CFD Analysis of Dual‐Layer PCM Roofs for Thermal Mitigation in Residential Buildings

This study presents a computational fluid dynamics analysis of dual‐layer phase change material (PCM) roofs for passive cooling in residential buildings under the hot and humid climate of Bangladesh. A three‐dimensional transient model was developed in ANSYS Fluent using the enthalpy–porosity approach to simulate coupled heat conduction, natural convection, and phase change under realistic boundary conditions. Rubitherm RT‐31, with a latent heat of 165 kJ/kg and a melting range of 302–307 K, was applied as two separate layers: one beneath the thermoplastic polyolefin membrane and another above the plaster ceiling. Simulations were carried out for Jashore, Dhaka, and Cox's Bazar on the hottest recorded day of 2024. The dual‐layer roof reduced ceiling peak temperatures by 6.6 K in Jashore, 4.7 K in Dhaka, and 3.25 K in Cox's Bazar, while delaying the thermal peak by approximately 2–3 h. Inner‐wall temperatures remained within 298–304 K, showing stable diurnal moderation. The upper PCM layer reached complete melting during the afternoon, while the lower layer attained a maximum liquid fraction of 0.45, creating a two‐stage buffering effect that extended cooling into the evening. Both layers fully solidified before dawn, confirming daily regeneration. Compared with a conventional roof, the dual‐layer configuration reduced conductive heat flux by nearly 38% and lowered estimated cooling energy demand by approximately 30%. These results demonstrate an effective, climate‐responsive solution for improving thermal comfort in tropical housing.