Water storage tank with submerged rigid tubular coil heat exchanger

Abstract

The invention relates to a water storage tank (1) comprising a cylindrical shell (1a) with a vertical longitudinal axis (ZZ'), a domed bottom (1b) closing one end of the shell (1a), and a heat energy exchanger with a tubular coil (4') immersed in the water of the tank (1) and transporting a heat transfer fluid between an inlet pipe (5) and an outlet pipe (6). The exchanger (4') comprises a first tubular section forming a cylindrical spiral whose turns (40') are coaxial with the longitudinal axis (ZZ') and a second tubular section in series with one end of the first tubular section. According to the invention, the second tubular section forms a spiral whose turns (41'a - 41'e) are coaxial with the longitudinal axis (ZZ') and have a decreasing radius of curvature such that an external envelope of the second section substantially follows the internal surface of the domed bottom (1b). Figure for abstract: Fig.2

Description

Title of the invention: Water storage tank with submerged rigid tubular coil heat exchanger Technical field

[0001] The present invention relates to the general field of water storage tanks, and more specifically to a water storage tank comprising a tubular coil heat energy exchanger intended to be immersed in the water of the tank in order to allow a transfer of heat energy with the water present in the tank in the vertically installed position.

[0002] The invention relates more particularly to a water storage tank comprising a shell of substantially cylindrical shape whose longitudinal axis is vertical in the installed position, a domed bottom closing one end of the shell, and a heat energy exchanger with a tubular coil intended to be immersed in the water of the tank to transport a heat transfer fluid between a heat transfer fluid inlet pipe and a heat transfer fluid outlet pipe, the heat transfer fluid inlet pipe and the heat transfer fluid outlet pipe being respectively connected to a first end and to a second end of the heat energy exchanger with a tubular coil. Technological background

[0003] Such tanks are used, for example, in domestic hot water storage tanks or domestic hot water heaters with vertical installation.

[0004] [Fig.l] schematically illustrates a known tank 1 for a hot water tank or heater installed in a vertical position. The tank 1 is conventionally produced by assembling a shell 1a, generally cylindrical in shape, whose longitudinal axis ZZ' is vertical in the installed position. The shell 1a is closed at its upper end and its base by two bottoms, respectively a lower bottom 1b and an upper bottom 1c.

[0005] In the following, we are interested in tanks for which at least one of the two bottoms, the lower bottom 1b in the non-limiting example of [Fig.l], is a domed type bottom. The bottoms 1b and 1c are generally of similar shape. The shell 1a and the two bottoms 1b and 1c are generally made of steel with an enamelled internal wall.

[0006] Feet 1d are fixed to the external part of the curved lower bottom 1b in order to place the tank 1 on the ground S and allow it to be kept in a vertical position.

[0007] The tank 1 illustrated by way of non-limiting example comprises an inlet tapping 2 for bringing cold water into the tank 1 (in the direction of the arrow F1), and an outlet tapping 3 for bringing heated water contained in the tank 1 out (in the direction of the arrow F1). direction of arrow F2). In this non-limiting example, the cold water enters the interior of the tank 1 through the inlet connection 2 which extends substantially horizontally at the level of the domed lower bottom 1b, and the heated water is taken at the level of the outlet connection 3, which here extends vertically through the upper bottom 1c of the tank 1.The water contained in the tank 1 is heated by a heat exchanger 4, here of the tubular coil type, intended to be immersed in the water of the tank 1 to transport a heat transfer fluid between a heat transfer fluid inlet pipe 5 and a heat transfer fluid outlet pipe 6 of an external heating system, the heat transfer fluid inlet pipe 5 and the heat transfer fluid outlet pipe 6 being respectively connected to a first end, here upper, and to a second end, here lower, of the tubular coil heat exchanger 4 in order to heat the water present in the lower part of the tank 1 in the installed position.The heat transfer fluid is heated by any heating system (not shown) external to the tank 1, comprising for example a heat pump, a solar energy heating system, or any other device making it possible to create, in a closed loop connection between the two ends of the tubular coil heat exchanger 4, a primary heating circuit. The heated heat transfer fluid enters the tubular heat exchanger (in the direction of arrow F3) at the inlet pipe 5, travels through the entire exchanger 4 heating the liquid contained in the tank 1, and leaves the exchanger (in the direction of arrow F4) at the outlet pipe 6. During its travel, the heated heat transfer fluid transfers heat to the walls of the exchanger, which in turn transfer their heat to the water contained in the tank 1. The heat transfer fluid used is for example water.

