GB2250356A

GB2250356A - Noise attenuation in ducting

Info

Publication number: GB2250356A
Application number: GB9026077A
Authority: GB
Inventors: Philip Alan Northfield
Original assignee: SARGENTS ACOUSTICS Ltd
Current assignee: SARGENTS ACOUSTICS Ltd
Priority date: 1990-11-30
Filing date: 1990-11-30
Publication date: 1992-06-03
Anticipated expiration: 2010-11-30
Also published as: GB9026077D0; GB2250356B

Abstract

A duct arrangement for use in a heating, ventilating or air conditioning system comprises a duct section defining a bend or corner, the section incorporating one or more flow-deflecting vanes 6 for guiding flow around the bend. The or each flow-deflecting vane is provided with or formed of a sound absorbent material. The flow deflecting vanes may be supported on a plate with the vanes and the plate constituting a removable fitting which can be inserted into the duct section. <IMAGE>

Description

DESCRIPTION OF INVENTION Improvements in or relating to ducting.

THE PRESENT INVENTION relates to ducting and more particularly relates to a noise attenuation device for use with ducting. Whilst the primary application for this invention will be in heating, ventilating and air conditioning systems, the invention may be used with ducting conveying media other than air. Thus, whilst the present document will make reference to air and air ducting, it is to be appreciated that the invention is not restricted to use with ducting conveying air.

Noise is generated as air flows through ducting in a building. The noise is generated by the plant that generates the air flow (i.e. the fan or impeller and the associated motor) and noise is generated in the ducting due to the energy used by the air to overcome resistance to flow offered by bends, changes in cross-section of the ducting and obstacles within the ducting. It is known to try and reduce the level of noise by including attenuators in the ducting or by designing the ducting in such a way as to minimize the energy lost by air flowing through the ducting.

However, this is a time consuming and costly exercise.

Bends in ducting present particular problems insofar as noise generation is concerned, since as the air changes direction tubulance is created which gives rise to noise.

It is known to provide turning or guide vanes in a bend in a ducting section in order to 'guide' the flow around the bend and improve the air flow characteristics. However, the turning vanes also tend to 'reflect' noise around the bend.

Providing noise attenuators in the ducting is often very difficult due to space limitations, particularly where the ducting is located in a space above a false ceiling.

Whilst providing sound absorbent material within ducting, for example on the interior of the ducting itself or in the form of webs, vanes or splitters extending axially, horizontally or vertically, of the ducting, absorbs some of the noise generated by the plant and present within the ducting, and some of the noise generated in the ducting, this also gives rise to an increased pressure drop within the flow since the noise attenuating material presents an obstacle to the flow and this results in increased running costs.

The present invention seeks to provide an improved arrangement which will afford adequate noise attenuation within ducting without severely impairing the air flow characteristics.

~According to one aspect of this invention there is provided a duct arrangement comprising a duct section defining a bend or corner, the duct section incorporating at least one flow deflecting vane provided with or formed of sound absorbent material.

Preferably a plurality of said vanes are provided, the vanes being aligned and extending across the region of said bend.

The or each vane may be made of a sound absorbent material, such as a foamed plastics material.

Alternatively the or each vane may be made of a metal or plastic and be provided with a sound absorbent material.

The sound absorbent material may be mounted on the exterior of the vane or may be contained within a hollow vane, at least part of the exterior of the vane being perforated. In this latter case an impermeable flexible membrane may be provided between the sound absorbent material and the perforated exterior of the vane.

Conveniently the sound absorbent material comprises an open structure acoustic material, such as glass or mineral fibre or a foamed plastics material.

Preferably the or each vane is mounted on a plate, the plate being inserted in position within the duct section.

Conveniently the or each vane is of crescent-shaped cross-section, having a predetermined internal radius and a predetermined external radius, the internal radius being greater than the external radius.

Advantageously the or each vane has a predetermined width and has an external radius equal to half the predetermined width and an internal radius equal to two thirds the predetermined width.

Preferably a plurality of vanes are incorporated in the duct section the spacing between the vanes being equal to two thirds the predetermined width of each vane.

The or each vane may comprise two substantially linear 0 arms extending at substantially 90 to each other, each arm presenting an outer face and an inner face, the outer face and the inner face diverging at approximately 110 at the free end of each arm.

According to a second aspect this invention provides a duct fitting for incorporation in ducting, the fitting comprising a plate carrying one or more upstanding flow deflecting vanes, the or each vane being provided with or formed of a sound absorbent material.

