Cooling device

Abstract

To provide a cooling device capable of improving cooling efficiency, the cooling device having an intermediate heat exchanger.SOLUTION: A cooling device 100 comprises: a two-stage compressor 1; a condenser or a gas cooler 2; a first expansion valve 3; an intermediate heat exchanger 4 that includes an evaporation part 4a evaporating a refrigerant expanded at the first expansion valve 3 and supplying it to a second compression part 1b, and a cooling part 4b cooling a remaining refrigerant out of the refrigerant having passed through the condenser or the gas cooler 2, and performing heat exchange between a refrigerant inside the evaporation part 4a and a refrigerant inside the cooling part 4b; a second expansion valve 5; an evaporator 6; and a control part 7 that controls adjustment of opening of the first expansion valve 3 on the basis of at least temperature of a refrigerant at an inlet of the evaporation part 4a of the intermediate heat exchanger 4.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a cooling device, and more particularly to a cooling device equipped with an intermediate heat exchanger. [Background technology]

[0002] 2. Description of the Related Art Conventionally, cooling devices equipped with an intermediate heat exchanger are known (see, for example, Patent Document 1).

[0003] The above-mentioned Patent Document 1 discloses a refrigeration device including a compressor, a condenser, a main expansion valve, an evaporator, an intermediate heat exchanger, and an electronic expansion valve that throttles the refrigerant supplied to the intermediate heat exchanger. In Patent Document 1, the refrigerant compressed by the compressor is condensed by the condenser, and then the refrigerant is supplied from the condenser to the intermediate heat exchanger. The intermediate heat exchanger includes a first portion and a second portion, and the refrigerant condensed by the condenser is supplied separately to the first portion and the second portion. An electronic expansion valve is provided in a flow path connecting the condenser and the first portion of the intermediate heat exchanger. On the other hand, an electronic expansion valve is not provided in a flow path connecting the condenser and the second portion of the intermediate heat exchanger. In the intermediate heat exchanger, heat exchange is performed between the refrigerant decompressed by the electronic expansion valve and supplied to the first portion and the refrigerant supplied to the second portion, and the refrigerant supplied to the first portion is evaporated and the refrigerant supplied to the second portion is cooled. The refrigerant cooled in the second portion is supplied to the evaporator via the main expansion valve. The refrigerant evaporated in the first portion is supplied to the compressor. Furthermore, the refrigeration device of Patent Document 1 controls the opening degree of the electronic expansion valve according to the difference between the detection result of a temperature detector set at the inlet or outlet of the compressor and a predetermined target temperature at the inlet and outlet of the high pressure side of the intermediate heat exchanger. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2009-192164 A Summary of the Invention [Problem to be solved by the invention]

[0005] In the case of a cooling device equipped with an intermediate heat exchanger as disclosed in Patent Document 1, the refrigerant supplied to the evaporator is cooled in the intermediate heat exchanger, thereby increasing the degree of supercooling of the refrigerant supplied to the evaporator and improving the cooling efficiency of the evaporator. Furthermore, when the heat exchange amount of the intermediate heat exchanger is maximum, the degree of supercooling of the refrigerant increases, and the cooling efficiency can be improved. However, since the refrigerant supercooled in the intermediate heat exchanger is evaporated in the evaporator and then supplied to the compressor, it is difficult to estimate whether the heat exchange amount of the intermediate heat exchanger is maximum or not from the temperature at the inlet or outlet of the compressor, and it is difficult to improve the cooling efficiency of the evaporator.

[0006] In addition, even if the air to be cooled in the evaporator is lower than the set temperature and it is desired to weaken the cooling in the evaporator, the refrigerant to be supplied to the evaporator is cooled in the intermediate heat exchanger, so that the evaporator may be overcooled. In this case, the compressor operation is repeatedly stopped and restarted. This causes uneven cooling, resulting in poor cooling efficiency.

[0007] The present invention has been made to solve the above-mentioned problems, and one object of the present invention is to provide a cooling device that is equipped with an intermediate heat exchanger and that can further improve cooling efficiency. [Means for solving the problem]

[0008] In order to achieve the above object, a cooling device according to a first aspect of the present invention includes a two-stage compressor including a first compression section that compresses a refrigerant and a second compression section that further compresses the refrigerant compressed by the first compression section, a condenser that condenses the refrigerant supplied from the second compression section or a gas cooler that cools the refrigerant supplied from the second compression section, a first expansion valve that receives a portion of the refrigerant condensed in the condenser or cooled in the gas cooler and expands the supplied refrigerant, and an expansion valve that evaporates the refrigerant expanded in the first expansion valve and supplies it to the second compression section. the refrigerant cooling unit includes an evaporator section that supplies refrigerant to the condenser or gas cooler, and a cooling section that cools the remaining refrigerant from the refrigerant that has passed through the condenser or the gas cooler, and is equipped with an intermediate heat exchanger that performs heat exchange between the refrigerant in the evaporator section and the refrigerant in the cooling section, a second expansion valve that is arranged downstream of the cooling section of the intermediate heat exchanger and expands the refrigerant, an evaporator that is arranged downstream of the second expansion valve and cools the space to be cooled by evaporating the refrigerant, and a control unit that performs control to adjust the opening of the first expansion valve based at least on the temperature of the refrigerant at the inlet of the evaporator section of the intermediate heat exchanger.

[0009] As described above, the cooling device according to a first aspect of the present invention includes a control unit that performs control to adjust the opening degree of the first expansion valve based at least on the temperature of the refrigerant at the inlet of the evaporator of the intermediate heat exchanger. This makes it possible to obtain the amount of change in the heat exchange amount of the intermediate heat exchanger by measuring the temperature of the refrigerant at the inlet of the evaporator of the intermediate heat exchanger, and therefore the heat exchange amount of the intermediate heat exchanger can be obtained based on the temperature of the refrigerant at the inlet of the evaporator of the intermediate heat exchanger. Therefore, the opening degree of the first expansion valve can be adjusted so that the heat exchange amount by the intermediate heat exchanger is maximized based on the temperature of the refrigerant at the inlet of the evaporator. As a result, the cooling efficiency can be further improved in a cooling device including an intermediate heat exchanger.

[0010] In the cooling device according to the above aspect, the control unit preferably performs control to adjust the aperture of the first expansion valve so as to improve the cooling efficiency of the intermediate heat exchanger, based at least on the temperature of the refrigerant at the inlet of the evaporator of the intermediate heat exchanger. With this configuration, the control unit adjusts the aperture of the first expansion valve so as to improve the cooling efficiency, so that the cooling efficiency of the intermediate heat exchanger can be further improved.

[0011] In this case, preferably, the control unit performs control to adjust the opening degree of the first expansion valve based on both the temperature of the refrigerant at the inlet of the evaporator of the intermediate heat exchanger and the temperature of the refrigerant at the outlet of the cooling unit of the intermediate heat exchanger. With this configuration, it is possible to obtain the temperature difference between the temperature of the refrigerant at the inlet of the evaporator and the temperature of the refrigerant at the outlet of the cooling unit of the intermediate heat exchanger. Here, it can be considered that the smaller the difference between the temperature of the refrigerant at the inlet of the evaporator of the intermediate heat exchanger and the temperature of the refrigerant at the outlet of the cooling unit of the intermediate heat exchanger, the greater the amount of heat exchange, since it can be said that the refrigerant in the cooling unit has been cooled to a temperature close to that of the refrigerant in the evaporation unit by the refrigerant in the evaporation unit. Therefore, the control unit can adjust the opening degree of the first expansion valve so as to reduce the temperature difference between the refrigerant at the inlet of the evaporator and the refrigerant at the outlet of the cooling unit, thereby increasing the amount of heat exchange and further improving the cooling efficiency of the intermediate heat exchanger.

