Recent Progress, Challenges, and Future Perspectives of Phase Change Materials for Building Thermal Energy Storage

Integrating phase change materials (PCMs) into building fabrics and thermal systems enables these components to store and release latent heat. This article presents a structured critical narrative review of 120 peer-reviewed sources published from 2004 to 2026, systematically retrieved from major academic databases. Evidence across experimental, numerical, and field studies was classified by scale and evaluated against material, system, economic, and environmental metrics. Crucially, our synthesis reveals that nominal enthalpy alone poorly predicts actual building value. At the material level, representative composites exhibit nominal enthalpies of 43.31–229.7 J g−1, yet usable capacity is often reduced by inactive supports, incomplete transitions, and heat-transfer limitations. Conductive additives can enhance thermal conductivity by up to 156.4%, but also displace active PCM and increase viscosity, cost, and embodied impacts. At building scale, concrete-based components yield modest peak-temperature reductions (1.0–1.81 °C), whereas a full-scale lightweight envelope achieved 5–8 °C attenuation in favorable seasons; however, PCM was active for only 20–28% of monitored time and remained melted during summer. An active 7000 L salt-hydrate installation delivered only 36% of nominal capacity, while a numerical heat-pump/PCM study reported up to 42% operating-cost reduction. These findings show that activated fraction, regeneration, and system boundary are more informative than nominal enthalpy alone. To bridge this gap, we propose an application-first pathway linking service conditions, containment, and heat-transfer design. Future priorities include standardized multiscale testing, multi-season matched field trials, transparent capacity definitions, and explicit life-cycle assessments.