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.

Description

CLAIM OF PRIORITY

This application claims priority to the U.S. patent application Ser. No. 11/715,255, filed Mar. 7, 2007, which claims the benefit of Korean Patent Application No. 10-2006-0021944 filed on Mar. 8, 2006, and also claims priority to the Korean Patent Application No. 2006-2149, filed Mar. 8, 2007 in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a variable air volume control apparatus for adjusting the volume of air supplied indoors appropriately in accordance with a set temperature of a room thermometer.

2. Description of the Related Art

In general, a variable air volume control apparatus is an important component in a variable air volume control system, which adjusts air volume to change room temperature, thereby maintaining pleasant indoor environment as well as preserving energy.

In such a variable air volume control apparatus, an air volume change ratio curve in accordance with an opening ratio of a damper is an important factor for adjusting the air volume according to temperature change indoors.

Therefore, the present invention aims to significantly improve the air volume change ratio curve such that it is changed from a conventional non-linear form to a linear form to realize precise control of the air volume. FIGS. 1 and 2 illustrate a conventional variable air volume control apparatus, in which a circular plate-shaped damper blade 230 is installed with a shaft 232 in a cylindrical duct 210. The conventional variable air volume control apparatus controls air volume through a following process.

A room thermometer 250 (not shown in detail) installed indoors senses room temperature and transmits information thereof (a signal) to a controller 260 (not shown in detail). The controller 260 which received the information computes the information and currently set temperature from the room thermometer 250 to calculate the air volume needed.

Then, the controller transmits a signal for an open angle corresponding to the air volume needed, to operational devices such as a motor or an actuator 240 which are then operated accordingly. Also, the controller measures the air volume at an inlet side via an air volume measurement device such as an anemometer or a differential pressure sensor installed at the inlet side and transmits the information (signal) to the controller 260.

The controller 260 receives the information (signal) from the air volume measurement device and rotates the shaft 232 of the operational device as much as, the excessive or deficient amount of air to adjust the open angle of the damper blade 230, thereby maintaining the air volume corresponding to the information (signal) from the room thermometer 250.

However, as shown in FIG. 1, the conventional air volume control apparatus 200 has drawbacks such as great imbalance between its opening ratio and its open area ratio corresponding to the open angle of the damper blade 230, air overflow, and friction between air flow and the inner surface of the duct 210. Thus, the air volume change ratio C is represented in a greatly deviating (distorted) curve rather than a line.

As shown in FIG. 3, the open area ratio curve B deviates greatly from the opening ratio line A, and thus the volume of air flowing through corresponding an open area is far from being in direct portion to the corresponding opening ratio. Therefore, the air volume change ratio C results in a curve which greatly deviates from the opening ratio line A.

As seen from the air volume change ratio curve, in a low opening ratio range of about 0 to 30%, i.e., in the range D1 of near closed state of the damper blade, the air volume change is too small with respect to the corresponding change of the opening ratio, thus difficult to adjust the air volume in this range.

Also, in a high opening ratio range of about 70 to 100%, i.e., in the range D2 of near open state of the damper blade, the air volume change is too small with respect to the corresponding opening ratio, thus difficult to accurately and precisely adjust the air volume.

In addition, in the opening ratio range of 30% to 70%, the air volume changes drastically with respect to even a small change in the open angle, i.e., the opening ratio of the damper blade, hindering precise control of the air volume.

Therefore, in order to exclude the tendency of too small an air volume change with respect to the opening ratio in the range D1 of near closed state of the damper blade and achieve a linear form in the entire range of the opening ratio, in the conventional air volume control apparatus shown in FIG. 2, the damper blade 230 installed with the shaft 232 inside the duct 210 is modified into an oval plate shape and the closed position of the damper blade in the duct 210 is shifted about 30 degrees to an angle θ1 so that an adjustable range of angle θ2 is thereby shifted to be 30 degrees to 90 degrees.

