Dual-path thermal optimization of PCM-cementitious envelope: Coupling latent heat capacity and structural insulation

Enhancing both thermal inertia and insulation without increasing wall thickness remains a major challenge in building thermal engineering. This study proposes an innovative dual-path optimization strategy for Phase Change Material–Cementitious Envelope (PCM-CE) systems by integrating spherical phase change macro-capsules (SPCMs) with extruded polystyrene (XPS) thermal insulation. A validated three-dimensional transient simulation model, incorporating a dynamically adjusted effective thermal conductivity to capture natural convection, was used to assess the effects of insulation placement and SPCM content under realistic sol–air boundary conditions. Results show that the external-insulation (ETIM) configuration enables pronounced synergy between thermal resistance and latent heat capacity: increasing SPCM content from 0 % to 20 % reduces temperature amplitude by 63.1 %, increases time lag by 72.2 %, and decreases heat flux amplitude by 70.0 %. In contrast, the internal-insulation (ITIM) configuration achieves less than one-third of these improvements due to phase-change activation mismatch. An optimal combination of 15 % SPCM and 10 mm XPS delivers comparable regulation to 20 % SPCM while reducing material use and cost. Energy storage analysis confirms that insulation placement exerts a greater influence on dynamic regulation than total storage capacity. The proposed framework—ETIM enabling full-cycle PCM activation, complemented by optimized SPCM content—offers a scalable, engineering-feasible solution for climate-adaptive retrofitting and high-performance new construction in high-diurnal-range regions.