Note: Descriptions are shown in the official language in which they were submitted.
CA 02478383 2007-04-27
TWO STAGE AIR FILTER
BACKGROUND OF THE INVENTION
The present invention relates generally to air filters, and in particular,
relates to air purification systems for commercial kitchens.
Air purification systems are primarily used to extract impurities, such as
grease, fi-om grease-laden air formed in commercial kitchens and other similar
environments during cooking. Grease extractors are typically a cleanable or
replaceable component of kitchen ventilation systems disposed above a cooking
area, such as a stove or the like. A fan in the ventilation system draws
grease-
laden air through the filter media which extracts the grease from the air
prior to
exhausting the air into the atmosphere. The extracted grease may run down the
filter wall and be collected for proper disposal, or the grease may be trapped
within the filter media that may be subsequently cleaned.
Conventionally, a primary air filter is mounted onto the hood of a cooking
area for the removal of large grease and other airborne particles before the
air
travels through the ductwork of a building and is ultimately expelled into the
outside environment. A secondary air filter is located at the outlet of the
building's
ductwork to remove additional smaller air impurities before the air is
released.
Various filters are available for such an air purification system.
Conventional centrifugal air filters cause air to enter a helical path in a
vortex chamber and subject the impurities to a centrifugal force. The
impurities
are propelled away from the vortex center and impinge upon chamber vwdlls. The
air exits the vortex chamber leaving the impurities behind in the chamber. One
such centrifugal air filter is described in U. S. Patent No. 6,251, 153
entitled
"Centrifugal Air Filter". Centrifugal air filters are advantageous in that the
extra.cted air impurities run down the filter wall and are collected for
proper
disposal, thereby minimizing the need for cleaning and other maintenance
efforts
that could cause down-time. While air filters of this type are effective at
removing
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large air impurities that may be flung against the side of the filter, smaller
impurities may remain in the air and travel ixlto the ductwork and fan of the
building.
Baffle filters define an enclosure having an inlet that receives grease laden
air. The enclosure defines a plurality of baffle plates that force the air to
abruptly
change the direction of travel several times prior to exiting the filter. As
the air
changes direction, grease and other impurities are propelled away from the air
stream and impinge upon the chamber walls. The grease may then run down into
a collection cup.
Another type of filter, known as an impact filter, traditionally includes a
wire mesh bed packed with filtration particles. As air is drawn through the
impact
filter, the media will trap impurities therein such that a cleaner air is
output. While
impact filters are successful at removing both large particles suitable for a
centrifugal fan along with sm.aller particles that may escape a centrifugal
fan,
depending on the filter media, they often accumulate a significant amount of
dirt
in a relatively short period of ti1ne. The accumulation presents a blockage to
the
air passing therethrough, which produces a significant pressure drop across
the
filter and limits the air flow rate through the purification system and
ultimately
the cleanliness of the air passing through. Impaet filters thus require
frequent
cleaning and maintenance.
While such air purification systems are suitable for their intended purpose,
grease and other volatile organic compounds (VOC's) tend to accumulate within
the ductwork, thereby necessitating frequent maintenance and cleaning.
It is thus desirable to provide a reliable air purification system that
removes both large and small particles from the air prior to the air entering
a
building's ductwork.
BRIEF SUMMARY OF THE INVENTTON
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The present invention provides an air purification system for receiving
incoming air
containing impurities and outputting purified air into ductwork of a building.
The system
includes a hood defining a hood outlet in communication with the ductwork. A
primary filter
member is mounted to the hood for receiving the incoming air, removing at
least a portion of
impurities therefrom, and outputting a primary airflow. A secondary filter
member is
mounted to the hood at a location downstream of the primary filter and
receives the primary
output airflow. The secondary filter member has a secondary filter media that
is operable to
remove impurities from the primary airflow and output a secondary airflow to
the hood outlet
that is cleaner than the primary airflow.
According to a first broad aspect of the present invention, there is provided
an air
purification system for receiving incoming air containing impurities and
outputting purified
air into ductwork of a building, the system comprising: a hood defining a hood
outlet in
communication with the ductwork; a primary filter member mounted to the hood
for
receiving the incoming air, removing at least a portion of the impurities
therefrom, and
outputting a primary airflow; and a secondary filter member mounted to the
hood at a
location downstream of the primary filter for receiving the primary output
airflow therefrom,
the secondary filter member having a secondary filter beads selected from the
group
consisting of silica, metal, glass, a diatomaceous earth, ceramic, and
zeolite, wherein the
beads are operable to remove impurities from the primary airflow and output a
secondary
airflow to the hood outlet that is cleaner than the primary airflow.
According to a second broad aspect of the present invention, there is provided
an air
filter chamber comprising: a top wall; a pair of side walls extending from
outer ends of the
top wall at one end and having distal ends at an opposite end in which the top
and side walls
are defined by inner and outer porous members enclosing a filtration media
therein; and a
front opening defined by distal ends of the side walls configured to receive
incoming impure
air, in which the air can flow from the opening into the top wall and side
walls; wherein the
side walls extend substantially perpendicular with respect to the front
opening.
