Method for operating a heating device and heating device

Abstract

In a method for operating a heating device with a resistance heating element with a high nominal power, which is arranged in a heating chamber, a part of the heating chamber itself or on the chamber is designed as a heating carrier so that it can be heated inductively. An induction heating coil is provided for this purpose. It partially heats the heating carrier to determine whether there is sufficient heat dissipation for operation of the resistance heating element because water flows through it. If it can be determined from a slow temperature rise during inductive heating that the heat dissipation is sufficient, heating operation with the high-power resistance heating element can begin. If the temperature rise is too rapid, the heat dissipation is insufficient, and the resistance heating element or the heating device will not operate.

Description

[0001] The invention relates to a method for operating a heating device and to a heating device specially designed to carry out this method.

[0002] DE 10 2018 203 609 A1 discloses a heating device comprising a heating chamber, in particular a tubular heating chamber, for fluid or water flowing through it. A heating support is arranged on this heating chamber, on which a resistance heating element is provided in a flat, distributed form. This resistance heating element is intended to be operable with a high power density in order to very rapidly heat fluid flowing through the heating chamber or present therein, in particular to boil and evaporate water. Due to the high power or power density of the resistance heating element, there is a risk that, if there is no fluid or water in the heating chamber, the heating support will become very hot very quickly and will be damaged and / or cause damage to the surrounding area, for example, to an electrical device in which the heating device is installed.Measurements with discrete temperature sensors on the resistance heating element or on the heating support can provide a remedy, but are not always sufficiently reliable.

[0003] Other temperature detection options operate over a wide area and, in particular, use leakage currents. However, this requires the resistance heating element to be operating and / or to heat up, which can also cause damage if the response is not fast enough. Overheating problems can arise not only when there is no fluid or water in the heating chamber, but also when the fluid velocity in the heating chamber is either very low or very high. It can also be problematic if heat transfer is disrupted by permanently or temporarily adhering dirt particles or films, such as a layer of limescale. Task and solution

[0004] The invention is based on the object of providing a method as mentioned above and a heating device suitable for carrying out this method, with which problems of the prior art can be avoided and, in particular, it is possible to avoid overheating of the heating device and, in particular, of a resistance heating element with even greater reliability.

[0005] This object is achieved by a method having the features of claim 1 and by a heating device designed to carry out this method having the features of claim 9. Advantageous and preferred embodiments of the invention are the subject of the further claims and are explained in more detail below. Some of the features are described only for the method or only for the heating device designed to carry it out. However, they are intended to be able to apply independently and independently of one another to both the method and the heating device. The wording of the claims is incorporated into the content of the description by express reference.

[0006] The heating device for carrying out the method comprises a metallic or metal-containing and inductively heatable or ferromagnetic heating support, which extends in an expansion surface and has a front and a back. At least one resistance heating element and / or an induction heating coil is arranged on the front or back of the heating support, for example, an aforementioned thick-film heating element, but optionally also another resistance heating element, for example, a tubular heater. The heating device comprises a heating chamber for the fluid to be heated, wherein the heating chamber is partially delimited by the heating support or borders on or rests against this heating support. Furthermore, the induction heating coil is provided on the heating device, in particular arranged such that it can inductively heat the aforementioned heating support and optionally also fluid located therein or flowing through it.Advantageously, the heating device has its own control or is connected to a control, wherein the control monitors or also controls the resistance heating element and the induction heating coil, in particular via a respective power supply.

[0007] In the method, the first step, when the fluid in the heating chamber is to be heated using the heating device and the resistance heating element with a high overall heat output, is to activate the induction heating coil to heat the heating support. A current and / or voltage through or at the induction heating coil is monitored and evaluated to determine a temperature change on the heating support. A changing temperature of the heating support results in changes in its ferromagnetic properties, which are expressed in the current and / or voltage across the induction heating coil. This is generally known from the prior art for inductive heating; see DE 10 2009 047 185 A1.

