GB2515109A

GB2515109A - A flow control apparatus for a HVAC system

Info

Publication number: GB2515109A
Application number: GB1310649.7A
Authority: GB
Inventors: James Ngai
Original assignee: Nuaire Ltd
Current assignee: Nuaire Ltd
Priority date: 2013-06-14
Filing date: 2013-06-14
Publication date: 2014-12-17
Anticipated expiration: 2033-06-14
Also published as: GB201310649D0; GB2515109B

Abstract

Flow control device through an air conditioning or ventilation device comprises a moveable main damper 12 with one or more auxiliary damper(s) 20, 22 at a sealing edge of the main damper and both the main damper and auxiliary damper(s) are arranged to control the flow of air passing through an outlet of the air conditioning or ventilation device. The auxiliary damper(s) is/are moveable relative to the main damper to vary the extent the auxiliary damper(s) restrict flow through the outlet. A biasing means (torsion spring) 36 bias the auxiliary damper(s) in a rest position and when the main damper rotates closed the auxiliary damper(s) rotate away from the rest position. Side panels 16 are located either side of the main damper and both the main damper and the auxiliary damper(s) are mounted to the side panels. Stops (32, fig 4) on the auxiliary damper(s) limit rotation of the auxiliary damper(s) and hold them in the rest position. The auxiliary damper(s) may comprise a curved leading edge 28. A plurality of main dampers each having auxiliary dampers may be used (fig 7) and are driven by a common drive (fig 8).

Description

A Flow Control Apparatus for a HVAC System The present invention relates to a flow control apparatus and in particular a damper assembly for a HVAC system.

HYAC (heating, ventilation, and air conditioning) systems utilise mechanical or "forced" ventilation to control indoor air quality, which is provided by an air handler. Conditioned air is supplied to multiple rooms via a series of ducts and vents, and it is necessary to be able to independently control the supply of air to each room. Automatic dampers are used to regulate airflow in order to independently modulate the flow of air in order to affect climate control. Dampers are typically operated by electric or pneumatic motors which in turn are controlled by the FIVAC control system.

A known damper mechanism 1 for controlling the airflow in a HVAC system is shown in is Figure 1. The damper mechanism 1 comprises damper blade 2 situated in an aperture 4 defined within a damper shut off plate 6. The damper blade 2 is rotatable within die aperture 4. Rotation of the damper blade 2 varies the effective size of the flow aperture 4 thereby causing a corresponding increase or decrease in the flow resistance and therefore a variance of the flow rate through the duct.

The damper blade 2 rotates between a fully open position in which the damper 2 is oriented substantially parallel to the flow and orthogonal to the plane of the damper plate 6, and a closed position in which the damper blade 2 abuts the damper plate 6 and closes the aperture 4. As the damper blade 2 approaches the closed position and the effective size of the flow aperture becomes very small, a small incremental change in the angular position of the damper blade 2 can cause a disproportionately large change in the flow rate relative to the change in the flow rate for a corresponding change in angular position when the damper blade 2 is in a more open position. This exponential change in the angular damper position against flow rate relationship close to the closed position makes fine control of flow rate very difficult in the close to closed condition.

In order to meet increasingly the increasingly tight design specifications of HVAC systems, it is important that air flow rates are able to be closely and accurately controlled across the full range of flow rates.

It is therefore desirable to provide an improved damper apparatus which addresses the above described problems and/or which offers improvements generally.

According to the present invention there is provided a damper apparatus as described in the accompanying claims.

In an embodiment of the invention there is provided a fluid flow control apparatus for a ventilation system comprising a first damper element defining a flow aperture; a second damper element movable relative to the first damper element between a closed configuration in which the aperture is closed by the second damper element and an open configuration in which a fluid pathway is defined between the first and second damper elements permitting fluid flow through the flow aperture, the second damper element being movable to variably restrict fluid flow through the flow aperture by varying the size of the fluid pathway; and a third damper element arranged relative to the second damper element to provide additional restriction of the flow through the fluid pathway.

