Test chamber

Abstract

Test chamber (10) for conditioning air, comprising a temperature-insulated test chamber (12) that can be closed off from the environment for receiving test material and a temperature control device (11) for temperature control of the test chamber, wherein a temperature in a temperature range of -80 °C to +180 °C can be established within the test chamber by means of the temperature control device, wherein the temperature control device comprises a cooling device (16) with a cooling circuit (17) with a refrigerant, a heat exchanger (18) arranged in the test chamber, a compressor (19), a condenser (20) and an expansion element (21), wherein the temperature control device (11) comprises a heating device (23) with a heater and a further heat exchanger (22), characterized in that the refrigerant is a nearly azeotropic refrigerant mixture consisting of a mass fraction of carbon dioxide and a mass fraction of at least one of the components ethene, hexafluoroethane, monofluoroethane, 1.1 Difluoroethene, fluoromethane and / or propane and / or xenon, wherein the refrigerant has a relative CO2 equivalent, based on 20 years, of < 2500, wherein a first bypass (43) with at least one further throttling element (44) is formed in the cooling circuit (17), wherein the first bypass (43) bridges the compressor (19) downstream of the compressor (19) and upstream of the condenser (20) in the direction of flow, wherein a pressure difference between a high-pressure side (26) and a low-pressure side (27) of the cooling circuit (17) can be equalized via the further throttling element (44).

Description

[0001] The invention relates to a test chamber for conditioning air, comprising a test chamber that can be closed off from the environment and is temperature-insulated for receiving the test specimen, and a temperature control device for temperature control of the test chamber, wherein a temperature in a temperature range of -80 °C to +180 °C, preferably -100 °C to +200 °C, can be established within the test chamber by means of the temperature control device, wherein the temperature control device comprises a cooling device with a cooling circuit with a refrigerant, a heat exchanger arranged in the test chamber, a compressor, a condenser and an expansion element, and wherein the temperature control device comprises a heating device with a heater and a further heat exchanger.

[0002] Such test chambers are regularly used to test the physical and / or chemical properties of objects, especially devices. For example, temperature test chambers or climate test chambers are known in which temperatures can be set within a range of -50 °C to +180 °C. In climate test chambers, desired climatic conditions can also be set, to which the device or the test specimen is then exposed for a defined period. Such test chambers are regularly, or partially, designed as mobile units, connected to a building only by the necessary supply lines and containing all the components required for temperature and climate control. Temperature control of the test chamber containing the test specimen is typically achieved via a recirculating air duct within the chamber.The recirculating air duct forms an air treatment chamber within the test chamber, in which heat exchangers are arranged to heat or cool the air flowing through the duct and / or the test chamber. A fan draws in the air from the test chamber and directs it through the recirculating air duct to the respective heat exchangers. The test specimen can thus be tempered or subjected to a defined temperature change. During a test interval, for example, the temperature can fluctuate between a maximum and a minimum temperature within the test chamber.

[0003] The refrigerant circulating in the cooling circuit must be suitable for use within the aforementioned temperature difference. Due to legal regulations, the refrigerant must not contribute significantly to ozone depletion in the atmosphere or global warming. Therefore, fluorinated gases and chlorinated substances are generally not permitted as refrigerants, making natural refrigerants or gases the only options. Furthermore, the refrigerant should be non-flammable to avoid complicating filling, shipping, and operation of the test chamber due to potential safety regulations. Using a flammable refrigerant also increases the cost of manufacturing a test circuit due to the necessary design modifications. Flammability, in this context, refers to the refrigerant's ability to react with ambient oxygen, releasing heat.A refrigerant is particularly flammable if it falls into fire class C according to the European standard EN2.

[0004] Furthermore, a refrigerant should have a relatively low CO2 equivalent, meaning its relative global warming potential (GWP) should be as low as possible to avoid indirect environmental damage from the refrigerant's release. The GWP indicates how much a given mass of a greenhouse gas contributes to global warming, using carbon dioxide as the reference point. The value describes the average warming effect over a specific period, in this case, 20 years for comparability. For the definition of the relative CO2 equivalent or GWP, please refer to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC), Accession Report, Appendix 8.A, Table 8.A.1.

