Patent Publication Number: US-11384965-B2

Title: Refrigeration cycle apparatus performing a refrigerant circulation operation using a liquid pump

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a U.S. national stage application of International Application PCT/JP2017/014107 filed on Apr. 4, 2017, the contents of which are incorporated herein by reference. 
     TECHNICAL FIELD 
     The present invention relates to a refrigeration cycle apparatus. 
     BACKGROUND 
     When a cooling operation is performed under such a condition that the temperature of outside air is low, it has been known that cooling performance is deteriorated if the operation is performed using a compressor. To address this, a refrigeration cycle apparatus has been known which can reduce an amount of consumed power by performing a refrigerant circulation operation using a liquid pump while utilizing coldness of outside air when the temperature of the outside air is low (for example, see Patent Literature 1). 
     PATENT LITERATURE 
     PTL 1: Japanese Patent Laying-Open No. 10-185342 
     However, in the cooling operation using the liquid pump as described in Patent Literature 1, saturated liquid is caused at an inlet of an indoor heat exchanger, with the result that a required amount of refrigerant is increased as compared with a case where the compressor is used therefor. Hence, the required amount of refrigerant for the operation using the liquid pump should be sealed in the refrigeration cycle apparatus. However, when such an amount of refrigerant is sealed, an excess of refrigerant circulates during the operation using the compressor, with the result that cooling performance may be decreased. 
     Moreover, when the refrigerant is insufficient during the operation using the liquid pump, the refrigerant flowing out from an air heat exchanger becomes two-phase refrigerant. Hence, gas is included in the refrigerant flowing from a refrigerant tank to the liquid pump. As a result, the liquid pump runs on idle and the liquid refrigerant is not transported accordingly. 
     SUMMARY 
     In view of the above, an object of the present invention is to provide a refrigeration cycle apparatus that can avoid a liquid pump from running on idle during a cooling operation using the liquid pump and that can avoid an excess of refrigerant from circulating during a cooling operation using a compressor. 
     A refrigeration cycle apparatus of the present invention is a refrigeration cycle apparatus comprising a refrigerant circuit, wherein the refrigerant circuit comprises: a compressor configured to compress refrigerant; an air heat exchanger configured to exchange heat between air and the refrigerant; a first throttle device; a water heat exchanger configured to exchange heat between the refrigerant and water; and a refrigerant tank and a liquid pump each connected to the first throttle device in parallel. The refrigerant circuit further comprises: a bypass pipe connected to the compressor in parallel; and a bypass valve configured to adjust an amount of the refrigerant flowing in the bypass pipe. During a first cooling operation, the compressor is in an operational state, the liquid pump is in a non-operational state, and an amount of the refrigerant allowing for existence of a liquid surface of the refrigerant in the refrigerant tank is accumulated in the refrigerant tank. During a second cooling operation, the compressor is in the non-operational state, the liquid pump is in the operational state, and the amount of the refrigerant allowing for the existence of the liquid surface of the refrigerant in the refrigerant tank is accumulated in the refrigerant tank. 
     According to the present invention, cooling performance can be prevented from being decreased, because the excessive amount of refrigerant obtained by subtracting the amount of refrigerant required for the first cooling operation from the amount of refrigerant sealed in the refrigerant circuit is accumulated in the refrigerant tank during the first cooling operation. According to the present invention, the liquid pump can be prevented from running on idle, because the liquid surface of the refrigerant exists in the refrigerant tank during the second cooling operation. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  shows a configuration of a refrigeration cycle apparatus of a first embodiment. 
         FIG. 2  shows states of components in the refrigeration cycle apparatus during a heating operation, a first cooling operation and a second cooling operation. 
         FIG. 3  is a P-h diagram during each of the first cooling operation and the second cooling operation. 
         FIG. 4  shows a flow of refrigerant during the heating operation. 
         FIG. 5  shows a flow of the refrigerant during the first cooling operation. 
         FIG. 6  shows a change in P-h of the refrigerant flowing in a refrigerant tank circuit  20  during the first cooling operation. 
         FIG. 7  shows a flow of the refrigerant during the second cooling operation. 
         FIG. 8  shows a configuration of a refrigeration cycle apparatus of a second embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     First Embodiment 
       FIG. 1  shows a configuration of a refrigeration cycle apparatus  1  of a first embodiment. 
     As shown in  FIG. 1 , refrigeration cycle apparatus  1  includes a refrigerant circuit RC 1  and a control device  60 . 
