WO1997034115A1

WO1997034115A1 - Damper for air flow adjustment

Info

Publication number: WO1997034115A1
Application number: PCT/SE1997/000445
Authority: WO
Inventors: Timo Kaasalainen; Örjan Gustafsson; Odd Strand
Original assignee: ABB Fläkt Aktiebolag
Priority date: 1996-03-15
Filing date: 1997-03-17
Publication date: 1997-09-18
Also published as: AU2185797A; FI981973A0; NO306646B1; FI981973A; SE508425C2; SE9600987L; NO984237D0; DE19781650T1; SE9600987D0; NO984237L

Abstract

An adjusting damper (1), preferably for ventilation plants and intended to be disposed in association with a duct (3), preferably in the vicinity of the duct's opening (8) into a connecting box (5), comprising a control means (15) which is arranged to be movable for the control of the gas flow rate through the duct (3). The control means (15) is axially movable along a tubular envelope (10) of a porous material which permits the through passage of the gas. The interior of the envelope (10) communicates with the duct (3). The flow rate through the duct (3) is controlled by the movement of the control means (15) so as to vary the surface area of the envelope (10) through which the gas passes, and hence the pressure drop across the adjusting damper (1).

Description

Damper for air flow adj ustment .

Ingress

The present invention is concerned with an adjusting damper, preferably for ventilation plants, intended to be disposed in association with a duct, preferably in the vicinity of said duct's opening into a connecting box, said damper to comprise a moveable control means provided for the control of a gas flow through the duct.

The adjusting damper is particularly suited for installation in ventilation plants that are subject to stringent requirements for low noise level and easy duct cleaning.

State of the art

Adjusting dampers are used e.g. for balancing supply air flow rates through different duct branches in a ventilation system. For aesthetic reasons it is desirable that the dampers be concealed from persons present in the ventilated spaces. The dampers are therefore located inside the ventilation duct behind or beyond the supply air terminal device through which the duct discharges into the space. It is moreover desirable that the duct can be cleared of obstructions in order to permit the convenient cleaning thereof. Adjusting dampers are therefore usually detachably arranged in the duct.

The supply air terminal device generally consists of some type of diffuser of which the function is to impart the desired throw and diffusion pattern to the air supplied to the space.

For the supply air terminal device to function optimally, the air from the duct must have a uniform velocity profile when it reaches the device. Therefore, a connecting box of rectangular section is often provided between the usually circular duct and the terminal device. The duct is connected to the connecting box at one of the short sides thereof and the supply air terminal device is likewise connected directly to the box through an opening in one of its longer sides. The purpose of the connecting box is to impart to the air reaching the supply air terminal device the most even velocity profile and the most uniform direction possible.

In order for the detachable adjusting damper to be easily accessible, it may be arranged inside the connecting box, e.g. by being inserted some distance into the opening of the circular duct. The adjusting damper is rendered accessible by removing the supply air terminal device, whereupon the damper is readily removed e.g. prior to cleaning of the duct. Patent application FI 90692 discloses an adjusting damper of the above-mentioned type. This prior damper comprises a central, elongated body having three radially disposed spokes at one end thereof. The damper is attached inside a circular duct by pushing said end some distance into the duct, with the extreme ends of the spokes butting on the walls of the duct. When the damper is attached to the duct, the opposite end of the body projects out of and away from the duct opening. A throttling device in the form of a circular disc, parallel to the plane of the duct opening, is disposed slidably along the body. The disc is fixed to a sleeve running axially along the body. The sleeve exhibits threads which, through a slot in the body envelope, engage with the threads of a screw disposed inside the body. By turning the screw the disc can be displaced towards and away from the duct opening. The flow rate through the duct is thus adjusted by moving the disc so as to set the appropriate size of gap between the disc and the duct opening. To ensure a certain base flow even when the adjusting damper is completely closed, the disc is perforated with circular holes.

The adjustment obtained by means of the adjusting damper described above is, however, highly non-linear. A given displacement of the disc at a large distance from the duct opening produces a much smaller change in the flow rate than an equally large displacement of the disc at a small distance from the opening. This non-linearity adds considerably to the difficulty of the adjustment process.

