Stationary liquid tank

Abstract

The invention relates to a stationary liquid tank (1) with a temperature control device (2) for temperature control of a liquid (3) in the liquid tank (1), which has at least one flat tube (5) externally connected to the liquid tank (1) in a heat-transferring manner, with channels (6) having a channel width bK and webs (7) having a web width bs, wherein the flat tube (5) is made of a material with a tensile strength Rm and has a burst pressure PBERST,IST, - wherein a heat distribution plate (10) is arranged between the flat tube (5) and the liquid tank (1), which is connected over a surface to the flat tube (5) and the liquid tank (1), or - wherein the flat tube (5) with the channels (6) and webs (7) is designed such that it satisfies the following equation, 1.2bK+Tolerance / bS−Tolerance≤Rm / PBERST,MIN with tolerance = manufacturing tolerance of the web thickness bs. This should enable increased heat transfer.

Description

[0001] The present invention relates to a stationary liquid tank. The invention also relates to a heat pump system with such a stationary liquid tank.

[0002] When using refrigerants, for example in stationary heat pump systems, the refrigerant charge is limited by various standards. Depending on the refrigerant, adhering to a maximum charge, the system's capacity, and structural requirements is not always easy with conventional components. Therefore, there is already a shift from round tube systems to flat tube systems in stationary applications. However, even here, the charge limit sometimes presents a challenge.

[0003] In stationary applications, for example, in domestic hot water heating systems for residential buildings, a heat exchanger or temperature control unit is wrapped around the hot water tank to heat it. With this design, installation, integration, and replacement in case of a defect are simpler than if the heat exchanger or temperature control unit were located inside the water tank. Additionally, direct contact between the (drinking) water and the heat exchanger, and thus contamination of the drinking water in the tank by substances from the heat exchanger, is prevented. Furthermore, in the event of a refrigerant leak, contamination of the drinking water is prevented, as the refrigerant escapes into the environment. Stationary liquid tanks with externally mounted flat tubes are known from documents CN 112 856 817 A and CN 112 902 445 A.

[0004] Nowadays, flat tubes with internal channels and intermediate webs are designed to just meet the burst pressures P BERST,MIN required by current standards, thus enabling a material-saving flat tube design.

[0005] A ratio of a channel width bK to a web width bS is calculated according to the following equation from the tensile strength Rm, the desired burst pressure PBURST,IST, and the manufacturing tolerance of the webs. b K + Toleranz / b S − Toleranz ≤ R m / P BERST , MIN . with P BERST,MIN = burst pressure required according to standardization and P BERST,IST = burst pressure maintained by the manufactured flat tube at nominal dimensions due to the web thickness.

[0006] When designing a heat exchanger or temperature control unit, it is sometimes impossible to achieve a desired heat flow while adhering to the requirements for the fill quantity and thus the internal volume of the heat exchanger. In the case of a heat exchanger wound around a stationary liquid tank, its flat tubes constitute the largest part of the internal volume.

[0007] During heat transfer from the refrigerant to the liquid being heated, or to the water, thermal conductivity in an enamel coating and a thermal interface material (thermal paste) accounts for a large portion of the thermal resistance. Depending on the heat transfer coefficient on the water side, the water side also represents a significant part of the total thermal resistance. The thermal resistance of the enamel and the thermal interface material can be reduced by increasing the thermal conductivity, reducing the layer thickness, and increasing the cross-sectional area. Thermal conductivity, as a material property, cannot be altered or is already optimized through material selection to the maximum possible for the application. The layer thickness is typically already as thin as possible for the application.Increasing the cross-sectional area as an effective measure to increase the transferred heat flow is not feasible with the current flat tube design while maintaining the required internal volume.

[0008] The present invention therefore deals with the problem of further developing a stationary liquid tank with a temperature control device in such a way that increased heat transfer between a flat tube of a temperature control device and the stationary liquid tank is enabled.

[0009] This problem is solved according to the invention by the subject matter of independent claim 1. Advantageous embodiments are the subject matter of the dependent claims.

