VENTILATION DEVICE WITH VARYING AIR VELOCITY

Abstract

A ventilation device 21 configured to be connected to a mouth of a ventilation duct 9 between the ventilation duct and an outside space. The ventilation device comprises an airflow opening 27 for passage of an airflow 30 between the ventilation device and the outside space. An air-permeable material 29 is arranged in the airflow opening 27.

Claims

1. A ventilation device configured to be connected to a mouth of a ventilation duct between the ventilation duct and an outside space, wherein the ventilation device comprises an airflow opening for passage of an airflow between the ventilation device and the outside space, wherein an air-permeable material is arranged in said airflow opening.

2. A ventilation device according to claim 1, wherein the air-permeable material is arranged in said airflow opening such that at least a portion of the airflow passes through the air-permeable material at passage between the ventilation device and the outside space.

3. A ventilation device according to claim 1, wherein the ventilation device comprises an outer body and a front cover, wherein the airflow opening is formed between a first edge of the outer body and a first side of the front cover.

4. A ventilation device according to claim 3, wherein the air-permeable material is arranged to affect the velocity profile of the airflow through the airflow opening, taken over a cross section of the airflow opening, to be such that the airflow velocity is lower at the first side of the front cover than at the first edge of the outer body.

5. A ventilation device according to claim 3, wherein the air-permeable material is arranged to affect the velocity profile of the airflow through the airflow opening, taken over a cross section of the airflow opening, to be such that the airflow velocity is lowest at the first side of the front cover and highest at the first edge of the outer body.

6. A ventilation device according to claim 3, wherein the air-permeable material is attached to the first side of the front cover.

7. A ventilation device according to claim 3, wherein the air-permeable material has such shape that at airflow through the airflow opening the airflow has a velocity profile, taken over a cross section of the air-permeable material in the airflow opening, such that the airflow velocity is lowest closest to the first side of the front cover and highest in the portion of the air-permeable material located furthest from the first side of the front cover.

8. A ventilation device according to claim 3, wherein the air-permeable material has a cross-sectional profile, taken over a cross section of the airflow opening, which is broadest closest to the first side of the front cover and tapers towards the first edge of the outer body.

9. A ventilation device according to claim 8, wherein the air-permeable material has a substantially triangular cross-sectional profile, taken over a cross section of the airflow opening.

10. A ventilation device according to claim 1, wherein the air-permeable material has a varying air-permeability beyond its cross-sectional profile, taken over a cross section of the airflow opening.

11. A ventilation device according to claim 1, wherein the air-permeable material comprises a porous material, such as a porous fiber material.

12. A ventilation device according to claim 11, wherein the porous material has a varying porosity beyond the cross-sectional profile of the air-permeable material, taken over a cross section of the airflow opening.

13. A ventilation device according to claim 3, wherein a size of the airflow opening is determined by the shortest distance between the first edge of the outer body and the first side of the front cover.

14. A ventilation device according to claim 1, wherein the size of the airflow opening is adjustable, whereby an airflow through the ventilation device can be adjusted.

15. A ventilation device according to claim 3, wherein the front cover is adjustably arranged relative to the outer body, whereby the size of the airflow opening is adjustable.

16. A ventilation device according to claim 1, wherein the air-permeable material covers, at least partially, the airflow opening.

17. A ventilation device according to claim 16, wherein the air-permeable material covers the airflow opening to at least ¼, preferably to ⅓, ½, or ¾, when the airflow opening is maximally open.

18. A ventilation device according to claim 14, wherein the air-permeable material covers, substantially completely, the airflow opening, when the airflow opening is maximally open.

19. A ventilation device according to claim 14, wherein the size of the airflow opening is continuously or stepwise adjustable between a maximally open position and a closed position, and values in between.

20. A ventilation device according to claim 1, wherein the air-permeable material is deformable.

21. A ventilation device according to claim 14, wherein the air-permeable material is arranged to get at least partially deformed relative to the size of the airflow opening.

22. A ventilation device according to claim 3, comprising an air duct defining element arranged centrally in the outer body such as to be at least partially surrounded by the outer body, wherein an airflow passage is formed between an outer side of the air duct defining element and an interior wall of the outer body.

23. A ventilation device according to claim 22, wherein the air duct defining element is a substantially cup-shaped element.

24. A ventilation device according to claim 23, wherein the cup-shaped element has the shape essentially of a truncated cone, arranged such that the cone base faces towards the first side of the front cover.

