Air conditioner

Abstract

An air conditioner, wherein, connected to a refrigerant circuit (C) for circulating a refrigerant are: an indoor heat exchanger (2); an outdoor heat exchanger (3); a heat-storage heat exchanger (4); a plurality of expansion valves (5) of which the degrees of opening can be adjusted; and switching valves (61), (62) for switching the flow path of the refrigerant circuit between a heat-storage heating operation in which the indoor heat exchanger and the heat-storage heat exchanger are caused to function as condensers and the outdoor heat exchanger is caused to function as an evaporator and a defrost heating operation in which the indoor heat exchanger and the outdoor heat exchanger are caused to function as condensers and the heat-storage heat exchanger is caused to function as an evaporator. The air conditioner comprises a heating capacity estimation means for estimating the heating capacity during the defrost heating operation and a control device (7) for controlling the plurality of expansion valves and the switching valves. The plurality of expansion valves include a first expansion valve (51) provided upstream of the outdoor heat exchanger during the defrost heating operation. During the defrost heating operation, the control device controls the degree of opening of the first expansion valve on the basis of the heating capacity estimated by the heating capacity estimation means.

Description

air conditioner

[0001] The present invention relates to an air conditioner.

[0002] In an air conditioner equipped with a heat storage heat exchanger that exchanges heat with a heat storage material by partially discharging refrigerant from a compressor, there is a technology that allows heating operation to continue even during defrosting operation by utilizing the heat stored in the heat storage material as a heat source (hereinafter also referred to as defrosting heating operation). In such an air conditioner, there is a technology that, during defrosting heating operation, detects the room temperature, condensation temperature, outdoor heat exchanger temperature, and discharge temperature and operates expansion valves disposed on the outlet side of the indoor heat exchanger and the outdoor heat exchanger to suppress insufficient heating capacity and defrosting capacity and the occurrence of liquid backflow, in which liquid refrigerant returns from the heat storage heat exchanger to the compressor (for example, Patent Document 1).

[0003] International Publication No. 2014 / 061134

[0004] Incidentally, when the building load is low (e.g., when the outdoor temperature is high during heating operation and the building volume is small, reducing the energy required for air conditioning operation), the required heating capacity is low. Generally, during defrosting operation, control prioritizes removing frost from the outdoor heat exchanger, and heating capacity is not as precisely controlled as during normal heating operation. This can lead to the room temperature rising or falling too high or too low relative to the set temperature, reducing comfort. Therefore, when the building load is low, the heating capacity often becomes excessive during defrosting heating operation. The air conditioner of Patent Document 1 does not anticipate cases where the heating capacity is excessive. Attempting to reduce the heating capacity by reducing the opening of the expansion valve on the outlet side of the indoor heat exchanger can increase the condensation temperature of the indoor heat exchanger, potentially resulting in excessive heating capacity and reducing comfort. While reducing the heating capacity by reducing the compressor rotation speed is also considered, this also reduces the defrosting capacity, lengthening the defrosting time and potentially reducing comfort.

[0005] Therefore, the present invention has been made to solve such problems, and has an object to provide an air conditioner that can maintain comfort during defrosting heating operation.

[0006] According to one aspect of the invention, there is provided an air conditioner in which a refrigerant circuit for circulating the refrigerant is connected to: a compressor for compressing the refrigerant; an indoor heat exchanger for exchanging heat between indoor air and the refrigerant; an outdoor heat exchanger for exchanging heat between outdoor air and the refrigerant; a heat storage heat exchanger for exchanging heat between a heat storage material and the refrigerant; a plurality of expansion valves with adjustable openings; and a switching valve for switching the flow path of the refrigerant circuit between a heat storage heating operation in which the indoor heat exchanger and the heat storage heat exchanger function as condensers and the outdoor heat exchanger function as an evaporator, and a defrost heating operation in which the indoor heat exchanger and the outdoor heat exchanger function as condensers and the heat storage heat exchanger function as an evaporator; the air conditioner is provided with: a heating capacity estimation means for estimating heating capacity during defrost heating operation; and a control device for controlling the plurality of expansion valves and the switching valves, the plurality of expansion valves including a first expansion valve provided upstream of the outdoor heat exchanger during defrost heating operation; and the control device controls the opening of the first expansion valve during defrost heating operation based on the heating capacity estimated by the heating capacity estimation means.

[0007] According to the air conditioner of the present invention, comfort can be maintained during defrosting heating operation.

[0008] FIG. 1 is a refrigerant circuit diagram of an air conditioner according to an embodiment of the present invention. FIG. 2 is a diagram showing a specific configuration of an indoor heat exchanger that constitutes the air conditioner according to the embodiment of the present invention. FIG. 3 is a refrigerant circuit diagram showing the flow of refrigerant when the air conditioner according to the embodiment of the present invention performs cooling operation. FIG. 4 is a refrigerant circuit diagram showing the flow of refrigerant when the air conditioner according to the embodiment of the present invention performs heating operation. FIG. 5 is a refrigerant circuit diagram showing the flow of refrigerant when the air conditioner according to the embodiment of the present invention performs heat storage heating operation. FIG. 6 is a refrigerant circuit diagram showing the flow of refrigerant when the air conditioner according to the embodiment of the present invention performs defrosting heating operation. FIG. 7 is a block diagram showing the internal configuration of a control device in an air conditioner according to an embodiment of the present invention. FIG. 8 is a flowchart showing the control flow of the defrosting heating operation of the first embodiment of the present invention. FIG. 9 is a flowchart showing the flow of estimating heating capacity in the defrosting heating operation of the first embodiment of the present invention. FIG. 10 is a flowchart showing the control flow of the defrosting heating operation of the second embodiment of the present invention. FIG. 11 is a flowchart showing the flow of estimating heating capacity in the defrosting heating operation of the second embodiment of the present invention. FIG. 12 is a flowchart showing the control flow of the defrosting heating operation of the third embodiment of the present invention. FIG. 13 is a flowchart showing the flow of estimating heating capacity in the defrosting heating operation of the third embodiment of the present invention.

[0009] [First Embodiment] The structure of an air conditioner S according to a first embodiment of the present invention will be described with reference to Figures 1 and 2. Figure 1 is a refrigerant circuit diagram of the air conditioner S. The air conditioner S includes a refrigerant circuit C that connects a compressor 1, an indoor heat exchanger 2, an outdoor heat exchanger 3, a heat storage heat exchanger 4, expansion valves 5 (51, 52, 53), and switching valves 6 (61, 62) and circulates the refrigerant. The air conditioner S also includes a control device 7 that controls the expansion valve 5 and the switching valve 6.

