Dual zone heat storage for district heating systems with reduced differential pressure variations at the intermediate roof

Abstract

Shown and described is a two-zone heat storage device for district heating systems, comprising a container (1) which can be connected to at least one heat-emitting system and at least one heat-absorbing system and which has a container wall (2) and a base (3), wherein the container (1) has an upper zone (4) and a lower zone (5), wherein an intermediate roof (6) is arranged between the upper zone (4) and the lower zone (5), wherein the lower zone (5) has at least one lower loading and unloading device (8) and at least one upper loading and unloading device (7), wherein the upper zone (4) and the lower zone (5) are connected to one another via at least one first equalizing line (11'), and wherein the upper zone (4) and the lower zone (5) can be filled with a heat transfer medium, as well as a method for operating a two-zone heat storage device.In order to be able to adjust the differential pressure at the intermediate roof within narrower tolerance limits during normal operation of the two-zone heat storage device, the two-zone heat storage device has a circulation pump (15) for flowing heat transfer medium through the at least one first equalization line (11') and a first equalization pump (16) for conveying heat transfer medium from the lower zone (5) into the upper zone (4), wherein the circulation pump (15) is designed to convey heat transfer medium from the upper zone (4) through the first equalization line (11') in the direction of the lower zone (5).

Description

[0001] The present invention relates to a two-zone heat storage unit for district heating systems, comprising a container which can be connected to at least one heat-emitting system and at least one heat-absorbing system and which has a container wall and a base, wherein the container has an upper zone and a lower zone, wherein an intermediate roof is arranged between the upper zone and the lower zone, wherein the lower zone has at least one lower loading and unloading device and at least one upper loading and unloading device, wherein the upper zone and the lower zone are connected to one another via a first equalizing line and wherein the upper zone and the lower zone can be filled with a heat transfer medium. The present invention further relates to a method for operating a two-zone heat storage unit.

[0002] District heating systems provide heat for heating and hot water supply, particularly for residential and office buildings. Heat suppliers such as combined heat and power plants generate heat at a relatively constant level and feed it into a district heating system. However, consumers' heat demand is significantly higher during the day than at night, and even during the day, the demand for district heating fluctuates considerably. For example, some consumers experience morning consumption peaks that are regularly around three times higher than the nighttime heat demand. Heat storage systems are used to absorb these power peaks while maintaining a nearly constant heat feed into the district heating systems. Heat can be added to these heat storage systems when consumer demand for heat is lower than the heat provided by the heat suppliers. Conversely, heat can be withdrawn from the heat storage systems during power peaks.A wide variety of heat storage systems for these applications are already known. During operation, such heat storage systems are filled with a fluid, such as water, that serves as a heat transfer medium. The fluid is relatively cold in the lower part of the storage system and relatively warm in the upper part. Heat is supplied by adding warm fluid to the upper part, while simultaneously removing cold fluid from the lower part of the heat storage system. If heat is to be removed from the storage system, warm fluid is removed from the upper part, while cold fluid is supplied to the lower part.

[0003] The present invention relates to a two-zone heat storage device, as described, for example, in EP 2 698 584 B1. Two-zone heat storage devices are formed from a container that is divided into an upper and a lower zone. An intermediate roof is arranged between the upper and lower zones, so that a first chamber is created in the upper zone and a second chamber in the lower zone. During operation, a heat transfer medium, such as water, which has a temperature of approximately 60 to 100 degrees Celsius, is located in the upper zone. During operation, the lower zone is also filled with the heat transfer medium, which, however, can have a temperature of over 100 degrees Celsius. Due to the dead weight of the heat transfer medium in the upper zone, pressure is exerted from the upper zone to the lower zone.This ensures that the heat transfer medium in the lower zone does not begin to boil, even at temperatures exceeding 100 degrees Celsius. Dual-zone heat storage systems therefore have the advantage of being able to store a heat transfer medium with a temperature exceeding 100 degrees Celsius without the need to pressurize the container.

[0004] The lower zone has at least one lower loading and unloading device and at least one upper loading and unloading device. If heat is to be added to the two-zone heat storage system, a hot heat transfer medium, such as hot water, is supplied to the lower zone via the upper loading and unloading device, while a relatively cold heat transfer medium, such as cold water, is removed via the lower loading and unloading device. When heat is removed from the two-zone heat storage system, this process is reversed.

