The new smart meter system is designed to replace the outdated configuration (a combination of relays, contactors, external CTs, and ammeters) to provide energy monitoring and on/off control for at least 4,000 air conditioning units installed in student dormitories. Energy consumption data is measured by the smart meters and transmitted to an energy management system, which converts the data into a preset format for monitoring and control by the university's building management system. Students can view their consumption data via a mobile app, recharge their balance, and pay for electricity. If the balance becomes negative, the university will remotely cut off the power supply to the student's dormitory.

The existing setup is based on outdated technology, composed of several discrete components (as shown in Figure 1), and cannot provide the necessary energy metering, billing management, and control functions. The facility manager is looking for an advanced and highly integrated IoT solution that can not only provide the required consumption management functions but also significantly reduce the number of components and installation costs. The new system should be able to manage operations centrally on an IoT platform, sharing consumption data, controlling the air conditioners based on real-time energy data, and allowing students to pay for electricity via a mobile app.

Proposed Solution:

CET has proposed a cost-effective solution by replacing the four discrete components (contactors, external CTs, relays, and ammeters) on-site with a single PMC-230 multifunction meter. The PMC-230 is CET's latest product for the low-voltage energy metering market. It features DIN Rail mounting, a compact structure, 63A direct connection (without external CT), and an internal UC3 disconnect relay for load management. The PMC-230 complies with IEC62053-21 Class 1 kWh accuracy standards and offers multifunctional measurements such as voltage, current, power, energy, power factor, frequency, and harmonic measurements, meeting and exceeding user requirements.

The RS-485 serial wiring connects all PMC-230 meters via a twisted pair on the same metering panel. The PMC-1302 ESG (Ethernet Serial Gateway) converts Modbus RTU data from the PMC-230 to IP-based Ethernet LAN. The PMC-1302 ESG supports efficient transmission of serial data packets between downstream devices on the RS-485 network and upstream applications on the Ethernet network. PecStar iEMS energy management software collects energy consumption data from the PMC-230 and provides it to the university's building management software through a Restful API, enabling real-time monitoring of each student's room energy usage and automatically controlling the air conditioners when the electricity balance becomes negative.