Upper-room Ultraviolet Germicidal Irradiation System Research Articles

Air disinfection performance of upper-room ultraviolet germicidal irradiation (UR-UVGI) system in a multi-compartment dental clinic

Multi-compartment dental clinics present significant airborne cross-infection risks. Upper-room ultraviolet germicidal irradiation (UR-UVGI) system have shown promise in preventing airborne pathogens, but its available application data are insufficient in multi-compartment dental clinics. Therefore, the UR-UVGI system's performance in a multi-compartment dental clinic was comprehensively evaluated in this study. The accuracy of the turbulence and drift flux models was verified by experimental data from ultrasonic scaling. The effects of the ventilation rate, irradiation zone volume, and irradiation flux on UR-UVGI performance were analyzed using computational fluid dynamics coupled with a UV inactivation model. Different patient numbers were considered. The results showed that UR-UVGI significantly reduced virus concentrations and outperformed increased ventilation rates alone. At a ventilation rate of six air changes per hour (ACH), UR-UVGI with an irradiation zone volume of 20% and irradiation flux of 5 μW/cm2 achieved a 70.44% average virus reduction in the whole room (WR), outperforming the impact of doubling the ventilation rate from 6 to 12 ACH without UR-UVGI. The highest disinfection efficiency of UR-UVGI decreased for WRs with more patients. The compartment treating patients exhibited significantly lower disinfection efficiency than others. Moreover, optimal UR-UVGI performance occurs at lower ventilation rates, achieving over 80% virus disinfection in WR. Additionally, exceeding an irradiation zone volume of 20% or an irradiation flux of 5 μW/cm2 notably reduces the improvement rates of UR-UVGI performance. These findings provide a scientific reference for strategically applying UR-UVGI in multi-compartment dental clinics.

Evaluation of upper-room ultraviolet germicidal irradiation system for air disinfection and energy conservation in multi-patient ward

High occupancy rates significantly increase the risk of airborne transmission of respiratory infectious diseases in multi-patient wards. While increasing air supply can effectively reduce airborne transmission, it also substantially raises energy consumption. Therefore, developing low-energy methods in multi-patient wards to suppress airborne transmission is essential. This study aims to evaluate the inactivation performance of upper-room ultraviolet germicidal irradiation (UVGI) against SARS-CoV-2 virus aerosols in a typical multi-patient ward using computational fluid dynamics at different ventilation rates, as well as its energy-saving effects. Upper-room UVGI reduced the virus aerosol concentrations, with a maximum decrease of up to 159 copies/m3 in the occupied zone (zone less than 2.1 m in height) observed at 8 ACH. However, increased ventilation rates limited the inactivation performance of upper-room UVGI. Two parameters of UVGI, irradiation height and irradiation flux, had been detailly evaluated. Elevating the irradiation height of upper-room UVGI could significantly enhance the inactivation performance. Increasing irradiation height from 0.3 to 0.6 m reduced the concentrations in the occupied zone by up to 11 copies/m3, while a further increase to 0.9 m decreased the concentrations by up to 55 copies/m3. However, increasing irradiation flux could only approximately linearly enhance the virus aerosol inactivation performance of upper-room UVGI. The energy consumption evaluation of upper-room UVGI shows that UVGI activation could conserve 100 kWh per year in one multi-patient ward, with a maximum saving of 333.7 kWh. These findings provide insights into the setups strategies and the energy-saving performance of upper-room UVGI systems in multi-patient wards.

Reducing airborne transmission of SARS-CoV-2 by an upper-room ultraviolet germicidal irradiation system in a hospital isolation environment

Upper-room ultraviolet germicidal irradiation (UVGI) technology can potentially inhibit the transmission of airborne disease pathogens. There is a lack of quantitative evaluation of the performance of the upper-room UVGI for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) airborne transmission under the combined effects of ventilation and UV irradiation. Therefore, this study aimed to explore the performance of the upper-room UVGI system for reducing SARS-CoV-2 virus transmission in a hospital isolation environment. Computational fluid dynamics and virological data on SARS-CoV-2 were integrated to obtain virus aerosol exposure in the hospital isolation environment containing buffer rooms, wards and bathrooms. The UV inactivation model was applied to investigate the effects of ventilation rate, irradiation flux and irradiation height on the upper-room UVGI performance. The results showed that increasing ventilation rate from 8 to 16 air changes per hour (ACH) without UVGI obtained 54.32% and 45.63% virus reduction in the wards and bathrooms, respectively. However, the upper-room UVGI could achieve 90.43% and 99.09% virus disinfection, respectively, with the ventilation rate of 8 ACH and the irradiation flux of 10 μW cm−2. Higher percentage of virus could be inactivated by the upper-room UVGI at a lower ventilation rate; the rate of improvement of UVGI elimination effect slowed down with the increase of irradiation flux. Increase irradiation height at lower ventilation rate was more effective in improving the UVGI performance than the increase in irradiation flux at smaller irradiation height. These results could provide theoretical support for the practical application of UVGI in hospital isolation environments.

