Field of the invention
[0001] The present invention refers to a plate heat exchanger and hydraulic assembly comprising
such a heat exchanger.
[0002] The invention has been developed with particular regard to, but not limited to, a
plate heat exchanger for use in a boiler for the instantaneous production of domestic
hot water and/or heating, as well as for use in a heat pump.
Technological background
[0003] A plate heat exchanger in a gas boiler has the function of transferring heat by conduction
from the hot water, heated by the burner, to the sanitary cold water entering the
boiler, while keeping the two fluids hydraulically separated. A plate heat exchanger,
hereinafter also referred to for brevity's sake as a heat exchanger, consists of plates,
typically in stainless steel, juxtaposed and welded together to form chambers for
water to pass. Each plate is in contact on one side with the hot water, heated by
the burner, and on the other side with the sanitary cold water.
[0004] A heat exchanger is provided with four ports: two are respectively for inlet and
outlet of the hot water heated by the burner, called primary circuit water, and the
other two ports are for inlet of sanitary cold water and outlet of sanitary hot water,
heated by the heat exchanger and ready to be supplied.
[0005] The four ports are normally provided on one face of the heat exchanger, in the four
corners. The heat exchange performance varies with the thermal length, which determines
the time for which the two fluids remain in contact. The number of plates is variable
and depends on the power it is wished to exchange. Of course the number of plates
cannot be increased indefinitely, as the space provided in a boiler to house the heat
exchanger is limited and standard. Exceeding these dimensions would require the design
and construction of a new boiler.
[0006] Four-channel valves to be used together with heat exchangers, for example for use
in a heat pump, are known. Typically slide valves are used, i.e. valves in which a
piston (the slide) slides back and forth in a seat in order to open and close the
connection ways. Although widely used, these valves have significant pressure drops.
Summary of the invention
[0007] An object of the invention is to overcome the problems of the known art and in particular
to increase the heat exchange efficiency. Another object is to provide a heat exchanger
with a size such that it can fit into a compact boiler. A further object is to realize
an inexpensive, simple, reliable in use and safe device.
[0008] According to a first aspect, a heat exchanger comprising a plurality of plates is
described. The plates can be fixed to each other to form first chambers and second
chambers. The first chambers are preferably hydraulically connected to each other
to form a primary circuit. The second chambers are preferably hydraulically connected
to each other to form a secondary circuit. The primary circuit is preferably hydraulically
separated from the secondary circuit. The heat exchanger preferably comprises at least
two ports for inlet and outlet of a fluid from the primary circuit and at least two
ports for inlet and outlet of a fluid from the secondary circuit.
[0009] According to one aspect, the ports are arranged along an approximately straight line.
A heat exchanger with such geometry turns out to have a significantly greater thermal
length than a traditional heat exchanger, in which the ports are arranged so as to
outline a rectangle. The new geometry in fact allows a better use of the available
space, while maintaining the possibility of mounting the heat exchanger in a hydraulic
assembly compatible with a standard DIN template. According to another aspect there
is described a heat exchanger in which the ports are all positioned on a same side
of the heat exchanger.
[0010] According to another aspect there is described a heat exchanger in which in at least
one chamber, defined between two contiguous plates, there is provided at least one
shoulder with open profile, for example U, V, L-shaped. A configuration of this type
allows the fluid flowing in the chamber to be conveyed along a predetermined path,
lengthening the thermal length of the heat exchanger without increasing the footprint
thereof. Preferably, the U-shaped shoulder is arranged so as to partially embrace
a connection hole between adjacent chambers and preferably has the concavity facing
outwards.
[0011] According to a further aspect there is described a heat exchanger in which each plate
has an elongated shape, with two long sides and two tapered ends. Tapered means that
the width of the plate is reduced when moving away from the centre of the plate itself.
