ES2966337T3 - Heat source unit and cooling apparatus - Google Patents

Abstract

According to the present invention, an oil recovery operation comprises a first operation of reducing the opening degree of a heat source expansion valve (28) and a second operation of increasing the opening degree of the heat source expansion valve (28). the heat source (28) after the first operation. . A controller (80) is configured to execute the second operation when a first condition is met during the first operation. The first condition includes at least one condition in which a difference ΔP between the pressure of a refrigerant on the downstream side of the heat source expansion valve (28) in a liquid pipe (43) and the pressure of a suction coolant from a compression element. (C) is less than a predetermined value. (Automatic translation with Google Translate, without legal value)

Description

DESCRIPTION

Heat source unit and cooling apparatus

Technical field

The present invention relates to a heat source side unit and a cooling apparatus.

Background of the technique

Patent Literature Document 1 describes a refrigeration apparatus configured to perform an oil recovery operation to return an oil stored in a use side heat exchanger to a compressor. Specifically, oil recovery operation involves reducing an opening degree of a first expansion valve in a liquid conduit. The refrigeration apparatus thus reduces a flow rate and a pressure of a refrigerant circulating through the use-side heat exchanger, and increases a degree of suction superheat. Accordingly, an opening degree of a use-side expansion valve gradually increases. The oil recovery operation also involves increasing the opening degree of the first expansion valve after the passage of a first predetermined time t1 from the reduction of the opening degree of the first expansion valve. The refrigeration device thus increases the flow rate of the refrigerant circulating through the heat exchanger on the use side. The refrigerant is made compatible with the refrigeration machine oil in the use side heat exchanger, and is returned together with the refrigeration machine oil to the compressor. PCT International Patent Application Document No. WO 2018/097138 A1 describes a heat source side unit according to the preamble of claim 1.

Citation List

patent literature

Patent Literature Document 1: Japan Patent Document No. JP 2018-084376 A.

Compendium of invention

<Technical problem>

As described in patent literature document 1, the refrigeration apparatus reduces the opening degree of the first expansion valve and, after the passage of the first predetermined time t1, determines that the opening degree of the expansion valve on the utilization side has increased. The cooling apparatus then increases the opening degree of the first expansion valve. However, this determination using a timer lacks precision in determining that the opening degree of the use side expansion valve has increased.

An object of the present invention is to improve the accuracy of determining that an opening degree of a use side expansion valve has increased in a first operation to reduce an opening degree of a source side expansion valve. heat, in an oil recovery operation.

<Problem Solution>

A heat source side unit according to the present invention is defined in claim 1. A first aspect is directed to a heat source side unit including a compression element (C), a liquid conduit (43) , a heat source side expansion valve (28) connected to the liquid conduit (43), and a heat source side heat exchanger (25). The heat source side unit is connected to a use side unit (70) that includes a use side heat exchanger (73) and a use side expansion valve (72) to constitute, together with the use side unit (70), a coolant circuit (10) configured to carry out a refrigeration cycle in which the heat source side heat exchanger (25) behaves as a radiator and the heat exchanger On the use side (73) it behaves like 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 to recover oil from the side heat exchanger. of use (73) in the refrigeration cycle. The oil recovery operation includes a first operation of reducing a degree of opening of the expansion valve on the heat source side (28), and a second operation of increasing the degree of opening of the expansion valve on the heat source side (28). heat source (28) after the first operation. The control unit (80) performs the second operation when a first condition is met in the first operation. The first condition includes at least one condition that a difference AP between a pressure of a refrigerant downstream of the heat source side expansion valve (28) in the liquid conduit (43) and a pressure of the sucked refrigerant in the compression element (C) has a value less than a predetermined value.

According to the first aspect, in the first operation, the first condition includes the condition that the difference AP between the refrigerant pressure downstream of the heat source side expansion valve (28) in the liquid conduit (43) and the pressure of the refrigerant sucked into the compression element (C) has a value lower than the predetermined value. This configuration thus improves the accuracy of determining that the opening degree of the utilization side expansion valve has increased.

According to a second aspect, in the first aspect, the first condition includes a condition that a degree of suction superheat has a value greater than a first value.

According to the second aspect, in the first operation, the first condition includes the condition that the degree of suction superheat is large. This configuration makes it possible to improve the precision of determining that the opening degree of the use side expansion valve (72) has increased.

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. of the start of the first operation when a second condition is met in the second operation, and the second condition includes a condition that a degree of suction superheat has a value less than a second value.

According to the third aspect, in the second operation, the second condition includes the condition that the suction superheat degree has a value less than the second value. This configuration makes it possible to improve the precision of determining that the oil has been returned to the compression element (C).

According to a fourth aspect, in any 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 of immediately before the start of the first operation when a second condition is met 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) in the liquid conduit (43) has a value greater than a predetermined value.

According to the fourth aspect, in the second operation, the second condition includes the condition that the refrigerant pressure downstream of the heat source side expansion valve (28) has a value greater than the predetermined value. This configuration makes it possible to improve the precision of determining that the oil has been returned to the compression element (C).

According to a fifth aspect, in any of the first to fourth aspects, a rate of growth of the degree of opening of the heat source side expansion valve (28) in the second operation is greater than a rate of decrease of the degree of opening. opening of the heat source side expansion valve (28) in the first operation.

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

A sixth aspect is directed to a refrigeration apparatus that includes the heat source side unit (20) according to any of the first to fifth aspects, and a use side unit (70) that includes a side heat exchanger of use (73) and an expansion valve on the use side (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 source side heat exchanger The heat exchanger (25) behaves like a radiator and the use side heat exchanger (73) behaves like an evaporator.

A seventh aspect is directed to the refrigeration apparatus according to the sixth aspect, wherein the use side expansion valve (72) is a thermostatic expansion valve.

Brief description of the drawings

FIG. 1 is a diagram of a duct system of a refrigeration apparatus including a heat source side unit according to the invention.

