Exploring dynamic thermal responses during indoor and outdoor walking in summer of a typical cold city of China: Effect of transient thermal stimulation on thermal pleasure

Abstract

Considering thermal alliesthesia, dynamic thermal environments contribute to improving thermal comfort. However, poor spatial organization may lead to uncomfortable stimuli and even pose health risks. The design of outdoor space in cold-climate cities often overlooks coping with hot weather. With the increasing frequency of extreme hot weather, limited shading in cold-climate cities intensifies thermal stimulations between indoor and outdoor areas, exacerbating thermal discomfort. This study examined pedestrians’ dynamic thermal perceptions during transitions between indoor environments and various outdoor areas, including UEB (underneath an elevated building), shaded, and sunlit areas. As a non-invasive technique, infrared facial thermography was used to capture temperature features from 7 facial regions during movement. The results showed that the buffering effect of UEB is superior to shade, which can effectively alleviate the thermal discomfort by 0.7 scales caused by direct sun exposure. The optimal spatial sequence conducive to thermal pleasure was indoor-UEB-sunlit-shade-indoor. When the thermal environment changed, thermal adaptation began to take effect at the 8th minute. Following abrupt changes in outdoor wind speed, both thermal pleasure and facial skin temperature response are delayed by approximately 4 min. For physiological parameters, eyes and cheeks showed the highest correlation with skin temperature. When combined with environmental variables and TSV as model inputs, they achieved a stacked ensemble learning model for predicting thermal pleasure (accuracy of 63%). The findings of this study can guide the passive design of urban walking environments and are attributed to the prediction of pedestrian thermal pleasure in real-time urban thermal comfort monitoring systems.