Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Counter-Flow Energy Recovery Ventilator (ERV) Core
Field of the Invention
[0001] The present invention relates to heat and humidity exchangers. Example
embodiments
provide energy recovery ventilator (ERV) cores comprising a water-permeable
membranes and
ERV systems that include such cores. The invention may be applied in any of a
wide variety of
applications where heat and humidity exchange is required. Examples include
heat and moisture
recovery in building ventilation systems, humidification and heat transfer in
fuel cells, separation
of gases, and desalination treatment of water.
Background
[0002] Heat and humidity exchangers (also sometimes referred to as
humidifiers) have been
developed for a variety of applications, including building ventilation
(HVAC), medical and
respiratory applications, gas drying, and more recently for the humidification
of fuel cell
reactants for electrical power generation. Many such devices involve the use
of a water-
permeable membrane across which heat and moisture may be transferred between
fluid streams
flowing on opposite sides of the membrane.
[0003] Planar plate-type heat and humidity exchangers use membrane plates that
are constructed
of planar, water-permeable membranes (for example, Nafion , cellulose,
polymers or other
synthetic membranes) supported with a spacer and/or frame. The plates are
typically stacked,
sealed and configured to accommodate intake and exhaust streams flowing in
either cross-flow
or counter-flow configurations between alternate plate pairs, so that heat and
humidity are
transferred between the streams via the membrane.
[0004] Other types of exchangers include hollow tube humidifiers and enthalpy
wheel
humidifiers. Hollow tube humidifiers have the disadvantage of high pressure
drop, and enthalpy
wheels tend to be unreliable because they have moving parts and tend to have a
higher leak rate.
[0005] A heat recovery ventilator (HRV) is a mechanical device that
incorporates a heat and
humidity exchanger in a ventilation system for providing controlled
ventilation into a building.
The heat and humidity exchanger heats or cools incoming fresh air using
exhaust air. Devices
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that also exchange moisture between the incoming fresh air and the exhaust air
are generally
referred to as Energy Recovery Ventilators (ERVs), sometimes also referred to
as Enthalpy
Recovery Ventilators. An ERV may remove excess humidity from the ventilating
air that is
being brought into a building or it may add humidity to the ventilating air.
ERVs may be used to
save energy and/or to improve indoor air quality in buildings.
[0006] ERVs typically comprise an enclosure, fans to move the air streams,
ducting, as well as
filters, control electronics and other components. The key component in the
ERV which transfers
the heat and humidity between the air streams is called the core or the
exchanger. The two most
common types of ERVs are those based on planar membrane plate-type devices and
those based
on rotating enthalpy wheel devices, both mentioned above. Planar plate-type
ERV cores use
layers of static plates that are sealed and configured to accommodate the
intake and exhaust
streams flowing in either cross-flow or counter-flow configurations between
alternate pairs of
plates.
[0007] FIG. 1 shows an example of a planar plate-type heat and humidity
exchanger made from
stacked planar sheets of membrane 3 with rigid corrugated spacers 6 inserted
between the
membrane sheets. The spacers maintain proper sheet spacing as well as defining
airflow channels
for wet and dry streams on opposite sides of each membrane sheet, in a cross-
flow
arrangement, as indicated by broad arrows 1 and 2 respectively. The stack is
encased within a
rigid frame 4.
[0008] A benefit of planar plate-type heat and humidity exchanger designs for
ERV, fuel cell,
and other applications, is that they are readily scalable because the quantity
(as well as the
dimensions) of the modular membrane plates can be adjusted for different end-
use applications.
Existing planar plate-type ERV cores are bulky and less effective than would
be desired in
facilitating enthalpy exchange.
[0009] Another approach to heat and humidity exchanger design is to
incorporate a pleated
water-permeable material in the exchanger. For example, US Patent No.
4,040,804 describes a
heat and moisture exchanger for exchanging heat and moisture between incoming
and outgoing
air for room ventilation. The exchanger has a cartridge containing a single
pleated sheet of water-
permeable paper. Air is directed in one direction along the pleats on one side
of the pleated
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paper, and the return air flows in the opposite direction along the pleats on
the other side of the
pleated paper. The ends of the cartridge are closed by dipping them in wax or
a potting
compound that can be cast and that adheres to the paper. The pleats are
separated or spaced, and
air passages between the folds are provided, by adhering grains of sand to the
pleated paper.
[0010] FIG. 2 shows an example of a heat and humidity exchanger suitable for
energy recovery
ventilator (ERV) applications which comprises a pleated water-permeable
membrane cartridge
disposed in a housing. A plastic flow field element can be disposed within
some or all of the
folds of the pleated membrane for directing the stream over the inner surfaces
of the folds, as
described in US Patent Application Publication No. 2008/0085437. The flow
field element
controls the relative flow paths of the two streams on opposite sides of the
membrane and
enhances flow distribution across one or both membrane surfaces. The flow
field elements can
also assist in supporting the pleated membrane and controlling the pleat
spacing within the
pleated membrane cartridge. In the embodiment shown in FIG. 2, a first fluid
stream is directed
in a U-shaped flow path 122 from an inlet port 124 on one face of housing 115
to an outlet port
128 on the same face of housing 115. The first fluid stream is thus directed
from inlet port 124
into a set of substantially parallel folds 126 on one side of pleated membrane
cartridge 120, then
along the length of the folds 126, and then out via port 128. A second fluid
stream is similarly
directed in a substantially U-shaped flow path 132 from an inlet port 134 to
an outlet port 138 on
the same face of housing 115 (both ports 134 and 138 being on the opposite
face of housing 115
from ports 124 and 128). The second fluid stream is directed from port 134
into a corresponding
set of substantially parallel folds 136 on the other side of pleated membrane
cartridge 120, then
along the length of the folds 136, and then out via port 138. The flow path
122 of the first fluid
stream is in a substantially counter-flow configuration relative to flow path
132 of the second
fluid stream.
[0011] There are also examples of ERV cores with stacked planar membrane
sheets that operate in a
substantially counter-flow configuration to transfer heat and humidity across
planar membrane
sheets. The membrane sheets can be interleaved with rigid plastic spacers that
define flow
channels as described in US Patent No. 7,331,376.
[0012] The flow field inserts or spacers used in the heat and humidity
exchangers described
above often provide controlled or directional gas flow distribution over the
membrane surface.