CFD modeling of room airflow effects on inactivation of aerosol SARS-CoV-2 by an upper-room ultraviolet germicidal irradiation (UVGI) system

Ultraviolet germicidal irradiation (UVGI) systems inactivate microorganisms indoors. Upper-room UVGI systems use wall- or ceiling-mounted fixtures to create an air disinfection zone above the occupied zone. The performance of upper-room UVGI systems varies with indoor airflow patterns induced by mechanical ventilation and thermal plumes from indoor heat sources. Little information is available on the effects of ventilation strategies on upper-room UVGI system performance for the control of viral aerosols in occupied spaces. This study simulated the effects of ventilation system characteristics in an office space on the ability of an upper-room UVGI system to inactivate viral aerosols with UV-C susceptibility representative of coronaviruses. UVGI reduced viral aerosol concentration by two orders of magnitude relative to the concentration without UVGI. Air change rates and air distribution strategy (mixing vs. displacement) had notable effects on the effectiveness of the UVGI system. For mixing ventilation, as the recirculation airflow rate increased from 0 to 5.3 h−1 for a room volume of 108 m3 with a fixed outdoor air change rate of 0.7 h−1, UVGI inactivation increased by 96.7%. Mixing ventilation with 100% outdoor air of 0.7 h−1 yielded airborne virus inactivation that was double that of displacement ventilation, due to enhanced air mixing.

Effect of ventilation strategy on performance of upper-room ultraviolet germicidal irradiation (UVGI) system in a learning environment

Upper-room ultraviolet germicidal irradiation (UVGI) system is recently in the limelight as a potentially effective method to mitigate the risk of airborne virus infection in indoor environments. However, few studies quantitatively evaluated the relationship between ventilation effectiveness and virus disinfection performance of a UVGI system. The objective of this study is to investigate the effects of ventilation strategy on detailed airflow distributions and UVGI disinfection performance in an occupied classroom. Three-dimensional computational fluid dynamics (CFD) simulations were performed for representative cooling, heating, and ventilation scenarios. The results show that when the ventilation rate is 1.1 h−1 (the minimum ventilation rate based on ASHRAE 62.1), enhancing indoor air circulation with the mixing fan notably improves the UVGI disinfection performance, especially for cooling with displacement ventilation and all-air-heating conditions. However, increasing indoor air mixing yields negligible effect on the disinfection performance for forced-convection cooling condition. The results also reveal that regardless of indoor thermal condition, disinfection effectiveness of a UVGI system increases as ventilation effectiveness is close to unity. Moreover, when the room average air speed is >0.1 m/s, upper-room UVGI system could yield about 90% disinfection effect for the aerosol size of 1 μm–10 μm. The findings of this study imply that upper-room UVGI systems in indoor environments (i.e., classrooms, hospitals) should be designed considering ventilation strategy and occupancy conditions, especially for occupied buildings with insufficient air mixing throughout the space.

Pulsating jet ventilation add-ons performance for reducing the contaminant spread in classrooms: Portable air cleaners vs. upper room UVGI

This paper examines the extent to which “add-on” cleaning devices in a classroom ventilated with a pulsating jet ventilation (PJV) system are able to reduce the contaminant spread risks between students when one of them is infected. Two types of “add-on” devices are investigated: portable air cleaners (PACs) and upper room ultraviolet germicidal irradiation (UR-UVGI) lamps. The cleaning effectiveness of each system is evaluated by comparing the contaminant concentration reduction ratio (CR) within the breathing layer in each group of students and the intake fraction (iF) with their corresponding values of standalone PJV operation under the same conditions. Detailed 3D computational fluid dynamic (CFD) models were developed and validated against published experimental data. A parametric analysis was performed by varying the PJV supply flowrate and its period of intermittency to establish the PJV operating conditions that maximize the cleaning and protection effectiveness of each “add-on” device at acceptable thermal comfort and CO2 levels.It was found that for maximum cleaning effectiveness, the PJV system is recommended to operate with an UR-UVGI system at supply flowrate between 250 l/s and 350 l/s with a range of intermittency periods between 4 min and 5 min. However, for a maximum protection against cross-contamination, the PJV system should operate with PAC devices at 400 m3/h for PJV flowrate ranging between 250 l/s and 350 l/s irrespective of the intermittency period with iFmax values between 1.47×10−4 and 0.67×10−4. The addition of “add-ons” resulted in a maximum of 7% increase in the overall energy consumption.

