WO2014131591A1

WO2014131591A1 - Heat pump and method for operating a heat pump

Info

Publication number: WO2014131591A1
Application number: PCT/EP2014/052293
Authority: WO
Inventors: Bernd Gromoll; Florian REISSNER
Original assignee: Siemens Aktiengesellschaft
Priority date: 2013-02-27
Filing date: 2014-02-06
Publication date: 2014-09-04
Also published as: DE102013203243A1

Abstract

The invention relates to a heat pump (12) with a fluid. Said heat pump (12) comprises at least one condensation device (8) for condensing the fluid, at least one expansion device (9) for expanding a fluid, at least one evaporation device (10) for evaporating the fluid and at least one compression device (7) for compressing the fluid. The condensation curve (18) of the fluid is inclined in the direction of increasing entropy at least in a major area of its path in the T-s-diagram (temperature-entropy). Said heat pump (12) comprises at least one heat guiding device (22) which can heat the fluid in the flow direction thereof (11) downstream of the evaporation device (10) and upstream of the compression device (7). The invention also relates to a method for operating a heat pump (12).

Description

description

Heat pump and method for operating a heat pump

The invention relates to a heat pump with a fluid, with at least one condensation device for condensing the fluid, with at least one expansion device for expanding the fluid, with at least one evaporation device for evaporating the fluid and with at least one compression device for compressing the fluid. The invention also relates to a method for operating such a heat pump.

A heat pump of the type mentioned at the beginning is used, for example, for heating buildings. A heat pump is a machine that uses technical work to absorb thermal energy in the form of heat from a lower temperature heat source and, together with the drive energy of the compressor, to dissipate waste heat to a higher temperature heat sink. Within a heat pump becomes a fluid conducted in a circular process. This cyclic process is also called thermodynamic vapor compression cycle.

In heat pump fluids are currently used, which are questionable from As ^¬ pekten of environmental protection, because they have a high global warming potential. Furthermore, some of the common fluids are flammable, sometimes hazardous to health or toxic. No fluid which has both very good environmental and safety properties is currently in commercial use in heat pumps.

CO ₂ is more environmentally safely and definitions according ^¬ has a Global Warming Potential of 1, however, is problematic for ther ^¬ modynamischer view, since its critical temperature is only about 31 ° C. Thus, above this temperature, the heat transfer to the heat sink does not occur in the context of a nearly isothermal condensation, that is, almost more constant Temperature, giving off the heat of condensation, but over a temperature range. As a result, the heat transfer to heat sinks that require a nearly constant temperature, such as steam generation affected. Furthermore, the pressure level for the usual for heat pumps tempera ^¬ ren in CO ₂ relatively high and thus requires a higher ap ^¬ para tive effort.

Object of the present invention is to provide a heat pump of the type mentioned, and a method for operating such a heat pump, in which fluids can be used that are environmentally friendly and safety-friendly, so have a low global warming potential and neither flammable nor are health ^¬ harmful.

This object is achieved by a heat pump with the features of patent claim 1 and by a method with the Merkma ^¬ len of claim 8. Advantageous ^{Ausgestaltun ¬} conditions with expedient developments of the invention are specified in the dependent claims.

The heat pump according to the invention comprises a fluid whose tau line is inclined at least in a predominant region of its course in the direction of increasing entropy in the Ts diagram. Furthermore, the heat pump comprises at least one Wär ^¬ mezuführeinrichtung, by means of which the fluid upstream in the flow direction downstream of the evaporation means and the compression means is heated.

The fact that heat is supplied to the fluid before its compression and after its evaporation, both the Tempe ^¬ rature and the entropy of the fluid is increased. As a result, the fluid can be compressed, that is, its pressure can be increased without a phase change occurring. Thus, the fluid is in a gaseous phase both before compression and after compression. The supply of energy in the form of heat is required in particular when the used fluid in its underlying Ts-diagram (temperature-entropy diagram) has a strongly overhanging 2-phase region. An overhanging 2-phase region is said to be when the tau line of the corresponding fluid is inclined in the direction of increasing entropy, at least in a predominant region of its course. The presence of the fluid in the form of a gas phase both before and after its compression is particularly advantageous because a Pha ^¬ senwechsel of the gas phase in a 2-phase region consisting of gas phase and liquid phase, damage to the compaction ^¬ processing device, in the form can lead, for example, liquid ^¬ slaps.

