Consumption Monitoring and Load Management for Student Hostel

A University in Hong Kong was looking for a Smart Metering Solution for its Student Hostel that could monitor the energy consumption and perform load management of individual air conditioners for bill management purpose.

Project Scope

The New Smart Metering System was designed to replace the outdated configuration (a combined circuitry of Relay, Contactor, External CT and Current Meter) to facilitate consumption monitoring and ON/OFF control for at least 4000 air conditioners installed inside student rooms. The consumption data would be measured by the Energy Meter, transmitted to an Energy Management System (EMS) and then converted in predefined format for the University’s Billing Management System to perform consumption monitoring and control. Students could use a mobile application to view the consumption data, top up the balance and pay for the electricity bill. The University would remotely disconnect the electricity to the student’s AC should the balance become negative.

Fig. 1 Old Configuration - A combination of Relay, External CT, Contactor and Current Meter
Fig. 2 New Configuration – PMC-230 only


The existing configuration was based on an outdated technology with a combination of several discrete components (Fig.1) that did not provide the necessary energy metering, billing management and control functions. The Facility Manager was looking for an advanced and highly integrated IoT solution that would not only provide the required consumption management features but also significantly reduce the number of components as well as installation costs. The new system should be able to centralize the management operation on an IoT Platform for consumption data sharing, ON/OFF control of air conditioner based on real-time energy data and electric bill payment through a mobile application.


CET proposed a cost-effective solution by using ONE PMC-230 Multifunction Meter to replace the FOUR discrete components (Contactor, External CT and Relay and Current Meter) on site.

  • PMC-230 is CET’s latest offer for the low voltage energy metering market featuring DIN Rail mount, compact construction, 63A Direct Connect without external CT and an internal UC3 Disconnect Relay for load management. The PMC-230 complies with the IEC62053-21 Class 1 kWh Accuracy Standard and is able to provide multifunction measurements such as Voltage & Current, Power & Energy, Power factor & Frequency as well as Harmonic measurements that not only fulfills but also exceeds user’s requirements.

The RS-485 serial wiring connected all PMC-230s through a twisted pair cable on the same metering panel where the Modbus RTU data from the PMC-230s are then converted to an IP-based Ethernet LAN through the PMC-1302 ESG (Ethernet-Serial Gateway).

  • PMC-1302 ESG supports the efficient transfer of serial packets between the downstream devices on the RS-485 network and the upstream applications on the Ethernet network.

The PecStar iEMS Energy Management Software collects the consumption data from the PMC-230s and then provides it to the University’s Billing Management Software via the Restful API for the continuous real-time monitoring of the energy consumption at each student room and the automatic load control of the air conditioner should the balance of the electric bill become negative.


The PMC-230 plays the critical role in this advanced and cost–effective solution to fulfill both the Energy Measurement and Load Management requirements in a compact DIN form factor. The overall solution lowered the materials cost, simplified the wiring tremendously and therefore reduced the installation cost as well as deployment time significantly.

The PMC-1302 ESG, PecStar iEMS and API automated the overall data exchange digitally with the latest IT communication technology and helped create a highly integrated and efficient platform which allowed the Billing Management Software to achieve centralized and continuous monitoring of energy consumption and real-time load control of the entire Student Hostel effortlessly.

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