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. 6.5 Demand controlled kitchen ventilation.Methods for ventilating a building are divided into mechanical/forced and natural types. Ventilation removes unpleasant smells and excessive moisture, introduces outside air, keeps interior building air circulating, and prevents stagnation of the interior air. Ventilating or ventilation (the "V" in HVAC) is the process of exchanging or replacing air in any space to provide high indoor air quality which involves temperature control, oxygen replenishment, and removal of moisture, odors, smoke, heat, dust, airborne bacteria, carbon dioxide, and other gases. HVAC is an important part of residential structures such as single family homes, apartment buildings, hotels, and senior living facilities medium to large industrial and office buildings such as skyscrapers and hospitals vehicles such as cars, trains, airplanes, ships and submarines and in marine environments, where safe and healthy building conditions are regulated with respect to temperature and humidity, using fresh air from outdoors. " 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 use of various technologies to control the temperature, humidity, and purity of the air in an enclosed space. 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.