JP7473775B2 - Heat source unit and refrigeration device - Google Patents

Description

This disclosure relates to a heat source unit and a refrigeration device.

The air conditioning system (refrigeration system) disclosed in Patent Document 1 has a refrigerant circuit to which a two-stage compression mechanism, an outdoor heat exchanger, an indoor heat exchanger, a switching mechanism, and an intermediate heat exchanger are connected. Such a refrigeration system can be switched between cooling operation and heating operation by the switching mechanism. In cooling operation, the indoor heat exchanger becomes an evaporator, and the outdoor heat exchanger becomes a radiator. In heating operation, the indoor heat exchanger becomes a radiator, and the outdoor heat exchanger becomes an evaporator.

JP 2009-229051 A

In a refrigeration system equipped with a refrigerant circuit as described in Patent Document 1, the outdoor heat exchanger is cooled during heating operation, which can cause frost to form. In such cases, it is necessary to periodically perform a defrost operation to remove the frost using the outdoor heat exchanger as a radiator. However, performing a defrost operation makes it impossible to continue heating operation.

The purpose of this disclosure is to suppress frost formation on the outdoor heat exchanger when the outdoor heat exchanger is operating as an evaporator.

A first aspect is a heat source unit including a heat source circuit (11) including a first compression section (21), a second compression section (22, 23), an intercooler (17), and a heat source heat exchanger (13), and configured to configure a refrigerant circuit (6) performing a refrigeration cycle by being connected to a utilization unit (50, 60) having a utilization heat exchanger (54, 64),
the first compression section (21) and the second compression section (22, 23) are connected to each other by an intermediate flow passage (41) connecting a discharge side of the second compression section (22, 23) and a suction side of the first compression section (21);
the intermediate flow path (41) includes an economizer (17) provided in the middle of the intermediate flow path (41), and a bypass flow path (25) having one end connected to a first connection portion (26) between the economizer (17) and a first compression section (21) and the other end connected to a second connection portion (27) between the economizer (17) and a second compression section (22, 23),
At least a portion of the bypass flow path (25) is arranged below or in the vicinity of a lower portion of the heat source heat exchanger (13), and the heat source circuit (11) includes a switching mechanism (K) capable of opening the bypass flow path (25) in a first operation in which the heat source heat exchanger (13) serves as an evaporator.

In the first mode, in the first operation, the high-temperature refrigerant compressed by the second compression section (22, 23) flows into the bypass flow path (25). The refrigerant that flows into the bypass flow path (25) passes near the lower part of the heat source heat exchanger (13). This heats the lower part of the heat source heat exchanger (13), thereby suppressing frost formation on the heat source heat exchanger (13).

In the second aspect, in the first aspect, the switching mechanism (K) is connected to the intermediate flow path (41) and includes an on-off valve (28) that can be adjusted so that the refrigerant flows to either the intermediate cooler (17) or the bypass flow path (25).

In the second embodiment, the switching mechanism (K) allows the refrigerant to flow through either the intermediate cooler (17) or the bypass flow path (25).

In the third aspect, in the first aspect, the switching mechanism (K) is connected to the intermediate flow path (41) and includes an opening/closing valve (28) whose opening is adjustable to adjust the flow rate of the refrigerant flowing through the bypass flow path (25).

In the third embodiment, the flow rate of the refrigerant flowing through the bypass flow path (25) can be adjusted by the switching mechanism (K).

The fourth aspect is the second or third aspect, further comprising a control unit (100) that performs a first control to open the bypass flow path (25) when a condition indicating that the outside air temperature is lower than a predetermined value is satisfied during the first operation.

In the fourth aspect, when conditions that make the heat source heat exchanger (13) prone to frosting are met, refrigerant is caused to flow through the bypass flow path (25), thereby making it possible to suppress frosting on the heat source heat exchanger.

A fifth aspect is any one of the first to fourth aspects, wherein the intermediate flow path (41) is
The refrigerant passage includes a first pipe (71) extending from a discharge side of the second compression section (22, 23) and connected to the second connection part (27), a second pipe (72) extending from the intercooler (17) side and connected to the second connection part (27), and a third pipe (73) connected to the second connection part (27) and constituting the bypass flow path (25), wherein an angle (β) formed between the first pipe (71) and the third pipe (73) is greater than an angle (α) formed between the first pipe (71) and the second pipe (72).

In the fifth aspect, the refrigerant flowing through the first pipe (71) is more likely to flow through the third pipe (73) than through the second pipe (72) at the second connection part (27). This allows the refrigerant to preferentially flow through the bypass flow path (25) in the first operation.

The sixth aspect is any one of the first to fifth aspects, in which the pressure loss of the refrigerant flowing through the bypass flow path (25) is smaller than the pressure loss of the refrigerant flowing through the flow path from the first connection part (26) through the intercooler (17) to the second connection part (27).

In the sixth aspect, in the first operation, the refrigerant discharged from the second compression section (22, 23) to the intermediate flow path (41) can be made to flow preferentially into the bypass flow path (25) rather than into the intermediate cooler (17).

The seventh aspect is any one of the first to sixth aspects, in which the first operation is a defrost operation in which the heat source heat exchanger (13) serves as an evaporator and the utilization heat exchanger (54, 64) serves as a radiator.

In the seventh aspect, during defrost operation in which frost is melted on the utilization heat exchanger (54, 64) and the heat source heat exchanger serves as an evaporator, frost formation on the heat source heat exchanger (13) can be suppressed.

The eighth aspect is any one of the first to seventh aspects, in which the heat source unit includes a fan (17a) that transports outdoor air to the intercooler (17), and the fan (17a) is stopped during at least a part of the first operation.

The ninth aspect is a refrigeration system including the heat source unit, the utilization unit (50, 60), and a communication pipe (2, 3, 4, 5) that connects the heat source unit and the utilization unit (50, 60), and the heat source unit is the heat source unit of any one of the first to eighth aspects.

FIG. 1 is a piping diagram of a refrigeration system according to an embodiment of the present invention. FIG. 2 is a three-dimensional perspective view showing a part of the configuration of the outdoor unit. FIG. 3 is a cross-sectional view taken along line III-III of FIG. FIG. 4 is a flowchart showing the relationship between each sensor, controller, and each device. FIG. 5 is a diagram corresponding to FIG. 1 and showing the flow of refrigerant during cooling operation. FIG. 6 is a diagram corresponding to FIG. 1 and showing the flow of refrigerant during cooling operation. FIG. 7 is a diagram equivalent to FIG. 1 showing the flow of refrigerant during cooling/cooling operation. FIG. 8 is a diagram corresponding to FIG. 1 and showing the flow of refrigerant during heating operation. FIG. 9 is a diagram equivalent to FIG. 1 showing the flow of refrigerant during heating/cooling operation. FIG. 10 is a view corresponding to FIG. 3 of the outdoor unit according to the first modified example. FIG. 11 is a piping diagram of a refrigeration system according to the second modification. FIG. 12 is a diagram showing the flow of refrigerant during the defrost operation.

