CHW Pump Pressure 3

[jrrocks]

Had a heated argument so just want to have clear understanding on this thing. When we are calculating pressure head for chilled water pump, we include all fittings and losses occur through the farthest route of CHW piping with corresponding flow including the return lines. My understanding is, this pressure is nothing but the differential pressure we have maintain across pump (Discharge - Suction Pump)to get the desired supply flow (as per pump selection or curve)

 

[LittleInch]

For a closed loop system where the pressure is maintained such that the highest point of the piping is kept at positive pressure - correct. You don't mention it specifically but also include losses through the AHU or whatever you plan to use the CHW for.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[SAK9]

Pump discharge pressure - Pump suction pressure= Differential head developed by the pump= System pressure drop

 

[jrrocks]

Thanks Folks...!!!

 

[lukaiENG]

Just pointing out a nuance - your index run may not be the furthermost point in the system. sometimes a closer item may have a higher pressure drop through it's coil and therefore become the system index. 99% of the time your statement is correct though.

 

[jrrocks]

Correct. Thanks.

 

[jrrocks]

What are the possible reasons if i received correct flow but not correct differential pressure (as per the pump performance curve)?

 

[LittleInch]

poor readings?

Different voltage

Variance in pump performance

Give us a bit of a clue here - how much different?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[BronYrAur]

Are you sure you are looking at the correct impeller size? Are you running at full rpm?

 

[jrrocks]

There are 3 pumps running. I could expect any one might have problem, but its unlikely that all three might have or may not have same issue. @pump 1: suction pressure is 2 bar and discharge is 5.3 bar. dP 3.3 bar. At 3.3 bar my flow to be 50 l/s as per performance curve, but in fact i am getting 75 l/s (which is req. as per design).

 

[BronYrAur]

I'm still confused by your reply. With three pumps (I assume in parallel) you will have a different flow characteristic than you would with only one pump running. Are you looking at the combined pump curves of all three in parallel?

 

[LittleInch]

Can you post pump curve.

Also check the electric current if you can and check all three pumps at the same time.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[jrrocks]

@BronYrAur
Yes these are in parallel. As per design Total flow required @ common Chiller supply header is 223 l/s. So three pumps in parallel (@ 75 l/s each , all are of same model/capacity)

 

[LittleInch]

You may well find that one pump is doing 50 and the other two 85... There are many many threads on this forum about parallel pumping issues and mismatch between supposedly "identical" units.

Lik eI said - post the pump curve if you have it and also try and see how many amps each pump is taking when operating in parallel. It's sometimes easier to measure Amps than fluid flow.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[willard3]

Have you checked the pump impellers for wear or other variances?

 

[jrrocks]

You are correct Williard.