

For very small buildings, contractors normally estimate the capacity and type of system needed and then design the system, selecting the appropriate refrigerant and various components needed. In modern buildings, the design, installation, and control systems of these functions are integrated into one or more HVAC systems. The means of air delivery and removal from spaces is known as room air distribution. HVAC systems can provide ventilation, and maintain pressure relationships between spaces.


HVAC systems can be used in both domestic and commercial environments. The three major functions of heating, ventilation, and air conditioning are interrelated, especially with the need to provide thermal comfort and acceptable indoor air quality within reasonable installation, operation, and maintenance costs.

" 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). HVAC system design is a subdiscipline of mechanical engineering, based on the principles of thermodynamics, fluid mechanics and heat transfer. Its goal is to provide thermal comfort and acceptable indoor air quality. Heating, ventilation, and air conditioning ( HVAC) is the technology of indoor and vehicular environmental comfort. The safety interlock switch is at the bottom left. The fan enclosure is directly behind the board, and the filters can be seen at the top. The wires connecting to the blue terminal block on the upper-right of the board lead to the thermostat. The control circuit in a household HVAC installation.
