Refrigeration Cycle Equipment

Abstract

This refrigeration cycle device causes a first refrigerant to circulate in a first refrigerant circuit, and cools a first target with the first refrigerant. The refrigeration cycle device comprises a first compressor, a first heat exchanger, an evaporator, a first valve, a first pressure detection device, a first temperature detection device, a control device, a liquid receiver, and a second refrigerant circuit. A second refrigerant is caused to circulate in the second refrigerant circuit. The second refrigerant circuit comprises a second compressor, a second heat exchanger, a second valve, and the first heat exchanger. The first compressor compresses the first refrigerant. The first heat exchanger causes heat exchange between the first refrigerant and the second refrigerant. The evaporator causes the first refrigerant to exchange heat with the first target. The first valve is provided on an upstream side from the evaporator in the first refrigerant circuit and, in an open state, allows the first refrigerant to flow to the evaporator. The first pressure detection device detects a first pressure, which is the pressure of the first refrigerant. The first temperature detection device detects a first temperature, which is the temperature of the first target in the evaporator. The control device controls the first compressor and the first valve. The second compressor compresses the second refrigerant. The second heat exchanger causes the second refrigerant to exchange heat with a third target, and the second valve reduces the pressure of the second refrigerant. If the first pressure is at or above a first threshold value pressure determined in advance, and the first temperature is at or below a threshold value temperature determined in advance, the control device controls the first valve to the open state.

Description

[Technical field]

[0001] The present disclosure relates to a refrigeration cycle device that uses carbon dioxide as a refrigerant. [Background technology]

[0002] In a refrigeration cycle device using carbon dioxide (R744) as a refrigerant, the refrigerant pressure is, for example, 10 [MPa], which is higher than when a refrigerant such as fluorocarbon is used. Therefore, components such as a heat exchanger, a container, and a refrigerant pipe in a refrigeration cycle device using R744 as a refrigerant are required to have high pressure resistance. In addition, such a refrigeration cycle device may be provided with various components to prevent the refrigerant pressure from exceeding the design pressure in the installation environment (for example, see Patent Document 1). Such components include a safety valve for releasing the refrigerant to the outside when the refrigerant pressure in the refrigerant circuit becomes high. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 6472527 Summary of the Invention [Problem to be solved by the invention]

[0004] However, the operation of the safety valve causes a large amount of gas refrigerant to accumulate inside the housing that forms the outer shell of the refrigeration cycle device, and workers, etc., may be suddenly exposed to a large amount of gas refrigerant when working on the refrigeration cycle device. In addition, after the refrigerant is released, it is necessary to process the refrigerant by refilling the refrigerant into the refrigerant circuit, and it may take some time for the refrigeration cycle device to resume operation.

[0005] The present disclosure has been made to solve the above-mentioned problems, and aims to provide a refrigeration cycle device that reduces the refrigerant pressure before the safety valve is activated, thereby preventing damage to the refrigeration cycle device, speeding up the resumption of operation, and improving safety. [Means for solving the problem]

[0006] A refrigeration cycle apparatus according to the present disclosure is a refrigeration cycle apparatus that circulates a first refrigerant, which is carbon dioxide, through a first refrigerant circuit and cools a first object with the first refrigerant, and includes a first compressor that compresses the first refrigerant, a first heat exchanger that exchanges heat with the first refrigerant discharged from the first compressor and a second object to cool the first refrigerant, an evaporator that exchanges heat with the first refrigerant and the first object, a first valve that is provided upstream of the evaporator in the first refrigerant circuit and reduces the pressure of the first refrigerant in an open state and circulates the reduced pressure first refrigerant through the evaporator, a first pressure detection device that detects a first pressure that is a pressure of the first refrigerant between the downstream side of the first compressor and the first valve, and a first pressure detection device that detects a pressure of the first refrigerant between the downstream side of the first compressor and the first valve and a second pressure detection device that detects a pressure of the first refrigerant in the evaporator. a control device for controlling the first compressor and the first valve, and a second refrigerant circuit for circulating a second refrigerant, wherein the second object is the second refrigerant, the second refrigerant circuit has a second compressor for compressing the second refrigerant, a second heat exchanger for causing the second refrigerant discharged from the second compressor to exchange heat with a third object and condense the second refrigerant, a second valve for reducing the pressure of the second refrigerant condensed in the second heat exchanger, and the first heat exchanger, wherein the first heat exchanger exchanges heat between the second refrigerant reduced in pressure by the second valve and the first refrigerant discharged from the first compressor, condensing the first refrigerant and evaporating the second refrigerant, and the control device When the first compressor is stopped, When the first pressure is equal to or higher than a predetermined first threshold pressure and the first temperature is equal to or lower than a predetermined threshold temperature, the first valve is controlled to an open state. Effect of the Invention

[0007] According to the refrigeration cycle device of the present disclosure, when the first pressure is equal to or higher than the first threshold pressure and the temperature of the first object is equal to or lower than the threshold temperature, the control device opens the first valve and circulates the first refrigerant to the evaporator. This reduces the first pressure of the first refrigerant in the first refrigerant circuit, such as the receiver. This suppresses the operation of the safety valve and damage to the refrigeration cycle device. By suppressing the operation of the safety valve and damage to the refrigeration cycle device, the refrigeration cycle device can quickly resume operation after normal refrigerant distribution is restored. In addition, by suppressing the operation of the safety valve, the release of the first refrigerant into the atmosphere is suppressed, so that workers or users are prevented from being exposed to the first refrigerant. This improves safety. [Brief description of the drawings]

[0008] [Figure 1] 1 is a schematic diagram showing a configuration example of a refrigeration cycle device according to a first embodiment. [Diagram 2] 2 is a block diagram illustrating a hardware configuration of a control device according to the first embodiment. FIG. [Diagram 3] 4 is a flowchart illustrating a flow of a pressure adjustment process performed by the refrigeration cycle apparatus according to the first embodiment. [Figure 4] FIG. 6 is a schematic diagram showing a configuration example of a refrigeration cycle device according to a second embodiment. [Diagram 5] 10 is a flowchart illustrating a flow of a pressure adjustment process performed by a refrigeration cycle apparatus according to a second embodiment. [Figure 6] FIG. 11 is a schematic diagram showing a configuration example of a utilization side device in the third embodiment. [Figure 7] FIG. 13 is a schematic diagram showing a configuration example of a utilization side device in the fourth embodiment. [Figure 8] FIG. 13 is a schematic diagram showing a configuration example of a refrigeration cycle device according to a fifth embodiment. [Figure 9] 13 is a flowchart illustrating a flow of a pressure adjustment process performed by a refrigeration cycle apparatus according to a fifth embodiment. [Figure 10] FIG. 13 is a schematic diagram showing a configuration example of a refrigeration cycle device according to a sixth embodiment. [Figure 11] 13 is a flowchart illustrating a flow of a pressure adjustment process performed by a refrigeration cycle apparatus according to a sixth embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, a refrigeration cycle device according to an embodiment will be described in detail with reference to the drawings.

[0010] Embodiment 1 1 is a schematic diagram showing a configuration example of a refrigeration cycle apparatus 100 according to a first embodiment. The refrigeration cycle apparatus 100 is a system that cools a first object, such as air or water, to a temperature desired by a user by using a first refrigerant. The first refrigerant is carbon dioxide (R744) refrigerant.

[0011] The refrigeration cycle apparatus 100 includes a first refrigerant circuit 1 in which a first refrigerant circulates, and a second refrigerant circuit 2 in which a second refrigerant circulates. The second refrigerant may be a highly available HFC refrigerant such as R32, R410A, or R448A, or a natural refrigerant such as R290 or R717 that poses few environmental problems. The refrigeration cycle apparatus 100 may not include the second refrigerant circuit 2.

[0012] The refrigeration cycle apparatus 100 includes a heat source device 3 and a user side device 4. The heat source device 3 and the user side device 4 are connected to each other by a first refrigerant pipe 5. The refrigeration cycle apparatus 100 also includes a control device 6. In FIG. 1, a housing forming the outer periphery of the heat source device 3 is shown by a dashed line rectangle, and an example is shown in which the control device 6 is installed inside the housing, but the control device 6 may be installed outside the housing. A part of the control device 6 may be provided in the heat source device 3, and the remaining part may be provided in the user side device 4. In this case, a part of the control device 6 in the heat source device 3 and the remaining part of the control device 6 in the user side device 4 may operate in cooperation with each other.

[0013] The first refrigerant circuit 1 has a first compressor 10, a primary side heat exchanger 11, an inter-refrigerant heat exchanger 12, a receiver 13, a first pressure reducing valve 14, an evaporator 15, and a gas-liquid separator 16, which are connected in sequence by a first refrigerant piping 5. The first compressor 10, the primary side heat exchanger 11, the inter-refrigerant heat exchanger 12, the receiver 13, and the gas-liquid separator 16 are disposed within the housing of the heat source equipment 3.

[0014] The first pressure reducing valve 14 and the evaporator 15 are disposed inside a housing forming the outer periphery of the utilization side device 4, which is indicated by a two-dot chain line square in Fig. 1. However, the first pressure reducing valve 14 may be provided outside the housing of the utilization side device 4.

[0015] The second refrigerant circuit 2 has a secondary side compressor 20, a secondary side condenser 21, a secondary side pressure reducing valve 22, and a refrigerant heat exchanger 12, which are connected in sequence by a second refrigerant pipe 7. The second refrigerant circuit 2 is disposed within the housing of the heat source device 3.

[0016] The first compressor 10 is a scroll type, rotary type, reciprocating type, screw type, or other compressor, and is an inverter compressor whose capacity can be controlled by an inverter. The first compressor 10 draws in the first refrigerant from the first refrigerant pipe 5 and compresses the drawn in first refrigerant. Then, the first compressor 10 discharges the compressed first refrigerant to the first refrigerant pipe 5.

[0017] The primary side heat exchanger 11 may be air-cooled or water-cooled. Examples of the air-cooled primary side heat exchanger 11 include a plate fin tube heat exchanger or a parallel flow condenser. Examples of the water-cooled primary side heat exchanger 11 include a shell and tube heat exchanger, a plate heat exchanger, or a double tube heat exchanger. The primary side heat exchanger 11 cools the first refrigerant by exchanging heat between the first refrigerant and air or water. The refrigeration cycle device 100 may not include the primary side heat exchanger 11. However, in order to reduce thermal stress on the refrigerant-to-refrigerant heat exchanger 12 caused by the first refrigerant discharged from the first compressor 10, it is desirable for the refrigeration cycle device 100 to include the primary side heat exchanger 11.