     Refrigerant circuit RC 1  includes a compressor  12 , a flow path switching device  13 , an air heat exchanger  14 , a first throttle device  15 , a water heat exchanger  16 , and an accumulator  17 , which are sequentially connected to one another via pipes. Refrigerant circuit RC 1  further includes a refrigerant tank circuit  20  connected to first throttle device  15  in parallel via a pipe. 
     Refrigerant circuit RC 1  further includes: a bypass pipe  30  connected to compressor  12 , flow path switching device  13 , and accumulator  17  in parallel; and a bypass valve  27  configured to adjust an amount of the refrigerant flowing in the bypass pipe. 
     Refrigerant tank circuit  20  includes a refrigerant tank  24  and a liquid pump  26  connected in series, refrigerant tank  24  and liquid pump  26  being disposed in this order relative to air heat exchanger  14 . 
     Refrigerant tank circuit  20  further includes: a second throttle device  23  disposed between air heat exchanger  14  and refrigerant tank  24 ; and a third throttle device  25  connected to liquid pump  26  in parallel. 
     In refrigerant circuit RC 1 , refrigerant involving a phase change, such as carbon dioxide and R410A, circulates. 
     Compressor  12  is configured to suction and compress low-pressure refrigerant and discharge the refrigerant as high-pressure refrigerant. Compressor  12  is an inverter compressor variable in a discharge capacity for the refrigerant, for example. 
     In a first state, flow path switching device  13  is configured to connect the discharge side of compressor  12  to air heat exchanger  14  and connect the suction side of compressor  12  to water heat exchanger  16  so as to form a first flow path in which the refrigerant discharged from compressor  12  flows to air heat exchanger  14 . In a second state, flow path switching device  3  is configured to connect the discharge side of compressor  12  to water heat exchanger  16  and connect the suction side of compressor  12  to air heat exchanger  14  so as to form a second flow path in which the refrigerant discharged from compressor  12  flows to water heat exchanger  16 . 
     Flow path switching device  13  switches between the first state and the second state in accordance with an instruction signal from control device  60 . Flow path switching device  13  is a device that has a valve body provided at the pipe in which the refrigerant flows and that is configured to switch between the above-described refrigerant flow paths by switching this valve body between opened and closed states. Flow path switching device  3  is also referred to as a “four-way valve”. 
     In air heat exchanger  14 , heat is exchanged between the refrigerant flowing in the flow path and air external to the flow path. A blower  11  is provided near air heat exchanger  14 . The heat exchange in air heat exchanger  14  is facilitated by air blown from blower  11 . Blower  11  includes a fan and a motor configured to rotate the fan. Blower  11  is a blower variable in rotating speed, for example. An amount of heat absorption of the refrigerant in air heat exchanger  14  can be adjusted by adjusting the rotating speed of the motor. 
     First throttle device  15  can decompress the high-pressure refrigerant. Examples of first throttle device  15  usable herein include a device having a valve body capable of adjusting a degree of opening, such as an electronic control type expansion valve. 
     Water heat exchanger  16  is connected to not only refrigerant circuit RC 1  but also a water circuit  46 , and is configured to exchange heat between the refrigerant flowing in the flow path and water flowing in water circuit  46 . The water flowing in water circuit  46  is heated or cooled by water heat exchanger  16 . The water flowing in water circuit  46  is used for indoor air conditioning, for example. 
     Accumulator  17  is a container configured to store the refrigerant therein, and is installed at the suction side of compressor  12 . Accumulator  17  has an upper portion connected to a pipe via which the refrigerant flows in and has a lower portion connected to a pipe via which the refrigerant flows out. Gas-liquid separation of the refrigerant is performed in accumulator  17 . The gas refrigerant resulting from the gas-liquid separation is suctioned to compressor  12 . By accumulator  17 , the liquid refrigerant can be prevented from being supplied to compressor  12 . 
     Bypass valve  27  is provided at the pipe that connects air heat exchanger  14  to water heat exchanger  16  in parallel with a path extending through accumulator  17 , compressor  12 , and flow path switching device  13 . 
     Second throttle device  23  can decompress the high-pressure refrigerant. Examples of second throttle device  23  usable herein include a device having a valve body capable of adjusting a degree of opening, such as an electronic control type expansion valve. Alternatively, examples of second throttle device  23  usable herein include a device with a fixed degree of opening, such as a capillary tube. 
