SHGC Requirements - Windows > GreenBuildingTalk - Green Building Forums on Insulating Concrete Forms (ICF), Structural Insulated Panels (SIP), Radiant Heating, Geothermal Heat Pumps, Solar Power

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Jelly

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Posts:274

06/18/2008 9:58 AM
So if I'm building in Zone 2, the IRC says I need an SHGC (solar heat gain coefficient) value of .40 or less for windows. Low-e glass is good, but not necessarily low enough of an SHGC value. An example of low SHGC glass is Cardinal's low E 366 http://www.cardinalcorp.com/products_coated_366/366.htm It has a low SHGC value, but the light transmission factor is only 66%. So has anyone built in Zone 2 since these new values have taken effect in the code? It seems like 66% light is actually kind of dark for a window. Does it look like a tinted window? What about other methods to block solar gain, like overhangs and shutters? Does it matter? Are all of us in Zone 2 doomed to have all dark windows in our houses? I've been in some new houses since the new code but the windows looked clear to me. Any ideas?

Brock

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Posts:209

06/18/2008 12:17 PM
I could be wrong but my understanding wasn’t that it blocked visible light, just 66% of the energy that comes in. So it reflects more UV and IR but still lets in visible light. I think in the visible spectrum they are in the 70-80% range, which is pretty darn clear. I know I don’t see any obvious “tinting” in our low-E windows, but if you open it and look at the light hitting the floor you can see where there is no glass it is a bit brighter. I stand corrected, just went and looked at the site. It looks like they do actually tint them more in the visible range. The jump from Low E to Low E 66 doesn’t look huge, but noticeable. Maybe you would have to have larger windows to get the same natural light in, which would defeat the purpose of the Low E 66. I just argued when we built and added as few windows as was allowed by code (and my wife). The best windows are 10 times worse then the worst wall insulation J

Green Bay, WI. - geothermal heated indoor pool with a small solar setup

Jelly

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Posts:274

06/18/2008 2:36 PM
where did you build Brock? Did you have an SHGC requirement? Cardinal seems to imply that the Low E 366 is almost as clear as regular Low E glass. If you don't really notice a tinted look with 75% visible spectrum then 66% visible spectrum is probably not that much different. Anyone else build recently with low SHGC requirements?

Brock

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Posts:209

06/18/2008 3:36 PM
We are up in Green Bay, WI at about 45* North. We have regular Low E's and had them in the last house as well and I can barely tell they are "tinted" and I work with lighting a lot at work (2000 seat theatre). Honestly the biggest thing I noticed when we got them last time was not getting the fading on the carpet and furniture in the sun areas. Also if you stood in the sun behind the windows it didn’t “feel” as warm as standing in the direct sunlight. In times we need heating, which is about 10 months a year, I have often wondered if that solar gain wouldn’t offset the heat loss in winter.

Green Bay, WI. - geothermal heated indoor pool with a small solar setup

Oberon

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Posts:18

06/21/2008 9:42 PM
Jelly, Think of it this way. A single pane of 1/8" clear glass has a VT of .9 or 90%. Add a second pane and the VT drops to 81%. Add a third pane and the VT drops to 73%. Add a 4th pane and VT drops to 66%. The VT published for Cardinal's 366 is based on two lites and the coating. So in essence, the coating affects the Visible Transmittance to the same degree as adding two more lites to a clear glass dual-pane IG unit.

tsmith

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Posts:3

07/04/2008 1:29 PM
I have seen Cardinal LowE 366, it is clear to slightly greenish. 66% is actually a high Vt for a glass with the SHGC that this glass has. The highest Vt that I know of with a sub .40 SHGC is Guardian RLE. This is an excellent product. performs well and Vt of 70% is excellent. I do not know what windows you have now, but either of these glazing systems are going to save you significant money in your cooling bills for this house and no matter what you will find these values as required under the next model energy codes in your area. Concrees is in the midts of passig a law that will make it so nationwide. Check H.R. 3221.

rancov

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Posts:18

11/08/2008 5:01 PM
Cardinals low-e 366 is a low solar gain, soft coat low-e glass. The 66 stands for 66% Vt (visible light transmitted through the glass) this is actually very high for a glass that has such a low SHGC. These days in order to judge a unit, you also need to calculate the LSG ration (light to solar gain ratio). This ratio will give you a better comparison between two glazing systems, The ideal ratio for a particular glass would be 1.5 and up. The ratio measures the amount of visible light passed through the glass relative to the amount of soalr heat gain passed through. For a more in depth explanation,, see: SHGC and Visible Light Transmission.

Randy

chebyrashka User is Offline

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Posts:13

11/12/2008 10:09 PM
I have this glass in windows I just installed, there isn't a noticeable darkness to them from my perspective. In terms of plants, I've heard it's more noticeable since it blocks out the energy they need to grow but even then it's negligable.

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