GB2528686A

GB2528686A - Air conditioning silencer and method of silencing an air conditioning unit

Info

Publication number: GB2528686A
Application number: GB1413324.3A
Authority: GB
Inventors: Phil Gillatt
Original assignee: SilentAire Group Ltd
Current assignee: SilentAire Group Ltd
Priority date: 2014-07-28
Filing date: 2014-07-28
Publication date: 2016-02-03
Also published as: GB201500593D0; GB2528734A; EP2980500A1; GB201413324D0

Abstract

An air conditioning silencer suitable to be placed at an inlet and / or outlet of an air conditioning unit 100, the silencer comprising a first flow restrictor 210 spaced from a second air flow restrictor 220 by a gap 230 and are arranged to create a non-linear air flow, and wherein the first and second flow restrictors are formed from sound absorbing material. The flow restrictors may be plates that extend across an air ducting and include equal sized apertures (fig 4) allowing air to pass therethrough. A third air flow restrictor 330 may be used. The silencer may be integral of a new air conditioning unit or may be retro fitted to existing air conditioning units, in particular having a reduced size and in use with individual hotel rooms. The apertures may be circular or other shapes and corresponding apertures in each restrictor do not substantially overlap, i.e. less than 30% overlap. The restrictors may be formed from acoustic foam having a thickness greater than 0.02m. A method of silencing and a vent grill 400 for use with an air conditioning system is also claimed.

Description

Air Conditioning Silencer and Method of Silencing an Air Conditioning Unit The present invention relates to a silencer for an air conditioning unit and in particular, though not exclusively, to a silencer that can be retro fitted to an existing air conditioning unit.

Air conditioning units are widely known. Typically, an air conditioning unit comprises a housing that houses a fan to pull air through an inlet, over a heat exchanger and out through an exit. The cooled air is expelled through the exit providing air conditioning to a room.

Operation of the air conditioning unit generates noise through movement of the various parts and air turbulence. It is known to silence the air conditioning unit by insulating the housing and reducing turbulence.

Air conditioning units are widely used in hotel rooms with a single unit in each room that circulates the air within the room. However, some air conditioning units can be too noisy for guests, particularly since the small size of the units means smaller fans must be used that operate at higher speeds creating greater air movement and therefore greater noise. It is often not practical for hotels to replace noisy air conditioning units and so a need exists for a method of silencing existing air conditioning units within a confined space and without easy access to the air conditioning unit itself. Typically, hotel rooms have around 0.15m between the air-conditioning unit and the bulkhead. Standard techniques of silencing the unit by fitting a long plenum are not possible. Here, the plenum is typically a box like structure with insulated sides.

It is an object of the present invention to attempt to overcome at least one of the above or other disadvantages. It is a further aim to provide a silencer for an air conditioning unit that does not involve using long sound proofed ducting.

According to the present invention there is provided an air conditioning silencer as set forth in the appended claims. Other features of the invention will be apparent from the dependent claims, and the description which follows.

An air conditioning silencer suitable to be placed at an outlet and/or inlet of an air conditioning unit, wherein the silencer includes a first air flow restrictor and a second air flow restrictor spaced from the first and arranged to create a plurality of substantially non-linear air flows. Although the non-linear air flows create turbulence, which is typically a source of noise generation at a frequency of around 50Hz -2000Hz, advantageously it has been found that by forming one of the restrictors and preferably both restrictors from a sound absorbing material such as acoustic foam, the sound generated by air movement on the supply side of the unit can be substantially reduced.

Acoustic foam is a term of art used to describe materials that absorb sound from turbulent air and airborne sound waves. Air movement noise is typically around 500Hz to 2000Hz. Materials can be classified with a sound absorbing coefficient. The more sound the material absorbs the better the sound silencing properties. The acoustic foam can be coated or covered with fabric to improve the sound absorption properties. The minimum sound absorption coefficient for the absorbing material is between 0.1 at 100Hz and 0.94 at 4kHz.

The sound absorption coefficient is measured in accordance with EN 150 11654:1997.

In the exemplary embodiments, ducting extends from the inlet I outlet to create an enclosed duct having substantially the same and consistent cross-section to the inlet I outlet.

