Patent Publication Number: US-2022214088-A1

Title: Refrigeration cycle apparatus

Description:
TECHNICAL FIELD 
     The present invention relates to a refrigeration cycle apparatus. 
     BACKGROUND ART 
     In a conventional refrigeration cycle apparatus, a four-way valve is configured to switch a flow channel by laterally sliding a flow channel switching piston that partitions a high-pressure side and a low-pressure side of a refrigerant circuit. For example, Japanese Patent Laying-Open No. 01-314870 (PTL 1) discloses a four-way valve configured to switch a flow channel by laterally sliding a flow channel switching piston that partitions a high-pressure side and a low-pressure side of a refrigerant circuit. 
     CITATION LIST 
     Patent Literature 
     PTL 1: Japanese Patent Laying-Open No. 01-314870 
     SUMMARY OF INVENTION 
     Technical Problem 
     In the four-way valve disclosed in the above publication, there is a gap between the flow channel switching piston and the installation surface along which the flow channel switching piston slides. This results in refrigerant leakage from the high-pressure side to the low-pressure side through this gap. 
     The present invention has been made in view of the above problem. An object of the present invention is to provide a refrigeration cycle apparatus that can reduce an amount of refrigerant leakage from a high-pressure side to a low-pressure side in a four-way valve. 
     Solution to Problem 
     A refrigeration cycle apparatus of the present invention includes a compressor, a four-way valve, a first outdoor heat exchanger, a first expansion valve, and an indoor heat exchanger. The compressor compresses the refrigerant. The four-way valve is connected to the compressor. The first outdoor heat exchanger is connected to the four-way valve. The first expansion valve is connected to the first outdoor heat exchanger. The indoor heat exchanger is connected to the first expansion valve and the four-way valve. The four-way valve is configured to switch between passing the refrigerant compressed by the compressor to the first outdoor heat exchanger and passing the refrigerant compressed by the compressor to the indoor heat exchanger. The four-way valve includes a casing, a first flow channel, a second flow channel, a flow channel switching piston, and a wall portion. The casing has an inner surface. The first flow channel and the second flow channel are disposed in the casing. The flow channel switching piston and the wall portion are disposed in the casing. The flow channel switching piston is configured to slide along the inner surface to switch between passing the refrigerant through the first flow channel and passing the refrigerant through the second flow channel. The wall portion is configured to slide along the inner surface together with the flow channel switching piston and is disposed with a space between the flow channel switching piston and the wall portion to cover the flow channel switching piston. 
     Advantageous Effects of Invention 
     According to the refrigeration cycle apparatus of the present invention, in the four-way valve, the wall portion is configured to slide along the inner surface together with the flow channel switching piston and is disposed with a space between the flow channel switching piston and the wall portion to cover the flow channel switching piston. The pressure of the refrigerant can thus be an intermediate pressure between a high-pressure side and a low-pressure side in the space between the wall portion and the flow channel switching piston. This can reduce an amount of refrigerant leakage from the high-pressure side to the low-pressure side in the four-way valve. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a refrigerant circuit diagram of a refrigeration cycle apparatus according to Embodiment 1. 
         FIG. 2  is a refrigerant circuit diagram of the refrigeration cycle apparatus according to Embodiment 1 during cooling operation. 
         FIG. 3  is a refrigerant circuit diagram of the refrigeration cycle apparatus according to Embodiment 1 during heating operation. 
         FIG. 4  is a refrigerant circuit diagram of a refrigeration cycle apparatus according to a comparative example. 
         FIG. 5  is a sectional view showing a configuration of a flow channel switching piston and its surroundings of the refrigeration cycle apparatus according to the comparative example. 
         FIG. 6  is a sectional view showing a configuration of a flow channel switching piston and its surroundings of the refrigeration cycle apparatus according to Embodiment 1. 
         FIG. 7  is a refrigerant circuit diagram of a refrigeration cycle apparatus according to Embodiment 2. 
         FIG. 8  is an enlarged sectional view taken along the line VIII-VIII of  FIG. 7 . 
         FIG. 9  is a refrigerant circuit diagram of the refrigeration cycle apparatus according to Embodiment 2 during cooling operation. 
         FIG. 10  is a graph showing a time that elapses before the completion of generation of an intermediate pressure in the refrigeration cycle apparatus according to Embodiment 1 for comparison with the refrigeration cycle apparatus according to Embodiment 2. 
         FIG. 11  is a graph showing a time that elapses before the completion of generation of an intermediate pressure in the refrigeration cycle apparatus according to Embodiment 2. 
