What is considered supply air in HVAC terminology?

In HVAC terminology, supply air refers specifically to the air that is delivered to the occupied space after being conditioned by the system. This air is typically cooled or heated, depending on the requirements of the space, and is essential for maintaining comfort and air quality.

When a system operates, it draws in air from the environment, conditions it—through cooling, heating, humidification, or dehumidification—and then circulates that air back into the areas where people are present, such as residences or commercial buildings. This process ensures that occupants are provided with a comfortable environment.

The other options present different aspects of airflow within an HVAC system: air returned to the system refers to the air that exits the occupied space and is sent back to be reconditioned; air being exhausted from a space indicates the removal of stale air; and air drawn from outdoors is used for ventilation purposes. However, none of these options directly describe supply air itself, making the identification of supply air as the conditioned air delivered to the space clear and appropriate.