[0010] The present invention is based on the general concept of achieving heat transfer between a flat tube of a temperature control unit of a stationary liquid tank and the liquid tank itself by increasing the heat transfer surface area without increasing the refrigerant volume. According to the invention, this is achieved by two alternative embodiments: firstly, by arranging a heat distribution plate between the flat tube and the liquid tank, and secondly, by integrating such a heat distribution plate into the flat tube through a correspondingly different geometric cross-sectional shape of the flat tube. The stationary liquid tank according to the invention has a temperature control unit for maintaining the temperature of the liquid in the tank, which can be used for both heating and cooling the liquid stored in the tank.The temperature control device, which constitutes a heat exchanger, comprises at least one flat tube externally connected to the liquid tank for heat transfer. The tube has internal channels with a channel width bK and webs with a web width bS. The flat tube is made of a material with a tensile strength Rm and has a burst pressure PBURST,IST. PSERST,MIN is the burst pressure required by the standard / specification. The burst pressure PSERST,IST of the flat tube must be higher. According to a first alternative embodiment of the stationary liquid tank according to the invention, the previously described heat distribution plate is arranged between the flat tube and the liquid tank and is connected to both the flat tube and the liquid tank over a surface area. Compared to, for example, a heat-conducting layer, the heat distribution plate has high thermal conductivity and is, for example, made of aluminum.It distributes the heat flow from the surface in contact with the flat tube to a larger area. This larger area is then conducted through the heat-conducting layer (which can be located between the heat distribution plate and the liquid tank), an enamel coating on the liquid tank, and the steel of the liquid tank. The heat-conducting layer has a thermal conductivity that is significantly lower than that of the flat tube material and / or the heat distribution plate. This enlarged surface area is also effective for heat transfer on the inner surface. A typical liquid tank wall consists of a steel core and an inner and outer enamel coating.

[0011] In an equivalent but alternative embodiment of the stationary liquid tank according to the invention, the flat tube with its channels and webs is designed such that it satisfies the following equation: 1 , 2 b K + Toleranz / b S − Toleranz ≤ R m / P BERST , MIN

[0012] In this solution, the web width bS is increased while maintaining the same channel size, thereby also increasing the outer dimensions of the flat tube and thus the contact area between the flat tube and the stationary liquid tank. The flat tube design according to the invention and the resulting design differs from previous flat tube designs in that the webs between the individual channels are so robust that they can withstand a significantly higher burst pressure PSERST,IST than required, for example, by current standards. The flat tube wall thickness remains unchanged compared to the previous design. Tests and calculations have shown that this embodiment is particularly advantageous when the lower tolerance limit of the web width is at least 20% greater than required to achieve the specified burst pressure PSERST,MIN.

[0013] Regardless of the chosen embodiment, the stationary liquid tank according to the invention offers the possibility of significantly improved heat transfer compared to previous liquid tanks due to the enlarged heat transfer surface on the tank's circumference, while maintaining the same internal volume of the flat tubes. This also provides a larger heat transfer surface on the tank's inner wall for the liquid stored within. Overall, this allows for an increase in heat flow without increasing the refrigerant volume. The second alternative embodiment offers the further significant advantage of relatively short heat conduction paths and thus a higher transferred heat flow. Additionally, the overall material usage is reduced, and the assembly forces required to clamp the heat exchanger around the liquid tank are lower.Additionally, manufacturing is simpler because no material-bonded connection between the flat tube and the heat distribution plate needs to be created, and positioning of the heat-conducting plate relative to the flat tubes during joining, for example by soldering, is unnecessary.

[0014] In the first alternative of the stationary liquid tank according to the invention, the heat distribution plate is connected to an outer surface of the liquid tank via a heat-conducting layer. The heat distribution plate has a thermal conductivity λv and a thickness dv, while the heat-conducting layer has a thermal conductivity λw and a thickness dw. To achieve the highest possible heat transfer from the temperature control device to the liquid tank and its contents, at least two flat tubes are wound parallel around the stationary liquid tank, with a distance s between two flat tubes. The following applies: 0 , 25 ⋅ λ V ⋅ d V / s < λ W ⋅ s / d W < 4 ⋅ λ V ⋅ d V / s or 8 R V > R W > 1 2 R V

