Effects of Shading and Ventilation Interactions on Outdoor Human Thermal Comfort

Urban heat intensification increasingly exacerbates outdoor thermal comfort, posing challenges for urban planning and climate adaptation. Shading and ventilation are recognized strategies to mitigate thermal stress. However, most studies rely on physical indicators without calibration to local subjective responses. In Taiwan’s hot-humid climate, such approaches may inadequately reflect actual comfort, and the interaction between ventilation and solar radiation remains insufficiently explored. Integrating subjective perceptions with environmental data is therefore critical to refine thermal comfort range and understand how shading and sun exposure modulate ventilation effects.

This study conducted field measurements (Air temperature, Globe temperature, Relative humidity, Wind speed) during the summer of 2025 at shaded and sun-exposed outdoor sites in Tainan, Taiwan. While simultaneously collecting participants’ personal characteristics and multi-dimensional subjective evaluations through questionnaire surveys, including Thermal Sensation Vote (TSV), Thermal Comfort Vote (TCV), Overall Comfort Vote (OCV), and environmental preference votes for temperature, wind, solar radiation, and humidity. Physiological Equivalent Temperature (PET) and mean radiant temperature (Tmrt) were calculated using RayMan Pro and ISO standard, respectively. Statistical analyses were then performed to examine discrepancies between objective physical conditions and subjective perceptions. Furthermore, considering human thermal adaptation under climate change, this study refines the conventional PET comfort range and establishes a localized assessment framework suitable for hot-humid environments.

Results indicate that shading effectively reduces Tmrt, while ventilation enhances convective heat loss and lowers perceived temperature. For PET, ventilated conditions consistently outperformed no-wind scenarios, with reductions of approximately 1°C and 0.7°C in shaded and sun-exposed sites, respectively. Analysis of subjective human responses indicated that under shaded conditions, when wind speed exceeded 0.3m/s, approximately 81% of participants reported thermal comfort, and overall comfort increased with higher wind speeds. In contrast, under sun-exposed conditions, even with increasing wind speeds, TCV and OCV rarely reached the comfort threshold, suggesting that high solar radiation is the dominant factor limiting the effectiveness of ventilation. Nevertheless, when wind speed ranged between 0.3 m/s to 0.9m/s, comfort levels improved for about 20% of participants. Furthermore, using the PET neutral temperature in previous studies as a reference, and accounting for warming trends and thermal adaptation associated with climate change, the subjectively adjusted results indicate that thermal tolerance increases in both shaded and sun-exposed environments.

This study demonstrates that the effectiveness of ventilation is strongly modulated by solar radiation. Under high-radiation conditions, shading should be prioritized to reduce thermal load, with ventilation serving as a complementary strategy to enhance overall comfort. The proposed PET adjustment model improves the accuracy of thermal comfort assessment in hot-humid climates, providing evidence-based guidance for urban planning and architectural design to optimize outdoor thermal environments.