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

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

FIG. 4 is a flow chart of an oil return operation.

Description of realizations

Embodiments of the invention will now be described with reference to the drawings. The following embodiments are examples of a preferred nature and are not intended to limit the scope of the present invention, the products to which the present invention applies, or the use of the present invention.

<General Settings>

A cooling apparatus (1) according to a first embodiment is configured to cool air as a cooling target. The term "cooling target," as used herein, may imply the air of a facility such as a refrigerator, freezer, or display case.

As illustrated in FIG. 1, the cooling apparatus (1) includes an outdoor unit (20) installed outdoors and two cooling installation units (70), each configured to cool the indoor air. The cooling apparatus (1) does not necessarily include two cooling installation units (70). For example, the cooling apparatus (1) may include a cooling installation unit (70). Alternatively, the cooling apparatus (1) may include three or more cooling installation units (70). The outdoor unit (20) is connected to the two cooling installation units (70) through a liquid connection pipe (14) and a gas connection pipe (13). In this way, a refrigerant circuit (10) is constituted in the refrigeration apparatus (1). A vapor compression refrigeration cycle is obtained, in such a way that a refrigerant circulates through the refrigerant circuit (10).

<Outdoor unit diagram>

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 external expansion valve (28).

The heat source side circuit (20a) includes a gas shut-off valve (11) and a liquid shut-off valve (12). The gas connection line (13) is connected to the gas shut-off valve (11). The liquid connection line (14) is connected to the liquid shut-off valve (12).

<Compression element and its peripheral structure>

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 variable capacity type. In the first compressor (21), power is supplied from a power source to an electric motor through an inverter circuit. The second compressor (22) and the third compressor (23) are each of a fixed capacity type.

The first compressor (21) has a discharge part to which a first discharge conduit (31) is connected. The first compressor (21) has a suction part to which a first suction conduit (34) is connected. The second compressor (22) has a discharge portion to which a second discharge duct (32) is connected. The second compressor (22) has a suction part to which a second suction conduit (35) is connected. The third compressor (23) has a discharge duct (33) to which a third discharge duct (33) is connected. The third compressor (23) has a suction part to which a third suction conduit (36) is connected.

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

A first check valve (CV1) is connected to the first discharge conduit (31). A second check valve (CV2) is connected to the second discharge conduit (32). A third check valve (CV3) is connected to the third discharge conduit (33). The first check valve (CV1), the second check valve (CV2) and the third check valve (CV3) each allow a flow of refrigerant from the discharge part of the corresponding compressor (21,22, 23) to the main discharge duct (37) and each prohibit a flow of refrigerant from the main discharge duct (37) to the discharge part of the corresponding compressor (21,22, 23).

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 line (39a). The oil return pipe (39a) has an outlet end connected to an injection circuit (I). The oil return passage (39a) is also connected to an oil return valve (39b), such as an electric valve. The oil separated by the oil separator (39) is returned to a compression chamber (an intermediate pressure part) of each compressor (21,22, 23) through the oil return duct (39a) and the injection (I).

<Four-way switching valve>

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 conduit (37). The second port (P2) is connected to an inlet end of the main suction conduit (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 shut-off valve (11).

The four-way switching valve (24) switches between a first state (a state indicated by a solid line in FIG. 1) and a second state (a state indicated by a dashed 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>

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 arranged 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 its peripheral structures>

The receiver (26) is configured to store the refrigerant. The receiver (26) is a vertically elongated airtight container.

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 circulating through the first flow path (27a) to exchange heat with the refrigerant circulating through the second flow path (27b).

A first conduit (41) is connected between a liquid end of the outdoor heat exchanger (25) and an upper part of the receiver (26). A fourth check valve (CV4) is connected to the first conduit (41). The fourth check valve (CV4) allows a flow of refrigerant from the outdoor heat exchanger (25) to the receiver (26) and prohibits a flow of refrigerant from the receiver (26) to the outdoor heat exchanger (25). ).

A second duct (42) is connected between a lower part of the receiver (26) and a first end of the first flow path (27a) of the subcooling heat exchanger (27). A third conduit (43) is connected between a second end of the first flow path (27a) and the liquid shut-off valve (12). The third conduit (43) is part of a liquid conduit. A fifth check valve (CV5) is connected to the third conduit (43). The fifth check valve (CV5) allows a flow of refrigerant from the second end of the first flow path (27 a) towards the liquid shut-off valve (12) and prohibits a flow of refrigerant from the liquid shut-off valve (12) towards the second end of the first flow path (27a).

The external expansion valve (28) is arranged between the second end of the first flow path (27a) and the fifth check valve (CV5) and is connected to the third conduit (43). The external expansion valve (28) is a heat source side expansion valve. The external expansion valve (28) is a decompression mechanism configured to decompress the refrigerant. The external expansion valve (28) is an electronic expansion valve.

A fourth conduit (44) is connected to the third conduit (43). The fourth conduit (44) has a first end connected to the third conduit (43) and located between the fifth check valve (CV5) and the liquid shut-off valve (12). The fourth conduit (44) has a second end connected to the first conduit (41) and located between the fourth check valve (CV4) and the receiver (26). A sixth check valve (CV6) is connected to the fourth conduit (44). The sixth check valve (CV6) allows a flow of refrigerant from the third conduit (43) to the first conduit (41) and prohibits a flow of refrigerant from the first conduit (41) to the third conduit (43).

A fifth conduit (45) is connected to the third conduit (43). The fifth conduit (45) has a first end connected to the third conduit (43) and located between the external expansion valve (28) and the fifth check valve (CV5). The fifth conduit (45) has a second end connected to the first conduit (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 conduit (45). The seventh check valve (CV7) allows a flow of refrigerant from the third conduit (43) to the first conduit (41) and prohibits a flow of refrigerant from the first conduit (41) to the third conduit (43).

