Patent Publication Number: US-2018045446-A1

Title: Method and Apparatus Taking into Account the Influence of Oil in an Air-Conditioning/Refrigeration Circuit

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority under 35 U.S.C. §119 from German Patent Application No. DE 10 2016 214 797.8, filed Aug. 9, 2016, the entire disclosure of which is herein expressly incorporated by reference. 
     BACKGROUND AND SUMMARY OF THE INVENTION 
     The invention generally relates to the field of refrigeration machines. In particular, the invention relates to the design of the components of an air-conditioning/refrigeration system, for example for a motor vehicle. 
     An air-conditioning system serves to maintain and to generate a pleasant indoor climate. The term air-conditioning system can be understood here to be a generic term for ventilation systems which set the temperature and air humidity and, if appropriate, the air quality to a setpoint value in a room and then keep it constant. Air-conditioning systems usually have a refrigeration machine which is operated by a compressor and has to be lubricated during operation by way of a lubricant. The lubricant usually at least partially enters the refrigerant conveyed by the compressor in the air-conditioning/refrigeration circuit. 
     In calculations of the fluid dynamics and thermodynamics of an air-conditioning/refrigeration circuit for the design of the components of an air-conditioning system, the refrigerant is generally represented as a pure material. However, in practice additives, for example oil, are added to the refrigerant as a lubricant for the compressor. The physical properties of the refrigerant-oil mixture differ to a certain extent significantly from those of the refrigerant as a pure material. If the real refrigerant-oil mixture is modeled as a pure material, i.e. the oil portion is ignored, during the design of the components of an air-conditioning/refrigeration system, the fluid dynamic and thermodynamic properties of the real refrigeration circuit can differ from those of the calculation. 
     For example, DE 10 2006 000 690 A1 discloses that the lubricant portion in the refrigerant has, to a certain extent, considerable effects on the functioning and the efficiency of a refrigeration system. It also discloses a device and a method in which the behavior of a lubricant portion in a refrigeration system can be determined with a largely small influence on the refrigeration system. 
     A calculation in which the refrigerant is represented as pure material and not as a refrigerant-oil mixture is, however, the preferred practice since numerous different effects, which are, to a certain extent, not completely captured or are difficult to capture, make physically correct representation of the influence of the oil in an oil model difficult. The influence of the oil which is not taken into account can adversely affect the refrigeration capacity which is necessary for an air-conditioning/refrigeration system which is to be designed. For example, if the influence of the oil is not taken into account, then the calculation results can be unrealistically good, with the result that the air-conditioning system is underdimensioned. A further problem is that measured values at a real air-conditioning/refrigeration system with a real refrigerant-oil mixture can only be transferred to a conditional degree to the calculations of the air-conditioning/refrigeration circuit with modeling of the refrigerant as a pure material. This impedes or prevents quantitative calibration of the calculation model on the basis of measured values on the test rig. 
     The use of computer-assisted design systems which simulate a system which is to be designed during the dimensioning and design of the components of an air-conditioning system is known, for example, from DE 10 2012 214 098 A1. 
     In order to precisely dimension and design the components of an air-conditioning/refrigeration circuit, an oil model which is as physically precise as possible is therefore necessary for the oil which is contained in the refrigerant-oil mixture. However, the model is very complex to produce and has to be newly produced for every oil. 
     An object of the present invention is to provide an improved method for designing an air-conditioning/refrigeration circuit, in particular for a motor vehicle, in which the abovementioned adverse effects of the oil portion in the refrigerant can preferably be avoided. An object of the present invention is, in particular, to improve the modeling of a component within a method for designing an air-conditioning/refrigeration circuit in such a way that the influence of the oil can be better taken into account. 
     These and other objects are achieved by the design method and test rig according to embodiments of the invention. Features and details which are described in relation to the design method according to the invention also apply of course in relation to a corresponding real test rig and to a computer-assisted system, and respectively vice versa, and therefore reference is and can always be made reciprocally with respect to the disclosure of the individual aspects. 
     With respect to the following statements it is to be noted that here the term “refrigerant” is used to refer to the pure refrigerant, i.e. without an oil portion. A real refrigerant, which contains oil, is correspondingly referred to here as a refrigerant-oil mixture. 