         FIG. 12  is a refrigerant circuit diagram of a refrigeration cycle apparatus according to Embodiment 3. 
         FIG. 13  is a p-h diagram of the refrigeration cycle apparatus according to Embodiment 3. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Embodiments of the present invention will be described below with reference to the drawings. Hereinbelow, identical or corresponding parts are identically denoted, and redundant description will not be repeated. The embodiments of the present invention will describe an air conditioner as an example refrigeration cycle apparatus. The refrigeration cycle apparatus is not limited to the air conditioner and may be, for example, a chiller. 
     Embodiment 1 
     A configuration of a refrigeration cycle apparatus  10  according to Embodiment 1 will be described with reference to  FIG. 1 .  FIG. 1  is a refrigerant circuit diagram of refrigeration cycle apparatus  10  according to Embodiment 1. Refrigeration cycle apparatus  10  according to Embodiment 1 mainly includes a compressor  1 , a four-way valve  2 , a first outdoor heat exchanger  3 , a first expansion valve, and an indoor heat exchanger  5 . Compressor  1 , four-way valve  2 , first outdoor heat exchanger  3 , the first expansion valve, and indoor heat exchanger  5  are connected by a pipe, thereby constituting a refrigerant circuit. 
     Compressor  1  is configured to compress refrigerant. Compressor  1  has an inlet  1   a  and an outlet  1   b . Compressor  1  is configured to compress the refrigerant sucked from inlet  1   a  and discharge the refrigerant from outlet  1   b . Compressor  1  may be configured to have a variable capacity. Compressor  1  may be configured to have a capacity that varies through adjustment of the rotation speed of compressor  1  based on an instruction from a controller (not shown). 
     Four-way valve  2  is connected to compressor  1 , first outdoor heat exchanger  3 , and indoor heat exchanger  5 . Four-way valve  2  is configured to switch between passing the refrigerant compressed by compressor  1  to first outdoor heat exchanger  3  and passing the refrigerant compressed by compressor  1  to indoor heat exchanger  5 . Specifically, four-way valve  2  is configured to switch a refrigerant flow so as to pass the refrigerant discharged from compressor  1  to first outdoor heat exchanger  3  during cooling operation and pass the refrigerant discharged from compressor  1  to indoor heat exchanger  5  during heating operation. 
     Four-way valve  2  includes a casing  21 , a first flow channel F 1 , a second flow channel F 2 , a flow channel switching piston  23 , a wall portion  24 , a partitioning member (pressure receiving portion)  25 , and a pilot valve  26 . 
     Casing  21  has a cylindrical shape. Casing  21  has an interior space. Casing  21  has an inner surface IS. Inner surface IS forms a valve seat of four-way valve  2 . 
     Casing  21  has a first connection port  22   a , a second connection port  22   b , a third connection port  22   c , a fourth connection port  22   d , a fifth connection port  22   e , and a sixth connection port  22   f . First connection port  22   a  is connected to outlet  1   b  of compressor  1 . Second connection port  22   b  is connected to inlet  1   a  of compressor  1 . Third connection port  22   c  is connected to first outdoor heat exchanger  3 . Fourth connection port  22   d  is connected to indoor heat exchanger  5 . First connection port  22   a , second connection port  22   b , third connection port  22   c , and fourth connection port  22   d  are in communication with inner surface IS. Second connection port  22   b  is disposed to be opposite to first connection port  22   a . Third connection port  22   c  and fourth connection port  22   d  are disposed to sandwich second connection port  22   b  therebetween. Second connection port  22   b , third connection port  22   c , and fourth connection port  22   d  are disposed on a straight line along the axis of casing  21 . Fifth connection port  22   e  is in communication with the interior space of casing  21 . Sixth connection port  22   f  is in communication with the interior space of casing  21 . 
     First flow channel F 1  and second flow channel F 2  are disposed in casing  21 . First flow channel F 1  is configured to pass the refrigerant from first connection port  22   a  to third connection port  22   c  and pass the refrigerant from fourth connection port  22   d  to second connection port  22   b . Second flow channel F 2  is configured to pass the refrigerant from first connection port  22   a  to fourth connection port  22   d  and pass the refrigerant from third connection port  22   c  to second connection port  22   b.    
     Flow channel switching piston  23  is disposed in casing  21 . Flow channel switching piston  23  forms a valve body of four-way valve  2 . Flow channel switching piston  23  includes a cover  23   a  and a bottom  23   b . Cover  23   a  is configured to cover bottom  23   b . A clearance between cover  23   a  and bottom  23   b  defines a flow channel. Flow channel switching piston  23  is configured to slide along inner surface IS. Flow channel switching piston  23  is configured to slide along inner surface IS to switch between passing the refrigerant through first flow channel F 1  and passing the refrigerant through second flow channel F 2 . Flow channel switching piston  23  may be formed of a thermoplastic resin. 
