Thermally insulating and sunlight selective aerogel film for window retrofits in hot regions

Glazed windows contribute up to 60% of energy losses from the building envelope. Designing energy-efficient retrofitting materials for windows that can block near-infrared radiation and retard environmental heat is crucial for reducing building energy loss and greenhouse gas emissions. Here, we proposed a visible transparent, near-infrared opaque, and thermal insulating silica aerogel film embedded with indium tin oxide (ITO) nanoparticles to reduce the energy consumption of buildings in hot regions. A coupled heat conduction, convection, and radiation transfer model was developed to assess how aerogel thickness, diameter, and concentration of ITO nanoparticle affect the optical and thermal performance of silica aerogel film on windows. The results show that a 5-mm-thick aerogel doped with 0.099 vol% ITO nanoparticles measuring 4 nm in diameter can achieve a U-value of 2.30 W/(m²·K), a solar heat gain coefficient of 0.60, a luminous transmittance of 0.60 and a near-infrared transmittance of 0.27. The proposed silica aerogel composite film can minimize energy loss without blocking visible solar energy, which has great potential as a retrofit to increase the energy efficiency of windows, particularly in hot regions.