[0008] The heating temperature of the water contained in the tank 1 is preferably regulated by means of one or more thermostats each extending through an opening made in the tank 1, such as the three thermostats 7 carried at the level of a wall of the shell 1a, to heat the water according to a set temperature.

[0009] In the case where the tank is intended for collective use in a building, a hot water loop runs continuously in the building, and the tank 1 may also have a tapping 8 used for the loop return.

[0010] The tank 1 further comprises an access hatch 9 closing a through opening made at chest height on the shell 1a. The through opening has a sufficiently large diameter, for example of the order of 400 millimeters, to allow a technician to inspect and maintain the interior of the tank and detect any traces of corrosion or scaling or to clean the interior thereof.

[0011] A hot water storage tank mostly operates by accumulation, that is to say, it does not heat the water continuously, but accumulates a quantity of hot water for daily needs and operates according to the principle of stratification. More precisely, cold water under pressure enters the tank 1 as it empties to meet domestic hot water needs. The cold water that enters is heated by the heat exchanger 4 and gradually rises to the top of the tank 1. Indeed, like air, hot water has a lower density than cold water. It is therefore lighter and naturally rises. On the other hand, cold water, naturally denser, remains at the bottom of the tank. It is this physical principle which is at the origin of the name stratification. Since the aim is to heat mainly the water contained at the bottom of the tank, it is necessary to provide a particular shape for the tubular coil heat exchanger 4.

[0012] To date, most tubular coil heat exchangers have the shape shown in [Fig.l] with: - a first tubular section forming a cylindrical spiral whose successive turns 40 (twelve turns in the example of [Fig.l]) are coaxial with the longitudinal axis ZZ', - a second tubular section also forming a cylindrical spiral, and whose successive turns 41 (three turns in the example of [Fig.l]) are coaxial with an axis AA' inclined at a non-zero angle relative to the longitudinal axis ZZ', and whose upper end is connected directly in series with a lower end of the first tubular section. In [Fig.l], the exchanger 4 is seen in section.

[0013] The first tubular section is fully positioned in the shell 1a while the second tubular section is inclined so as to cover part of the interior space of the shell 1a and part of the lower domed bottom 1b. With this configuration, the top of the exchanger 4 is at a distance hl from the ground.

[0014] However, a European regulation published in the official journal of August 15, 2021 now requires, in particular in the case where the primary circuit uses a heat pump, that the heat exchanger be included in the volume of the lower quarter of the tank 1. To clarify, the imaginary line H shown in [Fig.l], at the distance h above the ground S, shows the height limit not to be exceeded for the heat exchanger, in order to comply with this regulation.

[0015] Removing the turns 40 of the first tubular section located between the imaginary horizontal lines H and Hl of [Fig.l] would certainly make it possible to comply with this regulation, but at the cost of a drastic reduction in the exchange surface of the exchanger, and therefore in the power.

[0016] Furthermore, as seen in [Fig.l], the top of the exchanger 4 exceeds the lowest level of the through opening associated with the access hatch 9, consequently narrowing the passage so that a maintenance technician can properly inspect and maintain the interior of the tank. Summary of the invention

[0017] The present invention aims to overcome the drawbacks of known solutions.

[0018] This aim is achieved in accordance with the present invention, which relates to a water storage tank comprising a shell of substantially cylindrical shape whose longitudinal axis is vertical in the installed position, a domed bottom closing one end of the shell, and a heat energy exchanger with a tubular coil intended to be immersed in the water of the tank to transport a heat transfer fluid between a heat transfer fluid inlet pipe and a heat transfer fluid outlet pipe, the heat transfer fluid inlet pipe and the heat transfer fluid outlet pipe being respectively connected to a first end and to a second end of the heat energy exchanger with a tubular coil,said tubular coil heat exchanger comprising a first tubular section forming a cylindrical spiral whose turns are coaxial with the longitudinal axis and a second tubular section one end of which is connected in series with a first end of the first tubular section, characterized in that said second tubular section forms a spiral whose turns are substantially coaxial with the longitudinal axis and have a decreasing radius of curvature between a maximum radius of curvature and a minimum radius of curvature, so that an external envelope of the second section substantially follows the internal surface of the domed bottom.

[0019] In one possible embodiment, the domed bottom comprises a spherical cap, an edge radius and a cylindrical straight edge whose radius corresponds to the radius of the ferrule, at least a first turn of the second tubular section has a radius of curvature decreasing from the maximum radius of curvature and extends in the height of the cylindrical edge, and a last turn of the second tubular section has a radius of curvature decreasing from the minimum radius of curvature and extends in the height of the edge radius or of the spherical cap.