     Refrigerant tank  24  is a container configured to store the refrigerant therein. A flow inlet for the refrigerant in refrigerant tank  24  is connected to second throttle device  23  via a pipe. A flow outlet for the refrigerant in refrigerant tank  24  is connected to liquid pump  26  and third throttle device  25  via a pipe. In refrigerant tank  24 , gas-liquid separation of the refrigerant can be performed. For example, the flow inlet for the refrigerant in refrigerant tank  24  is disposed at the uppermost position of refrigerant tank  24  in the vertical direction, whereas the flow outlet for the refrigerant in refrigerant tank  24  is disposed at the lowermost position of refrigerant tank  24  in the vertical direction. 
     Third throttle device  25  is connected to the flow outlet of refrigerant tank  24  via a pipe. Third throttle device  25  can decompress the high-pressure refrigerant. Examples of third throttle device  25  usable herein include a device having a valve body capable of adjusting a degree of opening, such as an electronic control type expansion valve. 
     Liquid pump  26  is connected to the flow outlet of refrigerant tank  24  via a pipe. Liquid pump  26  supplies the liquid refrigerant in refrigerant tank  24  to water heat exchanger  16 . By liquid pump  26 , the pressure of the liquid refrigerant is increased. 
     Control device  60  controls switching among the first cooling operation, the second cooling operation, and the heating operation. 
     In the cooling operation of refrigeration cycle apparatus  1 , control device  60  performs control such that the first cooling operation is performed when a temperature T of outside air is more than or equal to a threshold value TH, and such that the second cooling operation is performed when temperature T of the outside air is less than threshold value TH. Temperature T of the outside air can be detected by a temperature sensor (not shown) disposed outdoor. 
     The first cooling operation is a vapor compression type refrigerant operation using compressor  12 . The second cooling operation is a circulation type cooling operation using liquid pump  26 . 
     When the temperature of the outside air is low, motive power for transporting the refrigerant in the cooling operation using liquid pump  26  is smaller than that in the cooling operation using compressor  12 . Hence, an amount of consumed power becomes small. 
     Assume that W 1  represents an amount of refrigerant required for refrigerant circuit RC 1  in the first cooling operation, W 2  represents an amount of refrigerant required for refrigerant circuit RC 1  in the second cooling operation, and W 3  represents an amount of refrigerant required for refrigerant circuit RC 1  in the heating operation. In this case, the following relation is satisfied: W 2 &gt;W 1 &gt;W 3 . Here, the expression “amount of refrigerant required” refers to an amount of refrigerant that is required to circulate in refrigerant circuit RC 1  in each operation. 
     Assume that W 2 +α represents an amount of refrigerant sealed in refrigerant circuit RC 1 . α represents an amount with which a liquid surface always exists in refrigerant tank  24  during the second cooling operation. In this way, during the second cooling operation, only the liquid refrigerant, rather than the gas refrigerant, can be supplied to liquid pump  26 . 
     During the first cooling operation, an excessive amount (W 2 +α-W 1 ) of refrigerant is accumulated in refrigerant tank  24 , whereas during the heating, an excessive amount (W 2 +α-W 3 ) of refrigerant is accumulated in refrigerant tank  24 . 
       FIG. 2  shows states of the components in the refrigeration cycle apparatus during the heating operation, the first cooling operation and the second cooling operation. 
       FIG. 3  is a P-h diagram during each of the first cooling operation and the second cooling operation. 
     When the temperature of the outside air is 35° C. and the water temperature is 7° C., the first cooling operation is performed in a cycle A. When the temperature of the outside air is −15° C. and the water temperature is 7° C., the second cooling operation is performed in a cycle B. 
     (Heating Operation) 
       FIG. 4  shows a flow of the refrigerant during the heating operation. 
     With reference to  FIG. 2  and  FIG. 4 , the following describes a flow of the refrigerant in the heating operation. 
     During the heating operation, compressor  12  is in the operational state (ON), liquid pump  26  is in the non-operational state (OFF), flow path switching device  13  is in the second state, first throttle device  15  is in the opened state, second throttle device  23  is in the fully closed state, third throttle device  25  is in the fully closed state, bypass valve  27  is in the fully closed state, and blower  11  is in the operational state (ON). 
     Since flow path switching device  13  is in the second state in the heating operation, the discharge side of compressor  12  is connected to water heat exchanger  16  to form the second flow path in which the refrigerant discharged from compressor  12  flows into water heat exchanger  16 . The refrigerant circulates in order of water heat exchanger  16 , first throttle device  15 , air heat exchanger  14 , and compressor  12 . Air heat exchanger  14  serves as an evaporator and water heat exchanger  16  serves as a condenser. 