Patent application FI 71614 discloses an adjusting damper exhibiting greater linearity of adjustment. This adjusting damper comprises a cylinder whose interior communicates with the opening of the circular duct into the connecting box. The cylinder extends from the duct opening centrally through the connecting box to the short side of said box opposite to said opening. Along a substantial portion of the length of the cylinder is disposed a plurality of holes passing through the cylinder wall. The duct is thus in communication with the connecting box through the holes. A cylindrical sleeve is arranged movably along the outer envelope of the cylinder. The inside diameter of the sleeve is essentially equal to the outside diameter of the cylinder, so that the holes occluded by the sleeve are blocked to the passage of air. The flow rate through the duct is adjusted by moving the sleeve along the cylinder so as to occlude the appropriate number of holes. Technical problem

The adjusting damper disclosed in FI 90692 and that disclosed in FI 71614 both exhibit problems with high noise level. When the air entering from duct strikes the walls of the connecting box it gives rise to a relatively loud and irritating noise. In order to reduce the noise as far as possible, the dimensions of the connecting box must unavoidably be increased. The reason is that the larger the connecting box is made, the quieter is the noise produced by the air stream striking its walls. This method of noise reduction, besides not providing adequate reduction, gives rise to expense and other drawbacks, as the dimensions of the connecting box must be increased, with the result that the box is more expensive, more awkward to handle, and has greater space requirements.

Both of the prior adjusting dampers also exhibit drawbacks with regard to the flow pattern arising in the connecting box. As indicated above, it is most important that the air flow reaching the diffuser of the supply air terminal device has a velocity profile that is as even as possible. With the adjusting damper according to FI 90692 in particular, the air flow after passing though the damper assumes a highly concentrated air flow direction. By far the greater part of the flow passes through the connecting box in a direction essentially parallel to the axis of the circular duct. This concentrated flow strikes the short side of the connecting box opposite the duct opening, giving rise to a highly turbulent flow pattern inside the connecting box. The flow reaching the supply air terminal device therefore exhibits very varied velocities, with the result that the diffusion pattern of the air flowing out from the supply air terminal device is not the intended one. With the adjusting damper according to FI 71614, the air flow passing through the perforations in the cylinder wall is imparted a certain radial deflection from the axial direction which it possesses as it leaves the duct opening. Even after passing through the cylinder wall, however, it retains a substantial axial component which, as with the damper according to FI 90692, gives rise to turbulent currents in the connecting box.

It is therefore an object of the present invention to disclose an adjusting damper which produces a low noise level and a desirable flow pattern in the connecting box and which permits simple adjustment and simple clearing of the duct for cleaning. Description of invention

The object is achieved by means of an adjusting damper of the type described in the ingress, characterised in that the control device is axially movable along a tubular envelope of porous material permitting the through passage of gas, and that the interior of the envelope communicates with the duct so that the flow rate through the duct can be controlled, via movement of the control means, by varying the surface area of the envelope through which the gas passes. By causing the air flow to pass through the porous material, a very good flow distribution is obtained. As it passes through the porous material, the air flow from the duct is divided into very fine jets. Four principal advantages over the prior art are obtained thereby. The noise arising from the air passing through the damper and striking the walls of the connecting box is of considerably lower volume. Moreover, said noise is of lower frequency, making it more amenable to reduction by means of insulation. Further, the fine jets produce an even, unimpeded air flow of substantially low turbulence in the connecting box, which in turn has the consequence that the diffusion pattern and throw of the air leaving the supply air terminal device will be those desired. The passage of the air through the porous material also causes the air flow out through the damper envelope to be substantially perpendicular to the envelope axis. In this way the whole of the connecting box, including the portion thereof nearest to the duct opening, is uniformly supplied with air over the entire length of the box. This, too, promotes the uniform velocity profile of the air supplied to the air terminal device.

The porous material through which the air is caused to pass may appropriately have a porosity between 10 and 60 pores per inch (conventionally abbreviated to ppi). The porosity may preferably be between 20 and 40 ppi. This gives a very fine subdivision of the air flow, while the pores are not so small as to present a risk of clogging.

