If the pressure exerted on the surface of a liquid body is reduced, the liquid will change to the gaseous state more readily, requiring less heat to evaporate.
Therefore, one of the first steps performed in the development of refrigeration systems was the identification of fluids whose boiling point is lower than that of water.
Fluids in which this characteristic has been identified are defined as "refrigerants".



The gas CFC-12 (R12) was one of the most widely used refrigerants until it was banned due to its highly destructive effect on the ozone layer (the layer that blocks most ultraviolet radiation).

The gas HCFC-22 (R22) combines excellent chemical and physical characteristics with high volumetric efficiency, ensuring its use in air-conditioning systems with low and medium capacity requirements. This gas is also under observation for its effects on the environment.

The gas CFC 114 is used in centrifugal compressors for air-conditioning systems.

The gas CFC 502 is one of those mixes that does not change its volumetric composition or its saturation temperature during evaporation, and, as it evaporates at lower temperatures than the other gases, is used in hermetic compressors.



The harmfulness of CFCs and HCFCs has been proven internationally, to the point where the Montreal protocol of 1992 resulted in the setting of production quotas, followed by their complete banning.
The search for alternative refrigerants has been focused on the category of hydrocarbons (HC), which are harmless to the environment but are extremely flammable, and therefore not suitable for residential applications; the category of the natural refrigerants (ammonia), which have good thermodynamic properties, low flammability but high toxicity; and finally the category of hydrofluorocarbons (HFC), which do not have an impact on the ozone layer, but do increase the greenhouse effect (quantity of CO2 in the air).

The gas HFC 134a (R134a) is used to replace CFC-12 in civil refrigeration applications, due to its low impact on the ozone layer, but it is not suitable for air-conditioning systems.

As a replacement for R22, the gases HFC 407C (R407c) or HFC 410A (R410a) are used, but in both cases the refrigeration and air-conditioning systems need to be converted accordingly. As well as these, the gas HFC 404A (R404A) is also used, however its potential effect on global warming is among the highest in the category of hydrofluorocarbons.