Heat pump and method for operating a heat pump

Abstract

The present invention relates to a heat pump and a method for operating a heat pump. According to the invention, after a refrigerant flow exits a subcooler (20) and before the refrigerant flow enters an evaporator (70), the refrigerant flow is divided into a first portion (1), which is passed through an intermediate heat exchanger (60), and a second portion (2), which bypasses this intermediate heat exchanger (60), wherein: a. the intermediate heat exchanger (60) facilitates heat exchange of the first portion (1) with refrigerant which is passed from the evaporator (70) to the compressor (50), b. the ratio of the first portion (1) to the second portion (2) is variably adjusted, and c. the first portion (1) and the second portion (2) are recombined to form a combined stream (3) before entering the expansion valve (80) or before entering the evaporator (70).

Description

[0001] The present invention relates to a method for operating a heat pump according to claim 1 and a heat pump according to claim 11.

[0002] A heat pump is a combined heat and power machine that, with the technical work of a compressor, absorbs thermal energy from a lower-temperature reservoir (usually the environment) and transfers it—along with the drive energy—as useful heat at a higher temperature to a system to be heated. Compression heat pumps are used primarily for heating purposes and offer the advantage of operating without emitting CO2. The CO2 footprint can be further reduced by operating the compressor with renewable energy, particularly through a photovoltaic system on the building to be heated.

[0003] Common heat pumps include a compressor, a condenser, a refrigerant receiver, a subcooler, an expansion valve, and an evaporator. A refrigerant is circulated through these elements in a refrigerant circuit.

[0004] Using the evaporator, the heat pump extracts heat from a heat reservoir in the environment, thereby increasing the enthalpy of the refrigerant. The heat source can be the air surrounding the evaporator, the ground, a body of water, or a waste heat source.

[0005] After flowing through the evaporator, the refrigerant is compressed by the compressor, increasing its temperature and pressure. The compressor's discharge pressure can be regulated so that the resulting saturated steam temperature is several degrees higher than the flow temperature of a heating system.

[0006] In the condenser, the refrigerant is then condensed by releasing heat in a heat exchange with a building to be heated. The refrigerant, which is now at least partially liquid, flows through a refrigerant receiver, which serves as a reservoir for liquid refrigerant, and then through a subcooler to further cool the refrigerant below the condensation point at the appropriate pressure. This subcooling further increases the enthalpy difference in such a cycle, thus increasing the heat that can be released by the heat pump to the higher temperature level of the heating system. After flowing through the subcooler, the refrigerant is passed through an expansion valve and expanded before being fed back to the evaporator.

[0007] Heat pumps are known that, in addition to the heat exchangers already described, also have an intermediate heat exchanger. The intermediate heat exchanger serves to exchange heat between the refrigerant flowing from the subcooler to the evaporator and the refrigerant flowing from the evaporator toward the compressor. Such an intermediate heat exchanger leads to further subcooling of the refrigerant flowing to the evaporator. Furthermore, the intermediate heat exchanger ensures that no liquid refrigerant flows from the evaporator to the compressor, since any liquid residue can be completely evaporated in this intermediate heat exchanger.Residual liquid refrigerant could damage the compressor, and accordingly, a larger surface area of ​​the evaporator can be utilized in such a cycle, since the provision of the intermediate heat exchanger ensures that any liquid refrigerant that might still leave the evaporator due to the large surface area used does not reach the condenser. In addition to the additional subcooling of the refrigerant upstream of the evaporator, the intermediate heat exchanger also ensures additional superheating of the refrigerant upstream of the compressor.

[0008] A disadvantage of such known heat pumps with an intermediate heat exchanger and corresponding methods for operating such known heat pumps is the fact that a heat pump must be able to operate with high efficiency at different operating points. For example, the preparation of hot water for a building requires a very high flow temperature in a circuit, such as a water circuit, which transfers the heat emitted by the heat pump from the heat pump's condenser. In heating mode for heating the building with radiators, a medium flow temperature is necessary, and in heating mode with underfloor heating, a low flow temperature is required. In extreme situations, for example, at an outside temperature of -14°C, a flow temperature of 70°C may be necessary for hot water preparation.Conversely, with an outside temperature of +12°C and underfloor heating, a flow temperature of 24°C may be sufficient for a building in heating mode.

