EP0275776B1 - Apparatus for controlling the superheating and calcination of a fluid heater, and fluid heater provided with such an apparatus - Google Patents

Abstract

An overheating and scaling control device for a fluid heating apparatus, such as a domestic water heater, removes the hot fluid in the heater when demand ceases. A piston (46) mobile within a case (28) separates the latter into two compartments (32, 36) respectively connected to the cold water supply pipe (16) and to the hot water discharge pipe (22). In operation, the pressure in pipe (16) is higher than the pressure in pipe (22) and piston (46) is moved to the left. On stopping, the pressures are equal in both pipes and spring (40) moves piston (46) to the right. Cold water is fed into the exchanger tube (20), so that the hot water contained in the latter is discharged into pipe (38) and compartment (36).

Description

The present invention relates to a device for controlling overheating and scaling for a fluid heating apparatus, serving essentially for the attenuation of overheating and scaling. The invention finds a particularly advantageous application in the case where this heating device is a domestic water heater or a gas boiler.

Figure 1 attached shows, seen in perspective, a domestic water heater of a type currently used called "wet room" water heater. This water heater, bearing the general reference 10, essentially consists of a metal tank 12, for example made of copper, arranged vertically and open at its lower and upper ends, thus defining a combustion chamber. A set of gas burners 14 is located under the tank and the burnt gases circulate from bottom to top inside the latter. The cold water arrives via a supply pipe 16 and then circulates along a coil 18 placed against the wall of the tank 12, but outside of the latter. The water therefore begins to heat by circulating in the coil 18, then arrives in an exchanger tube 20 placed at the top of the tank, in the zone through which the burnt gases exit. The water which has been preheated in the coil 18 is heated to the desired temperature in the exchanger 20. The hot water then returns to the user devices via a line 22.

Recently, a new type of water heater has appeared, such as the water heater 11 illustrated in FIG. 2 and called a "dry chamber" water heater. We find, as in the case of Figure 1, a metal tank 12 placed vertically and open at its lower and upper ends, as well as a set of gas burners 14 at the lower part of the tank. There is always the pipe 16 for the supply of cold water and the pipe 22 for the departure of hot water, but there is no longer a coil placed against the wall of the tank. This is fitted with an insulating mass 24 placed against its internal face and the pipe 16 opens directly into the exchanger tube 20 placed at the top of the tank at the point where the burnt gases exit. Compared to the device in FIG. 1, the device illustrated in FIG. 2 has the advantage of having a simpler device design, and therefore a lower mounting cost, and it allows material to be saved. causes the coil 18 to be removed.

However, in both cases, these devices still have a drawback which is the overheating of the water when the device is started up. It will be recalled that it is the flow of water in the exchanger 20, that is to say the opening and closing of the stop valve (not shown in FIGS. 1 and 2), which controls the starting or stopping the water heater. During operation, the water contained in the exchanger 20 is at an average temperature 25 ° C higher than the temperature of cold water. When the shut-off valve is closed, the water that remains inside the exchanger stores the heat radiated by the hot walls of the combustion chamber and that returned by the hot mass of the exchanger. This is why, after several tens of seconds of shutdown, the water can reach a maximum temperature close to 100 ° C.

It is therefore understandable that, if the appliance is restarted shortly after the previous stop, the temperature of the hot water at the outlet reaches very high values and risks exceeding the values fixed by the standards in force. For example, in France, standard NF D 35-322, applicable to water heaters, bathroom heaters, etc. stipulates that, the appliance being adjusted to its nominal heat flow rate and to a water flow rate corresponding to a temperature rise of 50 ° C, the temperature rise at the start of each draw-off must not exceed this speed value by more than 20 ° C. With current devices, and in particular dry chamber water heaters such as the one illustrated in FIG. 2, this value is often exceeded and can reach the boiling temperature of water within a few degrees, which doesn 'is of course not admissible. t

In document FR-A-1458 528, a heat exchanger is used to slightly cool the water leaving the heating body of a water heater while preheating the cold water which reaches the heating element, in order to avoid overheating during two successive draws.

