Systems theory approach for a reconstruction method to estimate the rate of air change by measuring the indoor radon concentration

Energy renovation works on buildings can cause disturbance of the indoor air quality. As part of the whole project to determine the rate of air change from measurements of radon concentration, a system-theoretical approach is developed, which makes it possible to determine the rate of air exchange from the measured temporal course of the radon activity concentration under everyday conditions, and bring it in connection with the indoor air quality. The determination of the rate of air exchange can be accomplished in two steps. The first step is an initial measurement of a few hours to calculate the radon source strength by low and constant air change rate. The radon source strength contains the complete characterization of the examination area. In the second step, using the reconstruction method [1], the rate of air change can be determinate from a long term measurement of radon concentration occurring under everyday conditions. In the context of this paper, a numerical method is developed using the systemtheoretical considerations, which determine an efficient source strength and reconstructs the rate of air change from the measured radon concentration course as noiseless as possible. The main challenges here are, identifying and highlighting relevant signal characteristics and the suitable choice of filter for suppression of artifacts and signal noise. This method could be verified by practical experiments in a constructed test chamber, and thus delivers a tool to determine the course of the air exchange rate from diverse noisy measurements of radon concentration course. (orig.)