Note: Descriptions are shown in the official language in which they were submitted.
` 204812~
.
AIR CANOPY VENTILATION SYSTEM
FIELD OF THE INVENTION
This invention relates to canopy venting systems,
and more particularly to canopy venting systems suitable for
use in controlling and containing noxious and undesirable
fumes produced by equipment, such as cooking surfaces and
laboratory equipment of diverse types.
DESCRIPTION OF THE RELATED ART
Systems for collecting fumes generated in laboratory
and cooking equipment are known in which an exhaust vent is
powered by a suction fan and located in a canopy above the
equipment and fumes are drawn upwardly by the exhaust vent for
discharge to the exterior of a building or after filtering are
returned to the immediate environment of the equipment. Such
systems may be combined with a venting means intended to
provide for a curtain of downflowing air from the front of
the canopy to decrease the air and fume flow into the room.
In application to cooking systems, such systems are designed
to be mounted on a wall above the stove cooking surface, with
considerable clearance therefrom, or to be integrally con-
structed with the stove, but nevertheless with the same
clearance.
~04312 1
For example, Canadian Patent No. 833,886 discloses
a ventilating hood structure for removing fumes from a seurce
located near the hood, including creating a low pressure zone
near the source of fumes and partially surrounding it -~ith a
supply of air under pressure, so as to entrain the fumes which
are thereafter removed from the zone by an exhaust fan which
creates the low pressure zone.
Canadian Patent No. 1,045,885 describes a kitchen
ventilator including a housing to be mounted above a kitchen
stove, and including means for producing a downwardly flowing
air curtain to restrain odors and fumes produced by cooking
on the stove.
U.S. Patent No. 4,050,368 (Eakes) discloses an in-
dustrial style exhaust system which uses an air curtain to
trap contaminated air and remove it. U.S. Patent No.
3,021,776 (Kennedy) discloses a laboratory fume hood using
different velocities of side moving air to trap fumes and
remove them. The use of this type of system has been banned
in some areas. U.S. Patent No. 3,131,687 (Kalla) describes
an air curtain type of ventilating system that uses directed
air to move contaminated air and is directed towards home
stove units. U.S. Patent Nos. 3,425,335 (Black) and 3,358,579
(Hauville) disclose laboratory fume hoods that exhaust
contaminated air to the outside. U.S. Patent No. 3,303,839
(Tavan) describes a portable vertical air curtain device that
3 20481 21
exhausts the contaminated air along with large volumes of room
alr .
In my U.S. Patent No. 5,042,456 granted August 27, l991,
an improved canopy venting system is disclosed as comprising
parallel side walls and a rear wall arranged to extend upwardly
from each side and the rear of a cooking surface, an upper canopy
surmounting the side and rear walls, vent means adjacent to and
extending substantially the whole length of a front edge of the
cooking surface, means connected to and adapted for driving a flow
of air through the vent means upwardly towards the upper canopy so
as to form in use an upwardly dlrected air curtain, exhaust means
disposed laterally inwardly from the plane of the air curtain for
continuously exhausting the upper portion of said air curtain
together with cooking fumes generated during operation of the
cooking surface upwardly through the upper canopy and means for
creating a supplementary air flow inwardly of the side walls to
improve the integrity of the vertical edges of the air curtain. In
one form of the system, the front of the upper canopy is disposed
rearwardly of the vent means and the vent means arranged to direct
the air curtain upwardly and rearwardly of the front of the upper
canopy.
SUM~IARY OF THE INVENTION
The present invention seeks to provide an air canopy
system, which possesses certain advantages and improvements over
that described in my U.S. Patent No. 5,042,456, particularly as
regards the uniformity and integrity of the air curtain and the
elimination of escape of fumes under even the most adverse
conditions, such as momentarily occurs when a cooking surface is
quickly covered with excessive fume generating products, such as
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4 20481 21
hamburgers.
The present invention additionally includes improved
exhaust means which provides for essentially uniform fume removal
lengthwise of the cooking surface and an improved exhaust fume flow
control arrangement, which maximizes the effectlveness of otherwise
conventional filter elements previously employed in the system.
More particularly, in one aspect, the invention herein
provides a canopy system for use in combination with equipment
producing fumes whose escape into the environment adjacent the
equipment is not desired, the equipment having front, rear and
sides and the system comprising rear and side walls adapted to
upstand from adjacent the rear and sides and an upper canopy
surmounting the rear and side walls and cooperating therewith to
define a volume for receiving fumes produced by the equipment.
