Heating unit for heating coffee machine water and related coffee machine

Abstract

The present invention relates to an heating unit (1) for heating coffee machine water, the heating unit (1) comprising: a boiler (2) defining a tank. (3) adapted to receive a volume of water, a heater (4) associated with the boiler (2) and configured to heat the volume of water to a predefined temperature, a heat exchanger (5) having a tubular duct (6) arranged at least partly within the tank (3) of the boiler (2), the tubular duct (6) setting one inlet (7) and one outlet (8) of the heat exchanger (5) in fluid communication with each other, the inlet (7) being configured to receive water at a first temperature from a water supply (9), the outlet (8) being configured to feed heated water at a second temperature to a brewing assembly (10) of a coffee machine (100), the second temperature being higher than the first temperature, the heating unit being characterized by the fact that the tank (3) is made of a first material having a respective first thermal conductivity, and that the tubular duct (6) is made at least partly of a second material having a second thermal conductivity greater than the first thermal conductivity.

Description

[0001] HEATING UNIT FOR HEATING COFFEE MACHINE WATER AND RELATED COFFEE MACHINE

[0002] Technical field of the Invention

[0003] The present invention relates to a heating unit for heating coffee machine water and to the coffee machine comprising such a unit.

[0004] Background Art

[0005] The use of espresso coffee machines having one or more brewing assemblies for the preparation of hot drinks and / or steam is known to the prior art.

[0006] The general operation of such machines involves cold water coming from the water supply being heated, pressurized and fed to the brewing assembly towards the ground coffee for the production of espresso coffee,

[0007] Considering the conditions of use of such coffee machines, it is necessary for the water to be brought to the optimum temperature and pressure conditions for coffee extraction in a short time, generally in a few seconds.

[0008] To this end, known coffee machines have a boiler and a heat exchanger that work together to heat the water intended to brew coffee up to a temperature of 90-95°C. The boiler collects a predefined volume of cold water which is heated by an electric resistance or a gas burner to a temperature of between 110°C and 120°C. The boiler is in fact designed so as to withstand high temperatures and pressures. The heat exchanger is arranged along a fluid path connecting the water supply to the brewing assembly and passes through the boiler.

[0009] The heat exchanger is generally defined by a coil or by a pipe immersed in the hot water and in the steam contained in the boiler.

[0010] In particular, the operation requires that the water passing through the heat exchanger be heated by the heat transferred from the hot water and from the steam in the boiler. The water is heated by conduction with heat transfer from the volume of water in the boiler to the heat exchanger and, therefore, to the water passing through the heat exchanger itself.

[0011] In the prior art, the boiler and the heat exchanger are generally made in a single body piece, made of copper or stainless steel, taking into account the need for rapid and efficient heating of the water intended for the brewing assembly,The Applicant has realized that known systems are not very efficient in terms of energy and versatility of use.

[0012] In fact, although copper has high thermal conductivity which facilitates the heating of the water passing through the heat exchanger, this high thermal conductivity causes excessive heat loss from the boiler to the outside environment.

[0013] On the other hand, using a material with lower thermal conductivity, such as stainless steel, allows this heat loss to be reduced at the expense of slower water heating for coffee brewing.

[0014] Object of the Invention

[0015] The Applicant realized the need to develop a solution that allows rapid heating of the water intended for the brewing assembly and reduced energy consumption. A further object of this description is to provide a heating unit and a coffee machine that allow heat loss to be reduced from the boiler to the surrounding environment.

[0016] A further object of this description is to provide a heating unit and a coffee machine that are versatile and easy to manufacture.

[0017] The aforementioned objects are achieved by the heating unit in accordance with claim 1.

[0018] The aforementioned objects are achieved by the coffee machine in accordance with claim 10.