     Wall portion  24  is disposed in casing  21 . Wall portion  24  is connected to flow channel switching piston  23 . Wall portion  24  is configured to slide along inner surface IS together with flow channel switching piston  23 . Wall portion  24  is disposed with a space SP between flow channel switching piston  23  and wall portion  24  to cover flow channel switching piston  23 . Space SP is provided as an intermediate layer between wall portion  24  and flow channel switching piston  23 . Wall portion  24  entirely covers flow channel switching piston  23 . In other words, wall portion  24  is disposed around flow channel switching piston  23  and is configured to surround flow channel switching piston  23 . Specifically, wall portion  24  forms a double structure together with flow channel switching piston  23 . Wall portion  24  may be formed of a thermoplastic resin. 
     Partitioning member  25  is connected to wall portion  24 . A first chamber  2   a  and a second chamber  2   b  are provided between casing  21  and partitioning member  25 . A pressure difference between first chamber  2   a  and second chamber  2   b  causes partitioning member  25  to slide. As partitioning member  25  slides, wall portion  24  and flow channel switching piston  23  slide. 
     Pilot valve  26  includes a first conduit  26   a , a second conduit  26   b , a third conduit  26   c , and a fourth conduit  26   d . Pilot valve  26  is configured to switch connection of first conduit  26   a , second conduit  26   b , third conduit  26   c , and fourth conduit  26   d  by a spring and an electromagnet that are built in pilot valve  26 . 
     First conduit  26   a  is connected to first connection port  22   a . Second conduit  26   b  is connected to second connection port  22   b . Third conduit  26   c  is connected to fifth connection port  22   e . Third conduit  26   c  is connected to first chamber  2  of casing  21  through fifth connection port  22   e . Fourth conduit  26   d  is connected to sixth connection port  22   f . Fourth conduit  26   d  is connected to second chamber  2   b  of casing  21  through sixth connection port  22   f.    
     First outdoor heat exchanger  3  serves to exchange heat between the refrigerant flowing in first outdoor heat exchanger  3  and the outdoor air. First outdoor heat exchanger  3  is connected to four-way valve  2  and first expansion valve  4 . First outdoor heat exchanger  3  functions as a condenser that condenses the refrigerant during cooling operation and as an evaporator that evaporates the refrigerant during heating operation. First outdoor heat exchanger  3  is a heat exchanger of plate fin tube type which includes a plurality of fins and a tube passing through the plurality of fins. 
     First expansion valve  4  is configured to expand the refrigerant condensed by the condenser to decompress the refrigerant. First expansion valve  4  is connected to first outdoor heat exchanger  3  and indoor heat exchanger  5 . First expansion valve  4  serves as a throttle device that decompresses the refrigerant condensed by first outdoor heat exchanger  3  during cooling operation and serves as a throttle device that decompresses the refrigerant condensed by indoor heat exchanger  5  during heating operation. First expansion valve  4  is, for example, a solenoid valve. 
     Indoor heat exchanger  5  serves to exchange heat between the refrigerant flowing in indoor heat exchanger  5  and the indoor air. Indoor heat exchanger  5  is connected to four-way valve  2  and first expansion valve  4 . Indoor heat exchanger  5  serves as an evaporator that evaporates the refrigerant during cooling operation and serves as a condenser that condenses the refrigerant during heating operation. Indoor heat exchanger  5  is a heat exchanger of plate fin tube type which includes a plurality of fins and a tube passing through the plurality of fins. 
     Next, an operation of refrigeration cycle apparatus  10  according to Embodiment 1 will be described with reference to  FIGS. 2 and 3 . 
     First, the cooling operation of refrigeration cycle apparatus  10  according to Embodiment 1 will be described with reference to  FIG. 2 .  FIG. 2  is a refrigerant circuit diagram of the refrigeration cycle apparatus according to Embodiment 1 during cooling operation. During cooling operation, the refrigerant circulates through the refrigerant circuit in order of compressor  1 , four-way valve  2 , first outdoor heat exchanger  3 , first expansion valve  4 , indoor heat exchanger  5 , and four-way valve  2 . 
     High-temperature, high-pressure gas refrigerant compressed by compressor  1  is discharged from compressor  1 , flows through four-way valve  2 , and radiates heat to the outdoor air to be condensed in first outdoor heat exchanger  3 , turning into high-pressure liquid refrigerant. This high-pressure liquid refrigerant flows into first expansion valve  4  and expands to be decompressed in first expansion valve  4 , turning into low-temperature, low-pressure gas-liquid-two-phase refrigerant. 