Such a geometry allows a better thermal performance with the same footprint. Preferably
each plate has an elongated shape, for example it may be approximately polygonal,
with two long sides and at least four short sides, or it may have two long sides and
two curved short sides, for example semi-circle or semi-ellipse. According to a further
aspect there is described a heat exchanger in which the plates have corrugations,
to increase the turbulence of the fluid flowing therein and therefore the performance.
Preferably the corrugations are successions of valleys and ridges, which can be arranged
with a herringbone pattern, preferably with opposing direction between adjacent plates.
[0012] There is further described is a hydraulic assembly comprising a heat exchanger with
some or all of the features described above and/or below, a circulation pump adapted
to cause the circulation of the primary fluid and a three-way valve located at the
inlet of the primary circuit.
[0013] According to another aspect, there is described a hydraulic assembly for a heat pump
comprising a heat exchanger having at least two ports for inlet and outlet of a fluid
from the primary circuit and at least two ports for outlet and inlet of a fluid from
the secondary circuit, a circulation pump for pumping the secondary fluid in the secondary
circuit of the heat exchanger and a four-way valve. The four-way valve can be configured
to maintain countercurrent primary flow and secondary flow in the heat exchanger.
Preferably, the four-way valve is interposed between the circulation pump and the
heat exchanger, to allow the pump to pump into the heat exchanger at one or other
port for inlet of a fluid from the secondary circuit.
[0014] Also described is a four-way valve, particularly suitable for use in a heat pump,
comprising a pair of opposing plates, provided with a total of four ports, and a rotating
plate interposed between them. The rotating plate has two through-holes, shaped in
such a way that, when the three plates are brought together and tightened, each through-hole
of the rotating plate connects a pair of ports. Preferably, the through-holes are
in the shape of a slot. By turning the rotating plate it is possible to change the
pairing of the ports.
[0015] The valve thus configured is particularly efficient for large flow rates and has
minimal pressure drops, significantly lower than a traditional four-way, slide valve.
In addition, the valve is easier to disassemble and inspect.
[0016] It should also be noted that the valve can be used for both water and for other coolants
such as for example those typically used in a heat pump.
Brief description of the drawings
[0017] Further features and advantages will become apparent from the following detailed
description of a preferred embodiment of the invention, with reference to the accompanying
drawings, given purely by way of non-limiting example, in which:
- Figure 1 shows a perspective view of a heat exchanger in a hydraulic assembly with
integrated pump,
- Figure 1a shows a perspective view of only the heat exchanger of Figure 1,
- Figure 1b shows a perspective view of the heat exchanger according to a variant,
- Figure 2 shows the heat exchanger of Figure 1a, sectioned along a plane perpendicular
to the plates that compose it,
- Figure 3 shows a front view of a first plate, with the path of the primary fluid displayed,
- Figure 4 shows a second plate, adjacent to the first plate referred to in Figure 3,
with the path of the secondary fluid displayed,
- Figure 5 shows the diagram of a heat pump, in summer operation and
- Figure 6 shows the diagram of the heat pump of Figure 5, in winter operation
- Figure 7 shows a heat exchanger assembly for the heat pump of Figures 5 and 6,
- Figure 8 shows an exploded view of the four-way valve particularly suitable for use
in the assembly of Figure 7, and
- Figure 9 and Figure 10 schematically show two positions of use of the four-way valve
of Figure 8.
Detailed description
[0018] Figure 1 depicts a heat exchanger 10 in a hydraulic assembly with integrated pump,
for use inside a gas boiler to heat water for a heating system and for sanitary use.
The heat exchanger is intended to exchange heat between a primary fluid, which flows
in a primary circuit, and a secondary fluid, which flows in a secondary circuit. The
primary and secondary fluid may be any fluid suitable for transferring heat, typically
steam and/or water. Preferably, the primary circuit provides for the entry of steam
and possibly water heated by a burner; the fluid cools (and possibly condenses) in
the circuit and then exits in the form of water. The secondary circuit instead provides
for the entry of cold water and the exit of hot water for sanitary use, heated by
the fluid of the primary circuit.