[0005] Carbon dioxide is not well-suited as a refrigerant for the temperature ranges intended for a test chamber, because its triple point is -56.6 °C, making it unsuitable for use below -55 °C. While mixtures of carbon dioxide with, for example, nitrous oxide can be used as refrigerants down to -70 °C, nitrous oxide damages the ozone layer.

[0006] EP 3 051 227 A1 describes a so-called storage room, which is temperature-insulated and to which a two-stage cooling system is connected. A low-temperature cooling circuit is designed to achieve temperatures as low as -86 °C. The cooling circuit comprises a compressor, a condenser, a capillary tube, and an evaporator. The evaporator is arranged within the space to be cooled, acting as a heat exchanger. Furthermore, the cooling circuit uses a refrigerant mixture of carbon dioxide and ethane with an azeotropic effect.

[0007] The standard DIN 8960 concerns refrigerants and contains a list of possible refrigerants with their respective properties.

[0008] DE 10 2009 010 329 A1 describes a control of a solenoid valve in a cooling circuit depending on a temperature measured by a sensor.

[0009] An excerpt from the textbook "The Refrigeration System Builder" deals with different types of bypass and expansion tank in a refrigeration circuit.

[0010] DE 196 54 790 C1 relates to a temperature control device for a test chamber with a heat exchanger located within a test chamber and allowing the test chamber to be cooled or heated. In particular, the temperature control device can set temperatures in a range between -100°C and +200°C. R404a or R23 is used as a refrigerant in the cooling system.

[0011] US patent 4,346,754 discloses a device for testing material strips, wherein these material strips are exposed to high or low temperatures by means of a temperature control device. The temperature control device is attached directly to the material strip.

[0012] A so-called two-component refrigerant is known from DE 10 2005 014 552 A1. This two-component refrigerant consists of a mixture of carbon dioxide and nitrous oxide. Furthermore, it is non-flammable and has a low GWP value. Its operating temperature is specified as down to -70°C.

[0013] Other refrigerant mixtures are known from US 5,744,052 A, US 2016 / 0018135 A1 and DE 693 06 905 T2.

[0014] The present invention is therefore based on the objective of proposing a test chamber with which temperatures down to at least -80 °C can be achieved, wherein the test chamber should be safe and environmentally friendly without additional costs in its manufacture.

[0015] This problem is solved by a test chamber having the features of claim 1.

[0016] The test chamber according to the invention for conditioning air comprises a test chamber that can be closed off from the environment and is temperature-insulated for receiving the test specimen, and a temperature control device for temperature control of the test chamber, wherein a temperature in a temperature range of -80 °C to +180 °C, preferably -100 °C to +200 °C, can be established within the test chamber by means of the temperature control device, wherein the temperature control device comprises a cooling device with a cooling circuit with a refrigerant, a heat exchanger arranged in the test chamber, a compressor, a condenser and an expansion element, wherein the temperature control device comprises a heating device with a heater and a further heat exchanger, wherein the refrigerant is a nearly azeotropic refrigerant mixture consisting of a mass fraction of carbon dioxide and a mass fraction of at least one of the components ethene, hexafluoroethane, monofluoroethane, 1.1 Difluoroethene, fluoromethane and / or propane and / or xenon, wherein the refrigerant has a relative CO2 equivalent, based on 20 years, of < 2500, preferably < 500, preferably < 10, wherein a first bypass with at least one further throttling element is formed in the cooling circuit, wherein the first bypass bridges the compressor downstream of the compressor and upstream of the condenser in the flow direction, wherein a pressure difference between a high-pressure side and a low-pressure side of the cooling circuit can be compensated via the further throttling element.

[0017] In the test chamber according to the invention, heat exchange with the surrounding environment is largely prevented by thermal insulation of the side walls, floor walls, and ceiling walls. The heat exchanger of the cooling circuit is located within the test chamber or in an air handling unit within the test chamber, so that air circulated by a fan can come into contact with the heat exchanger. This makes it possible to cool a volume of circulated air from the test chamber via the heat exchanger in the test chamber using the cooling device. The heat exchanger is, in turn, connected to or integrated into the cooling circuit, so that the refrigerant circulating in the cooling circuit flows through the heat exchanger. The cooling device further comprises the compressor, which can be, for example, a compressor unit, and the condenser for the compressed refrigerant, which is arranged downstream of the compressor in the direction of refrigerant flow.The compressed refrigerant, which is under high pressure after compression and is essentially gaseous, condenses in the condenser and is then essentially in a liquid state. The liquid refrigerant then flows through the expansion device, where it becomes gaseous again due to expansion caused by a pressure drop. It then flows through the heat exchanger, which is thereby cooled. Subsequently, the gaseous refrigerant is drawn back into the compressor and compressed again. An expansion device is understood to be an expansion valve, throttling device, throttle valve, or other suitable constriction of a fluid line.

