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.

In Scandinavia draught, cold and temperature changes are very general problems. About 50-70 % of responders in the questionnaires have reported about these adverse effects and this trend has increased during last decades. These problems are related to discomfort, accident risks and also indoor air quality. Reason behind problems in industrial buildings is mostly related to climate, draught at outer door openings and problems with ventilation.

The present state of ventilation design for industrial premises follows rules of thumb or other rules based on sometimes questionable experience. During the last years increasing effort has been successfully invested into research work to enlarge the theoretical and practical knowledge of industrial ventilation. One of the practical results of that research work has been national guidelines (in Germany e.g. VDI 3802) which give more or less detailed recommendations for the design process.

Large premises, such as airport tenninals or international conference centers, have high ceilings and large floor area. Most of passengers who use these facilities do not stay for a long time as they do in office blocks or residential housings, but occupy the buildings en masse for short periods of times.

The penetration of cold outdoor air into industrial buildings is a severe problem in countries having a cold, arctic or subarctic climate. The cold air, penetrating into the building mainly through the open doorways, causes discomfort to the workers, disturbs the functioning of the ventilation system and increases the energy and maintenance costs of the building. What even worse, the industrial process could be disturbed and even stopped, which could lead to high production and financial losses.