Control of an injection stream of a refrigerant for supplementary injection of the refrigerant into a compressor stage in a refrigerant circuit

Abstract

Control of an injection stream of a refrigerant for supplementary injection of the refrigerant into a compressor stage in a refrigerant circuit The invention relates to a controller (30) for controlling an opening degree of an injection expansion valve (22) for adjusting an injection stream (IJS) for supplementary injection of a refrigerant into a compressor stage (2). The controller (30) has a control output (37) outputting control signals (ODV; CLS) for adjusting said opening degree, a discharge controller module (50) that determines a first opening degree proposal (ODP1) for a new opening degree value (ODV) of the injection expansion valve (22) based on a discharge temperature (Td) of the refrigerant flowing out of the compressor stage (2), and superheat controller module (60) that determines, in parallel, a second opening degree proposal (ODP2) based on a superheat value of the injection stream (IJS). It further has a selector module (70) determining the larger one of said opening degree proposals (ODP1, ODP2) as the new opening degree value (ODV) and uses the latter for the next control signal (ODV; CLS). Further, it feeds back the new opening degree value (ODV) to both controller modules (50, 60). The invention also relates to a refrigerant cir- cuit (1; 100) and a method for controlling such an injection stream (IJS).

Description

[0001]

[0002] Control of an injection stream of a refrigerant for supplementary injection of the refrigerant into a compressor stage in a refrigerant circuit

[0003] The present invention relates to a controller for controlling an opening degree of an injection expansion valve for adjusting, in a refrigerant circuit with a compressor stage, an injection stream of a refrigerant for supplementary injection of the refrigerant into the compressor stage. The invention further relates to a refrigerant circuit and a method for controlling such an injection stream.

[0004] A refrigerant circuit typically includes a compressor, a condenser, a main expansion valve, and an evaporator. A main flow of the refrigerant is as follows: The compressed refrigerant is discharged from a discharge outlet of the compressor and flows to the condenser. In the condenser, the refrigerant condenses and releases heat. The liquid refrigerant flows from the condenser to the main expansion valve. The main expansion valve expands the refrigerant, and the expanded refrigerant reaches the evaporator. In the evaporator, the refrigerant evaporates and takes up heat. The refrigerant flows to a suction inlet of the compressor. In this way, the refrigerant is circulated along the main flow of the refrigerant in the refrigerant circuit.

[0005] It is known to add an economizer to the refrigerant circuit. The refrigerant flowing along the main flow from the condenser to the main expansion valve passes through a higher pressure branch of the economizer. Further, a part of the refrigerant is branched off from the main flow to an injection expansion valve for supplying a secondary flow. Said secondary flow can be branched off from the main flow upstream of the higher pressure branch or downstream of the higher pressure branch. The secondary flow is controlled by means of the injection valve. In more detail, an amount of the part of the refrigerant that is branched off from the main flow is adjusted by an opening of the injection expansion valve. The secondary flow passes the injection expansion valve and streams into a lower pressure

[0006] November 2025 D 200 P 2655 WO branch of the economizer. Since the injection expansion valve expand the secondary flow before the secondary flow reaches the lower pressure branch, depending on the opening degree of the injection valve, at least a part of the refrigerant in the secondary flow can evaporate. The refrigerant of the secondary flow in the lower pressure branch and the refrigerant in the higher pressure branch exchange heat. In more detail, in the economizer, heat is transferred from the refrigerant in the higher pressure branch to the refrigerant in the lower pressure branch. Therefore, a temperature of the refrigerant flowing out of the higher pressure branch of the economizer towards the main expansion valve is decreased due to the heat exchange in the economizer. Vice versa, a temperature of the refrigerant flowing out of the lower pressure branch of the economizer is increased due to the heat exchange in the economizer.

[0007] The refrigerant flowing out of the lower pressure branch of the economizer is supplied as an injection stream to an additional injection inlet of the compressor. Along a direction of the main flow of the refrigerant in the compressor from the suction inlet to the discharge outlet, the injection stream is injected into said main flow within the compressor between the suction inlet and the discharge outlet.

[0008] The injection stream flowing into the injection inlet of the compressor forms a supplementary injection (i.e. in addition to the main flow through the compressor supplied to the compressor via the suction inlet) of the refrigerant.

[0009] According to one approach, the opening degree is controlled in order to obtain a predetermined superheat of the refrigerant in the injection stream, for example 5 K. Said approach might be referred to as superheat control approach. It is known that such a supplementary injection of the refrigerant can increase the efficiency and / or performance of the refrigerant circuit. Since the refrigerant of the injection stream has always the predetermined superheat, this results in the supplementary injection of vaporized refrigerant into the compressor.

[0010] November 2025 D 200 P 2655 WO

[0011] In the case that the refrigerant of the injection stream is in vapor form, the supplementary injection might be referred to as "vapor injection".

[0012] By increasing the opening degree of the injection expansion valve, the secondary flow and hence the injection flow are increased. Since the secondary flow is larger, the refrigerant in the lower pressure branch of the economizer takes up more heat. As a consequence, the superheat of the injection stream of the refrigerant flowing from the lower pressure side of the economizer to the injection inlet can be decreased by increasing the opening degree of the injection expansion valve. Vice versa, by decreasing the opening degree of the injection expansion valve, the secondary flow through the lower pressure branch of the economizer resulting (downstream of the lower pressure branch of the economizer) in the injection stream is decreased. Accordingly, an injection temperature of the injection stream (i.e. a temperature of the refrigerant of the injection stream) increases.

[0013] According to another approach (which may be referred to as discharge temperature control approach), the supplementary injection of the refrigerant is controlled in order to limit a discharge temperature of the refrigerant flowing out of the discharge outlet of the compressor to a discharge temperature threshold, e.g. 121 °C. If the discharge temperature is too high, the performance of the compressor suffers. Excessive discharge temperatures may even come with an increased risk that the compressor is damaged. According to the discharge temperature control approach, the opening degree of the injection expansion valve is increased when the discharge temperature reaches the discharge temperature threshold. If the opening degree of the injection expansion valve is large enough, the refrigerant in the injection stream is in a state that allows cooling the refrigerant of the main flow within the compressor and hence pushing the discharge temperature down. For example, the refrigerant of the injection stream may be in a wet-steam area such that a liquid portion of the refrigerant can evaporate within the compressor

[0014] November 2025 D 200 P 2655 WO to reduce the temperature within the compressor and hence the discharge pressure.

[0015] In the case that the refrigerant of the injection stream is partially in liquid form and partially in vapor form (i.e. if it is in the wet-steam area), the supplementary injection might be referred to as "wet vapor injection".

[0016] The discharge temperature control approach can even be implemented without any economizer. In this case, a secondary flow of the refrigerant branched off from the main flow of the refrigerant, more specifically between the condenser and the main expansion valve, flows from the injection expansion valve to the injection inlet without passing an economizer.

[0017] In the case that the refrigerant of the injection stream is (at least substantially) in liquid form, the supplementary injection might be referred to as "liquid injection".

[0018] Each of the superheat control approach and the discharge temperature control approach has disadvantages.

[0019] Using the superheat control approach can result in excessive discharge temperatures of the refrigerant flowing out of the discharge outlet under some circumstances. This might increase the risk of damages of the compressor. Hence, the superheat control approach cannot reliably protect the compressor from damages.

[0020] Using the discharge temperature control approach means not to benefit from the efficiency advantages that the superheat control approach can provide, especially when the discharge temperature is well below the discharge temperature threshold.

[0021] November 2025 D 200 P 2655 WO

[0022] One might think of simply switching off a superheat controller module (for controlling the injection expansion valve in accordance with the superheat control approach) when the discharge temperature reaches the discharge temperature threshold and turning on a discharge temperature controller module (for controlling the injection expansion valve in accordance with the discharge temperature control approach) instead. Vice versa, the discharge temperature controller module could be switched off and the superheat controller module could be turned on instead when the discharge temperature falls below the discharge temperature threshold. However, such an approach can result in abrupt changes of the opening degree of the injection expansion valve when the responsibility of the controller modules changes. It takes will take some time until the controller module that just has been switched on provides a stable control. This might result in undesired effects and behavior of the system in the course of switching between the controller modules. This can impair the performance and even the reliability of the refrigerant circuit.

