Ups and downs
Elevators typically move in one of two ways; electric motors or hydraulics.
Tall buildings typically use an electric drive motor to move a cable attached to the elevator car at one end and a counterweight at the other. The cable is suspended over a pulley which attaches to the motor either directly or through gears. The weight suspended by the cable creates traction over the pulley, earning this type of system the name “traction elevator”. Principle 8 – Anti-weight
Traction elevators use brakes to hold the car in place at a given floor. These brakes are held open electrically and are closed by a spring. In the event of a power outage, the brakes will automatically engage. Principle 11 – Cushion In Advance
As an elevator car rides to the top of the building, all the weight of the cable adds to the weight of the counterweight. This upsets the balance between the car and the counterweight on tall buildings. To combat this, another cable or chain (called a compensator) is looped from the bottom of the car to the bottom of the counterweight. Principle 8 – Anti-weight
Shorter buildings usually use a hydraulic system that moves the car up and down like a jack. Principle 29 – Pneumatics and Hydraulics
Up Peak/Down Peak
Tall office buildings will often have “rush hours”, with employees rushing up into the building in the morning and rushing down at the end of day. To accommodate this, elevators prioritize their return to the ground floor in the morning. In the evening, the reverse is done, with the cars prioritizing a return to the top floor. Principle 15 – Dynamics
Although one big elevator could meet the needs of a building, the wait times would be intolerable. Most buildings have multiple elevators to handle a large load of passengers and to increase reliability. If one elevator fails or is in service, there is at least one more to handle the load. Principle 1 – Segmentation
Some very tall buildings divide the duty of ferrying passengers between express elevators that visit designated elevator lobby floor and local elevators that visit all the floors in between. Principle 3 – Local Quality
Most elevators follow a simple pattern of going to where the buttons are pushed on the floor selection panel inside, or if called from a floor, going to that floor. This is done in the order in which the floors pass by, going up and then going down.
Some very tall buildings will instead require a person to call the elevator by declaring which floor they wish to go to. This allows the elevator system to plan the route of its cars in advance. Principle 15 – Dynamics
<nerd_alert> This reminds me of the Happy Vertical People Transporter from Hitchhikers Guide to the Galaxy; elevators that can see into the future. </nerd_alert>
New highly efficient elevator systems can regenerate the majority of electricity they use, just like electric cars. For example, if a lightly loaded car travels to the top of the building, the motor will exert itself to slow that rate of climb against the counterweight’s tendency to accelerate travel. Rather than turning the exertion to heat, the motor can instead generate electricity to be recaptured for use elsewhere in the building.
Not only does this reduce the net use of electricity by the elevator, it can reduce the amount of heat created and the associated burden on the building’s cooling system. Principle 22 – Blessing in Disguise