[0019] Brief description of the drawings

[0020] Some embodiments and aspects of the invention will be described below with reference to the accompanying drawings, which are provided for illustrative purposes only and are therefore not limiting, wherein:

[0021] - Figure 1 is a perspective view of the heating unit according to the invention,

[0022] - Figure 2 shows a sectional view of the unit in Figure 1,

[0023] - Figure 3 is a perspective view of a detail of the unit according to the invention,

[0024] - Figure 4 illustrates a sectional view of the detail in Figure 3S- Figure 5 is a block diagram of a coffee machine according to the invention.

[0025] Detailed description

[0026] This description relates to a water heating unit 1 for a coffee machine 100. In particular, the heating unit 1 is configured to receive water from a water supply 9 and feed water to a brewing assembly of the coffee machine 100.

[0027] The heating unit 1 comprises a boiler 2 that defines a tank 3 adapted to receive a volume of water. The tank 3 is set in fluid communication with the water supply 9 to receive a predefined volume of water from such water supply 9.

[0028] In particular, the heating unit 1 has a feeding fluid path 23 connecting the boiler 2 to the water supply 9. The tank 3 of the boiler 2 is configured to be set in fluid communication with the water supply 9 by means of the feeding fluid path 23. According to one aspect, the heating unit 1 may comprise a first valve arranged along the feeding fluid path 23 to allow / prevent the supply of water to the boiler

[0029] In one embodiment, the tank 3 has a volume of between 0.3 liters and 3 liters, preferably of between 0.5 liters and 2.5 liters. The volume of water receivable by the boiler 2 is of between 0.3 liters and 3 liters, preferably of between 0.5 liters and 2.5 liters.

[0030] The heating unit 1 comprises a heater 4 associated with the boiler 2. In detail, the heater 4 is configured to heat said volume of water to a predefined temperature. According to one aspect, the heater 4 is configured to activate when the temperature of the water contained in the boiler 2 drops below a threshold value or the predefined temperature and / or to remain active until such predefined temperature is achieved.

[0031] In particular, the predefined temperature is equal to or greater than 90°C, preferably equal to or greater than 95 °C, and even more preferably equal to or greater than 100 °C. According to one aspect, the predefined temperature may be of between 90°C and 150°C, preferably of between 110°C and 120°C. The tank 3 of the boiler 2 may contain water in the liquid state and in the gaseous state. In other words, the boiler 2 may contain water and steam.The heater 4 may comprise an electric resistance arranged in the tank 3 of the boiler 2. The electric resistance is configured to heat the volume of water contained in the boiler 2.

[0032] In one embodiment, the heater 4 comprises a gas burner arranged externally to the boiler 2 and configured to heat the volume of water in the boiler 2 by means of the combustion of a gaseous fuel. The gas burner may be configured to use methane.

[0033] The heating unit 1 also comprises a heat exchanger 5 having a tubular duct 6. The heat exchanger 5 is constrained to the boiler 2. In detail, this tubular duct 6 is arranged at least partly within the tank 3 of said boiler 2.

[0034] The tubular duct 6 sets one inlet 7 and one outlet 8 of the heat exchanger 5 in fluid communication with each other. In particular, the inlet 7 of the heat exchanger 5 is configured to receive water at a first temperature from the water supply 9. The outlet 8 is configured to feed heated water at a second temperature to the brewing assembly 10 of the coffee machine 100.

[0035] The first temperature is variable, e.g. depending on the location of the water supply 9, the time of year or the time of day. The first temperature can be of between 6 °C and 20°C, preferably of between 8°C and 15°C.

[0036] The second temperature is higher than the first temperature, In particular, the second temperature may vary depending on the type of brewing assembly 10 of the coffee machine 100, the coffee blend, and the characteristics of the coffee machine 100. Specifically, the second temperature is of between 88°C and 96°C, preferably of between 90 °C and 95 °C, and even more preferably around 93 °C. The second temperature may be higher than 95°C, for example when water from the heat exchanger 5 is fed to a brewing assembly 10 for steam generation. The second temperature may be of between 110°C and 125°C, preferably of between 120°C and 125°C, when the heating unit 1 is used for steam generation, e.g. for frothing milk.

