Refrigeration and / or freezer device

Abstract

The present invention relates to a refrigerator and / or freezer with a cooled interior and with a refrigerant circuit which is designed to cool the cooled interior, wherein the refrigerant circuit comprises an evaporator, a compressor, a condenser and an adjustable expansion valve which is arranged between the condenser and the evaporator, wherein the refrigerant circuit further comprises a heat exchanger which is arranged and designed to enable heat transfer between the condenser outlet line and the evaporator outlet line, wherein a first temperature sensor for measuring the evaporation temperature and a second temperature sensor for measuring a second temperature are arranged in or on the heat exchanger and wherein a controller is provided which is designed to determine the difference between the two temperatures and to control the expansion valve based thereon.

Description

[0001] The present invention relates to a refrigerator and / or freezer having a cooled interior and having a refrigerant circuit designed to cool the cooled interior, wherein the refrigerant circuit comprises an evaporator, a compressor, a condenser and an adjustable expansion valve arranged between the condenser and the evaporator.

[0002] Adjustable expansion valves have long been used in refrigeration circuits, especially for larger cooling capacities, in order to be able to respond to the highly fluctuating operating conditions caused by different temperature levels or speed-controlled components (fans, compressors) and to significantly improve the efficiency and performance of the refrigerant circuit.

[0003] To operate the refrigeration circuit efficiently, it is necessary, on the one hand, that the refrigerant in the evaporator is evaporated as completely as possible, and, on the other hand, that the evaporator is filled predominantly with two-phase refrigerant. This means that both a two-phase leak of the refrigerant from the evaporator and overheating of large areas of the evaporator must be avoided simultaneously.

[0004] A known approach for actively controlling these adjustable expansion valves is superheat control, as disclosed, for example, in EP0147356 A2 and CN1380963A. In this prior art, the temperature at the evaporator outlet and the temperature at the evaporator inlet are measured for the purpose of superheat control. The degree of refrigerant superheat is determined from the difference between these two temperature values.

[0005] Reliably measuring the degree of superheat at the evaporator outlet is challenging depending on the design and size of the refrigeration circuit. Typically, and according to the aforementioned EP0147356 A2 and CN1380963A, this value is determined using two temperature sensors: one at the evaporator inlet (to determine the boiling point) and one at the evaporator outlet. The difference between the two temperatures determines the refrigerant superheat and is used as a control variable for controlling the expansion valve.

[0006] A significant disadvantage of determining superheat with two temperature sensors at the evaporator inlet and outlet is that the condition of the refrigerant at the evaporator outlet can only be reliably determined if the refrigerant is significantly superheated, i.e., by several degrees Kelvin. This is due, on the one hand, to measurement uncertainties and systematic measurement errors (pressure drop in the evaporator, difference between surface temperature and refrigerant temperature, environmental influences, etc.), and, on the other hand, to the fact that with a two-phase refrigerant outlet, no statement can be made about the outlet condition (vapor quality).

[0007] Another approach for detecting the transition point between single-phase and two-phase refrigerant outlet from the evaporator is known from US5502970A. It assumes that the refrigerant temperature fluctuates greatly in the region of the transition point from the two-phase mixture to pure vapor. The expansion valve is adjusted so that a sensor mounted at the evaporator outlet detects a widely fluctuating temperature signal. The refrigerant flow is controlled using a strategy aimed at achieving and maintaining a fluctuating superheat state. The control system ensures optimal use of the evaporator by ensuring that the refrigerant in the evaporator is in the liquid state.A temperature sensor at the evaporator outlet detects the refrigerant temperature, and the control system regulates the refrigerant flow so that the refrigerant transition point (the transition between the liquid state and the superheated state) is close to this sensor. Thus, a single sensor can be used to achieve a closed-loop control system.

[0008] In highly efficient refrigeration circuits, the temperature difference between the evaporator temperature and the ambient temperature (e.g., a refrigerated compartment) can be so small that the significant superheat required for efficient superheat control results in overheating of large areas of the evaporator. In these cases, the control variable for superheat at the evaporator outlet described above is no longer suitable as a control variable for expansion valves.

[0009] The present invention is therefore based on the object of developing a refrigerator and / or freezer of the type mentioned above in such a way that the refrigerant circuit can be operated with the highest possible efficiency.

