slide presentation from betterbricks/ashrae workshop

Fred Bauman, PECenter for the Built Environment (CBE)

All contents copyright (C) 2000 The Regents of the University of California

1

Designing UFAD SystemsBetterBricks Workshop, September 7-8, 2005

Designing Underfloor Air Distribution (UFAD) Systems

Workshop forBetterBricks

Cascadia Region of Green Building CouncilPuget Sound / Oregon Chapters of ASHRAE

Seattle – Sept. 7, Portland – Sept. 8, 2005

Fred Bauman, P.E.Center for the Built Environment, University of California, Berkeley

2

Acknowledgments

Taylor EngineeringAllan Daly

Pacific Gas & Electric Co.

ASHRAE

Course Development

Projects, ImagesArup, Flack + Kurtz, Nailor Industries, EH Price, Tate Access Floors, York International

3

Agenda9:00-9:10 Opening Comments9:10-9:30 Introduction 9:30-10:10 Diffusers and Stratification10:10-10:50 Underfloor Plenums10:50 -11:05 Break

11:05-11:45 Load Calculations, Energy11:45-12:00 Comfort and IAQ12:00 -1:00 Lunch

1:00-1:20 Horizontal and Vertical Distribution1:20-1:35 Commissioning and Operations1:35-1:50 Post-Occupancy Evaluations 1:50-2:05 How to Decide to Go with UFAD?2:05-2:15 Wrap-Up, Conclusions2:15 -2:30 Break

2:30-4:00 Panel Discussion

Introduction

9:10 – 9:30

5

CBE Organization

Industry/University Cooperative Research Center (I/UCRC)

National Science Foundation provides support and evaluation

Industry Advisory Board shapes research agenda

Semi-annual meetings emphasize interaction, shared goals and problem solving

6

CBE Industry Partners

Armstrong World Industries

Arup*

California Department of General Services

California Energy Commission

Charles M. Salter Associates

E.H. Price Ltd.

Flack + Kurtz, Inc.

HOK

Keen Engineering, Inc.

Pacific Gas & Electric Co.

RTKL

Skidmore Owings and MerrillSteelcase, Inc.Syska Hennessy GroupTate Access Floors Inc.*Taylor Engineering Team:

• Taylor Engineering• Guttmann & Blaevoet• Southland Industries• Swinerton Builders

TraneU.S. Department of Energy (DOE)*U.S. General Services Administration (GSA)*

York International Corporation

*founding partner



2


7

Overhead System

55°F-57°F

8

Underfloor air distribution system

61°F-65°F

9

Potential UFAD Benefits

Improved occupant comfort, productivity and health

Improved ventilation efficiency and indoor air quality

Reduced energy use

Reduced life-cycle building costs

Improved flexibility for building services

Reduced floor-to-floor height in new construction

10

Underfloor vs. Conventional Air Distribution System Design Issues

Underfloor air supply plenum

Air supplied into occupied zone near floor level

Higher supply air temperatures (for cooling)

Allows for occupant control

Properly controlled stratification leads to reduced energy use while maintaining comfort

Reduced space sensible heat load

Perimeter zone solutions are critical

Access floor improves flexibility and re-configurability

11

Current Barriers to UFAD Technology

Lack of familiarity by building industry

Higher first costs

Need for design guidelines and tools

Fundamental research needed on key issuesRoom air stratification

Underfloor plenums

Energy performance

Thermal comfort and ventilation effectiveness

Problems with applicable standards and codes

12

Room Air Stratification(cooling operation)



3


13

Floor Construction

14

Integrated Service Plenum

15

Underfloor Air & Power

PLUG & PLAY POWER and CONTROLS

Modular Wiring

VAV

Diffuser

16

Underfloor HVAC Concept

17

ASHRAE Research Project RP-1064:UFAD Design Guide

Project start: September 1999

Primary author – Fred Bauman

Contributing author – Allan Daly

Sponsored by ASHRAE and CBE

Technical oversight by TC 5.3, Room Air Distribution

Guide published by ASHRAE in December 2003

Available from ASHRAE bookstore

Developed ASHRAE Professional Development Seminar (PDS)

18

ASHRAE UFAD Design Guide

CONTENTS (243 pp.)1. Introduction2. Room Air Distribution3. Thermal Comfort and

Indoor Air Quality4. Underfloor Air Supply

Plenums5. UFAD Equipment6. Controls, Operation, and

Maintenance7. Energy Use8. Design, Construction, and

Commissioning

9. Perimeter and Special Systems

10. Cost Considerations11. Standards, Codes, and

Ratings12. Design Methodology13. Examples14. Future Directions15. Glossary16. References and

Annotated Bibliography17. Index



4


19

Development of UFAD Design Guide

Design Guide materialResearch (laboratory, field, simulation)

Design experience (literature, interviews, case studies)

Manufacturer’s literature

Includes UFAD and closely related task/ambient conditioning (TAC) systems

Covers topics in which important differences exist between UFAD and conventional overhead design

Identifies areas where more work is needed

20

Current status of UFAD technology

Strong interest due to several attractive featuresCurrent database of UFAD projects in North America

~300 installations

~50-55 million ft2

Routinely considered as HVAC design option

Ongoing research and experience in the field are generating new and improved information

Problems found in completed UFAD installations are often the same as those found in overhead buildings

Conservative design

Poor construction practice

Inadequate commissioning, controls, and operation

21

Raised floor and UFAD adoption

1995: Less than 3% of new office buildings had raised floors, UFAD a “fringe” element

2002: 7% of new offices used raised floors,15% of these with UFAD systems.

