Flooding of Ventilation Air and its Consequences

An air distribution system has two ends. To the inlet the capacity for the dilution of contaminants generated within the room is delivered. To the outlet the capacity for removal of the contaminants is delivered. The flow in a room is controlled by a driving flow. A driving flow does not need to be the supplied ventilation flow rate. A driving flow entrains ambient air, and the flow rate increases with the distance from the source. When the flow is driven by a jet the initial flow rate is the ventilation flow rate but when it is driven by a plume the initial flow rare is zero. Due to entrainment the flow rate increases with the distance from the source After a certain distance the flow rate in the driving flow is larger than the evacuation capacity. Thus, a surplus flow larger than the evacuation capacity is generated. The surplus flow cannot be evacuated immediately, and it returns to the room. This is flooding of ventilation air. It has several consequences for the air quality and air flow pattern in the room. The purpose of the paper is to present he mechanism for generation of surplus air, its consequences and the concepts related to this.