Calculating the risk of infection

In the light of the COVID-19 pandemic, there is a natural need to know more about the SARS-CoV-2 virus and how it develops. Ideally, we would like to look into the future and anticipate on that basis in order to limit the consequences. Building performance simulation models have been used for decades to calculate the energy demand of a building design. This may also allow us to say something about thermal comfort, for example in the event of overheating. We also use Computational Fluid Dynamics (CFD) technology to analyze the air flow in rooms and around buildings, for example ventilation efficiency. However, when it comes to ventilation and health, so far we find much less information on the prediction options. Ventilation, the flow rate/air exchange rate normally are boundary conditions and not part of the analysis of a design solution, unless it concerns fully naturally ventilated buildings. In practice, however, these are rarely designed and built. But when it comes to infections where airborne transmission is important, ventilation is crucial and depends, for example, on the use of a room and the risk that one wishes to accept. In that case, building code requirements or requirements as set out in prepared program of requirements for specific type of buildings, e.g. through labeling schemes, may not necessarily be sufficient. How do we deal with this? In this article we want to give a brief description of the model that may be used in that case, the Wells-Riley model.