Shifting the adjustable range of angle θ2 of the damper blade 230 to be from 30 degrees to 90 degrees, where an adjustable range is from 0 degrees to 60 degrees to yield 0% to 100% of air volume change, results in a drawback in which the adjustable range of angle is decreased by 33% from that with an adjustable range of 0 to 90 degrees to yield 0 to 100% of air volume change. This means that the adjustable range of angle is too small to allow precise control of air volume.

Therefore, rather than reducing the adjustable angle range of the variable air volume control apparatus 200, the adjustable angle range of 0 to 90 degrees should be maintained to yield the air volume change of 0 to 100% in order to more accurately and precisely control the air volume.

Also, in order to change the air volume curve into a linear form, the open area should be increased at the low opening ratio. This allows obtaining a linear air volume change in proportion to the opening ratio of the damper blade at a low opening ratio, thereby accurately and precisely controlling the air volume.

As confirmed above, the flow control damper is an essential component for adjusting the air volume introduced into the variable air volume control apparatus in an air conditioning system adopting a variable air volume control system. The capability of the flow control damper to linearly control the air volume plays a determining role in efficiently operating the variable air volume control apparatus.

Recently, the controller for the variable air volume control apparatus has been developed into a finely-operated electronic type, which is used in almost all air conditioning systems. However, if the variable air volume control apparatus does not have a linear flow characteristics of the flow control damper operated by the actuator 240, precise control of the variable air volume control apparatus cannot be efficiently realized, regardless of excellent capabilities and control of the controller of the variable air volume control apparatus and the highly accurate and reliable flow sensor for sensing air volume change at an inlet side of the variable air volume control apparatus or constant feedback control of the flow control damper by comparing and computing differential pressure signal from the flow sensor with the indoor temperature load change.

Air flows at the highest velocity in the central portion of a duct or conduit, and at a low velocity near the wall due to friction. Thus, when the damper blade is opened at the opening ratio of 100%, although the velocity may somewhat change, the air volume flowing per unit of time approximates to 100% with substantially no inflow or outflow loss.

When the damper blade's opening ratio decreases by 50%, i.e., the damper blade 230 is biased at 45 degrees, the air volume is also supposed to be decreased by 50%. However, the actual air volume turns out to be less than 50%. This is because when the damper blade 230 is biased at 50% (45 degrees) in a cylindrical duct, the resultant open area ratio is too small at 29.29%, and thus the resultant air volume is also small at about 40% (see FIG. 3).

Also, when the opening ratio of the damper blade is 30% or less, the resultant open area ratio is too small at 10% or less with too small an air volume, hindering precise control.

In addition, when the open angle of the damper blade 230 is 70% or more, the resultant open area is smaller than the directly proportional line whereas too large a volume of air flows, hindering precise control.

As described above, in the conventional variable air volume control apparatus 200, the air volume change with respect to the opening ratio of the damper blade 230 turns out to be a greatly deviating (distorted) curve C as shown in FIG. 3, rather than a line.

In FIG. 3, the graph shows the open area ratio and air volume change ratio with respect to the opening ratio, obtained by the above conventional variable air volume control apparatus.

Therefore, as shown in the graph in FIG. 3, with the conventional air volume control apparatus 200, in the opening ratio range of 30% to 40% or less, the actual open area ratio curve B deviates greatly from the ideal open area ratio, i.e., line A which is in direct proportion to the opening ratio of the damper blade 230. As a result, accurate control of air volume is difficult.

Therefore, the conventional air volume control apparatus 200 cannot accurately control the air volume introduced indoors, thus having difficulty in supplying fresh air indoors while consuming more energy.

In order to overcome such a problem, Korean Utility Model Registration No. 0346769 (entitled “Dome Type Air Damper Unit”) has been suggested. This conventional dome type air damper unit has a cylindrical body having flanges at opposed ends thereof. Inside the body, a wing unit, connected to a control unit, is connected to a plurality of wings at one side of the body, forming a dome-shape. The control unit adjusts the angle of the wings to operate the plurality of wings simultaneously, thereby changing an open area of an air outlet to adjust the air volume.

However, this conventional structure is structurally complex and expensive, yielding a non-linear air volume characteristics curve.

A different conventional technology has been suggested in Korean Utility Model Registration No. 0376799 (entitled “Variable Air Volume Control Apparatus”).

