Patent Publication Number: US-10767912-B2

Title: Refrigeration cycle apparatus

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a U.S. national stage application of PCT/JP2015/078656 filed on Oct. 8, 2015, the contents of which are incorporated herein by reference. 
     TECHNICAL FIELD 
     The present invention relates to a refrigeration cycle apparatus and particularly to a refrigeration cycle apparatus provided with a flow path switching apparatus configured to switch a flow of refrigerant discharged from a compressor to any of first and second heat exchangers. 
     BACKGROUND FIELD 
     Some refrigeration cycle apparatuses are configured to switch between cooling and heating by switching a flow of refrigerant discharged from a compressor to any of first and second heat exchangers. In such a refrigeration cycle apparatus, in general, a volume of a refrigerant flow path is greater in the first heat exchanger (an outdoor heat exchanger) than in the second heat exchanger (an indoor heat exchanger). In this case, since an optimal amount of refrigerant at which a coefficient of performance (COP) is maximized is greater in cooling than in heating, an amount of refrigerant is greater in cooling than in heating. Therefore, since an amount of refrigerant in cooling is excessive in heating, a refrigerant tank circuit which collects refrigerant excessive in heating to the refrigerant tank has been proposed. For example, Japanese Patent Laying-Open No. 2014-119153 (PTD 1) discloses such a refrigerant tank circuit. In an air conditioner described in this document, refrigerant excessive in heating is stored in a refrigerant tank (receiver) in the refrigerant tank circuit. 
     CITATION LIST 
     Patent Document 
     
         
         PTD 1: Japanese Patent Laying-Open No. 2014-119153 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     in the air conditioner described in the document, when refrigerant is collected to the refrigerant tank during cooling, the refrigerant is collected to the refrigerant tank in a gas-liquid two-phase state. Therefore, gas refrigerant in the refrigerant tank blocks inflow of liquid refrigerant. Since the refrigerant is not sufficiently collected to the refrigerant tank, the refrigerant excessive in heating remains in a refrigerant circuit. Therefore, when an operation of the air conditioner is switched from cooling to heating, liquid back which causes the liquid refrigerant to flow into the compressor is highly likely to occur. 
     Some refrigeration cycle apparatuses are provided with a defrosting mode for melting frost which adheres to the first heat exchanger (outdoor heat exchanger) which functions as an evaporator during heating. In the defrosting mode, refrigerant is circulated in a cycle the same as in cooling, that is, a cycle reverse to heating. Therefore, when the operation is switched from the defrosting mode to heating, liquid back is highly likely as in switching of the operation from cooling to heating. 
     The present invention was made in view of the problems above, and an object thereof is to provide a refrigeration cycle apparatus which can suppress occurrence of liquid back. 
     Solution to Problem 
     A refrigeration cycle apparatus according to the present invention comprises a refrigerant circuit, a refrigerant tank circuit, and a degassing pipe. The refrigerant circuit is configured by connecting a compressor, a flow path switching apparatus, a first heat exchanger, a decompressing apparatus, and a second heat exchanger. The refrigerant tank circuit is connected to the first and second heat exchangers in parallel with the decompressing apparatus. The degassing pipe has a first end and a second end. The flow path switching apparatus is configured to switch a flow of refrigerant discharged from the compressor to any of the first and second heat exchangers. The refrigerant tank circuit contains a refrigerant tank. The degassing pipe has the first end connected to the refrigerant tank and has the second end connected to at least any of the refrigerant circuit and the refrigerant tank circuit. 
     Advantageous Effects of Invention 
     According to the refrigeration cycle apparatus in the present invention, the refrigerant tank circuit is connected to the first and second heat exchangers in parallel with the decompressing apparatus. Therefore, the refrigerant is stored in the refrigerant tank and hence an amount of refrigerant which flows through the refrigerant circuit can be reduced. The refrigerant excessive in heating can thus be collected to the refrigerant tank. The degassing pipe has the first end connected to the refrigerant tank and has the second end connected to at least any of the refrigerant circuit and the refrigerant tank circuit. Therefore, the gas refrigerant in the refrigerant tank can escape through the degassing pipe. Therefore, blocking of inflow of liquid refrigerant by the gas refrigerant in the refrigerant tank is suppressed. Therefore, the liquid refrigerant can sufficiently be collected to the refrigerant tank. Thus, inflow into the compressor of the liquid refrigerant which flows in the refrigerant circuit can be suppressed. Therefore, occurrence of liquid back can be suppressed. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a circuit configuration diagram of one example of a refrigeration cycle apparatus in a first embodiment of the present invention. 
         FIG. 2  is a perspective view schematically showing a configuration of a refrigerant tank in the refrigeration cycle apparatus in the first embodiment of the present invention. 
         FIG. 3  is a circuit configuration diagram of another example of the refrigeration cycle apparatus in the first embodiment of the present invention. 
         FIG. 4  is a functional block diagram for illustrating a configuration of a control device in the refrigeration cycle apparatus in the first embodiment of the present invention. 
         FIG. 5  is a circuit configuration diagram showing a flow of refrigerant in a cooling mode of the refrigeration cycle apparatus in the first embodiment of the present invention. 
         FIG. 6  is a circuit configuration diagram showing a flow of refrigerant in one example of a refrigerant collection operation in the cooling mode and a defrosting mode of the refrigeration cycle apparatus in the first embodiment of the present invention. 
         FIG. 7  is a cross-sectional view showing a flow of refrigerant in a cooling collection operation in the refrigerant tank of the refrigeration cycle apparatus in the first embodiment of the present invention. 
         FIG. 8  is a circuit configuration diagram showing a flow of refrigerant in another example of the refrigerant collection operation in the cooling mode and the defrosting mode of the refrigeration cycle apparatus in the first embodiment of the present invention. 
         FIG. 9  is a circuit configuration diagram showing a flow of refrigerant in a heating mode of the refrigeration cycle apparatus in the first embodiment of the present invention. 
         FIG. 10  is a flowchart for illustrating a flow in the defrosting mode of the refrigeration cycle apparatus in the first embodiment of the present invention. 
         FIG. 11  is a timing chart for illustrating an operation of an actuator in the defrosting mode of the refrigeration cycle apparatus in the first embodiment of the present invention. 
         FIG. 12  is a diagram illustrating a high-pressure saturation temperature and a state of a degree of superheating on a suction side of the compressor in the defrosting mode in the first embodiment of the present invention. 
         FIG. 13  is a circuit configuration diagram showing a flow of refrigerant in a first refrigerant release operation in the defrosting mode of the refrigeration cycle apparatus in the first embodiment of the present invention. 
         FIG. 14  is a circuit configuration diagram showing a flow of refrigerant in a second refrigerant release operation in the defrosting mode of the refrigeration cycle apparatus in the first embodiment of the present invention. 
         FIG. 15  is a circuit configuration diagram of a refrigeration cycle apparatus in a second embodiment of the present invention. 