[0010] The compressor 1 compresses the refrigerant circulating through the refrigerant circuit C. The indoor heat exchanger 2 exchanges heat between the indoor air and the refrigerant. The outdoor heat exchanger 3 exchanges heat between the outdoor air and the refrigerant. Although the types of the compressor 1, indoor heat exchanger 2, and outdoor heat exchanger 3 will not be described here, various types of equipment may be used. The heat storage heat exchanger 4 is a heat exchanger that exchanges heat between a heat storage material and the refrigerant passing through the heat storage heat exchanger 4. The heat storage heat exchanger 4 is, for example, a fin-and-tube heat exchanger. The heat storage heat exchanger 4 is disposed inside a heat storage container filled with a heat storage material. The heat storage material may be, for example, liquid or solid, as long as it can exchange heat with the refrigerant flowing through the heat storage heat exchanger 4 and store heat.

[0011] The switching valve 6 switches the refrigerant circulation path in the refrigerant circuit C between, for example, a heat-storage heating operation in which the indoor heat exchanger 2 and the heat-storage heat exchanger 4 function as condensers and the outdoor heat exchanger 3 function as an evaporator, and a defrosting heating operation in which the indoor heat exchanger 2 and the outdoor heat exchanger 3 function as condensers and the heat-storage heat exchanger 4 function as an evaporator. The air conditioner S of this embodiment is provided with two switching valves 6 that switch the refrigerant flow based on instructions from a control device 7, which will be described later. That is, a first switching valve 61 is provided between the compressor 1 and the indoor heat exchanger 2. Furthermore, a second switching valve 62 is provided between the compressor 1 and the outdoor heat exchanger 3 or the heat-storage heat exchanger 4. The second switching valve 62 directs the refrigerant discharged from the compressor 1 to the outdoor heat exchanger 3 or the heat-storage heat exchanger 4.

[0012] The opening degree of the expansion valve 5 can be adjusted based on instructions from a control device 7, which will be described later, and a plurality of expansion valves 5 are provided in the air conditioner S in this embodiment. Specifically, a first expansion valve 51, a second expansion valve 52, and a third expansion valve 53 are provided. The first expansion valve 51 is provided upstream of the outdoor heat exchanger 3 in the direction in which the refrigerant flows during defrosting heating operation.

[0013] The second expansion valve 52 is provided between the indoor heat exchanger 2 and the outdoor heat exchanger 3. That is, the second expansion valve 52 is provided downstream of the indoor heat exchanger 2 in the direction of refrigerant flow during defrosting heating operation. Specifically, the second expansion valve 52 is provided in the refrigerant piping connecting the outdoor heat exchanger 3 and the indoor heat exchanger 2. The third expansion valve 53 is provided between the heat storage heat exchanger 4 and the outdoor heat exchanger 3. That is, the third expansion valve 53 is provided upstream of the heat storage heat exchanger 4 in the direction of refrigerant flow during defrosting heating operation. Specifically, the third expansion valve 53 is provided in the refrigerant piping connecting the heat storage heat exchanger 4 and the refrigerant piping connecting the indoor heat exchanger 2 and the outdoor heat exchanger 3.

[0014] In the following description, the first expansion valve 51 to the third expansion valve 53 will be referred to as the "expansion valve 5" when collectively describing them, and each individual expansion valve will be referred to by its respective name when describing them individually. Similarly, the switching valve 6 will be referred to as the "switching valve 6" when collectively describing the first switching valve 61 and the second switching valve 62, and each individual switching valve will be referred to by its respective name when describing them individually.

[0015] The indoor heat exchanger 2 is provided with a refrigerant temperature sensor 22 that detects the temperature of the refrigerant in the indoor heat exchanger 2. Fig. 2 shows the indoor heat exchanger 2 provided inside the indoor unit 10, which also includes a room temperature sensor 21 that detects the room temperature and an indoor fan 11 that blows the air that has exchanged heat with the refrigerant in the indoor heat exchanger 2 into the room. A gas-side refrigerant temperature sensor 23 that detects the temperature of the refrigerant flowing into the indoor heat exchanger 2 during defrosting heating operation is provided between the switching valve 61 and the indoor heat exchanger 2, and a liquid-side refrigerant temperature sensor 24 that detects the temperature of the refrigerant flowing out of the indoor heat exchanger 2 during defrosting heating operation is provided between the indoor heat exchanger 2 and the second expansion valve 52.

[0016] Next, the refrigerant circuit C of the air conditioner S will be described. The refrigerant circuit C is composed of each device, such as the compressor 1, and refrigerant piping that connects these devices and through which the refrigerant flows. Here, a first switching valve 61 is provided in the refrigerant piping that connects the compressor 1 and the indoor heat exchanger 2. In addition, a second switching valve 62 is provided in the refrigerant piping between the compressor 1 and the first switching valve 61, which directs the refrigerant discharged from the compressor 1 to the outdoor heat exchanger 3 or the thermal storage heat exchanger 4.

[0017] Furthermore, in the air conditioner S according to the embodiment of the present invention, a bypass circuit B is provided between the first switching valve 61 and the second switching valve 62. The bypass circuit B is provided with a check valve or the like so that the refrigerant flows only in the direction of the arrow as shown in Fig. 1. The control device 7 controls the opening degrees of the multiple expansion valves 5 to adjust the flow rate of the refrigerant circulating through the refrigerant circuit C. The control device 7 also switches the flow of the refrigerant circulating through the refrigerant circuit C by switching the multiple switching valves 6.

[0018] Before describing the functions of each part of the control device 7, the operating modes of the air conditioner S will be described in order using the circuit diagrams of the air conditioner S shown in Figures 3 to 6. In these circuit diagrams, the refrigerant circulation paths through which the refrigerant actually flows are indicated by solid lines. On the other hand, the refrigerant circulation paths and bypass circuit B that constitute the refrigerant circuit C but through which no refrigerant flows are indicated by dashed lines. The direction of the refrigerant circulating within the refrigerant circuit C is also indicated by arrows.

