Electrical heating assembly, water tank and heating systems comprising the electrical heating assembly, and use thereof

Abstract

The invention relates to an electrical heating assembly for a water tank of at least 20 liters volume for hot water storage, wherein the electrical heating assembly is insertable into the water tank and comprises: a heating circuitry configured to connect the electrical heating assembly to a power source, wherein the heating circuitry comprises an electrical resistor of a positive temperature coefficient, PTC, type; and a casing surrounding at least part of the heating circuitry including the electrical resistor and the casing configured to electrically isolate the heating circuitry from water when the at least part of the heating circuitry is inserted into the water tank and when the water tank is at least partially filled with water, wherein the electrical resistor is configured to, once a threshold temperature at the electrical resistor is reached, exponentially increase its electrical resistance with temperature.

Description

Field of the Invention

[0001] The invention relates to an electrical heating assembly for a water tank of at least 20 liters volume for hot water storage. The invention further relates to a water tank that comprises such electrical heating assembly, and to a use of such electrical heating assembly. Moreover, the invention further relates to an open loop domestic hot water heating system and to a closed loop heating water heating system.Background

[0002] At present, tanks for hot water production, for example for domestic hot water production or central heating water production for heating purposes, regularly use an electrical resistive element. The electrical resistive element may be a main heating device or a complementary heating device. For example, the main heating device that may be used is an electric water heater, or a heat pump, wherein the complementary heating device that may be used is a back-up heater associated to a heat pump.

[0003] Generally, there are two main types of electric heating systems, i.e. an immersion heater system and a non-submerged heater system.

[0004] The immersion heater system or immersion heater comprises a resistor immersible in water, wherein a resistive wire is enclosed in a tube, and an electrically non-conductive material is enclosed between the resistive wire and the tube. The whole assembly is immersed in water, i.e. the resistive wire heats the non-conductive material and the tube. The tube directly heats through its wall the water, i.e. in general the liquid in which it is immersed. The use of an electrically non-conductive element prevents a short-circuit between the resistive wire and the immersed tube, which is often made of stainless steel or copper for example. This is broadly equivalent to the solution used in a kettle.

[0005] The non-submerged heater system or non-submerged heater comprises a resistor that is positioned in an immersible sheath or casing. The resistor comprises a resistive wire as a heating element that is housed in an electrically non-conductive material and thermal conductive material, usually a ceramic. The resistive wire is positioned in the immersible sheath and the heat generated by the resistive wire is transmitted to the air in the sheath, then to the sheath and then to the water, i.e. in general to the liquid, when the immersible sheath is immersed into the water. This is a more high-end solution as compared to the immersion heater system, as it allows the customer to replace or access the resistor's electrical elements for example without having to empty the water from the water tank (i.e. the water tank into which the immersible sheath that houses the resistor is inserted), since the resistor, i.e. the resistive wire or heating element, may be removed or pulled out from the immersed sheath. Said in other words, as the heating element is not directly immersed (but rather indirectly, since it may be inserted into an immersed sheath), the customer can remove it quite easily. Moreover, as there is no direct contact between the heating element and the water in the water thank, as a contact surface between the water and the immersed sheath is important, and as a same material may be used for the sheath than for the water tank, there is no scale build-up on the heating element, which may be accelerated when there is a strong temperature gradient.

[0006] Regardless of the immersion heater or the non-submerged heater, an electrical resistance as heating element, for example the resistive wires, requires two control elements.

[0007] The first control element controls a heating, so that the heating element is active when heating is required. The heating element must be active when the water in the water tank is too cold, and it must stop when the water has reached a sufficient or predetermined temperature. The first control element is therefore a regulating element, often achieved by means of a temperature determining device. This may be a mechanical element that acts as a function of temperature, or a sensor and associated control system. Depending on product type and range, this element can be set to ensure a higher or lower setpoint heating temperature. Changing the setpoint temperature adjusts the equivalent volume of hot water (= volume of hot water at 40°C) available to a customer. For the same volume, it is therefore possible to adjust hot water production according to the customer's consumption. For example, the water in the water tank could be heated from 52°C to 65°C, providing a greater or lesser volume of water equivalent to 40°C (temperature of use).

[0008] The second control element is a safety element which ensures that, even in the event of failure of the first control element, the electric resistance will not continue to heat continuously. In the absence of control, the resistor's electric resistance could continue to heat up to an excessive water temperature, that may lead to a risk of water vaporization and even water tank explosion in the event of multiple failures. Moreover, there may be a risk of burns and premature water tank deterioration due to the water tank's unsuitability for such extensive water temperatures. The protection provided by the second control element is achieved by means of a triggering device, which is different from the first control element. This triggering device is usually a mechanical release, for example a blade made of a material whose elongation or volume depends on temperature. In the event of overheating, the blade deforms and disconnects a power supply from the resistor's booster, thus preventing overheating. Normally, such disconnection is a permanent disconnection that needs a manual resetting.

[0009] Hence, the first control element is necessary to ensure system operation and user comfort. The use of the second control element, i.e. of the safety thermostat for example, is required by safety standards.

[0010] These solutions are widely known and have been in use for several decades. They are reliable and economically optimized. However, whatever the type of heating system, there are the drawbacks that two separated types of regulation are required, i.e. the first control element (control system) and the second control element (safety system), which increases complexity.

[0011] Hence, in view of the safety standards to potentially be adjusted in future based on the availability of technological developments, there is need to overcome at least part of these drawbacks, i.e. there is need for a solution using a single control means instead of two control elements to reduce complexity.

[0012] Moreover, apart therefrom, there is a need in general for electrical heating assemblies of reduced complexity and, at the same time, of increased efficiency, reliability, applicability and safety, in particular when such electrical heating assemblies are used for heating water in a water tank that is used for hot water storage, wherein the water's temperature may need to maintained within a predetermined temperature range and wherein such water tank may have a water storage capacity between several tens to several thousand liters volume.

[0013] Hence, there is also need for improvement regarding the heating of water in a water tank for hot water storage by use of electrical heating assemblies. For example, there is need in ensuring that such stored hot water is safe for a customer. Thus, in relation thereto, there is further need for an accurate controlling of the heating, i.e. for an accurate controlling of the stored hot water's temperature. Moreover, there is still further need for an adjustable setting (i.e. temperature setting) of the stored hot water's temperature.Summary

[0014] In view of the above, it is an object of the present disclosure to address at least part of the above-outlined needs.

[0015] Therefore, there is provided, in a first aspect, an electrical heating assembly for a water tank, the water tank of at least 20 liters volume for hot water storage. The electrical heating assembly is at least partly insertable into the water tank and comprises a heating circuitry and casing. The heating circuitry is configured to connect the electrical heating assembly to a power source, wherein the heating circuitry comprises an electrical resistor of a positive temperature coefficient (PTC) type. The casing surrounds at least part of the heating circuitry including the electrical resistor and the casing is configured to electrically isolate the heating circuitry from water when the at least part of the heating circuitry is inserted into the water tank and when the water tank is at least partially filled with water. The electrical resistor is configured to, once a threshold temperature at the electrical resistor is reached, exponentially increase its electrical resistance with temperature.

[0016] First, it should be noted that in general the electrical heating assembly may be operable for heating water without using any additional control or safety systems. However, to meet current (December 2024) safety standard requirements (for example standard EN 60335), once a safety system was activated or triggered to avoid overheating, it is required that the safety system is to be reset by a manual reset. However, such manual reset is not possible with an electrical resistor of a PTC type (or with a PTC resistor). Therefore, it should be noted that according to several examples of the present disclosure, the electrical heating assembly may further comprise a safety system to satisfy safety standard requirements.

[0017] However, regardless of whether or not such safety system is included, since the electrical resistor of the PTC type avoids overheating due to its electrical resistance increasing exponentially with temperature once the threshold temperature at the electrical resistor is reached, the advantageous technical effect of a gain in lifetime is achieved.

[0018] Furthermore, when compared with conventional resistors, the application of the electrical resistor of the PTC type avoids the occurrence of current spikes each time the electrical heating assembly is started-up or switch on. This is advantageous for maintaining network stability, for example if several houses are occupied by water heaters that each draws current at start-up.

[0019] The water tank may be of any volume above 20 liters, for example 100 liters, 500 liters, 1,000 liters, 2,000 liters or even 5,000 liters.

[0020] The expression "for hot water storage" may be understood in that hot water is stored in the water tank. However, this does not exclude that, for example during usage of the stored hot water, water is flowing into the tank and / or that water is flowing out of the tank. Rather, the expression "for hot water storage" may be understood to distinguish the present water tank from a small-sized tank, for example of about one to five liters volume, which is embedded into a heating system's heating water circuit such as for instance inside an indoor heat pump unit, and which uses an auxiliary heating means for additionally heating the water circulating in the heating system's heating water circuit.

[0021] It shall be noted that in more detail, the electrical resistor may be configured to, once a threshold temperature at the electrical resistor is reached, exponentially increase its electrical resistance with temperature for a current to flow through the heating circuitry, wherein a temperature of the electrical resistor is associated with the current. Said in other words, if the temperature reaches the threshold temperature, the electrical resistance rises exponentially and as result a current flowing through the resistor stops, i.e. does not flow, or is reduced to almost or substantially stop.

[0022] Such configuration of the electrical resistor is achievable, since the electrical resistor of the PTC type, i.e. a PTC resistor said in other words. A PTC resistor is a resistive element whose electrical resistance value depends on temperature. It may generally be used as a temperature sensor, wherein the electrical resistance of such temperature sensor changes with temperature. Hence, by reading the electrical resistance value, the corresponding temperature can be determined.

[0023] In general, it shall be noted that PTC stands for positive-temperature-coefficient thermistors: the thermistor resistance evolves with the temperature. It has more or higher electrical resistance at higher temperatures. That means that it heats less (or not) when the temperature increases. Common electrical resistors (i.e. non-PTC resistors for example) have a similar heating capacity whatever the temperature may be (in a normal operational range). As a result, common electrical resistors produce a same heat during a heating of a system, i.e. of water in a water tank for example. Common electrical resistors are controlled by such first and second control elements as described above.

[0024] PTC ceramics are semiconductors whose resistance depends on temperature. In the case of PTC, its resistance increases with temperature (unlike at negative temperature coefficients, NTCs). Examples for PTC characterization curves are provided in Figure 16, which shows the electrical resistance over temperature. Figure 17 shows examples of characteristic features of such PTC characterization curve. For example, at a certain temperature T Rmin a PTC resistor may have a minimum electrical resistance R min . Further, at material-related Curie temperature or reference temperature T ref , the PTC resistor may have an electrical resistance R ref from which on the electrical resistance of the PTC resistors increases exponentially with temperature.

[0025] The PTC resistor can be used to control the heating assembly if the temperature at which the PTC resistor no longer produces heat is in the vicinity of a control temperature, e.g. a control temperature between 50 and 90°C (all types, including photovoltaic self-electricity production), in particular between 52 and 75°C (for standard water heating). Furthermore, contrary to standard use with historical regulation, using the PTC as a temperature regulator may allow to further increase safety, given that the PTC resistor used may be intrinsically designed and used to directly integrate this role.

[0026] The electrical heating assembly according to the first aspect is further advantageous in that it may participate in enabling, based on the electrical resistor being of the PTC type (also referred to as PTC resistor, for example a PTC ceramic), a self-regulation of temperature, as well as a passive protection against overheating. Hence, no overheating of the heating assembly is possible due to the PTC resistor, which may allow to increase a lifespan of the heating assembly. This may be based on the electrical resistance of PTC ceramics which increases with temperature, wherein the stabilization temperature is called the Curie temperature or reference temperature, and can vary according to the version of the PTC used.

[0027] According to several examples of the present disclosure, a temperature range in which the electrical resistance of the electrical resistor increases exponentially may comprises a range from 70°C to 400°C, preferably from 80°C to 270°C. At the upper end of the temperature range and higher, the electrical resistance may then remain (almost) constant with temperature.

[0028] It should be noted that the temperature range may depend on the certain type of PTC material (or mixture of different PTC materials). In general, different PTC materials may have different threshold temperatures and / or different gradients in temperature increase after the threshold temperature. However, it shall be note that the present disclosure is not limited to any certain type of PTC material. Rather, the present disclosure uses the physical characteristics of PTC materials in general.

[0029] Hence, a suitable temperature range may be selected and / or adjusted as appropriate.

[0030] According to several examples of the present disclosure, the electrical heating assembly may further comprise a control unit configured to control a temperature of the electrical resistor by applying a pulse width modulation signal at the electrical resistor and / or by controlling an increase and a decrease of an electrical current applied at the electrical resistor.

[0031] Similar to above, it should be noted that in general the electrical heating assembly may be operable for heating water without using any additional control or safety systems. However, without the control system or control unit, only one temperature (i.e. water heating temperature) could be set at the electrical resistor of the PTC type. Therefore, to be able to change this temperature, i.e. to achieve an adjustable setting, the control system or control unit is needed.

[0032] It should be noted that such application of pulse width modulation (PWM) may be linked to the use of a PTC or PTC resistor as a heating element and associated regulation, i.e. use of a power modulation system, based on a printed circuit board (PCB) with a power transistor, like triarc, MOSFET, IGBT, SSR, etc. In contrast to PTC resistors, resistors with a single resistive wire are controlled in On / Off mode, i.e. full power when on or no power when off. With the PTC resistor, however, it is possible to consider PWM control operation to adjust a power delivered according to need. In particular, PWM in general is possible with a classical resistive element, but PTC resistors are more adapted thanks to a fast reactivity and low current spike (to occur at a start-up for example). Such power delivery adjustment is not adapted with a single resistive wire, which is not suited to PWM control, which requires a large number of cycles, thereby reducing the single resistive wire's life. In addition to the PTC resistor, a power modulation system can be used to control one or more PMW signals applied to one or more PTC resistors to achieve a heating assembly having a precise heating power and control power consumption. For this purpose, a power electronics board may be added to the heating assembly, for example at the end of the heating assembly that is not inserted into the water tank, i.e. at the end of a PTC resistor module for example. This module could be based on a system of power transistors activated by a PWM signal. Each slot may activate the transistors that may act as switches. By varying a duration of the PWM signal's square-wave signal, a heating power of the PTC resistor can be modulated. This module can also provide feedback, like power consumption, instantaneous power, error message, etc., via LIN or CAN communication.

