Heat pump arrangement and method for operating a heat pump arrangement

Abstract

The invention relates to a heat pump arrangement (1) having a fluid circuit for a working fluid, which fluid circuit comprises an evaporator unit (2), a compressor arrangement (5) connected downstream of the evaporator unit (2), a condensing unit (8) connected downstream of the compressor arrangement (5), a return line (11) which connects an outlet of the condensing unit (8) to an inlet of the evaporator unit (2), and an expansion arrangement (12), located in the return line (11), for expanding the working fluid, wherein the expansion arrangement (12) has one or more expansion stages (13a 13b).

Description

[0001] Description

[0002] Heat pump arrangement and method for operating a heat pump arrangement

[0003] The present invention relates to a heat pump arrangement with a fluid circuit for a working fluid, which comprises an evaporator unit for transferring thermal energy from a heat source, in particular from a source fluid, to the working fluid, a compressor arrangement downstream of the evaporator unit for compressing the working fluid, a condensing unit downstream of the compressor arrangement for releasing thermal energy from the working fluid, in particular to a sink fluid, preferably for evaporating the sink fluid, a return line which connects an outlet of the condensing unit to an inlet of the evaporator unit, and an expansion arrangement provided in the return line for expanding the working fluid, wherein the expansion arrangement has one or more expansion stages.

[0004] The invention further relates to a method for operating a heat pump arrangement, in which a working fluid is guided through a fluid circuit, wherein thermal energy is transferred in an evaporator unit, in particular from a source fluid to the working fluid, wherein the working fluid is at least partially, in particular completely, evaporated, and the working fluid is subsequently compressed in a compressor arrangement, wherein the working fluid in the compressor arrangement passes through a plurality of compressor stages, in particular, and the working fluid is subsequently at least partially, in particular completely, liquefied in a condensation unit to release thermal energy, in particular to a sink fluid, and the working fluid is subsequently fed back to the evaporator unit via a return line, wherein the working fluid expands in an expansion arrangement provided in the return line, which expansion arrangement has one or more expansion stages.Heat pumps are based on the fundamental principle of absorbing thermal energy from a heat source by evaporating a working fluid and then compressing it and transferring it to a heat sink or sink fluid. To do this, the working fluid, which is usually gaseous after heat absorption, is pressurized to a higher level using a compressor with the absorbed thermal energy and then liquefied at a higher condensation temperature than the evaporation temperature. This exploits the fundamental property of fluids that with increased pressure, the evaporation or condensation temperature also increases. To return the working fluid to its original state at the end of its cycle, it is expanded, causing its pressure and temperature to drop again.

[0005] The coefficient of performance (COP) plays a key role in determining the efficiency of a heat pump. The COP is defined as the ratio of benefit to effort. The benefit corresponds to the amount of heat transferred to the heat sink, for example, to a sink fluid. The effort results from the work required by the compressor. The greater the difference between the evaporation and condensation temperatures of the fluid—i.e., the higher the temperature of the working fluid during heat transfer to a sink fluid—the lower the efficiency of the heat pump, as this requires more effort to compress the working fluid to the appropriate pressure level.

[0006] Heat pumps are increasingly being used in industrial processes, for example, to generate steam in industrial plants. The sink fluid, in this case water, is heated to temperatures of approximately 130 to 140 °C. This naturally requires appropriate compression of the working fluid, which is why the coefficient of performance of such high-temperature heat pumps is inherently rather low. The object of the invention is to create a heat pump arrangement of the type mentioned above and a method for operating such a heat pump arrangement, which allow efficient heating of a sink fluid even to high temperatures.

[0007] According to a first aspect of the present invention, this object is achieved in a heat pump arrangement of the type mentioned at the outset in that the heat pump arrangement has at least one flash gas line which connects the return line to the compressor arrangement parallel to the evaporator unit, so that a gaseous portion of the working fluid (flash gas) can be supplied from the return line to the compressor arrangement, bypassing the evaporator unit.

[0008] Accordingly, according to a first aspect, the object underlying the invention is achieved in a method of the type mentioned at the outset in that a gaseous portion of the working fluid is separated as flash gas from the return line from a liquid portion of the working fluid and is fed to the compressor arrangement through at least one flash gas line, bypassing the evaporator unit.

