Lagrangian modeling of inactivation of airborne microorganisms by in-duct ultraviolet lamps

Temporal and spatial far-ultraviolet disinfection of exhaled bioaerosols in a mechanically ventilated space

Far-UVC with a peak wavelength of 222 nm can potentially be used to inactivate exhaled bioaerosols in an efficient and safe manner. Therefore, this study aimed to experimentally explore the effectiveness of a 222 nm far-UVC light for inactivating bioaerosols, represented by E. coli, exhaled from a manikin in a chamber with mechanical ventilation. The spatial irradiance distribution from the far-UVC light was measured. The susceptibility constant (z-value) for E. coli under the far-UVC light was experimentally obtained. The temporal and spatial concentrations of the bioaerosols exhaled from the manikin were measured under three typical ventilation rates (4, 10, and 36 ACH). According to the results, when the far-UVC light was turned on, the bioaerosol concentrations were lower than those without the far-UVC light under all three ventilation rates, suggesting that far-UVC light can effectively disinfect E. coli under mechanical ventilation. However, the disinfection efficiency of the far-UVC light decreased as the ventilation rate increased, which indicated that the far-UVC light played a more important role in bioaerosol removal under a lower ventilation rate. In general, the results supported the feasibility of using 222 nm far-UVC light for disinfection of exhaled bioaerosols in mechanically ventilated spaces to reduce infection risks.

Review of component designs for post-COVID-19 HVAC systems: Possibilities and challenges

The globally occurring recurrent waves of the COVID-19 pandemic, primarily caused by the transmission of aerosolized droplets from an infected person to a healthy person in the indoor environment, has led to the urgency of designing new modes of indoor ventilation. To prevent cross-contaminations due to airborne viruses, bacteria, and other pollutants in indoor environments, heating ventilation and air-conditioning (HVAC) systems need to be redesigned with anti-pandemic components. The three vital anti-pandemic components for the post-COVID-19 HVAC systems, as identified by the authors, are: a biological contaminant inactivation unit, a volatile organic compound decomposition unit, and an advanced air filtration unit. The purpose of the current article is to provide an overview of the latest research outcomes toward designing these anti-pandemic components and pointing out the future promises and challenges. In addition, the role of personalized ventilation in minimizing the risk of indoor cross-contamination by employing various air terminal devices is discussed. The authors believe that this article will encourage HVAC designers to develop effective anti-pandemic components to minimize the indoor airborne transmission.

Indoor airborne disinfection with electrostatic disinfector (ESD): Numerical simulations of ESD performance and reduction of computing time

Airborne transmissions of infectious disease (e.g. SARS-CoV-2) in indoor environments may induce serious threat to public health. Air purification devices are necessary to remove and/or inactivate airborne biological species from indoor air environment. Corona discharge in an electrostatic precipitator is capable of removing particulate matter and disinfecting biological aerosols to act as electrostatic disinfector (ESD). The ions generated by ESD can effectively inactivate bacteria/viruses. However, the available research rarely investigated disinfection effect of ESD, and it is urgent to develop quantitative ESD design methods for building mechanical ventilation applications. This study developed an integrated numerical model to simulate disinfection performance of ESD. The numerical model considers the ionized electric field, electrohydrodynamic flow, and biological disinfection. The model prediction was validated with the experimental data (E. coli): Good agreement was observed. The validated model then was used to study the influences of essential design parameters (e.g. voltage, inlet velocity) of ESD on disinfection efficiency. The effects of modeling of electrophoretic force and EHD (electrohydrodynamic) flow patterns on disinfection efficiency and computing time were also analyzed. The disinfection efficiency of well-designed ESD (with space charge density of 3.6 × 10^-06 C/m³) could be as high as 100%. Compared with HEPA, ESD could save 99% of energy consumed by HEPA without sacrificing disinfection efficiency.