The European building performance directive EPBD is intending the implementation of an harmonized method for the evaluation of building energy performance. That is why a set of standards has been worked out addressing methods to calculate the performance of the building and its energy systems. In this paper the calculation method used to predict heat and cooling loads of the building and the indoor temperatures, respectively, has been analysed. Therefore the standardized calculation procedure has been implemented in simulation programme. The programme again has been verified to learn more about model accuracy, reliability and sensitivity. It was find from testing that model performance need to be improved. Also model accuracy is not satisfying.