Phase change materials walls: Smart thermal shields for energy-efficient buildings in semi-arid climates

• A numerical investigation of PCM-integrated walls was performed using ANSYS Fluent in the semi-arid climate of Marrakech. • Two PCMs with different melting points (16 °C and 29 °C) were evaluated individually and in combination. • The combined PCM1+PCM2 configuration achieved the best year-round performance, with up to 45 % heating and 30 % cooling energy savings. • Liquid fraction and natural convection analyses revealed complementary thermal behaviors of the two PCMs. • Results validate PCM walls as effective passive solutions for reducing building energy consumption in hot, dry climates. Improving the energy efficiency of buildings is a crucial issue in semi-arid regions where heating and cooling requirements are high. Phase change materials (PCMs) offer interesting prospects, but their effectiveness is often limited to one season when used individually. This study proposes a new hybrid configuration incorporating 2 PCMs with complementary melting points (29 °C and 16 °C) in the same wall, to ensure thermal comfort all year round. Using two-dimensional transient CFD simulations in ANSYS Fluent and an economic analysis based on the global discounted cost (LCC) over 9 years, four wall configurations were evaluated for the semi-arid climate of Marrakech: a reference wall, two walls with a single PCM, and the hybrid double PCM wall. The results show that the hybrid wall reduces summer indoor temperature peaks by25 %, improves winter night-time comfort by 15 %, and delivers annual energy savings of 21 % for cooling and 23 % for heating, compared with the reference wall. In economic terms, it also has the lowest LCC, confirming its cost-effectiveness and long-term efficiency. The originality of this work lies in the hybrid dual MCP strategy, which exploits the complementary nature of the melting temperatures to guarantee balanced and sustainable performance. These results highlight the potential of hybrid walls with dual PCMs as a passive, efficient solution adapted to hot and semi-arid climatic conditions.