Evaluating thermal sensation in outdoor environments - Different methods of coupling CFD and radiation modelling with a human body thermoregulation model

Thermal comfort is vital in outdoor spaces for social interaction and recreation. With increases in heat wave events and global warming, it becomes more essential to be able to assess heat stresses. Outdoor spaces have asymmetrical and transient environmental factors such as solar radiation, long-wave radiation and natural wind, which makes the thermal perception outdoors largely different from indoors. Traditional thermal comfort models have some limitations and less accuracy when applied to outdoor spaces. The current study focuses on developing a method to assess the human thermal interaction with the complex outdoor environment and the consequent thermal sensation. Computational Fluid Dynamics (CFD) and radiation modelling are coupled to the Joint System Thermoregulation (JOS-3) model to assess the skin temperature, based on which thermal sensation is predicted using the updated thermal comfort model developed by UC Berkeley. The proposed methodology is applied to assess the thermal sensation of human subjects standing in front of an outdoor radiant cooling hub. The important finding is that the one-way coupling, i.e., no skin temperature feedback to the CFD simulation, works reasonably well in the outdoor environment, and that convective heat transfer coefficients available from experimental studies can be coupled with CFD simulated environmental parameters to obtain more reliable convective heat exchange to avoid meshing the geometry of a human body in CFD and further reduce the computing cost.