AU2009230889A1

AU2009230889A1 - Variable air diffuser

Info

Publication number: AU2009230889A1
Application number: AU2009230889A
Authority: AU
Inventors: Ken Mccarthy
Original assignee: Yanek Pty Ltd
Current assignee: Yanek Pty Ltd
Priority date: 2008-04-03
Filing date: 2009-04-03
Publication date: 2009-10-08
Also published as: WO2009121145A1

Description

WO 2009/121145 PCT/AU2009/000412 1 VARIABLE AIR DIFFUSER This invention relates to a variable air diffuser which is used to vary the amount of chilled or heated air that may enter a room of a building for the 5 purpose of heating or cooling a room. Usually primary air or chilled or heated air is passed through a supply duct under the influence of an air blower or fan to a plenum chamber or housing. Subsequently the primary air is then passed through a variable air diffuser which has one or more damper blades or vanes that could be moved to either close off the flow of primary air 10 into a room or vary the amount of air flow into the room from a fully open position of the damper blade(s) to a partially open position. Examples of such variable air diffusers include US Patents 4,448,111, 4,800,804, 5,860,592, 6,176,435 and 6,581,847. US Patent 4,448,111 includes a plenum diffuser having a hinged 15 round inlet collar, an elongate housing to form a venturi, secondary air openings, a bottom plenum chamber and a pattern controller. There are also provided flow dampers located within the venturi which are hinged at a top end and abut each other to define a closed position. The volume of air flow through the venturi may be controlled by the size of the opening between the 20 dampers. Warm return air or induced air is caused to flow through the secondary air openings into a ceiling plenum when the dampers are closed. US Patent 4,800,804 refers to use of a single damper which was supported by guide posts for vertical movement of the damper toward or away from an air discharge aperture. The damper was therefore capable of 25 only linear movement. US Patent 5,860,592 referred to a variable air volume (VAV) conditioning system having at least one diffuser which was adapted for flow of supply air as well as ventilation air into a room through a discharge aperture. Ventilation air was discharged through a ventilation air opening 30 device positioned in a diffuser housing downstream of a diffuser flow control element such as a damper blade so that ventilation air is controlled independently of and decoupled from the variable flow rate of supply air WO 2009/121145 PCT/AU2009/000412 2 which is controlled by the damper blade. US Patent 6,176,435 refers to a thermally powered variable air volume diffuser having a diffuser housing and a thermally powered actuator assembly mounted therein which varies the size of a supply air discharge 5 opening. The actuator assembly comprises four thermal actuators and means operatively connecting the thermal actuators to a flow control disc defining the discharge opening. US Patent 6,581,847 also refers to use of a thermally powered actuator assembly used in VAV diffuser. There is provided a control device 10 for control of the actuator assembly which is an electric circuit controlling a heater. Reference may also be made to a variable air diffuser known as the "THERMA-FUSER" described at www.acutherm.com/therma-fuser application/how-it-works.php which has a thermal element operatively 15 connected to damper blades which is operational by sensing average space temperature. The thermal element contains a wax specially formulated to melt at room temperatures. Expansion of the wax pushes out an actuator shaft for the damper blades causing them to open. When the wax cools and contracts, a power spring causes the blades to close. Each of the damper 20 blades are pivotally mounted at a top end thereof to a stationary mounting. There is also provided a central baffle when a pair of blades is used to which both damper blades abut when in the closed position. Each damper blade is mounted on a pivot axle also located at a top end thereof, which is movable by the actuator shaft to open and by the power spring to close. The system 25 may be varied to include 2 slot 2 way VAV diffuser, 2 slot I way VAV diffuser or 1 slot I way VAV diffuser. However, each of the aforementioned conventional variable air diffusers is considered to be complicated in structure. For example, the "Therma-Fuser" described above had an actuator assembly which included 30 an operating shaft, thermal wax element and a power spring. It is therefore an object of the invention to provide a variable air diffuser which is of simple structure and is efficient in operation.

