EP4624832A1

EP4624832A1 - Heat source unit and refrigeration device

Info

Publication number: EP4624832A1
Application number: EP24756556.7A
Authority: EP
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: 2024-01-18
Publication date: 2025-10-01
Also published as: EP4624832A4; JP7485995B1; JP2024115907A; CN120584265A; CN120584265B; WO2024171705A1; US20250347447A1

Abstract

A heat-source-side circuit (11) of a heat source unit (10) includes a low-stage compressor (23), a high-stage compressor (21), a heat-source-side heat exchanger (13), a receiver (15), and a venting passage (37). The venting passage (37) connects an upper portion of the receiver (15) with an inlet of the high-stage compressor (21). A determination unit (103) of the heat source unit (10) determines that the amount of the refrigerant charged in a refrigerant circuit (6) is excessive based on the pressure and the degree of superheat of the refrigerant sucked into the high-stage compressor (21).

Description

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. The heat source unit includes a low-stage compressor, a high-stage compressor, a heat-source-side heat exchanger, and a receiver. The receiver is connected with a venting passage. The venting passage guides a gas refrigerant in the receiver to the high-stage compressor.
The heat source unit of Patent Document 1 is connected to a utilization-side unit by a pipe and forms a refrigerant circuit. In the refrigerant circuit, a refrigerant circulates to create a two-stage compression refrigeration cycle.

CITATION LIST

PATENT DOCUMENT

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

SUMMARY OF THE INVENTION

TECHNICAL PROBLEM

The length of the pipe connecting the heat source unit and the utilization-side unit depends on the building in which the heat source unit and the utilization-side unit are installed. In addition, the length of the pipe connecting the heat source unit and the utilization-side unit affects the appropriate value of the amount of refrigerant charged in the refrigerant circuit. Thus, when the heat source unit and the utilization-side unit are installed, the operator adjusts the amount of refrigerant charged in the refrigerant circuit.
However, the heat source unit of Patent Document 1 including the receiver and the venting passage does not have a function of determining whether the amount of refrigerant charged in the refrigerant circuit connected with the heat source unit is excessive.
An object of the present disclosure is to provide a heat source unit that includes a receiver and a venting passage where it is possible to determine that the amount of a refrigerant charged in a refrigerant circuit is excessive.

