TL;DR
Short cycling at low load means the chiller is hunting around its setpoint or the system load is below the minimum stable capacity. Widen the chilled water setpoint deadband and check the inlet guide vane minimum stop.
What you might see
- chiller starts and stops more than once per hour
- chilled water supply temperature oscillating
- surge or trip alarm appearing at low load
- starts logged significantly above design starts per day
Likely causes
Chilled water supply setpoint deadband too narrow, causing rapid start-stop hunting
System load below the chiller minimum stable capacity, triggering surge protection shutdown
Faulty chilled water supply temperature sensor giving unstable feedback to the controls
Inadequate chilled water loop volume providing too little thermal flywheel effect
Required tools
- Chiller controls access (Trane Tracer panel)
- Calibrated handheld thermometer
Safety first
- Adjusting chiller control parameters requires familiarity with the Tracer controls program. Incorrect surge protection settings can damage the compressor.
- Do not override surge protection limits without guidance from Trane service.
Procedure
- 1
Pull the start-stop log from the Tracer panel and count the number of starts in the last 24 hours. More than 4-6 starts per day is excessive for a centrifugal chiller.[1]
- 2
Check the current chilled water supply setpoint and the control deadband setting. Widen the deadband by 0.5 degrees C and observe whether cycling frequency decreases.[1]
- 3
Verify the chilled water supply temperature sensor calibration. Compare the panel reading to a calibrated handheld thermometer on the same piping.
- 4
Confirm the actual building cooling load by checking air handling unit valve positions and return water temperature. If load is near zero, enable a warm-weather setback or consider staging with a second smaller chiller.
- 5
Check the inlet guide vane minimum stop position. A minimum stop set too low allows the chiller to operate below its stable capacity range.
- 6
Review the surge protection parameters in the Tracer panel. If the chiller trips on surge at low load, the minimum stop needs to be raised to prevent operation in the surge zone.
- 7
If cycling persists after control adjustments, contact Trane service to review the controls program and compressor surge map.
Sources
Trane CenTraVac Chiller Operation and Maintenance Manual, Trane (Trane Technologies)
Trane CenTraVac Operation and Maintenance Manual, control system settings and surge protection (general)
View source
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