Test chamber and control method

Abstract

A method for conditioning the air in a test space of a test chamber and a test chamber are provided.SOLUTION: Wherein the cooling device (10) comprises a cooling circuit (11) with carbon dioxide as a refrigerant, a heat exchanger (12) in the test space, a compressor (13, 14), an oil device (41), a gas cooler (15) and an expansion valve (16), wherein a temperature in the test space is controlled and / or regulated by a control device of the test chamber, wherein oil is separated from the refrigerant by at least one oil separator (42) of the oil device and is conducted to the compressor by a supply device (43) of the oil device, in the cooling circuit, a pressure P of the refrigerant is produced while the compressor is at a standstill and at a temperature of the refrigerant which corresponds to the ambient temperature, in particular at least 20 °C.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a test chamber, in particular a climatic chamber, for conditioning the air and a method for conditioning the air in a test space of a test chamber, in particular a climatic chamber, for receiving test materials, the test space being sealable and insulated from the environment, in which a temperature in the range of -20°C to +180°C is established by a cooling device of a temperature control device of the test chamber, the cooling device comprising a cooling circuit using carbon dioxide as a refrigerant, a heat exchanger in the test space, a compressor, an oil device, a gas cooler and an expansion valve, the temperature in the test space being controlled and / or regulated by the control device of the test chamber, the oil being separated from the refrigerant by at least one oil separator of the oil device and being led to the compressor by a supply device of the oil device, and a refrigerant pressure P is generated in the cooling circuit when the compressor is stopped and at a refrigerant temperature corresponding in particular to the ambient temperature by at least 20°C. [Background technology]

[0002] This type of test chamber is regularly used to test the physical and / or chemical properties of objects, particularly devices. For example, test cabinets or climate test cabinets are known, the internal temperature of which can be set between -70°C and +180°C. In the case of climate test cabinets, desired climate conditions can additionally be set, to which devices or test materials are exposed for a predetermined time. The temperature of the test space containing the test material to be tested is regularly controlled in an air circulation duct within the test space. The air circulation duct forms an air handling space within the test space, in which a heat exchanger is arranged for heating or cooling the air flowing through the air circulation duct or test space. A fan or ventilator draws air from the test space and directs it through the air circulation duct to the respective heat exchanger. In this way, the test material can be temperature-controlled or exposed to desired temperature changes. In this case, the temperature can be varied, for example, between the maximum and minimum temperatures of the test chamber, during the test period. A test chamber of this type is known, for example, from Patent Document 1.

[0003] Refrigerants used in refrigeration circuits should have a fairly low CO2 equivalent value, i.e., the relative greenhouse potential or global warming potential (GWP) should be as low as possible to avoid indirect adverse effects on the environment if the refrigerant is released. Therefore, carbon dioxide (CO2) is also known to be used as a pure substance refrigerant. Carbon dioxide is available at low cost, is non-flammable, and has a GWP of 1, making it essentially environmentally neutral. The freezing point or triple point of carbon dioxide is -56.6°C, so temperatures lower than this cannot be achieved using carbon dioxide alone.

[0004] Carbon dioxide as a refrigerant has a very high volumetric cooling capacity, and even when using compressors with very low stroke volume flows, very high cooling capacities can be provided by the refrigeration circuit. In addition, the pressure range of a refrigeration circuit using carbon dioxide as a refrigerant is very high (up to 120 bar (12 MPa)) in transcritical operation, which is why the components required to form the refrigeration circuit are quite expensive.

[0005] Furthermore, chillers configured as what are called booster systems are known. In the cooling circuit of such chillers, a high-pressure compressor is always connected in series downstream of a low-pressure compressor, so that the refrigerant is compressed in stages, first by the low-pressure compressor and then by the high-pressure compressor. Due to the high demands for temperature control within the temperature range of the test space, the load demands frequently fluctuate during operation of the test chamber. Therefore, the cooling capacity generated by the compressor and expansion valve must be infinitely variable. At the same time, to extend the compressor's service life, it is desirable for the compressor to be switched on and off infrequently.

[0006] When the cooling system is operating, oil is supplied from the oil system to the cooling circuit. In this process, the oil is metered into the compressor housing of the compressor to lubricate the compressor's moving parts. The oil mixes with the refrigerant and reaches an oil separator in the cooling circuit downstream of the compressor in the refrigerant flow direction, where the oil in the refrigerant is separated through the oil separator and supplied back to the compressor in a circuit manner. To ensure sufficient lubrication of the compressor, oil must be continuously supplied to the compressor whenever the compressor is operating.

