What portion of supply air includes outdoor air and any recirculated air treated to maintain air quality?

The correct answer, ventilation air, is essential in HVAC systems because it refers to the portion of supply air that combines outdoor air with recirculated air that has been treated to uphold air quality standards. Ventilation air is crucial because it helps dilute indoor pollutants and provide fresh air to occupants, ensuring a healthy indoor environment. This air is subjected to conditioning processes such as filtration, heating, or cooling to optimize comfort and health.

Understanding ventilation air is important for compliance with building codes and standards, as it directly impacts energy efficiency and indoor air quality. Other options like environment air, exhaust air, and transfer air do not accurately describe the combination of outdoor and treated recirculated air used for maintaining air quality within a building. Environment air typically refers to the broader atmospheric conditions rather than a specific category of air involved in ventilation. Exhaust air pertains to air that is removed from a space, often for the sake of expelling stale or contaminated air, while transfer air concerns the movement of air between spaces without necessarily indicating any treatment for quality maintenance.