Displacement Ventilation - the Influence of the Characteristics of the Supply Air Terminal Device on the Airflow Pattern

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Abstract
Displacement ventilation is acknowledged to be an efficient system for the removal of contaminants and excess heat from occupied zones of rooms. However, airflow rates, temperature and the design of the air supply device strongly influence the parameters which determine thermal comfort. This paper reviews experiments and theoretical models which show the connection between these parameters. The width and shape of the air supply device have been varied, and a porous media has been used on the inlet area of the air supply device. The velocity and temperature profiles have been measured. The results presented show also that the flow can be described with respect to width and form of the profiles for temperature and velocity. The flow does not operate like a turbulent jet due to thermal stratification. It is shown that the Archimedes number of the supply air is the parameter which determines the air velocity in the area close to the floor. (The Archimedes number is here defined as the ratio between buoyancy and inertia forces.) The results show that it is possible to remove considerable amounts of excess heat from a room, typically 40-50 W/m2, without exceeding the limits for thermal comfort. However, this requires relatively high airflow rates and supply air terminal units at least along one of the walls.

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