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How to select right AHU for HVAC

Article By MG Cooling Solutions In HVAC - September 13, 2020

AIR HANDLING UNIT (A.H.U)

How to select right AHU for HVAC

The acronym A.H.U stands for air handling units that are found in a medium to large commercial and industrial buildings, located in the basement, on the roof, or the floor of buildings. The air handling unit is an assembly of air conditioning components like fans, cooling coils, filters, humidifiers, and dampers which are integrated and installed as a single unit connected to a system of metal ductwork that distributes the conditioned air. An air handling unit is used to circulate and re-condition air as part of a heating, ventilating, and air-conditioning system. The function of AHU is to take outside air, re-condition it, and supply it as fresh air to a building. All exhaust air is removed, which creates an acceptable indoor air quality. The AHU is used to control the following parameters

  • Temperature
  • Humidity
  • Air movement and circulation
  • Air cleanliness and air quality

There is a use of two types of air handling unit and they are: –

  1. DRAW-THROUGH – in this the fan pulls the air through the mixing box, filters, and cooling coil before discharging it from the fan outlet to the area to be cooled or to the ducting network. The design can be vertical or horizontal.
  2. BLOW-THROUGH-in this the fan blows the air through the mixing box, filters, and cooling coil before discharging it to the area being conditioned or the ducting system.

COMPONENTS OF AN AIR HANDLING UNIT

  1. SUPPLY FAN ­­- centrifugal fan type is used to circulate the conditioned air to various zones.
  2. FAN MOTOR – electric motor provides the rotating motion to the supply fan.
  3. COOLING COIL – cooling coil provide cooling and dehumidification of air. Both “direct expansion” cooling and “chilled water” cooling coils are used according to the system design. These coils are assembled in rows with different fin spacing. Aluminium fins and copper tubes are used in coil designing
  4. FILTERS – filters are used to eliminate contaminated particles of various sizes from the air. Different filters are used according to the application of the AHU system.

Panel filter is a flat and rectangular-shaped filter providing minimum low-efficiency filtration which is suitable for the air conditioning industry. The typical air velocity that moves through the filter is in the range of 2-3 m/s.

HEPA filter can achieve efficiencies up to 99.97% eliminating minute particles and airborne bacteria from the air. It is generally used in cleanroom applications such as semiconductor production floor, operating theatres, and critical processes.

Electrostatic filter uses highly charged electrodes that ionized the air to remove particles from the air.

  • HUMIDIFIERS   are usually used in cold days for maintaining a required hot climate or maintaining the comfort of the occupants in low humidity level of air. Humidifiers provide humidity either as hot vapor or water spray
  • DAMPERS are used to control the amount and direction of air before or after conditioning is achieved.
  • HEATING COIL is placed in AHU where hot liquid or vapor water from boilers is dispersed.
  • PREHEATING COIL placed at AHU entrance before cooling and heating coils. In hot days preheating coil reduces the entering fresh air’s relative humidity preventing the condensation of water vapor on the cooling coil. In cold days is also prevents the freezing of water inside the coil.
  • MIXING BOX is placed where fresh air is mixed with zone return air or with fresh conditioned air. It is performed to obtain the desired air temperature and humidity.
  • CENTRIFUGAL PUMPS are used for cooling and heating air processes. They maintain the pumping cycle of hot water from boilers to the heating or preheating coils and back to back to boilers and pumping cold water cycle from the chiller to the cooling coil in AHU and back to the chiller.
  • CONTROL SYSTEMS can vary from simple to advanced control systems that use the latest technologies. They usually control the temperature and humidity of the supply air to the zones. It also controls the damper system and even controls the fan rotation based on the required temperature and humidity in the zones and zone exit damper.
  • HOUSING/ CASING that contains all the above components of an AHU, made from metal and painted to prevent corrosion

 It is interesting to note that the configuration of the air handling unit can differ slightly in design and components according to the application and AHU capacity, but also the initial and running costs can affect the selection of various AHU components. For a cleaner and comfortable indoor environment, you will need an efficient AHU and for that, you will need MG COOLING solution assistance and we are here to support you, providing the perfect system and solutions for your facility.

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