<Injection circuit>

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 part of the compression element (C). The injection circuit (I) includes a branch duct (51), a regulation duct (52) and three injection ducts (53, 54, 55).

The branch conduit (51) has an inlet end connected to the third conduit (43) and located between the first flow path (27 a) and the outer expansion valve (28). The branch conduit (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 line (51). The injection valve (59) is an electronic expansion valve.

The regulating conduit (52) has an inlet end connected to an outlet end of the second flow path (27b). The regulation pipe (52) is connected to the outlet end of the oil return pipe (39a). The regulation duct (52) has an outlet portion connected to a respective inlet end of the first injection duct (53), the second injection duct (54) and the third injection duct (55).

The first injection duct (53) has an outlet end that communicates with the compression chamber of the first compressor (21). The second injection duct (54) has an outlet end that communicates with the compression chamber of the second compressor (22). The third injection duct (55) has an outlet end that communicates with the compression chamber of the third compressor (23).

A first electric valve (56) is connected to the first injection conduit (53). A second electric valve (57) is connected to the second injection line (54). A third electric valve (58) is connected to the third injection line (55). Each electric valve (56, 57, 58) is a flow adjustment valve. Each electric valve (56, 57, 58) adjusts the flow rate of the coolant that circulates through the corresponding injection pipe (53, 54, 55).

<Heat source side unit sensors>

The heat source side unit (20) includes a plurality of sensors for measuring 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 (65), a low pressure sensor (67), a liquid side pressure sensor (68) and an intermediate pressure sensor (69).

The first discharge temperature sensor (61) is configured to measure a temperature (Td1) of the coolant in the first discharge conduit (31). The second discharge temperature sensor (62) is configured to measure a temperature (Td2) of the coolant in the second discharge passage (32). The third discharge temperature sensor (63) is configured to measure a temperature (Td3) of the coolant in the third discharge passage (33). The high pressure sensor (64) is configured to measure a discharge pressure in the compression member (C) (i.e., a high pressure (HP) in the refrigerant circuit (10)). The suction temperature sensor (65) is configured to measure a temperature of the refrigerant sucked into the compression member (C). The low pressure sensor (67) is configured to measure a suction pressure in the compression member (C) (i.e., a low pressure (LP) in the refrigerant circuit (10)). The liquid side pressure sensor (68) is configured to measure a pressure (a liquid pressure (Ps)) of the liquid refrigerant in the third passage (43). The intermediate pressure sensor (69) is configured to measure a pressure (MP) of the coolant in the regulation duct (52) of the injection circuit (I).

The low pressure sensor (67) and the suction temperature sensor (66) constitute a suction superheat degree measuring unit for measuring a suction superheat degree (SSH) of the compression member (C). Specifically, the controller (80) obtains the degree of suction superheat (SSH) from a difference between a saturation temperature associated with the low pressure (LP) measured by the low pressure sensor (67) and the temperature measured by the suction temperature sensor (66).

The high pressure sensor (64) and the three discharge temperature sensors (61, 62, 63) constitute a discharge superheat degree measuring unit for measuring a discharge superheat degree (DSH) of the compression element ( C). Specifically, the controller (80) obtains the degree of discharge superheat (DSH) from a difference between a saturation temperature associated with the high pressure (HP) measured by the high pressure sensor (64) and the temperatures measured by the respective discharge temperature sensors (61,62, 63) (for example, an average value of these temperatures).

<Cooling installation unit

Each cooling installation unit (70) is a utilization side unit. Each cooling installation unit (70) includes a use side circuit (70a) and an indoor fan (F2).

The use side circuits (70a) are connected in parallel between the liquid connection conduit (14) and the gas connection conduit (13). Each use side circuit (70a) includes an open-close valve (71), an internal expansion valve (72) and an internal heat exchanger (73) arranged in this order from the liquid end to the liquid end. Of gas.

The opening-closing valve (71) is an electromagnetic opening-closing valve to open and close the use side circuit (70a). The open-close valve (71) is open during normal operation.

The internal expansion valve (72) is a use side expansion valve. The internal expansion valve (72) is a temperature sensitive automatic expansion valve. The internal expansion valve (72) has an adjustable opening degree according to the degree of superheating of the refrigerant that circulates out of the use side heat exchanger (73) that behaves as an evaporator. This degree of superheat corresponds to the degree of suction superheat (SSH) of the refrigerant sucked into the compression element (C).

As illustrated in FIG. 1, more specifically, the internal expansion valve (72) includes an expansion valve main body (72a), a thermostatic bulb (72b) and a capillary conduit (72c). The main body of the expansion valve (72a) is connected between the opening-closing valve (71) and the indoor heat exchanger (73) of the use side circuit (70a). The thermostatic bulb (72b) is in contact with a gas end duct of the use side heat exchanger (73). The main body of the expansion valve (72a) and the thermostatic bulb (72b) are connected to each other by means of the capillary conduit (72c) interposed between them. A change in the degree of superheat of the refrigerant circulating out of the indoor heat exchanger (73) that behaves as an evaporator causes a change in the pressure of the working fluid enclosed in each thermostatic bulb (72b) and capillary conduit (72c ). This change in internal pressure causes a displacement of a diaphragm of the main body of the expansion valve (72a), so that the opening degree of the internal expansion valve (72) is adjusted.

The indoor heat exchanger (73) is a use side heat exchanger. The indoor heat exchanger (73) is a fin and tube heat exchanger. The indoor fan (F2) is arranged near the indoor heat exchanger (73). The indoor fan (F2) provides indoor air that passes through the indoor heat exchanger (73). The indoor heat exchanger (73) causes the indoor air provided by the indoor fan (F2) to exchange heat with the refrigerant.

<Controller>

The outdoor unit (20) includes a controller (80). The controller (80) includes a microcomputer mounted on a control console, and a memory device (specifically, a semiconductor memory) that stores software to operate the microcomputer.