[0009] Conventional heat pumps with an intermediate heat exchanger have the disadvantage that they must be optimized for a specific operating point. If such an intermediate heat exchanger is designed too large for a specific operating point, the refrigerant supplied to the compressor may overheat. For example, at a flow temperature of 70°C, this so-called hot gas temperature can rise above 100°C, which can also damage the compressor. However, if such an intermediate heat exchanger is very small, its positive effect is reduced.

[0010] It is therefore an object of the present invention to provide a heat pump and a method for operating such a heat pump in which these problems are solved.

[0011] This object is achieved by a method for operating a heat pump according to claim 1 and by a heat pump according to the characterising part of claim 11.

[0012] In a method according to the invention, after the refrigerant flow exits the subcooler and before it enters the evaporator, the refrigerant flow is divided into a first portion, which is passed through the intermediate heat exchanger, and a second portion, which bypasses this intermediate heat exchanger. As is known, the intermediate heat exchanger serves to exchange heat between this first portion and refrigerant, which is passed from the evaporator to the compressor. According to the invention, however, the ratio of the first portion to the second portion is variably adjustable. The first portion and the second portion are recombined into a combined stream before entering the expansion valve or (if multiple expansion valves are provided) at the latest before entering the evaporator.

[0013] Such an inventive method offers the advantage that the heat pump can be variably optimized and adjusted for different operating points. For example, if a required flow temperature of 70°C is required, the heat pump can be operated practically without using the intermediate heat exchanger by routing the entire refrigerant flow past this intermediate heat exchanger. It is implemented as a bypass solution. In the other extreme case of low-temperature operation with a flow temperature of, for example, only 24°C, if, for example, only underfloor heating needs to be operated at an outside temperature of 12°C and hot water is not required or has already been prepared, the entire refrigerant flow of the heat pump can be routed through the intermediate heat exchanger.For flow temperatures that lie between such extreme values, the refrigerant flow is divided into the first part, which is passed through the intermediate heat exchanger, and the second part, which is passed past the intermediate heat exchanger.

[0014] A corresponding method for operating a heat pump according to the present invention thus results in the heat pump being able to operate with maximum efficiency at various operating points with very different flow temperatures. Accordingly, the intermediate heat exchanger can be freely dimensioned or designed for maximum performance, since the variable distribution of the refrigerant flow in every operating position ensures that, on the one hand, no liquid residues enter the compressor and, on the other hand, that the refrigerant supplied to the compressor does not overheat excessively. This protects the compressor from both liquid hammer and overheating in every operating situation. Therefore, the evaporator can also be operated efficiently thanks to its large surface area.The evaporation surface of the evaporator can be utilized up to 100% because, as already explained, any escaping liquid refrigerant can be evaporated and superheated in the intermediate heat exchanger at any operating point of the heat pump.

[0015] Corresponding advantages also arise for a heat pump according to the invention.

[0016] Further advantageous embodiments of the invention emerge from the subclaims.

[0017] Preferably, the first portion after passing through the intermediate heat exchanger and the second portion before entering the expansion valve are recombined and flow through the expansion valve as a combined stream. The size of the first portion and the second portion can be determined by the position of a three-way mixing valve or, alternatively, by the position of two valves or by the position of a single or multiple pulsed valves.

[0018] However, the first portion can also be recombined after flowing through the expansion valve, and the second portion after flowing through a second expansion valve before entering the evaporator. In this case, the size of the first portion and the second portion can be controlled by the position of the expansion valve and the position of the second expansion valve. Additional valves are then not necessary.

[0019] The first portion 1, which is passed through the intermediate heat exchanger 60, can assume the following values ​​in a particularly preferred embodiment of the process: a) 0% to 10% for heating hot water, b) 20% to 60% for pure heating operation with radiators, c) 80% to 100% for pure heating operation with underfloor heating, and the rest forms the second part (2).

[0020] The change in proportion 1 can be made continuously as requirements change.

[0021] In the process according to a), heating operation can also be provided at the same time.