[0007] Load fluctuations occur as a function of temperature changes in the test space, which also causes the compressor to shut down. Compressor shutdown occurs whenever cooling of the test space is required or when very high temperatures, for example, up to +180°C, are established. In this case, a fairly low-temperature refrigerant under high pressure can still be present in the cooling circuit, for example, in a storage device. This allows for rapid cooling of the heat exchangers in the test space, if required. When the compressor is shut down for an extended period of time, for example, when the test chamber is shut down, transported, or has not yet been started up, the refrigerant in the cooling circuit inevitably assumes ambient temperature. Depending on the ambient temperature, which can be, for example, 20°C, 35°C, or even 55°C during transport, a shutdown pressure of the refrigerant in the cooling circuit is created. In this case, there is a risk of exceeding the maximum allowable pressure of the refrigerant in the cooling circuit. Therefore, it is known to provide the cooling circuit with so-called shutdown cooling in order to cool at least a portion of the refrigerant to a pressure that does not exceed the maximum allowable pressure. Furthermore, one or more safety valves can be provided in the cooling circuit, through which the refrigerant can escape to the environment if the maximum allowable pressure is exceeded. These safety valves must be replaced after operation. This has the disadvantage that during transport, the cooling at rest is not active and may have to be powered, which is quite cost-intensive. To put the test chamber into operation, the refrigerant released via the safety valves must be replenished again in the cooling circuit to provide the required amount of refrigerant in the cooling circuit. For this purpose, appropriate maintenance of the test chamber is required. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] European Patent Application Publication No. 0344397 Summary of the Invention [Problem to be solved by the invention]

[0009] The object of the invention is therefore to propose a method for conditioning the air in the test space of a test chamber, and a test chamber, which allow for cheap operation and transportation. [Means for solving the problem]

[0010] This object is achieved by a method having the features of claim 1 and a test chamber having the features of claim 18.

[0011] The method of the present invention for conditioning the air in a test space of a test chamber, in particular a climate chamber, for receiving test materials, comprises: a test space that is sealable and insulated from the environment; a temperature in the test space ranging from -20°C to +180°C is established by a cooling device of a temperature control device of the test chamber; the cooling device comprises a cooling circuit using carbon dioxide as a refrigerant, a heat exchanger in the test space, a compressor, an oil device, a gas cooler, and an expansion valve; the temperature in the test space is controlled and / or regulated by the control device of the test chamber; oil is separated from the refrigerant by at least one oil separator of the oil device and is led to the compressor by a supply device of the oil device; a refrigerant pressure P is generated in the cooling circuit when the compressor is stopped and at a refrigerant temperature corresponding, in particular, to the ambient temperature by at least 20°C; a partial amount of carbon dioxide is absorbed by the oil; and the amount of carbon dioxide and / or the amount of oil in the cooling circuit for generating the pressure P is selected taking into account the partial absorption of the carbon dioxide.

[0012] If the temperature in the test space is to be increased during a test cycle starting from a relatively low temperature in the test space, for example, -20°C, the compressor can be turned off during operation of the test chamber. In this case, the low-temperature refrigerant, which is still compressed in the cooling circuit, often experiences a pressure difference between the high-pressure side portion of the cooling circuit, which runs from the compressor to the expansion valve in the direction of refrigerant flow, and the low-pressure side portion of the cooling circuit, which runs from the expansion valve to the compressor in the direction of refrigerant flow. If the compressor is turned off and / or the test chamber is shut down for an extended period of time, pressure equalization between the high-pressure and low-pressure sides of the cooling circuit occurs via the expansion valve or via a bypass section of the cooling circuit running between the high-pressure and low-pressure sides. Furthermore, the refrigerant is at ambient temperature. An ambient temperature of 20°C can be assumed as a reference in this case. When equalizing the pressure between the high-pressure and low-pressure sides, essentially the same refrigerant pressure P is generated in the cooling circuit.

[0013] Surprisingly, it has been found that the oil present in the cooling circuit together with the refrigerant is able to absorb a portion or a fraction of the refrigerant and / or carbon dioxide. This means that the carbon dioxide molecules are incorporated into the oil molecules. Absorption is carried out in the usable range, particularly at higher temperatures and / or at temperatures at least 20°C above, and this effect can be used to limit the shutdown pressure of the refrigerant. The volume of the cooling circuit with the amount of carbon dioxide and the amount of oil therein, as well as the temperatures of these substances, are important variables for generating the pressure P.