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However, the fluid flow paths across the membrane surface tend to be quite
tortuous and
turbulent, so the flow can be quite restricted and the pressure drop across
the overall apparatus
can be significant. If there are many closely-spaced ribs to support the
membrane, the ribs will
tend to impede or block the fluid flow, and also increase pressure drop. With
more widely-
spaced ribs the membrane can deflect into the channel also increasing the
pressure drop.
Therefore, the use of non-permeable flow field inserts is generally
undesirable.
[0013] Compact heat and humidity exchangers or HRV cores in which there is
heat transfer
between channels in two dimensions in counter-flow are described in US Patent
No. 5,725,051 in
which the heat transfer medium is a thermoformed rigid plastic sheet. The
plastic is impermeable
to water so there is no humidity transfer across the medium. In another
similar example, the heat
transfer medium is aluminum, but again there is no humidity transfer because
the medium is not
water-permeable.
[0014] As described above, conventional ERV cores with a water-permeable
membrane require a
spacer to support the membrane. Spacers generally impede or block heat and
moisture transfer
and they can increase the pressure drop if there is deflection of the membrane
into the channel.
[0015] The inventors have recognized that there remains a need for cost
effective and efficient
ERV systems and cores.
Summary
[0016] This invention has several aspects and encompasses a wide range of
specific
embodiments. Aspects of the invention provide building ventilation systems;
heat and humidity
exchangers; cores for heat and humidity exchangers; sub-assemblies for cores
of heat and
humidity exchangers; and methods for fabricating heat and humidity exchangers.
[0017] One example aspect provides a heat and humidity exchanger comprising a
core. The core
comprises a plurality of water vapor-permeable sheets. The sheets are layered
or stacked. at least
some of the sheets are pleated to provide a plurality of groups of channels
extending through the
core. Each of the plurality of groups of channels comprises channels defined
between two
adjacent ones of the sheets and extending along the pleats of at least one of
the pleated sheets. A
plurality of plenums is formed on opposed sides of the core. The plenums on
each of the opposed
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sides of the core are configured such that the channels of groups of channels
on opposing sides
of the same one of the sheets are fluidly connected to different ones of the
plenums. The plenums
are defined at least in part by manifold members attached along opposite edges
of the sheets, at
least one of the manifold members comprising a sheet that is connected to and
follows an edge of
one of the pleated water vapor-permeable sheets.
[0018] Another aspect provides a heat and humidity exchanger comprising a core
comprising a
plurality of channels. A first group of the plurality of channels extends from
a first plenum
through the core to a second plenum. A second group of the plurality of
channels extends from a
third plenum through the core to a fourth plenum. Each of the plurality of
channels in the first
group has walls in common with a plurality of the channels of the second group
and each of the
plurality of channels in the second group having walls in common with a
plurality of the
channels of the first group. The plurality of channels is defined by a
plurality of water vapor-
permeable membrane sheets. At least one of the water vapor-permeable membrane
sheets being
pleated. The pleated water vapor-permeable membrane sheet defines a plurality
of the walls of
each of a plurality of the first group of channels. The first and fourth
plenums are separated at
least in part by a manifold sheet that is connected to and follows an edge of
the pleated water
vapor-permeable membrane sheet.
[0019] Another aspect provides a heat and humidity exchanger comprising a core
comprising a
plurality of channels each having a triangular cross-section. A first group of
the plurality of
channels extends from a first plenum through the core to a second plenum. A
second group of the
plurality of channels extendsfrom a third plenum through the core to a fourth
plenum. Each of
the plurality of channels in the first group has walls in common with a
plurality of the channels
of the second group and each of the plurality of channels in the second group
has walls in
common with a plurality of the channels of the first group. Each of the common
walls is water
vapor-permeable.
[0020] Another aspect provides a heat and water vapor exchanger comprising a
core structure
comprising a plurality of layered water vapor permeable sheets attached
together to form a self-
supporting structure. A plurality of the layered water vapor permeable sheets
are pleated such
that triangular channels extend through the core. A manifold structure
comprises manifold
members attached along edges of the vapor permeable membrane sheets of the
core. The
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manifold members form stacked plenums such that channels extending through the
core between
different pairs of adjacent ones of the water vapor permeable membrane sheets
are in fluid
communication with different ones of the plenums.
[0021] Further aspects of the invention and features of example embodiments of
the invention
are described below.
Brief Description of the Drawings
[0022] The accompanying drawings illustrate non-limiting embodiments of the
invention.
[0023] FIG. 1 is an isometric view of a heat and humidity exchanger comprising
a stack of planar
membrane layers interleaved with rigid corrugated spacers (prior art).
[0024] FIG. 2 is an isometric view of a heat and humidity exchanger comprising
a pleated
membrane cartridge disposed in a housing (prior art).
[0025] FIG. 3 is a schematic cross-sectional view of a pleated water-permeable
membrane.
[0026] FIG. 4A is a schematic cross-sectional view illustrating two pleated
water-permeable
membrane sheets that can be joined to form a diamond-shaped channel. FIG. 4B
is a schematic
cross-sectional view illustrating four pleated water-permeable membrane sheets
arranged to form
an array of diamond-shaped channels. FIG. 4C is a schematic cross-sectional
view of a pleated
membrane combination like those shown in FIGS. 4A and 4B with flattened peaks.
FIG. 4D is a
non-isometric 3D view of an embodiment of an ERV core showing the central
pleated membrane
section with diamond- or parallelogram-shaped channels.
[0027] FIG. 5A is a schematic cross-sectional view illustrating two box-
pleated water-permeable
membrane sheets that can be joined to form channels of a square or rectangular
cross-section.
FIG. 5B is a schematic cross-sectional view illustrating four pleated water-
permeable membrane
sheets arranged to form an array of square- or rectangular-shaped channels.
[0028] FIG. 6A is a schematic cross-sectional view illustrating a pleated and
a flat sheet of
water-permeable membrane that can be joined to form channels of triangular
cross-section. FIG.
6B is a schematic cross-sectional view showing a stack of alternating pleated
and flat sheets of
water-permeable membrane forming a sub-assembly of channels of triangular
cross-section.
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[0029] FIG. 7A is a simplified exploded 3D view of a pair of pleated membranes
forming
parallel channels with a diamond-shaped cross-section, with manifold sections
attached to each
membrane sheet. FIG. 7B shows a simplified 3D partial cut-away view of the
assembly of FIG.
