Air Conditioning Equipment

Abstract

The air conditioner comprises a main circuit, a first bypass circuit that guides hot gas discharged from a compressor to each of a plurality of outdoor heat exchangers, a plurality of first opening / closing devices that open and close the first bypass circuit, and a plurality of second opening / closing devices that open and close the main circuit between the plurality of outdoor heat exchangers and a load side throttling device, and is capable of performing a cooling operation in which the refrigerant flow path switching device is set to a first state and the plurality of outdoor heat exchangers function as condensers, a heating operation in which the refrigerant flow path switching device is set to a second state and the plurality of outdoor heat exchangers function as evaporators, and a defrosting operation, and the defrosting operation includes a divided defrosting operation in which some of the outdoor heat exchangers function as evaporators and hot gas is introduced into the other outdoor heat exchangers, and a full defrosting operation in which hot gas is introduced into all of the plurality of outdoor heat exchangers, and in both the divided defrosting operation and the full defrosting operation, the refrigerant flow path switching device is set to the second state.

Description

[Technical field]

[0001] The present disclosure relates to an air conditioning apparatus. [Background technology]

[0002] Conventionally, in air-conditioning systems such as multi-air conditioners for buildings, for example, a refrigerant circuit is formed by connecting an outdoor unit, which is a heat source unit installed outside a building, to an indoor unit installed inside the building through piping, and the refrigerant is circulated through the refrigerant. Heat radiation and absorption of heat from the refrigerant are utilized to heat and cool the air, thereby heating or cooling the space to be air-conditioned.

[0003] When such a multi-air conditioner for buildings is in heating operation, the heat exchanger installed in the outdoor unit becomes an evaporator, and as a result of heat exchange between the low-temperature refrigerant and the air, moisture in the air condenses on the fins and heat transfer tubes of the heat exchanger, causing frost to form on the heat exchanger. When frost forms on the heat exchanger in this way, the air passage of the heat exchanger is blocked, and the heat transfer area of ​​the heat exchanger that exchanges heat with the air becomes smaller, causing a problem of insufficient heating capacity.

[0004] Therefore, in general, defrosting operation is performed by stopping the heating operation, switching the refrigerant flow using a refrigerant flow switching device, and using a heat exchanger installed in the outdoor unit as a condenser. However, the temperature inside the room drops during the heating stop period of the defrosting operation, and comfort decreases.

[0005] Patent Document 1 describes a method for performing defrosting operation without stopping heating operation by dividing multiple outdoor heat exchangers with on-off valves and providing an outdoor heat exchanger that performs defrosting and an outdoor heat exchanger that evaporates refrigerant flowing in from the indoor side. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] International Publication No. 2010 / 082325 Summary of the Invention [Problem to be solved by the invention]

[0007] In the technology of Patent Document 1, defrosting operation and heating operation can be performed simultaneously, but the capacity generated by the air conditioner is not increased, and the capacity is shared between the outdoor heat exchanger for defrosting and the outdoor heat exchanger for heating. When the heat required by the outdoor heat exchanger is large, such as when defrosting at a low outdoor temperature, the heating capacity decreases and the indoor discharge temperature decreases, resulting in a loss of comfort. For this reason, it may be necessary to flow the refrigerant in the opposite direction to the heating operation, make all the outdoor heat exchangers function as condensers, and complete the defrosting of all the outdoor heat exchangers in a short time. In this case, the heating operation is stopped, the refrigerant flow is switched by the refrigerant flow switching device, and then the defrosting operation is started. However, when switching the refrigerant flow switching device, it is necessary to reduce the pressure difference between the high-pressure side flow path and the low-pressure side flow path, and the compressor frequency needs to be slowed down, which is a problem in that it takes time to switch between the heating operation and the defrosting operation.

[0008] The present disclosure has been made to solve the above-mentioned problems, and has an object to provide an air conditioner that can shorten the time it takes to switch between heating operation and defrosting operation. [Means for solving the problem]

[0009] The air conditioner according to the present disclosure includes a main circuit having a compressor, a refrigerant flow switching device, a plurality of outdoor heat exchangers, a load side throttling device, and an indoor heat exchanger, and a hot gas discharged from the compressor is supplied to each of the plurality of outdoor heat exchangers. Dividea first bypass circuit that guides the hot gas to the outdoor heat exchanger, a plurality of first opening / closing devices that open and close the first bypass circuit corresponding to each of the plurality of outdoor heat exchangers, and a plurality of second opening / closing devices that open and close the main circuit between the plurality of outdoor heat exchangers and the load side throttling device corresponding to each of the plurality of outdoor heat exchangers, and the refrigerant flow switching device is capable of executing a cooling operation in which the plurality of outdoor heat exchangers function as condensers, a heating operation in which the refrigerant flow switching device is set to a second state and the plurality of outdoor heat exchangers function as evaporators, and a defrosting operation in which the hot gas is introduced into at least one of the plurality of outdoor heat exchangers via the first bypass circuit, and the defrosting operation includes a split defrosting operation in which some of the plurality of outdoor heat exchangers function as evaporators and the hot gas is introduced into other of the plurality of outdoor heat exchangers via the first bypass circuit, The refrigerant circulation in the main circuit is stopped, and all of the hot gas discharged from the compressor and flowing into the first bypass circuit is All of the outdoor heat exchangers Divide and a full defrosting operation to be introduced, and in both of the divided defrosting operation and the full defrosting operation, the refrigerant flow path switching device is set to the second state. Effect of the Invention

[0010] According to the present disclosure, the time required for switching between the heating operation and the defrosting operation can be shortened. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a refrigerant circuit diagram showing a circuit configuration in a cooling only operation mode of an air conditioner according to Embodiment 1. [Diagram 2] FIG. 1 is a refrigerant circuit diagram showing a circuit configuration in a full heating operation mode of an air conditioner according to Embodiment 1. [Diagram 3] FIG. 2 is a refrigerant circuit diagram showing a circuit configuration in a split defrosting operation mode of the air conditioner according to the first embodiment. [Figure 4] FIG. 2 is a refrigerant circuit diagram showing a circuit configuration in a full defrosting operation mode of the air conditioner according to the first embodiment. [Diagram 5]FIG. 4 is a refrigerant circuit diagram showing a circuit configuration of an air conditioner according to a modified example of the first embodiment. [Figure 6] FIG. 11 is a refrigerant circuit diagram showing a circuit configuration in a cooling only operation mode of an air conditioner according to embodiment 2. [Figure 7] FIG. 11 is a refrigerant circuit diagram showing a circuit configuration in a full heating operation mode of an air conditioner according to embodiment 2. [Figure 8] FIG. 11 is a refrigerant circuit diagram showing a circuit configuration in a split defrosting operation mode of an air conditioner according to embodiment 2. [Figure 9] FIG. 11 is a refrigerant circuit diagram showing a circuit configuration in a full defrosting operation mode of an air conditioner according to embodiment 2. [Figure 10] FIG. 11 is a refrigerant circuit diagram showing a circuit configuration in a cooling only operation mode of an air conditioner according to embodiment 3. [Figure 11] FIG. 11 is a refrigerant circuit diagram showing a circuit configuration in a cooling-dominated operation mode of an air conditioner according to embodiment 3. [Figure 12] FIG. 11 is a refrigerant circuit diagram showing a circuit configuration in a full heating operation mode of an air conditioner according to embodiment 3. [Figure 13] FIG. 11 is a refrigerant circuit diagram showing a circuit configuration in a heating-dominated operation mode of an air conditioner according to embodiment 3. [Figure 14] FIG. 11 is a refrigerant circuit diagram showing a circuit configuration in a split defrosting operation mode of an air conditioner according to embodiment 3. [Figure 15] FIG. 11 is a refrigerant circuit diagram showing a circuit configuration in a full defrosting operation mode of an air conditioner according to embodiment 3. [Figure 16] FIG. 11 is a refrigerant circuit diagram showing a circuit configuration in a cooling only operation mode of an air conditioner according to embodiment 4. [Figure 17] FIG. 11 is a refrigerant circuit diagram showing a circuit configuration in a cooling-dominated operation mode of an air conditioner according to embodiment 4. [Figure 18] FIG. 11 is a refrigerant circuit diagram showing a circuit configuration in a full heating operation mode of an air conditioner according to embodiment 4. [Figure 19] FIG. 11 is a refrigerant circuit diagram showing a circuit configuration in a heating-dominated operation mode of an air conditioner according to embodiment 4. [Figure 20] FIG. 11 is a refrigerant circuit diagram showing a circuit configuration in a split defrosting operation mode of an air conditioner according to embodiment 4. [Figure 21] FIG. 11 is a refrigerant circuit diagram showing a circuit configuration in a full defrosting operation mode of an air conditioner according to embodiment 4. [Figure 22] FIG. 11 is a refrigerant circuit diagram showing the circuit configuration of an air conditioner according to embodiment 5. [Diagram 23] FIG. 13 is a refrigerant circuit diagram showing the circuit configuration of an air conditioner according to embodiment 6. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, the embodiments of the present disclosure will be described with reference to the drawings. The present disclosure is not limited to the following embodiments, and can be modified in various ways without departing from the spirit of the present disclosure. The present disclosure includes all combinations of the configurations shown in the following embodiments that can be combined. In particular, the combination of components is not limited to the combinations in each embodiment, and the components described in one embodiment can be applied to another embodiment. In the following description, terms indicating directions (e.g., "upper", "lower", "right", "left", "front", "rear", etc.) are used as appropriate to facilitate understanding, but these are for explanation and do not limit the present disclosure. In each drawing, the same reference numerals are assigned to the same or equivalent parts, and this is common throughout the entire specification. In each drawing, the relative dimensional relationship or shape of each component may differ from the actual one.

[0013] Embodiment 1 <Configuration of the Air Conditioning Apparatus 100> An air conditioner according to the first embodiment will be described. FIG. 1 is a refrigerant circuit diagram showing a circuit configuration of an all-cooling operation mode of an air conditioner according to the present embodiment. The air conditioner 100 circulates refrigerant and performs air conditioning using a refrigeration cycle. The air conditioner 100 can select an all-cooling operation mode, an all-heating operation mode, or a defrosting operation mode. The all-cooling operation mode is an operation mode in which all operating indoor units 2 perform cooling. The all-heating operation mode is an operation mode in which all operating indoor units 2 perform heating. The defrosting operation mode is an operation mode in which the outdoor heat exchangers 12a, 12b in the outdoor unit 1 are defrosted. The defrosting operation mode includes a split defrosting operation mode and a all-defrosting operation mode, which will be described later.

[0014] 1, the air conditioner 100 has an outdoor unit 1, an indoor unit 2, and main pipes 5a, 5b that connect the outdoor unit 1 and the indoor unit 2. By connecting the outdoor unit 1 and the indoor unit 2 via the main pipes 5a, 5b, a main circuit 9 is formed that has a compressor 10, a refrigerant flow switching device 13, multiple outdoor heat exchangers 12a, 12b, a load side throttling device 25, and an indoor heat exchanger 26.

[0015] <Configuration of outdoor unit 1> The outdoor unit 1 has a compressor 10 that compresses and discharges a refrigerant. The outdoor unit 1 has a plurality of outdoor heat exchangers 12a, 12b that exchange heat between the refrigerant and outdoor air. The outdoor unit 1 has a heat source side blower 18 that supplies outdoor air to the outdoor heat exchangers 12a, 12b. In the outdoor heat exchangers 12a, 12b, the air supplied by the heat source side blower 18 exchanges heat with the refrigerant, and the refrigerant condenses or evaporates. The outdoor unit 1 has a refrigerant flow path switching device 13 that switches the flow path of the refrigerant depending on the operation mode. The outdoor unit 1 has an accumulator 19 that accumulates the refrigerant. The outdoor unit 1 has a first bypass circuit 20 that introduces hot gas to melt frost formed on the outdoor heat exchangers 12a, 12b. The outdoor unit 1 has a control device 60 that controls various devices.

