Test chamber and control method

Abstract

To provide a method for conditioning the air in a test space of a test chamber, and a test chamber capable of environmentally friendly operation even at low temperatures.SOLUTION: A test space is configured to be sealed from an environment and temperature-insulated. In the test space, a cooling device 10 of a temperature control device of a test chamber comprising 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, a gas cooler 15, and an expansion valve 17 downstream of the low-pressure compressor in a flow direction of the refrigerant, is used to establish a temperature in a temperature range of -20°C to +180°C within the test space, and a control device of the test chamber is used to control the temperature in the test space. Another cooling circuit 34 of the cooling device with another refrigerant, the heat exchanger in the test space, another compressor 35, another heat exchanger 36 and another expansion valve 37 are used to establish the temperature within the test space.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a test chamber for conditioning air, in particular a climate chamber, and to a method for conditioning air in a test space of the test chamber for receiving a test material, the test space being configured to be sealed and thermally insulated from the environment, 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, a gas cooler, and an expansion valve downstream of the low-pressure compressor in the refrigerant flow direction, using the cooling device of the temperature control device of the test chamber to establish a temperature in the test space in the temperature range from -20°C to +180°C and controlling the temperature in the test space using the control device of the test chamber.

Background Art

[0002] This type of test chamber is regularly used to test the physical and / or chemical properties of objects, in particular devices. For example, temperature test cabinets or climate test cabinets are known in which the temperature inside can be set in the range from -70°C to +180°C. In the case of a climate test cabinet, additional desired climate conditions can be set, and then a device or test material is exposed to these for a certain period of time. The temperature of the test space containing the test material is regularly controlled in the air circulation duct in the test space. The air circulation duct forms an air treatment space in the test space, where a heat exchanger for heating or cooling the air flowing through the air circulation duct or the test space is arranged. A fan or ventilator sucks the air in the test space and guides it through the air circulation duct to the respective heat exchanger. In this way, the test material can be temperature-controlled or exposed to a defined change in temperature. During the test interval, the temperature can vary, for example, between the maximum and minimum temperatures of the test chamber. This type of test chamber is known, for example, from Patent Document 1.

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

[0004] Furthermore, a cooling device configured as what is called a booster system is known. In the cooling circuit of the cooling device, since the high-pressure compressor is always connected in series downstream of the low-pressure compressor, the refrigerant is compressed stepwise by the low-pressure compressor and then by the high-pressure compressor. Since the requirements for temperature control within the temperature range of the test space are high, the load requirements vary frequently during the operation of the test chamber. Therefore, the cooling capacity generated by the compressor and the expansion valve must be infinitely variable. Nevertheless, it is desirable not to frequently switch the compressor on and off in order to extend the service life of the compressor.

[0005] Since carbon dioxide as a refrigerant has a very high volumetric cooling capacity, a very high cooling capacity is provided by the cooling circuit even when using a compressor with a very low stroke volume flow rate. In addition, the pressure range of the cooling circuit using carbon dioxide as a refrigerant is very high in transcritical operation (up to 120 bar), and therefore, the components required to form the cooling circuit are relatively expensive. Also, this type of cooling circuit has a complex structure, which requires a large installation space. Therefore, until now, the use of this type of cooling circuit with carbon dioxide as a refrigerant has only been reasonable for systems or test chambers with a correspondingly high cooling capacity, and thus a relatively large test space, or large device dimensions. Economical use in a relatively small system or a test space with a small volume, for example, a 25-liter test chamber, is not yet possible.

[0006] Furthermore, there is a problem that it is almost impossible to establish a very low temperature, for example, less than -50°C, in order to use carbon dioxide as a refrigerant or a majority of carbon dioxide in the refrigerant. This would require the use of refrigerants that are not so environmentally friendly and / or are flammable (A3) or highly flammable (A2L). In particular, when corresponding to fire class C according to European standard EN2 or classes A2, A2L and A3 of DIN 378 in the latest version at the priority date, the refrigerant is flammable.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0008] Therefore, an object of the present invention is to propose a method for conditioning air in the test space of a test chamber and a test chamber capable of environmentally friendly operation even at low temperatures.

[0009] This object is achieved by a method having the features of claim 1 and a test chamber having the features of claim 18.

Means for Solving the Problems

[0010] In a method according to the invention for conditioning air in a test space of a test chamber, in particular a climate chamber, for receiving test materials, the test space is configured to be sealed and thermally insulated from the environment, and a cooling device of a temperature control device of the test chamber is used, the cooling device including a cooling circuit having carbon dioxide as a refrigerant, a heat exchanger in the test space, a low-pressure compressor, and a high-pressure compressor, a gas cooler, and an expansion valve downstream of the low-pressure compressor in the refrigerant flow direction, to establish a temperature in a temperature range from -20°C to +180°C in the test space, and the temperature in the test space is controlled using a control device of the test chamber, and another cooling circuit of a cooling device with another refrigerant, a heat exchanger in the test space, another compressor, another heat exchanger and another expansion valve are used to establish the temperature in the test space.

