Air handling unit is a huge indoor unit of commercial air conditioning equipment. Air handling units are widely used in large facilities visited by many people, such as theaters and shopping malls. One of the reasons for that is that large facilities frequented by people are subject to strict regulations concerning the exhaustion of carbon dioxide and air cleanliness. A large facility needs to let large amounts of air into the building and use many blower fans to circulate the air. Air handling units are also used in factories and other workplaces where combustible gases are handled.