What is an Air handling Unit?
The Air Handling unit, or AHU, is a mechanical device that uses fans and heaters for Heating and cooling.
The AHU is responsible for moving hot or cold air from the space into the rest of the building.
It also draws air from ducts, filters it, and distributes it throughout the building via diffusers or strategically placed vents.
What are the types of Air Handling units?
Broadly speaking, we have two AHU units in use: “Draw-Through” or “Blow-Through.”
In the Draw-Through type, the fan pulls air through the mixing box, filters, and cooling coil. This is before discharging it from the fan outlet to the space to be conditioned or to the next stage in the air handling system.
In the Blow-Through type, the fan blows air through the mixing box, filters, and cooling coil before discharging into the conditioned space or the ducting system.
So, the section after the fan has positive pressure.
How does the AHU work?
To understand the proper operation of the AHU, it’s recommended to familiarize yourself with its parts and components, so you can understand its operating principles.
A- The body of the AHU:
The AHU’s housing is usually painted metal to prevent corrosion. This housing contains all AHU components, including the coil and fans. These components are insulated within the housing to prevent condensation.
B- The filter of the AHU:
The filters work to remove pollutants and contaminants from the air. A variety of filters are available to fit different AHUs, so we will see together the most common types of filters that are being used with the AHUs as follows:
HEPA Filters:
Businesses that are concerned about their staff and sensitive equipment often use HEPA filters. These filters are efficient at removing airborne bacteria and can remove viruses from the air.
Bag Filters:
Bag filters in AHUs play a vital role in the efficient operation of any HVAC system.
Its filtration accuracy can be considered medium to high.
They trap airborne particles, such as dust, mold spores, and bacteria, before they enter the ductwork.
Maintenance of bag filters ensures that air is clean, safe, and comfortable to breathe.
Bag filters need to be cleaned or replaced regularly to ensure the equipment operates efficiently.
Panel Filters:
The panel filters used in building air handling units (AHU) help control contaminants, maintain air quality, protect equipment from excessive dust, and conserve energy.
Its filtration accuracy can be considered low, with a minimum efficiency.
The filters work with other control elements, such as temperature and humidity controls. Their primary function is to allow or block the passage of air.
C- The Coils in the AHU:
As the AHU can be used for cooling or Heating or both of them, so to be used for cooling, we will need a cooling coil, and this coil will be supplied with chilled water from its bottom and then be returned to the system from the top side of the coil, as the chilled water network is a closed-loop network.
For the heating coil, it can be either an electric heating coil or a hot-water coil.
If you use a water-cooling coil or a water-heating coil in the same AHU, you will need a separate condensate drain point for each.
D- The fans of the AHU:
The AHU fan moves air to different sections of the building. There are a variety of fans available, depending on the AHU’s static pressure and air volume. The designer’s responsibility is to use software to select the right fan for the job.
For the same AHU, it can include multiple fans, such as one in the supply section and another in the return section.
Or, in other AHUs, you can find it includes only one fan in the supply section.
E- Humidifiers:
Humidifiers are devices that increase the moisture content of the air by spraying water into the air.
Humidifiers are a useful commodity, especially in winter, as they help combat dry air and dry nasal passages and also reduce static electricity.
Humidifiers can help increase well-being and support lung health. Humidification also helps reduce the risk of a cold by 50%. Plus helps reduce the risk of a cold by 50%.
F- Heat Recovery Wheel
In some cases, to save energy, the designer can use a heat recovery wheel or an energy economizer attached to the AHU, reducing the AHU’s total energy consumption.
Conclusion
In conclusion, the AHU is an integrated HVAC system component.
An air handling unit is a heating, ventilation, and air conditioning unit. An air handling unit also removes condensation from heat-exchange coils, filters air, provides make-up air, and recycles the air.
If you like to read about the sequence of operation or SOP of the AHU, please click on the following link:
The sequence of the Operation or SOP of an AHU
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