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Solar Cooling

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Posted by Swatsell on June 6, 2008, 11:42 pm
I've just recently started looking into different projects involving solar

I'm fascinated with parabolic reflectors and would like to try something.

Tell me if I'm off my nut here. Here's my idea.

A parabolic reflector concentrated on a sealed container using freon. Using
an evaporator buried underground to cool down expanded gas, a small metering
valve for expansion and a condensor coil and a fan blowing across it. Is
this a stupid idea?

Basically, parts from a small window unit A/C substituting a parabolic in
place of the compressor. I realize it would need additional cooling (maybe a
larger evaporator because of the additional heat along with the pressure.


Posted by Swatsell on June 7, 2008, 2:52 am
Well duh! I told you it was probably a stupid idea :) Just for that; I won't
share my other stupid idea for steam generation.

I thought the cooling effect was achieved when the freon flashed across the
expansion valve into the condensing unit.

Thanks Dow, I appreciate the feedback. I've been looking at the
Photovoltaics. It just seems like it costs a small fortune for the initial
investment and the output usually isn't that high. I priced a PV tonight at
Harbor Freight and Tools. It was $9.99 on sale. The output was 12 volts - 5
watts. The solar panels almost seem like a joke as far as cost vs output.

Thanks again,

Posted by Morris Dovey on June 7, 2008, 3:11 am
 [ Oops! Replied to sender by mistake. Apologies. ]

Swatsell wrote:

David wrote:

Not such a stupid idea - just not very workable. Don't be discouraged.

David kind of circled around the method I'd like to use. I want to use
solar energy (heat) to drive a Stirling engine to produce mechanical
energy - then use that mechanical energy to drive a second Stirling
engine in "backward" mode as a heat pump.

The efficiency wouldn't be fantastic, but I don't really care as long as
the thing produces cold air. :-)

Morris Dovey
DeSoto Solar
DeSoto, Iowa USA

Posted by Elihu on June 7, 2008, 5:54 am

Actually, it's a perfectly fine idea and would work just as well as any
three-way refrigerator you find in an RV.  When on propane, a small flame
heats one part of the circuit thereby creating flow.  And you're right, the
chilling effect is caused at expansioin.

Posted by Jeff on June 7, 2008, 1:58 pm
 Elihu wrote:

  But we aren't talking about a refrigerator, we are talking about an
air conditioner. It's one thing to buy an absorption fridge, it's
another thing to build an absorption chiller. Not to mention that it can
be dangerous as ammonia is usually one of the gases used. Take a look at
the plans for one.

Here's a treatise on a solar absorption chiller:

   Here's a single effect commercial unit:


Simplified diagram:


The COP of commercial units is about .7, yours will be less. Now lets
say you run a 6000 BTU AC for 8 hours, that's 48K BTUs, and you will
probably need twice that in heat input to run it. That's 100 SF or so of
collector, and all you've done is cool a small room or two, not a house.

   I think it is far more practical and far less expensive to mock up a
solar desiccant cooler using either LiBr or CaCl (road salt) brine as
the desiccant. All that operates very well at flat panel operating
temps. Plus it sanitizes the air.

   The more you crank numbers, the more sense adding
insulation/shading/radiant barriers makes!


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