WO 2009/121145 PCT/AU2009/000412 3 In one aspect of the invention there is provided a variable air diffuser having a plenum housing which is in fluid communication with supply air and/or return air wherein said plenum housing has a continuous peripheral wall and an opening for passage of supply and return air characterized in 5 that there is provided at least one damper blade having a first end and a second end wherein said at least one damper blade is pivotally mounted to the plenum housing or mounting structure proximal to the opening intermediate the first and second end to provide an inner end which is movable either manually or by a movable element of an actuator assembly 10 for opening and closing of an air access slot or aperture formed between an outer end of said at least one damper blade and an abutment for said at least one damper blade. The plenum housing may be cuboidal in shape having an end wall and a pair of opposed side walls and the opening discussed above. 15 However, the plenum housing may have a continuous peripheral wall of any suitable shape such as round or polygonal. Preferably there is provided an angled or lower pair of walls which each taper inwardly towards a vertical axis of the plenum housing to ultimately define the opening. The plenum housing may also be in fluid communication with a supply duct and/or a 20 return duct. Preferably the plenum housing is in fluid communication with the supply duct and optionally with a return duct. More preferably each of the above angled or lower pair of walls may be attached at an outer end thereof to a mounting element which may include a mounting socket or spigot for an adjacent damper blade. Each 25 mounting element may be the same structurally and thus, form the same or similar extrusion. Each of the mounting elements may also include one or more attachment apertures for attachment to an adjacent end wall or lower end bracket of the plenum housing or other structure contiguous until the plenum housing. Each of the mounting elements may include a locating 30 projection or socket for location of an adjacent side wall or lower wall of the plenum housing. Each mounting element may also include a lower abutment flange for abutment with a lower end of an adjacent damper blade.

WO 2009/121145 PCT/AU2009/000412 4 There also may be provided a central or intermediate mounting element or air baffle which also may have attachment aperture(s) for attachment to an adjacent end plate or lower end bracket of the plenum housing. The central mounting element or air baffle may function as an 5 abutment element for each damper blade if a pair of damper blades is required as well as a mounting element for 2 - 4 damper blades. The air baffle may also have one or more abutment flanges for abutment with an adjoining damper blade. The actuator assembly may be a drive shaft of a servo motor or 10 hydraulic motor connected to a damper blade by a suitable link assembly. Alternatively, the actuator assembly may be a flexible element shown hereinafter. On the other hand, each damper blade may be used manually. In another aspect of the invention therefore, there is provided a method of construction of a variable air diffuser structure which includes the 15 steps of: (i) connecting one or more mounting elements to an adjacent wall of a plenum housing; (ii) pivotally attaching one or more damper blades to an adjacent mounting element intermediate each end of a respective 20 damper blade; wherein in use the or each damper blade and the or each mounting element may be interchanged to provide a variable air diffuser with a variable structure having different air flow or air volume characteristics. Preferably there also may be used an intermediate or central air baffle 25 having one or more attachment apertures and also having one or more abutment surfaces for contacting an adjacent damper blade which also may be used interchangeably with the mounting element(s) and the damper blade(s). Reference may now be made to a preferred embodiment of the 30 invention as shown in the attached drawings wherein: FIG I is a perspective view of a variable air diffuser assembly constructed in accordance with the invention; WO 2009/121145 PCT/AU2009/000412 5 FIG 2 is a sectional view through line A-A of FIG 1 showing the variable air diffuser assembly of FIG 1 with a pair of damper blades in an open position and a two way air flow; FIG 3 is a similar view to FIG 2 showing a different embodiment to 5 that shown in FIG 2 with airflow in one direction only; FIG 4 shows a similar view to FIG 2 but showing four damper blades; FIG 5 shows a similar view to FIG 2 but with a single damper blade; FIG 6 shows a similar view to FIG 2 but showing a single damper blade and having a supply aperture and a return aperture for air flow; but 10 FIG 7 shows a similar view to FIG 6 but with a divided plenum allowing return air to be ducted; FIG 8 shows a similar view to FIG 2 having an upper end of each damper blade connected to a drive arrangement wherein the damper blades are in the open position; 15 FIG 9 is a similar view to FIG 8 but showing each damper blade in a position restricting air flow from the plenum chamber; FIG 10 is a top plan view of FIG 8; FIG 11 is a top plan view of FIG 9; FIG 12 shows a perspective view of another embodiment of a variable 20 air diffuser in accordance with the invention; FIG 13 shows a plan view of a link attached to an adjacent deflector blade made from bimetallic material in a non-operational position; FIG 14 shows a similar view to FIG 15 showing the link in an operational position; 25 FIG 15 is a similar view to FIG 2 which additionally illustrates a side mounted drive apparatus; and FIG 16 is a similar view to FIG 15 but showing the operation of three damper blades instead of two as shown in FIG 15, In the drawings as shown in FIGS 1-2 there is shown a variable air 30 diffuser 10 constructed in accordance with the invention having a plenum housing or duct 11 and a supply spigot 12 suitable for attachment or engagement with an air supply duct (not shown). The plenum housing 11 WO 2009/121145 PCT/AU2009/000412 6 has a top wall 13 and a pair of opposed side walls 14 and 15. There is also shown oblique walls 16 and 17 which each taper inwardly to a vertical axis 32 of the plenum housing 11 shown in FIG 2 to define an opening 5. Oblique wall 16 engages with an elongate side mounting member 18 and oblique wall 5 17 engages with an elongate side mounting member 19. Each of elongate mounting members 18 and 19 are also provided with attachment apertures or slots 20, 21, 22 and 23 for attachment by suitable fasteners (not shown) to a pair of end walls (not shown) of plenum housing 11. Top wall 13 engages with side walls 14 and 15 at 24 and 25. Each of oblique walls 16 and 17 10 engage with adjacent mounting members 18 and 19 at 26 and 27 wherein flanges or spigots 28 and 29 locate in support sockets 30 and 31. It will be appreciated that spigots 28 and 29 may be sockets and sockets 30 and 31 may also be spigots. Each of elongate mounting members 18 and 19 are provided with 15 inwardly directed (i.e. towards the vertical axis 32 of plenum housing 11) and upwardly extending flanges 33 and 34 which may engage with a pivotable damper blade 35 and 36 in an open position as shown in solid outline in FIG 2, wherein lower arcuate end 37 of each damper blade 35 and 36 abuts an adjacent flange 33 and 34 at 38. Each of elongate mounting members 18 20 and 19 may also be supported by adjoining flanges of adjacent reflector housings (not shown) which may be supported by longitudinal T bars (not shown). Each of pivotable damper blades 35 and 36 are pivotally attached to an adjacent support arm 48 of each elongate mounting member 18 and 19 25 by a pivot joint 45 wherein elongate socket 46 engages with elongate slot 47. However, it will also be appreciated that sockets 46 may form spigots or flanges and slots 47 may also form spigots or flanges. Each of damper blades 35 and 36 as shown in phantom have a closed position wherein each of arcuate lower ends 37 abut air baffle 49 at 50. Air baffle 49 also has 30 attachment apertures 51 and 52A for engagement with an aligned attachment aperture (not shown) of end bracket 40 shown in FIG 1 by a suitable fastener (not shown).