Preferably, the heat supply device comprises at least one heat exchanger through which the fluid flows, by means of which a heat quantity can be taken from the fluid after it has condensed and before it evaporates. Furthermore, it is at least partially supplied with ^¬ means of the heat exchanger the fluid after its evaporation and prior to its compression, the amount of heat.

A heat exchanger transfers heat from egg definition ^¬ nem stream of higher temperature to a material flow of lower temperature. Located on the one side of the heat-transferring surface of the heat exchanger after the ^¬ sen condensation and before the evaporation of warm fluid and on the other side of the heat transfer surface after its evaporation and prior to its compression in comparison to cold fluid, it can by the conditional heat exchange, the fluid is particularly easy to be placed in a state of higher temperature and higher entropy before its compression.

The heat exchanger is therefore flowed through both on its warm flow side leading, as well as on its side leading the cold flow of the fluid, with the difference that on the one hand, the fluid is warmer than on the other side. The heat transfer is particularly effective when the fluid in the flow direction flows shortly after the condensation device in the heat exchanger and dissipates a portion of its heat to the colder fluid on the other side of the heat exchanger. If the other side of the heat exchanger is arranged so that the heat is transferred to the colder fluid in the direction of flow shortly before the fluid enters the compression device, the heat losses are particularly low.

In other words, a part of the resulting product will process heat by means of fewer components and thus supplied in a particularly space- and weight-saving way to the fluid before the compression ^¬ sen. Thus, the equipment cost is reduced and material costs saved. As a further advantage, it has been shown that the amount of heat ^¬ in particular before the expansion of the fluid removable and the fluid after its evaporation and before its compression is at least partially supplied. Characterized in that the fluid before its expansion through the

Heat exchanger is withdrawn heat, there is a larger amount of transferable heat available. Expansion is thermodynamically an irreversible process. In other words, with respect to the Ts diagram of the fluid, this means that the entropy of the fluid increases. The greater the expansion work done, the greater the dissipation share. If, in other words, the fluid is deprived of energy in the form of heat by the heat exchanger before the expansion of the fluid, the expansion work performed during the expansion is also smaller. Since thus a ^¬ forth also occurring by expansion dissipation is smaller in absolute value, less occur thermal losses, and therefore the efficiency of the heat pump is improved. In a further advantageous embodiment of the invention, the heat supply device at least one Wärmeübertra ^¬ tion module, in particular at least one heat exchanger and / or at least one electric heating element. Such a heat transfer module, both as

Heat exchanger, as well as an electric heating element, can be ^{¬ designed in} particular as a PTC element, or another heating device is powered by an external source of energy. In the case of a cold start of the heat pump, the temperature of the fluid before its compression is not yet large enough that an at least partial phase ^¬ change of the fluid could be prevented during its compression. By supplying heat through the heat transfer ^¬ module, the fluid can vorkondi ^¬ tion before entering the compression ^¬ device even at a cold start of the heat pump, so that the fluid is present both before and after its compression in the gas phase. Especially effec- tive this phase shift is inhibited when the heat transfer ^¬ ^¬ temporally enforces this heat transfer module just before the beginning of compression by the compression device which can be configured as a compressor, takes place.

In a further advantageous embodiment, the heat pump comprises an expansion valve, by means of which the evaporator pressure and the overheating of the fluid flowing into the at least one evaporation ^{¬ device} is adjustable.

By means of an expansion valve, the evaporator pressure and the overheating of the fluid flowing into the evaporation device can be adjusted. In other words, the evaporator pressure and the overheating of the fluid can thus be controlled and / or regulated. Particularly precise, the evaporator pressure and the overheating of the fluid can be adjusted when a control of the evaporator pressure and overheating by z. B. with an automatic expansion valve

Evaporator pressure control, or an electronically controlled expansion valve with stepper motor control, or z. B. a thermostatically controlled expansion valve with sensor is controlled at the evaporator fluid outlet. Of particular advantage is that the heat pump ^¬ particular insbeson is used for providing industrial process heat, to heat the building or for heating water.

