Air flow model for sub-slab depressurization systems design

Soil gas pollutants (Radon, VOCs, etc...) entering buildings are known to pose serious health risks to building’s occupants, and various systems have been developed to lower this risk. Soil Depressurization Systems (SDS) are among the most efficient mitigation systems protecting buildings against soil pollutants. Two kinds of SDS are currently used: active and passive systems. Active systems are mainly use fans, which enables the mechanical sub-slab’s air extraction. Passive systems use natural thermal forces and wind effect to extract air from the sub-slab. Until now, no airflow model effective enough has been developed to help design those systems. In this paper, a novel method, based on analytical models of soil gas transfer, is presented to design Soil Depressurization Systems. The developed air flow models take into account various kinds of substructures: slab-on-grade and basement (supported slab and floating slab). These airflow models are integrated in a multizone airflow and heat transfer building code. This integration takes into account various parameters such as meteorological conditions (stack effect, wind), building characteristics (e.g. building envelope, airtightness…) and ventilation systems. Preliminary field verification results for extracted flow using passive sub-slab depressurization in an experimental house are presented and discussed. The results obtained show that, depending on local meteorological conditions and building characteristics, the airflow model is accurate enough, and represents a useful SDS design tool.