Bio-based chitin nanofiber films for passive cooling of windows in polluted cities

This study develops a bio-based chitin nanofiber (ChNF) film for passive daytime radiative cooling of building windows in a polluted city. The goal is to optimize the trade-offs between daylight preservation, investment cost, and cooling energy reduction considering air pollution effects on received solar irradiance. An aerosol-aware solar irradiance model including monthly aerosol optical depth (AOD) data was created. The best ChNF coverage on south-, north-, east-, and west-facing window surfaces was found using a three-objective optimization framework. The findings indicate that Tehran's yearly average AOD of 0.37 raises the diffuse percentage to 29% and decreases global solar irradiance by around 18%. The ideal configuration includes all south-facing windows and half of the west-facing windows covered by ChNF. The optimized configuration reduces yearly cooling demand by 28.2% (3111 kWh/year) at an installation cost of $187 with a payback period of 1.64 years and 62.6% daylight autonomy. Also, sensitivity analysis underscores the importance of air quality as a design factor and shows that the ideal west-facing coverage drops from 0.70 in clean air to 0.30 in highly polluted areas. The proposed framework is generalizable to other bio-derived materials and other polluted cities.