[0005] The density and thus the volume of heat transfer media such as water are temperature-dependent. In the temperature ranges relevant to this application, the density of fluids such as water decreases with increasing temperature. If heat is supplied to the two-zone heat storage unit according to the principle described above, the density of the heat transfer medium located in the lower zone decreases. To compensate for the volume change resulting from the changing density, two-zone heat storage units have at least one so-called first equalization line, which connects the upper zone with the lower zone. When heat is supplied, part of the heat transfer medium can escape into the upper zone through the at least one first equalization line.If heat is extracted from the dual-zone heat storage tank, causing the density of the heat transfer medium in the lower zone to increase, a portion of the heat transfer medium in the upper zone flows into the lower zone via at least one first equalizing line. This principle ensures that the minimum and maximum pressures of the lower zone are not exceeded or undercut, thus preventing evaporation and failure of the tank.

[0006] A key component of the two-zone storage tank is the intermediate roof, which separates the upper and lower zones. The intermediate roof is firmly attached to the tank and is pressurized with heat transfer medium on its top and bottom. Pressure acts on the intermediate roof from above due to the weight of the heat transfer medium in the upper zone. Internal pressure acts from below, which is created by the heat transfer medium in the lower zone. The pressure from above and the pressure from below creates a differential pressure at the intermediate roof. The intermediate roof is designed for a specific differential pressure range, so that during operation it must always be ensured that the differential pressure on the intermediate roof remains within the permissible range.

[0007] The differential pressure at the intermediate roof is determined, among other things, by the different weights of the water columns in the lower zone. As described above, the change in the density of the heat transfer medium when heat is extracted from or supplied to the two-zone heat storage system is compensated for by a fluid exchange between the upper zone and the lower zone via the at least one first equalization line. This results in a fluctuating temperature of the heat transfer medium located in the at least one first equalization line. This leads to changes in the density of the heat transfer medium located in the at least one first equalization line, which in turn leads to fluctuating ground pressure. In addition, the weight of the water column (when water is used as the heat transfer medium) in the lower zone changes when heat is extracted from and supplied to the two-zone heat storage system.into the two-zone heat storage tank, which also affects the differential pressure at the intermediate roof.

[0008] In addition to the normal fluctuations in the differential pressure at the intermediate roof that occur during operation, unforeseeable incidents can also affect the differential pressure at the intermediate roof. For example, pressure surges in the connected district heating system, which propagate via the connecting pipes into the dual-zone heat storage system, or differing flow rates in the loading and unloading systems, lead to fluctuations in the differential pressure at the intermediate roof. The intermediate roof must therefore be dimensioned to safely withstand the loads caused by incidents. Dimensioning the intermediate roof accordingly is complex and expensive.

[0009] Against this background, the present invention is based on the object of designing and developing the aforementioned and previously described dual-zone heat storage system in such a way that, during normal operation of the dual-zone heat storage system, the differential pressure at the intermediate roof can be adjusted within narrower tolerance limits, so that the design limits of the intermediate roof can be better utilized for fault situations. Furthermore, the invention is based on the object of specifying a method for operating a dual-zone heat storage system that ensures that the differential pressure at the intermediate roof remains within the narrowest possible limits during normal operation.

[0010] The above-mentioned object is achieved according to the invention by a two-zone heat storage device for district heating systems according to the preamble of claim 1, which has a circulation pump for flowing through the at least one first equalization line with heat transfer medium and a first equalization pump for conveying heat transfer medium from the lower zone into the upper zone, wherein the circulation pump is designed to convey heat transfer medium from the upper zone through the at least one first equalization line in the direction of the lower zone.

[0011] The above-mentioned object is further achieved according to the invention by a method for operating a corresponding two-zone heat storage device, in which a circulation pump causes a heat transfer medium to flow through at least one first equalizing line from an upper zone of the two-zone heat storage device in the direction of a lower zone of a two-zone heat storage device, when heat is supplied to the two-zone heat storage device, a first equalizing pump conveys heat transfer medium from the lower zone into the upper zone, and when heat is removed from the two-zone heat storage device, heat transfer medium flows from the upper zone through the at least one first equalizing line into the lower zone.

[0012] The invention has recognized that additional pumps can be used to set a substantially constant temperature in the at least one first equalization line, so that fluctuations in the pressure difference caused by loading and unloading processes at the intermediate roof can be reduced. In the present application, a constant temperature means a temperature which, although it can fluctuate over the course of the year, for example depending on the outside temperature and the associated temperature changes in the upper zone, but which is not subject to sudden changes caused by loading and unloading processes of the two-zone storage tank. By avoiding the sudden temperature changes in the at least one first equalization line that usually occur during loading and unloading, the sudden changes in the differential pressure at the intermediate roof that also usually occur during loading and unloading can be avoided.

