Air handler
Encyclopedia
HVAC
HVAC refers to technology of indoor or automotive environmental comfort. HVAC system design is a major subdiscipline of mechanical engineering, based on the principles of thermodynamics, fluid mechanics, and heat transfer...
) system. An air handler is usually a large metal box containing a blower
Fan (mechanical)
A mechanical fan is a machine used to create flow within a fluid, typically a gas such as air.A fan consists of a rotating arrangement of vanes or blades which act on the air. Usually, it is contained within some form of housing or case. This may direct the airflow or increase safety by preventing...
, heating or cooling elements, filter
Air filter
A particulate air filter is a device composed of fibrous materials which removes solid particulates such as dust, pollen, mold, and bacteria from the air. A chemical air filter consists of an absorbent or catalyst for the removal of airborne molecular contaminants such as volatile organic compounds...
racks or chambers, sound attenuators, and dampers
Damper (architecture)
A damper is a valve or plate that stops or regulates the flow of air inside a duct, chimney, VAV box, air handler, or other air handling equipment. A damper may be used to cut off central air conditioning to an unused room, or to regulate it for room-by-room temperature and climate control. Its...
. Air handlers usually connect to ductwork
Duct (HVAC)
Ducts are used in heating, ventilation, and air conditioning to deliver and remove air. These needed airflows include, for example, supply air, return air, and exhaust air. Ducts also deliver, most commonly as part of the supply air, ventilation air...
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 unit
Fan coil unit
A fan coil unit is a simple device consisting of a heating or cooling coil and fan. It is part of an HVAC system found in residential, commercial, and industrial buildings. Typically a fan coil unit is not connected to ductwork, and is used to control the temperature in the space where it is...
s. A larger air handler that conditions 100% outside air, and no recirculated air, is known as a makeup air unit (MAU). An air handler designed for outdoor use, typically on roofs, is known as a packaged unit (PU) or rooftop unit (RTU).
Blower/fan
Air handlers typically employ a large squirrel cage blowerCentrifugal fan
A centrifugal fan is a mechanical device for moving air or other gases. It has a fan wheel composed of a number of fan blades, or ribs, mounted around a hub. As shown in Figure 1, the hub turns on a driveshaft that passes through the fan housing...
driven by an AC induction electric motor
Electric motor
An electric motor converts electrical energy into mechanical energy.Most electric motors operate through the interaction of magnetic fields and current-carrying conductors to generate force...
to move the air. The blower may operate at a single speed, offer a variety of set speeds, or be driven by a Variable Frequency Drive
Variable frequency drive
A variable-frequency drive is a system for controlling the rotational speed of an alternating current electric motor by controlling the frequency of the electrical power supplied to the motor. A variable frequency drive is a specific type of adjustable-speed drive...
to allow a wide range of air flow rates. Flow rate may also be controlled by inlet vanes or outlet dampers on the fan. Some residential air handlers (central 'furnaces' or 'air conditioners') use a brushless DC electric motor
Brushless DC electric motor
Brushless DC motors also known as electronically commutated motors are electric motors powered by direct-current electricity and having electronic commutation systems, rather than mechanical commutators and brushes...
that has variable speed capabilities.
Multiple blowers may be present in large commercial air handling units, typically placed at the end of the AHU and the beginning of the supply ductwork (therefore also called "supply fans"). They are often augmented by fans in the return air duct ("return fans") pushing the air into the AHU.
Heating and/or cooling elements
Air handlers may need to provide heating, cooling, or both to change the supply air temperature depending on the location and the application.Smaller air handlers may contain a fuel-burning heater or a refrigeration
Refrigeration
Refrigeration is a process in which work is done to move heat from one location to another. This work is traditionally done by mechanical work, but can also be done by magnetism, laser or other means...
evaporator
Evaporator
An evaporator is a device used to turn the liquid form of some chemical into its gaseous form. For example, an evaporator is used in an air conditioning system to allow the compressed cooling chemical to evaporate from liquid to gas, absorbing heat in the process.-Uses:As stated above, an...
