Method for controlling a refrigeration circuit system based on isentropic temperature deviation, controller for a refrigeration circuit system and refrigeration circuit system

Abstract

Method for controlling a refrigeration circuit system based on isentropic temperature deviation, controller for a refrigeration circuit system and refrigeration circuit system The present invention relates to a method for controlling a refrigeration circuit system (1) including a compressor stage (2), an inlet sensor arrangement (3), and an outlet sensor arrangement (4). It includes determining, based on the inlet pressure (Pin) of the refrigerant flowing into a compression inlet (2in), a saturated vapor inlet condition (DWin), determining an isentropic outlet temperature (ToutIC) for the refrigerant flowing out of a compression outlet (2out), assuming an isentropic compression (ICC), determining an isentropic temperature deviation (Td) which is a difference of the outlet temperature (Tout) from the isentropic outlet temperature (ToutIC), and using the isentropic temperature deviation (Td) for controlling an inlet superheat (SHin) and / or an outlet superheat. In order to allow controlling the refrigeration circuit system (1) for particularly efficient and still reliable operation, the method comprises using a change in a slope of a relationship of the isentropic temperature deviation (Td) to the inlet superheat (SHin) for controlling the inlet superheat (SHin) and / or the outlet superheat. The invention further relates to a controller (20) for a refrigeration circuit system (1) and to a refrigeration circuit system (1).

Description

[0001]

[0002] Method for controlling a refrigeration circuit system based on isentropic temperature deviation, controller for a refrigeration circuit system and refrigeration circuit system

[0003] The present invention relates to a method for controlling a refrigeration circuit system, the refrigeration circuit system including a compressor stage with at least one compressor, an inlet sensor arrangement for providing inlet sensor information indicating at least an inlet pressure of the refrigerant flowing into a compression inlet, an outlet sensor arrangement for providing outlet sensor information indicating an outlet pressure and an outlet temperature of the compressed refrigerant flowing out of a compression outlet. The invention further relates to a controller for a refrigeration circuit system and a refrigeration circuit system.

[0004] Typically, a refrigeration circuit system includes a compressor, a condenser, an expansion valve, and an evaporator. The different units are fluidly connected in a refrigerant circuit. A refrigerant is circulated in the refrigerant circuit and compressed by the compressor. On the one hand, for efficient operation, a superheat of the refrigerant flowing out of the compressor should be low. The superheat of the refrigerant flowing out of the compressor can be briefly referred to outlet superheat. On the other hand, it should be avoided that liquid droplets of the refrigerant enter into the compressor or are formed in the compressor during compression of the refrigerant. Liquid refrigerant in the compressor decreases the efficiency and may even harm the compressor. The outlet superheat is affected by many different influences.

[0005] However, a major influence - for a given value of an inlet pressure of the refrigerant flowing into the compressor - is an inlet superheat. The inlet superheat is the superheat of the refrigerant flowing into the compressor. The inlet superheat can be adjusted by changing an opening degree of the expansion valve. In particular, it is aimed for an inlet superheat that is large enough to ensure that no liquid drops

[0006] October 2025 D 200 P 2635 WO of the refrigerant enter into the compressor or form in the compressor while the refrigerant is being compressed therein.

[0007] Usually, the refrigeration circuit system includes an inlet sensor arrangement for providing inlet sensor information including the inlet pressure and an inlet temperature and an outlet sensor arrangement for providing an outlet pressure and an outlet temperature. The inlet temperature is a temperature of the refrigerant flowing into the compressor. The outlet pressure is a pressure of the refrigerant flowing out of the compressor and the outlet temperature is a temperature of the refrigerant flowing out of the compressor.

[0008] The control of the refrigeration circuit system and especially of the inlet superheat as such are difficult. The refrigeration circuit system and especially the compressor are not thermodynamically "ideal" apparatuses. It is difficult to precisely predict the inlet superheat and / or the outlet superheat, in particular when the inlet superheat is low such that the refrigerant flowing out of the compressor is close to an inlet dew point. The inlet dew point is the (assumed) dew point for the refrigerant flowing into the compressor with the inlet pressure. An outlet dew point is the (assumed) dew point for the refrigerant flowing out of the compressor with the outlet pressure. Of course, due to the differences between the inlet pressure and the outlet pressure, the outlet dew point differs from the inlet dew point. When the inlet superheat is small (i.e. when the refrigerant flowing out of the compressor is close to the inlet dew point), even small differences in the inlet temperature and / or the inlet pressure can have substantial effects. Furthermore, especially the inlet temperature often fluctuates in this situation.

[0009] As mentioned above, the control of the refrigeration circuit system and especially of the inlet superheat is difficult. It is common practice to control the refrigeration circuit system and especially the opening degree of the expansion valve based on a pre-programmed scheme such that there is a pre-determined safety margin

[0010] October 2025 D 200 P 2635 WO between an inlet superheat set point and the assumed inlet dew point. The predetermined safety margin is comparatively high in order to ensure in any case that no liquid droplets enter the compressor or form in the compressor. Both the inlet superheat and the outlet superheat are hence typically or even in all operation conditions much larger than it would be necessary. This results in a suboptimal efficiency.

[0011] The problem underlying the invention is to allow controlling a refrigeration circuit system for particularly efficient and still reliable operation.

[0012] This problem is solved by a method for controlling a refrigeration circuit system, the refrigeration circuit system including a compressor stage with at least one compressor, an inlet sensor arrangement for providing inlet sensor information indicating at least an inlet pressure of the refrigerant flowing into a compression inlet, an outlet sensor arrangement for providing outlet sensor information indicating an outlet pressure and an outlet temperature of the compressed refrigerant flowing out of a compression outlet, wherein the method comprises the following steps:

[0013] - determining, based on the inlet pressure, a saturated vapor inlet condition assuming that the refrigerant would flow into the compression inlet at an inlet dew point for said inlet pressure,

[0014] - determining an isentropic outlet temperature for the refrigerant flowing out of the compression outlet, assuming an isentropic compression of the refrigerant from the saturated vapor inlet condition to the outlet pressure in the compressor stage,

[0015] - determining an isentropic temperature deviation which is a difference of the outlet temperature from the isentropic outlet temperature,

[0016] - using the isentropic temperature deviation for controlling an inlet superheat, which is a superheat of the refrigerant flowing into the compression inlet,

[0017] October 2025 D 200 P 2635 WO and / or an outlet superheat, which is a superheat of the refrigerant flowing out of the compression outlet.

[0018] The compression inlet is at an upstream side of the at least one compressor. The compression inlet can be an inlet of the compressor stage and / or an inlet of the at least one compressor.

[0019] The compression outlet is at a downstream side of the at least one compressor. The compression outlet can be an outlet of the compressor stage and / or an outlet of the at least one compressor.

[0020] It has been found in comprehensive studies that there is strong relation between the isentropic temperature deviation and a "critical inlet superheat". The critical inlet superheat is the minimum inlet superheat that allows stable control of the refrigeration circuit system without risking liquid droplets of the refrigerant in the compressor stage, in particular in the at least one compressor. In more detail, the following has turned out that for a plurality of different operational states (e.g. different fan speeds of a condenser of the refrigeration circuit system, different compressor speeds, different heating or cooling requirements, different condensing temperatures, different evaporating temperatures, and the like), at least as long as the refrigeration circuit system remains in the same configuration. A relationship of the isentropic temperature deviation to (with regard to) the inlet superheat is (at least substantially) a main linear relationship as long as the inlet superheat exceeds the critical inlet superheat. The relationship of the isentropic temperature deviation to the inlet superheat may be briefly referred to as "relevant relationship".

[0021] However, the relevant relationship distinctly changes as soon as the inlet superheat falls below the critical inlet superheat. Especially, a sudden change of a slope of the relevant relationship is detected at the critical inlet superheat. A

[0022] October 2025 D 200 P 2635 WO corresponding isentropic temperature deviation at the critical inlet superheat is also referred to as critical isentropic temperature deviations. If the actual outlet superheat falls below the minimum controllable outlet superheat, liquid droplets of the refrigerant are formed in the compressor stage (e.g. in the at least one compressor).

[0023] The disclosed approach makes use of this strong correlation for providing improved control of the refrigeration circuit system, e.g. by operating the refrigeration circuit system with an actual inlet superheat that is closer to or even corresponds to the critical inlet superheat.

[0024] The disclosed approach allows controlling the refrigeration circuit system for particularly efficient and still reliable operation, in particular in an easy and cost-efficient manner. No additional sensors are needed. The inlet sensor arrangement and the outlet sensor arrangement that are typically included in existing refrigeration circuit systems can be used and provide sufficient information for implementing the method.

[0025] The method helps to avoid liquid floodback at the compressor stage, especially at the at least one compressor. It helps to adjust the inlet superheat and / or the outlet superheat towards a minimum in an easy and well-controllable manner. As a consequence, a reliability of the compressor stage (e.g. of the at least one compressor) is improved.

[0026] Using the isentropic temperature deviation for controlling the inlet superheat and / or the outlet superheat may be understood to include cases of controlling the inlet superheat and / or the outlet superheat based at least the one of the critical isentropic temperature deviation and / or the minimum controllable outlet superheat. This might especially apply if the method includes determining the critical

[0027] October 2025 D 200 P 2635 WO isentropic temperature deviation and / or the minimum controllable outlet superheat.

[0028] The present invention uses the isentropic temperature deviation and hence does not need the inlet temperature as a control parameter. The inlet pressure is sufficient to calculate the inlet dew point and the saturated vapor inlet condition. As explained above, the inlet temperature is an instable and unreliable parameter, especially if the inlet superheat is small. Therefore, it is an advantage if the control is performed without using the inlet temperature as a control parameter. According to one aspect, the control using the isentropic temperature deviation is performed without using the inlet temperature as a control parameter.

[0029] The compressor stage includes the at least one compressor.

[0030] The critical temperature deviation may be larger than zero, for example at least 2 K, maybe at least 3 K. Additionally or alternatively, the critical temperature deviation may be less than 15 K, maybe less than 10 K.

[0031] According to one aspect, the compressor stage includes a single compressor, i.e. only the at least one compressor. In this case, the terms compressor stage and compressor (at least one compressor) can used synonymously.

[0032] According to one aspect, the compressor stage includes several compressors, e.g. at least two compressors.

[0033] Some of or all of the compressors can be connected in parallel. Additionally or alternatively, some or all of the compressors can be connected in series.

[0034] The refrigeration circuit system may be a heat pump system.

[0035] October 2025 D 200 P 2635 WO

[0036] The method can include operating the inlet sensor arrangement for providing the inlet sensor information indicating at least the inlet pressure (and optionally the inlet temperature), for example to the controller.

