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.