# Tilted Windows for Solar



## joe (Jan 12, 2006)

Does anyone have experience building or using a sunspace (as in a solar-heated home) with the windows mounted at a tilt? If so, did you have problems with leakage, etc? What type of glazing, frames, etc were used, and were there times in which it would have been good to be able to open the windows? Was the extra sunlight admitted by the tilt worth the extra work and cost when compared with vertical mounted windows (or patio doors)?


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## BeckyW (Mar 11, 2003)

Have you looked at Daniel Chiras' _The Solar House_? (published 2002 and I think there's a 2005 edition) 
It was recommended to me by solar engineer and has alot of info and websites for even more. There's a discussion in there on at least some of the issues you are pondering. 
Sorry. I'm in initial research myself so can't give you any answers. Hope this is a little help.
BW


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## WisJim (Jan 14, 2004)

The people that I know that built sunrooms/greenhouses with tilted glass, back in the 1970s and 1980s, wish that they had used vertical glass. Some of the later books on the subject list slanted glazing as one of the major pitfalls to avoid in building a solar building, unless you want to get more sun and heat in the summer, and less in the winter.


Problem areas: Strength of glazing, leakage of slanted glazing and framing, excess heat except in winter, as slanted glazing favors summer sun, and reflects more of winter sun, the opposite of what is usually wanted.


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## Jackpine Savage (Jul 4, 2002)

I'm in the process of designing a sunspace/greenhouse as well. If you are in a part of the country that has snow cover it sounds like vertical is the way to go, you will pick up some sunlight reflection off the snow. An excellent book to read is "The Homeowner's Complete Handbook For Add- On Solar Greenhouses and Sunspaces" by Andrew Shapiro.


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## joe (Jan 12, 2006)

Yes, I've read Chiras. Basically, he suggests that vertical is easier, cheaper, and more reliable. However, other authorities recommend tilted, but not with shoddy components.

I was considering a High Thermal Mass design such as this:
http://www.thenaturalhome.com/passivesolar.html


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## WisJim (Jan 14, 2004)

Most MODERN authorities warn against tilted glazing because it will overheat in summer, and give less than optimal results in winter. But if you want more heat in the summer, use tilted glazing.


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## joe (Jan 12, 2006)

>>Most MODERN authorities warn against tilted glazing because it will overheat in summer, and give less than optimal results in winter.<<

The recommendation to use tilted glass also included a recommendation to use shade cloth (available in different strengths) to prevent overheating in the summer.

I think that tilted glass looks goofy, and would prefer not to use it, but I want to be able to grow a garden in the sunspace in the winter (as discussed in the aforementioned HTM website.)


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## SolarGary (Sep 8, 2005)

Hi,
You don't say where you live, but assuming you are around latitude 40 degs, then if you want to maximize winter collection the ideal tilt would be about 40+15 = 55 degs. 

If you compare solar gain for the 55 deg tilt to a 90 deg tilt (vertical), in mid winter, the vertical glazing solar gain is about 92% of the ideal tilt gain -- so you only lose about 8% by making them vertical instead of tilting. The nice thing about vertical is that the solar gain in the summer is only about 1/3 as much as for the tilted glazing -- not to mention the fact that its easier to install, less likely to leak, and easier to shade. If you live in a climate where you get snow on the ground in the winter, the vertical glazing will actually gain more than the tilted glazing due to the favorable reflection off the ground. I'm probably a bit prejudiced on this, but I just don't see much advantage to the tilted glazing.

