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Chilled Water Reset Control Not Applied → Overcooling & Excess Power

Likely causes

Chiller CHWST setpoint fixed at 6 °C

Check: maintained even when load decreases, causing unnecessary COP drop

What to do: Change controller 'CHW Reset Enable' parameter to ON; configure reset range: when load ≤50%, raise setpoint +2 °C to operate at 8 °C

Return water temperature-based reset logic disabled

Check: controller parameter 'CHW Reset Enable' = OFF

What to do: Verify return water sensor connection: measure CHWRT sensor resistance (PT1000: 1000 Ω@0 °C), error within ±0.5 °C

Outdoor air temperature reset (OAT reset) sensor not connected

Check: setpoint stays fixed even as ambient drops

What to do: Activate OAT reset parameter: outdoor temp ≤10 °C → CHWST 8 °C; outdoor temp ≤0 °C → CHWST 10 °C

AHU-side valve over-opening pulls return temperature below setpoint

Check: controller always holds minimum setpoint

What to do: Optimize AHU valve opening: if return temperature is 2 °C below setpoint, reduce AHU valve opening by 20%

In multi-chiller parallel operation, reset applied to only one unit

Check: lead chiller alone adjusts, others run fixed

What to do: Power monitoring: confirm approximately 2–3% reduction in compressor power per 1 °C rise in setpoint

Field tip

Raising CHWST from 6 °C to 8 °C (2 °C increase) reduces chiller kW by approximately 4–6% — significant savings when converted to annual electricity cost.

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