     A core concept of the invention is a particular way of implementing the realization that an influence of the oil which is added to the refrigerant accounts for the fact that the thermal power which is transmitted to a component which is under consideration in the air-conditioning system is reduced or increased. Therefore, it is firstly proposed here to approximate an influence of the oil which is initially not captured in the calculation by correspondingly reducing the refrigerant mass flow which flows through a component under consideration. The reduction in the refrigerant mass flow which flows through the component is implemented according to the invention by way of a bypass which is attached parallel to the component. By use of this bypass, the portion of the refrigerant mass flow which is attributed to the influence of the oil is made to bypass the component during the calculation of the air-conditioning system and then fed again to the circuit. An influence of the oil which is not initially covered in the calculation can also be approximated by correspondingly increasing the refrigerant mass flow which flows through a component under consideration; an increase in a refrigerant mass flow which flows through the component can be represented computationally by defining a negative value for a portion of the mass flow which is directed through the bypass, with the result that the mass flow through the component is increased. 
     The quantity of the refrigerant which is conducted through the bypass is determined as a function of the fluid dynamic and thermodynamic conditions which prevail at the components of the air-conditioning system (in particular temperatures and pressures of the refrigerant) as well as the portion of oil in the refrigerant-oil mixture. In order to determine the quantity of the refrigerant which is conducted through the bypass it is proposed to take into account one or more of the following effects which are identified by the inventor and which can be attributed to the oil as a cause: mass flow defect, pre-evaporation, reduction in enthalpy, refrigerant solution. Of course, the invention is not restricted to these four effects and, when necessary, further effects can be taken into account in accordance with the principle proposed here. 
     It is to be noted here that in the design method according to the invention and the modeling according to the invention of one or more components of the air-conditioning/refrigeration circuit it is possible, if, for example, an oil portion of zero is to be explicitly considered (for example as a reference), to continue to use the method proposed here. That is, for example, the bypasses which are installed for each component can be maintained in a corresponding simulation model, i.e. for the case “without an oil portion” the simulation model does not have to be restructured. 
     The invention permits the influence of the oil to be approximately captured, and therefore the informative quality/accuracy to be improved to a relevant degree even in computer-assisted design systems, in particular in software applications which are available for this purpose, such as e.g. simulation programs for calculating the fluid dynamics and thermodynamics of a refrigeration process, or on a test rig for air-conditioning systems in which the influence of the oil is not taken into account. A reduction in the necessary additional expenditure for calibrating corresponding calculation components (evaporators, etc.) is also to be expected. 
     A first aspect of the invention therefore relates to a design method for an air-conditioning/refrigeration circuit having a refrigerant with an oil portion. At the design stage, only the presence of a pure refrigerant is assumed in a calculation of the air-conditioning/refrigeration circuit and the fluid-dynamic and thermodynamic influence of the oil portion for at least one circuit component of the air-conditioning/refrigeration circuit is approximated by reducing or increasing the refrigerant mass flow flowing through this circuit component. According to the invention, this mass flow reduction or mass flow increase is simulated by a bypass by which a bypass portion of the refrigerant mass flow is extracted from the circuit component at an extraction point upstream of the circuit component, e.g. a first valve, is made to bypass the circuit component and is then fed back to the circuit at a feed point, e.g. a second valve. A mass flow reduction is implemented computationally by defining a positive value for a portion of the mass flow which is conducted through the bypass. An increase in mass flow is correspondingly implemented by defining a negative value for a portion of the mass flow which is conducted through the bypass. 
     The bypass portion can be determined on the basis of the fluid dynamic and thermodynamic conditions at the components of the air-conditioning system, in particular at the extraction point, for example a first valve, at the feed point, e.g. a second valve and at the circuit component, and on the basis of the oil portion in the refrigerant-oil mixture. 
     The determination of the bypass portion is preferably based on at least one of the following effects: (a) portion of the refrigerant expelled by oil, here referred in abbreviated form as “mass flow defect”, (b) portion of changed quantity of refrigerant on the basis of hot or cold oil, referred to in abbreviated form as “pre-evaporization”, and (c) portion of the refrigerant dissolved in the oil, referred to here in abbreviated form as “refrigerant solution”. Each bypass portion which corresponds to a specific effect of the oil portion can be positive or negative. Overall, this results in an increase or decrease in the mass flow through the component under consideration. Even if the portions are explained below as a first, second and third portion, all the portions do not necessarily have to be taken into account. The words “first”, “second” and “third” do not define a sequence or valency but instead serve merely for the purpose of differentiation. 
     The effect referred to here as “mass flow defect” represents the fact that the oil in the real refrigerant-oil mixture expels a corresponding portion of the refrigerant, with the result that the overall mass flow of the refrigerant-oil mixture is reduced by the oil mass flow which can be described by means of the oil circulation rate (OCR). In order to represent the mass flow defect, the refrigerant mass flow ({dot over (m)}−Δ{dot over (m)}) of the refrigerant which flows through the component under consideration is reduced in the calculation approximately by a first portion Δ{dot over (m)} 1  which corresponds to the oil mass flow. This first portion Δ{dot over (m)} 1  is made to bypass the component with the bypass in order to obtain the mass flow. 
     