[0011] In the method according to the invention, by insulating the side walls, the floor wall and the ceiling wall, heat exchange with the environment of the test space is largely avoided. The heat exchanger is connected to or integrated into the cooling circuit such that the refrigerant circulating within the cooling circuit flows through the heat exchanger. Since the heat exchanger of the cooling circuit is arranged within the test space or in the air treatment space of the test space, the air in the test space is conditioned or temperature-controlled via the heat exchanger. A gas cooler is also integrated into the cooling circuit and is formed by the heat exchanger. The gas cooler is arranged downstream of the high-pressure compressor in the cooling circuit, and the compressed refrigerant is, after compression, under high pressure and is essentially gaseous or in vapor form or wet vapor and can be condensed in the gas cooler or condenser and then assumes an essentially liquid state of aggregation. It is also possible for the gaseous refrigerant not to condense in the gas cooler and to keep the gas cooler essentially in the gaseous state. The refrigerant is then only heated and exceeds the critical point (supercritical fluid). The gas cooler or heat exchanger in question can be equipped, for example, with means for cooling the refrigerant 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 made particularly compact. The refrigerant flows from the gas cooler through an expansion valve and through this, as a result of the pressure drop, expands and thus becomes gaseous, vapor or wet vapor again. In this process, the refrigerant flows through the heat exchanger and is consequently cooled. Here, the refrigerant absorbs heat from the test space via the heat exchanger. Subsequently, the gaseous refrigerant is suctioned and compressed again by the low-pressure compressor and the high-pressure compressor.

[0012] The term expansion valve refers to at least an expansion element, a throttling element, a throttle valve or another suitable constriction of a fluid conduit. The expansion valve and the other valves of the cooling circuit are preferably controllable.

[0013] The present invention intends to couple other cooling circuits of a cooling device to a heat exchanger in a test space. Other refrigerants in other cooling circuits are always separated from the refrigerant of the cooling circuit. The heat exchanger does not connect the respective cooling circuits. Thus, it is basically possible for the heat exchanger to form a first partial heat exchanger for the cooling circuit and a second partial heat exchanger for other cooling circuits. These partial heat exchangers can also be arranged at separate locations in the test space and then form a heat exchanger. Other cooling circuits have other heat exchangers, which form gas coolers for other refrigerants. The other refrigerant is then compressed through another compressor, cooled or liquefied in another heat exchanger, and can be used to cool the heat exchanger via another expansion valve. In this context, the other refrigerant of other cooling circuits is different from the refrigerant of the cooling circuit. The other refrigerant can be selected such that, using the other refrigerant, a temperature lower than the lowest temperature achievable using the refrigerant can be established. Overall, this enables a relatively low temperature to be established using a test chamber without requiring specific modifications to the cooling circuit. In this case, in particular, environmentally friendly carbon dioxide can continue to be used as the refrigerant. Other cooling circuits are in particular of a simple and compact design and can have refrigerants that are not as environmentally friendly as the other refrigerant. The cooling circuit can then operate for the major part of the operating time of the cooling device, whereas the other cooling circuit has to operate only when a relatively low temperature is to be achieved, which is usually not the case very often. The amount of the less environmentally friendly refrigerant of the cooling device can thus be substantially reduced in this way. Since the other cooling circuit operates only as required, energy can be saved. Safety-related technical measures that may be required are necessary only for a smaller part of the facility, thereby reducing costs.

[0014] Another bypass can be formed in the cooling circuit with at least another valve and another heat exchanger. In this case, 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. The refrigerant can be supplied to the low-pressure side via another valve, and the other refrigerant of the other cooling circuit can be cooled by the other heat exchanger. Therefore, the cooling circuit can be used to cool the other heat exchanger or the gas cooler of the other cooling circuit via another bypass. The other valve can be an expansion valve or a simple throttle valve. Therefore, in order to operate the other cooling circuit, a part of the cooling capacity of the cooling circuit can be used to condense, i.e., liquefy, the other refrigerant. The cooling circuit can thus be used particularly efficiently. However, in principle, it is also possible to cool the other heat exchanger in another way, for example, by air or water.

[0015] A reservoir for the other refrigerant can be connected to the other cooling circuit. In this case, the other refrigerant can be moved to the reservoir at a temperature in the temperature range of +50°C to +180°C in the test space. This also makes it possible to use a refrigerant that is not so environmentally friendly as the other refrigerant. If the refrigerant is flammable or highly flammable, the other refrigerant can be moved completely or mainly into the reservoir so that there is no or little other refrigerant in the heat exchanger. At higher temperatures in the test space, especially when there is a leak in the heat exchanger or the other cooling circuit in the test space, there is a risk that the other refrigerant will leak into the test space, and in this case, an explosive mixture can be formed in the test space. When the other cooling circuit is not operating, the other refrigerant can be moved to the reservoir so that additional safety-related technical features such as sensors are not required. The other refrigerant can be moved to the reservoir, for example, via other compressors, additional valves, etc. The reservoir can be a tank for holding the other refrigerant.

