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External thermal mass idea. Cool idea need help

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Posted by Saki on November 8, 2009, 7:11 am
This my idea, I have search the internet and can't find where someone
has done this. I am building a new house with radiant floor heat. It
is a 2000 sq ft concrete slab 4 inchs thick. It will be insulated
under the slab. I want to build and external slab also insulated 4
inchs under and around the slab that will have 2 layers of clear
corigated fiberglass cover (double pane window). The top of the
external slab will be painted black to attract the heat from the sun
(Greenhouse effect). Store the heat in the external that will have the
tubing built in so I can curculate water between the two slabs. I was
going to make it about 8 x 16 foot. How thick can the external slab
be? If I make it 2 ft thick will the heat penatrate 2 ft or is that
over kill. I want to use it as and external thermal mass battery or
make it 6 inchs thick and use it as an external solar generator.

Posted by Morris Dovey on November 8, 2009, 7:45 am
Saki wrote:

A better newsgroup for thermal questions is news:alt.solar.thermal

Where are you? A horizontal collector will not work well in winter if
you are far from the equator.

Morris Dovey
DeSoto Solar
DeSoto, Iowa USA

Posted by frigitar on November 10, 2009, 8:36 pm
Hmmm Im not sure what the schematic looks like here. The external
block you speak of is on the roof?
I think the first step will be to calculate the amount of radiant
power (or energy over the day) that falls on this wall. For best
results, you would use a collector itself. So say you had a wall that
was as good as a solar collector, you can use the area of the wall to
determine what it heats upto assuming no heat transfer.
Then use the common heat transfer equation to determine at what
thickness the temperature is maximum. This depends on the material you
use and rate of flow of water inside the wall.

However, in all fairness, i have to agree with Morris. I do not think
you will be getting a lot of heat during the winter (if its cold
enough for you to require heating) because the wall will lose most of
its heat to the atmosphere.No matter that its black, even solar
collectors which are made of selective surfaces and have very low
emissions do not work well in the winter unless they are vaccum

Cool idea though. I'd like to see where this goes.

Posted by bfunkdrt on November 25, 2009, 3:24 pm
 On Tue, 10 Nov 2009 12:36:03 -0800 (PST), frigitar

I am late to this party so may be my idea has been covered. If so

I'd approach this in a slightly different way. First I'd greatly
increase the mass of the house slab or use a water tank, pool, pond to
store the heat. Then use an asphalt drive way for the heater.

It's the storage area that has to be massive not the collector.


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