Minimum Outdoor Air Supply for Radon in High Rise Residential Buildings - Natural Ventilation v Air-Conditioning Unit

Natural ventilation, as a medium for air exchange between the indoor and outdoor environment, is known for its functions of providing outdoor ‘fresh’ air and removing indoor air pollutants. In this study, the minimum outdoor air ventilation rate required to maintain radon concentration at an acceptable level was determined.
Radon and air change per hour (ac/h) were measured simultaneously and systematically in a concrete high rise residential building (denoted as SP). The radon level and radon emanation rate of SP were about 435 Bq/m3 and 72.48 Bq/m2/h respectively. Modelling results showed that, for the action level of 200 Bq/m3 (according to WHO) and 150 Bq/m3 (HKEPD), the outdoor air supply in SP should exceed 0.61 ac/h and 0.88 ac/h respectively. The average background infiltration in SP was 0.36 ac/h and a window-type airconditioner can deliver 0.74 ac/h. In situ measurements showed that background infiltration in SP was inadequate to suppress indoor radon below 200 Bq/m3 but a well vented air-conditioner was sufficient to achieve that level