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stmbtwle

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Reply with quote  #1 
I've read with interest Gary's articles on the solar shed and evaporative/radiant cooling (thanks for the links SI) but it seems to me that it's highly likely that most of the cooling comes from the evaporative part.   Has anyone has tried straight RADIANT cooling (without the evaporation) and if so how well did it work.  Is it worth pursuing?

Living in Florida, I have reservations about evaporative cooling; among them:
High humidity
Water loss/cost
mineral buildup

Any information would be welcome.



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Willie, Tampa Bay

KevinH

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Reply with quote  #2 
Did you see the links at the end of this BIS page?:  http://www.builditsolar.com/Experimental/RadCoolSolShedTest/SolShedTest1.htm
They cover a radiant-only method and have test results.

I have also been thinking lately about whether some sort of radiant cooling would be practical or not.  Here in MN it usually gets cool at night, but the humidity also tends to be higher in the summer.  I can open the windows overnight or in the morning to cool the house, but that also raises the humidity so after closing up the house for the day I have to run the air conditioner for a while to bring the humidity back down.  I was thinking that an unglazed/uninsulated tube-type collector design could be used for cooling, but don't know if there would be enough benefit.  A radiator could probably bring 80F indoor air down to whatever the outdoor temp is (often in the 60's here), but that is a small temp difference compared to what we are doing with heating.  Also, there could be condensation inside the tubes and with the radiator facing the sky daytime heat would have to be vented.  Another option would be a simple backpass as a radiator.

Kevin H
MN
SolarInterested

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Reply with quote  #3 
Do you mean through a 'normal' panel? or a purpose built radiator. I don't think the former would work very well as the a normal panel (say copper/aluminum, glazed with double wall polycarb, polyiso insulation) is built to minimize heat loss. A purpose built radiator might work OK.
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stmbtwle

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Reply with quote  #4 
Yes Kevin that was the article I was talking about. However all I saw was EVAPORATIVE cooling and not so much RADIANT if at all. I'll have to check again.

Yes SI I was wondering if an existing already-installed collector could do double duty as a radiator at night. Building a dedicated radiator would not only increase cost but would take additional space, which I don't have.

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stmbtwle

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Reply with quote  #5 
Thanks Kevin, I found the link on the "night cool" tests near me. http://www.fsec.ucf.edu/en/publications/pdf/FSEC-CR-1692-07.pdf

They're very interesting and pretty much answered my question.  Even in an "ideal" test with new construction the results weren't that impressive to me, and I rather doubt that their test roof construction would pass our rather strict hurricane building codes anyway. For a retrofit, I don't think the energy savings would be worth the expense.  However a separate solar/collector radiator might still be made to work.  Mine has glass glazing which probably would not be conducive to IR radiation, but the twinwall glazing many of us use might be better.  Also a solar collector, being black, might actually be a better radiator than a white metal roof.  It would also cool down quicker than a hot attic.  

Anyway it will only take me an hour to hook up my collector/tank setup and try it out. 


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Solar is like the wind. It may be free, but putting it to work isn't!
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KevinH

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Reply with quote  #6 
SI,
Yes, I was thinking of using the equivalent of a tube-type hot air collector as a radiator, but without the glazing and insulated box.  Just tubes exposed on all sides with headers on the ends.  I still have the tube cores from my original collector.  I might do a quick test of this idea some time, but doubt if the amount of cooling would be worth it.

Willie,
I haven't studied the Night Cool test results, but thought it would be relevant to you since it was done in Florida.

Kevin H
MN
stmbtwle

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Reply with quote  #7 
I kinda doubt the direct radiant system would be worth it either, but a HEX system might. Use fan coils to move inside heat to storage during the day, then dump it into the cooler outside air at night with an auto fan/radiator or similar device. Wouldn't work this time of year but might in the spring and fall.
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SolarInterested

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Reply with quote  #8 
Quote:
Originally Posted by stmbtwle
... Building a dedicated radiator would not only increase cost but would take additional space, which I don't have.
Couldn't the radiator be as simple as a garden hose laying on the ground (or lawn)?

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Garage_Hermit

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Reply with quote  #9 
Nice one, Mike !

Or better still, suspended in the local watercourse...

G_H

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stmbtwle

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Reply with quote  #10 
The "watercourse" here is currently 90F (32C), and it doesn't get appreciably cooler at night.

The garden hose idea might even work.  I've even got a couple plastic pool heaters that might work.  Thanks for the suggestion.

Hmm the pool heaters might work pretty well. They're big, they're cheap, and they're NOT glazed. I bought them for an experimental collector, but even when covered with plastic film they didn't get the temperature I needed. As a radiator, though...

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Solar is like the wind. It may be free, but putting it to work isn't!
Willie, Tampa Bay
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