[0037] The method can include operating the outlet sensor arrangement for providing the outlet sensor information indicating at least the outlet pressure and the outlet temperature, for example to the controller.

[0038] The method may include determining the outlet superheat based on the outlet pressure and the outlet temperature. Especially, the method can include determining the outlet superheat based on the measured outlet pressure, the measured outlet temperature, and known properties of the refrigerant.

[0039] The known properties of the refrigerant might be considered by using

[0040] - at least one pressure-enthalpy diagram, such as a log(p)-h diagram (e.g. stored in a memory, for example of a controller) for the refrigerant,

[0041] - at least one look-up table (e.g. stored in the memory, for example of the controller) including known properties of the refrigerant, and / or

[0042] - at least one formula (e.g. stored in the memory, for example of the controller) considering known properties of the refrigerant.

[0043] Additionally or alternatively, the method may include determining the isentropic temperature deviation based on the outlet pressure and the outlet temperature.

[0044] According to one aspect, the method can include determining the inlet superheat based on the inlet pressure and the inlet temperature (even if the inlet temperature is not used as a control parameter). Especially, the method can include determining the inlet superheat based on the measured inlet pressure, the measured inlet temperature, and known properties of the refrigerant.

[0045] October 2025 D 200 P 2635 WO

[0046] According to one aspect, the method comprises adjusting, based at least on the isentropic temperature deviation, an outlet superheat set point for the outlet superheat and / or an inlet superheat set point for the inlet superheat. This allows particularly efficient and reliable but yet easy control of the refrigeration circuit system.

[0047] It is noted that the isentropic temperature deviation is a temperature difference defined for the outlet pressure. In other words, the isentropic temperature deviation intrinsically indicates a (fictious) ideal outlet superheat that would occur assuming the isentropic compression from the saturated vapor inlet condition (i.e. from a fictious, ideal, inlet superheat being zero) to the outlet pressure. In other words, the isentropic temperature deviation indicates to which extent the actual outlet superheat deviates from the ideal outlet superheat (resulting from the isentropic compression from the "ideal" inlet superheat = zero inlet superheat). The actual outlet superheat is sufficiently characterized by the combination of the outlet pressure and the isentropic temperature deviation. The isentropic temperature deviation is itself suitable as controlled variable and / or relevant parameter for controlling the refrigeration circuit system (at least for a given value of outlet pressure).

[0048] Additionally or alternatively, the method comprises using a critical isentropic temperature deviation for controlling the outlet superheat set point. The outlet superheat set point may be a controlled variable of the control. Especially when the inlet superheat is small (i.e. when the refrigerant flowing out of the compression outlet is close to an inlet dew point), the inlet temperature and hence the inlet superheat are fluctuating and hence less reliable and stable parameters for the control.

[0049] The critical isentropic temperature deviation may be determined based on a relationship of the isentropic temperature deviation to inlet superheat (i.e. the relevant

[0050] October 2025 D 200 P 2635 WO relationship). The critical isentropic temperature deviation is a meaningful but yet easy-to-use and sufficiently stable reference value. The method may rely on a pre-determined critical isentropic temperature deviation. For example, the critical isentropic temperature deviation may be measured in a factory and / or calculated in a factory and stored in a memory. Additionally or alternatively, the method may itself include measuring and / or calculating the critical isentropic temperature deviation. Exemplary possibilities for this are described below.

[0051] As noted above, the relevant relationship is very reproducible, even for various different operation conditions, at least as long a configuration of the refrigeration circuit system is not changed. The same applies with respect to the critical isentropic temperature deviation.

[0052] Since the critical isentropic temperature deviation is the same for different outlet pressures at least when the refrigeration circuit system is in the same configuration, a minimum controllable outlet superheat can be regarded as synonym of the critical isentropic temperature deviation. The minimum controllable outlet superheat for a given value of the outlet pressure can be simply calculated by adding the critical isentropic temperature deviation to the outlet dew point for that outlet pressure.

[0053] According to one aspect, the method comprises using a change in the slope of the relationship of the isentropic temperature deviation to the inlet superheat (i.e. the relevant relationship) for controlling the inlet superheat and / or the outlet superheat.

[0054] Especially, the critical isentropic temperature deviation may correspond to the isentropic temperature deviation at which the change in the slope of the relevant relationship (i.e. the relationship of the isentropic temperature deviation to the inlet superheat) occurs.

[0055] October 2025 D 200 P 2635 WO

[0056] The method may include comparing the isentropic temperature deviation with any one of, several of, or all of the following: The outlet superheat, the inlet superheat, and the critical isentropic temperature deviation.

[0057] Additional or alternatively, the method can include comparing the critical isentropic temperature deviation with any one of, several of, or all of the following: The outlet superheat, the inlet superheat, and the isentropic temperature deviation.

[0058] According to one aspect, the method may include using the relevant relationship for controlling the refrigeration circuit system, for example for adjusting the inlet superheat set point and / or the outlet superheat set point.

[0059] As explained above, the critical inlet superheat is closely related to the critical isentropic temperature deviation.

[0060] For example, the inlet superheat set point can be set to be within a range from the critical inlet superheat set point to an uppermost inlet superheat set point defined based on the critical inlet superheat set point. For example, the uppermost inlet superheat set point may be any one of, the lower one of, or the larger one of the following:

[0061] - The critical inlet superheat set point plus a temperature difference, wherein the temperature difference may be at least 0 K, e.g. at least 1 K or even at least 2 K, and / or 15 K at the maximum, maybe 10 K at the maximum or even 5 K at the maximum;

[0062] - The critical inlet superheat setpoint times a factor, wherein the critical inlet superheat set point may be indicated in Kelvin and the factor may be at least 1 ,0, e.g. at least 1 ,005 or even at least 1 ,01 , and / or 1 ,05 at the maximum, maybe 1 ,033 at the maximum or even 1 ,017 at the maximum.

[0063] October 2025 D 200 P 2635 WO

[0064] As explained above, the critical inlet superheat is also closely related to the minimum controllable outlet superheat.

[0065] The outlet superheat set point can be set to be within a range from the critical isentropic temperature deviation to an uppermost outlet superheat set point defined based on the critical isentropic temperature deviation. The uppermost outlet superheat set point may be any one of, the lower one of, or the larger one of the following:

[0066] - The critical isentropic temperature deviation plus a temperature difference, wherein the temperature difference may be at least 0 K, e.g. at least 1 K or even at least 2 K, and / or 15 K at the maximum, maybe 10 K at the maximum or even 5 K at the maximum;

[0067] - The critical isentropic temperature deviation times a factor, wherein the critical isentropic temperature deviation may be indicated in Kelvin and the factor may be at least 1 ,0, e.g. at least 1 ,005 or even at least 1 ,01 , and / or 1 ,05 at the maximum, maybe 1 ,033 at the maximum or even 1 ,017 at the maximum.

[0068] As noted above, the minimum controllable outlet superheat is closely related to the critical isentropic temperature deviation. Especially, the minimum controllable outlet superheat can correspond to the outlet dew point of the refrigerant at the outlet pressure plus the critical isentropic temperature deviation. In other words, the minimum controllable superheat corresponds to the refrigerant flowing out of the compression outlet having the outlet pressure, wherein the outlet temperature corresponds to the temperature at the dew point of the refrigerant at this outlet pressure plus the critical isentropic temperature deviation. Considering the outlet pressure, the minimum controllable superheat set point can be calculated from the critical isentropic temperature deviation and vice versa.

[0069] October 2025 D 200 P 2635 WO

[0070] The method may include determining the minimum controllable superheat set point based on the outlet pressure and the critical isentropic temperature deviation.

[0071] According to an aspect, the minimum controllable outlet superheat can be determined based on the critical isentropic temperature deviation and the outlet superheat set point can be set to be within a range from the minimum controllable outlet superheat to an uppermost outlet superheat set point defined based on the minimum controllable outlet superheat. For example, the uppermost outlet superheat set point may be any one of, the lower one of, or the larger one of the following:

[0072] - The minimum controllable outlet superheat plus a temperature difference, wherein the temperature difference may be at least 0 K, e.g. at least 1 K or even at least 2 K, and / or 15 K at the maximum, maybe 10 K at the maximum or even 5 K at the maximum;

[0073] - The minimum controllable outlet superheat times a factor, wherein the minimum controllable outlet superheat may be indicated in Kelvin and the factor may be at least 1 ,0, e.g. at least 1 ,005 or even at least 1 ,01 , and / or 1 ,05 at the maximum, maybe 1 ,033 at the maximum or even 1 ,017 at the maximum.

[0074] In one embodiment, the method comprises gradually lowering the outlet superheat with determining corresponding values of the isentropic temperature deviation and / or of the inlet superheat. Those values can be compared with the critical isentropic temperature deviation and / or the critical inlet superheat. This allows to approach towards the minimum controllable outlet superheat (and hence an optimum efficiency of operation) in a controlled manner.

[0075] Especially, the method can comprise gradually lowering the outlet superheat set point and determining the isentropic temperature deviation for at least several gradually lowered outlet superheat set points.

[0076] October 2025 D 200 P 2635 WO

[0077] The method can comprise setting an initial outlet superheat (set point). The outlet superheat can be set to the initial outlet superheat (set point) before gradually lowering the outlet superheat (set point).

[0078] The method can include preventing that the outlet superheat falls below the minimum controllable outlet superheat, that the inlet superheat falls below the critical inlet superheat, and / or that the isentropic temperature deviation falls below the critical isentropic temperature deviation.

[0079] The method may comprise adjusting the outlet superheat set point based on the isentropic temperature deviation and the critical isentropic temperature deviation. For example, the method can include reducing the outlet superheat set point gradually while the isentropic temperature deviation exceeds an outlet superheat threshold (which is based on the critical isentropic temperature deviation). The outlet superheat threshold may be the critical isentropic temperature deviation or correspond to the critical isentropic temperature deviation plus a safety margin. The safety margin can be at least 0,1 K, maybe at least 1 K, for example at least 2 K. It can be 15 K at the maximum, maybe 10 K at the maximum, for example even only 5 K at the maximum. The method can include gradually reducing the outlet superheat set point until the outlet superheat corresponds to or falls below the outlet superheat threshold.

[0080] The method may comprise adjusting the outlet superheat in order to match a target outlet superheat, which is the outlet superheat (for the respective given inlet pressure and the respective given outlet pressure) when the outlet temperature corresponds to the isentropic outlet temperature plus the critical isentropic temperature deviation plus (optionally) said safety margin.

