Technical field
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The invention concerns a heater and a heat pump system comprising such heater.
Background
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Heating of water in buildings, such as heating water of a central heating system or heating of water for domestic use, may be accomplished by means of a heat pump system. Often, an electrical back-up heater for additional heating of the water is needed. For instance, when the outside air temperature is too low, a heat pump system without an electrical back-up heater may not (be able to) extract enough heat from the air to heat the water to a target temperature. Thus, an electrical back-up heater is required to assist the heat exchanger circuit within a heat pump system to achieve the target temperature.
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Back-up tanks/heaters are conventionally made of steel which are durable and non-flammable. However, a steel tank is expensive, adds additional weight and is not desirable in terms of their carbon footprint and sustainability profile. Commonly known back-up-tanks made of thermoplastic materials for cost effectiveness compared to steel and for a reduced carbon footprint and improved sustainability profile compared to steel have the additional advantage of more flexibility in design compared to steel. However, such known back-up tanks have inherent risks due to the thermoplastic material commonly used. For example, in the event of leakage and system malfunction, known back-up tanks made of thermoplastic material have the risk of melting, electrical hazards, and possible fires. Existing safety systems, such as pressure sensors and thermal sensors are not sufficiently reliable in mitigating said risk. In case of a fire generated by the back-up heater, the severity of the fire may be increased further by the proximity of flammable refrigerant.
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Thus, there is a need for a (back-up) heater which has a reduced risk of melting, electrical hazards and fires, optionally if made of thermoplastic material, while allowing for flexibility in design.
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Hence, improvements as to the reliability and safety of a (back-up) heater are desired. These improvements may not be limited to a back-up heater, but may also apply to a heater in general.
Summary of the invention
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The present invention relates to a heater for connection to a liquid circuit and configured to heat liquid (of the liquid circuit), in particular as a back-up heater in addition to a heat pump unit, the heater comprising a tank for receiving liquid and having a tank wall extending (basically) in a longitudinal direction from a tank end and defining a liquid tank volume, the longitudinal direction (basically) running opposite or parallel to gravity, when the heater is installed on site, a first port and a second port for passage of liquid of the liquid circuit into and out of the tank, respectively, or out of and into the tank, respectively, at least one heating means having at least one heating element inside the tank for heating liquid inside the tank, the heating means extending at least partially in the longitudinal direction), and at least two hollow elements provided inside the tank and extending in the longitudinal direction, the at least two hollow elements each defining a (respective, e.g. different) liquid sub-volume (and for substantially separating the liquid sub-volume from the remaining liquid tank volume along the longitudinal direction), wherein the at least two hollow elements are in fluid communication with the remaining liquid tank volume at an opening of the respective hollow element, wherein the heater is configured, when installed on site, that one of the at least two hollow elements guides liquid along at least a part of the respective hollow element for flow of liquid along the heating elements of the heating means in the longitudinal direction, and the other one of the at least two hollow elements retains liquid in the tank in case of shortage of liquid in the tank, such that at least a part of the heating means remains immersed in liquid in the tank.
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A hollow element modifies/impacts the accommodation and/or flow of liquid in the tank. Specifically, a hollow element defines a liquid sub-volume and changes the direction/passage of the liquid e.g. by substantially surrounding the sub-volume and/or substantially guiding a flow of the liquid sub-volume, relative to the first and second ports, i.e. inlet port or the outlet port. This may be seen as increasing the minimal distance travelled by the liquid from the inlet to the outlet port. Accordingly, the passage of the liquid compared to when there is not such hollow element is changed.
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A hollow element may direct a sub-volume away from the input port so as to improve the liquid flow as to the heating by the at least one heating means and, hence, the heater may more efficiently and/or more homogeneously heat liquid inside the tank. In other words, a guiding tube may make the journey/path of the liquid along the heating means longer compared to when there is no such tube, which supports more stable and homogeneous heating of the liquid. Hence, by guiding liquid by way of a hollow element towards or along the heating means, the positions of the first and second ports can more freely be chosen and need, for example, no longer be on opposite ends of the tank in the longitudinal direction, as a hollow element may change the flow direction and flow path of the liquid, compared to a direct and less favourable passage of fluid with less heat absorption. For example, by way of a hollow element, more uniform liquid flow distribution may be achieved, resulting in less pressure drop in heater. More specifically, the guidance may help to direct liquid around the heating surface of the heating elements of the heating means along a "long path" so it ensures a better homogeneity of the heat exchange. In particular, it may reduce dead areas, i.e. areas which are not effective for heating (for example tourbillon in corners which are not heated).
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The tank may store a liquid sub-volume before the liquid would excessively drain through the outlet port, which would possibly expose the heating means. In this case, liquid would be missing in the tank. In particular, the amount of liquid may fall below the normal level of liquid, e.g. below the level of liquid defined by the sub-volume. This may be regarded as the tank being short of liquid. Reasons for liquid missing in the tank may be leakage of liquid outside the tank and, thus, loss of liquid through a port, hence, emptying the tank; or a non-working pump for pumping liquid in the liquid circuit, leading to no circulation and lowering of the level of liquid in the tank. If the liquid circuit is interrupted, i.e. if insufficient liquid is supplied via the inlet port, e.g. due to a liquid leak in the hydraulic system, an on-going draining of the hydraulic system or an interruption of the liquid circulation in the hydraulic system, this may lower the liquid received in the tank. These issues may all lead to the level of liquid falling below the normal level, in particular the tank volume not being sufficiently filled with liquid, and may be summarized as an (abnormal) shortage of liquid in the tank.