The present embodiment will be described below with reference to the drawings. Note that the following embodiment is essentially a preferred example and is not intended to limit the scope of the present invention, its applications, or its uses.

<<Embodiment>>
<overall structure>
The refrigeration system (1) according to the embodiment simultaneously cools an object to be cooled and conditions the air inside a room. The object to be cooled here includes the air inside equipment such as a refrigerator, a freezer, and a showcase. Hereinafter, such equipment will be referred to as a refrigeration facility.

As shown in FIG. 1, the refrigeration system (1) includes an outdoor unit (10) installed outside the room, an indoor unit (50) that performs air conditioning in the room, a cooling unit (60) that cools the air inside the room, and a controller (100). The refrigeration system (1) may have one indoor unit (50) or two or more indoor units (50) connected in parallel. FIG. 1 illustrates one cooling unit (60). The refrigeration system (1) may have two or more cooling units (60) connected in parallel. These units (10, 50, 60) are connected by four connecting pipes (2, 3, 4, 5) to form a refrigerant circuit (6).

The four connection pipes (2, 3, 4, 5) consist of a first liquid connection pipe (2), a first gas connection pipe (3), a second liquid connection pipe (4), and a second gas connection pipe (5). The first liquid connection pipe (2) and the first gas connection pipe (3) correspond to the indoor unit (50). The second liquid connection pipe (4) and the second gas connection pipe (5) correspond to the cooling unit (60).

In the refrigerant circuit (6), a refrigeration cycle is performed by circulating the refrigerant. In this embodiment, the refrigerant in the refrigerant circuit (6) is carbon dioxide. The refrigerant circuit (6) is configured to perform a refrigeration cycle in which the refrigerant reaches or exceeds its critical pressure.

<Outdoor unit>
The outdoor unit (10) is a heat source unit installed outdoors. The outdoor unit (10) has an outdoor fan (12) and an outdoor circuit (11). The outdoor circuit (11) has a compression element (C), a flow path switching mechanism (30), an outdoor heat exchanger (13), an outdoor expansion valve (14), a receiver (15), a cooling heat exchanger (16), and an intermediate cooler (17). As shown in FIG. 2, the outdoor unit (10) includes a base (18). The base (18) is a base on which the compression element (C) and the outdoor heat exchanger (13) are installed. A drain pan (19) formed in a groove shape is provided around the upper surface of the base (18). Condensation water from the outdoor heat exchanger (13) is stored in the drain pan (19).

Compression element
The compression element (C) compresses the refrigerant. The compression element (C) has a first compressor (21), a second compressor (22), and a third compressor (23). The compression element (C) is configured as a two-stage compression type. The second compressor (22) and the third compressor (23) constitute a low-stage side compressor. The second compressor (22) and the third compressor (23) are connected in parallel with each other. The first compressor (21) constitutes a high-stage side compressor. The first compressor (21) and the second compressor (22) are connected in series. The first compressor (21) and the third compressor (23) are connected in series. The first compressor (21) constitutes a first compression section (21), and the second compressor (22) and the third compressor (23) constitute a second compression section (22, 23). The first compressor (21), the second compressor (22), and the third compressor (23) are rotary compressors whose compression mechanisms are driven by motors. The first compressor (21), the second compressor (22), and the third compressor (23) are configured as variable displacement compressors whose operating frequency or rotation speed is adjustable.

The first compressor (21) is connected to a first suction pipe (21a) and a first discharge pipe (21b). The second compressor (22) is connected to a second suction pipe (22a) and a second discharge pipe (22b). The third compressor (23) is connected to a third suction pipe (23a) and a third discharge pipe (23b). The first suction pipe (21a) constitutes an intermediate pressure section between the first compression section (21) and the second compression section (22, 23).

The second suction pipe (22a) communicates with the cold storage unit (60). The second compressor (22) is a cold storage side compressor corresponding to the cold storage unit (60). The third suction pipe (23a) communicates with the indoor unit (50). The third compressor (23) is an indoor side compressor corresponding to the indoor unit (50).

<Flow path switching mechanism>
The flow path switching mechanism (30) switches the flow path of the refrigerant. The flow path switching mechanism (30) has a first pipe (31), a second pipe (32), a third pipe (33), a fourth pipe (34), a first three-way valve (TV1), and a second three-way valve (TV2). An inflow end of the first pipe (31) and an inflow end of the second pipe (32) are connected to a first discharge pipe (21b). The first pipe (31) and the second pipe (32) are pipes on which the discharge pressure of the compression element (C) acts. An outflow end of the third pipe (33) and an outflow end of the fourth pipe (34) are connected to a third suction pipe (23a) of the third compressor (23). The third pipe (33) and the fourth pipe (34) are pipes on which the suction pressure of the compression element (C) acts.

The first three-way valve (TV1) has a first port (P1), a second port (P2), and a third port (P3). The first port (P1) of the first three-way valve (TV1) is connected to the outlet end of the first pipe (31), which is the high-pressure flow path. The second port (P2) of the first three-way valve (TV1) is connected to the inlet end of the third pipe (33), which is the low-pressure flow path. The third port (P3) of the first three-way valve (TV1) is connected to the indoor gas side flow path (35).

The second three-way valve (TV2) has a first port (P1), a second port (P2), and a third port (P3). The first port (P1) of the second three-way valve (TV2) is connected to the outlet end of the second pipe (32), which is the high-pressure flow path. The second port (P2) of the second three-way valve (TV2) is connected to the inlet end of the fourth pipe (34), which is the low-pressure flow path. The third port (P3) of the second three-way valve (TV2) is connected to the outdoor gas side flow path (36).

The first three-way valve (TV1) and the second three-way valve (TV2) are motorized three-way valves. Each three-way valve (TV1, TV2) switches between a first state (state shown by solid lines in FIG. 1) and a second state (state shown by dashed lines in FIG. 1). In each three-way valve (TV1, TV2) in the first state, the first port (P1) and the third port (P3) are connected, and the second port (P2) is closed. In each three-way valve (TV1, TV2) in the second state, the second port (P2) and the third port (P3) are connected, and the first port (P1) is closed.

<Outdoor heat exchanger>
The outdoor heat exchanger (13) constitutes a heat source heat exchanger. The outdoor heat exchanger (13) is a fin-and-tube type air heat exchanger. As shown in FIG. 2, the outdoor heat exchanger (13) is installed on a drain pan (19) of a base (18). The outdoor fan (12) is disposed in the vicinity of the outdoor heat exchanger (13). The outdoor fan (12) transports outdoor air. The outdoor heat exchanger exchanges heat between the refrigerant flowing therein and the outdoor air transported by the outdoor fan (12).