[0014] In particular, higher temperatures cause a phase change of the carbon dioxide, which in turn causes a pressure increase due to thermal expansion. As a portion of the carbon dioxide is absorbed by the oil, the volume of the carbon dioxide decreases, resulting in a reduced pressure. According to the present invention, the amount or total amount of carbon dioxide and / or the amount or total amount of oil in the cooling circuit required to achieve the desired shutdown pressure or pressure P can be selected taking into account the absorption of the partial amount of carbon dioxide in the oil. This means that the amounts of carbon dioxide and oil are adjusted to one another to a degree that does not exceed the refrigerant pressure P in the cooling circuit at 20°C. Alternatively, this adjustment can be performed so as not to exceed the refrigerant pressure P in the cooling circuit at 35°C, preferably at 55°C. Therefore, again, structural measures are not required to prevent unacceptable high pressures from occurring during compressor shutdown. This can substantially simplify the design and, therefore, the manufacture of the cooling device. Furthermore, the test chamber can be more easily transported, and pre-startup testing and maintenance, which may involve refilling the cooling circuit with refrigerant, are not required.

[0015] In this way, a fraction of the carbon dioxide can be absorbed by the oil when the compressor is off and at a refrigerant temperature of at least 20° C. For example, depending on the oil and pressure used in the refrigeration circuit, the fraction of carbon dioxide can be between 2% and 35% of the total amount of carbon dioxide. In particular, it is advantageous to create a pressure P of 20 to 120 bar (2 to 12 MPa), preferably 40 to 50 bar (4 to 5 MPa), at 20° C. in the refrigeration circuit when the compressor is off.

[0016] The ratio of the amount of carbon dioxide to the amount of oil in the cooling circuit can be selected taking into account the absorption of a partial amount of carbon dioxide. In this case, the ratio or quotient of the amount of carbon dioxide to the amount of oil can be determined for each volume and pressure P of the cooling circuit at 20°C. Also, the ratio and / or respective amounts of oil and carbon dioxide can be selected for any other temperature of the refrigerant. In this case, the respective absorption rate of carbon dioxide in the oil can be taken into account.

[0017] The amount of oil in the cooling circuit can be selected to be greater than the amount of oil required for compressor operation. To ensure compressor operation with long idling times, the oil system must always have a sufficiently large required amount of oil to ensure continuous lubrication of the compressor during operation. In principle, it makes no sense to use a large amount of oil in the cooling circuit, as this would increase costs, reduce the total amount of carbon dioxide, and possibly require an oil separator suitable for larger volumes of oil. However, it has been discovered that increasing the total amount of oil in the cooling circuit allows the oil to absorb more carbon dioxide, which can be advantageously used to achieve pressure P during compressor shutdown. Therefore, other structural measures that may be required to limit pressure or reinforce the design of the cooling circuit can be omitted here, which allows for cheaper operation of the entire test chamber.

[0018] In the cooling circuit, the pressure of the refrigerant P is the maximum allowable refrigerant pressure P for the cooling circuit. max The maximum permissible pressure is understood to be the pressure within the meaning of the directives and technical regulations applicable to refrigeration circuits in general on the priority date, preferably in accordance with the Pressure Equipment Directive 2014 / 68 / EU and / or DIN EN 378. If the amounts of carbon dioxide and oil are selected in such a way that the maximum permissible pressure is not exceeded by absorption of carbon dioxide in the oil, then the otherwise usual structural safety measures can be omitted.

[0019] The refrigerant may not be cooled by the shutdown cooling or discharged from the cooling circuit by the safety valve when the compressor is off and the temperature of the refrigerant is at least 20°C. In this case, the shutdown cooling and / or the safety valve may be omitted. In this case, the problem of having to perform maintenance after transporting the test chamber to determine whether the refrigerant escaped to the environment through the safety valve no longer arises. In principle, a safety valve may still be present, but in this case the pressure of the refrigerant P may be less than the maximum allowable pressure P of the safety valve. max can be caused to be significantly smaller than

[0020] The oil is stored in a collector of the oil device, and the oil in the collector can be guided to the compressor via at least one supply valve in the supply line of the supply device. The supply valve can be controlled and / or adjusted, for example, by a control device. The collector can receive a partial amount and / or a predominant amount of the oil in the cooling circuit. In this case, the oil in the collector can be exposed to the same pressure as the refrigerant in the cooling circuit. In this case, carbon dioxide in the oil in the collector can be absorbed without further structural measures. The collector can be configured to store at least the total amount of oil in the cooling circuit. In this case, the oil in the collector simply needs to be discharged into the supply line via the supply valve, and the oil can then reach the compressor via the supply line.