[0037] The tank 3 of the heating unit 1 of the invention is made of a first material having a respective first thermal conductivity. The tubular duct 6 of the heat exchanger 5 is made at least partly of a second material having a respective second thermalconductivity. The first and second thermal conductivities are different from each other. In detail, the second thermal conductivity is greater than the first thermal conductivity.

[0038] According to one aspect, the first thermal conductivity and the second thermal conductivity differ from each other by an order of magnitude.

[0039] In particular, the first material may have a respective first thermal conductivity less than or equal to 100λ (W·m-1K-1), preferably less than 50λ (W·m-1K-1)4), and even more preferably of between 100λ (W·m4K4) and 10% (W-m4K ). In detail, the first thermal conductivity is of between 15λ (W·m-1K-1) and 17λ (W·m-1K-1), preferably equal to 15λ (W·m-1K-1).

[0040] According to one aspect, the second material may have a second thermal conductivity greater than or equal to 200λ (W·m-1K-1), preferably greater than 300λ (W·m-1K-1), and even more preferably of between 285λ (W·m-1K-1) and 420λ (W·m-1K-1). In detail, the second thermal conductivity is of between 390λ (W·m-1K-1) and 395λ (W·m-1K-1), preferably equal to 390λ (W·m-1K-1).

[0041] In one embodiment, the first material is steel. In particular, the first material is stainless steel for food-grade use, e.g. AISI 316 / 316L steel.

[0042] According to one aspect, the second material may be copper or aluminum. In detail, the second material is copper with thermal conductivity equal to approximately 390λ. The second material may also be aluminum with thermal conductivity equal to approximately 290λ. Preferably, the tubular duct 6 is entirely made of copper.

[0043] In one embodiment, the heat exchanger 5 comprises a first linking member 11 and a second linking member 12. These linking members 11, 12 are constrained to the tubular duct 6. In particular, the heat exchanger 5 and the boiler 2 are constrained to each other by means of the first linking member 11 and of the second linking member 12.

[0044] According to one aspect, the first linking member 11 defines the inlet 7 of the heat exchanger 5. In detail, this first linking member 11 is connectable to the water supply 9 through a first fluid path 13.The second linking member 12 defines the outlet 8 of the heat exchanger 5 and is connectable to the brewing assembly 10 through a second fluid path 14. The tubular duct 6 of the heat exchanger 5 joins and sets the first fluid path 13 in fluid communication with the second fluid path 14.

[0045] In particular, the first linking member 11 and the second linking member 12 have respective holes defining the inlet 7 and the outlet 8 of the heat exchanger 5. In one embodiment, the heating unit 1 comprises threaded flanges 2a, 2b arranged externally to the tank 3. Each of these threaded flanges 2a, 2b is associated with the linking members 11, 12 of the heat exchanger 5. In particular, the threaded flanges 2a, 2b are configured to connect to pipes defining the first fluid path 13 and the second fluid path 14. In detail, the inlet 7 is set in communication with the first fluid path 13 by means of a respective threaded portion 2a. Tire outlet 8 of the heat exchanger 5 is set in communication with die second fluid path 14 by means of a different respective threaded portion 2b.

[0046] The threaded flanges 2a, 2b may project from the outer surface of the tank 3 in order to facilitate their connection to these pipes and to promote any maintenance operations.

[0047] In particular, the water is at the first temperature along the first fluid path 13 and at the second temperature along the second fluid path 14. The water temperature varies from the first temperature to the second temperature as it passes through the tubular duct 6 of the heat exchanger 5.

[0048] In one embodiment, the heating unit 1 comprises a second valve 26 arranged along the first fluid path 13 and / or a third valve arranged along the second fluid path 14. The second valve 26 and the third valve are configured to allow / prevent the fluid passage along the respective fluid path.

