The effect of positive pressure on indoor air quality in a deeply renovated school building – a case study

This paper is a case study of ventilation and indoor air quality (IAQ) investigations in an extensively repaired comprehensive school in Finland. Our main hypothesis is that positive pressure between air indoors and outdoors can be used for decreasing the concentration of harmful chemical and microbiological agents in indoor air, as well as occupants´ complaints about IAQ, in a building waiting for new repairs or with unsolved IAQ problems. Research was undertaken on a building consisting of 12 classrooms, and served by one air handling unit. It found that the ventilation system was crucially unbalanced. However, IAQ measurements did not explain occupants´ symptoms, which were suspected to be related to the impurities leaked through the building envelope caused by the high negative pressure. To eliminate the potential harmful effects of the building related sources and infiltration airflows, the air handling unit was adjusted to generate a 5-7 Pa positive pressure for a period of 4 months. In the next planned phase of the study, moisture content of the structures during the heating season will be measured, as well as potential changes in perceived IAQ and microbial contamination.