An excel based calculation tool has been developed within the EU project Combisol. It implements the standard calculation method EN 15316-4-3 for solar combisystems, as defined for the Energy Performance of Buildings Directive (EPBD). A base case system and building were defined and a number of parametric studies were performed with this EPBD tool as well as TRNSYS for the same systems and boundary conditions. For all the simulations in this study, the EPBD tool predicted a greater solar contribution than detailed TRNSYS simulations predicted. The difference was greater for Stockholm (high latitude) and Madrid (high solar fraction). Other studies showed that the EPBD predicted changes in solar contribution due to changes in system size, orientation and azimuth as well as store size in the same way that TRNSYS does.