A synergistic angle-material-season strategy enabling thermochromic spectrally-selective envelopes for building year-round passive thermal regulation

To address the limitations of traditional building envelopes——whose static, monotonous thermal performance hinders adaptation to seasonal climate variations. This study adopts a systematic approach combining material development, structural design, and experimental validation, and investigates the coupling mechanism between spectrally selective coatings and angle-optimized envelopes, establishing an all-season dynamic thermal regulation system. With thermochromic microcapsules, titanium dioxide, and polyvinylidene fluoride as core functional materials, four types of temperature-responsive, spectrally selective coatings (TP-Coating, TPT-Coating, TT-Coating, and T-Coating) were successfully prepared via a matrix preparation-functional compounding-spin coating process. They respectively achieve high reflectance in summer, dynamic equilibrium in transitional seasons, and high absorption in winter—fulfilling the corresponding functional performances for different seasons. Based on these coatings, an angle-material synergistic control envelope structure was designed and built, incorporating Tianjin's solar altitude characteristics. It includes a horizontal surface with TP-Coating for summer, a 39° outward-inclined surface with TPT/TT-Coating for transitional seasons, and a 63° inward-inclined surface with T-Coating for winter. Constant and dynamic irradiation experiments demonstrate that this system significantly enhances the thermal adaptability of building envelopes. Compared to traditional rooms, it lowers the average room temperature by 2.72 °C in summer, raises it by 5.13 °C in winter, and reduces the amplitude of temperature fluctuations during transitional seasons by 18.23 %—all of which occur without external energy input, enabling efficient passive thermal regulation. This study overcomes traditional static envelope limitations by material-structural-seasonal synergy, providing an effective technical approach to reducing building heating and cooling energy consumption and achieving passive thermal comfort regulation.