Abstract
Radiative cooling is a natural process to cool down surfaces through the rejection of thermal radiation using the outer space as a cold sink, taking advantage of the transparency of the atmospheric windows (8–14 μm), which partially matches the infrared radiation band. With the development of new materials that have a high reflectivity of solar radiation, daytime radiative cooling can be achieved. This phenomenon depends on the optical properties of the surface and the local weather conditions. In this research, climatological data from 1791 weather stations were used to present detailed nighttime and all-day radiative cooling maps for the potential implementation of radiative cooling-based technologies. The paper offers a parametric study of the variation of the potential as a result of decreasing the solar reflectivity. The results show that southern Europe is the region with the highest potential while northern Europe holds more hours of available radiative cooling. After varying the solar reflectivity from 1 to 0.5 the average power reduces from 60.18 to 45.32 W/m2, and energy from 527.10 to 264.87 kWh/m2·year. For solar reflectivity lower than 0.5, all-day radiative coolers behave as nighttime radiative coolers, but power and energy values improve significantly for high values of solar reflectivity. Small variations of solar reflectivity have greater impacts on the potential at higher reflectivity values than at lower ones.
Highlights
Radiative cooling (RC) is a natural cooling process already used in 400 BC in ancient Iran for ice production [1]
Radiative cooling is known to be the process by which a surface reduces its temperature through the emission of thermal radiation into the outer space
In the first part of this section we present a comparison of the prediction maps for the cases of nighttime and all-day RC of an ideal reflective surface (ρ = 1)
Summary
Radiative cooling (RC) is a natural cooling process already used in 400 BC in ancient Iran for ice production [1]. Radiative cooling is known to be the process by which a surface reduces its temperature through the emission of thermal radiation into the outer space It benefits from the high transparency of the atmosphere in 8–14 μm wavelength range, named atmospheric window, which partially matches the peak of infrared radiation emitted by terrestrial bodies at ambient temperatures. This cooling process occurs when a net imbalance exists between the emitted and the absorbed heat; solar radiation, atmospheric radiation and parasitic losses (convection and conduction) accounted for in this net balance. We present twenty maps corresponding to seven maps of annual power, seven maps of annual energy production and six maps of percentage of RC hours over total annual hours
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