WO 2009/121145 PCT/AU2009/000412 7 Air baffle 49 also has feet 53 surrounding internal passage 54. There is also shown air supply apertures or slots 8 and 8A for passage of supply air from supply duct 12 which travels into a room (not shown) in directions as shown by the arrows. 5 FIG 3 shows a similar arrangement to that shown in FIG 2. There is shown air supply slots or apertures 9 and 9A which allow air to enter a room (not shown) in the same direction as shown by the arrows. However, the major difference between FIG 2 and FIG 3 is that damper blade 35 is shown attached to air baffle 49A instead of elongate 10 mounting member 18 by ball joint 45. Thus, air baffle 49A is now provided with an upwardly extended arcuate flange 64 which abuts with bottom end 37 of damper blade 35 in the open position as shown in full outline at 38 and abuts with elongate mounting member 18 in the closed position as shown at 65. Elongate mounting member 18 includes support socket 30A which 15 engages with flange 28A of oblique wall 16 as shown. Elongate mounting member 18 is also provided with feet 53 and internal passage 54A. Air baffle 49A is also provided with flange 48A and attachment apertures 51 and 52A. FIG 4 shows the use of four damper blades 80, 81, 82 and 83 which can be used to increase the volume of air being charged into a room through 20 supply slots 6A, 6B, 6C and 6D. Supply slots 6A and 6B show air being discharged into the room in the same direction while supply slots 6C and 6D show air being discharged into the room in the same direction but different to slots 6A and 6B. In this embodiment use is made of central air baffle 49 and two pairs of mounting members 18 and 19 as shown to achieve the desired 25 air flow and air direction shown. FIG 5 shows use of a single damper blade 70 with air flowing through a single supply slot 7A. Reference numerals are similar to those used in FIGS 2 and 3. FIG 6 shows an alternative embodiment using a single damper blade 30 70 attached to a mounting member 19 as shown in FIG 2 and hence, similar reference numerals are used as shown in FIG 2. FIG 6 shows that use of a single damper blade 70 may be used efficiently in accordance with the WO 2009/121145 PCT/AU2009/000412 8 invention. There is also shown not only a supply slot 7A but a return duct 7B which facilitates return room air to enter duct 7A because of different pressures that may prevail in the room.. FIG 7 shows a similar arrangement to that shown in FIG 6 again 5 having a supply slot or aperture 7C and a return slot or aperture 7B. However, this arrangement shows provision of a central partition 72 so that air flow from supply duct 12 may enter a room (not shown) through supply slot 7C. However, return air may enter return slot 7B and be directed to travel through return duct 73 by the partition 72. 10 In FIGS 8 - 11 is shown one form of actuator assembly for driving or actuating movement of the damper blades described in the above embodiments. Thus, there is provided servo motor 85 having a drive shaft 86 shown in FIG 8 which is pivotally attached to control lever 87 shown in FIGS 10-11 which is pivotally attached to links 58 at its ends 88 and 89. 15 Links 58 are in turn pivotally attached to damper blades 35 and 36 at 59. Thus, rotation of drive shaft 86 causes reciprocatable pivotal movement of control lever 87 which in turn, causes reciprocatable pivotal movement of links 58 to thereby cause damper blades 35 and 36 to have the movement shown in FIG 2. FIG 8 shows damper blades 35 and 36 in the open position 20 and FIG 9 shows damper blades 35 and 36 to be in the substantially closed position. In FIGS 12 - 14, there is shown another form of actuator assembly for the damper blades 35 and 36. In this embodiment there is shown blade 35 which has a link 90 formed of electroactive polymer or other material that 25 may flex as a result of an electric current being passed through from conductor element 91 having a pair of wires (not shown) that connect with connection pins 92 and 93 connectable to a source of electricity such as a battery or from a mains supply. Link 90 is pivotally attached to damper blade 35 at 89. Suitable materials that may form electroactive polymers or 30 materials include passive dielectrics, piezoelectric polymers, especially ferroelectric material, graft elastomers, liquid crystals and electrostrictive paper. Passive dielectrics comprise two conducting plates forming a WO 2009/121145 PCT/AU2009/000412 9 sandwich with a filling of resilient or springy insulating plastics material. When the plates are given opposite charges such as in a capacitor their mutual attraction squeezes the filling, causing it to do work. A new type of dielectric elastomer that