note to reviewers - ashrae.org library/technical resources/aedgs... · 8/31/2018 · 60%...

60% Preliminary Technical Refinement Draft – NOT FOR DISTRIBUTION

Note to Reviewers: This the second in the series of Zero Energy Advanced Energy Design Guides. This series of guides differs from previous guides in that it is based on an energy goal of zero energy. This shift represents a balance of energy consumption and energy supply in order to achieve a target EUI for energy consumption and ultimately a zero energy building with that balance. With this preliminary technical review, the Project Committee wishes to focus primarily on the technical details outlined in Chapter 5 and specifically requests feedback on those technical details and recommendations. As part of this review, input on specific questions about the content is being solicited. These questions are interspersed throughout the document in red text and brackets. Comments on any and all of the content/text in the document is solicited and appreciated. Please provide your comments on the input form and note the referenced text by line number. The Project Committee is actively looking for Case Studies to include in the final document. Names of buildings whose energy use meets the EUI targets in Table 3.1 are appreciated. If you were designing/constructing a zero energy office:

1. Which sections would you find most helpful? 2. Which sections would you find to be not helpful or unnecessary? 3. Are there sections that have too much detail or not enough detail? 4. Would the intended figures be helpful to using the guide? If not, are their other figures

that would be helpful? 5. Is the guide useful for practicing design professionals (e.g., architects, engineers)? 6. If the guide is not useful, how can it be more relevant? 7. Will this guide help transform the market such that zero energy buildingss are more

mainstream? Why or why not? Additional notes on the review document:

This preliminary draft has not been copy edited for typographical or punctuation errors. These will be addressed on the final draft.

There is currently no particular rhyme or reason to the numbering of the tables and figures other than to connect them to the appropriate text. All numbering in the document will be updated to a consistent numbering system prior to publication.

References to other sections of the Guide will be added prior to the next review. Many figures in the document are preliminary sketches and will be professionally

redrawn for the final document and hopefully the next review. Where indicated, some figures are placeholders only and do not accurately reflect the

information in this document. These will be updated with accurate data prior to the next review.


Advanced Energy Design Guide

For Small to Medium Office Buildings Achieving Zero Energy

60% Preliminary Technical Refinement Draft August 31, 2018

NOT FOR DISTRIBUTION American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. The American Institute of Architects Illuminating Engineering Society U.S. Green Building Council U.S. Department of Energy This is a draft document intended only for internal use by the Society, including review and discussion. It may not be copied or redistributed in paper or digital form or posted on an unsecured Web site without prior written permission from ASHRAE. ASHRAE has compiled this draft document with care, but ASHRAE has not investigated, and ASHRAE expressly disclaims any duty to investigate any product, service, process, procedure, design, or the like that may be described herein. The appearance of any technical data or editorial material in this draft document does not constitute endorsement, warranty, or guaranty by ASHRAE of any product, service, process, procedure, design, or the like, and ASHRAE expressly disclaims same. ASHRAE does not warrant that the information in this draft document is free of errors, and ASHRAE does not necessarily agree with any statement or opinion in this draft document.


This is an ASHRAE Design Guide. Design Guides are developed under ASHRAE’s Special Publication procedures and are not consensus documents. This document (SP 140) is an application manual that provides voluntary recommendations for consideration in achieving greater levels of energy savings relative to minimum standards

Project Committee

Paul Torcellini, Chair

Daniel Nall AIA Representative

Keith Boswell

AIA Representative

Carol Marriott ASHRAE Representative

Ronnie Moffitt

ASHRAE Representative

Michael Lane IES Representative

Jennifer Scheib IES Representative

Jackie Henke

USGBC Representative

Landry Watson USGBC Representative

Tony Hans Member-at-large

Tom Hootman Member-at-large

Merle McBride Member-at-large

Noah Pflaum Analysis Support

Lilas Pratt Staff Liaison

Steering Committee Tom Phoenix, Chair

Daniel Nall

AIA Representative

Mark Lien IES Representative

Brendan Owens USGBC Representative

Mick Schwedler ASHRAE Representative

Sarah Zaleski DOE Representative (Ex-Officio)

Lilas Pratt Staff Liaison

1


Table of Contents 2 3

Acknowledgements 4

Abbreviations and Acronyms 5

Foreword: A Message to Building Owners/Managers 6

Chapter 1 Introduction 7 WHY BUILD A ZERO ENERGY OFFICE BUILDING? 8

OCCUPANT SATISFACTION 9 SOUND FISCAL MANAGEMENT 10 ENVIRONMENTAL STEWARDSHIP 11

ZERO ENERGY DEFINITION 12 GOAL OF THIS GUIDE 13 SCOPE 14 ENERGY TARGETS AND BASELINE BUILDING 15 HOW TO USE THIS GUIDE 16 REFERENCES 17

Chapter 2 Rationale for Zero Energy 18 WHY ZERO ENERGY BUILDINGS 19

CONNECTION TO THE “WHY” OF THE BUILDING 20 BUT WHAT IS THE RETURN ON INVESTMENT 21 ZERO ENERGY FILTERS AND HOW TO OVERCOME 22 ARE ZERO ENERGY BUILDINGS THE TIPPING POINT 23 MYTHBUSTERS 24

HIGH PERFORMANCE BUILDINGS 25 LOADING ORDER FOR ZERO ENERGY SUCCESS 26 FUTURE PROOFING VERSUS MARKET RATES 27

FUNDAMENTAL PROJECT SUCCESS FACTORS 28 CULTURE & MINDSET 29 EVERYTHING NEEDS A CHAMPION 30 COLLABORATE & ITERATE 31 AIM FOR THE TARGET 32 EVEN BUILDINGS HAVE A BEDTIME 33 ENGAGE & EDUCATE 34

REFERENCES 35

Chapter 3: Zero Energy Buildings: Ongoing Performance 36 BUILDING THE TEAM AND PROCESS 37

HIRE THE TEAM 38 RFP WRITING 39 OPR AND BOD 40 PROCUREMENT 41 CERTIFICATIONS 42


PROJECT BUDGETING AND PLANNING 43 OPERATIONS SCHEDULE 44 ENERGY BASELINE – EUI 45 ENERGY MODELING 46 EDUCATION AND TRAINING 47 BUDGET AND VE 48 SCHEDULING 49 DUCK CURVE 50

PROJECT LEVEL GOALS AND PERFORMANCE 51

DEFINE THE ENERGY BOUNDARIES 52

ESTABLISH ENERGY-EFFICIENCY PRIORITIES 53

ESTABLISH TARGET EUI 54

IDENTIFY ENERGY-EFFICIENCY MEASURES 55

REDUCE ENERGY LOAD 56

CONFIRM THROUGH BUILDING SIMULATION 57

CONFIRM ON-SITE RENEWABLE ENERGY POTENTIAL 58

CALCULATE ENERGY BALANCE 59

VERIFY THE ENERGY GOAL 60 QUALITY ASSURANCE AND COMMISSIONING 61

COMMISSIONING DURING CONSTRUCTION 62 Building Envelope 63 Building Systems 64 Indoor Environmental Quality 65

MEASUREMENT AND VERIFICATION 66 POSTOCCUPANCY PERFORMANCE 67 ONGOING COMMISSIONING 68

REFERENCES 69

Chapter 4: Building Performance Simulation 70 INTRODUCTION 71 SIMULATION TEAM 72 SIMULATION TYPES 73 SIMULATION PROCESS AND STRATEGIES 74

CLIMATE 75 FORM AND SHAPE 76 WINDOW-TO-WALL RATIO 77 SHADING 78 ENVELOPE 79 USER BEHAVIOR 80 EQUIPMENT SCHEDULES AND LOADS 81 LIGHTING 82 NATURAL VENTILATION 83 INFILTRATION 84


DAYLIGHTING AUTONOMY AND GLARE ANALYSIS 85 RAY TRACE ANALYSIS 86 HEATING AND COOLING LOADS 87 MECHANICAL SYSTEMS COMPARISONS 88

REFERENCES AND RESOURCES 89

Chapter 5 How-to Strategies 90

BUILDING AND SITE PLANNING 91 OVERVIEW 92 SITE DESIGN STRATEGIES 93

BP1 Select Appropriate Building Site(s) 94 BP2 Optimize Building Siting Combined with Landscaping and Site Features 95 BP4 Climate-Responsive Building Shape 96 BP5 Minimize and Shade Surfaces Receiving Direct Solar Radiation for Cooling 97 BP6 Avoid Reflected Solar Glare 98 BP7 Optimize the Building for Natural Ventilation 99

BUILDING ORIENTATION 100 BP8 Optimize Orientation 101 BP9 Fenestration Orientation 102

BUILDING DESIGN STRATEGIES 103 BP10 Integrate Programmatic Elements for Minimal Energy Use 104 BP11 Office Use Considerations 105 B12 Provide Entrance Vestibules 106 BP13 Use Automatic Doors Appropriately 107

PLANNING FOR RENEWABLE ENERGY 108 BP14 General Guidance 109 BP15 Roof Form 110 BP16 Determine Required Roof Area for PV 111 BP17 Maximize Available Roof Area 112 BP18 Roof Durability 113 BP19 Roof Safety 114 BP20 Maintain Solar Access 115

REFERENCES 116

ENVELOPE 117 OVERVIEW 118 AIR BARRIER SYSTEM 119

EN1 Provide Continuous Air Leakage Control 120 EN2 Establish an Infiltration Goal 121

THERMAL MASS 122 EN3 General Guidance 123 EN4 Internal Thermal Mass 124 EN5 External Thermal Mass 125

ROOF CONSTRUCTION 126 EN6 Select Appropriate Roofing Materials 127 EN7 Cool Roofs and Warm Roofs 128

BUILDING INSULATION – OPAQUE COMPONENTS 129 EN8 General Guidance 130 EN9 Maintain Insulation Effectiveness 131 EN10 Roof Insulation 132


EN11 Mass Walls—Concrete and Masonry 133 EN12 Steel-Framed Walls and Wood-Framed Walls 134 EN13 Below-Grade Walls 135 EN14 Mass Floors 136 EN15 Framed Floors 137 EN16 Slab-on-Grade Floors—Unheated and Heated 138 EN17 Evaluate Doors 139 EN18 Person-Doors 140 EN19 Doors—Opaque, Non-Swinging 141

BUILDING INSULATION – THERMAL BRIDGING 142 EN20 General Guidance 143 EN21 Supporting Columns Below Floors 144 EN22 Wall Type Transitions 145 EN23 Cladding Attachment and Rainscreens 146 EN24 Shelf Angles 147 EN25 Other Structural Penetrations in Walls 148 EN26 Louvers 149 EN27 Opaque Wall and Vertical Fenestration Intersection 150 EN28 Intermediate Floor Edges without Balconies and Floor Overhangs 151 EN29 Balconies, Canopies and Floor Overhangs 152 EN30 Cavity Walls Above Roofs 153 EN31 Roof and Wall Intersections 154 EN32 Parapets 155 EN33 Roof Overhangs 156 EN34 Roof Edges 157 EN35 Through Wall Overflow Drains/Lambs Tongues 158 EN36 Through-Wall Scuppers 159 EN37 Roof Drains 160 EN38 Plumbing Vents 161 EN39 Roof Hatches 162 EN40 Equipment Pedestals and Other Structural Penetrations in Roofs 163 EN41 Mechanical Curbs 164 EN42 Skylight Curbs 165 EN43 Below Grade Piping and Conduit 166 EN44 Duct Bank Entrances 167 EN45 Miscellaneous Penetrations—Detailing Foam 168 EN46 Use Advanced Framing Techniques 169

BUILDING FENESTRATION 170 EN47 General Guidance 171 EN48 Consider Fenestration Early in the Process 172 EN49 Window to Wall Ratio 173 EN50 Select the Right Fenestration 174 EN51 U-Factor 175 EN52 Solar Heat Gain Coefficient (SHGC) 176 EN53 Visible Transmittance (VT) 177 EN54 Dynamic Glazing 178 EN55 Use Opaque Wall Assemblies in Place of Spandrel Panels 179 EN56 Evaluate Glazing Frame Alignment 180 EN57 Framing and Assembly U-Factors 181 EN58 Framing and Assembly Infiltration Rates 182 EN59 Air Barrier and Thermal Break Continuity 183 EN60 Operable Fenestration 184 EN61 Construction Sequencing 185



DAYLIGHTING 187 OVERVIEW 188 DESIGN APPROACH 189

DL1 Daylighting Design Methodology (Climate Zones: all) 190 DL2 Project Phase Tasks (Climate Zones: all) 191

GENREAL DESIGN CONSIDERATIONS 192 DL3 Building Footprint and Façade Orientation (Climate Zones: all) 193 DL4 Space Programming (Climate Zones: all) 194 DL5 Fenestration Function (Climate Zones: all) 195 DL6 Daylight Redirection (Climate Zones: all) 196 DL7 Shading and Glare Control (Climate Zones: all) 197 DL8 Fenestration Details (Climate Zones: all) 198 DL9 Interior and Exterior Surface Finishes (Climate Zones: all) 199 DL10 Electric Light Integration (Climate Zones: all) 200 DL11 Daylighting Performance Metrics and Analysis Tools (Climate Zones: all) 201 DL12 Open Offices (Climate Zones: all) 202 DL13 Private Offices (Climate Zones: all) 203 DL14 Conference Rooms (Climate Zones: all) 204 DL15 Corridors (Climate Zones: all) 205 DL16 Break Rooms and Restrooms (Climate Zones: all) 206

REFERENCES 207

LIGHTING CONTROLS 208 LC1 Goals for Office Lighting Controls 209

GOOD DESIGN PRACTICE 210 LC2 Separately Control Electric Light Distribution, Intensity, and Spectrum 211 LC3 Use an Occupant-Engaged Control Strategy 212 LC4 Photosensors 213 LC5 Vacancy / Occupancy Sensors 214 LC6 Use Information Available from the Lighting Control System 215 LC7 Measure and Verify Expected Lighting Power Profiles 216 LC8 Exterior Lighting Controls 217

REFERENCES 218

ELECTRIC LIGHTING 219 INTERIOR LIGHTING 220

New and Existing Buildings 221 Goals for Office Lighting 222

GOOD DESIGN PRACTICE 223 EL1 Savings and Occupant Acceptance 224 EL2 Light-Colored Interior Finishes 225 EL3 Task Lighting 226 EL4 Color Rendering Index (CRI) 227 EL5 Correlated Color Temperature (CCT) 228 EL6 Light Emitting Diodes (LED) 229 EL7 Exit Signs 230

SAMPLE DESIGN LAYOUTS FOR OFFICE BUILDINGS 231 EL8 Open-Plan Offices 232 EL9 Private Offices 233 EL10 Conference Rooms/Meeting Rooms 234


EL11 Corridors 235 EL12 Storage Areas 236 EL13 Lobbies 237 EL14 Twenty-Four-Hour Lighting 238

EXTERIOR LIGHTING 239 EL15 BUG Ratings 240 EL16 Exterior Lighting Power—Parking Lots and Drives 241 EL17 Exterior Lighting Power—Walkways, Pathways and Special Features 242 EL18 Exterior Lighting Power—Decorative Façade Lighting 243


PLUG LOADS AND POWER DISTRIBUTION SYSTEMS 245 OVERVIEW 246

PLUG LOAD MANAGEMENT 247 PL1 General Guidance 248 PL2 Establish a Plug and Process Load Management Policy 249 PL3 Install Plug Load Controls 250

EQUIPMENT SELECTION AND CONTROL 251 PL5 Choose Energy-Efficient Equipment 252 PL6 Occupancy Controls 253 PL7 Unnecessary Equipment (Climate Zones: all) (Tony) 254

BREAKROOM EQUIPMENT 255 PL8 Refrigerators 256 PL9 Vending Machines 257 PL10 Small Appliances 258

BUILDING PROCESS LOADS 259 PL11 Building Level Services and Telecommunications Systems 260 WORKSPACE Equipment 261 PL12 Laptop Computers 262 PL13 Printing Equipment 263 PL14 Audio/Visual Equipment (Climate Zones: all) 264 PERFORMANCE VERIFICATION 265 PL15 Monitor Plug Load Usage 266 PL16 Parasitic Loads (Climate Zones: all) 267

POWER DISTRIBUTION SYSTEMS 268 PL17 Rightsizing Power Distribution Systems 269


SERVICE WATER HEATING 271 OVERVIEW 272 SERVICE WATER HEATING SYSTEM TYPES 273 WH1 System Descriptions (Climate Zones: as indicated below) 274 GOOD DESIGN PRACTICE 275

WH2 Properly Size Equipment 276 WH3 Equipment Efficiency 277 WH4 Minimizing System Losses 278 WH5 Renewable and Heat Recovery Service Hot Water Sources 279 WH6 Pipe Insulation 280

REFERENCE AND RESOURCES 281

HVAC SYSTEMS AND EQUIPMENT 282


OVERVIEW 283 HVAC SYSTEM TYPES 284 HV1 System Descriptions (Climate Zones: as indicated below) 285 SYSTEM A - ROOFTOP MULTIZONE VAV WITH HYDRONIC HEATING (SMALL 286 OFFICE ONLY) 287 HV2 System Description 288 SYSTEM B – AIR SOURCE VARIABLE REFRIGERANT FLOW HEAT PUMP SYSTEM 289 WITH DOAS 290

HV3 System Overview 291 HV4 Sizing Indoor with Outdoor Units 292 HV5 Refrigerant Safety 293 HV6 Ambient Condition Considerations 294 HV7 Equipment Efficiencies 295

SYSTEM C – WATER AND GROUND SOURCE HEAT PUMP SYSTEM (GSHP) WITH 296 DOAS 297

HV8 – System Overview 298 HV9 Types of ground-source heat pump systems 299 HV10 Thermal storage in the ground 300 HV11 Configuration of Ground Heat Exchangers 301 HV12 Equipment efficiency 302 HV13 Water Piping and Pumping Strategies 303 HV14 Annual System Balance 304 HV15 Ground-source System Success Factors1 305

SYSTEM D – DOAS WITH SENSIBLE FANCOILS AND CHILLERS WITH WATERSIDE 306 ECONOMIZERS 307

HV16 System Overview 308 HV17 Chilled Water Equipment 309 HV18 Variable Primary Flow 310

DEDICATED OUTDOOR AIR SYSTEMS (100% Outdoor Air Systems) 311 HV19 System Overview 312 HV20 Sizing the DOAS for dehumidification 313 HV21 Delivery for Zone Level DCV 314 HV22 Discharge Air Temperature Control for DOAS 315 HV23 Exhaust Air Energy Recovery Options for DOAS 316 HV24 Advanced SOO for DOAS 317 HV25 Part Load Dehumidification Control 318 HV26 Ventilation Air Rate 319 HV27 Demand Control Ventilation Strategies 320 HV28 Carbon Dioxide (CO2) Sensors (Climate Zones: all) 321 HV29 Exhaust Air Systems (Climate Zones: all) 322 HV30 Relief vs Return Fans (Climate Zones: all) 323 HV31 Energy Recovery Frost Control (Climate Zones 4-8) 324 HV32 Indirect evaporative cooling (Climate Zones 2B, 3B, 4B, 5B) 325 HV33 Evaporative Condensers (Climate Zones 2B, 3B, 4B, 5B) 326

HVAC TIPS FOR ALL SYSTEM TYPES 327 HV34: Right Size Equipment 328 HV35: Economizer and Free Cooling 329 HV36 Heating and Cooling Loads in a Zero Energy Office Building 330 HV37 Waterside Economizer 331 HV38 Airside Economizer 332 HV39 Dynamic Control of the Ventilation and Energy Recovery Device 333


HV40 Natural Ventilation and Natural Free Cooling 334 HV41 Filters 335 HV42 Building Pressurization Control 336 HV43: Transport Energy - Air 337 HV44 Electronically Commutated motors 338 HV45: Transport Energy - Water 339 HV46: Ductwork Design and Construction 340 HV47: Duct Insulation 341 HV48: Duct Sealing and Leakage Testing and Balancing 342 HV49: Thermal Zoning 343 HV50: Infiltration (Climate Zones 7, 8) 344 HV51: System Level Control Strategies 345 HV52: Employ Proper Maintenance 346 HV53: Commission Systems and Equipment 347 HV54 Noise Control (Climate Zones: all) 348

THERMAL MASS 349 HV55 Concept Overview 350 HV56 Thermal Mass as Part of the Building Envelope or Internal to the Building 351 HV57 Active versus Passive Thermal Mass 352

REFERENCES 353

RENEWABLE ENERGY 354 OVERVIEW 355 COMMON TERMINOLOGY 356

RE1: Definitions 357 DESIGN STRATEGIES 358

RE2: System Design Considerations 359 RE3: System Sizing 360 RE4: Energy Storage (Batteries) 361 RE5: Mounting Options 362 RE6: Interconnection Considerations 363 RE7: Net Metering Options 364 RE8: Utility Considerations 365 RE9: Utility Rates 366

IMPLEMENTATION STRATEGIES 367 RE10: Purchasing Options 368 RE11: Purchasing the System 369 RE12: Negotiating Procurement 370 RE13: Commissioning the System 371


Appendix A Envelope Thermal Performance Factor 373

Appendix B International Climatic Zone Definitions 374 375 376 377

378


Acknowledgements 379 380 Note: Acknowledgements will be added prior to publication 381 382 383 384 385

386


Abbreviations and Acronyms 387 388 Abbreviations and Acronyms will be updated as part of the publication process 389 390 ACCA - Air Conditioning Contractors of America 391 ADA - Americans with Disabilities Act (United States) 392 A/E - Architectural/Engineering 393 AFUE - Annual Fuel Utilization Efficiency - dimensionless 394 AIA - American Institute of Architects 395 ASE - Annual sunlight exposure 396 ASTM - American Society for Testing and Materials 397 ANSI - American National Standards Institute 398 BOD - Basis of Design 399 Btu - British Thermal Unit 400 CD - Construction Documents 401 CHW - Chilled Water 402 c.i. - Continuous Insulation 403 Cx - Commissioning 404 CxA - Commissioning Authority 405 CFM - Cubic Feet per Minute 406 CM - Construction Manager 407 CMH - Ceramic Metal Halide 408 COP - Coefficient of Performance - dimensionless 409 CRI - Color Rendering Index 410 CRRC - Cool Roof Rating Council 411 D - Diameter - ft 412 db - Dry Bulb - F 413 DCKV - Demand Control Kitchen Ventilation 414 DL - Advanced Energy Design Guide Code for Daylighting 415 DOAS - Dedicated Outdoor Air System 416 DOE - Department of Energy (United States) 417 DX - Direct Expansion 418 Ec - Efficiency, combustion - dimensionless 419 ECM - Electronically Commutated Motor 420 EEPR - Electronic Evaporator Pressure Regulator 421 EEV - Electronic Expansion Valves 422 EER - Energy Efficiency Ratio - Btu/W-h 423 EF - Energy Factor - dimensionless 424 EIA - Energy Information Agency 425 Et - Efficiency, thermal - dimensionless 426 EL - Advanced Energy Design Guide Code for Electric Lighting 427 EN - Advanced Energy Design Guide Code for Envelope 428 EPR - Evaporator Pressure Regulator 429 EUI - Energy Use Intensity 430 EX - Advanced Energy Design Guide Code for Exterior Lighting 431 F - Slab Edge Heat Loss Coefficient per Foot of Perimeter – Btu/h∙ft∙oF 432 FC - Filled Cavity 433 FPI - Fins per inch 434


FPT - Functional Performance Testing 435 GC - General Contractor 436 GSHP - Ground Source Heat Pump 437 Guide - Advanced Energy Design Guide 438 HC - Heat Capacity - Btu/(ft2∙oF) 439 HGR - Hot Gas Reheat 440 HSPF - Heating Season Performance Factor – Btu/W∙h 441 HV - Advanced Energy Design Guide Code for HVAC Systems and Equipment 442 HVAC - Heating, Ventilating and Air-Conditioning 443 HW - Hot Water 444 HX - Heat Exchange 445 IES - Illuminating Engineering Society 446 in - Inch 447 IPLV - Integrated Part Load Value - dimensionless 448 kBtu/h - Thousands of British Thermal Units per Hour 449 kW - Kilowatt 450 LBNL - Lawrence Berkeley National Laboratory 451 LED - Light Emitting Diode 452 LPD - Lighting Power Density - W/ft2 453 Ls - Liner Systems 454 LSHX - Liquid Suction Heat Exchanger 455 LT - Low-temperature 456 N/A - Not Applicable 457 MA - Mixed Air 458 MBMA - Metal Building Manufacturers Association 459 MT - Medium-temperature 460 NEMA - National Electrical Manufacturers Association 461 NFRC - National Fenestration Rating Council 462 NR - No Recommendation 463 NREL - National Energy Renewable Laboratory 464 NZEB - Net Zero Energy Buildings 465 O&M - Operation and Maintenance 466 OPR - Owner’s Project Requirements 467 PC - Project Committee 468 PF - Projection Factor - dimensionless 469 PL - Advanced Energy Design Guide Code for Plug Loads 470 ppm - Part per million 471 psf - Pounds per square foot 472 PV - Photovoltaic 473 QA - Quality Assurance 474 R - Thermal Resistance - h∙ft2∙oF/Btu 475 SCT - Saturated Condensing Temperature 476 sDA - Spatial daylight autonomy 477 SEER - Seasonal Energy Efficiency Ratio – Btu/W-h 478 SET - Saturated Evaporator Temperature 479 SHGC - Solar Heat Gain Coefficient - dimensionless 480 SP - Special Project 481 SRI - Solar Reflectance Index - dimensionless 482


SSPC - Standing Standards Project Committee 483 SST - Saturated Suction Temperature 484 Std. - Standard 485 SWH - Service Water Heating 486 SZCV - Single Zone Constant Volume 487 SZVAV - Single Zone Variable Air Volume 488 TAB - Test and Balance 489 TC - Technical Committee 490 TD - Temperature Difference - F 491 TXV - Thermostatic Expansion Valve 492 U - Thermal Transmittance - Btu/h∙ft2∙oF 493 UPS - Uninterruptible Power Supply 494 USGBC - U. S. Green Building Council 495 VSD - Variable Speed Drive 496 VT - Visible Transmittance - dimensionless 497 W - Watts 498 wb - wet bulb 499 ”wg - Inches of Water Gauge 500 w.c. - Water Column 501 WH - Advanced Energy Design Guide Code for Service Water Heating 502 WSHP - Water Source Heat Pump 503 ZE - Zero Energy 504 ZEB - Zero Energy Building 505 506 507

508


Foreword: A Message to Building Owners/Managers 509 510 Note: Foreword will be added prior to publication 511 512 513 514 515 516


Chapter 1 Introduction 517 518 Zero energy buildings are about balance. Zero energy buildings are designed to balance low 519 energy consumption with on-site renewable energy production to meet their entire energy loads 520 over 12 months. Zero energy buildings are usually connected to the utility grid to provide 521 energy whenever renewable energy production is insufficient to meet required loads and to 522 return energy to the grid when renewable energy production exceeds the loads. This guide 523 provides insight on how to achieve a zero energy office building. 524 525 The qualities of a zero energy office building can create healthy, high-performance work 526 environments and allow occupants to be more productive as well as saving operational 527 expenses. As an organization, zero energy buildings can show corporate leadership impacting 528 customers, helping to retain employees and increasing client satisfaction. All these contribute 529 to minimizing the impact of the built environment. 530 531 WHY BUILD A ZERO ENERGY OFFICE BUILDING? 532 533 OCCUPANT SATISFACTION 534 535 Occupant satisfaction should be a key element for employers. Occupant salaries represent over 536 90% of the total cost of operating a business and satisfied occupants are less likely to see other 537 job opportunities. Occupant satisfaction is complex, but some aspects related to zero energy 538 buildings are increased comfort, access to daylighting, and the company’s environment 539 commitment shown through effective building design. Occupants have a large influence over 540 the success of a building, governing operations and many of the energy loads. They are the 541 champions for energy efficiency and can help achieve energy and environmental goals. They 542 are also the most valuable resource. 543 544 Productivity of occupants needs to be facilitated with a healthy, high performance work 545 environment. Zero energy buildings can be a vehicle to establish goals for the building, 546 including energy. 547 548 SOUND FISCAL MANAGEMENT 549 550 Zero energy buildings can substantially reduce the energy bills for a building. Often energy 551 costs are the largest controllable cost for a business. Reducing these costs has dramatic impact 552 on the bottom line. Zero energy office buildings can both reduce energy consumption 553 dramatically and mitigate the risk of future energy cost volatility. 554 555 As this guide will show, zero energy office buildings can have lower maintenance costs. 556 Effective design can create less complex buildings where heating, ventilating, air conditioning 557 and control systems may be operated and maintained by less highly skilled technicians, who are 558 generally easier to recruit. Maintenance costs are further reduced because the wall, window and 559 roof systems that achieve the low EUI essential to affordable zero energy buildings, and the 560 testing and commissioning needed to ensure that they are constructed and perform as designed, 561 should be more durable and require less long-term maintenance than standard construction. 562 Zero energy office buildings should have lower life-cycle costs than other like buildings, and 563 continue to conserve resources throughout their lives. 564


565 ENVIRONMENTAL STEWARDSHIP 566 567 Completing a zero energy office building, or an office building with the low EUI required to be 568 ready for zero energy when renewable energy sources are added, demonstrates leadership and 569 the clear commitment of companies to sustainability and environmental stewardship. A zero 570 energy office building signals a shift toward recognizing and protecting natural resources and 571 mitigating climate change to the entire community 572 573 ZERO ENERGY DEFINITION 574 575 There are a number of different terms in common use to describe buildings that achieve this 576 balance between energy consumption and production: zero energy, zero net energy, net zero 577 energy. The term used throughout this Guide is zero energy (ZE) for consistency with the 578 United States Department of Energy’s definition of zero energy. The specific definition of a 579 zero energy Building used in this Guide is based on source energy, as defined by the 580 Department of Energy (DOE 2015): 581 582

An energy-efficient building where, on a source energy basis, the actual annual 583 delivered energy is less than or equal to the on-site renewable exported energy. 584

585 The DOE definition provides a standard accounting method for zero energy using nationwide 586 average source energy conversion factors, facilitating a straightforward assessment of zero 587 energy performance of buildings. Although the DOE national averages do not take into account 588 regional differences in energy generation and production, nor precise differences in 589 transmission losses due to a project’s location, they provide an equitable and manageable 590 formula intended to facilitate scaling up of zero energy buildings across the country and 591 beyond. Because of its wide adoption across the country, using this definition also facilitates 592 alignment with federal policy and incentives as well as with many state and municipal 593 initiatives. 594 595 The guide provides target EUI information in both source energy and site energy. Both site and 596 source energy can be used to calculate the energy balance of a project. Site energy refers to the 597 number of units of energy consumed on the site and typically metered at the property line or the 598 utility meter. Source energy refers to the total amount of energy required to produce and 599 transmit a given amount of energy of each fuel type to the site. It takes into account the 600 efficiency of this process for each fuel source. It is calculated by multiplying the site energy of 601 each fuel source by a factor specific to that fuel. For example, for electrical energy, it takes 602 approximately 3 kWh of total energy to produce and deliver 1 kWh to the customer because the 603 production and distribution of electrical energy is roughly 33% efficient. On the energy 604 generation side of the equation, the on-site renewable energy generation is then also multiplied 605 by these same factors, to give credit to its greater efficiency. 606 607 The need to determine a specific energy boundary for a zero energy building and the use of the 608 DOE definition in calculating an energy balance is discussed in Chapter 3. Finally, achieving 609 zero energy is an operational goal that gets its basis in creating a building that is well designed 610 and achieves success during the operation—year after year. Unlike design goals, having a zero 611 energy building is long-lasting proof that the goal has been achieved. 612


613 GOAL OF THIS GUIDE 614 615 The goal of this Guide is to demonstrate that zero energy office buildings are attainable, and to 616 provide direction through recommendations, strategies, and solution packages for designing and 617 constructing zero energy office buildings in all climate zones. Unlike the Advanced Energy 618 Design Guides that preceded this one, there is no baseline model as zero energy is the absolute 619 energy target. 620 621 This Guide provides design teams with a methodology for achieving energy-savings goals that 622 are financially feasible, operationally workable, and otherwise readily achievable. Energy 623 efficiency and renewable energy technology is changing rapidly and what did not make sense 624 financially or technically a few years ago is feasible today. The result is a zero energy office 625 building that can be completed within a typical budget. This Guide provides a pathway to zero 626 energy and will help lead the way to a fundamental shift from buildings as consumers of energy 627 to buildings as producers of energy. 628 629 As demonstrated throughout this Guide, setting measurable goals is key to success. Setting 630 measurable goals is the first commitment towards completing a successful zero energy project 631 while maintaining a reasonable budget. The Guide is written from two key perspectives: 632 633

Achieving very low energy use intensity (EUI) is the primary goal, whether or not on-634 site renewable energy is a feasible goal in the near or long-term future of the facility. 635

Achieving zero energy performance in the first year of operation makes no sense if the 636 building is not maintained for the long term. 637

638 The intended audience of this Guide includes, building owners, developers, architects, design 639 engineers, energy modelers, contractors, facility managers, and building operations staff. Much 640 of the information provided in this Guide may be applicable to those seeking to achieve zero 641 energy on other building types as well as being applied to new as well as retrofit construction 642 projects. 643 644 SCOPE 645 646 The Guide was developed through a collaboration of the American Society of Heating, 647 Refrigerating and Air-Conditioning Engineers (ASHRAE), the American Institute of Architects 648 (AIA), the Illuminating Engineering Society (IES), the U.S. Green Building Council (USGBC), 649 with support from the U.S. Department of Energy (DOE). A project committee that represents a 650 diverse group of professionals and practitioners in HVAC, lighting, architectural, and building 651 owners drafted the guidance and recommendations presented in the guide. 652 653 This Guide provides user-friendly guidance for the construction of new, low energy small to 654 medium office building. Much of the guidance also applies to retrofits of existing buildings, 655 depending on the depth and breadth of the retrofit. That guidance addresses processes, polices, 656 strategies, and includes energy efficient targets and how-to recommendations. The guide 657 provides strategies and recommendations to help design and construction buildings to be ready 658 to accept renewable energy systems to meet their low energy loads. The recommendations in 659 this guide are voluntary and are not designed to be code-enforceable. As a result, they are not 660


intended to replace, supersede, or circumvent any applicable codes in the jurisdiction in which a 661 particular building is to be constructed. In addition, there are many pathways to zero energy and 662 as technologies improve more pathways will be developed. Therefore, the Guide provides ways, 663 but not the only ways, to achieve energy-efficient and zero energy office buildings. 664 665 The Guide applies to office buildings ranging from roughly 20,000 ft2 to 100,000 ft2 and under 666 75ft to the highest occupied floor. Many larger office buildings are made up of modules in this 667 size and therefore the guide can be extended to larger buildings. The guide does not cover 668 atypical spaces, such as process loads, food service, laboratories, and other spaces with higher 669 energy loads and ventilation requirements. Space types covered by the Guide for medium 670 office buildings include office areas, circulation, storage, break rooms (refrigerator, ice 671 machine, dishwasher, microwave, sink, small appliances, and vending), small data center, 672 workout room, conference and meeting spaces. The Guide will not consider specialty spaces 673 with extraordinary heat, large ventilation requirements or pollution generation. 674 675 The primary focus of this Guide is new construction. Much of the Guide may also be applicable 676 to buildings undergoing complete or partial renovation, additions, and or changes to one or 677 more building systems; however, upgrading existing exterior building envelopes to achieve the 678 low EUIs needed to make achieve zero energy is likely to be very challenging. 679 680 While this Guide focuses on energy consumption and energy production, it also strives to 681 improve other important aspects of sustainability, such as acoustics, indoor air quality (IAQ), 682 water conservation and quality, landscaping, and transportation. A zero energy building should 683 not compromise indoor environmental quality and should maintain minimums as defined by 684 other standards which will be discussed elsewhere in the Guide. Improving many of these 685 sustainability attributes also contributes to improving the educational experience of the students 686 and the work environment of the faculty and staff. 687 688 ENERGY TARGETS AND BASELINE BUILDING 689 690 To establish reasonable energy targets for achieving zero energy performance in all U.S. climate 691 zones, two prototypical office buildings were developed and analyzed using hourly building 692 simulations. These building models include a 20,000 and a 100,000 ft2 office building. Each 693 was carefully assembled to be representative of office building construction. Information was 694 drawn from a number of sources. A typical office building layout is shown in Figure 1-1. 695 696 697

[FIGURE TO BE ADDED] 698 699

Figure 1-1 Typical Office Plan 700 701 One set of hourly simulations was run for each prototype using the recommendations in this 702 guide (Torcellini et al. 2017). The prototypes were simulated in the climate zones adopted by 703 the International Energy Code Council (IECC) and ASHRAE in developing the energy codes 704 and standards. These include nine primary climate zones subdivided into moist, dry, and marine 705 regions for a total of 19 climate locations. All materials and equipment used in the simulations 706 are commercially available from two or more manufacturers. 707 708


The simulation results led to the determination of a target EUI for each of the 19 climate 709 locations. The target EUIs are shown in Figure 1-2. Figure 1-2(a) shows the site EUIs 710 comparison by climate zone and Figure 1-2(b) shows the source EUIs by climate zone. The 711 specific EUI target values are shown later in this Guide. 712 713 The EUI was verified to not exceed the amount of renewable solar energy that could be 714 generated by photovoltaic panels, reasonably accommodated on the roof of the prototype 715 building. These EUI’s are intended not as a prescriptive requirement, but as a starting point of 716 minimum performance that could be cost-effectively attained. Further optimization through 717 building simulation and integrated design is recommended to reach the lowest possible EUI for 718 the specific conditions of a particular project. 719 720

721

722 Figure 1-2(a) Site EUI Comparison by Climate Zone 723

724

725 Figure 1-2(b) Source EUI Comparison by Climate Zone 726

727 To facilitate reaching these EUI targets, the Guide then provides recommendations for the 728 design of the building configuration and of building components, including the building outside 729 envelope; fenestration; lighting systems (including electrical interior and exterior lights and 730


daylighting); heating, ventilation, and air-conditioning (HVAC) systems; building automation 731 and controls; outdoor air (OA) requirements; service water heating (SWH); renewable energy 732 generation systems, and plug and process loads. These recommendations are described in 733 Chapter 5. 734 735 HOW TO USE THIS GUIDE 736 737 This chapter (Chapter 1 Introduction) outlines the case for zero energy), how the guide was 738 developed, a general idea of what to expect in the guide, and how to use it. 739 740 Chapter 2 The Rationale for Zero Energy identifies the main principles fundamental to 741 implementing ZES. 742 743 Chapter 3, Zero Energy Buildings: Ongoing Performance outlines how to achieve a ZES from a 744 process standpoint, The chapter discusses how to determine a target EUI and provides 745 recommended EUI targets in both site and source energy. 746 747 Chapter 4 Building Performance Simulation provides information on how to incorporate 748 building simulation into the design process. While not definitive source for how to use 749 simulation tools, the chapter provides an overview on most relevant approaches for analyzing 750 the various components of design covered in the guide. 751 752 Chapter 5 How-to Strategies provides specific strategies and recommendations regarding the 753 design, construction, and operation of zero energy office buildings. The chapter has 754 suggestions about best design practices, how to avoid problems and how to achieve the energy 755 targets advocated in this guide. The chapter is organized into easy to follow how-to tips. 756

757 Appendices provide additional information: 758

Appendix A—Envelope Thermal Performance Factors 759 Appendix B—International Climate Zone Definitions 760 761

Case studies and technology example sidebars are interspersed throughout the Guide for 762 examples of how to achieve zero energy and to provide additional information relevant to that 763 goal. 764 765 The Zero Energy Buildings Resource Hub provides additional information, resources, and case 766 studies for zero energy buildings. (www.zeroenergy.org). 767 768 Note that this Guide is presented in Inch-Pound (I-P) units only; it is up to the individual user to 769 convert values to metric as required. 770 771 The recommendations in this Guide are based on typical prototype operational schedules and 772 industry best practices as well as typical costs and utility rates. The operational schedule, actual 773 costs, and utility rates of any one project may vary, and life-cycle cost analysis (LCCA) is 774 encouraged for key design considerations on each specific project to properly capture the unique 775 project costs and operational considerations. 776 777 778


REFERENCES 779 780 NREL Guide to NZEBs at http://www.nrel.gov/docs/fy10osti/44586.pdf 781 NREL/DOE Zero Energy Buildings Resource Hub (www.zeroenergy.org) 782 783 784 785 786 787 788


Chapter 2 Rationale for Zero Energy 789 790 There are many stakeholders in a new building project and all of these stakeholders view the 791 building from their perspective and may not see energy consumption and zero energy a primary 792 goal. This chapter highlights why zero energy buildings are important and the principles for 793 successfully achieving the zero energy goal. 794 795 WHY ZERO ENERGY BUILDINGS 796 797 Zero energy buildings are readily achievable within budget, are a good financial investment, can 798 help recruit and retain new employees, inspire staff, showcase a corporate mission and develop 799 a sense of pride amongst the occupants of the building. 800 801 The number of projects being initiated with zero energy as a project goal has increased 700% 802 percent from 2012 to 2018 (New Buildings Institute 2018), however, having the zero energy 803 goal survive the trials and tribulations of design, construction and occupancy continues to be a 804 sought-after result as few projects are achieving this ultimate performance goal. Owners are 805 discovering zero energy buildings are having an intense impact on the education of students, 806 inspiring a community, showcasing a city’s commitment to sustainability and assisting in 807 recruiting talented millennials for a growing company. This connection to the “why” of the 808 building puts zero energy in a different light. 809 810 CONNECTION TO THE “WHY” OF THE BUILDING 811 812 A beautifully designed, elongated and sweeping canopy gains attention, welcomes visitors and 813 becomes a signaled beacon at the entrance to an office building. The occupants are proud of the 814 entrance, enjoying entering through it each day and the architecture connects the purpose of the 815 building with the intentional improvement of those who occupy it. What is the return on 816 investment for the canopy? Similarly, what is the return on investment for upgrading to terrazzo 817 as the flooring of choice in the entrance lobby? Office buildings are incorporating a grocery list 818 of potential prioritized amenities in design and are including zero energy in the list. Many of 819 these betterments further the “Why” of the building, showcasing the occupant’s business vision 820 and mission and end up enhancing productivity and help recruit young talented employees. 821 822 BUT WHAT IS THE RETURN ON INVESTMENT 823 824 With the reduced cost of drastic energy reduction strategies and minimal cost for renewables, 825 the cost to obtain zero energy has dropped from over 20% of the project budget in 2009 to 826 reportedly 2% to 4% of the project budget on recent zero energy projects. Meanwhile, national 827 averages show project estimates are reportedly off by 4% or more from project bid results. In 828 this way, the cost to obtain zero energy can often be within the expected window for bid results. 829 Zero energy is making its way into the list of prioritized betterments which connect to the 830 “Why” of the building and are affordable on bid day. Figure 2-1 illustrates this point. 831 832 [Note to Reviewers: The data in the paragraph above was found for transportation projects but 833 will be reviewed and updated for vertical construction projects.] 834 835


836 Figure 2-1 Cost for Zero Energy Design as % of Project Cost 837

838 ZERO ENERGY FILTERS AND HOW TO OVERCOME 839 840 A project timeline for design, construction and one year of occupancy is typically in the range 841 of three years. The growth of the emerging zero energy project which list the performance goal 842 on day one of design will lead to numerous successful projects performing full zero energy, 843 however, there are many filters which can potentially remove the zero energy goal from the 844 project. As a project matures, the numerous filters and stages where zero energy is removed 845 include: 846 847

Owner RFQ: During the RFQ process the owner can document their desire for zero 848 energy. This aids in the prioritization of ZE to the successful Construction Manager, 849 Design-Build Team or Architect-Engineering Team. 850

First Project Estimate: Often, a Construction Manager or Project Estimator has no 851 incentive to estimate a project as under budget and subsequently, a project design team 852 could face scope reduction at every phase of the project. Each time threatening the ZE 853 goal expressed by the owner as a priority. 854

Bid/Value Engineering Phase: Similarly, a final bid and value engineering process 855 should focus on adding value to the project by cost shifting items not connected to the 856 mission/vision or “Why” of the building. 857

Construction: Potential cost over-runs, delayed schedules and change orders due to 858 scope creep could threaten the zero energy goal throughout the construction process. 859

Occupancy / Energy Verification: Owner training proves to greatly affect user energy 860 consumption and can positively impact the user’s connection to the zero energy goal. 861 Additional information is available in the later section on Owner Training. 862

863 Having an Energy Champion tied to the entire zero energy process can greatly assist in 864 overcoming filters created by those without zero energy project experience. 865 866 ARE ZERO ENERGY BUILDINGS THE TIPPING POINT 867


868 Diffusion of Innovations by Everett M. Rogers and later, Crossing the Chasm by Geoffrey 869 Moore discuss the Law of Innovation as the Bell Curve for when innovative ideas become 870 mainstream. Our population is broken into five segments that fall across a bell curve: 871 innovators, early adopters, early majority, late majority and laggards. [Start with Why, Simon 872 Sinek 2009]. 873 874 Simon Sinek suggests a tipping point for innovation in the 12% range and, as more and more 875 zero energy buildings successfully complete their three year process and the 700% growth in 876 emerging projects increases, this tipping point could be on the not too distant horizon. (See 877 Figure 2-2) 878 879

880 Figure 2-2 Bell Curve for Innovative Ideas Becoming Mainstream 881

882 883 [Note to Reviewers: The following sections are in outline form and will be completed for the 884 next review. Input on the outline is appreciated.] 885 886 MYTHBUSTERS 887 888 Give reasons to NOT do a zero energy building then refute them: 889

1. First Cost: Case studies of drastic energy reduction with renewables (ZE if available) 890 and cost reduction. NREL was under budget, Cincy Police was under budget, DOE Oak 891 Ridge 892

2. Profitability: Green Lease details and case studies of successes. (Need references?) 893 3. Lease: Will not be able to lease the building: info research on ZE tied to owner 894

preference and lease incentives. (Bullet Center info) 895 4. Market Value: Won’t help me with the mission of my owner/tenant: ZE helps entice 896

employees, increase retention, increase rental rates, vacancy rate will decrease. 897 5. Maintenance: My team cannot maintain cutting edge technologies. Strategies in this 898

guide are tried and true strategies that are market ready, sustainable with high durability. 899 (Need reference) 900

6. Future Proofing 901 7. Example projects don’t exist 902

903 904 905


HIGH PERFORMANCE BUILDINGS 906 907 As our understanding and collective definition of High Performance Buildings evolves – so 908 does the collective building industry science and our ability to measure empirical evidence to 909 this definition. Arguably to date, much of the built environment’s focus on performance was 910 focused prior to the ribbon cutting in the design and delivery of our spaces. Moving forward, 911 the collective understanding of the industry is that we must not only design and deliver spaces 912 with the capability of being high performance buildings, but also ensure that those performance 913 characteristics are measured and maintained through the life cycle of those projects. A complex 914 challenge for us all as a society, given all of the challenges of project delivery and eventual 915 ownership and operations reside amongst different parties of the process. Simply put, we as 916 building professionals cannot continue to believe that our responsibilities in a low-carbon future 917 end at project delivery – we must develop and foster relationships that allow for the continuous 918 measurement and improvement of our projects – and continue to develop the physical science of 919 the built environment. 920 921 The common components of High Performance Buildings are fairly integrated and have impacts 922 and correlations that are fairly notably connected. As our understanding of the science behind 923 our built environment improves, so does our further understanding of the interrelationships of 924 these characteristics. This design guide contemplates how best to design projects to achieve 925 zero energy performance, but as a collective we would never discourage broader topics in 926 sustainability and green building. Performance components of high performance buildings that 927 most directly associate with zero energy projects are commonly as follows: 928 929

Energy Efficiency. Energy Use Intensity (EUI) is the key performance goal for all 930 aspiring zero energy projects. It is the key driver of many decisions and design 931 parameters throughout the project delivery process. Providing strategies and measures 932 that directly reduce the consumption of energy should be the singular focus of the 933 project team. Energy Use Intensity for our buildings is comparable to a vehicle’s 934 efficiency in miles-per-gallon and we must focus a new industry effort to propagate and 935 increase understanding around the measurement and comparison of Energy Use 936 Intensity across all sectors of the built environment. 937

Water Efficiency. Reducing the consumption of indoor, outdoor and process water has a 938 number of direct connections with energy efficiency. Reducing indoor hot water 939 consumption has a direct reduction in consumption for domestic hot water heating – 940 which is likely no surprise to many. However, our understanding of the amount of 941 global carbon footprint of simply moving water from its source to the point of 942 consumption continues to expand our need to conserve all forms of water consumption 943 for all end uses. Although those aren’t directly connected to the performance of a zero 944 energy building – no one would deny this metric for High Performance Buildings and its 945 impact on our overall environment. Annual water consumption is easily tracked; 946 however, projects often do make a higher effort to measure the subordinate components 947 of this resource. 948

Materials Efficiency. We’ve always understood that High Performance Buildings 949 encourage materials efficiency in both the assembly of the project and also in the 950 reduction of waste departing that process. A new building science is the full 951 understanding of the actual embodied energy and carbon required to develop and deliver 952


the materials of our buildings. Our understanding of a low carbon future and high 953 performance buildings is expanding to understand how to best reduce this impact on our 954 environment. 955

Indoor environmental quality. High Performance Buildings have the ability to combine 956 air quality, lighting, views, acoustics and the overall indoor occupant experience into an 957 integrated manner. High quality indoor experiences encourage productive occupants 958 and significantly reduce impacts to building operations over time. A well designed, high 959 quality interior requires fewer buildings calls, modifications or operational testing – 960 reducing total cost of ownership and improving building energy performance. 961

Health & Wellness. Our expanding understanding of High Performance Buildings and 962 their direct correlation to occupant health and wellness is a young but undeniable 963 science. High Performing Buildings can directly impact occupant health and wellness 964 and encourage all facets of lifestyles. Healthy buildings can no longer be optional from 965 a robust definition of a High Performance Building. 966

967 [Question for Reviewers: Should the following section be shifted over to the project level goals 968 in Chapter 3?] 969 970 LOADING ORDER FOR ZERO ENERGY SUCCESS 971 972 Achieving a fully operational zero energy project requires a commitment to a design, delivery 973 and operational process. This process identifies opportunities and strategies in a manner that 974 can be overwhelming and confusing even to very seasoned industry professionals. A project 975 team that lacks discipline to a process or a hierarchy of decision making may find themselves 976 victim of project creep or budgetary issues, which have ended many valid attempts to achieve 977 fully zero energy projects. 978 979 Project teams that find success tend to employ both an energy champion and also define and 980 stay disciplined to a hierarchy of energy decision criteria – or a loading order. A loading order 981 can simply be defined as a simple set of rules to help fully understand decision making 982 processes for energy efficiency strategies and measures that may be considered for inclusion 983 into the project. 984 985 In general, for success in achieving zero energy, project teams utilize this most basic loading 986 order: 987 988

1. Energy Efficiency. This first category in the loading order would include all forms of 989 passive design and quite simply all static systems of the building. Any measure that can 990 be included in this category could conceivably reduce consumption for the building and 991 occupants for the life of building. These commonly do not require replacement or large 992 amounts of maintenance and are the best contributions to success of a zero energy 993 building. Measures in this category should be prioritized and employed as extensively 994 as possible. 995

2. Systems Efficiency. The next level of decision making for project teams include a 996 review and optimization of the systems of a project to consider all of the ways to 997 integrate solutions for project success. These include all components of buildings that 998 deliver basic services to the occupants or to the process of production for the purpose of 999


the space. Systems often have efficiencies that are available for cost premiums above 1000 market cost and should be considered in aggregate to determine the efficiencies that will 1001 bring the best Energy Use Intensity (EUI) reductions per cost in overall annual results. 1002

3. Renewables and Technologies. The last components of an overall basic loading order 1003 are renewable generation strategies and other technologies for management or 1004 measurement to improve awareness. In almost all zero energy projects, an onsite 1005 renewable generation component will be the final system required to move a project 1006 from a very high performance and low EUI building to zero or positive. These systems 1007 are clearly not considered market rate construction for code compliance and represent 1008 budgetary challenges to most zero energy project attempts. As new technologies 1009 develop and penetrate the market intended to facilitate the operation of buildings that are 1010 based on post-occupancy and subscription based models, project teams should take care 1011 to consider how these products or strategies relate to the overall loading order and their 1012 proven success in actually reducing consumption based on prior performance. Project 1013 teams should take care to understand an investment shift of capital expenditure to 1014 operations and maintenance that promises reductions in consumption require heavy 1015 scrutiny. 1016

1017 In general, project teams that use discipline in loading the measures and strategies for the 1018 project will find best reductions in EUI per dollar and often times, these choices will also 1019 represent the best return on investments. There are infinite solutions to achieving zero energy 1020 operational projects and none of them are discouraged, we simply are expressing that teams that 1021 stay disciplined to a loading order can best facilitate their decision making process throughout 1022 the complexity of design and project delivery. 1023 1024 FUTURE PROOFING VERSUS MARKET RATES 1025 1026 A final consideration for projects in achieving a zero energy operational project is the balance 1027 between staying at or near a market rate versus including some strategies, measures or efforts to 1028 avoid impacts of future technologies or services to the project. Often in project delivery, the 1029 installation of some infrastructure or measure during initial construction, although at a premium 1030 to the project, may represent an opportunity for future efficiency that would actually be a 1031 fraction of the cost it may require to retrofit that effort into an existing and operating building. 1032 Project teams anticipating future opportunities can weigh and consider as a group the impact on 1033 overall total cost of ownership and return on investment. When given the opportunity for future 1034 efficiencies, project teams may very well trade off dollars today that would result in immediate 1035 efficiencies for a greater opportunity at a future date. Energy professionals and the project 1036 energy champions should weigh these opportunities for inclusion the project. 1037 1038 FUNDAMENTAL PROJECT SUCCESS FACTORS 1039 1040 In every zero energy office project there are fundamental actions that contribute to its success. 1041 From the first consideration of zero energy, to design, to moving in occupants and through the 1042 days and years of operation, optimal performance requires attention and focus. Although there 1043 are numerous factors that will deliver zero energy success the six below are critical to 1044 achievement. 1045 1046


CULTURE & MINDSET 1047 1048 The first key to success is the belief and reinforcement of a culture and mindset that a zero 1049 energy office project is readily achievable within budget, is a good financial investment, can 1050 build national attention, invoke a sense of community and invigorate and inspire the work force 1051 occupying the building. To support this belief, the culture development starts in infancy when 1052 the project is first conceived of and extends through design and construction into operations. 1053 1054 To help start creating the culture a clear but flexible communications strategy is essential. It 1055 will educate, generate enthusiasm, develop new proponents for zero energy, and establish the 1056 key expectation that zero energy will be achieved and maintained. When crafting the strategy, 1057 be conscious to connect the benefits of zero energy to each individual stakeholder group (i.e. 1058 owner, architect, engineers, general contractor, facility maintenance team, and occupants) who 1059 will touch the project throughout its lifecycle. It is likely that the benefits will resonate with the 1060 stakeholders in different ways. 1061 1062 It is necessary from the outset to address head on those who believe that a zero energy office 1063 will automatically cost more than a typical high performance office, and that the risks of cost 1064 overruns, delays and eventual failure to achieve zero energy are too great. The first step in 1065 building confidence that zero energy will be achieved on budget and on schedule is to select 1066 your delivery method and start assembling the team and engraining in them the expectation for 1067 a zero energy project that is on budget and on schedule. 1068 1069 EVERYTHING NEEDS A CHAMPION 1070 1071 Ralph Waldo Emerson said, "Nothing great was ever achieved without enthusiasm." That holds 1072 true for bringing a zero energy building to life. 1073 1074 Be it an individual owner, landlord built or developer delivered, finding individuals with the 1075 vision, passion, persistence, and powers of persuasion to be a champion and lead the project 1076 through planning, design, construction, occupancy, and ongoing measurement and verification 1077 is critical to success. 1078 1079 This champion may appear in different ways. Ideally, the owner would be the champion 1080 establishing zero energy and other performance goals for the project. They would decide on a 1081 procurement methodology that helps select the best team to meet the goals. This team could be 1082 the architectural/engineering (A/E) firm or an expanded team that includes the contractor and 1083 facility managers, which has advantages in continuity of meeting performance goals. 1084 1085 As a zero energy project comes into focus consider including the role of zero energy champions 1086 in the scope of every outsourced member of the team (A/E, contractor, Cx agent, etc.). They 1087 will bring their specific expertise to the zero energy goal and steer the project through 1088 challenges that might put zero energy at risk during the life of the project. In the end, the owner 1089 also needs to be a champion, as zero energy is achieved through successful operations and not 1090 just design and construction. 1091 1092


COLLABORATE & ITERATE 1093 1094 Zero energy offices demand highly collaborative synergies among those who plan, design, 1095 construct, use, operate and maintain them. There are many project delivery methods including 1096 design-build, design-bid-build, Integrated Project Delivery, and construction manager at risk 1097 (CMR). Each one has benefits and potential issues that need to be addressed when selecting the 1098 most appropriate one. Regardless of deliver method, the process should be integrated from the 1099 outset. An integrated process "is highly collaborative. This approach requires the whole project 1100 team to think of the entire building and all of its systems together, emphasizing connections and 1101 improving communication among professionals and stakeholders throughout the life of a 1102 project. It breaks down disciplinary boundaries and rejects linear planning and design processes 1103 that can lead to inefficient solutions." (USGBC, 2014) 1104 1105 The advantages of integrated design in maximizing synergies across program, site, and system 1106 requirements have been noted for many building types, whether or not the goal is zero energy. 1107 Extensive guidance on integrated design methodology is available through the American 1108 Institute of Architects (AIA 2007) and elsewhere. For zero energy offices, finding synergies 1109 through integrated design is not just an enhancement but an essential strategy for achieving the 1110 low EUI needed within the budget available for a typical high performance office. Applying 1111 integrated design synergies to a zero energy office project creates a single integrated system, 1112 from which no major component can be removed or substantially altered without raising the 1113 EUI. 1114 1115 While prescriptive design guidance is useful to achieve many energy goals, to achieve zero 1116 energy as cost effectively as possible prescriptive strategies may no longer suffice. Rather, 1117 integrated design is required to reconcile the specifics of microclimate, site, program, available 1118 construction options and available renewable energy to develop an optimal solution that 1119 balances energy consumption with energy generation. With the development of zero energy 1120 buildings from performance-based rather than prescriptive criteria, the use of building 1121 simulation tools is essential as part of an iterative process of optimizing each system and 1122 component. This process is described in Chapter 4. 1123 1124 The extensive integration of multiple aspects of a zero energy office requires a collaborative 1125 process to maximize synergies for effective solutions. This process begins at the earliest stages, 1126 incorporating more detailed data and technical analysis when setting goals and developing the 1127 performance criteria. As predesign evolves through design and construction, an iterative process 1128 characterized by feedback loops, cycles between data analysis, building simulation, and design, 1129 to gradually optimize the design as more design data emerges. The repeated cycles through 1130 building simulation analyses to optimize the design are illustrated in Figure 3-1. Ultimately the 1131 feedback does not stop with occupancy but is carried over into post occupancy as the occupants 1132 develop the most efficient ways to run the building. 1133 1134


