Air conditioner

Abstract

This air conditioner comprises: a main circuit; a first bypass circuit that guides a 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 throttle device. The air conditioner is capable of executing a cooling operation in which a 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 defrosting operations. The defrosting operations include a split defrosting operation in which a portion of the outdoor heat exchangers is caused to function as an evaporator and the hot gas is introduced to the other outdoor heat exchangers, and a full defrosting operation in which the hot gas is introduced to all of the plurality of outdoor heat exchangers. In both the split defrosting operation and the full defrosting operation, the refrigerant flow path switching device is set to the second state.

Description

air conditioning equipment

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

[0002] Conventionally, in air conditioning systems such as multi-air conditioners for buildings, a refrigerant circuit is formed by connecting an outdoor unit, which is a heat source unit located outside a building, to an indoor unit located inside the building through pipes, and a refrigerant is circulated through the refrigerant. Heat dissipation and absorption of heat from the refrigerant are used 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 acts as 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, reducing the heat transfer area of ​​the heat exchanger that exchanges heat with the air, resulting in a problem of insufficient heating capacity.

[0004] Therefore, defrosting operation is generally 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, during the heating stop period of the defrosting operation, the temperature inside the room drops, reducing comfort.

[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.

[0006] International Publication No. 2010 / 082325

[0007] The technology disclosed in Patent Document 1 allows simultaneous defrosting and heating operations, but does not increase the capacity generated by the air conditioner. Instead, the capacity is shared between the outdoor heat exchanger used for defrosting and the outdoor heat exchanger used for heating. When defrosting is performed at low outdoor temperatures, for example, the outdoor heat exchanger requires a large amount of heat, resulting in a decrease in heating capacity and a drop in the indoor discharge temperature, resulting in a loss of comfort. For this reason, it may be necessary to flow refrigerant in the opposite direction to the heating operation, causing all outdoor heat exchangers to function as condensers, thereby completing defrosting of all outdoor heat exchangers in a short period of 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 initiated. However, switching the refrigerant flow switching device requires a reduction in the pressure difference between the high-pressure and low-pressure flow paths, which requires a slowdown in the compressor frequency, resulting in a time-consuming process for switching between the heating and defrosting operations.

[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 required to switch between heating operation and defrosting operation.

[0009] An 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 throttle device, and an indoor heat exchanger; a first bypass circuit that guides hot gas discharged from the compressor to each of the plurality of outdoor heat exchangers; 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 throttle device corresponding to each of the plurality of outdoor heat exchangers, and the air conditioner includes 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, and a cooling operation in which the refrigerant flow switching device is set to a second state and the plurality of outdoor heat exchangers function as condensers. The system is capable of executing a heating operation in which 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, and a full defrosting operation in which the hot gas is introduced into all of the plurality of outdoor heat exchangers via the first bypass circuit, and in both the split defrosting operation and the full defrosting operation, the refrigerant flow path switching device is set to the second state.

[0010] According to the present disclosure, the time required for switching between the heating operation and the defrosting operation can be reduced.

[0011] FIG. 1 is a refrigerant circuit diagram showing a circuit configuration in an all-cooling operation mode of an air conditioner according to Embodiment 1. FIG. 2 is a refrigerant circuit diagram showing a circuit configuration in an all-heating operation mode of an air conditioner according to Embodiment 1. FIG. 3 is a refrigerant circuit diagram showing a circuit configuration in a split defrosting operation mode of an air conditioner according to Embodiment 1. FIG. 4 is a refrigerant circuit diagram showing a circuit configuration in an all-defrosting operation mode of an air conditioner according to Embodiment 1. FIG. 5 is a refrigerant circuit diagram showing a circuit configuration in an all-cooling operation mode of an air conditioner according to Embodiment 2. FIG. 6 is a refrigerant circuit diagram showing a circuit configuration in an all-heating operation mode of an air conditioner according to Embodiment 2. FIG. 7 is a refrigerant circuit diagram showing a circuit configuration in an all-defrosting operation mode of an air conditioner according to Embodiment 2. FIG. 8 is a refrigerant circuit diagram showing a circuit configuration in an all-cooling operation mode of an air conditioner according to Embodiment 3. FIG. 9 is a refrigerant circuit diagram showing a circuit configuration in a cooling-dominated operation mode of an air conditioner according to Embodiment 3. FIG. 10 is a refrigerant circuit diagram showing a circuit configuration in an all-heating operation mode of an air conditioner according to Embodiment 3. 1 is a refrigerant circuit diagram showing the circuit configuration of a heating-dominated operation mode of an air conditioner according to Embodiment 3. FIG. 1 is a refrigerant circuit diagram showing the circuit configuration of a split defrost operation mode of an air conditioner according to Embodiment 3. FIG. 1 is a refrigerant circuit diagram showing the circuit configuration of a full defrost operation mode of an air conditioner according to Embodiment 3. FIG. 2 is a refrigerant circuit diagram showing the circuit configuration of a full cooling operation mode of an air conditioner according to Embodiment 4. FIG. 3 is a refrigerant circuit diagram showing the circuit configuration of a cooling-dominated operation mode of an air conditioner according to Embodiment 4. FIG. 4 is a refrigerant circuit diagram showing the circuit configuration of a full heating operation mode of an air conditioner according to Embodiment 4. FIG. 5 is a refrigerant circuit diagram showing the circuit configuration of a split defrost operation mode of an air conditioner according to Embodiment 4. FIG. 6 is a refrigerant circuit diagram showing the circuit configuration of a full defrost operation mode of an air conditioner according to Embodiment 4.

[0012] Embodiments of the present disclosure will be described below 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 and scope of the present disclosure. Furthermore, the present disclosure includes all possible combinations of the configurations shown in the following embodiments. In particular, the combinations of components are not limited to the combinations in each embodiment; components described in one embodiment can be applied to another embodiment. In the following description, directional terms (e.g., "up," "down," "right," "left," "front," "rear," etc.) are used as appropriate to facilitate understanding, but these are for explanatory purposes and do not limit the present disclosure. In each drawing, components designated with the same reference numerals are identical or equivalent, and this applies throughout the entire specification. Note that the relative dimensional relationships or shapes of each component in each drawing may differ from those in actuality.