[0019] A circulation pump 12 is positioned at the outlet of the primary circuit, to cause
the circulation of the primary fluid. A three-way valve 14 is instead placed at the
inlet of the primary circuit. The purpose of the three-way valve is to convey the
hot fluid coming from a primary heat exchanger inside the heat exchanger, if there
is a request for sanitary hot water. In the absence of a request for sanitary hot
water, on the other hand, the hot fluid coming from the primary exchanger is conveyed
towards the heating circuit.
[0020] A safety valve 18 ensures that the pressure of the system never exceeds a predetermined
pressure, for example 3 or 6 bar. A tap 20 instead allows a user to add water into
the primary circuit to reach an operating pressure.
[0021] Referring now to the following figures, a plate heat exchanger 10 according to the
invention comprises a plurality of alternating plates 30a, 30b, placed next to each
other and enclosed between a first end plate 32 and a second end plate 34, in opposing
position with respect to the end plate 32. The plates of the heat exchanger 10 are
produced by moulding a sheet metal and are subsequently brought together. The first
end plate 32, the second end plate 34, and the plates 30a, 30b of the heat exchanger
are permanently joined together to form a plate package. Preferably the joining between
the plates takes place by welding and more preferably by brazing, i.e. welding with
material addition. A particularly suitable brazing technology for the construction
of the heat exchanger 10 is copper foil technology.
[0022] Each plate has an elongated shape, with two long approximately parallel sides 2.
Preferably, each plate has an approximately polygonal shape, with two long sides and
at least four short sides, like in the figures. However, it is not excluded the possibility
of providing a plate with two straight long sides 2 and two curved short sides, for
example semi-circle or semi-ellipse or more generally two long sides 2 and two tapered
ends 4.
[0023] In the plate package, each pair of facing plates 30a, 30b, 32, 34 defines between
them a chamber 36, 38 for a fluid. The chambers 36 are connected to each other to
form the primary circuit 40 and the chambers 38 are connected to each other to form
the secondary circuit 42. The chambers 36 and 38 alternate such that each plate 30a,
30b serves as a dividing wall between the primary circuit 40 and the secondary circuit
42, thereby permitting a heat exchange between the primary fluid and the secondary
fluid.
[0024] The heat exchanger 10 is provided with four ports 44, 46, 48, 50, visible in Figure
1a. The ports 44 and 46 are for inlet and outlet of the fluid of the primary circuit,
respectively, while the ports 48 and 50 are for outlet and inlet of the fluid of the
secondary circuit, respectively. The four ports are preferably arranged in line with
each other, i.e. their axes all pass through a single straight or approximately straight
line. The four ports are preferably all positioned on the same side of the heat exchanger,
for example on the side of the first plate 32.
[0025] According to the variant of Figure 1b, the two ports 44, 46 of the primary circuit
are positioned on the side of the first end plate 32 and the two ports 48, 50 of the
secondary circuit are positioned on the side of the second end plate 34 (or vice versa).
Also in this variant the four ports are preferably arranged in line with each other,
i.e. their axes all pass through a single straight or approximately straight line.
[0026] Shoulders or partitions 52, 54, 60, 62 are provided between pairs of adjacent plates
to separate primary and secondary circuits between them, as known in the sector.
[0027] Figure 3 shows the course of the fluid within the primary circuit 40, in a chamber
36. Inside the chamber 36, and more specifically on the plate 30b, closed-profile
shoulders 52 and 54 are provided, which when the heat exchanger is assembled are welded
to the adjacent plate 30a, to separate the primary circuit from the secondary circuit.
The fluid enters from an inlet hole 65, near an end 4 of the heat exchanger. The fluid
is then directed towards the opposing end 4 of the heat exchanger, towards the outlet
hole 63. In the figure, the arrows indicate the path that the fluid approximately
travels in the chamber 36.
