Determination of pressure distribution and radon-laden soil-gas flow conditions induced by an active sub-slab depressurization system

A test-house was realised and equipped with an Active Sub-Slab Depressurization (ASD) systemwith two suction branches. As the active element, a centrifugal fan of power 136 W was used. Thecharacteristic point of operation of the fan was determined as 370 m/h air flow rate, with -120 Papressure drop in each suction branch with respect to the atmospheric pressure. The radon activityconcentration in the sub-slab region (in gravel) was increased by means of a flow-through radongassource of 3.7 MBq activity. Pressure distribution characteristics in the gravel-bed under theconcrete slab, induced by the ASD system, was determined. About 40 Pa of pressure drop on theaverage was established under the concrete slab (in gravel) of the test-house while the fan was inoperation. Similarly, the corresponding velocity distribution of the radon-bearing soil-gas wasalso determined, the soil-gas velocity was found roughly as 0.14 m/s, and the correspondingReynolds Number (Re) was calculated as 210, indicating that the flow was turbulent and thereforenon-Darcian. When the ASD system was not in operation, in other words when the fan was off, theReynolds Number was calculated as less than 10 (Re > 1)indicating that the flow was laminar [4]and therefore Darcian The corresponding soil-gas velocity was experimentally determinedapproximately as ~0.7x10? m/s.