refrigerant

Abstract

To provide an improved coolant for a cooling device, a test room for air conditioning including the coolant, and a method for using the coolant.SOLUTION: The present invention pertains to a coolant for a cooling device 10 having a cooling circuit 11 including at least one heat exchanger 12 inside which the coolant is subjected to phase transition. The coolant is a coolant mixture including a carbon dioxide portion, a difluoroethene portion, and a 1,1,1,2-tetrafluoroethane portion. In the coolant mixture, the carbon dioxide portion is 54-92 mole percent and the difluoroethene portion is 1-29 mole percent.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a refrigerant for a refrigeration system, a test chamber with the refrigerant, and the use of the refrigerant, the refrigerant being for a refrigeration system having a refrigerant circuit with at least one heat exchanger in which the refrigerant undergoes a phase transition, and consisting of a refrigerant mixture comprising a carbon dioxide portion, a fluoromethane portion, and a 1,1,1,2-trifluoroethane portion. [Background technology]

[0002] This type of refrigerant typically circulates in a closed refrigerant circuit of a refrigeration system and undergoes a series of changes into different states of matter. The refrigerant should be capable of being used within a given temperature difference in the refrigeration circuit. Conventionally, refrigerants consisting of a single component and refrigerants consisting of at least two components are known. Refrigerants are classified according to Section 6 of the latest edition of the German industry standard DIN 8960 as of the priority date of this application.

[0003] Legal regulations require that refrigerants not significantly contribute to atmospheric ozone depletion or global warming. This essentially means that fluorinated or chlorinated substances cannot be used as refrigerants, which is why natural refrigerants or gases are the preferred choice. Furthermore, refrigerants should be non-flammable so that the charging, transportation, and operation of refrigerant circuits are not complicated by safety regulations. Flammable refrigerants also make the construction of refrigerant circuits more expensive because of the structural measures required. Flammability refers to the refrigerant's ability to react with ambient oxygen, releasing heat. Refrigerants are flammable, particularly if they are classified as fire class C under European Standard EN 2 and classes A2, A2L, and A3 under DIN 378, the latest editions of which were in effect at the priority date of this case.

[0004] Furthermore, refrigerants should have a relatively low CO2 equivalent value, i.e., their relative global warming potential (GWP) should be as low as possible to avoid indirect damage to the environment if the refrigerant is released. GWP indicates the degree to which a defined amount of greenhouse gas contributes to global warming, with carbon dioxide being the benchmark. This value represents the average warming effect over a specific period, set here as 100 years for comparison. For a definition of CO2 equivalent or GWP, see the Intergovernmental Panel on Climate Change (IPCC), Assessment Report, Appendix 8.A, Table 8.A.1, latest edition as of the priority date.

[0005] Refrigerants with a low GWP, e.g., less than 2500, have the disadvantage of significantly lower refrigeration capacity in the temperature range of interest in refrigerant circuits than refrigerants with a relatively high GWP. Lower GWPs can be achieved with refrigerant mixtures that have a relatively high carbon dioxide fraction. However, these refrigerant mixtures, due to the mixture of different substances, have non-azeotropic properties, which are undesirable in many refrigerant circuits.

[0006] In non-azeotropic refrigerant mixtures, a phase transition occurs over a temperature range known as a temperature glide. The temperature glide is the difference between the boiling point and dew point temperatures at constant pressure. However, non-azeotropic refrigerant mixtures typically contain a large fraction of non-flammable components, characterized by a relatively high GWP. At first glance, carbon dioxide seems like a suitable component for refrigerant mixtures because of its non-flammability and low GWP. However, in mixtures of carbon dioxide with other components, a relatively large fraction of carbon dioxide is essential if the other components are flammable. This is a disadvantage because the freezing point of carbon dioxide is -56.6°C, making it nearly impossible to achieve temperatures down to -60°C at high carbon dioxide concentrations.

[0007] Furthermore, the use of a refrigerant should be as simple as possible, i.e., it should not require extensive technical reconstruction of the cooling system. In particular, for refrigerants with temperature gradients exceeding 3 K, the expansion elements and heat exchangers or evaporators of the refrigerant circuit in question must be adjusted to the evaporation temperature of the refrigerant and be correspondingly controlled. Furthermore, a distinction must be made between refrigerants designed for static operation of the cooling system, i.e., for cooling systems in which the temperature in the heat exchanger or evaporator remains essentially constant over a long period of time, and refrigerants designed for dynamic cooling systems that exhibit relatively rapid temperature changes in the heat exchanger. Such dynamic cooling systems are, for example, installed in a test chamber. This means that the refrigerant must be usable over a wide temperature range.

[0008] Test chambers are typically used to test the physical and / or chemical properties of objects, particularly devices. For example, temperature or climate test chambers are known, capable of setting temperatures ranging from -60°C to +180°C. In climate test chambers, desired climatic conditions can additionally be set, to which devices or test materials are exposed for a specified time. This type of test chamber is often or occasionally realized as a mobile device connected to a building via the necessary supply lines and equipped with all the necessary modules for temperature and climate control. The temperature of the test space holding the test material is typically controlled in a circulating air duct within the test space. The circulating air duct forms an air handling space within the test space, in which a heat exchanger is located to heat or cool the air flowing through the circulating air duct and the test space. A fan or blower draws air from the test space and directs it through the respective heat exchangers in the circulating air duct. In this way, the test material is temperature-controlled or exposed to specified temperature changes. During the test interval, the temperature can be repeatedly changed between the maximum and minimum temperatures of the test chamber. A test chamber of this kind is known, for example, from EP 0344397 A2.