[0020] In one possible embodiment, the maximum radius of curvature is equal to the radius of curvature of the turns of the first tubular section.

[0021] In one possible embodiment, the tubular coil heat exchanger has an oval or elliptical, or oblong, or rectangular cross-sectional profile. In this case, the longest axis of the cross-sectional profile is preferably perpendicular to the longitudinal axis.

[0022] Alternatively, the tubular coil heat exchanger has a circular cross-sectional profile.

[0023] In one possible embodiment, the first end and the second end of the tubular coil heat exchanger are connected respectively to the heat transfer fluid inlet pipe and the heat transfer fluid outlet pipe at two through openings made in the shell. The two through openings can be aligned vertically.

[0024] In one possible embodiment, the tank comprises a tubular connecting piece connecting a second end of the second tubular section and the heat transfer fluid outlet pipe. The second end of the second tubular section may be substantially located in a plane containing the longitudinal axis.

[0025] In one possible embodiment, the first tubular section forms a cylindrical spiral with a constant pitch, with a jump in turns at the level with the heat transfer fluid outlet pipe.

[0026] In one possible embodiment, the tank further comprises an access hatch closing a through opening made at man height on the shell, and said tubular coil heat energy exchanger extends entirely outside the access hatch.

[0027] In one possible embodiment, the tank further comprises an inlet tapping for bringing water into the tank, and an outlet tapping for bringing water contained in the tank out.

[0028] In one possible embodiment, the domed bottom closes the lower end of the shell in the installed position of the tank, and either the inlet pipe and the outlet pipe, or the inlet tapping and the outlet tapping, are connected to an external heating system. In one possible embodiment, said inlet tapping is made on the domed bottom, and the outlet tapping is made on an upper bottom closing an upper end of the shell.

[0029] In one possible embodiment, the domed bottom closes the upper end of the shell in the installed position of the tank; and either the inlet pipe and the outlet pipe, or the inlet tapping and the outlet tapping, are connected to an external cooling system. Brief description of the figures

[0030] The description which follows with reference to the appended drawings, given as non-limiting examples, will make it clear what the invention consists of and how it can be implemented. In the appended figures:

[0031] [Fig-1] [Fig.l], already written above, schematically illustrates a known tank for hot water storage tank, installed in a vertical position;

[0032] [Fig.2] [Fig.2] schematically illustrates the lower part of a tank of hot water storage according to a possible embodiment of the invention, installed in a vertical position;

[0033] [Fig.3] [Fig.3] illustrates two examples of cross sections for the exchanger tubular coil heat exchanger used in a tank in accordance with one embodiment of the present invention;

[0034] [Fig.4] [Fig.4] represents a perspective view of an assembly consisting of the tubular coil heat exchanger of [Fig.3] and a tubular connecting piece connecting the lower end of the exchanger and a heat transfer fluid outlet pipe;

[0035] [Fig.5] [Fig.5] represents a side elevation view of the whole of [Fig.4]

[0036] [Fig.6] [Fig.6] represents a bottom view of the whole of [Fig.4];

[0037] [Fig.7] [Fig.7] represents a top view of the whole of [Fig.4];

[0038] [Fig.8] [Fig.8] gives two comparative views of a water storage tank hot water of the prior art and a hot water storage tank of the same size in accordance with a possible embodiment of the invention with a heat exchanger of substantially the same power. Description of embodiment(s)

[0039] In the figures, identical or equivalent elements will bear the same reference signs.

[0040] [Fig.2] illustrates the lower part of a hot water storage tank according to a non-limiting embodiment in accordance with the invention, in a vertically installed position on a floor S. The heat energy exchanger (here a heat exchanger) is shown in section.

[0041] We thus find some of the elements already described with reference to [Fig.l], namely: - a tank 1, preferably made of steel, and preferably enamelled on its internal wall, the tank 1 comprising a shell 1a of generally cylindrical shape whose longitudinal axis ZZ' is vertical in the installed position; - a lower domed bottom 1b closing the ferrule 1a at its base; - preferably, feet Id to support the tank 1 on the ground S and keep it in a vertical position; - a heat energy exchanger with a tubular coil 4', intended to be immersed in the water of the tank 1 to transport a heat transfer fluid between a heat transfer fluid inlet pipe 5 and a heat transfer fluid outlet pipe 6 of an external heating system, the heat transfer fluid inlet pipe 5 and the heat transfer fluid outlet pipe 6 being respectively connected to a first end, here upper, and to a second end, here lower, of the tubular coil heat exchanger 4' in order to heat the water present in the lower part of the tank 1 in the installed position; - one or more thermostats 7 to control the temperature of the water contained in the tank 1; and - a visible partial access hatch 9 closing a through opening made at man height (for example, the center of which is approximately 900 millimeters above the ground) on the shell 1a.