25. A ventilation device according to claim 22, wherein the front cover is attached to the air duct defining element.

26. A ventilation device according to claim 3, wherein the first edge of the outer body has a dome-shape, preferably a convexly rounded shape, substantially without sharp edges.

27. A ventilation device according to claim 3, wherein the front cover has a substantially plane second side on the side opposite the first side.

28. A ventilation device according to claim 3, wherein the front cover has a size such that the front cover covers, at least substantially, the first edge of the outer body.

29. A ventilation device according to claim 28, wherein the front cover extends at least partially beyond the first edge of the outer body.

30. A ventilation device according to claim 3, wherein the front cover is configured such that air in an airflow out of or into the ventilation device flows substantially parallel to a surface of a wail or a ceiling in which the ventilation device is arranged.

31. A ventilation device according to claim 3, wherein the air-permeable material is at least partially fixated to the first side of the front cover via an adhesive material.

32. A ventilation device according to claim 1, wherein the air-permeable material has the shape of a disc, a ring, a peripheral ring with radially inwardly extending element, or the like.

33. A ventilation device according to claim 3, wherein the outer body has substantially circular-cylindrical shape.

34. A ventilation device according to claim 1, configured for mounting in a wail or in a ceiling, in particular in an interior wail or a ceiling.

35. A ventilation system, comprising at least one ventilation device according to claim 1, a ventilation duct to which said at least one ventilation device is connected, and a fan connected to the ventilation duct and arranged to be able to create an airflow through the ventilation device and the ventilation duct.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0051] FIG. 1 ventilation device according to the prior art, without attenuation;

[0052] FIG. 2 ventilation system according to the present disclosure;

[0053] FIG. 3A ventilation device with air-permeable material for reduced occurrence/generation of sound according to an embodiment of the present disclosure, expanded view, viewed from the side;

[0054] FIG. 3B ventilation device according to FIG. 3A, expanded view, viewed obliquely from the front;

[0055] FIG. 3C, D ventilation device according to FIGS. 3A, 3B, viewed obliquely from behind and obliquely from the front;

[0056] FIG. 3E ventilation device according to FIG. 3, viewed in section;

[0057] FIGS. 4A-4C detail of the airflow opening, e.g. according to FIG. 3, with air-permeable material of different thickness;

[0058] FIG. 4D detail of airflow opening according to FIG. 4C, with air-permeable material in the form of a ring.

[0059] FIGS. 5A-5C detail of successive degrees of closure of ventilation device;

[0060] FIGS. 6A-6C alternative embodiments of the air-permeable material according to the present disclosure;

[0061] FIG. 7 diagram of measurement data for valve without sound attenuation;

[0062] FIG. 8 diagram of measurement data for valve with porous air-permeable material with a shape according to FIG. 6A;

[0063] FIG. 9 diagram of measurement data for valve with air-permeable material with a shape according to FIG. 6B.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0064] The ventilation device disclosed here is described primarily as a feed air device. The technical teaching is, however, even applicable to exhaust air devices. Below, a ventilation system for feed air ventilation is described. Exhaust air ventilation works similarly.

[0065] FIG. 1 illustrates a ventilation device 1 according to the prior art. The ventilation device 1 includes a front cover 3 arranged in an outer body 5. The front cover 3 is usually adjustably arranged relative to the outer body 5, so that the size of a flow opening 7 can be adjusted. As described above, an airflow through the ventilation device 1 can be adjusted by adjusting the size of the airflow opening 7. As illustrated in FIG. 1, the ventilation device 1 may be mounted directly in a ventilation duct 9, the opening of which extends from a wall or a ceiling 11. In order to avoid air leakage along the outer sides of the outer body, the ventilation device 1 may be sealed against the wall 11 and/or the ventilation duct 9 by a sealing element 13. Examples of such a sealing element may be a foam rubber material, e.g. a foam rubber ring, or the like.

