HEAT SOURCE UNIT AND FREEZING APPARATUS

Abstract

 An oil recovery operation includes a first operation of decreasing an opening degree of a heat source-side expansion valve (28), and a second operation of increasing the opening degree of the heat source-side expansion valve (28), after the first operation. A control unit (80) performs the second operation when a first condition is established in the first operation. The first condition includes at least a condition that a difference ΔP between a pressure of a refrigerant downstream of the heat source-side expansion valve (28) on a liquid pipe (43) and a pressure of the refrigerant sucked in a compression element (C) has a value less than a predetermined value.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a heat source-side unit and a refrigeration apparatus.

BACKGROUND ART

[0002] Patent Literature 1 discloses a refrigeration apparatus configured to carry out an oil recovery operation for returning an oil stored in a utilization-side heat exchanger to a compressor. Specifically, the oil recovery operation involves decreasing an opening degree of a first expansion valve on a liquid pipe. The refrigeration apparatus thus reduces a flow rate and a pressure of a refrigerant flowing through the utilization-side heat exchanger, and increases a degree of suction superheating. Accordingly, an opening degree of a utilization-side expansion valve gradually increases. The oil recovery operation also involves increasing the opening degree of the first expansion valve after a lapse of a predetermined first time t1 from the decreasing of the opening degree of the first expansion valve. The refrigeration apparatus thus increases the flow rate of the refrigerant flowing through the utilization-side heat exchanger. The refrigerant is compatibilized with the refrigerating machine oil in the utilization-side heat exchanger, and is returned together with the refrigerating machine oil to the compressor.

CITATION LIST

PATENT LITERATURE

[0003] Patent Literature 1: JP 2018-084376 A

SUMMARY OF THE INVENTION

<Technical Problem>

[0004] As disclosed in Patent Literature 1, the refrigeration apparatus decreases the opening degree of the first expansion valve and, after the lapse of the predetermined first time t1, determines that the opening degree of the utilization-side expansion valve has increased. The refrigeration apparatus then increases the opening degree of the first expansion valve. However, this determination using a timer lacks accuracy in determining that the opening degree of the utilization-side expansion valve has increased.

[0005] An object of the present disclosure is to improve accuracy in determining that an opening degree of a utilization-side expansion valve has increased in a first operation for decreasing an opening degree of a heat source-side expansion valve, in an oil recovery operation.

<Solution to Problem>

[0006] A first aspect is directed to a heat source-side unit including a compression element (C), a liquid pipe (43), a heat source-side expansion valve (28) connected to the liquid pipe (43), and a heat source-side heat exchanger (25). The heat source-side unit is connected to a utilization-side unit (70) including a utilization-side heat exchanger (73) and a utilization-side expansion valve (72) to constitute, in conjunction with the utilization-side unit (70), a refrigerant circuit (10) configured to perform a refrigeration cycle in which the heat source-side heat exchanger (25) functions as a radiator and the utilization-side heat exchanger (73) functions as an evaporator. The heat source-side unit further includes a control unit (80) configured to control the heat source-side unit (20) to carry out an oil recovery operation of recovering an oil from the utilization-side heat exchanger (73) in the refrigeration cycle. The oil recovery operation includes a first operation of decreasing an opening degree of the heat source-side expansion valve (28), and a second operation of increasing the opening degree of the heat source-side expansion valve (28), after the first operation. The control unit (80) performs the second operation when a first condition is established in the first operation. The first condition includes at least a condition that a difference ΔP between a pressure of a refrigerant downstream of the heat source-side expansion valve (28) on the liquid pipe (43) and a pressure of the refrigerant sucked in the compression element (C) has a value less than a predetermined value.

[0007] According to the first aspect, in the first operation, the first condition includes the condition that the difference ΔP between the pressure of the refrigerant downstream of the heat source-side expansion valve (28) on the liquid pipe (43) and the pressure of the refrigerant sucked in the compression element (C) has a value less than the predetermined value. This configuration thus improves accuracy of a determination that the opening degree of the utilization-side expansion valve has increased.

[0008] According to a second aspect, in the first aspect, the first condition includes a condition that a degree of suction superheating has a value more than a first value.

[0009] According to the second aspect, in the first operation, the first condition includes the condition that the degree of suction superheating is large. This configuration enables improvement in accuracy of a determination that the opening degree of the utilization-side expansion valve (72) has increased.

[0010] According to a third aspect, in the first or second aspect, the control unit (80) performs a third operation of changing the opening degree of the heat source-side expansion valve (28) to the opening degree immediately before a start of the first operation when a second condition is established in the second operation, and the second condition includes a condition that a degree of suction superheating has a value less than a second value.

[0011] According to the third aspect, in the second operation, the second condition includes the condition that the degree of suction superheating has a value less than the second value. This configuration enables improvement in accuracy of a determination that the oil has been returned to the compression element (C).

[0012] According to a fourth aspect, in any one of the first to third aspects, the control unit (80) performs a third operation of changing the opening degree of the heat source-side expansion valve (28) to the opening degree immediately before a start of the first operation when a second condition is established in the second operation, and the second condition includes a condition that the pressure of the refrigerant downstream of the heat source-side expansion valve (28) on the liquid pipe (43) has a value more than a predetermined value.

[0013] According to the fourth aspect, in the second operation, the second condition includes the condition that the pressure of the refrigerant downstream of the heat source-side expansion valve (28) has a value more than the predetermined value. This configuration enables improvement in accuracy of a determination that the oil has been returned to the compression element (C).

[0014] According to a fifth aspect, in any one of the first to fourth aspects, an increasing speed of the opening degree of the heat source-side expansion valve (28) in the second operation is faster than a decreasing speed of the opening degree of the heat source-side expansion valve (28) in the first operation.

[0015] According to the fifth aspect, in the second operation, on the condition that the opening degree of the utilization-side expansion valve (72) increases, the oil in the utilization-side heat exchanger (73) can be quickly returned together with the refrigerant to the compressor (21, 22, 23).

[0016] A sixth aspect is directed to a refrigeration apparatus including the heat source-side unit (20) according to any one of the first to fifth aspects, and a utilization-side unit (70) including a utilization-side heat exchanger (73) and a utilization-side expansion valve (72). The heat source-side unit (20) and the utilization-side unit (70) are connected to constitute a refrigerant circuit (10) configured to perform a refrigeration cycle in which the heat source-side heat exchanger (25) functions as a radiator and the utilization-side heat exchanger (73) functions as an evaporator.

[0017] A seventh aspect is directed to the refrigeration apparatus according to the sixth aspect, in which the utilization-side expansion valve (72) is a thermostatic expansion valve.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] 

FIG. 1 is a diagram of a piping system in a refrigeration apparatus according to an embodiment.

FIG. 2 is a diagram (equivalent to FIG. 1) of a flow of a refrigerant during a cooling-facility operation.

FIG. 3 is a diagram (equivalent to FIG. 1) of a flow of the refrigerant during a defrosting operation.

FIG. 4 is a flowchart of an oil return operation.

