REFRIGERANT CIRCUIT

Description

[0001] The invention relates to a method for operating a refrigerant circuit, comprising at least one refrigerant compressor, which compresses refrigerant supplied to a suction connection to high pressure, so that a compressor mass flow of the refrigerant compressed to high pressure exits at a pressure connection, at least one high-pressure side heat-emitting heat exchanger with an inlet, to which the refrigerant circuit supplies the compressor mass flow, and with an outlet, from which a cooled total mass flow of refrigerant exits, at least one expansion unit, comprising an expansion-compression unit having an expander and a compressor stage, which expands an expansion mass flow of the total mass flow, guided from the refrigerant circuit in the direction of the suction connection of the refrigerant compressor, from high pressure to an expansion pressure,and at least one cooling stage with at least one heat-absorbing heat exchanger, to which the refrigerant circuit supplies a main mass flow comprised of the expansion pressure mass flow expanded by the expansion unit, and which the refrigerant circuit supplies to the suction connection of the refrigerant compressor after leaving the cooling stage, wherein an emergency operation unit is arranged in the refrigerant circuit, which comprises a bypass line bypassing the expansion compression unit and to which at least one expansion element is functionally assigned.

[0002] Such methods are known from EP 2 244 037 A1.

[0003] The problem with these is always how to operate them as optimally as possible.

[0004] This object is achieved according to the invention in a method of the type described at the outset in that the emergency operating unit is designed such that it detects an expansion fault of the expansion compression unit, that the emergency operating unit has a controller which transfers the emergency operating unit from the inactive state to the active state and that the emergency operating unit is designed such that in the event of a fault, in particular an expansion fault, of the expansion compression unit, it changes from an inactive state to an active state in which it generates an emergency expansion mass flow for operating the cooling stage by expanding the high-pressure refrigerant by means of the expansion element, which emergency expansion mass flow the bypass line supplies to the refrigerant circuit for forwarding to the cooling stage.

[0005] The advantage of the solution according to the invention is that the emergency operation unit according to the invention solves the problem that in the event of an expansion malfunction of the expansion unit, in particular of the expansion compression unit, the refrigerant circuit is no longer functional or only functional to a very limited extent, so that it cannot provide sufficient cooling capacity to the cooling unit and thus the cooling capacity provided by the refrigerant circuit during normal operation is lost, which would lead to considerable damage, for example, in refrigerant circuits for cooling systems, for example for temperature-sensitive goods.

[0006] Such a problem can be avoided by the emergency operation unit, since it is able to continue to provide at least a minimum cooling capacity due to the emergency expansion mass flow generated.

[0007] A wide variety of solutions are conceivable regarding the routing of the bypass line.

[0008] An advantageous solution provides that the bypass line of the emergency operation unit supplies the emergency expansion mass flow directly or indirectly to an expansion line of the refrigerant circuit that receives the expansion pressure mass flow.

[0009] This means that the bypass line does not necessarily have to flow directly into the expansion line, but can also flow into the refrigerant circuit upstream of the expansion line, for example, provided that it is ensured that the emergency expansion mass flow is indirectly fed to the expansion line.

[0010] Alternatively or additionally, it is preferably provided that the bypass line supplies the emergency expansion mass flow to a line of the refrigerant circuit which, during normal operation of the refrigerant circuit, carries the expansion pressure mass flow present at expansion pressure.

[0011] This ensures that the refrigerant circuit can continue to operate with the emergency expansion mass flow at least at a partial capacity, since the line carrying the expansion pressure mass flow during normal operation is supplied with the emergency expansion mass flow.

[0012] No further details have been provided so far regarding the function of the emergency operation unit.

[0013] The solution according to the invention provides that the emergency operation unit detects an expansion fault of the expansion compression unit.

[0014] Such an expansion disturbance can be detected, for example, by the expansion element itself.

[0015] For example, it is provided that the emergency operation unit detects a high pressure of the total mass flow or the expansion mass flow before it enters the expander.

[0016] In addition, an advantageous solution provides that the emergency operation unit detects a pressure difference between the high pressure of the total mass flow and / or the expansion mass flow before it enters the expander and a line section of the refrigerant circuit at expansion pressure.

[0017] In this case, the emergency operation unit detects a differential pressure, so that it is possible, for example, to use a known pressure relief valve as an expansion element, which, for example, reacts automatically to such a pressure difference and opens automatically when a certain level of the pressure difference is exceeded, thus generating the emergency expansion mass flow.

[0018] Another possibility is that the emergency operation unit detects a high pressure of the total mass flow or the expansion mass flow before it enters the expander in terms of its absolute value.

[0019] For this purpose, for example, a pressure sensor is provided.

[0020] In order to be able to detect an expansion fault of the expansion unit, it is furthermore expediently provided that the emergency operation unit compares the high pressure of the total mass flow or the expansion mass flow with a reference high pressure before it enters the expander.

[0021] A transition of the emergency operation unit from the inactive state to the active state can be advantageously realized in the solution according to the invention if the emergency operation unit has a control which transfers the emergency operation unit from the inactive state to the active state.

[0022] Such a control system, for example, compares the detected high pressure of the total mass flow or the expansion mass flow before it enters the expander with a stored reference pressure, for example.

[0023] In order to ensure that a defined operation of the refrigerant circuit is possible in the active state of the emergency operation unit, it is preferably provided that the emergency operation unit comprises at least one shutdown element for switching off the expansion compression unit.

[0024] This ensures that, for example, a leak in the expansion compression unit does not further disrupt the function of the refrigerant circuit and that faulty operation of the expander and compressor stage does not cause a disruption of the refrigerant circuit that could potentially counteract or disrupt the function of the emergency operation unit.

[0025] With regard to the arrangement of the shutdown element, a wide variety of solutions are conceivable.

[0026] An advantageous solution provides that the shutdown element of the emergency operation unit is arranged either before an expander inlet or after an expander outlet, so that it is primarily possible to switch off the expander of the expansion compression unit.

[0027] In addition, an advantageous solution provides that a switching element is arranged in the bypass line of the emergency operation unit, which creates a direct or indirect connection between an expansion element for generating the subcooling mass flow of the expansion unit and an expansion pressure output connection of the expansion unit.

[0028] This solution has the advantage that an expansion device already present in the expansion unit for generating a subcooling mass flow can be used by the emergency operation unit to generate the emergency expansion mass flow instead of the subcooling mass flow, thus eliminating the need for an additional expansion device. For example, it is provided that the switching element can be controlled by the control system of the emergency operation unit.

[0029] It is particularly advantageous if the switching element is a switching valve. Another advantageous solution provides for the switching element to be a 3 / 2-way valve, which connects either the bypass line or an expander outlet to the expansion pressure outlet connection. Preferably, a 3 / 2-way valve also serves to close the expander outlet when the bypass line is connected to the expansion pressure outlet connection, or to close the bypass line when the expander outlet is connected to the expansion pressure outlet connection.

[0030] Another advantageous solution provides for a pulsation damper unit to be arranged in the refrigerant circuit.

[0031] Such a pulsation damper unit has the great advantage of being able to dampen pulsations, in particular pulsations generated by the expansion-compression unit, in order to prevent damage and / or noise in the refrigerant circuit caused by such pulsations.

[0032] A variant of such a pulsation damper unit provides that it has a damper housing enclosing a damper chamber in which at least one gas bubble of refrigerant is formed and that the gas bubble absorbs pulsations via a pulsation transmission line leading to a line of the refrigerant circuit and is able to dampen them.

[0033] In the case of operation of the refrigerant circuit in the transcritical range, this usually leads to the refrigerant being in the transcritical range and thus transmitting the pulsations in this state.

[0034] However, pulsations are more serious when the refrigerant is in the subcritical range in the refrigerant circuit, as the pulsations then spread through the refrigerant in the liquid state.

[0035] For this reason, particularly in the case of operation of the refrigerant circuit in the subcritical range, it is provided that the gas bubble is located above a refrigerant bath and, in particular in this case, there is liquid refrigerant in the pulsation transmission line, which transfers the pulsations into the refrigerant bath of liquid refrigerant.

[0036] In order to ensure that a gas bubble is always present in the pulsation damper unit, it is preferably provided that the pulsation damper unit is provided with a heater to maintain the gas bubble of refrigerant, so that even during subcritical operation of the refrigerant circuit it can be ensured that the gas bubble dampening the pulsations is always present in the pulsation damper unit in sufficient size.

[0037] For example, the pulsation damper unit, in particular its damper housing, is heated by coupling the heating with a heat transport circuit, which extracts heat to a pressure in the range of high-pressure compressed refrigerant in the refrigerant circuit.

