Variable air volume control apparatus

Abstract

The invention relates to a variable air volume control apparatus which compensates an open area ratio to be in direct proportion to an opening ratio at a low opening ratio range according to an open angle of a damper blade to achieve accurate and precise air volume control. The variable air volume control apparatus includes a damper blade disposed rotatably within the duct for opening or closing an air flow path and an actuator for rotating the damper blade. The apparatus also includes an air flow path expansion mechanism having a curved surface for expanding the air flow path in accordance with an open angle of the damper blade. The invention allows obtaining the open area ratio in direct proportion to the opening ratio at the low opening ratio range through simple structural improvements, thereby improving linear characteristics of an air volume change ratio with respect to the opening ratio to more accurately and precisely control the air volume.

1 . A variable air volume control apparatus for varying air volume in a duct having a passageway therethrough defining an air flow path, comprising:
 a damper blade construction that has an outer circumference and is disposed within the duct to be rotatable between a fully closed position generally transverse to the duct and a fully open position generally aligned with the duct for opening or closing the air flow path through the duct;   an actuator for rotating the damper blade;   an air flow path expansion mechanism for providing an open area through which air can flow as the damper blade construction is opened and to control the air flow path in accordance with an open angle of the damper blade, said mechanism positioned at a point along the duct to form constrictor portion with a generally central rib portion and oppositely disposed side portions extending sidewardly from said rib portion along the duct, said rib portion projecting inwardly relative to said side portions and generally transversely to the duct towards the center of the duct to form a ridgeline to closely adjoin at least a portion of the outer circumference of said damper blade construction when said damper blade construction is in its fully closed position, said side portions including concavely curved surfaces facing inwardly towards the duct, said curved surfaces meeting at said ridgeline and extending sidewardly from said rib portion along the duct, said constrictor portion having an inner circumference at said ridgeline approximately the same as the outer circumference of said damper blade construction such that, when said damper blade construction is in its fully closed position, said constrictor portion and said damper blade construction generally close the air flow path through the duct;   whereby, as said damper blade construction is operated within a low opening ratio range of about 0% to 30%, the open air flow through the duct is increased in an approximately linear relationship with the opening ratio and said rib portion has a height at said ridgeline in the range of about 10% to 40% of the radius of the duct.   
     
     
         2 . The variable air volume control apparatus according to  claim 1 , wherein said rib portion has a height at said ridgeline in the range of about 12.5% to 32.5% of the radius of the duct. 
     
     
         3 . The variable air volume control apparatus according to  claim 1 , wherein said rib portion has a height at said ridgeline in the range of about 17.5% to 27.5% of the radius of the duct.