DESCRIPTION OF EMBODIMENTS

[0019] Embodiments will be described below with reference to the drawings. The following embodiments are preferable examples in nature and are not intended to limit the scope of the present invention, products to which the present invention is applied, or the use of the present invention.

<General configuration>

[0020] A refrigeration apparatus (1) according to a first embodiment is configured to cool air as a cooling target. The term "cooling target" as used herein may involve air in a facility such as a refrigerator, a freezer, or a showcase.

[0021] As illustrated in FIG. 1, the refrigeration apparatus (1) includes an outdoor unit (20) installed outdoors and two cooling facility units (70) each configured to cool inside air. The refrigeration apparatus (1) does not necessarily include two cooling facility units (70). For example, the refrigeration apparatus (1) may include one cooling facility unit (70). Alternatively, the refrigeration apparatus (1) may include three or more cooling facility units (70). The outdoor unit (20) is connected to the two cooling facility units (70) via a liquid connection pipe (14) and a gas connection pipe (13). A refrigerant circuit (10) is thus constituted in the refrigeration apparatus (1). A vapor compression refrigeration cycle is achieved in such a manner that a refrigerant circulates through the refrigerant circuit (10).

<Outline of outdoor unit>

[0022] The outdoor unit (20) is a heat source-side unit. The outdoor unit (20) is installed outdoors. The outdoor unit (20) includes a heat source-side circuit (20a) and an outdoor fan (F1). The heat source-side circuit (20a) mainly includes three compressors (21, 22, 23) constituting a compression element (C), a four-way switching valve (24), an outdoor heat exchanger (25), a receiver (26), a subcooling heat exchanger (27), and an outdoor expansion valve (28).

[0023] The heat source-side circuit (20a) includes a gas shutoff valve (11) and a liquid shutoff valve (12). The gas connection pipe (13) is connected to the gas shutoff valve (11). The liquid connection pipe (14) is connected to the liquid shutoff valve (12).

<Compression element and its peripheral structure>

[0024] In the first embodiment, the compression element (C) includes the three compressors (21, 22, 23). In the heat source-side circuit (20a), the three compressors (21, 22, 23) are connected in parallel. The three compressors (21, 22, 23) include a first compressor (21), a second compressor (22), and a third compressor (23). Each of the compressors (21, 22, 23) is, for example, a scroll compressor. The first compressor (21) is of a variable capacity type. In the first compressor (21), power from a power source is supplied to an electric motor via an inverter circuit. Each of the second compressor (22) and the third compressor (23) is of a fixed capacity type.

[0025] The first compressor (21) has a discharge portion to which a first discharge pipe (31) is connected. The first compressor (21) has a suction portion to which a first suction pipe (34) is connected. The second compressor (22) has a discharge portion to which a second discharge pipe (32) is connected. The second compressor (22) has a suction portion to which a second suction pipe (35) is connected. The third compressor (23) has a discharge pipe (33) to which a third discharge pipe (33) is connected. The third compressor (23) has a suction portion to which a third suction pipe (36) is connected.

[0026] The first discharge pipe (31), the second discharge pipe (32), and the third discharge pipe (33) each have an outlet end to which an inlet end of a main discharge pipe (37) is connected. The first suction pipe (34), the second suction pipe (35), and the third suction pipe (36) each have an inlet end to which an outlet end of a main suction pipe (38) is connected.

[0027] A first check valve (CV1) is connected to the first discharge pipe (31). A second check valve (CV2) is connected to the second discharge pipe (32). A third check valve (CV3) is connected to the third discharge pipe (33). Each of the first check valve (CV1), the second check valve (CV2), and the third check valve (CV3) permits a flow of the refrigerant from the discharge portion of the corresponding compressor (21, 22, 23) to the main discharge pipe (37) and prohibits a flow of the refrigerant from the main discharge pipe (37) to the discharge portion of the corresponding compressor (21, 22, 23).

[0028] The main discharge pipe (37) is provided with an oil separator (39). The oil separator (39) is configured to separate oil from the refrigerant compressed by the compression element (C). The oil separator (39) is connected to an inlet end of an oil return pipe (39a). The oil return pipe (39a) has an outlet end connected to an injection circuit (I). The oil return pipe (39a) is also connected to an oil return valve (39b) as an electric valve. The oil separated by the oil separator (39) is returned to a compression chamber (an intermediate-pressure portion) of each compressor (21, 22, 23) via the oil return pipe (39a) and the injection circuit (I).

<Four-way switching valve>

[0029] The four-way switching valve (24) has a first port (P1), a second port (P2), a third port (P3), and a fourth port (P4). The first port (P1) is connected to an outlet end of the main discharge pipe (37). The second port (P2) is connected to an inlet end of the main suction pipe (38). The third port (P3) is connected to a gas end of the outdoor heat exchanger (25). The fourth port (P4) is connected to the gas shutoff valve (11).

[0030] The four-way switching valve (24) is switched to a first state (a state indicated by a solid line in FIG. 1) and to a second state (a state indicated by a broken line in FIG. 1). In the four-way switching valve (24) switched to the first state, the first port (P1) communicates with the third port (P3) and the second port (P2) communicates with the fourth port (P4). In the four-way switching valve (24) switched to the second state, the first port (P1) communicates with the fourth port (P4) and the second port (P2) communicates with the third port (P3).

<Outdoor heat exchanger and its peripheral structure>

[0031] The outdoor heat exchanger (25) is a heat source-side heat exchanger. The outdoor heat exchanger (25) is a fin-and-tube heat exchanger. The outdoor fan (F1) is disposed near the outdoor heat exchanger (25). The outdoor fan (F1) provides outdoor air that passes through the outdoor heat exchanger (25). The outdoor heat exchanger (25) causes the outdoor air provided by the outdoor fan (F1) to exchange heat with the refrigerant.

<Receiver, subcooling heat exchanger, and their peripheral structures>

[0032] The receiver (26) is configured to store the refrigerant. The receiver (26) is a vertically elongated hermetic container.

[0033] The subcooling heat exchanger (27) includes a first flow path (27a) and a second flow path (27b). The subcooling heat exchanger (27) causes the refrigerant flowing through the first flow path (27a) to exchange heat with the refrigerant flowing through the second flow path (27b).

[0034] A first pipe (41) is connected between a liquid end of the outdoor heat exchanger (25) and a top portion of the receiver (26). A fourth check valve (CV4) is connected to the first pipe (41). The fourth check valve (CV4) permits a flow of the refrigerant from the outdoor heat exchanger (25) to the receiver (26) and prohibits a flow of the refrigerant from the receiver (26) to the outdoor heat exchanger (25).

[0035] A second pipe (42) is connected between a bottom portion of the receiver (26) and a first end of the first flow path (27a) of the subcooling heat exchanger (27). A third pipe (43) is connected between a second end of the first flow path (27a) and the liquid shutoff valve (12). The third pipe (43) makes up a part of a liquid pipe. A fifth check valve (CV5) is connected to the third pipe (43). The fifth check valve (CV5) permits a flow of the refrigerant from the second end of the first flow path (27a) to the liquid shutoff valve (12) and prohibits a flow of the refrigerant from the liquid shutoff valve (12) to the second end of the first flow path (27a).