[0010] This object is achieved by a refrigerator and / or freezer having the features of claim 1 and claim 2.

[0011] According to this, it is provided that the refrigerant circuit further comprises a heat exchanger which is arranged and designed to enable heat transfer between the condenser outlet line and the evaporator outlet line, wherein a first temperature sensor for measuring the evaporation temperature and a second temperature sensor for measuring a second temperature are arranged in or on the heat exchanger and wherein a controller is provided which is designed to determine the difference between the two temperatures and to control or regulate the expansion valve based thereon.

[0012] The invention is further directed to a refrigerator and / or freezer with a cooled interior and with a refrigerant circuit which is designed to cool the cooled interior, wherein the refrigerant circuit comprises an evaporator, a compressor, a condenser and an adjustable expansion valve which is arranged between the condenser and the evaporator, wherein the refrigerant circuit further comprises a heat exchanger which is arranged and designed to enable heat transfer between the condenser outlet line and the evaporator outlet line, wherein the evaporation temperature is derived from the information provided by the compressor and a temperature sensor for measuring a temperature is arranged in or on the heat exchanger and wherein a controller is provided which is designedto determine the temperature difference between the two temperatures and to control the expansion valve based on this.

[0013] The present invention relates to a variable or controlled variable which allows adjustable expansion valves to be controlled in such a way that the refrigeration circuit is operated efficiently even at small temperature differences between the evaporation temperature and the environment (e.g. refrigerated compartment).

[0014] While conventional superheat control refers to the temperature difference between the evaporator inlet and the evaporator outlet, the present invention defines as a new control parameter the temperature difference between the evaporation temperature, which is measured, for example, at the evaporator inlet, and the temperature measuring point within the said heat exchanger, which is also called "internal heat exchanger" below.

[0015] The internal heat exchanger is arranged and configured to transfer heat from the refrigerant flowing from the condenser toward the evaporator to the refrigerant flowing from the evaporator to the compressor.

[0016] In other words, the heat exchanger serves to superheat the refrigerant flowing out of the evaporator or to increase the degree of superheat of the refrigerant compared to the evaporator outlet.

[0017] The present invention is therefore based on the idea that the amount of heat transferred in the internal heat exchanger additionally superheats the refrigerant flowing out of the evaporator.

[0018] Measuring the temperature of this superheated refrigerant or a value correlated with it has the advantage that relatively low superheat levels at the evaporator outlet lead to significantly higher and thus more easily measurable superheat levels at the temperature measuring point in or on the heat exchanger.

[0019] It is conceivable that a correlation unit is present in which a correlation is stored between the said temperature difference and the degree of superheating of the refrigerant at the evaporator outlet.

[0020] Thus, the degree of superheating can be determined from the temperature difference between the evaporation temperature and the temperature of the superheated refrigerant in the heat exchanger.

[0021] It is also conceivable that the degree of superheating is calculated from the measured temperature difference.

[0022] Preferably, the temperature is measured in or on the heat exchanger line located between the evaporator outlet and the compressor inlet.

[0023] It is therefore conceivable to use the temperature in the suction line in the internal heat exchanger to obtain a suitable control parameter for the adjustable expansion valve.

[0024] "Adjustable" means that the free flow area for the refrigerant in the expansion valve can be changed. This can be achieved, for example, by an electric motor, such as a stepper motor, or by other suitable adjustment means.

[0025] To determine the control parameter, for example, a temperature sensor on the suction line (in the internal heat exchanger) and information about the evaporation temperature (e.g., from a temperature sensor at the evaporator inlet) are required. Using this control parameter, the state of the refrigerant at the evaporator outlet can be adjusted from two-phase (near vapor saturation) to significantly superheated. This allows for superheat levels that would otherwise be difficult or impossible to measure.

[0026] The second temperature sensor may be arranged on the line of the heat exchanger which is in flow connection with the evaporator outlet line.

[0027] The expansion valve is preferably arranged between the heat exchanger and the evaporator.

[0028] The expansion valve can also be located between the condenser and the heat exchanger.

[0029] The controller mentioned may be a control unit.

[0030] Preferably, however, the controller is a control unit designed to adjust the measured value of the temperature difference to a setpoint.