In order that the present invention may be more readily understood and so that further features thereof may be appreciated, the invention will now be described by way of example, with reference to the accompanying drawings, in which: FIGURE 1 is top plan view of a bend in ducting, showing one embodiment of the present invention; and FIGURE 2 is a top plan view of a turning vane forming part of a second embodiment of the present invention.

Referring initially to Figure 1 of the accompanying drawings part of an air duct in the form of a right angled bend 1 is illustrated. The bend comprises a first linear portion 2 and a second linear portion 3 which join at a right angle corner 4. Typically such ducting is of rectangular cross-section.

Mounted within the corner of the section of ducting illustrated is an air deflector assembly comprising a base plate 5 carrying a plurality of upstanding so-called turning vanes 6 designed to guide the flow of air around the bend and minimize energy losses in the flow.

The base plate 5 comprises a main portion 7 of generally rectangular form, terminating in a point or apex 8 designed to be received within the outer portion of the right angled corner 4, with the main portion 7 extending horizontally across the bend towards the inner portion of the right angled corner. Each of the turning vanes 6 is crescent-shaped in cross-section and has a width, when seen in plan view, as in Figure 1, W. The base plate 5 also has a width W. Thus, the turning vanes 6 extend across the full width of the base plate.

In the embodiment illustrated in Figure 1 of the drawings two crescent-shaped turning vanes 6 are provided, with a third turning vane being located on the apex 8 of the base plate 5 and having an arcuate inner face and a right angled outer face designed to be received snuggly within the corner 4. The turning vanes each have a height equivalent to the overall height of the duct within which they are to be received, the number of vanes present in the bend depending upon the width of the duct.It will be appreciated that the turning vanes are centred upon a line extending diagonally across the bend, the vanes being 2W equally spaced apart by a distance equal to Each of the two crescent-shaped turning vanes 6 has a radially outer skin 9 having a radius R1 which is equal W to 2 As mentioned above the outermost turning vane located upon the apex 8 of the base plate 5 defines a right-angled outer skin or wall 10 adapted to abut snuggly within the outermost corner of the bend in the duct. Each of the three turning vanes 6 has a radially inner, arcuate 2W skin 11 having a radius which is equal to 3.

The outer skin 9, 10 of the three turning vanes 6 may be solid or may be perforated and it is envisaged that this skin will be formed from an appropriate metal, such as galvanized steel or aluminium, although a rigid plastic material may be used. The inner skin 11 of each turning vane may also be formed from galvanized iron or aluminium and is perforated. The perforations may comprise a regular array of holes or may comprise an array of slots or the like or, alternatively, the skin may even be formed from flattened expanded metal. An impermeable flexible membrane in the form of a sheet of plastics material is located immediately behind the perforated inner skin 11 of each turning vane.

The inner and outer skin of each turning vane defines a hollow interior which accommodates a sound absorbing material 12 which may be an open acoustic absorbing material such as mineral wool, glass fibre, expanded plastics foam or the like. The plastics membrane behind the perforated inner skin of each vane prevents any of the sound absorbing material from falling out of the vane and being carried along in the air flow.

Thus, the air deflecting assembly comprises a plurality of turning vanes which serve not only to guide the flow of air around a bend in a duct but also serve to attenuate any noise generated in the duct, or generated by the plant and carried in the duct. The air deflecting, sound absorbing assembly comprising the base plate 5 and the upstanding turning vanes 6 may be pre-fabricated and subsequently inserted in position within a duct section as the duct is manufactured.

As air or any other gas flows through the duct, as indicated by arrows in Figure 1, it will be guided around the bend or corner 4 by the turning vanes and any noise generated in the duct, or generated by the plant and carried in the duct, will be attenuated or absorbed by the material within the turning vanes. It is to be appreciated that whilst the outer skin 9, 10 of the turning vanes may or may not be perforated, the inner skin 11 of each turning vane should, in the preferred embodiment illustrated, be perforated in order to allow the sound absorbing material 12 within the vanes to attenuate or absorb any duct - borne noise.

It will be appreciated that the present invention has the advantage of providing noise attenuation in the region of a bend in a duct without requiring the provision of an attenuator which accommodates additional space within the duct and which would give rise to an increased pressure drop in the flow. The arrangement of the present invention may be installed in the same physical space as an ordinary duct bend and gives virtually no increase in pressure drop in the flow. Since the turning vanes per se are already used in bends in ducting, the additional manufacturing and installation costs associated with the present invention are minimal.

Various modifications may be made to the arrangement described above without departing from the scope of the present invention. For example, each vane may comprise an element formed of metal having a facing of sound absorbent material adhered thereto. The sound absorbing material may comprise an appropriate expanded foamed plastics material.

