What is subcooling and why is it important?

• A. Subcooling is cooling of liquid refrigerant below its condensation temperature, increasing system efficiency and preventing flashing.
• B. Subcooling is heating of liquid refrigerant above condensation temperature.
• C. Subcooling is removing moisture from the refrigerant.
• D. Subcooling has no impact on system performance.

Answer: (A)

Subcooling is cooling the liquid refrigerant below its condensation (saturation) temperature after it has condensed. Keeping the liquid well below the condensation point ensures the liquid entering the expansion device is fully liquid, with minimal vapor.

This matters because, at throttling, any non-subcooled liquid can flash into vapor. Flash gas reduces the amount of liquid that actually absorbs heat in the evaporator, lowering the effective refrigeration capacity and making the system less efficient. By subcooling, you minimize flash, deliver more liquid to the evaporator, and improve overall performance and efficiency. It also helps stabilize operating pressures and reduces the likelihood of liquid being carried into the compressor.

Moisture removal and lack of impact on performance aren’t descriptions of subcooling, and heating above the condensation temperature wouldn’t be subcooling either.