Two zone heat storage for district heating systems with reduced differential pressure 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 unit, the two-zone heat storage unit has a circulation pump (15) for flowing heat transfer medium through the at least one first equalization line (11'), a first equalization pump (16) for conveying heat transfer medium from the lower zone (5) into the upper zone (4) and a second equalization pump (17) for conveying heat transfer medium from the upper zone (4) into 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.

[0003] 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.

[0004] 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.

[0005] 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.

[0006] 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.

[0007] 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.

[0008] 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.

[0009] 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.

[0010] 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.

[0011] 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 heat transfer medium through the at least one first equalization line, a first equalization pump for conveying heat transfer medium from the lower zone to the upper zone and a second equalization pump for conveying heat transfer medium from the upper zone to the lower zone.

[0012] 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, when heat is supplied to the two-zone heat storage device, a first equalizing pump conveys heat transfer medium from the lower zone to the upper zone, and when heat is removed from the two-zone heat storage device, a second equalizing pump conveys heat transfer medium from the upper zone to the lower zone.

[0013] The invention has recognized that the fluctuations in the pressure difference at the intermediate roof during loading and unloading processes can be reduced by additional pumps. According to the invention, when heat is supplied to the two-zone heat storage tank, the first equalizing pump pumps heat transfer medium from the lower zone to the upper zone, and when heat is removed from the two-zone heat storage tank, the second equalizing pump pumps heat transfer medium from the upper zone to the lower zone. The equalizing pumps should be controlled in such a way that it is always ensured that the volume equalization between the zones required during loading and unloading of the two-zone storage tank is completely carried out by the equalizing pumps. Accordingly, the temperature of the heat transfer medium in the at least one first equalizing line is not influenced by volume equalization between the zones. This has a positive effect on the differential pressure at the intermediate roof.

[0014] 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.

[0015] 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.

[0016] Particularly preferably, a control device for controlling the temperature of the heat transfer medium in the at least one first equalization line is provided. With active adjustment of the temperature of the heat transfer medium in the at least one first equalization line, the temperature can be approximated to the average temperature in the lower zone. The smaller the temperature difference between the heat transfer medium in the at least one first equalization line and in the lower zone, the lower the differential pressure at the intermediate roof. If the two-zone heat storage unit is fully loaded, so that the lower zone is hot throughout, the temperature in the at least one first equalization line should also be set relatively high, i.e. up to a maximum of boiling temperature. If the two-zone storage unit is completely discharged, so that the lower zone is relatively cold, the temperature in the at least one first equalization line can also be low, i.e.i.e., set to the return temperature. The return temperature corresponds to the temperature of the heat transfer medium flowing out of the two-zone heat storage tank via the lower loading and unloading device. The goal is always for the temperature in at least one first equalization line to approach the average temperature in the lower zone in order to reduce the differential pressure at the intermediate roof. In this way, the pressure difference at the intermediate roof can be set within even tighter tolerance limits, so that the intended design window of the intermediate roof can be better utilized as a reserve in case of emergency.

[0017] In a preferred embodiment of the invention, it is provided that a first pipeline originating from a pressure side of the circulation pump opens into an end region of the at least one first equalizing line assigned to the upper zone, a second pipeline connects a suction side of the circulation pump with the at least one first equalizing line in the lower zone, wherein the second pipeline preferably opens into the at least one first equalizing line at an end region of the at least one first equalizing line assigned to the lower zone, a third pipeline connects the suction side of the circulation pump with the lower zone, wherein the third pipeline opens into the lower zone in a lower region of the lower zone, a fourth pipeline connects the suction side of the circulation pump with a storage line provided on the upper loading and unloading device and the second,the third and fourth pipelines each have at least one control valve.,

[0018] In this advantageous embodiment of the invention, the circulation pump can selectively suck in heat transfer medium from the lower region of the at least one first equalizing line, from the lower region of the lower zone or from the storage line provided on the upper loading and unloading device, so that the temperature in the at least one equalizing line can be actively adjusted.

