An air handler, or air handling unit (often abbreviated to AHU), is a device used to condition and circulate air as part of a heating, ventilating, and air-conditioning (HVAC HVAC is an acronym that stands for the closely related functions of "Heating, Ventilating, and Air Conditioning"—the 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 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 objects from contacting the fan blades. Most fans are powered by electric motors, but other sources of power may be used, including hydraulic, heating or cooling elements, 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 or ozone. Air filters are used in applications racks or chambers, sound attenuators, and dampers 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 operation can be manual or automatic. Manual dampers. Air handlers usually connect to ductwork 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. As such, air ducts are one method of ensuring acceptable indoor air quality as well as thermal 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 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 installed, or serve multiple spaces. It is controlled or fan coil units. 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).
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Air handler components
Blower/fan
Air handlers typically employ a large squirrel cage blower A centrifugal fan is a mechanical device for moving air or 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. The gas enters from the side of the fan wheel, turns 90 degrees and accelerates due to centrifugal force as driven by an AC induction electric motor An electric motor uses electrical energy to produce mechanical energy, very typically through the interaction of magnetic fields and current-carrying conductors. The reverse process, producing electrical energy from mechanical energy, is accomplished by a generator or dynamo. Many types of electric motors can be run as generators, and vice versa 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 A variable-frequency drive is a system for controlling the rotational speed of an alternating current (AC) 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. Variable-frequency drives are also known as adjustable-frequency drives (AFD), 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 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 is the process of removing heat from an enclosed space, or from a substance, and moving it to a place where it is unobjectionable. The primary purpose of refrigeration is lowering the temperature of the enclosed space or substance and then maintaining that lower temperature. The term cooling refers generally to any natural or evaporator Within a downstream processing system, several stages are used to further isolate and purify the desired product. The overall structure of the process includes pre-treatment, solid-liquid separation, concentration, and purification and formulation. Evaporation falls into the concentration stage of downstream processing and is widely used to, placed directly in the air stream. Electric resistance 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 pumps A heat pump is a machine or device that moves heat from one location to another location (the 'sink' or 'heat sink') using mechanical work. Most heat pump technology moves heat from a low temperature heat source to a higher temperature heat sink. Common examples are food refrigerators and freezers, air conditioners, and reversible-cycle heat pumps are used too. Evaporative cooling Evaporative cooling is especially well suited for climates where the air is hot and humidity is low. For example, in the United States, the western/mountain states are good locations, with swamp coolers very prevalent in cities like Denver, Salt Lake City, Albuquerque, El Paso, Tucson, and Fresno where sufficient water is available. Evaporative is possible in dry climates too.
Large commercial air handling units contain coils A heat exchanger is a device 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. They are widely used in space heating, refrigeration, air conditioning, power plants, chemical plants, petrochemical plants, petroleum refineries, natural that circulate hot water Water is a chemical substance with the chemical formula H2O. Its 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 vapor or steam or steam Steam is either mist , or the gas phase of water (water vapor) for heating, and chilled water for cooling. The hot water or steam is provided by a central 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, and the chilled water is provided by a central chiller A chiller is a machine that removes heat from a liquid via a vapor-compression or absorption refrigeration cycle. A vapor-compression water chiller comprises the four major components of the vapor-compression refrigeration cycle . These machines can implement a variety of refrigerants. Absorption chillers use municipal water as the refrigerant and.
Filters
Air filtration 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 or ozone. Air filters are used in applications 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, 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 A high efficiency particulate air, or HEPA , filter is a type of high-efficiency air filter, electrostatic An electrostatic precipitator , or electrostatic air cleaner is a particulate collection device that removes particles from a flowing gas (such as air) using the force of an induced electrostatic charge. Electrostatic precipitators are highly efficient filtration devices that minimally impede the flow of gases through the device, and can easily, 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.
Humidifier
Humidification A humidifier is a household appliance that increases humidity in a single room or in the entire home. 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 entire house is often necessary in colder climates where continuous heating will make the air drier, resulting in uncomfortable air quality and increased static electricity Electrostatics is the branch of science that deals with the phenomena arising from 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.
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 dampers 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 operation can be manual or automatic. Manual dampers controlling the ratio between the return, outside, and exhaust air.
