Measured angular distribution of the emissivity and calculated radiation heat transfer of architectural coated flat glass Part 1. Theory

Abstract

International standards for the calculation of the central U value of coated multiple glazings are based on a model of radiative heat transfer allowing the behaviour at all angles to be predicted from emissivity measured at normal incidence. In order to provide a background for such standards, a theoretical and experimental study of the angular variation of total directional emissivity at room temperature of the relevant materials (including uncoated float glass and typical architectural coatings) has been undertaken in cooperation with TC 10 of the International Commission on Glass and with the Light and Energy Group of the Groupement Europeen des Producteurs de Verre Fiat. After illustrating the equations which correlate the optical constants with angular reflectivity and emissivity, the possibility of mathematically correlating the normal emissivity with the hemispherical and effective emissivity for different materials is discussed.