Chillew water pump 2

[MisterDonut]

Secondary pump speeds should modulate in response to the remote secondary loop differential pressure signal. The set point will need to be refined after testing and balancing, but 10 psi is a typical starting point. The differential pressure signal is typically measuring the pressure difference between the chilled water supply and the chilled water return at the point in the secondary loop that has the greatest pressure loss between it and the secondary pumps.

 

[hvacers]

Ideally i would place the DPT at the farthest unit in order to get the real picture at the end of the loop. and you can do testing from time to time and try to reduce the speed of the VFD as long as you dont go below your minimum delta P at the farthest unit

 

[xpsboy]

can you please let me know what will be my pump setpoint (psi) if I have 30mAq total head?

Also the diff. press transmitter will give signal to VFD to modulate the pump water flow? or pump will modulate base on temperature difference?

 

[xpsboy]

How to find the value of Differential Pressure Transmitter that will give signal to VFD to modulate?

Thanks in advance.

 

[MisterDonut]

The set point for the differential pressure must not be too high or control valves will not close properly and pump energy is wasted. Too low and some units will not have adequate performance because the control valve can’t accurately control the required flow to maintain the air-side set point.
To begin with, look at the unit closest to the sensor. Estimate the pressure differential through this unit’s coil, control valve and piping to and from the header. Assume the control valve is 80% open at maximum design flow. This amount is the pressure differential needed at that unit. Use that value as a starting point. If possible, test, adjust and balance the entire system and refine the set point as needed.

 

[xpsboy]

Misterdonut,
When you say estimate the pressure differential through the units coil, control valve and piping to and from the header - does it mean the Total Pump Head?

If I have 30m Aq (~100 ft of water) total pump head does it mean that is my diff. pressure sensor setting?

Thank you in advance.

 

[MisterDonut]

The differential pressure at the remote sensor will not be the same as the pressure developed at the pump because of the losses between the pump and the remote sensor.
The head required at the pump must overcome the losses in the supply and return piping as well as the losses through the control valves and coils. Some units are near the pump, so the piping losses between the pump and these units is lower. Some units are far from the pump, so there is more piping, and thus more piping losses, between the pump and these units. Each unit needs a certain amount of pressure differential between the supply and return piping so that water will flow through the control valve and coil. The set point to be maintained at the remote sensor must be enough to overcome the losses through the most remote unit.