I pasted in the Radiation On Collector runs for the 55 deg tilt and vertical below -- just compare the numbers in the column labeled "Total" -- if you want to play around with this more, you can download the program here:
http://www.builditsolar.com/Tools/RadOnCol/radoncol.htm


For the 55 deg tilt glazing:
Month by Month Summary of Sun on Collector
(100% sunny weather)

Collector Area: 1.0 (sqft)
Collector Azimuth: 0.0 (deg) measured from South
Collector Tilt: 55.0 (deg) measured from horiz
Latitude: 40.0 (deg)
Altitude above SL: 0.0 (ft) Above Sea Level

Date ---- Sun ---------------- Collector -----------------------
Month Day Direct Di- Total Direct Difuse Total
Normal fuse 
1 21 2192 127 2320 1841 100 1941
2 21 2600 156 2756 2059 122 2181
3 21 2917 207 3124 2074 163 2237
4 21 3095 302 3397 1829 237 2067
5 21 3162 384 3545 1602 302 1904
6 21 3181 426 3607 1495 335 1830
7 21 3061 416 3477 1546 327 1873
8 21 2914 354 3268 1730 279 2009
9 21 2713 252 2966 1936 198 2134
10 21 2429 176 2605 1944 138 2082
11 21 2121 133 2254 1785 105 1890
12 21 1974 113 2087 1683 89 1772
Sum 32359 3046 35404 21524 2397 23921

Radiation in BTU/day


For the Vertical glazing:
Month by Month Summary of Sun on Collector
(100% sunny weather)

Collector Area: 1.0 (sqft)
Collector Azimuth: 0.0 (deg) measured from South
Collector Tilt: 90.0 (deg) measured from horiz
Latitude: 40.0 (deg)
Altitude above SL: 0.0 (ft) Above Sea Level

Date ---- Sun ---------------- Collector -----------------------
Month Day Direct Di- Total Direct Difuse Total
Normal fuse 
1 21 2192 127 2320 1665 64 1729
2 21 2600 156 2756 1657 78 1735
3 21 2917 207 3124 1380 104 1484
4 21 3095 302 3397 864 151 1015
5 21 3162 384 3545 525 192 717
6 21 3181 426 3607 397 213 610
7 21 3061 416 3477 495 208 704
8 21 2914 354 3268 808 177 985
9 21 2713 252 2966 1277 126 1403
10 21 2429 176 2605 1571 88 1659
11 21 2121 133 2254 1618 67 1685
12 21 1974 113 2087 1586 57 1643
Sum 32359 3046 35404 13843 1523 15366

Radiation in BTU/day

Gary
www.BuildItSolar.com


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## joe (Jan 12, 2006)

Thanks, Gary.

Yes, the latitude is around 40 degrees (actually 37), so it's not up in the North. I, too am "leaning" towards vertical. However, I also want to do gardening in the sunspace, and I think that the tilted window is more appropriate for this. Or then again, it may be better to use vertical windows plus a few skylights to balance the light from the top to keep the plants happy. 

As for the tilted windows in the Summer, since I am trying to do some type of "high thermal mass annual heat storage" scheme, so having the extra heat is not necessarily a bad thing, and the plants growing in the area below the tilted windows will provide shade also.

The bottom line is that I am trying to get a feel for the practicality and cost tradeoffs. Although it sure would be neat to go totally solar, it may be more practical to simply burn some wood during the cold winter times. Also, a separate greenhouse may be better for the gardening than to try to do it in the sunspace. But the planters are a part of the "thermal mass" anyway, so some kind of plants, even if they are low-light houseplants, should go there. 

By the way, Gary, I like your site and encourage others on this list who are interested in solar to visit it.


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## mightybooboo (Feb 10, 2004)

Are you leaning towards an Earthship?

I really like the house/greenhouse all in one.

BooBoo


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## joe (Jan 12, 2006)

>>Are you leaning towards an Earthship?
I really like the house/greenhouse all in one.<<

I was thinking of something along the Earthship motif, but using typical construction materials like concrete block, etc.


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## mightybooboo (Feb 10, 2004)

Thats our plan too,its too involved getting the tire thing to pass muster.I like the Earthship design.
And reading here,I think vertical should probably be the way to go on the windows.

Helpful thread.

BooBoo


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## Jim-mi (May 15, 2002)

With vertical it would be easier to add a summer awning to keep from over heating.


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