US20250334310A1

US20250334310A1 - Heat source unit and refrigeration apparatus

Info

Publication number: US20250334310A1
Application number: US19/262,162
Authority: US
Inventors: Naoto Kimura; Iwao Shinohara; Masaaki Takegami; Tetsuya SHIRASAKI
Original assignee: Daikin Industries Ltd
Current assignee: Daikin Industries Ltd
Priority date: 2023-02-15
Filing date: 2025-07-08
Publication date: 2025-10-30
Also published as: EP4628816A8; JP2024115906A; JP7568955B2; CN120548446A; WO2024171704A1; EP4628816A1

Abstract

A heat source unit includes a heat-source-side circuit and a controller. In the heat-source-side circuit, an expansion valve is located between a heat-source-side heat exchanger and a receiver. while the compression element of the heat-source-side circuit is stopped, the controller controls the expansion valve based on one or both of a refrigerant pressure in the receiver and a refrigerant pressure in the heat-source-side heat exchanger.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a bypass continuation of PCT international application No. PCT/JP2024/001188, filed on Jan. 18, 2024, which claims benefit of Japanese patent application No. 2023-021806, filed on Feb. 15, 2023, the contents of each are incorporated herein by reference in their entirety.

TECHNICAL FIELD

The present disclosure relates to a heat source unit and a refrigeration apparatus.

BACKGROUND ART

Patent Document 1 discloses a heat source unit for a refrigeration apparatus. The heat source unit is connected to a utilization-side unit and performs a refrigeration cycle. The heat source unit includes devices such as a compressor, an outdoor heat exchanger, and a receiver.

CITATION LIST

Patent Document

- Patent Document 1: Japanese Unexamined Patent Publication No. 2022-152437

SUMMARY

A first aspect of the present disclosure is directed to a heat source unit connected to a utilization-side unit and configured to perform a refrigeration cycle. The heat source unit includes: a heat-source-side circuit including a compression element with one or more compressors, a heat-source-side heat exchanger, an expansion valve, and a receiver; and a controller configured to control the expansion valve, wherein in the heat-source-side circuit, the expansion valve is located between the heat-source-side heat exchanger and the receiver, and while the compression element is stopped, the controller controls the expansion valve based on one or both of a refrigerant pressure in the receiver and a refrigerant pressure in the heat-source-side heat exchanger.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a piping system diagram showing a configuration of a refrigeration apparatus according to a first embodiment.

FIG. 2 is a block diagram showing a configuration of a controller of a heat source unit according to the first embodiment.

FIG. 3 corresponds to FIG. 1 and shows a flow of a refrigerant in a cooling operation.

FIG. 4 corresponds to FIG. 1 and shows a flow of a refrigerant in a first heating operation.

FIG. 5 corresponds to FIG. 1 and shows a flow of a refrigerant in a second heating operation.

FIG. 6 corresponds to FIG. 1 and shows a flow of a refrigerant in a third heating operation.

FIG. 7 corresponds to FIG. 1 and shows a flow of a refrigerant in a pressure reduction operation.

FIG. 8 is a flowchart showing operation of the controller of the first embodiment.

FIG. 9 is a piping system diagram showing a configuration of a refrigeration apparatus according to a second embodiment.

DESCRIPTION OF EMBODIMENTS

Embodiments will be described with reference to the drawings. The following embodiments are merely exemplary ones in nature, and are not intended to limit the scope, applications, or use of the invention.

First Embodiment

A first embodiment will be described. A refrigeration apparatus (1) according to this embodiment can cool an object to be cooled, and can condition indoor air. The object to be cooled herein includes air in facilities such as a refrigerator, a freezer, and a show case.

—General Configuration of Refrigeration Apparatus—

As illustrated in FIG. 1 , the refrigeration apparatus (1) includes a heat source unit (10) placed outside, air-conditioning units (50) configured to perform air-conditioning of an indoor space, and cooling units (60) configured to cool inside air. The refrigeration apparatus (1) according to this embodiment includes one heat source unit (10), a plurality of cooling units (60), and a plurality of air-conditioning units (50). The refrigeration apparatus (1) may include one cooling unit (60) or one air-conditioning unit (50).
In the refrigeration apparatus (1), the heat source unit (10), the cooling units (60), the air-conditioning units (50), and the connection pipes (2, 3, 4, 5) connecting those units (10, 50, 60) constitute a refrigerant circuit (6).
In the refrigerant circuit (6), a refrigerant circulates to create a refrigeration cycle. The refrigerant in the refrigerant circuit (6) of this embodiment is carbon dioxide. The refrigerant circuit (6) is configured to perform the refrigeration cycle where the high pressure is higher than or equal to the critical pressure of the refrigerant.
The refrigerant charged in the refrigerant circuit (6) is not limited to carbon dioxide. The refrigerant circuit (6) may be charged with the so-called chlorofluorocarbon refrigerant.
In the refrigerant circuit (6), the plurality of air-conditioning units (50) are connected to the heat source unit (10) through a first liquid connection pipe (2) and a first gas connection pipe (3). In the refrigerant circuit (6), the plurality of air-conditioning units (50) are connected in parallel to each other.
In the refrigerant circuit (6), the plurality of cooling units (60) are connected to the heat source unit (10) through a second liquid connection pipe (4) and a second gas connection pipe (5). In the refrigerant circuit (6), the plurality of cooling units (60) are connected in parallel to each other.

—Heat Source Unit—

The heat source unit (10) includes an outdoor fan (12) and an outdoor circuit (11). The outdoor circuit (11) includes a compression element (C), a flow path switching mechanism (30), an outdoor heat exchanger (13), a first outdoor expansion valve (14 a), a receiver (15), a subcooling heat exchanger (16), an intercooler (17), and a bypass pipe (85). The outdoor circuit (11) is a heat-source-side circuit. The heat source unit (10) includes a controller (101).

The compression element (C) compresses a refrigerant. The compression element (C) includes a high-stage compressor (21), a first low-stage compressor (23), and a second low-stage compressor (22). The high-stage compressor (21), the first low-stage compressor (23), and the second low-stage compressor (22) are rotary compressors each including a compression mechanism that is driven by a motor. The compressors (21, 22, 23) are hermetic scroll compressors, for example. The high-stage compressor (21), the first low-stage compressor (23), and the second low-stage compressor (22) are configured as capacity-variable-type compressors each including a compression mechanism of which the rotational speed can be changed.
The compression element (C) performs two-stage compression. The first low-stage compressor (23) compresses the refrigerant sucked from the air-conditioning units (50) or the outdoor heat exchanger (13). The second low-stage compressor (22) compresses the refrigerant sucked from the cooling units (60). The high-stage compressor (21) sucks and compresses the refrigerant discharged from the first low-stage compressor (23) and the refrigerant discharged from the second low-stage compressor (22).
The high-stage compressor (21) is connected to a high-stage suction pipe (21 a) and a high-stage discharge pipe (21 b). The high-stage discharge pipe (21 b) is a discharge pipe through which the refrigerant discharged from the high-stage compressor (21) flows. The first low-stage compressor (23) is connected with a first low-stage suction pipe (23 a) and a first low-stage discharge pipe (23 b). The first low-stage suction pipe (23 a) is a suction pipe through which the refrigerant sucked into the first low-stage compressor (23) flows. The second low-stage compressor (22) is connected with a second low-stage suction pipe (22 a) and a second low-stage discharge pipe (22 b). In the compression element (C), the first low-stage discharge pipe (23 b) and the second low-stage discharge pipe (22 b) are connected to the high-stage suction pipe (21 a).
The second low-stage suction pipe (22 a) is connected to the second gas connection pipe (5). The second low-stage compressor (22) communicates with the cooling units (60) through the second gas connection pipe (5). The first low-stage suction pipe (23 a) communicates with the air-conditioning units (50) through the flow path switching mechanism (30) and the first gas connection pipe (3).
The compression element (C) includes a first low-stage pipe (24 c) and a second low-stage pipe (24 b). The first low-stage pipe (24 c) is a pipe through which the refrigerant flows to bypass the first low-stage compressor (23). One end of the first low-stage pipe (24 c) is connected to the first low-stage suction pipe (23 a), and the other end of the first low-stage pipe (24 c) is connected to the first low-stage discharge pipe (23 b). The first low-stage pipe (24 c) is provided in parallel with the first low-stage compressor (23). The second low-stage pipe (24 b) is a pipe through which the refrigerant flows to bypass the second low-stage compressor (22). One end of the second low-stage pipe (24 b) is connected to the second low-stage suction pipe (22 a), and the other end of the second low-stage pipe (24 b) is connected to the second low-stage discharge pipe (22 b). The second low-stage pipe (24 b) is in parallel with the second low-stage compressor (22).

