DE102017223127B3 - Heat transfer circuit with a cooling jacket for cooling a heat source of a drive motor - Google Patents

Abstract

The invention relates to a heat transfer circuit (1) for cooling a heat source (4), comprising a cooling jacket (6) with an inner jacket wall (12) which is in thermal contact with the heat source, and with an outer jacket wall (10), which together with the inner jacket wall delimits a jacket space (8), at least one heat transfer nozzle (14) which is arranged on the outer jacket wall and which is set up to inject heat transfer medium into the jacket space, at least one heat transfer outlet (24) arranged on the outer jacket wall is, and which is adapted for the discharge of heat transfer, and a drive motor and a method for cooling a heat source.

Description

The invention relates to a heat carrier circuit with a cooling jacket for cooling a heat source, in particular a drive motor of a motor vehicle, and a drive motor of a motor vehicle with such a heat transfer circuit and a method for cooling a heat source, in particular a drive motor of a motor vehicle.

The invention will be described below in the context of a reciprocating engine of a motor vehicle to be cooled, a classic application of a heat carrier circuit with a cooling jacket. However, the invention can also be used in other applications in which cooling by means of a cooling jacket seems to make sense. In particular, the invention can also be used for cooling an electric machine used as a drive motor in a motor vehicle.

Multi-cylinder reciprocating engines in motor vehicles often have a piston housing with a cooling jacket, in which around the cylinder outer walls around a certain distance another wall - the outer shell wall - is arranged. By means of the cylinder outer walls, which are formed as an inner jacket wall, and the outer jacket wall, a jacket space is delimited, which serves to dissipate the heat generated during combustion between the piston and the cylinder wall.

For heat dissipation, the jacket space in known cooling circuits for the mentioned motors flows through a suitable heat transfer medium, which is present in the liquid phase in order to allow the best possible convection. The cooling jacket of such cooling circuits usually has - depending on the engine concept - one or more feeds and one or more processes; the latter so that the heated heat carrier can be removed from the shell space. The cooling circuit is exchanged between the processes and the inlets at least with a heat transfer pump and a liquid-liquid or a liquid-air heat exchanger, so that the jacket space at any time sufficiently cool cooling liquid can be supplied.

The cooling circuits described above have, inter alia, the disadvantage that a relatively large mass of heat transfer medium is required in order to ensure a mass flow in the cooling jacket, which is sufficient to dissipate the operating heat of the reciprocating engine. Frequently, in such heat transfer circuits and the heat transfer temperature is not adapted to the thermal conditions of the heat engine to be cooled, but rather results randomly, which in turn requires a larger heat carrier mass in the cooling circuit. Normally, at least one adaptation of the upper limit temperature to be maintained by means of the cooling circuit to operation in hot countries takes place, so that the cooling circuit and in particular the heat carrier mass is oversized for most operating states in other countries.

In addition, a cooling of the reciprocating engine in its start-up phase is counterproductive for the quality of the aftertreated exhaust gases: the warm-up of the engine takes active cooling unnecessarily long, causing disadvantages in pollutant emission and friction, for example, by particle formation on cold walls or by later achievement the required operating temperature of a catalyst (light-off temperature).

With the problem of exhaust quality is already in the context of convection cooling the patent document DE 28 47 057 A1 apart. There, by way of example, an internal combustion engine with a cooling system is described that operates on the basis of an oil spray cooling. The cooling capacity is reduced during partial load operation of the engine by switching off part of the oil spray cooling. This is intended to increase the heat content in the combustion chamber, reduce the specific fuel consumption and shorten the warm-up period of the engine after the start, in particular the cold start.

Last but not least, such sized cooling circuits require high volume liquid coolers, which are difficult to accommodate in a confined space under the hood.

From the DE 3410261 A1 an evaporative cooling device for internal combustion engines with a cooling jacket is known, comprising a reservoir for receiving the liquid coolant, a condenser for re-cooling the coolant evaporated inside the cooling jacket and a coolant pump for conveying the liquid coolant within the cooling circuit, wherein the recooled in the condenser coolant in the Reservoir is fed back, wherein means are provided, by which the coolant is sprayed into the cooling jacket, if necessary, or can be injected.

