Refrigeration cycle device, and refrigeration cycle device control method

Abstract

A deterioration in user comfort when defrosting operation of an outdoor heat exchanger is performed is suppressed and also a decrease in defrosting capability is avoided. In starting defrosting operation, when a control unit (7) has determined that the temperature of a heat storage material acquired from a heat storage temperature sensor (HS) is equal to or less than the preset first threshold, the control unit (7) performs control to carry out reverse defrosting operation of defrosting an outdoor heat exchanger (3) by controlling a plurality of switching valves (6) such that a third pressure reduction mechanism (53) is brought into a closed state, the outdoor heat exchanger (3) functions as a condenser, and an indoor heat exchanger (2) functions as an evaporator, and when the control unit (7) has determined that the temperature of the heat storage material is higher than the first threshold, the control unit (7) performs control to carry out indoor-heat-exchanger bypass defrosting operation of defrosting the outdoor heat exchanger (3) by controlling the plurality of switching valves (6) such that a first pressure reduction mechanism (51) is brought into a closed state, the outdoor heat exchanger (3) functions as a condenser, and a heat accumulation heat exchanger (4) functions as an evaporator.

Description

TECHNICAL FIELD

[0001] The present invention relates to a refrigeration cycle device and a refrigeration cycle device control method.BACKGROUND ART

[0002] In general, when heating operation is performed in an air conditioner, a low temperature refrigerant flows to an outdoor heat exchanger. Therefore, when the temperature of the refrigerant falls below the dew point temperature of the outdoor air in a state in which the outdoor air temperature is equal to or less than the freezing temperature, for example, frost adheres to the outdoor heat exchanger, making heat exchange with the outdoor air difficult. Thus, when the heating operation is being performed, defrosting operation of removing the frost from the outdoor heat exchanger is regularly performed.

[0003] Such defrosting operation is operation required in operating an air conditioner. The defrosting operation is typically performed after stopping the heating operation. Specifically, when the defrosting operation is started, a refrigerant circuit is switched such that a refrigerant that has been discharged from a compressor is directly supplied to the outdoor heat exchanger to cause the outdoor heat exchanger to function as a condenser, thereby melting frost to perform defrosting. In the case of the defrosting operation, a high temperature refrigerant that has been supplied to the outdoor heat exchanger for defrosting is cooled to a low temperature by melting frost, and the low temperature refrigerant flows into an indoor heat exchanger.

[0004] When such defrosting operation is performed, the heating operation stops while the defrosting operation is being performed as described above, and therefore the room temperature gradually decreases, deteriorating user comfort. Further, each part, such as a pipe, of the indoor heat exchanger is cooled by the passage of the refrigerant that has been cooled to a low temperature by the defrosting of the outdoor heat exchanger. Therefore, even when the heating operation is started again after the defrosting operation, low temperature air is blown into a room until the indoor heat exchanger is warmed, which may impair comfort.

[0005] Thus, PTL 1 described later discloses the invention capable of continuing the heating operation even during the defrosting operation, thereby preventing the decrease in the room temperature due to the temporary stop of the heating operation and maintaining comfort.

[0006] More specifically, in the invention disclosed in PTL 1, a heat storage device is arranged separately from the indoor heat exchanger in a refrigeration circuit.

[0007] The total amount of heat that has been stored in the heat storage device is used only for the defrosting in the defrosting operation, thereby reducing the defrosting time and suppressing the decrease in the room temperature to a short period of time.CITATION LISTPatent Literature

[0008] PTL 1: JP H06-074618 ASUMMARY OF INVENTIONTechnical Problem

[0009] In the case of the air conditioner described in PTL 1 above, the inflow of the low temperature refrigerant into the indoor heat exchanger in the defrosting operation can be certainly avoided by utilizing the heat storage device. However, a heat source used for the defrosting is limited to the heat that has been stored in the heat storage device, and therefore the capability of the defrosting operation is considered to decrease as compared with a defrosting method using a refrigerant that has been discharged from a compressor as in conventional methods.

[0010] Herein, one of the heat sources for a refrigerant when the outdoor heat exchanger is defrosted is the indoor air. More specifically, in the defrosting operation, the refrigerant that has been cooled to a low temperature by the defrosting of the outdoor heat exchanger flows into the indoor heat exchanger. Then, the refrigerant absorbs heat by exchanging heat with the indoor air, a heat transfer tube of the indoor heat exchanger, or the like that has been warmed by the heating operation being performed up to the point before the defrosting operation and is utilized again for the defrosting of the outdoor heat exchanger.

[0011] However, in the case of the defrosting operation method as described in PTL 1, the heat of the indoor heat exchanger is not utilized for the defrosting operation. Therefore, particularly when heat is not sufficiently stored in the heat storage device, the defrosting capability significantly decreases, deteriorating comfort, e.g., the defrosting operation takes longer than before, for example.

[0012] It is an object of the present invention to provide a refrigeration cycle device and a refrigeration cycle device control method capable of suppressing the deterioration in user comfort when the defrosting operation of the outdoor heat exchanger is performed and also avoiding the decrease in defrosting capability.Solution to Problem

[0013] A refrigeration cycle device according to one aspect of the present invention includes: a refrigerant circuit configured to circulate a refrigerant, to which a compressor configured to compress the refrigerant; an indoor heat exchanger configured to exchange heat between the indoor air and the refrigerant; an outdoor heat exchanger configured to exchange heat between the outdoor air and the refrigerant; a heat accumulation heat exchanger configured to exchange heat between a heat storage material and the refrigerant; a plurality of pressure reduction mechanisms having an adjustable opening degree; and a plurality of switching valves configured to switch a circulation path of the refrigerant in the refrigerant circuit between heating operation in which the indoor heat exchanger and the heat accumulation heat exchanger are caused to function as condensers and the outdoor heat exchanger is caused to function as an evaporator and defrosting operation in which the outdoor heat exchanger is caused to function as a condenser and the indoor heat exchanger or the heat accumulation heat exchanger is caused to function as an evaporator are connected;

[0014] a heat storage temperature sensor configured to measure the temperature of the heat storage material; and

[0015] a control unit configured to control the plurality of switching valves,

[0016] the plurality of pressure reduction mechanisms having, in the circulation path of the refrigerant of the heating operation, a first pressure reduction mechanism provided on the downstream side of the indoor heat exchanger, a second pressure reduction mechanism provided on the upstream side of the heat accumulation heat exchanger, and a third pressure reduction mechanism provided on the downstream side of the heat accumulation heat exchanger, in which

[0017] in starting the defrosting operation, when the control unit has determined that the temperature of the heat storage material acquired from the heat storage temperature sensor is equal to or less than the preset first threshold, the control unit performs control to carry out reverse defrosting operation of defrosting the outdoor heat exchanger by controlling the plurality of switching valves such that the third pressure reduction mechanism is brought into a closed state, the outdoor heat exchanger functions as a condenser, and the indoor heat exchanger functions as an evaporator, and

[0018] when the control unit has determined that the temperature of the heat storage material is higher than the first threshold, the control unit performs control to carry out indoor-heat-exchanger bypass defrosting operation of defrosting the outdoor heat exchanger by controlling the plurality of switching valves such that the first pressure reduction mechanism is brought into a closed state, the outdoor heat exchanger functions as a condenser, and the heat accumulation heat exchanger functions as an evaporator.