[0033] Hence, power modulation makes it possible to precisely control the energy used by the heating assembly, which brings several advantages, like i) saving energy by avoiding power peaks (e.g. current spikes as indicated above), ii) avoiding potential overheating of the water that is being heated in the water tank, iii) avoiding overloading an electrical system of the building where the water tank including the heating assembly is installed, wherein the electrical system supplies power to the heating assembly, and iv) enabling intelligent control of a share of a totally availably power to be supplied to the heating assembly for example, wherein the intelligent control may be coupled with renewable energy sources for example.

[0034] According to several examples of the present disclosure, the control unit may further be configured to generate the pulse width modulation signal that corresponds to a first amount of electrical power and / or to control the electrical current to have a first amplitude that corresponds to the first amount of electrical power, wherein the first amount of electrical power is an adjustable share of a total amount of electrical power provided by the power source. Said in other words, the control unit may further be configured to use a first amount of electrical power for the pulse width modulation signal and / or the increase and the decrease, wherein the first amount of electrical power may be an adjustable share of a total amount of electrical power provided by the power source.

[0035] It should be noted that, for example, the total amount of electrical power may be a maximum amount of power providable by the power source. The power source may be a photovoltaic system for example.

[0036] Hence, power management may be improved, since an available amount of electrical power may be shared efficiently and appropriately among different power consumers (devices, like the heating assembly for example).

[0037] According to several examples of the present disclosure, the electrical resistor may comprise one or more PTC ceramic elements, wherein, if comprising at least two PTC ceramic elements, the at least two PTC ceramic elements are connected in parallel to each other.

[0038] It should be noted that a PTC ceramic element may also be understood as a PTC stone.

[0039] Hence, a heating power of the electrical resistor may be adapted or selected as required.

[0040] According to several examples of the present disclosure, the heating circuitry may comprise one or more PTC bundles, each PTC bundle of the one or more PTC bundles may comprise two or more PTC ceramic elements connected in parallel to each other. If comprising at least two PTC bundles, the at least two PTC bundles are connected in parallel or serial to each other.

[0041] It should be noted that to form a PTC bundle, PTC ceramics may be bonded in parallel between two conductive plates. In doing so, PTC ceramic stones are usable as a heating element for hot water cylinders for example. Such bundles may then be arranged or assembled on an insulating volumetric body, like on an insulating cylinder made of ceramic for example. A number of such arranged or assembled bundles and PTC ceramic stones per bundle may depends on the power required for the application of a certain water tank, for example from 1 ,000W to 3,000W or even to 10,000W and more for a residential application.

[0042] Hence, a heating power of the heating circuitry, i.e. the PTC resistors may be adapted or selected as required.

[0043] According to several examples of the present disclosure, the electrical heating assembly may further comprise an insulating volumetric body at least partly inserted into the casing, the insulating volumetric body comprising an outer surface that comprises one or more grooves, and wherein the one or more PTC bundles are assembled on the insulating volumetric body in that each PTC bundle is arranged in a respective groove of the one or more grooves.

[0044] It should be noted that, for example, a depth of the groove may be larger than a high of the PTC bundle when the PTC bundle is arranged in the groove. I.e., said in other words, the arranged PTC bundle may not be in contact with the casing when the insulating volumetric body is inserted into the casing. Preferably, the insulating volumetric body used to support the PTC bundles is ceramic, which is a thermal conductor and electrical insulator.

[0045] Hence, due to such design of the insulating volumetric body, a cross-section of the insulating volumetric body changes from a commonly used star shape to a cylinder, thereby further reducing an amount of air inside the casing. In this way, the heating assembly is more responsive (due to the reduction of no "unnecessarily" heated air) and a risk of creating hot air zones is avoided or reduced.

[0046] According to several examples of the present disclosure, the insulating volumetric body may be inserted into the casing, and a minimal distance between an assembled PTC bundle and an inner surface of the casing may be between 5.5 mm and 4.2 mm.

[0047] It should be noted that, in general and said in otherwords, it may be desirable to minimize a distance between an arranged PTC bundle and the inner surface of the casing to thus minimize an amount of air inside the casing. A reduced amount of air may allow for an increased heating efficiency, since a transfer of heat from the arranged PTC bundle to the water in the water tank via the insulating volumetric body, which may preferably be a ceramic, and the casing is increased if an amount of air is reduced. However, when the casing is in contact with water in the water tank, it has to be ensured that the arranged PTC bundle is not in contact with the casing.

[0048] Hence, it is enabled for an optimization of the design of the insulating volumetric body, by reducing a volume of air between a heating element, i.e. an arranged PTC bundle, and the inner surface of the casing. In doing so, it is enabled to reduce a distance between the arranged PTC bundle, i.e. the PTC resistor and the inner surface of the casing from, for example, 5.5 mm to 4.2 mm, allowing a smaller air gap. Thus, the proposed solution is more compact and minimizes the amount of air inside the casing, thereby reducing heat loss.

[0049] Such redesign or more compact design is easier to obtain based on using the PTC resistor compared to using a ferrous common resistor. The reason for that is because by using PTC resistors as heating elements, there is less risk of contact and of burn between the heating elements and the environment, i.e. between the heating elements and the casing or a user in case of maintenance. This allows for the above-indicated smaller distances between the arranged PTC bundles and the inner surface of the casing. As a result, this reduces a volume occupied by the heating assembly, in that it makes the heating assembly more compact and also limits the wall of air to be heated at the interface between the heating elements, i.e. the arranged PTC bundles, and the casing. As a further result, the heating assembly has less thermal inertia.

[0050] According to several examples of the present disclosure, the electrical heating assembly may further comprise one or more heating beams or heating modules that function as one or more heating elements. Each of such heating element of the one or more heating elements may include one or more of the PTC bundles that is / are overmolded with thermally conductive and electrically insulating material. Preferably the one or more of the PTC bundles are overmolded with magnesia. The casing may comprise or may be respective sheaths for each of such heating element of the one or more heating elements.

[0051] Hence, in this case, the PTC bundles may be overmolded in magnesia and may then be shielded with copper, stainless steel or enamelled steel as the respective sheath for example. In this case, the heating element may be understood as being in direct contact with the water in the water tank (since there is no air between the PTC bundle and the casing as in the previously outlined example), which may ensure optimum heat transfer from the PTC bundles to the water that is to be heated. The PTC resistor can take several different forms depending on the power required.

[0052] It should be noted for reasons of understandability that the respective sheaths may be in direct contact with water in the water tank, and that the PTC bundles are electrically isolated from the water due to being overmolded by an electrically insulating material. Thus, it may be said that the PTC bundles are in contact with the water in the water tank via a sheath and an electrically isolating overmolding material. In contrast thereto, it shall be pointed out for reasons of understandability that according to the example with the insulating volumetric body as outlined above in more detail, the PTC bundles may be arranged in grooves of an insulating volumetric body and that it may be said that the PTC bundles are not in contact with the water in the water tank, since the arranged PTC bundles are not in contact with the casing but an air space is provided between the arranged PTC bundles and the inner surface of the casing.

[0053] Hence, efficiency in heating water may be increased.

[0054] According to several examples of the present disclosure, the casing may comprise, or the respective sheaths may comprise at least one of copper, stainless steel, carbon steel and enameled steel.

[0055] Hence, water impermeability may be ensured.

[0056] According to several examples of the present disclosure, the electrical heating assembly may have a power rating in a range of 1,000 W to 10,000 W.

[0057] Hence, characteristics of the electrical heating assembly may be adjusted as required.

[0058] According to a second aspect, there is provided a water tank of at least 20 liters volume for hot water storage, wherein the water tank comprises an electrical heating assembly according to the first aspect.

[0059] The water tank according to the second aspect is advantageous in that it may participate in enabling, based on the electrical resistor being of the PTC type (also referred to as PTC resistor, for example a PTC ceramic), a self-regulation of temperature, as well as a passive protection against overheating. This may be based on the electrical resistance of PTC ceramics which increases with temperature, wherein the stabilization temperature is called the Curie temperature or reference temperature, and can vary according to the version of the PTC used. Hence, the use of PTC resistors could eliminate the need for a safety thermostat, i.e. for the second control element as mentioned above.

[0060] According to a third aspect, there is provided a domestic hot water heating system that comprises a water tank for storing domestic hot water. The water tank according to the second aspect.

[0061] The heating system according to the third aspect is advantageous in that it may participate in enabling, based on the electrical resistor being of the PTC type (also referred to as PTC resistor, for example a PTC ceramic), a self-regulation of temperature, as well as a passive protection against overheating. This may be based on the electrical resistance of PTC ceramics which increases with temperature, wherein the stabilization temperature is called the Curie temperature or reference temperature, and can vary according to the version of the PTC used. Hence, the use of PTC resistors could eliminate the need for a safety thermostat, i.e. for the second control element as mentioned above.

[0062] According to a fourth aspect, there is provided a central heating water heating system that comprises a water tank for storing water. The water tank according to the second aspect.

[0063] The heating system according to the fourth aspect is advantageous in that it may participate in enabling, based on the electrical resistor being of the PTC type (also referred to as PTC resistor, for example a PTC ceramic), a self-regulation of temperature, as well as a passive protection against overheating. This may be based on the electrical resistance of PTC ceramics which increases with temperature, wherein the stabilization temperature is called the Curie temperature or reference temperature, and can vary according to the version of the PTC used. Hence, the use of PTC resistors could eliminate the need for a safety thermostat, i.e. for the second control element as mentioned above.

[0064] According to a fifth aspect, there is provided a water heating system that comprises a domestic hot water heating system according to the third aspect and a central heating water heating system according to the fourth aspect.

[0065] The heating system according to the fifth aspect is advantageous in that it may participate in enabling, based on the electrical resistor being of the PTC type (also referred to as PTC resistor, for example a PTC ceramic), a self-regulation of temperature, as well as a passive protection against overheating. This may be based on the electrical resistance of PTC ceramics which increases with temperature, wherein the stabilization temperature is called the Curie temperature or reference temperature, and can vary according to the version of the PTC used. Hence, the use of PTC resistors could eliminate the need for a safety thermostat, i.e. for the second control element as mentioned above.

[0066] According to a sixth aspect, there is provided a use of an electrical heating assembly according to the first aspect for heating water in a water tank of at least 20 liters volume for hot water storage.

[0067] According to a seventh aspect, there is provided a method comprising the operation of the electrical heating assembly according to the first aspect for heating water in a water tank of at least 20 liters volume for hot water storage.

[0068] The use according to the sixth aspect and the method according to the seventh aspect are each advantageous in that each of the use and the method may participate in enabling, based on the electrical resistor being of the PTC type (also referred to as PTC resistor, for example a PTC ceramic), a self-regulation of temperature, as well as a passive protection against overheating. This may be based on the electrical resistance of PTC ceramics which increases with temperature, wherein the stabilization temperature is called the Curie temperature or reference temperature, and can vary according to the version of the PTC used. Hence, the use of PTC resistors could eliminate the need for a safety thermostat, i.e. for the second control element as mentioned above.

[0069] According to an eight, nineth and tenth aspect, there is provided a use of the heating systems according to the third, fourth and fifth aspects, respectively.

[0070] According to an eleventh, twelfth and thirteenth aspect, there is provided a method comprising the operation of the heating systems according to the third, fourth and fifth aspects, respectively.

[0071] The use according to the eight, nineth and tenth aspect and the method according to the eleventh, twelfth and thirteenth aspect are each advantageous in that each of the use and the method may participate in enabling, based on the electrical resistor being of the PTC type (also referred to as PTC resistor, for example a PTC ceramic), a self-regulation of temperature, as well as a passive protection against overheating. This may be based on the electrical resistance of PTC ceramics which increases with temperature, wherein the stabilization temperature is called the Curie temperature or reference temperature, and can vary according to the version of the PTC used. Hence, the use of PTC resistors could eliminate the need for a safety thermostat, i.e. for the second control element as mentioned above.

[0072] Optional features of the first aspect may form part of any of the second to thirteenth aspects, mutatis mutandis.

[0073] The indefinite article "a" or "an" does not exclude a plurality. In addition, the articles "a" and "an" as used herein should generally be construed to mean "one or more" unless specified otherwise or clear from the context to be directed to a singular form.

[0074] Unless specified otherwise, or clear from the context, the phrases "one or more of A, B and C", "at least one of A, B, and C", and "A, B and / or C" as used herein are intended to mean all possible permutations of one or more of the listed items. That is, the phrase "A and / or B" means (A), (B), or (A and B), while the phrase "A, B, and / or C" means (A), (B), (C), (A and B), (A and C), (B and C), or (A, B, and C).

[0075] The term "comprising" does not exclude other elements or steps. Furthermore, the terms "comprising", "including", "having" and the like may be used interchangeably herein.

[0076] The invention may include one or more aspects, examples or features in isolation or combination whether specifically disclosed in that combination or in isolation. Any optional feature or sub-aspect of one of the above aspects applies as appropriate to any of the other aspects.

