Relationship between indoor and outdoor temperatures in winter in the Hot Summer and Cold Winter Zone of China - Considering two sources of outdoor temperatures and different indoor heating methods

Thermal exposure is a global issue related to health. Environmental health studies often overlook indoor temperature in comparison to outdoor temperature. Exploring indoor and outdoor temperatures and their relationship is an important part to understand individual heat exposure. The aim of this study is to explore the indoor and outdoor temperatures and their relationship during winter, using weather station and ERA5-Land reanalysis outdoor temperature. Field experiments were conducted in both districting heating and non-district heating dwellings in the Hot Summer and Cold Winter zone of China, taking into account the influence of cold spells. Significant linear correlation was found between the weather station and reanalysis outdoor temperature. The indoor temperature of the district heating group was 8.4 °C higher than that of the non-district heating group. When the outdoor temperature approached 0 °C, the indoor-outdoor temperature difference of the district heating group was twice that of the non-district heating group. The non-district heating group experienced greater fluctuations in indoor temperature during the cold spell. The outdoor temperature could only partially explain indoor temperature, especially under the condition of district heating. The study suggests that outdoor temperature alone is insufficient when evaluating individual thermal exposure in winter. Furthermore, occupants with district heating and non-district heating may have different vulnerabilities, and thermal safeguard strategies in winter are suggested to be designed more targeted. This study may provides insights from the perspective of thermal environment for temperature and health studies.