Test room and control method

Abstract

The invention relates to a method and a test chamber for conditioning air in a test chamber, in particular a climate chamber, in a test space for receiving a test material, the test space being configured to be sealed and temperature-isolated from the environment, the cooling device (10) of the temperature control device of the test chamber comprises a cooling circuit (11) with carbon dioxide as a refrigerant, a heat exchanger (12) in the test space, a low-pressure compressor (13), a high-pressure compressor (14) downstream of the low-pressure compressor in the flow direction of the refrigerant, a gas cooler (15) and an expansion valve (17). The cooling device is used to establish a temperature in a temperature range of-20 DEG C to + 180 DEG C in the test space, and the control device of the test chamber is used to control the temperature in the test space. A further cooling circuit (34) of the cooling device serves to establish the temperature in the test space, the further cooling circuit having a further refrigerant, the heat exchanger, a further compressor (35), a further heat exchanger (36) and a further expansion valve (37).

Description

Field of the Invention

[0001] The present invention relates to a test chamber for conditioning air, in particular a climatic chamber, and to a method for conditioning air in a test space of the test chamber for receiving test materials, the test space being configured to be sealed and thermally insulated relative to the environment, the cooling device of the temperature control device of the test chamber comprising a cooling circuit using carbon dioxide as a refrigerant, a heat exchanger in the test space, a low-pressure compressor, and a high-pressure compressor downstream of the low-pressure compressor in the flow direction of the refrigerant, a gas cooler, and an expansion valve, the cooling device being used to establish a temperature in the test space within a temperature range of -20°C to +180°C, and the control device of the test chamber being used to control the temperature in the test space. Background Art

[0002] Such test chambers are often used to test the physical and / or chemical properties of objects, in particular devices. For example, there are known temperature test cabinets or climatic test cabinets in which temperatures in the range from -70°C to +180°C can be set. In the case of a climatic test cabinet, desired climatic conditions can additionally be set, and then a device or test material is exposed to the climatic conditions defined for a certain period of time. The temperature of the test space containing the test materials is regularly controlled in an air circulation duct in the test space. The air circulation duct forms an air treatment space in the test space, and a heat exchanger for heating or cooling the air flowing through the air circulation duct or the test space is provided in the air treatment space. A fan or a ventilator sucks the air in the test space and guides it through the air circulation duct to the corresponding heat exchanger. Thus, the test materials can be temperature-controlled or exposed to defined temperature variations. During a test interval, the temperature can vary, for example, between the maximum and minimum temperatures of the test chamber. For example, such a test chamber is known from EP0344397A2.

[0003] The refrigerant used in the cooling circuit should have a relatively low CO2 equivalent, i.e., the relative global warming potential (GWP) should be as low as possible to avoid indirect damage to the environment when the refrigerant is released. Therefore, it is also known that carbon dioxide (CO2) is used as a pure substance refrigerant. Carbon dioxide is available at low cost, is non-flammable, and is substantially environmentally neutral with a GWP of 1. Carbon dioxide has a freezing point temperature or triple point of -56.6°C, which makes it impossible to achieve lower temperatures by using carbon dioxide alone.

[0004] In addition, there is a known cooling device configured to be a so-called booster system. In the cooling circuit of the cooling device, a high-pressure compressor is always connected in series downstream of a low-pressure compressor, so that the refrigerant is compressed stepwise with the low-pressure compressor and then with the high-pressure compressor. Due to the high demand for temperature control within the temperature range of the test space, the load requirements fluctuate frequently during the operation of the test chamber. Therefore, the cooling capacity generated by the compressor and the expansion valve must be infinitely variable. However, in order to extend the service life of the compressor, it is desirable that the compressor is not switched on and off frequently.

[0005] Since carbon dioxide as a refrigerant has a very high volumetric cooling capacity, the cooling circuit provides a very high cooling capacity even when using a compressor with a very low displacement volume flow. In addition, in transcritical operation, the pressure range of the cooling circuit with carbon dioxide as a refrigerant is very high (up to 120 bar), which is why the components required to form the cooling circuit are relatively expensive. In addition, such a cooling circuit has a complex structure, which requires a large installation space. Therefore, so far, the use of such a cooling circuit with carbon dioxide as a refrigerant has only been meaningful for systems or test chambers with correspondingly high cooling capacities and thus relatively large test spaces or large device sizes. Economic use in relatively small systems or test chambers with a small test space volume (e.g., 25 liters) has not yet been possible.

[0006] In addition, there is the problem that it is almost impossible to establish a very low temperature, e.g., < -50 °C, for the use of carbon dioxide as a refrigerant or a majority of carbon dioxide in the refrigerant. This would require the use of less environmentally friendly and / or flammable (A3) or highly flammable (A2L) refrigerants. According to European standard EN2 or DIN 378 class A2, A2L, and A3 (in their latest versions at the priority date), a refrigerant is flammable, especially if it belongs to fire class C. Summary of the Invention

[0007] Therefore, an object of the present invention is to provide a method for regulating the air in the test space of a test chamber and a test chamber, which enable an environmentally friendly operation of the test chamber even at low temperatures.

[0008] This object is achieved by a method having the features of the present invention and a test chamber having the features of the present invention.

