EP3904785B1 - Test chamber and method for conditioning of air - Google Patents

Description

The invention relates to a method and a test chamber for conditioning air, with a test space that can be closed off from the environment and is temperature-insulated for receiving test material, and a temperature control device for temperature control of the test space, with the temperature control device being equipped with a cooling device, with a cooling circuit, with a zeotropic refrigerant , a heat exchanger arranged in the test chamber, a compressor, a condenser, a first expansion element and an internal heat exchanger, a temperature in a temperature range from -40 °C to +180 °C is formed inside the test chamber, with the internal heat exchanger being on a high-pressure side of the Cooling circuit in a direction of flow before the first expansion element and then the condenser, and on a low-pressure side of the cooling circuit in the direction of flow after the heat exchanger and before the compressor, is connected, the cooling circuit having a bypass m with at least one second expansion element, the bypass on the high-pressure side in the direction of flow following the condenser and in front of the internal heat exchanger, and on the low-pressure side following connected to the heat exchanger and before the internal heat exchanger.

Such methods and test chambers are regularly used to check the physical and/or chemical properties of objects, in particular devices. Thus, temperature test cabinets or climate test cabinets are known within which temperatures can be set in a range from -70°C to +180°C. In the case of climatic test chambers, additional desired climatic conditions can be set, to which the device or the test material is then exposed over a defined period of time. Such test chambers are regularly or partially designed as a mobile device, which is only connected to a building with the necessary supply lines and includes all the assemblies required for temperature control and air conditioning. Temperature control of a test room accommodating the test material to be tested is regularly carried out in a circulating air duct within the test room. The circulating air duct forms an air treatment space in the test space, in which heat exchangers are arranged for heating or cooling the air flowing through the circulating air duct or the test space. A fan sucks in the air in the test room and directs it in the circulating air duct to the respective heat exchangers. The test material can be tempered in this way or exposed to a defined temperature change. During a test interval, for example, a temperature can repeatedly change between a maximum temperature and a minimum temperature of the test chamber.

The refrigerant circulating in the cooling circuit must be such that it can be used in the cooling circuit within the aforementioned temperature difference. Furthermore, as a result of legal regulations, the refrigerant must not contribute significantly to ozone depletion in the atmosphere or global warming, and it must also be non-flammable. These provisions can be affected in particular by refrigerants or Refrigerant mixtures are met, which have a comparatively high mass fraction of carbon dioxide, these refrigerant mixtures have zeotropic properties due to the different substances mixed together, which in turn is undesirable. In a zeotropic refrigerant mixture, a phase transition takes place over a temperature range, the so-called temperature glide. A difference between the boiling temperature and the dew point temperature at constant pressure is considered a temperature glide. Since carbon dioxide has a freezing temperature or freezing point of -56.6 °C, a comparatively large temperature glide results in refrigerant mixtures with carbon dioxide as the main mixing partner to achieve temperatures down to -70 °C. Since a comparatively rapid temperature change at the heat exchanger must be implemented with a test chamber or a corresponding cooling device, it is necessary to adapt an expansion element and a heat exchanger or evaporator of the relevant cooling circuit to the evaporation temperature of the refrigerant. Such cooling devices cannot be operated as a mixture cascade system in which a zeotropic refrigerant is successively evaporated via an expansion element. Mixture cascade systems are only suitable for developing a significant static low temperature.

The known test chambers therefore regularly have an internal heat exchanger, which can be connected to a high-pressure side of the cooling circuit in a flow direction before the expansion element and then to the condenser, and to a low-pressure side of the cooling circuit in a flow direction before the compressor and then to the heat exchanger. The internal heat exchanger cools or so-called sub-cools the liquefied refrigerant on the high-pressure side.

Furthermore, a bypass can be provided, which has a second expansion element and forms a return injection device for refrigerant. Refrigerant can then be conducted via the bypass from the high-pressure side via the second expansion element into the low-pressure side upstream of the internal heat exchanger in the direction of flow, so that cooling of the refrigerant on the high-pressure side of the internal heat exchanger is increased. This lowering of a suction gas temperature upstream of the compressor on the low-pressure side of the internal heat exchanger means that greater subcooling can consequently be achieved. This supercooling is usually not monitored and no temperature is measured upstream of the first expansion device. The second expansion element is set in such a way that refrigerant is continuously metered via the second expansion element and subcooling is thus ensured during operation of the cooling circuit. Such a test chamber is, for example, from DE 10 2017 216 363 A1 known.