7A with two fluid streams following through the diamond-shaped channels in
counter-flow.
[0030] FIG. 8 is a plan view of the upper manifold/membrane assembly shown in
FIGs. 7A &
7B.
[0031] FIG. 9A is a cross-sectional view at location A-A in FIG. 8. FIG. 9B
shows a view
looking down the channels from a cross-section at location B-B in FIG. 8. FIG.
9C shows a view
looking down the channels from a cross-section at location C-C in FIG. 8. FIG.
9D is a cross-
sectional view at location D-D in FIG. 8 showing the zig-zag cross-section of
the pleated
membrane.
[0032] FIG. 10 is a diagram showing how the plenums created between adjacent
manifold
sections in a stacked core assembly (similar to that shown in FIG. 7)
correspond to the diamond-
shaped channels that they are supplying/discharging.
[0033] FIG. 11A is a simplified exploded isometric view of an assembly like
that of FIG. 7A, but
interleaved with an additional flat membrane sheet forming parallel channels
with a triangular-
shaped cross-section. FIG. 11B shows the flow of the two fluid streams on
opposite sides of a
manifold section that has ribs to direct the flow. FIG. 11C is a plan view
illustrating the flow
pattern of the two fluid streams in an assembly similar to the one shown in
FIG. 11A.
[0034] FIG. 12 is a diagram showing how the plenums created between the flat
membrane sheets
and adjacent manifold sections in a stacked core assembly (similar to that
shown in FIG. 11)
correspond to the triangular-shaped channels that they are
supplying/discharging.
[0035] FIG. 13 shows how the plenums created between adjacent manifold
sections in a stacked
core assembly similar to that shown in FIG. 5B would correspond to the square-
shaped channels
that they are supplying/discharging.
[0036] FIG. 14A is a plan view of a manifold/membrane subassembly with a
central pleated
membrane and a manifold section at each end, where the channels have a diamond
cross-section.
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FIG. 14B is a plan view of a manifold/membrane subassembly with a central
pleated membrane
and a manifold section at each end, where the channels have a triangular cross-
section.
[0037] FIG. 15 is a photo of a compression molded layer made entirely from a
formable water
permeable membrane.
[0038] FIG. 16 is a graph illustrating the performance of an ERV core
comprising a prototype
stacked pleated membrane core.
[0039] FIG. 17 is a graph illustrating the pressure drop for two prototype ERV
cores comprising
stacked triangular-pleated membranes.
[0040] FIG. 18 is a graph illustrating the performance of the two prototype
ERV cores
comprising stacked triangular-pleated membranes.
Detailed Description
[0041] FIGs. 1 and 2 are described above.
[0042] Performance of heat and humidity exchangers can be improved, and the
required heat and
humidity exchanger size can be reduced, by providing heat and humidity
exchanger
constructions that provide one or more of: enhancing flow distribution across
one or both
surfaces of heat and vapor exchange membranes; controlling the relative flow
paths of fluids on
opposite sides of heat and vapor exchange membranes; providing improved
support for heat and
vapor exchange membranes; reduced pressure drop across the heat and humidity
exchanger;
increased membrane surface area per unit volume of the exchanger; and/or
membranes that have
improved water transport and other properties.
[0043] Certain embodiments disclosed herein provide ERV cores with water-
permeable
membranes configured to allow multi-dimensional transfer of moisture as well
as heat. Multi-
dimensional transfer across a water-permeable membrane can provide more
efficient energy
recovery and allow the ERV core to be more compact for a given level of
performance.
Embodiments as described herein may be used to transfer heat and moisture
between two
streams flowing in a counter-flow configuration for more efficient energy
recovery.
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[0044] Designs and manufacturing methods as described herein may be applied to
provide ERV
core constructions that are free of spacers. In such constructions, thin,
flexible membranes may
be shaped and attached to one another to provide self-supporting layers and
core structures that
are robust enough to withstand significant pressure differentials.
[0045] FIG. 3 is a cross-sectional view showing a sheet of pleated water-
permeable membrane.
The pleated membrane defines the walls of channels through which a fluid
stream (e.g. wet or
dry air) can be directed to flow, and across which heat and humidity may be
exchanged. The
membrane may be attached to plastic manifold sections (as described in more
detail below) to
direct the fluid stream from inlet ports into the channels and from the
channels to outlet ports.
The membrane should be sufficiently thin to allow adequate exchange of heat
between the two
streams, driven by the temperature gradient between the streams. The membrane
is also water-
permeable to allow moisture to pass through the material, driven by the vapor
pressure
differential or water concentration gradient between the two streams. Thinner
membranes will
tend to have higher heat and moisture transport rates. Ideally the membrane is
also impermeable
to air, and contaminant gases, to prevent the mixing and crossover of the two
streams through the
membrane.
[0046] In the present approach, layers of pleated membrane are stacked to form
a sub-assembly
or cartridge for disposition in a heat and humidity exchanger. The pleated
membrane may be
prepared, for example, by folding a sheet of membrane such as with heat
and/pressure to provide
plastic deformation to the folded edge (e.g. with push-bar pleating
technology), or by forming a
membrane to have pleats, such as with gears or score-and-pleat rotary pleating
technology. The
angle of the pleats may be varied. For a constant channel hydraulic diameter,
larger pleat tip
angles allow more layers of membrane to be provided in a core of a certain
height, but with less
overall membrane area per layer. Conversely, for a constant channel hydraulic
diameter, smaller
pleat tip angles will provide more membrane area per layer but fewer layers
for the same core. In
some embodiments, the pleats are formed to have angles in the range of 70
degrees to 100
degrees. Some embodiments have pleat angles in the range of 50 to 70 degrees
(e.g. 60 degrees).
Pleat tip angles close to 60 degrees can advantageously provide improved heat
and mass transfer,
with the high use of membrane area, for a given core height..
