A validated numerical investigation of the ceiling fan's role in the upper-room UVGI efficacy

Publication date: April 2015
Source:Building and Environment, Volume 86
Author(s): George Pichurov , Jelena Srebric , Shengwei Zhu , Richard L. Vincent , Philip W. Brickner , Stephen N. Rudnick
This investigation quantifies the upper-room ultraviolet germicidal irradiation (UVGI) efficacy in a room with a ceiling-mounted fan that blew air either upwards or downwards at three rotational speeds. The numerical modeling deployed a steady-state passive scalar (Eulerian) and particle tracking (Lagrangian) CFD with a rotating reference frame. Two wall-mounted fixtures horizontally collimated the irradiance field, which was measured with a flat sensor and imported into the numerical models. This study predicted the UVGI efficacy under an extreme range of microorganism susceptibilities to define relationships between the system performance and operational parameters. A mathematical expression with general validity for fraction remaining under perfect air-mixing conditions was analytically developed and used as a performance benchmark. The CFD predictions were validated by the experimental data, expressed as a fraction remaining at the room exhaust for two different microorganisms. Numerical predictions were in a good agreement with the experimental data. In general, the Lagrangian predictions agreed better with the measured data than the Eulerian predictions. Inclusion of a rotating fan significantly improved UVGI performance, but there was no benefit from increasing the fan speed beyond certain values. For this investigation where the microorganism source is located below the fan, the UVGI system performed most efficiently when the fan blew upward, with the optimal performance achieved for the moderate rotational speed of 107 rpm. The highest upper-room UVGI efficacy for this fan setup is due to the airflow and UV light fields enabling a delivery of the highest amount of UV irradiation to the microorganism.