Note: Descriptions are shown in the official language in which they were submitted.
CA 02358004 2001-09-20
APPARATUS
Background of the Invention
This invention relates to heat exchangers.
The invention is more particularly concerned with heat exchangers for use in
building
ventilation systems.
Heat exchangers are used in building ventilation systems to transfer heat from
warm
air extracted from the building to cold air supplied to the building. In this
way, the amount of
energy needed to maintain the temperature within the building can be
minimized.
A common form of heat exchanger used in building ventilation systems comprises
a
stack of thin parallel plates spaced from one another to form two separate
flow paths between
alternate pairs of plates. The warm air is supplied along one path and a part
of its heat is
conducted through the thickness of the plates to the cold air supplied along
the other path.
The ideal heat exchanger should have a high efficiency of thermal transfer,
preferably
above about 90% and should produce only a low back pressure so as to reduce
energy
expenditure by the fans used to pass the air through the exchanger. The
exchanger should also
have a low leakage between the two air paths and be easy to manufacture at low
cost.
The plates used in heat exchangers usually have low projecting walls to
support the
plates spaced from one another and to enhance performance. In one arrangement,
the plates
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axe moulded with zigzag paths on opposite sides, the plates being arranged
with the paths out
of phase with one another so as to ensure that the flow paths are kept open.
Such an
arrangement may have a high efficiency but produces a high back pressure
because it results
in considerable interruption to the air flow path as it passes between the
intersecting walls on
facing plates.
Conventional heat exchangers have the edges of their plates bonded with one
another
such as by an adhesive, solvent or by ultrasonic welding. These processes can
produce
effective seals between the two flow paths but are relatively expensive and
require
specialised machinery.
Brief Summary of the Invention
It is an object of the present invention to provide an alternative heat
exchanger.
According to one aspect of the present invention there is provided a heat
exchanger
including a plurality of plate members stacked parallel above one another to
define two
separate fluid flow paths between alternate pairs of adjacent plate members,
and retaining
means for retaining the plate members with one another, the retaining means
including a
plurality of first and second surfaces facing one another between which edges
of respective
pairs of plate members are retained in sealing engagement with one another.
The first and second surfaces are preferably provided on projecting ribs
between
which edges of pairs of the plate members extend. The retaining means may
include two
imperforate side plates and may include four grille members located at each of
the inlets and
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outlets of the heat exchanger. The grille members may be slidable along the
plane of a face of
the exchanger, the grille members retaining an edge of adjacent plate members
in sealing
engagement and retaining a gap between retained pairs of plate members opening
into one of
the fluid flow paths. The heat exchanger preferably has inlet and outlet faces
on adjacent
faces of the exchanger. Respective grille members on adjacent faces may be
slidable towards
one another to form a seal between adjacent edges of the grille members. The
plate members
preferably have a plurality of internal walls defining multiple flow channels
therebetween
along the plate members. The internal walls and channels on one side of the
plate members
preferably have corresponding channels and walls on their opposite side. The
channels may
have a zigzag pattern. The plate members may have spacer means to retain
separation
between adjacent plate members over their surface. The spacer means may
include a
proj ection ~n a channel, an internal wall adj acent the proj ection being
reduced so that air flow
along the channels is not impeded by the projection. The plate members may be
vacuum
formed from plastics and may be of carbon-loaded uPVC. Preferably the plate
members are
of a black colour. The plate members may have six sides, four of the sides
being arranged to
be closed and two of the sides arranged to be open. Each plate member
preferably has a side
wall along the four closed sides, the side walls of adjacent plate members
nesting with one
another. Some of the side walls may have an M-shape profile. Each plate member
preferably
has a main section of rectangular shape and inlet and outlet sections of
triangular shape at
opposite ends. The inlet and outlet sections preferably have a plurality of
ribs extending
generally transverse to the direction of flow.
According to another aspect of the present invention there is provided a heat
exchanger including a plurality of plate members stacked parallel above one
another to define
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two separate fluid flow paths between alternate pairs of adjacent plate
members, each fluid
flow path opening at a respective inlet and outlet face of the exchanger, and
the exchanger
including at least one grille member slidable along the plane of a face of the
exchanger and
arranged to retain an edge of adjacent plate members as a pair in sealing
engagement and to
retain a gap between the pairs providing an opening into one of the fluid flow
paths.
The heat exchanger preferably has inlet and outlet faces on adjacent faces of
the
exchanger, respective grille members on adjacent faces being slidable towards
one another to
form a seal between adjacent edges of the grille members.