[0016] The compressor 10, the refrigerant flow switching device 13, the outdoor heat exchangers 12a and 12b, the opening and closing devices 15a and 15b, and the accumulator 19 are connected by the refrigerant piping 4. One end of the first bypass circuit 20 is connected to the refrigerant piping 4 between the discharge portion of the compressor 10 and the refrigerant flow switching device 13. The other end of the first bypass circuit 20 is branched into two flow paths. One flow path is connected between the outdoor heat exchanger 12a and the opening and closing device 15a. The other flow path is connected between the outdoor heat exchanger 12b and the opening and closing device 15b. The first bypass circuit 20 is provided with a plurality of opening and closing devices 11a and 11b. The opening and closing device 11a is provided in a flow path of the first bypass circuit 20 corresponding to the outdoor heat exchanger 12a. The opening and closing device 11b is provided in a flow path of the first bypass circuit 20 corresponding to the outdoor heat exchanger 12b.

[0017] The compressor 10 draws in a refrigerant and compresses the refrigerant to a high temperature and high pressure state. The compressor 10 is, for example, an inverter compressor whose capacity is controllable. The compressor 10 is controlled by a control device 60.

[0018] The refrigerant flow switching device 13 switches the refrigerant flow between a heating only operation mode and a cooling only operation mode. The refrigerant flow switching device 13 is controlled by the control device 60.

[0019] The outdoor heat exchangers 12a, 12b function as evaporators in the heating only operation mode, and function as condensers in the cooling only operation mode and the defrosting operation mode.

[0020] The accumulator 19 is provided on the suction side of the compressor 10. The accumulator 19 is a receiver that stores surplus refrigerant due to differences in operating conditions between the heating only operation mode, the cooling only operation mode, and the defrosting operation mode, and surplus refrigerant due to transient changes in operation.

[0021] The opening and closing devices 11a and 11b, during the defrosting operation mode, allow high-temperature gas refrigerant to flow from the discharge side of the compressor 10 through the refrigerant pipe 4 into the outdoor heat exchangers 12a and 12b. The opening and closing devices 11a and 11b are configured by, for example, a two-way valve, a solenoid valve, etc. The opening and closing devices 11a and 11b are controlled by a control device 60.

[0022] One of the opening and closing devices 15a, 15b is closed during the defrosting operation mode to prevent the low-pressure two-phase refrigerant from the indoor unit 2 from flowing into the outdoor heat exchangers 12a, 12b during defrosting. The opening and closing devices 15a, 15b may be configured with a device capable of opening and closing the refrigerant flow path, such as a two-way valve, a solenoid valve, or an electronic expansion valve capable of adjusting the flow rate. The opening and closing devices 15a, 15b are controlled by the control device 60.

[0023] The outdoor unit 1 is provided with an outdoor heat exchanger temperature sensor 43, a discharge temperature sensor 42, a discharge pressure sensor 40, and an outdoor air temperature sensor 46. The outdoor heat exchanger temperature sensor 43 detects the temperature of the refrigerant flowing out of the outdoor heat exchangers 12a and 12b during heating operation and defrosting operation, and detects the temperature of the refrigerant flowing into the outdoor heat exchangers 12a and 12b during cooling operation, and outputs a refrigerant temperature detection signal. The discharge temperature sensor 42 detects the temperature of the refrigerant discharged by the compressor 10, and outputs a refrigerant temperature detection signal. The discharge pressure sensor 40 detects the pressure of the refrigerant discharged by the compressor 10, and outputs a discharge pressure detection signal. The outdoor air temperature sensor 46 is provided in the air inflow portion of the outdoor heat exchangers 12a and 12b in the outdoor unit 1. The outdoor air temperature sensor 46 detects, for example, the outdoor air temperature, which is the temperature around the outdoor unit 1, and outputs an outdoor air temperature detection signal.

[0024] <Configuration of indoor unit 2> The indoor unit 2 has an indoor heat exchanger 26 and a load-side throttling device 25. The indoor heat exchanger 26 is connected to the outdoor unit 1 via the main pipes 5a and 5b. In each of the indoor heat exchangers 26, air supplied by a load-side blower (not shown) is heat-exchanged with the refrigerant to generate air for cooling or air for heating to be supplied to the indoor space. The load-side throttling device 25 can adjust the opening degree, for example, continuously or in multiple stages. For example, an electronic expansion valve is used as the load-side throttling device 25. The load-side throttling device 25 has the functions of a pressure reducing valve and an expansion valve. The load-side throttling device 25 reduces the pressure of the refrigerant to expand it. The load-side throttling device 25 is provided upstream of the indoor heat exchanger 26 in the flow of the refrigerant in the full cooling operation mode.

[0025] The indoor unit 2 has a load-side first temperature sensor 31 that detects the temperature of the refrigerant flowing into the indoor heat exchanger 26. The indoor unit 2 has a load-side second temperature sensor 32 that detects the temperature of the refrigerant flowing out from the indoor heat exchanger 26. The load-side first temperature sensor 31 and the load-side second temperature sensor 32 are composed of, for example, a thermistor. The load-side first temperature sensor 31 and the load-side second temperature sensor 32 each output a detection signal to the control device 60.

[0026] With the above configuration, the compressor 10, the refrigerant flow switching device 13, the indoor heat exchanger 26, the load side throttle device 25, and the outdoor heat exchangers 12a and 12b are sequentially connected by piping to form a main circuit 9 in which the refrigerant circulates. In addition, a first bypass circuit 20 is formed that causes high-temperature gas refrigerant discharged from the compressor 10 to flow into the outdoor heat exchangers 12a and 12b to be defrosted via the opening and closing devices 11a and 11b. Note that one indoor unit 2 is illustrated in FIG. 1. However, the number of indoor units 2 connected may be two or more. In addition, two or more outdoor units 1 may be connected in parallel.

[0027] The air conditioner 100 has a control device 60 configured with a microcomputer. Based on information detected by various detection means and instructions from a remote control, the control device 60 controls the drive frequency of the compressor 10, the rotation speed of the blower (including on and off), switching of the refrigerant flow switching device 13, opening and closing of the opening and closing devices 11a and 11b, the opening degree of the load side throttle device 25, and the like. In this way, each operation mode described later is executed.

[0028] 1 shows an example in which the control device 60 is installed in the outdoor unit 1, but is not limited to this. For example, the control device 60 may be provided for each unit, or may be provided for the indoor unit 2. When a control device 60 is provided for each unit, it is preferable to configure the control devices 60 to be connected to each other by wire or wirelessly so that information can be exchanged and to enable coordinated control.

[0029] Next, each operation mode executed by the air conditioning apparatus 100 will be described together with the flow of refrigerant.

[0030] <Full cooling operation mode> The cooling only operation mode executed by the air conditioner 100 will be described with reference to Fig. 1. In Fig. 1, the cooling only operation mode will be described using as an example a case in which a cold heat load is generated in the indoor heat exchanger 26. In Fig. 1, the flow direction of the refrigerant is indicated by solid arrows.

[0031] In the cooling only operation mode, the refrigerant flow switching device 13 is switched to the first state indicated by the solid line in Fig. 1. The opening and closing devices 11a and 11b are switched to the closed state to block the refrigerant. The opening and closing devices 15a and 15b are set to the open state.

[0032] When the compressor 10 is driven, the low-temperature, low-pressure refrigerant is compressed and discharged as a high-temperature, high-pressure gas refrigerant. The high-temperature, high-pressure gas refrigerant discharged from the compressor 10 flows into the outdoor heat exchangers 12a, 12b via the refrigerant flow switching device 13. The high-temperature, high-pressure gas refrigerant that flows into the outdoor heat exchangers 12a, 12b dissipates heat to the outdoor air in the outdoor heat exchangers 12a, 12b and becomes a high-pressure liquid refrigerant. The high-pressure liquid refrigerant that flows out of the outdoor heat exchangers 12a, 12b flows out of the outdoor unit 1.

[0033] The high-pressure liquid refrigerant flowing out from the outdoor unit 1 passes through the main pipe 5b and flows into the indoor unit 2, where it is expanded by the load-side throttling device 25 to become a low-temperature, low-pressure two-phase refrigerant. This two-phase refrigerant flows into the indoor heat exchanger 26, which operates as an evaporator, and cools the indoor air by absorbing heat from it, becoming a low-temperature, low-pressure gas refrigerant. The gas refrigerant flowing out from the indoor heat exchanger 26 passes through the main pipe 5a and flows back into the outdoor unit 1. The gas refrigerant that has flowed into the outdoor unit 1 passes through the refrigerant flow switching device 13 and the accumulator 19, and is sucked back into the compressor 10.

[0034] The control device 60 controls the opening degree of the load side throttling device 25 so that the superheat (degree of superheat), obtained as the difference between the temperatures detected by the load side first temperature sensor 31 and the load side second temperature sensor 32, is kept constant.

[0035] <Full heating operation mode> Fig. 2 is a refrigerant circuit diagram showing the circuit configuration in the full heating operation mode of the air conditioner according to this embodiment. The full heating operation mode executed by the air conditioner 100 will be described based on Fig. 2. In Fig. 2, the full heating operation mode will be described using an example in which a heat load is generated in the indoor heat exchanger 26. In Fig. 2, the flow direction of the refrigerant is indicated by solid arrows.

[0036] In the heating only operation mode, the refrigerant flow switching device 13 is switched to the second state indicated by the solid line in Fig. 2. The opening and closing devices 11a and 11b are switched to the closed state to block the refrigerant. The opening and closing devices 15a and 15b are set to the open state.

[0037] When the compressor 10 is driven, the low-temperature, low-pressure refrigerant is compressed and discharged as a high-temperature, high-pressure gas refrigerant. The high-temperature, high-pressure gas refrigerant discharged from the compressor 10 flows out of the outdoor unit 1 via the refrigerant flow switching device 13.

[0038] The high-temperature, high-pressure gas refrigerant flowing out from the outdoor unit 1 passes through the main pipe 5a and flows into the indoor unit 2, where it becomes liquid refrigerant while heating the indoor air by dissipating heat to the indoor air in the indoor heat exchanger 26. The liquid refrigerant flowing out from the indoor heat exchanger 26 is expanded in the load-side throttle device 25 and becomes low-temperature, medium-pressure two-phase refrigerant or liquid refrigerant, and flows back into the outdoor unit 1 through the main pipe 5b.

[0039] The low-temperature and medium-pressure two-phase refrigerant or liquid refrigerant that has flowed into the outdoor unit 1 flows into the outdoor heat exchangers 12a and 12b. The refrigerant that has flowed into the outdoor heat exchangers 12a and 12b absorbs heat from the outdoor air and becomes a low-temperature and low-pressure gas refrigerant, and is sucked into the compressor 10 again via the refrigerant flow switching device 13 and the accumulator 19.

[0040] The control device 60 controls the opening degree of the load side throttling device 25 so that the subcooling (degree of supercooling), obtained as the difference between the value obtained by converting the pressure detected by the discharge pressure sensor 40 into a saturation temperature, and the temperature detected by the load side first temperature sensor 31, is kept constant.

[0041] <Split defrost operation mode> The defrosting operation mode is implemented when the detection result of the outdoor heat exchanger temperature sensor 43 provided on the outlet side of the outdoor heat exchangers 12a, 12b is equal to or lower than a predetermined value. That is, when the detection result of the outdoor heat exchanger temperature sensor 43 becomes equal to or lower than a predetermined value (for example, equal to or lower than about -10°C) during the heating only operation mode, the control device 60 determines that a predetermined amount of frost has formed on the fins of the outdoor heat exchangers 12a, 12b, and implements the defrosting operation mode. The outdoor heat exchanger temperature sensor 43 may be provided on the inlet side of the outdoor heat exchangers 12a, 12b, and it is sufficient if it can measure the refrigerant evaporation temperature of the outdoor heat exchangers 12a, 12b in the heating only operation mode.

[0042] In addition, the determination of frost formation may be made, for example, when the saturation temperature converted from the suction pressure of the compressor 10 drops significantly compared to a preset outside air temperature, or when the temperature difference between the outside air temperature and the evaporation temperature remains equal to or greater than a preset value for a certain period of time.

