Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 0221~761 1997-09-17
Acoustical Dampening System
FIELD OF THE INVENTION
The present invention relates to an apparatus for noise suppression. In particular, the
apparatus includes an acoustical dampening system which is effective in noise suppression
in a wide range of frequencies. The invention also provides an effective enclosure design
for noise suppression in vertical and horizontal cooling systems.
BACKGROUND OF THE INVENTION
Process coolers in the oil, gas, petrochemical and other related industries require
substantial cooling of various liquid substances. Typically, hot substances are pumped into
a header, which is connected to a series of cooling coils with cooling fins, located within a
chamber through which high volumes of air are pumped through by rotating fans. The
forced air is drafted past the cooling coils and fins thereby transferring heat from the inside
of the pipes. In many installations, the air-flow required for the industrial process is very
high and necessitates large diameter fans, often in the range of 13 feet, with air flows in
the order of 250,000 cubic feet of air per minute passing through the fan systems.
These cooling systems may produce very high noise levels from the blades of the fan, the
air flowing past the coiling cools and fins, belts and/or gears, motors and any noise
transmitted through steel structures and/or from fluids flowing through the pipes. Noises
generated within a cooling system will escape with both the inflow and outflow portions of
the cooling system's air flow and may often exceed 100 dBA, which is well in excess of
acceptable noise level standards imposed in many regions. Jurisdictional regulations often
require that the average noise level around such a cooling installation does not exceed 40
dBA at night and 50 dBA during the day. Accordingly, there has been a need for acoustical
chambers which can effectively attenuate the noise levels while also providing effective
operation of the cooling system and, in particular, without creating excessive back pressure
on the cooling system.
In the design of an acoustical chamber which is effective in meeting the design goals of
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noise attenuation while maintaining normal operation of a cooling system, there has been a
need to develop an effective acoustical dampening system which can be readily formed
into an enclosure. In particular, there has been a need for an acoustical dampening system
having a baffle system in which noise in a wide range of frequencies can be effectively
attenuated and in particular is effective in attenuation of low frequency sound waves using
1/4 wave clipping functions.
In addition, the application of forced-draft horizontal and~ vertical coiling coil systems
varies in the market with such equipment serving a variety of applications, including but
not limited to the oil, gas, petrochemical, refrigeration, and air-conditioning industries. In
many of these applications, excessive noise levels may be produced in the vicinity of
cooling machinery which may be hazardous to workers or above legal limits.
In a typical cooling system, the majority of the noise at either the inlet or outlet of the
cooling system is projected either up or outwards. Furthermore, noise is typically
generated in a range of frequencies wherein the low frequency bands (16-31.5 Hz) being
the most difficult to attenuate.
Accordingly, there has been a need for a design of an acoustical chamber wherein the
majority of upwardly or outwardly projected noise is attenuated within a u-shaped trap. As
well, there has been a need for a design of acoustical chamber wherein the suppression of
specific low frequency noise is designed into the chamber by strategic designing the depth
or height of the chamber from the source noise to utilize 1/4 wave clipping functions so
that specific noise frequencies cannot be developed. For example, 31 Hz band sound will
have a wavelength of 10.7 meters with the 1/4 wave 2.6 meters in length. Accordingly,
there has been a need for a system of baffles to weave the low frequency sound wave into
a sound trap wherein the full length of sound wave cannot fully develop.
. .
Specifically, there has been a need for an acoustical dampening system having a system of
triangular baffles and adjacent planar acoustical panels having exposed acoustical
insulation providing an effective trapping system for a wide range of noise frequencies.
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A review of the prior art has revealed a number of references related to acoustical
dampening but none which specifically teach the structure of the present application, nor
the use of same to create an acoustical chamber in and around cooling coils.
For example, US Patent 5,317,113 teaches a wall and triangular baffle system. However,
this patent does not teach an acoustical dampening system in which the base surface of the
triangular baffle is reflective nor 1/4 wave clipping functionality. Still further, this patent
does not teach an acoustical chamber with managed air i~ow through it with noisesuppression.