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[0047] FIG. 4A is a cross-sectional view illustrating two pleated water-
permeable membrane
sheets that can be joined to form channels with a diamond-shaped cross-section
(or a
parallelogram-shaped cross-section). The peaks of one pleated membrane can be
attached to the
peaks of the adjacent pleated membrane, for example, by gluing, bonding, heat-
welding or
sealing. In this configuration, the joined pleated membrane sheets are self-
supporting and require
no spacer or supporting material other than the membrane itself. Adhering, or
otherwise
attaching, peaks in one pleated membrane sheet to peaks in adjacent membrane
sheets can
provide sufficient strength for the membrane channel to withstand a pressure
differential. In
some embodiments, a polyurethane glue is used to adhere the peaks of one
pleated membrane to
the corresponding peaks of an adjacent membrane. Other suitable glues or
adhesives can also be
used for the same purpose. Glues that are permeable to water vapor will allow
water transport to
occur even in the regions where the pleated membranes are attached to one
another. Glues that
are permeable to water vapor transfer may be of the class that are polymer-
based, with soft chain
sections that allow water to pass through, such as PermaxTM from Lubrizol.
Depending on the
membrane material, it may be possible to weld the pleated membrane sheets to
one another at the
peaks. For example, thermal, vibration or ultrasonic welding may be used.
[0048] FIG. 4B is a cross-sectional view illustrating four pleated water-
permeable membrane
sheets arranged to form an array of diamond-shaped channels. Two different
fluid streams can be
directed through alternate channels in a counter-flow configuration. Flow into
the plane of the
paper is indicated by a cross, and flow out of the plane of the paper is
indicated by a dot. In such
an array each diamond-shaped channel shares its walls with as many as four
other channels. Heat
and humidity can be transferred across all four walls of the channel through
the water-permeable
membrane. For a given channel, the flow in adjacent channels is in the
opposite direction to the
flow in the given channel. This is referred to as a counter-flow
configuration.
[0049] Each fluid stream is independent of the other and does not depend on
the peak-to- peak
adhesion of the pleated membranes to provide a seal, so there is reduced
potential for cross-
leakage between the two streams. If a peak seal were not perfect, any leak
into an adjacent
channel would be a channel carrying the same fluid, and would not cause mixing
of the two
streams or adversely affect heat or mass transfer.
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[0050] FIG. 4C is a cross-sectional view also showing an arrangement of water-
permeable
membrane sheets forming an array of diamond-shaped channels. In this example,
the peaks of
the diamonds, along the pleated lines of the membrane, are flattened to
provide a larger area for
attachment to peaks in adjacent membrane sheets. This embodiment can provide a
mechanically
stronger sub-assembly of membrane sheets with substantially the same sensible
and latent
transfer as the arrangement shown in FIG. 4B. An alternative to flattening the
peaks is to form
the peaks of one pleated membrane layer, with a small trough or valley that
extends along the
crests of the peaks. Peaks of an adjacent layer may then nest into the troughs
or valleys. Such
troughs or valleys may be formed in the crests on only one face of the pleated
membrane layer or
in the crests on both faces of the pleated membrane layer.
[0051] FIG. 4D shows a 3D representation of a stacked pleated membrane sub-
assembly with
diamond-shaped channels. Even though it can be made using a thin, flexible
membrane material,
the structure is self-supporting. This approach of stacking and gluing (or
otherwise attaching)
pleated membrane sheets provides a very high membrane surface area per unit
volume of the
exchanger providing a device with high effectiveness of heat and moisture
transfer.
[0052] FIG. 5A is a cross-sectional view illustrating two box-pleated water-
permeable membrane
sheets that can be joined to form channels with a square or rectangular cross-
section. In this
example, the box-pleats form a castellation, and the castellation pattern is
offset between
adjacent membrane sheets allowing the sheets to be joined to form square or
rectangular
channels. Each pleat line on one of the membrane sheets is glued, or otherwise
attached, to the
corresponding pleat line on an adjacent membrane sheet. Like the diamond
configuration
described above, the glued membrane sheets are self-supporting and require no
spacers or other
material to provide rigidity or support, and the channels are able to
withstand pressure
differentials.
[0053] FIG. 5B is a cross-sectional view illustrating four box-pleated water-
permeable
membrane sheets arranged to form an array of square-shaped or rectangular-
shaped channels.
Two different fluid streams can be directed through alternate channels in a
counter-flow
configuration. As before, flow into the plane of the paper is indicated by a
cross, and flow out of
the plane of the paper is indicated by a dot. Each channel shares its walls
with as many as four
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other channels. Heat and humidity can be transferred across all four walls
through the water-
permeable membrane.
[0054] The square- and diamond- shaped channels arrangements are topologically
and
functionally equivalent, and sub-assemblies with square channels can be
oriented during
assembly to provide diamond channels and vice versa. Other channel shapes such
as
parallelograms may also be created by stacking layers of pleated membranes.
[0055] In some embodiments, the pleated membrane sheets may be separated by a
mesh or other
suitable material, configured in a sheet or in strips arranged perpendicular
to the channels, or
other suitable configuration. This construction can be used instead of, or in
addition to, the use of
glue or welding along the pleat lines. This approach can reduce the tendency
for the pleats to slip
into one another during assembly and can provide structural support. This
construction can be
applied in the square or diamond arrangements described above.
[0056] FIG. 6A is a cross-sectional view showing a pleated water-permeable
membrane sheet
and a flat water-permeable membrane sheet positioned below it. The pleated
lines (the lower
peaks in the cross-sectional view) in the pleated membrane sheet can be glued,
welded or
otherwise attached to the flat membrane sheet to create parallel channels of
triangular cros s-
section. These channels each have three boundaries across which heat and
humidity can be
transferred. Stacking alternate sheets of pleated membrane and flat membrane
creates a
mechanically self-supported structure that requires no spacers or other
supporting material. In
this arrangement, again all flow channels walls are water-permeable allowing
heat and humidity
transfer to occur between all adjacent channels.
[0057] FIG. 6B is a cross-sectional view of a stack of membrane sheets in this
configuration with
the membranes forming an array of channels that are triangular in cross-
section. Two different
fluid streams can be directed through alternate channels in a counter-flow
configuration. As
before, flow into the plane of the paper is indicated by a cross, and flow out
of the plane of the
paper is indicated by a dot. Each channel shares its walls with as many as
three other channels.
Heat and humidity can be transferred across all three walls through the water-
permeable
membrane.
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[0058] The manufacturing method of pleating and then gluing, welding or
otherwise attaching
pleated membrane sheets to one another allows thinner membrane materials to be
used and still
have the strength to be self-supporting in the resulting 3D-structure. The
resulting sub-assembly
does not have to be held under tension. Furthermore this self-supporting
structure can provide
channels having walls that offer increased rigidity because they are supported
by other parts of
the structure even though the walls may be formed of a relatively thin,
flexible membrane
material. This increased rigidity may offer reduced pressure drop and improved
uniformity of
flow distribution through the core. Further, the structure facilitates
providing channels that have
consistent channel dimensions which further aids in achieving good uniformity
of flow among
the channels.
