Performance and Relative Humidity Impact of Cellulose‐Derivative Networks in All‐Day Passive Radiative Cooling

Abstract All‐day passive daytime radiative coolers (PDRC) offer a promising solution for energy‐free cooling of buildings and devices. This study investigates the use of various cellulose‐derivative networks to achieve optimal and stable cooling performance. These results showed that the mixed cellulose ester network has a maximum solar reflectance of 97%. While cellulose acetate network has a maximum infrared emissivity of 96% in the atmospheric transparency window band, which is a near‐perfect infrared emitter, the nitrocellulose network shows the highest cooling temperature, with a significant reduction of 14 °C from the ambient temperature and a power of 124 W·m⁻² during the daytime and at night of 7.7 °C and 72.8 W·m⁻². This study also analyzes the dampness's effect on the cooling performance of cellulose‐derivative networks. The cooling performance of the nitrocellulose network drops ≈ 3 °C (from 14 to 11.3 °C) when the relative humidity of the day exceeds ≈ 30% is observed. These findings indicate that the capacity of a material to absorb water from the surrounding air significantly influences its performance as a passive cooler, primarily due to changes in its optical properties. This is an important insight, as it highlights the need to consider environmental factors like relative humidity and sample hydrophobicity for PDRC systems.