Understanding Air Handling Units

Understanding Air Handling Units

One of the best ways to guarantee high-quality air in buildings is through the use of air handling units (AHUs). As a component of the ventilation, heating, and air conditioning system, AHUs are used to control and circulate the air. Any firm must prioritize having high-quality air to protect its workers’ health and safety and maximize production. AHUs are typically installed on the floors, roofs, or basements of medium to large industrial and commercial buildings. Numerous smaller AHUs operating in various parts of the building are typical.

What use does an air handling unit serve?

The air handling unit (AHU) is often a sizable metal box that is connected to the ductwork that distributes conditioned air inside a structure and returns it to the AHU. There are a lot of ventilators with various tasks inside this sizable metal box.

The room receives fresh air thanks to AHUs. The systems draw outside air into the system, filter it, and condition it (cooled by a cooling coil or heated by a heating coil).

The air from the rooms can be circulated to save electricity in areas with lesser hygiene requirements for air quality. A cooling/heat exchanger is typically installed on the AHU to increase capacity and reduce energy consumption.

How they operate

It is simplest to describe how AHUs operate by going through each component’s purpose in turn:


The housing, which is typically composed of metal and coated to avoid corrosion, houses every part of the AHU. To avoid condensation, the housing has insulation around the fans and coil.

Filters The air is purified using filters to remove impurities. There are various filters available for various AHUs:

  1. HEPA filters are frequently used in settings where businesses are particularly concerned about the safety of their personnel and sensitive equipment because they are effective at removing airborne bacteria and viruses from the air. 
  2. Bag filters offer medium to high filtration efficiency.
  3. Panel filters offer at least low filtration efficiency. 
  4. Electrostatic filters use highly charged electrodes to ionize the air. 
  5. Carbon filters eliminate odors and gasses.


The AHU’s fan distributes air to various parts of the structure. Different types of fans are available (forward Curved, Backward Curved, Airfoil, and Backward Inclined). Following the static pressure and air volume in the AHU, the designer will use software to choose the appropriate fan.

Technology has advanced over time to make greater use of energy and adhere to a greener agenda. Due to the ability to adjust the volume of air expelled based on demand, the variable air volume (VAV) system is well-liked. The fan’s speed will be low if the system and thermal loads are low, and it will increase if the loads are large.

Mixing Box

The outside air and the air that has been returned are combined in the mixing box, and the ideal mixture of air is then sent to the space for conditioning. This is a straightforward heat recovery technique. The choice of method to utilize will depend on the application. Other options include thermal wheels and cross-plate heat exchangers.

Condenser coil

The air is cooled and dried using a cooling coil. A chilled water cooling coil or a direct expansion cooling coil will be employed, depending on the AHU system.


Humidifiers are useful during the winter when indoor air can become excessively dry and uncomfortable:

A few popular humidifiers are:

  1. Grid Type Steam: Steam is produced by heating water.
  2. Water is heated using a pan and heating coil in a steam pan type. Water evaporation results in humidity.
  3. Spray Type, which contains a water-spraying spray nozzle

The following are the factors to consider while installing AHU

  1. Installation and commissioning: Hire the best specialists to install the AHU, and do not cut corners on commissioning because it will save you money.
  2. There is always a suitable option, whether it is produced in a factory or on-site (flatpack).
  3. Refurbishing existing devices will give them new life.
  4. To increase operating efficiencies and conserve energy, reconfigure or upgrade components. 

Types of the air handling unit

The “blow-through” and the “draw-through” air handling unit types are the two most common types.

Before the air enters the ducting network, the blow-through AHU’s fan forces the air through the mixing box, cooling coil, and filters.

The draw-through AHU can either be horizontal or vertical. Before the air enters the ducting network, it is pulled through the mixing box, cooling coil, and filters by a fan.

Bottom Line

The AHUs come in a variety of sizes. Terminal units, also known as fan coil units or blower units, are compact, straightforward machines. These appliances might be limited to a coil, blower, and air filter. A larger AHU that only treats 100% outside air is called a makeup air unit (MAU) or fresh air handling unit (FAHU). 

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