2004: 14% -15% have raised floors, ~ 45% of these with UFAD systems.

0%

4%

8%

12%

16%

20%

1995 1997 1999 2001 2003 2005Year

% o

f New

Offi

ce C

onst

ruct

ion

Raised FloorUFAD

22

How Many UFAD Projects are Installed?

Through 2000, approximately 80 projects representing some 20 million sq ft in US.

Between 2000-2002, the number of new projects represented another 25 million sq ft.

CBE currently maintains database of North American UFAD projects with over 300 installations representing 50-55 million sq ft.

The jobs are getting larger. The Bank One Center in Chicago (1.5 million sq ft) was completed in 2003 and several more projects over 1 million sq ft are now in design or under construction.

Diffusers and Stratification

9:30 – 10:10

24

Diffuser types

Swirl

Variable area (VA)

Swirl, horizontal discharge

Linear bar grille



5


25

Swirl floor diffuser

Swirl Diffusers

26

Personal control of swirl diffuserRotate face plate

27

Personal control of swirl diffuser

28

Individual Plenum Box

29

Office cubicles

One diffuser per workstation30

Too many!



6


31 32

Variable-AreaDiffuser

ProprietaryProduct

33

Variable Air Volume Performance

Maintain constant discharge velocity even as air reduces

CONSISTANT VELOCITY - VARIABLE VOLUME

34

Bar Grilles in Perimeter

35

Perimeter solution:Underfloor variable-speed fan-coil

Raised Access Floor

Return Air Plenum

Return Air Grille

Linear Bar Diffuser

Flex Duct

Fan Coil w/ ECM motor

Glazing

T

Heating Coil

No U/A diffusers in perimeter zones

36

Heating Loop Output

130°F

60°F

Discharge AirTemperatureSetpoint

Fan

Spee

d

Max Fan Speed

Design Fan Speed

30% Design Fan Speed

Lowest PossibleFan Speed(~15% Max

Fan Speed)

Deadband Cooling Loop Output

Airf

low

Design Airflow

30% Design Airflow

Minimum Airflow(due to pressurized plenum)

Airflow

Fan Speed

Variable Speed Fan-Coil Control



7


37 38

Perimeter solution:Underfloor variable-speed fan-coil

39

Perimeter solution – variable-area diffuserCooling mode

40

Perimeter solution – variable-area diffuserHeating mode

41

Task/Ambient Conditioning Systems

Desktop control for maximum occupant comfort control

Relatively rare in practice

42

Diffuser Code Compliance

In the past, technically only all-metal diffusers could meet all code flame spread and smoke ratings

For plastic diffusers:UL 94 (Flammability of Plastic Devices)

NFPA 90A (smoke developed index <= 50)

Smoke test protocol is NFPA 255 (burn 25 ft sample)

NFPA 90A exception (smoke optical density)

NFPA 262 or UL 2043 (new test for smoke generation from plastic diffusers in 2002 edition of NFPA 90A)



8


43

Room air stratification(cooling operation)

44

Overhead Air Distribution System

Mixing system tries to maintain uniform temperature and ventilation conditions throughout space

45

Displacement Ventilation System

Minimize mixing in occupied zone Stratification height (SH) separates upper and lower zones

46

Underfloor Air Distribution System

Increased mixing up to throw height (TH)Diffuser throw below stratification height (SH)

47


Diffuser throw above stratification level (SH)48

Air Patterns

displacement

swirl



9


49

Diffuser Comparison

ModelDischarge

Setting Airflow

Vertical Throw to

50 fpmClear Zone

Radius[ft3/min] [ft] [ft]

Vertical 100 4 - 6 1.5Vertical 75 2.5 - 4.5 1.5

Variable Vertical 150 8 2.0Area Full Spread 110 5 4.5

Vertical 75 / ft 25 -Vertical 40 / ft 18 -

Swirl

Bar

50

Room Air Stratification Testing

ApproachFull-scale laboratory tests of commercially available floor diffusers in realistic office setting.Study impact of various design and operating parameters on room air stratification (RAS).