The envelope may incorporate a cloth or matting of the porous material, which cloth or matting at least partly covers the outside or inside of a tubular stiffening device made of a rigid, perforated material. This provides a stable unit which is easily handled when inserting and removing, even if the porous material is soft or flimsy. With this design, moreover, the porous layer does not need to be made thicker, for the sake of stiffness, than is appropriate from the point of view of air flow.

The stiffening device appropriately comprises a perforated cylinder which can be brought into association with the duct, preferably detachably, by inserting one end of the cylinder into the duct opening. This provides a unit which is very simple to remove in order to clear the duct, e.g. for the purposes of duct cleaning. Moreover, this design permits simple, low-cost fabrication of the stiffening device. The stiffening device is appropriately fabricated from a steel band of width equal to the length of the stiffening device. Elongated transverse holes are punched in the band. The band is then cut to a length equal to the circumference of the stiffening device, and rolled and welded or riveted to form a perforated cylinder. The porous material can then be glued or slipped onto or into the cylinder.

The stiffening device is preferably provided with elongated parallel perforations extending axially thereof. Since the sole purpose of the stiffening device is to keep the porous envelope in place, the device should present the least possible obstruction to the air flow. It is therefore desirable that the stiffening device contain as little material as possible, with the elongated parallel perforations made as large as possible without unduly reducing the rigidity of the device.

The control means may comprise a piston, preferably consisting of two discs of perforated rigid material with an interjacent layer of porous material, which piston is arranged movably inside the tubular envelope. The axially movable piston permits very simple and precise linear adjustment of the flow rate. Moreover, the two perforated discs with interjacent porous material ensure a certain minimum base flow regardless of the damper setting and ensure that this base flow rate will also exhibit the desirable fine subdivision.

The control means may be either non-removably or removably arranged in the adjusting damper. The non-removable arrangement has the advantage that greater stiffness is imparted to the adjusting damper and that the damper is easier to handle when being inserted into and removed from the duct. A removable control means has the advantage that only the control means needs to be removed in order to clear the duct, e.g. for cleaning.

The adjusting damper will appropriately incorporate means for remotely causing axial movement of the control device. In this manner, adjustment can be carried out without the prior need to remove e.g. the supply air terminal device or other ventilation parts. These means may, e.g. if the control device is in the form of a piston, comprise a screw disposed axially inside the envelope, which screw engages with a thread in a preferably central hole passing through the piston and is joumalled in a retaining means which is preferably fixed to the envelope, the screw being arranged to be rotatable by turning a wire or spring attached thereto. This design offers very simple, precise, linear adjustment. During adjustment, only the wire or spring is brought out through the supply air terminal device, so that the operation may be conveniently accomplished by a person in the ventilated room without the removal of any ventilation components.

In another embodiment of the adjusting damper, the end of the damper opposite the duct opening may incorporate throttling or blocking of the axial flow and the control device may comprise a tubular sleeve coaxial with the envelope and arranged to be movable along the outside or inside thereof. In this embodiment, axial flow may be totally eliminated if desired.

The porous material may consist of reticulated polyurethane, i.e. polyurethane with open pores. This material has proved to impart very good flow characteristics and noise performance to the adjusting damper. The material is inexpensive and is available in a range of porosities by which the adjusting damper may be adapted to different operating conditions.

The adjusting damper according to the invention may additionally incorporate means for differential pressure measurement for the purpose of measuring the flow rate through the duct. Said means further facilitate the performance of the adjustment process in the ventilated space.

Description of figures

There follows a more particular description of an example of embodiment of the invention, reference being made to the attached drawings.

Fig. 1 shows a schematic longitudinal section through an embodiment of an adjusting damper according to the invention.

Fig. 2 shows a plan of the left end of the adjusting damper shown in Fig. 1.

The adjusting damper 1 shown in Figs. 1 and 2 comprises a cylindrical stiffening device 2 which is inserted into a circular ventilation duct 3 for the supply of air to a room 4 via a connecting box 5 and a supply air terminal device 6. In Fig. 1 the duct 3, the connecting box 5 and the supply air terminal device 6 are represented by broken lines. In Fig. 2 only the adjusting damper 1 is shown. In the example shown in the figures, the stiffening device 2 is kept in place in the duct 3 by friction fit alone. The damper is thus easily inserted and removed. Alternatively, that end of the stiffening device 2 which connects with the duct 3, and/or the duct itself, may be fitted with resilient lips, bayonet couplings or similar means for attaching the adjusting damper to the duct. The other end of the stiffening device 2 protrudes from the duct opening 8 into the connecting box 5.

