Differential Pressure Setpoint HWS/R

[mech711]

For a boiler plant with a BMS controlled differential bypass valve at the end of the loop and a Differential pressure sensor across the supply and return before the control valve. The loop consists of baseboard radiation with control valves on the return, fan coil units with a hot water coil and the pumps on the system have VFD's. How are the pumps controled? How do you obtain a differential pressure setpoint in the field and calculate one? The minimum flow through the boiler is 25 GPM the Differential bypass piping is 1-1/2" copper. Hopefully somebody can help.

 

[marcoh]

Differential setpoint should be based on the pressure differential where the differential pressure sensor is located through the piping, valves, fitting, coil etc. (IE not all the pipework back to the boiler)

Easiest way to control minimum flow is to install a flow meter at the boiler and a bypass valve controlled by the flow meter to maintain the minimum 25 gpm.

Have a look at the following article:

http://www.kirsner.org/kce/media/pdfs/PriSecChilWatr.pdf

 

[simsd]

What you do is you open up all of the control valves so that you have full flow. Make sure the bypass valve is fully closed. Then you take a reading from the input of the DP transmitter. This reading will become your setpoint as it simulates the worst case scenario.

Now put all of the valves back to auto and everything should take off. You should be able to see the changes in the system.

Any more questions, just let me know.