[0018] As it turns out, carbon dioxide can be used with a mass fraction of the refrigerant if it is mixed with a mass fraction of at least one of the components ethene, hexafluoroethane, monofluoroethane, 1,1-difluoroethene, fluoromethane, and / or propane and / or xenon. This refrigerant mixture then behaves like an azeotropic refrigerant mixture. An azeotropic mixture is a fluid consisting of two or more substances whose vapor phase has the same composition as the liquid phase. The azeotropic mixture has a definite boiling point, which is pressure-dependent, and behaves like a pure substance. In contrast, a zeotropic mixture is a fluid consisting of two or more substances whose vapor and liquid phase compositions always differ at vapor-liquid equilibrium. The dew point and boiling point do not intersect.At constant pressure, the phase transition of zeotropic mixtures occurs over a temperature range, the so-called temperature glide. In azeotropic mixtures, the dew point and boiling point lines touch at least at one point; that is, at this point, the composition of the vapor and liquid phases is the same. The vapor pressure and boiling point of a zeotropic mixture always lie between the vapor pressures and boiling points of the individual components, whereas in azeotropic mixtures, a pressure maximum or temperature minimum, or a pressure minimum or temperature maximum, occurs, which may lie outside the range limited by the values ​​of the individual components. Depending on one of the components of the refrigerant mixture, the refrigerant mixture can also exist as a zeotropic refrigerant mixture on the high-pressure side of the refrigeration circuit when it enters the condenser.

[0019] According to the invention, the refrigerant mixture enables the test chamber to be used in a temperature range from -80 °C to +100 °C, wherein the refrigerant mixture has a relative CO2 equivalent, based on 20 years, of < 2500 and is therefore only slightly harmful to the environment.

[0020] According to the invention, the temperature control device comprises a heating element with a heater and a second heat exchanger. The heating element can, for example, be an electric resistance heater that heats the second heat exchanger, thus enabling a temperature increase in the test chamber via the second heat exchanger. If the first and second heat exchangers can be selectively controlled by a control device for cooling or heating the air circulated in the test chamber, the temperature control device can then maintain a temperature within the test chamber in the range of -80 °C to +180 °C, preferably from -100 °C to +200 °C. In this way, a temperature constant of ± 0.3 to ± 0.5 K can be maintained in the test chamber during a test interval, regardless of the test specimen or its operating condition.A test interval, as used here, refers to a period within a complete test cycle during which the test specimen is exposed to a substantially constant temperature or climatic condition. The additional heat exchanger can be combined with the heat exchanger of the cooling circuit in such a way that a common heat exchanger body is formed, through which refrigerant flows and which incorporates heating elements of an electric resistance heater.

[0021] According to the invention, a first bypass with at least one further throttling element or capillary is formed in the cooling circuit, wherein the first bypass bypasses the compressor downstream of the compressor and upstream of the condenser in the flow direction, and wherein a pressure difference between a high-pressure side and a low-pressure side of the cooling circuit can be equalized via the further throttling element. The first bypass can additionally be equipped with an adjustable or controllable valve, for example, a solenoid valve. By connecting the high-pressure side and the low-pressure side via the further throttling element, it can be ensured that, in the event of a system shutdown, the highly compressed, gaseous refrigerant gradually flows from the high-pressure side to the low-pressure side of the cooling circuit. This ensures that a gradual pressure equalization between the high-pressure side and the low-pressure side also occurs when the expansion element is closed.The cross-section of the further throttling device can be dimensioned in such a way that an overflow of the refrigerant from the high-pressure side to the low-pressure side only minimally affects the normal operation of the cooling device.