[0022] Preferably, the size of the first portion and the second portion is regulated such that the evaporator is flooded with 90% to 100% liquid refrigerant, and any liquid refrigerant remaining in the refrigerant circuit after the evaporator is completely evaporated in the intermediate heat exchanger, and the gaseous refrigerant is preferably superheated in the process. This offers the advantage of maximum utilization of an evaporator surface or evaporator volume of the evaporator. Compared to known methods, the evaporator can be designed smaller, since the method according to the invention can always ensure full utilization of the evaporator at different operating points without overheating or liquid entrainment at the compressor.

[0023] The liquid fraction and / or the superheat of the refrigerant downstream of the intermediate heat exchanger is preferably determined in the refrigerant circuit by temperature and pressure sensors (preferably one each) arranged between the evaporator and the intermediate heat exchanger. Using the values ​​thus determined, the position of at least one expansion valve (or both) and / or the valves for dividing the refrigerant flow into the first and second portions can be controlled such that the evaporator is flooded with 90% to 100% liquid refrigerant.

[0024] In a further preferred embodiment of the method, a hot gas temperature of the refrigerant after the compressor is determined by means of a hot gas temperature sensor (T HG ), and a. the size of the first portion (1) and / or b. the position of the expansion valve (80) and / or c. the two expansion valves (80, 82) are regulated so that that it is 5 to 20 K, preferably 11 to 25 K, above the condensation temperature of the refrigerant on the high-pressure side of the refrigerant circuit. This allows the efficiency of the heat pump to be optimized at a wide range of operating points (according to different performance requirements).

[0025] In a preferred embodiment of a heat pump according to the invention, the control system has a three-way mixing valve in the branching or in the junction point.

[0026] Alternatively, the control may include a first valve in the first fluid line or in the third fluid line and a second valve (94) in the second fluid line (24).

[0027] Further alternatively, the control may comprise a pulsating valve in the first fluid line or in the third fluid line or in the second fluid line.

[0028] Instead of such valves for pure flow control, the control system can include an expansion valve in the second fluid line and a second expansion valve in the third fluid line. These expansion valves are designed not only to expand the refrigerant but also to regulate the flow rates.

[0029] Preferably, a temperature sensor and a pressure sensor are arranged in the refrigerant circuit between the evaporator and the intermediate heat exchanger.

[0030] In the present case, the invention is explained in more detail by way of example with reference to the attached figures.

[0031] It shows: Fig. 1 : a heat pump according to the invention, wherein the refrigerant flow is divided by means of a three-way mixing valve; Fig. 2 : a heat pump in which two valves are installed; and Fig. 3 : a heat pump in which two expansion valves are used. Fig. 4 : A heat pump in which the cooling circuit is supplemented with intermediate steam injection. This design can be used in all three variations.

[0032] Fig. 1 shows a first example of a heat pump according to the invention, which is controlled by means of a method according to the invention. As is known from the prior art, a refrigerant is passed through a condenser 40, which represents a heat exchanger by means of which the refrigerant releases heat to a secondary circuit. The secondary circuit is a heating circuit of a building that is to be heated and it has a flow VL and a return RL. Heating devices (not shown in detail) such as radiators, underfloor heating or a system for hot water preparation are connected to the flow VL and the return RL. A return temperature sensor T RL and a flow temperature sensor T VL are provided in each case in order to be able to monitor the flow temperature and the return temperature in this secondary circuit.This secondary circuit also includes a circulation pump 10, by means of which a corresponding secondary circuit fluid, for example water, is pumped through the secondary circuit. Depending on the ambient temperature and the desired temperature in an interior of the building or a desired hot water temperature, different flow temperatures are required, which can be between 24°C and 70°C. The corresponding heating of the secondary circuit fluid from the low return temperature T RL to the higher flow temperature T VL is achieved by heating the secondary circuit fluid via the condenser 40.

[0033] After the refrigerant passes through the condenser 40, the refrigerant flow of the predominantly liquid refrigerant at this point is fed to a refrigerant collector 30, which serves as a reservoir for liquid refrigerant. By providing such a reservoir, the heat pump shown can operate at different operating points, allowing more refrigerant to be involved in the heat pump cycle as heating demand increases.