[0043] The defrosting operation mode in this embodiment includes a split defrosting operation mode and a full defrosting operation mode. The split defrosting operation mode is an operation mode in which some of the outdoor heat exchangers 12a, 12b are defrosted. The full defrosting operation mode is an operation mode in which all of the outdoor heat exchangers 12a, 12b are defrosted. When the defrosting operation mode is performed, for example, if the outdoor air temperature is equal to or higher than a threshold temperature, the split defrosting operation mode is performed. On the other hand, if the outdoor air temperature is lower than the threshold temperature, the full defrosting operation mode, which will be described later, is performed.

[0044] Fig. 3 is a refrigerant circuit diagram showing a circuit configuration in the split defrost operation mode of the air conditioner according to this embodiment. In Fig. 3, the flow direction of the refrigerant is indicated by solid arrows. Fig. 3 shows the split defrost operation mode when defrosting the outdoor heat exchanger 12b. In the split defrost operation mode, the refrigerant flow path switching device 13 is maintained in the same second state as in the heating operation mode. The opening and closing device 11a is set to the closed state, the opening and closing device 11b is set to the open state, the opening and closing device 15a is set to the open state, and the opening and closing device 15b is set to the closed state.

[0045] The refrigerant discharged from the compressor 10 is divided into a refrigerant flowing to the first bypass circuit 20 and a refrigerant flowing to the indoor unit 2. The refrigerant flowing to the first bypass circuit 20 passes through the opening and closing device 11b, flows into the outdoor heat exchanger 12b, and is defrosted. The refrigerant that has completed the defrosting merges with the refrigerant that has passed through the outdoor heat exchanger 12a just before the refrigerant flow switching device 13, passes through the refrigerant flow switching device 13, passes through the accumulator 19, and is sucked into the compressor 10.

[0046] The refrigerant flowing to the indoor unit 2 passes through the refrigerant flow switching device 13, the indoor heat exchanger 26, and the load side throttling device 25, and returns to the outdoor unit 1. The refrigerant that has returned to the outdoor unit 1 passes through the opening and closing device 15a, flows into the outdoor heat exchanger 12a, and evaporates. The evaporated refrigerant merges with the refrigerant that has flowed out from the outdoor heat exchanger 12b just before the refrigerant flow switching device 13. In this way, in the split defrost operation mode, while defrosting a part of the outdoor heat exchanger 12b, heating is continued using the other outdoor heat exchanger 12a as a heat exchanger on the heat source side.

[0047] The determination of the end of the split defrost operation mode is performed using a timer. That is, when the execution time of the split defrost operation exceeds a threshold time, the control device 60 ends the split defrost operation mode and resumes the heating operation mode. However, when it is determined that the defrosting is not completed based on the outdoor air temperature sensor 46 or the outdoor heat exchanger temperature sensor 43, the operation mode is switched from the split defrost operation mode to the full defrost operation mode. This increases the defrosting capacity and shortens the defrosting time.

[0048] <Full defrost operation mode> FIG. 4 is a refrigerant circuit diagram showing a circuit configuration in the full defrost operation mode of the air conditioner according to this embodiment. In FIG. 4, the flow direction of the refrigerant is indicated by solid arrows. In the full defrost operation mode, the refrigerant flow switching device 13 is maintained in the second state, which is the same as in the heating operation mode, and the load side expansion device 25 is switched to the closed state to block the refrigerant. The opening and closing devices 11a and 11b are switched to the open state to allow the refrigerant to flow. The heat source side blower 18 and the load side blower (not shown) are stopped. In addition, by switching the opening and closing devices 11a and 11b to the open state and then closing the load side expansion device 25, it is possible to prevent blockage of the refrigerant flow path and suppress an increase in pressure.

[0049] The high-temperature, high-pressure gas refrigerant discharged from the compressor 10 is decompressed by the opening and closing devices 11a, 11b to a temperature higher than 0°C in terms of saturation temperature, and flows into the outdoor heat exchangers 12a, 12b. The high-temperature gas refrigerant that flows into the outdoor heat exchangers 12a, 12b melts the frost adhering to the outdoor heat exchangers 12a, 12b, and becomes a low-temperature gas refrigerant, a two-phase refrigerant with a low dryness, or a liquid refrigerant, and flows into the accumulator 19 via the refrigerant flow switching device 13. Of the refrigerant that flows into the accumulator 19, the liquid refrigerant remains in the accumulator 19, and the gas refrigerant flows into the suction section of the compressor 10.

[0050] The completion of defrosting of the outdoor heat exchangers 12a, 12b may be determined as the melting of the frost, for example, when a predetermined time has elapsed or when the temperature of the outdoor heat exchanger temperature sensor 43 reaches or exceeds a certain predetermined value (for example, 5°C). Note that the predetermined time may be set to be equal to or longer than the time required for all the frost to melt when high-temperature, high-pressure refrigerant is introduced, assuming that frost has formed on the entire outdoor heat exchangers 12a, 12b without any gaps.

[0051] Generally, when switching the flow path of the refrigerant flow path switching device 13, it is necessary to reduce the frequency of the compressor 10 and reduce the pressure difference between the high pressure side and the low pressure side. On the other hand, in this embodiment, when switching between the full heating operation mode, the divided defrost operation mode, and the full defrost operation mode, it is not necessary to switch the refrigerant flow path switching device 13, so there is no need to reduce the frequency of the compressor 10. Not reducing the frequency of the compressor 10 means that the refrigerant flow rate does not decrease. This reduces the time required for defrosting, improving user comfort.

[0052] In addition, in the divided defrost operation mode and the full defrost operation mode, the high-temperature, high-pressure gas refrigerant discharged from the compressor 10 is decompressed by the opening and closing devices 11a and 11b to a temperature higher than 0°C in terms of saturation temperature. However, if the size of the opening and closing devices 11a and 11b is small compared to the amount of gas refrigerant circulating, the pressure of the high-pressure gas refrigerant discharged from the compressor 10 will over-rise. For this reason, the size of the opening and closing devices 11a and 11b is selected according to the amount of gas refrigerant circulating in the divided defrost operation mode and the full defrost operation mode so that the pressure of the high-pressure gas refrigerant is lower than the operating pressure of the compressor 10. For example, when R410A refrigerant is used and the design pressure is 4.15 MPa, the size of the opening and closing devices 11a and 11b is selected so that the operating pressure is 3.8 MPa or less, which is lower than 4.15 MPa, taking into account pressure overshoot.

[0053] In addition, in the divided defrost operation mode and the full defrost operation mode, there may be a heat transfer tube path where frost is difficult to melt due to the influence of the difference in the amount of frost formed in each path of the heat transfer tubes of the outdoor heat exchangers 12a and 12b or the difference in the refrigerant flow rate in each path. In this case, the temperature of the gas refrigerant flowing out of the outdoor heat exchangers 12a and 12b rises above 0°C, which is the melting point of frost, and the temperature of the refrigerant sucked into the compressor 10 rises, so that the temperature of the refrigerant discharged from the compressor 10 rises excessively. In order to ensure reliability, such as preventing deterioration of the refrigeration oil, an upper limit value (e.g., 120°C) is set for the discharge temperature of the compressor 10. In this embodiment, when the temperature detected by the discharge temperature sensor 42 reaches a predetermined discharge temperature value (e.g., 110°C), the frequency of the compressor 10 is reduced to reduce the temperature of the refrigerant discharged from the compressor 10 so that the discharge temperature of the compressor 10 does not exceed the upper limit value. By controlling in this manner, the defrost operation can be stably performed.

[0054] <Modification of the first embodiment> 5 is a refrigerant circuit diagram showing a circuit configuration of an air conditioner according to a modified example of the present embodiment. In this modified example, opening and closing devices 11a and 11b are configured as electronic expansion valves capable of adjusting the refrigerant flow rate.

[0055] In the defrosting operation mode, the opening degree of the opening / closing devices 11a and 11b is adjusted so that the pressure of the gas refrigerant discharged from the compressor 10 becomes a predetermined pressure (for example, 3.0 MPa). When the defrosting operation progresses and most of the frost on the outdoor heat exchangers 12a and 12b melts and a portion remains, the outdoor heat exchangers 12a and 12b are heated and the low pressure increases, and the pressure of the high-pressure gas refrigerant discharged from the compressor 10 increases. When the pressure of the high-pressure gas refrigerant discharged from the compressor 10 increases above a predetermined value (for example, 3.8 MPa), the opening degree of the opening / closing devices 11a and 11b is increased. In this way, by making the opening / closing devices 11a and 11b electronic expansion valves capable of adjusting the refrigerant flow rate and adjusting the operating pressure of the gas refrigerant discharged from the compressor 10, the increase in pressure can be suppressed, and a stable defrosting operation can be performed.

[0056] As described above, the air conditioning apparatus 100 according to the present embodiment includes the main circuit 9, the first bypass circuit 20, a plurality of opening and closing devices 11a, 11b, and a plurality of opening and closing devices 15a, 15b. The main circuit 9 includes the compressor 10, the refrigerant flow switching device 13, a plurality of outdoor heat exchangers 12a, 12b, a load side throttling device 25, and an indoor heat exchanger 26. The first bypass circuit 20 guides hot gas discharged from the compressor 10 to each of the plurality of outdoor heat exchangers 12a, 12b. The plurality of opening and closing devices 11a, 11b are provided in the first bypass circuit 20 corresponding to each of the plurality of outdoor heat exchangers 12a, 12b. The plurality of opening and closing devices 11a, 11b open and close the first bypass circuit 20 corresponding to each of the plurality of outdoor heat exchangers 12a, 12b. The multiple opening and closing devices 15a, 15b are provided in the main circuit 9 between the multiple outdoor heat exchangers 12a, 12b and the load side throttling device 25 in correspondence with the multiple outdoor heat exchangers 12a, 12b, respectively. The multiple opening and closing devices 15a, 15b open and close the main circuit 9 between the multiple outdoor heat exchangers 12a, 12b and the load side throttling device 25 in correspondence with the multiple outdoor heat exchangers 12a, 12b, respectively. The multiple opening and closing devices 11a, 11b are an example of a first opening and closing device. The multiple opening and closing devices 15a, 15b are an example of a second opening and closing device.

[0057] The air conditioner 100 can perform a cooling operation, a heating operation, and a defrosting operation. In the cooling operation, the refrigerant flow switching device 13 is set to a first state, and the multiple outdoor heat exchangers 12a, 12b function as condensers. In the heating operation, the refrigerant flow switching device 13 is set to a second state, and the multiple outdoor heat exchangers 12a, 12b function as evaporators. In the defrosting operation, hot gas is introduced into at least one of the multiple outdoor heat exchangers 12a, 12b via the first bypass circuit 20. The defrosting operation includes a split defrosting operation and a full defrosting operation. In the split defrosting operation, some of the multiple outdoor heat exchangers 12a, 12b are made to function as evaporators, and hot gas is introduced into the other of the multiple outdoor heat exchangers 12a, 12b via the first bypass circuit 20. In the full defrosting operation, hot gas is introduced into all of the outdoor heat exchangers 12a, 12b via the first bypass circuit 20. In both the divided defrosting operation and the full defrosting operation, the refrigerant flow switching device is set to the second state.

[0058] According to this configuration, the refrigerant flow path switching device 13 is maintained in the second state in any of switching from heating operation to defrosting operation, switching from one of the split defrosting operation and the defrosting operation to the other during the defrosting operation, and switching from the defrosting operation to the heating operation. Therefore, it is not necessary to reduce the frequency of the compressor 10, which is required when switching the refrigerant flow path switching device 13. Therefore, the defrosting operation can be started promptly after the heating operation is ended, and the heating operation can be started promptly after the defrosting operation is ended. Therefore, the time during which the heating is stopped can be shortened, and the comfort of the user can be improved. In addition, since the split defrosting operation and the full defrosting operation can be selected, heating and defrosting can be performed efficiently.