[0021] The supply valve can be opened when the compressor is running, and closed when the compressor is stopped. In this case, no oil is further directed to the compressor while the compressor is stopped, so that as much oil as possible is available to absorb carbon dioxide. Depending on the compressor design, the amount of oil in the compressor can also be used to absorb carbon dioxide.

[0022] Oil can be metered to the compressor in a supply line leading to the compressor by a metering valve of the supply device. The metering valve can be installed directly on or adjacent to the compressor in the supply line. For example, the metering valve can limit the cross section of the supply line to an extent that only the amount of oil required for the compressor reaches the compressor. This can limit an unnecessarily high volumetric flow rate of oil in the supply line and line sections in the refrigerant flow direction from the compressor to the oil separator.

[0023] The amount of oil in the collector can be increased as the refrigerant temperature increases and decreased as the refrigerant temperature decreases due to the oil device. Consequently, the amount of oil in the collector can be varied in such a way that it is advantageously adjusted to the oil absorption rate, which depends on the refrigerant temperature and / or the ambient temperature during compressor operation or shutdown. In principle, the total amount of oil in the cooling circuit can be used to absorb carbon dioxide. At very low refrigerant temperatures, for example, 20°C, the absorption of carbon dioxide in the oil is negligible and is barely usable to generate the desired pressure P. Therefore, more oil can be used in the cooling circuit to lubricate the compressor. At high pressures in the cooling circuit, strong dilution of the oil, i.e., a decrease in the oil viscosity, can occur. In this regard, it is advantageous to always provide sufficient lubrication for the compressor during operation.

[0024] Furthermore, the oil fraction in the collector can be adjusted essentially linearly to the refrigerant temperature by the oil device. This linear adjustment can be performed via a supply valve and can be controlled and / or adjusted by a control device. The absorption rate of carbon dioxide in oil also behaves essentially linearly as a function of temperature and pressure, so the oil fraction in the collector can be advantageously adjusted to this ratio.

[0025] The collector's filling capacity can be at least as large as the volume of oil in the cooling circuit. In this case, the collector can receive all of the oil in the cooling circuit. In this case, there is no need for an external oil storage container connected to the collector, which may be present. In principle, however, it is also possible to adjust the oil volume via this type of storage container. The collector's filling capacity should be dimensioned so that it can receive the entire amount of oil when the coolant temperature is 35°C. During transportation of the test chamber, the ambient temperature may reach this value or even reach a maximum of 55°C.

[0026] Polyol ester oils can be used as the oil, which can be further supplemented with additives to improve compressor wear protection. Furthermore, polyol ester oils are well miscible with carbon dioxide, are highly thermally stable, have a very low evaporation temperature, and have excellent lubrication properties.

[0027] The cooling circuit can be realized to include a low-pressure compressor and a high-pressure compressor downstream of the low-pressure compressor in the refrigerant flow direction. In this case, an oil separator can be arranged in the cooling circuit downstream of the high-pressure compressor in the refrigerant flow direction and upstream of the gas cooler. In this case, the refrigerant can flow from the low-pressure compressor to the high-pressure compressor. The refrigerant can be sent to the low-pressure compressor and then to the high-pressure compressor, or to the high-pressure compressor alone, via a valve device. Depending on the load requirements, the low-pressure and high-pressure compressors can be operated together, or only the high-pressure compressor can be operated. Thus, during continuous operation of the test chamber, the low-pressure compressor can be temporarily turned off, thereby saving a large portion of the energy that would otherwise be required for the operation of the low-pressure compressor. By connecting the low-pressure and high-pressure compressors in series, the refrigerant can be compressed in stages.

[0028] Advantageously, pure carbon dioxide can be used as the refrigerant. Pure carbon dioxide has a GWP of 1, is non-flammable, non-hazardous, and available at low cost. Furthermore, carbon dioxide is a pure substance or an azeotrope, which allows for the advantageous implementation of the method and its variants in the first place.

[0029] The cooling circuit can be operated in a thermodynamically transcritical or subcritical state. The control device can be used to change the operating state appropriately depending on the cooling load requirements in the test space. In subcritical operation of the cooling circuit, the refrigerant is liquefied in the gas cooler below its critical point and expanded in the expansion valve to gas or wet vapor. The compressor, and if present, the high-pressure and low-pressure compressors, can be operated at least in a subcritical operating state. The subcritical operating state of the cooling circuit corresponds to partial load operation. In transcritical operating state, the refrigerant circulates in the cooling circuit essentially in a gaseous state. This means that the temperature difference is reduced to a level where the refrigerant does not liquefy in the gas cooler. Also, in transcritical operating state, the gas cooler reaches a pressure above the critical point of the refrigerant. For example, when a high cooling load is required, or when cooling from +180°C to -20°C is required, the cooling circuit can be operated in a transcritical state. When the cooling load demand in the test space is low, for example when the temperature is kept constant or the ambient temperature is low, it is advantageous to operate the cooling circuit in a subcritical state, which makes it possible to achieve increased efficiency, especially when the cooling load demand is low, as opposed to exclusively transcritical operation.

