Choosing Windows for Cold Climate
Picking Windows for Cold Canadian Climate – Energy Rating/U Factor/Solar Gain
I’m at the stage of picking windows for my project and I’m trying to wade through the choices. The main criteria is to meet the Canada Greener Homes Initiative criteria (https://natural-resources.canada.ca/energy-efficiency/energy-star-canada/about/participant-resources/technical-specifications/windows-doors-and-skylights-energy-starr-canada-proposed-technical-specification-draf/20950)
However, I’m struggling to pick between window options which focus on the Canadian Energy Rating (CSA A440.2 Standard) and simply the better (lower) U Factor.
Basically, how important is the solar gain component in my climate (7A)?
For example one of windows quoted has an Energy Rating of 35 which meets the grant criteria, but the U Factor is only 1.65 (W/m² – K) which is significantly above the 1.22 required for the grant (if not using ER). SHCG is 0.54.
Some people including some manufactures say that the ER system is a poor choice. (See: https://magicwindow.ca/blog/the-window-energy-rating-is-flawed-heres-why/) But then again I can read here that maybe the higher SHGC is actually beneficial for my winter climate. (See: https://www.greenbuildingadvisor.com/article/high-solar-gain-glazing)
Any pointers for climate 7A where we regularly see +40C to -40C?
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Replies
Insulated shutters would make the choice of glass largely irrelevant.
While I agree they would, they won't be used on this project.
Do you have any examples of insulated shutters?
Here’s a method from a builder in Fairbanks, Alaska. He built insulated shutters out of framing lumber and rigid foam. The parts cost about $500 for each shutter. There’s a helpful construction drawing of the assembly to see what he did. It's pretty slick.
CDNReno,
You may find these useful:
https://www.greenbuildingadvisor.com/article/buying-windows
https://www.greenbuildingadvisor.com/article/wanted-windows-for-a-northern-retrofit
https://www.greenbuildingadvisor.com/article/a-beginners-guide-to-high-performance-windows
We are looking at using roller shutters for some large southern windows that won't receive shading otherwise. Unfortunately, I haven't seen these very commonly in the US. If you are ordering European windows, it's an easy add. Manually operated or electric both available. I'm not sure if the electric ones are rated for standard North American 120v or only 220v that Europe uses.
https://www.windows24.com/roller-shutters/top-mounted.php
With that said, even in the cold, you don't want to overdo the solar gain. You can calculate the heat gain from the windows and compare to the Manual J result for that room. And remember that a bright sunny day will probably be a bit warmer than your design temp.
It really depends on the project details. Here in climate zone 6 I often find that using high-SHGC windows on all facades uses the least amount of energy over the course of the year compared to using low-SHGC windows on some facades, but the high-SHGC windows often lead to the need for more air conditioning in the warm months. If you don't have air conditioning, or if you just want to open the windows on moderately warm, sunny days, you might find that going with moderate- or low-SHGC windows is the better overall choice. You can use energy modeling to try out different combinations. I use BEopt, a free download paid for with tax dollars, but there are others available as well. Passive House modeling programs are probably the most accurate.
The house will have air conditioning, but I'm definitely more worried about winter heating costs than summer cooling costs.
It would still be a good idea to run an energy model to be sure, but unless you have more south- and west-facing glass than typical, you'll probably be happiest with high SHGC glass.
The increased sensible gain of a greater SHGC may increase run time of the AC a bit, but I can see that being somewhat advantageous in a climate like mine that has a lot of summer days where it's 70 and 100.1% humidity.
Definitely. Where it is contentious is on days when it's sunny, 70°F and dry--perfect weather for open windows--but high solar gain makes it 90°F inside if you don't run the a/c.
Good points have been brought up about high SHGC windows and possible over-heating. I've known a few people that went high SHGC, which is great in the winter, but then in the spring through fall, on warm sunny days, they have experienced over-heating and have to turn on the AC to cool the house off. Especially the swing seasons when the sun is low in the sky and overhangs don't work like they do in the summer. So there is an energy penalty at those times as the high SHGC overheats the house to the point where AC is needed.
In sunny warm climates like Arizona, in Zones 4, I recommend low to moderate SHGC windows. Elevation also plays a role. The sun is more intense at 4,000+ feet. Zones 5+ I can see using moderate to high but strategically placing the windows facing south with good overhangs. West windows are brutal in the summer as overhangs don't work and the west side gets blasted by the summer sun. Most builders/architects just put windows everywhere with no thought about solar gains or overheating. Even the best triple pane window (R-8) still doesn't come close to the code minimum wall (R-13).