[0034] After the refrigerant exits the refrigerant receiver 30, the refrigerant flow is passed through a subcooler 20, where heat exchange with the secondary circuit takes place again and the refrigerant is further cooled. Further subcooling can increase the enthalpy absorption of the refrigerant in the cycle and further reduce the vapor content in the refrigerant.

[0035] After the refrigerant exits the subcooler 20, the refrigerant reaches a branch 26, from which a first portion 1 is supplied to an intermediate heat exchanger 60 via a first fluid line 22, and a second portion 2 is passed past this intermediate heat exchanger 60 via a second fluid line 24. In order to vary the ratio of the first portion 1 to the second portion 2, a three-way mixing valve 90 is provided at a junction point 62. The three-way mixing valve 90 could alternatively also be provided in the branch 26.

[0036] At the junction point 62, the first portion 1, after flowing through the intermediate heat exchanger 60, is recombined with the second portion 2 to form a combined stream 3, which is fed to an expansion valve 80. The combined stream 3 is expanded by the expansion valve 80, and the refrigerant is liquefied as completely as possible before being fed to an evaporator 70. In the evaporator 70, the refrigerant undergoes heat exchange with a heat source, for example, the ambient air, a body of water, the ground, or a source of waste heat from a system. The heat exchange in the evaporator 70 evaporates the refrigerant at this point before being fed through the intermediate heat exchanger 60, which realizes the previously explained heat exchange with the first portion 1 of the refrigerant.

[0037] According to the present invention, the provision of the three-way mixing valve 90 adjusts the ratio between the first portion 1 and the second portion 2 depending on the operating situation. If high performance and high heat output are required from the heat pump, such as for the preparation of hot water, the heat pump according to the invention can be operated like a heat pump without an intermediate heat exchanger 60, in that the refrigerant is completely bypassed by the intermediate heat exchanger 60, thus having virtually no effect. Conversely, in a case where little heat output is required from the heat, for example, moderate outside temperatures and for operating an underfloor heating system without simultaneous hot water preparation, the refrigerant can be completely passed through the intermediate heat exchanger 60.In both cases, the intermediate heat exchanger 60 ensures, on the one hand, that the compressor 50 is not overheated and damaged by hot gas overheating, and, on the other hand, that no liquid refrigerant enters the compressor. The latter is ensured by the fact that, in the state of the evaporator 70, i.e., even if the evaporator 70 is completely flooded, any liquid refrigerant escaping from the evaporator is still evaporated in the intermediate heat exchanger 60 and even superheated to a specified superheat level before the refrigerant reaches the compressor 50.

[0038] After flowing through the compressor 50, the refrigerant is again fed to the condenser 40, thereby closing the circuit. To determine the liquid content and / or the superheating of the refrigerant downstream of the intermediate heat exchanger 60 in the refrigerant circuit, a temperature and pressure sensor T, P is provided between the evaporator 70 and the intermediate heat exchanger 60. Furthermore, a hot gas temperature sensor T HG is provided downstream of the compressor 50 and is arranged between the compressor 50 and the condenser 40. In addition, a pressure transmitter 72 is provided in the high-pressure region of the cooling circuit. A condensation pressure is determined using the pressure transmitter 72, and this pressure is converted into a temperature.

[0039] In the Fig. 2 An alternative embodiment is provided in which no three-way mixing valve is provided, but after the branch 26, a first valve 92 and a second valve 94 are provided both in the first fluid line 22, through which the first portion 1 flows, and in the second fluid line, through which the second portion 2 flows. The ratio of the first portion 1 to the second portion 2 can also be adjusted via the controllable position of these two valves 92 and 94. Alternatively, the first valve 92, which according to the illustration of the Fig. 2 installed after the intermediate heat exchanger 60, can also be arranged between the branch 26 and the intermediate heat exchanger 60. Alternatively, instead of the two valves 92 and 94, only one valve, in this case preferably a pulsed valve, for example a pulsed solenoid valve, can be provided between the branch 26 and the intermediate heat exchanger 60 or between the intermediate heat exchanger 60 and the junction point 62 in order to regulate the size of the first portion 1. Alternatively, such a pulsed valve can be provided in the section between the branch 26 and the junction point 62 through which the second portion 2 flows, in order to regulate the latter. In any case, the ratio of the first portion 1 to the second portion 2 can also be controlled or regulated by providing a single pulsed solenoid valve.