[0081] According to one aspect, the method can comprise controlling the inlet superheat indirectly by controlling the outlet superheat based at least on the isentropic

[0082] October 2025 D 200 P 2635 WO temperature deviation. As noted above, using the outlet superheat as controlled variable can be more robust and reliable in actual implementation. However, the outlet superheat is influenced by the inlet superheat. For example, when the inlet superheat increases for a given value of the inlet pressure, the outlet superheat for a given value of outlet pressure increases as well. Therefore, the output superheat can be adjusted by changing the inlet superheat. Further, the inlet superheat can be easily changed, for example, by changing an opening of an expansion valve in the refrigeration circuit system.

[0083] In one embodiment, the refrigeration circuit system comprises at least one evaporator for evaporating the refrigerant before it flows into the compression inlet (i.e. in the inlet of the compressor stage and / or in the inlet of the at least one compressor), wherein the method includes adjusting feeding of the at least one evaporator based at least on the isentropic temperature deviation. A thermodynamic state of the refrigerant flowing into the compression inlet can be influenced by adjusting the feeding of the at least one evaporator. Finally, said feeding can influence the inlet superheat, the outlet superheat, and the isentropic temperature deviation.

[0084] Especially if the method includes determining at least one of the critical isentropic temperature deviation and the minimum controllable outlet superheat, adjusting feeding of the at least one evaporator based at least on the isentropic temperature deviation may be understood to include cases of adjusting feeding of the at least one evaporator based on at least the one of the critical isentropic temperature deviation and / or the minimum controllable outlet superheat.

[0085] Additionally or alternatively, the refrigeration circuit system may further comprise at least one expansion valve for expanding refrigerant that has been compressed by the compressor stage, wherein the method includes controlling the at least one expansion valve based at least on the isentropic temperature deviation. Said controlling may include (and even consist of) adjusting an opening degree of the at

[0086] October 2025 D 200 P 2635 WO least one expansion valve based at least on the isentropic temperature deviation. This is an easy way to considerably affect the inlet superheat and hence also the outlet superheat and the isentropic temperature deviation.

[0087] Especially if the method includes determining at least one of the critical isentropic temperature deviation and the minimum controllable outlet superheat, controlling the expansion valve (e.g. adjusting the opening degree of the expansion valve) based at least on the isentropic temperature deviation may be understood to include cases of controlling the expansion valve (e.g. adjusting the opening degree of the expansion valve) based at least the one of the critical isentropic temperature deviation and / or the minimum controllable outlet superheat.

[0088] In a flow direction of the refrigerant, the expansion valve may be located upstream of the evaporator.

[0089] According to one aspect, the method includes controlling the refrigeration circuit system in (at least two) different configurations based on (at least two) different critical isentropic temperature deviations.

[0090] As an example, the method may include

[0091] - controlling the refrigeration circuit system in a first configuration of the refrigeration circuit system based on a first critical isentropic temperature deviation and / or a first minimum controllable outlet superheat and

[0092] - controlling the refrigeration circuit system in second configuration of the refrigeration circuit system based on a second critical isentropic temperature deviation and / or a second minimum controllable outlet superheat.

[0093] In one embodiment, the refrigeration circuit system may include a first heat exchanger and a second heat exchanger and may be switchable between the first configuration, in which the first heat exchanger is used as the condenser and the

[0094] October 2025 D 200 P 2635 WO second heat exchanger is used as the evaporator, and the second configuration, in which the second heat exchanger is used as the condenser and the first heat exchanger is used as the evaporator.

[0095] The method can include determining the inlet pressure (of the refrigerant flowing into the compression inlet), especially by means of the inlet sensor arrangement. If the compressor stage includes several compressors (at least two compressors), the method can include determining the (common) inlet pressure of the compressor stage. Additionally or alternatively, the method can include determining the individual inlet pressures at the inlets of the individual compressors. However, typically, the individual inlet pressures will be the same. Further, typically, the individual inlet pressures will be the same as the common inlet pressure of the whole compressor stage.

[0096] The method may be performed under control of a controller. It is referred to below regarding possible details of the controller.

[0097] The method can include determining the outlet pressure (of the refrigerant flowing out of the compression outlet), especially by means of the outlet sensor arrangement. If the compressor stage includes several compressors (at least two compressors), the method can include determining the (common) outlet pressure of the compressor stage. Additionally or alternatively, the method can include determining the individual outlet pressures at the outlets of the individual compressors. If the compressors are arranged in parallel, the common outlet pressure (of the compressor stage) can be an average of the individual outlet pressures. Especially if the individual compressors are of the same type and are operated in the same manner, the outlet pressures will be the same and further, the individual outlet pressures will be the same as the common outlet pressure of the whole compressor stage.

[0098] October 2025 D 200 P 2635 WO

[0099] For example, the first heat exchanger may be an indoor heat exchanger and the second heat exchanger may be an outdoor heat exchanger. In the first configuration, the refrigeration circuit system can be used for cooling with the indoor heat exchanger. In the second configuration, the refrigeration circuit system can be used for heating with the indoor heat exchanger.

[0100] The method may include determining the corresponding saturated vapor inlet condition and / or the inlet dew point based on the inlet pressure and known properties of the refrigerant.

[0101] Additionally or alternatively, the method may include determining the corresponding outlet dew point based on the outlet pressure and known properties of the refrigerant.

[0102] In one embodiment, the at least one compressor is a variable speed compressor. The method can include controlling the variable speed compressor (especially a speed of the variable speed compressor) based on the isentropic temperature deviation. This helps in improving the efficiency.

[0103] The problem mentioned above is further solved by a determination method for determining at least a critical isentropic temperature deviation for (at least one configuration of) a refrigeration circuit system, the refrigeration circuit system including a compressor stage with at least one compressor, an inlet sensor arrangement for providing inlet sensor information indicating at least an inlet pressure of the refrigerant flowing into a compression inlet, an outlet sensor arrangement for providing outlet sensor information indicating an outlet pressure and an outlet temperature of the compressed refrigerant flowing out of a compression outlet.

[0104] October 2025 D 200 P 2635 WO

[0105] As noted above, the compression inlet is at an upstream side of the at least one compressor. The compression inlet can be an inlet of the compressor stage and / or an inlet of the at least one compressor.

[0106] The compression outlet is at a downstream side of the at least one compressor. The compression outlet can be an outlet of the compressor stage and / or an outlet of the at least one compressor.

[0107] An inlet superheat is a superheat of a refrigerant flowing into compression inlet.

[0108] The determination method may include (for the at least one configuration of the refrigeration circuit system)

[0109] - determining, for a plurality of different inlet superheats, corresponding values of an isentropic temperature deviation;

[0110] - using (an influence of) a change in a slope of a relationship of the isentropic temperature deviation to the inlet superheat for determining the critical isentropic temperature deviation.

[0111] The method for controlling the refrigeration circuit system may include one or more steps of the determination method and vice versa. The method for controlling the refrigeration circuit system may include the determination method and vice versa. The definitions, explanations, embodiments, modifications, and advantages described with respect to the method for controlling the refrigeration circuit system may apply accordingly to the determination method and vice versa.

[0112] The determination method may include determining a minimum controllable outlet superheat based on the critical isentropic temperature deviation, especially based on the critical isentropic temperature deviation and a given (value of the) outlet pressure.

[0113] October 2025 D 200 P 2635 WO

[0114] For values of the isentropic temperature deviation above a value range with the change of the slope, the (relevant) relationship may include a main linear relationship. According to the main linear relationship, the isentropic temperature deviation increases linearly with increasing inlet superheat.

[0115] The determination method may include (for the at least one configuration of the refrigeration circuit system) successively setting a plurality of different inlet superheat setpoints for the inlet superheat.

[0116] The determination method can include measuring the different outlet pressures and outlet temperatures (of the refrigerant flowing out of the compression outlet) in the refrigeration circuit system being operated with the different inlet superheat setpoints.

[0117] According to one aspect, the determination method may include

[0118] - controlling the refrigeration circuit system successively with the plurality of different inlet superheats;

[0119] - mapping the different isentropic temperature deviations over the different inlet superheats (to determine the relationship of the isentropic temperature deviation to the inlet superheat); and

[0120] - determining the critical isentropic temperature deviation based on the change in the slope of the relationship of the isentropic temperature deviation to the inlet superheat.

[0121] In this approach, the change in the slope of the relationship of the isentropic temperature deviation to the inlet superheat is analyzed directly.

[0122] Especially, the determination method may include determining the critical isentropic temperature deviation to correspond to a value of isentropic temperature deviation where said change in the slope occurs.

[0123] October 2025 D 200 P 2635 WO

[0124] According to one aspect, the determination method may include

[0125] - setting an inlet superheat set point to an initial inlet superheat set point;

[0126] - gradually reducing the inlet superheat set point over time, especially (at least substantially) uniformly over time;

[0127] - mapping the different isentropic temperature deviations over time; and

[0128] - determining the critical isentropic temperature deviation based on a change of a slope in a relationship of the isentropic temperature deviation to the time.

[0129] In this approach, the influence of the change in the slope of the relationship of the isentropic temperature deviation to the inlet superheat is used indirectly. As time passes, the inlet superheat set points decrease. A specific passed time is an equivalent to a specific inlet superheat (set point), respectively. The change in the slope of the relationship of the isentropic temperature deviation to the inlet superheat is "transferred" into (reflects in) the change of the slope in the relationship of the isentropic temperature deviation to the time.

[0130] Naturally, the values of the inlet superheat set points and / or the values of the actual inlet superheat can be used directly even if gradually reducing the inlet superheat (set point) over time.

[0131] The determination method may include averaging of the critical isentropic temperature deviation determined under different operating conditions (but still for the at least one configuration of the refrigeration circuit system). As explained above, the critical isentropic temperature deviation is (at least substantially) the same for different operating conditions as long the configuration of the refrigeration circuit system is the same. However, determining the critical isentropic temperature deviation can be influenced by measurement errors. By averaging the results for the critical isentropic temperature deviation determined under different operating

[0132] October 2025 D 200 P 2635 WO conditions, the accuracy of the determination critical isentropic temperature deviation is increased.

[0133] According to one aspect, the determination method may include determining corresponding critical isentropic temperature deviations for (at least two) different configurations of the refrigeration circuit system. As explained above, the refrigeration circuit system may be operable in different configurations. For example, the different configurations may differ from each by different positions of at least one element of the heat system (e.g. the first heat exchanger) with respect to the compressor stage along a flow direction of the refrigerant. Especially, the determination method may include determining a first critical isentropic temperature deviation for a first configuration of the refrigeration circuit system in which a first heat exchanger of the refrigeration circuit system is operated to release heat from the refrigerant therein and determining a second critical isentropic temperature deviation for a second configuration of the refrigeration circuit system in which a second heat exchanger of the heat system is operated to transfer heat into the refrigerant therein.

