1. Field of the Invention
This invention relates, in general, to air conditioning systems. In particular, the invention relates to a central air conditioning system wherein the air-conditioning to a plurality of rooms is simultaneously carried out through a duct and a plurality of dampers by one central air conditioning apparatus.
2. Description of the Related Art
A conventional air conditioning system typically includes one heat source unit and a duct which is in communication with a plurality of rooms to be air-conditioned to simultaneously control the temperature in the plurality of rooms. The conventional air conditioning system usually is provided with an automatic air volume control function, i.e., a so-called VAV (variable air volume) system. In the VAV system, a damper and an air volume sensor are arranged in the diverging path formed between the duct and each room, and the opening degree of each damper is controlled on the basis of the air conditioning load of the corresponding room. Thus, the flow rate of air fed from the heat source unit to each room is controlled by the operation of the corresponding damper. The volume of air fed from the heat source unit also is controlled in accordance with the total air conditioning load of each room.
In the above-described conventional air conditioning system including the VAV system, the damper is closed to stop the air flow supplied from the heat source unit to the corresponding room when the air conditioning load of the corresponding room approaches zero. At this time, an air leakage noise occurs in the duct and is audible in the room. Thus, such air leakage noise causes an annoyance to people in the room. The air leakage noise occurs at a gap between the damper and the duct when the damper is closed. This is because the volume of air supplied from the heat source unit creates a relatively large temporary increase in the static pressure in the duct, as shown in FIG. 1. The noise continues until the volume of air in the duct gradually reduces to a point whrere the static pressure correspondes to the modified air conditioning load.