Where should duct static pressure sensors be placed in a VAV system?

The duct static pressure sensor for fan speed control should be placed approximately two-thirds to three-quarters of the distance down the main supply duct from the fan, at a point where it represents the pressure required by the most remote VAV box during design flow. ASHRAE Guideline 36 recommends an iterative reset strategy: the static pressure setpoint is continuously reset downward until at least one VAV box is near fully open (≥95% damper position), which ensures minimum fan energy while meeting all zone loads. Avoid placing the sensor too close to the fan discharge (which would overestimate system head and waste energy) or directly at a duct fitting (which creates inaccurate pressure readings due to turbulence). The sensor should be installed with a straight run of 5–7 duct diameters upstream and 2–3 diameters downstream for accurate measurement.