ABSTRACT
After the outbreak of COVID-19, it is worrisome that how to cope with the spread of the pandemic. Ventilation is the most important engineering control measure, ASHRAE, REHVA, SHASE and authoritative institutions in China have issued many documents on how to apply HVAC system to prevent and control the spread of COVID-19, and thus this paper summarizes the contents related to the ventilation rate and air distribution. Besides, traditional total volume ventilation has the disadvantages of insufficient ventilation rate, less efficiency for short-term exposure events at short range and high energy consumption during the pandemic. Source control based on advanced air distribution has the advantages of high control efficiency, personalized adjustable, fast response and high energy saving potential, which can make up the disadvantages of the total volume ventilation scheme. Therefore, this paper systematically summarizes the technical types of source control based on advanced air distribution in coping the spread of respiratory infectious diseases. Considering that the design of ventilation system in the post-pandemic era is facing the development of "combination of normal time and pandemic period", the advantages of applying source control in the post-pandemic era and the application schemes of source control in high-risk scenarios are discussed, and the directions that need to be further explored in order to implement the design concept of"combination of normal time and pandemic period" are also discussed. This paper aims to provide a reference for the compilation of subsequent guidelines, and to bring some new ideas and enlightenments to the ventilation design for future pandemic prevention. © 2022, Editorial Department of Journal of Hunan University. All right reserved.
ABSTRACT
It is important that efficient measures to reduce the airborne transmission of respiratory infectious diseases (including COVID-19) should be formulated as soon as possible to ensure a safe easing of lockdown. Ventilation has been widely recognized as an efficient engineering control measure for airborne transmission. Room ventilation with an increased supply of clean outdoor air could dilute the expiratory airborne aerosols to a lower concentration level. However, sufficient increase is beyond the capacity of most of the existing mechanical ventilation systems that were designed to be energy efficient under non-pandemic conditions. We propose an improved control strategy based on source control, which would be achieved by implementing intermittent breaks in room occupancy, specifically that all occupants should leave the room periodically and the room occupancy time should be reduced as much as possible. Under the assumption of good mixing of clean outdoor supply air with room air, the evolution of the concentration in the room of aerosols exhaled by infected person(s) is predicted. The risk of airborne cross-infection is then evaluated by calculating the time-averaged intake fraction. The effectiveness of the strategy is demonstrated for a case study of a typical classroom. This strategy, together with other control measures such as continuous supply of maximum clean air, distancing, face-to-back layout of workstations and reducing activities that increase aerosol generation (e.g., loudly talking and singing), is applicable in classrooms, offices, meeting rooms, conference rooms, etc.