       
         
           
             
               
                 Δ 
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                     m 
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                 OCR 
               
             
             ; 
             
               
                 where 
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                   Oil 
                 
                 
                   
                     m 
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     The effect referred to here as “pre-evaporization” represents the fact that comparatively hot oil (oil at correspondingly high temperature) influences a portion of the refrigerant by feeding heat into the refrigerant, in such a way that this portion no longer contributes, or only contributes to a limited degree to the fluid dynamic and thermodynamic processes (in particular thermal transfer process) in the component under consideration—e.g. by partial pre-vaporization. For example, this effect can be observed when the refrigerant expands in an expansion valve upstream of an evaporator. However, it is to be noted that the idea that the refrigerant is reduced (pre-evaporized) by a portion of the refrigerant through the presence of “hot” oil applies independently of an expansion process and/or of the presence of a valve. Analogously, comparatively cold oil (oil at a comparatively low temperature level) can bring about corresponding effects from the conduction of heat away from the refrigerant. For example, this effect can be observed when the refrigerant is fed in a compression device (e.g. compressor). However, it is also to be noted here that the idea that the refrigerant changes by a portion of the refrigerant as a result of the presence of “cold” oil applies independently of a compression process and/or of the presence of a compressor. In order to form the “pre-evaporization”, the refrigerant mass flow ({dot over (m)}−Δ{dot over (m)}) of the refrigerant which flows through the component is increased in the calculation approximately by a second portion Δ{dot over (m)} 2  which reduces or increases the effect of the pre-evaporization. This second portion Δ{dot over (m)} 2  is also made to bypass the component with the bypass in order to obtain the mass flow. 
     For example, for “hot” oil the “pre-evaporization” effect can be taken into account at an expansion device, e.g. an expansion valve, and an evaporation device, e.g. an evaporator, as follows: 
     
       
         
           
             
                 
             
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                       Refrigerant 
                     
                   
                 
               
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                     m 
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                 := 
                 
                   
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                       ( 
                       
                         1 
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                       m 
                       . 
                     
                     Refrigerant 
                   
                 
               
               ; 
               
                 
                   and 
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                     h 
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                 := 
                 
                   
                     
