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Description  |
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BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to kitchen ventilation systems, and more
particularly to an exhaust hood and associated ductwork for handling
cooking fumes generated during cooking with different types of cooking
appliances situated under the hood.
2. Description of the Prior Art
Various states in the United States have very specific guidelines for the
food service ventilation industry. Perhaps the most stringent guidelines
have been established by the State of Michigan. Among other aspects of the
guidelines are four categories of ventilation rates for different types of
cooking appliances as follows:
1. Low heat, low grease;
2. Grease producing;
3. Heat and grease producing;
4. High heat and grease producing.
In various food service establishments, it is the norm that appliances from
one, more than one, or even all categories will be found in a line under
the same exhaust hood. Therefore, different ventilation rates are needed
at different locations along the length of the hood in accordance with the
type of appliances in the line-up under the hood.
The State of Michigan as well as National Building Codes including BOCA
(Building Officials and Code Administration) ICBO (International
Conference of Building Officials) and Fire Prevention Codes NFPA (National
Fire Prevention Association), author codes regulating the manufacture of
commercial grease hoods, and all codes mentioned require that baffle type
grease filters, tested in accordance with Underwriters Laboratories
standards, be used. These filters remove from the ventilated air stream,
grease vaporized and emitted during the cooking process, and provide a
fire barrier between the portion of the hood exposed over the cooking
appliance, and the concealed portion of the hood located behind the grease
filters. Overlapping baffles, within each filter, create a barrier to
prevent the flames generated during a cooking appliance grease fire, from
passing directly through unobstructed openings into the ventilation duct
which runs through concealed building spaces above ceilings and into other
rooms. The overlapping baffles require the air passing through the filter
to change directions to maneuver around the baffles. These changes in
directions or turning of the air stream creates centrifugal forces at each
turn. This centrifugal force causes the heavier grease vapor and grease
droplets to be thrown against the opposing baffle. The grease is collected
on, or attaches, to the baffle face and drains down the baffle to a drip
trough, located beneath the filter. The trough is pitched for drainage of
the collected grease to a removable grease catch pan.
State of Michigan ventilation requirements require each filter manufacturer
to publish a chart indicating optimum performance. These charts indicate,
in accordance with manufacturer's testing, the optimum velocity range for
peak filter efficiency. Codes as well as good ventilation practice require
the filter be sized to the cubic feet per minute (cfm) being ventilated.
In addition, the guidelines and good practice require the filters to run
the full length of the ventilator exhaust chamber. When filters do not fit
the exact length of the exhaust chamber, the Michigan guideline limits the
space utilizing blank panels or filler panels, to complete the shortage in
filter length, to 16% of total filter area. Virtually all baffle filters
require the exhaust air to make a minimum of two turns around the baffles
as it passes through the filter from the intake or inlet face of the
filter to the exhaust or outlet face. The State of Michigan also requires
filter manufacturers to publish the velocities to be maintained that will
produce maximum grease extraction efficiency. This published report must
also include the net free area of each filter. The net free area is used
to determine which filter size will provide the required velocity at a
given ventilation air volume. Industry testing of various filters have
demonstrated these velocities, producing maximum grease extraction
efficiency, to be between 275 feet per minute (f.p.m.) minimum and 400
f.p.m. maximum.
An additional Michigan requirement is the pressure drop across the filters
be equal to or greater than 0.30" w.c. (water column) when using a single
duct collar in a hood length exceeding 10'-0". Lower pressure drops can be
accommodated by adding additional duct take offs. These additional take
offs add installation and maintenance expenses. As the ducts are above the
hood and therefore normally concealed above the ceiling there is often
insufficient space to accommodate the additional duct. The connecting duct
transport velocity is restricted by code to a minimum of 1,500 f.p.m. and
a normal maximum of 4,000 f.p.m. As a result of the combination of
requirements of the codes, it is very difficult to achieve ventilation in
a given hood where the cooking appliances under the hood are in different
categories. It is even more difficult to obtain optimum ventilation
performance and/or economy. In addition, if the requirements of the food
service establishment indicate a need for a different arrangement of
different categories of cooking units under the hood, it can be very
difficult to achieve the code-specified filter performance, much less
optimize the arrangement. Also, if different filters are used, they are
not likely to fit into the same grease filter frame, thus requiring
different hood designs. Therefore, if appliances are changed or relocated
under the hood, and more or less air is required, a new hood will be
required. Changes going from low heat and low grease, to heat and grease,
can be impossible because the smaller filters for the low heat and low
grease application creates such increased pressure drop that the fan
cannot provide the required volume of air flow for the larger filters.