[0023] Refrigerant circuits with injection expansion valves are known, e.g., from EP 3 901 539 B1 , US 2014 / 0 305 144 A1 , EP 4 635 765 A1 , and EP 4 517 220 A1.

[0024] It is desired to provide a particularly reliable, efficient, and smooth control of the supplementary injection even under changing conditions.

[0025] This problem is solved by a controller with the features according to claim 1 .

[0026] The controller is for controlling an opening degree of an injection expansion valve for adjusting, in a refrigerant circuit with a compressor stage, an injection stream of a refrigerant for supplementary injection of the refrigerant into the compressor stage. The compressor stage has a suction inlet and a discharge outlet for the refrigerant and further an injection inlet for receiving the injection stream.

[0027] November 2025 D 200 P 2655 WO

[0028] The controller comprises a discharge temperature controller module that is configured to determine a first opening degree proposal for a new opening degree value of the injection expansion valve based on a discharge temperature of the refrigerant flowing out of the compressor stage and the present opening degree value of the injection expansion valve.

[0029] Further, the controller comprises a superheat controller module that is configured to determine a second opening degree proposal for the new opening degree value of the injection expansion valve based on a superheat value of the injection stream and the present opening degree value.

[0030] The controller comprises a control output configured to output control signals for adjusting the opening degree of the injection expansion valve.

[0031] The superheat controller module is configured to determine the second opening degree proposal in parallel to the determination of the first opening degree proposal by the discharge temperature controller module.

[0032] Further, the controller comprises a selector module that is operatively connected to the discharge temperature controller module and the superheat controller module, wherein the selector module is configured

[0033] - to receive the first opening degree proposal and the second opening degree proposal,

[0034] - to determine the larger one of the first opening degree proposal and the second opening degree proposal as new opening degree value, wherein the controller is configured to use the new opening degree for the next control signal, and

[0035] - to feedback the new opening degree value to both the discharge temperature controller module and the superheat controller module as the present opening degree value.

[0036] November 2025 D 200 P 2655 WO

[0037] With the present invention, the control of the opening degree of the expansion valve is handed over between the discharge temperature controller module and the superheat controller module in an easy, reliable, and particularly smooth manner.

[0038] The present invention allows for bumpless control transition between the discharge temperature control approach and the superheat control approach. It allows for bumpless control transition between the vapor injection and the liquid injection.

[0039] With the present invention, the discharge temperature controller module and the superheat controller module can always run in parallel. Both controller modules always receive the new opening degree value that is actually to be used for the next opening degree of the injection expansion valve, despite of the new opening degree value corresponding to the first opening degree proposal or the second opening degree proposal. Further, the handover is triggered based on the comparison which one of the first opening degree proposal and the second opening degree proposal. This ensures that the handover occurs when the first opening degree proposal and the second opening degree proposal are quite similar. This would be, for example, not ensured if the change between using the first opening degree proposal or the second opening degree proposal for the next opening degree value would be made solely based on a predetermined discharge threshold, for example.

[0040] The present invention allows that changes between using the first opening degree proposal or the second opening degree proposal for the (next) opening degree value, in other words handing over actual control of the injection expansions valve

[0041] November 2025 D 200 P 2655 WO between the "outputs" of the two controller modules at various discharge temperatures and at different superheats.

[0042] The combination of the ongoing feedback of the new opening degree value to both controller models and the handover when the first opening degree proposal and the second opening degree proposal are quite similar leads to a very smooth, precise and yet reliable control of the opening degree of injection expansion valve. There is no abrupt change in the opening degree for the injection expansion valve even when the controller changes from using the first opening degree value for the new opening degree value instead of the second opening degree value that has been used as the present opening degree (and vice versa). Smooth transition of the behavior of the injection expansion valve and the whole refrigerant circuit when the responsibility for providing the new opening degree value is changed between the controller modules is ensured. This prevents unexpected and / or undesired effects due to said responsibility changes. This protects the elements of the refrigerant circuit. The focus of the control strategy is the compressor. The compressor stage is prevented from excessive discharge temperatures. Finally, the reliability and efficiency of the refrigerant system are increased.

[0043] The implementation can be done easily with an existing discharge temperature controller module (e.g. in the form of a corresponding software module) and an existing superheat controller module (e.g. in the form of a corresponding software module). It is not needed to develop and test a more complex new controller module.

[0044] The superheat controller module is provided in addition to the discharge temperature controller module. The modules are implemented individually. Hence, the discharge temperature controller module and the discharge temperature module can be kept simple. This allows a particularly cost-efficient implementation.

[0045] November 2025 D 200 P 2655 WO

[0046] If the discharge temperature is comparatively low, the first opening degree proposal provided by the discharge temperature controller output will be typically small or even zero. The second opening degree proposal provided by the superheat controller module may be larger. Hence, the selector module uses the second opening degree proposal for the new opening degree value. Hence, at this time, the actual opening degree and hence the control of the injection expansion valve is based on the superheat controller module. This ensures a high performance of the refrigerant circuit.

[0047] Naturally, if the discharge temperature raises, the first opening degree proposal provided by the discharge temperature controller module will typically become, at some point in time, larger than the second opening degree proposal. Accordingly, the selector module switches to using the larger first opening degree proposal for the new opening degree value. Hence, at this time, the actual opening degree and hence the control of the injection expansion valve is based on the discharge temperature controller module. This ensures protection of the refrigerant circuit, especially the compressor stage, from damages.

[0048] If the conditions change and the discharge temperatures decreases, the first opening degree proposal provided by the discharge temperature controller module will typically become, at some point in time, smaller than the second opening degree proposal. Accordingly, the selector module switches back to using the second opening degree proposal for the new opening degree value.

[0049] The controller can be configured to use the discharge temperature controller for liquid injection and / or wet vapor injection. The controller can be configured to use the superheat controller module for vapor injection. The present invention hence allows to expand an operational range (an operation map) of the compressor stage.

[0050] November 2025 D 200 P 2655 WO

[0051] The vapor injection boost cooling capacity and efficiency of the refrigerant circuit when the discharge temperature is low.

[0052] According to one aspect, wet vapor injection is used (only) when the discharge temperature is high. Otherwise the controller may aim for having superheat of the refrigerant in the injection stream.

[0053] When the compressor stage is operating at high pressure ratio (e.g. in the case of a low ambient temperature and a high discharge pressure), the compressor stage will be provided with additional cooling to maintain the high pressure ratio. This is obtained by adjusting the opening degree according to the (larger) first opening degree proposal under such circumstances. Even liquid injection is possible.

[0054] Under some operational conditions, both the first opening degree proposal and the second opening degree proposal might be zero. In this case, the new opening degree value is set to zero. The injection expansion valve is closed then.

[0055] The bumpless behavior is ensure by relying on the most demanding (the largest) one of the proposed valve opening degrees and feeding back the new opening degree value to both controller modules in any case. This makes the less demanding one of the controller modules more responsive when the priority shifts.

[0056] This is in particular beneficial when the discharge temperature gets high. Without the common feedback, during these circumstances, the discharge temperature controller module would not increase its first opening degree proposal from near closed. However, with the feedback, the discharge temperature controller module starts increasing from the current opening degree. This allows for a faster opening of the injection expansion valve. This is beneficial in order to quench the discharge temperature fast when the discharge temperature increases rapidly.

[0057] November 2025 D 200 P 2655 WO

[0058] The compressor stage includes at least one compressor.

[0059] In one embodiment, the compressor stage includes exactly one compressor. The suction inlet of the compressor stage can correspond to a suction inlet of said compressor. The discharge outlet of the compressor stage can correspond to a discharge outlet of said compressor.

[0060] According to one aspect, the compressor stage includes at least two compressors. The at least two compressors can be arranged in series. The suction inlet of the compressor stage can correspond to the suction inlet of the upstream compressor (the first compressor). The discharge outlet inlet of the compressor stage can correspond to the discharge outlet of the downstream compressor (the second compressor). The injection inlet may be in the upstream compressor (i.e. between the suction inlet and the discharge outlet of the upstream compressor). The injection inlet may be in the downstream compressor, (i.e. between the suction inlet and the discharge outlet of the upstream compressor). The injection inlet may be between the discharge outlet of the upstream compressor and the suction inlet of the downstream compressor.

[0061] In general, the injection inlet may be provided in the at least one compressor or between the at least one compressor and a further compressor of the compressor stage that is arranged in series with the art least one compressor.