According to a third broad aspect of the present invention, there is provided
a method
of removing impurities from an airflow in an air purification system disposed
upstream of a
building's ductwork, the air purification system being of the type having a
primary filter and a
secondary filter, the steps comprising: drawing incoming air having air
impurities into the
primary filter; removing air particles from the incoming airflow at the
primary filter to
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produce a primary airflow; outputting the primary airflow into a filter media
of the secondary
filter that includes filtering beads; removing air particles from the primary
airflow at the
secondary filter media to produce a secondary airflow; and outputting the
secondary airflow
into the ductwork.
According to a fourth broad aspect of the present invention, there is provided
in an air
purification system for removing airborne particles from an airflow prior to
emitting the
airflow into a buildings ductwork, the system including a hood defining a
space for receiving
incoming air having impurities and an outlet connected to the ductwork, and a
primary filter
mounted to the hood within the space, wherein the primary filter receives the
incoming air
and removes impurities prior to outputting once-filtered air towards the
outlet, the
improvement comprising: a secondary filter mounted within the hood and
disposed within
the space at a location downstream of the primary filter, the secondary filter
including a bed
of filtering beads through which the once-filtered air from the primary filter
flows, the
secondary filter entrapping airborne particles to output twice-filtered air
towards the outlet.
According to a fifth broad aspect of the present invention, there is provided
a method
of fabricating a two stage air purification system operable to receive
incoming air having air
impurities and outputting twice filtered air into the ductwork of a building,
the steps
comprising: providing a hood defining a hood outlet that is connectable to the
ductwork,
wherein the hood has a first filter mounted thereto to receive the incoming
air and output
once-filtered air toward the outlet; and mounting a second filter to the hood
at a location
downstream of the first filter to receive the once-filtered air and output the
twice-filtered air
toward the hood outlet, wherein the second filter has a media including filter
beads, and
wherein air can pass from the first filter to the second filter without
passing through any other
air filters.
According to a sixth broad aspect of the present invention, there is provided
an air
purification system for receiving incoming air containing impurities and
outputting purified
air into ductwork of a building, the system comprising: a hood defining a hood
outlet in
communication with the ductwork; a primary filter member mounted to the hood
for
receiving the incoming air, removing at least a portion of the impurities
therefrom, and
outputting a primary airflow; and a secondary filter member mounted to the
hood at a
location downstream of the primary filter for receiving the primary output
airflow therefore,
the secondary filter member having a inner and outer porous walls defining a
bed packed
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with secondary filter media operable to remove impurities from the primary
airflow and trap
therein the removed impurities and output a secondary airflow to the hood
outlet that is
cleaner than the primary airflow, wherein the filter media defines gaps
therebetween that are
sized to entrap the additional impurities therein.
According to a seventh broad aspect of the present invention, there is
provided an air
purification system for removing airborne particles from an airflow, the
system comprising:
a hood having an inlet for receiving the airflow from a space beneath the hood
and a hood
outlet for exhausting the airflow to a duct; a first filter mounted within the
hood and disposed
in the airflow to remove therefrom at least some of the airborne particles to
produce a first-
filtered airflow; and a second filter mounted within the hood and disposed
downstream of the
first filter to receive the first-filtered airflow, the second filter having a
porous filtration
chamber containing at least one filtration member and the first-filtered
airflow flows through
the filtration chamber and the filtration member removes airborne particles
from the first-
filtered airflow to produce second-filtered airflow that is exhausted through
the hood outlet,
wherein the airflow path between the first and second filters defines a
substantially straight
path; and wherein the filtration member is formed from a ceramic.
According to an eighth broad aspect of the present invention, there is
provided an air
purification system for removing airborne particles from an airflow, the
system comprising:
a hood having an inlet for receiving the airflow from a space beneath the hood
and a hood
outlet for exhausting the airflow to a duct; a first filter mounted within the
hood and disposed
in the airflow to remove therefrom at least some of the airborne particles to
produce a first-
filtered airflow; and a second filter mounted within the hood and disposed
downstream of the
first filter to receive the first-filtered airflow, the second filter having a
porous filtration
chamber containing at least one filtration member and the first-filtered
airflow flows through
the filtration chamber and the filtration member removes airborne particles
from the first-
filtered airflow to produce second-filtered airflow that is exhausted through
the hood outlet,
wherein the airflow path between the first and second filters defines a
substantially straight
path; and wherein the first filter is a centrifugal air filter presenting
baffle plates.
