Indoor radon source fluxes: Experimental tests of a two-chamber model

Abstract

Modeling houses as two coupled chambers, namely, the living area and basement, predicts more accurately the total indoor radon source flux from building materials and geology than a one-chamber model in houses with disparate radon concentrations. Three regional surveys found mean radon concentration ratios between basement and living area to range from 1.4 to 4.2, implying weak interchamber coupling in most cases. The invariability of second-order system parameters under steady infiltration but different initial conditions confirms the adequacy of the two-chamber model. The presence of a characteristic radon source flux was detected within the basements of two houses, in one case across different infiltration, coupling, and initial conditions. One-chamber models fit to two-chamber tracer gas data in one house show a source flux variation of a factor of 6 across changing coupling, while the two-chamber source flux variation was only a factor of 1.5. A substantial fraction of the apparent one-chamber living area source flux in these cases is the variable convective radon flux from the basement. The technique is not sensitive enough to detect living area source fluxes if either the interchamber coupling is strong or if the basement source flux is substantially larger.