It has been found that as a damper approaches the closed position against a shut off plate, * the increase in pressure loss and hence the reduction of flow rate is disproportionately large for a given movement of the damper. The third damper element advantageously provides additional flow restriction independently of the second damper element which creates a higher pressure loss across the damper assembly which produces a higher reduction in flow rate with the damper in a more open position. At this more open position the relative change in flow reduction for a given change in position of the damper is more gradual and therefore more easily and accurately controllable. The third damper element also lengthens the fluid pathway by defining an extension of the fluid pathway between the third damper and the second damper element thereby smoothing the pressure loss over a greater path length.

The third damper element is preferably movable relative to the second damper element to vary the extent to which the third damper element restricts the flow rate through the fluid pathway. As such the third damper element may be operated to increase the level of flow restriction it provides as the second damper element moves closer to the closed position to s avoid the damper having to move into the region of exponential pressure drop to achieve die required reduction in flow rate.

The third damper element is preferably movably mounted to the second damper element and arranged such that over a first range of movement of the second damper element the ía third damper element remains in a fixed rest position relative to the second damper element, and over a second range of movement between the first range of movement and the closed position the third damper element moves relative to the second damper element to variably restrict fluid flow through the fluid pathway. The third damper element is therefore able to be actuated by the movement of the second damper element. This IS advantageously obviates the requirement for a separate actuation means to control the movement of the third damper element, or a control system to independently monitor and control the position of the th.d damper element relative to the first and sccond damper elements. As such the cost of the system may be minimised, while the avoidance of complex mechanical and electrical coniponents also reduces failure rates and maintenance requirements.

The third damper element may be arranged such that over the second range of movement the third damper element engages the first damper element causing the third damper clement to move relative to the second damper element to variably restrict fluid flow through the fluid pathway. In this way the third damper element is automatically actuated by its engagement with the first damper element as soon as the second damper element reaches a predetermined distance from the first damper element.

The third damper clement also advantageous reduces noise emitted by the damper arrangement. The third damper element enables a given pressure drop to be achieved with the second damper element spaced a relatively greater distance from the first damper clement. The greater spacing and hence flow area reduces the velocity for the same flow rate, and hence reduces the noise of the system.

The second damper element is preferably rotatably mounted relative to the first damper element and rotates between the open and closed configurations, and the third damper element is rotatably mounted to the second damper element and rotates relative to the second damper element on engagement with the first damper element to variably restrict fluid flow through the fluid pathway.

The second damper element preferably comprises a primary damper blade having at least one end arranged to engage with the first damper element to close the aperture, and the ID third damper element comprises an auxiliary damper blade rotationally mounted to the primary damper plate such that its rotational axis is spaced from the end of the primary damper plate, and such that in the rest position a fluid flow channel is defined between the damper blade and the end of the damper plate. The rotational axis of the auxiliary blade is arranged parallel to the rotational axis of the primary damper blade.

The fluid flow control apparatus preferably further comprises biasing means arranged to rotationally bias the auxiliary damper to the rest position in a first rotational direction, which is preferably a torsion spring. The first damper element is a shut of plate and the auxiliary damper may he arranged such that when the primary damper is rotated towards the closed position in the second range of movement engagement of the auxiliary damper with the shut of plate causes the auxiliary damper to rotate away from the rest position in an opposing second rotational direction.

The fluid flow control apparatus preferably comprises first and second auxiliary damper blades mounted at opposing ends of the primary damper blade. The primary damper blade is mounted within the aperture and relative to the first damper element such that the first and second auxiliary damper blades engage opposing sides of the first damper element over the second range of movement, The use of a rotationally actuated damper enables the damper to be actuated by a drive means located outside the duct connected to the axis of the damper, rather than requiring an actuator located at least in art within the duct as required for linear actuation.

The primary damper preferably comprises a blade section and a pair of opposing side panels which extend past the ends of the blade section and wherein the auxiliary blades are mounted to the side panels at each end at a position spaced lengthwise from the end of the blade section. The side panels provide structural rigidity to the damper blade as well as forming a mounting bracket for the auxiliary damper.