[0008] Such a determined temperature change in the heating substrate is then compared with a predefined target value for a temperature change in order to determine the temperature increase and the duration of this temperature increase. Such a target value can simply indicate the time by which a temperature increases in °C when heating the heating substrate with the induction heating coil at a known power level, provided the fluid to be heated is present in the heating chamber, thus removing the heat from the heating substrate. Such a target value could, for example, be 70°C within 20 seconds.

[0009] A distinction is then made between two cases. If, in the first case, a specific temperature change for the heating carrier as described above remains below the specified value, i.e., a smaller temperature change or temperature increase is detected within a certain period of time, it is assumed that there is sufficient heat removal from the heating carrier. This means that the fluid or liquid to be heated is present in sufficient quantity on the heating carrier. The heating device is thus operated or enabled for subsequent heating operation in which the at least one resistance heating element is activated. It is advantageously operated at more than 50% of its rated power or maximum continuous power, in particular at the maximum continuous power.

[0010] In a second case, the correspondingly determined temperature change exceeds the aforementioned preset value. This means that the temperature can rise more sharply or to a higher value within the specified time. In this second case, it is assumed that there is insufficient heat dissipation from the heating support, particularly because there is no fluid to be heated in the heating chamber. Since the risk of damage would be too great in this case, the heating device with the resistance heating element is not activated or operated, and advantageously also not with the induction heating coil.

[0011] In the method according to the invention, the operation of the induction heating coil is used to check whether there is a sufficiently high heat dissipation at the heating carrier in the heating chamber, namely because the fluid to be heated is available in sufficient quantity. This check can take a few seconds; this will be explained in more detail below. If this is the case, i.e. there is a sufficiently high heat dissipation, then strong heating can be achieved using the resistance heating element with a considerably higher output, for example 10 to 30 times higher. If this is not the case, then the resistance heating element can be prevented from operating at its high output for safety reasons. The fluid to be heated can be a liquid, in particular water. Alternatively, it can also be a gas or air.

[0012] The changes in current and / or voltage detected at the induction heating coil for determining the temperature change do not need to be particularly precise. Under certain circumstances, it may even be acceptable that a starting temperature is not precisely known. With typically expected starting temperature values between 0°C and 100°C for water as a liquid, particularly between 10°C for very cold tap water and 50°C for already highly heated water, a detectable temperature change is still very easily detectable due to the electrical parameters of the induction heating coil.

[0013] In a further embodiment of the invention, the resistance heating element can be deactivated or remain deactivated while the induction heating coil is activated to heat the heating support in order to observe its possible temperature change or heat loss. This can prevent the temperature change on the heating support from being distorted due to its inductive heating.

[0014] Advantageously, an operator can be given a visual and / or acoustic signal as to whether or not the heating device with the resistance heating element is being activated, even if the operator has initiated this or entered a corresponding operating command. This information should be given to the operator, particularly in the event that the heating device or the resistance heating element is not being activated because the heat removal is too low due to the presumably lack of fluid on the heating support or in the heating chamber. After all, the operator expects the heating device to operate in such a way as to heat the fluid, so any deviation from this is of great interest. A signal can advantageously also contain the information that there is no fluid or not enough fluid in the heating chamber.This means an operator can potentially perform simple troubleshooting, such as opening supply valves or similar, to eliminate the problem and, for example, activate the heating system after a restart. Of course, this requires repeating the test to ensure sufficient heat dissipation at the heating element as before and passing it, so to speak.

[0015] Furthermore, it can be provided that fluid or additional, fresh fluid is only introduced into the heating chamber, or moved or pumped through the heating chamber, when the resistance heating element has actually been released for heating. This can eliminate unnecessary pumping of the fluid.

