ANGULAR EMISSIVITY AT ROOM-TEMPERATURE AND SPECTRAL REFLECTANCE AT NEAR NORMAL INCIDENCE OF FLOAT GLASS, BOROSILICATE GLASS AND GLASS-CERAMICS

An accurate investigation of the emissivity of uncoated flat glass (ne cessary to calculate the solar factor and the U value of glazing accor ding to standardized procedures) was performed in agreement with Group ement Europeen des Producteurs de Verre Flat, in support of CEN and IS O standardization activities. The total angular emissivity of a rang o f uncoated float glass samples was determined between 10 and 80 degree s C with an uncertainty of 0.5%. Both the normal and the hemispherical emissivity were nearly identical for all the samples investigated. No significant differences between the top and the bottom side were obse rved. Measurements sere also extended to borosilicate glass and glass- ceramic plates used for fire-resistant glazing, determining their ther mal conductivity and angular emissivity behaviour. In order to obtain additional information, also the spectral reflectance curves at near n ormal incidence between 2000 and 200 cm(-1) were obtained using a spec troradiometer. The fact that almost identical curves were obtained for a wide range of float glasses (both sides) as well as for the fire-re sistant materials confirms the correctness of the close emissivity val ues found. On the basis of the results obtained, a standard value of e psilon(n) = 0.900 and a epsilon(h)/epsilon(n), ratio = 0.936 is sugges ted for both float glass and for the two other materials.