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radiant heat design with solar thermal collectors - Page 2

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Posted by Eric Yancey on October 4, 2006, 1:38 pm
Thanks for your input Jeff.  I'm not that familiar with drainback systems so
I would need to do some research on that subject.  There is very little
chance of the water freezing in the slab.  We would have to experience
unusually cold temperatures for an extended time for the slab to get that
cold.  Also, if I keep the water heater in the loop, we would also have to
be without electricity for a long time to allow the system to be shut off.

Regarding tempering the water - this is something I was a little concerned
about.  My understanding is that you don't want to circulate fluid that is
hotter than 140F.  If this is the case, I'm wondering if constant
circulation will keep the temperatures at a reasonable level by transferring
as much heat as possible to the slab during peak solar time.  From what I
have read temperatures in some collectors can reach well over 200F -
something that probably wouldn't be good for my radiant system.

Thanks again!

Posted by Jeff on October 4, 2006, 2:23 pm
Eric Yancey wrote:

Google it up, it's where everyone is going. All that happens is when the
pump stops the water drains back to the reservoir. Simple eh? I wanted
to mention it because no one else had, probably because they thought you
had already considered that!

   Probably what you want is one loop through the solar collector and
then another loop through the radiant loops. Two pumps. No heat
exchangers. Common tank. Tanks can be cheaply- made of EPDM pond liner.
It's not a bad idea to store some heat.

  There is very little

Gary has some links on <URL: http://builditsolar.com  /> on radiant
heating. There is a design PDF that you can download (somewhere) with
more info. Not sure how it works, but you will want to do this.

Something about tempering tanks and tempering valves.

I'm not that far along so my knowledge of details is pretty bad! I'm
just now building collectors. Floor radiant is well suited to Solar
because of the lower temps needed.


   If this is the case, I'm wondering if constant

Posted by Robert Scott on October 4, 2006, 10:18 pm

Yes, it is simple.  But if site conditions require that the collector be placed
at a much higher level than the reservoir, then it will require a lot more pump
energy to circulate then water, as compared with a closed-loop system that does
not drain back.  This will require a larger pump and more electrical energy.

Robert Scott
Ypsilanti, Michigan

Posted by SJC on October 4, 2006, 10:46 pm

  In all the time on here I have never seen the difference in pumping power
expressed for similar systems, one closed loop and one drainback. I have
heard quotes of "only 35 watts" in a closed system, but that seemed a bit
low to me.

Posted by Solar Flare on October 5, 2006, 12:34 am
 Closed loop systems have to be filled the first time and it will take
a better pump to do this everytime maintenance has to be done.

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