Transient three-dimensional CFD modelling of ceiling fans: a comparison between detailed and simplified models

Ceiling fans have been widely used for decades for providing thermal comfort in warm environments. They are an effective means of completely avoiding the use of energyintensive air conditioning systems in milder environmental conditions and of reducing the use of such systems in more severe and hotter thermal environments. Ceiling fans can generate an immediate cooling effect on people, as they act on both sensible and latent heat exchange between the human body and the moved air. However, one of the major potential limitations of ceiling fans is that they generate non-uniform velocity profiles, and their effect is highly dependent on the mutual position between body and fan. Thus, it is essential to carefully evaluate the position in which they are installed to maximize their cooling effect where needed by people. CFD is a powerful technique for investigating the air velocity field generated by different ceiling fan configurations. Due to its high demand for computational power and the need for having stable models, previous studies proposed different approaches to model ceiling fans in CFD with some simplifications. As the available computational power increases, so does the possibility of creating more realistic models, but too little is known about when the benefits produced by more complex models are overtaken by their computational costs. The aim of this study was to compare the results obtained by using two approaches to include the ceiling fan into a CFD model, namely a detailed model of the geometry of the fan and a simplified implicit approach that emulates the effect of the fan only. The results illustrate that (a) both models capture the main regions of the air flow, (b) the implicit model provided considerably more accurate air speed values, (c) the computational time of the model with blades is one order of magnitude higher, and (d) fan geometry and meshing are the most critical issues in the model with blades.