Note: Descriptions are shown in the official language in which they were submitted.
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IMPROVED ACTIVE FIELD POLARIZED MEDIA AIR CLEANER
This application is a divisional of Canadian patent application Serial No.
2,635,804 filed internationally on December 29, 2006 and entered nationally on
June 27, 2008.
Field of Invention
The present invention relates generally to air cleaning systems and is
particularly directed
to air cleaners of the type that use an electrostatic field to polarize a
media and to polarize
particles to increase the particle collection efficiency on the media.
Background of the invention
The principal of electrostatic attraction has been used for many years to
enhance the
removal of contaminants from air streams. There are three primary categories
of air
electrostatic cleaners: electrostatic precipitators, passive electrostatic
filters and active field
polarized media air cleaners, which are sometimes known under different terms.
Electrostatic precipitators charge particles and then capture them on
oppositely charged
and/or grounded collection plates.
A passive electrostatic filter (also know as an electret) employs a media (or
combination of
different media) that through some combination of treatment and/or inherent
properties has
an electrostatic charge. Particles entering the filter media that have an
electrostatic charge
are attracted to the charged media filter materials that have the opposite
electrostatic
charge.
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An active field polarized media air cleaner uses an electrostatic field
created by a voltage
differential between two electrodes. A dielectric filter media is placed in
the electrostatic
field between the two electrodes. A dielectric material is an electrical
insulator or a
substance that is highly resistant to electric current that can also store
electrical energy. A
dielectric material tends to concentrate an applied electric field within
itself and is thus an
efficient supporter of electrostatic fields. The electrostatic field polarizes
both the media
fibers and the particles that enter, thereby increasing the efficiency of the
media and the air
cleaner. The efficiency of the filter is the percentage of particles removed
from the air
stream at a given particle size, or for a range of particle sizes.
A further electrostatic air filter design is disclosed in Canadian Patent No.
1,272,453, in
which a disposable rectangular cartridge is connected to a high voltage power
supply. The
cartridge consists of a conductive inner center screen, which is sandwiched
between two
layers of a dielectric fibrous material (either plastic or glass). The two
dielectric layers are,
in turn, further sandwiched between two outer screens of conductive material.
The
conductive inner center screen is raised to a high voltage, thereby creating
an electrostatic
field between the conductive inner center screen and the two conductive outer
screens that
are kept at an opposite or ground potential. The high voltage electrostatic
field polarizes
the fibers of the two dielectric layers.
The air cleaners may be installed in a variety of configurations and
situations, both as part
of a heating ventilating and air conditioning (HVAC) system and in standalone
air
moving/cleaning systems. In smaller HVAC systems (e.g. residential and light
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commercial), the air cleaner panels are often installed in a flat
configuration (perpendicular
to the airflow) or in angled filter tracks. In larger systems, banks of air
filters are typically
arranged in a V-bank configuration where multiple separate filters are
positioned to form a
Z-fold filter perpendicular to the axis of airflow.
Summary of the invention
The invention is embodied in improvements to active field polarized media air
cleaners.
AERODYNAMIC FRONT COWLING
In accordance with one aspect of the present invention, a V-bank configuration
of active
field polarized media air cleaners includes an aerodynamic front cowling
joining front
edges of adjacent active field polarized media panel air cleaners facing the
airflow. The
front cowling provides a lower form drag airflow to reduce filter static
pressure drop
(resistance to airflow). In addition, the hollow interior of the aerodynamic
front cowling
provides a recess for concealing the high voltage power supply inside the
aerodynamic
front cowling, providing protection and insulation of the electrical
components. Further,
the cowling serves as a wire chase for running both high and low voltage wires
between air
cleaner panels and adjacent air cleaner modules.
REAR DOUBLE HINGE AIR SEAL
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In accordance with another aspect of the present invention, a V-bank
configuration of
active field polarized media air cleaners includes a rear double hinge joining
rear edges of
adjacent active field polarized media air cleaners. The rear double hinge
provides a
positive seal between adjacent active field polarized media air cleaners,
thereby reducing
blow-by between adjacent active field polarized media air cleaners and
increasing
efficiency.
IMPROVED ELECTRODE FOR POLARIZED MEDIA AIR CLEANER
In accordance with another aspect of the present invention, the high voltage
electrode is
made from a conductive extruded plastic netting or other similar material that
provides for
significantly higher operational voltages and therefore higher efficiencies.
