renovating an existing home · exterior walls are 2x6 construction with 2 layers of 1” rigid foam...

Mary KrausAIA, LEED BD&C

Net Zero EnergyRenovating an Existing Home

KRAUS-FITCH ARCHITECTS, INC.Home – Community – Planet © Kraus-Fitch Architects, Inc. 2012

Summary

• What / why net zero?

• Steps for a net zero renovation

• Case study

• Other examples

• Conclusion

Net Zero Energy

•Net zero operational energy

•Net zero including embodied energy / lifecycle

•Ecological footprint

•Remember to look at the whole context!

What does it mean?

Why Net Zero Energy?

4 Examples:

• Renovation of small duplex home in Amherst

• Renovation of historic home in Northampton

• New home in Leverett

• New community in Berlin, MA

Steps for a Net Zero Home Renovation

1. Define your goals

2. Analyze existing conditions

3. Run energy modeling to evaluate different strategies

4. Identify solutions

5. Implement your chosen strategies

6. Evaluate performance and refine over time

A Note of Caution:

A house is a system, with many interrelated parts. Be sure to get expert advice before insulating, air sealing, etc., to avoid possible moisture and/or air quality problems.

My Home

What Was Our Starting Point?

Context: Cohousing, walk & bike commute

Small, energy-efficient home

Small, energy-efficient home

1. Net zero operational energy or net energy producing – heating, ventilation, hot water, electric plug loads

2. Learning: What would we do differently if building new?

Defining Our Goals

Utility Bills

Analyzing Existing Conditions

Specific electric loads


Energy audit: blower door test


Input for engineer

Modeling Energy Usage

Engineer’s modeling of existing conditions





Relative impact of different building components

Comparing different strategies


Comparing different strategies


•Air tightness: Good, but can be improved.

•Insulation levels: Already good, adding exterior foam would improve further but may not be best bang for buck.

•Windows: Double-glazed, low-e, need improvement.

Findings

• Ventilation: Exhaust-only ventilation has no heat recovery (and is ineffective)

• Heating system: Efficient, but fueled by non-renewable propane

• Hot water: Solar hot water system already in place, backed up with propane

• Electricity: Low usage, but can be improved (dehumidification of basement causing disproportionate use)

Findings

• Air leakage: 500 CFM 50 ( 0.2 air changes / hour)

• Insulation levels: R/24 walls w/ thermal break, R/34 roof

• Windows: Double-glazed, low-e (~R/3)

• Electric usage: 300 kwh/month

• Propane usage: 300 gal/year

Details

Consultant’s Recommendations

1. Targeted air sealing to reduce leakage ~15% EDIT2. High-grade interior storm windows3. Reduce electricity use from 300 to 200 kwh/month4. Replace exhaust-only ventilation with heat recovery

ventilation5. Replace gas boiler with minisplit heat pump6. Install solar electric: 5 kw of photovoltaics

Solution: One Way to Get to Zero

What We Did:

1. Targeted air sealing to reduce leakage ~15% - 20%2. Reduce electricity use (moderately)3. Replace exhaust-only ventilation with heat recovery

ventilation4. Replace gas boiler with minisplit heat pump5. Super insulated hot water tank6. Install solar electric: 5.9 kw of photovoltaics

Solution: One Way to Get to Zero

Setting up the blower door

Strategy 1 – Air Sealing

Feeling for leakage


Removing and sealing around cathedral ceiling penetrations


Stairwell light in cathedral ceiling


Caulking perimeter of second floor


Some tight areas – The joy of air sealing!


Interior door connecting to ceiling - an unlikely air path?


Leaks at range hood chase


A closeup. (Duct needs sealing, too!)


Weatherstripping exterior doors


Old refrigerator: 648 kwh/yr.

Replace existing refrigerator with Energy Star model

New refrigerator: 383 kwh/yr.

Strategy 2 – Reduce electric usage

Electricity Usage: Already using compact fluorescent bulbs & fixtures. Next step is to replace with LEDs.


Efficient appliances and conserving behaviors


Replace exhaust-only with heat recovery ventilation

Graphic: Popular Mechanics

Strategy 3 – Heat recovery ventilation

Replace exhaust-only with heat recovery ventilation

Strategy 3 – Heat recovery ventilation

Driven by PV; eliminates carbon fuel

Strategy 4 – Minisplit heat pump

Interior unit (above)

Exterior units (left)

Increases occupant comfort

Strategy 4 – Minisplit heat pump

Strategy 5

• Superinsulated electric water tank to back up solar hot water

Strategy 6 – Photovoltaics

• PV-ready roof

• 5.9 kW system powers both electric loads & heat pump

• Grid-tied

Results – Air Sealing

• Initial air leakage: 500 CFM 50 ( 0.2 air changes / hour)•Reduction in air leakage: 110 CFM 50

~20% improvement•BUT- Subsequent test after heating system renovations: 640 CFM 50 HMM – WHAT HAPPENED???