[0019] A refrigeration cycle device control method according to one aspect of the present invention includes:

[0020] in a refrigeration cycle device including: a refrigerant circuit configured to circulate a refrigerant, to which a compressor configured to compress the refrigerant; an indoor heat exchanger configured to exchange heat between the indoor air and the refrigerant; an outdoor heat exchanger configured to exchange heat between the outdoor air and the refrigerant; a heat accumulation heat exchanger configured to exchange heat between a heat storage material and the refrigerant; a plurality of pressure reduction mechanisms having an adjustable opening degree; and a plurality of switching valves configured to switch a circulation path of the refrigerant in the refrigerant circuit between heating operation in which the indoor heat exchanger and the heat accumulation heat exchanger are caused to function as condensers and the outdoor heat exchanger is caused to function as an evaporator and defrosting operation in which the outdoor heat exchanger is caused to function as a condenser and the indoor heat exchanger or the heat accumulation heat exchanger is caused to function as an evaporator are connected;

[0021] a heat storage temperature sensor configured to measure the temperature of the heat storage material; and

[0022] a control unit configured to control the plurality of switching valves,

[0023] the plurality of pressure reduction mechanisms having, in the circulation path of the refrigerant of the heating operation, a first pressure reduction mechanism provided on the downstream side of the indoor heat exchanger, a second pressure reduction mechanism provided on the upstream side of the heat accumulation heat exchanger, and a third pressure reduction mechanism provided on the downstream side of the heat accumulation heat exchanger,

[0024] after the heating operation has shifted to the defrosting operation, determining by the control unit whether the temperature of the heat storage material acquired from the heat storage temperature sensor is equal to or less than the preset first threshold,

[0025] when the temperature of the heat storage material has been determined to be equal to or less than the first threshold, performing control by the control unit to carry out reverse defrosting operation of defrosting the outdoor heat exchanger by controlling the plurality of switching valves such that the third pressure reduction mechanism is brought into a closed state, the outdoor heat exchanger functions as a condenser, and the indoor heat exchanger functions as an evaporator, and

[0026] when the temperature of the heat storage material has been determined to be higher than the first threshold, performing control by the control unit to carry out indoor-heat-exchanger bypass defrosting operation of defrosting the outdoor heat exchanger by controlling the plurality of switching valves such that the first pressure reduction mechanism is brought into a closed state, the outdoor heat exchanger functions as a condenser, and the heat accumulation heat exchanger functions as an evaporator.Advantageous Effects of Invention

[0027] The present invention can suppress the deterioration in user comfort when the defrosting operation of the outdoor heat exchanger is performed and also avoid the decrease in defrosting capability.BRIEF DESCRIPTION OF DRAWINGS

[0028] FIG. 1 is a refrigerant circuit diagram of a refrigeration cycle device according to an embodiment of the present invention;

[0029] FIG. 2 is a block diagram illustrating the internal configuration of a control unit in the refrigeration cycle device according to the embodiment of the present invention;

[0030] FIG. 3 is a refrigerant circuit diagram illustrating the flow of a refrigerant when the refrigeration cycle device according to the embodiment of the present invention performs heating and heat storage operation;

[0031] FIG. 4 is a refrigerant circuit diagram illustrating the flow of a refrigerant when the refrigeration cycle device according to the embodiment of the present invention performs reverse defrosting operation;

[0032] FIG. 5 is a refrigerant circuit diagram illustrating the flow of a refrigerant when the refrigeration cycle device according to the embodiment of the present invention performs indoor-heat-exchanger bypass defrosting operation;

[0033] FIG. 6 is a refrigerant circuit diagram illustrating the flow of a refrigerant when the refrigeration cycle device according to the embodiment of the present invention performs heating and defrosting operation;

[0034] FIG. 7 is a flowchart illustrating the flow of control when defrosting operation is performed in the refrigeration cycle device according to the embodiment of the present invention; and

[0035] FIG. 8 is a flowchart illustrating the flow of control when defrosting operation is performed in the refrigeration cycle device according to the embodiment of the present invention.DESCRIPTION OF EMBODIMENTS

[0036] The structure of a refrigeration cycle device S according to the embodiment of the present invention is described with reference to FIG. 1. FIG. 1 is a refrigerant circuit diagram of the refrigeration cycle device S according to the embodiment of the present invention. The refrigeration cycle device S includes a refrigerant circuit C to which a compressor 1, an indoor heat exchanger 2, an outdoor heat exchanger 3, a heat accumulation heat exchanger 4, a pressure reduction mechanism 5, and a switching valve 6 are connected and which circulates a refrigerant. Further, a control unit 7 controlling the switching valve 6 is provided.

[0037] The compressor 1 compresses a refrigerant circulating inside the refrigerant circuit C. The indoor heat exchanger 2 exchanges heat between the indoor air and a refrigerant. The outdoor heat exchanger 3 exchanges heat between the outdoor air and a refrigerant. Although structures of the compressor 1, the indoor heat exchanger 2, and the outdoor heat exchanger 3 are not described herein, devices of various structures can be adopted.

[0038] The heat accumulation heat exchanger 4 is a heat exchanger in which a heat storage material filled thereinside and a refrigerant passing through the heat accumulation heat exchanger 4 exchange heat. The heat storage material stores heat supplied from a refrigerant. The stored heat is used for heating operation or defrosting operation as described later. Further, a heat storage temperature sensor HS described later is provided at a position where the temperature of the heat storage material can be measured.