[0077] The above-described aspects will become apparent from, and elucidated with, reference to the detailed description provided hereinafter.Brief Description of the Drawings

[0078] A detailed description will now be given, by way of example only, with reference to the accompanying drawing, in which: Figure 1 shows a bundle of PTC resistors according to several examples of the present disclosure; Figure 2 shows an insulating volumetric body according to several examples of the present disclosure; Figure 3 shows, from a first perspective, the insulating volumetric body according to Figure 2, wherein several of the bundles according to Figure 1 are arranged in grooves of the insulating volumetric body; Figure 4 shows the insulating volumetric body according to Figure 3 from a second perspective; Figure 5 shows a heating assembly comprising the insulating volumetric body according to Figure 3 inserted in a casing according to several examples of the present disclosure; Figure 6 shows, from a first perspective, a cross section of the heating assembly according to Figure 5; Figure 7a shows an enlarged view of the cross section according to Figure 6; Figure 7b shows a comparative example; Figure 8a shows, from a second perspective, a cross section of the heating assembly according to Figure 5; Figure 8b shows, from a second perspective, a cross section of the comparative example according to Figure 7b; Figure 9 shows a heating assembly comprising heating modules according to several examples of the present disclosure; Figure 10 shows a cross section of a heating module according to Figure 9; Figure 11 shows a cross section of the heating assembly according to Figure 9; Figure 12 shows a heating assembly comprising heating modules according to several examples of the present disclosure; Figure 13 shows a cross section of the heating assembly according to Figure 12; Figure 14 shows an example for a pulse width modulation signal; Figure 15 shows an example for the usage of a share of a total amount of electrical power, the share to be supplied to a heating assembly according to several examples of the present disclosure; Figure 16 shows examples for PTC characterization curves; Figure 17 shows an example of characteristic points in a PTC characterization curve; Figure 18 comprises of Figures 18a, 18b and 18c, and shows different examples for water tanks according to several examples of the present disclosure; Figure 19 shows a diagram for the application of a domestic hot water tank that includes a heating assembly according to several examples of the present disclosure; Figure 20 shows a diagram for the application of a buffer tank that includes a heating assembly according to several examples of the present disclosure; and Figure 21 shows a diagram for the combined application of a domestic hot water tank that includes a heating assembly according to several examples of the present disclosure and a buffer tank that includes a heating assembly according to several examples of the present disclosure. Detailed Description

[0079] According to several examples of the present disclosure, one aspect is to use the physical characteristics of positive temperature coefficient (PTC) resistors to ensure that a predetermined maximum heating temperature generated or reached by an electrical heating assembly (or heating assembly as used herein further below) that comprises such PTC resistors is not to be exceeded. Such PTC resistors may be PTC stones, PTC ceramics or, more generally said, electrical resistors of the PTC type.

[0080] In view thereof, according to several examples of the present disclosure, there is provided an electrical heating assembly for a water tank of at least 20 liters volume for hot water storage. The electrical heating assembly is at least partly insertable into the water tank and comprises a heating circuitry and a casing. The heating circuitry is configured to connect the electrical heating assembly to a power source, wherein the heating circuitry comprises an electrical resistor of a PTC type. The casing surrounds at least part of the heating circuitry that includes the electrical resistor. Further, the casing is configured to electrically isolate the heating circuitry from water when the at least part of the heating circuitry is inserted into the water tank and when the water tank is at least partially filled with water. The electrical resistor is configured to, once a threshold temperature at the electrical resistor is reached, exponentially increase its electrical resistance with temperature.

[0081] In view thereof, referring to Figure 1, Figures 1 shows a bundle 100 of PTC resistors according to several examples of the present disclosure. In more detail, the bundle 100 100 comprises a first metal plate 131 that comprises, at one end of the first metal plate 131, a first electrical harness connection 111, a second metal plate 132 that comprises, at one end of the second metal plate 132, a second electrical harness connection 112, wherein the first metal plate 131 and the second metal plate 132 are arranged to face each other, and wherein the first electrical harness connection 111 and the second electrical harness connection 112 are arranged to face each other. Further, the bundle 100 comprises several electrical resistors of the PTC type, i.e. several PTC resistors, PTC ceramic elements, or PTC stones. In more detail, the bundle 100 comprises eight PTC stones 121 to 128 that are each arranged between the first metal plate 131 and the second metal plate 132. In more detail, the PTC stones 121 to 128 are bonded with conductive adhesive between the first metal plate 131 and the second metal plate 132. Hence, did PTC stones 121 to 128 are electrically connected in parallel to each other. The first electrical harness connection 111 and the second electrical harness connection 112 may be used to connect the bundle 100 to an electrical power source. Hence, said in other words, the first electrical harness connection 111, the first metal plate 131, the eight PTC stones 121 to 128 (wherein a number of PTC stones is not limited to eight and may be less than eight, for example one or more, or may be more than eight, for example nine or more), the second metal plate 132 and the second electrical harness connection 112 may be understood to form a heating circuitry. The PTC stones may be made of ceramic of different grades. A temperature range in which the electrical resistance of the PTC stones 121 to 128 increases exponentially may be from 70°C to 400°C, preferably from 80°C to 270°C.

[0082] According to several examples of the present disclosure, the above indicated heating assembly may comprise one or more of such PTC bundles 100. If there are at least two PTC bundles, the at least two PTC bundles are connected in parallel or serial to each other (depending on how there are supplied with electrical power from the power source).

[0083] Referring now to Figure 2, Figures 2 shows an insulating volumetric body 200 according to several examples of the present disclosure. The insulating volumetric body 200 comprises a substantial cylindrical shape having an outer surface 210. The insulating volumetric body 200, in more detail its outer surface 210, comprises one or more grooves 221 to 226. The one or more grooves 221 to 226 are each configured so that the PTC bundle 100 may be assembled or inserted or arranged in such groove. It shall be noted that the insulating volumetric body 200 may in general be of any shape, for example of a cuboid shape. Moreover, a number of grooves is not limited to six and there may be less than six, for example one or more grooves, or more than six, for example seven or more grooves. The insulating biometric body 200 is made of an insulating material and, preferably, also of a thermal conductive material, for example of a ceramic.

[0084] Referring now to Figure 3, Figure 3 shows an equipped or loaded insulating volumetric body 300. In more detail, the insulating volumetric body 200 according to Figure 2, wherein PTC bundles are arranged inside the grooves 221 to 226. In particular, a PTC bundle 100-1 is arranged in groove 221, a PTC bundle 100-2 is arranged in groove 222, a PTC bundle 100-3 is arranged in groove 223, a PTC bundle 100-4 is arranged in groove 224, a PTC bundle 100-5 is arranged in groove 225, and a PTC bundle 100-6 is arranged in groove 226. Figure 3 shows the equipped insulating volumetric body 300 from the perspective of the end of the substantial cylindrical shape of the insulating volumetric body 200 or 300 at which the insulating volumetric body 200 or 300 is intended to be inserted into a casing. Figure 4 shows the opposite end of the end shown in Figure 3. In more detail, referring now to Figure 4, Figure 4 shows the equipped insulating volumetric body 300 from the perspective of the end of the substantial cylindrical shape of the insulating volumetric body 200 or 300 at which the arranged bundles 100-1 to 100-6 are intended to be connected to an electrical power source. Accordingly, the bundle 100-1 comprises a first electrical harness connection 111-1 and a second electrical harness connection 112-1, the bundle 100-2 comprises a first electrical harness connection 111-2 and a second electrical harness connection 112-2, the bundle 100-3 comprises a first electrical harness connection 111-3 and a second electrical harness connection 112-3, the bundle 100-4 comprises a first electrical harness connection 111-4 and a second electrical harness connection 112-4, the bundle 100-5 comprises a first electrical harness connection 111-5 and a second electrical harness connection 112-5, and the bundle 100-6 comprises a first electrical harness connection 111-6 and a second electrical harness connection 112-6.

[0085] Referring now to Figure 5, Figures 5 shows a heating assembly 500 according to several examples of the present disclosure. The heating assembly 500 comprises the equipped insulating volumetric body 300 and a casing 510, into which the equipped insulating volumetric body 300 is inserted. The casing 510 is impermeable to water. Hence, the part of the equipped insulating volumetric body 300, or said in other words the part of the heating circuitry that is surrounded by the casing 510 is isolated from water. Referring now to Figure 6, Figures 6 shows a cross-sectional view of the heating assembly 500. As an example, to PTC bundles are illustrated in Figure 6, that is a first PTC bundle 100 -1 and a fourth PTC bundle 100-4. Wherein the first PTC bundle 100-1 comprises eight PTC stones 121-1 to 128-1, and wherein the fourth PTC bundle 100-4 comprises eight PTC stones 121-4 to 128-4. It shall be noted that each of the first PTC bundle 100-1 and the fourth PTC bundle 100-4 may be such PTC bundle 100 as shown in Figure 1. Referring now to Figure 7a, Figures 7a shows an enlarged view of the end of the heating assembly 500 in a cross-sectional view. This is according to a specific example developed by the inventors and the values indicated in Figure 7a thus correspond to the specific example. However, it shall be noted that the present disclosure is not limited to these certain values. In more detail, it is indicated in Figure 7a that a distance between PTC stones in different PTC bundles that are arranged opposite to each other, for example, as indicated in Figure 8a, an eighth position PTC stone (for example PTC stone 128-1) in the first PTC bundle 100-1 and an eighth position PTC stone (for example PTC stone 128-4) in the fourth PTC bundle 100-4, or an eighth position PTC stone (for example PTC stone 128-2) in the second PTC bundle 100-2 and an eighth position PTC stone (for example PTC stone 128-5) in the fifth PTC bundle 100-5, or an eighth position PTC stone (for example PTC stone 128-3) in the third PTC bundle 100-3 and an eighth position PTC stone (for example PTC stone 128-6) in the sixth PTC bundle 100-6, is 22.1 mm. In more detail, between such opposite PTC stones, a distance between the respective surfaces of the PTC stones that face towards the middle axis of the insulating volumetric body 200 is 22.1 mm. It shall be noted that according to several examples of the present disclosure such distance is not limited to 22.1 mm. For example, such distance of 22.1 mm may be understood as a lower limit distance. Moreover, Figure 7a indicates that a distance between a last PTC stone (for example the eighth PTC stone 128) in a PTC bundle and the outer surface of the casing 510 that is intended to be in contact with water to be heated, is 8.5 mm. It shall be noted that according to several examples of the present disclosure such distance is not limited to 8.5 mm. For example, such distance of 8.5 mm may be understood as a lower limit distance. Furthermore, it is indicated in Figure 7 that a distance between a PTC stone and the casing 510 is 4.2 mm. In more detail, it is indicated that a distance between a surface of a PTC stone that faces towards an outside of the insulating volumetric body 200, i.e. in a direction opposite to the direction towards the middle axis, and an inner surface of the casing 510 is 4.2 mm. It shall be noted that according to several examples of the present disclosure such distance is not limited to 4.2 mm. For example, such distance of 4.2 mm may be understood as a lower limit distance.

[0086] Comparative examples are shown in Figures 7b and 8b. In particular, current solutions with resistive wire elements (800-1 to 800-12) in a soapstone body 800 inserted into a casing 810 are shown. Accordingly, a minimum achievable distance between a resistive wire element 800-1 and the casing 510 is 5.5 mm (in comparison to 4.2 mm as illustrated in Figure 7a as an example).

[0087] Referring now to Figure 9, Figures 9 shows a heating assembly 900 comprising heating elements (also referred to as heating modules) 911 and 912 according to several examples of the present disclosure. However, the heating assembly 900 is not limited to have two such heating elements and may have one such heating element or three or more such heating elements. Further, such heating elements of the heating assembly 900 may not necessarily be identical, i.e. the different heating elements may have a different number of PTC bundles for example. Figure 10 shows a cross-sectional view of one such heating element 911. The heating element 911 as shown in Figure 10 comprises, from the inside to the outside, three PTC bundles 100-1, 100-2 and 100-3, wherein the three PTC bundles are overmolded in a thermally conductive and electrically insulating material 1020. It shall be noted that a number of PTC bundles may be different from three. Preferably, the thermally conductive and electrically insulating material 1020 is magnesia. Moreover, the thermally conductive and electrically insulating material 1020 is covered by a sheath 1011. Preferably, the sheath 1011 is in direct contact with the thermally conductive and electrically insulating material 1020, and there's no air between the sheath 1011 and the thermally conductive and electrically insulating material 1020.

[0088] As a mere example without being limited to these values, the heating element 911 may have a height of 15 mm and a width of 40 mm, wherein the minimum distances from the PTC stones to the inner surfaces of the thermally conductive and electrically insulating material 1020 is 3 mm in the width direction and 4 mm in the height direction. Figures 11 shows a cross-sectional view of the heating assembly 900 and illustrates the sheaths 1011 and 1012 of the respective heating elements 911 and 912.

[0089] Referring now to Figure 12, Figures 12 shows a heating assembly 1200 similar to the heating assembly 900 according to Figure 9, wherein the heating assembly 1200 according to Figure 12 comprises six heating elements (also referred to as heating modules) 1211 to 1216. Each heating element of the heating elements 1211 to 1216 comprises one PTC bundle overmolded in a thermally conductive and electrically insulating material, for example magnesia, and further comprises a respective sheath as indicated in Figure 13. In more detail, Figure 13 shows a cross-sectional view of the heating assembly 1200 and, in doing so, illustrates the respective sheaths 1311 to 1316 for the heating element 1211 to 1216.

[0090] According to several examples of the present disclosure, the casing 510 according to Figure 5 and the respective sheaths 1011, 1012 and 1311 to 1316 according to Figures 9 and 12 comprise at least one of copper, stainless steel, carbon steel and enamelled steel.

