Abstract:
A refrigeration cycle apparatus includes at least a compressor, a condenser, an internal heat exchanger configured to exchange heat between parts of refrigerant each having a different pressure, a refrigerant reservoir configured to store the refrigerant, a first pressure reducing device, an evaporator. The compressor, the condenser, the internal heat exchanger, the refrigerant reservoir, the first pressure reducing device, and the evaporator are sequentially connected to each other. The refrigeration cycle apparatus also includes a first pipe connecting the condenser and the refrigerant reservoir, and a second pressure reducing device provided to the first pipe between the internal heat exchanger and the refrigerant reservoir.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application is a U.S. national stage application of PCT/JP2014/069492 filed on Jul. 23, 2014, the contents of which are incorporated herein by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention relates to a refrigeration cycle apparatus including an internal heat exchanger. 
       BACKGROUND 
       [0003]    A related-art refrigeration cycle apparatus is generally known that includes an internal heat exchanger, in which refrigerant on a high-pressure side and refrigerant on a low-pressure side exchange heat, liquid refrigerant flowing into a pressure reducing device is subcooled, and gas refrigerant at an outlet of an evaporator is superheated to improve efficiency of a refrigeration cycle. 
         [0004]    In such a refrigeration cycle apparatus, to suppress a high pressure in a condenser, a degree of subcooling at a high-pressure side flow outlet of the internal heat exchanger is held at a predetermined value to suppress generation of subcooled liquid in the condenser and to enhance heat exchange efficiency (see Patent Literature 1). 
       PATENT LITERATURE 
       [0005]    Patent Literature 1: Japanese Unexamined Patent Application Publication No. 2011-052884 
         [0006]    In a related-art refrigeration cycle apparatus including an internal heat exchanger, to suppress a high pressure of a condenser during high temperature hot water output, generation of subcooled liquid in the condenser is suppressed. Thus, in subcooling operation, surplus refrigerant is generated in a refrigeration cycle. 
       SUMMARY 
       [0007]    The present invention has been made to solve such a problem, and an object of the present invention is to, in a refrigeration cycle apparatus including an internal heat exchanger, store surplus refrigerant generated in subcooling operation in a refrigerant reservoir having a minimum capacity. 
         [0008]    A refrigeration cycle apparatus according to one embodiment of the present invention includes at least a compressor, a condenser, an internal heat exchanger configured to exchange heat between parts of refrigerant each having a different pressure, a refrigerant reservoir configured to store the refrigerant, a first pressure reducing device, an evaporator. The compressor, the condenser, the internal heat exchanger, the refrigerant reservoir, the first pressure reducing device, and the evaporator are sequentially connected to each other. The refrigeration cycle apparatus also includes a first pipe connecting the condenser and the refrigerant reservoir, and a second pressure reducing device provided to the first pipe between the internal heat exchanger and the refrigerant reservoir. 
         [0009]    In the refrigeration cycle apparatus according to the one embodiment of the present invention, the refrigerant subcooled by the internal heat exchanger is decompressed into a saturated liquid or two-phase gas-liquid refrigerant similar to a saturated liquid by the second pressure reducing device and flows into the refrigerant reservoir. Surplus refrigerant can therefore be stored to the greatest extent, and thus, a capacity of the refrigerant reservoir can be reduced. Further, the refrigerant that flows in the refrigerant reservoir is not in a subcooled state, and thus mixes with a gas component to some extent, enabling the inside of the refrigerant reservoir to be prevented from becoming filled up. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0010]      FIG. 1  is a block diagram of a refrigeration cycle apparatus according to Embodiment 1 of the present invention. 
           [0011]      FIG. 2  is a Mollier diagram of the refrigeration cycle apparatus according to Embodiment 1. 
           [0012]      FIG. 3  is a Mollier diagram of Modified Example 1 of the refrigeration cycle apparatus according to Embodiment 1. 
           [0013]      FIG. 4  is a block diagram of Modified Example 2 of the refrigeration cycle apparatus according to Embodiment 1. 
           [0014]      FIG. 5  is a block diagram of Modified Example 3 of the refrigeration cycle apparatus according to Embodiment 1. 
           [0015]      FIG. 6  is a block diagram of a refrigeration cycle apparatus according to Embodiment 2 of the present invention. 
           [0016]      FIG. 7  is a Mollier diagram of the refrigeration cycle apparatus according to Embodiment 2. 
           [0017]      FIG. 8  is a block diagram of Modified Example 1 of the refrigeration cycle apparatus according to Embodiment 2. 
           [0018]      FIG. 9  is a block diagram of a refrigeration cycle apparatus according to Embodiment 3 of the present invention. 
           [0019]      FIG. 10  is a Mollier diagram of the refrigeration cycle apparatus according to Embodiment 3. 
           [0020]      FIG. 11  is a block diagram of a refrigeration cycle apparatus according to Embodiment 4 of the present invention. 
           [0021]      FIG. 12  is a Mollier diagram of the refrigeration cycle apparatus according to Embodiment 4. 
           [0022]      FIG. 13  is a block diagram of Modified Example 1 of the refrigeration cycle apparatus according to Embodiment 4. 
           [0023]      FIG. 14  is a Mollier diagram of Modified Example 1 of the refrigeration cycle apparatus according to Embodiment 4. 
           [0024]      FIG. 15  is a block diagram of a refrigeration cycle apparatus according to Embodiment 5 of the present invention. 
           [0025]      FIG. 16  is a Mollier diagram of the refrigeration cycle apparatus according to Embodiment 5. 
           [0026]      FIG. 17  is a block diagram of a refrigeration cycle apparatus according to Embodiment 6 of the present invention. 
           [0027]      FIG. 18  is a block diagram of a refrigeration cycle apparatus according to Embodiment 7 of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0028]    Embodiments of the present invention are described below with reference to the drawings. Note that, the present invention is not limited to the embodiments described below. 
       Embodiment 1 
     &lt;Configuration&gt; 
       [0029]      FIG. 1  is a block diagram of a refrigeration cycle apparatus according to Embodiment 1 of the present invention. 
         [0030]      FIG. 2  is a Mollier diagram of the refrigeration cycle apparatus according to Embodiment 1. 