There is means for producing an air curtain including an air
curtain directing means arranged to extend substantially between
the side walls in a forwardly spaced relationship from the front
for cooperation with the front to bound a make-up air receiving
inlet for permitting passage of air from the environment into the
volume and for cooperating with the side walls and the upper canopy
to bound an access opening for the volume. The air curtain
directing means directs an air curtain towards the upper canopy and
exhaust means having an exhaust inlet extends along an upper extent
of the rear wall for withdrawing fumes and air from the volume.
Still further the invention provides a canopy system for
use in combination with equipment producing fumes whose escape into
the environment is not desired, the system comprising in
combination means defining a volume disposed above the equipment
for receiving the fumes and an access opening adjacent one side of
}A
- 20~81 21
4A
the equipment for affording access to the volume from the
environment, the access opening having an upper edge, a lower edge
and opposite side edges. There is an inlet, filter means and an
outlet, the inlet and the access opening communicating with the
volume adjacent horizontally opposed sides of the equipment with
the lower edge being disposed vertically adjacent the equipment and
the inlet being disposed vertically remote from the equipment.
Suction means communicating with the outlet for drawing fumes and
air from the volume successively through the inlet, the filter
means and the outlet and discharging under pressure air filtered by
the filter means. A discharge discharges a portion of the filtered
air to the environment and means receives another portion of the
filtered air for creating an air curtain directed upwardly from
adjacent the lower edge and across the access opening between the
side edges towards the inlet. Means receives a further portion of
the filtered air for creating a filtered air flow directed from
adjacent the lower edge towards the inlet and intermediate the air
curtain and the equipment.
Further, the invention in another aspect pertains to a
system for use in combination with equipment producing fumes whose
escape into the environment is not desired and including air
filtering means having an inlet for receiving the fumes, air filter
means and an outlet and suction means connected to the outlet for
drawing the fumes through the inlet and through the filter means.
The improvement comprises the filter means including a cyclone
separating means having an axially directed air outlet having an
air flow axis and a generally rectangular filter means having a
filter inlet surface disposed normal to the air flow axis and
having a centrally disposed portion of the filter inlet surface
- 20481 21
4B
arranged in alignment with the air outlet. The filter inlet
surface is substantially larger than the cross-sectional area of
the air outlet and an equalization chamber of generally
parallelepiped configuration and communicates at opposite ends
thereof with the air outlet and substantially the whole of the
filter inlet surface. The opposite ends are spaced one from
another sufficiently to permit air passing into the equalization
chamber from the air outlet to diffuse outwardly and change its
flow direction to one- which is essentially normal to the filter
inlet surface to provide for relative uniform passage through the
filter inlet surface of air passing into the equalization chamber
from the air outlet.
A still further aspect of the invention provides a method
of preventing escape into the environment of fumes generated by
equipment, the method comprising providing an enclosure defining a
volume for receiving the fumes and an access opening for affording
access to the volume, the access opening having an upper edge, a
lower edge and opposite side edges, providing air filtering means
having an inlet communicating with the volume remotely of the
access opening and having air filter means and an outlet, providing
suction means connected to the outlet for drawing the fumes and air
from the volume through the inlet and through the filter means and
for discharging filtered air under pressure, conducting a portion
of the filtered air to the environment in an amount exceeding a
maximum volume of fumes expected to be generated by the equipment,
conducting a remaining portion of the filtered air in an amount
less than the portion to the lower edge for creating an air curtain
extending upwardly across the access opening between~the opposite
side edges for flow into the volume and to the opposite side edges
FA
2048l 21
4C
for creating flows of filtered air into the volume adjacent
opposite sides of the air curtain disposed adjacent the opposite
side edges, providing a makeup air inlet means extending along the
lower edge for creating a flow of air from the environment into the
volume between the air curtain and the equipment in response to
reduction in pressure within the volume incident to withdrawal of
the fumes and air from the volume in an amount exceeding an amount
of the remaining portion of the filtered air introduced into the
volume.