[0009] This aspect of the invention is based on the fundamental consideration that the working fluid, after liquefaction in the liquefaction unit, still has such a high temperature that its heat can be utilized. In particular, when the working fluid is in a completely liquid state after leaving the liquefaction unit, it can expand in a first expansion stage of the expansion arrangement or in an expansion device arranged in the flash gas line, whereby the pressure drops. As a result of the reduction in pressure, the evaporation temperature also drops, so that when flowing through the first expansion stage, part of the working fluid returns to the gaseous state. This gaseous portion (flash gas) can be separated off and fed directly to the compressor arrangement via a flash gas line, bypassing the evaporator unit.This allows the heat still present in the working fluid after the condensing unit to be used efficiently due to the high temperature at the existing pressure, which leads to a significant improvement in the coefficient of performance.

[0010] In a further embodiment, the compressor arrangement can have a plurality of, in particular exactly two, compressor stages, and the heat pump arrangement can comprise exactly one flash gas line, the flash gas line opening into the compressor arrangement between two consecutive, i.e. adjacent, compressor stages. In other words, the compressor arrangement comprises a plurality of compressor stages, in each of which the pressure of the working fluid increases step by step. The flash gas line therefore opens into the compressor arrangement between two consecutive compressor stages, the working fluid having a pressure between the compressor stages that corresponds to the pressure in the flash gas line.

[0011] The heat pump arrangement can also be characterized in that the compressor arrangement has a plurality of, in particular exactly three or four, compressor stages and the heat pump arrangement comprises a plurality of, in particular exactly two or three, flash gas lines running parallel to one another, wherein the various flash gas lines open into the compressor arrangement between different successive, i.e. mutually adjacent, compressor stages.In this embodiment, it is therefore provided not only to use one flash gas line to utilize the thermal energy present in the working fluid downstream of the liquefaction unit, but also to have several flash gas lines branched off in a cascade, in particular after different expansion stages of the expansion devices, or to provide corresponding expansion means within the flash gas lines in order to convert a portion of the working fluid into the gaseous state and to supply this portion as flash gas to the compressor arrangement between different successive compressor stages. In particular, a different pressure can prevail in each flash gas line, which corresponds to the pressure prevailing between the respective compressor stages.

[0012] Accordingly, in the process according to the invention, a gaseous portion of the working fluid can be separated in one stage or in several stages, in particular exactly in two or three stages, and can be fed to the compression arrangement, in particular between two successive compressor stages, bypassing the evaporator unit through a flash gas line.

[0013] In a further embodiment, a separator can be arranged in the return line, which is designed to separate a gaseous portion of the working fluid (flash gas) from a liquid portion of the working fluid, and one of the at least one flash gas line, in particular the only flash gas line or a first of several flash gas lines, can start from the separator, so that the liquid portion of the working fluid flows on into the return line and the gaseous portion of the working fluid can flow into the flash gas line. In other words, a separator can be provided directly in the return line, in particular after a first expansion stage of the expansion arrangement, by means of which separator the gaseous portion of the working fluid is separated from the liquid portion of the working fluid.The separator can then have two outlets, one of which is connected to the flash gas line through which the gaseous portion of the working fluid flows, and the other outlet is connected to the return line through which the liquid portion of the working fluid flows.

[0014] At least one of the flash gas lines, in particular a second flash gas line or a second and a third flash gas line, can branch off from the return line. In this or these flash gas lines, a separator can be arranged, which is designed to separate a gaseous portion of the working fluid (flash gas) from a liquid portion of the working fluid, so that the gaseous portion of the working fluid can flow further through the flash gas line in the direction of the compressor arrangement and the liquid portion of the working fluid can be returned to the return line. It is therefore also possible for a separator to be arranged not directly in the return line, but in the flash gas line, in order to separate the gaseous portion of the working fluid from the liquid portion of the working fluid there.

[0015] An expansion device can be provided upstream of the separator in the flash gas line to reduce the pressure of the working fluid in the flash gas line. In other words, an expansion device can be provided directly in the flash gas line upstream of the separator to convert a portion of the working fluid from the liquid to the gaseous state by lowering the pressure and thus also the evaporation temperature.

[0016] In a preferred embodiment, a first flash gas line can originate from a separator arranged in the return line. The separator is preferably arranged in the return line after a first expansion stage of the expansion arrangement. A second and optionally a third flash gas line can branch off directly from the return line, with a separator being arranged in each of the second and optionally the third flash gas lines. An expansion device is preferably arranged upstream of the separators in the second and optionally the third flash gas line(s) in the respective flash gas line.The separators arranged in the flash gas line have a (gas) outlet, from which the further flash gas line runs in the direction of the compressor arrangement and through which the gaseous portion of the working fluid flows, and a further (liquid) outlet, which is connected via a return line to the return line, through which the liquid portion of the working fluid can flow.