In this conventional variable air volume control apparatus, a shaft is disposed movable back and forth and connected to a guide lever of a damper actuator disposed outside of the apparatus body and operated by a room thermometer. Also, a pair of symmetrical air volume control dampers are split or joined in accordance with the movement of a pair of links that are connected to an end of the shaft. And an air conduit is installed to connect between an air inlet and a first air outlet, and is connected to a mixed air outlet.

However, this structure is structurally complex, thus difficult to manufacture, and expensive. Further, it uses a guide lever in a link structure, which makes noise and the resultant air volume change ratio curve has non-linear characteristics.

A different structure from the above is disclosed in U.S. Pat. No. 5,333,835 (entitled “Electric Motor Driven Air Valve”).

In this structure, a screw shaft is rotated by a motor to thereby move a damper blade connected to the screw shaft, adjusting the volume of air flowing between the open damper blade and the duct.

However, it is also difficult to accurately adjust the air volume according to the orbit of the damper blade with this conventional structure which is expensive and difficult to manufacture due to structural complexity.

SUMMARY OF THE INVENTION

The present invention has been made to solve the foregoing problems of the prior art and therefore an object of certain embodiments of the present invention is to provide a variable air volume control apparatus with excellent performance, capable of accurately adjusting air volume through simple structural improvements, and is low-cost.

Another object of certain embodiments of the invention is to provide a variable air volume control apparatus in which an air flow path is opened in proportion to opening ratio of a damper blade at a low opening ratio, thereby accurately adjusting air volume.

According to an aspect of the invention for realizing the object, there is provided a variable air volume control apparatus for varying air volume in a duct, including: a damper blade disposed rotatably within the duct for opening or closing an air flow path; an actuator for rotating the damper blade; 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.

Preferably, the curved surface of the air flow path expansion mechanism expands and compensates the air flow path such that an open area is in direct proportion to an opening ratio corresponding to an open angle of the damper blade.

Preferably, the air flow path expansion mechanism comprises a ring structure installed on an inner surface of the duct, and the damper blade has a circumference the same as that of the ring structure.

Preferably, the ring structure has a circular inner periphery.

Preferably, the ring structure has an oval shape in which a horizontal or an axial diameter of the damper blade is larger than a vertical diameter.

Preferably, the air flow path expansion mechanism is a part of the duct that is constricted inward.

Preferably, the air flow path expansion mechanism is a part of the duct that is bulged outward.

Preferably, the damper blade has an shaft shifted upward or downward from a center of the duct.

Preferably, the damper blade is installed in a rectangular duct.

Preferably, the curved surface of the air flow path expansion mechanism is formed to compensate an open area of (θ/90)−(1−COS θ) at a low opening ratio, where θ is an arbitrary angle at which damper blade open from a closed position of the damper blade.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

FIG. 1 illustrates a conventional air volume control apparatus;

FIG. 2 illustrates another conventional air volume control apparatus;

FIG. 3 is a graph showing the open area ratio and the air volume change ratio with respect to the opening ratio, obtained by the conventional variable air volume control apparatus;

FIG. 4 is an overall configuration view illustrating a variable air volume control apparatus according to the present invention;

FIG. 5 is a cross-sectional view illustrating the variable air volume control apparatus according to the present invention;

FIG. 6 is a graph showing the open area ratio and the air volume change ratio with respect to the opening ratio, obtained by the variable air volume control apparatus according to the present invention;

FIG. 7 is a cross-sectional view illustrating an alternative embodiment of the variable air volume control apparatus according to the present invention, in which an air flow path expanding mechanism having an oval inner periphery;

FIG. 8 is a side sectional view illustrating another alternative embodiment of the variable air volume control apparatus according to the present invention, in which the air flow path expansion mechanism is a part of the duct that is constricted inward;

FIG. 9 is a side sectional view illustrating yet another alternative embodiment of the variable air volume control apparatus in which the air flow path expansion mechanism is a part of the duct that is bulged outward;

FIG. 10 illustrates a further another alternative embodiment of the variable air volume control apparatus according to the present invention, in which a shaft of the damper blade is shifted downward; and

FIG. 11 is a side sectional view illustrating further another alternative embodiment of the variable air volume control apparatus according to the present invention including a rectangular duct.