[0049] In one embodiment, the heat exchanger 5 has a substantially cylindrical shape. In particular, the tubular duct 6 comprises a pipe with a circular cross-section. The circular cross-section of the tubular duct 6 has a diameter of between 34 mm and 32 mm. In detail, the tubular duct 6 has a circular cross-section with an inner diameter of 33 mm.In one embodiment, the first linking member 11 and the second linking member 12 are fitted on the tubular duct 6 at the opposite sides 6 a, 6b of the same tubular duct 6. In other words, the linking members 11, 12 define opposite ending portions of the heat exchanger 5.

[0050] In particular, the first linking member 11 and the second linking member 12 are arranged spaced apart from each other along a longitudinal axis A of the heat exchanger 5. The tubular duct 6 is arranged along such longitudinal axis A located between the first and the second linking members 11, 12.

[0051] In one embodiment, the first linking member 11 and the second linking member 12 are made of the first material. The tubular duct 6 may be entirely made of the second material. The first linking member 11 and the second linking member 12 may be welded to the boiler 2.

[0052] According to one aspect, the first linking member 11 and the second linking member 12 are constrained to the tubular duct 6 by means of a layer 15 of a third material. In detail, this third material is compatible with the first and second materials so as to constrain them stably together.

[0053] The third material may be a metal or a metal alloy. In particular, the third material is of the type of a filler metal or of a welding material. In one embodiment, the third material is a metal alloy comprising silver. This alloy allows the third material to be sufficiently elastic to allow for any thermal expansion of Hie tubular duct 6 and of the linking members 11, 12. For this purpose, the tubular duct 6. the first linking member 11, and the second linking member 12 define at least one expansion zone 11a, 12a or span between them.

[0054] The tubular duct 6 is configured to expand within the expansion zone Ila, 12a and / or to retract from the same expansion zone Ila, 12a as the predefined temperature and / or an inner temperature within the boiler 2 varies, In particular, during the heating of the water present in the boiler 2, the tubular duct 6 can expand in the expansion zone 11a, 12b.

[0055] According to one aspect, each linking member 11, 12 defines a respective expansion zone 11a, 12b or span at the respective side 6a, 6b of the tubular ductAdvantageously, the span Ila, 12a between the linking member and the duct 6 allows the tubular duct 6 to expand while maintaining a firm and stable constraint between the tubular duct 6 and the linking members 11, 12.

[0056] Usefully, each linking member 11, 12 is constrained to the tubular duct 6 by brazing or soldering.

[0057] In one embodiment, the first linking member 11 and the second linking member 12 are constrained to the boiler 2. preferably welded to the boiler 2 itself.

[0058] Since the linking members 11 and 12 are preferably made of stainless steel, which is the same material as the tank 3, it is possible to join the heat exchanger 5, and therefore the duct 6, to the tank 3 by welding (preferably TIG or laser welding with material addition) or by fusion (without material addition).

[0059] According to one aspect, the boiler 2 extends between one end 16 and an opposite end 17 along a direction of development X. The heat exchanger 5 extends transversely, preferably perpendicularly, to the direction of development X. Therefore, the longitudinal axis A of the heat exchanger 5 is perpendicular to the direction of development X.

[0060] In one embodiment, the boiler 2 has at least a first and a second opening 18, 19. These openings 18, 19 pass through a thickness of the boiler 2. In particular, the first linking member 11 and the second linking member 12 are constrained to the boiler 2 at these openings 18, 19, preferably by welding or fusion bonding. The first linking member 11 and the second linking member 12 pass through the first opening 18 and the second opening 19, respectively.

[0061] In particular, the openings 18, 19 are aligned with each other at the same distance from the end 16 of the boiler 2. In detail, the first opening 18 and the second opening 19 face each other.

[0062] According to one aspect, the first opening 18 and the second opening 19 are circular in shape. In detail, the first opening 18 and / or the second opening 19 has a maximum diameter equal to approximately 40 millimeters.

[0063] In one embodiment, the heating unit 1 comprises an additional heat exchanger 5*. In particular, the additional heat exchanger 5’ may be placed in series or in parallel with said heat exchanger 5. The additional heat exchanger 5’ comprises arespective tubular duct 6h a respective first linking member 11’ and a respective second linking member 12’. 'Hie additional heat exchanger 5’ is entirely similar to, or identical with, the heat exchanger 5 and will not be described further on. In particular, the two heat exchangers 5, 5’ are spaced apart from each other along the direction of development X.