[0016] It can be intended to operate other compressors at a temperature of less than at least -50°C within the test space. The operation of each compressor can be controlled by a control device. The cooling circuit can be operated down to a temperature of -50°C, and due to the triple point of carbon dioxide, it has become difficult to achieve lower temperatures. If it is necessary to establish a lower temperature in the test space, this can be achieved using other cooling circuits with other compressors. In this case, all compressors, i.e., the cooling circuit and the other cooling circuits, can be operated simultaneously.

[0017] The cooling circuit can have an internal heat exchanger, which can be connected to the high-pressure side of the cooling circuit downstream of the gas cooler and upstream of the expansion valve. The internal heat exchanger can be coupled to an intermediate-pressure bypass of the cooling circuit. The intermediate-pressure bypass can be connected to the high-pressure side downstream of the internal heat exchanger and upstream of the expansion valve upstream of the gas cooler, and to the intermediate-pressure side of the cooling circuit upstream of the high-pressure compressor and downstream of the low-pressure compressor. Another expansion valve can supply refrigerant from the high-pressure side through the internal heat exchanger to the intermediate-pressure side. Immediately downstream of the internal heat exchanger and upstream of the expansion valve, an intermediate-pressure bypass with another expansion valve can be connected to the circuit as a result. The refrigerant that has already passed through the internal heat exchanger can also be supplied and expanded through another expansion valve. The internal heat exchanger can also be connected downstream of another expansion valve in the intermediate-pressure bypass. The refrigerant expanded by another expansion valve flows through the internal heat exchanger and is consequently cooled. As a result, the internal heat exchanger on the intermediate-pressure side and thus the refrigerant on the high-pressure side of the internal heat exchanger are cooled. However, in principle, the intermediate-pressure bypass can also be connected to the cooling circuit such that the refrigerant flows through a further expansion valve and the internal heat exchanger downstream of the gas cooler and upstream of the internal heat exchanger. Downstream of the internal heat exchanger, the intermediate-pressure bypass can be connected between the low-pressure compressor and the high-pressure compressor such that the refrigerant sent through the intermediate-pressure bypass can be mixed with the refrigerant circulating in the cooling circuit at this location. By using the intermediate-pressure bypass together with the internal heat exchanger, it is possible to divert refrigerant through the intermediate-pressure bypass such that less refrigerant flows through the expansion valve, depending on the cooling load requirements of the control device. At the same time, the refrigerant flowing through the intermediate-pressure bypass can be used to temperature-control the refrigerant on the high-pressure side by means of the internal heat exchanger. The very high volumetric cooling capacity of carbon dioxide thus bypasses upstream of the heat exchanger and is used to cool the refrigerant on the high-pressure side when the cooling capacity required in the test space is reduced. This also makes it possible to make the test space smaller and to use a cooling circuit operating with carbon dioxide for a more compact test chamber.

[0018] Via the second expansion valve, the refrigerant can be supplied from the high-pressure side through the internal heat exchanger to the intermediate-pressure side such that the refrigerant becomes completely gaseous in the internal heat exchanger, i.e., is depressurized and / or the refrigerant arranged on the intermediate-pressure side is cooled. In this way, the compressed and highly superheated refrigerant can be cooled downstream of the low-pressure compressor. The second expansion valve can also cool the intermediate-pressure side of the internal heat exchanger in order to additionally cool the transcritical refrigerant arranged on the high-pressure side of the internal heat exchanger. Furthermore, the relatively cold refrigerant flowing through the intermediate-pressure bypass can then be introduced between the low-pressure compressor and the high-pressure compressor. When the low-pressure compressor is operating, the low-pressure compressor transports the refrigerant from the low-pressure side of the cooling circuit to the intermediate-pressure side, and at this point the refrigerant can already have a very high temperature. This can cause a thermal overload in the high-pressure compressor. This thermal overload can be avoided by mixing relatively colder refrigerant through the intermediate-pressure bypass.

[0019] The refrigerant on the high-pressure side can be subcooled using the internal heat exchanger. The enthalpy difference in the heat exchanger can be increased by this additional subcooling, which in turn leads to an increase in the cooling capacity of the heat exchanger. This makes it possible to efficiently establish particularly low temperatures in the test space.

[0020] Via the second expansion valve, the refrigerant can be supplied from the high-pressure side to the intermediate-pressure side such that the mass flow rate of the refrigerant in the high-pressure compressor is always greater than the mass flow rate of the refrigerant in the low-pressure compressor. If the refrigerant is subcooled by the internal heat exchanger, the mass flow rate transported through the high-pressure compressor can be significantly greater than the mass flow rate transported through the low-pressure compressor, so that no dissipation occurs in the heat exchanger. The reason for this is the significantly higher density of the refrigerant at the inlet of the high-pressure compressor 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 explained by the equation 0=m 高圧圧縮器 -(m 低圧圧縮器 +m 内部熱交換器 ) as described by.