     The high-temperature high-pressure refrigerant discharged from compressor  12  flows into water heat exchanger  16  via flow path switching device  13 . In water heat exchanger  16 , the high-temperature high-pressure refrigerant is decreased in temperature as a result of heat exchange with the water flowing in water circuit  46 , and flows out from water heat exchanger  16 . The refrigerant flowing out from water heat exchanger  16  is decompressed by first throttle device  15  to become low-temperature low-pressure refrigerant, and then flows into air heat exchanger  14 . 
     In air heat exchanger  14 , the low-temperature low-pressure refrigerant is increased in temperature as a result of heat exchange with air blown from blower  11 , and flows out from air heat exchanger  14 . The refrigerant flowing out from air heat exchanger  14  flows into accumulator  17  via flow path switching device  13 , and is subjected to gas-liquid separation in accumulator  17 . The gas refrigerant in accumulator  17  is suctioned to compressor  12 . 
     In the heating operation, the water flowing in water circuit  46  is heated by the refrigerant flowing in water heat exchanger  16 . This heated water is used for indoor heating, for example. During the heating, an excessive amount (W 2 +α-W 3 ) of refrigerant is accumulated in refrigerant tank  24 . The accumulation of the refrigerant in refrigerant tank  24  can be performed by controlling second throttle device  23  and third throttle device  25  just before starting the heating. Accordingly, the excess of refrigerant can be avoided from circulating in refrigerant circuit RC 1 . 
     (First Cooling Operation) 
       FIG. 5  shows a flow of the refrigerant during the first cooling operation. 
     With reference to  FIG. 2 ,  FIG. 3 , and  FIG. 5 , the following describes the flow of the refrigerant during the first cooling operation. 
     During the first cooling operation, compressor  12  is in the operational state (ON), liquid pump  26  is in the non-operational state (OFF), flow path switching device  13  is in the first state, first throttle device  15  is in the opened state, second throttle device  23  is in the opened state, and third throttle device  25  is in the opened state, bypass valve  27  is in the fully closed state, and blower  11  is in the operational state (ON). 
     Since flow path switching device  13  is in the first state in the first cooling operation, the discharge side of compressor  12  is connected to air heat exchanger  14  to form the first flow path in which the refrigerant discharged from compressor  12  flows into air heat exchanger  14 . The refrigerant circulates in order of air heat exchanger  14 , first throttle device  15 , water heat exchanger  16 , and compressor  12 . Air heat exchanger  14  serves as a condenser and water heat exchanger  16  serves as an evaporator. 
     The high-temperature high-pressure refrigerant discharged from compressor  12  flows into air heat exchanger  14  via flow path switching device  13  (Q 1  in the P-h diagram of  FIG. 3 ). In air heat exchanger  14 , the high-temperature high-pressure refrigerant is condensed as a result of heat exchange with air blown from blower  11 , and flows out from air heat exchanger  14  (Q 2  in the P-h diagram of  FIG. 3 ). The refrigerant flowing out from air heat exchanger  14  is decompressed by first throttle device  15  to become low-temperature low-pressure refrigerant, and then flows into water heat exchanger  16  (Q 3  in the P-h diagram of  FIG. 3 ). 
     In water heat exchanger  16 , the low-temperature low-pressure refrigerant is evaporated as a result of heat exchange with the water flowing in water circuit  46 , and flows out from water heat exchanger  16  (Q 4  in the P-h diagram of  FIG. 3 ). The refrigerant flowing out from water heat exchanger  16  flows into accumulator  17  via flow path switching device  13 , and is subjected to gas-liquid separation in accumulator  17 . The gas refrigerant in accumulator  17  is suctioned to compressor  12 . Compressor  12  is configured to suction and compress low-pressure refrigerant and discharge the refrigerant as high-pressure refrigerant. 
     Control device  60  detects a degree of superheating of the refrigerant flowing out from water heat exchanger  16 , and adjusts a degree of opening of first throttle device  15  such that the degree of superheating becomes a target value set in advance (superheating degree control). By increasing the degree of opening of first throttle device  15 , the degree of superheating of the refrigerant flowing out from water heat exchanger  16  can be decreased. By decreasing the degree of opening of first throttle device  15 , the degree of superheating of the refrigerant flowing out from water heat exchanger  16  can be increased. 
