AHU temperature control is hunting
AHU with a chilled water coil and modulating valve is stable at full load but starts hunting ±1.5°C around setpoint once the space load drops in the evenings. Valve appears to be overshooting and correcting repeatedly. Reasonably confident it's a tuning issue but want a sanity check on approach before I start adjusting gains on a live system.
Manufacturer
Trane
Controller
UC600
2 Answers
Demo Engineer · HVAC Controls Consultant
AcceptedClassic sign of proportional gain being too aggressive relative to the process at part load, since valve authority and coil response change with flow. Reduce gain first and observe, rather than adjusting integral time initially — it's easier to diagnose one variable at a time. Also confirm the valve isn't oversized for the reduced load, which alone can cause hunting no matter how it's tuned.
16 upvotes · 2026-08-06
Demo Engineer · Building Performance Engineer
Worth trending valve position alongside supply air temperature for a full day before changing anything — if the valve is fully closing and reopening repeatedly, that's a minimum flow or deadband issue rather than pure gain tuning.
7 upvotes · 2026-08-06