Thermosyphon Solar Hot Water Heater question about Expansion Tank

[jvithayapun]

In a thermosyphon solar hot water heater, assuming there is a backflow preventor/check valve from the city supply, does it require an expansion tank or does the storage tank above the collectors act as a tank for some expansion as well?

Thanks

 

[willard3]

No, you will require an expansion tank also.

Consider the effects to the panel and piping if you don't. Actually, the expanded water should weep out the PRV if you don't have an expansion tank....either that or it will cause pipe/joints to fail in the solar panel.

 

[jvithayapun]

ok. does it matter where the tank is positioned?

1) between the backflow preventer (from city supply) and storage tank?

2) or between the storage tank and the solar collector?

 

[jvithayapun]

On a side note, the storage tank has a pressure relief valve. does this not take care of the water expansion, therefore not needing an expansion tank?

 

[willard3]

If you don't pump, any place on the system side of the back flow preventer should work. Locate the place of zero pressure change in the system and put it there.

 

[photoengineer]

The PRV valve will sort of take care of the water expansion problem. The trouble is that the water expansion problem will happen every time water is heated, so you will be dripping water out all of the time.

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