1135 Figure 3-1 Integrated Design Process for a Zero Energy 1136

1137 1138 AIM FOR THE TARGET 1139 1140 Once the project budget is established and predesign program definition and concept design 1141 begins for the project, the zero energy design begins as well. This may occur after the hiring of 1142 the A/E team, for a design/bid/build or CMR project or as part of writing the RFP for a 1143 design/build project. This predesign process involves two types of tasks: data analysis which 1144 looks at project parameters (consumption data from similar projects, climate data for the site, 1145 etc.) and building simulation which simulates projected performance of the facility and impacts 1146 of various energy-efficiency measures. The building simulation process is described in Chapter 1147 4. Additional information and resources are provided in the NREL guide to zero energy 1148 buildings (Pless and Torcellini 2010). In an integrated process, these steps are typically 1149 iterative; that is, as each task is completed, they inform subsequent and previous tasks, requiring 1150 additional rounds of analysis as information becomes more complete. Through the iterations the 1151 EUI for the project will be established. 1152 1153 The team should use resources such as AIA 2030, the CBECS database and similar building 1154 performance data to establish the landscape of performance and a range for the project EUI. 1155 The EUI is the annual energy consumption of the project divided by the gross area of the project 1156 not including any renewable generation. Establishing the EUI involves evaluating the project 1157 parameters to determine a feasible target. More details on establishing the EUI is discussed in 1158 Chapter 3, however, the key is that once an EUI target is set it can then be the keystone around 1159 which discussions occur for system choices, equipment selections and other decisions are 1160 measured. It opens up the path to major paradigm shifts from selecting new HVAC systems, to 1161 modifying IT policies around wireless solutions and laptops over desktops, all decisions can be 1162


looked at through the lens of the impact to the EUI. It removes emotion from the discussions 1163 and facilitates performance based decisions. 1164 1165 EVEN BUILDINGS HAVE A BEDTIME 1166 1167 Zero energy buildings demand attention and clarity around their operating schedules. If 1168 mechanical systems are heating/cooling for full capacity when only 10% of the occupants are 1169 there, if the lights are on throughout the building when only one corner of one floor is occupied, 1170 if the copiers, monitors, and other equipment are on, even in sleep mode, overnight when no one 1171 is there, then achieving zero energy will be harder or perhaps unachievable. 1172 1173 Over the past decade the ability to have a flexible work schedule that allows for working at off 1174 hours of the day and working remote from the office have changed the typical use profiles of a 1175 building. The advent of co-sharing work environments has also impacted the use profiles by 1176 extending the operating hours to include evening and even weekend hours. 1177 1178 As part of the initial planning for an office, the project team must establish its assumptions and 1179 goals for the use of the building. This will allow the operations schedules to be defined for 1180 equipment and decisions can be made for the controls system that allow the building to shut 1181 itself down and stop drawing load when not required. 1182 1183 ENGAGE & EDUCATE 1184 1185 With all of the design and construction is done, the day occupants move in is not the end of the 1186 project, in some respects this is where it begins. Even with the most sophisticated controls 1187 systems, if the occupants haven't embraced the zero energy culture and aren't educated on what 1188 it means to work in a zero energy office the chances of achieving zero energy operations are 1189 significantly reduced. Just as there is a champion to drive the project from conception through 1190 to implementation, there needs to be a program that champions zero energy operations. 1191 Occupants need to be educated and not just on the day that they move in, but throughout the 1192 year. 1193 1194 Attention should be paid to creating a program that engages and educates occupants on the 1195 benefits of working in a zero energy office and what they can do to help ensure the zero energy 1196 status is achieved. Passive opportunities include building signage, real time displays of energy 1197 consumption and emailed updates on building performance. More active opportunities include, 1198 design phase workshops that extract goals and aspirations from these stakeholders to make them 1199 a part of the process, pre-move education sessions on zero energy, lunch and learn sessions that 1200 speak to the building performance, campaigns that focus on energy reduction targets, online 1201 communities where employees share their ideas and feedback, a zero energy champions 1202 programs, and celebrations when targets are achieved. Engaging occupants in the day in and 1203 day out requirements of operating a zero energy facility can lead to the long-term culture change 1204 that ensures success. 1205 1206 1207 REFERENCES 1208 1209


ASHRAE Guideline 10-2016, Interactions Affecting the Achievement of Acceptable Indoor 1210 Environments (ASHRAE 2016). 1211

ASHRAE Indoor Air Quality Guide: Best Practices for Design, Construction, and 1212 Commissioning (ASHRAE 2009) 1213

ANSI/ASHRAE Standard 55-2013, Thermal Environmental Conditions for Human Occupancy 1214 (ASHRAE 2013) 1215

1216 1217


Chapter 3: Zero Energy Buildings: Ongoing Performance 1218 1219 [Note to Reviewers: The following sections are in outline form and will be completed for the 1220 next review. Input on the outline is appreciated.] 1221 1222 BUILDING THE TEAM AND PROCESS 1223 1224

Hire the Team 1225 (team experience on this level, EUI performance, QUALITY energy modeler) 1226 1227 RFP writing 1228 1229 OPR and BOD 1230 1231 Procurement 1232 1233 Certifications 1234 (Energy Star, LEED, WELL, Living Building Net Zero Petal, etc.) 1235

1236 1237 [Note/Question for Reviewers: This chapter will likely include the EUI targets and additional 1238 information from the zero energy definition from DOE as shown in Table 3-1, and Figures 3-1 1239 and 3-2 below. Input on the placement of this information in the Guide is appreciated.] 1240 1241 1242 PROJECT BUDGETING AND PLANNING 1243 1244

Operations Schedule 1245 1246 Energy Baseline – EUI 1247

1248 Energy Modeling 1249 1250 Education and training 1251 1252 BUDGET and VE 1253 1254 Scheduling 1255 1256 Duck Curve 1257

1258 1259 PROJECT LEVEL GOALS AND PERFORMANCE 1260 1261

Define the Energy Boundaries 1262 1263 Establish Energy-Efficiency Priorities 1264 1265


Establish Target EUI 1266 (EUI Targets provided in this section – See Table 3-1 and Figure 3-1 below) 1267 1268 Identify Energy-Efficiency Measures 1269 1270 Reduce Energy Load 1271 1272 Confirm Through Building Simulation 1273 1274 Confirm On-Site Renewable Energy Potential 1275 1276 Calculate Energy Balance 1277 1278 Verify the Zero Energy Goal 1279

1280 1281 [Note to Reviewers: The Project Committee is actively looking for Case Studies to include in 1282 the final document. Names of buildings whose energy usages meets the EUI targets in Table 1283 3.1 are appreciated. Feedback on the EUI targets is also appreciated.] 1284 1285

Table 3-1 Target Energy Use Intensity (EUI) 1286

Climate zone

SITE ENERGY SOURCE ENERGY

0A 23.2 80 0B 27.6 96 1A 23.4 81 1B 25.7 89 2A 22.2 77 2B 22.8 79 3A 21.4 74 3B 21.1 73 3C 16.0 55 4A 21.7 75 4B 20.6 71 4C 17.3 60 5A 23.2 80 5B 22.9 79 5C 17.5 61 6A 27.7 96 6B 24.7 86 7 30.3 88 8 36.0 100

1287 1288 1289


1290 Figure 3-1 Climate Zone Map for US States and Counties 1291

Source: ASHRAE Standard 169, Normative Appendix B 1292 1293 1294 Site boundaries of energy transfer for zero energy accounting are illustrated in Figure 3-2 (taken 1295 from A Common Definition for Zero Energy Buildings). 1296 1297


1298 1299

Figure 3-2 Energy Balance Diagram 1300 Source: A Common Definition for Zero Energy Buildings 1301

1302 1303 [Questions for Reviewers: 1304 Is the following section enough information for the Guide on the topic of Quality Assurance and 1305 Commissioning or should a detailed appendix also be included? 1306 What topics would you suggest need to be expanded upon?] 1307 1308 QUALITY ASSURANCE AND COMMISSIONING 1309 1310 Zero energy is an operational goal and as a result, the success is obtained when the building 1311 actually performs to the EUI targets that have been specified and the renewable energy is shown 1312 to generate that amount of energy. In order to ensure the building achieves zero energy for a 1313 year requires strong Quality Assurance (QA) process and Commissioning (Cx). 1314 1315 QA is a systematic process of verifying the Owner’s Project Requirements (OPR), operational 1316 needs, and Basis of Design (BoD) and ensuring that the building performs in accordance with 1317 these defined needs. A strong QA approach begins with designating roles to help manage the 1318 QA process. The QA team can be in-house or outsourced. However, the building team should 1319 consider if creating a QA team made up of their own in-house technical experts, as well as 1320 external expertise, is possible. At a minimum, the QA team should include those responsible for 1321 the operation and maintenance of HVAC systems, building automation systems, lighting 1322 systems, building envelopes, audio/visual, information technology, security, and if applicable, 1323 kitchen operations. 1324

1325


The selection of external QA services should include the same evaluation process the owner 1326 would use to select other team members. Qualifications in providing QA services, past 1327 performance of projects, cost of services, and availability of the candidate are some of the 1328 parameters an owner should investigate and consider when making a selection. Owners may 1329 select a member of the design or construction team as the QA provider. While there are 1330 exceptions, in general most designers are not comfortable operating and testing assemblies and 1331 equipment and most contractors do not have the technical background necessary to evaluate 1332 performance. Cx requires in-depth technical knowledge of the building envelope and the 1333 mechanical, electrical, and plumbing systems and operational and construction experience. This 1334 function is best performed by a third party responsible to the owner because political issues 1335 often inhibit a member of the design or construction organizations from fulfilling this 1336 responsibility. 1337 1338 A critical role on the QA team, typically served by an external party, is that of the 1339 commissioning authority (CxA). The commissioning process encompasses the review, testing, 1340 and validation of a designated system to ensure that it performs as expected. In a high-1341 performance building, commissioning of the following components is a critical part of the QA 1342 process: 1343 1344

Building enclosure. Walls, roof, fenestration, slab 1345 Building systems. Heating, ventilation, air conditioning (HVAC), lighting and lighting 1346

controls, plug load management, renewable energy systems 1347 Indoor environmental quality. Air quality, light quality, acoustical performance In most 1348

cases, the CxA is directly contracted with the owner, so engaging a CxA is often done 1349 by way of a separate RFQ/P process. There are good reasons to consider engaging a 1350 CxA as early, if not earlier, than the design team itself. Typically, a CxA will contribute 1351 their technical expertise to the creation of the OPR. 1352

1353 The CxA also operates as an owner’s technical advocate during the design review process to 1354 help ensure that the requirements of the OPR are being met and that systems can be tested 1355 properly. They also provide a technical peer review of the construction documents for the 1356 systems being commissioned. This review provides an additional layer of quality assurance. 1357 1358 As the project proceeds through the stages of design, it is important that the QA team have 1359 ample opportunity to review the design and provide feedback. A log of the QA team’s 1360 comments should be kept, and noted issues should be resolved. The QA team’s review is 1361 intended to ensure that the design and supporting documents are developed in adherence to the 1362 OPR. 1363 1364 COMMISSIONING DURING CONSTRUCTION 1365

1366 The following multidisciplinary activities and the associated personnel should be considered for 1367 integrated approaches in traditional mechanical, electrical, and plumbing system Cx. 1368 Construction document specifications include requirements for Cx activities, such as 1369 participating in and documenting results, commissioning meetings, collaboration, and corrective 1370 actions. 1371

1372


Site-based Cx requires input from at least the following parties: the general contractor; 1373 the mechanical, electrical, controls, and test and balance (TAB) subcontractors; the 1374 CxA; the owner’s representative; and the mechanical, electrical, and lighting designers. 1375

Pre-functional test procedures usually require evaluation of motors and wiring by the 1376 electrical subcontractor and the manufacturer’s representative and evaluation of 1377 component performance by the manufacturer’s representative and the mechanical, TAB, 1378 and controls subcontractors. The CxA will generally sample to back-check the values 1379 reported in the pre-functional checklist results. 1380

Functional tests involve the CxA and the controls and TAB subcontractors at a 1381 minimum. 1382

1383 Besides the usual tests of control sequences, it is also important to document that the building is 1384 ready from an IAQ point of view, as it is necessary to remove the construction-related odors and 1385 off-gassing chemicals from the air volume of the space prior to permanent occupancy. This can 1386 be accomplished through physical testing in which concentrations of typical pollutants are 1387 measured and compared to health standards. It can also be proven (with agreement of all team 1388 members) through the careful documentation of preoccupancy purge procedures, which usually 1389 involve multiple hours of 100% ventilation air supply. 1390 1391 The selected contractors should build QA/QC plans to demonstrate how they plan to achieve the 1392 required performance, and should build in milestones for demonstrating performance as part of 1393 the commissioning process. 1394 1395 Specific and detailed commissioning tasks are found in documents published by ASHRAE 1396 (ASHRAE 2013b, 2015) and ASTM (ASTM 2012, 2016). However, a basic descriptions of 1397 each category follows. 1398 1399 Building Envelope 1400 The building envelope is a key element of zero energy design. It includes: walls, roofs, 1401 windows, doors, slabs, and foundations. Improper placement of insulation, improper sealing or 1402 lack of sealing at air barriers, wrong or poorly performing glazing and fenestration systems, 1403 incorrect placement of shading devices, misplacement of daylighting shelves, and 1404 misinterpretation of assembly details can significantly compromise the energy performance of 1405 the building. Therefore, at various points in the construction process, assembly testing or whole-1406 building testing may be performed to ensure the quality of the assembly construction. 1407 1408 Assembly testing performs air and moisture tests on individual components of a building, such 1409 as a wall, roof, or window. Large fans and/or spray racks are connected and inspected to 1410 determine the levels of air and moisture infiltration. 1411 1412 A mockup is a small sample of constructed wall or assembly that is used to demonstrate the 1413 process and product that will be constructed on a much larger scale. Mockups are constructed 1414 early in the construction process by the contractor, and inspected by the CxA, architect, and QA 1415 team for air and water infiltration so that any issues can be resolved before the construction of 1416 the actual assembly. If thorough mockup testing has been performed, more expensive assembly 1417 testing can often be deferred. However, complicated facades such as large curtain wall 1418 assemblies, or heavily articulated wall extrusions may warrant further testing to assure 1419 performance. 1420


1421 Whole building testing will use large fans (i.e., blower door tests) to determine the levels of 1422 leakage through the enclosure. Testing and remediation should be conducted to achieve the air 1423 infiltration rates specified in the OPR. Ideally, these are conducted at a point in time that allows 1424 for easy correction of the issue, such as before drywall is installed. 1425 1426 The results of the blower door test should be input into the as-built energy model for an accurate 1427 understanding of the energy loads. If the results of the blower door test do not meet the OPR 1428 criteria or contract requirements, specific leaks may be detected through the use of smoke 1429 testing and/or infrared thermography testing. The infrared testing will identify points of 1430 temperature differential at the building envelope, which typically correlate with points of 1431 infiltration. 1432 1433 Building Systems 1434 Building systems include HVAC, lighting, and renewable energy. Commissioning these 1435 systems involves testing the performance of the “active systems” of a building. Once the 1436 equipment has been successfully energized and started, the systems will undergo a series of 1437 tests, called functional performance testing (FPT) to determine if it is functioning as expected. 1438 1439 Buildings are subjected to a highly dynamic set of conditions that influence their performance 1440 including environmental conditions (seasonal) and internal conditions (fluctuating occupancy). 1441 The commissioning process attempts to replicate these conditions prior to occupancy, but it is 1442 not uncommon for follow-up commissioning work to occur as the seasons change to ensure 1443 performance in both heating and cooling seasons. 1444 1445 Indoor Environmental Quality 1446 Indoor Environmental Quality (IEQ) includes indoor air quality, lighting quality, acoustical 1447 performance, and thermal comfort. Commissioning of the indoor environmental quality (IEQ) is 1448 less common than enclosure or systems commissioning, but it is important to ensure that the 1449 zero energy building meets the environmental needs of the occupants. 1450 1451 Whereas systems and enclosure commissioning tests components and system performance, IEQ 1452 commissioning tests the outcomes of these systems’ performance from the perspective of the 1453 occupant needs. Testing should follow risk-based science for acceptable exposure and should 1454 include the following: 1455 1456

Indoor air quality: CO2, particulate matter, volatile organic compounds, formaldehyde, 1457 carbon monoxide, ozone, and radon. 1458

Lighting quality: brightness levels, contrast ratios, glare control, color quality, daylight 1459 efficacy 1460

Acoustical performance: HVAC noise criteria, reverberation time, sound transmission, 1461 sound amplification devices. 1462

Thermal comfort: air temperature, radiant temperature, thermal stratification, humidity, 1463 individual thermal comfort surveys. 1464

1465 MEASUREMENT AND VERIFICATION 1466 1467


The measurement and verification (M&V) period typically spans 12 to 24 months after 1468 substantial completion of the building. During this time, the CxA, design team, contractor, and 1469 energy modeler will work together with the owner to review the energy performance of the 1470 project. If anomalies are found between the expected performance from the calibrated model, 1471 and the actual performance, these should be identified and resolved. 1472 1473 Normal items that can cause a building to stray from the expected energy performance are 1474 associated with weather and use (i.e., occupancy patterns). A calibrated energy model inputs the 1475 actual data over a period of time to study if the building performed as expected. 1476 1477 The scope associated with measurement and verification is vital, but is often missed during the 1478 selection process. It’s important to discuss this scope with the team and identify who will be 1479 responsible for the tasks necessary to verify the building is on target to achieve zero energy and, 1480 if it is not, what the course of action is. 1481 1482 Every project should present a number of lessons learned. With zero energy projects in 1483 particular, it becomes important to document these. It is helpful to capture lessons learned and 1484 best practices from the zero energy design and use them to improve these standards. 1485 1486 Additionally, a number of publications and resources exist to support the greater adoption of 1487 zero energy practices and are always looking for excellent case studies. Development of case 1488 studies and lessons learned not only helps draw attention to the good work happening in zero 1489 energy design but it also provides valuable information to those districts that might seek to 1490 incorporate similar principles into their project. 1491 1492 POSTOCCUPANCY PERFORMANCE 1493 1494 Only after the project achieves a 12-month period of performance can it call itself a zero energy 1495 office building. However, it is important to continue to maintain the level of efficiency, if not 1496 improve on it year over year. As a result, successful projects often incorporate the following 1497 strategies: 1498 1499

Energy manager. Employ an energy manager to manage the performance of the building 1500 as well as serve as the resource to deliver continuous training and education to building 1501 occupants. 1502

Monitoring-based commissioning. This type of commissioning leverages software and 1503 connected devices to automate the diagnostic process during operations. These systems 1504 can identify anomalies in components or systems operating outside of their expected 1505 parameters. For example, if a pump that is supposed to vary its speed continuously runs 1506 at full speed for a few days, the system would identify it and notify the facility operator. 1507 This allows for the operator or CxA to address the issue quickly with minimal impact to 1508 the building’s energy performance. 1509

1510 ONGOING COMMISSIONING 1511 1512 Securing sufficient funds to maintain and operate buildings at optimal performance can often a 1513 challenge when having operational budget conversations. Sustaining zero energy performance 1514


and reducing energy consumption in the long term should be more important than saving money 1515 in the short term by reducing expenditures on maintenance. 1516 1517 Ensure that maintaining zero energy is included in the scope for the facility maintenance team if 1518 this service is outsourced. If the facility maintenance team is on-staff consider including 1519 performance bonuses for annual zero energy achievement. 1520 1521 REFERENCES 1522 1523 ASHRAE. 2013a. ANSI/ASHRAE Standard 169, Climatic Data for Building Design Standards. 1524

Atlanta: ASHRAE. 1525 ASHRAE Standard 202-2013 Commissioning Process for Buildings and Systems 1526 ASHRAE Guideline 0.2-2015 Commissioning Process for Existing Systems and Assemblies 1527 1528 ASTM E2813 - 12e1 Standard Practice for Building Enclosure Commissioning 1529 ASTM E2947 - 16a Standard Guide for Building Enclosure Commissioning 1530 1531 IFLI: International Living Future Organization, https://living-future.org/net-zero/certification/ 1532 1533 NREL 2010: Net Technical Report -Zero Energy Buildings: NREL/TP-550-44586 A 1534 Classification System Based June 2010 on Renewable Energy Supply Options 1535 (http://www.nrel.gov/docs/fy10osti/44586.pdf.) 1536 1537 UCLA School of Architecture and Urban Design (http://www.aud.ucla.edu/), Energy Design 1538 Tool (http://www.energy-design-tools.aud.ucla.edu/) 1539 1540 DOE DOE’s A Common Definition for Zero Energy Buildings available on the building page of 1541 the Office of Energy Efficiency and Renewable Energy on the DOE web site 1542 (https://energy.gov/eere/buildings/downloads/common-definition-zero-energy-buildings ) 1543 1544 1545 1546 1547 1548


Chapter 4: Building Performance Simulation 1549 1550 [Note to Reviewers: This chapter has been mostly copied from the K-12 ZE Guide. Input on 1551 appropriate changes for office buildings is requested.] 1552 1553 [Question for reviewers: What information on building performance simulation would be most 1554 helpful to the intended users of this guide (engineers, architects, design-building contractors, 1555 building owners and managers, building developers)?] 1556 1557 INTRODUCTION 1558 1559 Technological advancements have given designers the capability to access feedback almost 1560 instantly regarding the performance of their design. Within the context of a zero energy 1561 building, incorporating building performance simulation as a process is critical to optimizing 1562 the project design. 1563 1564 As a term, “building performance simulation” encompasses the numerous forms of 1565 computational simulation that may be conducted during the design process. “Energy modeling” 1566 is often referenced among designers and remains an accurate description of the simulation 1567 process used to study the energy performance of a building. However, high-performance 1568 buildings typically require other analyses to optimize the design. Some of the more common 1569 simulations cover lighting, daylighting, and natural ventilation strategies. While the energy 1570 impact of these design strategies is certainly of interest, particularly in a zero energy building 1571 (ZEB), it is not the only criteria that defines success. Lighting quality, thermal comfort, and 1572 indoor air quality are examples that should be modeled while meeting the energy goals. As a 1573 result, “building performance simulation” is a more accurate description for the process 1574 advocated in this chapter. 1575 1576 SIMULATION TEAM 1577 1578 Building performance simulation may be provided by engineering firms, architecture firms, or 1579 by dedicated specialists. Rather than focusing on which consultant should provide the 1580 simulation scope, it is more important to focus on the skill set and knowledge required to make 1581 appropriate and informed recommendations that result from the simulation process. A building 1582 should require analysis related to: 1583 1584

Climate 1585 Building Massing 1586 Energy 1587 Daylighting 1588 Lighting 1589 Mechanical systems sizing and selection 1590 Air movement 1591 Acoustics 1592 Heat and moisture migration 1593 Thermal comfort 1594

1595


The responsibility for modeling and evaluating the performance of the project in these areas will 1596 often be distributed among several team members as it is challenging for one person to be an 1597 expert in all areas. All of these factors can impact the energy performance and need thoughtful 1598 analysis during the design. Therefore, project leaders should ensure that their team has these 1599 capabilities available to support the design process. 1600 1601 SIMULATION TYPES 1602 1603 This chapter contains descriptions of simulations types used to evaluate and enhance design 1604 strategies that may be developed in response to performance targets set for the project. If the 1605 project is supported by a team capable of providing the capabilities noted in this chapter, then 1606 these performance targets represent the ideal outcomes that an iterative analysis should seek to 1607 achieve. 1608 1609 Analysis for zero energy buildings requires multiple instances of the energy model. Like a set 1610 of plans, the model follows the entire design process from conception through operations. 1611 These instances may include: 1612 1613

Baseline Model: typically used for comparison purposes. It represents a theoretical 1614 benchmark against which the proposed design can be studied. It can be used to calculate 1615 percent energy savings from “typical” design. As zero energy defines an absolute 1616 energy goal, baseline models are not necessary unless energy savings is needed for some 1617 other reason. It can also serve as a starting point for analysis as the code compliant 1618 building is the worst energy performing building that can be legally constructed. 1619

Design Model: intended to weigh trade-offs and evaluate strategies and features. These 1620 strategies are tested to determine the impact and progress towards meeting the goal. 1621 Ideally, this model is started at conceptual design and informs the form of the building. 1622 This model may not represent the final design as it may need to satisfy rules associated 1623 with showing code compliance. 1624

Predictive Model: While most modelers will try to satisfy the project needs with only the 1625 Design Models, the standards and codes to which they must adhere may require that 1626 they simulate aspects of the building that are not necessarily reflective of the actual 1627 project design. This model needs to meet the zero energy design goals including the 1628 renewable generation. It also includes passive strategies that are used to eliminate or 1629 reduce mechanical cooling requirements, or when the design team plans to use plug load 1630 reduction by selecting efficient equipment. The predictive model should match the final 1631 set of plans used for construction. 1632

Calibrated Model: created to reflect the most accurate set of conditions following 1633 construction and during the occupancy of the building. This should reflect as-installed 1634 equipment, as-tested performance information (such as enclosure leakage), and include 1635 actual weather and occupancy information. The calibrated model is ultimately used in 1636 the measurement and verification process to tune the building and ensure that it is 1637 operating properly. When deviations from actual performance exist, they can be 1638 compared against the calibrated model looking for issues to correct. 1639 1640

While the Baseline and Design models are common for most projects that incorporate building 1641 performance simulation, a Predictive and Calibrated model are critical for a zero energy project. 1642


As such, the inclusion of these models should be in the scope of the design. The model is a 1643 valuable tool to guide design and operational decisions for the entire life of the building and not 1644 just a code compliance tool. 1645 1646 SIMULATION PROCESS AND STRATEGIES 1647 1648 The value and appropriateness of simulation types varies based on the stage of the project. 1649 Simulations can provide data to make better decisions at critical steps in the design. The earlier 1650 the decisions are made, the less overall project cost is incurred. While it may take additional 1651 time up-front to prepare the simulation, these early decisions can streamline the design and 1652 operation of the building saving the project time as it unfolds. 1653 1654 Decisions from simulation, such as Form/Shape analysis are highly valuable at the early stages 1655 of a project. If left until later in the design process, such an analysis is unlikely to change the 1656 design. Likewise, certain studies, such as detailed plug load studies are probably more 1657 appropriate to analyze during the design development stage as equipment, audio/visual, 1658 information technology, and security needs have become more developed. These analysis 1659 should be done before HVAC is designed as it may inform the sizing and type of HVAC 1660 equipment. 1661 1662 The following section provides greater detail describing what is being analyzed, as well as 1663 where some opportunities may exist for a modeler to help provide valuable feedback to the 1664 design team. 1665 1666 CLIMATE 1667 1668 The location of the project dictates what climatic conditions represent opportunities or 1669 challenges. It is easier to achieve zero energy goals if the building uses the climate as a benefit, 1670 rather than working against the climate; therefore, thorough understanding of the site climate is 1671 a fundamental first step. Obtaining data from a weather station that reflects the local climate is 1672 a key starting point. If long-term weather data is available from the building site, it can also be 1673 used. When selecting a weather file, it is important to understand local climatic variations from 1674 that location. Ask local people about the weather patterns and confirm with data. Sometimes 1675 the best weather file is not the closest weather file. Mountains, canyons, bodies of water, and 1676 cities are examples of influences on micro-climates. 1677 1678 Projects with unique microclimate conditions may present additional challenges, particularly in 1679 the use of passive strategies such as natural ventilation or solar conditions. Review the available 1680 weather file(s) to determine if it is appropriately representative of the actual site conditions. 1681 (References: Olgyay, and Brown, DeKay) 1682 1683 Lastly, since the weather files use historical data, it may be worth considering future weather 1684 changes. Weather data files can be altered to test the sensitivity of building design elements 1685 into the future. An example may be a natural ventilation strategy may work for additional hours 1686 in a northern climate with higher ambient temperatures. 1687 1688


FORM AND SHAPE 1689 1690 A form and shape analysis examines the impact of the building’s geometry on the energy 1691 performance including the building energy consumption and energy production from 1692 photovoltaic systems. The building design team is able to quantitatively understand the total 1693 energy impact of many possible designs. The objective is to use the shape of the building to 1694 reduce the total energy loads. This information can add significant value to the overall 1695 discussion of which building form to select for the final building shape. 1696 1697 WINDOW-TO-WALL RATIO 1698 1699 Window to wall ratios (WWR) can be analyzed by applying increments in percentage of 1700 windows to the entire model, different façade orientations, or selected rooms. When applying 1701 the windows, the option to select the height, width, and spacing for the windows is available to 1702 create an accurate model. Windows can also be segregated into those that primary provide 1703 daylighting to offset electric lighting loads and view glass. 1704 1705 This study should reveal the optimum point between the increasing window to wall area ratio 1706 versus the change in energy usage and peak loads. Most models show that there is an energy 1707 minimum where daylighting provides the most benefit, yet solar gains are not excessive because 1708 of overglazing. Glazing types should be varied with respect to the solar heat gain coefficient 1709 (influencing solar gains), visible transmittance (influencing daylighting), and U-factor 1710 (influencing the heat transmission). For additional information on window-to wall ratios, see 1711 TBD in Chapter 5. 1712 1713 SHADING 1714 1715 Closely coupled to the window to wall ratio analysis is the shading analysis. In a building zone 1716 where the mechanical plant is primarily cooling a space, the modeler should analyze the impact 1717 of shading to reduce solar heat gains. While reducing the glass can help with this problem, 1718 overhangs can also be effective. Conversely, in a heating dominated climate, the modeler 1719 should review the impact of shading to ensure that it doesn’t adversely impact potentially 1720 beneficial passive solar heating. With a model, the length of the overhang can be determined 1721 such that it benefits the energy use as well as managing glare from the sun. 1722 1723 Take occupant comfort into account when performing a shading analysis or relying on solar 1724 gains for passive heating. Solar heat gain must be able to enter through the building skin and be 1725 absorbed into the building mass to be of benefit. If this heat gain is an occupied zone, occupant 1726 comfort could be compromised or shading systems could reduce the heat gain. 1727 1728 To be beneficial for passive solar gain, solar radiation cannot create excessive glare or 1729 overheating of spaces. Modeling can help determine this balance while using the solar gains to 1730 benefit the building. Sometimes, alternate technologies can help, such as Trombe walls. 1731 1732 Strategies related to shading techniques are discussed in Chapter 5. 1733 1734


ENVELOPE 1735 1736 The barrier between the outside elements and the indoors has a major impact on energy usage 1737 and peak loads. As the envelope’s insulating properties decrease, energy usage and peak loads 1738 increase. However, there is generally a point of diminishing returns between improvements to 1739 the building envelope reduction in energy use and peak loads. Since each building is impacted 1740 by many factors including form, climate, internal usage, and glazing; each building’s point of 1741 diminishing returns differs. However, the point of diminishing returns for each building can be 1742 found through careful analysis. 1743 1744 Simply comparing the insulation to the EUI may not tell the full story. At high levels of 1745 insulation, it may be possible to downsize or even eliminate mechanical equipment, which may 1746 justify greater levels of insulation. 1747 1748 By adjusting the constructions of the walls, roof, or windows in increments of one variable at a 1749 time, the calculated loads and simulations will show the optimal envelope values. Factors that 1750 should be analyzed include the construction assembly’s mass, R-value, and impact on building 1751 leakage. 1752 1753 A hygrothermal analysis may also be warranted, particularly with new or customized 1754 construction assemblies. The hygrothermal analysis will provide analysis of the heat and 1755 moisture migration through an assembly. This indicates potential condensation issues which 1756 could prematurely deteriorate the assembly and lead to biological growth. 1757 1758 Additionally, a hygrothermal analysis would indicate assembly surface temperatures. As the 1759 surface temperature influences occupant thermal comfort, this analysis can be utilized in 1760 conjunction with an ASHRAE 55 analysis to determine the impact of the studied assembly on 1761 occupant thermal comfort. This also includes thermal bridging analysis. Modeling thermal 1762 bridging is critical to examine compromises in the thermal envelope, especially when materials 1763 change. These are also locations where condensation is also likely to form. 1764 1765 USER BEHAVIOR 1766 1767 Estimating user behavior is an attempt to understand how a building occupant both react to their 1768 environment and also influence it with their active and passive behaviors. The objective is to 1769 mimic the occupant with operational schedules such that lights and HVAC are operated during 1770 “occupied” hours. It is a common fault of models that occupancy is underestimated which 1771 shows up in actual building operations as a building that uses too much energy. In addition, the 1772 number of occupants changes during the day and week, and this must be accounted for to 1773 properly model internal heat generated from the occupants. 1774 1775 Surveys and interviews with operations staff can be used to determine the actual building 1776 occupancy and schedules of use. Actual usage can vary substantially from the official operating 1777 hours, which affects the accuracy of the model. In addition to hours of operation, the way the 1778 maintenance staff operates a building has an impact on the energy use. The model should be 1779 aligned with the buildings specific operations policies as closely as possible. 1780 1781 EQUIPMENT SCHEDULES AND LOADS 1782 1783


Equipment schedules and loads are assumptions which help estimate the thermal gain and 1784 energy consumption. These includes plug loads, information technology, process loads, and any 1785 other load that is connected to an energy supply that is not HVAC or lighting. Equipment loads 1786 play a role in the calculation of room loads, while equipment schedules play an important part 1787 in estimating building energy usage. It is not unusual for these loads to be over half of the total 1788 energy consumption of the building. 1789 1790 Estimated equipment loads and schedules are provided in the ASHRAE Standard 90.1 User’s 1791 Manuals for different building types. When actual equipment loads are not available, these 1792 loads are considered acceptable substitutes; however, the model should be updated as the actual 1793 information becomes available during the design process. It is important to note that plug loads 1794 should not be considered unchangeable; modeling can show that reducing these loads can have 1795 a big impact on achieving the energy target. 1796 1797 Initial estimates for equipment loading and schedules help determine peak loads and energy use 1798 consumption. These values may be reduced through energy efficiency measures, but the longer 1799 this process is delayed, the more challenging it is to right size mechanical systems within the 1800 design schedule. For additional information on right sizing HVAC equipment, see TBD in 1801 Chapter 5. 1802 1803 LIGHTING 1804 1805 Building performance simulation should be used to help develop overall lighting strategies. The 1806 modeler should coordinate with the design team to evaluate the energy impact of appropriate 1807 lighting strategies, including lighting power density, illuminance levels, daylight harvesting, and 1808 other controls options. For more information on these metrics, see the Electric Lighting Section 1809 in Chapter 5. 1810 1811 NATURAL VENTILATION 1812 1813 If the project’s climate analysis indicates benefits to providing natural ventilation (including 1814 mixed-mode ventilation systems), further analysis may be required to determine the strategy’s 1815 impact on energy usage. 1816 1817 Modeling software has various levels of sophistication with regards to modeling natural 1818 ventilation. Determine the feasibility of using natural ventilation with the fastest, most 1819 reasonably accurate simulation methodologies first. to. Only after the strategy has been deemed 1820 feasible and worth pursuing should more sophisticated analyses, such as computational fluid 1821 dynamics (CFD) be considered. A CFD analysis is typically time consuming, and is a better 1822 strategy for optimizing the ventilation scheme, such as opening locations and sizes, rather than 1823 determining the feasibility of natural ventilation itself. Strategies related to Natural 1824 Ventilation are covered in Chapter 5. 1825 1826 INFILTRATION 1827 1828 Building performance simulation can be utilized to determine the merits of pursuing aggressive 1829 measures intended to reduce building air leakage. The modeler should discuss feasible air 1830 leakage rates with the design team, contractor and envelope commissioning agent, and model 1831 strategies against conventional approaches to determine the value of pursuing these strategies. 1832


1833 Actual, tested air leakage rates should be obtained from the commissioning agent and updated 1834 in the model to reflect the as-constructed conditions. See EN1 and EN2 in chapter 5 for more 1835 information on infiltration and air leakage control strategies. Additional information on air 1836 leakage testing is provided in the Commissioning during Construction section of Chapter 3. For 1837 design purposes, using leakage rates from previous buildings is a good start. See EN1 and EN2 1838 for more information on target leakage rates. This parameter can be varied and its impact on the 1839 overall energy target determined. If a tighter envelope is needed to meet the EUI target, then a 1840 strategy can be developed to achieve that performance goal. 1841 1842 DAYLIGHTING AUTONOMY AND GLARE ANALYSIS 1843 1844 An effective daylighting system is one in which the occupants don’t want the lights on. To 1845 achieve this level of effectiveness, detailed daylighting must be performed. Improvements in 1846 the efficiency of lighting technologies can reduce the impact of daylighting such that a balance 1847 of electric lighting and daylighting should be evaluated. This balance of lighting technologies, 1848 thermal performance of glass, and providing views may not fall within the capability of the 1849 simulation software utilized; but it is vital to the successful experience of the occupant. 1850 1851 Spatial daylight autonomy (sDA) is the desired metric to determine the accessibility occupants 1852 have to daylight on an annual basis. Additional information on these metrics is provided in 1853 DL3 in Chapter 5. 1854 1855 Glare analysis is the study of how the light levels impacting the space can have an effect on 1856 occupant comfort and ability to work. The data can be analyzed so that adjustments can be made 1857 to the building form, or shading in order to reduce glare levels, and increasing comfort for users. 1858 1859 RAY TRACE ANALYSIS 1860 1861 Ray tracing analysis is a daylighting analysis method which allows the user to see daylight 1862 levels over a period of time. 1863 1864 Ray tracing is done in a modeling program which allows designers to visually see how daylight 1865 changes over time in a space. This allows building designers to see how natural daylight levels 1866 will affect the users of the space, and when the space will need to be supplemented with 1867 artificial light. This allows the designer to alter the space to allow for more, or less, daylight 1868 levels to satisfy the occupant while using less energy. 1869 1870 HEATING AND COOLING LOADS 1871 1872 Heating and cooling loads, and the corresponding equipment sizing may be used as a proxy for 1873 energy performance. Larger heating and cooling plants will generally require more energy. 1874 Strategies that yield smaller plant sizes will also be found to reduce energy consumption. 1875 Therefore, analyses used to evaluate load reduction strategies should be included in the process. 1876 1877 A fundamental energy savings strategy is “right sizing” of mechanical equipment. Oversized 1878 equipment is responsible for energy waste. Therefore, it is important to align the calculated 1879 loads within the energy model and equipment sizing model if different software calculations are 1880


being performed. For additional information on sizing HVAC equipment, see HV3, HV8, and 1881 HV21. 1882 1883 MECHANICAL SYSTEMS COMPARISONS 1884 1885 A mechanical systems plant consists of the equipment that produce and distribute the heating 1886 and cooling such as: chillers, boilers, cooling towers, fans, and pumps. In this comparison 1887 process, multiple heating and cooling options are evaluated to determine the most effective 1888 solution for the project. 1889 1890 Plant comparisons help with effective decision making regarding the HVAC systems. The 1891 HVAC system components are the primary consumers of energy to create a conditioned space, 1892 however, they use energy in part because of plug loads, lighting loads, outside air requirements, 1893 and the building envelope. 1894 1895 1896 REFERENCES AND RESOURCES 1897 1898 Olgyay, Design with Climate (full reference needed) 1899 1900 Brown, DeKay; Sun, Wind, and Light (full reference needed) 1901 1902 CIBSE, AM10 Natural Ventilation in Non-Domestic Buildings (full reference needed) 1903 1904 NIST Report (full reference needed) 1905 1906 DOE Resource Page (full reference needed) 1907 1908 IBPSA (full reference needed) 1909 1910 AIA Guide to Modeling (full reference needed) 1911 AIA 2007: Integrated Project Delivery: A Guide, AIA, 2007, 1912 https://info.aia.org/SiteObjects/files/IPD_Guide_2007.pdf 1913 1914 1915 1916 1917


Chapter 5 How-to Strategies 1918 1919 There are many pathways to achieve a zero energy building, and more are becoming available 1920 as new technologies are developed. And, both renewable energy and existing energy efficiency 1921 technologies are advancing rapidly. This chapter outlines strategies to move a project towards 1922 zero, but success will come by finding synergies through the integrated design of all 1923 components that impact the energy consumption of the building. The objective is to achieve a 1924 low EUI target as specified in this Guide (see Table 3-1) and balance that with renewable 1925 energy. Even if renewable energy is only planned into a project, the decisions about energy 1926 efficiency will create a building ready for the future. Technologies are changing fast enough 1927 that prescribing a list of technologies will quickly become out of date and will not produce an 1928 economically competitive building to build. Many of the strategies needed to reach these low 1929 EUI targets are performance based, rather than prescriptive based, and the EUI targets are 1930 overall performance based targets. As a result, energy simulations play a key part in 1931 determining which technologies to use. 1932 1933 The differences between office size, construction classification, climate sensitivities, and 1934 regional practices make it impossible to address all the conditions that will be encountered in a 1935 typical office building project. The how-to information in this chapter is intended to provide 1936 guidance on strategies and good practices for achieving a zero energy office building. The 1937 guidance also includes cautions to help designers and other stakeholders avoid known problems 1938 and obstacles to energy-efficient construction. 1939 1940 Tables with recommended values are included throughout this chapter. These values may be 1941 used by designers and modelers as a starting point for zero energy projects. The strategies and 1942 recommendations for the chapter are summarized in Table 5-1 and include the corresponding 1943 how-to information and table numbers. The far right columns can be used to keep track of 1944 recommendations that building design is following ( column) and components that the 1945 building design doesn’t contain (X column). 1946 1947 [Note to Reviewers: This table will be filled in after the tips and strategies are finalized.] 1948 1949 Table 5-1 Summary of Strategies and recommendations 1950

Component How-to tips X

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1951 1952 BUILDING AND SITE PLANNING 1953 1954 OVERVIEW 1955 1956 Early phase design decisions have a profound impact on future building energy usage. With 1957 timely analysis and integrated planning, project teams can radically alter the trajectory for 1958 building energy usage by making smart and informed decisions which establish a solid 1959 framework for subsequent decisions and conservation measures. 1960 1961


During the early design phases, practitioners should employ a climate-responsive design 1962 approach that strives to design for efficiency while simultaneously satisfying or enabling the 1963 achievement of all project goals. The optimization process uses energy modeling and other tools 1964 to iterate design solutions and reconcile competing conservation measures. 1965 1966 SITE DESIGN STRATEGIES 1967 1968 BP1 Select Appropriate Building Site(s) 1969 There are many factors that affect the selection of potential building sites. These selection 1970 factors can be grouped into 2 categories: 1) Natural and 2) Human-made. each factor has 1971 evaluation criteria that influence the viability on whether the site is appropriate to support zero 1972 energy office building(s). Site Selection Factors should be evaluated for influence on building 1973 energy use and capability for renewable energy production. 1974 1975 Site Selection Factors include: 1976

1977 Natural Factors Human-Made Factors 1978 Topology/Terrain Parcel Shape 1979 Solar Exposure Adjacent Land Use 1980 Vegetation Zoning 1981 Climate/Micro Climate Transit 1982 Geology Regulations 1983 Soils Historic/Cultural 1984 Hydrology Utilities 1985 Ecologies Hazardous Materials 1986 Future Development 1987

1988 Some site factors directly influence design strategies and therefore affect building energy use or 1989 potential for renewable energy production. These factors should be prioritized when planning 1990 for a zero energy building. Include design professionals in the site selection process to discuss, 1991 evaluate, and determine all relevant considerations appropriately, including the opportunities 1992 and energy penalties associated with proposed sites. The ability to generate renewable energy 1993 sources such as solar, wind, geothermal, and water are influenced by Natural Site Factors. 1994 Building sites that are level or southward-facing are preferable to sites on slopes facing in other 1995 directions. Exposure for solar access should be evaluated for site generation potential and 1996 minimization of disturbing natural features. Be cognizant of the need to conserve and maintain 1997 Natural Features, forests, farmland, local ecologies, and undeveloped land parcels. 1998 1999 Where natural ventilation or wind power is desirable and reliable, climate and micro-climate 2000 assessments for each site should include a comparison of solar orientation and solar access, 2001 followed by wind speed and wind quality. Ideally, the local climate, solar access, potential 2002 shading issues would be studied as part of the site selection. Chapter 4 discusses modeling for 2003 climate analysis. Additional information on evaluating building sites for complete solar access 2004 is covered in TBD. 2005 2006 The site geology (rock types and depths), soils (types and properties), and hydrology (water 2007 above and below grade, and adjacent) to the site along with available site space will influence 2008 the viability for geothermal energy production or ground source heat dissipation or absorption. 2009

2010


Natural site features directly influence office building design strategies for energy use reduction 2011 and potential for renewable energy generation. Human-made factors such as access to transit 2012 and complimentary adjacent land uses can further reduce energy consumption beyond the 2013 building proper. 2014 2015 BP2 Optimize Building Siting Combined with Landscaping and Site Features 2016 Building siting is the practice of location, composition, and facing a building to maximize the 2017 positive site aspects and minimize the shortcomings. Siting must consider building orientation 2018 which is covered in TBD. Building siting and site features that should be considered or 2019 developed into an energy-efficient zero energy office building include the following: 2020 2021

1) Arrange building(s) on the site in a compact manner addressing solar access. 2022 Appropriate building site density allows open space for undisturbed natural site features 2023 and landscape. 2024

2) Plan for natural features 2025 a. Topology and Terrain 2026

i. For drainage: for sloped sites, halfway up the slope is preferred for 2027 drainage. For low slope sites consider natural drainage to minimize site 2028 disruptions and preparation. 2029

ii. Effect of landforms and plant forms on wind speed and wind quality, 2030 relative to natural ventilation and wind power 2031

iii. Beneficial effects of earth-berming on reduced cooling loads 2032 b. Solar Exposure 2033

i. Effect of landforms and plant forms on solar access and daylighting 2034 ii. Use of deciduous trees to provide beneficial shading of the sun in 2035

summer. But, be careful not to shade solar panels as trees grow to full 2036 height 2037

iii. Even when trees lose their leaves, shading from branches will impact 2038 passive solar gains as well as shade solar panels 2039

c. Wind and breezes: 2040 i. Use of dense evergreen trees and landscaping to reduce undesirable 2041

winter winds, which will reduce building infiltration 2042 ii. Use of trees and landscaping to funnel desirable breezes toward a 2043

building for cooling or ventilation 2044 iii. For sloped sites, cool or night – time air flows down. For low slope sites 2045

identify predominate wind direction to determine whether to incorporate 2046 or mitigate in the design. 2047

iv. Beneficial effects of plant-based evapotranspiration on thermal comfort 2048 d. Hydrology (Water) 2049

i. Proximity of water bodies to provide beneficial changes in temperature or 2050 humidity to the immediate microclimate 2051

ii. Proximity of water bodies for discharging heat 2052 e. Soils 2053

i. Thermal conductivity of the soil as it relates to the potential of ground-2054 source heating and cooling systems 2055

3) Plan for Human-made features 2056 a. Site access and parking: locate close to streets access and design to be pedestrian 2057

friendly. 2058


b. Hard surfaces: surfaces such as pavement can get hot. Consider the local climate 2059 and material use (pervious or impervious) in conjunction with solar heat gain and 2060 heat radiation. 2061

2062 2063

[FIGURE TO BE ADDED] 2064 2065

Figure BP-1 Site Analysis Diagram 2066 2067 BUILDING MASSING 2068 The articulation of a building’s physical form can affect energy use in many different ways 2069

2070 BP3 Optimize Surface Area to Volume Ratio 2071 Both energy use and building first costs are correlated to the efficiency of a building’s massing, 2072 which can be measured by the ratio of surface area (envelope) to volume, also known as the 2073 shape factor A/V (area to volume). The efficiency can also be measured by the ratio of surface 2074 area to floor area, known as shape factor A/A (area to area). 2075

2076 The reason to consider shape factor is because it quantifies the area of envelope compared to the 2077 quantity of conditioned space. The envelope is a source for a variety of thermal loads to the 2078 perimeter zones of the office building including heat gain and heat loss via transmission, 2079 infiltration through the envelope, and solar heat gain via windows. In this case, the envelope is 2080 an energy liability and by reducing the envelope area to a given area of conditioned space the 2081 envelope loads can be reduced, therefore saving energy. A sphere has the smallest ratio of 2082 surface area to volume. In more practical building terms, a cube has the smallest ratio and 2083 would minimize thermal losses through the building envelope. Also, multiple-story buildings 2084 have less roof area and therefore a more compact shape. It can also be beneficial to consider 2085 novel three-dimensional shapes, which can be designed so that the building is self-shading. 2086

2087 The envelope is also the interface for passive strategies such as natural ventilation and 2088 daylighting (refer to other tips). In this case, the envelope is an energy asset. By increasing the 2089 envelope area to a given quantity of conditioned space, more space can be passively 2090 conditioned, therefore saving energy. Refer to TBD for more information on climate-responsive 2091 shapes. 2092

2093 To optimize the shape factor is to balance the benefits of reducing envelope thermal loads and 2094 increasing passive conditioning capacity, or climate-responsiveness. Compact and climate-2095 responsive shapes each have their pros and cons, which must be weighed for each project. 2096 These are listed below and illustrated in Figure BP-2. 2097

2098 Compact Shape Pros 2099 Often effective in cold climates such as 7 and 8. 2100 Reduced quantity of envelope results in reduced heat loss and heat gain via transmission. 2101 Reduced quantity of envelope can reduce construction cost. 2102 Small compact footprints can still be effectively daylit and naturally ventilated. 2103 2104 Compact Shape Cons 2105


West and east facades are equal in area to other facades and represents a significant 2106 liability for solar heat gain when glazed. 2107

Large compact footprints are challenging to daylight and naturally ventilate. 2108 2109 Climate-Responsive Shape Pros 2110 Often effective in milder and warmer climates. 2111 All sizes of offices can be effectively daylit and naturally ventilated. 2112 More spaces can have access to views. 2113 Elongated east-west shapes have a reduced west and east façade areas and increased 2114

south and north façade areas offering effective opportunities for significant solar control. 2115 2116 Climate-Responsive Shape Cons 2117 Increased quantity of envelope results in increased heat loss and heat gain via 2118

transmission. However, strategically increasing the thermal performance of the envelope 2119 can effectively minimize this liability. 2120

Increased quantity of envelope can increase construction cost. 2121 2122 2123

2124 2125

Figure BP-2 Pros and Cons of Compact and climate-responsive shapes 2126 2127

With the above pros and cons in mind, there is a unique opportunity for climate-responsive 2128 shapes in cold climates. By designing 100% passively cooled buildings in climates with low 2129 summer time temperatures, the mechanical cooling can be eliminated from the project. This 2130 allows for a reduction in first cost and a reduction in overall energy use – a potential winning 2131 strategy for a zero energy building. Figure BP-3 is an example of this strategy in use. 2132

2133 2134

[IMAGE TO BE ADDED of RMI’s Basalt office] 2135 2136

Figure BP-3 RMI’s office in Basalt, Colorado 2137 – Climate Responsive Shape in Cold Climate 2138

2139


It is also important to consider an office building’s program and site when evaluating shape 2140 factor. First consider if the office building’s program is friendly to passive strategies or can be 2141 made passive friendly. Can the offices be open, rather than private? Open office environments 2142 are easier to naturally ventilate and daylight. Will the occupants be engaged in using operable 2143 windows and daylight to meet their indoor environmental needs? They may be responsible to 2144 operate the windows and/or control the interior blinds in conjunction with weather conditions 2145 and indoor environmental needs. (Refer to related PBs) 2146

2147 Next consider if the office building’s site is friendly to passive strategies. Does the site have 2148 access to daylight and to useable outdoor air flows? Are there sources of exterior noise or poor 2149 outdoor air quality that would limit the application of natural ventilation? (Refer to related PBs) 2150

2151 BP4 Climate-Responsive Building Shape 2152 Where a climate-responsive approach dictates, configure buildings as elongated rectangles, or as 2153 a series of such rectangles. These elongated rectangles have a narrow plan depth to permit cross 2154 natural ventilation and full daylighting. In very climate-responsive office buildings these floor 2155 depths can be as low as 30 feet or as high as 60 feet. These elongated rectangles need to be 2156 oriented properly, typically 20° plus-or-minus of east/west for the elongated axis (See BP9). 2157 The resulting shapes are sometimes referred to as “letter buildings” and resemble the shapes of 2158 letters such as C or E or H, etc. as shown in Figure BP-4. 2159

2160

2161 Figure BP-4 Letter Building Shapes 2162

2163 BP5 Minimize and Shade Surfaces Receiving Direct Solar Radiation for Cooling 2164 Minimize surfaces receiving direct solar radiation, especially during the cooling season. 2165 Prioritize the reduction of direct solar on glass, because of the direct solar gain in the space. But 2166 opaque envelope assemblies in hot climates can also benefit from shading or solar reflectance 2167 because of the sol-air temperature effect. Prioritize the control and reduction of orientations that 2168 receive the highest solar gains during the cooling season. Horizontal surfaces (roofs) receive the 2169


most solar radiation, which can be problematic for horizontal components of skylights, but also 2170 for roofs in hot climates. West facing facades receive the most solar radiation compared to 2171 south, east or north orientations and a good solar control strategy would be to eliminate or 2172 significantly reduce west glazing. (See Figure BP-5.) 2173

2174 [Note to Reviewers: The plan is to create graphs showing average annual solar radiation per 2175 orientation for each climate zone – similar to below, but perhaps simpler. Feedback on this 2176 concept is appreciated.] 2177

2178

2179 Figure BP-5 Average Annual Solar Radiation by Orientation 2180

2181 There are a variety of ways to provide shading for glazing and other envelope components 2182 including overhangs, shade structures, screens, double-skins, exterior blinds, landscaping and 2183 any number of imaginable solutions. To understand the effect of combining solar shading and 2184 solar heat gain coefficient (SHGC) for glazing refer to EN#. Shading also plays a significant 2185 role in daylight design and glare control. (Refer to DL#) Examples of shading strategies are 2186 shown in Figure BP-6. 2187

2188 2189

[PHOTOS TO BE ADDED showing examples of shading strategies] 2190 2191

Figure BP-6 Shading Strategy Examples 2192 2193

BP6 Avoid Reflected Solar Glare 2194 Unwanted solar reflection can come from many different sources and is often unavoidable. 2195 Building massing strategies that inadvertently reflect radiation from one part of a building to 2196 another should be avoided. In addition, avoid creating a situation where the new building causes 2197 a reflection problem on another building. 2198


2199 As an example, where a lower building volume is located on the southern side of a higher 2200 building volume, reflective roof or terrace surfaces below will reflect radiation into the higher 2201 portions of the building—likely giving rise to overheating, uncontrollable glare, and visual dis- 2202 comfort. This can also be a common problem with buildings with narrow courtyards and solar 2203 reflections from glazing on one building wing being reflected into another wing. 2204

2205 Reflected light can be beneficial for interior daylighting if effectively managed. Ensure that the 2206 reflecting surface is not generally visible to the building occupant. 2207

2208 BP7 Optimize the Building for Natural Ventilation 2209 Design building massing to make beneficial use of the wind for natural ventilation. In many 2210 climates there are significant time periods during which natural ventilation can play a role in 2211 cooling and bringing fresh air to offices and other spaces. See HV# for additional information 2212 on natural ventilation and mixed mode integration with HVAC systems. 2213

2214 As noted in BP3, providing a narrow depth floor plan (high surface area to floor area) and an 2215 open office environment are key first steps for integrating natural ventilation. Consider the 2216 variety of techniques for inducing natural ventilation through a space. Cross-ventilation is a 2217 common strategy that moves outside air through a space due to the pressure differential of the 2218 windward side (intake) and the leeward side (discharge). Stack-ventilation moves air through 2219 buoyancy created by a temperature difference, with air moving upward from cooler to warmer 2220 temperatures. This can be accomplished through the use of atriums, ventilation towers, or 2221 similar vertical openings, allowing outdoor air brought in from windows to move through the 2222 office space and discharged at the top of the atrium. The use of a solar chimney, which 2223 strategically uses solar radiation to further increase the temperature at the top of the discharge 2224 point, can increase the effectiveness of stack ventilation. Note that even low windows on the 2225 windward side and high windows on the leeward side can induce some stack, which can be 2226 effectively combined with cross-ventilation. A less effective, but still useable technique, is 2227 single sided ventilation which uses a high and low window on the same exterior wall to 2228 ventilate a shallow space, such as a private office. 2229

2230 Design guidance for natural ventilation can be found in a number of industry resources and 2231 technical reference books, including CIBSE’s Application Manuals, “AM10 Natural Ventilation 2232 in Non-Domestic Buildings (2005)” and “AM13 Mixed Mode Ventilation (2000).” Design for 2233 natural ventilation can be assisted with the use of modeling including computational fluid 2234 dynamics (CFD) and bulk air flow modeling. CFD modeling can provide detailed analysis of 2235 air and heat flows within a space for a specific scenario. Bulk air flow modeling provides a 2236 broader view of natural ventilation design and quantifies annual hourly air flows in and out of 2237 windows and between spaces. 2238

2239 Caution: Considerations need to be made for ambient exterior noise levels, outdoor air quality 2240 (EPA’s National Ambient Air Quality Standard), outside air temperatures, humidity, operable 2241 window air leakage, pest and allergens. 2242 2243 BUILDING ORIENTATION 2244

2245 BP8 Optimize Orientation 2246


Building orientation is the practice of locating a building and its associated shape, massing, and 2247 volume to maximize certain aspects of its surrounding site ranging from views (interior and 2248 exterior), visibility from public ways, and to capitalize on Natural Factors such as topography, 2249 solar access, wind patterns, and water use/conservation. Orientation influences passive and 2250 active solar design considerations such as daylighting, shading, and thermal mass as well as 2251 solar “view corridors” for onsite energy generation. These criteria should also be considered for 2252 hardscape and landscape features. Office building design is iterative and while traditionally 2253 driven by interior layouts and building floor plate efficiencies, siting and orientation are critical 2254 design parameters. Building energy use varies directly with building orientation, and orientation 2255 should be optimized during the early design process. Strategies for orientation relative to the 2256 solar path are well-understood; however, a comprehensive optimization also considers the 2257 effects of prevailing and seasonal winds relative to energy consumption without neglecting 2258 concerns relative to exterior borne noise and acoustics and reverberation time. Figure BP-7 2259 illustrates the effect of solar path on a building. 2260

2261 For optimal solar orientation in all climate zones in the Northern Hemisphere, select building 2262 sites and orient the building such that a rectangular footprint is elongated along an east-west 2263 axis. Solar azimuth and altitude vary depending on the time of the year. In the summer the sun 2264 rises slightly north of east and sets north of west and in the winter rises slightly south of east 2265 and sets south of west. Depending on the geographic location and the local climate the variation 2266 of the east-west axis can vary up to 20 degrees off of the east-west axis. This orientation 2267 achieves the following: 2268

2269 Minimizes unwanted and difficult-to-control radiation on the east- and west-facing sur- 2270

faces 2271 Maximizes access to beneficial solar radiation on the south side and diffuse sky 2272

conditions on the north side 2273 Facilitates shading strategies on the long, south-facing surface 2274 2275

For buildings where extensive east-west exposure is unavoidable, more aggressive energy 2276 conservation measures may be required in other building components to achieve energy goals. 2277

2278 Another Natural Factor to consider in orientation is prevailing breezes. Orientation considering 2279 wind direction can benefit from summer breezes for cooling and shield adverse winds in winter. 2280 Cold winds generally originate from the north and west, while coastal locations generally 2281 experience on shore flows. Orientation should consider the site climate micro climate wind 2282 directions per season. Figure BP-8 illustrates the effect of prevailing breezes on a building. 2283

2284 2285


2286 Figure BP-7 Effect of Solar Path on a Building 2287

[Note: Figure will be updated] 2288 2289

2290 Figure BP-8 Effect of Prevailing Breezes on a Buidling 2291

[Note: Figure will be updated] 2292 2293

BP9 Fenestration Orientation 2294 In most climate zones, windows should be located in south-facing surfaces, where solar 2295 radiation is readily controlled with proper overhangs; however, low-angle winter light may be a 2296 problem in northern climate zones with glare concerns. Openings in east- and west-facing walls 2297 should be optimized through iterative energy simulation as this radiation is very difficult to 2298


manage. Glare and summer heat gains are the predominant issues, and the typical solar control 2299 measure of overhangs are limited in their value. (See also TBD.) 2300