[0066] FIG. 2 schematically illustrates a ventilation system 15 of a type which is common in various properties, as described initially. The ventilation system 15 comprises a ventilation duct 9 to which a plurality of ventilation devices 1 are connected. As shown in FIG. 2, the ventilation device 1 may be connected at different positions along the ventilation duct 9. The ventilation duct 9 may have, as illustrated in FIG. 2, one or a plurality of branches to which one or more ventilation devices can be connected. The ventilation system 15 includes a fan 17. The fan 17 is arranged to generate a pressure in the ventilation system, so that forced ventilation can be obtained. As illustrated in FIG. 2, the ventilation system 15 can be installed in properties, e.g. in homes, and the ventilation duct 9 may extend over several different spaces for ventilation of those spaces. It may be a matter of feed air ventilation or exhaust air ventilation.

[0067] FIGS. 3A to 3E illustrate a ventilation device 21 configured to get a lower generation of sound as compared with the above described known ventilation device 1. The ventilation device 21 is configured to be connected to a ventilation duct 9, as described above for the known ventilation device 1. The ventilation device 21 can be used for various types of ventilation systems 15. For example, it can be attached to a ventilation system of the type illustrated in FIG. 2. It can be connected to existing ventilation systems. The ventilation device may be a feed air device or an exhaust air device, and can be designed for ceiling and/or wall mounting. If the ventilation device is mounted to a ventilation duct, the airflow opening 27 is the portion of the flow duct through the ventilation device 21 which is closest to the space to be ventilated. Thus, the airflow opening constitutes the ventilation device's mouth to the environment outside the ventilation duct. The airflow opening faces towards the space in which the ventilation device is arranged, and is the portion of the ventilation device which is located, flow-wise, furthest from the ventilation duct. The ventilation device can be used in various ventilation devices. The ventilation device may be designed as a feed air device or an exhaust air device. If the ventilation device is a feed air device, the airflow opening represents the airflow's last passage out of the ventilation device, i.e. the airflow opening corresponds to the last throttling in the ventilation system. If the ventilation device is an exhaust air device, the airflow opening represents the first passage of the air into the ventilation device, i.e. the airflow opening corresponds to the first throttling in the ventilation system. Generally, the airflow opening has the shape of a peripheral gap between two portions of the ventilation device.

[0068] The ventilation device 21 illustrated in FIGS. 3A-3E comprises essentially elements corresponding to those described above with reference to the known ventilation device illustrated in FIG. 1. However, the ventilation device 21 is provided with a porous air-permeable material 29 arranged in the airflow opening 27 to obtain sound attenuation. Said ventilation device will be described in more detail with reference to FIGS. 3A to 3E.

[0069] FIG. 3A shows an exploded view of the ventilation device 21. It comprises an outer body 25, a front cover 23, and a porous, air-permeable material 29. In the embodiment illustrated here, the ventilation device 21 also includes an element 31 for mounting of the front cover 23 on the outer body 25. Said element 31 is, as illustrated here, an air duct defining element, where an airflow passage 32 is formed between an outer side of the air duct defining element 31 and at least a portion of an interior wall of the outer body 25. The configuration of the element 31 will therefore affect the airflow through the ventilation device 21, both as regards airflow resistance and acoustic properties.

[0070] If the front cover 23 is attached to the outer body 25, an airflow opening 27 will be formed between a first side 23a of the front cover and a first edge 26 of the outer body. The front cover 23 is adjustably arranged relative to the outer body 25, whereby a size of the airflow opening 27 is adjustable. Said size is indicated by arrow 28 in FIG. 3E, FIGS. 4A-4D, and FIGS. 5A-5C.

[0071] FIG. 3B illustrates the ventilation device 21 in exploded view, viewed obliquely from the front. Here is also illustrated a threaded element 33, such as a screw, or other device for adjustable mounting of the air duct defining element 31 in the outer body 25. The air duct defining element 31 may be provided with an internal thread for adjustable mounting to the threaded element 33. Alternatively, the air duct defining element 31 may be positioned by means of screws or the like arranged on the threaded element 33 on both sides of the portion of the air duct defining element 31 which is intersected by the threaded element 33. As seen from e.g. FIGS. 3B and 3C, the air duct defining element 31 is arranged substantially centrally relative to the outer body 25, and is arranged to be located, at least partially, in the outer body 25. The front cover 23 is attached to the air duct defining element 31, and is thus adjustably arranged relative to the outer body 25. By adjustment of the front cover 23 relative to the first edge 26 of the outer body 25, a size 28 of the airflow opening is adjusted, which is illustrated clearly in FIG. 3E and FIGS. 5A-5C.

[0072] FIG. 3C illustrates the ventilation device 21, viewed obliquely from behind. FIG. 3D illustrates it, viewed obliquely from the front.