The flow path switching mechanism (30) is a mechanism configured to switch the flow paths in the refrigerant circuit (6) through which the refrigerant flows. The flow path switching mechanism (30) includes a first pipe (31), a second pipe (32), a third pipe (33), a fourth pipe (34), a first switching valve (81), and a second switching valve (82).
The inflow end of the first pipe (31) and the inflow end of the second pipe (32) are connected to the high-stage discharge pipe (21 b). The outflow end of the third pipe (33) and the outflow end of the fourth pipe (34) are connected to the first low-stage suction pipe (23 a).
The first switching valve (81) and the second switching valve (82) each switch the flow path of the refrigerant sucked into the first low-stage compressor (23) and the flow path of the refrigerant discharged from the high-stage compressor (21). The first switching valve (81) and the second switching valve (82) are four-way switching valves each having four ports.
The first port of the first switching valve (81) is connected to the outflow end of the first pipe (31). The second port of the first switching valve (81) is connected to the inflow end of the third pipe (33). The third port of the first switching valve (81) is closed. The fourth port of the first switching valve (81) is connected to one end of a first outdoor gas pipe (35). The other end of the first outdoor gas pipe (35) is connected to the first gas connection pipe (3).
The first port of the second switching valve (82) is connected to the outflow end of the second pipe (32). The second port of the second switching valve (82) is connected to the inflow end of the fourth pipe (34). The third port of the second switching valve (82) is connected to a second outdoor gas pipe (36). The fourth port of the second switching valve (82) is closed.
The first switching valve (81) and the second switching valve (82) each switch between a first state (the state indicated by the solid lines in FIG. 1 ) and a second state (the state indicated by the broken lines in FIG. 1 ). In the switching valves (81, 82) in the first state, the first port communicates with and the third port, and the second port communicates with the fourth port. In the switching valves (81, 82) in the second state, the first port communicates with the fourth port, and the second port communicates with the third port.
In the flow path switching mechanism (30), the first switching valve (81) and the second switching valve (82) may be three-way valves each having three ports.

The outdoor heat exchanger (13) serves as a heat-source-side heat exchanger. The outdoor heat exchanger (13) is a fin-and-tube air heat exchanger. The outdoor fan (12) is disposed near the outdoor heat exchanger (13). The outdoor fan (12) transfers outdoor air. The outdoor heat exchanger (13) exchanges heat between the refrigerant flowing therein and the outdoor air transferred by the outdoor fan (12).
The gas end of the outdoor heat exchanger (13) is connected with the second outdoor gas pipe (36). The liquid end of the outdoor heat exchanger (13) is connected with an outdoor flow path (O).

The outdoor flow path (O) includes a first outdoor pipe (o1), a second outdoor pipe (o2), a third outdoor pipe (o3), a fourth outdoor pipe (o4), a fifth outdoor pipe (o5), a sixth outdoor pipe (o6), a seventh outdoor pipe (o7), and an eighth outdoor pipe (o8).
One end of the first outdoor pipe (1) is connected to the liquid end of the outdoor heat exchanger (13). The other end of the first outdoor pipe (o1) is connected with one end of the second outdoor pipe (o2) and one end of the third outdoor pipe (o3). The other end of the second outdoor pipe (o2) is connected to the top of the receiver (15).
One end of the fourth outdoor pipe (o4) is connected to the bottom of the receiver (15). The other end of the fourth outdoor pipe (o4) is connected with one end of the fifth outdoor pipe (o5) and the other end of the third outdoor pipe (o3). The other end of the fifth outdoor pipe (o5) is connected with one end of the sixth outdoor pipe (o6) and one end of the eighth outdoor pipe (o8).
The other end of the eighth outdoor pipe (o8) is connected to the first liquid-side trunk pipe (4 a) of the second liquid connection pipe (4). The eighth outdoor pipe (o8) is a liquid pipe through which a liquid refrigerant downstream of the receiver (15) flows. The other end of the sixth outdoor pipe (o6) is connected to the first liquid connection pipe (2). One end of the seventh outdoor pipe (o7) is connected to an intermediate portion of the sixth outdoor pipe (o6). The other end of the seventh outdoor pipe (o7) is connected to an intermediate portion of the second outdoor pipe (o2).

The first outdoor pipe (o1) of the outdoor circuit (11) is provided with the first outdoor expansion valve (14 a). The third outdoor pipe (o3) of the outdoor circuit (11) is provided with a second outdoor expansion valve (14 b). The first outdoor expansion valve (14 a) and the second outdoor expansion valve (14 b) are electronic expansion valves of which the opening degree is variable. The first outdoor expansion valve (14 a) and the second outdoor expansion valve (14 b) are expansion valves provided in the outdoor circuit (11) as a heat-source-side circuit.

The receiver (15) serves as a container that stores the refrigerant. The receiver (15) is provided downstream of the first outdoor expansion valve (14 a). In the receiver (15), the refrigerant is separated into a gas refrigerant and a liquid refrigerant. The top of the receiver (15) is connected with the other end of the second outdoor pipe (o2) and one end of a venting pipe (37) described later.
The receiver (15) is covered with a thermal insulator (15 a). One of the examples of the thermal insulator (15 a) is glass wool. By covering the receiver (15) with the thermal insulator (15 a), it is possible to reduce the amount of heat transferred from the outdoor air to the refrigerant in the receiver (15) in a situation such as summer in which the outdoor air temperature is high.

The outdoor circuit (11) includes an intermediate injection circuit (49). The intermediate injection circuit (49) is a circuit configured to supply the refrigerant decompressed by the first outdoor expansion valve (14 a) to the high-stage suction pipe (21 a). The intermediate injection circuit (49) includes the venting pipe (37) and an injection pipe (38).
One end of the injection pipe (38) is connected to an intermediate portion of the fifth outdoor pipe (o5). The other end of the injection pipe (38) is connected to the high-stage suction pipe (21 a). The injection pipe (38) is provided with a decompression valve (40). The decompression valve (40) is an expansion valve of which the opening degree is variable.
The venting pipe (37) is a pipe configured to send the gas refrigerant of the receiver (15) to the high-stage suction pipe (21 a). The venting pipe (37) serves as a venting passage. Specifically, one end of the venting pipe (37) is connected to the top of the receiver (15). The other end of the venting pipe (37) is connected to an intermediate portion of the injection pipe (38). The venting pipe (37) is connected with a venting valve (39). The venting valve (39) is an electronic expansion valve of which the opening degree is variable.

The outdoor circuit (11) includes the subcooling heat exchanger (16). The subcooling heat exchanger (16) is a heat exchanger configured to cool the refrigerant (mainly the liquid refrigerant) separated in the receiver (15). The subcooling heat exchanger (16) is placed downstream of the receiver (15). The subcooling heat exchanger (16) has a first flow path (16 a) and a second flow path (16 b). The subcooling heat exchanger (16) exchanges heat between the refrigerant flowing through the first flow path (16 a) and the refrigerant flowing through the second flow path (16 b).
In the subcooling heat exchanger (16), the refrigerant flowing through the first flow path (16 a) is cooled. The first flow path (16 a) is connected to an intermediate portion of the fourth outdoor pipe (o4) serving as a liquid pipe through which the liquid refrigerant in the outdoor circuit (11) flows.
The second flow path (16 b) is included in the intermediate injection circuit (49). Specifically, the second flow path (16 b) is connected to part of the injection pipe (38) downstream of the decompression valve (40). The refrigerant that has been decompressed at the decompression valve (40) flows through the second flow path (16 b).

The intercooler (17) is connected to an intermediate flow path (41). One end of the intermediate flow path (41) is connected to the first low-stage discharge pipe (23 b) and the second low-stage discharge pipe (22 b). The other end of the intermediate flow path (41) is connected to the high-stage suction pipe (21 a).
The intercooler (17) is a fin-and-tube air heat exchanger. A fan (17 a) is disposed near the intercooler (17). The intercooler (17) exchanges heat between the refrigerant flowing therein and the outdoor air transferred from the fan (17 a).

The outdoor circuit (11) has 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), a seventh check valve (CV7), an eighth check valve (CV8), and a ninth check valve (CV9). The check valves (CV1 to CV9) allow the refrigerant to flow in the directions indicated by the respective arrows shown in FIG. 1 , and disallow the refrigerant to flow in the directions opposite thereto.
The first check valve (CV1) is connected to the high-stage discharge pipe (21 b). The second check valve (CV2) is connected to the second low-stage discharge pipe (22 b). The third check valve (CV3) is connected to the first low-stage discharge pipe (23 b). 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). The eighth check valve (CV8) is connected to the second low-stage pipe (24 b). The ninth check valve (CV9) is connected to the first low-stage pipe (24 c).