[0009] In a method for conditioning air in a test space for receiving a test material in a test chamber according to the invention, the test chamber being in particular a climate chamber, the test space being configured to be sealed and temperature-insulated relative to the environment, the cooling device of the temperature control device of the test chamber comprising a cooling circuit with carbon dioxide as the refrigerant, a heat exchanger in the test space, a low-pressure compressor and a high-pressure compressor downstream of the low-pressure compressor in the flow direction of the refrigerant, a gas cooler and an expansion valve, the cooling device being used to establish a temperature in the test space in the temperature range from -20 °C to +180 °C, the control device of the test chamber being used to control the temperature in the test space, wherein another cooling circuit of the cooling device is used to establish the temperature in the test space, the other cooling circuit having another refrigerant, the heat exchanger in the test space, another compressor, another heat exchanger and another expansion valve.

[0010] In the method according to the invention, heat exchange with the environment of the test space is largely avoided by means of insulating side walls, a bottom wall and a top wall. The heat exchanger is connected to or integrated into the cooling circuit such that the refrigerant circulating in the cooling circuit flows through the heat exchanger. The heat exchanger of the cooling circuit is arranged in the test space or in the air treatment space of the test space, so that the air in the test space is conditioned or temperature-controlled via the heat exchanger. The gas cooler is also integrated into the cooling circuit and is formed by a heat exchanger. The gas cooler is arranged in the cooling circuit downstream of the high-pressure compressor, the compressed refrigerant being at high pressure after compression and being substantially in gaseous or vapor form or as wet steam, so that it can be condensed in the gas cooler or condenser and then is substantially in a liquid aggregate state. It is also possible that the gaseous refrigerant does not condense in the gas cooler and leaves the gas cooler substantially in gaseous state. Then, the refrigerant is only heated and is above the critical point (supercritical fluid). The gas cooler or heat exchanger under discussion can be equipped with means for cooling the refrigerant, for example with air or water. In particular, the gas cooler can be an air-cooled finned tube heat exchanger. In this case, the gas cooler can be particularly compact. The refrigerant flows from the gas cooler via the expansion valve, through which the refrigerant again becomes gaseous, vapor or wet steam due to expansion caused by a pressure drop. In this process, the refrigerant flows through the heat exchanger, as a result of which the refrigerant is cooled. Here, the refrigerant absorbs heat from the test space via the heat exchanger. Subsequently, the gaseous refrigerant is sucked in and compressed again by the low-pressure compressor and the high-pressure compressor.

[0011] The term "expansion valve" refers at least to an expansion element, a throttling element, a throttle valve or another suitable constriction of a fluid conduit. The expansion valve and other valves of the cooling circuit are preferably controllable.

[0012] The invention aims to connect another cooling circuit of the cooling device to a heat exchanger within the test space. Another refrigerant in the another cooling circuit is always separated from the refrigerant of the cooling circuit. The heat exchanger is not connected to the corresponding cooling circuit. Thus, the heat exchanger can substantially form a first local heat exchanger for the cooling circuit and a second local heat exchanger for the another cooling circuit. These local heat exchangers can also be arranged at separate locations within the test space and then form the heat exchanger. The another cooling circuit has another heat exchanger which forms a gas cooler for the another refrigerant. Then, the another refrigerant can be compressed by the another compressor, cooled or liquefied in the another heat exchanger, and used to cool the heat exchanger via the another expansion valve. In this case, the another refrigerant of the another cooling circuit is different from the refrigerant of the cooling circuit. The another refrigerant can be selected such that the another refrigerant can be used to establish a lower temperature than the lowest temperature that can be established using the refrigerant. In summary, this enables a relatively low temperature to be established using the test chamber without the need for special modifications to the cooling circuit. In this case, it is possible to continue to use the environmentally friendly carbon dioxide as the refrigerant. The another cooling circuit can have a particularly simple and compact design and have a relatively less environmentally friendly refrigerant as the another refrigerant. Then, the cooling circuit can be operated during most of the operating time of the cooling device, while the another cooling circuit only needs to be operated when a relatively low temperature is to be reached, which is usually not a common situation. In this way, the amount of the relatively less environmentally friendly refrigerant of the cooling device can be significantly reduced. Since the another cooling circuit only operates when needed, energy can be saved. The safety-related technical measures that may be required are only necessary for a smaller part of the installation, which reduces costs.

[0013] Another bypass with at least one other valve and the other heat exchanger is formed in the cooling circuit, wherein the other bypass can be connected to the high-pressure side downstream of the gas cooler and upstream of the expansion valve and to the low-pressure side downstream of the heat exchanger and upstream of the low-pressure compressor, refrigerant can be metered into the low-pressure side via the other valve, and the other refrigerant of the other cooling circuit can be cooled in the other heat exchanger. Thus, the cooling circuit can be used to cool the other heat exchanger or the gas cooler of the other cooling circuit via the other bypass. The other valve can be an expansion valve or a simple throttle valve. Thus, a part of the cooling capacity of the cooling circuit can be used to condense (i.e., liquefy) the other refrigerant to operate the other cooling circuit. Thus, the cooling circuit can be used particularly efficiently. However, in principle, the other heat exchanger can also be cooled in another way, for example, by air or water.

[0014] A reservoir for the other refrigerant can be connected to the other cooling circuit, wherein the other refrigerant is moved to the reservoir at a temperature in the temperature range of +50 °C to +180 °C within the test space. This also makes it possible to use a relatively less environmentally friendly refrigerant as the other refrigerant. If the refrigerant is flammable or highly flammable, the other refrigerant can be moved entirely or mostly into the reservoir so that little or no other refrigerant is present in the heat exchanger. Especially at higher temperatures within the test space, in the case of a leak in the heat exchanger or the other cooling circuit within the test space, there is a risk of the other refrigerant leaking into the test space, in which case an explosive mixture may be formed within the test space. When the other cooling circuit is not in operation, the other refrigerant can be moved to the reservoir so that additional safety-related technical features (such as sensors, etc.) are unnecessary. For example, the other refrigerant can be moved to the reservoir via the other compressor, additional valves, etc. The reservoir can be a tank for holding the other refrigerant.