[0013] Furthermore, the invention has recognized that it is advantageous if the temperature of the heat transfer medium in the at least one first equalizing line is determined by the temperature of the upper zone. This is not subject to sudden changes due to loading and unloading processes, which would affect fluctuations in the differential pressure at the intermediate roof. Furthermore, the temperature of the heat transfer medium in a lower region of the upper zone is typically higher than the temperature in a lower region of the lower zone, so that the temperature difference between the heat transfer medium in the at least one first equalizing line and the lower zone is comparatively small if the temperature in the at least one first equalizing line is determined by the upper zone. This brings about a reduction in the differential pressure at the intermediate roof.

[0014] According to the invention, a first equalization pump pumps heat transfer medium from the lower zone to the upper zone when heat is supplied to the two-zone heat storage tank. The first equalization pump should be controlled in such a way that the volume equalization required when charging the two-zone heat storage tank from the lower zone to the upper zone is always completely carried out by the first equalization pump. Accordingly, the temperature in the at least one first equalization line is not affected when charging the two-zone heat storage tank. When discharging the two-zone heat storage tank, heat transfer medium must be transported from the upper zone to the lower zone.Since the circulation pump causes heat transfer medium to flow through the at least one first equalization line from the upper zone toward the lower zone, and the temperature in the at least one first equalization line is determined by the temperature of the upper zone, heat transfer medium can flow from the upper zone to the lower zone via the at least one first equalization line when the two-zone heat storage unit is discharged. Since in this case, only heat transfer medium flows from the upper zone to the lower zone, this process has no significant influence on the temperature in the at least one first equalization line.

[0015] In a dual-zone storage system according to the invention, a constant temperature can be maintained in the first, at least one, equalization line during charging and discharging of the storage system. This prevents large, sudden changes in ground pressure during charging and discharging of the dual-zone storage system. This, in turn, reduces fluctuations in the differential pressure at the intermediate roof.

[0016] Since the temperature in the at least one first equalizing line is determined by the temperature of the upper zone, a smaller temperature difference is established between the heat transfer medium located in the at least one first equalizing line and the heat transfer medium located in the lower zone of the two-zone heat storage system compared to the prior art. This smaller temperature difference has a positive effect on the load on the intermediate roof.

[0017] If the dual-zone heat storage system has more than one first equalization line, the circulation pump should be designed so that the circulation pump can flow through all of the first equalization lines. Alternatively, a separate circulation pump can be provided for each first equalization line.

[0018] Various embodiments of the dual-zone heat storage device and the method are described below. Each of the individual embodiments applies independently to the dual-zone heat storage device and the method. Furthermore, the individual embodiments can be combined with one another as desired.

[0019] Particularly preferably, the at least one first compensating line opens into the upper zone in the lower region of the upper zone, wherein in particular the end of the at least one first compensating line assigned to the upper zone is arranged in a lower half, preferably in a lower third, even more preferably in a lower quarter, particularly preferably in a lower fifth, further preferably in a lower tenth, and even more preferably in a lower twentieth of the upper zone. Any temperature fluctuations that may occur in the at least one first compensating line in this case have a comparatively minor effect on the differential pressure at the intermediate roof.

[0020] It is also advantageous if a pipe leading from the pressure side of the circulation pump flows into the upper zone in the lower half, preferably in the lower third, even more preferably in the lower quarter, and especially preferably in the lower fifth of the upper zone. The closer the pipe leading from the pressure side of the circulation pump flows into the upper zone at the intermediate roof, the less turbulence is caused in the hot layer of the upper zone below the water level.

[0021] A circulation line formed by the pipes extending from the pressure side and the suction side of the circulation pump can be relatively small in diameter compared to the at least one first equalizing line. The amount of heat transfer medium pumped by the circulation pump should be sufficiently large that the temperature in the at least one first equalizing line does not change significantly, even during loading and unloading processes.

[0022] In a preferred embodiment of the invention, it is provided that a pipeline extending from a suction side of the circulation pump opens into an end region of the at least one first compensation line assigned to the lower zone. In In this case, the circulation pump essentially completely circulates the at least one first equalization line with heat transfer medium, so that a substantially constant temperature is established throughout the entire at least one first equalization line. This has a positive effect on the pressure difference and pressure fluctuations at the intermediate roof.

[0023] Advantageously, a suction side of the first compensating pump is connected to the storage line provided at the lower loading and unloading device, with a pressure side of the first compensating pump particularly preferably being connected to the upper zone via a nozzle. In this configuration, the first compensating pump draws heat transfer medium directly from the storage line provided at the lower loading and unloading device when charging the two-zone heat storage unit and transports it to the upper zone. Accordingly, relatively cold heat transfer medium is transported from the lower zone to the upper zone. This has a positive effect on the thermal stratification in the lower zone.

