Estimating the germicidal effect of upper-room UVGI system on exhaled air of patients based on ventilation efficiency

Abstract

a b s t r a c tUpper room (UR)-ultraviolet germicidal (UVGI) systems, one of several disinfection applications of UV, target airborne infectious diseases in rooms of buildings such as healthcare facilities. Previous studies have introduced many experiments showing the germicidal effect of UR-UVGI systems. In this study, a novel numerical method of estimating the germicidal effect of UR-UVGI systems for air exhaled by ward patients was introduced. The method adopts and modifies the concept of ventilation efficiency because the germicidal effect depends upon how the air containing airborne infectious particles flows and stays within UV-radiated area. A case study based on a four-patient ward showed that UV doses were correlated with the age of the air exhaled by a source patient, as expected. Moreover, the UV doses were considerably affected by the position of the UR-UVGI system. Inactivation rates of the influenza virus estimated using the UV doses, were in the range of 48e74%, and those of Mycobacterium tuberculosis were 68e90% in the breathing area of a neighboring patient. The results indicate not directly the decreased concentration of airborne infectious particles, but the possibility of inactivation caused by the UR-UVGI system, which is useful for system optimization.

Application of CFD Simulation to Predicting Upper‐Room UVGI Effectiveness

“…As such, dose can be evaluated through a particle‐tracking approach using an algorithm to sum the dose along the trajectory or applied as a passive scalar tracer, through defining the rate of change in dose as a sink term . Either approach can be applied to the room air as a whole to optimize general coverage or the air from a particular source such as an infectious patient where the source location is known. This study applies a passive scalar approach where the dose distribution, D , depends on the irradiance field ( E ( x,y,z )) and the velocity vector field, U (m s −1 ), namely:…”

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

“…The present paper uses the first-order decay model in which the probability (P) of a microorganism to survive ultraviolet germicidal irradiation decreases exponentially with the quantity of the ultraviolet dose received (D, [J/m 2 ]), and the microorganisms' susceptibility to radiation (z, [m 2 /J]) [12,20]:…”

“…This approach calculated the dose received by inlet air, which is not identical to the dose received by microorganisms. To resolve this issue, Sung and Kato [12] calculated a transport equation for the dose received by air supplied from contaminant source using the concept of scales of ventilation efficiency [13,14]. Applying this dose in the decay ratio (equation (1)) produced different values for the viable mass fraction other than calculating it directly, such as in Ref.…”

Engineering control of respiratory infection and low-energy design of healthcare facilities

“…However studies also show the system can perform badly under different weather and operational conditions . Similarly there is a growing body of experimental (Xu et al 2003;NIOSH 2009) and computational (Noakes et al 2006;Sung and Kato 2011; studies with a small amount of field data ( Personalized ventilation is another approach where there could be some potential benefits in both energy and infection control. In the case of the short-range airborne route, traditional methods such as ventilation dilution are not effective, but there may be a role for alternatives such as personalized ventilation to provide near occupant protection (Sekhar et al 2005;Melikov 2004).…”