[0015] The following is preferred: 0 , 5 ⋅ λ V ⋅ d V / s < λ W ⋅ s / d W < 4 ⋅ λ V ⋅ d V / s or 4 R V > R W > R V

[0016] Here, RV is the axial thermal resistance in the heat distribution plate, approximately Rv = s / 2 / (λ V · d V ), and RW is the radial thermal resistance in the heat-conducting layer, approximately RW = d W / (λ W · s). Adhering to these relationships offers the significant advantage that the area between the flat tubes efficiently participates in heat transfer, thus increasing the heat flow between the flat tube and the liquid container. Simultaneously, fulfilling these relationships allows the heat distribution plate to be made only as thick as is necessary to maximize heat flow. This results in improved design in terms of installation space, weight, and cost.

[0017] Advantageously, a liquid tank according to the first alternative embodiment of the invention has a heat distribution plate that is soldered to the flat tube. Soldering between the heat distribution plate and the flat tube provides an optimized heat-transferring connection with an extremely short heat conduction path. Furthermore, compared to thermal paste (thermal conduction layer), solder has significantly improved thermal conductivity, thus enabling virtually unimpeded heat transfer between the flat tube and the heat distribution plate.

[0018] In a further advantageous embodiment of the stationary liquid tank according to the invention, the flat tube has insulation on an outer surface facing away from the stationary liquid tank. Such insulation can at least reduce heat loss or absorption from the environment, thereby significantly increasing the efficiency of the temperature control device. This type of insulation can be achieved, for example, by means of a suitable plastic coating or a type of housing, in particular made of plastic or mineral wool.

[0019] The temperature control device expediently includes a refrigerant circuit, with the flat tube(s) forming part of this circuit. The refrigerant, which theoretically could also be a coolant, can be used to control temperature, in particular to heat the contents of the stationary liquid tank.

[0020] In a further advantageous embodiment of the stationary liquid tank according to the invention, the flat tube is designed as an extruded profile or as a welded tube. The design as an extruded profile, for example made of aluminum, offers the significant advantage of producing the flat tube not only to a high standard but also cost-effectively. Furthermore, such extruded profiles can be produced in virtually any cross-sectional shape using appropriate dies.

[0021] The liquid tank features a steel core and both an inner and outer enamel coating. The enamel coating ensures hygienic storage of liquids, such as drinking water, within the tank.

[0022] The present invention is further based on the general concept of operating the described flat tube as part of a heat pump circuit, via which the liquid tank is heated. The use of such a liquid storage tank offers the advantage that a temperature-controlled liquid, for example hot water, can be stored for peak demand, and the heat pump system only needs to be dimensioned to heat the stored volume to the desired temperature over a longer period. In the described embodiment, contamination of the liquid tank with refrigerant or coolant is excluded, since any leakage would escape into the environment through the double-walled construction of the flat tube wall and the tank wall.

[0023] Further important features and advantages of the invention will become apparent from the dependent claims, the drawings and the associated description of the figures based on the drawings.

[0024] It is understood that the features mentioned above and those to be explained below can be used not only in the combinations specified, but also in other combinations or on their own, without leaving the scope of the present invention.

[0025] Preferred embodiments of the invention are shown in the drawings and are explained in more detail in the following description, wherein identical reference numerals refer to identical or similar or functionally identical components.

[0026] Each of these shows, schematically: Fig. 1 shows an external view of and a sectional view through a stationary liquid tank according to the invention with a temperature control device comprising several flat tubes, corresponding to a first alternative embodiment of the invention. Fig. 2 shows an external view of and a sectional view through a stationary liquid tank according to the invention with a temperature control device comprising several flat tubes, corresponding to a second alternative embodiment of the invention. Fig. 3 shows a cross-sectional view through a possible embodiment of a flat tube. Fig. 4 shows a sectional view through a wall of the stationary liquid tank with flat tubes, a heat distribution plate, and a heat-conducting layer, corresponding to a first alternative embodiment of the liquid tank according to the invention.