[0018] When the first refrigerant circuit 1 is provided with the primary side heat exchanger 11, the refrigerant-refrigerant heat exchanger 12 is provided downstream of the primary side heat exchanger 11. The refrigerant-refrigerant heat exchanger 12 is, for example, a plate type heat exchanger, and exchanges heat between the first refrigerant and the second refrigerant. The refrigerant-refrigerant heat exchanger 12 functions as a condenser in the first refrigerant circuit 1, and functions as an evaporator in the second refrigerant circuit 2. The first refrigerant condenses by releasing heat to the second refrigerant in the refrigerant-refrigerant heat exchanger 12. The second refrigerant evaporates by absorbing heat from the first refrigerant in the refrigerant-refrigerant heat exchanger 12. The refrigerant-refrigerant heat exchanger 12 is an example of a first heat exchanger. The second refrigerant that exchanges heat with the first refrigerant in the refrigerant-refrigerant heat exchanger 12 is an example of a second target. When the refrigeration cycle device 100 does not include the second refrigerant circuit 2, the primary side heat exchanger 11 is an example of a first heat exchanger, and condenses the first refrigerant by heat exchange with water or air. In this case, the air or water exchanging heat with the first refrigerant in the primary side heat exchanger 11 is an example of the second target.

[0019] The receiver 13 stores the first refrigerant. The receiver 13 is provided to store an excess of the first refrigerant that occurs due to seasonal changes, load fluctuations, or the like.

[0020] The first pressure reducing valve 14 is an electronic expansion valve, a temperature expansion valve, or the like. The first pressure reducing valve 14 reduces the pressure of the first refrigerant to expand it. The first pressure reducing valve 14 is an example of a first valve.

[0021] The evaporator 15 is a heat exchanger of a plate fin tube type, a shell and tube type, a plate type, or the like. The evaporator 15 exchanges heat between the first refrigerant, which has been brought to a low pressure state by the first pressure reducing valve 14, and a first object whose temperature the user desires to adjust, thereby cooling the first object. The first refrigerant absorbs heat from the first object in the evaporator 15 and evaporates.

[0022] The gas-liquid separator 16 is intended to prevent the first compressor 10 from drawing in the liquid first refrigerant from the first refrigerant pipe 5 on the side that draws in the first refrigerant. Hereinafter, the flow of the liquid first refrigerant into the first compressor 10 may be referred to as liquid return. Liquid return may occur due to fluctuations in the load of the utilization side device 4. Alternatively, liquid return may occur when the first compressor 10 starts and stops. It is preferable that the gas-liquid separator 16 is included in the first refrigerant circuit 1 to prevent liquid return, but it is not necessary.

[0023] In addition to the above, the first refrigerant circuit 1 may be provided with at least one of an oil separator, an oil return circuit from the oil separator, a check valve, a service operation valve, a safety device such as a sight glass, a strainer, a dryer, a high-pressure switch, a supercooling circuit for the liquid first refrigerant, and a liquid-gas heat exchanger, etc. The first refrigerant circuit 1 may also be provided with a four-way or three-way valve or the like that switches the flow direction of the first refrigerant to defrost the evaporator 15.

[0024] The secondary side compressor 20 is a scroll type, rotary type, reciprocating type, screw type, or other compressor, and is an inverter compressor whose capacity can be controlled by an inverter. The secondary side compressor 20 draws in the second refrigerant from the second refrigerant pipe 7 and compresses the drawn second refrigerant. Then, the secondary side compressor 20 discharges the compressed second refrigerant to the second refrigerant pipe 7. The secondary side compressor 20 is an example of a second compressor.

[0025] The secondary side condenser 21 may be air-cooled or water-cooled. Examples of the air-cooled secondary side condenser 21 include a plate fin tube heat exchanger or a parallel flow condenser. Examples of the water-cooled secondary side condenser 21 include a shell-and-tube heat exchanger, a plate heat exchanger, or a double-tube heat exchanger. The secondary side condenser 21 cools and condenses the second refrigerant by exchanging heat between the second refrigerant and a third object, which is air or water. The secondary side condenser 21 is an example of a second heat exchanger. In addition, when the refrigeration cycle device 100 includes the second refrigerant circuit 2, the air or water exchanging heat with the first refrigerant in the primary side heat exchanger 11 is an example of a fourth object.

[0026] The secondary pressure reducing valve 22 is an electronic expansion valve, a temperature expansion valve, or the like. The secondary pressure reducing valve 22 reduces the pressure of the second refrigerant to expand it. The secondary pressure reducing valve 22 is an example of a second valve.

[0027] In addition to the above, the second refrigerant circuit 2 may be provided with at least one of an oil separator, an oil return circuit from the oil separator, a check valve, a service operation valve, a sight glass, a strainer, a dryer, various sensors, safety devices such as a high-pressure switch, a liquid-gas heat exchanger, etc. In addition, the second refrigerant circuit 2 may be provided with a secondary-side gas-liquid separator in the second refrigerant pipe 7 on the side where the secondary-side compressor 20 sucks the second refrigerant.

[0028] The control device 6 controls the first compressor 10, the first pressure reducing valve 14, the secondary compressor 20, the secondary pressure reducing valve 22, etc. The control device 6 is connected by wire to each of the components, such as the first compressor 10, the first pressure reducing valve 14, the secondary compressor 20, and the secondary pressure reducing valve 22, and transmits control signals to each of the components, which operate based on the received control signals. The control device 6 may control at least one of the components, such as the first compressor 10, the first pressure reducing valve 14, the secondary compressor 20, and the secondary pressure reducing valve 22, by wireless communication.

[0029] Now, the design pressure of the first refrigerant circuit 1 through which the first refrigerant, which is R744 refrigerant, flows may be divided into a high-pressure portion, a liquid supply portion, and a low-pressure portion, or may be unified within the first refrigerant circuit 1. The high-pressure portion refers to the portion in the first refrigerant circuit 1 from when the first refrigerant is discharged from the first compressor 10 until the first pressure reduction. The liquid supply portion refers to the portion in the first refrigerant circuit 1 from when the discharged refrigerant is reduced in pressure once to the first pressure reducing valve 14, and generally the first pressure reduction is performed upstream of the receiver 13. The low-pressure portion refers to the portion in the first refrigerant circuit 1 from the first pressure reducing valve 14 to the first compressor 10. Whether the design pressure is determined for each of these portions or is determined to be common to each portion in the first refrigerant circuit 1, in either case, it is desirable to lower the design pressure of the liquid supply portion and the low-pressure portion that may be constructed by the customer in order to reduce the construction burden on the customer. Therefore, when the design pressure of the liquid sending portion and the low pressure portion and the design pressure of the high pressure portion are determined separately, the design pressure of the liquid sending portion and the low pressure portion is set to a pressure lower than the design pressure of the high pressure portion. For example, when R1234yf refrigerant is used as the second refrigerant, the pressure of the first refrigerant that brings about the optimal COP of the refrigeration cycle device 100 used in the F-class warehouse is about 3.3 [MPa], and the design pressure of the liquid sending portion and the low pressure portion may be set to 4.15 [MPa], which is equivalent to the case where the first refrigerant is, for example, R410A refrigerant that has high market circulation and versatility, or a pressure lower than 4.15 [MPa]. Here, the saturation temperature of R744 refrigerant at 4.15 [MPa] is 7.7 [℃], which is lower than the saturation temperature of other refrigerants such as R410A refrigerant. On the other hand, the temperature of the outside air, etc., may exceed 7.7 [℃] not only in summer but also in intermediate periods such as spring or autumn. Therefore, when the first refrigerant reaches the saturation temperature corresponding to the outside air temperature, the pressure may exceed the above-mentioned design pressure.

[0030] The refrigeration cycle device 100 can cool the first refrigerant in the refrigerant-refrigerant heat exchanger 12 by the second refrigerant flowing through the second refrigerant circuit 2, and can maintain the pressure of the first refrigerant discharged from the first compressor 10 below the design pressure. However, due to factors such as a failure of a component in the second refrigerant circuit 2 or a shortage of the second refrigerant, it may be impossible to reduce the pressure of the first refrigerant. In this case, a safety valve provided in the first refrigerant circuit 1 operates, and the first refrigerant is discharged to the outside of the first refrigerant circuit 1. The safety valve is provided at one or more locations among the first refrigerant pipe 5 on the discharge side of the first compressor 10, the receiver 13, an accumulator (not shown), the receiver 13 or the first refrigerant pipe 5 near the accumulator, and the first refrigerant pipe 5 within a range that can be sealed between valves. The discharged first refrigerant may remain in the housing of the heat source device 3, etc. Then, there is a possibility that workers performing work on the refrigeration cycle apparatus 100 will be suddenly exposed to a large amount of the accumulated first refrigerant. Furthermore, in order to restart the operation of the refrigeration cycle apparatus 100, it is necessary to reseal the first refrigerant in the first refrigerant circuit 1, and work for this, such as evacuation, takes time. Furthermore, once the safety valve is activated, maintenance, including replacement, is required, so it takes time to restart the operation of the refrigeration cycle apparatus 100.

[0031] Even if the pressure of the first refrigerant rises, the refrigeration cycle apparatus 100 according to the first embodiment suppresses the operation of the safety valve while suppressing damage to components constituting the first refrigerant circuit 1, such as the receiver 13 and the first refrigerant pipe 5, by suppressing the pressure of the first refrigerant below the design pressure before the operation of the safety valve. As a result, the refrigeration cycle apparatus 100 aims to quickly resume operation and improve safety. The configuration and functions of the refrigeration cycle apparatus 100 for this purpose will be described below.

[0032] The first refrigerant circuit 1 is provided with a first pressure detection device 17 that detects a first pressure, which is the pressure of the first refrigerant, between the discharge side of the first compressor 10 and the first pressure reducing valve 14. In the first embodiment, the first pressure detection device 17 is provided in the first refrigerant pipe 5 on the side where the first compressor 10 discharges the first refrigerant. Note that the first refrigerant circuit 1 may be provided with a plurality of first pressure detection devices 17. In this case, each of the first pressure detection devices 17 is provided at a plurality of locations in the first refrigerant circuit 1. The evaporator 15 is provided with a first temperature detection device 18 that detects a first temperature, which is the temperature of a first object that exchanges heat with the first refrigerant. For example, the first temperature may be the temperature inside a refrigerator or a freezer.

