Abstract
Subterranean temperature at a depth of 10 m is almost equal to the average outdoor air temperature of the same area. Therefore, if a building cooling trench is used as an outdoor air duct, outdoor air can be cooled in summer and warmed in winter. This energy-saving technique is often used in Japan. However, since the relative humidity in a cooling trench is high, microbe numbers tend to increase in summer. The present study sought to characterize the microbiome status in the cooling trench of such an office building in Japan. Specifically, we performed a metagenomic analysis in which we analyzed DNA directly upon collection from the environment, without intervening cultivation. The results showed the presence of bacteria of the genera Pseudomonas, Lactobacillus, Nesterenkonia, Staphylococcus, Deinococcus, Acinetobacter, Enhydorobacter, and Corynebacterium. Bacteria of the genera Nesterenkonia, Deinococcus, Enhydorobacter, and Corynebacterium predominated on the surface of the trench. Notably, bacteria of the genus Nesterenkonia constituted >50% of the organisms on the surface of the downstream end of the cooling trench. Principal coordinate analysis was used to compare bacterial inhabitants of outdoor air, indoor air from 2nd- and 3rdfloor offices, and the region downstream of the cooling trench. The results suggested that the microbiome of air in this cooling trench influenced indoor air within the building.
Highlights
The subterranean temperature at a depth of 10 m is almost equal to the annual average outdoor air temperature of the area
The level of airborne bacterial was highest inside the cooling trench, where bacteria achieved a concentration of 2500 cfu/m3
Our results suggested that the temperature, relative humidity, and the
Summary
The subterranean temperature at a depth of 10 m is almost equal to the annual average outdoor air temperature of the area. The cooling trench contained in the structure of an air circulation system allows air to pass into spaces made in underground concrete structures, providing heat exchange and an outdoor load. Subterranean heat originally was used in Japan as a source of heating for combatting snow accumulation in areas of heavy snowfall, the spread of ZEB (Net Zero Energy Buildings) in recent years has led to the use of subterranean heat as a mechanism for reducing air-conditioning cooling loads. If a building cooling trench uses as an outdoor air duct, outdoor air can be cooled in summer and warmed in winter. This energysaving technique often is used in Japan
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