Numerical modeling of upper-room UV germicidal irradiation — Validation and performance comparison under various airflow regimes in a generic enclosure

Given the critical importance of containing the spread of infectious airborne pathogens in indoor environments, ultraviolet germicidal irradiation (UVGI) has become increasingly adopted as a non-intrusive technology for controlling microbiologic infections in these settings. However, modeling the disinfection process of UVGI in indoor environments poses challenges because it involves multiple complex physical processes, which are additionally transient in nature. Computational fluid dynamics (CFD) simulations are frequently used to evaluate UVGI performance. Nevertheless, the modeling of such intricate systems is not straightforward and can often be computationally expensive. Here we demonstrate a relatively simple and computationally inexpensive approach using an Eulerian-Eulerian model in CFD to simulate airborne biopollutant transport and UVGI disinfection in a generic enclosure, representing a room. This approach incorporates volumetric biopollutant sinks based on first-order kinetics to approximate the decay of an airborne biopollutant under a UV irradiation field. Subsequently, we validate this numerical approach using recent experimental data from the literature. Finally, we discuss the transient behavior and performance of UVGI disinfection under various airflow regimes relevant to indoor building applications. Specifically, we explore the effects of air mixing, in order to support the biopollutant dispersion, ventilation supply, and the influence of a biopollutant source. The results underscore the significance of air mixing in enhancing the performance of UVGI disinfection under transient and non-equilibrium system conditions.