SignificanceControl of stratification is crucial to:

Proper designSystem sizingEnergy efficient operationThermal comfortIndoor air quality

51

Stratification test results Effect of airflow rate: constant load, swirl diffusers, interior zone

0

1

2

3

4

5

6

7

8

9

10

11

69 70 71 72 73 74 75 76 77 78 79 80 81 82

Room Temperature, °F

Hei

ght,

ft

1.0 cfm/sq. ft0.6 cfm/sq. ft0.3 cfm/sq. ft

5°F ∆TASHRAE Std.55-2004

Still satisfies vertical temperature difference (5°F) with 40% less air

52

Results – Interior office, swirl diffusers

RAS profiles for high room load, 6 workstationsNormalized to 65°F SAT and common deltaT

0

1

2

3

4

5

6

7

8

9

10

65 66 67 68 69 70 71 72 73 74 75 76 77 78 79


Hei

ght,

ft

High throw, 2 diffusers

Low throw, 8 diffusers

High throw, 2 diffusers

Low throw, 10 diffusers

Lowest throw, 7 DV diffusers

Delta T = 8°F Delta T = 13°F

Low room temperature

High room temperature

Swirl diffusers

53

Variable Area vs. Swirl

0

1

2

3

4

5

6

7

8

9

10

11

69 70 71 72 73 74 75 76 77 78 79 80 81 82


Hei

ght,

ft

SW-1SW-2VA-1VA-2VA-3

VA Diffuser

Swirl Diffuser

T e s t

R o o m L o a d W /ft 2

R o o m A ir f lo w c fm /f t 2

D if fu s e r f lo w ra te ,

(% o f d e s ig n )

5 0 f p m T h ro w

f t V A -1 2 .6 0 .8 7 0 % 7 V A -2 2 .9 0 .8 3 0 % ~ 7 V A -3 1 .8 0 .4 4 0 % ~ 7 S W -1 2 .5 0 .6 9 0 % ~ 4 S W -2 2 .7 0 .6 4 0 % ~ 2

Source: ASHRAE Journal May 2002

54

Stratification Test Results Effect of supply air temperature: constant load, swirl diffusers, interior zone



10


55

RAS Testing Results(Cooling performance)

The amount of stratification is primarily driven by room airflow relative to load, and throw height.

Stratification will increase as room airflow and/or diffuser throw height are reduced for constant heat input.

If too much air is delivered or throw height is too high, stratification will be reduced (approaching a well-mixed system), thereby compromising energy performance (increased fan energy, and lower RAT).

Optimized control strategies should promote stratification (reduce airflow requirements), while balancing this with comfort considerations (∆T < 3-4°F in occupied zone).

Due to stratification, consider increasing thermostat setpoint by 1-2°F, especially in interior zones.

56

RAS Testing Results (Perimeter zone cooling)

Key perimeter zone issuesSupply air temperature

Diffuser throw height, airflow rate, amount of mixing

Blinds up or blinds down

Net effect is that cooling air quantities in perimeter zones can be in the range of 25% less to 15% greater, depending on the amount of stratification and other operating conditions.

57

Perimeter Office1st floor, east perim

66

68

70

72

74

76

78

80

Tue

8/22

Wed

8/2

3

10'8'6'4'2'0'

Monitored Data from an Underfloor System

stratificationduring cooling

mode

mixingduringheatingmode

SensorLocations

noon6am 6pm

Stratification (in practice)

58

Controlling Room Air Stratification

GuidelinesPromote stratification (reduce airflow requirements), while maintaining comfort: ∆T < 3-4°F in occupied zone.

Don’t be too conservative! Airflow should be no greater than OH systems.

Provide controls to reduce airflow to interior (rather than raise setpoint only) in case sizing is too conservative.

Technology needsCooling airflow design tool

Impact of stratification on thermal comfort

Identify thermostat control strategies

Underfloor Plenums

10:10 – 10:50

60

Underfloor Air Supply Plenums

Room

Return Plenum



11


61

Plenum Design Variations

Pressurized plenumPassive diffusers

Most common approach and focus of current practice

Zero-pressure plenumActive (fan-powered) diffusers

Not as popular due to perceived higher costs

Fully ductedNot as popular due to high cost and lack of flexibility

Most designs are hybrid solutions

62

Airflow Performance Issues

Objective – deliver desired amount of airPressurized vs. zero-pressure

Reduced static pressure

Plenum height (obstructions)

Size of plenum zone

Air leakage

Plenum inlet conditions

Inlet velocity

Inlet direction (open, vanes, plates)

Location in zone

Number of inlets in zone

63

Underfloor Air Supply PlenumsResearch Results

Phase 1 – Airflow PerformanceObjective Investigate practical plenum configuration issues, including minimum plenum height, for which acceptable airflow performance can be achieved in pressurized underfloor plenums.

ApproachEmpirical experiments in full-scale underfloor air supply plenum test facility.

64

Full-Scale Plenum Test Facility

40'

80'

M M M

MM M M

M M

M

Flowmeasuring

station

Fan

23"x 23"Duct

Plenum inlet

Measurementpoint (typical)

Removablefloor panels (2)Obstruction #1

Obstruction #2

4' Underfloorbarrier

4" x 14" Floor grills(typical)

5' 10' 10' 10' 10' 10' 10' 10' 5'

Raised Floor

Concrete Slab

24'19'

14'10'

Section View

Plan View

65

Plenum Schematic Cross-Section

1-inch Floor Panel

Concrete Slab

1"

2"

2"

2"

2" Po

lysty

ren

e B

locks

2"3"

7"

Finish Floor Level

Plenum Schematic Cross-Section

66

Results

Airflow delivery is very uniform from an 8-inch pressurized underfloor plenum over a full range of supply volumes (0.5-1.5 cfm/ft2), even at a distance of 80 feet from the plenum inlet.