The controller (80) is configured to control each component of the outdoor unit (21,22, 23), based on an operating command and a measurement signal from each sensor. The controller (80) controls each component to change a cooling installation operation, a defrosting operation and an oil return operation. The cooling installation operation is an operation to make each cooling installation unit (70) cool the indoor air. The defrosting operation is an operation to melt frost from a surface of each indoor heat exchanger (73). The oil return operation is an operation to recover oil (i.e., refrigeration machine oil) from each indoor heat exchanger (73) and return the oil to each compressor (21, 22, 23).

During 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 to reduce the opening degree of the external expansion valve (28). The second operation is an operation to increase the opening degree of the external expansion valve (28). The third operation is an operation to return the opening degree of the outer expansion valve (28) to the opening degree immediately before the start of the first operation.

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 of which will be described later). The controller (80) determines whether the third operation is performed in the second operation. This determination is made based on a second condition (the details of which will be described later).

-Operations-

Next, a description of the operations that are carried out by the refrigeration apparatus (1) according to the first embodiment will be provided.

<Cooling installation operation>

During cooling installation operation, each compressor (21, 22, 23), the outdoor fan (F1) and each indoor fan (F2) are in operation. The four-way switching valve (24) is switched to the first state and the external expansion valve (28) is fully opened. Each opening-closing valve (71) opens. The opening degree of each internal expansion valve (72) is adjusted appropriately. Specifically, the opening degree of each indoor expansion valve (72) is adjusted so that the superheat degree of the refrigerant circulating out of the indoor heat exchanger (73) is maintained at a predetermined value. The opening degrees of the injection valve (59), the first electric valve (56), the second electric valve (57) and the third electric valve (58) are adjusted appropriately.

During the operation of the cooling installation, a first refrigeration cycle is reached, in which the outdoor heat exchanger (25) behaves as a radiator or a condenser and each indoor heat exchanger (73) behaves as a evaporator.

As illustrated in FIG. 2, during the operation of the cooling installation, when each compressor (21, 22, 23) compresses the refrigerant, then the refrigerant circulates to the outdoor heat exchanger (25). In the outdoor heat exchanger (25), the refrigerant dissipates heat to the outdoor air. After the refrigerant dissipates heat in the outdoor heat exchanger (25), the refrigerant circulates through the first conduit (41), the receiver (26) and the second conduit (42). The refrigerant then circulates through the first flow path (27a) of the subcooling heat exchanger (27).

When the injection valve (59) is opened, a part of the refrigerant from the third duct (43) flows to the branch duct (51). After the injection valve (59) decompresses the refrigerant from the branch duct (51), the refrigerant circulates to the second flow path (27b) of the subcooling heat exchanger (27). In the subcooling heat exchanger (27), the refrigerant of the second flow path (27b) exchanges heat with the refrigerant of the first flow path (27a). The refrigerant of the second flow path (27b) is evaporated by suction of heat from the refrigerant of the first flow path (27a). The refrigerant in the first flow path (27a) is cooled in this way, so that the degree of subcooling of the refrigerant increases.

The coolant then circulates through the second flow path (27b), the regulation duct (52) and each injection duct (53, 54, 55). Next, the refrigerant circulates into the compression chamber of each compressor (21,22, 23).

The cooled refrigerant from the first flow path (27a) circulates through the third conduit (43) and the liquid connection conduit (14), and then circulates to each cooling installation unit (70).

In each cooling installation unit (70), after the indoor expansion valve (72) decompresses the refrigerant, the refrigerant circulates to the indoor heat exchanger (73). In the indoor heat exchanger (73), the refrigerant evaporates by sucking heat from the indoor air. This cools the interior air.

After each use side heat exchanger (73) evaporates the refrigerant, the refrigerant circulates to the outdoor unit (20) through the gas connection pipe (13). Next, the refrigerant circulates through the main suction pipe (38) and circulates into each compressor (21,22, 23).

<Defrost operation>

During defrost operation, each compressor (21,22, 23), outdoor fan (F1) and each indoor fan (F2) are in operation. The four-way switching valve (24) is switched to the second state and each internal expansion valve (72) is fully opened. Each opening-closing valve (71) opens. The opening degree of the external expansion valve (28) is adjusted. As illustrated in FIG. 3, during defrosting operation, the refrigerant can circulate through the injection circuit (I) in a similar way as it does during cooling installation operation. However, the coolant does not necessarily circulate through the injection circuit (I) in such a way that the injection valve (59) is completely closed.

During the defrost operation, a second refrigeration cycle is reached, in which each indoor heat exchanger (73) behaves as a radiator or condenser and the outdoor heat exchanger (25) behaves as an evaporator.

As illustrated in FIG. 3, during defrosting operation, when each compressor (21, 22, 23) compresses the refrigerant, then the refrigerant circulates to each cooling installation unit (70) through the gas connection duct (13). In each cooling installation unit (70), the refrigerant circulates through the indoor heat exchanger (73). In the indoor heat exchanger (73), the refrigerant melts the frost on the surface of the indoor heat exchanger (73). When the refrigerant dissipates heat in each indoor heat exchanger (73), then the refrigerant circulates to the outdoor unit (20) through the liquid connecting pipe (14).

In the outdoor unit (20), the refrigerant circulates through the fourth duct (44), the receiver (26), the second duct (42), the first flow path (27a) of the subcooling heat exchanger ( 27) and the third duct (43), in this order. When the refrigerant leaves the third pipe (43), the external expansion valve (28) decompresses the refrigerant. Next, the refrigerant circulates through the fifth duct (45) and the outdoor heat exchanger (25), in this order. In the outdoor heat exchanger (25), the refrigerant evaporates by sucking heat from the outdoor air. After the outdoor heat exchanger (25) evaporates the refrigerant, the refrigerant circulates into each compressor (21, 22, 23) through the main suction line (38).