RESISTIVE CENTER SCREEN AND VARIABLE HIGH VOLTAGE POWER SUPPLY
In accordance with yet another aspect of the present invention, more than one
active field
polarized media air cleaners may share a single high voltage power supply. In
such
manner, if one active field polarized media air cleaner shorts out, the
resistance of the
center screen will limit the current drawn from the high-voltage power supply
by the short
circuit, thereby permitting the other active field polarized media air cleaner
sharing the
same power supply to continue operating normally.
Additionally, the high-voltage power supplies may be made variable so that an
optimal
voltage may be selected that provides an optimum electrostatic field without
arcing.
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DIELECTRIC MEDIA SUPPORT FRAME
In accordance with another aspect of the present invention, an active field
polarized media
air cleaner includes a dielectric media support frame having on one side a
recess or shelf
for holding the center screen and/or the filter media and on the other side a
protrusion for
creating a positive seal with the conductive holding frame that holds the
conductive outer
screens. The dielectric media support frame allows the center screen to extend
to the edge
of the filter media without shorting or arcing to the conductive outer screens
or to the
conductive holding frame, an arrangement that provides a more uniform
electrostatic field
throughout the filter media_ The border provided by the dielectric media
support frame also
prevents the spraying of corona at the edges of the center conductive screen.
The positive
seal between the dielectric media support frame and the conductive holding
frame reduces
air leakage (blow-by) between the conductive holding frame and the edge of the
filter
media. The dielectric media support frame can be made of either rigid or
flexible plastic
material.
FLAT CONDUCTIVE OUTER SCREEN
For a more uniform distance between electrodes and therefore a more uniform
field
throughout the active field polarized media air cleaner, the conductive outer
screen is made
relatively flat as compared to the flexible outer screens of prior art active
field polarized
media air cleaners. The flatness of the outer screen is achieved by using a
relatively rigid
material as compared to the dielectric filter material.
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IMPROVED HIGH VOLTAGE CONTACT
One of the problems in prior art active field polarized media air cleaners is
the area where
the high-voltage probe contacts the center screen. Typically in the prior art,
the high
voltage connection is made with a probe or clip that contacts the center
screen (or
electrode) over a relatively small area. In some cases, the contact becomes
poor. The
problem with this arrangement is that over time, the point of contact can arc,
spray and
erode the area of contact on the electrode and make less certain contact. As
this erosion
progresses, it can accelerate to the point where contact is no longer being
made. The
present invention overcomes this problem and maintains air cleaner integrity
by various
means making the high voltage contact a large area by means of a disc and/or
disc and
fastener that spreads the connection over a far wider surface of the
electrode. While
various embodiments of the invention will show the high-voltage contact area
as circular,
other shapes would work as well.
Also, there is a tendency to spray corona and/or arc in the region of the high-
voltage probe.
To reduce spraying and arcing in the region where the high-voltage probe
contacts the
center screen, a high-voltage probe enclosed in a high voltage shield is
provided.
Brief description of the drawings
Figure 1 is an isometric drawing of a plurality of active field polarized
media air cleaner
panels arranged in a V-bank configuration in accordance with the present
invention.
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Figure 2 is a cross-sectional view of a plurality of active field polarized
media air cleaner
filters arranged in a V-bank configuration in accordance with the present
invention.
Figure 3 is a detailed portion of a cross-sectional view of a plurality of
active field
polarized media air cleaner filters arranged in a V-bank configuration in
accordance with
the present invention illustrating insertion of replacement filter media into
a lower filter
holding frame.
Figure 4 is a detailed portion of a cross-sectional view of a plurality of
active field
polarized media air cleaner filters arranged in a V-bank configuration in
accordance with
the present invention illustrating insertion of replacement filter media into
an upper filter
holding frame.
Figure 5 is a schematic diagram of a plurality of active field polarized media
air cleaner
filters having resistive center screens and sharing common high-voltage power
supplies in
accordance with the present invention.
Figure 6 is a cross-sectional view of a front cowling for use on the top or
bottom of a stack
of active field polarized media air cleaner filters arranged in a V-bank
configuration in
accordance with the present invention.
Figure 7 is a cross-sectional view of a hinge section in accordance with the
present
invention for use in conjunction with the front cowling a figure 6.
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Figure 8 is a cross-sectional view of a front cowling for use with a plurality
of active field
polarized media air cleaner filters arranged in a V-bank configuration in
accordance with
the present invention.
Figure 9 is an assembly drawing of first and second active field polarized
media air
cleaners and a front cowling in accordance with the present invention.
Figure 10 is a cross-sectional view of a first portion of a double hinge in
accordance with
the present invention.
Figure 11 is a cross-sectional view of a second portion of a double hinge in
accordance
with the present invention.
Figure 12 is an assembly drawing of first and second active field polarized
media air
cleaners and a double hinge assembly in accordance with the present invention.
