When Ned and I were forming our company, Sustainable Growth, LLC, we met with our attorney, Jeff Agnor, several times. Jeff’s office was on the top floor of a very nice building with an impressive lobby and a revolving entrance door. Swinging doors flanked the revolving door on both sides (per life-safety code).
One day, as we were leaving, Ned used the revolving door and I used a swinging door. I asked him about it and in his characteristically diplomatic way he said “I try to use revolving doors when I can because they are more energy efficient.”
I was nearly floored. Not only had I not heard that before, but I immediately questioned it. How could it be? If anything, my intuition told me that a revolving door would be less efficient.
“MIT did a study,” Ned reiterated.
In 2006, a team of graduate students at MIT conducted an analysis of door use in one building on campus where they found that 23 percent of visitors used the revolving door. According to their calculations, the swinging door allowed as much as eight times more air to pass through than the revolving door. Applying average Boston weather to their equations, the MIT team found that if everyone who frequented that building over the course of a year 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.
The reason has to do with relative air pressures. Apparently a swinging door causes more of an air pressure imbalance and therefore much more air rushes in or out when this type of door is used.
So, how do you get people to use revolving doors?
First I checked to see what they do in Chicago where there are more revolving doors per capita than any other city I know of. As it turns out, they simply ask people to use them (see photo).
The MIT group was able to increase revolving-door usage by putting up signs, but the rates never rose above 63 percent. Interestingly, they found that a sign that politely asked people to use the door turned out to be more effective than one detailing the energy savings.
I wonder if anyone has determined how usage rates are affected if the revolving door is automatically powered and activated by a motion sensor. The potential savings that MIT documented would be more than enough to run the 250-watt motor typically used to power revolving doors.