The heat source unit (10) includes various sensors. The sensors include a high-pressure sensor (71), an intermediate-pressure sensor (72), a first low-pressure sensor (73), a second low-pressure sensor (74), a liquid refrigerant pressure sensor (75), and a high-stage suction temperature sensor (77).
The high-pressure sensor (71) is connected to the high-stage discharge pipe (21 b). The high-pressure sensor (71) detects the pressure of the refrigerant discharged from the high-stage compressor (21) (the pressure (HP) of the high-pressure refrigerant).
The intermediate-pressure sensor (72) is connected to part of the intermediate flow path (41) downstream of the intercooler (17). The intermediate-pressure sensor (72) detects the pressure of the refrigerant in the intermediate flow path (41). In other words, the intermediate-pressure sensor (72) detects the pressure of the refrigerant between the high-stage compressor (21) and the set of the second low-stage compressor (22) and the first low-stage compressor (23) (the pressure (MP) of the intermediate-pressure refrigerant).
The first low-pressure sensor (73) is connected to the second low-stage suction pipe (22 a). The first low-pressure sensor (73) detects the pressure of the refrigerant sucked by the second low-stage compressor (22) (the pressure (LP1) of the first low-pressure refrigerant).
The second low-pressure sensor (74) is connected to the first low-stage suction pipe (23 a). The second low-pressure sensor (74) detects the pressure of the refrigerant sucked by the first low-stage compressor (23) (the pressure (LP2) of the second low-pressure refrigerant).
The liquid refrigerant pressure sensor (75) is connected to the fourth outdoor pipe (o4). The liquid refrigerant pressure sensor (75) detects the pressure of the refrigerant flowing through the fourth outdoor pipe (o4). In other words, the liquid refrigerant pressure sensor (75) detects the pressure of the liquid refrigerant in the receiver (15).
The high-stage suction temperature sensor (77) is attached to the high-stage suction pipe (21 a). The high-stage suction temperature sensor (77) detects the temperature of the refrigerant flowing through the high-stage suction pipe (21 a). In other words, the high-stage suction temperature sensor (77) detects the temperature of the refrigerant sucked into the high-stage compressor (21).

The outdoor circuit (11) consists of the portions in which the upper limit design pressure is a first design pressure Pu1 and the portions in which the upper limit design pressure is a second design pressure Pu2.
Specifically, the upper limit design pressure of each of the first outdoor gas pipe (35), the second outdoor gas pipe (36), the flow path switching mechanism (30), the outdoor heat exchanger (13), and the first outdoor expansion valve (14 a) is the first design pressure Pu1. On the other hand, the upper limit design pressure of each of the outdoor flow path (O), the receiver (15), the subcooling heat exchanger (16), the venting pipe (37), the injection pipe (38), the venting valve (39), the decompression valve (40), the intermediate flow path (41), and the intercooler (17) is the second design pressure Pu2.
The first design pressure Pu1 is higher than the second design pressure Pu2. The first design pressure Pu1 is 12 MPa, for example. The second design pressure Pu2 is 9 MPa, for example.

As illustrated in FIG. 2 , the controller (101) includes a microcomputer (102) mounted on a control board, and a memory device (105) storing software for operating the microcomputer (102). The memory device (105) is a semiconductor memory. The controller (101) controls the components of the heat source unit (10).
The microcomputer (102) of the controller (101) functions as a receiver pressure control unit (103) by executing a program stored in the memory device (105). The receiver pressure control unit (103) conducts operation to hold the refrigerant pressure in the receiver (15) lower than the second design pressure Pu2 while the compression element (C) is stopped.

—Air-Conditioning Unit—

The air-conditioning unit (50) is a first utilization-side unit installed indoors. The air-conditioning unit (50) conditions air in an indoor space. The air-conditioning unit (50) includes an indoor fan (52) and an indoor circuit (51). The liquid end of the indoor circuit (51) is connected with the first liquid connection pipe (2). The gas end of the indoor circuit (51) is connected with the first gas connection pipe (3).
The indoor circuit (51) includes an indoor expansion valve (53) and an indoor heat exchanger (54) in the order from the liquid end to the gas end. The indoor expansion valve (53) is an electronic expansion valve of which the opening degree is variable. The indoor heat exchanger (54) is a fin-and-tube air heat exchanger. The indoor fan (52) is disposed near the indoor heat exchanger (54). The indoor fan (52) transfers indoor air. The indoor heat exchanger (54) exchanges heat between the refrigerant flowing therein and the indoor air transferred by the indoor fan (52).

—Cooling Unit—

The cooling unit (60) is a second utilization-side unit installed indoors. The cooling unit (60) is, for example, a refrigeration showcase placed in a store such as a convenience store. The cooling unit (60) may be a unit cooler configured to cool inside air in a refrigerator.
The cooling unit (60) includes a cooling fan (62) and a cooling circuit (61). The liquid end of the cooling circuit (61) is connected with the liquid-side branch pipe (4 c) of the second liquid connection pipe (4). The gas end of the cooling circuit (61) is connected with the gas-side branch pipe (5 c) of the second gas connection pipe (5).
The cooling circuit (61) includes a cooling expansion valve (63) and a cooling heat exchanger (64) in the order from the liquid end to the gas end. The cooling expansion valve (63) is an electronic expansion valve of which the opening degree is variable. The cooling heat exchanger (64) is a fin-and-tube air heat exchanger. The cooling fan (62) is disposed near the cooling heat exchanger (64). The cooling fan (62) transfers inside air. The cooling heat exchanger (64) exchanges heat between the refrigerant flowing therein and the inside air transferred by the cooling fan (62).

—Operation of Refrigeration Apparatus—

The operation of the refrigeration apparatus (1) will be described. The refrigeration apparatus (1) performs the cooling operation, the first heating operation, the second heating operation, and the third heating operation. The refrigeration apparatus (1) also performs the defrosting operation to defrost the outdoor heat exchanger (13), and the pressure reduction operation to reduce the refrigerant pressure in the receiver (15).

The cooling operation of the refrigeration apparatus (1) will be described with reference to FIG. 3 . In the cooling operation, the air-conditioning units (50) cool indoor spaces.
In the cooling operation, the first switching valve (81) and the second switching valve (82) are set to the first state, and the second outdoor expansion valve (14 b) is held in the closed state. In the cooling operation, the first low-stage compressor (23), the second low-stage compressor (22), and the high-stage compressor (21) are activated. In the cooling operation, in the refrigerant circuit (6), a refrigerant circulates to create a refrigeration cycle; the outdoor heat exchanger (13) functions as a radiator (a gas cooler); and the cooling heat exchanger (64) and the indoor heat exchanger (54) function as evaporators.
The refrigerant that has been discharged from the high-stage compressor (21) passes through the second switching valve (82) and flows into the outdoor heat exchanger (13), and dissipates heat to the outdoor air. The refrigerant that has passed through the outdoor heat exchanger (13) is decompressed while passing through the first outdoor expansion valve (14 a); thereafter passes through the receiver (15); and subsequently is cooled while passing through the first flow path (16 a) of the subcooling heat exchanger (16). Part of the refrigerant that has passed through the first flow path (16 a) of the subcooling heat exchanger (16) passes through the injection pipe (38) and flows into the second flow path (16 b) of the subcooling heat exchanger (16); then absorbs heat to evaporate; and thereafter flows into the high-stage suction pipe (21 a). The rest of the refrigerant that has passed through the first flow path (16 a) of the subcooling heat exchanger (16) flows into the first liquid connection pipe (2) and the second liquid connection pipe (4) separately.
The refrigerant flowing through the first liquid connection pipe (2) is distributed to the plurality of air-conditioning units (50). In each of the air-conditioning units (50), the refrigerant that has flowed into the indoor circuit (51) is decompressed while passing through the indoor expansion valve (53), and thereafter absorbs heat from the indoor air to evaporate in the indoor heat exchanger (54). Each of the air-conditioning unit (50) blows the air cooled in the indoor heat exchanger (54) into the indoor space.
The refrigerant that has flowed out of the indoor heat exchanger (54) of each of the air-conditioning units (50) flows and merges into the first gas connection pipe (3); thereafter flows into the first outdoor gas pipe (35) of the outdoor circuit (11); then passes through the first switching valve (81) and flows into the first low-stage suction pipe (23 a); and thereafter is sucked into and compressed in the first low-stage compressor (23).
The refrigerant flowing through the second liquid connection pipe (4) is distributed to the plurality of cooling units (60). In each of the cooling units (60), the refrigerant that has flowed into the cooling circuit (61) is decompressed while passing through the cooling expansion valve (63), and thereafter absorbs heat from the inside air and evaporates in the cooling heat exchanger (64). Each of the cooling units (60) blows the air cooled in the cooling heat exchanger (64) into the inside space.
The refrigerant that has flowed out of the cooling heat exchanger (64) of each of the cooling units (60) flows and merges into the second gas connection pipe (5); thereafter flows into the second low-stage suction pipe (22 a) of the outdoor circuit (11); and thereafter is sucked into and compressed in the second low-stage compressor (22).
The refrigerant that has been compressed in each of the first low-stage compressor (23) and the second low-stage compressor (22) dissipates heat to the outdoor air in the intercooler (17); merges with the refrigerant flowing through the injection pipe (38); and thereafter is sucked into the high-stage compressor (21). The high-stage compressor (21) compresses and discharges the sucked refrigerant.

