Low-e Storm Windows

Adam HadleyRegional Technical Forum

July 21, 2015

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Overview

Today, we are seeking RTF approval of a new Proven UES measure for Low-e Storm Windows

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Measure OverviewMeasure Developers BPA, PNNL, RTF

CAT Review Adam Hadley

Tech Sub-Com Review No

R&E Sub-Com Review No

Notes • This is a new measure for the RTF

• Low-e coating on storm windows have been commercially available since 2009 (PNNL)• Low-e pyrolytic coating is a hard ceramic coating (long-lasting,

durable)• Available at big-box home improvement stores

• Installations are permanent• Both Interior and Exterior Storm Windows Qualify• Often a DIY project• Field studies by DOE have shown significant savings

See PNNL Video for more details (Link)

From: Cort, K.A. “Low-E Storm Windows: Market Assessment and Pathways to Market Transformation.” PNNL. June 2013.

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Measure Specifications

• Storm windows must use glazing materials with an emissivity less than or equal to 0.22 and a solar transmittance greater than 0.55, as listed in the International Glazing Database (IGDB) managed by Lawrence Berkeley National Laboratory and measured in accordance with NFRC 300-14,NFRC 301-14 and NFRC 302-10.

• Storm windows must be of the same opening type as the existing prime window.• Storm window shall be permanently installed.• Storm windows shall be oriented with the low-e coating facing toward the interior of the house.• For installations with metal framed prime windows the storm window’s frame shall not be in direct

contact with the prime window frame.

Measure Identifiers• Existing Window Type

– Metal Frame, Single-pane– Wood (non-Metal) Frame, Single-pane– Metal Frame, Double-pane– Wood Frame, Double-pane– NFRC-rated U-0.30

• Heating Zones (1, 2, and 3)• Heating System Type

– Electric FAF– Electric Zonal or DHP– Heat Pump

This presentation gives results for these measures but CAT does not recommend their approval because determination of the baseline U-factor would likely require research (which is probably not worth the effort since the measures are not cost-effective).

Energy Savings• Same methodology as other weatherization (and windows)

measures– Calibrated SEEM runs– Measure interaction accounted for as per guidelines

• Note: No air leakage reduction assumed in savings calculations• U-factors and SHGC’s generated using NFRC window modeling

software (documented in PNNL Report)1

1Cort, KA; SH Widder, TD Culp. 2015. “Thermal and Optical Properties of Low-E Storm Windows and Panels.” PNNL-24444.2Assumes no low-e coating, but in practice, there would be windows by this definition with low-e coating.3U-Factor and SHGC for low-e storm window + NFRC-rated U-0.30 window based on a regression of the other data in the table.

Glazing Frame TypeMetal 1.09 0.41 0.66 0.52Wood 0.88 0.35 0.61 0.50Metal 0.69 0.33 0.63 0.48Wood 0.49 0.27 0.59 0.46

0.30 0.18 0.30 0.24

Baseline SHGC

SHGC with Low-e Storm

Single

Double

NFRC-rated u-0.30

Window Type Baseline U-Factor

U-Factor With Low-e Storm

3 3

2

Note: Wood Frame = non-metal frame

Note: Wood Frame = non-metal frame

Note: Wood Frame = non-metal frame

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Energy Savings: Other studies

• SEEM results are generally consistent with results from field studies for window types studied

Study N Heating System

Air Leakage Reduction

Atlanta 10 Gas furnace (9), FAF (1) 17%

Chicago 4 (1)Gas furnace (2) or boiler

(2)7%

Philadelphia 2 (2) Central gas 10%

PNNL Lab Homes 1 FAF 0%

(1) Six homes in study, but 2 had clear storms(2) Featured 2 multifamily buildings with a total of 101 units

0

5

10

15

20

25

30

35

40

SEEM, FAF,HZ1

SEEM,Zonal, HZ1

SEEM, HP,HZ1

Atlantastudy

SEEM, FAF,HZ2

SEEM,Zonal, HZ2

SEEM, HP,HZ2

ChicagoStudy

SEEM, FAF,HZ3

SEEM,Zonal, HZ3

SEEM, HP,HZ3

Hea

ting

Ener

gy S

avin

gs (%

)

Wood Frame, Single GlazedHZ1 HZ2 HZ3

0

5

10

15

20

25

30

35

SEEM, FAF,HZ1

SEEM, Zonal,HZ1

SEEM, HP,HZ1

Philidelphia SEEM, FAF,HZ2

SEEM, Zonal,HZ2

SEEM, HP,HZ2

SEEM, FAF,HZ3

SEEM, Zonal,HZ3

SEEM, HP,HZ3

Hea

ting

Ene

rgy

Savi

ngs

(%)

