EP2578965A1

EP2578965A1 - Freezing device

Info

Publication number: EP2578965A1
Application number: EP11789400.6A
Authority: EP
Inventors: Masaaki Takegami; Satoru Sakae; Ryuuji Takeuchi; Tetsuya Shirasaki
Original assignee: Daikin Industries Ltd
Current assignee: Daikin Industries Ltd
Priority date: 2010-05-31
Filing date: 2011-05-18
Publication date: 2013-04-10
Also published as: WO2011151985A1; EP2578965A4; JP2011252623A; JP4888583B2

Abstract

In a refrigeration apparatus including a refrigerant circuit (20) in which a plurality of compressors (21), a heat-source-side heat exchanger (25), an expansion mechanism (52), and a utilization-side heat exchanger (53) are connected in order, when one or more of the compressors (21) is a compressor in operation and other one or more of the compressors (21) is a stopped compressor, a control is performed to decrease the low pressure of an evaporator connected to the compressor in operation to less than the saturation pressure equivalent to the temperature of the stopped compressor itself or the ambient temperature of the stopped compressor. In such a manner, refrigerant liquefaction in the stopped compressor is reduced or prevented, thereby reducing operation failure or burnout upon a restart.

Description

TECHNICAL FIELD

The present invention relates to a refrigeration apparatus, and particularly relates to a refrigeration apparatus in which a plurality of compressors are connected together in a refrigerant circuit.

BACKGROUND ART

Conventionally, a refrigeration apparatus including a refrigerant circuit configured to perform a refrigeration cycle has been known. The refrigeration apparatus of this type has been broadly used for, e.g., a chiller configured to cool an inside of a compartment of a refrigerator in which food etc. are stored and an air conditioner configured to air-condition an inside of a room.
Patent Document 1 discloses a refrigeration apparatus in which an indoor unit and a cold-storage/freezing unit are provided. The refrigeration apparatus can perform an operation for cooling the cold-storage/freezing unit during an air-cooling operation, and can perform an operation for cooling the cold-storage/freezing unit during an air-heating operation.

CITATION LIST

PATENT DOCUMENT

PATENT DOCUMENT 1: Japanese Patent Publication No. 2007-078338

SUMMARY OF THE INVENTION

TECHNICAL PROBLEM

Suppose that a refrigeration apparatus in which a plurality of compressors are connected together is in the following operation state under the condition where an external air temperature is dropped to, e.g., about -10°C in a cold region: some of the compressors are in operation, whereas the other compressors are stopped. An evaporator connected to the compressor in operation is typically at about 5-10°C. Thus, if the external air temperature (if the compressors are accommodated in an outdoor unit, the temperature of the compressor itself or the ambient temperature of the compressor) is -10°C, the temperature-equivalent saturation pressure of the external air temperature is lower than the foregoing low pressure. As a result, since the internal pressure of the stopped compressor is lower than that of the compressor in operation, refrigerant may flow not into the compressor in operation but into the stopped compressor.
In the foregoing state, refrigerant gas is dissolved in low-temperature refrigerant oil accumulated in the stopped compressor, and then the resultant is condensed (the state in which refrigerant gas is dissolved in refrigerant oil and the resultant is condensed is hereinafter referred to as "refrigerant liquefaction"). This results in reduction in oil viscosity. As a result, when the stopped compressor is restarted, low-viscosity oil may be supplied to a mechanical sliding part of the compressor, thereby causing insufficient lubrication or burnout.
The present invention has been made in view of the foregoing, and it is an objective of the present invention to reduce or prevent, in a refrigeration apparatus including a plurality of compressors, refrigerant liquefaction in a stopped compressor to reduce operation failure or burnout upon a restart.

SOLUTION TO THE PROBLEM

A first aspect of the invention is intended for a refrigeration apparatus including a refrigerant circuit (20, 200) in which a plurality of compressors (21, 114), a heat-source-side heat exchanger (25, 115), an expansion mechanism (52, 153, 163), and a utilization-side heat exchanger (53, 154, 164) are connected in order.
The refrigeration apparatus includes a controller (9, 200) configured to decrease, when one or more of the compressors (21, 114) is a compressor in operation and other one or more of the compressors (21, 114) is a stopped compressor, if a saturation pressure equivalent to a temperature of the stopped compressor itself or an ambient temperature of the stopped compressor is lower than a low pressure of one of the heat exchangers serving as an evaporator connected to the compressor in operation, the low pressure of the evaporator connected to the compressor in operation to less than the saturation pressure equivalent to the temperature of the stopped compressor itself or the ambient temperature of the stopped compressor. The outlet pipe temperature of the compressor can be used as the temperature of the compressor itself, and, e.g., an external air temperature can be used as the ambient temperature of the compressor.
In the first aspect of the invention, when the temperature of the stopped compressor itself or the ambient temperature of the stopped compressor is dropped in, e.g., a cold region during the winter, and the saturation pressure equivalent to such a temperature is lower than the low pressure (evaporation pressure) of the compressor in operation, the control is performed to decrease the low pressure (evaporation pressure) of the compressor in operation to less than the temperature-equivalent saturation pressure. In such a manner, the low pressure of the compressor in operation becomes lower than the pressure of the stopped compressor. Thus, refrigerant flows into the compressor in operation, and does not flow into the stopped compressor.
A second aspect of the invention is intended for the refrigeration apparatus of the first aspect of the invention, in which the compressors (21, 114) and the heat-source-side heat exchanger (25, 115) are accommodated in a heat-source-side unit (2, 110), and, in an operation state in which the heat-source-side heat exchanger (25, 115) serves as a condenser, the controller (9, 200) performs a control based on a saturation pressure equivalent to an ambient temperature of the condenser having a temperature higher than an external air temperature. For example, the temperature of the compressor itself or the ambient temperature thereof may be used as the ambient temperature of the condenser.
In the second aspect of the invention, when the heat-source-side heat exchanger (25, 115) serves as the condenser, the temperature inside the heat-source-side unit (2, 110) is typically higher than the external air temperature. Thus, the control is performed based on the saturation pressure equivalent to the ambient temperature of the condenser having a temperature higher than the external air temperature.
A third aspect of the invention is intended for the refrigeration apparatus of the first aspect of the invention, in which the compressors (21, 114) and the heat-source-side heat exchanger (25, 115) are accommodated in a heat-source-side unit (2, 110), and, in an operation state in which the heat-source-side heat exchanger (25, 115) serves as an evaporator, the controller (9, 200) performs a control based on a saturation pressure equivalent to an ambient temperature of the evaporator having a temperature lower than an external air temperature. For example, the temperature of the compressor itself or the ambient temperature thereof may be used as the ambient temperature of the evaporator.
In the third aspect of the invention, when the heat-source-side heat exchanger (25, 115) serves as the evaporator, the temperature inside the heat-source-side unit (2, 110) is typically lower than the external air temperature. Thus, the control is performed based on the saturation pressure equivalent to the ambient temperature of the evaporator having a temperature lower than the external air temperature.
A fourth aspect of the invention is intended for the refrigeration apparatus of the first aspect of the invention, in which, in the refrigerant circuit (20), the heat-source-side heat exchanger (25) serves as a condenser, the utilization-side heat exchanger (53) serves as an evaporator, and only cooling is performed by the utilization-side heat exchanger (53).
In the fourth aspect of the invention, when the heat-source-side heat exchanger (25) serves as the condenser as in the second aspect of the invention, the temperature inside the heat-source-side unit (2) is typically higher than the external air temperature. Thus, the control is performed based on the saturation pressure equivalent to the ambient temperature of the condenser having a temperature higher than the external air temperature.
A fifth aspect of the invention is intended for the refrigeration apparatus of the first aspect of the invention, in which the refrigerant circuit (200) includes the heat-source-side heat exchanger (115) switchable to a condenser or an evaporator, a first utilization-side heat exchanger (154) switchable to a condenser or an evaporator, and a second utilization-side heat exchanger (164) configured as an evaporator, and the refrigerant circuit (200) is switchable between a first operation in which the first utilization-side heat exchanger (154) serves as the evaporator and the second utilization-side heat exchanger (164) and the heat-source-side heat exchanger (115) serve as the condensers, and a second operation in which the first utilization-side heat exchanger (154) and the heat-source-side heat exchanger (115) serve as the evaporators and the second utilization-side heat exchanger (164) serves as the condenser.
In the fifth aspect of the invention, when the heat-source-side heat exchanger (115) serves as the condenser or the evaporator as in the second and third aspects of the invention, the control is performed based on the saturation pressure equivalent to the ambient temperature of the condenser or the evaporator provided in the heat-source-side unit (110).

ADVANTAGES OF THE INVENTION

According to the present invention, when the temperature of the stopped compressor itself or the ambient temperature of the stopped compressor is dropped in, e.g., a cold region during the winter, and the saturation pressure equivalent to such a temperature is lower than the low pressure (evaporation pressure) of the compressor in operation, the control is performed to decrease the low pressure (evaporation pressure) of the compressor in operation to less than the temperature-equivalent saturation pressure. In such a manner, the low pressure of the compressor in operation becomes lower than the pressure of the stopped compressor. Thus, refrigerant flows into the compressor in operation, and does not flow into the stopped compressor. Consequently, in the refrigeration apparatus including the compressors (21, 114), refrigerant liquefaction in the stopped compressor can be reduced or prevented, thereby reducing operation failure or burnout upon a restart.
According to the second aspect of the invention, when the heat-source-side heat exchanger (25, 115) serves as the condenser, the temperature inside the heat-source-side unit (2, 110) is typically higher than the external air temperature. Thus, the control is performed based on the saturation pressure equivalent to the ambient temperature of the condenser having a temperature higher than the external air temperature. In such a manner, the decrease in internal pressure of the stopped compressor to less than the low pressure (evaporation pressure) of the compressor in operation can be also reduced or prevented. Thus, failure due to the refrigerant liquefaction in the stopped compressor can be reduced or prevented. For example, the low pressure may be set at the external air temperature-equivalent saturation pressure.
According to the third aspect of the invention, when the heat-source-side heat exchanger (25, 115) serves as the evaporator, the temperature inside the heat-source-side unit (2, 110) is typically lower than the external air temperature. Thus, the control is performed based on the saturation pressure equivalent to the ambient temperature of the evaporator having a temperature lower than the external air temperature. In such a manner, the decrease in internal pressure of the stopped compressor to less than the low pressure (evaporation pressure) of the compressor in operation can be also reduced or prevented. Thus, the failure due to the refrigerant liquefaction in the stopped compressor can be reduced or prevented.
According to the fourth aspect of the invention, the control is, as in the second aspect of the invention, performed based on the saturation pressure equivalent to the ambient temperature of the condenser having a temperature higher than the external air temperature. Thus, the failure due to the refrigerant liquefaction in the stopped compressor can be reduced or prevented.
According to the fifth aspect of the invention, the control is, as in the second and third aspects of the invention, performed based on the saturation pressure equivalent to the ambient temperature of the condenser or the evaporator having a temperature different from the external air temperature. Thus, the failure due to the refrigerant liquefaction in the stopped compressor can be reduced or prevented.
In order to reduce or prevent the refrigerant liquefaction, the compressors (21, 114) are typically heated by a crank case heater, and then refrigerant dissolved in refrigerant oil is separated from the refrigerant oil by evaporation. However, according to the first to fifth aspects of the invention, the crank case heater is not necessarily used, and therefore a device configuration can be simplified.

