Analysis of solar radiation and implementation of a calculation model for energy characterization of fenestration systems

In the last years, as fenestration and shading systems have become more complex and sophisticated, a great improvement of thermal and solar-optical performance has been required and as a consequence old methods of characterization have become inadequate. This evolution has yielded the introduction of new lumped parameters and the implementation of more sophisticated calculation models, which allow to evaluate the performance of fenestration and shading systems taking into account a large number of factors, such as the angular dependence of solar heat gain. The suitability and usefulness of new parameters and models for a wide use depend on the level of knowledge of the interaction between fenestration systems and the external environment. In the first part of this work an analysis of incident solar radiation on fenestration has been performed, by using the climatic data contained in the average monthly days of some sites representative of the main Italian climatic zones. The ratio of direct solar radiation to diffuse solar radiation has been analyzed for different orientations of glazed surfaces and for different periods in the year. Moreover, the relation between direct radiation and its incident angle has been analyzed. In the second part of this work a calculation model for the determination of the solar energy transmittance (TSET) of fenestration and shading systems has been developed. The model is based on a reference tool developed by CSTB, which has been modified by the authors in order to increase its flexibility, to adequate it to the existent national and international standard and recommendation, to take into account the angular dependence of solar heat gain through complex fenestration and shading systems. The combined application of the calculation model to some fenestration systems using the results of the external environment analysis has allowed to identify a wide range of cases and to obtain general rules about the applicability and usefulness of different calculation models depending on geometric and exposure features of glazed surfaces and on the period of the year.