What Is an Air Handling Unit and How Does It Work?

Medium- and large-sized industrial or commercial properties use an air handling unit (AHU) to condition and distribute fresh air throughout the building. An AHU is part of the larger HVAC system (heating, ventilating, and air conditioning). The device takes air from the outdoors, cleans and conditions it, and heats or cools it as needed. Once properly conditioned, the air is forced through ductwork inside the rooms of the building.

Most AHUs include an additional duct run that pulls dirty air out of the indoor spaces and discharges it back into the atmosphere. In some cases, a portion of the stale air is recirculated into the AHU and again put through the conditioning/distribution process. Recirculating the used air is an energy-saving technique, but it is not an option in every situation.

Maintaining clean and fresh air indoors is especially important considering how much time Americans spend indoors today. In fact, the EPA estimates that most of us spend around 90% of each day inside.

Air Handling Unit (AHU) Basics

AHUs are most useful in places that must house many people with limited natural ventilation sources, such as convention halls and hotel dining rooms. Units are also helpful for maintaining “clean rooms,” like laboratories and operating rooms.

In addition to managing the proper ventilation of indoor air, AHUs:

  • Filter and purify the interior air to maintain good indoor air quality
  • Control indoor temperatures
  • Monitor indoor humidity levels

AHUs are sometimes located in the basement of a building or on the roof.

The Parts of an Air Handling Unit (AHU)

Learning how the individual parts of an air handling unit work can help laypeople understand the system’s overall function.

  • Air Intake – The intake collects air from the outside to be treat and distribute indoors.
  • Filter – The type of filter depends on the purity requirements of the building. Air intended for a hospital surgical room requires a higher level of “cleaning” than air for a hotel conference room.
  • Fan – The fan expels the air from the AHU into the duct system that distributes the conditioned air.
  • Heat Exchangers – These devices transfer temperature between the air and the coolants used by the AHU.
  • The Cooling Coil – Air passes through the coils to cool before distribution. This process can cause condensation, which the AHU collects in a droplet separator.
  • Silencer – Special coatings are applied to the unit walls to help reduce the noise level while in operation.
  • Plenums – Plenums are strategically placed empty spaces within the unit where airflow is allowed to homogenize.

Are AHUs Energy-Efficient?

The ultimate goal of an air handling unit is to improve energy efficiency. Heat recovery units and specialized “run around” coils work together to pick up wasted heat and reprocess it through the AHU. This function reduces demand on the heating coils and controls energy use.

In order to save energy while cooling, indoor air mixes with outdoor air, reducing any extreme hot/cold contrast when the air reaches the cooling coil and making it possible for the unit to provide cool air with minimal energy use.

Want to Know More?

A properly installed AHU can create a more comfortable environment for employees, visitors, and clients while conserving energy use. If building new or retrofitting, we recommend installing an AHU. Better use of insulation during construction helps prevent heated or cooled air from escaping and lowers energy costs.

However, improved insulation can also lead to more deficient ventilation and air that is stale or too humid. Excessive moisture in the air is a literal breeding ground for mold and mildew growth. Contact The Severn Group today to learn more about the benefits of air handling units.

Also, check out our blog for more information about commercial HVAC management. It’s a great resource for technicians, operation/facility managers, and property owners.