| Air handler components | | | | commonly have provisions to allow the introduction |
| Blower/fan | | | | of outside air into, and the exhausting of air from the |
| Air handlers typically employ a large squirrel cage | | | | building. In temperate climates, mixing the right |
| blower driven by an AC induction electric motor to | | | | amount of cooler outside air with warmer return air |
| move the air. The blower may operate at a single | | | | can be used to approach the desired supply air |
| speed, offer a variety of set speeds, or be driven by | | | | temperature. A mixing chamber is therefore used |
| a Variable Frequency Drive to allow a wide range of | | | | which has dampers controlling the ratio between the |
| air flow rates. Flow rate may also be controlled by | | | | return, outside, and exhaust air. |
| inlet vanes or outlet dampers on the fan. Some | | | | Heat recovery device |
| residential air handlers (central 'furnaces' or 'air | | | | A heat recovery device heat exchanger of many |
| conditioners') use a brushless DC electric motor that | | | | types, may be fitted to the air handler between |
| has variable speed capabilities. | | | | supply and extract airstreams for energy savings and |
| Multiple blowers may be present in large commercial | | | | increasing capacity. These types more commonly |
| air handling units, typically placed at the end of the | | | | include for: |
| AHU and the beginning of the supply ductwork | | | | Cross Plate Heat exchanger: A sandwich of plastic or |
| (therefore also called "supply fans"). They are often | | | | metal plates with interlaced air paths. Heat is |
| augmented by fans in the return air duct ("return | | | | transferred between airstreams from one side of the |
| fans") pushing the air into the AHU. | | | | plate to the other. The plates are typically spaced at |
| Heating and/or cooling elements | | | | 4 to 6mm apart. Can also be used to recover coolth. |
| Air handlers may need to provide heating, cooling, or | | | | Heat recovery efficiency up to 70%. |
| both to change the supply air temperature depending | | | | Thermal Wheel: A slowly rotating matrix of finely |
| on the location and the application. | | | | corrugated metal, operating in both opposing |
| Smaller air handlers may contain a fuel-burning heater | | | | airstreams, heat is absorbed as air passes through |
| or a refrigeration evaporator, placed directly in the air | | | | the matrix in the exhaust airstream, during one half |
| stream. Electric resistance and heat pumps can be | | | | rotation, and released during the second half rotation |
| used as well. Evaporative cooling is possible in dry | | | | into the supply airstream in a continuous process. Can |
| climates. | | | | also be used to recover and coolth. Heat recovery |
| Large commercial air handling units contain coils that | | | | efficiency up to 85%. Wheels are also available with a |
| circulate hot water or steam for heating, and chilled | | | | hydroscopic coating to provide latent heat transfer |
| water for cooling. Coils are typically manufactured | | | | and also the drying or humidification of airstreams |
| from copper for the tubes, with copper or aluminium | | | | Run around coil: Two air to liquid heat exchanger coils, |
| fins to aid heat transfer. Cooling coils will also employ | | | | in opposing airstreams, piped together with a |
| eliminator plates to remove and drain condensate. | | | | circulating pump and using water or a brine as the |
| The hot water or steam is provided by a central | | | | heat transfer medium. This device, although not very |
| boiler, and the chilled water is provided by a central | | | | efficient, allows heat recovery between remote and |
| chiller. Downstream temperature sensors are typically | | | | sometimes multiple supply and exhaust airstreams. |
| used to monitor and control 'off coil' temperatures, in | | | | Heat recovery efficiency up to 50%. |
| conjunction with an appropriate motorised control | | | | Heat Pipe: Operating in both opposing air paths, using |
| valve prior to the coil. | | | | a confined refrigerant as a heat transfer medium. |
| Filters | | | | The 'pipe' is multiple sealed pipes mounted in a coil |
| Air filtration is almost always present in order to | | | | configuration with fins to increase heat transfer. Heat |
| provide clean dust-free air to the building occupants. | | | | is absorbed on one side of the pipe, by evaporation |