[0028] Figure 4 instead shows the course of the fluid within the secondary circuit 42, in
a chamber 38. Inside the chamber 38 shoulders 60 and 62, with closed-profile, are
provided to separate the primary circuit from the secondary circuit and there is also
provided a pair of shoulders 56, 58 with open profile, outlining a U. The U-shaped
shoulders 56, 58 are arranged so as to partially embrace the connection holes 64,
66 between adjacent chambers 38 and with the concavity facing outwards, more specifically
towards the shoulders 60, 62. The water enters from an inlet hole 66, is conveyed
from the U-shaped shoulder 58 towards an end 4 of the heat exchanger, where the shoulder
62 is located. The end 4 of the heat exchanger causes a reversal of the direction
of the flow of the fluid, which is directed towards the opposing end 4 of the heat
exchanger, where the shoulder 60 is located. The fluid is then conveyed inside the
U-shaped concavity of the shoulder 56 and then towards the outlet hole 64. Of course
the shoulders 56, 58 may also have a different shape, for example V- or L-shaped.
Overall it is sufficient that they direct the flow of the fluid towards an end 4 of
the heat exchanger.
[0029] Note that in the described heat exchanger the thermal length, i.e. the length along
which the two fluids have a heat exchange, is greater than the thermal length of a
known heat exchanger. In a known heat exchanger, with four ports placed at the vertices
of a rectangle, the thermal length is less than the length of the heat exchanger,
since there is no exchange near the primary and secondary fluid inlet and outlet ports.
In the heat exchanger of the invention instead the fluids flow side by side along
the entire length of the heat exchanger. Not only that: thanks to a U-shaped path
that the fluid of the secondary circuit travels near the ports 48, 50, the thermal
length is further increased.
[0030] Moreover, thanks to the specific shape and to the positioning of the ports of the
heat exchanger object of the present invention, with the same footprint it is possible
to insert into the boiler a longer heat exchanger, coupled to a hydraulic assembly
with an integrated pump.
[0031] Each plate has corrugations 70, understood as successions of valleys and ridges,
clearly visible in the section of Figure 2. The corrugations are generally with a
herringbone pattern, with opposing direction between the plates 30a and the plates
30b. In this way, two adjacent plates always have opposing corrugations. The corrugations
allow to create a series of tunnels, all communicating, for the fluid to pass in the
chambers 36, 38. Compared to the use of smooth plates, it has been noted that plates
with corrugations result in greater turbulence of the fluid and, therefore, a better
heat exchange.
[0032] As evident from a comparison between Figures 3 and 4, the fluids are predominantly
countercurrent, i.e. the primary fluid and the secondary fluid are directed in the
opposing direction. In this way the temperature difference between primary and secondary
fluid is relatively constant, with reduced swings. However, there are short stretches
in which the fluids are in phase, near the inlet 66 and outlet 64 holes.
[0033] The plates are preferably made of steel. Preferably each plate is obtained by moulding
from a metal sheet.
[0034] Finally, it should be noted that the heat exchanger described above, as shown in
Figure 1, has a layout compatible with a standard DIN template.
[0035] Referring now to Figures 5 and 6, the above-described heat exchanger 10 is also applied
in a heat pump. Figure 5 shows the summer mode operation diagram of a heat pump comprising
a heat exchanger 10.
[0036] In summer mode, in the secondary circuit there is fluid at temperature T1 in inlet
and fluid at temperature T2, lower than T1 in outlet. The temperature drop from T1
to T2 takes place inside the heat exchanger 10, thanks to the passage in its primary
circuit of another fluid, coolant, which enters the heat exchanger at temperature
T3 and exits at temperature T4, higher than T3 since it has absorbed heat from the
secondary fluid. While travelling along the circuit starting from the outlet of the
port 44 of the heat exchanger, the fluid at temperature T4 passes through a four-way
valve 90 and reaches a compressor 92. The compressor compresses the fluid, bringing
it to a higher pressure and, consequently, to a temperature T5, higher than T4.