         [0031]    As illustrated in  FIG. 1 , the refrigeration cycle apparatus according to Embodiment 1 includes a refrigerant circuit in which an outdoor unit  100  and a heat transfer unit  200  are connected via a gas connection pipe  4  and a liquid connection pipe  11 . 
         [0032]    A first pressure reducing device  101 , an evaporator  102 , a four-way valve  103 , and a compressor  104  are housed in the outdoor unit  100 . 
         [0033]    In the outdoor unit  100 , the evaporator  102  provided with a fan  102   a  and the four-way valve  103  are connected via a pipe  1 , the four-way valve  103  and a suction side of the compressor  104  are connected via a pipe  2 , and a discharge side of the compressor  104  and the gas connection pipe  4  are connected via a pipe  3 . Further, the liquid connection pipe  11 , the first pressure reducing device  101 , and the evaporator  102  are connected via a pipe  12 . 
         [0034]    Next, a condenser  201  (for example, water-refrigerant heat exchanger), an internal heat exchanger  202 , a second pressure reducing device  203 , and a refrigerant reservoir  204  are housed in the heat transfer unit  200 . 
         [0035]    In the heat transfer unit  200 , the gas connection pipe  4  and the condenser  201  are connected via a pipe  5 , and the condenser  201  and a high-temperature-side path  202   a  of the internal heat exchanger  202  are connected via a pipe  6 . Further, the high-temperature-side path  202   a  of the internal heat exchanger  202  and the second pressure reducing device  203  are connected via a pipe  7 , and the second pressure reducing device  203  and the refrigerant reservoir  204  are connected via a pipe  8 . Further, the refrigerant reservoir  204  and a low-temperature-side path  202   b  of the internal heat exchanger  202  are connected via a pipe  9 , and the low-temperature-side path  202   b  of the internal heat exchanger  202  and the liquid connection pipe  11  are connected via a pipe  10 . 
         [0036]    A pressure gauge P configured to detect a discharge pressure of the compressor is provided at a point b in  FIG. 1 , and thermometers T 1 , T 2 , and T 3  configured to detect temperatures of the refrigerant are provided at a point c, a point d, and a point e, respectively. 
       &lt;Operation&gt; 
       [0037]    Description is made with reference to  FIG. 1  and  FIG. 2 . Points a to h in  FIG. 1  correspond to state points a to h, respectively, on the Mollier diagram of  FIG. 2 . 
         [0038]    In the refrigeration cycle apparatus according to Embodiment 1, when the compressor  104  is driven, a high pressure vapor refrigerant b compressed by the compressor  104  is condensed by the condenser  201  into high pressure two-phase gas-liquid refrigerant c and flows into the high-temperature-side path  202   a  of the internal heat exchanger  202 . The high pressure two-phase gas-liquid refrigerant is cooled by medium pressure two-phase gas-liquid refrigerant in the internal heat exchanger  202  into subcooled liquid refrigerant d and flows into the second pressure reducing device  203 . The high pressure subcooled liquid refrigerant is decompressed in the second pressure reducing device  203  into medium pressure saturated liquid (or two-phase gas-liquid) refrigerant e and flows into the refrigerant reservoir  204 , and the refrigerant is discharged from the refrigerant reservoir  204  in a single-phase liquid state f. 
         [0039]    The single-phase liquid refrigerant discharged from the refrigerant reservoir  204  flows into the low-temperature-side path  202   b  of the internal heat exchanger  202 , becomes two-phase refrigerant g while cooling the high pressure two-phase gas-liquid refrigerant, and is discharged. The two-phase refrigerant g flows into the liquid connection pipe  11  and then flows into the first pressure reducing device  101 . The refrigerant is decompressed in the first pressure reducing device  101  into a low pressure two-phase refrigerant h and flows into the evaporator  102 . The refrigerant exchanges heat with air in the evaporator  102  to become low pressure vapor refrigerant a, and is sucked and compressed again by the compressor  104 . 
         [0040]    A controller (not shown) detects the temperatures of the refrigerant passing the points c, d, and e with the thermometers T 1 , T 2 , and T 3 , respectively, detects a measurement value of the discharge pressure of the compressor  104 , and exercises capacity control over the respective pressure reducing devices and the fan so that the refrigerant at the point d is held at a predetermined degree of subcooling (for example, 5 degrees C.), the refrigerant at the point c is in the two-phase gas-liquid state, and further, the refrigerant at the point e is the saturated liquid or the two-phase gas-liquid refrigerant similar to the saturated liquid. 
       &lt;Effects&gt; 
       [0041]    In the refrigeration cycle apparatus according to Embodiment 1, through increase of a quality (dryness) of the refrigerant at an outlet of the condenser  201  and discharge of the refrigerant from the condenser  201  in the two-phase gas-liquid state c, the inside of the condenser  201  has no subcooled liquid with an inferior heat transfer property to improve heat exchange ability of the condenser  201 . The heat exchange ability of the condenser  201  is improved, and thus, an upper limit of a tapping temperature can be raised from that of the related art (for example, from 55 degrees C. to 60 degrees C.). Further, a condensation pressure when the high temperature hot water is discharged can be set to be low, and thus, efficiency of the refrigeration cycle apparatus can be improved. 
         [0042]    Further, the refrigerant flows into the refrigerant reservoir  204  as the saturated liquid or the two-phase gas-liquid refrigerant similar to the saturated liquid, and thus, surplus refrigerant can be stored to the greatest extent. At this time, the refrigerant flows into the refrigerant reservoir  204  under a state in which a gas component is mixed in the refrigerant to some extent, and thus, the inside of the refrigerant reservoir can be prevented from becoming filled up. 
         [0043]    Further, the refrigerant at an outlet of the high-temperature-side path  202   a  of the internal heat exchanger  202  flows into the second pressure reducing device  203  as a single-phase liquid, and thus, flow rate controllability can be improved. 
         [0044]    Further, commonality of the configuration of the outdoor unit  100  can be achieved to reduce costs of the refrigeration cycle apparatus. 
       Modified Example 1 
       [0045]    Modified Example 1 of the refrigeration cycle apparatus according to Embodiment 1 is described with reference to  FIG. 3 . 