Metal Frame, Single GlazedHZ1 HZ2 HZ3

0

5

10

15

20

25

SEEM, FAF,HZ1

SEEM, Zonal,HZ1

SEEM, HP,HZ1

PNNL LabHomes

SEEM, FAF,HZ2

SEEM, Zonal,HZ2

SEEM, HP,HZ2

SEEM, FAF,HZ3

SEEM, Zonal,HZ3

SEEM, HP,HZ3

Hea

ting

Ener

gy S

avin

gs (%

)

Metal Frame, Double GlazedHZ1 HZ2 HZ3

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Measure Life• 20 years

– PNNL estimate, supported by • The 20 year warranty provided by the two leading manufacturers • A follow–up evaluation of 5 homes used in a field study in a low-income

neighborhood in Chicago, 10 years after installation 96 of 106 storm windows were present and in good condition.

– For details, see Culp, Thomas D. memo to Katie Cort. “Low-E storm window persistence in Chicago case study homes.” January 27, 2015.

• Note: The following measure specification is intended to help maintain measure life by reducing the chances of removal (and no subsequent re-installation) by the current or future occupant– “Storm windows must be of the same opening type as the existing

prime window.”

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Energy Savings: Staff Highlighted Area (1)• Issue: The energy savings calculation assumes the storm

windows are effective 100% of the year. However, storm windows could be left open (when the prime window is shut), almost eliminating savings in those instances

• Question: Should the RTF adjust for this?– Options:

• Yes: Include an adjustment factor in the savings estimate to account for storm windows not used correctly through the year

– Adjust savings by factor of 93/96 based on: Evaluation in Chicago found that 3 of 96 storm windows (that were still present and in good condition) were not fully closed in the middle of winter.

• Yes: Add an item in delivery verification to check whether the storm window is installed (closed where prime window is closed) during the heating season

– Where storm is open but prime window is closed, impact evaluation contractor would make an adjustment to the program savings

• No: Based on energy savings comparison with field studies (previous slide), assume issue is not significantStaff Recommendation

(Note: savings in this presentation do not reflect this adjustment)

Energy Savings: Staff Highlighted Area (2)• Issue: Cooling savings are -2% to 6% of heating savings• Question: Why are cooling savings negative? Should they be

included?– Background

• Field study results were highly variable and sometimes negative• Ben Larson confirmed

– SEEM shows reduced cooling load with decreased SHGC» Expected

– SEEM can show increased cooling load with decreased U-factor» Uh Oh, not expected! Why: House loses heat to the exterior (internal gains)

slower so more mechanical cooling is needed (this happens during mild conditions, which happens a lot in the PNW)

– Staff Recommendation• Remove cooling savings from the measure

– They are insignificant and unreliable– Model assumes a closed house; people open windows during the cooling season– Note savings in this presentation include cooling savings

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Energy Savings: Staff Highlighted Area (3)

• Issue: Savings do not currently reflect a reduction in whole-house infiltration rate but field studies all showed reductions

• Question: Should infiltration reduction be included in the analysis and if so, what value should be used?– Staff Recommendation

• Include an infiltration reduction of 10%– Roughly based on known field studies which show 7%, 10%, and 17%

average reductions

• “Back of the Envelope” savings estimate (using the existing UES values for infiltration reduction): Savings would increase over those shown here by 2%-10% in HZ 1

• Note: Savings in this presentation do not include infiltration reduction

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Measure Cost (2014$’s)

• Not a lot of data available for installation costs– Primary staff highlighted area is staff’s proposal for

inclusion of costs for DIY installations• Section 4.1.4 of Cost Guidelines says, “Labor should not

include installation labor provided by residential end users”• Staff disagrees with this in principle and proposes a DIY cost

of ½ of a professional install

Low-e Storm Window Costs Value (2014$'s) SourceMaterial Costs (per sq.ft.) $7.50 PNNL (see memo)Professional Installation Costs (per window) $60 PNNL (Wx installer informal survey)DIY Installation Rate 80% PNNL (via manufacturer interview)DIY Instllation Cost (per window) $30 Assumed as 1/2 professional installAverage window size (sq.ft.) 13.5 Analyst assumption (3 x 4.5)Average installation cost (per sq.ft.) $2.67 CalculatedTotal Installed Cost (per sq.ft.) $10.17 Calculated

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Note: Wood Frame = non-metal frame

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Note: Wood Frame = non-metal frame

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Note: Wood Frame = non-metal frame

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Proposed Motion

“I _________ move the RTF approve the measure specification, savings*, cost, and measure life for the Residential Low-e Storm Windows UES measures (except Wood frame, Double-Pane and NFRC-rated 0.30 u-factor applications) and

• Set the status to Active• Set the category to Proven• Set the sunset date to September 2019.”

