By Glen Tracy
Revolving doors can be up to eight times more energy-efficient than their hinged counterparts—all while allowing large numbers of people to pass in and out, boosting security, and adding architectural interest. In other words, not only can revolving doors efficiently handle bidirectional pedestrian traffic and reduce energy costs by maintaining an airlock, but they can also improve comfort for building occupants and offer more usable space at entrances compared to vestibules.
A revolving door generally consists of door wings that hang on a central shaft and rotate around a vertical axis within a cylindrical enclosure called a ‘drum’ (Figure 1). There are usually two, three, or four wings, typically incorporating glass. The opening of the drum enclosure is referred to as the ‘throat.’
Manual revolving doors rotate with push-bars, which cause all wings to move. Large-diameter revolving doors use a motor to rotate automatically, and can accommodate strollers, wheelchairs, and wheeled luggage. A speed control device (or ‘governor’) mounted in either the ceiling or floor prevents the door from moving at an unsafe speed.
Automatic revolving doors are powered above or below the central shaft, or along the perimeter. Sensors in the door wings and the enclosure frame ensure the speed with which the door revolves is controlled. Other sensors can prevent or minimize the force of impact of the door wing on users.
Revolving doors were invented in Philadelphia in 1888 by Theophilus Van Kannel to reduce air infiltration. His company’s original motto—“Always open, always closed”—refers to how these doors are always open to people, but closed to the elements.
A basic understanding of the way air behaves in a building sheds light on the benefits of revolving doors. Generally speaking, per the stack effect, air flows in and out of a building because of differences in air pressure and humidity. In the winter, heated air rises toward the top of the structure; as long as there are openings on the ground floor, cold air rushes in to replace the heated air. The opposite happens in the summer.
In 2006, a team of graduate students at the Massachusetts Institute of Technology (MIT) conducted an analysis of door use in one building on campus, where they found just 23 per cent of visitors used the revolving doors versus the available adjacent swinging doors. According to MIT’s calculations, the swinging door allowed as much as eight times more air to pass through the building than the revolving door (Figure 2).
According to the April 2009 MIT Tech Talk publication:
students indicated that if everyone were to use the revolving doors in this one building alone, MIT would save almost $7500 in natural gas a year. That’s enough to heat five houses over the same timeframe, and it also adds up to nearly 15 tons of CO2.
The MIT findings on how revolving door usage affects energy consumption are shown in Figure 3. A Toronto hospital project helps further illuminate these doors’ advantages.
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