[0013] Embodiment 1. <Configuration of Air Conditioning Apparatus 100> An air conditioner according to Embodiment 1 will be described. FIG. 1 is a refrigerant circuit diagram showing the circuit configuration of an air conditioner according to this embodiment in a cooling only operation mode. 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 conditioning apparatus 100 has an outdoor unit 1, an indoor unit 2, and main pipes 5a and 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 and 5b, a main circuit 9 is formed that has a compressor 10, a refrigerant flow switching device 13, multiple outdoor heat exchangers 12a and 12b, a load-side expansion 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 multiple 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, causing the refrigerant to condense or evaporate. The outdoor unit 1 has a refrigerant flow switching device 13 that switches the refrigerant flow path depending on the operating 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 that has 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 a refrigerant pipe 4. One end of a first bypass circuit 20 is connected to the refrigerant pipe 4 between the discharge port of the compressor 10 and the refrigerant flow switching device 13. The other end of the first bypass circuit 20 branches 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 it to a high-temperature, high-pressure state. The compressor 10 is configured, for example, as an inverter compressor whose capacity can be controlled. The compressor 10 is controlled by a control device 60.

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

[0019] The outdoor heat exchangers 12a and 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 excess refrigerant due to differences in operating conditions between the heating only operation mode, the cooling only operation mode, and the defrosting operation mode, as well as excess refrigerant due to transient changes in operation.

[0021] During the defrosting operation mode, the opening and closing devices 11a and 11b 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, two-way valves, solenoid valves, etc. The opening and closing devices 11a and 11b are controlled by the 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 equipped 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 and defrosting operations, and 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 from the compressor 10 and outputs a refrigerant temperature detection signal. The discharge pressure sensor 40 detects the pressure of the refrigerant discharged from the compressor 10 and outputs a discharge pressure detection signal. The outdoor air temperature sensor 46 is installed in the outdoor unit 1 at the air inlet portion of the outdoor heat exchangers 12a and 12b. 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 throttle device 25. The indoor heat exchanger 26 is connected to the outdoor unit 1 via main pipes 5a and 5b. In each indoor heat exchanger 26, air supplied by a load-side fan (not shown) exchanges heat with a refrigerant to generate air for cooling or air for heating to be supplied to the indoor space. The load-side throttle device 25 can adjust its opening degree, for example, continuously or in multiple stages. For example, an electronic expansion valve is used as the load-side throttle device 25. The load-side throttle device 25 functions as a pressure reducing valve and an expansion valve. The load-side throttle device 25 reduces the pressure of the refrigerant to expand it. The load-side throttle device 25 is located upstream of the indoor heat exchanger 26 in the refrigerant flow in the cooling only 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, refrigerant flow switching device 13, indoor heat exchanger 26, load-side expansion device 25, and outdoor heat exchangers 12a and 12b are sequentially connected by piping to form a main circuit 9 through which the refrigerant circulates. Also, a first bypass circuit 20 is formed, which allows high-temperature gas refrigerant discharged from the compressor 10 to flow into the outdoor heat exchangers 12a and 12b to be defrosted via opening and closing devices 11a and 11b. Note that FIG. 1 illustrates one indoor unit 2. However, two or more indoor units 2 may be connected. Furthermore, two or more outdoor units 1 may be connected in parallel.

[0027] The air conditioning apparatus 100 has a control device 60 configured by 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 (including on and off) of the blower, the switching of the refrigerant flow switching device 13, the opening and closing of the opening and closing devices 11a and 11b, the opening degree of the load-side expansion device 25, etc. In this way, each operation mode described below is executed.

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

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

[0030] <Cooling Only Operation Mode> The cooling only operation mode executed by the air conditioning apparatus 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 where a cooling 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 shown 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 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 has flowed into the outdoor heat exchangers 12a, 12b dissipates heat into the outdoor air in the outdoor heat exchangers 12a, 12b and becomes high-pressure liquid refrigerant. The high-pressure liquid refrigerant that has flowed out of the outdoor heat exchangers 12a, 12b flows out of the outdoor unit 1.

[0033] The high-pressure liquid refrigerant flowing out of 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 expansion 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 of 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 throttle 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, remains constant.

[0035] <Heating only operation mode> Fig. 2 is a refrigerant circuit diagram showing the circuit configuration of the heating only operation mode of the air conditioner according to this embodiment. The heating only operation mode executed by the air conditioner 100 will be described based on Fig. 2. In Fig. 2, the heating only operation mode will be described using as an example a case where a heating load is generated in the indoor heat exchanger 26. In Fig. 2, the direction of refrigerant flow 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, and 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 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 of 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 of 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, medium-pressure two-phase refrigerant or liquid refrigerant that has flowed into the outdoor unit 1 flows into the outdoor heat exchangers 12a, 12b. The refrigerant that has flowed into the outdoor heat exchangers 12a, 12b absorbs heat from the outdoor air and becomes a low-temperature, low-pressure gas refrigerant. The refrigerant then passes through the refrigerant flow switching device 13 and the accumulator 19 and is sucked into the compressor 10 again.

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

[0041] <Split Defrost Operation Mode> The defrost operation mode is implemented when the detection result of the outdoor heat exchanger temperature sensor 43, which is provided on the outlet side of the outdoor heat exchangers 12a and 12b, is below a predetermined value. That is, when the detection result of the outdoor heat exchanger temperature sensor 43 is below a predetermined value (e.g., approximately −10°C or below) while the heating only operation mode is being performed, the control device 60 determines that a predetermined amount of frost has formed on the fins of the outdoor heat exchangers 12a and 12b, and implements the defrost operation mode. The outdoor heat exchanger temperature sensor 43 may be provided on the inlet side of the outdoor heat exchangers 12a and 12b, as long as it can measure the refrigerant evaporation temperature of the outdoor heat exchangers 12a and 12b in the heating only operation mode.