[0091] Moreover, according to several examples of the present disclosure, each of the heating assemblies 500, 900 and 1200 according to Figures 5, 9 and 12 may further comprise a control unit. The control unit may be configured to control a temperature of the electrical resistor of the PTC type, i.e. of the one or more PTC stones of the one or more PTC bundles, by applying a pulse width modulation (PWM) signal 1400 at the electrical resistor and / or by controlling an increase and a decrease of an electrical current applied at the electrical resistor. Figures 14 shows an example for a PWM signal over time. The PWM signal and / or the changing electrical current may be provided by the power source that is connected to the PTC bundles via the respective first and second electrical harness connections. With the electrical resistor of the PTC type, it is possible to consider PWM control operation to adjust a power delivered (to the PTC stones) according to need. Thus, in addition to the electrical resistor of the PTC type, a power modulation system can be used to control one or more PMW signals applied to one or more PTC stones to achieve a heating assembly having a precise heating power and control power consumption. For this purpose, a power electronics board may be added to the heating assembly, for example at the end of the heating assembly where a bundle's respective first and second electrical harness connections are provided. Such power electronics board could be based on a system of power transistors activated by a PWM signal. Each slot may activate the transistors that may act as switches. By varying a duration of the PWM signal's square-wave signal, as illustrated in Figure 14, a heating power of the PTC stones can be modulated. This power electronics board could also provide feedback, like power consumption, instantaneous power, error message, etc., via LIN or CAN communication. Moreover, with reference to Figure 15, it shall be noted that PTC resistors may not be controlled in On / Off mode only, i.e. when full power (totally available power) is supplied in On-mode and when on o power is supplied in Off-mode. Rather, with a PTC resistor, it is possible to consider PWM control operation to adjust a power delivered according to need. In more detail, Figures 15 shows an example for the usage of a share P1 of a total amount of electrical power P3, the share P1 to be supplied to one of the heating assemblies 500, 900 and 1200 according to several examples of the present disclosure. Specifically, in a diagram Power (for example kW) over Time (for example hours), an amount of electrical power supplied to the heating assembly may be indicated by a graph G. The graph G has an inclination α greater than 0° and below 90°. With reference to above, an inclination of 90° may represent such On-mode where all available power, i.e. full power, is supplied to the heating assembly. In the diagram according to Figure 15, full power may be indicated by P3, so at On-mode, the graph G would have an inclination of α = 90° to rise at the time t from 0 to P3, and to then remain at the P3, i.e. at the power level 1520. In contrast thereto, the heating assembly according to several examples of the present disclosure allows for an inclination of α < 90°, for example of α = 50°, and further allows that an amount of electrical power P1 that is supplied to the heating assembly is below full power P3, i.e. the supplied electrical power may remain at a lower power level 1510 below the full power level 1520. The supplied electrical power may further be adjusted to another share P2 of the full power P3 and may remain on the corresponding power level 1530. The difference between the electrical power P1 and P2 may be S1, and the difference between the electrical power P2 and P3 may be S2. Hence, in case a power P1 is supplied to the heating assembly according to several examples of the present disclosure, still a power amount of S1 + S2 may be available for other devices / purposes.

[0092] Referring now to Figure 18, Figure 18 comprises a first part Figure 18a, a second part Figure 18b and a third part Figure 18c. In more detail, Figure 18a shows a domestic water tank 1800a that comprises, as generator, such heating assembly 500 according to Figure 5 for example (no additional coil inside the water tank 1800a). Figure 18b shows a domestic water tank 1800b that additionally comprises a coil inside the water tank 1800b as primary generator, wherein such heating assembly 500 according to Figure 5 for example is used as an electrical backup heater, i.e. a secondary generator. Figure 18c shows an example for a buffer tank 1800c that comprises such heating assembly 500 according to Figure 5 for example. In Figure 18, each of the water tanks 1800a, 1800b and 1800c are illustrated to comprise such heating assembly 500 according to Figure 5. However, each water tank 1800a, 1800b and 1800c may comprise such heating assembly 900 and / or 1200 instead and / or additionally. Based thereon, in the following, Figures 19 to 21 are described, wherein Figures 19 to 21 illustrate heating systems that use (see Figure 19) a domestic hot water tank for example according to Figure 18a or 18b, or that use (see Figure 20) a buffer tank for example according to Figure 18c, or that use (see Figure 21) both tanks, i.e. a domestic hot water tank according to Figure 18a or 18b and a buffer tank according to Figure 18c.

[0093] Referring now to Figure 19, Figure 19 shows, in a simplified manner for explanation purposes only, a diagram of a heating system 1900 for the application of a domestic hot water tank 1920 that includes a heating assembly 1922 according to several examples of the present disclosure. The domestic hot water in the domestic hot water tank 1920 is for alimentary purpose. In more detail, the heating system 1900 comprises a generator 1910, a domestic hot water tank 1920 and a pump 1930. The generator 1910 generates hot central heating water 1911 that flows from the generator 1910 to the domestic hot water tank 1920. The hot central heating water 1911 is for heat exchange only, and is not for alimentary purpose. In the domestic hot water tank 1920 there is provided a coil 1921 with central heating water inside. In more detail, the hot central heating water 1911 provided by the generator 1910 flows through the coil 1921 in the domestic hot water tank 1920. In doing so, the temperature of the hot central heating water 1911 decreases. The decrease in temperature is indicated by the greyscale, that is, hot water is indicated with grey and cold water is indicated with white, and the lighter the grey becomes the colder the water gets. Hence, Figure 19 illustrates that the hot central heating water 1911 inserts the coil 1921 in the domestic hot water tank 1920, cools down per heat exchange when flowing through the coil 1921, and exits the domestic hot water tank 1920 and the coil 1921 as cold central heating water 1912 that flows from the domestic hot water tank 1920 back to the generator 1910 by use of the pump 1930. The cold central heating water 1912 is for heat exchange only, and is not for alimentary purpose. The domestic hot water tank 1920 further comprises the heating assembly 1922. The heating assembly 1922 may be a heating assembly according to several examples of the present disclosure, for example one of the heating assemblies 500, 900 and 1200. Moreover, domestic cold water 1923 flows from the network into the domestic hot water tank 1920, gets heated by the heating assembly 1922 and the hot central heating water 1911 in the coil 1921, and may be stored in the domestic hot water tank 1920. Domestic hot water 1924 may then flow out of the domestic hot water tank 1920 for alimentary purposes. It should be noted that the central heating water does not mix with the domestic water.

[0094] Referring now to Figure 20, Figure 20 shows, in a simplified manner for explanation purposes only, a diagram of a heating system 2000 for the application of a buffer tank 2020 that includes a heating assembly 2023 according to several examples of the present disclosure. The central heating water according to Figure 20 is for heat exchange only, and is not for alimentary purpose. In more detail, the heating system 2000 comprises a generator 2010, a buffer tank 2020, several pumps 1931 and 1932, and several receptors 2041, 2042 and 2043 of the hot water. The generator 2010 generates hot central heating water 2011 that flows from the generator 2010 to the buffer tank 2020. In the buffer tank 2020 the received hot central heating water 2011 mixes with water stored or available in the buffer tank 2020. From the buffer tank 2020, hot central heating water 2021 flows to different receptors 2041, 2042 and 2043, which may be radiators and / or floor heating for example, which are for heat exchange only and not for alimentary purpose. Due to the heat exchange in the receptors, the hot central heating water 2021 cools down per heat exchange and returns to the buffer tank 2020 as cold central heating water 2022 via a first pump 2031. In the buffer tank 2020 there is provided a heating assembly 2023. The heating assembly 2023 may be a heating assembly according to several examples of the present disclosure, for example one of the heating assemblies 500, 900 and 1200. The cold central heating water 2022 gets heated in the buffer tank 2020 by the heating assembly 2023 and by mixing with the hot central heating water 2011. Moreover, cold central heating water 2012 flows from the buffer tank 2022 to the generator 2010 via a second pump 2032. Similar to Figure 19, a decrease in temperature is indicated by the greyscale, that is, hot water is indicated with grey and cold water is indicated with white, and the lighter the grey becomes the colder the water gets.

[0095] Referring now to Figure 21, Figure 21 shows, in a simplified manner for explanation purposes only, a diagram of a heating system 2100 that may be understood as a combination of the heating systems 1900 and 2000 according to Figures 19 and 20. In particular, the heating system 2100 comprises a generator 2110, a buffer tank 2120, several pumps 2131 and 2132, several receptors 2141 and 2142, a domestic hot water tank 2150, and a three-way-valve 2160. The domestic hot water in the domestic hot water tank 2150 is for alimentary purpose. Hot central heating water 2111 flows from the generator 2110 into the buffer tank 2120 (first part hot central heating water 2111a) and the domestic hot water tank 2150 (second part hot central heating water 2111b) via the three-way-valve 2160 (where the water flow is separated). From the buffer tank 2120, hot central heating water 2121 flows to the different 2141 and 2142, like radiators and / or floor heating for example, for heat exchange purposes, and flows as cold central heating water 2122 back to the buffer tank 2120 via a first pump 2131. In the buffer tank 2120, the received cold central heating water 2122 gets heated by the heating assembly 2123 included in the buffer tank 2120 and by mixing with the hot central heating water 2111 received the generator 2110. The heating assembly 2123 may be a heating assembly according to several examples of the present disclosure, for example one of the heating assemblies 500, 900 and 1200. From the buffer tank 2120, cold central heating water 2112a may be directed via the three-way-valve 2160 to flow back to the generator 2110, indicated as cold central heating water 2112, via a second pump 2132. Due to the three-way-valve 2160, the hot central heating water 2111 is directed to either flow to the domestic hot water tank 2150 or to the buffer tank 2120. In the domestic hot water tank 2150, the hot central heating water 2111b received from the generator 2110 flows through a coil 2151 provided in the domestic hot water tank 2150, exchanges heat with domestic water stored in the domestic hot water tank 2150 and thus cools down per heat exchange, and leaves the domestic hot water tank 2150 and the coil 2151 to flow back to the generator 2110 as cold central heating water 2112b. It should be noted that the water received from generator 2110 does not mix with the domestic water stored or available in the domestic hot water tank 2150. Moreover, domestic cold water 2153 for alimentary purpose flows from the network into the domestic hot water tank 2150, gets heated by a heating assembly 2152 included in the domestic water tank 2150 and by the hot central heating water 2111b in the coil 2151, and may be stored in the domestic hot water tank 2150. Domestic hot water 2154 may then flow out of the domestic hot water tank 2150 for alimentary purposes. The heating assembly 2152 may be a heating assembly according to several examples of the present disclosure, for example one of the heating assemblies 500, 900 and 1200. Similar to Figure 19, a decrease in temperature is indicated by the greyscale, that is, hot water is indicated with grey and cold water is indicated with white, and the lighter the grey becomes the colder the water gets. It shall be noted that the central heating water that flows into and out of the buffer tank 2120 and that flows through the coil 2151 is for heat exchange only, and is not for alimentary purpose.Reference Signs

[0096] 100PTC bundle 111first electrical harness connection 112second electrical harness connection 121 to 128PTC stones 131first metal plate 132second metal plate 200insulating volumetric body 210insulating volumetric body surface 221 to 226grooves 300equipped insulating volumetric body 500heating assembly 510casing 900heating assembly 911, 912heating elements 1020thermally conductive and electrically insulating material 1011,1012sheaths 1200heating assembly 1211 to 1216heating elements 1311 to 1316sheaths 1400pulse width modulation signal P1, P2, P3power values 1510 to 1530power levels T ref reference temperature 1800a, 1800bwater tanks 1900heating system 1910generator 1920domestic hot water tank 1921coil 1922heating assembly 1930pump 2000heating system 2010generator 2020buffer tank 2023heating assembly 2031,2032pumps 2041 to 2043receptors 2100heating system 2120buffer tank 2123heating assembly 2131,2132pumps 2141,2142receptors 2050domestic hot water tank 2051coil 2052heating assembly 2160three-way-valve

Examples

Embodiment Construction

[0079]According to several examples of the present disclosure, one aspect is to use the physical characteristics of positive temperature coefficient (PTC) resistors to ensure that a predetermined maximum heating temperature generated or reached by an electrical heating assembly (or heating assembly as used herein further below) that comprises such PTC resistors is not to be exceeded. Such PTC resistors may be PTC stones, PTC ceramics or, more generally said, electrical resistors of the PTC type.

[0080]In view thereof, according to several examples of the present disclosure, there is provided an electrical heating assembly for a water tank of at least 20 liters volume for hot water storage. The electrical heating assembly is at least partly insertable into the water tank and comprises a heating circuitry and a casing. The heating circuitry is configured to connect the electrical heating assembly to a power source, wherein the heating circuitry comprises an electrical resistor of a PTC...

Field of the Invention

[0001] The invention relates to an electrical heating assembly for a water tank of at least 20 liters volume for hot water storage. The invention further relates to a water tank that comprises such electrical heating assembly, and to a use of such electrical heating assembly. Moreover, the invention further relates to an open loop domestic hot water heating system and to a closed loop heating water heating system.Background

[0002] At present, tanks for hot water production, for example for domestic hot water production or central heating water production for heating purposes, regularly use an electrical resistive element. The electrical resistive element may be a main heating device or a complementary heating device. For example, the main heating device that may be used is an electric water heater, or a heat pump, wherein the complementary heating device that may be used is a back-up heater associated to a heat pump.

[0003] Generally, there are two main types of electric heating systems, i.e. an immersion heater system and a non-submerged heater system.

[0004] The immersion heater system or immersion heater comprises a resistor immersible in water, wherein a resistive wire is enclosed in a tube, and an electrically non-conductive material is enclosed between the resistive wire and the tube. The whole assembly is immersed in water, i.e. the resistive wire heats the non-conductive material and the tube. The tube directly heats through its wall the water, i.e. in general the liquid in which it is immersed. The use of an electrically non-conductive element prevents a short-circuit between the resistive wire and the immersed tube, which is often made of stainless steel or copper for example. This is broadly equivalent to the solution used in a kettle.

[0005] The non-submerged heater system or non-submerged heater comprises a resistor that is positioned in an immersible sheath or casing. The resistor comprises a resistive wire as a heating element that is housed in an electrically non-conductive material and thermal conductive material, usually a ceramic. The resistive wire is positioned in the immersible sheath and the heat generated by the resistive wire is transmitted to the air in the sheath, then to the sheath and then to the water, i.e. in general to the liquid, when the immersible sheath is immersed into the water. This is a more high-end solution as compared to the immersion heater system, as it allows the customer to replace or access the resistor's electrical elements for example without having to empty the water from the water tank (i.e. the water tank into which the immersible sheath that houses the resistor is inserted), since the resistor, i.e. the resistive wire or heating element, may be removed or pulled out from the immersed sheath. Said in other words, as the heating element is not directly immersed (but rather indirectly, since it may be inserted into an immersed sheath), the customer can remove it quite easily. Moreover, as there is no direct contact between the heating element and the water in the water thank, as a contact surface between the water and the immersed sheath is important, and as a same material may be used for the sheath than for the water tank, there is no scale build-up on the heating element, which may be accelerated when there is a strong temperature gradient.

