Figure 1 : Gearless Machine-Room-Less Revolution . Note the space-saving factor as technology advances . This increases usable spaces , which is crucially important in skyscrapers . ( Source : http :// www . otisworldwide . com ).
machines because motor controller technology had advanced enough so that it could regulate AC power , enabling smooth stopping , acceleration , and deceleration [ 9 , 12 , 24 ].
Geared and Gearless Motors High-rise buildings typically employ geared or gearless traction elevators capable of high or variable speed operation . In geared machines , the electric traction motor drives a reduction gearbox whose output turns a sheave over which the rope passes between the car and the counterweights . In contrast , in gearless elevators , the drive sheave is directly connected to the motor , thereby eliminating gear-train energy losses . Therefore , a major advantage of gearless motors is they save about 25 % more energy than geared motors . Gearless motors also run faster and enjoy greater longevity because they feature higher torque and run at lower RPMs . The major disadvantage of gearless elevators is cost : materials , installation , and maintenance are generally more expensive than for geared elevators . Despite the cost , more elevators today use AC gearless motor machines because they are more efficient and last longer [ 12 , 25 ].
Machine-Room-Less Technology Introduced in the mid-1990s , machine-room-less ( MRL ) technology was one of the biggest advances in elevator design since they went electric a century before . Manufacturers redesigned the motors and all other equipment normally housed in a machine room to fit into the hoistway , eliminating the need for a machine room . Earlier , elevator equipment was so massive that a dedicated machine room ( about eight feet tall or greater ) was required , usually placed above the hoistway atop a building ’ s roof . The machine room was costly because it needed to support heavy machinery ( Figure 1 ). Today , MRL elevators are increasingly common [ 14 , 26 ]. The MRL system becomes even more energy-efficient when it is combined with regenerative drives [ 14 , 26 ].
Regenerative Drives Regenerative drives are another remarkable advancement in energy-efficient elevator technology , providing the ability to recycle energy rather than waste it as heat . They work by capturing and converting the energy used from braking to maintain the elevator ’ s speed . More specifically , traction elevators use a counterweight to balance the weight of the elevator car and passengers . The counterweight is sized optimally , approximately to a car loaded to 40 %– 50 % of capacity . Hypothetically , if the counterweight is too heavy or too light , the elevator will overwork the motor and the braking system . Instead , a middle weight is effective at levelling energy use
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