Further still, another aspect of the invention provides
a method of preventing escape into the environment of fumes
generated by equipment, the method comprising providing an
enclosure defining a volume for receiving the fumes and an access
opening for affording access to the volume, the access opening
having an upper edge, a lower edge and opposite side edges,
providing air filtering means having an inlet arranged to
communicate with an upper extent of the volume, air filter means
and an outlet, the inlet being disposed remotely of and extending
lengthwise of the upper edge, providing suction means connected to
the outlet for drawing the fumes and air from the volume through
the inlet and through the filter means and for discharging filtered
air under pressure, discharging a portion of the filtered air to
the environment in an amount exceeding the maximum amount of fumes
expected to be generated by the equipment, conducting another
portion of the filtered air for creating an air curtain extending
along the lower edge and directed upwardly across the access
opening between the opposite side edges for receipt within the
volume and for creating air flows into the volume from~adjacent the
opposite side edges and conducting a further portion of the
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4D 20481 21
filtered air for creating a flow of filtered air extending along
the lower edge and directed into the volume intermediate the air
curtain and the equipment.
Still another aspect of the invention provides a device
connectable to a source of air under pressure for producing an air
curtain, the device comprising an air flow duct having an elongated
flow passage extending lengthwise thereof, an air inlet opening
adjacent one end of the elongated flow passage for connection to
the source and an elongated slot opening outwardly through the duct
and extending lengthwise of the elongated flow passage. First
plate means bridges the slot within the duct and defines closely
spaced parallel flow paths directed towards and arranged in flow
communication with -the elongated slot. Second plate means is
disposed in a generally parallel and spaced relation to the first
plate means to define a space therebetween arranged in flow
communication with the flow paths and having apertures extending
therethrough for delivering air from the elongated flow passage to
the space and therefrom through the parallel flow paths for exit
through the elongated slot to create the air curtain.
BRIEF DESCRIPTION OF THE DRAWINGS
The nature and mode of operation of the present invention
will now be more fully described in the following detailed
description taken with the accompanying drawings wherein:
Fig. 1 is a front elevational view of an air canopy
system formed in accordance with the present invention with
portions broken away to show its air filtering systemi
Fig. 2 is a sectional view taken generally along the line
2-2 in Fig. 1;
Fig. 3 is an enlarged sectional view taken generally
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4E 2048 1 2 1
along the line 3-3 in Fig. 2;
Fig. 4 is an enlarged sectional view taken generally
along the line 4-4 in Fig. 3;
rA
204~121
Fig. 5 is a sectional view taken generally along the
line 5-5 in Fig. 3;
Fig. 6 is a sectional view taken generally along the
line 6-6 in Fig. 2;
Fig. 7 is a sectional view taken generally along the
line 7-7 in Fig. l; and
Figs. 8 and 9 are views similar to Fig. 2, but
showing alternative forms of the present invention.
DETAILED DESCRIPTION
An air canopy system formed in accordance with the
present invention is generally designated as 10 and shown in
Figs. 1-3 as being arranged in association with fume producing
equipment 12, such as for instance a conventional cooking
equipment having an upwardly facing cooking surface 14 and
front, rear and opposite sides 16, 18 and 20, respectively.
Surface 14 may, for example, be in the form of a stationary
and movable grill or a griddle to which food is directly
applied for cooking purposes, a heating element on which
containers, such as frying pans, are intended to be placed,
or deep fryers.
System 10 generally includes rear and opposite side
walls 22 and 24 arranged to upstand from adjacent rear and
opposite sides 18 and 20 with any spaces present therebetween
being essentially filled by suitable filler plates 26 and 28
preferably arranged generally coplanar with cooking surface
14; an upper canopy or housing 30 surmounting rear wall 22 and
~a~3l2 i
side walls 24 and cooperating therewith to define a volume 32
for receiving fumes produced by equipment 12; air curtain
producing vent means 34 arranged to extend substantially
between side walls 24 in a forwardly spaced relationship to
front 16 for cooperation therewith to define a makeup air
receiving inlet or slot opening 36 for permitting passage of
air from the environment surrounding the system into volume
32 and for cooperation with side walls 24 and upper canopy 36
to bound an access opening 38, which affords user access to
volume 32 and cooking surface 14; and exhaust means 40 having
a filter inlet 42 for withdrawing fumes and air from volume
32. Makeup air may be suitably supplied to inlet 36, such as
by leaving the front of equipment 12 exposed to the environ-
ment, as shown in Figs. 1 and 2.
