HVAC (pronounced either "H-V-A-C" or "aetch-vak") is an acronym that stands for the closely related functions of "Heating, Ventilating, and Air Conditioning" - the technology of indoor or automotive environmental comfort. HVAC system design is a major 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 ventilating is dropped as in HACR (such as the designation of HACR-rated circuit breakers).