[0073] If a screw 33 or other threaded element is used for adjustable mounting of the air duct defining element 31, the position thereof may be continuously adjusted along with the screw 33. Alternatively, use may be made of another type of element which allows only stepwise adjustment of the position of the air duct defining element 31.

[0074] As illustrated here, the air duct defining element 31 is an essentially cup-shaped or cone-shaped element, and is an element separate from the front cover 23. However, according to other embodiments it might be configured to constitute a unit with the front cover. The air duct defining element 31 is arranged such that its broad portion faces towards the front cover, and its narrow portion faces towards the ventilation duct. If the air duct defining element 31 is shaped substantially like a truncated cone, it is arranged such that its base faces towards the first side 23a of the front cover. In the embodiment illustrated, the air duct defining element 31 is substantially hollow. However, other configurations are also possible.

[0075] Advantageously, the outer body 25 of the ventilation device has substantially circular-cylindrical shape. Advantageously, it has an outer diameter corresponding to an inner diameter of a ventilation duct to which it is to be mounted. Thus, the ventilation device can be designed for direct mounting in a ventilation duct. As there are standard dimensions of ventilation ducts, the ventilation device can be designed with corresponding standard dimensions. To facilitate direct mounting in a ventilation duct, the outer body 25 may be provided with mounting element 35, illustrated in FIGS. 3A and 3B as resilient element 35 with sufficient rigidity to make possible stable mounting in the ventilation duct. Sealing against wall or ceiling is accomplished the same way as for the known ventilation device illustrated in FIG. 1 by a sealing, e.g. a seal ring 13, positioned below the outer edge of the outer body.

[0076] FIG. 3E illustrates the ventilation device 21 cross-sectionally. It is seen from said illustration that the air-permeable material 29 is arranged such that at airflow through the airflow opening 27, at least a portion of the airflow passes through the air-permeable material 29. This is indicated in FIG. 3E by an arrow 30. The air-permeable material 29 is arranged such as to at least partially cover the airflow opening 27. In the embodiment according to FIG. 3E, the air-permeable material covers substantially the entire airflow opening 27.

[0077] The air-permeable material 29 is arranged such as to at least constitute a portion of the airflow opening 27. The airflow opening 27 has the shape of a peripheral gap between two portions of the ventilation device 21. The air-permeable material 29 is arranged such as to at least partially cover the gap of the airflow opening 27 between the two portions of the ventilation device 21. The airflow opening 27 has the shape of a peripheral gap between the front cover 23 and the outer body 25 of the ventilation device 21. The air-permeable material 29 is arranged such as to at least partially cover the gap of the airflow opening 27 between the front cover 23 and the outer body 25 of the ventilation device 21. The airflow opening 27 has the form of a peripheral gap between the first side 23a of the front cover and a first edge 26 of the outer body 25 of the ventilation device 21. The air-permeable material 29 is arranged such as to at least partially cover the gap of the airflow opening 27 between the first side 23a of the front cover and a first edge 26 of the outer body of the ventilation device 25. The air-permeable material 29 is disposed in the gap of the airflow opening 27. The air-permeable material 29 is disposed in the gap of the airflow opening 27 between the front cover 23 and the outer body 25 of the ventilation device. The air-permeable material 29 is disposed in the gap of the airflow opening 27 between the first side/inner side 23a of the front cover and the first edge 26 of the outer body of the ventilation device 25. In the embodiment according to FIG. 3E, the air-permeable material covers substantially the entire gap of the airflow opening 27.