Since vorzugswei the heat exchanger of the heat supply se completely into the fluid circuit of the heat pump eingebun to is the application of heat through an external Ener ^¬ gieversorgung of the heat transfer module is only as long as erfor ^¬ sary until the transferable heat of the heat exchanger is large enough to keep the temperature of the The fluid supply of the heat transfer module can be done FITS simply by supplying electrical energy, ie on the power supply of a building in which the heat used me pump will occur if the Wärmeübertra ^¬ tion module is designed as an electric heating element. However, the heat transfer module can also be designed as a heat exchanger, the heat transfer can be done by a suffi accordingly warm operating medium. In this case, however, must be taken into account that the heating of the fluid is slower than in an electric heater since the heating then depends on the temperature of the medium involved in the heat exchange.

It is particularly advantageous if the global warming Potenti al of the fluid is less than 10.

The smaller the global warming potential of the fluid used, the smaller is its influence on the Treibhausef ^¬ fect and thus on the climate. In this aspect, the use of so-called fluoroketones as a fluid is particularly recommended. Such fluoroketones are commonly used as insulating gas and fire-fighting agent and white ^¬ sen addition to a low global warming potential of a value less than 10, the safety especially Güns term properties, non-flammable and non-health- to be harmful to your health. Thus, such operating materials for heat pumps can be used future-proof within the legal framework conditions.

In the method according to the invention for operating a heat pump with a fluid, this fluid is condensed by means of at least one condensation device, expanded by means of at least one expansion device, evaporated by means of at least one evaporation device and compressed by means of at least one compression device. The

The tau line of the fluid in the Ts diagram is inclined in the direction of increasing entropy, at least in a predominant region of its course. The heat pump comprises at least one Wär ^¬ mezuführeinrichtung, by means of which the fluid is heated in the flow direction downstream of the vaporisation device and upstream of the compression device.

Take the advantage ^¬ le and preferred embodiments described for the inventive heat pump also apply to the inventive method and vice versa.

The description above mentioned features and combinations of features as well as mentioned below in the Figurenbe ^¬ letters and / or alone shown in the figures features and combinations of features can be used not only in the respectively specified combination but also in other combinations or in isolation, without the To leave frame of the invention.

Further advantages, features and details of the invention ^¬ be gathered from the claims, the following description of preferred embodiments and with reference to FIGS.

Showing:

1 schematically shows a cyclic process in the form of a thermodynamic vapor compression cycle for a heat pump and represents the state of the art. 2 shows the prior art, based on a Ts diagram for the conventional fluid R134a a conven- ^¬ nell run cycle of a heat pump. 3 shows a greatly overhanging 2-phase region on the basis of a T S diagram and the transfer of the fluid from the single-phase gas-phase in a 2-phase region when the cycle conven ^¬ tionally, that is guided without additional heating of the fluid before the ^¬ sen compaction.

4 shows schematically the cycle of the heat pump according to the invention with a heat supply device, the one

Heat exchanger and a heat transfer module comprises. 5 shows, based on a T-s diagram for a fluid with a strongly overhanging 2-phase region, the heat supply through a heat exchanger and / or by a heat transfer module and the subsequent compression of the fluid, wherein the fluid is present both before and after compression in the single-phase gas phase.