[0036] The outdoor expansion valve (28) is disposed between the second end of the first flow path (27a) and the fifth check valve (CV5) and is connected to the third pipe (43). The outdoor expansion valve (28) is a heat source-side expansion valve. The outdoor expansion valve (28) is a decompression mechanism configured to decompress the refrigerant. The outdoor expansion valve (28) is an electronic expansion valve.

[0037] A fourth pipe (44) is connected to the third pipe (43). The fourth pipe (44) has a first end connected to the third pipe (43) and located between the fifth check valve (CV5) and the liquid shutoff valve (12). The fourth pipe (44) has a second end connected to the first pipe (41) and located between the fourth check valve (CV4) and the receiver (26). A sixth check valve (CV6) is connected to the fourth pipe (44). The sixth check valve (CV6) permits a flow of the refrigerant from the third pipe (43) to the first pipe (41) and prohibits a flow of the refrigerant from the first pipe (41) to the third pipe (43).

[0038] A fifth pipe (45) is connected to the third pipe (43). The fifth pipe (45) has a first end connected to the third pipe (43) and located between the outdoor expansion valve (28) and the fifth check valve (CV5). The fifth pipe (45) has a second end connected to the first pipe (41) and located between the fourth check valve (CV4) and the outdoor heat exchanger (25). A seventh check valve (CV7) is connected to the fifth pipe (45). The seventh check valve (CV7) permits a flow of the refrigerant from the third pipe (43) to the first pipe (41) and prohibits a flow of the refrigerant from the first pipe (41) to the third pipe (43).

<Injection circuit>

[0039] The heat source-side circuit (20a) includes the injection circuit (I). The injection circuit (I) is configured to guide the intermediate-pressure refrigerant to the intermediate-pressure portion of the compression element (C). The injection circuit (I) includes one branch pipe (51), one relay pipe (52), and three injection pipes (53, 54, 55).

[0040] The branch pipe (51) has an inlet end connected to the third pipe (43) and located between the first flow path (27a) and the outdoor expansion valve (28). The branch pipe (51) has an outlet end connected to an inlet end of the second flow path (27b). An injection valve (59) is connected to the branch pipe (51). The injection valve (59) is an electronic expansion valve.

[0041] The relay pipe (52) has an inlet end connected to an outlet end of the second flow path (27b). The relay pipe (52) is connected to the outlet end of the oil return pipe (39a). The relay pipe (52) has an outlet portion connected to an inlet end of each of the first injection pipe (53), the second injection pipe (54), and the third injection pipe (55).

[0042] The first injection pipe (53) has an outlet end communicating with the compression chamber of the first compressor (21). The second injection pipe (54) has an outlet end communicating with the compression chamber of the second compressor (22). The third injection pipe (55) has an outlet end communicating with the compression chamber of the third compressor (23).

[0043] A first electric valve (56) is connected to the first injection pipe (53). A second electric valve (57) is connected to the second injection pipe (54). A third electric valve (58) is connected to the third injection pipe (55). Each electric valve (56, 57, 58) is a flow rate adjustment valve. Each electric valve (56, 57, 58) adjusts the flow rate of the refrigerant flowing through the corresponding injection pipe (53, 54, 55).

<Sensors of heat source-side unit>

[0044] The heat source-side unit (20) includes a plurality of sensors for detecting physical quantities of the refrigerant in the heat source-side circuit (20a). The sensors include at least a first discharge temperature sensor (61), a second discharge temperature sensor (62), a third discharge temperature sensor (63), a high-pressure sensor (64), a suction temperature sensor (65), a low-pressure sensor (67), a liquid-side pressure sensor (68), and an intermediate-pressure sensor (69).

[0045] The first discharge temperature sensor (61) is configured to detect a temperature (Td1) of the refrigerant in the first discharge pipe (31). The second discharge temperature sensor (62) is configured to detect a temperature (Td2) of the refrigerant in the second discharge pipe (32). The third discharge temperature sensor (63) is configured to detect a temperature (Td3) of the refrigerant in the third discharge pipe (33). The high-pressure sensor (64) is configured to detect a discharge pressure at the compression element (C) (i.e., a high pressure (HP) at the refrigerant circuit (10)). The suction temperature sensor (65) is configured to detect a temperature of the refrigerant sucked in the compression element (C). The low-pressure sensor (67) is configured to detect a suction pressure at the compression element (C) (i.e., a low pressure (LP) at the refrigerant circuit (10)). The liquid-side pressure sensor (68) is configured to detect a pressure (a liquid pressure (Ps)) of the liquid refrigerant in the third pipe (43). The intermediate-pressure sensor (69) is configured to detect a pressure (MP) of the refrigerant in the relay pipe (52) of the injection circuit (I).

[0046] The low-pressure sensor (67) and the suction temperature sensor (66) constitute a degree of suction superheating detection unit for detecting a degree of suction superheating (SSH) of the compression element (C). Specifically, the controller (80) derives the degree of suction superheating (SSH) from a difference between a saturation temperature associated with the low pressure (LP) detected by the low-pressure sensor (67) and the temperature detected by the suction temperature sensor (66).

[0047] The high-pressure sensor (64) and the three discharge temperature sensors (61, 62, 63) constitute a degree of discharge superheating detection unit for detecting a degree of discharge superheating (DSH) of the compression element (C). Specifically, the controller (80) derives the degree of discharge superheating (DSH) from a difference between a saturation temperature associated with the high pressure (HP) detected by the high-pressure sensor (64) and the temperatures detected by the respective discharge temperature sensors (61, 62, 63) (e.g., an average value of these temperatures).

<Cooling facility unit>

[0048] Each cooling facility unit (70) is a utilization-side unit. Each cooling facility unit (70) includes a utilization-side circuit (70a) and an inside fan (F2).

[0049] The utilization-side circuits (70a) are connected in parallel to the liquid connection pipe (14) and the gas connection pipe (13). Each utilization-side circuit (70a) includes an open-close valve (71), an inside expansion valve (72), and an inside heat exchanger (73) arranged in this order from the liquid end toward the gas end.

[0050] The open-close valve (71) is an electromagnetic open-close valve for making and breaking the utilization-side circuit (70a). The open-close valve (71) is open during a normal operation.

[0051] The inside expansion valve (72) is a utilization-side expansion valve. The inside expansion valve (72) is a temperature-sensitive automatic expansion valve. The inside expansion valve (72) has an opening degree adjustable in accordance with a degree of superheating of the refrigerant flowing out of the utilization-side heat exchanger (73) functioning as an evaporator. This degree of superheating corresponds to the degree of suction superheating (SSH) of the refrigerant sucked in the compression element (C).

