Evaluating coloured thermochromic windows for energy efficiency and visual comfort in buildings

• Coloured Thermochromic (TC) windows boost energy savings by up to 14% vs. double glazing. • TC windows improve annual daylight availability by 5–15%. • Red and grey TC designs offer optimal energy and daylight performance. • Multi-layer TC glazing adapts well across most of climates. In recent years, significant advancements have been made in thermochromic (TC) window technologies, particularly in vanadium dioxide (VO 2 )-based TC glazing. Innovations such as integrating pigments with polyurethane (PU) composite coatings have enabled colour modulation and improved colorimetric properties. However, their effects on building energy performance and indoor luminance environment are both critical for occupant comfort, health, and broader energy efficiency goals have been underexplored. This study evaluates conventional and coloured TC windows (blue, red, and grey), fabricated with one to three VO 2 layers, focusing both on building energy consumption and daylight performance. TC windows were assessed under three window-to-wall ratios of 30%, 60%, and 90% across three climatic conditions: Changsha, Ankara, and New York. Five key criteria were evaluated: energy savings, daylight availability, glare control, daylight uniformity, and colour quality. A multi-objective analysis revealed that the conventional 2-layer TC (TC2), 3-layer TC (TC3), red 3-layer TC (Red-TC3), and grey 2-layer TC (Grey-TC2) consistently outperformed other variants. These windows achieved up to 14% higher annual energy savings and 5–15% greater daylight availability (UDI 300-2000lux ) compared to standard double-glazed (DG) windows. The results highlight the strong potential of coloured TC windows as climate-adaptive solutions for reducing building operational energy demand and enhancing indoor environmental quality, contributing to future energy transition and sustainable building practices.