Refrigeration device

Abstract

The refrigeration device comprises: one or more first circuits through which a first refrigerant flows; and a second circuit through which a second refrigerant flows. The first circuits are each provided with: a compressor for compressing the first refrigerant; a condenser for condensing the compressed first refrigerant; a pressure reducer for reducing the pressure of the condensed first refrigerant; and an inter-refrigerant heat exchanger for exchanging heat between the pressure-reduced first refrigerant and the second refrigerant. The second circuit is provided with: the inter-refrigerant heat exchanger of the one or more first circuits; an evaporator that exchanges heat between the second refrigerant after heat exchange with the first refrigerant and a first object, cools the first object, and evaporates the second refrigerant; and a circulation device that circulates the second refrigerant in the second circuit. One of the one or more first circuits is an adjustment circuit. The adjustment circuit performs an operation to bring the first refrigerant at the outlet of the inter-refrigerant heat exchanger into a superheated state when the circulation device is stopped or performing a low-capacity operation.

Description

Refrigeration equipment

[0001] The present disclosure relates to a refrigeration system having a first circuit through which a first refrigerant circulates and a second circuit through which a second refrigerant circulates that exchanges heat with the first refrigerant.

[0002] In recent years, due to the revised Fluorocarbons Emission Reduction Act and carbon-neutral measures, etc., refrigeration systems using natural refrigerants such as R717 (ammonia) and R744 (carbon dioxide) are becoming more common. Specifically, Patent Document 1 shows a refrigeration system using R717 (ammonia) in the first circuit and R744 in the second circuit. Note that in household refrigerators or built-in showcases that use a small amount of refrigerant and have a sealed refrigeration cycle, a flammable refrigerant such as R290 (propane) may be used instead of R717 (ammonia).

[0003] On the other hand, known compressors for refrigeration systems include screw compressors, scroll compressors, and rotary compressors. While a single screw compressor can easily achieve a large capacity, its manufacturing costs are high. For this reason, there is a growing demand for load-distribution refrigeration systems, which use multiple scroll or rotary compressors to distribute the load, instead of central systems that use a single large-capacity compressor.

[0004] Japanese Patent Application Laid-Open No. 2008-309393

[0005] Consider a refrigeration system in which heat is exchanged between a refrigerant circulating through a first circuit and a refrigerant circulating through a second circuit, using R744 (carbon dioxide) as the refrigerant in the second circuit. Even if the design pressure of the second circuit is designed to be lower than the pressure corresponding to the saturation temperature of R744 (carbon dioxide) at anticipated ambient temperatures, the pressure of R744 (carbon dioxide) may rise above the design pressure even when the second circuit is stopped due to an increase in ambient temperature caused by an increase in air temperature, etc. Furthermore, even when the second circuit is operating at a low capacity, the refrigerant will not condense without the operation of the first circuit, and the pressure of the refrigerant in the second circuit may rise significantly. For this reason, the first circuit must be operated even when the second circuit is stopped or operating at a low capacity.

[0006] Here, when the second circuit is stopped or operating at a low capacity, the condensation heat release of R744 (carbon dioxide) is small, so the refrigeration capacity required for the first circuit is small, and the required capacity of the compressor in the first circuit is also small.

[0007] However, scroll compressors or rotary compressors do not have an internal capacity control mechanism like reciprocating compressors or screw compressors. When a compressor without a capacity control mechanism is installed in the first circuit, even when a single inverter compressor in the first circuit is operated at the minimum rotation speed, excessive capacity may occur. Refrigerants such as R717 (ammonia) or R290 (propane) in the first circuit may not fully evaporate in the refrigerant-to-refrigerant heat exchanger, potentially causing liquid return to the compressor. Generally, scroll compressors or rotary compressors have lower resistance to liquid return compared to reciprocating compressors or screw compressors, and therefore a means for suppressing liquid return as an alternative to a capacity control mechanism has been sought.

[0008] The present disclosure has been made to solve the above-mentioned problem, and aims to provide a refrigeration system that suppresses a pressure increase of the refrigerant in the second circuit while suppressing liquid return to the compressor in the first circuit.

[0009] A refrigeration system according to the present disclosure includes one or more first circuits through which a first refrigerant flows and a second circuit through which a second refrigerant flows, the first circuit including a compressor that compresses the first refrigerant, a condenser that condenses the compressed first refrigerant, a pressure reducer that depressurizes the first refrigerant after condensation, and an inter-refrigerant heat exchanger that exchanges heat between the depressurized first refrigerant and the second refrigerant, the second circuit including the inter-refrigerant heat exchangers of the one or more first circuits, an evaporator that exchanges heat between the second refrigerant after heat exchange with the first refrigerant and a first object to cool the first object and evaporate the second refrigerant, and a circulation device that circulates the second refrigerant through the second circuit, and at least one of the one or more first circuits is an adjustment circuit that operates to superheat the first refrigerant at an outlet of the inter-refrigerant heat exchanger when the circulation device is stopped or is operating at a low capacity below a threshold capacity.

[0010] According to the refrigeration apparatus of the present disclosure, it is possible to suppress a pressure increase of the refrigerant in the second circuit while suppressing liquid return to the compressor in the first circuit.

[0011] Fig. 1 is a circuit diagram showing an example of the configuration of a refrigeration device according to embodiment 1. Fig. 2 is a flowchart showing control of the refrigeration device according to embodiment 1. Fig. 3 is a ph diagram explaining the state of refrigerant when liquid return occurs in the first circuit according to embodiment 1. Fig. 4 is a ph diagram explaining the state of refrigerant when a bypass in the adjustment circuit according to embodiment 1 is opened. Fig. 5 is a circuit diagram showing an example of the configuration of a refrigeration device according to embodiment 2. Fig. 6 is a flowchart showing control of the refrigeration device according to embodiment 2.