[0059] The air conditioner 100 according to this embodiment further includes a control device 60 that controls the refrigerant flow switching device 13. When switching from heating operation to defrosting operation, the control device 60 switches to split defrosting operation if the outdoor air temperature is equal to or higher than a threshold temperature, and switches to full defrosting operation if the outdoor air temperature is below the threshold temperature. With this configuration, defrosting can be performed efficiently.

[0060] Embodiment 2 An explanation will be given of an air conditioner according to embodiment 2. In embodiment 2, only the changes from embodiment 1 will be explained.

[0061] <Configuration of outdoor unit 1> 6 is a refrigerant circuit diagram showing a circuit configuration in a full cooling operation mode of an air conditioner according to this embodiment. In addition to the components of embodiment 1, a second bypass circuit 21 is provided that connects a flow path between the outdoor heat exchanger 12a and the opening / closing device 15a and a flow path between the outdoor heat exchanger 12b and the refrigerant flow switching device 13. An opening / closing valve 16 is provided in the second bypass circuit 21. An opening / closing valve 17 is provided in the flow path between the second bypass circuit 21 and the refrigerant flow switching device 13. The opening / closing valve 16 and the opening / closing valve 17 are controlled by a control device 60.

[0062] <Full cooling operation mode> The refrigerant flow switching device 13 is set to the first state as in the first embodiment. In addition to the first embodiment, the on-off valve 16 is open, the on-off valve 17 is closed, the on-off device 15a is closed, and the on-off device 15b is open. The refrigerant that has passed through the refrigerant flow switching device 13 exchanges heat with the outside air in the outdoor heat exchanger 12a, passes through the on-off valve 16, passes through the outdoor heat exchanger 12b, passes through the on-off device 15b, and flows to the indoor unit 2. By arranging the two outdoor heat exchangers 12a and 12b in series, through which the high-pressure refrigerant flows and which act as condensers, the flow rate in the heat transfer tubes in the heat exchangers is increased, and the effect of promoting heat transfer is obtained.

[0063] <Full heating operation mode> FIG. 7 is a refrigerant circuit diagram showing the circuit configuration in the full heating operation mode of the air conditioner according to this embodiment. The refrigerant flow switching device 13 is set to the second state as in the first embodiment. In addition to the first embodiment, the on-off valve 16 is closed and the on-off valve 17 is open. The refrigerant flowing from the indoor unit 2 is divided and flows into the on-off device 15a and the on-off device 15b. By arranging two outdoor heat exchangers 12a, 12b in parallel, through which the low-pressure refrigerant flows and which act as evaporators, the flow rate in the heat transfer tubes in the heat exchangers is reduced, and the effect of reducing pressure loss is obtained.

[0064] <Split defrost operation mode> 8 is a refrigerant circuit diagram showing a circuit configuration in the split defrost operation mode of an air conditioner according to the present embodiment. The refrigerant flow path switching device 13 is set to the second state as in the first embodiment. In addition to the first embodiment, the on-off valve 16 is closed and the on-off valve 17 is closed. The flow of refrigerant in the split defrost operation mode is the same as in the first embodiment.

[0065] <Full defrost operation mode> 9 is a refrigerant circuit diagram showing the circuit configuration in the full defrost operation mode of an air conditioner according to this embodiment. The refrigerant flow path switching device 13 is set to the second state as in embodiment 1. In addition to embodiment 1, the on-off valve 16 is closed and the on-off valve 17 is closed. The flow of refrigerant in the full defrost operation mode is the same as in embodiment 1.

[0066] As described above, the air conditioning apparatus 100 according to this embodiment further includes the second bypass circuit 21 and the on-off valve 16. The second bypass circuit 21 connects the main circuit 9 between some of the outdoor heat exchangers 12a and the on-off device 15a corresponding to the outdoor heat exchanger 12a, and the main circuit 9 between the other outdoor heat exchanger 12b and the refrigerant flow switching device 13. The on-off valve 16 is provided in the second bypass circuit 21 and opens and closes the second bypass circuit 21. In cooling operation, the outdoor heat exchangers 12a, 12b are connected in series, and in heating operation, the outdoor heat exchangers 12a, 12b are connected in parallel.

[0067] According to this configuration, in the refrigerant flow during cooling operation, the outdoor heat exchangers 12a, 12b through which a high-pressure refrigerant flows are connected in series. This increases the refrigerant flow rate in the heat transfer tubes of the outdoor heat exchangers 12a, 12b, thereby providing the effect of promoting heat transfer. Also, in the refrigerant flow during heating operation, the outdoor heat exchangers 12a, 12b through which a low-pressure refrigerant flows are connected in parallel. This decreases the refrigerant flow rate in the heat transfer tubes of the outdoor heat exchangers 12a, 12b, thereby providing the effect of reducing pressure loss.

[0068] Embodiment 3 An air conditioner according to embodiment 3 will be described. Fig. 10 is a refrigerant circuit diagram showing the circuit configuration of an air conditioner according to this embodiment in a cooling only operation mode. Components having the same functions and actions as those in embodiment 1 or 2 are given the same reference numerals and descriptions thereof will be omitted.

[0069] As shown in Fig. 10, the air conditioner 200 has one outdoor unit 1 which is a heat source unit, multiple indoor units 2a, 2b, 2c, 2d, and a relay unit 3 provided between the outdoor unit 1 and the indoor units 2a to 2d. The outdoor unit 1 and the relay unit 3 are connected by multiple main pipes 5a, 5b through which a refrigerant flows. The relay unit 3 and each of the indoor units 2a to 2d are connected by multiple branch pipes 8a, 8b through which a refrigerant flows. The cold or hot heat generated by the outdoor unit 1 is supplied to each of the indoor units 2a to 2d via the relay unit 3.

[0070] In this embodiment, the outdoor unit 1 and the relay unit 3 are connected using two main pipes 5a, 5b, and the relay unit 3 and each of the indoor units 2a to 2d are connected using two branch pipes 8a, 8b. In this way, the outdoor unit 1 and the relay unit 3, and the relay unit 3 and the indoor units 2a to 2d are connected using two pipes each, so that the installation of the air conditioning apparatus 200 can be easily carried out.

[0071] <Configuration of outdoor unit 1> As in the first embodiment, the outdoor unit 1 has a compressor 10, a refrigerant flow switching device 13, outdoor heat exchangers 12a and 12b, an accumulator 19, opening and closing devices 11a and 11b, opening and closing devices 15a and 15b, and a heat source side blower 18. The compressor 10, the refrigerant flow switching device 13, the outdoor heat exchangers 12a and 12b, the accumulator 19, the opening and closing devices 11a and 11b, and the opening and closing devices 15a and 15b are connected by refrigerant piping 4.

[0072] Furthermore, a first connection pipe 22a, a second connection pipe 22b, and backflow prevention devices 14a, 14b, 14c, and 14d are provided in the outdoor unit 1. In this example, check valves are used as the backflow prevention devices 14a to 14d.

[0073] The first connection pipe 22a and the second connection pipe 22b are connected as follows in the refrigerant flow in the cooling only operation mode and the cooling main operation mode. One end of the first connection pipe 22a is connected to a refrigerant pipe downstream of the outdoor heat exchangers 12a, 12b and the opening and closing devices 15a, 15b and upstream of the main pipe 5b. The other end of the first connection pipe 22a is connected to a refrigerant pipe downstream of the main pipe 5a and upstream of the refrigerant flow switching device 13. One end of the second connection pipe 22b is connected to a refrigerant pipe downstream of the outdoor heat exchangers 12a, 12b and the opening and closing devices 15a, 15b and upstream of one end of the first connection pipe 22a. The other end of the second connection pipe 22b is connected to a refrigerant pipe downstream of the main pipe 5a and upstream of the other end of the first connection pipe 22a.

[0074] The backflow prevention device 14a is provided on the refrigerant piping between one end of the first connection piping 22a and one end of the second connection piping 22b. The backflow prevention device 14a prevents high-temperature, high-pressure gas refrigerant from flowing back from the first connection piping 22a to the outdoor heat exchangers 12a and 12b in the heating only operation mode and the heating main operation mode.

[0075] The backflow prevention device 14b is provided on the first connection pipe 22a. The backflow prevention device 14b prevents high-pressure liquid or gas-liquid two-phase refrigerant from flowing back from the refrigerant pipe on the outlet side of the backflow prevention device 14a to the accumulator 19 in the cooling only operation mode and the cooling main operation mode.

[0076] The backflow prevention device 14c is provided on the second connection pipe 22b. The backflow prevention device 14c prevents high-pressure liquid or gas-liquid two-phase refrigerant from flowing back from the refrigerant pipe on the inlet side of the backflow prevention device 14a to the accumulator 19 in the cooling only operation mode and the cooling main operation mode.

[0077] The backflow prevention device 14d is provided in the refrigerant piping between the other end of the first connection piping 22a and the other end of the second connection piping 22b. The backflow prevention device 14d prevents high-temperature, high-pressure gas refrigerant from flowing back from the flow path on the discharge side of the compressor 10 to the main pipe 5a in the heating only operation mode and the heating main operation mode.

[0078] In this way, by providing the backflow prevention devices 14a to 14d, the flow of the refrigerant flowing into the relay unit 3 can be made to flow in a constant direction regardless of the operation required by the indoor unit 2. In this example, check valves are used as the backflow prevention devices 14a to 14d, but the configuration of the backflow prevention devices 14a to 14d is not limited to this as long as it can prevent the backflow of the refrigerant. For example, an opening and closing device or a throttling device having a full closing function can also be used as the backflow prevention devices 14a to 14d.

[0079] <Configuration of indoor units 2a to 2d> The indoor units 2a to 2d have the same configuration, for example. The indoor unit 2a includes an indoor heat exchanger 26a and a load side throttling device 25a. The indoor unit 2b includes an indoor heat exchanger 26b and a load side throttling device 25b. The indoor unit 2c includes an indoor heat exchanger 26c and a load side throttling device 25c. The indoor unit 2d includes an indoor heat exchanger 26d and a load side throttling device 25d.

[0080] Each of the indoor heat exchangers 26a to 26d is connected to the outdoor unit 1 via the branch pipes 8a, 8b, the relay unit 3, and the main pipes 5a, 5b. In each of the indoor heat exchangers 26a to 26d, air for heating or air for cooling is generated by heat exchange between the air supplied by a load side blower (not shown) and the refrigerant to be supplied to the indoor space. The load side throttling devices 25a to 25d are capable of variably adjusting the opening degree, for example, continuously or in multiple steps. For example, an electronic expansion valve or the like is used as the load side throttling devices 25a to 25d. The load side throttling devices 25a to 25d have the functions of a pressure reducing valve and an expansion valve, and reduce the pressure of the refrigerant to expand it. The load side throttling devices 25a to 25d are provided upstream of the indoor heat exchangers 26a to 26d in the flow of the refrigerant in the cooling operation mode (for example, the full cooling operation mode).

[0081] The indoor units 2a to 2d are provided with first load temperature sensors 31a, 31b, 31c, and 31d and second load temperature sensors 32a, 32b, 32c, and 32d. The first load temperature sensors 31a to 31d detect the temperature of the refrigerant flowing into each of the indoor heat exchangers 26a to 26d. The second load temperature sensors 32a to 32d detect the temperature of the refrigerant flowing out from each of the indoor heat exchangers 26a to 26d. The first load temperature sensors 31a to 31d and the second load temperature sensors 32a to 32d are made of, for example, a thermistor. The first load temperature sensors 31a to 31d and the second load temperature sensors 32a to 32d output detection signals to the control device 60.

[0082] Although four indoor units 2a to 2d are illustrated in FIG. 10, the number of connected indoor units may be two, three, five or more.

[0083] <Configuration of Repeater 3> The relay unit 3 has a gas-liquid separator 29, a first relay throttling device 30, a second relay throttling device 27, a plurality of relay first opening and closing devices 23a, 23b, 23c, and 23d, and a plurality of relay second opening and closing devices 24a, 24b, 24c, and 24d.