Figure 13 is an assembly drawing of a double hinge assembly in accordance with
the
present invention.
Figure 14 is an isometric view of a conductive holding frame for use with an
active field
polarized media air cleaner in accordance with the present invention.
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Figure 15 is an isometric view of a retaining clip or elongated spline for use
in conjunction
an active field polarized media air cleaners in accordance with the present
invention.
Figure 16 is an assembly drawing illustrating the use of a dielectric media
support frame in
accordance with the present invention.
Figure 17 is a cross-sectional view of an assembly illustrating the use of a
retaining clip or
elongated spline to hold an conductive outer screen in a conductive holding
frame for use
in conjunction with the present invention.
Figure 18 is a cross-sectional view of a dielectric media support frame in
accordance with
the present invention.
Figure 19 is an assembly drawing showing a high-voltage probe and high-voltage
contact
screen in accordance with the present invention.
Figure 20 illustrates the use of the dielectric media support frame in
accordance with the
present invention.
Figure 21 illustrates the rigid conductive outer screen and conductive holding
frame
including a high-voltage probe and high-voltage contact shield in accordance
with the
present invention.
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Figure 22 is an assembly drawing illustrating the use of a dielectric media
support frame in
accordance with a second embodiment of the present invention.
Figure 23 is an assembly drawing illustrating the use of a dielectric media
support frame in
accordance with a third embodiment of the present invention.
Detailed description
A plurality of active field polarized media air cleaner panels (filters),
arranged in a V-bank
configuration 100, in accordance with the present invention is shown in figure
1. The
individual filter panels 101 may be referred to herein as either a "panel",
"filter" and/or an
"air cleaner." A plurality of active field polarized media air cleaners 101
are organized into
a plurality of stackable modules 102 each module having a width W, a height H
and a
depth D that is variable, depending on the application. In particular, the V-
bank 100 in
figure 1 contains eight stackable modules 102 each of which contains eight
individual
active field polarized media air cleaners for a total of 64 air cleaners.
A typical active field polarized media air cleaner is shown in figure 16. A
first pad of
fibrous dielectric material 16A is disposed above a center screen 110. On the
other side of
the center screen 110 is a second pad of dielectric filter material 16B. The
first pad of
dielectric filter material is attached to the dielectric media support frame
120 by a suitable
means such as adhesive material 121A or ultrasonic welding. Above the first
pad of
dielectric filter material 16A is a first conductive outer screen 12A. Below
the second pad
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of dielectric filter material 16B is a second conductive outer screen 12B. The
second pad of
dielectric filter material is attached to the dielectric media support frame
120 by a suitable
means, such as adhesive material 121B or ultrasonic welding. The first
conductive outer
screen 12A is held in place by a first conductive holding frame 116A. The
second
conductive outer screen 12B is held in place by a second conductive holding
frame 116B.
The filter media itself consists of a dielectric media support frame 120, a
first pad of
fibrous dielectric material 16A, a center screen 110 and second pad of
dielectric filter
material 16B. The filter holding frame that holds the filter media consists of
a first
conductive holding frame 116A with a first conductive outer screen 12A, and a
second
conductive holding frame 116B with a second conductive outer screen 12B.
In operation, one terminal of a high voltage power supply 108 is connected to
center screen
110. The other terminal of the high-voltage power supply 108 is coupled to the
first
conductive outer screen 12A and the second conductive outer screen 12B, which
is held
typically at ground potential.
Particles in the incoming air passing through dielectric filter material 16A
and 16B of the
active field polarized media air cleaner of figure 16 are polarized by the
electric field
therein and collected on the first and second pads of dielectric filter
material 16A, 16B.
AERODYNAMIC FRONT COWLING
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A cross-sectional view of an individual module 102 from figure 1 is shown in
figure 2.
Each of the individual active field polarized media air cleaners 110A, 110B,
110C, 110D,
110E, 110F, 110G and 110H are held in place in a V-bank formation. At the
front of the
module 102 a plurality of cowlings holds each filter in place. In particular,
there are two
end cowlings 104A and 104B at the top and bottom of module 102. In between the
two end
cowlings, there are three middle cowlings 106A, 106B and 106C. The aerodynamic
shape
of the cowlings provides for a lower form drag airflow thereby reducing the
static (air
resistance) of the filter.
A detailed view of a center cowling 106C is shown in figure 8. A removable cap
107A is
coupled to the body of the cowling 106C by a dovetail joint. The removable cap
permits
the insertion of a power supply 108C (not shown to scale). This shields the
electronics in
the power supply 108C from the air stream and insulates it from grounded
surfaces of the
outer filter holding frames and system housing. Further, the center cowling
106C provides
a chase or tray for both low and high voltage wires to be run between panels
or modules.
