What is An Air Handling Unit?

An Air Handling Unit (AHU) is used to re-condition and circulate air as part of a heating, ventilating and air-conditioning system. The basic function of the AHU is to take in outside air, re-condition it and supply it as fresh air to a building. All exhaust air is removed, which creates an acceptable indoor air quality. Depending on the required temperature of the re-conditioned air, the fresh air is either heated by a recovery unit or heating coil or cooled by a cooling coil.

In buildings where the hygienic requirements for air quality are lower, some of the air from the rooms can be re-circulated via a mixing chamber and this can result in significant energy savings. A mixing chamber has dampers for controlling the ratio between the return, outside and exhaust air.

AHUs connect to ductwork that distributes the conditioned air through the building and returns it to the AHU. A heat/cooling recovery exchanger is normally fitted to the AHU for energy savings and increasing capacity. An AHU designed for outdoor use, typically on roofs, is also known as a rooftop unit (RTU).

The AHU is a large metal box containing separate ventilators for supply and exhaust, heating coil, cooling coil, heating/cooling recovery system, air filter racks or chambers, sound attenuators, mixing chamber, and dampers.