Relation Between Spatial Age of Air Distribution and Indoor VOC Concentrations in a Classroom Assessed Using CFD

SUWHAN YEE, Donghyun Rim, Pennsylvania State University

     Abstract Number: 602
     Working Group: Aerosol Physics

Abstract
Approximately 90 % of human activity occurs indoors, rendering adequate ventilation essential to health and comfort. Ventilation performance is commonly characterized by the age of air, defined as the elapsed time since the supply air last entered the occupied zone. In this study, a steady-state CFD model of a classroom was employed to resolve the three-dimensional age-of-air field and to analyze the relation with volatile organic compounds (VOCs) emitted by occupants and transformed via ozone–terpene chemistry. The simulated age of air distribution is heterogeneous, spanning a few seconds adjacent to the supply diffuser to several hours along perimeter walls. Grid scale analysis confirmed an inverse relationship between the local age of air and VOC concentration. Areas with low age of air displayed a wide range of VOC levels. Locations closest to the emission source recorded the highest concentrations, whereas zones where the supply jet had mixed thoroughly with the indoor air showed much lower values because of dilution. In contrast, regions with high age of air were only weakly affected by the source, and the prolonged residence time encouraged ozone deposition surface reactions that further reduced VOC concentrations. The results demonstrate that spatial variations in age of air, combined with surface deposition processes, play a critical role in modulating indoor VOC accumulation. A detailed map of the local age of air patterns is essential for accurately identifying pollutant hotspots and optimizing ventilation strategies, whereas reliance on room averaged values is insufficient.