[0062] It is possible that the compressor stage includes several injection inlets.

[0063] For example, the compressor stage may include at least two (maybe identical) compressors that are arranged in series, and each of the compressors may include at least one injection inlet between its suction inlet and its discharge outlet, respectively.

[0064] November 2025 D 200 P 2655 WO

[0065] The refrigerant circuit may have an economizer. The economizer may have a higher pressure branch (for a main flow of the refrigerant from a condenser to a main expansion valve) and / or a lower pressure branch for the injection stream.

[0066] According to one aspect, the controller can comprise a discharge temperature sensor interface that is configured to operate a temperature detector (as a temperature sensor) for measuring the discharge temperature of the refrigerant flowing out of the compressor stage. Hence, the controller itself can directly operate the temperature detector for determining the discharge temperature. In general, various kinds of temperature detectors can be used. In one embodiment, the controller comprises a discharge temperature sensor interface that is configured to operate a resistance temperature detector, for example a PtIOOO, as a temperature sensor for measuring the discharge temperature of the refrigerant flowing out of the compressor stage. This allows for a particularly good compromise between cost-efficiency, reliability, and accuracy.

[0067] Additionally or alternatively, the controller can comprise an injection pressure interface that is configured to operate a pressure measurement means for measuring an injection pressure of the injection stream. Hence, the controller itself can directly operate the measurement means for determining the injection pressure. In general, various kinds of pressure means are usable. The pressure measurement means can include pressure sensor, a pressure transmitter, and / or a pressure transduce. Especially, the pressure measurement means can include a ratiometric pressure sensor. This allows for a particularly good compromise between cost efficiency, reliability, and accuracy.

[0068] Additionally or alternatively, the controller can comprise an injection temperature interface that is configured to operate a temperature detector (as a temperature sensor) for measuring an injection temperature of the injection stream. Hence, the

[0069] November 2025 D 200 P 2655 WO controller itself can directly operate the temperature detector for determining the injection temperature. In general, various kinds of temperature detectors are usable. In one embodiment, the controller comprises an injection temperature interface that is configured to operate a resistance temperature detector, e.g. a PtIOOO, as a temperature sensor for measuring an injection temperature of the injection stream. This allows for a particularly good compromise between cost efficiency, reliability, and accuracy.

[0070] Additionally or alternatively, the controller can comprise a temperature sensor interface that is configured to operate a temperature detector (as a temperature sensor) for measuring a temperature of the refrigerant flowing into the lower pressure branch of the economizer. Hence, the controller itself can directly operate the temperature detector for determining said temperature (which might be referred to as intermediate secondary flow temperature). In general, various kinds of temperature detectors are usable. In one embodiment, the controller comprises a temperature sensor interface that is configured to operate a resistance temperature detector, e.g. a PtIOOO, as a temperature sensor for measuring a temperature of the refrigerant flowing into the lower pressure branch of the economizer. This allows for a particularly good compromise between cost efficiency, reliability, and accuracy.

[0071] According to one aspect, the controller can comprise at least the discharge temperature sensor interface, the injection temperature interface, and at least one of the injection pressure interface and the temperature sensor interface (for measuring the temperature of the refrigerant flowing into the lower pressure branch). Hence, the controller itself includes all necessary interfaces that are needed for using the suitable detectors for measuring the discharge temperature and for providing measurement signals that are sufficient for calculating the superheat value of the injection stream.

[0072] November 2025 D 200 P 2655 WO

[0073] In one embodiment, the controller, for example the superheat controller module, is configured to calculate the superheat value of the injection stream, e.g. based on the injection temperature and at least one of the injection pressure and the temperature of the refrigerant flowing into the lower pressure branch of the economizer.

[0074] According to one aspect, the control output can be configured to provide control signals for driving an actuator of the injection expansion valve. Hence, injection expansion valve (especially the actuator thereof) can be directly functionally coupled to the controller. In general, various kinds of actuators can be used. In one embodiment, the control output is configured to provide control signals for driving a (e.g. bipolar) stepper motor as an actuator of the injection expansion valve.

[0075] In one embodiment, the controller is configured to be mounted on a DIN rail. This allows easy installation of the controller, e.g. in a control cabinet.

[0076] According to one aspect, the controller can comprise a microprocessor. For example, the controller can include a microcontroller unit (MCU) with at least one microprocessor. The allows for processing measurement signals and calculation directly within the controller. The controller can be configured to process code implementing the discharge temperature controller module, the superheat controller module, and / or the selector module with the microprocessor.

[0077] The controller can comprise a memory.

[0078] The controller can be configured to store (in the memory) a set point for the discharge temperature and / or a set point for the superheat of the refrigerant that is used for the supplementary injection.

[0079] November 2025 D 200 P 2655 WO

[0080] Additionally or alternatively, the memory can be configured to store (and especially include) information on thermodynamic properties of the refrigerant. The information on thermodynamic properties of the refrigerant may include information related to one of, several of, or all of the following:

[0081] - temperatures and / or pressures relevant for phase transitions of the refrigerant,

[0082] - transitions between a wet-steam area and a superheated gas area of the refrigerant,

[0083] - a saturated vapor line of the refrigerant,

[0084] - transitions between the wet-steam area and a subcooled liquid area of the refrigerant,

[0085] - a saturated liquid line of the refrigerant,

[0086] - pressure- and / or temperature-dependent enthalpy values of the refrigerant,

[0087] - a log(p)-h diagram of the refrigerant,

[0088] - and the like.

[0089] For example, the information on thermodynamic properties of the refrigerant may include at least (or even only) information related to the saturated vapor line of the refrigerant.

[0090] According to one aspect, the discharge temperature controller module can be implemented as a software module, e.g. as a software library. Additionally or alternatively, the superheat controller module can be implemented as a software module, e.g. as a software library. Since the controller modules as such work in a known manner, existing corresponding software libraries can be used. This allows for cost-efficient, reliable, and fast implementation. In one embodiment, the discharge temperature controller module is implemented as a software module and wherein the superheat controller module is implemented as an additional, separate software module.

[0091] November 2025 D 200 P 2655 WO

[0092] Additionally or alternatively, the selector module may be implemented as a software module, e.g. as a software library. The software module for the selector module may be separate from the software module for the discharge temperature controller module and the software module for the superheat controller module.

[0093] According to one aspect, the controller may be configured such that the discharge temperature controller module and the superheat controller module run in parallel despite of whether the first opening degree proposal or the second opening degree proposal is used as the next opening degree value. This facilitates fast and smooth switching between relying on the first opening degree proposal and the second opening degree proposal for the new opening degree value.

[0094] The discharge temperature controller module can be a proportional integral controller or a proportional integral derivative controller. This is a particularly easy and reliable implementation. The approach of using a proportional integral controller is more robust.

[0095] Additionally or alternatively, the superheat controller module can be a proportional integral controller or a proportional integral derivative controller. This is a particularly easy and reliable implementation. The approach of using a proportional integral controller is more robust.

[0096] The controller can be configured for use with different types of compressors, different refrigerants, different types of injection expansion valves, and / or different locations of branching off the secondary flow of refrigerant (e.g. upstream or downstream of the higher pressure branch of the economizer). This increases the versatility of the controller.

[0097] The problem indicated above is further solved by a refrigerant circuit, wherein the refrigerant circuit comprises a compressor stage, a condenser, an economizer,

[0098] November 2025 D 200 P 2655 WO and an injection expansion valve for adjusting an amount of refrigerant that is branched off downstream of the condenser and guided through a lower pressure branch of the economizer as an injection stream for supplementary injection into the compressor stage, where-in the compressor stage has a suction inlet and a discharge outlet for the refrigerant and further an injection inlet for receiving the injection stream, wherein refrigerant circuit includes the controller according to the present invention for controlling an opening degree of the injection expansion valve.

[0099] The embodiments, modifications, and advantages described with respect to the controller apply accordingly with respect to the refrigerant circuit, and vice versa.

[0100] The problem indicated above is further solved by a method according to claim 16.

[0101] The method is for controlling, in a refrigerant circuit with a compressor stage, an injection stream of a refrigerant for supplementary injection of the refrigerant into the compressor stage by means of a controller and an injection expansion valve, wherein the compressor stage has a suction inlet and a discharge outlet for the refrigerant and further an injection inlet receiving the injection stream.