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     where: 
     {dot over (Q)} Oil  is the quantity of heat of the oil which is output to the refrigerant; 
     Δh Refrigerant  is a difference between enthalpy values of the refrigerant; 
     cp Oil  is a specific thermal capacity; 
     T is a temperature; and 
     h Refrigerant  is an enthalpy value of the refrigerant. 
     It is to be noted that the second portion Δ{dot over (m)} 2  can also be defined negatively so that the bypass mass flow is therefore reduced by the corresponding portion, and the mass flow through the component is increased (even if the overall bypass mass flow continues to lead to a reduction in the mass flow through the component). The latter case would occur, for example, with a condensation device for which the term “pre-evaporization” would not apply but the treatment in terms of a formula is analogous. 
     The effect specified here “refrigerant solution” represents the fact that a portion of the refrigerant is dissolved in the oil and therefore no longer participates in the satisfactory processes such as, for example, evaporization. In order to represent the refrigerant solution, the mass flow ({dot over (m)}−Δ{dot over (m)}) of the refrigerant which flows through the component is reduced in the calculation approximately by a third portion Δ{dot over (m)} 3 . The third portion Δ{dot over (m)} 3  corresponds to the refrigerant dissolved in the oil and is also made to bypass the component with the bypass in order to obtain the mass flow. 
       Δ {dot over (m)}   3   _   :={dot over (m)}   Oil *γ Refrigerant solution ; with γ=γ( T;p ).  Formula
 
     where: 
     γ is a dimensionless factor; and 
     p is a pressure. 
     It is to be noted that the function γ=γ(T; p) can also be dependent on other components and not only on T and p. 
     A change in the material values of the refrigerant owing to an oil portion which is present in the real refrigerant-oil mixture is preferably allowed for in the calculation by virtue of the fact that the state variables and/or material values (e.g. temperature and/or enthalpy) are correspondingly changed at the outlet of the circuit component under consideration. The oil portion in the refrigerant-oil mixture changes the material values of the refrigerant, with the result that for example in the case of otherwise identical pressures and enthalpy values the presence of the oil means that the temperature of the refrigerant-oil mixture, for example at the outlet of a vaporization device, becomes higher than when there is only refrigerant. Correspondingly, the outlet temperature at the circuit component under consideration is changed or corrected in the calculation. For example analytical relationships, inter alia for correcting temperatures and enthalpies, can be established on the basis of material value correlations which represent the influence of the oil on the pure material for various thermodynamic states. 
     A refrigerant-side pressure loss which is directly dependent on the refrigerant mass flow through the component under consideration generally occurs in said component. In order to ensure that a refrigerant-side pressure loss is correctly represented by the component under consideration even in the case of a refrigerant mass flow which is corrected (reduced/increased) according to the invention, in the case of a correction (reduction/increase), caused by a mass flow bypass, of the refrigerant mass flow through the components a suitable correction of the refrigerant-side pressure loss can be performed. The correction can be implemented, for example, as a function of the oil portion. The correct representation of the pressure loss is important, for example, in a vaporization device, since the transmission of heat depends in some cases to a great extent on the pressure loss of the refrigerant across the vaporization device. 
     In one exemplary embodiment of the invention, the circuit component is a heat exchanger (such as, for example, primarily an evaporator, a condenser, internal heat exchangers, etc. but also lines or the like can function as heat exchangers). In particular, the component can be at least one from the group which is composed of: evaporization device (e.g. evaporator in the form of a heat exchanger for heating the refrigerant), compression device (e.g. compressor), expansion device (e.g. expansion valve), collecting device, precipitation device, condensation device or gas cooler including supercooling device (e.g. heat exchangers for cooling the refrigerant), lines and internal heat exchanger device. 
