The Wells-Riley equation has long been used to estimate infection risk in a range of environments.
In a report by the built Environment Research Group, the Wells-Riley model has been used to show that some building factors, particularly outdoor air ventilation rates, can be an important removal mechanism for airborne infectious agents (Chen et al., 2006; Escombe et al., 2007).
As an example, the table above shows the relationship between probability of infection, outdoor air ventilation rate, and quanta generation rate using the Wells-Riley model for a hypothetical 500m2 office building where adults are continuously in the presence of one infected individual for 8 hours.
It can be seen, that no amount of outdoor air ventilation could stop the most infectious disease from spreading (hypothetical q = 10,000/hr) while the risk of acquiring the common cold (q = 10/hr) could be reduced from 10% in a tight building, which has an outdoor air ventilation rate of 0.3 air changes per hour, to only 0.5% by increasing ventilation rates to 6 air changes per hour.
Simply put, the Wells – Riley equation shows that doubling the outdoor ventilation rate can reduce the infection rate in half.
All HVAC systems need to incorporate the minimum fresh air standards.
Energy Recovery Ventilators are becoming even more imperative as the expectation of indoor air quality gives due consideration to reducing infection rates.
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