[0052] As illustrated in FIG. 1, more specifically, the inside expansion valve (72) includes an expansion valve main body (72a), a feeler bulb (72b), and a capillary tube (72c). The expansion valve main body (72a) is connected between the open-close valve (71) and the inside heat exchanger (73) in the utilization-side circuit (70a). The feeler bulb (72b) is in contact with a gas-end pipe of the utilization-side heat exchanger (73). The expansion valve main body (72a) and the feeler bulb (72b) are connected to each other with the capillary tube (72c) interposed therebetween. A change in degree of superheating of the refrigerant flowing out of the inside heat exchanger (73) functioning as an evaporator causes a change in pressure of working fluid enclosed in each of the feeler bulb (72b) and the capillary tube (72c). This internal pressure change causes a displacement of a diaphragm of the expansion valve main body (72a), so that the opening degree of the inside expansion valve (72) is adjusted.

[0053] The inside heat exchanger (73) is a utilization-side heat exchanger. The inside heat exchanger (73) is a fin-and-tube heat exchanger. The inside fan (F2) is disposed near the inside heat exchanger (73). The inside fan (F2) provides inside air that passes through the inside heat exchanger (73). The inside heat exchanger (73) causes the inside air provided by the inside fan (F2) to exchange heat with the refrigerant.

<Controller>

[0054] The outdoor unit (20) includes a controller (80). The controller (80) includes a microcomputer mounted on a control board, and a memory device (specifically, a semiconductor memory) storing software for operating the microcomputer.

[0055] The controller (80) is configured to control each component of the outdoor unit (21, 22, 23), based on an operation command and a detection signal from each sensor. The controller (80) controls each component so as to switch a cooling-facility operation, a defrosting operation, and an oil return operation. The cooling-facility operation is an operation for causing each cooling facility unit (70) to cool the inside air. The defrosting operation is an operation for melting frost on a surface of each inside heat exchanger (73). The oil return operation is an operation for recovering the oil (i.e., the refrigerating machine oil) from each inside heat exchanger (73) and returning the oil to each compressor (21, 22, 23).

[0056] During the oil return operation, the controller (80) controls the outdoor unit (20) to perform a first operation, a second operation, and a third operation. The first operation is an operation for decreasing the opening degree of the outdoor expansion valve (28). The second operation is an operation for increasing the opening degree of the outdoor expansion valve (28). The third operation is an operation for returning the opening degree of the outdoor expansion valve (28) to the opening degree immediately before a start of the first operation.

[0057] The controller (80) determines whether to perform the second operation in the first operation. This determination is made based on a first condition (the details thereof will be described later). The controller (80) makes a determination as to whether to perform the third operation in the second operation. This determination is made based on a second condition (the details thereof will be described later).

-Operations-

[0058] Next, a description will be given of operations to be carried out by the refrigeration apparatus (1) according to the first embodiment.

<Cooling-facility operation>

[0059] During the cooling-facility operation, each compressor (21, 22, 23), the outdoor fan (F1), and each inside fan (F2) operate. The four-way switching valve (24) is switched to the first state, and the outdoor expansion valve (28) is fully opened. Each open-close valve (71) is opened. The opening degree of each inside expansion valve (72) is appropriately adjusted. Specifically, the opening degree of each inside expansion valve (72) is adjusted such that the degree of superheating of the refrigerant flowing out of the inside heat exchanger (73) is maintained at a predetermined value. The opening degrees of the injection valve (59), first electric valve (56), second electric valve (57), and third electric valve (58) are appropriately adjusted.

[0060] During the cooling-facility operation, a first refrigeration cycle is achieved, in which the outdoor heat exchanger (25) functions as a radiator or a condenser and each inside heat exchanger (73) functions as an evaporator.

[0061] As illustrated in FIG. 2, during the cooling-facility operation, when each compressor (21, 22, 23) compresses the refrigerant, then the refrigerant flows into the outdoor heat exchanger (25). In the outdoor heat exchanger (25), the refrigerant dissipates heat toward outdoor air. After the refrigerant dissipates heat in the outdoor heat exchanger (25), the refrigerant flows through the first pipe (41), the receiver (26), and the second pipe (42). The refrigerant then flows through the first flow path (27a) of the subcooling heat exchanger (27).

[0062] When the injection valve (59) is opened, a part of the refrigerant in the third pipe (43) flows into the branch pipe (51). After the injection valve (59) decompresses the refrigerant in the branch pipe (51), the refrigerant flows into the second flow path (27b) of the subcooling heat exchanger (27). In the subcooling heat exchanger (27), the refrigerant in the second flow path (27b) exchanges heat with the refrigerant in the first flow path (27a). The refrigerant in the second flow path (27b) evaporates by suction of heat from the refrigerant in the first flow path (27a). The refrigerant in the first flow path (27a) is thus cooled, so that the degree of subcooling of the refrigerant increases.

[0063] The refrigerant then flows through the second flow path (27b), the relay pipe (52), and each injection pipe (53, 54, 55). The refrigerant then flows into the compression chamber of each compressor (21, 22, 23).

[0064] The refrigerant cooled in the first flow path (27a) flows through the third pipe (43) and the liquid connection pipe (14), and then flows into each cooling facility unit (70).

[0065] In each cooling facility unit (70), after the inside expansion valve (72) decompresses the refrigerant, the refrigerant flows into the inside heat exchanger (73). In the inside heat exchanger (73), the refrigerant evaporates by suction of heat from the inside air. The inside air is thus cooled.

[0066] After each utilization-side heat exchanger (73) evaporates the refrigerant, the refrigerant flows into the outdoor unit (20) via the gas connection pipe (13). The refrigerant then flows through the main suction pipe (38) and flows into each compressor (21, 22, 23).

<Defrosting operation>

[0067] During the defrosting operation, each compressor (21, 22, 23), the outdoor fan (F1), and each inside fan (F2) operate. The four-way switching valve (24) is switched to the second state, and each inside expansion valve (72) is fully opened. Each open-close valve (71) is opened. The opening degree of the outdoor expansion valve (28) is adjusted. As illustrated in FIG. 3, during the defrosting operation, the refrigerant may flow through the injection circuit (I) in a manner similar to that during the cooling-facility operation. However, the refrigerant does not necessarily flow through the injection circuit (I) in such a manner that the injection valve (59) is fully closed.

[0068] During the defrosting operation, a second refrigeration cycle is achieved, in which each inside heat exchanger (73) functions as a radiator or a condenser and the outdoor heat exchanger (25) functions as an evaporator.

[0069] As illustrated in FIG. 3, during the defrosting operation, when each compressor (21, 22, 23) compresses the refrigerant, then the refrigerant flows into each cooling facility unit (70) via the gas connection pipe (13). In each cooling facility unit (70), the refrigerant flows through the inside heat exchanger (73). In the inside heat exchanger (73), the refrigerant melts frost on the surface of the inside heat exchanger (73). When the refrigerant dissipates heat in each inside heat exchanger (73), then the refrigerant flows into the outdoor unit (20) via the liquid connection pipe (14).