         FIG. 16  is a circuit configuration diagram showing a flow of refrigerant in one example of the refrigerant collection operation of the refrigeration cycle apparatus in the second embodiment of the present invention. 
         FIG. 17  is a circuit configuration diagram of a refrigeration cycle apparatus in a third embodiment of the present invention. 
         FIG. 18  is a circuit configuration diagram showing a flow of refrigerant in one example of the refrigerant release operation of the refrigeration cycle apparatus in the third embodiment of the present invention. 
         FIG. 19  is a circuit configuration diagram of a refrigeration cycle apparatus in a fourth embodiment of the present invention. 
         FIG. 20  is a circuit configuration diagram showing a state that refrigerant flows through a first pipe portion of the refrigeration cycle apparatus in the fourth embodiment of the present invention. 
         FIG. 21  is a circuit configuration diagram showing a state that refrigerant flows through a second pipe portion of the refrigeration cycle apparatus in the fourth embodiment of the present invention. 
         FIG. 22  is a circuit configuration diagram of a refrigeration cycle apparatus in a fifth embodiment of the present invention. 
         FIG. 23  is a circuit configuration diagram showing a state that refrigerant flows through the first pipe portion of the refrigeration cycle apparatus in the fifth embodiment of the present invention. 
         FIG. 24  is a circuit configuration diagram showing a state that refrigerant flows through the second pipe portion of the refrigeration cycle apparatus in the fifth embodiment of the present invention. 
         FIG. 25  is a cross-sectional view showing a configuration of a refrigerant tank of a refrigeration cycle apparatus in a sixth embodiment of the present invention. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Embodiments of the present invention will be described below with reference to the drawings. 
     First Embodiment 
     A configuration of a refrigeration cycle apparatus in a first embodiment of the present invention will initially be described. 
     Referring to  FIG. 1 , a refrigeration cycle apparatus  1  in the present embodiment mainly comprises a refrigerant circuit RC, a refrigerant tank circuit  12 , and a degassing pipe  30 . Refrigerant circuit RC and refrigerant tank circuit  12  implement a refrigeration circuit. 
     Refrigerant which varies in phase such as carbon dioxide or R410A circulates through the refrigeration circuit. Refrigeration cycle apparatus  1  exemplified in the first embodiment functions as a part of such a chilling unit that water in a water circuit  16  heated or cooled by a second heat exchanger  6  of refrigerant circuit RC is used for air conditioning of a room. 
     Refrigerant circuit RC is configured by connecting a compressor  2 , a flow path switching apparatus  3 , a first heat exchanger  4 , a decompressing apparatus  5 , second heat exchanger  6 , and an accumulator  7  sequentially through a pipe. 
     Compressor  2  suctions and compresses low-pressure refrigerant and discharges the refrigerant as high-pressure refrigerant. Compressor  2  is, for example, an inverter compressor of which volume of discharge of refrigerant is variable. An amount of circulation of refrigerant in refrigeration cycle apparatus  1  is controlled by regulating a volume of discharge from compressor  2 . 
     Flow path switching apparatus  3  is provided on a discharge side of compressor  2 . Flow path switching apparatus  3  is configured to switch a flow of refrigerant discharged from compressor  2  to any of first heat exchanger  4  and second heat exchanger  6 . Flow path switching apparatus  3  selectively performs an operation to allow connection of the discharge side of compressor  2  to first heat exchanger  4  and connection of a suction side of compressor  2  to second heat exchanger  6  so as to allow the refrigerant discharged from compressor  2  to flow to first heat exchanger  4  and an operation to allow connection of the discharge side of compressor  2  to second heat exchanger  6  and connection of the suction side of compressor  2  to first heat exchanger  4  so as to allow the refrigerant discharged from compressor  2  to flow to second heat exchanger  6 . Flow path switching apparatus  3  is an apparatus which has a valve disc provided in a pipe through which refrigerant flows and switches a flow path for the refrigerant as described above by switching between an opened state and a closed state of the valve disc. 
     First heat exchanger  4  is a refrigerant-air heat exchanger having a flow path through which refrigerant flows. In first heat exchanger  4 , heat is exchanged between the refrigerant which flows through the flow path and air outside the flow path. A fan  11  is provided in the vicinity of first heat exchanger  4 . Fan  11  serves to send air to first heat exchanger  4 . Heat exchange in first heat exchanger  4  is promoted by air from fan  11 . Fan  11  is, for example, a fan of which rotation speed is variable, and an amount of heat absorption by the refrigerant in first heat exchanger  4  is adjusted based on adjustment of a rotation speed of fan  11 . 
     Decompressing apparatus  5  reduces a pressure of high-pressure refrigerant. An apparatus provided with a valve disc of which opening position can be adjusted, such as an electronically controlled expansion valve, can be employed as decompressing apparatus  5 . 
     Second heat exchanger  6  is a refrigerant-water heat exchanger having a flow path through which refrigerant flows and a flow path through which water of water circuit  16  flows. In second heat exchanger  6 , heat is exchanged between the refrigerant and water. A plate-type heat exchanger can be employed as second heat exchanger  6 . 
     Refrigeration cycle apparatus  1  can operate while switching between cooling and heating. In a cooling mode, flow path switching apparatus  3  allows connection of the discharge side of compressor  2  to first heat exchanger  4 . The refrigerant discharged from compressor  2  flows to first heat exchanger  4 . First heat exchanger  4  functions as a condenser and second heat exchanger  6  functions as an evaporator. In a heating mode, flow path switching apparatus  3  allows connection of the discharge side of compressor  2  to second heat exchanger  6 . The refrigerant discharged from compressor  2  flows to second heat exchanger  6 . First heat exchanger  4  functions as an evaporator and second heat exchanger  6  functions as a condenser. First heat exchanger  4  functions as a heat source side heat exchanger and second heat exchanger  6  functions as a use side heat exchanger. Taking into account a load required in the cooling mode and the heating triode, first heat exchanger  4  is higher in capacity of heat exchange than second heat exchanger  6 . 
     Accumulator  7  is a container in which refrigerant is stored, and it is placed on the suction side of compressor  2 . A pipe in which the refrigerant flows is connected to an upper portion of accumulator  7  and a pipe out of which the refrigerant flows is connected to a lower portion of the accumulator. The refrigerant is subjected to gas-liquid separation in accumulator  7 . Gas refrigerant resulting from gas-liquid separation is suctioned into compressor  2 . 
     Refrigerant tank circuit  12  is connected to first heat exchanger  4  and second heat exchanger  6  in parallel with decompressing apparatus  5 . Refrigerant tank circuit  12  is a circuit which connects first heat exchanger  4  and decompressing apparatus  5  to each other and connects decompressing apparatus  5  and second heat exchanger  6  to each other. Refrigerant tank circuit  12  comprises a flow rate regulation apparatus  13 , a refrigerant tank  14 , and a valve  15 . Refrigerant tank circuit  12  is configured connecting flow rate regulation apparatus  13 , refrigerant tank  14 , and valve  15  in series through a pipe in the order of proximity to first heat exchanger  4 . 
