The residence time of aerosol reduces with an increase in the ventilation rate

According to a study “Modeling of dispersion of aerosolised air-borne pathogens exhaled in indoor spaces”, redesigning air conditioning systems in commercial buildings can limit Covid spread.

Scientists at the Indian Institute of Technology (IIT) in Delhi have discovered that increasing the ventilation rate of air conditioning systems in commercial buildings can help reduce the spread of Covid-19 in indoor spaces. The redesign reduces the residence time of pathogens. It is one of the first studies to estimate the likelihood of infection purely from a fluid dynamics perspective, considering the role of multiple occupants in pathogen spread. The findings are particularly significant given the recent surge in Covid-19 cases in India. According to Professor Amit Gupta, the study demonstrates that the residence time of aerosol is considerably reduced when ventilation rates are increased.

The research, which considers the effects of many occupants, is titled “Modeling of dispersion of aerosolised air-borne pathogens exhaled in indoor spaces” and has been published in the journal “Physics of Fluids”. Gupta recommends extending the operating hours of ventilation systems after closing time to minimise the concentration of pathogens and contaminants in the building space and stresses the importance of exhaust duct placement in classrooms.

The researchers recommend making provisions for increasing ventilation rates to reduce the risk of infection spread, especially during a pandemic. The highest possible ventilation rate that maintains comfort and HVAC system capacity should be used, and for classrooms, a ventilation rate equivalent to 9 air changes or more is recommended. The research team, which included Professor Supreet Singh Bagha and MTech student Praveen Sharma, conducted realistic airflow simulations in two representative classrooms at IIT Delhi, considering multiple occupants.