This study investigates the effectiveness of ventilation design strategies for general hospital wards in terms of virus removal capacity. A typical semi-enclosed six-bed general ward of Hong Kong hospitals and three respiratory viruses, namely Middle East respiratory syndrome coronavirus (MERS-CoV), severe acute respiratory syndrome coronavirus (SARS-CoV) and H1N1 influenza virus, were chosen for the computational fluid dynamics (CFD) simulation of airflow field and virus dispersion inside the ward. The results demonstrated that the location of an infected patient would affect the infection risks to other occupants and healthcare workers inside the same hospital ward, and an increased air change rate in the ward could reduce the risk of infection from direct contact and inhalation. It was found that an air change rate of 9 h À1 could effectively minimize the deposition and floating time of respiratory virus particles while maximizing energy efficiency. This study should provide a useful source of reference for the hospital management to mitigate the risk of infection with MERS or other airborne transmitted viruses through better ventilation design strategies.

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In practice, the drag coefficient of a particle is usually calculated using empirical relationships obtained by generalizing experimental data. This study demonstrates that using the default Stokes’ law settings in FLUENT to computationally predict the drag coefficients for bioaerosol deposition is not really appropriate: the average fractional bias is 7% and the average normalized mean square error is 15%. Comparatively, the errors for bacteria (−12% to 24%) are larger than those for fungi (−8% to 26%). These errors, however, can be minimized by selecting a suitable drag constant, which can be determined based on the bioaerosol diameter. The average drag constants for bacteria were shown by the results to vary from 0.25 to 3.1, which are much smaller than the default value of 24, whereas the values for fungi were generally larger and in a wider range. This study also investigated the correlation between the drag coefficient and Reynolds number for common indoor bioaerosols with diameters between 0.69 and 8.6 µm. The outcome of this study would therefore provide a good reference point for future estimation of the deposition distribution patterns of various common indoor bioaerosols.

Bioaerosol (i.e. biological aerosol) exposures in the office environment are associated with a wide range of health effects. The potential bioaerosol emission from mechanical ventilation and air conditioning (MVAC) systems can endanger the building occupants in office, especially as over 90% of commercial buildings in Hong Kong that are equipped with MVAC systems, due to the microbial growths inside MVAC systems, such as cooling coils and mixing chamber, were reported. This study evaluated the exposure risk of the bioaerosol emission from the MVAC systems to the building occupants. A two-phase flow computational fluid dynamics approach was adopted to simulate the emission, dispersion, deposition, and exhaustion of bioaerosol particles from the MVAC systems in a typical office cubicle by altering the ventilation strategies with four ventilation rates, four emission concentrations, and two microorganism species. The results reported that about 5% contribution of concentration level from the MVAC system including the ventilation rate is sufficient to dilute the biocontainment. This study suggested the importance of the maintenance strategies of MVAC systems for minimizing bioaerosol exposures in offices.

Potential bioaerosol infection risk associated with toilet flushing has not been sufficiently addressed in the design of residential washroom exhaust system. This study evaluates the performance of exhaust ventilation for residential washrooms in terms of air change rate, washroom size, washroom geometry, and locations of door louver, exhaust and water closet. Three bioaerosol species namely Escherichia coli (ATCC 10536), Serratia marcescens (ATCC 6911), and Cladosporium cladosporioides (ATCC 16022) are included in the simulations. By shortening the distance between the locations of exhaust and emission source (i.e. water closet), the fractional counts of bioaerosol particles exhausted can be increased. An increased air change rate and a louvered door can also improve the exhaust ventilation performance, yet with a longer time to steady state. This study should provide a useful source of reference for washroom exhaust designers to minimize bioaerosol infection risk. Practical application: This paper shows for residential washroom with an exhaust fan installed, the ventilation performance can be improved by an increased air change rate, and by shortening the distance between the locations of exhaust and emission source.

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