[0084] In a mixed cooling and heating operation mode with a large cooling load, gas-liquid separator 29 separates the high-pressure gas-liquid two-phase refrigerant generated in outdoor unit 1 into liquid refrigerant and gas refrigerant. Gas-liquid separator 29 causes the separated liquid refrigerant to flow into the lower piping in the figure to supply cold heat to some of the indoor units, and causes the separated gas refrigerant to flow into the upper piping in the figure to supply hot heat to some of the other indoor units. Gas-liquid separator 29 is provided at the inlet of relay unit 3 in the refrigerant flow.

[0085] The first intermediate throttling device 30 functions as a pressure reducing valve and an on-off valve. The first intermediate throttling device 30 reduces the pressure of the liquid refrigerant to a predetermined pressure, and opens and closes the flow path of the liquid refrigerant. The first intermediate throttling device 30 is capable of variably adjusting the opening degree, for example, continuously or in multiple stages. For example, an electronic expansion valve or the like is used as the first intermediate throttling device 30. The first intermediate throttling device 30 is provided in the piping through which the liquid refrigerant flows out from the gas-liquid separator 29.

[0086] The second intermediate throttling device 27 has the functions of a pressure reducing valve and an on-off valve. The second intermediate throttling device 27 opens and closes the refrigerant flow path in the heating only operation mode, and adjusts the bypass liquid flow rate according to the indoor load in the heating main operation mode. The second intermediate throttling device 27 is capable of variably adjusting the opening degree, for example, continuously or in multiple stages. For example, an electronic expansion valve or the like is used as the second intermediate throttling device 27. The second intermediate throttling device 27 is provided on the inlet side of the low-pressure side flow path in the heating only operation mode and the heating main operation mode.

[0087] The multiple relay unit first opening and closing devices 23a-23d are provided for each of the multiple indoor units 2a-2d (a total of four in this example). The relay unit first opening and closing devices 23a-23d open and close the flow path of the high-temperature and high-pressure gas refrigerant supplied to the indoor units 2a-2d, respectively. The relay unit first opening and closing devices 23a-23d are composed of, for example, solenoid valves. The relay unit first opening and closing devices 23a-23d are each connected to the gas side piping of the gas-liquid separator 29. Note that the relay unit first opening and closing devices 23a-23d may be a throttle device having a full closing function as long as they can open and close the flow path.

[0088] The multiple relay unit second opening and closing devices 24a-24d are provided for each of the multiple indoor units 2a-2d (a total of four in this example). The relay unit second opening and closing devices 24a-24d open and close the flow path of the low-temperature, low-pressure gas refrigerant flowing out from the indoor units 2a-2d, respectively. The relay unit second opening and closing devices 24a-24d are composed of, for example, solenoid valves. The relay unit second opening and closing devices 24a-24d are each connected to a low-pressure pipe that is connected to the outlet side of the relay unit 3. In addition, the relay unit second opening and closing devices 24a-24d may be a throttling device having a full closing function as long as they can open and close the flow path.

[0089] Furthermore, an inlet side pressure sensor 33 is provided on the inlet side of the first intermediate throttling device 30 in the relay unit 3. The inlet side pressure sensor 33 detects the pressure of the high-pressure refrigerant. An outlet side pressure sensor 34 is provided on the outlet side of the first intermediate throttling device 30. The outlet side pressure sensor 34 detects the intermediate pressure of the liquid refrigerant on the outlet side of the first intermediate throttling device 30 in the cooling-dominated operation mode.

[0090] In the air conditioner 200 shown in FIG. 10, the control device 60 also controls the operation of the entire air conditioner 200 based on detection signals from various sensors and instructions from a remote controller. For example, the control device 60 controls the drive frequency of the compressor 10, the rotation speed (including ON and OFF) of the blower, switching of the refrigerant flow switching device 13, opening and closing of the opening and closing devices 11a and 11b, the opening degree of the load side throttling device 25, and opening and closing of the relay first opening and closing devices 23a to 23d. The control device 60 also controls the opening and closing of the relay second opening and closing devices 24a to 24d, the opening and closing of the first relay throttling device 30, and the opening and closing of the second relay throttling device 27. This allows each operation mode to be executed, which will be described later. Note that the control device 60 in this example is provided in the outdoor unit 1, but the control device 60 may be provided in the indoor units 2a to 2d, or in the relay unit 3, or may be provided for each unit (for example, the outdoor unit 1, the indoor units 2a to 2d, and the relay unit 3).

[0091] We will now explain each operation mode executed by the air conditioner 200. The control device 60 is capable of performing cooling or heating operation independently in each of the indoor units 2a to 2d based on instructions from each of the indoor units 2a to 2d. In other words, the air conditioner 200 can perform the same operation (cooling operation or heating operation) in all of the indoor units 2a to 2d, and can also perform different operations in each of the indoor units 2a to 2d.

[0092] The operation modes executed by the air conditioner 200 are roughly classified into a cooling operation mode and a heating operation mode. The cooling operation mode includes a cooling only operation mode and a cooling-dominated operation mode. The heating operation mode includes a heating only operation mode and a heating-dominated operation mode.

[0093] The full cooling operation mode is an operation mode in which all of the indoor units 2a to 2d that are not stopped perform cooling operation. That is, in the full cooling operation mode, all of the indoor heat exchangers 26a to 26d that are not stopped function as evaporators. The cooling-dominated operation mode is a mixed cooling and heating operation mode in which some of the indoor units 2a to 2d perform cooling operation and some of the other indoor units 2a to 2d perform heating operation, and is an operation mode in which the cooling load is greater than the heating load. That is, in the cooling-dominated operation mode, some of the indoor heat exchangers 26a to 26d function as evaporators, and some of the other indoor heat exchangers 26a to 26d function as condensers.

[0094] The full heating operation mode is an operation mode in which all of the indoor units 2a-2d that are not stopped perform heating operation. That is, in the full heating operation mode, all of the indoor heat exchangers 26a-26d that are not stopped function as condensers. The heating-dominated operation mode is a mixed cooling and heating operation mode in which some of the indoor units 2a-2d perform cooling operation and other some of the indoor units 2a-2d perform heating operation, and is an operation mode in which the heating load is greater than the cooling load. Each operation mode will be described below.

[0095] <Full cooling operation mode> The cooling only operation mode executed by the air conditioner 200 will be described with reference to Fig. 10. In Fig. 10, the cooling only operation mode will be described using as an example a case in which a cooling load is generated only in the indoor heat exchanger 26a and the indoor heat exchanger 26b. Note that in Fig. 9, the flow direction of the refrigerant is indicated by solid arrows.

[0096] In the case of the cooling only operation mode, the control device 60 switches the refrigerant flow switching device 13 of the outdoor unit 1 to a first state in which the refrigerant discharged from the compressor 10 flows into the outdoor heat exchangers 12a, 12b.

[0097] First, low-temperature, low-pressure refrigerant is compressed by the compressor 10 and becomes a high-temperature, high-pressure gas refrigerant, which is then discharged. The high-temperature, high-pressure gas refrigerant discharged from the compressor 10 flows into the outdoor heat exchangers 12a, 12b via the refrigerant flow switching device 13. Then, in the outdoor heat exchangers 12a, 12b, the refrigerant becomes a high-pressure liquid refrigerant while dissipating heat to the outdoor air. The high-pressure liquid refrigerant flowing out of the outdoor heat exchangers 12a, 12b flows out of the outdoor unit 1 through the backflow prevention device 14a, and flows into the relay unit 3 through the main pipe 5b.

[0098] The high-pressure liquid refrigerant that flows into the relay unit 3 passes through the gas-liquid separator 29, the first relay throttling device 30, and the branch pipe 8b, and is expanded in the load side throttling devices 25a and 25b, becoming a low-temperature, low-pressure, gas-liquid two-phase refrigerant.

[0099] The refrigerant in a gas-liquid two-phase state expanded by the load-side throttle devices 25a and 25b flows into the indoor heat exchangers 26a and 26b acting as evaporators, respectively, and becomes a low-temperature, low-pressure gas refrigerant while absorbing heat from the indoor air and cooling the indoor air. At this time, the opening degree of the load-side throttle device 25a is controlled so that the superheat obtained as the difference between the temperature detected by the load-side first temperature sensor 31a and the temperature detected by the load-side second temperature sensor 32a is constant. Similarly, the opening degree of the load-side throttle device 25b is controlled so that the superheat obtained as the difference between the temperature detected by the load-side first temperature sensor 31b and the temperature detected by the load-side second temperature sensor 32b is constant.

[0100] The gas refrigerant flowing out from the indoor heat exchangers 26a, 26b passes through the branch pipe 8a and the relay second opening and closing devices 24a, 24b, flows out from the relay unit 3, and passes through the main pipe 5a to flow again into the outdoor unit 1. The refrigerant that has flowed into the outdoor unit 1 passes through the backflow prevention device 14d, the refrigerant flow switching device 13, and the accumulator 19, and is sucked into the compressor 10 again.

[0101] In the indoor heat exchanger 26c and the indoor heat exchanger 26d, which have no heat load, there is no need to flow refrigerant, and the corresponding load side throttling device 25c and the load side throttling device 25d are in a closed state. When a cold heat load occurs in the indoor heat exchanger 26c or the indoor heat exchanger 26d, the load side throttling device 25c or the load side throttling device 25d is opened to circulate the refrigerant. At this time, the opening degree of the load side throttling device is controlled so that the superheat obtained as the difference between the temperature detected by the load side first temperature sensor and the temperature detected by the load side second temperature sensor is constant, similar to the above-mentioned load side throttling device 25a or the load side throttling device 25b.

[0102] <Cooling-dominant operation mode> Fig. 11 is a refrigerant circuit diagram showing the circuit configuration of the air conditioner in the cooling-dominated operation mode according to this embodiment. In Fig. 11, the direction of refrigerant flow is indicated by solid arrows. Here, it is assumed that a cold heat load occurs only in the indoor heat exchanger 26a, and a hot heat load occurs only in the indoor heat exchanger 26b.

[0103] In the cooling-dominant operation mode, the control device 60 switches the refrigerant flow switching device 13 to a first state in which the refrigerant discharged from the compressor 10 flows into the outdoor heat exchangers 12a, 12b.

[0104] First, low-temperature, low-pressure refrigerant is compressed by the compressor 10 and becomes a high-temperature, high-pressure gas refrigerant, which is then discharged. The high-temperature, high-pressure gas refrigerant discharged from the compressor 10 flows into the outdoor heat exchangers 12a, 12b via the refrigerant flow switching device 13. Then, in the outdoor heat exchangers 12a, 12b, the refrigerant becomes a gas-liquid two-phase refrigerant while dissipating heat to the outdoor air. The refrigerant flowing out of the outdoor heat exchangers 12a, 12b flows into the relay unit 3 through the backflow prevention device 14a and the main pipe 5b.

[0105] The gas-liquid two-phase refrigerant flowing into the relay 3 is separated into a high-pressure gas refrigerant and a high-pressure liquid refrigerant by the gas-liquid separator 29. This high-pressure gas refrigerant flows through the relay first opening and closing device 23b and the branch pipe 8a, and then flows into the indoor heat exchanger 26b acting as a condenser. The high-pressure gas refrigerant dissipates heat into the indoor air, heating the indoor air and becoming a liquid refrigerant. At this time, the opening degree of the load side throttle device 25b is controlled so that the subcooling obtained as the difference between the value obtained by converting the pressure detected by the inlet side pressure sensor 33 into a saturation temperature and the temperature detected by the load side first temperature sensor 31b is constant. The liquid refrigerant flowing out from the indoor heat exchanger 26b is expanded by the load side throttle device 25b and flows through the branch pipe 8b.