[0033] The control device 6 is connected by wire to the first pressure detection device 17 and the first temperature detection device 18, and acquires the detection results from the first pressure detection device 17 and the first temperature detection device 18. Note that the control device 6 may acquire the detection results from both or one of the first pressure detection device 17 and the first temperature detection device 18 via wireless communication.

[0034] The control device 6 judges whether the first pressure detected by the first pressure detection device 17 is equal to or greater than a first threshold pressure. The first threshold pressure is less than the design pressure of each component of the first refrigerant circuit 1 and is less than the pressure at which a safety valve or a rupture disc (not shown) operates.

[0035] When the first pressure is equal to or higher than the first threshold pressure, the control device 6 determines whether the first temperature detected by the first temperature detection device 18 is equal to or lower than the threshold temperature. When the first temperature is equal to or lower than the threshold temperature, the control device 6 controls the first pressure reducing valve 14 to an open state. The open state is, for example, a fully open state. When the control device 6 controls the first pressure reducing valve 14 to an open state, the first refrigerant is reduced in pressure by the first pressure reducing valve 14 and flows into the evaporator 15.

[0036] Here, the threshold temperature is set, for example, by an experiment, based on the volume of the evaporator 15. Specifically, the threshold temperature is set so that the amount of the first refrigerant flowing into the evaporator 15 does not exceed the volume of the evaporator 15 when the first compressor 10 is stopped and the first pressure reducing valve 14 is open. The threshold temperature is also set based on the temperature of the water or air exchanging heat with the first refrigerant in the primary side heat exchanger 11. Hereinafter, the water or air in the primary side heat exchanger 11 may be described as the determination target. In setting the threshold temperature in the first embodiment, the temperature of the determination target is set to the expected maximum temperature or the maximum temperature in the experiment. When the determination target is air, for example, 43[°C] is cited as the maximum temperature. The temperature of the determination target may be determined based on the temperature of the second refrigerant in the second refrigerant circuit 2. Below, an example of setting the threshold temperature will be described in detail.

[0037] When the first compressor 10 stops and the first pressure reducing valve 14 is opened, the first refrigerant is in equilibrium in the first refrigerant circuit 1, and the pressure of the first refrigerant in the heat source device 3 and the pressure of the first refrigerant in the user side device 4 become uniform. When the first refrigerant is in an equal pressure state, the distribution of the amount of the first refrigerant in the first refrigerant circuit 1, that is, the amount of the first refrigerant in each of the heat source device 3 and the evaporator 15, is determined by the temperature of the determination object in the primary side heat exchanger 11 and the first temperature of the first object in the evaporator 15. The amount of the first refrigerant corresponds to the volume occupied by the first refrigerant. As described above, in the setting of the threshold temperature, the temperature of the determination object is set as the maximum temperature, so the amount of the first refrigerant in the evaporator 15 is determined based on the first temperature. That is, there is a correspondence between the volume of the first refrigerant in the evaporator 15 and the first temperature.

[0038] Here, when the temperature of the first refrigerant is lower than the condensation temperature of the first refrigerant, the higher the temperature of the portion of the first refrigerant circuit 1, the higher the liquid occupancy ratio of the first refrigerant at the same pressure. That is, when the temperature of the first refrigerant is lower than the condensation temperature, the volume occupied by the liquid first refrigerant in the portion of the first refrigerant circuit 1 where the temperature is high increases. On the other hand, when the temperature of the first refrigerant becomes higher than the condensation temperature, the volume of the first refrigerant increases while the volume of the first refrigerant circuit 1 is constant, and as a result, the pressure of the first refrigerant in the first refrigerant circuit 1 increases. In the first embodiment, in order to suppress an increase in the temperature of the first refrigerant in the evaporator 15, the threshold temperature is set to be equal to or lower than the condensation temperature of the first refrigerant.

[0039] Furthermore, in order to accommodate the first refrigerant in liquid form within the evaporator 15, the first temperature must be equal to or lower than the temperature corresponding to the volume of the first refrigerant in liquid form equal to the volume of the evaporator 15. However, since it is desirable to provide a margin for the evaporator 15, when X is a number greater than 0 and equal to or less than 1, the first temperature must be equal to or lower than the temperature corresponding to the volume of the first refrigerant equal to the product of X and the volume of the evaporator 15. For example, when X is 0.8, the capacity of the first refrigerant that the evaporator 15 can accommodate is up to 80% of the volume of the evaporator 15, and the first temperature must be equal to or lower than the temperature corresponding to the amount of the first refrigerant that is 80% of the volume of the evaporator 15. On the other hand, when X is 1, the capacity of the first refrigerant that the evaporator 15 can accommodate is up to the volume of the evaporator 15, and the first temperature must be equal to or lower than the temperature corresponding to the amount of the first refrigerant in the volume of the evaporator 15. Therefore, the threshold temperature is set to a temperature that is equal to or lower than the condensation temperature of the first refrigerant and corresponds to the product of the volume of the first refrigerant in liquid form, which is equal to the volume of the evaporator 15, and the above-mentioned X.

[0040] Here, an example has been shown in which the threshold temperature is set by determining the temperature of a determination object that exchanges heat with the first refrigerant in the primary side heat exchanger 11, but the threshold temperature may also be set by determining the temperature of a third object in the secondary side condenser 21.

[0041] The control device 6 may determine whether the first pressure is equal to or greater than the first threshold pressure at any time, or may determine whether the first pressure is equal to or greater than the first threshold pressure when an abnormality occurs in the second refrigerant circuit 2 and the secondary-side compressor 20 cannot operate. An abnormality occurs in the second refrigerant circuit 2 when, for example, the high-pressure switch is activated or the motor of the secondary-side compressor 20 breaks down, and in this case, an overcurrent is detected. The control device 6 can determine whether the secondary-side compressor 20 can operate by determining whether the high-pressure switch is activated or an overcurrent is detected. When the first compressor 10 is operating and a switch for operating the secondary-side compressor 20 is not turned on, the control device 6 starts the operation of the secondary-side compressor 20. However, the control device 6 may determine whether the first pressure is equal to or greater than the first threshold pressure together with or instead of starting the operation of the secondary-side compressor 20.

[0042] The control device 6 may determine whether the secondary compressor 20 is able to exert a refrigeration capacity for making the evaporation temperature of the second refrigerant in the refrigerant-to-refrigerant heat exchanger 12 a target evaporation temperature, and if the refrigeration capacity is not being exerted, may determine whether the first pressure is equal to or lower than a first threshold pressure. The target evaporation temperature is a target evaporation temperature of the second refrigerant in the refrigerant-to-refrigerant heat exchanger 12 for making the first pressure lower than the design pressure and lower than the pressure at which a safety valve or the like operates. The control device 6 determines the target evaporation temperature based on the first pressure detected by the first pressure detection device 17. Alternatively, a second temperature detection device (not shown) for detecting the temperature of the first refrigerant may be provided on the first refrigerant pipe 5 on the side where the first compressor 10 discharges the first refrigerant, and the control device 6 may determine the target evaporation temperature based on the detection result by the second temperature detection device instead of or together with the first pressure. Hereinafter, the refrigeration capacity for the secondary compressor 20 to make the evaporation temperature of the second refrigerant a target evaporation temperature may be referred to as a required refrigeration capacity. The case where the required refrigeration capacity cannot be obtained may occur due to, for example, leakage of the second refrigerant or a failure of the secondary-side compressor 20 or the secondary-side pressure reducing valve 22. The control device 6 judges whether the secondary-side compressor 20 is exerting the required refrigeration capacity as follows. A pressure detection device (not shown) that detects the pressure of the second refrigerant is provided in the second refrigerant pipe 7 on the outlet side of the second refrigerant from the refrigerant-to-refrigerant heat exchanger 12, and the control device 6 judges whether the secondary-side compressor 20 is exerting the required refrigeration capacity based on the detection result by the pressure detection device. Alternatively, a third temperature detection device (not shown) that detects the temperature of the second refrigerant may be provided in the second refrigerant pipe 7 on the outlet side of the second refrigerant from the refrigerant-to-refrigerant heat exchanger 12, and the control device 6 may judge whether the secondary-side compressor 20 is exerting the required refrigeration capacity based on the detection result by the third temperature detection device.

[0043] Hereinafter, the hardware configuration of the control device 6 in the first embodiment will be described with reference to Fig. 2. Fig. 2 is a block diagram illustrating the hardware configuration of the control device 6 in the first embodiment. The control device 6 can be configured, for example, by a processor 61, a memory 62, an input interface circuit 63, and an output interface circuit 64, which are connected to each other by a bus 60. The processor 61 is a CPU (Central Processing Unit) or an MPU (Micro Processing Unit), etc. The memory 62 is a ROM (Read Only Memory) or a RAM (Random Access Memory), etc.

[0044] The function of the control device 6 to acquire the detection results from each of the first pressure detection device 17 and the first temperature detection device 18 can be realized by the input interface circuit 63. The control device 6 may acquire the detection results from both or one of the first pressure detection device 17 and the first temperature detection device 18 by wireless communication. In this case, the control device 6 includes a wireless communication interface circuit instead of or in addition to the input interface circuit 63.

[0045] The function of the control device 6 performing processing based on the detection results from each of the first pressure detection device 17 and the first temperature detection device 18 can be realized by the processor 61 reading and executing various programs and data stored in the memory 62. The function of the control device 6 controlling components such as the first compressor 10 and the first pressure reducing valve 14 can be realized by an output interface circuit 64 connected to the components by wire, the processor 61, and the memory 62. The control device 6 may control the components by wireless communication. In this case, the control device 6 includes a wireless communication interface circuit instead of or in addition to the output interface circuit 64.

[0046] In addition to the above, all or part of the functions of the control device 6 may be realized by dedicated hardware such as a Complex Programmable Logic Device (CPLD) or a Field Programmable Gate Array (FPGA).