A heat recovery heat exchanger A heat exchanger is a device 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. They are widely used in space heating, refrigeration, air conditioning, power plants, chemical plants, petrochemical plants, petroleum refineries, natural, of many types, may be fitted to the air handler for energy savings and increasing capacity.
Controls
Controls A HVAC control system is a computerized control system for climate control in buildings. Stand alone control devices may be pneumatic or electronic. Some may have microprocessors, but to be considered a "control system" for the context of this article, computerized and networked are expected requirements. HVAC stands for heating, 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 A thermostat is a device for regulating the temperature of a system so that the system's temperature is maintained near a desired setpoint temperature. The name is derived from the Greek words thermos "hot" and statos "a standing". The thermostat does this by switching heating or cooling devices on or off, or regulating the or as complex as a 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. The control system is a computerized, intelligent network of electronic devices, designed to monitor and control the mechanical and lighting systems in a building system using BACnet BACnet is a communications protocol for building automation and control networks. It is an ASHRAE, ANSI, and ISO standard protocol or 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. It is used for the automation of various functions within buildings such as lighting and, for example.
Common control components include temperature sensors, humidity sensors, sail switches, actuators The efficiency of an actuator is a standard tool used to calculate or estimate the usefulness of any actuating mechanism. It is a dimensionless quantity which is generally lower than 1 expressing the energy conversion factor. For better explanation see Thermodynamic efficiency. Most of the wasted energy is thermally dissipated, 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.
Major manufacturers
- Carrier Corporation The Carrier Corporation is the world’s largest manufacturer and distributor of heating, ventilating and air conditioning systems, and a global leader in the commercial refrigeration and food service equipment industry. A wholly owned subsidiary of United Technologies Corporation, Carrier is a $12.5 billion company with over 43,000 employees (also makes Bryant and Payne brands)
- Citizen Industries
- Daikin Industries (also makes McQuay International)
- Engineered Air (North America)
- Fläkt Woods
- Huntair Inc. (worldwide) Leaders in Air Flow Management
- Johnson Controls Johnson 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 International Lennox International Inc. , through its subsidiaries, is a provider of climate control solutions for the heating, ventilation, air conditioning, and refrigeration markets around the world. The company began in Marshalltown, Iowa in 1895 and today is focused on four core businesses: Residential Heating & Cooling, Commercial Heating &
- Rheem (also makes Ruud)
- Trane
- Weger Air Solutions (Europe)
- Zamil Air Conditioners (Middle East)
See also
- HVAC HVAC is an acronym that stands for the closely related functions of "Heating, Ventilating, and Air Conditioning"—the 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
- Thermal comfort Human thermal comfort is defined by ASHRAE as the state of mind that expresses satisfaction with the surrounding environment . Maintaining thermal comfort for occupants of buildings or other enclosures is one of the important goals of HVAC design engineers
- Indoor air quality Indoor air quality is a term referring to the air quality within and around buildings and structures, especially as it relates to the health and comfort of building occupants
Categories: Heating, ventilating, and air conditioning Categories: Engineering thermodynamics | Heat transfer | Electro mechanical engineering | Building engineering | Automation | Temperature | Mechanical engineering Categories: Applied and interdisciplinary physics | Engineering disciplines
Sat, 12 Jun 2010 17:06:10 GMT+00:00
al.com (blog) He knows what he's doing," said dog handler Bart Rogers, who works for the veterinary sports medicine program. Holli, a female about the same age, ...
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Sat, 01 May 2010 01:39:22 GM
An AHU . air handler. unit is in a closet space for itself. There is a disconnect in the panel and one more in the front/part of the unit. Does there need to be an additional disconnect on the wall of the closet space also? ...
Q. Outside unit is a ten year old Trane xl1200 heat pump. Indoor air handler has bitten the dust. Looking at one for 3.5 ton 13 Max SEER. So far I have check out Goodman, Amana, Trane, and Carrier. Just want to know what others think. Thanks
Asked by Dechman - Sat Dec 1 10:31:44 2007 - - 2 Answers - 0 Comments
A. According to my source, Goodman and Amana have a 4 star rating out of 5. Maytag has a 5 star rating. For a complete list of ratings check out my source.
Answered by RICH @www.hvac-for-beginners.com - Sat Dec 1 12:14:13 2007
