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

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 (Tlum) and more stable solar modulation ability (ΔTsol) 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.