     This low-temperature, low-pressure gas-liquid-two-phase refrigerant flows into indoor heat exchanger  5 , absorbs heat from the indoor air to evaporate in indoor heat exchanger  5 , turning into low-pressure gas refrigerant. This low-pressure gas refrigerant returns to compressor  1  through four-way valve  2 , and is then compressed by compressor  1 . In this manner, the refrigerant circulates through the refrigerant circuit during cooling operation. 
     An operation of four-way valve  2  during cooling operation will now be described. During cooling operation, pilot valve  26  causes first chamber  2   a  of casing  21  to have a high pressure and second chamber  2   b  of casing  21  to have a low pressure. This causes flow channel switching piston  23  to slide together with partitioning member  25 , thus bringing first connection port  22   a  and third connection port  22   c  into communication with each other and also bringing second connection port  22   b  and fourth connection port  22   d  into communication with each other. This causes the refrigerant to flow from first connection port  22   a  to third connection port  22   c  and also flow from fourth connection port  22   d  to second connection port  22   b . In this manner, the refrigerant flows through first flow channel F 1  of four-way valve  2 . 
     Next, the heating operation of refrigeration cycle apparatus  10  according to Embodiment 1 will be described with reference to  FIG. 3 .  FIG. 3  is a refrigerant circuit diagram of the refrigeration cycle apparatus according to Embodiment 1 during cooling operation. During heating operation, the refrigerant circulates through the refrigerant circuit in order of compressor  1 , four-way valve  2 , indoor heat exchanger  5 , first expansion valve  4 , first outdoor heat exchanger  3 , and four-way valve  2 . 
     The high-temperature, high-pressure gas refrigerant compressed by compressor  1  is discharged from compressor  1 , flows through four-way valve  2 , and radiates heat to the indoor air to be condensed in indoor heat exchanger  5 , turning into high-pressure liquid refrigerant. This high-pressure liquid refrigerant flows into first expansion valve  4 , expands to be decompressed in first expansion valve  4 , turning into low-temperature, low-pressure gas-liquid-two-phase refrigerant. 
     This low-temperature, low-pressure gas-liquid-two-phase refrigerant flows into first outdoor heat exchanger  3 , and absorbs heat from the outdoor air to evaporate in first outdoor heat exchanger  3 , turning into low-pressure gas refrigerant. This low-pressure gas refrigerant returns to compressor  1  through four-way valve  2 , and is compressed by compressor  1 . In this manner, the refrigerant circulates through the refrigerant circuit during heating operation. 
     An operation of four-way valve  2  during heating operation will now be described. During heating operation, pilot valve  26  causes first chamber  2   a  of casing  21  to have a low pressure and second chamber  2   b  of casing  21  to have a high pressure. This causes partitioning member  25  and flow channel switching piston  23  to slide, thus bringing first connection port  22  and fourth connection port  22   d  into communication with each other and bringing second connection port  22   b  and third connection port  22   c  into communication with each other. This causes the refrigerant to flow from first connection port  22   a  to fourth connection port  22   d  and also flow from third connection port  22   c  to second connection port  22   b . In this manner, the refrigerant flows through second flow channel F 2  of four-way valve  2 . 
     Next, the functions and effects of refrigeration cycle apparatus  10  according to Embodiment 1 will be described while comparing with those of a comparative example. For convenience of description, four-way valve  2  during cooling operation will be described by way of example. 
     A configuration of refrigeration cycle apparatus  10  according to the comparative example will be described with reference to  FIG. 4 .  FIG. 4  is a refrigerant circuit diagram of refrigeration cycle apparatus  10  according to the comparative example. Refrigeration cycle apparatus  10  according to the comparative example has the same configuration and operation as those of refrigeration cycle apparatus  10  according to Embodiment 1 unless otherwise noted. Refrigeration cycle apparatus  10  according to the comparative example is different from refrigeration cycle apparatus  10  according to Embodiment 1 mainly in that it includes no wall portion of refrigeration cycle apparatus  10  according to Embodiment 1. 
     Referring to  FIG. 5 , description will be given of a leakage flow rate of the refrigerant that leaks from the high-pressure side to the low-pressure side in four-way valve  2  of refrigeration cycle apparatus  10  according to the comparative example. As indicated by the open arrow in  FIG. 5 , the refrigerant leaks from the high-pressure side to the low-pressure side through the gap between flow channel switching piston  23  and inner surface IS. 
     Generally, the relation among a flow rate coefficient Cv, a leakage flow rate Gr, and a pressure difference ΔP is represented by Expression (1) below. 
       [Math 1] 
         Gr∝Cv ×√{square root over (Δ P )}  (1)
 