     Flow rate regulation apparatus  13  reduces a pressure of high-pressure refrigerant. An apparatus provided with a valve disc of which opening position can be adjusted, such as an electronically controlled expansion valve, can be employed as flow rate regulation apparatus  13 . 
     Refrigerant tank  14  is a container in which refrigerant is stored. Refrigerant tank  14  can be, for example, columnar. As shown in  FIG. 2 , refrigerant tank  14  has an upper surface US, a bottom surface BS, and a side surface SS which connects upper surface US and bottom surface BS to each other. 
     Valve  15  has a valve disc provided in a pipe which constitutes refrigerant tank circuit  12  and switches between a conducting state and a non-conducting state of refrigerant by switching between an opened state and a closed state of the valve disc. For example, a bidirectional solenoid valve, an electronically controlled expansion valve of which opening position can be adjusted, or a valve unit in which a unidirectional solenoid valve and a check valve are provided in parallel can be employed as valve  15 . 
     Referring to  FIGS. 1 and 2 , degassing pipe  30  serves to evacuate gas refrigerant from refrigerant tank  14 . A capillary tube can be employed for degassing pipe  30 . Degassing pipe  30  may have a helically constructed portion. Since impact can thus be absorbed, break can be suppressed. 
     Degassing pipe  30  has a first end  30   a  and a second end  30   b . Degassing pipe  30  has first end  30   a  connected to refrigerant tank  14  and has second end  30   b  connected to at least any of refrigerant circuit RC and refrigerant tank circuit  12 . Degassing pipe  30  has first end  30   a  connected to an upper portion of refrigerant tank  14 . In  FIG. 2 , degassing pipe  30  has first end  30   a  connected to upper surface US of refrigerant tank  14 . Degassing pipe  30  may have first end  30   a  connected to side surface SS of refrigerant tank  14 . Degassing pipe  30  should only have first end  30   a  arranged at a height position above bottom surface BS of refrigerant tank  14 . 
     Degassing pipe  30  has second end  30   b  connected to at least any of refrigerant circuit RC and refrigerant tank circuit  12  between refrigerant tank  14  and second heat exchanger  6 . In  FIG. 1 , degassing pipe  30  has second end  30   b  connected to refrigerant tank circuit  12  between refrigerant tank  14  and second heat exchanger  6 . Degassing pipe  30  has second end  30   b  connected downstream from valve  15  in refrigerant circuit RC. Degassing pipe  30  may have a plurality of second ends  30   b . In this case, at least one of the plurality of second ends  30   b  may be connected to refrigerant circuit RC and at least another one of the plurality of second ends  30   b  may be connected to refrigerant tank circuit  12 . 
     A pipe which connects flow rate regulation apparatus  13  and refrigerant tank  14  to each other is connected to upper surface US of refrigerant tank  14 . A pipe which connects valve  15  and refrigerant tank  14  to each other is connected to bottom surface BS of refrigerant tank  14 . 
     Referring to  FIG. 3 , refrigeration cycle apparatus  1  in the present embodiment may have a suction pressure sensor  8 , a discharge pressure sensor  9 , a suction temperature sensor  10 , and a control device  20 . 
     Suction pressure sensor  8  which detects a pressure of refrigerant suctioned into compressor  2 , that is, refrigerant on a low-pressure side, is provided at a suction portion of compressor  2 . Suction pressure sensor  8  is provided at a position where it can detect a pressure of the refrigerant on the low-pressure side and an illustrated position of suction pressure sensor  8  is by way of example. 
     Discharge pressure sensor  9  which detects a pressure of the refrigerant discharged from compressor  2 , that is, the refrigerant on a high-pressure side, is provided at a discharge portion of compressor  2 . Discharge pressure sensor  9  is provided at a position where it can detect a pressure of the refrigerant on the high-pressure side and the illustrated position of discharge pressure sensor  9  is by way of example. 
     Suction temperature sensor  10  which detects a temperature of refrigerant suctioned into compressor  2 , that is, the refrigerant on the low-pressure side, is provided in the suction portion of compressor  2 . Suction temperature sensor  10  is provided at a position where it can detect a temperature of the refrigerant on the low-pressure side and the illustrated position of suction temperature sensor  10  is by way of example. Suction temperature sensor  10  is provided, for example, in a pipe in a lower portion of a shell of compressor  2  or on an inlet side of accumulator  7 . 
     Referring to  FIGS. 3 and 4 , control device  20  is responsible for overall control of refrigeration cycle apparatus  1 . Information detected by suction pressure sensor  8 , discharge pressure sensor  9 , and suction temperature sensor  10  is input to control device  20 . Control device  20  controls operations of compressor  2 , flow path switching apparatus  3 , decompressing apparatus  5 , flow rate regulation apparatus  13 , valve  15 , and fan  11 . 
     Control device  20  has a high-pressure saturation temperature detection unit  21 , a superheating degree detection unit  22 , and a refrigerant tank liquid amount detection unit  23  as functional blocks. Control device  20  has a memory  24 . 
     High-pressure saturation temperature detection unit  21  detects a high-pressure saturation temperature which represents a saturation temperature of high-pressure refrigerant on the discharge side of compressor  2  based on a pressure of the high-pressure refrigerant detected by discharge pressure sensor  9  and a conversion table of saturation temperatures under various pressures stored in memory  24 . 
     Superheating degree detection unit  22  detects a saturation temperature of refrigerant on the suction side based on a pressure of the refrigerant on the suction side of compressor  2  detected by suction pressure sensor  8  and the conversion table of saturation temperatures under various pressures stored in memory  24 . Superheating degree detection unit  22  detects a degree of superheating in the suction portion of compressor  2  by calculating a difference between the detected saturation temperature and the temperature of the refrigerant in the suction portion of compressor  2  detected by suction temperature sensor  10 . 
     Refrigerant tank liquid amount detection unit  23  detects an amount of liquid in refrigerant tank  14  based on the degree of superheating in the suction portion of compressor  2  detected by superheating degree detection unit  22  and a reference degree of superheating at the time when refrigerant tank  14  is full which is stored in memory  24 . 
     Control device  20  is implemented by a CPU (a central processing unit which is also referred to as a central processor, a processing device, an operation device, a microprocessor, a microcomputer, or a processor) which executes a program stored in memory  24 . 
     When control device  20  is implemented by the CPU, each function performed by control device  20  is performed by software, firmware, or combination of software and firmware. Software or firmware is described as a program and stored in memory  24 . The CPU performs each function of control device  20  by reading and executing the program stored in memory  24 . Memory  24  is, for example, a non-volatile or volatile semiconductor memory such as a RAM, a ROM, a flash memory, an EPROM, or an EEPROM. 