[0102] The method includes: receiving, with the controller, measurement signals indicating a discharged temperature of the refrigerant flowing out of the compressor stage, an injection temperature of the injection stream, and at least one of an injection pressure and a temperature of the refrigerant flowing into a lower pressure branch of an economizer, wherein the lower pressure branch is used for the injection stream; determining, with a discharge temperature controller module of the controller, a first opening degree proposal for a new opening degree value of the injection expansion valve based on the discharge temperature of the refrigerant flowing out

[0103] November 2025 D 200 P 2655 WO of the compressor stage and the present opening degree value of the injection expansion valve; determining in parallel, with a superheat controller module of the controller, a second opening degree proposal for the new opening degree value of the injection expansion valve based on the injection temperature, the present opening degree value, and the at least one of the injection pressure and the temperature (of the refrigerant flowing into the lower pressure branch of the economizer); receiving, with a selector module of the controller, the first opening degree proposal and the second opening degree proposal; determining, with the selector module, the larger one of the first opening degree proposal and the second opening degree proposal as new opening degree value; using the new opening degree value for providing, with the controller, a control signal for adjusting the opening degree of the injection expansion valve; and feeding back the new opening degree value to both the discharge temperature controller module and the superheat controller module as the present opening degree value.

[0104] The embodiments, modifications, and advantages described with respect to the controller and / or the refrigerant circuit apply accordingly with respect to the method, and vice versa.

[0105] Especially, the method may include: determining at a first time, with the selector module, that the first opening degree proposal is larger than the second opening degree proposal and hence determining the first opening degree as new opening degree value at the first time, and determining at a second time, with the selector module, that the second opening degree proposal is larger than the first opening degree proposal and hence determining the second opening degree as new opening degree value at the second time.

[0106] November 2025 D 200 P 2655 WO

[0107] The second time might be after or before the first time.

[0108] Additional features, advantages and possible applications of the invention result from the following description of exemplary embodiments and the drawings. All the features described and / or illustrated graphically here form the subject matter of the invention, either alone or in any desired combination, regardless of how they are combined in the claims or in their references back to preceding claims.

[0109] Preferred embodiments of the invention will now be described with reference to the drawings, in which:

[0110] Fig. 1 schematically shows an embodiment of a refrigerant circuit with a compressor stage, a condenser, an economizer, a main expansion valve, and an economizer, wherein a secondary flow for supplying refrigerant for a supplementary injection into the compressor stage is branched off from a main flow of the refrigerant upstream of a higher pressure branch of the economizer, wherein an injection stream into the compressor stage for the supplementary injection of the refrigerant is adjustable by varying an opening degree of an injection expansion valve;

[0111] Fig. 2 schematically shows a modified embodiment of the refrigerant circuit of Fig. 1 , wherein the secondary flow is branched off from the main flow of the refrigerant downstream of the higher pressure branch of the economizer;

[0112] Fig. 3 schematically shows a first embodiment of a controller according to the present invention for controlling the opening degree of an injection expansion valve in Figs. 1 and 2 for adjusting the injection flow;

[0113] November 2025 D 200 P 2655 WO

[0114] Fig. 4 schematically shows a structure of the controller according to Figs. 3 and 6,

[0115] Fig. 5 schematically shows steps of a method for controlling the opening degree of the injection expansion valve in Figs. 1 and 2; and

[0116] Fig. 6 schematically shows a second embodiment of a controller according to the present invention.

[0117] Fig. 1 schematically shows an embodiment of a refrigerant circuit 1.

[0118] The refrigerant circuit 1 comprises a compressor stage 2.

[0119] The compressor stage 2 has a compressor 2a, a suction inlet 3, and a discharge outlet 4. The compressor 2a includes a suction inlet and a discharge outlet. As the compressor stage 2 comprises, in this example, only one compressor 2a, the suction inlet of the compressor 2 is also a suction inlet 3 of the compressor stage 2 and the discharge outlet of the compressor 2 is also a discharge outlet 4 of the compressor stage 2.

[0120] The compressor stage 2 can be any compressor system or any compressor 2a having an intermediate pressure (a pressure between an inlet pressure at the suction inlet 3 and a discharge pressure at the discharge outlet 4). For example, the compressor 2a can be a scroll compressor or a screw compressor.

[0121] In operation, a main flow (or primary flow PF) of a refrigerant in the compressor 2a and hence in the compressor stage 2 is from the suction inlet 3 to the discharge outlet 4.

[0122] November 2025 D 200 P 2655 WO

[0123] The compressor 2a (and hence the compressor stage 2) comprises and additional injection inlet 5. Via the injection inlet 5, a supplementary injection of refrigerant into the compressor 2a and hence into the compressor stage 2 can be performed. An injection stream IJS of the refrigerant supplied into the injection inlet 5 joins the main flow of the refrigerant within the compressor stage 2 between the suction inlet 3 and the discharge outlet 4. By means of the injection stream IJS, the efficiency can be increased. Additionally or alternatively, the injection stream IJS can be used to decrease a discharge temperature Td (see Figs. 3, 5, and 6) of the refrigerant flowing out of the discharge outlet 4. This helps to operate the compressor stage 2 under suitable conditions and helps to prevent damages of the compressor 2a which are associated with excessively high discharge temperatures Td.

[0124] The refrigerant circuit 1 further comprises a fluid connection 7 with a temperature sensor 8 for measuring the discharge temperature Td. In Fig. 1 , the temperature sensor 8 is provided in-between the discharge outlet 4 and the condenser 9. In a modification (not shown), the temperature sensor 8 for measuring the discharge temperature Td could be provided directly at and / or in the discharge outlet 4 instead. In general, the temperature sensor 8 can be of various kinds. Especially, the temperature sensor 8 can include (or be) a resistance temperature detector, e.g. PtI OOO.

[0125] Further, the refrigerant circuit 1 comprises a condenser 9, which is fluidly connected to the compressor stage 2. More specifically, the condenser 9 is arranged downstream of the compressor stage 2. It is fluidly connected to the discharge outlet 4 of the compressor stage 2 via the fluid connection 7.

[0126] Still further, the refrigerant circuit 1 comprises an economizer 11. The economizer 11 is arranged downstream of the condenser 9. It is fluidly connected to the condenser 9 via a fluid connection 10.

[0127] November 2025 D 200 P 2655 WO

[0128] In Fig. 1 , there is a branch off point 20 in the fluid connection 10. A fluid connection 21 fluidly connects an injection expansion valve 22 with an actuator 23 with the branch off point 20. A part of the refrigerant can be branched off from a main flow of the refrigerant in order to create a secondary flow SF. The secondary flow SF is controllable by the injection expansion valve 22. For example, increasing the opening degree of the injection expansion valve 22 increases the part of the refrigerant that is branched off from the main flow of the refrigerant at the branch off point 20 and hence increases the secondary flow SF of the refrigerant. Vice versa, decreasing the opening degree of the injection expansion valve 22 decreases the part of the refrigerant that is branched off from the main flow of the refrigerant and hence decreases the secondary flow SF.

[0129] In principle, the injection expansion valve 22 can be of any kind that is controllable by a controller 30. The actuator 23 can be of any kind. Especially, the actuator 23 can be an electronic actuator. The actuator 23 might include an actuator motor 23B, for example a stepper motor, in particular a bipolar stepper motor. The injection expansion valve 22 might include an actuator driver 23A, e.g. a stepper motor driver.

[0130] The other part of the main flow of the refrigerant that is not branched off at the branch off point 20 can be still referred to as the main flow of the refrigerant (the secondary flow is extracted from the main flow) or as the primary flow PF of the refrigerant. In other words, the term primary flow PF can be used to specifically refer to the main flow of the refrigerant downstream of the branch-off point 20 and upstream of the injection inlet 5. Between the discharge outlet 4 of the compressor stage 2, the main flow of the refrigerant includes both the part of the refrigerant that constitutes the main flow of the refrigerant downstream of the branch off point 20 and upstream of the injection inlet 5 (i.e. the primary flow PF) and the

[0131] November 2025 D 200 P 2655 WO part of the refrigerant that constitutes the secondary flow SF / and hence provides the injection flow IJS).

