Discussing energy consumption monitoring and phase-separated metering of electricity

Abstract This paper introduces the functional characteristics of power meters and the selection scheme of power meters in the sub-metering of electricity in large public buildings. The communication function of power meters can be integrated with computers to form an electricity management system. Its powerful electricity reporting, curve analysis and graphic display functions make the application of power meters in the sub-metering of electricity in large public buildings increasingly widespread.  

Keywords: power meters, large public buildings, sub-metering of electrical energy  

0 Introduction  

Currently, according to statistics from relevant national departments, the average annual electricity consumption per square meter of building area in government office buildings and large public buildings is 85.4 kWh/m2, accounting for about 22% of the total electricity consumption in urban areas nationwide. The electricity consumption per square meter is 10 to 20 times that of ordinary residents and 1.5 to 2 times that of similar buildings in developed countries such as Europe and Japan.

On the one hand, my country's large public buildings consume enormous amounts of electricity; on the other hand, we lack direct data to provide reference for energy-saving decisions. To address this, Article 14 of the State Council Decree No. 531, the "Regulations on Energy Conservation in Public Institutions," clearly states that public institutions should implement an energy consumption metering system, distinguishing energy types, implementing separate metering for each household, category, and item, and monitoring energy consumption to promptly identify and correct energy waste. Jiangsu and Shanghai, among other places, have respectively issued the "Regulations on Energy Metering Design for Public Buildings in Jiangsu Province" (Su Jian Ke [2007] No. 217) and the "Notice on Further Strengthening the Technical Management of Energy-Saving Design for Civil Building Equipment in This City" (Hu Jian Jiao [2008] No. 828), further clarifying that major electrical facilities should be metered separately, and that metering for office buildings, shopping malls, dormitories, etc., should be done down to the economic accounting unit, while metering for medical wards, hotel rooms, and school classrooms should be done by floor or functional area, etc.

This demonstrates that implementing separate metering management of electricity consumption in large public buildings can promptly identify and correct electricity waste and provide data for building energy conservation assessments.

1. Power meters should be used for electricity metering in large public buildings.  

For large public buildings, electricity meters should be used for internal management, not for billing. The main characteristics of the two are summarized below (see Table 1).

Table 1 Comparison of Charged Electricity Meters and Power Meters

Power supply departments generally implement a one-meter-per-household billing system, meaning that the meters are installed by the power supply department. Therefore, in addition to a metering instrument license issued by the technical supervision bureau, these meters also require permission from the local provincial or municipal power department before installation and use. In the management of electricity in large public buildings, power supply departments typically install billing meters at the main incoming line.

Electricity meters are installed in addition to the user-installed billing meters, taking into account the needs of internal energy metering and energy-saving management, for internal energy management. Therefore, users can choose to purchase them independently, but should pay attention to whether the manufacturer has a metering license for the electricity meter (energy component). Electricity meters can collect sub-item energy data for each circuit, floor, or functional area, and complete the sub-item metering of energy in large public buildings through a background energy management system.

2. Selection Scheme of Power Meters in Sub-item Metering of Electricity  

Power meters are designed to meet the power monitoring and energy management needs of power systems, industrial and mining enterprises, public utilities, and intelligent large public buildings. They can measure all commonly used power parameters with high precision, such as three-phase voltage, three-phase current, active power, reactive power, frequency, power factor, and four-quadrant energy. A high-visibility LCD is used to display the measured parameters and the operating information of the power grid system. Power meters come in a wide variety of functions and models, with varying prices, and there are also many different energy metering solutions. Therefore, appropriate selection is crucial to achieve the best cost-effectiveness.

According to Document No. 114 of the Ministry of Housing and Urban-Rural Development, energy consumption data of large public buildings shall be classified and metered separately, and electricity shall be metered separately according to power consumption, lighting and socket consumption, air conditioning consumption and special consumption ^[1] . Therefore, for places such as dormitories, shops and wards where the metering should be down to the economic accounting unit, DDS1352 or DDSF1352 meters can be used;

The DDS1352 single-phase electricity meter, also known as ADL10, is a single-phase energy meter that is mounted on a DIN 35mm rail. It has a width of one module (18mm) and a maximum single-phase current of 30A. Its accuracy is class 1.0. Its advantages are small size and low price; its disadvantages are the lack of communication capabilities and inability to network.

The DDSF1352 single-phase electricity meter, also known as the ADL100, is a DIN 35mm rail mounter with four module widths. It has a maximum single-phase current of 80A, an accuracy class of 1.0, and features time-of-use (TOU) metering for peak, flat, and off-peak electricity rates. It includes an RS485 interface, supports Modbus or DL/T645 protocols, and can be networked. It is primarily used for metering single-phase electricity and is commonly found in distribution boxes. The appearance and application of the DDS1352 and DDSF1352 single-phase electricity meters are shown in Figure 1.

For electrical facilities, metering should be carried out separately according to the electricity consumption of windows and sockets, power consumption, air conditioning consumption, and special consumption. When metering school classrooms, medical wards, and hotel rooms by floor or functional area, DTSF1352 or ACR120EL meters can be selected.

The DTSF1352 three-phase four-wire meter (see Figure 2), also known as ADL300, is used for three-phase energy metering. It has the function of time-of-use multi-rate metering for peak, flat and valley energy. It is installed on a DIN35mm guide rail with a width of 7 modules. It can be installed in a lighting box or power box. The maximum three-phase current at one time is 80A. A current above 80A can be collected by a current transformer. The accuracy is 0.5 class. It has an RS485 interface, Modbus protocol or DL/T645 protocol, and can be networked ^[2] .