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For example, when a hollow element guides liquid away from the inlet port, the hollow element may be in fluid communication with the inlet port, so as to direct the inlet flow of fluid. The position of the opening of a hollow element may, in this case, represent a shifted inlet port. When a hollow element retains liquid from draining of the outlet port, at least a sub-volume of liquid is retained in the tank. The position of the opening of the hollow element may, in this case, determine the maximum level and, hence, the sub-volume, of the liquid retained in the tank. A hollow element may, in this case, be in fluid communication with the outlet port but the hollow element may, alternatively, be located within the tank without direct fluid communication to the outlet tank. Of course, a hollow element may, at the same time, fulfill both functions, namely guiding liquid away from the inlet port and preventing liquid from flowing through the outlet port.
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This may help to ensure that at least a part of the heating means, i.e. the heating elements having the heating surfaces, remains immersed in liquid and, thus, avoid that the heater is overly heating, as heat is not absorbed by the liquid, which may lead to damage such as melting e.g. of the tank, in particular if the tank is made of plastics. Hence, in case of shortage of liquid in the tank, e.g. leakage of liquid in the hydraulic system, it may be prevented that the heating element is not immersed. Rather, due to remaining immersion in liquid, at least a part of the heat may be transferred away from the heating means and, thus, be blocked e.g. from the tank walls. Often, as the liquid volume may be rather low (e.g. a few liters) with respect to the power of the heating element (e.g. a few kW such as 3, 6 or 9 kW), the liquid may not be able to absorb all the energy and may evaporate relatively quickly.
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Nevertheless, it will need some time to evaporate (e.g. tens of seconds) so it offers time for the safety counter-measure in the heater to react and prevent from further failure or risk: switch off the power, for example. Without retained liquid, no such "delay" would occur and the heater would heat the surrounding air very quickly and, within a few seconds, temperature would rise for hundreds of degrees and could burn the plastic, with a further risk then that the structure of the heater may fall down and/or that the heating surface of the heating elements of the heating means may be in contact with a flammable surface, such as a building, or even with people.
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According to the invention, the first hollow element may guide liquid away from the inlet port, and the second hollow element may prevent liquid from draining of the outlet port, so that both configurations pertaining to a hollow element are combined in the heater. In particular, the first and second hollow elements may cooperate to the effect that a potential disadvantage of a hollow element forming a hydraulic trap may be compensated by way of the second hollow element. More specifically, positioning the outlet port and/or a hollow element to avoid complete drainage of liquid through the outlet port in case of leakage in the liquid circuit may be disadvantageous as to the flow of liquid along the heating means. By way of another hollow element, the flow of fluid along the tank, and in particular along the heating means, may be strengthened and, thus, be improved. Also, the heater may be installed upside-down, i.e. its orientation may be swapped, meaning that it may be installed in the opposite direction: With two hollow elements, the first hollow element may have the retention/trap-function, while the second hollow element provides the guiding function. In opposite installation, the second hollow element may have the retention/trap-function, and the first hollow element may function as a guide. Hence, versatility of the heater is improved.
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Accordingly, the safety and reliability of the heater as to the heating may be improved and the heater may in particular be safer in case of shortage of fluid in the tank and, thus, more reliable than a prior art heater, while offering versatility.
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Hence, the invention is characterized by at least two hollow elements, i.e. at least first and second hollow elements. Whenever reference is made "a" hollow element in the following, this may relate to only the first or second hollow element and, alternatively, to both the first and second hollow elements.
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Heating means may refer to one heating element or may include several heating elements, which are preferably similar to each other. The function of a heating means (heating elements) is to heat the liquid in the tank.
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A hollow element extends (basically) in the longitudinal direction, which means that the hollow element may exclusively extend in the longitudinal direction or that the hollow element may extend i.a. in a direction which has at least a component in the longitudinal direction.
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The longitudinal direction may basically run in a direction opposite or parallel to the direction of gravity. The orientation may not be of relevance. However, in the drawings, the longitudinal direction is indicated as running opposite to gravity. Preferably, the longitudinal direction may (substantially) run opposite to the direction of gravity. The orientation of the longitudinal direction is opposite to gravity, while the longitudinal dimensioning is parallel to gravity. The longitudinal direction may (substantially) be the vertical direction. As such, the heater may preferably be installed vertical on site, but a small angle to the vertical is also possible.
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The opening of each hollow element may be open in basically a transverse plane perpendicular to the longitudinal direction, meaning that the opening faces the longitudinal direction or its opposite direction. The opening of the hollow element may be seen as a termination (of the impact) of the hollow element with respect to the sub-volume. The opening of the hollow element may represent an open end of the hollow element. The opening fluidly connects the liquid sub-volume as defined by the hollow element with the remaining liquid volume in the tank.
