The rate at which heat must be removed from an application under specified operating conditions, commonly expressed in W or kW.
Also called: heat load; thermal cooling load; required cooling duty.
Is a 3 kW chiller always enough for a 3 kW process?
Compare load with capacity specified at relevant conditions. Load is heat-removal demand; available capacity is what the system can supply at its stated fluid and heat-rejection conditions. A nameplate value at another operating point is not the same capacity claim.
Separate steady operation from startup cooldown and other transient demand. Heat pickup in a circulating fluid and cooling a fixed volume over time require different calculation boundaries. A machine’s electrical rating is not automatically the heat entering one coolant branch.
Estimating heat pickup from flow and temperature rise
For approximately steady single-phase flow, use mass flow, specific heat and the temperature rise across the defined load. The fluid identity matters: a water assumption cannot silently be substituted for a different glycol concentration or fluorinated fluid. The estimate represents that measured boundary, rather than every heat source on the line.
Use simultaneous, representative flow and temperature measurements. A small temperature difference makes measurement uncertainty particularly important. The calculation below addresses sensible heat at that boundary; additional sizing allowance needs an application-specific basis.
Heat pickup (W) ≈ mass flow (kg/s) × specific heat (J/kg·K) × return-minus-supply temperature (K).