[0022] If the refrigerant is non-flammable, the test chamber and, in particular, the cooling circuit can be designed more cost-effectively, as no special safety precautions regarding the refrigerant's flammability need to be observed. The refrigerant then cannot be classified as fire class C and / or refrigerant safety group A1. Furthermore, shipping and transporting the test chamber is simplified, as it can be filled with the refrigerant before transport, regardless of the mode of transport. With flammable refrigerant, filling may only be possible during commissioning at the installation site. Additionally, non-flammable refrigerants can be used even if ignition sources are present in the test chamber. Sensors for detecting a flammable atmosphere in the area of ​​the heat exchanger in the test chamber are then unnecessary. Such sensors are typically not temperature-stable.

[0023] It is also advantageous if the refrigerant is soluble in refrigeration oil. If the compressor is a conventional compressor, it can be located in an oil sump, which means that oil can be transported in the cooling circuit, at least in sections. An oil separator can be installed in the cooling circuit in the direction of refrigerant flow, through which the oil is returned to the compressor. The oil can be POE oil, PAG oil, PFPE oil, or mineral oil.

[0024] The refrigerant can have a temperature glide of less than or equal to 5 K, preferably 1 K. This can be the case if the refrigerant is a nearly azeotropic refrigerant mixture. The refrigerant has no temperature glide if it is a purely azeotropic refrigerant mixture. That is, a nearly azeotropic refrigerant mixture is understood here to be a refrigerant mixture with a temperature glide of less than or equal to 5 K, preferably 1 K. According to this definition, zeotropic refrigerant mixtures then have a temperature glide of > 5 K or > 1 K.

[0025] The mass fraction of carbon dioxide can range from 0.09 to 0.45 when mixed with ethene. If this is a binary refrigerant mixture, it can exhibit fully azeotropic behavior. This azeotropism favorably influences key refrigeration parameters. The refrigerant mixture can then be handled like a single-component refrigerant or a pure substance. The concentration difference between the liquid and vapor phases, as well as the temperature glide during isobaric evaporation or condensation, are negligibly small, which is advantageous for the design, construction, operation, and filling of the refrigeration circuit or test chamber.

[0026] The mass fraction of carbon dioxide can range from 0.35 to 0.63 in a mixture with hexafluoroethene. If it is a binary refrigerant mixture, it can behave completely azeotropically.

[0027] The mass fraction of carbon dioxide can range from 0.16 to 0.97 in a mixture with xenon. If it is a binary refrigerant mixture, it can behave completely azeotropically.

[0028] Furthermore, it is advantageous if the refrigerant mixture contains a cyclopropane component with a mass fraction of 0.03 to 0.2. In addition, the refrigerant mixture may contain additives for detecting leaks in the cooling circuit. These additives can be selected from helium and hydrogen or from the hydrocarbon group. Odorants or other detectable substances can also be included in the mixture.

[0029] The cooling system can include a further cooling circuit with another refrigerant, another compressor, another condenser, and another expansion element. This further cooling circuit can be coupled to the condenser of the first cooling circuit via an internal heat exchanger. Consequently, the cooling system can then have two circuits connected in series, forming a so-called cooling cascade. The further cooling system, or the further cooling circuit, can then cool the condenser of the first cooling circuit. This makes it possible to achieve particularly low temperatures in the test chamber. The further compressor in the further cooling circuit can also be a compressor.

[0030] The condenser can be designed with air cooling, water cooling, or another type of cooling fluid. In principle, the condenser can be cooled with any suitable fluid. The essential point is that the heat load generated at the condenser is dissipated via air or water cooling in such a way that the refrigerant can condense completely into a liquid.

[0031] A pressure equalization device for the refrigerant can be arranged in the cooling circuit, whereby a pressure of < 40 bar, preferably < 35 bar, can be maintained in the cooling circuit when the refrigerant temperature is uniformly maintained at 20 °C. If a further cooling circuit is present, it can also have such a pressure equalization device. Since comparatively large temperature differences can occur in the cooling circuit during operation, it is particularly advantageous if the pressure equalization device can compensate for these. In this way, very large temperature fluctuations and thus a change in the volume of the refrigerant, depending on the respective coefficient of expansion of the refrigerant, can be compensated for by the pressure equalization device. In particular, the pressure equalization device can be designed such that the temperature control device is intrinsically safe when de-energized, i.e.,that no standby cooling of the refrigerant is required. It is also possible to fully fill the cooling circuit and make it ready for operation before the test chamber is transported.

