[Greenbuilding] flat plat collectors

[Gary BIs]

Hi,
If the water actually filled the space between the absorber and the glass sheet, 
the pressure on the glass (and the absorber) would be quite high even if there 
were no pressure other than that due to gravity.  If the collector is 8 ft high, 
the pressure near the bottom would  be 3.5 psi, and at the mid point 1.75 psi.   
1.75 psi on a 4 ft by 8 ft high surface is about 8000 lbs.   In other words, you 
can't let the water actually fill the space between the absorber and glass 
unless you want to deal with very high loads on the glass.

The fins that take heat into the copper tubes on a conventional flat plate 
collector can be quite efficient -- its easy to get them up into the 95% fin 
efficiency area.  You can get an idea with this calculator:
http://www.builditsolar.com/References/Calculators/FinEficCalc/FinEficCalc.htm

I did a little work on a collector that is meant to spread the water out over 
the whole surface (as a glass one would):
http://www.builditsolar.com/Experimental/SolarShed/EPDMColTest.htm
I did not have a whole lot of success, but maybe there is something there with 
the right combination of the materials.  Or, the MTD collector may be doing 
well.  John C. is sending me an MTD kit to test side by side with a flat plate 
to get an idea how they compare.

Gary








On 12:59 PM, Clarke Olsen wrote:
> Does anyone have experience with, an opinion or knowledge of transparent exposed water collectors?
> That is, a flat plate solar water heater where, instead of running the water under a copper field absorber,
> the water runs between a glass face, and an absorbing surface. In such a device, the sun's heat would not
> have to flow through a copper sheet to be drawn-off with water, but would be taken from the very surface
> that absorbs it. A further development could be a dense black mesh in the cooling water, throughly scrubbed
> of it's heat. A glass plate exposed to 60+psi would not be pretty, but under low (drain-back) pressure...
> Clarke Olsen
> 373 route 203
> Spencertown, NY 12165
> USA
> 518-392-4640
> colsen at fairpoint.net
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