EP2321592B1 - Heat pump or refrigeration device and method for operating a heat pump or refrigeration device - Google Patents

Abstract

In a method for operating a heat pump or refrigeration device (1), a coolant is isothermally compressed using a fluid displacement compressor (2), then cooled, optionally condensed in the process, and then expanded. In a next step, the coolant is evaporated and finally fed back to the fluid displacement compressor (2). In order to improve the efficiency of the process, it is proposed that heat from the cooled coolant following compression is transferred to the heated coolant before the coolant is returned to the fluid displacement compressor (2), and thus the cycle is closed, and that the coolant is expanded in an engine comprising an operative connection to a hydraulic pump (31) for pumping a hydraulic fluid of the fluid displacement compressor (2). Further proposed as an apparatus is a heat pump/refrigeration device for carrying out the above method.

Description

The invention relates to a method for operating a heat pump or chiller, in which a refrigerant is compressed by means of a liquid piston compressor, then cooled and then expanded and vaporized in a next step and finally fed back to the liquid piston compressor. In addition, the invention relates in terms of device technology, a heat pump or chiller.

Heat pump or chiller processes have been part of the well-known state of the art for quite some time. In contrast to the widely used mechanical piston compressors, the use of liquid piston compressors attempts to realize an isothermal compression of the refrigerant in the closed loop process. By using a liquid piston, the compression space can be given generously sized and structurally very free surfaces to optimize heat transfer since there is no sealing problem when using a fluid as a "piston". For this reason, liquid-piston compressors can achieve a nearly isothermal compression. Another advantage of a liquid piston compressor is the fact that a phase transition in the compression from the vapor to the liquid state for such devices is unproblematic, since the liquid piston can take no "mechanical" damage even in so-called "liquid shocks". However, a prerequisite for the functioning of a liquid piston compressor is the use of immiscible fluids.

The US 2,772,543 as well as the US 1,766,998 Although chilling with these liquid piston compressors in principle an approximation of an isothermal compression would be possible, the cylinders of the prior art compressors, however, lack a special heat exchanger geometry, so that the compression in the known methods should be more or less polytopic in practice.

Disclosed in the broader field of the invention DE 26 10 063 A1 a heat pump with alcohol as refrigerant, liquid piston compressor and with an "internal heat exchanger" in which the refrigerant vapor is overheated on exiting the evaporator with warm condensate.

task

The invention has for its object to develop a method for operating a heat pump or chiller so that the efficiency of the process is further increased. The same object is the present invention in device-technical terms with respect to a heat pump and chiller based.

solution

With regard to a heat pump or chiller, the above object, starting from a method of the type described above, achieved in that heat of the cooled after compression refrigerant is transferred to the refrigerant before it is fed back to the liquid piston compressor and thus the cycle is closed and that the refrigerant is expanded in an engine having an operative connection to a hydraulic pump (31) by means of which a hydraulic fluid of the liquid piston compressor (2) is pumpable.

In the method according to the invention, heat that is still available after the cooling of the compressed refrigerant is transferred to the refrigerant that has evaporated again after the expansion. By such a process of internal heat transfer otherwise unused energy is used.

This advantage has an effect, in particular, on heat pumps or refrigerating machines which are operated in the transcritical range, for example with CO ₂ as refrigerant. The critical temperature of CO ₂ is 31 ° C. Above this temperature, no phase change to the liquid phase out is more possible, so that there is no ability of the refrigerant to release heat at the same temperature alone due to the phase change. As a result, CO _{2 is} at a very high level End temperature must be compressed, so that in the further course of the cycle, the waste heat can be delivered to a heat source with a specified temperature. The heat to be released in this case comes solely from the cooling of the hot gas and not from a phase change.

Due to this thermodynamic property of CO ₂ , the energy required for the compression is much higher than in conventional, but sometimes more environmentally harmful refrigerants, which undergo a phase change twice during the cycle. This fundamental disadvantage of CO ₂ as a refrigerant is now significantly reduced by the invention, since the process thermodynamically improved by the process of the internal transition of heat and the isothermal compression and thus the coefficient of performance of the relevant refrigerator or heat pump is increased.

According to one embodiment of the method according to the invention, it is provided that the refrigerant is alternately compressed by two liquid piston compressors, each having a working space whose common working fluid is reciprocated alternately from the working space of one liquid piston compressor into the working space of the other liquid piston compressor. In this way, a homogenization of the mass flow in the remaining process steps can be achieved.