         [0046]      FIG. 3  is a Mollier diagram of Modified Example 1 of the refrigeration cycle apparatus according to Embodiment 1. 
         [0047]    In Modified Example 1, as shown in  FIG. 3 , the refrigerant that is cooled by low pressure two-phase gas-liquid refrigerant in the internal heat exchanger  202  into the subcooled liquid refrigerant d and that flows into the second pressure reducing device  203  is decompressed in the second pressure reducing device  203  into low pressure saturated liquid refrigerant f, flows out of the refrigerant reservoir  204 , and flows into the low-temperature-side path  202   b  of the internal heat exchanger  202 . The refrigerant is heated in the internal heat exchanger  202  into two-phase refrigerant g, and flows into the first pressure reducing device  101 . At this time, the first pressure reducing device  101  is fully open. 
       &lt;Effects&gt; 
       [0048]    Modified Example 1 of the refrigeration cycle apparatus according to Embodiment 1 has, in addition to the effects of the refrigeration cycle apparatus according to Embodiment 1 described above, an effect that the refrigerant decompressed from a high pressure state (state d) to a low pressure state (state e) by the second pressure reducing device  203  causes an increased difference between the high pressure and the low pressure during heat exchange in the internal heat exchanger  202 , and thus, a heat exchange amount between the high pressure refrigerant and the low pressure refrigerant can be increased. 
         [0049]    Further, the refrigerant at the outlet of the high-temperature-side path  202   a  of the internal heat exchanger  202  is the single-phase liquid and flows into the second pressure reducing device  203 , and the first pressure reducing device  101  is controlled to be fully open, and thus, the flow rate controllability can be improved. 
       Modified Example 2 
       [0050]    Modified Example 2 of the refrigeration cycle apparatus according to Embodiment 1 is described with reference to  FIG. 4 . 
         [0051]      FIG. 4  is a block diagram of Modified Example 2 of the refrigeration cycle apparatus according to Embodiment 1. 
         [0052]    In Modified Example 2, as illustrated in  FIG. 4 , an air-refrigerant heat exchanger  201   a  is adopted as the condenser  201  provided with a fan  201   b.    
       &lt;Effects&gt; 
       [0053]    Modified Example 2 of the refrigeration cycle apparatus according to Embodiment 1 has, in addition to the effects of the refrigeration cycle apparatus according to Embodiment 1 described above, an effect that high pressure rise of the air-refrigerant heat exchanger can be suppressed. 
       Modified Example 3 
       [0054]    Modified Example 3 of the refrigeration cycle apparatus according to Embodiment 1 is described with reference to  FIG. 5 . 
         [0055]      FIG. 5  is a block diagram of Modified Example 3 of the refrigeration cycle apparatus according to Embodiment 1. 
         [0056]    In Modified Example 3, the first pressure reducing device  101  is provided to the pipe  10  in the heat transfer unit  200 . 
       &lt;Effects&gt; 
       [0057]    Even when the refrigeration cycle apparatus according to Modified Example 3 has such a configuration, effects similar to those of the refrigeration cycle apparatus according to Embodiment 1 described above can be obtained. 
       Embodiment 2 
     &lt;Configuration&gt; 
       [0058]      FIG. 6  is a block diagram of a refrigeration cycle apparatus according to Embodiment 2 of the present invention. 
         [0059]      FIG. 7  is a Mollier diagram of the refrigeration cycle apparatus according to Embodiment 2. 
         [0060]    As illustrated in  FIG. 6 , the refrigeration cycle apparatus according to Embodiment 2 includes a refrigerant circuit in which the outdoor unit  100  and the heat transfer unit  200  are connected via the gas connection pipe  4  and the liquid connection pipe  11 . 
         [0061]    The first pressure reducing device  101 , the evaporator  102 , the four-way valve  103 , and the compressor  104  are housed in the outdoor unit  100 . 
         [0062]    In the outdoor unit  100 , the evaporator  102  provided with the fan  102   a  and the four-way valve  103  are connected via the pipe  1 , the four-way valve  103  and the suction side of the compressor  104  are connected via the pipe  2 , and the discharge side of the compressor  104  and the gas connection pipe  4  are connected via the pipe  3 . Further, the liquid connection pipe  11 , the first pressure reducing device  101 , and the evaporator  102  are connected via the pipe  12 . 
         [0063]    Next, the condenser  201  (for example, water-refrigerant heat exchanger), the internal heat exchanger  202 , the second pressure reducing device  203 , and the refrigerant reservoir  204  are housed in the heat transfer unit  200 . 
         [0064]    In the heat transfer unit  200 , the gas connection pipe  4  and the condenser  201  are connected via the pipe  5 , and the condenser  201  and the high-temperature-side path  202   a  of the internal heat exchanger  202  are connected via the pipe  6 . Further, the high-temperature-side path  202   a  of the internal heat exchanger  202  and the second pressure reducing device  203  are connected via the pipe  7 , the second pressure reducing device  203  and a branch portion  205  are connected via the pipe  8 , and the branch portion  205  and the refrigerant reservoir  204  are connected via a pipe  8   a . The refrigerant reservoir  204  and a merging portion  206  are connected via a pipe  9   a , and the branch portion  205  and the low-temperature-side path  202   b  of the internal heat exchanger  202  are connected via a pipe  8   b . Further, the low-temperature-side path  202   b  of the internal heat exchanger  202  and the merging portion  206  are connected via a pipe  9   b , and the merging portion  206  and the liquid connection pipe  11  are connected via the pipe  10 . 
         [0065]    The pressure gauge P configured to detect the discharge pressure of the compressor is provided at the point b in  FIG. 6 , and the thermometers T 1 , T 2 , and T 3  configured to detect the temperatures of the refrigerant are provided at the point c, the point d, and the point e, respectively. 
       &lt;Operation&gt; 
       [0066]    Description is made with reference to  FIG. 6  and  FIG. 7 . Points a to g and A to C in  FIG. 6  correspond to state points a to g and A to C, respectively, on the Mollier diagram of  FIG. 7 . 
