Cooling performance of porous polymer radiative coating under different environmental conditions throughout all-year

Cooling terrestrial objects for thermoregulation is a significant challenge in this decade due to the rapidly increasing world energy consumption and human daily life demands. Furthermore, the conventional cooling technologies are energy-intensive, as predominantly vapor compression-based cooling systems consume a substantial amount of electricity. Therefore, the development of energy-efficient alternative cooling techniques with fewer environmental footprints is desirable. Here, we present a porous polymer coating with P(VDF-HFP) as a passive radiative cooler to investigate the cooling performance under various conditions. The reflectivity within the visible wavelength range (0.38-0.78 mu m) and the ultraviolet visible-near infrared wavelength range (0.25-2.5 mu m) of a 2.0 mm thick porous polymer radiative coating (PPRC) are about 98% and 94%, while the emissivity in the main atmospheric window (8-13 mu m) is up to about 97%, indicating that the proposed PPRC is a potential candidate to achieve a notable radiative cooling performance. By taking the meteorological location of Shanghai, China, as an example, the radiative cooling performance is tested for a whole year. The PPRC cooler can constantly exhibit excellent cooling performance throughout all-year and show the best in winter, followed by spring, autumn, and summer under typical fine weather conditions. We investigated quantitatively the impact of different environmental conditions, including cloud amount, air quality, relative humidity, and ambient temperature on the performance of the radiative cooler, which is essential for real-world deployment. For example, the PPRC cooler can achieve a temperature drop of up to about 6.9 degrees C at the relative humidity of 38% and only 3.9 degrees C at the relative humidity of 68% at 15:00-17:00 in summer when other environmental conditions are similar. As the passive cooling technique is expected to play an increasing role in the future, this work facilitates the fabrication of environmentally friendly PPRC cooler for energy-saving applications.

Automated summary

The study introduces a new porous polymer coating as a passive radiative cooler and evaluates its cooling performance under various conditions. Testing the radiative cooling performance in Shanghai for a whole year, the results show that the cooler can maintain excellent cooling effects throughout all seasons.