Effects of dynamic airflows on convective cooling of human bodies − Advances in thermal comfort assessment and engineering design

Abstract

Dynamic airflows, mainly characterized by turbulence and time-varying mean flow and direction, are increasingly recognized for their positive effects on enhancing the convective cooling of human body in warmer-than-neutral environments, especially at pedestrian-level outdoors where the turbulence is significant. There are two significant implications to sustainable cooling strategy development for thermal comfort: one is the design of novel mechanical fans indoors, and the other is the pedestrian level cooling via the utilization of wind-structure interactions. A literature review was thus conducted focusing on three main topics: dynamic airflows and convective heat transfer coefficient $h_c$, the accurate counting of the convective cooling impacts of dynamic airflows on comfort assessment, and dynamic airflow designs for thermal comfort. This review emphasizes the necessity of considering turbulence intensity, turbulence length scale, and other relevant dynamic airflows characteristics when estimating convective heat transfer over the human body, especially in outdoor pedestrian level. It is concluded that a 10 W/(m²·K) increase in whole-body $h_c$ caused by dynamic airflows is projected to result in a reduction of approximately 0.5 °C in the mean skin temperature and 1 scale in the thermal sensation vote when sedentary under 26.0 °C ≤ T_a ≤ 32.0 °C. Prevailing comfort prediction models and indices appear to have not adequately captured the convective cooling effects of dynamic airflows. Despite progress, application and design of indoor and outdoor dynamic airflows to achieve thermal comfort and energy efficiency under future warmer climates remains a complex challenge.