[0059] In the embodiments of stacked, pleated membrane sub-assemblies
described above the
pleated water-permeable membrane layers define a three-dimensional array of
parallel channels
arranged in a regular pattern. Each of the channel walls, defined by the
membrane material,
separates channels of first and second types, e.g. for carrying wet and dry
streams, respectively.
The two fluid streams can be directed through the channels so that the wet and
dry streams flow
in counter-flow to one another. This provides more efficient transfer of heat
and moisture with
high sensible and latent transfer.
[0060] In order to provide manifolds for supply and discharge of the gas
streams, the individual
sheets of pleated membrane can each be attached to a manifold section (before
they are stacked)
forming a manifold/membrane sub-assembly. The manifold/membrane sub-assemblies
may then
be stacked and glued together to form a core. The manifold section can be in
the form of a
unitary frame that borders the sheet of pleated membrane on all sides, or can
be in two (or more)
separate pieces that are, for example, attached to opposite ends of the
pleated membrane sheet.
[0061] The manifold section can be made of a different material than the
membrane, such as a
material that is not permeable to water or gas, and is stiffer and stronger
than the membrane. For
example, the manifold section material can be plastic, aluminum or any other
suitable material
that provides some structural support to the membrane and the stacked core,
while still providing
heat transfer in the manifold region. Preferably the material of the manifold
section is less than
0.012 inches (about 1/4 mm) in thickness. The manifold section may be made of
a flame retardant
material which will reduce the tendency for a flame to spread to the membrane
section and
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increase compliance with flammability requirements. For example, the manifold
section may be
made of aluminum or other metals; PVC, which is generally inherently self-
extinguishing; or a
plastic comprising one or more flame-retardant additives, such as magnesium
hydroxide.
[0062] Manifold sections may be made in a wide range of different ways. For
example, features
in manifold section(s) can be vacuum-formed or thermoformed or stamped
therein. In some
embodiments the manifold sections are formed with features and then attached
to the membrane.
Alternatively the manifold sections could be injection molded as separate
plastic pieces, and then
attached to the pleated membrane, or they could be injection molded directly
onto the edges of
the pleated membrane. The membrane can be adhered to the manifold section
using a suitable
glue, adhesive or other bonding agent, tape or the like. Some polyurethane-
based glues have
been found to be suitable for this purpose. Other types of adhesive can be
used, such as epoxies,
hot melts, cyanoacrylates, and even membrane coating materials that may also
be useful to
prevent or reduce cross-over contamination. Alternatively, depending on the
membrane and
manifold section material, it may be possible to thermally weld, vibration
weld, ultrasonically
weld, or otherwise bond the components together.
[0063] The attachment of the membrane to the manifold section should create a
leak-proof seal
to prevent cross-contamination between the two fluid streams. The bond should
be strong enough
to prevent delamination of the membrane from the manifold section when there
is a high
differential pressure between the fluid streams on opposite sides of the
membrane.
[0064] A benefit to this composite structure with pleated membrane adhered to
the transitioning
manifold sections is that the manifold sections may provide mechanical support
to the water
transfer membrane. Where manifold sections provide such mechanical support,
the core may be
self-supporting with reduced attachment between adjacent layers. Each layer
may be constructed
separately. The layers may each form a self-supporting structure, much like a
truss. The layers,
each including manifold sections and a moisture-exchange section may then be
stacked together
to form a heat and humidity exchanger.
[0065] The ratio of water-permeable membrane area to water impermeable
manifold material
area in the layers of the pleated membrane core assembly may be adjusted to
adjust the relative
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amounts of sensible heat and latent heat (moisture) that are transferred by
the pleated membrane
core. Increasing the area of water permeable membrane facilitates increased
moisture transfer.
[0066] In other embodiments the manifold section may comprise the same
material as the water
permeable membrane region, for example the manifold section may comprise a
water-permeable
membrane layer that is formable. This sheet of formable material may make up a
layer that
includes both a pleated region which will define counter-flow channels when
stacked together
with an adjacent layer and manifold regions that are configured so as, when
stacked together
with an adjacent layer, to direct a flow into channels at one end of the
pleated region and to
receive the flow on the other side of the pleated region (see FIG. 15 below,
for example). For
example, such a layer may be made of coated PET non-woven membrane, with
properties that
allow it to be molded or formed with pleats, ribs, bumps, and/or other out-of-
plane features
through the application of heat and/or pressure. Embodiments where a manifold
section is also
water-permeable permit increased humidity transfer due to the larger transfer
area. The transition
from the inlet or outlet to the center straight channels can follow the same
lofting as described
below, to transition from a wide rectangular area into alternating cells of
channels arranged
laterally.
[0067] The design of the manifold sections is such that, when they are stacked
in the assembled
core, they enable a first fluid stream to enter into alternate channels
laterally (a first type of
channel), and enable a second fluid stream (flowing through the core in the
opposite direction) to
exit from the other channels (second type of channel). Similarly at the other
face of the core, the
manifold receives the first fluid stream from the first channel type and
directs the second fluid
stream into the alternating channels of the second type. The two fluid streams
are fluidly isolated
from one another so that they do not mix. The manifolds can be designed to
ensure smooth flow
transition between the manifold regions and the channels so as to reduce or
minimize the overall
pressure drop through the exchanger device.
[0068] The manifold sections may be constructed to include features that
improve performance
of a heat and humidity exchanger by providing increased heat and/or humidity
transfer between
fluids and/or reduced pressure drop. For example:
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a. Ribs in intake manifold sections may be configured to direct flow evenly
into each
channel, and ribs in output manifold sections may be configured to allow flow
from
multiple channels to smoothly recombine into an output flow;
b. In embodiments where the manifold is bounded on one side by a flat membrane
sheet,
ribs in the manifold sections may be arranged to provide good support to the
membrane
sheet by providing closer rib-to-rib spacing especially in areas where the
membrane sheet
could sag;
c. Material of the manifold sections may be made thin (e.g. 0.004 inches to
0.012 inches -
about 0.01 cm to 0.03 cm). The use of thin materials for the manifold section
can enhance
the smoothness of the transitions from channels into the manifolds, increase
the cross-
sectional areas of plenums formed between the manifold sections, and also
improve heat
transfer through the material of the manifold sections.
