Space cooling is currently the fastest-growing end-user in buildings. The global warming trend combined with increased population and economic development will lead to accelerated growth in space cooling in the future, especially in China. The hot summer and cold winter (HSCW) zone is the most densely populated and economically developed region in China, but with the worst indoor thermal environment. Relatively few studies have been conducted on the actual measurements in the optimization of insulation design under typical intermittent cooling modes in this region. This case study was conducted in Chengdu—the two residences selected were identical in design, but the south bedroom of the case study residence had interior insulation (inside insulation on all opaque interior surfaces of a space) retrofitted in the bedroom area in 2017. In August 2019, a comparative on-site measurement was done to investigate the effect of the retrofit work under three typical intermittent cooling patterns in the real-life scenario. The experimental result shows that interior insulation provides a significant improvement in energy-saving and the indoor thermal environment. The average energy savings in daily cooling energy consumption of the south bedroom is 42.09%, with the maximum reaching 48.91%. In the bedroom with interior insulation retrofit, the indoor temperature is closer to the set temperature and the vertical temperature difference is smaller during the cooling period; when the air conditioner is off, the room remains a comfortable temperature for a slightly longer time.

In recent years, many scholars worldwide have carried out research related to the relationship between the construction of rural dwellings and the indoor thermal environment in response to the issue of building sustainability. China’s rural revitalization has developed rapidly in recent years. Although previous research showed that the poor indoor thermal environment of vernacular dwellings has negative effects on residents’ thermal comfort and health, it is poorly studied in terms of residents’ space usage habits, their thermal comfort satisfaction, and their thermal sensation. Linyi, the largest and most populous city in Shandong, China, was selected as the research area to investigate the thermal environment and space usage by using in-depth questionnaire interviews and systematical measurements. The results show that there are seasonal differences in space usage in a typical vernacular dwelling. The field measurements show that the indoor temperature is 0–5 °C in winter if there is no heating and 26 °C in summer. By comprehensive comparison, it is found that there is a contradiction between residential space usage and the functional layout; residents choose to use rooms with worse thermal conditions in winter. The analysis of the questionnaires shows that residents have higher satisfaction with the indoor thermal environment in summer than in winter, and the thermal comfort range of residents is 23.3~30 °C in summer and 11.25~17.5 °C in winter. Additionally, the neutral thermal temperature of the indoor space is 26.7 °C in summer and 14.4 °C in winter. Although residents have better adaptability to the cold climate, the measurement data in winter are still beyond the comfort range. We suggest that these results can be used as a reference and data base for improving the living environment of rural vernacular dwellings in Chinese cold regions.