The adaptive control of sunlight through photochromic smart windows could have a huge impact on the energy efficiency and daylight comfort in buildings. However, the fabrication of inorganic nanoparticle and polymer composite photochromic films with a high contrast ratio and high transparency/low haze remains a challenge. Here, a solution method is presented for the in situ growth of copper-doped tungsten trioxide nanoparticles in polymethyl methacrylate, which allows a low-cost preparation of photochromic films with a high luminous transparency (luminous transmittance T_lum = 91%) and scalability (30 × 350 cm²). High modulation of visible light (ΔT_lum = 73%) and solar heat (modulation of solar transmittance ΔT_sol = 73%, modulation of solar heat gain coefficient ΔSHGC = 0.5) of the film improves the indoor daylight comfort and energy efficiency. Simulation results show that low-e windows with the photochromic film applied can greatly enhance the energy efficiency and daylight comfort. This photochromic film presents an attractive strategy for achieving more energy-efficient buildings and carbon neutrality to combat global climate change.

Climate change will lead to more warm and hot days in the Netherlands. Climate adaptation measures are needed to reduce the vulnerability of urban areas. Moreover, proven adaptation measures, such as increased vegetated areas or water surfaces, are not always possible due to a lack of space or undesired aesthetic effects. An alternative option is to make use of coloured façades to create drafts and accelerate wind speed in a street canyon or on a square to attract fresh air from cooler places. Differences in colour and material types already influence the air flow in street canyons in an uncontrolled manner. If this thermal comfort principle can be implemented, it will potentially have a significant impact on many cities throughout the world. This paper presents the results of a first exploratory research based on measurements on scale models and at full scale. This pilot study indicates success of the intended draft principle, advocating further research.