Note: Descriptions are shown in the official language in which they were submitted.
1069749
Field of the Invention
This invention pertains generally to ventilating
. apparatus having an exhaust hood.
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Descriptian of the~Prior Art
Exhaust hoods in restaurant kitchens and the
like consist of a hood having an exhaust fan for drawing
fume laden air upwardly into the hood and through a filter.
S The amount of air which must be withdrawn is often prescribed
by building codes which may t~pically require that lO0 cubic
feet per minute be exhausted for every square foot of hood
opening area. The removal of conditioned room air places
a great load on the heating and air conditioning equipment
and is therefore very uneconomical and wasteful of energy~
Auxiliary air may be introduced directly into the hood to
reduce the conditioned room air removed, but known systems
have not been satisfactory.
Summary of the Invention
The novel ventilating apparatus supplies a major
portion, preferably about 80%, of the air that must be
exhausted through the hood from untempered air which it
draws directly from the environment outside the room.
This "free" outside air, never leaves the hood area. ~nly
about 20% of the total air requirement for ventilation is
tempered air which in a further aspect of the invention is
diffused into the room adjacent the hood from the main heat-
ing or air-conditioning system thereby eliminating the need
for a make-up air unit. Accordingly my appara~us conserves
considerable energy because it permits the use of primarily
untempered outside air to ventilate the cooking area. The
extensive use of cool outside air also reduces air pollution
in that it causes grease to congeal and collect on the grease
filter so that the air exhausted is cleaner. My apparatus
also reduces the accumulation of grease in the ducts and on
the roof of the building.
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Generally, in one feature of the present invention,
a hood enclosure includes a fume collection chamber having a
bottom opening and with a unique air intake chamber and an
air exhaust chamber on opposite sides. A filter forms a
common wall between the collection and exhaust chambers.
An air intake unit and an air exhaust unit are provided in
the chambers to introduce untempered air and to remove fume
laden air from the fume collection chamber. The air intake
chamber converges downwardly to increase the velocity of the
air and connects to a lateral discharge passageway along the
lower portion of the fume collection chamber. The discharge
passageway includes a smooth, curved lower deflection wall
and an upper wall to smoothly and continuously deflect the
air from the downward flow laterally and then at an upward
angle to the horizontal. The air flow from the passageway
is an upwardly inclined air curtain of fast moving air across
the fume collection chamber to the filter and exhaust chambers.
The chambers may be formed by inclined walls located within
suitable outer enclosure walls. Intake chamber walls are pre-
ferably insulated.
The air curtain functions in a manner similar toan ejector pump and causes the pressure inside the fume
collection chamber to be reduced below that which it would
be at if only the exhaust unit were providing the suction
therein. As a result the fume laden air arising from the
cooking surface is drawn into the fume collection chamber
and is exhausted through the exhaust unit with more effici-
ency than would be the case if only the exhaust unit were
being utilized. The passageway has a relatively narrow depth
in order to create a narrow, fast moving air stream. This
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air curtain prevents penetration thereof by the fumes
and provides an air pressure differential between the
moving stream and the surrounding ambient air. In
accor~ance with an additional, novel feature and aspect
of the invention~ a source of tempered secondary air is
injected into the room essentially about the enclosure
and directed toward the lower end of the hood to create an
air flow which entraps and carries fume laden air into the
hood rather than allowing it to become dispersed into the room.
Further objects, features and advantages of my
invention will be apparent from the following detailed de-
scription taken in conjunction with the accompanying drawings,
showing a preferred embodiment of an exhaust hood ventilating
apparatus exemplifying the principles of my invention.
Brief Description of the Drawings
In the drawings:
Fig. 1 is a perspective view of my exhaust hood
ventilating apparatus located above a stove or other cooking
surface;
Fig. 2 is a perspective view of a portion of the
apparatus of Fig. l;
Fig. 3 is a view taken generally along line 3-3
of Fig. ~; and
Fig. 4 is a view showing an island unit employing
this invention.