From the DE 10 2004 017 909 A1 is a device for cooling of at least one piston of an internal combustion engine by means of a lubricating oil pump, the oil from the lubricating oil circuit at least at the bottom at least one piston via a, having an outlet opening feed line, wherein the oil is supplied via at least one valve, wherein the at least one valve Check valve is what a supply of oil only from a defined pressure in the lubricating oil circuit permits and a control unit is provided, which ensures that the lubricating oil pump is controlled to provide a variable pressure in the lubricating oil circuit at different operating conditions of the internal combustion engine load-dependent, or at least one valve is a controllable solenoid valve and a control unit is provided, which ensures that the control the solenoid valve is carried out in dependence on the load of the internal combustion engine.

Against this background, it is an object of the invention to improve a heat carrier circuit with a cooling jacket, in particular for cooling a drive motor.

This object is achieved by a heat carrier circuit with the features of claim 1 and by a method for cooling a heat source according to the features of claim 8. A drive motor with such a heat transfer circuit is the subject of claim 7. Preferred embodiments of the invention are the subject of the dependent claims.

According to one aspect of the invention, a heat carrier circuit for cooling a heat source, in particular a drive motor of a motor vehicle such as a reciprocating engine or an electric machine is provided. The heat carrier circuit comprises: a) a cooling jacket having an inner jacket wall, which is in thermal contact with the heat source in particular, and which can be arranged around the heat source according to an embodiment, and from which in particular heat can be removed by means of the heat carrier, with a b) at least two heat transfer nozzles, which are arranged on the outer jacket wall, and which are adapted to inject heat carrier into the shell space, c) preferably at least one heat carrier outlet, which at the outer Jacket wall is arranged, and which is adapted to discharge the heat carrier.

Along a heat carrier line between the heat carrier outlet and the heat transfer nozzle d) a capacitor is arranged, which is adapted to condense, especially in the jacket wall, evaporated heat transfer medium.

According to a further aspect of the invention, a drive motor is provided with at least one reciprocating piston and with a heat carrier circuit according to an embodiment of the invention. The inner jacket wall is formed together with at least one cylinder for receiving a reciprocating piston.

According to a further aspect of the invention, a method is provided for cooling a heat source, in particular a drive motor such as a reciprocating piston engine or an electric machine, by means of a heat carrier circuit according to an embodiment of the invention. The method has at least the following steps: a) determination of a current temperature at at least one point, in particular a cooling point, of the inner jacket wall, in particular by means of a temperature determination, which can be designed in particular with a temperature sensor and / or with a temperature model, b) comparison the determined temperature with a predetermined threshold value, in particular a boiling temperature of the heat carrier, c) preferably releasing an injection of heat transfer medium into the jacket space when the threshold value is exceeded, d) adjusting a volume flow as a function of the determined temperature.

Among other things, the invention is based on the finding that convection cooling in conventional cooling jackets is not advantageous in every operating state of the vehicle engine, but, on the contrary, can prevent a rapid improvement of the exhaust gas quality, above all during a cold start of the engine.

The invention is based inter alia on the idea that convection is neither the only available method of heat removal from a heat source, nor in any operating state, the most efficient method.

Characterized in that in the heat carrier line beyond the heat transfer jacket, a condenser is arranged, which is adapted to condense vaporized heat carrier, the operating temperature of the surface to be cooled of the heat source on the one hand and the heat transfer medium used on the other hand be coordinated so that the heat carrier after injection evaporated by the heat transfer nozzle (s) when hitting the inner jacket wall to be cooled, that is, from the liquid to a vaporous state. Instead of a conventional cooler which has been streamed in by the wind, a condenser which is more favorable in terms of the required installation space is used. The condenser is preferably constructed structurally similar to a convective heat exchanger. Because of the very effective heat transfer during the phase change from gaseous to liquid, it can advantageously be made smaller than a convective cooling cooler. Before the condenser, a compressor must increase the pressure of the heat-carrying fluid and thereby raise its boiling point to allow its condensation.

The energy required for evaporation at least substantially corresponds to the heat energy dissipated.

In addition, it can be ensured in such a heat transfer circuit that relatively quickly after switching off the spray performance of the heat transfer (s) - and anyway before switching - within the mantle space substantially stationary air is present, which is not suitable, the inner shell wall, a large amount of heat but rather acts as a thermal insulator, at least compared to a liquid convection. In addition, it can be ensured that the drive motor, for example during cold start, reaches a temperature level as fast as possible, which enables efficient catalyst operation. When driving breaks or temporary shutdown of a motor within a hybrid electric hybrid drive, the ideal operating temperature of the drive can be advantageously obtained longer.