[0019] First, Figure 3 is a refrigerant circuit diagram showing the flow of refrigerant when the air conditioner S of the first embodiment is operating in cooling mode. During cooling mode, the indoor heat exchanger 2 functions as an evaporator, and the outdoor heat exchanger 3 functions as a condenser. The refrigerant compressed by the compressor 1 and discharged in a high-temperature, high-pressure state flows into the outdoor heat exchanger 3 via the first expansion valve 51 and the second switching valve 62, as indicated by the arrows in Figure 3. At this time, the first expansion valve 51 is fully open. The refrigerant discharged from the compressor 1 also flows through the first switching valve 61, but also passes through the bypass circuit B before flowing into the outdoor heat exchanger 3 via the second switching valve 62.

[0020] The refrigerant that flows into the outdoor heat exchanger 3 is cooled by outside air supplied by the rotation of an outdoor fan (not shown), and dissipates heat into the outside air. Part or all of the refrigerant is then condensed. The refrigerant that has dissipated heat into the outside air flows out of the outdoor heat exchanger 3 and passes through the second expansion valve 52, where it is decompressed to become a low-temperature, low-pressure refrigerant. The low-temperature, low-pressure refrigerant then flows into the indoor heat exchanger 2, where it exchanges heat with the indoor air.

[0021] Through heat exchange in the indoor heat exchanger 2, the refrigerant absorbs heat from the indoor air and evaporates, and the indoor air drawn into the indoor heat exchanger 2 is cooled and supplied into the room by the indoor fan 11, cooling the room. The refrigerant that has absorbed heat through heat exchange flows into the compressor 1 via the first switching valve 61. During cooling operation, the second expansion valve 52, through which the refrigerant condensed in the outdoor heat exchanger 3 passes, is controlled to an opening degree corresponding to the air conditioning capacity required of the air conditioner S. On the other hand, the third expansion valve 53 is controlled to be fully closed, so that the refrigerant flowing out of the outdoor heat exchanger 3 does not flow into the thermal storage heat exchanger 4.

[0022] Next, Figure 4 is a refrigerant circuit diagram showing the flow of refrigerant when the air conditioner S of the first embodiment is performing heating operation. As shown in Figure 4, refrigerant discharged from the compressor 1 flows into the indoor heat exchanger 2 via the first selector valve 61. Meanwhile, because the first expansion valve 51 is controlled to be fully closed, refrigerant does not flow to the outdoor heat exchanger 3 via the second selector valve 62, as in the cooling operation described above. In the indoor heat exchanger 2, heat is exchanged between the refrigerant and the air flowing into the indoor unit, and the heated air is supplied to the indoor space by absorbing heat from the refrigerant, thereby heating the room. Therefore, the indoor heat exchanger 2 functions as a condenser.

[0023] The refrigerant flowing out of the indoor heat exchanger 2 is reduced in pressure by passing through the second expansion valve 52, becoming a low-temperature, low-pressure refrigerant, which then flows into the outdoor heat exchanger 3. The outdoor heat exchanger 3 functions as an evaporator, and heat is exchanged between the refrigerant and the outdoor air. The refrigerant flowing out of the outdoor heat exchanger 3 flows into the compressor 1 via the second switching valve 62. In the air conditioner S according to the present invention, when the above-mentioned normal cooling operation or heating operation is performed, the thermal storage heat exchanger 4 does not function as a condenser or evaporator.

[0024] Next, FIG. 5 is a refrigerant circuit diagram showing the refrigerant flow when the air conditioner S of the first embodiment performs a heat storage heating operation. The heat storage heating operation is an operation in which heat is stored in the heat storage heat exchanger 4 by opening the first expansion valve 51 during heating operation and allowing a portion of the refrigerant discharged from the compressor 1 to flow into the heat storage heat exchanger 4. As shown in FIG. 5 , the refrigerant discharged from the compressor 1 flows into the indoor heat exchanger 2 via the first switching valve 61. The indoor heat exchanger 2 then exchanges heat between the refrigerant and the air flowing into the indoor unit, absorbing heat from the refrigerant and supplying the warmed air indoors. Therefore, the indoor heat exchanger 2 functions as a condenser. The refrigerant flowing out of the indoor heat exchanger 2 flows into the outdoor heat exchanger 3 via the second expansion valve 52. The outdoor heat exchanger 3 functions as an evaporator, where heat is exchanged between the refrigerant and the outdoor air. The refrigerant flowing out of the outdoor heat exchanger 3 flows into the compressor 1 via the second switching valve 62.

[0025] In the heat storage heating operation, the refrigerant discharged from the compressor 1 branches before reaching the first switching valve 61 and also flows into the heat storage heat exchanger 4 via the first expansion valve 51 and the second switching valve 62. The refrigerant that flows into the heat storage heat exchanger 4 exchanges heat with a heat storage material, so that heat of the refrigerant is stored in the heat storage material. The refrigerant that flows out of the heat storage heat exchanger 4 flows into the outdoor heat exchanger 3 via the third expansion valve 53.

[0026] Next, FIG. 6 is a refrigerant circuit diagram showing the refrigerant flow when the air conditioner S of the first embodiment performs defrosting heating operation. In defrosting heating operation, the first expansion valve 51 is opened during heating operation to allow a portion of the refrigerant discharged from the compressor 1 to flow into the outdoor heat exchanger 3, thereby melting frost on the outdoor heat exchanger 3. As shown in FIG. 6 , the refrigerant discharged from the compressor 1 flows into the indoor heat exchanger 2 via the first selector valve 61. Because the heating operation is performed here, the indoor heat exchanger 2 functions as a condenser, exchanging heat between the refrigerant and the air flowing into the indoor unit, absorbing heat from the refrigerant and supplying the heated air to the indoor space. The refrigerant discharged from the compressor 1 branches before reaching the first selector valve 61 and flows into the outdoor heat exchanger 3 via the first expansion valve 51 and the second selector valve 62. At this time, the opening of the first expansion valve 51 is adjusted based on a control process described below.

[0027] The high-temperature refrigerant from the compressor 1 flows into the outdoor heat exchanger 3, thereby performing a defrosting heating operation to melt frost adhering to the outdoor heat exchanger 3. The refrigerant flowing out of the indoor heat exchanger 2 flows into the heat-storage heat exchanger 4 via the second expansion valve 52 and the third expansion valve 53. The refrigerant flowing out of the outdoor heat exchanger 3 flows into the heat-storage heat exchanger 4 via the third expansion valve 53. In the heat-storage heat exchanger 4, heat exchange occurs between the flowing refrigerant and a heat storage material, and the refrigerant absorbs heat stored in the heat storage material and evaporates. The refrigerant flowing out of the heat-storage heat exchanger 4 flows into the compressor 1 via the second switching valve 62. The aperture of the second expansion valve 52 is set so that the refrigerant flowing out of the indoor heat exchanger 2, which functions as a condenser, is in a subcooled state. This makes it possible to simultaneously adjust the heating capacity of the indoor heat exchanger 2 and the defrosting capacity of the outdoor heat exchanger 3 during defrost heating operation without the need for complex control, simply by controlling the opening degree of the first expansion valve 51.