The center cowling 106C includes a first and second attachment points, 107B
and 107C. A
detailed view of an end cowling 104A is shown in figure 6. An end piece 109
(shown in
figure 7) is coupled to the end cowling 104A by a dovetail joint In other
embodiments of
the present invention, the dovetail may be of a variety of shapes such as "L"s
or "T"s or
alternately there may be no mating protrusion and the cowling would be bonded,
screwed
or otherwise attached to the filter holding frames.
A completed assembly of the aerodynamic front cowling coupled to the filter
holding
frames of two active field polarized media air cleaners is shown in figure 9.
First and
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second pads of dielectric filter material 16A 16B and a center screen 110A are
coupled to a
dielectric media support frame 120A. The dielectric media support frame 120A
is held in
place between an upper conductive frame 116A and a lower conductive frame
116B. The
lower conductive frame 116B is coupled to the attachment point 107B of the
center
cowling 106 by a dovetail joint.
Similarly, first and second pads of dielectric filter material 17A, 17B and a
center screen
110B are coupled to a dielectric media support frame 120B. The dielectric
media support
frame 120B is held in place between an upper conductive frame 116C and a lower
conductive frame 116D. The upper conductive frame 116C is coupled to the
attachment
point 107C of the center cowling 106 by a dovetail joint.
The center aerodynamic cowling 106 provides for lower form drag airflow over
the two
active field polarized media air cleaner panels. Further, it decreases
assembly time of the
modules.
REAR DOUBLE HINGE AIR SEAL
At the rear of the module 102 (figure 2) a plurality of double hinges holds
each filter in
place. Each double hinge is comprised of three hinges H1, H2 and H3. As shown
in figure
3, the first hinge H1 has a first attachment point coupled to an upper frame
112A, and a
second attachment point coupled to a lower frame 112B. The hinge H1 has a
pivot point
that permits the lower frame 112B to rotate away from the upper frame 112A so
as to
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allow a replacement filter media to be inserted into the active field
polarized media air
cleaner 110G.
Similarly, as shown in figure 4, the second hinge H2 has a first attachment
point coupled to
an upper frame 114A, and a second attachment point coupled to a lower frame
114B. The
hinge H2 has a pivot point that peimits the upper frame 114A to rotate away
from the
lower frame 114B so as to allow a replacement filter media to be inserted into
the active
field polarized media air cleaner 110H.
A third hinge H3 as a first attachment point coupled to the first hinge H1 and
a second
attachment point coupled to the second hinge H2. The third hinge H3 has a
third pivot
point such that the upper active field polarized media air cleaner (112A,
112B) can rotate
as a unit with respect to the lower active field polarized media air cleaner
(114A, 114B).
The use of double hinges at the rear of module 102 provides for flexibility in
mounting
active field polarized media air cleaners at different angles with respect to
each other. The
double hinge at the rear of the module 102 also provides a good air seal at
the rear of the
filters regardless of the different angles for mounting individual air
cleaners. The positive
seal provided by the double hinge at the rear of the filters reduces blow by,
i.e. the the
portion of the air stream passing by the filter arrangement without passing
through the
filter media.
The double hinge of the present invention is shown in further detail in
figures 10, 11, 12
and 13. Each hinge is formed by a plastic extrusion comprising rigid and
flexible plastic
regions. In figure 10, a first hinge has a first attachment point 140 and a
second attachment
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point 144. The first and second attachment points 140, 144 rotate with respect
to each other
around a pivot area 141. The attachment points 140, 144 are generally rigid
plastic or other
material components as compared to the more flexible material, typically
plastic, of the
pivot area 141. The pivot area 141 is typically made of flexible plastic,
which forms a
pivot point about which the first and second attachment points 140, 144 may
rotate. Other
combinations of materials, for example metal and rubber, are also possible.
As shown in figure 13, two of the hinges of the type shown in figure 10 are
used in
combination with a third hinge to form the double hinge of the present
invention. The first
of such hinges is shown as 140A having a pivot area 141A. The second of such
hinges is
shown as 140B having a pivot area 141B. A third hinge 142A in figure 13 (also
shown in
figure 11) has a first attachment point 142 and second attachment point 145,
which rotate
with respect to each other about pivot area 143. The first attachment point of
hinge 142A is
coupled via a dovetail joint to the first hinge 140A. The second attachment
point of hinge
142A is coupled via a dovetail joint to the second hinge 140B. The assembly of
the first
hinge 140A, the second hinge 140B and the third hinge 142A forms the double
hinge of
the present invention.