[0009] The refrigerant circulating in the refrigerant circuit must be suitable for use within the temperature range specified above. In particular, the dew point temperature of the refrigerant must not be higher than the lowest temperature to be achieved within the temperature range of the refrigerant circuit. This is because otherwise, the lowest temperature would not be achieved when the refrigerant evaporates in the heat exchanger used to cool the test space. The dew point temperature of an azeotropic refrigerant is reached immediately after the expansion element in the heat exchanger. A linear refrigerant circuit for the test space requires very high temperature stability of ±0.5 K or less to accurately control the temperature of the test chamber. This is not possible or can only be achieved to a limited extent using non-azeotropic refrigerants. In this case, a high degree of temperature stability cannot be achieved because, due to temperature differences within the test space in the region of the heat exchanger in the test apparatus, the dew point temperature or condensation point of the non-azeotropic refrigerant may shift locally as a function of temperature. This can lead to temperature changes during evaporation and temperature differences in the heat exchanger. When using non-azeotropic refrigerants, it is difficult to maintain spatial temperature differences of ±2 K or less. This is because the temperature stratification in the heat exchanger as described may also occur in the test space.

[0010] Refrigerants R23 and R469A are used as cryogenic refrigerants, especially for test chambers with temperatures down to -70°C. However, R23 has a GWP of 14,800, making this solvent unusable in the future. R369A has a significantly lower GWP of 1347, but its lower performance compared to R23 and its relatively large temperature gradient compared to R23 require reconfiguration of the test chamber refrigerant circuit.

[0011] Furthermore, refrigeration systems are known that continuously evaporate non-azeotropic mixed refrigerants, meaning that the refrigerant components are evaporated one after the other by means of an expansion element. These types of refrigeration systems, also called mixed fluid cascade systems, are suitable for realizing substantially static cryogenic systems.

[0012] WO 2017 / 157864 A1 discloses refrigerants containing, among other components, carbon dioxide and pentafluoroethane, for example, in a range of 30-70% by weight for carbon dioxide and 20-80% by weight for pentafluoroethane. Difluoromethane is also disclosed as a mixing partner.

[0013] DE 4116274 A1 discloses refrigerants containing carbon dioxide and difluoromethane as a mixing partner, for example fractions of (5-50) wt. % carbon dioxide and (25-70) wt. % difluoromethane. Summary of the Invention [Problem to be solved by the invention]

[0014] The object of the present invention is to provide a refrigerant for a cooling device that overcomes the drawbacks of the prior art, a test chamber using the refrigerant, and the use of the refrigerant. [Means for solving the problem]

[0015] This object is achieved by a refrigerant having the features of claim 1, a test chamber having the features of claim 16 and a method for using a refrigerant having the features of claim 17.

[0016] In a refrigerant for a cooling system having a cooling circuit with at least one heat exchanger, the refrigerant undergoes a phase transition in the heat exchanger. The refrigerant is a refrigerant mixture containing a carbon dioxide portion, a difluoromethane portion, and a 1,1,1,2-tetrafluoroethane portion. The carbon dioxide portion in the refrigerant mixture is (54 to 92) mole percent, the difluoromethane portion is (1 to 30) mole percent, and the 1,1,1,2-tetrafluoroethane portion is (1 to 29) mole percent.

[0017] The terms fraction and mole percent refer to mass fractions of a substance. Ranges given in mole % can also be interpreted as being given in % by mass.

[0018] Carbon dioxide (CO2) is also known as a refrigerant or component under the name R744. 1,1,1,2-Tetrafluoroethane (C2H2F4) is known as R134a. Pentafluoroethane (C2HF5) is known as R125. Difluoromethane (CH2F3) is known as R32. 2,3,3,3-Tetrafluoropropene is known as R1234fy. Fluoromethane (C3H2F4) is known as R41. Dichloro J Fluoroethane (C2H2F2Cl2) is known as R132. Ethane (C2H6) is known as R170. Fluoroform (CHF3) is known as R23. 1,1-difluoroethene (C2H2F2) is known as R1132a. Ethene (C2H4) is known as R1150. Fluoroethene (C2H3F) is known as R1141. Propane (C3H8) is known as R290. Propene (C3H6) is known as R1270. Hexafluoroethane (C2F6) is known as R161. And fluoroethane (CH2FCH3) is known as R161. These are based on the latest edition of the German industrial standard DIN 8960 as of the priority date of this application.

[0019] The present invention provides a refrigerant mixture of carbon dioxide and one or more fluorinated refrigerants that has a low GWP and is non-flammable or only limitedly flammable. The carbon dioxide fraction must be as small as possible, because otherwise the freezing point of the refrigerant mixture increases with the carbon dioxide fraction. However, a low carbon dioxide fraction reduces the GWP-reducing effect of carbon dioxide. This is why partially fluorinated refrigerants have improved flame retardant effects while having a significantly higher GWP than carbon dioxide.

[0020] A surprising discovery was that a sufficiently low GWP can be achieved by using a refrigerant mixture containing (54-90) mole percent carbon dioxide, (1-30) mole percent difluoromethane, and (1-29) mole percent 1,1,1,2-tetrafluoroethane. The adverse properties of carbon dioxide can be reduced by blending the components of the refrigerant mixture. In particular, the use of difluoromethane and 1,1,1,2-tetrafluoroethane with carbon dioxide in the described blend ratios allows for flexible blending of the refrigerant for different laboratory applications, such as adapting to existing refrigeration circuits, achieving specific cryogenic temperatures, or maintaining required temperature stability.

[0021] The carbon dioxide fraction of the refrigerant mixture may be greater than 69 mole percent. All ranges suggested for the carbon dioxide fraction may be limited to at least this amount of carbon dioxide.

[0022] Advantageously, the carbon dioxide content in the refrigerant mixture is (64 to 92) mol%, preferably (69 to 87) mol%, particularly preferably (74 to 82) mol%, which can further reduce the GWP of the refrigerant mixture.

[0023] The carbon dioxide portion in the refrigerant mixture may be (54 to 81) mole percent, preferably (59 to 76) mole percent, and particularly preferably (64 to 72) mole percent.

[0024] Advantageously, the difluoromethane portion may represent (1 to 25) mole percent, preferably (2 to 20) mole percent, particularly preferably (7 to 15) mole percent.

[0025] Alternatively, the difluoromethane portion may be (1 to 30) mole percent, preferably (5 to 25) mole percent, and particularly preferably (10 to 20) mole percent.