Uniformity (less than 10% variation) is preserved for solid obstructions with only 1.5 inches of clear space.



12


67

Air Flow Ratio: 8-inch plenum

70%

80%

90%

100%

110%

120%

130%

0 10 20 30 40 50 60 70 80

Distance from Fan Inlet (ft)

Del

iver

ed A

ir Fl

ow R

atio

(M

easu

red

flow

/Uni

form

flow

)

1.5 cfm/sf

1.0 cfm/sf

0.5 cfm/sf

68

Publication

“How Low Can You Go?”Air Flow Performance of

Low-Height Underfloor Plenums

F. Bauman, P. Pecora, and T. Webster Center for the Built Environment

University of California Berkeley, California

October 1999

PDF available from: www.cbe.berkeley.edu/underfloorair

69

Plenum Air Leakage

Air leakage from a pressurized plenum may impact energy use and can impair system performance if not accounted for.

Types of leakageLeakage between floor panelsLeakage due to poor sealing and construction

Floor Diffuser Floor Panel Air Leakage

70

Smoke TestAir leakage between Floor Panels

71

Air Leakage Test Setup

72

Carpet Tile Configurations

Aligned Offset



13


73

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1

Pressure (in. w.c.)

Air

Leak

age

(cfm

/ft2 )

Bare panelsAligned carpetOffset carpet

Air Leakage between Floor PanelsCarpet Tile Configurations

74

Thermal Performance IssuesPressurized Plenums

Objective – deliver air at the desired temperature using a minimum amount of energy

Plenum inlet conditionsSupply air temperature

Inlet velocity and direction

Thermal decayHeat transfer coefficients (slab and panels)

Velocity and residence time of air in plenum

Temperature profile in slab and floor panels

Temperature on underside of slab

Thermal storage strategies (nighttime pre-cooling)

75

Temperature variations in underfloor plenumTem

perature [F]

76

Ongoing Research on Underfloor Plenums

Phase 2 – Thermal Performance

CFD model of underfloor plenum

Full-scale experiments

Validate model vs. test facility

Study thermal performance (supply temperature variations and thermal storage control strategies)

77

Effect of Plenum Inlet Conditions

a)

Inlet

Diffusers

Diffusersb)

Inlet

Vanes

Plan view of plenum air flow patterns: (a) without inlet vanes, (b) with inlet vanes

78

Plenum Air Temperature – CFD Model

Focused jet

(°F)



14


79

CFD model: Particle visualization

Temperature (°F)

80

Full-Scale Plenum Test Facility

81

Underfloor plenum guidelines

Airflow delivery and pressure distributionQuite uniform across open pressurized plenum zone

LeakageAccount for leakage into occupied space in design airflow calculations

Careful attention to construction quality and sealing of plenum

Recommend leak test at end of construction (guidelines needed)

Thermal decay 50-65 ft (15-20 m) maximum to furthest diffuser

Plenum inlet conditions can be important

Break

10:50 – 11:05

Load Calculations,Energy

11:05 - 11:45

84

Does UFAD Require More Air?

Underfloor:Supply Temp: 63 F

Room Setpoint: 75 F

Space Heat Load: 17,297 Btu/hr

CFM = 17,291 Btu/hr = 1,335 CFM

1.1 Btu/hr-cfm-F x (75F-63F)

Overhead:Supply Temp: 55 F

Room Setpoint: 75 F

Space Heat Load: 17,297 Btu/hr

CFM = 17,297 Btu/hr = 786 CFM

1.1 Btu/hr-cfm-F x (75F-55F)

Assuming complete mixing:

Answer: No! The assumption of complete mixing is incorrect!



15


85

Overhead Air Distribution System

Mixing system tries to maintain uniform temperature and ventilation conditions throughout space

86


Increased mixing up to throw height (TH)Diffuser throw below stratification height (SH)

87

Heat Transfer in UFAD Systems

88

Energy Flows in Stratified UFAD System

BackgroundIn a conventional building using an overhead well-mixed system, 100% of the space heat gains are removed by warm return air leaving the room at ceiling level (heat extraction).

QuestionHow is heat removed from a stratified room in a multi-story building with UFAD?

ApproachAssumption of perfect mixing is no longer validSimplified first-law (energy balance) model

PublicationSubmitted to ASHRAE Transactions 2007

89

Cooling Operation of Overhead System

Heat gain into space

100%

Extraction 100%

90

Supply Supply PlenumPlenum

Ceiling-floor radiation

Floor-room convection

Return PlenumReturn Plenum

Return Return PlenumPlenum

Slab

Slab

Treturn

Treturn

Treturn

Tceiling

Tcarpet

Tplenum

Troom, near floor = 72°F

Slab-supply plenum conduction/convection

Slab-supply plenum conduction/convection

Floor-supply plenum conduction/convection

Return-ceiling convection

Return-slab convection

RoomRoom

Raised Floor Raised Floor PanelsPanels

Ceiling-slab radiation

0.6 cfm/ft2, 65°F

78°F

Simplified Model – Heat Transfer Pathways



16


91

Predicted Distribution of Room Cooling Load

Heat gain into space

100%

Extraction 57%

Through floor 14%

Through slab 29%

Total into plenum 43%

Baseline results – hung ceiling

92

EnergyPlus Modeling

Considering Radiation is KEY to making sense out of heat flows in UFAD systems (and all systems).

