The aim of this study is to clarify the influences of pollutants infiltration from concealed spaces upon indoor air quality in detached houses. The annual changes of pollutant concentrations were calculated using three leakage networks of wooden structures (A: a highly airtight wooden 2x4 stud structure, B: an airtight post-and-beam structure and C: a common post-and-beam structurer). The simulation program “Fresh” was used. The simulation program is based on three methods: a dynamic thermal calculation method using successive integration by Dr. Aratani, a calculation method of ventilation networks using Newmark-beta by Hayashi and Dr. Enai and a calculation method of pollutant concentrations using the ventilation networks by Hayashi. The annual changes of concentrations of pollutants which generate in the concealed spaces (beam spaces and a crawl space) in models with two ventilation systems (an exhaust ventilation system and an exhaust and supply ventilation system) are calculated using the weather data of Tokyo. These simulation results were compared with the measured infiltration ratios from concealed spaces.
The results are the followings:
1. The pollutants move upward by temperature difference and wind pressure and the pollutants infiltrate to the indoor spaces from the concealed spaces.
2. The influence of leakage networks and ventilation systems upon the concentrations of pollutants which generate in the concealed spaces, is not similar to the influence upon those of CO2 and CO which generate in the indoor spaces.
3. The indoor concentrations of pollutants from concealed spaces (beam spaces and a crawl space), are high in the case of the airtight houses (the equivalent leakage area: 2.8 cm2/m2) and the highly airtight houses (the equivalent leakage area: 0.3 cm2/m2), especially in those with exhaust ventilation systems.
4. The similar characteristics of indoor decompression by ventilation systems and infiltration from concealed spaces are seen both in the simulation results and the measurement results.
These results showed that it is necessary to prevent the pollutant infiltration from the concealed spaces according to the building standards on the sick house syndrome enforced in 2003. And the results showed that indoor air quality depends on the airtightness of houses and the decompression by ventilation systems. It is necessary to control air quality in the concealed spaces and to design ventilation networks in consideration of infiltration.