[0039] The pressure reduction mechanism 5 is formed such that the opening degree is adjustable and includes a plurality of pressure reduction mechanisms in the refrigeration cycle device S according to the embodiment of the present invention. Specifically, three pressure reduction mechanisms are provided. A first pressure reduction mechanism 51 is provided between the indoor heat exchanger 2 and the outdoor heat exchanger 3. A second pressure reduction mechanism 52 is provided between the compressor 1 and the heat accumulation heat exchanger 4 or the outdoor heat exchanger 3. A third pressure reduction mechanism 53 is provided between the heat accumulation heat exchanger 4 and the outdoor heat exchanger 3.

[0040] The switching valve 6 switches a circulation path of a refrigerant in the refrigerant circuit C between the heating operation and the defrosting operation. In the case of the heating operation, the indoor heat exchanger 2 and the heat accumulation heat exchanger 4 are caused to function as condensers and the outdoor heat exchanger 3 is caused to function as an evaporator. In the case of the defrosting operation, the outdoor heat exchanger 3 is caused to function as a condenser and the indoor heat exchanger 2 or the heat accumulation heat exchanger 4 is caused to function as an evaporator.

[0041] In the refrigeration cycle device S in the embodiment of the present invention, the switching valve 6 also includes a plurality of switching valves. More specifically, a first switching valve 61 is provided between the compressor 1 and the indoor heat exchanger 2. A second switching valve 62 is provided between the compressor 1 and the heat accumulation heat exchanger 4. A third switching valve 63 is provided between the compressor 1 and the outdoor heat exchanger 3.

[0042] Hereinafter, when these three pressure reduction mechanisms are collectively described, the three pressure reduction mechanisms are referred to as the “pressure reduction mechanism 5″ as appropriate, and, when each pressure reduction mechanism is described, each pressure reduction mechanisms is referred to as the name. Also for the switching valve 6, when these three switching valves are collectively described, the three switching valves are referred to as the ”switching valve 6″ as appropriate and, when each switching valve is described, each switching valve is referred to as the name.

[0043] The control unit 7 controls the opening degree of the plurality of pressure reduction mechanisms 5. The control of the opening degree of each pressure reduction mechanism by the control unit 7 enables the regulation of the flow rate of a refrigerant flowing through the refrigerant circuit C. As described above, the plurality of switching valves 6 is switched to switch the flow of the refrigerant circulating through the refrigerant circuit C.

[0044] By controlling the plurality of pressure reduction mechanisms 5 and the plurality of switching valves 6 as described above, the control unit 7 performs heating and heat storage operation of performing the heating operation and heat storage operation in parallel, for example. Further, the control when the defrosting operation of the outdoor heat exchanger 3 is performed is also performed by the control unit 7.

[0045] Next, the control contents performed by the control unit 7 are described in more detail. FIG. 2 is a block diagram illustrating the internal configuration of the control unit 7 in the refrigeration cycle device S according to the embodiment of the present invention. The control unit 7 includes a temperature detection unit 71, a storage unit 72, a determination unit 73, and a defrosting operation control unit 74.

[0046] The temperature detection unit 71 acquires the temperature of the heat storage material detected by the heat storage temperature sensor HS provided in the heat accumulation heat exchanger 4. The temperature of the heat storage material detected in the heat storage temperature sensor HS may be transmitted at each predetermined time interval from the heat storage temperature sensor HS to the temperature detection unit 71. Alternatively, the temperature detection unit 71 may conversely acquire the temperature of the heat storage material from the heat storage temperature sensor HS as required.

[0047] The storage unit 72 stores information for comparison with the temperature of the heat storage material acquired in the temperature detection unit 71. More specifically, in the storage unit 72, a first threshold and a second threshold are preset and stored. Both the first threshold and the second threshold are used when the determination unit 73 determines a mode of the defrosting operation carried out by the defrosting operation control unit 74 described later.

[0048] Although the relation between the first threshold and the second threshold can be set as desired, it is assumed in the embodiment of the present invention that the second threshold is set to a value higher than the value of the first threshold.

[0049] Herein, the “first threshold” is a value serving as the reference to be used to determine whether to perform reverse defrosting operation described later. Specifically, when the amount of heat stored in the heat storage material of the heat accumulation heat exchanger 4 is so small that there is a risk that the defrosting operation is prolonged, the first threshold is a value indicating the state. On the other hand, the “second threshold” is a value serving as the reference to be used to determine whether to perform heating and defrosting operation described later. Specifically, the second threshold is a value indicating a state in which the amount of heat stored in the heat storage material is large to such an extent that not only the defrosting operation but the heating operation can be performed in parallel. This is the reason why the second threshold is set to a value higher than the value of the first threshold as described above.

[0050] The determination unit 73 determines which operation mode is to be selected as the defrosting operation for the outdoor heat exchanger 3 using the temperature of the heat storage material acquired from the heat storage temperature sensor HS by the temperature detection unit 71 and the first threshold or the second threshold stored in the storage unit 72.

[0051] In the embodiment of the present invention, three modes of the reverse defrosting operation, indoor-heat-exchanger bypass defrosting operation, and the heating and defrosting operation that are described later are set as a mode of the defrosting operation. Then, the determination unit 73 selects any one of the operation modes by comparing the temperature of the heat storage material with the first threshold or the second threshold.

[0052] Information on the operation mode selected in the determination unit 73 is transmitted to the defrosting operation control unit 74. The defrosting operation control unit 74 controls the pressure reduction mechanism 5 and the switching valve 6 according to the operation mode received from the determination unit 73.

[0053] Next, various kinds of defrosting operation referred to above are described in order using the circuit diagram of the refrigeration cycle device S in the embodiment of the present invention. Prior to the description, the heating operation in the refrigeration cycle device S, which is the base, is first described using FIG. 3. FIG. 3 is a refrigerant circuit diagram illustrating the flow of a refrigerant when the refrigeration cycle device S according to the embodiment of the present invention performs the heating and heat storage operation. Herein, the heating and heat storage operation is operation in which heat is dissipated from a refrigerant to the heat storage material in the heat accumulation heat exchanger 4 while heating operation utilizing the indoor heat exchanger 2 as a condenser is being performed.

[0054] In the circuit diagrams used in the following description, including FIG. 3, the refrigerant circuit C through which a refrigerant actually flows is illustrated by the solid lines. On the other hand, the refrigerant circuit C which constitutes the refrigerant circuit C but through which no refrigerant flows is illustrated by the dashed lines. The directions of the refrigerant flowing in the refrigerant circuit C are indicated by the arrows.

