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This chapter introduces the role of thermal energy storage (TES) systems in enhancing building energy flexibility and demand-side management. Different forms of TES and their related storage media and materials were reviewed and the link between TES systems and energy flexibility was discussed. The role of TES systems in building energy flexibility and demand-side management was then addressed in terms of long-term (seasonal) and short-term storage applications. Different TES materials or media, such as sensible heat storage by water tanks, aquifers, and latent heat storage by various phase change materials can be considered. Furthermore, different techniques that can be utilized to manage the demand with the aid of TES systems are discussed. Different approaches, such as model predictive control as one of the most prominent ones, can be considered to maximize the benefit of TES in demand-side management, and hence energy flexibility.

High supercooling and single functionalization are the main barriers to the large-scale application of microencapsulated phase-change materials (PCMs) in the construction industry. To address these issues, we propose a new inorganic microencapsulated PCM, PW@CaWO4, which was synthesized via the in situ polymerization method using inorganic CaWO4 as shell and phase-change paraffin wax (PW) as core. We investigated the effects of different emulsifiers and core-to-shell ratios on microcapsule properties and found that the PW@CaWO4 microcapsules have regular spherical topography and good uniformity in particle size. During the synthesis process, the CaWO4 shell provides convenient conditions for heterogeneous nucleation of PW and effectively reduces the supercooling degree. The minimum supercooling degree of the PW@CaWO4 microcapsules is only 1.00 ± 0.08 °C, which is 3.41 °C lower than that of PW. Moreover, the PW@CaWO4 microcapsules can absorb ultraviolet radiation and exhibit fluorescence, which originates from the peculiar WO42– structure in the CaWO4 shell, eliminating the need for doping other light-activating ions into the shell. The newly prepared microcapsules possess several advantages, including suitable particle size, low supercooling, good heat storage, high thermal conductivity, good short-wave ultraviolet absorption, peculiar fluorescence, excellent proof of leakage, and so on. The microcapsules can be applied to fluorescent architectural energy-saving coatings.