The outdoor gas side flow path (36) is connected to the gas end of the outdoor heat exchanger (13). The outdoor flow path (O) is connected to the liquid end of the outdoor heat exchanger (13).

<Outdoor flow path>
The outdoor flow path (O) includes an outdoor first pipe (o1), an outdoor second pipe (o2), an outdoor third pipe (o3), an outdoor fourth pipe (o4), an outdoor fifth pipe (o5), an outdoor sixth pipe (o6), and an outdoor seventh pipe (o7). One end of the outdoor first pipe (o1) is connected to the liquid end of the outdoor heat exchanger (13). One end of the outdoor second pipe (o2) and one end of the outdoor third pipe (o3) are respectively connected to the other end of the outdoor first pipe (o1). The other end of the outdoor second pipe (o2) is connected to the top of the receiver (15). One end of the outdoor fourth pipe (o4) is connected to the bottom of the receiver (15). One end of the outdoor fifth pipe (o5) and the other end of the outdoor third pipe (o3) are respectively connected to the other end of the outdoor fourth pipe (o4). The other end of the outdoor No. 5 pipe (o5) is connected to the second liquid connecting pipe (4). One end of the outdoor No. 6 pipe (o6) is connected midway through the outdoor No. 5 pipe (o5). The other end of the outdoor No. 6 pipe (o6) is connected to the first liquid connecting pipe (2). One end of the outdoor No. 7 pipe (o7) is connected midway through the outdoor No. 6 pipe (o6). The other end of the outdoor No. 7 pipe (o7) is connected midway through the outdoor No. 2 pipe (o2).

<Outdoor expansion valve>
The outdoor expansion valve (14) is connected to the first outdoor pipe (o1). The outdoor expansion valve (14) is a pressure reducing mechanism for reducing the pressure of the refrigerant. The outdoor expansion valve (14) is a heat source expansion valve. The outdoor expansion valve (14) is an electronic expansion valve whose opening degree is variable.

Receiver
The receiver (15) constitutes a container for storing the refrigerant. In the receiver (15), the refrigerant is separated into a gas refrigerant and a liquid refrigerant. The other end of the second outdoor pipe (o2) and one end of a gas vent pipe (37) are connected to the top of the receiver (15). The other end of the gas vent pipe (37) is connected to the middle of the injection pipe (38). A gas vent valve (39) is connected to the gas vent pipe (37). The gas vent valve (39) is an electronic expansion valve whose opening is variable.

<Cooling heat exchanger>
The cooling heat exchanger (16) cools the refrigerant (mainly liquid refrigerant) separated in the receiver (15). The cooling heat exchanger (16) has a first refrigerant flow path (16a) and a second refrigerant flow path (16b). The first refrigerant flow path (16a) is connected to a portion of the outdoor fourth pipe (o4). The second refrigerant flow path (16b) is connected to a portion of the injection pipe (38).

One end of the injection pipe (38) is connected to the middle of the outdoor fifth pipe (o5). The other end of the injection pipe (38) is connected to the first suction pipe (21a) of the first compressor (21). In other words, the other end of the injection pipe (38) is connected to the intermediate pressure portion of the compression element (C). A pressure reducing valve (40) is provided in the injection pipe (38) upstream of the second refrigerant flow path (16b). The pressure reducing valve (40) is an expansion valve whose opening degree is variable.

In the cooling heat exchanger (16), heat is exchanged between the refrigerant flowing through the first refrigerant flow path (16a) and the refrigerant flowing through the second refrigerant flow path (16b). The refrigerant depressurized by the pressure reducing valve (40) flows through the second refrigerant flow path (16b). Therefore, in the cooling heat exchanger (16), the refrigerant flowing through the first refrigerant flow path (16a) is cooled.

<Intermediate flow path>
As shown in Fig. 1, the intermediate flow path (41) is a flow path connecting the suction side of the first compression section (21) and the discharge side of the second compression section (22, 23). Specifically, one end of the intermediate flow path (41) is connected to the second discharge pipe (22b) of the second compressor (22) and the third discharge pipe (23b) of the third compressor (23). The other end of the intermediate flow path (41) is connected to the first suction pipe (21a) of the first compressor (21). In other words, the other end of the intermediate flow path (41) is connected to the intermediate pressure section of the compression element (C).

The intermediate flow path (41) has an intermediate cooler (17) and a bypass flow path (25).

The intermediate cooler (17) is provided midway through the intermediate flow path (41). The intermediate cooler (17) is a fin-and-tube type air heat exchanger. A cooling fan (17a) is disposed near the intermediate cooler (17). The cooling fan (17a) transports outdoor air to the intermediate cooler (17). The refrigerant flowing inside the intermediate cooler (17) exchanges heat with the outdoor air transported by the cooling fan (17a).

As shown in Figs. 1 and 2, the bypass flow path (25) is provided so that the refrigerant flowing through the intermediate flow path (41) bypasses the economizer (17). Specifically, one end of the bypass flow path (25) is connected to a first connection part (26) between the economizer (17) and the first compression section (21). The first connection part (26) is provided between the outflow end of the economizer (17) and the first intake pipe (21a). The other end of the bypass flow path (25) is connected to a second connection part (27) between the economizer (17) and the second compression section (22, 23). The second connection part (27) is provided between the inflow end of the economizer (17) and the second discharge pipe (22b) and the third discharge pipe (23b).

The bypass flow path (25) is provided at the bottom of the outdoor heat exchanger (13). Specifically, as shown in FIG. 2 and FIG. 3, the bypass flow path (25) is inserted into the outdoor heat exchanger (13) from below the lowest heat transfer tube (13a) of the outdoor heat exchanger (13). The bypass flow path (25) is arranged in two rows below the lowest heat transfer tube (13a). The bypass flow path (25) includes an inlet pipe (25a) located in the right row at the front end of the outdoor heat exchanger (13) in FIG. 2 and an outlet pipe (25b) located in the left row. The bypass flow path (25) is connected to a U-shaped tube (25c) at the left end of the outdoor heat exchanger (13) in FIG. 2. As shown by the arrow in FIG. 2, the refrigerant in the bypass flow path (25) flows through the outdoor heat exchanger (13) and is sent to the first compressor (21).

The bypass flow passage (25) is provided with a bypass valve (28). The bypass valve (28) is an opening/closing valve whose opening can be adjusted to adjust the flow rate of the refrigerant flowing through the intercooler (17) and the bypass flow passage (25). The bypass valve (28) is, for example, a flow rate control valve (motorized valve) whose opening can be adjusted.

