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See Inside January 2009

How Do Elevators Work?

A look inside the complex machine that moves people up and down floors

Elevator installation is a mature business, yet change is under way as office space and energy get pricey. Most buildings that are taller than four stories use traction elevators. A motor at the top of the shaft turns a sheave—essentially a pulley—that raises and lowers cables attached to the cab and a counterweight. Gears connect the motor and sheave in slower systems. Faster elevators are gearless; the sheave is coupled directly.

Either way, the machinery typically fills an entire room above or beside the top of the shaft, occupying what could be prime penthouse space. But innovations are allowing builders to squeeze the equipment into the head of the shaft itself or against a side wall. “We are steadily shifting to gearless, machine room–less designs,” says Jeff Blain, senior project manager at Schindler Elevator in New York City. Some companies are using permanent-magnet gearless motors, which are smaller than traditional designs but have become just as powerful. And Otis Elevator in Farmington, Conn., has switched from wound steel cables to flat steel belts, allowing the sheave and motor to be downsized.

At the same time, manufacturers are exploiting gravity to save energy. A counterweight chosen to weigh about as much as a cab with 40 to 45 percent of a full load lessens the motor output needed. But when an empty elevator must go up, the heavier counterweight’s fall provides too much energy; massive resistors dissipate the excess energy as heat. The same resistance is needed when a full cab (heavier than the counterweight) is descending. New regenerative drives, however, convert the wasted energy into electricity. “We feed that energy back into the building’s electric grid for reuse,” says Leandre Adifon, vice president of elevator systems engineering and development at Otis.

Improved dispatch technology is upping human efficiency in buildings with multiple shafts. Office buildings are cramming more people into existing floors, but the increased population can slow elevator service. To compensate, installers are replacing the “up” and “down” push buttons in foyers with numbered display screens or touch pads. Would-be passengers push the floor number they want, and a computer tells them which elevator to take, grouping people going to the same or neighboring floors. The computer dispatches the elevators so each one travels to a small set of nearby floors, instead of randomly traveling far up and down. The scheme decreases wait time and energy consumption.

Did You Know ...
FAST FACT:
Toshiba Elevator claims to have the fastest passenger elevator, installed in Taipei 101, the 101-story building in Taiwan. Top climbing speed is 3,314 feet (1,010 meters) per minute, or roughly 100 floors in 26 seconds. A blower system adjusts the atmospheric
pressure inside the cab to minimize ear popping.

SAFETY FIRST:
An elevator cable is rated to hold 125 percent of the maximum full-car weight, and five or more cables suspend most cabs. Steel rope has become so strong that a one-half- or five-eighths-inch diameter is sufficient for a 3,500-pound load, typical in mid-rise buildings. New, flat, high-strength steel belts of similar strength may be less than one-fourth-inch thick.

SO INCLINED:
Certain elevators made by Otis move laterally as they rise, to follow the contour of unusual structures. Angled cables pull cabs along rails inclined at 39 degrees (from the horizontal) in the pyramidal Luxor Hotel in Las Vegas and at 30 degrees in the Eiffel Tower in Paris.

Note: This article was originally printed with the title, "New Designs Going Up".

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