Retrofitting Traditional Western Hunan Dwellings with Passive Strategies Based on Indoor Thermal Environment

The unique architectural style of Western Hunan traditional dwellings must be protected, and their poor indoor thermal environment should also be improved. This investigation sought to determine the optimal passive retrofitting methods for such timber-structure dwellings. An analysis of the thermal environment of a typical traditional dwelling in Western Hunan was carried out by field study and indoor thermal evaluation on the typically coldest and hottest days. Based on the test results, this study calculated the predicted mean vote (PMV) linear fit and the acceptable temperature ranges. Then, the optimum thicknesses of the envelope insulation layer and window-to-wall ratio were evaluated by numerical simulation software based on the thermal performance of different strategies. Finally, according to the thermal performance results of the orthogonal experiments and the calculated acceptable temperature, a final comprehensive retrofitting strategy, using ordinary insulating glass units (12-mm hollow layer), a 0.2 window-to-wall ratio improvement, a polyurethane foam insulation layer (10 mm) for the double-fir external wall envelope, and reed foil (80 mm) for the clay insulation layer roof, was optimized for the existing vernacular dwellings in rural areas of Western Hunan, which can decrease the annual load from 188.38 to 65.99 kW·h/m² and increase the acceptable temperature by 1,159 h over the whole year.