Using numerical simulation to predict ventilation efficiency in a model room

A computational fluid dynamics (CFD) code is used to simulate the air currents and the contaminant decay inside a small scale model room with forced ventilation through a simple supply and return. The numerical results are validated with flow visualization experiments and local clearance rate measurements by laser extinction. The comparisons show excellent agreement on the inlet side of the room and fair agreement on the outlet side. Based on the concept of local exponential tracer decay and mixing factor (m), an arithmetic average of m is proposed as a measure of overall air ventilation efficiency eta(m). The proposed definition has practical benefit in numerical simulation because it reduces computational time without sacrificing the concept of air ventilation effectiveness. Examples of application are demonstrated by evaluating eta(m) for different room configurations and ventilation arrangements. The calculated eta(m) correlate well with the time required for evacuating the contaminants in different room configurations. The results show that, for the room geometry studied, a ventilation system performs better when the inlet and the outlet are perpendicular to each other than when they are parallel to each other, and that partitions in the room can have a significant influence on ventilation performance. (C) 1998 Elsevier Science S.A. All rights reserved.