How to evaluate the refrigerating capacity of compressors?
Most compressor manufacturers express the capacity of their compressors using the "nominal capacity" of the motor, expressed in HP (1 Horse Power = 0.735 kW) which does not give precise information on the refrigerating capacity of the compressor. Regarding this refrigerating capacity, the first thing to stress is that, for a given compressor, its value is different according to the refrigerant used, due to different thermodynamic characteristics. Secondly, for a given refrigerant, two different methods are used to measure the refrigerating capacity of compressors: - European standard EN12900 foresees a capacity measure in air conditioning under the following conditions: evaporation temperature: 5°C, condensation temperature: 50°C, superheating at the suction level: 10°C, sub-cooling at the discharge level: 0°C; - ANSI/ARI Standard 500, more used in the refrigeration and air-conditioning sector, involves the following conditions: evaporation temperature: 7.2°C, condensation temperature: 54.4°C, superheating at the suction level: 11°C, sub-cooling at the discharge level: 8.3°C. For example, the capacity evaluation of Copeland's 17 ZR model compressors, suited for air conditioning, with R-407C as a refrigerant, gives the following results using EN 12900: nominal capacity: 1.5-30 HP, refrigerating capacity: 3.8-79.4 kW; the value of 1 HP varies between 2,333 and 2,646 kW. The capacity evaluation using ARI Standard with R-22 as a refrigerant shows, for the same nominal capacities, refrigerating capacities of 4.4 kW to 92 kW; the value of 1 HP varies from 2,766 to 3,066. So, to evaluate the refrigerating capacity of a compressor, it is impossible to just convert the HP into kW since, in the case of the compressors cited, the result can vary by up to 31.4%. (3.066/2.333); the standard used and then the refrigerant need to be checked.