The Explainer: Why Revolving Doors Save Energy.

Sometimes Slate's "The Explainer" explains random interesting shit...Here's one:

Right now, it's 71 degrees Fahrenheit in the Lantern's Manhattan office and 87 degrees outside. It takes a lot of electricity to cool this entire office building by 16 degrees—but it would take even more if people didn't use the two large revolving doors between the building lobby and the hot sidewalk outside.

Generally speaking, air flows in and out of a building because of differences in air pressure. (In the winter, heated air rises toward the top of a building, and—as long as there are any openings on the ground floor—cold air rushes in to replace it. The opposite happens in the summer, with the cold air flowing out the front doors.) Regular foot traffic in a large office building can result in air leaks of up to 30,000 cubic feet per minute.

How big a difference can using a revolving door make? In 2006, a team of graduate students at MIT conducted an analysis of door use in one building on campus, E25, where they found just 23 percent of visitors used the revolving doors. According to their calculations, the swinging door allowed as much as eight times more air to pass through the building than the revolving door. Applying average Boston weather to their equations, the MIT team found that if everyone used the revolving doors, it would save more than 75,000 kilowatt-hours of energy—about 1.5 percent of the total required to heat and cool the building—and prevent 14.6 tons of carbon dioxide from being emitted.* (By way of comparison, the EPA says an average American vehicle emits about six tons of carbon dioxide over a year.) The gains are also big enough that they could easily cover the energy needed to power an automatic revolving door like this one, which has a 250-watt motor.