Refrigeration cycle
Also known as: vapour-compression refrigeration cycle
Short definitionThe closed circuit in which refrigerant picks up heat in the evaporator and releases it in the condenser, kept going by the compressor and the expansion valve. All mechanical cooling, from cold rooms to air conditioners, runs on this loop.
Four jobs are done in sequence. The refrigerant evaporates at low pressure in the evaporator inside the room and takes up the heat of the air. The compressor squeezes this vapour, so pressure and temperature rise. In the condenser the vapour gives its heat to the outside air and turns to liquid. The expansion valve drops the liquid pressure and the refrigerant enters the evaporator again.
In a project the evaporator sits inside the room, the compressor and condenser in the condensing unit outside, and the valve at the evaporator inlet. Electricity use depends on the temperatures the heat is moved between: rejecting heat from a −20 °C freezer room to 35 °C outside air costs far more than from a 0 °C room. At commissioning, superheat at the evaporator outlet and subcooling at the condenser outlet are measured; if both are in range, the charge and valve setting are right.