[0031] The device may comprise a setting unit by means of which the degree of superheating of the refrigerant at the evaporator outlet and / or the temperature difference between the evaporation temperature and the temperature value in the heat exchanger can be set as a setpoint, wherein the setting unit is connected to the controller and wherein the controller is designed to control or regulate the expansion valve based on the setpoint.

[0032] Furthermore, it is conceivable that the device has a memory in which the degree of superheating of the refrigerant at the evaporator outlet and / or the said temperature difference is stored as a setpoint and that the setting unit is connected to the controller, wherein the controller is designed to control or regulate the expansion valve based on the setpoint.

[0033] It is conceivable that the value stored in the memory cannot be changed by the user, but can only be changed by a service technician or at the factory.

[0034] It should be noted here that the terms "a" and "an" do not necessarily refer to exactly one of the elements, although this is a possible interpretation, but can also refer to a plurality of the elements. Likewise, the use of the plural also includes the presence of the element in question in the singular, and conversely, the singular also encompasses several of the elements in question.

[0035] Furthermore, all features of the invention described herein may be combined with one another in any way or claimed in isolation from one another.

[0036] Further details and advantages of the invention are explained in more detail with reference to an embodiment shown in the drawing.

[0037] They show: Figure 1: a schematic representation of a refrigerant circuit of a refrigerator and / or freezer according to the invention and Figure 2: a representation of the correlation between the degree of superheating of the refrigerant and the vapor quality.

[0038] The Figure 1 The refrigeration circuit of a refrigerator and / or freezer according to the invention shown comprises at least one compressor 1, a condenser 2, an internal heat exchanger 3, a controllable expansion valve 4 and an evaporator 5, which serves to cool the cooled interior (not shown).

[0039] The refrigerant flows from the compressor 1 to the condenser 2, is liquefied there, and then flows through the internal heat exchanger 3 into the expansion valve 4. From there, the refrigerant enters the evaporator 5, where it is partially or completely evaporated. The line section from the condenser outlet to the evaporator inlet is called the condenser outlet line. From the evaporator 5, the refrigerant enters the internal heat exchanger 3, where it is heated and superheated by the liquid refrigerant from the condenser 2. The vaporous refrigerant heated in this way then returns to the compressor 1, forming a closed circuit. The line section between the evaporator outlet and the compressor inlet is called the evaporator outlet line.

[0040] The heat exchanger 3 is designed to enable heat transfer between these lines.

[0041] The refrigeration cycle according to Figure 1 is only exemplary in nature and can be extended as desired, e.g. by several condensers or the like.

[0042] To determine the controlled variable, a temperature sensor 8 is provided, which is attached to the connecting line between the evaporator 5 and the compressor 1. The measuring point of this temperature sensor 8 is located inside the internal heat exchanger 3.

[0043] In addition, information about the evaporation temperature is determined, which is obtained, for example, by a sensor at the evaporator inlet 6.

[0044] While the superheat control known from the prior art refers to the temperature difference between the evaporator inlet 6 and the evaporator outlet 7, the present invention defines as a new control parameter the temperature difference between the evaporation temperature (e.g. measured at the evaporator inlet 6) and the temperature measuring point 8 within the internal heat exchanger 3.

[0045] The amount of heat transferred in the internal heat exchanger 3 additionally superheats the refrigerant flowing from the evaporator 5 to the compressor 1.

[0046] According to the exemplary embodiment according to Figure 1 the use of the temperature in the suction line in the internal heat exchanger 3 to obtain a suitable control parameter for the adjustable expansion valve 4

[0047] Using this control parameter in the form of the temperature difference, the state of the refrigerant at the evaporator outlet 7 can be adjusted from two-phase (near vapor saturation) to significantly superheated. This allows for superheat levels that are difficult or impossible to measure.

[0048] In Figure 2 The vapor quality of the refrigerant at the evaporator outlet is plotted on the x-axis and the degree of superheat in K is plotted on the y-axis.

[0049] A superheat value of 0 means that the refrigerant is not yet superheated.

[0050] The vapor quality x is defined as the difference between the enthalpy at the evaporator outlet (hx ) and the enthalpy of boiling liquid (h L ), which is related to the specific evaporation enthalpy (hv - h L ): x = h x − h L / h V − h L

[0051] For x < 1, moist steam is present, for x > 1, superheated steam is present.

[0052] The black solid line represents the superheat at temperature measuring point 8 and the dashed line represents the superheat at the evaporator outlet 7. The hatched area indicates the condition at the evaporator outlet at which the refrigeration circuit operates most efficiently.