SOLUTION TO THE PROBLEM

A first aspect of the present disclosure is directed to a heat source unit (10) connected to a utilization-side unit (50, 60) and forming a refrigerant circuit (6) configured to perform a refrigeration cycle, the heat source unit (10) comprising: a heat-source-side circuit (11) including a low-stage compressor (23), a high-stage compressor (21), a heat-source-side heat exchanger (13), and a receiver (15); and a determination unit (103) configured to determine that an amount of a refrigerant charged in the refrigerant circuit (6) is excessive, wherein the heat-source-side circuit (11) includes a venting passage (37) that connects an upper portion of the receiver (15) with an inlet of the high-stage compressor (21), and the determination unit (103) determines that the amount of the refrigerant charged in the refrigerant circuit (6) is excessive based on a pressure and a degree of superheat of the refrigerant sucked into the high-stage compressor (21).
In the first aspect, the heat source unit (10) is connected to the utilization-side unit (50, 60) and forms the refrigerant circuit (6). In the heat-source-side circuit (11) of the heat source unit (10), the venting passage (37) connects the upper portion of the receiver (15) with the inlet of the high-stage compressor (21). If the amount of refrigerant charged in the refrigerant circuit (6) is excessive, the amount of the liquid refrigerant in the receiver (15) increases, and the liquid refrigerant together with the gas refrigerant is sucked into the high-stage compressor (21) through the venting passage (37). Thus, the state of the refrigerant sucked into the high-stage compressor (21) varies between when the amount of refrigerant charged in the refrigerant circuit (6) is excessive and when the amount of refrigerant charged in the refrigerant circuit (6) is appropriate. Then, the determination unit (103) determines that the amount of the refrigerant charged in the refrigerant circuit (6) is excessive based on the pressure and the degree of superheat of the refrigerant sucked into the high-stage compressor (21).
A second aspect of the present disclosure is an embodiment of the first aspect. In the second aspect, the determination unit (103) determines that the amount of the refrigerant charged in the refrigerant circuit (6) is excessive if a determination criterion is satisfied, and the determination criterion is that the pressure of the refrigerant sucked into the high-stage compressor (21) is higher than a reference pressure and that the degree of superheat of the refrigerant sucked into the high-stage compressor (21) is lower than a reference degree of superheat.
If the amount of refrigerant charged in the refrigerant circuit (6) is excessive, the liquid refrigerant in the receiver (15) together with the gas refrigerant is sucked into the high-stage compressor (21) through the venting passage (37). The larger the amount of liquid refrigerant flowing through the venting passage (37) is, the lower the degree of superheat of the refrigerant sucked into the high-stage compressor (21) is. In contrast, the higher the pressure of the refrigerant sucked into the high-stage compressor (21) is, the higher the degree of superheat of the refrigerant sucked into the high-stage compressor (21) is. Thus, if the degree of superheat of the refrigerant sucked into the high-stage compressor (21) is low while the pressure of the refrigerant sucked into the high-stage compressor (21) is relatively high, it can be determined that the amount of refrigerant charged in the refrigerant circuit (6) is excessive.
Then, the determination unit (103) of the second aspect determines that the amount of refrigerant charged in the refrigerant circuit (6) is excessive if the determination criterion "the pressure of the refrigerant sucked into the high-stage compressor (21) is higher than the reference pressure, and the degree of superheat of the refrigerant sucked into the high-stage compressor (21) is lower than the reference degree of superheat" is satisfied.
A third aspect of the present disclosure is an embodiment of the second aspect. In the third aspect, the refrigerant amount determination unit (103) repeatedly determines whether the determination criterion is satisfied, and determines that the amount of the refrigerant charged in the refrigerant circuit (6) is excessive if the determination criterion is satisfied twice or more within a predetermined time.
When the heat source unit is operating, the determination criterion might be accidentally satisfied even if the amount of refrigerant charged in the refrigerant circuit (6) is appropriate. Then, the determination unit (103) of the third aspect repeatedly determines whether the determination criterion is satisfied, and determines that the amount of the refrigerant charged in the refrigerant circuit (6) is excessive if the determination criterion is satisfied twice or more within a predetermined time. Thus, it is possible to reduce the possibility of erroneously determining that the amount of refrigerant charged in the refrigerant circuit (6) is excessive while the amount of refrigerant charged in the refrigerant circuit (6) is appropriate.
A fourth aspect of the present disclosure is an embodiment of any one of the first to third aspects. In the fourth aspect, the heat-source-side circuit (11) is charged with carbon dioxide as a refrigerant.
In the fourth aspect, carbon dioxide is used as a refrigerant in the heat-source-side circuit (11).
A fifth aspect of the present disclosure is directed to a refrigeration apparatus including: the heat source unit (10) of any one of the first to fourth aspects; and a utilization-side unit (50, 60) connected to the heat source unit (10).
In the fifth aspect, the heat source unit (10) and the utilization-side unit (50, 60) constitute the refrigeration apparatus (1).