[0042] In addition, frost formation may be determined, 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 above a preset value for a certain period of time.

[0043] The defrosting operation modes in this embodiment include 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 multiple outdoor heat exchangers 12a, 12b are defrosted. The full defrosting operation mode is an operation mode in which all of the multiple 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 the circuit configuration of the air conditioner in the split defrosting operation mode according to this embodiment. In Fig. 3, the refrigerant flow direction is indicated by solid arrows. Fig. 3 shows the split defrosting operation mode when defrosting the outdoor heat exchanger 12b. In the split defrosting operation mode, the refrigerant flow switching device 13 is maintained in the second state, the same 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 that flows into the first bypass circuit 20 and a refrigerant that flows into the indoor unit 2. The refrigerant that flows into the first bypass circuit 20 passes through the opening and closing device 11b and flows into the outdoor heat exchanger 12b for defrosting. The refrigerant that has completed 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 drawn 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 throttle 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 before reaching the refrigerant flow switching device 13. In this way, in the split defrost operation mode, heating is continued using the other outdoor heat exchanger 12a as the heat source-side heat exchanger while defrosting some of the outdoor heat exchangers 12b.

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

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

[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 above 0°C in terms of saturation temperature, and flows into the outdoor heat exchangers 12a, 12b. The high-temperature gas refrigerant that has flowed into the outdoor heat exchangers 12a, 12b melts frost adhering to the outdoor heat exchangers 12a, 12b, and becomes 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 has flowed 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, for example, when a predetermined time has elapsed or when the temperature of the outdoor heat exchanger temperature sensor 43 reaches or exceeds a predetermined value (for example, 5°C). The predetermined time may be set to be equal to or longer than the time required for all of 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 slow down 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 the present 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, and therefore it is not necessary to slow down the frequency of the compressor 10. Not slowing down the frequency of the compressor 10 means that the refrigerant flow rate does not decrease. This shortens the time required for defrosting and improves user comfort.

[0052] Furthermore, in the split 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, 11b to a temperature above 0°C in terms of saturation temperature. However, if the size of the opening and closing devices 11a, 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 excessively increase. For this reason, the size of the opening and closing devices 11a, 11b is selected according to the amount of gas refrigerant circulating in the split 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, if R410A refrigerant is used and the design pressure is 4.15 MPa, the size of the opening and closing devices 11a, 11b is selected so that the operating pressure is 3.8 MPa or less, lower than 4.15 MPa, taking pressure overshoot into consideration.

[0053] Furthermore, in the split defrosting operation mode and the full defrosting operation mode, there may be heat transfer tube paths where frost is difficult to melt due to differences in the amount of frost formed on each path of the heat transfer tubes of the outdoor heat exchangers 12a and 12b or differences 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, the melting point of frost. This increases the temperature of the refrigerant drawn into the compressor 10, causing the temperature of the refrigerant discharged from the compressor 10 to rise excessively. To ensure reliability, such as preventing deterioration of the refrigeration oil, an upper limit (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 lower 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. This control allows for stable defrosting operation.

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

[0055] In the defrosting operation mode, the opening degrees of the opening and closing devices 11a, 11b are adjusted so that the pressure of the gas refrigerant discharged from the compressor 10 becomes a predetermined pressure (e.g., 3.0 MPa). As the defrosting operation progresses, when most of the frost on the outdoor heat exchangers 12a, 12b melts and some remains, the outdoor heat exchangers 12a, 12b are heated, 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 (e.g., 3.8 MPa), the opening degrees of the opening and closing devices 11a, 11b are increased. In this way, by using the opening and closing devices 11a, 11b as 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, enabling stable defrosting operation.

[0056] As described above, the air conditioning apparatus 100 according to this embodiment includes a main circuit 9, a first bypass circuit 20, multiple opening and closing devices 11a, 11b, and multiple opening and closing devices 15a, 15b. The main circuit 9 includes a compressor 10, a refrigerant flow switching device 13, multiple outdoor heat exchangers 12a, 12b, a load-side expansion 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 multiple outdoor heat exchangers 12a, 12b. The multiple opening and closing devices 11a, 11b are provided in the first bypass circuit 20 corresponding to each of the multiple outdoor heat exchangers 12a, 12b. The multiple opening and closing devices 11a, 11b open and close the first bypass circuit 20 corresponding to each of the multiple outdoor heat exchangers 12a, 12b. The multiple opening and closing devices 15a, 15b correspond to the multiple outdoor heat exchangers 12a, 12b, respectively, and are provided in the main circuit 9 between the multiple outdoor heat exchangers 12a, 12b and the load-side expansion device 25. The multiple opening and closing devices 15a, 15b correspond to the multiple outdoor heat exchangers 12a, 12b, respectively, and open and close the main circuit 9 between the multiple outdoor heat exchangers 12a, 12b and the load-side expansion device 25. 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 conditioning apparatus 100 is capable of performing cooling operation, heating operation, and defrosting operation. In 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 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 defrosting operation, hot gas is introduced into at least one of the multiple outdoor heat exchangers 12a, 12b via the first bypass circuit 20. Defrosting operations include a split defrosting operation and a full defrosting operation. In split defrosting operation, some of the multiple outdoor heat exchangers 12a, 12b function as evaporators, and hot gas is introduced into the other 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 switching device 13 is maintained in the second state in all switching operations, including switching from heating operation to defrosting operation, switching from one of split defrosting operation and defrosting operation to the other during defrosting operation, and switching from defrosting operation to heating operation. This eliminates the need to reduce the frequency of the compressor 10, which is required when switching the refrigerant flow switching device 13. Therefore, the defrosting operation can be started promptly after the heating operation has ended, and the heating operation can be started promptly after the defrosting operation has ended. This shortens the time that heating is stopped, improving user comfort. Furthermore, the ability to select between split defrosting operation and full defrosting operation allows for efficient heating and defrosting.

[0059] The air conditioning apparatus 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. This configuration allows for efficient defrosting.

[0060] Embodiment 2 An air conditioning apparatus according to embodiment 2 will be described. In embodiment 2, only the changes from embodiment 1 will be described.

