GB2581720A

GB2581720A - Refrigeration Apparatus and Outdoor unit

Info

Publication number: GB2581720A
Application number: GB2006902.7A
Authority: GB
Inventors: Arii Yusuke; Saikusa Tetsuji; Hayasaka Motoshi
Original assignee: Mitsubishi Electric Corp
Current assignee: Mitsubishi Electric Corp
Priority date: 2017-11-29
Filing date: 2017-11-29
Publication date: 2020-08-26
Anticipated expiration: 2037-11-29
Also published as: WO2019106764A1; GB202006902D0; GB2581720B; JPWO2019106764A1; JP6833065B2; GB2581720C

Abstract

This refrigeration device has: a refrigeration circuit in which a compressor, a gas cooler, a liquid receiver, a low-pressure expansion valve and an evaporator are connected to refrigerant piping and a refrigerant is circulated; a high-pressure expansion valve provided between the gas cooler and the liquid receiver; an accumulator which is provided between the evaporator and the compressor and stores the refrigerant; a bypass circuit which connects a portion between the liquid receiver and the low-pressure expansion valve with the refrigerant inlet side of the accumulator; a bypass adjustment valve which is provided in the bypass circuit and adjusts the flow rate of the refrigerant; and a control device which performs a control for increasing the opening degree of the bypass adjustment valve when the amount of refrigerant stored between the discharge side of the compressor and the liquid receiver exceeds a predetermined threshold value.

Description

DESCRIPTION Title of Invention

REFRIGERATION APPARATUS AND OUTDOOR UNIT

Technical Field

[0001] The present disclosure relates to a refrigeration apparatus including a refrigerant circuit in which refrigerant circulates and an outdoor unit included in the refrigeration apparatus.

Background Art

[0002] As refrigerant for use in a refrigerating and air-conditioning apparatus, natural refrigerants that have a low global warming potential (GWP) and can be applied to countermeasures for a global warming problem has been paid attention. Among such natural refrigerants, R744 (CO2) refrigerant is refrigerant having a GWP of 1 and no toxicity. The R744 (CO2) refrigerant is refrigerant that can be applied to countermeasures against global warming, in place of HFC refrigerants such as R404A refrigerant having a GWP of approximately 4000 and R410A refrigerant having a GWP of approximately 2000.

[0003] As a refrigeration cycle apparatus using R744 (CO2) refrigerant, a refrigeration apparatus in which a pressure-reducing device is provided downstream of a gas cooler is known (see, for example, Patent Literature 1). The refrigeration apparatus described in Patent Literature 1 includes a refrigerant circuit in which a compressor, a gas cooler, a cascade heat exchanger, a second pressure-reducing device, a liquid receiver, a first pressure-reducing device, and an evaporator are connected in order by refrigerant pipes. The refrigeration apparatus includes a circuit that connects the liquid receiver and the compressor to each other, with an opening and closing valve located between the liquid receiver and the compressor.

[0004] In the refrigeration cycle apparatus using R744 (CO2) refrigerant, as disclosed in Patent Literature 1, the refrigerant is reduced in pressure in the outdoor unit, and then flows into the indoor unit through an extension pipe. In the refrigeration apparatus, the length of the extension pipe may vary in accordance with environments under which the refrigeration apparatus is installed, and the necessary amount of refrigerant may vary in accordance with the length of the extension pipe and use environments (outside-air temperature, interior temperature, etc.). Therefore, the liquid receiver is provided as a receiver that stores surplus refrigerant, to thereby adjust the amount of refrigerant. Citation List Patent Literature [0005] Patent Literature 1: Japanese Patent No. 4841288

Summary of Invention

Technical Problem [0006] The refrigeration apparatus disclosed in Patent Literature 1 may perform a supercritical cycle operation in which refrigerant does not change into liquid refrigerant no matter how much the refrigerant is compressed. In contrast, for example, the pressure of the refrigerant and the necessary amount of refrigerant change under certain operating conditions such as a change in ambient temperature. Therefore, it is hard to stably operate the refrigeration apparatus throughout the year In the case where refrigerant is reduced in pressure after flowing out of the gas cooler, a sufficient amount of refrigerant is not easily stored in the liquid receiver under certain use conditions including an ambient temperature. If refrigerant is not stored in the liquid receiver, the operation of a refrigeration cycle circuit may become unstable. This is because, for example, an excessive amount of refrigerant may be present in a region other than the liquid receiver. In particular, in the case where R744 (CO2) is used as refrigerant, a supercritical cycle may occur because of a change in ambient temperature. Therefore, the operation easily becomes unstable.

[0007] Embodiments of the present disclosure are applied to solve the above problems, and the present disclosure relates to a refrigeration apparatus and an outdoor unit that stably perform an operation under various use conditions such as a change in ambient temperature.

Solution to Problem [0008] A refrigeration apparatus according to an embodiment of the present disclosure includes: a refrigerant circuit in which a compressor, a gas cooler, a liquid receiver, a low-pressure expansion valve, and an evaporator are connected by refrigerant pipes, and refrigerant circulates; a high-pressure expansion valve provided between the gas cooler and the liquid receiver; an accumulator provided between the evaporator and the compressor to store refrigerant in the accumulator; a bypass circuit that connects a region between the liquid receiver and the low-pressure expansion valve to a refrigerant inlet side of the accumulator; a bypass regulating valve provided in the bypass circuit to regulate the flow rate of the refrigerant; and a controller that performs control to increase an opening degree of the bypass regulating valve, when the amount of refrigerant that is present in a region from a discharge side of the compressor to the liquid receiver exceeds a predetermined threshold.

[0009] An outdoor unit according to another embodiment of the present disclosure includes a compressor, a gas cooler, and a liquid receiver in a refrigerant circuit in which the compressor, the gas cooler, the liquid receiver, a low-pressure expansion valve, and an evaporator are connected by refrigerant pipes, and refrigerant circulates. The outdoor unit includes; a high-pressure expansion valve provided between the gas cooler and the liquid receiver; an accumulator provided between the evaporator and the compressor to store refrigerant; a bypass circuit connecting a region between the liquid receiver and the low-pressure expansion valve with a refrigerant inlet side of the accumulator; a bypass regulating valve provided in the bypass circuit to regulate the flow rate of the refrigerant; and a controller that performs control to increase the opening degree of the bypass regulating valve, when the amount of refrigerant that is present in a region from a discharge side of the compressor to the liquid receiver exceeds a predetermined threshold.

Advantageous Effects of Invention [0010] According to the embodiments of the present disclosure, even under various operating conditions such as a change in ambient temperature, the probability with which the operation becomes unstable due to surplus refrigerant in a liquid receiver can be reduced, and the operation can be stably performed.

Brief Description of Drawings

[0011] [Fig. 1] Fig. 1 is a refrigerant circuit diagram of a refrigeration apparatus according to Embodiment 1 of the present disclosure.

[Fig. 2] Fig. 2 is a functional block diagram illustrating a configuration example of a controller as illustrated in Fig. 1.

[Fig. 3] Fig. 3 is a refrigerant circuit diagram illustrating another configuration example of the refrigeration apparatus as illustrated in Fig. 1.

