Patent Description:
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.

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. A heat exchanger according to the preamble of claim <NUM> is disclosed in <CIT>.

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.

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.

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:.

<FIG> depicts a heat exchanger <NUM> 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 <NUM> is positioned at the outlet of the primary circuit, to cause the circulation of the primary fluid. A three-way valve <NUM> 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 <NUM> ensures that the pressure of the system never exceeds a predetermined pressure, for example <NUM> or <NUM> bar. A tap <NUM> 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 <NUM> according to the invention comprises a plurality of alternating plates 30a, 30b, placed next to each other and enclosed between a first end plate <NUM> and a second end plate <NUM>, in opposing position with respect to the end plate <NUM>. The plates of the heat exchanger <NUM> are produced by moulding a sheet metal and are subsequently brought together. The first end plate <NUM>, the second end plate <NUM>, 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 <NUM> is copper foil technology.

Each plate has an elongated shape, with two long approximately parallel sides <NUM>. 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 <NUM> and two curved short sides, for example semi-circle or semi-ellipse or more generally two long sides <NUM> and two tapered ends <NUM>.

In the plate package, each pair of facing plates 30a, 30b, <NUM>, <NUM> defines between them a chamber <NUM>, <NUM> for a fluid. The chambers <NUM> are connected to each other to form the primary circuit <NUM> and the chambers <NUM> are connected to each other to form the secondary circuit <NUM>. The chambers <NUM> and <NUM> alternate such that each plate 30a, 30b serves as a dividing wall between the primary circuit <NUM> and the secondary circuit <NUM>, thereby permitting a heat exchange between the primary fluid and the secondary fluid.

The heat exchanger <NUM> is provided with four ports <NUM>, <NUM>, <NUM>, <NUM>, visible in <FIG>. The ports <NUM> and <NUM> are for inlet and outlet of the fluid of the primary circuit, respectively, while the ports <NUM> and <NUM> 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 <NUM>.

According to the variant of <FIG>, the two ports <NUM>, <NUM> of the primary circuit are positioned on the side of the first end plate <NUM> and the two ports <NUM>, <NUM> of the secondary circuit are positioned on the side of the second end plate <NUM> (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 <NUM>, <NUM>, <NUM>, <NUM> are provided between pairs of adjacent plates to separate primary and secondary circuits between them, as known in the sector.

<FIG> shows the course of the fluid within the primary circuit <NUM>, in a chamber <NUM>. Inside the chamber <NUM>, and more specifically on the plate 30b, closed-profile shoulders <NUM> and <NUM> 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 <NUM>, near an end <NUM> of the heat exchanger. The fluid is then directed towards the opposing end <NUM> of the heat exchanger, towards the outlet hole <NUM>. In the figure, the arrows indicate the path that the fluid approximately travels in the chamber <NUM>.

<FIG> instead shows the course of the fluid within the secondary circuit <NUM>, in a chamber <NUM>. Inside the chamber <NUM> shoulders <NUM> and <NUM>, with closed-profile, are provided to separate the primary circuit from the secondary circuit and there is also provided a pair of shoulders <NUM>, <NUM> with open profile, outlining a U. The U-shaped shoulders <NUM>, <NUM> are arranged so as to partially embrace the connection holes <NUM>, <NUM> between adjacent chambers <NUM> and with the concavity facing outwards, more specifically towards the shoulders <NUM>, <NUM>. The water enters from an inlet hole <NUM>, is conveyed from the U-shaped shoulder <NUM> towards an end <NUM> of the heat exchanger, where the shoulder <NUM> is located. The end <NUM> of the heat exchanger causes a reversal of the direction of the flow of the fluid, which is directed towards the opposing end <NUM> of the heat exchanger, where the shoulder <NUM> is located. The fluid is then conveyed inside the U-shaped concavity of the shoulder <NUM> and then towards the outlet hole <NUM>. Of course the shoulders <NUM>, <NUM> 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 <NUM> 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 <NUM>, <NUM>, 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 <NUM>, understood as successions of valleys and ridges, clearly visible in the section of <FIG>. 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 <NUM>, <NUM>. 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 <FIG> and <FIG>, 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 <NUM> and outlet <NUM> 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 <FIG>, has a layout compatible with a standard DIN template.