[0070] In the outdoor unit (20), the refrigerant flows through the fourth pipe (44), the receiver (26), the second pipe (42), the first flow path (27a) of the subcooling heat exchanger (27), and the third pipe (43) in this order. When the refrigerant flows out of the third pipe (43), the outdoor expansion valve (28) decompresses the refrigerant. The refrigerant then flows through the fifth pipe (45) and the outdoor heat exchanger (25) in this order. In the outdoor heat exchanger (25), the refrigerant evaporates by suction of heat from the outdoor air. After the outdoor heat exchanger (25) evaporates the refrigerant, the refrigerant flows into each compressor (21, 22, 23) via the main suction pipe (38).

<Oil recovery operation>

[0071] Next, a specific description will be given of the oil recovery operation. The oil return operation is carried out when a predetermined condition is established in the cooling-facility operation. During the oil return operation, each compressor (21, 22, 23), the outdoor fan (F1), and each inside fan (F2) operate. The four-way switching valve (24) is switched to the first state. Each open-close valve (71) is opened. The opening degree of each inside expansion valve (72) is appropriately adjusted. Specifically, the opening degree of each inside expansion valve (72) is adjusted such that the degree of superheating of the refrigerant flowing out of the inside heat exchanger (73) is maintained at a predetermined value. The opening degrees of the injection valve (59), first electric valve (56), second electric valve (57), and third electric valve (58) are appropriately adjusted.

[0072] It should be noted that the oil recovery operation to be described below is an example of simultaneously recovering the oils from all the inside heat exchangers (73).

[0073] As illustrated in FIG. 4, when the controller (80) receives a command for carrying out the oil recovery operation, in step ST1, a storage unit of the controller (80) stores a current opening degree (pls1) of the outdoor expansion valve (28). This current opening degree (Pls1) corresponds to, for example, a maximum opening degree of the outdoor expansion valve (28). Next, in step ST2, the controller (80) performs the first operation.

[0074] The controller (80) performs the first operation to gradually decrease the opening degree of the outdoor expansion valve (28). Specifically, the controller (80) performs the first operation to decrease the opening degree of the outdoor expansion valve (28) stepwise every predetermined time ΔT1. It is assumed herein that EV1 represents a next opening degree (pulse) of the outdoor expansion valve (28) after a lapse of the predetermined time ΔT1, and EV1' represents a current opening degree (pulse) of the outdoor expansion valve (28). The controller (80) performs the first operation to decrease the opening degree of the outdoor expansion valve (28) such that a relation of EV1 = α × EV1' is satisfied every predetermined time ΔT1. The predetermined time ΔT1 is set at, for example, 15 seconds. In this relation, α is set at 0.75. In other words, in the first operation, the opening degree (pulse) of the outdoor expansion valve (28) decreases by 25% every 15 seconds. The controller (80) performs the first operation until the first condition is established in step ST3.

[0075] In the first operation, when the opening degree of the outdoor expansion valve (28) decreases, the outdoor expansion valve (28) decompresses the refrigerant. The decompression of the refrigerant reduces the flow rate and pressure of the refrigerant flowing through each utilization-side heat exchanger (73). This results in an increase of the degree of superheating of the refrigerant flowing out of each inside heat exchanger (73), so that the opening degree of each inside expansion valve (72) gradually increases.

[0076] In step ST3, the controller (80) determines whether the first condition for performing the second operation is established in the first operation. The first condition includes the following conditions (a) to (e). According to the first embodiment, when one of the conditions (a) to (e) is established, the processing proceeds to steps ST4 to S6 in which the controller (80) performs the second operation.

(a) A difference ΔP (= Ps - LP) between the liquid pressure (Ps) detected by the liquid-side pressure sensor (68) and the low pressure (LP) detected by the low-pressure sensor (67) has a value less than a predetermined value. This predetermined value is set at, for example, several hundred kilopascals.

(b) The degree of suction superheating (SSH) has a value more than a predetermined value (a first value). This first value is set at, for example, several ten degrees centigrade.

(c) The low pressure (LP) has a value less than a predetermined value. This predetermined value is set at several ten kilopascals.

(d) The high pressure (HP) has a value more than a predetermined value. This predetermined value is set at several hundred megapascals.

(e) A predetermined time t1 has elapsed after the first operation is performed. The predetermined time t1 is set at, for example, several minutes.

[0077] The condition (a) is a condition for determining that the opening degree of each inside expansion valve (72) has satisfactorily increased in the first operation. The liquid pressure (Ps) of the refrigerant downstream of the outdoor expansion valve (28) corresponds to the pressure at the inlet side of each inside expansion valve (72). The low pressure (LP) corresponds to the pressure at the outlet side of each inside expansion valve (72). Therefore, the difference ΔP corresponds to the pressure of the refrigerant decompressed by each inside expansion valve (72). The controller (80) thus accurately determines that the opening degree of each inside expansion valve (72) increases, on the condition that the difference ΔP has a value less than the predetermined value.

[0078] In addition, the condition (a) employs the pressure of the refrigerant as an index for the determination. The pressure of the refrigerant is higher in responsiveness than the temperature of the refrigerant. Therefore, the controller (80) quickly determines that the opening degree of each inside expansion valve (72) increases, on the condition (a) set as the first condition.

[0079] The condition (b) is a condition for determining that the opening degree of each inside expansion valve (72) has satisfactorily increased in the first operation. As described above, when the controller (80) performs the first operation to increase the degree of superheating of the refrigerant flowing out of each inside heat exchanger (73), the opening degree of each inside expansion valve (72) gradually increases. Nevertheless, when the degree of suction superheating (SSH) has a value more than the first value, it can be estimated that the opening degree of each inside expansion valve (72) satisfactorily increases or each inside expansion valve (72) is fully opened. The controller (80) thus accurately determines that the opening degree of each inside expansion valve (72) increases, on the condition that the degree of suction superheating (SSH) has a value more than the first value.

[0080] The condition (c) is a condition set from the viewpoint of protection of the refrigeration apparatus (1). When the controller (80) performs the first operation to decrease the opening degree of the outdoor expansion valve (28), the low pressure (LP) may excessively drop. In view of this, when the low pressure (LP) falls below a predetermined value in the first operation, the processing proceeds to steps ST4 to ST6 in which the controller (80) performs the second operation. The controller (80) thus increases the opening degree of the outdoor expansion valve (28) to suppress the drop of the low pressure (LP).

[0081] The condition (d) is a condition set from the viewpoint of protection of the refrigeration apparatus (1). When the controller (80) performs the first operation to decrease the opening degree of the outdoor expansion valve (28), the high pressure (HP) may excessively rise. In view of this, when the high pressure (HP) exceeds the predetermined value in the first operation, the processing proceeds to steps ST4 to ST6 in which the controller (80) performs the second operation.