[0024] In a particularly advantageous embodiment of the invention, a second, in particular external, equalization line is provided for connecting the upper zone with the lower zone, wherein the second equalization line has a shut-off valve, in particular arranged in a lower region of the second equalization line. This valve is shut off during normal operation of the two-zone heat storage tank. The valve of the second equalization line can be opened in the event of a malfunction, so that additional connection cross-section between the upper and lower zones is released and the flow of the equalization quantity is facilitated. This reduces the impact on the intermediate roof. Malfunctions include, for example, pressure surges in the connected district heating system, which continue into the tank via connecting lines.

[0025] Pressure surge events regularly spread so rapidly that timely detection via pressure measurements is difficult. For this reason, it is particularly advantageous to consider other scenarios that could lead to a pressure surge when controlling the valve of the second equalizing line. For example, a failure of a pump group can lead to a different flow rate in the upper and lower loading and unloading devices. In this case, it is advantageous to open the valve of the second equalizing line as a preventative measure. The same applies to the detection of a power failure.

[0026] Advantageously, the nominal width of the second compensating line corresponds at least to the nominal width of the at least one first compensating line, wherein the nominal width of the second compensating line is preferably at least 20 percent, more preferably at least 40 percent and even more preferably at least 60 percent larger than the nominal width of the at least one first compensating line.

[0027] This ensures that the second compensating line has a sufficiently large cross-section to absorb pressure surges.

[0028] Particularly preferably, the second equalization line is integrated, at least in sections, into the circulation of the heat transfer medium caused by the circulation pump in the at least one first equalization line. When the valve of the second equalization line is opened, the temperature in the at least one first and second equalization lines should be as similar as possible to avoid additional pressure surges when the valve of the second equalization line is opened. This can be achieved by allowing the heat transfer medium, which is conveyed by the circulation pump through the at least one first equalization line, to flow through the second equalization line, at least in sections.

[0029] Alternatively or additionally, the second equalizing line can have its own circulation device for the heat transfer medium to flow through the second equalizing line. This circulation device should ensure that a temperature comparable to that in the first equalizing line is maintained in the second equalizing line. If, for example, heat transfer medium from the upper zone flows through the at least one first equalizing line, it is advantageous if the circulation device of the second equalizing line also implements this.

[0030] In an advantageous embodiment of the method, the circulation pump is controlled. Since the circulation pump is configured so that, during operation, heat transfer medium flows from the upper zone through the at least one first equalizing line toward the lower zone, the circulation pump does not necessarily need to be controlled. The circulation pump can constantly pump heat transfer medium through the at least one first equalizing line. When discharging the two-zone heat storage system, the circulation pump can be switched off or turned down, as long as it is ensured that heat transfer medium flows through the first equalizing line from top to bottom.

[0031] Particularly preferably, the method according to the invention provides that a valve of a second equalization line is opened in the event of a fault event, in particular if a pressure surge, different flow rates in the lower loading and unloading device and the upper loading and unloading device, or a power failure is detected. The valve of the second equalization line is shut off during normal operation of the dual-zone heat storage system. It should only be opened in the event of a fault event, so that additional connection cross-section between the upper and lower zones is released and the flow of the equalization flow is facilitated. This reduces the impact on the intermediate roof during a fault event.

[0032] Particularly preferably, the second equalizing line is flowed through by a heat transfer medium at a temperature that essentially corresponds to the temperature of the heat transfer medium in the at least one first equalizing line. This can be achieved either by the circulation pump or a dedicated circulation device. A dedicated circulation device can be implemented, for example, with a bypass with free circulation.

[0033] Further features and advantages of the two-zone heat storage systems and the methods will become apparent from the following description of embodiments, with reference to the attached drawings.

[0034] The drawing shows, schematically, Fig. 1 shows a two-zone heat storage device according to the prior art in a vertical section, Fig. 2A shows a first embodiment according to the invention in a vertical section, Fig. 2B shows a second embodiment according to the invention in a vertical section and Fig. 2C shows a third embodiment according to the invention in a vertical section.

[0035] Fig. 1 shows a two-zone heat storage unit for district heating systems according to the prior art. The two-zone storage unit comprises a tank 1 having a tank wall 2 and a base 3. The tank 1 can be connected to a heat-emitting system (not shown here) and a heat-absorbing system (also not shown here).

[0036] The tank 1 is divided into an upper zone 4 and a lower zone 5. An intermediate roof 6 is arranged between the upper zone 4 and the lower zone 5. The upper zone 4 and the lower zone 5 are filled with water W during operation. The water W serves as a heat transfer medium. In addition, the dead weight of the water W in the upper zone 4 exerts pressure on the lower zone 5. This enables hot water W to be stored in the lower zone 5 at temperatures of over 100 degrees Celsius without the need to pressurize the tank 1.