[0055] When the refrigeration cycle device S performs the heating and heat storage operation, a refrigerant that has been discharged from the compressor 1 flows into the indoor heat exchanger 2 via the first switching valve 61. Then, heat is exchanged between the refrigerant and the air flowing into an indoor unit in the indoor heat exchanger 2, and the air that has been warmed by absorbing heat from the refrigerant is supplied to indoor space. Therefore, the indoor heat exchanger 2 functions as a condenser.

[0056] The refrigerant that has flowed out of the indoor heat exchanger 2 flows into the outdoor heat exchanger 3 through the first pressure reduction mechanism 51. The outdoor heat exchanger 3 functions as an evaporator, and heat is exchanged between the refrigerant and the outdoor air. The refrigerant that has flowed out of the outdoor heat exchanger 3 flows into the compressor 1 via the third switching valve 63.

[0057] The refrigeration cycle device S in the embodiment of the present invention is provided with the heat accumulation heat exchanger 4 in addition to the indoor heat exchanger 2 and the outdoor heat exchanger 3. When the heating and heat storage operation is carried out, the refrigerant that has been discharged from the compressor 1 not only flows into the indoor heat exchanger 2 as described above but flows into the heat accumulation heat exchanger 4 via the second pressure reduction mechanism 52 and the second switching valve 62.

[0058] In the heat accumulation heat exchanger 4, the refrigerant that has flowed into the heat accumulation heat exchanger 4 exchanges heat with the heat storage material, so that the heat of the refrigerant is stored in the heat storage material. The temperature of the heat storage material due to heat storage is detected in the heat storage temperature sensor HS and transmitted to the temperature detection unit 71 of the control unit 7 as appropriate as described above.

[0059] The refrigerant that has flowed out of the heat accumulation heat exchanger 4 after the heat exchange in the heat accumulation heat exchanger 4 flows into the outdoor heat exchanger 3 via the third pressure reduction mechanism 53. Further, the refrigerant flows out of the outdoor heat exchanger 3 and flows into the compressor 1 via the third switching valve 63.

[0060] The control unit 7 carries out control of the heating and heat storage operation in such a refrigeration cycle device S, and also carries out control of the operation of defrosting the outdoor heat exchanger 3. As described above, the control of the defrosting operation includes the plurality of modes. First, the reverse defrosting operation is described.

[0061] FIG. 4 is a refrigerant circuit diagram illustrating the flow of a refrigerant when the refrigeration cycle device S according to the embodiment of the present invention performs the reverse defrosting operation. The reverse defrosting operation is an operation mode in which the heating operation is switched to the cooling operation and the outdoor heat exchanger 3 is defrosted in the refrigeration cycle device S where the heating and heat storage operation is being carried out.

[0062] Specifically, in starting the defrosting operation, when the determination unit 73 has determined that the temperature of the heat storage material is equal to or less than the first threshold, the defrosting operation control unit 74 first brings the third pressure reduction mechanism 53 into a closed state.

[0063] In determining whether to perform the reverse defrosting operation, the determination unit 73 uses the first threshold. The first threshold is used to determine whether the heat that has been stored in the heat storage material of the heat accumulation heat exchanger 4 can be used for the defrosting operation of the outdoor heat exchanger 3.

[0064] As a result, when the temperature of the heat storage material transmitted by the heat storage temperature sensor HS is equal to or less than the first threshold, the determination unit 73 determines that the amount of heat stored in the heat storage material of the heat accumulation heat exchanger 4 is small, and the heat cannot be used for the defrosting operation of the outdoor heat exchanger 3.

[0065] Therefore, in such a case, the defrosting operation control unit 74 first controls the third pressure reduction mechanism 53 to be in a closed state as described above. Due to the fact that the third pressure reduction mechanism 53 is controlled as described above, the refrigerant discharged from the compressor 1 does not flow into the heat accumulation heat exchanger 4.

[0066] Then, the defrosting operation control unit 74 controls the plurality of switching valves 6 such that the outdoor heat exchanger 3 functions as a condenser and the indoor heat exchanger 2 functions as an evaporator and carries out the reverse defrosting operation of defrosting the outdoor heat exchanger 3.

[0067] Specifically, the defrosting operation control unit 74 controls both the first pressure reduction mechanism 51 and the second pressure reduction mechanism 52 to be in an open state. The defrosting operation control unit 74 also switches the first switching valve 61 such that the suction side of the compressor is connected to the indoor heat exchanger 2. Then, the defrosting operation control unit 74 switches the third switching valve 63 such that the discharge side of the compressor is connected to the outdoor heat exchanger 3.

[0068] Thus, the defrosting operation control unit 74 controls the plurality of pressure reduction mechanisms 5 and the plurality of switching valves 6. By the control, the high temperature refrigerant that has been discharged from the compressor 1 flows into the outdoor heat exchanger 3 via the second pressure reduction mechanism 52 and the third switching valve 63 as indicated by the arrows in FIG. 4.

[0069] Then, the heat of the refrigerant that has flowed into the outdoor heat exchanger 3 melts frost adhering to the outdoor heat exchanger 3. The refrigerant that has been cooled to a low temperature by melting the frost flows out of the outdoor heat exchanger 3 and flows into the indoor heat exchanger 2 via the first pressure reduction mechanism 51. The third pressure reduction mechanism 53 is controlled to be in closed state as described above, and therefore the refrigerant that has flowed out of the outdoor heat exchanger 3 does not flow into the heat accumulation heat exchanger 4.

[0070] Then, the refrigerant that has flowed into the indoor heat exchanger 2 exchanges heat with the air flowing into the indoor unit to evaporate, flows out of the indoor heat exchanger 2, and then flows into the compressor 1 via the first switching valve 61. When the heat that has been stored in the heat storage material of the heat accumulation heat exchanger 4 cannot be utilized, the defrosting operation of the outdoor heat exchanger 3 is performed using only the heat of the refrigerant that has been discharged from the compressor 1 without utilizing the heat that has been stored in the heat storage material.

[0071] Next, the control of the indoor-heat-exchanger bypass defrosting operation is described using FIG. 5. FIG. 5 is a refrigerant circuit diagram illustrating the flow of a refrigerant when the refrigeration cycle device S according to the embodiment of the present invention performs the indoor-heat-exchanger bypass defrosting operation.

