Air handler
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- AHU redirects here. For "ahu", the platform of stone used as a base for an Easter Island Statue or a group of such statues together, see: Moai.
1 - Supply duct
2 - Fan compartment
3 - Vibration isolator ('flex joint')
4 - Heating and/or cooling coil
5 - Filter compartment
6 - Mixed (recirculated + outside) air duct
An air handler, or air handling unit and often abreviated to AHU, is a device used as part of a heating, ventilating, and air-conditioning (HVAC) system. Usually, an air handler is a large metal box containing a blower, heating and/or cooling elements, filter racks or chambers, sound attenuators, and dampers. Air handlers usually connect to ductwork that distributes the conditioned air through the building, and returns it to the AHU. Sometimes AHUs discharge (supply) and admit (return) air directly to and from the space served, without ductwork.
Small air handlers, for local use, are called terminal units, and may only include an air filter, coil, and blower; these simple terminal units are called blower coils or fan coil units. Larger air handlers that condition 100% outside air, and no recirculated air, are known as makeup air units (MAUs). Air handlers designed for outdoor use, typically on roofs, are known as rooftop units (RTUs).
Air handlers usually contain a large squirrel cage blower driven by an AC induction electric motor. The blower may operate at a single speed, offer a variety of pre-set speeds, or be driven by a Variable Frequency Drive so as to allow a wide range of air flow rates. Some residential air handlers (central 'furnaces' or 'air conditioners') use a brushless DC electric motor that has variable speed capabilities.
If used to supply heat, the air handler may contain a fuel-burning heater or it may simply contain coils that are heated using circulating water or steam with the heat provided by a central boiler. Electric resistance and heat pumps are used too.
If used for cooling, the unit may a refrigeration evaporator, or simply a coil cooled by chilled water provided by a central chiller. Evaporative cooling is possible in dry climates too.
Air filtration may be via simple low-MERV pleated media, HEPA, electrostatic, or a combination of techniques. Gas-phase and ultraviolet air treatments may be employed as well.
Humidification may be provided. Air handlers commonly also provide provisions to allow the introduction of outside air into, and the exhausting of air from, the building. A heat recovery heat exchanger, of many types, may be fitted to the air handler for energy savings and increasing capacity.
Control may be as simple as an off/on thermostat to as complex as a building automation system using BACnet or LonWorks, for example.