According to a ninth broad aspect of the present invention, there is provided
an air
purification system for removing airborne particles from an airflow, the
system comprising:
a hood having an inlet for receiving the airflow and a hood outlet for
exhausting the airflow;
a first filter supported by the hood and positioned such that the airflow from
the inlet passes
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through the first filter and at least a portion of the airborne particles
therein are removed
therefrom to produce a once-filtered airflow; a second filter separately
connected to the hood
at a location downstream of the first filter to receive the once-filtered
airflow, the second
filter having a filtration chamber that contains a plurality of silica
filtration members that
remove some airborne particles from the once-filtered airflow to produce
second-filtered
airflow that is exhausted through the hood outlet; and wherein the first
filter is a centrifugal
air filter presenting a plurality of baffle plates.
According to a tenth broad aspect of the present invention, there is provided
an air
filter system for removing airborne particles from air, the combination
comprising: a hood
having a top wall and a vertical wall that join to define a hood chamber
having an inlet in its
bottom for receiving a flow of intake air containing airborne particles and an
outlet in its top
wall for exhausting the flow of air; a two-stage filter assembly mounted to
the hood and
disposed in the hood chamber to define an enclosed space that communicates
with the hood
outlet, the two-stage filter assembly including: a first filter for receiving
the flow of intake
air and being operable to remove airborne particles therefrom to produce once-
filtered
airflow; a second filter for receiving the once-filtered airflow and producing
twice-filtered air
that flows through the enclosed space to the hood outlet, the second filter
having a porous
filtration chamber containing a plurality of filtration members that remove
airborne particles
from the once-filtered airflow; and wherein the filtration members are formed
from a
ceramic.
According to an eleventh broad aspect of the present invention, there is
provided an
air filter system for removing airborne particles from air, the combination
comprising: a
hood having a top wall and a vertical wall that join to define a hood chamber
having an inlet
in its bottom for receiving a flow of intake air containing airborne particles
and an outlet in
its top wall for exhausting the flow of air; a two-stage filter assembly
mounted to the hood
and disposed in the hood chamber to define an enclosed space that communicates
with the
hood outlet, the two-stage filter assembly including: a first filter for
receiving the flow of
intake air and being operable to remove airborne particles therefrom to
produce once-filtered
airflow; a second filter for receiving the once-filtered airflow and producing
twice-filtered air
that flows through the enclosed space to the hood outlet, the second filter
having a porous
filtration chamber containing a plurality of filtration members that remove
airborne particles
from the once-filtered airflow; and wherein the first filter is a centrifugal
filter.
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According to a twelfth broad aspect of the present invention, there is
provided a
ventilation system for removing air from a food cooking area, the combination
comprising: a
hood disposed above said food cooking area, the hood having walls which define
a hood
chamber for receiving intake air containing airborne particles from the food
cooking area
below; a duct connected to an exhaust outlet on the hood for exhausting air
from the hood
chamber; and a two-stage filter assembly mounted to the hood and disposed in
the hood
chamber to filter airborne particles from intake air flowing from the food
cooking area to the
exhaust outlet, the filter assembly including: a first filter for receiving
the intake air and
being operable to remove airborne particles therefrom to produce once-filtered
airflow; and a
second filter for receiving the once-filtered airflow and producing a twice-
filtered air that
flows directly to the exhaust outlet, the second filter having a filtration
chamber containing a
regenerative filtration material selected from the group consisting of silica,
ceramic,
diatomaceous earth, and zeolite; and wherein the first filter comprises a
centrifugal filter.
According to a thirteenth broad aspect of the present invention, there is
provided a
ventilation system for removing air from a food cooking area, the combination
comprising: a
hood disposed above said food cooking area, the hood having walls which define
a hood
chamber for receiving intake air containing airborne particles from the food
cooking area
below; a duct connected to an exhaust outlet on the hood for exhausting air
from the hood
chamber; and a two-stage filter assembly mounted to the hood and disposed in
the hood
chamber to filter airborne particles from intake air flowing from the food
cooking area to the
exhaust outlet, the filter assembly including: a first filter for receiving
the intake air and
being operable to remove airborne particles therefrom to produce once-filtered
airflow; and a
second filter for receiving the once-filtered airflow and producing a twice-
filtered air that
flows directly to the exhaust outlet, the second filter having a filtration
chamber containing a
regenerative filtration material selected from the group consisting of silica,
ceramic,
diatomaceous earth, and zeolite; and wherein the first filter presents baffle
plates extending
into a path through which the intake air flows as it passes through the first
filter.
According to a fourteenth broad aspect of the present invention, there is
provided a
method for filtering air drawn from above a cooking area and into an exhaust
duct, the steps
comprising: producing once filtered air by passing the air through a first
filter which defines
by a plurality of walls an air flow path that causes airborne particles in the
air to impact the
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walls and be deposited on the walls and to thereby be removed from the air;
producing twice
filtered air by passing the once filtered air through a second filter
comprised of a plurality of
porous filtration members that absorb airborne particles in the once filtered
air; and
conveying the twice filtered air to the exhaust duct.
