What is subcooling?

The term "subcooling" has different meanings depending on the industry. In the medical field, it is viewed as a threatening and negative concept. In refrigeration and cooling technology, on the other hand, the situation is exactly the opposite: a significant level of subcooling is desirable.

Subcooling pertains to the state of the refrigerant in the refrigerant circuit. In a refrigeration system, subcooling is important because it leads to an improved energy balance of the system and protects certain components, thus ensuring the longevity of the refrigeration system.

How is refrigerant subcooled?

Subcooling occurs after the refrigerant has undergone its condensation process through the condenser, settled and formed a reserve in the refrigerant collector. After the refrigerant collector, the liquid refrigerant passes through another heat exchanger, where it is brought to a temperature below its saturation point (the boiling point at a given pressure). The use of an additional subcooler achieves this effect.
 

In a refrigeration system, it must be ensured that the refrigerant is entirely in a liquid state before the expansion device (injection valve). The transition from a liquid to a gaseous state should only occur in the evaporator. If the refrigerant is not completely liquid before the injection valve, it has a significant impact on the performance and efficiency of the refrigeration system.

How does pre-evaporation occur?

Pre-evaporation in a refrigeration system occurs when the pressure above the liquid refrigerant decreases. The saturation pressure is undershot, and the refrigerant starts to boil. This can occur due to pressure fluctuations in system operation or pressure drops in pipelines and components. Especially in vertical pipes, there is a natural pressure drop due to the difference in elevation, resulting in a significant pressure drop.

To prevent the problem of pre-evaporation and maintain the efficiency of the refrigeration system, adequate subcooling is essential.