October 7, 2011
Regenerative braking, which involves taking unwanted mechanical energy and turning it back into electricity instead of letting it dissipate as heat, is well established in cars like theToyota Prius and has lately made inroads in railway locomotives.
In both cases, an electric motor, which converts current into mechanical energy, briefly reverses its function to become a generator, converting mechanical energy into current. One problem for cars is that the flow of electricity is so great that batteries have trouble absorbing it.
For the last decade or so, companies have been using regenerative braking in elevators. Elevators normally use counterweights that are equal to the mass of a half-empty elevator car. If the car is going up with only one person in it, or coming down full, there is gravity to fight with and brakes have to be used.
Otis, the largest elevator manufacturer, points out that some elevators already capture this unwanted energy as electricity but then typically dissipate it as heat. The company and others sell models that put the current back into the building’s electrical grid, which has a far greater capacity to absorb sudden jolts of energy than car batteries do. Then it can be used to power other building systems.
Now, the idea has spread to escalators.
At a green building conference in Toronto on Wednesday, the company introduced an escalator that combines regenerative braking with a standby feature: the escalator slows down when no one is on it. The new model also uses LEDs for illumination, further cutting energy use. And Otis says it has a better lubricant system, too.
It is the first use of regenerative braking in an escalator, the company says. Avideo from Otis explains the concept.)
While the regenerative escalators are just edging into the market, Otis, a subsidiary of the United Technologies Corporation, said it recently sold 700 of its energy-efficient elevators for a housing project in Jiangsu, China.