Influences of radiation on the prediction of thermal environment in a transient buoyancy-driven natural ventilation classroom

Abstract

Computational fluid dynamics (CFD) simulations are performed to reveal the significant effects of radiation on predictive accuracy of thermal environment in a transient buoyancy-driven natural ventilation classroom. The present numerical method is verified by the experimental results. The time evolutions of airflow field, radiation heat flux, buoyancy force, and airflow rate are analyzed in detail. In addition, the effects of radiation on thermal comfort are evaluated by three different indices. It is found that radiation plays a critical role in the establishment of the indoor thermal environment. The proportion of radiation heat flux increases with the effective radiation area but decreases with the power of the occupants. Finally, the indoor space can be divided into five different occupied zones depending on how much radiated heat the occupants emit. Radiation can change the indoor heat flux distribution, directly leading to a smaller buoyancy force and ventilation rate. As a result, the thermal comfort except for any draft is linearly affected by both the power and the effective radiation area, and the greater the proportion of radiation heat flux is, the better the indoor thermal comfort is. These conclusions demonstrate that radiation has a noticeable impact on the dynamic evaluations of indoor thermal environment.