Note: Descriptions are shown in the official language in which they were submitted.
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BACKGROUND OF THE INVENTION
.
This invention relates to control units for
air distribution systems and, more particularly, to
damper arrangements for use in terminal control units
for air distribution systems.
It is well known that air flow terminal units
for air distribution systems are subject to self-
generated noise which may reach excessive levels,
particularly when air is being delivered at relatively
high velocities and pressures. Generally, it is necessary
to provide some sort of noise attenuation such as by
lining the interior of the unit with a sound-absorbing
material. Conventional porous materials used for this
purpose are capable of absorbing sound waves having
lengths up to four times the thickness of the material.
However, excessive thicknesses of the material are
required tjo attenuate low frequency sound which has
relatively long waves. For example, some low frequency
sound waves can be as long as 48 inches and require a
12 inch layer of sound-absorbing material. The size of
the housing required to accommodate a material of this
thickness obviates this approach as a practical solution
for many installations.
Prior art constructions have employed perforated
plates, located upstream and/or do~nstream of the control
damper, to break the mainstream into a plurality of
smaller streams having a higher frequency sound which
can be more easily attenuated. I~hile alleviating the
. problem in some cases, such prior art constructions are
not without disadvantages. The perforated plates can
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create excessive pressure drops and/or the divided air
- streams can subsequently mer~e back together before they
have passed through the damper or the air outlet.
Exemplary prior art constructions of control
arrangements which employ perforated members to minimize
noise generation are disclosed in U.S. Patents 3,911,958
(Logsdon), 3,750,839 (McNabney) and 2,807,329 (Caldwell).
SUMMARY OF THE INVENTION
One of the principal objects of the invention
is to provide an improved control unit for an air dis-
tribution system which can provide variable volume dis-
tribution without requiring a large amount of sound
- absorbing material to attenuate noise.
Another principal object of the invention is
to provide a control unit for an air distribution system
having a damper assembly which is arranged ~o minimize
noise generation and yet does not cause excessive
pressure drops.
Further objects, aspects and advantages of the
invention will become apparent to those skilled in the
art upon reviewing the following detailed description,
the drawing and the appended claims.
The control unit provided by the invention
comprises a housing having an inlet, an outlet and a
flow passage extending between the outlet and the inlet
and a flow control assembly disposed in the housing for
controlling the volume of air flowing through the flow
passage. The flow control assembly includes a damper
mounted for pivotal movement about an axis extending trans-
versely of the flow passage between an open position
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and a closed positio~ to shut off flow through the flow
passage, the damper having opposed transversely extending
outer edges. The damper further includes first and
second transversely extending perforate members, each
having a plurality of relatively small orifices and being
disposed in generally surrounding relationship with and in
close proximity to the arcuate travel path of the opposed
outer edges of the damper. Each of the first and second
perforate members has transversely extending open edge and
is arranged so that, during an initial portion of the
damper travel from the closed position to the open position,
the damper cooperates with the perforate me~bers to cause
substantially all the air flowing from the housing inlet to
the housing outlet to pass through the orifices and so that,
during a subsequent portion of the damper travel toward the
fully open position, an open flow passage exists between the
damper and the open edges.
In one embodiment, the damper is disposed substant-
ially parallel to the direction of flow through the flow
passage when in the fully open position and the perforate
members terminate in a transversely extending open edge
including at least a portion which is spaced from a longi-
tudinal plane extending through the damper pivot axis
parallel to the direction of flow so
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that an open flow passage exists between the open edges
and the damper when lt is in the fully open positior
These open edges preferably extend at an angle to the
above longitudinal plane so that the flow area of the
open flow passage gradually increasesas the damper
approaches the fully open position, resulting in a
gradual decrease in the static pressure required to force
air through the flow control assembly.
BRIEF DESCRIPTION OF THE DRAWINGS
. _ . _ . .
Fig. l is an exploded, perspective view,
partially fragmentary, of a control unit embodying the
invention.
. . .
Fig. 2 is a fragmentary, longitudinal séctional
view of the control unit illustrated in Fig. 1.
Fig. 3 is an elevation view of the outlet end -
of the air flow control assembly illustrated in Fig. 2.
