Elevatoring Issues & Considerations in Super Tall Buildings
Piston Effect & PreventionIn single shafts, the air displaced by the car is pushed into the narrow gap around the car. This can increase the speed of the air around the car to levels more than twice the speed of the car, causing noise. To reduce the noise level created by the air speed, pressure relief vent holes are needed. For speeds up to 2.5 mps, vent hole in the overhead walls are required and for speeds above 2.5 mps, vent hole above GF level specific to vendor drawings are required. Pressure relief holes can only be used if we have an adjacent hoistway or an adjacent air duct. If pressure relief holes are applied in fire protected hoistways, the holes must be supplied with automatic fire dampers.
Building Sway & PreventionBuilding sway may cause excessive sway in compensation ropes, over speed governor ropes, suspension ropes and traveling cables. In over 200m tall buildings and slender buildings of over 150m height, this may have an impact on the elevator design. However, rope resonance and traveling cable movement cannot be completely avoided in high-rise buildings. To minimize potential problems, the sway behavior of ropes and cables must be considered by vendors installing the equipment.
Stack Effect & PreventionStack effect is the movement of air in and out of the buildings and is driven by buoyancy. Buoyancy occurs due to a difference in indoor-to-outdoor air density resulting from temperature and moisture differences. In case of fire, especially, the stack effect needs to be controlled to prevent the spread of smoke. It helps drive natural ventilation, infiltration, and fires. It is essential that all elevator lobbies are well sealed to minimize stack effect.
Case Study: Guangzhou Chow Tai Fook (CTF) Finance CentreDevelopment of a High-Speed Lift in a Super Tall Building: The development of an Ultra-High-Speed Elevator that achieved the world’s fastest elevator with a speed of 1,200 m/min (Guinness record), included creating a heavy-duty drive system, highly reliable safety systems, elevator cars that provide users with a comfortable ride, and establishing construction techniques.
Elevators that travel at high speeds require larger equipment because of the resistance and losses that occur. Moreover, the greater weight of the rope required in taller buildings with longer elevator travel also has a major impact on the overall elevator. This section describes the traction machine and control panel that were made smaller by reducing losses and using a high-strength rope.
Drive Technologies: In terms of drive technologies, thin-profile motors are needed that combine a compact design with the high output required for elevators with a speed of 1,200 m/min. Accordingly, a new 330-kW permanent magnet synchronous motor was developed, which is among the world’s largest capacity motor. To achieve a thinner profile and reduce the electrical losses associated with higher speeds, the motor features a laminated core rotor and a split iron core that has a low torque ripple despite its large diameter. As a result, it was possible to make the traction machine 13% narrower while still having a rated output 1.3 times that of motors based on conventional technology.
To reduce the suspended load on the traction machine, a high-strength independent wire rope core (IWRC) was developed with newly designed materials and strand weave for use as the main rope holding up the elevator car. The new rope is 1.3 times stronger than ropes made using the previous technique, making it 30% lighter than the previous rope. Also developed a sheave with high strength and excellent wear durability.
Control Technologies: Having been made larger to provide the extra capacity needed for acceleration and deceleration control of the 330-kW permanent magnet synchronous motor, the control panel needed to be reduced in size so that it could fit inside the machine room. Accordingly, a high output of 2,200 kVA was achieved while keeping the dimensions equal or smaller to those of previous models by retaining the same dimensions for the individual control units as achieved on previous models and adopting a set parallel configuration that doubled the control unit output capacity, from 600 to 1,200 kVA, and connected two of these expanded control units in parallel.
The new control units were able to drive a single elevator at a speed of 600 m/min with a 3,600-kg carrying capacity. Because the capacity had been doubled from the previous 600 kVA to 1,200 kVA on the new control units, lift design adopted a configuration of four 1,400-A IGBT modules in parallel for the main converter and developed techniques for equalizing the current across these four IGBTs, reducing losses, and improving cooling performance. As well as increasing the number of rotations per minute, the 1,200-m/min elevator has a larger number of poles due to its larger diameter, and this means it has a higher motor current frequency.
Because the problem of current control delay arises when compensation for dead time in the upper and lower IGBT arms is performed by software, the resulting distortion of the current waveform with higher fifth- and seventh-order harmonics becomes a source of noise and vibration. To deal with this, a technique was developed that limits current waveform distortion to 1% or less by adjusting the phase of the dead time compensation voltage based on the motor current frequency.
Comfortable Elevators that Travel at Ultra-High Speed Over Long DistanceAt a speed of 1,200 m/min (72 kph), even minute bumps or warping in the guide rails have a major impact on elevator car vibration. The sensation of ear blockage resulting from the large pressure changes that occur in skyscrapers is also a source of user discomfort.
Techniques for Reducing Elevator Car Vibration: The method used in the past to reduce horizontal vibration of the elevator car involved an active guide unit that detected vibrations using an accelerometer attached to the bottom of the car and used an actuator in the guide unit on the underside of the car to suppress the vibrations by controlling the spring force. At 1,200 m/min, however, the periodic vibrational disturbances due to rail misalignment are shifted to a higher frequency, and these are prone to generating higher-order modes of vibration that include pitching and other rotational modes as well as translational vibration.