Performance of upper-room ultraviolet germicidal irradiation (UVGI) system in learning environments: Effects of ventilation rate, UV fluence rate, and UV radiating volume

• We study performance of upper-room ultraviolet germicidal irradiation (UVGI) systems. • Performance of upper-room UVGI system in a classroom varies with ventilation rate. • Non-uniform airflow pattern meaningfully influences the UVGI system performance. • UV radiating volume is more crucial for virus disinfection than UV fluence rate. • Doubling UV fluence rate from 25 to 50 μW∙cm-2 yields only moderate benefit. Previous studies show that upper-room ultraviolet germicidal irradiation (UVGI) systems can help contain infectious airborne viruses indoors. However, there has been a lack of research on the performance of an upper-room UVGI system in learning environments such as a school classroom. Since classrooms are more vulnerable to airborne transmission of diseases due to high occupancy for long hours, airborne infection characteristics are different from other occupied indoor environments (e.g., offices and residences). The objective of this study is to investigate UVGI system performance in a classroom considering detailed effects of ventilation rate, UV fluence rate, and UV radiating volume. Two analytical models, a one-zone and a two-zone material balance model, along with computational fluid dynamics (CFD) simulations, were employed to analyze viral aerosol concentrations under a representative range of classroom operating conditions. The CFD results show that increasing ventilation rate from 1.1 h –1 to 5 h –1 yields about 85% of airborne disinfection while doubling UV radiating volume results in a 60% disinfection. However, increasing UV fluence rate from 25 μW∙cm –2 to 50 μW∙cm –2 yields a moderate additional disinfection of 18%. Overall, the study results reveal that operating a UVGI system in an occupied classroom can markedly disinfect airborne viruses up to 96%, which is as effective as increasing ventilation rate more than five times. Furthermore, the results suggest that the one-zone and two-zone analytical models used in several previous studies could result in notably meaningful errors in analyzing viral aerosol concentrations, especially in occupied rooms with a highly non-uniform airflow distribution.

Evaluation of UR-UVGI System for Sterilization Effect on Microorganism Contamination in Negative Pressure Isolation Ward

A negative pressure isolation ward prevents the outflow of airborne microorganisms from inside the ward, minimizing the spread of airborne contamination causing respiratory infection. In response to recent outbreaks of severe acute respiratory syndrome (SARS) and Middle East respiratory syndrome (MERS), Korea has increased the number of these facilities. However, airborne contaminants that flow into the ward from adjacent areas may cause secondary harm to patients. In this study, the sterilization effect of upper-room ultraviolet germicidal irradiation (UR-UVGI) on microorganisms generated within the negative pressure isolation ward and those flowing inward from adjacent areas was evaluated through field experiments and computational fluid dynamics (CFD) analysis, to assess the potential of this approach as a supplementary measure to control such microorganisms. The sterilization effect was found to be not high because of high-level ventilation. CFD analysis under various conditions shows that the sterilization effect for indoor-generated microorganisms varies with the level of UV radiation, the source locations of the indoor-generated microorganisms, air supplies and exhausts, the UVGI system, and the airflow formed under the specified conditions. Our results show that when the UVGI system is installed in the upper part of the ward entrance, contaminated air from adjacent area is strongly sterilized.

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

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.

Modeling infection risk and energy use of upper-room Ultraviolet Germicidal Irradiation systems in multi-room environments

The effectiveness of ultraviolet irradiation at inactivating airborne pathogens is well proven, and the technology is also commonly promoted as an energy-efficient way of reducing infection risk in comparison to increasing ventilation. However, determining how and where to apply upper-room Ultraviolet Germicidal Irradiation devices for the greatest benefit is still poorly understood. This article links multi-zone infection risk models with energy calculations to assess the potential impact of a Ultraviolet Germicidal Irradiation installation across a series of inter-connected spaces, such as a hospital ward. A first-order decay model of ultraviolet inactivation is coupled with a room air model to simulate patient room and whole-ward level disinfection under different mixing and ultraviolet field conditions. Steady-state computation of quanta-concentrations is applied to the Wells–Riley equation to predict likely infection rates. Simulation of a hypothetical ward demonstrates the relative influence of different design factors for susceptible patients co-located with an infectious source or in nearby rooms. In each case, energy requirements are calculated and compared to achieving the same level of infection risk through improved ventilation. Ultraviolet devices are seen to be most effective where they are located close to the infectious source; however, when the location of the infectious source is not known, locating devices in patient rooms is likely to be more effective than installing them in connecting corridor or communal zones. Results show an ultraviolet system may be an energy-efficient solution to controlling airborne infection, particularly in semi-open hospital environments, and considering the whole ward rather than just a single room at the design stage is likely to lead to a more robust solution.