2301 North-facing fenestration can be used in all climate zones, but glazing specifications should be 2302 optimized and differentiated from glazing facing other directions. North-facing fenestration is 2303 ideal for daylighting and avoids solar heat gains. For information on glazing specification see 2304 the building fenestration section later in this chapter, specifically EN#. 2305

2306 Daylighting, ventilation, and potential heat gain should all be studied with energy simulations to 2307 properly size windows and specify the window glazing type. Fenestration orientation should be 2308 optimized through an iterative energy simulation process. 2309 2310 BUILDING DESIGN STRATEGIES 2311

2312 BP10 Integrate Programmatic Elements for Minimal Energy Use 2313 The manner in which building programmatic elements are arrayed, stacked, or otherwise 2314 aggregated can affect building energy usage. Strategies can vary greatly by climate zone, so 2315 early phase energy modeling is critical to understanding how zoning actually affects energy use. 2316

2317 The prototype medium size office building is composed as a speculative core and shell 100,000 2318 gross sq. ft. rectangular floor plate with a center core. The floor plate configuration can support 2319 either a single full floor tenant or multi-tenant office spaces. The only variant will be the use of 2320 an exit access tenant corridor for the multi-tenant arrangement that connects the two life safety 2321 egress stairs. 2322

2323 The center core consists of three passenger elevators (one is a swing cab for service), two life 2324 safety egress stairs that can be used as communicating stairs between floors, women’s and 2325 men’s toilet rooms, mechanical heating/cooling spaces (not sure yet if these are shafts or air 2326 handling units with supply/exhaust shafts), electrical risers and distribution rooms/closets, and 2327 telephone/information technology risers and distribution rooms. 2328

2329 The office lease space(s) consist of a nominal 42ft 6in lease span on all sides of the building 2330 floor plate. For the multi-tenant floor configuration, the exit access tenant corridor is sized as 5ft 2331 0in wide connecting the 2 life safety egress stairs. 2332

2333 The floor to floor height is 15ft 0in. The structural depth of the floor/beam assembly will be 2334 between 2ft 0in to 3ft 0in depending on the use of concrete or steel with composite 2335 concrete/metal deck. Fire protection sprinklers are light hazard and will be contained within the 2336 structural depth for vertical planning and design purposes. 2337

2338 Office uses within tenant spaces consist of open office work stations, private offices with 2339 partitions, conference/meeting rooms, coffee/break rooms, support spaces/office services/mail 2340 room, and a reception area. 2341

2342 BP11 Office Use Considerations 2343 Office layouts are not a one size fits all mentality. The current trend in office design is for 2344 flexible work spaces and community gathering spaces. Each type of tenant use – legal, 2345 financial, technology, medical and others will have different mixes of open and private offices. 2346 Office layouts go in and out of fashion and each tenant type has unique tendencies. The goal is 2347


to create a work environment that supports the goals of the tenant and supports energy 2348 efficiency in layout. 2349

2350 Either use historical as previously provided or see if the EUI is influenced by: 2351 1) Open office (low partition-say 5’-0” high) 2352 2) Open office (no partition) 2353 3) Enclosed offices (full height all opaque) 2354 4) Enclosed offices (full height/opaque perpendicular to the perimeter and transparent 2355

parallel) 2356 5) Conference/meeting rooms (side walls opaque-wall towards interior as glass) 2357 6) Coffee/break room (side walls opaque—wall towards interior as glass) 2358 7) Mail rooms (all opaque walls) 2359 2360

B12 Provide Entrance Vestibules 2361 Entrance vestibules are a technique to reduce air infiltration from people entering and existing 2362 the building. Vestibules should be considered on any doorway that is frequently used. Consider 2363 the following strategies for vestibules: 2364

2365 Orientation and Configuration. Orient vestibule openings to avoid unwanted infiltration by 2366 prevailing winds. The inner and outer doors in vestibules are generally oriented inline, for 2367 optimal pedestrian flow. Where practicable, configure the inner and outer doors at right angles 2368 to one another to further limit air infiltration during operation. 2369

2370 Vestibule Depths. Vestibule depths are generally a function of safe and accessible ingress and 2371 egress. Deeper vestibules offer the advantage of improved indoor environmental quality as they 2372 increase the walk-off surface available and in turn reduce the amount of dirt and moisture 2373 introduced to the interior. Deeper vestibules also offer the co-benefit of limiting the instances of 2374 simultaneous opening of inner and outer doors during passage. Vestibules that are 10 ft or more 2375 in clear inside depth are recommended. 2376

2377 Vestibule Construction. Configure vestibules such that the air, water, vapor, and thermal 2378 barriers are continuous from one side of the vestibule to the other (and from top to bottom), 2379 through the outer vestibule envelope, including openings. The inner vestibule envelope should 2380 be treated with equivalent concern for airtightness and insulation levels. This includes the door 2381 weather stripping. Fenestration in the inner vestibule envelope can generally be selected for U- 2382 factors equivalent to the exterior glass. SHGC values are not typically critical for the inner 2383 envelope glazing. 2384

2385 Vestibule Conditioning. The vestibule should be a semi-heated space and not mechanically 2386 heated to above 45°F. 2387

2388 BP13 Use Automatic Doors Appropriately 2389 Automatically operating doors (including “ADA doors” with push-button actuators) can be of 2390 great functional benefit when used appropriately. Automatic doors use additional energy, add 2391 construction costs, and can prove an impediment to daily use when not properly maintained or 2392 adjusted for non-automatic use. For these reasons, automatic doors should be selected and 2393 deployed with discretion, and the number of automatic doors provided should be limited to the 2394 quantity that is functionally necessary. Where automatic doors are specified, low-energy options 2395


are available in the marketplace. Capabilities of full-powered versus low-energy options should 2396 be examined to ensure the right choice is made with respect to end usage. 2397

2398 Be aware of applicable accessibility requirements and evaluate the energy use of automatic 2399 doors in relation to their use as component of a universal design (universally accessible) 2400 approach. 2401

2402 Where automatic doors are used in series at an exterior vestibule, ensure that the doors are 2403 controlled separately, or are otherwise programmed for asynchronous opening. 2404 2405 Vestibule doors should not be propped open as this defeats the purpose of the vestibule. 2406

2407 PLANNING FOR RENEWABLE ENERGY 2408 2409 BP14 General Guidance 2410 While other forms of renewable energy exist, solar systems or photovoltaic (PV) systems are 2411 the most prevalent and work in most building locations. PV systems are composed, in part, of 2412 PV panels or arrays. Ideally, the PV arrays are located on the roof to minimize the overall 2413 footprint. Planning for the array must begin with project conceptualization to ensure that an 2414 adequate roof area is reserved for renewable energy generation. A more detailed discussion on 2415 the use of PV is provided in the renewable energy section later in Chapter 5. 2416

2417 Other renewable technologies such as, but not limited to, wind power and micro-hydro- electric 2418 generation, may make sense in some regions or on some specific sites. Wind power should be 2419 evaluated for noise considerations. Wind power can be attached to the building, but structural 2420 and vibration considerations must be designed into the system. In addition, the energy 2421 generation from micro wind turbines is very low. Wind power does not scale down effectively 2422 as energy generation from wind is a function of the rotor diameter square and the wind speed 2423 cubed. 2424

2425 BP15 Roof Form 2426 PV panels may be mounted on flat roofs or pitched roofs. For pitched roofs, the slope should be 2427 within 30° of south to maximize the solar production. Single-sloping shed roofs are preferable 2428 to gable roofs since large portions of gable roof will have limited or no solar access. As panels 2429 will likely be mounted directly to the pitched roof, the pitch of the roof is critical. As a rule of 2430 thumb, the pitch should be approximately equal to the latitude. While there is an optimal angle 2431 for solar production, variations in roof pitch are not significant. In general, pitches should be 2432 maintained between 10° and 50°. Solar calculators can be used to estimate the production. 2433

2434 Flat roofs provide a lot flexibility for laying out PV arrays. The traditional method is to install 2435 roofs of south facing modules. This can optimize the energy generation of each module. 2436 However, the rows will require spacing so that the modules do not shade the row behind it. The 2437 spacing becomes larger as the tilt of the panel is increased. This installation method doesn’t 2438 optimize the energy generation for a given roof area, and for zero energy offices the area of roof 2439 for PV is often a constraint. An effective compromise is to layout modules on a dual tilt 2440 configuration with opposing modules facing east and west (see Figure BP-9). This prevents 2441 module self-shading, provides a higher power density per roof area, and is still relatively 2442 efficient for individual module energy generation. 2443

2444


2445 2446

Figure BP-9 Solar Panel Layout Options 2447 2448 2449 BP16 Determine Required Roof Area for PV 2450 Based on the modeled data developed by NREL, the approximate roof area needed for PV panel 2451 installation can be calculated in each climate zone (Torcellini et al. 2017). This area should be 2452 confirmed during the planning stages for the specific goals, project, and climate zone. 2453

2454 Table 5-2 indicates the required area for the two modeled office types in each climate zone. The 2455 area indicated in Table 5-2 represents the required PV collector area, which needs to be 2456 multiplied by a factor of 1.25 to account for spacing, aisles, and other installation requirements 2457 found on a typical office project. The table demonstrates that in most climate zones, for offices 2458 over two or three stories, it will be exceedingly difficult to achieve zero energy with only roof- 2459 top solar. 2460

2461 Caution: Individual projects may need to adjust the upgrade factor to account for the elements 2462 on the roof and how they are configured. 2463

2464 Early in the project, verify the goals relative to the PV area required for a zero energy office. 2465 Recognize that a building roof is never 100% available for PV; space is required for roof access, 2466 toplighting, plumbing vents, rooftop equipment that cannot be located elsewhere, and other 2467 miscellaneous elements. It is possible to arrange these elements to maximize the PV area, 2468 sometimes approaching 80% of the roof area. (See BP20.) 2469 2470 [Note/Question for Reviewers: The following table will be updated with office energy modeling 2471 results. The committee wouldlike to know if it would be useful to add the EUI target for each 2472 case.] 2473 2474 Table 5-2 PV Percent Area of Gross Floor Area 2475

Climate Zone Small Office* Medium Office*

0A 0B 1A 1B 2A 2B 3A 3B


Climate Zone Small Office* Medium Office*

3C 4A 4B 4C 5A 5B 5C 6A 6B 7 8

* Note: Table percentages are for the PV only and do not include the upgrade factor for 2476 aisles and other elements on the roof. 2477

2478 [Note to Reviewers: The following example calculations are placeholders and will be edited 2479 with data from the updated table for the next review.] 2480 2481 Using Table 5-2, the required percent of roof area required for PV can be calculated as follows: 2482

2483 Gross floor area × PV area % (Table 5-2) × upgrade factor = roof area required for PV Roof 2484 area required for PV / gross roof area = percentage of roof area needed 2485

2486 The calculations for a 2-story, medium office in climate zone 5B, are as follows: 2487 Gross floor area = 100,000 ft2 2488 Gross roof area = gross floor area / stories = 100,000 / 2 = 50,000 ft2 2489

2490 PV area % (from Table 5-2) = 20% Upgrade factor = 1.25 2491 Roof area required for PV = 100,000 ft2 × 0.20 × 1.25 = 25,000 ft2 2492 Percentage of roof area needed = 25,000 ft2 / 50,000 f ft2 = 50% 2493 2494 Some projects will not have the required roof area available for the PV system size needed for 2495 zero energy. Possible resolutions for this scenario include the following: 2496

2497 Lower the target EUI for the project 2498 Specify a higher-efficiency PV panel/system 2499 Supplement the rooftop array with a parking canopy array, a ground-mounted array or 2500

other form of on-site renewable energy. 2501 Reevaluate the massing and roof area assumptions to increase the building roof area 2502

(while simultaneously analyzing increased envelope loads and construction costs 2503 resulting from less efficient building massing) 2504

Perform a more detailed analysis that looks at available roof area and production needs 2505 2506

Additional information on specifying PV systems is provided in the renewable energy section, 2507 including tools to fine-tune the PV output based on orientation and module selection. 2508

2509 BP17 Maximize Available Roof Area 2510


Building infrastructure and building systems should be conceived in a coordinated way that 2511 minimizes the amount of rooftop equipment and number of roof penetrations. Toplighting 2512 strategies need to be balanced with project goals and weighed against the need for maximizing 2513 the area for renewables. For example, conventional toplighting approaches sacrifice roof area 2514 and reduce the rooftop solar capacity. Where sufficient daylighting can be provided from 2515 building vertical surfaces, roof area can be effectively dedicated to renewable generation. In 2516 general, the most cost-efficient PV systems have large areas of contiguous panels. 2517

2518 Consider the following strategies for maximizing available roof area: 2519 2520 Minimize rooftop daylight monitors. Monitors occupy valuable space and cast shade on 2521

adjacent roof areas, so use them sparingly and for maximum impact. Consider north- 2522 facing monitors so that the monitor roof can be used for PV mounting. Use the lowest 2523 height monitors practicable to avoid shadows. 2524

Use tubular daylighting systems strategically. As with monitors, deploy in critical or 2525 high- impact areas. Consider clustering units and relying on the flexibility of the light 2526 tubes to direct light to the locations needed. Arrange units such that they fit in between 2527 modules. 2528

Limit or avoid skylights, which, in addition to the concerns noted above, also increase 2529 cooling loads. 2530

Require rooftop coordination drawings from the construction team, starting with the 2531 solar shop drawing and including all equipment, penetrations, roof drains, and other 2532 miscellaneous items. Adjust items to maximize the solar panel locations. 2533

Avoid rooftop equipment to preserve roof space and to avoid shadows. Locate 2534 equipment on the ground, in mechanical rooms, in ceiling spaces, or in attics. Note that 2535 this strategy frequently necessitates the dedication of greater floor areas to mechanical 2536 spaces. This is also a preferred solution for maintenance personnel for improving 2537 serviceability of the equipment, which increases its overall service life and efficiency. 2538

Avoid rooftop intakes and exhausts. Relocate to walls, if possible. 2539

Evaluate strategies for aggregating equipment and aligning equipment installations to 2540 minimize disruptions to the PV layout. 2541

Coordinate equipment locations to fall along edges of or aisles between PV arrays, to 2542 minimize disruptions to the PV layout. 2543

Locate equipment in locations shaded by other building or site features that could not be 2544 otherwise used for efficient PV generation. 2545

Locate equipment items on the northern edge of roofs, or in other locations that will not 2546 cast shade on the PV installation. 2547

2548 BP18 Roof Durability 2549 Because the panels will generally rest on top of the roof surface and preclude easy roof 2550 replacement, specify the most durable roofing the project goals can support. To host a solar PV 2551 system, a roof must be able to support the weight of PV equipment. 2552

2553 Also important is determining whether the roof installation carries a warranty, and if the 2554 warranty includes contract terms involving solar installations. Consider roof warranties that are 2555


at least as long as the life expectancy of the PV array and be aware of the factors that distinguish 2556 roof durability and roof warranty (which are not always synonymous). 2557

2558 Consider including third-party roofing inspectors on the commissioning team to ensure roof 2559 installation quality and reduce the need for roof repairs after the PV installation is completed. 2560 Other considerations include: 2561

2562 Access. Provide walk-out or stair access to all roof areas with PV system components, 2563

whether code-required or not. 2564

Weight. Incorporate the PV system weights into the structural assumptions for the roof 2565 areas—even when an array is not expected to be installed immediately. A common 2566 assumption for solar array weight is 3 to 6 lb/ft2. 2567

Usage. Develop planning assumptions for any roof areas that will be occupied for the 2568 system demonstration or study. Areas intended for occupancy require greater structural 2569 capacity. 2570

Wind Loads. Analyze wind loads to ensure the roof structure and PV equipment are 2571 rated to withstand anticipated wind loads. 2572

2573 BP19 Roof Safety 2574 Be aware of applicable code requirements, fire department access requirements, and worker 2575 safety regulations. Any required guardrails or guarding parapets will cast shade and thus 2576 directly affect the location and placement of PV collectors. Conversely, roofs without guards or 2577 parapets will need to maintain significant clear areas around roof edges and will thus sacrifice 2578 roof area that could be otherwise used for solar-electric generation. 2579

2580 The renewable energy section later in this chapter provides technical recommendations for PV 2581 planning and installation. 2582

2583 BP20 Maintain Solar Access 2584 Pay particular attention to the many instances of conventional practice that sacrifice solar access 2585 and in turn reduce the production of solar electric power. Even small amounts of shading can 2586 reduce the output from solar PV systems, so locate the building and PV array to be entirely clear 2587 of shade from adjacent site features and surrounding vegetation, particularly on the south-facing 2588 side of the building. Note the following strategies: 2589

2590 Always calculate and analyze the solar path diagram, especially when working in 2591

unfamiliar locations. Pay particular attention in latitudes between the equator and 23.5° 2592 north (in the northern hemisphere) where direct sun will come entirely from the north for 2593 part of the year. 2594

Anticipate the buildable envelope of adjacent parcels. Secure solar easements or locate 2595 PV arrays entirely clear of the projected shade path. 2596

Anticipate the maximum/mature height of trees. Locate PV arrays entirely clear of the 2597 worst-case projected shade path. Do not rely on deciduous trees having dropped their 2598 leaves—plan the building/array location to receive unobstructed winter sun. 2599

Avoid towers, chimneys, or other appurtenances on the building that would impede solar 2600 access. 2601


Avoid shade thrown by parapets, monitors, stairwells, mechanical equipment, and other 2602 rooftop items. 2603

2604 REFERENCES 2605 2606 EPA. 2015. National Ambient Air Quality Standards Table. Washington, D.C.: U.S. Depart- 2607

ment of Energy. https://www.epa.gov/criteria-air-pollutants/naaqs-table. 2608 2609 2610 ENVELOPE 2611 2612 OVERVIEW 2613 2614 The building enclosure, or envelope, serves many functions, both aesthetic and performative. 2615 Architects and engineers rely on the envelope to provide a durable and visually appealing 2616 exterior while also managing the migration or transmission of water, water vapor, air, and 2617 thermal energy. This section provides strategies that ensure an air-tight and well-insulated 2618 building envelope. (ASHRAE Handbook). 2619 2620 Installation and commissioning are critical to the success of a high-performing building 2621 envelope and by extension the success of a zero-energy building. Further discussion of building 2622 envelope commissioning and other quality control efforts is provided in Chapter 3, Quality 2623 Assurance and Commissioning. 2624 2625 Figure 5-3 presents heating dominant and cooling dominant buildings by climate zone. This 2626 information can be quite useful as an intuitive starting point as one starts to evaluate appropriate 2627 building strategies for a specific project, and more specifically how climate in which a building 2628 is located changes the HVAC heating and cooling loads. 2629 2630 Cautions: 2631 Additional considerations include: 2632

Existing recommendations and warranties from manufacturers and manufacturer trade 2633 organizations may be tested. In many instances, dialogue with manufacturers and trade 2634 organizations will yield useful new understandings and opportunities. 2635

Adhere to applicable building codes and the underlying reference standards. These 2636 standards impose limits on the extents and application of combustible materials, and in 2637 particular on foam plastic insulation products. 2638

In many cases, specific tested assemblies may be required and slight variances may 2639 require engineering judgements from manufacturers to satisfy the authorities having 2640 jurisdiction (AHJ). 2641

2642 [Note to Reviewers: The following graph will be update graph with office energy model data – 2643 this is just a placeholder and uses data from a previous guide.] 2644 2645


2646 Figure 5-3 Heating and Cooling Loads by Climate Zone 2647

2648 2649 2650 AIR BARRIER SYSTEM 2651 2652 EN1 Provide Continuous Air Leakage Control 2653 An airtight envelope minimizes energy loads especially when the building is unoccupied. Even 2654 when it is occupied, an airtight building will allow for mechanical ventilation to provide the 2655 correct amount of ventilation based on occupancy rather than relying on external weather 2656 conditions through infiltration to provide fresh air. In addition, mechanical ventilation allows 2657 for heat recovery, which more than accounts for the fan energy (see HV#) 2658 2659 The air barrier system should be continuous over all surfaces of the building envelope including 2660 at the lowest floor, exterior walls, and the roof (see Figure 5-4). An air barrier system should 2661 also be provided for interior separations between conditioned spaces and semi-conditioned 2662 spaces. Semi-conditioned spaces maintain temperature or humidity levels that vary significantly 2663 from those in conditioned space. 2664 2665 Various methods for durable sealing of penetrations are available, including high performance 2666 tapes and liquid applied products. (Nordbye) 2667 2668 To maintain complete continuity, pay attention to those areas known to pose obstacles to 2669 continuity, notably: wall to roof transitions, wall to foundation transitions, wall to fenestration 2670 transitions, and the perimeter of all air barrier penetrations. A useful technique during the 2671 project development is to draw a continuous red line along the entire air barrier in the building 2672 sections to trace its location within each assembly and to identify areas of critical intersections. 2673 2674 The location of the air barrier within the assembly should be driven by climate conditions to 2675 avoid condensation within the assembly or on the interior surface. A hygrothermic analysis is 2676 recommended to confirm a proper placement of the air barrier. In many cases, the air barrier is 2677 coincident or co-planar with the insulating layers of the envelope. Recommendations on 2678 continuous insulation are shown in the sections that follow. 2679


2680

2681 Figure 5-4 Continuous Air Barrior 2682

2683 [Question for Reviewers: Would an air leakage rate of 0.15 cfm/ft2 of total envelope surface 2684 area at 75 Pa be a reasonable target to include in How to Tip EN2] 2685 2686 EN2 Establish an Infiltration Goal 2687 The recommended target air leakage rate is 0.25 cfm/ft2 of total envelope surface area at 75 Pa. 2688 Lower values are achievable, and should be considered in colder climates. The leakage goal 2689 should be established at a level that is as tight as can be expected given the anticipated 2690 construction. 2691 2692 THERMAL MASS 2693 2694 [Question for reviewers: How would you recommend organizing the coverage of thermal mass 2695 between the envelope section and the HVAC section?]. 2696 2697 EN3 General Guidance 2698 Thermal mass van be a useful passive cooling technique and it can improve thermal comfort 2699 and reduce energy use. Thermal mass is a property of a material that allows it to store thermal 2700 energy. Thermally massive materials have high densities and high specific heat capacities. They 2701 also have medium thermal diffusivity, which means the rate of heat flow through the material is 2702 moderate, and often matches a desired time delay for storing and releasing energy within a daily 2703 cycle. Materials with high thermal mass include masonry, stone, rammed earth, concrete and 2704 water. The advantage of thermal mass is in its ability to absorb thermal energy and temporarily 2705 store it before releasing it, and there by creating inertia against temperature fluctuations. 2706 2707


Two primary strategies for incorporating mass in the building structure include internal therma 2708 mass and external thermal mass. Internal therma mass can take many forms, but it is inside of 2709 the thermal envelope, and it is directly exposed to the space. Thermal mass can be exterior 2710 walls (inside the insulation layer), interior walls, slabs, and/or columns and beams. Thermal 2711 mass does not need to be deep to be effective, but it is more effective if it is distributed 2712 throughout the space. While these two approached are passive, thermal mass can also be made 2713 into thermally active surfaces (refer to HV#). 2714 2715 EN4 Internal Thermal Mass 2716 Exposing internal thermal mass within office spaces can create beneficial thermal energy lags 2717 that reduce cooling energy. Over the course of a day, in an office building dominated by 2718 cooling, people arrive to work, computers and lights turn on, and sun light enters through the 2719 windows. A portion of these heat gains can be absorbed by exposed thermal mass in the space 2720 and then released at night when the building is unoccupied. To release the thermal energy at 2721 night the mass needs to be exposed to air cooler than the temperature of the mass. In climates 2722 with diurnal temperature swings that go below the comfort zone at night a passive strategy 2723 known as night flushing (purging) can be used, which uses the cool night air to recharge the 2724 thermal mass. Night flushing can be accomplished passively or mechanically. An example of 2725 exposed thermal mass is shown in Figure 5-5. 2726

2727 2728

[PHOTO WILL BE ADDED 2729 of an office interior with exposed thermal mass] 2730

2731 Figure 5-5 Exposed Thermal Mass 2732

2733 2734 [Question for reviewers: Is the following EN4 External Thermal Mass tip useful enough to keep 2735 in the guide?] 2736 2737 EN5 External Thermal Mass 2738 In hot climates, mass veneers can be employed outboard of building thermal insulation to 2739 mitigate extreme swings caused by envelope gains. Conventional masonry cavity walls and 2740 insulated precast panels are examples of this construction and offer the co-benefit of a very 2741 durable exterior finish. The mass can absorb and store thermal energy during the day and 2742 release it back to the cooler exterior air at night. This reduces the amount of heat gain that is 2743 conducted through the insulated portion of the wall to in the interior environment. While 2744 external thermal mass can be a useful strategy for hot climates, it is important to prioritize 2745 exterior surfaces that reflect solar radiation and/or are shaded. 2746

2747 2748 2749

Phase Change Materials 2750

2751 In low mass buildings the use of phase change materials can offer similar 2752 benefits for passive cooling. While thermal mass absorbs and releases sensible 2753 heat (temperature changes with no change in material phase), phase change 2754


materials absorb and release latent heat (changes in material phase at constant 2755 temperature) and have high thermal energy storage densities. The melting point 2756 is designed to be a specific temperature to absorb heat from a space that is 2757 warming and in need of cooling. When the space temperature drops below the 2758 material’s melting point the thermal energy is released back into the space. A 2759 common strategy would to be include night flushing to remove this heat during 2760 unoccupied hours. 2761

2762 Phase change materials such as paraffin wax, slat hydrates and plant-based fatty 2763 acids are encapsulated to create a product that can integrated into construction 2764 assemblies. Phase change materials can be integrated into wall assemblies, 2765 ceiling assemblies and glazing assemblies. A common example is a membrane 2766 encapsulated with pockets of phase change material that can be laid over a 2767 ceiling in order to absorb and control internal heat gains. 2768

2769 [PHOTO TO BE ADDED of a typical PCM product] 2770

2771

2772 2773 ROOF CONSTRUCTION 2774 2775 EN6 Select Appropriate Roofing Materials 2776 There are a wide range of roofing choices available in the marketplace, and many factors affect 2777 the selection, specification, and detailing of a building’s roofing system. Roofing material 2778 properties can have a significant effect on building envelope loads, a building energy usage, and 2779 on a project’s microclimate. AEC teams should plan to optimize the roofing materials through 2780 energy modeling and an understanding of how roofing choices affect overall project goals. 2781

2782 The effects on an office’s indoor air quality (IEQ) should also be evaluated, particularly for flat 2783 roofs, as adhesives inside the building envelope (i.e., inboard of the membrane) can adversely 2784 affect the indoor environment and in turn occupant health and achievement. 2785

2786 Rooftop PV arrays can complicate roof maintenance and future roof replacement. See BP# for 2787 strategies on designing a long-lasting roof. 2788

2789 EN7 Cool Roofs and Warm Roofs 2790 To be considered a cool roof, a product must demonstrate a solar reflectance index (SRI) of 78 2791 or higher. A detailed explanation of the SRI calculation is available at the Cool Roof Rating 2792 Council at www.coolroofs.org. 2793

2794 In the past, cool roofs were generally lighter colored and had a smooth surface. The product 2795 category has expanded with technical advancements, and cool roofing materials are now 2796 available in a wider variety of colors and textures. Commercial roof products that qualify as 2797 cool roofs fall into three categories: single-ply, liquid-applied, and metal panels. Additional 2798 information is available from the Cool Roof Rating Council or the U.S. Department of Energy’s 2799 Guidelines for Selecting Cool Roofs (DOE 2010). 2800

2801


Cool roofs provide energy reductions in climate zones 0–4. Warm roofs, in contrast, reduce 2802 energy use modestly in climate zones 7 and 8. Differences in modeled energy usage between 2803 cool roofs and warm roofs are negligible in the remaining climate zones. Project teams should 2804 always model both roof types (and/or multiple types) to confirm the results for a specific 2805 building. Consider evaluating some roof areas separately, based on occupancy and scheduling. 2806

2807 It would seem intuitive that PV panels shade the roof and preclude the need for cool roofing, but 2808 the modeling that was done for this guide actually contradicts this perspective. While energy 2809 differences were more modest, the installation of PV panels did not change the relative 2810 difference in any climate zone. Also consider the roof’s effect on the productivity of the PVs. 2811 Elevated temperatures adversely affect solar production, so in many cases, cool roofs will 2812 improve the efficiency of the system and increase the amount of energy produced. The urban 2813 heat island effect should also be considered when selecting a roofing material. Individual 2814 project goals that favor a reduction in the heat island effect may warrant a slight energy penalty 2815 in the heating-dominated zones. 2816 2817 BUILDING INSULATION – OPAQUE COMPONENTS 2818 2819 EN8 General Guidance 2820 There are numerous insulation products available. There are many factors that are used to 2821 evaluate insulation including recycled content, recyclability, combustibility, outgassing, and R-2822 value. Insulation should be installed according to manufacturer’s specifications, and in some 2823 cases, provide an airtight wall construction. Structural components often decrease the 2824 effectiveness of the insulation causing thermal bridges. Continuous insulation can help reduce 2825 thermal bridging. For zero energy buildings, it is critical to meet the recommended U- factor for 2826 the envelope while considering all the other criteria for a successful envelope. 2827 2828 While increasing insulation beyond recommended levels will save energy, this reduction may 2829 be minimal, and efforts should be placed on other efficiency gains. Project teams should start 2830 with the recommended insulation levels (EN#) and model to see if additional insulation is 2831 effective at reducing the EUI. In addition, additional insulation can be compared to alternative 2832 energy conservation measures (ECMs) to provide the best energy savings strategy for the 2833 project budget. 2834 2835 The prescriptive climate zone recommendations provided in Table 5-3 represent one pathway 2836 for upgrading the thermal performance of the envelope. Alternative constructions that are less 2837 than or equal to the U-factor or F-factor for the appropriate climate zone construction are better. 2838 U-factors and F-factors that correspond to all recommendations are presented in Appendix A. 2839 For information on doors, see EN# to EN#. 2840 2841 EN9 Maintain Insulation Effectiveness 2842 To a certain extent, the effectiveness of any thermal envelope is a function of the installation 2843 quality, and designers, owners, and contractors must be vigilant in the proper installation 2844 referring to the manufacturer’s best practices. All insulation types can be susceptible to poor 2845 installation that impacts energy performance, condensation, and comfort. Insulation installations 2846 should be visibly inspected. Evaluate first cost, life-cycle costs, construction sequencing, and 2847 scheduling effects before finalizing the selection of any insulation system. 2848 2849 Table 5-3 Envelope Construction Factors 2850


Recommendations by Climate Zone Component 0 1 2 3 4 5 6 7 8 Roof U-factor 0.039 0.048 0.039 0.039 0.030 0.030 0.030 0.027 0.027

Walls above ground U-factor 0.124 0.077 0.077 0.064 0.061 0.052 0.047 0.047 0.035

Slab F-factor 0.730 0.730 0.730 0.730 0.494 0.494 0.485 0.400 0.400

Doors U-factor 0.370 0.370 0.370 0.370 0.352 0.352 0.352 0.352 0.352

2851 Two insulation types warrant special consideration relative to installation quality, and in turn 2852 insulation effectiveness: 2853

Rigid board insulation used in wall construction requires diligence to keep boards, level 2854 and square. Insulation must be cut neatly around openings and penetrations. Any gaps 2855 and edges must be thoroughly sealed with detailing foam or other appropriate insulating 2856 gap filler. 2857

Batt insulation is popular because of its low initial cost and ready availability. Thermal 2858 batt insulation should be combined with continuous insulation outboard of the framing 2859 cavities. 2860

2861 EN10 Roof Insulation 2862 Insulation entirely above deck is recommended. When relying on insulation installed entirely 2863 above the structural deck, carefully consider the consequences of the specified installation 2864 method. Mechanically attached layers and systems increase thermal bridging losses, and 2865 fasteners can penetrate the roofing system air barrier (in assemblies where the roof membrane is 2866 not being used as the continuous air barrier). Penetrations in an assembly’s air barrier can 2867 increase the susceptibility of the roofing layers to condensation and can reduce an assembly’s 2868 ability to resist a given uplift pressure. 2869 2870 Adhered layers (including insulation, substrate boards, and cover boards) eliminate thermal 2871 bridges and leave the air barrier intact. When relying on adhered systems, carefully weigh the 2872 energy-efficiency improvements against the increased VOCs inside the building envelope, the 2873 potentially degraded recyclability, and the more limited ability to disassemble the roof. In 2874 addition, ensure that the adhered installation meets related technical requirements defined by the 2875 building codes and third party stakeholders (such as insurers). 2876 2877 To minimize thermal losses and infiltration, board insulation should be installed in at least two 2878 layers staggering the joints. 2879 2880 If PV panels will be mounted to the roof, the roofing system must be able to handle uplift from 2881 the panels. Attachments for PV panels need to minimize thermal bridging (see EN#). Often, 2882 ballasted PV systems are used as they do not penetrate the roofing membrane. 2883 2884 EN11 Mass Walls—Concrete and Masonry 2885 For mass walls continuous exterior insulation is preferred over interior insulation as it limits 2886 moisture management issues, makes air barrier and insulation continuity easier, and better 2887 accommodates the use of the thermal mass for energy efficiency. Rigid board or sprayed-in-2888 place insulations are suitable for this application. All exterior walls should meet the U-factor 2889 recommendations in Table 5-3. 2890 For additional strategies relating to thermal mass see EN#, HV#, and HV#. 2891 2892


Option: In addition to the wall insulation options discussed in EN# and EN#, alternative or 2893 hybrid structures, such as insulated concrete forms (ICF’s) may also be used as long as the 2894 actual U-factor complies with the values in EN#. 2895 2896 EN12 Steel-Framed Walls and Wood-Framed Walls 2897 Cold-formed steel framing members are thermal bridges. Continuous insulation is the 2898 recommended method for insulating steel-framed stud walls to minimize thermal bridges. While 2899 wood studs are less conductive than steel, thermal bridging through the wood also decreases the 2900 effectiveness of stud cavity insulation; therefore, continuous exterior insulation is also 2901 recommended for wood-framed stud walls. Rigid board (suitable for exposure to moisture) or 2902 sprayed-in-place closed-cell polyurethane foam insulations are effective. 2903 2904 Alternative combinations of stud cavity insulation and continuous insulation can be used, 2905 provided that the proposed total wall assembly has a U-factor less than or equal to the U-factor 2906 for the appropriate climate zone construction listed in Appendix A, and provided that analysis 2907 demonstrates that vapor will not condense in the wall. Wall sheathing with integral insulation 2908 can provide exterior continuous insulation that simplifies wall construction. 2909 2910 Be sure to follow the manufacturer’s specifications to insure a quality installation for insulation 2911 used in stud wall cavities. 2912 2913 EN13 Below-Grade Walls 2914 Continuous exterior insulation is recommended for below-grade walls. Certain closed-cell foam 2915 insulations are suitable for this application. Continuous exterior insulation can reduce moisture 2916 management issues, makes air barrier and insulation continuity easier (where the above-grade 2917 primary thermal insulation or air barrier layers are outboard of the exterior wall construction), 2918 and better accommodates the use of the thermal mass. Below-grade walls must be insulated for 2919 their full depth. 2920 2921 When heated slabs are placed below grade, below-grade walls should meet the insulation 2922 recommendations for perimeter insulation according to the heated slab-on-grade construction. 2923 2924 Foam products are susceptible to termite damage. In this case, use products that are termite 2925 resistant. 2926 2927 EN14 Mass Floors 2928 Mass floors should be insulated continuously beneath the floor slab. As columns provide 2929 thermal bridges, the insulation should be turned down the column to grade. Note that this is in 2930 reference to supported mass floors. Slab-on-grade floors are addressed in EN#. 2931 2932 EN15 Framed Floors 2933 Insulation should be installed between the framing members and in intimate contact with the 2934 flooring system supported by the framing member in order to avoid the potential thermal short 2935 circuiting associated with open or exposed air spaces. Non-rigid insulation should be supported 2936 from below, in accordance with manufacturer’s recommendations, or in the absence thereof, no 2937 less frequently than 24 in. on center. Sprayed polyurethane insulation is also a suitable 2938 insulation type. 2939

2940 EN16 Slab-on-Grade Floors—Unheated and Heated 2941


Where slab edges or the enclosing stem walls are exposed to the exterior, rigid insulation should 2942 be used around the perimeter of the slab and should reach the footing. See Figure 5-5. 2943 2944 For heated slabs, continuous insulation should be placed below the slab as well. 2945 2946 To ensure thermal comfort requirements are met, always evaluate slab surface temperatures and 2947 adjust insulation levels and other variables until interior surface temperatures are within 9°F of 2948 the indoor air temperature. 2949 2950 Use termite-resistant products and strategies where below-grade insulation is recommended and 2951 where termite infestation poses a problem. 2952

2953

2954 Figure 5-5 Slab insulation. 2955

2956 EN17 Evaluate Doors 2957 Maximum U-factor values for doors are shown in Table 5-3. While there are no additional 2958 recommendations on U-factor and air leakage of doors, they do need to comply with ANSI/ 2959 ASHRAE/IES 90.1-2016 as a minimum requirement. This includes opaque non-swinging doors, 2960 opaque swinging doors, entrance doors (vertical fenestration). 2961

2962 Caution: Some thermally broken door assemblies have been known to show decreased 2963 durability compared to conventional product options. All doors should be carefully inspected 2964 prior to final acceptance to ensure that all weather stripping is tightly sealed to the door and to 2965 ensure that all sweeps and bottom seals are tightly contacting the threshold or sill. Consider 2966 using double sweeps to ensure an airtight installation. 2967 2968 EN18 Person-Doors 2969


Where exterior swinging doors are provided, single doors should be specified. Double swinging 2970 doors without a center post should be minimized and limited to areas where width is important, 2971 typically for moving large equipment. In that situation, consider removable center mullions, 2972 which can be more tightly sealed than door astragals. 2973 2974 EN19 Doors—Opaque, Non-Swinging 2975 When non-swinging doors are functionally required, use doors that have a U-factor of less than 2976 0.10, including edge effects and joints. A tight seal at the edges is critical to minimize 2977 infiltration. 2978 2979 Metal doors pose more challenges because they can have poor emissivity, resulting in a hot 2980 exterior surface from solar gains, which are transmitted through the door, increasing cooling 2981 loads and magnifying thermal comfort issues. Where steel doors are functionally required and 2982 are exposed to solar radiation, a high emissivity/reflectivity coating should be specified and 2983 proper solar shading should be provided. Specify insulated curtain slats and ensure that the 2984 installed unit has seals contacting the curtain slats. 2985 2986 Minimize or mitigate thermal bridging and air leakage between the door assembly’s perimeter 2987 components and the building framing. 2988 2989 2990 BUILDING INSULATION – THERMAL BRIDGING 2991 2992 EN20 General Guidance 2993 The design and construction of an effective building envelope requires a consistency in building 2994 assembles and construction sequencing that necessarily focuses on the continuous air barrier 2995 system and continuous insulation strategies. Continuous insulation is easily defeated or 2996 compromised by thermal bridging through the building envelope, so potential thermal bridges 2997 must be identified in advance of construction and in an integrated manner to eliminate, or at 2998 least mitigate, all bridging. 2999

3000

Energy Savings Due to Thermal Bridging 3001 3002

This table details energy savings due to thermal bridging for an office building that is 3003 9,000 ft2 gross floor area, 75ft wide, 40ft deep, 40ft tall, with a WWR=0.25 and windows R-3004

3 3005

3006


3007

3008 3009

3010 3011 Thermal bridging occurs when highly conductive elements connect internal and external 3012 surfaces. In general, this most often happens because of fastening systems, changes of 3013 construction types, or at corners. The types of bridging encountered varies considerably with 3014 construction type. The thermal conductivities of various materials are outlined in the chart 3015 shown in Table 5-4. 3016

3017 Thermal modeling at the detail level can be used to compare approaches and optimize solutions 3018 for thermal bridges. Fourier’s Law can also be used to compare conductive losses through 3019 simple bridges. 3020

3021 q = k A dT / s 3022

3023 where 3024

q = heat transfer, Btu/h 3025 k = thermal conductivity of a material, Btu/(h·ft·°F) 3026

A = heat transfer area, ft2 3027 dT = temperature gradient, °F 3028 s = material thickness, ft 3029

3030 Material densities are provided to help define the actual building material. In some cases, the 3031 density has an impact on the thermal conductivity. See ASHRAE Handbook—Fundamentals for 3032 more information (ASHRAE 2017). 3033 3034


Table 5-4 Envelope Material Conductivity 3035

Material Density (lb/ft2)

Thermal Conductivity (Btu·in/h·ft2·°F)

Polyisocyanurate 1.6–2.3 0.15–0.16 Extruded polystyrene 1.4–3.6 0.20 Expanded polystyrene 1.0–1.5 0.24–0.26 Cellulose 1.2–1.6 0.27–0.28 Polyurethane foam 0.45–0.65 0.26–0.29 Glass fiber batts 0.47–0.57 0.32–0.33 Wood 25 0.74–0.85 Gypsum sheathing 40 1.1 Brick—common 120 5.0 Brick—face 130 9.0 Concrete—sand/gravel 150 10–20 Stainless steel 494 96 Carbon steel (mild) 489 314 Aluminum (alloy 1100) 171 1536

3036 [Question for Reviewers: Is the following detailed thermal bridge analysis a useful addition to 3037 the guide?] 3038 3039 The following method provides for a more detailed adjustment of assembly U-factors for the 3040 simulation of thermal bridges. For the purpose of incorporating the effects of thermal bridges 3041 the clear-field U-factors of modeled assemblies need to be modified in accordance with the 3042 following equation. This modification shall be achieved in the simulation model by altering the 3043 conductance value assigned to any one or more insulation layers within the modeled assembly 3044 without altering the properties of modeled building material layers. 3045 3046

Utot = ( [ ( ∑ ψi ∙ Li ) + ( ∑ χj ∙ nj ) ] /Atotal ) +Uo 3047 where 3048

Utot = overall thermal transmittance including the effect of linear thermal bridges and point 3049 thermal bridges not included in the assembly’s Uo value, Btu/(h∙ft2∙oF) 3050

Uo = clear field thermal transmittance of the assembly, Btu/(h∙ft2∙oF) 3051

Atotal = total opaque projected surface area of the assembly, ft2 3052

ψi = Psi-factor, thermal transmittance for each type of linear thermal bridge, Btu/(h·ft·°F) 3053

Li = length of a particular linear thermal bridge as measured on the outside surface of the 3054 building envelope, ft 3055

χi = Chi-factor, thermal transmittance for each detail type of point thermal bridge, 3056 Btu/(h·°F) 3057

ni = the number of occurrences a particular type of point thermal bridge 3058 3059


Determination of Psi-factors and Chi-factors: Psi-factor (ψ) and Chi-factor (χ) values 3060 representative of an as-built thermal bridging condition shall be determined by one of the 3061 following: 3062

1. Values derived from models compliant with ISO 10211 using details representative of 3063 the actual construction and modeling assumptions consistent with accepted practice. 3064

2. Testing of the assembly in accordance with ASTM C1363 with and without the presence 3065 of the thermal bridge condition to determine a linear transmittance value or point 3066 transmittance value for the thermal bridge condition. 3067

3. Values as indicated in Table EN-XX 3068 3069

Table EN-XX Thermal Bridging Default Psi-Factors and Chi-Factors for Thermal 3070 Bridges 3071

Thermal Bridging Default Psi-Factors and Chi-factors for Thermal Bridges

Class of Construction -Wall, above

Grade

Thermal Bridge Type

Un-mitigated Default

Psi- Factor

Btu/(h·ft·°F)

Chi-Factor

Btu/(h·°F)

Psi- Factor

Btu/(h·ft·°F)

Chi-Factor

Btu/(h·°F)

Steel Framed

Parapet 0.289

N/A

0.151

N/A

Floor to Wall intersection 0.487 0.177

Relieving Angle 0.314 0.217 Wall to Vertical Fenestration intersection

0.262 0.112

Shading Device 0.402 0.117

Other Element N/A 1.73 N/A 0.91

Mass

Parapet 0.238

N/A

0.126

N/A



0.188 0.131



Wood-framed and Other

Parapet 0.032

N/A

0.032

N/A



0.150 0.099



3072 3073

Strategies for minimizing thermal bridges can be categorized as follows: 3074

Avoid possible thermal bridges by careful building planning and analysis of alternate 3075 construction methods. 3076

When bridges are unavoidable, use fewer, larger bridges. This might include further 3077 spacing for structural or stud elements. Use modeling to compare scenarios. 3078


Use the least conductive material when a bridge must be used. For example, stainless 3079 steel can be used in place of carbon steel for fasteners, brick ties, and structural clips. 3080 Plastic pipes can be used in lieu of metal pipes. Use Table 5-4 for comparing materials. 3081

Integrate nonconductive materials or spaces where conductive elements bridge the 3082 thermal barrier. Relatively nonconductive materials include fiber-reinforced plastic 3083 (FRP), some ceramic composites, and gypsum sheathing. 3084

Mitigate thermal bridges to the greatest extent possible, which generally entails the 3085 provision of additional insulation inboard and/or outboard of the bridging component 3086 including incorporating a layer of continuous insulation. 3087

3088 Thermal bridging is generally more problematic in areas with wider differences between indoor 3089 and outdoor temperatures. Thermal bridging should be evaluated as minimizing bridge- induced 3090 condensation leads to envelope degradation. 3091 3092 EN21 Supporting Columns Below Floors 3093 Exposed exterior columns as a result of supported elevated floors should be minimized as the 3094 exposed floors and thermal bridging from the columns is difficult to insulate. Where this detail 3095 is necessary, the column should be insulated continuously from the elevated floor insulation to 3096 grade, or in the event of an extraordinarily tall column, to a minimum of 1 ft per required R-3097 value to meet the necessary U-factor for the floor. For example, if R-20 is required, the column 3098 should be insulated to a minimum of 20 ft. 3099 3100 [Question for Reviewers: the following of the information on Thermal Bridging includes a lot 3101 of figures/illustrations. Are these illustrations useful? If not, what would be useful?] 3102 3103 EN22 Wall Type Transitions 3104 Transitions in the construction of exterior walls can pose special challenges to the continuity of 3105 the air and thermal barrier. Conventionally, such transitions have frequently occurred at or near 3106 finished grade. A true continuous thermal barrier is only achievable by installing below-grade 3107 insulation outboard of the basement wall directly connecting to the continuous wall insulation 3108 above. 3109 3110 Transitioning of masonry cavity walls requires special consideration and careful detailing. 3111 Cavity insulation should be carried in the same plane above and below grade and extended to 3112 the footings. The masonry cavity can be extended below grade to the same depth, or alternately 3113 an at- grade shelf angle may be used to minimize the extents of below-grade masonry. Figures 3114 5-6 through 5-8 detail the wall transition under various circumstances. Figure 5-6 illustrates 3115 continuous insulation to the foundation. Figure 5-7 illustrates continuous insulation to the 3116 foundation with masonry veneer. Figure 5-8 illustrates the wall transition where a shelf angle 3117 carries brick above grade. 3118 3119


3120 Figure 5-6 Wall transition with insulation continuous to foundation. 3121

3122 3123

3124 Figure 5-7 Wall transition with insulation. 3125

3126 3127


3128 Figure 5-8 Wall transition where shelf angle carries brick above grade. 3129

3130 EN23 Cladding Attachment and Rainscreens 3131 Thin building skins and rainscreens require attachment to the structure of the building. These 3132 attachment points can be sources of thermal bridging. Attachment systems should be evaluated 3133 based on their ability to meet the load requirements without compromising the thermal integrity 3134 of the envelope. 3135

3136 Where project circumstances cannot support the integration of proprietary attachment systems, 3137 consider the following: 3138

Avoid the use of continuous girts that penetrate the exterior insulation, causing thermal 3139 bridges and thereby increasing the U-factor of the wall assembly. 3140

Design attachment systems to minimize the number of attachment points and thermal 3141 bridges. Use calculations to compare the energy conducted through various attachment 3142 scenarios (unless thermal bridges are being comprehensively modeled and tested). 3143

Use nonconductive clips at all penetrations. Where nonconductive clips are not an 3144 option, use the least conductive option available (such as stainless steel in lieu of carbon 3145 steel). 3146

Ensure that all attachment points are thermally broken. Exterior sheathing is typically an 3147 adequate insulator in metal stud construction. 3148

Ensure that all cladding attachment systems are structurally sound. 3149 3150

As part of the design, it is important to integrate the architectural finishes with the energy 3151 features. If the facade treatment compromises the thermal integrity of the envelope, alternate 3152 treatments should be considered. Cross sections should be carefully examined to prevent these 3153 thermal bridges. 3154 3155


EN24 Shelf Angles 3156 Shelf angles are an especially problematic source of potential energy transfer through the 3157 building envelope. Conventionally, shelf angles are attached directly to the building structural 3158 frame or floor edge. In such an installation, a 3/8 in. steel angle can be responsible for as much 3159 heat loss as the entire story of insulated opaque envelope above. 3160 3161 Minimize the number and extents of shelf angles. Investigate strategies to avoid a shelf angle at 3162 each floor. 3163 3164 Where provided, shelf angles must be detailed and installed to minimize the interruption in the 3165 thermal barrier. In practice, shelf angles in high-performing envelopes are held off the building 3166 frame or floor edge by clips or proprietary structural components that allow insulation to pass 3167 between the shelf angle and the frame or floor edge as illustrated in Figure 5-10. Structural 3168 engineers should be retained that can help provide appropriate structural integrity without 3169 compromising the thermal envelope. 3170 3171 Clips or components carrying the shelf angle can be substantial in thickness and, because they 3172 penetrate the thermal barrier, they too should be selected to minimize the thermal bridging. 3173 Select such components to minimize conductivity through the envelope. Stainless steel can be 3174 an effective choice because carbon steel is approximately two and a half times as conductive as 3175 stainless steel. 3176 3177 Carefully research and address material compatibilities. 3178 3179

3180 Figure 5-10 Shelf angle installation. 3181

3182 EN25 Other Structural Penetrations in Walls 3183


An office building is likely to have multiple instances of structural penetrations in the building 3184 envelope. In practice, zero energy offices often require many penetrations to accommodate 3185 various types of exterior shading devices. Evaluate all such penetrations evaluated to determine 3186 the best strategy to balance the requirements of each penetration. 3187 3188 First, evaluate alternative support strategies that would eliminate the need to extend a 3189 conductive structural member through the envelope. 3190 3191 Where penetrations are unavoidable, use the least amount of penetrating material that meets 3192 structural requirements and use thermally broken structural connections. For smaller loads, 3193 high-strength bolts can sometimes provide sufficient capacity to accommodate continuous 3194 insulation between the interior and exterior structural members. Where the structural loads are 3195 more extensive, place nonconductive plates between the interior and exterior structural 3196 members and located in the plane of the wall insulation. 3197 3198 Where decoupling is not possible, insulate penetrating elements to the greatest degree possible, 3199 both inboard and outboard. See Figure 5-A. 3200 3201

3202 Figure 5-A 3203

3204 EN26 Louvers 3205 Penetrations in the envelope for exterior louvers and the associated ductwork are compromises 3206 in the thermal envelope. Consider the following when detailing louvered penetrations: 3207 3208

Consider a thermally broken louver 3209 Tie-in the building air barrier system to the duct. 3210 Use a flexible duct sleeve for a thermal break in the ductwork 3211 Insulate the duct all the way to the building thermal envelope and ensure complete tie-in 3212

with detailing foam 3213 3214 EN27 Opaque Wall and Vertical Fenestration Intersection 3215 Where opaque walls and vertical fenestration intersect and continuous insulation is present, 3216 align the outermost glazing layer within the thickness of the continuous insulation layer as 3217 shown in Figure 5-B. 3218 3219

3220 Figure 5-B 3221

3222


Where opaque walls and vertical fenestration intersect and continuous insulation is not present, 3223 align the outermost glazing layer within the thickness of the wall insulation layer and not more 3224 than 2 in. from the exterior side of the outermost insulation layer as shown in Figure 5-C 3225

3226 Figure 5-C 3227

3228 Exceptions to these details are shown in Figure 5-D and include: 3229

Intersections between vertical fenestration and opaque walls where all surfaces of the 3230 rough opening located between the edge of the frame of the vertical fenestration and the 3231 opaque wall insulation are either covered with a material having an R-3 minimum or 3232 covered with a wood framing member a minimum of 1.5 in. thick as shown in Figure 5-3233 D Exception 1. 3234

Intersections between vertical fenestration and opaque spandrel in a common 3235 fenestration framing system as shown in Figure 5-D Exception 2. 3236

Intersections between vertical fenestration and uninsulated opaque walls. 3237

3238 3239

3240 Exception 1 Exception 2 3241

Figure 5-D 3242 3243 3244 EN28 Intermediate Floor Edges without Balconies and Floor Overhangs 3245 For a wall with cavity insulation, extend the cavity insulation needs to extend to the underside 3246 of the floor deck. The cavity insulation can be interrupted by floor framing members and wall 3247 top and bottom plates or tracks as shown in Figure 5-E. 3248

3249 Figure 5-E 3250

3251 For a mass wall with integral insulation, extend the integral insulation to the underside of the 3252 floor deck. Where the intermediate floor deck extends through the integral insulation, aply 3253


additional insulation having a minimum rated R-value of insulation of R-5 to the full depth of 3254 the floor edge on the exterior side of the wall as shown in Figure 5-F. 3255 3256

3257 Figure 5-F 3258

3259 For a mass wall with insulation on the interior side, extend the insulation on the interior side of 3260 the wall up to the underside of the floor deck and apply additional insulation having a R-5 needs 3261 to the full depth of the floor edge at the interior face of the mass wall in alignment with 3262 insulation on the interior side of the wall or applied to the full depth of the floor edge on the 3263 exterior side of the wall as shown in Figure 5-G. 3264 3265

3266 Figure 5-G 3267

3268 For a mass wall with a minimum of 50 percent of the insulation on the exterior side and the 3269 remainder on the interior side, the insulation on the interior side of the wall can be interrupted 3270 by the intermediate floor as shown in Figure 5-H. 3271 3272

3273 Figure 5-H 3274

3275 EN29 Balconies, Canopies and Floor Overhangs 3276 Projecting or cantilevered balconies and walkways represent serious thermal breaks. 3277 Conventional engineering practice has relied on a cantilevered extension of the primary 3278 structural floor to support the balcony 3279

3280 Envelopes must include an effective thermal break between the balcony and the building wall in 3281 the plane of the wall insulation. While such a break can be engineered on a project-by-project 3282 basis, proprietary thermally broken structural components are available to serve this specific 3283 purpose. 3284

3285 Where a balcony or floor overhang is supported by point load connections, ensure that the full 3286 depth of the cavity insulation, integral insulation, and exterior continuous insulation on any wall 3287


passes between the attached balcony or floor overhang and the interior floor deck or primary 3288 structure as shown in Figure 5-I. 3289 3290

3291 Figure 5-I 3292

3293 Where a balcony or floor overhang is separately supported from the building structure, ensure 3294 that the full depth of the cavity insulation, integral insulation, and exterior continuous insulation 3295 on any wall passes between the attached balcony or floor overhang and the interior floor deck or 3296 primary structure as shown in Figure 5-J 3297 . 3298

3299 Figure 5-J 3300

3301 Canopies, like balconies, represent significant compromises to the building envelope when 3302 assembled in conventional fashion. Practitioners must carefully consider alternatives based on 3303 the specific circumstances of each project. To maximize building energy saving, consider the 3304 following: 3305

Evaluate if canopies can be supported by other than structural penetrations of the 3306 building envelope. Cantilevered canopies require significant amounts of highly-3307 conductive steel to penetrate the envelope and should be avoided. Ground-supported 3308 canopies, for example, can eliminate the need for complex insulating and sealing 3309 strategies. 3310

Where cantilevered canopies are unavoidable, thermally broken structural connections 3311 should be used. For smaller canopies, high-strength bolts can sometimes provide 3312 sufficient capacity to accommodate continuous insulation between the interior and 3313 exterior structural members. Where the structural loads are more extensive, 3314 nonconductive plates should be placed between the interior and exterior structural 3315 members and located in the plane of the wall insulation. 3316

Where non-thermally broken structural connections are used, building insulation should 3317 be wrapped around the entirety of the projecting canopy. This is most effective for 3318 smaller projections. When using this approach, all penetrations in the canopy need to be 3319 sealed and all recessed light fixtures should be fully enclosed and air-sealed. 3320

As a last resort, where none of the strategies above are implemented, insulate the 3321 penetrating/cantilevering structural member inboard and outboard of the wall envelope. 3322


Insulation should be extended a minimum of 6 ft on interior members (and connecting 3323 interior members). Insulation should be extended a minimum of 6 ft or the full length of 3324 the member (whichever is less) on exterior members. Sprayed polyurethane foam is the 3325 most practical insulation for such an application, though other more labor-intensive 3326 materials may also be used. 3327

3328 3329 EN30 Cavity Walls Above Roofs 3330 Upper story exterior walls that intersect lower roof planes are commonly encountered. Where 3331 the higher wall is a masonry cavity wall, conventional practice would allow the cavity wall 3332 veneer to bear on the roof structure. In this condition, the cavity wall veneer is likely to 3333 introduce a thermal discontinuity between the wall insulation and the roof insulation. To 3334 maintain a continuous insulating barrier, the higher cavity wall veneer should be carried on a 3335 stand-off shelf angle that allows the wall insulation to meet the roof insulation without a thermal 3336 bridge, as illustrated in Figure 5-9. 3337

3338 Figure 5-9 Cavity wall insulation. 3339

3340 EN31 Roof and Wall Intersections 3341 For roofs with insulation entirely above deck, extend the roof insulation without interruption to 3342 at least the exterior face of the wall insulation or extend the wall insulation without interruption 3343 to the top of the roof insulation as shown in Figure 5-K. 3344 3345


3346 Figure 5-K 3347

3348 EN32 Parapets 3349 Continuous air barriers and continuous insulation must be applied to parapets. Install insulation 3350 continuously on the outer face of the wall to the top of the parapet, horizontally beneath the 3351 parapet coping, and vertically on the back side of the parapet connecting to the roof insulation 3352 as illustrated in Figure 5-11. In practical terms, this can involve up to three or four insulation 3353 types to meet the individual requirements for the various surfaces. For tall parapet walls, consult 3354 with building envelope experts to ensure that air barrier and insulation layers are continuous 3355 without sacrificing other technical aspects of the design. 3356 3357

3358 Figure 5-11 Parapet insulation. 3359

3360 For a mass wall with integral insulation, extend the integral insulation to the top of the parapet 3361 below the coping and place an additional R-5 insulation on the roof side of the parapet 3362 extending from the top of the parapet below the coping to at least the top of the roof insulation 3363 as shown in Figure 5-L. 3364

3365 Figure 5-L 3366

3367


For a mass wall with insulation on the interior side, extend the insulation on the interior side of 3368 the wall to the underside of the roof deck and inward on the underside of the roof deck for at 3369 least 2 ft as shown in Figure 5-M. 3370 3371

3372 Figure 5-M 3373

3374 For parapets in the field of a roof apply R-5 insulation to both sides and top of the parapet as 3375 shown in Figure 5-N. 3376 3377

