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Pressurizing the Cars of High-Speed Express Elevators

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The possibility of pressurizing elevator cars in high-speed express elevators is often mentioned in articles about express elevators for tall buildings. “A New World’s Fastest: Shanghai Tower” (ELEVATOR WORLD India, 3rd Quarter 2013) mentions the pressurizing of cars and provides an interesting project in consideration of this topic. The express elevators for this tower may have a maximum contract speed of 18 mps.

The article mentions that the double-deck express elevators will reach contract speed after an acceleration period of 25 s. and travel at full speed during 10 s. If we assume the deceleration period is also 25 s., the total travel time to floor 119 (a distance of 565.4 m) is 60 s. This time probably includes time for door operation. A calculation with the usual standard rates for acceleration, deceleration, jerk, and times for door closing and opening confirms that the 60 s. door-to-door flight time (DDFT) is correct for the assumed contract speed of 18 mps..

The air pressure at floor-level zero will fluctuate in accordance with weather conditions; however, the air pressure on floor 119 will be about 58 millibars less, because air pressure declines by about 10.2 millibars per 100 m.

Control of Air Pressure

The time available for a gradual reduction of car air pressure during an up trip is the DDFT of 60 s., minus the time for door closing and opening (i.e., 54 s.). This means the car internal air pressure must be reduced by 1.07 millibars per second (58/54). This mode of air-pressure control provides a car internal air pressure as if it is a non-pressurized car traveling at a constant speed of 10.5 mps. During down trips, the car air pressure must be increased by 1.07 millibars per second.

Passenger Comfort

Airlines have undoubtably investigated the effects of air pressure on passengers, because gradually reducing air pressure in cabins and increasing it before landings is a standard practice. Airplanes usually have plenty of time for this procedure. For elevator passengers, the question is, “Which rate of change of car air pressure is safe and comfortable?” The author is under the impression that car speeds up to 12 mps can be tolerated by elevator passengers. If this assumption is correct, the pressurizing of the Shanghai Tower elevator cars enables a reduction of DDFT. If the maximum elevator speed that can be tolerated by the general public is less than 12 mps, the pressurizing of elevator cars is probably not attractive, because it introduces a serious technical problem for minimal time benefits.

Complex Technical Problem

“A New World’s Fastest: Shanghai Tower” mentions it may not be possible to use the maximum possible contract speed of 18 mps. This comment is not surprising, because the pressurizing of cars presents a complex technical problem that includes air-conditioning of the car interior. Also, a sudden change of air pressure due to a technical problem would have to be considered.

Conclusions

It is technically possible to realize a DDFT of 60 s. to the Shanghai Tower sky lobby. It would probably be the first group of express elevators that controls the internal air pressure of cars to minimize flight times. To put this DDFT of 60 s. into perspective, note that a contract speed of 12 mps will increase the DDFT to about 70 s. For a contract speed of 10 mps the DDFT will be approximately 73 s.

The round-trip times (RTTs) of the cars are positively affected by short DDFTs; however, the large cars of the express group under consideration cause long car loading and unloading times that negatively affect group performance. If we assume that the express group to floor 119 consists of four double-deck cars, their RTTs during heaviest simultaneous up and down traffic will be twice the DDFT of 60 s., plus two 25-s. periods for loading and unloading of, say, 20 passengers per deck at each terminal (i.e., a total RTT of 170 s.).

In this case, the theoretical minimum average departure interval will be 43 s., and the theoretical minimum average waiting time will be approximately 22 s. The maximum transport capacity of the group per 5 min. in both directions will be 282 passengers in both directions. The 25 s. for loading and unloading assumes the decks of the express cars have two sets of doors opposite each other to allow the loading doors to open about 5 s. after the opening of the unloading doors. This implies the 20-s. loading and unloading periods overlap by 15 s. If the decks have only one set of doors, the RTT will be at least 30 s. longer.

The four-large-car configuration is not the best possible optimum. An alternative group of six half-as-large triple-deck cars can be installed in the space required for four large double-deck cars. With a contract speed of 10 mps and unpressurized cars (with two sets of doors per deck), this group will deliver average RTTs of 171 s., plus 15 s. if having one set of doors. With two sets of doors, loading and unloading will take 12.5 s. per stop (25 s. for each round trip).The departure intervals will be approximately 29 s., and average waiting times will be approximately 15 s. The maximum capacity of this group per 5 min. will be 316 passengers in both directions.

The essential aspects of planning express groups and sky lobbies are described in Chapter 12 of your author’s book, The Planning and Performance of Groups of Elevators, published at website: elevatorgroup controls.com. Within, a six-car configuration with small triple-deck cars to reduce crowding at the main entrance and sky lobby floors and substantially increase service frequencies is presented. The author will greatly appreciate comments or questions from readers through EW at e-mail: editorial@elevatorworld.com.             

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