[0038] Another variant of a pulsation damper unit provides that the pulsation damper unit has a damper housing with a piston movable therein and two chambers adjacent to the piston on opposite sides and separated from each other by the piston, and that a gas bubble of refrigerant forms in at least one of the chambers.

[0039] In this case, the piston also serves to exert a damping effect through the gas bubble that forms in at least one of the chambers.

[0040] It is particularly advantageous if the piston itself in the damper housing is additionally loaded by elastic elements, for example springs, which hold the piston in an initial position, from which the piston can then move against the force effect of the elastic elements to dampen pulsations.

[0041] In order to achieve optimal pulsation damping in this case, it is preferably provided that each of the chambers is connected by means of a pulsation transmission line to different flows of refrigerant-carrying lines of the refrigerant circuit.

[0042] Thus, such a pulsation damper unit serves in particular to dampen pulsations by using a connection between different flows of refrigerant-carrying lines, which may, for example, also be at different pressure levels, to dampen pulsations in one of the two lines or in both of these lines, whereby these lines remain decoupled by the piston, but a pulsation in one of the lines can be transmitted to the other of the lines in a dampened manner and thus, in addition to the piston itself, a damping effect occurs through the coupling of the different flows of refrigerant-carrying lines.

[0043] For example, in such a case, it is provided that one pulsation transmission line is directly or indirectly connected to an inlet of the heat-dissipating heat exchanger and the other pulsation transmission line is directly or indirectly connected to an outlet of the heat-dissipating heat exchanger.

[0044] Furthermore, the damping effect of such a pulsation damper unit can be further improved if at least one pulsation transmission line is coupled to the refrigerant circuit via a throttle.

[0045] Another advantageous solution provides that an intermediate pressure collector is arranged between the expansion unit and the cooling stage, in whose bath a liquid phase of the refrigerant collects and in whose gas volume above the bath a gas phase of the refrigerant collects.

[0046] In this solution, the liquid phase is preferably fed to the cooling stage for expansion in the expansion device thereof.

[0047] In this case, the intermediate pressure receiver has the advantage that additional subcooling can be achieved by the refrigerant kept at intermediate pressure in the intermediate pressure receiver.

[0048] In the case of an intermediate pressure collector, it is preferably provided that an additional mass flow is discharged from the gas volume of the intermediate pressure collector.

[0049] Such an additional mass flow can be supplied in particular via an expansion device of the suction pressure line.

[0050] In addition, there is the possibility that the additional mass flow expanded by the expansion device additionally subcools a main mass flow led to the cooling stage in a heat exchanger, so that the main mass flow can be cooled even further.

[0051] Furthermore, it is preferably also possible within the scope of this solution for a deep-freeze stage in the form of a booster to be added to the cooling stage.

[0052] The provision of an intermediate pressure collector and an expansion device for controlling the additional mass flow discharged from the intermediate pressure collector also creates the possibility of regulating an intermediate pressure in the intermediate pressure collector to a specific pressure value by means of an intermediate pressure control that controls the expansion device.

[0053] In the solutions known from the prior art, regulation to a fixed pressure value of the intermediate pressure is usually carried out, which is in particular independent of the regulation or control of the high pressure in the total mass flow, which is carried out via the control assigned to the expansion unit.

[0054] However, in order to improve the COP (coefficient of performance), i.e. the ratio of cooling capacity to mechanical power used, especially in summer operation, or to expand a functional range of the expansion compression unit, especially in continued operation, several alternatives are conceivable.

[0055] One solution provides that the intermediate pressure control controlling the expansion device detects the pressure and / or the temperature of the total mass flow in the high-pressure discharge line as well as the value of the inlet pressure of the compressor stage and controls the intermediate pressure in such a way that a predetermined value of the inlet pressure suitable for these detected values ​​is set.

[0056] Another favorable solution provides that the pressure value to which the intermediate pressure in the intermediate pressure receiver is regulated by the intermediate pressure control is determined from a base value, for example a value in the range of 30 bar to 45 bar in the case of CO 2 as refrigerant, and additional values ​​with amounts, for example in the range of 0.5 bar to 7 bar in the case of CO 2 as refrigerant.

[0057] This solution has the advantage that additional efficiency increases are possible by adjusting the intermediate pressure and, for example, also due to the feedback on the expansion unit, in particular on an inlet pressure of the compressor stage.

[0058] For example, this is achieved by having the surcharge values ​​have positive values ​​for summer operation and negative values ​​for winter operation, with the amounts of the surcharge values ​​being within the range mentioned above.

[0059] Furthermore, it is advantageous if the size of the additional values ​​depends on the high pressure values ​​that occur when the high pressure is regulated.

[0060] This means that the size of the additional values ​​also varies depending on the values ​​set by the control of the high pressure by means of the expansion unit mentioned above.

[0061] For example, in summer operation, the additional values ​​are planned to be higher at high high pressure values ​​than at low high pressure values.

[0062] Furthermore, it is advantageously provided that in winter operation the additional values ​​are smaller at high high pressure values ​​than at low high pressure values.

[0063] The amounts of the surcharge values ​​are in the above-mentioned range of 0.5 bar to 7 bar.

[0064] No further details were given regarding the expansion unit itself, except that it comprises an expansion-compression unit with an expander and a compressor stage.

[0065] To control the high pressure of the total mass flow, it is particularly advantageous if an electrically operated control is provided which detects at least one of the following variables such as: an ambient temperature, a temperature of the mass flow of the refrigerant supplied to the expansion unit and / or the expander stage and an inlet pressure of the compressor stage, and according to this temperature and / or optionally this inlet pressure of the compressor stage, sets an inlet pressure of the expansion unit or the expander stage - and thus indirectly the high pressure of the total mass flow - and / or optionally an inlet pressure of the compressor stage by controlling the subcooling mass flow by means of the expansion element electrically controlled by the control.

[0066] The advantage of this solution is that it operates with high energy efficiency, since no throttling device is provided in the mass flow supplied to the expander stage to adjust the mass flow flowing to the expander stage.

[0067] Rather, the mass flow flowing to the expander stage and relevant for the inlet pressure of the expansion unit or the expansion compression unit is adjusted exclusively by controlling the subcooling mass flow by means of the expansion device controlled by the controller, so that during the expansion of the mass flow in the expander stage, maximum energy recovery takes place, which can be used to compress the subcooling mass flow in the compressor stage, so that at the same time optimal subcooling of the expanded mass flow takes place before its expansion.

[0068] In particular, the expansion element comprises an electrically driven servo motor.

[0069] With regard to measuring the temperature of the refrigerant mass flow, a wide variety of solutions are conceivable.

[0070] One solution provides that the control measures the ambient temperature and / or the temperature of the mass flow of the refrigerant before an inlet of the subcooling unit and / or before the latter enters the expander by means of a sensor.

[0071] Another solution that comprehensively records the temperature of the refrigerant mass flow involves measuring the temperature of the refrigerant mass flow with a sensor before it enters the subcooling unit and before it enters the expander.

[0072] Another solution provides that the control system detects the ambient temperature by means of a sensor and takes this into account alone or, where appropriate, in combination with the temperature of the mass flow of the refrigerant before it enters the subcooling unit and / or before it enters the expander for the control of the expansion device.

[0073] It is particularly advantageous if the control is an electronic control comprising a processor which electrically controls the expansion element by means of a control program, since with a processor the diverse correlations between the measured temperature and the subcooling mass flow to be controlled by the expansion element can be realized in a simple manner.

[0074] In particular, with this design of the control system, it is possible to always control the expansion device in such a way that the subcooling mass flow exits the subcooling unit in the superheated state, thus preventing partially liquid refrigerant in the subcooling mass flow from exiting the subcooling unit and being fed to the expansion stage.

[0075] In order to monitor the temperature of the subcooling mass flow leaving the subcooling unit, a sensor connected to the control system is provided in a connecting line between the subcooling unit and the compressor stage in order to detect an inlet pressure of the compressor stage, for example when it is to be controlled.

[0076] In the described solution, the control program is designed in particular in such a way that it comprises either an algorithm for determining the control of the expansion element or a stored correlation table which correlates the setting of the expansion element with the measured temperature of the supplied mass flow.

[0077] A particularly advantageous solution provides that the branch is arranged between the subcooling unit and the expansion-compression unit and branches off the subcooling mass flow from the total mass flow after the subcooling unit.

[0078] This solution is energetically advantageous because the diverted subcooling mass flow has also already been pre-cooled in the subcooling mass unit.

[0079] This solution is particularly advantageous for subcritical heat dissipation and allows for greater subcooling.

[0080] Furthermore, this solution has the advantage that pulsations emanating from the expansion compression unit are dampened by the supply line leading away from the branch with the expansion device.