[0026] Advantageously, the 1,1,1,2-tetrafluoroethane portion may represent (1 to 24) mole percent, preferably (1 to 19) mole percent, particularly preferably (6 to 14) mole percent.

[0027] Alternatively, the 1,1,1,2-tetrafluoroethane portion may be (1 to 20) mole percent, preferably (1 to 16) mole percent, and particularly preferably (4 to 12) mole percent.

[0028] According to another embodiment, the 1,1,1,2-tetrafluoroethane portion may be (1 to 29) mole percent, preferably (5 to 24) mole percent, particularly preferably (9 to 19) mole percent.

[0029] Further components may be pentafluoroethane and / or fluoromethane, which have been found to be particularly advantageous for adapting the refrigerant to different requirements.

[0030] The fluoromethane portion may be 1 to 15 mole percent, preferably 1 to 10 mole percent, and particularly preferably 1 to 5 mole percent.

[0031] Particularly advantageously, the pentafluoroethane portion may be 1 to 20 mole percent, preferably 1 to 15 mole percent, and particularly preferably 5 to 10 mole percent. The flame retardant effect of pentafluoroethane has been found to be relatively greater than that of carbon dioxide. Pentafluoroethane has an advantageously superior flame retardant effect compared to carbon dioxide. A disadvantage is that pentafluoroethane has a GWP of 3150, and therefore may have a higher GWP than other components of the refrigerant mixture.

[0032] The refrigerant mixture may consist of three components, or may consist of four or more components. Thus, the refrigerant mixture may be a ternary refrigerant mixture or a quinary refrigerant mixture. The refrigerant mixture may contain no other components beyond that.

[0033] The refrigerant may contain additional components dichlorodifluoroethane, ethane, ethene, fluoroethane, ethyne, propane, propene and / or fluoroethane in amounts of up to 30 mole percent each, preferably up to 20 mole percent each, particularly preferably up to 10 mole percent each, although improved properties can be achieved even with these relatively low proportions of said components.

[0034] The table below provides examples of refrigerants according to the above-described embodiments.

[0035] [Table 1]

[0036] In other embodiments, the refrigerant may have a temperature gradient of 5 K or less. The temperature gradient is related to the vapor pressure at 1 bar and may be between 0.5 K and 25 K. Particularly low temperature gradients of 5 K or less can be achieved using Refrigerants 1, 2, 3, and 4 shown in the table. Temperature gradients greater than 5 K can also be achieved using Refrigerants 1, 2, 3, and 4 shown in the table. For refrigerants with a temperature gradient greater than 5 K, an internal heat exchanger or recuperator may be required for safe operation and to achieve temperatures below -55°C in the refrigeration circuit. In contrast, for refrigerants with a temperature gradient of 5 K or less, an internal heat exchanger is not required to achieve the required refrigerant capacity. However, the compressor and refrigeration circuit piping may need to be adapted to the low density of the respective refrigerant at low evaporation temperatures. With these refrigerants, only relatively high temperatures may be achievable compared to refrigerants with a temperature gradient greater than 5 K.

[0037] The refrigerant may have a CO2 equivalent of less than 1400 over 100 years and / or may be flammable. As a result, the refrigerant may pose little harm to the environment. Furthermore, the refrigerant is particularly safe, allowing for more cost-effective design of refrigeration circuits and test chambers, since no special safety precautions need to be taken in terms of flammability.

[0038] In this case, the refrigerant must not be classified as at least Fire Class C and / or Refrigerant Safety Group A1. Furthermore, shipping and transport of the refrigeration circuit is facilitated by the fact that the refrigerant can be charged before transport, regardless of the means of transport. If a flammable refrigerant is used, charging may not be possible until start-up at the installation site. Also, non-flammable refrigerants can be used in the presence of ignition sources.

[0039] The test chamber for air conditioning according to the invention comprises a test space that serves to receive the test material and is sealable and temperature-insulated from the environment, and a temperature control device that controls the temperature of the test space. The temperature control device allows temperatures in the test space to be achieved in the range of -60°C to +180°C, preferably -70°C to +180°C, particularly preferably -80°C to +180°C. The temperature control device comprises a cooling device that includes a cooling circuit with the refrigerant of the invention, a heat exchanger, a compressor, a condenser, and an expansion element. Regarding the advantages of the test chamber according to the invention, reference is made to the description of the advantages of the refrigerant of the invention.

[0040] Unlike mixed fluid cascade systems, refrigerants containing all of their components can be evaporated at once by an expansion element. Since the freezing point of carbon dioxide is -56.6°C, refrigerant mixtures with a high carbon dioxide fraction are generally no longer suitable for achieving temperatures below -56.6°C. However, with the refrigerant according to the present invention, refrigerant dew points below -70°C can be achieved.

[0041] The refrigeration circuit may include an internal heat exchanger, which may be connected to the high-pressure side of the refrigeration circuit upstream of the expansion element and downstream of the condenser, and to the low-pressure side of the refrigeration circuit upstream of the compressor and downstream of the heat exchanger. By using the internal heat exchanger and cooling the liquefied refrigerant on the high-pressure side by the internal heat exchanger, temperatures below -56°C can be easily achieved. The evaporation temperature of the refrigerant cooled by the internal heat exchanger can be lowered in the expansion element compared to the evaporation temperature of the uncooled refrigerant. In this way, the refrigeration capacity transferred from the low-pressure side to the high-pressure side via the internal heat exchanger can be used at least partially, preferably exclusively, to lower the evaporation temperature of the refrigerant in the expansion element. Furthermore, refrigerants with a temperature gradient of more than 5 K can be used in the first place. This is because the dew point temperature of the refrigerant, the location of the dew point temperature of the refrigerant, or the location of condensation of the refrigerant can be moved into the internal heat exchanger. As a result of the temperature gradient of the non-azeotropic refrigerant, the refrigerant dew point temperature achieved may be relatively high, thus preventing the heat exchanger from being further cooled.

