Analysis of Ventilation Efficiency as Simultaneous Control of Radon and Carbon Dioxide Levels in Indoor Air Applying Transient Modelling

The impact of ventilation efficiency on radon ((222)Rn) and carbon dioxide (CO(2)) concentrations in the indoor air of a residential building was studied by applying transient data analysis within the CONTAM 3.4 program. Continuous measurements of (222)Rn and CO(2) concentrations, together with basic meteorological parameters, were carried out in an apartment (floor area about 27 m(2)) located in Ljubljana, Slovenia. Throughout the experiment (October 3–15), frequent ventilation (several times per day), poor ventilation (once to twice per day) and no ventilation scenarios were applied, and the exact ventilation and occupancy schedule were recorded. Based on the measurements, a transient simulation of (222)Rn and CO(2) concentrations was performed for six sets of scenarios, where the design ventilation rate (DVR) varied based on the ventilation requirements and recommendations. On the days of frequent ventilation, a moderate correlation between the measured and simulated concentrations (r = 0.62 for (222)Rn, r = 0.55 for CO(2)) was found. The results of the simulation indicated the following optimal DVRs: (i) 36.6 m(3) h(−1) (0.5 air changes per hour, ACH) to ensure a CO(2) concentration below 1000 ppm and a (222)Rn concentration below 100 Bq m(−3); and (ii) 46.9 m(3) h(−1) (0.7 ACH) to ensure a CO(2) concentration below 800 ppm. These levels are the most compatible with the 5C_Cat I (category I of indoor environmental quality, defined by EN 16798-1:2019) scenario, which resulted in concentrations of 656 ± 121 ppm for CO(2) and 57 ± 13 Bq m(−3) for (222)Rn. The approach presented is applicable to various types of residential buildings with high overcrowding rates, where a sufficient amount of air volume to achieve category I indoor environmental quality has to be provided. Lower CO(2) and (222)Rn concentrations indoors minimise health risk, which is especially important for protecting sensitive and fragile occupants.