Comparison of the hygrothermal performance of two light-framed timber structure buildings under different operation modes

Light-framed timber structure (LTS) buildings have been highly valued in recent years due to their low-carbon characteristics. However, the applicability of the building envelope is closely related to indoor and outdoor conditions. The hot summer and cold winter (HSCW) climate zone in China has high humidity and great temperature variation throughout the year, resulting in distinct outdoor environments in different seasons. The indoor environment is greatly affected by energy-consumption patterns and window-opening habits, which largely depend upon the regulation operations of occupants. All these interrelated factors lead to extremely complex boundary conditions on each side of the building envelope. Whether the structures of LTS buildings are applicable in this climate zone, therefore, needs to be carefully considered. In this study, two LTS buildings with different envelopes were established in Haining, China, situated in the HSCW climate zone, and selected as the study objects. Different operation modes were adopted to create a variety of indoor environments. Under each condition, the processes of heat and moisture transfer within the building envelopes and the indoor environment were monitored and compared. The comparison indicated that the building envelope with high moisture storage and insulation ability maintained a relatively stable indoor environment, especially when the environment changed abruptly. Conversely, if the outdoor environment was equable (e.g., relative humidity within the range of 30%-60%) or intermittent energy consumption modes were adopted, the building envelope with a low thermal inertia index and weak moisture-buffering ability performed better because it enabled a faster response of the indoor environment to air conditioning. Moreover, a high risk of moisture accumulation between the thermal insulation layer and other materials with a large water vapour transfer resistance factor was also identified, suggesting a higher requirement for the vapour insulation of the envelopes of LTS buildings.