System for heating hot water

Abstract

Hot water heating system (1), preferably intended for hard water, comprising: - a stainless steel water storage tank (2), - a stainless steel heat exchanger (3) and shaped to allow heat exchange between the water stored in the tank (2) and another fluid, for example heated by a heating generator (G), characterized in that the system (1) includes a cathodic protection device (4) comprising at least one anode (18, 19) and a means for generating an electric current (17) in said at least one anode (18, 19).

Description

technical field

[0001] This description falls within the scope of domestic hot water heaters and their protection against corrosion. Documents EP3441 695 A1 and US2018 / 356126 A1 disclose such hot water heaters. Previous technique

[0002] Generally, a hot water heater, preferably for domestic use, denoted DHW, includes a water storage tank and a heat exchanger designed to allow heat exchange between the water stored in the tank and another fluid heated by a heating generator.

[0003] Very high temperatures, reaching for example 1600°C, can be observed in the heat exchanger when the fluid inside is heated by the heating generator. Significant temperatures, up to 150°C, can be measured on the heat exchanger wall in contact with the water stored in the tank.

[0004] As is known, the high temperatures recorded on the wall of the heat exchanger in contact with the water stored in the tank create an accumulation of deposits on the wall of the heat exchanger in contact with the water stored in the tank.

[0005] The deposits are mainly due to the precipitation of ions contained in the water stored in the reservoir and consist mainly of calcium carbonate; this is known as limescale deposits.

[0006] Scale deposits are most frequently observed when the water stored in the tank is hard, that is, when the total hardness (TH) of the water stored in the tank is greater than 20°f.

[0007] The presence of deposits on the wall of the heat exchanger in contact with the water from the tank causes a degradation of the properties of the domestic hot water heater and reduces the lifespan of the domestic hot water heater.

[0008] For example, in the case of a domestic hot water heater with a stainless steel heat exchanger, the presence of deposits creates a cavity between the deposits and the stainless steel wall of the exchanger in contact with the water stored in the tank. This phenomenon is accentuated in the areas of the exchanger where the temperature is highest. This results in a concentration of salts contained in the water stored in the tank, particularly chlorides, on the exchanger wall. Consequently, corrosion phenomena can occur. More specifically, pitting corrosion, also known as differential aeration corrosion, as well as stress corrosion cracking and other forms of corrosion can be observed.

[0009] Corrosion causes leaks in the heat exchanger, quickly rendering the domestic hot water heater unusable.

[0010] Solutions to mitigate corrosion phenomena are known. For example, a water softener can be used upstream of the stainless steel domestic hot water heater, which reduces the concentration of calcium ions in the water contained in the domestic hot water heater and thus reduces the water hardness to a value below 20°f.

[0011] However, installing such a water softener is expensive. Furthermore, regular maintenance of the softener is necessary; otherwise, the aforementioned corrosion problems will occur. In addition, using a water softener can pose health problems, as consuming excessively soft water can lead to health issues. Summary

[0012] The purpose of this description is to address the aforementioned drawbacks.

[0013] For this purpose, the present description relates to a hot water heating system, preferably intended for hard water, comprising a stainless steel water storage tank, a stainless steel heat exchanger and configured to allow heat exchange between the water stored in the tank and another fluid, for example heated by a heating generator, the system comprising a cathodic protection device including at least one anode and a means of generating an electric current in said at least one anode, and finally the internal surface of the water storage tank, intended to be in contact with the water in the tank, is made of stainless steel, and the external surface of the heat exchanger, intended to be in contact with the water in the tank, is made of stainless steel.

[0014] Thanks to the cathodic protection system, the electrochemical potential of the heat exchanger can be lowered, thus passivating the stainless steel. This protects the heat exchanger against corrosion, particularly in the presence of scale deposits. In particular, the heat exchanger's lifespan is significantly increased, especially when the water stored in the tank is hard.

[0015] Furthermore, the system according to the present invention is derived from a simple manufacturing process, since the cathodic protection device can be added to a pre-existing assembly comprising the water storage tank and the heat exchanger.

[0016] Furthermore, the system as described herein is modular, insofar as at least one anode can be advantageously positioned according to the heat exchanger, thus preferentially protecting certain areas of the heat exchanger that might be more susceptible to corrosion. In addition, the current in at least one anode can be configured so that the system is adapted to different operating conditions.

[0017] According to another characteristic of the description, at least one anode is positioned opposite an area of ​​the heat exchanger whose skin temperature is above a threshold value when the system is in operation.

[0018] According to another characteristic of the description, the temperature threshold value is 120°C.

[0019] According to another characteristic of the description, at least one anode is positioned opposite an area of ​​the exchanger such that heat transfer between the water and the other fluid is greater than a threshold value when the system is in operation.

[0020] According to another characteristic of the description, the threshold value of heat transfer is 4 W / cm².