         [0067]    In the refrigeration cycle apparatus according to Embodiment 2, when the compressor  104  is driven, the high pressure vapor refrigerant b compressed by the compressor  104  is condensed by the condenser  201  into the high pressure two-phase gas-liquid refrigerant c and flows into the high-temperature-side path  202   a  of the internal heat exchanger  202 . The high pressure two-phase gas-liquid refrigerant is cooled by medium pressure two-phase gas-liquid refrigerant in the internal heat exchanger  202  into the subcooled liquid refrigerant d and flows into the second pressure reducing device  203 . The high pressure subcooled liquid refrigerant is decompressed in the second pressure reducing device  203  into the medium pressure saturated liquid (or two-phase gas-liquid) refrigerant e and flows into the branch portion  205 . 
         [0068]    The refrigerant that branches at the branch portion  205  flows into the refrigerant reservoir  204  and the low-temperature-side path  202   b  of the internal heat exchanger  202 . The refrigerant flowing into the refrigerant reservoir  204  flows out in the single-phase liquid state f. The refrigerant flowing into the internal heat exchanger  202  in a state A flows out in a state B while cooling the high pressure two-phase gas-liquid refrigerant. The refrigerant flowing out of the refrigerant reservoir  204  and the refrigerant flowing out of the internal heat exchanger  202  merge at the merging portion  206 . The refrigerant merging at the merging portion  206  in a state C flows into the liquid connection pipe  11  and flows into the first pressure reducing device  101 . The refrigerant in the state C is decompressed in the first pressure reducing device  101  into refrigerant in a state g, and flows into the evaporator  102 . The refrigerant exchanges heat with air in the evaporator  102  to become the low pressure vapor refrigerant a, and is sucked and compressed again by the compressor  104 . 
         [0069]    The controller (not shown) detects the temperatures of the refrigerant passing the points c, d, and e with the thermometers T 1 , T 2 , and T 3 , respectively, detects a measurement value of the discharge pressure of the compressor  104 , and exercises capacity control over the respective pressure reducing devices and the fan so that the refrigerant at the point d is held at a predetermined degree of subcooling (for example, 5 degrees C.), the refrigerant at the point c is in the two-phase gas-liquid state, and further, the refrigerant at the point e is the saturated liquid or the two-phase refrigerant similar to the saturated liquid. 
       &lt;Effects&gt; 
       [0070]    In the refrigeration cycle apparatus according to Embodiment 2, similarly to the refrigeration cycle apparatus according to Embodiment 1, through increase of the quality of the refrigerant at the outlet of the condenser  201  and discharge of the refrigerant from the condenser  201  in the two-phase gas-liquid state c, the inside of the condenser  201  has no subcooled liquid with an inferior heat transfer property to improve heat exchange ability of the condenser  201 . The heat exchange ability of the condenser  201  is improved, and thus, the upper limit of the tapping temperature can be raised from that of the related art (for example, from 55 degrees C. to 60 degrees C.). Further, the condensation pressure when the high temperature hot water is discharged can be set to be low, and thus, efficiency of the refrigeration cycle apparatus can be improved. 
         [0071]    Further, the refrigerant flows into the refrigerant reservoir  204  as the saturated liquid or the two-phase gas-liquid refrigerant similar to the saturated liquid, and thus, surplus refrigerant can be stored to the greatest extent. At this time, the refrigerant flows into the refrigerant reservoir  204  under a state in which a gas component is mixed in the refrigerant to some extent, and thus, the inside of the refrigerant reservoir can be prevented from becoming filled up. 
         [0072]    Further, the refrigerant at the outlet of the high-temperature-side path  202   a  of the internal heat exchanger  202  flows into the second pressure reducing device  203  as a single-phase liquid, and thus, flow rate controllability can be improved. 
         [0073]    Further, commonality of the configuration of the outdoor unit  100  can be achieved to reduce costs of the refrigeration cycle apparatus. 
         [0074]    In addition to those effects, by causing the refrigerant at the inlet of the low-temperature-side path  202   b  of the internal heat exchanger  202  to be in the two-phase state, the heat exchange amount in the internal heat exchanger can be increased. 
         [0075]    Further, through branching of the refrigerant at the branch portion  205 , the amount of the refrigerant flowing through the low-temperature-side path  202   b  of the internal heat exchanger  202  can be reduced to reduce the size of the internal heat exchanger  202 . 
       Modified Example 1 
       [0076]    Modified Example 1 of the refrigeration cycle apparatus according to Embodiment 2 is described with reference to  FIG. 8 . 
         [0077]      FIG. 8  is a block diagram of Modified Example 1 of the refrigeration cycle apparatus according to Embodiment 2. 
         [0078]    As illustrated in  FIG. 8 , Modified Example 1 is different from Embodiment 2 described above in that a third pressure reducing device  207  is provided to the pipe  8   b  between the branch portion  205  and the low-temperature-side path  202   b  of the internal heat exchanger  202 . 
       &lt;Effects&gt; 
       [0079]    In addition to the effects of Embodiment 2 described above, the third pressure reducing device  207  can control the flow rate of the refrigerant flowing through the low-temperature-side path  202   b  of the internal heat exchanger  202 , and thus, the degree of subcooling of the refrigerant at the outlet of the high-temperature-side path  202   a  of the internal heat exchanger  202  can be finely controlled. 
       Embodiment 3 
     &lt;Configuration&gt; 
       [0080]      FIG. 9  is a block diagram of a refrigeration cycle apparatus according to Embodiment 3 of the present invention. 
         [0081]      FIG. 10  is a Mollier diagram of the refrigeration cycle apparatus according to Embodiment 3. 
         [0082]    As illustrated in  FIG. 9 , the refrigeration cycle apparatus according to Embodiment 3 includes a refrigerant circuit in which the outdoor unit  100  and the heat transfer unit  200  are connected via the gas connection pipe  4  and the liquid connection pipe  11 . 
         [0083]    The first pressure reducing device  101 , the evaporator  102 , the four-way valve  103 , and the compressor  104  are housed in the outdoor unit  100 . 
         [0084]    In the outdoor unit  100 , the evaporator  102  provided with the fan  102   a  and the four-way valve  103  are connected via the pipe  1 , the four-way valve  103  and the suction side of the compressor  104  are connected via the pipe  2 , and the discharge side of the compressor  104  and the gas connection pipe  4  are connected via the pipe  3 . Further, the liquid connection pipe  11 , the first pressure reducing device  101 , and the evaporator  102  are connected via the pipe  12 . 