[0072] Herein, the “indoor-heat-exchanger bypass defrosting operation” is defrosting operation in which the refrigerant that has been used for the defrosting operation of the outdoor heat exchanger 3 is not caused to flow into the indoor heat exchanger 2 but is caused to flow into the heat accumulation heat exchanger 4, unlike the above-described reverse defrosting operation.

[0073] More specifically, in the case of the reverse defrosting operation, the heat that has been stored in the heat storage material of the heat accumulation heat exchanger 4 cannot be utilized for the defrosting operation. Therefore, the refrigerant that has been used in the defrosting operation of the outdoor heat exchanger 3 is sent to the compressor 1 via the indoor heat exchanger 2, not via the heat accumulation heat exchanger 4.

[0074] However, the temperature of the refrigerant flowing into the indoor heat exchanger 2 remains low, because the refrigerant is cooled to a low temperature by the defrosting operation for the outdoor heat exchanger 3. Therefore, each part, such as a pipe, of the indoor heat exchanger 2 that has been warmed by performing the heating and heat storage operation until then is cooled by the low temperature refrigerant to have a low temperature.

[0075] Therefore, even when the heating and heat storage operation is started again after the defrosting operation of the outdoor heat exchanger 3 has ended, the indoor heat exchanger 2 is not immediately warmed because each part of the indoor heat exchanger 2 is in a cold state. Accordingly, this may lead to a deterioration in user comfort, e.g., the supply of low temperature air into a room or the like, until the indoor heat exchanger 2 is warmed.

[0076] Then, the indoor-heat-exchanger bypass defrosting operation is performed as control capable of immediately supplying warm air into a room without deteriorating user comfort when the heating and heat storage operation is started again after the end of the defrosting operation while the decrease in the temperature of the indoor heat exchanger 2 is being prevented.

[0077] Specifically, the control of the indoor-heat-exchanger bypass defrosting operation is carried out when the determination unit 73 has determined that the temperature of the heat storage material is higher than the first threshold and is equal to or less than the second threshold. When the determination unit 73 has made such a determination, the defrosting operation control unit 74 first performs control to bring the first pressure reduction mechanism 51 into a closed state.

[0078] More specifically, due to the fact that the first pressure reduction mechanism 51 is brought into a closed state, the indoor heat exchanger 2 is prevented from being cooled by the flow of the refrigerant that has been used for the defrosting operation of the outdoor heat exchanger 3 in the defrosting operation into the indoor heat exchanger 2 as illustrated in FIG. 5.

[0079] Further, due to the fact that the first pressure reduction mechanism 51 is controlled to be in a closed state by the defrosting operation control unit 74, the low temperature refrigerant that has been used for the defrosting operation of the outdoor heat exchanger 3 flows into the heat accumulation heat exchanger 4 via the third pressure reduction mechanism 53. As described above, the determination unit 73 determines that the temperature of the heat storage material is higher than the first threshold. Therefore, the heat that has been stored in the heat accumulation heat exchanger 4 can be utilized for the defrosting operation of the outdoor heat exchanger 3.

[0080] Then, the defrosting operation control unit 74 performs control to switch the second switching valve 62 such that the outdoor heat exchanger 3 functions as a condenser and the heat accumulation heat exchanger 4 functions as an evaporator. Such control performed by the control unit 7 causes the refrigerant that has been discharged from the compressor 1 to flow into the outdoor heat exchanger 3 via the second pressure reduction mechanism 52 and the third switching valve 63, so that the defrosting operation is carried out.

[0081] Then, the refrigerant that has been used for the defrosting operation of the outdoor heat exchanger 3 flows into the heat accumulation heat exchanger 4 via the third pressure reduction mechanism 53 because the first pressure reduction mechanism 51 is controlled to be in a closed state and the third pressure reduction mechanism 53 is controlled to be in an open state. In the heat accumulation heat exchanger 4, the heat that has been stored in the heat storage material is absorbed by the refrigerant that has flowed into the heat accumulation heat exchanger 4, and, in this state, the refrigerant flows out of the heat accumulation heat exchanger 4. The refrigerant that has flowed out of the heat accumulation heat exchanger 4 returns to the compressor 1 via the second switching valve 62.

[0082] Thus, the refrigerant that has been cooled to a low temperature by the defrosting operation of the outdoor heat exchanger 3 does not flow into the indoor heat exchanger 2, and therefore the temperature of each part of the indoor heat exchanger 2 warmed by the heating and heat storage operation that has been performed before the defrosting operation does not decrease and the warm state can be maintained. Therefore, warm air can be supplied into a room even immediately after the switching from the defrosting operation to the heating and heat storage operation, and thus the deterioration in user comfort can be avoided.

[0083] Further, the refrigerant after the defrosting operation has been carried out flows into the heat accumulation heat exchanger 4 to exchange heat with the heat storage material, and therefore the heat that has been stored in the heat storage material can be utilized for the defrosting operation of the outdoor heat exchanger 3.

[0084] Further, when the determination unit 73 has determined that the temperature of the heat storage material is higher than the second threshold, the defrosting operation of the outdoor heat exchanger 3 is performed as described later. FIG. 6 is a refrigerant circuit diagram illustrating the flow of a refrigerant when the refrigeration cycle device S according to the embodiment of the present invention performs the heating and defrosting operation.

[0085] A case where the determination unit 73 has determined that the temperature of the heat storage material acquired from the heat storage temperature sensor HS is higher than the second threshold indicates that heat is sufficiently stored in the heat accumulation heat exchanger 4 to such an extent that the heat can be utilized for the heating operation in addition to the defrosting operation of the outdoor heat exchanger 3. Thus, when the temperature of the heat storage material is higher than the second threshold, the defrosting operation control unit 74 carries out the heating and defrosting operation in which the heating operation and the defrosting operation are simultaneously carried out.

[0086] Specifically, the determination unit 73 controls the plurality of switching valves 6 such that the indoor heat exchanger 2 and the outdoor heat exchanger 3 function as condensers and the heat accumulation heat exchanger 4 functions as an evaporator as is clear from the refrigerant circuit diagram illustrated in FIG. 6.

[0087] More specifically, to perform the heating operation, the defrosting operation control unit 74 controls the first switching valve 61 such that the refrigerant that has been discharged from the compressor 1 flows into the indoor heat exchanger 2. Since the defrosting operation is performed simultaneously with the heating operation, the defrosting operation control unit 74 switches the third switching valve 63 such that the refrigerant that has been discharged from the compressor 1 flows into the outdoor heat exchanger 3. Then, the third switching valve 63 switches the second switching valve 62 such that the refrigerant flows from the heat accumulation heat exchanger 4 to the compressor 1.