     As already mentioned above, the mass flow through the component can be increased computationally by defining a negative value for a portion Δ{dot over (m)} which is conducted through the bypass. This may possibly be expedient in the case of a condensation device as the component under consideration in order to represent the fact that the hot oil coming from the compression device has to be cooled in addition to the refrigerant. This could be approximated by a correspondingly increased refrigerant mass flow through the condensation device. For example, given the abovementioned partial effects, the mass flow defect would then continue to reduce the refrigerant mass flow through the component but the effect which was attributable to the “pre-evaporization” would be approximated by a negative sign as “additional condensation” and correspondingly increase the refrigerant mass flow through the component. It can also be apparent that a reduction in mass flow is also applicable to a condensation device. 
     A second aspect of the invention relates to a computer program having program code for carrying out a method according to the first aspect of the invention discussed above when the computer program is executed by a computer system. 
     A third aspect of the invention relates to a data carrier or a data stream with electronically readable control signals which can interact with a programmable computer system in such a way that the computer system carries out a method according to the first aspect of the invention discussed above. 
     A fourth aspect of the invention relates to a computer system for computer-assisted design of an air-conditioning/refrigeration circuit having at least one computing unit which is designed to carry out at least one of: (i) the execution of a computer program according to the second aspect of the invention, and (ii) the reading of the control signals of a data carrier or of a data stream according to the third aspect of the invention. 
     A fifth aspect of the invention relates to a test rig for generating measured values of an air-conditioning/refrigeration circuit, wherein the air-conditioning/refrigeration circuit is operated with a pure refrigerant, and the influence of an oil portion in a real refrigerant-oil mixture for at least one circuit component of the air-conditioning/refrigeration circuit is approximated by correcting (reducing/increasing) the refrigerant mass flow which flows through the circuit component in that a bypass by means of which a bypass portion of the refrigerant mass flow is extracted from the circuit at an extraction point, e.g. a first valve, upstream of the circuit component is provided on the circuit component, said bypass portion is made to bypass the circuit component and is then fed again to the circuit at a feed point, e.g. a second valve. 
     In one particular embodiment of the design method according to the first aspect of the invention, measured values at an air-conditioning/refrigeration circuit of the test rig according to the fifth aspect of the invention are used to calibrate the calculations in the design method. 
     Further advantages, features and details of the invention can be found in the following description in which an exemplary embodiment of the invention is described in detail with reference to the drawings. In this context, the features which are mentioned in the claims and in the description can each be essential to the invention individually per se or in any desired combination. Likewise, the features which are mentioned above and the features which are explained further below can each be used per se or in a plurality of combinations as desired. Functionally similar or identical parts or components are to a certain extent provided with the same reference symbols. The terms “on the left”, “on the right”, “at the top” and “at the bottom” which are used in the description of the exemplary embodiments relate to the drawings in an orientation with a normally readable designation of the figures or normally readable reference symbols. The exemplary embodiment which is shown and described is not to be considered as conclusive but instead has an exemplary character for explaining the invention. The detailed description serves to inform the person skilled in the art, and therefore known circuits, structures and methods are not shown or explained in detail in order to avoid making the present description more difficult to understand. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a simplified block diagram of an air-conditioning/refrigeration circuit with an exemplary embodiment of a bypass device for refrigerant at a vaporizer device as an exemplary component for approximating the influence of the oil portion in a real refrigeration-oil mixture at the vaporizer device. 
         FIG. 2  shows a bypass device for refrigerant on a component of an air-conditioning/refrigeration circuit in detail. 
         FIG. 3  is a flow diagram of a design method for an air-conditioning/refrigeration circuit by which the influence of the oil portion in a real refrigerant-oil mixture can be approximated. 
     
