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Grid Angle for Optimum Solar Interaction
Name: Byron B.
Status: Other
Age: 60s
Location: N/A
Country: N/A
Date: March 2004
Question:
I live in Dallas, Texas. I am constructing a pergula (patio with a wooden grid on the top). I would like to angle
1 x 6's on the top so that sunlight will come through during Jan 1 through Mar 15 but thereafter will be blocked or shaded during the summer months when the sun angle moves more directly overhead.
I assume that I can orient the boards on a true east-west line on their respective edges, but at what angle should I "tip" them to accomplish what I am trying to do? And what spacing should I use to that they effectively overlap during the "hot" months?
Replies:
Your latitude is 32 degrees, and you want to accept as much winter sun
as you can. At winter solstice, the sun is over a latitude of 23 degrees
south, and you want to pass as much sunlight as you can, so you should
orient your boards at 32+23=55 degrees from vertical (leaning south, of
course). At spring equinox in Dallas, the sun will be over the equator,
its rays making a 23-degree angle with your boards, and you want each
board to just barely shade the board below it, so the free space between
boards, s, should satisfy
s/w = tan(23 degrees) = .4245
where w is the width of the boards. For w = 5.5 in., s = 2.335 in., or
roughly 2 3/8 in.
Tim Mooney
Advanced Photon Source
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