As mentioned above, one of the Michigan requirements pertains to a minimum
pressure drop requirement when using a single duct collar in a hood length
exceeding ten feet. Lower pressure drops can be accommodated by adding
additional duct take-offs, but these additional take-offs add installation
and maintenance expense. Nevertheless, it is sometimes necessary. In
addition to state codes, installations must meet the requirements of local
government codes. There is a trend for governmental municipalities to
accept only hoods bearing the label of one of the nationally recognized
testing laboratories. Listed hoods bearing such labels have specifications
for placement of an exhaust duct opening collar within a limited range of
locations relative to the transverse center line of the hood. But problems
may arise at the hood installation site, because building codes prohibit
any installation such that roof joists, plumbing lines, electrical lines
or other devices would penetrate the exhaust duct running from the hood to
the roof-mounted fan. However, such building components typically run in
the space between ceiling above the hood, and the roof. Therefore it is
frequently a problem to coordinate the factory installed location of the
exhaust collar with the field location of obstructions. Consequently, it
is common to see in the field, a labeled hood which has been installed
with the factory located collar cutout welded closed and the duct welded
to the hood in a different location that was necessitated by structural
members or mechanical services already in the building and which could not
be moved. Such field welding of a collar is not in compliance with the
testing laboratory listing, and can put the burden of acceptance or
rejection on a local government code official who does not want that
burden or is not trained to make the necessary judgment.
In addition to the above-mentioned hood-to-duct connection problem
resulting from building mechanicals being in the ceiling space, the
routing of the duct to the roof-mounted exhaust fan can also be a
challenge. It sometimes involves turns in direction or long duct runs.
Codes require that a clean-out or access door be provided at each turn in
direction and at intervals no greater than twenty feet apart in long duct
runs. Typically the access doors include frames welded to the perimeter of
an opening cut into the wall of the duct. Then a door is screwed or
otherwise fastened to the frame. The welding is difficult to accomplish,
since the space available in which to work is very limited. Yet it is
desirable to install the clean-outs after the ducts are in place in the
building, to be certain that there is no conflict with other mechanicals
that would restrict access to them for clean-out. Since it is necessary to
route ductwork in the field, joints are inevitable. Building codes require
not only that the duct sections themselves be constructed with
liquid-tight continuous external welds at all seams and joints, but also
that all joints made in the field during installation must be made using
the same liquid-tight continuous external welds. As indicated above, these
code requirements make kitchen ventilation system installations difficult
and expensive.
Some efforts to address at least the problem of different requirements for
different types of cooking units have been made and the results disclosed
in some United States patents. For example, the U.S. Pat. No. 4,281,635
issued Aug. 4, 1981 to Gaylord, addresses the problem of different amounts
of air pollution by different cooking units, but does so in a water-wash
hood. Such hoods typically cost two to three times as much as canopy hoods
with dry filters. The Gaylord patent teaches the use of choke attachments
such as 60, 61 and 63, cut to a length corresponding to the combined width
of the low polluting cooking units with which a portion of the hood length
is associated. They are installed by spot welds, screws or "other suitable
means". They are used to throttle, choke or otherwise restrict the inlet
flow to that portion of the ventilator in which they are used. They can be
removed by removing the screws and burning off the spot welds, for
example.
Dry filters of the baffle type can be made along the lines shown generally
in U.S. Pat. No. 3,870,494 issued Mar. 11, 1975 to Doane. An approach to
providing different capacities in different portions of a hood using
baffle filters is to use a filter unit which is adjustable in itself. An
example is shown in U.S. Pat. No. 3,566,585 issued Mar. 2, 1971 to
Voloshen et al. Such filters have an adjustment screw 50 operable to
change the spacing between baffle members. But such filters are expensive,
and the adjustment feature is either not used or not effectively usable. A
McCauley U.S. Pat. No. 4,346,692 issued Aug. 31, 1982 uses adjustable
louvers or damper blades in the hood itself or in a make-up air module,
but not tailored to accommodate individual requirements of a variety of
types of cooking equipment under the hood. Similarly, the Neitzel et al.
U.S. Pat. No. 4,373,509 issued Feb. 15, 1983, provides adjustable dampers
in the hood to change relative amounts of fresh air and tempered air used
as make-up air in a kitchen ventilating system as various combinations of
cooking equipment are used.
The present invention is addressed to facilitating original installation of
a kitchen ventilation system, and minimizing the necessity of any changes
of hood or duct to accommodate changes in cooking equipment types and
combinations of types served by the exhaust hood in the system.