         [0085]    Next, the condenser  201  (for example, water-refrigerant heat exchanger), the internal heat exchanger  202 , the second pressure reducing device  203 , and the refrigerant reservoir  204  are housed in the heat transfer unit  200 . 
         [0086]    In the heat transfer unit  200 , the gas connection pipe  4  and the condenser  201  are connected via the pipe  5 , and the condenser  201  and the high-temperature-side path  202   a  of the internal heat exchanger  202  are connected via the pipe  6 . Further, the high-temperature-side path  202   a  of the internal heat exchanger  202  and the second pressure reducing device  203  are connected via the pipe  7 , and the second pressure reducing device  203  and the refrigerant reservoir  204  are connected via the pipe  8 . Further, the refrigerant reservoir  204  and the low-temperature-side path  202   b  of the internal heat exchanger  202  are connected via the pipe  9 , and a fourth pressure reducing device  208  is provided to the pipe  9 . Further, the low-temperature-side path  202   b  of the internal heat exchanger  202  and the liquid connection pipe  11  are connected via the pipe  10 . 
         [0087]    The pressure gauge P configured to detect a discharge pressure of the compressor is provided at the point b in  FIG. 9 , and the thermometers T 1 , T 2 , and T 3  configured to detect temperatures of the refrigerant are provided at the point c, the point d, and the point e, respectively. 
       &lt;Operation&gt; 
       [0088]    Description is made with reference to  FIG. 9  and  FIG. 10 . Points a to i in  FIG. 9  correspond to state points a to i, respectively, on the Mollier diagram of  FIG. 10 . 
         [0089]    In the refrigeration cycle apparatus according to Embodiment 3, when the compressor  104  is driven, the high pressure vapor refrigerant b compressed by the compressor  104  is condensed by the condenser  201  into the high pressure two-phase gas-liquid refrigerant c and flows into the high-temperature-side path  202   a  of the internal heat exchanger  202 . The high pressure two-phase gas-liquid refrigerant is cooled by the medium pressure two-phase gas-liquid refrigerant in the internal heat exchanger  202  into the subcooled liquid refrigerant d and flows into the second pressure reducing device  203 . The high pressure subcooled liquid refrigerant is decompressed in the second pressure reducing device  203  into the medium pressure saturated liquid (or two-phase gas-liquid) refrigerant e and flows into the refrigerant reservoir  204 , and the refrigerant is discharged from the refrigerant reservoir  204  in the single-phase liquid state f. 
         [0090]    The medium pressure liquid refrigerant in the single-phase liquid state f discharged from the refrigerant reservoir  204  flows into the fourth pressure reducing device  208  and is decompressed into the low pressure two-phase gas-liquid refrigerant g. The low pressure two-phase gas-liquid refrigerant g flows into the internal heat exchanger  202 , and exchanges heat while cooling the high pressure two-phase gas-liquid refrigerant from the condenser  201  to become the low pressure two-phase refrigerant h. The low pressure two-phase refrigerant h flows through the liquid connection pipe  11  and flows into the first pressure reducing device  101 . At this time, the first pressure reducing device  101  is controlled to be fully open, and the refrigerant flows out of the first pressure reducing device  101  in a state i and flows into the evaporator  102 . The refrigerant exchanges heat with air in the evaporator  102  to become the low pressure vapor refrigerant a, and is sucked and compressed again by the compressor  104 . 
         [0091]    The controller (not shown) detects the temperatures of the refrigerant passing the points c, d, and e with the thermometers T 1 , T 2 , and T 3 , respectively, detects a measurement value of the discharge pressure of the compressor  104 , and exercises capacity control over the respective pressure reducing devices and the fan so that the refrigerant at the point d is held at a predetermined degree of subcooling (for example, 5 degrees C.), the refrigerant at the point c is in the two-phase gas-liquid state, and further, the refrigerant at the point e is the saturated liquid or the two-phase refrigerant similar to the saturated liquid. 
       &lt;Effects&gt; 
       [0092]    In the refrigeration cycle apparatus according to Embodiment 3, similarly to the refrigeration cycle apparatus according to Embodiment 1, through increase of the quality of the refrigerant at the outlet of the condenser  201  and discharge of the refrigerant from the condenser  201  in the two-phase gas-liquid state c, the inside of the condenser  201  has no subcooled liquid with an inferior heat transfer property to improve heat exchange ability of the condenser  201 . The heat exchange ability of the condenser  201  is improved, and thus, an upper limit of the tapping temperature can be raised from that of the related art (for example, from 55 degrees C. to 60 degrees C.). Further, a condensation pressure when the high temperature hot water is discharged can be set to be low, and thus, efficiency of the refrigeration cycle apparatus can be improved. 
         [0093]    Further, the refrigerant flows into the refrigerant reservoir  204  as the saturated liquid or the two-phase gas-liquid refrigerant similar to the saturated liquid, and thus, surplus refrigerant can be stored to the greatest extent. At this time, the refrigerant flows into the refrigerant reservoir  204  under a state in which a gas component is mixed in the refrigerant to some extent, and thus, the inside of the refrigerant reservoir can be prevented from becoming filled up. 
         [0094]    Further, the refrigerant at the outlet of the high-temperature-side path  202   a  of the internal heat exchanger  202  flows into the second pressure reducing device  203  and the fourth pressure reducing device  208  as a single-phase liquid, and thus, flow rate controllability can be improved. 
         [0095]    Further, commonality of the configuration of the outdoor unit  100  can be achieved to reduce costs of the refrigeration cycle apparatus. 
         [0096]    In addition to the effects of the refrigeration cycle apparatus according to Embodiment 1 described above, the refrigerant decompressed from a high pressure state (state d) to a low pressure state (state g) by the fourth pressure reducing device  208  exchanges heat in the internal heat exchanger  202 . Thus, the decompressed refrigerant causes an increased difference between the high pressure and the low pressure in the internal heat exchanger  202 , and a heat exchange amount between the high pressure refrigerant and the low pressure refrigerant can be increased. 
         [0097]    Further, the refrigerant at the outlet of the refrigerant reservoir  204  is in the single-phase liquid state f and flows into the fourth pressure reducing device  208 . Further, the first pressure reducing device  101  is controlled to be fully open, and thus, the flow rate controllability can be improved. 