[0069] FIG. 7A shows a simplified exploded 3D view of an assembly 700
comprising a pair of
pleated membrane sheets 710 and 720 that, when stacked, form parallel channels
with a
diamond-shaped cross-section. Manifold sections 730 and 740 are attached to
each membrane
sheet. The two manifold sections form a plenum 750 between them, with a
rectangular opening
via which a first fluid stream can be supplied to the channels formed between
the two membrane
layers. The stacked manifold sections 730 and 740 are shaped to provide smooth
transition
regions 735 and 745 between the plenum 750, which has a rectangular cross-
section, and the
triangles that form half of each diamond-shaped channel. As another assembly
is stacked above
the one illustrated in FIG. 7A, a similar plenum is formed above the upper
manifold section 730,
for the second fluid steam which is exiting the diamond-shaped channels
defined in part by upper
surface of the upper membrane 710. Thus the stacked manifold sections form a
series of layered
plenums alternating for the first and second fluids respectively. FIG. 7B
shows a simplified 3D
partial cut-away view of two fluid streams following through the diamond-
shaped channels in
counter-flow. The first fluid stream (indicated by arrows 770) enters a first
set of diamond-
shaped channels 775 via the plenum formed between the two manifold sections
730 and 740, and
the second fluid stream (indicated by arrows 780) exits a second set of
diamond-shaped channels
785 via the plenum formed above the upper manifold section 730. The fluids are
in a cross-flow
configuration in the manifold region.
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[0070] FIG. 8 is a plan view of the upper manifold/membrane assembly shown in
FIGs. 7A &
7B.
[0071] FIGs. 9A-D are intended to illustrate the smooth transition from the
manifold region into
the channels. FIG. 9A is a cross-sectional view at location A-A in FIG. 8.
FIG. 9A shows the
plenum 750 for the first fluid stream 770 below the manifold section 730, and
the plenum for the
second fluid steam 780 above the manifold section 730. The first stream 770
enters the lower
plenum 750 and the second stream 780 exits the upper plenum, as indicated by
the broad arrows.
FIG. 9B shows a view looking down the channels from a cross-section at
location B-B in FIG. 8.
The plenum floor/roof is still flat at this point but gradually transitions
into a zig-zag cros s-
section to correspond to the membrane pleats. These transitions in the
transition region 735 of
manifold section 730 are visible in FIG. 9B as solid triangles above and below
the flat plane of
the plenum roof/floor. FIG. 9C shows a view looking down the channels from a
cross-section at
location C-C in FIG. 8. This shows the gradual shaping of the manifold section
in transition
region 735 into a wavy cross-section. At this point the waves are not quite as
deep as the zig-zag
membrane pleats, and the further slope of manifold transition regions 735 are
visible above and
below the wavy cross-section in FIG. 9C. FIG. 9D is a cross-sectional view at
location D-D in
FIG. 8 showing the zig-zag cross-section of the pleated membrane 710.
[0072] FIG. 10 shows how the plenums created between adjacent manifold
sections in a stacked
core assembly (similar to that shown in FIG. 7A) correspond to the diamond-
shaped channels
that they are supplying/discharging. The first fluid can flow in a straight
path between the
unshaded area of the channels of the first type and the supply plenum for the
first fluid.
Similarly, the second fluid can flow in a straight path between the unshaded
area of the channels
of the second and the discharge plenum for the second fluid. In this
embodiment there is a
straight path connection between the plenum and most of the cross-sectional
area of the
corresponding channels. This reduces the pressure drop by avoiding an abrupt
transition in the
direction of flow, and eliminating the need for a long transition region,
between the plenum and
the channel.
[0073] FIG. 11A shows a simplified exploded isometric view of an assembly 1100
like that of
FIG. 7A, but with an additional flat membrane sheet 1115 interposed between
the pair of pleated
membrane sheets 1110 and 1120 thereby forming parallel channels with a
triangular-shaped
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cros s-section. The pleated membranes 1110 and 1120 are preferably glued or
otherwise bonded
to the flat membrane sheet 1115 along the pleat lines, to improve structural
rigidity of the
assembly and to allow the membrane channels to better withstand pressure
differentials. The
bond along the pleat lines does not need to be leak-proof, however, as any
leak would be into an
adjacent channel of the same type (i.e. carrying the same fluid stream).
Manifold sections 1130
and 1140 are attached to each pleated membrane sheet. Plenums 1150 and 1155,
each with a
rectangular opening, are formed between each manifold section 1130 and 1140
and the adjacent
flat membrane sheet 1115, via which a first and second fluid streams can be
supplied to the
channels formed between the pleated and flat membrane layers. The manifold
sections 1130 and
1140 are shaped to provide smooth transition regions 1135 and 1145 between the
plenums,
which have a rectangular cross-section, and the triangular-shaped channels.
FIG. 11B shows the
flow of two fluid streams (in a cross-flow configuration) on opposite sides of
one manifold
section 1130a that in the illustrated embodiment has ribs 1190 to direct the
flow and support the
membrane 1115. FIG. 11C is a plan view illustrating the flow pattern of two
fluid streams in an
assembly similar to the one shown in FIG. 11A.
[0074] In the embodiment illustrated in FIG. 11A, the flat membrane sheet
extends into manifold
region. This can be advantageous as it allows heat and moisture transfer to
occur between the
fluid steams in adjacent plenums, as well as in the pleated membrane region.
However, without
adequate support in this region, deflection of the membrane can occur,
increasing the pressure
drop, and so it may be necessary to provide supporting ribs or features in the
manifold sections.
The flat sheet of membrane is attached to the edges of the adjacent manifold
sections to create a
leak-proof seal. Suitable adhesives, or welding techniques may be used, such
as for example,
thermal welding, vibration welding, ultrasonic welding, or RF welding.
[0075] In other similar embodiments, the flat membrane sheet does not extend
into the manifold
region, but is attached to manifold sections made from a different material.
These stack with the
manifold sections shown in FIG. 11A to define alternating plenums for the
first and second fluid
streams. In either case, the stacked manifold sections are shaped to provide
smooth transitions
between the plenums (which have a rectangular cross-section) and the
triangular-shaped
channels.
