Fenestration U's and S's: Picking the Right Window

Passive solar design requires having at least two different glazings available: low-U, low SHGC for cooling dominated locations, and low-U, high-SHGC for heating dominated locations. Both types exist, but for some reason only the former is US EnergyStar listed. Canadians list both.

When I replaced a patio door earlier this year, on a south wall with an overhang that blocks our very brief hot summer sun, I gave up a tax credit in order to get glazing that has the higher SHGC to improve winter solar capture. I didn't lose much credit, as previous work had come close to the cap.

 

Are you in a heating or a cooling climate? If the later, it probably makes sense to go with low E and not worry too much about passive heating. You need to be heating up a large object anyways (lots of thermal mass). Perhaps you could use the sun to heat water jugs or something similar during the day and bring them in as the sun starts to loose its effectiveness.

 

I can do the calculations for your particular case if you like, contact me off list.

There are a couple of different types of lo-e coating, you want hard coat (aka pyrolytic) for high SHGC, at the expense of a tiny bit of U-value.

If you have existing windows is your home, changing them is usually NOT cost effective. If you need better insulation from your windows you might think about interior storm windows. You can see my design here: Green Fret Consulting - Interior Storm Window They can be easily made for $1.25 per square foot, as opposed to the $50 or so per square foot you will be paying for new windows.

 

How about a window that switches?

Switchable Glazing Windows

I've seen some in action before. Power-wise, they're like the screens of e-readers: it takes a little bit of electricity to switch them, but they hold onto their light/dark setting after that without requiring continuous power.

 

Glad to hear this. It has been a while since I looked.