BRIEF DESCRIPTION OF THE DRAWINGS

[FIG. 1] FIG. 1 is a piping system diagram showing a configuration of a refrigeration apparatus according to a first embodiment.
[FIG. 2] FIG. 2 is a block diagram showing a configuration of a controller of a heat source unit according to the first embodiment.
[FIG. 3] FIG. 3 corresponds to FIG. 1 and shows a flow of a refrigerant in a cooling operation.
[FIG. 4] FIG. 4 corresponds to FIG. 1 and shows a flow of a refrigerant in a first heating operation.
[FIG. 5] FIG. 5 corresponds to FIG. 1 and shows a flow of a refrigerant in a second heating operation.
[FIG. 6] FIG. 6 corresponds to FIG. 1 and shows a flow of a refrigerant in a third heating operation.
[FIG. 7] FIG. 7 is a flowchart showing operation of the controller of the first embodiment.
[FIG. 8] FIG. 8 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 embodiments below are merely exemplary ones in nature, and are not intended to limit the scope, applications, or use of the present 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 target referred to herein includes air present 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 connection pipes (2, 3, 4, 5) connecting these 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 (14a), 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 (21a) and a high-stage discharge pipe (21b). The high-stage discharge pipe (21b) 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 (23a) and a first low-stage discharge pipe (23b). The first low-stage suction pipe (23a) 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 (22a) and a second low-stage discharge pipe (22b). In the compression element (C), the first low-stage discharge pipe (23b) and the second low-stage discharge pipe (22b) are connected to the high-stage suction pipe (21a).
The second low-stage suction pipe (22a) 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 (23a) 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 (24c) and a second low-stage pipe (24b). The first low-stage pipe (24c) is a pipe through which the refrigerant flows to bypass the first low-stage compressor (23). One end of the first low-stage pipe (24c) is connected to the first low-stage suction pipe (23a), and the other end of the first low-stage pipe (24c) is connected to the first low-stage discharge pipe (23b). The first low-stage pipe (24c) is provided in parallel with the first low-stage compressor (23). The second low-stage pipe (24b) is a pipe through which the refrigerant flows to bypass the second low-stage compressor (22). One end of the second low-stage pipe (24b) is connected to the second low-stage suction pipe (22a), and the other end of the second low-stage pipe (24b) is connected to the second low-stage discharge pipe (22b). The second low-stage pipe (24b) 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 (21b). 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 (23a).
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 (o1) 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 a first liquid-side trunk pipe (4a) 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 (14a). The third outdoor pipe (o3) of the outdoor circuit (11) is provided with a second outdoor expansion valve (14b). The first outdoor expansion valve (14a) and the second outdoor expansion valve (14b) are electronic expansion valves of which the opening degree is variable. The first outdoor expansion valve (14a) and the second outdoor expansion valve (14b) 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 (14a). 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 (15a). One of the examples of the thermal insulator (15a) is glass wool. By covering the receiver (15) with the thermal insulator (15a), 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 (14a) to the high-stage suction pipe (21a). 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 (21a). 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 (21a). 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) guides the refrigerant in the receiver (15) (mainly the gas refrigerant) to the high-stage suction pipe (21a) through the injection pipe (38). The venting pipe (37) serves as a venting passage that connects an upper portion of the receiver (15) with an inlet of the high-stage compressor (21).
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 (16a) and a second flow path (16b). The subcooling heat exchanger (16) exchanges heat between the refrigerant flowing through the first flow path (16a) and the refrigerant flowing through the second flow path (16b).
In the subcooling heat exchanger (16), the refrigerant flowing through the first flow path (16a) is cooled. The first flow path (16a) 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 (16b) is included in the intermediate injection circuit (49). Specifically, the second flow path (16b) 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 (16b).

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

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 (21b). The second check valve (CV2) is connected to the second low-stage discharge pipe (22b). The third check valve (CV3) is connected to the first low-stage 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). The eighth check valve (CV8) is connected to the second low-stage pipe (24b). The ninth check valve (CV9) is connected to the first low-stage pipe (24c).

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 (21b). 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 sucked into the high-stage compressor (21).
The first low-pressure sensor (73) is connected to the second low-stage suction pipe (22a). 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 (23a). 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 (21a). The high-stage suction temperature sensor (77) detects the temperature of the refrigerant flowing through the high-stage suction pipe (21a). In other words, the high-stage suction temperature sensor (77) detects the temperature of the refrigerant sucked into the high-stage compressor (21).