[0012] Embodiment 1. Figure 1 is a circuit diagram showing an example configuration of a refrigeration system 100 according to Embodiment 1. The refrigeration system 100 includes a plurality of first circuits 1 through which a first refrigerant circulates and a second circuit 2 through which a second refrigerant circulates. The first refrigerant in Embodiment 1 is a natural refrigerant or a refrigerant with a global warming potential of 1500 or less. The first refrigerant is, for example, R290 (propane) or R717 (ammonia). The first refrigerant may also be a single refrigerant selected from R1234yf, R1234ze, R32, and R290, a mixed refrigerant of two or more of these, a mixed refrigerant of any of these with another refrigerant, a mixed refrigerant containing R1132(E), or a mixed refrigerant containing R1123. Specifically, the first refrigerant may be a mixed refrigerant such as R516A, R445A, R444A, R454C, R444B, R454A, R455A, R457A, R459B, R452B, R454B, R447B, R447A, R446A, or R459A. The second refrigerant is R744 (carbon dioxide). The refrigeration system 100 cools a first object, such as air or water, in the load device 6 to a temperature desired by a user using the second refrigerant cooled by the first refrigerant.

[0013] The first circuit 1 has a compressor 10, a condenser 11, an expansion valve 12, and an inter-refrigerant heat exchanger 13, which are connected in series by a high-stage refrigerant pipe 3. The second circuit 2 has a receiver 20, a circulation device 21, an evaporator 22, and a plurality of inter-refrigerant heat exchangers 13, which are connected in series by a low-stage refrigerant pipe 4. Although the plurality of inter-refrigerant heat exchangers 13 in the second circuit 2 are connected in series in Fig. 1, they may be connected in parallel, or some of the plurality of inter-refrigerant heat exchangers 13 may be connected in parallel and the remaining inter-refrigerant heat exchangers 13 may be connected in series.

[0014] The receiver 20, the circulation device 21, and the plurality of first circuits 1 are arranged in the housing of the heat source device 5, which is indicated by a dashed rectangle in Fig. 1. The evaporator 22 is arranged in the housing of the load device 6, which is indicated by a dashed line in Fig. 1.

[0015] The refrigeration apparatus 100 further includes a control device 7. The control device 7 includes a CPU (Central Processing Unit) 70 and a memory 71. The control device 7 controls each of the multiple compressors 10, the multiple expansion valves 12, the circulation device 21, and actuators (not shown), etc., by wired or wireless communication via an input / output interface circuit (not shown).

[0016] The components of each of the first circuit 1 and the second circuit 2 will be described below. The compressor 10 is a scroll or rotary compressor, and is an inverter compressor whose capacity can be controlled by an inverter. The compressor 10 may be a compressor that does not have an internal mechanical capacity control mechanism. The compressor 10 draws a first refrigerant from the high-temperature refrigerant pipe 3 and compresses the drawn first refrigerant. The compressor 10 then discharges the compressed first refrigerant into the high-temperature refrigerant pipe 3.

[0017] The condenser 11 may be air-cooled or water-cooled. Examples of the air-cooled condenser 11 include a plate-fin coil heat exchanger, a parallel flow condenser, and an all-aluminum flat tube heat exchanger. When the condenser 11 is air-cooled, a blower 11a is provided to blow air to the condenser 11. FIG. 1 illustrates an air-cooled condenser 11 and the blower 11a. Examples of the water-cooled condenser 11 include a shell-and-tube heat exchanger, a brazed plate heat exchanger, and a double-tube heat exchanger. The condenser 11 cools the first refrigerant by exchanging heat between the first refrigerant and air or water. The condenser 11 may be installed separately as a remote condenser.

[0018] The expansion valve 12 may be an electronic expansion valve, an electric valve, a solenoid valve type expansion valve, a mechanical expansion valve, a capillary valve, etc. The expansion valve 12 is an example of a pressure reducer that reduces the pressure of the first refrigerant to expand it.

[0019] The refrigerant-to-refrigerant heat exchanger 13 is, for example, a brazed plate heat exchanger or a double-pipe heat exchanger, and exchanges heat between the first refrigerant and the second refrigerant. The refrigerant-to-refrigerant heat exchanger 13 functions as an evaporator in the first circuit 1 and as a condenser in the second circuit 2. The first refrigerant absorbs heat from the second refrigerant in the refrigerant-to-refrigerant heat exchanger 13 and evaporates. The second refrigerant releases heat to the first refrigerant in the refrigerant-to-refrigerant heat exchanger 13 and condenses.

[0020] The receiver 20 functions to send the second refrigerant in liquid form, rather than gaseous form, to the circulation device 21 to prevent breakdown of the circulation device 21. The receiver 20 stores the second refrigerant, and its volume is determined based on the internal volume of the entire second circuit 2, the amount of the second refrigerant, and the evaporation temperature of the evaporator 22 (described below). The volume is also set so that the second refrigerant is not released but maintained inside the refrigeration system 100 if the refrigeration system 100 malfunctions and stops operating. The volume can be changed based on the design pressure of the second circuit 2. Specifically, the volume can be reduced by increasing the design pressure of the second circuit 2, or increased by decreasing the design pressure. Depending on the daily refrigeration capacity, a safety valve or a fusible plug may be required, but is not shown.

[0021] The circulation device 21 is, for example, a pump that pumps the second refrigerant. When the circulation device 21 is a pump, the output of the electric motor is determined based on the pressure loss in the low-stage refrigerant pipe 4. If the output is too large, the pressure of the discharged second refrigerant increases, and the second refrigerant may not be in a two-phase state at the inlet of the evaporator 22. To prevent this, the output is determined so that two-phase refrigerant is supplied to the evaporator 22 due to the pressure loss in the distributor 22A provided upstream of the evaporator 22. The circulation device 21 may be inverter-driven or constant-speed driven.

[0022] The evaporator 22 may be a plate fin coil air heat exchanger, a brazed plate heat exchanger, a shell and tube heat exchanger, or the like, and as described above, a distributor 22A is provided upstream. When the evaporator 22 is a plate fin coil heat exchanger, a blower is provided to send air to the evaporator 22. The distributor 22A distributes the refrigerant among a plurality of heat transfer tubes (not shown) included in the evaporator 22. The distributor 22A reduces the pressure of the second refrigerant pressurized by the circulation device 21 to a predetermined appropriate pressure. A pressure reducing device such as an expansion valve may be provided upstream of the distributor 22A.

[0023] The low stock liquid pipe 4A, which is the low stock refrigerant pipe 4 connecting the upstream side of the load device 6 and the heat source device 5, has a pipe diameter set so that the pressure loss of the second refrigerant flowing therethrough is appropriate. Specifically, the pipe diameter of the low stock liquid pipe 4A is set so that the pressure loss of the second refrigerant is appropriate, taking into account the pressure loss of the second refrigerant in the distributor 22A. The low stock liquid pipe 4A is, for example, a copper pipe or a steel pipe.