[0017] In a further embodiment, superheating means for introducing heat into the flash gas can be arranged in at least one flash gas line, in particular in exactly one and / or in a first flash gas line. These can comprise a superheating heat exchanger which is arranged in the flash gas line. A branch line can branch off from the return line, in particular upstream of the expansion arrangement, which branch line opens into the superheating heat exchanger in order to transfer thermal energy from the working fluid to the flash gas and to superheat it. This means that the high temperature in the working fluid after it leaves the liquefaction unit can additionally be used to introduce thermal energy into the flash gas and to superheat it.

[0018] Accordingly, the method according to the invention can be configured such that the flash gas is superheated in at least one, in particular in exactly one and / or in a first flash gas line, in particular by heat transfer from the working fluid branched off from the return line. Through the superheating, additional thermal energy from the working fluid is supplied to the flash gas before it is introduced into the compressor arrangement, thereby further increasing the coefficient of performance of the heat pump arrangement.

[0019] The compressor arrangement can be designed as a turbo compressor with several compressor stages. Different pressures or pressure levels can prevail between the respective compressor stages, so that the pressure of the working fluid increases successively as it passes through. If the heat pump arrangement comprises several flash gas lines, a / the first flash gas line preferably opens into the compressor arrangement at a point with a higher pressure level than a / the second flash gas line. Correspondingly, in the return line starting from the liquefaction unit, the first flash gas line branches off first, followed by the second and, if necessary, a third and further flash gas line(s).

[0020] The expansion arrangement can comprise multiple expansion stages, with individual expansion stages being designed as adjustable throttles so that the flow rate of working fluid can be adjusted. Specifically, the expansion arrangement can have exactly two expansion stages arranged one after the other in the return line.

[0021] According to a second aspect of the present invention, the object underlying the invention is achieved in a heat pump arrangement of the type mentioned at the outset, wherein the heat pump arrangement further comprises a sink fluid supply line opening into the condensation unit, in that heat exchange means are provided which are designed to transfer thermal energy from the working fluid, which flows in the return line, in particular after the expansion arrangement or between two expansion stages of the expansion arrangement, to the sink fluid flowing in the sink fluid supply line in the direction of the condensation unit.

[0022] Accordingly, the object underlying the invention is achieved in a method of the type mentioned at the outset in that the sink fluid is heated before entering the condensation unit by a heat exchange with the working fluid flowing in the return line.

[0023] This aspect of the invention is based on the idea of ​​improving the coefficient of performance of the heat pump arrangement in that at least part of the sink fluid which flows in the direction of the condensing unit is already heated up before it enters the condensing unit, for which purpose the heat still present in the working fluid after it has flowed through the condensing unit is used. Specifically, the heat exchange means can comprise a heat exchanger device. The heat exchanger device can be arranged in the return line, in particular downstream of the expansion arrangement or between two expansion stages of the expansion arrangement, and the sink fluid supply line or a bypass line branching off from this and opening back into it can run through the heat exchanger device so that heat energy can be transferred from the working fluid to the sink fluid.

[0024] In a preferred embodiment, a bypass line runs through the heat exchanger device. In this case, not the entire amount of sink fluid is necessarily conducted through the heat exchanger device, but only a portion of it. A control means for adjusting the flow rate can be arranged in the sink fluid supply line between the branch of the bypass line and its inlet or in the bypass line in order to adjust the volume flow of sink fluid flowing through the bypass line. Accordingly, only the portion of the sink fluid that is branched off from the sink fluid supply line through a bypass line is heated in the heat exchanger device.

[0025] In principle, it is also conceivable to divert a volume flow of working fluid from the return line and feed it to a heat exchanger device arranged in the sink fluid supply line or in a bypass line to this, so that the heat exchanger device is not arranged directly in the return line. In this case, only a portion of the working fluid flowing through the return line is used for heat exchange with the sink fluid. In other words, the heat exchange means in this case comprise a working fluid bypass line branching off from the return line and re-entering it, which bypass line passes through the heat exchanger device.