The object of the present invention is to remedy these drawbacks by proposing a device for controlling overheating and scaling for a device for heating a fluid such as a water heater, a bath heater, a gas, etc.

• une conduite d'arrivée de fluide froid,
• une conduite de départ de fluide chaud,
• un échangeur communiquant d'une part avec ladite conduite d'arrivée de fluide froid et d'autre part avec ladite conduite de départ de fluide chaud, le fluide circulant, lorsque l'appareil fonctionne, de la conduite d'arrivée vers la conduite de départ à travers l'échangeur, et
• des moyens pour chauffer le fluide se trouvant dans l'échangeur.

Such an apparatus comprises, in a known manner:

• a cold fluid inlet pipe,
• a hot fluid flow pipe,
• an exchanger communicating on the one hand with said cold fluid inlet pipe and on the other hand with said hot fluid departure pipe, the fluid flowing, when the device is operating, from the arrival pipe to the flow through the interchange, and
• means for heating the fluid in the exchanger.

According to the main characteristic of the device for controlling overheating and scaling which is the subject of the invention, it comprises an enclosure of variable volume which can communicate with a cold fluid inlet pipe from the heating appliance, this enclosure being at least partially limited by a displaceable element having a first face subjected to the pressure prevailing in the cold fluid inlet pipe, and a second face subjected to a reference pressure, said element being displaceable under the effect of the pressure difference between its two faces.

The movable element can be constituted either by a deformable membrane, or by a piston movable inside a housing. In the first case, part of the cold fluid inlet pipe can be made of a flexible material, this material itself constituting the deformable membrane: in this case, the considered part of the cold fluid inlet pipe constitutes the enclosure of variable volume.

In a first embodiment of the invention, the second face of the displaceable element is subjected to the pressure prevailing in the hot fluid starting pipe. In another embodiment, concerning the case where the hot fluid starting pipe is in direct communication with the atmosphere, the second face of the displaceable element is subjected to atmospheric pressure.

In cases other than that where part of the cold fluid inlet pipe is made of flexible material, means are necessary to move the displaceable element so as to repel the liquid contained in said enclosure of variable volume in the exchanger so as to avoid overheating of the liquid and scaling of the exchanger. Preferably, a spring will be used as will be described below.

Finally, the invention also relates to a fluid heating device equipped with a device for controlling overheating and scaling as mentioned above.

The invention will be better understood on reading the description which follows, given purely by way of illustration and in no way limiting, with reference to the appended drawings, in which:

FIG. 1 is a schematic perspective view of a first type of water heater according to the prior art,

FIG. 2 is a view similar to FIG. 1 illustrating a second type of water heater of the prior art,

- Figures 3a and 3b are simplified diagrams illustrating the operation of a device according to the invention, in the case where the movable element is a deformable membrane, and where the second face thereof is subjected to the prevailing pressure in the hot fluid flow line,

- Figure 4 is a schematic view similar to the FIG. 3a in the case where the second face of the deformable membrane is subjected to atmospheric pressure,

FIG. 5 is a schematic view illustrating the device of the invention in the case where part of the cold fluid inlet pipe is made of a flexible material, and

- Figure 6 is a view similar to Figure 5, illustrating the case where the movable member is a movable piston inside a housing.

If we refer to Figures 3a and 3b, we find the pipe 16 for the cold water inlet, the exchanger 20 and the pipe 22 for the hot water outlet equipped with a valve 26. For greater clarity , the combustion chamber and the burners have not been shown in FIGS. 3a and 3b.