[0081] No further details have been provided so far regarding the design of the subcooling unit.

[0082] The subcooling unit can be designed in different ways.

[0083] One solution provides that the subcooling unit is designed as a heat exchanger unit and cools the mass flow of the refrigerant flowing to the expander stage by the subcooling mass flow passing through it in countercurrent.

[0084] Another advantageous solution provides that the subcooling unit is designed as a collecting tank in which a bath of liquid refrigerant of the subcooling mass flow is formed, which cools an element leading the mass flow of the refrigerant flowing to the expander stage through the bath, wherein a gas volume is formed above the bath, from which the gaseous subcooling mass flow is discharged.

[0085] This solution has the advantage that, on the one hand, the mass flow passing through the element is optimally subcooled and, on the other hand, by removing the subcooling mass flow from the gas volume, it can be ensured that no liquid refrigerant is supplied to the compressor stage for compression.

[0086] No further details have been provided so far regarding the connection between the expander and the compressor stage.

[0087] In principle, the expander and the compressor stage could be coupled, for example, by a generator motor unit.

[0088] However, a particularly advantageous solution provides that the expander and the compressor stage of the expansion compression unit are mechanically functionally coupled.

[0089] Such a mechanical functional coupling means that the energy generated in the expander is transferred directly to the compressor stage via a mechanical connection.

[0090] On the other hand, this solution also has the advantage that the inventive solution, namely the control of the mass flow expanded by the expander, can be easily controlled via the subcooling mass flow compressed by the compressor stage. In principle, the expander and the compressor stage can be formed by suitable types of rotary-driven machines.

[0091] A particularly advantageous solution provides for the expander and the compressor stage to be formed by a free-piston machine in which at least one free piston is freely movable in a piston chamber. The expansion-compression unit is preferably designed to have two piston chambers, each of which houses a free piston.

[0092] Furthermore, the free pistons are preferably movable in a coupled manner.

[0093] In the free-piston engine, it is preferably provided that a first free piston in the respective piston chamber separates a first expansion chamber and a first compression chamber from each other. Furthermore, it is advantageously provided that a second free piston in the respective piston chamber separates a second expansion chamber from a second compression chamber.

[0094] In order to operate the two free pistons in an advantageous manner, it is preferably provided that the two free pistons are arranged coaxially to one another in the piston chambers and are movable.

[0095] Advantageously, the first piston chamber is separated from the second piston chamber by a separating body.

[0096] Advantageous operation of the expansion compression unit can be achieved if the two expansion chambers are arranged adjacent to the separating body in the piston chambers.

[0097] Furthermore, it is preferably provided that the two compression chambers are arranged on the sides of the respective free pistons opposite the expansion chambers.

[0098] In principle, the free pistons can work independently of each other.

[0099] However, an advantageous solution provides that a coupling element coupling the free pistons extends through the separating body and is movable relative to it, in particular in a sealed manner.

[0100] In the simplest case, the coupling element is designed in such a way that it extends through the expansion chambers to the respective free piston.

[0101] With regard to the flow of refrigerant to the expansion chambers, it is preferably provided that these can be controlled by a slide system.

[0102] Such a slide system is designed, for example, as a change-over slide, so that in one slide position the refrigerant flows into one expansion chamber and flows out of the other expansion chamber and in the other slide position the refrigerant flows into the other expansion chamber and flows out of the other expansion chamber.

[0103] To control the slide system, it is preferably provided that the slide system can be controlled by a slide drive with which the two slide positions can be adjusted.

[0104] Such a slide drive can be carried out by an electrical control which detects at least one position of the free pistons by means of at least one position sensor assigned to them.

[0105] Alternatively, an advantageous solution provides that the slide drive can be controlled by a pressure difference between an expander inlet and an expander outlet.

[0106] Preferably, the slide drive is designed as a double-acting actuating cylinder, the piston of which is acted upon on the one hand by the pressure at the expander inlet and on the other hand by the pressure at the expander outlet.

[0107] To control such a drive unit, it is expediently provided that the slide drive can be controlled by a control slide, which controls the application of pressure to the piston at the expander inlet on the one hand and at the expander outlet on the other hand.

[0108] The control slide is preferably designed so that it detects the positions of the free pistons and moves accordingly.

[0109] In particular, it is provided that the control slide is movable by the free pistons.

[0110] In order to be able to supply the expansion unit preferably as a single, fully assembled unit and to install it in a refrigerant circuit, it is preferably provided that the expansion unit has a device base on which the subcooling unit and the expansion compression unit are arranged.

[0111] Furthermore, it is advantageous if the control unit is also arranged on the device base.

[0112] In addition, it is advantageous for installation if a high pressure inlet connection and an expansion pressure outlet connection are arranged on the device base.

[0113] Furthermore, in an advantageous solution, a high-pressure outlet connection is arranged on the device base, through which the compressed subcooling mass flow flows out when the expansion unit is installed.

[0114] A further advantageous solution provides for heat exchanger connection units to be provided on the device base, with which several high-pressure side heat exchangers can be connected.

[0115] In particular, each of the heat exchanger connection units is designed in such a way that it has a three-way valve and a bypass for the respective heat exchanger, so that the three-way valve makes it possible to control the flow through the respective heat exchanger.

[0116] In particular, it is provided that at least one of the heat exchanger connection units is connected to a high-pressure side heat exchanger that releases heat to the ambient air.

[0117] In principle, within the framework of the solution described so far, it is conceivable to operate the cooling stage without its own expansion device and to work in the cooling stage with the mass flow expanded by the expansion unit.

[0118] In this case, it is expedient if a phase separator is arranged following the cooling stage, the gas phase of which is fed to the refrigerant compressor from a suction pressure line.

[0119] Such a phase separator has the advantage that it prevents liquid refrigerant from being fed to the refrigerant compressor for compression.

[0120] Another advantageous solution provides that the cooling stage has at least one expansion element, so that it is possible to set the desired pressure in the cooling stage.

[0121] Further features and advantages of the invention are the subject of the following description and the drawings of some embodiments.

[0122] The drawing shows: Fig. 1 is a schematic representation of a first embodiment of a refrigerant circuit with a first embodiment of an expansion unit with a first embodiment of an emergency operation unit; Fig. 2 is an enlarged schematic representation of the first embodiment of an expansion unit with the first embodiment of an emergency operation unit; Fig. 3 is a schematic representation of a first embodiment of an expansion-compression unit; Fig. 4 is a schematic representation similar Fig. 3 a second embodiment of an expansion-compression unit; Fig. 5 a schematic representation of a second embodiment of the refrigerant circuit with a second embodiment of an emergency operation unit not covered by claim 1; Fig. 6 a schematic representation of the first embodiment of the expansion unit with a third embodiment of an emergency operation unit; Fig. 7 a schematic representation of the first embodiment of the expansion unit with a fourth embodiment of an emergency operation unit; Fig. 8 a schematic representation of the first embodiment of the expansion unit with a fifth embodiment of an emergency operation unit; Fig. 9 a schematic representation of a second embodiment of an expansion unit according to the invention with a sixth embodiment of an emergency operation unit; Fig.10 is a schematic representation of a third exemplary embodiment of an expansion unit according to the invention with the sixth embodiment of the emergency operation unit; Fig. 11 is a schematic representation of the first exemplary embodiment of the expansion unit with a seventh embodiment of an emergency operation unit in a first position of a 3 / 2-way valve; Fig. 12 is a schematic representation of the first exemplary embodiment of an expansion unit with the seventh embodiment of an emergency operation unit in a second position of the 3 / 2-way valve; Fig. 13 is a schematic representation of a fourth exemplary embodiment of an expansion unit; Fig. 14 is a schematic representation of a third exemplary embodiment of a refrigerant circuit; Fig. 15 is a schematic representation of a fourth exemplary embodiment of a refrigerant circuit and Fig. 16 is a schematic representation of a fifth exemplary embodiment of a refrigerant circuit.

[0123] A first embodiment of a refrigeration system, shown in Fig. 1 , comprises a refrigerant circuit, designated as a whole by 10, in which a refrigerant compressor unit, designated as a whole by 12, is arranged, which comprises, for example, at least one refrigerant compressor.

[0124] The refrigerant compressor unit 12 has a suction connection 14 and a pressure connection 16, wherein refrigerant compressed to high pressure PH1 is usually present at the pressure connection 16.

[0125] The term "high-pressure compressed refrigerant" means that the refrigerant has the highest pressure present in the refrigerant circuit.

