Regeneration is not a feature, it is a change in the drive

A traction elevator is counterweighted, which means that half the time it is being pulled rather than pushed. A full car going down and an empty car going up are both overhauling loads: gravity is doing the work, and the motor is holding the system back. In those moments the motor is a generator.

Where that energy goes today

In a conventional drive it goes into a braking resistor and leaves as heat. That heat has to be removed from wherever the drive lives, so the building pays twice: once for the energy it threw away, and again for the cooling that takes the heat back out.

A regenerative drive replaces the resistor with a unit that pushes that energy back into the building's electrical network, where the lighting and the air conditioning use it. Nothing about the car changes. The change is in the drive and in the control that goes with it.

Where it pays and where it does not

• High traffic, long travel and heavy cars regenerate the most, because they spend more time under overhauling conditions.
• A short residential building with three stops and light traffic recovers little: the car barely reaches rated speed before it decelerates.
• Hospitals and hotels benefit twice, because the equipment runs around the clock and the machine space is already fighting for cooling.
• The saving is not only the returned kilowatt-hours; it is also the cooling that no longer has to be installed and run.

Why it is a specification decision

Because it is the drive. Adding regeneration to an installed unit means changing the drive and, with it, the control and the electrical protections it was commissioned with. Choosing it at specification time costs a line in the schedule. Choosing it three years later costs a modernization.