[0024] The low-stage gas pipe 4B, which is the low-stage refrigerant pipe 4 connecting the downstream side of the load device 6 with the heat source device 5, has a pipe diameter set so that the pressure loss of the second refrigerant flowing therethrough is appropriate. Note that, if the pressure loss in the low-stage gas pipe 4B is large, the evaporation temperature of the first refrigerant on the first circuit 1 side in the refrigerant-to-refrigerant heat exchanger 13 decreases. This increases the power input by the motor of the compressor 10 in the first circuit 1, and reduces the coefficient of performance (COP) of the refrigeration system 100. Therefore, it is preferable that the pipe diameter of the low-stage gas pipe 4B be large.

[0025] When the first circuit 1 and the second circuit 2 are stopped due to a thermostat-off condition in the load device 6 or other reasons, the second refrigerant absorbs heat from the surrounding air, causing a rise in temperature and a corresponding increase in pressure of the second refrigerant. To prevent the pressure of the second refrigerant from rising to the design pressure of the second circuit 2, the compressors 10 in some or all of the first circuits 1 continue to operate even when the second circuit 2 is stopped. When the second circuit 2 is stopped, the amount of heat transferred from the second refrigerant to the first refrigerant in each refrigerant-to-refrigerant heat exchanger 13 is smaller than when the second circuit 2 is operating. This reduces the refrigeration capacity required by the first circuit 1 during operation and the required capacity of the operating compressor 10. Furthermore, even when the second circuit 2 is operating at a low capacity, the refrigeration capacity required by the operating first circuit 1 and the required capacity of the operating compressor 10 are also reduced. However, even if the compressor 10 in only one first circuit 1 operates at the minimum operating frequency, excessive refrigeration capacity may occur, and the first refrigerant may not be able to completely evaporate in the refrigerant-to-refrigerant heat exchanger 13, causing liquid return to the compressor 10. This liquid return may cause a malfunction of the compressor 10. The refrigeration system 100 according to the first embodiment further includes the following components to suppress liquid return to the compressor 10 when the second circuit 2 is stopped.

[0026] In the first embodiment, at least one first circuit 1 of the plurality of first circuits 1 is a regulating circuit 8 described below. The regulating circuit 8 has a bypass 14 and a regulating valve 15 in addition to the components included in the first circuit 1 described above. The bypass 14 is a path that guides a portion of the first refrigerant discharged from the compressor 10 downstream of the expansion valve 12 and upstream of the refrigerant-to-refrigerant heat exchanger 13. The bypass 14 is formed by piping that connects the downstream of the compressor 10 and upstream of the condenser 11 with the downstream of the expansion valve 12 and upstream of the refrigerant-to-refrigerant heat exchanger 13.

[0027] The regulating valve 15 is an opening / closing mechanism that opens and closes the bypass 14. The regulating valve 15 may have a valve element with an adjustable opening and function as a regulator that adjusts the flow rate of the first refrigerant. The regulating valve 15 may be an electronic expansion valve, an electric valve, a solenoid valve type expansion valve, a mechanical expansion valve, a capillary valve, or the like. However, since mechanical expansion valves are inferior to electronic types in terms of their ability to follow liquid return, electronic types are preferentially adopted in the first embodiment. In the case of a pressure reducing mechanism that does not have a flow rate adjustment function, such as a capillary valve, its function is limited, for example, it operates only when the operating frequency of the compressor 10 is at its minimum. The regulating valve 15 may have a circulating refrigerant amount, i.e., a diameter, that is different from or the same as that of the expansion valve 12.

[0028] 2 is a flowchart showing the control of the refrigeration system 100 according to Embodiment 1. In this embodiment, the control shown in FIG.

[0029] First, it is determined whether the second circuit 2 is operating (step S1). Whether the second circuit 2 is operating is the same as whether the circulation device 21 is operating, so in step S1, it may be determined whether the circulation device 21 is operating. If the second circuit 2 is stopped (step S1: NO), of the multiple first circuits 1, the first circuits 1 other than the adjustment circuit 8 are stopped (step S3), and the process proceeds to step S10. If the second circuit 2 is operating (step S1: YES), the process proceeds to step S2.

[0030] In step S2, it is determined whether the operating capacity of the circulation device 21 of the second circuit 2 is less than a threshold value. The threshold value of the operating capacity of the circulation device 21 is a value smaller than the maximum operating capacity of the circulation device 21 and is the operating capacity when the circulation device 21 performs low-volume operation. If the operating capacity of the circulation device 21 is less than the threshold value (step S2: YES), the first circuits 1 other than the adjustment circuit 8 among the multiple first circuits 1 are stopped (step S3), and the process proceeds to step S10. If the operating capacity of the circulation device 21 is not less than the threshold value (step S2: NO), the process proceeds to step S4.

[0031] In step S4, it is determined whether liquid return to the compressor 10 is occurring in any of the plurality of first circuits 1. When the refrigeration capacity to be supplied from one or more first circuits 1 to the second circuit 2 may be small, if the refrigeration capacity of one or more first circuits 1 is excessive, the first refrigerant cannot be evaporated completely in the refrigerant-to-refrigerant heat exchanger 13, and liquid return to the compressor 10 occurs.

[0032] Here, we will explain what happens when liquid return occurs in the first circuit 1. Figure 3 is a pH diagram that explains the state of the refrigerant when liquid return occurs in the first circuit 1 according to the first embodiment. In Figure 3, the vertical axis represents pressure P (MPa), and the horizontal axis represents specific enthalpy (kJ / kg). In Figure 3, points A, B, C, and D represent the state of the refrigerant at the suction section of the compressor 10 (i.e., the outlet of the refrigerant-to-refrigerant heat exchanger 13), the discharge section of the compressor 10, the outlet of the condenser 11, and the inlet of the refrigerant-to-refrigerant heat exchanger 13, respectively. When liquid return does not occur, the refrigerant circulates in a refrigeration cycle that starts at point A, passes through points B, C, and D, and returns to point A.