The intermediate flow path (41) has a first pipe (71), a second pipe (72), and a third pipe (73). The first to third pipes (71 to 73) are part of the intermediate flow path (41) extending in three directions from the second connection part (27). Specifically, the first pipe (71) extends from the discharge side of the second compression part (22, 23) and is connected to the second connection part (27). The second pipe (72) extends from the intermediate cooler (17) side and is connected to the second connection part. The third pipe (73) is connected to the second connection part (27) and constitutes the bypass flow path (25). The intermediate flow path (41) is configured such that the angle (β) between the first pipe (71) and the third pipe (73) is 180°, and the angle (α) between the first pipe (71) and the second pipe (72) is 90°. Specifically, the first pipe (71) extends horizontally toward the second connection portion (27). The second pipe (72) extends vertically upward from the second connection portion (27). The third pipe (73) extends horizontally from the second connection portion (27) on an extension of the first pipe (71).

In this manner, the intermediate flow path (41) is configured to branch into the bypass flow path (25) and the first flow path (29) to which the intercooler (17) is connected at the second connection part (27), and the bypass flow path (25) and the first flow path (29) merge again at the first connection part (26). The intermediate flow path (41) is configured so that the pressure loss of the refrigerant flowing through the bypass flow path (25) is smaller than the pressure loss of the refrigerant flowing through the first flow path (29). Specifically, the overall length of the bypass flow path (25) is shorter than the overall length of the first flow path (29).

<Oil separation circuit>
As shown in FIG. 1, the outdoor circuit (11) includes an oil separation circuit (42). The oil separation circuit (42) includes an oil separator (43), a first oil return pipe (44), a second oil return pipe (45), and a third oil return pipe (46). The oil separator (43) is connected to the first discharge pipe (21b) of the first compressor (21). The oil separator (43) separates oil from the refrigerant discharged from the compression element (C). The inflow end of the first oil return pipe (44) is connected to the oil separator (43). The outflow end of the first oil return pipe (44) is connected to the second suction pipe (22a) of the second compressor (22). The inflow end of the second oil return pipe (45) is connected to the oil separator (43). The outflow end of the second oil return pipe (45) is connected to the inflow end of the intermediate flow path (41). The third oil return pipe (46) includes a main return pipe (46a), a cooling-side branch pipe (46b), and an indoor branch pipe (46c). The inflow end of the main return pipe (46a) is connected to the oil separator (43). The outflow end of the main return pipe (46a) is connected to the inflow end of the cooling-side branch pipe (46b) and the inflow end of the indoor branch pipe (46c). The outflow end of the cooling-side branch pipe (46b) is connected to an oil reservoir in the casing of the second compressor (22). The outflow end of the indoor branch pipe (46c) is connected to an oil reservoir in the casing of the third compressor (23).

The first oil return pipe (44) is connected to a first oil amount control valve (47a). The second oil return pipe (45) is connected to a second oil amount control valve (47b). The cooling side branch pipe (46b) is connected to a third oil amount control valve (47c). The indoor side branch pipe (46c) is connected to a fourth oil amount control valve (47d).

The oil separated in the oil separator (43) is returned to the second compressor (22) via the first oil return pipe (44). The oil separated in the oil separator (43) is returned to the third compressor (23) via the second oil return pipe (45). The oil separated in the oil separator (43) is returned to the oil reservoirs in the casings of the second compressor (22) and the third compressor (23) via the third oil return pipe (46).

<non-return valve>
The outdoor circuit (11) includes a first check valve (CV1), a second check valve (CV2), a third check valve (CV3), a fourth check valve (CV4), a fifth check valve (CV5), a sixth check valve (CV6), and a seventh check valve (CV7). The first check valve (CV1) is connected to the first discharge pipe (21b). The second check valve (CV2) is connected to the second discharge pipe (22b). The third check valve (CV3) is connected to the third discharge pipe (23b). The fourth check valve (CV4) is connected to the second outdoor pipe (o2). The fifth check valve (CV5) is connected to the third outdoor pipe (o3). The sixth check valve (CV6) is connected to the sixth outdoor pipe (o6). The seventh check valve (CV7) is connected to the seventh outdoor pipe (o7). These check valves (CV1 to CV7) allow the refrigerant to flow in the direction of the arrow shown in FIG. 1, and prohibit the refrigerant from flowing in the opposite direction to the arrow.

<Indoor unit>
The indoor unit (50) is a utilization unit installed indoors. The indoor unit (50) has an indoor fan (52) and an indoor circuit (51). A first liquid connection pipe (2) is connected to a liquid end of the indoor circuit (51). A first gas connection pipe (3) is connected to a gas end of the indoor circuit (51).

The indoor circuit (51) has, in order from the liquid end to the gas end, an indoor expansion valve (53) and an indoor heat exchanger (54). The indoor expansion valve (53) is a first utility expansion valve. The indoor expansion valve (53) is an electronic expansion valve whose opening is variable.

The indoor heat exchanger (54) is a utility heat exchanger. The indoor heat exchanger (54) is a fin-and-tube type air heat exchanger. The indoor fan (52) is disposed near the indoor heat exchanger (54). The indoor fan (52) transports indoor air. The indoor heat exchanger (54) exchanges heat between the refrigerant flowing therethrough and the indoor air transported by the indoor fan (52).

<Refrigeration unit>
The refrigeration unit (60) is a utilization unit that cools the interior of the refrigerator. The refrigeration unit (60) has a refrigeration fan (62) and a refrigeration circuit (61). A second liquid connection pipe (4) is connected to a liquid end of the refrigeration circuit (61). A second gas connection pipe (5) is connected to a gas end of the refrigeration circuit (61).

The cold-setting circuit (61) has, in order from the liquid end to the gas end, a cold-setting expansion valve (63) and a cold-setting heat exchanger (64). The cold-setting expansion valve (63) is a second utilization expansion valve. The cold-setting expansion valve (63) is an electronic expansion valve whose opening is variable.

The cold-air heat exchanger (64) is a utilization heat exchanger. The cold-air heat exchanger (64) is a fin-and-tube type air heat exchanger. The cold-air fan (62) is disposed near the cold-air heat exchanger (64). The cold-air fan (62) transports the air inside the storage unit. The cold-air heat exchanger (64) exchanges heat between the refrigerant flowing therethrough and the air inside the storage unit transported by the cold-air fan (62).

Sensors
The refrigeration system (1) has various sensors, including an outdoor air temperature sensor (74). The outdoor air temperature sensor (74) detects the outdoor air temperature. The outdoor air temperature sensor (74) is provided near the outdoor fan (12).