[0126] From the pressure connection 16, a high-pressure line 18 carries a compressor mass flow V compressed by the refrigerant compressor unit 12 to high pressure PH1 to an inlet 24 of a high-pressure side heat-emitting heat exchanger, designated as a whole by 22, which releases heat in particular to the ambient air and thus cools the refrigerant, so that at an outlet 26 of the high-pressure side heat exchanger 22 there is a total mass flow G of refrigerant cooled by the high-pressure side heat exchanger 22, which is fed from a high-pressure discharge line 28 carrying refrigerant at a high pressure PH2, which is slightly lower than the high pressure PH1 due to the heat exchanger 22, to a high-pressure regulating expansion unit 32, designated as a whole by 32, which has a high-pressure inlet connection 34 connected to the high-pressure discharge line 28, an expansion pressure outlet connection 36 and a high-pressure outlet connection 38.

[0127] The expansion pressure outlet connection 36, which is at an expansion pressure PE, is connected to an expansion line 42, which in the case of Fig. 1 illustrated simplest embodiment leads to a cooling stage 62, which in the simplest case has a heat exchanger 64 which absorbs heat for cooling.

[0128] In this simplified embodiment, the heat-absorbing heat exchanger 64 is at the expansion pressure PE, so that no separate expansion valve is connected upstream of this heat exchanger 64.

[0129] To protect the refrigerant compressor unit 12, a phase separator 72 is connected downstream of the heat-absorbing heat exchanger 64, which is arranged in a suction pressure line 74 that leads from the cooling stage 62 to the suction connection 14 of the refrigerant compressor unit 12 and prevents liquid refrigerant from being sucked in by the refrigerant compressor unit 12 at the suction connection 14.

[0130] From the expansion pressure outlet connection 36, an expansion pressure mass flow EPM at expansion pressure PE thus flows through the expansion line 42 to the cooling stage 62 and from the cooling stage 62 in turn via the suction pressure line 74 to the refrigerant compressor unit 12.

[0131] In this case, the expansion pressure mass flow EPM does not correspond to the total mass flow, but rather the total mass flow G is divided in the expansion unit 32 into an expansion mass flow EM and a subcooling mass flow UM, which is discharged from the expansion unit 32 at the high-pressure outlet connection 38 at a return pressure PR as a subcooling return mass flow URM of a return line 78 and is supplied from there to the compressor mass flow V before it enters the heat-emitting high-pressure side heat exchanger 22.

[0132] The refrigerant circuits 10, which are described below, are all preferably designed for carbon dioxide, i.e. CO2, or ammonia, so that under common ambient conditions a transcritical cycle usually exists in which only before the expansion of the refrigerant through the expansion unit 32, for example by means of the heat exchanger 22, the refrigerant is cooled to a temperature which corresponds to isotherms running above the dew and boiling line or saturation curve, so that no liquefaction of the refrigerant occurs.

[0133] Only in the case of very low temperatures for cooling the high-pressure side heat-dissipating heat exchanger is it possible to carry out a subcritical cycle, so that in this case condensation of the refrigerant occurs at a temperature corresponding to an isotherm passing through the dew and boiling line or saturation curve of the refrigerant.

[0134] The first embodiment of the expansion unit 32 comprises, as shown in Fig. 2 shown enlarged, an expansion system 30 which has a device base designated as a whole by 82, on which the high pressure inlet connection 34, the expansion pressure outlet connection 36 and the high pressure outlet connection 38 are arranged.

[0135] Furthermore, in the expansion system 30, an expansion compression unit 84 is connected to the device base 82, which comprises an expander stage 86 and a compressor stage 88, which are integrated in the expansion compression unit 84 and rigidly coupled to one another.

[0136] The expansion compression unit 84 includes an expander inlet 92 and an expander outlet 94 connected to the expansion pressure output port 36, as well as a compressor inlet 96 and a compressor outlet 98, which in turn is connected to the high pressure output port 38.

[0137] Furthermore, in the expansion system 30, a subcooling unit 102 is arranged on the device base 82, which in the first embodiment is designed as a counterflow heat exchanger and has an inlet 104 and an outlet 106 for the mass flow to be cooled, in particular in this case the total mass flow G, as well as an inlet 112 and an outlet 114 for the subcooling mass flow UM guided as a counterflow through the heat exchanger.

[0138] The subcooling mass flow UM is branched off in the expansion system 30 at a branch 116 from the subcooled total mass flow G exiting at the outlet 106 of the subcooling unit 102, so that an expansion mass flow EM is guided from the branch 116 through a feed line to the expander inlet 92 and the subcooling mass flow UM is guided through a shut-off device 124 and an expansion device 122 driven by an actuator 123 in the feed line 126, in which the subcooling mass flow UM is expanded to a pressure PU, and then fed to the inlet 112 of the subcooling unit 102, wherein the subcooling mass flow UM in the subcooling unit 102 subcools the total mass flow G flowing from the inlet 104 to the outlet 106 in countercurrent and from the outlet 114 by means of a connecting line 128 to the compressor inlet 96 is supplied.

[0139] The mechanical energy released in the expander stage 86 by expansion of the expansion mass flow EM is fed directly to the compressor stage 88 in the expansion compression unit 84 by a mechanical functional coupling and leads therein to a compression of the subcooling mass flow UM from an inlet pressure EP of the compressor stage 88 to a return high pressure PR, which corresponds to or is higher than the pressure level PH1 in the high pressure line 18, so that the subcooling return mass flow URM can be fed from the high pressure outlet connection 38 via a high pressure return line 78 to the compressor mass flow V.

[0140] Furthermore, a controller 132 is provided in the expansion system 30, which on the one hand, for example with a sensor 134, which is in particular a temperature sensor, detects the temperature of the mass flow of the refrigerant before its expansion in the expansion stage 86 and, for example, controls the expansion element 122 according to this temperature by means of the actuator 123.

[0141] For this purpose, the sensor 134 is arranged, for example, between the branch 116 and the expander stage 86 as sensor 134 1.

[0142] Furthermore, the control is assigned a sensor 135 with which it is able to detect the inlet pressure EP.

[0143] Alternatively or additionally, the sensor 134 can also be used as sensor 134z between the high-pressure inlet connection 34 and the subcooling unit 102.

[0144] Alternatively or additionally, it is provided in particular that the sensor 134 as sensor 134s measures the ambient temperature, which significantly influences the temperature of the total mass flow G of the refrigerant at the outlet 26 of the heat exchanger 22, in particular due to the ambient air flowing through the heat exchanger 22.

[0145] The controller 132 can, for example, operate autonomously, so that the controller is part of the expansion system 30 installed as an independent unit in the refrigerant circuit.

[0146] However, it is also provided that the control 132 is coupled to an external controller 138, which - as in Fig. 1 shown - alternatively or in addition to the sensors 134, the temperature of the total mass flow G in the high-pressure compartment 28 and / or the temperature or pressure in the refrigerant compressor 12 is detected in order to control the actuator 123 directly or indirectly or by means of the controller 132.

[0147] The expansion element 122 serves to control the subcooling mass flow UM and thereby to regulate the high pressure PH2 at the high pressure inlet connection 34 and thus also the high pressure PH2 in the high pressure discharge line 28 in accordance with a relationship specified by the controller 132 and / or the external regulator 138, in particular stored therein as a file or algorithm, as a function of the respectively measured temperature of the refrigerant and thus as a function of the possibilities for cooling the refrigerant located on the high pressure PH2, for example as a function of the ambient temperature present for cooling in the heat exchanger 22.

[0148] The controller 132 and / or the external regulator 138 comprise, for example, a processor and a memory in which an algorithm or a correlation table is stored, by means of which a correlation between the settings of the expansion element 122 and the measured temperatures is stored, so that the settings of the expansion element 122, made by the actuator 123 controlled by the controller 132, result in the high pressure PH2 corresponding to the temperature being set at the high pressure inlet connection 34 and / or at the inlet 104 of the subcooling unit 102 and / or at the expander inlet 92.

[0149] The control of the high pressure PH2 by controlling the subcooling mass flow UM is possible because, due to the mechanical functional coupling of the expander 86 with the compressor stage 88, the expansion mass flow EM is directly correlated with the subcooling mass flow UM according to a fixed volume ratio, so that the expansion mass flow EM can be specified by specifying the subcooling mass flow UM. Typically, the subcooling mass flow UM comprises approximately 15% to 35% of the total mass flow G, so that the expansion mass flow EM comprises approximately 85% to 65% of the total mass flow G.

[0150] In particular, the high pressure PH2 is controlled such that in the subcooling unit 102 the temperature of the total mass flow G on the hot side, i.e. at the inlet 104, is only a few Kelvin, for example less than 4 Kelvin, even better less than 3 Kelvin, in particular one to two Kelvin, above the temperature of the subcooling mass flow UM at the outlet 114 of the subcooling unit 102 in order to essentially completely evaporate the refrigerant in the subcooling mass flow U.