Each auxiliary blade and the corresponding end of at [east one of the side panels to which it is mounted include corresponding stop features arranged to cooperate to limit rotation of the auxiliary blade in the first direction to hold the auxiliary blade in the rest position and to permit rotation of the auxiliary blade in the opposing sceond direction.

The first damper element is a preferably a shut off plate comprising spaced plate sections defining the flow aperture therebetween. Each plate section comprises a planar sealing surface arranged to be engaged by a corresponding sealing surface located at an end of the primary damper blade. The blade section of the primary damper blade comprises fIrst and second blade sections located on opposing sides of the rotational axis thai are offset from each other in a direction orthogonal to the length and width of the primary damper blade such that the scaling surface at the end of each blade section is arranged substantially parallel to the sealing surface of the shut off plate when in the closed position to optimise the sealing engagement thcrcbetwccn, In contrast, in pivoting damper arrangements of the prior art where a continuous fiat damper plate is used, the contact between the damper plate and the shut off plate is angled rather than parallel creating an edge contact of substantially smaller area which therefore has substantially less sealing efficiency.

Each auxiliary blade includes a curved leading edge configured for rolling engagement with the first damper element. This enables contact to be maintained between the damper blade and the shut off plate as the damper blade rotates and moves towards and away from the shut off plate.

The second and third damper elements are preferably operatively connected such that movement of the third damper elcmcnt is actuated by movement of the second damper element.

Preferably the first damper element defines a plurality of flow apertures. The second and third damper elements define a damper assembly, and the control apparatus comprises a plurality of damper assemblies corresponding to the plurality of flow apertures, The plurality of damper assemblies are arranged to cooperate with the first damper element to variably restrict flow through the plurality of respective flow apertures. Each of the plurality of damper assemblies preferably comprises a main damper blade having auxiliary damper blades at either end as dcscribcd above. The first damper element is a shutoff plate having a plurality of apertures in which each of the damper assemblies is rotationally mounted. The force acting on a damper blade for a given operating pressure is detennined by the size and hence the area of the blade. Preferably the rotational axes of the plurality of damper assemblies are arranged parallel to each other and aligned along a common plane.

Providing a plurality of blades located at a common Longitudinal position rather than a single blade reduces the stresses on each blade as the force acting on each blade for the same operating pressure is reduced due to the reduced area of the blade. Therefore, the blades can be formed from thinner material and require bearings of a lower strength specification than would be required for a single blade spanning the same duet.

Movement of the plurality of damper assemblies is preferably actuated by a common drive means. This enables the movement of the blades to be synehronised and coordinated.

Furthermore, the cost and complexity of the system is reduced as only a single motor or other actuator is required.

In another aspect of the invention there is provided a ventilation system comprising at least one enclosure defining a ventilation duct; a fluid flow control apparatus according to any preceding claim located within the duct and arranged such that fluid flow through the dud is caused to flow through the flow aperture of the first damper element.

The present invention will now be described by way of example only with reference to the following illustrative figures in which:

Figure us a damper arrangement of the prior art;

Figure 2 shows a isometric view of a damper arrangement according to an embodiment of the invention; Figure 3 shows the damper of Figure 2 hi the fully open position; Figure 4 shows the damper arrangement of' Figure 3 rotated closer to the closed position; Figure 5 shows the damper arrangement of Figure 4 having moved ftrther closer to the closed position with the auxiliary damper blades engaged with the shut off plate; and Figure 6 shows the damper arrangement of Figure 5 moved to the fully closed position.

Referring to Figure 2, a damper assembly 10 includes a main damper blade 12 having a length 1, a width w and a central axis of rotation A-A, The main damper blade 12 includes a stepped planar body 14 and opposing side panels 16. Rotational mountings 18 are located either side of the main body 14 along the rotational axis A-A for rotationally mounting the damper blade 12 within a ventilation duct.

Auxiliary damper blades 20 and 22 arc connected to the main damper blade 12 at either end of the main blade 12 taken lengthwise. The damper blades 20 and 22 are identical in constructions and are both connected to the respective end of the main blade 20 in the same manner. Therefore for conciseness the following description relates to the first auxiliary blade 20 only but is also applicable to the second blade 22.