The first heating operation of the refrigeration apparatus (1) will be described with reference to FIG. 4 . The first heating operation is an operation in which the air-conditioning units (50) heat indoor spaces. The first heating operation is performed in the operating state where the amount of heat dissipated from the refrigerant in the air-conditioning unit (50) is smaller than the amount of heat absorbed by the refrigerant in the cooling unit (60).
In the first heating operation, the first switching valve (81) is set to the second state; the second switching valve (82) is set to the first state; and the second outdoor expansion valve (14 b) is held in the closed state. In the first heating operation, the first low-stage compressor (23) is paused, and the second low-stage compressor (22) and the high-stage compressor (21) are activated. In the first heating operation, in the refrigerant circuit (6), a refrigerant circulates to create a refrigeration cycle; the indoor heat exchanger (54) and the outdoor heat exchanger (13) function as radiators (gas coolers); and the cooling heat exchanger (64) functions as an evaporator.
Part of the refrigerant that has been discharged from the high-stage compressor (21) passes through the first switching valve (81) and flows into the first outdoor gas pipe (35), and the rest of the refrigerant passes through the second switching valve (82) and flows into the second outdoor gas pipe (36).
The refrigerant flowing through the first outdoor gas pipe (35) is distributed to each air-conditioning unit (50) through the first gas connection pipe (3). In each of the air-conditioning units (50), the refrigerant that has flowed into the indoor circuit (51) dissipates heat to the indoor air in the indoor heat exchanger (54); thereafter is decompressed while passing through the indoor expansion valve (53); and then flows into the first liquid connection pipe (2). The refrigerant that has flowed from the air-conditioning unit (50) into the first liquid connection pipe (2) flows into the receiver (15) of the outdoor circuit (11). Each of the air-conditioning units (50) blows the air heated in the indoor heat exchanger (54) into the indoor space.
The refrigerant flowing through the second outdoor gas pipe (36) flows into the outdoor heat exchanger (13) and dissipates heat to the outdoor air. The refrigerant that has passed through the outdoor heat exchanger (13) is decompressed while passing through the first outdoor expansion valve (14 a), and thereafter flows into the receiver (15).
The refrigerant that has flowed out of the receiver (15) is cooled while passing through the first flow path (16 a) of the subcooling heat exchanger (16). Part of the refrigerant that has passed through the first flow path (16 a) of the subcooling heat exchanger (16) passes through the injection pipe (38) and flows into the second flow path (16 b) of the subcooling heat exchanger (16); then absorbs heat to evaporate; and thereafter flows into the high-stage suction pipe (21 a). The rest of the refrigerant that has passed through the first flow path (16 a) of the subcooling heat exchanger (16) flows into the second liquid connection pipe (4).
The refrigerant flowing through the second liquid connection pipe (4) is distributed to the plurality of cooling units (60). In each of the cooling units (60), the refrigerant that has flowed into the cooling circuit (61) is decompressed while passing through the cooling expansion valve (63), and thereafter absorbs heat from the inside air and evaporates in the cooling heat exchanger (64). Each of the cooling units (60) blows the air cooled in the cooling heat exchanger (64) into the inside space.
The refrigerant that has flowed out of the cooling heat exchanger (64) of each of the cooling units (60) flows and merges into the second gas connection pipe (5); thereafter flows into the second low-stage suction pipe (22 a) of the outdoor circuit (11); and thereafter is sucked into and compressed in the second low-stage compressor (22).
The refrigerant that has been compressed in the second low-stage compressor (22) dissipates heat to the outdoor air in the intercooler (17); then merges with the refrigerant flowing through the injection pipe (38); and thereafter is sucked into the high-stage compressor (21). The high-stage compressor (21) compresses and discharges the sucked refrigerant.

The second heating operation of the refrigeration apparatus (1) will be described with reference to FIG. 5 . The second heating operation is an operation in which the air-conditioning units (50) heat indoor spaces. The second heating operation is performed in the operating state where the amount of heat dissipated from the refrigerant in the air-conditioning unit (50) is balanced with the amount of heat absorbed by the refrigerant in the cooling unit (60).
In the second heating operation, the first switching valve (81) and the second switching valve (82) are set to the second state, and the second outdoor expansion valve (14 b) is held in the closed state. In the second heating operation, the first low-stage compressor (23) is paused, and the second low-stage compressor (22) and the high-stage compressor (21) are activated. In the second heating operation, in the refrigerant circuit (6), a refrigerant circulates to create a refrigeration cycle; the indoor heat exchanger (54) functions as a radiator (a gas cooler); the cooling heat exchanger (64) functions as an evaporator; and the outdoor heat exchanger (13) is paused.
The refrigerant that has been discharged from the high-stage compressor (21) passes through the first switching valve (81) and flows into the first outdoor gas pipe (35), and thereafter is distributed to the plurality of air-conditioning units (50) through the first gas connection pipe (3). In each of the air-conditioning units (50), the refrigerant that has flowed into the indoor circuit (51) dissipates heat to the indoor air in the indoor heat exchanger (54); thereafter is decompressed while passing through the indoor expansion valve (53); and then flows into the first liquid connection pipe (2). The refrigerant that has flowed from the air-conditioning unit (50) into the first liquid connection pipe (2) flows into the receiver (15) of the outdoor circuit (11). Each of the air-conditioning units (50) blows the air heated in the indoor heat exchanger (54) into the indoor space.
The refrigerant that has flowed out of the receiver (15) is cooled while passing through the first flow path (16 a) of the subcooling heat exchanger (16). Part of the refrigerant that has passed through the first flow path (16 a) of the subcooling heat exchanger (16) passes through the injection pipe (38) and flows into the second flow path (16 b) of the subcooling heat exchanger (16); then absorbs heat to evaporate; and thereafter flows into the high-stage suction pipe (21 a). The rest of the refrigerant that has passed through the first flow path (16 a) of the subcooling heat exchanger (16) flows into the second liquid connection pipe (4).
The refrigerant flowing through the second liquid connection pipe (4) is distributed to the plurality of cooling units (60). In each of the cooling units (60), the refrigerant that has flowed into the cooling circuit (61) is decompressed while passing through the cooling expansion valve (63), and thereafter absorbs heat from the inside air and evaporates in the cooling heat exchanger (64). Each of the cooling units (60) blows the air cooled in the cooling heat exchanger (64) into the inside space.
The refrigerant that has flowed out of the cooling heat exchanger (64) of each of the cooling units (60) flows and merges into the second gas connection pipe (5); thereafter flows into the second low-stage suction pipe (22 a) of the outdoor circuit (11); and then is sucked into and compressed in the second low-stage compressor (22).
The refrigerant that has been compressed in the second low-stage compressor (22) dissipates heat to the outdoor air in the intercooler (17); then merges with the refrigerant flowing through the injection pipe (38); and thereafter is sucked into the high-stage compressor (21). The high-stage compressor (21) compresses and discharges the sucked refrigerant.