Results – Energy DataMonth BEFORE: BEFORE AFTER Difference

Electric Propane Propane TOTAL TOTALkwh gal kwh equiv kwh kwh kwh

Dec 391 55 1485 1876 1090 -786

Jan 357 53.2 1436.4 1793.4 1347 -446.4

Feb 358 74.3 2006.1 2364.1 1053 -1311.1

Mar 346 52.3 1412.1 1758.1 751 -1007.1

Apr 313 33 891 1204 441 -763

May 218 8.3 224.1 442.1 247 -195.1

Jun 222 8.3 224.1 446.1 185 -261.1

]ul 367 8.3 224.1 591.1 187 -404.1

Aug 292 8.3 224.1 516.1 197 -319.1

Sep 253 0 0 253 166 -87

Oct 241 8.3 224.1 465.1 305 -160.1Nov 390 24.8 669.6 1059.6 623 -436.6

Totals 3748 334 9021 12769 6592 -6176.7

Monthly averages 312 28 752 1064 549 -515

Results – Energy Data

Date"4" on Net Meter - Usage from Grid

"10" on net meter - PV to Grid PV production

Net Usage from Grid (#4 - #10)

Total Electric Usage (Grid + PV)

(date of reading) reading

usage for period reading

for period reading

for period

net usage for period

net usage to date for period

12/3/2010 1534start data 1138start data 1354start data

1/1/2011 2428 894 1354 216 1766 412 678 678 10902/1/2011 3557 1129 1545 191 2175 409 938 1616 13473/4/2011 4393 836 1977 432 2824 649 404 2020 10534/4/2011 4961 568 2450 473 3480 656 95 2115 7515/3/2011 5288 327 2903 453 4047 567 -126 1989 4416/4/2011 5456 168 3478 575 4701 654 -407 1582 2477/5/2011 5576 120 4129 651 5417 716 -531 1051 1858/3/2011 5665 89 4783 654 6169 752 -565 486 1879/4/2011 5778 113 5423 640 6893 724 -527 -41 197

10/1/2011 5886 108 5865 442 7393 500 -334 -375 16611/5/2011 6129 243 6319 454 7909 516 -211 -586 30512/3/2011 6650 521 6685 366 8377 468 155 -431 623Totals 5116 5547 7023 -431 6592

Note: A 150-200 SF addition would cost the same.

Results – CostCost of RenovationItem Cost Rebates Tax Credit

(Fed)Tax Credit (MA)

PV $48,6010.00 $(10,500.00) $(14,580.30) $(1,000.00)

SDHW changes $3,818.40

Electric assoc. w/ PV & SDHW $750.00

Heat pumps $6,619.00 $(1,000.00)

HRV $3,125.00

Sale of old boiler $(2,300.00)

Misc carpentry $545.00

Gas disconnect $45.00

New refrigerator $736.40

Air sealing $135.00

Weatherstripping (by owner) $13.70

Total Cost $62,088.50

Totals: Rebates & Tax Credits $(11,500.00) $14,580.30) $(1,000.00)

Net Total Cost $35,008.20

Years to Payback: 9

Results – Cost

Payback for Renovation

kWh or gal Cost per unit Savings/year

Electricity Savings 3748 $0.17 $618.42

Propane Savings 334 $2.70 $901.80

SRECs $2,357.76

Total Revenues $3,877.98

Next Steps:

1. High-grade interior storm windows2. Further reduction to electrical usage

1. LED2. Induction Range

3. More air sealing4. Improved monitoring

Next Steps

1 – Interior Storm Windows

Power strip to control “vampire loads”

Graphic: Energy Federation, Inc.

2 – Further reduce electric usage

Change over to LED light bulbs


Graphics (l-r): GE, Switch, Philips

Change over to induction range

Graphics: GE


3 – More Air Sealing

4 – Improved Monitoring

http://www.brultech.comECM-1240 Home Monitor

A Review

Starting Point

• Small, energy-efficient duplex home• Built in1994 for approximately $56/SF • Compact fluorescent lighting • Exhaust-only ventilation• Spacious feeling in a compact floor plan• Solar hot water already installed