<Oil recovery operation>

A specific description of the oil recovery operation will be provided below. Oil return operation is carried out when a predetermined condition is met in the cooling installation operation. During oil return operation, each compressor (21, 22, 23), outdoor fan (F1) and each indoor fan (F2) are in operation. The four-way switching valve (24) is switched to the first state. Each opening-closing valve (71) opens. The opening degree of each internal expansion valve (72) is adjusted appropriately. Specifically, the opening degree of each indoor expansion valve (72) is adjusted so that the superheat degree of the refrigerant circulating out of the indoor heat exchanger (73) is maintained at a predetermined value. The opening degrees of the injection valve (59), the first electric valve (56), the second electric valve (57) and the third electric valve (58) are adjusted appropriately.

It should be noted that the oil recovery operation described below is an example of simultaneous recovery of the oils from all the indoor heat exchangers (73).

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

The controller (80) carries out the first operation to gradually reduce the opening degree of the external expansion valve (28). Specifically, the controller (80) performs the first operation to reduce the opening degree of the external expansion valve (28) in a step manner every predetermined time period AT1. It is assumed herein that EV1 represents the next opening degree (pulse) of the outer expansion valve (28) after the elapse of the predetermined time period AT1, and EV1' represents a current opening degree (pulse) of the external expansion valve (28). The controller (80) performs the first operation to reduce the opening degree of the external expansion valve (28) so that a ratio of EV1 = a x EV1' is satisfied every predetermined time period AT1. The default time period AT1 is set, for example, to 15 seconds. In this relationship, a is set to 0.75. In other words, in the first operation, the opening degree (pulse) of the external expansion valve (28) is reduced by 25% every 15 seconds. The controller (80) carries out the first operation until the first condition is met in step ST3.

In the first operation, when the opening degree of the external expansion valve (28) decreases, the external expansion valve (28) decompresses the refrigerant. Refrigerant decompression reduces the flow rate and pressure of the refrigerant circulating through each use side heat exchanger (73). This results in an increase in the superheat degree of the refrigerant circulating out of each indoor heat exchanger (73), so that the opening degree of each indoor expansion valve (72) gradually increases.

In step ST3, the controller (80) determines whether the first condition for performing the second operation is met 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 met, the processing proceeds to steps ST4 to S6, in which the controller (80) performs the second operation.

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

(b) The degree of suction superheat (SSH) has a value greater than a predetermined value (a first value). This first value is set, for example, to several tens of degrees Celsius.

(c) Low pressure (LP) has a value less than a predetermined value. This default value is set to several tens of kilopascals.

(d) High pressure (HP) has a value greater than a predetermined value. This default value is set to several hundred megapascals.

(e) A predetermined time t1 has elapsed after carrying out the first operation. The default time t1 is set, for example, to several minutes.

Condition (a) is a condition for determining that the opening degree of each internal expansion valve (72) has increased satisfactorily in the first operation. The liquid pressure (Ps) of the refrigerant downstream of the external expansion valve (28) corresponds to the pressure on the inlet side of each internal expansion valve (72). Low pressure (LP) corresponds to the pressure on the outlet side of each internal expansion valve (72). Therefore, the difference AP corresponds to the pressure of the refrigerant decompressed by each internal expansion valve (72). The controller (80) thus precisely determines that the opening degree of each internal expansion valve (72) increases, provided that the difference AP has a value less than the predetermined value.

Furthermore, condition (a) uses the pressure of the refrigerant as an index for the determination. Coolant pressure has a greater responsiveness than coolant temperature. Therefore, the controller (80) quickly determines that the opening degree of each internal expansion valve (72) increases, with condition (a) set as the first condition.

Condition (b) is a condition for determining that the opening degree of each internal expansion valve (72) has increased satisfactorily in the first operation. As described above, when the controller (80) carries out the first operation to increase the degree of superheating of the refrigerant circulating out of each indoor heat exchanger (73), the opening degree of each valve internal expansion (72) gradually increases. However, when the degree of suction superheat (SSH) has a value greater than the first value, it can be estimated that the opening degree of each internal expansion valve (72) increases satisfactorily or that each internal expansion valve (72 ) is completely open. The controller (80) thus precisely determines that the opening degree of each internal expansion valve (72) increases, provided that the degree of suction superheat (SSH) has a value greater than the first value.

Condition (c) is a condition established from the point of view of the protection of the refrigeration apparatus (1). When the controller (80) carries out the first operation to reduce the opening degree of the external expansion valve (28), the low pressure (LP) may drop excessively. In view of this, when the low pressure (LP) drops below a predetermined value in the first operation, the processing advances to steps ST4 to ST6, in which the controller (80) performs the second operation. The controller (80) thus increases the degree of opening of the external expansion valve (28) to suppress the drop in low pressure (LP).

Condition (d) is a condition established from the point of view of the protection of the refrigeration apparatus (1). When the controller (80) carries out the first operation to reduce the opening degree of the external expansion valve (28), the high pressure (HP) may increase excessively. In view of this, when the high pressure (HP) exceeds the predetermined value in the first operation, the processing advances to steps ST4 to ST6, in which the controller (80) performs the second operation.

Condition (e) is a condition for determining that the opening degree of each internal expansion valve (72) has increased satisfactorily in the first operation. In the first operation, the opening degree of each internal expansion valve (72) increases in each period of time. Therefore, the controller (80) determines that the opening degree of each internal expansion valve (72) increases, as long as condition (d) has been established as the first condition and the predetermined time t1 has elapsed. This predetermined time t1 is set appropriately long to the point that conditions (a) and (b) are met first. Condition (e) is a protection condition that causes the controller (80) to perform the second operation even when conditions (a) to (d) have not been met in a case where, for example, a sensor works wrongly or erroneously measures a value.

