Field measurement of indoor air quality and airborne microbes in a near-zero energy house with an earth tube in the cold region of Japan

Abstract

This study was conducted to evaluate the level of microbial contamination of indoor air during 3 years for two residences in one building equipped with heat recovery ventilation devices and located in Kimobetsu town of Hokkaido, Japan. This article documents a case study aimed at monitoring the microbes contaminations indoors for a safe use of energy saving ventilation devices and sanitary indoor air. This articles describes an investigative approach with three components. First, the authors evaluated the indoor air quality and microbial concentration by comparing the concentrations of particulate matter (PM10 and PM2.5), carbon dioxide, and airborne bacteria and fungi of indoor air and outdoor air during spring, summer and winter. Second, the microbial concentration inside an earth tube and a fixed sensible heat exchanger was evaluated by measuring the airborne microbial concentration of the supply air. Third, the authors assessed the possibility of microbial contamination inside the earth tube using the fungal index and by measuring temperature and relative humidity at the tube's outlet airflow. The results showed that the total concentration of airborne fungi was higher in summer than in spring or winter and that the fungal genera Cladosporium sp. and Penicillium sp. were dominant in the samples. Additionally, it was found that the environment inside the earth tube allowed easy growth of fungi from May to September with the highest fungal index measured in August. It was also confirmed that the earth tube did not affect the supply air for a building constructed 4 years ago.