[0042] Therefore, only a portion of the refrigerant may be evaporated in the heat exchanger, and the unusable portion of the refrigerant's wet vapor may be transferred to the internal heat exchanger. Overall, a refrigerant containing a fraction of carbon dioxide, while being environmentally friendly, has non-azeotropic properties and can be used to establish a low temperature in the test space. Furthermore, if a portion of the temperature gradient or a portion of the refrigerant's wet vapor is transferred from the test space heat exchanger to the internal heat exchanger, a non-azeotropic refrigerant can achieve relatively improved temperature stability. In this case, the cold capacity output through the heat exchanger can be generated in the section with only the temperature gradient. This means that a shift in the refrigerant's dew point in the cooling circuit has little effect on the temperature stability of the heat exchanger. Furthermore, a single heat exchanger can also be used to cool the fluid, i.e., air in this case, in the test space.

[0043] The heat exchanger can be dimensioned so that only a portion of the refrigerant can evaporate within the heat exchanger. This has the advantage that the dew point or dew point temperature of the refrigerant can be shifted from the heat exchanger to the internal heat exchanger. Due to the temperature gradient of the non-azeotropic refrigerant, the refrigerant partially evaporates in the heat exchanger, achieving a lower temperature within the heat exchanger than the remaining refrigerant evaporates within the internal heat exchanger.

[0044] In one embodiment of the test chamber, the heat exchanger may be located within the test space. In this case, the heat exchanger may be located in the air handling space of the test space so that the air circulated by the fan can come into contact with the heat exchanger. In this way, the amount of air circulated in the test space can be cooled directly within the test space by the cooling device via the heat exchanger. The test chamber may have a single cooling circuit as the only cooling circuit. In this case, the cooling circuit is directly connected to the test space.

[0045] In another embodiment of the test chamber, the condenser may be realized as a cascade heat exchanger of another cooling circuit of the cooling device. Thus, the test chamber may have at least two cooling circuits, where a cooling circuit may form the second stage of the cooling device, and another cooling circuit arranged upstream of the cooling circuit may form the first stage of the cooling device. In this case, the condenser functions as a cascade heat exchanger or a heat exchanger of the cooling circuit. This embodiment of the test chamber allows particularly low temperatures to be achieved in the test space.

[0046] The temperature control device may include a heating device comprising a heater and a heating heat exchanger within the test space. The heating device may be an electric resistance heater that heats the heating heat exchanger so that the temperature within the test space can be increased by the heating heat exchanger. If the heat exchanger and the heating heat exchanger can be specifically controlled by a control device for cooling or heating the air circulated within the test space, the temperature within the temperature range specified above can be established within the test space by the temperature control device. Temperature stability over time of ±1 K, preferably ±0.3 K to ±0.5 K, or less than ±0.3 K can be established within the test space during the test interval, regardless of the test material or its operating state. The test interval is a period of the entire test period during which the test material is exposed to substantially constant temperature or climatic conditions. The heating heat exchanger may be combined with a heat exchanger in a cooling circuit, thereby realizing a shared heat exchanger body through which a refrigerant can flow and which includes the heating element of the electric resistance heater. The condenser may be cooled by air, water, or other coolant. In principle, the condenser can be cooled using any suitable fluid, the essential aspect being that the heat load generated in the condenser can be released via cooling air or cooling water, allowing the refrigerant to condense until it is completely liquefied.

[0047] A first bypass having at least one controllable second expansion element may be implemented in the cooling circuit. In this case, the first bypass may be connected to the cooling circuit upstream of the internal heat exchanger and downstream of the condenser. The first bypass may be implemented as a controllable additional internal cooling system. The first bypass may form a reinjection device for the refrigerant, thereby recycling the refrigerant from the controllable second expansion element in the low-pressure internal heat exchanger. In this case, the first bypass may be connected to the low-pressure side of the cooling circuit upstream of the internal heat exchanger and downstream of the heat exchanger. The cooled refrigerant, or the refrigerant whose temperature level has been reduced by the second expansion element, may be guided through the internal heat exchanger to enhance cooling of the refrigerant on the high-pressure side of the internal heat exchanger. This also allows for more precise control of the cooling capacity of the internal heat exchanger.

[0048] The refrigeration circuit may also include a second bypass including at least one third expansion element. In this case, the second bypass bypasses the expansion element downstream of the condenser and upstream of the internal heat exchanger, and the refrigerant can be metered through the third expansion element upstream of the compressor on the low-pressure side of the refrigeration circuit to control the suction gas temperature and / or pressure of the refrigerant. In this way, overheating and damage to the compressor, which may be a compression device, can be prevented, among other things. As a result, the third expansion element can be operated to cool the gas refrigerant located upstream of the compressor by adding liquid refrigerant through the second bypass. The third expansion element is operated by a control device, which may itself be coupled to a pressure and / or temperature sensor upstream of the compressor in the refrigeration circuit. Particularly advantageously, a suction gas temperature of 30°C or less can be set via the second bypass. The refrigerant can also be metered to control the compressor's operating time. In principle, repeatedly switching a compressor or compression device on and off is disadvantageous. The operating life of the compressor may be extended if the compressor is operated for extended periods of time, for example, by directing the refrigerant through an expansion element or condenser via a second bypass, which delays automatic shutdown of the compressor and allows the compressor to operate for longer periods of time.

[0049] Another bypass, comprising at least one other expansion element, may be formed in the refrigeration circuit. The other bypass bypasses the compressor downstream of the compressor and upstream of the condenser, allowing the refrigerant suction gas temperature and / or suction gas pressure to be controlled upstream of the compressor on the low-pressure side of the refrigeration circuit and / or the pressure difference between the high-pressure side and the low-pressure side of the refrigeration circuit to be equalized. The second bypass may additionally comprise a settable or controllable valve, such as a magnetic valve. Connecting the high-pressure side and the low-pressure side via the other expansion element ensures that the compressed gaseous refrigerant flows gradually from the high-pressure side to the low-pressure side. This also ensures that the pressures on the high-pressure side and the low-pressure side are gradually equalized, even when the expansion element is closed. The cross-sectional dimensions of the other expansion element may be determined so that the refrigerant flowing from the high-pressure side to the low-pressure side only has a limited effect on the normal operation of the refrigeration device. At the same time, the refrigerant located upstream of the compressor may be cooled by adding liquid refrigerant via the other bypass.