[0012] In the cooling device according to the first aspect, preferably, the control unit performs control to adjust the aperture of the first expansion valve so that the difference between the temperature of the refrigerant at the inlet of the evaporator of the intermediate heat exchanger and the temperature of the refrigerant at the outlet of the cooling unit of the intermediate heat exchanger becomes a set value. Here, when the difference between the temperature of the refrigerant at the inlet of the evaporator of the intermediate heat exchanger and the temperature of the refrigerant at the outlet of the cooling unit of the intermediate heat exchanger is close to a minimum value, it can be considered that the refrigerant at the outlet of the cooling unit of the intermediate heat exchanger has been cooled to close to the temperature of the refrigerant at the inlet of the evaporator, and therefore it can be considered that the amount of heat exchange between the evaporator and the cooling unit has become maximum. Therefore, for example, by setting the set value so that the difference between the temperature of the refrigerant at the inlet of the evaporator of the intermediate heat exchanger and the temperature of the refrigerant at the outlet of the cooling unit of the intermediate heat exchanger becomes close to the minimum value, the aperture of the first expansion valve can be accurately adjusted so that the amount of heat exchange in the intermediate heat exchanger is maximized, and the cooling efficiency of the intermediate heat exchanger can be further improved.

[0013] In this case, preferably, the control unit performs control to adjust the opening of the first expansion valve so that the refrigerant temperature approaches a set value of the difference between the refrigerant temperature at the inlet of the evaporator section of the intermediate heat exchanger and the refrigerant temperature at the outlet of the cooling section of the intermediate heat exchanger. With this configuration, by setting a set value that maximizes the heat exchange amount of the intermediate heat exchanger in accordance with the operating conditions of the cooling device, the control unit can easily adjust the opening of the first expansion valve so that the heat exchange amount of the intermediate heat exchanger is maximized.

[0014] In the above configuration, the control unit is configured to perform control to adjust the aperture of the first expansion valve so that the difference between the refrigerant temperature at the inlet of the evaporator of the intermediate heat exchanger and the refrigerant temperature at the outlet of the cooling section of the intermediate heat exchanger becomes a set value, and the control unit is preferably configured to alternately perform a first control to reduce the aperture of the first expansion valve when the difference between the refrigerant temperature at the inlet of the evaporator of the intermediate heat exchanger and the refrigerant temperature at the outlet of the cooling section of the intermediate heat exchanger becomes close to the set value and the refrigerant temperature at the outlet of the cooling section of the intermediate heat exchanger increases, and a second control to increase the aperture of the first expansion valve when the difference between the refrigerant temperature at the inlet of the evaporator of the intermediate heat exchanger and the refrigerant temperature at the outlet of the cooling section of the intermediate heat exchanger is greater than close to the set value. With this configuration, the aperture of the first expansion valve can be adjusted so that the difference between the refrigerant temperature at the inlet of the evaporator of the intermediate heat exchanger and the refrigerant temperature at the outlet of the cooling section of the intermediate heat exchanger becomes close to the set value, and therefore the cooling device can be driven while maintaining a state in which the amount of heat exchange by the intermediate heat exchanger is maximized.

[0015] In the cooling device according to the first aspect, preferably, the control unit acquires the temperature of the refrigerant at the inlet of the evaporator, estimates the temperature of the refrigerant at the inlet of the evaporator of the intermediate heat exchanger from the relationship between the temperature of the refrigerant at the inlet of the evaporator and the temperature of the refrigerant at the inlet of the evaporator of the intermediate heat exchanger, and performs control to adjust the aperture of the first expansion valve based on the estimated temperature of the refrigerant at the inlet of the evaporator of the intermediate heat exchanger. With this configuration, for example, it is possible to estimate an optimal temperature of the refrigerant at the inlet of the evaporator of the intermediate heat exchanger based on the relationship between the temperature of the refrigerant at the inlet of the evaporator at which the amount of heat exchanged by the intermediate heat exchanger is maximized and the temperature of the refrigerant at the inlet of the evaporator of the intermediate heat exchanger, and adjust the aperture of the first expansion valve to achieve the optimal temperature. As a result, by acquiring the temperature of the refrigerant at the inlet of the evaporator, it is possible to further improve the cooling efficiency.

[0016] In this case, preferably, the control unit performs control to adjust the aperture of the first expansion valve so that the actual measured value of the temperature of the refrigerant at the inlet of the evaporator of the intermediate heat exchanger becomes the estimated temperature of the refrigerant at the inlet of the evaporator of the intermediate heat exchanger. With this configuration, it is only necessary to adjust the aperture of the first expansion valve to the estimated temperature, making it easy to adjust the aperture of the first expansion valve to an appropriate value for improving cooling efficiency.

[0017] In the cooling device according to the first aspect, the control unit is preferably configured to suppress cooling of the space to be cooled by controlling to close the first expansion valve when the temperature of the space to be cooled is equal to or lower than a set temperature and the rotation speed of the two-stage compressor is equal to or lower than a predetermined value. With this configuration, the cooling of the refrigerant by the intermediate heat exchanger can be stopped by closing the first expansion valve, so that even when the rotation speed of the two-stage compressor cannot be reduced, cooling of the space to be cooled can be suppressed without stopping the operation of the two-stage compressor. As a result, uneven cooling caused by repeatedly stopping and restarting the operation of the two-stage compressor can be suppressed, and the cooling efficiency of the cooling device can be improved.

[0018] A cooling device according to a second aspect of the present invention includes a two-stage compressor including a first compression section that compresses a refrigerant and a second compression section that further compresses the refrigerant compressed by the first compression section, a condenser that condenses the refrigerant supplied from the second compression section or a gas cooler that cools the refrigerant supplied from the second compression section, a first expansion valve that receives a portion of the refrigerant condensed in the condenser or cooled in the gas cooler and expands the supplied refrigerant, an evaporation section that evaporates the refrigerant expanded in the first expansion valve and supplies it to the second compression section, and a cooling section that evaporates the refrigerant that has passed through the condenser or the gas cooler. The cooling section cools the remaining refrigerant, and the cooling section cools the remaining refrigerant. The cooling section includes an intermediate heat exchanger that exchanges heat between the refrigerant in the evaporator section and the refrigerant in the cooling section, a second expansion valve that is arranged downstream of the cooling section of the intermediate heat exchanger and expands the refrigerant, an evaporator that is arranged downstream of the second expansion valve and cools the space to be cooled by evaporating the refrigerant, and a control section that is configured to suppress cooling of the space to be cooled by controlling the opening of the first expansion valve to be reduced when the temperature of the space to be cooled is below a set temperature and the rotation speed of the two-stage compressor is below a predetermined value.

[0019] The cooling device according to the second aspect of the present invention includes a control unit configured to suppress cooling of the space to be cooled by controlling the first expansion valve to close when the temperature of the space to be cooled is equal to or lower than a set temperature and the rotation speed of the two-stage compressor is equal to or lower than a predetermined value, as described above. This makes it possible to weaken the cooling of the refrigerant by the intermediate heat exchanger by reducing the opening degree of the first expansion valve, thereby suppressing cooling of the space to be cooled without stopping the operation of the two-stage compressor. As a result, it is possible to suppress uneven cooling caused by repeatedly stopping and restarting the operation of the two-stage compressor, thereby improving cooling efficiency.

[0020] In the cooling device according to the second aspect of the present invention, the control unit is preferably configured to suppress cooling of the space to be cooled by controlling to close the first expansion valve when the temperature of the space to be cooled is equal to or lower than a set temperature and the rotation speed of the two-stage compressor is equal to or lower than a predetermined value. With this configuration, cooling of the refrigerant by the intermediate heat exchanger can be stopped by closing the first expansion valve, so that cooling of the space to be cooled can be effectively suppressed without stopping the operation of the two-stage compressor.