[0033] Points A1 and B1 indicate the state of the refrigerant at the suction section of the compressor 10 (i.e., the outlet of the refrigerant-to-refrigerant heat exchanger 13) and the discharge section of the compressor 10, respectively, when liquid return occurs in the compressor 10. As can be seen from a comparison of points A and A1 in FIG. 3 , when liquid return occurs, the superheat of the refrigerant at the suction section (point A1) of the compressor 10 decreases, and the refrigerant may enter a gas-liquid two-phase state. Furthermore, as can be seen from a comparison of points B and B1 in FIG. 3 , when liquid return occurs, the superheat of the refrigerant at the discharge section (point B1) of the compressor 10 also decreases. Strictly speaking, when liquid return occurs, the low-pressure pressure is lower than when liquid return does not occur. However, for convenience, FIG. 3 illustrates the low-pressure pressure as being the same regardless of whether liquid return occurs or not.

[0034] As described above, the occurrence of liquid backflow is indicated by a change in the state of the refrigerant at the suction and discharge portions of the compressor 10. Therefore, in step S4 of Fig. 2, the occurrence of liquid backflow can be detected by determining whether the discharge superheat of the refrigerant discharged from the compressor 10 is equal to or less than a predetermined first reference value, or whether the suction superheat of the refrigerant drawn into the compressor 10 is equal to or less than a predetermined second reference value. Specifically, the occurrence of liquid backflow is detected based on the detection results of a pressure sensor that detects the pressure of the refrigerant and a temperature sensor that detects the temperature of the refrigerant, which are disposed between the refrigerant-to-refrigerant heat exchanger 13 and the compressor 10.

[0035] If liquid backflow has occurred in any of the multiple first circuits 1 (step S4: YES), proceed to step S5, and if liquid backflow has not occurred in any of the first circuits 1 (step S4: NO), return.

[0036] In step S5, liquid return suppression control is executed in the first circuit 1 where liquid return is occurring. Specifically, by reducing the refrigeration capacity of the refrigerant-to-refrigerant heat exchanger 13 in the first circuit 1 where liquid return is occurring, the refrigerant in the suction section of the compressor 10 becomes superheated, thereby suppressing liquid return to the compressor 10. Liquid return suppression control to achieve this includes reducing the operating capacity of the compressor 10, increasing the high pressure by reducing the rotation speed of the blower provided in the condenser 11, decreasing the opening of the expansion valve 12 to lower the low pressure, or performing two or more of these in combination. Such liquid return suppression control increases the superheat level in the suction section of the compressor 10, thereby suppressing liquid return to the compressor 10.

[0037] In step S6, it is determined whether or not the liquid return has been resolved. Whether or not the liquid return has been resolved is determined in the same manner as the determination of the presence or absence of liquid return in step S4. If the liquid return has been resolved (step S6: YES), the process returns, and if the liquid return has not been resolved (step S6: NO), the process proceeds to step S7.

[0038] In step S7, it is determined whether the duration of the liquid return is equal to or greater than a predetermined threshold. The duration of the liquid return is the time elapsed since it was determined in step S4 that the liquid return has occurred, and is counted by a timer (not shown) included in the control device 7. If the duration of the liquid return is less than the threshold (step S7: NO), the process returns to step S6. If the duration of the liquid return is equal to or greater than the threshold (step S7: YES), the process proceeds to step S8. The predetermined threshold may be variable.

[0039] In step S8, it is determined whether the first circuit 1 in which liquid return is continuing is the adjustment circuit 8. If liquid return is not continuing in the adjustment circuit 8 (step S8: NO), the first circuit 1 in which liquid return is occurring is stopped (step S9). That is, if liquid return is occurring in a first circuit 1 other than the adjustment circuit 8, the operation of the first circuit 1 in which liquid return is occurring is stopped. If liquid return is continuing in the adjustment circuit 8 (step S8: YES), the bypass 14 in the adjustment circuit 8 is opened (step S10).

[0040] In step S10, the regulating valve 15 provided in the bypass 14 of the regulating circuit 8 is controlled to an open state, and the bypass 14 is opened. Here, the processing of step S10 may be executed by transitioning from step S3 to step S10, or by transitioning from step S8 to step S10. In the former case, only the bypass 14 is opened without executing the liquid return suppression control, and in the latter case, the bypass 14 is opened while executing the liquid return suppression control. However, in the case of transitioning from step S8, the liquid return suppression control may be stopped depending on the operating state after the bypass 14 is opened.

[0041] Fig. 4 is a ph diagram illustrating the state of the refrigerant when the bypass 14 is opened in the regulation circuit according to Embodiment 1. In Fig. 4, the vertical axis represents pressure P (MPa), and the horizontal axis represents specific enthalpy h (kJ / kg).

[0042] 4 indicate the state of the refrigerant when only the bypass 14 is opened without performing the liquid return suppression control. Points A, B, C, and D indicate the state of the refrigerant at the suction port of the compressor 10, the discharge port of the compressor 10, the outlet of the condenser 11, and the outlet of the expansion valve 12, respectively. Point E indicates the state of the refrigerant at the outlet of the control valve 15, and point F indicates the state of the refrigerant at the inlet of the refrigerant-to-refrigerant heat exchanger 13 after the refrigerant from the expansion valve 12 and the refrigerant from the bypass 14 are joined together.

[0043] When the regulating valve 15 is opened and the bypass 14 is opened, a portion (Point B) of the first refrigerant discharged from the compressor 10 in the regulating circuit 8 passes through the regulating valve 15 of the bypass 14 without passing through the condenser 11 (Point E) and flows into the refrigerant-to-refrigerant heat exchanger 13 in a gaseous state. On the other hand, the remainder (Point B) of the first refrigerant discharged from the compressor 10 in the regulating circuit 8 is condensed and liquefied in the condenser 11 (Point C), becomes a two-phase gas-liquid state in the expansion valve 12, and flows into the refrigerant-to-refrigerant heat exchanger 13. Point F indicates a state in which the gaseous refrigerant that has passed through the regulating valve 15 and the two-phase gas-liquid refrigerant that has flowed out of the expansion valve 12 are mixed. When the gaseous refrigerant that has passed through the regulating valve 15 and the two-phase gas-liquid refrigerant that has flowed out of the expansion valve 12 are mixed, the specific enthalpy of the first refrigerant flowing into the refrigerant-to-refrigerant heat exchanger 13 is larger than when all of the first refrigerant that has flowed out of the compressor 10 passes through the condenser 11. This reduces the enthalpy difference between the refrigerants exchanging heat in the refrigerant-to-refrigerant heat exchanger 13, promoting evaporation of the first refrigerant. As a result, the first refrigerant flows out of the refrigerant-to-refrigerant heat exchanger 13 in a gaseous state, and liquid return to the compressor 10 is suppressed.