Description of the Preferred Embodiment
In Fig. 1, an exhaust hood apparatus 10 has a sub-
stantially rectangular hood enclosure 11 to be secured to a
wall above a stove or grill 12 in a kitchen. The enclosure 11
has a front longitudinal wall lla, a rear longitudinal wall llb,
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two ~ide walls llc and a top wall lld. The enclosure 11
has an open bottom preferably somewhat larger than the
area of the grill or stove in order to insure that a maximum
amount of vapors and grease particles rising upwardly will
be entrapped and pulled into the hood apparatus. Other
than the rectangular configuration may be utilized provided
that the bottom opening is adequately sized and shaped to
collect the rising vapors and fumes.
As best shown in Figs. 2 and 3, the enclosure 11 is
divided into three chambers.
The several walls of the hood apparatus 10 are
preferably made of heavy gauge sheet metal such as rolled
steel or stainless stell, to provide physical strength and
resistance to fire. The walls are preferably welded together,
although other methods of attachment may be utilized.
As shown in Figs. 2 and 3, interior walls 13 and
14 slant toward one another toward the top of the hood
enclosure in a general inverted V-shape. An intake chamber
15 is formed between walls lla, llc and lld. Chamber 15
receives untempered air under pressure which passes from
the air intake fan 16 (Fig. 1) through a duct 17 to an
opening in the top wall lld and then across chamber 15.
In Fig. 3, the air intake chamber 15 continually converges
from the top end of the chamber to the bottom end thereof.
This results in a smooth increase in the velocity of the
air at the bottom over the velocity of the air entering the
intake chamber. The air pressure and velocity is preferably
evenly distributed throughout the length of the intake
chamber 15 by an apertured distributor plate 18 across the
tope end and having a plurality of holes, preferably uniformly
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distributed. Plate lg minimizes differences in velocity
between the air that is exiting from the intake chamber
directly under the entrance of the duct 17 and the air that
is exiting from the intake chamber at the far ends of the
S chamber away from the duct opening. Walls of chamber 15
are advantageously insulated with material such as a fiber-
glass mat 19, to thereby prevent excessive cooling which
might create excessive condensation of moisture and grease
on the enclosure walls and interior walls.
A fume collection chamber 20 with a bottom opening
is defined by the interior walls 13 and 14 and the sidewalls
llc and is positioned to collect fumes, particles and
heated air arising from stove 12. The fumes are passed
through an opening 14a in wall 14 into an exhaus~ chamber
21 defined by the walls 14, llb and llc. The fumes are
drawn up through a duct 22 by an exhaust fan 23 which
exhausts the fumes into the atmosphere. Fan 23 is
sufficient in capacity to lower the air pressure in the
exhaust chamber 21 substantially below that of the surround-
ing atmosphere. A grease filter 24 is mounted in the open-
ing 14a between chamber 20 and chamber 21 to remove a
substantial portion of the grease. The filter 24 for a
kitchen may be any of the commonly employed types of grease
filters, which, for example, may utilize a stainless steel
mesh, and should extend substantially the length and width
of the wall 14 to allow maximum collection of fumes in the
filter.
The air in chamber 15 is deflected into the
chamber 20 by a unique lateral discharge passageway and
out therefrom through the filter 24. The passageway
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includes a deflector panel 25, of sheet metal or other
suitable material, which is mounted at the bottom end of
the intake chamber and extends substantially the length
of the bottom end of the intake chamber. Panel 25 is
curved along its width in a general U-shape and has a suffi-
cient curvature to smoothly deflect and redirect the air
from chamber 15 into the fume collection chamber 20 in a
direction at an angle upward from the horizontal~ A
throat panel 26 is mounted on the bottom end of the first
interior wall 13 and extends substantially the length of
the bottom end of the intake chamber. As shown in Fig. 3,
the throat panel 26 has horizontal portion 26a which is
attached to the first interior wall 13 and extends inwardly
into the fume collection chamber 20, and a portion 26b
which is bent upward from the horizontal portion. The
throat panel is mounted in proximity to the end of the
develctor panel 25 and the passageway ends in a narrow slot
therebetween. The deflector panel 25 is continuously curved
to continuously and smoothly deflect the air coming in
contact therewith from the narrow lower end of chamber 15
and to pass this air smoothly and continuously out through
the slot. The discharge passageway is desirably convergent
toward the slot, as shown in Fig. 3, to continuously increase
the velocity of the air advancing in the intake chamber
toward the slot.