[0032] A refrigerant reservoir with a throttling device or capillary can be connected to the low-pressure side of the cooling circuit. The refrigerant reservoir can then act as a pressure equalization device, for example, a container in which refrigerant can collect. Filling and emptying of the container can be accomplished via the throttling device, so that, depending on the condensation or evaporation rate of the refrigerant, a time-delayed pressure equalization occurs due to the slower flow of refrigerant through the throttling device.

[0033] A gas cooler can be installed on the high-pressure side of the refrigeration circuit, downstream of the compressor and upstream of the condenser. This allows the gaseous refrigerant, which is highly compressed by the compressor, to be cooled from a relatively high temperature level due to compression to a relatively lower temperature level. The gas cooler ensures condensation or liquefaction in the condenser, particularly with the refrigerant mixture used.

[0034] Furthermore, a second bypass with at least one first solenoid valve can be incorporated into the refrigeration circuit. This second bypass can bypass the compressor downstream of the condenser and upstream of the expansion device. The first solenoid valve allows for the metering of refrigerant to regulate the suction gas temperature and / or pressure of the refrigerant on the low-pressure side of the refrigeration circuit upstream of the compressor. This prevents, among other things, the compressor from potentially overheating and being damaged. Consequently, by actuating the first solenoid valve upstream of the compressor, the gaseous refrigerant can be cooled via the second bypass by adding liquid refrigerant.The first solenoid valve can be actuated by a control device, which in turn is coupled to a pressure and / or temperature sensor in the refrigeration circuit upstream of the compressor. It is particularly advantageous if a suction gas temperature of ≤ 30 °C can be set via the second bypass. The refrigerant can also be metered so that the compressor's operating time can be regulated. In principle, it is disadvantageous if the compressor is frequently switched on and off. A compressor's service life can be extended by operating it for longer periods. The second bypass allows refrigerant to bypass the compressor, for example, to delay automatic compressor shutdown and thus extend its operating time.

[0035] The refrigeration circuit can also include a third bypass with at least one second solenoid valve. This third bypass can bypass the expansion element upstream of the condenser in the direction of flow. The second solenoid valve allows for metering of refrigerant to control the suction gas temperature and / or pressure of the refrigerant on the low-pressure side of the refrigeration circuit upstream of the compressor. The third bypass can also include a throttling device or capillary to delay the flow of refrigerant.

[0036] The temperature control device can include a control unit with at least one pressure sensor and / or at least one temperature sensor in the cooling circuit, whereby solenoid valves can be actuated by the control unit depending on a measured temperature or pressure. The control unit can include data processing means that process sensor data and control the solenoid valves. The control of a function of the cooling unit can then also be adapted to the refrigerant used, for example, via a suitable computer program. Furthermore, the control unit can signal a malfunction and, if necessary, initiate a shutdown of the test chamber to protect the test chamber or the test specimen from damage caused by critical or undesired operating conditions of the test chamber.

[0037] A preferred embodiment of the invention is explained in more detail below with reference to the accompanying drawing.

[0038] The figure shows a schematic representation of a test chamber 10 with a circuit diagram of a temperature control device 11. The test chamber 10 comprises a test space 12, shown here only in sections, which is bounded and thermally insulated from an environment 14 by thermally insulated walls 13. A fan 15 is arranged inside the test space 12.

[0039] The temperature control device 11 comprises a cooling unit 16 with a cooling circuit 17 in which a refrigerant can circulate. The refrigerant is a nearly azeotropic refrigerant mixture consisting of a mass fraction of carbon dioxide and a mass fraction of at least one of the components ethene, hexafluoroethane, monofluoroethane, 1,1-difluoroethene, fluoromethane, and / or propane and / or xenon, wherein the refrigerant has a relative CO2 equivalent, based on a 20-year period, of < 10. The cooling unit 16 further comprises a heat exchanger 18, which is arranged in the test chamber 12, a compressor 19, a condenser 20, and an expansion element 21. In addition, a further heat exchanger 22 of a heating unit 23 of the temperature control device 11 is arranged in the test chamber 12. Thus, by means of the temperature control device 11, a temperature in a temperature range of -80 °C to +180 °C and also from -100 °C to +200 °C can be established within the test chamber 12.A line 24 indicates a spatial separation between a machine room 25 and the test room 12.

