Without this door the building would not function: the secret of skyscrapers
Most of us are sure that it is a design choice intended to convey luxury or regulate a crowd. A new video running on the web reveals that without this door, the skyscraper simply could not function, and it is directly related to your elevator.
The next time you arrive at an office tower or a luxury hotel, pay attention to the short moment when you are forced to slow down, squeeze in, and wait for your turn at the revolving glass door. It is annoying, it is slow, and it feels like an unnecessary design whim.
However, it is not a whim at all. A new video on the YouTube channel "Simple Why", which has accumulated many views on the web, explains that the revolving door is one of the smartest engineering creations in the building - and without it, the skyscraper you are standing in simply could not exist.
The building that acts like a chimney
The problem starts with simple physics. According to the video, a skyscraper actually acts like a giant chimney. In winter, the warm air inside the building rises up and escapes through cracks in the roof area, in elevator shafts, and in ventilation systems. This escape creates low pressure on the ground floor, which pulls cold air from outside in with force.
The phenomenon, which engineers call the "Stack effect", intensifies as the building gets taller. And here it gets extreme: on a cold winter day in an exceptionally tall tower, this invisible pressure can generate winds inside the lobby at speeds of up to 32 km/h.
The moment the door beats you
What is the practical meaning? Under such conditions, opening a regular entrance door might require a force of more than 45 kg. For a child, an elderly person, or someone dragging a suitcase, this is an almost impossible task. And every such opening also wastes all the air that was heated with effort at once, and lets in a freezing gust instead.
Here the revolving door comes into the picture, which is actually not a "door" in the usual sense at all. As the video explains, it is a continuous air lock, similar to the mechanism that exists in spaceships and submarines. People enter and exit continuously, but the building is never exposed to an open and large opening. At any given moment, the door is open to people but closed to air passage, and functions as a giant valve that maintains the air pressure in the building.
The inventor who simply did not like manners
There is also an amusing historical fact here. The inventor of the revolving door, an American named Theophilus Van Kannel who patented it in 1888, did not think about skyscrapers at all.
He simply did not like the social etiquette that requires holding the door for strangers, and wanted to avoid the cold wind that penetrates inside every time one does so. A solution to a small social problem that became, in retrospect, critical infrastructure in towers.
The second secret: why change elevators halfway?
The video also reveals another engineering mystery. In many towers, it is impossible to go up from the lobby directly to the top floor, and it is required to change elevators halfway, in what is called a "Sky Lobby". And the reason, it turns out, is not the separation between guests and employees.
The problem lies in the weight. In an elevator shaft 500 meters high, the steel cable alone can weigh close to 20 tons, equivalent to the weight of ten family cars. The taller the building, the more energy the engine wastes just on lifting the cable itself, until a technological limit is reached.
The solution, developed in the 60s, was to divide the building into vertical zones: you go up to a "Sky Lobby", and from there you transfer to another elevator that serves the next segment.
So the next time you enter a tall tower and get annoyed at the revolving door or the elevator change, it is worth remembering: these are not design nuisances, but the quiet engineering wonders thanks to which this huge building is even capable of standing.