[0134] The problem mentioned above is further solved by a controller for a refrigeration circuit system, the refrigeration circuit system including a compressor stage with at least one compressor, an inlet sensor arrangement for providing inlet sensor information indicating at least an inlet pressure of the refrigerant flowing into the a compression inlet, an outlet sensor arrangement for providing outlet sensor information indicating an outlet pressure and an outlet temperature of the compressed refrigerant flowing out of a compression outlet, and an expansion valve, wherein the controller comprises: a receiver for receiving the inlet sensor information and the outlet sensor information; a processor; and

[0135] October 2025 D 200 P 2635 WO a control output for controlling at least the expansion valve; wherein the controller is configured for

[0136] - determining, based on the inlet pressure, a saturated vapor inlet condition assuming that the refrigerant would flow into the compressor stage at an inlet dew point for said inlet pressure,

[0137] - determining an isentropic outlet temperature for the refrigerant flowing out of the compression outlet, assuming an isentropic compression of the refrigerant from the saturated vapor inlet condition to the outlet pressure in the compressor stage,

[0138] - determining an isentropic temperature deviation, which is a difference of the outlet temperature (Tout) from the isentropic outlet temperature, and

[0139] - controlling at least the expansion valve based at least on the isentropic temperature deviation.

[0140] The definitions, explanations, embodiments, modifications, and advantages described with respect to the method for controlling the refrigeration circuit system may apply accordingly to the controller and vice versa. In particular, the controller may be configured to control the refrigeration circuit system for performing the method according to the present invention.

[0141] The definitions, explanations, embodiments, modifications, and advantages described with respect to the determination method for determining at least one of a critical isentropic temperature deviation apply accordingly to the controller and vice versa. In particular, the controller may be configured to control the refrigeration circuit system for performing the determination method according to the present disclosure.

[0142] The controller can be used in any usual refrigeration circuit system. Most of the present refrigeration circuit system also include a suitable inlet sensor

[0143] October 2025 D 200 P 2635 WO arrangement, a suitable outlet sensor arrangement, and an expansion valve that can be controlled by a control output of a controller. Vice versa, the method and the determination method as disclosed are particularly advantageous because both of them can be easily implemented in existing refrigeration circuit systems by simply replacing an existing controller by the controller according to the present invention.

[0144] No new design of the refrigeration circuit system is necessary.

[0145] The controller can be even retrofitted to such existing refrigeration circuit system.

[0146] According to one aspect, the at least one compressor of the refrigeration circuit system may be a variable speed compressor. Accordingly, the controller is configured for controlling the (variable speed) compressor. For example, the controller (especially the control output) may be configured to adjust a speed setting for the at least one compressor for determining the critical isentropic temperature deviation and / or for adjusting the speed setting for the at least one compressor based at least on the isentropic temperature deviation. Accordingly, the controller is adapted to make use of the variable speed functionality of the at least one compressor in a synergistic manner.

[0147] The controller can be configured for determining, checking, and / or correcting a critical isentropic temperature deviation. The critical isentropic temperature may correspond to the isentropic temperature deviation at which a change in the slope of a (relevant) relationship between the isentropic temperature deviation to an inlet superheat occurs.

[0148] Additionally or alternatively, the controller can be configured for determining, checking, and / or correcting the critical isentropic temperature deviation using the

[0149] October 2025 D 200 P 2635 WO change in the slope of the relationship of the isentropic temperature deviation to the inlet superheat.

[0150] The controller can be configured to adjust an outlet superheat set point for an outlet superheat and / or an inlet superheat set point for an inlet superheat by controlling at least the expansion valve.

[0151] In one embodiment, the controller is switchable between

[0152] - a determination mode for determining, correcting and / or checking the critical isentropic temperature deviation (at least one critical isentropic temperature deviation) and / or at least one minimum controllable outlet superheat based on measurements and a

[0153] - a normal operation mode.

[0154] In one embodiment, the controller is configured to adjust the outlet superheat set point for the outlet superheat and / or the inlet superheat set point for the inlet superheat by controlling at least the expansion valve based at least on the isentropic temperature deviation. This allows a particularly easy but yet precise control using the existing refrigeration circuit system.

[0155] According to one aspect, the controller can be configured to control the expansion valve at least based on the actual isentropic temperature deviation and the critical isentropic temperature deviation (e.g. at least in the normal operation mode).

[0156] Additionally or alternatively, the controller can be configured to determine a critical isentropic temperature deviation (e.g. in the determination mode). It is referred to the corresponding disclosures regarding the determination method.

[0157] The controller may be configured for (e.g. in the determination mode) progressively decreasing the inlet superheat set point and / or the outlet superheat set

[0158] October 2025 D 200 P 2635 WO point to detect the change in the slope change in the relationship of the isentropic temperature deviation and the inlet superheat set point and / or the outlet superheat set point. The controller can include a corresponding algorithm (e.g. stored in a memory of the controller).

[0159] According to one aspect, the controller may be configured to control the refrigeration circuit system (e.g. at least an opening degree of the expansion valve) for maintaining a specific isentropic temperature deviation in operation. The controller be configured to perform control of the refrigeration circuit system with an isentropic temperature deviation loop control set point, e.g. for the inlet superheat setpoint and / or the outlet superheat set point. The controller can include a corresponding algorithm (e.g. stored in a memory of the controller).

[0160] The controller can include a learning machine, especially for improving the control.

[0161] According to one aspect, the controller may be configured to control the refrigeration circuit system based on different critical isentropic temperature deviations and / or minimum settable outlet superheat set points for different configurations of the refrigeration circuit system.

[0162] The controller may include at least one (cascade) regulation loop, e.g. cascade regulation loop on the inlet superheat, a (cascade) regulation loop on the outlet superheat, and / or a (cascade) regulation loop on the isentropic temperature deviation.

[0163] The problem mentioned above is further solved by a refrigeration circuit system including a compressor stage with at least one compressor, an inlet sensor arrangement for providing inlet sensor information indicating at least an inlet pressure of the refrigerant flowing into a compression inlet, an outlet sensor

[0164] October 2025 D 200 P 2635 WO arrangement for providing outlet sensor information indicating an outlet pressure and an outlet temperature of the compressed refrigerant flowing out of a compression outlet, and an expansion valve, wherein the refrigeration circuit system is configured for performing the method according to the present invention and / or the determination method according to the present invention and / or wherein the refrigeration circuit system includes the controller according to the present invention.

[0165] The definitions, explanations, embodiments, modifications, and advantages described with respect to the method for controlling the refrigeration circuit system may apply accordingly to the refrigeration circuit system and vice versa.

[0166] The definitions, explanations, embodiments, modifications, and advantages described with respect to the determination method for determining at least one of a critical isentropic temperature deviation apply accordingly to the refrigeration circuit system and vice versa.

[0167] The definitions, explanations, embodiments, modifications, and advantages described with respect to the controller may apply accordingly to the refrigeration circuit system and vice versa.

[0168] The refrigeration circuit system may include at least two heat exchangers that are fluidly connected in parallel to the expansion valve. This allows for implementing more heat transfer capacity in an easy and cost-efficient manner.

[0169] 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

[0170] October 2025 D 200 P 2635 WO 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.

[0171] Preferred embodiments of the invention will now be described with reference to the drawings, in which:

[0172] Fig. 1 schematically shows a refrigeration circuit system 1 with a compressor 2A, three heat exchangers 5, 7A, 7B, an expansion valve 6, a controller 20 for controlling the refrigeration circuit system 1 , and a switching valve 9, wherein one of the heat exchangers 5, 7A, 7B is fluidly connected to one side (a first side 61 ) of the expansion valve 6 and wherein the other two of the heat exchangers 5, 7A, 7B are fluidly connected to another side (a second side 62) of the expansion valve 6 in parallel, wherein a flow direction FD2A, FD2B of a refrigerant through the heat exchangers 5, 7A, 7B and the expansion valve 6 can be alternated with the switching valve 9;

[0173] Fig. 2 schematically shows a development of an inlet superheat set point SHinSP, an actual inlet superheat SHin, an isentropic temperature deviation Td, an oil superheat OilSH, and a difference DCP of an outlet temperature from a compressor polynomial calculation over time, wherein the inlet superheat set point is gradually reduced over time;

[0174] Fig. 3 shows a relationship of the isentropic temperature deviation Td to the inlet superheat SHin for a first configuration of the refrigeration circuit system 1 in Fig. 1 with the flow direction FD2A through the heat exchangers 5, 7A, 7B and the expansion valve 6, wherein there is a significant change of a slope of said relationship at a first critical isentropic temperature deviation TdCr(FD2A) and a corresponding first critical inlet superheat SHinCr(FD2A) for the first configuration;

[0175] October 2025 D 200 P 2635 WO

[0176] Fig. 4 is based on Fig. 3 and additionally shows the isentropic temperature deviation TdCr(FD2B) to the inlet superheat SHin for a second configuration of the refrigeration circuit system in Fig. 1 with the flow direction FD2B through the heat exchangers 5, 7A, 7B and the expansion valve 6;

[0177] Fig. 5 schematically shows aspects of the compression of the refrigerant by the compressor 2A and the control based on the isentropic temperature deviation Td in the refrigeration circuit system 1 of Fig. 1 ; and

[0178] Fig. 6 schematically shows one possible aspect of controlling the expansion valve 6 of the refrigeration circuit system 1 in Fig. 1 based on the isentropic temperature deviation Td.

[0179] Fig. 1 shows a refrigeration circuit system 1. It comprises a compressor stage 2 with a single compressor 2A for compressing a refrigerant that is circulated in a refrigerant circuit of the refrigeration circuit system 1 . The compressor stage 2 has a compression inlet 2in and a compression outlet 2out. Since there is only the single compressor 2A in this embodiment, the compression inlet 2in is both an inlet of the compressor stage 2 and an inlet of the individual compressor 2A. Similarly, the compression outlet 2out is both an outlet of the compressor stage 2 and an outlet of the individual compressor 2A. Refrigerant flows into the compressor stage 2 through the compression inlet 2in, the compressor stage 2 compresses the refrigerant, and the compressed refrigerant flows out of the compressor stage 2 via the compressor outlet 2out. Fig. 1 shows an (intended) compressor-part flow direction FD1 through the compressor stage 2 in operation.

[0180] The refrigeration circuit system 1 comprises an inlet sensor arrangement 3. The inlet sensor arrangement 3 is arranged directly upstream of the compression inlet

[0181] October 2025 D 200 P 2635 WO

[0182] 2in. Naturally, it could be also provided at the compression outlet 2in. The inlet sensor arrangement 3 includes at least one inlet pressure sensor 31 for measuring an inlet pressure Pin of the refrigerant flowing into the compression inlet 2in, hence into the compressor stage 2 and into the at least one compressor 2A. It further includes at least one inlet temperature sensor 32 for measuring an inlet temperature Tin of the refrigerant flowing into the compression inlet 2in, hence into the compressor stage 2 and into the at least one compressor 2A. The inlet sensor arrangement 3 generates inlet sensor information that indicates the inlet pressure Pin and the inlet temperature Tin. The inlet sensor arrangement 3 is electrically connected to the controller 20. The inlet sensor information is received by a receiver 22 of the controller 20.