[0042] Although not visible in [Fig.2], the tank 1 also comprises (see [Fig.8], view (b)) an upper bottom 1e, preferably also domed, to close the upper part of the shell 1a, an inlet connection 2 to allow cold water to enter the tank 1 (in the direction of the arrow F1), and an outlet connection 3 to allow heated water contained in the tank 1 to exit (in the direction of the arrow F2).

[0043] A non-limiting example of a heat energy exchanger (here heat) 4' according to the invention is shown in [Fig.2] and the various figures 4 to 7:

[0044] Like the heat exchanger 4 known from [Fig.l], the tubular coil heat energy exchanger 4' comprises a first tubular section forming a cylindrical spiral whose turns 40' are non-coplanar and coaxial with the longitudinal axis ZZ', as well as a second tubular section one end of which, here upper, is connected in series with a first end, here lower, of the first tubular section.

[0045] Nevertheless, here, and in accordance with the invention, the second tubular section forms a spiral whose turns 41'a, 41'b, 41'c, 41'd and 41'e are non-coplanar, and substantially coaxial with the longitudinal axis ZZ' and have a decreasing radius of curvature between a maximum radius of curvature and a minimum radius of curvature, so that an external envelope of the second section substantially follows the internal surface of the lower domed bottom 1b. In the non-limiting example of [Fig.2], corresponding to a tank with a capacity of approximately 2000 liters, the second section more precisely comprises four consecutive turns 41'a with an identical radius of curvature (forming a portion of a cylindrical spiral), connected to the lower end of the first section, followed by a turn 41'b whose radius of curvature decreases from the radius of curvature of turns 41'a, followed by a turn 41'c whose radius of curvature continues to decrease relative to turn 41'b, followed by a turn 41'd whose radius of curvature continues to decrease relative to turn 41'c, followed by a final turn 41'e whose radius of curvature continues to decrease relative to turn 41'd. Thus, turns 41'b to 41'e do not have a constant radius. In practice, to facilitate manufacturing, it is preferable to provide spokes in quarter turns. Thus, each turn 41'b to 41'e will then have four spokes with transition zones between each spoke.

[0046] In the non-limiting embodiment of [Fig.2], the heat energy exchanger 4' is particularly suitable for the lower domed bottom 1b of the type standardized so-called semi-elliptical, comprising a spherical cap, a square radius and a cylindrical straight edge whose radius corresponds to the radius of the ferrule 1a, for example a standardized GRC bottom (initials put for "with a large square radius").

[0047] Indeed, at least a first turn, here upper, of the second tubular section has a maximum radius of curvature (here the turns 41'a) and extends in the height of the cylindrical edge, the last turn 41'e, here lower, of the second tubular section has a minimum radius of curvature and extends in the height of the spherical cap, and the three intermediate turns 41'b, 41'c and 41'd have a radius of curvature which decreases.

[0048] In the non-limiting example of a tank illustrated in the figures, the maximum radius of curvature is equal to the radius of curvature of the turns 40' of the first tubular section. In other embodiments, particularly those in which the height of the cylindrical edge of the lower domed bottom is low, the maximum radius of curvature for the turns 41'a could be less than the radius of curvature of the turns 40'.

[0049] Furthermore, different profiles can be used for the first tubular section and the second tubular section. Preferably, the tubular coil heat exchanger 4' has a profile 43' of oval or elliptical section as shown in the two views (a) and (b) of [Fig.3]. In other variants not shown, the cross-section could be oblong or rectangular. In all these cases, this makes it possible, for an equal heat exchange surface, to further compact the exchanger 4' and reduce its intrinsic height. In this case, the axis of greatest length L of the profile of oval or elliptical cross-section is preferably perpendicular to the longitudinal axis ZZ'. For example, for a tank with a capacity of 1000 liters, we can choose an elliptical section profile in which the greatest length L of the ellipse is of the order of 50 to 60 millimeters, and the smallest length of the ellipse is 25 or 30 millimeters.

[0050] In the non-limiting example of the figures, it is practically entirely located in the height of the lower domed bottom 1b.

