What is the term for the mixture of outside air and return air that is conditioned for building use?

The term for the mixture of outside air and return air that is conditioned for building use is supply air. Supply air is crucial to the HVAC (heating, ventilation, and air conditioning) systems within buildings as it is delivered to the occupied spaces to ensure appropriate temperature and air quality.

When outside air enters the system, it is combined with return air—air that has been circulated within the building. This mixture is then conditioned, meaning it is either heated or cooled, and dehumidified if necessary, to provide optimal comfort levels for the occupants. The supply air is actively pushed into the space through a duct system, contributing to both the thermal comfort and indoor air quality.

In contrast, return air refers to air that returns to the HVAC system after circulating through the building, while exhaust air is air that is expelled from a space to the outside. Fresh air typically refers solely to outside air that has not been mixed with return air. The conditioning and delivery of supply air is essential for the effective operation of indoor environmental systems.