An air handler , or air handling unit (often abbreviated AHU ), is a device used to regulate and airflow as part of heating, ventilation , and AC (HVAC) systems. Air handlers are usually large metal boxes containing blowing, heating or cooling elements, filter shelves or cubicles, silencers, and silencers. Air handlers are usually connected to a ventilation duct system that distributes conditioned air through buildings and returns them to AHU. Sometimes AHU releases ( supplies ) and acknowledges (re) ) air directly to and from the space served without the need for air ducts.
Small air handlers, for local use, are called terminal units , and may include only air filters, coils, and blowers; These simple terminal units are called blower coils or fan coil units. Larger air handlers that require 100% of air outside, and no air is recirculated, known as air conditioning units ( MAU ). Air handlers designed for outdoor use, usually on the roof, are known as package units ( PU ) or roof units ( RTU ). Click here to watch AHU Animated Work on YouTube
Video Air handler
Construction
Air handlers are usually built around a framing system with metal infill panes that are required to customize component configurations. In its simplest form, frames can be made from ducts or metal parts, with a single-layer metal panel panel. Metal work is usually galvanized for long-term protection. For outer units some form of weather cover and additional sealing around the joints are provided.
Larger air handlers will be made from square-frame steel framing systems with insulated and double-insulated skin panels. The construction reduces heat loss or heat recovery from air handlers, and provides acoustic attenuation. Larger air handlers may be several meters long and are produced in a sectional way and therefore, for strength and rigidity, the steel base rail is provided under the unit.
Where supply and air extracts are required in equal proportions for a well-balanced ventilation system, it is common to supply and extract air handlers to join together, either in a side-by-side or stacked configuration .
Maps Air handler
Components
The main types of components are described here in the approximate order, from the return channel (input to AHU), through the unit, to the supply line (AHU output).
Filters
Air filtration is almost always available to provide clean, dust-free air for residents. This may be through a simple MERV low fold medium, HEPA, electrostatic, or a combination of techniques. Gas and ultraviolet phase air treatment can also be used.
Filtration is usually placed first in AHU to keep all downstream components clean. Depending on the level of filtration required, the filter will usually be arranged in two (or more) consecutive banks with a rough level panel filter provided in front of a high-quality filter bag, or other "final" filtration media. Filter panels are cheaper to replace and maintain, and thus protect the more expensive filter bags.
The life of the filter can be assessed by monitoring the pressure drop through the filter medium at the design air volume flow rate. This can be done using a visual display using a pressure gauge, or by a pressure switch connected to the alarm point on the building control system. Failure to replace the filter may ultimately lead to its collapse, since the force afforded by the fan overcame its innate strength, resulting in collapse and thus contamination from air controllers and downstream airways.
Heating and/or cooling elements
Air handlers may need to provide heating, cooling, or both to change the supply air temperature, and the humidity level depends on location and application. Such conditioning is provided by the heat exchanger coil in air flow of the air handling unit, such coils may be either indirectly or indirectly in relation to a medium that provides heating or cooling. effect.
Direct heat exchangers include them for gas-fired fuel-burning heaters or coolant evaporators, which are placed directly in the airflow. Electric resistance heaters and heat pumps can also be used. Evaporative cooling is possible in dry climates.
Indirect windings use hot water or steam for heating, and cold water for cooling (the main energy for heating and cooling is provided by the central plant elsewhere in the building). Coils are usually made from copper for tubes, with copper or aluminum fins to help heat transfer. The cooling coil will also use the eliminator plate to lift and dry the condensate. Hot water or steam is provided by the central boiler, and cold water is provided by the central chiller. Downstream temperature sensors are typically used to monitor and control "off coil" temperatures, along with appropriate motor control valves before the coil.
If dehumidification is required, then the cooling coil is used for over-cool so that dew points are reached and condensation occurs. A heating coil is placed after the cooling coil reheats the air (hence known as re-heat coil ) to the desired supply temperature. This process has the effect of reducing the relative humidity levels of the supply air.
In cold climates, where winter temperatures regularly fall below freezing, the frost coil or pre-heat is often used as the first stage of air treatment to ensure that the downstream filter or cold water coil is protected against freezing. Control the coil of ice in such a way that if a certain off-coil air temperature is not reached then all air controllers are turned off for protection.
Humidifier
Humidification is often necessary in cold climates where continuous heating will make the air drier, resulting in uncomfortable air quality and increased static electricity. Different types of humidification may be used:
- Evaporative: the dry air blown over the reservoir will evaporate some water. The rate of evaporation can be increased by spraying water into the baffles in the airflow.
- Vaporizer: steam or steam from the boiler blown directly into the airflow.
- Fog spray: water is dispersed by nozzles or other mechanical devices into fine droplets and carried by air.
- Ultrasonic: A fresh water tray in the air stream is attracted by an ultrasonic device that forms a mist or water mist.