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For separation of the liquid sub-volume from the remaining liquid tank volume upstream the opening, the respective hollow element is preferably configured so as to substantially exclude fluid communication with the remaining liquid in the tank except for at the opening. In particular, substantial separation of fluid may mean that the fluid in the hollow element does substantially not mix with the remaining fluid in the tank outside the hollow element. For example, if a hollow element is connected to the first port, fluid communication with the remaining liquid in the tank upstream the opening may substantially be excluded. It is preferable that the end of a hollow element opposite the opening is substantially sealed relative to the remaining liquid sub-volume. However, it is not excluded that there is a hole or channel or bypass for pressure equalization in the hollow element at the end opposite the opening of the hollow element. Accordingly, the separation of the sub-volume from the remaining volume of the tank is not necessarily a complete separation, but a substantial separation to the effect that the substantial flow of liquid is substantially guided/received by the hollow element. The separation of the sub-volume from the remaining liquid volume allows for guidance of the sub-volume and/or for retention of the liquid from draining off the lower port of the tank. Hence, the separation allows to avoid undesired emptying of the tank and, thus, exposure of the heating means, and/or for guidance of substantial liquid along the desired path, i.e. along the heating elements for absorption of heat by the liquid.
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A hollow element defines a cavity for receipt/guidance of liquid, here in particular of basically a sub-volume of the liquid in the tank. Each of the hollow elements may be a tube. Liquid may be stored in the cavity or may flow through the cavity. The hollow element does not need to define a cavity which is closed except for the opening. Rather, the hollow element may be configured to guide fluid along a longitudinal extension of the cavity.
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The hydraulic/liquid circuit refers to the circuitry of a heating system with liquid (water) to be heated. The liquid may not need to be pure water, but may include additives, such as glycol.
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When the heating system is a heat pump, this liquid is heated by the refrigerant and will be used via a closed-loop system to heat domestic hot water or for heating applications (floor heaters,...). When the heating system is an electric heater, in particular instantaneous electric water heater, this liquid is heated by the electric heater and is consumed via an opened-loop system for domestic applications (showers,...). Specifically, in constellations in which the tank would empty basically completing through drainage of liquid through the lower port upon leakage of liquid in the liquid circuit, a hollow element may be configured and located within the tank so that the tank does not empty completely via the lower port. Here, in case of leakage in the circuit and/or pump in the circuit off or damaged, the liquid will use the port which is the lowest (which can be the inlet or outlet port). In other words, the first and second ports may be used as inlet or outlet port, while, with respect to drainage and emptying of the tank, the lower port of the first and second ports, when installed on site, would function as drainage port (and, thus, as outlet port, irrespective of whether the lower port had been used as outlet or inlet port during the normal use). The first and second ports may serve for passage of liquid of the liquid circuit into and out of the tank, respectively. Alternatively, they may serve for passage of liquid of the liquid circuit into out of and into the tank, respectively. In some embodiments, the first and second ports may have both functions, but it is conceivable that in some embodiments each port may only have a single function, namely as outlet or inlet.
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An embodiment of the invention may optionally be described as follows: At least the first hollow element retains liquid in the tank at a position higher than the lowest point of the heating surface of the heating elements, when the heater is installed on site, and prevents liquid from draining off the lowest port of the first and second ports of the tank. A second hollow element may guide fluid along at least a part of the heating element(s), to avoid direct flow of the fluid to the outlet port, possibly avoiding at least a part of the heating means.
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The present invention is directed to a heater for heating liquid, in particular water. A preferred configuration of the invention is a back-up heater for heating water. A back-up heater is a heater used as a back-up solution to heat liquid/water in the event of heat pump unit insufficiency (e.g. in case of insufficient power, outside the heat pump's operating range, very cold temperatures outside, heat pump breakdown/fault heat etc.).
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The heating means may, at least most of its parts, be in direct or indirect contact with the liquid to be heated. For example, the heating elements of the heating means may completely be surrounded by the liquid, e.g., immersed in the liquid.
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Optionally, the heater is configured such that the at least two hollow elements and the first and second ports are arranged such that the lower port of the first and second ports or the opening of at least one of the at least two hollow elements is located above at least 70%, preferably 90% of the length of the heating elements in the longitudinal direction, when the heater is installed on site, so that at least a part of the heating means remains immersed in liquid in the tank, in case of shortage of liquid in the tank; and/or at least one of the at least two hollow elements has a length in the longitudinal direction of at least 50%, preferably of at least 80% of the length of the heating element(s) in the longitudinal direction, and the heater is configured such that the one of the at least two hollow elements and the heating means are arranged such that the one of the at least two hollow elements guides liquid (at least a part of the liquid; preferably substantially the entire liquid) along at least a part of the respective hollow element for flow of liquid along the heating element(s). Optionally, the opening of the one hollow element is above the lowest point of the at least one heating element, when the heater is installed on site.
