The influence of the concealed pollution sources upon the indoor air quality in houses

This report presents the results of investigations on the indoor air quality of common Japanese detached houses. It is necessary to control the emission rates from the interior materials and the ventilation rates to keep indoor concentration of VOC enough low. And it is also necessary to consider the influence of the pollution sources in the concealed spaces for better indoor air quality in some kinds of building structures and some kinds of ventilation systems. In this study the influences of the concealed pollution sources upon the indoor concentrations of pollutants were investigated using three detached houses with four ventilation systems and the following results were obtained. When the ventilation system was changed from the air-supply type to the air-exhaust type, the indoor concentrations of formaldehyde increased. The infiltration ratios: the ratios of the infiltration rate to the indoor space toward the emission rate of a pollutant in the concealed space were measured using the tracer-gas method. The ratios from the beam spaces and the partition were about 100% in most cases. The ratios from the crawl space under the first floor and the truss space under the roof were lower than those from the beam space and partitions in most cases, because those spaces have ventilation openings. But the ratio from the crawl space reached about 100% in the house without ventilation openings at the crawl space. And even in the house with ventilation openings at crawl space, the ratio reached 50% in the house with the exhaust-ventilation system. Therefore, it became clear that the use of the medicine to prevent the deterioration of the wooden structure and the white ants in the crawl spaces must be limited. The ratio from the envelope wall was changed with the pressure difference between inside and outside. These results showed that it is necessary to prevent infiltration from the concealed spaces and to control the emission rate from the concealed pollution sources.