SUMMARY OF THE INVENTION
According to a typical embodiment of the present invention, a hood located
over a row of cooking units of different types, has removable baffle type
grease filters of uniform height but of different widths and thicknesses
and with slots of different heights to handle the particular pollution
generating capabilities of the particular cooking units over which the
filters are situated. A removable grease drain channel having a length to
fit just inside the length of the hood and readily removable from the
hood, if desired, has locator members in it which are at spaced points
along the drain channel. The removable grease filters have a set of
partially punched knock-outs along the lower marginal portions of the
intake faces. When it is determined what particular filter is needed in a
particular location along the length of the hood, one of the knock-outs in
the filter corresponding to the locator member location in the drain
channel, is punched out so that, after the filters have been removed for
cleaning and upon reinstallation, only the correct filters can be placed
at any location along the hood. Means are provided at the outlet faces of
the filters to accommodate the different thicknesses of different filters
and keep the upper margins of the filters snug against the upper margins
of the hood inlet opening.
The hood outlet is provided with a field-installed collar assembly which
includes a flanged one-piece inner collar received up through a field-cut
opening in the top of the exhaust hood. Two half frames are driven in from
the top, bringing the one-piece collar into position, sealing a flange
thereon to a gasket to the top of the hood. Access door assemblies are
also field-installed using a one-piece door frame similar to the one-piece
inner collar frame, a two-piece hammer-in outer collar and a one piece
door bolted to the secured combination of the outer collar and inner door
frame. Exhaust duct sections have rolled edges which are formed to
hem-like configuration and are snapped together for end-to-end connection
of duct sections, and they have additional folds for interlocking to
prevent separation due to expansion or contraction of the duct sections in
response to hood and duct temperature changes.
Adjustable fire dampers are located inside the exhaust and make-up air
(mua) plenums. Each is movable through a range of motion which provides
different amounts of opening of the air flow path to and from the
respective plenum. Each is positionable at one of a group of selectable
positions in the range and which can be determined by a locating pin at
the location. The pins are heat fusable to permit automatic closure by the
damper in case of fire.
Adjustably positioned fire dampers are also located at the intake slot of
the make-up air diffusers along the length of the make-up air plenum. When
the required cfm of make-up air is lower than the design maximum, the
damper is closed to one of a plurality of possible preselectable pin
locations located on the damper guide. Closing this damper restricts the
opening, increasing the pressure drop through the opening and reducing the
volume of air being supplied from the make-up air plenum. When the
adjustable dampers at the intake slots of the diffusers distribute the
correct amount of air into each diffuser so that the air supplied through
the diffuser corresponds to the amount of air being exhausted through the
baffle filter directly opposite. In addition, the location of the fire
damper in the intake slot provides a fire break inside the plenum,
preventing the diffuser in the front of the make-up air plenum from
discharging out the face of the ventilator. Therefore, flames of a cooking
fire contained within the exhaust portion of the ventilator are prevented
from migrating back into the make-up air plenum and out the front of the
ventilator.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic front elevational view of the exhaust side of a
kitchen ventilation system according to a typical embodiment of the
present invention.
FIG. 2 is a schematic side elevational view thereof.
FIG. 3 is an enlarged vertical section through the exhaust portion of the
hood and duct assembly.
FIG. 3A is an enlarged fragmentary view showing filter locator slot and pin
combination.
FIG. 4 is an enlarged fragmentary sectional view of a snap joint in the
duct.
FIG. 5 is a further enlarged transverse section through a baffle-type
filter.
FIG. 6 is an intake face view of one of the four sizes of filters.
FIG. 7 is an intake face view of a second of the four sizes.
FIG. 8 is an intake face view of a third of the four sizes.
FIG. 9 is an intake face view of the fourth of the four sizes.
FIG. 10 is an enlarged fragmentary section through the top of the hood at
the exhaust collar to duct transition.
FIG. 11 is an exploded pictorial view of the exhaust collar parts before
assembly.
FIG. 12 is an enlarged fragmentary sectional view through the access door
portion of the exhaust duct assembly.
FIG. 13 is an exploded pictorial view of the access door components prior
to assembly into the exhaust duct.
FIG. 14 is a chart showing filter and locator pin arrangements for the hood
of FIG. 1.
FIG. 15 is a chart showing filter and pin arrangements for another line-up
of cooking equipment as could be on the opposite side of the line-up in
FIG. 1 in a canopy hood arrangement, if desired.
FIG. 16 is a cross sectional view through a ventilator similar to FIG. 2
but on a larger scale and also including a make-up air diffuser and fire
dampers in both the exhaust and make-up air sides of the hood.