Internal Loads Example(3.6 W/ft2)

Tsupply = 56Tplenum = 63Troom = 75Treturn = 76

System ∆T = 76-56 = 20Room ∆T = 75-63 = 13

18.8

17.8

16.2

17.4

22.5

24.223.9

29.1

24.4

24.3

24.3

23.8

23.8

17.4

13.4

23.6

0

20

40

60

80

100

120

140

160

180

10 15 20 25 30

56

63

75

76

∆Troom=13

∆Tsystem=20

75

93

Load Calculation/Energy Software Tools

Common load/energy calculation programsTrane Trace 700/Load 700

Carrier HAP

Elite

Wrightsoft RSC

DOE2.1, 2.2

No Underfloor Model in any of them!For load calculations, air volumes seem to work out to be the same as overhead calculations (so far…)

EnergyPlus UFAD system development underway!

94

Load Calc’s: What to do?!?

Designers need to understand the physics of these systems

“Standard” load calc’s seem to work(CAVEAT CAVEAT CAVEAT)

Must design systems that can react to dynamic load conditions

VAV system operation important

Resets seem to be very helpful

Systems must be commissioned to make sure they work

95

UFAD: Good Energy Performance

Cooling EnergyFree CoolingMechanical Cooling

Fan EnergyAir PressuresAir Volumes

Reheat EnergyLower ∆TLower Air-Volumes

96

More 100% Free Cooling

Mechanical cooling not required

due to warm supply air temperatures

65oFSupply Air Temperature

85oFReturn Air Temperature

<=65oFOutdoor Air Temperature

Cooling Coilis OFF



17


97

More Integrated Economizer Cooling

Higher return air temperature keepssystem at 100% outdoor air longer

65oFSupply Air Temperature

85oFReturn Air Temperature

65oF to <85oFOutdoor Air Temperature

Cooling Coilis On

98

Energy Advantages in the San Francisco Area

San Francisco Outdoor Temperature Distribution(Dry Bulb temperatures between 8am and 8pm)

0

50

100

150

200

250

300

33 37 39 41 43 45 47 49 51 53 55 57 59 61 63 65 67 69 71 73 75 77 79 81 83 85 87 89 91 93 95

Outdoor Dry Bulb Temperature [F]

Hou

rs

2217 Hours100% Economizer

99

UFAD in Other Climates

0

100

200

300

400

500

600

-25

-20

-15

-10 -5 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 10

0

0

100

200

300

400

500

600

-25

-20

-15

-10 -5 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 10

0

0

100

200

300

400

500

600

-25

-20

-15

-10 -5 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 10

0HV

AC

De

sig

n F

und

am

enta

ls

100

Economizer Savings Summary

Example Sensible Cooling Energy as a Function of Outside Air Temperature

0

5,000

10,000

15,000

20,000

25,000

30,000

35,000

50 55 60 65 70 75 80 85 90 95 100

Outside Air Temperature [oF]

Coo

ling

[Btu

]

OH system

UF system

101

Mechanical Cooling Energy Savings

Chiller energy decreases as the chilled water supply temperature increases – the compressor does less work 65oF

65oF

50oF62oF

102

Dehumidification

Chilled water supply temperature is determined by the lowest supply-air temperature needed.

If dehumidification is needed, this is likely to be 55oF or lower.

Affects both mechanical and free cooling.

55oF

55oF

40oF52oF



18


103

Mixing OH and UFAD Systems

Chilled water supply temperature is determined by the lowest supply-air temperature needed

If standard OH systems are used, this is likely to be 55oF.

Affects both mechanical and free cooling.

65oF

55oF

40oF52oF

104

System Type

Most UFAD perimeter systems still use reheat coils constant-speed or variable-speed fan units

HW or electric resistance heatUnducted – supplies underfloor air for cooling

VAV change-over air handlers are another more efficient option

Separate air handler per exposureControlled similar to “VVT” system

105

Reheat Energy

ExamplesItem Units Symbol / Equation OH UFAD

Heating Load [Btu/h] Qh 10,000 10,000System Supply Air Temp [F] Tsys 55 63Room Heating Setpoint [F] Tset 70 70Room Supply Air Temp [F] Tsupply 90 110

Supply Air Flow [CFM] Qh / (1.1 x (Tsupply-Tset)) 455 227Reheat [Btu/h] CFM x 1.1 x (Tset - Tsys) 7,500 1,750

23%

106

Structural Slab Thermal Storage

Building physics and anecdotal evidence suggest there is a strong coupling of plenum air and slab.

No validated mathematical models exist that can be used in design.

CBE, CEC, UCSD, and DOE working on it (EIEIO).