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

[0062] <Cooling-only operation mode> The refrigerant flow switching device 13 is set to the first state, as in embodiment 1. In addition to embodiment 1, 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 outside air in the outdoor heat exchanger 12a, passes through the on-off valve 16, the outdoor heat exchanger 12b, and 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 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.

[0063] <Heating only operation mode> Figure 7 is a refrigerant circuit diagram showing the circuit configuration of the air conditioner according to the present embodiment in heating only operation mode. The refrigerant flow 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 open. The refrigerant flowing from the indoor unit 2 is split 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 low-pressure refrigerant flows and which function as evaporators, the flow velocity in the heat transfer tubes in the heat exchangers is reduced, thereby achieving the effect of reducing pressure loss.

[0064] <Split defrost operation mode> Fig. 8 is a refrigerant circuit diagram showing the 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 embodiment 1. In addition to embodiment 1, the on-off valve 16 is closed and the on-off valve 17 is closed. The refrigerant flow in the split defrost operation mode is the same as in embodiment 1.

[0065] <Full defrost operation mode> Fig. 9 is a refrigerant circuit diagram showing the circuit configuration in the full 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 embodiment 1. In addition to embodiment 1, the on-off valve 16 is closed and the on-off valve 17 is closed. The refrigerant flow 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 a second bypass circuit 21 and an 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 devices 15a corresponding to the outdoor heat exchangers 12a, and the main circuit 9 between the other outdoor heat exchangers 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 multiple outdoor heat exchangers 12a, 12b are connected in series, and in heating operation, the multiple outdoor heat exchangers 12a, 12b are connected in parallel.

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

[0068] Embodiment 3 An air conditioner according to embodiment 3 will now be described. Fig. 10 is a refrigerant circuit diagram showing the circuit configuration of an air conditioner according to this embodiment in 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 their description will be omitted.

[0069] As shown in Figure 10, the air conditioning apparatus 200 has one outdoor unit 1 which is a heat source unit, multiple indoor units 2a, 2b, 2c, and 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 and 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 and 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, which makes it easy to install the air conditioning apparatus 200.

[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, 12b, an accumulator 19, opening and closing devices 11a, 11b, opening and closing devices 15a, 15b, and a heat source side blower 18. The compressor 10, the refrigerant flow switching device 13, the outdoor heat exchangers 12a, 12b, the accumulator 19, opening and closing devices 11a, 11b, and opening and closing devices 15a, 15b are connected by refrigerant piping 4.

[0072] Furthermore, a first connecting pipe 22a, a second connecting 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 connecting pipe 22a and the second connecting pipe 22b are connected as follows for the refrigerant flow in the cooling only operation mode and the cooling main operation mode: One end of the first connecting pipe 22a is connected to a refrigerant pipe downstream of the outdoor heat exchangers 12a, 12b and the opening / closing devices 15a, 15b and upstream of the main pipe 5b. The other end of the first connecting 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 connecting pipe 22b is connected to a refrigerant pipe downstream of the outdoor heat exchangers 12a, 12b and the opening / closing devices 15a, 15b and upstream of one end of the first connecting pipe 22a. The other end of the second connecting pipe 22b is connected to a refrigerant pipe downstream of the main pipe 5a and upstream of the other end of the first connecting pipe 22a.

[0074] The backflow prevention device 14a is provided on the refrigerant pipe between one end of the first connecting pipe 22a and one end of the second connecting pipe 22b. The backflow prevention device 14a prevents high-temperature, high-pressure gas refrigerant from flowing back from the first connecting pipe 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 connecting pipe 22a and 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 connecting pipe 22b and 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 on the refrigerant pipe between the other end of the first connecting pipe 22a and the other end of the second connecting pipe 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 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 they can prevent the backflow of refrigerant. For example, opening and closing devices or throttling devices with a fully closing function can also be used as the backflow prevention devices 14a to 14d.

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

[0080] Each of the indoor heat exchangers 26a-26d is connected to the outdoor unit 1 via branch pipes 8a-8b, a relay unit 3, and main pipes 5a-5b. In each of the indoor heat exchangers 26a-26d, heat exchange occurs between the refrigerant and air supplied by a load-side fan (not shown), generating air for heating or cooling to be supplied to the indoor space. The load-side throttle devices 25a-25d are capable of variably adjusting their opening, for example, continuously or in multiple stages. Examples of the load-side throttle devices 25a-25d include electronic expansion valves. The load-side throttle devices 25a-25d function as pressure-reducing valves and expansion valves, reducing the pressure of the refrigerant and expanding it. The load-side throttle devices 25a-25d are located upstream of the indoor heat exchangers 26a-26d in the refrigerant flow during cooling operation (e.g., full cooling operation).

[0081] The indoor units 2a to 2d are also provided with first load-side temperature sensors 31a, 31b, 31c, and 31d and second load-side temperature sensors 32a, 32b, 32c, and 32d. The first load-side 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-side temperature sensors 32a to 32d detect the temperature of the refrigerant flowing out of each of the indoor heat exchangers 26a to 26d. The first load-side temperature sensors 31a to 31d and the second load-side temperature sensors 32a to 32d are, for example, thermistors. Each of the first load-side temperature sensors 31a to 31d and the second load-side temperature sensors 32a to 32d outputs a detection signal to the control device 60.

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

[0083] <Configuration of relay unit 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 / closing devices 23a, 23b, 23c, and 23d, and a plurality of relay second opening / closing devices 24a, 24b, 24c, and 24d.

[0084] In a cooling and heating combined operation mode with a large cooling load, the gas-liquid separator 29 separates the high-pressure gas-liquid two-phase refrigerant generated in the outdoor unit 1 into liquid refrigerant and gas refrigerant. The 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. The gas-liquid separator 29 is provided at the inlet of the relay unit 3 in the refrigerant flow.

