Okay, it took us a few weeks but we found a total of 3 (!) window companies which make good enough insulated windows to be used in a Passive House. Two of them are in Canada and only one in the US.
This is the list of the finalists:
What they have in common is that they their frames all all made out of fiberglass, which makes them a lot stiffer than vinyl and the cavities can be insulated with foam. Stiffness is important for air-tightness.
All 3 window options come with a range of glazing options but so far only Thermotec provides all the necessary performance data for evaluating them in the Passive House Planning Package (the Excel-based modeling program for Passive Houses).
The PHPP asks for separate U-values for the frame and the glass, and SHGC (Solar Heat Gain Coefficient) for the glass alone, but the NFRC (National Fenestration Rating Council) is testing the complete window. While this is a somewhat understandable simplification (the space on standard window decals is limited), it is also not accurate enough for Passive House calculations because the frame-to-glass ratio changes with the window dimension and proportion.After days of harassing sales people at SeriousWindows and Fibertec, without any success in getting glass and frame data, we eventually did some improvisations…
assumption #1: As the U-values for a fiberglass frame and a triple gas-filled glass pane are not too different, we used the same U-value for both (insert loud outcry by any well-informed Passive House consultant here…)
assumption #2: Because the NFRC test size for a casement window is 600×1500mm and the frame thickness of the window is known, and assuming that the frames don’t contribute to solar gain, it’s possible to calculate the SHGC for the glass alone. In the case of the SeriousWindows glass 9 the SHGC overall was .33 which resulted in a .49 for the glass.
Using these numbers in the PHPP showed that the SW 925 series with glass #9 would work, not as well as Thermotec, but we have to consider the quotes we got for the 12 windows we need for 21 Greenpoint Ave:
- Thermotec: best performing window, best company know-how, no problem with oversized windows. quote: $12,688 (delivery excluded)
- SeriousWindows: smart light weight glass, short delivery time. quote: $8,950 (delivery included)
- Fibertec: slow response at first but now all good, limited in size due to weight of triple pane glass. quote: $9,452 (delivery included)
Update: We want to avoid importing windows from Europe but we found solid wood windows with insulated aluminum cladding from France. The company has a sales rep at the west coast and we asked them for a quote. Bieber Windows US Website
12/12/2009 We received the quote: 12 pcs casement windows 32″x72″ inswing: $37,647 plus $6,000 for the shipping (!)
note: 12 weeks to deliver windows which are shipped from overseas
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To read more about Passive House windows, check out this article from GreenBuildingAdvisor:
http://www.greenbuildingadvisor.com/blogs/dept/musings/passivhaus-windows
Great! Thank you.
assumption #1: As the U-values for a fiberglass frame and a triple gas-filled glass pane are not too different, we used the same U-value for both
I don’t claim to be a consultant or an expert but if the U-values of the frame and the glass were the same, why would PHPP bother accounting for them separately? The glass performs significantly better than the frame in every PH window I’ve looked at.
assumption #2: Because the NFRC test size for a casement window is 600×1500mm and the frame thickness of the window is known, and assuming that the frames don’t contribute to solar gain, it’s possible to calculate the SHGC for the glass alone.
Not too bad an assumption, I think, but the out-of-plane depth of the frame can affect the amount of shading.
Fascinating cost info, even for a European!
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