Sustainable latent heat thermal storage based on recycled construction material–PCM composites with a focus on building applications

The integration of renewable energy requires efficient thermal energy storage (TES) systems capable of mitigating intermittency and providing continuous heat. Latent Heat TES (LHTES) using phase change materials (PCMs) is attractive due to high energy density and near-constant operating temperatures. However, conventional PCMs face limitations including low thermal conductivity, leakage, high cost, and substantial embodied carbon (~4 kg CO₂/kg), restricting large-scale use. This research explores combining recycled construction materials with PCMs to develop sustainable, cost-effective, and high-performance latent heat storage solutions. Recycled concrete, ceramic, glass, and asphalt were assessed for thermophysical properties. Concrete offered high specific heat capacity for sustained energy storage, while ceramic enabled rapid energy release due to higher thermal diffusivity. Concrete and ceramic were selected for hybrid PCM composites. Ceramic–PCM composites (~60:40 volumetric ratio) were implemented in flat-plate solar collectors, latent heat storage modules, and building wall configurations. Embedding absorber tubes within the ceramic–PCM layer increased mean collector efficiency by ~8% and cumulative energy gain by 12%, highlighting the importance of heat exchanger positioning. Concrete–PCM composites accelerated charging and discharging by up to 75%, halved PCM consumption, and maintained structural stability, with finer concrete particles enhancing heat transfer. Studies on ceramic particle size showed finer particles improved charging rates by ~10%, minimized thermal stratification, and prevented overheating, while larger particles slowed energy release. PCM layers in building walls significantly reduced surface and indoor temperatures, improving thermal comfort and energy efficiency. These results demonstrate that recycled-material–PCM composites provide sustainable, cost-effective latent heat storage. While slightly reducing energy density compared with pure PCMs, they enhance heat transfer, charging/discharging power, and reduce embodied carbon, offering reliable and efficient TES solutions for renewable energy integration and building applications.