According to a further aspect of the present invention there is provided a
plate
member fob a heat exchanger according to the above one or other aspect of the
invention.
According to a fourth aspect of the present invention there is provided a
plate member
for a heat exchanger having a stack of plate members, the plate member having
a main
rectangular region having two parallel sides formed with walls shaped to nest
with
corresponding walls of adjacent plate members and having a plurality of flow
channels
extending generally longitudinally parallel to the parallel sides, and
triangular inlet and outlet
regions at opposite ends of the main region, the triangular regions each
having an edge
extending along one side adapted to nest with a corresponding edge of an
adjacent plate
member and each having an open side through which air can enter and leave from
between
adjacent plate members, the inlet and outlet regions being shaped to channel
air to and from
the flow channels.
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A heat exchanger assembly according to the present invention, will now be
described,
by way of example, with reference to the accompanying drawings.
Brief Description of the Drawi ~s
Figure 1 is a schematic plan view of the assembly;
Figure 2 is a perspective view of the heat exchanger unit;
Figure 3 is a perspective view of a top or base plate of the unit;
Figure 4 is a perspective view of a side plate of the unit;
Figure 5 is a perspective view of an end grille;
Figure 6 is a sectional side elevation of the grille of Figure 5 along the
line VI-VI of Figure 5;
Figure 7 is a perspective view of one type of heat exchanger plate;
Figure 8 is a perspective view of another type of heat exchanger plate;
Figure 9 is an enlarged plan view of a part of one of the heat exchanger
plates;
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Figure 10 is a cross-sectional side elevation of the plate along the line X-
X of Figure 9;
Figure 11 is a cross-sectional side elevation view of a lower, side part of
the heat exchanger unit showing how the exchanger plates are
retained by the side plates; and
Figure 12 is a cross-sectional side elevation view of an upper, end part of
the heat exchanger unit showing how the exchanger plates are
engaged by the grilles.
Detailed Description of the Preferred Embodiment
With reference first to Figures l and 2, the heat exchanger assembly has an
outer
housing 1 with two inlets 2 and 3 and two outlets 4 and 5 located at four
corners of the
housing. A heat exchange unit 6 is located in the housing l and defines two
separate air flow
paths 7 and 8 through the housing. The first flow path 7 extends from the
inlet 2 through the
exchange unit 6 to the outlet 4 in the opposite corner and, in use, receives
warm air exhausted
from a room. The second flow path 8 extends from the other inlet 3 to the
other outlet 3 and,
in use, receives cold air from outside. The exchange unit 6 operates to
transfer heat from the
air flowing along the first flow path 7 to air flowing along the second flow
path 8 so that the
fresh air supplied to the building is warmed. The assembly includes two
conventional electric
fans 10 and 11 located in the housing 1 at the two outlets 4 and 5 to draw air
along the
respective flow paths 7 and 8.
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The heat exchange unit 6 is of the counter-flow type having two parallel,
vertical
sides 61 and 62 and four end faces 63 to 66 providing the two inlets and
outlets. The unit 6
has a horizontal base 67 and top 68. Operation of the two fans 10 and 11
causes warm air
drawn in through the inlet 2 of the housing to flow in the inlet face 63,
through the unit 6 and
out of the diagonally opposite outlet face 65, from where it flows to the
outlet 4. Cold air
drawn in through the inlet 3 passes in the inlet face 64, through the unit 6
and out of the
diagonally opposite outlet face 66, from where it passes to the outlet 5.
With reference now also to Figures 3 to 12, the heat exchange unit 6 comprises
a
parallel stack of forty-four, six-sided heat exchanger plates 70. The plates
70 are contained
within a base plate 12, a top plate 13, two side plates 14 and 1 S and four
inlet grilles 16 to 19.
Each plate 70 is formed with walls at its edges to provide a seal around four
of its six sides,
leaving two diagonally-opposite sides open for inlet and outlet of air. The
heat exchanger
plates 70 are vacuum formed from a thin sheet of carbon-loaded uPVC of a black
colour,
which has a high thermal conductivity and is an efficient thermal radiator.
The plates 70 are
moulded with a pattern of internal walls to form channels therebetween on
opposite surfaces
that act to contain air flowing through the exchanger along defined paths
through the
exchange unit 6. The heat exchanger plates 70 are of two different types: a
lower type A and
an upper type B, which are stacked alternately one above the other. The
configuration of the
lower type of plate 70A will now be described with reference to Figure 7.
