Research on the performance of heat pump drying system with rock thermal energy storage

Heat pump drying systems are widely used in agriculture due to their high energy efficiency and cost-saving potential. This study develops a novel heat pump drying system integrated with a rock thermal energy storage bed to reduce energy consumption and enhance waste heat utilization. The system utilizes cost-effective and widely available rock materials (specific heat capacity of 2025 kJ/m3 & sdot;K) that exhibit high thermal capacity, excellent durability, and low thermal expansion. These properties contribute to long-term stability and lower maintenance costs. The system was evaluated under three drying modes: intermittent, delayed-intermittent, and continuous. The experimental data were processed using thermodynamic analysis methods, and the energy performance of each mode was evaluated through regression fitting models. Compared to continuous mode, SEC decreased by 11.98 % and 25.71 % in the intermittent and delayed intermittent modes. Correspondingly, total electricity consumption was reduced by 12.37 % and 26.51 %, and COP increased by 13.71 % and 11.60 %. Additionally, annual CO2 emissions were reduced by 11.17 % and 24.67 %. In delayed intermittent mode, extending the charging period improved thermal efficiency by 24.6 % and exergy efficiency by 9.97 %. These results demonstrate the benefits of integrating intermittent drying with rock thermal storage in improving energy efficiency and reducing environmental impact.