FIG. 12 illustrates a graph showing the improved air volume change ratio with respect to the opening ratio of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

As shown in FIG. 4, the variable air volume control apparatus 1 according to the present invention is installed inside a duct 10 through which outside air is introduced and includes a flow sensor 20 for sensing air flow from the outside, a damper blade 30 for adjusting air flow introduced indoors from the outside, and an actuator 40 for rotating the damper blade 30.

Also, the variable air volume control apparatus 1 includes a room thermometer 50 for detecting room temperature and a controller 60 for controlling the operation of the variable air volume control apparatus 1.

The flow sensor 20, the actuator 40 and the room thermometer 50 are electrically connected to the controller 60 to thereby be controlled.

Also, the variable air volume control apparatus 1 of the present invention includes an air flow path expansion mechanism 70 having a curved surface 70a for expanding the airflow path according to an open angle θ of the damper blade 30 as the damper blade 30 is opened.

The air flow path expansion mechanism 70 provides an open area through which air can flow as the damper blade construction 30 is opened, and to control the air flow path in accordance with an open angle of the damper blade 30. The air flow path expansion mechanism 70 is positioned at a point along the duct 10 so as to form constrictor portion with a generally central rib portion and oppositely disposed side portions extending sidewardly from the rib portion along the duct 10.

The rib portion projects inwardly relative to the side portions and generally transversely to the duct towards the center of the duct 10 to form a ridgeline to closely adjoin at least a portion of the outer circumference of the damper blade construction 30 when the damper blade construction 30 is in its fully closed position.

The side portions include concavely curved surfaces 70a facing inwardly towards the duct 10, the curved surfaces 70a meeting at the ridgeline and extending sidewardly from the rib portion along the duct 10.

The constrictor portion has an inner circumference at said ridgeline approximately the same as the outer circumference of said damper blade construction 30 such that, when said damper blade construction 30 is in its fully closed position, said constrictor portion and said damper blade construction 30 generally close the air flow path through the duct.

The curved surface 70a of the air flow path expansion mechanism 70 preferably expands and compensates the air flow path according to the open angle of the damper blade 30. In particular, in a low opening ratio range (hereinafter, referred to as the opening ratio of 0% to 30%), the curved surface 70a compensates for the area excluding an area corresponding to “1−COS θ” from the air flow path in accordance with the open area ratio in direct proportion to the open angle.

In addition, the air flow path expansion mechanism 70 preferably has a ring structure 74 installed on an inner surface of the duct, and the damper blade 30 has a circumference the same as an inner circumference of the ring structure 74.

That is, as shown in FIGS. 4 and 5, the air flow path expansion mechanism 70 is composed of a ring structure 74 installed on an inner surface of the duct 10, and the damper blade 30 has the inner circumference the same as the ring structure 74.

The air flow path expansion mechanism 70 can be installed on an inner surface of the duct 10 by a plurality of screws 72 penetrating through the duct 10 from the outside to fix the ring structure 74 on the inner side of the duct 10. The damper blade 30 is disposed inside the ring structure 74, and the rotation shaft 32 penetrates through the ring structure 74 and the duct 10 to enable rotation of the damper blade 30.

One end of the rotation shaft 32 is extended through the duct 10 and is connected to an operator 40 to be rotated forward and backward.

In addition, the air flow path expansion mechanism 70 has a curved surface 70a installed inside the duct 10 for expanding and compensating the air flow path for the area excluding an area corresponding to a cosine function (1−COS θ) of the open angle θ of the damper blade 30.

The curved surface 70a expands and compensates the open area for an area corresponding to (θ/90)−(1−COS θ) at a low opening ratio, i.e., 0% to 30%. At an opening ratio greater than 30%, the open area is no longer expanded or compensated. Thus at an opening ratio of up to 30%, the open area ratio is expanded and compensated to have directly proportional characteristics with respect to the opening ratio.

