Effects of air and water temperature on thermal comfort in showering: Experiments and modeling in a subtropical region

Showering is integral to the daily life and health of the residents. Proper showering practices can improve sleep quality and regulate mood, whereas excessive heat exposure during showering may pose thermal health risks. This study aimed to investigate the physiological and psychological thermal responses to environmental step changes and water flow impact during the showering process. The thermal responses of 11 subjects to showering under different water temperatures (32, 36, 40, 44 °C) and air temperatures (26, 34 °C) were studied, and two thermal sensation prediction methods were established. Three types of data including environmental parameters, physiological parameters and questionnaire survey were collected. The results showed that, under different conditions during the showering process, skin temperature varied by -2-4 °C, heart rate increased by 4-35 bpm, core temperature rose by 0.1-0.8 °C, thermal sensation vote ranged from -3.3-2.4, and the thermal comfort vote changed by -1.6-1.2. The skin temperature, air temperature, and relative humidity were significantly correlated with dynamic thermal sensation. Accordingly, the thermal sensation model TSV 1 (R 2 = 0.612, RMSE = 0.788) for the entire showering process can better predict the sensation in the step changes. To facilitate practical application, a simplified model TSV 2 (R 2 = 0.923) during the shower was developed based on water temperature, air temperature and relative humidity. Both models can be integrated with a thermal regulation model in smart water heaters to determine optimal shower water temperature and enable bathroom environmental regulation.