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Optionally, the first hollow element and the second hollow element at least partially overlap each other in the longitudinal direction and are distanced from each other in a transverse direction perpendicular to the longitudinal direction, and/or optionally extend in parallel and/or are tubular (cylindrical) or conical and/or are concentrically arranged. If the first and second hollow elements overlap each other at least partially in the longitudinal direction, the flow of liquid and storage of liquid may be improved as to the efficiency/protection of the heating means. Preferably, the first and second hollow elements are distanced from each other in the transverse direction, which is perpendicular to the longitudinal direction, so as to allow for flow of liquid in and outside of the hollow elements. In particular, the flow of liquid may specifically be guided by the hollow elements.
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In one embodiment, the first hollow element and the second hollow element may represent an inner and an outer hollow element, respectively, or vice versa. This means that the first hollow element may be located at least partially inside the second hollow element, or vice versa, and/or that the first hollow element may have a smaller cross-sectional area (e.g. smaller diameter) than the second hollow element (e.g. larger diameter).
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The hollow elements may each represent a tube, optionally extending in the longitudinal direction. The first hollow element and the second hollow element in a tubular configuration may have the same or preferably different radii. A first tube having a smaller radius may, seen in the radial direction, i.e. the transverse direction, be within the outer tube having a larger radius. Optionally, the tubes may extend at least partially, in parallel relative to each other and in the longitudinal direction. The first and second tubes may be arranged concentrically, in particular concentric relative to the center of the tank, seen in the transverse direction.
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Optionally, the heating means is, at least partially along the longitudinal direction, located between the first hollow element and the second hollow element, seen in the transverse direction. Hence, the first and second hollow elements may have a stronger impact on the liquid, e.g. the presence of the liquid and the flow of the liquid, in relation to the heating means. For example, guiding the flow of liquid and retaining liquid close to the heating means may both be improved if the first and second hollow elements sandwich the heating means. Accordingly, the liquid may more precisely be directed with respect to the heating means. In particular, if the heating element is positioned between an outer and an inner hollow element, at least in parts, this may help to reduce undesired energy transfer from the heating means to the tank wall (which may be sensitive to heat).
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An embodiment of the invention may optionally be described as follows: The first hollow element may retain liquid in the tank at a position higher than the lowest point of the heating surface of the heating elements and prevent liquid from draining off the lowest port of the tank. Optionally, in the inverted orientation of the heater, the second hollow element may retain liquid in the tank at a position higher than the lowest point of the heating surface of the heating elements and prevent liquid from draining off the lowest port of the tank.
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Optionally, the first port may be located in a first end section of the tank, and the second port may be located in a second end section of the tank, substantially opposite to each other, seen in the longitudinal direction, and lower than the first end section, when seen in the longitudinal direction, when the heater is installed on site.
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A hollow element may extend from the second port and/or the tank base/bottom (upwards) in the longitudinal direction to a retaining level at which the opening is located, when viewed in the longitudinal direction, when the heater is installed on site, wherein the heater may be configured such that the outside of the first hollow element and an outer counterpart (e.g. tank wall) retain liquid in the tank and prevent liquid from draining off the outlet/second port. Accordingly, a hydraulic trap may be formed between a hollow element and the counterpart, such as the tank wall. Here, the first hollow element may represent an (upward) extension or elongation from the outlet/second port to the opening. Accordingly, liquid is retained from draining through the outlet port up to the height of the opening of the first hollow element.
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Optionally, the heating means is at least partially located below the retaining level and, seen in the transverse direction, between the first hollow element and the outer counterpart, optionally the tank wall, such that the heater is configured to at least partially keep the heating means immersed in liquid, if the liquid circuit is interrupted and liquid drains off the outlet port. Accordingly, transfer of heat from the heating means to the liquid can at least partially be maintained, so as to avoid overheating of the heating means. In this case, a hollow element is in direct fluid communication with the outlet/second port, wherein the outer surface of the first hollow element, together with the outer counterpart act as hydraulic trap retaining liquid from draining of the outlet/second port in the height of the opening.
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Optionally, the opening of the second hollow element defines a guiding level, when viewed in the longitudinal direction, when the heater is installed on site, wherein the second hollow element is at least partially, seen in the longitudinal direction, located between the first hollow element and the tank wall, seen in the transverse direction, and the heater is configured to guide flow liquid in the tank from the first/inlet port downwards along at least a part of the second hollow element to the guiding level, then upwards at least to the retaining level along at least a part of the heating means and along at least a part of the first hollow element and the second hollow element, and then downwards and inside the first hollow element to the outlet/second port. Accordingly, by way of the first and second hollow elements, the liquid in the tank is guided, so as to improve transfer of heating from the heating means to the liquid and to allow for liquid to be retained in the tank at least partially surrounding the heating means in case of leakage through the outlet/second port.
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In another embodiment, when the first/inlet port may optionally be located in a first end section of the tank and the second/outlet port is located in a second end section of the tank substantially opposite to the first end section, seen in the longitudinal direction, and lower than the first end section, when viewed in the longitudinal direction, when the heater is installed on site, the first hollow element extends upwards from the tank bottom in the longitudinal direction and has the opening, which defines a retaining level, when viewed in the longitudinal direction, when the heater is installed on site, wherein the heater is configured to retain liquid in the tank at the retaining level inside the first hollow element, if the liquid circuit is interrupted and liquid drains off the second/outlet port. Accordingly, the inside of the first hollow element acts as a hydraulic trap. In this case, the second/outlet port is not in direct fluid communication with the inside of the first hollow element.
