AU2015100556A4 - Combined fan and attenuator unit - Google Patents

Abstract

Many indoor environments such as rooms, apartments, houses, offices and the like include outside air supply into the environment, and inside air extraction from the environment, as part of an HVAC system, to replace the air inside the environment. While it is desirable to replace the air within an environment such as a room, office, factory and the like, as quickly and as continuously as possible, there are effects associated with a strong air flow system that are desirable to avoid. The noise created by the air supply or extraction is one effect that is desirable to minimise. It is also desirable to minimise the size of the required equipment, such as fan units and ducting. One option to reduce the noise level produced by ducting is to use rectangular attenuator units in the ducting, and such, it is an object of the invention to provide an improved fan unit. 221 222 24 261 21 281 232 231

Description

COMBINED FAN AND ATTENUATOR UNIT Field of Invention 5 The invention relates to an improved fan and attenuator unit. More particularly, the invention relates to a combined fan and attenuator unit having a compact cross section. Background of the Invention 0 Many indoor environments such as rooms, apartments, houses, offices and the like include outside air supply into the environment, and inside air extraction from the environment, as part of an HVAC system, to replace the air inside the environment. While it is desirable to replace the air within an environment such as a room, office, factory and the like, as quickly and as continuously as possible, there are effects associated with a strong air flow system that are desirable to avoid. The noise created 5 by the air supply or extraction is one effect that is desirable to minimise. It is also desirable to minimise the size of the required equipment, such as fan units and ducting. One option to reduce the noise level produced by ducting is to use rectangular attenuator units in the ducting. Figure 1 shows a schematic illustration of a prior art rectangular attenuator unit 1. The 0 rectangular attenuator unit 1 comprises a housing defining a conduit in which acoustic attenuators 2 and 3 occupy a portion of the lateral space. Incoming air flow, the direction of which is indicated by the arrow 4 enters attenuator 1, passes through the airway 5 between the acoustic attenuator blocks 2 and 3, and leaves the attenuator unit 1 in the direction of arrow 6. The acoustic attenuator blocks 2 and 3 absorb sound from the air passing between them through the airway 5. 25 The design of the rectangular attenuator unit 1 is not suited for applications requiring an attenuator unit having a minimal cross sectional size, as a large portion of the conduit within the unit is occupied by the acoustic blocks, leaving less space within the unit for the airway. Furthermore, the rectangular unit 1 does not have any fan incorporated, meaning the fan must be spaced from the attenuator unit, limiting 30 the attenuator's ability to reduce noise. It is an object of the invention to provide an improved fan unit. Alternatively, it is an object of the invention to at least provide the public with a useful choice. 1 Summary of the Invention According to a first aspect of the invention there is provided a combined fan and attenuator unit, comprising: 5 a housing having at least one side wall defining a longitudinal conduit having a length, the housing comprising: an inlet through which a gas is able to enter the housing; an outlet, fluidly connected with the inlet via the conduit, through which a gas is able to exit the housing after passing through the conduit; o a fan within the housing configured to draw the gas through the conduit from the inlet to the outlet; an upstream attenuator portion comprising an upstream acoustic attenuator block occupying a first lateral side of the conduit such that the gas is able to flow past the upstream acoustic attenuator block between the upstream acoustic attenuator block and the at least one 5 side wall of the housing; a downstream attenuator portion comprising a downstream acoustic attenuator block occupying a second lateral side of the conduit, the second lateral side of the conduit being a different side of the conduit to the first lateral side, such that gas is able to flow past the downstream acoustic attenuator block between the downstream acoustic attenuator block and 0 the at least one side wall of the housing. Preferably, the second lateral side of the conduit is on an opposite side of the housing from the first lateral side of the conduit. 25 Preferably, the first lateral side is a top side and the second lateral side is a bottom side, or wherein the first lateral side is a bottom side and the second lateral side is a top side. Preferably, the conduit has a width and a height, the width greater than the height, and the upstream and/or downstream acoustic attenuator blocks occupy substantially the entire width of the conduit. 30 Preferably, the housing comprises a rectangular cross section. Preferably, the inlet comprises an orifice surrounded by an inlet spigot for connection to an inlet tube, and/or the outlet comprises an orifice surrounded by an outlet spigot for connection to an outlet tube. 35 2 Preferably, between the inlet and the upstream attenuator portion is an inlet plenum, and/or between the downstream attenuator portion and the outlet is an inlet plenum. Preferably, the upstream attenuator block and/or the downstream attenuator block comprise a porous 5 acoustic infill. More preferably, the porous acoustic infill is formed from fibreglass. Further aspects of the invention, which should be considered in all its novel aspects, will become apparent to those skilled in the art upon reading of the following description which provides at least one example of a practical application of the invention. 