US Patent 5,332,972 teaches a noise reduction unit for gas compressors which includes a
plurality of baffles for reducing noise around the inlet. This patent does not teach a noise
suppression system having a triangular baffle system.
Other patents such as US Patent 4,971,850, US Patent 2,659,808, US Patent 5,304,750,
US Patent 4,605,088, US Patent 3,068,535 and US Patent 4,298,090 each teach various
acoustical dampening systems but none are directed to the concept of managed sound
attenuation in conjunction with managed air flow.
SUMMARY OF THE INVENTION
In accordance with the invention, an acoustical dampening system is provided, the
acoustical dampening system comprising:
an acoustically dampening planar surface including a perforated and sound-reflective
outer surface exposing underlying acoustical insulation;
a plurality of triangular baffles in spaced relation from the planar surface, each
triangular baffle having first~ second and third sides, wherein the first side is generally
parallel to the planar surface and is sound reflective and the second and third surfaces
are perforated and expose underlying acoustical insulation.
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In further embodiments, the first, second and third sides of the triangular baffles have a
length, d, which defines a equilateral triangle, each triangular baffle is spaced from the
planar surface by a distance of approximately d/2 and/or are spaced from one another by a
distance of approximately d. In a further embodiment, the perforated surfaces of the planar
surface and second and third surfaces have a void fraction of 33-51%.
The apparatus may further comprise a u-shaped chamber adjacent the ends of the
triangular baffles, the u-shaped chamber having a perforated outer surface exposing
underlying acoustical insulation.
In a specific application, a noise suppression system is provided in a horizontal cooling
system having a fan rotating about a vertical axis for suppressing noise around the
horizontal cooling system, the noise suppression system comprising:
an inlet noise suppression system including
a first inlet noise suppression medium for suppressing noise in direct line-of
sight beneath the fan, the first inlet noise suppression medium including vertical
acoustical panels outside and below the fan;
a second inlet noise suppression medium for suppressing noise in direct line-of-sight above and outside the fan, the second inlet noise suppression medium
including an acoustically dampening planar surface including a perforated and
sound-reflective outer surface exposing underlying acoustical insulation and a
plurality of triangular baffles in spaced relation from the planar surface, eachtriangular baffle having first, second and third sides, wherein the first side is
generally parallel to the planar surface and is sound reflective and the second
and third surfaces are perforated and expose underlying acoustical insulation;
a third inlet noise suppression medium for suppressing noise outside the first
noise suppression medium and below the fan, the third inlet noise suppression
medium including a plurality of vertical and parallel acoustical panels including
a perforated and sound-reflective outer surface exposing underlying acoustical
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insulation below the fan and outside the first noise suppression medium.
In a further embodiment, an outlet noise suppression system is also provided including
a first outlet noise suppression medium for suppressing noise in direct line-of-sight above the fan, the first outlet noise suppression medium including an
acoustically dampening planar surface including a perforated and sound-
reflective outer surface exposing underlying acoustical insulation and a plurality
of triangular baffles in spaced relation from the planar surface, each triangular
baffle having first, second and third sides, wherein the first side is generallyparallel to the planar surface and is sound reflective and the second and third
surfaces are perforated and expose underlying acoustical insulation;
a second outlet noise suppression medium for suppressing noise including at
least one u-shaped chamber adjacent and outside the triangular baffles; and,
a third outlet noise suppression medium for a third inlet noise suppression
medium for suppressing noise below the second outlet noise suppression
medium, the third outlet noise suppression medium including a plurality of
vertical and parallel acoustical panels including a perforated and sound-
reflective outer surface exposing underlying acoustical insulation.
An inlet and o'utlet noise suppression system may also be provided for vertical cooling
systems.
