Experimental study on convective heat transfer coefficients for the human body exposed to turbulent wind conditions

Abstract

Ongoing urbanization and urban densification are leading to an increasing number of tall buildings, giving rise to an increasingly complex urban morphology which, in turn, is complicating the pedestrian-level wind environment of urban areas. As a key climatic element determining pedestrian outdoor thermal comfort, wind is represented in most of the existing outdoor comfort models, but its effects have been oversimplified to date. This study aims to examine how wind velocity and turbulence intensity affect convective heat loss over a human body. A wind tunnel with a turbulence-grid is used to simulate outdoor wind flow with turbulence intensity ranging from 13% to 36%, and wind velocity from 0.7 m/s to 6.7 m/s. Forced convective heat loss for individual body segments have been measured on a thermal manikin using a constant skin temperature regulation mode. Results for unit effect confirm that convective heat loss increases with turbulence intensity, which prompts us to make explicit the turbulence intensity when calculating the heat loss from human body. Ignoring turbulence causes the impact of wind on pedestrian thermal sensation to be underestimated by up to 50%. Based on the present data, regression formula derived from regular geometry for predicting convective heat transfer coefficients has been expanded to serve individual body segments. Accounting for the effect of both wind velocity and turbulence intensity, the accuracy of convective heat loss calculations in outdoor thermal comfort research would be improved.