     High-pressure saturation temperature detection unit  21 , superheating degree detection unit  22 , and refrigerant tank liquid amount detection unit  23  of control device  20  may be implemented partially by dedicated hardware and partially by software or firmware. When they are implemented by hardware, for example, a single circuit, a composite circuit, an ASIC, an FPGA, or combination thereof is employed. 
     An operation mode of the refrigeration cycle apparatus in the present embodiment will now be described. In each figure, a path through which refrigerant flows is shown with a bold line and a direction of flow of the refrigerant is shown with an arrow as appropriate. 
     [Cooling Mode] 
     A flow of refrigerant in the cooling mode will be described with reference to  FIG. 5 . The refrigerant at a high temperature and a high pressure discharged from compressor  2  flows into first heat exchanger  4  through flow path switching apparatus  3 . The refrigerant at a high temperature and a high pressure exchanges heat with air sent from fan  11  in first heat exchanger  4  to decrease in temperature, and flows out of first heat exchanger  4 . The refrigerant which flows out of first heat exchanger  4  is reduced in pressure in decompressing apparatus  5  to become refrigerant at a low temperature and a low pressure, and flows into second heat exchanger  6 . The refrigerant at a low temperature and a low pressure exchanges heat with water which flows through water circuit  16  in second heat exchanger  6  to increase in temperature, and flows out of second heat exchanger  6 . The refrigerant which flows out of second heat exchanger  6  flows into accumulator  7  through flow path switching apparatus  3  and subjected to gas-liquid separation in accumulator  7 . Gas refrigerant in accumulator  7  is suctioned into compressor  2 . 
     Thus, in the cooling mode, the refrigerant which flows through second heat exchanger  6  defined as the use side heat exchanger cools water which flows through water circuit  16  and this cooled water is used for cooling of the room. 
     An optimal amount of refrigerant in a rated operation in the cooling mode is greater than an optimal amount of refrigerant in a rated operation in the heating mode. Therefore, in the cooling mode, the refrigerant is not stored in refrigerant tank  14  but a total amount of refrigerant circulates through refrigeration cycle apparatus  1 . In the cooling mode, flow rate regulation apparatus  13  and valve  15  are frilly closed or in a state close to the fully closed state, and no refrigerant flows into or out of refrigerant tank circuit  12 . 
     [Cooling Mode-Refrigerant Collection Operation] 
     An optimal amount of refrigerant in the rated operation in the heating mode is smaller than an optimal amount of refrigerant in the rated operation in the cooling mode. Therefore, when the operation mode is switched from the cooling mode to the heating mode, a refrigerant collection operation in which the refrigerant excessive in the heating mode is collected to refrigerant tank  14  is performed in the cooling mode. 
     Referring to  FIG. 6 , in the refrigerant collection operation, flow rate regulation apparatus  13  and valve  15  are opened. Flow path switching apparatus  3  is maintained in a state that the discharge side of compressor  2  is connected to first heat exchanger  4 . Some of the refrigerant which flows from first heat exchanger  4  is branched upstream from decompressing apparatus  5  and flows into flow rate regulation apparatus  13 . The refrigerant is reduced in pressure in flow rate regulation apparatus  13  so that some of the refrigerant is converted to liquid refrigerant. The liquid refrigerant is stored in refrigerant tank  14 . 
     Referring to  FIGS. 6 and 7 , gas refrigerant flows into refrigerant tank  14  together with the liquid refrigerant. The gas refrigerant flows out of refrigerant tank  14  through degassing pipe  30 . The gas refrigerant flows through degassing pipe  30  toward second heat exchanger  6 . Since the gas refrigerant in refrigerant tank  14  escapes through degassing pipe  30 , the liquid refrigerant can sufficiently be stored in refrigerant tank  14 . When refrigerant tank  14  is filled up with the liquid refrigerant, the refrigerant collection operation ends. The filled up state means a state that eighty percent or more of a volume of refrigerant tank  14  is filled with liquid refrigerant. 
     Referring to  FIG. 8 , in the refrigerant collection operation, flow rate regulation apparatus  13  may be opened and valve  15  may be closed. Since valve  15  is closed in this case, the liquid refrigerant is more readily stored in refrigerant tank  14 . 
     [Heating Mode] 
     A flow of refrigerant in the heating mode will be described with reference to  FIG. 9 . The refrigerant at a high temperature and a high pressure discharged from compressor  2  flows into second heat exchanger  6  through flow path switching apparatus  3 . The refrigerant at a high temperature and a high pressure exchanges heat with water which flows through water circuit  16  in second heat exchanger  6  to decrease in temperature, and flows out of second heat exchanger  6 . The refrigerant which flows out of second heat exchanger  6  is reduced in pressure in decompressing apparatus  5  to become refrigerant at a low temperature and a low pressure, and flows into first heat exchanger  4 . The refrigerant at a low temperature and a low pressure exchanges heat with air sent from fan  11  in first heat exchanger  4  to increase in temperature, and flows out of first heat exchanger  4 . The refrigerant which flows out of first heat exchanger  4  flows into accumulator  7  through flow path switching apparatus  3  and is subjected to gas-liquid separation in accumulator  7 . Gas refrigerant in accumulator  7  is suctioned into compressor  2 . 
     Thus, in the heating mode, the refrigerant which flows through second heat exchanger  6  defined as the use side heat exchanger heats water which flows through water circuit  16  and heated water is used for heating a room. 
     In the heating mode, flow rate regulation apparatus  13  is fully closed or in a state close to the fully closed state, and valve  15  is fully opened. As described above, the refrigerant excessive during an operation in the heating mode is stored in refrigerant tank  14  and an amount of refrigerant which circulates through refrigerant circuit RC in the heating mode is smaller than an amount of refrigerant which circulates through refrigerant circuit RC in the cooling mode. 
     In the present embodiment, in both of the cooling mode and the heating mode described above, control device  20  controls decompressing apparatus  5  to set a degree of superheating. More specifically, superheating degree detection unit  22  of control device  20  detects a degree of superheating of refrigerant on an exit side of the heat exchanger which functions as the condenser, that is, on the suction side of compressor  2 , and control device  20  controls an opening position of decompressing apparatus  5  such that the detected degree of superheating is close to a target value. 
     [Defrosting Mode] 
     During an operation in the heating mode, frost may adhere to an outer surface of a pipe of first heat exchanger  4  which functions as the evaporator. Therefore, refrigeration cycle apparatus  1  operates in a defrosting mode in order to melt the frost that adheres. In the defrosting mode, as in the cooling mode, flow path switching apparatus  3  allows connection of the discharge side of compressor  2  to first heat exchanger  4  so as to allow refrigerant at a high temperature discharged from compressor  2  to flow to first heat exchanger  4 . Heat of the refrigerant thus melts frost. In the defrosting mode, the refrigerant at a low temperature flows into second heat exchanger  6  defined as the use side heat exchanger and therefore the defrosting mode desirably ends as early as possible. 