[0078] As is seen in FIGS. 3B and 3E, and in the detailed view in FIGS. 4A-4C, the first edge 26 of the outer body 25 has a dome-shape, preferably a convexly rounded shape, substantially without sharp edges. The size of the airflow opening 28 is defined as the shortest distance between the first side 23a of the front cover and the first edge 26 of the outer body. In the embodiment according to FIG. 3E, said size 28 is defined as the perpendicular distance between the first side 23a of the front cover and the closest portion of the rounded edge. This is illustrated in FIG. 3E, FIGS. 4A-4C, and FIGS. 5A-5C by arrow 28. A detailed view of the airflow opening is illustrated in FIGS. 4A-4D. Furthermore, in the embodiment according to FIGS. 4A-4D, an air-permeable material 29, 29c is arranged such as to partially cover the size 28 of the airflow opening at the maximally open position. As illustrated in FIGS. 4A-4C, the air-permeable material has a thickness 40, and it is possible to use air-permeable material of different thickness 40. FIGS. 4A-4C illustrate an air-permeable material 29, substantially in the form of a disc, for example according to the shape illustrated in FIG. 6A. FIG. 4D illustrates an air-permeable material 29c, e.g. as illustrated in FIG. 6C, substantially in the shape of a ring, the size and extent thereof substantially corresponding to the first edge 26 of the outer body. Alternatively, use may be made of an air-permeable material 29a, 29b having a shape as illustrated in FIG. 6B, where the peripheral ring 29a has a size and extent substantially corresponding to the first edge 26 of the outer body. The air-permeable material may be formed and arranged such as to cover the airflow opening to at least ¼, preferably to ⅓, ½, or ¾, when the airflow opening 27 is maximally open. Advantageously, it may be arranged such as to cover, substantially completely, the airflow opening 27 when the airflow opening is maximally open, as illustrated in FIG. 5A. This can be achieved in that the air-permeable material 29 may have a thickness extending over the whole or portion of the size 28 of the airflow opening. The air-permeable material need not necessarily have uniform thickness, but may have varying thickness.

[0079] In the embodiments illustrated in FIG. 3E, and FIGS. 4A-4D, and FIGS. 5A-5C, the air-permeable material 29, 29a, 29b, 29c is attached to the first side 23a of the front cover. When an airflow 30 flows through the ventilation device 21, at least a portion of said airflow will pass through the air-permeable material 29 on its way between the airflow opening 27 and the rear opening 34 of the ventilation device 21, or vice versa. If you look at the airflow velocity profile of the narrowest portion of the airflow opening, the airflow velocity is lower the further away from the first edge 26 of the outer body and the closer to the first side 23a of the front cover one comes. Thus, the air-permeable material contributes to give the airflow a lower velocity near the front cover 23.

[0080] As an example, we may consider the case of the exhaust air ventilation, which is illustrated by the arrow 30 in FIG. 3E and FIG. 4A. When air flows into the airflow opening 27, at least a portion of that airflow 30 will meet the air-permeable material 29, which, as illustrated in FIGS. 3E, 4A-4D, and 5A-5C, may cover, completely or partially, size 28 of the air flow opening. At its passage through the airflow opening 27, the airflow 30 will pass, at least partially, through the air-permeable material 29 before it reaches the air duct formed in the interior of the ventilation device 21. The portion of the airflow 30 which during its passage through the air-permeable material 29 has passed closest to the front cover 23, has traveled a longer distance through the air-permeable material 29 than the portion of the airflow which has flowed through the air-permeable material 29 closer to the first edge 26 of the outer body. The airflow that reaches the air duct inside the ventilation device 21 will therefore have a lower velocity in the duct the closer to the front cover it has been transported through the air-permeable material 29. Furthermore, the rounded shape of the first edge 26 of the outer body will affect the airflow velocity, as it will give rise to a gradual acceleration of the airflow 30 as it advances towards the rounded edge, and a gradual velocity reduction of the airflow 30 after the rounded edge. This reduces the degree of eddies and turbulence of the airflow 30. The air-permeable material 29, and also the rounded shape of the first edge 26 of the outer body, will therefore contribute to create a velocity profile of the airflow through the duct, which is advantageous as regards the sound effect level, in reducing the velocity of the airflow closest to surfaces inside the ventilation device.

[0081] In the case of feed air, the portion of the airflow 30 which during its passage through the air-permeable material 29 has passed closest to the front cover 23 will have traveled a longer distance through the air-permeable material 29 than the portion of the airflow which has flowed through the air-permeable material 29 closer to the first edge 26 of the outer body. The airflow which reaches the space will therefore have a lower velocity in the airflow opening the closer to the front cover it has been transported through the air-permeable material 29. The air-permeable material 29 may have different shapes to affect the airflow's velocity profile, taken over a cross section of the airflow opening, in the entire airflow opening. The airflow that reaches the space may have a velocity profile, taken over a cross section of the airflow opening, which has lower velocity closest to the first side 23a of the front cover 23 than at the first edge 26 of the outer body 25. The airflow that reaches the space may have a velocity profile, taken over a cross section of the airflow opening, which has the lowest velocity closest to the first side 23a of the front cover 23 and a highest velocity at the first edge 26 of the outer body 25. The shape of the air-permeable material 29 may be triangular. The shape of the air-permeable material 29 may be square. The shape of the air-permeable material 29 may be tapered from its base at the front cover towards the first edge 26 of the outer body 25. The porosity of the air-permeable material may vary to affect the airflow's velocity profile, taken over a cross section of the airflow opening. The porosity may vary to achieve the above velocity profiles in the airflow opening. The air-permeable material 29 may have different thickness 40 to affect the airflow's velocity profile, taken over a cross section of airflow opening 27.

