Replies

1. 
   Stu Turner | Sep 24, 2014 05:02pm | #1

   Hi Dave, not sure how much you want to get into the physics, but here is how the coatings function. Heat and light are forms of radiation that have different wavelengths. When something is not very warm (say, a human body) it emits low frequency radiation. When something is very hot (say, the sun) it emits high frequency radiation. Glass has the interesting property that it is transparent to a spectrum of frequencies that range from visible light (of course) to sunlight (which is high frequency radiation - heat), but glass is actually opaque to low frequency radiation. It absorbs this heat. Try looking through a window in the dark, with your night vision goggles on, and you will just see a solid surface that is the glass, not what is behind it. But coatings can be applied to the glass that change these properties. So a window can be made to (mostly) reflect high frequency radiation, you now have a "heat mirror". Or you can also have a coating that will mostly reflect low frequency radiation, which is nice for keeping the heat in your home from radiating out the windows. Most of these coatings are trying to balance these various benefits. If you have south facing windows that are appropriately shaded, you might want to allow in most of the sun's heat, and still do a decent job reflecting the home's heat back into the home. That is LoE180. The other coatings do a better job of reflecting the low wavelength heat, but also block most of the sun's heat. On the Cardinal site there is also a lot of talk about clarity - VT - because the coating make the windows very slightly more opaque, when you have triple pane windows with coatings you are talking about a window that is much less clear than a single pane of glass.

   So with triple pane windows it gets more complicated, because you can have different coatings on different panes inside the window. Using LoE180 on two panes is what you want for "passive solar" glass. I'm pretty sure most of the other coatings would be combined with 180 in your climate. There is also a LoE-i89 coating which is actually applied through a different process to interior of the pane facing your interior, which is a very good reflector of low freq radiation -- it can be added in to any window, as I believe it is transparent to solar heat.

2. 
   user-1137156 | Sep 24, 2014 06:05pm | #2

   Stu is right. A caution about I89 is: it dramatically increases the likely hood of condensation because it causes the inner surface to be significantly cooler than without it.

3. GBA Editor
   Martin Holladay | Sep 25, 2014 05:18am | #3

   Dave,
   Your window supplier should be able to tell you the net effect of different glazing options in terms of the U-factor of the window and the solar heat gain coefficient (SHGC) of the window. In the U.S., NFRC requirements call for these two numbers to be reported as whole-window numbers (including the frame). In Canada, some window manufacturers report glazing-only numbers, which are not directly comparable to NFRC's whole-window numbers.

   A low U-factor is always desirable, in all climate zones.

   In a classic cold-climate house, you usually want high-SHGC windows on the south side of the house (in your case, the southeast side), to bring in heat on sunny days during the winter. Ideally, your house has overhangs that provide shading of these windows during the summer.

   In most climates, it's safer to have low-SHGC windows on the west side of your house, to avoid overheating on hot summer afternoons.

   For more information on these issues, see All About Glazing Options.

4. 
   Stephen Thwaites | Sep 25, 2014 08:59am | #4

   Dave,

   If your goal is to minimize your energy bill, the answer, because you live in Canada, is easy.
   Just ask your supplier for the Energy Rating (ER) for the various glass options.
   Then pick the highest ER.

   Although similar approaches exist in Europe, in North America the ER is unique to Canada. It combines the effect of gains and losses over a heating season.

   As Martin suggests you may want to exercise comfort based judgement on the back NW facing windows. But keep in mind if you are replacing clear doubles, then even the highest solar gain triple will have a lower solar heat gain than your current windows. - so overheating will decrease from current levels.

   Hope that makes sense.

   thx
   Stephen Thwaites
   Thermotech Fiberglass Fenestration