[0082] The condition (e) is a condition for determining that the opening degree of each inside expansion valve (72) has satisfactorily increased in the first operation. In the first operation, the opening degree of each inside expansion valve (72) increases with a lapse of time. Therefore, the controller (80) determines that the opening degree of each inside expansion valve (72) increases, on the condition (d) that is set as the first condition and on which the predetermined time t1 has elapsed. This predetermined time t1 is set satisfactorily long to such an extent that the conditions (a) and (b) are established first. The condition (e) is a protective condition of causing the controller (80) to perform the second operation even when the conditions (a) to (d) are not established in a case where, for example, a sensor malfunctions or erroneously detects a value.

[0083] In step ST3, when one of the conditions (a) to (e) is established, the processing proceeds to step ST4. After a lapse of a predetermined time t2, the processing proceeds to step ST5. The predetermined time t2 is about several seconds. It should be noted that step S4 may be skipped and the processing may proceed from step ST3 to step ST5. In step ST5, the storage unit of the controller (80) stores the liquid pressure (Ps1) detected by the liquid-side pressure sensor (68). Next, in step ST6, the controller (80) performs the second operation.

[0084] The controller (80) performs the second operation to gradually increase the opening degree of the outdoor expansion valve (28). Specifically, the controller (80) performs the second operation to increase the opening degree of the outdoor expansion valve (28) stepwise every predetermined time ΔT2. It is assumed herein that EV2 represents a next opening degree (pulse) of the outdoor expansion valve (28) after a lapse of the predetermined time ΔT2, and EV2' represents a current opening degree (pulse) of the outdoor expansion valve (28). The controller (80) performs the second operation to increase the opening degree of the outdoor expansion valve (28) such that a relation of EV2 = β × EV2' is satisfied every predetermined time ΔT2. The predetermined time ΔT2 is set at, for example, 10 seconds. In this relation, β is set at 1.5. In other words, in the second operation, the opening degree (pulse) of the outdoor expansion valve (28) increases by 50% every 10 seconds. The controller (80) performs the second operation until the second condition is established in step ST7.

[0085] According to the first embodiment, as described above, the increasing speed of the opening degree of the outdoor expansion valve (28) in the second operation is faster than the decreasing speed of the opening degree of the outdoor expansion valve (28) in the first operation.

[0086] The controller (80) performs the second operation to increase the opening degree of the outdoor expansion valve (28), thereby increasing the flow rate and pressure of the refrigerant flowing through each inside heat exchanger (73). The second operation is performed when the condition that the opening degree of each inside expansion valve (72) has increased is established, except a case where the conditions (c) and (d) are established in step ST3. This configuration therefore satisfactorily secures the flow rate of the refrigerant flowing through each inside heat exchanger (73). The oil in each inside heat exchanger (73) is compatibilized with the liquid refrigerant or the refrigerant in the gas-liquid two-phase state, and then is sucked into each compressor (21, 22, 23). This configuration enables quick recovery of the oil from each inside heat exchanger (73).

[0087] As described above, the increasing speed of the opening degree of the outdoor expansion valve (28) in the second operation is faster than the decreasing speed of the opening degree of the outdoor expansion valve (28) in the first operation. This configuration therefore enables quick feed of the refrigerant to each inside heat exchanger (73) and quick recovery and return of the oil from each inside heat exchanger (73) and to each compressor (21, 22, 23) in a situation in which the opening degree of the inside expansion valve (72) is large.

[0088] The controller (80) performs the second operation until the second condition is established in step ST7.

[0089] In step ST7, the controller (80) determines whether the second condition for performing the third operation is established in the second operation. The second condition includes the following conditions (f) to (i). According to the first embodiment, when one of the conditions (f) to (i) is established, the processing proceeds to steps ST8 to ST9 in which the controller (80) performs the third operation.

[0090] (f) The current liquid pressure (Ps) has a value more than a predetermined value. Specifically, the current liquid pressure (Ps) is more than the liquid pressure (Ps1) × A. The liquid pressure (Ps1) is the pressure immediately before the start of the second operation and is stored in step ST5. The coefficient Ais set at, for example, 2.0.

[0091] (g) The degree of suction superheating (SSH) has a value less than a second value. Specifically, a state in which the degree of suction superheating (SSH) has a value less than the second value continues for a predetermined time t3. The second value is set at, for example, several degrees centigrade to about 10°C. The predetermined time t3 is set at, for example, about several ten seconds.

[0092] (h) The degree of discharge superheating (DSH) has a value less than a predetermined value. Specifically, a state in which the degree of discharge superheating (DSH) has a value less than the predetermined value continues for a predetermined time t4. The predetermined value is set at, for example, about several ten degrees centigrade. The predetermined time t4 is set at, for example, several ten seconds.

[0093] (i) A predetermined time t5 has elapsed after the second operation is performed. The predetermined time t5 is set at, for example, about several minutes. The predetermined time t5 is shorter than the predetermined time t1 on the condition (e).

[0094] The condition (f) is a condition for determining that the oil is recovered from each inside heat exchanger (73) and is returned to each compressor (21, 22, 23) in the second operation. The state in which the pressure (the liquid pressure (Ps)) of the refrigerant downstream of the outdoor expansion valve (28) has a value more than the predetermined value indicates that the opening degree of the outdoor expansion valve (28) is large. Specifically, the state in which the liquid pressure (Ps) is more than the liquid pressure (Ps1) immediately before the start of the second operation × A (A = 2.0) indicates that the opening degree of the outdoor expansion valve (28) has satisfactorily increased in the second operation. It can therefore be estimated that, when the condition (f) is established, the satisfactory amount of liquid refrigerant is fed to each inside heat exchanger (73), so that the oil is recovered from each inside heat exchanger (73) and is returned to each compressor (21, 22, 23). Therefore, the controller (80) accurately determines that the oil is recovered from each inside heat exchanger (73) and is returned to each compressor (21, 22, 23), by setting the condition that the liquid pressure (Ps) has a value more than the predetermined value (i.e., the liquid pressure (Ps1) × A).

[0095] In addition, the condition (f) employs the pressure of the refrigerant as an index. The pressure of the refrigerant is higher in responsiveness than the temperature of the refrigerant. Therefore, the controller (80) quickly determines that the oil is recovered from each inside heat exchanger (73) and is returned to each compressor (21, 22, 23) on the condition (f) set as the second condition.

[0096] The condition (g) is a condition for determining that the oil is recovered from each inside heat exchanger (73) and is returned to each compressor (21, 22, 23) in the second operation. The state in which the degree of suction superheating (SSH) has a value less than the predetermined value indicates that the liquid refrigerant is satisfactorily fed to each inside heat exchanger (73). It can be estimated that, when the state in which the degree of suction superheating (SSH) has a value less than the predetermined value continues for the predetermined time t3, the liquid refrigerant is continuously fed to each inside heat exchanger (73), so that the oil is returned together with the refrigerant to each compressor (21, 22, 23). Therefore, the controller (80) accurately determines that the oil is recovered from each inside heat exchanger (73) and is returned to each compressor (21, 22, 23), by setting the condition that the degree of suction superheating (SSH) has a value less than the predetermined value, specifically, this state continues for the predetermined time t3.

