Air flow models for sub-slab depressurization systems design

Publication date: May 2015
Source:Building and Environment, Volume 87
Author(s): Thierno M.O. Diallo , Bernard Collignan , Francis Allard
The entry of soil gas pollutants (Radon, VOCs, …) into buildings can cause serious health risks to inhabitants. Various systems have been developed to limit this risk. Soil Depressurization System (SDS) is one of the most efficient mitigation systems to prevent buildings against these pollutants. Two operating modes of SDS are currently used: active and passive systems. Active systems use a fan which enables to extract air from the sub-slab. Passive systems use the stack effect and the wind to extract air from the sub-slab. Until now, no airflow model has been developed that leads to the effective design of these systems. In this paper, an analytical method has been used to develop airflow models to design these systems. The developed models take into account different type of substructures. These models are integrated in a multizone airflow and heat transfer building code. This integration permits to take into account climate conditions (stack effect, wind), building envelope characteristics and ventilation systems. Preliminary field verification results for the extracted flow by the SDS in an experimental building are presented and discussed. The results show that the airflow models are accurate to design SDS. A first application of the models is illustrated by the impact of climate conditions on the operation of the passive SDS. A second application is illustrated by the study of the impact of the ventilation strategies (natural ventilation, exhaust ventilation, supply ventilation and balanced ventilation systems) on the passive SDS operation.