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 refrigerant amount determination unit (103) by executing the program stored in the memory device (105). The refrigerant amount determination unit (103) determines that the amount of refrigerant charged in the refrigerant circuit (6) is larger than an appropriate amount. In other words, the refrigerant amount determination unit (103) determines that the amount of refrigerant charged in the refrigerant circuit (6) is excessive.
Here, if the refrigeration apparatus (1) is installed in a building or the like, the heat source unit (10), the cooling units (60), and the air-conditioning units (50) are each placed at predetermined locations, and thereafter the connection pipes (2, 3, 4, 5) are provided between the cooling unit (60) and the heat source unit (10) and between the air-conditioning unit (50) and the heat source unit (10). As a result, the refrigerant circuit (6) is formed.
In general, the number of the cooling units (60), the number of the air-conditioning units (50), and the lengths of the connection pipes (2, 3, 4, 5) each depend on the building in which the refrigeration apparatus (1) is installed. On the other hand, the appropriate amount of refrigerant charged in the refrigerant circuit (6) varies with the number of the cooling units (60) in the refrigerant circuit (6), the number of the air-conditioning units (50) in the refrigerant circuit (6), and the lengths of the connection pipes (2, 3, 4, 5) in the refrigerant circuit (6). Thus, when the refrigeration apparatus (1) is installed, the operator needs to further charge the refrigerant circuit (6) with the refrigerant as needed.
If the operator further charges the refrigerant circuit (6) with the refrigerant, it is necessary to check whether the amount of refrigerant charged in the refrigerant circuit (6) is appropriate. Then, in a trial operation of the refrigeration apparatus (1) performed after the operator further charges the refrigerant circuit (6) with the refrigerant, the refrigerant amount determination unit (103) of the controller (101) determines that the amount of refrigerant charged in the refrigerant circuit (6) is excessive.

-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 a refrigerant flowing therethrough and 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 (4c) of the second liquid connection pipe (4). The gas end of the cooling circuit (61) is connected with the gas-side branch pipe (5c) 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) performs the defrosting operation to defrost the outdoor heat exchanger (13).

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 (14b) 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 (14a); thereafter passes through the receiver (15); and subsequently is cooled while passing through the first flow path (16a) of the subcooling heat exchanger (16). Part of the refrigerant that has passed through the first flow path (16a) of the subcooling heat exchanger (16) passes through the injection pipe (38) and flows into the second flow path (16b) of the subcooling heat exchanger (16); then absorbs heat to evaporate; and thereafter flows into the high-stage suction pipe (21a). The rest of the refrigerant that has passed through the first flow path (16a) 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 (23a); 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 (22a) 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 (14b) 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 (14a), 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 (16a) of the subcooling heat exchanger (16). Part of the refrigerant that has passed through the first flow path (16a) of the subcooling heat exchanger (16) passes through the injection pipe (38) and flows into the second flow path (16b) of the subcooling heat exchanger (16); then absorbs heat to evaporate; and thereafter flows into the high-stage suction pipe (21a). The rest of the refrigerant that has passed through the first flow path (16a) 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 (22a) 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 (14b) 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 (16a) of the subcooling heat exchanger (16). Part of the refrigerant that has passed through the first flow path (16a) of the subcooling heat exchanger (16) passes through the injection pipe (38) and flows into the second flow path (16b) of the subcooling heat exchanger (16); then absorbs heat to evaporate; and thereafter flows into the high-stage suction pipe (21a). The rest of the refrigerant that has passed through the first flow path (16a) 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 (22a) 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 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 (14a) 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 (16a) of the subcooling heat exchanger (16). The refrigerant that has passed through the first flow path (16a) 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 (16b) of the subcooling heat exchanger (16); then absorbs heat and evaporates; and thereafter flows into the high-stage suction pipe (21a).
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 (22a) 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 (14b); 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 (23a), 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.