[0030] The temperature control device allows a temperature in the test space to be established in the range of -40°C to +180°C, preferably -55°C to +180°C.

[0031] The test chamber according to the present invention, in particular a climate chamber, for conditioning air comprises a test space for receiving a test material, the test space being sealable and insulated from the environment, and a temperature control device for controlling the temperature of the test space, in which a temperature in the range of -20°C to +180°C can be established by the temperature control device, the temperature control device comprising a cooling device that uses carbon dioxide as a refrigerant, a heat exchanger in the test space, a compressor, an oil unit, a gas cooler, and an expansion valve, the test chamber having a control device for controlling and / or regulating the temperature in the test space, the oil being separated from the refrigerant by at least one oil separator of the oil unit and being led to the compressor by a supply device of the oil unit, a refrigerant pressure P can be generated in the cooling circuit when the compressor is stopped and at a refrigerant temperature corresponding in particular to the ambient temperature by at least 20°C, and a partial amount of carbon dioxide can be absorbed by the oil, and the amount of carbon dioxide and / or the amount of oil in the cooling circuit for generating the pressure P is selected taking into account the absorption of the partial amount of carbon dioxide. With regard to the advantages of the test chamber according to the invention, reference is made to the description of the advantages of the method according to the invention.

[0032] The oil device may have a collector for storing oil, which may be formed separately or integrally with the oil separator. If the collector and the oil separator are formed separately, the collector may be connected via a line, and oil is conducted from the oil separator to the collector in the line. If the collector and the oil separator are formed integrally, the collector may be formed directly on the oil separator, for example in a common housing.

[0033] The temperature control device may include a heating device having a heater and a heating heat exchanger in the test space. For example, the heating device may be an electric resistance heater that heats the heating heat exchanger so that a temperature increase in the test space is possible through the heating heat exchanger. If the heat exchanger and the heating heat exchanger can be controlled and / or adjusted in a targeted manner by the control device to cool or heat the air circulating in the test space, the temperature control device can establish a temperature in the test space within the temperature range specified above.

[0034] Further embodiments of the test chamber are evident from the characterizing recitations of the dependent claims which refer back to method claim 1.

[0035] In the following, preferred embodiments of the present invention will be described in more detail with reference to the accompanying drawings. [Brief explanation of the drawings]

[0036] [Figure 1] FIG. 1 shows one embodiment of a cooling device. [Figure 2] FIG. 2 shows a diagram of carbon dioxide being entrapped in refrigerant oil. DETAILED DESCRIPTION OF THE INVENTION

[0037] FIG. 1 shows a possible embodiment of a cooling device 10 of a test chamber (not shown in this example). The cooling device 10 comprises a cooling circuit 11 using carbon dioxide (CO2) as a refrigerant, a heat exchanger 12, a low-pressure compressor 13, a high-pressure compressor 14, a gas cooler 15, an expansion valve 16, and a valve device 17. In this example, the gas cooler 15 is configured in the form of a heat exchanger and is cooled by a heat transfer medium such as air or water. The heat exchanger 12 is arranged in an air handling duct (not shown in this example) of the test chamber so that a fan (not shown in this example) can circulate air in the test space through the heat exchanger 12. Furthermore, the cooling circuit 11 has a low-pressure side portion 18, an intermediate-pressure side portion 19, a high-pressure side portion 20, and an intermediate-pressure side portion 21. The pressure of the refrigerant in the low-pressure side portion 18 is relatively lower than that in the intermediate-pressure side portion 19. In the intermediate pressure side portion 19, the pressure of the refrigerant is relatively lower than that in the medium pressure side portion 21, and in the medium pressure side portion 21, the pressure of the refrigerant is relatively lower than that in the high pressure side portion 20.

