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How Do Air Handling Units Work? Understanding the Components and Functionality

Air handling units are essential components of a building’s ventilation system. So how do these units work?

Air handling units work by taking in air through ducts. The air then passes through dampers and filters to eliminate dust and other harmful particles. Heating and cooling coils regulate the air temperature. Finally, a series of ducts circulate clean air throughout the building.

The rest of this article will help you understand the workings of air handling units, their primary components, and where you can use them. Read on to learn more!

The Workings of Air Handling Units Explained

Air handling units (AHUs) are an essential part of modern heating, ventilation, and air conditioning (HVAC) systems. They provide the necessary climate control for residential, industrial, or commercial buildings.

AHUs are used to clean and circulate air, maintain temperature levels throughout a building, control humidity levels, and filter out contaminants from the air.

Fresh Air Is Drawn From Outside the Building

The first stage of air handling involves the intake of fresh air from outside. Air passes through ducts and filters found near the air intake. 

Here’s how the two components operate:

  • The ductwork transports air to and from the unit. The size and layout of the ductwork system vary depending on the size and design of the building.
  • The filters remove contaminants from the air. AHUs have different types of filters, each with its benefits.
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The Filtered Air Is Mixed With Fresh Air

The filtered air passes through a mixing chamber, where it mixes with clean air returning from the building. The mixing unit is usually a large chamber with a fan to facilitate the processing of air. The fan blows the air around and mixes it with the fresh air from outside.

Read: How Does Air Handling Unit Work?

The Preheating Coil Increases Air Temperature

When the air temperature drops below a certain level, the AHU’s heater automatically increases the air temperature, protecting the unit’s components from freezing and damage.

The preheated air moves into the bag filter, where it’s purified before it circulates back 

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into the building.

Airborne Particulates Are Eliminated Through the Bag Filter

The bag filter removes airborne particulates such as:

  • Dust
  • Dirt
  • Pollen
  • Smoke
  • Mold

Bag filters work by trapping particulates in the tiny spaces between fibers. Pre-filters and post-filters work together to remove even smaller particles from the air.

  • Pre-filters are located before the blower. It helps to protect the more delicate components of the AHU from damage.
  • The post-filter lies right after the blower. It helps remove any particulates the other filters may have missed.

Once the preheated air is filtered, it’s safe for circulation. However, it may be cooled again to maintain a stable room temperature.

Read: Why Is Indoor Air Quality Important?

The Cooling Coil Cools Down the Air

The cooling coil removes heat from the air in circulation. It does so by transferring heat from the air to the coil. Meanwhile, the refrigerant cools down the air to the desired set point in the cooling unit.

However, the ambient temperature inside the building may sometimes be low. If this is the case, the air is reheated to rise to the ideal temperature set point.

The Heating Coil Maintains Desired Air Temperature

The heating coil contains heat-transfer fluid. It heats the air cooled by the evaporator coil. This process ensures that the air circulated through the unit is at the set point temperature.

Without the heating coil, the AHU would be unable to maintain the proper temperature.

Read: Top Reasons Why A Portable Air Conditioner Fills With Water Quickly

The Air Goes Through the Supply Fan

Before clean air can circulate throughout the building, it goes through the supply fan first. Here’s how the supply fan functions:

  • It moderates the air in the unit by moving air through the ducts.
  • It distributes the conditioned air evenly.
  • It ensures proper ventilation of all areas in the building.

The type of fan used in an AHU depends on the application. Some common types of fans installed in AHUs are:

  • Centrifugal fan (forward-curved and backward-curved centrifugal fans)
  • Propeller fan
  • Vane axial fan

Typically, AHU fans are classified by their ability to:

Clean Air Circulates Throughout the Building

The supply chamber of the AHU circulates clean air to the building. It ensures that building occupants get fresh and clean air. Moreover, the air circulating from the supply chamber is neither too hot nor too cold, which is good for health.

Read: What Are 4 Basic Categories Of HVAC Systems?

What Are the Essential Components of Air Handling Units?

AHUs have several components that play specific roles. These work together to supply clean air throughout the building.

  • The filter. It removes contaminants from the air.
  • Air mixing plenum. It’s where returning air and air in the unit mix before flowing through the rest of the AHU.
  • Dampers. These control the air moving in and out of the unit.
  • The fan/blower. It provides the airflow necessary to circulate air throughout the AHU.
  • The coils. They heat or cool the air, depending on the temperature of the building.
  • The ductwork. It carries the conditioned air from the air handler unit to the various parts of the building.
  • Vibration isolators. The AHU sometimes creates a lot more noise than expected. Vibration isolators moderates this noise.
  • Pressure sensor. When the filters accumulate a certain amount of dirt, the pressure sensor activates to signal that they need to be replaced. 

Where Can You Use Air Handling Units?

Having an HVAC system installed in your home can be a huge convenience. That’s why I have written a detailed post regarding the need to air balance your HVAC system. It’s one way to ensure efficient air conditioning. 

AHUs are vital to any HVAC system. You can find AHUs in buildings such as:

  • Family homes
  • Large office buildings
  • Public halls
  • Healthcare buildings
  • Shelter homes
  • Classrooms
  • Hotels
  • Warehouses
  • Factories

What Role Do Air Handling Units Play in Buildings?

Air handling units ensure that air is filtered, heated, cooled, and distributed in a way that makes the interior comfortable and habitable. Specifically:

  • They improve overall air quality. AHUs remove contaminants from the air and improve the air quality for occupants in the building.
  • AHUs help regulate temperature. They provide heating and cooling mechanisms to maintain a comfortable indoor environment.
  • They control humidity levels. AHUs have humidity sensors that measure and regulate the air’s moisture level. They prevent condensation of the air, creating an overall comfortable indoor atmosphere.
  • AHUs improve ventilation. They control the amount of fresh air that enters the building.
  • AHUs reduce energy costs. Proper circulation of quality air inside the building maintains a comfortable temperature. It eliminates the need to install additional heating or cooling units.


In its most basic form, an air handling unit is used to move air from one place to another and regulate the temperature of that air. It filters fresh air before cooling or heating it. The air then goes through the ductwork and into the building. This process maintains the correct temperature and humidity.

AHUs have several components that maintain a continuous supply of clean, fresh air in the building. They make AHUs suitable for residential, industrial, and commercial use. These components include:

  • Air filters/dampers
  • Mixing Chamber
  • Heating and cooling coils
  • Fan
  • Ductwork