In step ST3, when one of conditions (a) to (e) is met, processing advances to step ST4. After the passage of a predetermined time t2, processing advances to step ST5. The default time t2 is approximately several seconds. It should be noted that step S4 can be omitted and processing can proceed from step ST3 to step ST5. In step ST5, the controller storage unit (80) stores the liquid pressure (Ps1) measured by the liquid side pressure sensor (68). Next, in step ST6, the controller (80) performs the second operation.

The controller (80) carries out the second operation to gradually increase the opening degree of the external expansion valve (28). Specifically, the controller (80) carries out the second operation to increase the opening degree of the outer expansion valve (28) in a step manner every predetermined time period AT2. It is assumed herein that EV2 represents the next degree of opening (pulse) of the outer expansion valve (28) after the passage of a predetermined period of time AT2, and EV2' represents a current degree of opening (pulse) of the external expansion valve (28). The controller (80) performs the second operation to increase the opening degree of the external expansion valve (28) so that a relationship of EV2 = p x EV2' is satisfied every predetermined time period AT2. The default time period AT2 is set to, for example, 10 seconds. In this relationship, p is set to 1.5. In other words, in the second operation, the opening degree (pulse) of the external expansion valve (28) increases by 50% every 10 seconds. The controller (80) carries out the second operation until the second condition of step ST7 is met.

According to the first embodiment, as described above, the speed of growth of the degree of opening of the external expansion valve (28) in the second operation is greater than the speed of decrease of the degree of opening of the expansion valve. exterior (28) in the first operation.

The controller (80) carries out the second operation to increase the degree of opening of the outdoor expansion valve (28), thus increasing the flow rate and pressure of the refrigerant circulating through each indoor heat exchanger ( 73). The second operation is performed when the condition that the opening degree of each internal expansion valve (72) has increased is met, except in the case where conditions (c) and (d) are met in step ST3. . Therefore, this configuration satisfactorily guarantees the flow rate of the refrigerant that circulates through each indoor heat exchanger (73). The oil from each indoor heat exchanger (73) is made compatible with the liquid refrigerant or with the refrigerant in a two-phase gas-liquid state, and is then sucked into the interior of each compressor (21,22, 23). This configuration makes possible rapid oil recovery from each indoor heat exchanger (73).

As described above, the speed of growth of the degree of opening of the external expansion valve (28) in the second operation is greater than the speed of decrease of the degree of opening of the external expansion valve (28) in the first operation. Therefore, this configuration makes possible a rapid supply of the refrigerant to each indoor heat exchanger (73) and a rapid recovery and return of the oil from each indoor heat exchanger (73) to each compressor (21, 22, 23). ) in a situation where the opening degree of the internal expansion valve (72) is large.

The controller (80) performs the second operation until the second condition of step ST7 is met.

In step ST7, the controller (80) determines whether the second condition for performing the third operation is met 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 met, the processing proceeds to steps ST8 to ST9 in which the controller (80) performs the third operation.

(f) The current liquid pressure (Ps) has a value greater than a predetermined value. Specifically, the current liquid pressure (Ps) is greater than the liquid pressure (Ps1) x A. The liquid pressure (Ps1) is the pressure immediately before the start of the second operation and is stored in step ST5. The coefficient A is set, for example, to 2.0.

(g) The degree of suction superheat (SSH) has a value less than a second value. Specifically, a state in which the degree of suction superheat (SSH) has a value less than the second value continues for a predetermined time t3. The second value is set, for example, to a few degrees Celsius up to approximately 10°C. The predetermined time t3 is set, for example, to approximately several tens of seconds.

(h) The degree of discharge superheat (DSH) has a value less than a predetermined value. Specifically, a state in which the degree of discharge superheat (DSH) has a value less than the predetermined value continues for a predetermined time t4. The default value is set, for example, to approximately several tens of degrees Celsius. The predetermined time t4 is set, for example, to several tens of seconds.

(i) A predetermined time t5 is allowed to elapse after performing the second operation. The predetermined time t5 is set, for example, to approximately several minutes. The predetermined time t5 is shorter than the predetermined time t1 of condition (e).

Condition (f) is a condition for determining that the oil is recovered from each indoor heat exchanger (73) and returned to each compressor (21,22, 23) in the second operation. The state in which the pressure (liquid pressure (Ps)) of the refrigerant downstream of the outer expansion valve (28) has a value higher than the predetermined value indicates that the opening degree of the outer expansion valve (28 ) is big. Specifically, the state in which the liquid pressure (Ps) is greater than the liquid pressure (Ps1) immediately before the start of the second operation x A (A = 2.0) indicates that the degree of opening of the External expansion valve (28) has increased satisfactorily in the second operation. Therefore, it can be estimated that, when condition (f) is met, the appropriate amount of liquid refrigerant is supplied to each indoor heat exchanger (73), so that oil is recovered from each indoor heat exchanger (73). interior (73) and is returned to each compressor (21, 22, 23). Therefore, the controller (80) precisely determines that oil is recovered from each indoor heat exchanger (73) and returned to each compressor (21,22, 23) by establishing the condition that the liquid pressure (Ps) is higher than the predetermined value (i.e., liquid pressure (Ps1) x A).

Furthermore, condition (f) uses the refrigerant pressure as an index. Coolant pressure has a greater responsiveness than coolant temperature. Therefore, the controller (80) quickly determines that the oil is recovered from each indoor heat exchanger (73) and returned to each compressor (21, 22, 23) with condition (f) set as the second condition. .

Condition (g) is a condition for determining that the oil is recovered from each indoor heat exchanger (73) and returned to each compressor (21, 22, 23) in the second operation. The state in which the degree of suction superheat (SSH) has a value less than the predetermined value indicates that the liquid refrigerant is satisfactorily supplied to each indoor heat exchanger (73). It can be estimated that, when the state in which the degree of suction superheat (SSH) has a value less than the predetermined value continues for the predetermined time t3, the liquid refrigerant is continuously supplied to each indoor heat exchanger (73 ), so that the oil is returned along with the refrigerant to each compressor (21,22, 23). Therefore, the controller (80) precisely determines that oil is recovered from each indoor heat exchanger (73) and returned to each compressor (21, 22, 23), by establishing the condition that the degree of suction superheat (SSH) has a value less than the predetermined value, specifically, that this state continues for the predetermined time t3.

