This study analyzed the transmission mechanism of the COVID-19 virus according to operating conditions of air conditioner in small restaurants using CFD. The main transmission route of COVID-19 is droplet transmission. The droplet transmission is mainly caused by droplets over 5 μm and is known to s...
This study analyzed the transmission mechanism of the COVID-19 virus according to operating conditions of air conditioner in small restaurants using CFD. The main transmission route of COVID-19 is droplet transmission. The droplet transmission is mainly caused by droplets over 5 μm and is known to settle within 2m. However, depending on indoor environmental conditions, droplets can move further and if the droplet is dried and floats in the air, it can be transmitted through the air (airborne transmission). Despite the long distance between the occupants, a secondary infection case occurred. The researchers suggested the virus had moved long distance due to the airflow from the air conditioner. The KDCA mentions that respiratory droplets can be transmitted through the air if they occur for a long time in a space where ventilation is improper, and WHO and CDC also mention the possibility of airborne infection. Therefore, in this study, the analysis case was selected by changing the operating conditions of the air conditioner for two transmission routes: airborne transmission and droplet transmission. A model was constructed and boundary conditions were selected based on actual cases of restaurants, one of the industries suffering from COVID-19. In the case of airborne transmission, airflow from Pthe primary infected person was defined as pollutant (virus), and for droplet transmission, droplet particles were defined as pollutants. Airflow was analyzed three-dimensionally using CFD with consideration of factors such as thermal effects caused by heat sources and changes in airflow caused by air conditioners. The main results are as follows.
1) Airflow and droplets (excluding 50 μm droplets) emitted from the mouth of the primary infected person rose to the ceiling, entered air conditioners, and were emitted in air conditioner airflow. When air conditioner airflow impacted a structure, eddy currents were formed and these increased the risk of infection by causing pollutant accumulation. If the air conditioner is not operated, pollutants rose to the ceiling due to rising airflow caused by indoor heat sources, but it stagnated around the primary infected person. Airflow generated by air conditioners spread the virus and expanded areas of infection risk.
2) Pollutant concentrations were lower where fresh air like infiltration was introduced, which indicates the importance of ventilation. In addition, when ventilating, it is important to keep the minimum amount of ventilation so that fresh air can spread throughout entire space.
3) In the case of droplets, the smaller the diameter, the more attached they were to the ceiling or located farther away. Conversely, as the diameter increased, the attachment rate to the floor increased. However, viruses in droplets can cause contact infections, and this should be borne in mind.
4) Currently, in small spaces in Korea, HVAC (Heating, Ventilation, and Air Conditioning) systems are designed and constructed mainly for temperature control such as cooling or heating. In addition, interest in indoor ventilation facilities is low in small spaces. According to the study, if the air conditioner is operated in an inappropriate ventilation space, indoor air may circulate through the space for a long time and pollutants may accumulate, resulting in poor air quality. In addition, in situations where infectious diseases such as COVID-19 occur, viruses discharged from infected people may continue to accumulate, increasing the risk of infection. As analyzed in this study, when ventilation is performed, the concentration of pollutants or viruses can be lowered through the inflow of fresh air. However, if external environmental conditions, such as summer or winter, are inappropriate for ventilation or if they are located underground, sufficient ventilation is difficult. In addition, small spaces are often not properly equipped with mechanical ventilation facilities. Therefore, it is necessary to install mechanical ventilation facilities to improve air quality as well as the existing method centered on temperature control. Therefore, bills or support policies for the installation of machine ventilation facilities such as heat exchangers should be prepared.
Studies have confirmed that air conditioners can spread the virus and expand the risk of infection. In addition, it is thought that countermeasures will be needed centering on places where the virus is expected to stagnate or attach due to air conditioner airflow. In this study, the effect of ventilation was confirmed and the necessity of satisfying the minimum ventilation volume was identified. In addition, as an alternative to ventilation, the installation of mechanical ventilation facilities such as a total heat exchanger was suggested as an alternative. However, since research using simulation has not been conducted in this case, future research requires research on various machine ventilation facilities such as the location or necessary performance of exhaust or air supply facilities of machine ventilation facilities. At this time, we are at the cusp of realizing a new normal and WITH-corona, We hope the results of this study are used as basic data to prepare prevention guidelines to reduce risks of infection by viruses like SARS-CoV-2 (COVID-19).