[0132] The economizer 11 comprises two fluid branches for the refrigerant. A first fluid branch thereof might be referred to as higher pressure branch 12. A second fluid branch thereof might be referred to as lower pressure branch 13. This is just a matter of nomenclature. In many operational conditions, a pressure of the refrigerant in the lower pressure branch 13 may be actually lower than a pressure of the refrigerant in the higher pressure branch 12. However, it is not excluded that the pressures in the lower pressure branch 13 and the higher pressure branch 12 can be at least substantially the same under some operational conditions. This could, for example, occur when the injection expansion valve 22 is fully open, i.e. when the opening degree of the injection expansion valve 22 is at its maximum.

[0133] The higher pressure branch 12 of the economizer 11 is fluidly connected to the condenser 9 (by the fluid connection 10).

[0134] Accordingly, in operation, the main flow of the refrigerant (in Fig. 1 , more exactly the primary flow PF) from the condenser 9 flows, via the fluid connection 10, into the higher pressure branch 12 of the economizer 11 .

[0135] The lower pressure branch 13 of the economizer 11 is fluid connected to the branch off point 20 via the fluid connection 21 including the injection expansion valve.

[0136] Accordingly, in operation, the secondary flow SF of the refrigerant flows from the branch off point 20 via the injection expansion valve 22 (which controls the secondary flow SF) into the lower pressure branch 13 of the economizer 11 .

[0137] November 2025 D 200 P 2655 WO

[0138] Typically (i.e. in most or even in all operational conditions), the injection expansion valve 22 will restrict the secondary flow SF. Accordingly, the injection expansion valve 22 expands the refrigerant of the secondary flow SF and reduces the pressure of the latter downstream of the injection expansion valve 22. Consequently, the pressure of the refrigerant (of the secondary flow SF) in the lower pressure branch 13 will be lower than the pressure of the refrigerant in the higher pressure branch 12. The refrigerant flowing out of the condenser is typically at least substantially in the liquid phase.

[0139] The expansion of the secondary flow SF by the injection expansion valve 22 hence allows that the expanded refrigerant downstream of the injection expansion valve 22 can at least partially evaporate and take up heat, for example in the lower pressure branch 13.

[0140] A heat exchange occurs between the refrigerant in the higher pressure branch 12 and the refrigerant in the lower pressure branch 13. In more detail, the refrigerant in the lower pressure branch 13 (i.e. the refrigerant of the secondary flow SF downstream of the injection expansion valve 22) will take up heat from the refrigerant in the higher pressure branch 12. At least a part of the refrigerant of the secondary flow SF may evaporate in the lower pressure branch.

[0141] The refrigerant circuit 1 further comprises a main expansion valve 15.

[0142] The main expansion valve 15 is arranged downstream of higher pressure branchi 2 of the economizer 11. A fluid connection 14 fluidly connects the main expansion valve 15 with the higher pressure branch 12.

[0143] Accordingly, in operation, the main flow of the refrigerant (in Fig. 1 , more specifically the primary flow PF of the refrigerant) flows from the higher pressure branch 12 to the main expansion valve.

[0144] November 2025 D 200 P 2655 WO

[0145] With respect to both Figs. 1 and 2, the heat exchange in the economizer 11 reduces a temperature of the refrigerant flowing through the higher pressure branch 12. Hence, the temperature main fluid flow (more precisely the primary fluid flow PF) reaching the main expansion valve 15 is (further) subcooled. This helps to increase the efficiency of the refrigerant circuit 1 .

[0146] The expansion valve 15 has an actuator 16, for example an electronic actuator.

[0147] The main expansion valve 15 expands the main flow of the refrigerant (more precisely the primary flow PF).

[0148] The refrigerant circuit 1 further comprises an evaporator 17. The evaporator 17 is arranged downstream of the main expansion valve 15 (along the main flow I the primary flow PF of the refrigerant).

[0149] Naturally, the main expansion valve 15 could be directly mounted to the economizer 11 or to the evaporator 17.

[0150] The expanded refrigerant flowing out of the expansion valve 15 flows into the evaporator 17. Since the pressure of the refrigerant (of the primary flow) is reduced while passing the expansion valve 15, said refrigerant can at least partially evaporate in the evaporator 17, at the same time taking up heat. Just for example, the evaporator 17 may be used in an air condition system to cool air and / or a transfer medium with the evaporator 17.

[0151] The suction inlet 3 of the compressor stage 2 is fluidly connected with the evaporator 17. For example, a fluid connection 18 connects the suction inlet 3 with an outlet of the evaporator 17.

[0152] November 2025 D 200 P 2655 WO

[0153] Accordingly, in operation, the refrigerant of the primary flow PF is returned from the evaporator 17 into to the compressor stage 2.

[0154] Apart from that, the injection stream IJS can be formed by refrigerant flowing out of the lower pressure branch 13 of the economizer 11. The injection stream IJS flows into the injection inlet 5 of the compressor stage 2. Hence, the injection stream IJS might be considered the downstream end portion of the secondary flow SF. The injection stream IJS (and hence the secondary flow SF) reunite within the compressor stage 2.

[0155] The injection inlet 5 is fluidly connected to the lower pressure branch 13 of the economizer 11 , in Fig. 1 via a fluid connection 24.

[0156] The refrigerant circuit 1 can comprise a pressure measurement means 25 for measuring a pressure of the refrigerant of the injection stream IJS. Said pressure is referred to as injection pressure Pij. The pressure measurement means 25 can be arranged at the fluid connection 24 to the injection inlet 5. In one example, the pressure measurement means 25 includes a pressure sensor, a pressure sensor and / or a pressure transducer. For example, the pressure measurement means 25 can include (or more specifically even consist of) a ratiometric pressure sensor.

[0157] Additionally or alternatively, the refrigerant circuit 1 can comprise a temperature sensor 27 for measuring a temperature Te of the refrigerant flowing into the lower pressure branch 13 of the economizer 11 . Said temperature sensor 27 can be of various kinds. Especially, the temperature sensor 27 can include (or be) a resistance temperature detector, e.g. a PtIOOO.

[0158] Further, the refrigerant circuit 1 comprises a temperature sensor 26 for measuring a temperature of the refrigerant of the injection stream IJS. Said temperature is referred to as injection temperature Tij. Said temperature sensor 26 can be of

[0159] November 2025 D 200 P 2655 WO various kinds. Especially, the temperature sensor 26 can include (or be) a resistance temperature detector, e.g. a PtIOOO.

[0160] In general, the refrigerant circuit 1 may include any combination of measurement means that are suitable for controlling a superheat of the injection flow based on measurement signals from the measurement means and for controlling the discharge temperature Td.

[0161] The refrigerant circuit 1 further comprises a controller 30. The controller 30 is functionally connected with the measurement means.

[0162] In this example, the controller 30 is connected to the temperature sensor 8 and operates the temperature sensor 8 for measuring the discharge temperature Td. Further, the controller 30 is connected to the temperature sensor 26 and operates the temperature sensor 26 for measuring the injection temperature Tij.

[0163] Still further, the controller 30 is connected to the temperature sensor 27 and operates the temperature sensor 27 for measuring the temperature Te. Additionally or alternatively, the controller 30 is connected to the pressure measurement means 25 and operates the pressure measurement means 25 for measuring the injection pressure Pij.

[0164] Apart from this, the controller 30 is (functionally) connected with the injection expansion valve, for example with the actuator 23. Especially, the controller 30 might be (functionally) connected with the actuator driver 23A.

[0165] The controller 30 is configured to provide control signals CLS for the opening degree of the injection expansion valve 22. Especially, the controller 30 is configured to send the control signals to the injection expansion valve 22 for adjusting the opening degree.

[0166] November 2025 D 200 P 2655 WO

[0167] The control signals CLS are at least based on a new opening degree value ODV which is determined by the controller 30 (see Fig. 3). The new opening degree value ODV corresponds to the desired opening degree that shall be set by the actuator 23 next.

[0168] The control signals CLS can include (even consist of) the respective new opening degree value ODV itself. The actuator driver 23A may convert the new opening degree value ODV into a signal that makes the actuator motor 23B (e.g. the stepper motor) move a valve element of the injection expansion valve 22.

[0169] The control signals CLS can include (or even consist of) signals that represent the new opening degree value ODV but differ from the new opening degree value ODV as such (see Fig. 6). By this, control signals CLS for injection expansion valves 22 requiring input of a specific type can be provided. Additionally or alternatively, as an example, the controller 30 may calculate the control signal CLS based on the new opening degree value ODV considering a non-linear opening behavior of the injection expansion valve 22 and / or the like.

