[Greenbuilding] Question about a window solar heater

LarenCorie LarenCorie at axilar.net
Thu Dec 1 12:53:45 PST 2011

From: "Bob Waldrop" <bwaldrop at cox.net>

> I recently came across this interesting take on the traditional
> solar window heater.

http://blog.imehrle.com/2011/02/10/solar-heating-made-easy----very-easy.aspx >

>  someone mentioned that since it hangs on the inside of a window,
> it blocks sunlight from the window. That person thought that the heat
> resulting from the flow of sunlight into a room without any obstruction
> in the window would be greater than the heat resulting from the
> operation of this device in a window, which would have the
> incidental effect of blocking some sunlight from the room.
> Is that correct?

Hi Bob;

  The net absorptance, of a flat black collector absorber,
and that of most rooms, is roughly the same.  However,
where it gets more complicated, is in the effect on heat
loss through the same window. While the sun is shining,
the collector probably significantly raises the air temper-
-ature adjacent to the glass, thereby producing greater
heat loss. However collectors may also (if built to do so)
serve as window insulation for all times when the window
would normally have more heat loss, than Solar gain. So,
the answer can go either way.   Another aspect is that it
may be advantageous to stratify Solar heated air, near
the ceiling, instead of having the direct sunlight turned
into heat at the floor level, where it can easily overheat
the whole room.  Higher temperatures near the ceiling
can store some of the heat in the thermal mass of the
upper drywall, releasing it a little more slowly, to carry
the daytime Solar heating, further into the evenings.

-Laren Corie-
   Natural Solar Building Design and
Solar Heating/Natural Cooling/Energy
 Efficiency Consultation Since 1975


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