An\nAll-Weather Sol<b>–</b>Gel Thermochromic\nEnergy-Saving Smart Window

Thermochromic smart windows achieve\nenergy conservation\nand emission\nreduction by regulating the energy exchange in buildings. However,\ntheir widespread application in architecture has been hindered by\nissues such as poor frost resistance, limited durability, high costs,\nrecycling challenges, and suitability only for specific climates (such\nas tropical climates). To address these challenges, we have successfully\ndeveloped a high-performance thermochromic window, which is an intelligent\nwindow based on a thermochromic solution of poly(vinyl alcohol) acetal\nand LiCl, encapsulated in a glass/thermal liquid/low-E structure.\nThis thermochromic window exhibits scalability, frost-resistance,\ndurability and all-climate adaptability (referred to as SFDA window,\nwith the thermochromic liquid termed SFDA liquid). First, the SFDA\nliquid reported here utilizes an efficient one-pot aqueous synthesis\ntechnique to directly produce a polyvinyl acetal solution. This process\nnot only supports large-scale production but also incorporates LiCl\nin situ, endowing the liquid with excellent frost resistance. Second,\nthe concentration is purposefully adjusted to the entangled concentration\nto facilitate the sol–gel transition, ensuring durability during\nlong-term use. Additionally, windows containing SFDA liquid demonstrate\nexcellent performance, maintaining up to approximately 84% light transmittance\nand 70.7% solar radiation at 20 °C. Third, our SFDA window achieves\nhigh-efficiency energy savings compared to traditional thermochromic\nwindows across all-weather conditions. Through indoor simulations,\nwe found that SFDA window can cut energy consumption by 64.6% relative\nto traditional glass windows in the summer. In the winter, compared\nto traditional glass windows, windows containing SFDA liquid can reduce\nheating energy consumption by 52.3%. In simulations conducted across\n33 cities worldwide, SFDA liquid windows achieved a total monthly\nenergy savings of 1179.8 MWh compared to commercial Low-E window.\nWith its outstanding energy efficiency, the SFDA smart window opens\nup a brand-new development pathway in the field of green economy.