-Operation of Controller-

As described above, in the trial operation of the refrigeration apparatus (1) performed after the refrigerant circuit (6) is further charged with the refrigerant, the refrigerant amount determination unit (103) of the controller (101) determines that the amount of refrigerant charged in the refrigerant circuit (6) is excessive. The refrigerant amount determination unit (103) of this embodiment determines that the amount of refrigerant charged in the refrigerant circuit (6) is excessive if the number of times the determination criterion is satisfied reaches the reference count Nc after the operation is started and before the reference time Hc passes.
The operation performed by the refrigerant amount determination unit (103) of the controller (101) will be described with reference to the flowchart of FIG. 7.

First, the refrigerant amount determination unit (103) performs the operation of step ST1. In the operation of step ST1, the refrigerant amount determination unit (103) resets the satisfaction count N to "zero." The satisfaction count N represents the number of times the determination criterion is satisfied.

Next, the refrigerant amount determination unit (103) performs the operation of step ST2. In the operation of step ST2, the refrigerant amount determination unit (103) starts measuring the elapsed time H.

Next, the refrigerant amount determination unit (103) performs the operation of step ST3. In the operation of step ST3, the refrigerant amount determination unit (103) compares the current elapsed time H with the reference time Hc. If the elapsed time H does not reach the reference time Hc (H < Hc), the refrigerant amount determination unit (103) performs the operation of step ST4. In contrast, if the elapsed time H reaches the reference time Hc (H ≥ Hc), the refrigerant amount determination unit (103) finishes the operation. The reference time Hc is 2 hours or more in one preferred embodiment.

In the operation of step ST4, the refrigerant amount determination unit (103) obtains the measurement value of the intermediate-pressure sensor (72) as the suction pressure Pm of the high-stage compressor (21), and obtains the measurement value of the high-stage suction temperature sensor (77) as the suction temperature Tm of the high-stage compressor (21).

Next, the refrigerant amount determination unit (103) performs the operation of step ST5. In the operation of step ST5, the refrigerant amount determination unit (103) calculates the degree of superheat of the refrigerant sucked into the high-stage compressor (21) (the degree of suction superheat SHm). The refrigerant amount determination unit (103) calculates the degree of suction superheat SHm by subtracting "the saturation temperature of the refrigerant at the suction pressure Pm" from "the suction temperature Tm."

Next, the refrigerant amount determination unit (103) performs the operation of step ST6. In the operation of step ST6, the refrigerant amount determination unit (103) determines whether the determination criterion is satisfied. The determination criterion is that "the suction pressure Pm of the high-stage compressor (21) is higher than the reference pressure Pc (Pm > Pc), and the degree of suction superheat SHm of the high-stage compressor (21) is lower than the reference degree of superheat SHc (SHm < SHc)." The reference pressure Pc is 5MPa, for example. The reference degree of superheat SHc is 5°C, for example.
If the determination criterion is satisfied, the refrigerant amount determination unit (103) performs the operation of step ST7. In contrast, if the determination criterion is not satisfied, the refrigerant amount determination unit (103) performs the operation of step ST3.
Here, if the amount of refrigerant charged in the refrigerant circuit (6) is excessive, the liquid refrigerant in the receiver (15) together with the gas refrigerant is sucked into the high-stage compressor (21) through the venting pipe (37). The larger the amount of liquid refrigerant flowing through the venting pipe (37) is, the lower the degree of superheat of the refrigerant sucked into the high-stage compressor (21) is.
In contrast, the higher the pressure of the refrigerant sucked into the high-stage compressor (21) is, the higher the degree of superheat of the refrigerant sucked into the high-stage compressor (21) is. Thus, if the degree of superheat of the refrigerant sucked into the high-stage compressor (21) is low while the pressure of the refrigerant sucked into the high-stage compressor (21) is relatively high, it can be determined that the amount of refrigerant charged in the refrigerant circuit (6) is excessive.
Then, the refrigerant amount determination unit (103) of this embodiment determines whether the determination criterion "the suction pressure Pm of the high-stage compressor (21) is higher than the reference pressure Pc (Pm > Pc), and the degree of suction superheat SHm of the high-stage compressor (21) is lower than the reference degree of superheat SHc (SHm < SHc)" is satisfied.