[0088] All of the first pressure reduction mechanism 51 to the third pressure reduction mechanism 53 are controlled by the defrosting operation control unit 74 to be in an open state. Thus, the refrigerant that has exchanged heat with the indoor air in the indoor heat exchanger 2 and the refrigerant that has been used for the defrosting operation for the outdoor heat exchanger 3 flow into the heat accumulation heat exchanger 4 via the third pressure reduction mechanism 53. Then, the refrigerant that has flowed out of the heat accumulation heat exchanger 4 returns to the compressor 1 via the second switching valve 62.

[0089] Due to the fact that the pressure reduction mechanism 5 and the switching valve 6 are controlled as described above on the assumption that a sufficiently high temperature refrigerant is stored in the heat accumulation heat exchanger 4, the heat that has been stored in the heat accumulation heat exchanger 4 can be utilized for the defrosting operation of the outdoor heat exchanger 3. Therefore, the heating operation can be performed simultaneously with the defrosting operation.

[0090] In each operation mode, such as the reverse defrosting operation, described so far, it is assumed that the heating operation is performed. On the other hand, when the heating operation is not performed, the refrigeration cycle device S is only required to focus on the defrosting operation. Thus, the defrosting operation performed during the stop of the heating operation is described later.

[0091] When a stop signal of the heating operation is received in the control unit 7, a determination as to whether to carry out the defrosting operation is made. For example, when the temperature the outdoor heat exchanger 3 is 0° C. or less and the heating operation has been performed for 30 minutes or more, it is anticipated that frost adheres to the outdoor heat exchanger 3. Thus, the control unit 7 determines that such a case requires the defrosting operation.

[0092] The condition under which the control unit 7 determines that the defrosting operation is required is not limited to the above-described condition, and various conditions can be set. The stop signal of the heating operation herein also includes a stop signal due to thermo-off in addition to the instruction of stopping the heating operation by a user using a remote control.

[0093] When the defrosting operation has been determined to be required as a result of determining whether the defrosting operation is required in the control unit 7, the temperature of the heat storage material detected by the heat storage temperature sensor HS is acquired via the temperature detection unit 71. Then, it is determined whether the acquired temperature of the heat storage material is equal to or less than the first threshold. When the temperature of the heat storage material is equal to or less than the first threshold, the above-described reverse defrosting operation is carried out.

[0094] On the other hand, when the temperature of the heat storage material shows a value larger than the first threshold, the indoor-heat-exchanger bypass defrosting operation is carried out. Then, when a separately-set condition for ending the defrosting operation is satisfied, the defrosting operation of the reverse defrosting operation or the indoor-heat-exchanger bypass defrosting operation ends.

[0095] Since the defrosting operation described herein is assumed to be performed in the state in which the heating operation stops as described above, the determination unit 73 does not compare the temperature of the heat storage material with the second threshold.

[0096] As described above, the defrosting operation during the heating operation or during the stop of the heating operation is described. The condition for ending the defrosting operation can be variously set, and one example is as follows. For example, when the case of the reverse defrosting operation is taken as an example, the defrosting operation ends after the elapse of a predetermined time (can be set as desired, e.g., 10 minutes) or when the temperature has become equal to or more than the temperature (can be set as desired, e. g., 10° C.) of the outdoor heat exchanger 3, after the reverse defrosting operation has started.Operation

[0097] Next, the flow of the control of the refrigeration cycle device S by the control unit 7 in the reverse defrosting operation, the indoor-heat-exchanger bypass defrosting operation, and the heating and defrosting operation described above is described using FIG. 7. FIG. 7 is a flowchart illustrating the flow of control when the defrosting operation is performed in the refrigeration cycle device S according to the embodiment of the present invention.

[0098] First, the control unit 7 determines whether the refrigeration cycle device S is in the heating operation (heating and heat storage operation) (ST1). More specifically, the control unit 7 confirms whether the stop signal of the heating operation described above has been received.

[0099] As a result, when the heating and heat storage operation has been determined to be carried out (ST1 YES), the control unit 7 carries out a determination as to whether the defrosting operation for the outdoor heat exchanger 3 is required (ST2). The flow of processing when the control unit 7 has determined that the refrigeration cycle device S is not in the heating operation (NO in ST1) is described later.

[0100] The condition under which the control unit 7 determines whether the defrosting operation is required during the heating operation can include, for example, a condition that the temperature of the outdoor heat exchanger 3 is −5° C. or less and that the heating operation has been performed for 60 minutes or more. Alternatively, in addition to the conditions of the temperature of the outdoor heat exchanger 3 and the operation time of the heating operation, a condition relating to the outdoor air temperature can be further added. Such a condition can be variously set.

[0101] The condition as to whether the defrosting operation is required during the heating operation and the condition as to whether the defrosting operation is required during the stop of the heating operation are different from each other. More specifically, during the heating operation, the defrosting operation is started when there is frost to such an extent that the defrosting is immediately required from the viewpoint of securing user comfort during the operation. On the other hand, when the heating operation stops, there is no restriction from such a viewpoint, and therefore the defrosting operation is started when there is even a small amount of frost such that, when the heating operation is started again, the operation can be performed in a frost-free state, for example. Therefore, the condition under which it is determined whether the defrosting operation is required is more stringent during the heating operation than during the stop of the heating operation.

[0102] When the defrosting operation for the outdoor heat exchanger 3 is not required as a result of the determination made by the control unit 7 (NO in ST2), the heating and heat storage operation is continued. On the other hand, when the control unit 7 has determined that the defrosting operation is required (YES in ST2), the defrosting operation for the outdoor heat exchanger 3 is started (ST3).

[0103] In the control unit 7, the temperature detection unit 71 acquires the temperature of the heat storage material from the heat storage temperature sensor HS and transmits the temperature to the determination unit 73 to determine the mode of the defrosting operation. Further, the determination unit 73 accesses the storage unit 72 to acquire the first threshold and the second threshold stored in advance in the storage unit 72.

[0104] Then, the determination unit 73 determines, based on the temperature of the heat storage material acquired from the temperature detection unit 71 and the first threshold and the second threshold acquired from the storage unit 72, how the temperature of the heat storage material relates to these thresholds.

