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Highly Insulating Windows


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Presentation by Christian Kohler, Lawrence Berkeley National Laboratory

On 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

  1. 1. <ul><li>Highly Insulating Windows </li></ul><ul><li>Christian Kohler </li></ul><ul><li>Windows and Daylighting Research Group </li></ul><ul><li>Lawrence Berkeley National Laboratory </li></ul><ul><li>June 11, 2009 </li></ul>
  2. 2. Windows and Daylighting Group <ul><li>10-15 researchers dedicated to windows research. Mostly DOE funded. </li></ul><ul><li>Engaged with industry since 1976 </li></ul><ul><li>State-of-the-art user facilities for testing and evaluation </li></ul><ul><li>Software used by over 8,000 users worldwide </li></ul>
  3. 3. Performance Indices <ul><li>Key performance indices </li></ul><ul><ul><li>U-factor </li></ul></ul><ul><ul><ul><li>Thermal resistance </li></ul></ul></ul><ul><ul><ul><li>Units Btu/hr-ft2-F </li></ul></ul></ul><ul><ul><ul><li>R-factor is inverse, U=0.2, R=1/0.2 = 5 hr-ft2-F/Btu </li></ul></ul></ul><ul><ul><li>SHGC </li></ul></ul><ul><ul><ul><li>Solar Gains </li></ul></ul></ul><ul><ul><ul><li>Ranges from 0-1, higher means more solar gains </li></ul></ul></ul><ul><ul><li>VT </li></ul></ul><ul><ul><ul><li>Visible Transmittance </li></ul></ul></ul><ul><ul><ul><li>Ranges from 0-1, higher means more daylight </li></ul></ul></ul>
  4. 4. Heat Transfer in Windows Conduction Radiation Conduction Convection Low-e coatings Special gas fills Multiple cavities Low conductance spacers Better frames
  5. 5. Whole window metrices <ul><li>Whole product vs center of glass </li></ul><ul><li>Window components </li></ul><ul><ul><li>Framing (structural) </li></ul></ul><ul><ul><li>Glazing (vision) </li></ul></ul><ul><li>Frame area can be 25% of total area </li></ul><ul><li>NFRC and ENERGY STAR require whole product numbers </li></ul>
  6. 6. 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
  7. 7. Performance Goals <ul><li>Heating Climates: </li></ul><ul><li>static high solar, hi-R (U=0.1 Btu/h-ft2-F) can meet ZEH goals </li></ul>
  8. 8. Benefits <ul><li>Areas near windows are often places of great temperature variation and discomfort </li></ul><ul><li>Conventional practice to avoid discomfort is to provide perimeter heating near windows </li></ul><ul><li>Perimeter heat may not be necessary with highly insulating windows </li></ul>Thermograms comparing a conventional dual-pane with a highly insulating window
  9. 9. LBNL / DOE Research <ul><li>Triple glazings </li></ul><ul><ul><ul><ul><li>Develop lower-cost, non-structural center layers </li></ul></ul></ul></ul><ul><li>Spacer interactions </li></ul><ul><li>High Performance Frames </li></ul><ul><ul><ul><ul><li>Collaboration with European researchers </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Focus on air leakage </li></ul></ul></ul></ul>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
  10. 10. Highly Insulating Frames <ul><li>Mostly driven by PassivHaus Institute in Germany </li></ul><ul><li>5 Windows being tested and simulated in Norway and US </li></ul><ul><li>Verify performance with US rating criteria </li></ul>
  11. 11. Low-e storm windows <ul><li>Pyrolytic Low-e coating (hard coat) </li></ul><ul><li>Does not degrade in non-sealed cavity </li></ul><ul><li>Identical installation cost to clear storms </li></ul>
  12. 12. Savings <ul><li>Whole house heating energy savings over a winter season in Chicago for new storms: </li></ul><ul><ul><li>Clear storm windows 8-18% </li></ul></ul><ul><ul><li>Low-e storm windows 19-27% </li></ul></ul><ul><li>Estimated U-values: </li></ul><ul><ul><li>Clear storm windows: 0.49 Btu/h-ft2-F </li></ul></ul><ul><ul><li>Low-e storm windows: 0.36 Btu/h-ft2-F </li></ul></ul>
  13. 13. 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
  14. 14. Thank You Christian Kohler, Windows and Daylighting Research Group Lawrence Berkeley National Lab