[0006] Regardless of the immersion heater or the non-submerged heater, an electrical resistance as heating element, for example the resistive wires, requires two control elements.

[0007] The first control element controls a heating, so that the heating element is active when heating is required. The heating element must be active when the water in the water tank is too cold, and it must stop when the water has reached a sufficient or predetermined temperature. The first control element is therefore a regulating element, often achieved by means of a temperature determining device. This may be a mechanical element that acts as a function of temperature, or a sensor and associated control system. Depending on product type and range, this element can be set to ensure a higher or lower setpoint heating temperature. Changing the setpoint temperature adjusts the equivalent volume of hot water (= volume of hot water at 40°C) available to a customer. For the same volume, it is therefore possible to adjust hot water production according to the customer's consumption. For example, the water in the water tank could be heated from 52°C to 65°C, providing a greater or lesser volume of water equivalent to 40°C (temperature of use).

[0008] The second control element is a safety element which ensures that, even in the event of failure of the first control element, the electric resistance will not continue to heat continuously. In the absence of control, the resistor's electric resistance could continue to heat up to an excessive water temperature, that may lead to a risk of water vaporization and even water tank explosion in the event of multiple failures. Moreover, there may be a risk of burns and premature water tank deterioration due to the water tank's unsuitability for such extensive water temperatures. The protection provided by the second control element is achieved by means of a triggering device, which is different from the first control element. This triggering device is usually a mechanical release, for example a blade made of a material whose elongation or volume depends on temperature. In the event of overheating, the blade deforms and disconnects a power supply from the resistor's booster, thus preventing overheating. Normally, such disconnection is a permanent disconnection that needs a manual resetting.

[0009] Hence, the first control element is necessary to ensure system operation and user comfort. The use of the second control element, i.e. of the safety thermostat for example, is required by safety standards.

[0010] These solutions are widely known and have been in use for several decades. They are reliable and economically optimized. However, whatever the type of heating system, there are the drawbacks that two separated types of regulation are required, i.e. the first control element (control system) and the second control element (safety system), which increases complexity.

[0011] Hence, in view of the safety standards to potentially be adjusted in future based on the availability of technological developments, there is need to overcome at least part of these drawbacks, i.e. there is need for a solution using a single control means instead of two control elements to reduce complexity.

[0012] Moreover, apart therefrom, there is a need in general for electrical heating assemblies of reduced complexity and, at the same time, of increased efficiency, reliability, applicability and safety, in particular when such electrical heating assemblies are used for heating water in a water tank that is used for hot water storage, wherein the water's temperature may need to maintained within a predetermined temperature range and wherein such water tank may have a water storage capacity between several tens to several thousand liters volume.

[0013] Hence, there is also need for improvement regarding the heating of water in a water tank for hot water storage by use of electrical heating assemblies. For example, there is need in ensuring that such stored hot water is safe for a customer. Thus, in relation thereto, there is further need for an accurate controlling of the heating, i.e. for an accurate controlling of the stored hot water's temperature. Moreover, there is still further need for an adjustable setting (i.e. temperature setting) of the stored hot water's temperature.Summary

[0014] In view of the above, it is an object of the present disclosure to address at least part of the above-outlined needs.

[0015] Therefore, there is provided, in a first aspect, an electrical heating assembly for a water tank, the water tank of at least 20 liters volume for hot water storage. The electrical heating assembly is at least partly insertable into the water tank and comprises a heating circuitry and casing. The heating circuitry is configured to connect the electrical heating assembly to a power source, wherein the heating circuitry comprises an electrical resistor of a positive temperature coefficient (PTC) type. The casing surrounds at least part of the heating circuitry including the electrical resistor and the casing is configured to electrically isolate the heating circuitry from water when the at least part of the heating circuitry is inserted into the water tank and when the water tank is at least partially filled with water. The electrical resistor is configured to, once a threshold temperature at the electrical resistor is reached, exponentially increase its electrical resistance with temperature.

[0016] First, it should be noted that in general the electrical heating assembly may be operable for heating water without using any additional control or safety systems. However, to meet current (December 2024) safety standard requirements (for example standard EN 60335), once a safety system was activated or triggered to avoid overheating, it is required that the safety system is to be reset by a manual reset. However, such manual reset is not possible with an electrical resistor of a PTC type (or with a PTC resistor). Therefore, it should be noted that according to several examples of the present disclosure, the electrical heating assembly may further comprise a safety system to satisfy safety standard requirements.

[0017] However, regardless of whether or not such safety system is included, since the electrical resistor of the PTC type avoids overheating due to its electrical resistance increasing exponentially with temperature once the threshold temperature at the electrical resistor is reached, the advantageous technical effect of a gain in lifetime is achieved.

[0018] Furthermore, when compared with conventional resistors, the application of the electrical resistor of the PTC type avoids the occurrence of current spikes each time the electrical heating assembly is started-up or switch on. This is advantageous for maintaining network stability, for example if several houses are occupied by water heaters that each draws current at start-up.

[0019] The water tank may be of any volume above 20 liters, for example 100 liters, 500 liters, 1,000 liters, 2,000 liters or even 5,000 liters.

[0020] The expression "for hot water storage" may be understood in that hot water is stored in the water tank. However, this does not exclude that, for example during usage of the stored hot water, water is flowing into the tank and / or that water is flowing out of the tank. Rather, the expression "for hot water storage" may be understood to distinguish the present water tank from a small-sized tank, for example of about one to five liters volume, which is embedded into a heating system's heating water circuit such as for instance inside an indoor heat pump unit, and which uses an auxiliary heating means for additionally heating the water circulating in the heating system's heating water circuit.

[0021] It shall be noted that in more detail, the electrical resistor may be configured to, once a threshold temperature at the electrical resistor is reached, exponentially increase its electrical resistance with temperature for a current to flow through the heating circuitry, wherein a temperature of the electrical resistor is associated with the current. Said in other words, if the temperature reaches the threshold temperature, the electrical resistance rises exponentially and as result a current flowing through the resistor stops, i.e. does not flow, or is reduced to almost or substantially stop.

[0022] Such configuration of the electrical resistor is achievable, since the electrical resistor of the PTC type, i.e. a PTC resistor said in other words. A PTC resistor is a resistive element whose electrical resistance value depends on temperature. It may generally be used as a temperature sensor, wherein the electrical resistance of such temperature sensor changes with temperature. Hence, by reading the electrical resistance value, the corresponding temperature can be determined.

[0023] In general, it shall be noted that PTC stands for positive-temperature-coefficient thermistors: the thermistor resistance evolves with the temperature. It has more or higher electrical resistance at higher temperatures. That means that it heats less (or not) when the temperature increases. Common electrical resistors (i.e. non-PTC resistors for example) have a similar heating capacity whatever the temperature may be (in a normal operational range). As a result, common electrical resistors produce a same heat during a heating of a system, i.e. of water in a water tank for example. Common electrical resistors are controlled by such first and second control elements as described above.

[0024] PTC ceramics are semiconductors whose resistance depends on temperature. In the case of PTC, its resistance increases with temperature (unlike at negative temperature coefficients, NTCs). Examples for PTC characterization curves are provided in Figure 16, which shows the electrical resistance over temperature. Figure 17 shows examples of characteristic features of such PTC characterization curve. For example, at a certain temperature T Rmin a PTC resistor may have a minimum electrical resistance R min . Further, at material-related Curie temperature or reference temperature T ref , the PTC resistor may have an electrical resistance R ref from which on the electrical resistance of the PTC resistors increases exponentially with temperature.

[0025] The PTC resistor can be used to control the heating assembly if the temperature at which the PTC resistor no longer produces heat is in the vicinity of a control temperature, e.g. a control temperature between 50 and 90°C (all types, including photovoltaic self-electricity production), in particular between 52 and 75°C (for standard water heating). Furthermore, contrary to standard use with historical regulation, using the PTC as a temperature regulator may allow to further increase safety, given that the PTC resistor used may be intrinsically designed and used to directly integrate this role.

[0026] The electrical heating assembly according to the first aspect is further advantageous in that it may participate in enabling, based on the electrical resistor being of the PTC type (also referred to as PTC resistor, for example a PTC ceramic), a self-regulation of temperature, as well as a passive protection against overheating. Hence, no overheating of the heating assembly is possible due to the PTC resistor, which may allow to increase a lifespan of the heating assembly. This may be based on the electrical resistance of PTC ceramics which increases with temperature, wherein the stabilization temperature is called the Curie temperature or reference temperature, and can vary according to the version of the PTC used.

[0027] According to several examples of the present disclosure, a temperature range in which the electrical resistance of the electrical resistor increases exponentially may comprises a range from 70°C to 400°C, preferably from 80°C to 270°C. At the upper end of the temperature range and higher, the electrical resistance may then remain (almost) constant with temperature.

[0028] It should be noted that the temperature range may depend on the certain type of PTC material (or mixture of different PTC materials). In general, different PTC materials may have different threshold temperatures and / or different gradients in temperature increase after the threshold temperature. However, it shall be note that the present disclosure is not limited to any certain type of PTC material. Rather, the present disclosure uses the physical characteristics of PTC materials in general.

[0029] Hence, a suitable temperature range may be selected and / or adjusted as appropriate.

[0030] According to several examples of the present disclosure, the electrical heating assembly may further comprise a control unit configured to control a temperature of the electrical resistor by applying a pulse width modulation signal at the electrical resistor and / or by controlling an increase and a decrease of an electrical current applied at the electrical resistor.

[0031] Similar to above, it should be noted that in general the electrical heating assembly may be operable for heating water without using any additional control or safety systems. However, without the control system or control unit, only one temperature (i.e. water heating temperature) could be set at the electrical resistor of the PTC type. Therefore, to be able to change this temperature, i.e. to achieve an adjustable setting, the control system or control unit is needed.

[0032] It should be noted that such application of pulse width modulation (PWM) may be linked to the use of a PTC or PTC resistor as a heating element and associated regulation, i.e. use of a power modulation system, based on a printed circuit board (PCB) with a power transistor, like triarc, MOSFET, IGBT, SSR, etc. In contrast to PTC resistors, resistors with a single resistive wire are controlled in On / Off mode, i.e. full power when on or no power when off. With the PTC resistor, however, it is possible to consider PWM control operation to adjust a power delivered according to need. In particular, PWM in general is possible with a classical resistive element, but PTC resistors are more adapted thanks to a fast reactivity and low current spike (to occur at a start-up for example). Such power delivery adjustment is not adapted with a single resistive wire, which is not suited to PWM control, which requires a large number of cycles, thereby reducing the single resistive wire's life. In addition to the PTC resistor, a power modulation system can be used to control one or more PMW signals applied to one or more PTC resistors to achieve a heating assembly having a precise heating power and control power consumption. For this purpose, a power electronics board may be added to the heating assembly, for example at the end of the heating assembly that is not inserted into the water tank, i.e. at the end of a PTC resistor module for example. This module could be based on a system of power transistors activated by a PWM signal. Each slot may activate the transistors that may act as switches. By varying a duration of the PWM signal's square-wave signal, a heating power of the PTC resistor can be modulated. This module can also provide feedback, like power consumption, instantaneous power, error message, etc., via LIN or CAN communication.

[0033] Hence, power modulation makes it possible to precisely control the energy used by the heating assembly, which brings several advantages, like i) saving energy by avoiding power peaks (e.g. current spikes as indicated above), ii) avoiding potential overheating of the water that is being heated in the water tank, iii) avoiding overloading an electrical system of the building where the water tank including the heating assembly is installed, wherein the electrical system supplies power to the heating assembly, and iv) enabling intelligent control of a share of a totally availably power to be supplied to the heating assembly for example, wherein the intelligent control may be coupled with renewable energy sources for example.

[0034] According to several examples of the present disclosure, the control unit may further be configured to generate the pulse width modulation signal that corresponds to a first amount of electrical power and / or to control the electrical current to have a first amplitude that corresponds to the first amount of electrical power, wherein the first amount of electrical power is an adjustable share of a total amount of electrical power provided by the power source. Said in other words, the control unit may further be configured to use a first amount of electrical power for the pulse width modulation signal and / or the increase and the decrease, wherein the first amount of electrical power may be an adjustable share of a total amount of electrical power provided by the power source.

[0035] It should be noted that, for example, the total amount of electrical power may be a maximum amount of power providable by the power source. The power source may be a photovoltaic system for example.

[0036] Hence, power management may be improved, since an available amount of electrical power may be shared efficiently and appropriately among different power consumers (devices, like the heating assembly for example).

[0037] According to several examples of the present disclosure, the electrical resistor may comprise one or more PTC ceramic elements, wherein, if comprising at least two PTC ceramic elements, the at least two PTC ceramic elements are connected in parallel to each other.

[0038] It should be noted that a PTC ceramic element may also be understood as a PTC stone.

[0039] Hence, a heating power of the electrical resistor may be adapted or selected as required.

[0040] According to several examples of the present disclosure, the heating circuitry may comprise one or more PTC bundles, each PTC bundle of the one or more PTC bundles may comprise two or more PTC ceramic elements connected in parallel to each other. If comprising at least two PTC bundles, the at least two PTC bundles are connected in parallel or serial to each other.

[0041] It should be noted that to form a PTC bundle, PTC ceramics may be bonded in parallel between two conductive plates. In doing so, PTC ceramic stones are usable as a heating element for hot water cylinders for example. Such bundles may then be arranged or assembled on an insulating volumetric body, like on an insulating cylinder made of ceramic for example. A number of such arranged or assembled bundles and PTC ceramic stones per bundle may depends on the power required for the application of a certain water tank, for example from 1 ,000W to 3,000W or even to 10,000W and more for a residential application.