[0105] First, the determination unit 73 determines whether the temperature of the heat storage material is equal to or less than the first threshold (ST4). When the determination unit 73 has determined that the temperature of the heat storage material is equal to or less than the first threshold (ST4 YES), the determination unit 73 instructs the defrosting operation control unit 74 to carry out the reverse defrosting operation.

[0106] The defrosting operation control unit 74 controls the third pressure reduction mechanism to be in a closed state based on the determination result made by the determination unit 73. Thus, the plurality of switching valves 6 is controlled such that the outdoor heat exchanger 3 functions as a condenser and the indoor heat exchanger 2 functions as an evaporator, and the reverse defrosting operation of defrosting the outdoor heat exchanger 3 is carried out (ST5).

[0107] On the other hand, when the determination unit 73 has determined that the temperature of the heat storage material has a value larger than the first threshold (NO in ST4), the determination unit 73 further compares the temperature of the heat storage material with the second threshold (ST6).

[0108] As a result, when the determination unit 73 has determined that the temperature of the heat storage material is equal to or less than the second threshold (YES in ST6), the determination unit 73 instructs the defrosting operation control unit 74 to carry out the indoor-heat-exchanger bypass defrosting operation.

[0109] The defrosting operation control unit 74 controls the first pressure reduction mechanism 51 to be in a closed state based on the determination result of the determination unit 73. Thus, the plurality of switching valves 6 is controlled such that the outdoor heat exchanger 3 functions as a condenser and the heat accumulation heat exchanger 4 functions as an evaporator, and the indoor-heat-exchanger bypass defrosting operation of defrosting the outdoor heat exchanger 3 is carried out (ST7).

[0110] On the other hand, when the determination unit 73 has determined that the temperature of the heat storage material has a value larger than the second threshold (NO in ST6), the heating and defrosting operation in which the heating operation and the defrosting operation are simultaneously performed is carried out (ST8).

[0111] Thus, the temperature of the heat storage material is compared with the first threshold or the second threshold, and any defrosting operation of the reverse defrosting operation, the indoor-heat-exchanger bypass defrosting operation, or the heating and defrosting operation described above is selected and carried out.

[0112] Then, while any defrosting operation among the above is being carried out, the control unit 7 determines, based on the above-described end condition, whether the frost of the outdoor heat exchanger 3 has melted and the defrosting operation may be ended (ST9).

[0113] When the control unit 7 has determined that the frost of the outdoor heat exchanger 3 has not sufficiently melted and the defrosting operation cannot be ended yet (NO in ST9), the defrosting operation that is being carried out is continued (ST10). On the other hand, when the control unit 7 has determined that the defrosting operation can be ended as a result of the determination (YES in ST9), the defrosting operation ends (ST11).

[0114] Although not illustrated in the flowchart in FIG. 7, the heating and heat storage operation may be started again after the defrosting operation has ended.

[0115] Next, the processing of the defrosting operation when the refrigeration cycle device S is not in the heating operation (NO in ST1), i.e., during the stop of the heating operation, is described using FIG. 8. FIG. 8 is a flowchart illustrating the flow of control when the defrosting operation is performed in the refrigeration cycle device S according to the embodiment of the present invention.

[0116] After the control unit 7 has determined that the stop signal of the heating operation is received and the refrigeration cycle device S is not in the heating operation, a determination as to whether the defrosting operation is required is first carried out by the determination unit 73 (ST21). The condition as to whether the defrosting operation is required herein is as described above.

[0117] When the defrosting operation has been determined to be required as the result of the determination (YES in ST21), the defrosting operation is started (ST22). At that time, in the control unit 7, the temperature detection unit 71 acquires the temperature of the heat storage material from the heat storage temperature sensor HS and transmits the temperature to the determination unit 73 to determine the mode of the defrosting operation. The determination unit 73 accesses the storage unit 72 to acquire the first threshold stored in advance in the storage unit 72.

[0118] The determination unit 73 determines whether the temperature of the heat storage material is equal to or less than the first threshold (ST23). When the determination unit 73 has determined that the temperature of the heat storage material is equal to or less than the first threshold (YES in ST23), the determination unit 73 instructs the defrosting operation control unit 74 to carry out the reverse defrosting operation.

[0119] On the other hand, when the determination unit 73 has determined that the temperature of the heat storage material has a value higher than the first threshold (NO in ST23), the determination unit 73 instructs the defrosting operation control unit 74 to perform the indoor-heat-exchanger bypass defrosting operation.

[0120] After these defrosting operation modes are carried out, a determination as to whether to end the defrosting operation is made as appropriate by the control unit 7 as shown in Step ST9 in FIG. 7 in any case. The flow of the control based on the determination result is as described above.

[0121] When the defrosting operation has been determined not to be required during the stop of the heating operation by the determination unit 73 (NO in ST21), the defrosting operation is not carried out and the processing ends.

[0122] As described above, a refrigeration cycle device and a refrigeration cycle device control method can be provided which can suppress the deterioration in user comfort when the defrosting operation of the outdoor heat exchanger is performed and also avoid the decrease in defrosting capability by carrying out the defrosting operation, among the plurality of defrosting operations modes, according to the current situation based on the temperature of the heat storage material provided in the heat accumulation heat exchanger 4.

[0123] This invention is not limited to the above-described embodiments as they are, and one example of the present invention is given. In the implementation stage, the invention can be embodied by modifying the constituent elements without deviating from the gist of the invention. Various alternations or modifications can be made to the above-described embodiments. Various inventions can be formed by combining the plurality of constituent elements disclosed in the above-described embodiments as appropriate.