The disadvantage here, however, is that due to the comparatively wide temperature range, with multi-stage cooling devices from -70 °C to +180 °C and with single-stage cooling devices from -40 °C to +180 °C, the cooling capacity required for supercooling varies greatly. Depending on the operating point of the cooling device, there may be fluctuations so that the supercooling may not be sufficient. If a larger amount of refrigerant is metered to the internal heat exchanger for supercooling the refrigerant on the high-pressure side via the second expansion element, the suction gas temperature before the compressor can drop to an unacceptable level.

The present invention is therefore based on the object of proposing a method and a test chamber for conditioning air which ensures stable operating behavior.

This object is achieved by a method having the features of claim 1 and a test chamber having the features of claim 16.

The method according to the invention for conditioning air is carried out with a test chamber with a test space that can be closed and temperature-insulated from the environment for receiving test material and a temperature control device for temperature control of the test space, with the temperature control device having a cooling device with a cooling circuit with a refrigerant, a Heat exchanger arranged in the test room, a compressor, a condenser, a first expansion element and an internal heat exchanger, a temperature in a temperature range of -40 °C to +180 °C is formed inside the test room, with the internal heat exchanger on a high-pressure side of the cooling circuit in one direction of flow before the first expansion element and then the condenser, and on a low-pressure side of the cooling circuit in the direction of flow following the heat exchanger and before the compressor, the cooling circuit having a bypass has at least one second expansion element, with the bypass being connected on the high-pressure side in the direction of flow downstream of the condenser and upstream of the internal heat exchanger, and on the low-pressure side downstream of the heat exchanger and upstream of the internal heat exchanger, with a control device of the temperature control device having a pressure sensor on the high-pressure side and with a temperature sensor on the high-pressure side downstream of the internal heat exchanger in the flow direction in the cooling circuit, regulates the second expansion element as a function of a pressure measured at the pressure sensor and a temperature measured at the temperature sensor.

In the method according to the invention, the side walls, floor walls and ceiling walls of the test room are thermally insulated, so that heat exchange with the surroundings of the test room is largely avoided. The heat exchanger is arranged in the test room, so that the cooling circuit runs at least in sections through the test room. In particular, the heat exchanger can be arranged in an air treatment room of the test room. The cooling device further has the Compressor, which can be a compressor, for example, and the compressor arranged downstream in the flow direction of the refrigerant condenser for the compressed refrigerant. The compressed refrigerant, which is under high pressure after compression and is essentially in gaseous form, condenses in the condenser and is then essentially in a liquid state. The liquid refrigerant continues through the internal heat exchanger and expansion device, again becoming gaseous through expansion due to a pressure drop. If it is a zeotropic refrigerant, only part of the refrigerant can possibly evaporate in the heat exchanger and an unusable part of a wet vapor component of the refrigerant can be relocated to the internal heat exchanger. The gaseous refrigerant is then sucked in again by the compressor and compressed. In principle, the method can also be carried out with an azeotropic refrigerant.

According to the invention, the temperature control device includes the control device with the pressure sensor and the temperature sensor, which are connected to the high-pressure side. A pressure of the refrigerant on the high-pressure side is measured via the pressure sensor. In principle, the pressure sensor can therefore be connected to any point in the cooling circuit on the high-pressure side. Since a temperature of the refrigerant in the course of the cooling circuit is regularly different, depending on the section of the cooling circuit, it is provided that the temperature sensor is arranged on the high-pressure side in the direction of flow after the internal heat exchanger and before the first expansion element. Accordingly, a temperature of the refrigerant is then measured immediately before the first expansion element. The control device now controls the second expansion element or a metering of refrigerant via the bypass from the high-pressure side to the low-pressure side to the internal heat exchanger as a function of a pressure measured at the pressure sensor and a temperature measured at the temperature sensor. By including pressure and temperature in the control it is only possible to reliably determine a state of the refrigerant upstream of the first expansion element and to enable sufficient supercooling of the refrigerant upstream of the first expansion element by means of the internal heat exchanger by controlling the second expansion element. It is thus always ensured that sufficient liquid refrigerant is available at the first expansion element and at the same time a suction gas temperature is not reduced too far. Critical operating states of the cooling device can thus be avoided with simple means.

