Two. An air curtain occurs as ventilation device utilized for separating ii climate zones from either every more. Commonly these are mounted above an entrance door around the shop etc. to keep cold air out & caring air around. It consists of heating elements (electric car or even hot water system) & a fan right sufficiency to install the high speed flow of air reaching the floor. Ambient (not heated) air curtains come typically utilized inside conjunction sustaining cold storages & refrigerated rooms.

Air flow across the door depends in wind forces, temperature differences & pressure differences. It may be illustrated when in the picture in the image below.