[0047] Hereinafter, the flow of the pressure adjustment process of the first refrigerant by the refrigeration cycle apparatus 100 according to the embodiment 1 will be described with reference to Fig. 3. Fig. 3 is a flowchart illustrating the flow of the pressure adjustment process by the refrigeration cycle apparatus 100 according to the embodiment 1. It is assumed that the first compressor 10 starts operating before step S1 in Fig. 3.

[0048] In step S1, the control device 6 determines whether or not the secondary side compressor 20 is operating. If the secondary side compressor 20 is operating (step S1: YES), the refrigeration cycle apparatus 100 shifts the process to step S4. If the secondary side compressor 20 is not operating (step S1: NO), in step S2, the control device 6 determines whether or not an abnormality has occurred in the second refrigerant circuit 2 and the secondary side compressor 20 is in an inoperable state. If the secondary side compressor 20 is in an inoperable state (step S2: YES), the refrigeration cycle apparatus 100 shifts the process to step S5.

[0049] If the secondary side compressor 20 is in an operable state (step S2: NO), in step S3, the control device 6 causes the secondary side compressor 20 to start operation. After the process of step S3, the refrigeration cycle apparatus 100 shifts the process to step S4. In step S4, the control device 6 determines whether or not the secondary side compressor 20 is exerting the required refrigeration capacity. If the secondary side compressor 20 is not exerting the required refrigeration capacity (step S4: NO), the refrigeration cycle apparatus 100 shifts the process to step S6. If the secondary side compressor 20 is exerting the required refrigeration capacity (step S4: YES), the refrigeration cycle apparatus 100 returns the process to step S1. In this case, the refrigeration cycle apparatus 100 may return the process from step S4 to step S1 after a predetermined first cycle time has elapsed.

[0050] In step S5, the control device 6 stops the first compressor 10. After the process of step S5, the refrigeration cycle apparatus 100 shifts the process to step S6. In step S6, the control device 6 judges whether the first pressure is equal to or higher than the first threshold pressure. If the first pressure is lower than the first threshold pressure (step S6: NO), the refrigeration cycle apparatus 100 returns the process to step S6. In this case, the refrigeration cycle apparatus 100 may return the process to step S6 after a predetermined second cycle time has elapsed. The second cycle time is equal to or lower than the first cycle time, but may be longer than the first cycle time. If the first pressure is lower than the first threshold pressure, the refrigeration cycle apparatus 100 may return the process to step S1 instead of step S6.

[0051] When the first pressure is equal to or higher than the first threshold pressure (step S6: YES), in step S7, the control device 6 judges whether or not the first temperature detected by the first temperature detection device 18 is equal to or lower than the threshold temperature. When the first temperature is not equal to or lower than the threshold temperature (step S7: NO), the refrigeration cycle apparatus 100 ends the pressure adjustment process. Note that the refrigeration cycle apparatus 100 may be provided with an alarm device, and when the first temperature is not equal to or lower than the threshold temperature, the control device 6 may control the alarm device to warn a user that the first refrigerant may be released from the first refrigerant circuit 1 by the operation of a safety valve or the like. When the first temperature is not equal to or lower than the threshold temperature and the first compressor 10 is operating, the control device 6 may stop the first compressor 10.

[0052] When the first temperature is equal to or lower than the threshold temperature (step S7: YES), in step S8, the control device 6 controls the first pressure reducing valve 14 to an open state. At this time, the control device 6 may stop the first compressor 10 when the first compressor 10 is operating. Note that the first refrigerant circuit 1 may include valves other than the first pressure reducing valve 14. In this case, when the first temperature is equal to or lower than the threshold temperature, the control device 6 controls all valves of the first refrigerant circuit 1 to an open state. After the process of step S8, the refrigeration cycle apparatus 100 ends the pressure adjustment process.

[0053] Here, after the process of step S8, the first object is heated by the first refrigerant in the evaporator 15, and the first temperature rises. Then, the temperature of the first refrigerant in the evaporator 15 also rises over time. As a result, the pressure of the first refrigerant in the evaporator 15 rises over time, and there is a risk that it may exceed the design pressure of the evaporator 15. To prevent such a situation, the volume of the evaporator 15 may be determined based on the expected time until the arrival of the worker. As described above, the threshold temperature is determined based on the volume of the evaporator 15, and the smaller the volume of the evaporator 15, the lower the threshold temperature becomes.

[0054] In addition, after the process of step S8 is performed, when the refrigeration cycle apparatus 100 resumes operation after the maintenance of the refrigeration cycle apparatus 100, a large amount of liquid first refrigerant may flow from the evaporator 15 into the heat source device 3. The amount of the liquid first refrigerant may be an amount that cannot be separated by the gas-liquid separator 16. The refrigeration cycle apparatus 100 performs the following process to prevent liquid return to the first compressor 10 when the operation is resumed. The control device 6 closes the first pressure reducing valve 14 and controls the first compressor 10 to operate at a predetermined minimum operating frequency, thereby circulating the first refrigerant through the first compressor 10. The volume of the gas-liquid separator 16 in the first embodiment is set so that the liquid first refrigerant does not flow into the first compressor 10 when the first compressor 10 operates at the minimum operating frequency. Alternatively, a liquid-gas heat exchanger (not shown) for evaporating the first refrigerant may be provided between the first compressor 10 and the evaporator 15. The first refrigerant circuit 1 may be provided with a flow path switching device such as a four-way valve (not shown) that changes the flow direction of the first refrigerant. Prior to resuming operation, the control device 6 controls the flow path switching device to reverse the flow direction of the first refrigerant from the flow direction during the refrigeration operation and causes the receiver 13 to recover the first refrigerant, and then the refrigeration cycle apparatus 100 may resume the refrigeration operation.

[0055] In the above, in the first embodiment, the control content has been described in which, when there is a malfunction in the secondary side compressor 20 (step S2: YES), the first compressor 10 is stopped, and when the first pressure is equal to or higher than the first threshold pressure (step S6: YES) and the first temperature is equal to or lower than the threshold temperature (step S7: YES), the first pressure reducing valve 14 is opened to allow the liquid first refrigerant to flow into the evaporator 15 and to exchange heat with the first target, thereby reducing the pressure of the first refrigerant. However, when the first temperature is higher than the threshold temperature, the safety valve may operate to protect the first refrigerant pipe 5 and the receiver 13 in the first refrigerant circuit 1, thereby reducing the pressure of the first refrigerant.

[0056] Embodiment 2 The refrigeration cycle apparatus 100 according to the second embodiment will be described in detail below. In the second embodiment, the same components as those in the first embodiment are denoted by the same reference numerals. In the second embodiment, the same configurations as those in the first embodiment and the same functions as those in the first embodiment will not be described unless there are special circumstances.

[0057] FIG. 4 is a schematic diagram showing a configuration example of a refrigeration cycle device 100 according to the second embodiment. The first refrigerant circuit 1 in the second embodiment has a first compressor 10, a low-stage heat exchanger 11A, a receiver 13, a first pressure reducing valve 14, an evaporator 15, and a gas-liquid separator 16, which are connected in sequence by a first refrigerant pipe 5. Each of the first compressor 10, the receiver 13, the first pressure reducing valve 14, the evaporator 15, and the gas-liquid separator 16 has the same configuration as in the first embodiment. The first compressor 10, the low-stage heat exchanger 11A, the receiver 13, and the gas-liquid separator 16 are provided in a housing that forms the outer shell of the heat source device 3. Note that in FIG. 4 as well, the housing of the heat source device 3 is indicated by a square drawn with a dashed line. The first pressure reducing valve 14 and the evaporator 15 are provided in the housing of the user side device 4, as in the first embodiment. Note that in FIG. 4 as well, the housing of the user side device 4 is indicated by a square drawn with a dashed line. The first pressure reducing valve 14 may be provided outside the housing of the utilization side device 4. Although an example in which the control device 6 is provided inside the housing of the heat source device 3 is also shown in FIG. 4, the control device 6 may be provided inside the housing of the utilization side device 4, or a part of the control device 6 may be provided in the heat source device 3 and the remaining part may be provided in the utilization side device 4.

[0058] The low-stage heat exchanger 11A may be air-cooled or water-cooled. The air-cooled low-stage heat exchanger 11A is, for example, a plate fin tube heat exchanger. The water-cooled low-stage heat exchanger 11A is, for example, a shell-and-tube heat exchanger, a plate heat exchanger, or a double-tube heat exchanger. The low-stage heat exchanger 11A is an example of a first heat exchanger. In addition, the air or water that cools the first refrigerant in the low-stage heat exchanger 11A is an example of a second target.

[0059] The refrigeration cycle apparatus 100 according to the second embodiment includes a refrigerant flow path 8 instead of the second refrigerant circuit 2. The refrigerant flow path 8 is connected to the first refrigerant circuit 1, and allows a first refrigerant to flow. The refrigerant flow path 8 has a high stage side compressor 20A, a high stage side condenser 21A, a high stage side pressure reducing valve 22A, and a receiver 13, which are connected in sequence by a first refrigerant piping 5. The refrigerant flow path 8 is disposed within a housing that forms the outer shell of the heat source equipment 3.

[0060] The high-stage compressor 20A is an inverter compressor, such as a scroll type, rotary type, reciprocating type, or screw type compressor, whose capacity can be controlled by an inverter. The high-stage compressor 20A compresses a first refrigerant from the low-stage heat exchanger 11A and a first refrigerant from a high-stage pressure reducing valve 22A, which will be described later. The high-stage compressor 20A is an example of a second compressor.

[0061] The high-stage condenser 21A may be an air-cooled condenser or a water-cooled condenser. Examples of the air-cooled high-stage condenser 21A include a plate-fin tube heat exchanger or a parallel flow condenser. Examples of the water-cooled high-stage condenser 21A include a shell-and-tube heat exchanger, a plate heat exchanger, or a double-tube heat exchanger. The high-stage condenser 21A cools and condenses the second refrigerant by exchanging heat between the second refrigerant and a fifth object, which is air or water. The gaseous first refrigerant discharged from the high-stage compressor 20A may be in a critical state, and in the high-stage condenser 21A, the first refrigerant loses heat to the fifth object in the critical state. When the high-stage condenser 21A is air-cooled, a sprinkler device (not shown) for cooling the first refrigerant may be installed. The high-stage condenser 21A is an example of a second heat exchanger.