[0027] According to the Fig. 1As well as 2 and 4, a stationary liquid tank 1 according to the invention has a temperature control device 2 for temperature control of a liquid 3, for example water 4, in the liquid tank 1. The temperature control device 2 has at least one, preferably several, flat tubes 5 with channels 6 connected externally to the liquid tank 1 in a heat-transferring manner, each having a channel width b K (cf. Fig. 3 The channels 6 are separated by intermediate webs 7, each with a web width bS. The flat tube(s) 5 are made of a material, for example, aluminum, with a tensile strength Rm and a burst pressure PBURST,IST. The burst pressure results from the tensile strength of the material and the selected geometry of the flat tube. PBURST,IST is the burst pressure that the flat tube 5 achieves.

[0028] The flat tubes 5 each open longitudinally into collectors 8, which are clamped against the stationary liquid tank 1 via a clamping device 9.

[0029] To enable better temperature control, in particular better heating or cooling of the liquid 3 stored in the liquid tank 1, without increasing the internal volume of the flat tubes 5, the invention provides for increasing the heat-transferring surface area between the temperature control device 2 and the liquid tank 1. According to a first alternative embodiment of the invention, a heat distribution plate 10 is arranged between the flat tubes 5 and the liquid tank 1, which is connected over a surface area to the flat tubes 5 on one side and to the liquid tank 1 on the other (see Figure 10). Fig. 1 and 4 ).

[0030] A heat distribution plate 10, which is soldered to the flat tubes 5 and thus ensures high heat transfer from them, can create a significantly increased thermal conductivity compared to a heat-conducting layer 11. Furthermore, the heat-conducting plate 10 distributes the heat flow introduced from a contact surface with the flat tubes 5 over a considerably larger area, whereby the heat flow is conducted across this larger area through the heat-conducting layer 11 and a wall of the liquid tank 1. Such a wall of the liquid tank 1 can, for example, consist of a steel core 12 and an inner and / or outer enamel coating 13 (see Figure 1). Fig. 4 ). Due to the larger heat-transferring surface of the heat distribution plate 10, an improved and increased heat transfer to the inside of the wall can also be achieved.

[0031] The heat distribution plate 10 is preferably connected to an outer side of the liquid tank 1 via the previously described heat-conducting layer 11, and has a thermal conductivity λ V and a thickness dv (see Fig. 4 The thermal conductivity layer 11 in turn has a thermal conductivity λW and a thickness dW.

[0032] If one considers the temperature control unit 1 according to the Fig. 1 As shown in Figures 4 and 5, it can be seen that several flat tubes 5 are arranged parallel to each other and wind around the stationary liquid tank 1. The at least two flat tubes 5 of the temperature control device 2 have a distance s between them (see Figure 4). Figs. 1 and 2 ) and are preferably arranged such that: (0.25 λ V · d V / s) < (λ W · s / d W ) < (4 λ W · d V / s), particularly preferably: (0.5 λ V · d V / s) < (λ W · s / d W ) < (2 λ V · d V / s).

[0033] In the second alternative embodiment of the stationary liquid tank 1 according to the invention, the flat tubes 5 with the channels 6 and the webs 7 are designed such that they satisfy the following equation: 1 , 2 b K + Toleranz / b S − Toleranz ≤ R m / P BERST , IST

[0034] The web width bS in each flat tube 5 is increased while maintaining the same channel size. This increases the outer dimension of the flat tube 5 and, consequently, the contact area available for heat transfer between the flat tube 5 and the liquid tank 1. The resulting flat tube design differs from previous designs in that the webs 7 between the individual channels 6 are so robust that they can withstand a significantly higher burst pressure PSERST,IST than the burst pressure PBERST,MIN required by current standards. This design becomes particularly advantageous if the burst pressure PBERST,MIN required for the application can be exceeded by 20% through appropriate adjustments to the web width bS and the channel width bK.

[0035] In general, such an embodiment according to the invention only makes sense if the permissible amount of refrigerant is limited in the application under consideration or if the cost per volume for liquid refrigerant is higher than for the heat exchanger material.