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a simplified block diagram of an example of an air-conditioning/refrigeration circuit  100  of an air-conditioning/refrigeration system which is arranged, for example, in a motor vehicle for air-conditioning the passenger compartment. The mass flow ({dot over (m)}) of the refrigerant circulates in the clockwise direction in the air-conditioning/refrigeration circuit  100  in  FIG. 1 . 
     Liquid refrigerant at a device  110  for collecting and/or filtering the refrigerant is fed to an expansion device  120  and relaxes. The refrigerant then evaporates in an evaporation device  130 . The evaporation device  130  is a heat exchanger, at which, for example, heat is extracted from air fed to the latter by evaporation of the refrigerant, and therefore the air is cooled and then fed, for example, to the passenger compartment. The heated refrigerant then passes further via a device  140  for filtering and/or drying the refrigerant to a compression device  150 , for example a mechanical compressor. The refrigerant is then conducted from the compression device  150  into a condensation device  160  in order to liquefy the usually gaseous refrigerant again. The condensation device  160  is usually a heat exchanger which is designed to extract heat from the refrigerant so that the latter condenses again. 
     It is to be noted that the air-conditioning/refrigeration circuit  100  in  FIG. 1  represents a simplified example for explaining the invention. Of course, the invention can also comply to an air-conditioning/refrigeration circuit which is designed in any other desired way. For example, the component  110  can also be designed, instead of or in addition to the component  140 , to dry the refrigerant. It is also possible to provide either only the component  110  or only the component  140 . The component  110  can have a supercooling section connected downstream of it, from which said section the coolant generally emerges in liquid form. The component  130  can also be cooled with water instead of air (referred to as a chiller). The component  140  can additionally have a collecting and precipitating function. 
     In the lower part of  FIG. 1 , an approximation device  170  (shown by dashed lines) is arranged to the air-conditioning/refrigeration circuit  100  for the purpose of illustration, in order to approximately take into account the influence of an oil portion of a real refrigerant-oil mixture. That is, the air-conditioning/refrigeration circuit  100  in  FIG. 1  is operated exclusively with a refrigerant without lubricant (oil portion). The air-conditioning/refrigeration circuit  100  can be a pure block circuit diagram for calculating a real air-conditioning/refrigeration circuit or a real air-conditioning/refrigeration circuit P in the form of a test rig. 
     It is to be noted that the approximation device  170  approximates only the influence of oil in the expansion and evaporation device  120 / 130 . In order to approximate the influence of oil in the entire air-conditioning/refrigeration circuit  100  an approximation device would have to be respectively introduced for each component of the air-conditioning/refrigeration circuit  100 . 
     The objective is to approximately represent the influence of the oil portion in a refrigerant in practice without the need for a separate oil model, in order thereby to design the air-conditioning/refrigeration circuit  100  correctly, i.e. be able to dimension its components correctly. 
     For this purpose, the approximation device  170 , which is explained in more detail in  FIG. 2 , is provided. The approximation device  170  takes into account the influence of the oil portion of a real refrigerant-oil mixture by causing part Δ{dot over (m)} of the refrigerant mass flow {dot over (m)} of the refrigerant to bypass a component of the air-conditioning/refrigeration circuit, with the result that the part Δ{dot over (m)} of the refrigerant does not have any effect at this component. In the exemplary embodiment illustrated in  FIG. 1 , the component of the air-conditioning/refrigeration circuit  100  which is under consideration is the evaporator  130 . 
     As explained above, by defining a negative value for a portion Δ{dot over (m)} of the mass flown {dot over (m)} which is conducted through the bypass  220  (see  FIG. 2 . also), the mass flow ({dot over (m)}−Δ{dot over (m)}) flowing through the component  210  can be increased. This can be expedient e.g. in the case of the condensation device  160  if the hot oil which comes from the compression device  150  has to be cooled in addition to the refrigerant. This can be approximated by correspondingly increasing the refrigerant mass flow in the component  210 . Here, with respect to the partial effects explained here, e.g. the mass flow defect would continue to reduce the refrigerant mass flow, but in a specific configuration it can be indicated that the portion which is to be fed back to “pre-evaporation” should be represented by an inverted sign as “additional condensation” and therefore the refrigerant mass flow through the condensation device  160  should be increased. 
       FIG. 2  shows an approximation device  200  with a bypass device  220  for a part Δ{dot over (m)} of the mass flow {dot over (m)} of the refrigerant at a component  210 , e.g. the evaporation device  130  of the air-conditioning/refrigeration circuit  100  in  FIG. 1 , in the detail for the approximation of the influence of an oil portion which is added to a real refrigerant. 
