Thermally adaptive windows for energy efficient buildings: High performance composite and multilayer vanadium dioxide window coatings

As populations increase and cities grow in size, reducing the energy consumption of the built environment is vital for reducing CO2 emissions and global warming. Heating and cooling loads account for > 40% of energy consumed within the built environment and window coatings with dynamic solar transmittance represent an excellent opportunity to reduce this load (by regulating solar heat gain). In particular, inorganic thermochromic coatings, based on the metal-insulator phase-transition of vanadium dioxide, offer long lifetimes (> 30 years) and can be passively integrated into a window system without additional electronics or power requirements. However, the application of vanadium dioxide as a dynamic window coating material has traditionally been hindered by its optical properties (i.e. low visible transparency and limited solar transmittance modulation) and phasetransition properties (i.e. wide phase-change hysteresis and high transition temperatures), along with practical concerns, such as determining optimal transition temperatures for a given location, and finding a production method that is suitable for the window coating industry. This thesis presents significant progress in addressing both the fundamental and practical issues of vanadium dioxide as a dynamic window coating material: (1) A simulation method is developed to investigate how the transition properties of thermochromic coatings affect their energy saving performance in different environments. (2) Scalable fabrication methods and high-throughput characterisation techniques are optimised to fabricate and characterise high purity vanadium dioxide based composite and multilayer coatings. (3) A method to control coating morphology is demonstrated to improve phase-transition properties. (4) An optically designed multilayer coating is experimentally demonstrated to improve optical properties (far exceeding previous literature performances). In light of the evidence presented, this thesis concludes that multilayer thin-film vanadium dioxide is the most viable morphology for thermochromic window coatings with high energy saving performances