In a suitable embodiment of the heat carrier circuit, this effect can even be amplified by means of the heat transfer compressor by the pump space of the jacket space is at least partially evacuated, which further reduces the heat extraction from the inner shell wall.

In order to be able to coordinate such a heat carrier cycle in particular to the typical operating temperatures of the surfaces to be cooled of internal combustion engines and / or electric motors, according to one embodiment, water, or a water-glycol mixture, is the main constituent of the heat carrier. Depending on the type of engine, various heat carriers are suitable, for example water, alcohols or refrigerants known from the field of air-conditioning technology

At the operating temperatures of internal combustion engines in the range of several 100 ° C is carried out with such a heat transfer easily evaporation on the inner shell wall when the heat transfer fluid impinges on it. At the operating temperatures of electric motors below 100 ° C, the use of, for example, an alcohol may cause a sufficient lowering of the evaporation temperature to ensure evaporation.

Thus, the operation of the cooling circuit to different operating conditions of the heat source to be cooled, in particular the drive motor, can be adjusted (for example, to a cold start), the heat carrier circuit to a control means which is adapted to a volume flow of the heat carrier through the heat transfer, in particular by means of a controlled valve, adapt. This can ensure that, for example, during a cold start, the inner shell wall is not sprayed with heat transfer, while after the warm-up phase of the engine heat transfer through the heat transfer in the shell space and applied to the inner shell wall to cool the engine.

The heat carrier circuit has a temperature determination for determining a current temperature of the inner jacket wall, wherein the control means is adapted to adjust the volume flow of the heat carrier as a function of the current and / or future expected temperature. As a result, a required volumetric flow of the heat carrier can be adapted to the cooling power required in the individual operating case, for example, in several stages or continuously graduated.

Preferably, the control means is adapted to increase the volume flow of the heat carrier, when the current temperature is higher than a predetermined threshold value. The predetermined threshold may be, for example, a boiling temperature of the heat carrier; In this case it can be ensured that the cooling can be used with optimal heat dissipation, as soon as a sufficient temperature for evaporation of the heat carrier is ensured on the inner shell wall.

In order to align the heat transfer circuit individually to those points of the inner shell wall, which relatively speaking require the highest cooling performance, according to one embodiment, a main spray of the heat transfer to a predetermined, especially relative to the remaining inner shell wall, hot cooling of the inner shell wall.

In order to be able to adequately cool, for example, an internal combustion engine having a plurality of cylinders, a heat carrier nozzle is arranged in each case at two or more points of the outer jacket wall. Preferably, in each case a heat transfer nozzle is arranged at a plurality of locations of the outer jacket wall, wherein in particular a plurality of heat transfer nozzles can be directed to a partial heat source, such as a cylinder of a reciprocating engine, preferably to different locations of the associated part of the inner shaft wall.

In order to enable a temperature-dependent operation with several cooled points, the temperature determination is set up to determine a current temperature at two or more points of the inner jacket wall.

So that the vaporized heat transfer medium in the heat transfer circuit does not generate too high a pressure, the heat transfer circuit according to one embodiment to a surge tank for receiving vaporized heat transfer in particular in the heat transfer between the / the throttle point (s) on the / the coolant nozzle (s) and the heat transfer medium Compressor is arranged.

According to one embodiment, the heat carrier circuit to a heat transfer compressor, which is preferably arranged in the heat transfer before the condenser, in particular its liquid container, and after the / the heat transfer (s). This can be ensured that, on the one hand, the condensation of the heat carrier is made possible and, on the other hand, the heat transfer nozzles are supplied with sufficient heat transfer under sufficient pressure to provide the required in each operating state heat transfer performance.

The volume flow of the heat carrier is adjusted, in particular by the heat transfer nozzles, by means of a valve and / or by means of a heat transfer compressor, which are arranged in the fluid flow in front of the heat transfer nozzle.

In a heat transfer circuit having a plurality of spaced-apart heat transfer nozzles according to an embodiment, each heat transfer nozzle is aligned with another predetermined cooling point of the inner jacket wall, wherein the current temperature can be determined for each of the predetermined cooling points.