As will be appreciated, advantageously, due to the arrangement of the restrictors, the length of the ducting can be substantially reduced from known plenums and can typically be less than 0.3m or less than 0.25m or less than 0.2m in length. The ducting can be lined with sound insulating material such as acoustic foam as with known plenums. The airflow restrictors are plates that extend across the ducting. That is, the air flow restrictors extend typically orthogonal to the sides of the ducting. The air flow restrictors therefore create turbulence by allowing air to freely pass through apertures formed through the air flow restrictors, whilst substantially restricting air movement through parts of the restrictor without apertures. The density of the holes to the cross sectional area of the duct is preferably between around 40% and 10%. Preferably, the density of the holes to the cross sectional area is around 20-40%. In the exemplary embodiments the air flow restrictors are plates sized to fit in the ducting and formed with apertures having a combined area of around 10% to 40% of the plate and preferably between 20% to 25%.

The aperture through the air flow restrictors can be formed from in a number of various ways. Preferably, each quarter of the air flow restrictor when viewed as a cross section orthogonally through the duct has an aperture density of not less than around 50% of the quarter having the greatest aperture density. The area may be divided into quarters for the aperture density by imaginary dividing lines that separate the air flow restrictor at equal distances along one axis, along the other axis or along both axis. Preferably the estimation of aperture density is approximately correct for two of the methods of separating the cross-sectional area into quarters or yet more preferably all three. Notwithstanding the approximation, it is preferable if the arrangement of the apertures across the restrictor is random. That is, there is no discernable geometric pattem to the layout of the apertures.

Although it can be envisaged the aperture having a complex shape, in the exemplary embodiments, the aperture is formed from a series of discrete apertures. Here, each aperture has an area of ± 50% of the mean aperture area, but preferably the aperture areas are substantially equally sized. In the exemplary embodiments, 5 to 10 apertures are provided.

Again, although a complex aperture outline is possible, in the exemplary embodiments a geometric shape such as a circle or a square is used. Preferably a circular hole is formed or drilled or punched, or cut to form each aperture.

In the exemplary embodiments, the air flow restrictors have a thickness in the direction of the air flow of at least 0.02m or at least 0.04m and preferably around 0.OSm. As mentioned, the air flow restrictors are suitably formed from acoustic foam. The first and second air flow restrictors are separated by a gap. The gap has a cross sectional area substantially the same as the ducting. The gap allows the air to mix. The gap spaces the first and second restrictors at least 190% of the thickness of the or each insulated air flow restrictor and preferably around 200%. Extending the gap distance increases the sound insulation factor, but the affect is limited above around 300% of the thickness of the restrictor. Importantly, the apertures through the first air flow restrictor and second air flow restrictor are not substantially aligned to thereby create the non-linear flow. That is, when viewed in the direction of the airflow, the apertures in the first air flow restrictor substantially cover closed areas of the second air flow restrictor. In the exemplary embodiments, some overlap is acceptable. It has been found that the overlap should be kept below 30% of the aperture area. That is, when the first restrictor is overlaid on the second restrictor, 70% or more of the aperture area of the first plate should overlay closed areas of the second restrictor. Preferably, in the embodiments having a plurality of discrete apertures, less than 30% of each aperture should overlay an aperture of the second restrictor.

In one exemplary embodiment a third airflow restrictor is provided spaced from the second air flow restrictor. The relationship between the second and third airflow restrictors is preferably substantially the same as the relationship between the first and second air flow restrictors.

In the exemplary embodiments, the supply of air into the room is expelled through a vent grill. The vent grill may be integral to the second airflow restrictor, or may be a decorative face plate. Consequently, according to a further exemplary embodiment, there is provided a vent grill for an air-conditioning duct. The vent grill is arranged to be connected to air conditioning ducting and have a generally planar construction in a main plane. The vent grill comprises a plurality of apertures arranged through a front face to provide a plurality of fluid passageways between a rear surface and the front face. Advantageously, the front face is arcuate such that an approximate plane of the front of one aperture is angled with respect to an approximate plane of the front of an adjacent aperture. This has been found to provide an improved airflow distribution into the room. In particular, an arrangement of adjacent apertures at an angle to each other such that an aperture towards an edge of the front face is arranged at a greater angle to the main plane than an aperture spaced further from the edge has been found to provide a divergent airflow distribution. Consequently, when installed in a room without direct, linear directionality from the air conditioning ducting to the area to be cooled, use of the improved vent grill enables a divergent flow to be achieved and thereby reaching the area more effectively.