[Fig. 4] Fig. 4 is a P-h chart indicating a state of refrigerant in the refrigerant circuit as illustrated in Fig. 1 in the case where an outside-air temperature is low. [Fig. 5] Fig. 5 is a P-h chart indicating the state of refrigerant in the refrigerant circuit as illustrated in Fig. 1 in the case where the outside-air temperature is high.

[Fig. 6] Fig. 6 is a flowchart indicating the procedure of control of a bypass regulating valve that is performed by a controller in Embodiment 1.

[Fig. 7] Fig. 7 is a flowchart indicating the procedure of control of a bypass regulating valve that is formed by a controller in Embodiment 2.

[Fig. 8] Fig. 8 is a schematic diagram for explaining a configuration of an accumulator as illustrated in Fig. 1.

[Fig. 9] Fig. 9 is a refrigerant circuit diagram illustrating another configuration example of the refrigeration apparatus as illustrated in Fig. 1.

[Fig. 10] Fig. 10 is a refrigerant circuit diagram illustrating still another configuration example of the refrigeration apparatus as illustrated in Fig. 1.

Description of Embodiments

[0012] Embodiment 1 A configuration of a refrigeration apparatus including an outdoor unit according to Embodiment 1 will be described. Fig. 1 is a refrigerant circuit diagram of the refrigeration apparatus according to Embodiment 1 of the present disclosure. A refrigeration apparatus 1 includes an outdoor unit 100 and an indoor unit 200 that are connected by a refrigerant circuit 5, and a controller 300 that controls devices in the refrigerant circuit 5. The indoor unit 200 is used to cool, for example, food. The indoor unit 200 may be a showcase in, for example, a supermarket, or a unit cooler installed in a cooling warehouse or a freezing warehouse.

[0013] The outdoor unit 100 includes a compressor 101 that compresses refrigerant and discharges the compressed refrigerant, a gas cooler 102 that causes heat exchange to be performed between refrigerant and outdoor air, a high-pressure expansion valve 103 that reduces the pressure of high-pressure refrigerant to a medium pressure, a liquid receiver 104, and a fan 102a. The high-pressure expansion valve 103 is provided between the gas cooler 102 and the liquid receiver 104. An accumulator 108 is provided on a refrigerant suction side of the compressor 101.

[0014] The compressor 101 is, for example, an inverter-type compressor whose capacity can be changed by changing its operating rotation speed. The gas cooler 102 is a heat exchanger that operates as a condenser. The gas cooler 102 is not limited to an air-cooled type gas cooler. The gas cooler 102 may be a gas cooler that causes heat exchanger to be performed between refrigerant and water. The following description is made by referring to by way of example the case where the gas cooler 102 is of an air-cooled type. The liquid receiver 104 is a container that stores high-pressure liquid refrigerant. The accumulator 108 stores refrigerant that has returned from the indoor unit 200, and separates gas refrigerant from the stored refrigerant. The fan 102a supplies outdoor air to the gas cooler 102.

[0015] In the outdoor unit 100, a first heat exchanger 105 is provided between the high-pressure expansion valve 103 and the liquid receiver 104. A second heat exchanger 106 is provided at a refrigerant pipe on a refrigerant outlet side of the liquid receiver 104. The first heat exchanger 105 is a heat exchanger that causes heat exchange to be performed between refrigerant and refrigerant to obtain medium-pressure liquid refrigerant. The second heat exchanger 106 is a heat exchanger that causes heat exchange to be performed between refrigerant and refrigerant to cause the refrigerant to be in a subcooled liquid state. The first heat exchanger 105 and the second heat exchanger 106 are each, for example, a plate heat exchanger or a double pipe; however, any element may be applied as each of the first heat exchanger 105 and the second heat exchanger 106, as long as it can cause heat exchange between refrigerant and refrigerant.

[0016] Furthermore, the outdoor unit 100 includes a bypass circuit 7 that connects a refrigerant outlet side of the second heat exchanger 106 to a refrigerant inlet side of the accumulator 108. The bypass circuit 7 extends from the refrigerant outlet side of the second heat exchanger 106 to the refrigerant inlet side of the accumulator 108 through the first heat exchanger 105 and a secondary side of the second heat exchanger 106.

In the bypass circuit 7, a bypass regulating valve 107 is provided upstream of a refrigerant inlet on the secondary side of the second heat exchanger 106. That is, the bypass regulating valve 107 is provided between a refrigerant outlet on a primary side of the second heat exchanger 106 and the refrigerant inlet on the secondary side of the second heat exchanger 106. The bypass regulating valve 107 is provided to regulate the flow rate of refrigerant that branches off from the refrigerant in the refrigerant circuit and reduce the pressure of medium-pressure refrigerant to change the medium-pressure refrigerant into low-pressure refrigerant.

[0017] A refrigerant pipe connected to the refrigerant outlet on the primary side of the second heat exchanger 106 is connected to the indoor unit 200 by an extension pipe 301. A refrigerant pipe connected to the refrigerant inlet of the accumulator 108 is connected to the indoor unit 200 by an extension pipe 302.

[0018] The indoor unit 200 includes a low-pressure expansion valve 201 and an evaporator 202. The low-pressure expansion valve 201 expands and evaporates medium-pressure liquid refrigerant. The evaporator 202 is a heat exchanger that causes heat exchange to be performed between refrigerant and air in an air-conditioned space. The extension pipe 301 is connected to a refrigerant inlet side of the low-pressure expansion valve 201 of the indoor unit 200. In the indoor unit 200, a refrigerant outlet of the low-pressure expansion valve 201 is connected to a refrigerant inlet of the evaporator 202 by a refrigerant pipe. A refrigerant outlet side of the evaporator 202 is connected to the extension pipe 302. A pipe that extends from the indoor unit 200 is connected to the extension pipe 302, which is connected to the outdoor unit 100. The extension pipe 301 is connected to the refrigerant inlet side of the accumulator 108 of the outdoor unit 100 by a refrigerant pipe. The compressor 101, the gas cooler 102, the liquid receiver 104, the low-pressure expansion valve 201, and the evaporator 202 are connected by refrigerant pipes, whereby the refrigerant circuit 5 is formed. In the refrigerant circuit 5, refrigerant is circulated.

[0019] As illustrated in Fig. 1, the refrigerant circuit 5 includes pressure sensors 112 to 114 that each measure the pressure of refrigerant. The pressure sensor 112 is provided at the refrigerant pipe on a refrigerant discharge side of the compressor 101. The pressure sensor 112 measures the discharge pressure of refrigerant discharged from the compressor 101. The pressure sensor 114 is provided at the refrigerant pipe on the refrigerant inlet side of the accumulator 108. The pressure sensor 114 measures the suction pressure of gas refrigerant sucked into the compressor 101. The pressure sensor 113 is provided between the high-pressure expansion valve 103 and the first heat exchanger 105. The pressure sensor 113 measures the pressure of refrigerant that flows out of the high-pressure expansion valve 103.

[0020] Fig. 2 is a functional block diagram illustrating a configuration example of the controller as illustrated in Fig. 1.