[0183] Further, the refrigeration circuit system 1 comprises an outlet sensor arrangement 4. The outlet sensor arrangement 4 is arranged directly downstream of the compression outlet 2out. Naturally, it could be also provided at the compression outlet 2out. The inlet sensor arrangement 4 includes at least one outlet pressure sensor 41 for measuring an outlet pressure Pout of the refrigerant flowing out of the compression outlet 2out, hence out of the compressor stage 2 and out of the at least one compressor 2A. It further includes at least one outlet temperature sensor 42 for measuring an outlet temperature Tout of the refrigerant flowing out of the compression outlet 2, hence out of the compressor stage 2 and out of the at least one compressor 2A. The outlet sensor arrangement 4 generates outlet sensor information that indicates the outlet pressure Pout and the outlet temperature Tout. The outlet sensor arrangement 4 is electrically connected to the controller 20. The outlet sensor information is received by the receiver 22 of the controller 20. Downstream of the compressor stage 2 and the outlet sensor arrangement 4, a switching valve 9 follows in the refrigerant circuit.

[0184] The switching valve 9 fluidly connects a compressor-part of the refrigeration circuit system 1 with a heat-exchanger-part of the refrigeration circuit system 1. The

[0185] October 2025 D 200 P 2635 WO switching valve 1 is configured to switch the refrigeration circuit system 1 between a first configuration with a first flow direction FD2A in the heat-exchanger-part and a second configuration with a second flow direction FD2B in the heat-exchanger- part.

[0186] The compressor-part includes the compressor stage 2, the inlet sensor arrangement 3, and the outlet sensor arrangement 4.

[0187] The refrigeration circuit system 1 includes at least two heat exchangers 5, 7A, 7B and an expansion valve 6. These elements are arranged in the heat-exchanger- part of the refrigeration circuit system 1. At least one heat exchanger 5 is fluidly connected to a first side 61 of the expansion valve 6 (i.e. to a first port of the expansion valve 6). At least one heat exchanger 7A, 7B is fluidly connected a second side 62 of the expansion valve 6 (i.e. to another port at an opposite end of the expansion valve 6 along an intended flow direction of the refrigerant through the expansion valve 6 in operation).

[0188] In this exemplary embodiment, the single heat exchanger 5 is fluidly connected to the first side 61 of the expansion valve 6, wherein two heat exchangers 7A, 7B are fluidly connected to the other, second side 62 of the expansion valve 6 in parallel. In modifications not shown, the heat exchanger 7B may be omitted or further heat exchangers may be fluidly connected to the second side 62 of the expansion valve 6. Apart from that, in modifications not shown, one or more further heat exchangers may be fluidly connected to the first side 61 of the expansion valve 6 in parallel to the heat exchanger 5.

[0189] An (intended) flow direction of the refrigerant through the heat exchangers 5, 7A, 7B and through the expansion valve 6 is switchable by means of the switching valve 9.

[0190] October 2025 D 200 P 2635 WO

[0191] In the first configuration, the refrigerant flow through the heat exchangers 5, 7A, 7B and through the expansion valve 6 (in operation) is along the first flow direction FD2A. The heat exchanger 5 operates as condenser and the heat exchangers 7A, 7B operate as evaporators. The refrigeration circuit system 1 pumps heat from the heat exchanger 5 to the heat exchangers 7A, 7B.

[0192] In the second configuration, the refrigerant flow through the heat exchangers 5, 7A, 7B and through the expansion valve 6 (in operation) is along the second flow direction FD2B. The heat exchangers 7A, 7B operate as condensers and the heat exchanger 5 operates as evaporator. The refrigeration circuit system 1 pumps heat from the heat exchangers 7A, 7B to the heat exchanger 5.

[0193] In the compressor-part of the refrigeration circuit system 1 , the compressor-part flow direction FD1 is the same in both configurations.

[0194] Optionally, the refrigeration circuit system 1 can include further sensors, for example, at least one of, several of, or all of the following:

[0195] - a sensor arrangement 81 directly at the first side 61 of (next to the one port of) the expansion valve 6 (i.e. directly downstream of the expansion valve 6 in the first configuration with the flow direction FD2A), wherein the sensor arrangement 81 can include at least one pressure sensor and / or at least one temperature sensor,

[0196] - a sensor arrangement 82 directly at the second side 62 of (next to the other port of) of the expansion valve 6 (i.e. directly upstream of the expansion valve 6 in the first configuration with the flow direction FD2A), wherein the sensor arrangement 82 can include at least one pressure sensor and / or at least one temperature sensor,

[0197] - a further sensor arrangement 83 arranged between the switching valve 9 and the compressor inlet 2in, wherein the sensor arrangement 83 can include at least one pressure sensor and / or at least one temperature sensor,

[0198] October 2025 D 200 P 2635 WO

[0199] - a sensor arrangement 84 arranged between the switching valve 9 and the heat exchanger 7A, wherein the sensor arrangement 84 can include at least one pressure sensor and / or at least one temperature sensor, and

[0200] - a sensor arrangement 85 arranged between the switching valve 9 and the heat exchanger 7B, wherein the sensor arrangement 85 can include at least one pressure sensor and / or at least one temperature sensor.

[0201] The controller 20 controls the operation of the refrigeration circuit system 1. The controller 20 includes an input 21 and a receiver 22 for receiving information from the sensor arrangements 3, 4, 81 , 82, 83, 84, 85. Especially, it is configured for receiving the inlet sensor information from the inlet sensor arrangement 3 and the outlet sensor information from the outlet sensor arrangement 4.

[0202] The controller 20 includes at least one processer 23. The processor 23 is connected to the receiver 22.

[0203] Further, the controller 20 can include a memory 25. It may be connected to the processor 23. The memory 25 may include information related to known properties of the refrigerant, for example at least one of, several of, or all of the following:

[0204] - at least one pressure-enthalpy diagram, such as a log(p)-h diagram for the refrigerant an / or a corresponding dataset,

[0205] - at least one look-up table including known properties of the refrigerant, and

[0206] - at least one formula (e.g. stored in the memory, for example of the controller) considering known properties of the refrigerant.

[0207] The known properties can, for example, include at least pressure-dependent dew points (i.e. condensing points / temperatures) of the refrigerant and / or information on phase-transition conditions of the refrigerant, especially between a superheated steam area SSA and a wet steam area WSA (see Fig. 5).

[0208] October 2025 D 200 P 2635 WO

[0209] Apart from that, the controller 20 may include at least one external communication interface 26. It may be connected to the processor 23. The communication interface 26 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.

[0210] The controller 20 also includes a control output 24. It can be connected to the processor 23. The control output 24 is configured for outputting control signals to at least one element of the refrigeration circuit system 1 . In particular, the controller 20 is configured to control at least an opening degree of the expansion valve 6 by means of the control output 24. In this embodiment, the controller 20 is further configured to control speeds of a fan 51 of the heat exchanger 5, a fan 71 A of the heat exchanger 7A, and / or a fan 71 B of the heat exchanger 71 B. Additionally or alternatively, the controller 20 can be configured to control the switching valve 9, in particular for switching between the first configuration and the second configuration of the refrigeration circuit system 1.

[0211] The compressor 2A can be a variable-speed compressor. The controller 20 can be configured to control the speed of the compressor 2A, e.g. via the control output 24.

[0212] Fig. 2 shows different values related to the operation of the refrigeration circuit system 1 of Fig. 1 in the first configuration. The refrigeration circuit system 1 was operated under certain operational conditions (e.g. a certain speed of the fan 51 , a certain speed of the fan 71 A, a certain speed of the fan 71 B, and / or a certain speed of the compressor 2A).

[0213] October 2025 D 200 P 2635 WO

[0214] As explained above, in the first configuration of the refrigeration circuit system 1 , the flow through the heat exchangers 5, 7A, 7B and the expansion valve 6 in operation occurs along the first flow direction FD2A.

[0215] To begin with, Fig. 2 shows an inlet superheat set point SHinSP for an inlet superheat SHin of the refrigerant.

[0216] The inlet superheat set point SHinSP is a controlled variable. The controller 20 operates the refrigeration circuit system 1 , trying that an (actual) inlet superheat SHin meets the inlet superheat set point SHinSP.

[0217] The inlet superheat SHin is a superheat of the refrigerant flowing into the compression inlet 2in, e.g. the superheat at the sensor inlet arrangement 3 and / or at the inlet of the compressor stage 2.

[0218] The inlet superheat SHin can be understood as a temperature difference between the (actual) inlet temperature Tin and an inlet dew point temperature TDWin. The inlet dew point temperature TDWin is the dew point temperature of the refrigerant at the inlet pressure Pin. The inlet temperature Tin, the inlet dew point temperature TDWin, and the inlet pressure Pin are indicated in Fig. 5.

[0219] It can be assumed an inlet condition of the refrigerant flowing in the compression inlet 2A (see point FSin in Fig. 5) is in the superheated steam area SSA (see Fig. 5).

[0220] The controller 20 determines the inlet dew point temperature TDWin based on the inlet sensor information, especially based on the inlet pressure Pin. For example, the controller 20 calculates the inlet dew point temperature TDWin from the inlet pressure Pin and / or looks up the corresponding inlet dew point temperature TDWin for the given inlet pressure Pin from the look-up table.

[0221] October 2025 D 200 P 2635 WO

[0222] Further, the controller 20 determines an isentropic temperature deviation Td for the refrigerant flowing out of the compression outlet 2out based on the inlet pressure Tin and the outlet pressure Pin.

[0223] In more detail, the controller 20 determines (e.g. calculates) an isentropic outlet temperature ToutIC for the refrigerant flowing out of the compression outlet 2out. This is explained referring to Fig. 5.

[0224] Firstly, it is assumed that the refrigerant flowing into the compression inlet 2in would be in a saturated vapor inlet condition DWin at the inlet pressure Pin. The saturated vapor inlet condition DWin for the inlet pressure Pin corresponds to the hypothetical situation that the refrigerant with the inlet pressure Pin would enter the compressor stage 2 with the inlet dew point temperature TDWin. This corresponds to the assumption that the refrigerant would enter the compressor stage 2 with zero inlet superheat SHin. Fig. 5 shows a dew line DWL that separates the wet steam area WSA from the superheated steam area SSA.

