[Greenbuilding] flat plat collectors

[Joe Killian]

  Hi Gary,
   I note your comment near the end of your B.I.S. post that an ordinary 
cotton bath towel spreads the water almost perfectly.
   I also note that John C. uses polyester felt.
   Seems the MTD collectors can work well with the right materials 
used.  And of course the upper layer of EDPM contains the water & water 
vapor so pressure against the glazing and heat loss via condensing on 
the glazing aren't an issue.
Joe

On 10/10/2011 8:05 AM, Gary BIs wrote:
> 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
>
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> 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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