It is envisaged that the vent grill would require improved distribution in one direction only. Typically when installed this would be in a horizontal direction. However, should the need arise, the vent grill could be arcuate in two orthogonal planes, wherein the approximate planes of adjacent apertures in both directions are angled.

In the exemplary embodiments, the apertures through the front face of the vent grill may be a grill or mesh but are preferably discrete apertures. Preferably, the apertures have a shape and area as described above. When the vent grill is separate to the second air flow restrictor, the apertures in the vent grill may have a similar overlapping relationship with the second air flow restrictor as described above. Preferably, for aesthetic reasons, the apertures may be uniformly spaced on the vent grill.

In the exemplary embodiments, the rear face of the vent grill is also arcuate. Suitably, the thickness of the front face is constant. For instance, the vent grill may be pressed or moulded from a flat sheet, though other forming processes are envisaged. Again, the apertures may be stamped or machined prior to forming the arcuate face or may be formed as part of the forming process.

For a better understanding of the invention, and to show how embodiments of the same may be carried into effect, reference will now be made, by way of example, to the accompanying diagrammatic drawings in which: Figure 1 is a plan schematic view of an air conditioning arrangement; Figures 2 and 3 are plan views of first and second air flow restrictors respectively; Figure 4 is a plan view showing the first and second reflectors overlaid; Figure 5 is a plan view of a vent grill; and Figure 6 is a plan view of the vent grill of Figure 4.

Referring to figure 1, an air conditioning arrangement comprises an air conditioning unit 100, a supply silencer 200, a return silencer 300 and a vent grill 400. The air conditioning unit is a standard unit that typically includes an air flow means 101, an inlet 102 and an outlet 104, and a heat exchanger 105. The air flow means 101 draws air in to the unit through the inlet 102, over the heat exchanger 105 and expels the air through the outlet 104. Silencers 200, 300 are attached to the outlet 104 and inlet 102 respectively. The silencers control the air flow to provide sound damping in a room being conditioned. The supply silencer 200 reduces air turbulence directly emitted in to the room. Applying a silencer to the return air reduces the noise level of the air travelling through the air conditioning unit 100 and therefore has an effect on the noise experienced within the room being conditioned.

It is envisaged that the silencers may be fitted as integral parts of new air conditioning units. However, the silencers are particularly suitable to be retro fitted to existing air conditioning units where access to the air conditioning unit 100 is not practical and where space is limited or at a premium for plenum ducting. Consequently, the silencers are particularly suitable for retrofitting within the hotel industry. Hotel room layouts are reasonably standard and typically use standard fan coil air conditioning unit packaged in a 0.2x0.7x0.62m envelope and housed in the ceiling space above the entrance hallway. Air is drawn in from the corridor and expelled out to one side of the room relative to the bed. Space for outlet or inlet ducting is limited by the bulkhead and is typically less than 0.3m at either side. Traditional box ducting with acoustic foam applied to each internal face of the ducting is not effective over such short distances.

Silencers 200 and 300 are substantially the same and so a description of only silencer 200 is given below. Silencer 300 is shown as having an additional gap between the silencer and inlet 102 as extra space is provided. However, a gap between airflow restrictors may also be increased. However, extending the gap to be greater than seven or eight times the thickness of air flow restrictors does not seem to have significant affect on the sound decrease.

Silencer 200 includes a first air flow restrictor 210 and a second airflow restrictor 220.

The air flow restrictors are spaced from each other to be separated by a gap 230. Air from the air-conditioning unit is passed through the first airflow restrictor 210 into the gap 230. The air continues to pass from the gap 230 through second airflow restrictor 220. The airflow restrictors restrict the air flow to cause turbulence air flow within the gap. The gap 230 provides an expansion for the air after exiting the first airflow restrictor. The airflow restrictors are arranged to provide a non-linear flow path, relative to the flow direction of the air approaching the first air flow restrictor. As the airflow approaching the first airflow restrictor will typically be orthogonal to the airflow restrictor, the first and second air flow restrictors are arranged to not substantially provide a straight fluid path across the gap.

