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Centrifugal Chiller Surging — Repeated Impact Noise and Vibration

Likely causes

Refrigerant flow drops below impeller minimum flow (surge line) during low-load operation

Check: Surging is identified by repeated 'bang-bang' impact sounds. Check compressor suction/discharge pressure ratio — below 2.0 indicates surge boundary. Check IGV (inlet guide vane) opening — surging is common when IGV is below 15~20% at loads under 20~30%

What to do: When surging occurs: manually open hot gas bypass valve immediately → increased flow escapes surge line. Set IGV minimum opening to 25~35% — prevent closing below this at low load. After load recovers, gradually close hot gas bypass

Cooling water temperature too low (<25°C) — condensing pressure drops sharply forming surge conditions

Check: Measure cooling water inlet temperature — below 25°C may cause condensing pressure to fall below spec (400~600 kPa depending on model). Check for cooling tower over-cooling in winter or night

What to do: Adjust cooling water temperature control valve — maintain minimum condensing pressure spec. Reduce cooling tower fan speed or stop some cells in winter to maintain cooling water 25~32°C. Check evaporator/condenser tube fouling factor — clean tubes if ≥0.0002

Field tip

For surging, open hot gas bypass before vibration spikes, then gradually close as load recovers. Ignoring it leads to impeller failure and bearing damage.

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