3378 Figure 5-N 3379

3380 Continuous parapet insulation poses several challenges, including the following: 3381

Where an air barrier or vapor retarder is used beneath the roof insulation, the multiple 3382 tie- ins can pose additional complexity 3383

High-performance assemblies may not be tested to specific NFPA requirements, and 3384 engineering judgments from product manufacturers may need to be solicited 3385

Wind uplift requirements in the building codes need to be considered 3386 3387 EN33 Roof Overhangs 3388 For a wall with exterior continuous insulation, extend the exterior continuous insulation to the 3389 underside of the roof deck and outward on the underside of the roof deck and overhang for a 3390 minimum of 2 ft or to the end of the roof overhang when the overhang is less than 2 ft. as shown 3391 in Figure 5-O. 3392 3393

3394 Figure 5-O 3395

3396 For a wall with cavity insulation, extend the cavity insulation to the underside of the roof deck. 3397 The cavity insulation can be interrupted by roof framing members and wall top plates or tracks 3398 as shown in Figure 5-P. 3399


3400

3401 Figure 5-P 3402

3403 For a mass wall with integral insulation, in addition to the integral insulation, apply an 3404 additional insulation of R-5 minimum to the interior surfaces of the wall and roof deck and 3405 extend a minimum of 2 ft along each surface as measured from the roof-wall intersection as 3406 shown in Figure 5-Q. 3407 3408

3409 Figure 5-Q 3410

3411 For a mass wall with insulation on the interior side, extend the insulation on the interior surface 3412 of the wall up to the underside of the roof deck and inward on the underside of the roof deck for 3413 a minimum of 2 ft as shown in Figure 5-R. 3414 3415

3416 Figure 5-R 3417

3418 EN34 Roof Edges 3419 Insulation (as well as air, water, and vapor control) must be continuous at roof edges, gravel 3420 stops, and similar conditions. Where wood cleating or nailers are necessary for anchorage, 3421 cleats should be attached outboard of the continuous insulation and fastened with oversize 3422 screws to the parapet structure. Where a nailer must be embedded in the thickness of the 3423 insulation, minimize compromises of the envelope by installing nailers in a discontinuous 3424 fashion only where required for structural integrity. 3425 3426 EN35 Through Wall Overflow Drains/Lambs Tongues 3427 Roof drains frequently break the building thermal barrier compromising building energy 3428 efficiency and providing a potential source for condensation within concealed areas of the 3429 building. Heat loss from such conditions can be clearly seen in thermographic imaging during 3430 the cold season. 3431


3432 When possible, designers should consider a roof water removal system that does not require 3433 internal drain leaders. Where internally routed roof drains are unavoidable, energy losses can be 3434 mitigated by using plastic pipes and by insulating the pipe inboard of the point where it exits the 3435 building envelope. 3436 3437 Like any penetration in the envelope, all gaps at the penetration should be insulated and sealed 3438 to the building air barrier system. 3439 3440 EN36 Through-Wall Scuppers 3441 Roof design often uses through-wall parapet scuppers, in part to avoid interior roof drains (see 3442 EN#). Such scuppers may penetrate the envelope twice: once on the front and once on the back 3443 of the parapet. To maintain continuity, insulation (and the air barrier) should wrap the entirety 3444 of the opening and provide a continuous connection to the insulation on both faces of the 3445 parapet, as illustrated in Figure 5-12. 3446

3447 Figure 5-12 Through-wall scupper insulation. 3448

3449 EN37 Roof Drains 3450 Roof drains are a unique source of energy loss (and internal building condensation) that can 3451 compromise the building envelope. These drain assemblies and the substantial connecting pipes 3452 can represent very large energy losses in flat-roofed buildings. The following strategies are 3453 recommended. 3454

3455 The inboard side of the drain assembly should be thoroughly insulated where it 3456

penetrates the thermal envelope. 3457


Where metal rain leaders are used, the leaders should be insulated inside the building to 3458 the point where they penetrate the floor below (see Figure 5-14). 3459

3460

3461 Figure 5-14 Roof drain insulation. 3462

3463 EN38 Plumbing Vents 3464 Plumbing vents penetrating the roof are often thermal bridges. Plumbing vent penetrations 3465 should be sealed and all gaps around the penetration should be filled, as illustrated in Figure 5-3466 13. Where nonconductive (plastic) pipe is used, additional pipe insulation is not necessary. 3467 When metal pipe is used, the pipe should be insulated to the top of the vent before being 3468 flashed. On the inboard side, metal pipe should be insulated for a minimum of 10 ft. 3469

3470

3471 Figure 5-13 Plumbing vent insulation. 3472

3473 EN39 Roof Hatches 3474 Roof hatches are another substantial source of unintended energy loss. Roof hatches can vary 3475 greatly by manufacturer and have conventionally been significantly underinsulated. Recent 3476 innovations have included thermally broken hatches that decouple the exposed outer portions of 3477 the unit from the base mounting. Consider roof access that does not require roof hatches or 3478 follow the following recommendations: 3479

3480


Select hatch covers with the maximum available insulation. Covers with at least R-18 3481 are available. 3482

Understand how the cover is structured and whether the cover is thermally broken. 3483 Select curbs with the maximum amount of insulation available. Curbs with at least R-18 3484

are available. 3485 Select thermally broken curb mounts. 3486 Consider whether supplemental insulation can be added to the outside of the curb and 3487

whether such an application affects the manufacturer’s warranty. 3488 Consider the quality of the hatch cover weather-stripping (airseal) and compare 3489

manufacturer’s infiltration data. 3490 3491 EN40 Equipment Pedestals and Other Structural Penetrations in Roofs 3492 Commercial construction projects frequently have structural components penetrating the roof 3493 and the roof insulation. Examples include guardrail supports, rooftop screens, PV panel support 3494 attachments, and custom equipment platforms. All such penetrations must be carefully detailed 3495 to minimize energy losses. 3496 3497 Rely on thermally broken structural connections, where a nonconductive plate is placed in the 3498 joint. The nonconductive plate should be located in the center of the roof insulation depth, if 3499 possible, to avoid complications with flashing and waterproofing. 3500 3501 EN41 Mechanical Curbs 3502 Apply the principles outlined in EN# to optimize the design, installation, and performance of 3503 each condition. Recognize that both conventional detailing and appropriate product availability 3504 are impediments to high-performance detailing or curbs. 3505 3506 Strive for airtightness and specify the highest level of insulation available for curbs. Also 3507 consider field-applied supplemental insulation on the outside of the curb. 3508 3509 EN42 Skylight Curbs 3510 Skylights are conventionally mounted on premanufactured curbs. Premanufactured curbs 3511 generally offer limited insulation levels, few insulation material choices, and few thermally 3512 broken options. Consider the following strategies: 3513 3514

Insulate the curb wall to at least the level required of opaque wall assemblies. Better, 3515 insulate to the level of the roof assembly. 3516

Apply additional insulation outboard of the curb, if possible, without creating 3517 condensation problems or voiding product warranties 3518

Specify or detail thermally broken curbs, anchoring, and attachments. 3519 3520 EN43 Below Grade Piping and Conduit 3521 All penetrations should be sealed. Depending on local climate, bury depth, and ground 3522 temperatures, penetrations may warrant insulation for a reasonable distance in one or both 3523 directions from the penetration. In additions, when sleeves are used, the wire or piping in the 3524 sleeve should be sealed to prevent infiltration. 3525 3526 EN44 Duct Bank Entrances 3527 Duct bank entrances create thermal bridges and can contribute to building energy losses. In 3528 most cases, duct banks enter the building at elevations shallow enough that the below-grade 3529


wall will be insulated. To mitigate thermal losses, duct bank casings should be held back from 3530 the below-grade wall so that the full thickness of wall insulation separates the casing from the 3531 building. Consider using plastic piping at the building penetration. 3532 3533 EN45 Miscellaneous Penetrations—Detailing Foam 3534 In general, all penetrations need to be insulated and air-sealed. Follow manufacturer’s 3535 recommendations, otherwise, seal gaps with expansive detailing foam and provide sealant at the 3536 exterior drainage plane and, if warranted, at the exterior skin. 3537

3538 EN46 Use Advanced Framing Techniques 3539 Many conventional wood-framed buildings are overbuilt structurally. This results in the use of 3540 more wood than is structurally necessary and also creates additional thermal bridges because 3541 each framing member represents a thermal bridge in the envelope assembly. 3542 3543 Advanced framing techniques aim to maximize structural and thermal performance. An 3544 example is to reduce the number of wood members used to frame building corners. Advanced 3545 framing also integrates considerations for airtightness into the construction process. A complete 3546 discussion of advanced framing techniques is available in Building Science Corporation’s 3547 Builder’s Guide series of publications (BSC, n.d.). Building resources are also available from 3548 Passive House Institute US (PHIUS 2017). 3549 3550 Although advanced framing techniques reduce the number of thermal bridges in a wood stud 3551 wall, using a layer of continuous insulation outboard of the stud is also recommended, as 3552 discussed in EN#. 3553

3554 BUILDING FENESTRATION 3555 3556 EN47 General Guidance 3557 Fenestration includes the light transmitting areas within a wall or roof assembly, including 3558 windows, skylights and glass doors. Vertical fenestration (or windows) includes glazing with a 3559 slope equal to or greater than 60° from the horizontal. Other glazing (sloping less than 60° from 3560 the horizontal) is considered a skylight. Clerestories, roof monitors, and other such fenestration 3561 fall in the vertical category. 3562 3563 Fenestration can be a source of natural ventilation that can reduce the need for mechanical 3564 cooling and ventilation in many climates and provide resiliency during power outages and other 3565 emergency events (see HV#). On the negative side, fenestration is a significant source of heat 3566 loss and gain through the building envelope. Designers should seek the right balance between 3567 the benefits of fenestration (views, daylighting, and natural ventilation) and the penalties (heat 3568 gain and loss) through iterative modeling and testing fenestration strategies. An effective 3569 window should provide more benefit from daylighting and natural ventilation than the adverse 3570 heat loss and gain from a weakened thermal envelope. 3571 3572 Additional guidance is provided in the daylighting section that follows (see DL#) 3573 3574

[SIDEBAR TO BE ADDED about daylighting, view and natural 3575 ventilation impact on office worker performance.] 3576

3577


In general, an optimized energy solution is to right-size the glass for daylighting and natural 3578 ventilation realizing that additional glazing is often desired for views. Balancing the amount of 3579 glass to meet architectural and energy goals requires careful energy simulations to evaluate the 3580 impact as it varies considerably by climate and fenestration orientation. 3581 3582 Glazing selection and fenestration sizing should be selected by varying these parameters with 3583 energy modeling to achieve the desired energy goals. Effectively designing the fenestration is 3584 one of the cornerstones of creating a zero energy office. See Chapter 4 for more modeling 3585 information. 3586

3587 EN48 Consider Fenestration Early in the Process 3588 The best way to achieve low-cost daylighting, views, and natural ventilation is to integrate 3589 fenestration early in the schematic design phase. The most economic and effective fenestration 3590 design requires coordination with the structural, mechanical, and electrical disciplines. This 3591 includes designing fenestration to help reduce peak cooling loads, which results in scaled-back 3592 mechanical systems providing first-cost savings. 3593 3594 With integration, common architectural components may serve dual functions, which reduces 3595 first costs. For example, a cool roofing material can serve as a waterproofing membrane, reflect 3596 solar radiation to reduce cooling loads, reduce roof temperatures to improve PV performance, 3597 but also boost lighting through vertical glazing in roof monitors. Only a comprehensive, well 3598 thought out approach will provide a low-cost system that achieves the desired benefits. 3599 3600 The opposite is true of nonintegrated designs. If the daylighting system is designed and bid as 3601 an alternative to a design with no daylighting, the daylighting strategy probably will not be as 3602 cost effective or resource efficient. If the designer thinks that the daylighting components have a 3603 good chance of being eliminated, he or she will be less likely to risk designing a smaller 3604 mechanical cooling system for fear of having to pay to redo the design. 3605 3606 EN49 Window to Wall Ratio 3607 The window-to-wall ratio (WWR) is the ratio of window area to above grade wall area 3608 (excluding parapets) for a building or a façade. 3609 3610 The WWR should be defined early in the design process, as it can have a profound effect on 3611 building energy performance. In fact, in many climates it may be the most important variable in 3612 delivering a cost-effective zero energy building. While the actual articulation of fenestration 3613 may not be developed until later in the design process, setting early goals for WWR for each 3614 façade can help you meet your energy target and construction budget. 3615 3616 While windows have many valuable benefits, including providing views, daylight, natural 3617 ventilation and aesthetics, they also represent a liability in terms of first cost and overall thermal 3618 performance. Glazing systems are often the highest cost envelope component for office 3619 buildings, and high-performance glazing systems and additional shading and daylighting 3620 devices increase this first cost. Glazing systems are also weak points in the thermal envelope 3621 with a significantly reduced R-value compared to opaque walls, accounting for the majority of 3622 an office building’s heat loss. Because they also directly emit solar radiation into the space, they 3623 account for virtually all of the solar heat gain for a building. High-performance glazing can help 3624 reduce this impact, but not as effectively as right-sizing the WWR. 3625 3626


In general, a good starting point for a WWR goal is 30%. This should be adjusted for climate 3627 zone, façade orientation and other design trade off considerations. It is good practice to reduce 3628 WWR on the east and west elevations compared to north and south elevations because east and 3629 west facades are difficult to control solar gains and glare and for northern latitudes (much of the 3630 U.S.) have higher incident solar striking the facades during the summer. (Refer to new solar 3631 radiation graphs in BP#.) 3632 3633 Typically, only a relatively small area of well-positioned windows is needed to provide daylight 3634 and natural ventilation. Predominantly overcast climates may require higher WWR for 3635 daylighting, but care must be taken to also design for sunny days in overcast climates. Providing 3636 for views usually drives the WWR higher than what is needed for daylight and natural 3637 ventilation. See the daylighting section (DL#) for a detailed discussion of glazing for 3638 daylighting and views. 3639 3640 Energy modeling and cost analysis should be used to optimize WWR and glazing performance 3641 to balance cost, thermal loads, natural ventilation, daylighting and views. This modeling needs 3642 to be completed early in the design process to have the greatest impact on design decisions. 3643 Options for modeling WWR include whole building energy simulations such as EnergyPlus as 3644 well as more specific modeling programs such as COMFEN (Lawrence Berkeley National 3645 Laboratory). See Chapter 4 for more information on Energy Simulation. 3646 3647

[TABLE OR GRAPH TO BE ADDED that shows correlation of WWR per climate, 3648 per façade and heating energy use and cooling energy use OR graphs that correlate WWR 3649

and SHGC for a fixed EUI or cooling energy and graphs that correlate WWR and U-factor] 3650 3651 EN50 Select the Right Fenestration 3652 The selection of window glazing should be considered separately for each orientation of the 3653 building. In addition, daylighting and view functions should be considered separately. The three 3654 main properties of fenestration assemblies that should be considered are as follows: 3655 3656

U-factor 3657 SHGC 3658 Visible transmittance (VT) 3659

3660 Table 5-5 shows the target values for U-factor, SHGC and VT. Fenestration products are 3661 available that exceed the minimum requirements in Table 5-5 and should be considered for zero 3662 energy office buildings. The interactions between the fenestration, other building components, 3663 and the energy goal require energy modeling to effectively make decisions. The graphs from 3664 EN# provide information on basic design trade-offs for glazing performance and WWR. 3665

3666 Table 5-5 Fenestration Criteria 3667 Recommendations by Climate Zone

0 1 2 3 4 5 6 7 8 Maximum U-Factor 0.45 0.45 0.45 0.45 0.36 0.36 0.34 0.31 0.28

Maximum SHGC 0.21 0.24 0.24 0.24 0.34 0.36 0.38 0.43 0.43

Minimum Ratio of VT/SHGC 1.10 1.10 1.10 1.10 1.10 1.10 1.10 1.10 1.10

3668


Structural performance, hurricane impact-resistant requirements, and durability should also be 3669 considered because they will affect fenestration product selection and the resulting energy 3670 performance. 3671

3672 EN51 U-Factor 3673 The U-factor is the rate of heat loss or gain through the window—the lower the value the better. 3674 The U-factor of a window or skylight depends not only on the number of panes of glazing and 3675 any special coatings, but also on the construction of the window frame. The best frames are 3676 constructed of non-metallic materials or have a thermal break that separates the interior portion 3677 of the frame from the exterior portion. 3678 3679 Ensure that all models and specifications reflect the assembly U-factor and avoid using the 3680 center-of-glass U-factors for comparisons. For manufactured fenestration, whether shipped 3681 assembled or site-assembled, look for a label or label certificate that denotes that the window U- 3682 factor is certified by the National Fenestration Rating Council (NFRC). This label/certificate 3683 will also include the SHGC and VT. During design, window manufacturers can be consulted for 3684 assembly U-factors, or they can be modeled using a software program called WINDOW (freely 3685 available by Lawrence Berkeley National Laboratory). 3686 3687 In colder climates, select a fenestration to avoid condensation and frosting. This requires an 3688 analysis to determine interior surface temperatures. Condensation can occur on the inner face of 3689 the glass whenever the inner surface temperature approaches the room dew-point temperature. 3690 This scenario is most likely in spaces with elevated humidity. Condensation is less likely for 3691 windows with low U-factors as the reduced heat loss translates to a higher glass surface 3692 temperature. This also translates to improved thermal comfort. During the winter if the interior 3693 surface temperature of glazing drops considerably lower than room temperature and the 3694 temperature of other interior surfaces, then a condition known as radiant asymmetry occurs. 3695 This can cause significant thermal comfort challenges, even when indoor air temperature is 3696 satisfactory. 3697 3698 In high-performing buildings, glazing will almost certainly include multiple panes of glass. In 3699 cold climates triple-pane windows should be strongly considered because double-pane insulated 3700 glazing will not typically meet the recommended or optimal U-factor. The most commonly 3701 specified spacers between glass panes are highly conductive aluminum; however, less 3702 conductive spacers are now available in the marketplace. 3703 3704 Additional improvements can be made with low conductivity window spacers as well as low 3705 conductivity window frames. The whole-window U-factor incorporates all these technologies 3706 and gives the best indication of window performance. (Refer to EN#) 3707 3708 3709

Maintain Internal Surface Temperatures 3710 3711 3712 A minimum R-value of insulation is required for each assembly of the exterior 3713 envelope, so as to maintain minimum internal surface temperatures. These are 3714 essential to maintain the thermal comfort of the interior. Where these minimum 3715 internal surface temperatures are not maintained, radiant and convective heat 3716


flows develop, causing drafts and variations in temperature throughout the 3717 space. These produce feelings of discomfort even if the average interior air 3718 temperature is adequate, which in turn can drive occupants to use additional 3719 energy. 3720 3721 The internal surface temperature can be calculated as follows: 3722 3723

Hi·(Ti – Tg) = U(Ti – To) 3724 3725 Where: 3726

Hi = interior film coefficient = 1.35 Btu/h·ft2°F (horiz. flow) or 1.031 (vertical 3727 flow) 3728 Ti = interior temperature (68) 3729 Tg = interior glass surface temperature (min. = 68 – 4 = 64) 3730 To = outdoor temperature 3731 U = U-factor of component 3732

3733 3734

EN52 Solar Heat Gain Coefficient (SHGC) 3735 Solar Heat Gain Coefficient is the fraction of solar radiation that is transmitted through glazing. 3736 The lower the SHGC the better the control for solar hear gain. As a starting point, the SHGC of 3737 fenestrations should comply with the SHGC delineated in Table 5-5. SHGC is ideally tuned to 3738 each elevation with the lowest value typically for west facing glass and the highest value 3739 typically for north facing glass. 3740

3741 Overhangs work to effectively reduce the SHGC of vertical fenestration on the east, south and 3742 west facades, but on the east and west, there are many times during the day when sunlight will 3743 shine under the overhang, causing glare and discomfort. The size of an overhang is commonly 3744 characterized by its projection factor (PF), which is the ratio of the distance the overhang 3745 projects from the window surface to its height above the sill of the window it shades. 3746

3747 The multipliers in Table 5-6 may be applied to the SHGC of the assembly to calculate the 3748 effective SHGC. For instance, if the NFRC-rated SHGC is 0.40 and the window is shaded by an 3749 overhang with a projection factor of 0.75, the effective SHGC would be 0.40 × 0.51 = 0.20. 3750

3751 While these reduce solar radiation on the east and west, there still may be a glare problem that 3752 can be assessed through the annual sunlight exposure (ASE) calculation (see DL#). 3753

3754


Table 5-6 SHGC Multipliers for Permanent Projections 3755

Projection Factor SHGC Multiplier (South, East, and

West Orientations) 0 to 0.10 1.00

>0.10 to 0.20 0.91

>0.20 to 0.30 0.82

>0.30 to 0.40 0.74

>0.40 to 0.50 0.67

>0.50 to 0.60 0.61

>0.60 to 0.70 0.56

>0.70 to 0.80 0.51

>0.80 to 0.90 0.47

>0.90 to 1.00 0.44

3756 3757 EN53 Visible Transmittance (VT) 3758 The visible transmittance (VT) is the fraction of the visible spectrum of sunlight that is 3759 transmitted through the glazing of a window, door, or skylight. As the VT is coupled to the 3760 SHGC, the ratio of VT to SHGC is often used. With advanced coatings, it is possible to block 3761 most of the radiation outside the visible spectrum while allowing visible light to pass through. 3762 Such glazing is known as spectrally selective, since it selectively allows some wave lengths to 3763 pass while blocking others. 3764 3765 The target value for VT/SHGC ratio as shown in Table 5-5 is 1.10 or higher. Most highly 3766 reflective glazing materials will fail to meet this requirement as they typically have a VT lower 3767 than the SHGC. Clear, green, or blue glass with low-e coatings will almost always comply with 3768 this requirement. Bronze or gray tinted glass with mirror like coatings will not. Relatively high 3769 VTs ensure that occupants can see out. The amount of daylighting that enters the building is 3770 directly proportional to the VT, so daylight apertures should have high VTs. The view windows 3771 below 7 ft do not require high light transmission glazing, so VT values between 0.25 and 0.75 3772 are acceptable, depending on the orientation and climatic zone. Glazing for view windows 3773 should be selected so that views are not hampered. 3774 3775 EN54 Dynamic Glazing 3776 Dynamic glazing is glass that can dynamically change its tint to best respond to real time solar 3777 conditions. There are several key dynamic glazing technologies in the market including 3778 electrochromic and thermochromic. Each technology has a unique process for varying glazing 3779 tint and has their own advantages and disadvantages. 3780 3781 Electrochromic glazing can allow a VT range of approximately 0.01 to 0.58, corresponding to a 3782 SHGC range of 0.09 to 0.41. These wide performance ranges allow for glass to be quite 3783 transparent (when there is no need for solar control) or approaching opaque (where complete 3784 solar control is needed) or ranges in between. This type of flexibility can significantly reduce 3785 annual solar heat gain while still optimizing for daylight and views. Dynamic glazing also 3786 provides glare control and can eliminate the need for conventional window interior blinds. 3787


3788 For cold climates dynamic glazing can be configured as triple-pane units to provide glazing 3789 with improved U-factor while having the benefit of dynamic control of VT and SHGC. 3790 3791 EN55 Use Opaque Wall Assemblies in Place of Spandrel Panels 3792 Glazing systems such as storefront and curtain wall accommodate a variety of building products 3793 that give designers aesthetic flexibility. Glazing systems, even with opaque or insulated panels, 3794 are significantly less energy efficient than conventional opaque wall assemblies. To improve 3795 envelope performance, glazing systems should be used only where transparency is required or 3796 desirable. 3797

3798 Where spandrel glass or opaque panels are used in these systems, the installations should follow 3799 the U-factor recommendations for opaque wall assemblies. In practice, this requires the use of 3800 oversize rabbet-edge panels (where insulated panels are glazed in) and supplemental insulation 3801 (where spandrel glass is used.) The latter approach poses technical challenges in terms of 3802 continuous insulation, and the condition is better addressed by an opaque wall system. When 3803 insulated panels are used, they must be sealed to the assembly to prevent airflow to the spandrel 3804 that would substantially reduce the U-factor. 3805

3806 EN56 Evaluate Glazing Frame Alignment 3807 Installing the fenestration outside of the plane of the wall insulation defeats the thermal break in 3808 the window frame. Fenestration should be installed to align the frame thermal break with the 3809 wall thermal barrier as illustrated in Figure 5-15. This will minimize the thermal bridging of the 3810 frame due to fenestration projecting inboard or outboard of the insulating layers in the wall. 3811 3812 In the same way, insulated exterior doors need to fall entirely within the exterior building 3813 insulation plane as illustrated in Figure 5-16. At door sills, the foundation insulation should 3814 extend all the way to the sill and the exterior walking surface must be held back to 3815 accommodate the insulation. (Note: the insulation is covered by the threshold.) 3816

3817 3818

3819 Figure 5-15 Top view of a window system to opaque wall connection. 3820


3821 3822

3823 Figure 5-16 Exterior door insulation installation. 3824

3825 3826

EN57 Framing and Assembly U-Factors 3827 The recommended fenestration U-factors in Table 5-5 are assembly U-factors that include the 3828 U-factor of the glass with the mullions and window frame including the edge-of-glass spacers. 3829 Window frames have significantly higher U-factors than the glazing. To achieve a low U-factor, 3830 window frame material, construction and design must all be considered. Aluminum is the most 3831 common window material for commercial offices but because it is highly conductive, it is poor 3832 performing compared with other frame materials such as wood and fiberglass. Frame U-factor is 3833 improved by introducing one or more thermal breaks into the frame assembly to separate the 3834 interior exposed portion of the frame from the exterior exposed portion of the frame. Figure 5-3835 X shows an example of a dual thermal barrier aluminum window frame. 3836

3837 3838

[IMAGE TO BE ADDED showing 3839 a dual thermal barrier aluminum window frame] 3840

3841 Figure 5-X Example of a Dual Thermal Barrier Aluminum Window Frame 3842

3843 It is typically easier to establish U-factors for factory-built window units than with storefront or 3844 curtain wall glazing systems. Sometimes modeling must be used to ensure that the window 3845 system selected can meet the recommended U-factors and will contribute effectively to meeting 3846 the overall energy performance of the building. Product manufactures may also be able to 3847 provide assembly level U-factors. Manufacturer-provided online calculators can also be used. 3848

3849 Seek to reduce the area of framing for any given area of glazing to reduce the impact of frames 3850 on thermal performance. Subdividing sections of glass with mullions introduces an even larger 3851


penalty. To maximize energy efficiency, intermediate mullions should generally be minimized. 3852 Note that mullions are helpful to separate daylighting glass from view glass and can be used as 3853 a mechanism to attach light shelves and blinds that can reduce glare without impacting the day- 3854 lighting. 3855 3856 The method of installation of the window system including factory-built windows, storefront, 3857 and curtain wall systems must be considered and accounted for in the overall energy modelling. 3858 Clips and bearing plates are integral to the installation and can be a source of thermal bridging 3859 between the window system and the exterior wall construction. These thermal bridges should be 3860 minimized (See also EN18). 3861

3862 EN58 Framing and Assembly Infiltration Rates 3863 Use frames and framing systems that, with glazing, meet infiltration recommendations. While 3864 the infiltration recommendations in this section include the entire envelope, windows are an 3865 important part of achieving the desired level of airtightness (EN#). Note that while storefront 3866 and curtain wall systems are frequently tested to the same level of airtightness, in practice, 3867 curtain wall is typically more airtight than storefront. 3868 3869 EN59 Air Barrier and Thermal Break Continuity 3870 Some fenestration types pose particular challenges or opportunities in regard to connectivity 3871 with the wall air barrier. 3872

3873 Conventional windows can be tied to the wall air barrier in a relatively straightforward way 3874 through the combination of self-adhering membranes, low-expansion foam insulation, and 3875 sealants. 3876 3877 Curtain wall is also well suited to air barrier continuity. Self-adhering membranes or silicone 3878 transition strips can be terminated directly in the glazing pocket and mechanically clamped by 3879 the pressure plate. Framing members generally have structural capacity and reinforcing is not 3880 required. 3881 3882 Storefront systems pose more challenges for air barrier continuity. Continuity is complicated by 3883 the nature of the extrusion, the method of bearing/attachment, and the method of draining and 3884 flashing the system. To maximize efficiency, consider the following strategies: 3885

3886

Always specify continuous filler plates on the concealed portion of the extrusion (to 3887 receive the air barrier.) Filler plates should be thermally broken or nonconductive. 3888

Size storefronts such that all units can be carried by mounting brackets. Use thermally 3889 broken bearing plates. Where bottom bearing units are unavoidable, use non-continuous 3890 bearing plates at the storefront shimming locations. 3891

Size storefronts such that steel reinforcement of mullions is not required. Steel 3892 reinforcement of jambs is typically not thermally broken and defeats framing systems 3893 that are otherwise thermally broken. 3894

Size storefront-mounted shading to avoid the need for steel reinforcing of the vertical 3895 mullions. Where shading devices would require mullion reinforcement, compare the 3896 energy penalty to that of other mounting strategies. 3897


Require secondary mechanical attachment of the self-adhering membrane or transition 3898 strip to the storefront filler plate (and ensure all parties understand the tight tolerances 3899 required to do so.) 3900

Never insulate inside the extrusion without the manufacturer’s written endorsement. 3901

Ensure that all glazing units are air-sealed by the fabricator per the manufacturer’s 3902 recommendations and can be represented by the manufacturer’s infiltrations test reports. 3903

3904 EN60 Operable Fenestration 3905 Operable fenestration offers personal comfort control and connections to the environment. 3906 Therefore, there should be a high level of integration between operable windows, envelope, and 3907 HVAC system design to maximize the energy benefits of this strategy. The envelope should be 3908 designed to take advantage of natural ventilation with well-placed operable openings. See HV# 3909 for guidance on interfacing operable windows with the HVAC system. See BP# for guidance on 3910 building and site planning as it relates to natural ventilation. 3911 3912 Operable units should meet fenestration requirements discussed elsewhere in this document (see 3913 TBD). 3914

3915 While screens may be used, note that they can significantly reduce the airflow (up to 40%) and 3916 air volume through fenestration openings. Screens also reduce the VT and SHGC and can 3917 impact daylighting. 3918 3919 EN61 Construction Sequencing 3920 A properly detailed building enclosure requires that building fenestration be installed prior to 3921 the building insulation and the building skin. This allows the wall air barrier system to be easily 3922 and thoroughly tied to the fenestration components minimizing infiltration issues. Critical issues 3923 that enable an early installation include an early start to fenestration submittals and shop 3924 drawings as well as adequate protection of the fenestration post-installation and throughout the 3925 remainder of construction. 3926 3927 Always consult with the fenestration manufacturer to vet the sequencing early in the process to 3928 ensure that all stakeholders understand the goals of the envelope installation and the benefits of 3929 a potentially alternative construction sequencing. 3930 3931 REFERENCES AND RESOURCES 3932 3933 ASHRAE. 2016. ANSI/ASHRAE/IES Standard 90.1-2016, Energy Standard for Buildings 3934

Except Low-Rise Residential Buildings. Atlanta: ASHRAE. 3935 ASHRAE. 2017. ASHRAE Handbook—Fundamentals. Chapter 24. Chapter 26, Heat, Air, and 3936

Moisture Control In Building Assemblies—Material Properties. Table 1, Building and 3937 Insulating Materials: Design Values. Atlanta: ASHRAE. 3938

ASTM. 2003. ASTM E2178-03, Standard Test Method for Air Permeance of Building Materi- 3939 als. West Conshohocken, PA: ASTM International. 3940

ASTM. 2011. ASTM E1980-11, Standard Practice for Calculating Solar Reflectance Index of 3941 Horizontal and Low-Sloped Opaque Surfaces. West Conshohocken, PA: ASTM Interna- 3942 tional. 3943


BSC. n.d. Builder’s Guide series. Joseph Lstiburek, ed. Building Science Corporation. https:// 3944 buildingscience.com/book-categories/builders-guides. Westford, MA: Building Science 3945 Corporation. 3946

Cool Roof Rating Council. http://coolroofs.org/. 3947 D’Annunzio, J. 2016. Thermal and dew point transfer: How to avoid issues related to steel- 3948

deck fasteners. Troy, MI: Building Enclosure. www.buildingenclosureonline.com/articles 3949 /85717-thermal-and-dew-point-transfer. 3950

DOE. 2010. Guidelines for selecting cool roofs. Oak Ridge, TN: Oak Ridge National Labora- 3951 tory. https://heatisland.lbl.gov/sites/all/files/coolroofguide_0.pdf. 3952

Nordbye, T. 2011a. Air sealing. Journal of Light Construction, January. Nordbye, T. 3953 2011b. Passive house. Journal of Light Construction, April. 3954

Nordbye, T. 2013. Air sealing without foam. Journal of Light Construction, May. 3955 Pallin, S., M. Kehrer, and A. Desjarlais. 2014. The energy penalty associated with the use of 3956

mechanically attached roofing systems. Presented at the Symposium on Building Envelope 3957 Technology. pp. 93–102. http://rci-online.org/wp-content/uploads/2014-BES-pallin-keh rer-3958 desjarlais.pdf. 3959

PHIUS. 2017. Software resources. Chicago: Passive House Institute U.S. www.phius.org/soft 3960 ware-resources 3961

3962 3963 DAYLIGHTING 3964 3965 OVERVIEW 3966 3967 Daylighting is both an energy efficiency and high performance building measure. In the context of 3968 high performance buildings, daylighting provides occupants with a connection to the outdoors 3969 through high quality views, intensity variation over space and time, and access to a full range of 3970 visible wavelengths. Daylighting also offers a layer to the lighting system that can be used to 3971 support demand response load reductions and wayfinding during prolonged grid outages. 3972 3973 In the context of zero energy office buildings, daylighting can lower the electric lighting EUI by 3974 about 25%. For example, the model developed for this Guide, which is grounded in real high 3975 performance lighting load profiles, results in an electric lighting EUI of 1.2 kBtu/ft2/yr for a mid-3976 latitude location. Without daylighting, the lighting EUI result would be 1.6 kBtu/ft2/yr. Compared 3977 to the whole building EUI target of approximately 20 kBtu/ft2/yr for the same location, 3978 daylighting reveals itself as a nontrivial but lower priority part of the energy measure portfolio. 3979 This relative lessening of the impact of daylighting as an energy efficiency measure is due to a 3980 recent increase in lighting system efficacy and higher resolution occupancy control. Additionally, 3981 window-to-wall ratio and solar heat gain (for hot climates) top the list of important zero energy 3982 design considerations, after plug loads and infiltration. Overglazing is not a cost-effective option 3983 for zero energy design. That said, glazing should and will be used on buildings for a variety of 3984 reasons and electric lighting use should decrease with the available resource as one of the many 3985 steps needed to reach zero energy. 3986 3987 To achieve the zero energy and high performance building goals, it is ever more important to 3988 consider daylighting as a measure which should be thoughtfully applied with equal consideration 3989 of energy use, environmental quality, and resiliency. 3990 3991


DESIGN APPROACH 3992 3993 DL1 Daylighting Design Methodology (Climate Zones: all) 3994 3995 The following tenets describe a daylighting design driven by multiple performance goals, zero 3996 energy being one. The methodology informs the specific recommendations given in the 3997 subsequent how-to tips. 3998

Each window provides a function, if not multiple, including high quality view and 3999 daylighting to replace or supplement electric lighting use during daytime hours, to 4000 occupants work area. 4001

Occupants are provided with access to ambient daylight and views through the use of a 4002 shallow floor plate and clear lines of sight. For example, all occupants are located within 4003 30 feet of a perimeter window and low partition heights at workstations and view 4004 preserving partition glass between office spaces are typical. 4005

Façade, interior, and electric lighting design decisions are made with an integrated 4006 system design approach. For example, workstations are retracted from windows and 4007 corridors are placed at the perimeter of open office areas so that the walkway and 4008 exterior shading elements work together to provide a buffer for occupant glare and heat 4009 control. 4010

The design is glare free on an annual basis since glare can negate all positive energy and 4011 occupant well-being effects. Glare from the sky and sun, as well as reflections off of 4012 building equipment are considered. 4013

Surface luminance balance is considered for a range of daylight, and electric lighting 4014 and daylight scenarios. Vertical surface lighting can enhance vertical illuminance at the 4015 eye and the perception of spaciousness; however, adjacent surface luminance ratios 4016 should be kept to a maximum of 20:1 relative to the daylight glazing to maintain visual 4017 comfort. 4018

Electric lighting near glazing turns off or dims during daylight hours. A more considered 4019 control strategy that includes daylight dimming of predefined electric lighting zones is 4020 incorporated in design but a basic check for lights off near all glazing such as entry 4021 doors, corridors, and stairways is an ingrained part of the setup and commissioning 4022 process. 4023

Electric lighting supports daylight distribution through workstation task lights or surface 4024 lighting that is controlled, manual-on by occupants when needed, allowing a flexibility 4025 for various occupant preferences and tasks, not requiring the system to automatically 4026 turn on to meet an illuminance criterion at the darkest location in the space, which is 4027 often not necessary throughout a day or year. (See the Lighting Controls section for a 4028 more general controls methodology.) 4029

4030 Figure 1-DL1 identifies two office buildings that exemplify many of the daylighting design 4031 tenets for zero energy. The National Renewable Energy Laboratory’s Research Support Facility 4032 (RSF) shows a solution appropriate for predominantly clear skies and the Bullitt Center shows a 4033 solution appropriate for predominately overcast skies. These examples show just two workable 4034 configurations. 4035 4036


[PHOTOS TO BE ADDED] 4037 4038

Figure 1-DL1 Examples of Zero Energy Daylighting Design 4039 4040 Additionally, the daylighting design approach might differ for a speculative versus build-to-suit 4041 office building. For speculative office space, the daylighting design need not provide the full 4042 task illuminance in all spaces. Daylight is used as a general layer of light for occupants to 4043 achieve a base task such as wayfinding and conversing with colleagues for as many spaces as 4044 possible. Try to accomplish this with a fairly consistent window-to-wall ratio on all facades of 4045 30% or less. Focus on balancing surface luminance and allowing access to high quality views. 4046 As tenants move interior partitions over time or use spaces for various visual tasks, the base 4047 daylight layer may need to be supplemented with electric light. 4048 4049 For a built-to-suit office, focus on full daylighting for areas with high illuminance/LPD 4050 requirements or high occupant use/density areas. The occupants of these areas can benefit from 4051 a continuous, higher saturation of daylight. The potentially higher window-to-wall ratio for one 4052 or two facades can be balanced with a lower window-to-wall ratio on other facades or other 4053 energy efficiency measures. 4054 4055 DL2 Project Phase Tasks (Climate Zones: all) 4056 Successful use of daylighting requires attention to the building design at every scale from building 4057 footprint to occupant task orientation as well as attention to integrated design decisions during 4058 each phase of the acquisition process. One or more team members must champion the expected 4059 daylighting outcomes by generating design ideas and validating expected outcomes throughout 4060 the process. 4061 4062 Predesign. During predesign, focus on building configuration studies and the shaping of the 4063 floorplate. The goal is to minimize floorplate depth and maximize access to daylight and view 4064 by strategically placing light wells, shafts, and atriums and orienting fenestration in a 4065 predominantly north- and south-facing direction. Maximize the amount of occupied space that 4066 has access to windows and minimize the distance from the building core to the perimeter. 4067 4068 The building footprint is the key factor for anticipating future design upgrades and 4069 improvements. A frequent challenge with existing buildings is their depth of floor plate, which 4070 prevents easy retrofits for daylighting, views, and natural ventilation. 4071

4072 Schematic Design. During the schematic design phase, focus on spatial considerations such as 4073 ceiling height, and articulation for clerestories, and space layout including occupants’ primary 4074 working orientation. Place space types that benefit from daylight and views, such as open and 4075 private offices and conference rooms, near the perimeter. 4076

4077 Design Development. During the design development phase, focus on envelope design to 4078 optimize quantity and quality of daylight while minimizing solar gains. The interior design 4079 focus is on surface reflectivity and optimizing furniture and partition layout to align with visual 4080 and thermal comfort requirements. 4081

4082 Construction Documents (CDs). Coordinate electric lighting and controls including the 4083 placement of manual-on switches for occupant zones, and verifying the placement of 4084


photosensors for automatically turning off or dimming lights in response to daylight. Verify 4085 glazing details such as visible light transmittance for each façade and window type. 4086 4087 Construction Administration (CAs). Walk through the building from the perspective of an 4088 occupant and identify any glare conditions or otherwise uncomfortable lighting scenes to 4089 address the issue before occupants cover windows or otherwise override the design. Look for 4090 small opportunities to turn lights off in response to daylight such as in vestibules or corridors 4091 with borrowed daylight from an adjacent office space. 4092 4093 GENREAL DESIGN CONSIDERATIONS 4094 4095 DL3 Building Footprint and Façade Orientation (Climate Zones: all) 4096 For the simplest daylighting design, the building should be elongated in the east-west direction, 4097 oriented within 15° of north and south directions. This allows for static shading solutions of 4098 reasonable size and daylight redirection devices that are most efficacious during typical daytime 4099 working hours. 4100 4101 In new buildings with site constraints or in a retrofit, east-west elongation and dominate façade 4102 orientations can work well with a more sophisticated shading solutions to block glare and heat 4103 gain from low-angle sun. If the design time is taken to develop a glare-free and workable east-4104 west daylighting solution then a benefit can be that electric lighting savings are realized during 4105 times of lower output from PV, aiding in a grid-friendly building design. 4106 4107 Metrics to guide footprint form, which set the stage for successful daylighting and views, 4108 include: 4109

Locate the maximum amount of occupied space within minimum distance to the 4110 building perimeter using 30 ft from occupant to perimeter as a guide. 4111

Locate 75% of the occupied space within 20 ft of the perimeter wall. 4112 Achieve a 60 ft floorplate depth where possible. 4113

4114 DL4 Space Programming (Climate Zones: all) 4115 In concert with the building orientation, identify the spaces that benefit most from daylighting 4116 (high occupant density and high LPD) and locate those spaces on the perimeter of the building. 4117 For typical offices, the first priority is to locate open office areas on the perimeter, preferably at 4118 the south perimeter to take advantage of redirected south sun. Locate private office spaces on 4119 the east- and west-facing perimeters or on the interior at the boundary of the secondary daylight 4120 zone. For private offices not on the window wall, place glazing along the private office wall that 4121 is parallel to perimeter wall, which allows views toward windows. Locate intermittently used, 4122 large conference rooms on the north or east façade to prevent the overlap of high occupant heat 4123 gain with high solar heat gain during afternoon peak load. Locate small huddle rooms, often the 4124 most used spaces in open office environments with group viewing of AV needs but for short 4125 periods of time, on north or west facades, or at the core of the building. Figure 1-DL4 shows a 4126 south-west corner of a floorplate designed with daylighting and views in mind. 4127 4128


4129 Figure 1-DL4 Typical Southwest Corner Floorplate for Daylighting & Views 4130

4131 DL5 Fenestration Function (Climate Zones: all) 4132 Daylighting apertures should be located as high in the space as possible to increase the ability to 4133 provide even, ambient illumination across the space. Daylighting apertures start at 7 ft or higher 4134 and extend to a minimum of 10 ft, and maintain a high visible transmittance (VT) of 60% or 4135 higher. Daylight windows are shown on the right side of Figure 1-DL5, and north clerestory 4136 windows are shown on the left side of the image. View windows should be located at eye level, 4137 although a sight line to daylighting apertures might be a necessary or desirable way to provide a 4138 view. View windows should have a VT of 30%-60% depending on the brightness of the scene 4139 being viewed (e.g., dense vegetation versus light concrete buildings). Openings for natural 4140 ventilation need to be located both low and high in the space. For these reasons, fenestration 4141 should be designed to separately serve specific functions instead of large spans of windows used 4142 solely for transparency or continuity. 4143 4144 4145


4146 Figure 1-DL5 Example of Clerestory (left of photo) 4147

and daylight windows (right of photo) 4148 (Image courtesy Dennis Schroder, NREL) 4149

4150 The total window-to-wall (WWR) ratio including both daylight and view windows should not 4151 exceed 40% for a zero energy office building. A WWR of 25% - 35% will enable sufficient 4152 daylighting and views in most office buildings while preventing excess heat transfer. Small 4153 increases in WWR have a relatively large impact on whole building EUI relative to other design 4154 parameters. For this reason, setting a WWR and working within that limit to achieve the 4155 maximum daylighting and views possible is an appropriate zero energy design approach. 4156 4157 DL6 Daylight Redirection (Climate Zones: all) 4158 Diffuse daylight from an overcast sky or clear sky through a daylight aperture starting at 7 ft 4159 AFF can be assumed to provide sufficient illuminance for occupants that work within the 4160 distance to the wall that is about one times the head height of the window, and partial daylight 4161 within two times the head height. (This perpendicular measure from the wall is part of a 4162 daylighting zone calculation, commonly referred to in energy codes and standards.) To provide 4163 ambient daylight to a greater zone depth, such as the recommended 60’ floorplate depth, 4164 daylight redirection devices are needed. These devices use direct sunlight and redirect it upward 4165 to create a luminous ceiling. This strategy is most effective on south facades in sunny climates 4166 however all locations and east and west orientations can benefit from sunlight redirection. 4167 4168 Optical louvers, shown in Figure 1-DL6, which are specifically designed shapes for redirecting 4169 sunlight of a given input angle, can be highly effective for maximizing the depth of penetration 4170 of sunlight onto the ceiling and for preventing direct sunlight from being transmitted or 4171 redirected down to the occupant’s visual field. If daylight windows are placed high on the wall 4172 and well out of the occupant visual field, as with clerestories or monitors, then treatments such 4173 as frit, etching, or translucent glass can be used to diffuse incoming sunlight. These treatments 4174 prevent glare and redirect daylight to room surfaces, but they do not create daylighting zones 4175 the size that is possible with view preserving glass. 4176 4177


For retrofits with curtain wall, consider applying a redirecting film or micro louvers to the 4178 portion above 7 ft and mount shades at 7 ft for the view portion of the window. 4179 4180 4181

4182 (a) Optical Louvers (b) Microstructure Applied Film 4183

Figure 1-DL6 4184 (Image courtesy Dennis Schroder, NREL) 4185

4186 4187 [Note for Reviewers: If annual metric description is moved to beginning of section, include sDA 4188 maps/zones for a range of solutions: view preserving glass, optical louvers, translucent and 4189 show typical daylight zone and surface luminance; show south zone larger then north for south 4190 redirection in sunny climate.] 4191 4192 DL7 Shading and Glare Control (Climate Zones: all) 4193 Uncontrolled solar heat gain is a major cause of energy use for cooling, particularly in warmer 4194 climates, and of thermal discomfort for occupants. Appropriate configuration of windows 4195 according to the orientation of the wall on which they are placed can significantly reduce these 4196 problems while simultaneously reducing or eliminating direct beam radiation that often 4197 contributes to unwanted heat gain and glare. 4198 4199 Unwanted solar heat gain is most effectively controlled on the outside of the building. 4200 Significantly greater energy savings are realized when sun penetration is blocked before it 4201 enters the windows. Horizontal overhangs at the top of the windows are most effective for 4202 south-facing facades and must continue beyond the width of the windows to adequately shade 4203 them. Table 1-DL7 has factors to approximate the impact of various size overhangs. Vertical 4204 fins can be effective for east and west facades to aid in glare control for early morning and late 4205 evening summer hours on the north façade. Additional exterior shading strategies include 4206 building self-shading, filtering, baffling through soffits, trellises, awnings, external light 4207 shelves, and vegetation. See Figure DLxx for sections of these strategies. The combined SHGC 4208 of the window and shading system should not exceed 0.25 for warm climates and should not 4209


exceed 0.45 for any climate. Window SHGC is a sensitive building design parameter for 4210 achieving zero energy. 4211 4212

Table 1-DL7 SHGC Multipliers for Permanent Projections 4213 Projection Factor

SHGC Multiplier (South, East, and West

Orientations) 0 to 0.10 1.00

>0.10 to 0.20 0.91 >0.20 to 0.30 0.82 >0.30 to 0.40 0.74 >0.40 to 0.50 0.67 >0.50 to 0.60 0.61 >0.60 to 0.70 0.56 >0.70 to 0.80 0.51 >0.80 to 0.90 0.47 >0.90 to 1.00 0.44

4214 Shading, filtering, or reflecting materials can be integrated into the glazing to reject unwanted 4215 solar gain. These include glazing that employ special coatings/constructions with selective 4216 transmission, as well as diffusing or opaque elements integral to the glazing, fritted patterns, 4217 fiber-fill, aerogel or interstitial louvers. 4218 4219 Interior blinds and shades are the least effective shading devices for limiting the window-driven 4220 cooling load in the space. However, these solutions are often employed as a cost-effective, 4221 controllable solution to mitigate glare and thermal discomfort for occupants especially for 4222 retrofits. When using such a solution, consider the use of top-down shades for view glass or 4223 blinds with tilt angle limits for daylight glass to maintain functionality of the windows as 4224 providing some daylight distribution and views throughout the entire day. 4225 4226 The success of daylighted offices depends on how occupants interact with the daylighting 4227 system, particularly for blinds and shades. If blinds are left closed, the daylighting and view 4228 potential will not be realized. If temporary darkening of a specific space is not functionally 4229 required, do not install shades or blinds. Unnecessary blinds results in reduced daylight 4230 performance, increased first costs, and higher long-term maintenance expenses. If blinds are 4231 necessary, consider including a mechanism to reset shade position or the clear, view preserving 4232 state at least once daily and, ideally, to the most efficient position at any given time of day when 4233 the space is unoccupied. 4234 4235 Figure 1-DL7 shows a combination of north-facing windows, hoods on south-facing view 4236 windows, and building self-shading on the west-facing windows, which enable a solution with 4237 no blinds, saving cost and maintaining views. 4238 4239 4240


4241 Figure 1-DL7 No Blind Shading Solution 4242 (Image courtesy Dennis Schroder, NREL) 4243

4244 [Note to Reviewers: If annual metric description is moved to beginning of section, add façade 4245 sections and ASE maps of shading strategies showing overhang (cooling load, south; glare; 4246 also showing projection factor calculation) fins (cooling load east-west; glare); hoods (no 4247 interior shades); vegetation, trellis; glazing integrated materials such as low-e or 4248 electrochromic; interior shades (glare and occupant comfort).] 4249 4250 DL8 Fenestration Details (Climate Zones: all) 4251 The specification and design details of the daylight and view windows are important to realizing 4252 a well daylighted, comfortable interior environments. The window specifications of SHGC, U-4253 factor, VT, and LSG should be considered for thermal performance as described in ENxx and as 4254 shown in the following window diagrams in Figure 1-DL8. Additional considerations include: 4255

Place all view glass above 3 ft AFF. Windows below the task plane rarely offer 4256 sustained benefit to occupants in terms of view and provide minimal contribution to 4257 usable daylight distribution on the task plane or visible surfaces. 4258

Align windows with office partition walls and the ceiling plane. This can reduce contrast 4259 near the apertures by allowing daylight to wash the adjacent ceiling and wall, which will 4260 in turn reflect more light onto the perimeter wall, reducing luminance ratios across that 4261 surface. 4262

Consider frame color, window well color and depth for reducing or enhancing contrast 4263 at the window wall. 4264

Screens for natural ventilation can decrease VT and view clarity. Compensate for the 4265 reduced daylighting efficacy through an increase in VT and by examining the screen 4266 effect in locations considered important for occupant views. 4267

4268 4269


4270

(G3: ~70% VT, G4: ~35% VT, G6: Solid wall) 4271 Figure 1-DL8 Example Window Diagrams (Images courtesy NREL) 4272

4273 [Question for Reviewers: Would it be helpful to add a side bar that talks about the calculation 4274 of WWR and the importance of being clear on interior versus exterior wall area, and frame 4275 type/size and its effect on thermal and daylighting performance. DL5 and DL8 can reference the 4276 sidebar.] 4277 4278 DL9 Interior and Exterior Surface Finishes (Climate Zones: all) 4279 For interior surfaces, select light colors (white is best) with a matte finish for interior walls and 4280 ceilings to increase light reflectance, mitigate glare, and reduce lighting and daylighting 4281 requirements. Minimum surface reflectances are shown in Table 1-DL9. The colors of the 4282 ceiling, walls, floor, and furniture have major impacts on the effectiveness of the daylighting 4283 strategy. 4284 4285 Table 1-DL9 Minimum Surface Reflectance 4286

Location Minimum Reflectance Wall segment above 7 ft 70%

Ceiling 70% (preferably 80%–90%) Light well or window well 80-90%

Floor 20% Furniture 50%

Walls segment below 7 ft 50% 4287


Consider a ceiling tile or surface that has a high reflectivity. Make sure that the ceiling tile 4288 reflectance includes the fissures within the acoustical tiles, as these irregularities affect the 4289 amount of light absorbed. Do not assume that the color of a tile alone dictates its reflectance. 4290 When selecting a tile, specify a minimum reflectivity. Most manufacturers will list the 4291 reflectance as if it were the paint color reflectance. The commissioning (Cx) provider should 4292 verify the reflectance. See ELx for additional information on interior finishes. 4293 4294 Consider the reflectance of the roofs, sidewalks, and other surfaces in front of the glazing areas. 4295 The use of lighter colors can increase daylighting resource at the glazing and, in some cases, 4296 reduce the glass area needed for roof monitors or clerestories. Note that a light-colored walkway 4297 or roofs in front of view windows may cause unwanted reflections and glare. The color might 4298 be a good design choice for the overall heat load of the site but additional glare control 4299 measures at the window or task location might be necessary. 4300 4301 DL10 Electric Light Integration (Climate Zones: all) 4302 Consider the use of lighting fixtures with an indirect component that more closely represents the 4303 same surface lighting effect as daylighting. Indirect lighting spreads light over the ceiling 4304 surface, which then reflects the light to the task locations; with the ceiling as the light source, 4305 indirect lighting is more uniform and can provide better glare control than fixtures with a 4306 predominantly direct component. 4307 4308 See The Lighting Controls section, LC3, for tips on daylighting control design and 4309 commissioning. Attention to this tip is critical for realizing the energy efficiency potential of 4310 daylighting. 4311 4312 [Questions for Reviewers: 4313 Should the following tip DL11 be moved toward the beginning of the section so that sDA and 4314 ASE metrics can be explained and referenced throughout the other tips? Or, should this remain 4315 last and only referenced in the space-by-space recommendations that give a specific solution? 4316 Also, is it appropriate to show sDA by hour to show opportunity for grid responsive design? 4317 4318 Should vertical illuminance at the eye be discussed as a proxy for indoor environmental 4319 quality? Too much indicates glare but too little shows lack of use of daylight for circadian 4320 rhythm entrainment?] 4321 4322 DL11 Daylighting Performance Metrics and Analysis Tools (Climate Zones: all) 4323 This Guide is designed to help achieve zero energy without energy modeling, but energy and 4324 daylighting modeling programs make evaluating energy-saving trade-offs faster and daylighting 4325 designs far more likely to be successful and accepted by occupants over time due to adequate 4326 distribution, and glare and heat gain control. 4327 4328 Daylighted spaces should provide a minimum of 300 lux for at least 50% of the operating 4329 hours. This illumination is then supplemented as needed by electric lighting. The spatial 4330 daylighting autonomy (sDA) for office spaces should be greater than 75% and greater than 55% 4331 for other regularly occupied spaces such as break rooms, conference rooms, and corridors (see 4332 Table DL3). Direct sunlight should not exceed 1000 lux (over ambient) for more than 250 hours 4333 per year. The ASE should not exceed the values shown in Table 1-DL11. 4334 4335


Table 1-DL11 Recommended Annual Daylighting Design Criteria 4336 Location Minimum

sDA300,50% Maximum

ASE1000,250 Open offices 75% 10% Private offices 75% 10% Conference rooms 55% 10% Corridors 55% 25% Break rooms and restrooms 55% 25%

4337

Annual Metric Descriptions 4338 4339 Point-in-time daylighting calculations (for example, workplane illuminance on 4340 December 21 at 9:00 am) can be useful for understanding best- or worst-case 4341 scenarios, but don't provide a good picture of whether a space or building is 4342 performing well on an annual basis. Dynamic daylight metrics take local climate and 4343 sunlight conditions into account, as well as detailed information about the size, shape 4344 and reflectances of the space, and the daylighting aperture shading and redirection 4345 devices. Two IESNA adopted metrics are helpful for evaluating daylighting 4346 distribution and glare/heat gain potential: spatial daylight autonomy (sDA) and 4347 annual sun exposure (ASE). Additional explanation on these metrics is available 4348 from IES (IES 2012). In summary: 4349 4350 Spatial daylight autonomy (sDA) is the percent of an analysis area that meets a 4351 minimum daylight illuminance level for a specified fraction of the operating hours 4352 per year. sDA can be calculated for any illuminance criterion and for any percentage 4353 of time, but the most common threshold is 300 lux for 50% of the time. Subscripts 4354 are commonly attached to indicate the illuminance criterion and percent of operating 4355 hours. An sDA300, 50% indicates that sDA is calculated for an illuminance of 300 lux 4356 and for 50% of the operating hours. If a daylighting design for an open office has an 4357 sDA300, 50% = 65, this means that 65% of the floor area meets this condition. 4358 Calculation of sDA requires software that can estimate the daylighting contribution 4359 at different points within the space for a range of sun and sky conditions representing 4360 the occupied window of the year; such software is offered by a number of vendors. 4361 Typically, lighting levels are calculated on an hourly basis for a 2 ft × 2 ft grid 4362 within the space. 4363 4364 Annual sunlight exposure (ASE) is a metric that describes the potential for visual 4365 discomfort in interior work environments. It is defined as the percent of an analysis 4366 area that exceeds a specified direct sunlight illuminance more than a specified 4367 number of hours per year. Like sDA, subscripts are commonly used to indicate the 4368 thresholds. ASE1000, 250 indicates that the thresholds are 1000 lux above the ambient 4369 lighting level for 250 hours per year. A well daylighted office space would have a 4370 high sDA and a low ASE. Both dynamic metrics are needed evaluate daylighting 4371 designs. sDA gauges if there is enough daylight and ASE gauges if there is not too 4372 much. sDA and ASE are now incorporated in common lighting analysis and design 4373 software packages, such as IESVE, Diva-for-Rhino, Daysim, Safairi, SPOT, and 4374 LightStanza. These tools are offered as examples and are not endorsed by ASHRAE 4375


or its AEDG partners. New tools are being offered each year so not all the available 4376 tools are included in the list. 4377 4378 Annual savings has to be calculated with an annual whole-building energy 4379 simulation tool after the daylighting design tools have been used to determine the 4380 illuminance in the spaces and after the windows have been appropriately sized. 4381 Current daylighting analysis tools do not help with heating and cooling loads or 4382 other energy uses; they predict only illumination levels and electric lighting use. 4383 However, at least one tool available produces an annual lighting power density 4384 (LPD) schedule grounded in the behavior of a specified lighting control system in 4385 response to a given daylighting design. The LPD schedule can be fed to the whole 4386 building energy simulation for an accurate picture of the electric lighting impact of 4387 daylighting (Guglielmetti, 2011). 4388 4389

4390 4391 SPACE-BY-SPACE RECOMMENDATIONS 4392 4393 [Question for Reviewers: The space by space recommendations intend to use photos to 4394 illustrate the concepts discussed. Is this the most helpful way to illustrate the concepts, or 4395 would other types of illustrations be helpful?] 4396 4397 DL12 Open Offices (Climate Zones: all) 4398 In climates with predominantly clear skies, the following set of design decisions will set the 4399 foundation for a glare-free, sufficiently daylighted work environment: 4400