The ACR120EL multi-function meter is used. This meter is embedded and can be installed on the door panel of a power box or low-voltage outgoing cabinet. The panel size is 80mm×80mm, and the specifications are 220/380V, 5A. The current is connected through a current transformer. The accuracy is 0.5 class. It can measure electrical parameters such as current, voltage, power, frequency, power factor, and four-quadrant energy. It has Modbus communication protocol.

For critical applications requiring harmonic detection, the ACR230ELH multifunction meter can be used. Specifically designed for incoming or critical outgoing circuits, the ACR230ELH is embedded in the distribution cabinet door panel, with a frame size of 96mm × 96mm. In addition to measuring all electrical parameters, it also features maximum demand, 2nd-31st order current and voltage harmonic components, voltage crest factor, current K-factor, telephone waveform factor, current and voltage imbalance, and positive/negative/zero sequence component analysis. Figure 3 shows the appearance of the ACR120EL and ACR230ELH multifunction meters and their practical application in low-voltage distribution cabinets.

3. System Networking  

Electricity meters can be used as internal management meters to replace a large number of traditional analog meters, and can also be used as front-end equipment of power monitoring systems to realize remote data acquisition and control. The RS485 communication interface conforms to industrial standards, making networking easy and convenient, and is an ideal choice for SCADA system integration. The power management system of large public buildings can realize the functions of power collection and power sub-metering by using fieldbus with fiber optic ring network, Ethernet or wireless networking according to the site conditions. The system uses computers, communication equipment and field power metering devices as basic tools, providing a basic platform for real-time data acquisition, remote management and control. It can form a complex power monitoring and power management system with detection and control equipment. The system mainly adopts a hierarchical distributed computer network structure, with a station control management layer, a network communication layer and a field equipment layer ^[3] (as shown in Figure 4).

The power meters are interconnected using shielded twisted-pair cables, forming a back-end monitoring and management system with communication servers, switches, and industrial-grade computers. This system enables monitoring of the power distribution system and management of individual electricity metering. The main functions of the system are:

(1) Real-time acquisition and display of operating parameters, such as voltage, current, power, power factor, active energy, etc., to provide a basis for metering management during normal operation and fault cause analysis when an accident occurs.

(2) Monitor the operating status of electrical equipment, such as the current open/closed status of various types of switches such as high-voltage and low-voltage incoming circuit breakers, and whether they are operating normally. If a fault is detected, an automatic alarm will be triggered.

(3) Record and count the electricity consumption of all equipment in the building, including power consumption, lighting and socket consumption, air conditioning consumption, special consumption and other electricity item metering, as well as time-of-use multi-rate metering, and generate electricity metering reports for users to query.

4 Application Cases

A library in Pudong, Shanghai, is a large, high-energy-consuming public building with a total floor area of ​​60,885 square meters. The library's power distribution system includes a high-voltage distribution room and a low-voltage distribution room. The high-voltage distribution room has 10 high-voltage distribution cabinets, and the low-voltage distribution room has 31 low-voltage distribution cabinets. Medium-voltage microprocessor-based protection devices are installed on the high-voltage incoming cabinets, PT cabinets, and outgoing cabinets. Power meters are installed on all other low-voltage circuits to perform sub-metering of electricity consumption in each circuit. Each floor is equipped with DTSF1352 DIN rail-mounted three-phase four-wire meters according to electricity usage type for sub-metering of electricity consumption. All medium-voltage microprocessor-based protection devices and power meters are networked via fieldbus. The central control room centrally monitors the electricity consumption of each circuit, tracks the data, and stores it in a database. This automatically generates daily, monthly, and annual electricity consumption reports, as well as sub-metering statistical reports, providing valuable information for management analysis and decision-making.

The project's energy sub-metering management system adopts a three-layer network structure. The station control layer serves as the direct human-machine interface, using an Advantech industrial computer as the monitoring host, along with an LCD monitor, printer, and other equipment. A SANTAK UPS power supply ensures the normal operation of the station control layer equipment for a certain period in the event of a power outage. The communication layer mainly consists of communication servers and switches. This layer acts as a bridge for data exchange, responsible for collecting and transmitting data from field equipment while relaying various commands from the host computer to the field equipment. The power meters in the field equipment layer primarily consist of ACR series multi-function meters and ADL series DIN rail meters. ACR series multi-function meters are used for low-voltage incoming circuits and important feeder circuits, while ADL series DIN rail meters are used for ordinary feeder circuits, power boxes, and lighting boxes, enabling sub-metering of energy across all circuits and floors.

The monitoring room's power management system collects data from each power circuit through transmission channels provided by field equipment and the communication system. The information is analyzed and processed, and provided to operators in various forms such as reports and graphs. This allows operators to easily grasp the system's operation and power usage status, perform sub-metering of power consumption, and promptly identify and correct power waste, thereby saving electricity. When needed, it also provides quick remote control methods to change equipment operating status and handle accident situations. Figure 5 shows the library's sub-metering query table, clearly displaying the power usage of each sub-item. Figure 6 is a pie chart showing the power consumption of library lighting, air conditioning, and sockets, intuitively displaying the percentage of each sub-item's power consumption.

5. Conclusion

With social development and the widespread application of electricity, power management has become an inevitable choice for the intelligent construction of large public buildings. This article introduces a power meter that can achieve sub-item metering and time-of-use multi-rate metering of electricity. It not only displays real-time electricity consumption but also has network communication capabilities, allowing it to form a power monitoring and energy management system with computers. It can analyze and process collected data, generating various power reports, analysis curves, and graphs, facilitating remote meter reading, analysis, and research, and providing a reference for energy-saving technologies in intelligent buildings. This power meter is reliable and stable in operation, and its high-definition LCD display greatly facilitates user operation. Power meters will undoubtedly play an increasingly important role in power management and sub-item metering of electricity in large public buildings.