Development of a non-stationary thermal environment analysis method for combined convection and radiation air conditioning

Advanced thermal environment simulation technology has been developing rapidly in recent years. The thermal environment simulation tools used in thermal engineering can be broadly classified into energy simulations and computational fluid dynamics programs. The combination of these approaches allows the high-accuracy prediction of a non-stationary thermal environment in a continuous space. The main feature of the coupled analysis method is that the radiation is calculated using energy simulation, which reduces the analysis load and makes transient analysis possible. Here, a method was devised for predicting the thermal environment of air conditioners and radiant panels, and its accuracy was verified. By coupling the convective heat transfer coefficient, the maximum mean absolute error of the proposed method was calculated to be 0.674 [-], which is acceptable considering the variable environmental conditions. Although in the acceptable range, this error is attributable to computational fluid dynamics, which is a steady-state analysis and does not fully track the non-stationarity of the radiant panel because of its stop–start nature. The results of this analysis are comprehensive, with the convective heat transfer coefficient calculated using the input conditions for each wall. Regarding the energy simulation, when temperature stratification occurred near a surface, such as the ceiling, a small error was induced because the reference temperature was set to the bulk temperature. However, as the overall trend was captured by the analysis method, these minor errors were deemed acceptable. These results show that the proposed method can be applied to a range of applications, including office spaces.