Angular-dependent measurements of the thermal radiation of the sky

Measurements were carried out to determine the incoming longwave radiation of the sky as a function of the zenith angle at the ZAE Bayern in Wurzburg. The obtained data allowed the adjustment of an existing model to regional climatic conditions. This model was used to compute the thermal heat losses for various buildings with respect to variations of the emissivities of outer wall surfaces as well as their orientation. Condensation of water vapour was also taken into account. It was found that the application of wall paints with emissivities of epsilon = 0.5 instead of normal paints (epsilon approximate to 0.9) would reduce the thermal heat losses by about 5%-25%. Poorly insulated buildings and south-facing walls show the greatest energy savings.