[0044] Points A2, B2, C2, D2, E2, and F2 each represent the state of the refrigerant when the bypass 14 is opened while the high-pressure increasing control, an example of liquid return prevention control, is being executed. As can be seen from a comparison of points D and D2 in Figure 4 , the liquid return prevention control increases the specific enthalpy at the outlet of the expansion valve 12, reducing the enthalpy difference between the refrigerants exchanging heat in the refrigerant-to-refrigerant heat exchanger 13 and contributing to preventing liquid return. Furthermore, as can be seen from a comparison of points E and E2, the specific enthalpy at the outlet of the bypass 14 also increases, contributing to an increase in the specific enthalpy of the first refrigerant in the refrigerant-to-refrigerant heat exchanger 13. These effects reduce the refrigeration capacity of the first circuit 1 in the refrigerant-to-refrigerant heat exchanger 13. Note that, for convenience of illustration, points F and F2 are shown at the same position in Figure 4 ; however, the state of the refrigerant at points F and F2 may differ depending on the operating state of the adjustment circuit 8. Furthermore, although opening the bypass 14 contributes to preventing liquid backflow as described above, depending on the operating state of the refrigeration system 100, liquid backflow may not be completely eliminated, or the degree of superheat of the refrigerant at the suction section of the compressor 10 may become too high. For this reason, it is advisable to monitor the degree of superheat at the suction section of the compressor 10 based on the state of the refrigerant detected by a pressure sensor or temperature sensor (not shown) provided between the refrigerant-to-refrigerant heat exchanger 13 and the compressor 10. Then, the opening degree of one or both of the expansion valve 12 and the regulating valve 15 is adjusted so that the degree of superheat does not deviate from the target value.

[0045] If the adjustment valve 15 is configured to be able to change its opening degree in multiple stages, in step S10, the opening degree of the adjustment valve 15 may be controlled according to the superheat degree of the first refrigerant required at the outlet of the refrigerant-to-refrigerant heat exchanger 13.

[0046] Returning to Fig. 2, in step S11 following step S10, it is determined whether or not the termination condition for opening the bypass 14 is met. Specifically, it is determined whether or not the liquid return in the adjustment circuit 8 has been resolved. Whether or not the liquid return has been resolved is determined in the same manner as the determination of the presence or absence of liquid return in step S4. If the termination condition for opening the bypass 14 is met (step S11: YES), the process proceeds to step S12; if the condition is not met (step S11: NO), operation continues with the bypass 14 open.

[0047] In step S12, the regulating valve 15 is closed to block the flow of refrigerant through the bypass 14. The liquid return suppression control and the opening of the bypass 14 are completed, and normal control is resumed, and the process returns.

[0048] The bypass 14 in the regulating circuit 8 may guide a portion of the first refrigerant discharged from the compressor 10 downstream of the condenser 11 and upstream of the expansion valve 12, instead of downstream of the expansion valve 12. That is, the bypass 14 may connect the downstream of the compressor 10 and upstream of the condenser 11 with the downstream of the condenser 11 and upstream of the expansion valve 12. In this case, too, the specific enthalpy of the refrigerant flowing into the refrigerant-to-refrigerant heat exchanger 13 increases, resulting in a decrease in the refrigeration capacity of the first circuit 1 at the refrigerant-to-refrigerant heat exchanger 13. Therefore, liquid return to the compressor 10 is suppressed when the second circuit 2 is stopped or operating at a low capacity.

[0049] When the plurality of first circuits 1 includes two or more regulating circuits 8, the control device 7 may alternately open the bypasses 14 in two or more regulating circuits 8 and operate the compressors 10 in step S10. The operation order of the compressors 10 in two or more regulating circuits 8 is determined by the control device 7 based on the operation rate or operation time of each compressor 10, or based on a predetermined order.

[0050] In embodiment 1, a case where the refrigeration device 100 includes multiple first circuits 1 has been described, but the refrigeration device 100 may include only one first circuit 1, in which case the one first circuit 1 is the adjustment circuit 8.

[0051] Here, whether the compressor 10 of the regulating circuit 8 is inverter-driven or operates at a constant rotation speed, the target evaporation temperature of the first refrigerant in the first circuit 1 for reducing the pressure of the second refrigerant in the second circuit 2 to a desired pressure is determined by design. Note that this evaporation temperature does not necessarily have to coincide with the target evaporation temperature of the first circuit 1 during normal cooling operation of the second circuit 2. The target evaporation temperature parameter also plays a role in determining the required minimum load of the first circuit 1.

[0052] The effects of the refrigeration system 100 according to the first embodiment will be described below. The refrigeration system 100 according to the first embodiment includes one or more first circuits 1 and one or more second circuits 2. A first refrigerant flows through each first circuit 1, and a second refrigerant flows through each second circuit 2. The first circuits 1 include a compressor 10, a condenser 11, an expansion valve 12, and an inter-refrigerant heat exchanger 13. The compressor 10 compresses the first refrigerant. The condenser 11 condenses the compressed first refrigerant. The expansion valve 12 expands the condensed first refrigerant. The inter-refrigerant heat exchanger 13 exchanges heat between the expanded first refrigerant and a second refrigerant. The second circuit 2 includes one or more inter-refrigerant heat exchangers 13 of the first circuits 1, an evaporator 22, and a circulation device 21. The evaporator 22 exchanges heat between the second refrigerant, which has exchanged heat with the first refrigerant, and a first object, thereby cooling the first object and evaporating the second refrigerant. The circulation device 21 circulates the second refrigerant in the second circuit 2. One of the one or more first circuits 1 is the adjustment circuit 8. The compressor 10 of the adjustment circuit 8 operates to superheat the first refrigerant at the outlet of the refrigerant-to-refrigerant heat exchanger 13 when the circulation device 21 is stopped or is operating at a low capacity where the circulation device 21 is operating at a capacity below a threshold.

[0053] When the circulation device 21 is stopped or is operating at a low capacity, the regulation circuit 8 operates to cool the second refrigerant in the refrigerant-to-refrigerant heat exchanger 13, thereby suppressing a rise in the pressure of the refrigerant in the second circuit 2. Furthermore, the regulation circuit 8 superheats the first refrigerant at the outlet of the refrigerant-to-refrigerant heat exchanger 13, thereby suppressing liquid return from the regulation circuit 8 to the compressor 10.