       Embodiment 4 
     &lt;Configuration&gt; 
       [0098]      FIG. 11  is a block diagram of a refrigeration cycle apparatus according to Embodiment 4 of the present invention. 
         [0099]      FIG. 12  is a Mollier diagram of the refrigeration cycle apparatus according to Embodiment 4. 
         [0100]    As illustrated in  FIG. 11 , the refrigeration cycle apparatus according to Embodiment 4 includes a refrigerant circuit in which the outdoor unit  100  and the heat transfer unit  200  are connected via the gas connection pipe  4  and the liquid connection pipe  11 . 
         [0101]    The first pressure reducing device  101 , the evaporator  102 , the four-way valve  103 , and the compressor  104  are housed in the outdoor unit  100 . 
         [0102]    In the outdoor unit  100 , the evaporator  102  provided with the fan  102   a  and the four-way valve  103  are connected via the pipe  1 , the four-way valve  103  and the suction side of the compressor  104  are connected via the pipe  2 , and the discharge side of the compressor  104  and the gas connection pipe  4  are connected via the pipe  3 . Further, the liquid connection pipe  11 , the first pressure reducing device  101 , and the evaporator  102  are connected via the pipe  12 . 
         [0103]    Next, the condenser  201  (for example, water-refrigerant heat exchanger), the internal heat exchanger  202 , the second pressure reducing device  203 , and the refrigerant reservoir  204  are housed in the heat transfer unit  200 . 
         [0104]    In the heat transfer unit  200 , the gas connection pipe  4  and the condenser  201  are connected via the pipe  5 , the condenser  201  and the high-temperature-side path  202   a  of the internal heat exchanger  202  are connected via the pipe  6 , and the high-temperature-side path  202   a  of the internal heat exchanger  202  and the branch portion  205  are connected via the pipe  7 . Further, the branch portion  205  and the second pressure reducing device  203  are connected via a pipe  7   a , the second pressure reducing device  203  and the refrigerant reservoir  204  are connected via the pipe  8   a , and the refrigerant reservoir  204  and the merging portion  206  are connected via the pipe  9   a . Further, the branch portion  205  and the third pressure reducing device  207  (closed during normal operation) are connected via a pipe  7   b . The third pressure reducing device  207  and the low-temperature-side path  202   b  of the internal heat exchanger  202  are connected via the pipe  8   b , the low-temperature-side path  202   b  of the internal heat exchanger  202  and the merging portion  206  are connected via the pipe  9   b , and the merging portion  206  and the liquid connection pipe  11  are connected via the pipe  10 . 
         [0105]    The pressure gauge P configured to detect a discharge pressure of the compressor is provided at the point b in  FIG. 11 , and the thermometers T 1 , T 2 , and T 3  configured to detect temperatures of the refrigerant are provided at the point c, the point d, and the point e, respectively. 
       &lt;Operation&gt; 
       [0106]    Description is made with reference to  FIG. 11  and  FIG. 12 . Points a to g and A to C in  FIG. 11  correspond to state points a to g and A to C, respectively, on the Mollier diagram of  FIG. 12 . 
       1) During High Pressure Rise Suppression Operation 
       [0107]    In the refrigeration cycle apparatus according to Embodiment 4, when the compressor  104  is driven, the high pressure vapor refrigerant b compressed by the compressor  104  is condensed by the condenser  201  into the high pressure two-phase gas-liquid refrigerant c and flows into the internal heat exchanger  202 . The high pressure two-phase gas-liquid refrigerant is cooled by the medium pressure two-phase gas-liquid refrigerant in the internal heat exchanger  202  into the subcooled liquid refrigerant d and flows into the branch portion  205 . The refrigerant branches from the branch portion  205  into the second pressure reducing device  203  and the third pressure reducing device  207 . The high pressure subcooled liquid refrigerant is decompressed in the second pressure reducing device  203  into the medium pressure liquid refrigerant e and flows into the refrigerant reservoir  204 . The refrigerant flows out in the single-phase liquid state f to flow into the merging portion  206 . 
         [0108]    The refrigerant flowing into the third pressure reducing device  207  flows out in the medium pressure two-phase gas-liquid refrigerant state A. The medium pressure two-phase gas-liquid refrigerant flows into the internal heat exchanger  202  to be in the state B while cooling the high pressure two-phase gas-liquid refrigerant from the condenser  201  and flows into the merging portion  206 . The superheated refrigerant B becomes the medium pressure two-phase gas-liquid refrigerant state C at the merging portion  206 , flows through the liquid connection pipe  11 , and flows into the first pressure reducing device  101 . The refrigerant is decompressed in the first pressure reducing device  101  into the low pressure two-phase gas-liquid refrigerant g and flows into the evaporator  102 . The refrigerant exchanges heat with air in the evaporator  102  to become the low pressure vapor refrigerant a, and is sucked and compressed again by the compressor  104 . 
         [0109]    The controller (not shown) detects the temperatures of the refrigerant passing the points c, d, and e with the thermometers T 1 , T 2 , and T 3 , respectively, detects a measurement value of the discharge pressure of the compressor  104 , and exercises capacity control over the respective pressure reducing devices and the fan so that the refrigerant at the point d is held at a predetermined degree of subcooling (for example, 5 degrees C.), the refrigerant at the point c is in the two-phase gas-liquid state, and further, the refrigerant at the point e is the saturated liquid or the two-phase refrigerant similar to the saturated liquid. 
       2) During Normal Operation (Third Pressure Reducing Device  207  is Closed) 
       [0110]    The high pressure single-phase liquid refrigerant c discharged from the condenser  201  flows into the second pressure reducing device  203  to be decompressed by the second pressure reducing device  203  into the medium pressure two-phase gas-liquid refrigerant e, and flows into the refrigerant reservoir  204 . The refrigerant flows out in the single-phase liquid state f, flows through the liquid connection pipe  11 , and flows into the first pressure reducing device  101 . The liquid refrigerant is decompressed in the first pressure reducing device  101  to be in the state g, and flows into the evaporator  102 . The low pressure vapor refrigerant a exchanging heat with air in the evaporator  102  is sucked and compressed again by the compressor  104 . 
