Effect of the envelope structure on the indoor thermal environment of low-energy residential building in humid subtropical climate: In case of brick–timber vernacular dwelling in China

The brick–timber structure plays a crucial role in creating a comfort indoor thermal environment for low-energy vernacular dwellings. Herein, the thermal environment of the dwelling was studied by DesignBuilder software and evaluated using Adaptive Predicted Mean Vote (APMV) index. These results revealed that the indoor damp and cold feelings intensified in winter, and the mountain as a natural wind barrier weakened the attack of the prevailing wind in winter. These results leaded that the wind speed of the tested room was lower than 0.1 m/s. The thermal comfort satisfactory days in a year accounts for 56.2%, and the overall level of indoor thermal environment was low in the rest of the year, especially in winter. The simple structure of the exterior envelope and the single material were the main reasons for the poor indoor thermal environment of naturally ventilated buildings. Therefore, optimization strategies such as increasing the insulation materials of the envelope and adopting insulating glass windows were proposed. Compared to that before the retrofitting, the overall thermal environment grade of the vernacular dwelling has been improved by 4.7% (grade I), -0.3% (grade II) and -4.3% (grade III), respectively. The poor thermal performance and airtightness of the envelope easily lead to the negative effect of outdoor cold, heat and water vapor entering the house, which affects the thermal environment grade. These conclusions provided a reference for the optimization of the thermal environment of existing low-energy vernacular dwellings in subtropical humid climate areas.