[0040] The cooling circuit 17 has a high-pressure side 26, which runs in the direction of refrigerant flow from the compressor 19 to the expansion element 21, and a low-pressure side 27, which runs from the expansion element 21 to the compressor 19. An oil separator 28 and a temperature sensor 29 are arranged in the cooling circuit 17 downstream of the compressor 19. Further downstream of the oil separator 28 in the cooling circuit 17, a pressure sensor 30 is arranged, followed by a gas cooler 31. In a pipe section 32 from the compressor 19 to the gas cooler 31, the refrigerant is gaseous and has a comparatively high temperature. The refrigerant compressed by the compressor 19 flows in the cooling circuit 17 to the condenser 20, which is cooled here via another cooling circuit 33, such that the gaseous refrigerant is liquefied in the condenser 20.In the direction of refrigerant flow, a shut-off valve 34 and a filter drier 35 for filtering and drying the refrigerant are located in the cooling circuit 17 after the condenser 20. The refrigerant then enters the cooling circuit 17 and passes to a solenoid valve 36 and the expansion device 21, which is self-regulating via a pressurized pipe section 37 and a temperature sensor 38. The refrigerant is therefore in a liquid state in a pipe section 39 of the cooling circuit 17. The expansion device 21, which is located in a supply line 40 with respect to the heat exchanger 18 and the compressor 19, is consequently controlled via the pipe section 37 and the temperature sensor 38, which are connected to a return line 41 of the cooling circuit 17. The expansion of the refrigerant downstream of the expansion element 21 cools the heat exchanger 18, whereby the refrigerant transitions into the gaseous state and is returned via the return line 41.a pipe section 42 is directed to compressor 19.

[0041] In the cooling circuit 17, a first bypass 43 with a throttling element 44 and a shut-off valve 45 is further arranged. The first bypass 43 bypasses the compressor 19, so that when the compressor 19 is at a standstill, a gradual pressure equalization between the high-pressure side 26 and the low-pressure side 27 takes place via the throttling element 44.

[0042] A second bypass 46 with a throttling device 47 and a solenoid valve 48 is connected to the first bypass 43 and also bypasses the compressor 19 upstream of the condenser 20 and the gas cooler 31. Refrigerant can then flow from the high-pressure side 26 to the low-pressure side 27 via the solenoid valve 48 and be metered so that the suction gas temperature and pressure in the pipe section 42 upstream of the compressor 19 are within the optimal range for the refrigerant. The first bypass 43 thus serves to allow cold, expanding gaseous refrigerant to flow through during system shutdowns, thereby equalizing the pressure. The second bypass 46 allows comparatively hot, gaseous refrigerant to flow into the return line 41 to regulate the suction gas temperature upstream of the compressor 19. The suction gas temperature here can be ≤ 30 °C.

[0043] A third bypass 49 intervenes in the cooling circuit 17 downstream of the condenser 20 or the filter drier 35, bypassing the expansion element 21. Refrigerant can be metered from the high-pressure side 26 to the low-pressure side 27 via a throttling device 50 and a solenoid valve 51, allowing the suction gas temperature and / or suction gas pressure of the refrigerant on the low-pressure side 27 upstream of the compressor 19 to be controlled. In contrast to the second bypass 46, the refrigerant metered via the third bypass 49 is liquid, which in particular allows a reduction in the suction gas temperature in the return line 41 after control by the solenoid valve 51.

[0044] The further cooling circuit 33 comprises another compressor 52, another condenser 53 and another expansion element 54 as well as an internal heat exchanger 55, by means of which cooling of the condenser 20 is accomplished.

