Empowering building flexibility service through thermal energy storage with ground source heat pump from demand side

: Thermal Energy Storage (TES) systems have gained significant attention in the buildings due to their flexibility services. This is because TES system can not only provide traditional heat supply, but also provide indirect electrical demand flexibility through thermal buffering. This feature makes the role of TES on the demand side more complex and diversified, which has not been systematically synthesized from a demand-side flexibility perspective in existing reviews. This review examines flexibility services provided by TES systems from a demand-side perspective, with particular attention to their integration with ground source heat pump (GSHP) systems in buildings. The concept of flexibility and key performance indicators on demand side is also considered. Subsequently, this review discuss different types of TES technologies in buildings, including sensible, latent, and thermochemical storage and how to model these in flexibility service. The flexibility service of TES equipment is mainly based on load shifting at the building technology level and demand-side response at the economic level both of which are analyzed in detail. The main TES systems service optimization strategies including data-driven control algorithms, and user-centric thermal comfort strategies are discussed. Finally, the challenges and direction in deploying TES systems for flexibility services are given. It is believed that this review will effectively assist researchers in better utilizing TES from demand side and expand the scope of what is traditionally considered as "building" or “thermal” subjects.