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BRIEFDESCRIPTION OF THE DRA WINGS
These and other features of the invention will be more apparent from the following
description in which reference is made to the appended drawings wherein:
Figure 1 is a schematic perspective diagram of an acoustical dampening system inaccordance with the invention; ~
Figurc 2 is a schematic perspective diagram of a triangular baffle in accordance with the
mventlon;
Figure 3 is an end view of a horizontal cooling system and acoustical dampening system
in accordance with the invention;
Figure 4 is a partial cross-sectional view of an inlet noise suppression system for a
horizontal cooling system in accordance with the invention;
Figure 5 is a schematic side view of the inlet and outlet noise suppression systems of a
horizontal cooling system in accordance with the invention;
Figure 6 is a plan view of an inlet noise suppression systems of a vertical cooling system
in accordance with the invention;
Figure 7 is a side view of an outlet noise suppression systems of a vertical cooling system
in accordance with the invention;
Figure 8 is a side view of a typical vertical cooling system including an inlet noise
suppression system and an outlet noise suppression system in accordance with the
mventlon.
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DETAILED DESCRIPTION OF THE INVENTION
With reference to Figure 1, an acoustical dampening system is described. The system 10
generally includes a flat planar surface 12 and a plurality of acoustical baffles 14 adjacent
the planar surface 12. As a result of the design of the planar surface 12 and baffles 14,
their relative dimensions and materials of construction, the combination is particularly
effective in attenuating or choking noise when installed around noisy industrial machinery
having large fans. Furthermore, the construction the acoustical dampening system 10 has a
high level of structural strength thus enhancing the installation of the acoustical
dampening system 10 as a modular component of a noise dampening enclosure.
The planar surface 12 includes an outer surface 12a which partially exposes an underlying
layer of acoustical insulation 12b. Thus, the outer surface 12 is preferably fabricated with
a plurality of evenly spaced openings 12c, as shown partially in Figure 1. The evenly
spaced openings 12c are typically circular and define a void fraction. The void fraction of
the planar surface is preferably in the order of 33-51%. The outer or back surface is also
preferably fabricated from a rigid and sound-reflective material such as galvanized sheet
metal to also provide structural integrity to the planar surface 12.
Each triangular baffle 14 of the plurality of triangular baffles is also fabricated to have
sufficient structural strength to span typical construction distances. Each baffle 14 has a
cross-section of an equilateral triangle with the base surface 14a parallel in orientation to
the planar su*ace 12. The base surface 14a is non-porous. The two outwardly projecting
surfaces 14b and 14c are porous having a void fraction in the range of 33-51% and also
expose underlying acoustical insulation 14d as described for the planar surface 12.
In accordance with the invention, it is preferred that the length of each side of the
triangular baffle 14 of the acoustical dampening system has a length d, where d is any
reasonable length as would be understood for a typical installation. In a typical in~t~ tion,
in and around a cooling system, d would be in the range of 1 foot. Each adjacent baffle 14
is spaced from one another by a distance d and the base surface 14a is spaced from the
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planar surface 12 by a distance d/2.
The outer surfaces of the baffles 14 are preferably fabricated from galvanized sheet metal
for its reflective and structural properties as well as for cost considerations.
Suitable acoustical insulation 12b and 14d for the underlying layers of the planar surface
12 and triangular baffles 14 are well known to those skilled in the art and may be chosen,
for example, from materials such as FIBREX 1240 (density of 4 pounds per cubic foot)
and FIBREX 1280 (density of 8 pounds per cubic foot).
In use, noise which is directed into the noise suppression system 10 will either hit the
perforated faces 14b andl4c of the baffle 14, where a proportion of the sound energy will
be absorbed and a majority of the rem~ining noise will be reflected against the perforated
acoustical surface 12, or it will be driven between the baffles 14 and hit the acoustical
surface 12 directly (whereby, again, some of the noise energy will be absorbed). Of the
noise hitting the acoustical surface 12, some of the noise energy will be absorbed by the
surface 12 with the remainder reflecting. A proportion of the reflected noise will strike the
back of the baffle 14a and reflect back to surface 12 in a relentless ricochet pattern.