[0037] In the upper zone 4 and the lower zone 5, thermal layers form in the water W, since warm water has a lower density than cold water in the relevant temperature range. Accordingly, relatively cold water W is found at the bottom of the upper zone 4 and the lower zone 5, while layers of relatively hot water W form in the upper area of ​​the upper zone 4 and the lower zone 5. The temperature in the lower area of ​​the lower zone 5 is largely determined by the return temperature. The return temperature is the temperature of the cold water that is introduced into the lower zone when the two-zone heat storage tank is discharged. Typically, the lower zone 5 at the bottom has a lower temperature than the upper zone 4 near the intermediate roof 6.

[0038] The intermediate roof 6 is made of a thermally insulating and waterproof material so that the water W cannot pass through the intermediate roof 6 from the upper zone 4 to the lower zone 5 and vice versa. Due to the thermally insulating properties of the intermediate roof 6, heat conduction between the water W located in the upper zone 4 and the water W located in the lower zone 5 is largely prevented.

[0039] The intermediate roof 6 is firmly connected to the tank 1, for example by welding. Pressure acts on the intermediate roof 6 from above due to the dead weight of the water W located in the upper zone 4. An internal pressure acts from below, which is created by the water W located in the lower zone 5. The pressure from above and the pressure from below create a differential pressure at the intermediate roof 6. The intermediate roof 6 is designed for a specific differential pressure range, so that during operation it must always be ensured that the differential pressure on the intermediate roof 6 remains within the permissible range.

[0040] The lower zone 5 has an upper loading and unloading device 7 and a lower loading and unloading device 8. The upper loading and unloading device 7 has an upper storage line 9, and the lower loading and unloading device 8 has a lower storage line 10. The heat transfer medium, which in the example shown is water W, can be introduced into the lower zone 5 and discharged therefrom through the loading and unloading devices 7 and 8. The upper storage line 9 is also referred to as the flow line, and the lower storage line 10 as the return line.

[0041] In Fig. 1 The flow directions that occur during heat dissipation are indicated by arrows. When heat is removed from the two-zone heat storage tank, warm water W exits the upper loading and unloading device 7 via the upper storage line 9. At the same time, essentially the same amount of cold water W, measured by weight, is introduced into the lower zone 5 via the lower loading and unloading device 8. The upper zone 4 and the lower zone 5 are connected to one another via a first equalizing line 11. Warm water has a lower density than cold water. Accordingly, when heat is removed from the two-zone heat storage tank, the density of the water W in the lower zone 5 decreases. To compensate for this density and associated volume difference, water W flows from the upper zone 4 through the first equalizing line 11 into the lower zone 5.

[0042] When heat is supplied to the two-zone heat storage tank, the described process is reversed. In this case, relatively hot water W is supplied to the lower zone 5 via the upper loading and unloading device 7, while relatively cold water W is discharged from the lower zone 5 via the lower loading and unloading device 8. The temperature change in the water W occurring in the lower zone 5 reduces the density of the water W, so that water W flows from the lower zone 5 to the upper zone 4 via the first equalization line 11.

[0043] The differential pressure at the intermediate roof 6 is determined, among other things, by the different weights of the water columns in the lower zone 5. When heat is extracted from and supplied to the dual-zone heat storage tank, fluctuations in the temperature of the water W in the first equalization line 11 occur. This leads to fluctuating ground pressure. Furthermore, the weight of the water column in the lower zone 5 changes when heat is extracted from and supplied to the dual-zone heat storage tank, which also affects the differential pressure at the intermediate roof 6.

[0044] A plate 12 is arranged above the first equalization line 11, which prevents the water W flowing from the lower zone 5 into the upper zone 4 from reaching the water surface in the upper zone 4. The first equalization line 11 has two further openings 13 in the upper zone 4 next to its upper end. These serve to direct the water W flowing from the lower zone 5 into the upper zone 4, where similar temperature conditions prevail. In this way, the formation of vortices and the associated disturbance of the thermal layers in the upper zone 4 can be reduced.

[0045] The first equalization line 11 is designed and arranged such that it ends just below the water level that occurs in the upper zone 4 when the two-zone heat storage tank is filled. This ensures that when the two-zone heat storage tank is filled, water W can always flow from the upper zone 4 to the lower zone 5 when heat is removed, and a pressure drop in the lower zone 5 is reliably prevented. The first equalization line 11 ends on the other side in the lower zone 5 just above the bottom 3 of the tank 1. This ensures that when heat is supplied to the two-zone heat storage tank, the coldest possible water W flows from the lower zone 5 to the upper zone 4.

