Solar-driven dual-mode cascading cycle based on ammonia complexation reaction for flexible seasonal thermal management

Flexible seasonal thermal management, including the summer refrigeration and winter heat pump with seasonal energy storage, is one of the promising routes to achieve the goal of buildings carbon neutrality. However, the previous sensible and latent heat storage technologies were unable to realize seasonal heating supply and refrigeration, and the single-stage sorption cycle was proven inefficient under the severe conditions of high condensation and sorption temperatures. To face the challenge, we propose a solar-driven flexible seasonal thermal management (FSTM) strategy enabled by the MnCl₂-CaCl₂-NH₃ cascading cycle based on ammonia complexation reaction, which can efficiently utilize the solar heat with severe temperature fluctuations to satisfy indoor summer refrigeration and winter heating supply with seasonal energy storage. Subsequently, we design a proof-of-concept FSTM device with two sorption reactors and an ammonia working tank. Experimental results exhibit that when the outdoor ambient temperature is as high as 35°C, the specific cooling capacity and coefficient of performance of FSTM are still up to 157 kJ∙kg^-1 and 0.11 respectively in summer, while the thermal energy storage density can exceed 100 kJ∙kg^-1 in winter with the highest sorption temperature of 90°C, which illustrates that the cascading cycle is suitable for harsh working conditions to achieve long-term thermal energy storage. Our work provides a promising low-carbon route for seasonal solar energy storage and thermal management of buildings.