may be used is described in 5 ACTUATOR 2004, 9 1h International Conference on New Actuators, 14 - 16 June 2004, Bremen Germany. Another material which is an electrically controlled polymer is described in US Patent 6,117,296. FIG 13 shows flexible link 90 in a non-operational position and FIG 14 shows link 90 flexing as a result of an electrical current. This will result in 10 moving damper blade 35 from a closed to open position or vice versa, or to vary the amount of air passing through the slot or aperture 94. In FIG 15, reference is made to an electronic controller 100 which controls operation of a drive motor 101 which is mounted to support bracket 102 at 103 and 104. The drive motor 101 is a stepper motor and has a drive 15 shaft (not shown) connected to a crank 105 which is only capable of limited oscillation or reciprocational movement between the open positions of each damper blades 35 and 36 shown in phantom and the closed positions of each damper blade 35 and 36, shown in full outline as already described above in relation to FIG 2. The crank 105 has link arm 106 attached to 20 damper blade 35 by blade clip 107. Link arm 106 is attached to one end 108 of crank 105 and there is provided another link arm 109 attached to another end 110 of crank 105. The oscillation of crank 105 is controlled by electronic controller 100. Link arm 109 is attached to damper blade 36 by blade clip 111. 25 In FIG 16 there are provided three damper blades 112, 113 and 114, which are each pivotally mounted to pivots comprising ball joints 46 mounted in adjacent sockets 47. Each of ball joints 46 are part of a stationary mounting member 117. There is also provided air slots 8B located between each mounting member 117. Each mounting member 117 is also provided 30 with flanges 118 which serve as abutments for each of damper blades 112, 113 and 114 when in the closed position as shown in solid outline in FIG 16, wherein each of damperblades 112,113 and 114 contact abutment flanges WO 2009/121145 PCT/AU2009/000412 10 118 at 115. Each of stationary mounting members 117 also have attachment apertures 119 and 120 for attachment to suitable supporting structure (not shown). There is also provided a plenum duct 11 connected to air spigot 12 b y brackets 121 wherein opposed walls 14 of plenum duct 11 5 are received in sockets 25 in brackets 121. Each of walls 14 taper inwardly as shown to form angled walls 122, which releasably engage with a respective stationary mounting member at 123. There is also provided as shown in FIG 15 controller 100, drive motor 101 and crank 105 as well as primary link 124 interconnecting end 126 of crank 105 and damper blade 112 10 with the aid of blade clip 111 and secondary or slave links 125 and 127 interconnecting damper blades 112 and 113 and 113 and 114, respectively with the use of blade clips 111. From the foregoing, it will be appreciated that the air diffuser assembly of the invention is extremely adaptable in use, thus, any number of damper 15 blades may be used. Thus, a single damper blade may be used as shown in FIGS 4, 5 and 6 where only a limited amount of supply air is required and where the direction of the supply air may also be varied as shown. In contrast, a pair of damper blades may be used as shown in FIGS 2 and 3 to push supply air into a room in the same or opposing directions. 20 Thus, the pair of damper blades may be centrally located in a room to provide an air flow of opposing directions whereas the same direction may be required in a corner or adjacent a cornice of a room. The amount of supply air may also be increased by using four damper blades as shown in FIG 7, which may also be in the same or opposing directions. The air 25 diffuser assembly may also be designed to facilitate the flow of return air as shown in FIGS 4 and 6. The invention also distinguishes over the prior art by having one or more damper blades which are connected intermediate their ends so as to allow one end to be moved by a suitable actuator assembly such as a servo 30 motor 85 as shown in FIGS 8 - 11 or by a flexible element as shown in FIGS 12 - 14 or by a drive or stepper motor 101 shown in FIGS 15 and 16 to open and close an access slot. This provides less risk of distortion and provides a WO 2009/121145 PCT/AU2009/000412 11 more positive or direct control of movement of the damper blades. Another advantage of the invention is that by use of a number of modular elements, i.e., one or more side mounting elements and one or more central mounting elements such as mounting members 18 and 19 or 5 117 and air baffle 49 or 49A an individual variable air diffuser can be designed to suit any particular application as may be required which is discussed above.