The auxiliary blade 20 has a width substantially equal to the width the of the body section 14 of the main damper blade 12. The auxiliary blade 20 is pivotalty connected at each side to the side panels 16. The pivotal connection between the auxiliary damper 20 and the side panels 16 comprises a cylindrical lug 24 extending from each end of the auxiliary damper which is rotatably received within a corresponding aperture 26 in the side panels 16,

S

The rotational axis of the auxiliary damper 20 is parallel to the rotational axis A-A of the main damper 12, The auxiliary damper 20 is elongate in the width wise direction with reference to the width w of the main damper having a greater width than length. Relative to the main damper 12 the auxiliary damper 20 has a distal leading end 28 that is upwardly curving away from the main damper 12 terminating at a distal edge 30. The proximal trailing end section 31 of the auxiliary damper 20 includes a stop portion 32 extending upwardly away from the main damper 12.

A torsion spring 36 is mounted on the auxiliary damper 20 centrally along its width and located along the axis of rotation. The spring 36 has a coiled cylindrical body portion mounted about a corresponding cylindrical lug of the auxiliary damper 20 located within a centrally located recess 38. The aims 40 of the torsion spring 36 extend downwardly and inwardly towards the body section 14 of the main damper 12.

As shown in Figure 3 the damper assembly 10 is pivotally mounted within an aperture 32 defined within a shutoff plate 34, which is located at a fixed location along the ducting of a ventilation system. The shutoff plate 34 engages the walls of the ducting at its outer edges such that all airflow for the dueting must flow through the aperture 32. The damper assembly 10 is pivotally mounted relative to the shutoff plate 34 by the pivotal mountings 18. The rotational axis A-A is located on the plane defined by the shutoff plate 34 at a central location within the aperture 32. In the open condition shown in Figure 3 the damper 10 is oriented substantially orthogonal to the plane of the shutoff plate 34 substantially parallel to the direction of flow through the aperture 32. This position represents the maximum effective size of the aperture 32 and minimum flow resistance and hence maximum flow through the aperture 32.

In the open condition the auxiliary damper 20 is in the disengaged rest position. The auxiliary damper 20 is rotationally biased to the rest position by the torsion spring 36 and is held in the disengaged position by the stops 32 which abut against the end projections of the side panels 16. The auxiliary damper 20 is rotationally mounted to the side panels 16 at a position spaced length wise from the end edge 40 of the body section 14 of the main damper 12. Specifically, the rotational axis of the auxiliary damper 20 is spaced length wise from the end 40 of the main body 14. In the disengaged position the auxiliary damper is substantially oriented transversely relative to the length wise plane of the main body 14. In this position, a gap 42 is defined bctwecn the inner surface 44 of the damper 20 and the end edge 40 of the main body 14. The gap 44 defines an air channel between the end of the main damper body 14 and the inner surface of the auxiliary damper 20, the inner surface being the surface facing the main body 14.

The position of the damper 10 is controlled by a rotational actuator connected to the to rotational mounts 18 of the main damper 12. Any suitable rotational actuator may be provided and may be connected to the damper 10 in any manner suitable to enable a rotational drive to be transferred to the damper to cause it to rotate about the rotational axis A-A. The damper 10 is rotated by the actuator in response to the control system of the HVAC system to control the size of the aperture 32 to achieve a desired flowrate. In the IS arrangement shown in Figure 4 the damper 10 has been moved to a position in which it is approaching the closed condition. The auxiliary damper 20 is in the disengaged rest condition such that the gap 44 between the auxiliary damper 20 and the body 14 of the main damper 12 is fully open. In this close to closed position a flow channel or gap 46 is defined between the end 40 of the main body 14 and the shutoff plate 34. A further gap 48 is defined between the distal end edge 30 of the auxiliary damper 20 and the shutoff plate 34. Without the auxiliary damper the airflow through the aperture 32 would pass through the gap 46 and continue past the damper 12 without further restriction. The presence of the auxiliary damper 20 provides additional down stream flaw restriction with the airflow being forced to flow through the gap 40 between the main body 14 of the damper 12 and the auxiliary damper 20 and through the gap 48 between the distal end edge 30 of the auxiliary damper 20 and the shutoff plate 34. The auxiliary damper 20 thereby creates a convoluted, elongated and narrowed airflow pathway. Forcing the airflow along this elongated pathway creates a higher pressure loss at the given angular position than would be achieved without the auxiliary damper 20 thereby producing a higher reduction of the flow rate. Therefore the damper begins to significantly restrict the flow at an earlier angular position than would be otherwise achieved allowing, for a given flow rate, the damper 12 to be maintained at greater angular distance from the shutoff plate 34. This allows the damper 12 to be controlled across a range of anguLar movenierit where the change of flow rate for a given angular displacement is not as great as is the case closer to the closed position at a smaller angular distance.