[0021] Therefore, the mass flow rate of the internal heat exchanger is the result of the difference in mass flow rate between the high-pressure compressor and the low-pressure compressor. The control device can be configured to always maintain this ratio through the control of the second expansion valve. In this way, a pressure drop on the intermediate pressure side can be prevented. This pressure drop on the intermediate side may lead to a change in the pressure ratio in the high-pressure compressor, which may cause the high-pressure compressor and / or the low-pressure compressor to exceed the intended operating threshold, which should be avoided.

[0022] For example, the second expansion valve can be controlled as a function of the pressure and / or temperature of the refrigerant arranged on the intermediate pressure side. The pressure and / or temperature can be measured using appropriate sensors. The second expansion valve can then be controlled by the control device or a regulating function of the control device such that the intake temperature of the high-pressure compressor and / or the pressure at the inlet side of the high-pressure compressor are within the required range. In this way, possible damage to the high-pressure compressor and / or the low-pressure compressor as a result of inappropriate temperature and pressure can be avoided by simple means.

[0023] If the cooling circuit can be operated in a partial load operating state, the pressure of the refrigerant on the high-pressure side can be reduced. In the partial load operating state, the cooling circuit does not operate at full load. Rather, since the cooling load requirements of the control device or the test space are decreasing, the expansion valve opens intermittently, i.e., it does not open permanently or fully. Since the refrigerant on the high-pressure side has a lower pressure, the final compression temperature of the high-pressure compressor may also be lower, which means that the amount of heat dissipated through the gas cooler is reduced via the environment in which the test chamber is located. As a result, the thermal load on the test chamber installation room, which may or may not be air-conditioned, can be reduced. In the partial load operating state, only a very low cooling capacity, for example less than 2% of the cooling capacity of the cooling circuit, and / or at a temperature in the test space of, for example, -10 °C or higher, is required. Since the output of the compressor can hardly be controlled, 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, by reducing the pressure of the refrigerant on the high-pressure side, a lower cooling capacity can be achieved without immediately switching off the compressor. In this way, frequent start intervals for the low-pressure compressor and the high-pressure compressor can be avoided, which is the reason why the compressor can be operated for a long service life.

[0024] Using a high-pressure valve of a cooling circuit arranged downstream of a gas cooler, gaseous and / or liquid refrigerant can be supplied into a storage tank for the refrigerant. The storage tank can be connected to the intermediate-pressure side of the cooling circuit upstream of a high-pressure compressor and downstream of a low-pressure compressor via an intermediate-pressure bypass of the cooling circuit. When the low-pressure compressor is switched off, gaseous refrigerant can be supplied from the storage tank to the intermediate-pressure side using an intermediate-pressure valve. Depending on the extraction point on the storage tank, liquid or gaseous refrigerant can be withdrawn from the storage tank. The liquid refrigerant can be sent through an expansion valve, where it can return to the gaseous state by expansion as a result of a pressure drop. In doing so, it flows through a heat exchanger, which is consequently cooled. In this embodiment of the cooling circuit, it can be defined that the high-pressure valve is arranged downstream of the gas cooler in the cooling circuit in order to supply gaseous and / or liquid refrigerant into the storage tank via the high-pressure valve. The storage tank is essentially a pressure vessel in which, when a phase boundary is formed, the liquid refrigerant is stored in a lower region 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 depressurized therein to cool the heat exchanger.

[0025] The cooling circuit can be operated in a thermodynamically subcritical or transcritical operating state. Depending on the cooling load requirements within the test space, the operating state can be changed accordingly using a control device. In the subcritical operation of the cooling circuit, the refrigerant is liquefied in the gas cooler below the critical point of the refrigerant, expanded by an expansion valve, and converted 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 partial load operation. In the transcritical operating state, the refrigerant essentially circulates through the cooling circuit in a gaseous state. This means that the temperature difference is reduced to such an extent that the refrigerant is not liquefied in the gas cooler. Also, in the transcritical operating state, the pressure in the gas cooler reaches a value above the critical point of the refrigerant. If there are high cooling load requirements, or if cooling from +180 °C to -20 °C is required, for example, the cooling circuit can be operated transcritically. If the cooling load requirements within the test space are low, 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 enables an increase in efficiency, especially in the case of particularly low cooling load requirements, for example, at low ambient temperatures, in contrast to exclusively transcritical operating states. The change between the subcritical and transcritical operating states is made possible in particular by an intermediate pressure bypass and an internal heat exchanger.

