Computational Hygrothermal Analysis of External Wall Behavior in Naturally Ventilated and Air-conditioned Historical Buildings in Thailand

Moisture in historical buildings has long been a significant problem in Thailand, causing damage to structural elements, wall materials, and indoor air quality. While some issues are attributed to inherited structural systems, many result from changes in space use, particularly the introduction of air-conditioning, which alters hygrothermal performance. This study examines heat and moisture transfer in historical buildings using computational hygrothermal analysis (WUFI), comparing air-conditioned and naturally ventilated cases, with and without wall-cutting interventions, in Thailand’s hot-humid climate. The results present the average water content (kg/m³) in exterior walls across three upper sections and one lower section under both conditions. The findings indicate that in air-conditioned historical buildings, water content in the middle and bottom sections of the upper exterior wall is influenced by dry, lower-temperature indoor conditions. The reduced relative humidity of conditioned air promotes higher evaporation, lowering the damp rise height and reducing water content by 2.83 and 5.13 kg/m³ in the middle and bottom sections of the upper wall, respectively, compared with naturally ventilated cases. The air-conditioning system has only a slight effect on the hygrothermal behavior of retrofitted walls after wall-cutting interventions, with an approximately 2 kg/m³ higher water content across all upper sections in the conditioned case compared with the naturally ventilated case. Meanwhile, wall cutting has a greater effect in unconditioned spaces, with larger reductions in water content above the cut but increased moisture below due to redistribution.