[0054] The regulating circuit 8 in the first embodiment is provided with a bypass 14 and a regulating valve 15. The bypass 14 guides a portion of the first refrigerant discharged from the compressor 10 downstream of the condenser 11 and upstream of the refrigerant-to-refrigerant heat exchanger 13. In the example of FIG. 1 , the bypass 14 guides a portion of the first refrigerant discharged from the compressor 10 downstream of the condenser 11 and the expansion valve 12 and upstream of the refrigerant-to-refrigerant heat exchanger 13. The regulating valve 15 is an opening / closing mechanism that opens and closes the bypass 14. When the circulation device 21 is stopped or is operating at a low capacity where the circulation device 21 is operating at a capacity below a threshold, the regulating valve 15 is opened in the compressor 10 of the regulating circuit 8, allowing the first refrigerant to flow through the bypass 14.

[0055] Because the regulating valve 15 is open, a portion of the first refrigerant discharged from the compressor 10 in the regulating circuit 8 flows into the refrigerant-to-refrigerant heat exchanger 13 in a gaseous state via the bypass 14 and the regulating valve 15 without passing through the condenser 11. Note that a portion of the first refrigerant may also flow into the expansion valve 12 in a gaseous state via the bypass 14 and the regulating valve 15. In this case, a portion of the first refrigerant flows out of the expansion valve 12 in a gaseous state and flows into the refrigerant-to-refrigerant heat exchanger 13. The remainder of the first refrigerant discharged from the compressor 10 in the regulating circuit is condensed and liquefied in the condenser 11, then becomes a gas-liquid two-phase state in the expansion valve 12, and flows into the refrigerant-to-refrigerant heat exchanger 13. Therefore, in the regulating circuit 8, the proportion of gas refrigerant in the refrigerant flowing into the refrigerant-to-refrigerant heat exchanger 13 is larger and the proportion of liquid refrigerant is smaller than in a case where all of the first refrigerant flowing out of the compressor 10 passes through the condenser 11. Therefore, even when the heat radiation amount of the second refrigerant in the refrigerant-to-refrigerant heat exchanger 13 is small, i.e., even when the second circuit 2 is stopped or operating at a low capacity, evaporation of the liquid first refrigerant is promoted in the refrigerant-to-refrigerant heat exchanger 13. Therefore, liquid return of the liquid first refrigerant from the refrigerant-to-refrigerant heat exchanger 13 to the compressor 10 is suppressed.

[0056] The regulating valve 15 opens when the circulation device 21 is stopped or is operating at a low capacity, or when it is determined that liquid is returning to the compressor 10 from the regulating circuit 8. This makes it possible to efficiently suppress liquid returning to the compressor 10.

[0057] The refrigeration system 100 according to the first embodiment includes a plurality of first circuits 1. The plurality of first circuits 1 include two or more regulating circuits. The compressors in the two or more regulating circuits operate in turn when the circulation device 21 is stopped or is operating at a low capacity. This prevents a specific regulating circuit 8 from having an increased number of starts and stops and an increased operating time compared to the other regulating circuits 8, thereby extending the life of the compressors 10 in each regulating circuit 8.

[0058] In the first embodiment, when the circulation device 21 of the second circuit 2 is stopped, the compressors 10 of the first circuit 1 other than the adjustment circuit 8 are stopped. This makes it possible to prevent the refrigeration capacities of the multiple first circuits 1 from becoming excessive relative to the second circuit 2.

[0059] The compressors 10 of the first circuits 1 in the first embodiment are compressors that do not have a mechanical capacity control mechanism inside, which makes it possible to reduce costs.

[0060] In the first embodiment, the first refrigerant is a natural refrigerant or a refrigerant with a global warming potential of 1500 or less, and the second refrigerant is R744 (carbon dioxide), thereby reducing the burden on the environment.

[0061] In the first embodiment, when the circulation device 21 is stopped, at least one of the operating frequency of the compressor 10 and the opening degree of the expansion valve 12 is determined based on the degree of superheat of the first refrigerant at the outlet of the refrigerant-to-refrigerant heat exchanger 13. This makes it possible to further suppress liquid return to the compressor 10.

[0062] The refrigeration system 100 in the first embodiment further includes a blower 11a for blowing air to the condenser 11. The conditions for determining the manipulated variable for the rotation speed of the blower 11a may include the degree of superheat of the first refrigerant at the outlet of the refrigerant-to-refrigerant heat exchanger 13. This makes it possible to further suppress liquid return to the compressor 10.

[0063] Embodiment 2. The configuration of a refrigeration system 200 according to embodiment 2 will be described below. In embodiment 2, the same components as those in embodiment 1 above will be assigned the same reference numerals. Furthermore, in embodiment 2, the same configurations as those in embodiment 1 and the same functions as those in embodiment 1 will not be described unless there are special circumstances.

[0064] 5 is a circuit diagram showing a configuration example of a refrigeration system 200 according to embodiment 2. The refrigeration system 200 according to embodiment 2 includes a plurality of first circuits 1A and a second circuit 2. The plurality of first circuits 1A all have the same circuit configuration, and none of them includes the bypass 14 and the adjustment valve 15 shown in embodiment 1.

[0065] In the second embodiment, at least one of the first circuits 1A is a regulating circuit 8A. The regulating circuit 8A can be operated at a lower capacity than the other first circuits 1A. Specifically, in this embodiment, the capacity of the compressor 10 in the regulating circuit 8A is smaller than the capacity of the compressor 10 in the other first circuits 1A. The capacity of the compressor 10 in the regulating circuit 8A is determined based on the minimum load required in the second circuit 2. The capacity based on this minimum load is a size required to maintain the pressure of the second refrigerant below the design pressure when the second circuit 2 is stopped. In the case of inverter drive, the capacity is determined based on the minimum load required at a minimum capacity or a specific capacity. Note that the compressor 10 in the regulating circuit 8A may operate at a constant rotational speed. Whether the compressor 10 in the regulating circuit 8A is inverter-driven or operates at a constant rotational speed, the target evaporation temperature of the first refrigerant in the first circuit 1 for reducing the pressure of the second refrigerant in the second circuit 2 to the desired pressure is determined by design. The evaporation temperature does not necessarily have to coincide with the target evaporation temperature of the first circuit 1 during normal cooling operation of the second circuit 2. The target evaporation temperature parameter also plays a role in determining the required minimum load of the first circuit 1.