[0021] In the cooling device according to the second aspect of the present invention, the control unit is preferably configured to control the first expansion valve to be opened less and the second expansion valve to be opened less when the temperature of the space to be cooled is equal to or lower than a set temperature and the rotation speed of the two-stage compressor is equal to or lower than a predetermined value, thereby suppressing cooling of the space to be cooled. With this configuration, the amount of refrigerant circulating can be reduced by reducing the opening of the second expansion valve, thereby reducing excess refrigeration capacity. As a result, it is possible to further suppress cooling of the space to be cooled without stopping the operation of the two-stage compressor. Effect of the Invention

[0022] According to the present invention, as described above, it is possible to provide a cooling device including an intermediate heat exchanger, which is capable of further improving the cooling efficiency. [Brief description of the drawings]

[0023] [Figure 1] FIG. 1 is a diagram showing a configuration of a cooling device according to a first embodiment and a third embodiment. [Diagram 2] 4 is a graph showing the relationship between the opening degree of the first expansion valve and the temperature of the evaporator section or the temperature of the cooling section. [Diagram 3] 4 is a flowchart of control by a control unit according to the first embodiment. [Figure 4] FIG. 11 is a diagram showing the configuration of a cooling device according to a second embodiment. [Diagram 5]4 is a graph showing a relationship between the inlet temperature of the evaporator and the inlet temperature of the evaporator. [Figure 6] 4 is a graph showing the relationship between the opening degree of the first expansion valve and the temperature at the inlet of the evaporator. [Figure 7] 10 is a flowchart of control by a control unit according to a second embodiment. [Figure 8] 4A and 4B are PH diagrams illustrating the cooling capacity when the first expansion valve is in an open state and a closed state, respectively. [Figure 9] 10 is a flowchart of control by a control unit according to a third embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings.

[0025] [First embodiment] The configuration of a cooling device 100 according to a first embodiment will be described with reference to FIGS.

[0026] As shown in Fig. 1, the cooling device 100 includes a two-stage compressor 1, a gas cooler 2, a first expansion valve 3, an intermediate heat exchanger 4, a second expansion valve 5, an evaporator 6, and a control unit 7. The cooling device 100 also includes an internal heat exchanger 8 and a strainer 9. The cooling device 100 is a device that cools a space to be cooled by a refrigerant. The cooling device 100 is used, for example, in a showcase, and the interior of the showcase is the space to be cooled. The refrigerant is, for example, carbon dioxide.

[0027] The two-stage compressor 1 includes a first compression section 1a and a second compression section 1b. The first compression section 1a compresses the low-pressure refrigerant supplied from the evaporator 6 via the internal heat exchanger 8 into a medium-pressure refrigerant. The second compression section 1b further compresses the medium-pressure refrigerant compressed in the first compression section 1a into a high-pressure refrigerant. The refrigerant compressed in the first compression section 1a is supplied to a cooler 12. The refrigerant compressed in the second compression section 1b is supplied to a gas cooler 2.

[0028] The cooler 12 cools the refrigerant brought to an intermediate pressure state in the first compression section 1a. The refrigerant cooled by the cooler 12 is supplied to the second compression section 1b. The gas cooler 2 cools the refrigerant brought to a high pressure state in the second compression section 1b to produce a low-temperature, high-pressure refrigerant. The refrigerant cooled by the gas cooler 2 is supplied to the intermediate heat exchanger 4.

[0029] The first expansion valve 3 is supplied with a portion of the refrigerant cooled by the gas cooler 2, and expands the supplied refrigerant. This results in a low-temperature, low-pressure refrigerant. The larger the opening of the first expansion valve 3, the greater the flow rate of the refrigerant supplied to the evaporation section 4a, and therefore the greater the amount of cooling. On the other hand, when the opening of the first expansion valve 3 becomes smaller, the flow rate decreases, and therefore the amount of cooling decreases.

[0030] The intermediate heat exchanger 4 includes an evaporator section 4a and a cooling section 4b. The evaporator section 4a is supplied with the refrigerant expanded in the first expansion valve 3. The cooling section 4b is supplied with the remaining refrigerant among the refrigerants cooled in the gas cooler 2 without passing through the first expansion valve 3. The intermediate heat exchanger 4 exchanges heat between the refrigerant in the evaporator section 4a and the refrigerant in the cooling section 4b. The refrigerant supplied to the evaporator section 4a is a refrigerant expanded by the first expansion valve 3 and in a low-pressure, low-temperature state. On the other hand, the refrigerant supplied to the cooling section 4b is a high-temperature refrigerant that does not pass through the first expansion valve 3. Therefore, heat exchange is performed between the refrigerant in the evaporator section 4a and the refrigerant in the cooling section 4b, the refrigerant in the evaporator section 4a evaporates, and the refrigerant in the cooling section 4b is cooled. The refrigerant cooled in the cooling section 4b is supplied to the internal heat exchanger 8. The refrigerant evaporated in the evaporator section 4a is supplied to the second compression section 1b.

[0031] The internal heat exchanger 8 exchanges heat between the refrigerant supplied from the cooling section 4b and the refrigerant that has passed through the evaporator 6. This allows the refrigerant supplied from the cooling section 4b to be cooled, and the degree of superheat of the refrigerant that has passed through the evaporator 6 to be increased.

[0032] The second expansion valve 5 expands the refrigerant cooled by the internal heat exchanger 8 to produce a low-pressure, low-temperature refrigerant. The larger the opening of the second expansion valve 5, the greater the flow rate of the refrigerant supplied to the evaporator 6. On the other hand, when the opening of the second expansion valve 5 becomes smaller, the flow rate becomes smaller. Therefore, the opening of the second expansion valve 5 affects the cooling capacity of the evaporator 6.

[0033] The evaporator 6 exchanges heat between the low-pressure, low-temperature refrigerant supplied from the second expansion valve 5 and the air in the space to be cooled, evaporating the refrigerant and cooling the air in the space to be cooled. The cooled air in the space to be cooled cools the space to be cooled. The refrigerant in the evaporator 6 becomes a low-pressure superheated state, and is further superheated in the internal heat exchanger 8 before being supplied to the first compression section 1a. A check valve 10 is provided in the flow path connecting the outlet side of the evaporator 6 and the internal heat exchanger 8.

[0034] The control unit 7 controls the operation of the cooling device 100 so that the temperature inside the showcase, which is the space to be cooled, becomes the set temperature. The control unit 7 controls the operation of the two-stage compressor 1 to adjust the flow rate and thereby adjust the cooling capacity of the evaporator 6. The control unit 7 also adjusts the opening degree of the first expansion valve 3 and the second expansion valve 5 to adjust the cooling capacity of the evaporator 6.

[0035] The strainer 9 is a mesh net provided in the refrigerant flow path to collect foreign matter in the refrigerant flow path.

[0036] The temperature measuring unit 11 is provided at the inlet of the evaporator unit 4a of the intermediate heat exchanger 4 and at the outlet of the cooling unit 4b of the intermediate heat exchanger 4. The temperature of the refrigerant measured by the temperature measuring unit 11 is transmitted to the control unit 7. The temperature measuring unit 11 is, for example, a thermistor.

[0037] The control unit 7 includes a CPU (Central Processing Unit). The control unit 7 performs control to adjust the opening degree of the first expansion valve 3 so as to improve the cooling efficiency of the intermediate heat exchanger 4 based on at least the temperature of the refrigerant at the inlet of the evaporator 4a of the intermediate heat exchanger 4. Specifically, the control unit 7 performs control to adjust the opening degree of the first expansion valve 3 based on both the temperature of the refrigerant at the inlet of the evaporator 4a of the intermediate heat exchanger 4 and the temperature of the refrigerant at the outlet of the cooling unit 4b of the intermediate heat exchanger 4.

[0038] FIG. 2 is a graph in which the temperature of the refrigerant is plotted on the vertical axis and the aperture of the first expansion valve 3 is plotted on the horizontal axis. As shown in FIG. 2, when the aperture of the first expansion valve 3 is gradually increased from the closed state, the amount of the refrigerant flowing into the evaporation section 4a increases, and the temperature of the refrigerant rises. On the other hand, the temperature of the refrigerant at the outlet of the cooling section 4b decreases because the amount of the refrigerant that is heat exchanged increases as the amount of the refrigerant flowing into the evaporation section 4a increases. However, after passing the optimum point (allowable value), the temperature of the refrigerant at the cooling section 4b starts to rise. The optimum point indicates the aperture of the first expansion valve 3 at which the difference ΔT between the temperature of the refrigerant at the inlet of the evaporation section 4a of the intermediate heat exchanger 4 and the temperature of the refrigerant at the outlet of the cooling section 4b of the intermediate heat exchanger 4 becomes the set value. The set value is, for example, the minimum value of the difference ΔT between the temperature of the refrigerant at the inlet of the evaporation section 4a of the intermediate heat exchanger 4 and the temperature of the refrigerant at the outlet of the cooling section 4b of the intermediate heat exchanger 4. The minimum value may be, for example, a predicted value obtained by simulation, or an actual measurement value based on past data.