[0050] Furthermore, the internal heat exchanger may be realized as a sub-cooler or heat exchanger, in particular as a plate heat exchanger. The sub-cooler may simply be realized by two lines of the cooling circuit in contact with each other.

[0051] The expansion element may have a throttle and a magnetic valve through which the refrigerant can be metered. The throttle may be a settable valve or a capillary through which the refrigerant is directed by the magnetic valve. The magnetic valve itself may be actuated by a controller.

[0052] The temperature control device may also include a control device with at least one pressure sensor and / or at least one temperature sensor in the cooling circuit. In this case, the magnetic valve can be activated by the control device as a function of the measured temperature and / or pressure. The control device may also include means for data processing, which process data sets from the sensors and control the magnetic valve. In this case, the functionality of the cooling device can also be adapted to the refrigerant used, for example, via a suitable computer program. Furthermore, the control device may signal a malfunction and, if necessary, initiate a shutdown of the test chamber, in order to protect the test chamber and the test materials from damage due to critical or undesirable operating conditions of the test chamber.

[0053] When a refrigerant mixture containing 54 to 92 mol% carbon dioxide, 1 to 30 mol% difluoromethane, and 1 to 29 mol% 1,1,1,2-tetrafluoroethane is used in accordance with the present invention, this refrigerant is used to condition the test space of the test chamber. This test space serves to receive the test material, is sealable from the environment, and is temperature-insulated. The cooling device of the test chamber temperature control device includes a cooling circuit with a refrigerant, a heat exchanger, a compressor, a condenser, and an expansion element, and is used to establish a temperature range of -60°C to +180°C, preferably -70°C to +180°C, and particularly preferably -80°C to +180°C, within the test space.

[0054] The internal heat exchanger of the refrigeration circuit may be connected to the high-pressure side of the refrigeration circuit upstream of the expansion element and downstream of the condenser, and to the low-pressure side of the refrigeration circuit upstream of the compressor and downstream of the heat exchanger, so that the high-pressure refrigerant is cooled using the internal heat exchanger, which can be used to lower the evaporation temperature in the expansion element.

[0055] When the evaporation temperature of the high-pressure refrigerant decreases, the suction pressure of the low-pressure refrigerant can be kept constant. Further system complexity, such as additional control of the suction pressure or control of the expansion element depending on the suction pressure, is not necessary in this case. In particular, the compressor can be operated at a constant power output regardless of the operating state of the refrigeration circuit. Long-term operation at a constant speed is crucial for a long service life, especially when a piston pump is used as the compressor.

[0056] The high-pressure refrigerant may be cooled by the low-pressure refrigerant at a constant suction pressure on the low-pressure side through the internal heat exchanger. Therefore, in the evaporative section of the cooling circuit, including the expansion element and the internal heat exchanger, the refrigerant can evaporate at a constant suction pressure. If the suction or evaporation pressure of the refrigerant is constant, the refrigerant can evaporate according to the refrigerant temperature gradient from the expansion element with a low evaporation temperature to the internal heat exchanger with a high evaporation temperature. The resulting dew point temperature may be higher than the temperature of the fluid being cooled or the temperature of the test space. Once the evaporation temperature of the refrigerant becomes the same as the temperature of the air to be cooled in the test space at the same suction pressure, the air cannot be further cooled. However, the dew point temperature reached in the other heat exchangers is lower than the liquid temperature of the refrigerant on the high-pressure side of the internal heat exchanger. This means that the liquid temperature of the refrigerant can be further lowered. Therefore, the evaporation temperature downstream of the expansion element can be lowered without changing the suction pressure, achieving further cooling of the air in the test space.

[0057] Only a portion of the refrigerant can be evaporated in the heat exchanger. That is, a first portion of the refrigerant passing through the expansion element can be evaporated in the heat exchanger, and a second portion of the refrigerant can be evaporated in the internal heat exchanger. The evaporative section of the cooling circuit, where the refrigerant evaporates, can extend from the expansion element to the internal heat exchanger. The evaporative section can pass through the internal heat exchanger, in which case the refrigerant condensation location can be located at the outlet of the internal heat exchanger upstream of the compressor. The ratio of the first portion to the second portion can vary as a function of the temperature in the test space or the heat exchanger during operation of the cooling circuit. For example, a relatively large difference between the temperature of the heat exchanger and the temperature in the test space can accelerate heating of the refrigerant in the heat exchanger, resulting in a shift of the refrigerant condensation location toward the inlet of the internal heat exchanger or the outlet of the heat exchanger upstream of the compressor. This shift in the condensation location can be acceptable if a relatively low temperature or target temperature has not yet been established in the test space. As the temperature of the heat exchanger approaches the temperature in the test space, the condensation location shifts and the second portion grows larger relative to the first portion.

[0058] The refrigerant can be metered and evaporated in the heat exchanger in a timely manner within a period of time. For example, the expansion element can be a magnetic valve configured to be controlled by a control device. The timely operation of the magnetic valve, i.e. the expansion element, allows for targeted supply of only small amounts of refrigerant to the heat exchanger. In particular, maintaining a low temperature often requires only a small amount of refrigeration capacity. The latter can be achieved by metering the refrigerant to evaporate in the heat exchanger. Such metering can be achieved particularly simply by timely opening and closing the expansion element within a period of time. Timely opening and closing particularly means repeating a certain procedure.