[0225] Secondly, an isentropic compression ICC of the refrigerant from the saturated vapor inlet condition DWin to the outlet pressure Pout by the compressor stage 2 is assumed. It is assumed that the refrigerant flowing out of the compression outlet 2out would have an ideal fluid outlet state FSoutIC with the outlet pressure Pout and the isentropic outlet temperature ToutIC. The isentropic outlet temperature ToutIC is the hypothetical temperature of the refrigerant that would occur at the compressor outlet 2out after the hypothetical isentropic compression ICC of the refrigerant from the saturated vapor inlet condition DWin at the inlet pressure Pin to the outlet pressure Pout. The isentropic outlet temperature ToutIC at the outlet pressure Pout corresponds also to a hypothetical outlet superheat. Said hypothetical outlet superheat is the difference between the isentropic outlet temperature ToutIC and a dew point temperature at the outlet pressure Pout.

[0226] October 2025 D 200 P 2635 WO

[0227] However, in normal operation, the refrigerant flowing into the compression inlet 2in with the inlet pressure Pin has a fluid inlet state FSin with an inlet superheat SHin that is larger than zero. In other words, the inlet temperature Tin is larger than the inlet dew point temperature TDWin. The inlet superheat SHin corresponds SHin = Tin - TDWin. There is an enthalpy difference between an actual enthalpy H(Pin, Tin) of the refrigerant flowing into the compression inlet 2in and an enthalpy H(Pin, TDWin) of the refrigerant at the saturated vapor inlet condition DWin.

[0228] Furthermore, a real compression RCL of the refrigerant by the compressor stage 2 is different from the ideal isentropic compression ICC. This is schematically shown in Fig. 5.

[0229] Finally, the outlet temperature Tout of the refrigerant flowing out of the compression outlet 2out is higher than the isentropic outlet temperature ToutIC.

[0230] The temperature difference between the outlet temperature Tout and the isentropic outlet temperature ToutIC is the isentropic temperature deviation Td.

[0231] The outlet superheat corresponds to Tout minus the dew point temperature at the outlet pressure Pout.

[0232] An enthalpy of the refrigerant in the ideal fluid outlet state FSoutIC is H(Pout, ToutIC). An enthalpy of the refrigerant flowing out of the compression outlet 2out is H(Pout, Tout).

[0233] Between the fluid outlet state FSout and the ideal fluid outlet state FSoutIC, there is an enthalpy difference AH(Td) which is related to the isentropic temperature difference Td.

[0234] October 2025 D 200 P 2635 WO

[0235] In tendency, a high temperature deviation Td is indicative of an unnecessary high outlet superheat and hence of an inefficient operation. However, as the real compression RLC is always “worse” than the ideal isentropic compression ICC, the isentropic temperature deviation Td approaching zero implies that the fluid state of the refrigerant flowing into the compression inlet 2in shifts into the wet steam area WSA (i.e. left of the saturated vapor inlet condition DWin in Fig. 5). This means that liquid droplets of refrigerant occur in the compressor stage 2.

[0236] It has now been found that there is a critical isentropic temperature difference TdCr(FD2A) which indicates very reliably (at least as long as the refrigeration circuit system 1 remains in the same configuration, e.g. in the first configuration) for various different operation conditions a lower threshold for the isentropic temperature deviation Td. When the isentropic temperature deviation Td falls below the critical isentropic temperature deviation TdCr(FD2A) in operation, there is a high risk of liquid droplets of refrigerant in the compressor stage 2. If the isentropic temperature deviation Td is instead kept larger than the critical isentropic temperature deviation TdCr(FD2A), no liquid droplets (at least no significant amount) can be found in the compressor stage 2. Hence, the critical isentropic temperature deviation TdCr(FD2A) is an indicator for operation of the refrigeration circuit system 1 in the corresponding configuration with optimum efficiency that can be realistically achieved.

[0237] For the purpose of finding the critical isentropic temperature deviation TdCr(FD2A), the controller 20 is configured to gradually reduce the inlet superheat set point SHinSP gradually over time.

[0238] In Fig. 2, the controller 20 starts at the time of 0 s (on the x-axis) with an initial inlet superheat set point SHinSP of about 8 K (on the y-axis). A minimum of the

[0239] October 2025 D 200 P 2635 WO inlet superheat set point SHinSP (about 2 K) is reached after a time of about 3200 s has expired.

[0240] The controller 20 calculates the (actual) inlet superheat SHin based on the inlet sensor information and the known properties of the refrigerant.

[0241] Furthermore, Fig. 2 shows an oil superheat OilSH and a difference DCP of the outlet temperature Tout from a compressor polynomial calculation over time.

[0242] The different curves in Fig. 2 reveal that liquid droplets of the refrigerant occur in the compressor stage 2 at the right side of the figure. In particular, the oil superheat OilSH falling below 8 K and a sharp bend in the curve of DSP at the same time (i.e. at a time of 3000 s) indicate the first occurrence of liquid droplets of refrigerant in the compressor stage 2 at this time. While the inlet superheat SHin is further reduced, the difference DCP value suddenly drops faster to larger negative values. Soon, the inlet superheat SHin cannot follow any further decrease of the inlet superheat set point SHinSP anymore. At the right end of Fig. 2, at times larger than 3800 s, there is so much liquid refrigerant in the compressor stage 2 that no supercooling of the refrigerant is possible anymore.

[0243] Common controllers rely on controlling refrigeration circuit systems, which are similar to the refrigeration circuit system 1 , based directly on the inlet superheat SHin as the controlled variable.

[0244] For good efficiency of the operation, it is desired to have the inlet superheat SHin as small as possible. However, it should be avoided that liquid droplets of the refrigerant "occur" in (i.e. enter into and / or form within) the compressor stage 2.

[0245] However, when the inlet superheat SHin becomes small, the inlet temperature Tin is an unreliable variable / parameter. The inlet temperature Tin tends to fluctuate.

[0246] October 2025 D 200 P 2635 WO

[0247] The control based directly on the inlet superheat SHin is not stable at low inlet superheats SHin. Therefore, it is not reliable to control the refrigeration circuit system 1 based directly on the inlet superheat SHin (needing measurement of the inlet temperature Tin as an essential parameter) as the controlled variable with particularly small inlet superheat SHin. Common controllers hence must operate with a rather large inlet superheat SHin in order to ensure reliable control.

[0248] Turning back to Fig. 2, there is a sudden change in a slope of the isentropic temperature Td at the point in time at which the first liquid droplets in the compressor stage 2 occur (i.e. at a time of about 3000 s in this example).

[0249] In more detail, at this time, the slope of the isentropic temperature deviation Td exhibits a significant step to a lower negative value.

[0250] Fig. 2 shows only one experiment at one set of specific operational conditions. The applicant has performed a plurality of many different experiments as shown in Fig. 2 under many different operational conditions.

[0251] Fig. 3 shows a relationship of the isentropic temperature deviation Td to the inlet superheat SHin for a plurality of experiments under different operational conditions (e.g. different speeds of the fan 51 , different speeds of the fan 71 A, different speeds of the fan 71 B, different speeds of the compressor stage 2, different condensing temperatures for the refrigerant, different evaporation temperatures for the refrigerant, etc.). For each data point in Fig. 3, for the respective inlet superheat SHin (x-axis-position of the respective data point), the corresponding values of the isentropic temperature deviation Td of a plurality of different experiments (such as the one shown in Fig. 2) were averaged to obtain the corresponding isentropic temperature deviation Td (y-axis position of the respective data point in Fig. 3). However, the refrigeration circuit system 1 was always in the first configuration (with flow direction F2DA) in these experiments.

[0252] October 2025 D 200 P 2635 WO

[0253] In other words, Fig. 3 shows a relationship Td = Td(SHin) for the first configuration of the refrigeration circuit system 1 .

[0254] The relationship of the isentropic temperature deviation Td to the inlet superheat SHin corresponds to a simple linear curve (a main linear function) for all inlet superheats SHin that exceed a critical inlet superheat SHinCr for the first configuration. This can be called a "main linear relationship" for the first configuration. The critical inlet superheat SHinCr for the first configuration can be briefly referred to as SHinCr(FD2A).

[0255] However, for inlet superheats SHin below the critical inlet superheat SHinCr(FD2A), the slope of the relationship has a larger value. In the first configuration, there is even a clear "secondary" linear function for SHin < SHinCr. In any case, there is a sudden change in the slope of the relationship at the critical inlet superheat SHinCr. The corresponding isentropic temperature deviation Td is the critical isentropic temperature deviation TdCr(FD2A).

[0256] It is a surprising fact that the value of SHinCr(FD2A) is the same (at least for the given first configuration of the refrigeration circuit system 1 ) even for various different operational conditions.

[0257] This knowledge can be advantageously used to control the refrigeration circuit system 1 based on the isentropic temperature deviation Td and / or the critical isentropic temperature deviation TdCr(FD2A) in the first configuration, especially in combination with the outlet superheat.

[0258] The controller 20 can be configured to calculate the outlet superheat from the outlet pressure Pout, the outlet temperature Tout, and the known properties of the refrigerant.

[0259] October 2025 D 200 P 2635 WO

[0260] The controller 20 can be configured to obtain a minimum controllable outlet superheat based on the outlet pressure Pout and the critical isentropic temperature deviation TdCrfor the given configuration of the refrigeration circuit system 1 (e.g. TdCr(FD2A) for the first configuration).

[0261] The minimum controllable outlet superheat (for the given inlet pressure Pi, the given outlet pressure Pout, and the given configuration) corresponds to the isentropic outlet temperature ToutIC (for the given inlet pressure Pin and a given outlet pressure Pout) plus the critical isentropic temperature deviation TdCr (for the given configuration, e.g. TdCr(FD2A) for the first configuration).

[0262] The controller 20 can be configured to set the outlet superheat set point based the critical isentropic temperature deviation TdCr, especially based on the minimum controllable outlet superheat (which can be obtained from the inlet pressure Pin, the outlet pressure Pout, and the critical isentropic temperature deviation TdCr).

[0263] For example, the controller 20 can be configured to set the outlet superheat set point directly to the minimum controllable outlet superheat (for the given configuration) and to control the refrigeration circuit system 1 based on the outlet superheat set point. This ensures particularly high efficiency of the operation of the refrigeration circuit system 1.

[0264] This is the same as and might be construed as (and vice versa) to setting - for a given value of the outlet pressure Pout - a set point for the temperature deviation Td to the critical isentropic temperature deviation TdCr (for the given configuration of the refrigeration circuit system 1 ).