[0021] According to another feature of the description, the system includes a burner for heating the other fluid.

[0022] According to another feature of the description, the heat exchanger includes a circulation duct having at least one cylindrical hearth, a return rod and / or a helical winding.

[0023] According to another characteristic of the description, at least one anode is positioned opposite the focal point.

[0024] According to another feature of the description, at least one anode is positioned opposite the return rod. Brief description of the drawings

[0025] Other features, details, and advantages will become apparent upon reading the detailed description below and analyzing the attached drawings, on which: Fig. 1 [ Fig. 1 ] is a schematic longitudinal cross-sectional view of a hot water preparation system according to the present invention. Fig. 2 [ Fig. 2 [ ] is a schematic perspective view of part of the hot water preparation system of the figure 1 . Fig. 3 [ Fig. 3 ] is a perspective view of a heat exchanger for the system of the figure 1 according to a first variant of the implementation. Fig. 4 [ Fig. 4 ] is a perspective view of a heat exchanger for the system of the figure 1 according to a second embodiment. Description of the implementation methods

[0026] The present description relates to a hot water preparation system, preferably for domestic use, referenced as 1. System 1 is preferably intended to supply hot water to a room, such as a domestic dwelling, individual or collective.

[0027] System 1 is particularly suited to hard water, i.e., water with a hardness of at least 20°f, or even greater than 30°f, or even in the order of 40°f.

[0028] As can be seen in the figures, system 1 mainly comprises a water storage tank 2, a heat exchanger 3 and a cathodic protection device 4, detailed below.

[0029] Tank 2 is preferably made from stainless steel.

[0030] As particularly visible on the Figures 1 And 2, the reservoir 2 has a general cylindrical shape comprising a longitudinal wall 5 extending between a bottom 6 and a top 7. The longitudinal wall 5 is delimited by an internal surface 5' and an external surface 5'.

[0031] Tank 2 further includes a cold water inlet fitting 8 and a hot water outlet fitting 9. Fitting 9 can be located at the top 7, while fitting 8 can be located at the bottom of tank 2, near the bottom 6, as illustrated in the figure 1 .

[0032] As already mentioned, the preparation system 1 includes a heat exchanger 3, made of stainless steel. In the illustrated embodiment, the heat exchanger 3 is in the form of a coil. However, the invention is not limited to this type of exchanger, and the exchanger 3 could, for example, be a plate heat exchanger.

[0033] As is apparent from figures 1 to 4 , the coil 3 includes a conduit 10 extending between an inlet 11 and an outlet 12.

[0034] The gas is advantageously a natural gas, consisting of a mixture of butane and propane, without limitation. However, the invention is not limited to a specific type of fluid, nor to a gaseous fluid, and the use of liquid water could be considered.

[0035] Inlet 11, also known as the cylindrical hearth, is equipped with a gas heating generator G, illustrated on the figure 1 The generator G is preferably a burner. Between the inlet 11 and the outlet 12, the conduit 10 includes a rod, called the return 13, followed by a helical winding 14. Gaseous fuels are introduced into the combustion chamber 11 where the fuels are heated, then hot fumes, resulting from the combustion of the gases, circulate in the winding 14 to the outlet 12.

[0036] The conduit 10 is delimited by a wall comprising an internal surface 15 and an external surface 16. The internal surface 15 is intended to be in contact with the gas, while the external surface 16 is intended to be in contact with the water stored in the tank 2.

[0037] As can also be seen from the figures, the exchanger 3 is immersed in the tank 2, which allows heat exchange between the water contained in the tank and the gas heated by the generator G, via surfaces 15 and 16. It is noted that the helical winding 14 ensures optimization of the exchanges between the two fluids.

[0038] Note that in the illustrated exchanger 3, the water from tank 2 and the gas are separated by a simple wall of the exchanger 3, which also contributes to an optimization of heat exchanges.

[0039] According to a first variant illustrated on the figure 3 And 4We have illustrated two variants of the implementation of the heat exchanger 3.

[0040] The helical winding 14 delimits an internal volume V. As visible at the figure 3 According to a first variant, the combustion chamber 11 is located outside the internal volume V, which optimizes the circulation of hot fumes from gas combustion within the winding 14 under the effect of gravity. Alternatively, as shown in the figure 4 , the hearth 11 is located in the internal volume V, which allows for a reduction in the footprint of the exchanger 3.

[0041] According to the present invention, each part of the tank 2 and the heat exchanger 3 intended to be in contact with the water in the tank is made of stainless steel. In other words, the internal surface 5' of the tank 2 and the external surface 16 of the heat exchanger 3 are made of stainless steel.

[0042] It is noted that, when system 1 is in heating mode, the gas heated by the burner G reaches very high temperatures, for example on the order of 1600°C. This results in a surface temperature 16 that can reach 150°C, a temperature subsequently referred to as the "water side skin temperature" or "water side surface temperature".