This study analyzed the transmission mechanism of the COVID-19 virus according to operating conditions of air conditioner in small restaurants using CFD. The main transmission route of COVID-19 is droplet transmission. The droplet transmission is mainly caused by droplets over 5 μm and is known to settle within 2m. However, depending on indoor environmental conditions, droplets can move further and if the droplet is dried and floats in the air, it can be transmitted through the air (airborne transmission). Despite the long distance between the occupants, a secondary infection case occurred. The researchers suggested the virus had moved long distance due to the airflow from the air conditioner. The KDCA mentions that respiratory droplets can be transmitted through the air if they occur for a long time in a space where ventilation is improper, and WHO and CDC also mention the possibility of airborne infection. Therefore, in this study, the analysis case was selected by changing the operating conditions of the air conditioner for two transmission routes: airborne transmission and droplet transmission. A model was constructed and boundary conditions were selected based on actual cases of restaurants, one of the industries suffering from COVID-19. In the case of airborne transmission, airflow from Pthe primary infected person was defined as pollutant (virus), and for droplet transmission, droplet particles were defined as pollutants. Airflow was analyzed three-dimensionally using CFD with consideration of factors such as thermal effects caused by heat sources and changes in airflow caused by air conditioners. The main results are as follows.
1) Airflow and droplets (excluding 50 μm droplets) emitted from the mouth of the primary infected person rose to the ceiling, entered air conditioners, and were emitted in air conditioner airflow. When air conditioner airflow impacted a structure, eddy currents were formed and these increased the risk of infection by causing pollutant accumulation. If the air conditioner is not operated, pollutants rose to the ceiling due to rising airflow caused by indoor heat sources, but it stagnated around the primary infected person. Airflow generated by air conditioners spread the virus and expanded areas of infection risk.
2) Pollutant concentrations were lower where fresh air like infiltration was introduced, which indicates the importance of ventilation. In addition, when ventilating, it is important to keep the minimum amount of ventilation so that fresh air can spread throughout entire space.
3) In the case of droplets, the smaller the diameter, the more attached they were to the ceiling or located farther away. Conversely, as the diameter increased, the attachment rate to the floor increased. However, viruses in droplets can cause contact infections, and this should be borne in mind.
4) Currently, in small spaces in Korea, HVAC (Heating, Ventilation, and Air Conditioning) systems are designed and constructed mainly for temperature control such as cooling or heating. In addition, interest in indoor ventilation facilities is low in small spaces. According to the study, if the air conditioner is operated in an inappropriate ventilation space, indoor air may circulate through the space for a long time and pollutants may accumulate, resulting in poor air quality. In addition, in situations where infectious diseases such as COVID-19 occur, viruses discharged from infected people may continue to accumulate, increasing the risk of infection. As analyzed in this study, when ventilation is performed, the concentration of pollutants or viruses can be lowered through the inflow of fresh air. However, if external environmental conditions, such as summer or winter, are inappropriate for ventilation or if they are located underground, sufficient ventilation is difficult. In addition, small spaces are often not properly equipped with mechanical ventilation facilities. Therefore, it is necessary to install mechanical ventilation facilities to improve air quality as well as the existing method centered on temperature control. Therefore, bills or support policies for the installation of machine ventilation facilities such as heat exchangers should be prepared.
Studies have confirmed that air conditioners can spread the virus and expand the risk of infection. In addition, it is thought that countermeasures will be needed centering on places where the virus is expected to stagnate or attach due to air conditioner airflow. In this study, the effect of ventilation was confirmed and the necessity of satisfying the minimum ventilation volume was identified. In addition, as an alternative to ventilation, the installation of mechanical ventilation facilities such as a total heat exchanger was suggested as an alternative. However, since research using simulation has not been conducted in this case, future research requires research on various machine ventilation facilities such as the location or necessary performance of exhaust or air supply facilities of machine ventilation facilities. At this time, we are at the cusp of realizing a new normal and WITH-corona, We hope the results of this study are used as basic data to prepare prevention guidelines to reduce risks of infection by viruses like SARS-CoV-2 (COVID-19).
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