, placed directly in the air stream. Electric resistance
Heating element
A heating element converts electricity into heat through the process of Joule heating. Electric current through the element encounters resistance, resulting in heating of the element....
and heat pump
Heat pump
A heat pump is a machine or device that effectively "moves" thermal energy from one location called the "source," which is at a lower temperature, to another location called the "sink" or "heat sink", which is at a higher temperature. An air conditioner is a particular type of heat pump, but the...
s can be used as well. Evaporative cooling is possible in dry climates.
Large commercial air handling units contain coils that circulate hot water
Water
Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...
or steam
Steam
Steam is the technical term for water vapor, the gaseous phase of water, which is formed when water boils. In common language it is often used to refer to the visible mist of water droplets formed as this water vapor condenses in the presence of cooler air...
for heating, and chilled water for cooling. Coils are typically manufactured from copper for the tubes, with copper or aluminium 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
Boiler
A boiler is a closed vessel in which water or other fluid is heated. The heated or vaporized fluid exits the boiler for use in various processes or heating applications.-Materials:...
, and the chilled water is provided by a central chiller
Chiller
A chiller is a machine that removes heat from a liquid via a vapor-compression or absorption refrigeration cycle. This liquid can then be circulated through a heat exchanger to cool air or equipment as required.-Use in air conditioning:...
. Downstream temperature sensors are typically used to monitor and control 'off coil' temperatures, in conjunction with an appropriate motorized control valve prior to the coil.
Filters
Air filtrationAir filter
A particulate air filter is a device composed of fibrous materials which removes solid particulates such as dust, pollen, mold, and bacteria from the air. A chemical air filter consists of an absorbent or catalyst for the removal of airborne molecular contaminants such as volatile organic compounds...
is almost always present in order to provide clean dust-free air to the building occupants. It may be via simple low-MERV
Minimum Efficiency Reporting Value
Minimum efficiency reporting value, commonly known as MERV rating is a measurement scale designed in 1987 by the American Society of Heating, Refrigerating and Air-Conditioning Engineers to rate the effectiveness of air filters...
pleated media, HEPA
HEPA
High-Efficiency Particulate Air or HEPA is a type of air filter. Filters that are awarded the HEPA accolade are used in various locations, whether in medical facilities, automotive vehicles, airplanes, home filters, or wherever very pure air is sought. The filter must satisfy certain standards of...
, electrostatic
Electrostatic precipitator
An electrostatic precipitator , or electrostatic air cleaner is a particulate collection device that removes particles from a flowing gas using the force of an induced electrostatic charge...
, or a combination of techniques. Gas-phase and ultraviolet air treatments may be employed as well.
It is typically placed first in the AHU in order to keep all its components clean. Depending upon the grade of filtration required, typically filters will be arranged in two (or more) banks with a coarse-grade panel filter provided in front of a fine-grade bag filter, or other 'final' filtration medium. The panel filter is cheaper to replace and maintain, and thus protects the more expensive bag filters.
The life of a filter may be assessed by monitoring the pressure drop through the filter medium at design air volume flow rate. This may be done by means of a visual display, using a pressure gauge, or by a pressure switch linked to an alarm point on the building control system. Failure to replace a filter may eventually lead to its collapse, as the forces exerted upon it by the fan overcome its inherent strength, resulting in collapse and thus contamination of the air handler and downstream ductwork.
Humidifier
HumidificationHumidifier
A humidifier is a household appliance that increases humidity in a single room or in the entire house. There are point-of-use humidifiers, which are commonly used to humidify a single room, and whole-house or furnace humidifiers, which connect to a home's HVAC system to provide humidity to the...
is often necessary in colder climates where continuous heating will make the air drier, resulting in uncomfortable air quality and increased static electricity
Electrostatics
Electrostatics is the branch of physics that deals with the phenomena and properties of stationary or slow-moving electric charges....
. Various types of humidification may be 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 onto baffles in the air stream.
- Vaporizer: steam or vapour from a boiler is blown directly into the air stream.
- Spray mist: water is diffused either by a nozzle or other mechanical means into fine droplets and carried by the air.
- Ultrasonic: A tray of fresh water 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.