The acoustical dampening system 10 is particularly effective in dampening noise when
forming a component of an enclosure around a cooling system 20 as shown in Figures 3-5.
With reference to Figures 3-5, a horizontal cooling tower includes a horizontal fan 22
which is rotated about a vertical axis for forcing air past cooling tubes 24. The cooling
system is elevated above ground level 26 and is supported on a foundation 28. Appropriate
structural supports are provided to support and define both an inlet charnber 30 and an
outlet chamber 32. The inlet chamber 30 has an inlet noise suppression system and the
outlet chamber has an outlet noise suppression system. As shown in Figures 3-5, outside
air is drawn into the cooling system 20 through the inlet chamber 30, through the fan 22
and upwardly through the outlet charnber 32.
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Within the inlet chamber 30, a first inlet noise suppression system is provided to receive
and attenuate noise in direct line of sight below the fan 22. The first inlet noise suppression
system includes vertical acoustical panels 30a around and outwardly of the fan 22
(typically 4 walls). The vertical panels 30a are constructed as the planar surface 12
described above, generally including a perforated outer surface of galvanized sheet metal
exposing a underlying layer of acoustical insulation on the fan side and plain metal on the
outside. The wall height of the vertical panel 3 Oa is flush with the bottom of the fan 22
and defines an inlet u-shaped region 30b by the panels 30a and the floor 30c which is
preferably designed to support 1/4 wave clipping functionality. The acoustical walls of the
first inlet noise suppression system provide both absorptive and reflective properties for
low, medium and high range noise frequencies. If necessary the floor 30c of the u-shaped
region 30b may include additional acoustical panels.
A second inlet noise suppression medium is positioned above and outward of the fan 22
and is intended to attenuate noise outwardly and above the fan 22. The second inlet noise
suppression system generally includes the acoustical dampening system 10 as described
above with the triangular baffles 14 extending from the outer edge of the fan 14 to the
outer wall 20a of the cooling system 20 which provides an air flow path which supports
the natural air flow with limited restriction. Rem~ining noise and partially suppressed
noise seeking to escape the cooling system 20 is driven directly into the baffle system 10.
The second inlet noise suppression medium also serves as a floor/ceiling between the inlet
30 and outlet 32 regions of the cooling system 20 and, accordingly, also serves to prevent
recirculation of waste heat within the cooling system 20.
A third inlet noise suppression medium is provided below the second inlet noise
suppression medium and outside and below the first inlet noise suppression system. The
third inlet noise suppression system includes a plurality of vertically spaced acoustical
baffles. Each baffle 34 includes a planar panel having perforations defining a void volume
as described above on both sides the panel exposing underlying acoustical insulation. The
panels 34 are placed suff1ciently far apart to enable adequate air flow past the baffles 34
for the air flow demands of the fan. Furthermore, the baffles 34 are supported above the
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ground level 26 at a height sufficient to allow air to enter the system from below. Noise
escaping the second inlet noise suppression medium will be forced into a tight, reflective
energy consuming pattern between the parallel baffles 34 attenuating rem~ining noise
upon each reflection.
Accordingly, air enters the air inlet chamber 30 by flowing upwardly past the vertical
baffles 34 whereby it undergoes a 90 degree bend and flows past and parallel to the second
inlet noise suppression medium. Air then flows downwa~dly into chamber 30 and then
upwardly through the fan 22.
After passing through the fan 22, air flows upwardly past the cooling coils 24 and into the
outlet chamber 32. As with the inlet chamber 30, the outlet chamber 32 includes a number
of noise suppression media to reduce the noise escaping the enclosure.
A first outlet noise suppression system is provided primarily in direct line of sight above
the fan 22, that is along the ceiling of the cooling system 20. As is shown, a horizontal
cooling system directs the air flow upwardly and accordingly, the majority of the noise
generated will similarly be directed upwardly.