[0042] Hence, a heating power of the heating circuitry, i.e. the PTC resistors may be adapted or selected as required.

[0043] According to several examples of the present disclosure, the electrical heating assembly may further comprise an insulating volumetric body at least partly inserted into the casing, the insulating volumetric body comprising an outer surface that comprises one or more grooves, and wherein the one or more PTC bundles are assembled on the insulating volumetric body in that each PTC bundle is arranged in a respective groove of the one or more grooves.

[0044] It should be noted that, for example, a depth of the groove may be larger than a high of the PTC bundle when the PTC bundle is arranged in the groove. I.e., said in other words, the arranged PTC bundle may not be in contact with the casing when the insulating volumetric body is inserted into the casing. Preferably, the insulating volumetric body used to support the PTC bundles is ceramic, which is a thermal conductor and electrical insulator.

[0045] Hence, due to such design of the insulating volumetric body, a cross-section of the insulating volumetric body changes from a commonly used star shape to a cylinder, thereby further reducing an amount of air inside the casing. In this way, the heating assembly is more responsive (due to the reduction of no "unnecessarily" heated air) and a risk of creating hot air zones is avoided or reduced.

[0046] According to several examples of the present disclosure, the insulating volumetric body may be inserted into the casing, and a minimal distance between an assembled PTC bundle and an inner surface of the casing may be between 5.5 mm and 4.2 mm.

[0047] It should be noted that, in general and said in otherwords, it may be desirable to minimize a distance between an arranged PTC bundle and the inner surface of the casing to thus minimize an amount of air inside the casing. A reduced amount of air may allow for an increased heating efficiency, since a transfer of heat from the arranged PTC bundle to the water in the water tank via the insulating volumetric body, which may preferably be a ceramic, and the casing is increased if an amount of air is reduced. However, when the casing is in contact with water in the water tank, it has to be ensured that the arranged PTC bundle is not in contact with the casing.

[0048] Hence, it is enabled for an optimization of the design of the insulating volumetric body, by reducing a volume of air between a heating element, i.e. an arranged PTC bundle, and the inner surface of the casing. In doing so, it is enabled to reduce a distance between the arranged PTC bundle, i.e. the PTC resistor and the inner surface of the casing from, for example, 5.5 mm to 4.2 mm, allowing a smaller air gap. Thus, the proposed solution is more compact and minimizes the amount of air inside the casing, thereby reducing heat loss.

[0049] Such redesign or more compact design is easier to obtain based on using the PTC resistor compared to using a ferrous common resistor. The reason for that is because by using PTC resistors as heating elements, there is less risk of contact and of burn between the heating elements and the environment, i.e. between the heating elements and the casing or a user in case of maintenance. This allows for the above-indicated smaller distances between the arranged PTC bundles and the inner surface of the casing. As a result, this reduces a volume occupied by the heating assembly, in that it makes the heating assembly more compact and also limits the wall of air to be heated at the interface between the heating elements, i.e. the arranged PTC bundles, and the casing. As a further result, the heating assembly has less thermal inertia.

[0050] According to several examples of the present disclosure, the electrical heating assembly may further comprise one or more heating beams or heating modules that function as one or more heating elements. Each of such heating element of the one or more heating elements may include one or more of the PTC bundles that is / are overmolded with thermally conductive and electrically insulating material. Preferably the one or more of the PTC bundles are overmolded with magnesia. The casing may comprise or may be respective sheaths for each of such heating element of the one or more heating elements.

[0051] Hence, in this case, the PTC bundles may be overmolded in magnesia and may then be shielded with copper, stainless steel or enamelled steel as the respective sheath for example. In this case, the heating element may be understood as being in direct contact with the water in the water tank (since there is no air between the PTC bundle and the casing as in the previously outlined example), which may ensure optimum heat transfer from the PTC bundles to the water that is to be heated. The PTC resistor can take several different forms depending on the power required.

[0052] It should be noted for reasons of understandability that the respective sheaths may be in direct contact with water in the water tank, and that the PTC bundles are electrically isolated from the water due to being overmolded by an electrically insulating material. Thus, it may be said that the PTC bundles are in contact with the water in the water tank via a sheath and an electrically isolating overmolding material. In contrast thereto, it shall be pointed out for reasons of understandability that according to the example with the insulating volumetric body as outlined above in more detail, the PTC bundles may be arranged in grooves of an insulating volumetric body and that it may be said that the PTC bundles are not in contact with the water in the water tank, since the arranged PTC bundles are not in contact with the casing but an air space is provided between the arranged PTC bundles and the inner surface of the casing.

[0053] Hence, efficiency in heating water may be increased.

[0054] According to several examples of the present disclosure, the casing may comprise, or the respective sheaths may comprise at least one of copper, stainless steel, carbon steel and enameled steel.

[0055] Hence, water impermeability may be ensured.

[0056] According to several examples of the present disclosure, the electrical heating assembly may have a power rating in a range of 1,000 W to 10,000 W.

[0057] Hence, characteristics of the electrical heating assembly may be adjusted as required.

[0058] According to a second aspect, there is provided a water tank of at least 20 liters volume for hot water storage, wherein the water tank comprises an electrical heating assembly according to the first aspect.

[0059] The water tank according to the second aspect is advantageous in that it may participate in enabling, based on the electrical resistor being of the PTC type (also referred to as PTC resistor, for example a PTC ceramic), a self-regulation of temperature, as well as a passive protection against overheating. This may be based on the electrical resistance of PTC ceramics which increases with temperature, wherein the stabilization temperature is called the Curie temperature or reference temperature, and can vary according to the version of the PTC used. Hence, the use of PTC resistors could eliminate the need for a safety thermostat, i.e. for the second control element as mentioned above.

[0060] According to a third aspect, there is provided a domestic hot water heating system that comprises a water tank for storing domestic hot water. The water tank according to the second aspect.

[0061] The heating system according to the third aspect is advantageous in that it may participate in enabling, based on the electrical resistor being of the PTC type (also referred to as PTC resistor, for example a PTC ceramic), a self-regulation of temperature, as well as a passive protection against overheating. This may be based on the electrical resistance of PTC ceramics which increases with temperature, wherein the stabilization temperature is called the Curie temperature or reference temperature, and can vary according to the version of the PTC used. Hence, the use of PTC resistors could eliminate the need for a safety thermostat, i.e. for the second control element as mentioned above.

[0062] According to a fourth aspect, there is provided a central heating water heating system that comprises a water tank for storing water. The water tank according to the second aspect.

[0063] The heating system according to the fourth aspect is advantageous in that it may participate in enabling, based on the electrical resistor being of the PTC type (also referred to as PTC resistor, for example a PTC ceramic), a self-regulation of temperature, as well as a passive protection against overheating. This may be based on the electrical resistance of PTC ceramics which increases with temperature, wherein the stabilization temperature is called the Curie temperature or reference temperature, and can vary according to the version of the PTC used. Hence, the use of PTC resistors could eliminate the need for a safety thermostat, i.e. for the second control element as mentioned above.

[0064] According to a fifth aspect, there is provided a water heating system that comprises a domestic hot water heating system according to the third aspect and a central heating water heating system according to the fourth aspect.

[0065] The heating system according to the fifth aspect is advantageous in that it may participate in enabling, based on the electrical resistor being of the PTC type (also referred to as PTC resistor, for example a PTC ceramic), a self-regulation of temperature, as well as a passive protection against overheating. This may be based on the electrical resistance of PTC ceramics which increases with temperature, wherein the stabilization temperature is called the Curie temperature or reference temperature, and can vary according to the version of the PTC used. Hence, the use of PTC resistors could eliminate the need for a safety thermostat, i.e. for the second control element as mentioned above.

[0066] According to a sixth aspect, there is provided a use of an electrical heating assembly according to the first aspect for heating water in a water tank of at least 20 liters volume for hot water storage.

[0067] According to a seventh aspect, there is provided a method comprising the operation of the electrical heating assembly according to the first aspect for heating water in a water tank of at least 20 liters volume for hot water storage.

[0068] The use according to the sixth aspect and the method according to the seventh aspect are each advantageous in that each of the use and the method may participate in enabling, based on the electrical resistor being of the PTC type (also referred to as PTC resistor, for example a PTC ceramic), a self-regulation of temperature, as well as a passive protection against overheating. This may be based on the electrical resistance of PTC ceramics which increases with temperature, wherein the stabilization temperature is called the Curie temperature or reference temperature, and can vary according to the version of the PTC used. Hence, the use of PTC resistors could eliminate the need for a safety thermostat, i.e. for the second control element as mentioned above.

[0069] According to an eight, nineth and tenth aspect, there is provided a use of the heating systems according to the third, fourth and fifth aspects, respectively.

[0070] According to an eleventh, twelfth and thirteenth aspect, there is provided a method comprising the operation of the heating systems according to the third, fourth and fifth aspects, respectively.

[0071] The use according to the eight, nineth and tenth aspect and the method according to the eleventh, twelfth and thirteenth aspect are each advantageous in that each of the use and the method may participate in enabling, based on the electrical resistor being of the PTC type (also referred to as PTC resistor, for example a PTC ceramic), a self-regulation of temperature, as well as a passive protection against overheating. This may be based on the electrical resistance of PTC ceramics which increases with temperature, wherein the stabilization temperature is called the Curie temperature or reference temperature, and can vary according to the version of the PTC used. Hence, the use of PTC resistors could eliminate the need for a safety thermostat, i.e. for the second control element as mentioned above.

[0072] Optional features of the first aspect may form part of any of the second to thirteenth aspects, mutatis mutandis.

[0073] The indefinite article "a" or "an" does not exclude a plurality. In addition, the articles "a" and "an" as used herein should generally be construed to mean "one or more" unless specified otherwise or clear from the context to be directed to a singular form.

[0074] Unless specified otherwise, or clear from the context, the phrases "one or more of A, B and C", "at least one of A, B, and C", and "A, B and / or C" as used herein are intended to mean all possible permutations of one or more of the listed items. That is, the phrase "A and / or B" means (A), (B), or (A and B), while the phrase "A, B, and / or C" means (A), (B), (C), (A and B), (A and C), (B and C), or (A, B, and C).

[0075] The term "comprising" does not exclude other elements or steps. Furthermore, the terms "comprising", "including", "having" and the like may be used interchangeably herein.

[0076] The invention may include one or more aspects, examples or features in isolation or combination whether specifically disclosed in that combination or in isolation. Any optional feature or sub-aspect of one of the above aspects applies as appropriate to any of the other aspects.

[0077] The above-described aspects will become apparent from, and elucidated with, reference to the detailed description provided hereinafter.Brief Description of the Drawings

[0078] A detailed description will now be given, by way of example only, with reference to the accompanying drawing, in which: Figure 1 shows a bundle of PTC resistors according to several examples of the present disclosure; Figure 2 shows an insulating volumetric body according to several examples of the present disclosure; Figure 3 shows, from a first perspective, the insulating volumetric body according to Figure 2, wherein several of the bundles according to Figure 1 are arranged in grooves of the insulating volumetric body; Figure 4 shows the insulating volumetric body according to Figure 3 from a second perspective; Figure 5 shows a heating assembly comprising the insulating volumetric body according to Figure 3 inserted in a casing according to several examples of the present disclosure; Figure 6 shows, from a first perspective, a cross section of the heating assembly according to Figure 5; Figure 7a shows an enlarged view of the cross section according to Figure 6; Figure 7b shows a comparative example; Figure 8a shows, from a second perspective, a cross section of the heating assembly according to Figure 5; Figure 8b shows, from a second perspective, a cross section of the comparative example according to Figure 7b; Figure 9 shows a heating assembly comprising heating modules according to several examples of the present disclosure; Figure 10 shows a cross section of a heating module according to Figure 9; Figure 11 shows a cross section of the heating assembly according to Figure 9; Figure 12 shows a heating assembly comprising heating modules according to several examples of the present disclosure; Figure 13 shows a cross section of the heating assembly according to Figure 12; Figure 14 shows an example for a pulse width modulation signal; Figure 15 shows an example for the usage of a share of a total amount of electrical power, the share to be supplied to a heating assembly according to several examples of the present disclosure; Figure 16 shows examples for PTC characterization curves; Figure 17 shows an example of characteristic points in a PTC characterization curve; Figure 18 comprises of Figures 18a, 18b and 18c, and shows different examples for water tanks according to several examples of the present disclosure; Figure 19 shows a diagram for the application of a domestic hot water tank that includes a heating assembly according to several examples of the present disclosure; Figure 20 shows a diagram for the application of a buffer tank that includes a heating assembly according to several examples of the present disclosure; and Figure 21 shows a diagram for the combined application of a domestic hot water tank that includes a heating assembly according to several examples of the present disclosure and a buffer tank that includes a heating assembly according to several examples of the present disclosure. Detailed Description

[0079] According to several examples of the present disclosure, one aspect is to use the physical characteristics of positive temperature coefficient (PTC) resistors to ensure that a predetermined maximum heating temperature generated or reached by an electrical heating assembly (or heating assembly as used herein further below) that comprises such PTC resistors is not to be exceeded. Such PTC resistors may be PTC stones, PTC ceramics or, more generally said, electrical resistors of the PTC type.

[0080] In view thereof, according to several examples of the present disclosure, there is provided an electrical heating assembly for a water tank of at least 20 liters volume for hot water storage. The electrical heating assembly is at least partly insertable into the water tank and comprises a heating circuitry and a casing. The heating circuitry is configured to connect the electrical heating assembly to a power source, wherein the heating circuitry comprises an electrical resistor of a PTC type. The casing surrounds at least part of the heating circuitry that includes the electrical resistor. Further, the casing is configured to electrically isolate the heating circuitry from water when the at least part of the heating circuitry is inserted into the water tank and when the water tank is at least partially filled with water. The electrical resistor is configured to, once a threshold temperature at the electrical resistor is reached, exponentially increase its electrical resistance with temperature.