Computational fluid dynamics modelling and optimisation of an upper-room ultraviolet germicidal irradiation system in a naturally ventilated hospital ward

Ultraviolet germicidal irradiation (UVGI) has been shown to be an effective technology for reducing the airborne bioburden in indoor environments and is already advocated as a potential infection control measure for healthcare settings. However, much of the understanding of UVGI performance is based on experimental studies or numerical simulation in mechanically ventilated environments. This study considers the application of an upper-room UVGI system in a naturally ventilated multi-bed hospital ward. A computational fluid dynamics model is used to simulate a Nightingale-type hospital ward with wind-driven cross-ventilation and three wall-mounted UVGI fixtures. A parametric study considering 50 different fixture configurations and three ventilation rates was carried out using a design of experiments approach. Each configuration was assessed by calculating the UV dose distribution over the ward and at each bed. Results show that dose is influenced by the location of the fixtures and the ventilation regime. Thermal effects are likely to be important at low ventilation rates and may reduce UV effectiveness. A metamodel-based numerical optimisation was applied at a ventilation rate of 6 air changes per hour. In this case, the optimum result is achieved when UVGI fixtures are mounted on the leeward wall at their lowest mounting height.

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.

Eggcrate UV: a whole ceiling upper-room ultraviolet germicidal irradiation system for air disinfection in occupied rooms

A novel whole ceiling upper-room ultraviolet germicidal irradiation (UVGI) system [eggcrate ultraviolet (UV)] has been developed that incorporates open-cell 'eggcrate'-suspended ceiling panels and bare UV lamps with a ceiling fan. Upper-room UVGI is more effective for air disinfection than mechanical ventilation at much lower installation and operating costs. Conventional upper-room UVGI fixtures employ multiple tightly spaced horizontal louvers to confine UV to the upper-room. These louvered fixtures protect occupants in the lower-room from UV-induced eye and skin irritation, but at a major cost to fixture efficiency. Using a lamp and ballast from a conventional upper-room UVGI fixture in the eggcrate UV system, the germicidal efficacy was markedly improved even though the UV radiation emitted by the lamp was unchanged. This fundamental change in the application of upper-room UVGI air disinfection should permit wider, more effective application of UVGI globally to reduce the spread of airborne infection.

Using Computational Fluid Dynamics Modeling to Evaluate the Design of Hospital Ultraviolet Germicidal Irradiation Systems for Inactivating Airborne Mycobacteria†

This research was conducted to evaluate the design of hospital ultraviolet germicidal irradiation (UVGI) systems and to assess their effectiveness for inactivating airborne mycobacteria. A computational fluid dynamics (CFD) model was developed and tested by simulating previous experiments measuring the effectiveness of a lab-based UVGI system. Model testing showed reasonable agreement with experimental measurements. The model captured trends similar to the experiments: Effectiveness of an upper-room UVGI system is higher when there is no ventilation compared with when there is ventilation, and wintertime ventilation conditions can markedly decrease the performance of an upper-room UVGI system. The CFD model was then applied to evaluate the design of three hospital patient rooms. A patient and an exam room with upper-room UVGI systems, and a patient room with an exhaust duct system were studied. Results showed that one of the UVGI systems was not very effective, due to the very efficient ventilation design. The other two configurations were reasonably to very effective at inactivating airborne mycobacteria. The most effective application was the one in which the room air-exchange rate was very low. CFD modeling can be useful for assessing whether hospital UVGI installations and ventilation systems are effective for infection control.

Minimizing the exposure of airborne pathogens by upper-room ultraviolet germicidal irradiation: an experimental and numerical study.

There has been increasing interest in the use of upper-room ultraviolet germicidal irradiation (UVGI) because of its proven effectiveness in disinfecting airborne pathogens. An improved drift flux mathematical model is developed for optimizing the design of indoor upper-room UVGI systems by predicting the distribution and inactivation of bioaerosols in a ventilation room equipped with a UVGI system. The model takes into account several bacteria removal mechanisms such as convection, turbulent diffusion, deposition and UV inactivation. Before applying the model, the natural die-off rate and susceptibility constants of bioaerosols were measured experimentally. Two bacteria aerosols, Escherichia coli and Serratia marcescens, were tested for this purpose. It was found out that the general decay trend of the bioaerosol concentration predicted by the numerical model agrees well with the experimental measurements. The modelling results agree better with experimental observations for the case when the UVGI inactivation mechanism dominates at the upper-room region than for the case without UVGI. The numerical results also illustrate that the spatial distribution of airborne bacteria was influenced by both air-flow pattern and irradiance distribution. In addition to predicting the local variation of concentration, the model assesses the overall performance of an upper-room UVGI system. This model has great potential for optimizing the design of indoor an upper-room UVGI systems.