[0043] As already mentioned, system 1 includes a cathodic protection device 4.

[0044] Device 4 includes at least one anode and a means 17 for generating an electric current in the anode. This is referred to as an impressed current anode. The means 17 is, for example, a DC voltage generator.

[0045] Said at least one anode is placed in the tank 2 opposite a zone of the heat exchanger 3 where the water-side surface temperature is greater than or equal to a threshold value. The threshold value is advantageously between 110°C and 150°C, preferably between 115°C and 125°C, and preferably still in the order of 120°C.

[0046] Alternatively or in combination, said at least one anode is placed in the tank 2 opposite an area of ​​the exchanger 3 where a surface heat power density value, representing the level of heat transfer between the water and the gas, is greater than or equal to a threshold value. The threshold value is advantageously between 3 W / cm² and 5 W / cm², preferably on the order of 4 W / cm².

[0047] According to an embodiment not shown, device 4 includes a single anode, preferably positioned opposite focal point 11. In the illustrated embodiment, device 4 includes a first anode 18, and a second anode 19.

[0048] The electric current generated by each anode lowers the potential of the stainless steel heat exchanger. This passivates the stainless steel and prevents corrosion under deposits. Despite highly aggressive conditions under limescale deposits, such as overheating, boiling, and salt concentration, System 1 provides long-lasting corrosion protection. To guarantee this durability, the system adapts to field operating conditions. The tank's potential is measured regularly to adjust the current as needed and ensure continuous protection.

[0049] Each anode is made of titanium (Ti), or titanium with a coating of mixed metal oxides (TiMMO). It should be noted that each anode is inert, meaning that it remains unchanged throughout the lifetime of system 1.

[0050] Each of the anodes has, for example, a cylindrical or conical surface. The height of the anode 18, 19 can, for example, be between 80 cm and 50 cm, preferably around 60 cm.

[0051] On the Figures 1 And 2 , the first anode 18 is positioned opposite the focal point 11 while the second anode 19 is positioned opposite the return pipe 13.

[0052] The current generation means 17 can supply both anodes 18, 19, or, alternatively, the device 4 includes a generator 17 dedicated to each anode 18, 19.

[0053] Each generator 17 is controlled by an electronic board, not shown.

[0054] The electronic board allows for self-adjustment of the system via an estimation of the potential of reservoir 2 at regular intervals, for example every second. Advantageously, at least one of the anodes acts as a sensor, the voltage drop across its terminals being measured when the anode is not supplied with electrical current.

[0055] The electronic board can therefore be configured to implement a control of the current to be imposed in each anode 18, 19 to obtain the setpoint value of the electrochemical potential to be reached from the measurement of the electrochemical potential within the storage tank 2. The value of current to be imposed in the anodes 18, 19 can be adjusted in real time.

[0056] As can be seen from the preceding description, system 1 is protected from any corrosion by means of the cathodic protection device 4.

Claims

1. Hot water heating system (1), preferably intended for hard water, comprising: - a stainless steel water storage tank (2), - a steel heat exchanger (3) designed to enable heat exchange between the water stored in the tank (2) and another fluid, for example heated by a heating generator (G), wherein: - the inner surface (5') of the water storage tank (2), designed to be in contact with the water in the tank, is made of stainless steel, the system (1) comprising a cathodic protection device (4) comprising at least one anode (18, 19) and a means of generating an electrical current (17) in said at least one anode (18, 19), characterised in that the heat exchanger is made of stainless steel and the outer surface (16) of the heat exchanger (6), which is intended to be in contact with the water in the tank, is made of stainless steel.

2. System (1) according to Claim 1, wherein said at least one anode (18, 19) is positioned opposite an area of the heat exchanger (3) where a skin temperature exceeds a threshold value when the system (1) is operational.

3. System (1) according to the preceding claim, wherein said temperature threshold value is 120°C.

4. System (1) according to one of the preceding claims, wherein said at least one anode (18, 19) is positioned opposite an area of the exchanger (3) such that heat transfer between the water and the other fluid exceeds a threshold value when the system (1) is operational.

5. System (1) according to the preceding claim, wherein the heat transfer threshold value is 4 W / cm2.

6. System (1) according to any one of the preceding claims, comprising a burner for heating said other fluid.

7. System (1) according to one of the preceding claims, wherein the heat exchanger (3) comprises a circulation duct having at least: - a cylindrical chamber (11), - a return pipe (13), - a helical winding (14).

8. System (1) according to the preceding claim, wherein said at least one anode (18, 19) is positioned opposite the chamber (11).

9. System (1) according to one of Claims 7 or 8, wherein said at least one anode (18, 19) is positioned opposite the return pipe (13).

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