How Does an Air Handling Unit Work?

Michael Rosario, Construction Tech Review

Many air handlers often bring in outside air to ensure that the room is still filled with fresh air rather than recycled air. It is vital to bring fresh air into a space to avoid high CO2 levels and stale air.

FREMONT, CA: An air handler comprises of a fan blowing air through a filter and heat exchanger. To do so, the air handler's fan draws unconditioned air from a building's confined spaces, such as an office, hallway, or classroom. Many air handlers often bring in outside air to ensure that the room is still filled with fresh air rather than recycled air. It is vital to bring fresh air into a space to avoid high CO2 levels and stale air. Both the return air and the outside air join the AHU through a mixing plenum. The mixing plenum is a portion of the air handler where the two airflows combine before going into the rest of the system.

After that, the air goes through a filter. Particles are stuck in the filter and separated from the air stream when the air flows through it. Filtration is one of the critical elements of an air handler because cleaning the air does two aspects:

• It prevents particle buildup from triggering mechanical problems. The buildup of dust and dirt within the air handler will wreak havoc on it, causing certain parts to malfunction. The energy efficiency of a dirty air

 the handler would be diminished as well.

• Improves the consistency of the air inside the home. The air filter eliminates pollutants from the air that reaches the house, resulting in improved air quality.

The air is then required to travel into a heat-exchanging coil. Depending on the type of air handler, the heat exchanger cools or heats the air in the process:

• Water flows through the coil in hydronic air handling systems. Depending on if the air handler is heating or cooling a room, the water may be either hot or cold. The coil's temperature increases as water passes into it. The coil heats or cools the air when it is blown over it by the fan.

• The refrigerant flows through the coil in Direct Expansion (DX) air handling systems. The heat is transferred directly between the refrigerant and the air blown by the fan.

Finally, the air handler pushes the clean, conditioned air into the enclosed space.