[0028] Next, FIG. 7 is a block diagram showing the functions of each part of the control device 7 of the first embodiment. The control device 7 includes a temperature detection unit 71, a storage unit 72, a determination unit 73, and a switching control unit 74. The temperature detection unit 71 acquires the room temperature detected by the room temperature sensor 21 provided in the indoor unit 10. The temperature detection unit 71 acquires the refrigerant temperature detected by the refrigerant temperature sensor 22 provided in the indoor heat exchanger 2. The refrigerant temperature detected by the refrigerant temperature sensor 22 during defrost heating operation is the condensation temperature of the indoor heat exchanger 2, which functions as a condenser. The temperature detection unit 71 also acquires the refrigerant temperature detected by the gas side refrigerant temperature sensor 23. The temperature detected by the gas side refrigerant temperature sensor 23 during defrost heating operation is the temperature of the refrigerant flowing into the indoor heat exchanger 2. The temperature detection unit 71 also acquires the refrigerant temperature detected by the liquid side refrigerant temperature sensor 24. The temperature detected by the liquid side refrigerant temperature sensor 24 during defrost heating operation is the temperature of the refrigerant flowing out of the indoor heat exchanger 2.

[0029] The memory unit 72 is configured with, for example, a semiconductor or a magnetic disk, and in a first embodiment described below, stores the refrigerant circulation amount during defrost heating operation based on changes in the rotation speed of the compressor 1. That is, the refrigerant circulation amount can be calculated by multiplying the rotation speed of the compressor 1 by the displacement volume by the suction density, and therefore the memory unit 72 stores, in a memory table, the refrigerant circulation amount corresponding to the rotation speed of the compressor 1 during defrost heating operation.

[0030] In a first embodiment described later, the storage unit 72 stores a heating capacity at the start of the defrosting heating operation, which is calculated by multiplying the refrigerant circulating amount at the start of the defrosting heating operation by the enthalpy difference between the inlet and outlet of the indoor heat exchanger 2 at the start of the defrosting heating operation. This heating capacity at the start of the defrosting heating operation is the initial value of the heating capacity in the first embodiment described later. The storage unit 72 also stores apertures of the first expansion valve 51 and the second expansion valve 52, which are determined according to the required capacity. The aperture of the first expansion valve 51 is the aperture required for the defrosting heating operation, and the aperture of the second expansion valve 52 is the aperture at which the refrigerant flowing out of the indoor heat exchanger 2, which functions as a condenser during the defrosting heating operation, is subcooled.

[0031] The determination unit 73 estimates the heating capacity during defrost heating operation. Specifically, in a first embodiment described below, the determination unit 73 calculates the enthalpy difference between the inlet and outlet of the indoor heat exchanger 2 based on the temperature of the refrigerant flowing into the indoor heat exchanger 2 (gas-side refrigerant temperature) and the temperature of the refrigerant flowing out of the indoor heat exchanger 2 (liquid-side refrigerant temperature) during defrost heating operation. Next, the determination unit 73 obtains the refrigerant circulation volume corresponding to the currently operating rotation speed of the compressor 1 from a storage table of the compressor 1 rotation speed and refrigerant circulation volume stored in the storage unit 72. Next, the determination unit 73 calculates the heating capacity by multiplying the enthalpy difference between the inlet and outlet of the indoor heat exchanger 2 by the refrigerant circulation volume corresponding to the currently operating rotation speed of the compressor 1. This heating capacity is the estimated heating capacity value in the first embodiment described below.

[0032] In a first embodiment described later, the determination unit 73 compares the heating capacity initial value stored in the memory unit 72 with the estimated heating capacity value, and determines whether the indoor heating capacity is excessive, insufficient, or appropriate based on the comparison result. The switching control unit 74 controls the opening degrees of the first expansion valve 51 and the second expansion valve 52 and performs switching control of the first changeover valve 61 and the second changeover valve 62 in accordance with the determination result received from the determination unit 73.

[0033] [Control of Defrosting and Heating Operation in First Embodiment] Next, the control flow of the defrosting and heating operation in the first embodiment will be described using the flowcharts shown in Figures 8 and 9. The control of the defrosting and heating operation in the first embodiment is characterized by estimating the heating capacity based on the enthalpy difference between the inlet and outlet of the indoor heat exchanger 2. First, the defrosting and heating operation is started in the air conditioner S (ST1). At that time, the switching control unit 74 controls the first expansion valve 51 and the second expansion valve 52 to predetermined opening degrees so as to form the refrigerant circuit shown in Figure 6, and performs switching control of the first switching valve 61 and the second switching valve 62, thereby executing the defrosting and heating operation. Next, the determination unit 73 estimates the heating capacity during the defrosting and heating operation (ST2).

[0034] As shown in FIG. 9 , the specific process for estimating the heating capacity during the defrost heating operation involves the temperature detection unit 71 acquiring the temperature of the refrigerant flowing into the indoor heat exchanger 2 (gas-side refrigerant temperature) and the temperature of the refrigerant flowing out of the indoor heat exchanger 2 (liquid-side refrigerant temperature) during the defrost heating operation (ST11). Next, the determination unit 73 calculates the enthalpy difference between the inlet and outlet of the indoor heat exchanger 2 based on the acquired gas-side and liquid-side refrigerant temperatures (ST12). Next, the determination unit 73 acquires the refrigerant circulation volume corresponding to the currently operating rotation speed of the compressor 1 from a storage table of compressor 1 rotation speeds and refrigerant circulation volumes stored in the storage unit 72 (ST13). Next, the determination unit 73 calculates the estimated heating capacity by multiplying the enthalpy difference between the inlet and outlet of the indoor heat exchanger 2 by the refrigerant circulation volume corresponding to the currently operating rotation speed of the compressor 1.