[0106] Thereafter, the medium-pressure liquid refrigerant that has been separated in the gas-liquid separator 29 and then expanded to an intermediate pressure in the first intermediate throttling device 30 joins with the liquid refrigerant that has passed through the load side throttling device 25b. At this time, the opening degree of the first intermediate throttling device 30 is controlled so that the pressure difference between the pressure detected by the inlet side pressure sensor 33 and the pressure detected by the outlet side pressure sensor 34 becomes a predetermined pressure difference (for example, 0.3 MPa).

[0107] The merged liquid refrigerant flows into the indoor unit 2a via the branch pipe 8b. The refrigerant in a gas-liquid two-phase state expanded by the load-side throttling device 25a of the indoor unit 2a flows into the indoor heat exchanger 26a acting as an evaporator, and becomes a low-temperature, low-pressure gas refrigerant while cooling the indoor air by absorbing heat from the indoor air. At this time, the opening degree of the load-side throttling device 25a is controlled so that the superheat obtained as the difference between the temperature detected by the load-side first temperature sensor 31a and the temperature detected by the load-side second temperature sensor 32a is constant. The gas refrigerant flowing out of the indoor heat exchanger 26a flows out of the relay unit 3 via the branch pipe 8a and the relay unit second opening and closing device 24a.

[0108] The gas refrigerant flowing out from the relay unit 3 passes through the main pipe 5a and flows again into the outdoor unit 1. The refrigerant flowing into the outdoor unit 1 passes through the backflow prevention device 14d, passes through the refrigerant flow switching device 13, and the accumulator 19, and is sucked again into the compressor 10.

[0109] In the indoor heat exchanger 26c and the indoor heat exchanger 26d, which have no heat load, there is no need to flow refrigerant, and the corresponding load side throttling device 25c and the load side throttling device 25d are in a closed state. When a cold heat load occurs in the indoor heat exchanger 26c or the indoor heat exchanger 26d, the load side throttling device 25c or the load side throttling device 25d is opened to circulate the refrigerant. At this time, the opening degree of the load side throttling device is controlled so that the superheat obtained as the difference between the temperature detected by the load side first temperature sensor and the temperature detected by the load side second temperature sensor is constant, similar to the above-mentioned load side throttling device 25a.

[0110] When a heating load occurs in the indoor heat exchanger 26c or the indoor heat exchanger 26d, the load side throttling device 25c or the load side throttling device 25d is opened to circulate the refrigerant. At this time, the opening degree of the load side throttling device is controlled, similarly to the above-mentioned load side throttling device 25b, so that the subcooling obtained as the difference between the value obtained by converting the pressure detected by the inlet side pressure sensor 33 into the saturation temperature and the temperature detected by the load side first temperature sensor is constant.

[0111] <Full heating operation mode> Fig. 12 is a refrigerant circuit diagram showing the circuit configuration of the air conditioner in the full heating operation mode according to this embodiment. In Fig. 12, the direction of refrigerant flow is indicated by solid arrows. Here, it is assumed that a heating load is generated only in the indoor heat exchanger 26a and the indoor heat exchanger 26b.

[0112] In the case of the full heating operation mode, the control device 60 switches the refrigerant flow switching device 13 to a second state in which the refrigerant discharged from the compressor 10 flows into the relay unit 3 without passing through the outdoor heat exchangers 12a and 12b.

[0113] First, a low-temperature, low-pressure refrigerant is compressed by the compressor 10 and discharged as a high-temperature, high-pressure gas refrigerant. The high-temperature, high-pressure gas refrigerant discharged from the compressor 10 passes through the refrigerant flow switching device 13 and the backflow prevention device 14b, and flows out of the outdoor unit 1. The high-temperature, high-pressure gas refrigerant flowing out of the outdoor unit 1 flows into the relay unit 3 through the main pipe 5b.

[0114] The high-temperature, high-pressure gas refrigerant that has flowed into the relay unit 3 flows through the gas-liquid separator 29, the relay unit first opening and closing devices 23a and 23b, and the branch pipe 8a, and then flows into the indoor heat exchanger 26a and the indoor heat exchanger 26b, which act as condensers. The refrigerant that has flowed into the indoor heat exchanger 26a and the indoor heat exchanger 26b dissipates heat to the indoor air, heating the indoor air and becoming a liquid refrigerant. The liquid refrigerant that has flowed out from the indoor heat exchanger 26a and the indoor heat exchanger 26b is expanded by the load-side throttling devices 25a and 25b, respectively, and flows back into the outdoor unit 1 through the branch pipe 8b, the second relay throttling device 27, which is controlled to be in an open state, and the main pipe 5a. At this time, the opening degree of the load-side throttling device 25a is controlled so that the subcooling obtained as the difference between the value obtained by converting the pressure detected by the inlet-side pressure sensor 33 into the saturation temperature and the temperature detected by the load-side first temperature sensor 31a is constant. Similarly, the opening degree of the load side throttle device 25b is controlled so that the subcooling obtained as the difference between the value obtained by converting the pressure detected by the inlet side pressure sensor 33 into a saturation temperature and the temperature detected by the load side first temperature sensor 31b remains constant.

[0115] The refrigerant that flows into the outdoor unit 1 passes through the backflow prevention device 14c and absorbs heat from the outdoor air in the outdoor heat exchangers 12a, 12b, becoming a low-temperature, low-pressure gas refrigerant, and is then sucked back into the compressor 10 via the refrigerant flow switching device 13 and the accumulator 19.

[0116] In the indoor heat exchanger 26c and the indoor heat exchanger 26d, which have no heat load, there is no need to flow refrigerant, and the corresponding load side throttling device 25c and the load side throttling device 25d are in a closed state. When a warm heat load is generated in the indoor heat exchanger 26c or the indoor heat exchanger 26d, the load side throttling device 25c or the load side throttling device 25d is opened to circulate the refrigerant. At this time, the opening degree of the load side throttling device is controlled so that the subcooling obtained as the difference between the value obtained by converting the pressure detected by the inlet side pressure sensor 33 into the saturation temperature and the temperature detected by the load side first temperature sensor is constant, similar to the above-mentioned load side throttling devices 25a and 25b.

[0117] <Heating-dominant operation mode> Fig. 13 is a refrigerant circuit diagram showing the circuit configuration of the air conditioner in the heating-dominated operation mode according to this embodiment. In Fig. 13, the direction of refrigerant flow is indicated by solid arrows. Here, it is assumed that a cold heat load occurs only in the indoor heat exchanger 26a, and a hot heat load occurs only in the indoor heat exchanger 26b.

[0118] In the heating-dominant operation mode, the control device 60 switches the refrigerant flow switching device 13 to a second state in which the refrigerant discharged from the compressor 10 flows into the relay unit 3 without passing through the outdoor heat exchangers 12a and 12b.

[0119] Low-temperature, low-pressure refrigerant is compressed by the compressor 10 and discharged as high-temperature, high-pressure gas refrigerant. The high-temperature, high-pressure gas refrigerant discharged from the compressor 10 passes through the refrigerant flow switching device 13 and the backflow prevention device 14b, and flows out of the outdoor unit 1. The high-temperature, high-pressure gas refrigerant flowing out of the outdoor unit 1 flows into the relay unit 3 through the main pipe 5b.

[0120] The high-temperature, high-pressure gas refrigerant that flows into the relay unit 3 flows through the gas-liquid separator 29, the relay unit first opening and closing device 23b, and the branch pipe 8a, and then flows into the indoor heat exchanger 26b, which acts as a condenser. The refrigerant that flows into the indoor heat exchanger 26b becomes liquid refrigerant while heating the indoor air by dissipating heat to the indoor air. The liquid refrigerant that flows out of the indoor heat exchanger 26b is expanded by the load side throttling device 25b and flows into the relay unit 3 through the branch pipe 8b. After that, most of it passes through the branch pipe 8b, and is expanded by the load side throttling device 25a, becoming a low-temperature, low-pressure, gas-liquid two-phase refrigerant. The remaining part of the liquid refrigerant is expanded by the second relay throttling device 27, which is also used as a bypass, becomes a liquid or gas-liquid two-phase refrigerant, and flows into the low-pressure piping on the outlet side of the relay unit 3.

[0121] The refrigerant in a gas-liquid two-phase state expanded by the load-side throttling device 25a flows into the indoor heat exchanger 26a acting as an evaporator, and becomes a gas refrigerant while absorbing heat from the indoor air and cooling the indoor air. The gas refrigerant flowing out of the indoor heat exchanger 26a passes through the branch pipe 8a and the second relay opening / closing device 24a, and merges with the remaining part of the refrigerant flowing out of the second relay throttling device 27. The merged refrigerant flows out of the relay device 3, passes through the main pipe 5a, and flows back into the outdoor unit 1. The refrigerant flowing into the outdoor unit 1 passes through the backflow prevention device 14c, and becomes a low-temperature, low-pressure gas refrigerant while absorbing heat from the outdoor air in the outdoor heat exchangers 12a and 12b. This gas refrigerant passes through the refrigerant flow switching device 13 and the accumulator 19, and is sucked back into the compressor 10.

[0122] At this time, the opening degree of the load side throttle device 25b is controlled so that the subcooling obtained as the difference between the value obtained by converting the pressure detected by the inlet side pressure sensor 33 into the saturation temperature and the temperature detected by the load side first temperature sensor 31b is constant. On the other hand, the opening degree of the load side throttle device 25a is controlled so that the superheat obtained as the difference between the temperature detected by the load side first temperature sensor 31a and the temperature detected by the load side second temperature sensor 32b is constant.

[0123] In addition, the opening degree of the second intermediate throttle device 27 is controlled so that the pressure difference between the pressure detected by the inlet side pressure sensor 33 and the pressure detected by the outlet side pressure sensor 34 becomes a predetermined pressure difference (for example, 0.3 MPa).

[0124] In the indoor heat exchanger 26c and the indoor heat exchanger 26d, which have no heat load, there is no need to flow refrigerant, and the corresponding load side throttling device 25c and the load side throttling device 25d are in a closed state. When a cold heat load occurs in the indoor heat exchanger 26c or the indoor heat exchanger 26d, the load side throttling device 25c or the load side throttling device 25d is opened to circulate the refrigerant. At this time, the opening degree of the load side throttling device is controlled so that the superheat obtained as the difference between the temperature detected by the load side first temperature sensor and the temperature detected by the load side second temperature sensor is constant, similar to the above-mentioned load side throttling device 25a.

[0125] When a heating load occurs in the indoor heat exchanger 26c or the indoor heat exchanger 26d, the load side throttling device 25c or the load side throttling device 25d is opened to circulate the refrigerant. At this time, the opening degree of the load side throttling device is controlled, similarly to the above-mentioned load side throttling device 25b, so that the subcooling obtained as the difference between the value obtained by converting the pressure detected by the inlet side pressure sensor 33 into the saturation temperature and the temperature detected by the load side first temperature sensor is constant.

[0126] <Split defrost operation mode> Fig. 14 is a refrigerant circuit diagram showing a circuit configuration in a split defrost operation mode of an air conditioner according to this embodiment. In Fig. 14, the refrigerant flow direction is indicated by solid arrows. Fig. 14 shows the split defrost operation mode when defrosting the outdoor heat exchanger 12b.

[0127] In the split defrost operation mode, the refrigerant flow switching device 13 is maintained in the second state, which is the same as in the full heating operation mode and the split heating operation mode. The opening / closing device 11a is set to the closed state, the opening / closing device 11b is set to the open state, the opening / closing device 15a is set to the open state, and the opening / closing device 15b is set to the closed state. As a result, a part of the refrigerant discharged from the compressor 10 flows into the outdoor heat exchanger 12b, and the outdoor heat exchanger 12b is defrosted.

[0128] <Full defrost operation mode> Fig. 15 is a refrigerant circuit diagram showing the circuit configuration in the full defrost operation mode of an air conditioner according to the present embodiment. In Fig. 15, the flow direction of the refrigerant is indicated by solid arrows.

