Key components that affect the energy use of this technology include motors, controls, and lighting. Both escalators and moving walkways are installed as pairs operating in opposite directions. They are usually driven by electric motors connected to the steps or belts and the handrail via a chain mechanism. Motor sizes depend on expected passenger load, but they typically vary between 10 and 20 horsepower (hp). Lighting can be implemented along the handrail as well as at the start and end to make the device more noticeable. There are a wide range of available efficiency technologies (Table 1).
Table 1: Efficient escalator technologies
Average potential electricity consumption savings for escalators and moving walkways can range as high as 50 percent per device. We have included LED energy savings with the caveat that they are only a percentage of lighting consumption.
Almost all of the electricity consumed by an escalator is used by its motor. AC induction motors between 7.5 to 15.0 kilowatts—10 to 20 hp—are the most common. Federal standards have been recently updated to mandate NEMA Premium—an efficiency level set by the National Electrical Manufacturers Association—as the baseline when replacing older models. Most escalator motors are oversized because they’re sized for maximum capacity (two people per step), but motors tend to operate inefficiently at the part-load conditions—between 25 and 50 percent of full-load capacity—that are more commonly seen.
Installing a smaller motor to match the load required can also reduce the energy consumed. If it isn’t possible to use a smaller motor, consider installing an adjustable-speed drive to reduce consumption at lower loads. The savings gained from replacing old motors with NEMA Premium models will depend on the number of operating hours, the motor’s horsepower, and the device’s typical load. For small motors with long operating hours, simple payback periods can be as short as 7 months.
Motor efficiency controllers
A motor efficiency controller (MEC) improves efficiency under part-load conditions. MECs optimize the efficiency of three-phase alternating current (AC) inverter-rated motors. Although motors typically operate optimally at 75 percent load, escalator motors often operate in underloaded conditions. Estimated savings from installing a MEC on an underloaded escalator ranges from 10 to 20 percent, with no savings being achieved if the escalator is loaded over 75 percent. MECs can only be used on inverter-rated motors, which are more expensive than general-purpose motors.
MECs’ variable-speed capability allows escalators to save energy during start-up and in slower-run modes. For down escalators, MECs also support regenerative braking operation, in which the motor acts as a generator when passengers are being transported downward, turning brake heat into energy that can be used to power other systems. Keep in mind that if the MEC is programmed for regenerative braking, the electrical distribution system must be protected from short circuits.
Additional energy can be saved if escalators can reduce speed when passengers aren’t present and increase speed to normal levels as they approach; it’s important to ensure that the speed won’t change once passengers are on board. This speed adjustment is accomplished with an intermittent drive that combines a sensor-based monitoring system with an adjustable-speed drive that regulates the frequency delivered to the motor. Three types of sensors are available: motion sensors, light barriers, or contact mats. Intermittent drives are not cost-effective in high-use areas because the volume of traffic allows very little opportunity for the escalator or walkway to slow or stop.
Updated safety standards. Prior to 2010, the American Society for Mechanical Engineers (ASME) maintained a federal policy standard (ASME A17.1) that prohibited the use of intermittent escalator drives. The prohibition was due to concerns that motion changes would cause passengers to lose their balance. The current standard—ASME A17.1-2010/CSA B44-10, allows the escalator speed to be changed as long as there are no passengers using the escalator (Table 2).
Table 2: ASME A17.1 escalator and moving walkway requirements
The standards of the American Society for Mechanical Engineers (ASME) were revised in 2010; they now allow variable-speed escalators to be used in commercial buildings.
Integrating intermittent drives. Coupling energy-efficient technologies can potentially result in larger benefits than if technologies are installed alone.
- Integrating with MECs. The MEC reduces energy use during full speed but low passenger load, and the intermittent drive reduces energy when passengers are not present. Together, these technologies work to increase motor life by reducing temperature and conductive losses.
- Integrating with regenerative drives. Regenerative drives allow for energy recovery from down escalators rather than dissipating waste heat. The recovered energy can be fed back into the building’s systems for use in lighting or other applications. Special care must be taken to ensure that power quality is maintained. According to the escalator manufacturer Schindler in its report on Regenerative Drive Upgrades (PDF), utilizing a regenerative drive can “reduce energy consumption by up to 50 percent when compared to a traditional escalator.”
Upgrading or replacing existing fluorescent lighting on escalator handrails and landing platforms with LEDs can be an opportunity for energy savings. The ACRP estimates that switching escalators to LED lighting from fluorescents will save 30 to 40 percent of lighting energy consumption, and the savings will persist over time because LEDs typically last 60 percent longer than fluorescents.