Abstract
Achieving a transition to maximize the utilization of radiative cooling as a passive cooling strategy is challenging for several regions worldwide, mainly due to unawareness, lack of government support, and extreme seasonal climatic variations. Being characterized by a variety of atmospheric conditions from tropical coastline to arid regions along with humid highland areas to regions with continental atmospheric conditions, Pakistan faces significant seasonal and daily variations in atmospheric parameters, such as solar irradiance, temperature, precipitation patterns, humidity, etc., making it a steppe country with diverse atmospheric conditions and an energy-intensive economy dominated by fossil fuels. Therefore, following United Nation's Sustainable Development Goals, here we investigate the radiative cooling potential resource map across Pakistan, providing it as a sustainable alternative to lower the cooling demand by maximizing the emitted thermal radiation to the deep space and minimizing solar irradiance absorption by utilizing the materials' inherent properties of being highly reflective within solar spectrum range and extremely emissive within the atmospheric window. A comprehensive comparison between annual, seasonal, diurnal, and nocturnal radiative cooling capability is conducted and analyzed across all provinces of Pakistan based on the variation in regional climatic conditions. The yearly average radiative cooling capacity varies from 69.39 to 96.41 W/m2 due to swift variation from humid continental to arid climatic regions, with a 24.27 % discrepancy in daytime and nighttime radiative cooling potentials owing to the significant influence of solar irradiance. An office building model incorporating radiative cooling coating at the rooftop is further implemented to illustrate the real-case scenarios of using radiative cooling coatings as a cool roof. Compared to traditional roofs, applying radiative cooling coatings on the rooftop of a single-storey office building can reduce the annual cooling load by 76.01 to 112.77 kWh/(m2.year) for various cities under diverse climatic conditions. The annual electricity savings in several cities are estimated to be 30.40 to 45.11 kWh/(m2.year) based on the refrigerator COP of 2.5. The application of radiative cooling coatings on rooftops induces the incremental cost of 24 $/m2, with a simple payback period of 5.32 to 7.89 years in response to annual electricity savings across varying meteorological conditions. Besides, the maximum carbon emissions reduction is estimated to be up to 27.77 kg/(m2.year) based on a carbon emission factor of 0.606 kgCO2/kWh. In the end, valuable insights are discussed based on policy recommendations and limitations for developing strategies to adapt the radiative cooling technology on a broader scale based on innovative solutions, spreading public awareness, and offering financial incentives.
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