In Fig. 2, side walls 24 are shown as having front
edges 24a, which incline upwardly and rearwardly towards upper
canopy 30. In a preferred form of the invention, side walls
24 serve to mount opposite front wall portions 44, which are
arranged to extend from adjacent front edges 24a in an
inwardly spaced relationship to the side walls and terminate
in rear edges 44a, which converge upwardly towards upper
canopy 30, as viewed in Fig. 1, and are upwardly and rear-
wardly inclined, as viewed in Fig. 2. Front wall portions 44
cooperate with the inwardly facing surfaces 24b of side walls
24 to define air flow passageways 46 whose front ends are
disposed in flow communication with vent slots 24c opening
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~_ 7
through facing surfaces 24b essentially parallel to front
edges 24a and whose rear ends open downwardly and rearwardly
in flow communication with volume 32. Flow of air into volume
32 through passageways 46 serves to stabilize the vertically
extending ends of the air curtain generated by vent means 34.
If desired, each of vent slots 24c may be replaced by a line
of spaced apart vent slots or holes, not shown, of desired
configuration.
Upper canopy 30 is best shown in Figs. 1, 2 and 6 as
being defined by upper ends or extensions of rear wall 22 and
side walls 24; a top wall 50; a front wall 54; a bottom wall
56, which is formed with an opening 58 communicating with
inlet 42; and channel portion 60, which depends from adjacent
the juncture of front wall 54 and bottom wall 56 and termi-
nates in a rearwardly facing free edge 62 disposed hori-
zontally intermediate vent means 34 and rear wall 22.
Preferably, the inner surface 60a of channel portion 60 is
preferably a smoothly curved generally cylindrical surface
arranged to define a vortex chamber 64 opening rearwardly
towards inlet 42. In the preferred form of the invention,
channel free edge 62, front wall portion rear edges 44a and
vent means 34 define the boundaries of access opening 38.
Further, the inner surface 60a and outer surface 60b of
channel portion 60 are preferably defined by separate panels
arranged in a spaced relationship to provide an air space or
~0~8121
_ 8
insulation receiving void 60c for purposes of reducing
transfer of heat from the inner surface to the outer surface.
Vent means 34 is best shown in Figs. 3-5 as includ-
ing an elongated, generally square cross-sectional channel 70,
which is arranged to extend between side walls 24 and has side
walls 70a-70d, opposite open ends 70e and a lengthwise
extending air curtain discharge slot 70f opening through side
wall 70a, which is in turn arranged in facing generally
parallel relationship to channel portion 60. Preferably,
channel 70, as viewed in section in Fig. 2, is tilted such
that a plane extending lengthwise of slot 70f and normal to
side wall 70a extends essentially parallel to and slightly
rearwardly of free edge 62 of channel portion 60. Arranged
within channel 70 is a first plate means in the form of a
honeycomb element 72 which defines uniformly arranged and
closely spaced parallel flow paths 72a arranged normal to side
wall 70a for supplying air uniformly to slot 70f; a second
plate means in the form of a relatively thin plate 74, which
is formed with flow openings 74a and disposed generally
parallel and in spaced relation to honeycomb element 72 to
form an air distributing space 76; and a pair of third plate
means 78 in the form of relatively thin plates, which co-
operate with plate 74 to define a pair of flow passages 80 of
progressively decreasing size or cross-section from channel
ends 70e towards a midportion of channel 70. In a presently
preferred construction, third plate means 78 is formed with
~48121
relatively uniformly arranged apertures 78a, which serve to
place flow passages 80 in flow communication with separate
volumes 84, which are disposed intermediate the third plate
means and side wall 70c and of progressively increasing volume
in directions away from channel ends 70e: and channel ends 70e
are bridged by fourth plate means 86 having a plurality of
apertures 86a, which define air inlet openings for flow
passages 80.
Alternatively, the pair of plates comprising the
third plate means 78 may be replaced by a single, apertured
plate extending along the whole of the length of channel 70
in which case air would be introduced into only one end of the
latter.
Further modifications of vent means 34 are possible,
such as for instance omission of one or the other of honeycomb
element 72 and second plate means 74, and the provision of a
solid or non-perforated third plate means 78. However, the
omission of the honeycomb element results in degradation of
the definition or uniformity of air curtain issuing through
slot 70f and, alternatively, the omission of the second plate
means results in the production of an air curtain which varies
lengthwise of the vent means. On the other hand, the use of
a non-perforated plate for the third plate means reduces the
uniformity of flow volume exiting the vent means lengthwise
thereof. Moreover, the illustrated construction is preferred
in that it provides for an easily fabricated and relatively
2~48121
-
low cost construction and the creation of a well defined air
curtain of desired air flow rate, which is relatively uniform
throughout the length of slot 70f.