FIG. 17 is a perspective view of a fire damper as used in the top of the
ventilator hood of FIG. 16.
FIG. 18 is a longitudinal sectional view through the fire damper.
FIG. 19 is a section through an adjustable fire damper at the make-up air
plenum.
FIG. 20 is a view from the bottom of the make-up air fire damper, with a
portion broken away to show the interior details.
DESCRIPTION OF THE PREFERRED EMBODIMENT
For the purposes of promoting an understanding of the principles of the
invention, reference will now be made to the embodiment illustrated in the
drawings and specific language will be used to describe the same. It will
nevertheless be understood that no limitation of the scope of the
invention is thereby intended, such alterations and further modifications
in the illustrated device, and such further applications of the principles
of the invention as illustrated therein being contemplated as would
normally occur to one skilled in the art to which the invention relates.
Referring now to the drawings in detail, and particularly FIGS. 1 and 2, a
portion of a building kitchen is shown with a floor 11, wall 12, ceiling
13 and roof 14. Four cooking units 16, 17, 18 and 19 are lined up in a row
under a wall-hung hood assembly 21. In this particular example, the
cooking units 16 and 19 can be surface ranges and/or ovens with griddles,
which are of the low heat, low grease category according to the
above-mentioned Michigan standards. Units 17 and 18 are deep fryers which
are in the heat and grease producing category.
Hood 21 is twelve feet long between its ends 22 and 23 and has an open
front essentially the same length except for the face flanges 24 and 26 at
each end. In this illustrated example, the hood has six filters spaced
along its length. They are filters 27, 28, 29, 31, 32 and 33. They occupy
the entire front opening according to a pattern which will be described.
Collected grease can flow down a drain 34 from the bottom of the hood to a
suitable receiver (not shown).
An exhaust duct assembly 36 is constructed between the top 37 of the hood
and a roof mounted blower assembly 38 mounted on a roof curb 39. The duct
assembly includes a field-installed collar assembly 41, double off-set 42,
joint 43, double elbow section 44, joints 46 and 47, and curb adaptor 48.
An access door assembly is provided in the end of the double elbow at 49.
Referring now to FIG. 5, the basic construction of a baffle filter of the
type used with the present invention is shown. This example is filter 29
and has four inlet slots 51 in the inlet face 52 thereof. These are
defined by inwardly turned baffles 53 and 54, for example. The slots 51
are represented schematically in FIG. 1 by the four vertical lines in
filter 29. Similarly, there are four vertical slots 56 in the outlet face
57 of the filter, each being formed by baffles such as 58 and 59,
respectively. The thickness of the filter will be referred to hereinafter
as the distance between the inlet upstream face 52 and the outlet
downstream face 57.
FIGS. 6, 7, 8 and 9 show four filters of the same basic construction as
shown in FIG. 5, FIG. 7 being filter 29 of FIG. 5. The distance between
the top 61 and bottom 62 of filter 29 is the same for all four of the
filters. But otherwise, these filters are different in various respects.
For convenience hereinafter, the filters of FIGS. 6, 7, 8 and 9 will be
referred to by model number, broadly stated as models one, two, three and
four, respectively. There are some differences in the slot lengths
(heights), most noticeable by comparing model one with model three. There
are also some differences in the number of slots. For example, model one
has nine slots 21 inches long, while model three has nine slots only 10
inches long. Also, the thickness of model one is 1.675 inches, while that
of model three is 1.495 inches. Thus, a more detailed model designation
can be used, designating the slot length, filter width, and filter
thickness. For example, model one can be designated 21/24/1.675,
signifying 21 (slot length)/24 (filter width)/1.675 (filter thickness).
Model two shown in FIG. 7 has slots which are 21 inches long in a filter
12 inches wide, and 1.927 inches thick. Therefore, a detailed model
designation for this model two filter would be 21/12/1.927. Model three
shown in FIG. 8 is 24 inches wide, has 9 slots that are 10 inches long,
and is 1.495 inches thick. Thus it is designated 10/24/1.495. Model four
is a filter 27 inches wide with nine slots 10 inches long, and is 1.495
inches thick. Therefore its detailed designation is 10/27/1.495.