[0039] The control unit 7 performs control to adjust the opening degree of the first expansion valve 3 so that a difference ΔT between the refrigerant temperature at the inlet of the evaporator section 4a of the intermediate heat exchanger 4 and the refrigerant temperature at the outlet of the cooling section 4b of the intermediate heat exchanger 4 becomes a set value. The difference ΔT is a set value that is set for each operating condition of the two-stage compressor 1.

[0040] The control unit 7 performs control to adjust the opening degree of the first expansion valve 3 so that the difference ΔT between the refrigerant temperature at the inlet of the evaporator 4a of the intermediate heat exchanger 4 and the refrigerant temperature at the outlet of the cooling unit 4b of the intermediate heat exchanger 4 approaches the vicinity of a set value. Specifically, the control unit 7 performs a first control to reduce the opening degree of the first expansion valve 3 when the difference between the refrigerant temperature at the inlet of the evaporator 4a of the intermediate heat exchanger 4 and the refrigerant temperature at the outlet of the cooling unit 4b of the intermediate heat exchanger 4 approaches the set value (in the case of FIG. 2, the minimum value of ΔT is the set value) and the refrigerant temperature at the outlet of the cooling unit 4b of the intermediate heat exchanger 4 rises. When the difference between the refrigerant temperature at the outlet of the cooling unit 4b of the intermediate heat exchanger 4 approaches the set value but the refrigerant temperature at the outlet of the cooling unit 4b of the intermediate heat exchanger 4 does not rise, it is considered that the difference has approached the set value due to the influence of a disturbance, and therefore the first control is not performed. The control unit 7 performs a second control to increase the opening degree of the first expansion valve 3 when the difference between the refrigerant temperature at the inlet of the evaporator section 4a of the intermediate heat exchanger 4 and the refrigerant temperature at the outlet of the cooling section 4b of the intermediate heat exchanger 4 becomes larger than near the set value. The control unit 7 is configured to alternately perform the first control and the second control. Near the set value includes, for example, a case where the temperature is the same as the set value, a case where the temperature is slightly higher than the set value (for example, set value +5°C), and a case where the temperature is slightly lower than the set value (for example, set value -5°C).

[0041] When the first expansion valve 3 opens from a closed state until the optimum point is reached, the difference between the temperature of the refrigerant at the inlet of the evaporator 4a of the intermediate heat exchanger 4 and the temperature of the refrigerant at the outlet of the cooling section 4b of the intermediate heat exchanger 4 becomes larger than the vicinity of the set value. In this case, the control unit 7 performs the second control to control the first expansion valve 3 to increase the opening degree. Furthermore, as the opening degree of the first expansion valve 3 is increased, the temperature of the refrigerant at the outlet of the cooling section 4b of the intermediate heat exchanger 4 begins to rise when the optimum point is exceeded. At this time, the control unit 7 performs the control to reduce the opening degree of the first expansion valve 3. Then, when the opening degree of the first expansion valve 3 is reduced and the temperature difference becomes larger than the vicinity of the set value, the control unit 7 performs the second control to increase the opening degree of the first expansion valve 3. In this manner, the first control and the second control are repeated to keep the operation of the intermediate heat exchanger 4 optimal.

[0042] The control of the control unit 7 in the first embodiment will be described with reference to Fig. 3. In step S1, the control unit 7 receives a control to turn on the power of the cooling device 100. In step S2, the opening degree of the first expansion valve 3 is increased.

[0043] In step S3, the step to be proceeded to differs depending on whether or not the difference between the refrigerant temperature at the inlet of the evaporator section 4a of the intermediate heat exchanger 4 and the refrigerant temperature at the outlet of the cooling section 4b of the intermediate heat exchanger 4 has reached a set value. If the set value has been reached, the process proceeds to step S4, and if the set value has not been reached, the process returns to step S2 and the opening degree of the first expansion valve 3 is further increased.

[0044] In step S4, the step to be followed differs depending on whether the outlet temperature of the cooling unit 4b has increased. If the outlet temperature of the cooling unit 4b has increased, the process proceeds to step S5. If not, the process returns to step S2, and the opening degree of the first expansion valve 3 is increased.

[0045] In step S5, the control unit 7 reduces the opening degree of the first expansion valve 3. In step S6, the step to be proceeded differs depending on whether the temperature difference between the refrigerant temperature at the inlet of the evaporator section 4a of the intermediate heat exchanger 4 and the refrigerant temperature at the outlet of the cooling section 4b of the intermediate heat exchanger 4 is greater than a set value. If it is greater than the set value, the process proceeds to step S7, and if it is equal to or less than the set value, the process returns to step S5. Then, in step S7, control is performed to adjust the opening degree of the first expansion valve 3. Specifically, the first control and the second control are repeated.

[0046] (Effects of the first embodiment) In the first embodiment, the following effects can be obtained.

[0047] In the first embodiment, the present invention relates to a two-stage compressor 1 including a first compression section 1a that compresses a refrigerant and a second compression section 1b that further compresses the refrigerant compressed by the first compression section 1a, a gas cooler 2 that condenses the refrigerant supplied from the second compression section 1b, a first expansion valve 3 to which a portion of the refrigerant cooled by the gas cooler 2 is supplied and which expands the supplied refrigerant, an evaporation section 4a that evaporates the refrigerant expanded in the first expansion valve 3 and supplies it to the second compression section 1b, and a cooling section 5a that evaporates the remaining refrigerant that has passed through the gas cooler 2. The intermediate heat exchanger includes an intermediate heat exchanger 4 including a cooling section 4b in which a refrigerant is cooled and performing heat exchange between the refrigerant in the evaporation section 4a and the refrigerant in the cooling section 4b, a second expansion valve 5 arranged downstream of the cooling section 4b of the intermediate heat exchanger 4 and expanding the refrigerant, an evaporator 6 arranged downstream of the second expansion valve 5 and cooling the space to be cooled by evaporating the refrigerant, and a control section 7 performing control to adjust the opening degree of the first expansion valve 3 based at least on the temperature of the refrigerant at the inlet of the evaporation section 4a of the intermediate heat exchanger 4. As a result, the amount of change in the heat exchange amount of the intermediate heat exchanger 4 can be obtained by measuring the temperature of the refrigerant at the inlet of the evaporation section 4a of the intermediate heat exchanger 4, and therefore the heat exchange amount of the intermediate heat exchanger 4 can be obtained based on the temperature of the refrigerant at the inlet of the evaporation section 4a of the intermediate heat exchanger 4. As a result, the opening degree of the first expansion valve 3 can be adjusted based on the temperature of the refrigerant at the inlet of the evaporation section 4a so that the heat exchange amount by the intermediate heat exchanger 4 is maximized. As a result, in the cooling device 100 including the intermediate heat exchanger 4, the cooling efficiency can be further improved.

[0048] Furthermore, in the first embodiment, as described above, the control unit 7 performs control to adjust the opening degree of the first expansion valve 3 so as to improve the cooling efficiency of the intermediate heat exchanger 4, based at least on the temperature of the refrigerant at the inlet of the evaporator section 4a of the intermediate heat exchanger 4. As a result, the control unit 7 adjusts the opening degree of the first expansion valve 3 so as to improve the cooling efficiency, and therefore the cooling efficiency of the intermediate heat exchanger 4 can be further improved.

