Tuesday, February 15, 2011

Evaluating Ordinary Window Screen as a Solar Air Heating Collector Absorber

This is a chance to exercise your Physics brain a bit.

A few people have used a couple layers of ordinary window screen as the absorber for solar air heating collectors.  This is the same stuff you put in windows to keep the bugs out.
Scott and I have been doing some testing of air heating collectors of various types, and to the surprise of some, the collector that uses the two layers of window screen as the absorber has done as well or better (so far) as other more complex absorbers.

The way these collectors work is shown in the diagram -- air enters the collector via the bottom vent and is routed to the glazing side of the screen absorber.  The screen has a little bit of pressure drop and this tends to spread the air evenly over the screen.  As the air works its way through the screen, it is heated, and eventually makes it way out the top vent located at the top back of the collector behind the screen. 
In an alternative to this picture, it has been suggested by Laren over at the Yahoo SimplySolar group that the screen is really quite open, and that much of the sun passes right through the screen and ends up getting absorbed instead by the back wall of the collector.  In this view, the screen still helps, in that it does absorb some of the solar, but, perhaps more importantly, it keeps the heated air from migrating back to the cold glazing where heat losses would be high.

I did a little test to measure how much of the incident sunlight 1, 2 and 3 layers of fiberglass and aluminum screen absorb, and some tentative conclusions and some questions come out of this.  So, take a minute to look at the results and see if you have any ideas to contribute on making these absorbers more efficient -- or, maybe you think there is a better option altogether?

The Window Screen as a Solar Absorber Test Stuff...

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