Claims

[1] Test chamber (10) for conditioning air, comprising a temperature-insulated test chamber (12) that can be closed off from the environment for receiving test material and a temperature control device (11) for temperature control of the test chamber, wherein a temperature in a temperature range of -80 °C to +180 °C can be established within the test chamber by means of the temperature control device, wherein the temperature control device comprises a cooling device (16) with a cooling circuit (17) with a refrigerant, a heat exchanger (18) arranged in the test chamber, a compressor (19), a condenser (20) and an expansion element (21), wherein the temperature control device (11) comprises a heating device (23) with a heater and a further heat exchanger (22), characterized by, that the refrigerant is a nearly azeotropic refrigerant mixture consisting of a mass fraction of carbon dioxide and a mass fraction of at least one of the components ethene, hexafluoroethane, monofluoroethane, 1.1 difluoroethene, fluoromethane and / or propane and / or xenon, wherein the refrigerant has a relative CO2 equivalent, based on 20 years, of < 2500, wherein a first bypass (43) with at least one further throttling element (44) is formed in the cooling circuit (17), wherein the first bypass (43) bypasses the compressor (19) downstream of the compressor (19) and upstream of the condenser (20) in the direction of flow, wherein a pressure difference between a high-pressure side (26) and a low-pressure side (27) of the cooling circuit (17) can be equalized via the further throttling element (44). [2] Test chamber according to claim 1, characterized by that a temperature within a temperature range of -100 °C to +200 °C can be achieved within the test chamber. [3] Test chamber according to claim 1 or 2, characterized by that the refrigerant has a relative CO2 equivalent, based on 20 years, of < 500. [4] Test chamber according to claim 3, characterized by that the refrigerant has a relative CO2 equivalent, based on 20 years, of < 10. [5] Test chamber according to one of the preceding claims, characterized by that the refrigerant is non-flammable. [6] Test chamber according to one of the preceding claims, characterized by that the refrigerant is soluble in refrigeration machine oil. [7] Test chamber according to one of the preceding claims, characterized by that the refrigerant has a temperature glide of less than or equal to 5 K, preferably 1 K. [8] Test chamber according to one of the preceding claims, characterized by , that the mass fraction of carbon dioxide is 0.09 to 0.45 when mixed with ethene. [9] Test chamber according to any one of claims 1 to 7, characterized by, that the mass fraction of carbon dioxide is 0.35 to 0.63 in a mixture with hexafluoroethene. [10] Test chamber according to any one of claims 1 to 7, characterized by , that the mass fraction of carbon dioxide is 0.16 to 0.97 in a mixture with xenon. [11] Test chamber according to one of the preceding claims, characterized by , that one component is cyclopropane, with a mass fraction of 0.03 to 0.

2. [12] Test chamber according to one of the preceding claims, characterized by , that the cooling device (16) has a further cooling circuit (33) with a further refrigerant, a further compressor (52), a further condenser (53) and a further expansion device (54), wherein the further cooling circuit (33) is coupled to the condenser (20) of the cooling circuit (17) by means of an internal heat exchanger (55). [13] Test chamber according to one of the preceding claims, characterized by, that the condenser (20, 53) is designed with air cooling or water cooling or another cooling fluid. [14] Test chamber according to one of the preceding claims, characterized by , that a pressure equalization device for the refrigerant is arranged in the cooling circuit (17), wherein a pressure of < 35 bar is formed in the cooling circuit (17) when the refrigerant temperature in the cooling circuit (17) is uniformly 20 °C. [15] Test chamber according to one of the preceding claims, characterized by , that a refrigerant reservoir with a throttling device is connected to a low-pressure side (27) of the cooling circuit (17). [16] Test chamber according to one of the preceding claims, characterized by , that in a high-pressure side (26) of the cooling circuit (17) a gas cooler (31) is arranged downstream of the compressor (19) and upstream of the condenser (20) in the direction of flow. [17] Test chamber according to one of the preceding claims, characterized by , that in the cooling circuit (17) a second bypass (46) with at least one first solenoid valve (48) is formed, wherein the second bypass (46) bypasses the compressor (19) in the flow direction from the condenser (20), wherein refrigerant can be metered via the first solenoid valve (48) in such a way that a suction gas temperature and / or a suction gas pressure of the refrigerant on a low-pressure side (27) of the cooling circuit (17) upstream of the compressor (19) can be controlled. [18] Test chamber according to one of the preceding claims, characterized by, that in the cooling circuit (17) a third bypass (49) with at least one second solenoid valve (51) is formed, wherein the third bypass (49) bridges the expansion element (21) in the flow direction downstream of the condenser (20) and upstream of the expansion element (21), wherein refrigerant can be metered via the second solenoid valve (51) in such a way that a suction gas temperature and / or a suction gas pressure of the refrigerant on a low-pressure side (27) of the cooling circuit (17) upstream of the compressor (19) can be controlled. [19] Test chamber according to claim 17 or 18, characterized by , that the temperature control device (11) comprises a control device with at least one pressure sensor (30) and / or at least one temperature sensor (29, 38) in the cooling circuit (17), wherein the solenoid valves (48, 51) can be actuated by means of the control device depending on a measured temperature or pressure.

Images