What is the optimal placement for a chilled water differential pressure sensor?

The differential pressure sensor for variable-speed secondary pump control should be installed across the supply and return mains at the most hydraulically remote coil (approximately 2/3 to 3/4 of the distance from the plant), measuring the differential pressure available at the end of the distribution system. The setpoint is typically maintained at the minimum pressure required by the “worst-case” control valve at design flow — plus any piping and fitting losses remaining to that valve. ASHRAE Guideline 36 recommends monitoring all control valve positions and resetting the DP setpoint downward until at least one valve reaches 90–95% open, analogous to the duct static pressure reset strategy for air systems. Installing the DP sensor at the plant or only partway down the main will cause the system to maintain excessive pressure at the remote coils, wasting pump energy and causing control valve hunting in near-plant circuits.