Referring now to <FIG> and <FIG>, the above-described heat exchanger <NUM> is also applied in a heat pump. <FIG> shows the summer mode operation diagram of a heat pump comprising a heat exchanger <NUM>.

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 <NUM>, 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 <NUM> of the heat exchanger, the fluid at temperature T4 passes through a four-way valve <NUM> and reaches a compressor <NUM>. 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 <NUM> and then reaches a condenser <NUM>, where it cools by evaporating. The fluid then reaches an expansion valve <NUM>, where the pressure decreases, cooling further and moving again to the temperature T3. The fluid may thus return to the heat exchanger <NUM> to cool the secondary circuit fluid. <FIG> 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 <NUM>, 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 <NUM> of the heat exchanger, the fluid at temperature T4' reaches the expansion valve <NUM>, where the pressure decreases, cooling down. The fluid then passes through the condenser <NUM>, where it cools further by evaporating, reaching a temperature T3', lower than T4'. The fluid then passes through the four-way valve <NUM>, which is now in a different configuration than it was in summer mode, to convey the fluid towards the compressor <NUM>. 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 <NUM> and can thus return to the heat exchanger <NUM> to heat the fluid of the secondary circuit.

<FIG> shows in detail the hydraulic assembly <NUM> constituting the secondary circuit. The hydraulic assembly <NUM> comprises a circulation pump <NUM>, which pushes the fluid that passes through it towards a four-way valve <NUM>. The four-way valve <NUM> may be configured to send the fluid coming from the pump <NUM> towards the port <NUM> or the port <NUM> of the heat exchanger, of choice. The ports <NUM> and <NUM> 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 <NUM> 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 <NUM> 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 <NUM> or <NUM>, 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 <NUM>, <NUM> is shown in <FIG>. The valve comprises two opposing plates <NUM>, <NUM>. The first plate <NUM> is provided with two ports <NUM>, <NUM> and the second plate <NUM> with two ports <NUM>, <NUM>. A rotating plate <NUM> is interposed between them and has two slotted through-holes <NUM> and <NUM>. The three plates are tightened together in use, such that each through-hole <NUM>, <NUM> each connects a port of the first plate <NUM> and a port of the second plate <NUM>. By turning the rotating plate <NUM>, it is possible to change the pairing of the ports, as better visible in the diagrams of <FIG>.

<FIG> are schematic and partial: they both show all the ports <NUM>, <NUM>, <NUM>, <NUM> but they do not show the cover plate <NUM>, such as to allow the display of the rotating plate <NUM> placed inside the valve.

In a first configuration (<FIG>), the through-hole <NUM> connects the ports <NUM> and <NUM>, while the through-hole <NUM> connects the ports <NUM> and <NUM>. In a second configuration (<FIG>), in which the rotating plate <NUM> is rotated by <NUM>° with respect to the position in which it is in the first configuration, the through-hole <NUM> connects the ports <NUM> and <NUM>, while the through-hole <NUM> connects the ports <NUM> and <NUM>. Seals <NUM> 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 <NUM>, <NUM>, 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 <NUM> for heat pump such as the one depicted in <FIG>, i.e. comprising a heat exchanger <NUM>. The hydraulic assembly <NUM> in turn finds particular but not exclusive use in a heat pump such as the one described above and illustrated in <FIG> and <FIG>.

Claim 1:
A heat exchanger comprising a plurality of plates (30a, 30b, <NUM>, <NUM>) fixed to each other to form first chambers (<NUM>) and second chambers (<NUM>), the first chambers being hydraulically connected to each other to form a primary circuit (<NUM>) and the second chambers (<NUM>) being hydraulically connected to each other to form a secondary circuit (<NUM>), hydraulically separated from the primary circuit, the heat exchanger further comprising at least two ports (<NUM> and <NUM>) for the inlet and outlet of a fluid from the primary circuit and at least two ports (<NUM> and <NUM>) for the outlet and inlet of a fluid from the secondary circuit, wherein said ports are arranged along an approximately straight line, characterised in that in at least one chamber (<NUM>) defined between two contiguous plates (30a, 30b) there is provided at least one shoulder with an open profile (<NUM>, <NUM>), it being arranged to partially embrace a connecting bore (<NUM>, <NUM>) between adjacent chambers and having a concavity facing outwards.