Claims

1. A variable air diffuser having a plenum housing which is in fluid communication with supply air and/or return air wherein said 5 plenum housing has a continuous peripheral wall and an opening for passage of supply and/or return air characterized in that there is provided at least one damper blade having a first end and a second end wherein said at least one damper blade is pivotally mounted to the plenum housing or mounting structure proximal to 10 the opening intermediate the first and second end to provide an inner end which is movable either manually or by a movable element of an actuator assembly for opening and closing of an air access slot or aperture formed between an outer end of said at least one damper blade and an abutment for said at least one 15 damper blade.

2. A variable air diffuser as claimed in claim 1, wherein the plenum housing is cuboidal in shape and wherein said continuous peripheral wall has an end wall and a pair of side walls and one of 20 said side walls is in fluid communication with a supply air and/or return air duct.

3. A variable air diffuser as claimed in claim 2 wherein each of said side walls remote from the end wall taper inwardly to form a pair of 25 angled walls which are spaced from each other substantially by said opening.

4. A variable air diffuser as claimed in any one of claims 1, 2 or 3, wherein the mounting structure has at least a pair of mounting 30 elements forming an extension of the plenum housing wherein at least one of the mounting elements includes a mounting socket or spigot for said at least one damper blade. WO 2009/121145 PCT/AU2009/000412 13

5. A variable air diffuser as claimed in claim 4, wherein the at least one of said mounting elements forms the abutment for said at least one damper blade. 5

6. A variable air diffuser as claimed in claims 4 or 5, wherein each mounting element is the same structurally and thus, forms a similar extrusion. 10

7. A variable air diffuser as claimed in claims 4, 5 or 6, wherein each mounting element has one or more attachment apertures for attachment to structure contiguous with the plenum housing.

8. A variable air diffuser as claimed in claims 4, 5, 6 or 7, wherein 15 each mounting element includes a locating socket or spigot for location of an adjacent wall of the plenum housing.

9. A variable air diffuser as claimed in claims 4, 5, 6, 7 or 8, wherein said at least one pair of mounting elements comprises a pair of 20 outer mounting elements and there is also provided a central or intermediate air baffle or mounting element which also forms an abutment for movement of the or each damper blade.

10. A variable air diffuser as claimed in claim 9, wherein the central or 25 intermediate air baffle or mounting element has one or more attachment apertures for attachment to an adjacent end plate or bracket of the plenum housing.