Referring to Figures 2 and 3, the non-linear air flow is achieved using off-set apertures through each airflow restrictor. Whilst the apertures may be a single aperture formed in a complex shape, in the exemplary embodiments, six or seven equally sized apertures have been found to be particularly suitable. It is believed, the apertures need to be a reasonable size to avoid creating too much turbulence and therefore noise that the system can't absorb.

However, the apertures cannot be too large as otherwise they would not create the turbulent flow into the gap. In the exemplary embodiments, the apertures are between 1.5% and 4.5% of the area of the airflow restrictor and preferably around 3.6%. Although any number of shapes is envisaged, the apertures are shown in the figures as being circular having a diameter between 0.09m and 0.05m and preferably around 0.08m based on a rectangular airflow restrictor having dimensions of 0.7m by 0.2m.

The apertures are randomly spaced but preferably have a generally even spread so that each quarter of the airflow restrictor has an aperture to area ratio of not less than around 50% of the aperture to area ratio of each of the other quarters. Here, the airflow restrictor can be divided into quarters by imaginary lines draw orthogonal to an axis and having equal areas.

The imaginary lines may be drawn along a first axis, or a second axis or may split the total airflow restrictor in to four by imaginary lines along the centre of the airflow restrictor in both axis.

The apertures of the exemplary embodiments are arranged to not substantially overlap in order to achieve the required non-linear flow, see Figure 4. By overlap, it is meant that when the two airflow restrictors are viewed from the direction of airflow approaching the first airflow restrictor, that is perpendicular to the first airflow restrictor, the apertures in the first airflow restrictor are arranged to cover portions of the second airflow restrictor. Some overlap of the apertures 219 is permissible whilst still achieving the non-linear air flow. It has been found that up to 30% overlap is allowable. That is up to 30% of the aperture area or of each aperture in one airflow restrictor is able to overlie a respective aperture in the other airflow restrictor.

The airflow restrictors are formed from a sound absorbing material. In the exemplary embodiments, acoustic foam having a thickness of O.05m was used and a sound absorption coefficient for the absorbing material is 0.18 at 100Hz, 0.44 ay 250Hz, 0.84 at 500Hz, 0.94 at 1000Hz, 0.87 at 2000Hz and 0.94 at 4000Hz. The sound absorption coefficient is measured in accordance with EN 150 11654:1997.

The gap 230 allows turbulent air to flow between the apertures of the airflow restrictors.

The gap extends the full cross section of the ducting. The width of the gap has been found to have an impact on the silencing function. If the gap is too small it is thought that the air does not have sufficient space to be turbulent and for sound absorption. If the gap is too large, the air is not sufficiently turbulent at the second airflow restrictor to be absorbed. It has been found that the gap having a thickness of between 190% and 300% of the thickness of the first airflow restrictor provides good sound absorption and a thickness of around 200% is particularly suitable.

In one exemplary embodiment, referring to silencer 300 of Figure 1, a third airflow restrictor 330 is provided after the first and second airflow restrictors 310, 320. The third airflow restrictor is substantially the same as the first and second airflow restrictors in terms of form and apertures and suitably has the same relationship with the second airflow restrictor as the second airflow restrictor has with the first airflow restrictor. The first and third airflow restrictors may have the same layout of apertures or may be different again. That is the first and third airflow restrictors may be substantially the same part separated by the second airflow restrictor with non-overlapping apertures to create non-liner flow between the first and second and second and third airflow restrictors.

It has been found that by utilising the silencers 200, 300 as described above, the operating noise of a standard air-conditioning unit can be reduced by around 10dB.

Referring to Figure 1, a vent grill is shown on the exit of the supply side to the room.

The vent grill is used to provide a decorative face plate to the exit of the air conditioning plenum and typically covers the join between the wall finish and opening for the air-conditioning plenum. It will be appreciated therefore that the vent grill 400 includes appropriate fixings and mountings as required. For instance, the vent grill may include a flange 410 arranged to fix flush to the wall. The flange therefore extends orthogonally to the flow path of the plenum. Referring to Figures 5 and 6, the exemplary vent grill is described.

