Applications of continuous radon monitors

A two month study was carried out during the early spring heating period of 1989, on a slab-on-grade home with an active sub-slab depressurization system to evaluate the required characteristics of a continuous radon monitor/controller. A pulsed ion chamber type radon monitor was used to measure the radon concentrations and a personal computer was used as data logger/controller. Radon levels in the house were monitored for four months in the summer and fall of 1988; prior, during and after mitigation. Based on these analyses, a 37 Bq/m3 (1 pCi/1) control band width was chosen for the active controller with 111 and 74 Bq/m3 (3 and 2 pCi/1) on/off switching points, respectively. Data compiled over a two month period demonstrated the efficacy of the continuous monitor controller system in maintaining an average radon concentration of 78 Bq/m3 (2.1 pCi/1) with an average fan on time of 29.3%. A 60 day composite summary of the controller data revealed a diurnal modulation on the fan duty cycle requirements. In this paper the minimum counting statistics and precision requirements for continuous radon monitors in controlling applications are presented