Figure 12 illustrates two active field polarized media air cleaner panels
coupled to a double
hinge. The upper 116A and lower 11613 conductive holding frames of a first
filter panel
115A are coupled to the first hinge 140A. In particular, the upper conductive
frame 116A
of the first filter panel 115A is typically an aluminum extrusion (or other
suitable material)
having a shape forming a dovetail joint coupled to the first attachment point
of the first
hinge 140A. The lower conductive frame 116B of the first filter panel 115A is
an
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aluminum extrusion having a shape forming a dovetail joint coupled to the
second
attachment point of the first hinge 140A. As will be discussed elsewhere, the
frames 116A,
116B may also be made of a non-conductive material.
Similarly, the upper conductive frame 116C of the second filter panel 115B is
an
aluminum extrusion having a shape forming a dovetail joint coupled to the
first attachment
point of the second hinge 140B. The lower conductive frame 116D of the second
filter
panel 115B is an aluminum extrusion having a shape forming a dovetail joint
coupled to
the second attachment point of the second hinge 140B.
Thus, the upper conductive frame 116A and the lower conductive frame 116B of
the first
filter panel 115A may rotate with respect to each other about pivot point 141A
of the first
hinge 140A. Similarly, the upper conductive frame 116C and the lower
conductive frame
116D of the second filter panel 115B may rotate with respect to each other
about pivot
point 141B of the second hinge 140B. Finally, by use of the double hinge of
the present
invention, the first filter panel 115A and the second filter panel 115B may
rotate with
respect to each other about pivot point 143 of the third hinge 142A.
Alternatively, the outer frame members 116A, 116B, 116C, 116D may be
constructed of
tubing or "L"s that arc formed, welded, or otherwise constructed into a
substantially
rectangular frame. The external screens (12A, 12B in figure 16) could then be
screwed,
welded, or otherwise secured to the frame members. Similarly the hinge and
cowling
assemblies could instead of dovetail joints, be screwed, bonded, or otherwise
secured to
the sides of the frame. Further, the "dovetail" as disclosed above could be a
"T" or "L" or
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other shape that would provide a positive attachment between the frame member
and the
hinge in the front or the cowling in the rear.
IMPROVED ELECTRODE DESIGN
While various air permeable materials and grids are described in the prior art
(e.g., for use
as the center screen), extruded plastic netting is not disclosed. Extruded
plastic neftings are
made from a wide variety of materials, with either low or high-density
polyethylene, being
among the most common. The extruded plastic netting is typically made
conductive by
adding carbon or other agents to the plastic resins. The resulting
conductivity is variable
and controllable depending on the specific formula used. Fire retardants are
also used to
make the material suitable for use as a center screen electrode in active
field polarized air
filtration applications. Extruded plastic netting material has been found to
have many
advantages from manufacturing and operational standpoints for use as an
electrode in an
active field polarized media air cleaner. The primary advantages of extruded
plastic netting
derive from the shape and form of the members of the netting (particularly the
lack of
sharp edge shapes formed around the openings of the netting).
When using high voltage potentials between electrodes, a number of factors
contribute to
the propensity for arcing, spraying and corona discharge and the point at
which it occurs.
The important factors include the shape, consistency, flatness, and spacing of
the members
or fibers of the electrodes. Sharp edges, burrs, kinks, stray fuzz or fibers,
points, etc. all
promote spraying and corona discharge. Because of its fabrication process,
extruded plastic
netting is substantially free of these defects. The resultant center screen
grid therefore
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allows for maximum operational voltages and therefore higher field strengths
and greater
filter efficiencies. Specifically, it has been found that a center screen made
from an
extruded plastic netting can carry an operational voltage 20-30% higher than a
carbon
impregnated foam and up to 40% higher than an aluminum screen. Although a low-
density polyethylene is an excellent material for this application, as it lies
substantially flat,
other materials substantially lacking in sharp features such as sharp edges,
burrs, kinks,
stray fuzz or fibers, points, etc. will also be appropriate.
RESISTIVE CENTER SCREEN AND VARIABLE HIGH VOLTAGE POWER SUPPLY
The aerodynamic cowlings shown in figure 2 are hollow, and, in each middle
cowling
106A, 106B and 106C there is a respective high-voltage power supply 108A, 108B
and
108C. The three high voltage power supplies 108A, 108B and 108C are shared
among the
eight active field polarized media air cleaners 110A, 110B, 110C, 110D, 110E,
110F,
110G and 110H. See figure 5. It should be noted that there could be one power
supply for
several or all panels in a module or all modules in an HVAC system or one
power supply
per panel. The goal is a balance between operational redundancy and overall
system cost.
