Article 30418 of alt.solar.thermal: Path: news.misty.com!not-for-mail From: nicksanspam@ece.villanova.edu Newsgroups: alt.solar.thermal Subject: South window shading in Texas Date: 5 May 2008 17:24:58 -0400 Organization: Villanova University Lines: 73 Message-ID: NNTP-Posting-Host: acadia.ece.villanova.edu X-Trace: max.inside.misty.com 1210019074 21587 153.104.44.130 (5 May 2008 20:24:34 GMT) X-Complaints-To: abuse@misty.com NNTP-Posting-Date: Mon, 5 May 2008 20:24:34 +0000 (UTC) Xref: news.misty.com alt.solar.thermal:30418 At 31.2 N. latitude, the min/max sun elevations at noon on 12/21 and 6/21 are 90-31.2+/-23.5 = 35.3 and 82.3 degrees above the horizon. We could pass all noon winter sun and shade all noon summer sun from a 1'-tall window under an S' opaque vertical separation under a W' wide horizontal overhang like this, viewed in a fixed font: . . . . . . \ . . W . Aw = 35.3 degrees, and tan(Aw) = S/W, - ----------------............................. | . | . . so S = Wtan(Aw). S| . | . . | . -| . | | . | | . | 1| . | | . south --> | | . | | . | | . | | . | | . | | . | | . \ | |. As = 82.3 degrees, tan(As) = (1+S)/W |............................... If W = (1+Wtan(Aw))/tan(As) = 0.1352+0.09573W = 0.1495', and S = 0.1059'. NREL recommends As = 108-lat and Aw = 71-lat, based on no shading at solar noon at 11/17 and 1/25 and complete shading at solar noon on 5/12 and 8/2, with a modification for southern states: if the first fall month with any heating degree days is October or later, NREL uses As = 92-lat and Aw = 66.5-lat to avoid any shading at noon on 12/21 and completely shade the window at noon from 3/26 to 9/18. As = 92-31.2 = 60.8 and Aw = 66.5-31.2 = 35.3 make W = 0.925' and S = 0.65'. This can be scaled. A 2'-tall window would have W = 1.85' and S = 1.3', and so on. We can get more winter solar gain by adding a diagonal reflector from the south edge of the overhang to the top of the window glazing or by eliminating separation S and tilting the overhang up to the south and making it wider. As = 2Aw (max) will put all the reflected dawn sun into the window, without wasting any winter sun. Aw = 35.3 makes W = 0.469 and S = 0.332. As = 2Aw = 70.6 = 90-lat+/-delta makes declination delta = +/-11.8 degrees = 23.5sin(360(284+N)/365) on the Nth day of the year, which makes full shade at noon between days N = 112 (April 22) and 233 (August 21), approximately. A perfect reflector would add 100S = 33% more dawn sun to the window. Tilting it more than the 12/21 noon sun elevation would likely increase the daily gain, while wasting some dawn sun, but midday sun is stronger, since it is closer to south and it travels through less atmosphere. Nick