[0046] In addition, the dual-zone heat storage unit has a discharge pipe 14, one end of which is located at an upper section of the lower zone 5 and the other end of which is located at an upper section of the upper zone 4. The discharge pipe 14 serves to vent the lower zone 5.

[0047] In Fig. 2A A first embodiment of a two-zone heat storage device according to the invention is shown, the structure of which largely corresponds to the structure of the two-zone heat storage device from Fig. 1 Thus, the two-zone heat storage device according to the invention comprises Fig. 2A also a container 1 with a container wall 2 and a base 3. The container 1 has an upper zone 4 and a lower zone 5, which are separated from each other by an intermediate roof 6. The lower zone 5 has an upper loading and unloading device 7 with an upper storage line 9 and a lower loading and unloading device 8 with a lower storage line 10, via which hot or cold water W is introduced into or removed from the lower zone 5 in the manner described above when heat is added or removed. The upper zone 4 and the lower zone 5 are connected to each other via a first equalizing line 11'. The Fig. 2A shown two-zone heat storage has a discharge pipe 14. The discharge pipe 14 is used to vent the lower zone 5. The Fig. 2 The two-zone heat storage tank shown is shown in a state filled with water W, although other heat transfer media may also be suitable.

[0048] In contrast to the prior art two-zone heat storage device, the two-zone heat storage device according to the invention has a circulation pump 15 for flowing water W through the first equalization line 11'. Furthermore, the two-zone heat storage device according to the invention comprises a first equalization pump 16 for conveying water W from the lower zone 5 to the upper zone 4.

[0049] The circulation pump 15 is connected on its suction side 17a via a pipe 18 to an end region 19 of the first equalizing line 11' assigned to the lower zone 5. The circulation pump 15 can thus suck in the water W located at the lower end 19 of the equalizing line 11'. A pipe 20 extending from a pressure side 17b of the circulation pump 15 opens into the upper zone 4 near the end 21 of the first equalizing line 11' assigned to the upper zone 4. However, it is also possible to arrange the pipe 20 such that it does not open into the upper zone 4 near the end 21 of the first equalizing line 11' assigned to the upper zone 4. During operation, the circulation pump 15 sucks water W from the lower area 19 of the equalizing line 11' and pumps it into the lower area of ​​the upper zone 4. There, water W flows from the upper zone 4 into the first equalizing line 11' in the direction of the lower zone 5.The temperature of the upper zone 4 is set in the first equalization line 11'.

[0050] In the embodiment shown here, the first equalizing line 11' opens into the upper zone 4 in the lower region of the upper zone 4, preferably in the lower tenth or a lower twentieth of the upper zone 4, i.e. well below the liquid level of the water W in the upper zone 4. The pipe 20 extending from the pressure side 17b of the circulation pump 15 also opens into the upper zone 4 in a lower region of the upper zone 4, preferably in the lower fifth of the upper zone 4. This avoids turbulence in the hot layer below the water level in the upper zone 4.

[0051] The first compensating pump 16 is connected on its suction side 22a via a pipeline 23 to a storage line 10 provided on the lower loading and unloading device 8. On its pressure side 22b, the first compensating pump 16 is connected to the upper zone 4 via a pipeline 24 and a nozzle 25.

[0052] The circulation pump 15 ensures that the first equalization line 11' is always flowed through with water W from the upper zone 4 towards the lower zone 5, so that the temperature in the first equalization line 11' is always determined by the upper zone 4. When heat is supplied to the two-zone heat storage tank, the first equalization pump 16 pumps water W from the lower storage line 10 into the upper zone 4, so that no significant temperature fluctuations occur in the equalization line 11'. When heat is removed from the two-zone heat storage tank, the circulation pump 15 can either be switched off briefly, so that the circulation of water W through the first equalization line 11' is briefly achieved through volume equalization. Alternatively, the circulation pump 15 can be turned down.Since during volume equalization during heat dissipation only water W flows from the upper zone 4 into the lower zone 5, the process has no significant influence on the temperature in the first equalization line 11'.

[0053] As a result, a relatively constant temperature can be set in the first equalization line 11', which only changes when the temperature of the water W in the upper zone 4 fluctuates. Such temperature fluctuations occur throughout the year, for example, due to a changing outside temperature. Short-term temperature jumps are not to be expected in the upper zone 4. By keeping the temperature in the first equalization line 11' at a relatively constant level, sudden changes in the differential pressure at the intermediate roof 6 can also be avoided.