[0015] It is intended that the other compressor operates within the test space at least at a temperature of < -50 °C. The operation of the corresponding compressor can be controlled by the control device. The cooling circuit can operate at temperatures up to -50 °C, and the triple point of carbon dioxide makes it difficult to reach lower temperatures. If it is necessary to establish a lower temperature within the test space, the other cooling circuit with the other compressor can be used to achieve this. In this case, all compressors, i.e., the cooling circuit and the other cooling circuit, can be operated simultaneously.

[0016] The cooling circuit may have an internal heat exchanger, which may be connected to the high-pressure side of the cooling circuit downstream of the gas cooler and upstream of the expansion valve, and the internal heat exchanger may be coupled to a medium-pressure bypass of the cooling circuit, and the medium-pressure bypass may be connected to the high-pressure side, downstream of the internal heat exchanger, upstream of the gas cooler and upstream of the expansion valve, and connected to the medium-pressure side of the cooling circuit, upstream of the high-pressure compressor and downstream of the low-pressure compressor, and via another expansion valve, refrigerant may be metered from the high-pressure side through the internal heat exchanger into the medium-pressure side. Immediately downstream of the internal heat exchanger and upstream of the expansion valve, the medium-pressure bypass and another expansion valve may thus be connected to the circuit. Then, the refrigerant that has passed through the internal heat exchanger may also be fed and expanded via the another expansion valve. The internal heat exchanger may also be connected in the medium-pressure bypass downstream of the another expansion valve. The refrigerant expanded at the another expansion valve flows through the internal heat exchanger, as a result of which it is cooled. Thus, the refrigerant in the internal heat exchanger in the medium-pressure side and thus in the high-pressure side of the internal heat exchanger is cooled. However, in principle, the medium-pressure bypass may also be connected to the cooling circuit downstream of the gas cooler and upstream of the internal heat exchanger, such that the refrigerant then flows through an additional expansion valve and the internal heat exchanger. Downstream of the internal heat exchanger, the medium-pressure bypass may be connected between the low-pressure compressor and the high-pressure compressor, such that the refrigerant routed via the medium-pressure bypass may be mixed with the refrigerant circulating in the cooling circuit at this location. By using the medium-pressure bypass with the internal heat exchanger, the refrigerant may be diverted through the medium-pressure bypass according to the cooling load requirements of the control device, such that less refrigerant flows through the expansion valve. At the same time, the refrigerant flowing through the medium-pressure bypass may be used to control the temperature of the refrigerant on the high-pressure side through the internal heat exchanger. Thus, when a smaller cooling capacity is required in the test space, the very high volumetric cooling capacity of carbon dioxide is diverted upstream of the heat exchanger and used to cool the refrigerant on the high-pressure side. This also allows the test space to be smaller and enables a cooling circuit operating with carbon dioxide to be used for a more compact test chamber.

[0017] Via the second expansion valve, refrigerant can be metered from the high-pressure side into the medium-pressure side via the internal heat exchanger such that the refrigerant becomes fully gaseous, i.e., decompressed, in the internal heat exchanger and / or the refrigerant located in the medium-pressure side is cooled. Thus, the compressed and highly superheated refrigerant can be cooled downstream of the low-pressure compressor. The second expansion valve can also cool the medium-pressure side of the internal heat exchanger to additionally cool the transcritical refrigerant located on the high-pressure side of the internal heat exchanger. Furthermore, the colder refrigerant flowing through the medium-pressure bypass can then be introduced between the low-pressure compressor and the high-pressure compressor. When the low-pressure compressor is in operation, it delivers refrigerant from the low-pressure side of the cooling circuit to the medium-pressure side, at which time the refrigerant can already have a very high temperature. This can result in a thermal overload at the high-pressure compressor. This thermal overload can be avoided by mixing relatively cold refrigerant via the medium-pressure bypass.

[0018] The internal heat exchanger can be used to subcool the refrigerant on the high-pressure side. The enthalpy difference at the heat exchanger can be increased by this additional subcooling, which in turn results in an increase in the cooling capacity of the heat exchanger. This enables the efficient establishment of particularly low temperatures within the test space.

[0019] Via the second expansion valve, refrigerant can be metered from the high-pressure side into the medium-pressure side such that the refrigerant mass flow rate at the high-pressure compressor is always greater than the refrigerant mass flow rate at the low-pressure compressor. If the refrigerant is subcooled due to the internal heat exchanger, no dissipation occurs at the heat exchanger because the mass flow rate delivered via the high-pressure compressor can be significantly greater than the mass flow rate delivered via the low-pressure compressor. The reason is that the density of the refrigerant at the inlet of the high-pressure compressor is significantly higher compared to the density of the refrigerant at the inlet of the low-pressure compressor. The mass flow rate in the cooling circuit can be described by the following equation: 0 = m 高压压缩机 – (m 低压压缩机 + m 内部热交换器 )). Thus, the mass flow rate of the internal heat exchanger is the result of the difference between the mass flow rate of the high-pressure compressor and the mass flow rate of the low-pressure compressor. The control device can be configured to always maintain this ratio by controlling the second expansion valve. In this way, a pressure drop on the medium-pressure side can be prevented. This pressure drop on the medium-pressure side can cause a change in the pressure ratio at the high-pressure compressor, which can cause the high-pressure compressor and / or the low-pressure compressor to exceed the expected usage threshold, which is to be avoided.