     Since an optimal amount of refrigerant is different between the cooling mode and the heating mode as described above, refrigeration cycle apparatus  1  operates in the heating mode with excessive refrigerant being stored in refrigerant tank  14 . In order to quit the defrosting mode in a short period of time, on the other hand, capability in the defrosting mode is desirably enhanced. In the present embodiment, in the defrosting mode, refrigerant in refrigerant tank  14  is released from refrigerant tank  14  to circulate, to thereby enhance defrosting capability. Therefore, when the operation mode returns from the defrosting mode to the heating mode, the refrigerant collection operation in which the refrigerant excessive in the heating mode is collected to refrigerant tank  14  is performed. The refrigerant collection operation in the defrosting mode is similar to the refrigerant collection operation in the cooling mode described above. 
     In succession, the defrosting mode will be described in further detail. 
     A general flow in the defrosting mode will be described with reference to FIG.  10 . When control device  20  starts the defrosting mode, it performs a refrigerant release operation in which refrigerant in refrigerant tank  14  is released by opening one of flow rate regulation apparatus  13  and valve  15  (S 1 ). In this refrigerant release operation, the refrigerant discharged from compressor  2  flows to first heat exchanger  4 . When a high-pressure saturation temperature is equal to or greater than a threshold value (S 2 ), control device  20  determines that defrosting is completed and performs the refrigerant collection operation for collecting the refrigerant to refrigerant tank  14  by opening both of flow rate regulation apparatus  13  and valve  15  (S 3 ). When an amount of liquid in refrigerant tank  14  reaches the threshold value (S 4 ), control device  20  quits the defrosting mode and returns to the heating mode. 
     An operation in the defrosting mode will further be described below with reference to  FIGS. 11 to 15 . 
     As shown in  FIG. 11 , in the heating mode, compressor  2  operates at a capacity determined based on a load in air conditioning. Flow path switching apparatus  3  allows connection of the discharge side of compressor  2  to second heat exchanger  6 . Decompressing apparatus  5  is set to an opening position at which a degree of superheating is controlled. Flow rate regulation apparatus  13  of refrigerant tank circuit  12  is fully closed or in a state close to the fully closed state. Valve  15  is opened. Flow rate regulation device  13  and valve  15  should only be in such a state that refrigerant tank  14  can be maintained in a full state in the heating mode and limitation to the example in  FIG. 11  is not intended. Refrigeration cycle apparatus  1  in the heating mode is as shown in  FIG. 9 . 
     [Defrosting Mode-First Refrigerant Release Operation] 
     When the defrosting mode is started, a first refrigerant release operation is initially performed. In the first refrigerant release operation, flow path switching apparatus  3  allows connection of the discharge side of compressor  2  to first heat exchanger  4  so that flow rate regulation apparatus  13  is controlled to the opened state and valve  15  is controlled to the closed state. Flow rate regulation apparatus  13  may fully be opened or may be set to an opening position slightly lower than the fully opened state in order to suppress liquid back to compressor  2 . A degree of superheating of decompressing apparatus  5  is controlled also in the defrosting mode. Though compressor  2  is enhanced in operation capacity for enhancing defrosting capability in the example in  FIG. 11 , control of capability of compressor  2  is not limited. 
     When the first refrigerant release operation is started as shown with a point. A in  FIG. 12 , relation in terms of high and low pressures is inverted with switching of a flow path by flow path switching apparatus  3  and hence a high-pressure saturation temperature is low. Though a low-pressure saturation temperature is lowered with lowering in high-pressure saturation temperature, a differential pressure is low because a temperature of water in water circuit  16  which flows through second heat exchanger  6  is high owing to a function in the heating mode before start of the defrosting mode. Therefore, as shown with a point B, a degree of superheating in the suction portion of compressor  2  is high. 
     As shown in  FIG. 13 , as valve  15  of refrigerant tank circuit  12  is closed and flow rate regulation apparatus  13  is opened, refrigerant tank  14  is connected to the high-pressure side of refrigerant circuit RC. Refrigerant circuit RC is in a state immediately after inversion of a low pressure and a high pressure, and the inside of refrigerant tank  14  which has been connected to the high-pressure side in the heating mode until immediately before is in a relatively high-pressure state. Therefore, liquid refrigerant is released from refrigerant tank  14 . Then, as shown with a point C in  FIG. 12 , a degree of superheating on the suction side of compressor  2  abruptly lowers. As shown with a point D in  FIG. 12 , as the first refrigerant release operation proceeds, the high-pressure saturation temperature increases to a inciting point (0° C.) of frost. The refrigerant stored in refrigerant tank  14  also circulates through refrigerant circuit RC so that defrosting capability is enhanced. 
     As shown with a point E in  FIG. 12 , when the degree of superheating on the suction side of compressor  2  lowers to a threshold value SH 1  which is a liquid release end criterion threshold value, control device  20  determines that release of the refrigerant in refrigerant tank  14  has been completed and quits the first refrigerant release operation. As shown in  FIG. 11 , when the first refrigerant release operation ends, flow rate regulation apparatus  13  is closed. 
     [Defrosting Mode-Second Refrigerant Release Operation] 
     Since refrigerant tank  14  releases the refrigerant toward the high-pressure side of refrigerant circuit RC in the first refrigerant release operation as described previously, liquid back is suppressed as compared with a case of release of the refrigerant toward the low-pressure side. When the inside of refrigerant tank  14  and the high-pressure side are equal to each other in pressure, however, the refrigerant may remain in refrigerant tank  14 , in order to further enhance defrosting capability, a second refrigerant release operation for releasing the refrigerant which remains in refrigerant tank  14  is performed. 
     As shown in  FIG. 11 , in the second refrigerant release operation, flow rate regulation apparatus  13  is controlled to the closed state and valve  15  is controlled to the opened state. Though compressor  2  is maintained in such a state that its operation capacity is high in the example in  FIG. 11 , control of capability of compressor  2  is not limited. Control of a degree of superheating of decompressing apparatus  5  is continued. 
     As shown in  FIG. 14 , by opening valve  15  of refrigerant tank circuit  12  and closing flow rate regulation apparatus  13 , refrigerant tank  14  is connected to the low-pressure side of refrigerant circuit RC. The refrigerant which remains in refrigerant tank  14  is released due to a difference in pressure between the inside of refrigerant tank  14  and a downstream side of valve  15  (a downstream side of decompressing apparatus  5 ). 
     As shown in  FIG. 12 , when the second refrigerant release operation is started, the refrigerant which remains in refrigerant tank  14  is released and the degree of superheating on the suction side of compressor  2  lowers. As shown with a point F in  FIG. 12 , when the degree of superheating on the suction side of compressor  2  lowers to a threshold value SH 2  which is a liquid release end criterion threshold value, control device  20  determines that release of the refrigerant in refrigerant tank  14  has been completed and quits the second refrigerant release operation. When the second refrigerant release operation ends, valve  15  is closed. 
