Heating, Ventilation and Air Conditioning (HVAC) 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 ventilating is dropped as in HACR (such as the designation of
HACR-rated circuit breakers).