Revolving Doors Aren’t Just Annoying, They’re Energy Saving Too [Hackaday]

View Article on Hackaday

While most of us have been content with swing and sliding doors for the vast majority of our needs around the home, the revolving door remains popular in a wide variety of contexts.

It’s a confounding contraption that always feels ready to snatch and ensnare the unwary user. However, these doors do have certain benefits that have allowed them to retain popularity in many public buildings around the world. Let’s dive in to why below.

You Spin Me Right Round

The revolving door dates back to the late 19th century, with two main patent filings occurring around that time. One H. Bockhacker in Germany filed a patent for a rotating cylindrical door in 1881. Meanwhile, the more well-known Theophilus Van Kannel was granted a patent in 1888 for a three-partition revolving door with all the major features we’re familiar with today.

Both of these inventors were keenly aware of the benefits of such a design. Their rotating doors were intended to allow entry and egress from a building without excessive exchange of air. Swing and sliding doors enable wind and rain to easily enter a building unless used in a dual-stage airlock design. In comparison, a rotating door that is sealed at the edges prevents this almost entirely. Only a small pocket of air is exchanged as each segment of the door rotates. Even better, a properly-designed rotating door won’t get blown open by the wind, and allows people to enter and exit a building at the same time. These benefits led to the adoption of rotating doors in many public buildings.

In fact, due to the lower amount of air exchange, the revolving door has become a key feature in many skyscrapers. These taller buildings are subject to what is referred to as the “chimney effect.” As the building’s HVAC system heats the air inside, this warm air rises as its buoyancy increases. This creates a pressure differential with a lower pressure at the base of the building. When a swing door is opened at ground level, this causes an in-rush of air. This then forces heated air out the top of the building in turn. This breeze is frustrating for occupants and bad for efficiency, as the fresh air must then be heated again, using more energy. The same effect happens in the warmer months, too, in reverse, as cooler air sinks through the building in the opposite direction.

The naturally-sealing design of a revolving door prevents this issue. While the door does not seal as well as a regular closed swing door, it exchanges far less air as it works compared to a swing door being open and closed repeatedly. The effect is noticeable even in smaller buildings. Larger buildings that are more subject to the chimney effect, with greater pressure differentials, will notice significantly greater benefit.

A simple study run by MIT in 2006  found that the benefits from revolving doors could be profound. Estimates were that solely using revolving doors in one building would save 74% of its current annual energy consumption on heating, cutting 15 tons of CO2 output.

It does highlight one of the pitfalls of the revolving door, however. In order to gain the benefits, the revolving door must be used in preference to swinging types. Even in buildings with revolving door entrances, many building codes mandate that swinging doors also be present. This is often wise practice, as revolving doors can be a liability in an emergency, prone to being jammed or overwhelmed by sudden rushes for the exits. However, if people regularly use the swing doors in preference to the revolving door, it’s not saving any energy at all.

It’s a simple fact that revolving doors often present a frustration to busy people. There’s a reason they don’t often appear in action films — after all, there’s pretty much no way to get through one in a hurry. Manually push-operated types can allow someone to push through quickly, but the rate must be limited mechanically to avoid injuring other people that may also be transiting the door at the same time. Alternatively, automatic doors can turn at a constant rate, but they must often be relatively slow in order to remain accessible to those who aren’t as mobile and quick as others. Careful provision must also be made for proper access by wheelchair users and those using other mobility aids.

Overall, revolving doors have an important role to play in our buildings. They may be slow and frustrating, particularly when the automatic ones randomly stop (looking at you, IKEA), but they can save us huge amounts on our energy bills. That’s good for the climate too, at a time when we need every last bit of efficiency we can get!