Successful reduction of indoor radon activity concentration via cross-ventilation: experimental data and CFD simulations.

Advanced computational fluid dynamics (CFD) simulations are essential for predicting airflow in ventilated spaces and assessing indoor air quality. In this study, a focus was set on techniques for the reduction of indoor radon-222 activity concentration [Rn], and it is demonstrated how true-to-scale 3D CFD models can predict the evolution of complex ventilation experiments. A series of ventilation experiments in an unoccupied flat on the ground floor of a residential block in Bad Schlema (Saxony, Germany) were performed. Specifically, the 'Cross-ventilation 100 %' experiment resulted in room-specific [Rn] reductions from ∼3000 to ∼300 Bq m. We quantitatively interpreted the results of the ventilation experiment using a CFD model with a k-ϵ turbulent stationary flow model characterised by the used decentralised ventilation system. The model was coupled with a transient transport model simulating indoor [Rn]. In a first approach, the model overestimated the decrease in the starting of the experiment and the steady state. Adjusting the model parameters inflowing radon and inlet velocity the model results are in a good agreement with the experimental values. In conclusion, this paper demonstrates the potential of CFD modelling as a suitable tool in evaluating and optimising ventilation systems for an effective reduction of elevated [Rn].