[0026] A second bypass with at least a 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, as well as to the low-pressure side downstream of the heat exchanger and upstream of the low-pressure compressor. By supplying the refrigerant to the low-pressure side via the third expansion valve, 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. Using the third expansion valve, the suction gas temperature and / or suction gas pressure upstream of the low-pressure compressor can be affected so that the final compression temperature of the low-pressure compressor is within the intended operating range for the low-pressure compressor. For example, if the temperature in the test space is to be reduced from, for example, +180 °C to a lower temperature, the suction gas temperature of the low-pressure compressor may rise particularly sharply. Since the heat exchanger is arranged in the test space, the refrigerant can flow from the heat exchanger to the low-pressure compressor at a particularly high temperature in the test space of +180 °C, for example, at this temperature. Before the severely superheated refrigerant is supplied to the low-pressure compressor, it can be cooled by the refrigerant supplied via the third expansion valve.

[0027] A control bypass having 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, as well as to the low-pressure side downstream of the heat exchanger and upstream of the low-pressure compressor. By supplying refrigerant to the low-pressure side via the control valve, 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, and / or the pressure difference between the high-pressure side and the low-pressure side of the cooling circuit can be made equal. Therefore, the control bypass is configured to be able to supply refrigerant from the high-pressure side to the low-pressure side via the control valve. The refrigerant can be superheated or in a gaseous state. Returning the superheated refrigerant from the high-pressure side to the low-pressure side by the control bypass is particularly advantageous if the cooling circuit is operating in a partial-load operating state. Since the expansion valve is rarely opened in this case, there is a risk that the suction pressure upstream of the low-pressure compressor will drop too much. When using carbon dioxide as the refrigerant, there is a possibility of forming dry ice at a pressure below 5.16 absolute bar, which can prevent the safe operation of the cooling circuit and damage the low-pressure compressor. Since the highly superheated refrigerant can be supplied via the control bypass to a point upstream of the low-pressure compressor directly downstream of the high-pressure compressor, the formation of dry ice can be effectively prevented. In addition, when, for example, the cooling device is not operating and the refrigerant will be heated as a result of temperature equalization with the environment, and there is a risk that an undesirable high pressure will build up in the cooling circuit, it is also possible to equalize the pressure difference between the high-pressure side and the low-pressure side of the cooling circuit via the control bypass.

[0028] The air in the test space can be dehumidified using a dehumidifier bypass of a cooling circuit including a dehumidifier valve and a second heat exchanger in the test space. This dehumidification can occur at some point during the test cycle, especially when the temperature in the test space is within the range above 0°C and below 100°C. When the temperature in the test space falls below or exceeds this range, water cannot condense on the second heat exchanger in the liquid phase, so the dehumidifier bypass does not function in these ranges. Therefore, the cooling circuit of the cooling device can establish a temperature from -20°C to +180°C in the test space during the test cycle and can be designed such that the dehumidification of the air by the dehumidifier bypass can be performed only in a partial range of this temperature range. Dehumidification occurs by supplying refrigerant from the high-pressure side of the cooling circuit to the low-pressure side of the cooling circuit via the dehumidifier valve. As a result, the second heat exchanger arranged downstream of the dehumidifier valve in the flow direction of the refrigerant in the dehumidifier bypass is cooled. Here, the control device can supply refrigerant via the dehumidifier valve such that a desired difference in temperature between the temperature of the air in the test space and the temperature of the second heat exchanger is achieved. This difference in temperature can be selected such that water from the air in the test space condenses on the second heat exchanger. Thereby, it becomes possible to perform the targeted dehumidification of the air in the test space essentially independently of the temperature established in the test space. The expansion valve and the dehumidifier valve can thus be controlled independently of each other using the control device. Subsequently, with a decrease in temperature in the test space, for example, more or less dehumidification may occur, whereby the relative humidity can be set or controlled more accurately. Overall, the climate test cycle can be performed much more accurately with just a few components in a compact test chamber.

[0029] 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 supplied from the high-pressure side through the dehumidifier valve to the low-pressure side so that the second heat exchanger is cooled. The dehumidifier valve can be, for example, an electronic expansion valve or a solenoid valve with a downstream throttle passing through a capillary, a nozzle, etc., or a thermostatic expansion valve. Optionally, the dehumidifier bypass can also be connected downstream of any internal heat exchanger downstream of the gas cooler. The dehumidifier bypass can thus be connected to the cooling circuit in parallel with the expansion valve and the heat exchanger. In this way, the dehumidifier bypass can have a particularly simple design.

[0030] 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 other cooling circuits. Pure carbon dioxide has a GWP of 1, is non-flammable, not dangerous, and is available at low cost. In addition, carbon dioxide is a pure substance or azeotropic, which enables an advantageous implementation of this method and its variations in the first place. On the other hand, it is almost impossible to provide a sufficient amount of gaseous refrigerant with a very small temperature difference with a refrigerant having azeotropic behavior, and thus the performance control of the high-pressure compressor will be almost impossible. R469A is a relatively environmentally friendly refrigerant, has a relatively low GWP, and is non-flammable due to its high carbon dioxide content. In particular, with other refrigerants, it becomes possible to establish temperatures up to -80 °C in the test space or in the heat exchanger.