[0016] In one embodiment of the invention, the aforementioned preset value for the temperature change can be a preset time. The induction heating coil can then be operated for this preset time to heat the heating carrier. After this preset time has elapsed, or even during it, a temperature increase or temperature change can be determined, i.e. less the course of the temperature change, but rather the final temperature after the preset time has elapsed. A check is then carried out to determine whether this temperature increase due to the inductive heating is above or below a preset value for the temperature increase. Thus, the preset value exists here for a period of time and for a temperature or temperature increase. If the temperature increase exceeds the preset value after the preset time, the heat removal from the heating carrier is insufficient. A desired heating operation using the resistance heating element would then cause overheating, which is not what should happen.Thus, the second case mentioned above would apply and the heating device would not be activated or would not operate.

[0017] Alternatively, it can be provided that heating is not primarily carried out for a predetermined time, but rather that a specific temperature change or predetermined temperature increase is achieved. This could be, for example, 40°C or 50°C or even more. The time required by the induction heating coil to heat the heating carrier by this temperature increase is then recorded. The evaluation then proceeds in principle as before. If the time is less than a predetermined time, heating is occurring too quickly and the entire heating device or the resistance heating element is not activated. In this way, a potential risk of excessive temperature buildup due to inductive heating can be avoided, as the specified temperature value can be set within an acceptable range.

[0018] In a further development of the invention, a predetermined time for both of the aforementioned alternatives can be between 10 seconds and 60 seconds, preferably between 15 seconds and 30 seconds. This avoids having to wait too long for the result of whether sufficient heat dissipation at the heating device is present for subsequent operation of the resistance heating element at high power. On the other hand, during this not inconsiderable time, other possible interference can be minimized or not have a disruptive effect.

[0019] For both of the aforementioned alternatives, a default value for the temperature change can generally be between 30°C and 150°C, preferably between 50°C and 95°C. If the fluid is initially at room temperature, heating to over 100°C would result. Particularly advantageously, a default value for the temperature change can be between 55°C and 80°C, so that when heating water that is approximately at room temperature, the boiling point of 100°C is just barely reached, or not at all.

[0020] In an embodiment of the invention, the induction heating coil for the heat dissipation test can be operated at a relatively low power compared to the resistance heating element. This can advantageously be a maximum of 20% of the maximum continuous power of the resistance heating element, and under certain circumstances even less than 10% of this maximum continuous power. This also ensures that, on the one hand, the induction heating coil heats the heating support relatively slowly and thus safely and in a manageable manner. Furthermore, a relatively high power can be provided for the resistance heating element as the maximum continuous power in order to be able to heat the fluid, especially water, very quickly and intensely in the then permitted heating mode.

[0021] In a further embodiment of the invention, it can be provided that for heating operation of the heating device at low power levels, i.e. for a relatively low desired heating of fluid in the heating chamber, where these low power levels are less than 20% of the maximum continuous power of the resistance heating element, only the induction heating coil is used. The power can then be designed for such heating operation. This has the advantage that, during its operation, a temperature change can continue to be monitored, thus avoiding or at least reducing the risk of potentially excessive heating. The resistance heating element with the much higher power would otherwise have to be operated in a pulsed manner, which could result in less uniform heating.

[0022] In yet another advantageous embodiment of the invention, it can be provided that the induction heating coil and the at least one resistance heating element, in particular all resistance heating elements of the heating device, are arranged next to one another or not one above the other in the heating chamber. It should be ensured that a fluid for heat removal, or that is to be heated, is present to the same extent in the area of both the induction heating coil and the resistance heating elements, or in neither of these areas. This way, potential problems with arranging the induction heating coil and resistance heating element in the same area of the heating chamber can be avoided, for example, because the resistance heating element responds to the induction heating coil, is inductively heated by it, or could disrupt its operation.Furthermore, the induction heating coil could be compromised or damaged by the typically higher temperatures of the resistance heating element, which could be mitigated by thermal insulation. For both the aforementioned thick-film heating elements and tubular heaters, these operating temperatures can exceed 150°C and sometimes even exceed 300°C, especially on their outer surfaces, even if the other side is used to heat water in an adjacent heating chamber.