As the damper 10 moves further closer to the closed position the distal end edge 30 of the auxiliary damper 20 engages the shutoff plate 34, as shown in figure 5. This closes the gap 48 between the auxiliary damper 20 and the shutoff plate 34 such that all airflow is now forced through the flow path defined by the gap 44 between the end of the main body 14 of the damper 12 and the auxiliary damper 20. This further restricts Lhe flow area and thereby further increases the pressure loss hence creates higher flow reduction. As the damper 10 continues to rotate, with the end of the auxiliary damper blade 30 engaged against the shutoff plate 34 the auxiliary damper blade 20 begins to rotate with the curved distal end surface section 28 enabling contact to be maintained between the auxiliary damper 20 and the shutoff plate 34 during rotation, As the distal end 30 of the auxiliary damper 20 rotates away from the main damper 12 the opposing trailing cnd 31 rotates downwardly towards the body 14 of the main damper 12 and begins to close the gap 44. At the same time the main body 14 of the main damper 12 continues to move towards the shutoff plate 34 and continues to close the gap 46. The distal end 30 of the auxiliary damper 20 has a nanower width than the trailing end 33 and therefore while the trailing end 33 is prevented from rotating in a first direction as biased by the torsion spring 36 by the stop 32 engaging with the side panels 16, in the opposing second direction the distal end 30 of the auxiliary damper 20 is able to rotate past the end lugs of the side panels 16 freely and without engagement with the stop 32 simultaneously moving away from the corresponding plugs of the side panels 16.

Figure 6 shows the damper 10 in the fully closed position! The main damper 12 is rotated to a position in which the distal ends 40 engage and seal against the adjacent sealing surfaces of the shutoff plate 34. The gap 46 between the main damper 12 and the shutoff plate 34 is thereby closed. The body section 14 of the main damper 12 includes a first end 42 and a second end 44 located on opposing sides of the central pivot axis 46. The first section 42 and second end section 44 include opposing inner faces 48 and 50 respectively with the inner face being defined as the surface facing the shutoff plate 34, with the corresponding first and second 32 and 44 engaging opposing sides of the shutoff plate 34.

The main body 14 is stepped at the longitudinal position of the pivot axis 46 such that the

II

inner faces 48 and 50 lie along a common longitudinal plane relative to the length L of the damper. The shutoff plate 34 includes corresponding first and second plate sections 52 and 54 located on opposing sides of the aperture 32. The first and second plate sections 52 and 54 of the shutoff plate 34 are offset transversely relative to the longitudinal axis L of the main body 14 when in the closed position when in the longitudinal such that a respeclive surfaces which are adjacent to and abut the end sections 40 of the main damper 12 when in the closed position lie along the same common plane. This off setting of the end sections 52 and 54 and the stepped configuration of the main body 14 ensures that the end seclions engage the shutoff plate in a parallel arrangement thereby maximising surface contact io and optimising seahng.

In the embodiment shown in Figure 7 a pair of dampers 1 lOa and 11 Gb are aligned a common longitudinal position along the length of the duet Ill. Bach damper 1 ba and 1 lOb is configured and interacts with the shutoff plate 134 as described above. The dampers 11 Oa and 11 Ob are arranged at spaced locations along the shutoff plate 134 transversely to the longitudinal axis of the duct 111. A pair of corresponding apertures I 32a and 1 32b are defined in the shutoff plate 132 in which the dampers 11 Oa and 11 Ob are respectively rotatably located.