[0031] Using a temperature control device, the temperature in the test space can be established in the temperature range from -50 °C to +180 °C, preferably from -80 °C to +180 °C, particularly preferably from -90 °C to +180 °C.

[0032] A test chamber according to the invention for conditioning air, in particular a climate chamber, comprises a test space for receiving a test material, which test space is configured to be sealed and thermally insulated from 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 in a temperature range from -20 °C to +180 °C, the temperature control device comprising a cooling circuit with carbon dioxide as refrigerant, a heat exchanger in the test space, a low-pressure compressor and a high-pressure compressor, a gas cooler, and an expansion valve downstream of the low-pressure compressor in the refrigerant flow direction, the test chamber comprising a control device for controlling the temperature in the test space, the cooling device comprising another cooling circuit with another refrigerant, a heat exchanger in the test space, another compressor, another heat exchanger and another expansion valve. 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.

[0033] The temperature control device can have a heating device with a heater and a heating heat exchanger in the test space. For example, the heating device can be an electrical resistance heater that heats the heating heat exchanger so that an increase in temperature in the test space is made possible via the heating heat exchanger. If the heat exchanger and the heating heat exchanger can be controlled by the control device in a targeted manner so as to cool or heat the air circulating within the test space, then the temperature in the temperature range specified above can then be established in the test space by the temperature control device.

[0034] The low-pressure compressor and the high-pressure compressor can share a housing. Furthermore, the low-pressure compressor and the high-pressure compressor can be driven by a shared motor, i.e., the same motor. The cooling device can in this case have a particularly compact design.

[0035] Other embodiments of the test chamber are apparent from the description of the features of the claims dependent on claim 1 of the method.

[0036] Hereinafter, a preferred embodiment of the present invention will be described in more detail with reference to the accompanying drawings.

Brief Description of the Drawings

[0037]

Figure 1

Figure 2

Embodiments for Carrying Out the Invention

[0038] FIG. 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 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 internal heat exchanger 16, and an expansion valve 17. In the present case, the gas cooler 15 is configured like a heat exchanger or a condenser and is cooled by a heat transfer medium such as air or water. The heat exchanger 12 is arranged in an air treatment duct so as to be able to cool the air in the test space by the heat exchanger 12 through an air treatment duct (not shown) of the test space of the test chamber. Further, the cooling circuit 11 has a low-pressure side 19, an intermediate-pressure side 20, and a high-pressure side 21. On the low-pressure side 19, the pressure of the refrigerant is relatively lower than that on the intermediate-pressure side 20. On the intermediate-pressure side 20, the pressure of the refrigerant is relatively lower than that on the high-pressure side 21.

[0039] The cooling circuit 11 further has an internal heat exchanger 16 downstream in the flow direction of the refrigerant and an intermediate pressure bypass 22 upstream of the expansion valve 17, and the intermediate pressure bypass 22 ends downstream of the low-pressure compressor 13 and upstream of the high-pressure compressor 14. A second expansion valve 23 is arranged in the intermediate pressure bypass 22. The second expansion valve 23 is connected upstream of the internal heat exchanger 16. Here, the refrigerant, which is essentially liquid, can be supplied from the gas cooler 15 through the high-pressure side 21 of the internal heat exchanger 16 and, if required, to the intermediate pressure side 20 of the internal heat exchanger 16 via the second expansion valve 23. In this process, the refrigerant on the high-pressure side 21 is subcooled to such an extent that a further lower temperature can be established at the expansion valve 17 or the heat exchanger 12. At the same time, the suction gas temperature of the high-pressure compressor 14 can be kept relatively low using the refrigerant flowing through the intermediate pressure bypass 22.

[0040] In addition, the cooling circuit 11 includes a second bypass 24 with 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 in the flow direction of the refrigerant, and also downstream of the heat exchanger 12 and upstream of the low-pressure compressor 13. By means of the third expansion valve 25, liquid refrigerant can be supplied beyond the expansion valve 17 and the heat exchanger 12 to the low-pressure side 19. This makes it possible to control the suction gas temperature and / or the suction gas pressure at the low-pressure side 19 upstream of the low-pressure compressor 13.

[0041] Furthermore, the cooling circuit 11 includes a control bypass 26 with 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. By means of the control bypass 26 or the control valve 27, refrigerant, in particular superheated refrigerant or gaseous refrigerant, can be supplied from the high-pressure side 21 to the low-pressure side 19 upstream of the low-pressure compressor 13 as a function of the operating state of the cooling circuit 11. Thereby, it is also possible to control the suction gas temperature and / or the suction gas pressure on the low-pressure side 19 upstream of the low-pressure compressor 13. Said control can be carried out by a control device (not shown) of the test chamber and sensors arranged in the cooling circuit 11, in particular pressure and temperature sensors.

