Revolving Door
From Sustainability
Contents |
Thank you for saving energy
On average 8x as much air is exchanged when a swing door is opened as opposed to a revolving door. That's 8x as much new air that needs to be heated or cooled and that's why using the revolving door is a great way to reduce energy requirements on campus.
Why should I use the revolving door?
You’ve probably seen the signs around campus saying “Help MIT save energy. Please use the revolving door.” But does it really make any difference? Absolutely. Our estimates show that if everyone used the revolving doors at E25 alone, MIT would save almost $7500 in natural gas amounting to nearly 15 tons of CO2. And that’s just from two of the 29 revolving doors on campus!
How does using the revolving door save energy?
The air that is inside a building has been “conditioned” to make it comfortable for the occupants. We call the equipment that does this “air conditioners” in the summer, but the air heating equipment in use during the winter and ventilation “make-up air” consumed year round is also conditioned air. Energy is required to condition air -- to make hot, moist air cold and dry in the summer and to make cold, dry air warm in the winter. Thus, whenever air is exchanged between inside and outside, air conditioning equipment has to work harder, using more energy.
The figure below illustrates how air is transferred in and out of a building. Cold air is more dense than warm, resulting in a pressure differential (“stack pressure”) that moves conditioned air through open doors and cracks in seals. Wind blowing on the building adds to this pressure differential.
The revolving door stops conditioned air from moving freely. An open swing door is like letting go of a balloon- the air rushes out of the opening. A revolving door is never open- seals remain in contact with the walls of the door at all times. Only the air in the chamber with the person going through the door is transferred.
How much energy does using the revolving door save?
Table 1. Potential savings in different revolving-door usage scenarios at E25
| Revolving-door usage | 50% | 75% | 100% |
|---|---|---|---|
| Saving of annual energy consumption | 14.5% | 38.7% | 74.0% |
| # of houses the saved energy can heat in one year | 1.0 | 2.7 | 5.1 |
| # of years the saved energy can light a 100W bulb | 5.8 | 15.3 | 29.0 |
| Tons of CO2 prevented | 3.0 | 7.7 | 14.6 |
The energy savings from using a revolving door are remarkable, given the three or four seconds over which is occurs. Note that the savings if everyone uses the revolving door don't amount to 88%, as you might expect from the 8x less air transferred through the revolving door as through the swing doors. That's because the revolving doors leak more than swing doors, lowering their overall efficiency slightly.
Energy savings depend on the weather- heating is less efficient than cooling and the indoor / outdoor temperature differential is larger in the winter than in the summer, so more energy is saved in the winter (see chart below). Windy days are worse than calm ones. Still, every time you walk through a door and you feel that rush of “wind,” you’re feeling energy leave the building. The chart below shows monthly-averaged total air leakages through building E25’s doors (revolving-door usage = 23.3%).
Average heat transfer per swing door passage: 78 Wh (267 BTU)
- 1.3 hours of light from a desk lamp
- 4.3 hours of light from a compact fluorescent bulb
- Driving a car 306 feet
- Half a mile jog
More information
For more information, please see the complete report here: [1]
References:
- American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. (2005). ASHRAE Handbook: Fundamentals. Atlanta: ASHRAE.
- Min, T. C. (1958). Winter infiltration through swinging-door entrances in multi-story buildings. Heating, Piping and Air Conditioning, 30 (2), 121-128.
- Power MIT: Real-time power and emissions data. Retrieved July 2006 from [2]
- Schutrum, L. F., et al. (1961). "Air infiltration through revolving doors.” ASHRAE Journal, 3 (11), 43-50.
- The Weather Underground, Inc. (2006). History for Boston, Massachusetts. Retrieved May 1, 2006 from [3].
- U.S. Department of Energy, Energy Information Administration. (2006, July 11). Average Retail Price of Electricity to Ultimate Customers by End-Use Sector, by State. Retrieved July 2006 from [4]
Revolving doors in the media:
How to Get Involved
- These signs are part of the campus component of the MIT Energy Initiative
- To get in contact with the student working-group responsible for this effort check out the Closing the Loop webpage or email closingtheloop@mit.edu
- Find out about other student efforts on energy and the environment check out the sustainability main page