     Expression (1) above is represented by Expression (2) with the use of a constant of proportion K, a high-pressure-side pressure P 1 , a low-pressure-side pressure P 2 , and a flow rate coefficient Cv 1  at a leakage spot in the sliding portion of flow channel switching piston  23 . High-pressure-side pressure P 1  is a pressure outside of flow channel switching piston  23 . Low-pressure-side pressure P 2  is a pressure inside of flow channel switching piston  23 . 
       [Math 2] 
         Gr=K×Cv   1 ×√{square root over ( P 1− P 2)}  (2)
 
     Referring to  FIG. 6 , description will be given of a leakage flow rate of the refrigerant that leaks from the high-pressure side to the low-pressure side in four-way valve  2  of refrigeration cycle apparatus  10  according to Embodiment 1. As indicated by the open arrows in  FIG. 6 , the refrigerant leaks from the high-pressure side to the low-pressure side through the gap between wall portion  24  and inner surface IS and through the gap between flow channel switching piston  23  and inner surface IS. The pressure outside of wall portion  24  is a high pressure, and the pressure inside of flow channel switching piston  23  is a low pressure. The pressure in space SP between wall portion  24  and flow channel switching piston  23  is an intermediate pressure. 
     Constant of proportion K, high-pressure-side pressure P 1 , a pressure Pm in space SP between wall portion  24  and flow channel switching piston  23 , a flow rate coefficient Cv 2  at a leakage spot in the sliding portion along which inner surface IS slides, and a leakage flow rate Gr′ at that spot is represented by Expression (3) below. High-pressure-side pressure P 1  is a pressure outside of wall portion  24 . 
       [Math 3] 
         Gr′=K×Cv   2 ×√{square root over ( P 1− Pm )}  (3)
 
     Constant of proportion K, low-pressure-side pressure P 2 , pressure Pm in space SP between wall portion  24  and flow channel switching piston  23 , flow rate coefficient Cv 1  at a leakage spot in the sliding portion of flow channel switching piston  23  on which inner surface IS slides, and a leakage flow rate Gr″ at that spot is represented by Expression (4) below. Low-pressure-side pressure P 2  is a pressure inside of flow channel switching piston  23 . 
       [Math 4] 
         Gr″=K×Cv   1 ×√{square root over ( Pm−P 2)}  (4)
 
     Since leakage flow rate Gr′ and leakage flow rate Gr″ are equal to each other (Gr′=Gr″) once the state of the refrigerant is stabilized, Expression (5) below is obtained by rearranging Expressions (3) and (4) above. 
     
       
         
           
             [ 
             
               Math 
               ⁢ 
               
                   
               
               ⁢ 
               5 
             
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                     Gr 
                     ′ 
                   
                   = 
                   
                     
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                               1 
                               
                                 Cv 
                                 1 
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                             ⁢ 
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                   ( 
                   5 
                   ) 
                 
               
             
           
         
       
     
     In Expression (5), the value of the term including the flow rate coefficient is smaller than that of flow rate coefficient Cv 1  as represented by Expressions (6) and (7) below. Thus, the leakage flow rate of the refrigerant decreases as wall portion  24  is provided. 
     When flow rate coefficient Cv 1  is not greater than flow rate coefficient Cv 2  (Cv 1 ≤Cv 2 ), the flow rate coefficient is represented by Expression (6) below. 
     
       
         
           
             [ 
             
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               6 
             
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                       1 
                     
                   
                 
               
               
                 
                   ( 
                   6 
                   ) 
                 
               
             
           
         
       
     
     When flow rate coefficient Cv 2  is not greater than flow rate coefficient Cv 1  (Cv 2 ≤Cv 1 ), the flow rate coefficient is represented by Expression (7) below. 
     