The third heating operation of the refrigeration apparatus (1) will be described with reference to FIG. 6 . The third heating operation is an operation in which the air-conditioning units (50) heat indoor spaces. The third heating operation is performed in the operating state where the amount of heat dissipated from the refrigerant in the air-conditioning unit (50) is larger than the amount of heat absorbed by the refrigerant in the cooling unit (60).
In the third heating operation, the first switching valve (81) and the second switching valve (82) are set to the second state, and the first outdoor expansion valve (14 a) is held in the fully-open state. In the third heating operation, the first low-stage compressor (23), the second low-stage compressor (22), and the high-stage compressor (21) are activated. In the third heating operation, in the refrigerant circuit (6), a refrigerant circulates to create a refrigeration cycle; the indoor heat exchanger (54) functions as a radiator (a gas cooler); and the cooling heat exchanger (64) and the outdoor heat exchanger (13) function as evaporators.
The refrigerant that has been discharged from the high-stage compressor (21) passes through the first switching valve (81) and flows into the first outdoor gas pipe (35), and thereafter is distributed to the plurality of air-conditioning units (50) through the first gas connection pipe (3). In each of the air-conditioning units (50), the refrigerant that has flowed into the indoor circuit (51) dissipates heat to the indoor air in the indoor heat exchanger (54); thereafter is decompressed while passing through the indoor expansion valve (53); and then flows into the first liquid connection pipe (2). The refrigerant that has flowed from the air-conditioning unit (50) into the first liquid connection pipe (2) flows into the receiver (15) of the outdoor circuit (11). Each of the air-conditioning units (50) blows the air heated in the indoor heat exchanger (54) into the indoor space.
The refrigerant that has flowed out of the receiver (15) is cooled while passing through the first flow path (16 a) of the subcooling heat exchanger (16). The refrigerant that has passed through the first flow path (16 a) of the subcooling heat exchanger (16) branches and flows into the fifth outdoor pipe (o5) and the third outdoor pipe (o3).
Part of the refrigerant flowing through the fifth outdoor pipe (o5) flows into the injection pipe (38), and the rest of the refrigerant flows into the eighth outdoor pipe (o8). The refrigerant flowing through the injection pipe (38) flows into the second flow path (16 b) of the subcooling heat exchanger (16); then absorbs heat and evaporates; and thereafter flows into the high-stage suction pipe (21 a).
The refrigerant flowing through the eighth outdoor pipe (o8) is distributed to the plurality of cooling units (60) through the second liquid connection pipe (4). In each of the cooling units (60), the refrigerant that has flowed into the cooling circuit (61) is decompressed while passing through the cooling expansion valve (63), and thereafter absorbs heat from the inside air and evaporates in the cooling heat exchanger (64). Each of the cooling units (60) blows the air cooled in the cooling heat exchanger (64) into the inside space.
The refrigerant that has flowed out of the cooling heat exchanger (64) of each of the cooling units (60) flows and merges into the second gas connection pipe (5); thereafter flows into the second low-stage suction pipe (22 a) of the outdoor circuit (11); and thereafter is sucked into and compressed in the second low-stage compressor (22).
The refrigerant flowing through the third outdoor pipe (o3) is decompressed while passing through the second outdoor expansion valve (14 b); then flows into the outdoor heat exchanger (13); and absorbs heat from the outdoor air and evaporates. The refrigerant that has passed through the outdoor heat exchanger (13) passes through the second switching valve (82) and flows into the first low-stage suction pipe (23 a), and thereafter is sucked into and compressed in the first low-stage compressor (23).
The refrigerant that has been compressed in each of the first low-stage compressor (23) and the second low-stage compressor (22) dissipates heat to the outdoor air in the intercooler (17); merges with the refrigerant flowing through the injection pipe (38); and thereafter is sucked into the high-stage compressor (21). The high-stage compressor (21) compresses and discharges the sucked refrigerant.

The defrosting operation of the refrigeration apparatus (1) will be described. The defrosting operation is an operation to defrost the outdoor heat exchanger (13). If the amount of frost on the outdoor heat exchanger (13) reaches a certain level or more in the third heating operation, the refrigeration apparatus (1) temporally pauses the third heating operation and performs the defrosting operation.
In the defrosting operation, the refrigerant circulates in the refrigerant circuit (6) similarly to the first heating operation. Specifically, the second switching valve (82) is set to the first state, and the outdoor heat exchanger (13) functions as a radiator (a gas cooler). The frost on the outdoor heat exchanger (13) is heated and melted by the refrigerant.

In a situation such as summer in which the outdoor air temperature is high, heat can be transferred from the outdoor air to the refrigerant in the receiver (15) while the refrigeration apparatus (1) is stopped, and then the refrigerant pressure might increase in the receiver (15). In such a case, the refrigeration apparatus (1) performs the pressure reduction operation to reduce the refrigerant pressure in the receiver (15).
The pressure reduction operation of the refrigeration apparatus (1) will be described with reference to FIG. 7 .
In the pressure reduction operation, the first switching valve (81) and the second switching valve (82) are set to the first state; the first outdoor expansion valve (14 a) and the venting valve (39) are held in the open state; and the second outdoor expansion valve (14 b) and the decompression valve (40) are held in the closed state. In the pressure reduction operation, the opening degrees of the first outdoor expansion valve (14 a) and the venting valve (39) are adjusted as appropriate.
In the pressure reduction operation, the first low-stage compressor (23) and the second low-stage compressor (22) are held in the stop state, and the high-stage compressor (21) is activated. In the pressure reduction operation, the outdoor fan (12) is activated, and the fan (17 a) is held in the stop state.
The high-stage compressor (21) sucks the refrigerant in the receiver (15) through the injection pipe (38) and the venting pipe (37). The high-stage compressor (21) compresses and discharges the sucked refrigerant. The refrigerant that has been discharged from the high-stage compressor (21) flows into the outdoor heat exchanger (13); then dissipates heat to the outdoor air; and thereafter passes through the first outdoor expansion valve (14 a). The refrigerant that has been decompressed while passing through the first outdoor expansion valve (14 a) flows into the receiver (15).
In this manner, in the pressure reduction operation, the gas refrigerant is sucked out of the receiver (15) by the high-stage compressor (21), and then the refrigerant that has been decompressed while passing through the first outdoor expansion valve (14 a) flows into the receiver (15). Thus, the refrigeration apparatus (1) performing the pressure reduction operation enables reduction in the refrigerant pressure in the receiver (15).

—Operation of Controller—

As described above, the refrigerant pressure might increase in the receiver (15) while the refrigeration apparatus (1) is stopped (in other words, while the compression element (C) is stopped). If the refrigerant pressure in the receiver (15) exceeds the second design pressure Pu2, the receiver (15) might be damaged and the refrigerant might leak into the atmosphere. Then, the receiver pressure control unit (103) of the controller (101) conducts operation to hold the refrigerant pressure in the receiver (15) lower than the second design pressure Pu2 while the compression element (C) is stopped.
Here, it is in a situation such as summer in which the outdoor air temperature is high that the refrigerant pressure in the receiver (15) increases while the compression element (C) is stopped. If the outdoor air temperature is high, the refrigeration apparatus (1) performs the cooling operation. When the refrigeration apparatus (1) performs the cooling operation, the first switching valve (81) and the second switching valve (82) of the flow path switching mechanism (30) are in the first state.
The operation performed by the receiver pressure control unit (103) of the controller (101) will be described with reference to the flowchart of FIG. 8 . The operation performed by the receiver pressure control unit (103) is the operation from step ST3 to step ST8 in FIG. 8 .

If a signal to stop the refrigeration apparatus (1) is input to the controller (101) by an operator, the controller (101) performs the operation of step ST1. In the operation of step ST1, the controller (101) stops the compression element (C). Specifically, the controller (101) stops all the compressors (21, 22, 23) constituting the compression element (C). A state in which the compression element (C) is stopped is a state in which all the compressors (21, 22, 23) constituting the compression element (C) is stopped.

Next, the controller (101) performs the operation of step ST2. In step ST2, the controller (101) turns the first outdoor expansion valve (14 a) and the second outdoor expansion valve (14 b) to the closed state in response to a stop of the compression element (C). For example, if the second outdoor expansion valve (14 b) is already in the closed state, the controller (101) switches the first outdoor expansion valve (14 a) from the open state to the closed state, and holds the second outdoor expansion valve (14 b) in the closed state. When the controller (101) performs the operation of step ST2, both the first outdoor expansion valve (14 a) and the second outdoor expansion valve (14 b) turn to the fully-closed state.
The time for the controller (101) to stop the compression element (C) and the time for the controller (101) to turn the first outdoor expansion valve (14 a) and the second outdoor expansion valve (14 b) to the closed state may be the same, or may be different.

