modelling

The concentrations of indoor pollutants should be maintained below recommended values at all occupied locations at any time. A design method based on minimal air change rates may not be satisfactory, since the ventilation effectiveness is determined not only by the nominal air exchange rate but also many other factors, such as the airflow pattern the space, location of contaminant sources, and properties of the contaminants. It is the objective of the present study to investigate numerically the effect of airflow patterns due to the various factors of ventilation effectiveness.

Results of 3-D computational fluid dynamic simulations of the air flows, temperature distribution and contaminant remove efficiencies for typical workstation configurations which include the option for localized supply of outdoor air will be presented. A typical office configuration including desks, partitions, localized heat and contaminant sources will be modelled. The results will be compared to similar simulations the same workstation environment using ceiling supply and return plenum configurations.

The paper discusses methods to set boundary conditions at the air supply opening in predictions of room air flows with computational fluid dynamics. The work is a part of the International Energy Agency project "Air Flow Patterns within Buildings", Annex 20. The air supply terminal in the Annex 20 project is a commercial diffuser which creates a stagnation region and a complicated wall jet below the ceiling. Fairly well predictions in the wall jet region were obtained replacing the diffuser by a simple opening which has the same momentum flow as in the diffuser.

Modern inlet devices applied in the field of ventilation of rooms are getting more complex in terms of geometry in order to fulfil the demand for thermal comfort of the occupants in the room and in order to decrease the energy consumption This expresses the need for more precise calculation of the flow jield. In order to apply CFD for this purpose it is essential to be able to model the inlet conditions precisely and effectively, in a way which is comprehensible to the manufacturer of inlet devices and in a way which can be coped by the computer resources.