[0023] In a further development of the invention, the heating support can be adapted to the shape of the heating chamber. If the heating chamber is a flat tube or a flat chamber with a flat exterior, the heating support can also be flat and level. The heating support can also possibly be part of the heating chamber or a corresponding container that serves as the heating chamber. In this case, another part can be saved, and the heat transfer from the inductively heated part to the fluid occurs more directly. Finally, the resistance heating element can be applied to the heating support, for example by screen printing or the like in the case of a thick-film heating conductor, or by winding and possibly soldering a tubular heater. It can also be a heating support separate from the heating chamber and then attached to it.This has the advantage that both the resistance heating element and the induction heating coil can be easily arranged on it, and the arrangement of the heating carrier on the heating chamber is also possible with good heat transfer. Since an induction heating coil can also act over a somewhat greater distance than a resistance heating element, it can also be arranged above the resistance heating element with some distance and, if necessary, thermal insulation in between. However, it can act on the same area of the heating carrier and thus also the heating chamber to heat it. For example, the distance from the induction heating coil to the heating carrier and / or to the heating chamber can be less than 1 cm. This distance is measured in a direction perpendicular to the expansion surface of the heating carrier and / or the induction heating coil.

[0024] If the heating chamber is a tube with a round, approximately round, or square cross-section, i.e., with a width similar to its height, the induction heating coil can also be wrapped around it, rather than just positioned on one side. This allows for relatively large-area and even heating of the heating chamber to test whether fluid is present in the heating chamber to provide sufficient heat dissipation for operating the resistance heating element.

[0025] As an alternative to an induction heating coil surrounding the heating chamber, it can also run in a surface parallel to an expansion surface of the heating support and / or the heating chamber. This surface can advantageously be a plane. In this case, the induction heating coil and the heating support, in particular the resistance heating element, can run in parallel planes. They do not necessarily have to run one above the other, but can also be arranged side by side.

[0026] If the heating chamber is designed as a tube, it can have an inlet at one end and an outlet at the other, opposite end. Such a tube can be designed with a relatively large diameter relative to its length; the length can be 5 to 25 times larger than the diameter. Alternatively, the heating chamber could also be designed as a spiral or meandering tube, in which case the length can be 50 to 200 times larger than the diameter.

[0027] In a further advantageous embodiment of the invention, the heating device can comprise ferritic material, for example, flat and / or wide ferrite rods, to direct or focus the magnetic field of the induction heating coil. Thus, the heating support can be arranged on one side of the induction heating coil, and the ferritic material on the other side. Likewise, another ferritic material can be provided behind the heating support to guide the magnetic field into the heating support as much as possible.

[0028] In addition to the aforementioned options as thick-film heating conductors and tubular heaters, a resistance heating element can also be designed as a so-called foil-like Kapton heating element.

[0029] For use in a water-conducting electrical appliance, such as a washing machine or dishwasher, the heating support preferably comprises or is made of magnetic stainless steel. Such a heating support can then potentially also form part of the heating chamber, meaning it can be in direct contact with the water therein.

[0030] These and other features emerge not only from the claims but also from the description and the drawings. The individual features may be implemented individually or in combination in an embodiment of the invention and in other fields, and may represent advantageous and individually protectable embodiments for which protection is claimed here. The division of the application into individual sections and subheadings does not limit the generality of the statements made therein. Brief description of the drawings

[0031] Embodiments of the invention are illustrated schematically in the drawings and explained in more detail below. The drawings show: Fig. 1 is a schematic representation of a washing machine having a heating device according to the invention, Fig. 2 is a first embodiment of a heating device according to the invention in a flat tube shape, and Fig. 3 is a second embodiment of a heating device according to the invention in a round tube shape. Detailed description of the implementation examples

[0032] In the Fig. 1A washing machine 11 is schematically shown as a water-conducting electrical household appliance in which the invention can be installed. The washing machine 11 has a housing 12, a drum receptacle 14 with a drum 15 therein, and a door 16 for closing the same. An inlet 18 leads into the drum receptacle 14 from a collecting funnel 19, which is arranged below a conventional detergent drawer 20. Detergent and other additives for a washing process can be dosed through this inlet. Water enters the detergent drawer 20 via a water line 22.