The device for controlling overheating and scaling according to the invention comprises a housing 28 inside which there is a deformable membrane 30 fixed in leaktight manner to the walls of this housing. This membrane separates the housing into a first compartment 32 communicating with the pipe 16 by a tube 34, and a second compartment 36 communicating with the hot water starting pipe 22 by a pipe 38. The latter opens into the pipe 22 upstream of valve 26 with respect to the direction of flow of water during operation of the device.

The device illustrated in Figures 3a and 3b operates as follows:

FIG. 3a corresponds to the case where the valve 26 is open and where the water circulates from line 16 to line 22 through the exchanger 20. Because the water is in motion, there is a loss of pressure between the point where the tube 34 opens into the line 16 and the point where the tube 38 opens into the line 22. The pressure is therefore higher in the line 16 than in the line 22. It follows that the pressure is more stronger in compartment 32 of housing 28 than in compartment 36 and, consequently, the membrane 30 is displaced to the right looking at Figure 3a.

Figure 3b corresponds to the case where the valve 26 is closed. As the water is no longer in motion, the pressure is the same in the pipes 16 and 22, as well as in the exchanger 20. As a result, the pressures on either side of the membrane 30 are equal. As has been expected, in the compartment 36, a spring 40 mounted so as to push the membrane 30 to the left, looking at FIGS. 3a and 3b, that is to say against the pressure prevailing in the compartment 32, when the valve 26 is closed, the spring 40 expands and pushes the membrane 30 to the left, looking at the figures. Thus, the water contained in the compartment 32, which is cold water, is pushed into the exchanger 20 and the hot water contained in the latter is expelled through the pipe 22 and the tube 38 into the compartment 36. The latter has seen its volume increase by the deformation of the membrane 30 and can therefore accommodate this body of water.

Thus, when the apparatus is stopped, the hot water contained in the exchanger tube 20 is replaced by cold water. Therefore, even if the walls of the combustion chamber are still hot, the temperature rise of the fluid contained in the exchanger 20 is limited and, when the heater is next started, there is no risk to have an excessive temperature rise. In the preferred embodiment, the dimensions of the housing 28, as well as the shape and deformation characteristics of the membrane 30 and the force of the spring 40, are determined so that the volume of water contained in the compartment 32 in the situation of FIG. 3a is substantially equal to the volume of water contained in the exchanger 20.

Figure 4 is a view similar to Figure 3a but, in this variant, the pipe 22 for starting hot water is not equipped with a valve such as the valve 26: it is in direct communication with the atmosphere . In this case, it is the pipe 16 which is equipped with a valve 42 upstream of the point where the tube 34 opens. The box 28 of FIG. 4 is similar to that of FIG. 3a. However, the pipe 38 is eliminated and the compartment 36 is in direct communication with the atmosphere, for example by means of a nozzle 43. FIG. 4 corresponds to the case where the device is in operation, that is that is to say that the valve 42 is open and the water circulates from the pipe 16 to the pipe 22. Due to the pressure drops, the water pressure in the pipe 16, and therefore in the compartment 32, is higher the pressure of the water at the outlet orifice 23 of the pipe 22, which is equal to atmospheric pressure. The membrane 30 is therefore pushed to the right when looking at the figure. When the valve 42 is closed, the pressure is the same in the pipe 16 downstream of the valve 42, as well as in the exchanger 20 and the pipe 22 and it is equal to atmospheric pressure. The spring 40 therefore pushes the membrane 30 to the left while looking at FIG. 4, which has the effect of driving out the cold water contained in the compartment 32 in the exchanger 20, while the hot water contained in the latter is hunted outside.