[0059] The evaporation temperature of the refrigerant on the high-pressure side can be lowered in a self-regulating manner. Depending on the heat exchanger temperature, refrigerant that no longer evaporates can be discharged from the heat exchanger in the flow direction. This is because the heat exchanger temperature is no longer sufficient to cause a phase transition in the refrigerant. This allows the wet vapor or liquid refrigerant to be re-evaporated in the internal heat exchanger, where the temperature difference between the high-pressure side and the low-pressure side can always be greater than in the internal heat exchanger. If the temperature of the liquid refrigerant upstream of the expansion element is lowered by the internal heat exchanger, i.e., by heat exchange in the internal heat exchanger, the energy density of the refrigerant upstream of the expansion element and the temperature difference achievable in the heat exchanger increase. In principle, the interaction between the expansion element, the heat exchanger, and the internal heat exchanger does not need to be controlled.

[0060] In particular, a constant suction pressure may be maintained while the internal heat exchanger reduces the evaporation temperature of the high pressure side refrigerant, and thus cooling of the high pressure side refrigerant via the internal heat exchanger may be used partially or exclusively to reduce the evaporation temperature of the refrigerant in the expansion element.

[0061] The dew point temperature of the refrigerant may be higher than the minimum temperature of the temperature range. In this case, in conventional test chambers, the minimum temperature of the temperature range cannot be established for this type of refrigerant, but a relatively high minimum temperature that substantially corresponds to the dew point temperature of the refrigerant can be established. However, in the test chamber according to the present invention, refrigerants with dew points higher than the minimum achievable temperature of the temperature range can be used, because the liquid temperature on the high-pressure side can be cooled by the internal heat exchanger. This means that the evaporation temperature of the refrigerant in the expansion element can be relatively low.

[0062] The refrigerant can be evaporated absolutely at a suction or evaporation pressure in the pressure range of 0.3 to 5 bar. The use of refrigerants in this pressure range allows for the production of cost-effective refrigeration circuits, since no special pressure-resistant modules and components need to be used to construct the low-pressure side of the refrigeration circuit.

[0063] The refrigerant can also be evaporated absolutely at suction or evaporation pressures in the range of 5 to 35 bar, and again the high pressure side can be constructed using modules and components that do not need to be adapted to relatively high pressures.

[0064] Further embodiments of the use are evident from the characterizing statements of the dependent claims of claim 1 of the device.

[0065] Preferred embodiments of the present invention will now be described in more detail with reference to the accompanying drawings. [Brief explanation of the drawings]

[0066] [Figure 1] FIG. 1 is a schematic diagram of a first embodiment of a cooling device. [Figure 2] FIG. 2 is a pressure-enthalpy diagram of the refrigerant. [Figure 3] FIG. 3 is a schematic diagram of a second embodiment of the cooling device. [Figure 4] FIG. 4 is a schematic diagram of a third embodiment of the cooling device. [Figure 5] FIG. 5 is a schematic diagram of a fourth embodiment of the cooling device. [Figure 6] FIG. 6 is a schematic diagram of a fifth embodiment of the cooling device. [Figure 7] FIG. 7 is a schematic diagram of a sixth embodiment of the cooling device. [Figure 8] FIG. 8 is a schematic diagram of a seventh embodiment of the cooling device. [Figure 9] FIG. 9 is a schematic diagram of an eighth embodiment of the cooling device. [Figure 10] FIG. 10 is a schematic diagram of a ninth embodiment of the cooling device. [Figure 11] FIG. 11 is a temperature-enthalpy diagram of the refrigerant. [Figure 12] FIG. 12 is a cycle time diagram for the expansion element. [Figure 13] Figure 13 is a temperature-surface diagram of the cooling circuit. DETAILED DESCRIPTION OF THE INVENTION

[0067] 1 shows a first embodiment of a cooling device 10 for a test chamber (not shown). The cooling device 10 comprises a cooling circuit 11 with a refrigerant, a heat exchanger 12, a compressor 13, a condenser 14 and an expansion element 15. The condenser 14 is cooled in this case by a further cooling circuit 16. The heat exchanger 12 is arranged in a test space (not shown) of the test chamber. Furthermore, the cooling circuit comprises a high-pressure side 17 and a low-pressure side 18, to which an internal heat exchanger 19 is connected.

[0068] FIG. 2 shows a pressure-enthalpy diagram (log p / h diagram) of the refrigerant circulating in the refrigeration circuit 11. The refrigerant is a non-azeotropic refrigerant. Looking at FIGS. 1 and 2 together, starting at position A, the refrigerant upstream of the compressor 13 is suctioned and compressed, thereby achieving a pressure downstream of the compressor 13 at position B. The refrigerant is compressed by the compressor 13 and then liquefied in the condenser 14 at position C. The refrigerant passes through an internal heat exchanger 19 on the high-pressure side 17, where it is further cooled, and reaches position C' upstream of the expansion element 15. The internal heat exchanger 19 allows the use of the wet vapor zone (position E to E') that cannot be used in the heat exchanger 12, further lowering the refrigerant temperature (position C' to C). The refrigerant is released in the expansion element 15 (position C' to D') and partially liquefied in the heat exchanger 12 (position D' to E). The wet refrigerant vapor then enters the internal heat exchanger 19 on the low-pressure side 18, where it is re-evaporated until it reaches the refrigerant's dew point temperature or dew point, as shown at point E'. Thus, a first subsection 20 of the refrigerant evaporator section 22 passes through the heat exchanger 12, and a second subsection 21 of the refrigerant evaporator section 22 passes through the internal heat exchanger 19. It is important that the suction pressure of the compressor 13 on the low-pressure side 18 remains constant across the evaporator section 22, even if the evaporator temperature at the expansion element 15 changes.

[0069] The refrigerant may be refrigerant 1, 2, 3, or 4 from the table above. These refrigerants contain no more than three or four components and, depending on their composition, have a high temperature gradient of more than 5 K. This is why the internal heat exchanger 19 is required for safe operation and to achieve temperatures below -55°C. As explained in connection with FIG. 1, with these refrigerants, the available cold capacity in the heat exchanger 12, i.e., the test space (not shown), is used to supplement the cooling of the liquid refrigerant upstream of the expansion element 15 in the internal heat exchanger 19. This effect is particularly pronounced when using refrigerants with a temperature gradient of more than 5 K, and the performance is correspondingly high. Control via a sophisticated sensor system is not required. However, due to the inertia of the cooling circuit 16 and the cooling device 10, dynamic load changes, i.e., temperature changes, are only possible to a limited extent. Furthermore, the refrigerant placed in the test space can be evaporated by the heating heat exchanger 12.