[0151] In order to be able to reliably monitor the temperature of the subcooling mass flow UM at the output 114, a sensor connected to the controller 132 is provided in particular in the connecting line 128.

[0152] However, it is also possible to use the controller 132 and / or 138 to detect the inlet pressure EP by means of the sensor 135 and to regulate it to a suitable value corresponding to the variables such as pressure and / or temperature of the total mass flow G and the size of the inlet pressure EP, wherein the suitable values ​​for the said variables are stored, for example, in the controller 132 and / or 138.

[0153] Due to the arrangement of the control unit 132, the expansion element 122, the subcooling unit 102 and the expansion-compression unit 84 on the device base 82, this unit forms a unit that can be mounted independently in the cooling circuit 10 and that regulates the operating states of the refrigerant circuit 10 by regulating the high pressure PH2 that is present on the output side of the heat-emitting heat exchanger 22.

[0154] As in Fig. 3 As shown, the expansion compression unit, designated as a whole by 84, is designed as a free piston machine having a cylinder housing 142 in which two separate piston chambers 144 and 146 are arranged, wherein a movable free piston 152, 154 is arranged in each piston chamber.

[0155] The free pistons 152 and 154 divide the respective piston chambers 144 and 146 into expansion chambers 162 and 164 and compression chambers 166 and 168.

[0156] Furthermore, the free pistons 152 and 154 are preferably mechanically coupled to one another in such a way that, when the first expansion chamber 162 has a maximum volume, the first piston 152 is positioned such that the first compression chamber 166 has a minimum volume and, at the same time, the second free piston 154 is positioned such that its expansion chamber 164 has a minimum volume while the compression chamber 168 has the maximum volume, or vice versa.

[0157] Thus, for example, an increase in the volume of the first expansion chamber 162 when it is subjected to the high pressure at the expander inlet 92 leads to a compression of refrigerant of the subcooling mass flow U in the first compression chamber 166, simultaneously to a displacement of the refrigerant in the second compression chamber 168 in the direction of the expander outlet 94 and to a suction of refrigerant in the second compression chamber 168 via the compressor inlet 96.

[0158] Conversely, pressurization of the second expansion chamber 164 by high-pressure refrigerant supplied via the expander inlet 92 results in compression of the refrigerant in the second compression chamber 168 and thus in displacement of the same to the compressor outlet 98, while at the same time displacement of the refrigerant in the first expansion chamber 162 takes place in the direction of the expander outlet 94 and suction of refrigerant in the first compression chamber 166 takes place via the compressor inlet 96.

[0159] Preferably, the first free piston 152 and the second free piston 154 are arranged coaxially to one another and move in piston chambers 144 and 146, which are also arranged coaxially to one another and are separated from one another by a separating body 148, wherein the separating body 148 is sealed by a coupling element 172 which couples the movement of the two free pistons 152 and 154.

[0160] In the simplest case, the coupling element 172 can be designed as a coupling rod which passes through the separating body 158 and moves with the free pistons 152, 154, which rod rests freely on the free pistons 152 and 154, i.e. is not firmly connected to them.

[0161] Due to the fact that when refrigerant flows in via the expander inlet 92, the pressure in this expansion chamber 162 or 164 acts on the respective free piston 152 or 154 and at the same time a pressure acts in the respective compression chamber 168 or 166 of the other free piston 154 or 152 which is higher than the pressure at the expander outlet 94, which is present in the respective expansion chamber 164 or 162, a pressure can be generated in the compression chamber 166 or 168 acted upon by the free piston 152 or 154 which is higher than the high pressure present at the expander inlet 92, so that the subcooling mass flow U can be compressed to a pressure present at the compressor outlet 98 which corresponds at least to the high pressure PH1 at the inlet 24 of the heat-dissipating heat exchanger or the pressure in the high pressure line 18, although the high pressure PH2,the expander inlet is available due to pressure losses in the heat exchanger 22 is slightly smaller than the high pressure PH1.

[0162] To connect the compression chambers 166 and 168 to the compressor inlet 96, supply lines 182 are provided which extend from the compressor inlet 96 and lead to the inlet valves 184 and 186 associated with the compression chambers 166 and 168, and the compressor outlet 98 is also connected to a pressure line 192 which leads from the outlet valves 194 and 196 associated with the compression chambers 166 and 168, respectively, to the compressor outlet 98.

[0163] An alternating connection between the expander inlet 92 and the expander outlet 94 with the expansion chambers 162 and 164 is made via a slide system 202 which is piston position controlled.

[0164] For example, the slide system 202 comprises a controller 203 which detects the positions of the free pistons 152 and 154, respectively, by means of position sensors 204 and 206 and controls, by means of an electric drive 207, a changeover slide valve designated as a whole by 208, which has two slide positions and, in one slide position, connects the expander inlet 92 to the expansion chamber 162 and the expander outlet 94 to the expansion chamber 164, and in the other slide position, connects the expander inlet to the expansion chamber 164 and the expander outlet 94 to the expansion chamber 162.

[0165] Alternatively, as in Fig. 4 represents, in a slide system 202' a pressure control of the changeover slide 208 is provided, wherein the drive 207' has a pressure-driven cylinder with a piston 205, which is controlled by an auxiliary slide 209 alternately acted upon on the one hand by the pressure at the expander inlet 92 and on the other hand by the pressure at the expander outlet 94 or vice versa, wherein the auxiliary slide 209 is also designed as a changeover slide and whose slide positions are determined by mechanical detection of the positions of the free pistons 152 and 154 in their end positions facing the separating body 148.

[0166] Since, for example, when the expansion compression unit 84 is designed as a free piston machine, malfunctions may occur so that no expansion pressure mass flow EPM or no sufficiently large expansion pressure mass flow EPM would be available for the cooling unit 62, no cooling capacity would be available at the cooling unit 62, so that the refrigerant circuit 10 would no longer be functional.

[0167] In addition, the high pressure PH1 and PH2 would rise to a level that would cause damage to the heat exchanger 22 and / or the refrigerant compressor 12.

[0168] For this reason, the refrigerant circuit 10 is provided with an emergency operation unit 230 which prevents this case.

[0169] A first embodiment of an emergency operation unit 230 provided in the expansion system 30 comprises, for example, an additional expansion element 232, which is arranged in a bypass line 234, which in turn is connected in parallel with the expander stage 86, in particular between its expander inlet 92 and expander outlet 94, and is designed as a pressure relief valve, which in turn opens when a predeterminable opening pressure PO is exceeded and then acts as an expansion element in the bypass line 234, so that an emergency operation expansion mass flow NEPM is supplied to the expansion line 42 through the expansion element in the bypass line 234, which can then absorb heat in the cooling unit 62, so that the refrigerant circuit 10 can continue to run in emergency operation ( Fig. 1 and Fig. 2 ).

[0170] The emergency operation expansion mass flow NEPM is selected such that a minimum cooling capacity is available at the cooling unit 62.

[0171] Particularly when using the free-piston machine as an expansion-compression unit 84, there is the problem of pulsations in the refrigerant circuit 10.

[0172] For this reason, in the first exemplary embodiment of the refrigerant circuit 10, a pulsation damper 260 is preferably connected to parts of the refrigerant circuit 10 adjacent to the expander stage 86, for example to the expansion line 42, which comprises a damper housing 262 enclosing a damper chamber 264, in which, at least in a subcritical operating state, a bubble 266 of gaseous refrigerant forms above a refrigerant bath 268 of liquid refrigerant, the refrigerant bath 268 being connected, for example, to the expansion line 42 via a pulsation transmission line 272.

[0173] The bubble 264 of gaseous refrigerant thus makes it possible to dampen pulsations in the expansion pressure mass flow EPM, which also affect the bath 268 of the refrigerant.

[0174] In order to ensure that the bubble 266 of gaseous refrigerant always forms in the damper housing 262 above the refrigerant bath 268 of liquid refrigerant, the damper housing 262 is preferably provided with a heater 274 in the area surrounding the bubble 266, which heater 274 supplies heat from the return line 78 to the damper housing 262 via a heat transport circuit 276 to maintain the bubble 266 of vaporous refrigerant.

[0175] In a second embodiment of a refrigerant circuit 10', shown in Fig. 5 A second embodiment of the emergency operation unit 230' is not part of the expansion system 30, as described in connection with the first embodiment of the refrigerant circuit 10 according to the invention, but a unit independent of the expansion system 30, wherein the expansion element 232 designed as a pressure relief valve is arranged in the bypass line 234', which in this case connects the high-pressure line 28 to the expansion line 42 and is thus connected in parallel to the entire expansion unit 32 ( Fig. 5 ).