The plate 70A has a main section 71 of rectangular shape with forty-three
internal
walls 72 of zigzag shape extending parallel with one another longitudinally of
the plate and
defining forty-two zigzag channels 73 extending along the plate between the
walls. The walls
CA 02358004 2001-09-20
72 project vertically on the upper surface of the plate and are moulded from
the material of
the plates so as to form a corresponding pattern of channels and walls on the
underside of the
plate.
At opposite ends of the main section 71, the plate 70A has an inlet and outlet
section
74 and 75, both of triangular shape. One side 76 of the inlet section 74 has a
raised edge wall
77, to close the side, and the other side 78 is open with a slightly lowered
edge 79. Where the
raised wall 77 meets the open side 78 there is a small step 177 aligned
longitudinally of the
plate. The surface of the inlet section 74 is ribbed with shallow, parallel
ribs 80 extending
laterally of the plate and generally transversely to the direction of air
flow. The inlet section
74 also has three higher raised walls 81 extending perpendicular to the open
side 78. These
ribs 80and walls 81 act to channel air entering the open side 78 substantially
evenly across
the row of ends of the zigzag channels 73. The ribs 80 also introduce a small
amount of
turbulence into the air flow. The outlet section 75 similarly has a closed
side 82 with a raised
wall 83, and an open side 84 which connects with the closed side via a step
183. The outlet
section 75 also has ribs 85 and walls 86 to help channel air emerging from the
zigzag
channels 73 to the open side 84 of the section. A location pip 87 projects
upwardly at
opposite ends of the plate 70A, just within the apex of the inlet and outlet
sections 74 and 75.
The two sides of the main section 71 are each closed by a raised wall 90
having an M-shape
profile (Figure 11) extending longitudinally along the plate.
The upper type of plate 70B (Figure 8) has similar surface formations, which
are
given the same number as the formations for plate 70A with the addition of a
prime '. The
inlet section 74' of the upper plate 70B is at the opposite end from that of
the lower plate 70A.
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The plates 70B are stacked alternately above the plates 70A and have a pattern
of zigzag
channels 73' identical with the channels 73 except that they are displaced
slightly laterally
such that the walls 72' align with the channels 73. In this way, the channels
defined by the
underside of the walls 72' are aligned with the channels 73 on the upperside
of the plates 70A
to form channels between adjacent plates of diamond shape in section. The top
of the internal
walls 72 on the plates 70A support the base of the channels 73' on the plates
70B.
Along the two sides, the main section 71' of the plate 70B has side walls 90'
of
reduced height and of M-shape in section, which nest on the top of the side
walls 90 of the
lower plates 70A.
The triangular inlet and outlet sections 74' and. 75' at the ends of the upper
plates 70B
are also similar to those of the lower plates 70A except that different ones
of the sides 76',
78', 82' and 84' are open and closed and the internal ribs 80', 85' and walls
81', 86' act to
channel air between the open sides 78', 84' and the ends of the zigzag
channels 73'. The inlet
and outlet sections 74' and 75' similarly have locating pips 87' the underside
of which are
engaged by the locating pips 87 on the lower plates 70A.
In order to ensure that the zigzag walls on adjacent plates do not nest with
one another
and thereby restrict flow, the pattern of zigzag walls is interrupted over the
surface of the
lower plate 70A by several raised pips 92 (Figures 9 and 10) located in
channels 73 between
the internal walls 72. The walls 72 in the region of these pips 92 is reduced
in height to form
notches 93 so that air flowing along the channels 73 can flow through the
notches into
adjacent channels and is not restricted by the presence of the pips.
CA 02358004 2001-09-20
The plates 70A and 70B are held together with one another in a stack by means
of the
bottom plate 12, top plate 13, side plates 14 and 1 S and the grilles 16 to
19. The side plates 14
and 15 (shown most clearly in Figures 4 and 11) are imperforate and moulded of
a rigid,
black ABS plastics material with twenty-three parallel ribs 95 extending
horizontally along
their length. The spacing between adjacent ribs 95 and their height are such
that each pair of
ribs receives between them the mated side walls 90 and 90' of a pair of plates
70A and 70B,
the facing surfaces 195 of adjacent ribs retaining and clamping the two walls
together to form
a secure seal.