A further increase in continuity can be achieved by temporarily storing the refrigerant in a high pressure accumulator after it has cooled and transferred further heat to the vaporized refrigerant.

The same effect of equalizing the process with respect to the refrigerant flow is obtained when the refrigerant is stored in a low-pressure accumulator after expansion before it is subsequently vaporized.

When the method according to the invention is used for refrigerants which undergo a phase change during the cycle, the refrigerant may already be present during cooling during the compression and / or subsequent transfer of heat to the vaporized refrigerant and / or during the subsequent cooling partially - condense.

A further significant increase in efficiency can be achieved in the process in question by the fact that the refrigerant after cooling and the heat transfer to the reheated refrigerant under work in an engine, in particular an expansion pump or an expansion turbine, is relaxed before it evaporates again or is heated.

While in the state of the art isenthalp with the help of a throttle relaxation of the refrigerant energy is lost, the previously unexploited expansion work can be used with the help of a relaxation machine. In conjunction with the compression of the refrigerant in a liquid piston compressor, the expansion work gained by the expansion machine can be advantageously used to pump the liquid used as working fluid into the liquid piston. The pumping work to be applied during the refrigerant compression is hereby reduced and the power requirement of the hydraulic pump or the hydraulic work to be performed by it is reduced.

By appropriate design of the surfaces of the liquid piston compressor and by appropriate control of the compression process (compression speed), the heat should be removed from the refrigerant during the compression in the liquid piston compressor so that the compression takes place isothermally. In this case, the heat dissipated from the compressor by means of a separate heat transfer medium from the heat of a heat sink, i. for example, to a consumer in the form of underfloor heating, or otherwise provided as process heat at a low temperature level, wherein the heat transfer medium is further heated after heating in the liquid piston compressor in the gas cooler for the refrigerant.

Starting from a known heat pump or chiller, the object of the invention is achieved by a heat exchanger, by means of which heat from the transcritical, the cooler leaving the refrigerant to the heater leaving the refrigerant is transferable.

With the help of such a so-called "internal heat exchanger" can increase the efficiency of the cycle, otherwise useful energy unused is used. This applies in particular to the use of CO ₂ as a refrigerant in accordance with the advantages already described above.

The pressure reducing means is an engine, in particular, an expansion pump or expansion turbine, which is arranged between the radiator and the heater. The expenditure on equipment is particularly low when a free-piston pump with self-switching valves is used as the expansion pump.

In order to use the power gained by the expansion machine directly to carry out the cyclic process, there is an operative connection, in particular a mechanical coupling, for example via a shaft, between the engine during expansion of the refrigerant and a hydraulic pump with which a hydraulic fluid is pumpable into a working space of the liquid piston compressor ,

embodiment

The invention will be explained in more detail below with reference to several exemplary embodiments, by means of which the heat pump process according to the invention is illustrated.

Fig. 1

einen Wärmepumpen-/Kältemaschinenprozess nach dem Stand der Technik in einem T-s-Diagramm mit dem Kältemittel R 134 a und isothermer Verdichtung mittels eines Flüssigkolbenverdichters,

Fig. 2

wie Figur 1, jedoch mit dem Kältemittel CO₂,

Fig. 3

einen erfindungsgemäßen Prozess in einem T-s-Diagramm mit dem Kältemittel R 134 a mit innerem Wärmeübertrager und arbeitsleistender Expansion,

Fig. 4

wie Figur 3, jedoch mit dem Kältemittel CO₂,

Fig. 5

eine schematische Anlagendarstellung einer Wärmepumpe/Kältemaschine mit innerem Wärmeübertrager und mit Expansionspumpe.

It shows:

Fig. 1

a heat pump / refrigerator process according to the prior art in a Ts diagram with the refrigerant R 134 a and isothermal compression by means of a liquid piston compressor,

Fig. 2

as FIG. 1 but with the refrigerant CO ₂ ,

Fig. 3

a process according to the invention in a Ts diagram with the refrigerant R 134 a with internal heat exchanger and work expansion,

Fig. 4

as FIG. 3 but with the refrigerant CO ₂ ,

Fig. 5

a schematic system representation of a heat pump / chiller with internal heat exchanger and with expansion pump.

