Revolving Door

A revolving door is a building entrance made of three or four door panels hung on a central shaft that rotates around a vertical axis inside a cylindrical enclosure, so that people pass through between two panels as the assembly turns. The design was meant to solve a practical building problem: it relieves the pressure of air rushing through tall buildings and lets large numbers of people pass in and out while acting as an airlock that cuts the heating and cooling lost through an ordinary hinged door. Theophilus Van Kannel of Philadelphia is credited with the invention, receiving US patent 387,571 on August 7, 1888 for a Storm-Door Structure with three rotating partitions sealed against drafts; the Franklin Institute awarded him its John Scott Legacy Medal in 1889, the first wooden revolving door was installed at a Manhattan restaurant in 1899, and Van Kannel was inducted into the National Inventors Hall of Fame in 2007.