A WWR of 30% on the south and north façades with separate punched windows for 4401 daylight and view 4402

Daylight windows on the south facades starting at 7 ft AFF extending up 3 ft with 4403 interior louvers optically designed to redirect sunlight onto ceiling at a 60 ft depth for all 4404 annual solar angles from 10 am to 2 pm 4405

Untreated daylight or clerestory windows on the north façade 4406

View windows shaded with exterior hoods that block all direct sun from striking the 4407 window from 10 am to 2 pm, April through September 4408

Workstations set back from the south perimeter wall to create a walkway that absorbs 4409 the direct winter sun, preventing the need for shades or blinds for glare control, as 4410 shown in Figure 1-DL12 4411

Low workstation partitions with light, diffuse interior finishes 4412

Indirect/direct electric fixtures with a manual-on control scheme and automatic daylight 4413 dimming to off on all rows of fixtures parallel to the south façade. 4414

4415


4416 Figure 1-DL12 Example of Walkway 4417

that Aborbs Direct Winter Sun 4418 (Image courtesy Dennis Schroder, NREL) 4419

4420 For climates with predominantly overcast skies, these parameters can shift slightly for a higher 4421 WWR allocated toward daylight windows or clerestory window, which, depending on the site 4422 context, can remain untreated if direct sun instances will be limited, welcomed, and if occupants 4423 have local workstation means to shade their visual field from direct sun. 4424 4425 The Daylighting Pattern Guide is a simple tool for design teams to gain a sense for the 4426 relationship between WWR, window placement, and resulting daylight performance: 4427 https://patternguide.advancedbuildings.net. 4428 4429 DL13 Private Offices (Climate Zones: all) 4430 Typical private offices need only a small WWR of 30% or less to provide adequate view and 4431 functional daylight. Place private offices on the north façade to prevent the need for shades or 4432 blinds. (Do provide small vertical fins, or some way to rotate monitors or working orientation 4433 for early morning and late afternoon summer sun that will strike the north façade.) Create low 4434 office walls as shown in Figure 1-DL13 and add clerestory glazing above the private offices to 4435 provide daylight to open office or core areas to the south. 4436 4437


4438 Figure 1-DL13 Example of Low Office Walls and Clerestory Glazing 4439

(Image courtesy Dennis Schroder, NREL) 4440 4441

DL14 Conference Rooms (Climate Zones: all) 4442 Place large conference rooms on the east façade and smaller conference rooms and huddle 4443 rooms, as shown in Figure 1-DL14, on the west façade. Use daylight redirection devices for 4444 larger conference rooms with automatic shades on view glass. Automatic shades, tied to the AV 4445 system are appropriate in high use spaces since manual control can lead to quick degradation of 4446 components. 4447 4448

4449 Figure 1-DL14 Huddle Room Example 4450 (Image courtesy Dennis Schroder, NREL) 4451

4452 DL15 Corridors (Climate Zones: all) 4453


Use borrowed or heavily filtered daylight to light corridors as shown in Figure 1-DL15. Place 4454 electric lighting on an open loop photocell and Cx the system to turn off for most daylight 4455 hours, maintaining the minimum required illuminance for safe navigation. Use accent lighting 4456 in main corridors to improve wayfinding and use other corridors as adaptation spaces for 4457 occupants in transition from exterior to interior. 4458 4459

4460 Figure 1-DL15 Filtered Daylight (left) and Borrowed Daylight (right) 4461

(Images courtesy Dennis Schroder, NREL) 4462 4463 DL16 Break Rooms and Restrooms (Climate Zones: all) 4464 For break rooms, use translucent ceiling or wall panels to borrow daylight from open offices or 4465 corridors, as shown in Figure 1-DL16. For restrooms use translucent daylight windows or 4466 tubular daylighting devices to provide high and even daylight to the space, overcoming 4467 partitions. In both spaces, only a base level of ambient daylight is needed for wayfinding and 4468 manual-on accent lighting can be provided at wash areas in restrooms or food preparation 4469 counters in break rooms. Often, occupants are quickly entering breakrooms to perform a simple 4470 task such as taking lunch out of a refrigerator. A 5 fc -10 fc ambient daylight condition is often 4471 sufficient to prevent a ten-to-fifteen minute on time for electric lighting for a minute or less of 4472 occupant use. 4473 4474


4475 Figure 1-DL16 Example of Translucent Ceiling 4476

(Image courtesy Dennis Schroder, NREL) 4477 4478 REFERENCES 4479 4480 Guglielmetti R, et al. 2011. Energy use intensity and its influence on the integrated daylighting 4481

design of a large net zero energy office building. Presented at the ASHRAE winter 4482 conference, Las Vegas, Nevada. 4483

IES. 2012. Approved Method: IES Spatial Daylight Autonomy (sDA) and Annual Sunlight 4484 Exposure (ASE), IES LM-83-12. NY: Illuminating Engineering Society of North America. 4485

IES. 2011. The Lighting Handbook, 10th ed. NY: Illuminating Engineering Society of North 4486 America. 4487

4488 [Note/Question for Reviewers: This preliminary draft provides guidance on lighting controls in 4489 the following standalone section separate from Daylighting and Electric Lighting. Is this the 4490 best way to organize this guidance?] 4491 4492 LIGHTING CONTROLS 4493 4494 LC1 Goals for Office Lighting Controls 4495 Zero energy office buildings are typically high performance buildings in that they aim to meet a 4496 variety of human wellbeing, environmental, and cost effectiveness goals. In a high performance 4497 building, the primary objectives for lighting control and sensor systems are to: (1) contribute to 4498 a comfortable and productive environment by providing dynamic lighting that responds to 4499 variation in occupants’ need for quantity, distribution, and spectrum of light depending on their 4500 task, individual preferences, or the time of day; and (2) support energy- and capital-cost-saving 4501 services by providing data about occupant and space patterns, and equipment performance to 4502 building information and control systems. In the pursuit of zero energy, an additional focus 4503 must be placed on providing electric light only at the time and quantity needed to meet the 4504


building goals. Additionally, the services made possible with a building-integrated or internet-4505 connected lighting control system should be selected based on the ability of the service to 4506 support zero energy operation over time. 4507 4508 The following tips highlight the most impactful steps toward realizing a high performance 4509 lighting control system for a zero energy target. 4510 4511 GOOD DESIGN PRACTICE 4512 4513 LC2 Separately Control Electric Light Distribution, Intensity, and Spectrum 4514 Leverage the lighting design’s lighting layers and solid state lighting color tunability to create a 4515 variety of scenes that are most appropriate for various tasks, and enable occupants to select the 4516 appropriate scene if the automatically selected scene is not sufficient. To control light 4517 distribution and intensity, separately switch or dim ambient, task, and accent lighting in each 4518 space. For this guide luminaire level lighting control (LLLC) luminaires are used in all open and 4519 private office spaces. LLLC’s allow individual or small groups of luminaires to have their own 4520 sequence of operations or response based on specific occupant behaviors or preferences. 4521 4522 To control light spectrum (change the color temperature – EL5), consider tunable white or full 4523 color tunable LED sources (https://www.energy.gov/eere/ssl/understanding-led-color-tunable-4524 products) for office areas where occupants work in one location for contiguous hours and have 4525 indirect connection to daylight. Spectral tuning can allow the lighting system to enhance the 4526 connection to daylight spectrum for partially daylit spaces, and enable circadian lighting for 4527 compliance with the WELL Building Standard certification. 4528 4529

Caution: Consider spectral tuning carefully. Open office spaces should only have pre-4530 programed color changing sequences based on time of day. Private offices under the 4531 control of a single occupant may have manual control, but the color temperature range 4532 should be limited as to not create a rainbow effect of colors emanating from the private 4533 offices. 4534

4535 The resolution of control (per fixture or zone, and spectral tuning type) for the selected 4536 luminaire and control equipment will inform lighting control protocol. Lighting control protocol 4537 descriptions are described by the IES (IES 2017). It is important to understand the pros and cons 4538 of the selected lighting control protocol and control system architecture for integration with 4539 building level information on control systems (see tip LC3). 4540 4541 Dimming is a common and affordable option for solid state lighting, typically implemented 4542 using the 0-10 V protocol. Dimming is an important function for effective daylighting and task 4543 tuning so take time to consider the control signal versus power curve of the specified driver. For 4544 example, if it is expected that a task will require a small amount of ambient light to balance 4545 luminance in a daylit area, ensure that the driver operates in the signal input range of 0%-10% 4546 versus cutting to off at 10% input signal. 4547 4548 In addition to dimming curves, consider potential dimming quality issues such as flicker, power 4549 quality, and color consistency. Set performance criteria for each parameter in the controls 4550 specification. 4551 4552 4553


Luminaire Level Lighting Control (LLLC) 4554 4555 LLLC luminaires at a minimum have an integral occupancy sensor, an integral 4556 daylight sensor, a dimming driver and individual control logic (with the ability to 4557 communicate with other luminaires – typically wirelessly) built into each luminaires. 4558 LLLC luminaires can be grouped to respond to occupancy patterns (e.g. lights over a 4559 row of open office cubicles), can be set to dim in response to increased daylight light 4560 levels in the space, and can be tuned to match user preferred light level in the space. 4561 4562 LLLC luminaires are initialized/commissioned using a handheld remote or 4563 smartphone which allow the grouping of luminaires, the setting of the daylight low 4564 setpoint, the occupancy sensitivity and timeout setting, and tuning the light level to 4565 match user preference. 4566 4567 The control logic allows luminaires to detect and share information with one another 4568 to adjust to occupancy and/or daylight in the space. The system will allow zoning of 4569 the luminaires and has the capability to adjust light levels either individually or in a 4570 zone. 4571 4572

4573 4574 LC3 Use an Occupant-Engaged Control Strategy 4575 As a default strategy for all zero energy offices, employ an “opt-in” or “occupant-engaged” 4576 lighting control strategy, which is characterized by manual-on settings on digital switches. The 4577 default and obvious control interface for the occupant should, when pressed, cause lights to turn 4578 on to the power level needed to perform the simplest visual task in the space (no more than 50% 4579 light output of ambient luminaires for a space type). Allow occupants to turn on additional 4580 zones, layers of light, or increase intensity of the ambient luminaires as needed for their task. 4581 This strategy allows occupants to consider the amount of light they need at a particular time and 4582 prevents the automatic-on of luminaires in spaces with borrowed daylight, for example, when 4583 an occupant is passing through. 4584 4585 An occupant-engaged control strategy is also characterized by automatic-off function using 4586 occupancy sensors for small areas and timeclock sweeps (automatic-off at a pre-programmed 4587 time) as an option for large areas with relatively consistent occupancy and schedules. 4588 4589 While an occupancy-engaged control strategy is a good starting point for many zero energy 4590 offices, do consider an LLLC automatic-on strategy in open office areas with limited daylight. 4591 An automatic-on scenario can prevent over lighting in some manual-on scenarios with large 4592 switching zones, such as when occupancy is intermittent and small zones can be lighted 4593 individually with maintained visual comfort. 4594 4595 LC4 Photosensors 4596 LLLC luminaires include integrated photosensors, or daylight sensors, which will meet all 90.1 4597 daylight control requirements. If not using LLLC luminaires locate a separate photocell in the 4598 center of each of the primary and secondary zones. Consider the primary daylighting zones 4599 when selecting and laying out fixtures to make sure that perimeter rows of fixtures can be 4600 turned off for most of the day. 4601


In all regularly occupied daylighted spaces such as staff areas, continuously dim rather than 4602 switch electric lights in response to daylight to minimize occupant distraction. Specify dimming 4603 ballasts that dim to at least 20% of full output and that have the ability to turn off when 4604 daylighting provides sufficient illuminance. Provide a means and a convenient location to 4605 override daylighting controls in spaces that are intentionally darkened to use overhead 4606 projectors or slides. 4607 4608 Photosensors should be specified for the appropriate illuminance range (indoor or outdoor) and 4609 must achieve a slow, smooth, linear dimming response from the dimming drivers. 4610 4611 In a closed-loop system, the interior photocell responds to the combination of daylight and 4612 electric light in the daylighted area. The best location for the photocell is above an unobstructed 4613 location such as the middle of the space. If using a lighting system that provides an indirect 4614 component, mount the photosensor at the same height as the luminaire or in a location that is 4615 not affected by indirect from the luminaire. 4616 4617 In an open-loop system, the photocell responds only to daylight levels but is still calibrated to 4618 the desired light level received on the work surface. The best location for the photosensor is on 4619 an easily accessible location on the roof with a clear view of the sky, facing the same direction 4620 as the primary façade of the controlled space. 4621 4622 The daylighting control system and photosensor should include a 15-minute time delay or other 4623 means to avoid cycling caused by rapidly changing sky conditions and a 1-minute fade rate to 4624 change the light levels by dimming. Automatic multilevel daylight switching may be used in 4625 environments that are not regularly occupied, such as hallways, storage rooms, restrooms, 4626 lounges, and lobbies. 4627 4628 Even a few days of occupancy with poorly calibrated controls can lead to permanent overriding 4629 of the system and loss of savings. Photosensor commissioning should be performed after 4630 furniture installation but prior to occupancy to ensure user acceptance. Scan the space and 4631 adjacent exterior environment for any highly reflective materials that could produce high 4632 illuminance on the photosensor. Shield the photosensor from view of these materials if possible. 4633 Evaluate the setpoint in a sunny daytime, overcast daytime, and nighttime condition to ensure 4634 the illuminance is maintained in each scenario. 4635 4636 The photosensor manufacturer and the quality assurance (QA) provider should be involved in 4637 the calibration. Document the calibration and Cx settings and plan for future recalibration as 4638 part of the maintenance program. 4639 4640 LC5 Vacancy / Occupancy Sensors 4641 Vacancy sensors (manual ON) are similar to occupancy sensors but require the user to manually 4642 turn the lights on when entering the space. Vacancy sensors are typically switch mounted as 4643 user input is required. 4644 4645 Occupancy sensors (automatic ON) can be switch mounted replacing the traditional wall switch, 4646 ceiling mounted or attached directly to each light luminaires. 4647 4648 Unless otherwise recommended, factory-set sensors should be set for medium to high sensitivity 4649 with a maximum 15-minute time delay (the optimum time to achieve energy savings without 4650


creating false OFF events). Work with the manufacturer for proper sensor placement, especially 4651 when partial-height partitions are present. 4652 4653 Periodically confirm that sensors are turning the lights off after the occupant leaves the space. 4654

4655 Switch mounted. Switch mounted sensors are typically use infrared technology to sense 4656

occupants. When using switch mounted sensors confirm that they are set to manual ON 4657 operation during installation as many manufacturers ship sensors with a default setting 4658 of automatic ON. 4659

4660 Caution: Confirm during space planning that switch mounted sensors line of sight to the 4661 occupant will not be blocked by furniture. If the line of sight is blocked use ceiling mounted 4662 occupancy sensors. 4663 4664 Ceiling mounted. Ceiling mounted occupancy sensors can use infrared technology, 4665

ultrasonic technology or both (Dual Technology) to sense occupants. Dual Technology 4666 sensors provide the best overall coverage. 4667

4668 Caution: Ceiling mounted sensors can see outside of spaces if the door is left open thereby 4669 turning on the lights when someone walks by the open door. Dual Technology sensor 4670 typically resolve this issue as both systems must sense the occupant entering the space. 4671

4672 LC6 Use Information Available from the Lighting Control System 4673 Identify the energy- and capital cost-saving applications that make use of lighting control 4674 system sensor data. Example data flow and applications include: 4675

Sending occupancy information to the building automation system to trigger HVAC 4676 setbacks 4677

Sending luminaire power and occupancy information as input to a fault detection and 4678 diagnostics (FDD) tool to assess sequence of operations or equipment failures 4679

Sending occupancy and assumed task information to a building control system during a 4680 demand response event to enable demand response without necessarily reducing the 4681 needed level of service by the electric lighting system 4682

Sending occupancy and assumed task information to a building control system to 4683 optimize the lighting control scene for enhanced occupant wellbeing (e.g., circadian 4684 lighting) and grid-friendliness, while maintaining a base level of electric lighting service 4685 for the occupant 4686

Sending occupancy information to facilities management tools as input for space 4687 utilization metrics to inform the programming for renovation and new occupancy. 4688

4689 Many of these applications are not off-the-shelf specifications but should be considered in the 4690 design process since product offerings are rapidly changing. Zero energy buildings are often a 4691 goal used in concert with other high performance goals such as “WELL”, grid-friendly, and 4692 resilient, all of which require a higher degree of information exchange that offered by 4693 traditional, stand-along lighting control systems. 4694 4695 When considering sensor, driver, and system controller selection, ensure compatibility between 4696 the lighting system and building controls (to the extent that control system integration is part of 4697 the zero energy maintenance strategy). Ensure that dimmable drivers are specified according to 4698


the protocol consistent with the lighting control system and using a dimming method 4699 appropriate for the common operating power of the source. 4700 4701 Coordination between the HVAC design, controls integrator, IT, and facilities maintenance staff 4702 is critical to the success and ongoing use of the applications. 4703 4704 LC7 Measure and Verify Expected Lighting Power Profiles 4705 The lighting power profile for a zero energy office building will typically look like Figure LC1. 4706 The base load should be very low at night (See EL14 Twenty-Four-Hour Lighting), lights 4707 gradually turn on in the morning, daylight dimming occurs during the day, and lights gradually 4708 turn on in the later afternoon as occupants and tasks require it. For non-vacancy/occupancy 4709 controlled lights an automatic sweep should turn all lights off at typically end-of-day. Provide 4710 for one- or two-hour override as needed. As occupants leave for the night, the only lighting load 4711 on periods should be brief as custodial or security staff enter spaces. 4712 4713

4714 Figure LC1 Example zero energy daily lighting load profile 4715

4716 Additional features of a zero energy lighting profile include: 4717

Low baseload. Perform a detailed inspection of potential always-on lighting that can be 4718 controlled to off such as elevator lights and vending machine lights. 4719

Switched egress lighting. Use UL-924 devices to allow egress lighting to be dimmed and 4720 switched in response to occupancy and daylighting. 4721

Lights off at night. The only sources that should be on at night are lights in vestibules or 4722 other points and pathways of entry. The lighted entry paths should lead to manual-on 4723 switches, which allow for all other lights to be off when the building is not in use. 4724

Atypical occupant types show as such. Security walkthroughs and other intermittent use 4725 of space should show up as approximately ten-minute spikes versus hour or more on-4726 time after hours. 4727


Daylighting “dip” and plateau midday to evening. Identify any sensor interactions with 4728 shadows or reflections that might be causing over or under dimming. If lights are all 4729 automatically turning on due to reduced daylight contribution in the afternoon, consider 4730 implementing a noontime sweep to turn all lights off. Enable occupants to manually turn 4731 on lights at any time after the sweep. 4732

Lights off next to windows. Lights at the perimeter of the building that are within the 4733 primary daylight zone of glazing (one window head height deep) are off during daytime 4734 hours. 4735

4736 These tips can be included in commissioning scope and included in ongoing commissioning 4737 procedures. 4738

4739 LC8 Exterior Lighting Controls 4740 Use photocell or astronomical time switches on all exterior lighting. If a building energy 4741 management system is being used to control and monitor mechanical and electrical energy use, 4742 it can also be used to schedule and manage outdoor lighting energy use. 4743 4744 Reduce the power of all parking lot lighting by at least 50% when no activity is detected for not 4745 longer than 15 minutes by using individual occupancy based controls. 4746 4747 Reduce the power of all remaining exterior lighting by at least 75% of the design level when no 4748 occupants are present between 9:00 p.m. and 6:00 a.m. This can be done with either time based 4749 or occupancy based controls. Lighting at building entries and exits may be left at full power, but 4750 by using occupancy based controls users will trigger the higher light level. The higher light 4751 level will identify to security that the area is or has recently been occupied. 4752

4753 4754 REFERENCES 4755 4756 IES. 2012. Lighting Control Protocols, ANSI/IES TM-23-17. NY: Illuminating Engineering 4757

Society of North America. 4758 4759 4760 ELECTRIC LIGHTING 4761 4762 INTERIOR LIGHTING 4763 4764 [Question for Reviewers: The Electric Lighting section outlines retrofit and renovation 4765 opportunities for existing buildings which are highlighted in blue text. Would this type of 4766 information be helpful in other sections as well? If so, in which sections would it be most 4767 helpful?] 4768 4769 New and Existing Buildings 4770 The electric lighting recommendations in Chapter 5 can be used in new construction, tenant 4771 improvement and retrofit projects with similar achievable savings. In tenant improvement and 4772 retrofit projects the daylighting potential is given by the existing building apertures and 4773 orientation but the daylight responsive control recommendations are still valid. Lighting layouts 4774 may need to be adjusted to work around existing structural, mechanical, pluming and sprinkler 4775


elements, but moving a luminaire 2 feet to one side will not adversely affect the lighting in the 4776 space. 4777

4778 Goals for Office Lighting 4779 The primary lighting goals for office lighting are to optimize the open office spaces for daylight 4780 integration, to control the lighting to respond to daylight and to the occupant and to provide 4781 appropriate lighting levels for the office functions while producing a vibrant environment. 4782 4783 GOOD DESIGN PRACTICE 4784 4785 EL1 Savings and Occupant Acceptance 4786 To meet the goals for office lighting, first the electric lighting system needs to respond to 4787 daylighting as it enters the spaces. Through automatic controls the electric lighting will decrease 4788 in intensity and power as the daylight increases in the morning. The system will automatically 4789 increase in the afternoon as the available daylight decreases. This decrease in the electric 4790 lighting intensity in the morning and increase in the afternoon is imperceptible with modern 4791 LED continuous dimming systems. Energy savings is dependent on many factors but typical 4792 savings for the first row of luminaires can be as high as 30%. 4793 4794 Secondly, the electric lighting needs to respond to the office worker by automatically turning 4795 off the lighting after they have left the space. One of the biggest wastes of lighting energy is 4796 leaving lights on in unoccupied spaces. Turning the lights on can be achieved either by 4797 manually using a switch or having the lights automatically turn on when the user enters the 4798 space (see LC2 Use and Occupant-Engaged Control Strategy). 4799 4800 Lastly, the combination of daylight and electric light needs to provide an appropriate lighting 4801 intensity for the office worker to accomplish their tasks. In computer dominated offices lighting 4802 levels can be reduced, but lower light levels can product a dull feeling environment. Selectively 4803 adding wall lighting by using wall sconces, art lighting or wall washing in larger open office 4804 spaces can create a more vibrant environment. 4805 4806 A good lighting control system will be invisible to the occupants, but users should be educated 4807 on the energy-saving benefits of the system and to spot and report systems that appear to be 4808 malfunctioning. 4809 4810 EL2 Light-Colored Interior Finishes 4811 For electrical lighting to be used efficiently, surfaces must have light-colored finishes. Ceiling 4812 reflectance should be at least 80% (preferably 90%), which in general means using smooth white 4813 acoustical tile or ceiling paint. The average reflectance of the walls should be at least 50%, which 4814 in general means using light tints or off-white colors for the wall surfaces, as the lower 4815 reflectance of doors, tack surfaces, windows and other objects on the walls will reduce the 4816 average. Floor surfaces should be at least 20%; for this there are many suitable surfaces. 4817

4818 In open-plan offices, cubicle partitions should also have a reflectance of at least 50%. Partitions 4819 between cubicles that are parallel to the window wall should be at least 50% translucent or be 4820 limited to 42 in. to maximize daylight potential. 4821

4822 In addition, take the shape and finish of the ceiling into account. A flat painted or acoustical tile 4823 ceiling is the most efficient; exposed roof structures, even if painted white, may significantly 4824


reduce the effective ceiling reflectivity. Make sure the ceiling and all components are painted a 4825 high-reflectance white. 4826

4827 Reflectance values are available from paint, carpet, and ceiling tile manufacturers. Reflectance 4828 should be verified by the QA provider. 4829 4830 EL3 Task Lighting 4831 If the space-planning recommendations in EL10-EL11 are followed by locating office spaces in 4832 the daylight zones, task lighting should not be needed during the daylight hours. In daylight 4833 zones, task lights should be evaluated on a needs basis and should not be automatically installed 4834 at each workstation. Connect all task lights to vacancy sensors (see LC4) to turn the lights off 4835 when the space is unoccupied. 4836

4837 Periodically confirm that task lights are controlled and are turned off during daylight hours and 4838 when occupants leave the spaces during non-daylight hours. 4839 4840 EL4 Color Rendering Index (CRI) 4841 The Color Rendering Index (CRI) is a scale measurement identifying a lamp’s ability to 4842 adequately reveal color characteristics of objects and people. The scale maximizes at 100, with 4843 100 indicating the best color-rendering capability. All lamps / lighting systems should be 4844 specified with an 80 CRI or greater. 4845

4846 4847

Color Rendition and Quality 4848 4849 With the traditional light sources of Incandescent, Fluorescent and High Intensity 4850 Discharge, CRI has been an acceptable metric to measure the relative ability of 4851 the light source to render colors. However, with LED light sources the CRI scale 4852 gives only a partial picture of how well colors are rendered. A new color metric 4853 being used in the lighting industry is described in IES TM-30-15 (IES 2015a) 4854 using the metrics of Fidelity Index and Gamut Index. 4855 4856 Fidelity Index (Rf) 4857 The fidelity index functions in a similar way to CRI, but instead of the eight 4858 pastel reference colors of CRI, it uses 99 reference colors in 16 bins and 4859 containing saturated hues. All LED sources should be specified with an 85 Rf or 4860 greater. At the time of this publication the majority of manufacturers are not yet 4861 consistently publishing fidelity data and are still using the CRI scale. 4862 4863 Gamut Index (Rg) 4864 The Gamut Index evaluates the extent to which the source increases or decreases 4865 mean color saturation in comparison to a reference source. The Gamut Index is 4866 based on a 100-plus-or-minus scale, where 100 it represents no change in 4867 saturation. All LED sources should be specified with an Rg as close to 100 as 4868 possible. 4869 4870 Caution: It is important to remember that CRI, Rf and Rg are only numbers and 4871 that for most office applications following the 80 CRI or greater, 85 Rf or greater 4872


and Rg as close to 100 will provide acceptable color environments. Additionally, 4873 these indexes do not take into account human preference. 4874

4875 4876 EL5 Correlated Color Temperature (CCT) 4877 CCT is a scale identifying a lamp’s relative warmth or coolness—the lower the color 4878 temperature the warmer the source and the higher the color temperature the cooler the source. It 4879 is best practice to specify one color temperature for lighting that is doing the same job, E.g.: all 4880 general light sources should be the same CCT source but accent lighting can be a different CCT 4881 from the general lighting. As shown in Figure EL5, CCT can range from a very warm 2000K to 4882 a very cool 6500K. For office applications specify a CCT in the 3000K to 5000K range. It is 4883 important to remember that these indexes do not take into account human preference. 4884

4885 The higher 4000K or 5000K color temperature will match the daylight color from windows and 4886 skylights more closely than the lower 3000K color-temperature sources. However, the high 4887 5000K source may produce an artificially cool-looking building at night. See Figure EL-5. 4888 4889

4890 Figure EL-5 Color Temperature Chart 4891

4892 EL6 Light Emitting Diodes (LED) 4893 LED is a solid-state semiconductor device that can produce a wide range of saturated colored 4894 light and can be manipulated with color mixing or phosphors to produce white light. To achieve 4895 the lighting power allowance (LPA) recommendations shown in the Sample Design Layouts for 4896 Office Buildings (EL10 – EL16) LED luminaires are used for all general, decorative, task and 4897 accent lighting. LED specifications are recapped in Table EL-1. 4898 4899 Table EL-1 LED Specifications 4900

Metric Recommendation (min)

Efficacy 125 LPW


End of Life L70 50,000+ hours CRI 80+

Fidelity & Gamut Rf above 85, Rg 90-110 Warranty 5+ years

4901

Efficacy. Efficacy of high color rendering white LED’s currently exceeds 125 lumens 4902 per watt (LPW) far exceeding that of T8 and T5 linear fluorescent. 4903

LED Life. The life of LED luminaires and how the life span is documented continues to 4904 evolve. LEDs gradually produce less light output over their life, and with the exception 4905 of catastrophic failures they don't typically “burn out.” Therefore, end of life is when an 4906 LED luminaire’s light output, or lumen maintenance, has diminished by a determined 4907 percentage; currently, 70% lumen maintenance, known as L70. When specifying an 4908 LED luminaire, look for a manufacturer L70 of greater than 50,000 hours tested per IES 4909 TM-21 (IES. 2011a). Some manufacturers are using L80 (a 20% reduction) or even L90 4910 (a 10% reduction) for life but in all cases 50,000 hours is a minimum rating to specify. 4911

Caution: Drivers and LED modules should have a minimum five year warranty that 4912 cover color shift and light output. 4913

Dimming. Unlike fluorescent switching, frequently turning an LED on and off does not 4914 hinder its expected life. Furthermore, LED luminaire and control manufacturers offer 4915 high-end trim and tuning. Under this condition, light output is reduced by a certain 4916 percentage, most often 20% reduction to 80% lumen output. The human eye sees a very 4917 small difference at 80% of typical office light levels and in many circumstances the 4918 luminaire’s light output can be further reduced. As an LED dims over time, additional 4919 energy will be applied to the luminaire to maintain the same light levels over the course 4920 of the luminaire’s life. High-end trim/tuning may reduce the energy over the lifetime of 4921 the luminaire by 10% or greater depending on the settings. 4922

Replacement. Not all LED luminaires are able to be relamped. Even when possible, the 4923 cost to relamp may exceed the cost of purchasing a new luminaire. Drivers and LED 4924 modules should be plug-in and removable. These quick disconnect boards provide an 4925 easy means of accessing and replacing drivers. 4926

Luminaire types should be minimized to reduce the amount of replacement stock 4927 required for different driver sizes, types, and LED light engines. 4928

Heat. Heat is a well-known factor in limiting the life of an LED. Be cautious about 4929 where luminaires are located to minimize excessive heat. LED luminaires can reach 4930 95°F ambient temperature at the ceilings. LED luminaires should be tested and rated at 4931 these higher temperatures. 4932

Phosphor. Some LED modules use remote phosphor technology that separates the 4933 phosphor disk from the LED emitters via an air space. By decoupling them, the 4934 phosphors stay cooler over life and there is substantially reduced degradation from heat. 4935 Heat degradation in LED luminaires is visible as color shift, meaning the modules are 4936 less prone to color shift over life than regular LEDs. 4937

Flicker. Flicker can be perceived or imperceptible. Excessive flicker may cause eye 4938 strain, headaches, impaired vision, or seizures. Studies have shown that people are 4939


sensitive to both 60 Hz flicker and a certain percentage of the population is sensitive to 4940 frequencies of up to 200 Hz or more (ASSIST 2015). 4941

Flicker occurs in luminaires from driver and/or dimming instability as well as voltage 4942 changes or external noise. IEEE Standard 1789-2015 provides a method for determining 4943 the maximum allowable percentage of flicker (IEEE 2015). While this standard is useful 4944 for specifications, a mockup of the luminaire and dimming control system is also 4945 valuable in most areas. 4946

4947 EL7 Exit Signs 4948 Use light-emitting diode (LED) exit signs or other sources that consume no more than 5 W per 4949 face. The selected exit sign and source should provide the proper luminance to meet all building 4950 and fire code requirements. 4951 4952 SAMPLE DESIGN LAYOUTS FOR OFFICE BUILDINGS 4953

4954 The 0.40 W/ft2 goal for LPA represents an average LPA for the entire building. Individual 4955 spaces may have higher power densities if they are offset by lower power densities in other 4956 areas as shown in Table EL-2 The example designs described below offer a way, but not the 4957 only way, that this watts-per-square-foot limit can be met. Daylighting (see DL12) is assumed in 4958 all open office areas. 4959

4960 Table EL-2 Interior Lighting Power Allowances 4961

Interior Spaces LPA

(W/ft2) Open Office 0.31 Private Office 0.42 Conference 0.77 Corridor 0.34 Active Storage 0.34 Restrooms 0.51 Break Rooms 0.47 Electrical/Mechanical 0.43 Stairway 0.58 Lobby 0.77 Elevator Lobby 0.46 Janitor 0.34 Classroom 0.42 Other Spaces 0.47 Average Building LPA 0.40

4962 The examples in EL8 through EL14 are based on a national “average” building space 4963 distribution. These averages are shown in Table EL-3. No building is average and each 4964 building will have a different space allocation. When following the recommendations below, 4965 adjust the standard space allocation to match the specific building’s space allocation. 4966

4967


Table EL-3 National Average Space Distribution 4968

Interior Spaces % of floor

area Open Office 50% Private Office 12% Conference 4% Corridor 8% Active Storage 6% Restrooms 3% Break Rooms 1% Electrical/Mechanical 4% Stairway 2% Lobby 4% Other Spaces 6%

4969 4970

EL8 Open-Plan Offices 4971 Space Planning. To maximize the energy savings from dimming the electric lighting in 4972 response to daylight, the open office workstations should be located on the north and south sides 4973 of the building. By maximizing daylight penetration workstations can be within the daylight 4974 zone. This generally limits the workstations to three deep from the window wall. Additionally, 4975 the partitions separating the workstations that are parallel to the window wall should be no taller 4976 than 42 inches or be at least 50% translucent above desk height to allow daylight to reach the 4977 second and third workstations. 4978 4979 Illumination level. The target lighting in open offices is 25-30 average maintained footcandles 4980 for ambient lighting, with approximately 50 fc provided on the desktop by a combination of 4981 LLLC luminaires and daylight. Supplemental task lighting is only required during non-daylight 4982 hours and must be vacancy sensor controlled. 4983

4984 Existing Building opportunity. Typically open office spaces are often controlled by local 4985 switches or a central time controller. Wireless controlled LLLC luminaires are a perfect 4986 opportunity for existing buildings as they mount and wire like a typical luminaire with hot, 4987 neutral and ground wires. The control of the luminaire is wireless so no additional control wires 4988 need to be installed in the ceiling or in the walls. 4989

4990 Sample Design. Open-plan office areas account for approximately 50% of the floor area and are 4991 designed to 0.31 W/ft2 including task lighting wattage (see EL5 for recommendations on task 4992 lighting). The desired lighting and energy target can be achieved by using one 25 watt, 125 4993 lumen per watt luminaire, for every 80 square feet of office area. 4994 4995 Use LLLC luminaires in all open office areas even if the luminaires fall outside the secondary 4996 daylight zone as the LLLC luminaires can be occupancy zoned and task tuned with luminaires 4997 in the daylight zones. LLLC luminaires exceed code requirements for daylight and occupancy 4998 control in the primary and secondary daylight zones (see the definitions of primary and 4999 secondary daylight zones near DL6). 5000 5001


Depending on the height of the partitions that separate the corridor from the workstations, it is 5002 possible that the corridor will be lighted by the workstation luminaires. At the low lighting 5003 power recommended for the open offices it is important to provide some vertical layer of 5004 lighting to the space. Highlight feature walls and corridor file areas with wall wash luminaires. 5005 See Figure EL10 for an example open-plan office layout. 5006

5007

5008 Figure EL10 Open-Plan Office Layout 5009

5010

Puget Sound Energy – Bothell Office LLLC Retrofit 5011 5012 The location is home to 80+ employees, and is comprised of open office space, 5013 private offices and conference rooms. The team recognized the clear business case for 5014 LED fixtures with luminaire level lighting controls. The LLLC luminaires allowed 5015 the team to significantly enhance employee satisfaction, modernize the building and 5016 enable seamless control over different areas. The retrofit involved replacing 84 T8 5017 fluorescent luminaires with 122 LED luminaires. 5018 5019 The Benefits 5020 Maximum Energy Savings. 70+% energy savings due to the integrated controls 5021

compared to the previous lighting system. Approximately half of the energy 5022 savings is from the integrated controls. 5023

Easy Installation and Control. PSE worked with a local contractor to install the 5024 luminaires and wireless integrated controls systems, which took two weeks during 5025 summer 2015. The luminaire installation was as simple as if luminaires were 5026 installed without controls, given that the wireless controls don’t require changing 5027 the existing circuits or installing separate occupancy or daylight sensors. 5028 Adjustments to customize light levels were simple thanks to the system’s wireless 5029 remote control. 5030

Increased Occupant Comfort 5031

Partitions separating workstations parallel to the window wall must be no taller than 36 inches or be at least 50% translucent above the desk height to let daylight deeper into the open office.

Partitions separating workstations perpendicular to the window wall may be higher to create a sense of privacy.

Use wall washing to light files and feature wall to create a vertical layer of light separate from the general office lighting.


5032

5033 Puget Sound Energy Offices 5034

(Photo courtesy of Puget Sound Energy) 5035 5036 Employees are now more comfortable, and expressed positive feedback in response to 5037 the improved light levels, better distribution of light and the new system’s dimming 5038 capabilities. Cleaning crews also benefit from the system’s occupancy sensing, and 5039 no longer need to wonder if staff are still in the office when they are finished cleaning 5040 as the lights are set to automatically shut off. 5041 5042

5043 5044 EL9 Private Offices 5045 Space Planning. Locate private offices on the east and west sides of the building as these spaces 5046 are the most difficult to control the daylight due to low sun angles and the tendency of tenants to 5047 close blinds. 5048 Illumination level. The target lighting in private offices is 25-30 average maintained footcandles 5049 for ambient lighting, with approximately 50 fc provided on the desktop by a combination of 5050 LLLC luminaires and daylight. Supplemental task lighting is only required during non-daylight 5051 hours and must be vacancy sensor controlled. 5052

5053 Existing Building opportunity. Typically private office spaces are often controlled by an 5054 occupancy sensor or, for vintage buildings, local switches. Wireless controlled LLLC 5055 luminaires are a perfect opportunity for existing buildings as they mount and wire like a typical 5056 luminaire with hot, neutral and ground wires. The control of the luminaire is wireless so no 5057 additional control wires need to be installed in the ceiling or in the walls. Replace the 5058 occupancy sensor or wall switch with a compatible switch or dimmer. 5059

5060 Sample Design. Private offices account for approximately 12% of the floor area and are designed 5061 to 0.42 W/ft2 including task lighting wattage (see EL5 for recommendations on task lighting). 5062

5063 The desired lighting and energy target can be achieved by using one 25 watt, 125 lumen per 5064 watt luminaires for 60 square feet. However, always use a minimum of two luminaires per 5065 office as one luminaire will not provide adequate lighting distribution in a typical private office. 5066


A local dimming wall controller near the desk location so the user can adjust the illumination 5067 level as desired. 5068

5069

5070 Figure EL1-EL9 Private Office Layout 5071

5072 EL10 Conference Rooms/Meeting Rooms 5073 Space Planning. Locate conference/meeting rooms on the east and west sides of the building as 5074 these spaces are the most difficult to control the daylight due to low sun angles and the tendency 5075 of tenants to close blinds. Larger conference rooms may also be located along the core of the 5076 building but provide translucent glass along the corridor wall to provide some connection to 5077 daylight. 5078 5079 Illumination level. The target lighting in conference rooms and meeting rooms is 25-30 average 5080 maintained footcandles. Use manual ON or automatic ON to 50% occupancy sensor local control. 5081

5082 Existing Building opportunity. Existing conference/meeting rooms may be controlled by 5083 switches, occupancy sensor or a multi-scene dimming controller. LED luminaires come 5084 standard with dimming drivers so if dimming is not currently available in the conference room 5085 it can be added through a 0-10v or wireless dimming controller. Some LED dimming drivers 5086 may be compatible with existing multi-scene controllers; consult with the controller 5087 manufacturer. 5088

5089 Sample Design. Conference rooms account for approximately 4% of the floor area and are 5090 designed to 0.77 W/ft2. A typical lighting layout for a conference room would be to provide task 5091 lighting on the table from lights located over the table. Using a pendant mounted direct/indirect 5092 luminaires over the table where the indirect lighting is separate from the downlight along with 5093 lighting on the presentation wall will provide a flexible lighting solution. See Figure EL1-5094 EL10. 5095 5096


5097 Figure EL1-EL10 Conference Rooms/Meeting Rooms Layout 5098

5099 EL11 Corridors 5100 Illumination level. The target lighting in corridors is 5–10 average maintained footcandles. 5101 Choose luminaires that light the walls and provide relatively uniform illumination. 5102

5103 Sample Design. In the virtual hall of the open office areas the LLLC luminaires can be 5104 continued at the same spacing as the open office. Alternately use a 15 watt LED downlight or 5105 combination of LED downlights, wall washers or wall sconces, one for every 45 square feet of 5106 the hallway. The downlight / wall washer / wall sconce option will provide a visually different 5107 layer of lighting making the space more interesting. 5108 5109 In other corridors, options include using the LLLC 25 watt 125 lumen per watt luminaires per 5110 75 square feet, or a 15 watt LED downlight or combination of LED downlights / wall washers / 5111 wall sconces, one for every 45 square feet of the hallway. See Figure EL1-EL10. 5112

5113


5114 Figure EL1-EL11 Corridor Layout 5115

5116 EL12 Storage Areas 5117 Illumination level. The target lighting in storage areas is 5–15 average maintained footcandles. 5118

5119 Sample Design. Storage areas account for approximately 6% of the floor area and are designed 5120 to 0.34 W/ft2. Use one 25 watt 125 lumen per watt LED luminaires per 75 square feet. Use a 5121 manual ON occupancy sensor. In more complex spaces where users may not be visible from a 5122 single location occupancy sensor, use a wireless ceiling mounted sensor with multiple sensors 5123 that communicate together. Note – LLLC luminaires can be used in these spaces which will 5124 allow occupancy communication and task tuning of the lighting in the space. See Figure EL1-5125 EL12. 5126

5127

5128 Figure EL1-EL12 Storage Area Layout 5129

5130 EL13 Lobbies 5131 Illumination level. The target lighting in lobby areas is 10–15 average maintained footcandles. 5132 Highlight wall surfaces and building directories. 5133

5134 Sample Design. Lobbies account for approximately 4% of the floor area and are designed to 5135 0.34 W/ft2. Lobbies provide the first impression to visitors so provide pendant or decorative 5136 ceiling lights over the reception desk. Note – if there is one receptionist use two luminaires one 5137 on each side to frame the receptionist, repeat spacing of luminaires if multiple receptionist 5138


locations. Highlight the feature wall behind the reception desk with LED wall washers or 5139 accent lights. 5140

5141 Lobbies may also have small phone spaces. Install downlights, pendants or 2x2 LED fixtures 5142 coupled with manual diming and occupancy sensors. Average the connected load in these 5143 spaces to 0.47 W/ft2, which is equivalent to about one 25 watt LED luminaires for every 60 ft2. 5144 See Figure EL1-EL13 5145

5146 5147

5148 5149

Figure EL1-EL13 Lobby Layout 5150 5151 Note: Lighting in the remainder of the office space is composed of various functions including 5152 restrooms, electrical/mechanical rooms, stairways, workshops, and others. Average the 5153 connected load in these spaces to 0.47 W/ft2, which is equivalent to about one 25 watt LED 5154 luminaires for every 60 ft2. Use occupancy sensors or timers where as required by 90.1. 5155 5156 EL14 Twenty-Four-Hour Lighting 5157 Night lighting or lighting left on 24 hours to provide emergency egress needs when the building 5158 is unoccupied should be designed to limit the total lighting power to 10% of the total LPA (0.04 5159 W/ft2). It should be noted that most jurisdictions also allow the application of occupancy sensor 5160 controls on egress lighting to further reduce electricity associated with lighting an unoccupied 5161 building. 5162 5163 EXTERIOR LIGHTING 5164 5165 With the publication of ASHRAE/IES Standard 90.1-2010, exterior lighting power allowances 5166 are now defined using lighting zones (LZs). There are five zones, as shown in Table EL-4. This 5167 guide assumes that the Advanced Energy Design Guide for Zero Energy Small to Medium 5168 Office Buildings will fall into Lighting Zone 3 or Lighting Zone 2. Refer to LC6 for exterior 5169 control recommendations. 5170

5171 Table EL-4 Exterior Lighting Zone Descriptions 5172

Lighting Zone

Description


0 Undeveloped areas within national parks, state parks, forest lands, rural areas, and other undeveloped areas as defined by the authority having jurisdiction

1 Developed areas of national parks, state parks, forest lands, and rural areas

2 Areas predominantly consisting of residential zoning, neighborhood business districts, light industrial buildings with limited nighttime use, and residential mixed-use areas

3 All other areas 4 High-activity commercial districts in major metropolitan areas as

designated by the local jurisdiction Source: Table 9.4.2-1 of ANSI/ASHRAE/IES 90.1-2016 (ASHRAE 2016) 5173

5174 Table EL-5 Exterior Lighting Power Allowances 5175

Exterior Areas LPA

(W/ft2) LZ3 & LZ4

LPA (W/ft2)

LZ2 Parking Lots and Drives 0.05 0.04 Walkways, Pathways, Stairs and Special Features

0.10 0.05

Decorative Façade Lighting

0.075 0.05

All other spaces 0.05 0.04 5176 Cautions: Calculate LPA only for areas intended to be lighted. For this Guide, areas that are 5177 lighted to less than 1 Lux (0.1 fc) are assumed to not be lighted and are not counted in the LPA 5178 allowance. For areas that are intended to be lighted, design with a maximum to minimum ratio 5179 of illuminance no greater than 30 to 1. Therefore, if the minimum light level is 0.1, then the 5180 maximum level in that area should be no greater than 3 fc. 5181 5182 For parking lot and grounds lighting, do not increase luminaire wattage in order to use fewer 5183 lights and poles. Increased contrast makes it harder to see at night beyond the immediate 5184 luminaires location. Flood lights and wall-packs should not be used, as they cause glare and 5185 unwanted light encroachment on neighboring properties. 5186 5187 Limit poles to 20 ft mounting height and use luminaires that provide all light below the 5188 horizontal plane to help eliminate light trespass and light pollution. All pole lights must 5189 integrate an occupancy sensor that reduces the power by at least 50% when no activity is 5190 detected for not longer than 15 minutes. 5191

5192 EL15 BUG Ratings 5193 BUG stands for back, uplight, and glare and is used to indicate how much spill light a luminaire 5194 may create, how much uplight it will produce, and its potential to create glare. Figure EL15 5195 shows an example of a luminaire’s BUG rating. This rating system is used by various 5196 municipalities as part of their night lighting ordinances to limit light trespass and reduce 5197 uplighting. The rating system is typically based on exterior lighting zones. 5198 5199


BUG ratings can also be used by designers to provide an appropriate exterior lighting solution. 5200 Balance is required when utilizing the glare aspect of this system. Too much glare can be 5201 unpleasant or even debilitating; however, efficacy may be significantly reduced when heavily 5202 frosted lenses are applied to reduce the glare rating. 5203 5204 Use forward throw optics or move exterior pole locations away from perimeter. This will reduce 5205 spill light and may provide greater flexibility in luminaire choice and spacing. 5206

5207

5208 (EL15) Exterior Fixture BUG Rating 5209

5210 EL16 Exterior Lighting Power—Parking Lots and Drives 5211 Limit exterior lighting power to 0.05 W/ft2 for parking lots and drives in LZ3 or to 0.04 W/ft2 in 5212 LZ2. Calculate only for paved areas, excluding grounds that are lighted to less than 0.1 fc. 5213 Use LED parking lot luminaires with a bi-level switching driver and exterior occupancy sensor 5214 that will reduce power by at least 50% when no activity is detected for 15 minutes. 5215 5216 Cautions: Parking lot lighting locations should be coordinated with landscape plantings so that 5217 tree growth does not block effective lighting from pole-mounted luminaires. 5218 5219 Parking lot lighting should not be significantly brighter than the lighting of the adjacent street. 5220 5221 EL17 Exterior Lighting Power—Walkways, Pathways and Special Features 5222 Limit exterior lighting power to 0.10 W/ft2 for walkways, pathways, plaza areas and special 5223 feature areas in LZ3, to W/ft2 for walkways, pathways, plaza areas and special feature areas in 5224 LZ2. Exclude grounds that are lighted to less than 0.1 fc. 5225 5226 EL18 Exterior Lighting Power—Decorative Façade Lighting 5227 Decorative façade lighting is lighting that highlights the building architecture and used 5228 sparingly if at all in a Zero Energy office buildings and when used should be limited to building 5229


entries. If façade lighting is used, limit the lighting power to 0.075 W/ft2 in LZ3 and to 0.05 5230 W/ft2 in LZ2 for the area intended to be illuminated to a light level no less than 0.1 fc. 5231 5232 REFERENCES AND RESOURCES 5233 5234 ASHRAE. 2016. ANSI/ASHRAE/IES Standard 90.1-2016, Energy Standard for Buildings 5235

Except Low-Rise Residential Buildings. Atlanta: ASHRAE. 5236 ASSIST. 2015. Recommended metric for assessing the direct perception of light source flicker. 5237

ASSIST Recommends 11(3). www.lrc.rpi.edu/programs/solidstate/assist/pdf/AR-5238 FlickerMetric.pdf. 5239

IEEE. 2015. IEEE Standard 1789-2015, IEEE Recommended Practices for Modulating Current 5240 in High-Brightness LEDs for Mitigating Health Risks to Viewers. Piscataway, NJ: IEEE. 5241 https://standards.ieee.org/findstds/standard/1789-2015.html. 5242

IES. 2011a. Projecting Long Term Lumen Maintenance of LED Light Sources, TM-21-11. New 5243 York: Illuminating Engineering Society. https://www.techstreet.com/standards/ies-tm-21 -5244 11?product_id=1810146. 5245

IES. 2015a. IES Method for Evaluating Light Source Color Rendition, TM-30-15. New York: 5246 Illuminating Engineering Society. https://www.techstreet.com/standards/ies-tm-30-15?pro 5247 duct_id=1900892 5248 5249 5250 PLUG LOADS AND POWER DISTRIBUTION SYSTEMS 5251 5252 OVERVIEW 5253

5254 Plug loads provide a significant opportunity for contributing to the overall building energy 5255 savings. Opportunities include strategies to: reduce the connected power with more efficient 5256 equipment, substitute for lower power equipment, reduce the amount of equipment, and control 5257 equipment so that it runs at reduced power or is off when not in use. 5258 5259 Controlling plug-load energy usage is critical to achieve a zero energy energy building. 5260 Depending on climate, plug loads represent 15%–30% of typical office building energy and that 5261 proportion tends to grow even higher with energy-efficient buildings as other uses such as 5262 lighting and HVAC are reduced. This point is illustrated in Figure PL-1. Plug equipment 5263 typically runs at normal operating power during occupied hours and in some cases may have the 5264 capability to partially power down when not in use. There is often potential to further reduce 5265 power during occupied hours when offices, cubicles, or other areas are not in use. Studies show 5266 that many types of plug-load equipment remain on at full power or reduced power even during 5267 unoccupied periods (Hart et al. 2004; Sanchez et al. 2007). 5268 5269 Often plug loads are overestimated when tenants are negotiating leases and even in owner 5270 occupied buildings. Studies show that requests for plug load can be in the range of 5-10 W/ft2 5271 when the demand, even in single occupant with a data center of less than .6W/ft2. (Sheppy, 5272 Gentile-Polese, and Gould, 2014) In order to reduce loads, two principal approaches are used: 5273

1. Select equipment with lower power demands and 5274

2. Control equipment so that it is on as little as possible when no one is using it. 5275 5276


The first step to take full advantage of the reduction potential is to consider what the plug load 5277 management plan will be for the building. 5278 5279 Office buildings likely cannot achieve the zero energy goal without effective plug and process 5280 load management. Plug and process loads (PPLs) account for the largest section of energy 5281 consumption in a commercial office building, typically consuming 30% of the total commercial 5282 building energy use, and this consumption is expected to grow to 35% by 2025 as the number 5283 and energy intensity of plug-in devices continue to increase. (DOE 2015) 5284 5285 As shown in Table PL-1, modeled analysis across all climate zones demonstrates that plug load 5286 equipment is always top three in consumption and therefore should always be one of the 5287 primary concerns in design and operations. 5288 5289 Table PL-1 Climate Zone EUI Breakdown by End Use 5290

Total Energy (kBtu/ft2-yr)

CZ Heating Cooling LightingPlug LoadEquipment

Fans Pumps Heat

Rejection Total

0A 0.3 10.4 1.5 8.2 2.0 0.9 0.0 23.2

0B 0.1 14.3 1.4 8.2 2.5 1.1 0.0 27.6

1A 0.0 10.9 1.3 8.2 2.1 0.9 0.0 23.4

1B 0.9 11.7 1.3 8.2 2.7 0.8 0.0 25.7

2A 1.0 9.0 1.3 8.2 1.9 0.8 0.0 22.2

2B 1.6 8.5 1.3 8.2 2.4 0.7 0.0 22.8

3A 3.8 5.5 1.3 8.2 1.9 0.5 0.0 21.4

3B 2.6 6.2 1.3 8.2 2.3 0.6 0.0 21.1

3C 1.1 3.3 1.3 8.2 1.7 0.3 0.0 16.0

4A 6.1 3.8 1.2 8.2 2.0 0.4 0.0 21.7

4B 3.8 4.4 1.2 8.2 2.5 0.4 0.0 20.6

4C 4.2 1.5 1.3 8.2 1.8 0.2 0.0 17.3

5A 8.9 2.5 1.2 8.2 2.0 0.3 0.0 23.2

5B 6.9 3.5 1.2 8.2 2.7 0.3 0.0 22.9

5C 5.3 0.8 1.3 8.2 1.8 0.1 0.0 17.5

6A 12.8 2.8 1.2 8.2 2.3 0.3 0.0 27.7

6B 10.0 2.3 1.2 8.2 2.6 0.3 0.0 24.7

7 15.6 2.4 1.2 8.2 2.6 0.3 0.0 30.3

8 22.2 1.2 1.4 8.2 2.8 0.2 0.0 36.0

5291 5292 PLUG LOAD MANAGEMENT 5293 5294 PL1 General Guidance 5295


PPLs in a typical commercial office include computers, copiers, telecommunications 5296 equipment, task lighting, break room appliances, etc. and performing a plug load inventory and 5297 implementing a load reduction strategy could reduce plug loads by up to 20-50%. 5298

5299 Effectively managing plug and process loads requires a full understanding of the building 5300 design and construction process along with developer/owner/tenant lease agreements and 5301 contracts. Process and Plug Loads can be divided into the following categories and energy 5302 reduction strategies focused individually throughout design and occupancy: 5303

Workstations consist of all electronic loads at individual open and private offices 5304 throughout the building. Energy users in these spaces include computers and monitors, 5305 phones, task lighting and device chargers. 5306

Break Rooms not only include appliances such as refrigerators, coffee makers, 5307 dishwashers, ice makers etc. but often include vending machines. 5308

Building Process Loads consist of centralized building system equipment often housed 5309 in the building’s Main Distribution Frame (MDF) such as telecommunications servers, 5310 routers, UPS’, as well as head-end equipment for fire alarm, security and digital 5311 surveillance. Building elevators (and potentially escalators) along with electric vehicle 5312 chargers are also included. 5313

5314 Successful implementation of energy reduction across PPLs can also be divided into the Design 5315 and Occupancy Stages. During design, the Energy Champion (reference Ch3) shall be 5316 integrated into the equipment procurement process. For the building process loads and break 5317 room equipment, this will often include integration with the building design engineer. Drastic 5318 energy reduction must be included as a priority in equipment selection. The Energy Champion 5319 will also need to be integrated into the equipment selection process for office workstation 5320 equipment and building branch circuit design for plug load management. During the occupancy 5321 phase, monitoring and reporting of process and plug load usage will incentivize occupants to 5322 reduce plug load usage even further so that zero energy goals are met. 5323 5324 Plug loads can be controlled either with a management plan requiring human actions or with a 5325 passive system where plug load devices are controlled by an automation system that removes 5326 human action from the equation. The management plan can be as simple as banning all 5327 extraneous devices and achieving buy-in through an education process explaining the “why” of 5328 plug load management. 5329 5330 PL2 Establish a Plug and Process Load Management Policy 5331 Develop a Plug and Process Load Management Policy for Design and Construction of the 5332 building. Implement this policy during design so that energy reduction is a partial decision 5333 maker in the selection process of all equipment. 5334 5335 The policy shall outline the priority of a zero energy goal and indicate all equipment selection 5336 must go through the Energy Champion and be selected in a way to optimize the opportunity for 5337 reaching zero energy. Selection of all equipment shall indicate energy savings per year 5338 comparisons and options for energy use reductions through optional modes of operation. 5339 5340 When designing the power distribution systems, keep in mind the options and desires of the 5341 facility maintenance staff for monitoring and measuring electricity use by group and type in the 5342


building. Seeing the power consumed in a building and being able to translate it into energy cost 5343 dollars helps impact user behavior and increase opportunities for savings. 5344 5345 PL3 Install Plug Load Controls 5346 Plug load controls minimize waste energy from devices being left on even when the user is not 5347 present, but provide power availability when needed. Automated controls are explicitly required 5348 by ANSI/ASHRAE/IES Standard 90.1-2010 and later versions, and by CEC Title 24 (CEC 5349 2016). Specifically, Standard 90.1 requires plug load control of 15 amp and 20 amp, 120 volt 5350 receptacles. 5351 5352 Generally, the requirement for plug load control is that 50% of the receptacles be controlled by 5353 an automatic shutoff device. Receptacles typically have a port that is uncontrolled and a port 5354 that is controlled. Plug monitors, task lighting, portable appliances, personal fans and even 5355 workstations into the controlled section of the receptacle. Connect computers with automatic 5356 sleep mode to the non-controlled circuit if necessary to maintain operations. Devices requiring 5357 continuous power such as servers or security equipment are not required to be part of the plug 5358 load control system and may be plugged into the uncontrolled section of the receptacle. For 5359 most applications, IT equipment should only be powered when it is needed and turned off when 5360 the building is not occupied. ENERGY STAR® settings can help deploy this option turning 5361 down power when equipment is not being used. 5362 5363 Plug load control devices may consist of time of day control, where receptacle circuits are 5364 controlled via a contactor relay or other power management device that is in turn controlled 5365 through a time of day schedule via the building automation system or a time clock. Controlled 5366 receptacles are required to be identified with a permanent, distinct marking to prevent a 24-hour 5367 load from being plugged into an interruptible outlet. A popular option is to integrate the plug 5368 load controls with the lighting control systems as many lighting control manufacturers 5369 incorporate an option to control local receptacle outlets. Lighting control systems also 5370 incorporate occupancy sensors that may be used as a further measure of plug load controls in 5371 individual spaces. While these solutions can control plug loads, occupant behavior must still be 5372 engaged to plug items into the correct type of outlet. 5373

5374 Caution: The use of smart plug strips, even with occupancy sensors built in, does not meet the 5375 intent of ANSI/ASHRAE/IES 90.1 and should not be considered as the primary source of plug 5376 load control. These devices can be used successfully as a secondary means of plug load control. 5377

5378 Plug load controllers should turn off devices at specific, programmed times, primarily when the 5379 building is unoccupied. The program should: 5380

Incorporate areas of 5000 ft2 or less. 5381 Provide manual override for late night, weekends, and holidays with the provision that 5382

the programmed state resumes after a set time of two hours. 5383 Program occupant sensors to turn off power within 10 minutes of occupants leaving a 5384

room. 5385 Turn off the devices 10 minutes after an occupant has left the room as sensed by the 5386

lighting control system, when the devices are controlled via the lighting control system. 5387 5388

