The results of indoor air quality surveys have showed that it was quite easy to fulfil the requirements of indoor climate standards and recommendations, even in office buildings where the workers experienced sick building symptoms, and complained that the reason for their symptoms was poor indoor air quality (1, 2). Many researchers consider that psychosocial factors may serve as moderators or mediators in the sick building syndrome process, either increasing or decreasing the vulnerability of the individual to environmental exposures (3, 4).

The control of emissions from open surface tanks is usually perfomed using simple exhaust systems or combined with push (1). In the first case the exhaust entries generate omnidirectional speed fields within the tank, which rapidly reduce efficiency as the distance increased and are recommended for tanks of less them 1 metre in length. In the push-pull systems, a curtain of air sweeps over the surface of the tank and drags emission towards the exhaust causing a jet wall which (2), when well formed, permits high capture efficiency (3).

When designing push-pull ventilation system as usual, it has been considered that supply airflow should be thoroughly exhausted by suction inlet. However, an escape of some of the supply airflow from an exhaust inlet could be permitted in the push-pull ventilation system, if all of the contaminants transported to the exhaust inlet do not escape and can be exhausted. In this study, we investigate appropriate flow rate for push-pull ventilation system by using CFD techniques.

This study is a part of a research project called 'Convective Flows and Vertical Temperature Gradient within Active Displacement Air Distribution'. The project and the two zone model developed have been introduced by Sandberg (1). The aim of this study was to examine the ventilation effectiveness with different elevations and horizontal positions of the heat sources within active displacement air distribution. This was studied by carrying out experiments using convective heaters and ordinary fluorescent tube lamps at several elevations as heat sources.