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

Abstract

The impact of ventilation efficiency on radon (222 Rn) and carbon dioxide (CO2 ) concentrations in the indoor air of a residential building was studied by applying transient data analysis within the CONTAM 3.4 program. Continuous measurements of222 Rn and CO2 concentrations, together with basic meteorological parameters, were carried out in an apartment (floor area about 27 m2 ) lo-cated 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 of222 Rn and CO2 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 for222 Rn, r = 0.55 for CO2 ) was found. The results of the simulation indi-cated the following optimal DVRs: (i) 36.6 m3 h−1 (0.5 air changes per hour, ACH) to ensure a CO2 concentration below 1000 ppm and a222 Rn concentration below 100 Bq m−3; and (ii) 46.9 m3 h−1 (0.7 ACH) to ensure a CO2 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 CO2 and 57 ± 13 Bq m−3 for222 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 CO2 and222 Rn concentrations indoors minimise health risk, which is especially important for protecting sensitive and fragile occupants.