[0038] Downstream of the gas cooler 15 in the refrigerant flow direction, the cooling circuit 11 further comprises an internal heat exchanger 22 and a high-pressure valve 23, through which the gaseous refrigerant is expanded and / or metered into a storage device 24. The storage device 24 is realized as a pressure vessel 25, in which a phase boundary 26 is formed between the liquid phase and the gaseous refrigerant. A flash gas bypass section 27 of the cooling circuit 11, which has a flash gas valve 28, is connected to the storage device 24 in such a way that the gaseous refrigerant can be taken from the storage device 24 and led to the intermediate-pressure side part 19 downstream of the low-pressure compressor 13 and upstream of the high-pressure compressor 14 in the refrigerant flow direction. Furthermore, a line section 29 is connected to the storage device 24 so that the liquid refrigerant can be taken from the storage device 24 and led to the expansion valve 16.

[0039] The refrigerant flowing from the gas cooler 15 to the high-pressure valve 23 can be subcooled by the internal heat exchanger 22, and in this case, the refrigerant flowing through the flash gas valve 28 into the intermediate-pressure section 19 upstream of the high-pressure compressor 14 can be superheated in the internal heat exchanger 22. This ensures that the gaseous refrigerant is located upstream of the high-pressure compressor 14, and that the high-pressure compressor 14 can only draw this refrigerant.

[0040] The cooling circuit 11 further comprises an intermediate-pressure bypass section 30 having an intermediate-pressure valve 31, which is connected to the line section 29 downstream of the storage device 24, to the cooling circuit 11, and / or to the intermediate-pressure side section 19 downstream of the low-pressure compressor 13 and upstream of the high-pressure compressor 14. Liquid refrigerant can be metered from the storage device 24 to the intermediate-pressure side section 19 by the intermediate-pressure valve 31, for example, if the temperature of the refrigerant is reduced upstream of the high-pressure compressor 14. The cooling circuit 11 further comprises a low-pressure bypass section 32 having a low-pressure valve 33, which is connected to the line section 29 downstream of the storage device 24 and to the low-pressure side section 18 immediately upstream of the low-pressure compressor 13 and downstream of the valve device 17. Liquid refrigerant can be metered from the storage device 24 to the low-pressure section 18 upstream of the low-pressure compressor 13 by the low-pressure valve 33, for example, when the refrigerant drawn by the low-pressure compressor 13 is cooled.

[0041] The cooling circuit 11 has a further bypass part 34 with a further valve 35. The further bypass part 34 is connected to the line section 29 downstream of the storage medium 24 and to the low-pressure part 18 of the cooling circuit 11 downstream of the heat exchanger 12 and upstream of the valve device 17. By means of the further valve 35, liquid refrigerant can be metered from the storage device 24 to the low-pressure part 18 upstream of the valve device 17. This makes it possible to cool the valve device 17 as needed and to provide a sufficient mass flow to the low-pressure compressor 13 or the high-pressure compressor 14.

[0042] Furthermore, the cooling circuit 11 has a regulating bypass section 36 with a regulating valve 37. The regulating bypass section 36 is connected to the intermediate pressure section 19 downstream of the low-pressure compressor 13 and upstream of the high-pressure compressor 14, and is also connected to the low-pressure section 18 of the cooling circuit 11 upstream of the low-pressure compressor 13 and downstream of the valve device 17. Refrigerant can be metered from the intermediate pressure section 19 to the low-pressure section 18 via the regulating valve 37. This makes it possible to regulate the suction gas temperature and / or suction gas pressure of the refrigerant in the low-pressure section 18 upstream of the low-pressure compressor 13 and to equalize the pressure difference between the intermediate pressure section 19 and the low-pressure section 18 of the cooling circuit 11, if necessary.

[0043] The valve device 17 is realized by a three-way valve 38. Depending on the temperature requirements of the test chamber control device (not shown), the control device operates the three-way valve 38 to direct the refrigerant flowing from the heat exchanger 12 directly to the low-pressure compressor 13 via a low-pressure line 39 directly connected to the three-way valve 38. After being compressed by the low-pressure compressor 13, the refrigerant travels to the high-pressure compressor 14 for further compression. The control device can also operate the three-way valve 38 to allow the refrigerant to reach the high-pressure compressor 14 by bypassing the low-pressure compressor 13 via a compressor bypass section 40 directly connected to the three-way valve 38. The compressor bypass section 40 is connected to the intermediate-pressure section 19 downstream of the low-pressure compressor 13 and upstream of the high-pressure compressor 14. Therefore, depending on the temperature requirements, the low-pressure compressor 13 can be operated together with the high-pressure compressor 14, or the high-pressure compressor 14 can be operated alone. In this case, the low-pressure compressor 13 is turned off, achieving significant energy savings. The high pressure compressor 14 is operated alone, in particular when a temperature of, for example, -20°C is to be established in the test space. The low pressure compressor 13 and the high pressure compressor 14 are operated together when a temperature of, for example, -50°C is to be established in the test space.

