EP4296602A1

EP4296602A1 - Plate heat exchanger and hydraulic assembly comprising such a heat exchanger

Info

Publication number: EP4296602A1
Application number: EP23179759.8A
Authority: EP
Inventors: Marco Rapaccioli
Original assignee: G20 Engineering Srl
Current assignee: G20 Engineering Srl
Priority date: 2022-06-24
Filing date: 2023-06-16
Publication date: 2023-12-27

Abstract

A heat exchanger comprises 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 comprises 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.

Description

Field of the invention

The present invention refers to a plate heat exchanger and hydraulic assembly comprising such a heat exchanger.
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

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.
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.
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.
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

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.
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.
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.
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.
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.
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.
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.
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.
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.
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

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

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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
The plates are preferably made of steel. Preferably each plate is obtained by moulding from a metal sheet.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.

Claims

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.
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.
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.
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).
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.
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).
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.
A heat exchanger according to any one of the preceding claims, wherein the plates have corrugations (70).
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).
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.
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.
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.
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.