[0035] Returning to FIG. 8 , the determination unit 73 compares the calculated estimated heating capacity with the initial heating capacity value stored in the memory unit 72 at the start of the defrost heating operation (ST3 in FIG. 8 ). If the comparison of the estimated heating capacity with the initial heating capacity value (ST4) reveals that the estimated heating capacity is greater than the initial heating capacity value (YES in ST4), the determination unit 73 determines that the room temperature is rising due to excessive heating capacity, reducing indoor comfort. The determination unit 73 then calculates the difference between the estimated heating capacity and the initial heating capacity value and calculates an opening control amount corresponding to this difference. The switching control unit 74 then controls the opening of the first expansion valve 51 by the opening control amount (ST5). On the other hand, if the initial heating capacity value is greater than the estimated heating capacity value or equal to the estimated heating capacity value (NO in ST4), the determination unit 73 determines whether the initial heating capacity value and the estimated heating capacity value are equal (ST6).

[0036] If the determination unit 73 determines that the initial heating capacity value and the estimated heating capacity value are equal (YES in ST6), the switching control unit 74 controls the first expansion valve 51 to maintain its opening (ST7). On the other hand, if the determination unit 73 determines that the initial heating capacity value and the estimated heating capacity value are not equal (NO in ST6), this corresponds to the case where the estimated heating capacity value is smaller than the initial heating capacity value. In this case, the determination unit 73 determines that the room heating capacity is insufficient, causing the room temperature to drop and reducing indoor comfort, calculates the difference between the initial heating capacity value, the estimated heating capacity value, and the initial heating capacity value, and calculates an opening control amount corresponding to this difference. The switching control unit 74 then controls the first expansion valve 51 to decrease its opening by the opening control amount (ST8).

[0037] While the defrosting and heating operation is being performed, the determination unit 73 determines whether the frost on the outdoor heat exchanger 3 has melted and it is acceptable to terminate the defrosting and heating operation based on preset termination conditions (ST9). If the determination unit 73 determines that the frost on the outdoor heat exchanger 3 has not melted and the defrosting and heating operation cannot be terminated yet (NO in ST9), the defrosting and heating operation continues (proceeding to ST2). On the other hand, if the determination result indicates that the defrosting and heating operation can be terminated (YES in ST9), the defrosting and heating operation is terminated (ST10).

[0038] Next, the effects of the defrosting heating operation of the first embodiment will be described. During the defrosting heating operation, the control prioritizes removing frost from the outdoor heat exchanger 3, so the heating capacity is not as precisely controlled relative to the set temperature as in the normal heat storage heating operation. This can lead to excessive room temperature rise or fall, reducing comfort. Therefore, when the outdoor temperature is high and the building volume is small, resulting in a low building load, the heating capacity during the defrosting heating operation may become excessive.

[0039] Therefore, the control device 7 of this embodiment calculates an estimated heating capacity based on the enthalpy difference between the inlet and outlet of the indoor heat exchanger 2 and the amount of refrigerant circulating during defrosting heating operation, and compares this estimated heating capacity with a preset initial heating capacity value.If it determines that the estimated heating capacity is excessive, it increases the opening of the first expansion valve 51, and if it determines that the estimated heating capacity is insufficient, it decreases the opening of the first expansion valve 51.

[0040] Therefore, by controlling the opening of the first expansion valve 51 to be larger when it is determined that the estimated heating capacity is excessive, part of the refrigerant flowing through the indoor heat exchanger 2 flows to the outdoor heat exchanger 3, reducing the indoor heating capacity and the room temperature, thereby suppressing a decrease in indoor comfort even when the building load is small. In addition, by causing part of the refrigerant flowing through the indoor heat exchanger 2 to flow to the outdoor heat exchanger 3, the defrosting time can be shortened.

[0041] Furthermore, by controlling the opening of the first expansion valve 51 to be smaller when it is determined that the estimated heating capacity is insufficient, the refrigerant flowing through the outdoor heat exchanger 3 flows to the indoor heat exchanger 2, increasing the indoor heating capacity and raising the room temperature, thereby suppressing a decrease in indoor comfort. Furthermore, by controlling the opening of the first expansion valve 51 based on the enthalpy difference between the inlet and outlet of the indoor heat exchanger 2, it is possible to simultaneously control the adjustment of the heating capacity of the indoor heat exchanger 2 and the defrosting capacity of the outdoor heat exchanger 3 during defrost heating operation.

[0042] Furthermore, the second expansion valve 52, which is located downstream of the refrigerant from the indoor heat exchanger 2, is fixed at an opening degree such that the refrigerant flowing out from the indoor heat exchanger 2, which functions as a condenser during defrost heating operation, is in a supercooled state. Therefore, no complex control is required, and the heating capacity of the indoor heat exchanger 2 and the defrosting capacity of the outdoor heat exchanger 3 during defrost heating operation can be adjusted simultaneously by simply controlling the opening degree of the first expansion valve 51.

[0043] Second Embodiment Next, a control flow of the defrosting heating operation of a second embodiment according to the present invention will be described using the flowcharts shown in FIGS. 10 and 11 . The control of the defrosting heating operation of the second embodiment is characterized by estimating the heating capacity based on the room temperature. The control device 7 of the second embodiment has the same configurations as the control device 7 of the first embodiment, including the temperature detection unit 71 and the switching control unit 74. The memory unit 72 of the control device 7 of the second embodiment stores a first threshold temperature and a second threshold temperature. The first threshold temperature is, for example, 2° C. higher than the room temperature (24° C.) set for the defrosting heating operation, and the second threshold temperature is, for example, 2° C. lower than the room temperature (24° C.) set for the defrosting heating operation.

[0044] The storage unit 72 of the control device 7 of the second embodiment also stores a heating capacity estimate for the first threshold temperature estimated from the first threshold temperature and a heating capacity estimate for the second threshold temperature estimated from the second threshold temperature. The storage unit 72 of the control device 7 of the second embodiment also stores the openings of the first expansion valve 51 and the second expansion valve 52 determined according to the required capacity. The opening of the first expansion valve 51 is the opening required for the defrosting heating operation, and the opening of the second expansion valve 52 is the opening at which the refrigerant flowing out of the indoor heat exchanger 2 functioning as a condenser in the defrosting heating operation is subcooled. The storage unit 72 of the control device 7 of the second embodiment also stores the opening of the second expansion valve 52 at which the refrigerant flowing out of the indoor heat exchanger 2 functioning as a condenser in the defrosting heating operation is subcooled. The storage unit 72 of the control device 7 of the second embodiment also stores data on the heating capacity estimate corresponding to changes in the indoor temperature.