[0085] The first intermediate throttle device 30 functions as a pressure reducing valve and an on-off valve. The first intermediate throttle 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 throttle device 30 is capable of variably adjusting its opening, for example, continuously or in multiple stages. An electronic expansion valve, for example, is used as the first intermediate throttle device 30. The first intermediate throttle device 30 is provided in the pipe through which the liquid refrigerant flows out from the gas-liquid separator 29.

[0086] The second intermediate throttling device 27 functions as 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 its opening, for example, continuously or in multiple stages. An electronic expansion valve, for example, 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 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 to 23d are provided for each of the multiple indoor units 2a to 2d (a total of four in this example). The relay unit first opening and closing devices 23a to 23d open and close the flow path of the high-temperature, high-pressure gas refrigerant supplied to the indoor units 2a to 2d, respectively. The relay unit first opening and closing devices 23a to 23d are configured, for example, with solenoid valves or the like. The relay unit first opening and closing devices 23a to 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 to 23d only need to be able to open and close the flow path, and may be a throttle device with a full-closing function.

[0088] The multiple relay unit second opening and closing devices 24a to 24d are provided for each of the multiple indoor units 2a to 2d (a total of four in this example). The relay unit second opening and closing devices 24a to 24d open and close the flow path of the low-temperature, low-pressure gas refrigerant flowing out from the indoor units 2a to 2d, respectively. The relay unit second opening and closing devices 24a to 24d are configured, for example, with solenoid valves or the like. The relay unit second opening and closing devices 24a to 24d are each connected to a low-pressure pipe that is connected to the outlet side of the relay unit 3. Furthermore, the relay unit second opening and closing devices 24a to 24d only need to be able to open and close the flow path, and may be a throttle device with a full-closing function.

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

[0090] In the air conditioning apparatus 200 shown in FIG. 10 , the control device 60 also controls the overall operation of the air conditioning apparatus 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 fan rotation speed (including on / off), the switching of the refrigerant flow switching device 13, the opening and closing of the opening and closing devices 11a and 11b, the opening degree of the load-side expansion device 25, and the opening and closing of the first relay opening and closing devices 23a-23d. The control device 60 also controls the opening and closing of the second relay opening and closing devices 24a-24d, the opening and closing of the first relay expansion device 30, and the opening and closing of the second relay expansion device 27, among other things. This allows the various operating modes described below to be executed. Note that, although the control device 60 in this example is provided in the outdoor unit 1, the control device 60 may also be provided in the indoor units 2a-2d, the relay unit 3, or each unit (e.g., the outdoor unit 1, the indoor units 2a-2d, and the relay unit 3).

[0091] We will now explain each operation mode executed by the air conditioning apparatus 200. The control device 60 is capable of independently performing cooling or heating operation 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 conditioning apparatus 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 conditioning apparatus 200 are broadly divided 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 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 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 to 2d that are not stopped perform heating operation. That is, in the full heating operation mode, all of the indoor heat exchangers 26a to 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 to 2d perform cooling operation and some of the indoor units 2a to 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] <Cooling Only Operation Mode> The cooling only operation mode executed by the air conditioning apparatus 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 direction of refrigerant flow is indicated by solid arrows.

[0096] In 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 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. It then becomes high-pressure liquid refrigerant in the outdoor heat exchangers 12a, 12b while dissipating heat to the outdoor air. The high-pressure liquid refrigerant flowing out of the outdoor heat exchangers 12a, 12b passes through the backflow prevention device 14a, flows out of the outdoor unit 1, 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 throttle device 30, and the branch pipe 8b, and is expanded by the load side throttle 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, 25b flows into the indoor heat exchangers 26a, 26b, which function as evaporators, and absorbs heat from the indoor air, cooling it and becoming a low-temperature, low-pressure gas refrigerant. The opening of the load-side throttle device 25a is controlled so that the superheat, calculated as the difference between the temperatures detected by the first load-side temperature sensor 31a and the second load-side temperature sensor 32a, remains constant. Similarly, the opening of the load-side throttle device 25b is controlled so that the superheat, calculated as the difference between the temperatures detected by the first load-side temperature sensor 31b and the second load-side temperature sensor 32b, remains constant.

[0100] The gas refrigerant flowing out of the indoor heat exchangers 26a, 26b passes through the branch pipe 8a and the second relay opening and closing devices 24a, 24b, flows out of the relay unit 3, and passes through the main pipe 5a to again flow 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 again sucked into the compressor 10.

[0101] In addition, 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 expansion device 25c and the load-side expansion device 25d are closed. When a cooling load is generated in the indoor heat exchanger 26c or the indoor heat exchanger 26d, the load-side expansion device 25c or the load-side expansion device 25d is opened to circulate the refrigerant. In this case, the opening degree of the load-side expansion device is controlled so that the superheat, which is obtained as the difference between the temperature detected by the first load-side temperature sensor and the temperature detected by the second load-side temperature sensor, is constant, as in the load-side expansion device 25a or the load-side expansion device 25b described above.

[0102] <Cooling-dominated operation mode> Fig. 11 is a refrigerant circuit diagram showing the circuit configuration of the air conditioner according to this embodiment in cooling-dominated operation mode. In Fig. 11, the direction of refrigerant flow is indicated by solid arrows. Here, it is assumed that a cooling load is generated only in indoor heat exchanger 26a, and a heating load is generated only in 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 and 12b.

[0104] First, low-temperature, low-pressure refrigerant is compressed by the compressor 10 and becomes 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. The refrigerant then dissipates heat to the outdoor air in the outdoor heat exchangers 12a, 12b, becoming a gas-liquid two-phase refrigerant. The refrigerant flowing out of the outdoor heat exchangers 12a, 12b passes through the backflow prevention device 14a and the main pipe 5b and flows into the relay unit 3.

