Radiative cooling computed for model atmospheres

Abstract

Calculations of spectral radiance are reported from several model atmospheres appropriate to different climatic conditions by use of the LOWTRAN 5 computer code. From these data we evaluate the radiative cooling power and the temperature drop below ambient temperature for horizontal surfaces that radiate toward the sky. The surfaces are ideal blackbodies or have ideal infrared-selective properties with zero reflectance in the 8-13-microm range and unity reflectance elsewhere. For freely radiating surfaces, the cooling power at ambient temperature lies between 58 Wm(-2) and 113 Wm(-2) for the different surfaces and model atmospheres. The maximum temperature difference for a device with a nonradiative heat transfer coefficient of 1 Wm(-2) K(-1) is between 11 and 21 degrees C for a blackbody and between 18 and 33 degrees C for an infrared-selective surface. For radiators arranged so that they intercept only the atmospheric zenith radiance, the cooling powers and temperature differences are higher than for freely radiating surfaces, the increase being largest for humid atmospheres. The influence of altered contents of water vapor was found to affect strongly the radiative cooling, whereas changes in ozone and aerosol abundance were less important. The significance of these results to different cooling applications is briefly discussed.

Solar Energy Materials

“…[74] The resource for this cooling has been evaluated through detailed calculations showing that the cooling power for a black-body surface is 80 to 120 W m ±2 , depending on the atmospheric conditions, when the surface is at ambient temperature. [75] If nothing but radiation exchange is considered, the surface can decrease to 14 to 26 C below the air temperature. In the presence of a non-radiative heat transfer equal to 1 W m ±2 K…”

Effect of clouds and dust storms on the sky radiation exchange for buildings located in hot–dry climates

“…Both cloud and dust conditions participate in changing the sky radiation conditions, then increasing effective sky temperature. In the literature, the lowest relative sky temperature was reported as -40 • C in the Atacama Desert of Chile (Eriksson and Granqvist 1982). Therefore, the minimum clear sky temperature of Saudi Arabia is considered to be the lowest measured temperature based on Maghrabi's (2012) measurements.…”

An ode to polyethylene

“…Recently, this challenge has been met by the development of spectrally selective surfaces that efficiently reflect sunlight and simultaneously emit mid-infrared radiation. [40][41][42][43][44][45][46][47] Broadband transparency of polyethylene ( Fig. 3) makes it an ideal optically neutral host material to achieve such spectral selectivity by embedding a variety of nanoscale and microscale particles into the polymer matrix.…”