In spaces with local lighting controls and no need for 24 hour power, use the lighting controls to 5389 provide on-off control of all the receptacles in a room, such as conference rooms and offices. In 5390


other spaces, the need for 24 hour power may require lighting controls for the controlled ports 5391 of the receptacles and uncontrolled wiring for the 24 hour loads. Consider if different workplace 5392 designs (offices, cubicles, touchdown spaces, etc.) should have any uncontrolled receptacles to 5393 allow for flexibility of use. Another wiring option is to use centrally controlled receptacle 5394 circuits from the circuit breaker panels, for example when time switch controls are used. 5395 Uncontrolled receptacle circuits are then run from the panel directly, bypassing the central 5396 control system. Dual wiring scenarios are more popular due to the flexibility they offer. 5397

5398 Caution: If end use metering is desired for measuring plug loads and lighting loads separately, 5399 care must be taken to not mix lighting and plug load circuits, especially if a lighting controller is 5400 used for plug load management. 5401

5402 Plug load control options include the following: 5403

Smart power strips sensing occupant with radio frequency or other BAS/Lighting 5404 control interface (no stand-alone power strips - must be plugged into a controlled 5405 receptacle port that is controlled by an automatic control system) 5406

Time switch controls 5407

Half switched outlets controlled via an automatic system 5408

Radio Frequency receptacle controls via occupancy sensor or power pack 5409

Contactor control through Building Automation System 5410

Compatibility with stand-alone or networked control systems in the building 5411

Written policies distributed to staff 5412

Enforcement of plug load management policy 5413

Signage reminding the importance of plug load management 5414

Competitions among employees 5415

Awareness of building occupants 5416

Education of users to ensure 24 hour operations continued power 5417

Removal of equipment not approved for use 5418 5419 Control equipment so that it is off when not in use. Options include occupancy-sensor 5420 controlled plug strips, outlets or circuits, occupancy-sensor-controlled vending machines, timer 5421 switches for equipment that is shared during occupied hours but can be off during unoccupied 5422 hours, and power management of computers and other devices, ensuring that sleep modes are 5423 fully active. Use of efficient low-voltage transformers and newer power management surge 5424 protectors can reduce phantom loads associated with low-voltage equipment (Lobato et al. 5425 2011). 5426 5427 EQUIPMENT SELECTION AND CONTROL 5428 5429 5430 PL5 Choose Energy-Efficient Equipment 5431 Purchase plug load devices that have a "sleep mode" option. In addition, select IT servers to be 5432 scalable to minimize wasted or unused power capacity. DC powered servers are commercially 5433 available and may be complimentary with a PV power system that also contains battery storage. 5434

5435


Select office equipment and appliances that require low energy usage. ENERGY STAR®-rated 5436 equipment typically has significantly lower operational wattage and may include improved 5437 sleep mode algorithms (EPA 2009). Desktop computers, laptops, printers, fax machines, copy 5438 machines, refrigerators, microwave ovens, coffeemakers, and dishwashers are typical equipment 5439 types used in offices that have ENERGY STAR ratings. Look for efficient equipment even if 5440 not rated by ENERGY STAR, such as high-output photocopying machines. Remember once 5441 any ENERGY STAR equipment is installed, the energy reduction settings must be enabled. 5442 Some equipment such as hard drives and printers can also be scheduled through internal 5443 software making it much easier to control and power down when not in use. 5444 5445 PL6 Occupancy Controls 5446 Consider the use of occupancy-based control of devices to reduce energy consumption when the 5447 equipment is not in use. Occupancy-sensor-controlled plug strips can be used to power down 5448 monitors and other items typically plugged in at individual workstations, such as fans, chargers, 5449 and task lighting (task lighting control is described in detail in EL5). Another approach well 5450 suited to individual enclosed offices is to control selected outlets with a room-based occupancy 5451 sensor. This approach can also reduce parasitic losses—small amounts of electricity used by 5452 appliances even when the appliances are switched off. Specific education that is ongoing can 5453 encourage occupants to plug the majority of their appliances into the occupancy-controlled plugs 5454 and ensure behavior doesn't change overtime leading to increased loads. 5455 5456 Use timer switches for central equipment that is unused during unoccupied periods but that 5457 should be available throughout occupied periods. Example equipment includes water coolers 5458 and central coffeemakers. 5459

5460 Choosing energy efficient equipment can result in substantial reduction in equipment power 5461 density relative to a representative building with non-ENERGY STAR and other unrated 5462 equipment with half of the computers desktops and half laptops. 5463 5464 The equipment power density values shown in Table 5-6 for a simulated medium office 5465 building of 53,600 ft2 show a reduction from 0.75 W/ft2 to 0.55 W/ft2 based on total wattage of 5466 equipment for the entire building, not just actual office area (Roberson et al. 2004). 5467

5468 [Question to Reviewers: Is this table helpful to clarify the importance that plug load plays in 5469 annual energy use?] 5470

5471 Table 5-6 Reduction in Equipment Wattage 5472

Plug Load Equipment Inventory

Baseline Efficient

Qty Plug Load, Each, W

Plug Load, W


Plug Load, W

Breakroom Equipment

Water cooler 8 350 2800 8 193 1544

Refrigerator 8 76 608 8 65 520

Vending machine 4 770 3080 4 770 3080

Coffeemaker 4 1050 4200 4 1050 4200


Plug Load Equipment Inventory

Baseline Efficient


Plug Load, W


Plug Load, W

Dishwasher

Microwave

Toaster Oven

Vending Machine

Technology

IT Server

Wi-Fi Antenna

Security Systems

Fire Alarm Panel

Phone Systems

Workspace Equipment

Computer—servers 8 65 520 8 54 432

Computer—desktopa 134 65 8710 89 54 4806

Computer—laptopa 134 19 2546 179 17 3043

Monitor—LCDs 8 35 280 8 24 192

Laser printer—network 8 215 1720 8 180 1440

Copy machine 4 1100 4400 4 500 2000

Fax machine 8 35 280 8 17 136

Multifunction Device

A/V Equipment

Other small appliances, chargers

250 4 1000 250 4 1000

Building Level Services

Elevators

Electric Vehicle Chargers

Total plug load, W 40,424 29,725

Plug load density, W/ft2 0.75 0.55 a Assumes shift toward higher proportion of laptops instead of desktop computers. 5473 b Values shown per unit are not full connected wattage and are reduced for estimates of seasonal usage and 5474 averages for a mix of devices 5475

5476 PL7 Unnecessary Equipment (Climate Zones: all) 5477 Determine whether there are pieces of equipment that operate as “nice-to-have” but which are 5478 not fundamental to the core function of the business. For example, large flat-screen TV arrays in 5479


lobby areas can be eliminated or at minimum placed on schedulers, and mechanically cooled 5480 drinking water can be replaced with filtered tap water. 5481 5482 BREAKROOM EQUIPMENT 5483 5484 PL8 Refrigerators 5485 Specify larger, solid door refrigerators in lieu of multiple mini-fridges. All refrigerators should 5486 be ENERGY STAR certified and operated at their suggested temperature settings, not at the 5487 highest cooling settings, in order to reduce energy use. (Sheppy, Lobato, Pless, Gentile Polese, 5488 Torcellini, 2013) 5489

5490 PL9 Vending Machines 5491 If the breakroom will include vending machines, they should be equipped with occupancy 5492 sensor control for lighting and for cooling operation. ENERGY STAR-rated vending machines 5493 include this type of control or can be retrofitted with add-on equipment. 5494

5495 PL10 Small Appliances 5496 Ensure small appliances (coffee makers, microwaves, water coolers, etc.) are carefully selected 5497 for their energy efficiency. These don't have to tie into a building level controls system as they 5498 are easily controlled with outlet timers to ensure they are off each night and on the weekends. 5499 5500 BUILDING PROCESS LOADS 5501 5502 PL11 Building Level Services and Telecommunications Systems 5503 Selection of building elevators should integrate slower travel speeds and minimized energy 5504 loads as well as incorporating active design principals which suggest centrally located and 5505 easily accessible stairwells. Selection of electric car chargers should note load impacts on the 5506 building electrical system and should be selected with the users charge time in mind to optimize 5507 the equipment’s use. 5508 5509 Energy reduction strategies in telecommunications design can achieve drastic energy reduction 5510 without compromising the goal of telecommunications systems. Numerous strategies mitigate 5511 or eliminate equipment runtime during unoccupied hours, increasing the longevity of the 5512 equipment, reduce costs and help achieve the zero energy goal. 5513 5514 Engage with the telecommunications team during design and reiterate the zero energy goal of 5515 the project. Successful collaboration between these two groups can lead to discovery of energy 5516 reduction strategies that do not compromise the “why” of the building yet will be crucial in 5517 achieving the zero energy goal. Strategies such as virtualization of servers, energy star settings 5518 in PC equipment, thin-clients and even wireless antenna shutdown during unoccupied hours can 5519 all have a drastic energy use impact. 5520 5521 WORKSPACE Equipment 5522 5523 PL12 Laptop Computers 5524 Select laptops with ENERGY STAR ratings. These laptop computers are designed to operate 5525 efficiently to extend battery life. Efficient operation includes lower connected wattage and 5526 effective power management. Desktop computers generally use significantly more energy and 5527 may not be necessary for most users. Involve the IT department or whichever department 5528


specifies equipment with the zero energy goals for the project as they can support the use of 5529 laptops and the removal of desktops as approved equipment. 5530

5531 Computer power management allows computers to go into minimum energy usage when not 5532 active or turn off during scheduled hours. Purchase individual devices with low power sleep 5533 modes, such as ENERGY STAR-rated laptops. Activate the power management in devices that 5534 don’t use these modes in their default setup. Network power management software allows 5535 central control for scheduled off hours and full activation of available power-saving modes 5536 while allowing the network management to turn units on for computer updates and 5537 maintenance. 5538 5539 PL13 Printing Equipment 5540 Consolidate printing services to minimize the number of required devices. One study provides 5541 information on a strategy being applied in a new office building to eliminate personal printing 5542 devices and consolidate printing services to a smaller number of multifunction devices that 5543 reduces connected power and provides anticipated reduction in energy usage (Lobato et al. 5544 2011). Use of multifunction devices that provide printing, copying, and faxing capabilities 5545 reduces power demand from multiple devices. The study indicates that printing services from 5546 these devices will be provided with 1 device per 60 occupants rather than 1 device per 40 5547 occupants, as in the building occupants’ old space. 5548

5549 PL14 Audio/Visual Equipment (Climate Zones: all) 5550 Conference room use is varied and often inconsistent. In order to ensure they are not drawing 5551 power when not in use, it is important to implement a controls system that will turn off 5552 equipment when the space is unoccupied and/or the equipment isn't needed for a meeting. Use 5553 occupancy sensors are an option to control the rooms during operating hours and tie the room 5554 equipment to an overall building controls system to allow it to be shut off outside of operating 5555 hours. In addition, choose energy efficient equipment for the conference rooms. There are 5556 energy efficient options for screens, projectors, conference room phone and video systems. 5557 (Sheppy, Lobato, Pless, Gentile Polese, Torcellini, 2013) 5558 5559 5560 PERFORMANCE VERIFICATION 5561 5562 PL15 Monitor Plug Load Usage 5563 All low voltage (120/208 V) power should be separately metered to display power consumed by 5564 each tenant or building section. These can be totaled on a daily or monthly basis to ensure that 5565 no “power creep” is occurring. Power creep occurs when staff adds equipment into the building 5566 (See PL2). As time goes on, additional equipment may be added, but old equipment must also 5567 be retired to keep the plug load within the energy budget. 5568

5569 Plug load consumption monitoring (controlled and non-controlled) should be part of the energy 5570 dashboard monitoring system along with the other major power systems (lighting and HVAC). 5571 The monitoring system should display the actual energy consumed, which can be compared 5572 with the predicted energy use for each of these systems. Corrective actions are necessary if the 5573 variance between predicted and actual cannot be reconciled by occupancy, hours of use, or other 5574 factors affecting energy consumption. 5575 5576 PL16 Parasitic Loads (Climate Zones: all) 5577


Reduce and eliminate parasitic loads. These loads include small energy usage from equipment 5578 that is nominally turned off but still using a trickle of energy. Transformers that provide some 5579 electronic devices with low-voltage direct current from alternating current plugs also draw 5580 power even when the equipment is off. Transformers are available that are more efficient and 5581 have reduced standby losses. Wall switch control of power strips, noted in PL3, cuts off all 5582 power to the plug strip, eliminating parasitic loads at that plug strip when the switch is 5583 controlled off. Newer power management surge protector outlet devices have low or no 5584 parasitic losses (Lobato et al. 2011). 5585 5586 POWER DISTRIBUTION SYSTEMS 5587 5588 PL17 Rightsizing Power Distribution Systems 5589 The 2014 National Electrical Code (NEC 2014) inserted a new provision that allows the design 5590 engineer to design to a lower general lighting load volt-ampere per area number when the 5591 facility is designed to comply with an energy code adopted by the local authority having 5592 jurisdiction. A power monitoring system is required when using this option that requires an 5593 alarm value be set to alert the building manager whenever the lighting loads exceed the values 5594 set by the energy code. When this exception is used, the designer may not apply any further 5595 demand factors in sizing the lighting infrastructure. This exception does allow new buildings to 5596 receive the first-cost benefit of designing to a smaller infrastructure. Lighting loads have fallen 5597 rapidly with the advent of lighting controls and LED lighting. In the 2017 NEC a new exception 5598 has been added to allow a further reduction in lighting load unit loads of one volt-amperes per 5599 square foot under certain conditions. (NFPA 2017) 5600 5601 5602

5603 Figure 5-41 (PL7) Typical medium office power distribution. (To Be Edited) 5604

5605 5606 Most small and medium office buildings are anticipated to be 120/208V Power distribution 5607 systems. It is noted that, where 277/480V systems are needed and a secondary transformer is 5608 used to step down the power from the higher voltage to the “plug load” voltage for receptacles, 5609


computers, and other devices that function at 120V, transformers fall under DOE minimum 5610 efficiency rules. The DOE efficiency standards apply at a single 35% load point, a common 5611 demand load point for transformers (DOE n.d.). However, this may result still in oversized 5612 transformers and higher than desirable losses due to lower efficiencies at light loads. When 5613 designing power distribution systems for larger offices, the step down transformers for plug 5614 loads should be sized as closely as possible within the National Electrical Code (NFPA 2017) 5615 requirements. When more heavily loaded, transformers operate more efficiently. Transformers 5616 should be specified to have a load loss profile that is higher under light loads to reduce energy 5617 losses. DOE 2016 transformer efficiencies will result in transformers with losses of only 1.6% 5618 to 1.26% (45 kVA to 112.5 kVA). Therefore, the use of a high efficiency transformer, operated 5619 close to its capacity in accordance with local electrical codes, will minimize energy losses in a 5620 zero energy office. The use of 100% rated devices on main services and large feeders may also 5621 help to reduce line losses. Transformers should be located so that they serve multiple electrical 5622 panelboards. Electrical closets should be stacked in order to reduce voltage drop. Lower 5623 temperature rise ratings and specialty transformers offering 30 to 50% reduction in losses may 5624 further reduce energy consumption due to transformer losses. Additionally, many designers add 5625 in a 20 to 25% “spare capacity” allowance to their plug load transformer sizing calculations. 5626 This may be eliminated to reduce oversizing, since the NEC minimum demand sizing 5627 requirements will result in a transformer oversized for the actual demand load. The engineer 5628 should study the usage patterns proposed for the office building and design accordingly. The 5629 transformer losses are an important part of the energy modeling and are considered in the 5630 overall energy target of the building. 5631 5632 REFERENCES AND RESOURCES 5633 5634 Plug and Process Loads Capacity and Power Requirements Analysis, Michael Sheppy and Luigi 5635

Gentile-Polese - National Renewable Energy Laboratory, Scott Gould - Stanford University, 5636 2014 5637

https://www.nrel.gov/docs/fy14osti/60266.pdf 5638 NREL - Assessing and Reducing Plug and Process Loads in Office Buildings, Sheppy, Lobato, 5639

Pless, Gentile Polese, Torcellini, 2013 5640 https://www.nrel.gov/docs/fy13osti/54175.pdf 5641 CEC. 2016. Building Energy Efficiency Program, Title 24. Sacramento: California Energy 5642

Commission. www.energy.ca.gov/title24/. 5643 DOE. n.d. U.S. Department of Energy, Energy Efficiency & Renewable Energy, Building 5644

Technology Office, Appliance and Equipment Standards, Distribution Transformers, 5645 https://www1.eere.energy.gov/buildings/appliance_standards/standards.aspx?productid 5646

=55&action=viewcurrent. 5647 EIA. 2012. Commercial Building Energy Survey, Energy Usage Summary. Washington, 5648

D.C.: 5649 U.S. Energy Information Administration. https://www.eia.gov/consumption/commercial/. 5650

NFPA. 2014. NFPA 70, National Electric Code. Quincy, MA: National Fire Protection 5651 Association. NFPA. 2017. NFPA 70, National Electric Code. Quincy, MA: National Fire 5652 Protection Association. www.nfpa.org/codes-and-standards/all-codes-and-standards/list-of-5653 codes 5654

-and-standards/detail?code=70. 5655 EPA. 2009. ENERGY STAR Qualified Products. www.energystar.gov/index.cfm?fuse 5656

action=find_a_product.html. Washington, DC: U.S. Environmental Protection Agency. 5657


Hart, R., S. Mangan, and W. Price. 2004. Who left the lights on? Typical load profiles in the 5658 21st century. 2004 ACEEE Summer Study on Energy Efficiency in Buildings. August 22–5659 27, Pacific Grove, CA. 5660

Lobato, C., S. Pless, M. Sheppy, and P. Torcellini. 2011. Reducing plug and process loads for a 5661 large-scale, low-energy office building: NREL’s Research Support Facility. ASHRAE 5662 Transactions 117(1):330–39. 5663

Maniccia, D., and A. Tweed. 2000. Occupancy Sensor Simulations and Energy Analysis for 5664 Commercial Buildings. Troy, NY: Lighting Research Center, Renssaelaer Polytechnic 5665 Institute. 5666

Roberson, J.A., C. Webber, M. McWhinney, R. Brown, M. Pinckard, and J. Busch. 2004. After-5667 hours power status of office equipment and energy use of miscellaneous plug-load 5668 equipment. LBNL-53729. Berkeley: Lawrence Berkeley National Laboratory. 5669

Sanchez, M.C., C.A. Webber, R. Brown, J. Busch, M. Pinckard, and J. Roberson. 2007. Space 5670 heaters, computers, cell phone chargers: How plugged in are commercial buildings? LBNL-5671 62397. Proceedings of the 2006 ACEEE Summer Study on Energy Efficiency in Buildings, 5672 August, Asilomar, CA. 5673

Thornton, B.A., W. Wang, M.D. Lane, M.I. Rosenberg, and B. Liu. 2009. Technical Support 5674 Document: 50% Energy Savings Design Technology Packages for Medium Office Buildings, 5675 PNNL-19004. Richland, WA: Pacific Northwest National Laboratory. 5676 www.pnl.gov/main/publications/external/technical_reports/PNNL-19004.pdf. 5677

Thornton, B.A., W. Wang, Y. Huang, M.D. Lane, and B. Liu. 2010. Technical Support 5678 Document: 50% Energy Savings for Small Office Buildings, PNNL-19341. Richland, WA: 5679 Pacific Northwest National Laboratory. 5680 www.pnl.gov/main/publications/external/technical_reports/PNNL-19341.pdf. 5681

5682 5683 SERVICE WATER HEATING 5684 5685 OVERVIEW 5686 5687 The first step to reducing the energy consumption of the service water heating system in an 5688 office is to reduce the demand for hot water. The simplest step to achieving this end is to 5689 specify low flow handwash and breakroom sinks and showerheads, if used. These fixtures 5690 should comply with the criteria in the EPA WaterSense program. Breakroom dishwashers 5691 should meet the criteria in Energy Star as shown in Table SWH-1. When hot water usage has 5692 been minimized the efficiency of the systems and equipment that provide the hot water can be 5693 addressed. 5694 5695 Water heating requirements for office buildings typically fall into the general category of 5696 distributed low-consumption fixtures, including hand wash and breakroom sinks, and small 5697 under-counter dishwashers. Some buildings may include showers, either for bicycle commuters 5698 or for operating staff. The first step for determining service water heating strategies is to 5699 develop an inventory of service water end-use applications in the facility. The second step is to 5700 establish the frequency of use and flow requirements for these end-uses. With that 5701 programmatic information the appropriate strategy for each end-use can be identified. Energy 5702 efficiency strategies for these applications should emphasize both the efficiency of generation of 5703 the hot water, and minimization of energy losses in delivering the hot water to its end use. In 5704


general, the distributed end uses should be served by simple local hot water generators to avoid 5705 the need for pumped loops to insure quick availability, 5706 5707 Table SWH-1 ENERGY STAR Criteria for Dishwashers 5708

Equipment Corresponding

Base Specification

High Temperature Efficiency Requirements***

High Temperature Efficiency Requirements**

Idle Energy Use*

Water Consumption

Idle Energy Use*

Water Consumption

Under Counter ENERGY

STAR <= 0.90 kW

<= 1.00 gal/rack

<= 0.50 kW <= 1.70 gal/rack

*Idle energy rate as measured with door closed and rounded to 2 significant digits 5709 **Machines designed to be interchangeable in the field from high temp to low temp, and vice versa, must meet both 5710 the high temp and low temp requirements to qualify 5711 5712 5713 SERVICE WATER HEATING SYSTEM TYPES 5714 5715 WH1 System Descriptions (Climate Zones: as indicated below) 5716 Several different types of water heating systems are used in office buildings. System selection 5717 depends upon fuel availability, fuel cost differentials in the location, and the magnitude of the 5718 loads to be served. The Energy Star system designates water heaters as either residential or 5719 commercial depending upon nominal energy input and water storage capacity. Depending upon 5720 end use and size, the water heaters in this guide may fall into either of these two categories. 5721 Systems considered in this Guide are as follows: 5722 5723 Gas-fired storage water heater 5724 This system consists of a water heater with a vertical or horizontal water storage tank. A 5725 thermostat controls the delivery of gas to the heater’s burner. The heater requires a vent to 5726 exhaust the combustion products. An electronic ignition is recommended to avoid the energy 5727 losses from a standing pilot. 5728 5729 Gas-fired instantaneous water heater 5730 This system consists of a water heater with minimal water storage capacity. Such heaters 5731 require vents to exhaust the combustion products. An electronic ignition is recommended to 5732 avoid the energy losses from a standing pilot. Instantaneous, point-of-use water heaters should 5733 provide water at a constant temperature regardless of input water temperature or flow rate. 5734 5735 Electric resistance storage water heater 5736 This system consists of a water heater consisting of a vertical or horizontal storage tank with 5737 one or more immersion heating elements. Thermostats controlling heating elements may be of 5738 the immersion or surface-mounted type. Electric resistance water heaters are not included in the 5739 Energy Star rating system. 5740 5741 Electric resistance instantaneous water heater 5742 This system consists of a compact under-cabinet or wall-mounted water heater with an insulated 5743 enclosure and minimal water storage capacity. A thermostat controls the heating element, which 5744 may be of the immersion or surface-mounted type. Instantaneous, point-of-use water heaters 5745 should provide water at a constant temperature regardless of input water temperature or flow 5746 rate. 5747


5748 Caution: These electric resistance instantaneous water heaters can save energy for small loads, 5749 such as restroom sinks, but larger systems should be avoided, as they may add to electrical 5750 demand charges if they operate coincidently with the peak load of the rest of the building. 5751 5752 Heat pump electric water heater (Climate Zones: 1, 2, 3, 4, 5, 6) 5753 A storage-type water heater using rejected heat from a heat pump as the heat source. Water 5754 storage is required because the heat pump is typically not sized for the instantaneous peak 5755 demand for service hot water. The heat source for the heat pump may be the interior air (within 5756 the kitchen is ideal because of the internal heat gain from cooking), which is beneficial in 5757 cooling-predominant climates; the circulating loop for a water-source heat pump (WSHP) 5758 system, also beneficial in cooling-dominated climates; or a ground-coupled hydronic loop. 5759 These types of water heaters should be considered for projects as alternatives to an electric 5760 resistance tank type water heater. Heat pump water heaters should have an Energy Factor of at 5761 least 2.2. Currently commercial (large heating capacity and/or storage capacity) heat pump 5762 water heaters are not included in the Energy Star program 5763 5764 Where electricity is the preferred energy source for SWH, consider specifying a heat pump 5765 water heater, meeting the Energy Star criteria for residential heat pump water heaters, for 5766 additional energy savings. Products, now available utilizing CO2 as a refrigerant have 5767 demonstrated much higher COP’s than systems using more common refrigerants, but even 5768 residential size versions of these products do not yet have an Energy Star rating as the official 5769 test procedures for the products have not yet been finalized. 5770 5771 GOOD DESIGN PRACTICE 5772 5773 WH2 Properly Size Equipment 5774 The water heating system should be sized to meet the anticipated peak hot-water load. In an 5775 office building, the hot water loads will usually be limited to low-flow distributed fixtures. 5776 Calculate the demand for each water heater based on the fixture units served by the heater 5777 according to local code. 5778 5779 Hot-water temperature requirements for vary by local and state code within the range of 100°F–5780 120°F. If showers are included in the program, the temperature of hot water provided should be 5781 100°F–110°F. Note that production of service hot water at temperatures below approximately 5782 135°F may result in bacterial growth in storage-type water heaters, so that end-uses with lower 5783 temperature requirements should be served from a storage-type heater with a thermostatic 5784 mixing valve. 5785 5786 In designing and evaluating the most energy-efficient hot-water system for the office building 5787 and the associated life-cycle costs, consider installing small local water heaters in most 5788 locations. Only in areas where large volumes of hot water are required (not in the scope of this 5789 document) should large water heaters systems be installed. 5790 5791 WH3 Equipment Efficiency 5792 Water heating equipment fuel source and efficiency should recognize the impact of site/source 5793 energy multipliers, both regionally and nationally. While the site/source multiplier for 5794 electricity, for almost all regions is greater than that of fossil fuels, for some applications, even 5795 electric resistance service water heating may be the more energy efficient selection. 5796


5797 Efficiency levels are provided in this Guide for gas-fired instantaneous, gas-fired storage, 5798 electric resistance instantaneous, and electric resistance storage water heaters and electric heat 5799 pump water heaters. Energy Star divides water heaters into residential and commercial 5800 classifications, and provides specifications for gas heaters and electric heat pump heaters. It no 5801 longer lists electric resistance heaters. Unfortunately, heat pump type water heaters are 5802 available only in larger tank sizes, and may not be appropriate for the small distributed end-5803 uses. 5804 5805 The small tank-type water heaters recommended for small distributed end-uses, in WH4, are 5806 classified as residential water heaters, under previous the Energy Star rating system, and are 5807 typically rated for the Uniform Energy Factor (EF) that reflects the ratio of the heat added to the 5808 delivered hot water to the total thermal input to the heater over a prescribed schedule of hot-5809 water delivery. 5810 5811 Commercial tank-type water heaters, suggested for central larger end-uses, and which will 5812 likely have a far different schedule of hot-water delivery, are currently rated by thermal 5813 efficiency (Et ) and standby heat loss. Standby heat losses are dependent upon tank volume and 5814 configuration in addition to jacket insulation value and are typically established by a 5815 standardized testing procedure. 5816 5817 For commercial gas-fired storage water heaters, the standby loss criteria is given by the 5818 following equation: 5819 5820 Standby Loss (Btu/hr) ≤ 0.84 * (Input Rate (Btu/hr) / 800) + 110 * √Volume (gal) 5821 5822 For gas-fired instantaneous water heaters, the EF and Et levels are nearly the same because there 5823 are no standby losses. The incorporation of condensing technology is recommended for all gas-5824 fired water heaters to achieve a minimum Et of 94%. For multi-story office buildings, 5825 incorporation of gas-fired instantaneous water heaters may be problematic because of flue and 5826 combustion air requirements. 5827 5828 Table WH-1 gives performance requirements for residential and commercial gas-fired water 5829 heaters of various capacities and sizes. 5830 5831 Table WH-1 Gas Water Heater Performance 5832

5833

Storage Volume

(gal)

Capacity, kBtu/h

UEF (Residential)

TE % (Commercial)

Standby Loss, Btu/h

(Commercial)

0.0 Varies 0.87 0.94 NA

55.0 70 0.68 NA NA

55.1 75 0.80 NA NA

140 75 NA 0.94 1380


The levels of performance specified in this Guide for gas water heaters require that the units be 5834 of the condensing type, not only recovering more sensible heat from the products of combustion 5835 but also recovering heat by condensing moisture from these gases. The construction of a 5836 condensing water heater as well as the water heater venting must be compatible with the acidic 5837 nature of the condensate for safety reasons. Disposal of the condensate should be done in a 5838 manner compatible with local building codes. 5839 5840 Efficiency metrics for residential and commercial high-efficiency electric storage water heaters 5841 are also provided in this Guide. These efficiency metrics represent premium products that have 5842 reduced standby losses, but which are no longer rated by Energy Star. Table WH-2 summarizes 5843 required EFs for electric resistance water heaters and thermal efficiency and standby loss limits 5844 for commercial electric resistance water heaters, according to a previous version of the Energy 5845 Star rating. Because these heaters are recommended only for distributed, small loads, 5846 performance ratings are given only for smaller size units. Standby losses for electric storage 5847 water heaters are calculated in the same way as for gas storage-type water heaters. 5848 5849 Table WH-2 Electric Resistance Water Heater Performance 5850

Storage Volume

(gal)

EF (Residential)

Et , % (Commercial)

Standby Loss, %/h

(Commercial)

0.0 0.98 0.98 NA

30 0.96 0.98 1.2

40 0.96 0.98 0.98

5851 Electric instantaneous water heaters are a more efficient alternative to high-efficiency storage 5852 water heaters for very-low-volume distributed end uses because they have no tank losses. In 5853 addition, they can be located near the end use, minimizing pipe losses. However, their impact 5854 on the first cost of electrical distribution may be significant and should be taken into account 5855 during design. For a bank of handwash sinks in a large restroom, an electric resistance heater 5856 with a small tank, (20 gals), would require a much less extensive electrical distribution approach 5857 than would providing an instantaneous electric resistance heater for each sink. A schematic of 5858 the proposed layout for serving a bank of handwash sinks in public restrooms is shown in 5859 Figure WH-1. 5860


5861 Figure WH-1 Hot Water Service for Bank of 5862

Hand-Wash Sinks with Local Point-of-Use Water Heater 5863 5864 Where unusually high hot-water loads (e.g., dishwashers) are present during periods of peak 5865 electrical use, electric heat-pump storage water heaters are recommended over electric 5866 instantaneous water heaters. Current Energy Star standards require heat pumps for all electric 5867 water heaters. Table WH-3 shows Energy Star performance requirements for residential heat 5868 pump type water heaters. Requirements for commercial heat pump water heaters have not yet 5869 be determined, but products are available in the market that deliver and EF higher than 3.0. For 5870 electric water heaters serving substantial water heating loads, this guide recommends using a 5871 product with the highest EF available for a competitive price. 5872 5873 Table WH-3 Performance Requirements 5874

Storage Volume

(gal)

UEF (Residential)

≤55 2.0

>55 2.16

5875 WH4 Minimizing System Losses 5876 Office SWH requirements most often consist of low-volume distributed end uses, such as hand-5877 wash and breakroom sinks. As was stated previously, the most important strategy for reducing 5878 hot water consumption is to provide water efficient fixtures. Aerated proximity faucets are 5879 available with a rated flow-rate as low as 0.35 gpm (1.32 l/m). These faucets not only have the 5880


benefit of a very low flow-rating but also initiate and curtail flow in response to the proximity 5881 of the object to be washed (hands, etc.). 5882 5883 The second most important strategy for reducing hot water consumption in office buildings is to 5884 eliminate the heat loss from pumped circulating loops that are required to minimizer hot water 5885 latency (period of time it takes to get hot water after faucet is opened). Pumped loops are 5886 required when the source of hot water is remote from the hot water end-use. Potential location 5887 for gas-fired water heaters, adjacent to office building end-uses such as hand-wash sinks, may 5888 be limited by flue and combustion air and local code requirements. 5889 5890 Low-volume end uses, including handwashing sinks, janitorial closets, and implement-washing 5891 sinks in the food preparation areas likely do not justify service from a central source with 5892 required recirculation and should be served with point-of-use water heaters, either 5893 instantaneous, for single fixtures, or small tank-type heaters for groupings of fixtures. 5894 5895 WH5 Renewable and Heat Recovery Service Hot Water Sources 5896 While solar thermal water heating and various types of heat recovery water heating are 5897 appropriate for occupancies with large centralized service water heating loads, they are difficult 5898 to accommodate to the small distributed end-uses that characterize office buildings. The 5899 recirculation pump energy required by the central location of the water heater might exceed the 5900 energy consumption required to generate the service hot water for these small end-uses, so that 5901 even if the heat source is “free” the net energy savings may be small or negative and the capital 5902 cost could be excessive. 5903 5904 WH6 Pipe Insulation 5905 All SWH piping should be installed in accordance with accepted industry standards. Required 5906 pipe insulation thickness should vary with the temperature of the water, the size of the pipe, and 5907 the thermal resistance of the insulation material per Table WH-4. 5908 5909 Table WH-4 Minimum Piping Insulation Thicknesses for SWH Systems 5910

Fluid Operating Temperature

Range, °F

Insulation Conductivity Nominal Pipe Size

Conductivity, Btu·in./h·ft2·°F

Mean Rating Temperature,

°F < 1 in. 1 to < 1 1/2 in. > 1 1/2 in.

141°F to 185°F 0.25 to 0.29 125 1.5 1.5 2.0

105°F to 140°F 0.22 to 0.28 100 1.0 1.0 1.5

For insulation outside the stated conductivity range, the minimum thickness (T) shall be determined as follows: T = r {( 1 + t / r )K/k – 1 }, where T = minimum insulation thickness (in.), r = actual outside radius of pipe (in.), t = insulation thickness listed in this table for applicable fluid temperature and pipe size, K = conductivity of alternate material at mean rating temperature indicated for the applicable fluid temperature (Btu·in./h·ft2·°F), and k = the upper value of the conductivity range listed in this table for the applicable fluid temperature. Data source: ASHRAE/IES Standard 90.1-2013, Table 6.8.3-1 5911 REFERENCE AND RESOURCES 5912 5913 ASHRAE. 2016. ANSI/ASHRAE/IES Standard 90.1-2016, Energy Standard for Buildings 5914

Except Low-Rise Residential Buildings. Atlanta: ASHRAE. 5915 ASHRAE. 2015. ASHRAE Handbook—HVAC Applications. Atlanta: ASHRAE 5916


5917 5918 HVAC SYSTEMS AND EQUIPMENT 5919 5920 OVERVIEW 5921 The design challenge of a Zero Energy HVAC system is maximizing energy efficiency. The 5922 lower the operating EUI is of the building, the less renewable energy is required to achieve zero 5923 energy which reduce first cost. Therefore strategies must be developed to address energy 5924 consumption with respect to cooling generation, heating generation, air distribution fan energy, 5925 water recirculation pump energy and outside air ventilation energy. 5926 5927 HVAC SYSTEM TYPES 5928 5929 HV1 System Descriptions (Climate Zones: as indicated below) 5930 Several different types of HVAC systems are used in office buildings. System selection depends 5931 upon building configuration, owner preference, zone configuration and the magnitude of the 5932 loads to be served. Several system types were examined and are recommended for the small 5933 office building. Systems considered in this Guide are as follows: 5934 5935

System A – Rooftop Multizone VAV with Hydronic Heating (Small Office Only) 5936 System B –Air Source Variable Refrigerant Flow Heat Pump System with DOAS 5937 System C – Water & Ground Source Heat Pump System (GSHP) with DOAS 5938 System D – Sensible Cooling Chilled Water Fancoils with DOAS 5939

5940 Details on each system are provided in this guide, along with specific recommendations for 5941 each system type. Overall tips for all system types is also present. Table HV-1 shows 5942 minimum recommendations for efficiency and requirements for all system types. Table HV-2 5943 through HV-4 show primary and secondary cooling and heating sources. 5944 5945


Table HV-1 Minimum Efficiency Recommendations by System Type 5946

5947 * Minimum recommended levels, 1)Certification with ISO standards, 2) Climates Where Water Source Used, 3) 5948 AHRI Standards, 4) See Table where WSHP applicable, 5) See Table XX where Boiler applicable 5949

GSHP cooling efficiency1 >18.0 EER at 59F entering water

GSHP heating efficiency1 >3.7 COP at 50F entering water

WSHP cooling efficiency1,4 >14.0 EER at 86F entering water

WSHP heating efficiency1,4 >4.6 COP at 68F at entering water

Terminal Fan ECM <0.38 W/CFM at DesignCompressor capacity control Multistage or VSD compressorWater circulation pumps VSD and NEMA premium efficiency <0.25 W/GPM at Design

Cooling tower/fluid cooler2,4 VSD on fans

Boiler efficiency2,5 Condensing boiler, >92% efficiency

<65,000 Btu/h; 15.0 SEER; 12.5 EER*>65,000 Btu/h and <135,000 Btu/h; 11.1 EER; 14.4 IEER*>135,000 Btu/h and <240,000 Btu/h; 10.7 EER; 13.7 IEER*<240,000 Btu/h; 10.1 EER; 12.5 IEER*<65,000 Btu/h; 8.5 HSPF*>65,000 Btu/h and <135,000 Btu/h; 3.4 COP*>135,000 Btu/h and <240,000 Btu/h; 3.2 COP*

Terminal Fan ECM <0.38 W/CFM at Design


Water circulation pumps VSD and NEMA premium efficiency <0.25 W/GPM at Design

Comply or exceed ASHRAE 90.1 2016<150 tons; 10.1 EER; 13.7 IPLV @AHRI Conditions<150 tons; 12.2 EER; 15.5 IPLV @55Chilled Water

Compressor Capacity Control Multi-stage or VSD compressorWater circulation pumps VSD and NEMA premium efficiency <0.25 W/GPM at DesignTerminal Fan ECM <0.38 W/CFM at Design


Air-cooled Rooftop Efficiency3 > 18 IEER

Compressor Capacity ControlMulti-stage or VSD compressor Minimum Turndown <20% of compressor capacity

Supply Fan Minimum Turndown <30% of design flow

Exhaust Energy Recovery3 A (humid) zones and C (marine) zones : 72% enthalpy reduction; B (dry)

zones: 72% dry-bulb temperature reduction

Gas Heat Gas Heat AFUE > 80%, modulating



Air Cooled DX Efficiency >5.2 ISMRE @AHRI 920 Conditions

Compressor Capacity ControlMulti-stage or VSD compressor Minimum Turndown <20% of compressor capacity

Supply Fan Minimum Turndown <30% of design flow

Exhaust Energy Recovery3 A (humid) zones and C (marine) zones : 72% enthalpy reduction;

B (dry) zones: 72% dry-bulb temperature reduction

DX Heat Pump >3.8 ISCOP @AHRI 920 ConditionsGas Heat Gas Heat AFUE > 80%, modulating



WATER & GROUND SOURCE HEAT PUMP SYSTEM (GSHP) WITH DOAS

ROOFTOP MULTIZONE VAV WITH HYDRONIC HEATING

DEDICATED OUTDOOR AIR SYSTEM

Ducted Air-cooled VRF multisplit with

heat recovery (cooling mode)3

Ducted Air-cooled VRF multisplit with

heat recovery (Heating Mode)3

SENSIBLE COOLING CHILLED WATER FANCOILS WITH DOAS

Air-cooled chiller efficiency

AIR SOURCE VARIABLE REFRIGERANT FLOW HEAT PUMP SYSTEM WITH DOAS


5950 [Note/Question to Reviewers: The following tables HV–2 through HV-4 have been added to 5951 make specific suggestions on how to apply this system type to each climate zone. Please 5952 comment if you find this table useful, is it understandable? Is there another way you would like 5953 to see these suggestions?] 5954 5955 Table HV-2: Recommendations for Rooftop Multizone VAV systems 5956

5957 5958 5959

VAV RTU, All Air VAV RTU w/Hyrdonic Heat

CZ System Designation System A System A

Primary Cooling source Air Source DX Air Source DX

First Stage Heating Source Exhaust Energy Recovery Exhaust Energy Recovery

Second Stage Heating Source Optional Gas Heat Optional Zone Hydronic Heat



Second Stage Heating Source Optional Gas Heat Optional Zone Hydronic Heat


First Stage Heating SourceExhaust Energy Recovery (Not Required Region 3C)

Exhaust Energy Recovery (Not Required Region 3C)

Second Stage Heating Source Gas Heat Zone Hydronic Heat












Second Stage Heating Source Gas Heat Zone Hydronic Heat +

Optional Unit Hydronic Heat

Primary Cooling source Optional (Air Source DX) Optional (Air Source DX)


Second Stage Heating Source Gas Heat Zone Hydronic Heat +

Optional Unit Hydronic Heat

Central Equipment

8

1

2

3

4

5

6

7


Table HV-3 - Recommendations for Zone Terminal Systems with DOAS 5960

5961 5962 5963

Air Source VRFGround Source Heat

PumpsSensible Cooling Hydronic Fancoils

CZ System Designation System B System C System D

Primary Cooling source Air Source DXWater source DX w/ Cooling

TowerAir Cooled Chiller or Water Cooled Chiller

w/ Cooling Tower

First Stage Heating Source Air Source DX Ground Source DX Electric ResistanceSecond Stage Heating

SourceNot Required Not Required Not Required

Primary Cooling source Air Source DXWater source DX w/ optional

cooling towerAir Cooled Chiller or Water Cooled Chiller

w/ Cooling Tower

First Stage Heating Source Air Source DX Ground Source DX Electric Resistance (Perimeter Zones)Second Stage Heating


Primary Cooling source Air Source DX Ground source DXAir Cooled Chiller or Water Cooled Chiller

w/ Cooling Tower

First Stage Heating Source Air Source DX Ground source DX Hydronic (4 pipe Perimeter Zones)Second Stage Heating



w/ Cooling Tower

First Stage Heating Source Air Source DX Ground source DX Hydronic (4 pipe Perimeter Zones)

Second Stage Heating Source

Optional Perimeter Zone Hydronic Heat(radiant, convective in space)

Not Required Not Required


w/ Cooling TowerFirst Stage Heating Source Air Source DX Ground source DX Hydronic (4 pipe Perimeter Zones)


Perimeter Zone Hydronic Heat (radiant, convective in space)



w/ Cooling Tower

First Stage Heating Source Air Source DX Ground source DX Hydronic ( 4 pipe Perimeter Zones)Second Stage Heating

Source Perimeter Zone Hydronic Heat (radiant, convective in space)


Primary Cooling source NA Ground source DXAir Cooled Chiller or Water Cooled Chiller

w/ Cooling Tower

First Stage Heating Source NAGround Source DX w/

Supplemental BoilerHydronic (4 pipe Perimeter Zones)


NA Not RequiredOptional Perimeter Zone Hydronic Heat

(radiant, convective in space)

Primary Cooling source NA NA Not Required

First Stage Heating Source NA NA Hydronic (2 pipe )Second Stage Heating

SourceNA NA

Perimeter Zone Hydronic Heat (radiant, convective in space)

Zone Terminal Equipment (used with DOAS)

5

6

7

8

1

2

3

4


Table HV-4 – Recommendations for DOAS Systems 5964

5965 5966 SYSTEM A - ROOFTOP MULTIZONE VAV WITH HYDRONIC HEATING (SMALL 5967 OFFICE ONLY) 5968 5969 HV2 System Description 5970 In this system, a packaged DX rooftop unit serves several individually controlled zones. Each 5971 thermal zone has a VAV terminal unit that is controlled to maintain temperature in that zone. 5972 The components of the rooftop unit are factory designed and assembled and include OA and 5973 return-air dampers, filters, fans, air to air exhaust energy recovery exchanger, a cooling coil, an 5974 optional heating source, compressors, a condenser, and controls. The components of the VAV 5975 terminal units are also factory designed and assembled and include an airflow-modulation 5976 device, controls, and possibly a heating coil, fan, or filter. 5977 5978 VAV terminal units are typically installed in the ceiling plenum above the occupied space or 5979 adjacent corridor. However, the equipment should be located to meet the acoustical goals of the 5980 space; fan power, ducting, and wiring should be minimized. 5981 5982

Air-cooled DX Cooling,

Air Source Heat Pump Ground Source Heat

Pump Hydronic Fan coils

CZ Compatible SystemsSYSTEM B SYSTEM C SYSTEM D

SYSTEM B SYSTEM C SYSTEM D

SYSTEM C SYSTEM D

Primary Cooling source Air Source DX NA NAAir Cooled Chiller or Water

Cooled Chiller w/ Cooling Tower

1 First Stage Heating Source Exhaust Energy Recovery NA NA Exhaust Energy Recovery

Second Stage Heating Source Not Required NA NA Not Required

Primary Cooling source Air Source DX Air Source DXWater source DX w/

supplemental cooling towerAir Cooled Chiller or Water

Cooled Chiller w/ Cooling tower

2 First Stage Heating Source Exhaust Energy Recovery Exhaust Energy Recovery Exhaust Energy Recovery Exhaust Energy Recovery

Second Stage Heating Source Electric resistnace heat (opt) Optional Air Source DX Ground Source DX Electric resistance heat (opt)

Primary Cooling source Air Source DX Air Source DXGround Source DX with optional

supplemental cooling towerAir Cooled Chiller or Water


3 First Stage Heating SourceExhaust Energy Recovery (Not Required Region 3C)




Second Stage Heating Source Indirect Gas Furnace Air Source DX Ground source DX Condensing Boiler

Primary Cooling source Air Source DX Air Source DX Ground source DXAir Cooled Chiller or Water



Second Stage Heating Source Indirect Gas Furnace Air Source DX Ground source DX Condensing Boiler




Second Stage Heating Source Indirect Gas Furnace Air Source DX Ground source DX Hydronic Heating Coil




Second Stage Heating Source Indirect Gas Furnace Air Source DX + Supplemental

Electric ResistanceGround source DX Condensing Boiler

Primary Cooling source Air Source DX NA Ground Source DX Air Cooled Chiller

First Stage Heating Source Exhaust Energy Recovery NA Exhaust Energy Recovery Exhaust Energy Recovery

Second Stage Heating Source Indirect Gas Furnace NAGround Source DX w/ Supplemental Boiler

Condensing Boiler

Primary Cooling source Optional (Air Source DX) NA NA Air Cooled Chiller (opt)

8 First Stage Heating Source Exhaust Energy Recovery NA NA Exhaust Energy Recovery

Second Stage Heating Source Indirect Gas Furnace NA NA Condensing Boiler

DOAS Options

7


All the VAV terminal units served by each rooftop unit are connected to a common air 5983 distribution system (see HV#). Cooling is provided by the centralized rooftop unit. Heating is 5984 provided by an electric convection heater in each space. 5985 5986 The cooling equipment, heating equipment, and fans should meet or exceed the efficiency levels 5987 listed in Table HV-1. In climate zones 7,8 where shown Indirect gas-fired furnaces providing 5988 morning warm-up should be condensing furnaces and have at least an 80% efficiency level as 5989 required in ASHRAE/IESNA Standard 90.1-2016 (ASHRAE 2016). Requirements for hydronic 5990 zone heating are shown table HV-1. For systems using gas-fired boilers, condensing boilers 5991 should be used. 5992 5993 For packaged VAV DX systems, fan power is usually incorporated into the IEER calculation. 5994 To achieve the required level of energy efficiency, air supply and delivery systems for the 5995 packaged VAV units should be designed to require no more than 2.0 in. w.c. external static 5996 pressure (ESP) and should include variable-frequency drives (VFDs) or other features that result 5997 in improved part-load performance. A reduced design supply air temperature (SAT) of 50°F is 5998 used to lower system airflow and the resultant pressure drop. To enhance economizer operation, 5999 SAT is reset up to 58°F in climate zones 1-3 and 61°F in other climate zones. 6000 6001 For the amount of outdoor air required for office spaces heat at the central unit is not needed 6002 with exception of morning warm up in cold climate zones. All the heat required during normal 6003 operation at the central roof top unit can be recovered from the exhaust air. The exhaust 6004 recovery exchanger should have means to reduce heat recovery to prevent overheating of the 6005 air. To prevent heating of outside air and recooling of the mixed air, incorporating the energy 6006 recovery into the rooftop unit. 6007 6008 Units will have air-side economizers in all climate zones except climate zone 1, with control 6009 based on either dry-bulb temperature sensors or enthalpy sensors. See the recommendations in 6010 Table HV-1 for the requirements in each climate zone. 6011 6012 For VAV systems, the minimum supply airflow to a zone must comply with local codes and the 6013 current versions of ASHRAE Standard 62.1 (for minimum OA flow) and ASHRAE/IES 6014 Standard 90.1 (for minimum turndown before reheat is activated) (ASHRAE 2010a, 2010b). 6015 6016 Ventilation optimization, a combination of zone demand-controlled ventilation (DCV) and 6017 system ventilation reset using the provisions of ASHRAE Standard 62.1, reduces OA during 6018 operation, see section HV# Demand Control Strategies. 6019 6020 SYSTEM B – AIR SOURCE VARIABLE REFRIGERANT FLOW HEAT PUMP 6021 SYSTEM WITH DOAS 6022 6023 HV3 System Overview 6024 This system is comprised of a fancoil in each thermal zone with air source heat pump and heat 6025 recovery units located outside the occupied space. It is also called a variable refrigerant flow 6026 (VRF) system. This type of equipment is available in pre-established increments of capacity. 6027 The components are factory assembled and include a filter, fan, refrigerant to air heat 6028 exchanger, compressor, and controls. A system example is shown in Figure HV-1. 6029 6030


Attributes that distinguish VRF from other DX system types are multiple indoor units connected 6031 to a common outdoor unit to achieve scalability, variable capacity, distributed control and 6032 recovered heat simultaneous heating and cooling (ASHRAE Handbook 2012, pg 18.1). The 6033 advantage is the ability to have individual zone control while also able to transfer energy from 6034 one indoor space to another using one energy source. 6035 6036 Terminal units are typically installed in each conditioned space, in the ceiling plenum within the 6037 space. However, the equipment should be located to meet the acoustical goals of the space, 6038 permit access for maintenance, and minimize fan power, ducting, and wiring. Consideration 6039 should also be given to any future modifications to the space. Piping supplying the terminal 6040 unit in the space will be refrigerant piping and will need trained technicians to reroute should 6041 any space reconfigurations require HVAC changes. 6042 6043

6044 Figure HV-1 Three-Pipe Heat Recovery VRF System Examples 6045

Source: Figure 4 from Chapter 18.2 of ASHRAE Systems handbook 2012 6046 6047 OA for ventilation is conditioned and delivered by a separate DOAS. This may involve ducting 6048 the OA directly to each fan coil, delivering it in close proximity to the fan-coil intakes, or 6049 ducting it directly to the occupied spaces. Depending on the climate, the dedicated OA unit 6050 may include components to filter, cool, heat, dehumidify, and/or humidify the outdoor air 6051 6052 HV4 Sizing Indoor with Outdoor Units 6053 Outdoor units are sized based on the higher of the peak cooling or heating load. The 6054 consideration for supplemental heating will be needed in climate zones where the outdoor 6055 ambient heating design temperature is below -4F and needs to be included in the sizing of the 6056 outdoor condenser systems. Derating of the outdoor systems also needs to be taken into account 6057 on both heating and cooling sizes. (ASHRAE Systems Handbook, 2016, Chapter 18) VSDs 6058


are highly recommended for at least one compressor on the outdoor unit. This will help with 6059 capacity control throughout the range of the equipment. 6060 6061 Indoor units will be selected based on the design considerations for the space which will be 6062 primarily based on the sound considerations of the space. Sizing for the indoor units takes into 6063 account the peak heating and cooling load in the space as well as the ration of the sensible to 6064 latent cooling load. Ventilation requirements and plans will affect the sizing of the indoor unit, 6065 if cooler air is supplied to the space, this allows the indoor unit to focus primarily on the 6066 sensible cooling load. (ASHRAE Systems Handbook, 2016, Chapter 18) 6067 6068 HV5 Refrigerant Safety 6069 All systems need to comply with ASHRAE Standard 15 to provide safeguards to protect 6070 occupants. It will require that the smallest space in which any indoor unit or piping is located 6071 has the ability to safely disperse the entire refrigerant charge of the VRF system in the event of 6072 leak or failure. Typical spaces that should be examined include bathrooms, electrical rooms, 6073 closets, small offices and egress spaces. As the engineer of record reviews the refrigerant safety 6074 applications for the equipment, they may make considerations of layout, condenser type and 6075 efficiency to minimize the amount of refrigerant required for the space. 6076 6077 Many options are available to address this requirement. Some spaces can be served by simple 6078 outdoor air ventilation. Multiple smaller spaces can be served by a single indoor unit increasing 6079 the conditioned space under consideration. Opening the smaller occupied space to an adjacent 6080 space that has a larger volume using a permanent opening. Details on compliance with 6081 ASHRAE Standard 15 are outside the scope of this document, however additional guidance and 6082 references should be considered, including “Applying VRF? Don’t Overlook Standard 15” 6083 (ASHRAE Journal, July 2012) 6084 6085 HV6 Ambient Condition Considerations 6086 In heating dominated climate zones, it is important to note that the capacity of the outdoor air 6087 source condensers is decreased in cooler temperatures. Condensers are rated at about 60% 6088 capacity at -4F (ASHRAE Systems Handbook 2016, page 18.9). Thus systems requiring heat 6089 below 40F design ambient conditions may need to include design considerations for the low 6090 ambient conditions. This could include low ambient kits, baffles or locating the system in an 6091 enclosed space such as a parking garage or equipment room to ensure the condenser can provide 6092 enough heating during the low ambient conditions. Furthermore, climates with operating 6093 temperatures below 0F definitely need low ambient design considerations or a back-up heating 6094 system. This would likely be electric resistance heating for simplicity of cost and controls. 6095 Low ambient design considerations should be implemented so as to not impact the cooling 6096 design conditions of the air source condenser. That is, the air source condenser will need 6097 unrestricted airflow in cooling mode. 6098 6099 During some temperature and humidity conditions, outdoor air source condensers can 6100 accumulate frost. Defrost cycles are available and are manufacturer dependent. Without 6101 defrosting, the condenser will not have enough airflow over the condenser coil surface and will 6102 not perform as designed. Some systems upon sensing frost will reverse the refrigerant flow to 6103 heat the condenser for a period of time. Whether installing the system indoors or using a defrost 6104 cycle, either way, considerations for heating during low ambient air conditions needs to be a 6105 part of the design. 6106 6107


HV7 Equipment Efficiencies 6108 Equipment should be rated in accordance with AHRI 1230. Equipment efficiencies should meet 6109 or exceed efficiencies listed in Table HV-1. 6110 6111 SYSTEM C – WATER AND GROUND SOURCE HEAT PUMP SYSTEM (GSHP) 6112 WITH DOAS 6113 6114 HV8 – System Overview 6115 A GSHP system consists of an exterior ground coupled heat exchanger, either in a vertical 6116 borehole, a horizontal trench, or submerged in a surface water feature, a water piping system 6117 connecting the ground heat exchanger to the GSHP heat pump unit, and thermal distribution to 6118 individual thermal zones. GSHP systems can be characterized as either “open loop” or “closed 6119 loop.” The systems described in this document are all “closed loop”. “Open loop” systems, 6120 because they introduce ground water into the thermal circulating loop present a number of 6121 additional challenges, mostly associated with ground water chemistry. Design of an “open 6122 loop” system should be done with the advice of experts, not only in ground thermal heat 6123 transfer, but also in ground chemistry and in some cases ground micro-biology. “Open loops” 6124 will not be treated in this document. 6125 6126 A GSHP system offers several other advantages for building owner when compared to a 6127 conventional WSHP system. In most climate zones, the GSHP system eliminates the need for 6128 boiler/cooling tower maintenance and chemical treatment, services that owners must contract to 6129 multiple service vendors. The central plant is substantially reduced in size, which lowers 6130 building sf and construction costs. The noise source of a cooling tower is removed, along with 6131 the hazard of a boiler. These advantages must be evaluated against the added cost of the ground 6132 heat exchanger. 6133 6134 HV9 Types of ground-source heat pump systems 6135 The simplest system utilizes multiple single package water-source heat pumps that are 6136 connected to the ground via the water circulating loop. Each thermal zone is provided with a 6137 separate GSHP terminal unit to provide zone cooling and heating. Supply and return ductwork 6138 connect the heat pump unit to the space for delivery of heating and cooling. GSHP units are 6139 available in pre-established increments of capacity. The components are factory assembled and 6140 include a filter, fan, refrigerant-to-air heat exchanger, compressor, refrigerant-to-water heat 6141 exchanger, and controls. The refrigeration cycle is reversible, allowing the same components to 6142 provide cooling or heating, at any time independent of the loop water temperature. Compressors 6143 and fans in the heat pump units should be variable speed to enhance energy efficiency. 6144 6145 Another popular option is to use water-source multi-split VRF heat pumps. This system 6146 employs a compressorized or “outdoor” unit that is connected to the ground circulating loop and 6147 to multiple fan coils in the zones via refrigerant piping. This system has the advantage that the 6148 “outdoor” unit may be located outside the conditioned space, in a closet or mechanical room, 6149 isolating the compressor noise. Each fan coil, or “indoor” unit, provides a separate thermal 6150 zone. The system can be configured with refrigerant-side heat recovery. With this system, 6151 when individual fan coils, connected to an “outdoor” unit, are in different modes of operation 6152 (heating and cooling), the smaller of the two load modes may be met with very little additional 6153 energy consumption. This feature can be very beneficial with a large floor plate office building, 6154 in which the interior zones are almost always in cooling mode even when the perimeter zone is 6155


in heating mode. Depending upon the floor plate configuration, refrigerant side heat recovery 6156 can be very beneficial in climate zones 2, 3, 4, 5, 6 and 7. 6157 6158 Both of the above options typically provide space conditioning through recirculated air. They 6159 are typically incorporated with separate Dedicated Outdoor Air Systems (DOAS) to manage 6160 ventilation. Heat pump units within the DOAS to condition ventilation air may also be 6161 connected to the ground loop. See HV4 Dedicated Outdoor Systems for additional information. 6162 6163 One further option is to connect the ground circulating loop to one or more water-to-water heat 6164 pumps, then circulate the hot or chilled water from the heat pumps to individual fan coils, 6165 chilled beams, radiant panels or thermally active floors located in the conditioned space. This 6166 system shares the advantage of locating the compressorized unit outside of the conditioned 6167 space, and also has the further advantage that no refrigerant is conveyed through the conditioned 6168 space, enabling the conditioning of very small volume spaces without a refrigerant purge 6169 system. 6170 6171 HV10 Thermal storage in the ground 6172 The primary means by which ground coupled heat pump systems reduce energy is through 6173 increased refrigeration system COP due to reduced temperature differential across which the 6174 system works. The annual ground temperature variation to which the heat exchangers are 6175 exposed are typically much narrower than the air temperature variations at the location. So, 6176 during cold weather, when the system is in heating mode, it will be extracting energy from a 6177 much warmer source than the air temperature. Similarly, in hot weather, when it is in cooling 6178 mode, it will be rejecting heat to a cooler sink than the air. Some ground-coupled heat pump 6179 systems may also save significantly fan energy compared with centralized air distribution 6180 because the pressure drop through the fan coils is significantly less than for central air handling 6181 units. 6182 6183 The water piping loop allows heat transfer between the heat pump units and the ground. For 6184 these systems, the mass of ground that is thermally coupled to the heat exchanger, acts as an 6185 annual thermal battery. During the heating season, heat is extracted from the ground by 6186 supplying the heat exchangers with water that has been cooled below ambient ground 6187 temperature. The ground warms this water, increasing its temperature before it is circulated 6188 back through the heat pump unit where it is chilled again. The heat pump unit conveys the heat 6189 extracted from the water to the conditioned space for space heating. In the summer, the process 6190 works in reverse. Water that is warmer than the ambient ground temperature is pumped through 6191 the heat exchanger where it is cooled and then returns to the heat pump unit where it is again 6192 heated by the heat exchanger with heat that has been extracted from the conditioned space for 6193 space cooling. 6194 6195 It is important to remember that the ground is not an infinite heat source or sink and that heat 6196 rejected into the ground and extracted from the ground must be in approximate balance over 6197 time to avoid long-term migration of the average ambient ground temperature. This 6198 phenomenon is particularly important for large scale deep borehole fields, where heat transfer 6199 through the ground surface, across the lateral boundaries of the well field and downward to the 6200 soil below the boreholes represents a very small percentage of the overall heat transfer into and 6201 out of the field. The ability of the ground to transfer and absorb heat is defined by three 6202 fundamental parameters, thermal conductance, specific heat and density, and a calculated 6203 parameter thermal diffusivity. In general, the greater the soil conductivity, the less length of 6204


ground heat exchanger is required for a given heat rejection or extraction capacity. Soils 6205 favorable to ground thermal storage should demonstrate both a high thermal conductivity, 6206 enabling heat to transfer from the heat exchanger far into the body of soil, and a high thermal 6207 capacity, resulting in reduced temperature change per unit of heat absorbed. Saturated ground, 6208 typically shows both enhanced thermal conductivity and increased thermal capacity compared 6209 with dry soil. Thermal diffusivity is calculated by the following formula and is used in the 6210 borehole sizing algorithm published in the ASHRAE publication Geothermal Heating and 6211 Cooling Design of Ground-Source Heat Pump Systems: 6212