The controller 300 is, for example, a microcomputer The controller 300 includes a central processing unit (CPU) and a memory, which are not illustrated. The controller 300 includes a refrigeration cycle unit 311, a storage determination unit 312, and an opening-degree control unit 313. When a program stored in the memory is executed by the CPU, the refrigeration cycle unit 311, the storage determination unit 312, and the opening-degree control unit 313 are configured in the refrigeration apparatus 1. The controller 300 may be provided in the outdoor unit 100.

[0021] The controller 300 is connected to the pressure sensors 112 to 114, the high-pressure expansion valve 103, the low-pressure expansion valve 201, the bypass regulating valve 107, the compressor 101, and the fan 102a wirelessly or by signal lines. Sensors not illustrated that measure the temperature and pressure of refrigerant may be provided in the refrigeration apparatus 1. These sensors are connected to the controller 300 wirelessly or by signal lines. For example, a temperature sensor that measures the temperature of refrigerant in the evaporator 202 or a pressure sensor that measures the pressure of refrigerant in the evaporator 202 may be provided.

[0022] The refrigeration cycle unit 311 controls, based on information on various sensors and setting information input by a user, the operating rotation speed of the compressor 101, the rotation speed of the fan 102a, and the opening degrees of the high-pressure expansion valve 103 and the low-pressure expansion valve 201. The storage determination unit 312 compares the amount of refrigerant that is present in a region from the discharge side of the compressor to the liquid receiver with a predetermined threshold and determines whether the amount of the refrigerant exceeds the threshold or not. In Embodiment 1, the storage determination unit 312 performs the determination based on a measurement value obtained by measurement by the pressure sensor 112. The opening-degree control unit 313 controls, based on the result of the determination by the storage determination unit 312, the opening degree of the bypass regulating valve 107. When the measurement value obtained by the pressure sensor 112 exceeds the threshold, the opening-degree control unit 313 increases the opening degree of the bypass regulating valve 107. When the measurement value obtained by the pressure sensor 112 is less than or equal to the threshold, the opening-degree control unit 313 decreases the opening degree of the bypass regulating valve 107. The refrigeration cycle unit 311 may give an instruction regarding the opening degree of the bypass regulating valve 107 to the opening-degree control unit 313 via the storage determination unit 312.

[0023] Fig. 2 illustrates the case where the controller 300 controls the low-pressure expansion valve 201. However, an indoor unit 200 manufactured by a manufacturer different from a manufacturer of the outdoor unit 100 may be connected to the outdoor unit 100. Therefore, it is also assumed that there is a case where a refrigerant device provided in the indoor unit 200 cannot be controlled from the outdoor unit 100.

[0024] In the case where natural refrigerant such as R744 (CO2) is used, when the ambient temperature is high, the refrigerant is made to be in a supercritical state. Thus, when the refrigerant is discharged from the compressor 101, the pressure of the refrigerant is very high. Furthermore, in the case where natural refrigerant such as R744 (CO2) is used, the internal pressure of the pipe may rise when the compressor 101 is in the stopped state, and whether the internal pressure of the pipe rises or not depends on the pressure of refrigerant that has been reduced by the high-pressure expansion valve 103. Therefore, as illustrated in Fig. 1, a first safety valve 109, a second safety valve 110, and a third safety valve 111 may be provided in the refrigerant circuit 5.

[0025] When the pressure in the refrigerant circuit 5 reaches a set value or more, the states of the first safety valve 109, the second safety valve 110, and the third safety valve 111 are switched from a closed state to an opened state. To be more specific, when the pressure in the refrigerant circuit 5 reaches the set value or more, the first safety valve 109, the second safety valve 110, and the third safety valve 111 are opened to release the high-pressure refrigerant into the atmosphere, thereby reducing the pressure in the refrigerant circuit 5, and avoiding breakage of the refrigerant pipe and a pressure container. The refrigerant released into the atmosphere does not cause any problem, since the refrigerant is natural refrigerant. The first safety valve 109 is provided on a refrigerant outlet side of the high-pressure expansion valve 103. The first safety valve 109 is provided, for example, between the liquid receiver 104 and the low-pressure expansion valve 201 and can promptly reduce the pressure by releasing liquid refrigerant. The second safety valve 110 is provided on the suction side of the compressor 101. The third safety valve 111 is provided on the discharge side of the compressor 101. Fig. 1 illustrates a configuration in which the first safety valve 109, the second safety valve 110, and the third safety valve 111 are provided in the refrigerant circuit 5. However, it suffices that at least one of the first safety valve 109, the second safety valve 110, and the third safety valve 111 is provided in the refrigerant circuit 5.

[0026] The bypass regulating valve 107 as illustrated in Fig. 1 is connected to the refrigerant inlet side of the accumulator 108, with the second heat exchanger 106 and the first heat exchanger 105 located in this order between the bypass regulating valve 107 and the accumulator 108. However, the bypass regulating valve 107 may be connected to the refrigerant inlet side of the accumulator 108, with the first heat exchanger 105 and the second heat exchanger 106 located in this order between the bypass regulating valve 107 and the accumulator 108.

[0027] Furthermore, in place of the bypass regulating valve 107 as illustrated in Fig. 1, two bypass regulating valves 107 may be provided in parallel. Fig. 3 is a refrigerant circuit diagram illustrating another configuration example of the refrigeration apparatus as illustrated in Fig. 1. A refrigeration apparatus la as illustrated in Fig. 3 includes two bypass circuits 7a and 7b, in place of the bypass circuit 7. The bypass circuit 7a extends from the refrigerant outlet side of the second heat exchanger 106 to the refrigerant inlet side of the accumulator 108 through the secondary side of the second heat exchanger 106. The bypass circuit 7b extends from the refrigerant outlet side of the second heat exchanger 106 to the bypass circuit 7a through the secondary side of the first heat exchanger 105. In the bypass circuit 7a, a bypass regulating valve 107a is provided between the refrigerant outlet side of the second heat exchanger 106 and the refrigerant inlet on the secondary side of the second heat exchanger 106. In the bypass circuit 7b, a bypass regulating valve 107b is provided between the refrigerant outlet side of the second heat exchanger 106 and the refrigerant inlet on the secondary side of the first heat exchanger 105.

[0028] In the refrigeration apparatus la as illustrated in Fig. 3, the accuracy of control of refrigerant that flows into the bypass circuits 7a and 7b is improved, as compared with the refrigeration apparatus 1 as illustrated in Fig. 1. In contrast, the number of expansion valves provided in the refrigeration apparatus 1 as illustrated in Fig. 1 is smaller than the number of expansion valves provided in the refrigeration apparatus la as illustrated in Fig. 3. Therefore, with the refrigeration apparatus 1 as illustrated in Fig. 1, the manufacturing cost of the apparatus is not high, and the control of the expansion valves is not complicated.

[0029] Next, the flow of refrigerant in the refrigerant circuit 5 will be explained. The compressor 101 compresses refrigerant and discharges the compressed refrigerant. The high-temperature, high-pressure gas refrigerant discharged from the compressor 101 flows into the gas cooler 102. In the gas cooler 102, the refrigerant exchanges heat with outdoor air, whereby heat of the refrigerant is removed by the outdoor air, and the refrigerant is changed into high-pressure liquid refrigerant or made to change to be in a supercritical state. The refrigerant that has flowed out of the gas cooler 102 is reduced in pressure by the high-pressure expansion valve 103 to change into medium-temperature, medium-pressure two-phase gas-liquid refrigerant.