Preferably, the volume flow of the heat carrier is distributed to the individual heat transfer nozzles such that a hotter predetermined cooling point is cooled more than a colder predetermined cooling point. In particular, the hotter exhaust side of an internal combustion engine may be cooled more than the cooler intake side.

In order to optimize the cooling effect application specific, according to an embodiment by means of a pressure control unit on the heat transfer compressor and / or by means of a selection of a suitable heat-carrying fluid, the one, especially in the application most suitable, boiling temperature of the heat carrier adjusted.

• 1 einen Wärmeträgerkreislauf für eine Hubkolbenmaschine gemäß einer beispielhaften Ausführung der Erfindung in einer Schemaansicht;
• 2 den Wärmeträgerkreislauf gemäß 1 entlang der dort eingezeichneten Schnittlinie B - B in einer Schemaansicht; und
• 3 den Wärmeträgerkreislauf gemäß 1 entlang der dort eingezeichneten Schnittlinie C - C in einer Schemaansicht.

Other features, advantages and applications of the invention will become apparent from the following description taken in conjunction with the figures. Show it:

• 1 a heat transfer circuit for a reciprocating engine according to an exemplary embodiment of the invention in a schematic view;
• 2 the heat transfer circuit according to 1 along the section line B - B drawn there in a schematic view; and
• 3 the heat transfer circuit according to 1 along the section line C - C drawn there in a schematic view.

In 1 is designed as a reciprocating engine drive motor 2 with a cooling circuit 1 for cooling several heat sources 4.1 . 4.2 . 4.3 and 4.4 (here the individual cylinders of the drive motor 2 ). The drive motor 2 is installed in a motor vehicle, not shown.

For cooling the heat sources 4 (So the cylinder walls), the heat transfer circuit 1 a cooling jacket 6 on. The cooling jacket 6 has a jacket space 8th on, which by an outer shell wall 10 and at least one inner jacket wall 12 - In the embodiment, one per heat source 4 - is demarcated. Each of the inner shell walls 12.1 . 12.2 . 12.3 and 12.4 stands in each case with its associated heat source 4.1 . 4.2 . 4.3 respectively. 4.4 in thermal contact and is each about this heat source 4 arranged around. In this way, the respective inner shell wall 12 absorb the heat of the respective heat source, so that it can be dissipated by the heat transfer circuit.

In the embodiment, the drive motor 2 designed as a four-cylinder reciprocating engine, which has a double housing structure: an inner housing structure forms the inner jacket walls of the cooling circuit; an outer casing structure is formed to mate with the inner casing walls 12.1 . 12.2 . 12.3 and 12.4 together the mantle room 8th formed.

On the outer jacket wall 10 is one or a plurality of heat transfer nozzles 14 arranged. Each of the heat transfer nozzles 14 is at least one cylinder of the drive motor 2 - Say at least one of the heat sources 4 - assigned. For example, a main spray axis (by way of example with the reference number 40 in 2 drawn) of the heat transfer nozzle 14 to the corresponding heat source, in particular to an associated cooling point 42 , to be aligned.

In the embodiment are both on a hot side 16 as well as on a cool side 18 of the drive motor 2 Heat transfer nozzles 14 arranged (compare in detail also 2 and 3 and the associated description).

Each of the heat transfer nozzles 14 is to the heat carrier line 20 the heat transfer circuit 1 connected, wherein in the inlet to each heat transfer nozzle 14 a valve 22 is arranged with which a volume flow of the associated to the associated heat transfer fluid 14 guided heat carrier can be regulated. This valve can be structurally integrated, for example, in the nozzle.

In the exemplary embodiment, the valves 22 at least substantially steplessly controllable and have electromagnetic actuators. Also conceivable are on-off valves or valves with two or more discrete opening stages.

On the outer jacket wall 10 is also a heat transfer outlet 24 arranged, for the discharge of heat transfer medium from the jacket space 8th is trained.

For complete training of the cooling circuit 1 this has a compensation volume in the exemplary embodiment 26 , a heat transfer compressor 28 and a capacitor 30 on. The heat transfer compressor 28 is in the heat transfer flow between the equalization volume 26 and the capacitor 30 arranged.

For controlling the valves 22 and the heat transfer compressor 28 the heat carrier circuit has a control means 32 on. For a temperature-based control of the cooling capacity of the cooling circuit 1 is the control means 32 set up on a temperature model 34 of the drive motor 2 (and in particular the heat sources 4 ).