The method can be carried out particularly easily if a pressure sensor and a temperature sensor are already installed at the appropriate point in the cooling circuit and the temperature control device has a control device. It is then only necessary to modify the control device accordingly in such a way that the second expansion element is controlled by the control device as a function of a pressure measured at the pressure sensor and a temperature measured at the temperature sensor.

Consequently, the high-pressure side refrigerant can be cooled by the internal heat exchanger. Since the internal heat exchanger is connected to the high-pressure side and the low-pressure side of the refrigeration cycle, the high-pressure-side refrigerant can be cooled by the low-pressure-side refrigerant flowing through the internal heat exchanger.

Refrigerant can be supplied to the internal heat exchanger via the second expansion element, it being possible for refrigerant to be supplied to the compressor from the low-pressure side of the internal heat exchanger. In order to ensure cooling or supercooling of the refrigerant on the high-pressure side in the internal heat exchanger or not to increase the temperature of the refrigerant above the boiling point of the refrigerant, the bypass is provided with the second expansion element, with the bypass and the second expansion element being connected Refrigerant is dosed on the low-pressure side in front of the internal heat exchanger and so a suction gas temperature can be further reduced.

The method can be used particularly advantageously if a refrigerant with a temperature glide of ≧5 K is used as the refrigerant. A zeotropic refrigerant can also be formed by a refrigerant mixture. Depending on the mixture composition of this refrigerant mixture, the refrigerant can have a temperature glide of ≥7 K to ≥15 K. The temperature glide is given here for an evaporation pressure of 1 bar.

For example, the refrigerant R469A or a mixture of the refrigerant R469A and the refrigerant R410A or R466A can be used. The refrigerant R469A consists of 35% by weight carbon dioxide, 32.5% by weight difluoromethane and 32.5% by weight pentafluoroethane and has a boiling temperature of -78.5 °C and a dew point temperature of -61.5 °C , so that temperatures down to -70 °C can be reached in a correspondingly adapted cooling circuit, for example in a multi-stage cooling device. The mixture of the refrigerant R469A and the refrigerant R410A or R466 can advantageously be used in a single-stage cooling device with only one cooling circuit. The proportion by mass of R449A in the refrigerant mixture can be 30 to 70 percent by mass, with the proportion by mass of the further refrigerant R410A or R466 in the refrigerant mixture being 30 to 70 percent by mass. Advantageously, the proportion by mass of R449A can be 50 percent by mass and the proportion by mass of R410A or R466 can be 50 percent by mass. The refrigerant(s) also meets the requirements of EU Regulation No. 5172014 on refrigerants in the version valid on the priority date. With regard to the designation of refrigerants, reference is made to DIN 8960 in the version last valid on the priority date.

It is particularly advantageous if the control device controls the second expansion element according to a reference variable, the reference variable can be a boiling temperature of the refrigerant or temperature of the subcooled refrigerant at the first expansion element. The control device can consequently form a control circuit or a controller which compares the command variable with a controlled variable or influences the second expansion element with a manipulated variable. Since the refrigerant in the cooling circuit is known in principle, the boiling temperature of the refrigerant at the measured pressure in the high-pressure side is also known, so that the boiling temperature of the refrigerant can advantageously be used as a reference variable. The control device can include means for data processing, for example a PLC control, a computer or the like, with the control device being able to run a computer program product or software that carries out the steps required to carry out the method.

The boiling temperature can be determined by the control device, in which case the control device can calculate the boiling temperature of the refrigerant for the pressure measured at the pressure sensor. Accordingly, it can be provided that the control device calculates the boiling temperature of the relevant refrigerant for the respective measured pressure and thus specifically determines the boiling temperature or the control variable.

The boiling temperature can be calculated particularly easily using a polynomial or a vapor pressure table. The polynomial or the vapor pressure table can then simulate a phase boundary line that corresponds to the boiling temperature or the saturation temperature at a saturation vapor pressure or boiling pressure. The polynomial or the vapor pressure table can be stored in the control device, so that a value for the boiling temperature can be derived for the measured pressure, which then corresponds to an assumed boiling pressure, or can be calculated by the control device.

The control device can calculate the command variable by adding the boiling temperature to a safety value of 5 K to 25 K, preferably 7 K to 15 K. The control device can determine the reference variable in such a way that a safety value is added to the boiling temperature, so that the reference variable is greater than the boiling temperature. If a range of, for example, 7 K to 15 K is assumed for the safety value, a command variable range results within which the control device controls the second expansion element. Adding the safety value to the reference variable can prevent the temperature of the refrigerant at the first expansion element from rising above the boiling temperature, for example as a result of a temperature control jump.

