The cooling process is done by the chillers. The main parts of chillers are: refrigerant, compressor, expansion valve, evaporator and condenser. The refrigerant absorbs the heat from one environment and carries it to the other. In general, the refrigerant is required to have the following properties.

• The latent heat of evaporation should be high and the evaporation temperature should be quite low.
• Its critical temperature and pressure must be high.
• It should not pollute the environment and should not damage the ozone layer.
• It should not be chemically active, should not react with the installation materials and the oil used, and should not impair the properties of the oil.
• It should not decompose chemically, it should not be flammable, explosive or poisonous.
• It should be cheap.
• In case of leakage, it should have a feature (such as odor, color) that allows it to be detected easily.
• Its specific volume should be small and its viscosity should be low.

The main refrigerants used today: R134a : R134a (CF2CH2F) is the closest alternative refrigerant to R12 in terms of thermodynamic and physical properties. Double compression is required for low temperature. The ozone depletion coefficient is zero, and it is one of the most used coolers today. It is used in vehicle air conditioners, domestic and commercial coolers. Since it is not compatible with mineral oils, it should be used with oils based on polyolester or polyolalkalinglycol.