The effect of object positions on ventilation performance.

The effect of the change in object positions (i.e. office furniture) on the air quality in a room was studied using zonal purging flow rates. In relation to the zonal purging flow rate in a room, the transfer probability from the inlet to a certain zone can provide information on the amount of fresh air from the inlet to the zone. In this study, the probability obtained from Markov chain theory was used to analyze the ventilation performance. Also, the mean ventilation effectiveness obtained from the transfer probability was compared with the traditional mean ventilation effectiveness for the room. The velocity fields in a two-dimensional parametric room (6m x 2.7m) were derived from CFD simulation under isothermal conditions. The velocity fields were used to calculate the interconnecting flow rate between zones, and to obtain the velocity data for the whole room and the occupied zone. Several different arrangements of objects (representing room furniture) were used to find the optimum location of the objects. It was found that the mean ventilation effectiveness using the zonal purging flow rate concept is in agreement with the traditional mean ventilation effectiveness. Findings from this paper show that the object positions can play a key role in influencing ventilation performance, either in a positive or in a negative way. Depending on the location of object and airflow pattern, the presence of an object may produce two opposite effects either a hindering of the airflow in a room or an improvement in the air distribution. Also, an increase in the object lengths and a decrease in the free volume of the room do not always mean that the ventilation effectiveness decreases. The zone where the maximum velocity in the occupied zone occurs was the optimum location of an object in the room investigated.