[0097] The condition (h) is a condition set from the viewpoint of protection of the refrigeration apparatus (1). When the controller (80) performs the second operation to increase the opening degree of the outdoor expansion valve (28), each compressor (21, 22, 23) may suck in the refrigerant in a wet state. In this case, the oil in each compressor (21, 22, 23) is diluted, which may result in lubrication failure of a sliding portion. In view of this, the controller (80) terminates the second operation on the condition that the degree of discharge superheating (DSH) has a value less than the predetermined value, specifically, this state continues for the predetermined time t4. Each compressor (21, 22, 23) is thus protected.

[0098] The condition (i) is a condition for determining that the oil is recovered from each inside heat exchanger (73) and is returned to each compressor (21, 22, 23) in the second operation. In the second operation, the opening degree of the outdoor expansion valve (28) increases with a lapse of time. Therefore, the controller (80) determines that the oil is recovered from each inside heat exchanger (73) and is returned to each compressor (21, 22, 23) on the condition (i) that is set as the second condition and on which the predetermined time t5 has elapsed. This predetermined time t5 is set satisfactorily long to such an extent that the conditions (f) and (g) are established first. The condition (1) is a protective condition of causing the controller (80) to terminate the second operation even when the conditions (f) and (g) are not established in a case where, for example, a sensor malfunctions or erroneously detects a value.

[0099] In step ST7, when one of the conditions (f) to (i) is established, the processing proceeds to step ST8 in which the controller (80) determines whether to continuously perform the second operation. When one of the conditions (j) to (1) is established in step ST8, the processing proceeds to step ST9. The condition (j) is a condition on which the high pressure (HP) has a value more than a predetermined value. The predetermined value is set at several megapascals. The condition (k) is a condition on which a maximum discharge temperature (TdMAX) has a value less than a predetermined value. The maximum discharge temperature (TdMAX) refers to a maximum value among temperatures (Td1, Td2, Td3) of the refrigerant detected by the respective discharge temperature sensors (61, 62, 63). This predetermined value is set at, for example, about 100°C. The condition (i) is a condition on which a predetermined time t6 has elapsed after the processing proceeds to step ST8. The predetermined time t6 is set at about several minutes. When the second condition is established in step ST7, the processing may proceed to step ST9 without the determination in ST8.

[0100] Next, in step ST9, the controller (80) performs the third operation. The controller (80) performs the third operation to return the opening degree of the outdoor expansion valve (28) to the opening degree (Psl1) immediately before the start of the first operation. This opening degree (Psl1) equals to the opening degree stored in step ST1. In the first embodiment, the opening degree (Psl1) corresponds to the maximum opening degree of the outdoor expansion valve (28). The oil recovery operation thus ends, and then the cooling-facility operation starts.

-Advantageous Effects of Embodiment-

[0101] The first embodiment provides a heat source-side unit including a compression element (C), a liquid pipe (43) (a third pipe), a heat source-side expansion valve (28) (an outdoor expansion valve) connected to the liquid pipe (43), and a heat source-side heat exchanger (25) (an outdoor heat exchanger). The heat source-side unit is connected to a utilization-side unit (70) (a cooling facility unit) including a utilization-side heat exchanger (73) (an inside heat exchanger) and a utilization-side expansion valve (72) (an inside expansion valve) to constitute, in conjunction with the utilization-side unit (70), a refrigerant circuit (10) configured to perform a refrigeration cycle in which the heat source-side heat exchanger (25) functions as a radiator and the utilization-side heat exchanger (73) functions as an evaporator. The heat source-side unit further includes a control unit (80) (a controller) configured to control the heat source-side unit (20) to carry out an oil recovery operation of recovering an oil from the utilization-side heat exchanger (73) in the refrigeration cycle. The oil recovery operation includes a first operation of decreasing an opening degree of the heat source-side expansion valve (28), and a second operation of increasing the opening degree of the heat source-side expansion valve (28), after the first operation. The control unit (80) performs the second operation when a first condition is established in the first operation. The first condition includes at least a condition that a difference ΔP between a pressure of a refrigerant downstream of the heat source-side expansion valve (28) on the liquid pipe (43) and a pressure of the refrigerant sucked in the compression element (C) has a value less than a predetermined value.

[0102] According to the first embodiment, the first condition includes the condition that the difference ΔP between the liquid pressure (Ps) and the low pressure (Ps) has a value less than the predetermined value. This configuration therefore enables an accurate determination that the opening degree of the inside expansion valve (72) increases.

[0103] In addition, this condition employs a pressure as an index and therefore is higher in responsiveness than a condition that employs a temperature as an index. This configuration therefore enables a quick determination that the opening degree of the inside expansion valve (72) increases.

[0104] In addition, the difference ΔP is obtained by the low-pressure sensor (67) and the liquid-side pressure sensor (68) in the heat source-side unit (20). This configuration therefore enables a determination that the first condition is established, irrespective of the specifications of the cooling facility unit (70). A determination similar to this determination is made even when the cooling facility unit (70) is replaced.

[0105] According to the first embodiment, the first condition includes a condition that a degree of suction superheating (SSH) has a value more than a first value.

[0106] According to the first embodiment, the first condition includes the condition that the degree of suction superheating (SSH) has a value more than the first value. This configuration therefore enables an accurate determination that the opening degree of the inside expansion valve (72) increases.

[0107] In addition, the degree of suction superheating (SSH) is obtained by the suction temperature sensor (66) and the low-pressure sensor (67) in the heat source-side unit (20). This configuration therefore enables a determination that the first condition is established, irrespective of the specifications of the cooling facility unit (70). A determination similar to this determination is made even when the cooling facility unit (70) is replaced.

[0108] According to the first embodiment, the control unit (80) performs a third operation of changing the opening degree of the heat source-side expansion valve (28) to the opening degree immediately before a start of the first operation when a second condition is established in the second operation, and the second condition includes a condition that a degree of suction superheating (SSH) has a value less than a second value.

[0109] According to the first embodiment, the second condition includes the condition that the degree of suction superheating (SSH) has a value less than the second value. This configuration therefore enables an accurate determination that the oil is recovered from the inside heat exchanger (73) and is returned to the compressor (21, 22, 23).

[0110] In addition, the degree of suction superheating (SSH) is obtained by the suction temperature sensor (66) and the low-pressure sensor (67) in the heat source-side unit (20). This configuration therefore enables a determination that the first condition is established, irrespective of the specifications of the cooling facility unit (70). A determination similar to this determination is made even when the cooling facility unit (70) is replaced.

[0111] According to the first embodiment, the control unit (80) performs a third operation of changing the opening degree of the heat source-side expansion valve (28) to the opening degree immediately before a start of the first operation when a second condition is established in the second operation, and the second condition includes a condition that the pressure of the refrigerant downstream of the heat source-side expansion valve (28) on the liquid pipe (43) has a value more than a predetermined value.