[0066] In the regulation circuit 8A, the capacity of the refrigerant-to-refrigerant heat exchanger 13 is small due to the small capacity of the compressor 10. In the second embodiment, in order to reduce pressure loss in the regulation circuit 8A, that is, to prevent a decrease in the evaporation temperature of the first refrigerant in the refrigerant-to-refrigerant heat exchanger 13 of the regulation circuit 8A, the refrigerant-to-refrigerant heat exchanger 13 of the regulation circuit 8A is installed at the most downstream position in the second circuit 2 among the plurality of refrigerant-to-refrigerant heat exchangers 13 of the first circuit 1A.

[0067] Fig. 6 is a flowchart showing the control of refrigeration device 200 according to embodiment 2. In this embodiment, the control shown in Fig. 6 is executed by control device 7. In Fig. 6, the processing other than steps S10A, S11A, and S12A is the same as Fig. 2, and therefore only steps S10A to S12A will be described here.

[0068] In step S10A, the capacity of the compressor 10 in the regulating circuit 8A is set to a specific value. The specific value is a predetermined value that prevents liquid from returning to the compressor 10 in the regulating circuit 8A and does not result in excessive capacity for the second circuit 2. Preferably, the specific value is a value smaller than the minimum capacity of the compressor 10 in the first circuit 1A other than the regulating circuit 8A.

[0069] In step S11A following step S10A, it is determined whether or not a termination condition for setting the capacity of the compressor 10 of the adjustment circuit 8A to a specific value is satisfied. Specifically, it is determined whether or not the liquid return in the adjustment circuit 8A has been resolved. Whether or not the liquid return has been resolved is determined in the same manner as the determination of the presence or absence of liquid return in step S4. If the termination condition is satisfied (step S11A: YES), the process proceeds to step S12A. If the termination condition is not satisfied (step S11A: NO), operation with the capacity of the compressor 10 of the adjustment circuit 8A set to a specific value is continued.

[0070] In step S12A, the setting of the capacity of the compressor 10 by the adjustment circuit 8A to the specific value is cancelled, normal control is restored, and the process returns.

[0071] The refrigeration system 200 according to the second embodiment may have one or more regulating circuits 8 according to the first embodiment, in addition to the multiple first circuits 1A. In this case, the control device 7 may operate either the compressors 10 of one or more regulating circuits 8 or the compressor 10 of the regulating circuit 8A when the circulation device 21 is stopped or is operating at a low capacity. Specifically, the control device 7 may alternately operate the compressors 10 of one or more regulating circuits 8 and the compressor 10 of the regulating circuit 8A. The operation order of the compressors 10 of one or more regulating circuits 8 and the compressors 10 of the regulating circuit 8A is determined by the control device 7 based on the operation rate or operation time of each compressor 10, or based on a predetermined order.

[0072] The effects of the refrigeration system 200 according to the second embodiment are described below. The regulating circuit 8A according to the second embodiment can be operated at a lower capacity than the first circuit 1A other than the regulating circuit 8A. Specifically, the capacity of the compressor 10 in the regulating circuit 8A according to the second embodiment is smaller than the capacity of the compressor 10 in the first circuit 1A other than the regulating circuit 8A. When the circulation device 21 is stopped or is operating at a low capacity, the compressor 10 in the regulating circuit 8A operates to superheat the first refrigerant at the outlet of the refrigerant-to-refrigerant heat exchanger 13. For example, when the compressor 10 is an inverter-type compressor, the compressor 10 in the regulating circuit 8A operates at a smaller displacement than the compressor 10 in the first circuit 1A other than the regulating circuit 8A.

[0073] When the circulation device 21 is stopped or is operating at a low capacity below the threshold, the regulation circuit 8A operates at a low capacity, whereby the second refrigerant is cooled in the refrigerant-to-refrigerant heat exchanger 13, thereby suppressing a rise in refrigerant pressure in the second circuit 2. Furthermore, because the refrigeration capacity of the regulation circuit 8A is small, the first refrigerant at the outlet of the refrigerant-to-refrigerant heat exchanger 13 can be superheated even when the circulation device 21 is stopped or is operating at a low capacity below the threshold, thereby suppressing liquid return to the compressor 10 in the regulation circuit 8A. Furthermore, because the capacity of the compressor 10 in the regulation circuit 8A is smaller than the capacity of the compressors 10 in the first circuit 1A other than the regulation circuit 8A, the refrigeration capacity exerted by the regulation circuit 8A is smaller than the refrigeration capacity of the other first circuits 1A. This prevents the refrigeration capacity of the regulation circuit 8A from becoming excessive relative to the second circuit 2.

[0074] In the present embodiment, the configuration in which the regulating circuit 8A can be operated at a lower capacity than the first circuits 1A other than the regulating circuit 8A has been described as being such that the capacity of the compressor 10 in the regulating circuit 8A is smaller than the capacity of the compressors 10 in the other first circuits 1A. In addition to this configuration, the capacities of the compressors 10 in all first circuits 1A including the regulating circuit 8A may be the same, and the opening degrees of the expansion valves 12 in the regulating circuit 8A may be different from those of the expansion valves 12 in the first circuits 1A other than the regulating circuit 8A, thereby operating the regulating circuit 8A at a lower capacity.

[0075] Furthermore, when the second circuit 2 is stopped, the compressors 10 of the first circuits 1 other than the regulating circuit 8 are stopped, and only the compressors 10 of the regulating circuit 8A are in operation. This makes it possible to prevent the refrigeration capacities of the multiple first circuits 1 from becoming excessive relative to the second circuit 2.

[0076] The capacity of the compressor 10 of the regulating circuit is determined based on the minimum load required in the second circuit 2. As a result, when the second circuit 2 is stopped, only the compressor 10 of the regulating circuit operates, thereby suppressing an increase in the pressure of the second refrigerant.

[0077] The refrigerant-to-refrigerant heat exchanger 13 of the adjustment circuit in the second embodiment is arranged at the most downstream position in the second circuit 2 among the plurality of refrigerant-to-refrigerant heat exchangers 13 of the first circuit 1A. This makes it possible to suppress pressure loss in the refrigerant-to-refrigerant heat exchanger 13 of the second circuit 2 during normal operation, resulting in a higher evaporation temperature in the adjustment circuit and suppressing an increase in power consumption.