The four models of filter can be combined in various ways to meet very
stringent ventilation requirements as specified by the State of Michigan,
for example, without disturbing the hood structure itself, because of
several features of the present invention. First of all, and referring to
FIG. 3, the back wall 63 of the hood has a lower margin defined by a bend
forward at 64 to define the bottom 66 of a gutter whose front wall 67
defines the front of the gutter. A grease drain trough 68 includes a rear
wall 69, closed ends 70, bottom 71, sloped down from the ends toward a
hole in the center above the grease drain 34, vertical front wall 72,
inclined wall 73, and down-turned flange 74 at the top front of the wall
73. This drain trough extends the full length of the hood from just inside
the left end wall 22 to just inside the right end wall 23 of FIG. 1. It is
supported by the down-turned flange 74 hooked over the top edge of the
front wall 67 of the hood gutter. The grease trough wall 73 has a
plurality of longitudinally spaced restrictor pins 75 welded to it and
projecting upward and to the rear therefrom. The shaft of each pin is
received in a slot 76 in the lower front face 52 of the filter. The head
75H of the pin is received through a slot-intercepting hole in the bottom
of the filter and can keep the filter front face from being sucked back
away from grease trough wall 73. The upper front face of the filter rests
against the in-turned lower marginal flange 77 at the upper front margin
78 of the hood opening. Thus, each of the filters is supported by its
intake face 52 resting against flange 77 at the top front of the margin of
the hood opening and against the wall 73 of the grease drain trough and by
the restrictor pin in the slot 76. An inclined lower rear wall 79 can be
provided on the filters to prevent premature engagement of the lower rear
edge of the filter with the front face of the trough wall 69 during
installation of the filter and which could interfere with the filter
location control feature of the restrictor pins.
The above description mentioned three different thicknesses of filters. One
feature of the present invention enables the use of all three thicknesses,
as well as others, if desired, in the same hood without modification. This
is achieved in part by the control provided by the restrictor pin heads,
and that accommodation of the inclined lower rear margin 79 of the thicker
filters, but also achieved in part by a method of holding the upper
portion of the filter snug against the flange 7. This is done by a rod 81
supported at spaced points by hanger posts 82. The rod has a top rib 83
extending along its length. A spacer ring or sleeve 84 is split at the top
so it can be pushed up over the rod 81 in the direction of arrow 86, and
come together against the rib 83. This ring is of a diameter such as to
snugly engage the upper rear downstream face 57 of the filter and hold it
snugly against the flange 77. Thus, the filter will adequately seal
against the upper margin of the hood opening regardless of the air flow
through it. As shown by the dotted lines at the top of the various filters
in FIG. 1, each of the "rings" can be an elongated split sleeve received
on the rod 81 such as at 84 for filter 29. Where a filter is a fairly wide
filter, such as the others in the hood, two such sleeves can be installed
on the rod to hold the upper marginal portion of the filter against the
hood flange 77.
The lower edge of each filter remains sealed against grease trough wall 73
as a result of the combination of the filter weight and the restrictor pin
heads. The drain trough 68 is sloped from its ends 70 downward toward the
center so that grease collected and running down the filter baffles and
out through the filter bottom holes such as 40 in the above-mentioned
Doane patent into the drain trough, can move toward the center and down
the drain tube 34 to a suitable collector (not shown).
As an example of how filters are selected according to the present
invention, it may be first helpful to give an example of requirements for
a conventional hood to meet the Michigan guidelines. Consider for example,
two identically sized hoods, each 12'0" long by 4'0" wide hung
back-to-back in island configuration over two line-ups of differently
arranged cooking appliances. For purposes of explanation, the two hoods
will be designated side A and side B. One exhaust duct is located equally
on the top centers of the hoods and sized at 20" square. Full end curtains
are on each end of each hood for minimum ventilation requirements, per the
Michigan guidelines, and for maximum efficiency. Given the requirements of
the Michigan guideline, the hoods each have 144" long exhaust chamber
front openings that must be closed with filters operating at velocities
between 275 and 400 f.p.m., and any area using blank filler panels cannot
exceed 16% of the filter area. Also, the pressure drop across the filters
must be at least 0.3" water gauge for a single duct opening in the 144"
length. Side A has a 36" length of heat and grease appliances below the
center of the hood (such as shown in FIG. 1), while the rest of side A of
the hood covers low heat and low grease appliances. The side B would
include low heat and low grease appliances under one-half of the length of
the hood, with heat and grease appliances under the other half. On both
sides, the distance from the cooking appliance surface to the bottom edge
of the hood is 3.5 ft. Using the Michigan guidelines, the cubic feet per
minute requirement would be:
1) Side A length of open front: 3' (over heat and grease
appliance).times.3.5' (height above appliance).times.125 f.p.m. (volume
through the 3'.times.3.5' opening required for heat and grease producing
equipment)=1,313 c.f.m. The rest of this side requires
9'.times.3.5'.times.50 f.p.m. (velocity required for low heat and grease
appliances)=1,575 c.f.m. Total for this side A of the hood equals 2,888
c.f.m.
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