The Air Exchange Efficiency of the Desk Displacement Ventilation Concept - Theory, Measurements and Simulations

The concept of air exchange efficiency of ventilation, a quantity entirely determined by the spatial distribution of the local mean age of air, is discussed. A divergence-type conservation equation for the local mean age of air is derived. This equation is solved numerically for a room ventilated by the desk displacement ventilation concept, using a CFO-routine. The CFO-calculated mean-age-of-air pattern is compared with mean age results from tracer experiments in a corresponding laboratory configuration. It is found that the air exchange efficiency of the air flow pattern induced by the desk displacement unit is only slightly above 0.5, the value for perfect mixing ventilation, for cooling situations.