Indeed, the vane itself may be fabricated solely from a suitable plastics material which is able to withstand high temperatures that may be experienced within a ducting system without deforming and without giving off toxic fumes, the plastics material being a sound absorbing material.

Whilst it is envisaged that the vanes illustrated in Figure 1 may be relatively cheap to produce, due to their relatively small size, these vanes may not provide optimum air flow characteristics. Figure 2 illustrates a vane 13 which, although probably more expensive to produce than the vanes shown in Figure 1, will provide superior results insofar as air flow characteristics are concerned. The vane 13 is symmetrical about an axis 14 which, when the vane is mounted in position in a bend in ductwork would extend diagonally across the bend. The vane 13 may again be considered as being 'crescent'-shaped and comprises two arms 15, 16 which, in the region of their extremities, are disposed substantially at right angles to each other. The vane 13 has a hollow interior defined between a solid rear or outer skin 17 and a perforated front or inner skin 18.

The hollow interior of the vane is filled with an appropriate sound absorbent material 19 in the same way as the vanes 6 of Figure 1. The rear skin of the vane has two linear portions positioned adjacent the ends of the arms 15, 16, the linear portions being interconnected by an arcuate portion in the central region of the vane. The front skin 18 of the vane is connected to the rear skin 17 at the free ends of the arms 15, 16, an angle of 110 being defined between the front and rear skin at the extremities of the arms 15, 16.

It is envisaged that a series of vanes 13 will be mounted upon a base plate such as the base plate 5 of Figure 1 such that the base plate and the vanes constitute a duct fitting in the form of a sound absorbing deflector assembly to be inserted in ducting.

Whilst the invention has been described with reference to preferred embodiments, it is to be appreciated that numerous further modifications may be made without departing from the scope of the present invention.

Claims

1. A duct arrangement comprising a duct section defining a bend or corner, the duct section incorporating at least one flow deflecting vane provided with or formed of sound absorbent material.

2. An arrangement according to Claim 1 wherein a plurality of said vanes are provided.

3. An arrangement according to Claim 2 wherein the vanes are aligned and extend across the region of said bend.

4. An arrangement according to any one of the preceding claims wherein the or each vane is made of a sound absorbent material.

5. An arrangement according to Claim 4 wherein the or each vane is made of a foamed plastics material.

6. An arrangement according to any one of Claims 1 to 3 wherein the or each vane is made of a metal and is provided with a sound absorbent material.

7. An arrangement according to Claim 6 wherein the sound absorbent material is mounted on the exterior of the vane.

8. An arrangement according to Claim 6 wherein the sound absorbent material is contained within a hollow vane, at least part of the exterior of the vane being perforated.

9. An arrangement according to Claim 8 wherein an impermeable flexible membrane is provided between the sound absorbent material and the perforated exterior of the vane.

10. An arrangement according to any one of the preceding claims wherein the sound absorbent material comprises an open structure acoustic material.

11. An arrangement according to Claim 10 wherein the sound absorbent material comprises glass or mineral fibre.

12. An arrangement according to Claim 10 wherein the sound absorbent material comprises a foamed plastics material.

13. An arrangement according to any one of the preceding claims wherein the or each vane is mounted on a plate, the plate being inserted in position within the duct section.

14. An arrangement according to any one of the preceding claims wherein the or each vane is of crescent-shaped crosssection, having a predetermined internal radius and a predetermined external radius, the internal radius being greater than the external radius.

15. An arrangement according to Claim 14 wherein the or each vane has a predetermined width and has an external radius equal to half the predetermined width and an internal radius equal to two thirds the predetermined width.

16. An arrangement according to Claim 15 wherein a plurality of vanes are incorporated in the duct section the spacing between the vanes being equal to two thirds the predetermined width of each vane.

17. An arrangement according to any one of the preceding claims wherein the or each vane comprises two substantially linear arms extending at substantially 900 to each other, each arm presenting an outer face and an inner face, the outer face and the inner face diverging at approximately 110 at the free end of each arm.

18. A duct fitting for incorporation in ducting, the fitting comprising a plate carrying one or more upstanding flow deflecting vanes, the or each vane being provided with or formed of a sound absorbent material.

19. A duct arrangement substantially as herein described, with reference to and as shown in Figure 1 or Figure 2 of the accompanying drawings.

20. A duct fitting substantially as herein described, with reference to and as shown in Figure 1 or Figure 2 of the accompanying drawings.

21. Any novel feature or combination of features disclosed herein.