Importantly, the vent grill includes a non-planar front face that has an arcuate profile. The arcuate profile is shown as being relative to an installed, horizontal direction. However, the arcuate profile may equally be arranged to be relative to the vertical direction or both. The result of arranging the front face to be arcuate is to achieve a more suitable directionality on the expelled air. With a planar front face, the air is directed in a substantially parallel fashion.

In contrast, by arranging the front face to be arcuate, the air is caused to be less collimated and to have a spread and directionality that better suits the position of the vent within the room. That is, typically the vent is situated above a corridor of a hotel room, directly opposite dead space, whereas using the vent grill 400, the conditioned air can be directed more efficiently towards the parts of the room that need to be cooled.

B

Referring to Figure 6, exit apertures 420 are formed on the front face. Because the front face is arcuate, the apertures each have an approximate plane angled with respect to adjacent apertures. Here the approximate plane is the plane comprising a tangent to the centre of the aperture. The figures show seven discrete apertures. However, the apertures are preferably as described herein in relation to the apertures of the first and second air flow restrictors.

Here, the relationship would be in terms of the apertures 42Oand area of the vent grill and the apertures of the air flow restrictor adjacent the vent grill. However, for aesthetic reasons it is preferable for the apertures 420 of the vent grill to be geometrically arranged on a regimented grid pattern.

Although a few preferred embodiments have been shown and described, it will be appreciated by those skilled in the art that various changes and modifications might be made without departing from the scope of the invention, as defined in the appended claims.

Claims

ClaIms 1. An air conditioning silencer suitable to be placed at an outlet and/or inlet of an air conditioning unit, wherein the silencer includes a first air flow restrictor and a second air flow restrictor spaced from the first and arranged to create a plurality of substantially non-linear air flows, wherein the first and second air flow restrictors are formed from a sound absorbing material.
2. The air conditioning silencer of claim 1, wherein the air flow restrictors are plates that extend across an air ducting, orthogonal to sides of the ducting.
3. The air conditioning silencer of claim 1 or 2, wherein the airflow restrictors include apertures to allow air to pass through.
4. The air conditioning silencer of claim 3, wherein the density of the apertures to the area of the airflow restrictor is between 10% and 30%.
5. The air conditioning silencer of claim 4, wherein a quarter of the airflow restrictor has an aperture density of not less than 50% of a quarter having the greatest aperture density.
6. The air conditioning silencer of any of claims 3 to 5, wherein each aperture is substantially equally sized.
7. The air conditioning silencer of any preceding claim wherein the air flow restrictors have a thickness of greater than 0.02m.
8. The air conditioning silencer of claim 7 wherein the gap spaces the first and second air flow restrictors between 190% and 300% of the thickness of the air flow restrictors.
9. The air conditioning silencer of any of claims 3 to 8 wherein less than 30% of the area of the apertures in one air flow restrictor is aligned with the aperture area of the other airflow restrictor.
10. The air conditioning silencer of any preceding claim including a third airflow restrictor.
11. A method of silencing an air conditioning unit comprising fitting an air conditioning silencer of any preceding claim to an inlet or outlet of an air conditioning unit.
12. The method of silencing an air conditioning unit of claim 11, wherein the method comprises installing the silencer in the plenum of an existing air conditioning installation.
13. A vent grill for use with an air conditioning system, the vent grill having a generally planar construction in a main plane and including a plurality of apertures arranged through a front face to provide a plurality of fluid passageways between a rear surface and the front face, wherein the front face is arcuate such that an approximate plane of the front of one aperture is angled with respect to an approximate plane of the front of an adjacent aperture.
14. The vent grill of claim 13, wherein the density of the apertures to the area of the vent grill is between 10% and 30%.
15. The vent grill of claim 14, wherein a quarter of the airflow restrictor has an aperture density of not less than 50% of a quarter having the greatest aperture density.
16. The vent grill of any of claimsl3 to 15 wherein each aperture is substantially equally sized.
17. An air conditioning unit including a silencer as claimed in any of claims ito 10 and / or a vent grill of any of claims 13 to 16.