BRIEF DESCRIPTION OF THE DRAWINGS

[FIG. 1] FIG. 1 is a refrigerant circuit diagram of a refrigeration apparatus of a first embodiment.
[FIG. 2] FIG. 2 is a cross-sectional view illustrating a main part of a compression mechanism of a compressor of the first embodiment.
[FIG. 3] FIG. 3 is a flowchart illustrating a control of the compressor of the first embodiment.
[FIG. 4] FIG. 4 is a refrigerant circuit diagram of a refrigeration apparatus of a second embodiment.
[FIG. 5] FIG. 5 is a refrigerant circuit diagram illustrating a flow of refrigerant in an air-cooling operation in the second embodiment.
[FIG. 6] FIG. 6 is a refrigerant circuit diagram illustrating a flow of refrigerant in an air-heating operation in the second embodiment.
[FIG. 7] FIG. 7 is a refrigerant circuit diagram illustrating a flow of refrigerant in a cold-storage/freezing operation in the second embodiment.
[FIG. 8] FIG. 8 is a refrigerant circuit diagram illustrating a flow of refrigerant in a cooling/air-cooling operation in the second embodiment.
[FIG. 9] FIG. 9 is a refrigerant circuit diagram illustrating another flow of refrigerant in the cooling/air-cooling operation in the second embodiment.
[FIG. 10] FIG. 10 is a refrigerant circuit diagram illustrating a flow of refrigerant in a first cooling/air-heating operation in the second embodiment.
[FIG. 11] FIG. 11 is a refrigerant circuit diagram illustrating a flow of refrigerant in a second cooling/air-heating operation in the second embodiment.
[FIG. 12] FIG. 12 is a refrigerant circuit diagram illustrating a flow of refrigerant in a third cooling/air-heating operation in the second embodiment.

DESCRIPTION OF EMBODIMENTS

Embodiments of the present invention will be described in detail below with reference to drawings.

«First Embodiment of the Invention»

A first embodiment of the present invention will be described.

A refrigeration apparatus (1) of the present embodiment is configured to cool a plurality of refrigerated storages. Referring to FIG. 1, the refrigeration apparatus (1) includes an outside-compartment unit (heat-source-side unit) (2), a plurality of in-compartment units (utilization-side units) (3), and a controller (9) which is a control section. The outside-compartment unit (2) is placed outside, and each of the in-compartment units (3) is placed in a corresponding one of the refrigerated storages. An outside-compartment circuit (20) is provided in the outside-compartment unit (2), and an in-compartment circuit (50) is provided in each of the in-compartment units (3). A refrigerant circuit (10) of the refrigeration apparatus (1) is configured such that the plurality of in-compartment circuits (50) are connected in parallel to the outside-compartment circuit (20) to perform a vapor compression refrigeration cycle.
Specifically, the outside-compartment circuit (20) and the in-compartment circuits (50) are connected together through a first communication pipe (14) and a second communication pipe (15). One end of the first communication pipe (14) is connected to a first stop valve (11) provided at one end of the outside-compartment circuit (20). The other end of the first communication pipe (14) is branched, and the first communication pipe (14) is, at the branched ends thereof, connected to one ends of the in-compartment circuits (50). One end of the second communication pipe (15) is connected to a second stop valve (12) provided at the other end of the outside-compartment circuit (20). The other end of the second communication pipe (15) is branched, and the second communication pipe (15) is, at the branched ends thereof, connected to the other ends of the in-compartment circuits (50).

<Outside-Compartment Unit>

In the outside-compartment circuit (20) of the outside-compartment unit (2), the followings are provided: first to third compressors (21a, 21b, 21c); an outside-compartment heat exchanger (heat-source-side heat exchanger) (25); a receiver (27); a supercooling heat exchanger (28); and a supercooling pressure reducing valve (pressure reducing unit) (29).
All of the compressors (21 a, 21 b, 21 c) are high-pressure dome type hermetic scroll compressors. In each of the compressors (21a, 21b, 21c), the followings are provided: a compression mechanism having a compression chamber (4a, 4b, 4c) (see FIG. 2) with an intermediate port (5, 6, 7) opening in an intermediate-pressure position; and an electric motor configured to drive the compression mechanism.
The electric motor of the first compressor (variable capacity compressor) (21a) is connected to an inverter configured to freely change the rotation speed of the electric motor in a predetermined range. The inverter can adjust the rotation speed of the electric motor to increase/decrease the operational capacity of the first compressor (21a). The inverter is not connected to the electric motors of the second and third compressors (fixed capacity compressors) (21b, 21c), and the rotation speeds of such electric motors are maintained constant. Thus, the operational capacities of the second and third compressors (21b, 21c) are maintained constant.
FIG. 2 is a cross-sectional view illustrating a main part of the compression mechanism (47) of the first compressor (21a). Since the compression mechanisms of the second and third compressors (21b, 21c) have the same configuration as that of the compression mechanism (47) of the first compressor (21 a), the description thereof will not be repeated.
Referring to FIG. 2, the compression mechanism (47) includes a fixed scroll (41) and a movable scroll (42) engaged with the fixed scroll (41). In addition, the compression mechanism (47) has first and second compression chambers (43, 44) formed and divided by engagement of a fixed wrap (41a) provided in the fixed scroll (41) and a movable wrap (42b) provided in the movable scroll (42).
A space formed between an inner peripheral surface of the fixed wrap (41a) and an outer peripheral surface of the movable wrap (42b) is the first compression chamber (43), and a space formed between an outer peripheral surface of the fixed wrap (41a) and an inner peripheral surface of the movable wrap (42b) is the second compression chamber (44). The compression chambers (43, 44) are formed such that the volume of each of the compression chambers (43, 44) is increased/decreased with orbital motion of the movable scroll (42).
An inlet port (45) is formed at the outer periphery of the fixed scroll (41). The inlet port (45) is configured so as to intermittently communicate with both of the compression chambers (43, 44) in association with the orbital motion of the movable scroll (42). In addition, an outlet port (46) is formed in a center part of the fixed scroll (41). The outlet port (46) is configured so as to intermittently communicate with both of the compression chambers (43, 44) in association with the orbital motion of the movable scroll (42).
The intermediate port (5) is formed in the fixed scroll (41). The intermediate port (5) is configured so as to intermittently communicate with the first compression chamber (43) in association with the orbital motion of the movable scroll (42).
Specifically, when the first compression chamber (43) is in the intermediate-pressure position in which the first compression chamber (43) communicates with neither the inlet port (45) nor the outlet port (46), the intermediate port (5) and the first compression chamber (43) communicate with each other. When the first compression chamber (43) is in a position other than the intermediate-pressure position, the intermediate port (5) and the first compression chamber (43) are isolated from each other.
Outlet pipes (22a, 22b, 22c) are connected respectively to outlet sides of the compressors (21a, 21b, 21c). A check valve (CV) is provided in each of the outlet pipes (22a, 22b, 22c). The outlet pipes (22a, 22b, 22c) are connected together through an outlet junction pipe (22). The check valve (CV) is provided in such a direction that only a flow of refrigerant from each of the compressors (21a, 21 b, 21 c) toward the outlet junction pipe (22) is allowed.
In each of the outlet pipes (22a, 22b, 22c), a corresponding one of oil separators (38a, 38b, 38c) is provided upstream of the check valve (CV). The oil separator (38a, 38b, 38c) is configured to separate refrigerant oil from refrigerant discharged from the compressor (21a, 21b, 21c). Oil return pipes (39a, 39b, 39c) are connected respectively to the oil separators (38a, 38b, 38c). These three oil return pipes (39a, 39b, 39c) are joined together at one end of an oil return junction pipe (39). The other end of the oil return junction pipe (39) is connected to a second injection pipe (38) which will be described later. In each of the oil return pipes (39a, 39b, 39c), a check valve (CV) and a capillary tube (CP) are provided in this order from a side closer to the oil separator (38a, 38b, 38c)
The check valve (CV) provided in the oil return pipe (39a, 39b, 39c) is provided in such a direction that only a flow of refrigerant oil toward the oil return junction pipe (39) is allowed.
Inlet pipes (23a, 23b, 23c) are connected respectively to inlet sides of the compressors (21a, 21b, 21c). The inlet pipes (23a, 23b, 23c) are connected to an inlet junction pipe (23). The inlet junction pipe (23) is connected to the second stop valve (12).
One end of the outside-compartment heat exchanger (25) is connected to a top part of the receiver (27) through a first refrigerant pipe (32). The outside-compartment heat exchanger (25) is a cross fin type fin-and-tube heat exchanger. An outside-compartment fan (26) is provided near the outside-compartment heat exchanger (25). The outside-compartment heat exchanger (25) is configured to exchange heat between outside-compartment air sent by the outside-compartment fan (26) and refrigerant flowing through the outside-compartment heat exchanger (25).
The supercooling heat exchanger (28) includes a high-pressure flow path (28a) and an intermediate-pressure flow path (28b). The supercooling heat exchanger (28) is configured to exchange heat between refrigerant flowing through the high-pressure flow path (28a) and refrigerant flowing through the intermediate-pressure flow path (28b).
An inlet end of the high-pressure flow path (28a) is connected to a bottom part of the receiver (27). An outlet end of the high-pressure flow path (28a) is connected to the first stop valve (11) through a second refrigerant pipe (33). On the other hand, inlet and outlet ends of the intermediate-pressure flow path (28b) are connected to an injection circuit (40).
The injection circuit (40) is configured to inject refrigerant to each of the compressors (21a, 21b, 21c). The injection circuit (40) includes a first injection pipe (branched pipe) (37), the second injection pipe (38), and first to third branched injection pipes (37a, 37b, 37c).
The first injection pipe (37) is branched from the second refrigerant pipe (33), and is connected to the inlet end of the intermediate-pressure flow path (28b). The supercooling pressure reducing valve (pressure reducing unit) (29) is provided in the first injection pipe (37). The supercooling pressure reducing valve (29) is an electronic expansion valve, the degree of opening of which is adjustable.
The outlet end of the intermediate-pressure flow path (28b) is connected to one end of the second injection pipe (38). The second injection pipe (38) is, at the other end thereof, branched into the first to third branched injection pipes (37a, 37b, 37c). The first to third branched injection pipes (37a, 37b, 37c) are connected respectively to the intermediate ports (5, 6, 7) of the compressors (21a, 21b, 21c).
A first flow control valve (30a) is provided in the first branched injection pipe (37a), and a second flow control valve (30b, 30c) is provided in each of the second and third branched injection pipes (37b, 37c). The first flow control valve (30a) is an electronic expansion valve, the degree of opening of which is adjustable. The second flow control valves (30b, 30c) are openable solenoid valves.
The receiver (27) is, as described above, arranged between the outside-compartment heat exchanger (25) and the supercooling heat exchanger (28), and is configured to temporarily store high-pressure refrigerant condensed in the outside-compartment heat exchanger (25).
Various sensors and pressure switches are provided in the outside-compartment circuit (20). Specifically, in each of the outlet pipes (22a, 22b, 22c), an outlet pipe temperature sensor (61) and a high-pressure switch (62) are provided. The outlet pipe temperature sensor (61) is configured to detect the temperature of the outlet pipe (22a, 22b, 22c), and the high-pressure switch (62) is configured to detect a discharge pressure and to bring the refrigeration apparatus (1) to an emergency stop under an extremely-high pressure.
At a junction of the outlet pipes (22a, 22b, 22c) (i.e., at an inlet end of the outlet junction pipe (22)), a discharge pressure sensor (64) configured to detect the discharge pressures of the compressors (21a, 21b, 21c) is provided. At a junction of the inlet pipes (23a, 23b, 23c) (or near the junction), a suction pressure sensor (65) configured to detect the suction pressures of the compressors (21a, 21b, 21c) is provided. An external air temperature sensor (67) configured to detect an external air temperature (specifically the temperature inside the outside-compartment unit (2)) is provided near the outside-compartment fan (26). A low-pressure switch (63) is provided in the inlet pipe (23b).
In addition, a first liquid temperature sensor (68) is provided in the second refrigerant pipe (33). The first liquid temperature sensor (68) is configured to detect the temperature of liquid refrigerant.

