Pressure sensors locaiton for Variable pumping 1

[remp]

I have a variable pumping system with 2 port valve arranagment on all the air handling unit coils for a chilled water system. The pipe run is over 300m with branches to different building every 30 meters. Where should i position the differential pressure sensor for controling the variable speed dirve of the pump? Should it be before the first branch take off or at the end of line or elsewhere?

 

[DRWeig]

At the worst-case coil, farthest from the pump (and with the most pressure drop). Otherwise, your controller will have no way of meeting that coil's needs.

Good on ya,

Goober Dave

 

[coldmaster]

If you don't have pressure independent flow control valves you may be better off with the sensor "2/3" of the way down the main run. Differential pressure setpoint should be determined based on full flow and 100% system demand. I don't think you want to control the system based on any one coil's branch piping.

 

[EnergyProfessional]

You also can do some trim&respond (like in VAV systems) to reduce the set-pressure if demand is low. then the coil with the largest opening position will determine set-pressure.

 

[mauricestoker]

You may want to place more than one dP, especially if running variable loading on multiple branches. If you did the thermal loading, minimum and maximum loads should be apparent, by location. If toughest run is the same on min and max, a single dP might do.

 

[marcoh]

I usually try try to locate the DP sensor near the end of the index run. If there are significant branches (or multiple potential index runs) install a DP sensor on each one and control to maintain pressure at all locations.

I used to locate the sensor 2/3 between first and last take-off but on one project had an issue with starving the end AHU's at part load conditions. The pipework distribution on that specific project was complex and loads highly variable but ever since then have always put the DP sensor at the end without an issue.

If you really want to optimise energy consumption you should use an algorithm to automatically reset the differential pressure setpoint as low as possible.

But if you have different buildings I think you will potentially have problems maintaining acceptable pressures in all buildings and you should be considering tertiary pumping to each building, or look differential-pressure-control-valves serving each individual building.