Performance test of an active sub-slab depressurization system developed for a radon test-house

A radon Test-House was realised and equipped with an Active Sub-Slab Depressurization (ASD)system to test and quantify its performance as a radon remediation measure. As active element, acentrifugal fan of power 136 W was used. The characteristic point of operation of the fan wasdetermined as 370 m/h air flow rate, with 120 Pa pressure drop in each suction branch withrespect to the atmospheric pressure. The radon activity concentration in the sub-slab region (ingravel) was artificially increased by means of a flow-through radon-gas source of 3.7 MBqactivity. When the performance of the system was tested under an indoor concentration of ~17x10Bq/m, a 75% reduction of the initial concentration was observed within 60 min , although theradon enrichment process in the sub-slab region was going on, and then the concentration kept ondecreasing. A considerable radon-concentration increase inside the test-house was never observedwhile the ASD system was in operation. A pressure drop of about 40 Pa was established under theconcrete slab of the test-house while the fan was in operation. For the sake of comparison, astatistical analysis of single radon measurements (each 10 min) was realised to monitor thevariation of radon-concentration in time, both when the ASD was on and off. The mean radonconcentrationwas found as 133 Bq/m while the ASD was off, although the same quantity wasdetermined as 15 Bq/m when the ASD was on. The occurrence probabilities of EPA action level(148 Bq/m) was determined as 60% and