The air curtain issuing through slot 70f diverges or
5increases slightly in width, as channel 70 is viewed in cross-
section, as it flows upwardly towards upper canopy 30 with
slot 70f being arranged to direct most of the air comprising
the air curtain to enter volume 32 rearwardly of free edge 62
of channel portion 60 except for that portion of the air
10forming the forward or outer boundary of the air curtain which
is directed towards the channel portion immediately forwardly
of its free edge. The vertical side edges of the air curtain
flow upwardly along the facing surfaces of front wall portions
44, with air issuing into volume 32 through the rear ends of
15flow passageways 46 adjacent rear edges 44a tending to prevent
degradation/separation of the vertical edges of the air
curtain, which might otherwise occur due to turbulence induced
frictional effects as the air curtain edges flow upwardly
along the front wall portions.
20As by way of example of the presently preferred
construction, an air curtain flow rate of 550fpm may be
provided having a variation in flow throughout the length of
an approximately 8 foot channel not exceeding about plus or
minus 10% by providing the channel with approximately 2 1/2
25inch by 2 1/2 inch cross-section having a 3/4 inch wide air
discharge slot; a one inch thick honeycomb element having flow
~04~121
11
paths of nominal 3/16 inch width; second and third plates
having 1/16 inch diameter apertures arranged on 1/8 inch
centers; a distribution space having a thickness of 1/8 inch;
and a fourth plate having 3/16 inch diameter apertures
arranged on 3/8 inch centers. This arrangement is adapted to
prevent the outflow of fumes through access opening 38, when
channel 70 is inclined such that the air passing through
discharge slot 70f creates an air curtain whose outwardly
facing boundary, i.e. the boundary facing the environment, is
directed towards channel surface 60b immediately adjacent free
edge 62.
Exhaust means 40 is shown in Figs. 1, 2, 6 and 7 as
including an inlet portion 90, which depends below upper
canopy bottom wall 56 and a main filter portion 92, which is
arranged within upper canopy 30 and placed in communication
with the inlet portion via bottom wall opening 58.
Inlet portion 90 includes a housing 94 serving to
define inlet 42, which is arranged to extend downwardly from
adjacent bottom wall 56 and horizontally essentially between
side walls 24 and to face downwardly and forwardly towards
canopy free edge 62. Housing 94 serves to removably mount a
plurality of primary or first filter panels 96, which are of
generally rectangular configuration and arranged in an
abutting end-to-end, coplanar relationship throughout the
length of inlet 42, and a plurality of fixed position,
generally rectangular, coplanar flow distributor panels 98a-
2~8121
12
98c, which are spaced from each other and side walls 24 to
define flow openings lOOa-lOOd connecting a first volume 102
bounded by the distributor panels and the filter panels and
a second volume 104 bounded by the distributor panels and the
rear of the housing. Filter panels 96 may be, if desired,
commercially available metal mesh or baffle type panels which
may be removed for cleaning on a periodic basis. Grease
ten~ing to collect on distributor panels 98a-98c and/or the
interior surfaces of housing 94 may collect adjacent the
bottom of the housing and, if desired, be drained therefrom
via suitable means, not shown.
Distributor panels 98a-98c are sized and arranged
relative to bottom wall opening 58, such as to cooperate with
volumes 102 and 104 to provide for a relatively uniform inflow
of fumes and air through inlet 42 throughout its length. As
by way of example of a presently preferred construction
adapted for use with an installation measuring approximately
8 feet between side walls 24, panels 98a-98c may have hori-
zontal dimensions of 12, 30 and 21 inches, respectively, and
flow openings may have horizontal dimensions of 5/8, 1, 2 1/4
and 29 1/8 inches, respectively, for the case where bottom
wall opening 58 has a horizontal dimension of 13 inches and
its center is spaced 21 1/2 inches from the right hand side
wall 24, as viewed in Fig. 6.
Main filter portion 92 includes in combination a
secondary filter 108; an equalization chamber 110; a tertiary
2a4sl2l
_ 13
filter stage 112 comprised of two or more glass-fiber mat
filters of generally rectangular plan view configuration and
of progressively decreasing mesh; a quaternary filter stage
114 comprised for instance of an activated charcoal type
filter or a chemical deodorizer of the pellet or liquid type;
and suction fan 116 operable to draw fumes and air in succes-
sion through inlet portion 90 and main filter portion 92 and
discharge filtered air under pressure. Secondary filter 108
has its inlet communicating with bottom wall opening 58 and
operates as a centrifuge causing incoming fumes and air to
rapidly change directions and separate therefrom the bulk of
grease remaining in the air stream prior to discharge thereof
through an axial discharge opening 120 opening centrally
through one end of equalization chamber 110. Grease separated
from the airstream, while passing through secondary filter
108, may be permitted to flow by gravity for collection in
housing 94 and/or collected in a removable drip pan, not
shown.
