Low-Tech Solar Water Heater on the Roof

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rberq
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Post Fri. Jun. 27, 2008 1:08 pm

I have a 34' x 38' low pitched garage roof that gets almost full sun. I would like to buy several hundred feet of heavy black garden hose and snake it back and forth on the roof. Then, install an indirect water heater to front-end my regular water heater, and pump water round and round through the tank coil and the hose during the day when the sun is shining. Non-freeze months only, of course. I would take the whole thing down come Fall.

Two questions:
(1) Do I need an expansion tank on the hose circuit, or can I get away with just under-filling the circuit a bit?
(2) What should I use for a pump, and where would I get one?

Opinions and warnings are welcome, along with the above information!

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traderfjp
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Post Fri. Jun. 27, 2008 3:44 pm

What is the rise? Try **Broken Link(s) Removed** they have panels made for pool heaters that are not too much money and will work better then a garden hose.

rberq
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Post Sat. Jun. 28, 2008 7:12 pm

Total rise about 18 feet. But the hose would be full of water, so wouldn't the pump just have to overcome resistance to flow, rather than having to actually lift the water?


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coalkirk
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Post Sun. Jun. 29, 2008 10:01 am

I have thought of doing something like that. I know when I turn on my hose after it has laid on the deck in the sun, I can't hold onto the metal nozzle it gets so hot. Recovery is the issue.

CapeCoaler
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Post Sun. Jun. 29, 2008 1:35 pm

If you put the second tank on the roof higher than the hose, natural convection will circulate the hot water. You will also need a swing check valve to prevent the water tank cooling at night, flow reversal. Run a standard boiler circulator from the inside tank to the outside tank, simple solar differential controller will make your life easy. For the solar loop, leave it open to atmosphere with a reserve tank for expansion. This will keep the expanding hot water from sucking air into the tank at night. PRV on the pump line at the highest point, if power or pump fails you will blow the line with out one. Use PEX for the pumped line and you can keep it simple. You might want to experiment with making a manifold and making a few shorter runs to keep the water temps lower. A single run will have higher temps with higher heat loss.

rberq
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Post Sun. Jun. 29, 2008 5:46 pm

Thanks for the ideas. One thing I don't understand in what you said: Leaving the solar loop open to the atmosphere with a reserve tank sounds a lot like the radiator overflow tank on my car but without the pressurizing radiator cap. If I do that, then why do I need a pressure relief valve on the pump circuit, which after all IS the solar loop circuit? The reserve tank would serve as an unlimited expansion tank, no?


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traderfjp
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Post Sun. Jun. 29, 2008 6:02 pm

Here pic of the panel I'm using for my pool. The cost is 221.00 for a 4 x 8 panel. By the time you buy the house, manifold, etc. You'll be close to that I'm sure. I'm not sure if I would go through the trouble of mounting atank on the roof. I would just run a plastic line to the panel with a circulator in the line. You would need a control that will shut off the pump and a solenoid to shuttoff any flow from convection. You'll also need a relief valve somewhere and a few check valves. I'd say your low tech solar HW heater is going to cost close to 600.00 installed. They have copper panels that are made to be used with an indirect tank but then your talking bucks for that. Good luck.
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CapeCoaler
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Post Sun. Jun. 29, 2008 11:15 pm

My assumption was the circulator was on the coiled part of both tanks creating a closed circuit.

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