Acrel Smart Building Elevator Energy Consumption Optimization and Energy Feedback Metering Control Solution

Elevators are typical potential energy loads. Under specific operating conditions, the traction machine motor switches from power consumption to power generation, continuously producing regenerative electrical energy. This primarily occurs in three scenarios: first, heavy-load downward travel, where the car's load exceeds the counterweight's mass, and gravitational potential energy drives the car downward, reversely rotating the motor to generate electricity; second, light-load or no-load upward travel, where the counterweight is heavier than the car, causing it to descend and pull the car upward, again reversely driving the motor to produce electricity; third, deceleration and braking, where the elevator decelerates before reaching the target floor, rapidly releasing its mechanical kinetic energy and converting it into electrical energy.

Practical project verification has shown that after installing energy feedback devices on building elevators, the average energy saving rate for a single elevator can reach 30%, and can exceed 40% under optimal conditions. For commercial buildings or residential complexes equipped with multiple elevators, the economic and social benefits of energy conservation are significant, offering high promotional and application value.

Figure 1: Elevator Power Generation Scenarios: Heavy-load Downward and Light-load Upward (Schematic Diagram)

I. Principle of Energy Recovery

Conventional unmodified elevators lack an energy recovery function. The regenerative electrical energy generated during elevator operation continuously raises the DC bus voltage of the variable frequency drive (VFD). To ensure safe equipment operation, the system dissipates this excess energy as heat through braking resistors. This not only wastes a large amount of electrical energy but also continuously increases the ambient temperature in the elevator machine room, accelerating equipment aging and compromising the overall operational stability of the elevator.

After installing a dedicated elevator energy feedback device, the regenerative electrical energy can be recovered, purified, and fed back into the grid for reuse. The complete energy recovery process consists of three main steps:

1. Energy Capture: The AC power generated by the elevator during operation is converted to DC power by the VFD's rectifier and temporarily stored in the DC link capacitors of the VFD, achieving the initial collection of regenerative energy.

2. Intelligent Inversion: When the VFD's DC bus voltage reaches a system-set threshold, the energy feedback device activates preferentially (with priority over the braking resistor). Utilizing core components like an IGBT full-bridge inverter and a DSP microprocessor, the device inverts the DC bus voltage into three-phase AC power that matches the building's low-voltage grid in frequency, phase, and voltage.

3. Purification and Feedback: The inverted AC power is filtered and purified through components like filter reactors to effectively eliminate harmonic pollution. After ensuring the power quality meets standards, the power is safely fed back into the building's public AC grid, achieving waste-to-energy reuse.

Figure 2: Schematic Diagram of Elevator Energy Recovery

II. Relevant Standards Requirements

The national standard GB/T 32271-2015, "Elevator energy feedback device," specifically governs the technical parameters, test methods, and safety performance of elevator energy-saving feedback equipment. It is applicable to uncontrolled rectifier variable voltage and variable frequency (VVVF) elevators with rated voltages up to 400V in TN-S power supply systems. The standard imposes mandatory constraints on core indicators such as device energy efficiency, power quality, and operational safety. Specific requirements are as follows:

Efficiency Classification Requirements: Three levels of efficiency standards are defined based on load conditions: conversion efficiency ≥85% at 25% load, ≥90% at 50% load, and ≥95% at 100% rated load.

Power Quality Requirements: The Total Harmonic Distortion of current (THDi) fed back to the grid must be ≤5%. Additionally, specific limits are set for the content of odd and even harmonics to prevent pollution of the public grid.

Power Factor Requirements: When the device's output power reaches 50% of its rated power, the operating power factor must be ≥0.90 to ensure grid operational efficiency.

Safety Protection Functions: The equipment must be equipped with comprehensive protection mechanisms, including anti-islanding, overvoltage, undervoltage, short-circuit, and open-circuit protection. It should also be capable of handling fault scenarios like abnormal grid frequency, ensuring the safe and stable operation of both the device and the grid.

This standard also specifies the test platform, conditions, and measurement methods for verifying these indicators. It requires the use of high-precision bidirectional energy meters for simultaneous metering at the DC input and AC output terminals of the device. By comparing the DC input active energy with the AC output active energy, the actual conversion efficiency of the energy feedback device is calculated to ensure the equipment meets performance standards.