Therefore, the present arrangement provides for two or more panels to share a
single power
supply without one panel being able to adversely impact the operation of the
other panels
sharing the same power supply.
In accordance with one aspect of the present invention, the center screen of
each active
field polarized media air cleaner is resistive rather than conductive. As
shown in figure 5,
the eight active field polarized media air cleaners 110A, 110B, 110C, 110D,
110E, 110F,
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110G and 110H are represented by the symbols for a resistor. In particular,
high-voltage
power supply 108A is coupled to the center screen for the three active field
polarized
media air cleaners 110A, 110B and 110C. High-voltage power supply 108B is
coupled to
the center screen for the two active field polarized media air cleaners 110D
and 110E.
Finally, high-voltage power supply 108C is coupled to the center screen for
the three active
field polarized media and cleaners 110F, 110G and 110H.
The shared high-voltage power supply in combination with a resistive center
screen and.
active field polarized media air cleaner permits the filters to still continue
to operate in the
event that the center screen of one of the air cleaners is shorted to ground.
For example, if
the center screen of filter 110H were shorted to ground (as illustrated by
short circuit 110S)
the remaining resistance of the portion of the center screen between the short
110S and
high-voltage power supply, would permit high-voltage power supply 108C to
continue
operating. Thus, even if the center screen of filter 110H has been shorted to
ground, the
other filters connected to the same power supply (namely 110F and 110G) would
continue
to operate.
If, as in the prior art, the center screen was highly conductive, then a short
circuit of one of
the center screens would result in the collapse of the voltage from the high-
voltage power
supply thereby disabling all of the filters connected to thc same high-voltage
power supply.
To avoid a short circuit in the center screen of one filter from disabling
other filters, prior
art banks of filters provided for one power supply per filter. The resistive
center electrode
(screen) could be made of a variety of materials. For example, an extruded
plastic net or
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carbon impregnated foam or mesh. In a further embodiment of the invention the
center
screen would have odor-absorbing properties, such as a carbon impregnated foam
or mesh.
Furthermore, high-voltage power supplies 108A, 108B and 108C are made
variable. That
is, the output voltage provided by power supply 108A to the center screens of
active field
polarized media air cleaners 110A, 110B and 110C is adjustable. Similarly, the
output
voltage provided by power supply 108B to the center screens of active field
polarized
media air cleaners 11013 and 110E is adjustable. In similar manner the output
voltage
provided by power supply 108C to the center screens of active field polarized
media air
cleaners 110F, 110G and 110H is adjustable.
Adjustability of the high-voltage potential applied to the center screens of
the active field
polarized media air cleaners permits an optitnintion of electrostatic field
strength.
Generally speaking, the highest possible voltage before arcing occurs is the
most desirable
choice. However, the highest possible voltage is dependent on several factors
such as
altitude and humidity. A higher voltage level is desirable where the filters
are installed at a
sea level location. Conversely, at higher altitude a lower voltage is
desirable. The optimum
voltage is also related to humidity. In dryer climates, a higher voltage may
be applied to
the filters without arcing. In climates experiencing higher humidity
conditions a lower
voltage to prevent arcing is desirable. The adjustability of high-voltage
power supplies
108A, 108B and 108C permits the selection of an optimal electrostatic field
under
appropriate altitude and climate conditions. Further, the arcing voltage will
be a function of
the materials of both the charged electrode and the media. Variability of the
power supply
allows for the optimization of the voltage depending on the materials used as
well.
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DIELECTRIC MEDIA SUPPORT FRAME
A cross-sectional view of a dielectric media support frame 120 in accordance
with the
present invention is shown in figure 18. The dielectric media support frame,
which is
typically formed by extrusion, includes vertical flanges 120A and 120D. The
dielectric
media support frame 120 also includes horizontal flanges or shelves 120C1 and
120C2.
The horizontal flanges or shelves 120C1 and 120C2 form a recess 122. Opposite
the recess
122 is a protrusion 124 having flexible fins 126 on both sides.
Figure 16 illustrates the use of the dielectric media support frame of the
present invention
in an active field polarized media air cleaner. A first function of the
dielectric media
support frame 120 is to permit the center screen 110 of an active field
polarized media air
cleaner to extend all the way to the edge of the filter media. Another
function of the
dielectric media support frame 120 is to prevent arcing to the upper or lower
conductive
holding frames 116A, 116B and reduce the spraying of corona at the edges of
the center
conductive screen 110. To accomplish these functions, the center screen 110 is
held in
place on one of the shelves 120C1, 120C2 forming the recess 122 of the
dielectric media
support frame 120.
