Comparison and modification of measurement and simulation techniques for estimating Tmrt in summer and winter in a severely cold region

Abstract

Abstract Mean Radiant Temperature (Tmrt) is a crucial indicator to assess urban radiant and thermal environments. In this study, Tmrt derived from the globe thermometer method and three simulation models (SOLWEIG, RayMan, and ENVI-met) were analyzed and modified based on the standard six-directional method (Tmrt(six)). Performances of the techniques were compared for two contrasting seasons, summer and winter, and at sites with different degrees of openness. The accuracies of each method were assessed via patterns in time series, coefficient of determination, root mean square error, and Willmott index of agreement. Results showed that globe thermometer method was more suitable for estimating Tmrt in summer than winter, and it showed better performance in more open spaces. The simulation inaccuracies were mainly reflected in winter. Comparatively, SOLWEIG exhibited the best performance in correlation and discrepancy; RayMan presented an advantage in describing the trend consistency of Tmrt than ENVI-met; ENVI-met simulated Tmrt closer to Tmrt(six) than RayMan. Principle-based causes of the techniques’ inaccuracies were analyzed. Correlation and cluster analyses were applied for the globe thermometer method, and global radiation showed the strongest correlation and nearest distance with globe temperature, followed by air temperature. Sensitivity and components analyses were utilized for the simulation models involving isotropic and anisotropic issues considering direct and diffuse radiation, solar position, and surrounding environment. Based on the characteristics of different techniques, multiple nonlinear (introducing equivalent globe temperature) and unary linear regressions were utilized to modify globe thermometer and simulation results, respectively. Both modifications significantly improved Tmrt determination accuracies.