[0062] The high-stage side pressure reducing valve 22A is an electronic expansion valve, a thermal expansion valve, or the like. The high-stage side pressure reducing valve 22A is an example of a second valve. The high-stage side pressure reducing valve 22A reduces the pressure until the first refrigerant is liquefied. The first refrigerant after pressure reduction by the high-stage side pressure reducing valve 22A is in a two-phase state. Of the two phases, the first refrigerant that is a saturated gas mixes with the gaseous first refrigerant of the first refrigerant that flows out of the low-stage side heat exchanger 11A, and the mixed gaseous first refrigerant is sucked into the high-stage side compressor 20A.

[0063] The first refrigerant that is a saturated liquid after being reduced in pressure by the high-stage side pressure reducing valve 22A and the liquid first refrigerant that flows out from the low-stage side heat exchanger 11A are stored in the receiver 13. The receiver 13 is disposed downstream of the low-stage side heat exchanger 11A and the high-stage side pressure reducing valve 22A and upstream of the first pressure reducing valve 14.

[0064] In the second embodiment, in addition to the above, at least one of an oil separator, an oil return circuit from the oil separator, a check valve, a service operation valve, a sight glass, a strainer, a dryer, and a safety device such as a high-pressure switch may be installed in both or one of the first refrigerant circuit 1 and the refrigerant flow path 8. In addition, the first refrigerant circuit 1 may be provided with a four-way valve or a three-way valve that switches the flow direction of the first refrigerant to defrost the evaporator 15.

[0065] In the second embodiment, the first refrigerant in a saturated liquid state flows out from the heat source equipment 3. Then, due to a pressure loss of the first refrigerant in the first refrigerant piping 5 connecting the heat source equipment 3 and the utilization side equipment 4, flash gas may be generated upstream of the first pressure reducing valve 14. For this reason, the refrigeration cycle apparatus 100 may include a subcooling heat exchanger or a liquid-gas heat exchanger, etc., not shown.

[0066] The control device 6 controls the first compressor 10, the first pressure reducing valve 14, etc., as in the first embodiment, and also controls the high-stage side compressor 20A and the high-stage side pressure reducing valve 22A. The control device 6 is connected by wire to each of the components, such as the high-stage side compressor 20A and the high-stage side pressure reducing valve 22A, and transmits control signals to each of the components, which operate based on the received control signals. The control device 6 may control at least one of the components, such as the high-stage side compressor 20A and the high-stage side pressure reducing valve 22A, by wireless communication.

[0067] In the second embodiment, similarly to the first embodiment, the first refrigerant circuit 1 is provided with a first pressure detection device 17, which detects a first pressure. Also, the evaporator 15 is provided with a first temperature detection device 18, which detects a first temperature. Similarly to the first embodiment, the control device 6 acquires detection results from the first pressure detection device 17 and the first temperature detection device 18. Then, when the first pressure detected by the first pressure detection device 17 is equal to or higher than the first threshold pressure and the first temperature detected by the first temperature detection device 18 is equal to or lower than the threshold temperature, the control device 6 opens the first pressure reducing valve 14. Note that, similarly to the first embodiment, the threshold temperature in the second embodiment is equal to or lower than the condensation temperature of the first refrigerant. Here, the threshold temperature in embodiment 1 was set by determining the temperature of the determination object in the primary side heat exchanger 11, whereas the threshold temperature in embodiment 2 is set by determining the water or air in the low stage side heat exchanger 11A, or the fifth object in the high stage side condenser 21A.

[0068] The control device 6 in the second embodiment may determine whether the first pressure is equal to or greater than the first threshold pressure at any time, or may determine whether the first pressure is equal to or greater than the first threshold pressure when the high-stage compressor 20A is in an inoperable state. The control device 6 can determine whether the high-stage compressor 20A is in an inoperable state by determining whether an overcurrent is detected or the like. The overcurrent occurs when the high-pressure switch is activated or when the motor of the high-stage compressor 20A breaks down. When the first compressor 10 is operating and the switch for operating the high-stage compressor 20A is not turned on, the control device 6 starts the operation of the high-stage compressor 20A. However, the control device 6 may determine whether the first pressure is equal to or greater than the first threshold pressure together with or instead of starting the operation of the high-stage compressor 20A.

[0069] The hardware configuration of the control device 6 of the second embodiment is illustrated in Fig. 2, similarly to the first embodiment. The content of the hardware configuration of the control device 6 of the second embodiment is similar to the content of the hardware configuration of the control device 6 of the first embodiment described with reference to Fig. 2.

[0070] Hereinafter, the flow of the adjustment process of the pressure of the first refrigerant by the refrigeration cycle apparatus 100 according to the second embodiment will be described with reference to Fig. 5. Fig. 5 is a flowchart illustrating the flow of the pressure adjustment process by the refrigeration cycle apparatus 100 according to the second embodiment. It is assumed that the first compressor 10 starts operating before step S11 in Fig. 5.

[0071] In step S11, the control device 6 determines whether the high stage side compressor 20A is operating. If the high stage side compressor 20A is operating (step S11: YES), the refrigeration cycle apparatus 100 returns the process to step S11. The refrigeration cycle apparatus 100 may return the process to step S11 after the first cycle time has elapsed.

[0072] When the high-stage compressor 20A is not operating (step S11: NO), in step S12, the control device 6 determines whether the high-stage compressor 20A is in an inoperable state. When the high-stage compressor 20A is in an inoperable state (step S12: YES), the refrigeration cycle apparatus 100 shifts the process to step S14. When the high-stage compressor 20A is in an operable state (step S12: NO), in step S13, the control device 6 causes the high-stage compressor 20A to start operating. After the process of step S13, the refrigeration cycle apparatus 100 returns the process to step S11. At this time, the refrigeration cycle apparatus 100 may return the process to step S11 after the first cycle time has elapsed. Note that, after the process of step S13, the refrigeration cycle apparatus 100 may shift the process to step S15 instead of step S11.

[0073] The processes of steps S14 to S17 are the same as the processes of steps S5 to S8. The process of the refrigeration cycle apparatus 100 when restarting operation after the process of step S17 and after the maintenance of the refrigeration cycle apparatus 100 is also the same as the process of the refrigeration cycle apparatus 100 when restarting operation in the above-mentioned embodiment 1. The volume of the gas-liquid separator 16 in embodiment 2 may be determined so that the liquid first refrigerant does not flow into the first compressor 10 when the first compressor 10 operates at the lowest operating frequency, as in embodiment 1. Alternatively, in embodiment 2, a liquid-gas heat exchanger (not shown) for evaporating the first refrigerant may be provided between the first compressor 10 and the evaporator 15. The first refrigerant circuit 1 may be provided with a flow path switching device, as in embodiment 1. The control device 6 may control the flow path switching device prior to restarting operation to reverse the flow direction of the first refrigerant to the flow direction during the freezing operation, to cause the receiver 13 to recover the first refrigerant, and then the refrigeration cycle apparatus 100 may resume operation.

[0074] Embodiment 3 The refrigeration cycle apparatus 100 according to the third embodiment will be described in detail below. In the third embodiment, the same components as those in the first and second embodiments are denoted by the same reference numerals. In the third embodiment, the same configurations as those in the first and second embodiments and the same functions as those in the first and second embodiments will not be described unless there are special circumstances.

[0075] FIG. 6 is a schematic diagram showing a configuration example of the utilization side device 4 in the third embodiment. The configuration of the refrigeration cycle apparatus 100 according to the third embodiment is the same as that of the first and second embodiments, except for the utilization side device 4. The first refrigerant circuit 1 in the third embodiment includes a bypass path 1A for the first refrigerant flowing out from the receiver 13 to bypass the first pressure reducing valve 14. The bypass path 1A is provided with a first on-off valve 14A. The first on-off valve 14A is an electronic expansion valve, a temperature expansion valve, a solenoid valve, or the like. In an open state, the first on-off valve 14A allows the first refrigerant to flow from the receiver 13 to the evaporator 15, and in a closed state, blocks the flow of the first refrigerant from the receiver 13 to the evaporator 15. The first on-off valve 14A is an example of a first valve.

[0076] 6 shows an example in which the first pressure reducing valve 14, the bypass path 1A, and the first on-off valve 14A are arranged inside the housing of the utilization side device 4, but the first pressure reducing valve 14, the bypass path 1A, and the first on-off valve 14A may be arranged outside the utilization side device 4. Alternatively, the first pressure reducing valve 14 may be arranged inside the housing of the utilization side device 4, and a part of the bypass path 1A may be arranged inside the housing of the utilization side device 4. In this case, the first on-off valve 14A may be arranged inside the housing of the utilization side device 4 or outside the utilization side device 4.

[0077] When the first pressure is equal to or higher than the first threshold pressure and the first temperature is equal to or lower than the threshold temperature, the control device 6 in the third embodiment controls the first pressure reducing valve 14 to an open state, or controls the first on-off valve 14A to an open state while controlling the first pressure reducing valve 14 to an open state. This makes it possible to transfer the first refrigerant to the evaporator 15 even when the first refrigerant does not flow to the evaporator 15 through the first pressure reducing valve 14 due to a malfunction of the first pressure reducing valve 14, for example. Therefore, an increase in the pressure of the first refrigerant in the first refrigerant circuit 1 can be suppressed.

[0078] Embodiment 4 The refrigeration cycle apparatus 100 according to the fourth embodiment will be described in detail below. In the fourth embodiment, the same components as those in the first to third embodiments are denoted by the same reference numerals. In the fourth embodiment, the same configurations as those in the first to third embodiments and the same functions as those in the first to third embodiments will not be described unless there are special circumstances.

[0079] FIG. 7 is a schematic diagram showing a configuration example of the utilization side device 4 in the fourth embodiment. The configuration of the refrigeration cycle apparatus 100 according to the fourth embodiment is the same as that of the first to third embodiments, except for the utilization side device 4. FIG. 7 shows a case where the first refrigerant circuit 1 does not include a bypass path 1A, but the first refrigerant circuit 1 in the fourth embodiment may include a bypass path 1A. The refrigeration cycle apparatus 100 in the fourth embodiment further includes a second on-off valve 14B. The second on-off valve 14B is, for example, a solenoid valve. The second on-off valve 14B is provided in the first refrigerant circuit 1 upstream of the first pressure reducing valve 14, and in an open state, the second on-off valve 14B allows the first refrigerant to flow through the evaporator 15, and in a closed state, blocks the flow of the first refrigerant. The second on-off valve 14B is an example of a third valve.