6213

6214 Where: α = thermal diffusivity 6215 κ = thermal conductance 6216 ρ = density 6217 cp = specific heat 6218 6219 Thermal diffusivity describes the rate at which the soil temperature changes over time in 6220 response to heat gain. Higher thermal diffusivity is weakly consistent with higher effective soil 6221 thermal resistance over time. Table HV-5 typical values for several types of soil. 6222 6223 Table HV-5 Thermal Properties of different soil types2 6224

Soil Thermal Conductivity Thermal Diffusivity Moisture /Texture Btu/fthr°F W/m-°F ft2/day 106m2/s

Basalt 0.98 1.70 0.70 0.65

Shale 1.21 2.10 0.90 0.84

Limestone 1.62 2.80 1.26 1.17 Dry sand 0.23 0.40 0.27 0.25 Dry clay/silt 0.29 0.50 0.33 0.31 Dry loam 0.52 0.90 0.46 0.43 Saturated sand 1.39 2.40 0.89 0.83 Saturated clay/silt 0.98 1.70 0.54 0.50 6225 Based upon soil samples taken from a test bore, the thermal parameters of the soil can be 6226 established. Using those parameters, and detailed load profiles from the building energy model, 6227 the required length of ground heat exchanger can be calculated, using either the method in the 6228 ASHRAE publication Geothermal Heating and Cooling Design of Ground-Source Heat Pump 6229 Systems, or detailed computer simulation of the ground. 6230 6231 HV11 Configuration of Ground Heat Exchangers 6232 Ground heat exchangers can be configured in vertical or horizontal boreholes or horizontal 6233 trenches as shown in Figure HV-2. 6234 6235


6236 Figure HV-2 GSHP Vertical Water Loop Diagram 6237

Source: ASHRAE (2011b)1 6238 6239 A typical vertical bore hole ground heat exchanger includes many vertical pipe bores, each 200 6240 to 500 ft deep. Multiple vertical pipe bores are circuited together with horizontal piping which 6241 is then routed to the building and the heat pump devices. An example of three different 6242 circuiting arrangements is shown in Figure HV-3, appropriate to different sizes of borehole 6243 fields. 6244 6245 Individual vertical bore-hole heat exchangers have typically been U-tubes, sized as shown in 6246 Figure HV-3. The sizing algorithms in the ASHRAE publication1 enable borehole sizing based 6247 on standard U-tube design or concentric heat exchangers. Concentric or co-axial heat 6248 exchangers are designed to maximize the thermal coupling between the circulating fluid and the 6249 ground. These devices typically have an outer tube that is designed to fill the entire borehole so 6250 that grout is utilized only for void-filling between the borehole face and the tube. This 6251 arrangement minimizes the grout thermal resistance and maximizes the heat transfer area of 6252 tubing. The fluid flows down the length of the heat exchanger through an inner tube, made of a 6253 material with somewhat higher thermal resistance to minimize short-circuit heat exchange 6254 between the tubes. The fluid flows upward from the bottom of the heat exchanger between the 6255 outer wall and the inner tubing. Some products equip the outer wall of the inner tube with 6256 vanes to generate turbulent flow in the fluid flowing upward back to the surface, thus increasing 6257 heat transfer between the outer wall and the fluid. Testing of these devices indicates that the 6258 effective borehole length to achieve a certain capacity can be reduced by as much as 20% 6259 compared with standard U-tube heat exchangers imbedded in thermally conductive grout.4 6260 Products utilizing this strategy are available from multiple manufacturers. 6261


6262 Figure HV-3 Three options for Closed-loop 6263 Heat Pump Vertical Ground-loop circuits.1 6264

6265 Horizontal heat exchangers come in many configurations, but most examples seek to maximize 6266 the length of tubing that is inserted into a trench. As a result, the so-called “slinky” 6267 configuration is often utilized. While the adjacency of individual loops to one another results in 6268 a much less than optimal mass of soil influenced by each unit length of tubing, the very low cost 6269 of the tubing per unit length compared with the cost of trenching dictates this configuration. 6270 Horizontal heat exchangers are often utilized for projects with a large area of external grounds 6271 that will be disturbed for other reasons, such as construction of extended parking structures. An 6272 example of a “slinky” coil in a trench is shown in Figure HV-4. 6273


6274 Figure HV-4 Horizontal heat exchange coil in a trench3 6275

6276 HV12 Equipment efficiency 6277 The heat pump unit efficiencies should meet or exceed the efficiency levels noted in Table HV-6278 1. Efficiency levels listed for ground-source heat pumps are based on “ground loop” test 6279 conditions according to ASHRAE/ARI/ISO Standard 13256-1-1998, Water-Source Heat Pumps 6280 Testing and Rating for Performance (ASHRAE 1998). The heat pumps should be provided 6281 with variable speed compressors and fans to increase part-load efficiency. 6282 6283 HV13 Water Piping and Pumping Strategies 6284 A GSHP survey (Caneta Research 1995) reported that installed pumping power varied from 6285 0.04 to 0.21 hp/ton of heat pump power. (ASHRAE HVAC Applications Handbook, 2015, 6286 Chapter 34) The piping material, pipe sizing, water velocity and water solution used will all 6287 effect the design efficiency. The piping system can be steel or various plastic materials. Good 6288 water quality is important to minimize fouling factor and avoid clogging of heat exchangers. A 6289 steel piping system will require chemical treatment to inhibit corrosion. The heat transfer fluid 6290 may be water with some additives or it may be a water/anti-freeze mixture. Anti-freeze should 6291 be included in the fluid only when design analysis indicates a danger of freezing because of 6292 high heating loads for the heat pump system along with a low undisturbed ground temperature. 6293 Successfully designed piping systems that can reduce the total system pressure drop below 46 6294 feet TDH flowing 3 GPM/ton are Graded as "A" by the ASHRAE HVAC Applications 6295 Handbook, 2015, Chapter 34. 6296 6297 Two water pumping strategies are most common, centrally pumped or distributed pumped. The 6298 centrally pumped system normally includes a minimum of three variable speed pumps operating 6299 in a lead/lag arrangement, with each sized at 50% of peak flow to provide redundancy for space 6300


heating operation. Pumps should be configured with variable speed and heat pump devices 6301 should be equipped with shut off valves to block flow when compressors are not active. Other 6302 options for increasing system part load pumping efficiency are modulating valves for each heat 6303 pump device controlled to maintain a constant temperature differential for water flowing 6304 through the device (suitable for larger heat pumps), or a controller that varies pump speed to 6305 maintain a maximum temperature differential across the heat pump device at greatest part load. 6306 6307 A decentralized water pumping system eliminates the central pumps and utilizes a small inline 6308 water pumps at each heat pump unit. The water pump operates only when the heat pump unit 6309 compressor is operating. Variable water flow is accomplished without the need for variable 6310 speed pumps and water pressure controls, thus eliminating the additional system pressure drop 6311 imposed by the water pressure sensor. It also simplifies the variable flow controls system. 6312 6313 HV14 Annual System Balance 6314 Very few climate zones strike a perfect balance between heat rejected to the ground heat 6315 exchanger and heat absorbed from it. A properly designed ground heat exchanger can 6316 accommodate an imbalance between heat rejected and heat absorbed. However, in the extreme 6317 climate zones, larger imbalances will exist and a hybrid system should be considered to insure 6318 the ground heat exchanger does not deliver too hot or too cold loop water, impacting the 6319 operation of the heat pump units. 6320 6321 For example, in a cooling-dominated climate (such as climate zones 1 or 2), a large amount of 6322 heat will be rejected to the ground during the cooling season and a smaller amount of heat will 6323 be extracted from the ground during the heating season. This imbalance can cause the 6324 temperature of the ground surrounding the ground heat exchanger to rise to levels that 6325 adversely affect system efficiency. 6326 6327 Conversely, in a heating-dominated climate (such as climate zones 6 or 7), a relatively small 6328 amount of heat is rejected to the ground during the cooling season, but a much larger amount 6329 of heat will be extracted from the ground during the heating season. In this case, the ground 6330 temperature may become too cold, adversely affecting both system efficiency and, sometimes, 6331 system capacity. 6332 6333 A hybrid approach involves adding a fluid cooler to the loop for a system that is installed in a 6334 cooling-dominated climate, or adding a boiler to a system in a heating-dominated climate. 6335 Fluid coolers should be added to the ground circulating loop in series with and upstream of the 6336 ground heat exchangers, while boilers should be added to the building circulating system, in 6337 parallel or independent of heat pump supply to the space. A hybrid design will reduce the 6338 system efficiency so design strategies that improve energy performance should first be 6339 considered. 6340 6341 Table HV-6 shows water recharge rates for ground loops 6342 6343


Table HV-6 Water recharge rates for ground loops 6344

6345 6346 HV15 Ground-source System Success Factors1 6347 The system efficiency of ground-coupled heat pump (GCHP) systems can be exceptionally 6348 high in larger buildings if: 6349

High-efficiency, extended range heat-pumps are used 6350

The ground and surface-water heat exchangers are of sufficient depth and length and 6351 located in mediums so that liquid temperatures entering the heat pumps are much more 6352 moderate than the outdoor air temperature, 6353

The air distribution system is designed and installed so that the required fan power is 6354 small (< 15% of total system power [heat pump + fan + pump power]), and 6355

The water distribution system is designed and installed so that the required pump power 6356 is small (< 10% of total system power [heat pump + fan + pump power]). 6357

6358 SYSTEM D – DOAS WITH SENSIBLE FANCOILS AND CHILLERS WITH 6359 WATERSIDE ECONOMIZERS 6360

6361 HV16 System Overview 6362 In this system, a separate fan coil unit is used for each thermal zone. Components are factory 6363 assembled and include filters, a fan, heating and cooling coils, controls, and possibly OA and 6364 return air dampers. 6365 6366 Fan coils are typically installed in each conditioned space, in the ceiling plenum (or some other 6367 noncritical space), or in a closet or hallway adjacent to the space. However, the equipment 6368 should be located to meet the acoustical goals of the space, permit access for maintenance, and 6369 minimize fan power, ducting, and wiring. 6370 6371 All the fan coils are connected to a common water distribution system. Cooling is provided by a 6372 centralized water chiller. Heating is provided by either a centralized boiler, heat recovery chiller 6373 or electric resistance heat. In climate zones 1 and 2, where heating loads are quite low, the cost 6374


effectiveness of a boiler heating system should be examined, and it may be more cost effective 6375 to use heat recovery chillers or solar hot water heating in lieu of a hot-water heating system 6376 because of the minimal heating requirements. 6377 6378 OA for ventilation is conditioned and delivered by a separate dedicated OA system. This may 6379 involve ducting the OA directly to each fan coil, delivering it in close proximity to the fan-coil 6380 intakes, or ducting it directly to the occupied spaces. Depending on the climate, the dedicated 6381 OA unit may include components to filter, cool, heat, dehumidify, and/or humidify the outdoor 6382 air. 6383

6384 HV17 Chilled Water Equipment 6385 The cooling equipment, heating equipment, and fans should meet or exceed the efficiency levels 6386 in Tables HV-1. 6387 6388 Chillers should include variable frequency drives on the compressors to provide continuous 6389 unloading. Chillers should incorporate controls capable of accommodating variable evaporator 6390 water flow while maintaining control of leaving chilled-water temperature. 6391 6392 Water-cooled chillers and cooling towers were not analyzed for this Guide. A system including 6393 a water-cooled chiller, condenser water pump, and cooling tower all with sufficient efficiency 6394 and integrated controls may give the same or better energy performance as an air-cooled chiller. 6395 Large office spaces considering water-cooled chillers should follow the ASHRAE Green Guide 6396 (2013) 6397 6398 HV18 Variable Primary Flow 6399 Variable speed pumps in a chiller system offer significant operating costs savings as the pumps 6400 will be optimized to respond to the changing in load conditions. Chillers will need to be 6401 selected for the minimal flow requirement of the system plus large turn down on the water side 6402 to ensure continued performance at lower flow rates. To optimize pump energy savings reset 6403 the differential pressure to maintain discharge air temperature at the terminal units or air 6404 handlers with at least one control value in a fully open condition. The will achieve flow to 6405 every unit while achieving pump savings at low load conditions (ASHRAE, 2015) 6406 6407 DEDICATED OUTDOOR AIR SYSTEMS (100% Outdoor Air Systems) 6408 6409 HV19 System Overview 6410 There are many advantages of using a DOAS with a zero energy office building. DOAS can 6411 simplify ventilation control and design, improve humidity control and allow for sensible cooling 6412 only terminal equipment (ASHRAE DOAS Guideline 2017). The DOAS also can be equipped 6413 with high-efficiency filtration systems with static pressure requirements above the capability of 6414 zone terminal HVAC equipment. One of the energy-saving features of DOAS is the separation 6415 of ventilation air conditioning from zone air conditioning and the ease of implementation of 6416 exhaust air energy recovery. Terminal HVAC equipment heats or cools recirculated air to 6417 maintain space temperature. Terminal equipment may include fan-coil units, WSHPs, zone-6418 level air handlers, or radiant heating and/or cooling panels. 6419 6420 The DOAS includes two ductwork systems, one to supply outdoor air to the thermal zones and 6421 the second to exhaust air from the thermal zones. The DOAS is variable flow to help achieve 6422 energy targets. All building exhaust air is normally returned to the DOAS, including restroom 6423


exhaust. Special exhaust systems such as range hoods and fume hoods are ducted outdoors 6424 independently. Where possible the DOAS unit should be located within the building thermal 6425 envelope to maximize the available roof area for the solar system. 6426 6427 Dedicated outdoor air systems (DOASs) can reduce energy use by decoupling the 6428 dehumidification and conditioning of OA ventilation from sensible cooling and heating in the 6429 zone. The OA is conditioned by a separate DOAS that is designed to dehumidify the OA and to 6430 deliver it dry enough (with a low enough dew point) to offset space latent loads, thus providing 6431 space humidity control (Mumma 2001; Morris 2003). 6432 6433 There are many possible 100% outdoor air system (100% OAS) configurations (see Figure HV- 6434 XXX for a few typical ones). 6435 6436 HV20 Sizing the DOAS for dehumidification 6437 The DOAS is sized to remove all the space latent load. This will enable independent 6438 dehumidification control of the space and this will allow for energy saving measures for the 6439 terminal cooling equipment. 6440 6441 The primary space latent load for most offices will be from the space occupants. For example a 6442 seated active office worker will add 0.19 lb/h to the space that will need to be removed 6443 (ASHRAE Fundamentals handbook). If the office has a lot of visitors, these people will 6444 increase the moisture load in addition to increased infiltration (Dehumidification handbook). 6445 The dew point temperature of the supply air of the DOAS will need be below the dew point 6446 temperature of the space to account for the water vapor added to the space from these loads and 6447 others. 6448 6449 For systems B VRF and GSHP system C the cooling coil in the terminal equipment will be cold 6450 enough for some coincidental dehumidification and condensate when there is a call for cooling. 6451 However, sizing and utilizing the DOAS to control humidity will allow for the cycling of fan on 6452 only for the need for cooling. This will require the ventilation system to have separate delivery 6453 to the space from the terminal equipment (See the following section on DOAS ventilation 6454 delivery). 6455 6456 For the sensible cooling fan coil system B the DOAS is sized to condition space dew point 6457 below the chilled water temperature of the terminal equipment. This prevent condensation on 6458 the terminal equipment. Keeping cooling coils dry will reduce the required energy to cool the 6459 space. This will reduce the filtration requirements of the terminal equipment. ASHRAE 6460 Standard 62.1 section 5.8 requires MERV 8 or higher filters of devices with wetted surfaces 6461 through which air is supplied to an occupiable space. Not having these higher filtration 6462 requirements will reduce terminal fan energy to cool the space. 6463 6464 Because the DOAS does all the dehumidification the chilled water cooling the space can be at a 6465 higher temperature (55-57F). This can improve the chiller efficiency >20% over tradition 44F 6466 chilled water system resulting in additional cooling energy savings. 6467 6468


6469 Figure HV-XXX Typical DOAS Configurations 6470

6471 HV21 Delivery for Zone Level DCV 6472 DOAS can also be used in conjunction with multiple-zone recirculating systems, such as 6473 centralized VAV air handlers SYSTEM A but most often VAV systems do not use separate 6474 ventilation systems. DOAS can reduce energy use in primarily three ways: 6475

They often avoid the high OA intake airflows at central air handlers needed to satisfy the 6476 multiple spaces equation of ASHRAE Standard 62.1 (ASHRAE 2016) and enable zone 6477 by zone demand control ventilation 6478


They eliminate (or nearly eliminate) simultaneous cooling and reheat that would 6479 otherwise be needed to provide adequate dehumidification in humid climates, and 6480

With constant-volume zone units (heat pumps, fan-coils), they allow the unit to cycle 6481 with load without interrupting ventilation airflow. 6482

6483 A drawback DOAS is that they cannot provide air-side economizing. This is more significant in 6484 drier climates where 100% OA can be used for economizing without the concern of raising 6485 indoor humidity levels. 6486 6487 To realize these savings how the ventilation is delivered to the space needs to be considered. 6488 To control the amount of ventilation to each zone a zone damper or air valve is needed. In 6489 most cases flow measurement will be needed. This will allow for the outside air to be reduced 6490 during off peak occupancy and is especially beneficial to office buildings which often have a 6491 high variance of occupancy. In many cases the outside air during stand-by mode, occupied 6492 hours with no one present, the amount of outdoor air can be reduced to the area outdoor air rate, 6493 in some cases it may be reduced to zero (ASHRAE standard 62.1 2016). This air valve may be 6494 in the DOAS duct work before the diffusers serving the zone or it may be incorporated into the 6495 terminal equipment. Incorporating into the terminal unit will enable a broader range of 6496 ventilation control. By mixing in some return air, this will prevent airflow from falling below 6497 diffusers the minimum recommended air flow and prevent the dumping of cool ventilation air. 6498 The DOAS unit job is to deliver dehumidified air as required by the zones. This is 6499 accomplished by DOAS pressurizing the duct work to the minimum pressure required to deliver 6500 the air. The static pressure set point in the system supply duct work is reset based on position of 6501 the air valves in the system. This ensures the minimum fan power is used to deliver ventilation 6502 to the space. The air valves flow rate are recalculated based on number of occupants. 6503 Occupancy population can be measured by CO2 sensors or occupancy sensors or both 6504 depending on the zone. For more on DCV calculations see section HV27. See Figures HV-5 6505 and HV-6. 6506

6507 Figure HV-5 – Modulating damper with airflow measurement 6508

6509 6510


6511 Figure HV-6 – DOAS Supply Fan controlled with VSD 6512

6513 There is a minimum turn down allowed for the DOAS unit. The DOAS equipment will have a 6514 turn down limit. This turn down can be as low as 30% of design flow and should be confirmed 6515 with manufacturer as the limit will depend on the fan, DX system, or other components in the 6516 DOAS system. For proper building pressure control the minimum ventilation rate should also 6517 not fall below the required exhaust sources. For offices this often is the restroom exhaust flow. 6518 The minimum positions set on the ventilation air valves should be set not to allow the DOAS to 6519 turn down below this minimum during occupied hours. 6520 6521 HV22 Discharge Air Temperature Control for DOAS 6522 Consider delivering the conditioned OA cold (not reheated to neutral) whenever possible and 6523 reheat only when needed. For most offices the amount of outside air required will not overcool 6524 the space if delivered cooler than the space. When the discharge air temperature supplied from 6525 the DOAS unit is cooler than room temperature the zone air distribution effectiveness is not 6526 penalized. Also, providing cold (rather than neutral) air from the DOAS offsets a portion of the 6527 space sensible cooling loads, allowing the terminal HVAC equipment to be downsized and use 6528 less energy (Mumma and Shank 2001; Murphy 2006). Adding reheat even if this reheat is from 6529 recovered energy wastes energy if cooling is needed in the space. ASHRAE 90.1-2016 section 6530 6.5.2.6 restricts heating the ventilation air above 60F when majority of zones served by the 6531 DOAS require cooling. Reheating the dehumidified air (to a temperature above the required 6532 dew point) may be warranted. 6533 6534

if the reheat consumes very little energy (using energy recovery, solar thermal source, 6535 etc.) and none of the zones are in the cooling mode, 6536

if all of the zones are in the heating mode, or 6537 if, for those zones in the cooling mode, the extra cooling energy needed (to offset the 6538

loss of cooling due to delivering neutral-temperature ventilation air) is offset by higher-6539 efficiency cooling equipment and the reduction in heating energy needed for those zones 6540 in the heating mode (this is more likely to be true on an annual basis if the reheat in the 6541 DOAS is accomplished via air-to-air or condenser heat recovery). 6542

6543 In addition, implementing reset control strategies and exhaust air energy recovery (see HV23) 6544 can help minimize energy use. 6545 6546 HV23 Exhaust Air Energy Recovery Options for DOAS 6547 Exhaust air energy recovery can provide an energy-efficient means of reducing the latent and sensible 6548 OA cooling loads during peak summer conditions. It can also reduce the OA heating load in mixed 6549 and cold climates. HVAC systems that use exhaust air energy recovery should to be resized to account 6550 for the reduced OA heating and cooling loads (see ASHRAE [2008a]). 6551


6552 Energy recovery devices should have a total effectiveness of 75% for climates where total energy 6553 recovery is required. For climates where sensible recovery is require a sensible effectiveness of 75% is 6554 required. These minimum effectiveness values should be achieved with no more than 0.85 in. w.c. static 6555 pressure drop on the supply side and 0.65 in. w.c. static pressure drop on the exhaust side. 6556 6557 Sensible energy recovery devices transfer only sensible heat. Common examples include coil loops, 6558 fixed-plate heat exchangers, heat pipes, and sensible energy rotary heat exchangers (sensible energy 6559 wheels). Total energy recovery devices transfer not only sensible heat but also moisture (or latent heat)—6560 that is, energy stored in water vapor in the airstream. Common examples include total energy rotary 6561 heat exchangers and fixed-membrane heat exchangers. Energy recovery devices should be selected to 6562 avoid cross-contamination of the intake and exhaust airstreams. For rotary heat exchangers, minimizing of 6563 cross-contamination can be achieved by designing the intake outside air system pressure higher than the 6564 exhaust system pressure. The use of purge, flushing the rotary exchangers with excess outside air, should 6565 be avoided as this will increase DOAS and exhaust fan energy. 6566 6567 For maximum benefit, the system should provide as close to balanced outdoor and exhaust airflows as is 6568 practical, taking into account the need for building pressurization. Office restroom exhaust will be a large 6569 portion of the exhaust air, this required toilet exhaust shall be utilized along with the exhaust air needed 6570 for building pressure relief. 6571 6572 Conditioned ventilation air should be delivered to space cold (not reheated to neutral) whenever 6573 possible, if space loads indicate reheat is required adding a second exhaust energy recovery 6574 exchanger will reduce cooling energy. The reheat recovered in this configuration will result in 6575 precooling the outside air reducing the amount of wasted sensible cooling that would occur by 6576 using a reheat coil. See Figure HV-7. 6577 6578

6579

6580 Figure HV-7 Example Exhaust Air Energy Recovery Configurations 6581

6582 6583


HV24 Advanced SOO for DOAS 6584 When the outdoor air conditions are above the DOAS supply dew point temperature set point, the 6585 DOAS unit will be in dehumidification and cooling mode. When the outdoor air dew point is below set 6586 point but above supply temperature set point the unit will be in cooling mode, if below supply air 6587 temperature the unit will be in heating mode. 6588 6589 Figure HV-8 and Table HV-8 are the typical modes for a DOAS unit (DOAS Guide ASHRAE 2017). 6590 DOAS with exhaust energy recovery for OA preconditioning should be controlled to prevent the transfer 6591 of unwanted heat to the outdoor airstream during mild outdoor conditions when cooling in the space is 6592 still required, shown as “ventilation only” mode. There should also be a mechanism to control the 6593 amount of heat recovered during heating mode to prevent overheating the air. 6594

6595

6596 Figure HV- 8 - DOAS Unit Control Modes 6597

(Source ASHRAE DOAS Guide 2017) 6598 6599 Table HV-8 DOAS Unit Control Modes 6600

6601 (Source ASHRAE DOAS Guide 2017) 6602

6603 6604 DOAS with exhaust energy recovery for OA preconditioning and reheat (Figure HV#) should be 6605 controlled to similar with added stages for reheat (Moffitt AT-15-C047, 2015) 6606 6607


HV25 Part Load Dehumidification Control 6608 For the systems that use DOAS (see Table HV-4) the DOAS should be designed to dehumidify 6609 the OA so that it is dry enough (has a low enough supply air dew point) to offset the latent loads 6610 in the spaces. The DOAS should be dehumidifying and provide the ventilation air at this supply 6611 air dew point set point whenever the outdoor air is above this condition. This helps avoid high 6612 indoor humidity levels without additional dehumidification enhancements in the zone terminal 6613 units. The BAS may reset the DOAS supply air dew point set point if it finds the space is being 6614 over or under dehumidified. For systems with sensible only cooling devices, it will be critical 6615 to keep the space below the required dew point to prevent condensation from forming. For 6616 these systems it may be necessary to add limits to the DOAS turn down from DCV to keep the 6617 space dehumidified. 6618 6619 VAV systems typically dehumidify effectively over a wide range of indoor loads, as long as the 6620 VAV rooftop unit continues to provide cool, dry air at part-load conditions. One caveat: use 6621 caution when resetting the SAT upward during the cooling season. Warmer supply air means 6622 less dehumidification at the coil and higher humidity in the space. If SAT reset is used, include 6623 one or more zone humidity sensors to disable the reset if the relative humidity within the space 6624 exceeds 60%. 6625 6626 HV26 Ventilation Air Rate 6627 The zone-level outdoor airflows and the system-level intake airflow should be determined based 6628 on the most recent edition of ASHRAE Standard 62.1 (ASHRE 2010a) but should not be less 6629 than the values required by local code unless approved by the authority having jurisdiction. The 6630 number of people used in computing the breathing zone ventilation rates should be based on 6631 known occupancy, local code, or the default values listed in Standard 62.1. 6632 6633 Caution: The occupant load, or exit population, used for egress design to comply with the fire 6634 code is typically much higher than the zone population used for ventilation system design. 6635 Using occupant load rather than zone population to calculate ventilation requirements can result 6636 in significant overventilation, oversized HVAC equipment, and excess energy use. Buildings 6637 with multiple-zone recirculating ventilation systems can be designed to account for recirculated 6638 OA as well as system population diversity using the Ventilation Rate Procedure of ASHRAE 6639 Standard 62.1 (ASHRAE 2007a). In effect, the multiple-zone recirculating ventilation system 6640 design approach allows ventilation air to be calculated on the basis of how many people are in 6641 the building (system population at design) rather than the sum of how many people are in each 6642 space (sum-of-peak zone population at design). Using the Ventilation Rate Procedure can 6643 reduce the energy required to condition ventilation air in office buildings. Refer to 62.1 User’s 6644 Manual for specific guidance (ASHRAE 2007b). 6645 6646 For all zones, time-of-day schedules in the building automation system (BAS) should be used to 6647 introduce ventilation air the DOAS should deliver the conditioned OA directly to each zone, to 6648 the intake of each individual terminal unit or directly to the space as shown in Figure XXX (see 6649 HV#). Each zone should have ventilation flow measurement. Zones that are configured with 6650 DOAS ducted directly to zone have the advantage air can be delivered to the space even when 6651 the terminal unit fan is not running so that the unit can cycle for cooling or heating load without 6652 interrupting ventilation. However, the zone diffusers will have a minimum turndown for the 6653 ventilation air to be delivered properly. Zones that are configured with DOAS in series with the 6654 terminal unit will allow for very low ventilation flows and ensure the air is properly delivered. 6655 6656


HV27 Demand Control Ventilation Strategies 6657 DCV can reduce the energy required to condition OA for ventilation. To maintain acceptable 6658 IAQ, the setpoints (limits) and control sequence must comply with ASHRAE Standard 62.1 6659 (ASHRAE 2016a). Refer to Appendix A of that standard for specific guidance (ASHRAE 6660 2016b). 6661 6662 Office buildings can have high variability in occupancy and the amount of OA should be con-6663 trolled. Occupancy status can be determined by 1) a time-of-day schedule in the BAS or 2) an 6664 occupancy sensor (such as a motion detector) that indicates when a zone is occupied or 6665 unoccupied. The Occupancy level can be indicated by or 1) a carbon dioxide (CO2) sensor, as a 6666 proxy for ventilation airflow per person, that measures the change in CO2 levels in a zone rela-6667 tive to the levels in the OA or 2) occupant counting. A controller will then operate the OA to 6668 maintain proper ventilation to the zone. The design ventilation rates for the occupied period 6669 should be based upon full occupancy and should be calculated in accordance with Section 6 of 6670 Standard 62.1-2016. This level then will be reduced based on actual occupancy as measured. 6671 In many cases the outside air during stand-by mode, occupied hours with no one present, the 6672 amount of outdoor air can be reduced to the area outdoor air rate, in some cases it may be 6673 reduced to zero. 6674 6675 CO2 sensors should be used in zones that are densely occupied and have highly variable 6676 occupancy patterns during the occupied period, such as conference rooms or meeting areas or 6677 open offices. For the other zones, occupancy sensors should be used to reduce ventilation when 6678 a zone is temporarily unoccupied. For all zones, time-of-day schedules in the BAS should be 6679 used to introduce ventilation air only when a zone is expected to be occupied. 6680 6681 For systems with DOAS the zone ventilation rate will vary directly based on the measured zone 6682 population. 6683 Voz =(Rp x Pz) + (Ra x Az) / Ez 6684 Ez = air distribution effectiveness of the zone 6685 Az = area of the zone 6686 Rp = outdoor airflow rate required per person 6687 Ra = outdoor airflow rate required per unit area 6688 Pz = zone population 6689 6690 Multiple-zone recirculating systems such as VAV systems SYSTEM A require special attention 6691 to ensure adequate OA is supplied to all zones under varying loads. Employing DCV in a 6692 DOAS requires an automatic damper, a CO2 sensor, and an airflow measurement device for 6693 each DCV zone. If the automatic damper selected is of the pressure-independent type, by 6694 definition it has flow measurement capability. 6695


6696 6697 Control of a DCV system to match airflow volume to occupancy requires a continuous search 6698 algorithm for the controller. The controller continuously calculates the volume required in the 6699 space based upon the measured CO2 concentration differential and then updates the volume 6700 setpoint to the pressure-independent damper controller. The following equation gives the 6701 required volume in the space based upon the measured CO2 differential: 6702 6703 The above equation has been extracted from 62.1 2016 Appendix A. The control system for the 6704 DOAS must be able to calculate the required ventilation rate for each zone based upon the 6705 above equation then reset the flow setpoint for the zone to the calculated value. The procedure 6706 for a multizone VAV system is somewhat more complicated. The system will require a flow 6707 measurement device on the OA inlet for the VAV air handler. The controller must then 6708 calculate the actual OA flow to each control zone based upon the percentage of OA in the 6709 supply air to the zone. The system must calculate the required OA flow for each zone. 6710 6711 HV28 Carbon Dioxide (CO2) Sensors (Climate Zones: all) 6712 The number and location of CO2 sensors for DCV can affect the ability of the system to 6713 accurately determine the building or zone occupancy. A minimum of one CO2 sensor per zone 6714 is recommended for systems with greater than 500 cfm of OA. Multiple sensors may be 6715 necessary if the ventilation system serves spaces with significantly different occupancy 6716 expectations. Where multiple sensors are used, the ventilation should be based on the sensor 6717 recording the highest concentration of CO2. 6718 6719 Sensors used in individual spaces should be installed on walls within the space. Multiple spaces 6720 with similar occupancies may be represented by an appropriately located sensor in one of the 6721 spaces. The number and location of sensors should take into account the sensor manufacturer's 6722 recommendations for their particular products as well as the projected usages of the spaces. 6723 Sensors should be located such that they provide a representative sampling of the air within the 6724 occupied zone of the space. For example, locating a CO2 sensor directly in the flow path from 6725 an air diffuser would provide a misleading reading concerning actual CO2 levels (and 6726 corresponding ventilation rates) experienced by the occupants. 6727 6728 The OA CO2 concentration can have significant fluctuation in urban areas. OA CO2 con-6729 centration should be monitored using a CO2 sensor located near the position of the OA intake. 6730 CO2 sensors should be certified by the manufacturer to have an accuracy to within ±50 ppm, 6731 factory calibrated, and calibrated periodically as recommended by the manufacturer. 6732


6733 HV29 Exhaust Air Systems (Climate Zones: all) 6734 Zone exhaust airflows (for restrooms, janitorial closets, and break rooms) should be determined 6735 based on the current version of ASHRAE Standard 62.1 but should not be less than the values 6736 required by local code unless approved by the authority having jurisdiction. 6737 6738 Central exhaust systems for restrooms, janitorial closets, and break rooms should be interlocked 6739 to operate with the air-conditioning system, except during unoccupied periods. Such a system 6740 should have a motorized damper that opens and closes with the operation of the fan. The 6741 damper should be located as close as possible to the duct penetration of the building envelope to 6742 minimize conductive heat transfer through the duct wall and avoid having to insulate the entire 6743 duct. During unoccupied periods, the damper should remain closed and the exhaust fan turned 6744 off, even if the air-conditioning system is operating to maintain setback or setup temperatures. 6745 Design exhaust ductwork to facilitate recovery of energy recovery (see HV**) from exhaust 6746 taken from spaces with air quality classification of 1 or 2 (e.g., restrooms) per Table 6.1 of 6747 Standard 62.1 (ASHRAE 2016a). This exhaust air along with the relief air exhausted to 6748 properly pressurize the building should both be used to recover energy. The exhaust fan shall 6749 have variable speed capability. The zone exhaust airflows with required minimum flow by 6750 code should be measured and controlled with dampers to ensure these minimums are 6751 maintained as the exhaust fan speed is reduced to maintain building pressure. This will occur 6752 when demand control ventilation is implemented. See Figure HV-9. 6753 6754

6755 Figure HV-9 – Exhaust air measurement 6756

6757 HV30 Relief vs Return Fans (Climate Zones: all) 6758 Relief (rather than return) fans should be used when necessary to maintain building 6759 pressurization during economizer operation. Relief fans reduce overall fan energy use in most 6760 cases, as long as return dampers are sized correctly. 6761

6762 HV31 Energy Recovery Frost Control (Climate Zones 4-8) 6763 Energy recovery heat exchangers have a risk of frosting. This occurs when the exhaust air is 6764 cooled below condensing point. Total recovery devices can help minimize this risk by 6765 transferring water vapor from the exhaust air to the supply air. The primary factor that will 6766 cause frosting conditions is the humidity of exhaust air from the space. To accurately predict 6767 frosting risk entering exhaust air conditions at design should be calculated. Over estimating the 6768


indoor relative humidity of the office will reduce the amount of energy recover and initiate frost 6769 prevention measures when not needed. Table HV-7 shows an example frost chart for a 75% 6770 total effective energy recovery wheel. Frost prevention is accomplished by either preheating the 6771 outdoor air to the predicted frost point or reducing the energy recovery capacity to reduce risk 6772 of exhaust air condensing. For example in table HV-7 given when utilizing electric preheat 6773 before the energy exchanger at an indoor design relative humidity of 30% RH, the outdoor air 6774 needs to be preheated to -3F not 32F to prevent frosting. 6775 6776 Table HV-7 - Example Frost point for Energy Wheel 6777 with 75% total effectiveness and 70F space conditions 6778

Indoor Relative Humidity Outdoor Air Temperature

40% 5F 30% -3F 20% -14F 15% -22F

6779 6780

HV32 Indirect evaporative cooling (Climate Zones 2B, 3B, 4B, 5B) 6781 In dry climates, incoming ventilation air can be precooled using indirect evaporative cooling. 6782 For this strategy, the incoming ventilation air (the primary airstream) is not humidified; instead, 6783 a separate stream of air (the secondary or heat rejection stream) is humidified, dropping its 6784 temperature, and is used as a heat sink to reduce the temperature of the incoming ventilation air. 6785 6786 The source of the heat rejection stream of air can be either OA or exhaust air from the building. 6787 If the air source is exhaust air, this system becomes an alternative for HV12. 6788 6789 Sensible heat transfer between the ventilation airstream and the evaporatively cooled secondary 6790 airstream can be accomplished using plate or tubular air-to-air heat exchangers, heatpipes, or a 6791 pumped loop between air coils in each stream (often called a ….). For indirect evaporative 6792 coolers that use exhaust air as the secondary stream, the evaporative cooler can also function for 6793 sensible heat recovery during the heating season. If a runaround loop is used for heat transfer 6794 both for indirect evaporative cooling and heat recovery, the circulating fluid should incorporate 6795 antifreeze levels appropriate to the design heating temperature for that location. 6796 6797 Indirect evaporative cooling has the advantage that indoor air quality (IAQ) is not affected, as 6798 the evaporative cooling process is not in the indoor airstream. Air quality is not as critical for 6799 the exhausted secondary airstream as it is for the ventilation stream entering the occupied space. 6800 6801 Indirect evaporative coolers should be selected for at least 90% evaporative effectiveness for the 6802 evaporatively cooled airstream and for at least 65% heat transfer efficiency between the two 6803 airstreams. 6804 6805 Indirect evaporative coolers should also be selected to minimize air pressure drop through the 6806 heat exchangers 6807 6808


HV33 Evaporative Condensers (Climate Zones 2B, 3B, 4B, 5B) 6809 Evaporative condensers on rooftop DX packaged units (SYSTEMS A and DOAS units) can be 6810 considered in dry climates to improve energy efficiency. These devices take advantage of the 6811 low ambient wet-bulb temperature in order to improve energy efficiency by coupling convective 6812 heat rejection with the evaporation of water off of wetted heat rejection condenser coils. In dry 6813 climates, up to 40% reduction in energy use can result. 6814 6815 Generally speaking, all of the wetted components and the condenser section should be designed 6816 for corrosion resistance to ensure reasonable equipment life. Some air-cooled package 6817 equipment can be retrofitted with evaporative precooler before the condensing coil. A direct 6818 evaporative cooling media is placed before the condensing coil. This pad is sprayed with water 6819 pumped through nozzles. The extra pressure drop to the condenser fan air flow needs to be 6820 considered. 6821 6822 Drawbacks to the system include extra first costs, extra weight that arises from the extra 6823 equipment and the water in the sump, additional controls, and the need to provide water 6824 treatment regimens. 6825 6826 HVAC TIPS FOR ALL SYSTEM TYPES 6827 6828 HV34: Right Size Equipment 6829 The key to rightsizing systems and equipment is the application of strategic factors that will 6830 impact the load calculation process, rather than the utilization of rule of thumb “safety factors”. 6831 These strategic factors include: 6832 6833

Critical service requirement which refers to the selection of environmental design 6834 criteria that are input to the load calculation. These include both external and internal 6835 environmental conditions, ventilation rates and other variables. While normal HVAC 6836 sizing criteria use 2% conditions (conditions warmer than all but 2% of hours at the 6837 location) and 99% heating conditions (conditions colder than 99% of hour), Certain 6838 functions may require different “strategic factors.” Outdoor air systems with energy 6839 recovery should be designed to 1% wet-bulb conditions to recognize actual 6840 dehumidification requirements. 6841

6842 Uncertainty factors which should be applied to descriptive parameters for which some 6843

uncertainty exists. These might include the U-factor of a wall in an existing building. 6844 Analysis might reveal a range of U-factors for a given wall, depending on the exact 6845 material used, the exact dimensions and the quality of the construction. For the load 6846 calculation, an informed decision should be made about the likely “worst” U-factors that 6847 might result from this construction. Uncertainty factors may also be applied to 6848 parameter estimations for future use and operation different form the initial program. 6849 They may also be applied to diversity assumptions described below. As a general rule, 6850 uncertainty factors should be applied directly to parameters for which the designer has 6851 uncertainty concerning the actual parameter value. They should be directed at 6852 minimizing the risk of uncertainty for specific parameters that affect the load. 6853

6854 Diversity assumptions which include both the spatial and temporal aspects of diversity. 6855

Diversity factors reduce, the magnitude of overall loads because they establish the extent 6856


to which peak load component values are not applicable over the entire extent of the 6857 building operation. As an example, in an auditorium, either the hall or the lobby can 6858 have a certain maximum occupant density, but, they almost certainly will not have 6859 maximum occupancy simultaneously. Similarly, certain areas of an office building may 6860 have equipment power densities as high as 3 or 4 W/ft2 (0.28 to 0.37 W/m2), but almost 6861 certainly, the entire building will not. Determination of these diversity factors is an 6862 exercise that should involve the architect, engineer and owner, to avoid future 6863 disagreement. It is important to note that diversity factors are independent of schedules 6864 and as such must be reviewed with the schedules to ensure that the appropriate level of 6865 fluctuation is accounted for only once (especially when the schedule is a percent of load 6866 type of schedule). While agreed-upon schedules capture known temporal variation of 6867 load components, diversity factors capture the uncertain variance of these components. 6868 Diversity assumptions, like uncertainty factors, should be applied to the actual 6869 parameters that are diversely allocated rather than any value resultant to a subsequent 6870 calculation. 6871

6872 Diversity factors may also be applied in sequence as the fraction of the building area to 6873 which they are applied becomes greater, because the likelihood that all served areas will 6874 be operating at peak intensity becomes less as the area grows larger. From a systems 6875 standpoint, this approach may mean that no diversity factor for plug loads is applied for 6876 single terminal units, while a moderate diversity factor (90%) is applied to sizing trunk 6877 ducts, a 70% plug load diversity factor is applied for serving central air handling units 6878 and a 50% factor is used for sizing the chiller plant. 6879

6880 Redundancy factor which reflects the need to upsize components or distribution 6881

systems to accommodate continued operation during a planned or unplanned component 6882 outage. A typical application of a redundancy factor is a design that meets the heating 6883 load requirement with two boilers each sized at 75% of the calculated heating load. 6884 Even if one of the boilers fails, the building will remain comfortable throughout most 6885 weather conditions and will be, at least, minimally habitable in the most extreme 6886 conditions. Redundancy factors almost always involve meeting capacity requirements 6887 with more than one piece of equipment. If the capacity requirement is met by a large 6888 number of units, as is often the case with a modular boiler plant, a prudent redundancy 6889 requirement may be met without upsizing the plant to any extent or affecting operating 6890 efficiency. Meeting the load with more, smaller units, furthermore, may increase part 6891 load operating efficiency. Once again, this factor is determined in concert with the entire 6892 project team, including the owner. 6893 6894 Safety factor multipliers should not be applied to calculations that use those parameters, 6895 because they, then, multiplicatively enlarge loads resulting from values for which the 6896 engineer has great confidence. Safety factors should also not be applied so that they 6897 serially expand previously applied safety factors. Applying safety factors at the end of 6898 calculations can also result in larger central equipment (e.g. chillers, boilers) but with no 6899 ability to deliver that capacity to conditioned spaces. 6900

6901 HV35: Economizer and Free Cooling 6902 Important strategies for achieving the low EUI consistent with Zero Energy Office buildings 6903 involve reduction in heat gain and loss through the building envelope and with reduction in 6904


building thermal loads through energy recovery for ventilation air. Inappropriate use of energy 6905 or heat recovery may actually be counterproductive in moderate weather, because the 6906 conditioning savings for outdoor air may be outweighed by additional fan energy for the 6907 pressure drop through the recovery device. 6908 The requirement for “balanced” ventilation typically means utilizing constant exhaust for 6909 kitchen and bathrooms and excluding certain variable exhaust appliances such as clothes dryers 6910 from the comfort envelope or providing make-up air by some other means, such as a direct 6911 outdoor air make-up connection for the dryer. The annual energy consumption limits, expressed 6912 as site or primary energy, dictate a highly efficient heating, cooling and ventilation system, even 6913 though there are few specific systems requirements. The ventilation rates assumed in the 6914 standards, typically 0.3 air changes per hour, are significantly lower than those required by the 6915 relevant ASHRAE Standards. The PHIUS standard also has a comprehensive checklist that 6916 includes numerous site observations and measurements by a certified “rater” and the HVAC 6917 contractor that resemble a commissioning script. In summary, the stated HVAC requirements 6918 of the standards are as follows: 6919

Sufficient energy efficiency to enable the building to meet the calculated annual energy 6920 consumption requirement 6921

Balanced ventilation system (supply/exhaust) using energy or heat recovery unit with a 6922 certified minimum recovery efficiency and fan energy limit. 6923

Compliance with a number of specific detailed requirements listed in the checklist 6924 6925 Despite this minimal list of specific requirements, the reality of providing comfort conditioning 6926 in a building with a very high performance envelope and very low internal heat gains introduces 6927 a new level of complexity to HVAC system design for the project. 6928 6929 HV36 Heating and Cooling Loads in a Zero Energy Office Building 6930 The extremely high performance building envelope required for this building type results in 6931 very low heating loads, despite the very low user equipment power density implied by the EUI 6932 limitation. An important characteristic of the resulting load profile is a very low balance point 6933 temperature, defined as the outdoor ambient dry bulb temperature at which heat losses through 6934 the envelope balance internal and solar heat gains. Reduced infiltration is a significant 6935 contributor to this load reduction. It is mandated in the standard through various specifications 6936 of air barriers and required architectural details and requires on-site verification through blower 6937 doors or other means. Figure HV-10 provides a qualitative illustration of relative values of 6938 balance point temperature for different levels of building envelope performance. 6939 6940 The upshot of the low balance point temperature is the need to exploit available free cooling 6941 opportunities whenever exterior conditions permit to avoid excessive cooling energy 6942 consumption. In residential applications, operable windows might suffice, but for other types of 6943 applications, airside economizer is almost mandatory. Obviously, for a building seeking 6944 certification under one of the standards, the ERV/HRV requirement is counter-productive for 6945 the provision of free-cooling during certain exterior conditions. HRV and ERV devices with 6946 controllable recovery capabilities, either in the form of supply air bypass or speed control for 6947 wheel-type heat exchangers enable the ventilation system to provide free cooling when it is 6948 needed. 6949 6950


6951 Figure HV-10. Heating Requirements for Different 6952

Envelope Performance Levels as a Function of Outdoor Temperature 6953 6954 HV37 Waterside Economizer 6955 Waterside economizer is only applicable for systems that incorporate water cooled refrigeration 6956 and transport of cooling to space cooling devices, air handling units, fan coils, radiant panels or 6957 chilled beams) using chilled water cooling. The cooling tower is used to create chilled water 6958 sufficiently cold to meet the cooling requirement. However, achieving the required level of free 6959 cooling with waterside economizer is not the sure thing that many have assumed it is. Careful 6960 selection of cooling tower, heat exchanger and cooling coil is required to raise the threshold 6961 outdoor wet-bulb temperature at which free cooling can be achieved. 6962 6963 The first step for determining waterside economizer performance is to establish the room 6964 sensible part load fraction at waterside economizer conditions. Reduced window solar control 6965 requirements and increased envelope thermal performance requirements required for zero 6966 energy performance will tend to increase that part load fraction. 6967 6968 After the room sensible part load fraction has been established, along with the potential for 6969 supply air temperature reset, the total coil part load fraction can be calculated. Note that 6970 locations with relatively mild design conditions, such as Los Angeles and Seattle, will be 6971 challenged in that their total coil part load fraction will tend to be high. Decreasing the part 6972 load fraction helps achieve economizer compliance in two ways; a lower space sensible load 6973 fraction enables supply air temperature reset to increase the difference between the ambient wet 6974 -bulb temperature and the supply air temperature, and a lower total coil load fraction enables a 6975 closer approach of the leaving cooling tower water temperature to the ambient wet bulb 6976 temperature. 6977 6978


Selection of the space heat transfer strategy comes next, and this selection can be done in 6979 concert with the heat exchanger selection and the cooling tower selection. The strategy for the 6980 space heat exchanger is to increase the thermal coupling between the device and the space, 6981 minimizing the approach of the leaving supply air temperature to the entering cooling water 6982 temperature. Radiant panels and chilled beams are typically designed for 55°F (12.8°C) chilled 6983 water, enhancing the opportunity for waterside economizer. 6984 6985 Fan coil systems that provide only sensible cooling and that derive all dehumidification from 6986 Dedicated Outdoor Air Systems (DOAS) can also be designed for 55°F (12.8°C) chilled water. 6987 Because the coils in these fan coils are not dehumidifying and are dry, pressure drop for any 6988 given coil will be reduced as much as 65% compared with wet coils. These coils should be 6989 selected with more rows and a denser fin pattern, while observing the air pressure drop 6990 limitations of the fan coil, to reduce the approach of the leaving air temperature to the entering 6991 chilled water temperature to no more than 3°F (1.7°C). 6992 6993 For air handling units, using 8 row, 10 fpi coils to minimize supply air temperature approach to 6994 the entering chilled water temperature is a powerful strategy. Combined with reducing the coil 6995 face velocity to no more than 430 fpm (2.2 m/s) the robust coil enables reduction of the 6996 approach of the coil leaving air dry bulb temperature to the chilled water entering temperature to 6997 4°F (2.2°C) during waterside economizer operating conditions (ambient wet-bulb temperature 6998 below 45°F (7.2°C)). 6999 7000 For the heat exchanger, a 2°F (1.1°C) approach is desirable, if it can be achieved. For the 7001 cooling tower, the strategy is to define the most cost effective way of achieving the required 7002 cooling water supply temperature to the cooling coil. Cost effectiveness analyses for various 7003 options for each of these components can lead the designer to the optimal means of achieving 7004 compliance. 7005 7006 The ASHRAE 90.1 outdoor condition requirement for meeting the entire cooling load with 7007 waterside economizer is arbitrary. For office buildings, it does not vary with climate zones for 7008 buildings, and, thus, is not related to the frequency distribution of wet bulb temperatures in any 7009 location. However, an effective economizer function is a powerful tool in reducing energy 7010 consumption and cost. At a minimum, a Zero Energy office building designed with waterside 7011 economizer should meet the ASHRAE 90.1 requirement that it to provide full cooling at an 7012 outdoor ambient condition of 50°F (10.0°C) dbt/45°F (7.2°C) wbt. Depending upon the 7013 climate, the designer may seek to achieve even greater performance for the waterside 7014 economizer. 7015 7016 HV38 Airside Economizer 7017 Airside economizer is typically more effective than waterside economizer, because it provides 7018 free cooling at higher enthalpy ambient conditions than waterside economizer. The strategy of 7019 airside economizer is to substitute outdoor air for the recirculated air that returns from the space 7020 whenever that substitution results in a reduced load on the cooling coil. Airside economizer is 7021 not subject to the same approach temperature overheads as is waterside economizer. Airside 7022 economizer, furthermore, does not entail water consumption and provides increased energy 7023 savings compared with water side economizer because no cooling tower fans or water pumps 7024 are required for its operation. Unfortunately, airside economizer is typically difficult to realize 7025 with either chilled water or DX fan coils, because of the extensive ductwork required to transfer 7026 outdoor air to the fan coil, that is typically located in the space to be served. 7027


7028 Control of airside economizer is a hotly contested issue, particularly with respect to the impact 7029 of sensor errors and calibration issues for enthalpy and humidity sensors. ASHRAE Standard 7030 90.1 has published the following specifications for control of airside economizer. The table 7031 (Table HV-8) has been truncated to include only options that utilize dry bulb temperature 7032 sensors only, because owners and operators of small to medium office buildings may not wish 7033 to assume the burden of maintaining humidity sensors. 7034 7035 Table HV-8 Recommended Control for Airside Economizer 7036

7037 (recommendation that single zone VAV AHU’s that are provided with minimum outdoor air 7038 through DOAS also have economizer outdoor air intake that is not routed through DOAS) 7039 (Source: ASHRAE Standard 90.1) 7040 7041 HV39 Dynamic Control of the Ventilation and Energy Recovery Device 7042 Demand ventilation control seeks to reduce outdoor air flow to the minimum required by 7043 ASHRAE Standard 62.1-2016 whenever that reduction would result in a reduction of load on 7044 the heating coil or cooling coil. When outdoor air conditions are beneficial, however, 7045 ventilation control should maximize outdoor airflow based upon the economizer controls shown 7046 in Table HV-8 even though outdoor airflow may be insufficient to meet the entire cooling load. 7047 7048 Further energy savings in office building may be achieved by controlling the energy recovery 7049 function of the DOAS unit to maximize free cooling. For the DOAS, disable energy recovery 7050 whenever outdoor conditions are such that increasing the ventilation rate will reduce the cooling 7051 load required to maintain comfort settings. Energy recovery disabling controls should follow 7052 the economizer logic shown in Table HV-8. When outdoor air dry bulb temperature falls below 7053 freezing, the energy recovery function can be re-initiated, and controlled to maintain a minimum 7054 outdoor air supply temperature set point of 35 - 40°F (1.7 – 4.4°C). The energy recovery 7055 function therefore serves as pre-heat freeze protection function for the air handling system. 7056 Should mixed return air and outdoor air fall below the supply air set-point at any time, while 7057 outdoor air is at minimum flow, based upon ASHRAE Standard 62.1-2016, energy recovery can 7058 be ramped up until the mixed air temperature rises to the supply air temperature set-point. 7059 7060 HV40 Natural Ventilation and Natural Free Cooling 7061 Natural ventilation and natural free cooling should be recognized as separate but related 7062 functions. Ventilation is a regulated function, providing specific rates of outdoor airflow to 7063 specific occupancies and specific populations. Cooling is the maintenance of thermal 7064 conditions, but, in most circumstances, is not a regulated activity. While both of these activities 7065 usually occur together, it is quite possible, and sometimes desirable, to have natural free cooling 7066 in concert with mechanical ventilation, to ensure that all space occupants have adequate 7067 ventilation. 7068


7069 Natural ventilation through operable windows, skylights, operable vents in the building 7070 envelope can be a very effective energy conservation strategy, but it requires either 7071 sophisticated and often expensive automatic control systems, or well trained and attentive 7072 building occupants to avoid costing more energy than is saved. Clearly, excess outdoor air 7073 inflow to the building, when exterior conditionings are inopportune, increases building energy 7074 consumption. On the other hand, de-energizing the building conditioning system when exterior 7075 conditions can be used to maintain interior comfort requirements can result in significant energy 7076 savings. 7077 7078 The recognized limitations of ambient conditions to maintain interior comfort requirements, 7079 with operable windows, are a upper dry bulb temperature limit of 68°F (20°C), and a lower 7080 temperature limit of 48°F (8.9°C), Ambient temperatures higher than this limit cannot provide 7081 adequate cooling, especially to spaces significantly inboard of the building envelope, while 7082 temperatures below the limit result in diminished comfort conditions adjacent to the window. 7083 Another limitation to natural conditioning is the humidity content of the ambient air. If the dew 7084 point temperature of the ambient air is greater than approximately 62°F (16.7°C), the interior 7085 relative humidity resulting from natural ventilation will likely be too high to maintain comfort. 7086 7087 If natural ventilation is being considered as a strategy for reducing energy consumption and 7088 providing a better work environment, it is recommended that the building design be modeled 7089 using a CFD program. To successfully integrate this strategy, building orientation should align 7090 with prevailing wind patterns. (This may conflict with the best daylighting orientation.) Air inlet 7091 and outlet openings should be positioned to promote air flow thru the rooms. The design team 7092 will usually model several architectural design approaches to maximize thermal comfort in the 7093 zone. Figure HV11 is an example of CFD modeling for a office environment. 7094 7095

7096 Figure HV-11 CFD model for a an office building 7097

Graphic reprinted with permission of Syska Hennessy 7098 7099 Natural conditioning can be used in office buildings in concert with interior thermal mass to 7100 reduce daytime cooling needs. If the overnight dry bulb temperature falls below 60°F (15.6°C), 7101 the building can be “flushed” overnight to cool the internal thermal mass and the resulting 7102 cooling will be “stored” to reduce daytime cooling needs. The designer should recognize, 7103 however, that, just as there is internal thermal mass, there is also internal “moisture” mass. The 7104


porous materials in the space, including carpets, fabrics, paper and unsealed wood have the 7105 ability to absorb moisture from humid air, slowly released that moisture when exposed to less 7106 humid air. In humid climates, overnight low dry bulb temperatures may be coincident with very 7107 high relative humidity, so that overnight flushing may purge the building of sensible heat while 7108 charging it with moisture that will later appear as latent load for the air conditioning system. In 7109 dry climates, overnight “flushing” in concert with thermal mass, can result in significant energy 7110 savings. 7111 7112 Natural ventilation has less cooling capacity than mechanical cooling, and therefore it is even 7113 more important to design carefully to limit internal and envelope loads. Utilization of natural 7114 conditioning may also be limited by unusually poor outdoor air quality, or high degrees of 7115 outside noise. Natural ventilation works best when the building owner and occupants are well 7116 educated about what to expect about the building performance, and be willing to become an 7117 active and integral part of the building operation. 7118 7119 HV41 Filters 7120 Another requirement of the HVAC system is to ensure that the air delivered to the conditioned 7121 space is relatively clean. This improves system performance (by keeping the coils cleaner, for 7122 example) and keeps the air distribution system relatively clean to ensure a healthy learning 7123 environment for the building occupants. Some of the contaminants that affect IAQ can be 7124 classified as particulates, gases, or biologicals. The methods and technologies for effectively 7125 controlling these contaminants differ, so it is important to define the contaminants of concern 7126 for a given facility. 7127 7128 Comply with at least the minimum requirements for particulate filtration and air cleaning de-7129 fined by ANSI/ASHRAE Standard 62.1 (ASHRAE 2016c). For equipment with wetted 7130 surfaces a MERV 8 filter is required by minimum. For more information on using air cleaning 7131 to improve the indoor environment beyond minimum requirements, refer to Indoor Air Quality 7132 Guide: Best Practices for Design, Construction, and Commissioning (ASHRAE 2009). Filters 7133 add to fan energy of the systems. Some ways to reduce this added energy is to increase the 7134 face area of the filter. For central equipment, the DOAS SYSTEAM or central VAV air handler 7135 SYSTEM A, an angled filter rack will greatly increase the face area and reduce pressure drop. 7136 For terminal equipment, designing the system such the equipment is used only for sensible 7137 cooling as in sensible fan coil system D will reduce the filtration requirements and terminal 7138 energy. For the VRF(SYSTEM B) and GSHP (SYSTEMC), the equipment should be sized to 7139 maximize the MERV 8 filter area. 7140 7141 Use a filter differential pressure gage to monitor the pressure drop across the DOAS or VAV 7142 unit filters and send an alarm if the predetermined pressure drop is exceeded. Filters should be 7143 replaced when the pressure drop exceeds this alarm value. Fan energy is a large portion of the 7144 HVAC system, the predetermined pressure drop should be set to maximize energy use for the 7145 zero energy office building. A filter manufacturer's recommendations for replacement may be 7146 based on maximum life vs energy. A pressure gage may not be possible across the filters on 7147 the terminals units such as heat pumps, VRF, and fan-coil units because accurate sensing is not 7148 possible. For this equipment scheduled filter changes should be in place to minimize fan energy 7149 for this equipment. The gauges should be checked and the filters should be visually inspected at 7150 least once every three months. 7151 7152