     [Defrosting Mode-Continued Defrosting Operation] 
     When release of the refrigerant from refrigerant tank  14  ends, a continued defrosting operation is performed. As shown in  FIG. 11 , in the continued defrosting operation, flow rate regulation apparatus  13  and valve  15  are controlled to the closed state. Control of compressor  2  and decompressing apparatus  5  similar to before is continued. 
     The operation in the defrosting mode promotes melting of frost which has adhered to first heat exchanger  4  and the high-pressure saturation temperature increases as shown in  FIG. 12 . As shown with a point G in  FIG. 12 , when the high-pressure saturation temperature reaches a threshold value T 1  representing a defrosting end criterion threshold value, control device  20  determines that defrosting has been completed and quits the continued defrosting operation. 
     [Defrosting Mode-Refrigerant Collection Operation] 
     As described above, in the defrosting mode, defrosting capability is improved by circulating the refrigerant in refrigerant tank  14 . In returning to the heating mode, the refrigerant collection operation in which the refrigerant excessive in the heating mode is collected to refrigerant tank  14  is performed. 
     As shown in  FIG. 11 , in the refrigerant collection operation, flow rate regulation apparatus  13  and valve  15  are controlled to the opened state. Flow path switching apparatus  3  is maintained in such a state that the discharge side of compressor  2  is connected to first heat exchanger  4 . Control of a degree of superheating of decompressing apparatus  5  is continued. Compressor  2  is relatively low in operation capacity. Since operation capability of compressor  2  is lowered in the refrigerant collection operation in the present embodiment, a speed of circulation of the refrigerant is low and the refrigerant tends to be stored in refrigerant tank  14 . 
     When refrigerant tank  14  is full owing to the refrigerant collection operation, liquid refrigerant flows in on a downstream side of second heat exchanger  6  and the degree of superheating on the suction side of compressor  2  stars to lower as shown with a point H in  FIG. 12 . When the degree of superheating on the suction side of compressor  2  lowers to a threshold value SH 3  representing a collection end criterion threshold value by making use of a phenomenon as shown with a point I in  FIG. 12 , control device  20  determines that refrigerant tank  13  is full and quits the refrigerant collection operation. 
     Though an example in which the continued defrosting operation is performed between the refrigerant release operation and the refrigerant collection operation is shown in  FIG. 11 , frost may also totally be molten during the refrigerant release operation depending on an amount of frost which adheres in first heat exchanger  4 . Therefore, when control device  20  detects the high-pressure saturation temperature reaching T 1  representing the defrosting end criterion threshold value during the refrigerant release operation, control device  20  stops the refrigerant release operation and makes transition to the refrigerant collection operation. 
     [Resumption of Heating Mode] 
     As shown in  FIG. 11 , when the defrosting mode ends, the heating mode is resumed. Specifically, capability of compressor  2  is controlled depending on a required load. Since second heat exchanger  6  defined as the use side heat exchanger has been cooled in the defrosting mode, in general, compressor  2  is operated with its operation capability being high at the time of resumption of the heating mode. Flow path switching apparatus  3  allows connection of the discharge side of compressor  2  to second heat exchanger  6 . Control of the degree of superheating of decompressing apparatus  5  is continued. Flow rate regulation apparatus  13  of refrigerant tank circuit  12  is fully closed or set to an opening position close to the fully closed state and valve  15  is opened. 
     As set forth above, according to the present embodiment, since the refrigerant in refrigerant tank  14  is released in the defrosting mode, an amount of refrigerant which circulates through refrigerant circuit RC increases and defrosting capability can be enhanced. With defrosting capability being enhanced, a time period for the defrosting operation can be shortened. 
     The refrigerant collection operation may end based on subcooling (a degree of subcooling) at an exit of first heat exchanger  4 . The refrigerant collection operation may end when subcooling at the exit of first heat exchanger  4  is equal to or smaller than a prescribed value. Specifically, subcooling at the exit of first heat exchanger  4  is measured, and the refrigerant collection operation may end when subcooling is towered to the prescribed value. 
     A function and effect of the refrigeration cycle apparatus in the present embodiment will now be described. 
     According to refrigeration cycle apparatus  1  in the present embodiment, refrigerant tank circuit  12  is connected to first heat exchanger  4  and second heat exchanger  6  in parallel with decompressing apparatus  5 . Therefore, refrigerant is stored in refrigerant tank  14  and hence an amount of refrigerant which flows through refrigerant circuit RC can be reduced. The refrigerant excessive in heating can thus be collected to refrigerant tank  14 . Degassing pipe  30  has first end  30   a  connected to refrigerant tank  14  and has second end  30   b  connected to at least any of refrigerant circuit RC and refrigerant tank circuit  12 . Therefore, gas refrigerant in refrigerant tank  14  can escape through degassing pipe  30 . Therefore, blocking of inflow of liquid refrigerant by the gas refrigerant in refrigerant tank  14  is suppressed. Therefore, the liquid refrigerant can sufficiently be collected to refrigerant tank  14 . Thus, inflow into compressor  2  of the liquid refrigerant which flows in refrigerant circuit RC can be suppressed. Therefore, occurrence of liquid back can be suppressed. Therefore, failure of compressor  2  due to liquid back can be suppressed. 
     In refrigeration cycle apparatus  1  in the present embodiment, degassing pipe  30  has second end  30   b  connected to at least any of refrigerant circuit RC and refrigerant tank circuit  12  between refrigerant tank  14  and second heat exchanger  6 . Therefore, degassing pipe  30  has second end  30   b  connected to the low-pressure side of refrigerant circuit RC. The gas refrigerant in refrigerant tank  14  can thus escape through degassing pipe  30  to the low-pressure side of refrigerant circuit RC. Therefore, the liquid refrigerant can reliably be collected to refrigerant tank  14 . 
     In refrigeration cycle apparatus  1  in the present embodiment, valve  15  of refrigerant tank circuit  12  is arranged between refrigerant tank  14  and second heat exchanger  6 . Therefore, storage of the liquid refrigerant in refrigerant tank  14  can be facilitated by closing valve  15 . 
     In refrigeration cycle apparatus  1  in the present embodiment, an amount of refrigerant which flows through refrigerant circuit RC can be reduced. Therefore, refrigeration cycle apparatus  1  can be configured without accumulator  7 . In refrigeration cycle apparatus  1 , accumulator  7  can be reduced in size even though accumulator  7  is provided. Therefore, a machine compartment of refrigeration cycle apparatus  1  where accumulator  7  is generally installed can be reduced in size. Therefore, refrigeration cycle apparatus  1  can be space-saving. A weight of refrigeration cycle apparatus  1  can thus be reduced. A footprint of refrigeration cycle apparatus  1  can be made smaller. An amount of refrigerant of refrigeration cycle apparatus  1  can be reduced. 
     Second Embodiment 
     A configuration of refrigeration cycle apparatus  1  in a second embodiment of the present invention will be described with reference to  FIG. 15 . Features the same as in the first embodiment have the same reference characters allotted and description will not be repeated unless otherwise specified, which is also applicable to third to sixth embodiments. 
