I am learning a lot about windows, not the computer kind, but the house kind. The one feature that I have to pay attention to for the south side windows is the solar heat gain coefficient (shgc). The shgc rating ranges from 1.0 down. A rating of one means clear glass and 100% of solar heat going through. The lower the number, the less solar heat. Unfortunately, the higher the number, generally the more heat leaks out also. So most windows today have a low shgc. Ones that I specced out had a .29-.35 shgc. This mean only 29 to 35 percent of the solar energy is getting through. This is much too low. So far, and quite frankly I haven't started to seriously look, the highest shgc stock window I have found is .45, still to low. I am looking for .60 and above.
With these high shgc windows come two complications. The first is the heat loss factor. It is pointless to try to heat the house passively if much of my heat is going to leave through the windows. Therefore I need to have insulated shades that I can pull down at night to minimize heat loss, or get those windows that have them internally installed.
The second issue, which segues into the second topic in this post, is the zero energy challenge. I have decided (from advice given to me from Peter Harding our energy consultant), to enter the house in the Connecticut zero energy challenge. This is a contest for new constructions, with a grand prize of 10,000 dollars to the most energy efficient house. A link with all the details is here: http://www.ctzeroenergychallenge.com/about.htm
As far as I can tell from the existing contestants, I am the only contestant who is doing his own general contracting. Every other contestant is a building company.
Excavation -silt fence construction to start Monday!
Wish me luck, and
Thanks for reading.
Sam
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I'm sure you know more about this now than I do, but would have though you would have wanted the most energy efficient windows you could find. I thought that greenhouses worked by allowing visible light in, which would be absorbed by things inside the house, which would then re-radiate in the infrared, to which the window glass is opaque (hence preventing heat loss).
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That's right. But today's windows block both light coming in as well as heat/energy going out. So as a passive solar builder, I'm sort of in a quandry; I need to have lots of solar heat come in, but that means a much less efficient window which will allow lots of heat to leave. The trick here, I think is to insulate the curtins. During the day, curtins are open allowing for the sun to heat up the slab, at night, the curtins closed, trapping the heat inside.
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