Re: [GBlist] south wall glazing

[Speireag Alden <Joshua.M.Alden.91@alum.dartmouth.org>]

Sgrìobh j. gann:

>In designing/building a passive solar structure, what is the optimum 
>angle of the glazing ?  (40 o latitude).  Or does it matter??

     It does matter, somewhat, but as you go north the optimal angle 
gets closer to vertical.  At 40 degrees north latitude, the angle of 
the sun at noon on the summer solstice will be 73 degrees above the 
horizon.  The angle at noon the winter solstice will be 27 degrees 
above the horizon.  If you set your windows at 63 degrees from 
horizontal, you'd be getting that winter solstice sun smack into them 
at right angles.

     However, remember that this is not a linear function; it's a sine 
function.  The first few degrees don't matter a whole lot.  We can 
situate our houses fifteen degrees in either direction of south 
without affecting solar gain more than a few percent.  The same is 
true of the vertical angle.  Even out to thirty degrees it won't 
matter a *whole* lot:  only about 13%.

     There's another factor:  seals.

     If memory serves, keeping the window seals from failing on glass 
which is other than vertical is a pain, especially if it's exposed to 
the elements directly.  It's such a pain, in fact, that many builders 
have despaired of doing it and just re-seal them every so often. 
This is building unnecessary maintenance into the design, which is 
not good design technique.

     Also, too much sun can make summertime cooling very difficult.

     If you set the windows vertically and put them under 
appropriately sized eaves, you can have your winter sun and your 
summer shade, too!  There is a 46 degree difference between the peak 
angle at summer solstice and the lowest angle at winter solstice.  So 
your degree of insolation changes without your having to lift a 
finger, and you don't have to worry nearly as much about the seals, 
both of which are Good Building Design.

-Speireag.
-- 
Speireag Alden, aka Joshua Macdonald Alden

If the biota, in the course of aeons, has built something we like but 
do not understand, then who but a fool would discard seemingly 
useless parts?  To keep every cog and wheel is the first precaution 
of intelligent tinkering.   -- Aldo Leopold, _A Sand County Almanac_ 

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