[0078] The first and second embodiments have been described above. In addition to the above, the refrigeration apparatus 100 according to the first embodiment and the refrigeration apparatus 200 according to the second embodiment may each be provided with the following components. Specifically, the second circuit 2 may be provided with existing components such as a safety valve, a pressure relief device, or a rupture disc (not shown) as a measure against a pressure increase of the second refrigerant. Furthermore, the second circuit 2 may be provided with a component that prevents the pressure of the second refrigerant from exceeding the design pressure when the system is stopped, or with a component that releases the second refrigerant to the outside of the second circuit 2 when the pressure of the second refrigerant increases to prevent damage to the second circuit 2.

[0079] Additionally, one or more existing detectors may be provided to detect leaks of the first and / or second refrigerant.

[0080] 2 and 6, after step S2, the pressure of the second refrigerant in the second circuit 2 may be detected. If the pressure of the second refrigerant is equal to or greater than a predetermined threshold, the process may proceed to step S9 or step S9A, and if the pressure of the second refrigerant is less than the predetermined threshold, the process may return. The threshold value for the pressure of the second refrigerant is a value smaller than the design pressure of the second circuit 2. In this way, when the second circuit 2 is stopped, the regulation circuit 8 operates only if the pressure of the second refrigerant becomes equal to or greater than the threshold due to the influence of the ambient temperature, etc. This prevents unnecessary operation of the regulation circuit 8, contributing to energy savings.

[0081] Although the embodiments have been described above, the contents of the present disclosure are not limited to the embodiments and include conceivable equivalents. Furthermore, the configurations described in the first and second embodiments and their modifications can be combined with each other as long as the functions and operations are not impaired.

[0082] 1, 1A First circuit, 2 Second circuit, 3 High-stage refrigerant piping, 4 Low-stage refrigerant piping, 4A Low-stage liquid piping, 4B Low-stage gas piping, 5 Heat source device, 6 Load device, 7 Control device, 8 Adjustment circuit, 8A Adjustment circuit, 10 Compressor, 11 Condenser, 11a Blower, 12 Expansion valve, 13 Refrigerant heat exchanger, 14 Bypass, 15 Adjustment valve, 20 Receiver, 21 Circulation device, 22 Evaporator, 22A Distributor, 70 CPU, 71 Memory, 100, 200 Refrigeration device.

Claims

1. A refrigeration system comprising: one or more first circuits through which a first refrigerant circulates; and a second circuit through which a second refrigerant circulates, wherein the first circuit is provided with: a compressor that compresses the first refrigerant, a condenser that condenses the compressed first refrigerant, a pressure reducer that depressurizes the first refrigerant after condensation, and an inter-refrigerant heat exchanger that exchanges heat between the depressurized first refrigerant and the second refrigerant; and the second circuit is provided with: the inter-refrigerant heat exchangers of the one or more first circuits; an evaporator that exchanges heat between the second refrigerant, after heat exchange with the first refrigerant, and a first object to cool the first object and evaporate the second refrigerant; and a circulation device that circulates the second refrigerant in the second circuit, wherein at least one of the one or more first circuits is an adjustment circuit that operates to superheat the first refrigerant at the outlet of the inter-refrigerant heat exchanger when the circulation device is stopped or is operating at a low capacity where the circulation device is operating at a capacity below a threshold value.

2. The refrigeration system of claim 1, wherein the adjustment circuit is provided with a bypass that guides a portion of the first refrigerant discharged from the compressor downstream of the condenser and upstream of the refrigerant-to-refrigerant heat exchanger, and an opening / closing mechanism that opens and closes the bypass, and when the circulation device is stopped or is performing the low-capacity operation, the opening / closing mechanism is in an open state, allowing the first refrigerant to circulate through the bypass.

3. The refrigeration system according to claim 2, wherein the bypass guides a portion of the first refrigerant discharged from the compressor downstream of the condenser and the pressure reducer and upstream of the refrigerant-to-refrigerant heat exchanger.

4. A refrigeration device according to claim 2 or 3, wherein the opening and closing mechanism is set to an open state when it is determined that liquid is returning to the compressor in the adjustment circuit.

5. A refrigeration system as claimed in any one of claims 2 to 4, comprising a plurality of said first circuits, said plurality of first circuits including two or more said adjustment circuits, and wherein each of said compressors in said two or more adjustment circuits operates in turn when said circulation device is stopped or when said circulation device is performing said low capacity operation.

6. The refrigeration system of claim 1, wherein when the circulation device is stopped or when the circulation device is operating at a low capacity, the regulation circuit operates at a lower capacity than the first circuit other than the regulation circuit.

7. The refrigeration system according to claim 6, wherein the capacity of the compressor in the regulating circuit is smaller than the capacity of the compressor in the first circuit other than the regulating circuit.

8. A refrigeration device as described in claim 6 or claim 7, comprising a plurality of the first circuits, wherein the refrigerant-to-refrigerant heat exchanger of the adjustment circuit is arranged at the most downstream position in the second circuit among the refrigerant-to-refrigerant heat exchangers of the plurality of first circuits.

9. A refrigeration system according to any one of claims 1 to 8, wherein when the circulation device is stopped, the compressor of the first circuit other than the adjustment circuit is stopped.

10. A refrigeration system according to any one of claims 1 to 9, wherein the compressor of the first circuit is a compressor that does not have a mechanical capacity control mechanism inside.

11. A refrigeration device according to any one of claims 1 to 10, wherein the first refrigerant is a natural refrigerant or a refrigerant with a global warming potential of 1500 or less, and the second refrigerant is R744.

12. A refrigeration system as described in any one of claims 1 to 11, wherein at least one of the operating frequency of the compressor and the opening degree of the pressure reducer is determined based on the degree of superheat of the first refrigerant at the outlet of the refrigerant-to-refrigerant heat exchanger when the circulation device is stopped.

13. A refrigeration system according to any one of claims 1 to 12, further comprising a blower for blowing air to the condenser, wherein the rotation speed of the blower is controlled based on conditions including the degree of superheat of the first refrigerant at the outlet of the refrigerant-to-refrigerant heat exchanger.

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