Air doors use powerful blowers to create curtains of air that can be used to separate two different environments. An air door can be used in between different climate controlled zones in a structure or to separate the interior of a building from the exterior. The force of the downwards air pressure tends to prevent air from either side of the curtain from penetrating it, though high winds can reduce the efficiency. Common uses of an air door are to keep insects or dust from entering a building or to improve the efficiency of a heating, ventilation, and air conditioning (HVAC) system.
Most air doors consist of a powerful blower fan that is mounted on a ceiling or the top of a door frame and oriented towards the floor. When the device is switched on, it blows air downwards at a high velocity. This can prevent air on one side of the curtain from mixing with air on the other side. While this is less efficient than a physical door with a good seal, it can also allow people, vehicles, and other objects to move unimpeded between the two different environments.
The ability of air doors to effectively separate two environments depends largely on the strength of the blower fan. A blower with a higher velocity will tend to keep two volumes of air from mixing, especially on the exterior of a building where there might be winds present. These strong blowers can be uncomfortable for people to walk under, so weaker, less efficient units are often used in commercial facilities.
When an air door is used inside a structure, it is often intended to separate two climate controlled zones. One way that air doors are commonly used is to prevent freezers or cooler rooms from warming up each time the door is opened. This can increase the efficiency of not only the cooling system for the freezer but also the heating system for the rest of the building. In other cases, the air door is placed on the exterior of the building where it can preserve the interior temperature or keep dust, insects, and other undesirable objects from entering.
An air door can be placed in a doorway by itself or be used in conjunction with a physical door. When an air door is used by itself, it is typically set to blow constantly. These are often used at loading dock entrances where the doors remain open throughout the business day. Air doors that are used in conjunction with physical doors can be set to turn on only when the door is open. These are often used in commercial stores and other facilities where customers come and go throughout the day.