In Figure 5, there is shown schematically in broken lines and in perspective a water heater similar to that of Figure 2 with the tank 12 and the burners 14 supplied by a pipe 15. We also find the pipe 16 of arrival cold water, the exchanger 20 at the upper part of the tank 12 and the pipe 22 for the start of hot water equipped with the valve 26. In this variant, part 44 of the pipe 16 is made of a flexible material and constitutes a deformable membrane which can deform under the effect of pressure differences between its first face or internal face, which is in contact with cold water, and its second face or external face. The housing 28 surrounds the part 44 of the pipe 16 and it is fixed in leaktight manner to the latter. It is therefore the interior of the part 44 which constitutes the first compartment 32 and the volume located between the membrane 44 and the housing 28 which constitutes the second compartment 36. The latter is in communication with the pipe 22 for starting water. hot by a tube 38: this opens into the pipe 22 at a point located upstream from the valve 26 and which can be, for example, near the outlet of the exchanger 20 at the top of the tank 12.

The operation of the device illustrated in FIG. 5 is practically the same as the operation of the devices illustrated in FIGS. 3a, 3b and 4.

When the valve 26 is open and the water circulates from the pipe 16 to the pipe 22 through the exchanger 20, there is a pressure loss between the part 44 of the pipe 16 and the pipe 22. The pressure of the water is therefore stronger in the part 44 of the pipe 16 than in the pipe 22. The membrane 44 therefore swells and occupies the position 44a shown in solid lines in FIG. 5. When the valve 26, l is closed water no longer circulates and the pressure is the same in line 16, exchanger 20 and line 22. The membrane 44 therefore returns to its normal position 44b, shown schematically in broken lines in the drawing. This has the effect of expelling into the exchanger 20 the cold water contained in the compartment 32 and the part of the pipe 16 located between the latter and the exchanger, while the hot water which was contained in the exchanger is driven along the line 38 into the compartment 36.

In this case also, an arrangement similar to that of FIG. 4 can be adopted, the tube 38 and the valve 26 being omitted and the compartment 36 being placed in direct communication with the atmosphere.

FIG. 6 is a view similar to FIG. 5, but, in this variant, the displaceable element consists of a piston 46 movable inside the housing 28. As in FIG. 5, the line shows the tank 12, the burners 14 and the gas inlet pipe 15. There are also the pipe 16 for cold water inlet, the exchanger tube 20 and the pipe 22 for hot water departure fitted with a valve 26 The case 28 is again found, but the deformable membrane is replaced by a piston 46 which is mobile inside this case. We finds the first compartment 32 communicating with the pipe 16 by a tube 34 and the second compartment 36 communicating with the pipe 22 by a tube 38 which opens into the latter at a point located upstream of the valve 26. We still see the spring 40 , placed in compartment 36 and arranged so as to push the piston to the right, looking at Figure 6.

This figure corresponds to the case where the valve 26 is open and therefore where the water circulates from the pipe 16 to the pipe 22 through the exchanger 20. In this case, the pressure in the pipe 16, and therefore in the compartment 32 , is greater than the pressure prevailing in the line 22 and therefore in the compartment 36. Under the effect of this pressure difference, the spring 40 being suitably calibrated, the piston 46 moves to the left, looking at FIG. 6. When the valve 26 is closed, the pressure is the same in the pipe 16, the exchanger 20 and the pipe 22 and, consequently, it is the same in the compartments 32 and 36. Under the action of the spring 40, the piston 46 moves to the right while looking at the figure and the cold water is expelled into the tube 34 and the pipe 16: this has the effect of expelling the hot water contained in the exchanger 20 in the tube 38 and, from there , in compartment 36.

FIG. 6 also shows a diaphragm 48 placed on the tube 34, this diaphragm being intended to control the flow of cold water.

As a test, a device was produced in accordance with that of FIG. 6 mounted on a water heater with a nominal power of 8.7 kW. The diaphragm 48, placed on the tube 34 between the pipe 16 and the housing 28, had a diameter of 4 mm. The housing 28 was a cylindrical housing 150 mm long and 25 mm in diameter, the piston having a length of 15 mm. The spring used had a stiffness of 15 newtons per meter (N / m). The superheat measured on the device not equipped with the attenuation device according to the invention was 31.5 ° C. while with the device of the invention, the maximum superheat was only 13 ° C.

