HVAC

Rooftop HVAC unit with view of fresh air intake vent

Ventilation duct with outlet diffuservent. These are installed throughout a building to move air in or out of a room.

The control circuit in a household HVAC installation. The wires connecting to the blue terminal block on the upper-right of the board lead to the thermostat. The fan enclosure is directly behind the board, and the filters can be seen at the top of the image. The safety interlock switch is at the bottom left.

Heating, ventilation, and air conditioning (HVAC)^[1] is the technology of indoor and vehicular environmental comfort. Its goal is to provide thermal comfort and acceptable indoor air quality. HVAC system design is a subdiscipline of mechanical engineering, based on the principles of thermodynamics, fluid mechanics, and heat transfer. "Refrigeration" is sometimes added to the field's abbreviation, as HVAC&R or HVACR, or "ventilation" is dropped, as in HACR (as in the designation of HACR-rated circuit breakers).