A Review

Strategies

• Careful modeling to determine strategies• Targeted air sealing• Reducing plug loads (old refrigerator and

dehumidifier were energy hogs)• New air-source heat pumps to replace

propane boiler• New HRV to replace exhaust-only ventilation• Super-insulated electric water tank as new

backup for solar hot water• 5.9 kw PV array to cover all energy uses

A Review

Results

• Exceeded zero net: net energy producing by 430 kwh/year

• Total energy use reduced by 23%• New refrigerator alone saved ~40 kwh/month• Original tight construction (improved, then undermined)• Basement dehumidification using heat pump is

more efficient & effective• Comfort improved (pleasant heating system)

A Review

Costs:

• Total cost before rebates: $62,100• Cost after rebates & tax credits: $35,000• Yearly revenue from SRECs: $2,400• Yearly cost savings on utilities: $1,500• Payback: 9 years

A Review

Next Steps

• Interior storm windows• More air sealing• LED lighting• Magnetic induction range • Further reduction in plug loads• Improved monitoring

Northampton Residence – Gut Renovation

Before & After

Before & After

Complete Gut Renovation

Note: Gas cooktop & open fireplace door not recommended

Interior

Note thick walls

Interior

Interior

Ground-source heat pump fueled by PVs

Mechanical System

Attempting net zero for heating, cooling, hot water & electric loads; appear to be at 50%+.

New Leverett Home

Interior

Interior

Ground-source heat pump fueled by PVs

Mechanical System

New Community in Berlin, MA

Simple massing simplifies air sealing and insulation details

14” TJI roof rafters provide for 14” of dense packed cellulose insulation

Penetrations for bathroom, kitchen and plumbing vents need to be detailed to ensure air tightness

Exterior walls are 2x6 construction with 2 layers of 1” rigid foam on the outside, further enhanced with a rain screen detail under the siding.

Exterior sheathing is the air barrier –so it is taped at all seams and sealed at all edges and rough openings.

Insulated rim joists and window headers

Triple glazed windows are detailed carefully for air tightness with pre-fabricated corner flashing.

Fully insulated slab and slab edge

Wall Section

OSB sheathing is taped for air sealing prior to the installation of rigid exterior insulation, strapping (right) and exterior siding.

Detailing

What makes a tight, well-insulated building envelope?(Some general information)

Double stud wall for thicker insulation

Wall Construction

Triple-glazed window w/insulated fiberglass frame & sash

High-Performance Windows

And don’t forget air sealing!

Comparison of a 1,400 SF home (2,700 SF including conditioned basement & attic) in New England with four levels of insulation & air-tightness:

Base case (better than Energy Star)• R-16 walls, R-35 roof, R-3 windows, R-5 foundation walls, 0.30 CFM50 infiltration39,000 BTU / hour design heat loss

• Annual heat load of 71 million BTU • ~640 gallons of fuel at 80% efficiency.

Well insulated & very tight (equal to that at Mosaic Commons Cohousing)• R-31 walls, R-48 roof, R-5 windows, R-10 foundation walls, 0.18 CFM50 infiltration• 24,600 BTU / hour design heat loss • Annual heat load of 44 million BTU • ~400 gallons of fuel at 80% efficiency.• 62% of base case

Super insulation & even tighter• R-40 walls, R-55 roof, R-5 windows, R-30 foundation walls, 0.10 CFM50 infiltration15,500 BTU / hour design heat loss

• Annual heat load of 20 million BTU • ~185 gallons of fuel at 80% efficiency.• 29% of base case

German “passivhaus”• Estimated at approximately 15% of base case

Calculations provided by Marc Rosenbaum, Energysmiths

Insulation & Air Tightness Levels

Closing Thoughts

What does a hero look like?

(You know, the kind of person who is helping to “save the world” . . .)

YOU

Whether you go all the way to net zero, or substantially improve your home’s performance, whatever you do will reduce your footprint and help us all learn more.

The strategies you select will depend upon your home and your personal goals.

Net Zero?

It’s not just the house, it’s how you live there!

Remember

Technical Credits:Mary KrausLaura Fitch

Photo Credits:Mike AprilJanice DoyamaJohn FabelLaura FitchMary KrausJen LuckRebecca Reid

© Kraus-Fitch Architects, Inc. 2006

KRAUS-FITCH ARCHITECTS, INC.

Home – Community – Planet

Mary Kraus, AIA, [email protected]

110 Pulpit Hill Road

Amherst, MA 01002

413-549-5799

www.krausfitch.com

Center for Ecological Technology (CET), energy audit & air sealing, (413) 586-7350, www.cetonline.org

Solar Store of Greenfield, (413) 772-3122, http://solarstoreofgreenfield.com/

Energy Federation, Inc., www.efi.org

North Quabbin Energy, “Winserts” interior storm windows, www.northquabbinenergy.org/wordpress/

Northeast Solar Design Associates (PV), www.nesolardesign.com

Kraus-Fitch Architects, Inc., (413) 549-5799,

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