0 Brief Description of the Drawings One or more embodiments of the invention will be described below by way of example only, and without intending to be limiting, with reference to the following drawings, in which: 5 Figure 1 is a schematic illustration of a prior art rectangular attenuator; Figure 2 is a schematic illustration of a combined fan and attenuator unit according to one embodiment of the invention; and 0 Figure 3 is a schematic illustration of a combined fan and attenuator unit according to another embodiment of the invention. Detailed Description of Preferred Embodiments of the Invention 25 Embodiments of the invention provide for a combined fan and attenuator unit that generates low noise output and that can fit in small spaces. It uses a unique combination of an 'acoustic mirror' attenuator structure and cross-flow fan arrangement to obtain low noise performance and a low cross-sectional profile. This low profile enables the unit to be installed within confined ceiling voids and to fit between 30 typical timber floor joist framing. Acoustic performance may be further enhanced by housing the fan in a heavy steel enclosure to minimise 'radiated' sound. The unit may be used for supply or extraction of air where low noise is desirable or necessary. Applications such as high quality domestic and apartment fresh air supply and bathroom extract are typical uses, among many others. 3 Figure 2 shows a schematic illustration of a rectangular attenuator unit 11. The attenuator unit 11 of comprises an attenuator block 12 within a housing defining a conduit through which a gas such as air can pass. The conduit has an inlet through which air enters the attenuator unit in a direction generally indicated by the arrow 14. Air passes through the conduit along an airway 15 past the acoustic 5 attenuator block 12, which absorbs sound from the air as it passes. The air then exits from the attenuator unit from an outlet in a direction generally indicated by arrow 16. The attenuator unit 11 is approximately half the lateral width of the prior art attenuator shown in Figure 1, yet the acoustic attenuator bock 12 is the same width as attenuator block 2. Therefore, the airway 15 0 is half the width of the airway 5. The attenuator units 1 and 11 have substantially the same acoustic performance, yet the total width of attenuator unit 11 has been halved. This reduction in size without reduction in acoustic performance is at least partly attributable to an "acoustic mirror" effect, whereby sound waves within the airway 15 are reflected off the reflecting plane 17 and attenuated by the attenuator block 12. Since the width of the airway 15 is half the width of the airway 5, the total distance 5 travelled from the edge of the attenuator block 12 to the reflecting plane 17 and back to the attenuator block 12 is the same distance as the width of the airway 5. Figure 3 shows a side schematic illustration of a combined fan and attenuator unit 20. The combined fan and attenuator unit comprises a housing 21. The housing 21 defines a conduit having an inlet 221 fluidly 0 connected with an outlet 231. Gas, such as air, can enter the conduit formed within the housing through inlet 221, and exit through outlet 231. In this embodiment the housing comprises four side walls to form a rectangular cross section. 25 The combined fan and attenuator unit 20 comprises a fan 26 within the housing 21 and configured to draw air through the conduit from the inlet 221 to the outlet 231. The direction of airflow into the inlet 221 is generally indicated by the arrow 22, and the direction of airflow from the outlet 231 is generally indicated by the arrow 23. 30 In this embodiment the inlet 221 and the outlet 231 are each defined by a spigot extending outwards from the housing around an orifice. Also in this embodiment, the region of the conduit most proximate the inlet 221 is an inlet plenum or space 222. Likewise, the region of the conduit most proximate the outlet 231 is an outlet plenum 232. The inlet and outlet plenums advantageously allow a space for airflow to smoothly transition between the conduit within the housing and the spigots. 4 The spigots are intended in this embodiment for connection to flexible tubing or other fluid connection means to receive and release air flow. The inlet and outlet in other embodiments could be shaped in any configuration, such as orifices, diffusers, filters etc. 5 The combined fan and attenuator unit 20 comprises an upstream attenuator portion 27 of the conduit, between the inlet 221 and the fan 26. Furthermore, the combined fan and attenuator unit 20 comprises a downstream attenuator portion 28 of the conduit, between the fan 26 and outlet 231. 0 An upstream acoustic attenuator block 24 occupies a portion of the volume within the conduit within the upstream attenuator portion 27, such that air flowing through the conduit must flow past the upstream attenuator block 24. Likewise, a downstream attenuator block 25 occupies a portion of the volume within the conduit within the downstream attenuator portion 28, such that air flows past the downstream attenuator block 25 as it flows through the conduit. 