SHGC of north-facing windows?
thrifttrust
| Posted in Green Products and Materials on
I’m beginning the search for windows for my new home in Detroit, CZ5. South windows will have a high SHGC. West windows will have a low SHGC. The east windows get summer shading from a large oak tree so will have a high SHGC. My question is about north windows. Of course they won’t be subjected to sunlight, but my first thought is that a window with a low SHGC will better reflect indoor heat back inside? I would prefer to be wrong because high SHGC windows let in more light.
Douglas Higden
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Search and download construction details
Replies
Doug,
While I'll defer to others who may have better logic or more complete understanding I'm using high SHGC windows on the North because they experience solar gain, by reflected sunlight, sufficient to offset the slightly higher loss by conduction. Exactly where in the Detroit metro area are you building? I'm a grad of Southfield high school and Wayne State University..
Douglas,
The answer to your question has nothing to do with "reflecting heat."
At night, the thermal performance of your windows can be assessed by looking at a single metric: U-factor. The lower the U-factor, the better the thermal performance.
During the daytime, things get more complicated. A north-facing window gets a little bit of direct sunlight (perhaps) near the hours of sunrise and sunset in late June. Otherwise, all its gets is reflected light.
On a very bright sunny day in winter, a north-facing window can get quite a bit of reflected light, especially if the ground is snow-covered. In theory, you want your north-facing window to have a high SHGC to take advantage of this reflected light in winter -- but in practice, there isn't a lot of available heat from north-facing windows, so the SHGC isn't too important.
My advice is to choose glazing for your north-facing windows with a low U-factor and a high VT (visible transmittance) -- and don't worry too much about its SHGC.
Douglas,
I agree with everything Martin said. None the less the particular choices I faced had the same u factor 0.15 but SHGC of 0.21 with vt=48% or SHGC 0.46 with vt=58%.
EDIT in other words lowest u is first priority but SHGC breaks ties.
Thanks, I agree, low U value and high VT seems the way to go.
Those are impressive window numbers Jerry. What style and brand are they?
Actually, my lot is in the north east corner of Southfield, (Thirteen Mile and Greenfield.) but it is in the Birmingham school district. I went to Cooley High in Detroit, My spouse, one of my children and many of my friends are WSU alum. Where's your place?
Doug,
Those are for fixed (non operable) style that matches casements with u=0.17 from either Enerlux (fiberglass frame) and Wasco (UPC frame) I'll probably go with the Wasco, significantly lower cost. Both are thick triple pane (1/2" spacis between glass) with two low e coatings.
I'm building in Saddieville Ky. which is almost midway between Lexington Ky and Cincinatti OH. i
Thanks Jerry, I'd seen the Wasco website but it wasn't sure they were available outside Wisconsin. The Enerlux windows are impressive. There site has the best descriptions of various glass assemblies I've found. Although I would prefer fiberglass, I fear I'll have to settle for vinyl. Do you have ball park square foot prices tor these brands?
Doug,
I've never bothered to compute/sq ft. I just request quotes for my needs, Wasco responded in a day, Enerlux took a week. Wasco is a lot closer to you and they'll ship anywhere. FWIW Wasco uses European, UPC frame material. like Intus but they offer a US type out swing casement, I'm too old to adapt to "inswing"