Numerical modeling of indoor environment with a ceiling fan and an upper-room ultraviolet germicidal irradiation system

This study proposes a numerical modeling method for the indoor environment with ceiling fans and upper-room ultraviolet germicidal irradiation (UR-UVGI) fixtures. The numerical modeling deployed steady-state Computational Fluid Dynamics (CFD) with a rotating reference frame to simulate the rotation of fan blades. CFD was validated with experimental data of velocity field and fraction of microorganism remaining at the exhaust diffuser. The fraction of microorganism remaining represented the ratio of the concentration of airborne microorganisms measured with UVGI turned on to the one measured with UVGI turned off. According to the validation results, the CFD model correctly reproduced the air movement induced by the rotation of ceiling fan. When the ambient ventilation rate was 2 ACH (air changes per hour) or 6 ACH, the CFD model accurately predicted the average vertical speeds in the section 2.44 m above the floor with the errors less than 10%, regardless of the ceiling fan's rotational direction or speed. In addition, the simulation results showed that the fraction of microorganism remaining increased with the ambient air exchange rate when the fan blew air downward with a rotational speed as high as 235 rpm, which corresponded with the experimental results. Furthermore, the simulation results accurately predicted the fraction of microorganism remaining when the ambient air exchange rate was 2 ACH. We conclude that this novel numerical model can reproduce the effects of ceiling fans and UR-UVGI fixtures on indoor environment, and should aid in the investigation of the impact of ceiling fans on UR-UVGI disinfection efficacy.