To determine a control deviation, the control device can subtract the temperature measured at the temperature sensor as a control variable from the boiling temperature, the control device being able to control the second expansion element with a control variable depending on the control deviation. A control deviation can be determined particularly easily by subtracting the measured temperature from the calculated boiling temperature. Depending on the control deviation, the control device can then control the second expansion element with a manipulated variable and thus influence a quantity of refrigerant metered via the second expansion element.

Consequently, the second expansion element can be controlled using the manipulated variable when the measured temperature is higher than the command variable or the boiling temperature, and the manipulated variable cannot be controlled when the measured temperature is lower than the command variable. If there is no control with the manipulated variable, a manipulated variable or an output level is then 0%. However, the second expansion element can still be opened far enough for the coolant to flow through the second expansion element and continuous supercooling is ensured. A further opening of the second expansion organ only occurs if the measured temperature is higher than the reference variable. Otherwise the second expansion element is in normal operation. Deviating from this, it can also be provided that the second expansion element is closed completely when the measured temperature is lower than the reference variable.

The control device can limit the manipulated variable to a maximum value. This then ensures that the second expansion element is not opened so far that, in the event of a failure of the temperature sensor or the pressure sensor, the second expansion element is opened so far by the control device that the cooling device is damaged.

The second expansion element can be controlled particularly advantageously with a PID controller of the control device. The PID controller may be a PID controller in a series structure or a PID controller in a parallel structure. The PID controller is easy to implement and easy to adapt. The PID controller can be implemented particularly easily within the framework of digital control with the control device.

In the process, the temperature control device can be used to set a temperature in a temperature range from -50 °C to +180 °C, preferably from -70 °C to +180 °C, particularly preferably from -80 °C to +180 °C, within the Test room are trained. The temperature range from -50 °C to +180 °C can still be achieved by a single-stage cooling device with just one cooling circuit. A multi-stage cooling device with at least two or more cooling circuits connected in the manner of a cascade can be used for the remaining, lower temperature ranges. Furthermore, by means of the temperature control device, a temperature in a temperature range from -80° C. to +180° C., preferably -80° C. to +220° C., can be formed inside the test chamber. A temperature in a temperature range from <+60 °C to +220 °C within the test chamber can also be reduced to a temperature of -70 °C or -80 °C by means of the temperature control device. That Refrigerant is strongly heated in the heat exchanger due to the comparatively high temperature in the test chamber, which is why the cooling circuit can be technically adapted to a refrigerant heated in this temperature range in terms of its design, at least on a low-pressure side of the cooling circuit. Otherwise, a refrigerant heated in this way can no longer be optimally used on the high-pressure side of the cooling circuit. Furthermore, it can also be provided that a temperature constancy of +/-1 K +/-0.3 K to +/-0.5 K is formed in the specified temperature range during a test interval in the test room. A test interval is understood here as a time segment of a complete test period in which the test material is exposed to a substantially constant temperature or climatic condition.

An expansion element is understood to mean at least one expansion valve, throttle element, throttle valve or another suitable narrowing of a fluid line.

The first expansion element and the second expansion element can each be formed from a throttle element and a magnetic valve, it being possible for refrigerant to be metered by means of the control device via the respective throttle element and the magnetic valve. The throttling element can be an adjustable valve or a capillary, via which refrigerant is then conducted by means of the magnetic valve. The solenoid valve can in turn be actuated by means of the control device. Actuation can take place in such a way that the solenoid valve is actuated via a manipulated variable for dosing refrigerant.

The test chamber according to the invention for conditioning air comprises a test space that can be closed and temperature-insulated from the environment for receiving test material, and a temperature control device for temperature control of the test space, the temperature control device comprising a cooling device with a cooling circuit with a refrigerant, a heat exchanger arranged in the test space, a Compressor, a condenser, a first expansion device and an internal one Has a heat exchanger, wherein a temperature in a temperature range from -40 °C to +180 °C can be formed within the test chamber by means of the temperature control device, wherein the internal heat exchanger is on a high-pressure side of the cooling circuit in a flow direction before the first expansion element and subsequently the condenser, and on a low-pressure side of the cooling circuit in the direction of flow downstream of the heat exchanger and upstream of the compressor, the cooling circuit having a bypass with at least one second expansion element, the bypass on the high-pressure side in the flow direction downstream of the condenser and upstream of the internal heat exchanger and on the low-pressure side is connected downstream of the heat exchanger and upstream of the internal heat exchanger, with the temperature control device downstream of a control device having a pressure sensor on the high-pressure side and a temperature sensor on the high-pressure side in the direction of flow lgend the internal heat exchanger in the cooling circuit, the second expansion element being controllable by means of the control device as a function of a pressure measured at the pressure sensor and a temperature measured at the temperature sensor. For 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.