[0026] In a further embodiment of the heat pump arrangement according to both aspects of the invention, a heat exchanger device can be arranged in the sink fluid supply line, which is connected to a line system of a source fluid in such a way that heat can be transferred from the source fluid to the sink fluid. A heat exchange can thus take place before the sink fluid enters the condensation unit by using the source fluid directly to preheat the sink fluid. Accordingly, in the method according to the invention, the sink fluid can be heated by a heat exchange with the source fluid before entering the condensation unit.

[0027] In a specific embodiment, the heat exchanger device in the sink fluid supply line can be arranged upstream of heating the sink fluid by heat exchange with the working fluid in the return line. In other words, in a first step, the sink fluid can be preheated by heat transfer from the source fluid, and in a second step, at least a portion of the sink fluid can be heated by heat transfer from the working fluid in the return line.

[0028] A reheating line can branch off from the return line, in particular between two expansion stages of the expansion arrangement, and opens into a heat exchanger unit arranged between the evaporator unit and the compressor arrangement in order to transfer thermal energy to the working fluid flowing from the evaporator unit to the compressor arrangement, in particular to superheat it. In other words, the heat exchanger unit can be arranged in a working fluid line which connects an outlet of the evaporator unit to an inlet of the compressor arrangement. A return line can originate from the heat exchanger unit and, in particular downstream of the expansion arrangement, open back into the return line in order to allow the branched off working fluid to flow back into the return line.This design represents a further possibility to optimize the coefficient of performance of the heat pump arrangement, since in this way the heat still present in the working fluid in the return line can be used efficiently.

[0029] Correspondingly, the method according to the invention can be characterized in that the working fluid is heated, in particular superheated, after leaving the evaporator unit and before entering the compressor arrangement by heat exchange with working fluid which is branched off from the return line.

[0030] The heat pump arrangement can include a desuperheating device, which is arranged upstream of the condensing unit in order to be able to reduce the temperature of the working fluid to the condensation temperature. The desuperheating device can be arranged in a working fluid line which connects an outlet of the compressor arrangement to an inlet of the condensing unit. Accordingly, in the method according to the invention, the temperature of the working fluid can be reduced to its condensation temperature before it enters the condensing unit.

[0031] For further details of the invention, reference is made to the dependent claims and the following description of exemplary embodiments with reference to the drawings. The drawings show:

[0032] Figure 1 shows a first embodiment of a heat pump arrangement according to the invention in a schematic representation;

[0033] Figure 2 shows a second embodiment of a heat pump arrangement according to the invention in a schematic representation; and

[0034] Figure 3 shows a third embodiment of a heat pump arrangement according to the invention in a schematic representation.

[0035] Figure 1 shows a high-temperature heat pump arrangement 1 according to the present invention with a fluid circuit for a working fluid. This comprises an evaporator unit 2 for transferring thermal energy from a heat source, in this case a source fluid, to the working fluid. The evaporator unit 2 is designed as a counter-rotating heat exchanger, into which a source fluid supply line 3 opens and from which a source fluid return line 4 branches off.

[0036] The fluid circuit further comprises a compressor assembly 5 downstream of the evaporator unit 2 for compressing the working fluid. The compressor assembly 5 is designed as a turbocompressor and comprises two compressor stages 6a, 6b. The two compressor stages 6a, 6b are driven by a motor 7.

[0037] The fluid circuit further comprises a condensing unit 8 which is modeled after the compressor arrangement 5 and is designed as a multi-stage heat exchanger in the present case. In the condensing unit 8, thermal energy is transferred from the working fluid to a sink fluid, in this case water, to evaporate the sink fluid. For this purpose, a sink fluid supply line 9 opens into the condensing unit 8 to feed the sink fluid into the condensing unit 8. A sink fluid vapor line 10 runs from the condensing unit 8 and transports the evaporated sink fluid to corresponding systems in which it is required. A desuperheater (not shown) can be connected upstream of the condensing unit 8, by means of which the working fluid is cooled to its condensation temperature.

[0038] After flowing through the condensation unit 8, the working fluid is at least substantially liquid and flows through a return line 11, which connects an outlet of the condensation unit 8 to an inlet of the evaporator unit 2. An expansion arrangement 12 is provided in the return line 11, which in this case has two expansion stages 13a, 13b for expanding the working fluid.

[0039] In the evaporator unit 2, thermal energy from the source fluid is transferred to the working fluid, which is conducted in the fluid circuit, wherein the working fluid evaporates at least partially, in particular completely. The working fluid is then compressed in the compressor arrangement 5 to a higher pressure level, so that its temperature also rises, before it is subsequently liquefied at least partially, in particular completely, in order to release thermal energy to the sink fluid in the condensation unit 8. The working fluid is then fed back to the evaporator unit 2 via the return line 11, wherein the working fluid expands in the two expansion stages 13a, 13b of the expansion arrangement 12, which is provided in the return line 11.