[0070] FIG. 3 shows a schematic diagram of the simplest embodiment of the cooling device 23, which is self-regulating. The cooling device 23 comprises a cooling circuit 24 with a heat exchanger 25, a compressor 26, a condenser 27, an expansion element 28, and an internal heat exchanger 29. Depending on the temperature in the heat exchanger 25, refrigerant that has not completely evaporated escapes the heat exchanger 25. This is because the temperature in the heat exchanger 25 or in the test space (not shown) is insufficient to cause a phase transition. In this case, the refrigerant that is still liquid is re-evaporated in the internal heat exchanger 29, because the temperature difference here must always be greater than the temperature difference in the heat exchanger 25. As the heat exchange in the internal heat exchanger 29 reduces the temperature of the liquid refrigerant upstream of the expansion element 28, the energy density in the heat exchanger 25 and therefore the achievable temperature difference increase. The cooling device 23 does not require sophisticated controls such as sensors.

[0071] FIG. 4 shows a cooling device 30 that differs from the cooling device of FIG. 3 in that it includes a first bypass 31 and a second bypass 32. A controllable second expansion element 33 is arranged in the first bypass 31, which is configured as an additional internal cooling system 34. The first bypass 31 is connected to the cooling circuit 24 immediately downstream of the condenser 27 and upstream of the internal heat exchanger 29, and downstream of the heat exchanger 25 and upstream of the internal heat exchanger 29. The first bypass 31 thus bypasses the expansion element 28 together with the heat exchanger 25, which is supplied with evaporated refrigerant via the second expansion element 33. The intake gas mass flow introduced into the internal heat exchanger 29 can be additionally cooled by the first bypass 31 in the event of a high intake gas temperature, which may be due to the heat exchanger 25. In this way, evaporation of the refrigerant upstream of the expansion element can be prevented. The first bypass 31 can therefore be used to react to changing loads on the cooling device 30. The second bypass 32 has a third expansion element 35 and is connected to the cooling circuit 24 downstream of the condenser 27 and upstream of the internal heat exchanger 29, and downstream of the internal heat exchanger 29 and upstream of the compressor 26. This allows the intake gas mass flow upstream of the compressor 26 to be reduced sufficiently via the second bypass 32 to avoid unacceptably high final compression temperatures.

[0072] Figure 5 shows a cooling device 36, which differs from the cooling device of Figure 4 in that it includes another bypass 37. The other bypass 37 includes another expansion element 38 and is connected to the cooling circuit 24 downstream of the condenser 27 and upstream of the internal heat exchanger 29, and downstream of the internal heat exchanger 29 and upstream of the compressor 26.

[0073] The first bypass 31 makes it possible to react to changing loads. Thus, the suction gas mass flow is introduced into the internal heat exchanger 29, and in the event of a high suction gas temperature, which may be caused by the heat exchanger 25, additional cooling can be achieved by reinjection via the first bypass 31. This ensures that no evaporation occurs upstream of the expansion element 28. Furthermore, reinjection via the other bypass 37 ensures that the suction gas temperature upstream of the compressor 26 is sufficiently reduced to avoid excessively high compression end pressures. This allows the use of refrigerants with temperature gradients of more than 5 K in cryogenic applications, even with highly dynamic load changes.

[0074] Figure 6 shows a cooling device 39 which differs from the cooling device of Figure 5 in that it has another cooling device 40. The other cooling circuit 40 serves to cool a condenser 41 of a cooling circuit 42. The condenser 41 is implemented in this case as a cascade heat exchanger 43.

[0075] 7 shows a cooling device 44 comprising a cooling circuit 45 and another cooling circuit 46, and in particular an internal heat exchanger 47 in the cooling circuit 45. In this case, the heat exchanger 48 is located in an insulated test chamber (not shown).

[0076] 8 shows a schematic diagram of the simplest embodiment of a cooling device 49 without an internal heat exchanger. The cooling circuit 50 of the cooling device 49 is realized by a compressor 51, a condenser 52, an expansion element 53 and a heat exchanger 54 in an insulated test space of a test chamber (not shown).

[0077] The refrigerant circulating in the refrigeration circuit 50 may be any one of refrigerants 1, 2, 3 or 4 in the table above. These refrigerants do not contain more than three or four components and have a temperature gradient of 5 K or less depending on their composition. This is why an internal heat exchanger is not required for safe operation and to achieve temperatures below -55°C. Due to the low density of each refrigerant, the low evaporation temperatures require appropriate matching of the compressor 51 and the piping of the refrigeration circuit 50.

[0078] Figure 9 shows a chiller 55 which differs from the chiller of Figure 8 in that it includes a first bypass 56 having a first expansion element 57 and a second bypass 58 having a second expansion element 59. The first bypass 56 and second bypass 58 may be used as described in connection with Figure 4. Thus, the suction temperature of the compressor 51 and the evaporating pressure can be set or controlled by the first expansion element 57 and the second expansion element 59.

[0079] Figure 10 shows a cooling device 60 which differs from the cooling device of Figure 9 in that it includes an additional bypass 61 with an additional expansion element 62. The additional expansion element 62 makes it possible to further reduce the intake gas temperature and thus indirectly the compression end temperature.

[0080] Furthermore, the effective temperature gradient of the refrigerant used can be advantageously reduced in all cooling systems based on the cooling systems shown in Figures 3 to 8. As can be seen from the diagram in Figure 11, the temperature gradient is not linear, and most refrigerants have a temperature gradient of more than 5 K. In Figure 11, arrow 63 marks the pipe section of the cooling circuit that passes through the heat exchanger in the test space. By reducing the effective temperature gradient in the heat exchanger, the temperature in the test space can be stabilized. Complete evaporation can be achieved, for example, by utilizing superheat in the compressor suction line. Furthermore, ideally, the energy contained in the refrigerant can be utilized by targeted reheating of the refrigerant or by using a liquid separator to increase the efficiency of the installation.

