Air-gap controlled smart window for spectral and angular selective modulation of solar radiation

Active smart windows that dynamically control solar radiation are efficient in reducing building energy consumption. In particular, spectrally selective modulation is crucial for preserving visible light transparency while modulating near-infrared (near-IR) solar gain, thus broadening the applicability of smart windows. When combined with angular selective modulation, the energy-saving potential can be further enhanced. In this study, we propose a novel smart window that offers spectral and angular selectivity capable of switching between summer and winter modes. In summer mode, the window maintains high transmittance for normally incident visible light while increasing reflectance for both normally incident near-IR light and obliquely incident visible and near-IR light. Conversely, in winter mode, high transmittance is preserved across the visible and near-IR spectral ranges, regardless of the angle of incidence. This selective modulation is achieved by adjusting the air gap between two thin-film-coated layers, with the optimal structure determined through multi-objective optimization. The optimized gap-switching window (GSW) can control the normally incident near-IR transmittance by approximately 0.5 and oblique visible light transmittance by 0.22 while maintaining high normal incident visible light transmittance ( ∼ 0.7). The GSW is predicted to reduce annual energy consumption by up to 29.2%, offering promising energy-saving solutions in zero-energy buildings. This study aims to provide novel mechanisms to modulate solar radiation and facilitate the development of smart windows with enhanced spectral and angular control. • A smart window featuring both spectral and angular selectivity is proposed. • In summer, the window reflects solar radiation, except for normal visible light. • In winter, high transmittance is preserved across wide spectral and angular ranges. • The optimum design reduces annual energy use in zero-energy buildings by up to 29.2%.