[0040] The heat pump assembly 1 further comprises a flash gas line 14, which connects the return line 11 to the compressor assembly 5 downstream of the first expansion stage 13a of the expansion assembly 12. In this way, a gaseous portion of the working fluid (flash gas) can be supplied from the return line 11 to the compressor assembly 5, bypassing the evaporator unit 2. Specifically, the flash gas line 14 opens into the compressor assembly 5 between the two compressor stages 6a, 6b.

[0041] The working fluid, which is completely liquid after flowing through the liquefaction unit 8, becomes partially gaseous again through the expansion stage 13a, since the boiling temperature also decreases due to the reduction in pressure.

[0042] To separate the gaseous portion of the working fluid (flash gas), a separator 15 is arranged in the return line 11 after the first expansion stage 13a. This separator is designed to separate a gaseous portion of the working fluid from a liquid portion of the working fluid. The flash gas line 14 extends from the separator 15, so that the liquid portion of the working fluid flows further into the return line 11 and the gaseous portion of the working fluid flows into the flash gas line 14 in the direction of the compressor arrangement 5.

[0043] Furthermore, superheating means are arranged in the flash gas line 14 in order to introduce additional heat into the flash gas and to superheat it. Specifically, the superheating means comprise a superheating heat exchanger 16. A branch line 17 branches off from the return line 11 upstream of the first expansion stage 13a and opens into the superheating heat exchanger 16 in order to transfer thermal energy from the working fluid to the flash gas and to superheat it. The working fluid flowing through the branch line 17 is then returned to the return line 11 via a return line 18 in which an expansion device 19 for expanding the working fluid is arranged. The return line 18 opens into the return line 11 downstream of the first expansion stage 13a.

[0044] Furthermore, an adjustable expansion device 20 is arranged in the flash gas line 14 between the superheat heat exchanger 16 and the compression arrangement 5 in order to adapt the pressure of the flash gas to the pressure between the compressor stages 6a, 6b and to control the volume flow of the flash gas in the flash gas line 14.

[0045] By separating a gaseous portion of the working fluid from the return line 11 and introducing it into the compressor arrangement 5 while bypassing the evaporator unit 2, the heat present in the working fluid after leaving the condensing unit 8 can be used efficiently, which leads to an improved coefficient of performance of the heat pump arrangement 1.

[0046] Furthermore, a reheating line 21 branches off from the return line 11 between the two expansion stages 13a, 13b of the expansion arrangement 12 and opens into a heat exchanger unit 22 arranged between the evaporator unit 2 and the compressor arrangement 5 in order to transfer thermal energy to the working fluid flowing from the evaporator unit 2 to the compressor arrangement 5 and to superheat this. The heat exchanger unit 22 is connected again to the return line 11 via a return line 23 so that the working fluid flowing through the heat exchanger unit 22 and giving off its heat can be led back into the return line 11 through the return line 23. An expansion device 24 for expanding the working fluid is also arranged in the return line. The return line 23 opens downstream of the expansion arrangement 12, i.e. after both expansion stages 13a, 13b, into the return line 11.

[0047] Furthermore, a heat exchanger device 25 is arranged in the sink fluid supply line 9 and is connected to the line system of the source fluid in such a way that heat can be transferred from the source fluid to the sink fluid. Specifically, for this purpose, a branch (C) is arranged in the source fluid supply line 3 and is connected to an inlet (C) of the heat exchanger device 25, and an inlet (D) is arranged in the source fluid return line 4 and is connected to an outlet (D) of the heat exchanger device 25. In this way, the sink fluid can be preheated directly by the source fluid.

[0048] Figure 2 shows a second exemplary embodiment of a high-temperature heat pump arrangement according to the invention. This differs from the heat pump arrangement 1 of Figure 1 in that it comprises not just one flash gas line 14, but two parallel flash gas lines 14, 26. The compressor arrangement 5 in this case comprises three compressor stages 6a, 6b, 6c.

[0049] The first flash gas line 14, which extends from the separator 15 to the compressor arrangement 5, is designed identically to the first exemplary embodiment in Figure 1. Downstream of the separator 15, from which the first flash gas line 14 originates, the second flash gas line 26 branches off from the return line 11. In this flash gas line 26, an expansion device 27 is initially provided in order to reduce the pressure of the working fluid in the flash gas line 26. This reduces the boiling temperature, so that part of the liquid working fluid returns to the gaseous state.

