Impact of the filtration system on the indoor-outdoor particles concentration relationships in an air conditioned office building

The objective of this study is to measure the impact of various classes of filters in the HVAC system on the IAQ in an office building. It aims at understanding outdoor-indoor concentrations and filtration relashionships in order to guide filtration system designs.
Various filters classified G4, F7 and F9 (according to the standard EN 779), new and used, were placed in the HVAC system of an office building ventilated with 100 % outdoor air and located in the suburb of Lyon (southeast France). Particle size distributions were measured outdoors, indoors and in the return duct of the ventilation system (balanced ventilation system).
These data were used to investigate filtration efficiency and relationships between indoor and outdoor particle concentrations.
Results show a dramatic reduction of fine particle using high efficiency filters (F7, F9). As for larger particles (> 1 μm) no significant improvement of IAQ is measured, indoor air can even present higher concentrations of large particles due to the presence of various indoor sources.
A high efficiency filtration system can then be used sucessfully to reduce indoor exposures to fine particles but its impact on total particles concentration is limited. This solution has to be taken into account and integrated in a global approach for a better IAQ.