The dimensions of the slot between the deflector
panel 25 and the throat panel 26 are important to the proper
operation of my exhaust ventilating apparatus 10. I have
determined that for normal kitchen ventilation usage it is
preferably that the slot width be no more than about two
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inches wide, in which case the maximum velocity of the air
flowing out of the slot would be in ~he range of 950 ft./min-
ute. A one inch slot can be utilized by increasing the air
flow to a maximum velocity of about 1250 ft./minute. The
slot between the throat panel 26 and deflector panel 25
should be so oriented that the stream or curtain of air
emerging therefrom strikes the grease filter 24 approximately
perpendicular thereto.
~s shown in Fig. 3, the throat panel 26 may have
an upturned portion 26b to also act as a grease gutter or
trough for grease that may congeal and sccumulate on the
first interior wall 13. The throat panel 26 may decline
slightly from one end of the hood enclosure to the other so
that grease accumulating on the throat panel may flow to a
grease collector (not shown) where it can be removed. A
similar grease gutter 27 is also provided at the bottom of
the rear wall llb. A horizontal bottom panel 28 i5 located
underneath the deflector panel 25 and is preferably kept fairly
narrow so that the major portion of ~he fumes arising from
the stove flow naturally up into the chamber 20.
If all of the air exhausted from the hood were
provided from the conditioned air in the room, a substantial
heat loss during the winter and a similar cooling loss during
the summer would result. The moving stream of air issuing
from the slot between panels 25 and 26 in my ventilating
apparatus 10 will tend to mix somewhat with the air which it is
in contact with and will carry this air and any particles
of grease or fumes which are intermixed therewith into the
grease filter 24 and therethrough to the exhause chamber 21.
~y ventilating hood apparatus will thus draw more fume laden
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106~3749
air into the exhaust chamber 21 than would a similar exhaust
hood apparatus without the stream of forced air which utilized
only the suction produced by the exhaust fan 23. Since the
air that is discharged through the slot is provided from
outside air and does not require heating or cooling in any
way, there is a very substantial decrease in the heat load
on the heating and air conditioning system.
I have determined that my exhaust hood ventilating
apparatus functions most efficiently when approximately 80%
of the air drawn out through the exhaust fan 23 is provided
by air forced through the slot between the throat panel 26
and the deflector plate 25, and 20% of such air is provided
by heated or cooled air which is forced into the room in
which the exhaust hood ventilating apparatus 10 is situated.
In the illustrated embodiment, this heated or cooled air
is provided by the ducts 29 wherein a continuous outlet or
spaced outlets for the tempered air are provided a various
positions around the ventilating enclosure. The secondary
source of tempered air preferably forced into the room at
"a short distance from the exhaust hood enclosure and above
the opening, creates an auxiliary flow toward the exhaust
hood opening to entrain the particles of air and pull them
into the hood rather than allowing them to disperse through-
out the room. This auxiliary air is preferably forced into
the room rather than simply being drawn in by suction from
the ventilating apparatus.