[0082] The front cover 23 may further have a substantially plane second side 23b on the side opposite the first side 23a. This has turned out to have a beneficial effect on the airflow through the ventilation device, as it contributes to direct the airflow parallel to a wall or a ceiling on which the ventilation device is arranged. The front cover 23 may have one of several possible shapes. In the illustrated example, the front cover has square shape. Other possible shapes are rectangular or other polygonal shape, circular or oval. The front cover 23 may advantageously have a size such that the front cover 23 covers, at least substantially, the first edge 26 of the outer body. In the embodiment illustrated, the front cover extends at least partially beyond the first edge 26 of the outer body. In the example illustrated, the front cover 23 is substantially plane. As indicated by the dashed line in FIG. 4A, it is also possible to design the front cover 23 with a bent peripheral edge 23c.

[0083] In the embodiment according to FIG. 3E, the air duct defining element 31 is shaped as a hollow element having substantially the shape of a truncated cone. The truncated cone 31 is configured such that the front cover 23 can be attached to an inner side of the cone 31 via one or more radially resilient elements 37, such as clips or the like, provided on the first side 23a of the front cover 23. The resilient elements 37 may consist of, for example, metal bands. The element 31 comprises at least an inner edge 39 against which the radially resilient elements 37 can abut to attach the front cover to the cone. Thereby, the front cover can be easily dismounted from the element 31, which may be advantageous as regards cleaning or replacing the air-permeable material.

[0084] The air-permeable material 29 is disposed between the first side 23a of the front cover 23 and the air duct defining element 31. As seen in FIG. 3E, where the air-permeable material is deformable, it is fixated between a peripheral edge of the base of the air duct defining element 31, where said peripheral edge abuts substantially against the first side 23a of the front cover. The radially resilient elements 37 may be configured such as to also contribute to keep the air-permeable material in place. This provides a stable mechanical mounting of the air-permeable material 29, while at the same time the air-permeable material 29 can be easily replaced.

[0085] As described above, the size of the airflow opening is adjustable, whereby an airflow through the ventilation device can be adjusted. The size of the airflow opening is continuously or stepwise adjustable between a maximally open position and a closed position, and values in between. The ventilation device may be configured such that the size of the airflow opening cannot be adjusted to more than maximally open position, i.e. the maximum distance between the first side 23a of the front cover and the first edge 26 of the outer body has been reached, and the ventilation device cannot be opened more. At the maximally closed position, the shortest possible distance between the first side 23a of the front cover and the first edge 26 of the outer body 25 has been reached. Ideally, essentially no airflow is possible through the ventilation device 21 in the closed position, when the airflow opening 27 has its minimum/smallest size 28.

[0086] The air-permeable material 29 is arranged such that air in an airflow through the ventilation device 21 is spread towards the first side of the cover. This can be realized through the porosity of the air-permeable material. Furthermore, the porous air-permeable material is advantageously a fiber material, wherein the individual fibers are directed substantially randomly. This contributes to distribute and spread an airflow flowing through the air-permeable material, and to thereby affect the sound pattern that occurs at airflow through the ventilation device.

[0087] The air-permeable material 29 may be deformable, and may be arranged to get at least partially deformed relative to the size 28 of the airflow opening 27. This is illustrated in FIGS. 5A-5C, where the size 28 of the airflow opening is successively reduced. This is particularly advantageous if the porous air-permeable material has such thickness as to cover the entire airflow opening when maximally open, i.e. when the ventilation device is completely open and the airflow opening 27 has its maximum/largest size 28. The air-permeable material 29 gets deformed when its thickness 40 in non-deformed state is greater than the size 28 of the airflow opening 27. If the size 28 of the airflow opening 27 decreases, the air-permeable material 29 will abut against the first edge 26 of the outer body 25, when the thickness 40 of the air-permeable material 29 corresponds the size 28 of the airflow opening 27. If the size 28 of the airflow opening 27 is reduced further, the air-permeable material 29 gets deformed and its thickness is reduced so as to correspond to the size 28 of the airflow opening 27. When the size 28 of the airflow opening 27 is increased, the thickness of the air-permeable material 29 will increase correspondingly until it regains its thickness 40 in non-deformed state. If the size 28 of the airflow opening 27 increases further thereafter, a distance will be created between the first edge 26 of the outer body 25 and the air-permeable material 29.