[0081] In view thereof, referring to Figure 1, Figures 1 shows a bundle 100 of PTC resistors according to several examples of the present disclosure. In more detail, the bundle 100 100 comprises a first metal plate 131 that comprises, at one end of the first metal plate 131, a first electrical harness connection 111, a second metal plate 132 that comprises, at one end of the second metal plate 132, a second electrical harness connection 112, wherein the first metal plate 131 and the second metal plate 132 are arranged to face each other, and wherein the first electrical harness connection 111 and the second electrical harness connection 112 are arranged to face each other. Further, the bundle 100 comprises several electrical resistors of the PTC type, i.e. several PTC resistors, PTC ceramic elements, or PTC stones. In more detail, the bundle 100 comprises eight PTC stones 121 to 128 that are each arranged between the first metal plate 131 and the second metal plate 132. In more detail, the PTC stones 121 to 128 are bonded with conductive adhesive between the first metal plate 131 and the second metal plate 132. Hence, did PTC stones 121 to 128 are electrically connected in parallel to each other. The first electrical harness connection 111 and the second electrical harness connection 112 may be used to connect the bundle 100 to an electrical power source. Hence, said in other words, the first electrical harness connection 111, the first metal plate 131, the eight PTC stones 121 to 128 (wherein a number of PTC stones is not limited to eight and may be less than eight, for example one or more, or may be more than eight, for example nine or more), the second metal plate 132 and the second electrical harness connection 112 may be understood to form a heating circuitry. The PTC stones may be made of ceramic of different grades. A temperature range in which the electrical resistance of the PTC stones 121 to 128 increases exponentially may be from 70°C to 400°C, preferably from 80°C to 270°C.

[0082] According to several examples of the present disclosure, the above indicated heating assembly may comprise one or more of such PTC bundles 100. If there are at least two PTC bundles, the at least two PTC bundles are connected in parallel or serial to each other (depending on how there are supplied with electrical power from the power source).

[0083] Referring now to Figure 2, Figures 2 shows an insulating volumetric body 200 according to several examples of the present disclosure. The insulating volumetric body 200 comprises a substantial cylindrical shape having an outer surface 210. The insulating volumetric body 200, in more detail its outer surface 210, comprises one or more grooves 221 to 226. The one or more grooves 221 to 226 are each configured so that the PTC bundle 100 may be assembled or inserted or arranged in such groove. It shall be noted that the insulating volumetric body 200 may in general be of any shape, for example of a cuboid shape. Moreover, a number of grooves is not limited to six and there may be less than six, for example one or more grooves, or more than six, for example seven or more grooves. The insulating biometric body 200 is made of an insulating material and, preferably, also of a thermal conductive material, for example of a ceramic.

[0084] Referring now to Figure 3, Figure 3 shows an equipped or loaded insulating volumetric body 300. In more detail, the insulating volumetric body 200 according to Figure 2, wherein PTC bundles are arranged inside the grooves 221 to 226. In particular, a PTC bundle 100-1 is arranged in groove 221, a PTC bundle 100-2 is arranged in groove 222, a PTC bundle 100-3 is arranged in groove 223, a PTC bundle 100-4 is arranged in groove 224, a PTC bundle 100-5 is arranged in groove 225, and a PTC bundle 100-6 is arranged in groove 226. Figure 3 shows the equipped insulating volumetric body 300 from the perspective of the end of the substantial cylindrical shape of the insulating volumetric body 200 or 300 at which the insulating volumetric body 200 or 300 is intended to be inserted into a casing. Figure 4 shows the opposite end of the end shown in Figure 3. In more detail, referring now to Figure 4, Figure 4 shows the equipped insulating volumetric body 300 from the perspective of the end of the substantial cylindrical shape of the insulating volumetric body 200 or 300 at which the arranged bundles 100-1 to 100-6 are intended to be connected to an electrical power source. Accordingly, the bundle 100-1 comprises a first electrical harness connection 111-1 and a second electrical harness connection 112-1, the bundle 100-2 comprises a first electrical harness connection 111-2 and a second electrical harness connection 112-2, the bundle 100-3 comprises a first electrical harness connection 111-3 and a second electrical harness connection 112-3, the bundle 100-4 comprises a first electrical harness connection 111-4 and a second electrical harness connection 112-4, the bundle 100-5 comprises a first electrical harness connection 111-5 and a second electrical harness connection 112-5, and the bundle 100-6 comprises a first electrical harness connection 111-6 and a second electrical harness connection 112-6.

[0085] Referring now to Figure 5, Figures 5 shows a heating assembly 500 according to several examples of the present disclosure. The heating assembly 500 comprises the equipped insulating volumetric body 300 and a casing 510, into which the equipped insulating volumetric body 300 is inserted. The casing 510 is impermeable to water. Hence, the part of the equipped insulating volumetric body 300, or said in other words the part of the heating circuitry that is surrounded by the casing 510 is isolated from water. Referring now to Figure 6, Figures 6 shows a cross-sectional view of the heating assembly 500. As an example, to PTC bundles are illustrated in Figure 6, that is a first PTC bundle 100 -1 and a fourth PTC bundle 100-4. Wherein the first PTC bundle 100-1 comprises eight PTC stones 121-1 to 128-1, and wherein the fourth PTC bundle 100-4 comprises eight PTC stones 121-4 to 128-4. It shall be noted that each of the first PTC bundle 100-1 and the fourth PTC bundle 100-4 may be such PTC bundle 100 as shown in Figure 1. Referring now to Figure 7a, Figures 7a shows an enlarged view of the end of the heating assembly 500 in a cross-sectional view. This is according to a specific example developed by the inventors and the values indicated in Figure 7a thus correspond to the specific example. However, it shall be noted that the present disclosure is not limited to these certain values. In more detail, it is indicated in Figure 7a that a distance between PTC stones in different PTC bundles that are arranged opposite to each other, for example, as indicated in Figure 8a, an eighth position PTC stone (for example PTC stone 128-1) in the first PTC bundle 100-1 and an eighth position PTC stone (for example PTC stone 128-4) in the fourth PTC bundle 100-4, or an eighth position PTC stone (for example PTC stone 128-2) in the second PTC bundle 100-2 and an eighth position PTC stone (for example PTC stone 128-5) in the fifth PTC bundle 100-5, or an eighth position PTC stone (for example PTC stone 128-3) in the third PTC bundle 100-3 and an eighth position PTC stone (for example PTC stone 128-6) in the sixth PTC bundle 100-6, is 22.1 mm. In more detail, between such opposite PTC stones, a distance between the respective surfaces of the PTC stones that face towards the middle axis of the insulating volumetric body 200 is 22.1 mm. It shall be noted that according to several examples of the present disclosure such distance is not limited to 22.1 mm. For example, such distance of 22.1 mm may be understood as a lower limit distance. Moreover, Figure 7a indicates that a distance between a last PTC stone (for example the eighth PTC stone 128) in a PTC bundle and the outer surface of the casing 510 that is intended to be in contact with water to be heated, is 8.5 mm. It shall be noted that according to several examples of the present disclosure such distance is not limited to 8.5 mm. For example, such distance of 8.5 mm may be understood as a lower limit distance. Furthermore, it is indicated in Figure 7 that a distance between a PTC stone and the casing 510 is 4.2 mm. In more detail, it is indicated that a distance between a surface of a PTC stone that faces towards an outside of the insulating volumetric body 200, i.e. in a direction opposite to the direction towards the middle axis, and an inner surface of the casing 510 is 4.2 mm. It shall be noted that according to several examples of the present disclosure such distance is not limited to 4.2 mm. For example, such distance of 4.2 mm may be understood as a lower limit distance.

[0086] Comparative examples are shown in Figures 7b and 8b. In particular, current solutions with resistive wire elements (800-1 to 800-12) in a soapstone body 800 inserted into a casing 810 are shown. Accordingly, a minimum achievable distance between a resistive wire element 800-1 and the casing 510 is 5.5 mm (in comparison to 4.2 mm as illustrated in Figure 7a as an example).

[0087] Referring now to Figure 9, Figures 9 shows a heating assembly 900 comprising heating elements (also referred to as heating modules) 911 and 912 according to several examples of the present disclosure. However, the heating assembly 900 is not limited to have two such heating elements and may have one such heating element or three or more such heating elements. Further, such heating elements of the heating assembly 900 may not necessarily be identical, i.e. the different heating elements may have a different number of PTC bundles for example. Figure 10 shows a cross-sectional view of one such heating element 911. The heating element 911 as shown in Figure 10 comprises, from the inside to the outside, three PTC bundles 100-1, 100-2 and 100-3, wherein the three PTC bundles are overmolded in a thermally conductive and electrically insulating material 1020. It shall be noted that a number of PTC bundles may be different from three. Preferably, the thermally conductive and electrically insulating material 1020 is magnesia. Moreover, the thermally conductive and electrically insulating material 1020 is covered by a sheath 1011. Preferably, the sheath 1011 is in direct contact with the thermally conductive and electrically insulating material 1020, and there's no air between the sheath 1011 and the thermally conductive and electrically insulating material 1020.

[0088] As a mere example without being limited to these values, the heating element 911 may have a height of 15 mm and a width of 40 mm, wherein the minimum distances from the PTC stones to the inner surfaces of the thermally conductive and electrically insulating material 1020 is 3 mm in the width direction and 4 mm in the height direction. Figures 11 shows a cross-sectional view of the heating assembly 900 and illustrates the sheaths 1011 and 1012 of the respective heating elements 911 and 912.

[0089] Referring now to Figure 12, Figures 12 shows a heating assembly 1200 similar to the heating assembly 900 according to Figure 9, wherein the heating assembly 1200 according to Figure 12 comprises six heating elements (also referred to as heating modules) 1211 to 1216. Each heating element of the heating elements 1211 to 1216 comprises one PTC bundle overmolded in a thermally conductive and electrically insulating material, for example magnesia, and further comprises a respective sheath as indicated in Figure 13. In more detail, Figure 13 shows a cross-sectional view of the heating assembly 1200 and, in doing so, illustrates the respective sheaths 1311 to 1316 for the heating element 1211 to 1216.

[0090] According to several examples of the present disclosure, the casing 510 according to Figure 5 and the respective sheaths 1011, 1012 and 1311 to 1316 according to Figures 9 and 12 comprise at least one of copper, stainless steel, carbon steel and enamelled steel.

[0091] Moreover, according to several examples of the present disclosure, each of the heating assemblies 500, 900 and 1200 according to Figures 5, 9 and 12 may further comprise a control unit. The control unit may be configured to control a temperature of the electrical resistor of the PTC type, i.e. of the one or more PTC stones of the one or more PTC bundles, by applying a pulse width modulation (PWM) signal 1400 at the electrical resistor and / or by controlling an increase and a decrease of an electrical current applied at the electrical resistor. Figures 14 shows an example for a PWM signal over time. The PWM signal and / or the changing electrical current may be provided by the power source that is connected to the PTC bundles via the respective first and second electrical harness connections. With the electrical resistor of the PTC type, it is possible to consider PWM control operation to adjust a power delivered (to the PTC stones) according to need. Thus, in addition to the electrical resistor of the PTC type, a power modulation system can be used to control one or more PMW signals applied to one or more PTC stones to achieve a heating assembly having a precise heating power and control power consumption. For this purpose, a power electronics board may be added to the heating assembly, for example at the end of the heating assembly where a bundle's respective first and second electrical harness connections are provided. Such power electronics board could be based on a system of power transistors activated by a PWM signal. Each slot may activate the transistors that may act as switches. By varying a duration of the PWM signal's square-wave signal, as illustrated in Figure 14, a heating power of the PTC stones can be modulated. This power electronics board could also provide feedback, like power consumption, instantaneous power, error message, etc., via LIN or CAN communication. Moreover, with reference to Figure 15, it shall be noted that PTC resistors may not be controlled in On / Off mode only, i.e. when full power (totally available power) is supplied in On-mode and when on o power is supplied in Off-mode. Rather, with a PTC resistor, it is possible to consider PWM control operation to adjust a power delivered according to need. In more detail, Figures 15 shows an example for the usage of a share P1 of a total amount of electrical power P3, the share P1 to be supplied to one of the heating assemblies 500, 900 and 1200 according to several examples of the present disclosure. Specifically, in a diagram Power (for example kW) over Time (for example hours), an amount of electrical power supplied to the heating assembly may be indicated by a graph G. The graph G has an inclination α greater than 0° and below 90°. With reference to above, an inclination of 90° may represent such On-mode where all available power, i.e. full power, is supplied to the heating assembly. In the diagram according to Figure 15, full power may be indicated by P3, so at On-mode, the graph G would have an inclination of α = 90° to rise at the time t from 0 to P3, and to then remain at the P3, i.e. at the power level 1520. In contrast thereto, the heating assembly according to several examples of the present disclosure allows for an inclination of α < 90°, for example of α = 50°, and further allows that an amount of electrical power P1 that is supplied to the heating assembly is below full power P3, i.e. the supplied electrical power may remain at a lower power level 1510 below the full power level 1520. The supplied electrical power may further be adjusted to another share P2 of the full power P3 and may remain on the corresponding power level 1530. The difference between the electrical power P1 and P2 may be S1, and the difference between the electrical power P2 and P3 may be S2. Hence, in case a power P1 is supplied to the heating assembly according to several examples of the present disclosure, still a power amount of S1 + S2 may be available for other devices / purposes.

[0092] Referring now to Figure 18, Figure 18 comprises a first part Figure 18a, a second part Figure 18b and a third part Figure 18c. In more detail, Figure 18a shows a domestic water tank 1800a that comprises, as generator, such heating assembly 500 according to Figure 5 for example (no additional coil inside the water tank 1800a). Figure 18b shows a domestic water tank 1800b that additionally comprises a coil inside the water tank 1800b as primary generator, wherein such heating assembly 500 according to Figure 5 for example is used as an electrical backup heater, i.e. a secondary generator. Figure 18c shows an example for a buffer tank 1800c that comprises such heating assembly 500 according to Figure 5 for example. In Figure 18, each of the water tanks 1800a, 1800b and 1800c are illustrated to comprise such heating assembly 500 according to Figure 5. However, each water tank 1800a, 1800b and 1800c may comprise such heating assembly 900 and / or 1200 instead and / or additionally. Based thereon, in the following, Figures 19 to 21 are described, wherein Figures 19 to 21 illustrate heating systems that use (see Figure 19) a domestic hot water tank for example according to Figure 18a or 18b, or that use (see Figure 20) a buffer tank for example according to Figure 18c, or that use (see Figure 21) both tanks, i.e. a domestic hot water tank according to Figure 18a or 18b and a buffer tank according to Figure 18c.

