Concept

The sun crosses the horizon significantly lower in the winter and higher in the summer. We can take advantage of this fact by designing solar homes with southern overhangs to admit more sun through the window in the winter and shade the window in the summer.

This is not perfect because the heat cycle lags the sun cycle by about a month, i.e. June 21st is the longest day but the hottest day is about July 21st – statistically. Same in the winter: December 21st is the shortest day but January 21st is the coldest.

Moderate use of overhangs to reduce the sun energy coming through the southern windows in the summer helps keep the house cooler, but be careful not to jeopardize winter heating. This is important in our climate, where heating is the main focus, but cooling is still a concern.

Application

My goals were

#1 windows would be 100% unshaded at solar noon each day, November 21st through February 1st, the coldest period of the year, and

#2 would be 100% shaded at solar noon on July 21st, the hottest day of the year.

I accomplished these goals with the use of a very nifty on-line tool at http://www.susdesign.com/overhang. See Solar Window Overhang & Shading for more details.

To use the tool enter basic window and overhang dimensions and location. Then click through the months to see shading patterns. Very nifty. Christopher Gronbeck, a solar consultant, provides this and other tools and appreciates a small donation, if you find his site helpful, as I did.

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