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Presentation by Christian Kohler, Lawrence Berkeley National LaboratoryOn Thursday June 11th, the Alliance to Save Energy hosted a webinar for Alliance Associates and others interested in opportunities for window energy efficiency. Moderated by the Alliance’s Vice President for Programs Jeff Harris, speakers representing research, industry and low-income weatherization highlighted options that can minimize window heat loss far beyond common practice. The focus was on high-end R-5 window technologies, but lower-cost products, such as low-E storm windows, and the specific needs of low-income weatherization programs were also discussed. The five presenters’ different perspectives converged in the message that there is a great need for more energy-efficient windows and that advanced technologies and their integration in incentive and weatherization programs can bring far greater savings within reach.
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Highly Insulating Windows
Christian KohlerWindows and Daylighting Research Group
Lawrence Berkeley National Laboratory
June 11, 2009
Windows and Daylighting GroupWindows 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
Performance IndicesPerformance 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
Heat Transfer in WindowsHeat Transfer in Windows
Conduction
Radiation
Conduction
Convection
Low-e coatings
Special gas fillsMultiple cavities
Low conductance spacersBetter frames
Whole window metricesWhole window metrices
• Whole product vs center of glass
• Window components—Framing (structural)—Glazing (vision)
• Frame area can be 25% of totalarea
• NFRC and ENERGY STAR require whole product numbers
Highly Insulating Windows - rangeHighly Insulating Windows - range
Whole window U-factor
0.10 0.20 0.30 0.500.40
No heat transfer
Standard double-pane windows
Typical ENERGY STAR
windows
Highly insulating windows
0.35 = Northern ENERGY STAR
benchmark
Performance GoalsPerformance Goals
Heating Climates: static high solar, hi-R (U=0.1 Btu/h-ft2-F) can meet ZEH goals
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
70
75
80
85
90
95
100
105
110
115
120
125
130
135
140
145
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
SH G C
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
U-f
act
or
Minneapolis, MN - Com bined Annual Heating and Cooling Energy (MBtu)
w indow s use energy
w indow s provide energy
Co
mb
ine
d A
nn
ua
l He
atin
g a
nd
Co
olin
g E
ne
rgy
(MB
tu)
doub le clear
low ga in low -e A r double ,h igh ga in low -e A r double
sing le clear
low ga in low -e A r trip le
target perform ance reg ion
typ ica l Energy S tar
m oderate ga in low -e K r trip le (acrylic center layer)
BenefitsBenefits
• 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
LBNL / DOE ResearchLBNL / 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
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
Low-e storm windowsLow-e storm windows
• Pyrolytic Low-e coating (hard coat)
• Does not degrade in non-sealed cavity
• Identical installation cost to clear storms
SavingsSavings
• 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 StormsCost 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, [email protected]
Windows and Daylighting Research Group
Lawrence Berkeley National Lab