[0030] The pressure of the refrigerant is reduced by the high-pressure expansion valve 103 such that the pressure of the refrigerant on the refrigerant outlet side of the high-pressure expansion valve 103 becomes constant. It is therefore possible to reduce the design pressure resistances of pipes and devices such as the liquid receiver 104, the first heat exchanger 105, the second heat exchanger 106, and the extension pipes 301 and 302. As a result, the thickness of the refrigerant pipes for use in the refrigeration apparatus 1 can be reduced, and the manufacturing cost of the refrigeration apparatus 1 can be reduced. Furthermore, the high-pressure expansion valve 103 reduces the pressure of the refrigerant once. Therefore, in the case where the high-pressure expansion valve 103 reduces the pressure of the refrigerant to a refrigerant pressure (for example, 4.15 MPa) equivalent to that of refrigerant such as HFC adopted by existing refrigeration apparatuses, devices and pipes provided in existing refrigeration apparatuses can be applied as devices and pipes of the refrigeration apparatus 1, which include the extension pipes 301 and 302. Since pipes and devices that are used for HFC are manufactured in volume and thus inexpensive, the manufacturing cost of the refrigeration apparatus 1 is not high.

[0031] The refrigerant that has flowed out of the high-pressure expansion valve 103 exchanges heat with refrigerant on the secondary side in the first heat exchanger 105 to change into medium-pressure liquid refrigerant, and the medium-pressure liquid refrigerant flows into the liquid receiver 104. In the liquid receiver 104, the medium-pressure liquid refrigerant is separated into gas refrigerant and liquid refrigerant, and only saturated liquid refrigerant flows into the second heat exchanger 106. In the second heat exchanger 106, the liquid refrigerant exchanges heat with the refrigerant on the secondary side to change into medium-pressure subcooled liquid refrigerant.

Then, the medium-pressure subcooled liquid refrigerant flows out of the second heat exchanger 106.

[0032] The refrigerant that has flowed out of the second heat exchanger 106 branches into two refrigerants. One of the two refrigerants flows into the bypass circuit 7, and the other flows out of the outdoor unit 100. The refrigerant that has flowed into the bypass circuit 7 is reduced in pressure by the bypass regulating valve 107 to change into low-temperature, low-pressure two-phase gas-liquid refrigerant. The two-phase, gas-liquid refrigerant flows through the secondary side of the second heat exchanger 106 and the first heat exchanger 105, and exchanges heat with refrigerant on the primary side. The refrigerant that has flowed out of the first heat exchanger 105 flows into the refrigerant inlet of the accumulator 108.

[0033] The refrigerant that has flowed out of the outdoor unit 100 flows into the indoor unit 200 through the extension pipe 301. The refrigerant that has flowed into the indoor unit 200 is reduced in pressure by the low-pressure expansion valve 201 to change into low-temperature, low-pressure two-phase gas-liquid refrigerant. The two-phase gas-liquid refrigerant evaporates in the evaporator 202 to change into low-pressure gas refrigerant. After flowing out of the evaporator 202, the gas refrigerant returns to the outdoor unit 100 through the extension pipe 302. The refrigerant that has returned to the outdoor unit 100 is separated into gas refrigerant and liquid refrigerant in the accumulator 108, and the gas refrigerant returns to the compressor 101 [0034] Next, it will be described what control is performed by the controller 300 on each of devices provided in the refrigerant circuit 5. The control as described below is merely an example and may be different from control that is performed in the case where, for example, abnormality occur in the refrigeration apparatus 1.

[0035] Control of the compressor 101 will be explained. The refrigeration cycle unit 311 controls the rotation speed of the compressor 101 such that a low pressure measured by the pressure sensor 114 becomes constant. To be more specific, when the low pressure increases, the refrigeration cycle unit 311 increases the rotation speed of the compressor 101. When the low pressure decreases, the refrigeration cycle unit 311 decreases the rotation speed of the compressor 101. Because of this control, the low pressure becomes constant. The low pressure varies in accordance with the load of a cooling target such as a showcase, a cooling warehouse, or a freezing warehouse. In the case where, for example, the number of items to be cooled is large and as a result the load of a cooling target is high, the low pressure tends to be high. In contrast, in the case where the load of the cooling target is low, the low pressure tends to be low.

It should be noted that the refrigeration cycle unit 311 may monitor an evaporating temperature, instead of the low pressure.

[0036] Control of the fan 102a will be described. The refrigeration cycle unit 311 controls the rotation speed of the fan 102a based on a condensing temperature. In the case where, for example, the outside air temperature is high, the condensing temperature tends to be high. In this case, the refrigeration cycle unit 311 increases the rotation speed of the fan 102a. In the case where, for example, the outside air temperature is low, the condensing temperature tends to be low. In this case, the refrigeration cycle unit 311 decreases the rotation speed of the fan 102a.

[0037] Then, control of the high-pressure expansion valve 103 will be described. The refrigeration cycle unit 311 controls the opening degree of the high-pressure expansion valve 103 such that pressure measured by the pressure sensor 113 becomes constant.

When the pressure measured by the pressure sensor 113 is higher than a predetermined threshold, the refrigeration cycle unit 311 decreases the opening degree of the high-pressure expansion valve 103. When the pressure measured by the pressure sensor 113 is lower than the threshold, the refrigeration cycle unit 311 increases the opening degree of the high-pressure expansion valve 103.

[0038] However, if the opening degree of the high-pressure expansion valve 103 is excessively decreased, circulation of refrigerant is restricted, and as a result the refrigerant inlet side of the high-pressure expansion valve 103 is clogged with the refrigerant. In this case, the discharge pressure of the compressor 101 is excessively increased. Therefore, in the case of decreasing the opening degree of the high-pressure expansion valve 103, the opening degree of the high-pressure expansion valve 103 must be controlled such that it is not excessively decreased. The discharge pressure of the compressor 101 is measured by the pressure sensor 112, as illustrated in Fig. 1.

[0039] In the case where the pressure measured by the pressure sensor 113 is controlled to be constant, the control for achieving this is not limited to the control of the opening degree of the high-pressure expansion valve 103, and the opening degree of the bypass regulating valve 107 may be controlled. To be more specific, when the pressure measured by the pressure sensor 113 is higher than the threshold, the refrigeration cycle unit 311 increases the opening degree of the bypass regulating valve 107 to release the high-pressure refrigerant toward the suction side of the compressor 101 to reduce the pressure. This control can also reduce the pressure measured by the pressure sensor 113. Therefore, the pressure measured by the pressure sensor 113 may be adjusted by combining the control of the high-pressure expansion valve 103 and that of the bypass regulating valve 107.

[0040] Although it is described above that the refrigeration cycle unit 311 controls the compressor 101 and the fan 102a separately, controls suitable for conditions may be combined and applied to set an optimal rotation speed of each of devices.

