Flexibility assessment of grid-interactive commercial buildings considering multi-zone thermal coupling

Commercial buildings, characterized by substantial cooling loads and thermal inertia, serve as vital flexible resources for low-carbon power systems. However, existing approaches often fail to capture thermo-electric coupling under multi-zone thermal interactions and neglect user-side efficiency, which necessitates a more robust flexibility assessment framework. This paper proposes a thermo-electro-efficiency coupled framework to evaluate the summer demand response of grid-interactive commercial buildings. We develop a multi-zone third-order RC model with explicit inter-zone and public-area heat transfer, which is combined with a building-level HVAC model to correlate available cooling capacity, part-load ratio, and variable COP. Implementation of this strategy during demand response events yields significant efficiency gains. Specifically, it achieves a 4.6% higher COP retention than an aggressive rule-based baseline, with strict adherence to indoor thermal comfort limits. Furthermore, sensitivity and Pareto analyses delineate efficiency-oriented, balanced, and deep-response operating regimes. These insights provide a practical foundation for flexibility evaluation and pre-event strategy formulation.