[0064] In one embodiment, the heating unit 1 comprises a control unit 21 in signal communication with the heater 4 and configured to command the switching on and off of such heater 4. In detail, the control unit 21 is set in signal communication with the electric resistance and / or with the gas burner.

[0065] In addition, the heating unit 1 may comprise at least one temperature sensor and / or a pressure sensor 25 associated with the tank 3 of the boiler 2 and configured to generate temperature and / or pressure data representative of the temperature and / or pressure value in the boiler 2.

[0066] The control unit 21 is set in signal communication with this temperature and / or pressure sensor 25 and configured to:

[0067] - receive such temperature and / or pressure data from the temperature sensor and / or from the pressure sensor 25,

[0068] - receive operating parameters representative of one or more of the following: such predefined temperature, a temperature threshold value, a pressure limit value,

[0069] - generate an on / off signal based on a comparison between such temperature and / or pressure data and said operating parameters,

[0070] - control the switching on / off of the heater 4 based on such on / off signal.

[0071] For example, the control unit 21 can be configured to activate the heater 4 when the temperature measured by the temperature sensor 25 is lower than the predefined temperature.

[0072] Furthermore, for example, the control unit 21 may be configured to deactivate the heater 4 when the inner pressure of the boiler 2 measured by the pressure sensor is higher than a pressure limit value.

[0073] In one embodiment, the heating unit 1 comprises a safety valve associated with the tank 3 of the boiler 2 and configured to allow / prevent the fluid from escapingfrom the tank. For example, the safety valve can be configured to allow the steam and / or hot water to escape from the tank to the outside environment in an automatic and / or controlled manner.

[0074] The safety valve may be of the solenoid valve type and set in signal communication with the control unit 21. The control unit 21 may be configured to activate the safety valve to allow a release of steam and / or water from the boiler 2 when the inner pressure of the boiler exceeds the pressure limit value.

[0075] In accordance with a further embodiment, the heating unit 1 is configured to prevent corrosion phenomena within the boiler 2. For this purpose, the boiler 2 comprises a sacrificial anode 27 intended to be associated with a fitting 26 preferably positioned at the tank 3.

[0076] This sacrificial anode 27 is made of a material having a lower electrochemical potential than the material of which the tank 3 is made, e.g. stainless steel. In this way, the anode 27 serves as a galvanic protection element. In particular, the sacrificial anode 27 serves as a lightning rod, attracting and concentrating on itself any parasitic currents (also known as Foucault currents) that may be generated within the boiler 2 during the operation thereof. By concentrating the oxidation process on itself, the anode 27 corrodes in a preferential manner, thus preserving the soundness of the other metal parts of the boiler 2 and of the heat exchanger 5. Advantageously, the sacrificial anode 27 is fitted in a removable manner into the fitting of the safety valve 26, thus allowing for easy inspection and replacement during periodic maintenance operations. This ensures long-lasting and effective protection against corrosion, significantly increasing the service life and reliability of the whole heating unit 1.

[0077] According to one aspect, one or more of the first valve, the second valve, and the third valve may be of the solenoid valve type and set in signal communication with the control unit 21. The control unit 21 is configured to command the operation of such first, second, and third valves and, therefore, the passage of fluid along the respective fluid paths.

[0078] In one embodiment, the heating unit 1 comprises a return fluid path 24 connecting the brewing assembly 10 to the tank 3 of the boiler 2. The brewing assembly 10may be configured to substantially send water at the second temperature to the boiler 2 through such return fluid path 24.

[0079] In particular, the return fluid path 24 may at least, partly define a thermosiphon circulation path. In other words, the return fluid path 24 allows hot water to maintain the brewing assembly 10 at an optimal temperature for brewing beverages, such as coffee, even during standby times, i.e., times when the brewing assembly is not in use. According to one aspect, the return fluid path 24 advantageously allows hot water to exchange heat with the brewing assembly 10 even when the pumping means are not activated.