If the operation of step ST2 is ended, the receiver pressure control unit (103) of the controller (101) performs the operation of step ST3. In the operation of step ST3, the receiver pressure control unit (103) obtains the value measured by the high-pressure sensor (71) as the refrigerant pressure Phx in the outdoor heat exchanger (13). In a state in which the second switching valve (82) of the flow path switching mechanism (30) is in the first state and the compression element (C) is stopped, the value measured by the high-pressure sensor (71) shows the refrigerant pressure Phx in the outdoor heat exchanger (13).
The controller (101) performs the operation of step ST2, whereby the first outdoor expansion valve (14 a) is in the closed state. Even when the first outdoor expansion valve (14 a) and the second outdoor expansion valve (14 b) are in the closed state, the refrigerant in the outdoor heat exchanger (13) flows out little by little through the compressors (21, 22, 23) constituting the compression element (C), and thus the refrigerant pressure Phx in the outdoor heat exchanger (13) decreases gradually.
In the operation of step ST3, the receiver pressure control unit (103) determines whether the condition “the obtained refrigerant pressure Phx in the outdoor heat exchanger (13) is lower than a predetermined first pressure P1 (Phx<P1)” is satisfied. If this condition is not satisfied, the receiver pressure control unit (103) performs the operation of step ST3 again. On the other hand, if this condition is satisfied, the receiver pressure control unit (103) performs the operation of step ST4.
The first pressure P1 is lower than the second design pressure Pu2 (9 MPa in this embodiment), the upper limit design pressure of the receiver (15). The first pressure P1 of this embodiment is 5 MPa, for example.
In the operation of step ST3, the receiver pressure control unit (103) may determine whether the condition “the obtained refrigerant pressure Phx in the outdoor heat exchanger (13) is lower than or equal to the first pressure P1 (Phx≤P1)” is satisfied. In this case, the receiver pressure control unit (103) substantially determines whether the condition “the obtained refrigerant pressure Phx in the outdoor heat exchanger (13) is lower than the first pressure P1 (Phx<P1)” is satisfied and whether the condition “the obtained refrigerant pressure Phx in the outdoor heat exchanger (13) is equal to the first pressure P1 (Phx=P1)” is satisfied.

In the operation of step ST4, the receiver pressure control unit (103) switches the first outdoor expansion valve (14 a) from the closed state to the open state. Specifically, the receiver pressure control unit (103) increases the opening degree of each of the first outdoor expansion valve (14 a) and the second outdoor expansion valve (14 b) from zero to a predetermined opening degree. This predetermined opening degree may be the fully-open degree, or may be an opening degree lower than the fully-open degree.
The operation of step ST3 and step ST4 is the first operation performed by the receiver pressure control unit (103). The first operation is an operation to turn the first outdoor expansion valve (14 a) and the second outdoor expansion valve (14 b) to the open state if the refrigerant pressure Phx in the outdoor heat exchanger (13) becomes lower than the first pressure P1.
When the first outdoor expansion valve (14 a) and the second outdoor expansion valve (14 b) turn to the open state, the receiver (15) and the outdoor heat exchanger (13) communicate with each other through the fourth outdoor pipe (o4), the third outdoor pipe (o3), and the first outdoor pipe (o1). As a result, the refrigerant pressure in the receiver (15) becomes substantially equal to the refrigerant pressure Phx in the outdoor heat exchanger (13). Thus, if the refrigerant pressure Phx in the outdoor heat exchanger (13) is lower than the predetermined first pressure P1, the refrigerant pressure in the receiver (15) is also lower than the first pressure P1.
Here, in a situation in which the outdoor air temperature is high, heat is transferred from the outdoor air to the refrigerant in the receiver (15). As a result, the liquid refrigerant in the receiver (15) might evaporate, and the refrigerant pressure in the receiver (15) might increase.
If the first outdoor expansion valve (14 a) and the second outdoor expansion valve (14 b) are in the closed state, most of the gas refrigerant produced as a result of evaporation of the liquid refrigerant in the receiver (15) remains in the receiver (15). On the other hand, if the first outdoor expansion valve (14 a) and the second outdoor expansion valve (14 b) are in the open state, and the refrigerant pressure in the receiver (15) increases as a result of evaporation of the liquid refrigerant in the receiver (15), part of the refrigerant in the receiver (15) flows out of the receiver (15); then passes through the second outdoor expansion valve (14 b) and the first outdoor expansion valve (14 a) in order; and then flows toward the outdoor heat exchanger (13). Thus, if the first outdoor expansion valve (14 a) and the second outdoor expansion valve (14 b) are in the open state, the refrigerant pressure increases less in the receiver (15) than if the first outdoor expansion valve (14 a) and the second outdoor expansion valve (14 b) are in the closed state.

If the operation of step ST4 is ended, the receiver pressure control unit (103) performs the operation of step ST5. In the operation of step ST5, the receiver pressure control unit (103) obtains the value measured by the liquid refrigerant pressure sensor (75) as the refrigerant pressure Prv in the receiver (15). As described above, the value measured by the liquid refrigerant pressure sensor (75) is substantially equal to the pressure of the liquid refrigerant in the receiver (15). Thus, the value measured by the liquid refrigerant pressure sensor (75) shows the refrigerant pressure Prv in the receiver (15).
When the outdoor air temperature becomes high while the refrigeration apparatus (1) is stopped, the temperature of the outdoor heat exchanger (13) becomes high, and accordingly the refrigerant pressure in the outdoor heat exchanger (13) becomes high. When the refrigerant pressure Phx in the outdoor heat exchanger (13) becomes high, the refrigerant pressure Prv in the receiver (15) that communicates with the outdoor heat exchanger (13) becomes high as well.
Then, in the operation of step ST5, the receiver pressure control unit (103) determines whether the condition “the obtained refrigerant pressure Prv in the receiver (15) is higher than a predetermined second pressure P2 (Prv>P2)” is satisfied. If this condition is not satisfied, the receiver pressure control unit (103) performs the operation of step ST5 again. On the other hand, if this condition is satisfied, the receiver pressure control unit (103) performs the operation of step ST6.
The second pressure P2 is lower than the second design pressure Pu2 (9 MPa in this embodiment), the upper limit design pressure of the receiver (15). The second pressure P2 is higher than the first pressure P1 (5 MPa in this embodiment). The second pressure P2 of this embodiment is 7 MPa, for example. The second pressure P2 of this embodiment is lower than the critical pressure (7.38 MPa) of carbon dioxide used as the refrigerant.
In the operation of step ST5, the receiver pressure control unit (103) may determine whether the condition “the obtained refrigerant pressure Prv in the receiver (15) is higher than or equal to the second pressure P2 (Phx≥P2)” is satisfied. In this case, the receiver pressure control unit (103) substantially determines whether the condition “the obtained refrigerant pressure Prv in the receiver (15) is higher than the second pressure P2 (Phx>P2)” is satisfied and whether the condition “the obtained refrigerant pressure Prv in the receiver (15) is equal to the second pressure P2 (Phx=P2)” is satisfied.

In the operation of step ST6, the receiver pressure control unit (103) switches the first outdoor expansion valve (14 a) from the open state to the closed state. In other words, the receiver pressure control unit (103) turns the first outdoor expansion valve (14 a) to the fully-closed state. If the first outdoor expansion valve (14 a) turns to the closed state, the receiver (15) and the outdoor heat exchanger (13) are disconnected by the first outdoor expansion valve (14 a). In the operation of step ST6, the receiver pressure control unit (103) may switch the second outdoor expansion valve (14 b) from the open state to the closed state, or may hold the second outdoor expansion valve (14 b) in the open state.
The operation of step ST5 and step ST6 is the second operation performed by the receiver pressure control unit (103). The second operation is an operation to turn the first outdoor expansion valve (14 a) to the closed state if the refrigerant pressure Prv in the receiver (15) becomes higher than the second pressure P2.
The outdoor heat exchanger (13) is a heat exchanger configured to exchange heat between the refrigerant and the outdoor air, and includes fins that improves heat exchange with the outdoor air. That is, the area of part of the outdoor heat exchanger (13) that is in contact with the outdoor air is large. Thus, the refrigerant pressure Phx in the outdoor heat exchanger (13) is likely to be affected by the outdoor air temperature.
In contrast, the receiver (15) is covered with the thermal insulator (15 a). The thermal insulator (15 a) prevents heat transfer from the outdoor air to the refrigerant in the receiver (15). Thus, the refrigerant pressure Prv in the receiver (15) is less likely to be affected by the outdoor air temperature than the refrigerant pressure Phx in the outdoor heat exchanger (13).
However, if the first outdoor expansion valve (14 a) is in the open state, the receiver (15) communicates with the outdoor heat exchanger (13), and thus the refrigerant pressure Prv in the receiver (15) becomes substantially equal to the refrigerant pressure Phx in the outdoor heat exchanger (13).
Thus, in the operation of step ST6, in order to reduce an increase in the refrigerant pressure Prv in the receiver (15), the receiver pressure control unit (103) switches the first outdoor expansion valve (14 a) to the closed state to disconnect the receiver (15) and the outdoor heat exchanger (13).
The operation performed by the receiver pressure control unit (103) in step ST5 and in step ST6 is the second operation. The second operation is an operation to turn the first outdoor expansion valve (14 a) to the closed state if the refrigerant pressure Prv in the receiver (15) becomes higher than the second pressure P2.

