A Multi-Tracer Technique for Studying Rates of Ventilation, Air Distribution Patterns, and Air Exchange Efficiencies

A multiple tracer system has been utilized within commercial buildings to monitor ventilation rates, air exchange efficiencies, age of air at multiple indoor locations, and the fractions of air at a monitoring point that entered the building through a particular air handler and by infiltration. To label the incoming air, a distinct tracer gas is injected at a constant rate into each mechanically supplied outside-air or supply air stream. Gas chromatographs monitor tracer gas concentrations versus time in the major airstreams of the air handlers. Small "local samplers" at various indoor locations are utilized to monitor local ages of air. The standard methods of applying age distribution theory are modified to process the multiple tracer data. The experimental system and methods of data analysis are described, and the results of investigations in an office building when the ventilation systems maximized and minimized the recirculation of indoor air are reviewed. The standard deviation in the age of air measured at different locations within this office building is from 25% to 40% of the mean age. Our measurements did not yield evidence of substantial short-circuiting or displacement flow patterns.