Fig. 4 is a reduced plan view of one of the
perforated members prior to being formed into an arcuate
shape.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The control unit of the invention will be
described in connection with an air distribution system
wherein cool air is delivered to the interior of a
building. However, it can be appreciated that it can
be used for other applications, such as in systems
delivering heated air.
Referring to Fig. l, the control unit 10
includes a main shell or housing 12 which carries an
air flow control assembly 14. The housing 12 has top
- 30 and bottom walls 16 and 18, side walls 20 and 22, and
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an open inlet end 24 in which the flow control assembly
14 is received and an open outlet end 26 which is
connected, in the usual manner, to an alr diffuser (not
shown) or the like through which air is delivered into
a room or other area being serviced. The interior of
the housing 12 is lined with a relatively thin layer of
a porous sound-absorbing material 28, such as neoprene-
backed, flexible glass fiber, for acoustical purposes.
As a guide, this material can be approximately 1/2 inch
thick and has a density of approximately 1.5 lb. per
cubic foot.
The flow control assembly 14 includes an end
plate 30 which, after installation of the flow control
assembly inside the housing 12, covers the inlet end 24
of the housing and carries a collar 32 for attachment
to a flexible duct 34 of the air distributi.~g system
(Fig. 2): The flow control assembly 14 also includes
top and bqttom walls 36 and 38, side walls 40 and 42
and an open outlet end 44. These walls define an open
plenum 45. Air entering the plenum 45 through the
collar 32 is discharged therefrom into the interior
of the housing 12 through the flow control assembly
outlet 44 and thereafter flows out through the housing
outlet 26. The portion of the inner surface of the
end plate 30 located inside the plenum 35 is covered
with a layer of sound-absorbing material 46 for
acoustical purposes.
The volume of air discharged into the housing 12
is controlled by a damper assembly 48 located near the
outlet 44 of the flow control assembly 14. More speci-
fically, the damper assembly 48 lncludes an imperforate
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damper blade 50 carried on a shaft 52 which extends
between and is suitably journaled in the side walls
40 and 42 for pivotal movement about the pivot axis
53 provided by the shaft 52. The opposite ends of
the damper blade 50 are spaced a small distance from
the respective side walls 40 and 42 so as to provide
free pivotal movement of the damper blade between a
closed position (shown by dashed lines in Fig. 2) to
shut off flow through the outlet 44 and a fully open
position (not shown) where the damper blade is sub-
stantially parallel to the direction of flow from
inlet collar 32 to the outlet 44 of the flow control
assembly 14.
When the damper blade 50 is in the closed
position, the peripheral edge portions thereof are
seated against a series of damper gaskets, including a
laterally extending top gasket 54 mounted on a flange 56
depending from the top 36, a laterally extending bottom
gasket 58 mounted on a flange 60 extending upwardly
from the bottom 38, and a pair of vertically extending
end gaskets 62 and 64 mounted on each of the side walls
40 and 42.
Partially surrounding the damper blade 50 is
a diffuser assembly including a pair of perforate
members 66 and 68, each having an arcuate cross section.
One of the perforated members 66 is located upstream of
the damper blade pivot axis 53 and the other perforated
member 68 is located downstream of the damper blade
pivot axis 53. In order to reduce the static pressure
losses when the damper blade 50 is in or close to the
fully open position, the perforate members 66 and 68
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preferably e~tend through an arc of less than 90 as
will be explalned in mo-.-e detai]. below.
Each of the perforated members 66 and 68
include a plurality of orifices 70. When the damper blade
50 is located at a position intermediate the closed and
fully open positions to meter the volume of air being
delivered through the outlet 26, such as in the solid
line position sho~n in Fig. 2, substantially all of the
main air stream flows through the orifices 70 in each of
the perforated members 66 and 68 and is divided into a
plurality of smaller streams. These small air streams
have higher frequency sound and, hence, shorter wave
lengths which can be attenuated by the sound-absorbing
material 28 lining the housing 12. The inner curvate
surfaces of the perforate members preferably are disposed
in parallel relationship to the longitudinal edges of the
damper blade 50 and are spaced therefrom at a sufficient
clearance to permit free pivotal movement of the damper
blade without allowing an excessive flow of air around
the edges of the damper blade with the resultant genera-
tion of long wave frequency sound.
