Ask Habitat: What's an Elevator "Regen Drive" and Does It Save Money?

HABITAT ANSWERS: New elevator technology is making it easier to recapture some of the energy typically wasted in day-to-day operations.

There are three ways that an elevator loses energy and a "regen" drive saves it:

Loss: anytime the elevator decelerates — i.e., when it reaches its destination – energy is created. In a typical elevator system, that energy is dissipated as heat through a device called a heat resister. 

Gain: With a regen drive, the energy is captured and sent back to the power grid. 

Loss: whenever an empty or lightly loaded elevator goes up, the motor spins but the elevator's counter-weight is doing most of the work. 

Gain: A regen drive can allow the motor to essentially act as a generator, creating power which also goes back to the grid.

Loss: when a heavy elevator goes down, the motor spins but gravity is doing most of the work. 

Gain: A regen drive can again generate power to the grid.

Elevators do not use a large amount of power compared to a building's total load, with experts estimating that in a residential building, they amount to only about five percent of total energy use. Regardless, a regen drive generally can use 20 to 40 percent less electricity to power elevators. In addition, if a regen drive is in place and the energy does not have to be dissipated as heat, the building sees some savings because the equipment rooms do not have to be cooled as much.

How much a regen drive system can cost can also have a huge range, based on a wide variety of factors, such as the type of system installed, the existing condition of the elevators, the size of the building, and the demand. Parts alone can cost between $7,000 and $12,000 per elevator.

A few experts are installing data-loggers to track elevator usage so that those buildings will know their elevator energy use and can decide if the regen drives are worth it and what technology to install. In one building, a simulation model showed that the regen drives would not save enough energy to make them economically viable. But the data tracking actual energy usage also showed that the elevators consumed four times more energy than the simulation showed.

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Photo: KONE Corp. Licensed under Creative Commons Attribution-Share Alike 3.0 Unported.