One in the plant diagram according to FIG. 5 schematically illustrated heat pump / chiller 1 has in the cycle of the refrigerant (here: CO ₂ ) a liquid piston compressor 2, a gas cooler 3 / condenser an internal heat exchanger 4, a high-pressure accumulator 5, an expansion pump 42, a Low-pressure accumulator 7, an evaporator 8 and check valves 9 to 12 on. The following process takes place in the form of a cycle through the aforementioned components and the interconnecting lines:

The isothermally compressed CO ₂ in the liquid piston compressor is fed via a line 13 to the gas cooler 3, in which condensation may occur depending on the compression end temperature of the refrigerant. Due to the comparatively low critical temperature of CO ₂ (31 ° C.), however, condensation typically does not take place either during the compression or in the downstream gas cooler 3 / "condenser", that is to say the wet steam area is not reached in these process steps.

Thus, after the cooled CO _{2 has} reached the inner heat exchanger 4 via a line 1, heat is transferred there to the refrigerant after it has left the evaporator 8. Via a further line 15, the refrigerant passes from the inner heat exchanger into a high-pressure accumulator 5, from which it passes through a line 16 to the expansion pump 42, in which an ideal isentropic expansion of the refrigerant takes place, which occurs during the expansion in the wet steam area. Via a line 17, the expanded refrigerant enters the low-pressure accumulator 7, from where it passes through a line 18 into the evaporator and evaporates there under heat absorption. Subsequently, the refrigerant is conducted via a line 18 to the already mentioned inner heat exchanger 4 and heated there before it flows back via the line 19 back to the liquid piston compressor 2.

The liquid piston compressor 2 has two cylinders 20, 21 each defining a working space, which are connected in parallel to each other. From the line 19 branches off the inflow line 22 of the cylinder 20, in which the check valve 10 is arranged, which allows only an influx into the cylinder 20. Via the line 23, in which there is only one outflow permitting check valve 9, the refrigerant passes from the cylinder 20 into the conduit 13 and thus back into the gas cooler 3 / condenser.

Cylinder 21 is connected via a conduit 24 serving for the inflow to the conduit 19 and via the conduit 25 serving for the outflow to the conduit 13 Here, the check valves 11 and 12 allow only an inflow or outflow of the refrigerant.

On the underside of the cylinders 21 and 22, respectively, hydraulic lines 24 and 25 are connected, which open into a respective working chamber 26, 27 formed by the interior of the cylinders 20, 21. In the interior of the work spaces 26, 27 is located below the hydraulic fluid, on the mirror S, the more or less strongly compressed refrigerant is. The hydraulic fluid is selected so that it is neither miscible nor dissolved in the refrigerant.

The hydraulic lines 24 and 25 lead to a four-way hydraulic valve 28, from which in turn depart two hydraulic lines 29, 30 which are connected to the suction or pressure side of a hydraulic pump 31. Depending on the switching position of the four-way hydraulic valve 28, now hydraulic fluid pressure is removed from one of the two cylinders 20, 21 and pumped under pressure into the other of the two cylinders 20, 21, whereby in the latter cylinder a compression stroke is performed, whereas in the other cylinder, the vaporized and preheated refrigerant is sucked.

Both cylinders 20, 21 are surrounded on their outer side by a double jacket 32 to 33 and provided in their interior with a heat exchanger bundle 34, 35. The double shells 32 to 33 or heat exchanger bundles 34, 35 are connected to discharge lines 36, 37 and supply lines 38, 39.

The heated during the compression process heat transfer medium is passed after passing a located in the respective switching position three-way valve 39 from a circulation pump 40 to a consumer 41, which may be, for example, a floor heating or a consumer of process heat at low temperature level. From the consumer, the cooled heat transfer medium reaches the gas cooler 3, from which it is already preheated, in order subsequently to be returned to the liquid piston compressor 2, where it is reheated in the course of the isothermal compression of the refrigerant and its circuit thus closes. The heat transfer medium is depending on the switching position of the three-way valve 39 each only by those cylinders 20 and 21st in which the isothermal compression of the refrigerant is taking place. Alternatively, both cylinders are constantly flowed through.