As shown in Figure 8, the dampers 11 Oa and 11 Oh are lined to a common drive means via a drive train arrangement 150. The drive train arrangement 150 includes a first drive axle 152 connected to a drive means which may be an electric motor or any other suitable rotational actuator. The drive axle 152 is connected to a drive gear 154 which is configured to rotate with the drive axle 152. The drive gear 152 is meshingly connected to two driven gears 1 56a and 1 56b. The driven gears 1 56a and 1 56h are each connected respectively to the rotationa[ mountings 11 8a and 11 8b of the respective dampers 11 Oa and 11Gb, A rotational drive input from the drive axle 152 is transmitted to the dampers 11 Ga and 11Gb via the gear train to cause synchronised and coordinated movement of the dampers 11 Oa and IlOb.

The damper assembly includes a mounting assembly 160 for rotationally supporting the dampers 11 Oa and 11 Ob and for mounting the dampers within a dueting Ill. The mounting assembly 160 includes a first mounting plate 162 and second mounting plate 164 located on opposing sides of the dampers 11 Os and II Oh. The first mounting plate 162 is frnmed to defined a housing for containing the drive mechanism 150 for the dampers 1 lOa and 11 Oh. The first mounting plate includes a main side panel 166 and end panels 168. The main panel 166 rotationally supports the dampers llOa and liOb and thc drive axle 152.

The end panels 168 space the main panel 166 from the side walls of the duct Ill to accommodate the gears of the drive mechanism 150 while also acting as shutoff plates to prevent airflow between the main panel 166 and the side walls of the duct 111, thereby ensuring that all airflow is directed through the apertures 132. The second nTlounting plate 164 is arranged in a similar manner with a smaller spacing between the main panel and the side walls of the duct 111 enabled by the absence of drive gears on that opposing side. The first and second mounting plates 162 and 164 are interconnected by the shutoff plate 134.

As such that damper assembly forms a self-contained preassembled unit that can be easily inserted into a ducting arrangement without complicated assembly requirements. It will be appreciated that this assembly could also be applied to a single damper arrangement. It will also be appreciated that the above embodiment could also include morc than two dampers, and that multiple damper assemblies may be located at spaced locations along the length of a duct, and operated by a single drive means if required.

Whilst cndeavouring in the foregoing specification to draw attention to those features of the invention believed to be of particular importance it should be understood that the Applicant claims protection in respect of any patentable feature or combination of features hereinbefore referred to and/or shown in the drawings whether or not particular emphasis has been placed thereon.