[0170] Fig. 2 shows a modified refrigerant circuit 100. The modified refrigerant circuit 100 differs from the refrigerant circuit 1 shown only in that the branch off point 20 is arranged downstream of the higher pressure branch 12 of the economizer 11 , more precisely between the higher pressure branch 12 and the main expansion valve 15. Apart from that, the refrigerant circuit 100 is the same as the refrigerant circuit 1. Accordingly, Fig. 2 uses the same reference signs as Fig. 1 and, apart from describing the difference to Fig. 1 , no further explanation concerning the refrigerant circuit 100 in Fig. 2 are necessary.

[0171] The controller 30 is described in more detail referring to Figs. 3 to 6.

[0172] November 2025 D 200 P 2655 WO

[0173] The controller 30 may comprise a controller housing (see Fig. 3).

[0174] Fig. 3 shows, inter alia, a functional structure of the controller 30. The controller 30 comprises a discharge temperature sensor interface 31 that is configured to operate the temperature sensor 8 for measuring the discharge temperature Td. Further, it comprises a, injection temperature sensor interface 33 that is configured to operate the temperature sensor 26 for measuring the injection temperature Tij.

[0175] Still further, the controller 30 comprises at least one of (maybe both of) an injection pressure interface 32 to operate the pressure measurement means 25 for measuring the injection pressure Pij and a temperature sensor interface 34 for measuring the temperature Te.

[0176] The controller 30 has a control output 37 for outputting the control signals CLS.

[0177] The controller comprises a discharge temperature controller module 50 and a superheat controller module 60.

[0178] The discharge temperature controller module 50 is configured to determine a first opening degree proposal ODP1 for the new opening degree value ODV of the injection expansion valve 22 based on a discharge temperature Td and a present opening degree value ODV of the injection expansion valve 22. The discharge temperature Td is obtained via the discharge temperature sensor interface 31 .

[0179] The discharge temperature controller module 50 may be a proportional integral controller or a proportional integral derivative controller. It can be implemented as a software module, e.g. as a software library.

[0180] The discharge temperature controller module 50 watches the discharge temperature Td and the present opening degree of the injection expansion valve 22

[0181] November 2025 D 200 P 2655 WO

[0182] (represented by the present opening degree value ODV). The first opening degree proposal ODP1 is determined in order to keep the discharge temperature below pre-determined discharge temperature threshold Tdt. The discharge threshold Tdt may be different for different compressor stages 2, especially for different types of the compressor 2a, and / or for different refrigerants.

[0183] The discharge temperature threshold Tdt may be pre-stored and / or user-settable, e.g. via a user interface 42 (optional, see Fig. 4). The discharge temperature threshold Tdt may be stored in the memory 39 of the controller 30 (see Fig. 4) and / or obtained by the controller 30 via an (optional) communication interface 40.

[0184] The controller 30 may include several stored discharge temperature thresholds Tdt (e.g. for different compressor stages 2, different types of compressors 2a, and / or different refrigerants).

[0185] The discharge temperature threshold Tdt to be used may be selectable by a user.

[0186] The controller 30 may comprise a selection functionality for assisting the user in the selection of the suitable discharge temperature threshold Tdt. For example, the selection functionality may offer the user to select the compressor stage 2, the type of the compressor 2a, and / or the type of refrigerant and then automatically select and / or set the suitable discharge temperature threshold Tdt.

[0187] An output 51 of the discharge temperature controller module 50 outputs the first opening degree proposal ODP1.

[0188] The superheat controller module 60 is configured to determine a second opening degree proposal ODP2 based on a superheat value of the injection stream IJS.

[0189] November 2025 D 200 P 2655 WO

[0190] The superheat value corresponds to a superheat (if any) of the refrigerant in the injection stream IJS. When there is currently no superheat of the refrigerant in the injection stream IJS, the superheat value might be zero (or even negative). When there is currently any superheat of the refrigerant in the injection stream IJS, the superheat value corresponds to said superheat.

[0191] The controller 30, in particular the superheat controller module 60 determine the superheat value based on the measurement signals from the measurement means.

[0192] For example, the controller may determine the superheat values based on the injection temperature Tij and at least one of the injection pressure Pij and the temperature Te.

[0193] For example, for determining the superheat value based on the temperature Te and the injection temperature Tij, it might be assumed that the refrigerant of the secondary flow SF that flows into the lower pressure branch is in the wet-steam area, i.e. consist of a liquid-vapor mixture of the refrigerant. If the injection temperature Tij is the same as the temperature Te, there is no superheat of the injection stream. The superheat value may be set to zero. If the injection temperature Tij is larger than the temperature Te, the difference Tij - Te might be considered the superheat value.

[0194] As a further example, the superheat value may be determined based on the injection pressure Tij and the injection pressure Pij. The controller 30 may determine the superheat value based on said measurement signals in combination with information on thermodynamic properties of the refrigerant. The information on the thermodynamic properties of the refrigerant may be stored in the controller 30, for example in a memory 39 and / or obtained by the controller 30 via the communication interface 40, for example from an external server. The information on the

[0195] November 2025 D 200 P 2655 WO thermodynamic properties may include one of, several off, or all of the following: at least one formula, at least one look-up table, at least one simulation model, at least one log(p)-h diagram and / or corresponding information, and the like.

[0196] The superheat controller module 60 may be a proportional integral controller or a proportional integral derivative controller. It can be implemented as a software module, e.g. as a software library.

[0197] The superheat controller module 60 watches the present opening degree of the injection expansion valve 22 (represented by the present opening degree value ODV). It further watches the superheat value (or, for example, directly the injection temperature Tij and at least one of the injection pressure Pij and the temperature Te, which can be considered equivalent to watching the superheat value). The second opening degree proposal ODP2 is determined by the superheat controller module 60 in order to maintain a pre-determined superheat target SHt of the (refrigerant in) the injection stream IJS.

[0198] The superheat target SHt may be different for different compressor stages 2, especially for different types of the compressor 2a, and / or for different refrigerants.

[0199] The superheat target SHt may be pre-stored and / or user-settable, e.g. via the user interface 42 (optional, see Fig. 4). The superheat target SHt may be stored in the memory 39 of the controller 30 and / or obtained by the controller 30 via the communication interface 40.

[0200] The controller 30 may include several stored superheat target SHt (e.g. for different compressor stages 2, different types of compressors 2a, and / or different refrigerants).

[0201] The superheat target SHt to be used may be selectable by a user.

[0202] November 2025 D 200 P 2655 WO

[0203] The controller 30 may comprise a selection functionality for assisting the user in the selection of the suitable superheat target SHt. For example, the selection functionality may offer the user to select the compressor stage 2, the type of the compressor 2a, and / or the type of refrigerant and then automatically select and / or set the suitable superheat target SHt.

[0204] An output 61 of the superheat controller module 60 outputs the second opening degree proposal ODP1.

[0205] The controller 30 further comprises a selector module 70. The selector module 70 is configured to ongoingly receive, e.g. with a first input 71 , the first opening degree proposals ODP1 from the discharge temperature controller module 50. Further, the selector module 70 is configured to ongoingly receive, e.g. with a second input 72, the second opening degree proposals ODP2 from the superheat controller module 60.

[0206] In every cycle, the selector module 70 compares the first opening degree proposal OPD1 and the second opening degree proposal ODP2 that are received in this cycle. It determines which of the first opening degree proposal OPD1 and the second opening degree proposal ODP2 is larger in this cycle and determines the larger one of these values as the new opening degree value ODV for the injection expansion valve 22.

[0207] In every cycle, the selector module 70 then outputs the new opening degree value ODV as feedback to both the discharge temperature controller module 50 and the superheat controller module 60 to be used as the present opening degree value ODV in the next cycle. The ensures that both controller modules 50, 60 always "follow" actual the opening degree of the injection expansion valve 22.

[0208] November 2025 D 200 P 2655 WO

[0209] The discharge temperature controller module 50 may comprise an input 52 for receiving the new opening degree value ODV (from the selector module 70). The superheat controller module 60 may comprise an input 62 for receiving the new opening degree value ODV (from the selector module 70).