107

Reduced Fan Power

Underfloor plenum is the primary air distribution route

UFAD systems use less ductwork than OH systems

Primary fan pressure reduced 1/2 to 1 in. H2O, a reduction of about 25%

Substantial energy savings on primary fan power possible, however this may be offset by fan-powered boxes or terminals used in perimeter zones

108

Fan Energy Savings: Air Volumes

Calculations and practice suggest that UFAD systems do not require more air than OH systems due to stratification

But…

There are many unknowns associated with load calc’s

It appears that built projects in case studies provide too much air

Further research will allow us to design for reduced air volumes



19


Comfort and IAQ

11:45 – 12:00

110

Thermal ComfortVariations in Individual Preferences

Clothing

Activity level

Body weight & size

Personal preferences

111

Thermal Comfort

Light office activity, light jacket, slacks

Sedentary, Skirt, blouse, pantyhose

112

Personal Control

Field research: Occupants with no control are twice as sensitiveto temperature changes

Less control = more hot/cold complaints

113

Thermal Comfort

Traditional approachSatisfy up to 80% of building occupants

Underfloor approachAllow personal control of the local thermal environment satisfy up to 100% of occupants reduce occupant complaints

Existing fan-driven (TAC) supply outlets provide sizable range of temperature control:desktop 13°F (7°C); floor 9°F (5°C)

Passive diffusers (no fan power) don’t provide as much local temperature control, but improve perception of individual control

114

Occupant Control Issues

Supply outlet design (swirl, jet)

Passive (pressurized plenum) vs. active (local fan-driven) diffusers

Understandable and easy to use

Frequency of adjustment

Response rate

Range of control

Task/ambient control integration



20


115

Comfort Standards(Impact of stratification on thermal comfort)

ASHRAE 55 and ISO 7730 define a 5°F (3ºC) limit on vertical air stratification The limit was based on Olesen’s study in 1979 on 16 college students

116

Ongoing Comfort Research

CBE advanced thermal comfort model indicates that greater stratification (> 5°F) may be acceptable in middle of comfort zone.

New research is needed to define comfort criteria in stratified environments

Impact of stratification over full range of comfort zone temperatures

Comfort with and without personal control

Impact of localized heating or cooling (TAC systems) on thermal comfort

117

Indoor Air Quality

Traditional approachProvide uniform ventilation throughout space

Underfloor approachFresh air is delivered closer to the occupants

Floor-to-ceiling air flow pattern provides improved IAQ in occupied zone (up to 6 ft [1.8 m])

Local air supply improves air motion, preventing sensation of stagnant air (associated w/ poor IAQ)

118

Room Air Stratification(cooling operation)

119

Air Change Effectiveness (ACE)

ACE = age of air at return (τreturn) / age of air at breathing level (τbl)

τreturn

τbl

120

Indoor air quality

Air change effectiveness (ACE)Overhead (OH) systems(0.8 heating, 1.0 cooling)

Displacement ventilation (DV) (0.7 heating, 1.2 cooling)

Underfloor air distribution(no data available yet: 0.7 heating, 1.0 cooling)

Task/ambient conditioning(up to 2.7 for desktop supply)

Local air motion improves perceived air quality



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121

Research needed

Ventilation performance in UFAD systemsLack of quantitative data on ventilation performance of current-generation UFAD systems

ASHRAE TC 5.3 is preparing research work statement for proposed laboratory and computational fluid dynamics (CFD) study of ventilation performance of stratified systems (UFAD and displacement ventilation)

CBE is seeking funding to conduct field study (with Lawrence Berkeley Laboratory) of ventilation effectiveness and pollutant removal efficiency in existing UFAD office building

Lunch

12:00 - 1:00

Horizontal and VerticalDistribution

1:00 – 1:20

124

Plenum Distribution Criteria

General, uniform air distribution

Relatively equal supply air temperature to each diffuser

Relatively equal pressure in plenum

125

Horizontal Distribution

Layout Example:

Initial Plan –Large amount of

ductwork

126



22


127

Shafts

Horizontal Distribution

Layout Example:

Final plan employs multiple shafts to reduce ductwork in the

floor

128

50 foot radius

129

“Air Highways”

130

“Air Highway” Cross Section

131

Large Air Highway

132

Air Highway Construction



23


133

Air Highway Goals

Lower costsLess sheet metal

Lower labor rates of floor installers

Lower pressure dropLarger effective duct area

Reduced coordination and conflicts

Leak-free

134

Air Highway Limitations

Questionable actual cost savings

Familiarity of construction by floor contractors, general contractor

Code equivalence to a ductCrossing corridors

Construction coordinationNot complete until floor tiles installedDamage by other trades

Limited pressure capability

Leakage!!!!