[0041] Next, the state of the refrigerant in the refrigeration cycle circuit in Embodiment 1 will be explained. Fig. 4 is a P-h chart illustrating the state of the refrigerant in the refrigerant circuit as illustrated in Fig. 1 in the case where the outside air temperature is low. Fig. 5 is a P-h chart illustrating the state of the refrigerant in the refrigerant circuit as illustrated in Fig. 1 in the case where the outside air temperature is high. In the P-h charts of Figs. 4 and 5, the horizontal axis represents enthalpy h [KJ/Kg], and the vertical axis represents pressure P [MPa]. For the sake of explanation, in Figs. 4 and 5, numbers 1 to 7 are allocated to states of the refrigerant in the P-h charts.

[0042] A step from state 1 to state 2 is a compression step of compression by the compressor 101. In the step from state 1 to state 2, the refrigerant is compressed, the pressure of the refrigerant increases, and the enthalpy increases because of the power of the compressor 101. A step from state 2 to state 3 is a condensation step of condensation by the gas cooler 102. In this step, high-temperature, high-pressure gas refrigerant transfers heat at the gas cooler 102, and the enthalpy thus decreases. When an ambient temperature around the gas cooler 102 is low, the refrigerant condenses and changes into liquid refrigerant, as illustrated in Fig. 4. In the case where the ambient temperature around the gas cooler 102 is high, the refrigerant is made to be in a supercritical state, as illustrated in Fig. 5. In both the above cases, the pressure hardly decreases at the gas cooler 102.

[0043] A step from state 3 to step 4 is a pressure-reduction step of pressure-reduction by the high-pressure expansion valve 103. The pressure of the refrigerant is reduced by the high-pressure expansion valve 103 in the pressure-reduction step. Therefore, the pressure of the refrigerant is reduced. However, the refrigerant does not work for the outside, and the enthalpy thus does not change. Furthermore, after the pressure of the refrigerant is reduced, the refrigerant changes into two-phase gas-liquid refrigerant. In the step from state 4 to state 5, the first heat exchanger 105 causes heat exchange to be performed between refrigerant and refrigerant to obtain saturated liquid refrigerant, and the saturated liquid refrigerant flows into the liquid receiver 104.

[0044] A step from state 5 to step 6 is a heat exchange step of heat exchange at the second heat exchanger 106. At the second heat exchanger 106, the saturated liquid refrigerant that has flowed out of the liquid receiver 104 exchanges heat with refrigerant to change into subcooled liquid refrigerant. It should be noted that in a freezer, in accordance with environments in which the freezer is installed, a longer extension pipe may be used or the difference in level between the position of an indoor unit and that of an outdoor unit may be great. In such a case, when the refrigerant in the saturated liquid state (state of no subcooling) flows out of the outdoor unit and pass through the extension pipe, the state of the refrigerant changes into a two-phase gas-liquid state because of a pressure loss. For example, in the case where a plurality of indoor units are installed, if refrigerant in the two-phase gas-liquid state is distributed to the plurality of indoor units, a failure may occur in distribution of the refrigerant to the indoor units or a failure may occur in expansion at expansion valves in the indoor units. Therefore, it is preferable that refrigerant that has been subcooled at the second heat exchanger 106 be made to flow out of the outdoor unit.

[0045] A step from state 6 to state 7 is a pressure-reduction step of pressure-reduction by the low-pressure expansion valve 201 of the indoor unit 200. As in the step from state 3 to state 4, the pressure of the refrigerant is reduced by the low-pressure expansion valve 201 in the pressure-reduction step. However, the refrigerant does not work for the outside, and the enthalpy thus does not change. Finally, a step from state 7 to state 1 is an evaporation step of evaporation by the evaporator 202 of the indoor unit 200. In the evaporation step, at the evaporator 202, the refrigerant receives heat from the outside, and evaporates. At this time, although the pressure of the refrigerant does not change, the enthalpy increases since the refrigerant receives heat.

[0046] As described above, the P-h chart varies in accordance with the ambient temperature around the gas cooler 102, as illustrated in Figs. 4 and 5. In the P-h chart, the duration of the step from state 2 to state 3 in the case where the outside air temperature is high (the case illustrated in Fig. 5) is shorter than that in the case where the outside air temperature is low (the case illustrated in Fig. 4). That is, the value by which the enthalpy decreases in the case where the outside air temperature is high is smaller than that in the case where the outside air temperature is low.

[0047] In general, in order to increase the duration of the step from state 2 to state 3 and increase the value by which the enthalpy decreases, a larger heat exchanger is applied, or the amount of air to be sent by of a fan that supplies air to the heat exchanger is increased. However, no matter how much the size of the heat exchanger and the amount of air from the fan are increased, the temperature of refrigerant that flows in the gas cooler 102 cannot be reduced to a temperature below the ambient temperature around the gas cooler 102. Under conditions that the ambient temperature around the gas cooler 102 is high and the refrigerant is made to be in a supercritical state at the gas cooler 102, even if the temperature of the refrigerant drops to the same level as the ambient temperature around the gas cooler 102, a great enthalpy difference cannot be obtained at the gas cooler 102 in terms of the properties of refrigerant.

[0048] From the above, in the case where the outside air temperature is high, the duration of the step from state 2 to state 3 needs to be short. It is therefore necessary to increase the duration of the step from state 4 to state 5 after the refrigerant flows out of the high-pressure expansion valve 103. That is, it is necessary to improve the efficiency of heat exchange between the refrigerant and the outdoor air at the first heat exchanger 105, and reduce the enthalpy.

[0049] To reduce the enthalpy, the size of the first heat exchanger 105 needs to be increased or the temperature at the refrigerant inlet on the secondary side of the first heat exchanger 105 needs to be lowered. To lower the temperature at the refrigerant inlet on the secondary side of the first heat exchanger 105, it suffices that the bypass regulating valve 107 is controlled such that the temperature of the refrigerant that flows out of the bypass regulating valve 107 is lowered. On the other hand, if the size of the first heat exchanger 105 is increased, the manufacturing cost of the apparatus is also increased. Furthermore, because the temperature of refrigerant that flows through the bypass regulating valve 107 is equal to the saturation temperature (evaporating temperature) corresponding to the low pressure, for example, in the case where the apparatus is used for cooling, the evaporating temperature increases to be high. Therefore, it is hard to lower the temperature of the refrigerant that flows out of the bypass regulating valve 107.

[0050] Thus, when the ambient temperature around the gas cooler 102 is high and the evaporating temperature is high, there is a case where heat exchange cannot be sufficiently performed in the step from state 4 to state 5 and refrigerant that flows into the liquid receiver 104 is not in the saturated liquid state. In this case, liquid refrigerant cannot be sufficiently stored in the liquid receiver 104. In the case where liquid refrigerant cannot be sufficiently stored in the liquid receiver 104, there is no place for storing surplus refrigerant. Therefore, the refrigeration cycle circuit becomes unstable, and abnormality such as an increase in the pressure of the refrigerant may occur in each of components. In particular, it should be noted that if the discharge pressure measured by the pressure sensor 112 increases, abnormality may occur in the refrigerant circuit 5.

