Background The air flow around and through a building with several rooms belongs among the most difficult issues of the aerodynamic. Exemplary for the complexity of the influences are the interaction between adjacent buildings, the overlap of wind and thermal lift, as well as the simple effect of an open or closed inner door. In the specialist literature but also in the relevant standards, such as EN 15242:2007, the physical models to calculate the determination of air flow rates in buildings are described in detail. For the practical application of these algorithms for example in the planning of ventilation systems a description of mathematical approaches for iterative processes is missing. As suggested and commissioned by the European Ventilation Industry Association (EVIA) an Excel tool to calculate the air flow rates in buildings including infiltration on the basis of EN 15242 was made by the authors. This Excel tool is generally applicable even after reviewing this standard in the course of the EPBD mandate 480 (the future EN 16798-7 ”Energy performance of buildings – Part 7: Ventilation for buildings – Module M5-1, M5-5, M5-6, M5-8 – Calculation methods for the determination of air flow rates in buildings including infiltration”).
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