[0105] The gas-liquid two-phase refrigerant flowing into the relay unit 3 is separated into high-pressure gas refrigerant and high-pressure liquid refrigerant by the gas-liquid separator 29. This high-pressure gas refrigerant passes through the relay unit first opening / closing device 23b and the branch pipe 8a before flowing into the indoor heat exchanger 26b, which functions as a condenser. The high-pressure gas refrigerant radiates heat to the indoor air, heating it and becoming liquid refrigerant. At this time, the opening degree of the load-side throttle device 25b is controlled so that the subcooling, which is 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 of 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 separated in the gas-liquid separator 29 and then expanded to an intermediate pressure in the first intermediate throttle device 30 joins with the liquid refrigerant that has passed through the load side throttle device 25b. At this time, the opening degree of the first intermediate throttle 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 two-phase gas-liquid refrigerant expanded by the load-side throttle device 25a of the indoor unit 2a flows into the indoor heat exchanger 26a, which functions as an evaporator, and absorbs heat from the indoor air, cooling it and becoming a low-temperature, low-pressure gas refrigerant. At this time, the opening degree of the load-side throttle device 25a is controlled so that the superheat, calculated as the difference between the temperatures detected by the first load-side temperature sensor 31a and the second load-side temperature sensor 32a, remains constant. The gas refrigerant flowing out of the indoor heat exchanger 26a flows through the branch pipe 8a and the second relay unit opening / closing device 24a and flows out of the relay unit 3.

[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, the refrigerant flow switching device 13, and the accumulator 19, and is again sucked into the compressor 10.

[0109] In addition, 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 expansion device 25c and the load-side expansion device 25d are closed. When a cooling load is generated in the indoor heat exchanger 26c or the indoor heat exchanger 26d, the load-side expansion device 25c or the load-side expansion device 25d is opened to circulate the refrigerant. In this case, the opening degree of the load-side expansion device is controlled, similar to the load-side expansion device 25a described above, so that the superheat, obtained as the difference between the temperature detected by the first load-side temperature sensor and the temperature detected by the second load-side temperature sensor, is constant.

[0110] When a heating load is generated in the indoor heat exchanger 26c or 26d, the load-side throttle device 25c or 25d is opened to circulate the refrigerant. In this case, the opening degree of the load-side throttle device is controlled, similarly to the load-side throttle device 25b described above, so that the subcooling, which is 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 first load-side temperature sensor, is constant.

[0111] <Heating only operation mode> Fig. 12 is a refrigerant circuit diagram showing the circuit configuration in the heating only operation mode of the air conditioner 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 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, low-temperature, low-pressure refrigerant is compressed by the compressor 10 and becomes high-temperature, high-pressure gas refrigerant, which is then discharged. 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 flows into the relay unit 3 passes through the gas-liquid separator 29, the first relay unit opening / closing devices 23a and 23b, and the branch pipe 8a before flowing into the indoor heat exchangers 26a and 26b, which function as condensers. The refrigerant that flows into the indoor heat exchangers 26a and 26b dissipates heat into the indoor air, heating the indoor air and becoming liquid refrigerant. The liquid refrigerant that flows out of the indoor heat exchangers 26a and 26b is expanded by the load-side expansion devices 25a and 25b, respectively, and flows through the branch pipe 8b, the second relay expansion device 27 (which is controlled to an open state), and the main pipe 5a before flowing back into the outdoor unit 1. At this time, the opening degree of the load-side expansion device 25a is controlled so that the subcooling, which is 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 first load-side 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 while absorbing heat from the outdoor air in the outdoor heat exchangers 12a and 12b, becomes 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 exchangers 26c and 26d, which have no heat load, there is no need for refrigerant to flow, and the corresponding load-side throttle devices 25c and 25d are closed. When a warming load is generated in the indoor heat exchanger 26c or the indoor heat exchanger 26d, the load-side throttle device 25c or the load-side throttle device 25d is opened to circulate the refrigerant. In this case, the opening degree of the load-side throttle device is controlled, as with the load-side throttle devices 25a and 25b described above, so that the subcooling, which is 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 first load-side temperature sensor, remains constant.

[0117] <Heating-dominant operation mode> Fig. 13 is a refrigerant circuit diagram showing the circuit configuration in heating-dominant operation mode of the air conditioner according to this embodiment. In Fig. 13, the direction of refrigerant flow is indicated by solid arrows. Here, it is assumed that a cooling load is generated only in indoor heat exchanger 26a, and a heating load is generated only in 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 becomes high-temperature, high-pressure gas refrigerant, which is then discharged. 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 that flows 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 passes through the gas-liquid separator 29, the first relay unit opening / closing device 23b, and the branch pipe 8a before flowing into the indoor heat exchanger 26b, which functions as a condenser. The refrigerant that flows into the indoor heat exchanger 26b dissipates heat into the indoor air, heating it and turning into liquid refrigerant. The liquid refrigerant that flows out of the indoor heat exchanger 26b is expanded by the load-side throttle device 25b and flows into the relay unit 3 via the branch pipe 8b. Most of the refrigerant then passes through the branch pipe 8b and is expanded by the load-side throttle device 25a, turning into low-temperature, low-pressure, two-phase gas-liquid refrigerant. The remaining liquid refrigerant is expanded by the second relay throttle device 27, which also serves as a bypass, turning into liquid or two-phase gas-liquid refrigerant and flowing into the low-pressure pipe on the outlet side of the relay unit 3.

[0121] The gas-liquid two-phase refrigerant expanded by the load-side throttle device 25a flows into the indoor heat exchanger 26a, which functions as an evaporator, and becomes gas refrigerant by absorbing heat from the indoor air, 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 portion of the refrigerant that flowed out of the second relay throttle device 27. The merged refrigerant flows out of the relay unit 3, passes through the main pipe 5a, and flows back into the outdoor unit 1. The refrigerant that flows into the outdoor unit 1 passes through the backflow prevention device 14c, and becomes 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 again drawn into the compressor 10.

[0122] At this time, the opening degree of the load-side expansion 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. On the other hand, the opening degree of the load-side expansion 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 throttling 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 (e.g., 0.3 MPa).

[0124] In addition, 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 expansion device 25c and the load-side expansion device 25d are closed. When a cooling load is generated in the indoor heat exchanger 26c or the indoor heat exchanger 26d, the load-side expansion device 25c or the load-side expansion device 25d is opened to circulate the refrigerant. In this case, the opening degree of the load-side expansion device is controlled, similar to the load-side expansion device 25a described above, so that the superheat, obtained as the difference between the temperature detected by the first load-side temperature sensor and the temperature detected by the second load-side temperature sensor, is constant.

