Performance
Refrigerant mass flow from capacity
- where
- refrigerant mass flow (kg/s)
- refrigeration capacity (kW)
- enthalpy leaving the evaporator (kJ/kg)
- enthalpy entering the evaporator (kJ/kg)
Explain this equation
Works out how much refrigerant must circulate to give a required cooling capacity. Use it for sizing pipework and checking compressor selections.
Each kilogram of refrigerant absorbs h₁ − h₄ in the evaporator. Dividing the required capacity in kW (kJ/s) by that gives kilograms per second; the calculator also multiplies by 3600 for kg per hour.
This is the capacity equation rearranged for mass flow.
Sense check: 7.5 kW with 150 kJ/kg of refrigerating effect needs 0.05 kg/s, 180 kg/h.
Watch out: the refrigerating effect depends strongly on the condensing temperature and subcooling, so take h₄ at the real operating conditions.
Works out the refrigerant mass flow needed for a given cooling capacity, for line sizing, valve selection and velocity checks.
Enter your values to see the result.
Good to know
Q in kW divided by kJ/kg gives kg/s. Feed the result into the pipe velocity check with the density at line conditions.
Common mistake
Using compressor power instead of evaporator capacity, or condenser enthalpies.
Limits
Steady-state energy balance.
Sources
Results are calculations from the published methods and figures shown, and depend on the data you enter. Follow the equipment manufacturer’s data, CIBSE guidance, BS EN 378, the F-gas Regulations and your company procedures. Refrigerant work needs the correct F-gas certification.