[0045] 10 , in the control of the defrosting heating operation in the second embodiment, the defrosting heating operation is first started in the air conditioner S (ST21). At that time, the switching control unit 74 controls the first expansion valve 51 and the second expansion valve 52 to a predetermined opening degree, and the refrigerant discharged from the compressor 1 flows into the indoor heat exchanger 2 via the first switching valve 61, and high-temperature refrigerant from the compressor 1 flows into the outdoor heat exchanger 3, thereby executing the defrosting operation to melt the frost adhering to the outdoor heat exchanger 3. Next, the determination unit 73 estimates the heating capacity during the defrosting heating operation (ST22).

[0046] 11 , the specific process for estimating the heating capacity during defrosting heating operation is as follows: the temperature detection unit 71 acquires the current room temperature detected by the room temperature sensor 21 provided in the indoor unit 10 (ST41). Next, the determination unit 73 acquires a heating capacity estimate corresponding to the current room temperature from data of heating capacity estimates corresponding to changes in the room temperature stored in the memory unit 72 (ST42). Next, returning to FIG. 10 , the determination unit 73 compares the current room temperature with the first threshold temperature (ST23 in FIG. 10 ).

[0047] If the determination unit 73 compares the current room temperature with the first threshold temperature (ST24) and determines that the current room temperature is equal to or higher than the first threshold temperature (YES in ST24), the determination unit 73 determines that the room heating capacity is excessive, causing the room temperature to rise and reducing indoor comfort, calculates the difference between the heating capacity estimate and the heating capacity estimate for the first threshold temperature, and calculates an opening control amount corresponding to this difference.The switching control unit 74 then controls the first expansion valve 51 to increase its opening by the opening control amount (ST25).On the other hand, if the current room temperature is lower than the first threshold temperature (NO in ST24), the determination unit 73 compares the current room temperature with the second threshold temperature (ST26).

[0048] If the determination unit 73 compares the current room temperature with the second threshold temperature (ST27) and determines that the current room temperature is equal to or lower than the second threshold temperature (YES in ST27), the determination unit 73 determines that the room heating capacity is insufficient, causing the room temperature to drop and reducing indoor comfort, calculates the difference between the estimated heating capacity and the estimated heating capacity at the second threshold temperature, and calculates an opening control amount corresponding to this difference.The switching control unit 74 then controls the opening of the first expansion valve 51 to be reduced by the opening control amount (ST28).If the current room temperature is higher than the second threshold temperature (NO in ST27), the switching control unit 74 controls the opening of the first expansion valve 51 to be maintained (ST29).

[0049] While the defrosting and heating operation is being performed, the determination unit 73 determines whether the frost on the outdoor heat exchanger 3 has melted and it is acceptable to terminate the defrosting and heating operation based on preset termination conditions (ST30). If the determination unit 73 determines that the frost on the outdoor heat exchanger 3 has not sufficiently melted and the defrosting and heating operation cannot be terminated yet (NO in ST30), the defrosting and heating operation continues (proceeding to ST22). On the other hand, if the determination result indicates that the defrosting and heating operation can be terminated (YES in ST30), the defrosting and heating operation is terminated (ST31).

[0050] The effect of the defrosting heating operation of the second embodiment will be described. When the control device 7 of the second embodiment determines that the room temperature during the defrosting heating operation is equal to or higher than the first threshold temperature, it determines that the estimated heating capacity is excessive and controls to increase the opening of the first expansion valve 51. When the control device 7 determines that the room temperature during the defrosting heating operation is equal to or lower than the second threshold temperature, it determines that the estimated heating capacity is insufficient and controls to decrease the opening of the first expansion valve 51.

[0051] Therefore, by controlling the first expansion valve 51 to be larger when it is determined that the estimated heating capacity is excessive, part of the refrigerant flowing through the indoor heat exchanger 2 flows to the outdoor heat exchanger 3, reducing the indoor heating capacity and the room temperature, so that it is possible to suppress a decrease in indoor comfort even when the building load is small. In addition, by having part of the refrigerant flowing through the indoor heat exchanger 2 flow to the outdoor heat exchanger 3, it is possible to shorten the defrosting time.

[0052] Furthermore, by controlling the first expansion valve 51 to be smaller when it is determined that the estimated heating capacity is insufficient, the refrigerant flowing through the outdoor heat exchanger 3 flows to the indoor heat exchanger 2, increasing the indoor heating capacity and raising the room temperature, thereby suppressing a decrease in indoor comfort. Furthermore, in the second embodiment, by controlling the opening of the first expansion valve 51 based on the room temperature during defrosting heating operation, it is possible to simultaneously control the adjustment of the heating capacity of the indoor heat exchanger 2 and the defrosting capacity of the outdoor heat exchanger 3 during defrosting heating operation.

[0053] Furthermore, the second expansion valve 52, which is located downstream of the refrigerant from the indoor heat exchanger 2, is set to a fixed opening value so that the refrigerant flowing out from the indoor heat exchanger 2, which functions as a condenser during defrost heating operation, is in a supercooled state.Therefore, no complex control is required, and the heating capacity of the indoor heat exchanger 2 and the defrosting capacity of the outdoor heat exchanger 3 during defrost heating operation can be adjusted simultaneously by simply controlling the opening of the first expansion valve 51.

[0054] [Third embodiment] Next, the flow of control of the defrosting heating operation of a third embodiment according to the present invention will be described using the flowcharts shown in Figures 11 and 12. The control of the defrosting heating operation of the third embodiment is characterized by estimating the heating capacity based on the condensation temperature of the indoor heat exchanger 2. The memory unit 72 of the control device 7 of the third embodiment stores the condensation temperature of the indoor heat exchanger 2, which functions as a condenser during the defrosting heating operation, at the start of the defrosting heating operation, and an initial value of the heating capacity of the defrosting heating operation based on this condensation temperature.

[0055] As in the first and second embodiments, the storage unit 72 of the control device 7 of the third embodiment stores the opening degrees of the first expansion valve 51 and the second expansion valve 52 determined according to the required capacity. The storage unit 72 of the third embodiment also stores data on an estimated value of heating capacity corresponding to the condensing temperature of the indoor heat exchanger 2 that functions as a condenser during defrosting heating operation.