The perforate members 66 and 68 are arranged
so that there is an open flow passage for the air when
the damper blade 50 is in the fully open position. More
specifically, the open or lower edge 72 of the upstream
perforate member 66 and the open or upper edge 74 of the
downstream perforate member 68 terminates short of the
; arcuate travel path of the outer edges of the damper
blade 50. That is, these edges are circumferentially
spaced rrom a longitudinal plane (designated by reference
numeral 76 in ~ig. 2) extending through the damper blade
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pivot axis 53 parallel to the direc~ion cf flow. Thus,
when ~he damper blade 50 is in the fully open position,
an open flow passage exists between the open edges of
the perforate members and the outer edges of the damper
blade through which air can flow from the plenum 45 to
th~ outlet 44 without passing through the orifices 70
of the perforate members. This open flow passage
minimizes the static pressure loss when the damper
blade 50 is fully open to provide maximum volume flow,
but does not cause the generation of low frequency
sound because of the low pressure drop which exists
when the damper blade is in a fully open position.
The open edges of the perforate members 66
- and 68 preferably are arranged so they are not parallel
to the damper blade 50 when it is in the fully open
position. More specifically, the lower edge 72 of the
upstream perforate member 66 extends upwardly from the
lowermost end (the left end as viewed in Fig. 3) at an
angle (e.g., 5 to 10) to the longitudinal plane 76
and the upper edge 74 of the downstream perforate member
68 extends downwardly from an uppermost end (the right
end as viewed in Fig. 3) at an angle to the longitudinal
plane 76. These edges preferably are generally parallel
to each other as shown. Thus, once the damper blade 50
has been moved to a position where an open flow passage
(designated by reference numerals 78 in Fig. 3) exists
between the damper blade 50 and the edges 72 and 74 of
the perforate member 68, the flow area of this passage
gradually increases as the damper blade subsequently
moves toward the fully open position. This results in
a gradual decrease in the static pressure required to
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force th~ a'r through t~e damper assembly 4~,.
In the specific construction illustrated, the
opening defined by the open edges of the perforate
members 66 and 6~ has a rhomboid shape with respect to
the direction of flow. It should be understood that the
open edges of the perforate members can be arranged to
provide an opening having a wide variety of shapes so
long as an open flow passage exists as the damper blade
approaches the fully open position.
As shown in Fig. 4, the orifices 70 in the
perforate plates preferably are arranged in a plurality
of rows 80 and 82 which are parallel to each other but
not parallel to the straight edge of the perforate
member, i.e., top edge 84 of the upstream perforate
member 66 and the lower edge 86 of the downstream per-
forate member 68. Also, the orifices 70 in adjacent
rows 80 and 82 preferably are staggered. As a guide,
the orifices 70 can be sized to provide about 22 % open
area in each of the perforate members, e.g., 3/32 inch
' 20 diameter holes on 3/16 inch staggered centers.
In addition to performing the sound attenuation
function described above, the perforate members reduce
the amount of torque required to maintain a centrally
pivoted damper blade in a partially closed position.
That is, the aerodynamic characteristics of a centrally
pivoted damper blade are such that air flowing therepast
normally causes the blade to assume a partially closed
position once it has been moved from a position parallel
to the direction of flow. In order to overcome this
torque, the means for adjusting the damper blade position
must be relatively large. By partially surrounding or
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encasing the damper blade, the perforate members alter the . :~
aerodynamic characteristics so that this torque is reduced
substantially and smaller blade positioning means can be
used.
~ile a centrally pivoted damper blade has
been illustrated and described, and is preferred because
of the ease of manufacture, off-center pivoted damper
blades can be used. In that case, the curvate inner
surfaces of the perforate members are arranged to be
substantially parallel to the travel path of the respec-
tive edge of the damper blade so as to avoid the creation
of large openings between the damper blade and the per-
forate members which can result in the generation of long
; wave frequency sound.
Although a preferred embodiment of the invention
has been illustrated and described in detail, it should
be understood that various alterations and modifications
can be made thereto without departing from the spirit of
the invention or the scope of the appended clsims.
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