The cooling device can be designed with just one cooling circuit. In this embodiment of a test chamber, it is possible to set low temperatures for a number of cooling circuits in the test room, for example -40° C. or down to -50° C., without a large outlay on structural equipment.

The condenser can be designed as a cascade heat exchanger of a further cooling circuit of the cooling device, wherein the further cooling circuit can have a further refrigerant, the cascade heat exchanger, a further compressor, a further condenser and a further expansion element. Accordingly, the test chamber can then have at least two cooling circuits, wherein the cooling circuit can form a second stage of the cooling device and the further cooling circuit, which is then upstream of the cooling circuit, can form a first stage of the cooling device. The condenser then serves as a cascade heat exchanger or heat exchanger for the cooling circuit. In this embodiment of a test chamber, it is possible to develop particularly low temperatures in the test space, for example -70°C.

The temperature control device can have a heating device with a heater and a heating heat exchanger in the test chamber. The heating device can be an electrical resistance heater, for example, which heats the heating and heat exchanger in such a way that the heating and heat exchanger allows the temperature in the test chamber to be increased. If the heat exchanger and the heating heat exchanger can be specifically controlled by the control device for cooling or heating the air circulating in the test room, a temperature in the above-mentioned temperature range can be formed inside the test room by means of the temperature control device. The heating heat exchanger can be combined with the heat exchanger of the cooling circuit in such a way that a common heat exchanger body is formed, through which the refrigerant can flow and which has heating elements of an electrical resistance heater. The condenser can be designed with air cooling or water cooling or another cooling liquid if the condenser is not designed as a cascade heat exchanger. In principle, the condenser can be cooled with any suitable fluid. It is essential that the heat load occurring at the condenser is dissipated via air cooling or water cooling in such a way that the refrigerant can condense so that it is liquefied.

The cooling circuit can have a further bypass with at least one third expansion element, the further bypass on the high-pressure side downstream of the compressor in the direction of flow and upstream of the condenser, and on the low-pressure side downstream of the internal heat exchanger and upstream of the compressor, such that a suction gas temperature and/or a suction gas pressure of the refrigerant can be regulated on the low-pressure side upstream of the compressor, and/or that a pressure difference between the High-pressure side and the low-pressure side can be compensated. The further bypass can additionally be equipped with an adjustable or controllable valve, for example a solenoid valve. By connecting the high-pressure side and the low-pressure side via the third expansion element, it can be ensured that when the system is at a standstill, the compressed and gaseous refrigerant gradually flows from the high-pressure side to the low-pressure side of the cooling circuit. This ensures that even when the expansion device is closed, there is a gradual pressure equalization between the high-pressure side and the low-pressure side. A cross section of the third expansion element can be dimensioned in such a way that an overflow of the refrigerant from the high-pressure side to the low-pressure side affects normal operation of the cooling device only insignificantly. The third expansion element can be actuated by the control device, which in turn can be additionally coupled to a further pressure sensor which is arranged in the cooling circuit in a direction of flow directly in front of the compressor. It is particularly advantageous if a suction gas temperature of ≦30° C. can be set via the additional bypass. The refrigerant can also be metered in such a way that the operating time of the compressor can be regulated. In principle, it is disadvantageous if the compressor or compressor is switched on and off many times. A service life of the compressor can be extended if it is operated for longer periods of time. The refrigerant can be routed past the expansion element or the condenser via the further bypass, for example in order to delay an automatic switch-off of the compressor and to extend the service life of the compressor.

The internal heat exchanger can be designed as a supercooling section or a heat exchanger, in particular a plate heat exchanger. The sub-cooling section can already be formed by two line sections of the cooling circuit that are in contact with one another.

Further advantageous embodiments of a test chamber result from the feature descriptions of the subclaims that refer back to claim 1 .

