A “thermometer” for effective sky temperature

Abstract

The measurement of sky emissivity or effective sky temperature is essential toward assessing the potential for radiative cooling. Such measurements have been made with radiometers[l,2] for a variety of locations throughout the United States. On summer nights, for example, desert skies can have effective sky temperatures as much as 35K below ambient dry bulb temperature[3], which attests to the impressive potential for radiative cooling. It is the purpose of this paper to propose a simple experimental technique for the determination of effective sky temperature-a method that requires a relatively unsophisticated and inexpensive apparatus. This method is based on elementary theoretical considerations of heat exchange between a radiator and the nocturnal sky. The nighttime heat exchange between a radiator at temperature T and its surroundings can be expressed by