Chilled water and heating piping

[tscna88]

Hi all,

I have two separate systems one heating and one chilled water both are primary-secondary loop systems with VFD guided pumps on the secondary. Both have Differential pressure switches on the end of the loops controlling the speed of the pumps. I have no original engineering data on these DP settings and I believe someone has changed them without thinking. I am not not having any issue's other than on low load days it appears that the VFD's are running a little higher than I would see?
My question is, how can I determine, or what information is needed, to determine what the Chilled water and Hot water system differential setting should be at the end of the run. Right now they have the CW at 10psi and the HW at 20 psi. I am assuming that I would need to know the total head loss with all of the valves open? I guess if I had the list of information and how to figure it I could make sure the DP setting in the BAS is correct and not over or underkill.

 

[BigInch]

Differential pressure switches at the end of the run?
Where's the "end of the run"?
Differential pressure across what?
Maybe if you made a diagram and posted it here, somebody could help.

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[tscna88]

At the last unit we measure DP accross supply and return to maintain a set DP for the pump VFD.

 

[BigInch]

No sys diagram?
You might want to ask this question in the HVAC forum. Maybe they know what you're trying to do.

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[Bally91304]

If this an air conditioning system, you might set the control to maintain a 10 degree F delta T (temperature rise or drop) in the water through the coil of the end unit.