Method and limits

Cooling duty is the sensible heat balance on the evaporator: Q = ṁ · c_p · ΔT, taking chilled water density as 1.0 kg/L and c_p as 4.186 kJ/kg·K, so Q(kW) = flow(L/s) × 4.186 × ΔT(K). One ton of refrigeration is 3.517 kW. COP is duty divided by electrical input; kW/TR is the reciprocal expressed per ton.

The accuracy of this calculation is set almost entirely by ΔT. At a 5.5 K design difference, a ±0.2 K sensor error on either probe is a ±3.6% error in duty, and a ±0.5 K pair error is over 9%. Calibrate the supply and return probes against each other before trusting an efficiency figure, and take flow from a commissioned meter rather than a pump curve.

The part-load curve drawn here is a generic centrifugal characteristic for orientation only. Real part-load behaviour depends on compressor type, VSD fitment and condenser water temperature, and the certified IPLV or NPLV curve from the manufacturer should replace it. The tool evaluates one steady-state point; it does not detect refrigerant loss on its own — a persistent rise in kW/TR at constant load and condenser temperature is the symptom to watch for, which needs trending over weeks.