[0112] According to the first embodiment, the second condition includes the condition that the liquid pressure (Ps) of the refrigerant downstream of the outdoor expansion valve (28) on the third pipe (43) has a value more than the predetermined value. This configuration therefore enables a determination that the opening degree of the outdoor expansion valve (28) satisfactorily increases. This configuration thus enables an accurate determination that the oil is recovered from the inside heat exchanger (73) and is returned to the compressor (21, 22, 23).

[0113] In addition, this condition employs a pressure as an index and therefore is higher in responsiveness than a condition that employs a temperature as an index. This configuration therefore enables a quick determination that the oil is returned to the compressor (21, 22, 23).

[0114] In addition, the pressure (Ps) is obtained by the low-pressure sensor (67) and the liquid-side pressure sensor (68) in the heat source-side unit (20). This configuration therefore enables a determination that the first condition is established, irrespective of the specifications of the cooling facility unit (70). A determination similar to this determination is made even when the cooling facility unit (70) is replaced.

[0115] Particularly in the first embodiment, the current liquid pressure (Ps) is compared with the liquid pressure (Ps1) immediately before the start of the second operation. This configuration therefore enables a reliable determination that the opening degree of the outdoor expansion valve (28) has satisfactorily increased in the second operation.

[0116] According to the first embodiment, an increasing speed of the opening degree of the heat source-side expansion valve (28) in the second operation is faster than a decreasing speed the opening degree of the heat source-side expansion valve (28) in the first operation.

[0117] According to the first embodiment, in the second operation, the control unit (80) quickly increases the opening degree of the outdoor expansion valve (28) in the situation in which the opening degree of the inside expansion valve (72) is large. This configuration therefore enables quick recovery and return of the oil from the inside heat exchanger (73) and to the compressor (21, 22, 23).

[0118] In addition, in the first operation, the controller (80) gradually decreases the opening degree of the outdoor expansion valve (28). This configuration therefore enables avoidance of an excessive rise of the high pressure (HP) and an excessive drop of the low pressure (LP) owing to an excessive decrease in opening degree of the outdoor expansion valve (28).

«Other Embodiments»

[0119] The first condition only has to include at least the condition (a), and preferably includes the condition (b). The second condition preferably includes the condition (f) or the condition (g).

[0120] The refrigeration apparatus (1) according to the first embodiment is configured to cool inside air. The refrigeration apparatus (1) may alternatively be an air conditioning apparatus configured to condition indoor air or a refrigeration apparatus configured to cool inside air and condition indoor air at the same time.

[0121] The utilization-side expansion valve (72) is a temperature-sensitive automatic expansion valve. The utilization-side expansion valve (72) may alternatively be an expansion valve configured to adjust the opening degree, based on the degree of superheating of the evaporated refrigerant. The utilization-side expansion valve (72) may alternatively be an electronic expansion valve.

[0122] The utilization-side heat exchanger (73) is an air heat exchanger configured to cause the refrigerant to exchange heat with air. The utilization-side heat exchanger (73) may alternatively be a heat exchanger configured to cause the refrigerant to exchange heat with a predetermined heating medium (e.g., water).

[0123] While the embodiments and modifications have been described herein above, it is to be appreciated that various changes in form and detail may be made without departing from the spirit and scope presently or hereafter claimed. In addition, the foregoing embodiments and modifications may be appropriately combined or substituted as long as the combination or substitution does not impair the functions of the present disclosure. The foregoing ordinal numbers such as "first", "second", and "third" are merely used for distinguishing the elements designated with the ordinal numbers, and are not intended to limit the number and order of the elements.

INDUSTRIAL APPLICABILITY

[0124] As described above, the present disclosure is useful for a heat source-side unit and a refrigeration apparatus.

REFERENCE SIGNS LIST

[0125] 

10: refrigerant circuit

20: outdoor unit (heat source-side unit)

20a: heat source-side circuit

25: outdoor heat exchanger (heat source-side heat exchanger)

28: outdoor expansion valve (heat source-side expansion valve)

43: third pipe (liquid pipe)

70: cooling facility unit (utilization-side unit)

72: inside expansion valve (utilization-side expansion valve)

73: inside heat exchanger (utilization-side heat exchanger)

80: controller (control unit)

Claims

1. A heat source-side unit comprising:

a compression element (C);

a liquid pipe (43);

a heat source-side expansion valve (28) connected to the liquid pipe (43); and

a heat source-side heat exchanger (25),

the heat source-side unit being connected to a utilization-side unit (70) including a utilization-side heat exchanger (73) and a utilization-side expansion valve (72) to constitute, in conjunction with the utilization-side unit (70), a refrigerant circuit (10) configured to perform a refrigeration cycle in which the heat source-side heat exchanger (25) functions as a radiator and the utilization-side heat exchanger (73) functions as an evaporator,

the heat source-side unit further comprising:

a control unit (80) configured to control the heat source-side unit (20) to carry out an oil recovery operation of recovering an oil from the utilization-side heat exchanger (73) in the refrigeration cycle,

wherein

the oil recovery operation includes

a first operation of decreasing an opening degree of the heat source-side expansion valve (28), and

a second operation of increasing the opening degree of the heat source-side expansion valve (28), after the first operation,

the control unit (80) performs the second operation when a first condition is established in the first operation, and

the first condition includes at least a condition that a difference ΔP between a pressure of a refrigerant downstream of the heat source-side expansion valve (28) on the liquid pipe (43) and a pressure of the refrigerant sucked in the compression element (C) has a value less than a predetermined value.

2. The heat source-side unit according to claim 1, wherein
the first condition includes a condition that a degree of suction superheating has a value more than a first value.

3. The heat source-side unit according to claim 1 or 2, wherein

the control unit (80) performs a third operation of changing the opening degree of the heat source-side expansion valve (28) to the opening degree immediately before a start of the first operation when a second condition is established in the second operation, and

the second condition includes a condition that a degree of suction superheating has a value less than a second value.

4. The heat source-side unit according to any one of claims 1 to 3, wherein

the control unit (80) performs a third operation of changing the opening degree of the heat source-side expansion valve (28) to the opening degree immediately before a start of the first operation when a second condition is established in the second operation, and

the second condition includes a condition that the pressure of the refrigerant downstream of the heat source-side expansion valve (28) on the liquid pipe (43) has a value more than a predetermined value.

5. The heat source-side unit according to any one of claims 1 to 4, wherein
an increasing speed of the opening degree of the heat source-side expansion valve (28) in the second operation is faster than a decreasing speed of the opening degree of the heat source-side expansion valve (28) in the first operation.

6. A refrigeration apparatus comprising:

the heat source-side unit (20) according to any one of claims 1 to 5; and

a utilization-side unit (70) including a utilization-side heat exchanger (73) and a utilization-side expansion valve (72),

wherein

the heat source-side unit (20) and the utilization-side unit (70) are connected to constitute a refrigerant circuit (10) configured to perform a refrigeration cycle in which the heat source-side heat exchanger (25) functions as a radiator and the utilization-side heat exchanger (73) functions as an evaporator.

7. The refrigeration apparatus according to claim 6, wherein
the utilization-side expansion valve (72) is a thermostatic expansion valve.

Drawing