Transparent passive-cooling composite films for indoor and outdoor spaces

• DOI: 10.1016/j.coco.2020.100611
• Publication Date: 2020-12-29T12:36:06Z
• Authors: Lina Cui; Canyi Huang; Hong Xia; Yiping Qiu; Qing-Qing Ni
• Keywords: Passive cooling; Glazing; Ultraviolet

Abstract Energy expenditure in buildings and transportation is about 63% of all global energy consumption, making them major targeted sectors for energy conservation and carbon dioxide (CO2) emission reduction. To save energy in cooling of automobiles and buildings, transparent passive-cooling films with 90-nm-diameter zinc oxide (ZnO) particles dispersed in low density polyethylene were manufactured. These films filter out the high-energy region of visible light (Vis), block ultraviolet (UV) light, and allow infrared light to pass through by utilizing light scattering due to nanoparticles (NPs) and refraction from lamellar crystals in the film. Transmissivities of the films decrease as NP concentration, film thickness, and crystallinity increase. Passive-cooling performance tests show that the films have a temperature reduction (ΔT) of up to 14.95 °C around midday, which is substantially better than that reported for similar films. The volume involved in the passive-cooling test is found to be critically important. ΔT initially declines exponentially and then levels-off as the enclosed volume to window area ratio, or specific volume (SV), increases. An empirical model is proposed for the relationship between ΔT and SV for more appropriate measurements of passive-cooling performance. SVs of passenger cars and office buildings are located within the most sensitive range of the ΔT-SV curve of the fabricated films.