A new mathematical model for irradiance field prediction of upper-room ultraviolet germicidal systems

There has been an increasing interest in the use of upper-room ultraviolet germicidal irradiation (UVGI) system because of its proven disinfection effect for airborne microorganisms. To better design and explore further potential applications of UVGI systems, it is of critical importance to predict the spatial UV intensity in enclosures. In this paper, we developed a new mathematical model to predict spatial radiation intensity for upper-room ultraviolet germicidal irradiation systems. The detail geometries of the lamp and the reflector were removed and replaced by introducing a fictitious irradiation surface near louver slots. The view factor approach was applied to evaluate the UV irradiance in a three-dimensional space with different louver configurations. With this approach no detail meshing of the fixture is required and this leads to significant simplification of the entire systems from modeling perspectives. To validate the model, experiments were performed in a full-scale environmental controlled chamber in which one UVGI fixture was mounted on a sidewall. The UV irradiance was measured by a radiometer. The results predicted by the present model agree very well with the experimental measurements. Factors affect the accuracy of the model was also discussed.

Method to evaluate UV dose of upper-room UVGI system using the concept of ventilation efficiency

Several countermeasures against the prevalence of infectious diseases have recently been issued, and one of them, the ultraviolet germicidal irradiation (UVGI) system, has been carefully considered for building environments especially. Besides experimental methods to evaluate the germicidal performance of upper air UVGI systems, this research introduces two numerical methods using the concept of ventilation performance, and illustrates the methods with a ward model. The first calculates the average residence time of air using the concept of local purging flow rate (L-PFR) which is multiplied by the average UV intensity of the upper area to obtain a UV dose. The other calculates the UV dose with the distributional UV intensity and deals with UV intensities as contaminant sources. The results of the illustrative cases with a ward model show that the method using the L-PFR concept could not clearly identify the difference in UV doses for each case with different exhaust opening setups, although the other could. The results from the method using the distributional UV intensity indicated the layout of ventilation openings and upper-room UVGI systems are important to optimize the germicidal performance.

Use of CFD Modelling to Optimise the Design of Upper-room UVGI Disinfection Systems for Ventilated Rooms

The installation of upper-room ultraviolet germicidal irradiation (UVGI) devices in ventilated rooms has the potential to reduce transmission of infections by an airborne route. However, the performance of such devices is dependant on several factors including the location of the lamp and the ventilation airflow in the room. This study uses a CFD model to evaluate the performance of UVGI devices by considering the cumulative UV-C dose received by the bulk room air in a ventilated room. By evaluating the UV dose rather than the resulting micro-organism inactivation the methodology can be used to optimise UVGI systems at the design stage, particularly when the source location of bioaerosol contaminants is not known. The study investigates the relationships between the lamp location, lamp power, ventilation system and room heating in a small, ventilated room. The results show that with ventilation air supplied at low level and extracted at high level the UVGI system performs better than with the air supplied at high level and extracted close to the floor. In addition the results show the presence of a heater in the room is unlikely to have a detrimental effect on performance and may promote mixing to increase the extent of disinfection.

05/02857 Transport properties of non-spherical nanoparticles studied by Brownian dynamics: theory and numerical simulations

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.

A quantitative method for evaluating the germicidal effect of upper room UV fields

With the general increase in the worldwide incidence of tuberculosis there is increasing interest in the use of upper room ultraviolet germicidal irradiation (UVGI) systems to disinfect air. A number of researchers have demonstrated experimentally the ability of such systems to inactivate airborne microorganisms. However, relatively little theoretical work has been done to explain the results observed and few models exist to describe the performance of upper room UVGI systems. This paper presents a new model, which can be used both to design such systems and to evaluate their germicidal effectiveness. A theoretical study is undertaken, which indicates that although upper room UVGI systems work well at lower ventilation rates, they are of limited benefit in highly ventilated applications. The paper also demonstrates and quantifies the relationship between inter-zonal air velocity and room ventilation rate. In particular, the paper shows that under steady-state conditions the number of passes made by bioaerosol particles through an upper room UV field is independent of the ventilation rate.