In the operation of step ST7, the refrigerant amount determination unit (103) updates the satisfaction count N. Specifically, the value obtained by adding "1" to the satisfaction count N up to then is newly defined as the satisfaction count N.

Next, the refrigerant amount determination unit (103) performs the operation of step ST8. In the operation of step ST8, the refrigerant amount determination unit (103) compares the satisfaction count N with the reference count Nc. If the criterion "the satisfaction count N is more than or equal to the reference count Nc (N ≥ Nc)" is satisfied, the refrigerant amount determination unit (103) performs the operation of step ST9. In contrast, if this criterion is not satisfied, the refrigerant amount determination unit (103) performs the operation of step ST3. The reference count Nc is an integer that is more than or equal to "2." The reference count Nc is five or more in one preferred embodiment.

If the criterion in the operation of step ST8 is satisfied, this means that the satisfaction count N of the determination criterion in the operation of step ST6 reaches the reference count Nc before the elapsed time H reaches the reference time Hc. Then, in the operation of step ST9, the refrigerant amount determination unit (103) determines that the amount of refrigerant charged in the refrigerant circuit (6) is excessive, and then warns the operator about this determination. For example, the refrigerant amount determination unit (103) displays a predetermined remark on a display of a remote control of the refrigeration apparatus (1) in order to warn the operator that the amount of refrigerant charged in the refrigerant circuit (6) is excessive.

-Feature (1) of First Embodiment-

In the heat source unit (10) of this embodiment, the refrigerant amount determination unit (103) of the controller (101) automatically determines that the amount of refrigerant charged in the refrigerant circuit (6) of the refrigeration apparatus (1) is excessive. Thus, it is possible to reduce the number of steps required to install the refrigeration apparatus (1). In addition, since it is possible to correctly determine whether the amount of refrigerant charged in the refrigerant circuit (6) of the refrigeration apparatus (1) is excessive, the refrigeration apparatus (1) can reliably exhibit its full performance.

-Feature (2) of First Embodiment-

When the refrigeration apparatus (1) is operating while the pressure of the refrigerant sucked into the high-stage compressor (21) is relatively low, the degree of superheat of the refrigerant sucked into the high-stage compressor (21) might be relatively low even if the amount of refrigerant charged in the refrigerant circuit (6) is appropriate. In contrast, when the operation is being conducted while the pressure of the refrigerant sucked into the high-stage compressor (21) is relatively high, the degree of superheat of the refrigerant sucked into the high-stage compressor (21) is also high if the amount of refrigerant charged in the refrigerant circuit (6) is appropriate.
Thus, if the degree of superheat of the refrigerant sucked into the high-stage compressor (21) is low while the pressure of the refrigerant sucked into the high-stage compressor (21) is relatively high, the amount of liquid refrigerant flowing from the receiver (15) toward the high-stage compressor (21) through the venting pipe (37) is relatively large. Thus, it can be determined that the amount of refrigerant charged in the refrigerant circuit (6) is excessive.
Then, the refrigerant amount determination unit (103) of this embodiment determines that the amount of refrigerant charged in the refrigerant circuit (6) is excessive based on not only the degree of superheat of the refrigerant sucked into the high-stage compressor (21) but both the pressure and the degree of superheat of the refrigerant sucked into the high-stage compressor (21). Thus, according to this embodiment, it is possible to reduce the possibility of erroneously determining that the amount of refrigerant charged in the refrigerant circuit (6) is excessive while the amount of refrigerant charged in the refrigerant circuit (6) is appropriate.

