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Evilroyslade

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Reply with quote  #1 
Hope my diagram explains my horizontal PVC pipe idea of pumping cold to the top and letting the cold water in the top pipe drain back to the barrel picking up heat along the way.  I assume my pump shuts off and any cold water in the pumps pipe will drain back into the barrel. I'm trying to  simplify and make the drain back bullet proof. The input pipe will have a T-vent to allow air behind the water when the pump shuts off. 
The submerged pump will be primed as long as I have water in the barrel, the 12V pump will run off a battery that's charged by a 45amp solar panel. The pump pipe will be 3/8 and the PVC will be 1/2 pipes at a 1 inch slope per 8 ft pipe back to the barrel. No flat spots or inclines.

Any suggestions or criticism will be appreciated.

Clyde 20161206_211220.jpeg   


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SolarInterested

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Reply with quote  #2 
Gary from Build-It-Solar has done some testing on drain back of serpentine piping which indicates that you might be able to get away without the tee vent:
http://www.builditsolar.com/Experimental/SerpentineDrainback/SerpentineDrainbackTest.htm

Filling the collector from the bottom up would ensure the pipes are completely full of water at all times which, I'm guessing, would give better heat transfer.

I'm not sure that having the pump in the storage tank is a good idea. See the comments by JamieF in his build topic:
http://simplysolar.supporttopics.com/post/jamies-long-road-to-solar-7175299?trail=290


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stmbtwle

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Reply with quote  #3 
Quite similar to my setup.

Usually the inlet to the collector is at the bottom and the outlet at the top, this is to better purge air from the system.

PVC can't take the heat and IMO cpvc is marginal. consider copper or PEX.

you don't really need a battery, it just adds cost and hassle. The PV panel can power the pump itself. If there's no sun, there's no heat, either.

you don't really need a vent at the collector as long as the return is above the level of the water in the storage tank. That is your vent. A vent at the top of the collector breaks the siphon and will require slightly more power, this MIGHT be an issue if you collector is on the roof. Otherwise it won't hurt.

I see no mention of an absorber plate or fins. You need something to capture the sunlight and transfer it to the pipes. They don't work very well by themselves.

For easy-to-build (and cheap), consider an ARETHA. There's a whole lot less plumbing involved.

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Evilroyslade

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Reply with quote  #4 
Thank you Solarinterested. Great feedback and links to greater details. Excellent answers to my concerns. I will proceed and document my results. I will use the submerged 12v pump since the pump failure Jaime had was caused by a lack of water, my configuration has the pump under 50 gals of water and not likely to run dry. My little pump will lift 9 feet for this setup so it would not push a full panel of water out the top. 
Clyde

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Evilroyslade

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Reply with quote  #5 
Thank you Stmbtwle,      I will use CPCV rated to 180F with a panel mechanical vent set at 180F to start with, flashing will be aluminum and 6mm twin wall polycarbonate.  I considered copper (Expensive - my skills) and Pex again (Expensive and UV issues).  I chose CPVC to start with on this panel, later I would consider a solar vacuum tube system or the copper pipe panel.  Panel frame is metal 2x4's, 1 inch AP foil faced foam sheathing all painted hi temp flat black. The battery is optional until later when I start pumping the hot water through a radiator. I will check ARETHA before building my panel.

Clyde 

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SolarInterested

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Reply with quote  #6 
Clyde here are some more links for you. Pay particular attention to costs of the heat exchanger in the panel vs normal piping and fins. I know it surprised me that the HX was less.

ARETHA Project, solar panel with car radiator (link)
ARETHA type collector compared to cpvc-flashing collector (link)
Willie's Cinefoil dual pass ARETHA (link)

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stmbtwle

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Reply with quote  #7 
My experience with submerged pumps is heat. While the pump can handle 212F or 100C, the MOTOR can't. When the water temperature hits 160F or so, the submerged motor will shut down and your collector will stagnate. If the pump is NOT submerged, the motor won't overheat. Of course the heat tolerance will vary from pump to pump. Check the specs.
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Evilroyslade

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Reply with quote  #8 
Good info but not likely to pump 212F in the bottom of 100 gals of two barrel system. I already have an external pump but drilling holes in my barrels would make more points of for leaks so I will try the submersible pump. I hope to avoid stagnation using mechanical vents using auto thermostat (s).  Later I will shut the system down when the barrel water on top reaches a lower temp assuming I can eliminate stagnation with the thermostats.  I read up on the ARETHA design and I'm not seeing the dollar savings or a more bullet proof system. I will stay up to date with ARETHA.
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stmbtwle

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Reply with quote  #9 
It's not the 212F you're worried about, it's the 160F which your collector can easily obtain. When the electronics in the pump gets to around that temperature it shuts down. USUALLY it will run again after it cools down but not always. Check the specs on your pump.

For the holes in the tank I use nylon 'through-hull' fittings. To seal them you can use 3M 5200 or a rubber gasket on the inside. Both work well. Some through hulls have pipe thread, simply cut off the hose barb and screw on the fitting of your choice.

The ARETHA is still in the experimental stage, the newer version has the HEX assembly mounted outside what is really just an air heater. Probably not as efficient as the internal HEX but it would be even easier to build, and repair if needed. Pictures here:

https://www.facebook.com/Aretha-Project-307885346030194/?ref=ts&fref=ts&__nodl

I've used computer fans in mine and they have handled the heat with no problem though I've always mounted them on the "cool" side of the HEX. After nearly two seasons on my hot tub the fan was still running, though the aluminum HEX failed from the chlorine.

Cost is relative. An ARETHA will cost more than a CPVC collector of the same size but it's a LOT less work, and IMO more durable. What is YOUR time worth?

If I ever get caught up on the Honeydoos I want to build a larger one, 8 x 8. However as I'm in Florida it's not at the top of my list.

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Evilroyslade

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Reply with quote  #10 
Good FB ARETHA I'll follow it now and stay up to date. If my submergible pump specs aren't higher than 160f I will use the external with a bulkhead fitting in the barrel hole, after thinking about it I will drill the holes and put fittings in while the tank is empty in case I have to use the external pump. since I retired my time is worth $-100 every time I go to Harbor freight and Home Depot [smile]  
Thanks Willie for all your feedback, looks like you will miss all our up north winter sports living in Tampa.  

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