Enlightenment of re-entry airflow: The path of the airflow and the airborne pollutants transmission in buildings. (15th May 2021)

• Record Type: Journal Article
• Authors: Tung, C.W.; Mak, C.M.; Niu, J.L.; Hung, K.; Wu, Yan; Tung, Nam; Wong, H.M.
• Is Part Of: Building and environment. Volume 195(2021)
• Publication Date: 2021-05-15
• Subjects: Re-entry airflow -- New dual-zone model -- Apparent air changes per hour -- Semi-open corridor -- Fade-out index; Buildings -- Environmental engineering -- Periodicals; Building -- Research -- Periodicals; Constructions -- Technique de l'environnement -- Périodiques; Electronic journals; 696
• DOI: 10.1016/j.buildenv.2021.107760
• Languages: English
• ISSNs: 0360-1323

Abstract

Abstract: Viable aerosols in the airflow may increase the risk of occupants contracting diseases. Natural ventilation is common in buildings and is accompanied by re-entry airflow during the ventilation process. If the re-entry airflow contains toxic or infectious species, it may cause potential harm to residents. One of the Covid-19 outbreaks occurred in a public residential building at Luk Chuen House (LC-House) in Hong Kong. It is highly suspected that the outbreak of the disease is related to the re-entry airflow. The study attempts to explain and discuss possible causes of the outbreak. In order to understand the impact of airflow on the outbreak, a public residential building similar to LC-House was used in the study. Two measurements M − I and M − II with the same settings were conducted for a sampling unit in the corridor under low and strong wind conditions respectively. The sampling unit and the tracer gas carbon dioxide (CO2 ) were used to simulate the index unit and infectious contaminated airflow respectively. The CO2 concentrations of the unit and corridor were measured simultaneously. Two models of Traditional Single-zone model (TSZ-model) and New Dual-zone model (NDZ-model) were used in the analysis. By comparing the ACH values obtained from the two models, it is indicated that the re-entry airflow of the unit is related to the corridor wind speeds and this provides a reasonable explanation for the outbreak in LC-House, and believes that the results can help understand the recent frequent cluster outbreaks in other residential buildings. Highlights: The dual-zone model can more accurately describe the ventilation of the room. The newly introduced fade-index shows the airflow characteristics of the corridor. The integration of TSZ-model and NDZ-model can quantify re-entry airflow. Re-entry airflow is a wind speed depending sub-airflow in ventilation. Re-entry airflow cannot be neglected during studying Covid-19 spread in buildings.