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Summary
Over the last century the use of escalators and moving walkways has grown from the start of the invention to the world wide implementation nowadays. They are used at shopping malls, stations, airports etcetera. Many of the currently installed systems are outdated, due to their long lifespan. The older types of escalators operate very inefficient leading to high energy consumption. Therefore energy saving methods that can be implemented to the system are needed. Popular options are to stop or slow down the escalator when it carries no passengers. This is achieved with a light sensor detecting the presence of passengers. These methods have proven to be effective and are applied to reduce energy consumption. The objective of this report is to describe the search for energy saving methods that are able to work on a system continuously running at constant nominal speed. Information about the working principle of escalators, the flow of passengers and the essence of induction motors is important to identify areas suitable for additional energy saving methods. Escalators are powered by an induction motor that gives its torque through the gearbox to the step chain. An average escalator operating full time uses about 45,000 kWh annually. Due to the highly fluctuating passenger flow the maximal power of the system is not required on every moment. The energy consumption can be separated in fixed and variable energy consumption, fixed to drive the system in no-load condition and variable energy for the transport of passengers. The fixed energy counts for 70% of the used energy and the variable for 30%. A standard escalator always runs at full power, this power however is only required at maximum passenger flow. Certain energy saving methods make the supplied power to the drive depends on the load (passengers). To start up the induction motor of the escalator a controlling device is necessary to apply the torque regulated to the steps. These devices can also be used to control the speed of system (slow down method) or to control the voltage supplied during operation.
There are three categories in which energy can be saved: - Good housekeeping
- Accurate design of the system
- Installation of energy efficient equipment
Good housekeeping is ment in the sense of well system maintenance and operational choices. The automatic start/stop and slow down methods are ways to operate the system. Up to 50% reduction in energy consumption is possible when the systems are stopped when no load is present. Similarly the slow down method results in an energy reduction of 40%. These methods however are not applicable to an escalator running at continuous speed. A look at the design provides methods to reduce the weight of the system, use highly efficient gear and implement LED lighting. With a reduction in step weight, energy savings in the fixed use of energy can be made, the weight reduction leads to lower resistance and a lower dead weight transportation. The efficiency of new gear types is up to 10% higher than the previously used gear. LED lighting is up to 40 – 80% more energy efficient and has a very long lifespan as compared to conventional light tubes.
5 Energy efficient equipment that can be installed is a type of voltage control or the option of using regenerated power. Voltage control during operation can be accomplished in two ways, by a delta-star operation or a soft starter. The delta-star switches the power supply to a lower level when the motor has a low load thereby reducing the used energy resulting in savings up to 25%. By adjusting the supplied voltage to the passenger flow with a soft starter savings up to 40% are possible. The regeneration of power is possible if a downward escalator is fully loaded (maximum passenger flow). The gravitational force of the passengers is more than required to overcome the friction of the system and drive it at nominal speed. The additionally generated power by ‘negative’ power consumption of the motor can be used to drive for instance an upward escalator.
An evaluation of these methods shows that the simultaneous use of different methods is possible. LED lighting for instance is very easy to implement at low costs that will pay back in a few years. Because of the commonly fluctuating passenger flow voltage control is the most promising method. Energy savings up to 40% enable a payback of only 3 years. The design of an efficient system is possible with new gear types and low weight steps, to apply these efficient systems to an existing system is more expensive due to the relatively large amount of labour to reinstall steps and gear. The other systems exist of a box with electronic devices to control the motor power supply.
This report presents several new ways to enable energy savings for continuously running escalators and moving walkways. The inefficient way of always running at maximum power of the older
escalators provides possibilities to intervene .The performance of the drive can seriously be improved by application of these energy saving methods.