[0044] The heat exchanger 12 is preferably realized with only one exchanger body (not shown in this example), and only one line of the cooling circuit 11 runs inside the exchanger body. The surface area of ​​the exchanger body can therefore be fully used with the cooling circuit 11, which is why the temperature difference between the atmosphere of the test space and the atmosphere of the heat exchanger 12 can be considerably small when a temperature change is to be established in the test space. Furthermore, a heating device (not shown in this example) comprising a heater and a heating heat exchanger is provided in the test space.

[0045] The cooling system 10 further includes an oil unit 41. The oil unit 41 includes an oil separator 42 and a supply unit 43. The supply unit 43 is realized by a supply line 44 having a supply valve 45 and metering valves 46 and 47. The oil separator 42 further includes a collector (shown diagrammatically in this example) integrally formed with the oil separator 42, but details thereof are not shown. The oil in the cooling circuit 11 serves to lubricate the low-pressure compressor 13 and the high-pressure compressor 14 during operation. The oil separator 42 is arranged downstream of the high-pressure compressor 14 and upstream of the gas cooler 15 in the cooling circuit 11 in the refrigerant flow direction, and separates the oil from the refrigerant and / or carbon dioxide flowing through the oil separator 42. The oil in the collector is led via the supply valve 45 to the supply line 44, from which it is led to the low-pressure compressor 13 and the high-pressure compressor 14. Metering valves 46 and 47 are located in the supply line 44 immediately upstream of the low-pressure compressor 13 and the high-pressure compressor 14, respectively, and the metering valves 46, 47 allow the desired amount of oil to be introduced into the respective compressors 13 and 14 to lubricate them, where the oil returns to the cooling circuit 11 and to the oil separator 42. In this way, the oil circulates in the circuit 48 of the oil unit 41.

[0046] If the compressors 13, 14 are switched on, a temperature of the refrigerant close to the ambient temperature, for example 20° C., occurs during a prolonged shutdown of the compressors 13, 14. Furthermore, pressure equalization is achieved in the cooling circuit 11, for example via the further bypass 34 and the regulating bypass 36, so that a fairly uniform pressure P of the refrigerant prevails in the cooling circuit 11. In this process, a partial amount of carbon dioxide is absorbed by the oil, in particular by the oil in the oil separator 42 and / or the collector, so that the amount and / or volume of carbon dioxide in the cooling circuit 11 is reduced until the pressure P reaches the maximum permissible pressure P for the cooling circuit 11. max Therefore, there is no need to provide shutdown cooling or to reduce the pressure to the maximum allowable pressure P on the cooling circuit 11. max There is no need to provide a safety valve to limit the

[0047] The diagram in FIG. 2 shows the ratio of the pressure P (bar) to the temperature T (°C) of the refrigerant in the cooling circuit 11. It can be seen that a certain weight percentage of the total amount of carbon dioxide in the cooling circuit 11 is absorbed by the oil. This is shown by a characteristic curve field with parameters in weight percentage in this example. For example, if the cooling circuit 11 has a volume of approximately 70 liters of carbon dioxide and 7 liters of oil, a mass of 9.7 kg of carbon dioxide results. The weight percentage of carbon dioxide absorbed in the oil is, for example, 28 weight percent or mass percent at a temperature of 21.8°C and a pressure of 43 bar (4.3 MPa). In this case, the oil absorbs a mass of 1.9 kg of carbon dioxide. Therefore, 7.8 kg of carbon dioxide remains in the cooling circuit. In contrast, if the absorption of carbon dioxide in the oil is ignored, the pressure would be approximately 40 bar (4 MPa).

Claims

1. A method for conditioning the air in a test space of a test chamber, in particular a climate chamber, for receiving test materials, said test space being sealable and insulated against the environment, in which a temperature ranging from -20°C to +180°C is established by a cooling device (10) of a temperature control device of the test chamber, said cooling device (10) using carbon dioxide (CO ) as a refrigerant. ２ ), a heat exchanger (12) in the test space, a compressor (13, 14), an oil unit (41), a gas cooler (15) and an expansion valve (16), the temperature in the test space being controlled and / or regulated by a control device of the test chamber, oil being separated from the refrigerant by at least one oil separator (42) of the oil unit and being led to the compressor by a supply device (43) of the oil unit, and a pressure P of the refrigerant is generated in the cooling circuit when the compressor is stopped and at a temperature of the refrigerant corresponding in particular to the ambient temperature by at least 20° C., a partial amount of carbon dioxide is absorbed by the oil, and the amount of carbon dioxide and / or the amount of oil in the cooling circuit (11) for generating a pressure P is selected taking into account the absorption of the partial amount of carbon dioxide.