[0080] In one embodiment, the boiler 2 has additional through openings passing through a thickness of the boiler 2. In particular, one or more of these openings is adapted to receive the heater, preferably the electric resistance. The heater can be arranged to project into the interior of the tank from one of these openings in the boiler. Furthermore, the heater may have a portion passing through this opening with means for the electrical connection to an electric supply.

[0081] According to one aspect, one or more of the additional openings are adapted to be associated with a removable cap for emptying and / or maintaining the boiler. For example, one of the additional openings may allow a technician to perform maintenance operations within the boiler through the same additional opening. In one embodiment, the temperature sensor and the pressure sensor 25 may be arranged at respective ones of said additional openings projecting into the interior of the boiler 2.

[0082] The present invention also relates to the coffee machine 100 comprising the heating unit 1 in accordance with any of the embodiments described herein. The machine 100 comprises a brewing assembly 10. In particular, the brewing assembly 10 is configured to receive hot water at the second temperature from the heating unit 1 and to brew a quantity of beverage, e.g. espresso coffee.

[0083] The machine 100 comprises a first fluid path 13 connecting the inlet 7 of the heat exchanger 5 to the water supply 9. and a second fluid path 14 connecting the outlet 8 of the heat exchanger 5 to the brewing assembly 10.In addition, the machine 100 comprises pumping means 22 arranged along the first fluid path 13, These pumping means 22 are configured to receive water at the first temperature from the water supply 9 and to feed such water at the first temperature to the inlet 7. These pumping means may also be arranged along the fluid path for feeding the boiler to send water to the boiler 2 itself.

[0084] In detail, the brewing assembly 10 is configured to receive water at the second temperature from the outlet 8 of the heat exchanger 5 through such second fluid path 14.

[0085] The present invention also relates to the method of manufacturing the heating unit 1 in accordance with any of the embodiments described. The method comprises one or more of the following phases:

[0086] - providing a tank made of a first material having a first thermal conductivity, preferably of stainless steel,

[0087] ~ providing a tubular duct 6 at least partly made of a second material having a second thermal conductivity greater than the first thermal conductivity, preferably of copper,

[0088] - constraining the tubular duct 6 inside the tank 3.

[0089] In one embodiment, the method comprises one or more of the following phases: - making one or more openings 18, 19 passing through the thickness of the tank 3,

[0090] - axially positioning the heat exchanger 5 at these openings 18, 19 and constraining it to the tubular duct 6 so that the inlets 7 and the outlet 8 may be accessible from outside the boiler 2.

[0091] Furthermore, the method comprises the phases of:

[0092] - connecting the inlet 7 to the water supply 9 by means of a first fluid path 13, - connecting the outlet 8 to the brewing assembly of a coffee machine 100 by means of a second fluid path 14.

[0093] In one embodiment, the method involves constraining the steel linking members 11 and 12 to opposite sides of the tubular duct 6 made of copper, preferably by welding or brazing using a third material, e.g. a silver alloy.Since the linking members 11 and 12 are preferably made of stainless steel, which is the same material as the tank 3, it is possible to join the duct 6 to the tank 3 by welding (preferably TIG or laser welding with material addition) or by fusion (without material addition).