       &lt;Effects&gt; 
       [0111]    In the refrigeration cycle apparatus according to Embodiment 4, in the high pressure rise suppression operation, similarly to the refrigeration cycle apparatus according to Embodiment 1, through increase of the quality of the refrigerant at the outlet of the condenser  201  and discharge of the refrigerant from the condenser  201  in the two-phase gas-liquid state c, the inside of the condenser  201  has no subcooled liquid with an inferior heat transfer property to improve heat exchange ability of the condenser  201 . The heat exchange ability of the condenser  201  is improved, and thus, an upper limit of the tapping temperature can be raised from that of the related art (for example, from 55 degrees C. to 60 degrees C.). Further, a condensation pressure when the high temperature hot water is discharged can be set to be low, and thus, efficiency of the refrigeration cycle apparatus can be improved. 
         [0112]    Further, the refrigerant flows into the refrigerant reservoir  204  as the saturated liquid or the two-phase gas-liquid refrigerant similar to the saturated liquid, and thus, surplus refrigerant can be stored to the greatest extent. At this time, the refrigerant flows into the refrigerant reservoir  204  under a state in which a gas component is mixed in the refrigerant to some extent, and thus, the inside of the refrigerant reservoir can be prevented from becoming filled up. 
         [0113]    Further, the refrigerant at the outlet of the high-temperature-side path  202   a  of the internal heat exchanger  202  flows into the second pressure reducing device  203  and the third pressure reducing device  207  as a single-phase liquid, and thus, flow rate controllability can be improved. 
         [0114]    Further, commonality of the configuration of the outdoor unit  100  can be achieved to reduce costs of the refrigeration cycle apparatus. 
         [0115]    In addition to the effects described above, the third pressure reducing device  207  can control the flow rate of the refrigerant flowing through the low-temperature-side path  202   b  of the internal heat exchanger  202 , and thus, the degree of subcooling at the point d can be finely controlled. 
         [0116]    Further, in the normal operation, through control of the degree of subcooling at the outlet of the condenser  201  with the temperature and the pressure at the outlet of the condenser  201 , the heat exchange amount of the condenser  201  can be improved. 
       Modified Example 1 
       [0117]    Modified Example 1 of the refrigeration cycle apparatus according to Embodiment 4 is described with reference to  FIG. 13  and  FIG. 14 . 
         [0118]      FIG. 13  is a block diagram of Modified Example 1 of the refrigeration cycle apparatus according to Embodiment 4. 
         [0119]      FIG. 14  is a Mollier diagram of Modified Example 1 of the refrigeration cycle apparatus according to Embodiment 4. 
         [0120]    As illustrated in  FIG. 13 , Modified Example 1 is different from Embodiment 4 described above in that the merging portion  206  of the pipe  9   b  is provided on a downstream side of the second pressure reducing device  203 . Specifically, the second pressure reducing device  203  and the merging portion  206  are connected via the pipe  8   a , the merging portion  206  and the refrigerant reservoir  204  are connected via a pipe  8   c , and the refrigerant reservoir  204  and the liquid connection pipe  11  are connected via the pipe  10 . 
       &lt;Effects&gt; 
       [0121]    In addition to the effects of Embodiment 4 described above, the refrigerant at the outlet of the refrigerant reservoir  204  in the single-phase liquid state f flows into the first pressure reducing device  101 , and thus, the flow rate controllability can be prevented from being lowered. 
       Embodiment 5 
     &lt;Configuration&gt; 
       [0122]      FIG. 15  is a block diagram of a refrigeration cycle apparatus according to Embodiment 5 of the present invention. 
         [0123]      FIG. 16  is a Mollier diagram of the refrigeration cycle apparatus according to Embodiment 5. 
         [0124]    As illustrated in  FIG. 15 , the refrigeration cycle apparatus according to Embodiment 5 includes a refrigerant circuit in which the outdoor unit  100  and the heat transfer unit  200  are connected via the gas connection pipe  4  and the liquid connection pipe  11 . 
         [0125]    In the refrigeration cycle apparatus according to Embodiment 5, the fourth pressure reducing device  208  is provided to the pipe  9   a  of the heat transfer unit  200  of the refrigeration cycle apparatus according to Embodiment 4. 
       &lt;Operation&gt; 
       [0126]    Description is made with reference to  FIG. 15  and  FIG. 16 . Points a to h and A to C in  FIG. 15  correspond to state points a to h and A to C, respectively, on the Mollier diagram of  FIG. 16 . 
       1) During High Pressure Rise Suppression Operation 
       [0127]    The high pressure vapor refrigerant b compressed by the compressor  104  is condensed by the condenser  201  into the high pressure two-phase gas-liquid refrigerant c and flows into the internal heat exchanger  202 . The high pressure two-phase gas-liquid refrigerant is cooled by the medium pressure two-phase gas-liquid refrigerant in the internal heat exchanger  202  into the subcooled liquid refrigerant d and flows into the branch portion  205 . The refrigerant branches from the branch portion  205  into the second pressure reducing device  203  and the third pressure reducing device  207 . The high pressure subcooled liquid refrigerant is decompressed in the second pressure reducing device  203  into the medium pressure liquid refrigerant e and flows into the refrigerant reservoir  204 . The refrigerant flows out in the medium pressure liquid refrigerant state f. The medium pressure liquid refrigerant flows into and is decompressed by the fourth pressure reducing device  208  into the low pressure two-phase gas-liquid refrigerant g, and flows into the merging portion  206 . 
         [0128]    The refrigerant flowing into the third pressure reducing device  207  is decompressed and flows out in the low pressure two-phase gas-liquid refrigerant state A. The low pressure two-phase gas-liquid refrigerant flows into the internal heat exchanger  202  and exchanges heat while cooling the high pressure two-phase gas-liquid refrigerant from the condenser  201 . The refrigerant in the state B flowing out of the internal heat exchanger  202  flows into the merging portion  206 . The refrigerant in the state B becomes the low pressure two-phase gas-liquid refrigerant C at the merging portion  206 , flows through the liquid connection pipe  11 , and flows into the first pressure reducing device  101 . At this time, the first pressure reducing device  101  is controlled to be fully open, and the refrigerant flows out of the first pressure reducing device  101  in a state h and flows into the evaporator  102 . The refrigerant exchanges heat with air in the evaporator  102  to become the low pressure vapor refrigerant a, and is sucked and compressed again by the compressor  104 . 