Physical quantities detected by other sensors (not shown) include the temperature/pressure of the high-pressure refrigerant in the refrigerant circuit (6), the temperature/pressure of the refrigerant in the gas-liquid separator (15), the temperature/pressure of the low-pressure refrigerant, the temperature/pressure of the intermediate-pressure refrigerant, the temperature of the refrigerant in the outdoor heat exchanger (13), the temperature of the refrigerant in the cold heat exchanger (64), the temperature of the refrigerant in the indoor heat exchanger (54), the temperature of the air inside the storage unit, and the temperature of the indoor air.

<controller>
The controller (100) is a control unit. As shown in Fig. 4, the controller (100) includes a microcomputer mounted on a control board and a memory device (specifically, a semiconductor memory) that stores software for operating the microcomputer. The controller (100) controls each device of the refrigeration system (1), such as the cooling fan (17a) and the bypass valve (28), based on detection signals from various sensors. The operation of the refrigeration system (1) is switched by the control of each device by the controller (100).

- Driving operation -
A detailed description will be given of the operation of the refrigeration system (1). The operation of the refrigeration system (1) includes cooling operation, cooling operation, cooling/cooling operation, heating operation, heating/cooling operation, and defrost operation.

In cooling operation, the cooling unit (60) is operated and the indoor unit (50) is stopped. In cooling operation, the cooling unit (60) is stopped and the indoor unit (50) performs cooling. In cooling/cooling operation, the cooling unit (60) is operated and the indoor unit (50) performs cooling. In heating operation, the cooling unit (60) is stopped and the indoor unit (50) performs heating. In defrost operation, the indoor unit (50) is operated and an operation is performed to melt frost on the surface of the indoor heat exchanger (54).

<Cold operation>
As shown in FIG. 5, in the cooling operation, the first three-way valve (TV1) is in the second state, and the second three-way valve (TV2) is in the first state. The outdoor expansion valve (14) is opened at a predetermined opening degree, the opening degree of the cold-setting expansion valve (63) is adjusted by controlling the degree of superheat, the indoor expansion valve (53) is fully closed, and the opening degree of the pressure reducing valve (40) is appropriately adjusted. The outdoor fan (12), the cooling fan (17a), and the cold-setting fan (62) are operated, and the indoor fan (52) is stopped. The first compressor (21) and the second compressor (22) are operated, and the third compressor (23) is stopped. In the cooling operation, a refrigeration cycle is performed in which the refrigerant compressed by the compression element (C) releases heat in the outdoor heat exchanger (13) and evaporates in the cold-setting heat exchanger (64).

The refrigerant compressed by the second compressor (22) is cooled by the intermediate cooler (17) and then sucked into the first compressor (21). The refrigerant compressed by the first compressor (21) releases heat in the outdoor heat exchanger (13), flows through the receiver (15), and is cooled by the cooling heat exchanger (16). The refrigerant cooled by the cooling heat exchanger (16) is decompressed by the cold expansion valve (63) and then evaporates in the cold heat exchanger (64). As a result, the air inside the storage unit is cooled. The refrigerant evaporated in the cooling heat exchanger (16) is sucked into the second compressor (22) and compressed again.

The bypass valve (28) is fully closed. During cooling operation, the refrigerant that flows from the second compression section (22, 23) into the intermediate flow path (41) does not flow into the bypass flow path (25).

<Cooling operation>
As shown in Fig. 6, in the cooling operation, the first three-way valve (TV1) is in the second state, and the second three-way valve (TV2) is in the first state. The outdoor expansion valve (14) is opened at a predetermined opening, the cold-setting expansion valve (63) is fully closed, the opening of the indoor expansion valve (53) is adjusted by controlling the superheat degree, and the opening of the pressure reducing valve (40) is appropriately adjusted. The outdoor fan (12), the cooling fan (17a), and the indoor fan (52) are operated, and the cold-setting fan (62) is stopped. The first compressor (21) and the third compressor (23) are operated, and the second compressor (22) is stopped. In the cooling operation, a refrigeration cycle is performed in which the refrigerant compressed by the compression element (C) releases heat in the outdoor heat exchanger (13) and evaporates in the indoor heat exchanger (54).

The refrigerant compressed by the third compressor (23) is cooled by the intermediate cooler (17) and then sucked into the first compressor (21). The refrigerant compressed by the first compressor (21) releases heat in the outdoor heat exchanger (13), flows through the receiver (15), and is cooled by the cooling heat exchanger (16). The refrigerant cooled by the cooling heat exchanger (16) is reduced in pressure by the indoor expansion valve (53) and then evaporates in the indoor heat exchanger (54). As a result, the indoor air is cooled. The refrigerant evaporated in the indoor heat exchanger (54) is sucked into the third compressor (23) and compressed again.

The bypass valve (28) is fully closed. During cooling operation, the refrigerant that flows from the second compression section (22, 23) into the intermediate flow path (41) does not flow into the bypass flow path (25).

<Cooling/cooling operation>
As shown in Fig. 7, in the cooling/cooling operation, the first three-way valve (TV1) is in the second state, and the second three-way valve (TV2) is in the first state. The outdoor expansion valve (14) is opened at a predetermined opening degree, the opening degrees of the cold-setting expansion valve (63) and the indoor expansion valve (53) are adjusted by controlling the degree of superheat, and the opening degree of the pressure reducing valve (40) is appropriately adjusted. The outdoor fan (12), the cooling fan (17a), the cold-setting fan (62), and the indoor fan (52) are operated. The first compressor (21), the second compressor (22), and the third compressor (23) are operated. In the cooling/cooling operation, a refrigeration cycle is performed in which the refrigerant compressed by the compression element (C) releases heat in the outdoor heat exchanger (13) and evaporates in the cold-setting heat exchanger (64) and the indoor heat exchanger (54).

The refrigerant compressed by the second compressor (22) and the third compressor (23) is cooled by the intermediate cooler (17) and then sucked into the first compressor (21). The refrigerant compressed by the first compressor (21) dissipates heat in the outdoor heat exchanger (13), flows through the receiver (15), and is cooled by the cooling heat exchanger (16). The refrigerant cooled by the cooling heat exchanger (16) is divided into the cold-setting unit (60) and the indoor unit (50). The refrigerant decompressed by the cold-setting expansion valve (63) evaporates in the cold-setting heat exchanger (64). The refrigerant evaporated in the cold-setting heat exchanger (64) is sucked into the second compressor (22) and compressed again. The refrigerant decompressed by the indoor expansion valve (53) evaporates in the indoor heat exchanger (54). The refrigerant evaporated in the indoor heat exchanger (54) is sucked into the third compressor (23) and compressed again.