In addition, such a curved surface 70a extends from a portion of the duct 10 corresponding to an end portion of the damper blade 30 vertically positioned to a portion of the duct 10 corresponding to an end portion of the damper blade 30 horizontally positioned. In the upper region with respect to the rotation shaft 32, the curved surface 70a is installed in the air inlet side or the front side of the duct, and in the lower region, it is installed in the air outlet side or the backside of the duct 10.

When the damper blade 30 is opened at an arbitrary open angle θ at a low opening ratio (0 to 30%), conventionally, the damper blade 30 is opened by an open area ratio corresponding to 1−COS θ. However, according to the present invention, as shown in FIG. 4, the curved surface 70a of the ring structure 74 compensates the open area ratio by (θ/90)−(1−COS θ) to obtain a linear open area ratio approximating to the opening ratio.

As said damper blade construction 30 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 as shown in FIGS. 6 and 12.

Further, said rib portion may have a height at said ridgeline in the range of about 10% to 40% of the radius of the duct 10.

Preferably, said rib portion may have a height at said ridgeline in the range of about 12.5% to 32.5% of the radius of the duct 10.

More preferably, said rib portion may have a height at said ridgeline in the range of about 17.5% to 27.5% of the radius of the duct 10.

In addition, rather than having a ring structure 74 with a circular inner periphery, the air flow path expansion mechanism 70 can have a ring structure 76 with an oval inner periphery in which the diameter of the portion of the shaft 32 of the damper blade is larger than the vertical diameter.

Such a structure as shown in FIG. 7 ensures more space in the air flow path of the duct 10 while facilitating installation of the rotation shaft 32 of the damper blade.

In addition, the air flow path expansion mechanism 70 may preferably be a part of the duct 10 having a constricted part 78. As shown in FIG. 8, the duct 10 is machined to have the constricted part 78 constricted inward of the duct 10. The curved surface 70a of the air flow path expansion mechanism 70 expands and compensates for an area of the air flow path excluding the area corresponding to “1−COS θ” at a low opening ratio range, i.e., 0 to 30%, in accordance with the open area ratio in direct proportion to the opening ratio.

Such a structure does not require an additional ring structure, and can be formed by machining the duct 10, and thus can be adopted in the present invention without additional costs of material.

The constricted part 78 also has the curved surface 70a for additionally compensating the open area ratio by (θ/90)−(1−COS θ).

Alternatively; the air flow path expansion mechanism 70 can be a structure in which the duct 10 is machined to have a bulged part 80 bulged outward of the duct 10. When the damper blade is open in an open angle θ at a low opening ratio (0 to 30%), conventionally, the damper blade is opened by an open area ratio corresponding to 1−COS θ. However, as shown in FIG. 9, with this bulged part 80 bulged outward of the duct 10, the curved surface 70a of the bulged part 80 compensates the open area ratio by (θ/90)−(1−COS θ) to result in a linear open area ratio approximating to the opening ratio:

Such a structure does not require an additional ring structure, and can be formed by machining the duct 10, and thus can be adopted in the present invention without additional costs of material. Also, the structure does not cause decrease in the air volume in the duct 10.

In addition, according to a certain embodiment of the present invention, the damper blade 30 has its rotation shaft 32 shifted upward or downward from a center P of the duct 10.

As shown in FIGS. 10 (a) and 10(b), the rotation shaft 32 is shifted in a predetermined distance L downward from the center P of the duct 10.

In this case, the damper blade 30 may be a structure other than a circular plate, but the air flow path expansion mechanism 70 may still be a ring structure having an inner periphery the same as the outer periphery of the damper blade 30, or a part of the duct 10 having a constricted part.

In the above, a downwardly shifted position of the damper blade 30 is presented, but an upwardly shifted position can also be adopted.

The invention is also effectively applicable to a duct 10′ having a rectangular cross-section in addition to a circular cross-section. In this case, the air flow path expansion means 70 can be composed of first and second curved structures 82a and 82b separated into upper and lower parts rather than a ring structure, and can be fixed to the upper and lower inner surfaces of the duct 10′, respectively.

