An investigation of air inlet types in mixing ventilation

Previous studies have shown that dispersion of contaminant concentrations strongly depends on air inlet types. However, these studies were performed computationally, not experimentally. Thus, the purpose of the current research is to obtain contaminant concentrations in a room, to perform qualitative and quantitative comparison for a wall jet (WJ) air inlet and a ceiling diffuser (CD) air inlet, and to determine more efficient inlet and outlet configuration. Here, the effect of air inlet types in mixing ventilation was investigated in an experimental room under two conditions, with no occupant and with an occupant present north of the source. A heated mannequin, producing a total heat load of 120 W, represented an occupant. Tracer gas (99.5% propylene) concentrations were monitored automatically at 144 sampling points with a photoionization detector. Three flow rates (5.5, 3.3, and 0.9 m3/min) were employed. Experimental results for the 0.9 m3/min are not reported here because concentration measurements with time in preliminary tests did not reach a stationary condition even over periods of 5 h due to dominant airflow by natural convection rather than by forced convection. Results have shown that the air inlet type is an important physical determinant to the distribution of airborne contaminant concentrations because they generate different airflow patterns and thus different spatial concentration patterns. This investigation enhanced understanding of the interactions of concentration field, airflow, and air inlet types. The findings of the study can be applied to practical areas; for example, it was shown that CD air supply system minimizes occupant exposure from hazards in office buildings, hospitals, and schools, if sources are located under ceiling diffuser inlets.