-Feature (3) of First Embodiment-

When the refrigeration apparatus (1) is operating, the determination criterion for the refrigerant amount determination unit (103) (see step ST6 in FIG. 7) might be accidentally satisfied even if the amount of refrigerant charged in the refrigerant circuit (6) is appropriate. Then, the refrigerant amount determination unit (103) of this embodiment repeatedly determines whether the determination criterion is satisfied, and then determines that the amount of refrigerant charged in the refrigerant circuit (6) is excessive if the satisfaction count N of the determination criterion reaches the reference count Nc before the elapsed time H reaches the reference time Hc. Thus, according to this embodiment, it is possible to reduce the possibility of erroneously determining that the amount of refrigerant charged in the refrigerant circuit (6) is excessive while the amount of refrigerant charged in the refrigerant circuit (6) is appropriate.

<<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. 8, 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 (22a), and the second low-stage discharge pipe (22b) 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) includes a first port connected to the high-stage discharge pipe (21b), a second port connected to the first low-stage suction pipe (23a), 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. 8) and a second state (the state indicated by the broken lines in FIG. 8). 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, and a defrosting 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.

-Operation of Controller-

The refrigerant amount determination unit (103) of the controller (101) performs the same operation as that of the first embodiment. Thus, the refrigerant amount determination unit (103) of this embodiment performs the operation shown in FIG. 7 and determines that the amount of refrigerant charged in the refrigerant circuit (6) is excessive.

<<Other Embodiments>>

The refrigerant amount determination unit (103) of the first and second embodiments may be configured to determine that the amount of refrigerant charged in the refrigerant circuit (6) is excessive if the determination criterion is successively satisfied for a predetermined time. In addition, the refrigerant amount determination unit (103) of this variation may be configured to periodically determine whether the determination criterion is satisfied; and regard the determination criterion as being successively satisfied for a predetermined time and thus determine that the amount of refrigerant charged in the refrigerant circuit (6) is excessive if the number of times the determination criterion is successively satisfied reaches a predetermined value.
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)
15: Receiver
21: High-Stage Compressor
23: First Low-Stage Compressor (Low-Stage Compressor)
37: Venting Pipe (Venting Passage)
50: Air-Conditioning Unit (Utilization-Side Unit)
60: Cooling Unit (Utilization-Side Unit)
101: Controller
103: Refrigerant Amount Determination Unit (Determination Unit)

Claims

A heat source unit (10) connected to a utilization-side unit (50, 60) and forming a refrigerant circuit (6) configured to perform a refrigeration cycle, the heat source unit (10) comprising:
a heat-source-side circuit (11) including a low-stage compressor (23), a high-stage compressor (21), a heat-source-side heat exchanger (13), and a receiver (15); and

a determination unit (103) configured to determine that an amount of a refrigerant charged in the refrigerant circuit (6) is excessive,

wherein

the heat-source-side circuit (11) includes a venting passage (37) that connects an upper portion of the receiver (15) with an inlet of the high-stage compressor (21), and

the determination unit (103) determines that the amount of the refrigerant charged in the refrigerant circuit (6) is excessive based on a pressure and a degree of superheat of the refrigerant sucked into the high-stage compressor (21).
The heat source unit of claim 1, wherein
the determination unit (103) determines that the amount of the refrigerant charged in the refrigerant circuit (6) is excessive if a determination criterion is satisfied, and

the determination criterion is that the pressure of the refrigerant sucked into the high-stage compressor (21) is higher than a reference pressure and that the degree of superheat of the refrigerant sucked into the high-stage compressor (21) is lower than a reference degree of superheat.
The heat source unit of claim 2, wherein
the refrigerant amount determination unit (103) repeatedly determines whether the determination criterion is satisfied, and determines that the amount of the refrigerant charged in the refrigerant circuit (6) is excessive if the determination criterion is satisfied twice or more within a predetermined time.
The heat source unit of any one of claims 1 to 3, wherein
the heat-source-side circuit (11) is charged with carbon dioxide as a refrigerant.
A refrigeration apparatus comprising:
the heat source unit (10) of any one of claims 1 to 4; and

a utilization-side unit (50, 60) connected to the heat source unit (10).