Heating, Ventilating, and Air Conditioning (HVAC) equipment perform heating and/or cooling for residential, commercial or industrial buildings. The HVAC system may also be responsible for providing fresh outdoor air to dilute interior airborne contaminants such as odors from occupants, volatile organic compounds (VOC's) emitted from interior furnishings, chemicals used for cleaning, etc. through ventilation; and providing proper building air pressurization.

HVAC systems generally have a few basic design elements
  • Outside air intake
  • Air handling unit—a system of fans, heating and cooling coils, air-flow control dampers, air filters, etc.
  • Air distribution system
  • In general, outside ("supply") air is drawn into a building's HVAC system through the air intake by the air handling unit (AHU). Once in the system, supply air is filtered to remove particulate matter (mold, allergens, dust), heated or cooled, and then circulated throughout the building via the air distribution system
  • In many buildings, the air distribution system also includes a return air system so that conditioned supply air is returned to the AHU ("return air") where it is mixed with supply air, re-filtered, re-conditioned, and re-circulated throughout the building.
  • This is usually accomplished by drawing air from the occupied space and returning it to the AHU by :
    • Ducted returns, wherein air is collected from each room or zone using return air devices in the ceiling or walls that are directly connected by ductwork to the air-handling unit; or
    • Plenum returns, wherein air is collected from several rooms or zones through return air devices that empty into the negatively pressurized ceiling plenum (the space between the drop ceiling and the real ceiling); the air is then returned to the air-handling unit by ductwork or structural conduits.
  • Finally, some portion of the air is exhausted from the building. The air exhaust system might be directly connected to the AHU and/or may be stand-alone
In commercial/ industrial applications, following methods are used to maintain fresh air throughout the facility.
  • Forced Ventilation via AHU's and ductwork.
    • "Mechanical" or "forced" ventilation is provided by an air handling unit and ducting used to control indoor air quality. Excess humidity, odors, and contaminants can often be controlled via dilution or replacement with outside air.
  • Air cooling / humidification especially in dry areas with air washers.
    • This is the process of adding moisture to the air by using a whole house humidifier. During the winter months, heated air can make that space too dry. Adding moisture protects furnishings and reduces static electricity. While in Summers, especially in dry areas, adding humidity with air flow gives some drop in temperature and comfort.
  • Simple air circulations with high volume exhaust fans
    • Exhaust fan to draw the air through the facility and blow it into the space.
  • Air Conditioning
    • Centralized air conditioning
      • In central air conditioning, the heat-exchanger is typically placed inside the central furnace / AC unit which is then used to distribute hot / chilled air throughout any residence or commercial building. Central (ducted) air conditioning offers whole-house or large-commercial-space cooling, and often offers moderate multi-zone temperature control capability by the addition of air-louver-control boxes.
    • Centralized air conditioning
      • Slipt AC's with IDU & ODUs Split" up into two components: the compressor and condenser are part of an external unit while the evaporative coil is part of the indoor AHU (Air Handling Unit). These are generally mounted high on the walls. The units are connected with tubing which circulates the refrigerant. The tubing, along with an electric and drain line, is run through a 3-inch hole hidden behind the indoor unit
    • Centralized air conditioning
      • Simple window or single split unit Compressor, condenser, expansion valve and other components work as a single unit that is cuboid in shape Suitable for cooling areas which are less than 300 sq. ft. in size. Very economical. Installation costs are low as well