135

The need for

Plenum Dividers

Sheet metal plenum dividers subdivide UF plenum

Purpose:Provide more interior control zones

Reduce length of air travel to perimeter UFTsReduced temperature degradation

Allow off-hour isolationMeet Title 24 25000 ft2 isolation area limitation

136

Plenum Dividers

Plenum DividersMaximum 25000 ft2 area per zone

137

Recommendations

Use as little underfloor ductwork as possibleMinimize cost

Minimize conflicts

50 feet from discharge to last outlet seems to be the consensus (more research being done)

Use many vertical shafts to try to eliminate horizontal ductwork

Cost of fire/smoke dampers offset by eliminated ductwork

Reduced velocity leaving shaft, reduces noise

Commissioning and Operations1:20 – 1:35



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139

Plenum Air Leakage

Conduct leakage tests in underfloor plenumBlower panel with variable-speed test fan

Maintain design plenum pressure (e.g., 0.05 in. H2O)

Test #1 – Total leakageFloor panels, electrical outlets, carpet tiles installed according to typical design specifications

Seal all diffusers

Test #2 – Construction quality leakageSeal all openings and gaps on raised floor surface

Floor leakageSubtract Test #2 result from Test #1 result

140

Acceptable Leakage Rates

Construction quality leakage

Not to exceed 0.05 cfm/ft2 at 0.05 in H2O (e.g., 1,000 cfm for a 20,000 ft2 floor plate)

Floor leakage

Not to exceed 0.10 cfm/ft2 at 0.05 in H2O(e.g., 17% leakage for an interior zone with 0.6 cfm/ft2

design airflow)

Consider testing a full-scale mock-up prior to construction. Apply corrections and sealing methods to remaining underfloor plenums and test again.

141

Airflow and Room Air Stratification

No cooling airflow design tool yet available

Systems are commonly oversized, often as a result of over-estimation of design loads

Conduct measurements of vertical temperature profile during fully loaded conditions

Use “stratification measurement tree” consisting of string or pole with several temperature sensors at regular intervals

Prior to measurements, operate building long enough (up to one week) to ensure thermal mass of structural slab is in equilibrium

If stratification in the occupied zone (up to 6 ft) is not at least 3°F, further adjustments should be made

142

Adjusting Stratification(at peak load)

AdjustAirflow quantity

Plenum pressure max setpoint

# of diffusers

TStat setpoint

Goal∆T ~ 3-4°F in occupied zone

Equivalent comfort (same average temperature)

143

Other Considerations

Close coordination between designers, contractors, commissioning agents, and building operators

Building operators must be properly trained on UFAD design and operation

Raise TStat setpoints to avoid overcooling (interior zones)

Avoid overriding higher airflows into open plenum – impacts the entire plenum zone

If plenum air temperature is too high, corrections may be needed

Account for temperature gain to plenum supply air, particularly in key areas

Perimeter zones

Conference rooms

BMS should allow easy retrieval and review of archived trend logs to evaluate system performance

Post-Occupancy Evaluations

1:35 – 1:50



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145

CBE occupant satisfaction survey

CBE’s occupant satisfaction survey offers a systematic, cost-effectiveway of measuring how satisfied occupants are with their workplace environments.

146

Survey implementation

Survey notification via email

Occupants respond to web-based survey Data sent to

SQL server database

Results reported online

147

Satisfaction with indoor air qualityOccupant survey results

- 3 30

+0.88 mean satisfaction7 UFAD bldgs, 1,344 responses

+0.23 mean satisfaction152 overhead bldgs, 25,749 responses

Reference: www.cbesurvey.org

How satisfied are you with the air quality in your workspace (i.e. stuffy/stale air, cleanliness, odors)?

148

Satisfaction with thermal comfortOccupant survey results

- 3 30


-0.21 mean satisfaction152 overhead bldgs, 25,749 responses


How satisfied are you with the temperature in your workspace?

149

Satisfaction with lightingOccupant survey results

- 3 30




How satisfied are you with the amount of light in your workspace?

150

Satisfaction with acoustic qualityOccupant survey results

- 3 30

-0.16 mean satisfaction7 UFAD bldgs, 1,344 responses



How satisfied are you with the noise level in your workspace?



26


151

Satisfaction with cleanlinessOccupant survey results

- 3 30




How satisfied are you with the general cleanliness of the overall building?

152

CBE UFAD project databasewww.cbe.berkeley.edu/underfloorair/casestudies.htm

~300 projects in North AmericaWeb-based questionnaire collecting key building characteristics ~32 buildings under active study; 13 have completed operations section of questionnaire

153

UFAD building operations questionnaireCompleted by facility managers

Based on your knowledge of how the UFAD system has been operating and your experience in other non-UFAD buildings, how much better or worse is this building in comparison to conventional buildings with respect to:

Much better Much worse3 -30

Operations issue NMean

response

0.1513Effort and cost of maintenance

0.5413Hot and cold complaints

0.6213Overall performance of UFAD system

0.6713Energy use

0.9213Making changes to tenant space

154

UFAD building operations questionnaireCompleted by facility managers

Based on your experience with this building, indicate how serious of a problem the following have been:

No problem Serious problem3 -30

Operations issue NMean

response

-0.1713Air leakage from construction joints

0.1713Plenum airflow and thermal decay

0.9213Air leakage from panel joints

1.2513Dust and dirt in plenum

1.6713Temp. stratification in occupied spaces

2.0813Moisture, mold, related problems

How to Decide toGo with UFAD?