- Wet media: The fine-grained media in the airflow is kept moist with fresh water from the header pipe with a series of small outlets. As the air passes through the medium, it enters the water into fine droplets. This type of humidifier can be quickly clogged if the main air filtration is not well maintained.
Mixing space
To maintain indoor air quality, air handlers usually have provisions to allow the introduction of exterior air into, and exhausting air from the building. In temperate climates, mixing the right amount of cold outer air with warm return air can be used to approach the desired supply air temperature. Therefore, a mixing chamber is used which has a silencer that controls the ratio between return, outer, and exhaust air.
Blower/fan
Air handlers usually use a large cage blower powered by an AC induction electric motor to drive the air. Blowers can operate at a single speed, offer a wide range of set speeds, or are driven by variable frequency drivers to allow for varying airflow rates. The flow rate can also be controlled by the inlet propeller or damper outlet on the fan. Some residential air handlers in the United States (center "furnace" or "AC") use a brushless DC electric motor that has variable speed capability. Air handlers in Europe and Australia and New Zealand now usually use curved fans backward without scrolling or "fan plug". It is driven using high efficiency EC (commutated electronic) motors with built in speed control.
Some blowers can be present in large commercial air handling units, usually placed on the AHU end and the start of the supply line channel (hence also called "supply suppliers"). They are often augmented by fans in the back air channel ("return fans") pushing air into the AHU.
Balancing
Unbalanced fans wobble and vibrate. For fans of air conditioning at home, this can be a big problem: very reduced air circulation in the vents (due to wobble loss of energy), uninterrupted efficiency, and increased noise. Another major problem in unbalanced fans is the longevity of the bearings (attached to the fan and the shaft) are disrupted. This can cause failure to occur well beyond the bearing life expectancy.
Weights can be strategically placed to improve the fine spin (for ceiling fans, experiments and placement errors usually solve the problem). Air-conditioned home/center fans or other large fans are usually taken to the store, which has a special counterweight for more complex balancing (trial and error can cause damage before the correct point is found). The fan motor itself usually does not vibrate.
Heat recovery device
Heat recovery heat exchangers can be fitted to air handlers between supply and airflow extracts for energy savings and capacity building. These types are more common including to:
- Recuperator, or Plate Heat exchanger: Sandwich of plastic or metal plate with interlaced air lane. Heat is transferred between the airflow from one side of the plate to the other. Plates are usually spaced 4 to 6mm. Heat recovery efficiency up to 70%.
- Thermal Wheel, or Rotary heat exchanger: Corrugally corrugated corrugated metal matrix, operating in the two opposite air currents. When the air handling unit is in heating mode, heat is absorbed as the air passes through the matrix in the exhaust air stream, for one and a half rotations, and is released during the second half rotation into the supply airflow in a continuous process. When the air handling unit is in cooling mode, the heat is released when air passes through the matrix in the exhaust airflow, for one half of rotation, and is absorbed during the second half-round into the supply airflow. Heat recovery efficiency up to 85%. The wheels are also available with a hydroscopic coating to provide latent heat transfer and also drying or moisture flow.
- Run the coil around: Two air to a liquid heat exchanger, in opposition to airflow, is supplied along with a circulating pump and uses water or brine as a heat transfer medium. This device, though not very efficient, allows heat recovery between the remote and sometimes some supplies and airflow flue. Heat recovery efficiency up to 50%.
- Heat Pipe: Operates on both opposing air lanes, using limited refrigerant as a heat transfer medium. The heat pipe uses several sealed pipes fitted in a coil configuration with fins to improve heat transfer. Heat is absorbed on one side of the pipe, by evaporating the refrigerant, and released on the other side, by condensing the refrigerant. The conditioned coolant flows by gravity to the first side of the pipe to repeat the process. The heat recovery efficiency is up to 65%.
Control
Controls are required to regulate every aspect of the air controller, such as: air flow rate, air supply supply, mixed air temperature, humidity, air quality. They may be as simple as an off/on thermostat or as complex as a building automation system using BACnet or LonWorks, for example.
Common control components include temperature sensors, humidity sensors, sail switches, actuators, motors, and controllers.
Vibration isolator
Blowers in an air handler can create large vibrations and a large area of ​​the channel system will send this noise and vibration to the occupants of the building. To avoid this, the vibration isolator (flexible part) is usually inserted into the conduit immediately before and after air handling and often also between the fan compartment and the remaining AHU. The rubber-like material of this section allows the components of the air handler to vibrate without transmitting this movement to the attached channel.
The fan compartment can be further isolated by placing it on the spring suspension, which will reduce the vibration transfer through the floor.
Primary producer
- Operator Company (also Bryant and Payne brand)
- CIAT Group
- Daikin Industries (also McQuay International, Goodman, and Airfel)
- Emerson Network Power
- Johnson Controls (also the York International brand)
- Lennox International
- Rheem (also Ruud)
- Trane
- TROX
- Mafna Air Technologies Inc.
- Air Engineered
See also
- HVAC
- Thermal comfort
- Indoor air quality
References
Source of the article : Wikipedia
0 Comments