What type of air is conveyed to or from occupied areas through ducts not associated with heating or air-conditioning?

The correct choice is environmental air, which refers to air that is brought into or removed from occupied spaces through ducts that are not specifically associated with heating or cooling processes. This type of air typically includes fresh air introduced to improve indoor air quality or to ensure adequate ventilation.

Environmental air is critical for ensuring that living and working spaces maintain acceptable levels of oxygen, dilute indoor pollutants, and regulate humidity levels. In systems designed for ventilation, this air may come from outside sources as part of a mechanical ventilation strategy to maintain comfort and health standards indoors.

The other types of air mentioned—return air, supply air, and recirculated air—are primarily linked with heating, ventilation, and air conditioning (HVAC) systems where temperature regulation and comfort control are the main objectives. Return air is the air that is taken back from the occupied space to be filtered and conditioned before being reintroduced. Supply air is the conditioned air delivered into the space. Recirculated air is air that is reused within the system after going through filtering and conditioning processes. While these types of air play vital roles in HVAC systems, they do not pertain to the definition of environmental air, which focuses on the broader scope of indoor air quality and ventilation, rather than temperature control.