Mixing chamber
In order to maintain indoor air quality, air handlers commonly have provisions to allow the introduction of outside air into, and the exhausting of air from the building. In temperate climates, mixing the right amount of cooler outside air with warmer return air can be used to approach the desired supply air temperature. A mixing chamber is therefore used which has dampersDamper (architecture)
A damper is a valve or plate that stops or regulates the flow of air inside a duct, chimney, VAV box, air handler, or other air handling equipment. A damper may be used to cut off central air conditioning to an unused room, or to regulate it for room-by-room temperature and climate control. Its...
controlling the ratio between the return, outside, and exhaust air.
Heat recovery device
A heat recovery device heat exchangerHeat exchanger
A heat exchanger is a piece of equipment built for efficient heat transfer from one medium to another. The media may be separated by a solid wall, so that they never mix, or they may be in direct contact...
of many types, may be fitted to the air handler between supply and extract airstreams for energy savings and increasing capacity. These types more commonly include for:
- RecuperatorRecuperatorA recuperator is a special purpose counter-flow energy recovery heat exchanger positioned within the supply and exhaust air streams of an air handling system, or in the exhaust gases of an industrial process, in order to recover the waste heat...
, or Plate Heat exchanger: A sandwich of plastic or metal plates with interlaced air paths. Heat is transferred between airstreams from one side of the plate to the other. The plates are typically spaced at 4 to 6mm apart. Can also be used to recover coolth. Heat recovery efficiency up to 70%. - Thermal WheelThermal wheelA Thermal Wheel, also known as a Rotary heat exchanger, or Rotary air-to-air enthalpy wheel, or Heat recovery wheel, is a type of energy recovery heat exchanger positioned within the supply and exhaust air streams of an air handling system, or in the exhaust gases of an industrial process, in order...
, or Rotary heat exchanger: A slowly rotating matrix of finely corrugated metal, operating in both opposing airstreams. When the air handling unit is in heating mode, heat is absorbed as air passes through the matrix in the exhaust airstream, during one half rotation, and released during the second half rotation into the supply airstream in a continuous process. When the air handling unit is in cooling mode, heat is released as air passes through the matrix in the exhaust airstream, during one half rotation, and absorbed during the second half rotation into the supply airstream. Heat recovery efficiency up to 85%. Wheels are also available with a hydroscopic coating to provide latent heat transfer and also the drying or humidification of airstreams - Run around coilRun around coilthumb|right|300px|A run-around coil installation, serving [[air handler|air handling units]] on the roof of an office buildingA run-around coil is a type of energy recovery heat exchanger most often positioned within the supply and exhaust air streams of an air handling system, or in the exhaust...
: Two air to liquid heat exchanger coils, in opposing airstreams, piped together with a circulating pump and using water or a brine as the heat transfer medium. This device, although not very efficient, allows heat recovery between remote and sometimes multiple supply and exhaust airstreams. Heat recovery efficiency up to 50%. - Heat PipeHeat pipeA heat pipe or heat pin is a heat-transfer device that combines the principles of both thermal conductivity and phase transition to efficiently manage the transfer of heat between two solid interfaces....
: Operating in both opposing air paths, using a confined refrigerant as a heat transfer medium. The 'pipe' is multiple sealed pipes mounted in a coil configuration with fins to increase heat transfer. Heat is absorbed on one side of the pipe, by evaporation of the refrigerant, and released at the other side, by condensation of the refrigerant. Condensed refrigerant flows by gravity to the first side of the pipe to repeat the process. Heat recovery efficiency up to 65%.
Controls
ControlsHVAC control system
-Direct digital control:Central controllers and most terminal unit controllers are programmable, meaning the direct digital control program code may be customized for the intended use. The program features include time schedules, setpoints, controllers, logic, timers, trend logs, and alarms...
are necessary to regulate every aspect of an air handler, such as: flow rate of air, supply air temperature, mixed air temperature, humidity, air quality. They may be as simple as an off/on thermostat
Thermostat
A thermostat is the component of a control system which regulates the temperature of a system so that the system's temperature is maintained near a desired setpoint temperature. The thermostat does this by switching heating or cooling devices on or off, or regulating the flow of a heat transfer...
or as complex as a building automation
Building automation
Building automation describes the functionality provided by the control system of a building. A building automation system is an example of a distributed control system...
system using BACnet
BACnet
BACnet is a communications protocol for building automation and control networks. It is an ASHRAE, ANSI, and ISO standard protocol....
or LonWorks
LonWorks
LonWorks is a networking platform specifically created to address the needs of control applications. The platform is built on a protocol created by Echelon Corporation for networking devices over media such as twisted pair, powerlines, fiber optics, and RF...