[0054] Furthermore, setting the temperature in the first equalization line 11' at the level of the upper zone 4 reduces the pressure difference at the intermediate roof 6 compared to setting a temperature level of the lower area of ​​the lower zone 5, since the temperature in the lower area of ​​the upper zone 4 is regularly higher than the temperature in the lower area of ​​the lower zone 5 and thus closer to the average temperature in the lower zone 5. For this reason, the design limits of the intermediate roof 6 can be better utilized for fault situations.

[0055] In Fig. 2B a second embodiment of a two-zone heat storage device according to the invention is shown, the structure of which largely corresponds to the structure of the two-zone heat storage device from Fig. 2A The Fig. 2B The embodiment shown differs from the one in Fig. 2A shown two-zone heat storage tank by a second external equalization line 26, which connects the upper zone 4 with the lower zone 5. In the Fig. 2B In the circuit diagram shown on the left, the second compensating line 26 is shown as a thick line.

[0056] The second equalization line 26 has a nominal diameter of the same order of magnitude as that of the first equalization line 11' and, during normal operation, is sealed off by a valve 27 located in the lower area of ​​the second equalization line 26. If a fault occurs, the valve 27 opens as quickly as possible and releases an additional connecting cross-section between the upper zone 4 and the lower zone 5 in order to facilitate equalizing flows between the upper zone 4 and the lower zone 5. This reduces the impact on the intermediate roof 6. Fault events include, for example, pressure surges in the connected district heating system, which continue into the tank 1 via connecting lines.

[0057] The pressure surges caused by accidental events can spread so quickly that timely detection via normal pressure measurements in the dual-zone storage tank is not possible. For this reason, other scenarios that could lead to a pressure surge are also considered when controlling the valve 27 of the second equalizing line 26. For example, a failure of a pump group can lead to a different flow rate in the upper and lower loading and unloading devices 7, 8, so it is advantageous to preventively open the valve 27 of the second equalizing line 26 in the event of a pump group failure. The same applies to the detection of a power failure.

[0058] The temperature in the second equalization line 26 and the first equalization line 11' should be as identical as possible when opening the valve 27 of the second equalization line 26, in order to avoid additional pressure surges caused by different temperatures when opening. In order to set the water temperature in the two equalization lines 11', 26 to as identical a level as possible, the second equalization line 26 is Fig. 2B In the embodiment shown, the first equalizing line 11' is integrated into the circulation of the first equalizing line 11'. This is achieved by the pipe 20 extending from the pressure side 17b of the circulation pump 15 opening into the second equalizing line 26 above the fitting 27 of the second equalizing line 26.

[0059] In the Fig. 2B In the illustrated embodiment, during normal operation, the circulation pump 15 draws water from the lower region of the first equalization line 11' and pumps it through the upper part of the second equalization line 26 into the upper zone 4. By withdrawing water W at the lower end of the first equalization line 11', water W continuously flows from the upper zone 4 into the first equalization line 11'. As a result, the upper zone 4 determines both the temperature in the first equalization line 11' and, at least to a large extent, that of the second equalization line 26.

[0060] The Fig. 2C The embodiment shown differs from the one in Fig. 2Billustrated two-zone heat storage tank only insofar as the second equalizing line 26 is not integrated into the circulation by the circulation pump 15, but has its own circulation device. In the case shown here, the circulation device is provided by a pipe 28 which connects the sections of the second equalizing line 26 upstream of the valve 27 of the second equalizing line 26 and downstream of the valve 27 of the second equalizing line 26. The pipe 28 has a significantly smaller nominal diameter than the second equalizing line 26 and can be opened and closed using a valve 29. When the valve 29 is opened, the pipe releases a connecting cross-section between the upper zone 4 and the lower zone 5 and is freely circulated. Alternatively, the circulation device can also be equipped with its own pump. List of reference symbols:

[0061] 1 Tank 2 Tank wall 3 Floor 4 Upper zone 5 Lower zone 6 Intermediate roof 7 Upper loading and unloading device 8 Lower loading and unloading device 9 Storage line of the upper loading and unloading device 7 10 Storage line of the lower loading and unloading device 8 11 First equalizing line 11' First equalizing line 12 Plate 13 Openings 14 Discharge pipe 15 Circulation pump 16 First equalizing pump 17a Suction side of the circulation pump 15 17b Pressure side of the circulation pump 15 18 Pipe 19 End area of ​​the first equalizing line 11' assigned to lower zone 5 20 Pipe 21 End of the first equalizing line 11' assigned to upper zone 4 22a Suction side of the first equalizing pump 16 22b Pressure side of the first equalizing pump 16 23Pipe 24Pipe 25Pipe connection 26Second compensation line 27Valve of the second compensation line 26 28Pipe 29Valve of the pipe 28

