China's elevator industry has developed rapidly, but the high energy consumption problem cannot be ignored. According to incomplete statistics, in 2013, only 1.92% of the more than 600,000 elevators in use nationwide were energy-efficient. By 2015, if all elevators in the country were still non-energy-efficient, my country's elevators would consume approximately 80 billion kilowatt-hours of electricity, equivalent to the annual power generation of the Three Gorges Dam. These figures illustrate the critical importance of energy conservation in elevators. The following introduces six ways to achieve energy conservation in elevators and six new energy-saving technologies.
In-run variable speed technology
The rated power of an elevator traction motor is designed based on the maximum output power of the traction motor under full load or no load conditions. When the car and counterweight have the same weight, the traction motor theoretically only needs to overcome the static friction on the traction sheave, and its output power does not reach full load and still has a margin.
Assuming the motor power remains constant, and the car and counterweight weights are consistent, the elevator speed can be increased relatively according to changes in the number of passengers. Compared to traditional elevators operating at rated speed, variable speed technology can appropriately increase the elevator speed (by approximately 1.6 times). This relatively reduces passenger waiting and riding time, contributing to energy conservation and environmental protection.
Energy feedback technology
Energy feedback technology converts the regenerative energy generated when the elevator car is lightly loaded while ascending or fully loaded while descending, along with the kinetic energy generated by the motor braking, into electrical energy through multiple rectification techniques and feeds it back into the power grid to power other electrical equipment within the same local area network. This reduces energy consumption and is environmentally friendly. Based on this principle, an experimental "hybrid electric elevator" has been developed, which stores the fed-back electricity in a specially designed "battery" to power other electrical equipment within the power grid.
Single shaft double car operation technology
To improve elevator carrying efficiency and shaft utilization in high-rise buildings, single-shaft dual-car technology has emerged in recent years. Based on car location and operating conditions, it can be divided into three types: super double-decker linked car, adjustable double-car linkage, and independent operation of each car.
The working principle of single-shaft dual-car technology is that two independent cars in the same shaft are monitored by an intelligent control system through sensors to prevent collisions, allowing them to operate independently and safely, while also increasing carrying capacity and achieving energy savings.
Objective: Layer-selection intelligent technology
Efficient operation and scheduling through intelligent diversion at destination floors can effectively improve elevator operating efficiency and reduce passenger waiting or riding time.
The destination floor selection intelligent technology consists of modules such as a group control unit, a destination floor selector, and a floor indicator. Based on expert systems, fuzzy logic, and neural network control technology, it has functions such as dynamic distributed elevator waiting, peak self-identification, dynamic zoning service, configurable service layers, selectable allocation strategies, and timely forecasting.
Wireless power transmission and wireless signal transmission technologies
By using wireless power transmission and wireless signal transmission methods, elevators can be made to operate without a traveling elevator car. This can save on elevator costs and improve a series of safety and energy-saving issues such as load balance, signal interference, and safety performance during elevator operation.
The elevator car travels along with the elevator, connecting the car to the elevator machine room control cabinet for power and signal transmission. Through the interaction of current transformers on each floor's shaft wall and the car's top, the current frequency is increased, generating a high-frequency magnetic field in the magnetic core coil. When the car's secondary coil approaches, an induced current is generated, which is then rectified into direct current to charge the battery, providing power to the elevator car and landing doors.
The elevator car-side switch signals are collected by the existing signal acquisition device and then hardwired to the car-side wireless signal transmission device. The antenna transceiver transmits the signal to the landing door-side wireless signal transmission device, and then the signal is connected to the monitoring center via a wired connection. The monitoring center sends the elevator car-side switch signals in the reverse order. This method enables the transmission of wireless signals to the elevator car without a traveling elevator, thereby achieving elevator safety and energy saving.
Reduce standby power consumption
Foreign research institutions conducted energy consumption tests on 150,000 operating elevators. The report shows that standby energy consumption accounts for the largest share of total elevator energy consumption, approximately 58%. This demonstrates that reducing standby energy consumption has a significant effect on improving elevator energy efficiency.
Optimize reconfiguration
The average load rate of an elevator is approximately 20% of its rated load, and the currently accepted elevator balance coefficient is 40%-50%. After extensive testing and analysis, industry experts suggest that the balance coefficient can be optimized to 0.35 for traction drive, 0.21 for energy regeneration device, and 0.30 for hydraulic elevator, indicating that optimizing the counterweight configuration can also reduce the energy consumption of the elevator during operation.
Energy Feedback
In elevator energy feedback, energy recovery rates generally range from 20% to 40%, depending on the elevator type, usage frequency, and load capacity. Currently, national elevator energy consumption standards have not yet been released. Energy feedback energy saving utilizes a PWM active inverter method, adding an ERB device to the terminals of the original resistive braking unit of the elevator voltage inverter to achieve energy feedback. This method is suitable for elevators with large load capacities and high usage frequency.
Optimize the selection and management of elevators.
Optimizing the layout of elevator types, quantities, operation, and stopping floors based on the building's nature, target users, usable area, traffic flow, and destination can achieve energy-saving effects and is the most practical approach.
Develop new energy-saving technologies
The application of new technologies such as linear motors, linear inverters, and high-efficiency reducers in elevators can also save elevator energy consumption.
Linear elevator
Linear motors can directly convert electrical energy into mechanical energy for linear motion without any conversion devices. A linear elevator driven by a linear motor, put into use in Tokyo, Japan in 1990, has a load capacity of 600 kg, a speed of 1.75 m/s, and a lifting height of 22.90 m.
The new generation of linear motor driven, traction-free elevators requires no machine room, counterweight, or traction ropes, and has the advantages of simple structure, easy maintenance, no noise, no pollution, and energy saving of 60%.
Therefore, linear motor-driven elevators without traction steel ropes may become the future development direction for elevators in high-rise buildings.
Six ways to save energy in elevators
Elevator energy saving refers to reducing energy consumption during elevator operation, especially energy consumption in standby mode, and improving elevator operating efficiency.
Ideal weight balance
If the elevator car and counterweight are balanced during vertical movement, the motor only needs to overcome the resistance of the elevator's sliding and rotating parts, making the elevator most energy-efficient. However, the load inside the elevator car is a variable. Ideally, the counterweight should also change accordingly with the load inside the car, but implementing this technology is very difficult.
Elevator energy conservation remains a long and arduous task.
my country has introduced a series of laws and regulations concerning elevator energy conservation. For example, in 2004, the Ministry of Finance and the National Development and Reform Commission jointly formulated the "Implementation Opinions on Government Procurement of Energy-Saving Products"; the "Energy Conservation Law" stipulates that energy conservation reviews and supervision should be implemented for high-energy-consuming special equipment; the State Council's "Regulations on Safety Supervision of Special Equipment" has designated elevators as high-energy-consuming special equipment, and they are expected to be included in the government procurement energy conservation list in the future; the State Administration for Quality Supervision, Inspection and Quarantine is about to release the "Elevator Energy Efficiency Utilization Evaluation Indicators and Testing Methods" for assessing elevator energy conservation. The emergence of these laws and regulations fully demonstrates my country's high regard for elevator energy conservation.
Currently, my country has become the country with the largest promotion and use of energy-saving elevators in the world. Relevant departments have stated that they will promote and popularize energy-saving elevators nationwide within a certain period. Surveys show that if energy-saving elevators are first applied to government and relevant department buildings and public buildings across the country, and the electricity generated by these elevators is recycled and reused, based on an average energy saving rate of 30%, 9 billion kilowatt-hours of electricity can be saved annually. The task of promoting elevator energy-saving technology is arduous, but the future is bright.