The first outlet noise suppression system includes the acoustical noise suppression system
10 as described above along the inclined ceiling surface of the cooling system 20. As such,
the triangular baffles 14 are parallel with respect to the roof line and may be inclined with
respect to the horizontal. Accordingly, the majority of noise which reflects off the roof
surface will tend towards either the upper or the lower region of the roof. Optional
kneewall vertical baffles 32a may be provided in certain buildings if the air outlet remains
in line-of-sight with outer areas of the fan 22.
The inclined baffles 14, in conjunction with a u-shaped area 40 (a second outlet noise
suppression medium) at the lower region of the roof, provides an acoustical choke for the
reflected sound propagating along the underside of the roof. The u-shaped region 40
supports 1/4 wave clipping functionality.
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A third outlet noise suppression medium is provided beneath the u-shaped region 40 and
includes a plurality of horizontal baffles as vertical baffles 34 described above. The
horizontal baffles 42 allow outflowing air to flow along their surfaces and exit the cooling
system 20. The third outlet noise suppression medium traps the noise that is reflected from
the ceiling and noise which escapes the u-shaped regions 40 by setting up a tight reflective
pattern between adjacent panels. A second u-shaped region 40a may be provided in the
lower region of the outlet chamber. The vertical spacing, thickness and length of the
horizontal baffles is determined by the final noise suppression demands and which also
permits adequate air flow for the demands of the fan 22. Floor baffle 44 may be provided
for further sound attenuation.
All joints at intersecting walls, floors and ceilings are acoustically sealed as is understood
by those skilled in the art.
The length of baffles, the space between baffles, the noise coefficient properties of the
acoustical insulation, the reflective properties of the perforated sheeting can all be selected
according to the desired noise suppression for a particular installation.
In a vertical cooling system, that is a cooling system having a fan rotating about a
horizontal axis, first, second and third inlet noise suppression and first, second and third
outlet noise suppression systems are provided to permit adequate air flow and noise
suppression in a manner similar to those described above for a horizontal cooling system
20.
Specifically, in a vertical cooling system and as shown in Figures 6 - 8, a vertical cooling
system 48 includes an inlet portion 48a as shown in Figure 6 and an outlet portion 48b as
shown in Figure 7. A fan 50 is mounted on a horizontal axis and directs air across coiling
coils 52. As shown, the inlet noise suppression system includes a first inlet noise
suppression medium consisting of a number of parallel spaced baffles 54 which are
generally parallel to the flow of air towards the fan, the baffles 54 for attenuating a portion
of the noise in a direct line of sight with the fan 50 and to direct the noise directly into the
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acoustical choke. A second inlet noise suppression medium includes the acoustical
dampening system 10 as described above with u-shaped chambers 56 which provide 1/4
wave clipping functionality. A third noise suppression medium includes a plurality of
parallel baffles 58 at the entrance to the cooling system 48 at 90 degrees to the first noise
suppression medium baffles 54 as is described above.
At the outlet 48b and as shown in Figure 7, an outlet noise suppression system is shown.
In this embodiment, a fan (not shown) is below the outlet noise suppressian system.
Directional baffles 60 direct airflow and noise directly upward into an acoustical choke 12,
14 as described above. Noise which escapes the acoustical choke is attenuated in the outlet
baffle system 60.
It is also understood that in the design of an acoustical chamber, knowledge of the
existence of a particular noise frequency will assist in the design of the chamber.
Accordingly, the depth or size of an acoustical choke, u-shaped chamber and baffle system
can be adjusted to deal with a specific frequency, and specifically to prevent low frequency
noise from weaving around baffles to escape suppression.
The terms and expressions which have been employed in this specification are used as
terms of description and not of limitations, and there is no intention in the use of such
terms and expressions to exclude any equivalents of the features shown and described or
portions thereof, but it is recognized that various modifications are possible within the
scope of the claims.