[0037] The fluid exiting the compressor passes again into the four-way valve 90 and then
reaches a condenser 94, where it cools by evaporating. The fluid then reaches an expansion
valve 96, where the pressure decreases, cooling further and moving again to the temperature
T3. The fluid may thus return to the heat exchanger 10 to cool the secondary circuit
fluid. Figure 6 shows the winter mode operation diagram of the same heat pump.
[0038] In winter mode, there is fluid at temperature T1' in inlet and fluid at temperature
T2', higher than T1' at outlet. The temperature increase from T1' to T2' takes place
inside the heat exchanger 10, thanks to the heat exchange with the fluid of the primary
circuit, which enters the heat exchanger at temperature T5' and exits at temperature
T4', lower than T5'. While travelling along the circuit starting from the outlet of
the port 46 of the heat exchanger, the fluid at temperature T4' reaches the expansion
valve 96, where the pressure decreases, cooling down. The fluid then passes through
the condenser 94, where it cools further by evaporating, reaching a temperature T3',
lower than T4'. The fluid then passes through the four-way valve 90, which is now
in a different configuration than it was in summer mode, to convey the fluid towards
the compressor 92. The compressor compresses the fluid, bringing it to a higher pressure
and, consequently, to a temperature T5', higher than T3' and T4'. The fluid exiting
the compressor passes again in the four-way valve 90 and can thus return to the heat
exchanger 10 to heat the fluid of the secondary circuit.
[0039] Figure 7 shows in detail the hydraulic assembly 100 constituting the secondary circuit.
The hydraulic assembly 100 comprises a circulation pump 102, which pushes the fluid
that passes through it towards a four-way valve 104. The four-way valve 104 may be
configured to send the fluid coming from the pump 102 towards the port 48 or the port
50 of the heat exchanger, of choice. The ports 44 and 46 of the heat exchanger are
intended to be connected to a closed primary circuit for a fluid of a heat pump, as
described above.
[0040] The heat pump, as seen, can be used in heating (winter) or cooling (summer) mode,
by reversing the direction of the fluid in the primary circuit. Since, however, a
heat exchanger operates more efficiently when primary and secondary fluid are in countercurrent,
the four-way valve 104 allows to reverse the direction of the secondary fluid to adapt
it to that of the primary circuit, defined by the mode of operation (heating or cooling).
This results in a maximum efficiency of the heat pump.
[0041] It should also be noted that it is possible to reverse the position of the four-way
valve 104 and of the heat exchanger, obtaining a similar result, i.e. that the fluid
of the secondary circuit and of the primary circuit are always countercurrent. In
this second case, the valve would cause the fluid of the primary circuit to always
enter from the same port 44 or 46, regardless of the mode of operation and, therefore,
of the direction of travel of the fluid in its circuit.
[0042] An exploded view of the four-way valve 90, 104 is shown in Figure 8. The valve comprises
two opposing plates 110, 112. The first plate 110 is provided with two ports 114,
116 and the second plate 112 with two ports 118, 120. A rotating plate 122 is interposed
between them and has two slotted through-holes 124 and 126. The three plates are tightened
together in use, such that each through-hole 124, 126 each connects a port of the
first plate 110 and a port of the second plate 112. By turning the rotating plate
122, it is possible to change the pairing of the ports, as better visible in the diagrams
of Figures 9 and 10.
[0043] Figures 9 and 10 are schematic and partial: they both show all the ports 114, 116,
118, 120 but they do not show the cover plate 112, such as to allow the display of
the rotating plate 122 placed inside the valve.
[0044] In a first configuration (Figure 9), the through-hole 124 connects the ports 116
and 118, while the through-hole 126 connects the ports 114 and 120. In a second configuration
(Figure 10), in which the rotating plate 122 is rotated by 90° with respect to the
position in which it is in the first configuration, the through-hole 124 connects
the ports 114 and 118, while the through-hole 126 connects the ports 116 and 120.