[0088] If the air-permeable material 29 gets deformed, also its porosity might be changed. The air-permeable material 29 may be configured such that the porosity changes differently over its shape, when it is deformed.

[0089] FIGS. 6A-6C illustrate some different embodiments of the air-permeable material 29. Other geometries are also conceivable. It is common to all embodiments that the thickness of at least the portion of the air-permeable material 29 disposed in the airflow opening 27 may be adapted to cover substantially the whole or a portion of the size of the airflow opening. Alternatively, or in addition to a mechanical attachment via clamping of the air-permeable material 29 to the first side 23a of the front cover 23, the air-permeable material can be attached to the first side 23a of the front cover 23, for example via adhesive material.

[0090] As shown in FIG. 6A, the air-permeable material 29 may have the shape of a circular disc. Such an embodiment makes possible a mechanical attachment of the air-permeable filter as described above with reference to FIG. 3E.

[0091] FIG. 6B shows an embodiment in which the air-permeable material 29 has a carriage-wheel-like configuration. The outer portion 29a will be located in the air-flow opening 27. The spokes 29b make possible mechanical attachment as described above.

[0092] FIG. 6C shows an embodiment in which the air-permeable material has essentially a ring shape. The extent 29c of air-permeable material in radial direction may have different values.

[0093] FIGS. 7-9 illustrate graphs of the relationship between airflow (l/s) (the x-axis) out of the ventilation device, here configured as an air supply device, and the maximum degree of pressure throttling Δp.sub.t (Pa) (the y-axis) that can be implemented without exceeding a certain sound effect level L.sub.w (dB(A)). The oblique lines extending across the diagram in the y-direction represent different opening degrees of the respective ventilation devices, i.e. different values of the size of the airflow opening, stated in mm. The lines with value designations 20, 25, 30, etc., represent measured sound effect level generated by the respective ventilation devices. The graphs in FIGS. 7-9 are all measured for ventilation ducts with the dimension 125 mm diameter. What differentiates the ventilation devices is the presence or absence of a porous air-permeable material.

[0094] For ventilation ducts with the dimension 125 mm, the standard flow is set at 20 l/s. Maximum recommended sound effect level is 30 dB(A).

[0095] In FIG. 7, the ventilation device has no air-permeable material. Here it is seen that in order to obtain an airflow of 20 l/s at 20 mm airflow opening, a pressure drop of about 13 Pa over the ventilation device is called for. 20 mm airflow opening is generally the maximum opening degree of a ventilation device as described here. However, other sizes are conceivable. As described above, the ventilation device furthest from the fan is as a standard set with maximum airflow opening. Furthermore, the diagram shows that at airflow of 20 l/s and sound limitation at 30 dB(A), a throttling of about 35 Pa can be achieved at 14 mm airflow opening. This is the maximum value to which the pressure can be throttled without exceeding the threshold value of 30 dB(A) when an airflow of 20 l/s desired. The operational range of said ventilation device is therefore limited to between 13-35 Pa.

[0096] FIG. 8 shows a corresponding diagram for a ventilation device with an air-permeable material in the form of a 5 mm thick filter material in the shape of a circular disc. From here it is apparent that the operational range lies between 25 Pa and about 68 Pa.

[0097] FIG. 9 shows a corresponding diagram for a ventilation device with an air-permeable material in the form of a 10 mm thick filter material in the shape of a wagon wheel as illustrated in FIG. 5B. From here it is seen that the operational range lies between 25 Pa and about 140 Pa.

[0098] The presence of a porous air-permeable material thus broadens the operational range of the ventilation system so that appropriate pressure distribution can be set in the ventilation system while at the same time a specified airflow distribution is achieved, and standards for sound effect levels are not exceeded.

[0099] The invention is not limited to the examples of embodiments described above and illustrated in the drawings, but may be freely varied within the scope of the appended claims.