Posted by NobodyUKnow on November 14, 2003, 1:08 am
Has anyone tried making their own solar pool heaters? I have
some 1/2" drip irrigation tubing that I'm tempted to coil up and
lay in the sun and play around with it to see if it does anything
as a cheap homebrew solar panel. If anything, it makes a cool
little science project for the kids ;-)
A Quick and dirty calculation says the following:
- 250ft of tubing yields approx 10sqft of surface area when laid
out as a flat coil
- 250ft of tubing will fit in a ~4ft diameter circle
- if assume 250btu/hr/sqft of solar radiation, I should be able
to extract about 2500btu/hr in bright sunlight--enough to
heat about 325 gallons 1F per hour
- Obviously I don't expect 100% efficiency, so actual performance
is probably quite a bit less.
I assume the thin-wall 60psi tubingis plenty good since my pool
pump runs nowhere close to that, and heat transfer efficiency is a bit
better than the thick-wall stuff. I also assume tubing works far
better than something like ABS pipe that some folks have tried
Tubing goes for $0 for a 500ft roll at Home Depot, so this
stuff is fairly cheap. If it doesn't work out, I'll just reuse
the tubing for my drip irrigation that I need to put in next
summer regardless :-)
Since 250ft of tubing fits in a 4ft dia coil, I can squeeze 2
coils (20sqft) in a 4'x8' space and run them in parallel since
flow rate and head loss aren't terribly good through each
coil, nor can they compare with the real thing. It's not as
space efficient as a normal rectangular panel, but for $0
versus $50-$00 for a 32sqft real panel, it's not bad.
any comments/suggestions from prior experience?
I'm not a fluids/thermal guy by profession, so please correct
me if I'm wrong in any of the assumptions :-)
Posted by Mitch Dickson on November 14, 2003, 6:32 am
Iffin you get an old satellite dish, and iffin you screw the offset
declination all the way in so it will acurately track the ecliptic, and
iffin you wind the coil on the surface of the dish for a form, and iffin you
get a suntracker, you will multiply the "catch" power by 8 or 10 times :)
"Come by and sit a spell with me at www.volstate.net/~mitch/ "
Posted by Duane C. Johnson on November 14, 2003, 12:14 pm
What you are describing is essentially a tracked flat plate
thermal collector without any transparent insulation.
The tracking will increase the output but not as much as
you say. In Minnesota this would be from 100% in summer to
40% in winter. Ok, pool heating isn't needed ion winter.
The basic problem with the coiled uninsulated collector
is the low initial efficiency. Yes, the collection temperature
is low, which increases the efficiency, but the losses are
Since you have the dish you should use the concentrating
ability to dramatically increase the efficiency. Even though
you don't need the high temperatures that are possible the
thermal losses are much lower than with flat plates. At low
temperatures you won't need the transparent insulation to
get high efficiency.
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Posted by Renewablelife on November 17, 2003, 2:50 am
Where you planing to place it at the bottom of the pool?
If so you would loose a lot of the heat from reflection on the water
surface. If not you are just spilling water on the area you are laying it.
Remember it is drip irrigation tube, hence the water leaks out.