Experimental study on the control effects of different strategies on particle transportation in a conference room: Mechanical ventilation, baffle, portable air cleaner, and desk air cleaner

To control the spread and transmission of airborne particles (especially SARS-CoV-2 coronavirus, recently) in the indoor environment, many control strategies have been employed. Comparisons of these strategies enable a reasonable choice for indoor environment control and cost-effectiveness. In this study, a series of experiments were conducted in a full-scale chamber to simulate a conference room. The control effects of four different strategies (a ventilation system (320 m3/h) with and without a baffle, a specific type of portable air cleaner (400 m3/h) and a specific type of desk air cleaner (DAC, 160 m3/h)) on the transportation of particles of different sizes were studied. In addition, the effects of coupling the ventilation strategies with five forms of indoor airflow organization (side supply and side or ceiling return, ceiling supply and ceiling or side return, floor supply and ceiling return) were evaluated. The cumulative exposure level (CEL) and infection probability were selected as evaluation indexes. The experimental results showed that among the four strategies, the best particle control effect was achieved by the PAC. The reduction in CEL for particles in the overall size range was 22.1% under the ventilation system without a baffle, 34.3% under the ventilation system with a baffle, 46.4% with the PAC, and 10.1% with the DAC. The average infection probabilities under the four control strategies were 11.3–11.8%, 11.1–11.8%, 9.1–9.5%, and 18.2–19.7%, respectively. Among the five different forms of airflow organization, the floor supply and ceiling return mode exhibited the best potential ability to remove particles.

Experimental study on the control effects of different strategies on particle transportation in a conference room: Mechanical ventilation, baffle, portable air cleaner, and desk air cleaner.

To control the spread and transmission of airborne particles (especially SARS-CoV-2 coronavirus, recently) in the indoor environment, many control strategies have been employed. Comparisons of these strategies enable a reasonable choice for indoor environment control and cost-effectiveness. In this study, a series of experiments were conducted in a full-scale chamber to simulate a conference room. The control effects of four different strategies (a ventilation system (320 m3/h) with and without a baffle, a specific type of portable air cleaner (400 m3/h) and a specific type of desk air cleaner (DAC, 160 m3/h)) on the transportation of particles of different sizes were studied. In addition, the effects of coupling the ventilation strategies with five forms of indoor airflow organization (side supply and side or ceiling return, ceiling supply and ceiling or side return, floor supply and ceiling return) were evaluated. The cumulative exposure level (CEL) and infection probability were selected as evaluation indexes. The experimental results showed that among the four strategies, the best particle control effect was achieved by the PAC. The reduction in CEL for particles in the overall size range was 22.1% under the ventilation system without a baffle, 34.3% under the ventilation system with a baffle, 46.4% with the PAC, and 10.1% with the DAC. The average infection probabilities under the four control strategies were 11.3-11.8%, 11.1-11.8%, 9.1-9.5%, and 18.2-19.7%, respectively. Among the five different forms of airflow organization, the floor supply and ceiling return mode exhibited the best potential ability to remove particles.

A Method to Generate Experimental Aerosol with Similar Particle Size Distribution to Atmospheric Aerosol

The SARS-CoV virus spreads in the atmosphere mainly in the form of aerosols. Particle air filters are widely used in indoor heating, ventilation, and air-conditioning (HVAC) systems and filtration equipment to reduce aerosol concentration and improve indoor air quality. Requirements arise to rate filters according to their mass-based filtration efficiency. The size distribution of test aerosol greatly affects the measurement results of mass-based filtration efficiency and dust loading of filters, as well as the calibration of optical instruments for fine-particle (PM2.5) mass concentration measurement. The main objective of this study was to find a new method to generate a chemically nontoxic aerosol with a similar particle size distribution to atmospheric aerosol. We measured the size distribution of aerosols generated by DEHS (di-ethyl-hexyl-sebacate), PSL (poly-styrene latex), olive oil, and 20% sucrose solution with a collision nebulizer in a wide range of 15 nm–20 μm. Individually, none of the solutions generated particles that share a similar size distribution to atmospheric aerosol. We found that the 20% sucrose solution + olive oil mixture solution (Vss:Voo = 1:2) could be used to generate a chemically nontoxic aerosol with similar particle number/volume size distribution to the atmospheric aerosol (t-test, p < 0.05). The differences in the mass-base filtration efficiency measured by the generated aerosol and the atmospheric aerosol were smaller than 2% for MERV 7, 10, 13, and 16 rated filters. The aerosol generated by the new method also performed well in the calibration of optical-principle-based PM2.5 concentration measurement instruments. The average relative difference measured by a tapered element oscillating microbalance (TEOM) and a Dusttrak Model 8530 (calibrated by aerosol generated by the new method) was smaller than 5.8% in the real-situation measurement.

Experimental study on the control effect of different ventilation systems on fine particles in a simulated hospital ward.

In recent years, a large number of respiratory infectious diseases (especially COVID-19) have broken out worldwide. Respiratory infectious viruses may be released in the air, resulting in cross-infection between patients and medical workers. Indoor ventilation systems can be adjusted to affect fine particles containing viruses. This study was aimed at performing a series of experiments to evaluate the ventilation performance and assess the exposure of healthcare workers (HW) to virus-laden particles released by patients in a confined experimental chamber. In a typical ward setting, four categories (top supply and exhaust, side supply and exhaust) were evaluated, encompassing 16 different air distribution patterns. The maximum reduction in the cumulative exposure level for HW was 70.8% in ventilation strategy D (upper diffusers on the sidewall supply and lower diffusers on the same sidewall return). The minimum value of the cumulative exposure level for a patient close to the source of the contamination pertained to Strategy E (upper diffusers on the sidewall supply and lower diffusers on the opposite sidewall return). Lateral ventilation strategies can provide significant guidance for ward operation to minimizing the airborne virus contamination. This study can provide a reference for sustainable buildings to construct a healthy indoor environment.