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SUB-SLAB DEPRESSURISATION: OVERVIEW OF IMPORTANT FAN
CHARACTERISTICS ILLUSTRATED BY LABORATORY MEASUREMENTS

A.Bossaer, C.Delmotte, P.Voordecker, B.Ingelaere, L.Calberg and P.Wouters
Division of Building Physics and Indoor Climate
Belgian Building Research Institute (BBRI), Rue de la Violette 21-23, 1000 Bruxelles

Within the Belgian Radon Programme the Belgian Building Research Institute is responsible for the
investigation of techniques for prevention and mitigation of radon problems in dwellings. One of the
most regular actions is the installation of a sub-slab depressurisation (SSD) system. As there are no
ready-to-use systems available on the Belgian market, a system has to be designed for every specific
situation. In this case, one of the most difficult points is the choice of an appropriate fan.
Important characteristics are the relation between air flow and pressure difference, the fan power, the
acoustical performances, the durability, the electrical protection, etc. Some of these characteristics
have an influence on the effectiveness of the radon reduction (e.g. air flow vs. pressure difference),
while other parameters are important from the point of view of the occupant (e.g. acoustics,
consumption).
Within the Belgian Radon Programme some of these performances (air flow vs. pressure difference,
fan power vs. pressure difference, acoustics) were measured in the laboratory for a number of fans
(10) available on the Belgian Market. Moreover a comparison was made with two ready-to-use SSD-systems
sold abroad.
The paper will discuss the different characteristics in detail and use the measurement results of the 12
fans as illustrations.
The study revealed that only a limited number of fans is appropriate to be used for a sub-slab
depressurisation. Some remarkable findings:
- Some fans with a high power (and as a consequence a high consumption) seemed to operate at
about the same working point as fans with a much lower power. This means that the fan power is
certainly not a good point of reference to evaluate the efficiency from the radon point of view.
- There seemed to be a very important difference from the acoustical point of view. It is important to
keep in mind that a silent fan will be necessary to assure that the occupier will not stop the
extraction due to irritating noise. The laboratory tests showed that it is possible to reduce the sound
level importantly by the installation of a simple silencer.
Key words: Radon, sub-slab depressurisation, fan, fan power, acoustics, airflow.