42 n BUILDING SERVICES March 2024 www.drivesncontrols.com How regeneration can boost lift efficiencies The UK Government set an objective to halve the energy use of new buildings by 2030. It’s widely accepted in the industry that elevators represent between 3–7% of a building’s energy consumption, so the use of regeneration to improve the energy eciency of elevators and escalators can play a part in achieving these targets. Elevators are designed for durability and daily use, but this doesn’t always guarantee eciency. For building owners, improving an elevator’s ROI can mean one of two things. The rst is modernisation – if an ageing lift breaks down frequently and becomes unreliable, upgrading to a newer lift system featuring advanced, intelligent control technology can help cut operating costs, improve ride quality, and extend the lift’s lifecycle. Then, there is the energy-saving element. This includes the use of low-energy lighting, such as LEDs, and gearless permanent magnet (PM) motor designs that use less electricity. Finally, there are regenerative drives that convert into useful power the energy that was traditionally lost as heat through dynamic braking resistors. Implementing some, or all, of the above to meet green building rating systems can help building owners to increase the rental value of their properties. Therefore, while they might not see an immediate ROI from retrotting energy-saving components, the nancial benet can become more tangible in the longer term. Energy management In most lifts, the counterweight is sized so that if a half-load is placed in the cabin, and the mechanical brake is released, the lift doesn’t move. The counterweight is heavier than the cabin so, for example, with an empty cabin travelling upwards, the motor would overhaul and push energy backwards. Similarly, if the cabin is full loaded and travelling downwards, it will be heavier than the counterweight – again, overhauling the motor. When the motor overhauls, it requires negative torque and creates energy that would historically have been fed to resistors and dissipated as heat. Not only is the energy lost as heat, but further energy is required from building systems such as HVAC to manage the heat and keep the equipment cool. In elevator applications, this process occurs to some extent on every run and this energy must be managed properly to prevent drive faults and other equipment damage. The Building Research Establishment Environmental Assessment Method (Breeam) is one example of an assessment method that is used to determine sustainability levels of buildings. Those that receive a high Breeam rating will often have lower running costs because they’re naturally more ecient. Also, the higher rating also results in a more pleasant working environment, so tenants are not only more likely to pay more for the property, but are also likely to stay longer in the building. Ecient elevators with operating speeds above 0.15m/s can contribute up to three Breeam points by meeting the criteria published in the Energy section of the Breeam assessment – specically, Ene 06. The use of regeneration on these elevators can contribute one of those points. Line regeneration We can’t turn electricity meters backwards, but we can slow them down and harness the excess energy, rather than letting it go to waste. Regenerative braking systems reclaim the energy generated from the overhauling motor and supply it back to the three-phase AC power system so it can be used elsewhere in the building. Regenerative systems are usually wired in parallel with a variable-speed drive, either as part of a new control system or as a retrot to an existing drive. Standby consumption is minimal and, such systems in can meet the Breeam credit criteria for saving more energy than the standby consumption. Breeam credit aside, once a regenerative braking system has been installed, its ROI (return on investment) comes down to physics. For example, an elevator in a school with two ¡oors could be used a handful of times each day. But in high-rise buildings such as London’s Shard, lifts are used every day and by almost every visitor. The ROI will be quicker purely because the lifts are used more often and travel/regenerate for longer. n Brian Preston, general manager of the elevator drive specialist CP Automation, explores how regenerative braking systems can improve lift eciency and deliver signicant benets for building owners. Capturing braking energy from high-rise lifts can deliver signicant benets
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