An air handler or air handling unit (AHU), is a device used to regulate and circulate air as part of a heating, ventilating, and air-conditioning (HVAC) system. An air handler is usually a large metal box containing a blower, heating, or cooling elements, filter or chambers, sound attenuators, and dampers. Air handlers usually connect to a ductwork ventilation system 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
Construction
The air handler is normally constructed around a framing system with metal infill panels as required to suit the configuration of the components. In its simplest form the frame may be made from metal channels or sections, with single skin metal infill panels. The metalwork is normally galvanized for long term protection. For outdoor units some form of weatherproof lid and additional sealing around joints is provided.
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Filter's
MERV measures a filter's arrestance ,a filter's ability to remove large airborne particles from the air , and dust-spot efficiency, its ability to remove small airborne particles , and assigns a number based on the filter's ability to remove the particles. Several types of air filters are common in commercial HVAC systems:
FIBERGLASS FILTER=This throwaway air filter is the most common type. Layered fiberglass fibers are laid over each other to form the filter media and typically are reinforced with a metal grating that supports the fiberglass to prevent failure and collapse.
POLYESTER AND PLEATED FILTERS= These filters are similar to fiberglass filters but typically have a higher resistance to airflow and a superior dust-stopping ability.
HIGH EFFICIENCY PARTICULATE ARRESTANCE (HEPA) FILTERS= These units filter the air passing through them at a very fine scale.
WASHABLE AIR FILTERS. These products are not as common and rely on the build-up of dust along the cloth to improve the efficiency of the filter. Industrial processes involving high volumes of coarse dust are typical applications.
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Heating or Cooling Elements
AHU may need to provide heating, cooling, or both to change the supply air temperature, and humidity level depends on the location and the application. Such condition is provided by heat exchanger coils within the air handling unit air stream, such coils may be direct or indirect in relation to the medium providing the heating or cooling effect
Direct heat exchangers include those for gas-fired fuel-burning heaters and/or a refrigeration evaporator, placed directly in the air stream. Electrical resist heaters and heat pumps can be used as well. Evaporative cooling is possible in dry climates.
Humidification is often necessary in colder climates where continuous heating will make the air drier, resulting in
Vaporizer: steam or vapor from a boiler is blown directly into the air stream.
Spray mist: water is diffused either by a nozzle or other Methods into fine droplets and carried by air.
Ultrasonic: A tray of freshwater in the airstream is excited by an ultrasonic device forming a fog or water mist.
Wetted medium: A fine fibrous medium in the airstream is kept moist with fresh water from a header pipe with a series of small outlets. As the air passes through the medium it entrains the water in fine droplets. This type of humidifier can quickly clog if the primary air filtration is not maintained in good order.
Construction
The air handler is normally constructed around a framing system with metal infill panels as required to suit the configuration of the components. In its simplest form the frame may be made from metal channels or sections, with single skin metal infill panels. The metalwork is normally galvanized for long term protection. For outdoor units some form of weatherproof lid and additional sealing around joints is provided.
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Filter's
MERV measures a filter's arrestance ,a filter's ability to remove large airborne particles from the air , and dust-spot efficiency, its ability to remove small airborne particles , and assigns a number based on the filter's ability to remove the particles. Several types of air filters are common in commercial HVAC systems:
FIBERGLASS FILTER=This throwaway air filter is the most common type. Layered fiberglass fibers are laid over each other to form the filter media and typically are reinforced with a metal grating that supports the fiberglass to prevent failure and collapse.
POLYESTER AND PLEATED FILTERS= These filters are similar to fiberglass filters but typically have a higher resistance to airflow and a superior dust-stopping ability.
HIGH EFFICIENCY PARTICULATE ARRESTANCE (HEPA) FILTERS= These units filter the air passing through them at a very fine scale.
WASHABLE AIR FILTERS. These products are not as common and rely on the build-up of dust along the cloth to improve the efficiency of the filter. Industrial processes involving high volumes of coarse dust are typical applications.
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Heating or Cooling Elements
AHU may need to provide heating, cooling, or both to change the supply air temperature, and humidity level depends on the location and the application. Such condition is provided by heat exchanger coils within the air handling unit air stream, such coils may be direct or indirect in relation to the medium providing the heating or cooling effect
Indirect coils use hot water or steam for heating, and chilled water for cooling (prime energy for heating and cooling is provided by central plant elsewhere in the building). Coils are Mostly manufactured from copper for the tubes, with copper or aluminum fins to aid heat transfer. Cooling coils will also employ eliminator plates to remove and drain condensate. The hot water or steam is provided by a central boiler, and the chilled water is provided by a central chiller.
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HumidificationHumidification is often necessary in colder climates where continuous heating will make the air drier, resulting in
uncomfortable air quality and increased static electricity.
Types of Humidification used:
Evaporative: dry air blown over a reservoir will evaporate some of the water. The rate of evaporation can be increased by spraying the water on the air stream.
Evaporative: dry air blown over a reservoir will evaporate some of the water. The rate of evaporation can be increased by spraying the water on the air stream.
Vaporizer: steam or vapor from a boiler is blown directly into the air stream.
Spray mist: water is diffused either by a nozzle or other Methods into fine droplets and carried by air.
Ultrasonic: A tray of freshwater in the airstream is excited by an ultrasonic device forming a fog or water mist.
Wetted medium: A fine fibrous medium in the airstream is kept moist with fresh water from a header pipe with a series of small outlets. As the air passes through the medium it entrains the water in fine droplets. This type of humidifier can quickly clog if the primary air filtration is not maintained in good order.
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