[0042] Figure 2 shows a pressure-enthalpy diagram (log-p-h diagram) of the refrigerant circulating in the cooling circuit 11 with respect to the operating state of the cooling circuit 11 when the low-pressure compressor 13 and the high-pressure compressor 14 are operating. In the diagram, a 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.

[0043] Figure 2 shows the supercritical operating state of the cooling circuit 11. Starting from position A, the refrigerant is taken in and compressed by the low-pressure side 19 equipped with the low-pressure compressor 13, and reaches the pressure corresponding to position B downstream of the low-pressure compressor 13. The refrigerant is then taken 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 the trans-critical state and is liquefied or the superheat is reduced. 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 F), and the refrigerant evaporates in the heat exchanger 12 (from position F to position A). Another part of the refrigerant flows through the intermediate-pressure bypass 22, where again the refrigerant expands at 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 intermediate-pressure bypass 22 mixes with the refrigerant from the low-pressure compressor 13.

[0044] Furthermore, a dehumidifier bypass 31 equipped with a dehumidifier valve 32 and a second heat exchanger 33, which is also arranged in the test space, is arranged in the cooling circuit 11. The air in the test space can be dehumidified by the second heat exchanger 33 or the dehumidifier bypass 31. For this purpose, the test chamber has a control device (not shown) that can control the temperature and / or relative humidity in the test space. For this purpose, the control device can operate the expansion valve 17 and especially the second expansion valve 23. Thereby, it becomes possible to perform a climate test that can very accurately establish the dehumidification or relative humidity in the test space with the cooling device 10, whether the temperature in the test space is constant or decreasing.

[0045] Also, the cooling device 10 includes another cooling circuit 34 equipped with another refrigerant, a heat exchanger 12, another compressor 35, another heat exchanger 36, and another expansion valve 37. R469A is used here as the other refrigerant. Alternatively, a carbon dioxide-based refrigerant or a flammable refrigerant can be used as the other refrigerant. The other cooling circuit 34 is used for additional cooling of the test space via the heat exchanger 12.

[0046] Another bypass 38 with another valve 39 is formed in the cooling circuit 11. The another bypass 38 extends through 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 to the low-pressure side 19 downstream of the heat exchanger 12 and upstream of the low-pressure compressor 13. Here, the another valve 39 can be used to supply refrigerant to the low-pressure side 19 or to the another heat exchanger 36. Thereby, another refrigerant in another cooling circuit 34 is cooled in the another heat exchanger 36 and is liquefied by condensation. When a temperature below -50°C is to be established in the test space, the another cooling circuit 34 can then be operated. Thereby, it becomes possible to establish a temperature up to -80°C in the test space.

Explanation of Signs

[0047] 10 Cooling device, 11 Cooling circuit, 12 Heat exchanger, 13 Low-pressure compressor, 14 High-pressure compressor, 15 Gas cooler, 16 Internal heat exchanger, 17 Expansion valve, 19 Low-pressure side, 20 Intermediate-pressure side, 21 High-pressure side, 22 Intermediate-pressure bypass, 23 Second expansion valve, 24 Second bypass, 25 Third expansion valve, 26 Control bypass, 27 Control valve, 28 Boiling line, 29 Dew condensation line, 30 Critical point, 31 Dehumidifier bypass, 32 Dehumidifier valve, 33 Second heat exchanger, 34 Another cooling circuit, 35 Another compressor, 36 Another heat exchanger, 37 Another expansion valve, 38 Another bypass, 39 Another valve

Claims

1. 1. A method for conditioning the air in a test chamber for receiving a test material, in particular a test space of a climatic chamber, comprising: the test space is configured to be sealed and insulated from the environment; A cooling device (10) for the temperature control device of the test chamber, said cooling device being configured to cool the temperature control device by using carbon dioxide (CO ２ Establishing a temperature in the test space in the temperature range from -20°C to +180°C by means of a cooling device comprising a cooling circuit (11) using refrigerant gas of 0.1% psi (1.0) as a refrigerant, a heat exchanger (12) in the test space, a low-pressure compressor (13), a high-pressure compressor (14), a gas cooler (15), and an expansion valve (17) downstream of the low-pressure compressor in the flow direction of the refrigerant, 13. A method for controlling the temperature in the test space using a controller for the test chamber, comprising: establishing the temperature in the test space using another cooling circuit (34) of the cooling device with another refrigerant, the heat exchanger in the test space, another compressor (35), another heat exchanger (36) and another expansion valve (37).

2. a further bypass (38) is formed in said cooling circuit (11) with at least one further valve (39) and said further heat exchanger (36); the other bypass is connected to a high pressure side (21) downstream of the gas cooler (15) and upstream of the expansion valve (17) and to a low pressure side (19) downstream of the heat exchanger (12) and upstream of the low pressure compressor (13), and supplies refrigerant to the low pressure side via the other valve; 2. The method of claim 1, characterized in that the other refrigerant of the other cooling circuit (34) is cooled in the other heat exchanger.