[0051] Based on the refrigerant circuit 5, the pressure of refrigerant in the refrigerant circuit 5, and a change in the enthalpy, it is described above with reference to Figs. 4 and 5 that the refrigeration cycle may become unstable. Under conditions that the ambient temperature around the gas cooler 102 is high and the evaporating temperature is high, heat exchange at the first heat exchanger 105 is insufficient. Therefore, liquid refrigerant cannot be sufficiently stored in the liquid receiver 104, and no place to store surplus refrigerant is present. This causes the refrigeration cycle circuit to be unstable. In view of the above cause, the refrigeration apparatus 1 according to Embodiment 1 prevents the refrigeration cycle circuit from becoming unstable, by controlling the bypass regulating valve 107 to change the place for storing surplus refrigerant from the liquid receiver 104 to the accumulator 108.

[0052] It will be described what control is performed on the bypass regulating valve 107 by the controller 300 in the refrigeration apparatus 1 according to Embodiment 1. Fig. 6 is a flowchart illustrating the procedure of the control of the bypass regulating valve that is performed by the controller in Embodiment 1.

[0053] In step ST1, the storage determination unit 312 determines whether the pressure measured by the pressure sensor 112 exceeds a set threshold. The threshold is, for example, 10 MPa. That is, in step ST1, the storage determination unit 312 determines whether or not the discharge pressure of refrigerant in the compressor 101 exceeds the threshold.

[0054] Normally, the saturation temperature corresponding to a pressure that is measured by the pressure sensor 112 is slightly higher than or equal to the ambient temperature around the gas cooler 102. In the case where the saturation temperature is higher than the ambient temperature around the gas cooler 102, the difference between the saturation temperature and the ambient temperature is, for example, 5 to 10 degrees Celsius. In the case where the saturation temperature is greatly higher than the ambient temperature around the gas cooler 102, the controller 300 determines that the pressure measured by the pressure sensor 112 has risen because no refrigerant is stored in the liquid receiver 104 and surplus refrigerant stays in a region from the discharge port of the compressor 101 to the gas cooler 102.

[0055] When it is determined in step ST1 that the pressure measured by the pressure sensor 112 is higher than the threshold, the opening-degree control unit 313 performs control in step ST2. In step ST2, the opening-degree control unit 313 increases the opening degree of the bypass regulating valve 107. Thus, the amount of refrigerant that flows through the bypass regulating valve 107 increases, and the amount of refrigerant that is returned to the refrigerant inlet of the accumulator 108 increases. As a result, surplus refrigerant can be accumulated in the accumulator 108. In step S12, the controller 300 may perform control such that the opening degree of the bypass regulating valve 107 does not reach a threshold for the maximum opening degree or more. The threshold for the maximum opening degree, which is smaller than the opening degree of the valve in the case where the valve is fully opened, is stored in a memory not illustrated in the controller 300.

[0056] In contrast, when it is determined step ST1 that the pressure measured by the pressure sensor 112 is lower than or equal to the threshold, the opening-degree control unit 313 determines that heat exchange is sufficiently performed between refrigerant and outdoor air at the first heat exchanger 105 and refrigerant is stored in the liquid receiver 104. Then, the opening-degree control unit 313 performs control in step ST3.

In step ST3, the opening-degree control unit 313 decreases the opening degree of the bypass regulating valve 107. Thus, the amount of refrigerant that flows through the accumulator 108 decreases. After steps ST2 and 513, the step to be carried out by the controller 300 returns to step ST1 indicated in Fig. 6 (step ST4).

[0057] When the opening degree of the bypass regulating valve 107 is increased by the control in step ST2 and the amount of refrigerant that flows to the accumulator 108 through the bypass circuit 7 excessively increases, the amount of refrigerant that flows into the indoor unit 200 through the extension pipe 301 decreases. If the amount of refrigerant that flows in the indoor unit 200 decreases, the amount of heat exchange at the evaporator 202 decreases, whereby a cooling capacity decreases. Therefore, in the case where surplus refrigerant is sufficiently stored in the liquid receiver 104, and the refrigeration apparatus 1 can be stably operated, when the opening degree of the bypass regulating valve 107 is decreased, the cooling capacity is more greatly improved. However, if the opening degree of the bypass regulating valve 107 is decreased such that the bypass regulating valve 107 is fully closed, heat exchange cannot be performed at the first heat exchanger 105 or the second heat exchanger 106. Thus, in step 513 indicated in Fig. 6, in the case of decreasing the opening degree of the bypass regulating valve 107, the opening-degree control unit 313 performs control such that the opening degree of the bypass regulating valve 107 is decreased to be greater than or equal to a threshold for a minimum opening degree, and the bypass regulating valve 107 is not fully closed. The threshold for the minimum opening degree is stored in the memory not illustrated in the controller 300.

[0058] As described above, if the liquid receiver 104 becomes unable to store surplus refrigerant, the controller 300 increases the opening degree of the bypass regulating valve 107, whereby the surplus refrigerant that cannot be stored in the liquid receiver 104 can be accumulated in the accumulator 108. In particular, in the case where the discharge pressure of the compressor 101 unexpectedly increases, the discharge pressure can be reduced. As a result, the operation of the refrigeration apparatus 1 becomes stable. It should be noted that in order that surplus refrigerant be stored in the accumulator 108, it is preferable that the capacity of the accumulator 108 be larger than or equal to the capacity of the liquid receiver 104.

[0059] The outdoor unit 100 according to Embodiment 1 performs, in the case where the discharge pressure of the compressor 101 exceeds a threshold, control to increase the opening degree of the bypass regulating valve 107 in the bypass circuit 7 that connects the refrigerant outlet side of the liquid receiver 104 and the refrigerant inlet side of the accumulator 108.

[0060] According to Embodiment 1, even in the case where the ambient temperature is high and the discharge pressure of the compressor 101 unexpectedly rises, surplus refrigerant that cannot be stored in the liquid receiver 104 can be moved to the accumulator 108. Therefore, even under various operating conditions such as variations in the ambient temperature, the probability with which the operation becomes unstable due to the surplus refrigerant in the liquid receiver 104 can be reduced, and the operation can be stably performed. As a result, the reliability of the refrigeration apparatus 1 can be improved.

[0061] Because the pressure of R744 (CO2) refrigerant is high during the operation, the pressure capacity of pipes and devices in the refrigeration cycle circuit needs to be increased. By contrast, in the refrigeration apparatus 1 according to Embodiment 1, after reduced in pressure once, refrigerant that flows out of the gas cooler 102 flows out to the indoor unit 200. Therefore, as a device through which refrigerant reduced in pressure flows, a device of an existing refrigeration apparatus can be applied, and design pressure resistances of an extension pipe and an indoor unit can be reduced. Thus, the manufacturing cost can be reduced, and a high technique is not required to install devices. Furthermore, in Embodiment 1, the amount of surplus refrigerant in the liquid receiver 104 is reduced, and complicated control is not required to stably operate the refrigeration apparatus 1. Therefore, the refrigeration apparatus 1 can be made at a lower cost and can be stably operated under simpler control.