[0020] For example, the second expansion valve can be controlled based on the pressure and / or temperature of the refrigerant located in the medium-pressure side. Appropriate sensors can be used to measure the pressure and / or temperature. Then, the second expansion valve can be controlled by the control device or the adjustment feature of the control device such that the intake temperature of the high-pressure compressor and / or the pressure on the inlet side of the high-pressure compressor is within the required range. In this way, possible damage to the high-pressure compressor and / or the low-pressure compressor due to inappropriate temperature and pressure can be avoided by a simple device.

[0021] If the cooling circuit can be operated in a part-load operation state, the pressure of the refrigerant on the high-pressure side can be reduced. In the part-load operation state, the cooling circuit is not operated at full load. Rather, due to the reduced cooling load requirement of the control device or the test space, the expansion valve opens intermittently, i.e., not permanently or fully open. Since the refrigerant on the high-pressure side has a lower pressure, the final compression temperature of the high-pressure compressor can also be lower, which means that the heat emitted via the gas cooler is reduced via the environment in which the test chamber is located. As a result, the heat load on the room in which the test chamber is installed can be reduced, and the room in which the test chamber is installed may or may not be equipped with air conditioning equipment. In the part-load operation state, only a very low cooling capacity is required, for example, less than 2% of the cooling capacity of the cooling circuit, and / or at a temperature of, for example, ≥ -10 °C in the test space. Since it is almost impossible to control the output of the compressor, when a low cooling capacity is required and / or when there is a small temperature difference between the target temperature and the actual temperature in the test space, a lower cooling capacity is achieved by reducing the pressure of the refrigerant on the high-pressure side without having to immediately shut down the compressor. In this way, frequent start-stop intervals of the low-pressure compressor and the high-pressure compressor can be avoided, which is why the compressor can operate with a long service life.

[0022] The high-pressure valve provided in the cooling circuit downstream of the gas cooler can be used to meter gaseous and / or liquid refrigerant into a storage tank for the refrigerant. The storage tank can be connected to the medium-pressure side of the cooling circuit upstream of the high-pressure compressor and downstream of the low-pressure compressor via a medium-pressure bypass of the cooling circuit, and a medium-pressure valve can be used to meter gaseous refrigerant from the storage tank into the medium-pressure side when the low-pressure compressor is shut down. Depending on the extraction point on the storage tank, liquid or gaseous refrigerant can be tapped from the storage tank. The liquid refrigerant can continue to be conveyed via the expansion valve, where, due to the pressure drop, the liquid refrigerant can expand back to the gaseous state. In doing so, it flows through the heat exchanger, as a result of which it is cooled. In this embodiment of the cooling circuit, it can be provided that the high-pressure valve is provided in the cooling circuit downstream of the gas cooler to meter gaseous and / or liquid refrigerant into the storage tank via the high-pressure valve. The storage tank is substantially a pressure vessel, wherein when a phase boundary is formed, the liquid refrigerant is stored in the lower region of the pressure vessel and the gaseous refrigerant is stored in the upper region of the pressure vessel. Depending on the extraction point, liquid or gaseous refrigerant can be extracted from the storage tank. Thus, the liquid refrigerant can be supplied to the expansion valve and decompressed therein in order to cool the heat exchanger.

[0023] The cooling circuit can be operated in a thermodynamically subcritical or transcritical operating state. Depending on the cooling load requirements in the test space, the control device can be used to change the operating state accordingly. In the subcritical operation of the cooling circuit, the refrigerant is liquefied in the gas cooler at a temperature below the critical point of the refrigerant, and expands at the expansion valve and is transformed into a gas phase or wet steam. The high-pressure compressor and the low-pressure compressor can be operated at least in the subcritical operating state or at low ambient temperatures. The subcritical operating state of the cooling circuit corresponds to part-load operation. In the transcritical operating state, the refrigerant circulates in the cooling circuit substantially in a gaseous state. This means that the temperature difference is reduced to such an extent that the refrigerant does not liquefy in the gas cooler. In addition, in the transcritical operating state, a pressure above the critical point of the refrigerant is reached at the gas cooler. For example, if there are high cooling load requirements or a cooling from +180 °C to -20 °C is required, the cooling circuit can be operated transcritically. If there are low cooling load requirements in the test space, for example, if the temperature is to be kept constant, or if the ambient temperature is low, the cooling circuit can be operated subcritically. This allows for an increase in efficiency, especially in the case of low cooling load requirements (e.g., at low ambient temperatures), compared to just the transcritical operating state. The change between the subcritical operating state and the transcritical operating state can be achieved especially by means of the medium-pressure bypass and the internal heat exchanger.

[0024] A second bypass with at least one third expansion valve can be formed in the cooling circuit, and the second bypass can be connected to the high-pressure side downstream of the internal heat exchanger or the gas cooler and upstream of the expansion valve and to the low-pressure side downstream of the heat exchanger and upstream of the low-pressure compressor, and the suction gas temperature and / or suction gas pressure of the refrigerant on the low-pressure side of the cooling circuit upstream of the low-pressure compressor can be controlled by metering the refrigerant into the low-pressure side via the third expansion valve. The third expansion valve can be used to influence the suction gas temperature and / or suction gas pressure upstream of the low-pressure compressor such that the final compression temperature of the low-pressure compressor is within the desired operating range of the low-pressure compressor. For example, if the temperature in the test space is to be reduced, e.g., from +180 °C to a lower temperature, the suction gas temperature of the low-pressure compressor can increase particularly sharply. Since the heat exchanger is located in the test space, for example, at a particularly high temperature of +180 °C in the test space, the refrigerant can flow from the heat exchanger to the low-pressure compressor at this temperature. Before the severely superheated refrigerant is fed to the low-pressure compressor, it can be cooled by the refrigerant metered via the third expansion valve.