[0051] Nevertheless, a gain in compactness is obtained thanks to the invention even in the case where the tubular coil heat energy exchanger 4' has a circular cross-sectional profile.

[0052] In all cases, the heat energy exchanger is made from tubes generally made of steel and preferably enameled on their external and / or internal wall. The tubes are preferably rigid.

[0053] The two tubular sections may be designed as a single piece, for example, they may be formed from a single tube. Alternatively, they may also be manufactured by successively connecting several tubes to each other, for example by welding, brazing or gluing.

[0054] The pitch used for the turns of the first section and / or the second section can be constant.

[0055] In the non-limiting embodiment of [Fig. 2] and of figures 4 to 7, the first end and the second end of the tubular coil heat exchanger 4' are connected respectively to the heat transfer fluid inlet pipe 5 and to the heat transfer fluid outlet pipe 6 at two through openings made on the same side of the shell, and preferably aligned vertically.

[0056] In other embodiments not shown, the heat transfer fluid inlet pipe 5 and the heat transfer fluid outlet pipe 6 could be placed at two through openings made on two different axes, for example diametrically opposite.

[0057] Furthermore, in this embodiment, the tank 1 also comprises a tubular connection piece 43' which connects a second end, here lower, of the second tubular section (i.e. the end of the last turn 41'e) to the heat transfer fluid outlet pipe 6.

[0058] The lower end of the second tubular section (i.e. the end of the last turn 41'e) is preferably substantially located in a plane containing the longitudinal axis ZZ', as is particularly visible in Figures 2 and 5. This advantageously simplifies the assembly of the tubular connecting piece 43'.

[0059] In the non-limiting embodiment illustrated, the first tubular section forms a cylindrical spiral with a constant pitch, with a turn jump 42' at the level of the outlet pipe 6 of the heat transfer fluid, so as to be positioned substantially in height and angularly with this outlet pipe 6. This advantageously makes it possible to place the outlet pipe 6 at the level of the cylindrical shell, and consequently to simplify manufacturing.

[0060] Whatever the embodiment, the solution proposed by the invention makes it possible to obtain a very compact heat exchanger 4' and to optimize the placement of this exchanger in the tank to comply in particular with recent regulatory constraints. These advantages are particularly visible in [Fig.8] which shows side by side two tanks of the same capacity placed on the same horizontal ground S, one equipped with a heat exchanger 4 according to the known art described with reference to [Fig.l] (view (a) of [Fig.8]), the other equipped with an exchanger 4' according to an embodiment of the invention combining the two sections set out above and the choice of an elliptical transverse profile to produce the turns of the two sections (view (b) of [Fig.8]). The imaginary line H has also been shown in [Fig.8].It is noted in this figure that the embodiment in accordance with the invention presented in view (b) complies with the regulatory constraint since the upper level of the exchanger 4' is substantially at the same level as this imaginary line H. In addition, the tubular coil heat exchanger 4' extends entirely below the level of the . access hatch 9. The entire through opening associated with this hatch is therefore accessible to a maintenance technician, which greatly facilitates the inspection of the general condition of the interior of the tank as well as its maintenance. At the level of the liquid inlets / outlets, we note that only the positioning of the heat transfer fluid inlet pipe (arrow F3) needs to be modified.

[0061] Although the invention has been more particularly described in the case of a hot water storage tank as shown in [Fig.2], the principles of the present invention are applicable to variants of tanks, without departing from the scope of the claims:

[0062] For example, in the explanation relating to the tank in [Fig.l] and that relating to the tank in [Fig.2], it was assumed that the domestic hot water was that present in the tank, and that the serpentine exchanger was connected, via the inlet and outlet pipes, to a primary circuit, here a heating system external to the tank. In a variant not shown, the tank could be part of the primary circuit, in which case it is the inlet tapping and the outlet tapping which must be connected to the external heating system, and the heated domestic water would then pass through the serpentine exchanger.

[0063] Furthermore, it was also assumed that the tank was intended for the storage of hot water, which explains: - on the one hand, positioning of the 4' exchanger in the lower part of the tank, of the inlet tapping in the lower part, of the outlet tapping in the upper part, and positioning of the inlet pipe above the outlet pipe. - on the other hand, the use of an external heating system. In a variant not shown, the tank could be intended for the storage of cold water, in which case the previous positions would have to be reversed, and an external cooling system used instead of the external heating system. Of course, the exchanger 4' would then be a cold exchanger, and its position would be reversed along a horizontal plane compared to the positions shown in the figures. In other words, the second section would then be intended to follow the domed bottom closing the upper end of the shell.