[0176] In the first exemplary embodiment of a refrigerant circuit, a third embodiment of an emergency operation unit 230" is assigned to the first exemplary embodiment of the expansion unit 30, which is designed such that the expansion element 232 is arranged in a bypass line 234" which is connected in parallel to the expander stage 86 and a shut-off element 236 arranged upstream of the expander inlet 92, so that when the expansion element 232 is opened, it is possible to deactivate the expander stage 86 and thus the entire expansion compression unit 84 via the shut-off valve 236, so that only the emergency operation expansion mass flow NEPM flows from the high-pressure inlet connection 34 to the expansion pressure outlet connection 36.

[0177] Because the expander stage 86 is deactivated by the shut-off element 236, the compressor stage 88 is also deactivated, so that no subcooling return mass flow URM flows to the high-pressure line 18 via the high-pressure outlet connection 38 and the return line 78.

[0178] In this embodiment, it is necessary to actively control the expansion element 232 and the shut-off element 236, for example by an emergency operation control 238, which detects the high pressure PH2 present in the refrigerant circuit 10 upstream of the expander stage 86, for example the high pressure between the outlet 106 of the subcooling unit 102 and the expander inlet 92 by means of a sensor 242 ( Fig. 6 ).

[0179] In a fourth embodiment of an emergency operation unit 230''', shown in Fig. 7 the shut-off element 236 is not arranged in front of the expander inlet 92, but immediately after the expander outlet 94 and the bypass line 234‴ is thus connected in parallel to the expander stage 86 with the shut-off element 236, which is arranged following the expander outlet 94.

[0180] In this case too, the control 238 is provided on the one hand to control the expansion element 232 and the shut-off element 236.

[0181] In a fifth embodiment of an emergency operation unit 230''', shown in Fig. 8 the emergency operation unit 230ʺʺ comprises the expansion element 237 and the shut-off element 236.

[0182] In this embodiment, in the same way as in the third embodiment, the shut-off element 236 is arranged in front of the expander inlet 92 in order to deactivate the expander stage 86 by interrupting the expansion mass flow EM flowing into the expander stage 86, while the bypass line 234ʺʺ connects the supply line 126, into which the subcooling mass flow UM enters after flowing through the expansion element 122, and the expansion pressure output connection 36.

[0183] In this case, a further shut-off element 237 is provided in the bypass line 234ʺʺ, while the expansion element 122 provided for the expansion of the subcooling mass flow UM also serves as an expansion element for the emergency operation unit 230ʺʺ and therefore determines the emergency expansion mass flow NEPM, which is led to the expansion pressure output connection 36, bypassing the expander 86.

[0184] In this case, too, the emergency operation control 238 is required, which controls the shut-off elements 236 and 237 when the sensor 242 detects an undesirable increase in the high pressure PH2.

[0185] In a sixth embodiment of an emergency operation unit 230" associated with a second embodiment of an expansion unit 32', shown in Fig. 9 , the emergency expansion unit 230ʺʺ′ is also formed by the bypass line 234''''' with the shut-off element 237, while the shut-off element 236 is arranged directly following the expander outlet 94, so that the bypass line 234''''' is led from the supply line 126 to the expansion pressure outlet connection 36 and opens into a bypass line between the shut-off element 236 and the expansion pressure outlet connection 36.

[0186] In this second embodiment of the expansion unit 32', the pulsation transmission line 272 also opens into this bypass line, which is led to a pulsation damper 260 which is designed in the same way as described in connection with the first embodiment, wherein in this case the heat transport circuit 276 is also part of the expansion system 30 and extracts heat from a bypass line between the compressor outlet 98 and the high-pressure outlet connection 38 and supplies it to the heater 274.

[0187] In a third embodiment, shown in Fig. 10 , the expansion system 30 is provided with the emergency operation unit 230ʺʺ′ according to the sixth embodiment, so that in this regard, reference can be made in full to the explanations of the sixth embodiment.

[0188] In contrast to the first exemplary embodiment, however, a pulsation damper unit 280 is provided between the high-pressure inlet connection 34 and the high-pressure outlet connection 38, which pulsation damper unit has a damper housing 282 in which a piston 284 is arranged, which separates a first chamber 286 arranged in the damper housing 282 from a second chamber 288, wherein, for example, the first chamber 282 is connected to the high-pressure inlet connection 34 via a first pulsation transmission line 292 and the second chamber 288 is connected to the high-pressure outlet connection 38 via a second pulsation transmission line 294.

[0189] The pulsation damper unit 280 is thus able to dampen pulsations propagating to the high-pressure inlet port 34 or to the high-pressure outlet port 38 by transmitting the pulsation through the piston, wherein the piston 284 is preferably mounted between two spring-elastic damping elements 296 and 298, which are arranged in the chambers 286 and 288, respectively.

[0190] An eighth embodiment of an emergency operation unit 230‴‴′, shown in Fig. 11 and Fig. 12 , is based in principle on the fifth embodiment of the emergency operation unit 230"", wherein in this case the emergency operation unit 230‴‴ has a bypass line 234‴‴ which leads from the supply line 126 to a 3 / 2-way valve 235 which is able to either connect the expander outlet 94 to the expansion pressure output connection 36 and close the bypass line 234‴‴′ or to connect the bypass line 234‴‴ to the expansion pressure output connection 36 and close the expander outlet 94, wherein the 3 / 2-way valve 235 is also controlled by the controller 238, which, for example, detects the high pressure of the expansion mass flow EM before it enters the expander.

[0191] In this embodiment, too, the expansion element 122, which is actually intended for the expansion of the subcooling mass flow UM, serves as an expansion element for the emergency operation unit 230‴‴ in the case of emergency operation.

[0192] In a fourth embodiment of an expansion unit 32‴ shown in Fig. 13 , the expansion unit 32‴ is modified in such a way that the branch 116' is arranged between the high-pressure inlet connection 34 and the inlet 104 of the subcooling unit 102 and thus the subcooling mass flow UM is branched off from the total mass flow G before flowing through the subcooling unit 102, wherein in the same way as in the preceding exemplary embodiments the shut-off element 124 and the expansion element 122 are provided, which are arranged between the branch 116‴ and the inlet 112 for the counterflow flowing through the subcooling unit 102.

[0193] This embodiment of the expansion unit 32‴ is also controlled by the controller 132 in the same way as in the first embodiment.

[0194] This fourth embodiment can also be provided with emergency operating units, for example with an emergency operating unit 230 according to the first embodiment, and the expansion element 232 designed as a pressure relief valve.

[0195] However, the expansion unit 32‴ can also be provided with emergency operation units 230', 230", 230‴, 230ʺʺ, 230ʺʺ′, 230‴‴ and 230‴‴′ and / or with pulsation damper units 260, 280, as described in connection with the preceding embodiments of the refrigerant circuit 10, so that reference is made in this regard to the preceding explanations regarding these emergency operation units.

[0196] In a third embodiment of a refrigerant circuit 10", shown in Fig. 14 , those elements which are identical to those of the first embodiment are provided with the same reference numerals, so that with regard to the description, reference can be made in full to the explanations relating to these in connection with the first embodiment.

[0197] However, the third embodiment is provided with the third embodiment of the emergency operation unit 230", with regard to which reference is made to the above explanations regarding this third embodiment. In contrast to the first embodiment, in the third embodiment, the expansion line 42 does not lead directly to the cooling stage 62, but rather to an intermediate pressure collector 44, in which a bath 46 of liquid refrigerant forms at expansion pressure PE, from which liquid refrigerant is supplied via a liquid line 48 to the cooling stage 62", which in this case comprises not only the heat-absorbing heat exchanger 64, but also a shutdown element 68 and an expansion element 66.

[0198] Furthermore, a gas volume 52 of refrigerant is formed in the intermediate pressure collector 44 above the bath 46, from which an additional mass flow Z is supplied to the suction line 74 via an expansion element 54.

[0199] The intermediate pressure collector 44 makes it possible to divide the expansion mass flow E at expansion pressure PE into a main mass flow H, which is fed via the liquid line to the cooling stage 62", and a gaseous additional mass flow Z, which is fed via the expansion element 54 to the suction pressure line 74, so that the temperature of the main mass flow H reaching the cooling stage 62" can be adjusted by means of the expansion element 54.

[0200] In the third embodiment, a pulsation damper 260 is also assigned to the high-pressure discharge line 28, which in the first embodiment of the refrigerant circuit 10 according to Fig. 1 , which is assigned to the expansion line 42, so that with regard to its function, reference can be made in full to the above explanations.

[0201] Alternatively, the pulsation damper 260 can also be arranged in the area of ​​the expansion unit 32 or even integrated into the expansion system 30.

