For the Evaluation of Thermal Environmental Indices in Outdoor Spaces during Heatwaves : A Modified Regression Equation Study

Purpose: PMV and UTCI are key indices encompassing all major factors for assessing human thermal comfort. However, due to the complexity of calculations and significant errors arising from the inclusion of all these factors, there is a need for research on simpler indices that can be more easily applied. Therefore, in this study, we propose a modified formula for analyzing and evaluating thermal comfort in outdoor spaces during heatwaves, based on data collected in actual outdoor environments. Method: Employing the Stepwise method in multiple regression analysis, we analyzed existing PMV and UTCI to derive a modified regression model. Temperature (Ta), radiant temperature (Tr), relative humidity (RH), metabolic rate (Met), and clothing insulation (Clo) were used as variables. Result: The PMV equation demonstrated 99.3% explanatory power, while the UTCI equation showed 99.7%. The significance of deriving these formulas lies in the fact that they are based on data collected from outdoor environments rather than theoretical values. Especially considering the high accuracy but challenging usability of PMV and UTCI as evaluation metrics, once the reliability of the modified regression equations is confirmed, they are expected to be widely utilized in future research.