A preferred embodiment of the invention is explained in more detail below with reference to the attached drawing.

Fig. 1

eine schematische Darstellung einer ersten Ausführungsform einer Kühleinrichtung;

Fig. 2

eine schematische Darstellung einer zweiten Ausführungsform einer Kühleinrichtung.

Show it:

1

a schematic representation of a first embodiment of a cooling device;

2

a schematic representation of a second embodiment of a cooling device.

the 1 shows a schematic representation of a cooling device 10 with a cooling circuit 11, within which a refrigerant can circulate. The refrigerant is a zeotropic refrigerant with a temperature glide of ≧5 K. The cooling device 10 includes a further cooling circuit 12 which is connected upstream of the cooling circuit 11 . The cooling circuit 11 comprises a heat exchanger 14 arranged in a test space 13 of a test chamber (not shown in detail here), a compressor 15, a condenser 16, a first expansion element 17 and an internal heat exchanger 18. The cooling circuit 11 has a high-pressure side 19, which extends in the direction of flow of the refrigerant runs from the compressor 15 to the first expansion element 17 and a low-pressure side 20, which runs from the first expansion element 17 to the compressor 15. In a pipe section 21 from the compressor 15 to the condenser 16, the refrigerant is gaseous and has a comparatively high temperature. The refrigerant compressed by the compressor 15 flows into the cooling circuit 11 via an oil separator 22 to the condenser 16, the gaseous refrigerant being liquefied in the condenser 16. In the direction of flow of the refrigerant, the internal heat exchanger 18 follows the condenser 16 in the cooling circuit 11, the refrigerant therefore being in the liquid state in a pipe section 23 of the cooling circuit 11 between the condenser 16 and the first expansion element 17. Expansion of the refrigerant downstream of the first expansion element 17 cools the heat exchanger 14, with the refrigerant then changing into the gaseous aggregate state in a pipe section 24 between the first expansion element 17 and the heat exchanger 14 and via a pipe section 25 from the heat exchanger 14 to the compressor 15 is conducted.

In the cooling circuit 11 the internal heat exchanger 18 is connected to the tube sections 23 and 25 on the high-pressure side 19 and the low-pressure side 20 of the cooling circuit 11 . The refrigerant on the high-pressure side 19 flows so closely past the refrigerant on the low-pressure side 20 in the internal heat exchanger 18 that an exchange of thermal energy occurs in the internal heat exchanger 18 . The internal heat exchanger 18 is used here to supercool the refrigerant on the high-pressure side 19 with the refrigerant on the low-pressure side 20. This supercooling is ensured by a bypass 26, which is formed from a pipe section 27 with a second expansion element 28. The bypass 26 or the pipe section 27 is connected on the high-pressure side 19 in the direction of flow after the condenser 16 and before the internal heat exchanger 18, and on the low-pressure side 20 after the heat exchanger 14 and before the internal heat exchanger 18. Refrigerant can thus be metered or expanded from the high-pressure side 19 to the low-pressure side 20 via the second expansion element 28 and conducted into the internal heat exchanger 18 .

Furthermore, a pressure sensor 29 for measuring the pressure of the low-pressure side 20 is arranged in the pipe section 25 immediately before the compressor 15 , and a pressure sensor 30 for measuring the pressure of the high-pressure side 19 is arranged in the pipe section 21 immediately following the compressor 15 . A temperature sensor 31 is arranged in the pipe section 23, following the internal heat exchanger 18 and directly in front of the first expansion element 17, with which a temperature of the refrigerant is measured.

Another bypass 32 with a third expansion element 33 is also connected in the cooling circuit 11 . The further bypass 32 runs from the high-pressure side 19 in the direction of flow after the compressor 15 and before the condenser 16, to the low-pressure side 20 after the internal heat exchanger 18 and before the compressor 15. Via the further bypass 32 or the third expansion element 33, a Suction gas temperature and / or a suction gas pressure of the refrigerant on the low-pressure side 20 before the compressor 15 is regulated and, if necessary, a pressure difference between the high-pressure side 19 and the low-pressure side 20 can be compensated.

The other cooling circuit 12 is filled with another refrigerant and includes another compressor 34, another condenser 35 and another expansion element 36. The condenser 16 of the cooling circuit 11 is integrated into the further cooling circuit 12 that a cascade heat exchanger 37 through the Capacitor 16 is formed.