The four grilles 16 to 19 (shown most clearly in Figures 5, 6 and 12) are each
of
similar cor~struction, having twenty-three horizontal, parallel cross-bars 97
spaced apart from
one another to form slots 98 through which air can enter between adjacent
pairs of plates. The
external surface of the cross-bars 97 is rounded to give an aerodynamic
profile promoting
free flow of air into the slots 98. Internally, each cross-bar 97 has a recess
99 with opposite
facing surfaces 199 between which the edges of a pair of plates 70A and 70B
are received
and retained together in sealing engagement. The grilles 16 to 19 are
assembled on the unit 6
by aligning one end of the recesses 99 with the corners of the exchanger
plates 70A and 70B
where they are supported by the side plates 14 and 15 so that the edges of a
pair of plates
locates in respective recesses. The grilles 16 to 19 are then slid along their
length, parallel to
the edge of the plates 70A and 70B, towards the apex. Where two grilles 16 and
19, 17 and
18 meet at the apex, they clamp onto the steps 177 and 183 on the plates 70A
and 70B to
ensure a good sealing fit along the end of the unit 6. Each grille 16 to 19
has an L-shape ledge
100 along the vertical edge, which locates at the apex. Each grille 16 to 19
also has an angled
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ledge 101 along its opposite edge, which overlaps the edge of the adjacent
side plate 14, 15.
Along the top and bottom vertical edge of each grille 16 to 19 extends a
channel 102 with
clips 103, which fasten onto the edges of the top and bottom plates 13 and 12.
Similarly, the
top and bottom plates 13 and 12 both have channels 104 along their sides with
clips 105
(Figure 11), which fasten onto the top and bottom edges of the side plates 14
and 15.
Considering the grilles 16 and 19 at one end of the unit 6, one of these
grilles 16 seals
together the edge 84 of each lower plate 70A to the edge 84' of the upper
plate 70B directly
below it. The slots 98 in the grille 16, therefore, open into spaces between
the upper surface
of the lower plates 70A and the lower surfaces of the upper plates so that the
air flow path 7
extends between these surfaces. The adjacent grille 19, however, seals
together the edge 83 of
each lower,plate 70A to the edge 83' of the upper plate 70B directly above it
so that the slots
98 in the grille open into the air flow path 8 extending between the upper
surface of the upper
plates and the lower surface of the lower plates. The warm air flowing along
flow path 7
flows along the channels 73, 73' in a direction that is parallel to but
opposite from the cold air
flowing along the flow path 8. Heat in the exhaust air flow path 7 is
conducted through the
thickness of the plates 70A and 70B into the inlet air flow path 8. The
construction and
arrangement of the plates 70A and 70B ensure that the heat only has to flow
through a single
layer of material between adj acent flow paths.
The unit 6 is assembled by clipping the side plates 14 and 15 into the base
plate 12
and then sliding a pair of heat exchange plates 70A and 70B into the gaps
between the ribs 95
along the side plates, with the plates being located together by engagement of
the pip 87 in
the lower plate in the corresponding location point 87' in the upper plate.
When all the pairs
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of plates 70 have been slid into position, the top plate 13 is clipped onto
the upper edge of the
side plates 14 and 15. The grilles 16 to 19 are then slid into place in the
manner previously
described. In this way, the entire unit 6 can be assembled without the use of
adhesives,
solvents and without having to weld or bond components together.
The heat exchanger unit 6 has six vertical edge proj ections 111 to 116
located around
its surface and provided on the grilles 16 to 19 and side plates 14 and 15.
These projections
are a close sliding fit in channels 211 to 216 formed on the inside surface of
the housing 1,
which is of a foamed plastics material, so that the unit 6 can be slid down
into the housing.
The engagement of the projections 111 to 116 in the channels 211 to 216 forms
a seal
preventing passage of air between the outside of the exchange unit 6 and the
inside of the
housing 1.
The arrangement of the present invention has several advantages. The manner in
which the plates are retained together at their edges avoids the need for any
adhesive or
welding, thereby considerably simplifying assembly and reducing costs. The
aligned, zigzag
air flow paths on the upper surface of one plate and the lower surface of an
adjacent plate
enables a relatively low back-pressure to be achieved, whilst the spacer pips
ensure that the
air flow paths remain open. Previous exchange plates with zigzag paths have
been arranged
out of phase with one another so that the walls on adjacent plates cross and
support one
another. This previous arrangement produces considerable air flow disturbance
and results in
relatively high back-pressure compared with the arrangement of the present
invention. By
sliding the grilles into position the alignment of the grilles with the
individual plates is
considerably simplified compared with alternative arrangements.