A general objective of the present invention is to provide an air purification
assembly
achieving an improved extraction of airborne impurities from an airflow prior
to the airflow
traveling within the internal ductwork of a building. By providing a first
filter member for
removing impurities and a second filter member for removing additional
impurities, a cleaner
air is output to the ductwork, thus reducing the frequency of maintenance to
the ductwork.
These and other objects and advantages of the invention will be apparent from
the
description that follows. In the description reference is made to the
accompanying drawings
which form a part hereof and in which there is shown by way of illustration,
and not
limitation, embodiments of the invention. Such embodiments do not necessarily
represent the
full scope of the invention. Reference should therefore be made to the claims
herein for
interpreting the scope of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
Reference is hereby made to the following figures in which like reference
numerals
correspond to like elements throughout, and in which:
Fig. I. is side elevation view of a ventilation hood having a primary air
filter and
secondary air filter constructed in accordance with the preferred embodiment;
Fig. 2 is an exploded perspective view of the ventilation hood illustrated in
Fig. 1 to
further illustrate the primary air filter;
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[00151 Fig. 3 is a cut away front perspective view of the primary cross
sectional
view of the primary air filter illustrated in Fig. 1;
100161 Fig. 4 is a sectional side elevation view of the air filter illustrated
in Fig.
3 taken along line 4-4;
[00171 Fig. 5 is a perspective view of the hood illustrated in Fig. 1 with a
portion
cut away showing the removal of the filters;
100181 Fig. 6 is a perspective view of the secondary air filter illustrated in
Fig. 1
showing the inlet;
[00191 Fig. 7 is a perspective view of the secondary air filter illustrated in
Fig. 1
showing the outlet;
[00201 Fig. 8 is a sectional side elevation view of the secondary air filter
illustrated in Fig. 7; taken along the line 8-8;
[0021] Fig. 9 is an illustration of a porous filter media used in the
secondary air
filter in accordance with the preferred embodiment;
100221 Fig. 10 is an illustration of a nonporous filter media used in the
secondary air filter in accordance with an alternate embodiment; and
[00231 Fig. 11 is a side elevation view of a ventilation hood constructed in
accordance with an alternate embodiment of the invention.
DETAILED DESCRIPTION OF THE INVENTION
100241 Referring initially to Fig. l, an air purification system 10 suitable
for
extracting grease and other particles, such as VOC'S, from grease-laden air is
mounted on an angle at one end of a ventilation hood 12 that is disposed above
a
food cooking area (not shown). Hood 12 defines an outlet to a duct collar 27
that
provides an interface from the hood to the ductwork system (not shown) of the
building. In particular, a primary air filter 18 is angularly mounted within
the hood
12 that, along with the interior walls of the hood, defines an enclosure 21
disposed
between the filter and outlet duct'collar 27. The enclosure 21 ensures that
only
filtered air is able to travel into the duct collar 27. A secondary filter 22
is also
angularly mounted within the hood at a location within the enclosure between
the
primary filter 18 and the duct collar 27. In particular, lower and upper guide
rails
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126 and 127, respectively, extend laterally across the hood 12 and supports
the outer
ends of the filter 22, as will be described in more detail below.
[00251 During operation, a fan (not shown) draws grease-laden air 16 into the
hood 12 and through the primary air filter 18 to remove large particles from
the air.
The partially cleaned air 20 is subsequently drawn through the secondary air
filter 22
for the removal of smaller particles from the air that were not removed by the
primary filter 18. "Clean" air 24 is thus expelled from the hood 12 through
the duct
collar 27 and travels through the internal ductwork and out the building.
Advantageously, the internal ductwork of the building does not accumulate dirt
and
grease as quickly as conventional systems that use a secondary filter at the
outlet of
the building's ductwork.
[00261 Referring particularly to Figs. 2-4, the primary air filter 18 has a
front
wall 26 and a rear wall 28 joined at its perimeter by a top wall 30, bottom
wall 32,
and opposing sidewalls 34. The cavity formed by the walls 26, 28, 30, 32, and
34 is
divided into a plurality of separate vortex chambers 35.
[00271 Each vortex chamber 35 has a pair of inlets 36 located at opposite ends
38 of the vortex chambers 35, and a single outlet 39 located at the midpoint
of the
chamber 35. Grease-laden air 16 enters a vortex chamber 35 through the pair of
inlets 36 formed in the filter front wall 26, and exits the chamber 35 through
the
outlet 39 formed in the filter rear wall 28. The filter 18 captures the grease
by
directing the grease-laden air 16 along a helical path through the vortex
chambers
35. The helical path causes the grease particles suspended in the air to
impinge
against the chamber walls and then flow along the chamber wall to a collection
point. Forming the inlets 36 proximal opposing chamber ends 38 prevents the
air 16
entering each inlet 36 from passing directly to the outlet 39 and avoiding the
helical
path. This ensures that a maximum amount of grease is extracted from the air
16.