HV42 Building Pressurization Control 7153 The HVAC system is to ensure that the building is properly pressurized. Uncontrolled 7154 infiltration or exfiltration through the building envelope can cause cooling and heating loads to 7155 increase and do harm to the building. Each zone of the building with a DOAS or central VAV 7156 system will have a central relief fan that should modulate to maintain building pressure for that 7157 zone (See sections HV DOAS, HV2 – SYSTEM A, HV29 exhaust air systems). Controlling the 7158 zone pressure directly will control infiltration and exfiltration and also ensure that the exhaust 7159 energy available is recovered. The building envelope needs to be sealed properly (See EN#) so 7160 the HVAC system and DOAS unit can work effectively. 7161 7162 HV43: Transport Energy - Air 7163 Fan motors should meet at least IE3 efficiency or NEMA Premium efficiency. EC motors may 7164 be an appropriate choice for many small units to increase efficiency. 7165 7166 Fan systems should meet or exceed the efficiency levels listed in Table HV-1. Depending on the 7167 HVAC system type, the efficiency level is expressed in terms of either a maximum power (W) 7168 per cubic foot per minute of supply air (for systems where fan power is not included in the 7169 packaged HVAC unit efficiency calculation) or a maximum ESP loss (for packaged systems 7170 where fan power is included in the EER calculation). 7171 7172 HV44 Electronically Commutated motors 7173 Electronically commutated motors (EC motors) electronically control the voltage and current. 7174 They have a permanent magnet applied to the motor and a stator with electrical windings that 7175 generate a rotating magnetic field. As the rotor moves, it commutates the stator windings (ie; 7176 switches phases of the magnetic poles. (ASHRAE Journal March 2004). EC motors operate 7177 without slip-losses, as opposed to AC induction motors, and therefore are inherently more 7178 efficient. In addition, the electronic commutation provides a convenient means for speed 7179 control. Minimum full-load efficiency requirements for a PSC motor, per ASHRAE 90.1-2016 7180 range from 65% to 85% depending upon motor size. while the full load efficiency of an EC 7181 motor will range from 70-90%. However, efficiency of a PSC motor drops dramatically in part-7182 load conditions, often falling below 40%, while the efficiency of an electronically commutated 7183 motor remains high. Market factors have driven cost and price down of these motors, and 7184 manufacturers now manufacture EC motors up to 15hp. They are also more reliable, have an 7185 inherent soft start and a longer motor life. (AHSRAE Journal, May 2016) 7186 7187 HV45: Transport Energy - Water 7188 Hydronic systems should be designed for variable flow and be capable of reducing pump flow 7189 rates to 30% or less of the design flow rate. Care should be taken to maintain the minimum flow 7190 through each chiller, as defined by the chiller manufacturer. 7191 7192 Piping should be sized to comply with the pipe sizing limitations listed in Table 6.5.4.5 of 7193 ASHRAE/IES Standard 90.1 (ASHRAE 2016). Using a smaller pipe size increases the pressure 7194 drop through the pipe, increases the velocity through the pipe, and may cause erosion to occur if 7195 velocity is too high. A larger pipe size results in additional pump energy savings but increases 7196 the installed cost of the pipe. In systems that operate for longer hours, larger pipe sizes are often 7197 very economical. 7198 7199 Energy use and installed costs are typically both reduced by selecting chilled water (CHW) ∆T 7200 of 12°F to 20°F rather than the traditional 10°F (ASHRAE Handbook 2010). This will save 7201


pump energy, permit the reduction of pipe sizes (reducing installation cost), and minimize pump 7202 heat added to the water because of the use of reduced pump horsepower, but it will also affect 7203 cooling coil performance. This can be overcome by lowering the chilled-water temperature to 7204 deliver the same air conditions leaving the coil. Chilled water temperature setpoints should be 7205 selected based on a life-cycle analysis of pump energy, fan energy, and desired air conditions 7206 leaving the coil. 7207 7208 HV46: Ductwork Design and Construction 7209 Good duct design practices result in lower energy use. Low pressure loss and low air leakage in 7210 duct systems are critical to lowering the overall fan energy. Lowering the pressure needed to 7211 overcome dynamic pressure and friction losses will decrease the fan motor size and the needed 7212 fan energy. Refer to the “Duct Design” chapter (F21) of the 2017 ASHRAE Handbook—7213 Fundamentals (ASHRAE 2017) for detailed data and practices. 7214 7215 Dynamic losses result from flow disturbances, including changes in direction, duct-mounted 7216 equipment, and duct fittings or transitions. Designers should reevaluate fitting selection 7217 practices using the ASHRAE Duct Fitting Database (ASHRAE 2008b), a program that contains 7218 more than 220 fittings. For example, using a round, smooth radius elbow instead of a mitered 7219 elbow with turning vanes can often significantly lower the pressure loss. Elbows should not be 7220 placed directly at the outlet of the fan. To achieve low loss coefficients from fittings, the flow 7221 needs to be fully developed, which is not the case at the outlet of a fan. To minimize the system 7222 effect, straight duct should be placed between the fan outlet and the elbow. 7223 7224 Be sure to specify 45° entry branch tees for both supply and return/exhaust junctions. The total 7225 angle of a reduction transition is recommended to be no more 45°. The total angle of an 7226 expansion transition is recommended to be 20° or less. 7227 7228 Poor fan performance is most commonly caused by improper outlet connections, nonuniform 7229 inlet flow, and/or swirl at the fan inlet. Look for ways to minimize the fan/duct system interface 7230 losses, referred to as system effect losses. Be sure the fan outlet fittings and transitions follow 7231 good duct design and low pressure loss practices. Project teams must address space 7232 requirements for good, low-pressure duct design in the early programming and schematic 7233 design phases. Allow enough space for low-pressure drop fittings and locate air-handling units 7234 that result in short, straight duct layouts. Avoid the use of close-coupled fittings. 7235 7236 The use of flexible duct should be limited because these ducts will use more fan energy than a 7237 metal duct system. Recent research has shown that flexible duct must be installed with less than 7238 4% compression to achieve less than two times the pressure loss of equivalent-sized metal 7239 ductwork (Abushakra et al. 2004; Culp and Cantrill 2009). If the compression is more than 7240 30%, the pressure loss can exceed nine times the pressure loss of metal ductwork. In addition, 7241 Lawrence Berkeley National Laboratory (LBNL) has shown that the loss coefficients for bends 7242 in flexible ductwork have a high variability from condition to condition, with no uniform trends 7243 (Abushakra et al. 2002). Loss coefficients ranged from a low of 0.87 to a high of 3.3 (for com-7244 parison purposes, a die-stamped elbow has a loss coefficient of 0.11). If a project team decides 7245 to use flexible duct, the following is advised: 7246 7247

Limit the use of flexible duct to connections between duct branches and diffusers or 7248 VAV terminal units. 7249


Flexible sections should not exceed 5 ft in length (fully stretched). 7250 Install the flexible duct without any radial compression (kinks). 7251 Do not use flexible duct in lieu of fittings. 7252

7253 Where permissible, consider using plenum return systems with lower pressure loss. Whenever 7254 using a plenum return system, design and construct the exterior walls to prevent uncontrolled 7255 infiltration of humid air from outdoors (Harriman et al. 2001). 7256 7257 HV47: Duct Insulation 7258 Duct insulation should be installed to ensure conditioned air reaches the space with minimal 7259 losses as possible. In addition, all airstream surfaces should be resistant to mold growth and 7260 resist erosion, according to the requirements of ASHRAE Standard 62.1. 7261 7262 The following ductwork should be insulated: 7263 7264

All supply air ductwork 7265 All outdoor air ductwork 7266 All exhaust and relief air ductwork between the motor-operated damper and penetration 7267

of the building exterior 7268 7269 For Zero Energy buildings, supply, exhaust and outside air ductwork should never be located 7270 outside the thermal envelope, in attics, crawl spaces or on the roof. 7271 7272 Low-energy-use ductwork design involves short, direct, and low-pressure-drop runs. The 7273 number of fittings should be minimized and should be designed with the least amount of 7274 turbulence produced. (In general, the first cost of a duct fitting is approximately the same as 12 7275 ft of straight duct that is the same size as the upstream segment.) Excessive noise from 7276 ductwork airflow is a direct result of air turbulence. Round duct is preferred over rectangular 7277 duct due to sound considerations. However, space (height) restrictions may require flat oval 7278 ductwork to achieve the low-turbulence qualities of round ductwork. Alternatively, two parallel 7279 round ducts may be used to supply the required airflow. 7280 7281 Air should be ducted through low-pressure ductwork with a system pressure classification of 7282 less than 2 in. w.c. Rigid ductwork is necessary to maintain low pressure loss and reduce fan 7283 energy. When a unit is serving multiple zones, supply air should be ducted to diffusers in each 7284 individual space. 7285 7286 In general, the following sizing criteria should be used for duct system components: 7287

Diffusers and registers, including balancing dampers, should be sized with a static 7288 pressure drop not to exceed 0.08 in. w.c. Oversized ductwork increases installed cost 7289 but reduces energy use due to lower pressure drop. 7290

Supply ductwork should be sized with a pressure drop no greater than 0.08 in. w.c. 7291 per 100 lf. 7292

Return ductwork should be sized with a pressure drop no greater than 0.04 in. w.c. 7293 per 100 lf. 7294

Exhaust ductwork should be sized with a pressure drop no greater than 0.05 in. w.c. 7295 per 100 lf. 7296


Flexible ductwork should be of the insulated type and should be 7297 limited to connections between duct branches and diffusers or between duct 7298

branches, 7299 limited to 5 ft (fully stretched length) or less, 7300 installed without any kinks, 7301 installed with a durable elbow support when used as an elbow, and 7302 installed with no more than 15% compression from fully stretched length. 7303

Hanging straps, if used, need to use a saddle to avoid crimping the inside cross-7304 sectional area. For ducts 12 in. or smaller in diameter, use a 3 in. saddle; those larger 7305 than 12 in. should use a 5 in. saddle. 7306

Long-radius elbows and 45° lateral take-offs should be used wherever possible. The 7307 angle of a reduction transition should be no more than 45° (if one side is used) or 7308 22.5° (if two sides are used). The angle of expansion transitions should be no more 7309 than 15° (laminar air expands approximately 7°). 7310

7311 HV48: Duct Sealing and Leakage Testing and Balancing 7312 The ductwork should be sealed in accordance with ASHRAE/IES Standard 90.1. All duct joints 7313 should be inspected to ensure they are properly sealed and insulated, and the ductwork should 7314 be leak tested at the rated pressure. The leakage should not exceed the allowable cfm/100 ft2 of 7315 duct area for the seal and leakage class of the system’s air quantity apportioned to each section 7316 tested. 7317 7318 After the system has been installed, cleaned, and placed in operation, the system should be test-7319 ed, adjusted, and balanced (TAB) in accordance with ASHRAE Standard 111 (ASHRAE 7320 2008a) or SMACNA’s TAB manual (SMACNA 2002). 7321 7322 This will help to ensure that the correctly sized diffusers, registers, and grilles have been 7323 installed, that each space receives the required airflow, and that the fans meet the intended 7324 performance. The balancing subcontractor should certify that the instruments used in the 7325 measurement have been calibrated within 12 months before use. A written report should be 7326 submitted for inclusion in the operations and maintenance (O&M) manuals. 7327 7328 HV49: Thermal Zoning 7329 The HVAC systems discussed in this guideline simplify thermal zoning because each thermal 7330 zone has a respective terminal unit. The temperature sensor for each zone should be installed in 7331 a location that is representative of the entire zone. 7332 7333 Thermal zoning should also consider building usage during the unoccupied hours. Depending 7334 on the office schedule, the building may be used for alternative events, and/or include non 7335 regular scheduled work hour programs. It is important to identify the spaces that may typically 7336 be used for these events and arrange the building design so that they are isolated in one area. 7337 This will minimize the equipment they will have to operate and limit the DOAS unit ventilation 7338 air supplied during these periods. 7339 7340 Arranging similar occupancies on the same building exposure provides the design team with the 7341 option of using one terminal unit to serve two offices. Each office can be provided with a 7342 temperature sensor and the unit responds to the average condition. This design approach is often 7343 used to reduce first cost and long term maintenance cost. 7344


7345 7346 HV50: Infiltration (Climate Zones 7, 8) 7347 Infiltration is one of the largest contributors to HVAC energy in climate 7 and 8, see HV45 o 7348 building pressurization. Sealing the build to avoid unnecessary HVAC energy usage will be 7349 key to a zero energy HVAC design, particularly in climate zones 7 and 8, however all climates 7350 will benefit. We recommend sealing and testing the building envelope to no larger than 0.15 7351 cfm per square foot of exterior wall area at 75Pa (0.3” w.c.). A stretch goal would be to achieve 7352 Passive House Criteria of 0.08 cfm per square foot of exterior wall area. 7353 7354 7355 HV51: System Level Control Strategies 7356 System level control strategies exploit the concept that conditioning and ventilation are for the 7357 health and comfort of the occupants and control setpoints may be modified in pursuit of energy 7358 savings when occupants aren’t present. Having a setback temperature for unoccupied periods 7359 during the heating season or a setup temperature during the cooling season can help save energy 7360 by avoiding the need to operate heating, cooling, and ventilation equipment. A good design 7361 approach is to equip each zone with a zone temperature sensor and then use a system-level 7362 controller that coordinates the operation of all components of the system. This system-level 7363 controller contains time-of-day schedules that define when different areas of the building are 7364 expected to be unoccupied. During these times, the system is shut off and the temperature is 7365 allowed to drift away from the occupied setpoint. Similarly, when occupants are not present, 7366 ventilation may not be required, and DOAS system delivery to the space may be eliminated. 7367 This control strategy is different than demand controlled ventilation in that some ventilation is 7368 required during the occupied period even no occupants are present. 7369 7370 Optimal start uses a system-level controller to determine the length of time required to bring 7371 each zone from the current temperature to the occupied setpoint temperature. The controller 7372 waits as long as possible before starting the system so that the temperature in each zone reaches 7373 the occupied setpoint just in time for occupancy. This strategy reduces the number of hours that 7374 the system needs to operate and saves energy by avoiding the need to maintain the indoor 7375 temperature at the occupied setpoint when the building is unoccupied. Controlling energy usage 7376 outside of normal operating hours is most successful when the usage culture can be change. 7377 Refer to Chapters 2 and 3 for more information on achieving culture change. 7378 7379 Control systems should include the following: 7380

Control sequences that easily can be understood and commissioned 7381

Use of the room motion sensor to setback temperatures during the occupied period when 7382 no usage is occurring in the room. Also many times a room may be scheduled "on" 7383 during the unoccupied period for a function. The room motion sensor will again insure 7384 the unit only operates when the room is occupied. 7385

A user interface that facilitates understanding and editing of building operating 7386 parameters and schedules 7387

Optimal start systems as a means to limit demand during start-up so the peak demand is 7388 not inadvertently set during start-up. 7389

Sensors that are appropriately selected for range of sensitivity and ease of calibration 7390


Means to effectively convey the current status of systems operation and of exceptional 7391 conditions (faults) 7392

Means to record and convey history of operations, conditions, and efficiencies 7393

Means to facilitate diagnosis of equipment and systems failures 7394

Means to document preventive maintenance 7395 7396 HV52: Employ Proper Maintenance 7397 Continued performance and control of O&M costs require a maintenance program. The O&M 7398 manuals provide information that the O&M staff uses to develop this program. Detailed O&M 7399 system manual and training requirements are defined in the OPR and executed by the project 7400 team to ensure the O&M staff has the tools and skills necessary. The level of expertise typically 7401 associated with O&M staff for buildings covered by this Guide is generally much lower than 7402 that of a degreed or licensed engineer, and they typically need assistance with development of a 7403 preventive maintenance program. The CxA/QA provider can help bridge the knowledge gaps of 7404 the O&M staff and assist the owner with developing a program that will help ensure continued 7405 performance. The benefits associated with energy-efficient buildings are realized when systems 7406 perform as intended through proper design, construction, operation, and maintenance. 7407 7408 HV53: Commission Systems and Equipment 7409 After the system has been installed, cleaned, and placed in operation, it should be commissioned 7410 to ensure that the equipment meets the intended performance and that the controls operate as 7411 intended. The commissioning authority (CxA) provider should provide a fresh perspective that 7412 allows identification of issues and opportunities to improve the quality of the CDs and verify that 7413 the OPR is being met. Issues identified in the design review can be more easily corrected early in 7414 the project, providing potential savings in construction costs and reducing risk to the team. 7415 7416 Performance testing is essential to ensure that commissioned systems are properly implemented. 7417 Unlike most appliances these days, none of the mechanical/electrical systems in a new facility 7418 are “plug and play.” Functional test procedures are often written in response to the contractor’s 7419 detailed sequence of operations. The CxA will supervise the controls contractor running the 7420 equipment through its operations to prove adequate automatic reaction of the system to 7421 artificially applied inputs. The inputs simulate a variety of extreme, transition, emergency, and 7422 normal conditions. 7423 7424 If possible, it is useful to operate and monitor key aspects of the building for a one-month 7425 period just before contractor transfer to verify energy-related performance and the final setpoint 7426 configurations in the O&M documents. This allows the building operator to return the systems 7427 to their original commissioned states (assuming good maintenance) at a future point, with 7428 comparative results. 7429 7430 Final acceptance generally occurs after the CxA issues in the issues log have been resolved 7431 except for minor issues the owner is comfortable with resolving during the warranty period. 7432 7433 HV54 Noise Control (Climate Zones: all) 7434 Acoustical requirements may necessitate attenuation of the supply and/or return air, but the 7435 impact on fan energy consumption should also be considered and, if possible, compensated for 7436 in other duct or fan components. Acoustical concerns may be particularly critical in short, direct 7437 runs of ductwork between the fan and supply or return outlet. (See Figures HV-9 and HV-19) 7438


7439 Avoid installation of the air-conditioning or heat pump units above occupied spaces. Consider 7440 locations above less critical spaces such as storage areas, restrooms, corridors, etc. (See Figure 7441 HV-9 and Figure HV-10) 7442 7443 ASHRAE Handbook—HVAC Applications (ASHRAE 2007c) is a potential source for 7444 recommended background sound levels in the various spaces that make up office buildings. 7445 7446

7447 Figure HV-9 Typical Noise Paths for 7448

Rooftop-Mounted HVAC Units 7449 7450

7451 Figure HV-10 Typical Noise Paths for Interior-Mounted HVAC Units 7452

7453 THERMAL MASS 7454 7455 HV55 Concept Overview 7456 The thermal mass of the building structure can be incorporated into the building conditioning 7457 system in several ways both to improve comfort and to reduce energy consumption. Thermal 7458 mass generally tends to mitigate temperature swings that might result from a mismatch between 7459


conditioning level and thermal loads at any specific time. Thermal mass reduces the total 7460 thermal loads over time when the impact of intermittent exterior conditions (sun or air 7461 temperature) can be “stored” to offset the impact of later conditions that might drive the space 7462 temperature in the opposite direction. The perfect example of such “storage’ is the impact of a 7463 massive exterior wall on the building internal temperature, when the diurnal exterior 7464 temperature oscillates across the comfort band. Night-time heat losses and daytime heat gains 7465 to some extent cancel one another in their journey across the depth of the wall, resulting in a 7466 much smaller temperature swing on the interior surface of the wall that may well stay within the 7467 comfort band. 7468 7469 HV56 Thermal Mass as Part of the Building Envelope or Internal to the Building 7470 The example just given is of thermal mass in the building envelope. The thermal mass is part of 7471 the envelope that separates the building interior environment from the ambient external 7472 environment. External mass will, in effect, “average” the impact of ambient external conditions 7473 on the interior environment. In effect, it will reduce the peak conditioning demand on the 7474 space, but may amplify the minimum conditioning demand. This strategy is most effective 7475 when the ambient diurnal temperature traverses the comfort zone. 7476 7477 Internal thermal mass is mass that is entirely contained within the building envelope. While it is 7478 often said that internal thermal mass tends to mitigate interior temperature swings, one must 7479 remember that heat transfer between the thermal mass and the air must be driven by temperature 7480 difference. Therefore, to “exercise” the thermal mass, to make use of its thermal storage 7481 capacity, the air must be warmer than the thermal mass to drive heat into it, and must be colder 7482 than the thermal mass to extract heat from it. As a result, the cycling of air temperature must 7483 necessarily have a greater amplitude than the cycling of the thermal mass temperature. For 7484 certain types of occupancies, cycling of air temperature may be acceptable; for others not, 7485 especially if the cycling extends outside of the comfort range. In any event, if the ambient 7486 diurnal temperature cycle does not traverse the temperature of the internal cycle, thermal mass 7487 will have little effect on the daily heat transfer across the building envelope and little effect on 7488 total conditioning required. 7489 7490 Exceptions to this statement are passive solar heating systems in which short wave solar 7491 radiation is transmitted through windows or skylights and directly heat internal mass. This heat 7492 is stored and over time is released into the internal environment, avoiding the need for high 7493 internal air temperature to charge the mass. Solar heated thermally massive elements will also 7494 exchange heat through long wave radiation with other surfaces in the space, If those other 7495 surfaces are also massive, the rate of discharge of the absorbed solar energy will be further 7496 attenuated and extended over time. Designers using this strategy should be cautious of thermal 7497 discomfort that can result from direct solar penetration into the space and visual discomfort that 7498 can result from direct solar glare. 7499 7500 Thermally massive elements in a space will dampen variation in space mean radiant 7501 temperature, improving comfort even with significant changes in space air temperature. If the 7502 thermal mass has significant area in the space, its relatively invariant surface temperature can 7503 reduce fluctuations in mean radiant temperature, resulting in improved thermal comfort. 7504 Interior thermal mass is particularly effective in spaces with significant solar gain, because it 7505 dampens the peak conditioning loads or temperature variations that might occur due to highly 7506 variable solar heat gains. 7507 7508


One additional advantage to internal thermal mass is that it can reduce the rate at which internal 7509 temperatures rise as cooling capacity for the space is reduced, facilitating adaption of the 7510 building to minimizing electrical demand during the 4:00pm to 9:00pm period when the utility 7511 generation profile will include fewer renewable assets. Upon receipt of a signal from the utility 7512 that their renewable generation fraction has fallen below a certain threshold, thermostat set-7513 points can be raised, with the realization that a thermally massive building will conform to the 7514 new temperature more slowly than a less massive one. 7515 7516 HV57 Active versus Passive Thermal Mass 7517 Passive thermal mass is thermal mass whose temperature is driven by convective or radiant 7518 interaction with the air or the sun. Heat transfer into or out of the mass is not under active 7519 control, and is usually driven by variation in air temperature or radiant flux. Exploitation of 7520 internal thermal mass, therefore, usually requires a larger variation of internal air temperature 7521 than the variation of temperature in the thermal mass. 7522 7523 Active thermal mass on the other hand, can be used to moderate interior air temperature 7524 variations. Typically, the active thermal mass is charged or discharged with embedded hydronic 7525 tubes or air passages. Conditioning fluid is passed through these conduits to control the 7526 temperature of the thermal mass independently of the air temperature. Examples of active 7527 thermal mass elements include floor slabs, ceiling slabs, and, even the entire internal horizontal 7528 structures of buildings. The thermal mass can dampen significant variations in thermal loads, 7529 resulting in less variation of comfort conditions. Thermal mass can be pre-cooled before the 7530 start of the day to mitigate daytime cooling requirements. Conditioning to the thermal mass can 7531 be terminated before the end of the day and thermal mass will maintain space conditions until 7532 the end of the operating period. Using natural ventilation at night to pre-cool building spaces for 7533 day-time use is discussed in HV19. Active thermal mass can be used as the primary vehicle to 7534 maintain the heat balance of a space and constrain internal temperatures within the comfort 7535 range. Note that active thermal mass neither ventilates, nor, hopefully dehumidifies, so that air 7536 systems are required to provide these two functions of the building environmental system. The 7537 heating and cooling sources for active thermal mass may require a significantly lower deviation 7538 from the average interior temperature because of the extensive surface area available of the 7539 massive element. Commonly active thermal mass elements are cooled with chilled water no 7540 cooler than 60°F and heated with hot water no warmer than 110°F, temperatures that can be 7541 generated much more efficiently than conventional heating and cooling sources. 7542 7543 Thermal storage is a special case of active thermal mass wherein both the charging of the 7544 thermal mass is actively controlled and the coupling of the thermal mass to the space is also 7545 controlled. This strategy can be used to create conditioning potential independently of space 7546 operation and to apply the conditioning to the space in the most energy efficient way. 7547 7548 Active thermal mass is particularly effective when natural conditioning assets do not occur 7549 simultaneously with building conditioning requirements. Examples of these assets include low 7550 overnight dry-bulb temperatures, and solar heat gain. 7551 7552 [Note to Reviewers: References have not been fully updated, and will be updated prior to the 7553 90% draft. If you have additional resources you think we should be referencing and adding, 7554 please let us know] 7555 7556 REFERENCES 7557


7558 Steve Kavanaugh and Kevin Rafferty, Geothermal Heating and Cooling Design of Ground-7559

Source Heat Pump Systems, RP-1674, ASHRAE, 2014 7560

Andújar Márquez JM, Martínez Bohórquez MÁ, Gómez Melgar S. Ground Thermal Diffusivity 7561 Calculation by Direct Soil Temperature Measurement. Application to very Low Enthalpy 7562 Geothermal Energy Systems. Passaro VMN, ed. Sensors (Basel, Switzerland). 7563 2016;16(3):306. doi:10.3390/s16030306, p.11.. 7564

Zhang, C.; Yang, W.; Yang, J.; Wu, S.; Chen, Y. Experimental Investigations and Numerical 7565 Simulation of Thermal Performance of a Horizontal Slinky-Coil Ground Heat Exchanger. 7566 Sustainability 2017, 9, 1362, Creative Commons image 7567

Jasmin Raymond, Serge Mercier, Luc Nguyen, “Designing coaxial ground heat exchangers with 7568 a thermally enhanced outer pipe”, Geothermal Energy, December, 2015. 7569

7570 7571 RENEWABLE ENERGY 7572 7573 [Note to Reviewers: This section has been copied from the K-12 ZE Guide. Input on 7574 appropriate changes for office buildings is requested.] 7575 7576 OVERVIEW 7577 7578 The cost of renewable energy has dropped rapidly in the last decade driven by declining costs of 7579 wind and solar. For most building owners, photovoltaic (PV) is a highly versatile renewable 7580 energy source and for many has provided the capability for buildings to become zero energy. 7581 For purposes of this guide, PV systems will be considered as the primary renewable energy 7582 source for getting to a zero energy building. While some small scale wind, micro-hydro, and 7583 biomass is available, it is fairly limited. Buildings should evaluate whether these sources are 7584 economically viable in their area. 7585 7586 Since 2010, the cost of photovoltaic power generation has dropped more than half as prices of 7587 PV panels and systems equipment have seen prices decrease due to worldwide implementation 7588 and manufacturing improvements (NREL 2016). Solar energy is increasing geometrically. In 7589 2016 the installed capacity is in excess of 300 Gigawatts having increased 75 GW in the 7590 previous year (IEA 2016). The bottom line is that buildings that have not looked at PV in the 7591 last year should revisit as the costs are dropping dramatically. 7592 7593 Other renewable energy systems, such as biomass, and the purchase of renewable energy 7594 certificates (RECs), do not meet the definition of on-site renewable energy and thus are not 7595 considered for this design guide. . 7596 7597 COMMON TERMINOLOGY 7598 7599 PV systems are made up of an array of Photovoltaic (PV) modules which use sunlight to 7600 produce electricity. This electricity is generated as direct current (DC) and must be converted to 7601 alternating current (AC) and synchronized with the local utility grid in order to be used in 7602 commercial power applications like an office building. PV power generation systems are 7603 flexible, and can be configured in any size to suit the loads of the facility. Besides the PV 7604


modules that combine to make the PV array, other equipment is required such as inverters to 7605 convert DC to AC, energy storage devices, maximum power point trackers (included in many 7606 inverters), disconnecting and combining equipment, mounting hardware, metering, and 7607 monitoring. A diagram of a typical PV AC system is shown in Figure 5-49. 7608 7609

7610

7611 Figure 5-49 Typical PV AC System Diagram. 7612

7613 RE1: Definitions 7614 Understanding common terms from the renewable energy field is useful when discussing the 7615 use of renewable energy for a zero energy building. 7616 7617 Renewable energy refers to energy that is produced from a fuel source that cannot be exhausted, 7618 like sunlight or wind. Coal and natural gas are two fuel sources which have limited supplies 7619 and are considered non-renewable. 7620 7621 Photovoltaic (PV) refers to a type of energy production which uses light to directly generate 7622 electricity. PV power is generally produced through the use of sunlight striking a 7623 semiconductor material like the chips used in electronics, to produce a direct current across the 7624 junction in the semi-conductor. More can be found about Photovoltaic panels and materials 7625 used in creating PV panels at the NASA Science webpage: https://science.nasa.gov/science-7626 news/science-at-nasa/2002/solarcells. 7627 7628 Standalone PV systems are those PV systems which are not intended to operate in parallel with 7629 a utility grid, and typically are used for small applications in conjunction with battery storage. 7630 These are not applicable for commercial PV systems. 7631 7632 Interactive or Grid-Tied PV systems are those which operate in parallel with the AC utility grid, 7633 whether directly to a utility transformer to back feed directly into the grid, or where 7634 interconnected to the facility main switchboard or panelboard in order to offset power 7635 consumption in the facility. Interactive PV systems must be synchronized with the grid voltage 7636


and phase to ensure that issues of flicker, harmonic distortion, frequency and voltage 7637 fluctuations do not occur. The PV system is required to be disconnected from the grid 7638 whenever voltage, frequency do not meet utility requirements for stability, or when there are 7639 utility power outages and/or grid disturbances. 7640 7641 Wind power is the production of electricity from wind and is considered a renewable source. 7642 More information can be found about wind power production at the DOE office of Energy 7643 Efficiency and Renewable Energy website under Energy Basics: 7644 https://energy.gov/eere/energybasics/articles/wind-energy-technology-basics 7645 7646 Energy storage is a device with the capability of storing energy such as batteries. 7647 7648 "Net" metering is where the PV power generated is used to offset power consumption at the 7649 facility Net metering allows excess energy to be stored in the form of credits which are then 7650 used to balance electricity pulled from the utility grid. For most applications net-metered PV 7651 systems are sized to match the consumption of the building (or less) such that excess energy is 7652 not produced on an annual basis. For the building to claim the renewable attributes of the PV 7653 system, the building must retain the RECs. 7654 7655 "Sell all" metering is metering of the PV system where all of the power generated is sold to the 7656 utility and is not used to directly offset facility electricity consumption. Compensation is an 7657 important component of the Sell All system. 7658 7659 Renewable energy certificates (RECs) are also sometimes called renewable energy credits, 7660 renewable electricity certificates, green tags, or tradable renewable certificates. These 7661 certificates allow a mechanism to purchase renewable energy to and from the electricity grid 7662 and documents that one Megawatt-hour (MWh) of electricity has been generated by a renewable 7663 energy source and fed into a shared electric grid that transports electricity to customers. Also 7664 known as “SREC’s when solar energy is the source of the renewable energy power generation. 7665 7666 Solar renewable energy certificates are those specifically generated by solar energy. 7667 7668 Ground mounted refers solar energy photovoltaic systems that are mounted at grade level, 7669 commonly on “tables” which are structurally anchored to the ground by concrete foundations 7670 and steel supports which hold the PV panels in place and keep them from wind driven uplift 7671 forces. Ground mounted PV systems may also include parking canopies and building canopies 7672 which provide protection from weather elements such as sun and rain. Typically, the use of 7673 ground mounted solar for building applications is limited to sites with large areas of available 7674 ground to install the PV panels. PV panels which are ground mounted are usually installed at an 7675 angle of around 30 degrees, whereas roof mounted PV panels are mounted at approximately a 7676 10-degree tilt. A small, ground mounted demonstration PV system is useful for educational 7677 purposes when the majority of the PV system is on the roof or in a non-visible location. Note 7678 that all electrical components should be enclosed by a grounded, protective fence. 7679 7680 DESIGN STRATEGIES 7681 7682 RE2: System Design Considerations 7683 PV panels are specified with two distinct guarantees: performance and product manufacturing. 7684 Performance guarantees are for a power output performance over time. The panel will degrade 7685


over a nominal 25 year system life, so it is important to compare different manufacturers’ 7686 warrantees for degradation of power production over the same time period. Manufacturing 7687 warrantees are usually for a period of one to five years and cover manufacturing defects, not 7688 performance. Tier 1 panels should be specified. 7689 7690 Other considerations include: 7691

Types of PV panels, efficiencies, and quality 7692 Orientation and panel tilt 7693 Number of inverters and number of panels 7694 Rebates and tax credits, if any are applicable 7695 Type and quality of inverters 7696 Type and quality of energy storage, if any 7697 Type of wire and conduit and wire management systems 7698 Point of connection to building main power switchboard or at utility transformer 7699 Size and configuration of customer or utility transformers to accommodate PV power 7700

input 7701 Accessibility of roof and height 7702 Remote shut down from building fire alarm system and by code officials in order to 7703

disconnect all power in and on the building. 7704 Type of roof, flat or standing seam metal roof 7705 Additional architectural or structural engineering associated with mounting of PV panels 7706

on roof 7707 Location of inverters on roof or in utility yard 7708 Removal of trees to eliminate shading 7709

7710 Solar-ready design is rooted in determining the optimal placement of potential future solar 7711 technology. See BP17-23 for additional information regarding how building orientation, roof 7712 form, and shading considerations affect system design. 7713 7714 RE3: System Sizing 7715 Determine the size of the PV system needed to achieve zero energy use status. Sizing should be 7716 based on the projected energy consumption of the building. An additional allowance should be 7717 made if batteries are included to account for their inefficiencies. Size PV systems based on the 7718 orientation, solar irradiance and shading studies of the site. 7719 7720 Consider the use of metering separate from the inverter meter. Separate utility grade electricity 7721 meters are generally more accurate and easier to calibrate than internal inverter meters. An 7722 external metering system is an important part of the overall monitoring and measurement and 7723 verification system for the building. 7724 7725 Ideally, a PV system should be sized slightly larger than the predicted loads. In many cases, 7726 shadows are not fully accounted for and buildings use more energy than estimates. . 7727 7728 RE4: Energy Storage (Batteries) 7729 Battery storage can be an effective means to reduce peak demand charges. However, the use of 7730 battery storage is not an effective renewable energy generation source as batteries require 7731 energy to recharge daily and after every discharge. Life expectancy of current technologies 7732


(Lithium Ion) is about ten years or less, depending on number of discharges. Flow batteries will 7733 soon be commercially available with an even longer life of over 1,000 discharges. 7734 7735 The use of energy storage is currently at a 20-year payback period and will definitely trend 7736 downwards over the next ten years. Until the payback period reaches less than ten years, 7737 battery storage may not be financially desirable from an energy production standpoint. 7738 7739 RE5: Mounting Options 7740 Once the size of the renewable energy system is determined, the building site can be evaluated 7741 for PV panels. Determining if there is adequate space for the PV modules and equipment is the 7742 next most important consideration after sizing considerations. (See also BP19 and BP20.) PV 7743 panels may be used as shading devices or building integrated as roof material and power 7744 production. The PV system can be mounted a number of different ways on the building 7745 property. Examples of different mounting options are shown in Figures 5-50 and 5-51. 7746 7747 The most used location is on the roof of the building. Roof mounted PV systems are typically 7748 used for the larger systems necessary to complete the zero energy equation, as roof areas are 7749 large spaces that are not being used for other purposes. At the time of building construction, 7750 minimizing the amount of non-solar rooftop equipment will maximize the available area for 7751 installing a solar PV system in the future. See BP19-BP20 for information on determining and 7752 maximizing the required roof area for PV installation. (reference) 7753 7754 Also important is determining whether the roof installation carries a warranty, and if the 7755 warranty includes contract terms involving solar installations. 7756 7757 The type of roof system used can affect the cost of solar installations. To host a solar PV 7758 system, a roof must be able to support the weight of PV equipment and the system should be 7759 mounted so as to minimize the impacts of wind loads and maintain solar access. One reason 7760 that flat roof PV systems are only tilted at 10 degrees is to minimize wind loading on the roof 7761 and PV system. It also minimizes the shading of the PV panels on other PV panels. See BP21-7762 BP23 for more information on roof durability and maintaining solar access. 7763 7764 Covering parking areas may provide another location for siting PV systems. In addition in hot 7765 sunny climates, parking canopies created by PV panels can serve a dual purpose of shading cars 7766 which reduces fuel consumption from air-conditioning, and power generation (Figure 5-51). 7767 7768 Ground mounted PV systems are seen in larger PV power generation systems but are only an 7769 option where the site can provide adequate real estate without jeopardizing other functions such 7770 as athletic fields and parking. PV systems require considerable space for panels and equipment. 7771 A rough rule of thumb is 2.5 acres for a 500KW system, depending on shading factors, module 7772 efficiency, location, and orientation. 7773 7774 Additionally, assessing the potential PV system size and corresponding energy production 7775 output can inform building design and result in optimized system sizing at a later date. 7776

NREL’s PV Watts and System Advisor Model (SAM) are online, interactive tools that can be 7777 used to explore system sizing and output potential. (NREL-PV, NREL-SAM) 7778

7779


7780 Figure 5-50 (RE5) Roof Mounted PV System 7781

Photo reproduced by permission of Stantec 7782 7783 7784

7785 Figure 5-51 (RE5) PV Canopy Mounted PV System 7786

Photo by Dennis Schroeder, NREL Image 48750 7787 7788 When establishing the location for the PV panel arrays, shading must be considered. Shading 7789 studies take into account obstructions from trees, adjacent buildings, towers, power lines, or 7790 even rooftop HVAC equipment or antennas. Minimal shading at all times is best, but essential 7791 during the middle day peak generation period. The arrays should be oriented for peak solar 7792 energy harvesting. See also BP17. 7793 7794 RE6: Interconnection Considerations 7795 PV systems for commercial use fall into two categories: sell all, where the energy produced 7796 is connected to a utility grid and sold to a utility company, i.e., not consumed at the site; and 7797 net metered, where the energy produced is consumed at the site and any excess is not 7798 compensated by the utility company. Both system types are metered to determine the 7799 amount of renewable energy produced. With a sell all system, excess energy produced during 7800


a grid failure must be controlled. Inverters should be programmed to limit power output to 7801 the demand energy use during times of grid failure. 7802 7803 The interconnection point is where the renewable energy system connects to the commercial 7804 power system. For a sell all system this is at the utility transformer, either a dedicated one or 7805 the same utility transformer used for the building service. When contemplating a sell all PV 7806 system for a zero energy building, involve the utility company early, as soon as the system 7807 size is known. The transformer size for the building service will need to be increased to 7808 accept the PV power generated on site and if not addressed in the planning stages, can result 7809 in a too small transformer being installed. The larger transformer may also impact fault 7810 currents and impedance on the building’s electrical power distribution systems. If the building 7811 site is using a net metered system, the point of interconnection is usually made at the main 7812 switchboard for the building. The switchboard will need to be upsized in order to 7813 accommodate the power from the renewable energy system. Space for AC inverters will need 7814 to be accommodated, either on the roof, on the ground, or in the main electrical room. Bus 7815 connection ampacity sizing must take into consideration building demand load and PV load, 7816 plus 20%. 7817 7818 Standoff mounting is often used for slant roof-top mounted solar systems. These standoffs are 7819 attached to the roof for support rails, to which the PV modules are mounted. Standoff 7820 arrays with panels typically add anywhere from 3 to 5 pounds per square foot; however, they 7821 can be designed to coincide with the roof structure. Be cautious that the thermal integrity of the 7822 roof is not compromised with the PV system. 7823 7824 Ballasted systems are much heavier than standoff systems, and are used for flat-roof- 7825 mounted systems. The roof must be specifically engineered for the number of ballasts, ballast 7826 locations, types, effect on roof structural sizing, seismic concerns, and wind loading. Uplift is a 7827 primary concern for PV arrays, especially in high-wind areas like tornado alleys or hurricane 7828 zones. The effect of the PV arrays and their attachment points must be considered when 7829 designing the roof and building structure. The typical tilt for a flat-roof-mounted system is 10° 7830 to minimize uplift. For safety purposes, PV panels should not be mounted within 8 to 10 ft of 7831 the roof edge, depending on local jurisdictions and fire department requirements. Roofs may 7832 require fall protection railings for roof mounted equipment. Access to the roof should be more 7833 than a vertical ladder with roof hatch. Full walk-up stair access should be provided. 7834 7835 Roof mounted systems should be planned around the replacement of the panels at 25-year life, 7836 and for the roof replacement. The roof selection should be made with consideration that PV 7837 panels will be covering a large portion of the roof for the life of the PV system. Access 7838 should be provided to the roof for periodic maintenance of the PV. 7839 7840 Rack mounting for panels are typically used for ground mounted systems that do not use 7841 tracking. Rack mounting is not common on smaller projects and is commonly used for large 7842 utility scale generation projects over 1MW. 7843 7844 A discussion of wind turbines as a renewable energy system are not included in this guide. 7845 While in Kansas, Iowa, South Dakota, Oklahoma, Nebraska, and parts of Texas wind power 7846 generates a significant portion of electricity produced—more than 20% of power production in 7847 some cases (Jossi 2017)—these are utility-grade turbines beyond the capabilities of most 7848


building systems to maintain. Wind turbines large enough to produce power for a zero energy 7849 office building are inappropriate for properties in urban and suburban areas. 7850 7851 RE7: Net Metering Options 7852 With a net metered, grid connected system, PV power is produced and used by the facility first, 7853 before the facility imports energy from the utility grid, and before the facility exports PV energy 7854 to the grid. Net metering or net energy metering (NEM), allows owners of PV power 7855 generation systems to “send” that energy when it is generated, for “use” at a later date. A 7856 typical PV single line diagram is shown in Figure 5-52. The diagram illustrates a net metered 7857 system. For example, if you have a PV system which generates power during the day in excess 7858 of your load, then you may send the excess power in the form of credits which can be applied in 7859 the future. Often the credits, if they remain after a 12 month period, are converted to a 7860 monetary credit according to the utility rate tariff. 7861 7862 Annual net metering allows power credits that are generated and exported during weekends to 7863 be used when the building is fully engaged. Net metering uses a bi-directional meter which 7864 measures power flowing in two directions – from the PV power generation system to the utility 7865 grid, and from the utility grid to the customer’s electrical load. With systems of this size, utility 7866 fault current and impedance studies are commonly required to minimize negative impacts to the 7867 grid. With battery storage systems, the inverter or charge controller will regulate the battery 7868 charging during the day when PV power is being produced. In addition, the inverter must 7869 disconnect any electrical panel boards that have PV or battery inputs from the utility for stand-7870 alone operation much like an emergency generator system. 7871 7872 Check with the latest Public Utility Commission, state laws, and utility rules governing 7873 renewable energy systems in your jurisdiction for the current status of net metering policies. 7874 PV system sizes affect application fees and sometimes, utility rates. PV systems will be larger 7875 for extreme climate zones and possibly fall into a different regulatory category. Implementation 7876 of PV systems and net metering are highly location specific across the US. Utilities may be 7877 concerned about the effect of PV system inverters on the grid, which may act to destabilize the 7878 grid from the intermittent nature of renewable power generation. The issue of flicker in power 7879 grids connected to PV systems comes from rapidly moving clouds across PV panels, which 7880 results in uncontrolled power generation. Inverters are increasingly being required to limit 7881 excess energy exported to the grid, and to shut down under unstable conditions. 7882

7883

7884


Figure 5-52 (RE7) Typical PV single line diagram 7885 7886 RE8: Utility Considerations 7887 Coordinate with the local utility company to determine the proposed contract demand for the 7888 project. This will be based on the design team’s load calculation for the building from the 7889 energy model with all loads considered – such as, HVAC, lighting, plug, IT, and exterior 7890 lighting. 7891 7892 Initiate discussion with the local utility company as soon as the decision is made to build a zero 7893 energy building to understand the grid connection and PUC requirements. Coordinate with 7894 local utility to understand the local rates, including demand charges, and discover any 7895 restrictions to connecting the grid, or if there are zoning issues regarding ground mounted PV 7896 systems or wind turbines. 7897 7898 The interconnection agreement with the utility will be affected by the size of the PV system, the 7899 grid characteristics, and how much energy will be exported to the grid. Verify with the utility 7900 the fees charged for the utility interconnection fee, the feasibility study, and the metering 7901 charges. The term of the agreement should be specifically addressed, such as 10, 15, or 25 7902 years. Understand the implications of a long-term utility rate agreement as part of the contract 7903 demand agreement. 7904 7905 Easements may be required by the utility company. The requirements vary from state to state 7906 but must be filed prior to construction of the PV system. 7907 7908 Questions to ask the utility company include: 7909

Can power be exported to the grid? 7910 Is there a power limit for exporting electricity to the grid? 7911 What additional facility charges, if any, will there be if the PV system ties directly to the 7912

utility transformer? 7913 What will the utility pay for excess power exported to the grid? 7914 How will having a PV system affect the building’s electricity rate? 7915 When do they require the filing of a report on the planned construction with their 7916

distribution department? 7917 7918 It is important to get answers in writing. Staff change, PUC rules and regulations change, but 7919 original agreements are usually honored if in writing. 7920 7921 Caution: Legal agreements are more durable than a written memorandum of understanding 7922 between an owner and a utility company. 7923 7924 RE9: Utility Rates 7925 Questions to ask regarding utility rates include: 7926

What is the rate type: Time of Use, flat rate, peak demand charges, uninterruptible, or 7927 interruptible rate 7928

What are peak and off peak demand charges? 7929 What are peak and off peak electric rates? 7930 When do the peak and off peak rates and demand charges occur summer and winter? 7931

Time of day? 7932


Is there a minimum contract kWh demand consumption clause in the utility contract? 7933 Typically this is the contract demand established by the energy model, design team, 7934 owner, and utility. 7935

7936 These answers should be communicated to the design team as part of the energy modeling 7937 efforts. 7938 7939 IMPLEMENTATION STRATEGIES 7940 7941 RE10: Purchasing Options 7942 Determine whether to purchase the PV system outright or to enter into a power purchase a 7943 agreement (PPA) with a solar developer, who will furnish, install, and maintain the PV system 7944 for you under a lease or lease purchase agreement. 7945 7946 Caution: If you go with a lease or purchase agreement, remember to maintain ownership of the 7947 renewable energy certificates (RECs). 7948 7949 Determine maintenance staff capabilities and current and projected maintenance work load for 7950 providing on-going maintenance for the PV system. Consider contracting with the PV installer 7951 for an ongoing maintenance contract. Decide if you want to include a Performance Bond for the 7952 term of the PV system guarantee and warranty. 7953 7954 Consider an insurance policy to cover damage from high winds, hail, baseballs, and target 7955 practice. 7956 7957 RE11: Purchasing the System 7958 Write the technical specs and Request for Proposal (RFP) for the PV system. Include a 7959 checklist for panel and inverter efficiencies, AC and DC system sizing, number of inverters, 7960 metering, monitoring, approximate layout, interconnection point, and warranty and power 7961 production guarantee requirements. Consider using a template PPA RFP such as available from 7962 the Solar Energy Industry Association. 7963 7964 Negotiate and bid the system, including doing homework on the warranty and guarantee 7965 offered, the PV products, the technologies, the equipment efficiencies, metering, monitoring, 7966 system configuration and guaranteed power production. 7967 7968 Verify system provider qualifications, including certifications and references. Some questions 7969 to ask to verify contractor qualifications include: 7970 7971

Are they accredited with electrical contracting license in your state, with adequate 7972 liability insurance? 7973

Do they have Workers Compensation insurance and are they OHSA compliant with 7974 safety policies in effect and a designated safety officer? 7975

Does the bid tabulation include the RFP checklist, the equipment included in the bid, 7976 and a schedule of values for the equipment, installation, metering, monitoring, and 7977 maintenance agreement? 7978

Is the system performance estimates included for daily, weekly, monthly, and annually? 7979 Are they members of industry associations? 7980


How many similarly sized systems have they installed? 7981 Are they experienced in working with your local utility company? 7982 Will any of the work be subcontracted to another firm? 7983 What specific equipment are they proposing for your project? 7984 Does it meet the requirements of the RFP? 7985 What exceptions did they note with their bid? 7986 Has a detailed analysis of the load generation been included to confirm sizing is 7987

adequate to achieve zero energy, taking into account specific project limitations and 7988 conditions? 7989

Is the metering and monitoring system sufficiently detailed in the bid? 7990 What is the monitoring and metering agreement? 7991 Has a complete project team including contact information and team structure, been 7992

included? 7993 7994 RE12: Negotiating Procurement 7995 There are many system considerations open for negotiation during the procurement process. 7996 7997 Output limiting factors include: 7998

DC vs. AC system sizing. Typically use a 15% efficiency factor when converting from 7999 DC to AC power. Module efficiencies are improving and some reports of well over 8000 46% efficiency are being achieved in laboratories. Present commercial efficiency is 8001 about 20%. 8002

Safety considerations for PV systems 8003 Safety considerations for wind turbines 8004 Lightning protection 8005 System sizing for optimal energy production 8006 System sizing for peak reduction 8007 Flicker and why it matters – power quality considerations 8008 Grid interactive only 8009 Grid interactive with battery storage 8010 Energy storage 8011 Battery types 8012

8013 Educational factors include: 8014

Monitoring of power production 8015 Graphics display 8016

o PV and how it works 8017 o Carbon production showing the reduction in carbon from the energy strategies 8018

for lighting, HVAC, and renewable energy versus the baseline energy 8019 consumption 8020

o Solar irradiance 8021 o Weather station 8022 o Carbon reduction 8023 o Impact on natural environment 8024 o Carbon trading for students 8025 o Real time monitoring 8026


8027 Installation considerations include: 8028

Maintenance considerations for roof replacement 8029 Maintenance considerations for PV panel replacement 8030 Maintenance and location of inverters and combiner boxes 8031 Fire safety and signage considerations 8032 Electrical fusing and protection 8033 Financing models 8034

o Solar developer 8035 o Tax breaks 8036 o Private-public partnerships 8037

Bidding methods 8038 o Included with construction documents 8039 o Included as stand-alone contract 8040 o Bid with construction vs. as post building completion 8041

8042 RE13: Commissioning the System 8043 Once the system is installed, provide independent commissioning of the PV system to verify 8044 performance, grounding, overcurrent protection, and overall functionality. Perform a 8045 reconciliation of predicted energy production versus actual at monthly and one year intervals. 8046 Analyze factors affecting energy production like weather, cleanliness of panels, inverter 8047 performance and component failure, and meter drift. Perform remediation to return PV system 8048 to peak operating performance. 8049 8050 8051 REFERENCES AND RESOURCES 8052 8053 8054 Midwest: Midwest Energy News, Industry Report, Frank Jossi, 2017: 8055

http://midwestenergynews.com/2017/04/19/industry-report-midwest-and-great-plains-lead-8056 wind-energy-expansion/ 8057

NREL 2016: U.S. Solar Photovoltaic System Cost Benchmark: Q1 2016 Ran Fu, Donald 8058 Chung, Travis Lowder, David Feldman, Kristen Ardani, and Robert Margolis National 8059 Renewable Energy Laboratory (NREL) https://www.nrel.gov/docs/fy16osti/66532.pdf 8060

NREL PV: NREL PVWatts Calculator, http://pvwatts.nrel.gov/. 8061

NREL SAM: NREL System Advisor Model (SAM), 2010, https://sam.nrel.gov/ 8062

NREL, Solar Ready: An Overview of Implementation Practices, 8063 https://www.nrel.gov/docs/fy12osti/51296.pdf 8064 8065 NREL, Solar Ready Buildings Planning Guide, https://www.nrel.gov/docs/fy10osti/46078.pdf 8066 8067

Solar Energy Industry Association PPA RFP Template 8068 https://www.seia.org/sites/default/files/2017-8069 10/SEIA%20C%2BI%20PPA%20v2.0.docx 8070

8071

8072


Appendix A Envelope Thermal Performance Factor 8073 8074 The envelope information in the tables in the guide present a prescriptive or target construction 8075 option for each of the opaque envelope measures discussed. Table A-1 presents U-factors for 8076 above-grade components and F-factors for slab-on-grade floors that correspond to the 8077 prescriptive construction options. 8078 8079 Procedures to calculate U-factors are presented in ASHRAE Handbook—Fundamentals 8080 (ASHRAE 20xx), and expanded U-factor, C-factor, and F-factor tables are presented in 8081 Appendix A of ASHRAE/IES Standard 90.1 (ASHRAE 20xx). 8082 8083 Alternate constructions found in ANSI/ASHRAE/IES Standard 90.1-2016, Appendix A provide 8084 an equivalent method for meeting the specifications of this Guide provided they are less than or 8085 equal to the thermal performance factors listed in Table A-1. 8086 8087

OPAQUE CONSTRUCTION OPTIONS Roof Assemblies Walls, Above Grade Slabs

Insulation Above Deck Steel Framed Unheated R U R U R-in (vertical) F

20 c.i. 0.048 7.6 c.i. 0.123 0 0.73 25 c.i. 0.039 15.2 c.i. 0.071 15 - 36 0.480 30 c.i. 0.032 13 + 7.5 c.i. 0.064 30 - 54 0.400 35 c.i. 0.028 13 + 8.0 c.i. 0.062 40 c.i. 0.025 13 + 10.0 c.i. 0.052 Heated - Fully Insulated

13 + 12.0 c.i. 0.047 7.5 0.64 Metal Building 13 + 18.8 c.i. 0.035 15 0.44

19 +10 FC 0.041 20 0.373 19 +11 Ls 0.037 Metal Building25 + 8 Ls 0.037 13 0.124 25 + 11 Ls 0.031 16 + 6.5 c.i. 0.077 30 +11 Ls 0.029 16 + 9.8 c.i 0.062

25+11+11 Ls 0.026 30 0.052 25 + 10 0.047

25 + 13 c.i. 0.035

Mass Walls 7.6 c.i. 0.123 15.0 c.i. 0.076 19.6 c.i. 0.062 20.0 c.i. 0.060 28.0 c.i. 0.046 39.2 c.i. 0.034

8088 Note: All information in this appendix is in Inch-Pound (IP) units. For Slabs, the “in” refers to 8089 the depth of the vertical slab edge insulation. See Standard 90.1 for additional explanation. 8090 All units used in the table are defined in the Abbreviations and Acronyms of the Guide. 8091

8092


Appendix B International Climatic Zone Definitions 8093 8094 The following tables show the climate zone definitions that are applicable to any location. The 8095 information is from ANSI/ASHRAE Standard 169-2013, A3 Climate Zone Definitions. 8096 Weather data is needed in order to use the climate zone definitions for a particular city. 8097 Weather data for a number of cities in Canada and Mexico are available on the AEDG webpage 8098 (under Additional Information). Weather data by city are available for a large number of 8099 international cities on the 2013 Handbook-Fundamental CD. 8100 8101

CZ Name Thermal Criteria

0 Extremely Hot 10,800 < CDD50F

1 Very Hot 9000 < CDD50F < 10,800

2 Hot 6300 < CDD50F < 9000

3 Warm CDD50F < 6300

and HDD65F < 3600

4 Mixed CDD50F < 6300

and 3600 < HDD65F < 5400

5 Cool CDD50F < 6300

and 5400 < HDD65F < 7200

6 Cold 7200 < HDD65F < 9000

7 Very Cold 9000 < HDD65F < 12600

8 Subarctic/Artic 12600 < HDD65F

8102 CDD50F = Cooling degree-day to a base temperature of 50F 8103 HDD50F = Heating degree-day to a base temperature of 50F 8104 8105 Determine the moisture zone (Marine, Dry or Humid) 8106

a. If monthly average temperature and precipitation data are available, use the Marine, Dry 8107 and Humid definitions below to determine the moisture zone (C, B or A). 8108 8109

b. If monthly or annual average temperature information (including degree-days) and only 8110 annual precipitation (i.e. annual mean) are available, use the following to determine the 8111 moisture zone 8112

1. If thermal climate zone is 3 and CDD50oF < 4500, climate zone is Marine (3C). 8113 2. If thermal climate zone is 4 and CDD50oF < 2700, climate zone is Marine (4C). 8114 3. If thermal climate zone is 5 and CDD50oF < 1800, climate zone is Marine (5C). 8115

8116 c. If only degree-day information is available, use the following to determine the moisture 8117

zone. 8118 1. If thermal climate zone is 3 and CDD50oF < 4500, climate zone is Marine (3C). 8119 2. If thermal climate zone is 4 and CDD50oF < 2700, climate zone is Marine (4C). 8120 3. If thermal climate zone is 5 and CDD50oF < 1800, climate zone is Marine (5d). 8121


8122 Marine (C) Zone Definition – Locations meeting all four of the following criteria: 8123 8124

a. Mean temperature of coldest month between 27°F (–3°C) and 65°F (18°C) 8125 8126

b. Warmest month mean < 72°F (22°C) 8127 8128

c. At least four months with mean temperatures over 50°F (10°C) 8129 8130

d. Dry season in summer. The month with the heaviest precipitation in the cold season has 8131 at least three times as much precipitation as the month with the least precipitation in the 8132 rest of the year. The cold season is October through March in the Northern Hemisphere 8133 and April through September in the Southern Hemisphere. 8134

8135 Dry (B) Definition – Locations meeting the following criteria: 8136

a. Not Marine (C). 8137 8138

b. If 70% or more of the precipitation, P, occurs during the high sun period, then the 8139 dry/humid threshold is: P < 0.44 x (T - 7) 8140 8141

c. If between 30% and 70% of the precipitation, P, occurs during the high sun period, then 8142 the dry/humid threshold is: P < 0.44 x (T – 19.5) 8143

8144 d. If 30% or less of the precipitation, P, occurs during the high sun period, then the 8145

dry/humid threshold is: P < 0.44 x (T – 32), where 8146 8147

P = annual precipitation, in 8148 T = annual mean temperature, oF 8149 8150 Summer or high sign = April through September in the Northern Hemisphere and 8151 October through March in the Southern Hemisphere. 8152 8153 Period 8154 8155 Winter or cold season = October through March in the Northern Hemisphere and 8156 April through September in the Southern Hemisphere. 8157

8158 Humid (A) Definition – Locations that are not Marine (C) and not Dry (B). 8159