Energy efficiency of PCM-based fresh air-heating systems using solar heat thermal energy storage in different climatic zones

Substantial energy is required to heat cold outdoor air introduced by fresh-air ventilation systems of buildings during winter. To address this issue, an innovative fresh-air preheating strategy is proposed by integrating a phase change material (PCM)-based thermal storage unit into the ventilation system, enabling solar thermal energy to be stored and later utilized to preheat cold outdoor air in winter. A three-dimensional numerical model of the solar thermal storage-coupled fresh-air heating system is developed and rigorously validated against experimental data. On this basis, the system performance under winter operating conditions is simulated and evaluated for cities in different climate zones using hourly meteorological data. The numerical results demonstrate that the proposed fresh-air system with PCM-based solar thermal storage can significantly reduce fresh-air heating energy consumption. For example, an average energy-saving rate of approximately 16% is achieved over the entire winter in hot summer and cold winter regions like Chongqing, and savings exceed 23% in cold regions such as Beijing, and the system energy consumption is reduced by about 15% in severe-cold regions such as Harbin. By partially shifting the nighttime fresh-air heating load to daytime hours and utilizing solar-derived heat, the system mitigates heating demand, lowers operating costs, and reduces carbon emissions. For instance, in severe-cold regions, the maximum achievable energy saving reaches 333 GJ with a corresponding carbon reduction of 8.4 t. These findings confirm the broad applicability of the proposed PCM thermal storage-coupled fresh-air system and its potential to substantially reduce ventilation heating energy use and associated carbon emissions in the built environment.