[0053] The advantages of this new control variable lie, on the one hand, in the ability to measure two-phase evaporator outlet conditions. This means that the measured superheat at the evaporator outlet 7 is zero in this case, but a measurable superheat is still present at the temperature measuring point 8, as can be seen from Figure 2 emerges.

[0054] Only when the liquid content at the evaporator outlet is relatively high (vapor quality significantly below 1) does the superheat at temperature measuring point 8 become zero.

[0055] Relatively low superheat levels at the evaporator outlet 7, on the other hand, lead to significantly higher and thus more easily measurable superheat levels at the temperature measuring point 8.

[0056] The new control parameter results in an almost linear relationship over a wide range of the evaporator outlet state, which on the one hand makes it possible to adjust the expansion valve more quickly and on the other hand to control the expansion valve in such a way that the refrigerant at the evaporator outlet has only a very low superheat or even exits with a small amount of liquid, so that the refrigerant circuit can be operated particularly efficiently.

Claims

1. A refrigerator and / or freezer having a cooled interior and a refrigerant circuit designed to cool the cooled interior, wherein the refrigerant circuit comprises an evaporator, a compressor, a condenser and an adjustable expansion valve arranged between the condenser and the evaporator, characterized in that the refrigerant circuit further comprises a heat exchanger which is arranged and designed to enable heat transfer between the condenser outlet line and the evaporator outlet line, wherein a first temperature sensor for measuring the evaporation temperature and a second temperature sensor for measuring a second temperature are arranged in or on the heat exchanger and wherein a controller is provided which is designed to determine the temperature difference between the two temperatures and to control the expansion valve based thereon.

2. A refrigerator and / or freezer having a cooled interior and a refrigerant circuit designed to cool the cooled interior, wherein the refrigerant circuit comprises an evaporator, a compressor, a condenser and an adjustable expansion valve arranged between the condenser and the evaporator, characterized in that the refrigerant circuit further comprises a heat exchanger which is arranged and designed to enable heat transfer between the condenser outlet line and the evaporator outlet line, wherein the evaporation temperature is derived from the information provided by the compressor and a temperature sensor for measuring a temperature is arranged in or on the heat exchanger and wherein a controller is provided which is designed to determine the temperature difference between the two temperatures and to control the expansion valve based thereon.

3. Refrigerator and / or freezer according to claim 1 or 2, characterized in that a correlation unit is present in which a correlation is stored between the temperature difference and the degree of superheating of the refrigerant at the evaporator outlet.

4. Refrigerator and / or freezer according to one of the preceding claims, characterized in that a computing unit is provided which is designed to calculate the degree of superheating of the refrigerant at the evaporator outlet from the temperature difference.

5. Refrigerator and / or freezer according to one of the preceding claims, characterized in that the second temperature sensor is arranged on the line of the heat exchanger formed by the evaporator outlet line.

6. Refrigerator and / or freezer according to one of the preceding claims, characterized in that the expansion valve is located between the heat exchanger and the evaporator.

7. Refrigerator and / or freezer according to one of the preceding claims, characterized in that the expansion valve is located between the condenser and the heat exchanger.

8. Refrigerator and / or freezer according to one of the preceding claims, characterized in that the expansion valve is electronically or electrically adjustable.

9. Refrigerator and / or freezer according to one of the preceding claims, characterized in that the controller is a control unit.

10. Refrigerator and / or freezer according to one of the preceding claims, characterized in that the controller is a control unit.

11. Refrigerator and / or freezer according to one of the preceding claims, characterized in thatan adjustment unit is provided by means of which the degree of superheating of the refrigerant at the evaporator outlet and / or the temperature difference can be set as a setpoint, and that the adjustment unit is connected to the controller, wherein the controller is designed to control or regulate the expansion valve based on the setpoint.

12. Refrigerator and / or freezer according to one of the preceding claims, characterized in that the device has a memory in which the degree of superheating of the refrigerant at the evaporator outlet and / or the temperature difference is stored as a setpoint and that the setting unit is connected to the controller, wherein the controller is designed to control or regulate the expansion valve based on the setpoint.

13. Refrigerator and / or freezer according to claim 12, characterized in that the value stored in the memory cannot be changed by the user.

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