Effect of Filter Type in Ventilation Systems on NO2 Concentrations in Classrooms
This study was conducted to assess how different filter types in the ventilation system affect the indoor NO2 concentrations. Measurements were carried out in two classrooms and air intakes in a primary school located in Oslo, Norway. A regular F7 particle filter and an F7 combination filter with activated charcoal lining were compared. NO2 concentrations were measured for five weeks during winter 2017 in a cross-over study design to compare: (1) NO2-levels in classrooms with regular filter (RF) versus combination filter (CF); (2) indoor/outdoor ratio with regular filter versus combination filter. One-hour average concentrations are reported during operating time of the ventilation system (6:00–23:00) and during hours with high (>40 µg/m3) outdoor NO2 concentrations. The measured average NO2 concentrations in both classrooms with an RF were significantly higher than with a CF. The median CF/RF ratios for the two classrooms were 0.50 and 0.81 during hours with high NO2 concentrations, and 0.48 and 1.00 during the period the ventilation system was operational. During hours with high NO2 concentrations, the median indoor/outdoor ratios for the two classrooms with an RF were above 1.00, while the corresponding ratios with a CF were 0.78 and 0.75. Our results demonstrate that a combination filter is more efficient than a regular filter in reducing NO2 concentrations in classrooms during hours with high outdoor concentrations.
KeywordsNO2 Ventilation Filtration School Filter efficiency Indoor Outdoor
We would like to thank Camfil AS who provided the filters and guidance in how to install them in the ventilation system. This paper is based on the master thesis by Kristian Fredrik Nikolaisen, and was a part of the BEST VENT project. BEST VENT is funded by the Research Council of Norway EnergiX program under Grant 255375/E20 together with the following industry partners: Undervisningsbygg Oslo KF, GK Inneklima AS, DNB Næringseiendom AS, Erichsen & Horgen AS, Hjellnes Consult AS, Multi-consult AS, Interfil AS, Camfil Norge AS, Swegon AS, Belimo Automasjon Norge AS, NEAS AS, and Norsk VVS Energi- og Miljøteknisk Forenings Stiftelse for forskning.
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