Ventilation performance evaluation using passively-generated carbon dioxide as a tracer gas.

Tracer gases are commonly used to evaluate the performance of ventilation systems. One way to reduce the time, complexity, and cost of such experiments is to use the carbon dioxide generated by occupants as a tracer gas. In this paper, a method for using the carbon dioxide generated by occupants as a tracer gas for determining the effective supply air flow rate to a zone or the relative air-change effectiveness of a zone is described. The approach is to make use of a model of the accumulation dynamics and a model of the way that occupants generate carbon dioxide. The carbon dioxide accumulation dynamics are modeled as a first-order perfect-mixing process with bypass. The rate at which occupants generate carbon dioxide is modeled as an integrated random process. Sudden changes in the rate at which carbon dioxide is generated in a zone that occur when occupants enter and leave are detected using statistical techniques. The detector is used to adjust the gains of an estimator that determines either the effective supply air flow rate or the relative air-change effectiveness and also the rate at which occupants generate carbon dioxide. This can be done even when the rate at which occupants generate carbon dioxide changes with time and when the concentration of carbon dioxide in the supply air changes with time. The performance of the strategy is demonstrated with experimental results on a room in a working building.