[0025] A control bypass with at least one control valve can be formed in the cooling circuit, and the control bypass can be connected to the high-pressure side downstream of the high-pressure compressor and upstream of the gas cooler and to the low-pressure side downstream of the heat exchanger and upstream of the low-pressure compressor, and can control the suction gas temperature and / or suction gas pressure of the refrigerant on the low-pressure side of the cooling circuit upstream of the low-pressure compressor, and / or can balance the pressure difference between the high-pressure side and the low-pressure side of the cooling circuit by metering refrigerant provided to the low-pressure side via the control valve. Thus, the control bypass is configured such that the refrigerant can be fed from the high-pressure side to the low-pressure side via the control valve. The refrigerant can be superheated or gaseous. If the cooling circuit is operated in a part-load operation state, it is particularly advantageous to return superheated refrigerant from the high-pressure side to the low-pressure side via the control bypass. Since the expansion valve is rarely opened in this case, there is a risk that the suction pressure upstream of the low-pressure compressor drops too much. When using carbon dioxide as the refrigerant, dry ice can form at an absolute pressure below 5.16 bar, which can disrupt the safe operation of the cooling circuit and may damage the low-pressure compressor. Since highly superheated refrigerant can be fed directly downstream of the high-pressure compressor to the point upstream of the low-pressure compressor via the control bypass, the formation of dry ice can be effectively prevented. In addition, for example, when the cooling device is not in operation and there is a risk that the refrigerant will be heated due to equilibrium with the ambient temperature and an undesirably high pressure will accumulate in the cooling circuit, the pressure difference between the high-pressure side and the low-pressure side of the cooling circuit can also be balanced via the control bypass.

[0026] The dehumidifier bypass of the cooling circuit can be used to dehumidify the air in the test space. The dehumidifier bypass includes a second heat exchanger and a dehumidifier valve in the test space. This dehumidification can occur at a point during a test cycle, particularly whenever the temperature in the test space is in the range of >0°C to <100°C. If the temperature in the test space is below or above this range, water cannot condense out in liquid form on the second heat exchanger, so the dehumidifier bypass does not function within these ranges. Thus, the cooling circuit of the cooling device can be designed such that a temperature between -20°C and +180°C can be established in the test space during a test cycle, and air dehumidification can be carried out via the dehumidifier bypass only within a portion of this temperature range. Dehumidification is carried out by metering the refrigerant from the high-pressure side of the cooling circuit to the low-pressure side via the dehumidifier valve. This results in the cooling of the second heat exchanger, which is arranged downstream of the dehumidifier valve in the flow direction of the refrigerant in the dehumidifier bypass. The control device can now meter the refrigerant via the dehumidifier valve such that a desired temperature difference is achieved between the temperature of the air in the test space and the temperature of the second heat exchanger. This temperature difference can be selected such that water from the air in the test space condenses on the second heat exchanger. This enables targeted dehumidification of the air in the test space to be carried out substantially independently of the temperature established in the test space. Thus, the expansion valve and the dehumidifier valve can be controlled independently of each other using the control device. Then, a decrease in the temperature in the test space can be accompanied by, for example, more or less dehumidification, whereby the relative humidity can be set or controlled more precisely. In summary, climate test cycles can be carried out much more accurately with just a few components in a compact test chamber.

[0027] The dehumidifier bypass can be connected to the high-pressure side of the cooling circuit downstream of the gas cooler and upstream of the expansion valve and to the low-pressure side of the cooling circuit downstream of the heat exchanger and upstream of the low-pressure compressor, and the refrigerant can be metered from the high-pressure side to the low-pressure side via the dehumidifier valve such that the second heat exchanger is cooled. The dehumidifier valve can be an electronic expansion valve or a solenoid valve having a downstream throttling device such as a capillary, nozzle, etc., or the dehumidifier valve can be a thermostatic expansion valve. Optionally, the dehumidifier bypass can also be connected downstream of any internal heat exchanger downstream of the gas cooler. Thus, the dehumidifier bypass can be connected in parallel with the expansion valve and the heat exchanger to the cooling circuit. In this way, the dehumidifier bypass can be of a particularly simple design.

[0028] A non-fluorinated refrigerant, preferably pure carbon dioxide, can be used as the refrigerant in the cooling circuit, and / or R469A can be used as another refrigerant in the other cooling circuit. Pure carbon dioxide has a GWP of 1, is non-flammable, non-hazardous and can be obtained at low cost. In addition, carbon dioxide is a pure substance or azeotropic, which first makes it possible to advantageously implement the method and its variations. On the other hand, refrigerants with azeotropic behavior can hardly provide a sufficient amount of gaseous refrigerant at a very low temperature difference and thus hardly allow performance control of the high-pressure compressor. R469A is a relatively environmentally friendly refrigerant with a relatively low GWP and is non-flammable due to its high carbon dioxide content. In particular, the other refrigerant allows the establishment of temperatures up to -80 °C in the test space or at the heat exchanger.