The stiffening device 2 is usually made of sheet metal, but various plastics or fibreglass may also be used. The stiffening device 2 further exhibits a plurality of punched longitudinal perforations 9 through its surface. A layer 10 of porous material is applied around the outside of the stiffening device 2, extending for a portion of its length. The porous layer consists of a matting of reticulated polyurethane wrapped once around the stiffening device 2 and attached thereto. Alternatively, the matting may be formed into a cylinder held by a glued joint or seam, and slipped over the stiffening device. The layer may in this case be held in place by the friction between the inner surface of the matting and the external surfaces of the stiffening device. The matting thus forms an envelope enclosing the stiffening device. The polyurethane envelope 10 incorporates a multitude of open pores and has a porosity of 30 ppi (pores per inch).

At the end of the adjusting damper 1 opposite to the duct opening 8 there is provided a retaining means 11 disposed at the inside wall of the stiffening device 2. The retaining means 11 comprises two radial legs 12, each of which is attached to the stiffening device 2. The legs 12 may for example be spot welded, riveted or glued to the stiffening device 2, but they may also be held by friction fit so as to be detachable. At the centre of the retaining means 11, where the legs 12 meet, there is an axial bushing 13. Rotatably joumalled in the bushing 13 is a screw 14 disposed coaxially with the stiffening device 2. Around the screw 14 is a control device having the form of a piston 15. The piston 15 comprises two essentially circular discs 16 of diameter substantially equal to the inside diameter of the stiffening device 2. One or more perforations 17 pass axially through the discs 16. The total area of the perforations 17 is between 10% and 40% and preferably between 20% and 30% of the cross-sectional area of the piston. Between the discs 16 is a layer 18 of porous material. The porous material is of the same type as that enclosing the stiffening device 2. Passing centrally through the piston 15 is a piston bushing 19 provided with threads (not shown). The threads engage with the threads of the screw 14 so that a turning motion of the screw 14 is converted into an axial motion of the piston 15. To prevent rotation of the piston 15, a radial groove (not shown) may be made in the periphery of the piston 15, to engage with an axial guide (not shown) in the stiffening device 2. The axial guide may consist, for example, of an axial strip of metal located between two of the punched perforations 9 and bent some distance radially inward of the envelope of the stiffening device.

At the end of the screw 14 opposite to the duct opening 8 there is an elongated helical spring 20. The helical spring 20 is flexible but relatively rigid in torsion in order to transfer a turning motion to the screw 14. The helical spring 20 is long enough to protrude through the air terminal device 6. Hence adjustment can be carried out by turning the helical spring 20 when the loose end thereof is located in the room 4. The helical spring 20 may of course be replaced with a wire or by other elongated elements which are flexible and capable of transferring turning motions.

The adjusting damper 1 may also incorporate means for flow rate measurement by differential pressure measurement. These means consist, in the illustrated example, of a test probe 21, joumalled on that end of the screw 14 which is nearer to the duct opening 8. The test probe 21 comprises a throttling disc (not shown) disposed parallel to the cross-sectional plane of the duct 3. Two measuring tubes 22a, 22b are arranged with their mouths at the throttling disc, one on each side (upstream and downstream) thereof. The mouths of the two measuring tubes are disposed so that their planes are substantially parallel to the throttling disc and so arranged that they lead away from the upstream and the downstream sides, respectively, of the disc. The two test tubes 22a, 22b extend from the measuring probe 21, parallel to the screw 14, through holes in the piston 15, and past the retaining means 11. The test tubes 22a, 22b are moreover anchored to the retaining means 11 and may be used as guides for the piston 15 to prevent rotation thereof as the screw 14 is turned. In this way it is possible to dispense with any other guides for the piston 15 as described above. The test tubes 22a, 22b are moreover connected at their ends distant from the test probe to respective^" measuring tubes 23a and 23b. The measuring tubes 23a, 23b are long enough for their unattached ends to be drawn into the room 4 through the air terminal device 6, e.g. during adjustment, and connected to a device for differential pressure measurement. By this means adjustment can be simply carried out from the room 4 with the aid of simultaneous flow rate measurement.

