A liquid sub-cooler is fitted in a cooling plant in order to increase the performance of the evaporator. Sub-cooled liquid lowers the refrigerant inlet temperature to the evaporator.
Liquid sub-cooling is an application often used in refrigeration plants for heat transfer between the suction and liquid lines, and to decrease the liquid to below its boiling temperature/condensing temperature.
The purpose is to utilize the temperature difference between the suction line at the evaporation temperature (plus super-heating) and the liquid line at the condensing temperature.
The energy exchanged in the liquid sub-cooler increases the performance of the evaporator, since it lowers the refrigerant inlet temperature to the evaporator.