The bypass valve (28) is fully closed. In cooling/cooling operation, the refrigerant that flows from the second compression section (22, 23) into the intermediate flow path (41) does not flow into the bypass flow path (25).

<Heating operation>
As shown in Fig. 8, in the heating operation, the first three-way valve (TV1) is in the first state, and the second three-way valve (TV2) is in the second state. The indoor expansion valve (53) is opened at a predetermined opening degree, the cold-setting expansion valve (63) is in a fully closed state, the opening degree of the outdoor expansion valve (14) is adjusted by controlling the degree of superheat, and the opening degree of the pressure reducing valve (40) is appropriately adjusted. The outdoor fan (12) and the indoor fan (52) are operated, and the cooling fan (17a) and the cold-setting fan (62) are stopped. The first compressor (21) and the third compressor (23) are operated, and the second compressor (22) is stopped. In the heating operation, a refrigeration cycle is performed in which the refrigerant compressed by the compression element (C) releases heat in the indoor heat exchanger (54) and evaporates in the outdoor heat exchanger (13).

The refrigerant compressed by the third compressor (23) flows through the bypass flow path (25) and is then sucked into the first compressor (21). The refrigerant compressed by the first compressor (21) dissipates heat in the indoor heat exchanger (54). As a result, the indoor air is heated. The refrigerant that has dissipated heat in the indoor heat exchanger (54) flows through the receiver (15) and is cooled in the cooling heat exchanger (16). The refrigerant cooled in the cooling heat exchanger (16) is decompressed by the outdoor expansion valve (14) and then evaporates in the outdoor heat exchanger (13). The refrigerant that has evaporated in the outdoor heat exchanger (13) is sucked into the third compressor (23) and compressed again.

The bypass valve (28) is fully open. During heating operation, the refrigerant that flows from the second compression section (22, 23) into the intermediate flow path (41) does not flow into the intercooler (17).

<Heating/Cooling Operation>
As shown in Fig. 9, in the heating/cooling operation, the first three-way valve (TV1) is set to the first state, and the second three-way valve (TV2) is set to the second state. The indoor expansion valve (53) is opened at a predetermined opening degree, the opening degrees of the cold-setting expansion valve (63) and the outdoor expansion valve (14) are adjusted by controlling the degree of superheat, and the opening degree of the pressure reducing valve (40) is appropriately adjusted. The outdoor fan (12), the cold-setting fan (62), and the indoor fan (52) are operated, and the cooling fan (17a) is stopped. The first compressor (21), the second compressor (22), and the third compressor (23) are operated. In the heating/cooling operation, a refrigeration cycle is performed in which the refrigerant compressed by the compression element (C) releases heat in the indoor heat exchanger (54) and evaporates in the cold-setting heat exchanger (64) and the outdoor heat exchanger (13).

The refrigerant compressed in the second compressor (22) and the third compressor (23) flows through the intermediate cooler (17) and is then sucked into the first compressor (21). The refrigerant compressed in the first compressor (21) dissipates heat in the indoor heat exchanger (54). As a result, the indoor air is heated. The refrigerant that dissipates heat in the indoor heat exchanger (54) flows through the receiver (15) and is cooled in the cooling heat exchanger (16). A portion of the refrigerant cooled in the cooling heat exchanger (16) is depressurized in the outdoor expansion valve (14) and then evaporates in the outdoor heat exchanger (13). The refrigerant that has evaporated in the outdoor heat exchanger (13) is sucked into the third compressor (23) and compressed again.

The remaining refrigerant cooled in the cooling heat exchanger (16) is decompressed in the cold expansion valve (63) and then evaporates in the cold heat exchanger (64). As a result, the air inside the cabinet is cooled. The refrigerant evaporated in the cold heat exchanger (64) is sucked into the second compressor (22) and compressed again.

The opening of the bypass valve (28) is appropriately adjusted by the controller (100). During heating/cooling operation, the refrigerant that flows from the second compression section (22, 23) into the intermediate flow path (41) also flows through the bypass flow path (25).

- Issues with defrosting outdoor heat exchangers -
The first operation includes a heating operation and a heating/cooling operation. Here, the first operation is an operation in which the outdoor heat exchanger (13) serves as an evaporator. In the conventional refrigeration system (1), if frost forms on the outdoor heat exchanger (13) during the first operation, it is necessary to perform a defrost operation in which the outdoor heat exchanger (13) serves as a radiator. In the defrost operation, the frost on the outdoor heat exchanger (13) can be melted by the heat radiation from the outdoor heat exchanger (13).

However, there is a problem in that performing the defrost operation makes it impossible to continue the first operation (heating operation) and the heating/cooling operation.

In consideration of these issues, the refrigeration system (1) of this embodiment performs the following control to suppress frost formation on the outdoor heat exchanger (13) during the first operation.

- Control of the first operation -
In the first operation, the controller (100) appropriately adjusts the opening of the bypass valve (28) and the rotation speed of the cooling fan (17a). Specifically, when the controller (100) receives a command to perform the first operation, the controller (100) opens the bypass valve (28). As a result, substantially all of the refrigerant discharged from the second compression section (22, 23) to the intermediate flow path (41) in the first operation flows into the bypass flow path (25). While the first operation is being performed, the cooling fan (17a) is stopped.

In the first operation, the controller (100) performs the first control. The first control is a control in which the bypass valve (28) is opened when the outside air temperature sensor (74) detects that the outside air temperature is lower than a predetermined value. Here, the predetermined value is, for example, 0°C. Specifically, when the outside air temperature sensor (74) detects that the outside air temperature is below 0°C, the controller (100) executes the first control.

In the first operation, the high-temperature refrigerant compressed in the second compression section (22, 23) flows into the intermediate flow path (41). Of the refrigerant that flows into the intermediate flow path (41), an amount of refrigerant that corresponds to the opening degree of the bypass valve (28) flows into the bypass flow path (25). The high-temperature refrigerant that flows into the bypass flow path (25) circulates through the lower part of the outdoor heat exchanger (13) and dissipates heat to the outdoor heat exchanger (13). Thereafter, this refrigerant merges with the refrigerant that has passed through the intermediate cooler (17) at the first connection part (26). The merged refrigerant is sucked into the first compressor (21).

In cooling operation, cooling operation, and cooling/cooling operation, the outdoor heat exchanger (13) functions as a radiator. The bypass valve (28) is fully closed by the controller (100). Therefore, in operations other than the first operation, the refrigerant discharged from the second compression section (22, 23) to the intermediate flow path (41) does not flow through the bypass flow path (25). The entire amount of refrigerant passes through the intercooler.