[0036] The channels 6 themselves can have a square cross-section, as is the case according to the Figs. 1 to 4 as shown, although theoretically they could also have a rectangular, non-square, or round cross-section. To achieve the most efficient temperature control of the liquid 3 in the liquid tank 1, additional insulation 14, for example a polystyrene shell, can be provided on the flat tubes 5 on an outer side facing away from the stationary liquid tank 1 (see figure). Fig. 1The temperature control unit 2 can also have a refrigerant circuit, with the flat tubes 5 forming part of this refrigerant circuit. Alternatively, it is of course also conceivable that the temperature control unit 2 has a coolant circuit, with the flat tubes 5 forming part of the coolant circuit in this case.

[0037] To manufacture the flat tubes 5 cost-effectively yet to a high standard, they can be designed as extruded profiles, in particular as aluminum extruded profiles, or alternatively as welded tubes. The aluminum extruded profile design, in particular, allows for virtually any configuration of the channels 6 and the webs 7 arranged between them.

[0038] The stationary liquid tank 1 can, for example, be part of a heat pump system 15. Overall, with the temperature control device 2 and the stationary liquid tank 1 according to the invention, a significantly improved temperature control of the liquid 3 can be achieved while maintaining the same (internal) volume of the flat tubes 5.

Claims

1. Stationary liquid tank (1) for a stationary heat pump system (15) having a tempering device (2) for tempering a liquid (3) in the liquid tank (1), the tempering device having at least one flat tube (5) which is connected to the outside of the liquid tank (1) in a heat-transmitting manner and which has channels (6) with a respective channel width bK and webs (7) with a respective web width bS, - wherein between the flat tube (5) and the liquid tank (1), a heat distribution plate (10) is arranged which is connected over its entire surface to the flat tube (5) and the liquid tank (1), - wherein the heat distribution plate (10) is connected to an outer side of the liquid tank (1) via a heat-conducting layer (11), - wherein the heat distribution plate (10) has a thermal conductivity λv and a thickness dv, - wherein the heat-conducting layer (11) has a thermal conductivity λw and a thickness dw, - wherein at least two flat tubes (5) are wound in parallel around the stationary liquid tank (1), wherein a spacing s is provided between two flat tubes (5), - wherein, for the ratio of thermal conductivity of the heat distribution plate (10) in the axial direction and the heat distribution plate (10) in the radial direction, the following applies: 0.25 ⋅ λ v ⋅ d v / s < λ w ⋅ s / d w < 4 ⋅ λ v ⋅ d v / s , or - wherein the flat tube (5) is made of a material having a tensile strength Rm, - wherein the flat tube (5) has a bursting pressure PBERST,MIN as required by the standard / specification, - wherein the flat tube (5) with the channels (6) and webs (7) is designed such that it satisfies the following equation 1.2 b k + tolerance / b s − tolerance ≤ R m / P BERST , MIN where tolerance = manufacturing tolerances.

2. Stationary liquid tank according to claim 1, first alternative, characterized in that - the following applies: (0.5 · λv · dv / s) < (λw · s / dw) < (2 · λv · dv / s).

3. Stationary liquid tank according to claim 1, first alternative, or according to claim 2, characterized in that the heat distribution plate (10) is soldered to the flat tube (5).

4. Stationary liquid tank according to any one of the preceding claims, characterized in that the channels (6) have a square, a rectangular or a round cross-section.

5. Stationary liquid tank according to any one of the preceding claims, characterized in that the flat tube (5) has an insulation (14) on an outer side facing away from the stationary liquid tank (1).

6. Stationary liquid tank according to any one of the preceding claims, characterized in that the tempering device (2) has a refrigerant circuit, wherein the flat tube (5) forms a part of the refrigerant circuit.

7. Stationary liquid tank according to any one of the preceding claims, characterized in that the flat tube (5) is designed as an extruded profile or as a welded tube.

8. Stationary liquid tank according to any one of the preceding claims, characterized in that the liquid tank (1) has a wall with a steel core (12) and an internal and / or external enamel coating (13).

9. Stationary liquid tank according to any one of the preceding claims, characterized in that the stationary liquid tank (1) is designed as a water tank, in particular as a service water tank.

10. Heat pump system (15) having a stationary liquid tank (1) according to any one of the preceding claims.

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