         [0129]    The controller (not shown) detects the temperatures of the refrigerant passing the points c, d, and e with the thermometers T 1 , T 2 , and T 3 , respectively, detects a measurement value of the discharge pressure of the compressor  104 , and exercises capacity control over the respective pressure reducing devices and the fan so that the refrigerant at the point d is held at a predetermined degree of subcooling (for example, 5 degrees C.), the refrigerant at the point c is in the two-phase gas-liquid state, and further, the refrigerant at the point e is the saturated liquid or the two-phase refrigerant similar to the saturated liquid. 
       2) During Normal Operation (Third Pressure Reducing Device  207  is Fully Closed) 
       [0130]    The high pressure single-phase liquid refrigerant c flowing out of the condenser  201  flows into the second pressure reducing device  203  to be decompressed by the second pressure reducing device  203  into the medium pressure two-phase gas-liquid refrigerant e. The refrigerant then flows into the refrigerant reservoir  204 , flows out in the single-phase liquid state f, and flows into the first pressure reducing device  101 . The liquid refrigerant is decompressed in the first pressure reducing device  101  to be in the state h, and flows into the evaporator  102 . The refrigerant exchanges heat with air in the evaporator  102  to become the low pressure vapor refrigerant a, and is sucked and compressed again by the compressor  104 . 
       &lt;Effects&gt; 
       [0131]    In the refrigeration cycle apparatus according to Embodiment 5, similarly to the refrigeration cycle apparatus according to Embodiment 1, through increase of the quality of the refrigerant at the outlet of the condenser  201  and discharge of the refrigerant from the condenser  201  in the two-phase gas-liquid state c, the inside of the condenser  201  has no subcooled liquid with an inferior heat transfer property to improve heat exchange ability of the condenser  201 . The heat exchange ability of the condenser  201  is improved, and thus, an upper limit of the tapping temperature can be raised from that of the related art (for example, from 55 degrees C. to 60 degrees C.). Further, a condensation pressure when the high temperature hot water is discharged can be set to be low, and thus, efficiency of the refrigeration cycle apparatus can be improved. 
         [0132]    Further, the refrigerant flows into the refrigerant reservoir  204  as the saturated liquid or the two-phase gas-liquid refrigerant similar to the saturated liquid, and thus, surplus refrigerant can be stored to the greatest extent. At this time, the refrigerant flows into the refrigerant reservoir  204  under a state in which a gas component is mixed in the refrigerant to some extent, and thus, the inside of the refrigerant reservoir can be prevented from becoming filled up. 
         [0133]    Further, the refrigerant at the outlet of the high-temperature-side path  202   a  of the internal heat exchanger  202  flows into the second pressure reducing device  203  and the third pressure reducing device  207  as a single-phase liquid, and thus, flow rate controllability can be improved. 
         [0134]    Further, commonality of the configuration of the outdoor unit  100  can be achieved to reduce costs of the refrigeration cycle apparatus. 
         [0135]    Further, in the refrigeration cycle apparatus according to Embodiment 5, the third pressure reducing device  207  causes the internal heat exchanger  202  to exchange heat between the low pressure refrigerant and the high pressure refrigerant, and thus the heat exchange amount can be improved. 
       Embodiment 6 
     &lt;Configuration&gt; 
       [0136]      FIG. 17  is a block diagram of a refrigeration cycle apparatus according to Embodiment 6 of the present invention. 
         [0137]    As illustrated in  FIG. 17 , in the refrigeration cycle apparatus according to Embodiment 6, the outdoor unit  100 , a high pressure rise suppression unit  300 , and the heat transfer unit  200  are connected via the gas connection pipe  4 , a first liquid connection pipe  11   a , and a second liquid connection pipe  11   b.    
         [0138]    The first pressure reducing device  101 , the evaporator  102 , the four-way valve  103 , and the compressor  104  are housed in the outdoor unit  100 . 
         [0139]    The condenser  201  (for example, water-refrigerant heat exchanger) is housed in the heat transfer unit  200 . 
         [0140]    The internal heat exchanger  202 , the second pressure reducing device  203 , and the refrigerant reservoir  204  are housed in the high pressure rise suppression unit  300 . 
         [0141]    The configuration of connecting pipes is similar to that in Embodiment 1. 
       &lt;Operation&gt; 
       [0142]    Operation of the refrigeration cycle apparatus according to Embodiment 6 is similar to that in Embodiment 1. 
       &lt;Effects&gt; 
       [0143]    The refrigeration cycle apparatus according to Embodiment 6 has, in addition to the effects of Embodiment 1, independently providing the high pressure rise suppression unit  300  achieves commonality of the configuration of the outdoor unit  100  and the configuration of the heat transfer unit  200 . Further, commonality of the configuration of the outdoor unit  100  and the configuration of the heat transfer unit  200  enables cost reduction. 
       Embodiment 7 
     &lt;Configuration&gt; 
       [0144]      FIG. 18  is a block diagram of a refrigeration cycle apparatus according to Embodiment 7 of the present invention. 
         [0145]    As illustrated in  FIG. 18 , in the refrigeration cycle apparatus according to Embodiment 7, the outdoor unit  100 , the high pressure rise suppression unit  300 , and a plurality of heat transfer units  200  connected in parallel with the outdoor unit  100  are connected via the gas connection pipe  4 , the first liquid connection pipe  11   a , and the second liquid connection pipe  11   b.    
         [0146]    The configuration of connecting pipes is similar to that in Embodiment 1. 
       &lt;Operation&gt; 
       [0147]    Operation of the refrigeration cycle apparatus according to Embodiment 7 is similar to that in Embodiment 1. 
       &lt;Effects&gt; 
       [0148]    The refrigeration cycle apparatus according to Embodiment 7 has, in addition to the effects of Embodiment 1, an effect that one outdoor unit  100  and one high pressure rise suppression unit  300  can suppress high pressure rise of the condensers  201  of the plurality of heat transfer units  200 .