To deal with this, a vertical active system was developed with upper and lower active guide units that have accelerometers and actuators installed at four locations (top, bottom, left, and right). The control system was built to be able to suppress different modes of vibration by designing it using the H∞ control technique to allow for sensitivity to horizontal vibration due to people and variations in the elevator parameters. Testing on a vibrator test rig demonstrated that the new vertical active system can suppress rotational as well as translational modes of vibration, and that this ability to suppress a number of different modes of vibration works even when higher speeds cause the frequency of vibration to increase.
Techniques for Reducing Noise in Elevator Car: Faster elevator speeds increase the level of aerodynamic noise, causing more noise to propagate into the interior of the elevator car. The predicted increase in interior noise when changing from 600 m/min to 1,200 m/min was more than 15 dB, reaching a level similar to that experienced when standing next to a major highway. Minimizing this increased interior noise level requires suppression measures for both the noise source and transmission path.
To reduce noise at its source, use of computational fluid dynamics techniques acquired through development work in the railway industry to evaluate the surface pressure fluctuations that cause aerodynamic noise, and developed a streamlined capsule that reduces these fluctuations by approximately 50% compared to previous models. Moreover, because an elevator car is subject to increased horizontal vibration when passing its counterweight, experiencing wind pressure that increases with the square of the speed, reducing the noise and vibration caused by this passing is one of the challenges associated with increasing elevator speed. Accordingly, to suppress interior noise and reduce vibration, the counterweight was fitted with a streamlining cover and an opening that reduces wind pressure by about 30%.
The noise reduction measures relating to the transmission path involved both, improving the acoustic insulation in the ceiling, side walls, and other parts of the car to reduce transmitted noise, and developing an airtight car by minimizing gaps around the door and elsewhere to reduce airborne noise transmission. Testing in a wind tunnel and on actual elevators verified that these techniques had succeeded in reducing internal noise.
Reducing Sensation of Ear Blockage caused by Air Pressure Changes: The changes in air pressure associated with taller buildings and faster speeds can cause user discomfort in elevator cars such as ear blockage, and the effect of pressure changes on the human body are more severe in skyscrapers of 500 m or more. Because this sensation of ear blockage is more noticeable when the elevator is descending than when it is ascending, it is necessary to place a limit on the descent speed. Moreover, to reduce this discomfort, a method of controlling air pressure inside the elevator car was adopted that prevents the sensation of ear blockage from becoming more severe by forcing a rapid change in car air pressure to prompt users to swallow, which helps equalize the pressure in their ears.
Using an air pressure simulator to conduct sensory evaluations: Testing of the rate of change in air pressure and the sensation of ear blockage was performed by using an air pressure simulator to conduct sensory evaluations. To control the interior air pressure, an air pressure control system was developed made up of a pressurizer and a depressurizer mechanism. The difficulty with this air pressure control system was that it needed to minimize control tolerance while still providing the fast response needed to achieve rapid changes in air pressure. To solve this problem, a control technology was developed with two degrees of freedom in which feedforward control is used for a fast response and control tolerance is minimized by combining feedback control with the generation of control commands in a way that takes account of the change in volume of structural components due to pressure differences. This succeeded in making air pressure control both accurate and responsive.
Safety Features for Ultra-High-Speed Operation
- Brake: A brake lining was developed that is able to bring the elevator car to a safe halt even if it gets as hot as 400°C.
- Safety Device: Decelerating an elevator traveling at 1,200 m/min to a full halt requires approximately 4.8 times as much braking energy. A laminated ceramic wedge was developed that is able to withstand the heat and wear caused by braking and to bring the elevator car to a halt without exceeding the maximum rate of deceleration specified by the regulations.
- Oil Buffer: The greater impact force resulting from the faster elevator speed means that the height of the oil buffers needs to be increased. Using the old design, a 1,200-m/min elevator would require an oil buffer of 24 m or more, causing extra construction work and making future replacement difficult. The problem was resolved by developing an oil buffer that uses a telescopic configuration with a four-stage plunger to shorten its overall height, to 15 m or less, in this case.
- Delivery of Fully Assembled Traction Machines
- Joint Assembly Test of Elevator Car Prior to Installation at factory
- Guide Rail Construction Technique to reduce compression pressure
- Simulation Evaluation trials – Off and Onsite testing
- Electronic ETSD - an emergency terminal speed-limiting device, ETSD monitors the elevator car location and speed as it approaches the end of the hoistway and decelerates the car if its speed at a specified distance from the end of the hoistway exceeds a specified limit.
Traffic Study, Analysis & PlanningTo recommend an ideal vertical transportation system where the handling capacity equals the traffic flow at the critical period with acceptable waiting interval. Key considerations include:
- quantity of service – handling capacity
- quality of service – waiting interval
- traffic flow – up peak
- group operation