[0029] The temperature control device can be used to establish a temperature in the test space within a temperature range of -50 °C to +180 °C, preferably -80 °C to +180 °C, particularly preferably -90 °C to +180 °C.

[0030] A test chamber (in particular a climatic chamber) for conditioning air according to the invention comprises: a test space for receiving a test material, the test space being configured to be sealed and temperature-insulated with respect to the environment; and a temperature control device for controlling the temperature of the test space, the temperature control device being configured to establish a temperature in the test space within a temperature range of -20 °C to +180 °C, the temperature control device comprising a cooling device having a cooling circuit with carbon dioxide as the refrigerant, a heat exchanger in the test space, a low-pressure compressor and a high-pressure compressor downstream of the low-pressure compressor in the flow direction of the refrigerant, a gas cooler and an expansion valve, the test chamber comprising a control device for controlling the temperature in the test space, wherein the cooling device comprises another cooling circuit having another refrigerant, the heat exchanger in the test space, another compressor, another heat exchanger and another expansion valve. Regarding 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.

[0031] The temperature control device can have a heating device and a heating heat exchanger in the test space, the heating device having a heater. For example, the heating device can be a resistance heater that heats the heating heat exchanger so that an increase in the temperature in the test space can be achieved via the heating heat exchanger. If the heat exchanger and the heating heat exchanger can be controlled in a targeted manner by the control device to cool or heat the air circulating in the test space, a temperature within the temperature range specified above can be established in the test space by the temperature control device.

[0032] The low-pressure compressor and the high-pressure compressor can share a housing. In addition, the low-pressure compressor and the high-pressure compressor can be driven by a common (i.e., the same) motor. In this case, the cooling device can have a particularly compact design.

[0033] Other embodiments of the test chamber are apparent from the description of other features of the present invention. Description of the Drawings

[0034] Hereinafter, a preferred embodiment of the present invention will be explained in more detail with reference to the accompanying drawings.

[0035] Figure 1 is a schematic illustration of a cooling device; Figure 2 is a pressure-enthalpy diagram of the operating state of a cooling circuit. Detailed Description of the Invention

[0036] Figure 1 Shows a possible embodiment of a cooling device 10 for a test chamber (not shown). The cooling device 10 includes a cooling circuit 11 with carbon dioxide (CO2) as the refrigerant, a heat exchanger 12, a low-pressure compressor 13, a high-pressure compressor 14, a gas cooler 15, an internal heat exchanger 16, and an expansion valve 17. In the present case, the gas cooler 15 is configured as a heat exchanger or condenser 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) of the test space of the test chamber such that the air in the test chamber circulating via this air handling duct can be cooled by the heat exchanger 12. In addition, the cooling circuit 11 has a low-pressure side 19, a medium-pressure side 20, and a high-pressure side 21. In the low-pressure side 19, the pressure of the refrigerant is relatively lower than in the medium-pressure side 20, and in the medium-pressure side 20, the pressure of the refrigerant is relatively lower than in the high-pressure side 21.

[0037] The cooling circuit 11 also has an internal heat exchanger 16 downstream in the flow direction of the refrigerant and a medium-pressure bypass 22 upstream of the expansion valve 17, the medium-pressure bypass 22 terminating downstream of the low-pressure compressor 13 and upstream of the high-pressure compressor 14. A second expansion valve 23 is provided in the medium-pressure bypass 22. The second expansion valve 23 is connected upstream of the internal heat exchanger 16. The substantially liquid refrigerant can now be fed from the gas cooler 15 through the high-pressure side 21 of the internal heat exchanger 16 and, if required, metered via the second expansion valve 23 into the medium-pressure side 20 of the internal heat exchanger 16. In this process, the refrigerant on the high-pressure side 21 is subcooled to such an extent that a lower temperature can be established at the expansion valve 17 or the heat exchanger 12. At the same time, the refrigerant flowing through the medium-pressure bypass 22 can be used to keep the suction gas temperature of the high-pressure compressor 14 relatively low.

[0038] In addition, the cooling circuit 11 includes a second bypass 24 having a third expansion valve 25. The second bypass 24 is connected to the cooling circuit 11 downstream of the internal heat exchanger 16 and upstream of the expansion valve 17 and downstream of the heat exchanger 14 and upstream of the low-pressure compressor 13 in the refrigerant flow direction. Via the third expansion valve 25, the liquid refrigerant can be fed to the low-pressure side 19 via the expansion valve 17 and the heat exchanger 12. This enables the suction gas temperature and / or the suction gas pressure in the low-pressure side 19 upstream of the low-pressure compressor 13 to be controlled.

[0039] In addition, the cooling circuit 11 includes a control bypass 26 having a control valve 27. The control bypass 26 is connected to the cooling circuit 11 downstream of the high-pressure compressor 14 and upstream of the gas cooler 15 and downstream of the heat exchanger 12 and upstream of the low-pressure compressor 13 in the refrigerant flow direction. Via the control bypass 26 or the control valve 27, the refrigerant, in particular the superheated refrigerant or the gaseous refrigerant, can be fed from the high-pressure side 21 to the low-pressure side 19 upstream of the low-pressure compressor 13 depending on the operating state of the cooling circuit 11. This also enables the suction gas temperature and / or the suction gas pressure in the low-pressure side 19 upstream of the low-pressure compressor 13 to be controlled. The control can be carried out by a control device (not shown) of the test chamber and sensors located in the cooling circuit 11, in particular pressure sensors and temperature sensors.