(00281 In accordance with the preferred embodiment, the filter 18 includes a
tray-shaped base 40 with the filter front wall 26, and a top wall 30, bottom
wall 32,
and side walls 34 defining the filter perimeter. The walls 30, 32, and 34
extend
rearwardly and substantially perpendicular from the front wall 26 to form a
tray
cavity 41. Dividers 42 dividing the cavity 41 and defining the vortex chambers
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in cooperation with the base 40 are mounted in the cavity 41. The base 40 is
preferably formed from a single sheet of material to eliminate seams and
facilitate
cleaning the filter front wall 26.
100291 The pairs of inlets 36 are formed in the front wall 26 and provide an
entry
for the grease-laden air 16 into the chambers 35. The inlet pairs 36 are
spaced along
the front wall substantially parallel to the base side walls 34. Preferably,
the front
wall 26 is deformed rearward to form vortex generators 44 at each inlet 36.
The
vortex generators 44 direct air 16 entering the inlet 36 into a helical path
inside the
chamber 35 toward the chamber center 46.
[00301 The dividers 42 are retained in the cavity 41 by folding flaps 48 over
the
dividers 42 inserted therein. Looking particularly at Fig. 4, the flaps 48 are
formed
on rear edges of the base top 30, bottom 32, and sides 34 which are folded
over to
retain the interlocked dividers 42 in the base cavity 41. Advantageously,
folding the
flaps over the dividers minimizes air leaks from the chambers 35. The flaps 48
are
secured at each base corner and sides using methods known in the art, such as
using
tack welds, spot welds, screw type fasteners, and the like, to prevent the
flaps 48
from inadvertently releasing the dividers 42.
[0031] Grease impinged onto the vortex chamber walls drains out of the
chamber 35 through apertures 50 punched in the base bottom 32 at the end 38 of
each chamber 35. During heavy grease loading of the filter, similar to heavy
duty
cooking, the vortex generators 44 can become loaded with grease. This heavy
loading of grease may develop into runs down the front wall 26. To prevent the
runs
from running completely down the entire front face 26, small louvers 52 are
formed,
such as by punching into the front face just below the vortex generators 44 at
each
inlet 36 proximal the filter top. Two rows of staggered louvers 52 are used to
cover
the entire surface (left to right). The staggered louvers 52 assure any runs
from the
vortex generators 44 will be caught by a louver.
[00321 The louvers 52 need only be formed on the top portion of the filter,
and
not the bottom, making the filter top to bottom orientation specific. However,
if the
louvers are not required, the apertures 50 can be punched in the base top 30
and
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bottom 32 allowing the filter 18 to be mounted in the hood 12 without
reference to the
filter top 30 or bottom 32 orientation.
To simplify the filter assembly 18 and reduce assembly costs, the vortex
chambers 35 axe formed by interlocking dividers 42 which are inserted into the
cavity
41. The elongated L-shaped dividers 42 are inserted into the tray cavity 41
and
cooperate with the base 40 and adjacent dividers 42 to form the elongated
vortex
chambers 35. Each divider 42 extends the width of the base 40 and has a side
wall
substantially parallel to the base side walls 34 and a rear wa1137
substantially parallel
to the front wall 22 to form the filter rear wall 28. The rear wall of each
divider 42 is
disposed above a different pair of inlets 36 and has a notch fonmed generally
centrally
therein defining the chamber outlet 39. Edges of the divider rear wall and
side walls
are bent inward and abut the base 40 or adjacent divider 42 to minimize air
leaks.
The dividers 42 are preferably formed from the same material using the same
processes as the base 40 and are interlocked to simplify the filter assernbly
18. Tabs
formed in each divider 42 extend into slots formed in the adjacent divider 42
to lock
adjacent dividers 42 together. The tab and slot construction eliminates a need
to spot
weld or otherwise secure each individual divider 42 in the cavity 41,
By providing a vortex chamber 35 having front inlets 36 and a rear outlet 39,
the air enters and exits the filter 18 in substantially parallel directions to
enable the air
to easily enter the secondary filter 22, as will be described in more detail
below. This
arrangement furthermore provides a more compact filter 18 relative to an air
filter in
which the air exits the air filter substantially perpcndicular to the air
entering the
filter, such as through the chamber ends. Purtherinore, a rear outlet air
filter does not
require a specially adapted ventilation hood to channel air exiting the
chamber ends
into the hood.
In another embodiment, the hasc, dividers or portions thereof are coated with
a dry lubricant, such as described in U. S. Patent 6,050, 258 entitled
"Exhaust fan
with dry lubricant coating".
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100371 It should be appreciated that conventional centrifugal filters are not
capable of removing all grease and other impurities from grease-laden air. For
this
reason, a secondary filter has been conventionally installed at the outlet of
a
building's ductwork to further remove pollutants before the air is emitted
into the
environment. However, the partially cleansed air output by the primary filter
leaves
grease, dirt, and sludge on the interior of the ductwork and in the plenum of
the
hood, thereby necessitating frequent cleaning and maintenance.
