Elevator and Escalator Consulting Engineers
How Fast Can We Go?
As the world gets squeezed more and more for space with more and more people populating our planet there is an increasing tendency towards higher buildings in some of the more densely populated urban areas of the world.
This tendency is also fueled, apart from practical considerations of space, by the desire to have the "tallest building in the world" or at least if not the tallest, one of the tallest. To some extent the prestige of a city or its degree of modernity is measured by the height of its buildings.
As part of this "higher-high-rise" trend, a few elevator companies have begun experimenting with faster elevators. Consideration is being given to elevators traveling at speeds of 1000 and 2000 metres per minute.
Unfortunately, as elevators travel faster, the air pressure changes faster. The experience is similar to flying in an unpressurized airplane. The change of pressure with change in altitude can be quite uncomfortable because of the problems it causes to the inner ear.
Each person reacts differently to the pressure change; it is a purely individual and subjective phenomenon. There is no absolute criterion that will fit all people.
When the PanAm building was constructed in New York City after the Second World War, Westinghouse, the elevator contractor designed the high rise group to travel at 1800 fpm (550 metres per minute). It was reported that the elevator passengers found the pressure change sufficiently uncomfortable that their complaints led to a reduction of the speed to 1600 fpm (490 meters per minute). If this is to be believed then this could be considered the upper limit of acceptable elevator speed.
On the other hand it was also rumoured that the speed was reduced because there were problems with the speed control system. Take your pick.
In any case, there is a limit.
Japanese researchers have published information indicating that their tests show that much higher speeds (and consequently much higher pressure changes) can be tolerated. These tests were made with volunteers (at least we assume they were volunteers) in pressure chambers. The terminology used is of course significant. A test subject may accept pressure changes that the average high rise office occupant would not. One could expect more reluctance to experience discomfort from someone paying top prices for luxury office space.
Perhaps the answer is indeed that if we wish to keep one hundred percent of the building population happy, we will have to either accept the 490 to 500 metre per minute speed limit or find means to channel passengers through space locks and pressure chambers so as to maintain acceptable pressure change.
A more practical alternative that may be explored in the coming years is the balancing of the pressure of buildings from the top to bottom.
Tall buildings tend to act as chimneys. In most cases - particularly in cold weather - cold air comes in at the base of the building, is heated and rises to the top of the building. At the upper floors of the building the air “exfiltrates” through various fissures - particularly in the curtain wall - to the external atmosphere. There is normally a neutral point in the vertical rise of the building where the internal building air pressure equals the external pressure. The vertical pressure spectrum will vary with external and internal temperature changes, wind conditions and other miscellaneous factors. If there are elevator shafts running non-stop from top to bottom of the building it becomes difficult to maintain a constant pressure within these hoistways. And a constant hoistway pressure is desirable if we wish minimize the pressure on the middle ear and thus achieve a comfortable ride for the elevator passenger.
It would be theoretically possible to install horizontal “gates” at various points up the hoistway that would effectively seal off much of the hoistway and thus defeat the stack effect. These gates would be designed to automatically open in front of the elevator cab and close behind it as the cab moves up and down the hoistway. Since nothing like this has been attempted to date there would obviously be teething problems, even assuming that the basic premise has validity. This would be, however, one avenue to explore for future high rise buildings.
If we could by these means obtain and maintain a zero vertical pressure gradient, then the biological human body limitations to elevator speed would be removed and there would be no speed limit.
Another, and perhaps more practical approach, is to not have continuous vertical shafts through the building. Although there is often some passenger resistance to transferring from one elevator group to another there may not be any reasonable alternative in a high rise building (over one or two hundred floors). Obviously this does not directly answer the question of “How Fast Can We Go?” since the various groups with their reduced travel would operate at “normal” (by this we mean five to seven metres per second) velocities. In this way, we avoid the question.