[0125] When a heating load is generated in the indoor heat exchanger 26c or 26d, the load-side throttle device 25c or 25d is opened to circulate the refrigerant. In this case, the opening degree of the load-side throttle device is controlled, similarly to the load-side throttle device 25b described above, so that the subcooling, which is 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 first load-side temperature sensor, is constant.

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

[0127] In the split defrosting 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 portion 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 defrosting operation mode> Fig. 15 is a refrigerant circuit diagram showing the circuit configuration in the full defrosting operation mode of the air conditioner according to the present embodiment. In Fig. 15, the direction of refrigerant flow 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 a closed state to block the refrigerant. The opening and closing devices 11a and 11b are switched to an open state to allow the refrigerant to flow. The heat-source-side blower 18 and a load-side blower (not shown) are stopped. By closing the load-side expansion devices 25a to 25d after switching the opening and closing devices 11a and 11b to an open state, blockage of the refrigerant flow path can be prevented and a rise in pressure can be suppressed.

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

[0131] In the heating operation mode, the indoor heat exchangers 26a to 26d operate as condensers, so a large amount of refrigerant is present in the indoor heat exchangers 26a to 26d. This allows excess refrigerant to be stored in the indoor heat exchangers 26a to 26d, thereby reducing the amount of excess refrigerant remaining in the accumulator 19.

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

[0133] Furthermore, a decrease in refrigerant density due to pressure loss does not occur, and high-density gas refrigerant can flow into the suction portion of the compressor 10. This increases the amount of refrigerant circulating from the compressor 10, improving defrosting capacity. Immediately after switching from the defrosting operation mode to the heating operation mode, 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 portion of the compressor 10 than in a case where excess refrigerant does not flow into the outdoor heat exchangers 12a and 12b, increasing the amount of refrigerant circulating in the compressor 10. This increases the supply of high-temperature, high-pressure gas refrigerant flowing into the indoor heat exchangers 26a to 26d, speeding up the start of heating operation, and improving user comfort.

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

[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 / closing devices 23a to 23d, the relay second opening / 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 air conditioning apparatus according to embodiment 4 will be described. In embodiment 4, only the changes from embodiment 3 will be described.

[0137] <Configuration of outdoor unit 1> Fig. 16 is a refrigerant circuit diagram showing the circuit configuration in cooling-only operation mode of an air conditioner according to this embodiment. Fig. 17 is a refrigerant circuit diagram showing the circuit configuration in cooling-dominated operation mode of an air conditioner according to this embodiment. In addition to the components of Embodiment 3, a second bypass circuit 21 is provided that connects the flow path between the outdoor heat exchanger 12a and the opening / closing device 15a and the 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 valves 16 and 17 are controlled by the control device 60.

[0138] <Cooling Operation Mode> In both the cooling-only operation mode and the cooling-dominant 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 outside air in the outdoor heat exchanger 12a, passes through the on-off valve 16, the outdoor heat exchanger 12b, and 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 high-pressure refrigerant flows and which function as condensers, the flow rate in the heat transfer tubes in the heat exchangers is increased, thereby achieving the effect of promoting heat transfer.

[0139] <Heating Operation Mode> Figure 18 is a refrigerant circuit diagram showing the circuit configuration in the heating-only operation mode of an air conditioner according to this embodiment. Figure 19 is a refrigerant circuit diagram showing the circuit configuration in the heating-dominated operation mode of an air conditioner according to this embodiment. In both the heating-only operation mode and the heating-dominated operation mode, the refrigerant flow switching device 13 is set to the second state. In addition to the functions of Embodiment 1, 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 low-pressure refrigerant flows and which function as evaporators, the flow velocity in the heat transfer tubes in the heat exchangers is reduced, thereby achieving the effect of reducing pressure loss.

[0140] <Divided defrosting operation mode> Fig. 20 is a refrigerant circuit diagram showing the circuit configuration of the divided defrosting operation mode of the air conditioner according to the present embodiment. In the divided defrosting operation mode, as in the heating only operation mode and the heating-dominant 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 closed.

[0141] <Full defrosting operation mode> Fig. 21 is a refrigerant circuit diagram showing the circuit configuration in the full defrosting operation mode of the air conditioner according to the present embodiment. In the full defrosting operation mode, as in the full heating operation mode and the heating-dominant 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 closed.

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

[0143] As shown in Figure 22, the relay unit 3 of the air conditioning apparatus 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 relay heat exchanger 35b via heat medium piping 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 relay heat exchangers 35a and 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 exchangers 35a and 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 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 switching devices 50a to 50d, four second heat medium flow 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 exchangers 35a and 35b function as condensers or evaporators. The relay heat exchangers 35a and 35b exchange heat between the refrigerant and the heat medium, transferring cold 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 switching device 39a in the refrigerant circuit 101. The relay heat exchanger 35a heats the heat medium during combined cooling and heating operation. The relay heat exchanger 35b is provided between the relay throttling device 38b and the relay flow switching device 39b in the refrigerant circuit 101. The relay heat exchanger 35b cools the heat medium during combined cooling and heating 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 relay heat exchanger 35a in terms of the refrigerant flow during cooling operation. The intermediate throttling device 38b is provided upstream of the relay heat exchanger 35b in terms of the refrigerant flow during cooling operation. Each of the intermediate throttling devices 38a and 38b is composed of an electronic expansion valve or the like whose opening degree is changeable.

[0148] The on-off device 36a and the on-off device 36b are composed of two-way valves or the like, and open and close the refrigerant pipe 4. The on-off device 36a is provided on the inlet side of the refrigerant pipe 4. The on-off device 36b is provided on the refrigerant pipe 4 connecting the inlet side and outlet side of the refrigerant.

[0149] The relay flow path switching device 39a and the relay flow path switching device 39b are configured with 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 flowing 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 controllable capacity, for example.