       
         
           
             [ 
             
               Math 
               ⁢ 
               
                   
               
               ⁢ 
               7 
             
             ] 
           
         
       
       
         
           
             
               
                 
                   
                     
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                             1 
                             
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                   = 
                   
                     
                       
                         
                           2 
                         
                         2 
                       
                       ⁢ 
                       
                         Cv 
                         2 
                       
                     
                     &lt; 
                     
                       Cv 
                       1 
                     
                   
                 
               
               
                 
                   ( 
                   7 
                   ) 
                 
               
             
           
         
       
     
     As described above, according refrigeration cycle apparatus  10  of Embodiment 1, in our-way valve  2 , wall portion  24  is configured to slide along the inner surface together with flow channel switching piston  23  and is disposed with space SP between flow channel switching piston  23  and wall portion  24  to cover flow channel switching piston  23 . The pressure of the refrigerant in space SP between wall portion  24  and flow channel switching piston  23  can thus be an intermediate pressure between the high-pressure side and the low-pressure side. This can reduce an amount of the refrigerant that leaks from the high-pressure side to the low-pressure side in four-way valve  2 . The amount of the refrigerant flowing into indoor heat exchanger  5  can thus be increased. As a result, heat exchange performance can be improved. 
     According to refrigeration cycle apparatus  10  of Embodiment 1, first flow channel F 1  is configured to pass the refrigerant from first connection port  22   a  to third connection port  22   c  and pass the refrigerant from fourth connection port  22   d  to second connection port  22   b . Second flow channel F 2  is configured to pass the refrigerant from first connection port  22   a  to fourth connection port  22   d  and pass the refrigerant from third connection port  22   c  to second connection port  22   b . This allows flow channel switching piston  23  to switch between passing the refrigerant from first connection port  22   a  to third connection port  22   c  and also from fourth connection port  22   d  to second connection port  22   b , and passing the refrigerant from first connection port  22   a  to fourth connection port  22   d  and also from third connection port  22   c  to second connection port  22   b.    
     In refrigeration cycle apparatus  10  according to Embodiment 1, wall portion  24  and flow channel switching piston  23  are each formed of a thermoplastic resin. The thermoplastic resin has a thermal conductivity of 0.2 to 0.5 (W/mK). On the other hand, a HFC refrigerant, such as R32, has a thermal conductivity of 0.02 (W/mK) in the gas phase. Thus, the HFC refrigerant in the gas phase has a higher heat insulation capacity than the thermoplastic resin. Thus, as the refrigerant fills a gap between wall portion  24  and flow channel  23 , refrigeration cycle apparatus  10  according to Embodiment 1 has more improved heat insulation performance than in the case where wall portion  24  and the flow channel switching piston are each formed of only the thermoplastic resin. This can reduce a heat loss in four-way valve  2 . 
     Embodiment 2 
     Embodiment 2 has the same configuration and operation as well as functions and effects as those of Embodiment 1 unless otherwise noted. Thus, the same components of Embodiment 2 as those of Embodiment 1 are denoted by the same reference numerals, and redundant description will not be repeated. Embodiment 2 is different from Embodiment 1 mainly in that it includes a first intermediate pressure channel. 
     The configuration of refrigeration cycle apparatus  10  according to Embodiment 1 will be described with reference to  FIGS. 7 and 8 .  FIG. 7  is a refrigerant circuit diagram of refrigeration cycle apparatus  10  according to Embodiment 2.  FIG. 8  is an enlarged sectional view taken along the line VIII-VIII of  FIG. 7 . 
     Refrigeration cycle apparatus  10  according to Embodiment 2 further includes a first channel R 1 , a second channel R 2 , and a first intermediate pressure channel M 1 . First channel R 1  connects first outdoor heat exchanger  3  to first expansion valve  4 . First channel R 1  is configured by connecting first outdoor heat exchanger  3  to first expansion valve  4  by a pipe. Second channel R 2  connects compressor  1  to first outdoor heat exchanger  3 . Second channel R 2  is configured by connecting compressor  1  to first outdoor heat exchanger  3  by a pipe. Specifically, second channel R 2  is configured by connecting compressor  1  to first outdoor heat exchanger  3  by a pipe through four-way valve  2 . First channel R 1  and second channel R 2  are disposed on the high-pressure side of the refrigerant circuit. 