[0019] While the heat transfer medium in the upper loading and unloading device and the associated storage line is relatively hot, the heat transfer medium located in the lower region of the lower zone is relatively cold. If the heat transfer medium in the at least one first equalization line is to be set hotter, the valves in the second and third pipelines are closed, while the valve in the fourth pipeline is opened. If a reduction in the temperature of the heat transfer medium in the at least one first equalization line is desired, the valves in the second and fourth pipelines are closed and the valve in the third pipeline is opened. If the temperature is to be kept constant, only the valve in the second pipeline is opened.In this preferred embodiment of the invention, the temperature in the at least one first equalization line can be actively adjusted to the average temperature in the lower zone without the need for further heating or cooling devices to influence the temperature of the heat transfer medium in the at least one first equalization line.

[0020] Alternatively, the third and fourth pipes can also be connected to other locations in the dual-zone heat storage system where relatively cold or relatively hot heat transfer medium can be removed. For example, it would also be possible to connect the second pipe to a storage line of the lower loading and unloading device (also called a return line) and the third pipe to an upper area of ​​the lower zone. It is only important that relatively hot and relatively cold heat transfer medium can be provided on the suction side of the circulation pump as needed, in order to actively adjust the temperature in the at least one first equalization line.

[0021] If the two-zone heat storage system has more than one first equalization line, it should preferably be ensured that the heat transfer medium in all first equalization lines can be actively adjusted according to the principle described above.

[0022] When the second pipeline opens into the at least one first equalizing line at an end region of the at least one first equalizing line assigned to the lower zone, the circulation pump essentially completely circulates the heat transfer medium through the at least one first equalizing line, so that a substantially constant temperature is established throughout the at least one first equalizing line. This has a particularly positive effect on the pressure difference at the intermediate roof.

[0023] In the embodiment of the invention described above, it is particularly advantageous if a sensor for measuring the temperature of the heat transfer medium is arranged on the pressure side of the circulation pump. This sensor helps determine which valves in the second, third, and fourth pipelines should be opened or closed. Alternatively, a corresponding sensor can also be arranged at another suitable location. The control device can open and close the second, third, and fourth pipelines based on the values ​​measured by the sensor.

[0024] Particularly preferably, the at least one first equalizing 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 equalizing line associated with 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. In this way, the differential pressure at the intermediate roof can be particularly effectively reduced.

[0025] Preferably, the circulation pump is designed to transport heat transfer medium from the upper zone through the at least one first equalizing line toward the lower zone. In this case, the temperature in the at least one first equalizing line could also be determined solely by the temperature in the upper zone. In this way, it would be possible to reduce the fluctuations in the differential pressure at the intermediate roof even without actively controlling the temperature in the at least one first equalizing line.

[0026] The temperature in the upper zone is relatively constant. In this application, a relatively constant temperature means a temperature that may fluctuate throughout 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 due to charging and discharging processes in the two-zone storage tank. By avoiding the sudden temperature changes in the at least one first equalization line that usually occur during charging and discharging, the sudden changes in the differential pressure at the intermediate roof that also usually occur during charging and discharging can be avoided if the temperature in the at least one first equalization line is determined by the temperature in the upper zone.

[0027] Furthermore, in this case, a smaller temperature difference occurs 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 dual-zone heat storage system compared to the prior art dual-zone heat storage systems. This smaller temperature difference has a positive effect on the load on the intermediate roof.

[0028] 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.

[0029] Preferably, a pressure side of the second compensating pump is connected to the storage line provided on the lower loading and unloading device, with a pipe extending from the suction side of the second compensating pump preferably being connected to the nozzle of the upper zone. A corresponding embodiment of the invention also has a positive effect on the thermal stratification of the lower zone.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] This ensures that the second compensation line has a sufficiently large cross-section to absorb pressure surges.