5 The attenuator blocks may comprise a porous acoustic infill, for example high density fibreglass, which may be held within a structure such as steel sheet 262 with a hole in the surface of the attenuator block that faces the conduit. The sound is then free to travel into the infill. In other embodiments the infill may be held within a steel sheet having a surface perforated with holes to enable the sound to travel 0 into the infill. Where high density fibreglass is used, a particularly high density layer may be formed on the surface exposed to the conduit to minimise fibre erosion. In other embodiments other suitable acoustic infills may be used, such as materials formed from fine, tangled fibres with a suitable flow resistivity. 25 In this embodiment, the upstream attenuator block 24 occupies a first lateral side of the conduit so that air must flow past the upstream attenuator block 24 on a second lateral side of the conduit. In this embodiment the second lateral side of the conduit is directly across the housing from the first lateral side. In particular, the first lateral side is a top side, and the second lateral side is a bottom side. 30 The wall of the housing 21 opposite from the upstream attenuator block 24 acts as an acoustic mirror, and is identified as upstream acoustic mirror 271. The upstream acoustic mirror 271 reflects sound back towards the upstream attenuator block 24. This enhances the acoustic performance of the upstream 5 attenuator portion 27 to the performance of a conventional attenuator with one attenuator block on either side of a conduit, yet the attenuator portion 27 takes up half the size. Likewise, the wall of housing 21 opposite the downstream attenuator block 25 acts as an acoustic 5 mirror, and is identified as downstream acoustic mirror 281. Downstream acoustic mirror 281 reflects sound back towards the downstream attenuator block 25. This enhances the acoustic performance of the downstream attenuator portion 28 to that of a conventional attenuator with one attenuator block on either side of a conduit, yet the attenuator portion 28 takes up half the size. O The fan 26 is mounted on a mounting plate 261. In this way, the fan can easily be added to the unit assembly by fastening the plate to a corresponding hole in the housing 21. The fan 26 is a fan that blows air radially, although any suitable fan may be used. Within the unit, the intake of the fan corresponds to an intake plate 262, which substantially fills the gap between the attenuator blocks 24 and 25, so that all air passing between the attenuator portions 27 and 28 must pass through the fan. The fan 26 is 5 advantageously positioned on one side of the conduit, in line with attenuator block 24, which helps reduce the sound of the fan that can travel back out of the inlet 22. This positioning also makes it easy to remove the fan from the housing through a hole in the near side of the conduit, for example for cleaning, maintenance or replacement purposes. The fan 26 is oriented so that the intake of the fan is perpendicular to the axis of the conduit, which the applicant has identified can provide a higher flow 0 rate than other orientations. The housing may be formed from steel sheet, and may be galvanised. Moreover, the fan can be housed in heavy gauge steel sheet to reduce fan noise radiated from the unit. 25 Preferred embodiments of the invention provide a combined fan and attenuator unit that combines the advantageous effects of the inventor's acoustic mirror design while allowing for the fan to be positioned between two attenuator blocks, yet also allowing for the fan to draw air through the unit. Combination fan and attenuator units according to various embodiments of the invention may be 30 different widths to provide for different air flow capacities, while the height may be the same between different embodiments so that the different units can all fit within small spaces within the ceiling or floor. 6 The unit in one particular embodiment may be substantially 250mm wide, 150mm deep and 1500mm long. In some embodiments the unit may be configured to run in two speed modes, to provide different flow 5 rates at different times, such as 25 I/s and 100 I/s. In some embodiments, it may be that a gas other than air flows through the combined fan and attenuator unit, or that the air has a different composition to the air that is typically found in nature. The unit can therefore be used to supply or extract any suitable gas, while minimising noise. 0 Unless the context clearly requires otherwise, throughout the description and the claims, the words "comprise", "comprising", and the like, are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense, that is to say, in the sense of "including, but not limited to". 5 The entire disclosures of all applications, patents and publications cited above and below, if any, are herein incorporated by reference. Reference to any prior art in this specification is not, and should not be taken as, an acknowledgement or any form of suggestion that that prior art forms part of the common general knowledge in the field of 0 endeavour in any country in the world. The invention may also be said broadly to consist in the parts, elements and features referred to or indicated in the specification of the application, individually or collectively, in any or all combinations of two or more of said parts, elements or features. 25 Where in the foregoing description reference has been made to integers or components having known equivalents thereof, those integers are herein incorporated as if individually set forth. It should be noted that various changes and modifications to the presently preferred embodiments 30 described herein will be apparent to those skilled in the art. Such changes and modifications may be made without departing from the spirit and scope of the invention and without diminishing its attendant advantages. It is therefore intended that such changes and modifications be included within the present invention. 7