[0049] In the first embodiment, as described above, the control unit 7 performs control to adjust the opening degree of the first expansion valve 3 based on both the refrigerant temperature at the inlet of the evaporator 4a of the intermediate heat exchanger 4 and the refrigerant temperature at the outlet of the cooling unit 4b of the intermediate heat exchanger 4. This makes it possible to obtain the temperature difference between the refrigerant temperature at the inlet of the evaporator 4a and the refrigerant temperature at the outlet of the cooling unit 4b of the intermediate heat exchanger 4. Here, the smaller the difference between the refrigerant temperature at the inlet of the evaporator 4a of the intermediate heat exchanger 4 and the refrigerant temperature at the outlet of the cooling unit 4b of the intermediate heat exchanger 4, the more the refrigerant in the cooling unit 4b is cooled to a temperature close to that of the refrigerant in the evaporator 4a, and therefore the greater the amount of heat exchange can be considered to be. Therefore, the control unit 7 can adjust the opening degree of the first expansion valve 3 so that the temperature difference between the refrigerant temperature at the inlet of the evaporator 4a and the refrigerant temperature at the outlet of the cooling unit 4b is reduced, thereby increasing the amount of heat exchange and further improving the cooling efficiency of the intermediate heat exchanger 4.

[0050] Furthermore, in the first embodiment, as described above, the control unit 7 performs control to adjust the opening degree of the first expansion valve 3 so that the difference between the refrigerant temperature at the inlet of the evaporator section 4a of the intermediate heat exchanger 4 and the refrigerant temperature at the outlet of the cooling section 4b of the intermediate heat exchanger 4 becomes a set value. Here, when the difference between the refrigerant temperature at the inlet of the evaporator section 4a of the intermediate heat exchanger 4 and the refrigerant temperature at the outlet of the cooling section 4b of the intermediate heat exchanger 4 is close to a minimum value, it can be considered that the refrigerant at the outlet of the cooling section 4b of the intermediate heat exchanger 4 has been cooled to close to the refrigerant temperature at the inlet of the evaporator section 4a, and therefore it can be considered that the amount of heat exchange between the evaporator section 4a and the cooling section 4b has become maximum. Therefore, for example, by setting the set value so that the difference between the temperature of the refrigerant at the inlet of the evaporator section 4a of the intermediate heat exchanger 4 and the temperature of the refrigerant at the outlet of the cooling section 4b of the intermediate heat exchanger 4 is close to a minimum value, the opening of the first expansion valve 3 can be accurately adjusted so that the heat exchange amount of the intermediate heat exchanger 4 is maximized, thereby further improving the cooling efficiency of the intermediate heat exchanger 4.

[0051] Furthermore, in the first embodiment, as described above, the control unit 7 performs control to adjust the opening degree of the first expansion valve 3 so as to approach a set value of the difference between the refrigerant temperature at the inlet of the evaporator section 4a of the intermediate heat exchanger 4 and the refrigerant temperature at the outlet of the cooling section 4b of the intermediate heat exchanger 4. In this way, by setting a set value at which the cooling efficiency of the intermediate heat exchanger 4 is optimized according to the operating conditions of the cooling device 100, the control unit 7 can easily adjust the opening degree of the first expansion valve 3 so as to optimize the cooling efficiency.

[0052] In the first embodiment, as described above, the control unit 7 is configured to alternately perform a first control for reducing the aperture of the first expansion valve 3 when the difference between the refrigerant temperature at the inlet of the evaporator 4a of the intermediate heat exchanger 4 and the refrigerant temperature at the outlet of the cooling unit 4b of the intermediate heat exchanger 4 becomes close to a set value and the refrigerant temperature at the outlet of the cooling unit 4b of the intermediate heat exchanger 4 increases, and a second control for increasing the aperture of the first expansion valve 3 when the difference between the refrigerant temperature at the inlet of the evaporator 4a of the intermediate heat exchanger 4 and the refrigerant temperature at the outlet of the cooling unit 4b of the intermediate heat exchanger 4 is greater than close to the set value. This makes it possible to adjust the aperture of the first expansion valve 3 so that the difference between the refrigerant temperature at the inlet of the evaporator 4a of the intermediate heat exchanger 4 and the refrigerant temperature at the outlet of the cooling unit 4b of the intermediate heat exchanger 4 becomes close to the set value, and therefore the cooling device 100 can be driven while maintaining an optimal cooling efficiency.

[0053] [Second embodiment] Next, the configuration of a cooling device 200 according to a second embodiment of the present invention will be described with reference to Figures 4 to 7. In the cooling device 200 of the second embodiment, the control unit 7 acquires the temperature of the refrigerant at the inlet of the evaporator 6, estimates the temperature of the refrigerant at the inlet of the evaporator section 4a of the intermediate heat exchanger 4 from the relationship between the temperature of the refrigerant at the inlet of the evaporator 6 and the temperature of the refrigerant at the inlet of the evaporator section 4a of the intermediate heat exchanger 4, and performs control to adjust the opening degree of the first expansion valve 3 based on the estimated refrigerant temperature at the inlet of the evaporator section 4a of the intermediate heat exchanger 4. Note that the same components as those in the first embodiment are denoted by the same reference numerals as those in the first embodiment, and description thereof will be omitted.

[0054] 4, in a cooling device 200 of the second embodiment, a temperature measuring unit 11 is disposed at the inlet of an evaporator 6. The temperature of the refrigerant at the inlet of the evaporator 6 affects the cooling capacity of the evaporator 6.

[0055] Fig. 5 is a graph showing the relationship between the inlet temperature of the evaporator 6 and the inlet temperature of the evaporator section 4a of the intermediate heat exchanger 4 when the coefficient of performance (COP), which is calculated by dividing the cooling capacity by the power consumption, is optimized. The temperature of the evaporator section 4a of the intermediate heat exchanger 4 is plotted on the vertical axis, and the inlet temperature of the evaporator 6 is plotted on the horizontal axis. This graph shows the relationship between the refrigerant temperature at the inlet of the evaporator 6 and the inlet temperature of the refrigerant at the inlet of the evaporator section 4a of the intermediate heat exchanger 4. Note that the operating conditions of the two-stage compressor 1 are different between the solid line and the dashed line.

[0056] The control unit 7 acquires the refrigerant temperature at the inlet of the evaporator 6 from the relationship between the refrigerant temperature at the inlet of the evaporator 6 and the refrigerant temperature at the inlet of the evaporator section 4a of the intermediate heat exchanger 4 shown in Fig. 5, and estimates the refrigerant temperature at the inlet of the evaporator section 4a of the intermediate heat exchanger 4 from the relationship between the refrigerant temperature at the inlet of the evaporator 6 and the refrigerant temperature at the inlet of the evaporator section 4a of the intermediate heat exchanger 4. Specifically, the temperature measurement unit 11 acquires the refrigerant temperature at the inlet of the evaporator 6, and the value of the evaporator section 4a is acquired on the graph in Fig. 5 to be used as an estimated value. This estimated value is the ideal refrigerant temperature at which energy consumption efficiency is optimized.

[0057] FIG. 6 is a graph in which the temperature of the evaporator 4a is plotted on the vertical axis and the opening degree of the first expansion valve 3 is plotted on the horizontal axis. As shown in FIG. 6, when the opening degree of the first expansion valve 3 increases, the temperature of the evaporator 4a increases. The control unit 7 adjusts the opening degree of the first expansion valve 3 under the relationship shown in FIG. 6 so that the current temperature of the evaporator 4a becomes the temperature of the evaporator 4a estimated from the temperature of the refrigerant at the inlet of the evaporator 6. As shown in FIG. 6, when the current temperature of the evaporator 4a is lower than the temperature of the evaporator 4a estimated from the temperature of the refrigerant at the inlet of the evaporator 6, the control unit 7 controls the opening degree to be larger. Also, when the current temperature of the evaporator 4a is higher than the temperature of the evaporator 4a estimated from the temperature of the refrigerant at the inlet of the evaporator 6, the control unit 7 controls the opening degree to be smaller.

