An Air Handling Unit is used to condition and circulate air as part of a heating, ventilating, and air-conditioning system. The basic function of the AHU is take in outside air, condition it and supply fresh air to a building. All exhaust air is discharged, which secures an acceptable indoor air quality. Depending on the required temperature of the conditioned air, the fresh air is either heated by a recovery unit or heating coil, or cooled by a cooling coil. A factory-made encased assembly consisting of a fan or fans and other necessary equipment to perform one or more of the functions of circulating, cleaning, heating, cooling, humidifying, dehumidifying and mixing of air Energy Saving In buildings, where the hygienic requirements for air quality are lower, some of the air from the rooms can be re-circulated by a mixing chamber, and result in significant energy savings. Ductwork AHUs connect to ductwork that distributes the conditioned air through the building, and returns it to the AHU.Mixing chamber has dampers for controlling the ratio between the return, outside, and exhaust air. Recovery Exchanger 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.