The test chamber, which is not shown in detail here, has a control device with which the cooling device 10 can be controlled. The control device is coupled to the pressure sensor 29, the pressure sensor 30, the temperature sensor 31, the first expansion element 17 and the second expansion element 28. In particular, a pressure is measured by the control device via the pressure sensor 30 and a temperature of the refrigerant is measured via the temperature sensor 31 and the second expansion element 28 is controlled with a manipulated variable. The controller determines a Boiling temperature of the refrigerant at the temperature sensor 31 in that the control device calculates the boiling temperature for the pressure measured at the pressure sensor 30 . This calculation is done using a polynomial or a vapor pressure table. The boiling temperature is a reference variable according to which the control device controls the second expansion element 17 . The control device determines a control deviation by subtracting the temperature measured at the temperature sensor 31 as a control variable from the boiling temperature, the control device controlling the second expansion element 28 as a function of this control deviation using the manipulated variable.

Provision is made for the second expansion element 28 to be controlled only when the measured temperature is higher than the reference variable. If the measured temperature is lower than the reference variable, the second expansion element 28 is not controlled with the manipulated variable, or the second expansion element 28 is then operated as usual. By controlling the second expansion element when a control deviation occurs due to a higher temperature at the temperature sensor 31, it can be ensured that the refrigerant is always supercooled upstream of the first expansion element 17 to such an extent that the refrigerant is not heated to the boiling point. The cooling circuit 11 and thus the cooling device 10 can be operated safely and without major temperature fluctuations. If the pressure sensor 30 and the temperature sensor 31 are already present in a cooling circuit, it is only necessary to design or adapt the control device in such a way that a corresponding control of the second expansion element 28 can be carried out. In this way, operational reliability of the cooling device 10 can be significantly improved with simple means.

the 2 shows a schematic representation of a cooling device 40. In contrast to the cooling device from FIG Fig.1 only the cooling circuit 11 is provided here. The cooling device 40 is therefore in one stage educated. The cooling circuit 11 is operated as described above. With the cooling device 40, it is possible to form low temperatures in the test room, for example -40.degree. C. to -50.degree.

Claims (21)

