Undercooling or Subcooling of Refrigerant: Sometimes, the refrigerant after condensation process is cooled below the saturation temperature before expansion by throttling. Such a process is called undercooling or subcooling of the refrigerant. The ultimate effect of undercooling is to increase the value of coefficient of performance.

The process of undercooling is generally brought about by circulating more quantity of cooling water through the condenser or by using water colder than the main circulating water. Sometimes this process is also brought about by employing a heat exchanger. In actual practice, the refrigerant is superheated after compression and undercooled before throttling.