Equalization chamber 110 is required to have a
height and depth, as viewed in Figs. 6 and 7, respectively,
which correspond essentially to the plan view dimensions of
planar inlet surface 112a of the first filter element of
tertiary filter stage 112. Equalization chamber 110 is also
required to have a length, as measured lengthwise of main
filter portion 92 or axially of the air stream passing through
discharge opening 120, which is sufficient to permit the air
14 2048~ 21
stream to diffuse outwardly and change its flow direction to one
which is essentially normal to the surface of the filter inlet
surface 112a. Chamber llO is shown in Figs. 6 and 7 as being
generally parallelepiped in configuration and defined by surface
llOa, which extends outwardly of discharge opening 120 in facing
relation to filter inlet surface 112, upper and lower surfaces llOb
and llOc and side surfaces llOd and llOe. Below a given minimum
length, which is determined by the plan view dimensions of filter
inlet surface 112a, the size of discharge opening 120 and the rate
of flow of the air stream passing through the discharge opening, it
has been found that only the central portion of the filter inlet
surface effectively acts on the air stream for filtering purposes.
Above such given minimum length, the whole inlet surface of first
filter element becomes effective for filtering purposes, as can be
visually observed by the collection of grease particles on the
surface of the filter element over time, when placed at varying
distances from discharge opening 120. As by way of example, for an
equalization chamber having a fixed height and depth of 24 and 24
inches, respectively; a generally square discharge opening of
approximately 11 inches on edge and an air stream velocity through
the discharge opening of approximately 1250 ft./min., first filter
element 112a must be placed 6 inches or more from the discharge
opening to assume essentially uniform coating of the first filter
element with grease particles.
By again making reference to Figs. 2 and 6, it will
be noted that the discharge of fan 116 is connected to
a main distribution duct 124, which extends lengthwise of upper
canopy 30 and has its opposite ends flow connected to branch
ducts 126, which extend downwardly and forwardly through side
2Q1~21
walls 24 for flow communication with the inlet ends of
passages 80 via apertures 86a. The forward ends of branch
ducts also communicate with the lower ends of additional ducts
128, which are arranged to extend upwardly along and rear-
wardly of side wall front edges 24a and are lengthwise slotted
to define vent slots 24c.
In accordance with a preferred form of the inven-
tion, that portion of the discharge from suction fan 116 which
is not required to create and stabilize the air curtain, is
discharged directly to the immediate environment or to a
stack, via opening 130, and makeup air admitted to volume 32,
as required to maintain some predetermined overall flow
through the system. In this respect, it will be understood
that the quantity of makeup air drawn into volume 32 by
suction fan 116 operating at some given speed is automatically
regulated or controlled by the quantity of fumes generated
during various stages of a cooking or grilling operation; the
requirement for makeup air being decreased with an increase
in volume of fumes being generated. Makeup air is introduced
into volume 32 via slot 36 and beneath channel portion 60, due
principally to the natural tendency of the forward boundary
of the air curtain to draw or frictionally drag ambient air
for movement therewith upwardly towards the channel portion.
Inflow of ambient air rearwardly into volume 32 along outer
surface 60b may also occur under certain conditions existing
within the volume.
~4~121
16
In operation, suction fan 116 would normally be
energized when cooking surface 14 is initially heated prior
to being placed in use, so as to create a steady state
condition, wherein volumes of filtered air are continuously
supplied by suction fan 116 to main distribution duct 124 for
creating and stabilizing the air curtain and exhausted to the
environment via opening 130. In that the volume of air
supplied to main distribution duct 124 is less than the volume
of air drawn through filter inlet 42, a negative pressure
tends to develop within volume 32 with the result that makeup
air is drawn into volume 32 via makeup air receiving inlet 36
and beneath channel portion 60. While operating conditions
are expected to vary due to different installation require-
ments, it has been found that satisfactory operating condi-
tions may normally be achieved in cooking environments tested
to date by exhausting about two-thirds of the filtered air to
the atmosphere, directing about one-third of the filtered air
to distribution duct 124 and sizing inlet 36 and directing the
air curtain such that about one-half of the required makeup
air is introduced through the inlet and the other one-half
introduced below channel portion 60. Of the latter, about
two-thirds is drawn in by the normal operation of the air
curtain and about one-third is drawn in due to the reduced
pressure condition created within volume 32. Of the one-third
of the filtered air recirculated via duct 124, about ninety
percent is used to form the air curtain and about five percent
~8121
-
17
is supplied to each of vent slots 24c, in order to stabilize
the vertical side edges of the air curtain.
