Tracer gas experiment for local mean ages of air from individual supply inlets in a space with multiple inlets

We investigate the supply characteristics of incoming air via individual inlets in a ventilated space with multiple inlets. Theoretical considerations are given to determine the relations between the local mean age (LMA) of the total supply air and the individual LMA of each supply air inlet. Tracer gas experiments are conducted in a simplified livestock model with two supply inlets and one exhaust outlet. Transient concentration responses at internal points are measured after tracer gas injection one inlet at a time, and for simultaneous tracer injection at both inlets. The spatial distributions of LMAs and steady concentrations are obtained by tracer injections from each supply inlet, which demonstrate the supply characteristics of the individual inlets in the space. We have found that the overall LMA is the weighted average of the LMA by each inlet, and the weighting factor for the average is the corresponding steady state concentration at a given point. Experiments repeated for various airflow rates show that the nondimensional steady concentrations remain nearly constant regardless of the total airflow rate, but are greatly influenced by the airflow ratio between inlets. The local mean ages are found to increase proportionally with respect to the nominal time constant. Experimental procedures and results are verified by the fact that the total LMA measured at the exhaust is in good agreement with the theoretical nominal time constant of the space.

► We consider ventilation effectiveness in a space with multiple inlets.
► We derive theoretical relations between overall LMA and the LMAs from each inlet.
► Tracer gas experiment is conducted to verify the relations in a scaled model.
► The overall local mean age is the weighted average of the LMAs from each inlet.
► The weighting factors are the corresponding steady concentrations at a point.