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Optionally, the heating means is at least partially located below the retaining level and, seen in the transverse direction, inside a hollow element, such that the heater is configured to at least partially keep the at least one heating means, preferably all heating elements, more preferably the entire heating means, immersed in liquid in case of shortage of liquid in the tank. This helps to void situation in which the heating means basically ceases to transfer heat to the liquid and transfers heat to air within the tank.
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Optionally, the heater comprises a second hollow element, and the opening of second hollow element represents a guiding level, when viewed in the longitudinal direction, when the heater is installed on site,
wherein the second hollow element is at least partially, seen in the longitudinal direction, located inside the first hollow element, seen in the transverse direction, and the heater is configured to flow liquid in the tank from the first/inlet port downwards along at least a part of the second hollow element to the guiding level, then upwards at least to the retaining level along at least a part of the heating means and then downwards and outside the first hollow element to the second/outlet port. Accordingly, by way of the first and second hollow elements, the liquid in the tank is guided, so as to improve transfer of heat from the heating means to the liquid and to allow for liquid to be retained in the tank at least partially surrounding the heating means in case of leakage, e.g. through the second/outlet port or somewhere else in the hydraulic circuit.
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In any embodiment, the heater may comprise a thermostat to measure the temperature of the liquid inside the tank, optionally located within at least one of the first hollow element and the second hollow element, further optionally at the tank end. The thermostat measures the temperature of the liquid and can, as such, serve as an indicator of abnormal situations. If the thermostat is located at the end of the tank and/or at a first hollow element or a second hollow element, it may remain preferably immersed in liquid, even in case of leakage of liquid through the second/outlet port of the tank and, accordingly, continue to provide reliable temperature measurement results. In particular, if the thermostat is immersed in liquid, thermal conduction and, thus, temperature detection, is quicker. However, it may not be necessary to have the thermostat immersed in the liquid in case of a leakage: The thermostat may be above the retained liquid level and may nevertheless identify leakage because of the steam generated by the heating elements. Further, the thermostat is not necessarily in direct contact with the liquid, but it may be included in a sleeve immersed in the liquid, to provide for an indirect measurement.
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Optionally, the tank wall and/or the tank end may comprise at least two guiding features/shapes such as recesses, extruded parts and/or cavities, to (further) improve liquid flow distribution inside the tank by reducing/avoiding dead zones. An example of such embodiment may be an entity comprising first and second hollow elements. The first and second hollow elements are substantially tubular, wherein the second hollow element represents an inner tube, and the first hollow element represents an outer tube, in which the inner tube is concentrically received. The inner tube is sealed to the tank end. At the interface between the tank end and the tank wall, guiding features with e.g. spoon-shaped buckets are provided to allow for better whirling of the fluid inside the tank. Thanks to these (optionally: three) guiding features/shapes (for instance extruded parts, recesses or cavities), a better flow distribution inside the tank may be achieved and the path of the liquid along the heating means may be increased.
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Optionally, an end of a hollow element opposite to the opening in the longitudinal direction abuts an end of the tank, and is optionally sealed to the end. While the tank end may be at an upper or lower end of the tank, an end of a hollow element may abut the tank end, in particular in the transverse direction, i.e. perpendicular to the longitudinal direction. The tank end may be understood as tank bottom or tank head.
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Optionally, the tank end may be included in the flange of the heater. Optionally, the heating means may extend from the flange towards the inside of the tank. Optionally, the end of a hollow element is sealed to a tank end, in particular to the effect that the opening of a hollow element represents the substantially only fluid communication with the remaining liquid for the sub-volume.
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Optionally, the tank is made of (thermos)plastics, preferably PPS, and/or the first and/or second hollow elements are made of metal, in particular stainless steel or copper. Further optionally, a hollow element (the first or second hollow element, e.g. the outer hollow element) may be made of stainless steel, as this allows for welding to the flange (which also comprises stainless steel), and the second hollow element (first or second hollow element, e.g. the inner hollow element) may be made of copper, which may be preferable in terms for manufacture. The outer hollow element may be understood here as a hollow element closer to the tank wall than to the inner hollow element. In general, making the tank and/or the first hollow element and/or the second hollow element of plastics may reduce the costs and may allow for versatile functions. The tank and/or at least a part of the flange may be made of plastics. The tank may be formed as a single piece of plastics, at least the tank shell and the tank end. A "cap" of the tank, e.g. flange, may be separate from the remaining tank. Nevertheless, temperature restrictions need to be borne in mind. The outer hollow element has also a benefit in terms of safety, as it reduces the risk of tank melting in case of temperature rise inside the tank in particular if the tank is made of plastics. Indeed, the hollow elements acts as a physical barrier between the heating means and the tank wall in particular if the tank is made of plastics.
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Optionally, the heating means is a resistive heating means. In other words, the heating means may be an electrical heating means. The heating means may have helicoidal or U-shaped heating elements, wherein this may in particular relate to the resistive path.
