Refrigeration guide
How to Calculate Refrigeration Capacity
Use refrigerant mass flow and the evaporator enthalpy difference to calculate a stated refrigerant-side heat-transfer rate.
Start with the correct boundary
For a refrigerant-side evaporator calculation, capacity is the refrigerant mass flow multiplied by the refrigerating effect: the enthalpy increase from evaporator inlet to outlet. Both state points must come from the same refrigerant and operating condition.
Formula
Capacity (kW) = mass flow (kg/s) × enthalpy difference (kJ/kg)
The units collapse directly to heat-transfer rate. This is thermal capacity, not compressor electrical input or a final equipment selection.
Numeric example
At 10 lb/min and 40 BTU/lb across the evaporator, capacity is 60 × 10 × 40 = 24,000 BTU/h. That equals 7.03 kW thermal or 2 nominal refrigeration tons. Convert only after confirming the state-point basis.
What to document
| Item | Why it matters |
|---|---|
| Refrigerant and property source | Enthalpy and saturation values are fluid-specific. |
| Evaporator inlet/outlet points | They define the enthalpy difference and calculation boundary. |
| Mass-flow basis | It must represent the same refrigerant stream and condition. |
| Rating condition | Capacity changes as temperatures, pressure drops, airflow, and controls change. |
Common mistakes
- Mixing a mass flow from one condition with enthalpies from another.
- Using thermal kW as electrical demand.
- Generating refrigerant properties from a generic value rather than an identified source.
- Using a calculated capacity as a building-load or equipment-selection approval.
Related tools and references
- Refrigeration Capacity Calculator
- BTU to Tons Calculator
- Refrigeration Units and Measurement Reference
- How to Calculate HVAC Load
Sources and scope
Use a validated property source for the actual refrigerant. This calculation does not generate state points, diagnose a system, or replace a qualified design or service procedure.