[0202] In a fourth embodiment of a refrigerant circuit 10''', shown in Fig. 15 , which are identical to those of the first and second embodiments, are provided with the same reference numerals, so that with regard to the description thereof, reference can be made in full to the statements on the first and second embodiments.

[0203] In addition to the features of the second embodiment, the fourth embodiment is provided with the pulsation damper unit 280, which in this embodiment is connected in parallel to the heat exchanger 22 and thus dampens pulsations between the high-pressure line 18 and the high-pressure discharge line 28.

[0204] The pulsation damper unit 280 is designed identically to the pulsation damper unit 280 integrated in the third embodiment of the expansion unit 32" ( Fig. 10 ), so that reference can be made in full to the above statements in this regard. In addition, however, a throttle 302 is provided between the second pulsation transmission line 294 and the high-pressure line 18 in order to achieve an improved damping effect.

[0205] In a fifth embodiment of a refrigerant circuit 10", shown in Fig. 16 , those elements which are identical to those of the first and second embodiments are provided with the same reference numerals, so that with regard to the description thereof, reference can be made in full to the statements relating to the first and second embodiments.

[0206] In contrast to the second exemplary embodiment, the additional mass flow Z from the gas volume 52 is not fed directly to the suction pressure line 74 via the expansion element 54, but is again guided through a subcooler 58 provided in the liquid line 48, which further subcools the main mass flow H flowing in the liquid line 48. Furthermore, the cooling stage 62‴ is designed, for example, as a normal cooling stage, and a deep cooling stage 212 is additionally provided, which has a heat-absorbing heat exchanger 214 as well as a shutdown element 218 and an expansion element 216.

[0207] The refrigerant expanded in the deep-freeze stage 212 is fed via a suction pressure line 224 to a deep-freeze compressor unit 222, which compresses the refrigerant again to such an extent that it can be fed to the suction pressure line 74 for the refrigerant compressor unit 12 for compression to high pressure.

[0208] In addition, a subcooler 226 is preferably provided in the suction pressure line 224 of the deep-freeze compressor unit 212, which subcooler further subcools the refrigerant supplied to the deep-freeze stage 212 via the liquid line 48 before it enters the deep-freeze stage 212, namely by means of the expanded refrigerant emerging from the deep-freeze stage 212 and guided in the suction pressure line 224.

[0209] In connection with the third, fourth and fifth embodiments according to the Fig. 14 , 15 and 16 The solution described the presence of the intermediate pressure collector 44 and also the supply of the additional mass flow Z via the expansion device 54 to the suction pressure line 74 as well as the control of the temperature of the main mass flow H.

[0210] This control of the temperature of the main mass flow H comprises the control of an intermediate pressure PM in the intermediate pressure collector 44 by means of the expansion element 54, which in this case can be controlled via an intermediate pressure control 55.

[0211] In principle, in the third, fourth and fifth embodiments, according to the Fig. 14 , 15 and 16 It is possible, on the one hand, to control the high pressure PH2 in the high pressure discharge line by means of the controls 132 and / or 138 in accordance with an optimal operation of the expansion unit 32 at the respective temperature of the refrigerant in the high pressure discharge line 28 and, for example, the respective outside temperature, and to set only a constant intermediate pressure PM in the intermediate pressure collector 44 with the intermediate pressure control 55.

[0212] The efficiency of the refrigerant circuit can be increased by the above-mentioned detection of the inlet pressure EP of the compressor stage 88 by means of the controls 132, 138.

[0213] However, the refrigerant circuit 10 can also be optimized with regard to the achievable COP, i.e. the ratio of cooling capacity to the mechanical power used, in particular in summer operation, and with regard to the extension of the functional operation of the expansion compression unit, in particular in winter operation, by additional operating state-dependent control of the intermediate pressure PM, which affects the inlet pressure EP of the compressor stage 88 due to the volume ratios of the expansion compression unit 84.

[0214] In this operating condition-dependent control of the intermediate pressure PM, for example, the intermediate pressure PM is controlled by means of the intermediate pressure control 55 and the expansion element 54 to a pressure value which results on the one hand from a basic value which is generally set once and from additional values ​​to this basic value which vary depending on the operating condition.

[0215] For example, the base value for CO2 as a refrigerant is in the range of 30 bar to 45 bar, so that a value from this range, for example 35 bar, is set as the base value, and the additional values ​​for CO2 as a refrigerant have amounts in the range of 0.5 bar to 7 bar.

[0216] In principle, the surcharge values ​​could be fixed values ​​from the range of surcharge values ​​provided for them, but it is particularly advantageous if the surcharge values ​​vary within this specified range depending on the operating condition.

[0217] In addition, a differentiation is preferably made between summer operation and winter operation, with the additional values ​​having positive values ​​for summer operation and negative values ​​for winter operation, so that, for example, the values ​​for CO2 as a refrigerant are in the range of 0.5 bar to 7 bar for summer operation and in the range of -0.5 bar to -7 bar for winter operation.

[0218] It is particularly advantageous if the size of the additional values ​​depends on the values ​​within the control range of the high pressure PH2 and therefore varies depending on the values ​​of the high pressure PH2.

[0219] In particular, it is intended that the surcharge values ​​are higher at high high pressure values ​​than at low high pressure values.

[0220] For example, in the case of CO2 as a refrigerant during summer operation, additional values ​​in the range of +0.5 bar to +3 bar result, provided that the high pressure PH2 has values ​​in the range of 75 bar to 80 bar, and additional values ​​in the range of +3 bar to +7 bar, provided that the high pressure PH2 has values ​​in the range greater than 80 bar, preferably values ​​greater than 80 bar to 120 bar.

[0221] For example, in summer operation, with a high pressure PH2 in the range of 80 bar, an additional value in the range of 3 bar is used, while with a high pressure PH2 in the range of 90 bar, an additional value in the range of 5 bar is used.

[0222] In the same way, the additional values ​​for winter operation are, for example, in the range of -0.5 bar to -3 bar, provided that the high pressure PH2 is in the range of 55 bar to 65 bar and the additional values ​​are in the range of -3 bar to -5 bar, provided that the high pressure PH2 is in the range of less than 50 bar to 40 bar.

[0223] In particular, during winter operation, for example, at a high pressure PH2 in the range of 60 bar, an additional value in the range of -3 bar is used and at a high pressure in the range of 50 bar, an additional value in the range of -5 bar is used.

[0224] In the above examples of summer and winter operation, the base value is preferably always the same.

[0225] The above control of the intermediate pressure PM thus has the following consequences in summary: By changing the intermediate pressure PM, the inlet pressure EP at the compressor stage 88 changes and thus a subcooler output of the subcooling unit 102.

[0226] If the intermediate pressure PM is increased, the inlet pressure EP at the compressor stage 88 increases and thus the subcooling mass flow UM and thus the subcooler capacity of the subcooling unit 102 is increased, so that the COP also increases.

[0227] If the intermediate pressure PM is reduced, the inlet pressure EP at the compressor stage 88 also decreases. However, the pressure difference at the expander stage 86 is increased and thus the functional range of the expansion compression unit 84 is also increased.

[0228] In the case of an alternative solution according to Fig. 16 It is provided that the intermediate pressure control 55 detects the variables, in particular the temperature and / or the pressure of the total mass flow G in the high-pressure discharge line 28 as well as the value of the inlet pressure EP of the compressor stage 88 and, depending thereon, controls the intermediate pressure PM in order to regulate to a predetermined value of the inlet pressure EP that is suitable for the detected variables and, for example, stored in the intermediate pressure control 55.

[0229] All compressor units can be any compressor or combination of compressors (parallel, in series, multi-stage).

[0230] Likewise, one or more of the compressors can be provided with a power control, which can be achieved by switching off compressors, by mechanical power control (for example switching off, in particular cyclical switching off of parts (cylinder banks) of a compressor) or by speed control of the compressor.