[0034] 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.

[0035] 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 of at least one first equalizing line is set in the second equalizing line.

[0036] In an advantageous embodiment of the method, a control device increases the temperature of the heat transfer medium in the at least one first equalization line when heat is supplied to the two-zone heat storage device and reduces the temperature of the heat transfer medium in the at least one first equalization line when heat is removed from the two-zone heat storage device, wherein the temperature of the heat transfer medium in the at least one first equalization line is preferably adjusted to the average temperature of the heat transfer medium in the lower zone.

[0037] In this way, the temperature in the at least one first equalizing line can be brought closer to the average temperature of the lower zone. The smaller the temperature difference between the heat transfer medium in the at least one first equalizing line and in the lower zone, the lower the differential pressure at the intermediate roof. Accordingly, the intended design window of the intermediate roof can be better utilized as a reserve in case of emergency.

[0038] In a particularly advantageous embodiment of the method, a control valve of a second pipeline connecting a suction side of the circulation pump and the first equalization line is opened when the temperature of the heat transfer medium in the at least one first equalization line is to be kept at a constant level, a control valve of a third pipeline connecting the suction side of the circulation pump and a lower region of the lower zone is opened when the temperature of the heat transfer medium in the at least one first equalization line is to be reduced, and a control valve of a fourth pipeline connecting the suction side of the circulation pump and a storage line provided on an upper loading and unloading device is opened when the temperature of the heat transfer medium in the at least one first equalization line is to be increased.

[0039] In this advantageous embodiment of the method, the circulation pump selectively sucks in heat transfer medium from the lower region of the at least one first equalizing line, from the lower region of the lower zone or from the storage line provided on the upper loading and unloading device, so that the temperature in the at least one equalizing line can be actively adjusted.

[0040] While the heat transfer medium in the storage line provided for the upper loading and unloading device is relatively hot, the heat transfer medium located in the lower region of the lower zone is relatively cold. If the heat transfer medium in the at least one first equalization line is to be set hotter, the valves in the second and third pipes are closed, while the valve in the fourth pipe is opened. If a reduction in the temperature of the heat transfer medium in the at least one first equalization line is desired, the valves in the second and fourth pipes are closed and the valve in the third pipe is opened. If the temperature is to be kept constant, only the valve in the second pipe is opened.In this preferred embodiment of the invention, the temperature in the at least one first equalization line can be actively adjusted to the average temperature in the lower zone without the need for further heating or cooling devices to influence the temperature of the heat transfer medium in the at least one first equalization line.

[0041] Alternatively, the third and fourth pipes can also be connected to other locations in the dual-zone heat storage system where relatively cold or relatively hot heat transfer medium can be removed. For example, it would also be possible to connect the second pipe to a storage line of the lower loading and unloading device (also called a return line) and the third pipe to an upper area of ​​the lower zone. It is only important that relatively hot and relatively cold heat transfer medium can be provided on the suction side of the circulation pump as needed, in order to actively adjust the temperature in the at least one first equalization line.

[0042] Particularly preferably, the method according to the invention provides for a valve of a second equalization line to be 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 are 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.

[0043] Particularly preferably, the second equalizing line is flowed through by a heat transfer medium at a temperature that substantially corresponds to the temperature of the heat transfer medium in the at least one first equalizing line. This can be done either by the circulation pump or a dedicated circulation device.

[0044] 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.

[0045] 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 and Fig. 2B shows a second embodiment according to the invention in a vertical section.

[0046] 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).

[0047] 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.

[0048] 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 located 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.

[0049] Typically, the lower zone 5 at ground level has a lower temperature than the upper zone 4 near the intermediate roof 6.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] 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.

[0058] 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.

[0059] 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. 2A 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.

[0060] 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 into the upper zone 4 and a second equalization pump 17 for conveying water W from the upper zone 4 into the lower zone 5.