[0093] Referring now to Figure 19, Figure 19 shows, in a simplified manner for explanation purposes only, a diagram of a heating system 1900 for the application of a domestic hot water tank 1920 that includes a heating assembly 1922 according to several examples of the present disclosure. The domestic hot water in the domestic hot water tank 1920 is for alimentary purpose. In more detail, the heating system 1900 comprises a generator 1910, a domestic hot water tank 1920 and a pump 1930. The generator 1910 generates hot central heating water 1911 that flows from the generator 1910 to the domestic hot water tank 1920. The hot central heating water 1911 is for heat exchange only, and is not for alimentary purpose. In the domestic hot water tank 1920 there is provided a coil 1921 with central heating water inside. In more detail, the hot central heating water 1911 provided by the generator 1910 flows through the coil 1921 in the domestic hot water tank 1920. In doing so, the temperature of the hot central heating water 1911 decreases. The decrease in temperature is indicated by the greyscale, that is, hot water is indicated with grey and cold water is indicated with white, and the lighter the grey becomes the colder the water gets. Hence, Figure 19 illustrates that the hot central heating water 1911 inserts the coil 1921 in the domestic hot water tank 1920, cools down per heat exchange when flowing through the coil 1921, and exits the domestic hot water tank 1920 and the coil 1921 as cold central heating water 1912 that flows from the domestic hot water tank 1920 back to the generator 1910 by use of the pump 1930. The cold central heating water 1912 is for heat exchange only, and is not for alimentary purpose. The domestic hot water tank 1920 further comprises the heating assembly 1922. The heating assembly 1922 may be a heating assembly according to several examples of the present disclosure, for example one of the heating assemblies 500, 900 and 1200. Moreover, domestic cold water 1923 flows from the network into the domestic hot water tank 1920, gets heated by the heating assembly 1922 and the hot central heating water 1911 in the coil 1921, and may be stored in the domestic hot water tank 1920. Domestic hot water 1924 may then flow out of the domestic hot water tank 1920 for alimentary purposes. It should be noted that the central heating water does not mix with the domestic water.

[0094] Referring now to Figure 20, Figure 20 shows, in a simplified manner for explanation purposes only, a diagram of a heating system 2000 for the application of a buffer tank 2020 that includes a heating assembly 2023 according to several examples of the present disclosure. The central heating water according to Figure 20 is for heat exchange only, and is not for alimentary purpose. In more detail, the heating system 2000 comprises a generator 2010, a buffer tank 2020, several pumps 1931 and 1932, and several receptors 2041, 2042 and 2043 of the hot water. The generator 2010 generates hot central heating water 2011 that flows from the generator 2010 to the buffer tank 2020. In the buffer tank 2020 the received hot central heating water 2011 mixes with water stored or available in the buffer tank 2020. From the buffer tank 2020, hot central heating water 2021 flows to different receptors 2041, 2042 and 2043, which may be radiators and / or floor heating for example, which are for heat exchange only and not for alimentary purpose. Due to the heat exchange in the receptors, the hot central heating water 2021 cools down per heat exchange and returns to the buffer tank 2020 as cold central heating water 2022 via a first pump 2031. In the buffer tank 2020 there is provided a heating assembly 2023. The heating assembly 2023 may be a heating assembly according to several examples of the present disclosure, for example one of the heating assemblies 500, 900 and 1200. The cold central heating water 2022 gets heated in the buffer tank 2020 by the heating assembly 2023 and by mixing with the hot central heating water 2011. Moreover, cold central heating water 2012 flows from the buffer tank 2022 to the generator 2010 via a second pump 2032. Similar to Figure 19, a decrease in temperature is indicated by the greyscale, that is, hot water is indicated with grey and cold water is indicated with white, and the lighter the grey becomes the colder the water gets.

[0095] Referring now to Figure 21, Figure 21 shows, in a simplified manner for explanation purposes only, a diagram of a heating system 2100 that may be understood as a combination of the heating systems 1900 and 2000 according to Figures 19 and 20. In particular, the heating system 2100 comprises a generator 2110, a buffer tank 2120, several pumps 2131 and 2132, several receptors 2141 and 2142, a domestic hot water tank 2150, and a three-way-valve 2160. The domestic hot water in the domestic hot water tank 2150 is for alimentary purpose. Hot central heating water 2111 flows from the generator 2110 into the buffer tank 2120 (first part hot central heating water 2111a) and the domestic hot water tank 2150 (second part hot central heating water 2111b) via the three-way-valve 2160 (where the water flow is separated). From the buffer tank 2120, hot central heating water 2121 flows to the different 2141 and 2142, like radiators and / or floor heating for example, for heat exchange purposes, and flows as cold central heating water 2122 back to the buffer tank 2120 via a first pump 2131. In the buffer tank 2120, the received cold central heating water 2122 gets heated by the heating assembly 2123 included in the buffer tank 2120 and by mixing with the hot central heating water 2111 received the generator 2110. The heating assembly 2123 may be a heating assembly according to several examples of the present disclosure, for example one of the heating assemblies 500, 900 and 1200. From the buffer tank 2120, cold central heating water 2112a may be directed via the three-way-valve 2160 to flow back to the generator 2110, indicated as cold central heating water 2112, via a second pump 2132. Due to the three-way-valve 2160, the hot central heating water 2111 is directed to either flow to the domestic hot water tank 2150 or to the buffer tank 2120. In the domestic hot water tank 2150, the hot central heating water 2111b received from the generator 2110 flows through a coil 2151 provided in the domestic hot water tank 2150, exchanges heat with domestic water stored in the domestic hot water tank 2150 and thus cools down per heat exchange, and leaves the domestic hot water tank 2150 and the coil 2151 to flow back to the generator 2110 as cold central heating water 2112b. It should be noted that the water received from generator 2110 does not mix with the domestic water stored or available in the domestic hot water tank 2150. Moreover, domestic cold water 2153 for alimentary purpose flows from the network into the domestic hot water tank 2150, gets heated by a heating assembly 2152 included in the domestic water tank 2150 and by the hot central heating water 2111b in the coil 2151, and may be stored in the domestic hot water tank 2150. Domestic hot water 2154 may then flow out of the domestic hot water tank 2150 for alimentary purposes. The heating assembly 2152 may be a heating assembly according to several examples of the present disclosure, for example one of the heating assemblies 500, 900 and 1200. Similar to Figure 19, a decrease in temperature is indicated by the greyscale, that is, hot water is indicated with grey and cold water is indicated with white, and the lighter the grey becomes the colder the water gets. It shall be noted that the central heating water that flows into and out of the buffer tank 2120 and that flows through the coil 2151 is for heat exchange only, and is not for alimentary purpose.Reference Signs

[0096] 100PTC bundle 111first electrical harness connection 112second electrical harness connection 121 to 128PTC stones 131first metal plate 132second metal plate 200insulating volumetric body 210insulating volumetric body surface 221 to 226grooves 300equipped insulating volumetric body 500heating assembly 510casing 900heating assembly 911, 912heating elements 1020thermally conductive and electrically insulating material 1011,1012sheaths 1200heating assembly 1211 to 1216heating elements 1311 to 1316sheaths 1400pulse width modulation signal P1, P2, P3power values 1510 to 1530power levels T ref reference temperature 1800a, 1800bwater tanks 1900heating system 1910generator 1920domestic hot water tank 1921coil 1922heating assembly 1930pump 2000heating system 2010generator 2020buffer tank 2023heating assembly 2031,2032pumps 2041 to 2043receptors 2100heating system 2120buffer tank 2123heating assembly 2131,2132pumps 2141,2142receptors 2050domestic hot water tank 2051coil 2052heating assembly 2160three-way-valve

Examples

Embodiment Construction

[0079]According to several examples of the present disclosure, one aspect is to use the physical characteristics of positive temperature coefficient (PTC) resistors to ensure that a predetermined maximum heating temperature generated or reached by an electrical heating assembly (or heating assembly as used herein further below) that comprises such PTC resistors is not to be exceeded. Such PTC resistors may be PTC stones, PTC ceramics or, more generally said, electrical resistors of the PTC type.

[0080]In view thereof, according to several examples of the present disclosure, there is provided an electrical heating assembly for a water tank of at least 20 liters volume for hot water storage. The electrical heating assembly is at least partly insertable into the water tank and comprises a heating circuitry and a casing. The heating circuitry is configured to connect the electrical heating assembly to a power source, wherein the heating circuitry comprises an electrical resistor of a PTC...

Claims

1. An electrical heating assembly (500; 900; 1200) for a water tank (1800a; 1800b) of at least 20 liters volume for hot water storage, wherein the electrical heating assembly (500; 900; 1200) is at least partly insertable into the water tank (1800a; 1800b) and comprises: a heating circuitry (111, 112, 121 to 128, 131, 132) configured to connect the electrical heating assembly (500; 900; 1200) to a power source, wherein the heating circuitry (111, 112, 121 to 128, 131, 132) comprises an electrical resistor (121 to 128) of a positive temperature coefficient, PTC, type; and a casing (510; 1011, 1012; 1311 to 1316) surrounding at least part of the heating circuitry (111, 112, 121 to 128, 131, 132) including the electrical resistor (121 to 128) and the casing (510; 1011, 1012; 1311 to 1316) configured to electrically isolate the heating circuitry (111, 112, 121 to 128, 131, 132) from water when the at least part of the heating circuitry (111, 112, 121 to 128, 131, 132) is inserted into the water tank (1800a; 1800b) and when the water tank (1800) is at least partially filled with water, wherein the electrical resistor (121 to 128) is configured to, once a threshold temperature (Tref) at the electrical resistor (121 to 128) is reached, exponentially increase its electrical resistance with temperature.

2. The electrical heating assembly according to claim 1, wherein a temperature range in which the electrical resistance of the electrical resistor (121 to 128) increases exponentially comprises a range from 70°C to 400°C, preferably from 80°C to 270°C.

3. The electrical heating assembly according to claim 1 or 2, further comprising a control unit configured to control a temperature of the electrical resistor by applying a pulse width modulation signal (1400) at the electrical resistor and / or by controlling an increase and a decrease of an electrical current applied at the electrical resistor.

4. The electrical heating assembly according to claim 3, wherein the control unit is further configured to generate the pulse width modulation signal (1400) that corresponds to a first amount of electrical power (P1; 1510) and / or to control the electrical current to have a first amplitude that corresponds to the first amount of electrical power (P1; 1510), wherein the first amount of electrical power (P1; 1510) is an adjustable share of a total amount of electrical power (P3; 1520) provided by the power source.

5. The electrical heating assembly according to any of claims 1 to 4, wherein the electrical resistor comprises one or more PTC ceramic elements (121 to 128; 121-1 to 128-1; 121-4 to 128-4), wherein, if comprising at least two PTC ceramic elements, the at least two PTC ceramic elements are connected in parallel to each other.

6. The electrical heating assembly according to any of claims 1 to 5, wherein the heating circuitry comprises one or more PTC bundles (100; 100-1 to 100-6), each PTC bundle of the one or more PTC bundles comprises two or more PTC ceramic elements connected in parallel to each other, wherein, if comprising at least two PTC bundles, the at least two PTC bundles are connected in parallel or serial to each other.

7. The electrical heating assembly according to claim 6, further comprising an insulating volumetric body (200) inserted into the casing (510), the insulating volumetric body (200) comprising an outer surface (210) that comprises one or more grooves (221 to 226), and wherein the one or more PTC bundles (100; 100-1 to 100-6) are assembled on the insulating volumetric body (200) in that each PTC bundle is arranged in a respective groove of the one or more grooves (221 to 226).

8. The electrical heating assembly according to claim 7, wherein a minimal distance between an assembled PTC bundle and an inner surface of the casing is between 5.5 mm and 4.2 mm.

9. The electrical heating assembly according to claim 6, further comprising one or more heating elements (911, 912; 1211 to 1216), wherein each heating element of the one or more heating elements includes one or more of the PTC bundles (100-1, 100-2, 100-3) overmolded with thermally conductive and electrically insulating material (1020), preferably overmolded in magnesia, and wherein the casing (1011, 1012; 1311 to 1316) comprises respective sheaths for each heating element of the one or more heating elements.

10. The electrical heating assembly according to claim 9, wherein the casing comprises or the respective sheaths comprise at least one of copper, stainless steel, carbon steel and enamelled steel.

11. The electrical heating assembly according to any of claims 1 to 10, wherein the electrical heating assembly has a power rating in a range of 1,000 W to 10,000 W.

12. A water tank (1800a; 1800b; 1800c; 1920; 2020; 2120; 2150) of at least 20 liters volume for hot water storage, wherein the water tank (1800a; 1800b; 1800c; 1920; 2020; 2120; 2150) comprises an electrical heating assembly (500; 900; 1200; 1922; 2023; 2123; 2152) according to any of claims 1 to 11.

13. A domestic hot water heating system (1900; 2100) comprising a water tank (1920; 2150) for storing domestic hot water, the water tank according to claim 12.

14. A central heating water heating system (2000; 2100) comprising a water tank (2020; 2120) for storing central heating water, the water tank according to claim 12.

15. Use of an electrical heating assembly (500; 900; 1200; 1922; 2023; 2123; 2152) according to any of claims 1 to 11 for heating water in a water tank (1800a; 1800b; 1920; 2020; 2120; 2150) of at least 20 liters volume for hot water storage.

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