2 shows the heat transfer circuit 1 along the section line B - B. From this illustration it can be seen that on the hot side 16 every cylinder (every heat source 4 ) - on the hot exhaust outlet side 36 of the cylinder is - for example, a heat transfer fluid 14 is more arranged than on the cool side 18 standing on the cool mixture inlet side 38 the cylinder is located. Each one along the height of the mantle space 8th arranged valves 22 can by means of the control means 32 be controlled separately, preferably in dependence on the temperature model 34 and / or depending on an already past operating time or the duration since a cold start of the drive motor 2 ,

The reference numbers of the valves 22 and the heat transfer nozzle 14 in 2 (and analogously in 3 ) explain themselves as follows: The letter af stands for the height in the mantle space 8th , the lowered first digit stands for the assigned heat source; the subscript second digit 16 or 18 stands for the arrangement on the hot side 16 or the cool side 18 ,

The temperature model 34 is set up in the embodiment, the control means 32 separate from each refrigeration point 42 the inner jacket wall 12 on which a heat transfer nozzle 14 is directed to provide a current operating temperature of this cooling point.

The control means 32 is in turn set up, based on this provided operating temperature, a heat carrier inlet to the corresponding heat transfer nozzle 14 partially or completely free or block. The location for which the temperature is determined in each case, preferably that cooling point 42 to which the associated main spray axis 40 is directed.

Additionally or alternatively to such a temperature model, at one, some, or each of these locations, the inner shell wall may 12 a suitable temperature sensor may be provided which is connected to the control means 32 connected is.

Hereinafter, the operation of the invention by way of example with reference to the representations of 1 and 2 explains:

The in 1 illustrated cooling circuit 1 is formed and the operating temperature of the surface to be cooled of the inner jacket wall (and the thermally connected heat sources 4 ) that the heat transfer medium - in the embodiment, a water-glycol mixture - at least partially, preferably completely evaporated when hitting the inner shell wall.

Thus, the cooling takes place - compared with a conventional liquid cooling jacket - to a much lower (or no) proportion by means of convective heat transfer and to a much higher proportion (or completely) by the action of the evaporation energy during the phase transition of the heat carrier from liquid to gaseous.

To achieve this, is the heat transfer compressor 28 adapted to pressurize the heat carrier and in the (suitable branching) heat transfer line 20 through the capacitor 30 towards the valves 22 to promote.

Depending on the cooling power requirement of the individual cooling points to be cooled (by way of example with the reference numeral 42 in 2 as the point of impact of the respective main spray axis 40 drawn) are the corresponding valves 22 , if necessary partially, opened or closed. When opening one of the valves 22 gives the associated heat transfer nozzle 14 a heat transfer spray with a large number of small liquid drops in the direction of the point to be cooled. Because of the high temperature of the inner shell wall 12 at the point to be cooled, the small drops evaporate. In doing so, they absorb the required evaporation energy by absorbing heat from the inner shell wall 12 dissipate.

So lies in the mantle room 8th a mixture of liquid spray and a vapor phase of the heat carrier before. A pressure control by means of a pressure control unit 29 at the compressor in conjunction with a suitable choice of the heat-carrying fluid determined in the embodiment, an optimum evaporation temperature. More heat carrier per time (= volume flow) is sprayed when more cooling capacity is required. The control means 32 calculated as a function of the prevailing operating temperatures of the areas of the inner jacket wall to be cooled 12 and / or the heat source to be cooled 4 , Which volume flow of the heat carrier through which of the valves 22 in the mantle room 8th is initiated.

By the pressure in the mantle space 8th the heat transfer steam is through the heat transfer outlet 24 further into the heat transfer circuit 1 promoted, with the compensation volume 26 Can compensate for pressure differences.

Downstream of the heat transfer steam passes through a compressor 28 in the condenser 30 where the compressed heat transfer medium is condensed by releasing its latent heat energy to the ambient air or the wind. Depending on the intended line length may optionally between the capacitor 30 and the heat transfer nozzles may be provided with an additional pump (not shown) in the heat transfer stream. The condensed heat transfer medium is then transferred via the heat transfer nozzles 14 back into the mantle room 8th sprayed.

3 shows the heat transfer circuit 1 along the section line C - C. It can be seen from this illustration that the arrangement of the heat transfer nozzle 14 a matrix of nozzles, by means of which the drive motor 2 Depending on its operating state (in particular the different operating temperatures of the heat sources and their parts) can be cooled slender according to the respective need for cooling capacity.