Condition (h) is a condition established from the point of view of the protection of the refrigeration apparatus (1). When the controller (80) carries out the second operation to increase the opening degree of the external expansion valve (28), each compressor (21,22, 23) can suck the refrigerant in a wet state. In this case, the oil in each compressor (21, 22, 23) is diluted, which can cause lubrication failure of a sliding part. In view of this, the controller (80) terminates the second operation on the condition that the degree of discharge superheat (DSH) has a value less than the predetermined value, specifically, that this state continues for the predetermined time t4. Each compressor (21,22, 23) is thus protected.

Condition (i) is a condition for determining that the oil is recovered from each indoor heat exchanger (73) and returned to each compressor (21, 22, 23) in the second operation. In the second operation, the opening degree of the external expansion valve (28) increases with the passage of time. Therefore, the controller (80) determines that the oil is recovered from each indoor heat exchanger (73) and returned to each compressor (21,22, 23) with condition (i) set as the second condition and in which the predetermined time t5 has elapsed. This predetermined time t5 is set appropriately long to the point that conditions (f) and (g) are satisfied first. Condition (l) is a protection condition that causes the controller (80) to terminate the second operation even when conditions (f) and (g) have not been met in a case where, for example, a sensor works wrongly or erroneously measures a value.

In step ST7, when one of the conditions (f) to (i) is met, the processing proceeds to step ST8 in which the controller (80) determines whether the second operation should be performed continuously. When one of the conditions (j) to (l) is met in step ST8, processing advances to step ST9. Condition (j) is a condition in which the high pressure (HP) has a value greater than a predetermined value. The default value is set to several megapascals. Condition (k) is a condition in 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 the temperatures (Td1, Td2, Td3) of the coolant measured by the respective discharge temperature sensors (61,62, 63). This default value is set, for example, to approximately 100°C. Condition (i) is a condition in which a predetermined time t6 has elapsed after processing has advanced to step ST8. The default time t6 is set to approximately several minutes. When the second condition is met in step ST7, processing can proceed to step ST9 without the determination of ST8.

Next, in step ST9, the controller (80) performs the third operation. The controller (80) carries out the third operation to return the opening degree of the external expansion valve (28) to the opening degree (Psl1) immediately before the start of the first operation. This opening degree (Psl1) is equal to the opening degree stored in step ST1. In the first embodiment, the opening degree (Psl1) corresponds to the maximum opening degree of the external expansion valve (28). In this way the oil recovery operation ends and at that moment the cooling installation operation begins.

-Advantageous effects of realization-

The first embodiment provides a heat source side unit including a compression element (C), a liquid conduit (43) (a third conduit), a heat source side expansion valve (28) (a outdoor expansion valve) connected to the liquid conduit (43), and a heat source side heat exchanger (25) (an outdoor heat exchanger). The heat source side unit is connected to a use side unit (70) (a cooling installation unit) which includes a use side heat exchanger (73) (an indoor heat exchanger) and a use side expansion valve (72) (an internal expansion valve) to constitute, together with the use side unit (70), a refrigerant circuit (10) configured to carry out a refrigeration cycle in which The heat source side heat exchanger (25) behaves as a radiator and the use side heat exchanger (73) behaves 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 to recover oil from the exchanger. of use side heat (73) in the refrigeration cycle. The oil recovery operation includes a first operation of reducing an opening degree of the heat source side expansion valve (28), and a second operation of increasing the opening degree of the source side expansion valve. of heat (28) after the first operation. The control unit (80) performs the second operation when a first condition is met in the first operation. The first condition includes at least one condition that a difference AP between a pressure of a refrigerant downstream of the heat source side expansion valve (28) in the liquid conduit (43) and a pressure of the sucked refrigerant in the compression element (C) has a value less than a predetermined value.

According to the first embodiment, the first condition includes the condition that the difference AP between the liquid pressure (Ps) and the low pressure (Ps) has a value less than the predetermined value. Therefore, this configuration makes possible a precise determination that the degree of opening of the internal expansion valve (72) increases.

Additionally, this condition uses a pressure as an index and is therefore more responsive than a condition that uses a temperature as an index. Therefore, this configuration makes possible a quick determination that the degree of opening of the internal expansion valve (72) increases.

Furthermore, the difference AP is obtained by means of the low pressure sensor (67) and the liquid side pressure sensor (68) of the heat source side unit (20). Therefore, this configuration makes it possible to determine that the first condition is met, regardless of the specifications of the cooling installation unit (70). A determination similar to this determination is made even when the cooling installation unit (70) is replaced.

According to the first embodiment, the first condition includes a condition that a suction superheat (SSH) degree has a value greater than a first value.

According to the first embodiment, the first condition includes the condition that the suction superheat (SSH) degree has a value greater than the first value. Therefore, this configuration makes possible a precise determination that the degree of opening of the internal expansion valve (72) increases.

Furthermore, the degree of suction superheat (SSH) is obtained by means of the suction temperature sensor (66) and the low pressure sensor (67) of the heat source side unit (20). Therefore, this configuration makes it possible to determine that the first condition is met, regardless of the specifications of the cooling installation unit (70). A determination similar to this determination is made even when the cooling installation unit (70) is replaced.

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 the start of the first operation when a second condition is met in the second operation, and the second condition includes a condition that a degree of suction superheat (SSH) has a value less than a second value.

According to the first embodiment, the second condition includes the condition that the suction superheat (SSH) degree has a value less than the second value. Therefore, this configuration makes possible an accurate determination that the oil is recovered from the indoor heat exchanger (73) and returned to the compressor (21,22, 23).

