Dewdrop and evaporation rates were measured in the inner space of an old mound located in the Gifu Prefecture, Japan. The measurement was carried out using five evaporation sensors that were recently developed by the present authors. Spatial temperature variability was observed over the wall surface of the space. It was clearly found that the dewdrop and the evaporation occur at the lower and the higher temperature parts on the wall surface, respectively. The total amount of the dewdrop was almost equal to the total evaporation in the space. This nature indicates that the vapor condensed as dewdrop on the lower temperature part in the space is continuously supplied by the evaporation from the higher temperature part. It can be concluded that the temperature variability is the most important agent that creates dewdrop in the underground space.
A numerical simulation technique by which the temperature distribution over the wall surface of an underground spase can be calculated is also proposed in this paper. The main part of the technique is the numerical calculation of the unsaturated groundwater flow and the heat transfer around the space. The spatial distribution of the dewdrop and the evaporation rates over the wall surface and the seasonal change of the distribution were successfully estimated by this technique.