[0062] Embodiment 2 Regarding Embodiment 1, it is described above that the controller 300 controls the bypass regulating valve 107 to move surplus refrigerant in the liquid receiver 104 to the accumulator 108, whereby an increase in the discharge pressure of the compressor 101 can be reduced and the refrigeration apparatus 1 can thus operate stably. In Embodiment 2, the controller 300 controls the bypass regulating valve 107 to improve the return of refrigerating machine oil discharged from the compressor 101 to the compressor 101, thus improving the reliability of the refrigeration apparatus 10. The refrigeration apparatus 1 according to Embodiment 2 has the same configuration as or a similar configuration to that of the refrigeration apparatus 1 according to Embodiment 1. Therefore, regarding Embodiment 2, a detailed description concerning the same configuration as or the similar configuration to that of Embodiment 2 will be omitted, and differences in, for example, operation between Embodiments 1 and 2 will be described in detail.

[0063] In the case where natural refrigerant such as R744 (CO2) is used in a refrigeration apparatus, there is a case where refrigerating machine oil for improving the lubricity of a compressor does not melt together with refrigerant and is separated in two phases, although whether or not such a case occurs depends on the temperature and pressure at which the refrigerating machine oil is used. In general, refrigerant discharged from a compressor also contains refrigerating machine oil. Therefore, oil discharged from the compressor 101 flows through the gas cooler 102, etc. and is then stored in the liquid receiver 104. The liquid receiver 104 serves to separate the refrigerant into gas refrigerant and liquid refrigerant. Therefore, many liquid receivers are each configured to cause refrigerant to flow into each liquid receiver from an upper side thereof and flow out from a lower side of each liquid receiver. In such a liquid receiver, the refrigerant and the refrigerating machine oil are separated into two phases; and the oil stays in an upper side of the liquid receiver, and the refrigerant stays in a lower side of the liquid receiver Therefore, the oil that has flowed into the liquid receiver 104 does not return to the compressor 101 and is thus stored in the liquid receiver 104.

[0064] Regarding Embodiment 2, it will be described how the controller 300 returns oil stored in the liquid receiver 104 to the compressor 101 applying the control as described above regarding Embodiment 1. Fig. 7 is a flowchart illustrating the procedure of the control of the bypass regulating valve that is performed by the controller in Embodiment 2.

[0065] In step ST11, the storage determination unit 312 determines whether the operating time of the compressor 101 exceeds a set time. The set time is, for example, two hours. In the case where the operating time of the compressor 101 exceeds the set time, the storage determination unit 312 determines that a certain amount of refrigerating machine oil is discharged from the compressor 101 and the amount of refrigerating machine oil stored in the compressor 101 is reduced to a predetermined threshold or less. The set time and the threshold for the amount of stored refrigerating machine oil are stored as data in the memory not illustrated in the controller 300. It should be noted that the determination whether or not the amount of refrigerating machine oil stored in the compressor 101 is less than or equal to the threshold is not limited to the determination in step ST11 indicated in Fig. 7. An oil-level sensor may be provided in the compressor 101, and the storage determination unit 312 may determine the amount of refrigerating machine oil stored in the compressor 101, based on a measurement value obtained by measurement by the oil-level sensor.

Furthermore, the operating time may be a continuous operating time or an integrated value of intermittent operating time.

[0066] When it is determined in step ST11 that the operating time of the compressor 101 exceeds the set time, the opening-degree control unit 313 performs control in step ST12. In step ST12, the opening-degree control unit 313 increases the opening degree of the bypass regulating valve 107 as in step ST2 indicated in Fig. 6. Therefore, the amount of refrigerant that flows through the bypass regulating valve 107 increases, and the amount of refrigerant that is returned to the refrigerant inlet of the accumulator 108 increases. Thus, refrigerant stored in the liquid receiver 104 is moved to the accumulator 108, and refrigerating machine oil stored in the liquid receiver 104 is also moved together with the refrigerant to the accumulator 108.

[0067] Then, in step 5T13, the storage determination unit 312 determines whether or not a certain time elapses from the time when the control in step ST12 is performed. The certain time is, for example, five minutes. When it is determined in step ST13 that the certain time does not elapse, the opening-degree control unit 313 maintains the opening degree of the bypass regulating valve 107. In contrast, when it is determined in step S113 that the certain time elapses, the storage determination unit 312 determines that the refrigerant and the refrigerating machine oil stored in the liquid receiver 104 are sufficiently moved to the accumulator 108. Based on the result of the determination, the opening-degree control unit 313 performs control in step ST14. In step S114, the opening-degree control unit 313 decreases the opening degree of the bypass regulating valve 107. Since the opening degree of the bypass regulating valve 107 is decreased, the refrigerant accumulated in the accumulator 108 is sent to the liquid receiver 104.

[0068] The principle of returning of the refrigerating machine oil accumulated in the accumulator 108 to the compressor 101 will be described. Fig. 8 is a schematic diagram for explaining the configuration of the accumulator as illustrated in Fig. 1.

[0069] The accumulator 108 includes an inflow pipe 21 into which mixed liquid of refrigerant and refrigerating machine oil flows and an outflow pipe 22 from which gas refrigerant flows to the compressor 101. In the accumulator 108, in order to separate the refrigerant into two-phase gas-liquid refrigerant and extract only gas refrigerant from an upper side of the accumulator 108, a refrigerant suction port of the outflow pipe 22 is located above the oil level of the refrigerating machine oil obtained by the above separation. Furthermore, the accumulator 108 normally has a small hole 23 for returning refrigerating machine oil accumulated in a bottom portion of the accumulator 108 to the compressor 101 via a pipe not illustrated.

[0070] In steps ST12 to S113, the refrigerant and the refrigerating machine oil stored in the liquid receiver 104 moves to the accumulator 108. In the accumulator 108, the refrigerating machine oil is accumulated in the upper portion, and the refrigerant is accumulated in the lower portion. Therefore, the refrigerating machine oil has not yet returned to the compressor 101. Thus, after step ST13, the opening-degree control unit 313 decreases the opening degree of the bypass regulating valve 107 in step ST14. Therefore, the refrigerant accumulated in the accumulator 108 is sent out toward the liquid receiver 104, and the liquid levels of the refrigerant and the refrigerating machine oil accumulated in the accumulator 108 lower. When the position of a lower surface of the refrigerating machine oil lowers to a position close to the small hole 23 at the bottom of the accumulator 108, the refrigerating machine oil re-returns to the compressor 101. [0071] It should be noted that the determination in step ST13 is described above as the determination in the case where a parameter for determining whether or not refrigerant in the liquid receiver 104 is accumulated in the accumulator 108 is time. However, the parameter is not necessarily time. Sensors that measures the temperature, the pressure, and the liquid level of refrigerant at each of components may be provided, and at least one of the temperature, the pressure, and the liquid level of refrigerant may be used as the parameter [0072] When it is determined in step ST11 indicated in Fig. 7 that the operating time of the compressor 101 does not exceed the set time, the opening-degree control unit 313 performs control in step ST15. In step ST15, the opening-degree control unit 313 decreases the opening degree of the bypass regulating valve 107. However, in step S115 indicated in Fig. 7, when decreasing the opening degree of the bypass regulating valve 107, the opening-degree control unit 313 performs control such that the opening degree becomes higher than or equal to the threshold for the minimum opening degree, and the bypass regulating valve 107 is not fully closed, as in step 5T3 illustrated in Fig. 6 as described above in Embodiment 1. After steps ST14 and ST15, the step to be carried out by the controller 300 returns to step ST11 indicated in Fig. 7 (step 5T16).