[0080] 7 shows an example in which the first pressure reducing valve 14 and the second on-off valve 14B are disposed inside the housing of the utilization side device 4, but the first pressure reducing valve 14 and the second on-off valve 14B may be disposed outside the utilization side device 4. Alternatively, the first pressure reducing valve 14 may be disposed inside the housing of the utilization side device 4, and the second on-off valve 14B may be disposed outside the utilization side device 4.

[0081] When the first refrigerant circuit 1 includes the bypass passage 1A, the bypass passage 1A may be a path that causes the first refrigerant to bypass the first pressure reducing valve 14 and the second on-off valve 14B. Alternatively, the bypass passage 1A may be a path that causes the first refrigerant to bypass only the first pressure reducing valve 14, and the second on-off valve 14B may be provided upstream of the first pressure reducing valve 14 and the first on-off valve 14A. In other words, the second on-off valve 14B may be provided upstream of a position where the first refrigerant flowing out of the receiver 13 flows into the bypass passage 1A.

[0082] When the first pressure is equal to or higher than the first threshold pressure and the first temperature is equal to or lower than the threshold temperature, the control device 6 controls the second on-off valve 14B to an open state.

[0083] The effects of the refrigeration cycle apparatus 100 according to the first to fourth embodiments will be described below. The refrigeration cycle apparatus 100 according to the first to fourth embodiments circulates a first refrigerant, which is carbon dioxide, through a first refrigerant circuit 1, and cools a first object with the first refrigerant. The refrigeration cycle apparatus 100 includes a first compressor 10, a first heat exchanger, an evaporator 15, a first valve, a first pressure detector 17, a first temperature detector 18, and a control device 6. The first compressor 10 compresses and discharges the first refrigerant. The first heat exchanger exchanges heat between the first refrigerant discharged from the first compressor 10 and a second object, thereby cooling the first refrigerant. The evaporator 15 exchanges heat between the first refrigerant and the first object. The first valve is provided upstream of the evaporator 15 in the first refrigerant circuit 1, and in an open state, reduces the pressure of the first refrigerant and causes the reduced pressure first refrigerant to flow through the evaporator 15. The first pressure detection device 17 detects a first pressure which is the pressure of the first refrigerant between the downstream side of the first compressor 10 and the first valve. The first temperature detection device 18 detects a first temperature which is the temperature of a first object in the evaporator 15. The control device 6 controls the first compressor 10 and the first valve. The control device 6 controls the first valve to an open state when the first pressure is equal to or higher than a predetermined first threshold pressure and the first temperature is equal to or lower than a predetermined threshold temperature.

[0084] According to the above configuration, when the first pressure is equal to or higher than the first threshold pressure and the first temperature is equal to or lower than the threshold temperature, the control device 6 controls the first valve to be open, so that the first refrigerant flows into the evaporator 15. The first temperature is equal to or lower than the threshold temperature, and the first refrigerant exchanges heat with the first object in the evaporator 15, so that the first pressure of the first refrigerant in the first refrigerant circuit 1 is reduced compared to when the first valve is closed and the first refrigerant does not flow into the evaporator 15. Therefore, the operation of the safety valve is suppressed, and damage to components in the first refrigerant circuit 1 is suppressed. In addition, since the operation of the safety valve is suppressed, the release of the first refrigerant is suppressed, so that workers, users, etc. are prevented from being suddenly exposed to the first refrigerant. This improves safety.

[0085] The threshold temperature in the first to fourth embodiments is a temperature lower than the condensation temperature of the first refrigerant when the first refrigerant is in an equal pressure state in the first refrigerant circuit 1. In the first embodiment, the first refrigerant condenses in the primary side heat exchanger 11 or the inter-refrigerant heat exchanger 12, and in the second embodiment, the first refrigerant condenses in the high stage side condenser 21A. However, by setting the threshold temperature lower than the condensation temperature of the first refrigerant, the first refrigerant is further cooled in the evaporator 15. Therefore, the refrigeration cycle apparatus 100 can further reduce the first pressure. Therefore, the refrigeration cycle apparatus 100 can suppress damage to components in the first refrigerant circuit 1 or operation of the safety valve.

[0086] The threshold temperature in the first to fourth embodiments is set so that the amount of the first refrigerant flowing into the evaporator 15 when the first compressor 10 is stopped and the first valve is open does not exceed the volume of the evaporator 15. This allows the evaporator 15 to store the first refrigerant and also prevents damage to the evaporator 15.

[0087] The first compressor 10, the first heat exchanger, the first valve, and the evaporator 15 in the first to fourth embodiments are connected by the first refrigerant pipe 5 through which the first refrigerant flows. The first threshold pressure is a pressure that is lower than the design pressure of each of the first compressor 10, the first heat exchanger, the first valve, the evaporator 15, and the first refrigerant pipe 5, and is lower than the pressure at which the safety valve or the rupture disc operates. When the first pressure is equal to or higher than the first threshold pressure and the first temperature is equal to or lower than the threshold temperature, the control device 6 controls the first valve to an open state, so that the first refrigerant is guided to the evaporator 15. Therefore, before the first pressure reaches a pressure that may damage components in the first refrigerant circuit 1 and before the first pressure reaches a pressure at which the safety valve or the like operates, the first refrigerant exchanges heat with the first object in the evaporator 15, and the first pressure is reduced. Therefore, damage to components in the first refrigerant circuit 1 is suppressed, and the operation of the safety valve or the like is suppressed.

[0088] The refrigeration cycle apparatus 100 according to the first to fourth embodiments further includes a receiver 13 for storing the first refrigerant, downstream of the first heat exchanger and upstream of the first valve in the first refrigerant circuit 1. This allows the refrigeration cycle apparatus 100 to reduce the first pressure in the first refrigerant piping 5 and the like, and suppresses damage to the first refrigerant piping 5 and the like, or operation of the safety valve.

[0089] The first compressor 10, the first heat exchanger, the receiver 13, the first valve, and the evaporator 15 in the first to fourth embodiments are connected by the first refrigerant pipe 5 through which the first refrigerant flows. The first threshold pressure is a pressure that is lower than the design pressure of each of the first compressor 10, the first heat exchanger, the receiver 13, the first valve, the evaporator 15, and the first refrigerant pipe 5, and is lower than the pressure at which the safety valve or the rupture disc operates. When the first pressure is equal to or higher than the first threshold pressure and the first temperature is equal to or lower than the threshold temperature, the control device 6 controls the first valve to an open state, so that the first refrigerant is guided to the evaporator 15. Therefore, before the first pressure reaches a pressure that may damage components in the first refrigerant circuit 1 and before the first pressure reaches a pressure at which the safety valve or the like operates, the first refrigerant exchanges heat with the first object in the evaporator 15, and the first pressure is reduced. Therefore, damage to components in the first refrigerant circuit 1 is suppressed, and the operation of the safety valve or the like is suppressed.

[0090] The refrigeration cycle apparatus 100 according to the first, third, and fourth embodiments further includes a second refrigerant circuit 2 that circulates a second refrigerant. The second object is the second refrigerant. The second refrigerant circuit 2 includes a second compressor, a second heat exchanger, a second valve, and the first heat exchanger. The second compressor compresses the second refrigerant. The second heat exchanger exchanges heat with the second refrigerant discharged from the second compressor and a third object to condense the second refrigerant. The second valve reduces the pressure of the second refrigerant condensed in the second heat exchanger. The first heat exchanger exchanges heat between the second refrigerant reduced in pressure by the second valve and the first refrigerant discharged from the first compressor 10 to condense the first refrigerant and evaporate the second refrigerant. In the first heat exchanger, the first refrigerant is cooled by the second refrigerant, and the first pressure is reduced. Therefore, damage to components in the first refrigerant circuit 1 or operation of the safety valve is suppressed.

[0091] The first refrigerant circuit 1 in the first, third, and fourth embodiments further includes a primary side heat exchanger 11. The primary side heat exchanger 11 cools the first refrigerant by exchanging heat with a fourth object. Since the first refrigerant is cooled in the primary side heat exchanger 11 and the first heat exchanger, the first pressure is reduced. Therefore, the refrigeration cycle apparatus 100 can suppress damage to components in the first refrigerant circuit 1 or operation of a safety valve.

[0092] In the first, third and fourth embodiments, when the second compressor is not exerting the required refrigeration capacity, the control device 6 determines whether the first pressure is equal to or higher than the first threshold pressure, and when the first pressure is equal to or higher than the first threshold pressure and the first temperature is equal to or lower than the threshold temperature, controls the first valve to be open. This suppresses the rise in the first pressure even when a malfunction occurs in the second refrigerant circuit 2 and the first refrigerant cannot be cooled by the second refrigerant. Therefore, the refrigeration cycle device 100 can suppress damage to components in the first refrigerant circuit 1 or the operation of the safety valve.

[0093] The refrigeration cycle apparatus 100 according to the second to fourth embodiments further includes a refrigerant flow path 8 that is connected to the first refrigerant circuit 1 and that circulates the first refrigerant. The refrigerant flow path 8 has a second compressor, a second heat exchanger, and a second valve. The second compressor compresses the first refrigerant. The second heat exchanger exchanges heat with the first refrigerant discharged from the second compressor with a fifth object, and condenses the first refrigerant. The second valve reduces the pressure of the first refrigerant condensed in the second heat exchanger. The receiver 13 is provided downstream of the second valve. The second compressor compresses the first refrigerant from the first heat exchanger and the second valve. This suppresses an increase in the first pressure of the first refrigerant in the first refrigerant circuit 1 on the heat source device 3 side, and suppresses damage to the refrigeration cycle apparatus 100.

[0094] In the first to fourth embodiments, when the second compressor is in an inoperable state, the control device 6 stops the first compressor, determines whether the first pressure is equal to or higher than the first threshold pressure, and controls the first valve to an open state when the first pressure is equal to or higher than the first threshold pressure and the first temperature is equal to or lower than the threshold temperature. This suppresses an increase in the first pressure even when the second compressor is inoperable and the first refrigerant is not cooled. Therefore, the refrigeration cycle device 100 can suppress damage to components in the first refrigerant circuit 1 or operation of the safety valve.