Claims

1. A method for operating a refrigerant circuit (10), comprising at least one refrigerant compressor (12), which compresses refrigerant fed at a suction connection (14) to high pressure (PH1) such that a compressor mass flow (V) of the refrigerant compressed to high pressure (PH1) exits at a pressure connection, at least one heat-emitting heat exchanger (22) on the high-pressure side, having an inlet (24) to which the refrigerant circuit (10) feeds the compressor mass flow (V) and having an outlet (26) from which a cooled total mass flow (G) of refrigerant exits, at least one expansion unit (32), comprising an expansion compression unit (84), which has an expander stage (86) and a compressor stage (88) and which expands an expansion mass flow (EM) of the total mass flow (G), conducted by the refrigerant circuit (10) in the direction of the suction connection (14) of the refrigerant compressor (14), starting from high pressure (PH2) to an expansion pressure (PE), and at least one cooling stage (62) having at least one heat-absorbing heat exchanger (64) to which the refrigerant circuit (10) feeds a main mass flow (H) comprised by the expansion pressure mass flow (EM) expanded by the expansion unit (32), and which is fed by the refrigerant circuit (10) after leaving the cooling stage (62) to the suction connection (14) of the refrigerant compressor (12), wherein an emergency operation unit (230) is arranged in the refrigerant circuit (10) and comprises a bypass conduit (234) bypassing the expansion compression unit (84) with which is functionally associated at least one expansion element (232, 122), characterised in that the emergency operation unit (230) is configured such that it detects an expansion disruption of the expansion compression unit (84), in that the emergency operation unit (230) has a controller (238) which transfers the emergency operation unit (230) from the inactive state into the active state, and in that the emergency operation unit (230) is configured so that, in the event of a disruption, in particular an expansion disruption, it transfers the expansion compression unit (84) from an inactive state into an active state, in which said expansion compression unit, by expansion of the refrigerant placed under high pressure by means of the expansion element (232, 122), generates an emergency expansion mass flow (NEPM) for operating the cooling stage (62), said emergency expansion mass flow being fed by the bypass conduit (234) to the refrigerant circuit (10) for forwarding to the cooling stage (62).

2. A method in accordance with claim 1, characterised in that the bypass conduit (234) of the emergency operation unit (230) directly or indirectly feeds the emergency expansion mass flow (NEPM) to an expansion conduit (42) of the refrigerant circuit (10) receiving the expansion pressure mass flow (EPM).

3. A method in accordance with the preceding claims, characterised in that the bypass conduit (234) feeds the emergency expansion mass flow (NEPM) to a conduit of the refrigerant circuit (10) conducting, in normal operation of the refrigerant circuit (10), the expansion pressure mass flow (EPM) present at expansion pressure (PE).

4. A method (10) in accordance with the preceding claims, characterised in that the emergency operation unit (230) detects a high pressure (PH2) of the total mass flow (G), exiting from the outlet (26) of the heat exchanger (22), or of the expansion mass flow (EM) prior to its entry into the expander stage (86).

5. A method in accordance with the preceding claims, characterised in that the emergency operation unit (230) detects a pressure difference between the high pressure (PH2) of the total mass flow (G) or the expansion mass flow (EM) prior to its entry into the expander stage (86) and a conduit portion (42) of the refrigerant circuit (10) at expansion pressure (PE).

6. A method in accordance with the preceding claims, characterised in that the emergency operation unit (230) detects a high pressure of the total mass flow (G) or of the expansion mass flow (EM) prior to its entry into the expander stage (86) in respect of its absolute value.

7. A method in accordance with the preceding claims, characterised in that the emergency operation unit (230) compares the high pressure of the total mass flow (G) or of the expansion mass flow (EM), prior to its entry into the expander stage (86), with a reference high pressure.

8. A method in accordance with the preceding claims, characterised in that the emergency operation unit (230) comprises at least one switch-off element (235, 236, 237) for switching off the expansion compression unit (84), in that in particular the switch-off element (235, 236, 237) of the emergency operation unit (2300 is arranged either upstream of an expander inlet (92) or downstream of an expander outlet (94).

9. A method in accordance with the preceding claims, characterised in that a switch element (235, 237) is provided in the bypass conduit (234) of the emergency operation unit (230) and establishes a direct or indirect connection between an expansion member (122) for generating the supercooling mass flow (UM) of the expansion unit (32) and an expansion pressure outlet connection (36) of the expansion unit (32), in that in particular the switch element is actuatable by the controller (238) of the emergency operation unit (230), in that in particular the switch element is a switch valve, in that in particular the switch element (235) is a 3 / 2 directional valve, which either connects the bypass conduit (234) or an expander outlet to the expansion pressure outlet connection (36).

10. A method in accordance with the preceding claims, characterised in that an intermediate pressure collector (44) is arranged between the expansion unit (32) and the cooling stage (62), in the bath (46) of which intermediate pressure collector there collects a liquid phase of the refrigerant and in the gas volume (52) of which intermediate pressure collector disposed above the bath (46) there collects a gas phase of the refrigerant, in that in particular an additional mass flow (Z) is discharged from the gas volume (52) of the intermediate pressure collector (44), in that in particular the additional mass flow (Z) is fed via an expansion member (54) to the intake pressure conduit (74), in that in particular the additional mass flow (Z) expanded by the expansion member (54) cools, in a heat exchanger (58), a main mass flow (H) conducted to the cooling stage (62).

11. A method in accordance with claim 10, characterised in that an intermediate pressure controller (55) actuating the expansion member (54) detects the pressure and / or the temperature of the total mass flow (G) in the high-pressure discharge conduit (28) and the inlet pressure (EP) of the compressor stage (88) and controls the intermediate pressure (PM) so that there is established a value of the inlet pressure (EP) predefined for the detected variables.

12. A method in accordance with claim 10 or 11, characterised in that, by means of an intermediate pressure controller (55) actuating the expansion member (54), an intermediate pressure (PM) in the intermediate pressure collector (44) is controlled to a pressure value that is determined by the intermediate pressure controller (55) from a base value, for example a value in the range from 30 bar to 45 bar, and additional values having absolute values, for example in the range of 0.5 bar to 7 bar, in that in particular the additional values in summer operation have positive values and in winter operation have negative values, in that in particular the magnitude of the additional values is dependent on the values of the high pressure that establish during control of the high pressure, in that in particular in summer operation the additional values with high values of the high pressure (PH2) are greater than with low values of the high pressure (PH2), in that in particular in winter operation the additional values with high values of the high pressure (PH2) are smaller than with low values of the high pressure (PH2).

13. A method in accordance with the preceding claims, characterised in that the expansion unit (32) comprises an expansion system (30) which has a supercooling unit (102) for supercooling the total mass flow of the refrigerant fed to the expansion unit (32), the expansion compression unit (84) comprising the expander stage (86) and the compressor stage (88), has a branch (116), which branches off a supercooling mass flow (UM) from the total mass flow (G) fed to the expansion unit (32) and is connected to a feed conduit (126), which conducts the supercooling mass flow (UM) to an inlet (112) of the supercooling unit (102), has an expansion member (122, 124) which is provided in the feed conduit (126) and which expands the supercooling mass flow (UM) to a supercooling pressure (PU), and has a connection conduit (128), which feeds the supercooling mass flow (U) exiting from the supercooling unit (102) to the compressor stage (88), which in turn compresses the supercooling mass flow (U) to a return high pressure (PR), which corresponds to least one high pressure (PH1) of the compressor mass flow (V), to which the supercooling mass flow (U) is fed.

14. A method in accordance with the preceding claims, characterised in that the refrigerant circuit (10) has an electrically operating controller (132, 138), which detects at least one of the following variables, such as: an ambient temperature, a temperature of the mass flow of the refrigerant fed to the expansion unit (32) and / or the expander stage (86), and an inlet pressure (EP) of the compressor stage (88), and, in accordance with this temperature and / or as applicable this inlet pressure (EP) of the compressor stage (88), establishes an inlet pressure of the expansion unit (32) or of the expander stage (86) and / or as applicable an inlet pressure (EP) of the compressor stage (88) by controlling the supercooling mass flow (UM) by means of the expansion member (122) electrically actuated by the controller (132, 138), in that in particular the controller (132, 138) measures the ambient temperature and / or the temperature of the mass flow of the refrigerant upstream of an inlet (104) of the supercooling unit (102) and / or upstream of an expander inlet (92) by means of a sensor (134), in that in particular the controller (132, 138) is an electronic controller (132, 138) comprising a processor, which controller electrically actuates the expansion member (122) by means of a control program, in that in particular the branch (116) is arranged between the supercooling unit (102) and the expansion compression unit (84) and branches off the supercooling mass flow (U) from the total mass flow (G) downstream of the supercooling unit (102), in that in particular the supercooling unit (102) is formed as a heat exchanger and cools the mass flow of the refrigerant flowing to the expander (86) by the supercooling mass flow U conducted in counter current through said heat exchanger.

15. A method in accordance with the preceding claims, characterised in that the expander stage (86) and the compressor stage (88) of the expansion compression unit (84) are mechanically functionally coupled.

16. A method in accordance with the preceding claims, characterised in that the expander stage (86) and the compressor stage (88) are formed by a free-piston machine, in which at least one free piston (152, 154) is freely movable in a piston chamber (144, 146), in that in particular the expansion compression unit (84) has two piston chambers (144, 146), in each of which a free piston (152, 154) is movable.