The air curtain is a powerful airflow generated by a high-speed motor driving through the flow or centrifugal wind wheel to form an "invisible door curtain". 

       Divide indoor and outdoor into two independent temperature areas to create comfortable indoor environment, maintain indoor air conditioning and purify indoor air, save electricity, and make air circulation, can effectively isolate dust, smoke, odor, insects and microbes, etc. 

To prevent the outflow of cold (or warm) air, it can save electricity and effectively prevent the leakage of cold (warm) gas. The indoor and outdoor air can be divided into two independent temperature areas. When the air conditioner is running for a long time, the auxiliary circulation can adjust the temperature. 

Definitions

       The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) defines an air door as follows: "In its simplest application, an air curtain is a continuous broad stream of air circulated across a doorway of a conditioned space. It reduces penetration of insects and unconditioned air into a conditioned space by forcing an air stream over the entire entrance. The air stream layer moves with a velocity and angle such that any air that tries to penetrate the curtain is entrained. Air curtain effectiveness in preventing infiltration through an entrance generally ranges from 60 to 80%".

       The Air Movement and Control Association defines an air curtain as: "A directionally-controlled airstream, moving across the entire height and width of an opening, which reduces the infiltration or transfer of air from one side of the opening to the other and/or inhibits flying insects, dust or debris from passing through".

With air curtain or without air curtain.

       Following the laws of physics, the light heated air on the left of the image, goes up by natural convection and escapes to the cooler side while the heavier unheated cold air penetrates from the outside flowing through the floor. As the air tends to equalize temperatures and pressures and the warm inside are not thermally protected from the outside, the air mixes and we can’t see two separate thermal areas. In this situation we waste lots of energy and the heater is not able to keep comfortable the internal area.

The air jet of the air curtain placed on top, clearly divide the warm and the cold area in two thermal zones. The air curtain keeps internal environment on the left side of the image at comfortable warm temperature and avoids cold air penetration from the outside. In this second situation, the air curtain saves up to 80% of the energy given by the heater placed on the left wall.

Important Note: Poorly designed air curtains, wrong selected units (less powerful) or inadequate installation will lose part or even all the advantages and became worse than unprotected door.