Chiller Capacity and Water Flow Calculation

The heat carried by a water circuit is calculated from mass flow, specific heat and the entering/leaving temperature difference. This calculation does not by itself establish the available capacity of a selected chiller at every operating condition.

Heat load formula

Q = ρ × cp × V̇ × ΔT

Q is in kW; density ρ is in kg/m³; cp is in kJ/kg·K; volumetric flow V̇ is in m³/s; ΔT is in K or °C. Assuming water density of 1000 kg/m³ and cp of 4.18 kJ/kg·K, with flow in m³/h: Q ≈ 1.16 × flow × ΔT.

Example: 100 kW with a 5 °C difference

Flow ≈ 100 / (1.16 × 5) = 17.24 m³/h. This water-only estimate assumes constant properties. For example, 20 °C entering water and 15 °C leaving water give a 5 °C difference.

Limits of preliminary sizing

Confirm leaving water temperature, ambient or condenser water temperature, glycol concentration, fouling allowance, flow limits and load profile. A pump also requires a pressure-loss calculation. Glycol mixtures need the actual density and specific heat. Use process data rather than a universal capacity margin.

Cooling capacity versus electrical power

A 100 kW cooling capacity is not a 100 kW electrical input. COP is cooling capacity divided by electrical input at stated conditions and measurement boundaries. Confirm whether fans and pumps are included.

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