LIST OF REFERENCE NUMBERS

1

Cooling circuit

2

drive motor

4

heat source

6

cooling jacket

8th

shell space

10

outer jacket wall

12

inner jacket wall

14

Wärmeträgerdüse

16

hot side

18

cool side

20

Heat transfer line

22

Valve

24

Heat transfer medium outlet

26

compensating volume

28

Heat carrier compressor

29

Pressure control unit

30

capacitor

32

control means

34

temperature model

36

Exhaust outlet

38

Mixture inlet side

40

Hauptsprühachse

Claims (12)

Heat transfer circuit (1) for cooling a heat source (4), the heat transfer circuit comprising: - a cooling jacket (6) with an inner jacket wall (12), which is in thermal contact with the heat source, and with an outer jacket wall (10), which together with the inner jacket wall a jacket space (8) defines, - at least two heat transfer nozzles (14) which is arranged at different locations of the outer jacket wall, and which is adapted to inject heat carrier into the shell space, - at least one heat transfer outlet (24) is arranged on the outer jacket wall, and is arranged for the discharge of heat transfer medium, - a heat transfer line (20) along which a condenser (30) is arranged between the heat transfer and the heat transfer fluid, which is adapted to condense vaporized heat carrier, a control means (32) which is adapted to a volume flow of the heat carrier through the A temperature determination (34) for determining a current temperature at different points of the inner jacket wall (12), wherein the control means is adapted to adjust the volume flow of the heat carrier in dependence on current temperatures, characterized in that the Control means (32) is adapted to adjust the volume flow through each of the heat transfer nozzles (14) by means of a respective valve (22), wherein the valves are each arranged in fluid flow in front of the corresponding heat transfer nozzle (14). Heat transfer circuit (1) according to Claim 1 , characterized in that a Main component of the heat carrier water or a water-glycol mixture is. Heat transfer circuit (1) according to one of the preceding claims, characterized in that the control means is adapted to increase the volume flow of the heat carrier, when the current temperature is higher than a predetermined threshold value. Heat transfer circuit (1) according to one of the preceding claims, characterized in that a Hauptsprühachse (40) of the heat transfer nozzle is aligned with a predetermined, hot cooling point (42) of the inner almond wall. Heat transfer circuit (1) according to one of the preceding claims, characterized by a surge tank (26) for receiving vaporized heat transfer medium, which is arranged in the heat transfer flow between the heat carrier outlet and the condenser. Heat transfer circuit (1) according to one of the preceding claims, characterized by a heat transfer compressor (28), which is arranged in the heat transfer flow between the condenser and the / the heat transfer (s). Drive motor (2) with at least one reciprocating piston and with a heat carrier circuit (1) according to one of the preceding claims, characterized in that the inner jacket wall (12) is formed together with at least one cylinder (4) for receiving a reciprocating piston. Method for cooling a heat source (4) of a drive motor (2) by means of a heat carrier circuit (1) according to one of the preceding Claims 1 to 6 characterized by the steps of: - determining a current temperature at at least one point of the inner jacket wall (12), - comparing the determined temperature with a predetermined threshold value, - releasing an injection of heat transfer medium into the jacket space (8) when the threshold value is exceeded, Adjusting the volume flow as a function of the determined temperature. Method according to the preceding Claim 8 , characterized in that the volume flow by means of a valve (22) and / or by means of a heat transfer compressor (28) is adjusted, which is arranged in the fluid flow in front of the heat transfer nozzle (14) / are. Method according to one of the preceding Claims 8 or 9 , characterized in that in a heat transfer circuit with a plurality of spaced heat carrier nozzles (14) each heat transfer to another predetermined cooling point (42) of the inner shell wall (12) is aligned, wherein the current temperature can be determined for each of the predetermined cooling points. Method according to one of the preceding Claims 8 to 10 , characterized in that the volume flow of the heat carrier is distributed to the individual heat transfer nozzles (14), that a hotter predetermined cooling point is cooled more than a colder predetermined cooling point. Method according to one of the preceding Claims 8 to 11 , characterized in that a boiling temperature of the heat carrier is adjusted by means of a pressure control unit (29) on the heat transfer medium compressor (28) and / or by means of a selection of a suitable heat-carrying fluid.

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