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[0076] FIG. 12 shows how the plenums created between the flat membrane sheets
and adjacent
manifold sections in a stacked core assembly (similar to that shown in FIG.
11A) correspond to
the triangular-shaped channels that they are supplying/discharging. The first
fluid can flow in a
straight path between unshaded area of the channels of the first type and the
supply plenum for
the first fluid. Similarly, the second fluid can flow in a straight path
between the unshaded area
of the channels of the second type and the discharge plenum for the second
fluid. Once again, in
this embodiment there is a straight path connection between the plenum and
most of the cros s-
sectional area of the corresponding channels.
[0077] A manifolding arrangement similar to those described above can be
provided for box-
pleated membrane sub-assemblies, such as shown in FIG. 5B. FIG. 13 shows how
the plenums
created between adjacent manifold sections in such a stacked core assembly
would correspond to
the square-shaped channels that they are supplying/discharging. The first
fluid can flow in a
straight path between unshaded area of the channels of the first type and the
supply plenum for
the first fluid. Similarly, the second fluid can flow in a straight path
between the unshaded area
of the channels of the second type and the discharge plenum for the second
fluid. In this
embodiment there is a straight path connection between the plenum and about
50% of the cross-
sectional area of the corresponding channels.
[0078] The manifold sections can have features formed in one or both surfaces
to direct the flow
from the plenums into the corresponding channels, such as the ribs shown in
FIG. 11B. Such
features can, for example, improve flow distribution. They can also support
the membrane if it
extends into this region (for example, as in the embodiments illustrated in
FIG. 11A). Features
that will promote mixing or turbulence of the fluid streams can also be
incorporated into the
manifold sections to improve performance. The use of vacuum-formed or
thermoformed
manifold entrance and exit sections allows a variety of counter-flow sizes to
be produced with
varying channel heights without significant investment in tooling (such as
would be the case with
injection molded separators currently in use).
[0079] In illustrated embodiments the manifold members are each connected to
the core along a
first edge, have an up-turned wall along a second edge and a down-turned wall
along a third edge
such that, when stacked together the manifold members form a column of plenums
that open
alternately to sides corresponding to the first and second edges.
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[0080] FIG. 14A is a plan view of a manifold/membrane subassembly 1400 with a
central
pleated membrane 1410 and manifold sections 1430 and 1440 attached at each
end, where the
channels have a diamond cross-section. The manifold sections 1430 and 1440
include ribs on
one side to direct the fluid stream into the respective channels. FIG. 14B is
a plan view of a
manifold/membrane subassembly 1450 with a central pleated membrane 1460 and
manifold
sections 1480 and 1490 attached at each end, where the channels have a
triangular cross-section.
In this embodiment the manifold sections 1480 and 1490 include ribs on both
sides of the
midplane of the manifold section to direct the fluid streams into the
respective triangular-shaped
channels.
[0081] The assembled core can be potted along the sides and ends. It can be
encased in a metal
or plastic frame which can also assist in blocking flame spread to allow for
compliance with
flammability standards. A metal frame can also act as a heat sink. For ERV
applications the core
can be housed in an enclosure, which can also house fans to move the air
streams, ducting, as
well as filters, control electronics and other components.
[0082] The present membrane cores are readily manufacturable and can be
readily scaled to
different sizes, as the pleated membrane can be cut to different sizes to suit
the particular end-use
application and the number of layers in the stack can be varied.
[0083] Any membrane material that can be pleated and has the requisite water-
permeability and
other properties, is suitable for use in the above-described pleated membrane
cores. Membranes
that have been used or suggested for ERV applications include cellulose films;
cellulose fibre or
glass fibre papers or porous polymer films that are coated or impregnated with
a hydrophilic
polymer or a hydrophilic polymer-desiccant mixture; thin film composites
manufactured via
interfacial polymerization; laminated membranes made from a blown film on a
non-woven
support layer; laminated membranes comprising an ionomer film bonded to a
porous support;
and sulphonated and carboxylated ionomer films. Other materials involve
applying a water-
permeable coating to the microporous substrate. Composite membrane materials
comprising a
porous desiccant-loaded polymer substrate that is coated on one surface with a
water-permeable
polymer have been found to be particularly suitable for ERV and similar
applications. Examples
of such membranes are described in published PCT Application No.
W02010/132983.
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Membranes of this type can retain a pleat once folded, which tends to increase
the strength of the
membrane channels in the core designs described herein.
[0084] In some embodiments, a membrane that is formable or can be corrugated
may be used.
Engineered composite membrane materials which can be formed to create features
and hold
various structures, may allow increased performance and decreased cost in
membrane-based
devices such as those described herein. For example, the use of a electrospun
nanofibrous
membrane on a formable backer in a counter-flow heat and humidity transfer
device takes
advantage of the formable property of the membrane. A number of methods may be
available
with which to form the membrane, e.g. with channels or other features, (with
or without the use
of heat) such as compression molding, vacuum forming or stamping.
[0085] FIG. 15 is a photo of a layer made entirely from a formable water
permeable membrane
comprising a coated nanofibrous layer on a polyester spunbond nonwoven fabric
support layer.
The layer comprises manifold regions at each end, and a central section with
straight channels,
all made of the same material. The features were formed in the membrane layer
by heating it
(80 C) in a compression mold. Such layers can be stacked to form an ERV core
assembly In a
specific example embodiment, sheets of polyester spunbond nonwoven fabric
(Smash Specialty
Nonwoven Y15100) were obtained from Asahi Kasei. These materials are designed
for
formability under low heat (<100 C). Coatings of PAN nanofibres were deposited
on these
support layers with three different loadings. The nanofibrous layers were then
impregnated with
aqueous solutions of a polyetherpolyurethane co-polymer at three
concentrations (13, 15, and
17% by weight). The materials were dried in an oven at 50 C.
Experimental Examples
Example 1: First Prototype ERV Core ¨ Multi-Directional Transfer
[0086] Multi-directional transfer was demonstrated using a prototype with a
vacuum-formed
corrugated plastic spacer designed to have approximately the same heat
transfer as a pleated
membrane. The prototype showed the predicted increase in heat transfer
compared to a counter-
flow design with only vertical (1-dimensional) transfer for the same pressure
drop. The increase
was due to the multi-dimensional nature of the transfer.