[0061] The first compensating pump 16 is connected on its suction side 18a via a pipeline 19 to a storage line 10 provided on the lower loading and unloading device 8. On its pressure side 18b, the first compensating pump 16 is connected to the upper zone 4 via a pipeline 20 and a nozzle 21.

[0062] The second compensating pump 17 is connected on its suction side 22a via a pipe 23 to the nozzle 21 of the upper zone 4 and on its pressure side 22b via a pipe 24 to the storage line 10 provided on the lower loading and unloading device 8.

[0063] The balancing quantities to be shifted between the upper and lower zones 4, 5 during loading and unloading of the two-zone heat storage tank are pumped into the respective zone via the first balancing pump 16 and the second balancing pump 17. When heat is supplied to the two-zone heat storage tank, the first balancing pump 16 pumps water W from the lower storage line 10 into the upper zone 4, so that no temperature fluctuations occur in the balancing line 11'. When heat is removed from the two-zone heat storage tank, the second balancing pump 17 pumps water from the upper zone 4 via the lower storage line 10 into the lower zone 5. The balancing pumps 16, 17 are controlled so that no balancing quantities are shifted via the first balancing line 11'.

[0064] A first pipeline 26 originating from a pressure side 25b of the circulation pump 15 opens into an end region 27 of the first equalizing line 11' assigned to the upper zone 4.

[0065] The circulation pump 15 of the Fig. 2A The two-zone heat storage unit shown can be supplied with water W on its suction side 25a via three pipes. A second pipe 28 connects the suction side 25a of the circulation pump 15 to a lower region 29 of the first equalization line 11'. A third pipe 30 connects the suction side 25a of the circulation pump 15 to the lower region of the lower zone 5. A fourth pipe 31 establishes a connection between the suction side 25a of the circulation pump 15 and the storage line 9 of the upper loading and unloading device 7. The second, third and fourth pipes 28, 30, 31 are brought together at the suction side 25a of the circulation pump 15. The pipes 28, 30, 31 each have a control valve 32, 33, 34.Accordingly, depending on which control valve 32, 33, 34 is open or closed, the circulation pump 15 can suck water W from the lower region 29 of the first equalization line 11', from the lower region of the lower zone 5 or from the storage line 9 of the upper loading and unloading device 7 and pump it into the end region 27 of the first equalization line 11' assigned to the upper zone 4.

[0066] While the water W in the storage line 9 provided on the upper loading and unloading device 7 is relatively hot, the water W located in the lower region of the lower zone 5 is relatively cold. If the temperature in the first equalization line 11' is to be increased, the valves 32, 33 in the second and third pipes 28, 30 are closed, while the valve 34 of the fourth pipe 31 is opened. If a reduction in the temperature of the water W in the first equalization line 11' is desired, the valves 32, 34 of the second and fourth pipes 28, 31 are closed and those of the third pipe 30 are opened. If the temperature in the first equalization line 11' is to be kept constant, only the valve 32 of the second pipe 28 is opened.In this way, the pressure difference at the intermediate roof 6 can be set within even narrower tolerance limits, so that the intended design window of the intermediate roof 6 can be used even better as a fault reserve.

[0067] Alternatively, the third and fourth pipes can also be connected to other locations in the dual-zone heat storage system where relatively cold or relatively hot water W can be discharged. For example, it would also be possible to connect the third pipe to the storage line 10 of the lower loading and unloading device 8 and the fourth pipe to an upper area of ​​the lower zone 5. It is only important that relatively hot and relatively cold heat transfer medium can be provided on the suction side 25a of the circulation pump 15 as needed in order to actively adjust the temperature in the first equalization line 11'.

