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GPG OUTBRIEF 25
Lightweight Quad-Pane Windows
If you missed our last webinar, on a Green Proving Ground (GPG) assessment of lightweight quad-pane windows, a recording of the webinar and presentation slides are now available.
Many thanks to all the presenters and to the participants for their thoughtful questions, some of which are answered below:
Q: Can the technology be integrated with blast-resistant or bullet-proof glass?
A: Yes. The quad-pane insulated glass unit (IGU) can be fabricated to meet bomb-blast requirements and ASTM F 2248-03 standards. The fiberglass frame is still undergoing blast-resistance testing. The glass can also be incorporated into other frame systems that are > 1 3/8". For bullet-proof glass, wider glass pockets (> 2.0") are needed.
Q: Because quad-pane windows are lighter and thinner than double-pane windows, are they as resistant to severe weather?
A: The two outer panes of glass are of standard thickness and surround two inner one-millimeter glass panes.The units should perform similarly in hail and other weather events. The quad-pane IGUs have not been hurricane-rated.
Q: Is there a concern with gas leakage?
A: This is always a concern with multi-pane glass units. Research indicates 1% leakage per year, therefore the insulating value should remain high throughout the windows' 20-year lifespan.
Q: How does the weight of thin quad-pane compare to that of a thin triple-pane?
A: The quad-pane with thin glass is about 15% heavier than the thin triple-pane and equivalent to a standard double-pane. The suspended film configuration is about one pound lighter per square foot than the thin-glass configuration.
Weight of thin-glass windows < 16 square feet:
• triple-pane – 3.7 lbs/sf
• quad-pane – 4.3 lbs/sf
Weight of thin-glass windows > 16 square feet:
• triple-pane – 5.3 lbs/sf
• quad-pane – 5.9 lbs/sf
Q: Can the solar heat gain coefficient (SHGC) be modified and what SHGC was used to calculate energy savings?
A: The windows come with two SHGC options optimized for hot and cold climates. Windows with a high SHGC collect solar heat more effectively and are more broadly recommended for cold climates. Windows with a low SHGC block heat gain more effectively and are better suited to hot climates. Modeling assumed a SHGC of 0.20 for climate zones 1A to 3C and 0.46 for climate zones 4A to 6A.
Q: Is there an improvement in resistance to fire penetration or an increase in sound protection?
A: Fire penetration is the same as a double-pane window because the primary barrier is the outer panes. There should be an increase in sound protection over a triple- or double-pane window, though this was not measured in the testbed evaluation.
Q: What is the long-term durability compared to standard IGUs?
A: The lifespan of a quad-pane window is similar to that of a standard IGU. The technology we tested comes with a 10-year warranty; the manufacturer claims a minimum 20-year lifespan.
Q: Are the windows commercially available? And, if so, in what sizes and for what applications?
A: The quad-pane windows evaluated in this assessment were provided by Alpen High-Performance Products. They are commercially available and manufactured in the United States. The integrated units with fiberglass frames are available in sizes as large as 50 square feet. The thin glass is also available without the fiberglass frame and can be used in curtain-wall applications. However, the fiberglass frame contributes to the improved thermal performance, so energy savings would not be as high.
Reference to any specific commercial product, process or service does not constitute or imply its endorsement, recommendation or favoring by the United States Government or any agency thereof.
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