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Example 2: Second Prototype ERV Core ¨ Pleated Membrane
[0087] A second prototype was made using pleated membrane in the counter-flow
section, with
thermoformed plastic manifold sections for the entrances and exits. A
polyurethane glue was
used to attach the membrane to the manifold sections. When compared on a
normalized flow
basis, the heat transfer compared favorably to state-of-the-art commercial HRV
cores. The
prototype performed better in moisture transfer than commercially available
cores.
[0088] The graph shown in FIG. 16 shows the performance of an ERV core,
comprising this
second prototype stacked pleated membrane, as a function of flow rate. The
graph shows the
effectiveness of sensible heat and latent (moisture) transfer for the pleated
membrane core.
Example 3: Third and Fourth Prototype ERV Cores
[0089] A third prototype was made with triangular channels in a core with a
larger footprint size.
A fourth prototype was also built with taller triangular channels.
[0090] Dimensions of the channels may be selected to provide a desired balance
between rate of
heat and mass transfer and pressure drop. The third prototype triangular-
pleated membrane core
had a pitch, or layer-to-layer membrane spacing, of 3.2 mm in the straight
counter-flow section.
This resulted in a channel entrance height of approximately 1.6 mm. Such a
small height
signifies a relatively low hydraulic diameter in the entrance and exit areas
of each layer, resulting
in a pressure drop that was higher than desired. The fourth prototype was
constructed to
demonstrate that pressure drop can be reduced by providing different channel
dimensions. In the
fourth prototype, the layer-to-layer spacing was 4.5 mm. This increased the
entrance and exit
heights of the manifolds to approximately 2.2 mm. The reduction in pressure
drop achieved in
the fourth prototype versus the third prototype is illustrated in FIG. 17.
[0091] With an increase in pitch spacing in the center channel section, fewer
layers would be
incorporated for the same overall height, or volume, of core. A reduction in
number of layers
would result in a reduction in the overall membrane surface area in the core,
reducing the
transport area and diminishing performance. However, this was compensated in
the fourth
prototype by incorporating more tightly spaced pleats (less distance between
pleats) in the
pleated counter flow sections, thereby packing more membrane in the straight
counter-flow
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section in the middle of the core. By going from about a 90 pleat tip angle
to about a 60 pleat
tip angle, enough membrane was incorporated into the fourth prototype to
offset the reduction in
the number of layers.
[0092] An ERV is typically operated in laminar flow in the layers of the core,
so heat and mass
transfer is only a function of hydraulic diameter and Nusselt number (a type
of dimensionless
temperature gradient), which is constant for a given geometry if the flow is
laminar. As
discussed in the literature (e.g., Int. J. Heat Mass Transfer, Vol. 18, pp.
849-862, 1975), for
triangular ducts in laminar flow the Nusselt number will decrease as one moves
away from an
equilateral triangle. The change of pleat angle from 90 to 60 in the fourth
prototype therefore
also compensated for the decrease in number of layers.
[0093] The graph shown in FIG. 18 shows the performance of these third and
fourth prototype
ERV cores, as a function of flow rate. The graph shows the effectiveness of
sensible heat and
latent (moisture) transfer was quite similar for the two prototypes.
[0094] Heat and humidity exchangers as described herein may be applied, for
example, to
exchange heat and humidity between a flow of fresh air entering a building and
a flow of air
being vented from a building.
[0095] While a number of exemplary aspects and embodiments have been discussed
above,
those of skill in the art will recognize certain modifications, permutations,
additions and sub-
combinations thereof. It is therefore intended that the following appended
claims and claims
hereafter introduced are interpreted to include all such modifications,
permutations, additions
and sub-combinations as are within their true spirit and scope.
Interpretation of Terms
[0096] Unless the context clearly requires otherwise, throughout the
description and the claims:
= "comprise," "comprising," and the like are to be construed in an
inclusive sense, as
opposed to an exclusive or exhaustive sense; that is to say, in the sense of
"including,
but not limited to".
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= "connected," "coupled," or any variant thereof, means any connection or
coupling,
either direct or indirect, between two or more elements; the coupling or
connection
between the elements can be physical, logical, or a combination thereof.
= "herein," "above," "below," and words of similar import, when used to
describe this
specification shall refer to this specification as a whole and not to any
particular
portions of this specification.
= "or," in reference to a list of two or more items, covers all of the
following
interpretations of the word: any of the items in the list, all of the items in
the list, and
any combination of the items in the list.
= the singular forms "a," "an," and "the" also include the meaning of any
appropriate
plural forms.
[0097] Words that indicate directions such as "vertical," "transverse,"
"horizontal," "upward,"
"downward," "forward," "backward," "inward," "outward," "vertical,"
"transverse," "left,"
"right," "front," "back" ," "top," "bottom," "below," "above," "under," and
the like, used in this
description and any accompanying claims (where present) depend on the specific
orientation of
the apparatus described and illustrated. The subject matter described herein
may assume various
alternative orientations. Accordingly, these directional terms are not
strictly defined and should
not be interpreted narrowly.
[0098] Where a component (e.g. a core, structure, plenum, fan, duct, etc.) is
referred to above,
unless otherwise indicated, reference to that component (including a reference
to a "means")
should be interpreted as including as equivalents of that component any
component which
performs the function of the described component (i.e., that is functionally
equivalent), including
components which are not structurally equivalent to the disclosed structure
which performs the
function in the illustrated exemplary embodiments of the invention.
[0099] Specific examples of systems, methods and apparatus have been described
herein for
purposes of illustration. These are only examples. The technology provided
herein can be applied
to systems other than the example systems described above. Many alterations,
modifications,
additions, omissions and permutations are possible within the practice of this
invention. This
invention includes variations on described embodiments that would be apparent
to the skilled
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addres see, including variations obtained by: replacing features, elements
and/or acts with
equivalent features, elements and/or acts; mixing and matching of features,
elements and/or acts
from different embodiments; combining features, elements and/or acts from
embodiments as
described herein with features, elements and/or acts of other technology;
and/or omitting
combining features, elements and/or acts from described embodiments.
[0100] It is therefore intended that the following appended claims and claims
hereafter
introduced are interpreted to include all such modifications, permutations,
additions, omissions
and sub-combinations as may reasonably be inferred. The scope of the claims
should not be
limited by the preferred embodiments set forth in the examples, but should be
given the broadest
interpretation consistent with the description as a whole.