An alternate embodiment of a dielectric media support frame 120X in accordance
with the
present invention is shown in figure 22. In lieu of a recess, the dielectric
media support
frame 120X has a single horizontal flange or shelf 120Z. The first pad of
dielectric filter
material 16A, the center screen 110 and the second pad of dielectric filter
material 168 rest
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on shelf 120Z. The first pad of dielectric filter material is attached to the
dielectric media
support frame 120 by a suitable means such as adhesive material 121X or
ultrasonic
welding.
Yet another alternate embodiment of a dielectric media support frame 120Y in
accordance
with the present invention is shown in figure 23. In figure 23 the use of
adhesive material
(121A and 121B in figure 16, or 121X in figure 22) is eliminated. The recess
122Y is made
large enough so that the first pad of dielectric filter material 16A, the
center screen 110 and
the second pad of dielectric filter material 16B are positioned in the recess
122Y of the
dielectric media support frame 120Y.
Alternatively, the insulating/conductive properties of the dielectric media
support frame
(120 in figure 16) and the upper and lower conductive holding frames (116A,
116B in
figure 16) could be reversed. That is, the media support frame 120 could be
conductive (or
not a complete insulator) and the upper and lower holding frames 116A, 116B
could be an
insulator (i.e. a dielectric or non-conductive material) or be insulated by
having a holding
clip wrap around the mating surfaces of the holding frames or by having an
insulating
material applied to them. In the latter case, the media support frame 120 may
be omitted
with the center screen 110 sandwiched between upper 116A and lower 116B non-
conducting and/or insulated holding frames.
A second function of the dielectric media support frame is to form a positive
seal between
the upper conductive holding frame 116A and the lower conductive holding frame
116B.
For the latter purpose, the protrusion 124 and flexible fins 126 of the
dielectric media
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support frame form a positive seal between the upper conductive holding frame
116A and
the lower conductive holding frame 116B. Alternatively, the protrusion from
the dielectric
media support frame could press against the upper conductive holding frame
116A and/or
the lower conductive holding frame 116B rather than being pressed between the
upper and
lower conductive holding frames 116A, 116B. In general, protrusion 124 is any
shape that
creates a positive seal between the media support frame 120 and the holding
frame(s)
116A, 116B.
FLAT CONDUCTIVE OUTER SCREEN
A first conductive outer screen 12A is held in place by the upper conductive
frame 116A.
A second conductive outer screen 12B is held in place by the lower conductive
frame
116B. For the sake of clarity, the retaining clips (118 in figures 15 and 17)
that hold the
outer screens 12A and 12B to upper and lower conductive frames 116A and 116B
respectively are omitted in figure 16. A cross-sectional view of the retaining
clip 118 is
illustrated in figure 15. A detail view of how the retaining clip 118 is
assembled with the
conductive frame 116 is shown in figure 17. First, the conductive outer screen
12 is
inserted into the recess of the conductive holding frame 116. Thereafter, the
retaining clip
118 is rotated into place. The retaining clip 118 holds the conductive outer
screen 12 in the
conductive holding frame 116. The retaining clip 118 is an elongated spline
that runs the
entire length of the frame.
The conductive outer screen 12 (in figure 17) is made of a sufficiently rigid
material so as
to lie substantially flat when placed against the pad of fibrous dielectric
material (16A or
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16B in figure 16). The conductive outer screen 12 permits air to flow through
it. The
conductive outer screen 12 may be made of perforated solid sheet material or
of expanded
sheet material, for example expanded metal. Expanded metal is sheet material
that is slit
and pulled apart so that the slits stretch open to form passageways for
airflow.
The conductive outer screen 12A, 12B being relatively rigid compared to the
pad of
fibrous dielectric material 16A, 16B, compresses the dielectric material
preventing a
bowing or "pillow" effect. Thus, when the conductive holding screens 116A and
116B are
closed around the pads of dielectric filter material 16A and 16B, the
conductive outer
screens 12A and 12B are substantially flat and substantially parallel to each
other.
Substantially flat conductive outer screens 12A, 12B provides for a more
uniform field
throughout the active field polarized media air cleaner. In the prior art, the
outer screen
flexes into a pillow shape, in which case the maximum high-voltage is limited
by the
minimum spacing (typically near the edges). In the prior art, most of the
screen area in the
middle of the active field polarized media air filter will be much further
away from the
center screen (as compared to the area near the edges) thus reducing the
electrostatic field
which in turn reduces the efficiency of the filter. As compared to the prior
art, the
electrostatic field of the present invention will be more uniform throughout
the filter media
and can be sustained at a higher voltage and therefore support a greater
electrostatic field.