The heat pump / chiller 1 has an expansion pump 42. The refrigerant taken from the high-pressure accumulator 5 is expanded by means of the expansion pump 42 designed as a free-piston pump before the expanded refrigerant is returned to the low-pressure accumulator and the process via the evaporation, preheating to condensation temperature, isothermal compression and cooling runs identically as in FIG. 5 ,

In contrast to the expansion valve in which an isenthalp relaxation takes place, when expansion in the expansion pump work is released, which can be used, for example, that an operative connection between the expansion pump 42 and the hydraulic pump 31 is made to their power requirements when pumping the hydraulic fluid to reduce the compression of the refrigerant or directly to pump a partial flow itself. Overall, therefore, the coefficient of performance of the heat pump / chiller 1 can be further improved by means of the expansion pump 42.

The effect of the inner heat exchanger 4 in the refrigerant circuit is to be illustrated by a comparison of the cycle processes in each case in a Ts diagram. FIG. 3 according to the process in the heat pump / chiller 1 according to FIG. 5 illustrates how the refrigerant from point A is isothermally compressed to point B. In this case, the idealized, horizontally extending line AB intersects the wet-steam line 43, whose section on the right of the maximum 44 is referred to as a dew-line 45 and whose section 46 on the left of the maximum 44 is referred to as a boiling line. From the intersection point 47 between tau line 45 and line AB, the refrigerant is thus in the post-vaporized area. Starting from point B, the refrigerant in the internal heat exchanger 4 is isobarically cooled along boiling line 46 until point C is reached. In the expansion pump 42, the refrigerant is now polytropically expanded and thus reaches point D with a correspondingly reduced temperature. Without expansion pump, that is, throttling via an expansion valve ( FIG. 5 ) is dashed along the the point D 'reached, which is characterized by a greater entropy - due to the isenthalic relaxation.

From point D or D 'an evaporation of the refrigerant takes place (at the same temperature), until on the dew line 45 the point E is reached. Starting from this point, the refrigerant is again isobarically heated in the inner heat exchanger 4, in order finally to reach the state point A again, whereby the cycle is closed.

In contrast, in a conventional chiller / heat pump process with isothermal compression, but without an internal heat exchanger, the compressed refrigerant is expanded isenthalp from the point b lying on the boiling line 46. Subsequently, point d is achieved on the same isotherm as it is also present during evaporation, when the medium has previously been cooled in an internal heat exchanger. In addition, the process without internal heat exchanger from point e on the tau line runs steeper upward on the "upper isotherm" along which even in the presence of an internal heat exchanger to point b or B would be compressed. To make the two processes better comparable, are also in the diagram according to FIG. 3 the state points a, b, d, e registered and dashed, also the lines bd and ea.

While the FIGS. 1 and 3 show the cycles with R 134 A as the refrigerant form the Figures 2 and 4 a comparison of the processes when using CO ₂ as a refrigerant. It is clear that by the internal heat exchanger 4, the relaxation of a lower temperature level (point C ') starts, as is the case in b' without internal heat exchanger. For CO ₂ as a refrigerant, neither the in FIG. 2 illustrated process according to the prior art still in the in FIG. 4 process according to the invention during the isothermal compression reaches the wet steam area. The line A'-B 'and the line a'-b' are located above the wet steam line of CO ₂ . The wet steam area is reached only during the relaxation, the point D '* is achieved without exploiting the expansion work in an isenthalp relaxation, whereas when using an expansion pump a polytropic relaxation is achieved, which is steeper than the line C'-D' * and to point D 'on the same Isotherms leads. For better comparability are in FIG. 4 also the points a ', b', d ', e' off FIG. 2 registered and in FIG. 3 also the points a, b, d, e.