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However, the heater of the invention is optionally adaptable to both electric and hydraulic back-up configurations. This means that, instead of an electric, i.e. resistive, heating means, the heating means may rely on hydraulic heating. The latter may mean that the liquid (water) of the main circuit, i.e. entering/exiting the first and second ports, may mix with water of a secondary (hot water) circuit or that the secondary (hot water) circuit is also heated by the electric heating means.
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Optionally, the heater may comprise an external insulation layer.
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The liquid circuit may represent a main water flow circuit. A secondary water flow circuit may flow between secondary water flow ports also through the tank and may also be heated by means of the heating means.
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Optionally, one of the first and second ports is at the (side) wall (shell) of the tank and the other one of the first and second ports is at a tank end This allows for a simple shape of the hollow elements, e.g. as straight tubes and, thus, for easy manufacture. For example, no bending or corners of the tube may be necessary
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The invention is also directed to a heat pump system comprising the heater of the invention. Specifically, the heat pump system of the invention comprises a liquid circuit comprising a heat pump unit for heating (optionally also for cooling liquid) and further comprising the heater of the invention, wherein the heater of the invention optionally represents a back-up heater for (selective) additional heating of the liquid of the liquid circuit.
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The invention, in general, refers to any kind of heat pump system, including at least one ground source (water)- and/or air source-heat pump unit. The heat pump units may be indoor or outdoor units. A heat pump unit of the heat pump system may be a split unit or a monobloc unit. The heat pump system may be configured to heat air or water (of a closed loop or of an open loop, such as domestic hot water), while the heater as part of the system may heat liquid (e.g. water) directly, possibly for later heat exchange with air or another liquid.
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Detailed embodiments and further advantages and features related to the present invention are described in the following, wherein these examples shall not be regarded as limiting the invention.
Brief description of the drawings
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- Fig. 1(a)
- shows a cross-sectional view of a heater of an embodiment of the invention, Fig. 1(b) shows a cross-sectional view an entity of a heater of the invention, and Fig. 1(c) shows a perspective view of the outside of a heater of the invention.
- Fig. 2(a), 2(b) and 2(c)
- show cross-sectional views of a heater of an embodiment of the invention in a first orientation and first flow direction, wherein Fig. 2(a) shows the structure, Fig. 2(b) additionally indicates the flow of liquid, and Fig. 2(c) additionally indicates the level of liquid as retained.
- Fig. 3(a), 3(b) and 3(c)
- show cross-sectional views of a heater of an embodiment of the invention in a first orientation and second flow direction, wherein Fig. 3(a) shows the structure, Fig. 3(b) additionally indicates the flow of liquid, and Fig. 3(c) additionally indicates the level of liquid as retained.
- Fig. 4(a), 4(b) and 4(c)
- show cross-sectional views of a heater of an embodiment of the invention in a second orientation and first flow direction, wherein Fig. 4(a) shows the structure, Fig. 4(b) additionally indicates the flow of liquid, and Fig. 4(c) additionally indicates the level of liquid as retained.
- Fig. 5(a), 5(b) and 5(c)
- show cross-sectional views of a heater of an embodiment of the invention in a second orientation and second flow direction, wherein Fig. 5(a) shows the structure, Fig. 5(b) additionally indicates the flow of liquid, and Fig. 5(c) additionally indicates the level of liquid as retained.
- Fig. 6
- shows another embodiment of a heater of the invention, wherein Fig. 6(a) represents a cross-sectional view and Fig. 6(b) is a perspective view of a lower region of the heater of an embodiment of the invention.
- Fig. 7(a)
- shows a side view of an upper part of a tank of an embodiment of the invention, and Fig. 7(b) shows a perspective view of a tank of an embodiment of the invention.
Detailed description
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Figure 1(a) shows a cross-sectional view of a heater 1 of an embodiment of the invention. The heater 1 may have a cylinder shape and so it may be understood that most of the shape of the whole heater 1 be imagined with a revolution of this view around the central vertical axis, with the exception of the elements on the side of the shell such as the port 11. The tank 2 forms a cylinder. The heater 1 comprises the tank 2 for receiving liquid. The tank 2 has a tank wall 16 which runs along the longitudinal direction I and has a tank end 4 in the transverse direction t, which represents an upper end in the orientation of Fig. 2(a). The transverse direction t is perpendicular to the longitudinal direction I, and the longitudinal direction I is opposite to gravity, when the heater 1 is installed on site.
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Two hollow elements, namely the tubes 14 and 15, are provided. More specifically, the hollow element 15 represents a first hollow element, and the hollow element 14 represents a second hollow element.
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The heater 1 comprises first 10 and second 11 ports for passage of liquid into or out of the tank 2. By way of the ports 10, 11, the heater 1 is connected to a liquid/hydraulic circuit (not shown), which circuit may be a primary water circuit. The first port 10 is on the top of the tank 2, wherein the second port 11 is in the tank wall 16 close to the bottom 17 of the tank 2. The first port 10 may function as inlet port and the second port 11 may function as outlet port, or vice versa, during normal use.