In Figure 1, the cycle of a heat pump 12 is shown schematically. The fluid is conveyed in a flow direction 11 through the heat pump 12. An evaporator, which is designed as an evaporator 10, vaporizes the fluid so that it assumes a vapor state 1. In this vapor state 1, the fluid enters a ^{Verdichtungseinrich ¬} tion, which is designed as a compressor 7. By the compressor 7, the fluid is compressed to a compression state 3 and flows in this compressed state in a condenser, which is designed as a condenser 8. Through the condenser 8, the fluid is converted into a condensed compression state 5, and finally ^¬ in an expansion device, which is designed as an expansion valve 9, expands. As a result, the fluid assumes a state of expansion to 6, wherein it was in this ^¬ turn to the evaporator is supplied to the tenth The fluid is thus continuously during the operation of the heat pump 12 lent according to the direction of the arrow, which represents the flow direction 11 schematically, promoted by the heat pump 12. FIG 2 illustrates a Ts diagram 23 illustrating entspre ^¬ accordingly the image plane to the right, ie, on the abscissas axis ^¬ entropy and 14 on the image plane up to, ie on the axis of ordinates a temperature. 13 The TS plot 23 is used to represent a dew line 18, a boiling line 19, as well as different aggregate states of the fluid. The dew line 18 delimits a gas phase 15 from a two-phase region 16, wherein in the two-phase region 16 the fluid is present both in the liquid state and in the gaseous state. The boiling line 19 delimits the 2-phase region 16 from a liquid phase 17. The illustrated Ts diagram 23 illustrates in FIG. 2 a fluid whose dew line 18 has a negative gradient.

In other words, the dew line 18 extends at least predominantly according to the image plane to the left of an axis ^¬ intersection point 24 in which the dew line 18 intersects with the Abs ^¬ zissenachse.

Also shown schematically in FIG. 2 are various thermodynamic states of the fluid, this fluid assuming these different states as a result of the flow through the compressor 7, the condenser 8, the expansion valve 9 and the evaporator 10. Starting from Dampfzu ^¬ stand 1, the compression state 3 of the fluid is achieved according to the flow direction 11 by compression within the compressor 7. The compression state 3 is located within the gas phase 15, which is why the compressor takes 7 kei ^¬ ne damage from liquid slugging in consequence of a phase ^¬ change. The illustrated connecting lines between the individual states are shown as straight connecting lines in FIG. 2, FIG. 3 and FIG. 5, but may also run in a curved manner. Starting from the compression state 3, the condenser 8 condenses the condensed state 5, which is located on the Siedelinie. ^Starting from this condensed compression state 5, the expansion state 6 is achieved by the passage of the fluid through the expansion valve 9. Starting from this expansion state 6, the vapor state 1 of the fluid is again achieved by supplying energy in the evaporator 10. Thus, the cycle of the heat pump 12 is closed.

FIG. 3 illustrates in essential parts the contents of FIG. 2, for which reason only the differences will be discussed below. The Ts diagram 23 shown in FIG. 3 illustrates the curves of the boiling line 19 and the tau line 18 of a fluid having a strongly overhanging 2-phase region 16. Thus, the 2-phase region 16 shown in FIG. 3 depends at least in accordance with the image plane with respect to the axis intersection point 24 essentially strong right over. In other words, the dew point line is 18 with respect to the image plane at least in the Wesent ^¬ union right of the axis intersection point 24 is carried out starting from the vapor state 1 in accordance with the method described in FIG 1, the conventional circuit of the heat pump 12 is a compression of the fluid by the compressor 7, so is the compression ^¬ condition 3 of the fluid in the two-phase region 16. Accordingly, it can cause damage, such as liquid shocks in the compressor 7, so the compression device.

To avoid liquid shocks when using fluids with strongly overhanging 2-phase region, it is recommended to use a heat pump according to the form shown in FIG. 4 shows at least in large part the structure shown schematically in FIG. In the following, therefore, only the differences will be discussed. Thus, a heat supply device 22 is provided in FIG 4 in the flow direction 11 after the evaporator 10 and in the flow direction in front of the compressor 7, which includes a heat exchanger 20 and a heat transfer module 21. In this case, the individual components of the heat supply device 22, that is to say the heat exchanger 20 and the heat transfer module 21, can also be arranged in a different order than that shown be. The heat transfer module 21 essentially serves to increase the fluid temperature when the heat pump 12 is started. When starting the heat pump 12, the fluid temperatures required for heat transfer by means of the heat exchanger 20 have not yet been reached, so that the heat transfer module 21 transfers the heat to the fluid. The transferred heat is sufficient to increase the fluid temperature such that even during the compression of the fluid by the compressor 7 no phase change occurs. However, the heat transfer module 21 can also be used in addition to the heat exchanger 20 for fluid heating. While the heat exchanger 20 takes out the fluid at a point heat and adding them at other Stel ^¬ le, the heat transfer module 21 is preferential as ^¬ executed as a heating element with an external power supply. Alternatively, however, the heat exchanger 20 may be designed as a heating element with external power supply and the heat transfer ^¬ module 21 as a heat exchanger.