2. 2. The method according to claim 1, characterized in that the partial amount of the carbon dioxide is absorbed by the oil during shutdown of the compressor (13, 14) and at a temperature of the refrigerant of at least 20°C.

3. 3. The method according to claim 1 or 2, characterized in that the ratio between the amount of carbon dioxide and the amount of oil in the cooling circuit (11) is selected taking into account the absorption of the partial amount of carbon dioxide.

4. 4. The method according to claim 1, wherein the amount of oil in the cooling circuit (11) is selected to be greater than the amount of oil required for the operation of the compressors (13, 14).

5. 5. The method according to claim 1, wherein in the cooling circuit (11), the pressure P of the refrigerant is less than or equal to the maximum allowable pressure Pmax of the refrigerant for the cooling circuit.

6. 6. The method according to claim 1, wherein the refrigerant is neither cooled by shutdown cooling nor discharged from the cooling circuit by a safety valve during the shutdown of the compressors and at a temperature of the refrigerant of at least 20°C.

7. 7. The method according to claim 1, wherein oil is stored by a collector of the oil device (41), and the oil in the collector is led to the compressors (13, 14) via at least one supply valve (45) in a supply line (44) of the supply device (43).

8. 8. The method according to claim 7, characterized in that the supply valve (45) is opened when the compressors (13, 14) are running and the supply valve is closed when the compressors (13, 14) are stopped.

9. 9. A method according to claim 7 or 8, characterized in that oil is metered to the compressors in the supply line (44) leading to the compressors (13, 14) by means of metering valves (46, 47) of the supply device (43).

10. 10. The method according to claim 7, wherein the fractional amount of oil in the collector is increased with an increase in the temperature of the refrigerant and is decreased with a decrease in the temperature of the refrigerant by the oil device (41).

11. 11. Method according to any one of claims 7 to 10, characterized in that the oil fraction in the collector is adjusted essentially linearly with respect to the temperature of the refrigerant by the oil device (41).

12. 12. Method according to any one of claims 7 to 11, characterized in that the filling volume of the collector is at least as large as the volume of oil in the cooling circuit (11).

13. 13. The method according to any one of claims 1 to 12, characterized in that a polyol ester oil is used as the oil.

14. 14. The method according to any one of claims 1 to 13, characterized in that the cooling circuit is realized to have a low-pressure compressor (13) and a high-pressure compressor (14) downstream of the low-pressure compressor in the flow direction of the refrigerant.

15. Pure carbon dioxide (CO ２ 15. The method according to claim 1, wherein a mixture of 100% by weight of ethanol and 100% by weight of ethanol is used as the refrigerant.

16. 16. The method according to any one of claims 1 to 15, characterized in that the cooling circuit (11) is operated in a thermodynamically transcritical or subcritical state.

17. 17. The method according to any one of claims 1 to 16, characterized in that the temperature control device establishes a temperature in the test space in the temperature range of -40°C to +180°C, preferably -55°C to +180°C.

18. A test chamber, in particular a climate chamber, for conditioning the atmosphere, comprising a test space for receiving a test material, the test space being sealable and insulated against the environment, and a temperature control device for controlling the temperature of the test space, in which a temperature in the range of -20°C to +180°C can be established by means of the temperature control device, the temperature control device comprising a cooling device (10), a cooling circuit (11) using carbon dioxide as a refrigerant, a heat exchanger (12) in the test space, compressors (13, 14), and an oil device (4). a cooling device (10) comprising an oil cooler (1), a gas cooler (15) and an expansion valve (16), the test chamber having a control device for controlling and / or regulating the temperature in the test space, wherein oil can be separated from the refrigerant by at least one oil separator (42) of the oil device and can be led to the compressor by a supply device (43) of the oil device, and a pressure P of the refrigerant can be generated in the cooling circuit when the compressor is stopped and at a temperature of the refrigerant that corresponds in particular to the ambient temperature by at least 20° C., A test chamber characterized in that a portion of the carbon dioxide can be absorbed by the oil, and the amount of carbon dioxide and / or the amount of oil in the cooling circuit for generating a pressure P is selected taking into account the absorption of the portion of the carbon dioxide.

19. 19. A test chamber according to claim 18, characterized in that the oil device (41) has a collector for storing oil, the collector being formed separately or integrally with the oil separator (42).

20. 20. The test chamber according to claim 18 or 19, characterized in that the temperature control device comprises a heating device in the test space, the heating device having a heater and a heating heat exchanger.

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