Comparing the effects of sun and wind on outdoor thermal comfort: A case study based on longitudinal subject tests in cold climate region

Sun and wind are important physical factors that influence outdoor thermal comfort. This study compared the impact of sun and wind on outdoor thermal sensation by analyzing 3546 samples of subject test data during a case study in a cold climate city Tianjin, China. The data was collected from subject tests conducted under air temperatures ranging from 3.8 °C to 35.2 °C (mean 20.2 °C), wind from 0 to 4.8 m/s (mean 0.6 m/s), mean radiant temperature 1.8 to 68.9 °C (mean 36.8 °C) in Tianjin, China. In this particular study, the sun was found to be a more significant factor than wind during the test. Standardized linear regression of the pooled dataset revealed that the contributions of air temperature, sun, wind, and humidity to thermal sensation were 56%, 29.4%, 8.8%, and 5.9%, respectively. When compared under different air temperature ranges, the effect of sun was more than two times greater that of wind. When the air temperature was in the range of 5-10 °C, solar exposure increased the thermal sensation by more than 2 units, but a reduction in wind speed had no observable effect on thermal sensation. When the air temperature was as high as 30-35 °C, increasing the wind by up to 2 m/s lowered the thermal sensation in the shade, but not in the sun. A summary of pedestrian level wind measured in real urban spaces in 28 previous studies indicated that urban spaces generally have low wind speeds, with the median value of mean wind speed of 0.8 m/s. The results of this study provide useful information for designs to creating comfortable urban open spaces.