Efficient indoor radon reduction by over pressure ventilation

Since new radon risk maps for Germany were published in 2021, in Saxony the highest spatial accumulation of precautionary areas can be found. Reasons are the geological subsoil like the Ore Mountains, as well as a historical mining industry and intensive uranium mining from 1946 to 1990.

Close to a heap, various ventilation experiments for indoor radon reduction were performed in a two-room flat (ground floor) in Bad Schlema (Germany). As an innovative approach to eliminate indoor radon and prevent new radon from entering, the focus is on creating an over pressure within the flat. This developed ventilation mode, which aims to ensure that more fresh air enters the room than leaves it, is called differential pressure mode with a forced over pressure.

Therefore, a decentralised ventilation system with heat-recovery from inVENTer (Germany) was installed. Throughout numerous different ventilation experiments, radon activity concentrations [Rn] were continuously measured in all rooms (including basement and balcony) using Radon Scout Plus devices from SARAD (Germany). Thereby, room-specific radon behaviour with and without ventilation was found.

Despite a strong seasonal trend with significantly higher indoor radon levels in Sep.-Nov. and Dec.-Feb. than in June-Aug., an overall reduction of indoor radon of up to 80 % was achieved. Important to mention is that different ventilation modes in combination with different fan performance levels resulted in different indoor radon reductions.

Here, in particular, the experiments with forced over pressure (up to +5 Pa) led to significant results in summer and winter, even in rooms with higher [Rn]. For example, measured [Rn] of 7.000 Bq/m³ within the kitchen could be reduced to 300 Bq/m³ and maintained for the entire duration of the respective ventilation experiment.

In this work, the performed experiments as well as the room-specific ventilation effect will be presented. Furthermore, this work analyses the dependencies between the reduction of indoor radon activity concentration and the corresponding environmental parameters.