     First intermediate pressure channel M 1  connects first channel R 1  or second channel R 2  to space SP of four-way valve  2 . First intermediate pressure channel M 1  is configured by connecting first channel R 1  or second channel R 2  to space SP of four-way valve  2  by a pipe. First intermediate pressure channel M 1  includes an on-off valve MB. On-off valve MB is configured to open and close the first intermediate pressure channel. On-off valve MB is, for example, a solenoid valve. In Embodiment 2, first intermediate pressure channel M 1  connects first channel R 1  to space SP of four-way valve  2 . 
     Next, an operation of refrigeration cycle apparatus  10  according to Embodiment 2 will be described with reference to  FIG. 9 . For convenience of description, refrigeration cycle apparatus  10  during cooling operation will be described by way of example. 
     At the start of operation (at the activation of a compressor), on-off valve MB of first intermediate pressure channel M 1  is opened. On-off valve MB is opened for a certain period of time for generating an intermediate pressure and is closed after a lapse of the certain period of time. As a result, an intermediate pressure is generated immediately at the start of operation in space SP of four-way valve  2 . 
     Next, the functions and effects of refrigeration cycle apparatus  10  according to Embodiment 2 will be described while comparing with those of refrigeration cycle apparatus  10  according to Embodiment 1. 
     Referring to  FIGS. 10 and 11 , description will be given of the state before the completion of generation of an intermediate pressure at four-way valve  2  in refrigeration cycle apparatus  10  according to Embodiment 2.  FIG. 10  is a graph showing a time that elapses before the completion of generation of an intermediate pressure in the refrigeration cycle apparatus according to Embodiment 1 for comparison with refrigeration cycle apparatus  10  according to Embodiment 2.  FIG. 11  is a graph showing a time that elapses before the completion of generation of an intermediate pressure in refrigeration cycle apparatus  10  according to Embodiment 2. 
     Referring to  FIG. 10 , refrigeration cycle apparatus  10  according to Embodiment 1 includes no first intermediate pressure channel M 1 , and accordingly, an intermediate pressure is generated gradually from the pressure at the time of stop of operation in four-way valve  2 . This results in a longer time (t 1 ) that elapses before the completion of generation of an intermediate pressure than in Embodiment 2. 
     Referring to  FIG. 11 , in refrigeration cycle apparatus  10  according to Embodiment 2, as on-off valve MB of first intermediate pressure channel M 1  is opened at the start of operation, the pressure in space SP is equal to a high pressure in four-way valve  2 . As on-off valve MB is closed, the pressure in space SP in four-way valve  2  decreases from the high pressure to the intermediate pressure. This can reduce the time (t 1 ) that elapses before the completion of generation of the intermediate pressure more than in Embodiment 1. 
     As described above, according to refrigeration cycle apparatus  10  of Embodiment 2, first intermediate pressure channel M 1  connects first channel R 1  or second channel R 2  to space SP of four-way valve  2 , and on-off valve MB is configured to open and close first intermediate pressure channel M 1 . Thus, as the high-pressure refrigerant is passed from first channel R 1  or second channel R 2  to space SP of four-way valve  2 , an intermediate pressure can be generated immediately in space SP. 
     According to refrigeration cycle apparatus  10  of Embodiment 2, first intermediate pressure channel M 1  connects first channel R 1  to the space. The refrigerant, the temperature of which has decreased due to heat radiation to the outdoor air in first outdoor heat exchanger  3 , can thus be passed to space SP of four-way valve  2 . This can restrain heat transfer from the refrigerant flowing through space SP of four-way valve  2  to the refrigerant flowing in flow channel switching piston  23 . 
     Embodiment 3 
     Embodiment 3 has the same configuration and operation as well as functions and effects as those of Embodiment 1 unless otherwise noted. Thus, the same components of Embodiment 3 as those of Embodiment 1 are denoted by the same reference numerals, and redundant description will not be repeated. Embodiment 3 is different from Embodiment 1 mainly in that it includes a second intermediate pressure channel, a second expansion valve, and a second outdoor heat exchanger. 
     The configuration of refrigeration cycle apparatus  10  according to Embodiment 3 will be described with reference to  FIG. 12 .  FIG. 12  is a refrigerant circuit diagram of refrigeration cycle apparatus  10  according to Embodiment 3. 
