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The conventional way to fabricate current sub-ambient daytime radiative cooling (SDRC) systems is to maximally suppress the cooler's solar absorption and substantially improve its selective emissivity only in the atmospheric transparency window. This greatly limits the selection of materials and their practical applications. In this paper, an alternative method, which combines sunlight-triggered fluorescent cooling, particle scattering, and broadband infrared radiation, was presented for creating serial eco-friendly coatings with the SDRC effect with conventional cost-effective building materials. The presence of conventional fluorescent pigments in the coating composition increased the effective direct-normal solar reflectance via sunlight-excited fluorescent emissions to the level required for SDRC. When applied to various substrates, the serial coatings exhibited distinct SDRC effects under direct and strong sunlight in typical temperate monsoon climate regions such as Beijing. The observed sub-ambient temperature reduction of the coating with yellow–green fluorescence over an aluminium plate was 3.5 °C under a peak solar intensity of 996 W/m2, yielding a cooling power of 45.7 W/m2 under a peak solar intensity of 981 W/m2. Compared with the conventional cool white coatings, the large-scale application of the coating to urban surfaces is predicted to reduce a city's air temperature by approximately 1 °C and thereby decrease the Heat Island Intensity. Additionally, the method proposed in this paper was generic and expanded the SDRC design paradigm, thereby promoting SDRC as a viable energy-efficient technology. Image 1 • Fluorescent emissions increase the effective solar reflectance to an ideal level. • Fluorescent cooling is crucial for sub-ambient daytime radiative cooling (SDRC). • FR coatings over various substrates exhibit distinct SDRC effect. • The SDRC effect on an aluminium plate is 3.5 °C on a clear hot sunny day. • The cooling power is 45.7 W/m2 under a peak solar intensity of 981 W/m2. [ABSTRACT FROM AUTHOR]

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 °C with a maximum value of 12.4 °C under a peak solar intensity of 999 W/m2. Moreover, during the coldest day in winter, the maximum sub-ambient temperature reduction during the midday hours was 5.3 °C. The maximum difference between the lowest temperatures of the coated and uncoated scale-model buildings' room interiors was 1.5–1.6 °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. Image 1 • The FR coating exhibits a distinct SDRC effect under real working conditions. • The FR coating over a concrete roof surface shows a more notable SDRC effect. • The SDRC design does not necessarily result in detrimental effects in winter. • The FR coating has excellent durability and outstanding self-cleaning properties. [ABSTRACT FROM AUTHOR]

Waterborne and solvent-based coatings with prominent passive subambient daytime radiative cooling (RC) coatings were fabricated to conserve cooling energy in the summer. Concurrently, water- and alcohol-based superamphiphobic self-cleaning coatings were manufactured and introduced into the RC coatings as topcoats. The contact angles of water and n -hexadecane of the superamphiphobic topcoat containing coating systems were 163.4° and 151.4°, respectively; additionally, the sliding angles of water and n -hexadecane of these systems were 2° and 9°, respectively. Moreover, the introduction of a transparent superamphiphobic topcoat to the RC coatings did not affect their originally high solar reflectance but improved their emissivity values in the atmospheric transparency window, wavelengths between 2.5 and 24 μm, and the entire infrared spectrum due to the presence of plenty of silicon-oxygen bonds formed via hydrolysis and/or alcoholysis reactions and the subsequent co-polycondensation of tetraethoxysilane and 1H,1H,2H,2H-perfluorodecyltriethoxysilane. The solar reflectance of the coating system was 0.986, which is the highest recorded worldwide. The emissivity of the superamphiphobic RC coatings in the atmospheric transparency window was 0.954. The superamphiphobic RC coatings possessed excellent static and dynamic non-wetting capabilities, significantly improving their water resistance, waterproofing properties, and anti-graffiti performance. Additionally, the superamphiphobic RC coatings exhibited outstanding self-cleaning properties, preventing the coating surfaces from being contaminated by dust, soiling, grime, and water/oil-soluble pollutants, thereby enabling them to maintain an extremely high solar reflectance. Water- and alcohol-based superamphiphobic radiative cooling coatings with solar reflectance up to 0.986 were fabricated. The emissivity in the atmospheric transparency window and thereby the overall emissivity were increased to 0.954 and 0.96, respectively, due to the introduction of transparent superamphiphobic topcoats. The contact angles of water and n -hexadecane were 163.4°and 151.4°, respectively, while the sliding angles of water and n -hexadecane were 2°and 9°, respectively. [Display omitted] •The superamphiphobic coating with subambient daytime radiative cooling was produced. •The solar reflectance of the coating was up to 0.986 •The coating's emissivity in the atmospheric transparency window was 0.954 •The coating's contact angles of water and n-hexadecane were higher than 150°. •The coating's sliding angles of water and n-hexadecane were lower than 10°. [ABSTRACT FROM AUTHOR]

Highlights: [•] Two waterborne cool white coatings for building energy efficiency were prepared. [•] The solar reflectance of cool coatings S1 and S2 is respective 0.879 and 0.892. [•] The predicted industrial limits for practical reflective cool white coatings are 0.91. [•] The coatings integrate multiple cooling principles and show super cooling effect. [•] Radiant heat flux may be significantly reduced by use of cool white coatings. [Copyright &y& Elsevier]

Abstract: The physicochemical properties of two newly developed dirt-resistant cool white coatings were systematically measured in light of the relevant standard testing methods, and the influences of dirt accumulation and washing on the long-term cooling performance of cool coatings were investigated and discussed. Both cool white coatings owe their outstanding physicochemical properties to the optimized formulations, high glass transition temperature and minimum film formation temperature of selected aqueous self-curing acrylic emulsions. The high solid content was also influential. Dirt accumulation leads to a decline in the cooling performance of coatings, which may be almost fully restored by simply washing the coatings with a mild soap solution. [Copyright &y& Elsevier]