[0124] For example, some constituent elements may be deleted from all of the constituent elements described in the embodiments. Further, constituent elements across different embodiments may be combined as appropriate, and such altered or modified forms can also be included in the present invention. The embodiments and the modifications thereof are included in the scope and the gist of the invention, and are included in the scope of the invention described in each claim and equivalents thereof.REFERENCE SIGNS LIST1: compressor

[0126] 2: indoor heat exchanger

[0127] 3: outdoor heat exchanger

[0128] 4: heat accumulation heat exchanger

[0129] 5: pressure reduction mechanism

[0130] 51: first pressure reduction mechanism

[0131] 52: second pressure reduction mechanism

[0132] 53: third pressure reduction mechanism

[0133] 6: switching valve

[0134] 61: first switching valve

[0135] 62: second switching valve

[0136] 63: third switching valve

[0137] 7: control unit

[0138] 71: temperature detection unit

[0139] 72: storage unit

[0140] 73: determination unit

[0141] 74: defrosting operation control unit

[0142] C: refrigerant circuit

[0143] HS: heat storage temperature sensor

[0144] S: refrigeration cycle device

Claims

1. A refrigeration cycle device comprising:a refrigerant circuit configured to circulate a refrigerant, to whicha compressor configured to compress the refrigerant;an indoor heat exchanger configured to exchange heat between indoor air and the refrigerant;an outdoor heat exchanger configured to exchange heat between outdoor air and the refrigerant;a heat accumulation heat exchanger configured to exchange heat between a heat storage material and the refrigerant;a plurality of pressure reduction mechanisms having an adjustable opening degree; anda plurality of switching valves configured to switch a circulation path of the refrigerant in the refrigerant circuit between heating operation in which the indoor heat exchanger and the heat accumulation heat exchanger are caused to function as condensers and the outdoor heat exchanger is caused to function as an evaporator and defrosting operation in which the outdoor heat exchanger is caused to function as a condenser and the indoor heat exchanger or the heat accumulation heat exchanger is caused to function as an evaporator are connected;a heat storage temperature sensor configured to measure a temperature of the heat storage material; anda control unit configured to control the plurality of switching valves,the plurality of pressure reduction mechanisms having, in the circulation path of the refrigerant of the heating operation, a first pressure reduction mechanism provided on a downstream side of the indoor heat exchanger, a second pressure reduction mechanism provided on an upstream side of the heat accumulation heat exchanger, and a third pressure reduction mechanism provided on a downstream side of the heat accumulation heat exchanger, whereinin starting the defrosting operation, when the control unit has determined that a temperature of the heat storage material acquired from the heat storage temperature sensor is equal to or less than a preset first threshold, the control unit performs control to carry out reverse defrosting operation of defrosting the outdoor heat exchanger by controlling the plurality of switching valves such that the third pressure reduction mechanism is brought into a closed state, the outdoor heat exchanger functions as a condenser, and the indoor heat exchanger functions as an evaporator, andwhen the control unit has determined that the temperature of the heat storage material is higher than the first threshold, the control unit performs control to carry out indoor-heat-exchanger bypass defrosting operation of defrosting the outdoor heat exchanger by controlling the plurality of switching valves such that the first pressure reduction mechanism is brought into a closed state, the outdoor heat exchanger functions as a condenser, and the heat accumulation heat exchanger functions as an evaporator.

2. The refrigeration cycle device according to claim 1, wherein, when the control unit has determined that the temperature of the heat storage material is higher than a second threshold set to be higher than the first threshold, the control unit controls the plurality of switching valves such that the indoor heat exchanger and the outdoor heat exchanger function as condensers and the heat accumulation heat exchanger functions as an evaporator and performs heating and defrosting operation of simultaneously carrying out the heating operation and the defrosting operation.

3. The refrigeration cycle device according to claim 1, whereinduring stop of the heating operation,when the control unit has determined that the temperature of the heat storage material is equal to or less than the first threshold, the control unit performs control to carry out the reverse defrosting operation,when the control unit has determined that the temperature of the heat storage material is higher than the first threshold, the control unit performs control to carry out the indoor-heat-exchanger bypass defrosting operation.

4. A refrigeration cycle device control method comprising:in a refrigeration cycle device including:a refrigerant circuit configured to circulate a refrigerant, to whicha compressor configured to compress the refrigerant;an indoor heat exchanger configured to exchange heat between indoor air and the refrigerant;an outdoor heat exchanger configured to exchange heat between outdoor air and the refrigerant;a heat accumulation heat exchanger configured to exchange heat between a heat storage material and the refrigerant;a plurality of pressure reduction mechanisms having an adjustable opening degree; anda plurality of switching valves configured to switch a circulation path of the refrigerant in the refrigerant circuit between heating operation in which the indoor heat exchanger and the heat accumulation heat exchanger are caused to function as condensers and the outdoor heat exchanger is caused to function as an evaporator and defrosting operation in which the outdoor heat exchanger is caused to function as a condenser and the indoor heat exchanger or the heat accumulation heat exchanger is caused to function as an evaporator are connected;a heat storage temperature sensor configured to measure a temperature of the heat storage material; anda control unit configured to control the plurality of switching valves,the plurality of pressure reduction mechanisms having, in the circulation path of the refrigerant of the heating operation, a first pressure reduction mechanism provided on a downstream side of the indoor heat exchanger, a second pressure reduction mechanism provided on an upstream side of the heat accumulation heat exchanger, and a third pressure reduction mechanism provided on a downstream side of the heat accumulation heat exchanger,after the heating operation has shifted to the defrosting operation,determining by the control unit whether the temperature of the heat storage material acquired from the heat storage temperature sensor is equal to or less than a preset first threshold,when the temperature of the heat storage material has been determined to be equal to or less than the first threshold, performing control by the control unit to carry out reverse defrosting operation of defrosting the outdoor heat exchanger by controlling the plurality of switching valves such that the third pressure reduction mechanism is brought into a closed state, the outdoor heat exchanger functions as a condenser, and the indoor heat exchanger functions as an evaporator, andwhen the temperature of the heat storage material has been determined to be higher than the first threshold, performing control by the control unit to carry out indoor-heat-exchanger bypass defrosting operation of defrosting the outdoor heat exchanger by controlling the plurality of switching valves such that the first pressure reduction mechanism is brought into a closed state, the outdoor heat exchanger functions as a condenser, and the heat accumulation heat exchanger functions as an evaporator.

5. The refrigeration cycle device control method according to claim 4 comprising:when the control unit has determined that the temperature of the heat storage material is higher than the a second threshold set to be higher than the first threshold, controlling the plurality of switching valves such that the indoor heat exchanger and the outdoor heat exchanger function as condensers and the heat accumulation heat exchanger functions as an evaporator and performing heating and defrosting operation of simultaneously carrying out the heating operation and the defrosting operation by the control unit.

6. The refrigeration cycle device control method according to claim 4 further comprising:determining by the control unit whether the refrigeration cycle device is in the heating operation,in a case where the control unit has determined that the refrigeration cycle device is in the stop of the heating operation,when the control unit has determined that the temperature of the heat storage material is equal to or less than the first threshold, performing control by the control unit to carry out the reverse defrosting operation, andwhen the control unit has determined that the temperature of the heat storage material is higher than the first threshold, performing control by the control unit to carry out the indoor-heat-exchanger bypass defrosting operation.

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