[0129] In the full defrost operation mode, the refrigerant flow switching device 13 is maintained in the second state, which is the same as in the full heating operation mode and the split heating operation mode. The load side expansion devices 25a to 25d are switched to the closed state to block the refrigerant. The opening and closing devices 11a and 11b are switched to the open state to allow the refrigerant to flow. The heat source side blower 18 and the load side blower (not shown) are stopped. By switching the opening and closing devices 11a and 11b to the open state and then closing the load side expansion devices 25a to 25d, it is possible to prevent the refrigerant flow path from being blocked and suppress an increase in pressure.

[0130] The flow path of the high-temperature, high-pressure gas refrigerant discharged from the compressor 10 is connected to the flow path of the indoor heat exchangers 26a-26d via the backflow prevention device 14b, the main pipe 5b, the gas-liquid separator 29, the first relay opening and closing devices 23a-23d, and the branch pipe 8a. The refrigerant that existed during the heating operation mode is retained between the load side throttling devices 25a-25d in the closed state and the gas-liquid separator 29 due to the pressure of the high-temperature, high-pressure gas refrigerant discharged from the compressor 10, which is higher than the pressure of the indoor heat exchangers 26a-26d.

[0131] In the heating operation mode, since the indoor heat exchangers 26a to 26d operate as condensers, a large amount of refrigerant is present in the indoor heat exchangers 26a to 26d. As a result, the surplus refrigerant can be stored in the indoor heat exchangers 26a to 26d, and the amount of surplus refrigerant remaining in the accumulator 19 can be reduced.

[0132] In this embodiment, as in the first and second embodiments, during the defrosting operation mode, the amount of excess refrigerant in the accumulator 19 can be reduced by retaining the excess refrigerant in the indoor heat exchangers 26a-26d. If the lengths of the main pipes 5a, 5b are long due to restrictions on the installation environment of the air conditioning apparatus 200, the amount of excess refrigerant increases. For this reason, by retaining the excess refrigerant in the indoor heat exchangers 26a-26d, it is possible to prevent liquid refrigerant from overflowing from the accumulator 19 and flowing into the suction section of the compressor 10.

[0133] In addition, the refrigerant density does not decrease due to pressure loss, and high-density gas refrigerant can flow into the suction section of the compressor 10. This increases the amount of refrigerant circulating discharged from the compressor 10, improving the defrosting capacity. Also, immediately after switching from the defrosting operation mode to the heating operation mode, the excess refrigerant held in the indoor heat exchangers 26a to 26d can be evaporated in the outdoor heat exchangers 12a and 12b. This allows more gas refrigerant to flow into the suction section of the compressor 10 than in the case where the excess refrigerant does not flow into the outdoor heat exchangers 12a and 12b, increasing the amount of refrigerant circulating in the compressor 10. This allows the supply amount of high-temperature, high-pressure gas refrigerant flowing into the indoor heat exchangers 26a to 26d to be increased, which speeds up the start of the heating operation and improves user comfort.

[0134] In the defrosting operation mode of the third embodiment, the first relay throttling device 30, the relay second opening and closing devices 24a to 24d, and the load side throttling devices 25a to 25d may be closed. This prevents the high-temperature, high-pressure gas refrigerant discharged from the compressor 10 from condensing and staying in the refrigerant piping including the main pipe 5a between the outlet side of the relay 3 and the backflow prevention device 14c, which has a lower temperature than the refrigerant discharged from the compressor 10. Therefore, a large amount of high-temperature, high-pressure gas refrigerant discharged from the compressor 10 can be made to flow into the outdoor heat exchangers 12a and 12b, improving the defrosting capacity. Also, instead of the load side throttling devices 25a to 25d, the second relay throttling device 27 may be closed and the load side throttling devices 25a to 25d may be opened, and the same effect is obtained.

[0135] In the defrosting operation mode of embodiment 3, the first relay throttle device 30, the second relay throttle device 27, the relay first opening and closing devices 23a to 23d, the relay second opening and closing devices 24a to 24d, and the load side throttle devices 25a to 25d may all be closed, and the same effect will be achieved.

[0136] Embodiment 4 An explanation will be given of an air conditioner according to embodiment 4. In embodiment 4, only the changes from embodiment 3 will be explained.

[0137] <Configuration of outdoor unit 1> FIG. 16 is a refrigerant circuit diagram showing a circuit configuration in a cooling-dominated operation mode of an air conditioner according to this embodiment. FIG. 17 is a refrigerant circuit diagram showing a circuit configuration in a cooling-dominated operation mode of an air conditioner according to this embodiment. In addition to the components of the third embodiment, a second bypass circuit 21 is provided that connects a flow path between the outdoor heat exchanger 12a and the opening / closing device 15a and a flow path between the outdoor heat exchanger 12b and the refrigerant flow switching device 13. An opening / closing valve 16 is provided in the second bypass circuit 21. An opening / closing valve 17 is provided in the flow path between the second bypass circuit 21 and the refrigerant flow switching device 13. The opening / closing valve 16 and the opening / closing valve 17 are controlled by a control device 60.

[0138] <Cooling operation mode> In both the cooling only operation mode and the cooling main operation mode, the refrigerant flow switching device 13 is set to the first state. In addition to the first embodiment, the on-off valve 16 is open, the on-off valve 17 is closed, the on-off device 15a is closed, and the on-off device 15b is open. The refrigerant that has passed through the refrigerant flow switching device 13 exchanges heat with the outside air in the outdoor heat exchanger 12a, passes through the on-off valve 16, passes through the outdoor heat exchanger 12b, passes through the on-off device 15b, and flows to the indoor unit 2. By arranging the two outdoor heat exchangers 12a and 12b in series, through which the high-pressure refrigerant flows and which function as condensers, the flow rate in the heat transfer tubes in the heat exchangers is increased, and the effect of promoting heat transfer is obtained.

[0139] <Heating operation mode> FIG. 18 is a refrigerant circuit diagram showing a circuit configuration in the heating-dominated operation mode of an air conditioner according to this embodiment. FIG. 19 is a refrigerant circuit diagram showing a circuit configuration in the heating-dominated operation mode of an air conditioner according to this embodiment. In both the heating-dominated operation mode and the heating-dominated operation mode, the refrigerant flow switching device 13 is set to the second state. In addition to the first embodiment, the on-off valve 16 is closed and the on-off valve 17 is open. The refrigerant flowing from the indoor unit 2 is divided and flows into the on-off device 15a and the on-off device 15b. By arranging two outdoor heat exchangers 12a and 12b in parallel, through which low-pressure refrigerant flows and which function as evaporators, the flow rate in the heat transfer tubes in the heat exchangers is reduced, and the effect of reducing pressure loss is obtained.

[0140] <Split defrost operation mode> Fig. 20 is a refrigerant circuit diagram showing a circuit configuration in the split defrost operation mode of the air conditioner according to this embodiment. In the split defrost operation mode, like the full heating operation mode and the heating-dominant operation mode, the refrigerant flow path switching device 13 is set to the second state. In addition to the first embodiment, the on-off valve 16 is closed and the on-off valve 17 is closed.

[0141] <Full defrost operation mode> Fig. 21 is a refrigerant circuit diagram showing a circuit configuration in the full defrost operation mode of the air conditioner according to this embodiment. In the full defrost operation mode, like the full heating operation mode and the heating-dominant operation mode, the refrigerant flow path switching device 13 is set to the second state. In addition to the first embodiment, the on-off valve 16 is closed and the on-off valve 17 is closed.

[0142] Embodiment 5. An air conditioner according to embodiment 5 will be described. Fig. 22 is a refrigerant circuit diagram showing the circuit configuration of an air conditioner according to this embodiment. In embodiment 5, the same explanation as in embodiments 1 to 4 will be omitted, and only the characteristic parts will be described.

[0143] As shown in FIG. 22, the relay unit 3 of the air conditioner 300 has relay heat exchangers 35a and 35b that exchange heat between a refrigerant and a heat medium such as water or brine. A liquid heat medium such as water or brine is used as the heat medium. The indoor units 2a to 2d have indoor heat exchangers 26a to 26d, respectively. The indoor heat exchangers 26a to 26d are connected to the relay heat exchanger 35a and the relay heat exchanger 35b via a heat medium pipe 70 that circulates the heat medium. As a result, a heat medium circuit 102 is formed between the relay unit 3 and the indoor units 2a to 2d.

[0144] The outdoor unit 1 and the relay unit 3 are connected via main pipes 5a and 5b through which a refrigerant flows. The main pipes 5a and 5b are connected to a relay heat exchanger 35a and a relay heat exchanger 35b provided in the relay unit 3. The relay unit 3 and each of the indoor units 2a to 2b are connected via heat medium pipes 70 through which a heat medium flows. The heat medium pipes are connected to the relay heat exchanger 35a and the relay heat exchanger 35b.

[0145] The relay unit 3 has two relay heat exchangers 35a, 35b, two relay throttling devices 38a, 38b, two opening and closing devices 36a, 36b, and two relay flow path switching devices 39a, 39b as components of a refrigerant circuit 101. The relay unit 3 has two pumps 41a, 41b, four first heat medium flow path switching devices 50a to 50d, four second heat medium flow path switching devices 51a to 51d, and four heat medium flow control devices 52a to 52d as components of a heat medium circuit 102.

[0146] The relay heat exchanger 35a and the relay heat exchanger 35b function as a condenser or an evaporator. The relay heat exchanger 35a and the relay heat exchanger 35b exchange heat between the refrigerant and the heat medium, and transfer the cold heat or hot heat generated in the outdoor unit 1 and stored in the refrigerant to the heat medium. The relay heat exchanger 35a is provided between the relay throttling device 38a and the relay flow path switching device 39a in the refrigerant circuit 101. The relay heat exchanger 35a is used to heat the heat medium during the cooling and heating mixed operation. The relay heat exchanger 35b is provided between the relay throttling device 38b and the relay flow path switching device 39b in the refrigerant circuit 101. The relay heat exchanger 35b is used to cool the heat medium during the cooling and heating mixed operation.

[0147] The intermediate throttling device 38a and the intermediate throttling device 38b function as pressure reducing valves or expansion valves, and reduce the pressure of the refrigerant to expand it. The intermediate throttling device 38a is provided upstream of the intermediate heat exchanger 35a in the flow of the refrigerant during cooling operation. The intermediate throttling device 38b is provided upstream of the intermediate heat exchanger 35b in the flow of the refrigerant during cooling operation. Each of the intermediate throttling device 38a and the intermediate throttling device 38b is composed of an electronic expansion valve or the like whose opening degree can be changed.

[0148] The opening and closing device 36a and the opening and closing device 36b are composed of a two-way valve or the like, and open and close the refrigerant piping 4. The opening and closing device 36a is provided on the inlet side of the refrigerant piping 4. The opening and closing device 36b is provided on the refrigerant piping 4 that connects the inlet side and the outlet side of the refrigerant.

[0149] The relay flow path switching device 39a and the relay flow path switching device 39b are composed of a four-way valve or the like, and switch the refrigerant flow depending on the operation mode. The relay flow path switching device 39a is provided downstream of the relay heat exchanger 35a in the refrigerant flow during cooling only operation. The relay flow path switching device 39b is provided downstream of the relay heat exchanger 35b in the refrigerant flow during cooling only operation.

[0150] The pumps 41a and 41b pressurize and circulate the heat medium passing through the heat medium piping 70. The pump 41a is provided on the heat medium piping 70 between the relay heat exchanger 35a and the plurality of second heat medium flow switching devices 51a to 51d. The pump 41b is provided on the heat medium piping 70 between the relay heat exchanger 35b and the plurality of second heat medium flow switching devices 51a to 51d. Each of the pumps 41a and 41b is configured to have a capacity controllable, for example.

[0151] The four first heat medium flow switching devices 50a to 50d are composed of three-way valves or the like, and switch the flow path of the heat medium. The first heat medium flow switching devices 50a to 50d are provided in a number corresponding to the number of indoor units 2. In the first heat medium flow switching devices 50a to 50d, one of the three sides is connected to the relay heat exchanger 35a, one of the three sides is connected to the relay heat exchanger 35b, and one of the three sides is connected to the heat medium flow control devices 52a to 52d, respectively. The first heat medium flow switching devices 50a to 50d are provided on the outlet side of the heat medium flow path of the indoor heat exchangers 26a to 26d, respectively. In FIG. 22, the first heat medium flow switching device 50a, the first heat medium flow switching device 50b, the first heat medium flow switching device 50c, and the first heat medium flow switching device 50d are illustrated from the bottom in correspondence with the indoor units 2a to 2d.

