Hydronics Primary/Secondary loops - secondary loop pump placement question
Hydronics Primary/Secondary loops - secondary loop pump placement question
(OP)
I read it is not desirable to install a centrifugal secondary loop pump in the return line of hydronic system as it decreases static pressure in the loop upon pump startup. (see attachment "rule #2")
The engineering firm that designed a system at our plant placed the pump in the return line - the system is already constructed but nothing ran yet.
Can someone give me an idea how we could know if the pump placement is an issue here? Is the concern of decrease in static pressure about cavitation in the secondary pump?
The engineering firm that designed a system at our plant placed the pump in the return line - the system is already constructed but nothing ran yet.
Can someone give me an idea how we could know if the pump placement is an issue here? Is the concern of decrease in static pressure about cavitation in the secondary pump?





RE: Hydronics Primary/Secondary loops - secondary loop pump placement question
Why don't you post a sketch of the system?
RE: Hydronics Primary/Secondary loops - secondary loop pump placement question
RE: Hydronics Primary/Secondary loops - secondary loop pump placement question
Thanks for reply. The secondary circulator is in the secondary circuit. A simplified sketch is provided in the last post.
Perhaps the normal placement in hydronics is in the supply to provide some desired pressure to secondary loop? We only require a given flow so perhaps our placement does not matter per the sketch?
RE: Hydronics Primary/Secondary loops - secondary loop pump placement question
RE: Hydronics Primary/Secondary loops - secondary loop pump placement question
1. With the pump on the discharge end, you would have to pressurize the common loop to force water into the secondary loop.
2. Difficult to fill the loop on startup.
3. Low suction pressure at the pump.
4. Pump suction problem if pump is installed on the multistory downleg.
5. If the common piping loop was long, you may not have much pressure to push liquid into the secondary loop where you tee off.
6. Centrifugal pumps are designed to pump, not to pull liquid.
7. In general, it is advisable to minimize the length of the pump suction lines.
8. Potential for problems with installations in multistory structures, but may not be a problem on single story structures.
Agree that the pump at the end of the secondary loop is incorrect.
RE: Hydronics Primary/Secondary loops - secondary loop pump placement question
Part of the problem is that the terms "supply" and "return" and "primary" and "secondary" can have whatever meaning you want them to have.
RE: Hydronics Primary/Secondary loops - secondary loop pump placement question
RE: Hydronics Primary/Secondary loops - secondary loop pump placement question
Hence, yes, often not a good idea, but can be done depending on the particular issues of your system.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.