<In-Compartment Unit>

The two in-compartment units (3) have the same configuration. The in-compartment circuit (50) is provided in each of the in-compartment units (3). In the in-compartment circuit (50), a heating pipe (51), an in-compartment expansion valve (52), and an in-compartment heat exchanger (utilization-side heat exchanger) (53) are provided in this order from one end toward the other end.
The heating pipe (51) is attached to a drain pan (55) provided below the in-compartment heat exchanger (53). The drain pan (55) is configured to collect condensation water dropped from the in-compartment heat exchanger (53). The heating pipe (51) is attached to the drain pan (55) so that ice blocks formed by freezing the condensation water can be melted by using heat of high-pressure refrigerant flowing through the heating pipe (51).
The in-compartment expansion valve (52) is an electronic expansion valve, the degree of opening of which is adjustable.
The in-compartment heat exchanger (53) is a cross fin type fin-and-tube heat exchanger, and an in-compartment fan (54) is provided near the in-compartment heat exchanger (53). The in-compartment heat exchanger (53) is configured to exchange heat between in-compartment air sent by the in-compartment fan (54) and refrigerant flowing through the in-compartment heat exchanger (53).
Three temperature sensors are provided in the in-compartment circuit (50). Specifically, an evaporation temperature sensor (72) configured to detect the evaporation temperature of refrigerant is provided in a heat transfer pipe of the in-compartment heat exchanger (53). A refrigerant temperature sensor (73) configured to detect the temperature of gas refrigerant is provided near a gas inlet/outlet end of the in-compartment circuit (50). An in-compartment temperature sensor (74) configured to detect an in-compartment temperature is provided near the in-compartment fan (54).

Detection values of the foregoing sensors, the high-pressure switch (62), and the low-pressure switch (63) are input to the controller (9). Based on such detection values, the controller (9) controls an operation of the refrigeration apparatus (1) while controlling driving of the compressors (21a, 21b, 21c) and the fans (26, 54), switching the various valves (24, 29, 31, 52, SV), and adjusting the degrees of opening of the various valves (24, 29, 31, 52, SV).
In an operation state in which the outside-compartment heat exchanger (25) serves as a condenser, when the condition where the temperature-equivalent saturation pressure of an external air temperature (more specifically the temperature inside the outside-compartment unit (2), the temperature of a stopped compressor itself, or the ambient temperature of the stopped compressor) is lower than the low pressure (evaporation pressure) of a compressor in operation is satisfied, the controller (9) perform a control for decreasing the low pressure of the compressor in operation to less than the temperature-equivalent saturation pressure. That is, the controller (9) performs the control based on the saturation pressure equivalent to the temperature around the condenser having a temperature higher than the external air temperature. Note that the outlet pipe temperature of the compressor can be used as the temperature of the compressor itself, and, e.g., the temperature around the outside-compartment heat exchanger (25) or the external air temperature can be used as the ambient temperature of the compressor.

Operation

The operation of the refrigeration apparatus (1) will be described below. The refrigeration apparatus (1) is configured to perform a cooling operation for maintaining an inside of each of the refrigerated storages at a predetermined temperature (e.g., 5°C).
In the cooling operation, at least one of the three compressors (21 a, 21b, 21c) is driven, and the inside of the compartment is cooled by each of the in-compartment units (3). First, the case where all of the three compressors (21 a, 21 b, 21 c) are driven will be described. In addition, the degrees of opening of the supercooling pressure reducing valve (29) and the in-compartment expansion valve (52) are adjusted as necessary. Each of the solenoid valves (SV) is opened/closed depending on the operation state.
In the cooling operation, when the first to third compressors (21a, 21b, 21c) are driven, refrigerant flows in a direction indicated by solid arrows illustrated in FIG. 1 in the refrigerant circuit (10). In such a state, the outside-compartment heat exchanger (25) functions as a condenser, and each of the in-compartment heat exchangers (53) functions as an evaporator. In such a manner, the vapor compression refrigeration cycle is performed in the refrigerant circuit (10).
Specifically, high-pressure gas refrigerant compressed in the first to third compressors (21a, 21b, 21c) is discharged through the outlet pipes (22a, 22b, 22c). The high-pressure gas refrigerant discharged through the outlet pipes (22a, 22b, 22c) flows into the oil separators (38a, 38b, 38c). In each of the oil separators (38a, 38b, 38c), refrigerant oil is separated from the high-pressure refrigerant. After the separated refrigerant oil is temporarily stored in each of the oil separators (38a, 38b, 38c), such refrigerant oil flows into the second injection pipe (38) through the oil return pipes (39a, 39b, 39c) and the oil return junction pipe (39). Meanwhile, the high-pressure refrigerant from which the refrigerant oil is separated flows out from the oil separators (38a, 38b, 38c), and flows of such high-pressure refrigerant are joined together at the outlet junction pipe (22).
The high-pressure refrigerant joined at the outlet junction pipe (22) flows into the outside-compartment heat exchanger (25). In the outside-compartment heat exchanger (25), the high-pressure refrigerant is condensed by exchanging heat with outside-compartment air. After the condensed refrigerant passes through the first refrigerant pipe (32), the receiver (27), and the high-pressure flow path (28a) of the supercooling heat exchanger (28) in this order, such refrigerant flows into the second refrigerant pipe (33). Part of the refrigerant flowing into the second refrigerant pipe (33) flows into the first injection pipe (37), and the remaining refrigerant flows into the first communication pipe (14) through the first stop valve (11).
After the supercooling pressure reducing valve (29) reduces the pressure of the high-pressure refrigerant flowing into the first injection pipe (37) to a predetermined pressure to change such refrigerant into intermediate-pressure refrigerant, the intermediate-pressure refrigerant flows into the intermediate-pressure flow path (28b) of the supercooling heat exchanger (28). In the supercooling heat exchanger (28), heat is exchanged between the intermediate-pressure refrigerant and high-pressure refrigerant flowing through the high-pressure flow path (28a). Thus, the high-pressure refrigerant is cooled, resulting in an increase in degree of supercooling of the high-pressure refrigerant. Meanwhile, the intermediate-pressure refrigerant is heated into gas refrigerant. After the gas refrigerant flows out from the supercooling heat exchanger (28), a flow of the gas refrigerant is branched into the first to third branched injection pipes (37a, 37b, 37c) through the second injection pipe (38).
After the flow rate of the intermediate-pressure refrigerant flowing into the first branched injection pipe (37a) is adjusted by the first flow control valve (30a), such refrigerant is injected to the first compression chamber (43) of the first compressor (21a) which is in the intermediate-pressure position.
In addition, after the flow rate of the intermediate-pressure refrigerant flowing into each of the second and third branched injection pipe (37b, 37c) is adjusted by a corresponding one of the second and third flow control valves (30b, 30c), such refrigerant is injected to each of the compression chambers of the second and third compressors (21b, 21c) which are in the intermediate-pressure position.
Meanwhile, a flow of the high-pressure refrigerant flowing into the first communication pipe (14) is branched into the in-compartment circuits (50). The high-pressure refrigerant flowing into the in-compartment circuit (50) flows through the heating pipe (51). At the same time, in the drain pan (55), ice blocks formed by freezing condensation water are melted by the refrigerant flowing through the heating pipe (51). This further supercools the high-pressure refrigerant flowing through the heating pipe (51). After the in-compartment expansion valve (52) reduces the pressure of the high-pressure refrigerant flowing out from the heating pipe (51) to change such refrigerant into low-pressure refrigerant, the low-pressure refrigerant flows into the in-compartment heat exchanger (53).
In the in-compartment heat exchanger (53), the low-pressure refrigerant is evaporated by exchanging heat with in-compartment air. This cools the in-compartment air. The refrigerant evaporated in the in-compartment heat exchanger (53) re-flows into the outside-compartment circuit (20) through the second communication pipe (15). The low-pressure refrigerant flowing into the outside-compartment circuit (20) flows into the inlet junction pipe (23), and then flows into each of the compressors (21 a, 21b, 21c) through a corresponding one of the inlet pipes (23a, 23b, 23c). The low-pressure refrigerant flowing into each of the compressors (21a, 21b, 21c) is changed into high-pressure refrigerant by being compressed to a predetermined pressure together with intermediate-pressure refrigerant flowing into each of the compressors (21 a, 21b, 21c) through a corresponding one of the intermediate ports (5, 6, 7). Then, the high-pressure refrigerant is re-discharged from the compressors (21a, 21b, 21c). Refrigerant circulates as described above, thereby performing the cooling operation for maintaining the inside of each of the refrigerated storages at the predetermined temperature.

Suppose that one or two of the three compressors (21a, 21 b, 21 c) are in operation, and the other compressor(s) (21 a, 21b, 21 c) is stopped. If an external air temperature (more specifically the temperature inside the outside-compartment unit (2)) is dropped to a low temperature of about -10°C in a cold region during the winter, the temperature of the stopped compressor is also dropped to about -10°C. If the evaporation temperature of an evaporator connected to the compressor in operation is about 0-5°C, the stopped compressor has a temperature lower than that of the compressor in operation. Thus, since the saturation pressure equivalent to the temperature of the stopped compressor is lower than the low pressure (evaporation pressure) of the compressor in operation, refrigerant may flow into the stopped compressor. In such a case, refrigerant is melted in refrigerant oil accumulated in the compressor, and the refrigerant oil is diluted. Thus, there is a possibility that insufficient lubrication occurs upon a restart.
In the present embodiment, under the condition where the saturation pressure equivalent to the temperature of the stopped compressor itself or the ambient temperature of the stopped compressor is lower than the low pressure of the compressor in operation, the controller (9) performs the control for decreasing the low pressure of the compressor in operation to less than the temperature-equivalent saturation pressure.
First, a control in a normal operation will be briefly described.
(1) When the compressors (21a, 21b, 21c) are controlled based on a difference between an in-compartment temperature or a room temperature and a set temperature, a PID control is performed based on a value represented by the following equation: $Hz = f (Tset - Th 1)$

where "Tset" represents the set temperature, "Th1" represents a suction temperature, and "Hz" represents the frequency of the compressor.
(2) When loads of the compressors (21 a, 21b, 21 c) are controlled based only on the set temperature, the PID control is performed based on a value represented by the following equation: $Hz = f (LP - Target LP)$

where the target LP is set at f(Set Temperature - 10) and is regarded as a saturation pressure equivalent to a value lower than the set temperature by 10K. Note that the "LP (low pressure)" does not mean the suction pressure of the compressor, but means the evaporation pressure of the evaporator.
Next, a control for reducing or preventing the refrigerant liquefaction in the stopped compressor(s) will be described with reference to a flowchart illustrated in FIG. 3. First, it is, at step ST1, determined whether or not the low pressure LP of the compressor in operation is smaller than a value obtained according to a value f(Ta). The value f(Ta) is a function of an external air temperature, and may relate to an external air temperature-equivalent saturation pressure. Alternatively, in the configuration in which a compressor and an outdoor heat exchanger is accommodated in an outdoor unit, the value f(Ta) may relate to the saturation pressure equivalent to the temperature of the compressor itself or the saturation pressure equivalent to the ambient temperature of the compressor.
If the determination result at step ST1 is "YES," the process proceeds to step ST2. When the process proceeds to step ST2, the external air temperature-equivalent saturation pressure is higher than the low pressure (evaporation pressure) of the compressor in operation, and therefore refrigerant does not flow into the stopped compressor. Thus, in any of the cases (1) and (2), the control described above is performed.
If the determination result at step ST1 is "NO," the process proceeds to step ST3 to correct the temperature represented by "(Ta)." In the present embodiment, an outdoor heat exchanger serves as a condenser. It is assumed that the temperature inside the outdoor unit is higher than an external air temperature. Thus, in the case (1), the PID control is performed based on the value represented by the following equation: $Hz = f (LP - Target LP)$
where Target LP = f(Ta). A control similar to the foregoing is performed in the case (2).
In the foregoing manner, refrigerant does not flow into the stopped compressor. Thus, the refrigerant liquefaction does not occur, and refrigerant oil is not diluted.

Advantages of the Embodiment

According to the present embodiment described above, refrigerant does not flow into the stopped compressor. Thus, the refrigerant liquefaction does not occur, and refrigerant oil is not diluted. As a result, insufficient lubrication or burnout upon a restart of the compressor does not occur, thereby increasing device stability.
When an in-compartment temperature is dropped by decreasing the low pressure (evaporation pressure) of the compressor in operation, the refrigeration apparatus enters a "thermo-off state" (i.e., a resting state in which the compressors are stopped and only air blowing is performed), and the in-compartment temperature is not further dropped. In such a state, since all of the compressors are stopped, refrigerant does not circulate in the refrigerant circuit. Thus, even if the temperature of the stopped compressor itself or the ambient temperature of the stopped compressor is low, the refrigerant liquefaction due to refrigerant flowing into the compressor(s) can be reduced or prevented.
As described above, in the refrigeration apparatus of the present embodiment configured such that the in-compartment heat exchanger (53) only performs cooling in the refrigerant circuit in which the outside-compartment heat exchanger (25) serves as a condenser and the in-compartment heat exchanger (53) serves as an evaporator, the refrigerant liquefaction in the stopped compressor(s) can be reduced or prevented, thereby increasing the device stability.
In order to reduce or prevent the refrigerant liquefaction, a compressor (21) is typically heated by a crank case heater, and then refrigerant dissolved in refrigerant oil is separated from the refrigerant oil by evaporation. However, according to the present embodiment, the crank case heater is not necessarily used, and therefore a device configuration can be simplified. Note that it is not a requirement in the present embodiment that the crank case heater is not used, and the crank case heater may be used in combination with the control described in the present embodiment depending on the situation.

«Second Embodiment of the Invention»

A second embodiment of the present invention will be described.
A refrigeration apparatus (100) of the second embodiment is installed in, e.g., a convenience store. Referring FIG. 4, the refrigeration apparatus (100) includes an outdoor unit (110) installed outside, an indoor unit (150) configured to air-condition an in-store space, two in-compartment units (160a, 160b) each configured to cool an inside of a compartment, and a booster unit (180). The two in-compartment units (160a, 160b) are a first in-compartment unit (160a) for cold storage, and a second in-compartment unit (160b) for freezing.
An outdoor circuit (111), an indoor circuit (152), a first in-compartment circuit (161a), a second in-compartment circuit (161b), and a booster circuit (181) are provided in the outdoor unit (110), the indoor unit (150), the first in-compartment unit (160a), the second in-compartment unit (160b), and the booster unit (180), respectively. In the refrigeration apparatus (100), the outdoor circuit (111), the indoor circuit (152), the first in-compartment circuit (161a), the second in-compartment circuit (161b), and the booster circuit (181) are connected together through four communication pipes (201, 202, 203, 204) to form a refrigerant circuit (200) configured to perform a vapor compression refrigeration cycle. The first in-compartment circuit (161a) and the second in-compartment circuit (161b) are connected together in parallel. In addition, the second in-compartment circuit (161b) and the booster circuit (181) are connected together in series.
In the refrigerant circuit (200), a utilization-side heat exchanger for an air conditioning system and a utilization-side heat exchanger for a cold-storage/freezing system are provided. As later-described compressors (114a, 114b, 114c), a compressor connected to the utilization-side heat exchanger for the air conditioning system and a compressor connected to the utilization-side heat exchanger for the cold-storage/freezing system are provided.
The four communication pipes (201, 202, 203, 204) are a first liquid communication pipe (201), a second liquid communication pipe (202), a first gas communication pipe (203), and a second gas communication pipe (204). One end of the first liquid communication pipe (201) is connected to a first liquid stop valve (205) of the outdoor circuit (111), and the other end of the first liquid communication pipe (201) is connected to the indoor circuit (152). One end of the second liquid communication pipe (202) is connected to a second liquid stop valve (206) of the outdoor circuit (111). The other end of the second liquid communication pipe (202) is, at two branched parts thereof, connected to the first in-compartment circuit (161a) and the second in-compartment circuit (161b). One end of the first gas communication pipe (203) is connected to a first gas stop valve (207) of the outdoor circuit (111), and the other end of the first gas communication pipe (203) is connected to the indoor circuit (152). One end of the second gas communication pipe (204) is connected to a second gas stop valve (208) of the outdoor circuit (111). The other end of the second gas communication pipe (204) is, at two branched parts thereof, connected to the first in-compartment circuit (161a) and the second in-compartment circuit (161b). The second in-compartment circuit (161b) and the booster circuit (181) are connected together through a gas connection pipe (194).

In the outdoor circuit (111), a compression mechanism (140), an outdoor heat exchanger (115), and a receiver (112) are provided. The compression mechanism (140) includes the variable capacity compressor (114a), the first fixed capacity compressor (114b), and the second fixed capacity compressor (114c). In the compression mechanism (140), outlet sides of the compressors (114a, 114b, 114c) are connected together. In addition, inlet sides of the compressors (114a, 114b, 114c) are connected to a third four-way valve (133) which will be described later. In the second embodiment, the variable capacity compressor (114a) serves as a first compressor (114a). In addition, the first fixed capacity compressor (114b) and the second fixed capacity compressor (114c) serve as second and third compressors (114b, 114c), respectively.
Power is supplied to the variable capacity compressor (114a) through an inverter. The variable capacity compressor (114a) is configured to adjust the operational capacity thereof in a stepwise manner by changing the output frequency of the inverter. On the other hand, each of the first and second fixed capacity compressors (114b, 114c) is configured such that an electric motor is operated at a constant rotation speed, and the operational capacity thereof is unchangeable.
The variable capacity compressor (114a) serves as an in-compartment compressor configured to suck refrigerant evaporated in the in-compartment units (160a, 160b). The variable capacity compressor (114a) is a compressor exclusively for the inside of the compartment. The second fixed capacity compressor (114c) serves as an indoor compressor configured to suck refrigerant evaporated in the indoor unit (150) in an air-cooling operation. The second fixed capacity compressor (114c) is a compressor exclusively for an inside of a room. In addition, the first fixed capacity compressor (114b) serves as an in-compartment compressor when the third four-way valve (133) which will be described later is in a first state, and serves as an indoor compressor when the third four-way valve (133) is in a second state. That is, the first fixed capacity compressor (114b) is used as both of an in-compartment compressor and an indoor compressor.
In the compression mechanism (140), if an in-compartment load which is a total cooling load in in-compartment heat exchangers (164a, 164b) for cold-storage/freezing is relatively small, only the variable capacity compressor (114a) is set as the in-compartment compressor, and the operational capacity of the variable capacity compressor (114a) is adjusted such that, e.g., the pressure of an inlet pipe (157a) of the variable capacity compressor (114a) is maintained at a constant value. As a result, the operational capacity of the variable capacity compressor (114a) is adjusted depending on the in-compartment load. When the in-compartment load exceeds the maximum value of the operational capacity of the variable capacity compressor (114a), the first fixed capacity compressor (114b) is also set as the in-compartment compressor. In such a state, the total operational capacity of the in-compartment compressors is adjusted by the variable capacity compressor (114a).
When an air-cooling load in an indoor heat exchanger (154) is relatively small, only the second fixed capacity compressor (114c) is set as the indoor compressor. When the cooling load is increased, the first fixed capacity compressor (114b) is also set as the indoor compressor. Note that the first fixed capacity compressor (114b) is preferentially used as the in-compartment compressor when both of the in-compartment load and the air-cooling load are large.
The variable capacity compressor (114a), the first fixed capacity compressor (114b), and the second fixed capacity compressor (114c) are, e.g., high-pressure dome type hermetic scroll compressors. Each compressor (114) includes a scroll compression mechanism (47) similar to that described with reference to FIG. 2. The detailed description of the compression mechanism (47) is not repeated.
A first outlet pipe (156a) of the variable capacity compressor (114a), a second outlet pipe (156b) of the first fixed capacity compressor (114b), and a third outlet pipe (156c) of the second fixed capacity compressor (114c) are connected to an outlet junction pipe (121). The outlet junction pipe (121) is connected to a first four-way valve (131). A branched outlet pipe (122) is branched from the outlet junction pipe (121). The branched outlet pipe (122) is connected to a second four-way valve (132).
In each outlet pipe (156), an oil separator (137a, 137b, 137c), a high-pressure switch (139a, 139b, 139c), and a check valve (CV1, CV2, CV3) are arranged in this order from a side closer to the compressor (114). Each high-pressure switch (139) is configured so as to bring the compressor (114) to an emergency stop under an extremely-high pressure. Each check valve (CV1, CV2, CV3) is configured to prevent a flow of refrigerant toward the compressor (114).
The first inlet pipe (157a) of the variable capacity compressor (114a) is connected to the second gas stop valve (208). A third inlet pipe (157c) of the second fixed capacity compressor (114c) is connected to the second four-way valve (132). A second inlet pipe (157b) of the first fixed capacity compressor (114b) is connected to the third four-way valve (133). A low-pressure switch (139d) is provided in the second inlet pipe (157b). A first branched inlet pipe (158a) is branched from the first inlet pipe (157a). A second branched inlet pipe (158b) is branched from the third inlet pipe (157c). Both of the first branched inlet pipe (158a) and the second branched inlet pipe (158b) are connected to the third four-way valve (133). Check valves (CV7, CV8) each configured to prevent a flow of refrigerant from a side closer to the third four-way valve (133) is provided respectively in the first branched inlet pipe (158a) and the second branched inlet pipe (158b).
The outdoor heat exchanger (115) is a cross fin type fin-and-tube heat exchanger. The outdoor heat exchanger (115) serves as a heat-source-side heat exchanger. An outdoor fan (123) configured to send outdoor air to the outdoor heat exchanger (115) is provided near the outdoor heat exchanger (115). In the outdoor heat exchanger (115), heat is exchanged between refrigerant and outdoor air.
A gas inlet/outlet side of the outdoor heat exchanger (115) is connected to the first four-way valve (131). A liquid inlet/outlet side of the outdoor heat exchanger (115) is connected to a top part of the receiver (112) through a first liquid pipe (124). In the first liquid pipe (124), a solenoid valve (228) configured to prevent a flow of refrigerant toward the outdoor heat exchanger (115) is provided.
The receiver (112) is an elongated hermetic container. In the receiver (112), high-pressure refrigerant condensed in, e.g., the outdoor heat exchanger (115) is temporarily stored. One end of a second liquid pipe (125) is connected to a bottom part of the receiver (112). The second liquid pipe (125) is, at the other end thereof, branched into a first branched pipe (126) and a second branched pipe (127).
The first branched pipe (126) is connected to the first liquid stop valve (205). The first branched pipe (126) communicates with the indoor circuit (152) through the first liquid communication pipe (201). In the first branched pipe (126), a check valve (CV10) configured to prevent a flow of refrigerant toward the second liquid pipe (125) is provided. A third branched pipe (128) connected to part of the first liquid pipe (124) between the solenoid valve (228) and the receiver (112) is branched from the first branched pipe (126). In the third branched pipe (128), a check valve (CV11) configured to prevent a flow of refrigerant toward the first branched pipe (126) is provided.
The second branched pipe (127) is connected to the second liquid stop valve (206). The second branched pipe (127) communicates with each of the in-compartment circuits (161a, 161b) through the second liquid communication pipe (202). A second intermediate heat exchanger (117) which will be described later is connected to the second branched pipe (127). A fourth branched pipe (129) and an injection pipe (branched pipe forming an injection circuit) (130) are branched from the second branched pipe (127).
The fourth branched pipe (129) is branched from part of the second branched pipe (127) between the second intermediate heat exchanger (117) and the second liquid stop valve (206). The fourth branched pipe (129) is, at an end opposite to the end connected to the second branched pipe (127), connected to part of the first liquid pipe (124) between the outdoor heat exchanger (115) and the solenoid valve (228). In the fourth branched pipe (129), a check valve (CV9) configured to prevent a flow of refrigerant toward the second intermediate heat exchanger (117), and a first outdoor expansion valve (166) which is an electronic expansion valve, the degree of opening of which is adjustable, are provided in this order from a side closer to the second intermediate heat exchanger (117). A communication pipe (129a) is connected to part of the fourth branched pipe (129) between the check valve (CV9) and the first outdoor expansion valve (166) and to part of the first liquid pipe (124) between the solenoid valve (228) and the receiver (112). In the communication pipe (129a), a check valve (CV17) configured to prevent a flow of refrigerant from the first liquid pipe (124) toward the fourth branched pipe (129) is provided.
The injection pipe (130) is branched from part of the second branched pipe (127) between a branched part of the fourth branched pipe (129) and the second liquid stop valve (206). The injection pipe (130) forms an injection path. The injection pipe (130) includes a main injection pipe (130d) extending from the second branched pipe (127), a left branched injection pipe (130a) branched from the main injection pipe (130d) and connected to an intermediate port (5) of the variable capacity compressor (114a), a right branched injection pipe (130c) branched from the main injection pipe (130d) and connected to an intermediate port (6) of the second fixed capacity compressor (114c), and a middle branched injection pipe (130b) branched from the main injection pipe (130d) and connected to an intermediate port (7) of the first fixed capacity compressor (114b).
In the main injection pipe (130d), a second outdoor expansion valve (pressure reducing unit) (167) is provided. The second outdoor expansion valve (167) is an electronic expansion valve, the degree of opening of which is adjustable. In the second outdoor expansion valve (167), the pressure of refrigerant flowing from the second branched pipe (127) to the main injection pipe (130d) is reduced to an intermediate pressure in the refrigeration cycle.
In each of the branched injection pipes (130a, 130b, 130c), an electronic expansion valve (211, 212, 213) is provided as a flow control valve.
In the second embodiment, a first intermediate heat exchanger (116) configured to cool refrigerant supplied to all of the indoor heat exchanger (154) and the in-compartment heat exchangers (164), and the second intermediate heat exchanger (117) configured to cool refrigerant supplied only to the in-compartment heat exchangers (164) are provided.
The first intermediate heat exchanger (116) is configured to exchange heat between refrigerant flowing through a first flow path (116a) and refrigerant flowing through a second flow path (116b). The first intermediate heat exchanger (116) is, e.g., a double-pipe heat exchanger. In the first intermediate heat exchanger (116), the first flow path (116a) is connected to the second liquid pipe (125), and the second flow path (116b) formed on an inner side relative to the first flow path (116a) is connected to part of the main injection pipe (130d) downstream of the second outdoor expansion valve (167). In the heat exchange in the first intermediate heat exchanger (116), high-pressure refrigerant of the second liquid pipe (125) is cooled by intermediate-pressure refrigerant of the main injection pipe (130d).
The second intermediate heat exchanger (117) is configured to exchange heat between refrigerant flowing through a first flow path (117a) and refrigerant flowing through a second flow path (117b). The second intermediate heat exchanger (117) is, e.g., a plate heat exchanger. In the second intermediate heat exchanger (117), the first flow path (117a) is connected to the second branched pipe (127), and the second flow path (117b) is connected to part of the main injection pipe (130d) downstream of the first intermediate heat exchanger (116). In the heat exchange in the second intermediate heat exchanger (117), high-pressure refrigerant of the second branched pipe (127) is cooled by intermediate-pressure refrigerant of the main injection pipe (130d).
A first port (P1) of the first four-way valve (131) is connected to the outlet junction pipe (121), a second port (P2) of the first four-way valve (131) is connected to a fourth port (P4) of the second four-way valve (132), a third port (P3) of the first four-way valve (131) is connected to the outdoor heat exchanger (115), and a fourth port (P4) of the first four-way valve (131) is connected to the first gas stop valve (207). A first port (P1) of the second four-way valve (132) is connected to the branched outlet pipe (122), a second port (P2) of the second four-way valve (132) is connected to the third inlet pipe (157c), and the fourth port (P4) of the second four-way valve (132) is connected to the second port (P2) of the first four-way valve (131). A third port (P3) of the second four-way valve (132) is a closed port. A first port (P1) of the third four-way valve (133) is connected to a high-pressure pipe (136) connected to the outlet junction pipe (121), a second port (P2) of the third four-way valve (133) is connected to the second inlet pipe (157b), a third port (P3) of the third four-way valve (133) is connected to the second branched inlet pipe (158b), and a fourth port (P4) of the third four-way valve (133) is connected to the first branched inlet pipe (158a).
Each of the first to third four-way valves (131, 132, 133) is switchable between the first state (see a state indicated by a solid line in FIG. 4) in which the first port (P1) and the third port (P3) communicate with each other and the second port (P2) and the fourth port (P4) communicate with each other, and the second state (see a state indicated by a dashed line in FIG. 4) in which the first port (P1) and the fourth port (P4) communicate with each other and the second port (P2) and the third port (P3) communicate with each other.
In the second embodiment, the first oil separator (137a) is provided in the first outlet pipe (156a), the second oil separator (137b) is provided in the second outlet pipe (156b), and the third oil separator (137c) is provided in the third outlet pipe (156c). Each oil separator (137) is a hermetic container, and is configured to separate refrigerant oil from refrigerant discharged from a corresponding one of the compressors (114).
A first oil return pipe (142) is connected to the first oil separator (137a), a second oil return pipe (143) is connected to the second oil separator (137b), and a third oil return pipe (144) is connected to the third oil separator (137c). Each of the oil return pipes (142, 143, 144) is configured to send refrigerant oil separated in the oil separator (137) to an intermediate-pressure compression chamber of the compressor (114) through the injection pipe (130). The oil return pipes (142, 143, 144) are joined together, and the joined oil return pipes (142, 143, 144) are connected to the injection pipe (130). Refrigerant oil is injected to each compressor (114) through a corresponding one of the intermediate ports (5, 6, 7).
In the first oil return pipe (142), a check valve (CV12) configured to prevent a flow of refrigerant oil returning back to the first oil separator (137a), and a capillary tube (141a) configured to reduce the pressure of high-pressure refrigerant oil to an intermediate pressure are provided in this order from a side closer to the first oil separator (137a). In the second oil return pipe (143), a check valve (CV13) configured to prevent a flow of refrigerant oil returning back to the second oil separator (137b), and a capillary tube (141b) configured to reduce the pressure of high-pressure refrigerant oil to an intermediate pressure are provided in this order from a side closer to the second oil separator (137b). In the third oil return pipe (144), a check valve (CV 14) configured to prevent a flow of refrigerant oil returning back to the third oil separator (137c), and a capillary tube (141c) configured to reduce the pressure of high-pressure refrigerant oil to an intermediate pressure are provided in this order from a side closer to the third oil separator (137c).
Various sensors are provided in the outdoor unit (110). Specifically, a discharge pressure sensor (118) is provided in the outlet junction pipe (121). A discharge temperature sensor (not shown in the figure) is provided in each outlet pipe (156). A first suction pressure sensor (119a) and a first suction temperature sensor (120a) are provided in the first inlet pipe (157a). A second suction pressure sensor (119b) and a second suction temperature sensor (120b) are provided in the third inlet pipe (157c). A liquid temperature sensor (172) and an intermediate-pressure sensor (173) are provided in the injection pipe (130). Detection values of the foregoing sensors are input to a controller (210) which will be described later.

In the indoor circuit (152), an indoor expansion valve (153) and the indoor heat exchanger (154) are provided in this order from a liquid inlet/outlet end to a gas inlet/outlet end of the indoor circuit (152). The indoor expansion valve (153) is an electronic expansion valve, the degree of opening of which is adjustable. In addition, the indoor heat exchanger (154) is a cross fin type fin-and-tube heat exchanger. The indoor heat exchanger (154) serves as a second utilization-side heat exchanger (154). An indoor fan (155) configured to send indoor air to the indoor heat exchanger (154) is provided near the indoor heat exchanger (154). In the indoor heat exchanger (154), heat is exchanged between refrigerant and indoor air.
In the indoor circuit (152), an evaporation temperature sensor (221) is provided in a heat transfer pipe of the indoor heat exchanger (154). In addition, a gas temperature sensor (222) is provided near the gas inlet/outlet end of the indoor circuit (152). An room temperature sensor (223) is provided in the indoor unit.

<In-Compartment Unit>

In each of the first in-compartment circuit (161a) and the second in-compartment circuit (161b), an in-compartment expansion valve (163a, 163b) and the in-compartment heat exchanger (164a, 164b) are provided in this order from a liquid inlet/outlet end to a gas inlet/outlet end of the in-compartment circuit (161a, 161b). Each of the in-compartment expansion valves (163a, 163b) is an electronic expansion valve, the degree of opening of which is adjustable. Each of the in-compartment heat exchangers (164a, 164b) is a cross fin type fin-and-tube heat exchanger. The in-compartment heat exchanger (164a) of the first in-compartment circuit (161a) serves as a first utilization-side heat exchanger (164a). An in-compartment fan (165a, 165b) configured to send in-compartment air to the in-compartment heat exchanger (164a, 164b) is provided near the in-compartment heat exchanger (164a, 164b). In each of the in-compartment heat exchangers (164a, 164b), heat is exchanged between refrigerant and in-compartment air.
In each of the in-compartment circuits (161a, 161b), an evaporation temperature sensor (224a, 224b) is provided in a heat transfer pipe of the in-compartment heat exchanger (164a, 164b). In addition, a gas temperature sensor (225a, 225b) is provided near the gas inlet/outlet end of the in-compartment circuit (161a, 161b). An in-compartment temperature sensor (226a, 226b) is provided in the in-compartment unit.

In the booster circuit (181), a booster compressor (186) is provided, the operational capacity of which is variable. In an outlet pipe (178) of the booster compressor (186), an oil separator (187), a high-pressure switch (188), and a check valve (CV 15) are provided in this order from a side closer to the booster compressor (186). An oil return pipe (192) provided with a capillary tube (191) is connected to the oil separator (187). In addition, in the booster circuit (181), a bypass pipe (195) bypassing the booster compressor (186) is provided. In the bypass pipe (195), a check valve (CV16) is provided.

In the operation state in which the outdoor heat exchanger (115) serves as a condenser or an evaporator under the condition where the temperature-equivalent saturation pressure of an external air temperature (more specifically the temperature inside the outdoor unit (110), the temperature of a stopped compressor itself, or the ambient temperature of the stopped compressor) is lower than the low pressure of a compressor in operation, the controller performs a control for decreasing the low pressure of the compressor in operation to less than the temperature-equivalent saturation pressure. That is, the controller (210) performs the control based on the saturation pressure equivalent to the temperature around the condenser having a temperature higher than the external air temperature or the saturation pressure equivalent to the temperature around the evaporator having a temperature lower than the external air temperature. Note that the outlet pipe temperature of the compressor can be used as the temperature of the compressor itself, and, e.g., the temperature around the outside-compartment heat exchanger (25) or the external air temperature can be used as the ambient temperature of the compressor.
The other details of the control are basically the same as those of the first embodiment.

Operation

Next, an operation of the refrigeration apparatus (100) will be described according to operation type. The refrigeration apparatus (100) is configured such that seven types of operation mode can be set. Specifically, the following operations can be selected: <i> an air-cooling operation only for cooling air by the indoor unit (150); <ii> an air-heating operation only for heating air by the indoor unit (150); <iii> a cold-storage/freezing operation only for cooling an inside of each of compartments by the first in-compartment unit (160a) and the second in-compartment unit (160b); <iv> a cooling/air-cooling operation for cooling the inside of each of the compartments by the first in-compartment unit (160a) and the second in-compartment unit (160b) and cooling air by the indoor unit (150); <v> a first cooling/air-heating operation for cooling, without using the outdoor heat exchanger (115), the inside of each of the compartments by the first in-compartment unit (160a) and the second in-compartment unit (160b) and heating air by the indoor unit (150); <vi> a second cooling/air-heating operation performed when there is an extra air-heating capacity of the indoor unit (150) in the first cooling/air-heating operation; and <vii> a third cooling/air-heating operation performed when the air-heating capacity of the indoor unit (150) lacks in the first cooling/air-heating operation.

<Air-Cooling Operation>

In the air-cooling operation, the second fixed capacity compressor (114c) is, referring to FIG. 5, operated with the first four-way valve (131) and the second four-way valve (132) being set to the first state. The in-compartment expansion valves (163) are set to a closed state. During the air-cooling operation, the degree of opening of the indoor expansion valve (153) is controlled such that the degree of superheating of refrigerant which passed through the indoor heat exchanger (154) reaches the target degree of superheating (e.g., 5°C). The same applies to the cooling/air-cooling operation which will be described later.
In the air-cooling operation, the vapor compression refrigeration cycle is performed, in which the outdoor heat exchanger (115) serves as a condenser and the indoor heat exchanger (154) serves as an evaporator. Note that, if a cooling capacity lacks in the air-cooling operation, the first fixed capacity compressor (114b) is also operated. In such a case, the third four-way valve (133) is set to the second state, and the first fixed capacity compressor (114b) serves as an indoor compressor. The variable capacity compressor (114a) is stopped at all times.
Specifically, in the air-cooling operation, refrigerant discharged from the second fixed capacity compressor (114c) is condensed in the outdoor heat exchanger (115), and then flows into the indoor circuit (152) through the receiver (112). After the pressure of the refrigerant flowing into the indoor circuit (152) is reduced by the indoor expansion valve (153), such refrigerant is evaporated by absorbing heat from indoor air in the indoor heat exchanger (154). The indoor air cooled by the refrigerant is supplied to the in-store space. The refrigerant evaporated in the indoor heat exchanger (154) is sucked into the second fixed capacity compressor (114c), and then is re-discharged. Note that the evaporation temperature of refrigerant in the indoor heat exchanger (154) is, e.g., about 10°C.

<Air-Heating Operation>

In the air-heating operation, the second fixed capacity compressor (114c) is, referring to FIG. 6, operated with the first four-way valve (131) being set to the second state and the second four-way valve (132) being set to the first state. The in-compartment expansion valves (163) are set to the closed state.
In the air-heating operation, the vapor compression refrigeration cycle is performed, in which the indoor heat exchanger (154) serves as a condenser and the outdoor heat exchanger (115) serves as an evaporator. Note that, if an air-heating capacity lacks in the air-heating operation, the first fixed capacity compressor (114b) is also operated. In such a case, the third four-way valve (133) is set to the second state. The variable capacity compressor (114a) is stopped at all times.
Specifically, refrigerant discharged from the second fixed capacity compressor (114c) flows into the indoor circuit (152), and then is condensed by dissipating heat to indoor air in the indoor heat exchanger (154). The indoor air heated by the refrigerant is supplied to the in-store space. After the pressure of the refrigerant condensed in the indoor heat exchanger (154) is reduced by the first outdoor expansion valve (166), such refrigerant is evaporated in the outdoor heat exchanger (115). Then, the refrigerant is sucked into the second fixed capacity compressor (114c), and then is re-discharged.

<Cold-Storage/Freezing Operation>

In the cold-storage/freezing operation, the variable capacity compressor (114a) is, referring to FIG. 7, operated with the first four-way valve (131) being set to the first state. The indoor expansion valve (153) is set to the closed state. During the cold-storage/freezing operation, the degree of opening of the in-compartment expansion valve (163a, 163b) is controlled such that the degree of superheating of refrigerant which passed through the in-compartment heat exchanger (164a, 164b) reaches the target degree of superheating (e.g., 5°C). The same applies to the cooling/air-cooling operation and the cooling/air-heating operation which will be described later.
In the cold-storage/freezing operation, the vapor compression refrigeration cycle is performed, in which the outdoor heat exchanger (115) serves as a condenser and the in-compartment heat exchanger (164) serves as an evaporator. Note that, if an in-compartment cooling capacity lacks in the cold-storage/freezing operation, the first fixed capacity compressor (114b) is also operated. In such a case, the third four-way valve (133) is set to the first state, and the first fixed capacity compressor (114b) serves as an in-compartment compressor. The second fixed capacity compressor (114c) is stopped at all times.
Specifically, in the cold-storage/freezing operation, refrigerant discharged from the variable capacity compressor (114a) is condensed in the outdoor heat exchanger (115). Then, the refrigerant condensed in the outdoor heat exchanger (115) is distributed to the first in-compartment circuit (161a) and the second in-compartment circuit (161b) after passing through the receiver (112).
After the pressure of the refrigerant flowing into the first in-compartment circuit (161a) is reduced by the in-compartment expansion valve (163a), such refrigerant is evaporated by absorbing heat from in-compartment air in the in-compartment heat exchanger (164a). The in-compartment air cooled by the refrigerant is supplied to a compartment of a cold-storage showcase. Meanwhile, after the pressure of the refrigerant flowing into the second in-compartment circuit (161b) is reduced by the in-compartment expansion valve (163b), such refrigerant is evaporated by absorbing heat from in-compartment air in the in-compartment heat exchanger (164b). The in-compartment air cooled by the refrigerant is supplied to a compartment of a freezer showcase. The refrigerant evaporated in the in-compartment heat exchanger (164b) is compressed by the booster compressor (186). The refrigerant evaporated in the in-compartment heat exchanger (164a) and the refrigerant compressed by the booster compressor (186) are joined together. Subsequently, such refrigerant is sucked into the variable capacity compressor (114a), and then is re-discharged.
In the cold-storage/freezing operation, the evaporation temperature of refrigerant in the in-compartment heat exchanger (164a) is set at, e.g., 5°C, and the evaporation temperature of refrigerant in the in-compartment heat exchanger (164b) is set at, e.g., -30°C. Since the refrigerant flowing out from the in-compartment heat exchanger (164b) is compressed by the booster compressor (186), the temperature of the refrigerant is about 5°C when joining other refrigerant at the second gas communication pipe (204).
In the cold-storage/freezing operation, if the first fixed capacity compressor (114b) serves as an in-compartment compressor, a refrigeration cycle using a single refrigerant supply source is performed. In such a refrigeration cycle, refrigerant evaporated in the in-compartment heat exchanger (164a) is sucked into the variable capacity compressor (114a) and the first fixed capacity compressor (114b).

In the cooling/air-cooling operation, the variable capacity compressor (114a) and the second fixed capacity compressor (114c) are operated with the first four-way valve (131) and the second four-way valve (132) being set to the first state. In the cooling/air-cooling operation, the vapor compression refrigeration cycle is performed, in which the outdoor heat exchanger (115) serves as a condenser and the indoor heat exchanger (154) and the in-compartment heat exchangers (164) serve as evaporators.
Note that, if there are an extra air-cooling capacity of the indoor unit (150) and an extra cooling capacity of the in-compartment unit (160) in the cooling/air-cooling operation, the first fixed capacity compressor (114b) is stopped. If the cooling capacity of the in-compartment unit (160) lacks, the first fixed capacity compressor (114b) is, referring to FIG. 8, operated with the third four-way valve (133) being set to the first state. In such a case, the first fixed capacity compressor (114b) serves as an in-compartment compressor. If the air-cooling capacity of the indoor unit (150) lacks, the first fixed capacity compressor (114b) is, referring to FIG. 9, operated with the third four-way valve (133) being set to the second state. In such a case, the first fixed capacity compressor (114b) serves as an indoor compressor.
Specifically, in the cooling/air-cooling operation, refrigerant discharged from the variable capacity compressor (114a) and the second fixed capacity compressor (114c) is condensed in the outdoor heat exchanger (115). Then, the refrigerant condensed in the outdoor heat exchanger (115) is distributed to the first in-compartment circuit (161a), the second in-compartment circuit (161b), and the indoor circuit (152) after passing through the receiver (112).
The refrigerant distributed to the first in-compartment circuit (161a) and the second in-compartment circuit (161b) circulates in the similar manner to that of the cold-storage/freezing operation. Subsequently, the refrigerant is sucked into the variable capacity compressor (114a), and then is re-discharged. The refrigerant distributed to the indoor circuit (152) circulates in the similar manner to that of the air-cooling operation. Subsequently, the refrigerant is sucked into the second fixed capacity compressor (114c), and then is re-discharged.
In the cooling/air-cooling operation, the evaporation temperature of refrigerant in the indoor heat exchanger (154) is, e.g., about 10°C. The evaporation temperature of refrigerant in the in-compartment heat exchanger (164a) of the first in-compartment circuit (161a) is set at, e.g., 5°C, and the evaporation temperature of refrigerant in the in-compartment heat exchanger (164b) of the second in-compartment circuit (161b) is set at, e.g., -30°C. The evaporation temperature of refrigerant in the indoor heat exchanger (154) is higher than that in the in-compartment heat exchanger (164a) of the first in-compartment circuit (161a).
In the cooling/air-cooling operation, a refrigeration cycle using double refrigerant supply sources is performed. In such a refrigeration cycle, refrigerant evaporated in the in-compartment heat exchanger (164a) of the first in-compartment circuit (161a) is sucked into the variable capacity compressor (114a), and refrigerant evaporated in the indoor heat exchanger (154) having an evaporation temperature higher than that of the in-compartment heat exchanger (164a) is sucked into the second fixed capacity compressor (114c). If the first fixed capacity compressor (114b) serves as an indoor compressor, the refrigerant evaporated in the indoor heat exchanger (154) is also sucked into the first fixed capacity compressor (114b). In addition, in the cooling/air-cooling operation, if the first fixed capacity compressor (114b) serves as an in-compartment compressor, a refrigeration cycle using a single refrigerant supply source is performed. In such a refrigeration cycle, refrigerant evaporated in the in-compartment heat exchanger (164a) is sucked into the variable capacity compressor (114a) and the first fixed capacity compressor (114b).

In the first cooling/air-heating operation, the variable capacity compressor (114a) is, referring to FIG. 10, operated with the first four-way valve (131) being set to the second state and the second four-way valve (132) being set to the first state. If an in-compartment cooling capacity lacks in the first cooling/air-heating operation, the first fixed capacity compressor (114b) is also operated. In such a case, the third four-way valve (133) is set to the first state, and the first fixed capacity compressor (114b) serves as an in-compartment compressor. In the first cooling/air-heating operation, the vapor compression refrigeration cycle is performed, in which the indoor heat exchanger (154) serves as a condenser and the in-compartment heat exchangers (164) serve as evaporators. During the first cooling/air-heating operation, cooling capacities (evaporation heat amounts) of the first in-compartment unit (160a) and the second in-compartment unit (160b) and an air-heating capacity (condensation heat amount) of the indoor unit (150) are brought into balance, resulting in heat recovery of 100%.
Specifically, refrigerant discharged from the variable capacity compressor (114a) is condensed by dissipating heat to indoor air in the indoor heat exchanger (154). The refrigerant condensed in the indoor heat exchanger (154) is distributed to the first in-compartment circuit (161a) and the second in-compartment circuit (161b). The refrigerant distributed to the first in-compartment circuit (161a) and the second in-compartment circuit (161b) circulates in the similar manner to that of the cold-storage/freezing operation. Subsequently, the refrigerant is sucked into the variable capacity compressor (114a), and then is re-discharged.
If the first fixed capacity compressor (114b) serves as an in-compartment compressor in the first cooling/air-heating operation, a refrigeration cycle using a single refrigerant supply source is performed. In such a refrigeration cycle, refrigerant evaporated in the in-compartment heat exchanger (164a) is sucked into the variable capacity compressor (114a) and the first fixed capacity compressor (114b). The same applies to the second and third cooling/air-heating operations which will be described later.

If there is an extra air-heating capacity in the first cooling/air-heating operation, the second cooling/air-heating operation is, referring to FIG. 11, performed by switching the second four-way valve (132) to the second state. In the second cooling/air-heating operation, the outdoor heat exchanger (115) is operated as a condenser. The same settings as those of the first cooling/air-heating operation are established in the second cooling/air-heating operation, except for the setting for the second four-way valve (132).
In the second cooling/air-heating operation, part of refrigerant discharged from the variable capacity compressor (114a) flows into the outdoor heat exchanger (115). The refrigerant flowing into the outdoor heat exchanger (115) is condensed by dissipating heat to outdoor air. The refrigerant condensed in the outdoor heat exchanger (115) joins refrigerant condensed in the indoor heat exchanger (154), and the resultant is distributed to the first in-compartment circuit (161a) and the second in-compartment circuit (161b). In the second cooling/air-heating operation, extra condensation heat is dissipated in the outdoor heat exchanger (115) without bringing cooling capacities (evaporation heat amounts) of the first in-compartment unit (160a) and the second in-compartment unit (160b) and an air-heating capacity (condensation heat amount) of the indoor unit (150) into balance.

If an air-heating capacity lacks in the first cooling/air-heating operation, the third cooling/air-heating operation is, referring to FIG. 12, performed in such a manner that the second fixed capacity compressor (114c) is operated with the second four-way valve (132) being set to the first state and the first outdoor expansion valve (166) being set to an open state. In the third cooling/air-heating operation, the vapor compression refrigeration cycle is performed, in which the indoor heat exchanger (154) serves as a condenser and the in-compartment heat exchangers (164) and the outdoor heat exchanger (115) serve as evaporators.
In the third cooling/air-heating operation, refrigerant condensed in the indoor heat exchanger (154) is distributed not only to the first in-compartment circuit (161a) and the second in-compartment circuit (161b) but also to the outdoor heat exchanger (115). After the pressure of the refrigerant distributed to the outdoor heat exchanger (115) is reduced by the first outdoor expansion valve (166), such refrigerant is evaporated in the outdoor heat exchanger (115). Subsequently, the refrigerant is sucked into the second fixed capacity compressor (114c), and then is re-discharged. In the third cooling/air-heating operation, heat equivalent to an evaporation heat shortage is absorbed in the outdoor heat exchanger (115) without bringing cooling capacities (evaporation heat amounts) of the first in-compartment unit (160a) and the second in-compartment unit (160b) and an air-heating capacity (condensation heat amount) of the indoor unit (150) into balance.

<Low-Pressure Control Operation>

Suppose that one or two of the three compressors (114a, 114b, 114c) are in operation, and the other compressor(s) is stopped. If an external air temperature (more specifically the temperature inside the refrigeration apparatus (100)) is dropped to a low temperature of about -10°C in a cold region during the winter, the temperature of the stopped compressor is also dropped to near -10°C. If the evaporation temperature of an evaporator connected to the compressor in operation is about 0-5°C, the stopped compressor has a temperature lower than that of the compressor in operation. Thus, since the saturation pressure equivalent to the temperature of the stopped compressor is lower than the low pressure (evaporation pressure) of the compressor in operation, refrigerant may flows into the stopped compressor. In such a case, refrigerant is melted in refrigerant oil accumulated in the compressor, and the refrigerant oil is diluted. Thus, there is a possibility that insufficient lubrication occurs upon a restart.
In the present embodiment, under the condition where the saturation pressure equivalent to the temperature of the stopped compressor itself or the saturation pressure equivalent to the ambient temperature of the stopped compressor is lower than the low pressure of the compressor in operation, the controller (210) performs the control for decreasing the low pressure of the compressor in operation to less than the temperature-equivalent saturation pressure.
First, a control in a normal operation will be briefly described.
(1) When the compressors are controlled based on a difference between an in-compartment temperature or a room temperature and a set temperature, a PID control is performed based on a value represented by the following equation: $Hz = f (Tset - Th 1)$

where "Tset" represents the set temperature, "Th1" represents a suction temperature, and "Hz" represents the frequency of the compressor.
(2) When loads of the compressors are controlled based only on the set temperature, the PID control is performed based on a value represented by the following equation: $Hz = f (LP - Target LP)$

where the target LP is set at f(Set Temperature - 10) and is regarded as a saturation pressure equivalent to a value lower than the set temperature by 10K. Note that the "LP (low pressure)" does not mean the suction pressure of the compressor, but means the evaporation pressure of the evaporator.
Next, a control for reducing or preventing refrigerant liquefaction in the stopped compressor when the outdoor heat exchanger (115) serves as a condenser will be described with reference to the flowchart illustrated in FIG. 3. First, it is, at step ST1, determined whether or not the low pressure LP of the compressor in operation is lower than a value f(Ta). The value f(Ta) may relate to the saturation pressure equivalent to an external air temperature ta, or may relate to, in the configuration in which a compressor and an outdoor heat exchanger are accommodated in an outdoor unit, the saturation pressure equivalent to the ambient temperature of the compressor.
If the determination result at step ST1 is "YES," the process proceeds to step ST2. When the process proceeds to step ST2, the external air temperature-equivalent saturation pressure is higher than the low pressure (evaporation pressure) of the compressor in operation, and therefore refrigerant does not flow into the stopped compressor. Thus, in any of the cases (1) and (2), the control described above is performed.
If the determination result at step ST1 is "NO," the process proceeds to step ST3 to correct the temperature represented by "(Ta)." In the present embodiment, the outdoor heat exchanger serves as a condenser. It is assumed that the temperature inside the outdoor unit is higher than an external air temperature. Thus, in the case (1), the PID control is performed based on the value represented by the following equation: $Hz = f (LP - Target LP)$

where Target LP = f(Ta). A control similar to the foregoing is performed in the case (2).
When the outdoor heat exchanger serves as an evaporator, the PID control is, at step ST3, performed based on a value represented by the following equation: $Hz = f (LP - cooler LP)$

where Target LP = Evaporator LP. A control similar to the foregoing is performed in the case (2).
In the foregoing manner, refrigerant does not flow into the stopped compressor. Thus, the refrigerant liquefaction does not occur, and refrigerant oil is not diluted.

Advantages of the Second Embodiment

According to the second embodiment described above, refrigerant does not flow into the stopped compressor as in the first embodiment. Thus, the refrigerant liquefaction does not occur, and refrigerant oil is not diluted. As a result, insufficient lubrication or burnout upon a restart of the compressor does not occur, thereby increasing stability of the apparatus (100).
When an in-compartment temperature is dropped by decreasing the low pressure (evaporation pressure) of the compressor in operation, the apparatus (100) enters a "thermo-off state" (i.e., a resting state in which the compressors are stopped and only air blowing is performed), and the in-compartment temperature is not further dropped. That is, overcooling does not occur. In such a state, since all of the compressors (114) are stopped, refrigerant does not circulate in the refrigerant circuit (200). Thus, even if the temperature of the stopped compressor itself or the ambient temperature of the stopped compressor is low, a flow of refrigerant into each compressor can be reduced or prevented.
When an in-compartment temperature is dropped by decreasing the low pressure (evaporation pressure) of the compressor in operation, the apparatus (100) enters a "thermo-off state" (i.e., a resting state in which the compressors are stopped and only air blowing is performed), and the in-compartment temperature is not further dropped. In such a state, since all of the compressors (114) are stopped, refrigerant does not circulate in the refrigerant circuit (200). Thus, even if the temperature of the stopped compressor itself or the ambient temperature of the stopped compressor is low, a flow of refrigerant into each compressor can be reduced or prevented.
As described above, the present embodiment describes the refrigeration apparatus (100) which includes the outdoor heat exchanger (heat-source-side heat exchanger) (115) switchable to a condenser or an evaporator, the in-compartment heat exchanger (first utilization-side heat exchanger) (164) switchable to a condenser or an evaporator, and the indoor heat exchanger (second utilization-side heat exchanger) (154) configured as an evaporator, and which includes the refrigerant circuit switchable between the first operation in which the first utilization-side heat exchanger (164) serves as the evaporator and the second utilization-side heat exchanger (154) and the heat-source-side heat exchanger (115) serve as the condensers, and the second operation in which the first utilization-side heat exchanger (164) and the heat-source-side heat exchanger (115) serve as the evaporators and the second utilization-side heat exchanger (154) serves as the condenser. In any of the operations in which the outdoor heat exchanger serves as the condenser or the evaporator, the refrigerant liquefaction in the stopped compressor can be reduced or prevented, thereby increasing the device stability.
In order to reduce or prevent the refrigerant liquefaction, the compressor (114) is typically heated by a crank case heater, and then refrigerant dissolved in refrigerant oil is separated from the refrigerant oil by evaporation. However, according to the present embodiment, the crank case heater is not necessarily used, and therefore a device configuration can be simplified. Note that it is not a requirement in the present embodiment that the crank case heater is not used, and the crank case heater may be used in combination with the control described in the present embodiment depending on the situation.

«Other Embodiment»

Each of the foregoing embodiments may be configured as follows.
In each of the foregoing embodiments, the three compressors (21a, 21b, 21c) (114a, 114b, 114c) are provided in the outside-compartment circuit (20). However, the present invention is not limited to such a configuration. Two compressors or four or more compressors may be used.
In each of the foregoing embodiments, the control is performed based on the temperature of the compressor itself or the ambient temperature of the compressor. However, the low pressure of the compressor may be controlled based on an actual outside-compartment temperature.
Each of the foregoing embodiments has described the control under the condition where the external air temperature is dropped to about -10°C. However, in the present invention, when one or more of a plurality of compressors are in operation, and the other compressor(s) is stopped, if the external air temperature-equivalent saturation pressure is, regardless of the external air temperature, lower than the low pressure (evaporation pressure) of the compressor in operation, the control may be performed to decrease the low pressure to less than the external air temperature-equivalent saturation pressure.
The foregoing embodiments have been set forth merely for the purpose of preferred examples in nature, and are not intended to limit the scope, applications, and use of the invention.

INDUSTRIAL APPLICABILITY

As described above, the present invention is useful for the refrigeration apparatus including the plurality of compressors and configured to perform the vapor compression refrigeration cycle.

DESCRIPTION OF REFERENCE CHARACTERS

1: Refrigeration Apparatus
2: Heat-Source-Side Unit
9: Controller (Control Section)
20: Refrigerant Circuit
21: Compressor
25: Heat-Source-Side Heat Exchanger
52: Expansion Mechanism
53: Utilization-Side Heat Exchanger
100: Refrigeration Apparatus
110: Heat-Source-Side Unit
114: Compressor
115: Heat-Source-Side Heat Exchanger
153: Expansion Mechanism
163: Expansion Mechanism
164: Utilization-Side Heat Exchanger
200: Refrigerant Circuit
210: Controller (Control Section)

Claims

A refrigeration apparatus including a refrigerant circuit (20, 200) in which a plurality of compressors (21, 114), a heat-source-side heat exchanger (25, 115), an expansion mechanism (52, 153, 163), and a utilization-side heat exchanger (53, 154, 164) are connected in order, the refrigeration apparatus comprising:
a controller (9, 200) configured to decrease, when one or more of the compressors (21, 114) is a compressor in operation and other one or more of the compressors (21, 114) is a stopped compressor, if a saturation pressure equivalent to a temperature of the stopped compressor itself or an ambient temperature of the stopped compressor is lower than a low pressure of one of the heat exchangers serving as an evaporator connected to the compressor in operation, the low pressure of the evaporator connected to the compressor in operation to less than the saturation pressure equivalent to the temperature of the stopped compressor itself or the ambient temperature of the stopped compressor.
The refrigeration apparatus of claim 1, wherein
the compressors (21, 114) and the heat-source-side heat exchanger (25, 115) are accommodated in a heat-source-side unit (2, 110), and
in an operation state in which the heat-source-side heat exchanger (25, 115) serves as a condenser, the controller (9, 200) performs a control based on a saturation pressure equivalent to an ambient temperature of the condenser having a temperature higher than an external air temperature.
The refrigeration apparatus of claim 1, wherein
the compressors (21, 114) and the heat-source-side heat exchanger (25, 115) are accommodated in a heat-source-side unit (2, 110), and
in an operation state in which the heat-source-side heat exchanger (25, 115) serves as an evaporator, the controller (9, 200) performs a control based on a saturation pressure equivalent to an ambient temperature of the evaporator having a temperature lower than an external air temperature.
The refrigeration apparatus of claim 1, wherein
in the refrigerant circuit (20), the heat-source-side heat exchanger (25) serves as a condenser, the utilization-side heat exchanger (53) serves as an evaporator, and only cooling is performed by the utilization-side heat exchanger (53).
The refrigeration apparatus of claim 1, wherein
the refrigerant circuit (200) includes the heat-source-side heat exchanger (115) switchable to a condenser or an evaporator, a first utilization-side heat exchanger (154) switchable to a condenser or an evaporator, and a second utilization-side heat exchanger (164) configured as an evaporator, and
the refrigerant circuit (200) is switchable between a first operation in which the first utilization-side heat exchanger (154) serves as the evaporator and the second utilization-side heat exchanger (164) and the heat-source-side heat exchanger (115) serve as the condensers, and a second operation in which the first utilization-side heat exchanger (154) and the heat-source-side heat exchanger (115) serve as the evaporators and the second utilization-side heat exchanger (164) serves as the condenser.