--Effects of the embodiment--
In the embodiment, a heat source unit including a heat source circuit (11) including a first compression section (21), a second compression section (22, 23), an intercooler (17), and a heat-source heat exchanger (13), and configured to configure a refrigerant circuit (6) performing a refrigeration cycle by being connected to a utilization unit (50, 60) having a utilization heat exchanger (54, 64), is configured as follows: Specifically, the first compression section (21) and the second compression section (22, 23) are connected to each other by an intermediate flow path (41) that connects the discharge side of the second compression section (22, 23) and the suction side of the first compression section (21). The intermediate flow path (41) includes an economizer (17) provided in the middle of the intermediate flow path (41), and a bypass flow path (25) having one end connected to a first connection portion (26) between the economizer (17) and a first compression section (21) and the other end connected to a second connection portion (27) between the economizer (17) and a second compression section (22, 23). At least a portion of the bypass flow path (25) is disposed below the heat source heat exchanger (13). The heat source circuit (11) includes a switching mechanism (K) that enables the bypass flow path (25) to be opened in a first operation in which the heat source heat exchanger (13) serves as an evaporator.

In this embodiment, in the first operation, the high-temperature refrigerant compressed in the second compression section (22, 23) flows into the bypass flow path (25). The refrigerant that flows into the bypass flow path (25) flows through the lower part of the outdoor heat exchanger (13). Therefore, frost formation on the outdoor heat exchanger (13) can be suppressed in the first operation.

In addition, in the first operation, the high-temperature refrigerant compressed by the second compression section exchanges heat with the outdoor heat exchanger (13) in the bypass passage (25). Therefore, there is no need to cool this refrigerant by the intercooler (17). As a result, in the first operation, the operating power of the cooling fan (17a) can be reduced, which in turn leads to energy savings.

In this embodiment, the switching mechanism (K) is connected to the intermediate flow path (41) and includes an opening/closing valve (bypass valve (28)) whose opening is adjustable to adjust the flow rate of the refrigerant flowing through the bypass flow path (25).

In this embodiment, the bypass valve (28) can adjust the flow rate of the refrigerant flowing into the intermediate cooler (17) and the bypass flow path (25).

In addition, the suction temperature of the refrigerant into the first compressor (21) can be adjusted by adjusting the flow rate of the refrigerant flowing into the intercooler (17) and the bypass flow path (25).

In this embodiment, the control unit (100) (controller) performs a first control to open the bypass flow path (25) when a condition indicating that the outside air temperature is lower than a predetermined value is satisfied during the first operation.

In this configuration, for example, when the outdoor air temperature falls below 0°C, there is a possibility that frost will form on the outdoor heat exchanger (13) during the first operation. Even in this case, the opening of the bypass valve (28) is adjusted to allow high-temperature refrigerant to flow into the bypass passage (25). This makes it possible to suppress frost formation on the outdoor heat exchanger (13).

In the embodiment, a first pipe (71) extends from the discharge side of the second compression section (22, 23) and is connected to the second connection section (27), a second pipe (72) extends from the intercooler (17) side and is connected to the second connection section (27), and a third pipe (73) is connected to the second connection section (27) and constitutes the bypass flow path (25), and the angle (β) between the first pipe (71) and the third pipe (73) is larger than the angle (α) between the first pipe (71) and the second pipe (72).

In this embodiment, the refrigerant in the first pipe (71) flowing from the second compression section (22, 23) is more likely to flow toward the third pipe (73) than toward the second pipe (72) at the second connection part (27). This allows the refrigerant to preferentially flow into the bypass passage (25) in the first operation. As a result, when the bypass valve (28) is opened, the high-temperature refrigerant quickly flows through the bypass passage (25). Therefore, frost formation on the outdoor heat exchanger (13) can be reliably suppressed in the first operation.

In this embodiment, the pressure loss of the refrigerant flowing through the bypass flow path (25) is smaller than the pressure loss of the refrigerant flowing through the flow path from the first connection part (26) through the intercooler (17) to the second connection part (27).

In this embodiment, in the first operation, the refrigerant discharged from the second compression section (22, 23) to the intermediate flow path (41) can flow preferentially through the bypass flow path (25) where the compression loss is small. This allows the refrigerant to quickly flow into the bypass flow path (25) in the first operation.

In this embodiment, the heat source unit (10) includes a fan (17a) (cooling fan) that transports outdoor air to the intercooler (17), and in the first operation, the fan (17a) is stopped.

In this mode, the amount of refrigerant flowing through the intercooler (17) decreases during the first operation. Therefore, energy can be saved by stopping the cooling fan (17a).

<<Variation 1>>
10 , the bypass flow path (25) of the first modification is disposed near the lower part of the outdoor heat exchanger (13). Specifically, the bypass flow path (25) is disposed in the drain pan (19). The refrigerant flowing into the bypass flow path (25) flows near the lower part of the outdoor heat exchanger (13).

In this first modification, too, frost formation on the outdoor heat exchanger (13) can be suppressed in the first operation. Even if frost forms on the outdoor heat exchanger (13), the frost can be defrosted by the first operation.

<<Variation 2>>
As shown in Fig. 11, the utilization unit of the refrigeration system (1) of the second modification includes only a cooling unit (60). In the heat source circuit (11) of the second modification, the third port (P3) of the first three-way valve (TV1) communicates with the second gas connection pipe (5). The low-stage compressor includes only the second compressor (22).

In the refrigeration system (1) of the second modified example, cooling operation is normally performed. The cooling operation is a refrigerant cycle operation in which the outdoor heat exchanger (13) serves as a radiator and the cooling heat exchanger (64) serves as an evaporator.

As shown in FIG. 12, the first operation is a defrost operation in which the cold-conditioning heat exchanger (64) serves as a radiator and the outdoor heat exchanger (13) serves as an evaporator. During the cold-conditioning operation, when frost forms on the cold-conditioning heat exchanger (64), the frost is removed from the cold-conditioning heat exchanger (64) by the defrost operation.

In defrost operation, the first three-way valve (TV1) is in the first state, and the second three-way valve (TV2) is in the second state. The cold-setting expansion valve (63) is fully open, and the pressure reducing valve (40) is fully closed. The outdoor fan (12) and the cold-setting fan (62) are operated, and the cooling fan (17a) is stopped.

The refrigerant compressed by the second compressor (22) flows through the bypass flow path (25) and is then sucked into the first compressor (21). The refrigerant compressed by the first compressor (21) dissipates heat in the cold-dissipating heat exchanger (64). As a result, the frost on the surface of the cold-dissipating heat exchanger (64) is heated from the inside. The refrigerant used to defrost the cold-dissipating heat exchanger (64) evaporates in the outdoor heat exchanger (13), is then sucked into the second compressor (22) and compressed again.