[0058] The control of the control unit 7 in the second embodiment will be described with reference to Fig. 7. In step S11, the control unit 7 receives control to turn on the power of the cooling device 100. In step S12, the control unit 7 acquires the inlet temperature of the evaporator 6. In step S13, the control unit 7 estimates the inlet temperature of the evaporator 4a from the acquired temperature of the evaporator 6. In step S14, the opening degree of the first expansion valve 3 is adjusted so that the temperature becomes the temperature acquired in step S13.

[0059] The other configurations of the second embodiment are similar to those of the first embodiment.

[0060] (Effects of the second embodiment) As described above, in the second embodiment, there is provided a two-stage compressor 1 including a first compression section 1a that compresses a refrigerant and a second compression section 1b that further compresses the refrigerant compressed by the first compression section 1a, a gas cooler 2 that cools the refrigerant supplied from the second compression section 1b, a first expansion valve 3 to which a portion of the refrigerant cooled by the gas cooler 2 is supplied and which expands the supplied refrigerant, an evaporation section 4a that evaporates the refrigerant expanded in the first expansion valve 3 and supplies it to the second compression section 1b, and a remaining portion of the refrigerant that has passed through the gas cooler 2. The intermediate heat exchanger includes an intermediate heat exchanger 4 including a cooling section 4b in which the refrigerant in the evaporator section 4a is cooled and performs heat exchange between the refrigerant in the evaporator section 4a and the refrigerant in the cooling section 4b, a second expansion valve 5 arranged downstream of the cooling section 4b of the intermediate heat exchanger 4 and expanding the refrigerant, an evaporator 6 arranged downstream of the second expansion valve 5 and cooling the space to be cooled by evaporating the refrigerant, and a control section 7 performing control to adjust the opening degree of the first expansion valve 3 based at least on the temperature of the refrigerant at the inlet of the evaporator section 4a of the intermediate heat exchanger 4. As a result, the amount of change in the heat exchange amount of the intermediate heat exchanger 4 can be obtained by measuring the temperature of the refrigerant at the inlet of the evaporator section 4a of the intermediate heat exchanger 4, and therefore the heat exchange amount of the intermediate heat exchanger 4 can be obtained based on the temperature of the refrigerant at the inlet of the evaporator section 4a of the intermediate heat exchanger 4. As a result, the opening degree of the first expansion valve 3 can be adjusted based on the temperature of the refrigerant at the inlet of the evaporator section 4a so that the heat exchange amount by the intermediate heat exchanger 4 is maximized. As a result, in the cooling device 200 including the intermediate heat exchanger 4, the cooling efficiency can be further improved.

[0061] In the second embodiment, as described above, the control unit 7 acquires the temperature of the refrigerant at the inlet of the evaporator 6, estimates the temperature of the refrigerant at the inlet of the evaporator section 4a of the intermediate heat exchanger 4 from the relationship between the temperature of the refrigerant at the inlet of the evaporator 6 and the temperature of the refrigerant at the inlet of the evaporator section 4a of the intermediate heat exchanger 4, and performs control to adjust the opening degree of the first expansion valve 3 based on the estimated temperature of the refrigerant at the inlet of the evaporator section 4a of the intermediate heat exchanger 4. Thereby, for example, based on the relationship between the temperature of the refrigerant at the inlet of the evaporator 6 at which the amount of heat exchanged by the intermediate heat exchanger 4 is maximized and the temperature of the refrigerant at the inlet of the evaporator section 4a of the intermediate heat exchanger 4, it is possible to estimate the optimal temperature of the refrigerant at the inlet of the evaporator section 4a of the intermediate heat exchanger 4, and adjust the opening degree of the first expansion valve 3 so that the optimal temperature is obtained. As a result, by acquiring the temperature of the refrigerant at the inlet of the evaporator 6, it is possible to further improve the cooling efficiency.

[0062] In the second embodiment, as described above, the control unit 7 performs control to adjust the aperture of the first expansion valve 3 so that the actual measurement value of the refrigerant temperature at the inlet of the evaporator section 4a of the intermediate heat exchanger 4 becomes the estimated refrigerant temperature at the inlet of the evaporator section 4a of the intermediate heat exchanger 4. This makes it possible to easily adjust the aperture of the first expansion valve 3 to an appropriate value for improving cooling efficiency, since it is only necessary to adjust the aperture of the first expansion valve 3 to the estimated temperature.

[0063] Other effects of the second embodiment are similar to those of the first embodiment.

[0064] [Third embodiment] Next, the configuration of a cooling device 300 according to a third embodiment of the present invention will be described with reference to Fig. 1, Fig. 8 and Fig. 9. In the cooling device 300 of the third embodiment, the control unit 7 is configured to suppress cooling of the space to be cooled by controlling the first expansion valve 3 to be smaller when the temperature of the space to be cooled is equal to or lower than a set temperature and the rotation speed of the two-stage compressor 1 is equal to or lower than a predetermined value. Note that the same components as those in the first embodiment are given the same reference numerals as those in the first embodiment and the description thereof will be omitted. The predetermined value is the minimum rotation speed.

[0065] In the third embodiment, the control unit 7 adjusts the opening degree of the first expansion valve 3 based on the temperature inside the showcase, which is the space to be cooled. A thermometer for measuring the internal temperature is provided inside the showcase, and the control unit 7 acquires the measurement result of the thermometer.

[0066] When the cooling device 300 is driven, the control unit 7 sets the rotation speed of the two-stage compressor 1 to the maximum rotation speed in order to cool the inside of the showcase. This increases the flow rate of the refrigerant, improving the cooling capacity of the evaporator 6 and allowing the inside of the showcase to be cooled rapidly. When the temperature inside the showcase reaches the set temperature, the control unit 7 performs PID control to maintain the temperature close to the set temperature. In this case, the control unit 7 repeatedly increases and decreases the rotation speed of the two-stage compressor 1 based on the temperature inside the showcase.

[0067] When the temperature inside the showcase falls below the set temperature, the control unit 7 reduces the rotation speed of the two-stage compressor 1. This reduces the flow rate of the refrigerant supplied to the evaporator 6, thereby suppressing the cooling capacity of the evaporator 6.

[0068] When the temperature inside the showcase falls below the set temperature even after the rotation speed of the two-stage compressor 1 is reduced to a predetermined value, the control unit 7 controls the first expansion valve 3 to be closed by gradually decreasing the opening degree. By closing the first expansion valve 3, cooling in the intermediate heat exchanger 4 stops, so that the specific enthalpy of the refrigerant supplied to the evaporator 6 further increases, and the cooling capacity of the evaporator 6 can be further suppressed. The predetermined value of the rotation speed of the two-stage compressor 1 is the minimum rotation speed. Closing the first expansion valve 3 means that the first expansion valve 3 is brought into a closed state in which the opening area is zero.

[0069] Fig. 8(A) shows the case where the first expansion valve 3 is in an open state, and Fig. 8(B) shows the case where the first expansion valve 3 is in a closed state. As shown in Fig. 8(B), since the first expansion valve 3 is closed, no cooling occurs in the intermediate heat exchanger 4, and the specific enthalpy does not decrease significantly. Therefore, the cooling capacity can be suppressed.

[0070] The control of the control unit 7 in the third embodiment will be described with reference to Fig. 9. In step S21, the control unit 7 receives a control to turn on the power of the cooling device 300. In step S22, the control unit 7 starts preparations for starting the cooling device 300.

[0071] In step S23, the control unit 7 operates the two-stage compressor 1 at the maximum rotation speed so that the temperature inside the showcase becomes the set temperature. In step S24, the step to be followed differs depending on whether the temperature inside the showcase becomes equal to or lower than the set temperature. If the temperature becomes equal to or lower than the set temperature, the process proceeds to step S25, and if not, the process returns to step S23.

[0072] In step S25, the control unit 7 starts PID control. In step S26, the step to be followed differs depending on whether the rotation speed of the two-stage compressor 1 is the minimum rotation speed and is equal to or lower than the set temperature. If the rotation speed of the two-stage compressor 1 is the minimum rotation speed and is equal to or lower than the set temperature, the process proceeds to step S29, and if not, the process proceeds to step S27.