Claims (9)

1. A combined fan and attenuator unit, comprising: a housing having at least one side wall defining a longitudinal conduit having a length, 5 the housing comprising: an inlet through which a gas is able to enter the housing; an outlet, fluidly connected with the inlet via the conduit, through which a gas is able to exit the housing after passing through the conduit; a fan within the housing configured to draw the gas through the conduit from the inlet 0 to the outlet; an upstream attenuator portion comprising an upstream acoustic attenuator block occupying a first lateral side of the conduit such that the gas is able to flow past the upstream acoustic attenuator block between the upstream acoustic attenuator block and the at least one side wall of the housing; 5 a downstream attenuator portion comprising a downstream acoustic attenuator block occupying a second lateral side of the conduit, the second lateral side of the conduit being a different side of the conduit to the first lateral side, such that gas is able to flow past the downstream acoustic attenuator block between the downstream acoustic attenuator block and the at least one side wall of the housing. 0

2. The combined fan and attenuator unit as claimed in claim 1, wherein the second lateral side of the conduit is on an opposite side of the housing from the first lateral side of the conduit.

3. The combined fan and attenuator unit as claimed in claim 1 or claim 2, wherein the first lateral 25 side is a top side and the second lateral side is a bottom side, or wherein the first lateral side is a bottom side and the second lateral side is a top side.

4. The combined fan and attenuator unit as claimed in any one of the previous claims, wherein the conduit has a width and a height, the width greater than the height, and the upstream and/or 30 downstream acoustic attenuator blocks occupy substantially the entire width of the conduit.

5. The combined fan and attenuator unit as claimed in any one of the previous claims, wherein the housing comprises a rectangular cross section. 35

6. The combined fan and attenuator unit as claimed in any one of the previous claims, wherein: 8 the inlet comprises an orifice surrounded by an inlet spigot for connection to an inlet tube; and/or the outlet comprises an orifice surrounded by an outlet spigot for connection to an outlet tube. 5

7. The combined fan and attenuator unit as claimed in any one of the previous claims, wherein: between the inlet and the upstream attenuator portion is an inlet plenum; and/or between the downstream attenuator portion and the outlet is an inlet plenum. 0

8. The combined fan and attenuator unit as claimed in any one of the previous claims, wherein the upstream attenuator block and/or the downstream attenuator block comprises a porous acoustic infill.

9. The combined fan and attenuator unit as claimed in claim 8, wherein the porous acoustic infill is 5 formed from fibreglass. 9