Which of the following describes a direct expansion cooling system?

A direct expansion cooling system operates by allowing refrigerant to directly expand within the cooling coils. In this process, the refrigerant absorbs heat from the surrounding air as it evaporates, effectively cooling the air that is blown over these coils. This method is common in air conditioning units and is effective for providing immediate cooling. The efficiency of this system comes from the direct contact between the refrigerant and the air, allowing for rapid heat exchange.

Other options describe different systems or processes that do not align with the principles of direct expansion cooling. For instance, systems that cool water before distribution refer to chilled water systems, which are distinct from direct expansion systems and do not involve refrigerant expanding within coils. Similarly, methods for increasing air humidity relate to humidification processes, which are not a characteristic of direct expansion cooling where the goal is primarily to reduce temperatures rather than increase moisture levels. Lastly, a process requiring no refrigerants describes air systems or other non-refrigerant-based methods, which fundamentally differ from the direct expansion approach that relies on the phase change of a refrigerant for cooling.