[0050] Downstream of the expansion device 27 in the flash gas line is a separator 28, which is designed to separate a gaseous portion of the working fluid from a liquid portion of the working fluid. In this way, the gaseous portion of the working fluid can flow further through the flash gas line 26 in the direction of the compressor arrangement 5, and the liquid portion of the working fluid can be returned to the return line 11 after the second expansion stage 13b through a corresponding return line 29, in which an in particular adjustable expansion device 30 is arranged.

[0051] In the further course of the flash gas line 26, in the same way as in the first flash gas line 14, an expansion device 20, in particular an adjustable one, is provided.

[0052] The first flash gas line 14 opens into the compressor arrangement 5 between the two compressor stages 6b and 6c, whereas the second flash gas line 26 opens into the compressor arrangement 5 between the compressor stages 6a and 6b.

[0053] Furthermore, heat exchange means are provided which are designed to transfer thermal energy from the working fluid flowing in the return line 11 to the sink fluid flowing in the sink fluid supply line 9. Specifically, the heat exchange means comprise a heat exchanger device 31 which is arranged downstream of the first expansion stage 13a of the expansion arrangement 12 in the return line 11. A bypass line 32 (E) branches off from the sink fluid supply line 9 after the heat exchanger device 25, runs through the heat exchanger device 31 and opens back into the sink fluid supply line 9 (F), so that thermal energy can be transferred from the working fluid to the sink fluid.

[0054] In the sink fluid supply line 9, between the branch of the bypass line 32 and its inlet, a control means 33 for adjusting the flow rate is arranged in order to adjust the volume flow of sink fluid flowing through the bypass line 32. The control means 33 can, for example, be in the form of an adjustable throttle. In this way, the sink fluid can be heated before entering the condensing unit 8 by direct heat exchange with the working fluid in the return line 11, whereby the heat present in the working fluid in the return line 11 is advantageously utilized and the coefficient of performance of the heat pump arrangement 1 is increased.

[0055] Figure 3 shows a further exemplary embodiment of a heat pump arrangement 1 according to the invention. This differs from the exemplary embodiment in Figure 2 only in that the heat exchanger unit 22 arranged between the evaporator unit 2 and the compressor arrangement 5 is omitted, so that overheating of the working fluid between the evaporator unit 2 and the compressor arrangement 5 does not occur. As a result, under certain circumstances, it is possible in particular to dispense with a complex desuperheating device (not shown in Figures 1 and 2), which is arranged upstream of the condensing unit 8 in order to reduce the temperature of the working fluid to its condensation temperature.

[0056] In particular, it has been found that the efficient use of the heat still present in the working fluid after leaving the condensation unit 8 via the at least one flash gas line 14, 26 and the heat exchanger device 31 results in a significantly more favorable coefficient of performance, so that under certain circumstances the heat exchanger unit 22 and the superheating of the working fluid after the evaporator unit 2 can be dispensed with. This significantly reduces the equipment complexity, particularly for such a desuperheating device.

[0057] Although the invention has been illustrated and described in detail by the preferred embodiment, the invention is not limited to the disclosed examples and other variations can be derived therefrom by those skilled in the art without departing from the scope of the invention.

Claims

Patent claims 1. Heat pump arrangement (1) with a fluid circuit for a working fluid, which comprises an evaporator unit (2) for transferring thermal energy from a heat source, in particular from a source fluid, to the working fluid, a compressor arrangement (5) downstream of the evaporator unit (2) for compressing the working fluid, a condensing unit (8) downstream of the compressor arrangement (5) for transferring thermal energy from the working fluid, in particular to a sink fluid, preferably for evaporating the sink fluid, a return line (11) which connects an outlet of the condensing unit (8) to an inlet of the evaporator unit (2), and an expansion arrangement (12) provided in the return line (11) for expanding the working fluid, wherein the expansion arrangement (12) has one or more expansion stages (13a, 13b), characterized in that the heat pump arrangement (1) comprises at least one flash gas line (14, 26),which connects the return line (11) to the compressor arrangement (5) parallel to the evaporator unit (2), so that a gaseous portion of the working fluid (flash gas) can be supplied from the return line (11) to the compressor arrangement (5) bypassing the evaporator unit (2).