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The heater 1 further comprises heating means 3 which is basically located inside the tank 2 and heats liquid inside the tank 2. The heating means 3 extends in the longitudinal direction I and is, in the figures, an electric heater, with resistive heating elements running helically around an axis in the longitudinal direction I. In other words, a resistive helix forms the heating means 3 in figure 1.
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In any embodiment, the heater 1 may have resistive heating elements 3, e.g. having a U-shape or helicoidal shape, i.e. in the form of a helix. For example, having different stages of helicoidal elements in the longitudinal direction I may be preferable compared to U-shaped elements for heating uniformity when controlled separately. Helicoidal shape may also be preferred for compacity reason compared to U-shaped elements. As the bending of tube may be limited for mechanical reasons, the helicoidal shape may offer denser presence of heating elements for the same volume.
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Electrical connections 7 for the heating means 3 pass through the flange 8. The flange 8 represents the lower end of the heater 1 and includes the tank bottom 17.
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The heater 1 further comprises secondary flow ports 12a, 12b, which may be connected to a secondary water circuit, liquid of which may also be heated by the heating means 3. Alternatively or additionaly, the heater 1 may, by means of the secondary flow ports 12a and 12b serve as a "hydraulic mixing device", as the secondary water circuit may mix with the liquid circuit of the first and second ports, 10,11.
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The heater 1 of figure 1(a) (and of any other figure) comprises a thermostat 13 which is located inside a thermostat housing which extends in the longitudinal direction I, from the flange 8 of the tank 2. The thermostat may be located inside the thermostat housing's outermost end, i.e. at the end of the thermostat housing opposite to the flange 8.
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Figure 1(b) shows an entity comprising first and second hollow elements 14, 15, the heating means 3 as well as the flange 8 in detail, of the heater of Fig. 1(a). The first and second hollow elements 14, 15 are substantially tubular, wherein the second hollow element 14 represents an inner tube, and the first hollow element 15 represents an outer tube, in which the inner tube 14 is concentrically received. The outer tube 15 is sealed to the bottom 17 and, thus, to the flange 8 and extends upwards, until the termination of the tube forms an opening 15a. The inner tube 14 has a tube end 14b which is for abutting and sealing with an upper end 4 of the tank 2. The opposite termination of the inner tube 14 represents the opening 14a.
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Figure 1(c) shows a perspective view of a heater 1 of the invention, having the first port 10 on top, and the second port 11 at lower part of the tank wall 16, wherein the electrical connection 7 including the flange 8 is located at the bottom of the heater 1. This may correspond to a perspective view of the tank 2 shown in figure 1(a).
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Figures 2(a) to 2(c) show the same heater 1 as shown in Fig. 1, wherein additionally the direction of flow of liquid is indicated in Fig. 2(b) and the resulting retained level of liquid is indicated in Fig. 2(c). A level Ir until which liquid is retained in the tank even in case of shortage of liquid is shown and almost extends along the entire length of the heating means 3. More specifically, in the orientation of the heater 1 in figure 2(a), the flange 8 of the heater is at the lower end. This corresponds to the orientation of the entity shown in figure 1. When connected to a liquid circuit (not shown) in a first flow direction, liquid enters via the first port 10 on top of the heater and flows along the inner tube 14 until the opening 14a is reached. Accordingly, the inlet port 10 is positioned in an upper end section 6, and the outlet port is positioned in the lower end section 9. At the opening 14a, the tube 14 terminates and the termination is regarded as an approximate end of the guidance of the liquid flow inside the tube 14. Figure 2(a) indicates the corresponding level of guidance Ig. Upon exit through the opening 14a, the liquid is being heated, while flowing upwards along the outer side of the inner tube 14. At that time, the liquid is surrounded by the outer tube 15, which prevents the liquid from directly exiting the heater 1 through the outlet 11 at the lower end. Rather, the liquid has to pass along the heating means 3, which allows the liquid to absorb further heat. When the flow of liquid reaches the opening 15a of the outer tube 15, the liquid can flow downwards between the outer surface of the outer tube 15 to the second port 11. Up to the opening 15a of the outer tube 15, liquid would be stored inside the outer tube 15 if the liquid circuit is interrupted and liquid leaks. Hence, the outer tube 15 represents a hydraulic trap which captures a sub-volume of liquid in the tank 2 and prevents the sub-volume from passing through the lower port 11.
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Figures 3(a) to 3(c) show the same heater 1 as shown in Fig. 1, wherein additionally the direction of flow of liquid is indicated in Fig. 3(b) and the resulting retained level of liquid is indicated tin Fig. 3(c). Compared to Fig. 2, the same tank 2 is used, wherein the direction of flow is inversed. When connected to a liquid circuit (not shown) in a second flow direction opposite to the first flow direction shown in Fig. 2(b), liquid exits via the first port 10 on top of the heater after flowing along the inner tube 14. Accordingly, during normal use, the outlet port 10 is positioned in an upper end section 6, and the inlet port 11 is positioned in the lower end section 9. At the opening 14a, the tube 14 terminates and the termination is regarded as an approximate end of the guidance of the liquid flow inside the tube 14. Figure 3(a) indicates the corresponding level of guidance Ig. Before entry into the opening 14a, the liquid is being heated, while flowing downwards along the outer side of the inner tube 14. At that time, the liquid is surrounded by the outer tube 15, after liquid has entered the tank 2 via the inlet port 11 at the lower end. Rather, the liquid has to pass along the heating means 3, which allows the liquid to absorb further heat. After entry through the port 11, the liquid flows upwards between the outer surface of the outer tube 15 and the tank wall 16. Up to the opening 15a of the outer tube 15, liquid will be stored inside the outer tube 15 if the liquid circuit is interrupted and liquid leaks. Hence, the outer tube 15 represents a hydraulic trap which captures a sub-volume of liquid in the tank 2 and prevents the sub-volume from draining through the lower port 11.
