How To Calculate Refrigerant Amounts

Heat pumps transfer energy by forcing a refrigerant through differing pressures. The refrigerant absorbs latent heat of vaporization when it evaporates and releases it elsewhere when it liquefies. Each refrigerant has its own heat transfer rate, a value that describes how much heat it absorbs per unit weight. Specifications typically state this value using the standard scientific unit of kilojoules per kilogram (kj/kg). Simple conversions apply this transfer rate to construction and manufacturing measurements.

Step 1

Multiply your heat transfer requirement, measured in British Thermal Units, by 1.055 to convert it to kilojoules. If you must move, for instance, 250,000 BTUs in a given amount of time: 250,000 x 1.055 = 263,750 kj.

Step 2

Divide this amount of heat by the refrigerant's heat transfer rate. If the refrigerant moves, for instance, 170 kj/kg, then: 263,750 / 170 = 1,551 kg.

Step 3

Multiply this weight by 2.2 to convert it to pounds: 1,551 x 2.2 = 3,412 lb.

Step 4

Divide this weight by the number of cycles the system will go through during the time period. If if will cycle the refrigerant, for instance, 20 times: 3,412 / 20 = approximately 170 pounds. The system therefore needs 170 pounds of refrigerant.