[0095] The first valve in the first to fourth embodiments is a first pressure reducing valve 14 that, in an open state, reduces the pressure of the first refrigerant flowing through the evaporator 15. This reduces the pressure of the first refrigerant flowing into the evaporator 15. Therefore, damage to the evaporator 15 is suppressed.

[0096] The refrigeration cycle apparatus 100 according to the first to fourth embodiments further includes a first pressure reducing valve 14. The first pressure reducing valve 14 is provided upstream of the evaporator 15 in the first refrigerant circuit 1, and in an open state, causes the first refrigerant to flow through the evaporator 15 and reduces the pressure of the first refrigerant. The first refrigerant circuit 1 includes a bypass passage 1A for the first refrigerant flowing to the evaporator 15 to bypass the first pressure reducing valve 14. The first valve is provided in the bypass passage 1A. When the first pressure is equal to or higher than a first threshold pressure and the first temperature is equal to or lower than a threshold temperature, the control device 6 controls the first pressure reducing valve 14 to an open state. As a result, even if a malfunction occurs in the first valve and it cannot be controlled to an open state, the first pressure reducing valve 14 is opened, so that the first refrigerant can be transferred to the evaporator 15. Therefore, when the first pressure is equal to or higher than the first threshold pressure and the first temperature is equal to or lower than the threshold temperature, the first refrigerant flows into the evaporator 15 in a state where the pressure of the first refrigerant is reduced by the first pressure reducing valve 14, and the pressure of the first refrigerant in the first refrigerant circuit 1 is reduced. Therefore, the refrigeration cycle apparatus 100 can suppress damage to components in the first refrigerant circuit 1, or suppress the operation of a safety valve or the like.

[0097] The refrigeration cycle apparatus 100 according to the first to fourth embodiments may further include a second on-off valve 14B as described below. The second on-off valve 14B is provided in the first refrigerant circuit 1 upstream of the first pressure reducing valve 14, and allows the first refrigerant to flow through the evaporator 15 in the open state, and blocks the flow of the first refrigerant in the closed state. The control device 6 controls the second on-off valve 14B to the open state when the first pressure is equal to or higher than a first threshold pressure and the first temperature is equal to or lower than a threshold temperature.

[0098] Embodiment 5. The refrigeration cycle apparatus 100 according to the fifth embodiment will be described in detail below. In the fifth embodiment, the same components as those in the first to fourth embodiments are denoted by the same reference numerals. In the fifth embodiment, the same configurations as those in the first to fourth embodiments and the same functions as those in the first to fourth embodiments will not be described unless there are special circumstances.

[0099] FIG. 8 is a schematic diagram showing a configuration example of the refrigeration cycle apparatus 100 according to the fifth embodiment. In the fifth embodiment, the first pressure detection device 17 is provided at the inlet of the receiver 13. The first pressure detection device 17 may be provided in the receiver 13. The first pressure detection device 17 of the fifth embodiment detects the first pressure of the first refrigerant in the receiver 13. The refrigeration cycle apparatus 100 of the fifth embodiment further includes a second pressure detection device 17A that detects the first pressure of the first refrigerant discharged from the first compressor 10. The second pressure detection device 17A is provided, for example, in the first refrigerant pipe 5 on the discharge side of the first compressor 10. The configuration of the refrigeration cycle apparatus 100 according to the fifth embodiment shown in FIG. 8 is the same as the configuration of the refrigeration cycle apparatus 100 according to the first embodiment shown in FIG. 1, except for the first pressure detection device 17 and the second pressure detection device 17A.

[0100] The user side device 4 of the refrigeration cycle apparatus 100 according to the fifth embodiment may be the same as that of the third to fourth embodiments and may be the one shown in Fig. 6 or 7. The hardware configuration of the control device 6 according to the fifth embodiment is exemplified by Fig. 2, similarly to the first to fourth embodiments.

[0101] The control device 6 of the fifth embodiment determines whether or not the first pressure obtained by the first pressure detection device 17 is equal to or greater than the first threshold pressure when the first compressor 10 is stopped. The first threshold pressure in the first embodiment is determined based on the design pressure of the receiver tank 13. That is, the first threshold pressure is a pressure less than the design pressure of the receiver tank 13. When the first pressure is equal to or greater than the first threshold pressure, the control device 6 determines whether or not the first temperature is equal to or less than the threshold temperature, and when the first temperature is equal to or less than the threshold temperature, controls the first pressure reducing valve 14 to an open state.

[0102] When the first compressor 10 is operating, the control device 6 of the fifth embodiment determines whether the first pressure detected by the second pressure detection device 17A is equal to or greater than the second threshold pressure. The second threshold pressure is determined based on the design pressures of the first compressor 10 and the first refrigerant piping 5. That is, the second threshold pressure is determined to be less than the design pressure of the first compressor 10 and less than the design pressure of the first refrigerant piping 5. The second threshold pressure is equal to or greater than the first threshold pressure.

[0103] Hereinafter, the pressure adjustment process by the refrigeration cycle apparatus 100 according to the fifth embodiment will be described with reference to Fig. 9. Fig. 9 is a flowchart illustrating the flow of the pressure adjustment process by the refrigeration cycle apparatus 100 according to the fifth embodiment. The processes in steps S21 to S22 are similar to the processes in steps S1 to S2 described above. If the secondary side compressor 20 is in an inoperable state in step S22 (step S22: YES), the refrigeration cycle apparatus 100 transfers the process to step S23. The process in step S23 is similar to the process in step S5.

[0104] If the secondary side compressor 20 is in an operable state (step S22: NO), in step S24, the control device 6 determines whether or not the first compressor 10 is stopped. If the first compressor 10 is stopped (step S24: YES), the refrigeration cycle apparatus 100 transfers the process to step S26. The processes of steps S26 to S28 are the same as the processes of steps S6 to S8 described above.

[0105] When the first compressor 10 is not stopped (step S24: NO), in step S25, the control device 6 determines whether or not the first pressure obtained by the second pressure detection device 17A is equal to or higher than the second threshold pressure.

[0106] When the first pressure obtained by the second pressure detection device 17A is not equal to or greater than the second threshold pressure (step S25: NO), the refrigeration cycle apparatus 100 returns the process to step S21. When the first pressure obtained by the second pressure detection device 17A is equal to or greater than the second threshold pressure (step S25: YES), the refrigeration cycle apparatus 100 shifts the process to step S26.

[0107] When the first compressor 10 is operating, the pressure of the refrigerant in each of the discharge portion of the first compressor 10 and the receiver 13 is substantially equal, but when the first compressor 10 stops in step S23 or when it is determined in step S24 that the first compressor 10 is stopped, the pressure of the refrigerant in the receiver 13 may become higher than the pressure of the refrigerant in the discharge portion of the first compressor 10 over time due to a check valve (not shown) in the discharge portion of the first compressor 10. In the fifth embodiment, the control device 6 compares the first pressure in the receiver 13 with the first threshold pressure in step S26, and when the first pressure is equal to or higher than the first threshold pressure, the refrigeration cycle apparatus 100 performs the process of step S27 and step S28, thereby making it possible to maintain the first pressure in the receiver 13 below the design pressure of the receiver 13 even when the operation of the first compressor 10 is stopped.

[0108] The following describes effects of the refrigeration cycle apparatus 100 according to the fifth embodiment. The first pressure detection device 17 of the fifth embodiment detects the first pressure of the first refrigerant in the receiver 13. When the first compressor 10 is stopped, the control device 6 controls the first valve to an open state if the first pressure is equal to or higher than a first threshold pressure and the first temperature is equal to or lower than a threshold temperature.

[0109] According to the above configuration, even if the first pressure of the first refrigerant in the receiver 13 rises while the first compressor 10 is stopped, if the first temperature is equal to or lower than the threshold temperature, the first refrigerant in the receiver 13 flows through the evaporator 15. Therefore, an excessive rise in the first pressure in the receiver 13 is suppressed, and the receiver 13 can be protected.

[0110] The refrigeration cycle apparatus 100 according to the fifth embodiment further includes a second pressure detection device 17A that detects the first pressure of the first refrigerant discharged from the first compressor 10. When the first pressure of the first refrigerant discharged from the first compressor 10 is equal to or higher than a second threshold pressure determined in advance while the first compressor 10 is in operation, the control device 6 determines whether the first pressure of the first refrigerant in the receiver 13 is equal to or higher than the first threshold pressure, and controls the first valve to an open state when the first pressure of the first refrigerant in the receiver 13 is equal to or higher than the first threshold pressure and the first temperature is equal to or lower than the threshold temperature. The first threshold pressure is determined based on the design pressure of the receiver 13. The second threshold pressure is determined based on the design pressure of the first compressor 10. The first pressure may change when the first refrigerant flows from the first compressor 10 to the receiver 13. However, when the first pressure of the first refrigerant discharged from the first compressor 10 is high, there is a risk that the first pressure of the first refrigerant flowing into the receiver 13 will exceed the design pressure of the receiver 13. When the first pressure detected by the second pressure detection device 17A is equal to or higher than the second threshold pressure, the first pressure detected by the first pressure detection device 17 is equal to or higher than the first threshold pressure, and the first temperature is equal to or lower than the threshold temperature, the control device 6 opens the first valve, so that the first refrigerant flows through the evaporator 15. This protects the receiver 13 as well as the evaporator 15.

[0111] Embodiment 6 The refrigeration cycle apparatus 100 according to the sixth embodiment will be described in detail below. In the sixth embodiment, the same components as those in the first to fifth embodiments are denoted by the same reference numerals. In the sixth embodiment, the same configurations as those in the first to fifth embodiments and the same functions as those in the first to fifth embodiments will not be described unless there are special circumstances.

[0112] FIG. 10 is a schematic diagram showing a configuration example of a refrigeration cycle apparatus 100 according to a sixth embodiment. In the sixth embodiment, a first pressure detection device 17 is provided in the receiver 13. The first pressure detection device 17 of the sixth embodiment detects the first pressure of the first refrigerant in the receiver 13. The configuration of the refrigeration cycle apparatus 100 according to the sixth embodiment is the same as the configuration of the refrigeration cycle apparatus 100 according to the second embodiment shown in FIG. 4, except for the location of the first pressure detection device 17. However, the configuration of the refrigeration cycle apparatus 100 according to the sixth embodiment may be shown in FIG. 4, as in the second embodiment. That is, the first pressure detection device 17 may be provided in the first refrigerant pipe 5 on the discharge side of the first compressor 10. Alternatively, the refrigeration cycle apparatus 100 according to the sixth embodiment may include the first pressure detection device 17 provided in the receiver 13 and another pressure detection device (not shown) provided in the first refrigerant pipe 5 on the discharge side of the first compressor 10, etc.

