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foil backing in colector

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Posted by samuel chamberlain on November 11, 2006, 7:01 pm
Any help appreciated :
Having all ready made a test liquid collector I am now ready to make a
large size collector (8x4 ft) , the book I used for design tips has the
title : solar water heating a diy guide .
page 11 step 16 instructs me to : taking care that there is no gap
between the insulation layer and collector surface , place the pipework
(with fins) on top .
I have 2 main questions about the above step :
(1) is there an advantage in placing the clips one way or the other ?
i.e pipe showing top/bottom .
(2) what is the function of the foil face if it is placed in contact
with the collector ?
thanks in advance samuel .

Posted by SJC on November 11, 2006, 8:37 pm

   I have no idea what this book is, but if they tell you to put the foil face in
contact with the solar thermal collector, I would question the validity of that.
An air gap or vacuum is a good insulator. The insulation acts as a trapped air
gap. If you put the foil face of the insulation in contact with a hot solar
collector, I would say you reduced the insulation value. You also do not have
a radiant barrier that can reflect IR back.

Posted by samuel chamberlain on November 11, 2006, 8:55 pm
 SJC wrote:

Yes this did worry me some what so in the test panel I used timber
beading as stand-offs . thank you SJC for your reply , samuel .

Posted by Solar Flare on November 13, 2006, 2:58 am
 Engineering ignorance?

Seriously, like SJC and daestrom said, if the plate/pipes touch the
you lose the effect of the radiant barrier.  Yoiu need a
small air gap to reduce thermal conduction, and the foil barrier to
reflect the radiant heat.

Posted by daestrom on November 11, 2006, 10:57 pm

Looks pretty?

Seriously, like SJC said, if the plate/pipes are in contact with the foil,
you lose the whole purpose of having a radiant barrier.  Normally you want a
small air gap to reduce conduction/convection, and the foil barrier to
reduce radiant heat transfer.


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