vapourcompression

Vapour compression refrigeration, or vapor-compression cycle, is a widely used method of removing heat from a low-temperature space by circulating a refrigerant through a closed loop that changes phase between liquid and vapor. The cycle uses a compressor to raise the refrigerant’s pressure and temperature, enabling heat rejection at a condenser and heat absorption in an evaporator.

In operation, the evaporator absorbs heat from the area to be cooled as the low-pressure liquid refrigerant evaporates into vapor. The vapor is compressed by a compressor, increasing its pressure and temperature. The hot, high-pressure vapor releases latent and sensible heat in a condenser as it condenses back to a liquid. The liquid then passes through an expansion device, which drops its pressure and temperature, creating a cold, low-pressure mixture that returns to the evaporator to begin the cycle again.

Key components are the compressor, condenser, expansion device (capillary tube or thermostatic or electronic expansion valve), and evaporator. Systems may include additional heat exchangers, filters, and control sensors. The cycle is used for refrigeration and air conditioning, and when reversed, forms a heat pump for space heating.

Performance is expressed by the coefficient of performance (COP) for cooling or energy efficiency ratings. Actual COP depends on operating conditions, ambient temperature, and refrigerant properties. Efficiency improvements come from optimized compressors, better heat exchangers, variable-speed drives, and precise electronic expansion control.

Environmental and safety considerations center on refrigerant selection. CFCs and HCFCs have ozone depletion potential and are being phased out; many systems now use lower-GWP refrigerants such as HFCs, hydrofluoroolefins, or natural substances like ammonia or carbon dioxide, each with trade-offs in flammability or toxicity.