As mentioned above, it is most desirable that the
slot between the throat panel and the deflector panel be less
than approximately two inches wide for the volumes of air
normally exhausted in hoods utilized in kitchens and other
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similar applications. The narrow stream o~ air issuing
from the slot will not tend to disperse substantially
before reaching the grease filter 24. For a narrow slot
and wherein the deflector panel and the throat panel con-
verge smoothly and continuously toward the slot, the airstream issuing therefrom can develop substantially laminar
flow for some distance from the slot. The capability of ob-
taining laminar flow is enhanced because the air issuing
from the slot is issuing into a moving stream of air
produced by the air being drawn up into the exhaust
chamber 21 and through the fan 23. Thus the relative
velocity of the air issuing from the slot and the surround-
ing ambient air is less than the absolute velocity at which
the air exists from the slot. Even if the flow issuing from
the slot is turbulent, the flow will be relatively narrow
and fast moving with minimal development of vortexes and
eddys. Such smooth flow is desirable since it avoids ex-
tensive mixing of the air curtain with the fume laden air
arising from below, and also avoids penetration of the air
curtain by the fume laden air so that very little of the
fumes reach the interior walls 13 and 14. It is desirable
to minimize the vortexing of the fume laden air, since such
vortexing results in deposits of grease on the interior walls
and also substantially reduces the pressure drop developed
in the fume collection chamber 20.
It is preferable that the second interior wall 14
be at an angle greater than 45~ with the horizontal so that
grease that does accumulate either on the filter 24 or on
the interior wall 14 flows downwardly into the grease gutter
27 or is trapped in the filter, and does not form into large
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droplets which fall from the interior wall into the food
preparation surface below.
In Fig. 4, the present invention is sho~m applied
to an island unit which is spaced from the several walls of a
room and permits the user to move completely about the grill 12.
In Fig. 4, corresponding elements of the embodiment of Figs. 1 -
3 will be identified by corresponding numbers for simplicity
and clarity.
In the embodiment of Fig. 4, the hood apparatus 10
includes a substantially rectangular hood enclosure 11 adapted
to be secured from the celing above the island type grill 12.
Within the enclosure, a first fume collection chamber 20 is formed
to one side of the unit and second similar fume collection
chamber 20' is formed to the opposite side. The collection
chamber 20 is formed by walls 13 and 14. Fume collection chamber
20' is similarly formed by reversely positioned walls 13' and 14'
suc'n that the filters 24 and 24' are located adjacent to the
central portion of the rectangular enclosure 11. They form the
opposite side walls of a centrally located exhaust chamber 21.
~0 A common duct 22 is operative to exhaust the fumes into the
atmosphere. Supply chambers 15 and 15' are similarly formed to
the opposite ends of the rectangular enclosure and are connected
to individual air entrance ducts 1/ and 17'. These ducts may
be supplied from a common fan or from individual fans. The
fume collection chambers 20 and ~0' are thus constructed as
essentially mirror images about a central vertical plane. In
accordance with the embodiment of the invention, a continuous
secondary tempered air duct 29 is mounted in complete encircle-
ment about the hood enclosure 11. The duct 29 is located in
upwardly spaced relation to the lower end of the enclosure 11 and
is provided with an éssentially continuous bottom air diffuser
opening which developes a soft velocity air curtain about the
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total hood enclosure. The air flow is shown by both solid and
dotted lines ~0, with the dotted lines indicating the air flow
to the backside of the encircling duct 29. The secondary tempered
air difusser is located in upward relation and particularly,
generally at the ceiling line. The spaced location results in
significant reduction in the velocity so as to avoid objectionable
drafts over the cooks and other personnel. In a preferred constru~
ction as applied to a kitchen area, the secondary tempered air
again is selected to provide about 20% of the total air exhausted
by the hood apparatus, the other gO% being supplied via the ducts
17 and 17'
The invention with the ability of minimizing drafts
and dispersion of the fumes has been found to be particularly
significant in island units where they may be located centrally
of the room and particularly subjected to the effects of door
openings and the like.
This application is a division of Canadian applica-
tion Serial No. 246,367 filed February 23, 1976.