[0073] In step S27, the steps to be followed differ depending on whether it is the time to start defrosting the showcase. If it is the time to start defrosting, the process proceeds to step S28, where the process waits for the operation of cooling the inside of the showcase to remove the frost on the evaporator 6. If it is not the time to start defrosting, the process returns to step S25.

[0074] In step S29, control is performed to close the first expansion valve 3. Then, in step S30, if the temperature reaches or exceeds the set temperature within the set time, the process returns to step S25, and if the temperature is below the set temperature even after the set time has elapsed, the process proceeds to step S31 to temporarily stop the two-stage compressor 1, and the process returns to step S25.

[0075] Furthermore, in the third embodiment, when the temperature of the space to be cooled is equal to or lower than a set temperature and the rotation speed of the two-stage compressor 1 is equal to or lower than a predetermined value, the control unit 7 may reduce the opening of the second expansion valve 5 in addition to the first expansion valve 3. Reducing the opening of the second expansion valve 5 does not include the case where the second expansion valve 5 is closed (a state where the opening area is 0), but only includes the case where it is not closed. Furthermore, the opening of the first expansion valve 3 and the opening of the second expansion valve 5 are appropriately adjusted according to the situation.

[0076] The other configurations of the third embodiment are similar to those of the first embodiment.

[0077] (Effects of the third embodiment) As described above, in the third embodiment, there is provided a two-stage compressor 1 including a first compression section 1a that compresses a refrigerant and a second compression section 1b that further compresses the refrigerant compressed by the first compression section 1a, a gas cooler 2 that cools the refrigerant supplied from the second compression section 1b, a first expansion valve 3 to which a portion of the refrigerant cooled by the gas cooler 2 is supplied and which expands the supplied refrigerant, an evaporation section 4a that evaporates the refrigerant expanded in the first expansion valve 3 and supplies it to the second compression section 1b, and a remaining portion of the refrigerant that has passed through the gas cooler 2. The intermediate heat exchanger includes an intermediate heat exchanger 4 including a cooling section 4b in which the refrigerant in the evaporator section 4a is cooled and performs heat exchange between the refrigerant in the evaporator section 4a and the refrigerant in the cooling section 4b, a second expansion valve 5 arranged downstream of the cooling section 4b of the intermediate heat exchanger 4 and expanding the refrigerant, an evaporator 6 arranged downstream of the second expansion valve 5 and cooling the space to be cooled by evaporating the refrigerant, and a control section 7 performing control to adjust the opening degree of the first expansion valve 3 based at least on the temperature of the refrigerant at the inlet of the evaporator section 4a of the intermediate heat exchanger 4. As a result, the amount of change in the heat exchange amount of the intermediate heat exchanger 4 can be obtained by measuring the temperature of the refrigerant at the inlet of the evaporator section 4a of the intermediate heat exchanger 4, and therefore the heat exchange amount of the intermediate heat exchanger 4 can be obtained based on the temperature of the refrigerant at the inlet of the evaporator section 4a of the intermediate heat exchanger 4. As a result, the opening degree of the first expansion valve 3 can be adjusted based on the temperature of the refrigerant at the inlet of the evaporator section 4a so that the heat exchange amount by the intermediate heat exchanger 4 is maximized. As a result, in the cooling device 300 including the intermediate heat exchanger 4, the cooling efficiency can be further improved.

[0078] In the third embodiment, as described above, the control unit 7 is configured to suppress cooling of the space to be cooled by controlling the first expansion valve 3 to be smaller when the temperature of the space to be cooled is equal to or lower than the set temperature and the rotation speed of the two-stage compressor 1 is equal to or lower than a predetermined value. As a result, since the cooling of the refrigerant by the intermediate heat exchanger 4 can be stopped by closing the first expansion valve 3, even when the rotation speed of the two-stage compressor 1 cannot be reduced, it is possible to suppress cooling of the space to be cooled without stopping the drive of the two-stage compressor 1. As a result, it is possible to suppress uneven cooling caused by repeatedly stopping and restarting the operation of the two-stage compressor 1, and therefore it is possible to improve the cooling efficiency of the cooling device 300.

[0079] In the third embodiment, as described above, the control unit 7 is configured to suppress cooling of the space to be cooled by controlling to close the first expansion valve 3 when the temperature of the space to be cooled is equal to or lower than the set temperature and the rotation speed of the two-stage compressor 1 is equal to or lower than a predetermined value. As a result, since the cooling of the refrigerant by the intermediate heat exchanger 4 can be stopped by closing the first expansion valve 3, even when the rotation speed of the two-stage compressor 1 cannot be reduced, it is possible to effectively suppress cooling of the space to be cooled without stopping the drive of the two-stage compressor 1.

[0080] In the third embodiment, as described above, when the temperature of the space to be cooled is equal to or lower than the set temperature and the rotation speed of the two-stage compressor is equal to or lower than a predetermined value, the control unit 7 controls the first expansion valve 3 to reduce the opening degree and controls the second expansion valve 5 to reduce the opening degree, thereby suppressing the cooling of the space to be cooled. By reducing the opening degree of the second expansion valve 5, the amount of refrigerant circulating can be reduced, and therefore the excessive refrigeration capacity can be reduced. As a result, the cooling of the space to be cooled can be further suppressed without stopping the operation of the two-stage compressor 1.

[0081] Other effects of the third embodiment are similar to those of the first embodiment.

[0082] [Variations] The embodiments disclosed herein should be considered to be illustrative and not restrictive in all respects. The scope of the present invention is indicated by the claims, not by the description of the embodiments above, and further includes all modifications (variations) within the meaning and scope of the claims.

[0083] For example, in the above first to third embodiments, an example has been shown in which the aperture of the first expansion valve 3 is adjusted based on both the refrigerant temperature at the inlet of the evaporator section 4a of the intermediate heat exchanger 4 and the refrigerant temperature at the outlet of the cooling section 4b of the intermediate heat exchanger 4, but the present invention is not limited to this. In the present invention, the aperture of the first expansion valve 3 may be adjusted based only on the refrigerant temperature at the inlet of the evaporator section 4a of the intermediate heat exchanger 4. Furthermore, instead of the refrigerant temperature at the outlet of the cooling section 4b of the intermediate heat exchanger 4, the aperture of the first expansion valve 3 may be adjusted based on another temperature and the refrigerant temperature at the inlet of the evaporator section 4a of the intermediate heat exchanger 4.

[0084] Furthermore, in the above first to third embodiments, an example has been shown in which the minimum value of the difference between the refrigerant temperature at the inlet of the evaporator section 4a of the intermediate heat exchanger 4 and the refrigerant temperature at the outlet of the cooling section 4b of the intermediate heat exchanger 4 is set as the set value, but the present invention is not limited to this. In the present invention, the set value of the difference between the refrigerant temperature at the inlet of the evaporator section 4a of the intermediate heat exchanger 4 and the refrigerant temperature at the outlet of the cooling section 4b of the intermediate heat exchanger 4 may be calculated in accordance with the operating conditions.

[0085] In the above first to third embodiments, the cooling device 100 (200, 300) is used in a showcase, but the present invention is not limited to this. In the present invention, the cooling device 100 (200, 300) may be used to cool a vending machine or the interior of a room.

[0086] Further, in the above first to third embodiments, the internal heat exchanger 8 and the strainer 9 are provided as examples, but the present invention is not limited to this. The present invention does not necessarily have to include the internal heat exchanger 8 and the strainer 9.

[0087] In the first to third embodiments, the refrigerant is carbon dioxide, but the present invention is not limited to this. The refrigerant in the present invention may be propane or the like other than carbon dioxide.

[0088] Further, in the above first to third embodiments, an example was shown in which the gas cooler 2 was provided, but the present invention is not limited to this. In the present invention, when the refrigerant is other than carbon dioxide, a condenser may be provided.

[0089] Further, in the above first to third embodiments, examples have been shown in which the cooler 12 is provided, but the present invention is not limited to this.

