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, a centrifugal fan of power 136 W was used. The characteristic point of operation of the fan was determined as 370 m³/h air flow rate, with -120 Pa pressure drop in each suction branch with respect to the atmospheric pressure. The radon activity concentration in the sub-slab region (in gravel) was artificially increased by means of a flow-through radon-gas sourceof 3.7 MBq activity. When the performance of the system of the system was tested under an indoor concentration of ~17x10³ Bq/m³, a 75% reduction of the initial concentration was observed within 60 min, although the radon enrichment process in the sub-slab region was going on, and then the concentration kept on decreasing. A considerable radon-concentration increase inside the test-house was never observed while the ASD system was in operation. A pressure drop of about 40 Pa was established under the concrete slab of the test-house while the fan was in operation. For the sake of comparison, a statistical analysis of single radon measurements (each 10 min) was realised to monitor the variation of radon-concentration in time, both when the ASD was on and off. The mean radonconcentration was found as 133 Bq/m³ while the ASD was off, although the same quantity was determined as 15 Bq/m³ when the ASD was on. The occurrence probabilities of EPA action level (148 Bq/m³) was determined as 60% and <1% when ASD was off and on respectively. Similarly, the repetition frequencies of EPA action level was determined as 100 when ASD was off, although this level was not reached at all when the ASD was on.