Effects of thermal histories on human thermal adaptation to district heating environments: A cross-sectional investigation in the severe cold zone, China

Understanding personalized thermal comfort is critical for creating comfortable indoor environments and achieving energy efficiency. Thermal history has a significant impact on human thermal adaptation, but it has received insufficient attention. Combining field investigation and statistical analysis, this study introduces the thermal neutral rate (TNR) and thermal comfort and acceptability rate (TCAR) to analyze the differences in thermal and humidity responses and adaptability among groups with different thermal histories in northern China. Results show that as subjects acclimatize to indoor environments, their thermal neutral temperature rises, and humid sensation votes approach 'neutral' conditions. Participants with no prior northern thermal history require up to 1 year to adapt to district heating environments, while adaptation to humid environments may take 2–3 years. The thermal neutral temperature of the un-adapted subjects was 18.0 °C, and post-adaptation, it varied within the range of 20.2–21.4 °C. For engineers designing indoor environments, maintaining temperatures within the range of 19.1–22.3 °C meets the comfort and acceptability requirements of participants with different thermal histories in the office. These findings provide evidence for understanding human thermal adaptation mechanisms and give recommended heating temperature ranges for comfortable indoor environments in office buildings in the severe cold zone.