As shown in FIG. 11, in such a structure, the first and second curved structures 82a and 82b have curved surfaces, respectively, for compensating the conventional open area ratio of “1−COS θ” into the open area ratio corresponding to “θ/90”, where each of the curved surfaces compensates the open area ratio by (θ/90)−(1−COS θ).

As shown in FIG. 4, the air volume control apparatus 1 with the above described configuration is operated in the range from the vertical position of the damper blade 30 to completely block the air flow path at 0 degrees to an arbitrary angle θ at which the damper blade 30 is opened to the horizontal position of the damper blade 30 to completely open the air flow path at 90 degrees.

As the air volume control apparatus 1 is operated as above, when the damper blade 30 is open in an arbitrary angle θ (at a low opening ratio of about 0 to 30%), the actual open area ratio created by the damper blade 30 equals to a sum of the conventional open area ratio corresponding to (1−COS θ) and an open area ratio corresponding to θ/90−(1−COS θ) compensated by the air flow expansion mechanism 70 at the arbitrary angle. As a result, this summed open area ratio corresponds to θ/90, which yields an open area ratio directly proportional to an arbitrary angle θ, i.e., opening ratio of the damper blade 30.

FIG. 6 illustrates a graph showing the improved open area ratio and air volume change ratio with respect to the opening ratio by the present invention.

The open area ratio curve B′ shown in FIG. 6, improved by the present invention is in direct proportion to the opening ratio curve A at a low opening ratio (0 to 30%).

FIG. 12 illustrates a graph showing the improved air volume change ratio with respect to the opening ratio of the present invention.

In FIG. 12, curves C1, C2, and C3 respectively represent cases in which the rib portion has a height at the ridgeline equal to 10%, 22.5% and 40% of the radius of the duct 10, and a curve C4 represents a case in which there is no rib portion in duct 10 according to the prior art.

As shown in FIG. 12, in a case which the rib portion has a height at the ridgeline equal to 22.5% of the radius of the duct 10, the air volume change ratio of curves C2 has an almost linear relationship with the opening ratio curve A at a low opening ratio.

Also, as shown in FIG. 12, the air volume change ratio of curves C1 and C3, improved by the present invention, is increased in an approximately linear relationship with the opening ratio curve A at a low opening ratio (0 to 30%).

However, the air volume change ratio of curve C4, according to the prior art, deviates greatly from the opening ratio curve A.

As described above, in the present invention, when the damper blade 30 is open in an arbitrary angle θ from a closed position completely blocking the air flow path, for example, open at 9° (at the opening ratio of 10%), the air flow path expansion mechanism 70 expands and compensates the open area of the air flow path by 9/90−(1−COS 9°). When the damper blade 30 is further opened up to 27° (the opening ratio of 30%), the air flow expansion mechanism 70 expands and compensates the open area of the air flow path by 27/90−(1−COS 27°), thereby increasing air volume.

In addition, at the opening ratio of 30% (27° or more, the present invention yields the open area ratio curve that is similar to the open area ratio curve B with respect to the opening ratio of the damper blade 30 without any compensation.

As described above, the open area ratio with respect to the opening ratio is improved significantly from the conventional curve B to have direct proportional characteristics at an opening ratio of 30% or less, i.e., an open angle of 27° or less.

Thereby, at an opening ratio of 0 to 50%, the air volume change ratio with respect to the opening ratio is improved to have linear characteristics to achieve more accurate and precise air volume control.

As set forth above, certain embodiments of the present invention attains the open area ratio approximate to opening ratio through simple structural improvements by the air flow path expansion mechanism, thereby achieving more accurate and precise air volume control.

Also, according to certain embodiments of the invention, installing the simple air flow path expansion mechanism allows accurate control of the air volume and a low-cost air volume control apparatus having excellent capabilities.

Certain exemplary embodiments of the invention have been explained and shown in the drawings as presently preferred. The invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. While the present invention has been shown and described in connection with the preferred embodiments, it will be apparent to those skilled in the art that modifications and variations can be made without departing from the spirit and scope of the invention as defined by the appended claims.

Claims

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.