In the defrost operation, the bypass valve (28) is fully open. In the defrost operation, the refrigerant that flows from the second compression section (22, 23) into the intermediate flow path (41) does not flow into the intercooler (17). Therefore, the refrigerant compressed by the second compressor (22) flows near the lower part of the outdoor heat exchanger (13). Therefore, even in the defrost operation of the second modification, frost formation on the outdoor heat exchanger (13) can be suppressed.

Other Embodiments
In the above embodiment, the following configuration may be adopted.

In this embodiment, the intermediate flow path (41) is configured so that the angle β between the first pipe (71) and the third pipe (73) is 180°, and the angle α between the first pipe (71) and the second pipe (72) is 90°. However, the intermediate flow path (41) may be configured so that the angle β is greater than the angle α.

In the embodiment, the length of the bypass flow path (25) is shorter than the length of the first flow path (29). However, the intermediate flow path (41) only needs to be configured so that the pressure loss of the refrigerant flowing through the bypass flow path (25) is smaller than the pressure loss of the refrigerant flowing through the first flow path (29). For example, the bypass flow path (25) may be configured so that the inner diameter is larger than the inner diameter of the first flow path (29). This makes the pressure loss of the refrigerant flowing through the bypass flow path (25) lower than the pressure loss of the refrigerant flowing through the first flow path (29). As a result, the refrigerant can be preferentially circulated through the bypass flow path (25).

In this embodiment, the bypass valve (28) is connected to the bypass flow path (25). However, the bypass valve (28) may be connected to the first flow path (29). When the entire amount of refrigerant that has flowed into the intermediate flow path (41) is to be caused to flow into the bypass flow path (25), the bypass valve (28) may be controlled to be fully closed.

In the embodiment, the bypass valve (28) is a flow rate control valve. However, the bypass valve (28) may be an on-off valve that can adjust the refrigerant to flow to either the intercooler (17) or the bypass flow path (25). In this case, the bypass valve (28) is, for example, a solenoid valve. This makes it possible to control the refrigerant to flow to the bypass flow path (25) in the first operation. As a result, when the outdoor heat exchanger (13) functions as an evaporator, frost formation on the outdoor heat exchanger (13) can be steadily suppressed.

In this embodiment, the cooling fan (17a) is stopped during the first operation. However, the cooling fan (17a) may be operated during part of the first operation.

The indoor heat exchanger (54) does not have to be an air heat exchanger that exchanges heat between air and a refrigerant. The indoor heat exchanger (54) may be, for example, a heating heat exchanger that heats water or brine using a refrigerant.

The cold-air heat exchanger (64) does not have to be an air heat exchanger that exchanges heat between air and a refrigerant. The cold-air heat exchanger (64) may be, for example, a cooling heat exchanger that cools water or brine using a refrigerant.

Although the embodiments and modifications have been described above, it will be understood that various modifications of form and details are possible without departing from the spirit and scope of the claims. Furthermore, the above embodiments and modifications may be combined or substituted as appropriate as long as the functionality of the subject matter of this disclosure is not impaired. The descriptions "first," "second," "third," etc. described above are used to distinguish the words to which these descriptions are attached, and do not limit the number or order of the words.

As explained above, the present disclosure is useful for refrigeration devices.

K switching mechanism 1 refrigeration device 6 refrigerant circuit 11 heat source circuit 13 outdoor heat exchanger (heat source heat exchanger)
17 Intercooler 17a Cooling fan (fan)
21 First compressor (first compression section)
22 Second compressor (second compression section)
23 Third compressor (second compression section)
25 Bypass flow path 26 First connection part 27 Second connection part 28 Bypass valve (on-off valve)
30: flow path switching mechanism 41: intermediate flow path 50: indoor unit (utilization unit)
60 Refrigeration unit (utilization unit)
54 Indoor heat exchanger (utilization heat exchanger)
64 Refrigeration heat exchanger (utilization heat exchanger)
71 First pipe 72 Second pipe 73 Third pipe 100 Controller (control unit)

Claims (6)

A heat source unit including a heat source circuit (11) including a first compression section (21), a second compression section (22, 23), an intercooler (17), and a heat source heat exchanger (13), and which constitutes a refrigerant circuit (6) performing a refrigeration cycle by being connected to a utilization unit (50, 60) having a utilization heat exchanger (54, 64),
the first compression section (21) and the second compression section (22, 23) are connected to each other by an intermediate flow passage (41) connecting a discharge side of the second compression section (22, 23) and a suction side of the first compression section (21);
The intermediate flow path (41)
an intermediate cooler (17) provided midway through the intermediate flow path (41);
a bypass flow path (25) having one end connected to a first connection portion (26) between the economizer (17) and the first compression section (21) and the other end connected to a second connection portion (27) between the economizer (17) and the second compression section (22, 23),
at least a portion of the bypass flow path (25) is located at or near a lower portion of the heat source heat exchanger (13);
the heat source circuit (11) includes a switching mechanism (K) capable of opening the bypass flow path (25) in a first operation in which the heat source heat exchanger (13) functions as an evaporator;
The switching mechanism (K)
an on-off valve (28) connected to the intermediate flow path (41) and adjustable so that a refrigerant flows into either the intermediate cooler (17) or the bypass flow path (25);
The intermediate flow path (41)
a first pipe (71) extending from a discharge side of the second compression section (22, 23) and connected to the second connection section (27);
a second pipe (72) extending from the intercooler (17) side and connected to the second connection portion (27);
a third pipe (73) connected to the second connection portion (27) and constituting the bypass flow path (25),
an angle (β) between the first pipe (71) and the third pipe (73) is larger than an angle (α) between the first pipe (71) and the second pipe (72),
The heat source unit, wherein the on-off valve (28) is connected to the third pipe (73) and is not connected to the second pipe (72). In claim 1 ,
The on-off valve (28)
The heat source unit, characterized in that the opening degree of the bypass passage (25) is adjustable so as to adjust the flow rate of the refrigerant flowing through the bypass passage (25). In claim 1 or 2 ,
a control unit (100) performing a first control of opening the bypass flow path (25) when a condition indicating that the outside air temperature is lower than a predetermined value is established, during the first operation. In any one of claims 1 to 3 ,
The heat source unit, wherein the first operation is a defrost operation in which the heat source heat exchanger (13) serves as an evaporator and the utilization heat exchanger (54, 64) serves as a radiator. In any one of claims 1 to 4 ,
The heat source unit includes a fan (17a) that transports outdoor air to the intercooler (17),
The heat source unit, wherein the fan (17a) is stopped during at least a part of the first operation. A refrigeration system comprising the heat source unit, the utilization unit (50, 60), and communication piping (2, 3, 4, 5) connecting the heat source unit and the utilization unit (50, 60),
A refrigeration system, wherein the heat source unit is the heat source unit according to any one of claims 1 to 5 .

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