[0033] An outlet 30, optionally with a valve, leads out from the bottom of the drum holder 14. Water can flow through a water line 22 into a filter 28. The filtered water can be pumped further through a further water line 22 by a pump 26, and specifically through a further water line 22 into the heating device 24 according to the invention. There, in the exemplary embodiment shown here, the water can be heated continuously; advantageously, it passes through the heating device 24 several times, pumped by the pump 26. Alternatively, the heating device 24 can also be designed as a somewhat larger container or with a larger volume, so that stagnant water therein can be heated. This is therefore an example of heating water; alternatively, air or another gas can also be heated in a heating device according to the invention.

[0034] The washing machine 11 also has a controller 32 and an operating device 34. The power supply to the heating device 24 can be provided in the controller 32, which is connected to the heating device 24 in a manner not shown. The method according to the invention can also be carried out by determining a temperature change in the heating device by monitoring and evaluating the current and voltage at an induction heating coil of the heating device 24. The operating device 34, in turn, can have operating elements and a display, which can be used, in particular, to indicate to an operator in the manner described above if no further, stronger heating takes place due to an excessively rapid temperature change after heating with the induction heating coil.

[0035] The Fig. 2shows a heating device 24 according to the invention in a first embodiment. The heating device 24 is designed for continuous operation and has a pipe 36, which may have a flat rectangular cross-section. An inlet 37 leads into the pipe and an outlet 38 leads out, both of which are correspondingly Fig. 1connected to a water pipe 22. The pipe 36 forms within its interior, between inlet 37 and outlet 38, a heating chamber 40 as described above. The fluid to be heated here is water, possibly also washing liquor. The pipe 36 or the heating chamber 40 is delimited by pipe walls 41, whereby the upper pipe wall and lower pipe wall 41 shown here are flat or even due to their rectangular cross-section. The pipe walls 41 are each provided with an insulating layer 42, which primarily provides electrical insulation. For this purpose, the insulating layer 42 can be glass-like or ceramic. Furthermore, it can comprise plastic, Teflon, or silicone, depending on the temperature resistance.

[0036] A resistance heating element 44 is arranged at the bottom of the lower pipe wall 41 or on its insulation layer 42. This element consists of thick-film heating conductors 45, which can be applied to the insulation layer 42 in the usual way using a thick-film process. In this case, the pipe wall 41 forms the heating support according to the invention mentioned above. As an alternative to applying the resistance heating element 44 directly and permanently to the pipe wall 41 or to the pipe 36, it can also be applied to a separate component, which is then attached to the pipe wall 41 with the best possible heat conduction. The resistance heating element 44 is also supplied with power via the controller 32. For example, it can have a maximum continuous power of 0.5 kW to 2 kW and thus quickly and intensely heat water in the pipe 36 or water flowing through it.

[0037] An induction heating coil 48 is arranged on the opposite upper side of the tube 36, or on the upper tube wall 41 and the insulation layer 42 there. This coil is formed from individual coil turns 49. If the tube 36 has a flat, rectangular cross-section with a width that is, for example, twice or three times the height, sufficient space is provided for both the resistance heating element 44 and the induction heating coil 48 to be arranged only on the corresponding side. The induction heating coil 48 can then be formed from several coil turns 49, flat and spiral with a very elongated shape in the direction from the inlet 37 to the outlet 38. Ferrite rods 51 are arranged above the induction heating coil 48. These shield the magnetic field upwards or conduct it in a known manner. In this case, the tube 36 with its tube wall 41 consists of a suitable material that can be inductively heated.For example, it can be made of a nickel-iron alloy. This should be sufficiently corrosion-resistant to allow water to pass through it. Otherwise, it would have to be appropriately coated or lined on the inside. In an alternative embodiment, a flat plate made of such a material can be arranged between the insulation layer 42 and the pipe wall 41. This plate can be inductively heated and then, in turn, heats the pipe wall 41 and thus the heating chamber 40 therein via direct heat conduction.

