Window choice problem with new Canadian regulations
When I get my current house sold I will be building a 1240 sq ft, single-level house for me and my wife. It will be very close to Passivhaus and also close to Net Zero. I used to build energy efficient houses in Ireland prior to coming to Canada in 2007 and this proposed place will be built similar.
The problem I have is the introduction of new window regulations for BC. I attended a seminar last week in regards to this and, to cut it brief, as of this coming December any window and door fitted into a BC house will have to comply with NAFS 08 and the Canadian supplement. NAFS is supposed to give an overall standard for North America, except it doesn’t! The Canadian supplement will mean more extensive, and expensive, testing. In my eyes this may well prevent European manufacturers of high performing windows and doors selling into BC for Passivhaus construction.
Anyway, in my proposed house I may now have to accept a poorer performing window and pay more for the privilege. I am a certified energy advisor and have modeled the house with the Hot2000 software. This gives a heat loss of around 12000 Btus. However, Hot2000 is not particularly good at modeling windows, although this is supposed to be rectified when the updated version becomes available next year.
Can anyone please tell me just how much of a difference SHG makes between say 0.4 and 0.5 on a 4 ft x 3 ft triple-glazed window facing southwest? Is it reasonably substantial or not, or am I, maybe, making too much of the regulation change?
There is a lot of sun in the area that I will be building in, southeast BC.
Many thanks for any advice.
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Replies
Ray,
Q. "Can anyone please tell me just how much of a difference SHG makes between say 0.4 and 0.5 on a 4 ft x 3 ft triple-glazed window facing southwest?"
A. There are too possible ways to answer your question: roughly and precisely. The rough answer is, "Not much." The precise answer is, "You didn't give us enough information to answer the question."
The question can be answered precisely with PHPP software. However, we need to know the U-factors of the two options; I doubt if they are identical. We also need to know how much shading the window gets, and the type of roof overhang.
Finally, we need to know the total area of the south-facing glazing (as well as a great many other characteristics of the house) to determine whether the house is at risk of overheating (and would therefore benefit from glazing that has a lower SHGC) or whether the house has so little south-facing glazing that it makes sense to maximize the window's SHGC.
An easier approach than the PHPP spreadsheet may be to run a conventional Manual J load calc for the room in question or the entire home, room by room. Done properly (beware GIGO, Garbage In, Garbage Out), a load calc will account for all the issues Martin raised.
Thanks to you both for your answers.
Martin, I've attached a floor plan and other information regarding the location of the build. Specs for the house are as follows; insulated raft to R24 min, walls from outside to in will be hardyplank, 1x4 strapping for air gap, 3" Roxul Comfortboard, 1/2"ply, 2x6 to 9'high with R22 Roxul batts, Intello+ air/vapour barrier, 2x4 to 8' high for cable runs etc, after which R14 Roxul batts added. There will be a 1' void above the ceiling of 8' for hrv ducting. R70 blown cellulose in the attic. Roof is gable end to gable end.
European window quotes are giving an overall U value of 0.14 with solar heat gain of either 0.5 or 0.64. The actual glazed area is U value of either 0.08 or 0.10. I can get u values of 0.14 from Canadian manufacturers but the high SHG seems to be a bit more of a problem.
The windows will be' in-betweenies' and overhang to the side windows approx 2'6". Overhang to the rear windows will be determined after the first summer with blinds/awnings fitted as necessary. Unilux can supply shading as an option for their windows.
The front of the house faces north-east, glazing areas are N.East 12sq ft,S.east 40 sq ft, S.west 44 sq ft and N.west 12 sq ft.
As I said, I'm just somewhat angry at the choices of windows being somewhat restricted due to the Canadian supplement and the extra testing and pricing involved. It looks to me as if some of the European manufacturers will abandon the Canadian market due to this.
Many thanks for your help and advice again.
Ray,
It sounds like you are building an excellent house. Unfortunately, I don't have time to run your calculations for you. In most cases, owner/builders who don't have experience running energy modeling software hire an energy consultant (for example, a HERS rater) to run the software for them.
However, I stand by my earlier statement -- based on "pretty good house" principles -- that the difference between the two window choices is "not much."
For more information on this issue, see these two articles:
Study Shows That Expensive Windows Yield Meager Energy Returns
Energy Modeling Isn’t Very Accurate