2. Heat pump arrangement (1) according to claim 1, characterized in that the compressor arrangement (5) has several compressor stages (6a, 6b, 6c) and the heat pump arrangement (I) comprises exactly one flash gas line (14), wherein the flash gas line (14) opens into the compressor arrangement (5) between two successive compressor stages (6a, 6b, 6c), or that the compressor arrangement (5) has a plurality of compressor stages (6a, 6b, 6c) and the heat pump arrangement (1) comprises a plurality of, in particular exactly two or three, flash gas lines (14, 26) running parallel to one another, wherein the various flash gas lines (14, 26) open into the compressor arrangement (5) between different adjacent compressor stages (6a, 6b, 6c).

3. Heat pump arrangement (1) according to one of the preceding claims, characterized in that in the return line (II) a separator (15) is arranged downstream of an expansion stage (13a, 13b) of the expansion arrangement (12), which separator is designed to separate a gaseous portion of the working fluid (flash gas) from a liquid portion of the working fluid, and one of the at least one flash gas line (14), in particular a first of a plurality of flash gas lines (14), extends from the separator (15), so that the liquid portion of the working fluid can flow further into the return line (11) and the gaseous portion of the working fluid can flow into the flash gas line (14).

4. Heat pump arrangement (1) according to one of the preceding claims, characterized in that at least one of the flash gas lines (26), in particular a second flash gas line (26) or a second and a third flash gas line (26), branches off from the return line (11) and in this flash gas line (26) a separator (28) is arranged, which is designed to separate a gaseous portion of the working fluid (flash gas) from a liquid portion of the working fluid, so that the gaseous portion of the working fluid can flow further through the flash gas line (26) in the direction of the compressor arrangement (5) and the liquid portion of the working fluid can be returned to the return line (11), wherein, in particular, in the flash gas line (14) upstream of the separator (28) an expansion device (27) is provided in order to reduce the pressure of the working fluid in the flash gas line.

5. Heat pump arrangement (1) according to one of the preceding claims, characterized in that in at least one flash gas line (14), in particular in exactly one and / or in a first flash gas line (14), superheating means for introducing heat into the flash gas are arranged, wherein, in particular, the superheating means comprise a superheating heat exchanger (16) and a branch line (17) branches off from the return line (11), preferably upstream of the expansion arrangement (12), which branch line opens into the superheating heat exchanger (16) in order to transfer thermal energy from the working fluid to the flash gas and to superheat it.

6. Heat pump arrangement (1) with a fluid circuit for a working fluid, which comprises an evaporator unit (2) for transferring thermal energy from a heat source, in particular from a source fluid, to the working fluid, a compressor arrangement downstream of the evaporator unit (2), in particular with several compressor stages (6a, 6b, 6c) for compressing the working fluid, a condensing unit (8) downstream of the compressor arrangement (5) for releasing thermal energy from the working fluid to a sink fluid, preferably for evaporating the sink fluid, and a return line (11) which connects an outlet of the condensing unit (8) to an inlet of the evaporator unit (2), and an expansion arrangement (12) provided in the return line (11) for expanding the working fluid, wherein the expansion arrangement (12) has one or more expansion stages (13a, 13b), in particular according to one of the preceding claims, wherein the heat pump arrangement (1) further has a sink fluid supply line (9) opening into the condensation unit (8), characterized in that heat exchange means are provided which are designed to transfer thermal energy from the working fluid flowing in the return line (11), in particular downstream of the expansion arrangement (12) or between two expansion stages (13a, 13b) of the expansion arrangement (12), to the sink fluid flowing in the sink fluid supply line (9).

7. Heat pump arrangement (1) according to claim 6, characterized in that the heat exchange means comprise a heat exchanger device (31).

8. Heat pump arrangement (1) according to claim 7, characterized in that the heat exchanger device (31) is arranged in the return line (11), in particular downstream of the expansion arrangement (12) or between two expansion stages (13a, 13b) of the expansion arrangement (12) and the sink fluid supply line (9) or a bypass line (32) branching off from it and opening into it again runs through the heat exchanger device (31), so that heat energy can be transferred from the working fluid to the sink fluid.

9. Heat pump arrangement (1) according to claim 8, wherein a bypass line (32) runs through the heat exchanger device (31), characterized in that in the sink fluid supply line (9) between the branch of the bypass A control means (33) for adjusting the flow rate is arranged in the line (32) and its inlet or in the bypass line (32) in order to be able to adjust the volume flow of sink fluid flowing through the bypass line (32).

