A Unified Virtual Battery Modeling Framework for Flexibility Characterization of Building HVAC Systems

The heating, ventilation and air-conditioning (HVAC) systems dominate building’s energy consumption and meanwhile exhibit substantial operational flexibility that can be exploited for providing grid services. However, this goal is largely hindered by the difficulty to characterize the system’s operating flexibility due to the complex building thermal dynamics, physical operating limits and human comfort constraints. To address this challenge, this paper develops a unified virtual battery (VB) modeling framework for characterizing the operating flexibility of both single-zone and multi-zone building HVAC systems, enabling responsive buildings to function like virtual batteries. Specifically, a physically meaningful representation state is first identified to represent building thermal conditions under thermal comfort constraints and then a VB model is established for characterizing the operating flexibility of single-zone HVAC systems. We subsequently extend the VB modeling framework to multi-zone HVAC systems and establish zone VB models to characterize the heterogeneous zonal operating flexibility. We further develop a systematic method to aggregate the zone VB models into a unified VB model. The proposed VB model enables a low-order storage-like representation of the operational flexibility of both single-zone and multi-zone buildings. Case studies demonstrate that the VB model can well capture the building thermal dynamics under varying HVAC control policies. In addition, the VB model is validated through demand response (DR) of buildings. The optimal DR strategies can be obtained from the low-order and low-complexity VB model, and the building’s committed DR can be efficiently decomposed to zone-level control inputs while maintaining human thermal comfort.