Compressor
Also known as: refrigeration compressor
Short definitionThe machine that drives the refrigeration cycle. It draws low-pressure vapour from the evaporator, compresses it and discharges it to the condenser at high pressure; most of the electricity the system uses goes here.
To reject the heat collected from the room, the refrigerant has to be warmer than the outside air. The compressor makes that happen: it draws in the vapour, compresses it and raises its pressure and temperature. By housing there are hermetic, semi-hermetic and open types; by mechanism there are reciprocating, scroll, screw and rotary types. The compressor accounts for 80–90% of the plant’s electricity use.
Selection rests on three figures: the cooling capacity required, the evaporating temperature and the refrigerant. As the evaporating temperature falls, the capacity of the same machine falls too; a compressor that is enough for a 0 °C room does only about half that work in a −25 °C room. Freezer rooms therefore use a low-temperature series and, where needed, a two-stage or economised model. Liquid at the suction, poor oil return and frequent starts shorten its life.