The development of ventilation strategies for moisture problems, the reduction of the heating and cooling demands, the guarantee of hygrothermal and hygienic comfort in building constructions as well as the performance and the durability of building components are questions which are related to the strong interactions between the climate conditions, the building use and the building envelope. These questions can be answered with the help of efficient building simulation tools before building construction or retrofit. Until now, models which used the generic concepts of object-oriented -equation-based modelling language standards like Modelica for the simulation of the hygrothermal behaviour and the interactions between building components and building envelope were missing in building physics. In the thesis, the advantages of the generic concepts of Modelica were used to develop a flexible building physics library. This model library was validated and was used to develop a controlled ventilation system that minimises the risk of mould growth while ensuring hygrothermal and hygienic comfort in building rooms. This seminar will give a short overview about the results of this thesis. Audio of this presentation is available at http://www.vimeo.com/18478714. The slides may be downloaded separately at the link below.