[0064] Furthermore, it has also been assumed that the heat exchanger 4' was the only heating means. In a variant not shown, the tank 1 could have another main heating means, located in the lower part of the tank, and the heat exchanger 4' could be part of an additional heating means, located in the upper part of the tank, and its position would be reversed along a horizontal plane relative to the positions shown in the figures so that its second section would follow the domed bottom closing the upper end of the shell. The other main heating means could also be a heat exchanger according to figures 2 to 7 of the invention.

Claims

Claims

1. Water storage tank (1) comprising a shell (1a) of substantially cylindrical shape whose longitudinal axis (ZZ') is vertical in the installed position, a domed bottom (1b) closing one end of the shell (1a), and a tubular coil heat energy exchanger (4') intended to be immersed in the water of the tank (1) to transport a heat transfer fluid between a heat transfer fluid inlet pipe (5) and a heat transfer fluid outlet pipe (6), the heat transfer fluid inlet pipe (5) and the heat transfer fluid outlet pipe (6) being respectively connected to a first end and to a second end of the tubular coil heat energy exchanger (4'),said tubular coil heat exchanger (4') comprising a first tubular section forming a cylindrical spiral whose turns (40) are coaxial with the longitudinal axis (ZZ') and a second tubular section one end of which is connected in series with a first end of the first tubular section, characterized in that said second tubular section forms a spiral whose turns (41'a - 41'e) are substantially coaxial with the longitudinal axis (ZZ') and have a decreasing radius of curvature between a maximum radius of curvature and a minimum radius of curvature, so that an external envelope of the second section substantially follows the internal surface of the domed bottom (1b), in which the tubular coil heat exchanger (4') has a profile (44') of oval or elliptical, or oblong, or rectangular cross-section,the axis of greatest length (L) of the cross-sectional profile being perpendicular to the longitudinal axis (ZZ').,

2. Tank (1) according to claim 1, in which the domed bottom (1b) comprises a spherical cap, an edge radius and a cylindrical straight edge whose radius corresponds to the radius of the shell (la), in which at least a first turn (40') of the second tubular section has a radius of curvature decreasing from the maximum radius of curvature and extends in the height of the cylindrical edge, and in which a last turn (41'e) of the second tubular section has a radius of curvature decreasing from the minimum radius of curvature and extends in the height of the edge radius or of the spherical cap.

3. A tank (1) according to claim 2, wherein the radius of curvature maximum is equal to the radius of curvature of the turns (40') of the first tubular section.

4. Tank (1) according to any one of the preceding claims, in which the first end and the second end of the tubular coil heat energy exchanger (4') are connected respectively to the heat transfer fluid inlet pipe (5) and to the heat transfer fluid outlet pipe (6) at two through openings made in the shell (la).

5. Tank (1) according to claim 4, in which the two through openings are aligned vertically.

6. Tank (1) according to any one of the preceding claims, comprising a tubular connecting piece (43') connecting a second end of the second tubular section and the heat transfer fluid outlet pipe (6).

7. Tank (1) according to claim 6, in which the second end of the second tubular section is substantially located in a plane containing the longitudinal axis (ZZ').

8. Tank (1) according to any one of the preceding claims, in which the first tubular section forms a cylindrical spiral with constant pitch, with a turn jump (42') at the level with the outlet pipe (6) of the heat transfer fluid.

9. Tank (1) according to any one of the preceding claims, further comprising an access hatch (9) closing a through opening made at man height on the shell (la), in which said tubular coil heat energy exchanger (4') extends entirely outside the access hatch (9).

10. A tank (1) according to any preceding claim, further comprising an inlet tapping (2) for bringing water into the tank (1), and an outlet tapping (3) for bringing water contained in the tank (1) out.

11. Tank (1) according to claim 10, in which: - the domed bottom (1b) closes the lower end of the shell (1a) in the installed position of the tank; and - either the inlet pipe (5) and the outlet pipe (6), or the inlet tapping (2) and the outlet tapping (3), are connected to an external heating system.

12. Tank (1) according to claim 11, in which said inlet tapping (2) is made on the domed bottom (1b), and the outlet tapping (3) is made on an upper base (the) closing an upper end of the ferrule (the).

13. Tank (1) according to claim 10, in which: - the domed bottom closes the upper end of the shell (la) in the installed position of the tank; and - either the inlet pipe (5) and the outlet pipe (6), or the inlet tapping (2) and the outlet tapping (3), are connected to an external cooling system.

Images