Angle-dependent microstructural vanadium dioxide film for thermochromic smart windows: from materials to buildings

Abstract

The thermal properties, optical properties and energy-saving effects of vanadium dioxide (VO₂) thermochromic films can be affected by the incident angle, especially for the microstructural films. This study investigates the influence of incident angle on optical and thermal properties of microstructural VO₂ films through both experimental and numerical methods, and further proposes an integrated method to calculate the energy consumption by considering the angle-dependent effect for both material and building. The microstructural VO₂ film was measured to have a lower temperature inside a model house compared to the one with normal glass, and their discrepancy reached 1.8 °C at an incident angle of 60°. When the incident angle changed, the microstructural VO₂ film exhibited an improved average luminous transmittance (T_lum) and more stable solar modulation ability (ΔT_sol) than the planar film. Considering the angle-dependent material and building characteristics in building energy simulation, the application of microstructural VO₂ film was predicted to reduce the heating and cooling loads by 42.4 kWh/m² per year compared to those of the normal glass, and gave a lower lighting load than that of the planar VO₂ film. This study will contribute to accurate calculations considering angle-dependent material and building characteristics in thermochromic smart window applications.