Thermal and heat transfer characteristics of a packed-bed CTES system using encapsulated PCM capsules for peak-load management

This study explores a packed-bed cool thermal energy storage (CTES) system that uses spherical PCM capsules filled with distilled water and incorporates a helical coil to retrieve cold energy through air circulation. The system is designed to deliver efficient cooling performance, ensuring a reliable supply of cold energy even during electricity outages. The research investigates the influence of HTF flow rates (100 l/h, 200 l/h, and 300 l/h) during charging and air discharge velocities (2, 4, and 6 m/s) on the system’s thermal performance. Results indicate that higher HTF flow rates accelerate the charging process, reducing the time to full PCM solidification from 3.44 h at 100 l/h to 2.49 h at 300 l/h, while lower flow rates decrease the pressure drop from 0.78 kN/m² to 0.53 kN/m², highlighting a trade-off between rapid energy storage and pumping efficiency. Energy analysis indicates that the PCM stores the majority of the cold energy, with latent heat contributing over 60% of the total 9857 kJ, demonstrating the effectiveness of the hybrid sensible-latent storage approach. During discharging, air temperature and humidity reductions were most significant at 4 m/s, with temperature decreasing from 34.93°C to 25.44°C and humidity from 55–47%, indicating optimized cooling and moisture removal. Comparisons with conventional air-conditioning reveal that the CTES system can deliver equivalent cooling using pre-stored energy, reducing peak electricity demand while maintaining thermal comfort. The study confirms that careful selection of HTF flow rates and discharge velocities enables efficient energy storage and retrieval, making the proposed CTES system a practical and sustainable solution for continuous indoor cooling under intermittent power supply conditions.