[0151] The four first heat medium flow switching devices 50a to 50d are configured with three-way valves or the like and switch the flow path of the heat medium. The number of first heat medium flow switching devices 50a to 50d corresponds to the number of indoor units 2. One of the three sides of each of the first heat medium flow switching devices 50a to 50d 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 a heat medium flow control device 52a to 52d. The first heat medium flow switching devices 50a to 50d are respectively provided on the outlet side of the heat medium flow path of the indoor heat exchangers 26a to 26d. Note that 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 shown, from bottom to top, corresponding to the indoor units 2a to 2d.

[0152] The four second heat medium flow switching devices 51a to 51d are configured with three-way valves or the like and switch the flow path of the heat medium. The number of second heat medium flow switching devices 51a to 51d corresponds to the number of indoor units 2. One of the three sides of each 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 each of the indoor heat exchangers 26a to 26d. The second heat medium flow switching devices 51a to 51d are respectively provided on the inlet side of the heat medium flow path of each of the indoor heat exchangers 26a to 26d. Note that in FIG. 22, the second heat medium flow switching devices 51a, 51b, 51c, and 51d are shown from the bottom to correspond to the indoor units 2a to 2d.

[0153] The four heat medium flow control devices 52a to 52d are configured with devices such as two-way valves that can control 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 of the heat medium flow control devices 52a to 52d is connected to the indoor heat exchangers 26a to 26d, and the other 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 paths of the indoor heat exchangers 26a to 26d. Note that 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 shown, from bottom to top, corresponding to the indoor units 2a to 2d. The four heat medium flow control devices 52a to 52d may also 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 the detection by the sensors are sent to the control device 60, for example.

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

[0156] The air conditioning apparatus 300 has four cooling and heating operation modes, just like the air conditioning apparatus 200 described in embodiment 3. The first is an all-cooling operation mode in which all of the indoor units 2 that are driven can perform cooling operation. The second is an all-heating operation mode in which all of the indoor units 2 that are driven can perform heating operation. The third is a cooling-dominated operation mode that is executed when the cooling load is greater in combined cooling and heating operation. The fourth is a heating-dominated operation mode that is executed when the heating load is greater in combined 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 to 27d that are 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 to 2d that form a heat medium circuit 102 between the relay unit 3 and the indoor units 2a to 2d.

[0158] Sixth embodiment An air conditioning apparatus according to a sixth embodiment will be described. Fig. 23 is a refrigerant circuit diagram showing the circuit configuration of an air conditioning apparatus according to this embodiment. In the sixth embodiment, the same explanations as in the first to fifth embodiments will be omitted, and only the characteristic parts will be described.

[0159] <Configuration of outdoor unit 1> In addition to the configuration of embodiment 5, a second bypass circuit 21 is provided that connects the flow path between the outdoor heat exchanger 12a and the opening / closing device 15a and the 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 valves 16 and 17 are controlled by a control device 60.

[0160] <Cooling operation mode> In both the cooling-only operation mode and the cooling-dominant 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 outside air in the outdoor heat exchanger 12a, passes through the on-off valve 16, the outdoor heat exchanger 12b, and 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 high-pressure refrigerant flows and which function as condensers, the flow rate in the heat transfer tubes in the heat exchangers is increased, and heat transfer is promoted.

[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 the two outdoor heat exchangers 12a, 12b, which function as evaporators through which low-pressure refrigerant flows, in parallel, the flow velocity in the heat transfer tubes in the heat exchangers is reduced, thereby achieving the effect of reducing pressure loss.

[0162] <Divided defrosting operation mode> In the divided defrosting operation mode, similarly to 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 closed.

[0163] <Full defrost operation mode> In the full defrost operation mode, similarly to the full heating operation mode and the heating-dominant 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.

[0164] REFERENCE SIGNS LIST 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 Relay unit first opening / closing device, 23c Relay unit first opening / closing device, 23d Relay unit first opening / closing device, 24a Relay unit second opening / closing device, 24b Relay unit second opening / closing device, 24c Relay unit second opening / closing device, 24d Relay unit second opening / closing device, 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 Second load side temperature sensor, 32a Second load side temperature sensor, 32b Second load side temperature sensor, 32c Second load side temperature sensor, 32d Second load side 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 throttle device, 38b Relay throttle 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,51d second heat medium flow switching device, 52a heat medium flow control device, 52b heat medium flow control device, 52c heat medium flow control device, 52d heat medium flow 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 cooling system comprising: 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 guides hot gas discharged from the compressor to each of the plurality of outdoor heat exchangers; 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 throttle device corresponding to each of the plurality of outdoor heat exchangers, wherein the cooling system is capable of performing 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; 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, wherein the defrosting operation includes: an air conditioning apparatus including: a divided defrosting operation in which some of the plurality of outdoor heat exchangers are caused to function as evaporators and the hot gas is introduced into other of the plurality of outdoor heat exchangers via the first bypass circuit; and a full defrosting operation in which the hot gas is introduced into all of the plurality of outdoor heat exchangers via the first bypass circuit, wherein the refrigerant flow path switching device is set to the second state in both the divided defrosting operation and the full defrosting operation.

2. An air conditioning apparatus as described in claim 1, further comprising a control device that controls the refrigerant flow path switching device, wherein, when switching from the heating operation to the defrosting operation, the control device switches to the split defrosting operation if the outside air temperature is equal to or higher than a threshold temperature, and switches to the full defrosting operation if the outside air temperature is below the threshold temperature.

3. An air conditioning apparatus as described in claim 1 or claim 2, further comprising: a second bypass circuit connecting the main circuit between some of the plurality of outdoor heat exchangers and second opening / closing devices corresponding to some of the outdoor heat exchangers among the plurality of second opening / closing devices, and the main circuit between other outdoor heat exchangers of the plurality of outdoor heat exchangers and the refrigerant flow path switching device; and an opening / closing valve opening and closing the second bypass circuit, wherein the plurality of outdoor heat exchangers are connected in series during the cooling operation, and the plurality of outdoor heat exchangers are connected in parallel during the heating operation.

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