It can therefore be seen that the device which is the subject of the invention has particularly advantageous advantages, the main one of which is to reduce the rise in temperature observed when the heating appliance is started up. On the other hand, as the temperature of the water contained in the exchanger is lower, this results in a reduction of the scale deposit in the exchanger, and therefore an increased reliability and a longer service life of the device.

Finally, it is understood that the invention is not limited to the single embodiments which have just been described, but that variants can be envisaged without departing from the scope of the invention. This is how any fluid heating device (water heater, bath heater, gas boiler, etc.) can be equipped with a device for controlling overheating and scaling in accordance with invention.

In addition, it is possible to use or not a diaphragm such as the diaphragm 48 of FIG. 6 mounted on the tube 34. This same tube 34 can open into the pipe 16 at any point thereof upstream of the exchanger 20, provided however, in cases similar to that of FIG. 4 where the pipe 22 communicates directly with the atmosphere, that it opens downstream of the valve 42. As for the tube 38, it can lead into the pipe 22 at any point downstream of the exchanger 20, provided however that this point is located upstream of the valve 26 in the case where the hot water starting pipe is equipped with such a valve.

It will also be recalled that, in most cases, the cold water inlet pipe 16 is equipped with a pressure-reducing device (not shown in the drawings), used to control the supply of combustible gas. The tube 34 can open into the pipe 16 both upstream and downstream of this pressure reducing device.

In the examples which have been described above, the enclosure of variable volume is constituted by the first compartment of a housing fitted with either a deformable membrane or a movable piston. In either case, the second compartment can be placed in communication either with the hot fluid flow pipe, or with the atmosphere. One could possibly, without departing from the scope of the invention, delete the second compartment of the housing and limit it to the first compartment in the case where the second face of the membrane or of the piston is subjected to atmospheric pressure.

Claims (9)

1. Device for controlling overheating and scale formation for a fluid heating apparatus, characterized in that this device has a variable volume enclosure (32) which can communicate with a supply pipe for cold fluid from the heating apparatus, said enclosure (32) being at least partly limited by a displaceable element (30) having a first face exposed to the pressure prevailing in the cold fluid supply pipe and a second face exposed to a reference pressure, said element (30) being displaceable under the effect of the pressure difference between its two faces.
2. Device according to claim 1, characterized in that said displaceable element is a deformable membrane or diaphragm (30).
3. Device according to claim 1, characterized in that said displaceable element is a piston (46) mobile within a case (28).
4. Device according to any one of the claims 1 to 3, characterized in that it also has means for displacing the displaceable element (30), so as to reduce the volume of said variable volume enclosure (32).
5. Device according to claim 4, characterized in that said displacement means comprise a spring (40) having a first end fixed to the displaceable element (30) and a second end fixed to an element, which is itself fixed with respect to the remainder of the apparatus.
6. Apparatus for heating a fluid comprising a cold fluid supply pipe (16), a hot fluid discharge pipe (22), an exchanger (20) communicating on the one hand with said cold fluid supply pipe (16) and on the other with said hot fluid discharge pipe (22), the fluid circulating when the apparatus is in operation from supply pipe (16) to discharge pipe (22) through exchanger (20) and means (14) for heating the fluid in exchanger (20), characterized in that it is equipped with an overheating and scaling control device according to any one of the claims 1 to 6.
7. Device according to claim 6, characterized in that part (44) of the cold fluid supply pipe (16) is made from a flexible material and thus constitutes a deformable diaphragm, said part (44) of the supply pipe constituting the varialbe volume enclosure (32).
8. Device according to any one of the claims 6 and 7, characterized in that the second face of the displaceable element is exposed to the pressure prevailing in the hot fluid discharge pipe (22).
9. Device according to any one of the claims 6 to 8, characterized in that the hot fluid discharge pipe (22) is directly linked with the atmosphere, so that the second face of the displaceable element (30) is exposed to atmospheric pressure.

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