Claims

CLAIMS1. A fluid flow control apparatus for a ventilation system comprising: a first damper element defining a flow aperture; a second damper element movable relative to the first damper element between a closed configuration in which the aperture is closed by the second damper element and an open configuration in which a fluid pathway is defined between the first and second damper elements permitting fluid flow through the flow aperture, the second damper element being movable to variably restrict fluid flow through the flaw aperture by varying the size of the fluid pathway; and a third damper element arranged relative to the second damper element to provide additional restriction of the flow through the fluid pathway.
2. A fluid flow control apparatus according to claim 1 wherein the third damper is element is movable relative to the second damper element to vary the extent to which the third damper element restricts the flow rate through the fluid pathway.
3. A fluid flow control apparaLus according to claim 2 wherein the third damper element is movably mounted to the second damper element and arranged such that over a first range of movement of the second damper element the third damper element remains in a fixed rest position relative to the second damper element, and over a second range of movement between the first range of movement and the closed position the third damper element moves relative to the second damper element to variably restrict fluid flow through the fluid pathway.
4. A fluid flow control apparatus according to claim 3 wherein the third damper element is arranged such that over the second range of movement the third damper element engages the first damper element causing the third damper element to move relative to the second damper element to variably restrict fluid flow through the fluid pathway.
5. A fluid flow control apparatus according to claim 4 wherein the second damper element is rotatably mounted relative to the first damper element and rotates between tile open and closed configurations, and the third damper element is rotatably mounted to the second damper element and rotates relative to the second damper element on engagement with the first damper element to variably restrict fluid flow though the fluid pathway.
6. A fluid flow control apparatus according to claim 5 wherein the second damper element comprises a primary damper blade having at least one end arranged to engage with the first damper element to close the aperture, and the third damper element comprises an auxiliary damper blade rotationally mounted to the primary damper plate such that its rotational axis is spaced from the end of the primary damper plate, and such that in the rest position a fluid flow channel is defined between the damper blade and thc end of the damper plate.
7. A fluid flow control apparatus according to claim 6 further comprising biasing means arranged to rotationally bias the auxiliary damper to the test position in a first rotational direction and wherein the auxiliary damper is arranged such thai when the is primary damper is rotated towards the closed position in the second range of movement engagement of the auxiliary damper with the first damper element causes the auxiliary damper to rotate away from the rest position in an opposing second rotational direction.
S. A fluid flow control apparatus according to claim 7 comprising first and second auxiliary damper blades mounted at opposing ends of the primary damper blade, wherein the primary damper blade is mounted relative to the first damper element such that the first and second auxiliary damper blades engage opposing sides of the first dampcr element over the second range of movement.
9. A fluid flow control apparatus according to claim S wherein the primary damper comprises a blade section and a pair of opposing side panels which extend past the ends of the blade section and wherein the auxiliary blades are mounted to the side panels at each end at a position spaced lengthwise from the end of the blade section.
10. A fluid flow control apparatus according to claim 9 wherein each auxiliary blade and the corresponding end of at least one of the side panels to which it is mounted include corresponding stop features arranged to cooperate to limit rotation of the auxiliary blade in the first direction to hold the auxiliary blade in the rest position and to permit rotation of the auxiliary blade in the opposing second direction.
11. A fluid flow control apparatus according to claim 10 wherein the first damper s element is a shut off plate comprising spaced plate sections defining the flow aperture therebetween, each plate section comprises a sealing surface arranged to be engaged by a corresponding sealing surface located at an end of the primary damper blade, and wherein the blade section of the primary damper blade comprises first and second blade sections located on opposing sides of the rotational axis that are offset from each other in a direction orthogonal to the length and width of the primary damper blade such that the sealing surface at the end of each blade section is arranged substantially parallel to the sealing surface of the shut off plate when in the closed position to optimise the sealing engagement therebetween.
12. A fluid flow control apparatus according to claim 11 wherein each auxiliary blade includes a curved leading edge configured for rolling engagement with the first damper element.
13. A fluid flow control apparatus according to any preceding claim wherein the second and third damper elements are operatively connected such that movement of the third dampcr clement is actuated by movement of the second damper element.
14. A fluid flow control apparatus according to any preceding claim wherein the first damper element defines a plurality of flow apertures, the second and third damper elements define a damper assembly, and the control apparatus comprises a plurality of damper assemblies corresponding to the plumlity of flow apertures and arranged to cooperate with the first damper element to variably restrict flow through the plurality of flow apertures.
15. A fluid flow control apparatus according to claim 14 wherein movement of the plurality of damper assemblies is actuated by a common drive means.
16. A fluid flow control apparatus according to claim 15 wherein the coniinon dive means is arranged to cause synchronised movement of the plurality of damper assemblies. lb
17, A fluid flow apparatus according to any one of claims 14 to 16 wherein the rotational axes of the plurality of damper assemblies are arranged parallel to each other and aligned along a common plane.
18. A ventilation system comprising: at least one enclosure defining a ventilation duet; a fluid flow control apparatus according to any preceding claim located within the duet and arranged such that fluid flow through the duct is caused to flow through the flow aperture of the first damper element.
19. A fluid flow control apparatus substantially as hereinbefore described with reference to, and/or as shown in figures 2 to 6.
20. A ventilation system substantially as hereinbefore described with reference to, and/or as shown in figures 2 to 6.