Ammonia refrigeration systems are gaining popularity these days due to their various advantages such as lower evaporation temperature and less environmental stress comparing with other industrial refrigeration. An ammonia refrigeration cycle is basically an absorption refrigeration cycle in which ammonia is used as the refrigerant. In the absorption cycle a heat source is utilised to provide the energy which is required to run the cooling system. These refrigerators have gained a wide popularity in industries since they reduce the electricity expenditure.

An ammonia refrigerator is similar to a regular compression refrigerator in that the refrigeration happens due to the evaporation of a liquid with a sub-zero boiling point. When a liquid evaporates or boils, it absorbs heat and this happens either until the entire liquid volume is boiled or until the area to be cooled reaches the sub-zero boiling point of the refrigerant. However there exists a difference between the two types of refrigeration in the manner by which the gas is changed into a liquid form for re-use. In an absorption refrigerator this is done by utilising heat, and as such no moving parts exist.

The refrigeration cycle typically starts at the evaporator. Here anhydrous, liquefied ammonia is entered. Anhydrous ammonia refrigeration systems contains no water and hence its boiling point is sub-zero. The evaporator also contains another gas (usually hydrogen) and the presence of this gas results in the lowering of ammonia’s the partial pressure. The total pressure in the entire system remains constant, but now the pressure is exerted by both ammonia and hydrogen. Ammonia is inert with respect to hydrogen, and hence the hydrogen is preset only to create a void which maintains the system pressure. Since the boiling point of any substance changes with its pressure, the boiling point of ammonia is lowered due to the decrease in its partial pressure. Thus ammonia can now boil at a pressure below room temperature. When ammonia boils and evaporates, it removes some of the heat present and this result in the refrigeration effect.