Comparative evaluation of PET and mPET models for outdoor walking in hot-humid climates

In light of escalating climate change, causing more frequent and severe heatwaves, outdoor walking during the hot weather poses risks of heat stress and health issues. Evaluating pedestrian thermal comfort and physiological responses across varying outdoor environments is crucial. Physiologically Equivalent Temperature (PET) is a widely utilized thermal index, while modified PET was proposed to improve the application in high humidity regions. There has been a lack of comparative evaluations assessing the ability of PET and mPET models to predict physiological responses. This study aims to systematically evaluate the performance of PET and mPET in outdoor walking scenarios. Three typical outdoor environments and two age groups have been considered. Using the measured skin temperature (Tskin) and core temperature (Tcore) as benchmark, this study finds that mPET outperforms PET in dynamic walking processes, irrespective of environmental settings and personnel characteristics. The root mean square errors (RMSE) of Tskin based on PET and mPET estimations were 3.66 °C and 1.04 °C, respectively. While for Tcore, PET and mPET models presented RMSE of 2.02 °C and 0.24 °C, separately. Sensitivity tests highlighted the impact of personal characteristics (e.g., age, sex, weighting, height, etc.) on thermos-physiological responses. PET model overestimated Tcore and Tskin in all outdoor walking scenarios, indicating its limitations. This study contributes by (1) bridging the gap between theoretical modelling and practical applications, aiding in model selection for specific walking scenario; (2) providing valuable insights for improving physiological models, and designing health-conscious urban environments.