1

Wärmepumpe/Kältemaschine

2

Flüssigkeitskolbenverdichter

3

Gaskühler/Kondensator

4

Innerer Wärmeübertrager

5

Hochdruckspeicher

7

Niederdruckspeicher

8

Verdampfer

9

Rückschlagventil

10

Rückschlagventil

11

Rückschlagventil

12

Rückschlagventil

13

Leitung

14

Leitung

15

Leitung

16

Leitung

17

Leitung

18

Leitung

19

Leitung

20

Zylinder

21

Zylinder

22

Leitung

23

Leitung

24

Hydraulikleitung

25

Hydraulikleitung

26

Arbeitsraum

27

Arbeitsraum

28

Vier-Wege-Hydraulikventil

29

Hydraulikleitung

30

Leitung

31

Hydraulikpumpe

32

Doppelmantel

33

Doppelmantel

34

Wärmetauscherbündel

35

Wärmetauscherbündel

36

Abfuhrleitung

37

Abfuhrleitung

38

Zufuhrleitung

39

Drei-Wege-Ventil

40

Umwälzpumpe

41

Verbraucher

42

Expansionspumpe

43

Nassdampflinie

44

Maximum

45

Taulinie

46

Siedelinie

47

Schnittpunkt

In the figures are

1

Heat pump / chiller

2

Liquid piston compressor

3

Gas cooler / condenser

4

Internal heat exchanger

5

High-pressure accumulator

7

Low-pressure accumulator

8th

Evaporator

9

check valve

10

check valve

11

check valve

12

check valve

13

management

14

management

15

management

16

management

17

management

18

management

19

management

20

cylinder

21

cylinder

22

management

23

management

24

hydraulic line

25

hydraulic line

26

working space

27

working space

28

Four-way hydraulic valve

29

hydraulic line

30

management

31

hydraulic pump

32

jacketed

33

jacketed

34

heat exchanger bundle

35

heat exchanger bundle

36

discharge line

37

discharge line

38

supply line

39

Three-way valve

40

circulating pump

41

consumer

42

expansion pump

43

Wet steam line

44

maximum

45

dew line

46

boiling

47

intersection

Claims (10)

1. A method for operating a heat pump or refrigeration device (1) wherein a coolant is compressed by means of a fluid displacement compressor (2), is subsequently cooled and optionally condensed and then expanded and, in a next step, is evaporated and finally fed back to the fluid displacement compressor (2), characterized in that heat from the coolant, which is pre-cooled after the compression, is transferred to the evaporated coolant before said coolant is fed again to the fluid displacement compressor (2), and thus the cycle is closed, and that the coolant is expanded in an engine comprising an operative connection to a hydraulic pump (31) by means of which a hydraulic fluid of the fluid displacement compressor (2) can be pumped.
2. The method according to claim 1, characterized in that the fluid displacement compressor (2) has two operating chambers which are separated from each other, and that the coolant is alternatingly compressed in one of the two operating chambers, the common hydraulic fluid of which is alternatingly pumped back and forth from the one operating chamber (26, 27) into the other operating chamber (26, 27).
3. The method according to any one of the preceding claims, characterized in that the coolant is stored temporarily in a high pressure storage (5) after it has been cooled and has transferred further heat to the evaporated coolant.
4. The method according to any one of the preceding claims, characterized in that after expansion, the coolant is stored temporarily in a low pressure storage (7) before it is subsequently evaporated.
5. The method according to any one of the preceding claims, characterized in that the coolant condensates during cooling and/or during transferring heat to the evaporated coolant and/or during the compression.
6. The method according to any one of the preceding claims, characterized in that the coolant after the cooling and the heat transfer to the evaporated coolant is expanded under the performance of work in an engine, in particular an expansion pump (42) or an expansion turbine, before it is evaporated or heated.
7. The method according to any one of the preceding claims, characterized in that heat is extracted from the coolant during the compression in the fluid displacement compressor (2) in such a manner that the compression takes place isothermally and that the heat dissipated from the coolant by means of a separate heat transfer medium is fed to a heat sink, wherein the heat transfer medium, after heating in the fluid displacement compressor (2), is further heated in the cooler (3) for the coolant.
8. A heat pump or refrigeration device (1) with a fluid displacement compressor (2) for compressing a coolant while dissipating heat to a heat transfer medium materially separated from the coolant, a cooler (3) for reducing the temperature of the compressed coolant, a pressure reduction device for expanding the cooled coolant, an evaporator (8) for evaporating the expanded coolant, and lines connecting the aforementioned components so that the coolant can be conveyed in the cycle, and with a heat exchanger by means of which heat can be transferred from the coolant leaving the cooler to the coolant leaving the evaporator, characterized in that the pressure reduction device is an engine, in particular an expansion pump (42) or an expansion turbine which is arranged between the cooler (3) and the evaporator (8) and comprises an operative connection to a hydraulic pump (31) by means of which a hydraulic fluid of the fluid displacement compressor (2) can be pumped.
9. The heat pump or refrigeration device (1) according to the preceding claim, characterized in that the expansion pump (4) is a free piston pump with self-switching valves.
10. The heat pump or refrigeration device (1) according to any one of the claims 8 and 9, characterized by an operative connection, in particular a mechanical coupling, between the engine, which acts during the expansion of the coolant, and a hydraulic pump (31) by means of which a hydraulic fluid can be pumped into an operating chamber of the fluid displacement compressor (2).

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