[0068] In order to be able to adjust the temperature particularly precisely, the two-zone heat storage tank has a Fig. 2A A sensor (not shown) for measuring the water temperature is provided. Alternatively, the temperature sensor can also be arranged at another suitable location. Furthermore, a control device is provided for controlling the temperature of the water W in the first equalization line 11'. The control device opens and closes the control valves 32, 33, 34 based on the values ​​measured by the temperature sensor. The aim is for the temperature in the first equalization line 11' to approach the average temperature in the lower zone 5 in order to reduce the differential pressure at the intermediate roof 6.

[0069] 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 devices 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 35, 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 35 is shown as a thick line.

[0070] The second equalization line 35 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 36 located in the lower area of ​​the second equalization line 35. If a fault occurs, the valve 36 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.

[0071] 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 36 of the second equalizing line 35. 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 36 of the second equalizing line 35 in the event of a pump group failure. The same applies to the detection of a power failure.

[0072] The temperature in the second equalization line 35 and the first equalization line 11' should be as identical as possible when opening the valve 36 of the second equalization line 35, 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', 35 to as identical a level as possible, the second equalization line 35 is Fig. 2B shown embodiment integrated into the circulation of the first compensating line 11'.

[0073] The second equalization line 35 is integrated into the circulation of the first equalization line 11' by forking the first pipeline 26, which extends from the pressure side 25b of the circulation pump 15, into two pipelines, one pipeline leading into the second equalization line 35 and the other pipeline leading into the first equalization line 11'. Orifices 37 are provided at the fork so that, for example, half of the water W coming from the pressure side 25b of the circulation pump 15 is directed into the first equalization line 11' and the other half into the second equalization line 35. On the suction side 25a of the circulation pump 15, a bifurcation takes place in the second pipe 28, wherein one pipe opens into the end region of the first equalizing pipe 11' assigned to the lower zone 5 and the other pipe opens into the second equalizing pipe 35 above the fitting 36 of the second equalizing pipe 35.Here, too, orifices 37 are provided which ensure that the first pipeline 28 is fed, for example, half with water W from the first equalizing line 11' and half with water W from the second equalizing line 35. List of reference symbols:

[0074] 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 17 Second equalizing pump 18a Suction side of the first equalizing pump 16 18b Pressure side of the first equalizing pump 16 19 Pipe 20 Pipe 21 Nozzle 22a Suction side of the second equalizing pump 17 22b Pressure side of the second equalizing pump 17 23 Pipe 24 Pipe 25a Suction side of the circulation pump 15 25bPressure side of the circulation pump 15 26First pipe 27End section of the first equalization pipe 11' assigned to the upper zone 4 28Second pipe 29End section of the first equalization pipe 11' assigned to the lower zone 5 30Third pipe 31Fourth pipe 32Control valve of the secondPipeline 28 33Control valve of the third pipeline 30 34Control valve of the fourth pipeline 31 35Second balancing line 36Valve of the second balancing line 35 37Orifices

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'), a first equalizing pump (16) for conveying heat transfer medium from the lower zone (5) into the upper zone (4) and a second equalizing pump (17) for conveying heat transfer medium from the upper zone (4) into the lower zone (5).

2. Two-zone heat storage according to claim 1, characterized in that a control device for controlling the temperature of the heat transfer medium in the at least one first compensation line (11') is provided.

3. Two-zone heat storage according to claim 1 or 2, characterized in thata first pipeline (26) extending from a pressure side (25b) of the circulation pump (15) opens into an end region (27) of the at least one first equalizing line (11') assigned to the upper zone (4), a second pipeline (28) connects a suction side (25a) of the circulation pump (15) with the at least one first equalizing line (11') in the lower zone (5), wherein the second pipeline (28) preferably opens into the at least one first equalizing line (11') at an end region (29) of the at least one first equalizing line (11') assigned to the lower zone (5), a third pipeline (30) connects the suction side (25a) of the circulation pump (15) with the lower zone (5), wherein the third pipeline (30) opens into the lower zone (5) in a lower region of the lower zone (5), and a fourth pipeline (31) connects the suction side (25a) connects the circulation pump (15) to a storage line (9) provided on the upper loading and unloading device (7),wherein the second, third and fourth pipelines (28, 30, 31) each have at least one control valve (32, 33, 34).