[0090] In the second embodiment, an example is shown in which the relationship between the inlet temperature of the evaporator 6 when the energy consumption efficiency is optimized and the refrigerant temperature at the inlet of the evaporator section 4a of the intermediate heat exchanger 4 is used, but the present invention is not limited to this. For example, the relationship between the inlet temperature of the evaporator 6 and the refrigerant temperature at the inlet of the evaporator section 4a of the intermediate heat exchanger 4 when the opening degree of the first expansion valve 3 is constant may be used.

[0091] In the second embodiment, the temperature measuring unit 11 is provided at the outlet of the cooling unit 4b, but the present invention is not limited to this. For example, the temperature measuring unit 11 does not have to be provided at the outlet of the cooling unit 4b.

[0092] In the third embodiment, the predetermined value of the rotation speed of the two-stage compressor 1 is the minimum rotation speed, but the present invention is not limited to this. In the present invention, the predetermined value of the rotation speed of the two-stage compressor 1 may be higher than the minimum rotation speed.

[0093] In the above third embodiment, the control unit 7 closes the first expansion valve 3 (brings it to a closed state) when the temperature of the space to be cooled is equal to or lower than the set temperature and the rotation speed of the two-stage compressor 1 is equal to or lower than a predetermined value, but the present invention is not limited to this. In the present invention, when the temperature of the space to be cooled is equal to or lower than the set temperature and the rotation speed of the two-stage compressor 1 is equal to or lower than a predetermined value, the opening degree of the first expansion valve 3 may be reduced so that the first expansion valve 3 does not enter a closed state, thereby reducing supercooling and lowering excessive refrigeration capacity.

[0094] In addition, in the above-described third embodiment, an example having the configuration of the first embodiment has been described, but the present invention is not limited to this. In the present invention, the third embodiment does not necessarily have to have the configuration of the first embodiment. [Explanation of symbols]

[0095] 1. Two-stage compressor 1a First compression section 1b Second compression section 2 Gas cooler 3. First expansion valve 4 Intermediate heat exchanger 4a Evaporation section 4b Cooling section 5 Second expansion valve 6. Evaporator 7 Control section 100, 200, 300 chillers

Claims

1. A two-stage compressor including a first compression section that compresses a refrigerant and a second compression section that further compresses the refrigerant compressed by the first compression section; a condenser that condenses the refrigerant supplied from the second compression unit, or a gas cooler that cools the refrigerant supplied from the second compression unit; a first expansion valve to which a portion of the refrigerant condensed in the condenser or cooled in the gas cooler is supplied and which expands the supplied refrigerant; an intermediate heat exchanger including an evaporation section that evaporates the refrigerant expanded in the first expansion valve and supplies the refrigerant to the second compression section, and a cooling section that cools the remaining refrigerant of the refrigerant that has passed through the condenser or the gas cooler, and performs heat exchange between the refrigerant in the evaporation section and the refrigerant in the cooling section; a second expansion valve disposed downstream of the cooling portion of the intermediate heat exchanger and configured to expand a refrigerant; an evaporator disposed downstream of the second expansion valve and configured to evaporate a refrigerant to cool a space to be cooled; a control unit that performs control to adjust an opening degree of the first expansion valve based at least on a temperature of a refrigerant at an inlet of the evaporator of the intermediate heat exchanger.

2. 2. The cooling device according to claim 1, wherein the control unit performs control to adjust an opening degree of the first expansion valve so as to improve a cooling efficiency of the intermediate heat exchanger, based at least on a temperature of the refrigerant at an inlet of the evaporator of the intermediate heat exchanger.

3. 3. The cooling device according to claim 2, wherein the control unit performs control to adjust an opening degree of the first expansion valve based on both a temperature of the refrigerant at an inlet of the evaporator section of the intermediate heat exchanger and a temperature of the refrigerant at an outlet of the cooling section of the intermediate heat exchanger.

4. 4. The cooling device according to claim 3, wherein the control unit adjusts an opening degree of the first expansion valve so that a difference between a temperature of the refrigerant at an inlet of the evaporator section of the intermediate heat exchanger and a temperature of the refrigerant at an outlet of the cooling section of the intermediate heat exchanger becomes a set value.

5. 5. The cooling device according to claim 4, wherein the control unit performs control to adjust an opening degree of the first expansion valve so that the refrigerant temperature approaches a set value of a difference between a temperature of the refrigerant at an inlet of the evaporator section of the intermediate heat exchanger and a temperature of the refrigerant at an outlet of the cooling section of the intermediate heat exchanger.

6. 5. The cooling device according to claim 4, wherein the control unit is configured to alternately perform a first control of reducing the opening degree of the first expansion valve when a difference between a temperature of the refrigerant at an inlet of the evaporator section of the intermediate heat exchanger and a temperature of the refrigerant at an outlet of the cooling section of the intermediate heat exchanger becomes close to a set value and the temperature of the refrigerant at the outlet of the cooling section of the intermediate heat exchanger increases, and a second control of increasing the opening degree of the first expansion valve when a difference between a temperature of the refrigerant at the inlet of the evaporator section of the intermediate heat exchanger and a temperature of the refrigerant at the outlet of the cooling section of the intermediate heat exchanger is greater than close to a set value.

7. 2. The cooling device according to claim 1, wherein the control unit acquires a temperature of the refrigerant at an inlet of the evaporator, estimates a temperature of the refrigerant at the inlet of the evaporator of the intermediate heat exchanger from a relationship between the temperature of the refrigerant at the inlet of the evaporator and a temperature of the refrigerant at the inlet of the evaporator of the intermediate heat exchanger, and performs control to adjust an opening degree of the first expansion valve based on the estimated temperature of the refrigerant at the inlet of the evaporator of the intermediate heat exchanger.

8. 8. The cooling device according to claim 7, wherein the control unit performs control to adjust an opening degree of the first expansion valve so that an actual measurement value of a temperature of the refrigerant at an inlet of the evaporator of the intermediate heat exchanger becomes equal to an estimated temperature of the refrigerant at the inlet of the evaporator of the intermediate heat exchanger.

9. The cooling device according to claim 1, wherein the control unit is configured to suppress cooling of the space to be cooled by controlling the first expansion valve to close when the temperature of the space to be cooled is below a set temperature and the rotation speed of the two-stage compressor is below a predetermined value.

10. A two-stage compressor including a first compression section that compresses a refrigerant and a second compression section that further compresses the refrigerant compressed by the first compression section; a condenser that condenses the refrigerant supplied from the second compression unit, or a gas cooler that cools the refrigerant supplied from the second compression unit; a first expansion valve to which a portion of the refrigerant condensed in the condenser or cooled in the gas cooler is supplied and which expands the supplied refrigerant; an intermediate heat exchanger including an evaporation section that evaporates the refrigerant expanded in the first expansion valve and supplies the refrigerant to the second compression section, and a cooling section that cools the remaining refrigerant of the refrigerant that has passed through the condenser or the gas cooler, and performs heat exchange between the refrigerant in the evaporation section and the refrigerant in the cooling section; a second expansion valve disposed downstream of the cooling portion of the intermediate heat exchanger and configured to expand a refrigerant; an evaporator disposed downstream of the second expansion valve and configured to evaporate a refrigerant to cool a space to be cooled; a control unit configured to suppress cooling of the space to be cooled by controlling the opening of the first expansion valve to be reduced when the temperature of the space to be cooled is below a set temperature and the rotation speed of the two-stage compressor is below a predetermined value.

11. The cooling device according to claim 10, wherein the control unit is configured to suppress cooling of the space to be cooled by controlling the first expansion valve to close when the temperature of the space to be cooled is equal to or lower than a set temperature and the rotation speed of the two-stage compressor is equal to or lower than a predetermined value.

12. The cooling device according to claim 10, wherein the control unit is configured to suppress cooling of the space to be cooled by controlling the first expansion valve to reduce an opening degree and controlling the second expansion valve to reduce an opening degree when the temperature of the space to be cooled is below a set temperature and the rotation speed of the two-stage compressor is below a predetermined value.

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