In order for the adjusting damper 1 to give as low a noise level and as uniform a flow pattern as possible, it is desirable for the air flow through the damper 1 to be obstructed as little as possible by the stiffening device 2. Thus it is desirably for as large a proportion as possible of the envelope of the stiffening device 2 to consist of perforations. At the same time, the stiffening device 2 must comprise sufficient highly rigid material to ensure the adequate mechanical strength of the adjusting damper. Normally between 65 % and 95 %, and preferably between 80% and 85% , of the envelope of the stiffening device 2 along the active length of the adjusting damper consists of punched perforations. By the active length of the adjusting damper is meant here the axial extension thereof along which the piston 15 can be moved and along which air can pass radially through the damper 1.

During adjustment of the air flow rate through the duct 3, the unattached ends of the helical spring 20 and of the measuring tubes 23a, 23b are brought out of the connecting box through the supply air terminal device 6 into the room. The measuring tubes 23a, 23b are connected to a differential pressure gauge. By turning the helical spring 20, and hence the screw 14, clockwise or counterclockwise, the piston 15 is moved towards or away from the opening 8 of the duct 3 in the connecting box 5. Varying portions of the porous envelope 10 of the adjusting damper 1 are thereby exposed to the air flow passing through the duct 3. When the piston 15 is moved away from the opening 8 the exposed sμrface area is increased, causing the pressure drop across the adjusting damper to decrease. This increases the flow rate through the duct 3 and hence the supply air flow into the room. When the piston 15 is moved towards the opening 8 the exposed surface area is reduced, causing the pressure drop across the adjusting damper 1 to increase and the air flow rate to decrease. The correct flow rate is simply set by measuring the magnitude of the flow rate by means of the differential pressure gauge.

Even if the piston 15 is moved all the way to or past the duct opening 8 into the duct 3, a certain base flow is ensured inasmuch as air can pass through the perforations 17 in the piston 15 via the interjacent layer 18 of porous material. At the installation of the damper 1, the total cross-sectional area of these perforations 17 is chosen to suit the operating conditions. If appropriate, the two discs 16 of the piston 15 may be mutually rotatable. The base flow can then be determined by rotating the two discs in relation to each other so that their respective perforations overlap so as to form the appropriate total cross-sectional area. Inasmuch as the air passing^' through the damper 1 is caused to pass through the porous material, a very fine subdivision of the air flow is obtained. This gives a smooth flow of air through the connecting box 5, with little turbulence. As a result of this, the flow reaching the supply air terminal device 6 has a very uniform velocity profile over the entire cross-section. The supply air terminal device 6 will thus be operating under good conditions to generate exactly the desired throw and diffusion pattern. The fine subdivision of the air flow in the connecting box 5 also results in a considerably lower volume of sound being generated in the connecting box 5 than has previously been possible. The sound is moreover of lower frequency, which means that it is easily reduced by applying sound insulation to the exterior of the connecting box. The combined effect of these factors is that the connecting box 5 can be made smaller and hence cheaper and with less space requirements.

Other embodiments of the adjusting damper are also possible within the terms of the claims.

For example, the adjusting damper may be modified for the control of the exhaust air flow rate out of a room. In this case, the porous envelope will often be chosen to have a lower porosity, i.e. larger pores, to avoid clogging of the adjusting damper by dust and other impurities in the exhaust air.

The adjusting damper may also be installed in a ventilation duct not in the immediate vicinity of a connecting box. In this case, one end of the adjusting damper may be inserted into a duct section having a certain inside cross-sectional area. This duct section is connected to a duct section of greater cross-sectional area. The active length of the adjusting damper is disposed in the duct section of greater cross-sectional area so that the air can pass freely through the porous envelope surface.

