Window shading in a cool climate - is it needed?
I'm designing a small up/down duplex in a mountain climate with cold winters and cool summers. Do I really need or want window shading overhangs with a relatively high south glazing ratio (13%)?
Today is a fine June day with weather that is not at all out of the ordinary for the area. Today's high is about 10C. The indoor temperature is 15C. A little extra solar heat gain would be quite desirable now, not to mention in March, April, May, September and October. Since solar shading is the same in mid-August as mid-April, I'm pretty hesitant to block the solar gain that I want in April in order to stay a little cooler in August. HOT2000 is definitely indicating that I will need more heat if I block a good portion of the solar heat gain in March and April.
I'm assuming that I can control overheating by just opening a window or in extreme cases opening windows and running bathroom and kitchen exhausts, plus the HRV in exhaust mode. It is probably only hot enough that I would normally consider closing windows during the day for one or two weeks per year. Humidity is low, so not a concern.
Up/down duplex, 800sqft interior per unit
13% unshaded S windows with high SHGC
4% unshaded E&W windows with low SHGC
250 sq ft of 2.75" Gypcrete per unit as thermal mass, plus some doubled drywall
R44 walls, R80 ceiling, R40 floor over unheated basement
50N in SE British Columbia, 4400 HDD (Celsius)
Can provide HOT2000 modelling details if it helps
My plan is to use a small, high roof overhang on the S side for the top floor providing minimal shading and no shading on the bottom floor. If those 1-2 weeks of hot weather per year are just unbearable, I'd consider adding shading in the future. Most guidelines would indicate I'm headed in a bad direction, but I'm not so sure they apply to my specific climate. I know that builders on the nearby Canadian prairie use significant shading in a similar heating climate, but their summers are much hotter than mine.
I have read with interest A Contrarian View of Passive Solar Design, but I'm designing with far less solar mass and without active heat transfer techniques (and I'm leary of any techniques running air through slabs). I'm also not a big fan of adjustable awnings.
Does anyone know of other examples of this working? Am I crazy to consider this?
Posted Jun 17, 2014 2:55 PM ET
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