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Figures 4(a) to 4(c) show the heater 1 in the inverted orientation, i.e. "upside down", in which liquid enters via the first port 10 and exits via the second port 11 in the tank bottom 17. In this orientation, the inner tube 14 ensures that liquid is retained at the level Ir and does not drain through the lower port 11 once the level Ir has been reached. Accordingly, at least two thirds of the heating means 3, seen in the longitudinal direction I, remain immersed in liquid.
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The outer tube 15 runs downwards from the flange 8 and guides liquid entering the tank 2 via the port 10 downwards. Accordingly, the outer tube 15 guides liquid from the first port 10 downwards up to the level Ig at the opening 15a. The liquid is guided, by way of the outer side of the inner tube 14 and the inner side of the outer tube 15, along the heating means 3.
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Figures 5(a) to 5(c) show the heater 1 in the same orientation as in Fig. 4, but with opposite flow direction. In Fig. 5, liquid enters via the port 11 in the tank bottom 17 and exits via the port 10 . In this orientation, the inner tube 14 ensures that liquid is retained at the level Ir and does not drain through the lower port 11 once the level Ir has been reached. Accordingly, at least two thirds of the heating means 3, seen in the longitudinal direction I, remain immersed in liquid.
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The outer tube 15 runs downwards from the flange 8 and guides liquid entering the tank 2 via the port 11 downwards, after having flow upwards inside the inner tube 14. The liquid is guided, by way of the outer side of the inner tube 14 and the inner side of the outer tube 15, along the heating means 3.
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When comparing the embodiments of figures 2 and 3, on the one hand, and of figures 4 and 5, on the other hand, it is evident that the inner and outer tubes 14, 15 may be seen as switching functions in that, in figure 2 and 3, it is the inner tube 14 which primarily guides the liquid and the outer tube 15 prevents the liquid from completely draining through the lower port 11. In figures 4 and 5, it is the outer tube 15 which primarily guides the liquid, and the inner tube 14 prevents liquid from completely draining through the lower port 11.
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Figure 6 shows embodiments having an inner tube 14 and an outer tube 15. In figure 6(a), the inner tube 14 extends between heating elements of the heating means 3, when seen in the transverse direction t (which may be seen as a radial direction). Accordingly, on the inside and the outside of the inner tube 14, a part of the heating means 3 is present, so that liquid can be heated when passing on both sides of the inner tube 14.
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Figure 6(b) shows a realization of the opening 14a in that the inner tube 14 does not terminate abruptly, but the wall of the inner tube 14 has openings between tube walls extending further in the longitudinal direction I, namely up to the end 4 of the tank 2. The extended tube wall may represent feet and a connection to the tank end 4.
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Fig. 7(a) shows a side view of an upper part of a tank of an embodiment of the invention, and Fig. 7(b) shows a perspective view of a tank of an embodiment of the invention, wherein inner entities are visible. More specifically, the tank wall 16 and/or the tank end 4 comprises at least two guiding features 18, such as recesses, extruded parts and/or cavities, to (further) improve liquid flow distribution inside the tank 2 by reducing/avoiding dead zones. An example of such embodiment is an entity comprising first and second hollow elements 14, 15. The first and second hollow elements 14, 15 are substantially tubular, wherein the second hollow element 14 represents an inner tube, and the first hollow element 15 represents an outer tube, in which the inner tube 14 is concentrically received. The inner tube 14 is sealed to the tank end 4. At the interface between the tank end 4 and the tank wall 16, 3 three guiding features with e.g. spoon-shaped bucket, are provided to allow for better whirling of the fluid inside the tank 2.
Reference signs
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- 1
- (back-up) heater
- 2
- tank
- 3
- heating means
- 4
- tank end
- 5
- thermal insulation
- 6
- first end section
- 7
- electrical connection
- 8
- flange
- 9
- second end section
- 10
- first (inlet) port
- 11
- second (outlet) port
- 12a, 12b
- secondary water flow ports
- 13
- thermostat
- 14
- inner tube (hollow element)
- 14a
- opening of inner tube
- 14b
- end of inner tube
- 15
- outer tube (hollow element)
- 15a
- opening of outer tube
- 15b
- end of inner tube
- 16
- tank wall
- 17
- tank bottom
- 18
- guiding feature
- I
- longitudinal direction
- t/r
- transverse / radial direction
- Ig
- guiding level
- Ir
- retaining level