[0038] In the heating device 24 according to the invention according to the Fig. 2On one side of the heating chamber 40, a resistance heating element 44 is provided. This element has a very high output and is primarily designed for quickly heating water in the heating chamber. However, it should only operate when there is actually water or liquid in the heating chamber 40, which guarantees good and sufficient heat dissipation, so that operation of the resistance heating element 44 is possible without problems. To ensure that heat dissipation is sufficiently high not only at the bottom of the heating chamber 40, but also in the upper area near the induction heating coil 48, the tube 36 or the heating chamber 40 must actually be completely filled. Otherwise, the temperature of the upper tube wall 41 would increase too quickly and too much.

[0039] For the method according to the invention, it can be provided that the induction heating coil 48 is first operated for a predetermined duration of, for example, 20 seconds. It can inductively heat the upper tube wall 41 of the tube 36 with a heating output of approximately 100 W to 200 W. This is controlled by the controller 32. The current and voltage at the induction heating coil 48 are monitored in order to determine a temperature or a temperature change of the inductively heated material on the tube wall 41 from their change. If the temperature has increased by, for example, 60°C after the predetermined time of 20 seconds at a default value of 80°C, whereby the absolute starting temperature and the absolute end temperature play no significant role since they lie within expected ranges, it is assumed that the heating chamber 40 is full of water.Thus, the upper pipe wall 41 is also in contact with the water, so that good heat removal from it has occurred; thus, the first case according to the invention applies, and operation of the resistance heating element 44 at full power is possible. To carry out the method, it is advantageous not to pump water through the heating chamber 40, but rather to allow the water to stand still therein. Alternatively, water can be pumped through during this method in order to rule out possible sources of error such as a defective pump 26. It can then be assumed that the temperature change within the specified time is even smaller, for example, only 30°C. The water flowing past repeatedly or continuously removes a great deal of heat from the upper pipe wall 41 and causes only a slow and slight increase in temperature.For this purpose, the possibility of a continuous water flow can also be tested in this variant.

[0040] If, for example, the temperature had increased by 100°C or more within 20 seconds, sufficient heat dissipation was not occurring. The fault could be due, for example, to a missing or insufficient water supply. Thus, the second case according to the invention applies: operation of the resistance heating element 44 at full power should be avoided. In fact, the resistance heating element 44 should not be operated at all. A corresponding error message should appear on the display of the control device 34.

[0041] Alternatively, when monitoring the time and temperature change at the upper pipe wall 41 below the induction heating coil 48, the time elapsed until the pipe wall 41 has heated up by 20°C or 30°C can also be recorded. If this takes at least a predetermined time, for example, 20 seconds or 30 seconds, the specified time value has also been exceeded. This is a clear sign that sufficient heat removal has occurred, thus the first case according to the invention applies again. If this occurs faster than this time, the second case according to the invention applies.

[0042] The resistance heating element 44 can then heat at full power and heat the water in the pipe or heating chamber 40, advantageously in a continuous flow. The previously described test has shown that sufficient heat dissipation is achieved by the presence of water in the heating chamber 40. This may even have been determined in a continuous flow, so that the functional test can be carried out with a high degree of certainty.

[0043] In the Fig. 2 Below the right-hand area of the resistance heating element 44, it is shown that all or some of the coil windings 49', which are shown in dotted lines, can also be provided below the lower tube wall 41. This is intended to indicate that the induction heating coil can alternatively be wound at least partially around the entire circumference of the tube 36. Furthermore, this can also be provided in areas where a resistance heating element is provided on the tube.

[0044] In the Fig. 3An alternative embodiment of a heating device 124 according to the invention is shown. Here, a tube 136 with inlet 137 and outlet 138 is actually round or has a round-cylindrical cross-section. The tube 136 forms a heating chamber 140 inside it for flowing water or for heating water as it flows through. The tube 36 or its surrounding tube wall 141 is made of stainless steel, which cannot be heated inductively. The outside of the tube wall 141 is provided in the right-hand area with an insulating layer 142 all the way around, which can be designed as previously described. A circumferential resistance heating element 144 is applied to this insulating layer 142. Individual heating conductors 145 of the resistance heating element 144 can either be applied using a thick-film process, which is also possible all the way around. Alternatively, a resistance heating element 144 can be wound in the form of heating wires or tubular heaters.When using tubular heaters, the insulation layer 142 can be omitted.