1:50 – 2:05

156

Cost considerations – UFAD vs. overhead

Accurate first and life-cycle cost estimates are crucial early in design process

Added first cost of raised floor system can be offset (in part) by reduction in ductwork and electrical/telecomm installation costs

Recent projects have demonstrated that first costs for UFAD can be very comparable to overhead systems

Range from $1.00-1.50/ft2 reduction to $4.00-6.00/ft2 premium

Well-recognized that raised floor systems reduce life-cycle costs associated with churn

As more designers become familiar with UFAD and more manufacturers enter the market, costs will come down further



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157

Relative costs

$-

$50

$100

$150

$200

$250

Cost of Labor Cost of Energy Incremental Cost of UFAD

Offi

ce B

uild

ing

Cos

t per

Squ

are

Foot

A 1% Savings in Productivity

~1 year payback

158

Ongoing CBE UFAD Cost Analysis Project

Objective: Develop comprehensive first and life-cycle cost model for UFAD systems

Funded by U.S. GSA

Began summer 2002, ~$450K budget

Project statusFirst cost model complete

Development of life-cycle cost model underway

Complete model and total cost analysis complete by September 2006

159

Approach - Affected first cost elements

The model evaluates each affected element and computes the UFAD to overhead (OH) system cost difference

Access Floor: Installation of access floors & carpets

Façade & structure: Allowance for reducing floor-to-floor height

HVAC: Cooling and heating loads calculation for sizing and pricing tenant area HVAC costs

Electrical: Power distribution and voice and data differences

Raised Core: Raised slab in core (non-UFAD) area

Ceiling Treatments: Ceiling cavity paint, lighting, acoustical treatment, fireproofing steel beams, and sprinklers

Furniture: Difference between system-powered and conventional furniture

160

Comparison of electrical first costsCBE first cost model

$0.41$2.09

$0.38

$2.72$0.76

$1.91

$10.06$6.80

$10.06$6.80

$10.06 $6.80

$1.83

$1.78$1.83

$1.78$1.83

$1.78

-$2.27-$1.45 -$2.13

-$1.23-$3.00

$0

$2

$4

$6

$8

$10

$12

$14

$16

OH: Pow

er po

le, po

wered

UFAD: Con

venti

onal,

non-p

owere

d

UFAD: Con

venti

onal,

powere

d

UFAD: Mod

ular, n

on-po

wered

UFAD: Mod

ular, p

owere

d

UFAD: Mod

ular, n

on-po

wered,

RF labo

r

Elec

tric

al c

ost,

$/G

sf

-$20-$18-$16-$14-$12-$10-$8-$6-$4-$2$0

Workstation - LaborWorkstation - MaterialV&D - LaborV&D - MaterialElectrical - LaborElectrical - Material

Cost differential, $/Gsf

161

When to Use Underfloor Air?

Office buildings -- all are possible but best for:Open office plans

Owner Occupied Buildings

Dry, Mild ClimatesEnergy benefits best in mild climates without high humidity levels – little or no chiller plant savings in humid climates

162


Spec Office Buildings – not as commonGrowing number of successful projects in recent years

Multiple tenants with diverse loads and full height walls may be a problem depending on system design

If first costs are higher than conventional systems, it is important to developer for UFAD building to command higher rents



28


163


Churches, Theaters, Auditoriums True displacement if supplied under seats at low velocity

Trading Floors

Tall spacesBanks

In recent years, increased number of projectsLibraries

Schools

Court Houses

Institutional

Wrap-Up,Conclusions

2:05 – 2:15

165

Last Thoughts…

Significant energy savings possibleDepends strongly on climate

Depends on designing the systems correctly

More Research NeededLoad calc’s

Stratification

Underfloor plenum

Energy Simulation will be KeySlab, plenum, stratification

166

Underfloor Air Technology Websitewww.cbe.berkeley.edu/underfloorair

Objective:Develop and maintain website dedicated to providing a complete and unbiased description of underfloor air distribution technology

Audience:- engineers and architects- building owners- developers- CBE partners and clients- manufacturers and rep’s- facility managers- corporate real estate- researchers

167

Underfloor Air Technology Website

Key Features:

- simple graphical tools highlighting basic concepts

- technical overviews explaining process, benefits and limitations

- detailed summaries of research on UFAD and related technologies

- guidelines for applying the technology

- case studies of existing systems

168

Current Research by CBE

Design toolsWhole-building energy simulation program (EnergyPlus):Ongoing 3-year project sponsored by California Energy Commission (CEC), U.S. DOE, CBE, and York (completion in June 2006)

Cooling airflow design tool:New project sponsored by CEC and others (completion in Nov. 2006)

Field Studies -- Whole-building performance dataOngoing field study of Calif. State office building sponsored by Calif. State Dept. of General Services (completion in Dec. 2006)

Cost analysis toolOngoing 4-year project sponsored by U.S. GSA to develop first and life-cycle cost model comparing UFAD with OH systems (completion in Sept. 2006)



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169

Conclusions

Large and growing interest in underfloor air distribution

More information and experience is needed comparing UFAD to conventional overhead systems

Developments are underway addressing technology needs

Research on key fundamental issues

New and revised design guidelines and tools

Improved training of construction and operations personnel

Revised standards and codes as appropriate

Greater familiarity and understanding within building industry

Questions?

Fred [email protected]

CBE websitewww.cbe.berkeley.edu

Underfloor air technology website www.cbe.berkeley.edu/underfloorair

CBE occupant survey websitewww.cbesurvey.org

slide presentation from betterbricks/ashrae workshop

Documents