     Control device  60  controls second throttle device  23  and third throttle device  25  such that the amount of the refrigerant circulating in refrigerant circuit RC 1  becomes a predetermined amount during the first cooling operation. For example, when starting the first cooling operation, control device  60  fully opens second throttle device  23  and fully closes third throttle device  25  until an amount (WX=(W 2 +α-W 1 )) of refrigerant obtained by subtracting, from the amount (W 2 +α) of sealed refrigerant, amount W 1  of refrigerant required to circulate in refrigerant circuit RC 1  in the first cooling operation is accumulated in refrigerant tank  24 . When amount WX of refrigerant is accumulated in refrigerant tank  24 , control device  60  fully closes second throttle device  23 . 
     Alternatively, during the first cooling operation, instead of the refrigerant flowing into and then remaining in refrigerant tank  24 , the refrigerant may flow into refrigerant tank  24  and then may flow out from refrigerant tank  24  with amount WX of refrigerant remaining in refrigerant tank  24 . In this case, the pressure and enthalpy of the refrigerant flowing out from refrigerant tank circuit  20  are the same as the pressure and enthalpy of the refrigerant flowing out from first throttle device  15 . Therefore, the change from Q 2  to Q 3  in the P-h diagram of  FIG. 3  represents not only changes in pressure and enthalpy of the refrigerant flowing via first throttle device  15  but also changes in pressure and enthalpy of the refrigerant flowing via refrigerant tank circuit  20 . 
       FIG. 6  shows a change in P-h of the refrigerant flowing in refrigerant tank circuit  20  during the first cooling operation. 
     Q 2 , which represents the pressure and enthalpy of the refrigerant flowing into second throttle device  23 , corresponds to Q 2  in  FIG. 3 . 
     By throttling the refrigerant by second throttle device  23 , the two-phase refrigerant flows into refrigerant tank  24  (QX in  FIG. 6 ). The liquid refrigerant is accumulated in the lower portion of refrigerant tank  24 . The liquid refrigerant in the lower portion of refrigerant tank  24  is exhausted by third throttle device  25 . 
     Control device  60  adjusts the degree of opening of second throttle device  23  and the degree of opening of third throttle device  25  so as to accumulate amount WX of refrigerant in refrigerant tank  24 . In this way, although the refrigerant flows into refrigerant tank  24  and flows out from refrigerant tank  24 , amount WX of refrigerant is always accumulated in refrigerant tank  24 . Also in this way, the degree of subcooling of the refrigerant flowing out from air heat exchanger  14  is decreased. 
     It should be noted that in addition to or instead of control device  60  controlling second throttle device  23  and third throttle device  25  to accumulate amount WX of refrigerant in refrigerant tank  24 , control device  60  may control second throttle device  23  and third throttle device  25  in the following manner. 
     Control device  60  may be configured to detect the degree of subcooling of the refrigerant flowing out from air heat exchanger  14 , and also adjust the degree of opening of third throttle device  25  such that the degree of subcooling becomes a target value set in advance (subcooling control). By increasing the degree of opening of third throttle device  25 , the degree of subcooling of the refrigerant flowing out from air heat exchanger  14  can be increased. By decreasing the degree of opening of third throttle device  25 , the degree of subcooling of the refrigerant flowing out from air heat exchanger  14  can be decreased. 
     Further, control device  60  may be configured to adjust the degree of opening of second throttle device  23  such that a pressure difference (differential pressure) between the pressure at the inflow side of second throttle device  23  and the pressure of refrigerant tank  24  becomes a predetermined amount (differential pressure control). As the degree of opening of second throttle device  23  is more decreased, the differential pressure can be more increased. 
     Alternatively, control device  60  may be configured to set the degree of opening of second throttle device  23  to a fixed degree of opening. When the fixed degree of opening is employed, a capillary tube may be used as second throttle device  23 , instead of the electronic control type expansion valve. 
     In the first cooling operation, the water flowing in water circuit  46  is cooled by the refrigerant flowing in water heat exchanger  16 . The cooled water is used for indoor cooling, for example. 
     (Second Cooling Operation) 
       FIG. 7  shows a flow of the refrigerant during the second cooling operation. 
     With reference to  FIG. 2 ,  FIG. 3 , and  FIG. 7 , the following describes the flow of the refrigerant during the second cooling operation. 
     During the second cooling operation, compressor  12  is in the non-operational state (OFF), liquid pump  26  is in the operational state (ON), flow path switching device  13  is in the first state, first throttle device  15  is in the fully closed state, second throttle device  23  is in the fully opened state, and third throttle device  25  is in the fully closed state, bypass valve  27  is in the opened state, and blower  11  is in the operational state (ON). 