[0073] As described above, in Embodiment 2, the controller 300 increases the opening degree of the bypass regulating valve 107, whereby refrigerant and refrigerating machine oil stored in the liquid receiver 104 can be moved to the accumulator 108.

Therefore, depletion of oil in the compressor 101 can be avoided, and the reliability of the refrigeration apparatus 1 can also be improved.

[0074] Regarding Embodiments 1 and 2, it is described above as the configuration examples illustrated in Figs. 1 and 3 that the first safety valve 109, the second safety valve 110, and the third safety valve 111 are provided in the refrigerant circuit 5.

However, since safety valves are relatively expansive, one or more of the safety valves may be replaced with other elements.

[0075] Fig. 9 is a refrigerant circuit diagram illustrating another configuration example of the refrigeration apparatus as illustrated in Fig. 1. As illustrated in Fig. 9, in a refrigeration apparatus lb, a capillary tube 116 is provided in a circuit that bypasses the high-pressure expansion valve 103. Furthermore, a check valve 115 is provided at a pipe that connects the refrigerant inlet side of the accumulator 108 and the refrigerant outlet side of the second heat exchanger 106. The check valve 115 allows the refrigerant to flow from the suction side of the compressor to the refrigerant outlet side of the high-pressure expansion valve, and prevents the refrigerant from flowing in the opposite direction to the above flow direction. The circuit that bypasses the high-pressure expansion valve 103 serves as a valve corresponding to the third safety valve 111, and the check valve 115 serves as a valve corresponding to the second safety valve 110. Unlike the configuration example illustrated in Fig. 1, the refrigeration apparatus lb includes neither the second safety valve 110 nor the third safety valve 111. The refrigeration apparatus lb adopts inexpensive components such as the capillary tube 116 and the check valve 115, in place of the second safety valve 110 and the third safety valve 111.

[0076] The high-pressure expansion valve 103 is, for example, an electronic expansion valve whose opening degree can be adjusted, and is fully closed when not supplied with current, for example, because of a power failure. In this example, the capillary tube 116 is provided in parallel with the high-pressure expansion valve 103. Therefore, even when the high-pressure expansion valve 103 is fully closed because it is not supplied with current, for example, due to a power failure, the gas cooler 102 and the first heat exchanger 105 in the refrigerant circuit 5 can be bypassed. Therefore, refrigerant stored in a flow passage from the compressor 101 to the high-pressure expansion valve 103 flows to the refrigerant outlet side of the high-pressure expansion valve 103. Furthermore, since the check valve 115 is provided as illustrated in Fig. 9, when the pressure of refrigerant in a region from the low-pressure expansion valve 201 to the suction side of the compressor 101 is higher than the pressure of refrigerant in a region from the high-pressure expansion valve 103 to the low-pressure expansion valve 201, the refrigerant flows toward the first safety valve 109. Therefore, with the use of the capillary tube 116 and the check valve 115, when the pressure of the refrigerant in the refrigerant circuit 5 rises, the refrigerant flows toward the first safety valve 109, and safety for the case where the pressure of the refrigerant rises can be ensured. It should be noted that in place of the capillary tube 116, a solenoid valve, which is closed when supplied with current and is opened when a power failure occurs, may be used.

[0077] Furthermore, the refrigeration apparatus lb of Embodiment 2 may include the refrigerant circuit 5 in which the compressor 101, the gas cooler 102, the low-pressure expansion valve 201, and the evaporator 202 are connected by refrigerant pipes such that refrigerant circulates and the first safety valve 109 provided between the gas cooler 102 and the low-pressure expansion valve 201. The check valve 115 is provided at the pipe that is connected in parallel with the low-pressure expansion valve 201 and the evaporator 202, and safety for the case where the pressure of refrigerant rises can thus be ensured. In the case where the high-pressure expansion valve 103 is provided between the gas cooler 102 and the low-pressure expansion valve 201, by providing the capillary tube 116 in parallel with the high-pressure expansion valve 103, safety for the case where the pressure of refrigerant rises can be ensured. In the case where the liquid receiver 104 is provided of downstream of the gas cooler 102 in the flow of refrigerant, by providing the first safety valve 109 downstream of the liquid receiver 104 in the flow of refrigerant, the pressure can be promptly reduced.

[0078] Furthermore, in the configuration examples illustrated in Figs. 1, 3, and 9, the first heat exchanger 105 is provided on the refrigerant inlet side of the liquid receiver 104, the first heat exchanger 105 may be replaced by another element. Fig. 10 is a refrigerant circuit diagram illustrating still another configuration example of the refrigeration apparatus illustrated in Fig. 1.

[0079] As illustrated in Fig. 10, a refrigeration apparatus 1 c includes two bypass circuits 7a and 7c in place of the bypass circuit 7 as illustrated in Fig. 1. The configuration of the bypass circuit 7a is the same as that of the bypass circuit 7a as illustrated in Fig. 3, and its detailed description will thus be omitted. A pipe that releases gas refrigerant from an upper portion of the liquid receiver 104 is provided in the bypass circuit 7c. The pipe joins the bypass circuit 7a and is then connected to the refrigerant inlet side of the accumulator 108. The bypass circuit 7c includes a bypass regulating valve 107c. The refrigeration apparatus lc does not include the first heat exchanger 105 that is provided as illustrated in Fig. 1.

[0080] The bypass circuit 7c as illustrated in Fig. 10 serves to release refrigerant gas from the upper portion of the liquid receiver 104, and can obtain the same advantage as the first heat exchanger 105. To be more specific, the controller 300 adjusts the opening degree of the bypass regulating valve 107c, whereby refrigerant and refrigerating machine oil in the liquid receiver 104 can be moved toward the accumulator 108. In the refrigeration apparatus lc as illustrated in Fig. 10, the accuracy of control of refrigerant that flows out to the bypass circuits 7a and 7c can be improved, as compared with the refrigeration apparatus 1 as illustrated in Fig. 1. In contrast, the number of expansion valves provided in the refrigeration apparatus 1 as illustrated in Fig. 1 is smaller than the number of expansion valves provided in the refrigeration apparatus lc as illustrated in Fig. 10. Therefore, in the refrigeration apparatus 1 as illustrated in Fig. 1, the manufacturing cost is not high, and the control of the expansion valves is not complicated.

Reference Signs List [0081] 1, la to lc refrigeration apparatus, 5 refrigerant circuit, 7, 7a to 7c bypass circuit, 21 inflow pipe, 22 outflow pipe, 23 small hole, 100 outdoor unit, 101 compressor, 102 gas cooler, 102a fan, 103 high-pressure expansion valve, 104 liquid receiver, 105 first heat exchanger, 106 second heat exchanger, 107, 107a to 107c bypass regulating valve, 108 accumulator, 109 first safety valve, 110 second safety valve, 111 third safety valve, 112 to 114 pressure sensor, 115 check valve, 116 capillary tube, 200 indoor unit, 201 low-pressure expansion valve, 202 evaporator, 300 controller, 301, 302 extension pipe, 311 refrigeration cycle unit, 312 storage determination unit, 313 opening-degree control unit