[00381 In accordance with the preferred embodiment, a secondary filter 22 is
mounted within the hood at a position downstream of primary filter 18 within
the
enclosure 21, and receives the partially cleaned air (primary airflow) 20 from
the
primary filter. It should be appreciated that the term "downstream" is used
herein
with reference to the direction of airflow 16, 20, and 24. As will be
described in
more detail below, secondary filter 22 is an impact filter whose filter media
includes
beads (either porous or nonporous) that remove additional impurities from the
air 20.
It should be appreciated, however, that the term "filter media" is broadly
used herein
to define any filter mechanism that is operable to remove air-borne particles,
including the structure of centrifugal filter 18. Clean air (secondary
airflow) 24 is
thus output and received by a duct collar 27 that extends from the hood 12 and
connects to the buildings internal ductwork. The air 24 may thus travel
directly out
the building without being further cleansed, thereby increasing the time
interval
between regular duct cleanings and reducing the risk of fire. Furthermore,
because
the secondary filter 18 is disposed within the hood 12, it is more accessible
to the
user, for example, when the filter is to be cleaned.
100391 Referring now to Figs. 6-8, the secondary air filter 22 includes a
frame 61
that defines a front face 60 operable to receive incoming air. The front face
60 has
an outer periphery defined by a top wall 62, bottom wall 64, and opposing end
walls
66. A rear surface 68 is disposed opposite the front face 60, and allows
cleaned air
to exit the filter 22. The cavity formed by the walls 60, 62, 64, and 66 is
partitioned
into two outer air intake chambers 70 and 72, and a middle air intake chamber
74 by
dividers 71 and 73 that extend across the front face 60. The front face 60
defines an
inlet to the three chambers. It will become appreciated from the description
below
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that the shape of intake chambers 70, 72, and 74 provide a greater surface
area to the
incoming air, thereby increasing the efficiency of the filter 22 over
conventional flat
filter designs.
[00401 The rear surface 68 is used herein to collectively identify the
respective
rear walls of each intake chamber, it being appreciated that the rear surface
is not
necessarily a flat or continuous wall. For instance, the rear surface 68 at
the outer
chamber 70 is defined by first and second outer walls 75 and 77, respectively.
In
particular, first wal175 extends outwardly from the front end 80 of the bottom
wall
64 at a 45 angle. The second wall 77 extends inwardly at a 90 angle from the
distal end of wa1175 to the front face 60 of the chamber 70 (and thus defines
a 45
angle with respect to the front face 60). The first and second walls 75 and
77, along
with the front face 60, define a substantially right triangle when viewed in
cross
section, as illustrated in Fig. 8.
100411 The first wa1175 is defined by a pair of inner and outer wire mesh
screens
76 and 78 that extend parallel to each other and spaced apart to fonn a gap
therebetween that houses a filter media 89. Likewise, the second wall 77 is
defined
by a pair of inner and outer wire mesh screens 82 and 84, respectively, that
are
connected to the outer ends of screens 76 and 78, respectively. Screens 82 and
84
extend parallel to each other, and are spaced apart to form a continuous gap
with
screens 76 and 78. The distal ends of screens 76 and 78 are sealed by an outer
clip
86, and the distal ends of screens 82 and 84 are sealed by an inner clip 88.
The
enclosure defined by two pairs of screens and clips 86 and 88 ensures that air
passing through chamber 70 will pass through the filter media 89.
100421 The rear surface 68 at the middle chamber 74 is defined by two side
walls 90 that extend perpendicularly outwardly from the front face 60, and a
laterally extending top wal192 that joins the outer ends of walls 90. Walls 90
and
92, along with front face 60, define a substantially rectangular chamber 74
when
viewed in cross section. Side walls 90 include inner and outer wire mesh
screens 94
and 96, respectively, that are offset from one another a predetermined
distance to
define a space therebetween that houses the filter media 89. Upper wall 92
includes
and inner and outer pair of screens 98 and 100, respectively, that are
connected to
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the outer ends of inner and outer screens 94 and 96, respectively, and are
offset to
define a gap therebetween that is also occupied by the filter media 89. The
inner
ends of screens 94 and 96 are sealed by clips 102 to define an enclosure to
ensure
that all air entering into the middle chamber 74 will pass through the filter
media 89.
100431 Outer chamber 72 is similar to chamber 70, and is defined by a first
wall
104 that extends outwardly from the front end 81 of bottom wall 62 at a 45
angle.
A second wall 106 extends inwardly at a 90 angle from the distal end of wall
75
towards the front face 60 of the chamber 72. For instance, the rear surface 68
is thus
defined at the outer chamber 72 by the first and second walls 104 and 106,
respectively. The first and second walls 75 and 77, along with the front face
60,
define a substantially right triangle when viewed in cross section.