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

4. A method according to any one of claims 1 to 3, characterised in that the other compressor (35) is operated at a temperature in the test space of at least less than -50°C.

5. the cooling circuit (11) comprises an internal heat exchanger (16) 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 is coupled to an intermediate pressure bypass (22) of the cooling circuit; the intermediate pressure bypass is 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); 5. The method according to claim 1, further comprising the step of: supplying refrigerant from the high pressure side to the intermediate pressure side via the internal heat exchanger using a second expansion valve (23).

6. 6. The method according to claim 5, characterized in that via the second expansion valve (23), the refrigerant is supplied from the high pressure side (21) through the internal heat exchanger (16) to the intermediate pressure side (20) such that the refrigerant becomes completely gaseous in the internal heat exchanger and / or the refrigerant arranged on the intermediate pressure side is cooled.

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

8. 8. The method according to claim 5, wherein refrigerant is supplied from the high pressure side (21) via the second expansion valve (23) to the intermediate pressure side (20) in such a way that the mass flow rate of refrigerant in the high pressure compressor (14) is always greater than the mass flow rate of refrigerant in the low pressure compressor (13).

9. 9. The method according to claim 5, wherein the second expansion valve (23) is controlled as a function of the pressure and / or the temperature of the refrigerant arranged on the intermediate pressure side (20).

10. supplying gaseous and / or liquid refrigerant into a storage tank for refrigerant by means of a high-pressure valve of the cooling circuit arranged downstream of the gas cooler, the storage tank is connected to an intermediate pressure side of the cooling circuit upstream of the high pressure compressor and downstream of the low pressure compressor via an intermediate pressure bypass of the cooling circuit; 5. The method according to claim 1, characterized in that when the low pressure compressor is shut off, an intermediate pressure valve is used to supply gaseous refrigerant from the storage tank to the intermediate pressure side.

11. 11. The method according to any one of the preceding claims, characterized in that the cooling circuit (11) is operated in a thermodynamically sub-critical or trans-critical operating state.

12. The cooling circuit (11) is provided with a second bypass (24) having at least a third expansion valve (25), the second bypass is connected to a 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 a low pressure side (19) downstream of the heat exchanger (12) and upstream of the low pressure compressor (13); 12. The method according to claim 1, characterized in that a suction gas temperature and / or a suction gas pressure of the refrigerant in the low pressure side of the cooling circuit upstream of the low pressure compressor is controlled by supplying refrigerant to the low pressure side via the third expansion valve.

13. The cooling circuit (11) is provided with a controlled bypass (26) having at least one control valve (27), the controlled bypass is connected to a high pressure side (21) downstream of the high pressure compressor (14) and upstream of the gas cooler (15) and to a low pressure side (19) downstream of the heat exchanger (12) and upstream of the low pressure compressor (13); 13. The method according to claim 1, characterized in that a suction gas temperature and / or a suction gas pressure of the refrigerant in the low pressure side of the cooling circuit upstream of the low pressure compressor is controlled by supplying refrigerant to the low pressure side via the control valve and / or equalizing the pressure difference between the high pressure side and the low pressure side of the cooling circuit.

14. 14. The method according to claim 1, characterized in that the air in the test space is dehumidified by means of a dehumidifier bypass (31) of the cooling circuit (11), comprising a dehumidifier valve (32) and a second heat exchanger (33) in the test space.

15. 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); 15. The method according to claim 14, characterized in that refrigerant is supplied from the high pressure side through the dehumidifier valve (32) to the low pressure side so that the second heat exchanger (33) is cooled.

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

17. 17. The method according to any one of claims 1 to 16, characterized in that, with the temperature control device, a temperature in the test space is established in the temperature range of -50°C to +180°C, preferably -80°C to +180°C.

18. a test chamber for conditioning the atmosphere, in particular a climatic chamber, said test chamber being a test space for receiving a test material, said test space being configured to be sealed and insulated from the environment; a temperature control device for controlling a temperature of the test space; Including, the temperature control device is configured to establish a temperature within the test space in a temperature range of −20° C. to +180° C.; The temperature control device includes a cooling device (10); The cooling device comprises a cooling circuit (11) using carbon dioxide as a refrigerant, a heat exchanger (12) in the test space, a low-pressure compressor (13), a high-pressure compressor (14), a gas cooler (15), and an expansion valve (17) downstream of the low-pressure compressor in the flow direction of the refrigerant, The test chamber includes a controller for controlling the temperature in the test space. The cooling device comprises a separate cooling circuit (34) with a separate refrigerant, the heat exchanger in the test space, a separate compressor (35), a separate heat exchanger (36) and a separate expansion valve (37).

19. 20. The test chamber of claim 18, wherein the temperature control device includes a heating device having a heater and a heating heat exchanger in the test space.

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