Integration of radiative cooling and solar heating in thermal management films for year-round energy savings

Abstract

The application of zero-emission passive radiative coolers is a crucial step toward global carbon neutrality. However, a single radiative cooling function cannot meet the thermal requirements under various weather conditions. We present a dual-mode thermal management film that integrates passive radiative cooling and heating functions through its porous polymer surface for cooling and a light-to-heat conversion surface enabled by graphene and carbon nanotubes for heating. The surfaces of the dual-mode film were physically flipped, positioning the corresponding surface toward solar radiation to obtain the desired functionality. In the cooling surface, the film achieves sub-ambient cooling of ≈13.3 °C under 853.88 W m–2 of sunlight, thanks to its high solar reflectance (0.92) and mid-infrared emissivity (0.95). In the heating surface, it uses high solar absorption (0.90) to increase the temperature by 11.4 °C and generates Joule heating at various voltage levels. According to EnergyPlus software estimates, buildings with roofs covered in the film could reduce CO2 emissions by 1.109 billion metric tons, equivalent to 3% of current global CO2 emissions. This study offers a promising solution to climate challenges and holds great potential for energy savings and carbon reduction.