Quantification of moisture flux from the wall surface in contact with the ground in a semi-underground space based on measurements and hygrothermal analysis

Abstract

Relative humidity tends to be high in underground spaces. One possible cause for this is the moisture flux from the ground, whose effects have rarely been explicitly evaluated. To quantify the influence of moisture flux from the ground on indoor humidity, we performed a year-round field measurement of an unoccupied semi-underground apartment and developed a whole-building hygrothermal analysis of the target room and the surrounding ground. The larger measured annual average indoor absolute humidity than that of outdoor air indicated that the moisture transferred from the ground increased indoor humidity. Furthermore, the calculation results reproducing the measured indoor humidity confirmed the significant influence of moisture flux from the ground on indoor climate by comparing the results of a model in which the moisture flux from the ground was hypothetically masked out. The calculated indoor air moisture balance showed that the moisture flux from the envelopes in contact with the ground was more dominant than that from other envelopes or outdoor air, and that it accounted for more than 80% of the total indoor moisture gain, except in July. The moisture flux was highest in winter (October–January) because the higher temperature of the walls in contact with the ground accelerated moisture evaporation owing to the heat capacity of the ground. This study quantitatively demonstrated the influence of the moisture flux from the ground in a real, uninhabited underground room and the mechanism of its seasonal variations. The findings will contribute to developing countermeasures against high humidity in underground spaces.