Generic method for creating waterborne coatings with sub-ambient daytime cooling-Part II: Cooling effect under real working conditions and key physical properties

摘要

Current sub-ambient daytime radiative cooling (SDRC) designs are generally evaluated in a well-insulated apparatus to suppress heat convection and conduction with the surrounding environment. In a companion study, we experimentally demonstrated that serial waterborne coatings, which combined particle scattering, sunlight-excited fluorescence, and mid-infrared broadband radiation, exhibited pronounced SDRC effects on various substrates installed on a well-designed rooftop setup under different climatic conditions. In this study, we experimentally show that the coating with yellow-green fluorescence (termed as the FR coating) can achieve meaningful SDRC under real working conditions. When applied to a concrete scale-model building, the FR coating showed a significant SDRC effect compared with other substrates installed on the rooftop cooling device and an assembled corrugated steel house. The average decrease in sub-ambient temperature under direct sunlight was 10.1 +/- 1.4 degrees C with a maximum value of 12.4 degrees C under a peak solar intensity of 999 W/m(2). Moreover, during the coldest day in winter, the maximum sub-ambient temperature reduction during the midday hours was 5.3 degrees C. The maximum difference between the lowest temperatures of the coated and uncoated scale-model buildings' room interiors was 1.5-1.6 degrees C. Therefore, excessive heating energy consumption in the winter might be completely compensated for or exceeded by the cooling energy savings in the summer in areas that require both heating and cooling depending on the season. Additionally, the coating possesses excellent weather and salt spray resistance, self-cleaning capabilities, and excellent visible appearance, which are essential for practical applications.