100441 The first wall 104 is defined by a pair of an inner and outer wire mesh
screens 108 and 110 that extend parallel to each other and spaced apart to
form a gap
therebetween that houses filter media 89. Likewise, the second wall 106 is
defined
by a pair of inner and outer wire mesh screens 112 and 114, respectively, that
are
connected to the outer ends of screens 76 and 78, respectively, and are also
spaced
apart to house the filter media. Screens 112 and 114 extend parallel to each
other,
and are spaced apart to define a gap that houses filter media 89. The distal
ends of
screens 76 and 78 are sealed by outer clip 86, and the distal ends of screens
82 and
84 are sealed by inner clip 88. The enclosure defined by two pairs of screens
and
clips 86 and 88 ensures that all air entering chamber 72 passes through the
filter
media.
100451 During operation, incoming air 20 is received normal to the front face
60
of secondary filter 22 and is directed into each of the chambers 70, 72, and
72. Air
20 then passes through the inner screens defining the chamber walls, where
airborne
particles are removed by the filter media prior to exiting filter 22 via the
outer
screens. Clean secondary air 24 is then directed through the duct collar 27
and
through the building's internal ductwork system before being expelled into the
outdoor environment.
100461 The inner and outer screens that define the walls of chambers 70, 72,
and
74 are preferably spaced apart a distance less than one inch, and preferably
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1/2 inch in accordance with the preferred embodiment, though it should be
appreciated that any distance could be used in accordance with the present
invention.
Advantageously, it has been determined that the inner and outer screens may be
positioned far enough apart that the pressure drop across the secondary filter
22 is no
greater than 2 in H20 for a given airflow with a packed bed of filter media,
as is
described in more detail below.
[00471 Because air flowing through the filter 22 may exert a significant
amount
of pressure on the chamber walls, the outer surfaces of the outer screens of
each
chamber are supported by walls 116 that extend between end walls 66 at the
junction
between two screens. Walls 116 further act to seal each interface to ensure
that all
air entering the secondary filter 22 passes through the filter media 89. The
screens
are further supported by laterally extending beams 118 that join the midpoints
of
walls 116. A pair of walls 120 extends along the front face 60 and encapsulate
clips
88 and 102 to provide a seal at the interface between outer chambers 70 and 72
and
middle chamber 74. Walls 116 thus further prevent the incoming air 20 from
flowing through the filter 22 without passing through the filter media 89.
100481 While the chamber walls have been described herein as being defined by
inner and outer wire mesh screens, it should be appreciated that the walls
could be
made out of any suitable porous material that is able to provide an adequate
air flow
rate therethrough.
100491 Referring now to Figs. 9 and 10, the filter media 89 comprises
generally
spherical beads 91 that are capable of absorbing grease from the incoming air
20.
During manufacturing, a first end plate 66 is attached to walls 62 and 64. The
beads
91 are poured between the inner and outer chamber screens at the other end to
produce a packed bed of beads or any alternative material suitable for use in
combination with the present invention. The second end plate 66 is
subsequently
attached to enclose the chamber walls. It should be appreciated that the
diameter of
the beads may vary, but a diameter between 1 and 4 mm is currently
contemplated.
The beads 91 are capable of removing smaller air impurities that were not
removed
by the primary filter 18. Advantageously, because end plates 66 are attached
to the
frame via nuts and bolts (not shown), an end user is able to remove the end
plate 66
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and the used beads 91, and insert new beads 91 into the filter without having
to
replace the entire filter 22.
100501 Referring to Fig. 9 in particular, beads 91 are porous, and may
comprise
silica gel, a ceramic, a diatomaceous earth, zeolite, or any other porous
material
deemed suitable and durable enough to be made into a bead-like form and packed
into a filtration device. Silica gel is used in accordance with the preferred
embodiment because of its high affinity to grease in comparison to water
vapor.
While silica gel has been used in the past as an oil filter, the present
invention
recognizes that silica gel may further be used for the removal of grease and
other
impurities (e.g., VOC's) from grease-laden air.
100511 During operation, grease-laden air 20 enters through the chamber walls
and passes through the beads 91. The beads 91 act as baffles that cause the
incoming air to make several sudden changes in direction such that the grease
and
other particles suspended in the air impinge against the beads and are
absorbed into
the interstices 124 of the filter media 89 during normal operation.
Advantageously,
because the impurities are stored within each bead 89, the gaps between
adjacent
porous beads are free of dirt, thereby enabling air to easily pass through the
filter 22
without producing a significant pressure drop across the chamber walls. Once
the
beads become saturated, grease may begin to accumulate within the air gaps
located
between adjacent beads 91. Accordingly, it may be desirable to install a
collection
cup (not shown) to receive any grease that accumulates, as will now be
described
with reference to Fig. 10.