Claims

1. A two-zone heat storage device for district heating systems, comprising a container (1) connectable to at least one heat-emitting system and at least one heat-absorbing system, having a container wall (2) and a base (3), wherein the container (1) has an upper zone (4) and a lower zone (5), wherein an intermediate roof (6) is arranged between the upper zone (4) and the lower zone (5), wherein the lower zone (5) has at least one lower loading and unloading device (8) and at least one upper loading and unloading device (7), wherein the upper zone (4) and the lower zone (5) are connected to one another via at least one first equalizing line (11'), and wherein the upper zone (4) and the lower zone (5) can be filled with a heat transfer medium, characterized in thatthe two-zone heat accumulator has a circulation pump (15) for flowing heat transfer medium through the at least one first equalizing line (11') and a first equalizing pump (16) for conveying heat transfer medium from the lower zone (5) into the upper zone (4), wherein the circulation pump (15) is designed to convey heat transfer medium from the upper zone (4) through the first equalizing line (11') in the direction of the lower zone (5).

2. Two-zone heat storage according to claim 1, characterized in thatthe at least one first compensating line (11') opens into the upper zone (4) in the lower region of the upper zone (4), wherein in particular an end (21) of the at least one first compensating line (11') assigned to the upper zone (4) is arranged in a lower half, preferably in a lower third, more preferably in a lower quarter, particularly preferably in a lower fifth, further preferably in a lower tenth and even more preferably in a lower twentieth of the upper zone (4).

3. Two-zone heat storage according to claim 1 or 2, characterized in that a pipeline (20) extending from the pressure side (17b) of the circulation pump (15) opens into the upper zone (4) in the lower half, preferably in the lower third, more preferably in the lower quarter and particularly preferably in the lower fifth of the upper zone (4).

4. Two-zone heat storage according to one of the preceding claims, characterized in thata pipeline (18) connects a suction side (17a) of the circulation pump (15) to the at least one first equalizing line (11') in the lower zone (5), wherein the pipeline (18) preferably opens into the at least one first equalizing line (11') at an end region (19) of the at least one first equalizing line (11') assigned to the lower zone (5).

5. Two-zone heat storage according to one of the preceding claims, characterized in that a suction side (22a) of the first compensating pump (16) is connected to a storage line (10) provided on the lower loading and unloading device (8), wherein particularly preferably a pressure side (22b) of the first compensating pump (16) is connected to the upper zone (4) via a nozzle (25).

6. Two-zone heat storage according to one of the preceding claims, characterized in thata second, in particular external, compensating line (26) is provided for connecting the upper zone (4) to the lower zone (5), wherein the second compensating line (26) has a valve (27) for shutting off, in particular arranged in a lower region of the second compensating line (26).

7. Two-zone heat storage according to claim 6, characterized in that the nominal width of the second compensating line (26) corresponds at least to the nominal width of the at least one first compensating line (11'), wherein the nominal width of the second compensating line (26) is preferably at least 20 percent, more preferably at least 40 percent and even more preferably at least 60 percent larger than the nominal width of the at least one first compensating line (11').

8. Two-zone heat storage according to claim 6 or 7, characterized in thatthe second compensating line (26) is at least partially integrated into the circulation of the heat transfer medium through the at least one first compensating line (11') caused by the circulation pump (15).

9. Two-zone heat storage device according to one of claims 6 to 8, characterized by that the second compensating line (26) has its own circulation device for flowing heat transfer medium through the second compensating line (26).

10. Method for operating a two-zone heat storage device according to one of claims 1 to 9, characterized in thata circulation pump (15) causes a heat transfer medium to flow through at least one first equalizing line (11') from an upper zone (4) of the two-zone heat accumulator in the direction of a lower zone (5) of a two-zone heat accumulator, when heat is supplied to the two-zone heat accumulator, a first equalizing pump (16) conveys heat transfer medium from the lower zone (5) into the upper zone (4), and when heat is removed from the two-zone heat accumulator, heat transfer medium flows from the upper zone (4) through the at least one first equalizing line (11') into the lower zone (5).

11. Method according to claim 10, characterized in that the circulation pump (15) is controlled.

12. Method according to one of claims 10 or 11, characterized in thata valve (27) of a second compensating line (26) is opened in the event of a fault event, in particular when a pressure surge, different flow rates in a lower loading and unloading device (8) and an upper loading and unloading device (7) or a power failure are detected.

13. Method according to claim 12, characterized in that the second equalization line (26) is flowed through with heat transfer medium having a temperature which substantially corresponds to the temperature of the heat transfer medium in the at least one first equalization line (11').

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