4. Two-zone heat storage according to one of the preceding claims, characterized in that a sensor for measuring the temperature of the heat transfer medium is arranged on the pressure side (25b) of the circulation pump (15).

5. Two-zone heat storage according to one of the preceding claims, characterized in that the 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 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).

6. Two-zone heat storage according to one of the preceding claims, characterized in that the circulation pump (15) is designed to transport heat transfer medium from the upper zone (4) through the at least one first equalizing line (11') towards the lower zone (5).

7. Two-zone heat storage according to one of the preceding claims, characterized in that a suction side (18a) 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 (18b) of the first compensating pump (16) is connected to the upper zone (4) via a nozzle (21).

8. Two-zone heat storage according to one of the preceding claims, characterized in thata pressure side (22b) of the second compensating pump (17) is connected to the storage line (10) provided on the lower loading and unloading device (8) and preferably a pipe (23) extending from the suction side (22a) of the second compensating pump (17) is connected to the nozzle (21) of the upper zone (4).

9. Two-zone heat storage device according to one of the preceding claims, characterized in that a second, in particular external, compensating line (35) is provided for connecting the upper zone (4) to the lower zone (5), wherein the second compensating line (35) has a valve (36) for shutting off, in particular arranged in a lower region of the second compensating line (35).

10. Two-zone heat storage according to claim 9, characterized in thatthe nominal width of the second compensating line (35) 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 (35) 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').

11. Two-zone heat storage according to claim 9 or 10, characterized in that the second compensating line (35) is at least partially integrated into the circulation of the heat transfer medium caused by the circulation pump (15) through the at least one first compensating line (11').

12. Two-zone heat storage device according to one of claims 9 to 11, characterized in that the second compensating line (35) has its own circulation device for flowing heat transfer medium through the second compensating line (35).

13. Method for operating a two-zone heat storage device according to one of claims 1 to 12, characterized in that a circulation pump (15) causes a heat transfer medium to flow through at least one first equalizing line (11'), when heat is supplied to the two-zone heat accumulator, a first equalizing pump (16) conveys heat transfer medium from the lower zone (5) to the upper zone (4), and when heat is removed from the two-zone heat accumulator, a second equalizing pump (17) conveys heat transfer medium from the upper zone (4) to the lower zone (5).

14. Method according to claim 13, characterized in thata control device increases the temperature of the heat transfer medium in the at least one first equalization line (11') when heat is supplied to the two-zone heat accumulator and reduces the temperature of the heat transfer medium in the at least one first equalization line (11') when heat is removed from the two-zone heat accumulator, wherein the temperature of the heat transfer medium in the at least one first equalization line (11') is preferably adjusted to the average temperature of the heat transfer medium in the lower zone (5).

15. Method according to claim 13 or 14, characterized in thata control valve (32) of a second pipeline (28) connecting a suction side (25a) of the circulation pump (15) and the at least one first equalizing line (11') is opened when the temperature of the heat transfer medium in the at least one first equalizing line (11') is to be kept at a constant level, a control valve (33) of a third pipeline (30) connecting the suction side (25a) of the circulation pump (15) and a lower region of the lower zone (5) is opened when the temperature of the heat transfer medium in the at least one first equalizing line (11') is to be reduced, and a control valve (34) of a fourth pipeline (31) connecting the suction side (25a) of the circulation pump (15) and a storage line (9) provided on an upper loading and unloading device (7) is opened when the temperature of the heat transfer medium in the at least one first equalizing line (11') is to be increased.

16. Method according to one of claims 13 to 15, characterized in that a valve (36) of a second compensating line (35) 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 the upper loading and unloading device (7) or a power failure are detected.

17. Method according to claim 16, characterized in that the second equalization line (35) 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').

Images