Refrigerant is the life blood of the vapor compression cycle. It is the fluid that flows continuously through the refrigeration cycle or vapor compression cycle absorbing heat from the low temperature reservoir and throwing it to the atmosphere or any other high temperature reservoir. For different temperature conditions and applications different refrigerants are found to be suitable. There is no ideal refrigerant that can be used in all the conditions.
1) Safe properties: The refrigerants that are used in refrigerating and air-conditioning systems should be harmless to the environment and not contribute to the depletion of the ozone layer, or to the increase in earth’s warming potential also called the greenhouse effect. Since many years a number of chlorofluorocarbons (CFCs) have been used as the refrigerants that cause excessive damage to the ozone layer when they are leaked to the atmosphere. What makes CFCs even more damaging is that they have a very long atmospheric life, which in certain cases can be 100 years. This means that once this refrigerant is leaked in the atmosphere it will keep on damaging it for 100 years.
2) Toxicity: Refrigerants are used extensively in household and commercial refrigeration and air-conditioning systems. These units lie in close proximity to human beings, and technicians frequently come in contact with the refrigerants. Hence it is vital that the refrigerants used in refrigeration and air-conditioning systems should be non-toxic in nature, so that even if they are leaked in the atmosphere they won’t have any damaging effects to human life. Presently, ammonia is the only toxic refrigerant being used to a large extent though its applications are limited to packing plants, ice plants and large cold storage facilities.
3) Flammability and explosiveness: Most of the refrigerants being used today are non-explosive and nonflammable. This is again very important to ensure the safety of humans that are using the refrigerating and air-conditioning systems. Ammonia is slightly flammable and explosive, but its effects can be nullified by taking some precautionary measures.
4) Economic considerations: The refrigerant used in the vapor compression cycle of the refrigeration or air-conditioning system should produce maximum refrigerating effect. That’s means it should have high coefficient of performance and consume less power for producing certain refrigerating effect. The cost of the refrigerant itself should be low enough.
Earlier refrigerants had very damaging effects for the atmosphere, but now a number of new and safe refrigerants have been discovered and are fast replacing the older ones. In some developing countries the damaging refrigerants are still being used extensively though their use has been restricted.