If the operation of step ST6 is ended, the receiver pressure control unit (103) performs the operation of step ST7. In the operation of step ST7, the receiver pressure control unit (103) obtains the value measured by the liquid refrigerant pressure sensor (75) as the refrigerant pressure Prv in the receiver (15). As described above, the value measured by the liquid refrigerant pressure sensor (75) shows the refrigerant pressure Prv in the receiver (15).
As described above, the receiver (15) is covered with the thermal insulator (15 a). Thus, the refrigerant pressure Prv in the receiver (15) is relatively less likely to be affected by the outdoor air temperature. However, if the outdoor air temperature becomes extremely high (for example, over 35° C.), the refrigerant pressure Prv in the receiver (15) increases as a result of evaporation of the liquid refrigerant in the receiver (15).
Then, in the operation of step ST7, the receiver pressure control unit (103) determines whether the condition “the obtained refrigerant pressure Prv in the receiver (15) is higher than a predetermined third pressure P3 (Prv>P3)” is satisfied. If this condition is not satisfied, the receiver pressure control unit (103) performs the operation of step ST3 again. On the other hand, if this condition is satisfied, the receiver pressure control unit (103) performs the operation of step ST8.
The third pressure P3 is lower than the second design pressure Pu2 (9 MPa in this embodiment), the upper limit design pressure of the receiver (15). The third pressure P3 is higher than the second pressure P2 (7 MPa in this embodiment). The third pressure P3 of this embodiment is 7.5 MPa, for example.
In the operation of step ST7, the receiver pressure control unit (103) may determine whether the condition “the obtained refrigerant pressure Prv in the receiver (15) is higher than or equal to the third pressure P3 (Prv≥P3)” is satisfied. In this case, the receiver pressure control unit (103) substantially determines whether the condition “the obtained refrigerant pressure Prv in the receiver (15) is higher than the third pressure P3 (Prv>P3)” is satisfied and whether the condition “the obtained refrigerant pressure Prv in the receiver (15) is equal to the third pressure P3 (Prv=P3)” is satisfied.

In the operation of step ST8, the receiver pressure control unit (103) allows the refrigeration apparatus (1) to perform a pressure reduction operation. In other words, the receiver pressure control unit (103) controls the components of the heat source unit (10) so that the refrigeration apparatus (1) performs the pressure reduction operation.
As described above, in the pressure reduction operation of the refrigeration apparatus (1), the high-stage compressor (21) sucks the refrigerant in the receiver (15) through the injection pipe (38) and the venting pipe (37). In other words, the gas refrigerant in the receiver (15) is sucked out of the receiver (15) by the high-stage compressor (21).
The operation of step ST7 and step ST8 is the third operation performed by the receiver pressure control unit (103). The third operation is an operation to activate the compression element (C) to suck the gas refrigerant in the receiver (15) into the compression element (C) through the venting pipe (37) if the refrigerant pressure Prv in the receiver (15) becomes higher than the third pressure P3.
When the refrigeration apparatus (1) performs the pressure reduction operation, the gas refrigerant is discharged from the receiver (15), and the refrigerant pressure Prv in the receiver (15) decreases. If the refrigerant pressure Prv in the receiver (15) becomes sufficiently low (for example, lower than 5 MPa), the receiver pressure control unit (103) stops the high-stage compressor (21) in order to end the pressure reduction operation of the refrigeration apparatus (1).

—Feature (1) of First Embodiment—

In the refrigeration apparatus (1) of this embodiment, the receiver pressure control unit (103) of the controller (101) switches the first outdoor expansion valve (14 a) and the second outdoor expansion valve (14 b) to the closed state in response to a stop of the compression element (C), and thereafter performs the first operation. The first operation is an operation to turn the first outdoor expansion valve (14 a) and the second outdoor expansion valve (14 b) to the open state if the refrigerant pressure in the outdoor heat exchanger (13) becomes lower than the first pressure.
If the first outdoor expansion valve (14 a) and the second outdoor expansion valve (14 b) turn to the open state, the receiver (15) communicates with the outdoor heat exchanger (13) through the first outdoor expansion valve (14 a) and the second outdoor expansion valve (14 b). Thus, even if the liquid refrigerant in the receiver (15) evaporates and the refrigerant pressure in the receiver thus increases because of a factor such as an increase in the outdoor air temperature, the refrigerant in the receiver (15) can move to the outdoor heat exchanger (13) through the first outdoor expansion valve (14 a) and the second outdoor expansion valve (14 b). As a result, an increase in the refrigerant pressure in the receiver (15) is reduced.
In this manner, according to this embodiment, an increase in the refrigerant pressure in the receiver (15) can be reduced while the refrigeration apparatus (1) is stopped, and thus it is possible to prevent damage to the receiver (15) in advance and secure the reliability of the refrigeration apparatus (1).

—Feature (2) of First Embodiment—

In the refrigeration apparatus (1) of this embodiment, the receiver pressure control unit (103) of the controller (101) performs the second operation after performing the first operation. The second operation is an operation to turn the first outdoor expansion valve (14 a) to the closed state if the refrigerant pressure in the receiver (15) becomes higher than the second pressure.
As described above, the receiver (15) is covered with the thermal insulator (15 a). Thus, the refrigerant pressure in the receiver (15) is less likely to be affected by the outdoor air temperature than the refrigerant pressure in the outdoor heat exchanger (13). Thus, in order to reduce an increase in the refrigerant pressure in the receiver (15), the receiver pressure control unit (103) switches the first outdoor expansion valve (14 a) to the closed state to disconnect the receiver (15) and the outdoor heat exchanger (13). As a result, in a situation in which the outdoor air temperature is high, an increase in the refrigerant pressure in the receiver (15) can be reduced.
Thus, according to this embodiment, an increase in the refrigerant pressure in the receiver (15) can be reduced while the refrigeration apparatus (1) is stopped, and thus it is possible to prevent damage to the receiver (15) in advance and secure the reliability of the refrigeration apparatus (1).

—Feature (3) of First Embodiment—

In the refrigeration apparatus (1) of this embodiment, the receiver pressure control unit (103) of the controller (101) performs the third operation after performing the second operation. The third operation is an operation to activate the high-stage compressor (21) to suck the gas refrigerant in the receiver (15) into the high-stage compressor (21) through the venting pipe (37) if the refrigerant pressure in the receiver (15) becomes higher than the third pressure.
When the receiver pressure control unit (103) performs the third operation, the gas refrigerant is discharged from the receiver (15), and the refrigerant pressure in the receiver (15) decreases. Thus, according to this embodiment, an increase in the refrigerant pressure in the receiver (15) can be reduced while the refrigeration apparatus (1) is stopped, and thus it is possible to prevent damage to the receiver (15) in advance and secure the reliability of the refrigeration apparatus (1).

—Feature (4) of First Embodiment—

In the refrigeration apparatus (1) of this embodiment, the receiver pressure control unit (103) of the controller (101) controls the first outdoor expansion valve (14 a) and the second outdoor expansion valve (14 b) in the first operation and the second operation, and allows the refrigeration apparatus (1) to perform the pressure reduction operation if the first operation and the second operation fail to reduce an increase in the refrigerant pressure in the receiver (15). Thus, the refrigeration apparatus (1) can perform the pressure reduction operation with a reduced frequency than if the receiver pressure control unit (103) does not perform the first operation and the second operation.
When the refrigeration apparatus (1) performs the pressure reduction operation, the high-stage compressor (21) is activated and thus electric power is consumed. On the other hand, according to this embodiment, the refrigeration apparatus (1) can perform the pressure reduction operation with a reduced frequency than if the receiver pressure control unit (103) does not perform the first operation and the second operation. Thus, according to this embodiment, the pressure reduction operation that consumes electric power can be performed with a reduced frequency, and electric power consumption of the refrigeration apparatus (1) can be reduced.

Second Embodiment

A second embodiment will be described. Here, the differences between the refrigeration apparatus (1) of this embodiment and the refrigeration apparatus (1) of the first embodiment will be described.