Furthermore, the degree of suction superheat (SSH) is obtained by means of the suction temperature sensor (66) and the low pressure sensor (67) of the heat source side unit (20). Therefore, this configuration makes it possible to determine that the first condition is met, regardless of the specifications of the cooling installation unit (70). A determination similar to this determination is made even when the cooling installation unit (70) is replaced.

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 the start of the first operation when a second condition is met 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) in the liquid passage (43) has a value higher than a predetermined value.

According to the first embodiment, the second condition includes the condition that the liquid pressure (Ps) of the refrigerant downstream of the external expansion valve (28) in the third conduit (43) has a value greater than the predetermined value. Therefore, this configuration makes it possible to determine that the opening degree of the external expansion valve (28) increases satisfactorily. This configuration thus allows for a precise determination of which oil is recovered from the indoor heat exchanger (73) and returned to the compressor (21, 22, 23).

Additionally, this condition uses a pressure as an index and is therefore more responsive than a condition that uses a temperature as an index. Therefore, this configuration makes possible a rapid determination that oil is returned to the compressor (21,22, 23).

Furthermore, the pressure (Ps) is obtained by means of the low pressure sensor (67) and the liquid side pressure sensor (68) of the heat source side unit (20). Therefore, this configuration makes it possible to determine that the first condition is met, regardless of the specifications of the cooling installation unit (70). A determination similar to this determination is made even when the cooling installation unit (70) is replaced.

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. Therefore, this configuration makes possible a reliable determination that the opening degree of the external expansion valve (28) has satisfactorily increased in the second operation.

According to the first embodiment, a rate of growth of the opening degree of the heat source side expansion valve (28) in the second operation is greater than a rate of decrease of the opening degree of the heat source side expansion valve (28) in the second operation. heat source (28) in the first operation.

According to the first embodiment, in the second operation, the control unit (80) rapidly increases the opening degree of the outer expansion valve (28) in the situation where the opening degree of the inner expansion valve (72) ) is big. Therefore, this configuration makes possible a rapid recovery and return of the oil from the indoor heat exchanger (73) to the compressor (21,22, 23).

Furthermore, in the first operation, the controller (80) gradually reduces the opening degree of the external expansion valve (28). Therefore, this configuration makes it possible to avoid an excessive increase in the high pressure (HP) and an excessive drop in the low pressure (LP) due to an excessive reduction in the opening degree of the external expansion valve (28).

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The first condition only needs to include at least condition (a), and preferably includes condition (b). The second condition preferably includes condition (f) or condition (g).

The cooling apparatus (1) according to the first embodiment is configured to cool indoor air. The cooling apparatus (1) may alternatively be an air conditioning apparatus configured to condition indoor air or a refrigeration apparatus configured to cool indoor air and condition indoor air at the same time. The use side expansion valve (72) is a temperature sensitive automatic expansion valve. The use side expansion valve (72) may alternatively be an expansion valve configured to adjust the degree of opening based on the degree of superheat of the evaporated refrigerant. The use side expansion valve (72) may alternatively be an electronic expansion valve.

The use side heat exchanger (73) is an air heat exchanger configured to cause the refrigerant to exchange heat with the air. The use 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).

Although the embodiments and modifications have been described hereinbefore, it should be appreciated that different changes can be made in the form and details without departing from the scope of the present invention, as defined in the attached claims.

Industrial applicability

As described above, the present invention is useful for a heat source side unit and for a refrigeration apparatus.

List of reference signs

10: coolant circuit

20: outdoor unit (heat source side unit)

20a: heat source side circuit

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

28: external expansion valve (heat source side expansion valve)

43: third conduit (liquid conduit)

: cooling installation unit (use side unit)

: indoor expansion valve (use side expansion valve) : Indoor heat exchanger (use side heat exchanger) : controller (control unit)

Claims (7)

1. A heat source side unit comprising: a compression element (C); a liquid conduit (43); a heat source side expansion valve (28) connected to the liquid conduit (43); and a heat source side heat exchanger (25), the heat source side unit being connectable to a use side unit (70) including a use side heat exchanger (73) and a use side expansion valve (72) to constitute, together with the use side unit (70), a coolant circuit (10) configured to carry out a refrigeration cycle in which the heat source side heat exchanger (25) behaves as a radiator and the heat exchanger On the use side (73) it behaves like 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 to recover oil from the use side heat exchanger (73) in the refrigeration cycle , in which oil recovery operation includes a first operation of reducing a degree of opening of the heat source side expansion valve (28), and a second operation of increasing the degree of opening of the heat source side expansion valve (28) after the first operation, characterized in that The control unit (80) performs the second operation when a first condition is met in the first operation, and because The first condition includes at least one condition that a difference AP between a pressure of a refrigerant downstream of the heat source side expansion valve (28) in the liquid conduit (43) and a pressure of the sucked refrigerant 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 superheat has a value greater 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 the start of the first operation when a second condition is met. in the second operation, and The second condition includes a condition that a degree of suction superheat has a value less than a second value. 4. The heat source side unit according to any 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 the start of the first operation when a second condition is met. in the second operation, and The second condition includes a condition that the refrigerant pressure downstream of the heat source side expansion valve (28) in the liquid passage (43) has a value greater than a predetermined value. 5. The heat source side unit according to any of claims 1 to 4, wherein a growth rate of the opening degree of the heat source side expansion valve (28) in the second operation is greater 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 of claims 1 to 5; and a use side unit (70) including a use side heat exchanger (73) and a use side expansion valve (72), in which 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 source side heat exchanger The heat exchanger (25) behaves like a radiator and the use side heat exchanger (73) behaves like an evaporator. 7. The refrigeration apparatus according to claim 6, wherein The use side expansion valve (72) is a thermostatic expansion valve.