Multizone Age-of-Air Analysis

Age-of-air is a technique for evaluating ventilation that has been actively used for over 20 years. Age-of-air quantifies the time it takes for an elemental volume of outdoor air to reach a particular location or zone within the indoor environment. Age-of-air is often also used to quantify the ventilation effectiveness with respect to indoor air quality. In a purely single zone situation this use of age-of-air is straightforward, but application of age-of-air techniques in the general multizone environment has not been fully developed. This article looks at expanding those single-zone techniques to the more complicated environment of multizone buildings and in doing so develops further the general concept of age-of-air. The results of this analysis show that the nominal age-of-air, as often used, cannot be directly used for determining ventilation effectiveness unless specific assumptions are made regarding source distributions. The results herein will allow improved accuracy of age-of-air calculations in complex environments. The link between local age-of-air and ventilation effectiveness is hereby improved and the ability to use age-of-air measurement to estimate distribution effectiveness is increased. Use of these results will improve the design of future measurement efforts using tracer gases in multizone environments.