     For this purpose, a branching device  212 , for example a first three-way valve  172  in  FIG. 1 , for branching off the part Δ{dot over (m)} of the mass flow {dot over (m)} of the refrigerant is located upstream of the component  210 , for example of the evaporation device  130  in  FIG. 1 , and a feed device  214 , for example a second three-way valve  176  in  FIG. 1 , for feeding back the part Δ{dot over (m)} of the mass flow {dot over (m)} of the refrigerant is located downstream of the component  210 . The part Δ{dot over (m)} of the mass flow {dot over (m)} of the refrigerant, which is branched off at the branching device  212 , is conducted through the bypass device  220  ( 174  in  FIG. 1 ) about the component  210  to the feed device  214 . 
     The approximation device  200  ( 170  in  FIG. 1 ) is based on the realization that a significant influence of the oil which is added as lubricant to the real refrigerant for mechanical components of the air-conditioning/refrigeration circuit consists in the fact that the thermal power which is transmitted to a component under consideration is reduced or increased; for example the thermal power is to be reduced in the evaporation device  130  in  FIG. 1  and increased in the condensation device  160  in  FIG. 1 . 
     Therefore, it is proposed here to approximate a power-reducing or power-increasing effect owing to the oil portion, which is initially not captured in a calculation with a pure refrigerant, by correspondingly reducing or increasing the coolant mass flow {dot over (m)} flowing through the components of the air-conditioning/refrigeration circuit. The reduction Δ{dot over (m)} or increase−Δ{dot over (m)} of the refrigerant mass flow flowing through the component  210  is converted in  FIG. 2  by the bypass device  220  which is mounted parallel to the component  210 . 
     The bypass device  220  can be an additional component in a calculation model of a computer system with a computer-assisted design of an air-conditioning/refrigeration circuit or a real bypass on a test rig P of an air-conditioning/refrigeration circuit. Measured values of such a test rig P can then be used to calibrate the calculation model. During the calculation of the air-conditioning/refrigeration system, the ineffective portion Δ{dot over (m)} of the refrigerant/mass flow {dot over (m)} can be made to bypass the component  210  and then be fed again to the air-conditioning/refrigeration circuit by way of the bypass device  220 . That is to say in the component  210 , the part {dot over (m)}−Δ{dot over (m)} of the refrigerant mass flow {dot over (m)} acts in the component  210 . 
     Provided downstream of the component  210  in  FIG. 2  is also a correction device  230  by which the influence of the oil portion on the temperature or enthalpy of the refrigerant owing to the changed material values is represented. A temperature correction is e.g. then expedient if the value is a sensor value of a temperature measuring point, such as is used, for example, for the closed-loop control of a valve. 
     The part Δ{dot over (m)} of the refrigerant which is fed through the bypass  220  is determined as a function of the fluid dynamic and thermodynamic conditions, in particular temperatures and pressures of the refrigerant which are present at the component  210  and optionally at further locations of the air-conditioning/refrigeration circuit  100  in  FIG. 1  (e.g. expansion device  120 ), and of the oil portion in the refrigerant-oil mixture. In order to determine the part Δ{dot over (m)} it is possible to take into account one or more of the effects which can be attributed as a cause to the oil. These are in particular the effects explained in the general part such as the mass flow defect, pre-vaporization, reduction in enthalpy and refrigerant solution. 
     The component  220  can be a heat exchanger like the evaporation device  130  or the condensation device  160  in  FIG. 1 . The component  220  can, however, also be the expansion device  120 , the collecting device  110 , the compression device  150  and/or an internal heat exchanger (not shown) as well as the lines of the circuit. It is to be noted that it is also the case that these are only examples without limitation. That is to say in principle the bypass concept can be applied for any component of the air-conditioning/refrigeration circuit  100  in  FIG. 1 , thus e.g. also for the components  110 ,  140  as well as further or alternative and, if appropriate, future components. 
     The invention advantageously permits the influence of the oil to be approximately captured, and therefore the informative quality/accuracy to be sufficiently improved, for example in computer-assisted design systems, particularly in software applications which are available for this such as e.g. simulation programs for calculating the fluid dynamics and thermodynamics of a refrigeration process, or on a test rig for air-conditioning systems in which the influence of the oil is not taken into account. A reduction in the additional expenditure which is necessary for the calibration of corresponding calculation components (such as e.g. the evaporation device  130 , etc.) is also to be expected. 
       FIG. 3  shows a flow diagram of a design method for an air-conditioning/refrigeration circuit by means of which the influence of the oil portion which is added to a real refrigerant can be approximated. 