[0056] The determination unit 73 of the third embodiment estimates the heating capacity during defrosting heating operation. Specifically, this process obtains a heating capacity estimate corresponding to the refrigerant temperature (condensing temperature) detected by the refrigerant temperature sensor 22 from heating capacity estimate data stored in the memory unit 72. The determination unit 73 also compares whether the temperature difference between the current room temperature and the room temperature a predetermined time ago (e.g., one minute ago) is within a predetermined temperature range (e.g., 2°C). The determination unit 73 also compares the current refrigerant temperature with the refrigerant temperature (condensing temperature) at the start of the defrosting heating operation.

[0057] 12 , in the control of the defrosting heating operation in the third embodiment, the defrosting heating operation is first started in the air conditioner S (ST51). At that time, the switching control unit 74 controls the first expansion valve 51 and the second expansion valve 52 to predetermined opening degrees, and the refrigerant discharged from the compressor 1 flows into the indoor heat exchanger 2 via the first switching valve 61, and high-temperature refrigerant from the compressor 1 flows into the outdoor heat exchanger 3, thereby executing the defrosting operation to melt the frost adhering to the outdoor heat exchanger 3. Next, the determination unit 73 estimates the heating capacity during the defrosting heating operation (ST52).

[0058] 13, the specific process for estimating the heating capacity during defrosting heating operation is as follows: temperature detection unit 71 acquires the current condensing temperature detected by refrigerant temperature sensor 22 (ST71). Next, determination unit 73 acquires a heating capacity estimate corresponding to the current condensing temperature from the heating capacity estimate data stored in memory unit 72 (ST72). Next, returning to FIG. 12, determination unit 73 calculates the temperature difference between the current room temperature and the room temperature a predetermined time ago (ST53).

[0059] Next, the determination unit 73 compares the temperature difference between the room temperature and the temperature within a predetermined temperature range (e.g., 2°C). If the temperature difference between the room temperature and the temperature within the predetermined temperature range is equal to or less than the predetermined temperature range (YES in ST54), the determination unit 73 compares the current condensing temperature with the condensing temperature at the start of the defrosting heating operation (ST55). If the current condensing temperature is higher than the condensing temperature at the start of the defrosting heating operation (YES in ST56), the determination unit 73 determines that the room heating capacity is excessive, causing the room temperature to rise and reducing indoor comfort. The determination unit 73 calculates the difference between the estimated heating capacity and the initial heating capacity, and calculates an opening control amount corresponding to this difference. The switching control unit 74 then controls the first expansion valve 51 to increase its opening by the opening control amount (ST57).

[0060] If the current condensing temperature is equal to or lower than the condensing temperature at the start of the defrosting heating operation (NO in ST56) or is lower than the condensing temperature at the start of the defrosting heating operation (YES in ST58), the determination unit 73 determines that the room heating capacity is insufficient, causing the room temperature to drop and the room comfort to decrease. The determination unit 73 calculates the difference between the estimated heating capacity and the initial heating capacity, and calculates an opening control amount corresponding to this difference. The switching control unit 74 then controls the opening of the first expansion valve 51 to be reduced by the opening control amount (ST59). If the current condensing temperature and the condensing temperature at the start of the defrosting heating operation are equal (NO in ST58), the switching control unit 74 controls the opening of the first expansion valve 51 to be maintained (ST60).

[0061] While the defrosting and heating operation is being performed, the determination unit 73 determines whether the frost on the outdoor heat exchanger 3 has melted and it is acceptable to terminate the defrosting and heating operation based on preset termination conditions (ST61). If the determination unit 73 determines that the frost on the outdoor heat exchanger 3 has not melted sufficiently and the defrosting and heating operation cannot be terminated yet (NO in ST61), the defrosting and heating operation continues (proceeding to ST52). On the other hand, if the determination result indicates that the defrosting and heating operation can be terminated (YES in ST61), the defrosting and heating operation is terminated (ST62).

[0062] The effect of the defrosting heating operation of the third embodiment will be described. Assume that the current room temperature during the defrosting heating operation is 24°C, and the room temperature a predetermined time ago was 23°C. There is not much temperature difference between the current room temperature and the room temperature a predetermined time ago. However, if the current condensing temperature of the indoor heat exchanger 2 is higher than the condensing temperature at the start of the defrosting heating operation, the estimated heating capacity is determined to be excessive, and control is performed to increase the opening of the first expansion valve 51. On the other hand, if the current condensing temperature of the indoor heat exchanger 2 is lower than the condensing temperature at the start of the defrosting heating operation, the estimated heating capacity is determined to be insufficient, and control is performed to decrease the opening of the first expansion valve 51. Therefore, in the third embodiment, by monitoring changes in the condensing temperature of the indoor heat exchanger 2, whether the heating capacity is excessive or insufficient can be estimated from the condensing capacity even when the room temperature change is small. This makes it possible to prevent the room temperature from rising too high or dropping too low, thereby preventing a decrease in indoor comfort.

[0063] Also, as in the first and second embodiments, by controlling the aperture of the first expansion valve 51 based on the room temperature during defrosting heating operation, it is possible to simultaneously control and adjust the heating capacity of the indoor heat exchanger 2 and the defrosting capacity of the outdoor heat exchanger 3 during defrosting heating operation. Furthermore, the second expansion valve 52, which is arranged downstream of the refrigerant from the indoor heat exchanger 2, is set to a fixed aperture value such that the refrigerant flowing out of the indoor heat exchanger 2, which functions as a condenser during defrosting heating operation, is in a subcooled state. Therefore, complex control is not required, and the heating capacity of the indoor heat exchanger 2 and the defrosting capacity of the outdoor heat exchanger 3 during defrosting heating operation can be simultaneously adjusted by simply controlling the aperture of the first expansion valve 51.

[0064] [Fourth embodiment] In the first to third embodiments, the estimated heating capacity is calculated based on the enthalpy difference between the inlet and outlet of the indoor heat exchanger 2 and the amount of refrigerant circulating during defrosting heating operation, the estimated heating capacity is calculated based on the room temperature detected by the room temperature sensor 21, or the estimated heating capacity is calculated based on the condensing temperature of the indoor heat exchanger 2 and the room temperature.