[0265] October 2025 D 200 P 2635 WO

[0266] According to an aspect, the controller 20 can be configured to set the outlet superheat set point to a value corresponding to the minimum controllable outlet superheat plus a safety margin and to control the refrigeration circuit system 1 based on the outlet superheat set point. The safety margin can be at least 0,1 K, maybe at least 1 K, for example at least 2 K. It can be 15 K at the maximum, maybe 10 K at the maximum, for example even only 5 K at the maximum.

[0267] This is the same as and might be construed as (and vice versa) setting - for the given value of the outlet pressure Pout - a set point for the temperature deviation Td to the critical isentropic temperature deviation TdCr (for the given configuration of the refrigeration circuit system 1 ) plus the safety margin.

[0268] Further, the safety margin for the outlet superheat may be calculated based on a function of a difference of the (actual) outlet superheat to the minimum controllable outlet superheat. Additionally or alternatively, the safety margin (for the outlet superheat set point and / or the isentropic temperature deviation set point) can be calculated based on a function of the isentropic temperature deviation Td. In other words, the safety margin may be auto-adaptive (e.g. for ensuring smoother control).

[0269] An example for the control of the outlet superheat is schematically illustrated in Fig. 6. The controller 20 ongoingly adjusts the outlet superheat set point. The controller 20 configured to set a new outlet superheat set point based on the present outlet superheat plus an outlet superheat correction offset SHoutCO. This is done repeatedly. The next value of the outlet superheat set point corresponds to the present outlet superheat plus the outlet superheat correction offset SHoutCO, respectively. The controller 20 calculates the outlet superheat correction offset SHoutCO based on a function of the (actual) isentropic temperature deviation Td. The outlet superheat correction offset SHoutCO is constant at a value Y2 when the isentropic temperature deviation Td is larger than an upper threshold X2.

[0270] October 2025 D 200 P 2635 WO

[0271] The upper threshold X2 can be in the range from 5 K to 15 K, for example X2 = 15 K or X2 = 10 K. Y2 may be negative. Just for example, Y2 may be in the range from - 5 k to - 0,5 K, e.g. Y2 = - 2K.

[0272] In one exemplary embodiment, SHoutCO (Td > X2) = Y2 = - 2 K. This means that the controller 20 automatically sets the next outlet superheat set point to 2 K below the present outlet superheat as long as the isentropic temperature deviation Td is larger than X2. As a consequence, in the case that there is a high outlet superheat, the outlet superheat set point (and hence the actual outlet superheat) is gradually reduced step by step over time.

[0273] For values of the isentropic temperature deviation Td being smaller than X2, the outlet superheat correction offset SHoutCO in Fig. 6 might be calculated as a function SHoutCO (Td), in this example as SHoutCO (Td) = (Y2-Y1 ) / (X2-X1 )*(Td- X2) + Y2. For example, Y1 = 4 K and / or Y1 = TdCr. Additionally or alternatively, for example, X1 = 4 K and / or X1 = TdCr. It is noted that a slope (Y2-Y1 ) / (X2-X1 ) of the function is negative and that Y2 is negative in Fig. 6.

[0274] Whenever the isentropic temperature deviation Td is larger than a value X3, the new outlet superheat set point is reduced (by the controller 20) below the present outlet superheat. Hence, the controller 20 controls the refrigeration circuit system 1 to reduce the outlet superheat in such situations.

[0275] Whenever the isentropic temperature deviation Td is smaller than the value X3, the new outlet superheat set point is raised (by the controller 20) above the present outlet superheat. Hence, the controller 20 controls the refrigeration circuit system 1 to increase the outlet superheat in such situations.

[0276] October 2025 D 200 P 2635 WO

[0277] In other words, the controller 20 operates the refrigeration circuit system 1 to approach and maintain the isentropic pressure difference Td at the value X3. In principle, X3 can correspond to the critical isentropic temperature deviation TdCr, e.g. TdCr(FD2A) for the refrigeration circuit system 1 being in the first configuration and TdCr(FD2B) for the refrigeration circuit system 1 being in the second configuration. In practice, X3 might be a bit above the critical isentropic temperature deviation TdCr, e.g. in the range from 0,1 K to 6 K above the critical isentropic temperature deviation TdCr. X3 might be referred to as the "target isentropic temperature deviation" of the control. Naturally, it corresponds to a "target outlet superheat", which is the hypothetical outlet superheat (for the given outlet pressure Pout) plus X3.

[0278] The controller 20 can be configured to adjust the outlet superheat in order to match the target outlet superheat, which is the outlet superheat (for the respective given inlet pressure Pin and the respective given outlet pressure Pout) at the outlet temperature Tout corresponding to the isentropic outlet temperature ToutIC plus the critical isentropic temperature deviation TdCr plus (optionally) an additional safety margin.

[0279] The controller 20 controls the expansion valve 6, and optionally the speed of the compressor stage 2, the fan 51 , the fan 71 A, and / or the fan 71 B accordingly.

[0280] If the refrigeration circuit system 1 in Fig. 1 is in the first configuration, the controller 20 adjusts a feeding of the heat exchanger 5, which is used as evaporator in the first configuration, by adjusting the opening degree of the expansion valve 6.

[0281] If the refrigeration circuit system 1 in Fig. 1 is in the second configuration, the controller 20 adjusts a feeding of the parallel heat exchangers 7A, 7B, which are

[0282] October 2025 D 200 P 2635 WO used as parallel evaporators in the second configuration, by adjusting the opening degree of the expansion valve 6.

[0283] Of course, this is only one example for using the isentropic temperature deviation Td (and optionally also the critical isentropic temperature deviation TdCr) for controlling the refrigeration circuit system 1. For example, the function shown in Fig. 6 may be modified to be non-linear, shifted along the x-axis, and / or the like.

[0284] Fig. 4 is based on Fig. 3. It shows additional data points for the refrigeration circuit system 1 of Fig. 1 operating in the second configuration. In principle, the same main linear relationship as for the first configuration applies. However, the critical isentropic temperature deviation TdCr(FD2B) for the second configuration is a bit higher than the critical isentropic temperature deviation TdCr(FD2A) for the first configuration, see area AR1 in Fig. 4.

[0285] The critical isentropic temperature deviation TdCr(FD2A) for the first configuration may be briefly referred to as first critical isentropic temperature deviation. The critical isentropic temperature deviation TdCr(FD2B) for the second configuration may be briefly referred to as second critical isentropic temperature deviation.

[0286] For example, the first critical isentropic temperature deviation TdCr(FD2A) is 4,2 K and the second critical isentropic temperature deviation TdCr(FD2B) is 6 K. These are just examples. The difference results from a less ideal flow of the refrigerant in the second configuration. As the two heat exchangers 7A, 7B operate as evaporators in parallel, this causes additional fluctuations.

[0287] Of course, a difference of the (second) minimum controllable outlet superheat for the second configuration minus the (first) minimum controllable outlet superheat for the first configuration corresponds (if assuming the same outlet pressures Pout) is the same as a difference of the second critical isentropic

[0288] October 2025 D 200 P 2635 WO temperature deviation TdCr(FD2B) minus the first critical isentropic temperature deviation TdCr(FD2A).

[0289] In general, the refrigeration circuit system 1 might include more heat exchangers and / or might be configured to operate in more different configurations. Accordingly, the controller 20 can be configured to control the refrigeration circuit system 1 in various different configurations based on various corresponding critical isentropic temperature differences Td.

[0290] According to an aspect, the memory 25 may store one or more critical isentropic temperature deviations TdCr(FD2A), TdCr(FD2B) and / or one or more minimum controllable outlet superheats. The values may be determined based on measurements by the manufacturer and / or calculated by the manufacturer and prestored. Additionally or alternatively, they can be determined based on measurements after installation and be stored.

[0291] The controller 20 may be configured for operating the refrigeration circuit system 1 to determine at least one critical isentropic temperature deviation TdCr(FD2A), TdCr(FD2B) and / or at least one minimum controllable outlet superheat based on measurements, e.g. as described above. Especially, the controller 20 may be configured for operating the refrigeration circuit system 1 to determine, respectively for several configurations of the refrigeration circuit system 1 , a corresponding critical isentropic temperature deviation TdCr(FD2A), TdCr(FD2B) and / or a corresponding minimum controllable outlet superheat based on measurements, e.g. as described above.

[0292] The controller 20 may be able to intermittently (e.g. periodically) determine and / or check said values. For example, the controller 20 may from time to time carefully reduce the isentropic temperature deviation Td below the critical isentropic temperature deviation TdCr to check, correct, and / or re-determinate the critical

[0293] October 2025 D 200 P 2635 WO isentropic temperature deviation TdCr. Accordingly, the controller 20 may be from time to time carefully reduce the outlet superheat below the minimum controllable outlet superheat to check, correct, and / or re-determinate the minimum controllable outlet superheat. Said reductions(s) allow to detect the low end of the main linear relationship, e.g. the sudden change in the slope of the isentropic temperature difference.

[0294] For example, the controller 20 may be switchable between

[0295] - a determination mode for determining and / or checking the at least one critical isentropic temperature deviation TdCr(FD2A), TdCr(FD2B) and / or at least one minimum controllable outlet superheat based on measurements and a

[0296] - normal operation mode.

[0297] In the embodiment shown in Fig. 1 , the compressor stage 2 includes the single compressor 2A.

[0298] In modifications (not shown), the compressor stage 2 can include several compressors, e.g. at least one further compressor that is connected with the inlet of the compression stage 2 and to the outlet of the compression stage 2 in parallel to the compressor 2A.

[0299] In principle, it is sufficient to provide the inlet sensor information indicating at least the common inlet pressure (i.e. the common inlet pressure of the whole compressor stage 2 I the inlet pressure at the inlet of the compressor stage 2). Similar, it is sufficient to provide the outlet sensor information indicating the common outlet pressure and the common temperature outlet (i.e. the outlet pressure of the whole compressor stage 2 I the outlet pressure and the outlet temperature at the outlet of the compressor stage 2). Naturally, if all compressors are of the same type and are operated identically, the occurrence of liquid droplets of refrigerant is expected to start under at least substantially the same conditions. If the compressors

[0300] October 2025 D 200 P 2635 WO are of different types and / or are not operated identically, the control can be configured to prevent the occurrence of liquid droplets of refrigerant in the compressor that is most prone to this issue (e.g. by a control based on the critical isentropic temperature deviation and / or the minimum stable superheat for this specific compressor).

[0301] Additionally or alternatively, the inlet sensor information may indicate the individual inlet pressure for at least one of the compressors, maybe the individual inlet pressures for all compressors. Further additionally or alternatively, the outlet sensor information may indicate the individual outlet pressure and the individual outlet pressure for the at least one of the compressors, maybe the individual outlet pressures for all compressors and / or the individual outlet temperatures for all compressors.

