Thermal conductivity of float glass at room temperature

Abstract

When the heat transfer coefficient of multiple glazings is to be determined, it is important to know the exact thermal conductivity value of the glasses used for building purposes. The values given for flat glass lie between 0.8 and 1.15 W/(m K ) . The thermal conductivity of 11 float glass samples of 4 different colours, manufactured in 5 European countries, has been determined in the temperature range between 10 and 90 °C with an uncertainty of less than 1.5 %. At 10 °C, the mean value of all glasses investigated amounts to 1.022 W/ (m K); the individual values vary between 1.033 and 1.017 W/(m K) . On the basis of the composition, the basicity and the density, the measurement results could be well interpreted by known theoretical considerations. The slight variation of the thermal conductivity values obtained by measurement is in agreement with the values calculated from the composition and the density and can be explained by the fact that all float glasses are of nearly the same composition. By interpolation of the measurement data, coefficients could be determined to calculate the thermal conductivity from the oxide composition. The investigation has shown that - at 10 °C - a value of 1.02 W/(m K) can be applied for the thermal conductivity of flat glasses used for building purposes, independent of their colour or manufacturer.