[0065] 2 , the heating capacity during the defrosting heating operation may be estimated based on the air volume sent out from the indoor fan 11, which sends into the room the air that has exchanged heat with the refrigerant in the indoor heat exchanger 2. That is, the estimated heating capacity during the defrosting heating operation can be calculated based on the temperature difference between the room temperature detected by the room temperature sensor 21 provided in the indoor unit 10 and the refrigerant temperature detected by the refrigerant temperature sensor 22, and the air volume of the indoor fan 11. If the estimated heating capacity is calculated based on the air volume sent out from the indoor fan 11 and used to control the defrosting heating operation in the first to third embodiments, more precise and quick control of the defrosting heating operation can be achieved than if the estimated heating capacity was calculated based only on the room temperature and the temperature of the refrigerant flowing through the indoor heat exchanger 2.

[0066] The present invention is not limited to the above-described embodiment, but merely illustrates one example of the present invention. In the implementation stage, the components can be modified and embodied without departing from the spirit of the invention, and various changes and improvements can be made to the above-described embodiment. Furthermore, various inventions can be formed by appropriately combining multiple components disclosed in the above-described embodiment. For example, some components may be omitted from all of the components shown in the embodiment. Furthermore, components from different embodiments may be appropriately combined, and such changes or improvements can also be included in the present invention. These embodiments and their modifications are within the scope and spirit of the invention, and are also included in the scope of the invention and its equivalents as set forth in the claims.

[0067] REFERENCE SIGNS LIST 1 Compressor 2 Indoor heat exchanger 3 Outdoor heat exchanger 4 Heat storage heat exchanger 5 Expansion valve 6 Switching valve 7 Control device 10 Indoor unit 11 Indoor fan 21 Room temperature sensor 22 Refrigerant temperature sensor 23 Gas side refrigerant temperature sensor 24 Liquid side refrigerant temperature sensor 51 First expansion valve 52 Second expansion valve 53 Third expansion valve 61 First switching valve 62 Second switching valve B Bypass circuit C Refrigerant circuit S Air conditioner

Claims

1. A refrigerant circuit for circulating a refrigerant is connected to: a compressor for compressing the refrigerant; an indoor heat exchanger for exchanging heat between indoor air and the refrigerant; an outdoor heat exchanger for exchanging heat between outdoor air and the refrigerant; a heat storage heat exchanger for exchanging heat between a heat storage material and the refrigerant; a plurality of expansion valves with adjustable openings; and a switching valve for switching a flow path of the refrigerant circuit between a heat storage heating operation in which the indoor heat exchanger and the heat storage heat exchanger function as condensers and the outdoor heat exchanger function as an evaporator, and a defrost heating operation in which the indoor heat exchanger and the outdoor heat exchanger function as condensers and the heat storage heat exchanger function as an evaporator; heating capacity estimating means for estimating heating capacity during the defrost heating operation; and a control device for controlling the plurality of expansion valves and the switching valve, wherein the plurality of expansion valves include a first expansion valve provided upstream of the outdoor heat exchanger during the defrost heating operation, The air conditioner, characterized in that the control device controls the opening degree of the first expansion valve based on the heating capacity estimated by the heating capacity estimation means during the defrosting heating operation.

2. The air conditioner according to claim 1, characterized in that the control device increases the opening of the first expansion valve when it determines that the heating capacity estimated by the heating capacity estimation means is excessive.

3. The air conditioner according to claim 1, characterized in that the control device reduces the opening of the first expansion valve when it determines that the heating capacity estimated by the heating capacity estimation means is insufficient.

4. An air conditioner as described in claim 1, characterized in that it is provided with an enthalpy difference calculation means for calculating an enthalpy difference based on the inlet side enthalpy of the indoor heat exchanger and the outlet side enthalpy of the indoor heat exchanger, and the heating capacity estimation means estimates the heating capacity based on the enthalpy difference calculated by the enthalpy difference calculation means.

5. An air conditioner as described in claim 1, further comprising a room temperature sensor for detecting the room temperature, and wherein the heating capacity estimation means estimates the heating capacity based on the room temperature detected by the room temperature sensor.

6. The air conditioner of claim 5, characterized in that when the room temperature detected by the room temperature sensor becomes equal to or higher than a predetermined first threshold, the control device determines that the heating capacity estimated by the heating capacity estimation means is excessive, and when it determines that the heating capacity is excessive, increases the opening of the first expansion valve.

7. The air conditioner of claim 5, characterized in that when the room temperature detected by the room temperature sensor falls below a predetermined second threshold, the control device determines that the heating capacity estimated by the heating capacity estimation means is insufficient, and when it determines that the heating capacity is insufficient, reduces the opening of the first expansion valve.

8. An air conditioner as described in claim 1, characterized in that it is equipped with a room temperature sensor that detects the temperature inside the room, and an indoor heat exchanger temperature sensor that detects the temperature of the indoor heat exchanger, and the heating capacity estimation means estimates the heating capacity based on the temperature of the indoor heat exchanger detected by the indoor heat exchanger temperature sensor.

9. The air conditioner of claim 8, characterized in that the control device determines that the heating capacity estimated by the heating capacity estimation means is excessive if the temperature difference between the current indoor temperature detected by the room temperature sensor and the indoor temperature a predetermined time ago is within a predetermined range and the temperature of the indoor heat exchanger detected by the indoor heat exchanger temperature sensor is higher than the temperature at the start of the defrost heating operation, and increases the opening of the first expansion valve if it determines that the heating capacity is excessive.

10. The air conditioner of claim 8, characterized in that the control device determines that the heating capacity estimated by the heating capacity estimation means is insufficient when the temperature difference between the current indoor temperature detected by the room temperature sensor and the indoor temperature a predetermined time ago is within a predetermined range and the temperature of the indoor heat exchanger detected by the indoor heat exchanger temperature sensor is lower than the temperature at the start of the defrost heating operation, and when it determines that the heating capacity is insufficient, reduces the opening of the first expansion valve.

11. An air conditioner as described in claim 8, further comprising an air volume calculation means for calculating the volume of air sent out from an indoor fan that blows the air that has exchanged heat with the refrigerant in the indoor heat exchanger into the room, and wherein the heating capacity estimation means estimates the heating capacity based on the temperature difference between the room temperature detected by the room temperature sensor and the temperature of the indoor heat exchanger detected by the indoor heat exchanger temperature sensor, and the air volume calculated by the air volume calculation means.

12. An air conditioner as described in any one of claims 1 to 11, characterized in that the multiple expansion valves are provided downstream of the indoor heat exchanger during the defrosting heating operation, and include a second expansion valve whose opening is set to a fixed value during the defrosting heating operation.

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