Occupant generated carbon dioxide as a measure of dilution ventilation efficiency

The time rate of decay of occupant generated carbon dioxide after workers have left a work area can be used in indoor air quality screening. Tests in a dilution chamber proved the goodness-of-fit of a limited exponential decay model. Correlation coefficients for the log-linear plots of the chamber tests approached unity as did the ratios of actual airflow to calculated flow. The model was used to estimate the number of air changes per unit time at the point of sample collection. Multiplying the number of air changes per minute by the room volume gave the effective ventilation rate. Dividing the actual quantity of air entering the space by the effective quantity provided a measure of ventilation effectiveness, i.e., a measure of mixing. The number of room air changes measured by carbon dioxide decay was positively correlated with the evaluator's qualitative assessment of the ventilation effectiveness in several offices and laboratories.