Secondary Refrigerants:

In some of the refrigeration systems, the refrigerant is not put into direct utilization. It is done mostly out of security considerations. As an instance, this is not wanted to use toxic refrigerants as ammonia in home air- conditioning & home refrigeration systems. Also, in some of the cases the size of the refrigerated space can be so big that direct refrigeration can be uneconomical. In such of the case, an indirect way is working. The refrigerants utilized in this way do not flow through the cyclic process & referred to like secondary refrigerants. Commonly the refrigerants utilized in this way are water & brine solutions of calcium or sodium. Therefore this permits the utilization of a smaller size refrigerator along a considerably less amount of refrigerant. Also, as the refrigerant does not come in direct contact, cheaper grade materials may be utilized for the heat exchanger.

Because of its toxicity, ammonia may not be utilized as a refrigerant in residential air conditioners. Hence, the usual practice is to chill brine over the evaporator coil & then air is cooled through passing over the brine coil. This technique removes the dangers of toxification on account of ammonia leakage into the air streams.

Sodium chloride brine solutions are most frequent up to - 15 ⁰C when calcium chloride brine solutions may be utilized up to - 50 ⁰C. Though, these solutions are very caustic to metals such as copper, brass and aluminium. In place of them, sometimes definite chemicals called antifreeze are utilized with water to stop clogging.