     Since compressor  12  is non-operational although flow path switching device  13  is in the first state in the second cooling operation, compressor  12  does not discharge the refrigerant. 
     The refrigerant circulates in order of liquid pump  26 , water heat exchanger  16 , bypass valve  27 , and air heat exchanger  14 . As with the first cooling operation, air heat exchanger  14  serves as a condenser and water heat exchanger  16  serves as an evaporator. 
     The liquid refrigerant discharged from liquid pump  26  flows into water heat exchanger  16  (Q 5  in the P-h diagram of  FIG. 3 ). 
     The liquid refrigerant is evaporated as a result of heat exchange with the water flowing in water circuit  46  in water heat exchanger  16 , and flows out from water heat exchanger  16  (Q 6  in the P-h diagram of  FIG. 3 ). 
     The high-temperature high-pressure refrigerant having flown out from water heat exchanger  16  is decompressed in bypass valve  27 , and flows into air heat exchanger  14  (Q 7  in the P-h diagram of  FIG. 3 ). 
     In air heat exchanger  14 , the high-temperature high-pressure refrigerant is condensed as a result of heat exchange with air blown from blower  11 , and flows out from air heat exchanger  14  (Q 8  in the P-h diagram of  FIG. 3 ). 
     Since second throttle device  23  is fully opened, the refrigerant having flown out from air heat exchanger  14  flows into refrigerant tank  24  with the pressure and enthalpy thereof being substantially unchanged. 
     The liquid refrigerant in refrigerant tank  24  is suctioned into liquid pump  26 , and the liquid refrigerant increased in pressure is discharged and flows into water heat exchanger  16  (Q 5  in the P-h diagram of  FIG. 3 ). 
     Here, amount a of liquid refrigerant is always accumulated in refrigerant tank  24 . Therefore, the liquid surface always exists in refrigerant tank  24 . Accordingly, during the second cooling operation, only the liquid refrigerant, rather than the gas refrigerant, can be supplied to liquid pump  26 . 
     During the second cooling operation, as with the first cooling operation, the water flowing in water circuit  46  is cooled by the refrigerant flowing in water heat exchanger  16 . The cooled water is used for indoor cooling, for example. 
     It should be noted that control device  60  may control the degree of opening of bypass valve  27  such that the degree of subcooling of the refrigerant flowing out from air heat exchanger  14  becomes more than or equal to 0. By decreasing the degree of opening of bypass valve  27 , the degree of subcooling is increased. By increasing the degree of opening of bypass valve  27 , the degree of subcooling is decreased. In this case, an electronic control type expansion valve may be used for bypass valve  27 . By using the electronic control type expansion valve, the degree of subcooling is adjusted to facilitate attaining a liquid state at the inlet of liquid pump  26 . 
     According to the present embodiment, since the excess of refrigerant is accumulated in the refrigerant tank during the first cooling operation as described above, performance during the first cooling operation can be suppressed from being decreased. Moreover, since the liquid surface always exists in refrigerant tank  24  during the second cooling operation, the liquid pump can be avoided from running on idle. 
     Second Embodiment 
       FIG. 8  shows a configuration of a refrigeration cycle apparatus of a second embodiment. 
     A refrigeration cycle apparatus  2  of  FIG. 8  is different from refrigeration cycle apparatus  1  of  FIG. 1  in that a refrigerant circuit RC 2  of refrigeration cycle apparatus  2  of  FIG. 8  includes a valve  51 . 
     In the first embodiment, when the refrigerant flows into compressor  12  during the second cooling operation, the refrigerant is cooled by compressor  12  and the refrigerant may be accumulated in compressor  12 . As a result, the amount of refrigerant to circulate becomes insufficient, with the result that gas refrigerant may be suctioned to liquid pump  26 . In the present embodiment, such a problem can be avoided by valve  51 . 
     Valve  51  is disposed between compressor  12  and a branch point D of a path from water heat exchanger  16  to compressor  12  and a path from water heat exchanger  16  to bypass value  27 . 
     Control device  61  fully opens valve  51  in the heating operation and the first cooling operation, and fully closes valve  51  in the second cooling operation. Accordingly, the refrigerant can be avoided from flowing into compressor  12  during the second cooling operation. 
     The embodiments disclosed herein are illustrative and non-restrictive in any respect. The scope of the present invention is defined by the terms of the claims, rather than the embodiments described above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.