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Green Energy Living

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Reply with quote  #1 
I have a similar problem to Giel's because I have a lot of trees around my house I needed to mount my solar panels on the roof which is about 15 ft higher than my 200 gallon water tank inside my laundry room. I tried using three different submersible pond pumps all of which did not work. They did not have enough head pressure even though when you put them in a bucket of water they really move a lot of water around very fast. It appeared they would be powerful enough. The problem with other pumps is that they have so much power that the water would move too quickly through the panel so the heat output or heat rise would not be very much. I also have a grundfos 3 speed pump but the problem with that is I used a plywood and pond liner tank there is no way that I can think of to mount the pump below the waterline so it can be primed to suck the water out of the tank AND STILL DRAIN WATER BACK INTO THE TANK when the pump stops FOR A DRAINBACK SO NO WATER REMAINS IN THE PANEL TO FREEZE.. sorry for the caps but I had to emphasize that. I really liked the idea of the submersible pump because you don't need to prime it and as soon as the pump stops the water automatically drains back because of gravity. It seems impossible to have a pump that wouldn't need to be primed amd have enough head pressure to bring the water up that high but yet be slow enough that the water can heat up sufficiently and still allow the water to drain back in the tank.
Any suggestions?. Thank you very much

stmbtwle

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Reply with quote  #2 
You can mount the pump outside the tank if your water line leads out the top of the tank and then down to the pump which must be located below the water level in the tank. You will have to prime it but it should maintain its prime. The water will only drain back to the level of the water in the tank. The pump and this "dip" in the line MUST be located inside where it won't freeze.

Even with a slow pump, you'll only get a temp rise of a couple degrees between the tank and the collector output. However this adds up as the tank gets warmer as you are recirculating the heated water.

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Solar is like the wind. It may be free, but putting it to work isn't!
Willie, Tampa Bay
SolarInterested

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Reply with quote  #3 
The BuildItSolar site has some info

Rules for Plumbing a Drain Back System
https://www.builditsolar.com/Projects/SpaceHeating/DHWplusSpace/PlumbingDesign.htm


and see "High Head Drainback System Pumps" under
https://www.builditsolar.com/Projects/SpaceHeating/Components.htm#Pumps

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Both temperature rise and airflow are integral to comparing hot air collectors
Green Energy Living

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Reply with quote  #4 
Thank you, that's a good point and that's good advice. I will follow that
Bruce

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Reply with quote  #5 
I am using the Grundfos 3 speed hooked up just like the drawing above in the BIS site and it works great.  I installed it with a drain to outside and can fill the tank from outside the basement wall.  I have been using it for 3 or 4 years and it has never lost its prime.  
Green Energy Living

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Posts: 33
Reply with quote  #6 
I hooked up my grundfos 3 speed pump however even the grundfos pump does not have enough power to get the water up and back, however if I plug in my submersible pond pump in conjunction with the grundfos 3 speed pump it does have enough power to get the water up and back through the solar panels. Then I can shut off my submersible pump and then the grundfos pump will continue to circulate the water at a slower rate of flow. I was going to drill a 1 inch hole through the thin metal backing and insulation on my solar panel to place a snap disc switch to start both pumps when the temperature in the solar panel gets to be above 100 degrees. However I need to figure out how to shut the submersible pump off after approximately two minutes after the snap disc switch turns on both pumps after reaching the temperature of a hundred degrees in the solar panel. Can anybody think about how to shut the submersible pump off after 2 minutes? Thank you
stmbtwle

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Reply with quote  #7 
I've seen adjustable delay modules in an air conditioner, don't know if they could be made to work.

An idea would be to put the second pump on a separate snap disk with a higher setting. Any time the first pump fails to start circulation, the collector will start to overheat, and the second pump will kick in. Once flow starts the collector will cool a bit and the #2 pump will stop. It will also give you a "two speed" system.

Yet another setup (possibly better) would be some sort of flow sensor in the return line. The marine industry uses them to set off an alarm if they lose coolant flow.

Someone else might have a better idea.

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Solar is like the wind. It may be free, but putting it to work isn't!
Willie, Tampa Bay
Green Energy Living

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Reply with quote  #8 
Thank you, if the flow sensor exists, I think that would be a perfect idea. because once the water starts going back into the tank the grundfos pump can handle it from there. I will see if I can find one on Amazon or ebay
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