IMPROVED HIGH VOLTAGE CONTACT WITH CENTER SCREEN
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As indicated in figure 16, a first terminal of a high-voltage power supply 108
is coupled to
the center screen 110. In the prior art, a high-voltage probe would pass
through the
conductive outer screen, piercing the pad of fibrous dielectric material 16A
or sliding
between the two pads 16A and B to make contact by pressing against the center
screen
110. Often, such contacts were unreliable. If the high-voltage probe failed to
make contact
with the center screen, then there would be no electrostatic field across the
pads of
dielectric filter material 16A, 16B greatly reducing the filter efficiency.
Furthermore, the
sharp point of a high-voltage probe often resulted in the spraying of corona
and/or arcing
to the conductive outer screens 12A, 12B. Further, because the center screen
material is
typically sparse and air permeable and because the contact area was relatively
small, arcing
could lead to an erosion of the center screen and a loss of contact.
In accordance with the present invention, a conductive disc is attached to the
center screen
in the area where the high voltage probe would make contact. See figure 19.
Adding a
contact area to the center screen allows for the use of a more resilient
material and further,
increase the area of contact with the charged electrode (center screen).
When a relatively sparse filter media material is used, a piercing or
penetrating high-
voltage probe may be employed, and the disc(s) would be on either side of the
center
screen. However, with denser filter media, it is preferable to have one
conductive disc
press against the denser filter media and another conductive disc press
against the center
screen. The two conductive discs would be mechanically an electrically
connected to each
other.
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In accordance with the present invention, a high-voltage contact protected by
a high-
voltage shield to reliably contact the center screen is shown in figure 19. A
rivet 136 is
passed through a hole in the center screen 13. A conductive disk (e.g.
titanium) 133
secures the rivet 136 to the center screen 13, which provides a good
connection between
the rivet 136 and the charged electrode or center screen 13. Alternatively, a
second metallic
disk can be placed beneath the head of the rivet.
In a further embodiment of the invention, a high-voltage probe 130 passes
through the
conductive outer screen 12A and terminates in a high-voltage contact 134. A
high-voltage
shield of insulating dielectric material 132A surrounds the high-voltage
contact 134.
Similarly, a high-voltage shield of insulating dielectric material 132B
surrounds lower end
of the rivet 136 and the metallic disk 133. Alternatively, the high-voltage
probe may be
routed on the inside of the conductive outer screens 116A, 116B.
A top view of the filter media in figure 19 is shown in figure 20. A
dielectric media
support frame 120 surrounds the pad of dielectric filter material 16A. The
rivet or
attachment means 136 passes through the pad of dielectric filter material 16A.
A top view of the frame that holds the filter media in figure 19 is shown in
figure 21. Four
conductive outer filter holding frame pieces 116 and four plastic end caps 128
form a
frame to hold the conductive outer screen 12. The high-voltage contact 134 is
positioned
within the insulating high-voltage shield 132A.
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In operation, when the conductive outer filter holding frames 116A and 116B
(figure 19)
are closed around the filter media (120, 16A, 13 and 16B) the high-voltage
contact 134
contacts the head of the rivet 136. Also, the high-voltage shields 132A and
132B slightly
compress the pads of dielectric filter material 16A and 16B. The high-voltage
contact 134
assures a reliable connection with the head of the rivet 136. The insulating
high-voltage
shields I32A, 132B reduce the spraying of corona from the tip of the high-
voltage contact
134. Furthermore, the insulating high-voltage shields 132A, 132B reduce the
chances of
arcing from the high-voltage contact 134 to the conductive outer screens 12A
and 12B.
The high-voltage contact 134 is typically made of rigid titanium or other
resilient material.
In making contact with the head of the rivet 136, the center screen 13 may
flex slightly.
Alternatively, the high-voltage contact 134 can be a spring contact to reduce
the flexing of
the center screen 13. Alternative arrangements for the contact area 136 on the
center screen
13 include a conductive disk on the top side of the center screen 13, a pair
of conductive
discs, one on the top and the other on the bottom of the center screen, with a
fastener
passing through the center screen and holding the two discs together. The key
point is that
the rigidity of the high-voltage probe 134 or the rigidity of the external
conductive outer
screens or both in conjunction force a positive mechanical contact between the
end of the
high-voltage probe 134 and the disc or disc/rivet combination 136. The result
is a firm
contact that cannot be compromised by vibration, or media movement or center
screen
(electrode) movement.
