Effect of Solar Radiation Model on the Predicted Energy Performance of Buildings

The building energy balance is strictly connected with the solar irradiation. Therefore, a reliable estimation of the global irradiation incident on various tilted surfaces is essential in order to account for the solar heat gains. In many meteorological stations, only global solar radiation on a horizontal plane is monitored while, in some stations, also the direct and diffuse components are collected. However, only few stations measure the solar radiation incident on tilted surface. For these reasons, a variety of mathematical and empirical models have been proposed in the literature for both the subdivision of horizontal solar radiation into direct and diffuse components (horizontal diffuse irradiance models) and for the calculation of irradiation on tilted surfaces (irradiance models for tilted surfaces). Nevertheless, there is no pair of models that can provide results with the same reliability for different worldwide localities. This topic has been widely discussed in the literature by means of solar model validation against experimental data for a particular location. Little is still known about the propagation of these model uncertainties through the building energy balance. This research work investigates the extent to which the choice of solar radiation models affects the predicted energy performance of a set of simplified reference buildings. By means of a full factorial plan, a set of 72 simplified residential buildings is defined by changing the insulation and thermal inertia of opaque components, the windows surface and orientations and the solar heat gain coefficient of glazing. Moreover, a full combination of 22 horizontal diffuse irradiance models coupled with 12 irradiance models for tilted surfaces is implemented and used as a pre-processor of solar data used in building energy simulation codes (i.e. TRNSYS). Starting from these data, the hourly dynamic energy simulations were performed for several European locations. In particular, the Europe region has been divided in 5 zones considering the classes of annual solar radiation and, for each zone, a representative city was identified and used for this work. Finally, the distribution of monthly energy needs and peak loads are studied and discussed by means of statistical techniques, in order to generalize the found discrepancies and to correlate the deviations to the building envelope characteristics