| It may be via simple low-MERV pleated media, HEPA, | | | | of the refrigerant, and released at the other side, by |
| electrostatic, or a combination of techniques. | | | | condensation of the refrigerant. Condensed |
| Gas-phase and ultraviolet air treatments may be | | | | refrigerant flows by gravity to the first side of the |
| employed as well. | | | | pipe to repeat the process. Heat recovery efficiency |
| It is typically placed first in the AHU in order to keep | | | | up to 65%. |
| all its components clean. Depending upon the grade of | | | | Controls |
| filtration required, typically filters will be arranged in | | | | Controls are necessary to regulate every aspect of |
| two (or more) banks with a coarse-grade panel filter | | | | an air handler, such as: flow rate of air, supply air |
| provided in front of a fine-grade bag filter, or other | | | | temperature, mixed air temperature, humidity, air |
| 'final' filtration medium. The panel filter is cheaper to | | | | quality. They may be as simple as an off/on |
| replace and maintain, and thus protects the more | | | | thermostat or as complex as a building automation |
| expensive bag filters. | | | | system using BACnet or LonWorks, for example. |
| The life of a filter may be assessed by monitoring | | | | Common control components include temperature |
| the pressure drop through the filter medium at design | | | | sensors, humidity sensors, sail switches, actuators, |
| air volume flow rate. This may be done by means of | | | | motors, and controllers. |
| a visual display, using a pressure gauge, or by a | | | | Vibration isolators |
| pressure switch linked to an alarm point on the | | | | The blowers in an air handler can create substantial |
| building control system. Failure to replace a filter may | | | | vibration and the large area of the duct system |
| eventually lead to its collapse, as the forces exerted | | | | would transmit this noise and vibration to the |
| upon it by the fan overcome its inherent strength, | | | | occupants of the building. To avoid this, vibration |
| resulting in collapse and thus contamination of the air | | | | isolators (flexible sections) are normally inserted into |
| handler and downstream ductwork. | | | | the duct immediately before and after the air handler |
| Humidifier | | | | and often also between the fan compartment and |
| Humidification is often necessary in colder climates | | | | the rest of the AHU. The rubberized canvas-like |
| where continuous heating will make the air drier, | | | | material of these sections allow the air handler to |
| resulting in uncomfortable air quality and increased | | | | vibrate without transmitting much vibration to the |
| static electricity. Various types of humidification may | | | | attached ducts. |
| be used: | | | | The fan compartment can be further isolated by |
| Evaporative: dry air blown over a reservoir will | | | | placing it on a spring suspension, which will mitigate |
| evaporate some of the water. The rate of | | | | the transfer of vibration through the floor. |
| evaporation can be increased by spraying the water | | | | Major manufacturers |
| onto baffles in the air stream. | | | | Carrier Corporation (also makes Bryant and Payne |
| Vaporizer: steam or vapour from a boiler is blown | | | | brands) |
| directly into the air stream. | | | | Citizen Industries |
| Spray mist: water is diffused either by a nozzle or | | | | Daikin Industries (also makes McQuay International) |
| other mechanical means into fine droplets and carried | | | | Engineered Air (North America) |
| by the air. | | | | Flkt Woods |
| Ultrasonic: A tray of fresh water in the airstream is | | | | Johnson Controls (also makes York International |
| excited by an ultrasonic device forming a fog or | | | | brand) |
| water mist. | | | | Lennox International |
| Wetted medium: A fine fibrous medium in the | | | | Nortek (makers of Huntair, Nordyne, Temtrol, |
| airstream is kept moist with fresh water from a | | | | Ventrol, and other brands) |
| header pipe with a series of small outlets. As the air | | | | Rheem (also makes Ruud) |
| passes through the medium it entrains the water in | | | | Robatherm GMBH |
| fine droplets. This type of humidifier can quickly clog | | | | Trane |
| if the primary air filtration is not maintained in good | | | | Weger Air Solutions (Europe) |
| order. | | | | Zamil Air Conditioners (Middle East) |
| Mixing chamber | | | | Haakon Industries Inc. |
| In order to maintain indoor air quality, air handlers | | | | |