[0040] Figure 2 A pressure-enthalpy diagram (log-P-H diagram) of the refrigerant circulating in the cooling circuit 11 is shown for the operating state of the cooling circuit 11 when the low-pressure compressor 13 and the high-pressure compressor 14 are operating. In this diagram, the specific enthalpy is shown on the abscissa and the logarithmically scaled pressure is shown on the ordinate. The boiling line 28 marks the transition from saturated liquid to wet steam, and the dew line 29 marks the transition from wet steam to saturated steam. The boiling line 28 and the dew line 29 meet at the critical point 30.

[0041] Figure 2Shows the supercritical operating state of the cooling circuit 11, in which, starting from position A, the refrigerant is sucked in by the low-pressure compressor 13 from the low-pressure side 19 and compressed, resulting in a pressure corresponding to position B downstream of the low-pressure compressor 13. Then, the refrigerant is sucked in by the high-pressure compressor 14 downstream of position C and compressed to position D. As a result, the refrigerant flows through the gas cooler 15 in a transcritical state and is liquefied or desuperheated. Thereafter, the refrigerant passes through the internal heat exchanger 16 and reaches position E. A part of the liquid refrigerant flows through the expansion valve 17, where the refrigerant expands (from position E to position F), and the refrigerant evaporates in the heat exchanger 12 (from position F to position A). Another part of the refrigerant flows through the medium-pressure bypass 22, where the refrigerant also expands in the second expansion valve 23 (from position E to position G), and the refrigerant evaporates in the internal heat exchanger 16 (from position G to position C). At position C, the refrigerant from the medium-pressure bypass 22 is mixed with the refrigerant from the low-pressure compressor 13.

[0042] In addition, a dehumidifier bypass 31 with a dehumidifier valve 32 and a second heat exchanger 33 also located in the test space are provided in the cooling circuit 11. The air in the test space can be dehumidified by passing through the second heat exchanger 33 or the dehumidifier bypass 31. For this purpose, the test chamber has a control device (not shown), with which the temperature and / or relative humidity in the test space can be controlled. For this, the control device can in particular activate the expansion valve 17 and the second expansion valve 23. This enables the cooling device 10 to be used to perform climate tests, in which the dehumidification or relative humidity in the test space can be very accurately established even when the temperature in the test space is constant or decreasing.

[0043] In addition, the cooling device 10 includes another cooling circuit 34, which has another refrigerant, a heat exchanger 12, another compressor 35, another heat exchanger 36, and another expansion valve 37. Alternatively, a carbon dioxide-based refrigerant or a flammable refrigerant can be used as the other refrigerant. The other cooling circuit 34 is used to additionally cool the test space via the heat exchanger 12.

[0044] Another bypass 38 with another valve 39 is formed in the cooling circuit 11. The another bypass 38 extends via another heat exchanger 36 and is connected to the high-pressure side 21 downstream of the gas cooler 15 and upstream of the expansion valve 17 and is connected to the low-pressure side 19 downstream of the heat exchanger 12 and upstream of the low-pressure compressor 13. The another valve 39 can now be used to meter refrigerant into the low-pressure side 19 or into the another heat exchanger 36. This cools another refrigerant of another cooling circuit 34 in the another heat exchanger 36 and liquefies it by condensation. When a temperature below -50 °C is to be established in the test space, then the another cooling circuit 34 can be put into operation. This makes it possible to establish a temperature of up to -80 °C in the test space.

Claims

1. A method for conditioning the air in a test space of a test chamber for receiving test material, the test chamber being in particular a climate chamber, the test space being configured to be sealed and temperature-isolated relative to the environment, the cooling device (10) of the temperature control device of the test chamber comprising a cooling circuit (11) with carbon dioxide (CO2) as refrigerant, a heat exchanger (12) in the test space, a low-pressure compressor (13) and a high-pressure compressor (14) located downstream of the low-pressure compressor in the flow direction of the refrigerant, a gas cooler (15) and an expansion valve (17), the cooling device (10) being used to establish a temperature in the test space within a temperature range of -20°C to +180°C, the control device of the test chamber being used to control the temperature in the test space, It is characterized in that A further cooling circuit (34) of the cooling device is used to establish the temperature in the test space, the further cooling circuit (34) having another refrigerant, the heat exchanger in the test space, another compressor (35), another heat exchanger (36) and another expansion valve (37).

2. The method according to claim 1, It is characterized in that A further bypass (38) having at least one further valve (39) and the further heat exchanger (36) is formed in the cooling circuit (11), the further bypass (38) being connected to the high-pressure side (21) downstream of the gas cooler (15) and upstream of the expansion valve (17) and to the low-pressure side (19) downstream of the heat exchanger (12) and upstream of the low-pressure compressor (13), the refrigerant being metered into the low-pressure side via the further valve and the further refrigerant of the further cooling circuit (34) being cooled in the further heat exchanger.

3. The method according to claim 1 or 2, It is characterized in that A reservoir for the further refrigerant is connected to the further cooling circuit (34), the further refrigerant being moved to the reservoir when the temperature in the test space is within a temperature range of +50°C to +180°C.

4. The method according to any one of the preceding claims, It is characterized in that The further compressor (35) is operated at least at a temperature of <-50°C in the test space.

