Controlling variable primary or secondary chilled water pump speeds relies heavily on differential pressure (DP) feedback. Mislocating the DP sensor causes secondary pump cycling, inadequate flow at remote cooling coils, or wasted pumping energy.

Understanding where and how to place differential pressure transmitters across a hydronic loop is essential for balancing energy efficiency with occupant comfort.

1. Comparison Matrix: Sensor Placement Strategies

2. Calculating Setpoints & Preventing Pump Hunting

When positioning the DP transmitter at the 2/3 position of the longest hydraulic run:

• Setpoint Calculation: Set the DP control setpoint equal to the design pressure drop across the control valve and coil at design flow (GPM), typically 5 to 15 PSI (35 to 100 kPa).
• Proportional-Integral (PI) Tuning: Use a longer integral time constant on pump speed control loops to prevent pump hunting caused by rapid valve movements across the system.
• Fail-Safe Logic: If the remote DP sensor signal drops offline or experiences a fault, configure the BMS to default pump speed to a pre-set safe minimum (e.g., 70–80% speed) and trigger a high-priority alarm.