     Refrigeration cycle apparatus  10  according to Embodiment 3 further includes a first channel R 1  and a second intermediate pressure channel M 2 . First channel R 1  connects first outdoor heat exchanger  3  to first expansion valve  4 . First channel R 1  is configured by connecting first outdoor heat exchanger  3  to first expansion valve  4  by a pipe. First channel R 1  includes a second expansion valve  4   a . Second expansion valve  4   a  is configured to expand the refrigerant condensed in the condenser to decompress the refrigerant. Second expansion valve  4   a  is connected to first outdoor heat exchanger  3 . Second expansion valve  4   a  is, for example, a solenoid valve. 
     Second intermediate pressure channel M 2  connects first channel R 1  to space SP of four-way valve  2 . Second intermediate pressure channel M 2  is configured by connecting first channel R 1  to space SP of four-way valve  2  by a pipe. Second intermediate pressure channel M 2  is always opened. Second intermediate pressure channel M can thus include no on-off valve. Second intermediate pressure channel M 2  is connected to between first expansion valve  4  and second expansion valve  4   a  in first channel R 1 . 
     First channel R 1  includes a second outdoor heat exchanger  3   a . Second outdoor heat exchanger  3   a  serves to exchange heat between the refrigerant flowing in second outdoor heat exchanger  3   a  and the outside air. Second outdoor heat exchanger  3   a  is disposed between first expansion valve  4  and second expansion valve  4   a  in first channel R 1 . Second intermediate pressure channel M 2  is connected to between second expansion valve  4   a  and second outdoor heat exchanger  3   a  in first channel R 1 . 
     Next, an operation of refrigeration cycle apparatus  10  according to Embodiment 3 will be described with reference to  FIGS. 12 and 13 . For convenience of description, refrigeration cycle apparatus  10  during cooling operation will be described by way of example. 
     The high-temperature, high-pressure gas refrigerant compressed by compressor  1  flows through four-way valve  2  and is condensed in first outdoor heat exchanger  3 , turning into high-temperature liquid refrigerant. This high-temperature liquid refrigerant flows into second expansion valve  4   a  and expands to be decompressed in expansion valve  4   a , turning into gas-liquid-two-phase refrigerant. 
     This gas-liquid-two-phase refrigerant flows into second outdoor heat exchanger  3   a  and is condensed in second outdoor heat exchanger  3   a , turning into high-temperature liquid refrigerant. This high-temperature liquid refrigerant flows into first expansion valve  4  and expands to be decompressed in first expansion valve  4 , turning into low-temperature, low-pressure gas-liquid-two-phase refrigerant. 
     This low-temperature, low-pressure gas-liquid-two-phase refrigerant flows into indoor heat exchanger  5  and absorbs heat from the indoor air to evaporate in indoor heat exchanger  5 , turning into low-pressure gas refrigerant. This low-pressure gas refrigerant returns to compressor  1  through four-way valve  2  and is compressed by compressor  1 . In this manner, the refrigerant circulates through the refrigerant circuit during cooling operation. 
     Next, the functions and effects of refrigeration cycle apparatus  10  according to Embodiment 3 will be described. 
     According to refrigeration cycle apparatus  10  of Embodiment 3, second intermediate pressure channel M 2  is connected to between first expansion valve  4  and second expansion valve  4   a  in first channel R 1 . Thus, the pressure between first expansion valve  4  and second expansion valve  4   a  can generate an intermediate pressure in space SP of four-way valve  2 . 
     According to refrigeration cycle apparatus  10  of Embodiment 3, second intermediate pressure channel M 2  is connected to between second expansion valve  4   a  and second outdoor heat exchanger  3   a  in first channel R 1 . Thus, a part of the leakage flow rate of the refrigerant in four-way valve  2  is collected by first channel R 1  and condensed in second outdoor heat exchanger  3   a . The collected refrigerant flows into indoor heat exchanger  5 , and accordingly, the amount of the refrigerant flowing through indoor heat exchanger  5  can be increased. 
     It should be construed that the embodiments disclosed herein are given by way of illustration in all respects, not by way of limitation. It is therefore intended that the scope of the present invention is defined by claims, not only by the embodiments described above, and encompasses all modifications and variations equivalent in meaning and scope to the claims. 
     REFERENCE SIGNS LIST 
     
         
         
           
               1  compressor;  1   a  inlet;  1   b  outlet;  2  four-way valve;  3  first outdoor heat exchanger;  3   a  second outdoor heat exchanger;  4  first expansion valve;  4   a  second expansion valve;  5  indoor heat exchanger;  10  refrigeration cycle apparatus;  21  casing;  22   a  first connection port;  22   b  second connection port;  22   c  third connection port;  22   d  fourth connection port;  22   e  fifth connection port;  22   f  sixth connection port;  23  switching piston;  24  wall portion;  25  partitioning member;  26  pilot valve; F 1  first flow channel; F 2  second flow channel; IS inner surface; M 1  first intermediate pressure channel; M 2  second intermediate pressure channel; R 1  first channel; R 2  second channel; SP space.