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Old 09-25-20, 04:16 AM   #9
Hong Kong
Join Date: May 2010
Location: Hong Kong
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Originally Posted by SDMCF View Post
Jeff, how do you see such problems happening? I have no experience with drainback systems so I can only guess.

It seems to me there are 2 ways: a failure to pump fluid into the collectors because of pump or power failure, or collector temperature rising rapidly before the system can react and pump fluid. Have I missed something?

Failure to pump is a problem in any system, so not unique to tubes or drainback.

Slow reaction at first seems surprising, but thinking about it I can understand how this might happen. The temperature sensors on mine are at the (outlet) end of the manifold. Without fluid in the system to dampen the temperature rise the end of each tube could conceivably get very hot before the temperature rises is conducted as far as the temperature sensor. If I hold in my hand the end of a tube that is normally inserted into the manifold, with the tube in full sun the end quite quickly becomes too hot to handle.

I had not considered that before, so I was lucky that I did not (could not with my layout) opt for a drainback solution.
There are advantages and disadvantages to both systems. If drainback is done right, I sincerely believe it will eventually be simpler in construction, more reliable, more failsafe, cheaper to build and maintan and even more efficient.

I am really tired of watching energy lost in heat exchangers. I need a better system, and that is what I will build.
Space heating/cooling and water heating by solar, Annual Geo Solar, drainwater heat recovery, Solar PV (to grid), rainwater recovery and more ...
Installing all this in a house from 1980, Copenhagen, Denmark. Living in Hong Kong. Main goal: Developing "Diffuse Light Concentration" technology for solar thermal.
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