1. A method for conditioning air, said method being carried out by means of a test chamber having a temperature-insulated test space (13) which is capable of being sealed against an environment and serves to receive test material, and a temperature control device for controlling the temperature of the test space, a temperature in a temperature range of -40 °C to +180 °C being established within the test space by means of the temperature control device having a cooling device (10, 40) having a cooling circuit (11) comprising a refrigerant, a heat exchanger (14) disposed in the test space, a compressor (15), a condenser (16), a first expansion element (17) and an internal heat exchanger (18), the internal heat exchanger being connected to a high-pressure side (19) of the cooling circuit upstream of the first expansion element and downstream of the condenser, and to a low-pressure side (20) of the cooling circuit downstream of the heat exchanger and upstream of the compressor, the cooling circuit having a bypass (26) having at least one second expansion element (28), the bypass being connected to the high-pressure side downstream of the condenser and upstream of the internal heat exchanger, and to the low-pressure side downstream of the heat exchanger and upstream of the internal heat exchanger,
   characterized in that
   a controlling system of the temperature control device controls the second expansion element by means of a pressure sensor (30) at the high-pressure side and by means of a temperature sensor (31) at the high-pressure side downstream of the internal heat exchanger in the cooling circuit as a function of a pressure measured at the pressure sensor and of a temperature measured at the temperature sensor.
2. The method according to claim 1,
   characterized in that
   the refrigerant of the high-pressure side (19) is cooled by means of the internal heat exchanger (18).
3. The method according to claim 1 or 2,
   characterized in that
   refrigerant is supplied to the internal heat exchanger (18) via the second expansion element (28), refrigerant being supplied to the compressor (15) from the low-pressure side (20) of the internal heat exchanger.
4. The method according to any one of the preceding claims, characterized in that
   a refrigerant having a temperature glide of ≥ 5 K is used as refrigerant.
5. The method according to any one of the preceding claims, characterized in that
   R469A or a mixture of the refrigerant R469A and the refrigerant R410A or R466A is used as refrigerant.
6. The method according to any one of the preceding claims, characterized in that
   the controlling system controls the second expansion element (28) according to a reference variable, the reference variable being a boiling temperature of the refrigerant or a temperature of the subcooled refrigerant at the first expansion element (17).
7. The method according to claim 6,
   characterized in that
   the boiling temperature is determined by means of the controlling system, the controlling system calculating the boiling temperature of the refrigerant for the pressure measured at the pressure sensor (30).
8. The method according to claim 7,
   characterized in that
   the boiling temperature is calculated by means of a polynomial or a vapor pressure table.
9. The method according to any one of claims 6 to 8, characterized in that
   the controlling system calculates the reference variable by adding a safety value of 5 K to 25 K, preferably 7 K to 15 K, to the boiling temperature.
10. The method according to any one of claims 6 to 9, characterized in that
    the controlling system subtracts the temperature measured at the temperature sensor (31) as a controlled variable from the boiling temperature in order to determine a control deviation, the controlling system controlling the second expansion element (28) as a function of the control deviation by means of a manipulated variable.
11. The method according to claim 10,
    characterized in that
    the second expansion element (28) is controlled by means of the manipulated variable when the measured temperature is higher than the reference variable, and in that no controlling is carried out by means of the manipulated variable when the measured temperature is lower than the reference variable.
12. The method according to claim 10 or 11,
    characterized in that
    the controlling system limits the manipulated variable to a maximum value.
13. The method according to any one of the preceding claims, characterized in that
    the second expansion element (28) is controlled by means of a PID controller of the controlling system.
14. The method according to any one of the preceding claims, characterized in that
    a temperature in a temperature range of -50 °C to +180 °C, preferably of -70 °C to +180 °C, especially preferably of -80 °C to +180 °C, is established within the test space.
15. The method according to any one of the preceding claims, characterized in that
    the first expansion element (17) and the second expansion element (28) are each composed of a throttle and a magnetic valve, refrigerant being metered by means of the controlling system via the respective throttle and the magnetic valve.
16. A test chamber for conditioning air, said test chamber comprising a temperature-insulated test space (13) which is capable of being sealed against an environment and serves to receive test material, and a temperature control device for controlling the temperature of the test space, the temperature control device having a cooling device (10, 40) having a cooling circuit (11) comprising a refrigerant, a heat exchanger (14) disposed in the test space, a compressor (15), a condenser (16), a first expansion element (17) and an internal heat exchanger (18), a temperature in a temperature range of -40 °C to +180 °C being capable of being established within the test space by means of the temperature control device, the internal heat exchanger being connected to a high-pressure side (19) of the cooling circuit upstream of the first expansion element and downstream of the condenser, and to a low-pressure side (20) of the cooling circuit downstream of the heat exchanger and upstream of the compressor, the cooling circuit having a bypass (26) having at least one second expansion element (28), the bypass being connected to the high-pressure side downstream of the condenser and upstream of the internal heat exchanger, and to the low-pressure side downstream of the heat exchanger and upstream of the internal heat exchanger, characterized in that
    the temperature control device comprises a controlling system having a pressure sensor (30) at the high-pressure side and a temperature sensor (31) at the high-pressure side downstream of the internal heat exchanger in the cooling circuit, the second expansion element being controlled by means of the controlling system as a function of a pressure measured at the pressure sensor and of a temperature measured at the temperature sensor.
17. The test chamber according to claim 16,
    characterized in that
    the cooling device (40) is realized with only one cooling circuit (12).
18. The test chamber according to claim 16,
    characterized in that
    the condenser (16) is realized as a cascade heat exchanger (37) of another cooling circuit (12) of the cooling device (10), the other cooling circuit having another refrigerant, the cascade heat exchanger, another compressor (34), another condenser (35) and another expansion element (36).
19. The test chamber according to any one of claims 16 to 18, characterized in that
    the temperature control device has a heating device having a heater and a heating heat exchanger in the test space.
20. The test chamber according to any one of claims 16 to 19, characterized in that
    the cooling circuit (11) has another bypass (32) having at least one third expansion element (33), the other bypass being connected to the high-pressure side (19) downstream of the compressor (15) and upstream of condenser (16), and to the low-pressure side (20) downstream of the internal heat exchanger (18) and upstream of the compressor in such a manner that a suction gas temperature and/or a suction gas pressure of the refrigerant is/are controllable at the low-pressure side upstream of the compressor, and/or in such a manner that a pressure difference between the high-pressure side and the low-pressure side is compensable.
21. The test chamber according to any one of claims 16 to 20, characterized in that
    the internal heat exchanger (18) is realized as a subcooling section or a heat exchanger, in particular a plate heat exchanger.

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