High-performance subambient radiative cooling enabled by optically selective and thermally insulating polyethylene aerogel
Recent progress in passive radiative cooling technologies has substantially improved cooling performance under direct sunlight. Yet, experimental demonstrations of daytime radiative cooling still severely underperform in comparison with the theoretical potential due to considerable solar absorption and poor thermal insulation at the emitter. In this work, we developed polyethylene aerogel (PEA)—a solar-reflecting (92.2% solar weighted reflectance at 6 mm thick), infrared-transparent (79.9% transmittance between 8 and 13 μm at 6 mm thick), and low-thermal-conductivity (kPEA = 28 mW/mK) material that can be integrated with existing emitters to address these challenges. Using an experimental setup that includes the custom-fabricated PEA, we demonstrate a daytime ambient temperature cooling power of 96 W/m2 and passive cooling up to 13°C below ambient temperature around solar noon. This work could greatly improve the performance of existing passive radiative coolers for air conditioning and portable refrigeration applications.
Subambient cooling is vital for minimizing food shortage, promoting human well-being, and driving sustainable economic growth (1). Lack of and inadequate refrigeration of perishable food products in developing countries are still responsible for more than 40% of postharvest food spoilage, leading to unnecessary greenhouse gas emissions, biodiversity and habitat loss, as well as water consumption (2). Moreover, air conditioning use in buildings is poised to surge in hotter parts of the world with growing populations and economic activity, further increasing the world’s energy consumption and CO2 emissions (1). Fortunately, passive, affordable, and more efficient cooling solutions have the potential to reduce food spoilage as well as meet space cooling energy needs without any CO2 emissions. One approach that has generated notable interest in recent years is radiative cooling (3–23)—a passive cooling solution that relies on the natural emission of infrared (IR) radiation of terrestrial o