Pumping water to a height in a closed loop circuit
Pumping water to a height in a closed loop circuit
(OP)
I have a tank of water with a variable speed pump to pump water to solar collectors on the roof. The return pipe from the collectors comes back to the tank creating a closed flow loop. The roof is 15m above the tank. I am expecting the flow to run through the system if the pump just compensates the pressure drop due to friction in the pipe (because the fluid circuit is a closed loop). Whereas this doesn't happen. If the pump slows down and generates a head below a certain threshold the flow in the return pipe from the collectors separates. I am guessing that at the top of the circuit the pressure drops below the vapor pressure of water. Can anyone clarify on this and let me know how to run water at low flow rates in such cases?





RE: Pumping water to a height in a closed loop circuit
you've answered your own question. The system pressure ( usually maintained by some sort of expansion tank or bladder) needs to be at a pressure where the top of the system is at a positive pressure compared to atmosphere, so > 0.1 barg.
The easiest way for you is to have a tank located at the high point and keep it topped up to a level above the highest bit of piping.
Remember - More details = better answers
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RE: Pumping water to a height in a closed loop circuit
This was discussed recently:
http://www.eng-tips.com/viewthread.cfm?qid=393312
RE: Pumping water to a height in a closed loop circuit
It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)
RE: Pumping water to a height in a closed loop circuit
RE: Pumping water to a height in a closed loop circuit
http://westank.com/hydropneumatic-tanks/
RE: Pumping water to a height in a closed loop circuit
I've got a 300L tank mounted horizontally on my roof and there were no changes/structural reinforcing done when it was installed.
Question to the OP- can you pressurised the ground based tank? If it can handle pressure- close it up and run a small line up to a header tank to provide the required system pressure. Top up from the header tank. May require further thought if your area is subject to freezing temperatures.
As a chem eng/metallurgist the first part of any answer I give starts with "It Depends"
RE: Pumping water to a height in a closed loop circuit
If you live in a mainly heating climate, your main storage tank needs to be inside your house, not on the roof. The expansion tank on the roof is only needed to ensure the system remains liquid full without having thermal expansion problems so it should be small. If you're in a mainly cooling climate, the opposite is true.
RE: Pumping water to a height in a closed loop circuit