Digital Twin System for Urban Building Energy Efficiency: A Case Study in Shenzhen

Digital twin technology is increasingly recognized as a cornerstone for sustainable digital cities, enabling real-time integration between physical environments and their virtual counterparts. This study develops a Unity-based digital twin system that integrates Internet of Things (IoT) devices with occupancy-centric control (OCC) to enhance building energy performance and provide insights at the urban scale. The system incorporates temperature sensors and millimeter-wave radar for accurate occupancy detection, enabling automatic regulation of air conditioning and lighting. A digital twin platform was implemented to mirror the office environment, visualize realtime operations, and quantify energy performance. A four-month field experiment in Shenzhen showed that the OCC strategy reduced total electricity consumption by 11.9%. In terms of specific end-uses, the system shortened HVAC runtime by 2 5. 9 6 % and lighting runtime by 1 3. 3 6 %; these runtime reductions translated into the overall electricity savings observed, without compromising occupant comfort. When extrapolated to Shenzhen's office building stock, the findings suggest annual savings of over 12 GWh per million square meters of office area. This study demonstrates that digital twin platforms, when combined with IoT-driven occupancy sensing, can effectively bridge building-level innovations and city-scale sustainability goals, offering a scalable pathway for digital urban energy management.