100521 In particular, the filter media 89 may alternatively comprise nonporous
beads 93, such as metallic beads, glass beads, or any other nonporous material
suitable for use with the present invention. In accordance with this
embodiment, the
airborne grease and other impurities impinge against the beads and accumulate
within the air gaps 125 fonned between adjacent beads. As impurities
accumulate,
the pressure drop across chamber walls begins to rise until the drop is
sufficiently
great that incoming air drives the grease off the beads 89. The filter 22
would
include a collection cup (not shown) to capture the impurities when nonporous
beads
91 are used.
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[00531 It should be appreciated that still other filter media 89 could be used
with
the secondary filter 22. For example, the filter media 89 could comprises a
porous
ceramic structure that is in the shape of the interior defined by any of walls
75, 77,
90, 92, 104, and 106 such that the walls are fabricated around the ceramic
structure.
In accordance with this embodiment, incoming air 20 passes through the porous
structure, whose pores absorb the impurities that were not removed by the
primary
filter 18. A ceramic filter media has been found to exhibit a sufficient
affinity to
grease in comparison to water vapor, and is thus suitable for use as a filter
media in
secondary filter 22.
[00541 Both the primary and secondary filters may be regenerated using a
commercial dishwasher and standard dishwasher detergents to remove grease and
VOC's. In some instances, such as the case where the pores extend completely
through the beads, the filter should be soaked in a solution of commercial
detergent
in order to break down the grease which has been absorbed prior to removal of
the
grease in a commercial dishwasher.
100551 Referring to Fig. 5, both the primary and secondary filters 18 and 22
rest
on guide rails 126 and 127 that facilitate their removal from the hood 12.
Fig. 5
illustrates the removal of the secondary filter 22, though it should be
appreciated that
the primary filter 18 is removable in the same manner. In particular, a pair
of
handles 128 extends from the front of end walls 66 to enable the easy removal
and
transport of filter 22. Guide rails 126 and 127 are spaced a sufficient
distance such
that a user may lift filter 22 up against the lower edge of upper guide rails
127 to
provide clearance to swivel bottom wall 64 past the corresponding lower guide
rail
126. Once one wal164 has been disengaged from the guide rails 126 and 127, the
upper wal162 may be easily removed from engagement with its set of guide
rails. It
should be appreciated that a similar system may be used to removably mount the
primary filter 18.
[00561 Referring now also to Fig. 11, a flat secondary filter 122 could be
installed downstream of primary filter 18 in accordance with an alternate
embodiment of the invention. However, it should be appreciated that hoods
having
only the primary air filter 18 installed are currently commercially
manufactured in
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systems that employ a secondary filter at the outlet of a building's internal
ductwork
system. Because secondary filter 122 is flat, it would have to be elongated
more
than filter 22 in order to provide a great enough surface area to effectively
and
reliably clean the air 20 while supporting a sufficient air flow rate.
However, the
position of primary filter 18 in conventional systems would not allow for a
sufficiently elongated secondary filter to be installed within enclosure 21.
Accordingly, primary filter 18 would need to be moved back within the hood 12
in
order to accommodate a further elongated secondary filter 122. The
installation of a
flat secondary filter 122 would thus necessitate that the manufacturing
process of
hood 12 be modified, which would consume additional expense and resources.
100571 Advantageously, the chamber walls 75, 77, 90, 104, and 106 of filter 22
extend at least partially outwardly from the front face 60. Filter 22 thus
utilizes the
lateral distance allowed by the conventional hood 14 along with the available
depth
within the enclosure 21 to achieve a greater surface area than flat filter 122
without
occupying a greater amount of lateral space within the hood 12. Conventional
filter
walls have been known to extend up to 45 from the front surface. However, the
walls 90 of secondary filter 22 extend up to 90 from the front face, it being
appreciated that any angle greater than 45 with respect to the front surface
60 will
provide a greater surface area than the prior art. The increased surface area
achieved
by the walls of chambers 70, 72, and 74 enables a greater flow rate through
the filter
22 and also achieves a high efficiency. The preferred embodiment thus enables
the
installation of secondary filter 22 in the hood 12 without having to modify
conventional manufacturing and assembly of the hood/primary filter assembly.
[00581 While the present invention has been described with reference to a
primary centrifugal air filter 18 and a secondary impact air filter 22, it
should be
appreciated that other filters could be used in an air purification system
having a first
stage that collects a large portion of the larger size airborne particles and
a
subsequent stage or stages that removes smaller particles not removed in the
first
stage and non-particle contaminants such as Volatile Organic Compounds prior
to
the air entering a building's internal ductwork. For example, filters 18 and
22 could
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comprise any one of a centrifugal filter, a baffle filter, an impact filter,
or any other
like filter suitable for removing airborne impurities.
[00591 The above has been described as a preferred embodiment of the present
invention. It will occur to those that practice the art that many
modifications may be
made without departing from the spirit and scope of the invention. In order to
apprise the public of the various embodiments that may fall within the scope
of the
invention, the following claims are made.