11. A variable air diffuser as claimed in claims 9 or 10, wherein there 30 is provided said pair of outer mounting elements and there is provided a pair of damper blades wherein each damper blade is pivotally attached to an adjacent outer mounting element by a WO 2009/121145 PCT/AU2009/000412 14 respective mounting socket or spigot and each of an outer mounting element and the central or intermediate mounting element form abutments for movement of a respective damper blade located therebetween. 5

12. A variable air diffuser as claimed in claims 9 or 10, wherein there is provided a pair of damper blades wherein one of said damper blades is pivotally attached to the central or intermediate mounting element by said mounting socket or spigot and the other of said 10 damper blades is pivotally attached to an adjacent outer mounting element by said mounting socket or spigot and a respective outer mounting element and the central or intermediate mounting element both form abutments for a respective damper blade located therebetween. 15

13. A variable air diffuser as claimed in claims 9 or 10 wherein there is provided two pairs of respective outer and inner mounting elements and the central or intermediate mounting element is located between each of said two pairs of mounting elements and 20 there is provided a pair of outer damper blades and a pair of inner damper blades wherein each outer damper blade is pivotally attached to an adjacent outer mounting element and each inner damper blade is pivotally attached to an adjacent inner mounting element and each of the outer mounting elements and the central 25 or intermediate mounting element form abutments for each outer damper blade and each of the inner mounting elements and the central or intermediate mounting element form abutments for each inner damper blade. 30

14. A variable air diffuser as claimed in claims 4, 5, 6, 7 or 8, wherein said at least one damper blade comprises a single damper blade and there is provided a pair of said mounting elements wherein WO 2009/121145 PCT/AU2009/000412 15 said single damper blade is pivotally attached to an adjacent mounting element and both of said mounting elements form a respective abutment for said single damper blade. 5

15. A variable air diffuser as claimed in claim 9, wherein there is provided a single damper blade and said central or intermediate air baffle or mounting element and an adjacent outer mounting element form abutments for said single damper blade which is pivotally attached to said adjacent outer mounting element. 10

16. A variable air diffuser as claimed in claim 15, wherein said central or intermediate air baffle or mounting element forms an extension of a partition dividing the plenum chamber into a return air duct and a supply air duct. 15

17. A variable air diffuser as claimed in any one of claims 4 - 16, wherein there is provided an additional mounting element which does not form an extension of the plenum housing and which is located adjacent to a respective outer mounting element to 20 thereby form a return air duct.

18. A variable air diffuser as claimed in any one of claims I - 17, wherein the or each damper blade has a body part and an end flange which in use form an abutment for the damper blade(s). 25

19. A variable air diffuser as claimed in any one of claims 1 - 18, wherein the actuator assembly comprises a servo motor having a drive shaft which is pivotally attached to a control lever which is pivotally attached to a pair of links at each end of the control lever 30 and wherein each link has an end remote from its attachment to the control lever wherein each remote end is pivotally attached to an adjacent damper blade. WO 2009/121145 PCT/AU2009/000412 16

20. A variable air diffuser as claimed in any one of claims I - 18, wherein the actuator assembly comprises a stepper motor driving a crank, which is reciprocatable in motion and which at one end 5 thereof is pivotally attached to a link which link is pivotally attached to an adjacent damper blade.

21. A variable air diffuser as claimed in claim 20, wherein there is provided a plurality of damper blades and one damper blade is 10 directly attached to said crank by a primary link and the remaining damper blades are pivotally attached to secondary links wherein each secondary link is attached to said primary link.

22. A method of construction of a variable air diffuser which includes 15 the steps of: (i) connecting one or more mounting elements to an adjacent wall of a plenum housing; (ii) pivotally attaching one or more damper blades to an adjacent mounting element intermediate each end of a 20 respective damper blade; wherein in use, the or each damper blade and the or each mounting element may be interchanged to provide a variable air diffuser with a variable structure having different air flow or air volume characteristics. 25

23. A method as claimed in claim 22, wherein there is also utilised an intermediate or central mounting element which is also attached to the plenum housing or extension thereof and having one or more abutment surfaces for contacting an adjacent damper blade 30 wherein the intermediate or central mounting element is used interchangeably with the mounting element(s) and the damper blade(s). WO 2009/121145 PCT/AU2009/000412 17

24. A method as claimed in claims 22 or 23 wherein each mounting element has a body part and an end flange which in use forms an abutment for the damper blade(s).