[0210] In the embodiment shown in Fig. 3, the controller 30 outputs the new opening degree value ODV directly as the control signal for the injection expansion valve 22. In this example, the actuator drive 23A of the actuator 23 converts the new opening degree value ODV into the signal that makes the actuator motor 23B (e.g. the stepper motor) move the valve element of the injection expansion valve 22.

[0211] The selector module 70 can be implemented as a software module, e.g. as a software library.

[0212] Fig. 6 shows a slight modification of the embodiment shown in Fig. 3. The only difference is that the selector module outputs the control signals CLS separately from the internal feedback output of the new opening degree value ODV. Outputs 73A, 73B for feeding the new opening degree ODV are separate. The control signals CLS are different from the new opening degree values ODV but still are based on and are in accordance with the corresponding new opening degree values ODV. With this approach, for example, the control signals CLS can be adapted for injection expansion valves 22 that need control signals CLS of a different type than the new opening degree values ODV.

[0213] Apart from that, the modified embodiment shown in Fig. 6 corresponds to the one shown in Fig. 3. Accordingly, the same reference signs are used in Fig. 6 and no further explanations are necessary.

[0214] November 2025 D 200 P 2655 WO

[0215] Turning now to Fig. 4, the controller 30 comprises a sensor interface 35 for operating the measurement means. It comprises the discharge temperature sensor interface 31 , the injection temperature sensor interface 33, and at least one of (maybe both of) the injection pressure interface 32 and the temperature sensor interface 34 for measuring the temperature Te.

[0216] The controller 30 further includes a microprocessor 36 that is operatively coupled to the sensor interface 35. The microprocessor 36 may be used for executing the discharge temperature controller module 50, the superheat controller module 60, and / or the selector module 70.

[0217] The controller 30 can also comprise the memory 39, which is operatively coupled to the microprocessor 39 in Fig. 4. As indicated above, the memory 39 may be configured to store (an actually provided pre-stored with) at least one temperature discharge threshold Tdt and / or at least one superheat target SHt.

[0218] Further, the controller 30 can include the control output 37. The control output may include a connector terminal 38 for data connection and / or electrical connection with the injection expansion valve 22.

[0219] According to one aspect, the controller optionally includes the communication interface 40. It may be connected to the processor 36. The communication interface 40 may be configured for data exchange with external electronic devices. It may be configured for wired and / or wireless communications. For example, it might include a bus interface (such as a fieldbus interface and / or a CAN bus interface), a local area network interface, a Bluetooth ® interface, and / or the like. The external interface controller 40 may include at least one connector terminal 45, e.g. at least one RJ-45 connector.

[0220] November 2025 D 200 P 2655 WO

[0221] Optionally, the controller 30 comprises the user interface 42. The user interface 42 may comprise a screen, e.g. a touchscreen, buttons, and / or sound-generating means. The user interface 42 may be detachable. In the latter case, it can be sufficient that the controller 30 comprises a mount for detachably mounting the user interface 42. The user interface 42 can be adapted to be user for generating input to the controller 30 and / or to present information to the user, e.g. including graphic output (for example via the screen / touchscreen) and / or audio output.

[0222] Finally, a method for operating the refrigerant circuit 1 (and accordingly the refrigerant circuit 100) is briefly summed up with respect to Fig. 5.

[0223] In step S1A, the discharge temperature controller module 50 receives the discharge temperature Td and the present opening degree ODV. The present opening degree of the present cycle corresponds to the new opening degree value ODV determined in the preceding cycle.

[0224] In step S2A, the discharge temperature controller module 50 determines the first opening degree proposal ODP1 based on the discharge temperature Td and the present opening degree ODV. Step S2A may be performed according to a proportional integral controller or according to a proportional integrative derivative controller.

[0225] In step S1 A and / or S2A, the discharge temperature controller module 50 may also obtain (not shown) the discharge temperature threshold Tdt to be used, e.g. from the memory 39. If there are several discharge temperature thresholds Tdt in the memory 39, there may be an additional information, e.g. in the memory 39, which of them is to be used. For example, the discharge temperature threshold Tdt to be used may be flagged.

[0226] November 2025 D 200 P 2655 WO

[0227] In the same cycle, in step S1 B, the superheat controller module 60 receives the measurement signals that are suitable for superheat control. For example, it receives the injection temperature Tij and the present opening degree ODV; and it further receives at least one of the injection pressure Pij and the temperature Te.

[0228] In step S2B, the superheat controller module 60 determines the second opening degree proposal ODP2 based on said measurement signals. Step S2B may be performed according to a proportional integral controller or according to a proportional integrative derivative controller.

[0229] In step S1 B and / or S2B, the superheat controller module 60 may also obtain (not shown) the superheat target SHt to be used, e.g. from the memory 39. If there are several superheat targets SHt in the memory 39, there may be an additional information, e.g. in the memory 39, which of them is to be used. For example, the superheat target SHt to be used may be flagged.

[0230] Step S1 B and / or S2B may include calculating the superheat value.

[0231] In step S3, the selector module 70 receives the first opening degree proposal ODP1 and the second opening degree proposal ODP2 and determines the larger one of the first opening degree proposal ODP1 and the second opening degree proposal ODP2. Fig. 5 exemplarily shows the check ODP2 >= ODP1 . Similarly, it can be checked for ODP2 > ODP1 , OPD2 <= ODP1 , or ODP2 < ODP1 instead. In any case, the selector module 70 sets the larger one of ODP1 and ODP2 as the new opening degree value ODV for the present cycle. If ODP1 = ODP2, then anyway ODV = ODP1 = ODP2 applies.

[0232] Accordingly, if ODP2 < ODP1 , the new opening degree value ODV is set to the first opening degree proposal ODP1 in step S4A. Else, the new opening degree value ODV is set to the second opening degree proposal ODP2 in step S4B.

[0233] November 2025 D 200 P 2655 WO

[0234] The new opening degree value ODV is provided as feedback to both of the discharge temperature controller module 50 and the superheat controller module 60. The feedback opening degree value ODV of this cycle is used as the present opening degree value ODV in the next cycle.

[0235] Further, in step S5, the control output 37 outputs the control signal(s) CLS based on the new opening degree value ODV to the injection expansion valve 22.

[0236] If the injection expansion valve 22 is suitable for being controlled with the new opening degree value ODV, the new opening degree value ODV can be directly used as the control signal CLS. Otherwise, the control signal CLS may be generated based on the new opening degree value ODV to represent, on the one hand, the desired opening degree of the injection expansion valve 22 and to be, on the other hand, be suitable as input for the injection expansion valve 22 (for setting the desired opening degree).

[0237] The controller 30 can be suitable to be used with different types of injection expansion valves 22 and hence be configured to generate different control signals CLS depending on which type of injection expansion valve 22 is used.

[0238] It is noted that steps S1 B and S2B are performed in addition to steps S1A and S2A in every cycle, despite of whether ODP1 or ODP2 is chosen as the new opening degree value ODV in this cycle. The discharge temperature controller module 50 and the superheat controller module 60 always run in parallel.

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[0240] List of reference signs:

[0241] 1 , 100 refrigerant circuit

[0242] 2 compressor stage

[0243] 2a compressor

[0244] 3 suction inlet

[0245] 4 discharge outlet

[0246] 5 injection inlet

[0247] 7, 10, 14, 18, 21 , 24 fluid connection

[0248] 8 temperature sensor

[0249] 9 condenser

[0250] 11 economizer

[0251] 12 higher pressure branch

[0252] 13 lower pressure branch

[0253] 15 main expansion valve

[0254] 16 actuator

[0255] 17 evaporator

[0256] 20 branch off point

[0257] 22 injection expansion valve

[0258] 23 actuator

[0259] 23A actuator driver

[0260] 23B actuator motor

[0261] 25 pressure measurement means

[0262] 26, 27 temperature sensor

[0263] 30 controller

[0264] 30a controller housing

[0265] 31 discharge temperature sensor interface

[0266] 32 injection pressure interface

[0267] 33 injection temperature sensor interface

[0268] 34 temperature sensor interface

[0269] 35 sensor interface

[0270] November 2025 D 200 P 2655 WO

[0271] 36 microprocessor

[0272] 37 control output

[0273] 38 connector terminal

[0274] 39 memory

[0275] 40 communication interface

[0276] 41 connector terminal

[0277] 42 user interface

[0278] 50 discharge temperature controller module

[0279] 51 , 61 , 73A, 73B output

[0280] 52, 62, 71 , 72 input

[0281] 60 superheat controller module

[0282] 70 selector module 70

[0283] CLS control signal

[0284] ODP1 first opening degree proposal

[0285] ODP2 second opening degree proposal

[0286] ODV opening degree value

[0287] Pij injection pressure

[0288] S1A, S2A, S1 B, S2B step

[0289] S3, S4A, S4B, S5 step

[0290] Td discharge temperature

[0291] Te temperature

[0292] Tij injection temperature

[0293] November 2025 D 200 P 2655 WO

Claims

Claims:1 . A controller (30) for controlling an opening degree of an injection expansion valve (22) for adjusting, in a refrigerant circuit (1 ; 100) with a compressor stage (2), an injection stream (IJS) of a refrigerant for supplementary injection of the refrigerant into the compressor stage (2), wherein the compressor stage (2) has a suction inlet (3) and a discharge outlet (4) for the refrigerant and further an injection inlet (5) for receiving the injection stream (IJS), wherein the controller (30) comprises: a discharge temperature controller module (50) that is configured to determine a first opening degree proposal (ODP1 ) for a new opening degree value (ODV) of the injection expansion valve (22) based on a discharge temperature (Td) of the refrigerant flowing out of the compressor stage (2) and the present opening degree value (ODV) of the injection expansion valve (22); a superheat controller module (60) that is configured to determine a second opening degree proposal (ODP2) for the new opening degree value (ODV) of the injection expansion valve (22) based on a superheat value of the injection stream (IJS) and the present opening degree value (ODV); and a control output (37) configured to output control signals (ODV; CLS) for adjusting the opening degree of the injection expansion valve (22); characterized in that the superheat controller module (60) is configured to determine the second opening degree proposal (ODP2) in parallel to the determination of the first opening degree proposal (ODP1 ) by the discharge temperature controller module (50), andNovember 2025 D 200 P 2655 WOthat the controller (30) comprises a selector module (70) that is operatively connected to the discharge temperature controller module (50) and the superheat controller module (60), wherein the selector module (70) is configured- to receive the first opening degree proposal (ODP1 ) and the second opening degree proposal (ODP2),- to determine the larger one of the first opening degree proposal (ODP1 ) and the second opening degree proposal (ODP2) as new opening degree value (ODV), wherein the controller (30) is configured to use the new opening degree for the next control signal (ODV; CLS), and- to feedback the new opening degree value (ODV) to both the discharge temperature controller module (50) and the superheat controller module (60) as the present opening degree value (ODV).

2. The controller (30) according to claim 1 , wherein the controller (30) comprises a discharge temperature sensor interface (31 ) that is configured to operate a resistance temperature detector as a temperature sensor (8) for measuring the discharge temperature (Td) of the refrigerant flowing out of the compressor stage (2).

3. The controller (30) according to any one of the preceding claims, wherein the controller (30) comprises an injection pressure interface (32) that is configured to operate a pressure measurement means (25) for measuring an injection pressure (Pij) of the injection stream (IJS).

4. The controller (30) according to any one of the preceding claims, wherein the controller (30) comprises an injection temperature interface (33) that is configured to operate a resistance temperature detector as a temperature sensor (26) for measuring an injection temperature (Tij) of the injection stream (IJS).November 2025 D 200 P 2655 WO5. The controller (30) according to any one of the preceding claims for controlling the opening degree of the injection expansion valve (22) for adjusting, in the refrigerant circuit (1 ; 100) having an economizer (11 ) with a higher pressure branch (12) for a main flow of the refrigerant from a condenser (9) to a main expansion valve (15) and a lower pressure branch (13) for the injection stream (IJS), characterized in that the controller (30) comprises a temperature sensor interface (34) that is configured to operate a resistance temperature detector as a temperature sensor (27) for measuring a temperature (Te) of the refrigerant flowing into the lower pressure branch (13) of the economizer (11 ).

6. The controller (30) according to any one of the preceding claims, wherein the control output (37) is configured to provide control signals (ODV; CLS) for driving a bipolar stepper motor as an actuator (23) of the injection expansion valve (22).

7. The controller (30) according to any one of the preceding claims, wherein the controller (30) is configured to be mounted on a DIN rail.

8. The controller (30) according to any one of the preceding claims, wherein the controller (30) comprises a microprocessor (36).

9. The controller (30) according to any one of the preceding claims, wherein the controller (30) comprises a memory (39) and is configured to store a set point for the discharge temperature (Td) and / or a set point for the superheat of the refrigerant that is used for the supplementary injection.

10. The controller (30) according to any one of the preceding claims, wherein the discharge temperature controller module (50) is implemented as a softwareNovember 2025 D 200 P 2655 WOmodule and wherein the superheat controller module (60) is implemented as an additional, separate software module.11 . The controller (30) according to any one of the preceding claims, wherein the selector module (70) is implemented as a software module.

12. The controller (30) according to any one of the preceding claims, wherein the controller (30) is configured such that the discharge temperature controller module (50) and the superheat controller module (60) run in parallel despite of whether the first opening degree proposal (ODP1 ) or the second opening degree proposal (ODP2) is used as the next opening degree value (ODV).

13. The controller (30) according to any one of the preceding claims, wherein the discharge temperature controller module (50) is a proportional integral controller or a proportional integral derivative controller.

14. The controller (30) according to any one of the preceding claims, wherein the superheat controller module (60) is a proportional integral controller or a proportional integral derivative controller.

15. A refrigerant circuit (1 ; 100) for a refrigerant, wherein the refrigerant circuit (1 ; 100) comprises a compressor stage (2), a condenser (9), an economizer (11 ), and an injection expansion valve (22) for adjusting an amount of refrigerant that is branched off downstream of the condenser (9) and guided through a lower pressure branch of the economizer (11 ) as an injection stream (IJS) for supplementary injection into the compressor stage (2), wherein the compressor stage (2) has a suction inlet (3) and a discharge outlet (4) for the refrigerant and further an injection inlet for receiving the injection stream (IJS),November 2025 D 200 P 2655 WOwherein refrigerant circuit (1 ; 100) includes the controller (30) according to any one of the preceding claims for controlling an opening degree of the injection expansion valve (22).

16. A method for controlling, in a refrigerant circuit (1 ; 100) with a compressor stage (2), an injection stream (IJS) of a refrigerant for supplementary injection of the refrigerant into the compressor stage (2) by means of a controller (30) and an injection expansion valve (22), wherein the compressor stage (2) has a suction inlet (3) and a discharge outlet (4) for the refrigerant and further an injection inlet (5) receiving the injection stream (IJS), wherein the method includes: receiving, with the controller (30), measurement signals indicating a discharged temperature (Td) of the refrigerant flowing out of the compressor stage (2), an injection temperature of the injection stream (IJS), and at least one of an injection pressure (Pij) and a temperature (Te) of the refrigerant flowing into a lower pressure branch (13) of an economizer (11 ), wherein the lower pressure branch (13) is used for the injection stream (IJS); determining, with a discharge temperature controller module (50) of the controller (30), a first opening degree proposal (ODP1 ) for a new opening degree value (ODV) of the injection expansion valve (22) based on the discharge temperature (Td) of the refrigerant flowing out of the compressor stage (2) and the present opening degree value (ODV) of the injection expansion valve (22); determining in parallel, with a superheat controller module (60) of the controller (30), a second opening degree proposal (ODP2) for the new opening degree value (ODV) of the injection expansion valve (22) based on the injectionNovember 2025 D 200 P 2655 WOtemperature (Tij), the present opening degree value (ODV), and the at least one of the injection pressure (Pij) and the temperature (Te); receiving, with a selector module (70) of the controller (30), the first opening degree proposal (ODP1 ) and the second opening degree proposal (ODP2); determining, with the selector module (70), the larger one of the first opening degree proposal (ODP1 ) and the second opening degree proposal (ODP2) as new opening degree value (ODV); using the new opening degree value (ODV) for providing, with the controller (30), a control signal (ODV; CLS) for adjusting the opening degree of the injection expansion valve (22); and feeding back the new opening degree value (ODV) to both the discharge temperature controller module (50) and the superheat controller module (60) as the present opening degree value (ODV).

17. The method according to claim 16, wherein the method further includes adjusting the opening degree of the expansion valve (22) based on the control signal (ODV; CLS) by means of an actuator (23).November 2025 D 200 P 2655 WO

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