[0045] The left section of tube 136 has a slipped-on nickel-iron tube 153, which has a tight fit for the best possible heat transfer from the nickel-iron tube 153 to the tube wall 141. A thermal insulation 154 is applied circumferentially to this nickel-iron tube 153, for example, wound, slipped on as a separate component, or applied in a layering process. A support tube 155 is, in turn, slipped and secured over this thermal insulation 154. The support tube 155 can be made of temperature-resistant plastic and should, in any case, be permeable to magnetic field lines.

[0046] An induction heating coil 148 is wound onto the support tube 155 with several coil turns 149, forming a single assembly. This finished assembly can then simply be slid onto the tube 136 or the nickel-iron tube 153 or the thermal insulation 154, and if necessary, fixed there. Thus, the induction heating coil 148 does not need to be wound directly onto the tube 136 or the aforementioned layers located thereon. Ferrite rods 151 are provided outside the induction heating coil 148 to guide the magnetic field.

[0047] In the embodiment of a heating device 124 shown here, the induction heating coil 148 on the one hand and the resistance heating element 144 on the other hand are spatially separated, at least in the direction of the liquid to be heated, namely arranged next to each other. Even if in the Fig. 3While it is shown that both are approximately the same length, this may be different in practice. In particular, the right-hand section with the resistance heating element 144 is advantageously significantly longer than the left-hand section with the induction heating coil 148.

[0048] Due to the design of tube 136 as a heating chamber 140, with its advantageous horizontal arrangement, it is possible to ensure that, either when the water is still in the tube 136 or when water is flowing through it, this water is equally present or absent in both the area of the induction heating coil 148 and the area of the resistance heating element 144. Thus, the test for the temperature change due to heating by the induction heating coil 148 can be carried out with equal reliability in both cases. Thus, the induction heating coil 148 can be used to determine a heat loss that would also apply to the operation of the resistance heating element 144 at high power levels.

[0049] As previously explained, the resistance heating element 144 can be designed for a very high maximum continuous power, for example, more than 0.5 kW, in particular up to 2 kW, or for power densities of 50 W / cm 2 to 100 W / cm 2 . However, if water flowing through the pipe 36 is only to be heated slightly, it can be provided that this water is heated only by operating the induction heating coil 148. This is then possible with a significantly lower power; the induction heating coil can, for example, have a continuous power of 200 W. Thus, the induction heating coil 148 can be used not only for a heat removal test, but also actually for heating operation. This can generally be provided for temperatures below 50°C or even below 40°C, in which case heating is only provided inductively by means of the induction heating coil 148.This can be advantageous, for example, when heating water in a washing machine that has been mixed with enzymes for a better cleaning process. Such enzymes generally shouldn't be exposed to higher temperatures for optimal effectiveness.

Claims

1. Method for operating a heating device, the heating device comprising: - a metallic and inductively heatable or ferromagnetic heating carrier which runs in an expansion surface and has a front side and a back side, - at least one resistance heating element on the front side or on the back side of the heating carrier, - a heating chamber for fluid which is partially delimited by the heating carrier or adjoins the heating carrier, - an induction heating coil on the heating device, with the following steps: - the induction heating coil is activated to heat the heating carrier, - current and / or voltage is passed through oron the induction heating coil are monitored and evaluated to determine a temperature change on the heating carrier and a resulting change in its ferromagnetic properties based on the current and / or voltage curve, - a specific temperature change in the heating carrier is compared with a predetermined target value for a temperature change with regard to temperature increase and duration of the temperature increase, - a distinction is made between: + if in a 1. case a specific temperature change for the heating carrier remains below the target value, it is assumed that there is sufficient heat removal from the heating carrier and the heating device is operated by activating the at least one resistance heating element, + exceeds in a 2. caseIf the determined temperature change exceeds the specified value, it is assumed that there is insufficient heat removal from the heating carrier and the heating device is not activated or operated by activating at least one resistance heating element.