[0081] The diagram of Figure 12 shows another advantageous method of opening and closing the expansion element in time intervals, in this way allowing the heat exchanger to be supplied with a small amount of refrigerant which evaporates in the heat exchanger when relatively little cooling capacity is required to maintain the temperature.

[0082] The diagram shown in Figure 13 illustrates the utilization of the superheat of the refrigerant in the suction line 66 of the compressor. The arrow 64 marks the progression of the temperature rise as the refrigerant passes through the heat exchanger, more precisely across the heat exchanger surface 65, more precisely across its surface 66. The electronic expansion element ensures superheat in the suction line, while the temperature drops downstream of the heat exchanger.

Claims

1. A refrigerant for a cooling device (10, 23, 30, 36, 39, 44, 49, 55, 60) having a refrigeration circuit (11, 24, 42, 50) including at least one heat exchanger (12, 25, 48, 54) in which a phase transition of the refrigerant occurs, The refrigerant is carbon dioxide (CO 2 ) moiety and difluoromethane (CH 2 F 2 ) moiety and 1,1,1,2-tetrafluoroethane (C 2 H 2 F 4 ) portion, The refrigerant mixture is characterized in that the carbon dioxide portion is (54 to 81) mole percent, the difluoromethane portion is (10 to 20) mole percent, and the 1,1,1,2-tetrafluoroethane (C 2 H 2 F 4 ) portion is (1 to 29) mole percent.

2. The refrigerant of claim 1, A refrigerant characterized in that the carbon dioxide portion of the refrigerant mixture is (59 to 76) mole percent.

3. The refrigerant according to claim 1 or 2, A refrigerant characterized in that the 1,1,1,2-tetrafluoroethane portion is (1 to 24) mole percent.

4. The refrigerant according to claim 1 or 2, A refrigerant characterized in that the 1,1,1,2-tetrafluoroethane portion is (1-20) mole percent.

5. The refrigerant according to claim 1 or 2, A refrigerant characterized in that the 1,1,1,2-tetrafluoroethane portion is (5-24) mole percent.

6. A refrigerant for a cooling device (10, 23, 30, 36, 39, 44, 49, 55, 60) having a cooling circuit (11, 24, 42, 50) including at least one heat exchanger (12, 25, 48, 54) in which a phase transition of the refrigerant occurs, The refrigerant is a refrigerant mixture that includes a carbon dioxide (CO2) portion, a difluoromethane (CH2F2) portion, a 1,1,1,2-tetrafluoroethane (C2H2F4) portion, and other components; The other component is pentafluoroethane (C 2 HF 5 ) and / or fluoromethane (CH 3 F) The refrigerant mixture has a carbon dioxide portion of (54 to 92) mole percent and a difluoromethane portion of (1 to 29) mole percent; A refrigerant characterized in that the fluoromethane portion is (1-15) mole percent.

7. The refrigerant of claim 6, A refrigerant characterized in that the pentafluoroethane portion is (1-20) mole percent.

8. The refrigerant according to any one of claims 1 to 7, A refrigerant characterized by having a temperature gradient of 5K or less.

9. The refrigerant according to any one of claims 1 to 8, The refrigerant has a relative CO2 emission of less than 1400 for 100 years. 2 Refrigerants characterized by having an equivalent mass and / or being non-flammable.

10. an environmentally sealable and temperature insulated test space serving to receive a test sample; a temperature control device for controlling the temperature of the test space, the temperature control device allows a temperature in the test space to be achieved in the range of −60° C. to 180° C.; 10. A test chamber for air conditioning, wherein the temperature control device comprises a cooling device (10, 23, 30, 36, 39, 44, 49, 55, 60) including a cooling circuit (11, 24, 42, 50) with a refrigerant according to any one of claims 1 to 9, a heat exchanger (12, 25, 48, 54), a compressor (13, 26, 51), a condenser (14, 27, 41, 52), and an expansion element (15, 28, 53).

11. Carbon dioxide (CO 2 ) moiety (54-81) mole percent and difluoromethane (CH 2 F 2 ) moiety (10-20) mole percent and 1,1,1,2-tetrafluoroethane (C 2 H 2 F 4 1. A method for air conditioning a test space in a test chamber, comprising: the test space serves to receive a test sample and is environmentally sealable and temperature insulated; A method of using a refrigerant, wherein a cooling device (10, 23, 30, 36, 39, 44, 49, 55, 60) of the temperature control device of the test chamber, including a cooling circuit (11, 24, 42, 50) with a refrigerant, a heat exchanger (12, 25, 48, 54), a compressor (13, 26, 51), a condenser (14, 27, 41, 52), and an expansion element (15, 28, 53) are used to achieve a temperature in the test space in the temperature range of -60°C to +180°C.

12. The method of use according to claim 11, The high-pressure side refrigerant is cooled by an internal heat exchanger (19, 29, 47) of the cooling circuit (11, 24, 42, 50), the cooling circuit is connected to a high-pressure side (17) of the cooling circuit upstream of an expansion element (15, 28) and downstream of a condenser (14, 27, 41, 52), and to a low-pressure side (18) of the cooling circuit upstream of a compressor (13, 26) and downstream of a heat exchanger (12, 25, 48); Cooling of the refrigerant on the high pressure side is utilized to reduce the evaporation temperature in the expansion element using an internal heat exchanger. A method for using a refrigerant, characterized by:

13. 13. The method of claim 11 or 12, A method of using a refrigerant, characterized in that only a portion of the refrigerant evaporates in the heat exchanger (12, 25, 48, 54).

14. The use method according to any one of claims 11 to 13, A method for using a refrigerant, characterized in that the refrigerant is metered and evaporated in time within a time interval in the heat exchanger (12, 25, 48, 54) by means of the expansion element (15, 28, 53).

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