What describes a Direct Expansion system in HVAC?

A Direct Expansion (DX) system in HVAC is properly described by the statement that indoor air is directly cooled within the system. This type of cooling system works by circulating indoor air through a series of evaporator coils filled with refrigerant. As the indoor air passes over these coils, the refrigerant absorbs heat, thereby cooling down the air before it is circulated back into the living space.

The effectiveness of a Direct Expansion system lies in its ability to provide rapid cooling by directly engaging with the air within the occupied environment, making it highly efficient for immediate temperature control. This contrasts with systems that may rely on external air or other means of heating and cooling. Understanding this principle is vital for selecting and optimizing HVAC units in various settings, particularly in commercial applications where precise climate control is essential.

In this context, other options do not adequately characterize the Direct Expansion system. Using outdoor air solely for cooling, relying on heat pumps, or operating with steam for heating refers to different methods and systems, which differ fundamentally from how DX systems function.