While staying at a resort hotel, last week, I saw an interesting behavior in response to an interesting design solution. The entry level elevator lobby had two elevators, two hall call stations, and two elevator position indicators. The two call stations were less than four feet apart.
Guest Behavior
A hotel guest approached the elevators and without hesitation pressed the UP button on both call stations. I thought it odd that the guest felt the need to press both buttons. So I stood and watched as other guests tried to use the elevators. I saw the same behavior repeated several times. Each time, the second elevator arrived at an empty lobby (except for me). No passengers boarded. Soon afterward, both elevators were called to another floor. The position indicators gave this away.
Curious, I began exploring. The elevator lobby was arranged identically on all floors, two cars, two call stations, and two position indicators. (7th floor lobby shown in photo) I thought perhaps one car may have been a service car. No, both cabs were identical, fitted out as passenger cars.
Simplex Controls
The controls for both cars were a simplex type - meaning each call station calls only one car. When the call buttons on both stations were pressed, both elevators responded. Only one car collected any passengers.
Operating both cars to respond to a passenger call on the same floor is a complete waste of energy. One car chases the other, only to find no passengers. Then the process is repeated. It would be interesting to check the elevator control records, especially if the cars included a weight sensor to see how may "empty" trips were made in a day, a week, or a year. Then calculate the energy that was totally wasted and the unnecessary wear and tear on the machine. The annual operating costs are likely double what they should be.
Select the Right Controls
Use simplex controls for a single car. Use duplex controls (single call station) for two adjacent cars. Use group controls (one or more call stations tied together) for more than two cars in a single bank of elevators. Duplex and group controls will dispatch a single car to each hall call. The controls analyze each car's position and direction of travel to select the most efficient response to each call.
Elevators consume a lot of energy. Today's electronic controls are designed to minimize the expended energy while minimizing the passenger wait time.
Providing simplex controls on adjacent elevators keeps the power companies and elevator service companies happy. Owners, however, deserve a better design solution to help minimize operating costs.