Seals 128 ensure tightness and thus allow the two circuits to be kept separated from
each other.
[0045] Note that the ports can all be provided on one of the two plates 110, 112, the other
being solid, without changing the functionality of the valve.
[0046] The four-way valve shown here can be sized for the passage of water or of a coolant
and finds particular but not exclusive use in a hydraulic assembly 100 for heat pump
such as the one depicted in Figure 7, i.e. comprising a heat exchanger 10. The hydraulic
assembly 100 in turn finds particular but not exclusive use in a heat pump such as
the one described above and illustrated in Figures 5 and 6.
[0047] Of course, while the principle of the invention remains intact, the forms of implementation
and the details of realisation may vary widely from what is described and illustrated,
without thereby departing from the scope of the invention.
1. A heat exchanger comprising a plurality of plates (30a, 30b, 32, 34) fixed to each
other to form first chambers (36) and second chambers (38), the first chambers being
hydraulically connected to each other to form a primary circuit (40) and the second
chambers (38) being hydraulically connected to each other to form a secondary circuit
(42), hydraulically separated from the primary circuit, the heat exchanger further
comprising at least two ports (44 and 46) for the inlet and outlet of a fluid from
the primary circuit and at least two ports (48 and 50) for the outlet and inlet of
a fluid from the secondary circuit, wherein said ports are arranged along an approximately
straight line.
2. A heat exchanger according to the preceding claim, wherein the ports (44, 46, 48,
50) are all positioned on the same side of the heat exchanger.
3. A heat exchanger according to claim 1, wherein the ports (44, 46, 48, 50) are positioned
partly on a first side of the heat exchanger and partly on an opposing side.
4. A heat exchanger according to any one of the preceding claims, wherein in at least
one chamber (38) defined between two contiguous plates (30a, 30b) there is provided
at least one shoulder with an open profile (56, 58).
5. A heat exchanger according to any preceding claim, wherein the shoulder with an open
profile is arranged to partially embrace a connecting bore (64, 66) between adjacent
chambers and preferably has a concavity facing outwards.
6. A heat exchanger according to any one of the preceding claims, wherein each plate
has an elongated shape, with two long sides (2) and two tapered ends (4).
7. A heat exchanger according to any one of the preceding claims, wherein each plate
has an elongated shape that is approximately polygonal, having two long sides (2)
and at least four short sides, or has two long sides and two curved short sides.
8. A heat exchanger according to any one of the preceding claims, wherein the plates
have corrugations (70).
9. A heat exchanger according to any of the preceding claims, wherein the corrugations
are successions of valleys and ridges, arranged in a herringbone pattern, with opposite
direction between adjacent plates (30a , 30b).
10. A hydraulic assembly comprising a heat exchanger according to any one of the preceding
claims, a circulation pump (12) for circulating the primary fluid, and a three-way
valve placed at the inlet of the primary circuit.
11. A hydraulic assembly for a heat pump comprising a heat exchanger (10) having at least
two ports (44 and 46) for inlet and outlet of a primary fluid from a primary circuit
and at least two ports (48 and 50) for outlet and inlet of a secondary fluid from
a secondary circuit, a circulation pump (102) for pumping the secondary fluid in the
secondary circuit of the heat exchanger, and a four-way valve (104) configured to
maintain countercurrent primary flow and secondary flow in the heat exchanger.
12. A hydraulic assembly according to any preceding claim wherein the four-way valve is
interposed between the circulation pump (102) and the heat exchanger, to allow the
pump to pump the secondary fluid in the heat exchanger into one or other port (48
and 50) for inlet of a fluid from the secondary circuit.
13. A hydraulic assembly according to claim 11 or 12, wherein the heat exchanger is a
heat exchanger according to any one of claims 1 to 9.