     In refrigeration cycle apparatus  1  in the present embodiment, degassing pipe  30  has second end  30   b  connected to refrigerant circuit RC between second heat exchanger  6  and compressor  2 . In  FIG. 15 , degassing pipe  30  has second end  30   b  connected to refrigerant circuit RC between second heat exchanger  6  and flow path switching apparatus  3 . Degassing pipe  30  has second end  30   b  connected downstream from second heat exchanger  6  and on a low-pressure side relative to refrigerant tank  14  in refrigerant circuit RC. 
     Referring, to  FIG. 16 , the refrigeration cycle apparatus in the present embodiment, degassing pipe  30  has second end  30   b  connected downstream from second heat exchanger  6  and on the low-pressure side relative to refrigerant tank  14  in refrigerant circuit RC. Therefore, gas refrigerant in refrigerant tank  14  escapes through degassing pipe  30  toward a lower-pressure side of refrigerant circuit RC. 
     In refrigeration cycle apparatus  1  in the present embodiment, degassing pipe  30  has second end  30   b  connected to refrigerant circuit RC between second heat exchanger  6  and compressor  2 . Therefore, degassing pipe  30  has second end  30   b  connected to the lower-pressure side of refrigerant circuit RC. Gas refrigerant in refrigerant tank  14  can thus escape through degassing pipe  30  toward the lower-pressure side of refrigerant circuit RC. Therefore, liquid refrigerant can more reliably be collected to refrigerant tank  14 . A time period for collection of the liquid refrigerant can be shortened. 
     Third Embodiment 
     A configuration of refrigeration cycle apparatus  1  in a third embodiment of the present invention will be described with reference to  FIG. 17 . In refrigeration cycle apparatus  1  in the present embodiment, degassing pipe  30  has second end  30   b  connected to refrigerant circuit RC between compressor  2  and first heat exchanger  4 . In  FIG. 17 , degassing pipe  30  has second end  30   b  connected to refrigerant circuit RC between compressor  2  and flow path switching apparatus  3 . Degassing pipe  30  has second end  30   b  connected downstream from compressor  2  and on the high-pressure side relative to refrigerant tank  14  in refrigerant circuit RC. 
     Referring to  FIG. 18 , in the refrigeration cycle apparatus in the present embodiment, degassing pipe  30  has second end  30   b  connected downstream from compressor  2  and on the high-pressure side relative to refrigerant tank  14  in refrigerant circuit RC. Therefore, a pressure of gas refrigerant discharged from compressor  2  is applied to the inside of refrigerant tank  14  through degassing pipe  30 . Flow rate regulation apparatus  13  is closed and valve  15  is opened. Therefore, the liquid refrigerant is released from refrigerant tank  14  while the pressure of the gas refrigerant discharged from compressor  2  is applied to the inside of refrigerant tank  14  through degassing pipe  30 . 
     In refrigeration cycle apparatus  1  in the present embodiment, degassing pipe  30  has second end  30   b  connected to refrigerant circuit RC between compressor  2  and first heat exchanger  4 . Therefore, a pressure of the gas refrigerant discharged from compressor  2  is applied to the inside of refrigerant tank  14  through degassing pipe  30 . Thus, when liquid refrigerant is released from refrigerant tank  14  in the cooling mode, refrigerant tank  14  can reliably be evacuated. When the liquid refrigerant is similarly released from refrigerant tank  14  also in the defrosting mode, refrigerant tank  14  can reliably be evacuated. 
     Fourth Embodiment 
     A configuration of refrigeration cycle apparatus  1  in a fourth embodiment of the present invention will be described with reference to  FIG. 19 . In refrigeration cycle apparatus  1  in the present embodiment, degassing pipe  30  is provided with a first pipe portion  31 , a second pipe portion  32 , and a valve portion VP. First pipe portion  31  has a first end  31   a  and a second end  31   b . Second pipe portion  32  has a first end  32   a  and a second end  32   b.    
     First pipe portion  31  has first end  31 . a  connected to refrigerant tank  14 . First pipe portion  31  has first end  31   a  connected to the upper surface of refrigerant tank  14 . First pipe portion  31  has second end  31   b  connected to at least any of refrigerant circuit RC and refrigerant tank circuit  12  between refrigerant tank  14  and second heat exchanger  6 . In  FIG. 19 , first pipe portion  31  has second end  31   b  connected to refrigerant tank circuit  12  between refrigerant tank  14  and second heat exchanger  6 . First pipe portion  31  has second end  31   b  connected downstream from valve  15  in refrigerant tank circuit  12 . 
     Second pipe portion  32  has first end  32   a  connected to refrigerant tank  14 . Second pipe portion  32  has first end  32   a  connected to the upper surface of refrigerant tank  14 . Second pipe portion  32  has second end  32   b  connected to refrigerant circuit RC between compressor  2  and first heat exchanger  4 , in  FIG. 19 , second pipe portion  32  has second end  30   b  connected to refrigerant circuit RC between compressor  2  and flow path switching apparatus  3 . Second pipe portion  32  has second end  32   b  connected downstream from compressor  2  and on the high-pressure side relative to refrigerant tank  14  in refrigerant circuit RC. 
     Valve portion VP is configured to allow refrigerant to flow to one of first pipe portion  31  and second pipe portion  32  and not to allow the refrigerant to the other thereof. Valve portion VP is connected between first end  31   a  and second end  31   b  of first pipe portion  31 . Valve portion VP is connected also between first end  32   a  and second end  32   b  of second pipe portion  32 . Valve portion VP has a valve disc and switches between a conducting state and a non-conducting state of the refrigerant by switching between an opened state and a closed state of the valve disc. For example, a bidirectional solenoid valve can be employed for valve portion VP. Valve portion VP is electrically connected to control device  20 . An operation of valve portion VP is controlled by control device  20 . 
     Referring to  FIG. 20 , valve portion VP connected to first pipe portion  31  is opened and valve portion VP connected to second pipe portion  32  is closed, so that liquid refrigerant can sufficiently be stored in refrigerant tank  14  in the refrigerant collection operation. 
     Referring to  FIG. 21 , valve portion VP connected to first pipe portion  31  is closed and valve portion VP connected to second pipe portion  32  is opened, so that a pressure of gas refrigerant discharged from compressor  2  is applied to the inside of refrigerant tank  14  through second pipe portion  32  when liquid refrigerant is released from refrigerant tank  14 . 