, for example.
Common control components include temperature sensors, humidity sensors, sail switches, actuator
Actuator
An actuator is a type of motor for moving or controlling a mechanism or system. It is operated by a source of energy, usually in the form of an electric current, hydraulic fluid pressure or pneumatic pressure, and converts that energy into some kind of motion. An actuator is the mechanism by which...
s, motors, and controllers.
Vibration isolators
The blowers in an air handler can create substantial vibration and the large area of the duct system would transmit this noise and vibration to the occupants of the building. To avoid this, vibration isolators (flexible sections) are normally inserted into the duct immediately before and after the air handler and often also between the fan compartment and the rest of the AHU. The rubberized canvas-like material of these sections allow the air handler to vibrate without transmitting much vibration to the attached ducts.The fan compartment can be further isolated by placing it on a spring suspension, which will mitigate the transfer of vibration through the floor.
European Market
The European market of air handling units (AHU) is dominated by Germany and the Northern Countries, where are located the main manufacturers, and reaches a total of 1 343.06M€.The number of units sold, by range of capacity, is split as following :
- ≤ 5.000 m3/h : 55%
- 5.001 - 15.000 m3/h : 31%
- 15.001-30.000 m3/h : 10%
- 30.001 - 50.000 m3/h : 3%
- ≥ 50.001 m3/h : 1%
The market by country is split in 2010 as following:
| Countries | Sales Volume in M€ | Share |
|---|---|---|
| Benelux | 111.06 | 8.3% |
| France | 94.34 | 7.0% |
| Germany | 323.00 | 24.0% |
| Italy | 76.08 | 5.7% |
| Portugal | 23.81 | 1.8% |
| Russia, Ukraine and CIS countries | 130.59 | 9.7% |
| Scandinavia and Baltic countries | 240.60 | 17.9% |
| Spain | 49.58 | 3.7% |
| Turkey | 38.53 | 2.9% |
| UK and Ireland | 102.88 | 7.7% |
| Eastern Europe | 152.60 | 11.4% |
Major manufacturers
- GEA GroupGEA GroupGEA Group AG , headquartered in Bochum, Germany, is one of the largest system providers for food and energy processes with about €4.4 billion in 2009 revenue. The company focuses on process technology and components for demanding production processes in various end markets...
- Carrier CorporationCarrier CorporationThe Carrier Corporation is one of the world’s largest manufacturers and distributors of heating, ventilating and air conditioning systems, and a global leader in the commercial refrigeration and food service equipment industry...
(also makes Bryant and Payne brands) - Daikin IndustriesDaikin Industriesis a Japan-based multinational corporation present in Japan, China, Australia, India, Southeast Asia, Europe, and North America.The company was founded in 1924 by Akira Yamada in Osaka, Japan. Daikin has centrally been a chemical corporation, where its focus has been on air conditioning systems...
(also makes McQuay InternationalMcQuay InternationalMcQuay International is a global corporation that designs, manufacturers and sells heating, ventilation and air conditioning products, systems, parts and services for commercial buildings. Since 2006 McQuay has been a subsidiary of Daikin Industries, Ltd....
brands) - Johnson ControlsJohnson ControlsJohnson Controls, Inc. is a company, based in Milwaukee, Wisconsin, USA. It was founded in 1885 by professor Warren S. Johnson, inventor of the first electric room thermostat....
(also makes York International brand) - Lennox InternationalLennox InternationalLennox International Inc. is an American company. Through its subsidiaries, it is a provider of climate control products for the heating, ventilation, air conditioning, and refrigeration markets around the world...
- RheemRheemRheem is a privately held manufacturing company that started in 1927 as a supplier of packagings to the petroleum industry.-Divisions:*Rheem Water Heating*Ruud Water Heating*Rheem Air conditioning*Ruud Air Conditioning Division*Solahart*Raypak...
(also makes Ruud) - TraneTraneTrane Inc. is a subsidiary of Ingersoll Rand and is the successor company to the American Standard Companies. It is a global provider of heating, ventilating and air conditioning systems and building management systems and controls under the Trane and American Standard brand names...
- Air Design