When a cooking operation commences, fumes are
generated or received within volume 32, which, together with
filtered air introduced into such volume via main distribution
duct 124 and the makeup air, are drawn through filter inlet
42 and pass successively through filter panels 96, secondary
filter 108, equalization chamber 110, tertiary filter stage
112 and quaternary filter stage 114 before entering suction
fan 116. It is intended that grease be removed from the air
stream by the time it has passed through tertiary filter stage
112 such that quaternary filter 114 can effectively perform
its deodorizing function to ensure that filtered air dis-
charged from suction fan 116 is both free of grease and
noxious fumes.
As previously indicated, the present system is self-
regulating from the standpoint that the volume of makeup air
drawn into volume 32 tends to decrease, as the volume of fumes
generated during the cooking operation increases, whereby
pressure within volume 32 tends to remain relatively constant
and the position and configuration of the air curtain flowing
upwardly across access opening 38 tends to remain relatively
stable. The flow parameters are chosen such that makeup air
will always be drawn through inlet 36 during contemplated fume
generation conditions, since it is critical to the present
invention that a flow of air be continuously maintained above
~a4~l2l
18
the fume generating surface for purposes of directing fumes
rearwardly and upwardly towards filter inlet 42.
At certain times during a cooking operation when
very large volumes of fumes are momentarily generated, as for
instance immediately after high fat content food products,
such as hamburgers, are placed on cooking surface 14, it is
critical to the trouble free operation of the system that flow
of fumes within volume 32 be controlled to prevent the upper
extent of the air curtain from being deflected forwardly, such
as would permit the escape of fumes to the environment from
beneath channel portion 60.
In accordance with the present invention, flow of
excessive fumes within volume 32 is controlled in such a
manner as to tend to counteract pressure forces otherwise
tending to produce outward deflection of the upper extent of
the air curtain. Specifically, when fumes are generated in
a volume which might overburden the system, the fumes quickly
rise towards canopy bottom wall 56 and upon impingement
thereagainst divide for flow rearwardly for immediate removal
through filter inlet 42 and forwardly towards channel portion
60 whose curved inner surface 60e imparts a downwardly and
rearwardly directed movement to the fumes, i.e. counter-
clockwise directed rotation, as viewed in Fig. 2. In effect,
a flow vortex is created and the flow of fumes rearwardly over
free edge 62 tends to lower the effective pressure adjacent
the rear portion of outer surface of channel portion 60,
2 ~
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19
thereby counteracting the buildup of pressure within volume
32 otherwise tending to outwardly displace the upper portion
of the air curtain. Thus, the shape and placement of channel
portion surface 60a allows trouble-free operation of the
system, even under extreme momentary fume qeneration condi-
tions.
The present system may be designed for given fume
generating equipment whose maximum fume generating volume or
capacity is known and in this case, suction fan 116 may have
a predetermined constant speed and discharge opening 130 may
have a predetermined size. Alternatively, it is anticipated
that suction fan speed and/or discharge opening size may be
made adjustable to accommodate a given system for efficient
operation with different equipment and/or to accommodate its
use with a single piece of equipment having a very wide range
of fume generation operating conditions.
The canopy system thus far described is suitable for
use with many fume generating installations. However, it has
been found that small amounts of fumes may escape to the
environment from beneath channel portion 60 during operating
conditions under which channel portion outer surface 60b
becomes hot, due either to overall high operating temperature
of cooking equipment and/or placement of a high heat generat-
ing source adjacent the forward portion of surface 14 imme-
diately below the channel portion. Tests have determined that
escape of fumes is caused by a convection flow pattern
~R 3121
generated immediately adjacent surface 60b when same is heated
to a sufficiently high temperature, and this pattern tends to
draw fumes outwardly of volume 32 for flow outwardly and
upwardly along channel portion outer surface 60b.
