Which of the following terms describes the process of reducing a refrigerant temperature to increase its density?

Subcooling refers to the process where the temperature of a refrigerant is lowered below its condensing temperature, while it is still in the liquid state. This reduction in temperature increases the density of the refrigerant, which is beneficial in HVAC systems as it enhances the refrigerant’s ability to absorb heat during its evaporation phase.

By subcooling the liquid refrigerant, you ensure that more of the refrigerant enters the evaporator in a denser liquid form, which maximizes the system’s efficiency and cooling capacity. The subcooled liquid can absorb more heat from the environment before it vaporizes, leading to a more effective refrigeration cycle. This is vital in commercial air conditioning applications to maintain optimal performance and energy efficiency.

The other terms relate to different processes. Superheating involves heating a vapor to increase its temperature above the boiling point, which does not increase density; ejector ventilation pertains to a method of moving air within a system rather than changing refrigerant state; and thermal expansion refers to the process of cooling fluids but does not directly relate to increasing refrigerant density through cooling. Thus, subcooling is the most appropriate term for the process described in the question.