*Savings methodology and inputs are being approved here. Savings values will change after removing the cooling savings, adding infiltration reduction, and making the 93/96 adjustment as discussed today; staff will bring back the final results in a Management Update presentation.

Additional Information on Low-E Storm Window Measure

SH Widder, PNNL

Effect of Mounting Method for Metal Frame Windows

• ~10% increase in U-Factor if metal storm window is mounted directly on metal prime window

Source: Cort, KA; SH Widder, TD Culp. 2015. “Thermal and Optical Properties of Low-E Storm Windows and Panels.” PNNL-24444.

Assumed U-Factor based on thermally

broken installation

Installation Info for Low-E Storm Windows

• BASC– Exterior:

https://basc.pnnl.gov/resource-guides/low-e-exterior-storm-windows

– Interior: https://basc.pnnl.gov/resource-guides/low-e-permanent-interior-storm-windows

• Manufacturer Websites– e.g. Larson:

http://www.larsondoors.com/storm_windows/how_to_install_instructions/

International Glazing Database (IGDB)

• The IGDB is a database of measured optical data for glazing products. – Maintained/QA’d by LBNL on behalf of DOE for use in NFRC rating of

fenestration products• NFRC-qualified products subject to periodic verification testing and noted

with a (#) symbol in the database

– Manufacturers of glazing products submit data collected from a certified laboratory to LBNL for review and inclusion in the database

• Data collected in accordance with NFRC 300 (solar optical properties), 301 (IR properties), and 302 (reporting).

• Submitted data is subject to review by LBNL and a peer-review by other manufacturers.

– Glazing samples are also retained for later reconfirmation or challenges of the listed properties.

• Major manufacturers of low-e storm windows use glazing with similar optical properties

• Other, smaller manufacturers of low-e storm windows include ProVia, Allied Window, Harvey Building Products, Thermolite Windows– Not sure what type of glazing they use

Optical Properties of Low-E Storm Windows

Manufacturer Typical Products Glazing Emissivity1 Solar Transmittance1

LarsonExterior and interior clear and low-e storm windows and doors

AGC Comfort Select 0.148 0.689

QuantaExterior and interior clear and low-e storm windows

Pilkington Energy Advantage 0.164 0.748

Pilkington Solar-E 0.166 0.419

AGC Comfort Select 0.148 0.689

1 As listed in the IGDB, v.41

Solar Heat Gain• Both low solar heat gain and high solar heat gain

low-e storm windows available– Low solar gain windows have same emissivity, but

~20-50% lower SHGC

• Low solar heat gain low-e storm windows will impact savings could impact savings by ~50%– Will vary based on house size, climate, prime window

sq.ft. and orientation, low-e window optical properties, etc

Air Leakage• Air leakage is extremely variable

(studies report 0-50% infiltration reduction)

• Not well correlated to savingsbased on field studies

• RESFEN1 modeling suggests that air infiltration may account for approximately 23%of total HVAC energy savings

1RESFEN is a residential energy modeling tool maintained by LBNL to help consumers and builders pick the most energy-efficient and cost-effective window for a given application. See http://windows.lbl.gov/software/resfen/resfen.html

U-Factor Validation• SEEM U-factor assumptions based on NFRC

modeling using WINDOWS/THERM (see PNNL Report)1

– Validated based on testing in LBNL’s MoWiTT thermal chamber test facility based on measured heat flux and correcting for air infiltration2

1Cort, KA; SH Widder, TD Culp. 2015. “Thermal and Optical Properties of Low-E Storm Windows and Panels.” PNNL-24444.2Klems, JH. 2002. Measured Performance of Storm Windows. Lawrence Berkeley National Lab.

Attachment Energy Rating Council (AERC)

• Consortium effort led by Window Covering Manufactures Association (managed by DOE)

• During the next 4 years AERC activities include:– Prioritize product types and performance indices (storm

windows are slated to be first product under evaluation)– Characterize the key material properties of window

attachment products (e.g., transmittance, reflectance, and emissivity)

– Conduct product performance simulations and evaluate procedures to used to rate window attachments

Launched in 2015, an independent rating, certification, labeling and performance verification program for fenestration attachments sponsored by DOE.