## The Elevator

The IL Centreâ€™s elevator uses a hydraulic system to raise and lower passengers. The cylinder can be seen through a window in the side of the elevator shaft. Elevator power use is monitored using the IL Centreâ€™s Live Building system.

A piston as tall as the elevator shaft (three stories) is mounted in a cylinder. To raise the elevator, a pump pushes hydraulic fluid into the pipe beneath the cylinder and the elevator rises.

When the car travels down, a valve opens and the fluid re-enters the holding tank; the weight of the car pushes the fluid out of the pipe, and the diameter of the return pipe determines the rate of descent.

The elevator motor needs power to move the elevator up, but not down. The graph to the right shows its power use for the past hour. Each spike is a trip upwards. The greater the number of passengers, the more power required to do the work of raising the car.

### Alternatives

Rope-and-counterweight elevators work on a see-saw principle. The work of pulling the car up is performed not only by a motor, but also by a counterweight moving in the opposite direction. Each time the elevator moves downwards, it puts potential energy into the counterweight by pulling it upwards. The average hydraulic elevator takes about 20kW to move people upwards, while a rope and counterweight takes 7.5kW. And while the hydraulic elevator only spends energy on the way up, and rope and counterweight systems use energy for both up and down, the combined total -- 15kW -- still represents a 25% energy savings over hydraulic elevators.

While rope-and-counterweight systems are more energy-efficient, the control mechanisms are complex and the elevator requires many more safety mechanisms, meaning that the installation cost is typically much higher. And while a hydraulic elevator is mechanically simpler, it is feasible only for buildings with few floors; the cylinder has to be as tall as the highest floor, which means the pipe below must be drilled into the ground the same number of floors deep.