—Configuration of Refrigeration Apparatus—

As illustrated in FIG. 9 , the refrigeration apparatus (1) of this embodiment does not include the cooling units (60) of the first embodiment. In the refrigerant circuit (6) of the refrigeration apparatus (1) of this embodiment, one heat source unit (10) and the plurality of air-conditioning units (50) are connected by the first liquid connection pipe (2) and the second gas connection pipe (5).
The heat source unit (10) of this embodiment does not include the second low-stage compressor (22), the second low-stage suction pipe (22 a), and the second low-stage discharge pipe (22 b) of the first embodiment. The compression element (C) of this embodiment includes the first low-stage compressor (23) and the high-stage compressor (21), but does not include the second low-stage compressor (22).
The heat source unit (10) of this embodiment includes a switching valve (80) instead of the flow path switching mechanism (30) of the first embodiment. Similarly to the first switching valve (81) and the second switching valve (82) of the first embodiment, the switching valve (80) is a four-way switching valve. The switching valve (80) has a first port connected to the high-stage discharge pipe (21 b), a second port connected to the first low-stage suction pipe (23 a), a third port connected to the second outdoor gas pipe (36), and a fourth port connected to the first outdoor gas pipe (35).
The switching valve (80) switches between a first state (the state indicated by the solid lines in FIG. 9 ) and a second state (the state indicated by the broken lines in FIG. 9 ). In the switching valve (80) in the first state, the first port communicates with the third port, and the second port communicates with the fourth port. In the switching valve (80) in the second state, the first port communicates with the fourth port, and the second port communicates with the third port.

—Operation of Refrigeration Apparatus—

The refrigeration apparatus (1) of this embodiment performs a cooling operation, a heating operation, a defrosting operation, and a pressure reduction operation.
In the cooling operation, the switching valve (80) is set to the first state. In the refrigerant circuit (6) in the cooling operation, the first low-stage compressor (23) and the high-stage compressor (21) are activated; the outdoor heat exchanger (13) functions as a radiator (a gas cooler); and the indoor heat exchanger (54) of each of the air-conditioning units (50) functions as an evaporator.
In the heating operation, the switching valve (80) is set to the second state. In the refrigerant circuit (6) in the heating operation, the first low-stage compressor (23) and the high-stage compressor (21) are activated; the indoor heat exchanger (54) of each of the air-conditioning units (50) functions as a radiator (a gas cooler); and the outdoor heat exchanger (13) functions as an evaporator.
The defrosting operation is an operation to defrost the outdoor heat exchanger (13). If the amount of frost on the outdoor heat exchanger (13) reaches a certain level or more in the heating operation, the refrigeration apparatus (1) temporally pauses the heating operation and performs the defrosting operation.
In the defrosting operation, the refrigerant circulates in the refrigerant circuit (6) similarly to the cooling operation. Specifically, the switching valve (80) is set to the first state, and the outdoor heat exchanger (13) functions as a radiator (a gas cooler). The frost on the outdoor heat exchanger (13) is heated and melted by the refrigerant.
In the pressure reduction operation, the switching valve (80) is set to the first state. Similarly to the first embodiment, in the pressure reduction operation, the first outdoor expansion valve (14 a) and the venting valve (39) are held in the open state, and the second outdoor expansion valve (14 b) and the decompression valve (40) are held in the closed state. In the pressure reduction operation, the first low-stage compressor (23) is held in the stop state; the high-stage compressor (21) is activated; the outdoor fan (12) is activated; and the fan (17 a) is held in the stop state.

—Operation of Controller—

If both the high-stage compressor (21) and the first low-stage compressor (23) that constitute the compression element (C) are stopped, the receiver pressure control unit (103) of the controller (101) performs the same operation as that of the first embodiment.
Specifically, the receiver pressure control unit (103) performs the first operation and the second operation if the compression element (C) stops. In the first operation and the second operation, the receiver pressure control unit (103) controls the first outdoor expansion valve (14 a) and the second outdoor expansion valve (14 b) in order to reduce an increase in the refrigerant pressure in the receiver (15). If the first operation and the second operation fail to reduce an increase in the refrigerant pressure in the receiver (15), the receiver pressure control unit (103) performs a third operation. In the third operation, the receiver pressure control unit (103) allows the refrigeration apparatus (1) to perform a pressure reduction operation.

OTHER EMBODIMENTS

—First Variation—

In the receiver pressure control unit (103) of the controller (101) of the first and second embodiments, the second pressure that is used to determine whether to close the first outdoor expansion valve (14 a) in the second operation is set lower than the critical pressure of carbon dioxide serving as the refrigerant. The second pressure may be set higher than or equal to the critical pressure of carbon dioxide. However, the second pressure needs to be lower than the third pressure.
If the second pressure is lower than the critical pressure of carbon dioxide, the difference between the second pressure and the third pressure is relatively large. Thus, the time required for the refrigerant pressure in the receiver (15) to rise from the second pressure to the third pressure becomes longer, and thus the refrigeration apparatus (1) can perform the pressure reduction operation with a reduced frequency.
On the other hand, if the second pressure is higher than the critical pressure of carbon dioxide, the refrigerant pressure in the outdoor heat exchanger (13) is higher than the critical pressure of carbon dioxide at the time when the receiver pressure control unit (103) closes the first outdoor expansion valve (14 a) in the second operation, which means that the refrigerant in the outdoor heat exchanger (13) is in a supercritical state. Thus, even if the outdoor air temperature rises thereafter, the refrigerant does not evaporate in the outdoor heat exchanger (13), and thus a sharp rise in the refrigerant pressure in the outdoor heat exchanger (13) is avoided.

—Second Variation—

In the heat source unit (10) of the first and second embodiments, the compression element (C) may be configured to perform a single-stage compression. The compression element (C) of this variation includes one compressor or a plurality of compressors connected in parallel to each other.
In the outdoor circuit (11) of this variation, the venting pipe (37) is connected to an injection port or a suction port of the compressor constituting the compression element (C). The injection port is a port to introduce the refrigerant into the compression chamber of the compressor that is in course of compression. The suction port is a port to introduce the refrigerant into the compression chamber of the compressor that is in course of suction.
While the embodiments and variations thereof have been described above, it will be understood that various changes in form and details may be made without departing from the spirit and scope of the claims. The foregoing embodiments and variations thereof may be combined or replaced with each other without deteriorating the intended functions of the present disclosure. In addition, the expressions of “first,” “second,” “third,” . . . , in the specification and claims are used to distinguish the terms to which these expressions are given, and do not limit the number and order of the terms.

INDUSTRIAL APPLICABILITY

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

DESCRIPTION OF REFERENCE CHARACTERS

- 1 Refrigeration Apparatus
- 10 Heat Source Unit
- 11 Outdoor Circuit (Heat-Source-Side Circuit)
- 13 Outdoor Heat Exchanger (Heat-Source-Side Heat Exchanger)
- 14 a First Outdoor Expansion Valve (Expansion Valve)
- 15 Receiver
- C Compression Element
- 21 High-Stage Compressor (Compressor)
- 22 Second Low-Stage Compressor (Compressor)
- 23 First Low-Stage Compressor (Compressor)
- 37 Venting Pipe (Venting Passage)
- 50 Air-Conditioning Unit (Utilization-Side Unit)
- 60 Cooling Unit (Utilization-Side Unit)
- 101 Controller

Claims

1. A heat source unit connected to a utilization-side unit and configured to perform a refrigeration cycle, the heat source unit comprising:

a heat-source-side circuit including a compression element with one or more compressors, a heat-source-side heat exchanger, an expansion valve, and a receiver; and

a controller configured to control the expansion valve,

wherein

in the heat-source-side circuit, the expansion valve is located between the heat-source-side heat exchanger and the receiver, and

while the compression element is stopped, the controller controls the expansion valve based on one or both of a refrigerant pressure in the receiver and a refrigerant pressure in the heat-source-side heat exchanger.

2. The heat source unit of claim 1, wherein

the controller switches the expansion valve to a closed state in response to a stop of the compression element, and thereafter performs a first operation to turn the expansion valve to an open state if the refrigerant pressure in the heat-source-side heat exchanger becomes lower than a first pressure.

3. The heat source unit of claim 2, wherein

after performing the first operation, the controller performs a second operation to turn the expansion valve to a closed state if the refrigerant pressure in the receiver becomes higher than a second pressure.

4. The heat source unit of claim 3, wherein

the heat-source-side circuit includes a venting passage configured to send a gas refrigerant in the receiver to the compression element, and

after performing the second operation, the controller performs a third operation to activate the compression element to suck the gas refrigerant in the receiver into the compression element through the venting passage if the refrigerant pressure in the receiver becomes higher than a third pressure.

5. The heat source unit of claim 1, wherein

the heat-source-side circuit is charged with carbon dioxide as a refrigerant.

6. A refrigeration apparatus comprising:

the heat source unit of claim 1; and

a utilization-side unit connected to the heat source unit.