Limitations of Employing a Unified Physiological Equivalent Temperature Scale for Assessing Thermal Comfort in Taiwan’s Cwa Urban Climate

Taiwan’s national reference for outdoor thermal comfort assessment originates from a single non-urban site in a Cfa zone, whereas the country’s most heat-vulnerable metropolitan areas lie in the Cwa zone. Conventional thermal comfort evaluations rely on single standardized scales, which may not fully reflect variation across different climates and outdoor contexts. This study employed the modified physiologically equivalent temperature (mPET) thermal index as a thermal comfort indicator and established a regionally adaptive and mPET-based thermal perception scale suitable for Taiwan’s Cwa climate. Field studies were conducted in two representative Cwa sites—Zhongxing New Village and the Central Taiwan Science Park—and encompassed seven outdoor spaces with distinct spatial functions and microclimatic characteristics. Microclimatic measurements, questionnaire surveys, and user count observations were considered to examine the relationships among thermal conditions, thermal sensation, thermal comfort, and spatial behavior. The results indicate that a neutral temperature for these sites is 23.3 °C mPET and that a 90