Patent Publication Number: US-2022221196-A1

Title: Air conditioner

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a Continuation of PCT International Application No. PCT/JP2020/036084, filed on Sep. 24, 2020, which claims priority under 35 U.S.C. 119(a) to Patent Application No. 2019-180832, filed in Japan on Sep. 30, 2019, all of which are hereby expressly incorporated by reference into the present application. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to an air conditioner. 
     BACKGROUND ART 
     Hitherto, as an example of an air conditioner that has a refrigerant circuit constituted to be switchable between a cooling operation and a heating operation and that performs a multistage compression refrigeration cycle, there exists an air conditioner such as that described in PTL 1 (Japanese Unexamined Patent Application Publication No. 2016-11780). In such an air conditioner, increasing operation efficiency by cooling with an intermediate cooler a high-temperature refrigerant that has been subjected to multistage compression may be considered. 
     SUMMARY 
     An air conditioner according to a first aspect includes a compression mechanism, a heat-source-side unit, a plurality of use-side units, and a control unit. The compression mechanism has a first compression unit and a second compression unit that is disposed on a discharge side of the first compression unit. The heat-source-side unit has a first heat-source-side heat exchanger and a second heat-source-side heat exchanger. The plurality of use-side units switches between a cooling operation and a heating operation. The control unit performs switching between a first operation, a second operation, and a third operation by switching a flow of a refrigerant at the heat-source-side unit. The control unit, at a time of the first operation, switches the flow of the refrigerant so that the first heat-source-side heat exchanger functions as a radiator and the second heat-source-side heat exchanger functions as an intermediate cooler. The control unit, at a time of the second operation, switches the flow of the refrigerant so that the first heat-source-side heat exchanger and the second heat-source-side heat exchanger function as evaporators. The control unit, at a time of the third operation, switches the flow of the refrigerant so that the first heat-source-side heat exchanger functions as the radiator and the second heat-source-side heat exchanger functions as the evaporator. Alternatively, the control unit, at the time of the third operation, switches the flow of the refrigerant so that the first heat-source-side heat exchanger functions as the evaporator and the second heat-source-side heat exchanger functions as a radiator. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic structural view of an air conditioner  1  according to a first embodiment of the present disclosure. 
         FIG. 2  is a block diagram of a control unit  120  according to the first embodiment of the present disclosure. 
         FIG. 3  is a schematic structural explanatory view of the operation of the air conditioner  1  when a first operation is performed. 
         FIG. 4  is a schematic structural explanatory view of the operation of the air conditioner  1  when a second operation is performed. 
         FIG. 5  is a schematic structural explanatory view of the operation of the air conditioner  1  when a third A operation is performed. 
         FIG. 6  is a schematic structural explanatory view of the operation of the air conditioner  1  when a third B operation is performed. 
         FIG. 7  is a schematic structural explanatory view of the operation of the air conditioner  1  when a third C operation is performed. 
         FIG. 8  is a schematic structural view of an air conditioner  1 A according to Modification 1A. 
         FIG. 9  is a block diagram of a control unit  120  according to Modification 1A. 
         FIG. 10  is a schematic structural view of an air conditioner  1 S according to second embodiment of the present disclosure. 
         FIG. 11  is a schematic structural explanatory view of the operation of the air conditioner  15  when a second S operation is performed. 
         FIG. 12  is a schematic structural explanatory view of the operation of the air conditioner  15  when a third S operation is performed. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     An air conditioner according to an embodiment of the present disclosure is described below with reference to the drawings. Note that embodiments and modifications below are specific examples of the present disclosure, do not limit the technical scope of the present disclosure, and are changeable as appropriate within a scope that does not depart from the spirit. 
     First Embodiment 
     (1) Overall Structure 
       FIG. 1  is a schematic structural view of an air conditioner  1  according to a first embodiment of the present disclosure. In the air conditioner  1 , a refrigerant circuit  30  is constituted by a compression mechanism  15 , a heat-source-side unit  100 , a plurality of use-side units  101   a ,  101   b , and  101   c , branch units  70   a ,  70   b , and  70   c , and a control unit  120 . The air conditioner  1  is constituted to be capable of freely selecting between a cooling operation and a heating operation for each use-side unit. A refrigerant that acts in a supercritical region (here, a CO 2  refrigerant or a CO 2  mixed refrigerant) is sealed in the refrigerant circuit  30 . 
     (2) Detailed Structure 
     (2-1) Compression Mechanism 
     The compression mechanism  15  has a first compression unit  11  and a second compression unit  12 . The compression mechanism  15  sucks in a low-pressure refrigerant in a refrigeration cycle by a suction pipe  8 , and compresses the refrigerant by the first compression unit  11  and the second compression unit  12 . The low-pressure refrigerant in the refrigeration cycle, after being compressed to an intermediate pressure in the refrigeration cycle by the first compression unit  11 , is discharged to an intermediate connection pipe  9 . The refrigerant that has been discharged to the intermediate connection pipe  9  is sucked into the second compression unit  12 . The refrigerant that has been sucked into the second compression unit  12 , after being compressed to a high pressure in the refrigeration cycle, is discharged to a discharge pipe  10 . 
     The intermediate connection pipe  9  is a pipe to which the refrigerant compressed to the intermediate pressure in the refrigeration cycle at the first compression unit  11  is discharged. The intermediate connection pipe  9  is connected to a second intermediate-connection-pipe branch pipe  9   b  and a first intermediate-connection-pipe branch pipe  9   a  via a second heat-source-side switching mechanism  5   b . The second intermediate-connection-pipe branch pipe  9   b  is a pipe that connects the intermediate connection pipe  9  and a second heat-source-side heat exchanger  82  to each other via the second heat-source-side switching mechanism  5   b . The first intermediate-connection-pipe branch pipe  9   a  is a pipe that connects the intermediate connection pipe  9  and the second compression unit  12  to each other via the second heat-source-side switching mechanism  5   b.    
     The discharge pipe  10  is a pipe to which the refrigerant compressed to the high pressure in the refrigeration cycle by the second compression unit  12  is discharged. The discharge pipe  10  branches into a high-low-pressure gas-refrigerant connection pipe  3  and a liquid-refrigerant connection pipe  2 . 
     (2-2) Heat-Source-Side Unit 
     The heat-source-side unit  100  is installed on the roof of, for example, a building, or around, for example, a building. The heat-source-side unit  100  is connected to the use-side units  101   a ,  101   b , and  101   c  via the liquid-refrigerant connection pipe  2 , the high-low-pressure gas-refrigerant connection pipe  3 , a low-pressure gas-refrigerant connection pipe  4 , a liquid-side cutout valve  90 , a first gas-side cutout valve  91 , a second gas-side cutout valve  92 , and the respective branch units  70   a ,  70   b , and  70   c , and constitutes a part of the refrigerant circuit  30 . 
     The heat-source-side unit  100  primarily has a first heat-source-side heat exchanger  81 , the second heat-source-side heat exchanger  82 , a pipe  9   c  for sending to a suction side of the second compression unit (hereunder, injection pipe  9   c ), an economizer pipe  21 , an economizer heat exchanger  61 , a first heat-source-side expansion mechanism  24   a , a second heat-source-side expansion mechanism  24   b , a first heat-source-side switching mechanism  5   a , the second heat-source-side switching mechanism  5   b , a third heat-source-side switching mechanism  5   c , and an accumulator  95 . 
     (2-2-1) 
     A heat-source-side heat exchanger is a heat exchanger that performs heat exchange between, for example, a refrigerant and outdoor air, and, here, is divided into the first heat-source-side heat exchanger  81  and the second heat-source-side heat exchanger  82 . The first heat-source-side heat exchanger  81  is a heat exchanger that functions as an evaporator or a radiator of a refrigerant. The first heat-source-side heat exchanger  81  is connected to the first heat-source-side switching mechanism  5   a  by the liquid-refrigerant connection pipe  2 . The second heat-source-side heat exchanger  82  is a heat exchanger that functions as an intermediate cooler or an evaporator of a refrigerant. The second heat-source-side heat exchanger  82  is connected to the second heat-source-side switching mechanism  5   b  by the second intermediate-connection-pipe branch pipe  9   b . A liquid side of the first heat-source-side heat exchanger  81  and a liquid side of the second heat-source-side heat exchanger  82  are connected to each other via a liquid-refrigerant-connection-pipe branch pipe  84 . 
     The injection pipe  9   c  is a pipe that causes an intermediate-pressure refrigerant in the refrigeration cycle that has flowed from the second heat-source-side heat exchanger  82  that functions as an intermediate cooler to return to the second compression unit  12 . 
     The economizer pipe  21  is a pipe that branches off from the liquid-refrigerant connection pipe  2  and merges with the first intermediate-connection-pipe branch pipe  9   a . The economizer pipe  21  includes a third heat-source-side expansion mechanism  24   c . Here, the third heat-source-side expansion mechanism  24   c  is constituted by an electric expansion valve whose opening degree can be adjusted. The opening degree of the third heat-source-side expansion mechanism  24   c  is adjusted as appropriate by the control unit  120  in accordance with an operation state. 
     The economizer heat exchanger  61  is a heat exchanger that is disposed between the heat-source-side unit  100  and the use-side units  101   a ,  101   b , and  101   c . Here, the economizer heat exchanger  61  is a double-pipe-type heat exchanger or a plate-type heat exchanger. A refrigerant that flows in the economizer pipe  21  and a refrigerant that flows in the liquid-refrigerant connection pipe  2  exchange heat with each other at the economizer heat exchanger  61 . A refrigerant that has radiated at the first heat-source-side heat exchanger  81  that functions as a radiator of the refrigerant further radiates and is subcooled at the economizer heat exchanger  61 . 
     The first heat-source-side expansion mechanism  24   a  and the second heat-source-side expansion mechanism  24   b  are mechanisms that are disposed at the refrigerant circuit  30  and that expand a refrigerant that flows between the use-side heat exchangers  102   a ,  102   b , and  102   c  and the heat-source-side heat exchangers  81  and  82 . Here, the first heat-source-side expansion mechanism  24   a  and the second heat-source-side expansion mechanism  24   b  are each constituted by an electric expansion valve whose opening degree can be adjusted. The opening degree of the first heat-source-side expansion mechanism  24   a  and the opening degree of the second heat-source-side expansion mechanism  24   b  are each adjusted as appropriate by the control unit  120  in accordance with an operation state. 
     The first heat-source-side switching mechanism  5   a , the second heat-source-side switching mechanism  5   b , and the third heat-source-side switching mechanism  5   c  are mechanisms for switching a direction of flow of a refrigerant in the refrigerant circuit  30 . More specifically, the control unit  120  is a mechanism for switching between a radiation operation state and an evaporation operation state. The radiation operation state is a state in which the control unit  120  causes the first heat-source-side heat exchanger  81  to function as a radiator and the second heat-source-side heat exchanger  82  to function as a radiator or an intermediate cooler of a refrigerant. The evaporation operation state is a state in which the control unit  120  causes the first heat-source-side heat exchanger  81  and the second heat-source-side heat exchanger  82  to function as evaporators of a refrigerant. 
     Here, the first heat-source-side switching mechanism  5   a , the second heat-source-side switching mechanism  5   b , and the third heat-source-side switching mechanism  5   c  are each a four-way switching valve. Note that a fourth port  5   ad  of the first heat-source-side switching mechanism  5   a  and a fourth port  5   cd  of the third heat-source-side switching mechanism  5   c  are closed, and the first heat-source-side switching mechanism  5   a  and the third heat-source-side switching mechanism  5   c  each function as a three-way valve. 
     (2-3) Use-Side Units 
     The use-side units  101   a ,  101   b , and  101   c  are installed on a ceiling inside, for example, a building by being embedded, suspended, or the like, or are installed on an indoor wall surface by wall hanging or the like. The use-side units  101   a ,  101   b , and  101   c  are connected to the heat-source-side unit  100  via the liquid-refrigerant connection pipe  2 , the high-low-pressure gas-refrigerant connection pipe  3 , the low-pressure gas-refrigerant connection pipe  4 , the liquid-side cutout valve  90 , a first gas-side cutout valve  91 , the second gas-side cutout valve  92 , and the respective branch units  70   a ,  70   b , and  70   c ; and constitute a part of the refrigerant circuit  30 . 
     The first use-side unit  101   a  has a first use-side heat exchanger  102   a  and a first use-side expansion mechanism  103   a . The second use-side unit  101   b  has a second use-side heat exchanger  102   b  and a second use-side expansion mechanism  103   b . The third use-side unit  101   c  has a third use-side heat exchanger  102   c  and a third use-side expansion mechanism  103   c . The use-side heat exchangers  102   a ,  102   b , and  102   c  are each a heat exchanger that processes indoor air-conditioning load (heat load) by causing a refrigerant and indoor air to exchange heat with each other. Here, the use-side expansion mechanisms  103   a ,  103   b , and  103   c  are each constituted by an electric expansion valve. The opening degrees of the use-side expansion mechanisms  103   a ,  103   b , and  103   c  are each adjusted as appropriate by the control unit  120  in accordance with an operation state. 
     Note that, although, in the present embodiment, the air conditioner  1  including three use-side units  101   a ,  101   b , and  101   c  is described, the present disclosure is also applicable to an air conditioner including a larger number of use-side units than three use-side units. 
     (2-4) Branch Units 
     The branch units  70   a ,  70   b , and  70   c  are installed, for example, near the use-side units  101   a ,  101   b , and  101   c , respectively, inside, for example, a building. The branch units  70   a ,  70   b , and  70   c  are interposed between the liquid-refrigerant connection pipe  2 , the high-low-pressure gas-refrigerant connection pipe  3 , and the low-pressure gas-refrigerant connection pipe  4 , the use-side units  101   a ,  101   b , and  101   c  and the heat-source-side unit  100 ; and constitute a part of the refrigerant circuit  30 . The branch units  70   a ,  70   b , and  70   c  are installed at a corresponding one of the use-side units  101   a ,  101   b , and  101   c . Alternatively, a plurality of use-side units each having the same switching timing between a cooling operation and a heating operation are connected to one branch unit. 
     The branch units  70   a ,  70   b , and  70   c  each primarily have a first branch path including a corresponding one of first branch-unit switching valves  71   a ,  72   a , and  73   a , and a second branch path including a corresponding one of second branch-unit switching valves  71   b ,  72   b , and  73   b . The first branch-unit switching valves  71   a ,  72   a , and  73   a  are each an electromagnetic valve that switches communication/non-communication between the high-low-pressure gas-refrigerant connection pipe  3  and a corresponding one of the use-side heat exchangers  102   a ,  102   b , and  102   c . The second branch-unit switching valves  71   b ,  72   b , and  73   b  are each an electromagnetic valve that switches communication/non-communication between the low-pressure gas-refrigerant connection pipe  4  and a corresponding one of the use-side heat exchangers  102   a ,  102   b , and  102   c.    
     (2-5) Control Unit 
     The control unit  120  controls the operations of devices of each part that constitutes the air conditioner  1 . The control unit  120  is constituted by joining a heat-source-side control unit  111 , a use-side control unit  104 , and a branch-side control unit  74  by a communication line (see  FIG. 2 ). 
     The heat-source-side unit  100  has the heat-source-side control unit  111  that controls the operation of each part that constitutes the heat-source-side unit  100 . The heat-source-side control unit  111  includes a microcomputer and various electric components, which are provided for controlling the heat-source-side unit  100 , the microcomputer having a CPU (Central Processing Unit), a memory, and the like. The CPU reads a program that is stored in the memory or the like and performs a predetermined calculation in accordance with the program. Further, in accordance with the program, the CPU is capable of writing a calculated result to the memory and reading information stored in the memory. The heat-source-side control unit  111  is constituted to be capable of exchanging a control signal or the like with the use-side control unit  104  of the use-side units  101   a ,  101   b , and  101   c  via the communication line. 
     The use-side units  101   a ,  101   b , and  101   c  have the use-side control unit  104  that controls the operation of each part that constitutes the use-side units  101   a ,  101   b , and  101   c . The use-side control unit  104  includes a microcomputer and various electric components, which are provided for controlling the use-side units  101   a ,  101   b , and  101   c , the microcomputer having a CPU (Central Processing Unit), a memory, and the like. The CPU reads a program that is stored in the memory or the like and performs a predetermined calculation in accordance with the program. Further, in accordance with the program, the CPU is capable of writing a calculated result to the memory and reading information stored in the memory. The use-side control unit  104  is constituted to be capable of exchanging a control signal or the like with the heat-source-side unit  100  via the communication line. The use-side control unit  104  is constituted to be capable of receiving, for example, signals regarding the operation and the stoppage of the air conditioner  1 , and signals related to various settings, the signals being sent from a remote controller (not shown) for operating the use-side units  101   a ,  101   b , and  101   c.    
     The branch units  70   a ,  70   b , and  70   c  have the branch-side control unit  74  that controls the operation of each part that constitutes the branch units  70   a ,  70   b , and  70   c . The branch-side control unit  74  includes a microcomputer and various electric components, which are provided for controlling the branch units  70   a ,  70   b , and  70   c , the microcomputer having a CPU (Central Processing Unit), a memory, and the like. The CPU reads a program that is stored in the memory or the like and performs a predetermined calculation in accordance with the program. Further, in accordance with the program, the CPU is capable of writing a calculated result to the memory and reading information stored in the memory. The branch-side control unit  74  is constituted to be capable of exchanging a control signal or the like with the use-side control unit  104  of the use-side units  101   a ,  101   b , and  101   c.    
     Structural devices of the air conditioner  1  that is controlled by the control unit  120  includes, for example, the compression units  11  and  12 , the heat-source-side switching mechanisms  5   a ,  5   b , and  5   c , the heat-source-side expansion mechanisms  24   a ,  24   b , and  24   c , the use-side expansion mechanisms  103   a ,  103   b , and  103   c , the first branch-unit switching valves  71   a ,  72   a , and  73   a , and the second branch-unit switching valves  71   b ,  72   b , and  73   b.    
     The air conditioner  1  is capable of performing switching between a first operation, a second operation, and a third operation, which are described below, by control of the control unit  120 . 
     Specifically, when switching the operation of each use-side unit, the control unit  120  switches the states of the heat-source-side heat exchangers  81  and  82  from the difference between the total of operating-device capacities of the use-side heat exchangers that function as evaporators of a refrigerant and the total of operating-device capacities of the use-side heat exchangers that function as radiators of a refrigerant. 
     When ΔQ=the operating-device capacities of the use-side heat exchangers that function as evaporators of a refrigerant—the operating-device capacities of the use-side heat exchangers that function as radiators of a refrigerant,
 
if ΔQ is larger than a first threshold value c 1 , the control unit  120  causes the first heat-source-side heat exchanger  81  and the second heat-source-side heat exchanger  82  to function as radiators of a refrigerant.
 
If ΔQ is less than or equal to the first threshold value c 1  and is greater than or equal to a second threshold value c 2 , the control unit  120  causes the first heat-source-side heat exchanger  81  to be a radiator and the second heat-source-side heat exchanger  82  to be an evaporator.
 
If ΔQ is less than the second threshold value c 2 , the control unit  120  causes the first heat-source-side heat exchanger  81  and the second heat-source-side heat exchanger  82  to function as evaporators of a refrigerant.
 
     When a state in which both the high pressure and the low pressure of the user-side heat exchangers during the operation are lower than a target pressure Pb has continued for a predetermined time, the control unit  120  increases the number of heat-source-side heat exchangers that function as evaporators. 
     When a state in which both the high pressure and the low pressure of the user-side heat exchangers during the operation are higher than the target pressure Pb has continued for a predetermined time, the control unit  120  increases the number of heat-source-side heat exchangers that function as radiators. 
     (3) Operation of Air Conditioner 
     Next, the operation of the air conditioner  1  according to the present embodiment is described. The air conditioner  1  according to the present embodiment conditions air due to the control unit  120  performing switching between the first operation, the second operation, and the third operation. 
     The first operation is an operation in which only use-side heat exchangers that function as evaporators of a refrigerant (use-side units that perform a cooling operation) exist (all cooling operation). 
     The second operation is an operation in which only use-side heat exchangers that function as radiators of a refrigerant (use-side units that perform a heating operation) exist (all heating operation). 
     The third operation is an operation in which a use-side unit that performs a cooling operation and a use-side unit that performs a heating operation exist (simultaneous cooling-and-heating operation). The third operation includes a third A operation, a third B operation, and a third C operation. 
     The third A operation is an operation in which, although both a use-side heat exchanger that functions as an evaporator of a refrigerant and a use-side heat exchanger that functions as a radiator of a refrigerant exist, the load on an evaporation side is large as a whole (predominant cooling operation). 
     The third B operation is an operation in which, although both a use-side heat exchanger that functions as a radiator of a refrigerant and a use-side heat exchanger that functions as an evaporator of a refrigerant exist, the load on a radiation side is large as a whole (predominant heating operation). 
     The third C operation is an operation in which, although both a use-side heat exchanger that functions as an evaporator of a refrigerant and a use-side heat exchanger that functions as a radiator of a refrigerant exist, an evaporation load and a radiation load are equal to each other as a whole (equivalent cooling-heating operation). 
     (3-1) First Operation 
     Here, operations that are performed when the first operation is performed are described by giving as an example a case in which the control unit  120  causes the first use-side heat exchanger  102   a  and the third use-side heat exchanger  102   c  to function as evaporators of a refrigerant and perform a cooling operation and in which the control unit  120  causes the operation of the second use-side heat exchanger  102   b  to be stopped (see  FIG. 3 ). 
     In the first operation, the control unit  120  determines that the first heat-source-side heat exchanger  81  is to function as a radiator of a refrigerant and the second heat-source-side heat exchanger  82  is to function as an intermediate cooler of a refrigerant. The control unit  120  switches the first heat-source-side switching mechanism  5   a , the second heat-source-side switching mechanism  5   b , and the third heat-source-side switching mechanism  5   c  to a radiation operation state (state shown by the solid lines of the first heat-source-side switching mechanism  5   a , the second heat-source-side switching mechanism  5   b , and the third heat-source-side switching mechanism  5   c  in  FIG. 3 ). The control unit  120  closes the first branch-unit switching valves  71   a ,  72   a , and  73   a  and the second branch-unit switching valve  72   b , and opens the second branch-unit switching valves  71   b  and  73   b.    
     In such a state of the refrigerant circuit  30  (regarding flow of a refrigerant, see the arrows at the refrigerant circuit  30  of  FIG. 3 ), a low-pressure refrigerant in a refrigeration cycle is sucked into the first compression unit  11  from the suction pipe  8 . The low-pressure refrigerant in the refrigeration cycle that has been sucked into the first compression unit  11 , after being compressed to an intermediate pressure in the refrigeration cycle at the first compression unit  11 , is discharged to the intermediate connection pipe  9 . The intermediate-pressure refrigerant in the refrigeration cycle that has been discharged to the intermediate connection pipe  9  from the first compression unit  11  flows through the second intermediate-connection-pipe branch pipe  9   b  via the second heat-source-side switching mechanism  5   b , and is sent to the second heat-source-side heat exchanger  82  that functions as an intermediate cooler. The refrigerant that has been sent to the second heat-source-side heat exchanger  82  that functions as an intermediate cooler exchanges heat with, for example, outdoor air and is cooled at the second heat-source-side heat exchanger  82 . The intermediate-pressure refrigerant in the refrigeration cycle that has been cooled at the second heat-source-side heat exchanger  82  is sent to the second compression unit  12  via the injection pipe  9   c  and the first intermediate-connection-pipe branch pipe  9   a . The intermediate-pressure refrigerant in the refrigeration cycle that has been sent to the second compression unit  12  is sucked into the second compression unit  12  and is compressed to a high pressure in the refrigeration cycle at the second compression unit  12 . The refrigerant that has been compressed to a high pressure in the refrigeration cycle at the second compression unit  12  is discharged to the discharge pipe  10 . Here, the high-pressure refrigerant in the refrigeration cycle that has been discharged to the discharge pipe  10  from the second compression unit  12  is compressed to a pressure that is higher than the critical pressure of the refrigerant by a double-stage compression operation by the compression units  11  and  12 . The high-pressure refrigerant in the refrigeration cycle that has been discharged to the discharge pipe  10  from the second compression unit  12  flows through the liquid-refrigerant connection pipe  2  and is sent to the first heat-source-side heat exchanger  81  that functions as a radiator. The high-pressure refrigerant in the refrigeration cycle that has been sent to the first heat-source-side heat exchanger  81  exchanges heat with, for example, outdoor air and radiates at the first heat-source-side heat exchanger  81 , and is sent to the first heat-source-side expansion mechanism  24   a . The high-pressure refrigerant in the refrigeration cycle that has been sent to the first heat-source-side expansion mechanism  24   a  has its pressure reduced at the first heat-source-side expansion mechanism  24   a  and is sent to the economizer heat exchanger  61  via the liquid-refrigerant connection pipe  2 . At this time, a part of the refrigerant that flows in the liquid-refrigerant connection pipe  2  branches and flows in the economizer pipe  21 . 
     The refrigerant that has branched and that has flowed in the economizer pipe  21  from the liquid-refrigerant connection pipe  2  has its pressure reduced to an intermediate pressure in the refrigeration cycle at the third heat-source-side expansion mechanism  24   c , and is sent to the economizer heat exchanger  61 . The refrigerant whose pressure has been reduced to an intermediate pressure in the refrigeration cycle at the third heat-source-side expansion mechanism  24   c  exchanges heat with the refrigerant that flows in the liquid-refrigerant connection pipe  2  at the economizer heat exchanger  61 . The intermediate-pressure refrigerant in the refrigeration cycle that has exchanged heat with the refrigerant that flows in the liquid-refrigerant connection pipe  2  at the economizer heat exchanger  61  is sent to the first intermediate-connection-pipe branch pipe  9   a . The intermediate-pressure refrigerant in the refrigeration cycle that has been sent to the first intermediate-connection-pipe branch pipe  9   a  is sucked into the second compression unit  12 . 
     The refrigerant whose pressure has been reduced at the first heat-source-side expansion mechanism  24   a  and that has been sent to the economizer heat exchanger  61  via the liquid-refrigerant connection pipe  2  exchanges heat with the refrigerant that flows in the economizer pipe  21  and is cooled at the economizer heat exchanger  61 . The refrigerant that has been cooled at the economizer heat exchanger  61  is sent to the use-side expansion mechanisms  103   a  and  103   c  via the liquid-refrigerant connection pipe  2 . The refrigerant that has been sent to the use-side expansion mechanisms  103   a  and  103   c  via the liquid-refrigerant connection pipe  2  has its pressure reduced and becomes a low-pressure refrigerant in a gas-liquid two-phase state in the refrigeration cycle at the use-side expansion mechanisms  103   a  and  103   c . The low-pressure refrigerant in the refrigeration cycle whose pressure has been reduced at the use-side expansion mechanisms  103   a  and  103   c  is sent to the use-side heat exchangers  102   a  and  102   c . The low-pressure refrigerant in the refrigeration cycle that has been sent to the use-side heat exchangers  102   a  and  102   c  exchanges heat with, for example, indoor air and evaporates at the use-side heat exchangers  102   a  and  102   c  that function as evaporators of the refrigerant. The low-pressure refrigerant in the refrigeration cycle that has evaporated at the use-side heat exchangers  102   a  and  102   c  is sucked into the first compression unit  11  again via the low-pressure gas-refrigerant connection pipe  4 , the accumulator  95 , and the suction pipe  8 . In this way, the first operation is performed. 
     (3-2) Second Operation 
     Here, operations that are performed when the second operation is performed are described by giving as an example a case in which the control unit  120  causes the first use-side heat exchanger  102   a  and the third use-side heat exchanger  102   c  to function as radiators of a refrigerant and perform a heating operation and in which the control unit  120  causes the operation of the second use-side heat exchanger  102   b  to be stopped (see  FIG. 4 ). 
     In the second operation, the control unit  120  determines that the first heat-source-side heat exchanger  81  and the second heat-source-side heat exchanger  82  are to function as evaporators of a refrigerant. The control unit  120  switches the first heat-source-side switching mechanism  5   a , the second heat-source-side switching mechanism  5   b , and the third heat-source-side switching mechanism  5   c  to an evaporation operation state (state shown by the solid lines of the first heat-source-side switching mechanism  5   a , the second heat-source-side switching mechanism  5   b , and the third heat-source-side switching mechanism  5   c  in  FIG. 4 ). The control unit  120  closes the first branch-unit switching valve  72   a  and the second branch-unit switching valves  71   b ,  72   b , and  73   b  and opens the first branch-unit switching valves  71   a  and  73   a.    
     In such a state of the refrigerant circuit  30  (regarding flow of a refrigerant, see the arrows at the refrigerant circuit  30  of  FIG. 4 ), a low-pressure refrigerant in a refrigeration cycle is sucked into the first compression unit  11  from the suction pipe  8 . The low-pressure refrigerant in the refrigeration cycle that has been sucked into the first compression unit  11 , after being compressed to an intermediate pressure in the refrigeration cycle at the first compression unit  11 , is discharged to the intermediate connection pipe  9 . The intermediate-pressure refrigerant in the refrigeration cycle that has been discharged to the intermediate connection pipe  9  from the first compression unit  11  flows through the first intermediate-connection-pipe branch pipe  9   a  via the second heat-source-side switching mechanism  5   b , and is sucked into the second compression unit  12 . The refrigerant sucked into the second compression unit  12 , after being compressed to a high pressure in the refrigeration cycle at the second compression unit  12 , is discharged to the discharge pipe  10 . Here, the high-pressure refrigerant in the refrigeration cycle that has been discharged from the second compression unit  12  is compressed to a pressure that is higher than the critical pressure of the refrigerant by a double-stage compression operation by the compression units  11  and  12 . The high-pressure refrigerant in the refrigeration cycle that has been discharged from the second compression unit  12  is sent to the use-side heat exchangers  102   a  and  102   c  via the high-low-pressure gas-refrigerant connection pipe  3  and the third heat-source-side switching mechanism  5   c . The high-pressure refrigerant in the refrigeration cycle that has been sent to the use-side heat exchangers  102   a  and  102   c  exchanges heat with, for example, indoor air and radiates at the use-side heat exchangers  102   a  and  102   c  that function as radiators of the refrigerant. The high-pressure refrigerant in the refrigeration cycle that has radiated at the use-side heat exchangers  102   a  and  102   c  is sent to the use-side expansion mechanisms  103   a  and  103   c . The high-pressure refrigerant in the refrigeration cycle that has been sent to the use-side expansion mechanisms  103   a  and  103   c  has its pressure reduced at the use-side heat expansion mechanisms  103   a  and  103   c . The refrigerant whose pressure has been reduced at the use-side expansion mechanisms  103   a  and  103   c  is sent to the first heat-source-side expansion mechanism  24   a  and the second heat-source-side expansion mechanism  24   b  via the liquid-refrigerant connection pipe  2  or the liquid-refrigerant connection-pipe branch pipe  84 . The refrigerant that has been sent to the first heat-source-side expansion mechanism  24   a  and the second heat-source-side expansion mechanism  24   b  has its pressure reduced and becomes a low-pressure refrigerant in a gas-liquid two-phase state in the refrigeration cycle at the first heat-source-side expansion mechanism  24   a  and the second heat-source-side expansion mechanism  24   b . The low-pressure refrigerant in the refrigeration cycle whose pressure has been reduced at the first heat-source-side expansion mechanism  24   a  and the second heat-source-side expansion mechanism  24   b  is sent to the first heat-source-side heat exchanger  81  and the second heat-source-side heat exchanger  82 . The low-pressure refrigerant in the refrigeration cycle that has been sent to the first heat-source-side heat exchanger  81  and the second heat-source-side heat exchanger  82  exchanges heat with, for example, outdoor air and evaporates at the first heat-source-side heat exchanger  81  and the second heat-source-side heat exchanger  82  that function as evaporators of the refrigerant. The low-pressure refrigerant in the refrigeration cycle that has evaporated at the first heat-source-side heat exchanger  81  is sucked into the first compression unit  11  again via the first heat-source-side switching mechanism  5   a , the accumulator  95 , and the suction pipe  8 . The low-pressure refrigerant in the refrigeration cycle that has evaporated at the second heat-source-side heat exchanger  82  is sucked into the first compression unit  11  again via the second heat-source-side switching mechanism  5   b , the accumulator  95 , and the suction pipe  8 . In this way, the second operation is performed. 
     (3-3) Third Operation 
     Next, the third operation is described in terms of three operations, that is, the third A operation, the third B operation, and the third C operation. 
     (3-3-1) Third A Operation 
     The 3 third A operation is an operation in which, although both a use-side heat exchanger that functions as an evaporator of a refrigerant and a use-side heat exchanger that functions as a radiator of a refrigerant exist, the load on an evaporation side is large as a whole (predominant cooling operation). 
     Here, operations that are performed when the third A operation is performed are described by giving as an example a case in which the control unit  120  causes the first use-side heat exchanger  102   a  and the second use-side heat exchanger  102   b  to function as evaporators of a refrigerant and perform a cooling operation and in which the control unit  120  causes the third use-side heat exchanger  102   c  to function as a radiator of a refrigerant and perform a heating operation (see  FIG. 5 ). 
     In the third A operation, the control unit  120  determines that the first heat-source-side heat exchanger  81  is to function as a radiator and the second heat-source-side heat exchanger  82  is to function as an evaporator of a refrigerant. The control unit  120  switches the first heat-source-side switching mechanism  5   a  to a radiation operation state (state shown by the solid line of the first heat-source-side switching mechanism  5   a  in  FIG. 5 ) and switches the second heat-source-side switching mechanism  5   b  and the third heat-source-side switching mechanism  5   c  to an evaporation operation state (state shown by the solid lines of the second heat-source-side switching mechanism  5   b  and the third heat-source-side switching mechanism  5   c  in  FIG. 5 ). The control unit  120  closes the first branch-unit switching valves  71   a  and  72   a  and the second branch-unit switching valve  73   b  and opens the first branch-unit switching valve  73   a  and the second branch-unit switching valves  71   b  and  72   b.    
     In such a state of the refrigerant circuit  30  (regarding flow of a refrigerant, see the arrows at the refrigerant circuit  30  of  FIG. 5 ), a low-pressure refrigerant in a refrigeration cycle is sucked into the first compression unit  11  from the suction pipe  8 . The low-pressure refrigerant in the refrigeration cycle that has been sucked into the first compression unit  11 , after being compressed to an intermediate pressure in the refrigeration cycle at the first compression unit  11 , is discharged to the intermediate connection pipe  9 . The intermediate-pressure refrigerant in the refrigeration cycle that has been discharged to the intermediate connection pipe  9  from the first compression unit  11  flows through the first intermediate-connection-pipe branch pipe  9   a , and is sent to the second compression unit  12 . The intermediate-pressure refrigerant in the refrigeration cycle that has been sent to the second compression unit  12  is sucked into the second compression unit  12  and is compressed to a high pressure in the refrigeration cycle at the second compression unit  12 . The refrigerant that has been compressed to a high pressure in the refrigeration cycle at the second compression unit  12  is discharged to the discharge pipe  10 . Here, the high-pressure refrigerant in the refrigeration cycle that has been discharged to the discharge pipe  10  from the second compression unit  12  is compressed to a pressure that is higher than the critical pressure of the refrigerant by a double-stage compression operation by the compression units  11  and  12 . A part of the high-pressure refrigerant in the refrigeration cycle that has been discharged to the discharge pipe  10  is sent to the first heat-source-side heat exchanger  81  via the liquid-refrigerant connection pipe  2  and the first heat-source-side switching mechanism  5   a  from the discharge pipe  10 , and the remaining part is sent to the third use-side heat exchanger  102   c  via the high-low-pressure gas-refrigerant connection pipe  3  and the third heat-source-side switching mechanism  5   c.    
     The high-pressure refrigerant in the refrigeration cycle that has been sent to the first heat-source-side heat exchanger  81  from the discharge pipe  10  exchanges heat with, for example, outdoor air and radiates at the first heat-source-side heat exchanger  81  that functions as a radiator of the refrigerant, and is sent to the first heat-source-side expansion mechanism  24   a . The high-pressure refrigerant in the refrigeration cycle that has been sent to the first heat-source-side expansion mechanism  24   a  has its pressure reduced at the first heat-source-side expansion mechanism  24   a . A part of the refrigerant whose pressure has been reduced at the first heat-source-side expansion mechanism  24   a  is sent to the economizer heat exchanger  61  via the liquid-refrigerant connection pipe  2 , and the remaining part is sent to the second heat-source-side expansion mechanism  24   b.    
     The refrigerant whose pressure has been reduced at the first heat-source-side expansion mechanism  24   a  and that has been sent to the second heat-source-side expansion mechanism  24   b  has its pressure reduced at the second heat-source-side expansion mechanism  24   b  and is sent to the second heat-source-side heat exchanger  82 . The refrigerant that has been sent to the second heat-source-side heat exchanger  82 , after evaporating at the second heat-source-side heat exchanger  82  that functions as an evaporator of the refrigerant, returns to the first compression unit  11  again via the second heat-source-side switching mechanism  5   b , the accumulator  95 , and the suction pipe  8 . 
     A part of the refrigerant whose pressure has been reduced at the first heat-source-side expansion mechanism  24   a  and that has been sent to the economizer heat exchanger  61  via the liquid-refrigerant connection pipe  2  branches and flows in the economizer pipe  21 . 
     The refrigerant that has branched and that has flowed in the economizer pipe  21  from the liquid-refrigerant connection pipe  2  has its pressure reduced to an intermediate pressure in the refrigeration cycle at the third heat-source-side expansion mechanism  24   c , and is sent to the economizer heat exchanger  61 . The refrigerant whose pressure has been reduced to an intermediate pressure in the refrigeration cycle at the third heat-source-side expansion mechanism  24   c  exchanges heat with the refrigerant that flows in the liquid-refrigerant connection pipe  2  at the economizer heat exchanger  61 . The intermediate-pressure refrigerant in the refrigeration cycle that has exchanged heat with the refrigerant that flows in the liquid-refrigerant connection pipe  2  at the economizer heat exchanger  61  is sent to the first intermediate-connection-pipe branch pipe  9   a . The intermediate-pressure refrigerant in the refrigeration cycle that has been sent to the first intermediate-connection-pipe branch pipe  9   a  is sucked into the second compression unit  12 . 
     The refrigerant whose pressure has been reduced at the first heat-source-side expansion mechanism  24   a  and that has been sent to the economizer heat exchanger  61  via the liquid-refrigerant connection pipe  2  exchanges heat with the refrigerant that flows in the economizer pipe  21  and is cooled at the economizer heat exchanger  61 . The refrigerant that has been cooled at the economizer heat exchanger  61  is sent to the use-side expansion mechanisms  103   a  and  103   b  via the liquid-refrigerant connection pipe  2 . 
     On the other hand, the high-pressure refrigerant in the refrigeration cycle that has been sent to the third use-side heat exchanger  102   c  from the discharge pipe  10  exchanges heat with, for example, indoor air and radiates at the third use-side heat exchanger  102   c  that functions as a radiator of the refrigerant. The high-pressure refrigerant in the refrigeration cycle that has radiated at the third use-side heat exchanger  102   c  is sent to the third use-side expansion mechanism  103   c . The high-pressure refrigerant in the refrigeration cycle that has been sent to the third use-side expansion mechanism  103   c  has its pressure reduced at the third use-side heat expansion mechanism  103   c , and flows in the liquid-refrigerant connection pipe  2 . The refrigerant that has flowed in the liquid-refrigerant connection pipe  2  merges with the refrigerant that has exchanged heat at the economizer heat exchanger  61 . The refrigerant that has merged at the liquid-refrigerant connection pipe  2  is sent to the use-side expansion mechanisms  103   a  and  103   b.    
     The refrigerant that has been sent to the use-side expansion mechanisms  103   a  and  103   b  has its pressure reduced and becomes a low-pressure refrigerant in a gas-liquid two-phase state in the refrigeration cycle at the use-side expansion mechanisms  103   a  and  103   b . The low-pressure refrigerant in the refrigeration cycle whose pressure has been reduced at the use-side expansion mechanisms  103   a  and  103   b  is sent to the use-side heat exchangers  102   a  and  102   b . The low-pressure refrigerant in the refrigeration cycle that has been sent to the use-side heat exchangers  102   a  and  102   b  exchanges heat with, for example, indoor air and evaporates at the use-side heat exchangers  102   a  and  102   b  that function as evaporators of the refrigerant. The low-pressure refrigerant in the refrigeration cycle that has evaporated at the use-side heat exchangers  102   a  and  102   b  is sucked into the first compression unit  11  again via the low-pressure gas-refrigerant connection pipe  4 , the accumulator  95 , and the suction pipe  8 . In this way, the third A operation is performed. 
     (3-3-2) Third B Operation 
     Here, operations that are performed when the third B operation is performed are described by giving as an example a case in which the control unit  120  causes the first use-side heat exchanger  102   a  and the second use-side heat exchanger  102   b  to function as radiators of a refrigerant and perform a heating operation and in which the control unit  120  causes the third use-side heat exchanger  102   c  to function as an evaporator of a refrigerant and perform a cooling operation (see  FIG. 6 ). 
     In the third B operation, the control unit  120  determines that the first heat-source-side heat exchanger  81  and the second heat-source-side heat exchanger  82  are to function as evaporators of a refrigerant. The control unit  120  switches the first heat-source-side switching mechanism  5   a , the second heat-source-side switching mechanism  5   b , and the third heat-source-side switching mechanism  5   c  to an evaporation operation state (state shown by the solid lines of the first heat-source-side switching mechanism  5   a , the second heat-source-side switching mechanism  5   b , and the third heat-source-side switching mechanism  5   c  in  FIG. 6 ). The control unit  120  closes the first branch-unit switching valve  73   a  and the second branch-unit switching valves  71   b  and  72   b , and opens the first branch-unit switching valves  71   a  and  72   a  and the second branch-unit switching valve  73   b.    
     In such a state of the refrigerant circuit  30  (regarding flow of a refrigerant, see the arrows at the refrigerant circuit  30  of  FIG. 6 ), a low-pressure refrigerant in a refrigeration cycle is sucked into the first compression unit  11  from the suction pipe  8 . The low-pressure refrigerant in the refrigeration cycle that has been sucked into the first compression unit  11 , after being compressed to an intermediate pressure in the refrigeration cycle at the first compression unit  11 , is discharged to the intermediate connection pipe  9 . The intermediate-pressure refrigerant in the refrigeration cycle that has been discharged to the intermediate connection pipe  9  from the first compression unit  11  flows through the first intermediate-connection-pipe branch pipe  9   a  via the second heat-source-side switching mechanism  5   b . The refrigerant that has flowed in the first intermediate-connection-pipe branch pipe  9   a  is sucked into the second compression unit  12 , and, after being compressed to a high pressure in the refrigeration cycle at the second compression unit  12 , is discharged to the discharge pipe  10 . Here, the high-pressure refrigerant in the refrigeration cycle that has been discharged from the second compression unit  12  is compressed to a pressure that is higher than the critical pressure of the refrigerant by a double-stage compression operation by the compression units  11  and  12 . The high-pressure refrigerant in the refrigeration cycle that has been discharged to the discharge pipe  10  is sent to the use-side heat exchangers  102   a  and  102   b  via the high-low-pressure gas-refrigerant connection pipe  3  and the third heat-source-side switching mechanism  5   c . The high-pressure refrigerant in the refrigeration cycle that has been sent to the use-side heat exchangers  102   a  and  102   b  exchanges heat with, for example, indoor air and radiates at the use-side heat exchangers  102   a  and  102   b  that function as radiators of the refrigerant. The high-pressure refrigerant in the refrigeration cycle that has radiated at the use-side heat exchangers  102   a  and  102   b  is sent to the use-side expansion mechanisms  103   a  and  103   b . The high-pressure refrigerant in the refrigeration cycle that has been sent to the use-side expansion mechanisms  103   a  and  103   b  has its pressure reduced at the use-side heat expansion mechanisms  103   a  and  103   b . A part of the refrigerant whose pressure has been reduced at the use-side expansion mechanisms  103   a  and  103   b  is sent to the first heat-source-side expansion mechanism  24   a  and the second heat-source-side expansion mechanism  24   b  from the liquid-refrigerant connection pipe  2 , and the remaining part is sent to the third use-side expansion mechanism  103   c  from the liquid-refrigerant connection pipe  2 . 
     The refrigerant that has been sent to the first heat-source-side expansion mechanism  24   a  and the second heat-source-side expansion mechanism  24   b  has its pressure reduced and becomes a low-pressure refrigerant in a gas-liquid two-phase state in the refrigeration cycle at the first heat-source-side expansion mechanism  24   a  and the second heat-source-side expansion mechanism  24   b . The low-pressure refrigerant in the refrigeration cycle whose pressure has been reduced at the first heat-source-side expansion mechanism  24   a  and the second heat-source-side expansion mechanism  24   b  is sent to the first heat-source-side heat exchanger  81  and the second heat-source-side heat exchanger  82  that function as evaporators of the refrigerant. The low-pressure refrigerant in the refrigeration cycle that has evaporated at the first heat-source-side heat exchanger  81  is sucked into the first compression unit  11  again via the first heat-source-side switching mechanism  5   a , the accumulator  95 , and the suction pipe  8 . The low-pressure refrigerant in the refrigeration cycle that has evaporated at the second heat-source-side heat exchanger  82  is sucked into the first compression unit  11  again via the second heat-source-side switching mechanism  5   b , the accumulator  95 , and the suction pipe  8 . 
     On the other hand, the refrigerant that has branched from the liquid-refrigerant connection pipe  2  and that has been sent to the third use-side expansion mechanism  103   c  has its pressure reduced and becomes a low-pressure refrigerant in a gas-liquid two-phase state in the refrigeration cycle at the third use-side expansion mechanisms  103   c . The low-pressure refrigerant in the refrigeration cycle whose pressure has been reduced at the third use-side heat exchanger  103   c  is sent to the third use-side heat exchanger  102   c . The low-pressure refrigerant in the refrigeration cycle that has been sent to the third use-side heat exchanger  102   c  exchanges heat with, for example, indoor air and evaporates at the third use-side heat exchanger  102   c  that functions as an evaporator of the refrigerant. The low-pressure refrigerant in the refrigeration cycle that has evaporated at the third use-side heat exchanger  102   c  is sent to the first compression unit  11  again via the low-pressure gas-refrigerant connection pipe  4 , the accumulator  95 , and the suction pipe  8 . 
     (3-3-3) Third C Operation 
     Here, operations that are performed when the third C operation is performed are described by giving as an example a case in which the control unit  120  causes the first use-side heat exchanger  102   a  to function as a radiator of a refrigerant and perform a heating operation, in which the control unit  120  causes the operation of the second use-side heat exchanger  102   b  to be stopped, and in which the control unit  120  causes the third use-side heat exchanger  102   c  to function as an evaporator of a refrigerant and perform a cooling operation (see  FIG. 7 ). 
     In the third C operation, the control unit  120  determines that the first heat-source-side heat exchanger  81  is to function as a radiator of a refrigerant and the second heat-source-side heat exchanger  82  is to function as an evaporator of a refrigerant. The control unit  120  determines that the radiation load and the evaporation load of the respective first heat-source-side heat exchanger  81  and second heat-source-side heat exchanger  82  are small. The control unit  120  switches the first heat-source-side switching mechanism  5   a  to a radiation operation state shown by the solid line in  FIG. 7  and switches the second heat-source-side switching mechanism  5   b  and the third heat-source-side switching mechanism  5   c  to an evaporation operation state shown by the solid lines in  FIG. 7 . The control unit  120  closes the first branch-unit switching valves  72   a  and  73   a  and the second branch-unit switching valves  71   b  and  72   b , and opens the first branch-unit switching valve  71   a  and the second branch-unit switching valve  73   b.    
     In such a state of the refrigerant circuit  30  (regarding flow of a refrigerant, see the arrows at the refrigerant circuit  30  of  FIG. 7 ), a low-pressure refrigerant in a refrigeration cycle is sucked into the first compression unit  11  from the suction pipe  8 . The low-pressure refrigerant in the refrigeration cycle that has been sucked into the first compression unit  11 , after being compressed to an intermediate pressure in the refrigeration cycle at the first compression unit  11 , is discharged to the intermediate connection pipe  9 . The intermediate-pressure refrigerant in the refrigeration cycle that has been discharged from the first compression unit  11  is sent to the second compression unit  12  via the second heat-source-side switching mechanism  5   b . The intermediate-pressure refrigerant in the refrigeration cycle that has been sent to the second compression unit  12  is compressed to a high pressure in the refrigeration cycle at the second compression unit  12 , and is discharged to the discharge pipe  10 . Here, the high-pressure refrigerant in the refrigeration cycle that has been discharged from the second compression unit  12  is compressed to a pressure that is higher than the critical pressure of the refrigerant by a double-stage compression operation by the compression units  11  and  12 . A part of the high-pressure refrigerant in the refrigeration cycle that has been discharged to the discharge pipe  10  from the second compression unit  12  is sent to the first heat-source-side heat exchanger  81  via the first heat-source-side switching mechanism  5   a , and the remaining part is sent to the first use-side heat exchanger  102   a  via the third heat-source-side switching mechanism  5   c.    
     The high-pressure refrigerant in the refrigeration cycle that has been sent to the first heat-source-side heat exchanger  81  via the first heat-source-side switching mechanism  5   a  exchanges heat with, for example, outdoor air and radiates at the first heat-source-side heat exchanger  81  that functions as a radiator of the refrigerant. The high-pressure refrigerant in the refrigeration cycle that has radiated at the first heat-source-side heat exchanger  81  has its pressure reduced at the first heat-source-side expansion mechanism  24   a . The refrigerant whose pressure has been reduced at the first heat-source-side expansion mechanism  24   a  is sent to the second heat-source-side expansion mechanism  24   b . The refrigerant that has been sent to the second heat-source-side expansion mechanism  24   b  has its pressure reduced and becomes a low-pressure refrigerant in a gas-liquid two-phase state in the refrigeration cycle at the second heat-source-side expansion mechanism  24   b . The low-pressure refrigerant in the refrigeration cycle whose pressure has been reduced at the second heat-source-side expansion mechanism  24   b  is sent to the second heat-source-side heat exchanger  82 . The low-pressure refrigerant in the refrigeration cycle that has been sent to the second heat-source-side heat exchanger  82  exchanges heat with, for example, outdoor air and evaporates at the second heat-source-side heat exchanger  82  that functions as an evaporator of the refrigerant. The low-pressure refrigerant in the refrigeration cycle that has evaporated at the second heat-source-side heat exchanger  82  is sucked into the first compression unit  11  again via the second heat-source-side switching mechanism  5   b , the accumulator  95 , and the suction pipe  8 . 
     On the other hand, the high-pressure refrigerant in the refrigeration cycle that has been sent to the first use-side heat exchanger  102   a  from the discharge pipe  10  exchanges heat with, for example, indoor air and radiates at the first use-side heat exchanger  102   a  that functions as a radiator of the refrigerant. The high-pressure refrigerant in the refrigeration cycle that has radiated at the first use-side heat exchanger  102   a  is sent to the first use-side expansion mechanism  103   a . The high-pressure refrigerant in the refrigeration cycle that has been sent to the use-side expansion mechanism  103   a  has its pressure reduced at the first use-side expansion mechanism  103   a . The refrigerant whose pressure has been reduced at the first use-side expansion mechanism  103   a  is sent to the third use-side expansion mechanism  103   c  via the liquid-refrigerant connection pipe  2 . The refrigerant that has been sent to the third use-side expansion mechanism  103   c  has its pressure reduced and becomes a low-pressure refrigerant in a gas-liquid two-phase state in the refrigeration cycle at the third use-side expansion mechanism  103   c . The low-pressure refrigerant whose pressure has been reduced at the third use-side expansion mechanism  103   c  is sent to the third use-side heat exchanger  102   c . The low-pressure refrigerant in the refrigeration cycle that has been sent to the third use-side heat exchanger  102   c  exchanges heat with, for example, indoor air and evaporates at the third use-side heat exchanger  102   c  that functions as an evaporator of the refrigerant. The low-pressure refrigerant in the refrigeration cycle that has evaporated at the third use-side heat exchanger  102   c  is sucked into the first compression unit  11  again via the low-pressure gas-refrigerant connection pipe  4 , the accumulator  95 , and the suction pipe  8 . In this way, the third C operation is performed. 
     (4) Modifications 
     Next, modifications of the air conditioner  1  according to the present embodiment are described. Note that structures that are the same as those of the first embodiment above are given the same reference numerals and detailed descriptions thereof are omitted. 
     (4-1) Modification 1A 
     In the above embodiment, the heat-source-side unit  100  of the air conditioner  1  is described as having a first heat-source-side heat exchanger  81  and a second heat-source-side heat exchanger  82 . However, the structure of the air conditioner  1  is not limited thereto, and, for example, in an air conditioner  1 A, a heat-source-side heat exchanger may be divided into a first heat-source-side heat exchanger  81 , a second heat-source-side heat exchanger  82 , and a third heat-source-side heat exchanger  83  (see  FIGS. 8 and 9 ). 
     In this case, a refrigerant circuit  30 A of the air conditioner  1 A further has a fourth heat-source-side switching mechanism  5   d , a fourth heat-source-side expansion mechanism  24   d , and a third gas-side cutout valve  93 . 
     The fourth heat-source-side switching mechanism  5   d  is a mechanism for switching a direction of flow of a refrigerant in the refrigerant circuit  30 A. More specifically, the control unit  120  is a mechanism for switching between a radiation operation state and an evaporation operation state. The radiation operation state is a state in which the control unit  120  causes the first heat-source-side heat exchanger  81  to function as a radiator of a refrigerant, the second heat-source-side heat exchanger  82  to function as an intermediate cooler or a radiator of a refrigerant, and the third heat-source-side heat exchanger  83  to function as a radiator of a refrigerant. The evaporation operation state is a state in which the control unit  120  causes the first heat-source-side heat exchanger  81 , the second heat-source-side heat exchanger  82 , and the third heat-source-side heat exchanger  83  to function as evaporators of a refrigerant. 
     Here, the fourth heat-source-side switching mechanism  5   d  is a four-way switching valve. A fourth port  5   dd  of the fourth heat-source-side switching mechanism  5   d  is closed, and the fourth heat-source-side switching mechanism  5   d  functions as a three-way valve. 
     The fourth heat-source-side expansion mechanism  24   d  is a mechanism that is disposed at the refrigerant circuit  30 A and that expands a refrigerant that flows between the use-side heat exchangers  102   a ,  102   b , and  102   c  and the heat-source-side heat exchangers  81 ,  82 , and  83 . Here, the fourth heat-source-side expansion mechanism  24   d  is constituted by an electric expansion valve whose opening degree can be adjusted. The opening degree of the fourth heat-source-side expansion mechanism  24   d  is adjusted as appropriate by the control unit  120  in accordance with an operation state. 
     (4-2) Modification 1B 
     In the above embodiment, the first heat-source-side switching mechanism  5   a , the second heat-source-side switching mechanism  5   b , the third heat-source-side switching mechanism  5   c , and the fourth heat-source-side switching mechanism  5   d  are each described as being a four-way switching valve. However, in the present disclosure, four-way switching valves do not necessarily need to be used as flow-path switching valves. For example, other types of switching valves, such as electromagnetic valves, electric valves, three-way valves, or five-way valves, may be used as the flow-path switching valves. 
     (5) Features 
     (5-1) 
     In an air conditioner that includes a compression mechanism including a plurality of compression units, a heat-source-side heat exchanger that is divided to function as an evaporator or a radiator, and use-side units, and that is constituted to be capable of performing switching between a cooling operation and a heating operation for each use-side unit, increasing operation efficiency by cooling a refrigerant that is compressed by the plurality of compression units by a heat exchanger that functions as an intermediate cooler may be considered. In particular, in an air conditioner that performs a supercritical refrigeration cycle in which the pressure becomes higher than the critical pressure of a refrigerant, since the temperature of the refrigerant that is discharged from the compression mechanism is increased, reducing the temperature of the refrigerant that is discharged from the compression mechanism by cooling the refrigerant with an intermediate cooler may be considered. However, when a heat-source-side heat exchanger that is divided to function as an evaporator or a radiator is further divided to form a heat exchanger that functions as an intermediate cooler, costs are increased. In the air conditioner  1  of the first embodiment of the present disclosure, the second heat-source-side heat exchanger  82  that functions as an intermediate cooler at the time of the first operation functions as an evaporator of a refrigerant at the time of the second operation and the third operation. In this way, one heat exchanger is constituted to function as an intermediate cooler or an evaporator in accordance with an instruction of the control unit  120 . Therefore, since it is no longer necessary to further divide a heat-source-side heat exchanger to form a heat exchanger that functions as an intermediate cooler, an increase in costs is suppressed. 
     (5-2) 
     The air conditioner  1  of the first embodiment according to the present disclosure may have a first heat-source-side heat exchanger  81 , a second heat-source-side heat exchanger  82 , and a third heat-source-side heat exchanger  83  by dividing a heat-source-side heat exchanger. By dividing the heat-source-side heat exchanger in this way, the heat-source-side heat exchanger is capable of properly processing the heat loads of the use-side units. 
     Even in the air conditioner  1 A having a third heat-source-side heat exchanger by further dividing a heat-source-side heat exchanger, increasing operation efficiency by cooling a refrigerant that is compressed by the plurality of compression units with a heat exchanger that functions as an intermediate cooler may be considered. The air conditioner  1 A according to the first embodiment of the present disclosure is such that the second heat-source-side heat exchanger  82  functions as an intermediate cooler or an evaporator in accordance with an instruction of the control unit  120 . Therefore, since it is no longer necessary to further divide a heat-source-side heat exchanger to form a heat exchanger that functions as an intermediate cooler, an increase in costs is suppressed. 
     Second Embodiment 
     Next, an air conditioner  1 S as a second embodiment of the present disclosure is described. Note that, in order to distinguish this embodiment from the other embodiment, in the present embodiment, the letter “S” is sometimes added. The air conditioner  1  according to the first embodiment has been described as including a second heat-source-side heat exchanger  82  that functions as an intermediate cooler of a refrigerant and an evaporator of a refrigerant. As shown in  FIG. 10 , the second embodiment differs from the first embodiment in that a heat-source-side unit  100 S has a bypass pipe  20 . Excluding this point, the structure of the second embodiment is substantially the same as the structure of the first embodiment. Therefore, in the second embodiment, structures differing from those of the first embodiment are described, and the other descriptions are omitted. 
     (6) Detailed Structure 
     (6-1) Intermediate Connection Pipe 
     An intermediate connection pipe  9 S is a pipe to which is discharged a refrigerant that has been compressed to a high pressure in a refrigeration cycle at a first compression unit  11 , and that branches into a first intermediate-connection-pipe branch pipe  9   a S and a second intermediate-connection-pipe branch pipe  9   b S. The second intermediate-connection-pipe branch pipe  9   b S is a pipe that connects the intermediate connection pipe  9 S and a second heat-source-side heat exchanger  82 S to each other via a second heat-source-side switching mechanism  5   b S. The first intermediate-connection-pipe branch pipe  9   a S is a pipe that connects the intermediate connection pipe  9 S and a second compression unit  12  to each other. 
     (6-2) Heat-Source-Side Unit 
     The heat-source-side unit  100 S is installed on the roof of, for example, a building, or around, for example, a building. The heat-source-side unit  100 S is connected to use-side units  101   a ,  101   b , and  101   c  via a liquid-refrigerant connection pipe  2 , a high-low-pressure gas-refrigerant connection pipe  3 , a low-pressure gas-refrigerant connection pipe  4 , a liquid-side cutout valve  90 , a first gas-side cutout valve  91 , a second gas-side cutout valve  92 , a fifth gas-side cutout valve  94 , and respective branch units  70   a ,  70   b , and  70   c , and constitutes a part of a refrigerant circuit  30 S. 
     The heat-source-side unit  100 S primarily has a first heat-source-side heat exchanger  81 , the second heat-source-side heat exchanger  82 S, an injection pipe  9   c  for sending to a suction side of the second compression unit  12  a refrigerant that has flowed in the second heat-source-side heat exchanger  82 S, an economizer pipe  21 , an economizer heat exchanger  61 , a first heat-source-side expansion mechanism  24   a , a second heat-source-side expansion mechanism  24   b , a first heat-source-side switching mechanism  5   a , the second heat-source-side switching mechanism  5   b S, a third heat-source-side switching mechanism  5   c , and the bypass pipe  20 . 
     (6-2-1) 
     The second heat-source-side heat exchanger  82 S is a heat exchanger that functions as an intermediate cooler, an evaporator, or a radiator of a refrigerant. The second heat-source-side heat exchanger  82 S is connected to the second heat-source-side switching mechanism  5   b S by the second intermediate-connection-pipe branch pipe  9   b S. A liquid side of the first heat-source-side heat exchanger  81  and a liquid side of the second heat-source-side heat exchanger  82 S are connected to each other via a liquid-refrigerant-connection-pipe branch pipe  84 . 
     A fourth port  5 bdS of the second heat-source-side switching mechanism  5   b S is closed, and the second heat-source-side switching mechanism  5   b S is a four-way switching valve that functions as a three-way valve. Note that the second heat-source-side switching mechanism  5   bs  may be a three-way valve instead of a four-way switching valve. 
     The bypass pipe  20  is a pipe that branches off from the first intermediate-connection-pipe branch pipe  9   a S and that is connected to a discharge pipe  10 . A refrigerant that has been discharged to the second intermediate-connection-pipe branch pipe  9   b S from the first compression unit  11  and that has flowed in the first intermediate-connection-pipe branch pipe  9   a S passes through the bypass pipe  20  to flow in the use-side units  101   a ,  101   b , and  101   c , or the first heat-source-side heat exchanger  81  without being sucked into the second compression unit  12 . 
     A control unit  120  controls the operations of devices of each part that constitutes the air conditioner  1 S. The air conditioner  15  is capable of performing switching between a first S operation, a second S operation, and a third S operation, which are described below, by control of the control unit  120 . 
     (7) Operation of Air Conditioner 
     Next, the operation of the air conditioner  15  according to the present embodiment is described. The air conditioner  15  according to the present embodiment conditions air due to the control unit  120  performs switching between the second S operation and the third S operation. 
     The second S operation is an operation in which only use-side heat exchangers that function as radiators of a refrigerant (use-side units that perform a heating operation) exist (all heating operation). 
     The third S operation is an operation in which a use-side unit that performs a cooling operation and a use-side unit that performs a heating operation exist (simultaneous cooling-and-heating operation). 
     (7-1) Second S Operation 
     Here, operations that are performed when the second S operation is performed are described by giving as an example a case in which the control unit  120  causes the first use-side heat exchanger  102   a  and the third use-side heat exchanger  102   c  to function as radiators of a refrigerant and perform a heating operation and in which the control unit  120  causes the operation of the second use-side heat exchanger  102   b  to be stopped (see  FIG. 11 ). 
     In the second S operation, the control unit  120  determines that the first heat-source-side heat exchanger  81  and the second heat-source-side heat exchanger  82 S are to function as evaporators of a refrigerant. The control unit  120  switches the first heat-source-side switching mechanism  5   a , the second heat-source-side switching mechanism  5   b S, and the third heat-source-side switching mechanism  5   c  to an evaporation operation state (state shown by the solid lines of the first heat-source-side switching mechanism  5   a , the second heat-source-side switching mechanism  5   b S, and the third heat-source-side switching mechanism  5   c  in  FIG. 11 ). The control unit  120  closes a first branch-unit switching valve  72   a  and second branch-unit switching valves  71   b ,  72   b , and  73   b  and opens first branch-unit switching valves  71   a  and  73   a.    
     In such a state of the refrigerant circuit  30 S (regarding flow of a refrigerant, see the arrows at the refrigerant circuit  30 S of  FIG. 11 ), a low-pressure refrigerant in a refrigeration cycle is sucked into the first compression unit  11  from the suction pipe  8 . The low-pressure refrigerant in the refrigeration cycle that has been sucked into the first compression unit  11 , after being compressed to a high pressure in the refrigeration cycle at the first compression unit  11 , is discharged to the intermediate connection pipe  9 S. Here, the high-pressure refrigerant in the refrigeration cycle that has been discharged to the intermediate connection pipe  9 S from the first compression unit  11  is compressed to a pressure that is higher than the critical pressure of the refrigerant by a compression operation by the first compression unit  11 . The high-pressure refrigerant in the refrigeration cycle that has been discharged to the intermediate connection pipe  9 S from the first compression unit  11  flows through the first intermediate-connection-pipe branch pipe  9   a S, and flows in the bypass pipe  20 . The high-pressure refrigerant in the refrigeration cycle that has flowed in the bypass pipe  20  is sent to the use-side heat exchangers  102   a  and  102   c  via the high-low-pressure gas-refrigerant connection pipe  3  and the third heat-source-side switching mechanism  5   c . The high-pressure refrigerant in the refrigeration cycle that has been sent to the use-side heat exchangers  102   a  and  102   c  exchanges heat with, for example, indoor air and radiates at the use-side heat exchangers  102   a  and  102   c  that function as radiators of the refrigerant. The high-pressure refrigerant in the refrigeration cycle that has radiated at the use-side heat exchangers  102   a  and  102   c  is sent to the use-side expansion mechanisms  103   a  and  103   c . The high-pressure refrigerant in the refrigeration cycle that has been sent to the use-side expansion mechanisms  103   a  and  103   c  has its pressure reduced at the use-side heat expansion mechanisms  103   a  and  103   c . The refrigerant whose pressure has been reduced at the use-side expansion mechanisms  103   a  and  103   c  is sent to the first heat-source-side expansion mechanism  24   a  and the second heat-source-side expansion mechanism  24   b  via the liquid-refrigerant connection pipe  2  or the liquid-refrigerant connection-pipe branch pipe  84 . The refrigerant that has been sent to the first heat-source-side expansion mechanism  24   a  and the second heat-source-side expansion mechanism  24   b  has its pressure reduced and becomes a low-pressure refrigerant in a gas-liquid two-phase state in the refrigeration cycle at the first heat-source-side expansion mechanism  24   a  and the second heat-source-side expansion mechanism  24   b . The low-pressure refrigerant in the refrigeration cycle whose pressure has been reduced at the first heat-source-side expansion mechanism  24   a  and the second heat-source-side expansion mechanism  24   b  is sent to the respective first heat-source-side heat exchanger  81  and second heat-source-side heat exchanger  82 S. The low-pressure refrigerant in the refrigeration cycle that has been sent to the first heat-source-side heat exchanger  81  and the second heat-source-side heat exchanger  82 S exchanges heat with, for example, outdoor air and evaporates at the first heat-source-side heat exchanger  81  and second heat-source-side heat exchanger  82 S that function as evaporators of the refrigerant. The low-pressure refrigerant in the refrigeration cycle that has evaporated at the first heat-source-side heat exchanger  81  is sucked into the first compression unit  11  again via the first heat-source-side switching mechanism  5   a , an accumulator  95 , and the suction pipe  8 . The low-pressure refrigerant in the refrigeration cycle that has evaporated at the second heat-source-side heat exchanger  82 S is sucked into the first compression unit  11  again via the second heat-source-side switching mechanism  5   b S, the accumulator  95 , and the suction pipe  8 . In this way, the second S operation is performed. 
     (7-2) Third S Operation 
     Next, the third S operation is described. Here, as an example of the third S operation, a description is given of a case in which, although both a use-side heat exchanger that functions as a radiator of a refrigerant and a use-side heat exchanger that functions as an evaporator of a refrigerant exist, an operation (predominant heating operation) in which the load on a radiation side is large as a whole is performed. 
     Here, as an example of the predominant heating operation, a description is given of a case in which the control unit  120  causes the first use-side heat exchanger  102   a  and the second use-side heat exchanger  102   b  to function as radiators of a refrigerant and perform a heating operation and in which the control unit  120  causes the third use-side heat exchanger  102   c  to function as an evaporator of a refrigerant and perform a cooling operation (see  FIG. 12 ). 
     In such an operation, the control unit  120  determines that the first heat-source-side heat exchanger  81  is to function as an evaporator and the second heat-source-side heat exchanger  82 S is to function as a radiator of a refrigerant. The control unit  120  switches the second heat-source-side switching mechanism  5   bs  to a radiation operation state shown by the solid line in  FIG. 12  and switches the first heat-source-side switching mechanism  5   a  and the third heat-source-side switching mechanism  5   c  to an evaporation operation state shown by the solid lines in  FIG. 12 . The control unit  120  closes the first branch-unit switching valve  73   a  and the second branch-unit switching valves  71   b  and  72   b , and opens the first branch-unit switching valves  71   a  and  72   a  and the second branch-unit switching valve  73   b.    
     In such a state of the refrigerant circuit  30 S (regarding flow of a refrigerant, see the arrows at the refrigerant circuit  30 S of  FIG. 12 ), a low-pressure refrigerant in a refrigeration cycle is sucked into the first compression unit  11  from the suction pipe  8 . The low-pressure refrigerant in the refrigeration cycle that has been sucked into the first compression unit  11 , after being compressed to a high pressure in the refrigeration cycle at the first compression unit  11 , is discharged to the intermediate connection pipe  9 S. Here, the high-pressure refrigerant in the refrigeration cycle that has been discharged to the intermediate connection pipe  9 S from the first compression unit  11  is compressed to a pressure that is higher than the critical pressure of the refrigerant by a compression operation by the first compression unit  11 . The high-pressure refrigerant in the refrigeration cycle that has been discharged to the intermediate connection pipe  9 S from the first compression unit  11  branches and flows through the second intermediate-connection-pipe branch pipe  9   b S and the first intermediate-connection-pipe branch pipe  9   a S. 
     The high-pressure refrigerant in the refrigeration cycle that has flowed in the second intermediate-connection-pipe branch pipe  9   b S from the intermediate connection pipe  9 S is sent to the second heat-source-side heat exchanger  82 S that functions as a radiator of the refrigerant, and exchanges heat with, for example, outdoor air and radiates at the second heat-source-side heat exchanger  82 S. The high-pressure refrigerant in the refrigeration cycle that has radiated at the second heat-source-side heat exchanger  82 S has its pressure reduced at the second heat-source-side expansion mechanism  24   b , and is sent to the first heat-source-side expansion mechanism  24   a . The refrigerant that has been sent to the first heat-source-side expansion mechanism  24   a  has its pressure reduced at the first heat-source-side expansion mechanism  24   a , and becomes a low-pressure refrigerant in the refrigeration cycle. The low-pressure refrigerant in the refrigeration cycle whose pressure has been reduced at the first heat-source-side expansion mechanism  24   a  is sent to the first heat-source-side heat exchanger  81 . The low-pressure refrigerant in the refrigeration cycle that has been sent to the first heat-source-side heat exchanger  81  exchanges heat with, for example, outdoor air and evaporates at the first heat-source-side heat exchanger  81  that functions as an evaporator of the refrigerant. The low-pressure refrigerant in the refrigeration cycle that has evaporated at the first heat-source-side heat exchanger  81  is sucked into the first compression unit  11  again via the first heat-source-side switching mechanism  5   a , the accumulator  95 , and the suction pipe  8 . 
     On the other hand, the refrigerant that has flowed to the first intermediate-connection-pipe branch pipe  9   a S from the intermediate connection pipe  9 S flows in the bypass pipe  20 . The high-pressure refrigerant in the refrigeration cycle that has flowed in the bypass pipe  20  is sent to the use-side heat exchangers  102   a  and  102   c  via the high-low-pressure gas-refrigerant connection pipe  3  and the third heat-source-side switching mechanism  5   c . The high-pressure refrigerant in the refrigeration cycle that has been sent to the use-side heat exchangers  102   a  and  102   b  exchanges heat with, for example, indoor air and radiates at the use-side heat exchangers  102   a  and  102   b  that function as radiators of the refrigerant. The high-pressure refrigerant in the refrigeration cycle that has radiated at the use-side heat exchangers  102   a  and  102   b  is sent to the use-side expansion mechanisms  103   a  and  103   b . The high-pressure refrigerant in the refrigeration cycle that has been sent to the use-side expansion mechanisms  103   a  and  103   b  has its pressure reduced at the use-side heat expansion mechanisms  103   a  and  103   b . A part of the refrigerant whose pressure has been reduced at the use-side expansion mechanisms  103   a  and  103   b  is sent to the first heat-source-side expansion mechanism  24   a  from the liquid-refrigerant connection pipe  2 , and the remaining part is sent to the third use-side expansion mechanism  103   c  from the liquid-refrigerant connection pipe  2 . 
     The refrigerant that has been sent to the first heat-source-side expansion mechanism  24   a  has its pressure reduced and becomes a low-pressure refrigerant in a gas-liquid two-phase state in the refrigeration cycle at the first heat-source-side expansion mechanism  24   a . The low-pressure refrigerant in the refrigeration cycle whose pressure has been reduced at the first heat-source-side expansion mechanism  24   a  is sent to the first heat-source-side heat exchanger  81 . The low-pressure refrigerant in the refrigeration cycle that has evaporated at the first heat-source-side heat exchanger  81  that functions as an evaporator is sucked into the first compression unit  11  again via the first heat-source-side switching mechanism  5   a , the accumulator  95 , and the suction pipe  8 . 
     The refrigerant that has branched from the liquid-refrigerant connection pipe  2  and that has been sent to the third use-side expansion mechanism  103   c  has its pressure reduced and becomes a low-pressure refrigerant in a gas-liquid two-phase state in the refrigeration cycle at the third use-side expansion mechanism  103   c . The low-pressure refrigerant in the refrigeration cycle whose pressure has been reduced at the third use-side heat exchanger  103   c  is sent to the third use-side heat exchanger  102   c . The low-pressure refrigerant in the refrigeration cycle that has been sent to the third use-side heat exchanger  102   c  exchanges heat with, for example, indoor air and evaporates at the third use-side heat exchanger  102   c  that functions as an evaporator of the refrigerant. The low-pressure refrigerant in the refrigeration cycle that has evaporated at the third use-side heat exchanger  102   c  is sent to the first compression unit  11  via the low-pressure gas-refrigerant connection pipe  4 , the accumulator  95 , and the suction pipe  8 . In this way, the predominant heating operation, which is an example of the third S operation, is performed. 
     (8) Features of Second Embodiment 
     (8-1) 
     In an air conditioner that includes a compression mechanism including a plurality of compression units, a heat-source-side heat exchanger that is divided to function as an evaporator or a radiator, and a plurality of use-side units, and that is constituted to be capable of performing switching between a cooling operation and a heating operation for each use-side unit, increasing operation efficiency by cooling a refrigerant that is compressed by the plurality of compression units by a heat exchanger that functions as an intermediate cooler may be considered. In particular, in an air conditioner that performs a supercritical refrigeration cycle in which the pressure becomes higher than the critical pressure of a refrigerant, since the temperature of the refrigerant that is discharged from the compression mechanism is increased, reducing the temperature of the refrigerant that is discharged from the compression mechanism by cooling the refrigerant with an intermediate cooler may be considered. However, when a heat-source-side heat exchanger that is divided to function as an evaporator or a radiator is further divided to form a heat exchanger that functions as an intermediate cooler, costs are increased. In the air conditioner  1   s  according to the second embodiment of the present disclosure, the second heat-source-side heat exchanger  82 S that functions as an intermediate cooler at the time of the first operation functions as an evaporator of a refrigerant or a radiator of a refrigerant at the time of the second operation or the third operation. In this way, since one heat exchanger functions as an intermediate cooler, an evaporator, or a radiator in accordance with an instruction of the control unit  120 , it is no longer necessary to further divide a heat-source-side heat exchanger into a heat exchanger that functions as an intermediate cooler. Therefore, an increase in costs is suppressed. 
     (8-2) 
     The second heat-source-side heat exchanger  82  of the first embodiment above functions as an evaporator of a refrigerant and as an intermediate cooler of a refrigerant. In general, when a heat-source-side heat exchanger is to be divided into a radiator and an evaporator, the heat-source-side heat exchanger is divided so that the proportion of the evaporator is small. Even in the present disclosure, the second heat-source-side heat exchanger  82  that functions as an evaporator and as an intermediate cooler is divided so that the size proportion is smaller than that of the first heat-source-side heat exchanger  81 . 
     Although both a use-side heat exchanger that functions as a radiator of a refrigerant and a use-side heat exchanger that functions as an evaporator of a refrigerant exist, when an operation in which the load on a radiation side is large as a whole (predominant heating operation) is to be performed, a heat-source-side heat exchanger needs to process predominantly the load on the radiation side. In such a case, when, as in the third B operation of the first embodiment, the second heat-source-side heat exchanger  82  that has been divided so that the size proportion is smaller than that of the first heat-source-side heat exchanger  81  processes the load on the radiation side, the operation efficiency may be reduced. 
     The air conditioner  1 S according to the second embodiment of the present disclosure has a bypass pipe  20  for bypassing the second compression unit  12 . Therefore, the second heat-source-side heat exchanger  82 S functions as a radiator of a high-pressure refrigerant in a refrigeration cycle. Consequently, since the air conditioner  15  is such that the second heat-source-side heat exchanger  82 S that is smaller than the first heat-source-side heat exchanger  81  is capable of functioning as a radiator, it is possible to suppress a reduction in operation efficiency when the predominant heating operation is performed. 
     Although the embodiments of the present disclosure have been described above, it is to be understood that various changes can be made to the forms and details without departing from the spirit and the scope of the present disclosure described in the claims. The present disclosure is one that allows various disclosures to be provided by combining as appropriate a plurality of structural elements that are disclosed in each of the embodiments above. For example, some of the structural elements may be omitted from all of the structural elements that are described in each of the embodiments. Further, structural elements of different embodiments may be combined as appropriate. 
     REFERENCE SIGNS LIST 
     
         
         
           
               1 ,  1 A,  1 S air conditioner 
               2  liquid-refrigerant connection pipe 
               3  high-low-pressure gas-refrigerant connection pipe 
               4  low-pressure gas-refrigerant connection pipe 
               10  discharge pipe 
               11  first compression unit 
               12  second compression unit 
               15  compression mechanism 
               20  bypass pipe 
               21  economizer pipe 
               61  economizer heat exchanger 
               70   a ,  70   b ,  70   c  branch unit 
               81  first heat-source-side heat exchanger 
               82 ,  82 S second heat-source-side heat exchanger 
               83  third heat-source-side heat exchanger 
               100  heat-source-side unit 
               101   a ,  101   b ,  101   c  use-side unit 
               120  control unit 
           
         
       
    
     CITATION LIST 
     Patent Literature 
     
         
         PTL 1: Japanese Unexamined Patent Application Publication No. 2016-11780