10. Heat pump arrangement (1) according to one of the preceding claims, wherein the heat pump arrangement has a sink fluid supply line (9) opening into the condensation unit (8), characterized in that a heat exchanger device (25) is arranged in the sink fluid supply line, which is connected to a line system of a source fluid in such a way that heat can be transferred from the source fluid to the sink fluid.

11. Heat pump arrangement (1) according to one of the preceding claims, characterized in that a reheating line (21) branches off from the return line (11), in particular between two expansion stages (13a, 13b), which opens into a heat exchanger unit (22) arranged between the evaporator unit (2) and the compressor arrangement (5) in order to transfer thermal energy to the working fluid flowing from the evaporator unit (2) to the compressor arrangement (5), in particular in order to superheat it, wherein, in particular, the reheating line (21) opens into the return line (11) after leaving the heat exchanger unit (22), wherein a control valve for adjusting the flow rate is preferably arranged in the reheating line (21).

12. Heat pump arrangement (1) according to one of the preceding claims, characterized in that the compressor arrangement (5) comprises or consists of a turbo compressor, and / or that a desuperheating device is connected upstream of the condensing unit (8) in order to be able to reduce the temperature of the working fluid to the condensation temperature.

13. Method for operating a heat pump arrangement (1), in particular a heat pump arrangement (1) according to one of the previous claims, in which a working fluid is guided through a fluid circuit, wherein thermal energy is transferred in an evaporator unit (2), in particular from a source fluid to the working fluid, wherein the working fluid is at least partially evaporated, and the working fluid is subsequently compressed in a compressor arrangement (5), wherein the working fluid in the compressor arrangement (5) passes through in particular several compressor stages, and the working fluid is subsequently at least partially liquefied in a liquefaction unit (8) to release thermal energy, in particular to a sink fluid, and the working fluid is subsequently fed back to the evaporator unit (2) via a return line (11), wherein the working fluid expands in an expansion arrangement (12) which has one or more expansion stages (13a, 13b), characterized inthat a gaseous portion of the working fluid is separated as flash gas from the return line (11) from a liquid portion of the working fluid and is fed to the compressor arrangement (5) through at least one flash gas line (14, 26), bypassing the evaporator unit (2), in particular between two compressor stages (6a, 6b, 6c).

14. The method according to claim 13, characterized in that a gaseous portion of the working fluid is separated in one stage or in several, in particular exactly in two or three stages and is fed back to the compression arrangement by bypassing the evaporator unit (2) through a respective flash gas line (14, 26), and / or that the working fluid is completely liquefied in the liquefaction unit (8) and subsequently in an expansion ion stage (13a, 13b) of the expansion arrangement (12), wherein a part of the working fluid is converted into the gaseous state, and / or that the flash gas is superheated in at least one flash gas line (14), in particular in exactly one and / or in a first flash gas line (14), preferably by heat transfer from working fluid branched off from the return line (11).

15. A method for operating a heat pump arrangement (1), in particular a heat pump arrangement according to one of claims 1 to 12, in which a working fluid is guided through a fluid circuit, wherein thermal energy is transferred in an evaporator unit (2), in particular from a source fluid to the working fluid, wherein the working fluid is at least partially evaporated, and the working fluid is subsequently compressed in a compression arrangement comprising, in particular, several compressor stages (6a, 6b, 6c), and the working fluid is subsequently at least partially liquefied in a liquefaction unit (8) to release thermal energy to a sink fluid, and the working fluid is subsequently fed back to the evaporator unit (2) via a return line (11), wherein the working fluid expands in an expansion arrangement (12) having one or more expansion stages (13a, 13b),wherein the method is designed in particular according to one of claims 13 or 14, characterized in that the sink fluid is heated before entering the condensing unit (8) by a heat exchange with the working fluid flowing in the return line (11).

16. The method according to claim 15, characterized in that only a part of the sink fluid, which is branched off from the sink fluid supply line (9) through a bypass line (32), is heated.

17. Method according to one of claims 13 to 16, characterized in that the sink fluid is heated by heat exchange with the source fluid before entering the condensation unit (8), and / or that the working fluid is heated, in particular superheated, after leaving the evaporator unit (2) and before entering the compressor arrangement (5) by heat exchange with working fluid which is branched off from the return line (11), and / or that the temperature of the working fluid is reduced to its condensation temperature before it enters the condensation unit (8).

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