[0302] Working with the individual inlet pressure, the individual outlet pressure, and the individual outlet temperature for the at least one compressor (e.g. the compressor 2A) allows a control that specifically prevents liquid droplets of the refrigerant occurring in this at least one compressor.

[0303] For example, the inlet sensor arrangement can be provided at the (individual) inlet of the compressor that is most prone to liquid droplets of the refrigerant occurring therein and the outlet sensor arrangement can be provided at the (individual) outlet of the same compressor.

[0304] Working with the individual inlet pressures, the individual outlet pressures, and the individual outlet temperatures for all compressors allows a control that precisely prevents liquid droplets of the refrigerant occurring in any one of the compressors, especially even if the compressors are of different type and / or operated differently (e.g. with different compressor speeds). This also allows individual control of the compressors (e.g. individual compressor speeds, individual power-on

[0305] October 2025 D 200 P 2635 WO or power up depending on present power requirements of the refrigeration circuit system 1 , and the like).

[0306] In any embodiment, the sensor arrangements can be modified accordingly to pro- vide the necessary values.

[0307] October 2025 D 200 P 2635 WO

[0308] List of reference signs:

[0309] 1 refrigeration circuit system

[0310] 2 compressor stage

[0311] 2A compressor

[0312] 2in compression inlet

[0313] 2out compression outlet

[0314] 3 inlet sensor arrangement

[0315] 4 outlet sensor arrangement

[0316] 5, 7A, 7B heat exchanger

[0317] 6 expansion valve

[0318] 9 switching valve

[0319] 20 controller

[0320] 21 input

[0321] 22 receiver

[0322] 23 processor

[0323] 24 control output

[0324] 25 memory

[0325] 26 external communication interface

[0326] 31 inlet pressure sensor

[0327] 32 inlet temperature sensor

[0328] 41 outlet pressure sensor

[0329] 42 outlet temperature sensor

[0330] 61 first side

[0331] 62 second side

[0332] 51 , 71A, 71 B fan

[0333] 81 , 82, 83, 84, 85 sensor arrangement

[0334] AR1 area

[0335] FD1 , FD2A, FD2B flow direction

[0336] DCP difference of the outlet temperature Tout from a compressor polynomial calculation

[0337] October 2025 D 200 P 2635 WO

[0338] DWL dew point line

[0339] DWin saturated vapor inlet condition

[0340] FSin fluid inlet state

[0341] FSoutIC ideal fluid outlet state

[0342] FSout fluid outlet state

[0343] H(Pin, Tin), H(Pin, TDWin) enthalpy

[0344] H(Pout, ToutIC), H(Pout, Tout) enthalpy

[0345] AH(Td) enthalpy difference

[0346] ICC ideal isentropic compression

[0347] OilSH oil superheat

[0348] Pin inlet pressure

[0349] Pout outlet pressure

[0350] RLC real compression

[0351] SHin inlet superheat

[0352] SHinCr(FD2A), SHinCr(FD2B) critical inlet superheat

[0353] SHinSP inlet superheat set point

[0354] SHoutCO outlet superheat correction offset

[0355] SSA saturated steam area

[0356] Td isentropic temperature deviation

[0357] TdCr, TdCr(FD2A), TdCr(FD2B) critical isentropic temperature deviation

[0358] TDWin inlet dew point temperature

[0359] Tin inlet temperature

[0360] Tout outlet temperature

[0361] ToutIC isentropic outlet temperature

[0362] WSA wet steam area

[0363] X3 target isentropic temperature deviation

[0364] October 2025 D 200 P 2635 WO

Claims

Claims1. Method for controlling a refrigeration circuit system (1 ), the refrigeration circuit system (1 ) including a compressor stage (2) with at least one compressor (2A), an inlet sensor arrangement (3) for providing inlet sensor information indicating at least an inlet pressure (Pin) of the refrigerant flowing into a compression inlet (2in), an outlet sensor arrangement (4) for providing outlet sensor information indicating an outlet pressure (Pout) and an outlet temperature (Tout) of the compressed refrigerant flowing out of a compression outlet (2out), wherein the method comprises the following steps:- determining, based on the inlet pressure (Pin), a saturated vapor inlet condition (DWin) assuming that the refrigerant would flow into the compression inlet (2in) at an inlet dew point for said inlet pressure (Pin),- determining an isentropic outlet temperature (ToutIC) for the refrigerant flowing out of the compression outlet (2out), assuming an isentropic compression (ICC) of the refrigerant from the saturated vapor inlet condition (DWin) to the outlet pressure (Pout) in the compressor stage (2),- determining an isentropic temperature deviation (Td) which is a difference of the outlet temperature (Tout) from the isentropic outlet temperature (ToutIC),- using the isentropic temperature deviation (Td) for controlling an inlet superheat (SHin), which is a superheat of the refrigerant flowing into the compression inlet (2in), and / or an outlet superheat, which is a superheat of the refrigerant flowing out of the compression outlet (2out), characterized in that the method comprises using a change in a slope of a relationship of the isentropic temperature deviation (Td) to the inlet superheat (SHin) for controlling the inlet superheat (SHin) and / or the outlet superheat.October 2025 D 200 P 2635 WO2. Method according to claim 1 , wherein the method comprises adjusting, based at least on the isentropic temperature deviation (Td), an outlet superheat set point for the outlet superheat and / or an inlet superheat set point (SHinSP) for the inlet superheat (SHin).

3. Method according to claim 2, wherein the method comprises using a critical isentropic temperature deviation (TdCr(FD2A), TdCr(FD2B)) for controlling the outlet superheat set point (SHOutSP).

4. Method according to claim 3, wherein the critical isentropic temperature deviation (TdCr(FD2A), TdCr(FD2B)) is determined based on a relationship of the isentropic temperature deviation (Td) to the inlet superheat (SHin).

5. Method according to claim any one of the preceding claims, wherein the method comprises gradually lowering the outlet superheat with determining corresponding values of the isentropic temperature deviation (Td) and / or of the inlet superheat (SHin).

6. Method according to any one of the preceding claims, wherein the method comprises controlling the inlet superheat (SHin) indirectly by controlling the outlet superheat based at least on the isentropic temperature deviation (Td).

7. Method according to any one of the preceding claims, for the refrigeration circuit system (1 ) further comprising at least one evaporator (5, 7A, 7B) for evaporating the refrigerant before it flows into the compression inlet (2in), wherein the method includes controlling feeding of the at least one evaporator (5, 7A, 7B) based at least on the isentropic temperature deviation (Td).

8. Method according to any one of the preceding claims, for the refrigeration circuit system (1 ) further comprising at least one expansion valve (6) forOctober 2025 D 200 P 2635 WOexpanding refrigerant that has been compressed by the compressor stage (2), wherein the method includes controlling the at least one expansion valve (6) based at least on the isentropic temperature deviation (Td).

9. Controller (20) for a refrigeration circuit system (1 ), the refrigeration circuit system (1 ) including a compressor stage (2) with at least one compressor (2A), an inlet sensor arrangement (3) for providing inlet sensor information indicating at least an inlet pressure (Pin) of the refrigerant flowing into a compression inlet (2in), an outlet sensor arrangement (4) for providing outlet sensor information indicating an outlet pressure (Pout) and an outlet temperature (Tout) of the compressed refrigerant flowing out of a compression outlet (2out), and an expansion valve (6), wherein the controller (20) comprises: a receiver (22) for receiving the inlet sensor information and the outlet sensor information; a processor (23); and a control output (24) for controlling at least the expansion valve (6); wherein the controller (20) is configured for- determining, based on the inlet pressure (Pin), a saturated vapor inlet condition (DWin) assuming that the refrigerant would flow into the compression inlet (2in) at an inlet dew point for said inlet pressure (Pin),- determining an isentropic outlet temperature (ToutIC) for the refrigerant flowing out of the compression outlet (2out), assuming an isentropic compression (ICC) of the refrigerant from the saturated vapor inlet condition (DWin) to the outlet pressure (Pout) in the compressor stage (2),- determining an isentropic temperature deviation (Td) which is a difference of the outlet temperature (Tout) from the isentropic outlet temperature (ToutIC),October 2025 D 200 P 2635 WOcontrolling at least the expansion valve (6) based at least on the isentropic temperature deviation (Td), characterized in that the controller (20) is configured for determining, checking, and / or correcting a critical isentropic temperature deviation (TdCr(FD2A), TdCr(FD2B)), wherein the critical isentropic temperature deviation TdCr(FD2A), TdCr(FD2B)) corresponds to the isentropic temperature deviation (Td) at which a change in a slope of a relationship between the isentropic temperature deviation (Td) to an inlet superheat (SHin) occurs.

10. The controller (20) according to claim 9, wherein the controller (20) is configured for determining, checking, and / or correcting the critical isentropic temperature deviation (TdCr(FD2A), TdCr(FD2B)) using the change in the slope of the relationship of the isentropic temperature deviation (Td) to the inlet superheat (SHin).

11. The controller (20) according to claim 9 or 10, wherein the controller (20) is switchable between- a determination mode for determining, correcting, and / or checking the critical isentropic temperature deviation (TdCr(FD2A), TdCr(FD2B)) and / or at least one minimum controllable outlet superheat based on measurements and a- normal operation mode.

12. Controller (20) according to any one of the claims 9 to 11 , for the refrigeration circuit system (1 ) with the at least one compressor (2A) being a variable speed compressor, wherein the control output (21 ) is further configured for controlling the at least one compressor (2A).

13. Controller (20) according to any one of the claims 9 to 12, wherein the controller (20) is configured to adjust an outlet superheat set point for the outletOctober 2025 D 200 P 2635 WOsuperheat and / or an inlet superheat set point (SHinSP) for the inlet superheat (SHin) by controlling at least the expansion valve (6) based at least on the isentropic temperature deviation (Td).

14. Controller (20) according to any one of the claims 9 to 13, wherein the controller (20) is configured to control the expansion valve (6) at least based on the isentropic temperature deviation (Td) and the critical isentropic temperature deviation (TdCr(FD2A), TdCr(FD2B)).

15. Refrigeration circuit system (1 ) including a compressor stage (2) with at least one compressor (2A), an inlet sensor arrangement (3) for providing inlet sensor information indicating at least an inlet pressure (Pin) of the refrigerant flowing into a compression inlet (2in), an outlet sensor arrangement (4) for providing outlet sensor information indicating an outlet pressure (Pout) and an outlet temperature (Tout) of the compressed refrigerant flowing out of a compression outlet (2in), and an expansion valve (6), characterized in that the refrigeration circuit system (1 ) is configured for performing the method according to any one of the claims 1 to 8 and / or in that the refrigeration circuit system (1 ) includes the controller (20) according to any one of the claims 9 to 14.October 2025 D 200 P 2635 WO

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