The T-s diagram 23 shown in FIG. 5 clarifies, just like FIG. 3, the courses of the boiling line 19 as well as the

Dew line 18 of a fluid with strong overhanging 2- phase region 16. However, the following is to be scheduled on the differences ^¬ de if, instead of the heat pump schematically illustrated conventional 1 NEN the heat pump schematically illustrated in FIG 4 with the additional pre see ^¬ in FIG Heat supply 22 is used. Starting from the vapor state 1 by means of the heat supply means, that is by means of the heat exchanger 20 or the Wärmeübertragungsmo ^¬ duls 21 or the combination of both the fluid heat conces- leads, so that the fluid takes a heated vapor state 2 at ^¬. This heated vapor state 2 lies in the region of the single-phase gas phase 15 and thus corresponding to the image plane to the right of the dew line 18. If the fluid is supplied from the heated vapor state 2 to the compressor 7, this results in a compression of the fluid to the heated compression state 4. the heated Verdichtungszu ^¬ stand 4 is, as already the heated vapor state 2 within the range of single-phase gas phase 15. On the other Ren words thus the fluid remains in its compression by the compressor 7 in the gas phase 15 and there is no phase change in the 2-phase region 16. This will prevent ^¬ the that the compressor 7 damage z. B. takes in the form of liquid shocks.

Claims

claims

1. Heat pump (12) with a fluid, with at least one Kon ^¬ densationseinrichtung (8) for condensing the fluid, with at least one expansion device (9) for expanding the fluid, with at least one evaporation means (10) for vaporizing the fluid and with at least a compression device (7) for compressing the fluid,

characterized in that

the vapor line (18) of the fluid in at least one predominant area of its course in the direction of increasing entropy (14) in the Ts diagram is inclined, wherein the pump (12) we ^¬ nigstens includes a heat supply means (22), by means of which the fluid in the Flow direction (11) downstream of the evaporation device (10) and upstream of the compression device (7) is heated.

2. Heat pump (12) according to claim 1, characterized in that the heat supply means (22) comprises at least one of the fluid flowed through heat exchanger (20), by means of which the fluid after its condensation and before the evaporation, a heat quantity can be removed and wel ^¬ chem the fluid after its evaporation and before its compression, the amount of heat is at least partially supplied.

3. Heat pump (12) according to claim 2, characterized in that the amount of heat is removable, in particular before the expansion of the fluid and the fluid after its evaporation and prior to its compression at least partially.

4. Heat pump (12) according to one of claims 1 to 3, characterized in that the heat supply device (22) wenigs ^¬ least one heat transfer module (21), in particular at least one heat exchanger and / or at least one electric heating element.

5. heat pump (12) according to one of claims 1 to 4, characterized in that the heat pump (12) an expansion valve (9), by means of which the evaporator pressure and the overheating of the at least one evaporator (10) inflowing fluid is adjustable.

6. heat pump (12) according to one of claims 1 to 5, characterized in that the heat pump (12) in particular for Be ^¬ provision of industrial process heat, for heating buildings or for hot water treatment can be used.

7. Heat pump (12) according to any one of claims 1 to 6, characterized in that the global warming potential of the fluid is less than 10.

8. A method for operating a heat pump (12) with a fluid having at least one condensation device (8) for condensing the fluid, with at least one expansion device (9) for expanding the fluid, with at least one evaporation device (10) for vaporizing the fluid and at least one compression device (7) for compressing the fluid,

characterized in that

the tau line (18) of the fluid is tilted in the direction of rising entropy (14) in the Ts diagram at least in a predominant region of its course, wherein the heat pump (12) comprises at least one heat supply device (22) by means of which the fluid is in its Flow direction (11) downstream of the evaporation device (10) and upstream of the compression device (7) is heated.