Highly Insulating Windows Christian Kohler Windows and Daylighting Research Group Lawrence Berkeley National Laboratory June 11, 2009

Highly Insulating Windows

Christian Kohler

Windows and Daylighting Research Group

Lawrence Berkeley National Laboratory

June 11, 2009

Windows and Daylighting Group 10-15 researchers dedicated to windows research. Mostly DOE funded. Engaged with industry since 1976 State-of-the-art user facilities for testing and evaluation Software used by over 8,000 users worldwide

10-15 researchers dedicated to windows research. Mostly DOE funded.

Engaged with industry since 1976

State-of-the-art user facilities for testing and evaluation

Software used by over 8,000 users worldwide

Performance Indices Key performance indices U-factor Thermal resistance Units Btu/hr-ft2-F R-factor is inverse, U=0.2, R=1/0.2 = 5 hr-ft2-F/Btu SHGC Solar Gains Ranges from 0-1, higher means more solar gains VT Visible Transmittance Ranges from 0-1, higher means more daylight

Key performance indices

U-factor

Thermal resistance

Units Btu/hr-ft2-F

R-factor is inverse, U=0.2, R=1/0.2 = 5 hr-ft2-F/Btu

SHGC

Solar Gains

Ranges from 0-1, higher means more solar gains

VT

Visible Transmittance

Ranges from 0-1, higher means more daylight

Heat Transfer in Windows Conduction Radiation Conduction Convection Low-e coatings Special gas fills Multiple cavities Low conductance spacers Better frames

Whole window metrices Whole product vs center of glass Window components Framing (structural) Glazing (vision) Frame area can be 25% of total area NFRC and ENERGY STAR require whole product numbers

Whole product vs center of glass

Window components

Framing (structural)

Glazing (vision)

Frame area can be 25% of total area

NFRC and ENERGY STAR require whole product numbers

Highly Insulating Windows - range Whole window U-factor 0.10 0.20 0.30 0.50 0.40 No heat transfer Standard double-pane windows Typical ENERGY STAR windows Highly insulating windows 0.35 = Northern ENERGY STAR benchmark

Performance Goals Heating Climates: static high solar, hi-R (U=0.1 Btu/h-ft2-F) can meet ZEH goals

Heating Climates:

static high solar, hi-R (U=0.1 Btu/h-ft2-F) can meet ZEH goals

Benefits Areas near windows are often places of great temperature variation and discomfort Conventional practice to avoid discomfort is to provide perimeter heating near windows Perimeter heat may not be necessary with highly insulating windows Thermograms comparing a conventional dual-pane with a highly insulating window

Areas near windows are often places of great temperature variation and discomfort

Conventional practice to avoid discomfort is to provide perimeter heating near windows

Perimeter heat may not be necessary with highly insulating windows

LBNL / DOE Research Triple glazings Develop lower-cost, non-structural center layers Spacer interactions High Performance Frames Collaboration with European researchers Focus on air leakage 2 sealed gas gaps at different temperatures and pressures with standard glass, unit is thicker and heavier low-e thin glass or plastic held by spacer spacer low-e only 2 paths for gas loss

Triple glazings

Develop lower-cost, non-structural center layers

Spacer interactions

High Performance Frames

Collaboration with European researchers

Focus on air leakage

Highly Insulating Frames Mostly driven by PassivHaus Institute in Germany 5 Windows being tested and simulated in Norway and US Verify performance with US rating criteria

Mostly driven by PassivHaus Institute in Germany

5 Windows being tested and simulated in Norway and US

Verify performance with US rating criteria

Low-e storm windows Pyrolytic Low-e coating (hard coat) Does not degrade in non-sealed cavity Identical installation cost to clear storms

Pyrolytic Low-e coating (hard coat)

Does not degrade in non-sealed cavity

Identical installation cost to clear storms

Savings Whole house heating energy savings over a winter season in Chicago for new storms: Clear storm windows 8-18% Low-e storm windows 19-27% Estimated U-values: Clear storm windows: 0.49 Btu/h-ft2-F Low-e storm windows: 0.36 Btu/h-ft2-F

Whole house heating energy savings over a winter season in Chicago for new storms:

Clear storm windows 8-18%

Low-e storm windows 19-27%

Estimated U-values:

Clear storm windows: 0.49 Btu/h-ft2-F

Low-e storm windows: 0.36 Btu/h-ft2-F

Cost effectiveness – Low-e Storms Total Window Cost Annual Energy Savings Simple Payback (yrs) House 2- Low-E $1,738 $490 3.5 House 3- Clear $1,344 $111 12.1 House 4- Clear $2,661 $317 8.4 House 5- Low-E $1,738 $341 5.1

Thank You Christian Kohler, CJKohler@lbl.gov Windows and Daylighting Research Group Lawrence Berkeley National Lab