2. Method according to claim 1, characterized in that for the time during which the induction heating coil is activated to heat the heating carrier, at least one resistance heating element on the heating carrier remains deactivated or no resistance heating element on the heating carrier is activated and heating.

3. Method according to claim 1 or 2, characterized in that is signaled optically and / or acoustically to an operator if the heating device is either activated or not, whereby this information is preferably displayed to an operator if the heating device is not activated.

4. Method according to one of the preceding claims, characterized in that a fluid is only introduced into the heating chamber or moved through the heating chamber when heating operation occurs at the heating device by activating at least one resistance heating element.

5. Method according to one of the preceding claims, characterized in thatthe preset value for the temperature change in a preset time is such that the induction heating coil is operated for this preset time to heat the heating carrier and then a temperature increase is determined after the expiry of this preset time, wherein the preset value includes a specific temperature increase after the expiry of this preset time, and then it is checked whether, after the expiry of the preset time and heating of the heating carrier during the preset time with the induction heating coil, the temperature of the heating carrier is above or below the preset value for the temperature increase, wherein in the event that the determined temperature increase is above the preset value, there is insufficient heat removal from the heating carrier and according to the 2nd case, no activation or operation of the heating device takes place, wherein preferably the preset time is between 10 seconds and 60 seconds, preferably between 15 seconds and 30 seconds.

6. Method according to claim 5, characterized in that a default value for the temperature change is between 30°C and 150°C, preferably between 50°C and 95°C, in particular between 55°C and 80°C.

7. Method according to one of the preceding claims, characterized in that the induction heating coil heats the heating device carrier with a low power which is less than 20% of a maximum continuous power of the resistance heating element, preferably less than 10% of a maximum continuous power of the resistance heating element.

8. Method according to one of the preceding claims, characterized in that for heating operation of the heating device with low power levels which are below 20% of a maximum continuous power of the at least one resistance heating element, the heating support is heated only with the induction heating coil and the at least one resistance heating element on the heating support remains deactivated, preferably no resistance heating element is activated.

9. Heating device which is designed to carry out the method according to one of the preceding claims and has: - a metallic and inductively heatable or ferromagnetic heating carrier which runs in an expansion surface and has a front side and a back side, - at least one resistance heating element on the front side or on the back side of the heating carrier, wherein the resistance heating element is preferably selected from the group: thick-film heating element, tubular heating element, Kapton heating element - a heating chamber for fluid which is partially delimited by the heating carrier or borders on the heating carrier, - an induction heating coil on the heating device.

10. Heating device according to claim 9, characterized in thatthe induction heating coil is arranged at a distance of less than 1 cm from the heating support, preferably measured in a direction that is perpendicular to an extension surface of the heating support and / or the induction heating coil.

11. Heating device according to claim 9 or 10, characterized in that the induction heating coil runs in a surface which is parallel to an extension surface of the heating carrier, wherein preferably this surface is a plane and the induction heating coil and the heating carrier run in parallel planes.

12. Heating device according to one of claims 9 to 10, characterized in that the heating chamber is a tube with an inlet at one end and an outlet at the other opposite end, with the heating support resting against one side of the tube.

13. Heating device according to one of claims 9 to 12, characterized in thaton one side of the induction heating coil the heating support is arranged and on the other side of the induction heating coil ferritic material is arranged, in particular in the form of flat and / or wide ferrite rods.

14. Heating device according to one of claims 9 to 13, characterized in that the induction heating coil and the resistance heating element are arranged next to each other with a distance of at least 0.5 cm such that the induction heating coil does not heat the heating carrier in the area of the resistance heating element.

15. Heating device according to one of claims 9 to 14, characterized in that the heating support has or is made of magnetic stainless steel.

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