1. Supply Air:

Definition:  Air distributed from the HVAC system into the conditioned space.
Function:  Delivers heated or cooled air to maintain the desired indoor temperature and air quality.
Path:  Moves from the HVAC unit through ducts and vents into various rooms.

2. Return Air:

Definition: Air drawn from the conditioned space back into the HVAC system.
Function: Returns indoor air to the HVAC unit for reconditioning (heating, cooling, filtering) and recirculation.
Path: Travels from rooms through return ducts and vents back to the HVAC unit.

3. Exhaust Air:

Definition: Air expelled from the building to the outside.
Function: Removes stale, contaminated, or excess air to improve indoor air quality.
Path: Extracted from areas like bathrooms or kitchens and directed outside via exhaust ducts and fans.

4. Fresh Air:

Definition: Outdoor air brought into the building.
Function: Introduces outside air to dilute indoor pollutants and replenish oxygen levels.
Path: Enters through fresh air intakes, often filtered and conditioned by the HVAC system before mixing with indoor air.