[0040] A further embodiment of a heat pump according to the invention is described in Fig. 3 In this case, two expansion valves 80 and 82 are provided, wherein the expansion valve 80 serves to expand the second portion 2 and the second expansion valve 82 to expand the first portion 1. The second expansion valve 82 is therefore provided for a third fluid line 28, which (as already in the Fig. 1 and 2 shown) carries the first portion of refrigerant from the intermediate heat exchanger 60 to the junction point 62. The expansion valve 80 is accordingly provided in the second fluid line 24, which, as already shown in the Fig. 1 and 2 shown, is led from the branch 26 to the junction point 62 and here directs the second part 2.

[0041] This means that for all heat pumps shown, the Fig. 1 bis 3 and the associated inventive methods each have the advantage that the proportion of refrigerant passed through the intermediate heat exchanger 60 can be variably adjusted and / or regulated, depending on the flow temperature required by the heat pump. If a high flow temperature is required, such as for hot water preparation or for hot water preparation in combination with an active heating system that has radiators, the refrigerant flow can be completely bypassed by the intermediate heat exchanger 60 to the evaporator 70. The refrigerant then arrives at the evaporator 70 already so subcooled that further subcooling by the intermediate heat exchanger 60 is not necessary.Conversely, in a case where little heating power is required from the heat pump, the entire refrigerant is passed through the intermediate heat exchanger 60 before flowing into the evaporator 70, where it is further subcooled to improve the efficiency of the heat pump.

[0042] Fig. 4 . shows a heat pump corresponding to the heat pump of the Fig 1, in which the circuit is supplemented with an intermediate vapor injection. Such an intermediate vapor injection can be used in all heat pumps and methods of the present invention. The liquefied refrigerant is divided behind the condenser 40 into a main stream 96 and an injection stream 98. Both streams 96 and 98 are passed through a heat exchanger 100 for heat exchange with each other. The smaller injection stream 98 is expanded by means of an expansion valve 102 and subcools the main stream 96 in the heat exchanger 100. The evaporated injection stream 98 is then injected into the compressor 50. The additional subcooling of the main stream 96 increases the amount of heat that the heat pump can release, so that the vapor injection results in even better efficiency overall. List of reference symbols

[0043] 1First part 2Second part 3Combined flow 10Circulation pump 20Subcooler 22First fluid line 24Second fluid line 26Branch 28Third fluid line 30Refrigerant receiver 40Condenser 50Compressor 60Intermediate heat exchanger 62Joint point 70Evaporator 72Pressure transmitter 80Expansion valve 82Second expansion valve 90Three-way mixing valve 92First valve 94Second valve TRLReturn temperature sensor TVLSupply temperature sensor THGHot gas temperature sensor 96Main flow 98Injection flow 100Heat exchanger 102Expansion valve

Claims

1. Method for operating a heat pump, wherein in the course of the method: a refrigerant cyclically passes through a refrigerant circuit in which the refrigerant flows through a compressor (50), a condenser (40), a refrigerant receiver (30), a subcooler (20), an expansion valve (80) and an evaporator (70), wherein after the refrigerant flow exits the subcooler (20) and before the refrigerant flow enters the evaporator (70), the refrigerant flow is divided into a first portion (1), which is passed through an intermediate heat exchanger (60), and a second portion (2), which bypasses this intermediate heat exchanger (60), wherein: a. the intermediate heat exchanger (60) mediates heat exchange of the first portion (1) with refrigerant which is passed from the evaporator (70) to the compressor (50), b. the ratio of the first part (1) to the second part (2) is variably adjusted, and c.the first portion (1) and the second portion (2) are recombined into a combined stream (3) before entering the expansion valve (80) or before entering the evaporator (70).

2. Method according to claim 1, characterized in that the first portion (1) after passing through the intermediate heat exchanger (60) and the second portion (2) before entering the expansion valve (80) are recombined and flow through this as a combined stream (3).

