Optically-switchable thermally-insulating VO<inf>2</inf>-aerogel hybrid film for window retrofits

Abstract

Developing easy-to-install energy-efficient window retrofitting materials is important for reducing the heating and cooling loads of buildings. However, it is very challenging to achieve window retrofits that are simultaneously thermally insulating, visible-light transparent, and dynamically switchable in solar transmission. Here, a visibly transparent and thermally insulating film was proposed to reduce the energy loss through windows. By embedding insulator–metal phase transition vanadium dioxide (VO2) nanoparticles inside an ultralow thermal conductivity aerogel film, the thermal insulation performance is greatly improved in such thermochromic film while the solar transmission can be dynamically switched in response to ambient conditions. A coupled heat conduction and solar radiation heat transfer model was developed to evaluate the effect of geometric features such as film thickness, nanoparticle size, and concentration on the thermal and optical performance of the proposed films. It was shown that a 3.0 mm thick film could achieve a low U-value of ~ 3.0 W/(m2K), and a high luminous transmittance of > 60% and a solar modulation ability of ~ 20%. This film improves the performance of single-pane windows by reducing the energy loss, improving thermal comfort, and avoiding moisture condensation in cold climates and overheating in hot climates.