Claims

CLAIMS1) Heating unit (1) for heating coffee machine water, said heating unit (1) comprising:a boiler (2) defining a tank (3) adapted to receive a volume of water,a heater (4) associated with said boiler (2) and configured to heat said volume of water to a predefined temperature,a heat exchanger (5) having a tubular duct (6) arranged at least partly within the tank (3) of said boiler (2), said tubular duct (6) setting one inlet (7) and one outlet (8) of said heat exchanger (5) in fluid communication with each other, said inlet (7) being configured to receive water at a first temperature from a water supply (9). said outlet (8) being configured to feed heated water at a second temperature to a brewing assembly (10) of a coffee machine (100), said second temperature being higher than the first temperature,the heating unit being characterized by the fact thatsaid tank (3) is made of a first material having a respective first thermal conductivity, and thatsaid tubular duct (6) is made at least partly of a second material having a second thermal conductivity greater than the first thermal conductivity.2) Heating unit (1) according to the preceding claim, wherein said heat exchanger (5) comprises a first linking member (11) and a second linking member (12) constrained to said tubular duct (6), and wherein:the first linking member (11) defines the inlet (7) and can be connected to said water supply through a first fluid path (13),the second linking member (12) defines the outlet (8) and can be connected to said brewing assembly (10) through a second fluid path (14).3) Heating unit (1) according to the preceding claim, wherein said first linking member (11) and said second linking member (12) are fitted on said tubular duct (6) at the opposite sides (6a, 6b) of said tubular duct (6).4) Heating unit (1) according to claim 2 or 3, wherein said tubular duct (6), the first linking member (11) and the second linking member (12) define at least one expansion zone (1 la, 12a), said tubular duct (6) being configured to expandwithin said expansion zone (1 la, 12a) and / or to retract from said expansion zone (Ila, 12a) upon changing a temperature within the boiler and / or said predefined temperature,5) Heating unit (1.) according to any of the preceding claims 2 to 4, wherein the first linking member (11) and the second linking member (12) are made of said first material and / or constrained to said tubular duct (6) by means of a layer (15) of a third material.6) Heating unit (1) according to any of the preceding claims, wherein the boiler (2) extends between one end (16) and an opposite end (17) along a direction of development (X), said heat exchanger (5) extending transversely, preferably perpendicularly, to said direction of development (X),7) Heating unit (1) according to any of the preceding claims when dependent on claim 2, wherein said boiler (2) has at least a first and a second opening (18, 19) passing through a thickness of said boiler (2), said first linking member (11) and said second linking member (12) being constrained to and passing through said first and second opening (18. 19), respectively.8) Heating unit (1) according to any of the preceding claims, wherein:said first material has a respective first thermal conductivity less than or equal to 100λ, and / orsaid first material has a respective first thermal conductivity comprised between 100λ and 10λ, and / orsaid second material has a respective second thermal conductivity greater than or equal to 200λ, and / orsaid second material has a respective second thermal conductivity comprised between 285λ and 420λ.9) Heating unit (1) according to any of the preceding claims, wherein: said heating unit (1.) comprises an additional heat exchanger (5’) placed in series or in parallel with said heat exchanger (5), and / orsaid heater (4) comprises an electrical resistance arranged in the tank (3) of said boiler (2) and configured to heat said volume of water contained in the boiler (2).10) Heating unit (1) according to any of the preceding claims, wherein the first material is steel.11) Heating unit. (1) according to any of the preceding claims, wherein the second material is copper or aluminum.12) Heating unit (1) according to any of the preceding claims, comprising a sacrificial anode (27) associated with said tank (3) and configured to protect said tank (3) from corrosion.13) Heating unit (1) according to the preceding claim, wherein said tank (3) comprises a fitting (26) and wherein said sacrificial anode (27) is fitted in a removable manner into said fitting (26).14) Heating unit (1) according to claim 12 or 13, wherein said sacrificial anode (27) is configures to attract any parasitic currents generated within said tank (3), serving as a protection against galvanic corrosion.15) Coffee machine (100) comprising:a heating unit (1) according to any of the preceding claims,a brewing assembly (10),a first fluid path (13) connecting the inlet (7) of said heat exchanger (5) to said water supply (9),a second fluid path (14) connecting the outlet (8) of said heat exchanger (5) to said brewing assembly (10),pumping means (22) arranged along said first fluid path (13) and configured to receive water at the first temperature from said water supply (9) and to feed said water at the first temperature to said inlet (7). whereinsaid brewing assembly (10) is configured to receive water at the second temperature from the outlet (8) of said heat exchanger (5) through said second fluid path (14).

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