     In refrigeration cycle apparatus  1  in the present embodiment, valve portion VP connected to first pipe portion  31  is opened and valve portion VP connected to second pipe portion  32  is closed, so that liquid refrigerant can sufficiently be stored in refrigerant tank  14  in the refrigerant collection operation. Flow into compressor  2  of liquid refrigerant which flows through refrigerant circuit RC can thus be suppressed. Valve portion VP connected to first pipe portion  31  is closed and valve portion VP connected to second pipe portion  32  is opened, so that a pressure of gas refrigerant discharged from compressor  2  is applied to the inside of refrigerant tank  14  through second pipe portion  32  when liquid refrigerant is released from refrigerant tank  14 . Refrigerant tank  14  can thus reliably be evacuated when liquid refrigerant is released from refrigerant tank  14 . By switching valve portion VP, in refrigerant collection operation, flow into compressor  2  of liquid refrigerant which flows in refrigerant circuit RC can be suppressed and refrigerant tank  14  can reliably be evacuated when liquid refrigerant is released from refrigerant tank  14 . 
     Fifth Embodiment 
     A configuration of refrigeration cycle apparatus  1  in a fifth embodiment of the present invention will be described with reference to  FIG. 22 . In refrigeration cycle apparatus  1  in the present embodiment, degassing pipe  30  is provided with first pipe portion  31 , second pipe portion  32 , and valve portion VP. First pipe portion  31  has first end  31   a  and second end  31   b . Second pipe portion  32  has first end  32   a  and second end  32   b.    
     First pipe portion  31  has first end  31   a  connected to refrigerant tank  14 . First pipe portion  31  has first end  31   a  connected to the upper surface of refrigerant tank  14 . First pipe portion  31  has second end  31   b  connected to refrigerant circuit RC between second heat exchanger  6  and compressor  2 . In  FIG. 22 , first pipe portion  31  has first end  31   a  connected to refrigerant circuit RC between second heat exchanger  6  and flow path switching apparatus  3 . First pipe portion  31  has second end  31   b  connected downstream from second heat exchanger  6  and on the low-pressure side relative to refrigerant tank  14  in refrigerant circuit RC. 
     Second pipe portion  32  has first end  32   a  connected to refrigerant tank  14 . Second pipe portion  32  has first end  32   a  connected to the upper surface of refrigerant tank  14 . Second pipe portion  32  has second end  32   b  connected to refrigerant circuit RC between compressor  2  and first heat exchanger  4 . In  FIG. 12 , second pipe portion  32  has second end  30   b  connected to refrigerant circuit RC between compressor  2  and flow path switching apparatus  3 . Second pipe portion  32  has second end  32   b  connected downstream from compressor  2  and on the high-pressure side relative to refrigerant tank  14  in refrigerant circuit RC. 
     Valve portion VP is configured to allow refrigerant to flow to one of first pipe portion  31  and second pipe portion  32  and not to allow the refrigerant to flow to the other thereof. Valve portion VP is connected between first end  31   a  and second end  31   b  of first pipe portion  31 . Valve portion VP is connected also between first end  31   a  and second end  31   b  of first pipe portion  31 . Valve portion VP has a valve disc and switches between a conducting state and a non-conducting state of the refrigerant by switching between the opened state and the closed state of the valve disc. For example, a bidirectional solenoid valve can be employed for valve portion VP. Valve portion VP is electrically connected to control device  20 . An operation of valve portion VP is controlled by control device  20 . 
     Referring to  FIG. 23 , valve portion VP connected to first pipe portion  31  is opened and valve portion VP connected to second pipe portion  32  is closed, so that gas refrigerant in refrigerant tank  14  can escape through first pipe portion  31  toward the lower-pressure side of refrigerant circuit RC. 
     Referring to  FIG. 24 , valve portion VP connected to first pipe portion  31  is closed and valve portion VP connected to second pipe portion  32  is opened, so that a pressure of gas refrigerant discharged from compressor  2  is applied to the inside of refrigerant tank  14  through second pipe portion  32  when liquid refrigerant is released from refrigerant tank  14 . 
     In refrigeration cycle apparatus  1  in the present embodiment, valve portion VP connected to first pipe portion  31  is opened and valve portion VP connected to second pipe portion  32  is closed, so that gas refrigerant in refrigerant tank  14  can escape through first pipe portion  31  to the lower pressure side of refrigerant circuit RC in the refrigerant collection operation. The liquid refrigerant can thus more reliably be collected to refrigerant tank  14 . Valve portion VP connected to first pipe portion  31  is closed and valve portion VP connected to second pipe portion  32  is opened, so that a pressure of gas refrigerant discharged from compressor  2  is applied to the inside of refrigerant tank  14  through second pipe portion  32  when liquid refrigerant is released from refrigerant tank  14 . Thus, refrigerant tank  14  can reliably be evacuated when liquid refrigerant is released from refrigerant tank  14 . By switching valve portion VP, in the refrigerant collection operation, liquid refrigerant can more reliably be collected to refrigerant tank  14  and refrigerant tank  14  can reliably be evacuated when liquid refrigerant is released from refrigerant tank  14 . 
     Sixth Embodiment 
     A configuration of refrigerant tank  14  of refrigeration cycle apparatus  1  in a sixth embodiment of the present invention will be described with reference to  FIG. 25 . 
     In refrigeration cycle apparatus  1  in the present embodiment, refrigerant tank  14  is provided with a main body portion  141  and a tubular portion  142  connected to main body portion  141 . Tubular portion  142  is arranged on a side of first heat exchanger  4  shown in  FIG. 1  relative to main body portion  141 . Tubular portion  142  is connected to first heat exchanger  4  through a pipe. Main body portion  141  is connected to first heat exchanger  4  with tubular portion  142  being interposed. Degassing pipe  30  has first end  30   a  connected to tubular portion  142 . For example, a T tube can be employed for tubular portion  142 . Tubular portion  142  has an inner diameter, for example, not smaller than 25 mm and not greater than 35 mm. As the inner diameter is greater, efficiency in gas-liquid separation of refrigerant can be improved. 
     In refrigeration cycle apparatus  1  in the present embodiment, degassing pipe  30  has first end  30   a  connected to tubular portion  142 . Therefore, degassing pipe  30  is not connected to main body portion  141 . Therefore, a hole for degassing pipe  30  does not have to be provided in refrigerant tank  14 . Therefore, a structure for connection between refrigerant tank  14  and degassing pipe  30  is simplified. Therefore, cost can be reduced. 
     It should be understood that the embodiments disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims rather than the description above and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims. 
     REFERENCE SIGNS LIST 
       1  refrigeration cycle apparatus;  2  compressor;  3  path switching apparatus;  4  first heat exchanger;  5  decompressing apparatus;  6  second heat exchanger;  7  accumulator;  8  suction pressure sensor;  9  discharge pressure sensor;  10  suction temperature sensor;  11  fan;  12  refrigerant tank circuit;  13  flow rate regulation apparatus;  14  refrigerant tank;  15  valve;  16  water circuit;  20  control device;  21  high-pressure saturation temperature detection unit;  22  superheating degree detection unit;  23  refrigerant tank liquid amount detection unit;  24  memory;  30  degassing pipe;  30   a ,  31   a ,  32   a  first end;  30   b ,  31   b ,  32   b  second end;  31  first pipe portion;  32  second pipe portion;  141  main body portion;  142  tubular portion; RC refrigerant circuit; and VP valve portion