3. Method according to claim 2, characterized in that the size of the first portion (1) and the second portion (2) is determined by the position of a three-way mixing valve (90).

4. Method according to claim 2, characterized in that the size of the first portion (1) and the second portion (2) is determined by the position of two valves (92, 94) or by the position of a single pulsed valve.

5. Method according to claim 1, characterized in thatthe first portion (1) after flowing through the expansion valve (80) and the second portion (2) after flowing through a second expansion valve (82) are recombined before entering the evaporator (70).

6. Method according to claim 5, characterized in that the size of the first portion (1) and the second portion (2) is regulated by the position of the expansion valve (80) and the position of the second expansion valve (82).

7. Method according to one of the preceding claims, characterized in that the first portion (1), which is passed through the intermediate heat exchanger (60), assumes the following values: d) 0% to 10% for heating hot water, e) 20% to 60% for pure heating operation with radiators, f) 80% to 100% for pure heating operation with underfloor heating, and the remainder forms the second portion (2).

8. Method according to one of the preceding claims, characterized in thatthe size of the first portion (1) and the second portion (2) is regulated so that the evaporator (70) is flooded with 90% to 100% liquid refrigerant, and after the evaporator (70) in the refrigerant circuit remaining liquid refrigerant is completely evaporated in the intermediate heat exchanger (60), and the gaseous refrigerant is preferably superheated in the process 9. Method according to claim 8, characterized in that the liquid content and / or the superheating of the refrigerant after the intermediate heat exchanger (60) in the refrigerant circuit is determined by temperature (T) and pressure sensors (P) arranged between the evaporator (70) and the intermediate heat exchanger (60).

10. Method according to one of the preceding claims, characterized in that a hot gas temperature of the refrigerant after the compressor (50) by means of a hot gas temperature sensor (T HG) is determined, and via d. the size of the first portion (1) and / or e. the position of the expansion valve (80) and / or f. the two expansion valves (80, 82) is regulated so that it is 5 to 20 K, preferably 11 to 25 K above the condensation temperature of the refrigerant on the high-pressure side of the refrigerant circuit.

11. Method according to the preceding claims characterized in that a condensation pressure is determined by means of a pressure transmitter (72), wherein a determined pressure is converted into a temperature.

11. A heat pump comprising a refrigerant circuit in which a compressor (50), a condenser (40), a refrigerant collector (30), a subcooler (20), at least one expansion valve (80), and an evaporator (70) are arranged in succession, wherein, after the subcooler (20) and before the at least one expansion valve (80), a branch (26) into a first fluid line (22) and a second fluid line (24) is provided for dividing the refrigerant flow into a first portion (1), which is guided through an intermediate heat exchanger (60), and a second portion (2), which bypasses this intermediate heat exchanger (60), wherein: a. the intermediate heat exchanger (60) is designed such that heat exchange can take place between the first portion (1) and refrigerant, which is guided from the evaporator (70) to the compressor (50), characterized in thatb. a control is provided to variably adjust the ratio of the first portion (1) to the second portion (2), and c. a third fluid line (28) is provided, by means of which the first portion (1) after passing through the intermediate heat exchanger (60) and before the second portion (2) enters the expansion valve (80) or before it enters the evaporator (70) at a merging point (62) is recombined with the latter to form a combined stream (3).

12. Heat pump according to claim 11, characterized in that the control has a three-way mixing valve (90) in the branch (26) or in the junction point (62).

13. Heat pump according to claim 11, characterized in that the control includes a first valve (92) in the first fluid line (22) or in the third fluid line (28) and has a second valve (94) in the second fluid line (24).

14. Heat pump according to claim 11, characterized in thatthe control comprises a pulsating valve in the first fluid line (22) or in the third fluid line (28) or in the second fluid line (24).

15. Heat pump according to claim 11, characterized in that the control comprises the expansion valve (80) in the second fluid line (24) and a second expansion valve (82) in the third fluid line (28).

16. Heat pump according to one of claims 11 to 15, characterized in that a temperature (T) and a pressure sensor (P) are arranged in the refrigerant circuit between the evaporator (70) and the intermediate heat exchanger (60).

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