The foregoing condition may be alleviated by
artificially cooling surface 60b, but alternatively, the
external surface of channel portion 60 may be reconfigured in
the manner shown in Fig. 8. Specifically, in this alternative
construction, channel portion outer surface 60b' is defined
by a generally planar first panel portion 60d arranged to
extend downwardly and forwardly from adjacent rear edge 62;
a generally planar second panel portion 60e arranged to extend
upwardly and forwardly from adjacent the first panel portion;
a smoothly curved third panel portion 60f arranged to extend
upwardly from adjacent the second panel portion; and a
generally planar fourth panel portion 60g arranged to extend
upwardly and rearwardly from adjacent the third panel portion
towards front wall 54. With first panel portion 60d arranged
in the manner shown in Fig. 8, it is adapted to reflect heat
2 0 downwardly and rearwardly into volume 3 2, and if it becomes
sufficiently hot that a convective flow pattern is initiated,
such convective flow pattern will tend to draw makeup air into
the volume, as opposed to drawing fumes into the environment.
Moreover, first panel portion 60d is adapted to deflect or
direct the air stream impinging thereon rearwardly into volume
32 whenever it is temporarily displaced forwardly as a result
~gl21
21
of momentary high pressure condition within the volume
generated by the creation of excessive fumes. of less
operational significance, is the provision of the corner
defined by panel portions 60d and 60e, which tends to create
a weak counterclockwise rotating vortex adjacent the outer
edge of panel portion 60d, as viewed in Fig. 8, which tends
to retard escape of any "puff" of fumes, which might otherwise
tend to escape past the boundary established by the air
curtain at the initiation of an excessive fume generation
condition.
Also in Fig. ~, equipment 12 is shown as being a gas
fired cooking unit from which combustion gases are vented
directly upwardly into the rear of volume 32 via a discharge
140. For equipment wherein the volume of combustion gases may
be varied incident to normal equipment operation, it may be
desired to direct the exhaust gases directly to housing 94 via
a conduit 140a in order to limit their affect on the typical
flow pattern depicted in Fig. 8, wherein arrows 150 designate
the flow of fumes generated adjacent cooking surface 14,
arrows 152 designate makeup air entering through inlet 36 and
serving to force the fumes to flow rearwardly within volume
32, arrows 154 designate the air screen, arrows 156 designate
makeup air tending to be drawn into volume 32 by the air
screen and arrow 158 designates makeup air tending to be drawn
in beneath channel portion 60 as a result of low pressure
conditions existing within volume 32 and due to any convective
22 20481 21
flow pattern resulting from the heating of first panel portion
60d. For installations where code requirements necessitate
exhausting combustion gases to the atmosphere via a stack, not
shown, discharge 140 may be fitted with a conduit 140b exiting
volume 32 for connection to such stack. For this latter
situation, operation of the present canopy system is no
different for the case of gas fired cooking equipment than for
electric powered cooking equipment generally depicted in Fig.
2.
Fig. 9 illustrates an alternative canopy system
particularly adapted for use in those situations where it is
necessary to minimize the amount of makeup air introduced into
volume 32, due to the cost of heating or cooling air present
in the environment in which the equipment 12 is located. This
construction departs from that illustrated in Figs. 2 and 8
in the absence of inlet 36 or blocking thereof in order to
prevent or at least substantially reduce the inflow of makeup
air to volume 32 between cooking surface 14 and vent means
34', and in modification of the vent means to create both the
previously described air curtain and a secondary air curtain
or flow pattern designated by arrows 152', which serves, in
place of makeup air previously introduced through inlet 36,
to direct fumes 150 rearwardly within volume 32. With this
construction, volume 32 would receive about two-thirds
filtered air and about one-third makeup air under steady state
conditions, and flows would be selected to ensure the intro-
2~4812~
_ 23
duction of makeup air under all operating conditions expected
to be encountered during use. Vent means 34' is generally
depicted in Fig. 9 as including a channel 70' having angularly
related side walls 70a and 70a', which are formed with air
discharge slots 70f and 70f' for producing the air curtain and
secondary air curtain, respectively. The interior of channel
70' may be similar in construction to that described with
reference to channel 70 with changes in aperture sizing of the
honeycomb elements associated with slots 70f and 70f' being
lo made, if desired to vary the flow characteristics of the air
curtains. Alternatively, wholly independent flow passages may
be provided to supply air to slots 70f and 70f'.
