Can buildin hydronic hot water pump vfd be controlled by a flow meter?

[tlsps]

For energy savings, a vfd is replacing the constant speed motor controller for the building hot water pump. Usually, dp switches are installed at the pump output and 2/3rds out into the system. In this case, the line is in a pipe chase that will not allow DP installation on the piping anywhere near the end of the line. The piping is cast iron.
Q1: Can a strap-on flow meter be used at the 2/3rds location? It can be installed since no cutting or welding would be required, but not sure if flow measurement will provide an accurate way to control the pump speed.
Q2: Can DP switches be installed at the pump suction and discharge in lieu of 2/3rds? Will the nearby locations provide enough input on what the system needs really are?

 

[marcoh]

The function of the prump is to provide differetial pressure across the control valve so you should measure the system pressure.

Taking a step back though are the control valves 2 way or 3 way valves as it sounds as if the exising system is a constant flow system.

 

[tlsps]

We are changing out the valve as part of the VFD upgrade.

 

[mauricestoker]

Are you sure you're not confusing air side and hydronic side? Or, are you considering 2/3 of highest hydraulic run?

I'd recommend considering valve percentage open to run the pump.

 

[tlsps]

Yes, 2/3 highest hydraulic run. How does valve percentage work? There are 20 AHU coils on the hot water circuit.

 

[KiwiMace]

A flowmeter is not applicable unless you are controlling to a flow setpoint. In this case, you do not know at any given point in time what this flow should be.

Thus the pressure or valve position inputs already mentioned.

 

[tlsps]

Ok. I am interested in the valve percentage open control, but don't know the concept. How would that control scheme work, and would it require replacing all control valves, or just one? If one, where should it be located?
Thanks to all, by the way. Very helpful input.