The control means, instead of being in the form of a piston moveable inside the surrounding porous envelope, may be formed as a cylindrical sleeve. Said sleeve may be arranged to be movable inside the envelope, in which case the outside diameter of the sleeve will be essentially equal to the inside diameter of the envelope. Alternatively, the sleeve may be arranged to be movable outside the envelope, in which case the inside diameter of the sleeve will be essentially equal to the outside diameter of the envelope. In both these embodiments, axial air flow through the adjusting damper needs to be prevented, e.g. by a throttle or obstruction at the end of the damper opposite to the duct opening. In this embodiment, axial movement of the sleeve may be brought about e.g. by threads on the sleeve engaging with threads arranged on the envelope or the stiffening device, so that rotation of the sleeve results in an axial movement thereof. The porous envelope need not necessarily extend for the entire active length of the adjusting damper. By covering only that portion of the adjusting damper which is located nearest to the duct opening in the connecting box, the desired fine subdivision of the air flow is obtained in the most sensitive part of the connecting box, nearest to the duct opening. At the same time this arrangement permits, if desired, a greater maximum flow rate through the uncovered portion of the adjusting damper, which portion exhibits a lower flow resistance. In this way it is possible to combine desirable flow distribution with a large maximum flow rate in the same adjusting damper.

Claims

1. An adjusting damper (1), preferably for ventilation plants and intended to be disposed in association with a duct (3), preferably in the vicinity of the duct opening (8) into a connecting box (5), which adjusting damper (1) comprises a control means (15) which is arranged to be movable for the purpose of controlling the gas flow rate through the duct (3), characterised in that the control means (15) is movable axially of a tubular envelope (10) of porous material which permits the through passage of the gas and that the interior of the envelope (10) is in communication with the duct (3), so that the flow rate through the duct can be controlled, via movement of the control means (15), by varying the surface area of the envelope (10) through which the gas passes.

2. An adjusting damper according to claim 1, characterised in that the porous material has a porosity of between 10 and 60 ppi and preferably between 20 and 40 ppi.

3. An adjusting damper according to claim 1 or 2, characterised in that the envelope (10) comprises a cloth or matting of the porous material, which cloth or matting covers at least part of the outside or inside of a tubular stiffening device (2) of a rigid, perforated material.

4. An adjusting damper according to claim 3, characterised in that the stiffening device (2) comprises a perforated cylinder which can be disposed in relation to the duct (3), preferably detachably, by inserting one end of the cylinder into the opening (8) of the duct (3).

5. An adjusting damper according to either of claims 3 or 4, characterised in that the stiffening device (2) has axially elongated, parallel openings (9).

6. An adjusting damper according to any of claims 1-5, characterised in that the control means comprises a piston (15), preferably comprising two discs (16) of perforated rigid material with an interjacent layer (18) of porous material, which piston (15) is arranged to be movable inside the tubular envelope (10).

7. An adjusting damper according to any of claims 1-6, characterised in that the control means (15) is non-removably arranged in the adjusting damper (1) so that it accompanies the adjusting damper when the latter is removed from the duct (3).

8. An adjusting damper according to any of claims 1-6, characterised in that the control means (15) is removably arranged in the adjusting damper to permit clearing of the envelope (10) and of the duct (3).

9. An adjusting damper according to any of claims 1-8, characterised by means (13, 14,

19, 20) for remotely bringing about axial movement of the control means (15).

10. An adjusting damper according to claim 9, characterised in that said means comprise a screw (14) disposed axially inside the envelope (19), which screw (14) engages with a threaded device (19) in a hole passing through and preferably centrally of the control means

(15) having the form of a piston, and is joumalled in a retaining means (11), which is preferably fixed to the adjusting damper, said screw (14) being arranged to be rotatable by turning a wire or spring (20) connected to the screw (14).

11. An adjusting damper according to any of claims 1-5, characterised in that the end of the adjusting damper opposite to the opening (8) of the duct (3) is equipped with means to throttle or block the through passage of gas and that the control means comprises a tubular sleeve which is arranged coaxial with the envelope so as to be moveable along the outside or inside of the envelope (10).

12. An adjusting damper according to any of claims 1-10, characterised in that the porous material consists of reticulated polyurethane.

13. An adjusting damper according to any of claims 1-11, characterised by means (21, 22a, 22b, 23a, 23b) for differential pressure measurement for the purpose of measuring the flow rate through the duct 3.