[0152] The four second heat medium flow switching devices 51a to 51d are composed of three-way valves or the like, and switch the flow path of the heat medium. The second heat medium flow switching devices 51a to 51d are provided in a number corresponding to the number of indoor units 2. One of the three sides of the second heat medium flow switching devices 51a to 51d is connected to the relay heat exchanger 35a, one of the three sides is connected to the relay heat exchanger 35b, and one of the three sides is connected to the indoor heat exchangers 26a to 26d, respectively. The second heat medium flow switching devices 51a to 51d are provided on the inlet side of the heat medium flow path of the indoor heat exchangers 26a to 26d, respectively. In FIG. 22, the second heat medium flow switching device 51a, the second heat medium flow switching device 51b, the second heat medium flow switching device 51c, and the second heat medium flow switching device 51d are illustrated from the bottom in correspondence with the indoor units 2a to 2d.

[0153] The four heat medium flow control devices 52a to 52d are composed of two-way valves capable of controlling the opening area, and control the flow rate through the heat medium pipe 70. The heat medium flow control devices 52a to 52d are provided in a number corresponding to the number of indoor units 2. One side of the heat medium flow control devices 52a to 52d is connected to the indoor heat exchangers 26a to 26d, and the other side is connected to the first heat medium flow switching devices 50a to 50d, respectively. The heat medium flow control devices 52a to 52d are provided on the outlet side of the heat medium flow path of the indoor heat exchangers 26a to 26d. In FIG. 22, the heat medium flow control device 52a, the heat medium flow control device 52b, the heat medium flow control device 52c, and the heat medium flow control device 52d are illustrated from the bottom in correspondence with the indoor units 2a to 2d. The four heat medium flow control devices 52a to 52d may be provided on the inlet side of the heat medium flow paths of the indoor heat exchangers 26a to 26d.

[0154] Various sensors (not shown) are installed in the repeater 3. Signals related to detection by the sensors are sent to the control device 60, for example.

[0155] The indoor units 2a to 2d are included in the heat medium circuit 102. The indoor units 2a to 2d have, for example, the same configuration as one another. The indoor units 2a to 2d each have an indoor heat exchanger 26a, 26b, 26c, 26d. Each of the indoor heat exchangers 26a to 26d is connected to the relay unit 3, which is connected to the relay unit 3 by piping via a branch pipe 8a and a branch pipe 8b. In each of the indoor heat exchangers 26a to 26d, air supplied by a load-side blower (not shown) is heat-exchanged with the heat medium, and cooling air or heating air to be supplied to an indoor space is generated.

[0156] The air conditioner 300 has four cooling and heating operation modes, just like the air conditioner 200 described in embodiment 3. The first is a full cooling operation mode in which all of the indoor units 2 that are driven are capable of performing cooling operation. The second is a full heating operation mode in which all of the indoor units 2 that are driven are capable of performing heating operation. The third is a cooling-dominated operation mode that is executed when the cooling load is greater in mixed cooling and heating operation. The fourth is a heating-dominated operation mode that is executed when the heating load is greater in mixed cooling and heating operation.

[0157] According to the fifth embodiment, the relay unit 3 has a relay heat exchanger 35a and a relay heat exchanger 35b that exchange heat between a refrigerant and a heat medium. The air conditioning apparatus 300 has a plurality of indoor heat exchangers 26a-27d connected to the relay heat exchanger 35a and the relay heat exchanger 35b of the relay unit 3 by heat medium piping 70 through which the heat medium circulates, and includes one or more indoor units 2a-2d that configure a heat medium circuit 102 between the relay unit 3 and the air conditioning apparatus 300.

[0158] Embodiment 6 An air conditioner according to embodiment 6 will be described. Fig. 23 is a refrigerant circuit diagram showing the circuit configuration of an air conditioner according to this embodiment. In embodiment 6, the same explanations as in embodiments 1 to 5 will be omitted, and only the characteristic parts will be described.

[0159] <Configuration of outdoor unit 1> In addition to the configuration of the fifth embodiment, a second bypass circuit 21 is provided to connect a flow path between the outdoor heat exchanger 12a and the opening / closing device 15a and a flow path between the outdoor heat exchanger 12b and the refrigerant flow switching device 13. An opening / closing valve 16 is provided in the second bypass circuit 21. An opening / closing valve 17 is provided in the flow path between the second bypass circuit 21 and the refrigerant flow switching device 13. The opening / closing valve 16 and the opening / closing valve 17 are controlled by a control device 60.

[0160] <Cooling operation mode> In both the cooling only operation mode and the cooling main operation mode, the refrigerant flow switching device 13 is set to the first state. In addition to the fifth embodiment, the on-off valve 16 is open, the on-off valve 17 is closed, the on-off device 15a is closed, and the on-off device 15b is open. The refrigerant that has passed through the refrigerant flow switching device 13 exchanges heat with the outside air in the outdoor heat exchanger 12a, passes through the on-off valve 16, passes through the outdoor heat exchanger 12b, passes through the on-off device 15b, and flows to the indoor unit 2. By arranging the two outdoor heat exchangers 12a and 12b in series, through which the high-pressure refrigerant flows and which function as condensers, the flow rate in the heat transfer tubes in the heat exchanger is increased, and the effect of promoting heat transfer is obtained.

[0161] <Heating operation mode> In both the heating only operation mode and the heating main operation mode, the refrigerant flow switching device 13 is set to the second state. In addition to the fifth embodiment, the on-off valve 16 is closed, and the on-off valve 17 is open. The refrigerant flowing from the indoor unit 2 is divided and flows into the on-off device 15a and the on-off device 15b. By arranging in parallel the two outdoor heat exchangers 12a, 12b through which the low-pressure refrigerant flows and which function as evaporators, the flow velocity in the heat transfer tubes in the heat exchangers is lowered, and the effect of reducing pressure loss is obtained.

[0162] <Split defrost operation mode> In the divided defrost operation mode, similarly to the full heating operation mode and the heating main operation mode, the refrigerant flow switching device 13 is set to the second state. In addition to the fifth embodiment, the on-off valve 16 is closed and the on-off valve 17 is closed.

[0163] <Full defrost operation mode> In the full defrost operation mode, similarly to the full heating operation mode and the heating main operation mode, the refrigerant flow switching device 13 is set to the second state. In addition to the fifth embodiment, the on-off valve 16 is closed, and the on-off valve 17 is closed. [Explanation of symbols]

[0164] 1 outdoor unit, 2 indoor unit, 2a indoor unit, 2b indoor unit, 2c indoor unit, 2d indoor unit, 3 relay unit, 4 refrigerant piping, 5 main pipe, 5a main pipe, 5b main pipe, 8a branch pipe, 8b branch pipe, 10 compressor, 11a opening / closing device, 11b opening / closing device, 12a outdoor heat exchanger, 12b outdoor heat exchanger, 13 refrigerant flow switching device, 14a backflow prevention device, 14b backflow prevention device, 14c backflow prevention device, 14d backflow prevention device, 15a opening / closing device, 15b opening / closing device, 16 opening / closing valve, 17 opening / closing valve, 18 heat source side blower, 19 accumulator, 20 first bypass circuit, 21 second bypass circuit, 22a first connecting pipe, 22b second connecting pipe, 23a relay unit first opening / closing device, 23b Repeater first switchgear, 23c Repeater first switchgear, 23d Repeater first switchgear, 24a Repeater second switchgear, 24b Repeater second switchgear, 24c Repeater second switchgear, 24d Repeater second switchgear, 25 Load side throttle device, 25a Load side throttle device, 25b Load side throttle device, 25c Load side throttle device, 25d Load side throttle device, 26 Indoor heat exchanger, 26a Indoor heat exchanger, 26b Indoor heat exchanger, 26c Indoor heat exchanger, 26d Indoor heat exchanger, 27 Second relay throttle device, 29 Gas-liquid separator, 30 First relay throttle device, 31 Load side first temperature sensor, 31a Load side first temperature sensor, 31b Load side first temperature sensor, 31c Load side first temperature sensor, 31d Load side first temperature sensor, 32 load side second temperature sensor, 32a load side second temperature sensor, 32b load side second temperature sensor, 32c load side second temperature sensor, 32d load side second temperature sensor, 33 inlet side pressure sensor, 34 outlet side pressure sensor, 35a relay heat exchanger, 35b relay heat exchanger, 36a opening and closing device, 36b opening and closing device, 38a relay throttling device, 38b relay throttling device, 39a relay flow path switching device, 39b relay flow path switching device, 40 discharge pressure sensor, 41a pump, 41b pump, 42 discharge temperature sensor, 43 outdoor heat exchanger temperature sensor, 46 outdoor air temperature sensor, 50a first heat medium flow path switching device, 50b first heat medium flow path switching device, 50c first heat medium flow path switching device, 50d first heat medium flow path switching device, 51a second heat medium flow path switching device, 51b Second heat medium flow switching device, 51c Second heat medium flow switching device, 51dSecond heat medium flow switching device, 52a heat medium flow rate control device, 52b heat medium flow rate control device, 52c heat medium flow rate control device, 52d heat medium flow rate control device, 60 control device, 70 heat medium piping, 100 air conditioner, 101 refrigerant circuit, 102 heat medium circuit, 200 air conditioner, 300 air conditioner.

Claims

1. a main circuit having a compressor, a refrigerant flow switching device, a plurality of outdoor heat exchangers, a load side throttle device, and an indoor heat exchanger; a first bypass circuit that divides and guides the hot gas discharged from the compressor to each of the outdoor heat exchangers; a plurality of first opening and closing devices that open and close the first bypass circuit corresponding to each of the plurality of outdoor heat exchangers; a plurality of second opening / closing devices each corresponding to the plurality of outdoor heat exchangers and configured to open and close the main circuit between the plurality of outdoor heat exchangers and the load side throttle device; Equipped with a cooling operation in which the refrigerant flow switching device is set to a first state and the plurality of outdoor heat exchangers function as condensers; a heating operation in which the refrigerant flow switching device is set to a second state and the plurality of outdoor heat exchangers function as evaporators; a defrosting operation in which the hot gas is introduced into at least one of the outdoor heat exchangers via the first bypass circuit; The defrosting operation includes: a divided defrosting operation in which some of the outdoor heat exchangers among the plurality of outdoor heat exchangers are caused to function as evaporators and the hot gas is introduced into the other outdoor heat exchangers among the plurality of outdoor heat exchangers via the first bypass circuit; a full defrosting operation in which the refrigerant circulation in the main circuit is stopped, and all of the hot gas discharged from the compressor and flowing into the first bypass circuit is introduced separately into all of the plurality of outdoor heat exchangers, The air conditioning apparatus, in which the refrigerant flow switching device is set to the second state in both the divided defrosting operation and the full defrosting operation.

2. A control device for controlling the refrigerant flow path switching device is further provided.

2. The air conditioning apparatus according to claim 1, wherein, when switching from the heating operation to the defrosting operation, the control device switches to the split defrosting operation if an outdoor air temperature is equal to or higher than a threshold temperature, and switches to the full defrosting operation if the outdoor air temperature is lower than the threshold temperature.

3. a second bypass circuit connecting the main circuit between some of the outdoor heat exchangers and a second opening / closing device corresponding to the some of the outdoor heat exchangers among the plurality of second opening / closing devices, and the main circuit between another of the plurality of outdoor heat exchangers and the refrigerant flow switching device; an on-off valve that opens and closes the second bypass circuit, In the cooling operation, the plurality of outdoor heat exchangers are connected in series, The air conditioner according to claim 1 or 2, wherein in the heating operation, the plurality of outdoor heat exchangers are connected in parallel.