     The design method serves, for example, to design the air-conditioning/refrigeration circuit  100  in  FIG. 1 , which contains a refrigerant which contains an oil portion, for example for lubricating the condensation device  150 . 
     In the design in step S 1 , only a pure refrigerant, i.e. without an oil portion, is assumed in the calculation of the air-conditioning/refrigeration circuit  100 . 
     In a step S 2 , the fluid dynamic and thermodynamic influence of the oil portion is approximated for at least one circuit component such as the evaporation device  130  in  FIG. 1  of the air-conditioning/refrigeration circuit  100  by means of a refrigerant mass flow {dot over (m)}−Δ{dot over (m)} which is e.g. reduced and flows through the circuit component  130 . The step S 2  can be carried out here for any component at which the influence of the oil is to be approximated. 
     Then, in a step S 3  the air-conditioning/refrigeration circuit  100  is calculated taking into account the reduction/increase in the refrigerant flowing through the component. The influence of the oil is thus approximated in the calculation by the bypass  174 . The bypass  174  therefore constitutes a workaround as a replacement for an oil model in the calculation. In this context, in step S 3  the calculation is carried out in such a way that by means of the bypass  174  the bypass portion Δ{dot over (m)} of the refrigerant mass flow {dot over (m)} is extracted from the circuit  100  at the branch  172  upstream of the circuit component  130 , made to bypass the circuit component  130  and then fed again to the circuit  100  at the junction  176  downstream of the component  130 . The step S 3  is also carried out for each component at which the influence of the oil is to be approximated. 
     The bypass portion Δ{dot over (m)} is determined in the example in  FIG. 1  on the basis of the fluid dynamic and thermodynamic conditions at the valve  120  and the circuit component  130  as well as the oil portion in the refrigerant-oil mixture. During the determination of the bypass portion Δ{dot over (m)}, a first portion of the refrigerant is determined which corresponds to the portion of the refrigerant (mass flow defect) expelled by the oil. Further, during the determination of the bypass portion Δ{dot over (m)}, a second portion of refrigerant is taken into account that is influenced (e.g. pre-vaporized) due to hot oil in such a way that it no longer functions as intended (pre-vaporization). Finally, during the determination of the bypass portion Δ{dot over (m)}, a third portion of refrigerant is taken into account which is dissolved in the oil (refrigerant solution). 
     Further, in a step S 4 , a change in the material values of the refrigerant owing to the oil portion in the calculation is taken into account in that the outlet temperature and/or enthalpy at the circuit component  130  is correspondingly corrected or changed in the calculation. 
     The method can optionally have a step S 5  in which the model on which the calculation is based is corrected on the basis of measurement data of a real test rig P. 
     The method, which is described above, can also particularly advantageously be used on a real test rig P for testing an air-conditioning/refrigeration circuit  100  and measuring on the air-conditioning/refrigeration circuit  100 . The test rig P is then essentially constructed as shown in  FIG. 1 , i.e. it contains all the components shown there. 
     On the test rig, the air-conditioning/refrigeration circuit  100  is operated with a pure refrigerant. The influence of an oil portion in a real refrigerant-oil mixture is approximated for at least one circuit component  130  of the air-conditioning/refrigerant circuit  100  by correction of the refrigerant mass flow flowing through the circuit component  130 . For this purpose, a bypass portion Δ{dot over (m)} of the refrigerant mass flow {dot over (m)} at the valve  172  upstream of the circuit component  130  is extracted from the air-conditioning/refrigeration circuit  100  at the circuit component with the bypass  174 , is made to bypass the circuit component  130  and is then fed again to the air-conditioning/refrigeration circuit  100 . Measured values can particularly advantageously be used at the air-conditioning/refrigeration circuit  100  of the test rig P to calibrate the calculations in the design method. 
     It is to be noted that the design method described here can also be embodied in a computer program. The computer program then has program code for carrying out the design method described here when the computer program is executed by a computer system. The computer program can also be embodied on a data carrier or in a data stream, wherein the data carrier or the data stream has electronically readable control signals which can interact with a programmable computer system in such a way that the computer system carries out the design method described here. Correspondingly, the design method can be embodied in a computer system for computer-assisted design of an air-conditioning/refrigeration circuit with at least one computing unit, wherein the at least one computing unit is designed to execute the specified computer program and/or to read the control signals of the specified data carrier or of a specified data stream. 
     The foregoing disclosure has been set forth merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof.