Patent Publication Number: US-2022221205-A1

Title: Refrigeration cycle device

Description:
TECHNICAL FIELD 
     The present disclosure relates to a refrigeration cycle device that performs a vapor compression refrigeration cycle by using a refrigerant. 
     BACKGROUND 
     Hitherto, as described in, for example, PTL 1 (Japanese Unexamined Patent Application Publication No. 2002-107011), a refrigeration cycle device that performs a vapor compression refrigeration cycle by using a refrigerant has been known. Usually, many such refrigeration cycle devices include a heat source unit that is a heat source (for example, heat source machine A in PTL 1), and a use unit that uses heat energy that is supplied from the heat source unit (for example, indoor units B1 to Bi in PTL 1). The heat source unit and the use unit are separated from each other. In order to circulate a refrigerant between the heat source unit and the use unit, the heat source unit and the use unit are connected by a long metal connection pipe (for example, first connection pipe C and second connection pipe D in PTL 1). 
     SUMMARY 
     A refrigeration cycle device, according to one or more embodiments, includes a heat source unit that has a compressor and a heat-source-side heat exchanger; one first use unit that is installed by being separated from the heat source unit and that has a first use-side heat exchanger; a first connection flow path that connects the heat source unit and the first use unit and causes a refrigerant to flow; and a second connection flow path that connects the heat source unit and the first use unit and causes a refrigerant whose specific enthalpy is smaller than a specific enthalpy of the refrigerant that flows in the first connection flow path to flow. The heat source unit, the first use unit, the first connection flow path, and the second connection flow path constitute a refrigerant circuit that includes the compressor, the heat-source-side heat exchanger, and the first use-side heat exchanger and that repeats a vapor compression refrigeration cycle. The refrigerant circuit uses a refrigerant whose saturation pressure is 4.5 MPa or higher when a saturation temperature reaches 65° C., or a refrigerant whose critical temperature is 65° C. or lower. The first connection flow path includes a metallic first connection pipe and a metallic second connection pipe, and is formed so that a refrigerant flows from one of the heat source unit and the first use unit to both of the first connection pipe and the second connection pipe, and so that both refrigerants that each flow in a corresponding one of the first connection pipe and the second connection pipe each flow from the corresponding one of the first connection pipe and the second connection pipe to the other of the heat source unit and the first use unit. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a circuit diagram showing an example of a structure of an air conditioner according to a first embodiment. 
         FIG. 2  is a circuit diagram showing an example of a structure of an air conditioner according to a second embodiment. 
         FIG. 3  is a circuit diagram showing an example of a structure of an air conditioner according to Modification C. 
         FIG. 4  is a circuit diagram showing another example of a structure of the air conditioner according to Modification C. 
         FIG. 5  is a schematic view showing an example of a structure of an air conditioner according to Modification E. 
         FIG. 6  is a schematic view for describing brazing for installing a first connection pipe and a second connection pipe. 
         FIG. 7  is a partial enlarged perspective view of a heat source unit according to Modification F. 
         FIG. 8  is a partial enlarged view showing a first connection part and a second connection part of the heat source unit in  FIG. 7 . 
         FIG. 9A  is a perspective view showing an example of a first use unit according to Modification G. 
         FIG. 9B  is a side view of the first use unit in  FIG. 9A . 
         FIG. 10  is a partial enlarged view of the first use unit in  FIG. 9A . 
         FIG. 11  is a partial enlarged view showing an example of a first connection part and a second connection part according to Modification H. 
         FIG. 12A  is a partial enlarged view showing another example of the first connection part and the second connection part according to Modification H. 
         FIG. 12B  is a partial enlarged perspective view showing in enlarged form a part of the first connection part and the second connection part in  FIG. 12A . 
         FIG. 13  is a perspective view of a branch socket according to Modification H. 
         FIG. 14  is a plan view for describing displacement of ends of the branch socket in FIG.  13 . 
         FIG. 15A  is a schematic view showing an example of a special-purpose coil according to Modification I. 
         FIG. 15B  is a schematic view showing an example of a special-purpose straight pipe according to Modification I. 
         FIG. 16A  is a schematic view showing another example of the special-purpose coil according to Modification I. 
         FIG. 16B  is a schematic view showing another example of the special-purpose straight pipe according to Modification I. 
         FIG. 17  is a perspective view showing an example of a special-purpose socket. 
         FIG. 18  is a perspective view showing heat-insulating materials according to Modification K. 
         FIG. 19  is a perspective view showing a mounted state of a first connection pipe, a second connection pipe, and a metallic pipe in the heat-insulating materials in  FIG. 18 . 
         FIG. 20  is a diagram for describing heat-insulating materials according to Modification L. 
         FIG. 21  is a front view showing examples of the heat-insulating materials in  FIG. 20 . 
         FIG. 22  is a front view showing another example of each heat-insulating material in  FIG. 20 . 
     
    
    
     DETAILED DESCRIPTION 
     First Embodiment 
     (1) General Description 
       FIG. 1  shows an air conditioner  1  as an example of a refrigeration cycle device. The refrigeration cycle device here is a device that circulates a refrigerant and repeats a vapor compression refrigeration cycle. Although, in the embodiments below, the air conditioner  1 , which is a refrigeration cycle device, is described, the refrigeration cycle device is not limited to the air conditioner  1 . The refrigeration cycle device is applicable to, for example, a heat-pump water heater, a refrigerator, and a cooling apparatus that cools an interior. 
     The air conditioner  1  shown in  FIG. 1  includes a heat source unit  10  and a use unit  30 . The use unit  30  includes one first use unit  31 . The first use unit  31  is installed by being separated from the heat source unit  10 . The heat source unit  10  has a compressor  11  and a heat-source-side heat exchanger  12 . The first use unit  31  has a first use-side heat exchanger  41 . 
     The air conditioner  1  includes a first connection flow path  50  and a second connection flow path  80 . In a state in which the air conditioner  1  repeats the vapor compression refrigeration cycle, the specific enthalpy of a refrigerant that flows in the second connection flow path  80  is smaller than the specific enthalpy of a refrigerant that flows in the first connection flow path  50 . The first connection flow path  50  includes a metallic first connection pipe  51  and a metallic second connection pipe  52 . A refrigerant that flows in the air conditioner  1  passes through the first connection flow path  50  and the second connection flow path  80  to circulate between the heat source unit  10  and the first use unit  31 . In other words, the heat source unit  10 , the first use unit  31 , the first connection flow path  50 , and the second connection flow path  80  constitute a refrigerant circuit  100 . 
     The refrigerant circuit  100  includes the compressor  11 , the heat-source-side heat exchanger  12 , and the first use-side heat exchanger  41 . At the refrigerant circuit  100 , the vapor compression refrigeration cycle is repeated. At the refrigerant circuit  100 , a refrigerant whose saturation pressure is 4.5 MPa or higher when the saturation temperature reaches 65° C., or a refrigerant whose critical temperature is 65° C. or lower is used. Examples of refrigerants whose saturation pressure is 4.5 MPa or higher when the saturation temperature reaches 65° C. are, for example, carbon dioxide based mixed refrigerants (such as carbon dioxide+R32 and carbon dioxide+R1234ze). Examples of refrigerants whose critical temperature is 65° C. or lower are carbon dioxide, R23, and R1123. 
     The air conditioner  1  has a structure capable of switching between a heating operation and a cooling operation. In the heating operation, a refrigerant flows to both of the first connection pipe  51  and the second connection pipe  52  from the heat source unit  10 . In the heating operation, the refrigerant that flows in both of the first connection pipe  51  and the second connection pipe  52  further flows to the one first use unit  31  from the first connection pipe  51  and the second connection pipe  52 . 
     In the cooling operation, a refrigerant flows to both of the first connection pipe  51  and the second connection pipe  52  from the one first use unit  31 . In the cooling operation, both refrigerants that each flow in a corresponding one of the first connection pipe  51  and the second connection pipe  52  each further flow to the heat source unit  10  from the corresponding one of the first connection pipe  51  and the second connection pipe  52 . 
     In the air conditioner  1 , a refrigerant that flows between the heat source unit  10  and the one first use unit  31  can be divided by the first connection pipe  51  and the second connection pipe  52 . Therefore, compared with when a refrigerant that flows between the heat source unit  10  and the first use unit  31  flows in one connection pipe, it is possible to reduce the pipe diameters of the first connection pipe  51  and the second connection pipe  52 . 
     The heat source unit  10  and the first use unit  31  are each separated and transported to a construction site. The heat source unit  10  is installed, for example, on a roof of a building or an outer periphery of a house. The first use unit  31  is installed, for example, in a room inside a building or inside a house. The first connection pipe  51  and the second connection pipe  52  are bent along, for example, a wall, a floor, or a ceiling, and is disposed at a building or a house, and are connected to the heat source unit  10  and the first use unit  31 . Compared with when construction is performed with one connection pipe, it is easier to process the thin first connection pipe  51  and the thin second connection pipe  52  at a site. For example, when one thick connection pipe is used and is to be bent to install the connection pipe, it is difficult to bend the thick connection pipe, and, for example, a bent elbow needs to be brazed, as a result of which construction time is increased and thus costs are increased. In contrast, the air conditioner  1  including the thin first connection pipe  51  and the thin second connection pipe  52  is such that the pipes can sometimes be installed by a bending operation at a construction site, and can reduce construction time and improve work efficiency at the time of construction related to the first connection pipe  51  and the second connection pipe  52 . 
     (2) Detailed Structure 
     (2-1) First Connection Flow Path  50  and Second Connection Flow Path  80   
     The first connection flow path  50  shown in  FIG. 1  includes, in addition to the metallic first connection pipe  51  and the metallic second connection pipe  52 , a first branch pipe  53  and a single pipe  54 . The first connection pipe  51  and the second connection pipe  52  are main pipe parts, and the first branch pipe  53  and the single pipe  54  are pipes other than the main pipes. In other words, the first branch pipe  53  and the single pipe  54  are connection pipes for connecting the first connection pipe  51  and the second connection pipe  52 , which are main pipe parts, to the heat source unit  10 . Therefore, the first branch pipe  53  is disposed near the heat source unit  10 . The single pipe  54  is shorter than the first connection pipe  51  and the second connection pipe  52 . The length of the single pipe  54  is, for example, 1 m or less. 
     One end of the single pipe  54  is connected to a shutoff valve  22  of the heat source unit  10 . The other end of the single pipe  54  is connected to a first in and out port of the first branch pipe  53 . A second in and out port of the first branch pipe  53  is connected to one end of the first connection pipe  51 , and a third in and out port thereof is connected to the second connection pipe  52 . The other end of the first connection pipe  51  and the other end of the second connection pipe  52  are connected to the first use unit  31 . A flow path cross-sectional area of a collecting pipe formed from the first connection pipe  51  and the second connection pipe  52  is greater than or equal to 90% of a flow path cross-sectional area of the single pipe  54 . In order to obtain a suitable pressure loss at the first connection pipe  51  and the second connection pipe  52 , a flow path cross-sectional area that is the total of the flow path cross-sectional area of the first connection pipe  51  and the flow path cross-sectional area of the second connection pipe  52  may be larger than the flow path cross-sectional area of the single pipe  54 . 
     When the air conditioner  1  is performing a heating operation, a refrigerant flows toward the single pipe  54  from the shutoff valve  22 . In this case, a refrigerant that has flowed into the first branch pipe  53  from the single pipe  54  is divided at the first branch pipe  53  by the first connection pipe  51  and the second connection pipe  52 . When the air conditioner  1  is performing a cooling operation, a refrigerant flows toward the shutoff valve  22  from the single pipe  54 . 
     The first connection pipe  51  and the second connection pipe  52  may each have an outside diameter of 12.7 mm or less. The pipe type may be a soft pipe (O material of a copper pipe) that is easily bent. When the refrigerant is carbon dioxide, a ½H material of a copper pipe may have a thickness that is greater than or equal to 12% of the outside diameter thereof, an O material of a copper pipe may have a thickness that is greater than or equal to 20% of the outside diameter thereof, and stainless steel may have a thickness that is greater than or equal to 7.5% of the outside diameter thereof. The definitions of temper designations “½H” and “0” comply with JIS-H3300. When carbon dioxide is a refrigerant, that is, a refrigerant whose state becomes a supercritical state, the pressure inside the pipes tends to increase compared with that when a refrigerant that is not used in a supercritical state is used. However, as long as the pipes have the aforementioned thicknesses, even if the pipes are used with a refrigerant in a supercritical state, the pipes can be provided with sufficient pressure resistance. In this way, when carbon dioxide is a refrigerant, the thicknesses of the first connection pipe  51  and the second connection pipe  52  tend to increase. However, by keeping down the outside diameters to 12.7 mm or less, the first connection pipe  51  and the second connection pipe  52  can be bent by a bender. For example, when the outside diameters of the connection pipes become 15 mm or greater, it becomes difficult to perform a bending operation at a site, and it becomes necessary to, for example, use a special-purpose socket that is bent in an L shape. 
     The second connection flow path  80  shown in  FIG. 1  includes one metallic pipe  81 . One end of the metallic pipe  81  is connected to the shutoff valve  21 , and the other end thereof is connected to one end of an indoor expansion valve  43 . Since the specific enthalpy of a refrigerant that flows in the second connection flow path  80  is smaller than the specific enthalpy of a refrigerant that flows in the first connection flow path  50 , the flow rate of the refrigerant that flows in the second connection flow path  80  is smaller than the flow rate of the refrigerant that flows in the first connection flow path  50 . Compared with the total of the flow path cross-sectional area of the first connection pipe  51  and the flow path cross-sectional area of the second connection pipe  52  in the first connection flow path  50 , the cross-sectional area of the second connection flow path  80  may be smaller, and even one metallic pipe  81  can be made thin. Therefore, the outside diameter of both or one of the first connection pipe  51  and the second connection pipe  52  may be substantially the same as the outside diameter of the metallic pipe  81 . Here, “substantially the same” means that, for example, the outside diameter difference is within plus or minus 10%. In order to prevent a mix-up of pipes, the covering color of the metallic pipe  81  may differ from that of the connection pipe, among the first connection pipe  51  and the second connection pipe  52 , whose outside diameter is substantially the same as that of the metallic pipe  81 . For example, the covering color of the first connection flow path  50  is a warm-color-based color, and the covering color of the second connection flow path  80  is a cold-color-based color. The material of the metallic pipe  81  is, for example, copper or stainless steel. The overall length of the metallic pipe  81  is substantially the same as the overall length of the first connection pipe  51  and the overall length of the second connection pipe  52 . 
     (2-2) Heat Source Unit  10   
     The heat source unit  10  shown in  FIG. 1  includes, in addition to the compressor  11  and the heat-source-side heat exchanger  12  above, a four-way valve  13 , a first expansion valve  14 , a second expansion valve  15 , a third expansion valve  16 , a subcooling heat exchanger  17 , a receiver  18 , and the shutoff valves  21  and  22 . 
     A discharge port of the compressor  11  and a first port of the four-way valve  13  are connected to each other. One inlet/outlet of the heat-source-side heat exchanger  12  is connected to a second port of the four-way valve  13 . One end of the first expansion valve  14  is connected to the other inlet/outlet of the heat-source-side heat exchanger  12 , and one inlet/outlet of a main flow path  17   a  of the subcooling heat exchanger  17  is connected to the other end of the first expansion valve  14 . One end of the second expansion valve  15  is connected to the other inlet/outlet of the main flow path  17   a  of the subcooling heat exchanger  17 , and the shutoff valve  21  is connected to the other end of the second expansion valve  15 . One end of the third expansion valve  16  is connected to a flow path that connects the other end of the first expansion valve  14  and the one inlet/outlet of the main flow path  17   a  of the subcooling heat exchanger  17 . The other end of the third expansion valve  16  is connected to one inlet/outlet of a cooling flow path  17   b  of the subcooling heat exchanger  17 . The other inlet/outlet of the cooling flow path  17   b  is connected to a flow path that connects a third port of the four-way valve  13  and an inlet of the receiver  18 . An outlet of the receiver  18  is connected to a suction port of the compressor  11 . A fourth port of the four-way valve  13  is connected to the shutoff valve  22 . 
     The compressor  11  is capable of compressing a refrigerant sucked in from the suction port and discharging a refrigerant in a supercritical state from the discharge port. The four-way valve  13  is capable of switching between a state in which the first port and the second port communicate with each other and the third port and the fourth port communicate with each other (state show by solid lines) and a state in which the first port and the fourth port communicate with each other and the second port and the third port communicate with each other (state shown by broken lines). The heat-source-side heat exchanger  12 , for example, causes heat to be exchanged between outdoor air and a refrigerant. The first expansion valve  14 , the second expansion valve  15 , and the third expansion valve  16  are constituted so that their opening degrees are changeable. The first expansion valve  14 , the second expansion valve  15 , and the third expansion valve  16  make it possible to adjust the degree of decompression/expansion as a result of changing the opening degrees. The first expansion valve  14 , the second expansion valve  15 , and the third expansion valve  16 , for example, in a fully open state, do not perform a decompression/expansion operation and simply pass a refrigerant therethrough. The subcooling heat exchanger  17  causes heat to be exchanged between a refrigerant that flows in the main flow path  17   a  and a refrigerant that flows in the cooling flow path  17   b . The receiver  18  can accumulate a refrigerant. 
     (2-3) First Use Unit  31   
     The first use unit  31  shown in  FIG. 1  includes, in addition to the first use-side heat exchanger  41  above, the indoor expansion valve  43 , a first on-off valve  44 , and a second on-off valve  45 . The one end of the indoor expansion valve  43  is connected to the other end of the metallic pipe  81 , and the other end of the indoor expansion valve  43  is connected one inlet/outlet of the first use-side heat exchanger  41 . One end of the first of-off valve  44  and one end of the second on-off valve  45  are connected to the other inlet/outlet of the first use-side heat exchanger  41 . The first use-side heat exchanger  41 , for example, causes heat to be exchanged between indoor air and a refrigerant. The indoor expansion valve  43  is constituted so that its opening degree is changeable. The indoor expansion valve  43  makes it possible to adjust the degree of decompression/expansion as a result of changing the opening degree, and, for example, in a fully open state, does not perform a decompression/expansion operation and simply passes a refrigerant therethrough. The first on-off valve  44  and the second on-off valve  45  are capable of opening and closing a flow path. 
     (3) Overall Operation 
     The air conditioner  1  shown in  FIG. 1  is constituted to switch between a cooling operation and a heating operation by switching a flow path by the four-way valve  13 . At the time of the cooling operation, the first port and the second port of the four-way valve communicate with each other and the third port and the fourth port of the four-way valve  13  communicate with each other. In both the cooling operation and the heating operation, the shutoff valves  21  and  22  are open. 
     (3-1) Heating Operation 
     In a normal heating operation mode, the first on-off valve  44  and the second on-off valve  45  are in an open state. When a refrigerant is carbon dioxide, at the time of the heating operation, the compressor  11  compresses the refrigerant to a supercritical state and discharges the refrigerant. The high-temperature, high-pressure refrigerant in the supercritical state discharged from the compressor  11  passes through the first port and the fourth port of the four-way valve  13 , passes through the shutoff valve  22 , and flows into the first connection flow path  50 . At the first connection flow path  50 , the refrigerant in the supercritical state flows into the first branch pipe  53  from the single pipe  54 . At the branch pipe  53 , the refrigerant is split into a refrigerant that flows in the first connection pipe  51  and a refrigerant that flows in the second connection pipe  52 . The refrigerants that each flow in a corresponding one of both of the first connection pipe  51  and the second connection pipe  52  flow into the first use-side heat exchanger  41  via a corresponding one of the first on-off valve  44  and the second on-off valve  45 . The refrigerant that has entered the first use-side heat exchanger  41  exchanges heat with indoor air at the first use-side heat exchanger  41  to apply heat to the indoor air. At this time, the first use-side heat exchanger  41  functions as a heat dissipater. The heated indoor air heats the interior of a room. The refrigerant in the supercritical state that has exited from the first use-side heat exchanger  41  is decompressed and expanded at the indoor expansion valve  43 , and flows into the heat source unit  10  via the second connection flow path  80  and the shutoff valve  21 . 
     The second expansion valve of the heat source unit  10  is in a fully open state. The refrigerant that has passed through the second expansion valve  15  flows into the main flow path  17   a  of the subcooling heat exchanger  17 . The refrigerant that has flowed into the main flow path  17   a  of the subcooling heat exchanger  17  is divided into a refrigerant that flows into the first expansion valve  14  from the main flow path  17   a  and a refrigerant that flows into the cooling flow path  17   b  via the third expansion valve  16 . The refrigerant that flows in the cooling flow path  17   b , by being decompressed and expanded at the third expansion valve  16 , has a low temperature, and takes away heat from the refrigerant that flows in the main flow path  17   a . The refrigerant that has taken away heat at the cooling flow path  17   b  flows into the receiver  18 . The refrigerant that has flowed into the first expansion valve  14  from the main flow path  17   a  is decompressed and expanded and becomes a low-temperature, low-pressure refrigerant at the first expansion valve  14 . The low-temperature, low-pressure refrigerant exchanges heat with outdoor air or the like and obtains heat from the outdoor air at the first use-side heat exchanger  41 . The refrigerant that has obtained heat and that has been converted into a gas flows into the receiver  18 . The gaseous refrigerant in a refrigerant that is stored in the receiver  18  is sucked in from the suction port of the compressor  11 . 
     (3-2) Cooling Operation 
     In a normal cooling operation mode, the first on-off valve  44  and the second on-off valve  45  are in an open state. When a refrigerant is carbon dioxide, at the time of the cooling operation, the compressor  11  compresses the refrigerant to a supercritical state and discharges the refrigerant. The refrigerant in the supercritical state discharged from the compressor  11  dissipates heat at the heat-source-side heat exchanger  12 . The first expansion valve  14  is in a fully open state. The refrigerant that has passed through the first expansion valve  14  is divided into a refrigerant that flows into the main flow path  17   a  of the subcooling heat exchanger  17  and a refrigerant that flows into the cooling flow path  17   b  via the third expansion valve  16 . Since the refrigerant that flows in the cooling flow path  17   b , by being decompressed and expanded at the third expansion valve  16 , has a low temperature, heat is taken away from the refrigerant that flows in the main flow path  17   a . The refrigerant that has passed through the main flow path  17   a  of the subcooling heat exchanger  17  is decompressed and expanded and becomes a liquid refrigerant in a subcooled state at the second expansion valve  15 . 
     The refrigerant in the subcooled state that has flowed into the indoor expansion valve  43  via the second connection flow path  80  and the shutoff valve  21  from the second expansion valve  15  is decompressed and expanded and becomes a low-temperature, low-pressure refrigerant at the indoor expansion valve  43 . The low-temperature, low-pressure refrigerant flows into the first use-side heat exchanger  41  from the indoor expansion valve  43 . At the first use-side heat exchanger  41 , the refrigerant exchanges heat with indoor air or the like and takes away heat from the indoor air. The air whose heat has been taken away cools the interior of a room. The refrigerant that has obtained heat and that has been converted into a gas flows into both of the first connection pipe  51  and the second connection pipe  52  from the first use-side heat exchanger  41 . The refrigerants that have each flowed into a corresponding one of both of the first connection pipe  51  and the second connection pipe  52  merge at the first branch pipe  53 , and the merged refrigerant passes through the single pipe  54  and the shutoff valve  22  and flows into the heat source unit  10 . The refrigerant that has passed through the shutoff valve  22  flows into the receiver  18  via the fourth port and the third port of the four-way valve  13 . The gaseous refrigerant in a refrigerant that is stored in the receiver  18  is sucked in from the suction port of the compressor  11 . The refrigerant that has flowed out of the cooling flow path  17   b  flows into the receiver  18 . 
     (3-3) Oil-Return Operation Mode 
     In an oil-return operation mode, the air conditioner  1  closes one of the first on-off valve  44  and the second on-off valve  45 , and causes a refrigerant to flow in one of the first connection pipe  51  and the second connection pipe  52 . For example, by closing the second on-off valve  45  and causing a refrigerant to flow in only the first connection pipe  51 , the flow velocity of the flow of the refrigerant can be made higher than that when the refrigerant is caused to flow in both of the first connection pipe  51  and the second connection pipe  52 . Since the flow velocity is increased, oil in the first connection pipe  51  can be returned in a short time. Even when, in order to return oil from the second connection pipe  52 , an oil-return operation, in which a refrigerant is caused to flow in only the second connection pipe  52  by closing the first on-off valve  44 , is performed, the same effects are realized. Since a liquid refrigerant does not flow in the first connection pipe  51  and the second connection pipe  52 , the effect of quickly returning oil by increasing the flow velocity of the refrigerant is noticeable. 
     Second Embodiment 
     (4) General Description 
     As shown in  FIG. 1 , the air conditioner  1  according to the first embodiment above has been described as one in which the use unit  30  includes one first use unit  31 . In contrast, an air conditioner  1  shown in  FIG. 2  includes a plurality of use units  30 . 
     The air conditioner  1  shown in  FIG. 2  includes a heat source unit  10  and the plurality of use units  30 . The plurality of use units  30  include first use units  31  and second use units  32 . In order to simplify the illustration,  FIG. 2  shows the air conditioner  1  including two use units  30  (one first use unit  31  and one second use unit  32 ). However, the plurality of use units of the air conditioner  1  are not limited to two use units  30 . The air conditioner  1  can be constituted to include three or more use units  30 . 
     The first use unit  31  and the second use unit  32  are each installed by being separated from the heat source unit  10 . The heat source unit  10  has a compressor  11  and a heat-source-side heat exchanger  12 . The first use unit  31  has a first use-side heat exchanger  41 . The second use unit  32  has a second use-side heat exchanger  42 . A general description of a first connection flow path  50  and a second connection flow path  80  of the air conditioner  1  of the second embodiment is the same as that of the first embodiment and thus is not given. 
     The refrigerant circuit  100  includes the compressor  11 , the heat-source-side heat exchanger  12 , the first use-side heat exchanger  41 , and the second use-side heat exchanger  42 . Even in the refrigerant circuit  100  of the second embodiment, a refrigerant that is of the same type as the refrigerant that is used in the refrigerant circuit  100  of the first embodiment is used. 
     The air conditioner  1  has a structure capable of switching between a heating operation and a cooling operation. In the heating operation, a refrigerant flows to both of the first connection pipe  51  and the second connection pipe  52  from the heat source unit  10 . In the heating operation, the refrigerant that flows in both of the first connection pipe  51  and the second connection pipe  52  further flows to the one first use unit  31  from the first connection pipe  51  and the second connection pipe  52 . In addition, the refrigerant that flows in both of the first connection pipe  51  and the second connection pipe  52  flows to the one second use unit  32  from the first connection pipe  51  and the second connection pipe  52 . 
     In the cooling operation, a refrigerant flows to both of the first connection pipe  51  and the second connection pipe  52  from the one first use unit  31 . In addition, the refrigerant flows to both of the first connection pipe  51  and the second connection pipe  52  from the one second use unit  32 . In the cooling operation, both refrigerants that each flow in a corresponding one of the first connection pipe  51  and the second connection pipe  52  each further flow to the heat source unit  10  from the corresponding one of the first connection pipe  51  and the second connection pipe  52 . 
     In the air conditioner  1 , a refrigerant that flows between the heat source unit  10  and each of the one first use unit  31  and the one second use unit  32  can be divided by the first connection pipe  51  and the second connection pipe  52 . Therefore, compared with when a refrigerant that flows between the heat source unit  10  and each of the first use unit  31  and the second use unit  32  is caused to flow by using one connection pipe, it is possible to reduce the pipe diameters of the first connection pipe  51  and the second connection pipe  52 . 
     (5) Detailed Structure 
     (5-1) First Connection Flow Path  50  and Second Connection Flow Path  80   
     Since the second connection flow path  80  of the second embodiment shown in  FIG. 2  can be constituted similarly to the second connection flow path  80  of the first embodiment shown in  FIG. 1 , a description thereof is not given. 
     The first connection flow path  50  shown in  FIG. 2  includes, in addition to the metallic first connection pipe  51  and the metallic second connection pipe  52  above, a first branch pipe  53 , a single pipe  54 , a second branch pipe  55 , a third branch pipe  56 , and joints  61 ,  62 ,  63 , and  64 . Since the first connection pipe  51 , the second connection pipe  52 , the first branch pipe  53 , and the single pipe  54  of the first connection flow path  50  of the second embodiment have been described in the first embodiment, they are not described here. 
     The other end of each of the first connection pipe  51  and the second connection pipe  52  communicates with the first use unit  31 . The other end of each of the first connection pipe  51  and the second connection pipe  52  also communicates with the second use unit  32 . In order to perform such a connection, the second branch pipe  55 , the third branch pipe  56 , and the joints  61 ,  62 ,  63 , and  64  are interposed between the other end of each of the first connection pipe  51  and the second connection pipe  52  and each of the first use unit  31  and the second use unit  32 . Here, although the second branch pipe  55 , the third branch pipe  56 , and the joints  61 ,  62 ,  63 , and  64  are constituted by separate components, several of them may be formed all at once as one component. For example, the second branch pipe  55  and the third branch pipe  56  may be formed all at once as one component. The joints  61  to  64  are short metallic pipes, such as short copper pipes, and are shorter than the first connection pipe  51  and the second connection pipe  52 . 
     The other end of the first connection pipe  51  is connected to a first in and out port of the second branch pipe  55 . The other end of the second connection pipe  52  is connected to a first in and out port of the third branch pipe  56 . A second in and out port of the second branch pipe  55  and the other end of the first on-off valve  44  of the first use unit  31  are connected to each other by the joint  61 , and a second in and out port of the third branch pipe  56  and the other end of the second on-off valve  45  of the first use unit  31  are connected to each other by the joint  62 . A third in and out port of the second branch pipe  55  and the other end of a first on-off valve  47  of the second use unit  32  are connected to each other by the joint  63 , and a third in and out port of the third branch pipe  56  and the other end of a second on-off valve  48  of the second use unit  32  are connected to each other by the joint  64 . 
     (5-2) Heat Source Unit  10   
     A structure of the heat source unit  10  of the second embodiment can be the same as the structure of the heat source unit  10  of the first embodiment. 
     (5-3) First Use Unit  31  and Second Use Unit  32   
     The second use unit  32  shown in  FIG. 2  has the same structure as the first use unit  31 . In other words, the second use unit  32  includes the second use-side heat exchanger  42 , an indoor expansion valve  46 , the first on-off valve  47 , and the second on-off valve  48 , which correspond to the first use-side heat exchanger  41 , the indoor expansion valve  43 , the first on-off valve  44 , and the second on-off valve  45  of the first use unit  31 , respectively. Therefore, here, the second use unit  32  is not described. One end of the indoor expansion valve  46  of the second use unit  32  is also connected to the other end of a metallic pipe  81  of the second connection flow path  80 . Note that branch pipes and the like are also provided in the second connection flow path  80 . 
     (6) Operation of Air Conditioner  1   
     Similarly to the air conditioner  1  shown in  FIG. 1 , the air conditioner  1  shown in  FIG. 2  is also constituted to switch between a cooling operation and a heating operation by switching a flow path by a four-way valve  13 . The air conditioner  1  shown in  FIG. 2  is capable of performing a cooling operation and a heating operation by using not only the first use unit  31  but also the second use unit  32 . 
     When the air conditioner  1  performs a heating operation by using the second use unit  32 , for example, the air conditioner  1  performs control so that a refrigerant does not flow in the first use unit  31  by closing the first on-off valve  44  and the second on-off valve  45  of the first use unit  31 . When the air conditioner  1  performs a cooling operation by using the second use unit  32 , for example, the air conditioner  1  performs control so that a refrigerant does not flow in the first use unit  31  by closing the indoor expansion valve  43  of the first use unit  31 . 
     When the air conditioner  1  performs a heating operation by using the first use unit  31 , for example, the air conditioner  1  performs control so that a refrigerant does not flow in the second use unit  32  by closing the first on-off valve  47  and the second on-off valve  48  of the second use unit  32 . When the air conditioner  1  performs a cooling operation by using the first use unit  31 , for example, the air conditioner  1  performs control so that a refrigerant does not flow in the second use unit  32  by closing the indoor expansion valve  46  of the second use unit  32 . 
     The operations of the air conditioner  1  when performing a cooling operation or a heating operation by using the second use unit  32  or both of the first use unit  31  and the second use unit are also the same as the operations of the air conditioner  1  when performing a cooling operation or a heating operation by using the first use unit  31 . Therefore, here, descriptions thereof are not given. 
     In an oil-return operation mode, the air conditioner  1  closes one pair of a pair of the first on-off valves  44  and  47  and a pair of the second on-off valves  45  and  48 , and causes a refrigerant to flow in one of the first connection pipe  51  and the second connection pipe  52 . For example, by closing the second on-off valves  45  and  48  and causing a refrigerant to flow in only the first connection pipe  51 , the flow velocity of the flow of the refrigerant can be made higher than that when the refrigerant is caused to flow in both of the first connection pipe  51  and the second connection pipe  52 . Since the flow velocity is increased, oil in the first connection pipe  51  can be returned in a short time. Even when, in order to return oil from the second connection pipe  52 , an oil-return operation, in which a refrigerant is caused to flow in only the second connection pipe  52  by closing the first on-off valves  44  and  47 , is performed, the same effects are realized. 
     (7) Modifications 
     (7-1) Modification A 
     In the first embodiment and the second embodiment, a case in which a refrigerant is carbon dioxide and the state of the refrigerant when discharged from the compressor is a supercritical state has been described. However, such a refrigerant is not limited to carbon dioxide. A refrigerant whose critical temperature is 65° C. or lower is used as such a refrigerant. Examples of such a refrigerant other than carbon dioxide are R23 and R1123. 
     (7-2) Modification B 
     In the first embodiment and the second embodiment, the air conditioner  1  using a refrigerant whose critical temperature is 65° C. or lower has been described. However, the refrigerant that is used in the air conditioner  1  is not limited to a refrigerant whose critical temperature is 65° C. or lower, and may be a refrigerant whose saturation pressure is 4.5 MPa or higher when the saturation temperature reaches 65° C. When such a refrigerant is used, at the time of a heating operation, the state of the refrigerant that flows in the first connection pipe  51  and the second connection pipe  52  is a gaseous state. Although the refrigerant that flows in the first connection pipe  51  and the second connection pipe  52  is not in a supercritical state as it is in the first embodiment and the second embodiment, the pressure is very high at 4.5 MPa or higher. In order to withstand such a high pressure, as with the case in which the refrigerant is carbon dioxide, if an attempt is made to install a pipe by using one connection pipe, the thickness of the pipe must be increased, as a result of which construction becomes difficult. A refrigeration cycle device using a refrigerant whose saturation pressure is 4.5 MPa or higher when the saturation temperature reaches 65° C. provides effects that are the same as those of the air conditioners  1  of the first embodiment and the second embodiment by separating the first connection pipe  51  and the second connection pipe  52  as in the first embodiment and the second embodiment. 
     (7-3) Modification C 
     In the first embodiment and the second embodiment above, in a heating operation, refrigerants that flow in the first connection pipe  51  and the second connection pipe  52  merge at each of the first use unit  31  and the second use unit  32 . In a cooling operation, the refrigerant that has been split in each of the first use unit  31  and the second use unit  32  flows as refrigerants in a corresponding one of the first connection pipe  51  and the second connection pipe  52 . 
     However, as shown in  FIGS. 3 and 4 , refrigerants may merge or a refrigerant may be split outside the first use unit  31  or the second use unit  32 . When such a structure is formed, an air conditioner  1  in  FIG. 3  includes a fourth branch pipe  71  and a joint  65 . A first in and out port of the fourth branch pipe  71  and the other inlet/outlet of the first use-side heat exchanger  41  are connected to each other by the joint  65 . The other end of the first connection pipe  51  is connected to a second in and out port of the fourth branch pipe  71 , and the other end of the second connection pipe  52  is connected to a third in and out port of the fourth branch pipe  71 . 
     In a heating operation, a refrigerant flows into both of the first connection pipe  51  and the second connection pipe  52  as refrigerants from the heat source unit  10 , and the refrigerants that each flow in a corresponding one of both of the first connection pipe  51  and the second connection pipe  52  merge at the fourth branch pipe  71 . The merged refrigerant formed at the fourth branch pipe  71  flows into the first use unit  31  via the joint  65 . In a cooling operation, a refrigerant flows to the fourth branch pipe  71  via the joint  65  from the first use unit  31 . At the fourth branch pipe  71 , the refrigerant that has flowed out of the first use unit  31  is split into refrigerants, and the refrigerants flow into a corresponding one of both of the first connection pipe  51  and the second connection pipe  52 . In the cooling operation, both refrigerants that each flow in a corresponding one of the first connection pipe  51  and the second connection pipe  52  each further flow to the heat source unit  10  from the corresponding one of the first connection pipe  51  and the second connection pipe  52 . 
     An air conditioner  1  in  FIG. 4  includes a fourth branch pipe  71 , a fifth branch pipe  72 , joints  65  and  66 , and refrigerant pipes  57   a ,  57   b ,  58   a , and  58   b . A first in and out port of the fourth branch pipe  71  and the other inlet/outlet of the first use-side heat exchanger  41  are connected to each other by the joint  65 . A first in and out port of the fifth branch pipe  72  and the other inlet/outlet of the second use-side heat exchanger  42  are connected to each other by the joint  66 . A second in and out port of the second branch pipe  55  is connected to a second in and out port of the fourth branch pipe  71  by the refrigerant pipe  57   a , and a second in and out port of the third branch pipe  56  is connected to a third in and out port of the fourth branch pipe  71  by the refrigerant pipe  58   a . A third in and out port of the second branch pipe  55  is connected to a second in and out port of the fifth branch pipe  72  by the refrigerant pipe  57   b , and a third in and out port of the third branch pipe  56  is connected to a third in and out port of the fifth branch pipe  72  by the refrigerant pipe  58   b . The joints  65  and  66  and the refrigerant pipes  57   a ,  57   b ,  58   a , and  58   b  are short metallic pipes, such as short copper pipes, and are shorter than the first connection pipe  51  and the second connection pipe  52 . Note that, in the air conditioners  1  in  FIGS. 3 and 4 , the fourth branch pipe  71  and the fifth branch pipe  72  may be directly connected to a corresponding one of the first use unit  31  and the second use unit  32  without using a corresponding one of the joints  65  and  66 . 
     In a heating operation, a refrigerant flows to both of the first connection pipe  51  and the second connection pipe  52  from the heat source unit  10 . The refrigerant that flows in the first connection pipe  51  is split at the second branch pipe  55 . The refrigerant that flows in the second connection pipe  52  is split at the third branch pipe  56 . A part of the refrigerant that has been split off at the second branch pipe  55  and a part of the refrigerant that has been split off at the third branch pipe  56  merge at the fourth branch pipe  71 , and the merged refrigerant flows in the first use unit  31 . The remaining part of the refrigerant that has been split off at the second branch pipe  55  and the remaining part of the refrigerant that has been split off at the third branch pipe  56  merge at the fifth branch pipe  72 , and the merged refrigerant flows in the second use unit  32 . 
     In a cooling operation, a refrigerant flows to the fourth branch pipe  71  via the joint  65  from the first use unit  31 . A refrigerant flows to the fifth branch pipe  72  via the joint  66  from the second use unit  32 . At the fourth branch pipe  71 , the refrigerant that has flowed out of the first use unit  31  is split into parts. The parts of the split refrigerant each flow into a corresponding one of the second branch pipe  55  and third branch pipe  56  via a corresponding one of the refrigerant pipes  57   a  and  58   a . At the fifth branch pipe  72 , the refrigerant that has flowed out of the second use unit  32  is split into parts. The parts of the split refrigerant each flow into a corresponding one of the second branch pipe  55  and third branch pipe  56  via a corresponding one of the refrigerant pipes  57   b  and  58   b . A part of the refrigerant that has flowed out of the first use unit  31  and a part of the refrigerant that has flowed out of the second use unit  32  merge at the second branch pipe  55 , and the merged refrigerant flows in the first connection pipe  51 . The remaining part of the refrigerant that has flowed out of the first use unit  31  and the remaining part of the refrigerant that has flowed out of the second use unit  32  merge at the third branch pipe  56 , and the merged refrigerant flows in the second connection pipe  52 . In other words, the refrigerant that has flowed out of the first use unit  31  flows in both of the first connection pipe  51  and the second connection pipe  52  via the fourth branch pipe  71 , the second branch pipe  55 , and the third branch pipe  56 . The refrigerant that has flowed out of the second use unit  32  flows in both of the first connection pipe  51  and the second connection pipe  52  via the fifth branch pipe  72 , the second branch pipe  55 , and the third branch pipe  56 . 
     (7-4) Modification D 
     In the first embodiment, the second embodiment, and the modifications above, the main pipes of the first connection path  50  are described as being constituted by two connection pipes, that is, the first connection pipe  51  and the second connection pipe  52 . However, the main pipe parts of the first connection flow path  50  are not limited to two main pipe parts and may be three or more main pipe parts. 
     (7-5) Modification E 
     In the embodiments and the modifications above, the single pipe  54  has been described as being shorter than the first connection pipe  51  and the second connection pipe  52  and as having a length of, for example, 1 m or less. However, the single pipe  54  may be longer than the first connection pipe  51  and the second connection pipe  52  and may have a length that is, for example, greater than 1 m. 
     For example, as shown in  FIG. 5 , the heat source unit  10  is installed on a roof of a building BL. A first use unit  31 , a second use unit  32 , a third use unit  33 , and the other use units (a fourth use unit and units in the order after the fourth use unit are not shown) are disposed on each of a first floor G 1  to a sixth floor G 6 . Here, for simplifying the description, the structures of and pipe installations with respect to the first use unit  31 , the second use unit  32 , the third use unit  33 , and the other use units on each of the first floor G 1  to the sixth floor G 6  are described as being the same. In  FIG. 5 , a part of the second connection flow path  80  is not shown. 
     The single pipe  54  that is connected to the heat source unit  10  extends to the first floor G 1  from the roof. A first connection pipe  51  and a second connection pipe  52  are installed so as to be separated from the single pipe  54  on each of the first floor G 1 , the second floor G 2 , the third floor G 3 , the fourth floor G 4 , the fifth floor G 5 , and the sixth floor G 6 . 
     When a flow of a refrigerant at the time of a heating operation is taken as an example, for example, a refrigerant discharged from one heat source unit  10  passes along the single pipe  54  (vertical connection pipe) and is split at a first branch pipe  53  on the sixth floor G 6 . 
     On the sixth floor G 6 , as shown by symbols, the refrigerant that has been split at the first branch pipe  53  flows in the first connection pipe  51  and the second connection pipe  52  that are installed on the sixth floor G 6 , and is split by a second branch pipe  91  and a third branch pipe  92  on the sixth floor  6 G. A part of the refrigerant that has been split off at the second branch pipe  91  and a part of the refrigerant that has been split off at the third branch pipe  92  merge at a fourth branch pipe  71  that is connected to the first use unit  31  on the sixth floor G 6 , and the merged refrigerant flows in the first use unit  31  on the sixth floor G 6 . Here, although a description is given with regard to only the first use unit  31  on the sixth floor G 6 , a refrigerant also flows to the first use unit  31  on each of the first floor G 1  to the fifth floor G 5  via a first branch pipe  53 , a second branch pipe  91 , a third branch pipe  92 , and a fourth branch pipe  71  as in the case of the first use unit  31  on the sixth floor G 6 . 
     On the fourth floor G 4 , as shown by symbols, the refrigerant that has been split at a first branch pipe  53  flows in the first connection pipe  51  and the second connection pipe  52  that are installed on the fourth floor G 4 , and is split by a second branch pipe  93  and a third branch pipe  94  on the fourth floor G 4 . A part of the refrigerant that has been split off at the second branch pipe  93  and a part of the refrigerant that has been split off at the third branch pipe  94  merge at a fifth branch pipe  72  that is connected to the second use unit  32  on the fourth floor G 4 , and the merged refrigerant flows in the second use unit  32  on the fourth floor G 4 . Here, although a description is given with regard to only the second use unit  32  on the fourth floor G 4 , a refrigerant also flows to the second use unit  32  on each of the first floor G 1  to the third floor G 3 , the fifth floor G 5 , and the sixth floor G 6  via a first branch pipe  53 , a second branch pipe  93 , a third branch pipe  94 , and a fifth branch pipe  72  as in the case of the second use unit  32  on the fourth floor G 4 . 
     On the second floor G 2 , as shown by symbols, the refrigerant that has been split at a first branch pipe  53  flows in the first connection pipe  51  and the second connection pipe  52  that are installed on the second floor G 2 , and is split by a second branch pipe  95  and a third branch pipe  96  on the second floor G 2 . A part of the refrigerant that has been split off at the second branch pipe  95  and a part of the refrigerant that has been split off at the third branch pipe  96  merge at a sixth branch pipe  73  that is connected to the third use unit  33  on the second floor G 2 , and the merged refrigerant flows in the third use unit  33  on the second floor G 2 . Here, although a description is given with regard to only the third use unit  33  on the second floor G 2 , a refrigerant also flows to the third use unit  33  on each of the first floor G 1  and the third floor G 3  to the sixth floor G 6  via a first branch pipe  53 , a second branch pipe  95 , a third branch pipe  96 , and a sixth branch pipe  73  as in the case of the third use unit  33  on the second floor G 2 . Note that, since the structure of each third use unit  33  is the same as the structures of each first use unit  31  and each second use unit  32 , here, the structure of each third use unit  33  is not described. 
     Note that, in order to make it possible to perform sophisticated pipe installations, an O material may be used for the first connection pipe  51  and the second connection pipe  52  on each of the floors G 1 , G 2 , G 3 , G 4 , G 5 , and G 6 . 
     (7-6) Modification F 
       FIG. 6  schematically shows an example of a method of connecting the shutoff valve  22  of the heat source unit  10  shown in  FIG. 4  to the first branch pipe  53 , the first connection pipe  51 , and the second connection pipe  52 . In the example shown in  FIG. 6 , the first branch pipe  53  has the single pipe  54 . In this case, a site worker performs brazing on three portions indicated by thick arrows in  FIG. 6  at the place of installation of the heat source unit  10 . When the single pipe  54  is prepared separately from the first branch pipe  53 , the site worker needs to perform brazing on four portions. 
     Therefore, an air conditioner  1  according to Modification F includes a heat source unit shown in  FIG. 7 . The heat source unit  10  in  FIG. 7  has a heat-source-unit casing  10   c . The compressor  11  and the heat-source-side heat exchanger  12  shown in  FIG. 4  are accommodated in the heat-source-unit casing  10   c . As shown in  FIGS. 7 and 8 , the heat source unit  10  has a first connection part  10   a  that is connected to the first connection pipe  51 , and a second connection part  10   b  that is connected to the second connection pipe  52 . The first connection part  10   a  and the second connection part  10   b  are two separated connection portions extending from the shutoff valve  22 . It is possible to say that a structure corresponding to the first branch pipe  53  having the first connection part  10   a  and the second connection part  10   b  and to the single pipe  54  is connected to the shutoff valve  22  and is accommodated in the heat-source-unit casing  10   c . Therefore, a refrigerant that flows via the shutoff valve  22  flows in each of the first connection part  10   a  and the second connection part  10   b . The specific enthalpy of the refrigerant that flows via the shutoff valve  22  is larger than the specific enthalpy of a refrigerant that flows via the shutoff valve  21 . The first connection part  10   a  and the second connection part  10   b  are each disposed in the heat-source-unit casing  10   c . A third connection part  10   d  that communicates with the shutoff valve  21  is disposed in the heat-source-unit casing  10   c . The third connection part  10   d  is connected to the metallic pipe  81  of the second connection flow path  80 . The first connection part  10   a , the second connection part  10   b , and the third connection part  10   d  are covered and protected by the heat-source-unit casing  10   c  so as not to be directly exposed to wind and rain. In order to facilitate connection of the first connection pipe  51  and the second connection pipe  52 , the first connection part  10   a , the second connection part  10   b , and the third connection part  10   d  are disposed near an opening  10   e  of the heat-source-unit casing  10   c.    
     (7-7) Modification G 
       FIGS. 9A and 9B  shows an indoor unit that is installed on a ceiling with the first use unit  31  shown in  FIG. 4  being used as an example. An air conditioner  1  according to Modification G includes a first use unit  31  shown in  FIGS. 9A and 9B . The first use unit  31  in  FIGS. 9A and 9B  has a first-use-unit casing  31   c . The first use-side heat exchanger  41  shown in  FIG. 4  is accommodated in the first-use-unit casing  31   c . The first use unit  31  sucks in indoor air from a lower-side suction port  31   s  facing the interior of a room, and, after heat exchange at the first use-side heat exchanger  41  disposed in the interior, blows out conditioned air from a blow-out port  31   t . As shown in  FIG. 10 , the first use unit  31  has a first connection part  31   a  that is connected to the first connection pipe  51 , and a second connection part  31   b  that is connected to the second connection pipe  52 . The first connection part  31   a  and the second connection part  31   b  are two separated connection portions extending from the other inlet/outlet of the first use-side heat exchanger  41 . It is possible to say that a structure corresponding to the fourth branch pipe  71  having the first connection part  31   a  and the second connection part  31   b  and to the joint  65  is connected to the first use-side heat exchanger  41  and is accommodated in the first-use-unit casing  31   c . Therefore, a refrigerant that flows via the other inlet/outlet of the first use-side heat exchanger  41  flows in each of the first connection part  31   a  and the second connection part  31   b . The specific enthalpy of the refrigerant that flows via the other inlet/outlet of the first use-side heat exchanger  41  is larger than the specific enthalpy of a refrigerant that flows via one inlet/outlet of the first use-side heat exchanger  41  that is connected to the indoor expansion valve  43 . The first connection part  31   a  and the second connection part  31   b  are each disposed in the first-use-unit casing  31   c.    
     Since, unlike the heat source unit  10  that is disposed outdoors, the first use unit  31  is installed indoors, the first connection part  31   a  and the second connection part  31   b  may be disposed outside the first-use-unit casing  31   c . A third connection part  31   d  that communicates with the indoor expansion valve  43  may be disposed in the first-use-unit casing  31   c . The third connection part  31   d  is connected to the metallic pipe  81  of the second connection flow path  80 . At the first use unit  31 , the third connection part  31   d  may be disposed outside the first-use-unit casing  31   c.    
     Note that the structure of the heat source unit  10  of Modification F and the structure of the first use unit  31  of Modification G may be simultaneously applied to one air conditioner  1 . 
     (7-8) Modification H 
       FIG. 11  shows another form of each of the first connection part  10   a  and the second connection part  10   b  shown in  FIG. 7  and another form of each of the first connection part  31   a  and the second connection part  31   b  shown in  FIG. 10 . The structural concept of the other form of each of the first connection part  10   a  and the second connection part  10   b  and the structural concept of the other form of each of the first connection part  31   a  and the second connection part  31   b  are the same. Therefore, in the description below, the other form of each of the first connection part  10   a  and the second connection part  10   b  is described, and the other form of the first connection part  31   a  and the second connection part  31   b  is not described. 
     The first connection part  10   a  and the second connection part  10   b  have an expanded first connection end  51   a  and an expanded second connection end  52   a , respectively. The inside diameter of the expanded first connection end  51   a  is substantially equal to the outside diameters of the first connection parts  10   a  and  31   a , and the inside diameter of the expanded second connection end  52   a  is substantially equal to the outside diameters of the second connection parts  10   b  and  31   b . At the time of brazing, in order to reduce the amount of heat that escapes to an adjacent connection part, the first connection parts  10   a  and  31   a  and the corresponding second connection parts  10   b  and  31   b  are offset from each other in a pipe diameter direction of the first connection pipe  51  by a first prescribed value mr 1  or more. In other words, a displacement amount di 1  between the first connection parts  10   a  and  31   a  and the corresponding second connection parts  10   b  and  31   b  is greater than or equal to the prescribed value mr 1  in the pipe diameter direction. In the description above, the displacement amount di 1  in the pipe diameter direction has been described as a displacement amount between the first connection parts  10   a  and  31   a  and the corresponding second connection parts  10   b  and  31   b . However, from a different point of view, the first connection end  51   a  of the first connection pipe  51  and the second connection end  52   a  of the second connection pipe  52  may be understood as being disposed by the displacement amount di 1  greater than or equal to the prescribed value mr 1  in the pipe diameter direction of the first connection pipe  51 . 
       FIGS. 12A and 12B  show another form of each of the first connection part  10   a  and the second connection part  10   b  shown in  FIG. 7  and another form of each of the first connection part  31   a  and the second connection part  31   b  shown in  FIG. 10 . The first connection part  10   a  has at an end thereof a connection end  10   m  that is connected to a first connection end  51   b  of the first connection pipe  51 . The connection end  10   m  and the first connection end  51   b  are fastening components that are fastened to each other. More specifically, the connection end  10   m  of the first connection part  10   a  is a hexagon nut, and the first connection end  51   b  of the first connection pipe  51  is a hexagon bolt. The second connection part  10   b  has at an end thereof a connection end  10   n  that is connected to a second connection end  52   b  of the second connection pipe  52 . The connection end  10   n  and the second connection end  52   b  are fastening components that are fastened to each other. More specifically, the connection end  10   n  of the second connection part  10   b  is a hexagon nut, and the second connection end  52   b  of the second connection pipe  52  is a hexagon bolt. 
     A displacement amount di 2  in a pipe diameter direction of the first connection part  10   a  shown in  FIG. 12A  is set to be greater than or equal to a prescribed value mr 2  in a pipe axis direction shown in  FIG. 12B . In this case, the prescribed value mr 2  in the pipe axis direction is the height of the hexagon nut. A displacement amount di 3  in the pipe diameter direction of the first connection part  10   a  shown in  FIG. 12A  is set to be greater than or equal to a prescribed value mr 3  in the pipe diameter direction shown in  FIG. 12B . In this case, the prescribed value mr 3  in the pipe diameter direction is a diagonal distance of the hexagon nut. 
     In the description above, the displacement amount di 2  in the pipe axis direction has been described as a displacement amount between the connection ends  10   m  and  10   n . However, from a different point of view, the first connection end  51   b  and the second connection end  52   b  may be understood as being disposed by the displacement amount di 2  greater than or equal to the prescribed value mr 2  in the pipe axis direction of the first connection pipe  51 . In addition, the first connection end  51   b  and the second connection end  52   b  may be understood as being disposed by the displacement amount di 3  greater than or equal to the prescribed value mr 3  in the pipe diameter direction of the first connection pipe  51 . As long as at least one of such prescribed value mr 2  in the pipe axis direction and such prescribed value mr 3  in the pipe diameter direction is provided, a tool for fastening the connection end  10   m  and the first connection end  51   b  to each other and the connection end  10   n  and the second connection end  52   b  to each other, in this case, a hexagon wrench can be used. As long as both the prescribed value mr 2  in the pipe axis direction and the prescribed value mr 3  in the pipe diameter direction are provided, it is possible to smoothly fasten the connection end  10   m  and the first connection end  51   b  to each other and the connection end  10   n  and the second connection end  52   b  to each other by using the tool. 
     Regarding the first connection end  51   b  of the first connection pipe  51  and the second connection end  52   b  of the second connection pipe  52 , in order to provide the displacement amount di 2  in the pipe axis direction and the displacement amount di 3  in the pipe diameter direction, a branch socket  200 , shown in  FIGS. 13 and 14 , may be used. 
     The branch socket  200  includes a Y-shaped copper pipe  210  and a Y-shaped heat-insulating section  220  that covers the copper pipe  210 . Here, although the branch socket  200  including the copper pipe  210  is described, the copper pipe  210  may be substituted by another metallic pipe. The heat-insulating section  220  is made of, for example, resin. The heat-insulating section  220  has two separated columnar portions  221  and  222  extending in the same direction. An end  223  of the longer columnar portion  221  and an end  224  of the shorter columnar portion  222  are offset from each other by an amount di 4  in a pipe axis direction of the copper pipe  210 . The displacement amount di 4  is set to be greater than or equal to the first prescribed value mr 2 . The ends  223  and  224  are offset from each other by an amount di 5  in a pipe diameter direction of the copper pipe  210 . The displacement amount di 5  is set to be greater than or equal to the third prescribed value mr 3 . The first connection pipe  51  and the second connection pipe  52  having the same length are brazed to the copper pipe  210  by being inserted up to the ends  223  and  224  of the two corresponding columnar portions  221  and  222 . Regarding the first connection pipe  51  and the second connection pipe  52  that have been inserted in this way, the first connection end  51   b  and the second connection end  52   b , which are ends differing from the brazed ends, can be fixed at the positions shown in  FIG. 12A . 
     (7-9) Modification I 
     In the first embodiment, the second embodiment, and the modifications above, the case in which, at an installation site of the air conditioner  1 , the first connection pipe  51  and the second connection pipe  52  are brazed to, for example, the first branch pipe  53  has been described. However, special-purpose coils  300  and  350  and special-purpose straight pipes  400  and  450  that are shown in a corresponding one of  FIGS. 15A, 15B, 16A, and 16B  and in which connection pipes and branch pipes are previously connected and fixed may be prepared. The special-purpose coils  300  and  350  and the special-purpose straight pipes  400  and  450  differ from each other in that a first connection pipe  51  and a second connection pipe  52  of each of the special-purpose coils  300  and  350  are spirally formed, whereas a first connection pipe  51  and a second connection pipe  52  of each of the special-purpose straight pipes  400  and  450  are linearly formed. Regarding the special-purpose coils  300  and  350 , a site worker can stretch and contract the special-purpose coils  300  and  350  by changing the lengths of the first connection pipe  51  and the second connection pipe  52 . 
     The special-purpose coil  300  and the special-purpose straight pipe  400  are each, for example, one product in which the first connection pipe  51 , the second connection pipe  52 , the first branch pipe  53 , and the fourth branch pipe  71  of the first connection flow path  50 , which are shown in  FIG. 3 , are previously integrated all at once. Such a special-purpose coil  300  and such a special-purpose straight pipe  400  are manufactured at, for example, a factory. The special-purpose coil  300  and the special-purpose straight pipe  400  are transported, for example, to an installation site of the air conditioner  1  from the factory. Therefore, by using the special-purpose coil  300  or the special-purpose straight pipe  400 , it is possible to omit brazing of two branch pipes and two connection pipes at the installation site of the air conditioner  1 . 
     The special-purpose coil  350  and the special-purpose straight pipe  450  are each, for example, one product in which the first connection pipe  51 , the second connection pipe  52 , and the first branch pipe  53  of the first connection flow path  50 , which are shown in  FIGS. 1 to 4 , are previously integrated all at once. Such a special-purpose coil  350  and such a special-purpose straight pipe  450  are manufactured at, for example, a factory. The special-purpose coil  350  and the special-purpose straight pipe  450  are transported, for example, to an installation site of the air conditioner  1  from the factory. Therefore, by using the special-purpose coil  350  or the special-purpose straight pipe  450 , it is possible to omit brazing of one branch pipe and two connection pipes at the installation site of the air conditioner  1 . 
     Note that the special-purpose coils  300  and  350  and the special-purpose straight pipes  400  and  450  may incorporate the single pipe  54 . The special-purpose coil  350  and the special-purpose straight pipe  450  may be used in parts of the first connection pipe  51 , the second connection pipe  52 , and the fourth branch pipe  71 . The special-purpose coil  350  and the special-purpose straight pipe  450  may be used in portions of the joints  61  and  62  and the second branch pipe  55  shown in  FIG. 2 , or in portions of the joints  63  and  64  and the third branch pipe  56  shown in  FIG. 2 . 
     (7-10) Modification J 
     In the first embodiment, the second embodiment, and the modifications above, the case in which, when the air conditioner  1  is to be installed at an installation site, an end portion of one pipe and an end portion of one pipe are brazed to each other has been described. However, the first connection pipe  51  and the second connection pipe  52  may be connected to each other by using a special-purpose socket that is capable of brazing a plurality of pipes all at once.  FIG. 17  shows the first connection pipe  51  and the second connection pipe  52  and the first connection part  10   a  and the second connection part  10   b  of the heat source unit  10  being connected to a special-purpose socket  500 . The special-purpose socket  500  is made of, for example, a metal, such as copper or stainless steel. The special-purpose socket  500  is formed by, for example, deforming a metallic cylindrical body. The special-purpose socket  500  includes a first insertion part  501  having an inside diameter substantially equal to the outside diameter of the first connection pipe  51 , a second insertion part  502  having an inside diameter substantially equal to the outside diameter of the second connection pipe  52 , a third insertion part  503  having an inside diameter substantially equal to the outside diameter of the first connection part  10   a , and a fourth insertion part  504  having an inside diameter substantially equal to the outside diameter of the second connection part  10   b . The first connection pipe  51 , the second connection pipe  52 , the first connection part  10   a , and the second connection part  10   b  are inserted into and brazed to the first insertion part  501 , the second insertion part  502 , the third insertion part  503 , and the fourth insertion part  504  of the special-purpose socket  500 , respectively. In this case, the first connection pipe  51 , the second connection pipe  52 , the first connection part  10   a , and the second connection part  10   b , that is, four components can be used by two brazing operations. As a result of the brazing operations, a refrigerant is prevented from leaking outside the special-purpose socket  500 , the first connection pipe  51 , the second connection pipe  52 , the first connection part  10   a , and the second connection part  10   b . Therefore, not only a portion where an end portion of the special-purpose socket  500 , the first connection pipe  51 , and the second connection pipe  52  are close to each other, but also a portion of the end portion of the special-purpose socket  500  close to the first connection pipe  51  and the second connection pipe  52  is sealed by a brazing material. Similarly, not only a portion where an end portion of the special-purpose socket  500 , the first connection part  10   a , and the second connection part  10   b  are close to each other, but also a portion of the end portion of the special-purpose socket  500  close to the first connection part  10   a  and the second connection part  10   b  is sealed by a brazing material. When connection by such a special-purpose socket  500  is performed, a refrigerant primarily flows between the first connection pipe  51  and the first connection part  10   a  and between the second connection pipe  52  and the second connection part  10   b . However, a refrigerant is allowed to leak in the special-purpose socket  500 . For example, when a refrigerant flows to the first connection pipe  51  and the second connection pipe  52  from the heat source unit  10 , a refrigerant that has exited from the first connection part  10   a  need not be made to flow only to the first connection pipe  51  and may be made to flow to the second connection pipe  52 . Similarly, a refrigerant that has exited from the second connection part  10   b  may be made to flow to the first connection pipe  51 . 
     Here, the case in which the first connection flow path  50  including two connection pipes, that is, the first connection pipe  51  and the second connection pipe  52 , which are disposed in parallel, is connected by the special-purpose socket  500  has been described. 
     However, the number of connection pipes of the first connection flow path  50  that can be connected by a special-purpose socket is not limited to two. When the first connection flow path  50  includes three or more connection pipes, the three or more connection pipes may be brazed all at once by one special-purpose socket. Here, although the case in which the first connection pipe  51  and the first connection part  10   a  are connected to each other and the second connection pipe  52  and the second connection part  10   b  are connected to each other by the special-purpose socket  500  has been described, what can be connected by the special-purpose socket  500  is not limited to the first connection part  10   a  and the second connection part  10   b  of the heat source unit  10 . For example, the first connection pipe  51  and the first connection part  31   a  of the first use unit  31  may be connected to each other and the second connection pipe  52  and the second connection part  31   b  of the first use unit  31  may be connected to each other by the special-purpose socket  500 . 
     (7-11) Modification K 
     In the air conditioners  1  according to the first embodiment, the second embodiment, and the modifications above, the number of pipes included in the first connection flow path  50  is larger than that in air conditioners known in the art. Therefore, in order to reduce the time and effort to thermally insulate the first connection flow path  50 , as shown in  FIG. 18  and  FIG. 19 , the air conditioner  1  is constituted to include heat-insulating materials  601 ,  602 , and  603 . The heat-insulating materials  601 ,  602 , and  603  have corresponding ones of grooves  611  to  616  that correspond with a corresponding one of the first connection pipe  51 , the second connection pipe  52 , and the metallic pipe  81  of the second connection flow path  80 . A heat-insulating-material assembly  600  is one in which the first heat-insulating material  601 , the second heat-insulating material  602 , and the third heat-insulating material  603  have been assembled. The first heat-insulating material  601  has the grooves  611  and  612 , which correspond to the first connection pipe  51  and the second connection pipe  52 , respectively, in a first surface  621 . The second heat-insulating material  602  has the grooves  613  and  614 , which correspond to the first connection pipe  51  and the second connection pipe  52 , respectively, in a first surface  622 . The second heat-insulating material  602  has the groove  615 , which corresponds to the metallic pipe  81 , in a second surface  623  on a side opposite to the first surface  622 . The third heat-insulating material  603  has the groove  616 , which corresponds to the metallic pipe  81 , in a first surface  624 . When the first heat-insulating material  601 , the second heat-insulating material  602 , and the third heat-insulating material  603  are assembled, a column having three holes is formed. The materials of the heat-insulating materials  601 ,  602 , and  603  are hard resin or semi-hard resin, or materials that are moldable and stretchable and contractible. 
     The first surface  621  of the first heat-insulating material  601  and the first surface  622  of the second heat-insulating material  602  are put together and the first connection pipe  51  and the second connection pipe  52  are sandwiched by the heat-insulating materials  601  and  602 . The first connection pipe  51  is fitted to the groove  611  of the heat-insulating material  601  and the groove  613  of the heat-insulating material  602 . The grooves  611  and  613  are put together and form a columnar hole. The diameter of the hole formed by the grooves  611  and  613  is substantially the same as or slightly larger than the outside diameter of the first connection pipe  51 . Therefore, the heat-insulating materials  601  and  602  can cover a periphery of the first connection pipe  51 . The second connection pipe  52  is fitted to the groove  612  of the heat-insulating material  601  and the groove  614  of the heat-insulating material  602 . The grooves  612  and  614  are put together and form a columnar hole. The diameter of the hole formed by the grooves  612  and  614  is substantially the same as or slightly larger than the outside diameter of the second connection pipe  52 . Therefore, the heat-insulating materials  601  and  602  can cover a periphery of the second connection pipe  52 . 
     The second surface  623  of the second heat-insulating material  602  and the first surface  624  of the third heat-insulating material  603  are put together and the metallic pipe  81  is sandwiched by the heat-insulating materials  602  and  603 . The metallic pipe  81  is fitted to the groove  615  of the heat-insulating material  602  and the groove  616  of the heat-insulating material  603 . The grooves  615  and  616  are put together and form a columnar hole. The diameter of the hole formed by the grooves  615  and  616  is substantially the same as or slightly larger than the outside diameter of the metallic pipe  81 . Therefore, the heat-insulating materials  602  and  603  can cover a periphery of the metallic pipe  81 . 
     (7-12) Modification L 
     The second branch pipe  55  and the third branch pipe  56  in  FIG. 2  may be constituted to be accommodated in a heat-insulating-material assembly  700  including a first heat-insulating material  701  and a second heat-insulating material  702  and described below using  FIGS. 20 and 21 . 
     The heat-insulating material  701  has a plurality of grooves  711  corresponding to the second branch pipe  55 , and the heat-insulating material  702  has a plurality of grooves  712  corresponding to the third branch pipe  56 . The heat-insulating-material assembly  700  is one in which the first heat-insulating material  701  and the second heat-insulating material  702  have been assembled. The first heat-insulating material  701  has the grooves  711 , which correspond to the second branch pipe  55 , in a first surface  721 . The second heat-insulating material  702  has the grooves  712 , which correspond to the third branch pipe  56 , in a first surface  722 . When the first heat-insulating material  701  and the second heat-insulating material  702  are assembled, a Y-shaped member having two Y-shaped holes is formed. The materials of the heat-insulating materials  701  and  702  are hard resin or semi-hard resin, or materials that are moldable and stretchable and contractible. The first surface  721  of the first heat-insulating material  701  and the first surface  722  of the second heat-insulating material  702  are put together and the second branch pipe  55  and the third branch pipe  56  are sandwiched by the heat-insulating materials  701  and  702 . The second branch pipe  55  is fitted to the grooves  711  of the heat-insulating material  701 . Each groove  711  is deeper than the height of the second branch pipe  55 . Therefore, a periphery of the second branch pipe  55  is covered by the first heat-insulating material  701 . The third branch pipe  56  is fitted to the grooves  712  of the heat-insulating material  702 . Each groove  712  is deeper than the height of the third branch pipe  56 . Therefore, a periphery of the third branch pipe  56  is covered by the second heat-insulating material  702 . The second branch pipe  55  and the third branch pipe  56  are joint portions of the first connection pipe  51  and the second connection pipe  52 . 
     As shown in  FIG. 22 , the second branch pipe  55  and the third branch pipe  56  may be covered by two of a heat-insulating material  703 , a heat-insulating material  704 , and a heat-insulating material  705 . As shown in  FIG. 22 , the air conditioner  1  is constituted to include the heat-insulating materials  703 ,  704 , and  705 . The heat-insulating material  703  has a plurality of grooves  713  corresponding to the second branch pipe  55 , the heat-insulating material  704  has a plurality of grooves  714  and  715  corresponding to a corresponding one of the second branch pipe  55  and the third branch pipe  56 , and the heat-insulating material  705  has a plurality of grooves  716  corresponding to the third branch pipe  56 . A heat-insulating-material assembly  750  is one in which the first heat-insulating material  703 , the second heat-insulating material  704 , and the third heat-insulating material  705  have been assembled. The first heat-insulating material  703  has the grooves  713 , which correspond to the second branch pipe  55 , in a first surface  723 . The second heat-insulating material  704  has the grooves  714 , which correspond to the second branch pipe  55 , in a first surface  724 . The second heat-insulating material  704  has the grooves  715 , which correspond to the third branch pipe  56 , in a second surface  725  on a side opposite to the first surface  724 . The third heat-insulating material  705  has the grooves  716 , which correspond to the third branch pipe  56 , in a first surface  726 . When the first heat-insulating material  703 , the second heat-insulating material  704 , and the third heat-insulating material  705  are assembled, a Y-shaped member having two Y-shaped holes is formed. The materials of the heat-insulating materials  703 ,  704 , and  705  are hard resin or semi-hard resin, or materials that are moldable and stretchable and contractible. 
     The first surface  723  of the first heat-insulating material  703  and the first surface  724  of the second heat-insulating material  704  are put together and the second branch pipe  55  is sandwiched by the heat-insulating materials  703  and  704 . The second branch pipe  55  is fitted to the grooves  713  of the heat-insulating material  703  and the grooves  714  of the heat-insulating material  704 . The grooves  713  and  714  are put together and form a Y-shaped hole. The diameter of the hole formed by the grooves  713  and  714  is substantially the same as or slightly larger than the outside diameter of the second branch pipe  55 . Therefore, the heat-insulating materials  703  and  704  can cover a periphery of the second branch pipe  55 . The third branch pipe  56  is fitted to the grooves  715  of the heat-insulating material  704  and the grooves  716  of the heat-insulating material  705 . The grooves  715  and  716  are put together and form a Y-shaped hole. The diameter of the hole formed by the grooves  715  and  716  is substantially the same as or slightly larger than the outside diameter of the third branch pipe  56 . Therefore, the heat-insulating materials  704  and  705  can cover a periphery of the third branch pipe  56 . 
     Here, a description has been given by taking the second branch pipe  55  and the third branch pipe  56  as examples of joint portions to which the heat-insulating materials  701  and  702  or the heat-insulating materials  703  to  705  are applied. However, the joint portions to which the heat-insulating materials  701  and  702  or the heat-insulating materials  703  to  705  are applied are not limited to the second branch pipe  55  and the third branch pipe  56 . For example, with the fourth branch pipe  71  and the fifth branch pipe  72  shown in  FIG. 4  as joint portions, heat-insulating materials, such as the heat-insulating materials  701  and  702  or the heat-insulating materials  703  to  705 , may be applied to the fourth branch pipe  71  and the fifth branch pipe  72 . The refrigerant pipes  57   a  and  57   b  can be considered as first connection pipes included in the first connection flow path  50 , and the refrigerant pipes  58   a  and  58   b  can be considered as second connection pipes included in the first connection flow path  50 . 
     (8) Features 
     (8-1) 
     In the air conditioner  1 , which is a refrigeration cycle device, described above, a refrigerant that flows between the heat source unit  10  and one first use unit  31  is divided by the first connection pipe  51  and the second connection pipe  52 . A refrigerant that flows in the main pipe parts of the first connection flow path  50  at the time of a heating operation is a high-temperature, high-pressure refrigerant in a supercritical state or a high-temperature, high-pressure gas refrigerant having a pressure of 4.5 MPa or higher. Compared with when a main pipe part of the first connection flow path  50  in which such a high-temperature, high-pressure refrigerant flows is constituted by one connection pipe, it is possible to reduce the pipe diameters of the first connection pipe  51  and the second connection pipe  52 , which constitute the main pipe parts. As a result, at a site, processing of the main pipe parts of the first connection flow path  50  constituted by the thin first connection pipe  51  and the thin second connection pipe  52  is facilitated. For example, the thin first connection pipe  51  and the thin second connection pipe  52  are easily bent along a building. When the air conditioner  1  is to be installed, work efficiency at the time of construction related to the first connection pipe  51  and the second connection pipe  52  is improved. 
     (8-2) 
     The thin first connection pipe  51  and the thin second connection pipe  52  above each may have an outside diameter of 12.7 mm or less. The first connection pipe  51  and the second connection pipe  52 , which have an outside diameter of 12.7 mm or less, are easily processed. Therefore, the air conditioner  1  including the first connection pipe  51  and the second connection pipe  52 , each having an outside diameter of 12.7 mm or less, can improve work efficiency at the time of construction. 
     (8-3) 
     In the air conditioner  1  of the second embodiment, since a large amount of refrigerant, which is the total amount of refrigerant that flows in one first use unit  31  and one second use unit  32 , is divided by the first connection pipe  51  and the second connection pipe  52  and flows, compared with when a large amount of refrigerant in a plurality of use unit  30  flows in one connection pipe, the air conditioner  1  is considerably effective in facilitating construction by reducing the pipe diameters of the first connection pipe  51  and the second connection pipe  52 . 
     (8-4) 
     The first connection flow path  50  of the air conditioner  1  above has main pipe parts including the first connection pipe  51  and the second connection pipe  52 . The first connection pipe  51  and the second connection pipe  52 , which are main pipe parts, are common to the first use unit  31  and the second use unit  32 . For example, the first use unit  31  and the second use unit  32  may be disposed in a room on the first floor of a building and the heat source unit may be disposed on a roof of the building. In this case, the first connection pipe  51  and the second connection pipe  52 , which are main pipe parts, are installed up to the room on the first floor of the building from the roof of the building. The first connection pipe  51  and the second connection pipe  52  that are installed in this way each have, for example, a length exceeding the height of the building. Even when the first connection pipe  51  and the second connection pipe  52  are constituted by connecting a plurality of straight pipes at a site, connection is facilitated by reducing the pipe diameters. 
     (8-5) 
     In the air conditioner  1  of the second embodiment, for example, when heating is performed at the second use unit  32  without performing heating at the first use unit  31 , the first on-off valve  44 , which is a first valve, and the second on-off valve  45 , which is a second valve, are closed. When the first on-off valve  44  and the second on-off valve  45  are closed in this way, sound can be suppressed from being transmitted through the first connection pipe  51  and the second connection pipe  52  and propagation of sound to the first use unit  31 . By suppressing sound that is transmitted to the first use unit  31  from the first connection pipe  51  and the second connection pipe  52 , it is possible to improve quietness of the first use unit  31 . 
     For example, when heating is performed at the first use unit  31  without performing heating at the second use unit  32 , the first on-off valve  47 , which is a first valve, and the second on-off valve  48 , which is a second valve, are closed. When the first on-off valve  47  and the second on-off valve  48  are closed in this way, sound can be suppressed from being transmitted through the first connection pipe  51  and the second connection pipe  52  and propagation of sound to the second use unit  32 . By suppressing sound that is transmitted to the second use unit  32  from the first connection pipe  51  and the second connection pipe  52 , it is possible to improve quietness of the second use unit  32 . 
     (8-6) 
     The air conditioners  1  according to the first embodiment and the second embodiment can, by combining the first connection pipe  51  and the second connection pipe  52  having different outside diameters, increase the range of selection of the first connection pipe  51  and the second connection pipe  52  suitable for the amount of refrigerant that flows. For example, the outside diameters of metallic pipes that can be supplied at all times by metallic pipe manufacturers are generally discrete. Therefore, when obtaining from a manufacturer metallic pipes used for the first connection pipe  51  and the second connection pipe  52  suitable for the amount of refrigerant that circulates in the air conditioner  1 , a combination of metallic pipes having different outside diameters may be more suitable for the amount of refrigerant that circulates. When the outside diameters are selected so that a suitable pressure loss occurs at the first connection pipe  51  and the second connection pipe  52 , the first connection pipe  51  and the second connection pipe  52  may be applied as those having different outside diameters to the air conditioner  1 . In order to obtain a suitable pressure loss at the first connection pipe  51  and the second connection pipe  52 , the flow path cross-sectional area that is the total of the flow path cross-sectional area of the first connection pipe  51  and the flow path cross-sectional area of the second connection pipe  52  may be larger than the flow path cross-sectional area of the single pipe  54 . 
     (8-7) 
     As described in Modification D, the first connection flow path  50  may be constituted to include three or more connection pipes as main pipe parts. For example, when the first connection flow path  50  includes a third connection pipe in addition to the first connection pipe  51  and the second connection pipe  52 , compared with when the first connection flow path  50  includes only the first connection pipe  51  and the second connection pipe  52 , the outside diameter of each pipe can be further reduced. When the first connection flow path  50  includes the third connection pipe in addition to the first connection pipe  51  and the second connection pipe  52 , for example, bending of the main pipe parts of the first connection flow path  50  is further facilitated compared with when the first connection flow path  50  includes two main pipe parts, and work efficiency at the time of construction is easily improved. 
     (8-8) 
     The air conditioner  1  of the first embodiment can, by causing a refrigerant to flow in the first connection pipe  51  by opening the first on-off valve  44  and not causing a refrigerant to flow in the second connection pipe  52  by closing the second on-off valve  45 , increase the flow velocity of the refrigerant that flows in the first connection pipe  51  compared with that when the refrigerant is caused to flow in both connection pipes. By causing a refrigerant to flow in the second connection pipe  52  by opening the second on-off valve  45  and not causing a refrigerant to flow in the first connection pipe  51  by closing the first on-off valve  44 , it is possible to increase the flow velocity of the refrigerant that flows in the second connection pipe  52  compared with that when the refrigerant is caused to flow in both connection pipes. In this way, by causing a refrigerant to flow in the first connection pipe  51  and the second connection pipe  52 , for example, as long as a predetermined operating mode is an operating mode in which an oil return operation is performed, the air conditioner  1  of the first embodiment can end the oil return operation in a short time. 
     The air conditioner  1  of the second embodiment can, by causing a refrigerant to flow in the first connection pipe  51  by opening the first on-off valves  44  and  47  and not causing a refrigerant to flow in the second connection pipe  52  by closing the second on-off valves  45  and  48 , increase the flow velocity of the refrigerant that flows in the first connection pipe  51  compared with that when the refrigerant is caused to flow in both connection pipes. By causing a refrigerant to flow in the second connection pipe  52  by opening the second on-off valves  45  and  48  and not causing a refrigerant to flow in the first connection pipe  51  by closing the first on-off valves  44  and  47 , it is possible to increase the flow velocity of the refrigerant that flows in the second connection pipe  52  compared with that when the refrigerant is caused to flow in both connection pipes. In this way, by causing a refrigerant to flow in the first connection pipe  51  and the second connection pipe  52 , for example, as long as a predetermined operating mode is an operating mode in which an oil return operation is performed, the air conditioner  1  of the second embodiment can end the oil return operation in a short time. 
     (8-9) 
     The air conditioner  1  may be constituted so that the covering color of the metallic pipe  81  differs from that of the connection pipe, among the first connection pipe  51  and the second connection pipe  52 , whose outside diameter is substantially the same as that of the metallic pipe  81 . In such a structure, even if the outside diameter of the first connection pipe  51  and/or the outside diameter of the second connection pipe  52  and the outside diameter of the metal pipe  81  are substantially the same, it is possible to reduce a mix-up of the metallic pipe  81  and the first connection pipe  51  and/or the second connection pipe  52  at the time of construction. 
     (8-10) 
     The air conditioner  1 , which is a refrigeration cycle device, has the first connection part  10   a  or  31   a , which is connected to the first connection pipe  51 , and the second connection part  10   b  or  31   b , which is connected to the second connection pipe  52 , at at least one of the heat source unit  10  shown in  FIG. 7  and the first use unit  31  shown in  FIG. 10 . The air conditioner  1  having such a structure makes it possible to directly connect the first connection pipe  51  and the second connection pipe  52  to at least one of the heat source unit  10  and the first use unit  31 . As a result, it is possible to improve work efficiency of an installation worker at a site where the air conditioner  1  is to be installed. 
     (8-11) 
     As shown in  FIGS. 7 and 10 , the first connection part  10   a  or  31   a  and the second connection part  10   b  or  31   b  are disposed inside at least one of the heat-source-unit casing  10   c  and the first-use-unit casing  31   c . The air conditioner  1  having such a structure is such that the first connection part  10   a  or  31   a  and the second connection part  10   b  or  31   b , disposed inside at least one of the heat source casing  10   c  and the first use unit casing  31   c , are protected by a corresponding one of the heat-source-unit casing  10   c  and the first-use-unit casing  31   c.    
     (8-12) 
     As shown in  FIG. 11  and  FIG. 12A , the connection ends  10   m  and  31   m  of the corresponding first connection parts  10   a  and  31   a  are disposed so as to be offset from a corresponding one of the connection ends  10   n  and  31   n  of the corresponding second connection parts  10   b  and  31   b  by the prescribed value mr 1  or more, mr 2  or more, or mr 3  or more in at least one of the pipe diameter direction and the pipe axis direction of a corresponding one of the first connection part  10   a  and the first connection part  31   a . The air conditioner  1  having such a structure facilitates a connection operation or a brazing operation using a tool for the first connection parts  10   a  and  31   a  and the second connection parts  10   b  and  31   b  due to the connection end  10   m  of the first connection part  10   a  and the connection end  31   m  of the first connection part  31   a  being offset from a corresponding one of the connection end  10   n  of the second connection part  10   b  and the connection end  31   n  of the second connection part  31   b  by the prescribed value mr 1  or more, mr 2  or more, or mr 3  or more in at least one of the pipe diameter direction and the pipe axis direction. As a result, it is possible to improve work efficiency of an installation worker at a site where the air conditioner  1  is to be installed. 
     (8-13) 
     The first connection pipe  51  has the first connection ends  51   a  and  51   b  into which a refrigerant flows from one of the heat source unit  10  and the first use unit  31 . The second connection pipe  52  has the second connection ends  52   a  and  52   b  into which a refrigerant flows from one of the heat source unit  10  and the first use unit  31 . The first connection parts  51   a  and  51   b  and the corresponding connection ends  52   a  and  52   b  are disposed so as to be offset from each other by the prescribed value mr 1  or more, mr 2  or more, or mr 3  or more in at least one of the pipe diameter direction and the pipe axis direction of the first connection pipe  51 . The air conditioner  1  having such a structure facilitates a connection operation or a brazing operation using a tool for the first connection pipe  51  and the second connection pipe  52  due to the first connection ends  51   a  and  51   b  and the corresponding second connection ends  52   a  and  52   b  being offset from each other by the prescribed value mr 1  or more, mr 2  or more, or mr 3  or more in at least one of the pipe diameter direction and the pipe axis direction. As a result, it is possible to improve work efficiency of an installation worker at a site where the air conditioner  1  is to be installed. 
     (8-14) 
     The branch socket  200  in  FIGS. 13 and 14  has a form that allows the first connection ends  51   a  and  51   b  and the corresponding connection ends  52   a  and  52   b  to be disposed so as to be offset from each other by the prescribed value mr 1  or more, mr 2  or more, or mr 3  or more in at least one of the pipe diameter direction and the pipe axis direction of the first connection pipe  51  is realized. In the air conditioner  1  having such a structure, since the first connection ends  51   a  and  51   b  and the corresponding second connection ends  52   a  and  52   b  can be offset from each other by the prescribed value mr 1  or more, mr 2  or more, or mr 3  or more due to the form of the branch socket  200 , for example, a standard for the prescribed value of a gauge or the like is no longer required, as a result of which a connection operation of connecting the first connection pipe  51  and the second connection pipe  52  is facilitated. 
     (8-15) 
     The air conditioner  1  includes the plurality of heat-insulating materials  601 ,  602 , and  603  having corresponding ones of grooves  611  to  616  that correspond with a corresponding one of the first connection pipe  51 , the second connection pipe  52 , and the metallic pipe  81  of the second connection flow path  80  shown in  FIGS. 18 and 19 . The plurality of heat-insulating materials  601  to  603  cover the periphery of a corresponding one or ones of the first connection pipe  51 , the second connection pipe  52 , and the second connection flow path  80 . In this way, since it is possible to save time and effort to form the grooves  611  to  616  in a corresponding one of the heat-insulating materials  601  to  603  due to the grooves  611  to  616  of the corresponding one of the heat-insulating materials  601  to  603 , it is possible to reduce the number of manhours for a heat-insulation operation using the heat-insulating materials  601  to  603 . 
     (8-16) 
     The air conditioner  1  includes the plurality of heat-insulating materials  701  and  702  or the plurality of heat-insulating materials  703 ,  704 , and  705 , each including corresponding ones of the grooves  711 ,  712 ,  713 ,  714 , and  715  corresponding to a corresponding one of the second branch pipe  55  and the third branch pipe  56 , which are joint portions of the first connection pipe  51  and the second connection pipe  52  shown from  FIG. 20  to  FIG. 22 . The plurality of heat-insulating materials  701  and  702  or the plurality of heat-insulating materials  703  to  705  cover a corresponding one or ones of the second branch pipe  55  and the third branch pipe  56 . In this way, since it is possible to save time and effort to form the grooves  711  to  716  in a corresponding one of the heat-insulating materials  701  to  706  due to the grooves  711  to  716  of the corresponding one of the heat-insulating materials  701  and  702  or the corresponding one of the heat-insulating materials  703  to  705 , it is possible to reduce the number of manhours for a heat-insulation operation using the heat-insulating materials  701  to  706 . 
     (8-17) 
     When the heat-insulating materials  601 ,  602 , and  603  shown in  FIGS. 18 and 19  or the heat-insulating materials  701 ,  702 ,  703 ,  704 , and  705  shown from  FIG. 20  to  FIG. 22  are resin heat-insulating materials that are stretchable and contractible, the lengths of the heat-insulating materials  601  to  603 , the heat-insulating materials  701  and  702 , and the heat-insulating materials  703  to  705  are easily made to correspond with the lengths of the first connection pipe  51  and the second connection pipe  52 , and a heat-insulation operation can be facilitated. 
     (8-18) 
     The first connection flow path  50  shown in each of  FIGS. 15A, 15B, 16A, and 16B  includes a corresponding one of the special-purpose coils  300  and  350  and the special-purpose straight pipes  400  and  450  in which at least one end of the first connection pipe  51  and one end of the second connection pipe  52  merge and are integrated with each other. In this way, when the special-purpose coils  300  and  350  or the special-purpose straight pipes  400  and  450  merge at least one end of the first connection pipe  51  and one end of the second connection pipe  52  and integrate them with each other, it is possible to reduce the number of brazing portions required for installing the air conditioner  1 . 
     (8-19) 
     The first connection flow path  50  shown in  FIG. 17  includes the special-purpose socket  500  that makes it possible to braze the first connection pipe  51  and the second connection pipe  52  all at once. In such a structure, by brazing the first connection pipe  51  and the second connection pipe  52  all at once by the special-purpose socket  500 , it is possible to reduce the number of brazing portions required for installing the air conditioner  1  compared with when the first connection pipe  51  and the second connection pipe  52  are individually brazed. 
     Although the disclosure has been described with respect to only a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that various other embodiments may be devised without departing from the scope of the present invention. Accordingly, the scope of the invention should be limited only by the attached claims. 
     REFERENCE SIGN LIST 
     
         
         
           
               1  air conditioner (example of refrigeration cycle device) 
               10  heat source unit 
               10   a ,  31   a  first connection part 
               10   b ,  31   b  second connection part 
               10   c  heat-source-unit casing 
               10   m ,  10   n ,  31   m ,  31   n  connection end 
               11  compressor 
               12  heat-source-side heat exchanger 
               31  first use unit 
               31   c  first-use-unit casing 
               32  second use unit 
               41  first use-side heat exchanger 
               42  second use-side heat exchanger 
               44  first on-off valve (example of first valve) 
               45  second on-off valve (example of second valve) 
               50  first connection flow path 
               51  first connection pipe 
               51   a ,  51   b  first connection end 
               52  second connection pipe 
               52   a ,  52   b  second connection end 
               54  single pipe 
               80  second connection flow path 
               81  metallic pipe 
               200  branch socket 
               300 ,  350  special-purpose coil 
               400 ,  450  special-purpose pipe 
               500  special-purpose socket 
               601  to  603 ,  701  to  702 ,  703  to  705  heat-insulating material 
               611  to  616 ,  711  to  712 ,  713  to  716  groove 
           
         
       
    
     CITATION LIST 
     Patent Literature 
     PTL 1: Japanese Unexamined Patent Application Publication No. 2002-107011