[Greenbuilding] flat plat collectors

[Gary BIs]

Hi Joe,
Yes -- I'm eager to see how the traditional flat plate compares to the MTD -- I 
think that the the MTD might do fine.

I'm probably a bit prejudiced on this, but I think from a life and long term 
maintenance point of view, the traditional flat plate may have some advantages.  
I'm just a little concerned about keeping the trickle tube trickling over 20 years.

Gary

On 12:59 PM, Joe Killian wrote:
>  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
>>
>>
>>
>>
>>
>>
>>
>>
>> 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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>
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