Impact of room heat load on ventilation effectiveness and probability of transmission of airborne diseases on the example of chosen scenarios

The Wells-Riley model is commonly used to assess the probability of viral transmission, taking into account various factors. One of these factors is the ventilation effectiveness, which is commonly assumed to be constant. This article proposes to consider the variability of ventilation efficiency and the inclusion of an additional factor, the dependence of the variability of ventilation efficiency on the variable room heat load and the type of air distribution system in the room, in this established model. The study presents several scenarios simulating probability of airborne transmission of the Omicron variant of the SARS-CoV-2 (causing COVID-19) for typical rooms, such as an office, classroom, and auditorium, for different typical air distribution patterns ('up-up' and 'down-up'), for heat load conditions of two extreme climatic situations: summer (15 August) and winter (31st December), as well as for the maximum and minimum attendance and different types of lighting and room equipment. The study demonstrates that the variability of ventilation effectiveness, depending on the variability of the room's heat load and the air distribution system in the room, influences the probability of pathogen transmission. For an airflow system 'up- up' in classroom, the probability result after 7 h is 15.9 % in winter with minimal heat load (ventilation efficiency from 0.78 to 0.83) and 13.8 % in summer maximum heat load (ventilation efficiency constant and equal to 1.0). to 1.0). For an airflow system 'down- up' in auditorium, the probability result after 4 h is 3.8 % in winter with minimal internal heat gains (ventilation efficiency from 0.82 to 0.92) and 2.8 % in summer maximum internal heat gains (ventilation efficiency from 1.01 to 1.26). This study shows that neglecting this parameter may lead to an underestimation of the transmission risk, thus this article recommends that at least simplifies heat load model should be included in future analyses, and scenarios with different room heat loads should be evaluated separately.