[0113] The user side device 4 of the refrigeration cycle apparatus 100 according to the sixth embodiment is similar to that of the third to fourth embodiments, and may be as shown in Fig. 6 or 7. The hardware configuration of the control device 6 according to the sixth embodiment is exemplified by Fig. 2, similar to that of the first to fifth embodiments.

[0114] The first pressure detection device 17 of the sixth embodiment detects a first pressure of the first refrigerant in the receiver 13. Then, when the first compressor 10 is stopped and the first pressure obtained by the first pressure detection device 17 is equal to or higher than a first threshold pressure and the first temperature is equal to or lower than a threshold temperature, the control device 6 controls the first pressure reducing valve 14 to an open state and causes the first refrigerant to flow through the evaporator 15.

[0115] Hereinafter, the pressure adjustment process by the refrigeration cycle apparatus 100 according to the sixth embodiment will be described with reference to FIG. 11. FIG. 11 is a flowchart illustrating the flow of the pressure adjustment process by the refrigeration cycle apparatus 100 according to the sixth embodiment. The processes in steps S31 to S32 are similar to the processes in steps S11 to S12 described above. If the high stage side compressor 20A is in an inoperable state in step S32 (step S32: YES), the refrigeration cycle apparatus 100 transfers the process to step S33. The processes in steps S33 to S36 are similar to the processes in steps S14 to S17. If the high stage side compressor 20A is in an operable state in step S32 (step S32: NO), the refrigeration cycle apparatus 100 returns the process to step S31.

[0116] The effects of the refrigeration cycle apparatus 100 according to the sixth embodiment will be described below. The first pressure detection device 17 of the sixth embodiment detects the first pressure in the receiver 13. When the first compressor 10 is stopped, if the first pressure is equal to or higher than the first threshold pressure and the first temperature is equal to or lower than the threshold temperature, the control device 6 controls the first valve to an open state. As a result, even if the first pressure of the first refrigerant in the receiver 13 rises while the first compressor 10 is stopped, if the first temperature is equal to or lower than the threshold temperature, the first refrigerant in the receiver 13 flows through the evaporator 15. Therefore, an excessive rise in the first pressure in the receiver 13 is suppressed, and the receiver 13 can be protected.

[0117] Although the embodiments have been described above, the contents of the present disclosure are not limited to the embodiments and include a range of conceivable equivalents. [Explanation of symbols]

[0118] 1 first refrigerant circuit, 1A bypass path, 2 second refrigerant circuit, 3 heat source equipment, 4 utilization side equipment, 5 first refrigerant piping, 6 control device, 7 second refrigerant piping, 8 refrigerant flow path, 10 first compressor, 11 primary side heat exchanger, 11A low stage side heat exchanger, 12 refrigerant heat exchanger, 13 receiver, 14 first pressure reducing valve, 14A first on-off valve, 14B second on-off valve, 15 evaporator, 16 gas-liquid separator, 17 first pressure detection device, 17A second pressure detection device, 18 first temperature detection device, 20 secondary side compressor, 20A high stage side compressor, 21 secondary side condenser, 21A high stage side condenser, 22 secondary side pressure reducing valve, 22A high stage side pressure reducing valve, 60 bus, 61 processor, 62 memory, 63 input interface circuit, 64 output interface circuit, 100 refrigeration cycle device.

Claims

1. A refrigeration cycle device that circulates a first refrigerant, which is carbon dioxide, through a first refrigerant circuit and cools a first object with the first refrigerant, a first compressor that compresses the first refrigerant; a first heat exchanger that exchanges heat between the first refrigerant discharged from the first compressor and a second object to cool the first refrigerant; an evaporator for exchanging heat between the first refrigerant and the first object; a first valve that is provided in the first refrigerant circuit upstream of the evaporator, the first valve reducing the pressure of the first refrigerant in an open state and allowing the reduced pressure first refrigerant to flow through the evaporator; a first pressure detection device that detects a first pressure, which is a pressure of the first refrigerant between a downstream side of the first compressor and the first valve; a first temperature detection device that detects a first temperature, which is a temperature of the first object in the evaporator; A control device that controls the first compressor and the first valve; a second refrigerant circuit for circulating a second refrigerant; Equipped with The second object is the second refrigerant, The second refrigerant circuit includes: a second compressor that compresses the second refrigerant; a second heat exchanger that exchanges heat between the second refrigerant discharged from the second compressor and a third object to condense the second refrigerant; a second valve for reducing the pressure of the second refrigerant condensed in the second heat exchanger; The first heat exchanger; having The first heat exchanger is a heat exchange is performed between the second refrigerant decompressed by the second valve and the first refrigerant discharged from the first compressor, so that the first refrigerant is condensed and the second refrigerant is evaporated; The control device includes: a first valve being controlled to an open state when the first pressure is equal to or greater than a predetermined first threshold pressure and the first temperature is equal to or less than a predetermined threshold temperature when the first compressor is stopped.

2. The first refrigerant circuit includes: The refrigeration cycle apparatus according to claim 1 , further comprising a primary side heat exchanger that cools the first refrigerant by exchanging heat with a fourth object.

3. 3. The refrigeration cycle apparatus according to claim 1, further comprising a receiver for storing the first refrigerant, the receiver being located downstream of the first heat exchanger in the first refrigerant circuit and upstream of the first valve.

4. The first pressure sensing device is The refrigeration cycle apparatus according to claim 3 , wherein the first pressure of the first refrigerant in the receiver is detected.

5. a second pressure detection device that detects the first pressure of the first refrigerant discharged from the first compressor, The control device includes: When the first compressor is operating, if the first pressure of the first refrigerant discharged from the first compressor is equal to or higher than a predetermined second threshold pressure, it is determined whether the first pressure of the first refrigerant in the receiver is equal to or higher than the first threshold pressure; When the first pressure of the first refrigerant in the receiver is equal to or higher than the first threshold pressure and the first temperature is equal to or lower than the threshold temperature, the first valve is controlled to an open state; The first threshold pressure is determined based on a design pressure of the receiver, The refrigeration cycle apparatus according to claim 4 , wherein the second threshold pressure is determined based on a design pressure of the first compressor.

6. The control device includes: When the second compressor is operating and the second compressor is not exerting a required refrigeration capacity, it is determined whether the first pressure is equal to or higher than the first threshold pressure; 3. The refrigeration cycle apparatus according to claim 1, wherein the first valve is controlled to an open state when the first pressure is equal to or higher than the first threshold pressure and the first temperature is equal to or lower than the threshold temperature.

7. A refrigeration cycle device that circulates a first refrigerant, which is carbon dioxide, through a first refrigerant circuit and cools a first object with the first refrigerant, a first compressor that compresses the first refrigerant; a first heat exchanger that exchanges heat between the first refrigerant discharged from the first compressor and a second object to cool the first refrigerant; an evaporator for exchanging heat between the first refrigerant and the first object; a first valve that is provided in the first refrigerant circuit upstream of the evaporator, the first valve reducing the pressure of the first refrigerant in an open state and allowing the reduced pressure first refrigerant to flow through the evaporator; a first pressure detection device that detects a first pressure, which is a pressure of the first refrigerant between a downstream side of the first compressor and the first valve; a first temperature detection device that detects a first temperature, which is a temperature of the first object in the evaporator; A control device that controls the first compressor and the first valve; a receiver for storing the first refrigerant, the receiver being located downstream of the first heat exchanger in the first refrigerant circuit and upstream of the first valve; a refrigerant flow path connected to the first refrigerant circuit and through which the first refrigerant flows; Equipped with The refrigerant flow path is A second compressor that compresses the first refrigerant; A second heat exchanger that exchanges heat between the first refrigerant discharged from the second compressor and a fifth object to condense the first refrigerant; a second valve for reducing the pressure of the first refrigerant condensed in the second heat exchanger; having The receiver is provided downstream of the second valve, The second compressor is compressing the first refrigerant from the first heat exchanger and the second valve; The control device includes: a first valve being controlled to an open state when the first pressure is equal to or greater than a predetermined first threshold pressure and the first temperature is equal to or less than a predetermined threshold temperature when the first compressor is stopped.

8. The refrigeration cycle apparatus according to claim 7 , wherein the first pressure detection device detects the first pressure in the receiver.

9. the first compressor, the first heat exchanger, the receiver, the first valve, and the evaporator are connected by a first refrigerant piping through which the first refrigerant flows; The first threshold pressure is 4. The refrigeration cycle apparatus according to claim 3, wherein the pressure is lower than a design pressure of each of the first compressor, the first heat exchanger, the receiver, the first valve, the evaporator, and the first refrigerant pipe, and is lower than a pressure at which a safety valve or a rupture disc operates.

10. The first compressor, the first heat exchanger, the receiver, the first valve, and the evaporator are connected by a first refrigerant piping through which the first refrigerant circulates; The first threshold pressure is 9. The refrigeration cycle apparatus according to claim 7 or 8, wherein the pressure is lower than a design pressure of each of the first compressor, the first heat exchanger, the receiver, the first valve, the evaporator, and the first refrigerant pipe, and is lower than a pressure at which a safety valve or a rupture disc operates.

11. The control device includes: When the second compressor is in a state where it cannot operate, the first compressor is stopped, and it is determined whether the first pressure is equal to or greater than the first threshold pressure; 9. The refrigeration cycle apparatus according to claim 1, wherein the first valve is controlled to an open state when the first pressure is equal to or higher than the first threshold pressure and the first temperature is equal to or lower than the threshold temperature.

12. The refrigeration cycle apparatus according to claim 1 , wherein the threshold temperature is lower than a condensation temperature of the first refrigerant in a pressure-equal state in the first refrigerant circuit.

13. The threshold temperature is 9. The refrigeration cycle device according to claim 1, wherein an amount of the first refrigerant flowing into the evaporator when the first compressor is stopped and the first valve is open is set so as not to exceed a volume of the evaporator.

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