What is an Air Curtain and What is the Purpose of an Air Curtain?
Theophilus van Kannel patented the rotating door in 1888, claiming that it would keep “noxious effluvia” and “baleful miasmas” out of a building when the postman came and went. The rotating door also made it unnecessary for one person to hold a door open for another (legend has it that Van Kannel had grown tired …
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