5. The method according to any one of the preceding claims, It is characterized in that The cooling circuit (11) has an internal heat exchanger (16) which is connected to the high-pressure side (21) of the cooling circuit downstream of the gas cooler (15) and upstream of the expansion valve (17), the internal heat exchanger being coupled to an intermediate-pressure bypass (22) of the cooling circuit, the intermediate-pressure bypass being connected to the high-pressure side downstream of the internal heat exchanger or the gas cooler and upstream of the expansion valve and to the intermediate-pressure side (20) of the cooling circuit upstream of the high-pressure compressor (14) and downstream of the low-pressure compressor (13), a second expansion valve (23) being used to meter refrigerant from the high-pressure side into the intermediate-pressure side via the internal heat exchanger.

6. The method according to claim 5, It is characterized in that Via a second expansion valve (23), refrigerant is metered from the high-pressure side (21) through the internal heat exchanger (16) into the medium-pressure side (20), so that the refrigerant becomes completely gaseous in the internal heat exchanger and / or the refrigerant in the medium-pressure side is cooled.

7. A method according to claim 5 or 6, It is characterized in that The internal heat exchanger (16) is used to subcool the refrigerant on the high-pressure side (21).

8. The method according to any one of claims 5 to 7, It is characterized in that Refrigerant is metered from the high-pressure side (21) to the medium-pressure side (20) via the second expansion valve (23), so that the mass flow of the refrigerant at the high-pressure compressor (14) is always greater than the mass flow of the refrigerant at the low-pressure compressor (13).

9. The method according to any one of claims 5 to 8, It is characterized in that The second expansion valve (23) is controlled according to the pressure and / or temperature of the refrigerant in the intermediate pressure side (20).

10. The method according to any one of claims 1 to 4, It is characterized in that The high-pressure valve of the cooling circuit, which is arranged downstream of the gas cooler, is used to provide gaseous and / or liquid refrigerant in a metered manner to a storage tank for refrigerant, and the storage tank is connected to the medium-pressure side of the cooling circuit upstream of the high-pressure compressor and downstream of the low-pressure compressor via a medium-pressure bypass of the cooling circuit. The medium-pressure valve is used to provide gaseous refrigerant from the storage tank to the medium-pressure side in a metered manner when the low-pressure compressor is turned off.

11. The method according to any one of the preceding claims, It is characterized in that The cooling circuit (11) operates in a thermodynamically subcritical or transcritical operating state.

12. The method according to any one of the preceding claims, It is characterized in that A second bypass (24) having at least one third expansion valve (25) is formed in the cooling circuit (11), the second bypass being connected to the high-pressure side (21) downstream of the internal heat exchanger (16) or the gas cooler (15) and upstream of the expansion valve (17) and to the low-pressure side (19) downstream of the heat exchanger (12) and upstream of the low-pressure compressor (13), the suction gas temperature and / or the suction gas pressure of the refrigerant on the low-pressure side of the cooling circuit upstream of the low-pressure compressor being controlled by metering the refrigerant into the low-pressure side via the third expansion valve.

13. The method according to any one of the preceding claims, It is characterized in that A control bypass (26) having at least one control valve (27) is formed in the cooling circuit (11), the control bypass being connected to the high-pressure side (21) downstream of the high-pressure compressor (14) and upstream of the gas cooler (15) and to the low-pressure side (19) downstream of the heat exchanger (12) and upstream of the low-pressure compressor (13), controlling the suction gas temperature and / or suction gas pressure of the refrigerant on the low-pressure side of the cooling circuit upstream of the low-pressure compressor and / or balancing the pressure difference between the high-pressure side and the low-pressure side of the cooling circuit by metering the refrigerant into the low-pressure side via the control valve.

14. The method according to any one of the preceding claims, It is characterized in that The dehumidifier bypass (31) of the cooling circuit (11) is used to dehumidify the air in the test space, and the dehumidifier bypass (31) includes a second heat exchanger (33) and a dehumidifier valve (32) in the test space.

15. The method according to claim 14, It is characterized in that The dehumidifier bypass (31) is connected to the high-pressure side (21) of the cooling circuit (11) downstream of the gas cooler (15) and upstream of the expansion valve (17) and to the low-pressure side (19) of the cooling circuit downstream of the heat exchanger (12) and upstream of the low-pressure compressor (13), and refrigerant is metered from the high-pressure side to the low-pressure side via the dehumidifier valve (51), so that the second heat exchanger (33) is cooled.

16. The method according to any one of the preceding claims, It is characterized in that A non-fluorinated refrigerant, preferably pure carbon dioxide (CO2), is used as the refrigerant in the cooling circuit (11), and / or R469A is used as the further refrigerant in the further cooling circuit (34).

17. A method according to any one of the preceding claims, It is characterized in that The temperature control device is used to establish a temperature in the test space in a temperature range of -50°C to +180°C, preferably -80°C to +180°C.

18. A test chamber for conditioning air, in particular a climate chamber, comprising: a test space for receiving a test material, the test space being configured to be sealed and temperature isolated from an environment; and a temperature control device for controlling the temperature of the test space, the temperature control device being configured to establish a temperature within a temperature range of -20°C to +180°C in the test space, the temperature control device comprising a cooling device (10), the cooling device (10) having a cooling circuit (11) with carbon dioxide as a refrigerant, a heat exchanger (12) in the test space, a low-pressure compressor (13), and a high-pressure compressor (14) downstream of the low-pressure compressor in the flow direction of the refrigerant, a gas cooler (15), and an expansion valve (17), the test chamber comprising a control device for controlling the temperature of the test space, It is characterized in that The cooling device comprises a further cooling circuit (34) having a further refrigerant, the heat exchanger in the test space, a further compressor (35), a further heat exchanger (36) and a further expansion valve (37).

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

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