III. Selection Scheme for Elevator Energy Feedback Energy Metering

According to the national standard's technical requirements and considering the operational characteristics of elevator energy feedback systems, retrofit projects require the deployment of metering devices on both the DC side (device input) and the AC side (device grid-connection output). This setup covers data monitoring needs for power generation, feedback quantity, power quality, and conversion efficiency. Specifically, the DC side monitors DC voltage, DC current, and bidirectional DC regenerative energy. The AC side monitors three-phase voltage, three-phase current, bidirectional active energy, reactive power, and apparent power. Simultaneously, power quality parameters such as current harmonic distortion, individual harmonic content, power factor, and DC component are monitored across the entire system.

(1) AC Grid-Connection Side Metering Scheme (for Overall Elevator Energy Consumption and Feedback Energy Statistics)

• Installation Location: At the 380V three-phase incoming line of the elevator distribution panel and the grid-connection terminal of the energy feedback device

• Core Purpose: To meter the electrical energy drawn from the grid and the regenerative energy fed back to the grid by the elevator. This allows for calculating the overall elevator energy consumption and energy-saving benefits, providing data support for energy efficiency assessments.

1. Wired Networking Scheme (Standard for New Projects):

• Selected Device: DTSD1352 Three-Phase Rail-Mounted Energy Meter.

• Device Advantages: Supports three-phase four-wire metering, offers 0.5S class high-precision four-quadrant bidirectional metering. Can be used with external split-core current transformers. Suitable for batch retrofit projects for elevators in new residential complexes and commercial buildings. Wired networking is stable and reliable, suitable for standardized engineering construction.

Figure 3: DTSD1352 Three-Phase AC Rail-Mounted Energy Meter

2. Wireless IoT Scheme (for Retrofit Projects with Difficult Wiring):

• Selected Device: ADW300 Series Wireless IoT Power Meter.

• Device Advantages: Optional 4G, Wi-Fi communication modules support TCP bidirectional transparent transmission, allowing data to be directly uploaded to the cloud platform. Requires no complex wiring and supports installation without power outage, suitable for energy-saving retrofits of elevators in older residential areas or standalone buildings.

Figure 4: ADW300 Three-Phase AC IoT Energy Meter

(2) DC Feedback Bus Side Metering Scheme (for Regenerative DC Energy Statistics)

• Installation Location: On the DC540V/750V bus side inside the energy feedback device.

• Core Purpose: To independently meter the elevator's DC regenerative generation and calculate the conversion efficiency of the energy feedback device. Also suitable for scenarios integrating elevator energy storage systems (capacitor/lithium battery), for real-time monitoring of DC energy data during storage device charging/discharging.

• Selected Device: DJSF1352-RN Bidirectional DC Rail-Mounted Energy Meter.

  Device Advantages: Voltage measurement range covers DC 0~1000V, supports connection to 75mV shunts and 0~20mA/0~10V Hall sensors. Optional dual-channel DC input can simultaneously monitor regenerative generation and energy storage charging/discharging. Available in accuracy classes 0.5 and 1.0 to meet high-precision testing requirements.

Figure 5: DJSF1352-RN DC Energy Meter and Matching Hall Sensor

(3) Data Acquisition and Transmission Scheme

Wired metering devices require dedicated data acquisition equipment to centrally collect, parse, and upload field instrument data to the cloud, ensuring stable data transmission.

• Selected Devices: ANet-1E2SM-4G, AWT100-4G Data Concentrators.

• Device Advantages: The downstream side is compatible with the RS485 interface and the Modbus-RTU standard protocol, adaptable to all on-site smart instruments. The upstream side supports both 4G wireless and Ethernet transmission methods. Features a rail-mounting design suitable for various equipment room scenarios, with flexible device model selection based on the requirements of the superior platform.

Figure 6: ANet-1E2SM-4G and AWT100-4G Data Acquisition Scheme

IV. Elevator Energy Feedback Management System Solution

The solution is complemented by the Acrel-EIoT Energy IoT SaaS Cloud Platform, a self-developed, lightweight intelligent management platform. It supports multi-protocol device access and multi-terminal synchronous access. It integrates comprehensive functions such as real-time energy monitoring, equipment efficiency analysis, power quality diagnosis, fault alarm push notifications, and automatic generation of data reports, enabling remote visualization, digitalization, and intelligent management of the elevator energy feedback system. Users can quickly complete device commissioning via a mobile app QR code scan. Energy consumption data, operational parameters, and energy-saving statistical results can be accessed anytime via the computer WEB interface or mobile devices.

Figure 7: Acrel-EIoT Energy IoT Cloud Platform

System Hardware and Software Device Selection Summary Table: