Air conditioning device

Abstract

This air conditioning device comprises: an outdoor unit having a compressor, a flow path switching device, a heat source-side heat exchanger, and an accumulator; an indoor unit having a throttle device and a load-side heat exchanger; a relay device which is connected between the outdoor unit and the indoor unit, and which switches a flow of refrigerant according to an operating condition; a refrigerant circuit in which the outdoor unit, the relay device, and the indoor unit are connected by piping, and in which a refrigerant circulates; a control device which controls the refrigerant circuit; a discharge temperature detection device which detects the temperature of refrigerant discharged from the compressor; a discharge pressure detection device which detects the pressure of refrigerant discharged from the compressor; an inlet temperature detection device which detects the temperature of refrigerant flowing into the accumulator; and a suction pressure detection device which detects the pressure of refrigerant being sucked in by the compressor. During a defrost operation, the control device switches the flow path switching device so that refrigerant discharged from the compressor flows into the heat source-side heat exchanger, and fully closes the throttle device. After returning from the defrost operation to a heating operation, the control device performs a first determination process to determine whether a difference between the temperature detected by the discharge temperature detection device and a condensation temperature converted from the pressure detected by the discharge pressure detection device is at least a first threshold which is a preset value, and whether a difference between the temperature detected by the inlet temperature detection device and an evaporation temperature converted from the pressure detected by the suction pressure detection device is at least a second threshold which is a preset value. If the conditions of the first determination process are not met, the control device decreases the opening degree of the throttle device.

Description

air conditioning equipment

[0001] The present disclosure relates to an air conditioner capable of defrosting operation.

[0002] 2. Description of the Related Art Conventionally, air conditioners have been proposed that defrost a heat exchanger in an outdoor unit when frost forms on the heat exchanger during heating operation (see, for example, Patent Document 1).

[0003] In Patent Document 1, if a defrost request is made for any of the outdoor unit's multiple heat exchangers during heating operation, the flow path switching mechanism of only the heat exchanger for which defrosting is requested is switched, and the high-temperature refrigerant discharged from the compressor is introduced directly into the heat exchanger for which defrosting is requested, thereby performing defrosting operation.

[0004] Patent No. 5029001

[0005] In Patent Document 1, the throttling device of the indoor unit is open during defrosting operation, so the liquid refrigerant that had accumulated in the heat exchanger of the indoor unit during heating operation flows into the outdoor unit through the throttling device of the indoor unit. If the amount of liquid refrigerant flowing into the outdoor unit becomes large, there is a problem that the liquid refrigerant flows back into the compressor of the outdoor unit.

[0006] The present disclosure has been made to solve the above-mentioned problems, and has an object to provide an air conditioner that can suppress liquid backflow into the compressor.

[0007] An air conditioner according to the present disclosure includes an outdoor unit having a compressor, a flow switching device, a heat source side heat exchanger, and an accumulator; an indoor unit having a throttling device and a load side heat exchanger; a relay unit connected between the outdoor unit and the indoor unit and switching the flow of refrigerant depending on the operating conditions; a refrigerant circuit in which the outdoor unit, the relay unit, and the indoor unit are connected by piping and in which the refrigerant circulates; a control device for controlling the refrigerant circuit; a discharge temperature detection device that detects the temperature of the refrigerant discharged from the compressor; a discharge pressure detection device that detects the pressure of the refrigerant discharged from the compressor; an inlet temperature detection device that detects the temperature of the refrigerant flowing into the accumulator; and a suction pressure detection device that detects the pressure of the refrigerant drawn into the compressor. The control device switches the flow path switching device so that the refrigerant discharged from the compressor flows into the heat source side heat exchanger during defrost operation and fully closes the throttling device, and after returning from the defrost operation to the heating operation, performs a first judgment process to determine whether the difference between the temperature detected by the discharge temperature detection device and the condensation temperature converted from the pressure detected by the discharge pressure detection device is greater than or equal to a first threshold value which is a predetermined value, and whether the difference between the temperature detected by the inlet temperature detection device and the evaporating temperature converted from the pressure detected by the suction pressure detection device is greater than or equal to a second threshold value which is a predetermined value, and if the conditions of the first judgment process are not met, reduces the opening of the throttling device.

[0008] In the air conditioning apparatus according to the present disclosure, the control device switches the flow path switching device and fully closes the throttling device during defrost operation so that refrigerant discharged from the compressor flows into the heat source-side heat exchanger. After returning to heating operation from defrost operation, the control device performs a first determination process to determine whether excessive liquid refrigerant is returning to the outdoor unit. If the conditions of the first determination process are not met, the control device reduces the opening of the throttling device. In this way, by fully closing the throttling device of the indoor unit during defrost operation, liquid refrigerant accumulated in the indoor unit does not flow to the outdoor unit, thereby suppressing liquid backflow to the compressor. Furthermore, if excessive liquid refrigerant is returning from the indoor unit to the outdoor unit after returning to heating operation from defrost operation, the control device reduces the opening of the throttling device of the indoor unit to suppress excessive liquid refrigerant returning from the indoor unit to the outdoor unit and suppressing liquid backflow to the compressor.

[0009] Fig. 1 is a schematic diagram showing an example of a refrigerant circuit configuration of an air conditioner according to an embodiment. Fig. 2 is a schematic diagram for explaining the flow of refrigerant during cooling only operation in the air conditioner of Fig. 1. Fig. 3 is a schematic diagram for explaining the flow of refrigerant during cooling-dominated operation in the air conditioner of Fig. 1. Fig. 4 is a schematic diagram for explaining the flow of refrigerant during heating only operation in the air conditioner of Fig. 1. Fig. 5 is a schematic diagram for explaining the flow of refrigerant during heating-dominated operation in the air conditioner of Fig. 1. Fig. 6 is a flowchart showing control processing after returning from defrost operation to heating operation in an air conditioner according to an embodiment.

[0010] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. Note that the present disclosure is not limited to the embodiments described below. Also, the size relationships of the components in the drawings may differ from those in reality.

[0011] Embodiment. An air conditioning apparatus 100 according to an embodiment will be described below. The air conditioning apparatus 100 is installed in, for example, a building or an apartment building, and is capable of performing cooling or heating operation using a refrigerant circuit 101 that circulates a refrigerant. In particular, the air conditioning apparatus 100 according to the embodiment can perform only cooling, only heating, or both simultaneously for multiple air-conditioned spaces. Furthermore, the air conditioning apparatus 100 according to the embodiment can perform defrost operation to remove frost that has formed on the heat source-side heat exchanger 13 during heating operation.

[0012] [Configuration of air conditioning apparatus 100] Figure 1 is a schematic diagram showing an example of the refrigerant circuit configuration of an air conditioning apparatus 100 according to an embodiment. The air conditioning apparatus 100 according to embodiment 1 comprises an outdoor unit 10, multiple indoor units 20a, 20b, a relay unit 30, and a control device 40. The example of Figure 1 shows a case where the air conditioning apparatus 100 is configured with one outdoor unit 10, two indoor units 20a, 20b, and one relay unit 30.

[0013] In the air conditioning apparatus 100, the outdoor unit 10 and the relay unit 30 are connected by a first main pipe 1 and a second main pipe 2. The relay unit 30 and the indoor unit 20a are connected by a first branch pipe 5a and a second branch pipe 6a, and the relay unit 30 and the indoor unit 20b are connected by a first branch pipe 5b and a second branch pipe 6b. In this manner, the outdoor unit 10, the relay unit 30, and the indoor units 20a and 20b are connected by their respective pipes to form a refrigerant circuit 101 through which the refrigerant circulates. Note that the number of indoor units 20a and 20b is not limited to this example and may be three or more. The number of outdoor units 10 and relay units 30 may also be, for example, two or more. Furthermore, the type of refrigerant used in the air conditioning device 100 is not particularly limited, and any of the following may be used: natural refrigerants such as carbon dioxide, hydrocarbons, or helium; chlorine-free alternative refrigerants such as HFC410A, HFC407C, or HFC404A; or fluorocarbon refrigerants such as R22 or R134a that are used in existing products.

[0014] (Outdoor unit 10) The outdoor unit 10 is provided to supply heat to the indoor units 20. The outdoor unit 10 includes a compressor 11, a flow path switching device 12, a heat source side heat exchanger 13, and an accumulator 14. Furthermore, the outdoor unit 10 includes check valves 15a, 15b, 15c, 15d, a first connecting pipe 3, and a second connecting pipe 4 so that the flow of refrigerant flowing into the relay unit 30 can be unidirectional regardless of the request of the indoor units 20.

[0015] The compressor 11 draws in low-temperature, low-pressure gas refrigerant, compresses it, and discharges it into a high-temperature, high-pressure state. The compressor 11 may be, for example, an inverter compressor whose capacity, or the amount of refrigerant delivered per unit time, can be controlled by changing the drive frequency. The drive frequency of the compressor 11 is controlled by the control device 40.

[0016] Compressor 11 is not limited to an inverter type, and may be, for example, a constant speed type compressor or a compressor that combines an inverter type and a constant speed type. Compressor 11 may be any type that can compress the drawn refrigerant to a high pressure state, and may be, for example, a reciprocating, rotary, scroll, or screw type compressor.

[0017] The flow path switching device 12 is, for example, a four-way valve, and switches between cooling operation and heating operation by switching the direction of refrigerant flow. The switching of the flow path switching device 12 is controlled by the control device 40. Note that the flow path switching device 12 is not limited to this example, and may be configured by combining other valves, such as two-way valves or three-way valves.

[0018] The heat source-side heat exchanger 13 exchanges heat between the refrigerant and a fluid such as outdoor air or water. Specifically, during cooling operation, the heat source-side heat exchanger 13 functions as a condenser that radiates heat from the refrigerant to the outdoor air to condense and liquefy the refrigerant. During heating operation, the heat source-side heat exchanger 13 functions as an evaporator that evaporates the refrigerant into gas and absorbs heat from the outdoor air as heat of vaporization.

[0019] When the heat source-side heat exchanger 13 is an air-cooled heat exchanger, the outdoor unit 10 is provided with a blower (not shown), such as a heat source-side fan, for supplying outdoor air to the heat source-side heat exchanger 13. The rotation speed of the heat source-side fan is controlled by the control device 40, thereby controlling the condensation capacity or evaporation capacity of the heat source-side heat exchanger 13.

[0020] Furthermore, when the heat source-side heat exchanger 13 is a water-cooled heat exchanger, the outdoor unit 10 is provided with a water circulation pump (not shown) for circulating a fluid such as water and supplying it to the heat source-side heat exchanger 13. The rotation speed of the water circulation pump is controlled by the control device 40, thereby controlling the condensation capacity or evaporation capacity of the heat source-side heat exchanger 13.

[0021] The accumulator 14 is provided on the low-pressure side, which is the suction side, of the compressor 11. The accumulator 14 stores excess refrigerant generated due to differences in operating conditions between cooling operation and heating operation, excess refrigerant due to transient changes in operation, and the like.

[0022] The first connecting pipe 3 connects the second main pipe 2 downstream of the check valve 15a with the first main pipe 1 downstream of the check valve 15b. The second connecting pipe 4 connects the second main pipe 2 upstream of the check valve 15a with the first main pipe 1 upstream of the check valve 15b. The junction of the second connecting pipe 4 and the second main pipe 2 is shown as junction a, the junction of the first connecting pipe 3 and the second main pipe 2 as junction b (downstream of junction a), the junction of the second connecting pipe 4 and the first main pipe 1 as junction c, and the junction of the first connecting pipe 3 and the first main pipe 1 as junction d (downstream of junction c).

[0023] Check valve 15a is provided between junction a and junction b and allows refrigerant to flow only in the direction from the outdoor unit 10 to the relay unit 30. Check valve 15b is provided between junction c and junction d and allows refrigerant to flow only in the direction from the relay unit 30 to the outdoor unit 10. Check valve 15c is provided in the first connecting pipe 3 and allows refrigerant to flow only in the direction from junction d to junction b. Check valve 15d is provided in the second connecting pipe 4 and allows refrigerant to flow only in the direction from junction c to junction a.

[0024] (Indoor units 20a, 20b) The indoor units 20a, 20b supply heat from the outdoor unit 10 to a cooling load or a heating load, respectively, to cool or heat the space to be air-conditioned. The indoor unit 20a is equipped with an expansion device 21a and a load-side heat exchanger 22a. The indoor unit 20b is equipped with an expansion device 21b and a load-side heat exchanger 22b.

[0025] In the following description, when there is no need to particularly distinguish between the indoor units 20a and 20b, they will be simply referred to as "indoor unit 20." Furthermore, since the expansion device 21a and the expansion device 21b have the same configuration, and the load-side heat exchanger 22a and the load-side heat exchanger 22b have the same configuration, the following description will be given taking the expansion device 21a and the load-side heat exchanger 22a as examples.

[0026] The expansion device 21a functions as a pressure reducing valve and an expansion valve, and reduces the pressure of the refrigerant and expands it by adjusting the flow rate of the refrigerant. The expansion device 21a is configured as a valve whose opening degree can be controlled, such as an electronic expansion valve. In this case, the opening degree of the expansion device 21a is controlled by the control device 40.

[0027] The load-side heat exchanger 22a exchanges heat between the refrigerant and a fluid such as indoor air or water. Specifically, during cooling operation, the load-side heat exchanger 22a functions as an evaporator that evaporates the refrigerant to gasify it and absorbs heat from the outdoor air as heat of vaporization. During heating operation, the load-side heat exchanger 22a functions as a condenser that radiates heat from the refrigerant to the indoor air and condenses the refrigerant to liquid.

[0028] The indoor unit 20a is provided with a blower (not shown), such as a load-side fan, for supplying indoor air to the load-side heat exchanger 22a. The rotation speed of the load-side fan is controlled by the control device 40, thereby controlling the evaporation capacity or condensation capacity of the load-side heat exchanger 22a.

[0029] (Relay unit 30) The relay unit 30 switches the flow of refrigerant depending on the operating conditions, so as to distribute low-temperature refrigerant to the indoor units 20 performing cooling operation and high-temperature refrigerant to the indoor units 20 performing heating operation.

[0030] The relay unit 30 includes a gas-liquid separator 31, a first throttling device 32, a second throttling device 33, first on-off valves 34a, 34b, and second on-off valves 35a, 35b. In the following description, when there is no need to particularly distinguish between the first on-off valves 34a, 34b and the second on-off valves 35a, 35b, they will be simply referred to as the "first on-off valve 34" and the "second on-off valve 35" as appropriate.

[0031] The relay unit 30 is also provided with a connection pipe 7, a connection pipe 8, and a relay pipe 9. The connection pipe 7 connects the gas side of the gas-liquid separator 31 to the first on-off valve 34, and is a pipe through which gas refrigerant flows. The connection pipe 8 connects the liquid side of the gas-liquid separator 31 to the indoor unit 20, and is a pipe through which liquid refrigerant flows. The relay pipe 9 is provided to relay the connection pipe 7 and the connection pipe 8.

[0032] The gas-liquid separator 31 is provided in the second main pipe 2, and is connected to the connecting pipe 7 and the connecting pipe 8. The gas-liquid separator 31 separates the two-phase refrigerant flowing through the second main pipe 2 into gas refrigerant and liquid refrigerant. The gas refrigerant separated in the gas-liquid separator 31 is supplied to the first on-off valve 34 via the connecting pipe 7. The liquid refrigerant separated in the gas-liquid separator 31 is supplied to the first throttle device 32 via the connecting pipe 8.

[0033] The first throttle device 32 is provided in the connecting pipe 8. The first throttle device 32 functions as a pressure reducing valve and an expansion valve, and reduces the pressure and expands the refrigerant by adjusting the flow rate of the refrigerant. The first throttle device 32 is configured by a valve whose opening degree can be controlled, such as an electronic expansion valve. In this case, the opening degree of the first throttle device 32 is controlled by the control device 40.

[0034] The second throttling device 33 is provided in the relay pipe 9. The second throttling device 33 functions as a pressure reducing valve and an expansion valve, and reduces the pressure and expands the refrigerant by adjusting the flow rate of the refrigerant. The second throttling device 33 is configured by a valve whose opening degree can be controlled, such as an electronic expansion valve. In this case, the opening degree of the second throttling device 33 is controlled by the control device 40.

[0035] The first on-off valves 34a, 34b are provided to control the supply of refrigerant to the indoor units 20a, 20b for each operation mode, and are provided between the connection pipe 7 and the first branch pipes 5a, 5b. That is, the first on-off valves 34a, 34b are connected on one side to the gas-liquid separator 31 and on the other side to the load-side heat exchangers 22a, 22b of the indoor units 20a, 20b, respectively, and are controlled to pass or not pass the refrigerant.

[0036] The second on-off valves 35a, 35b also control the supply of refrigerant to the indoor units 20a, 20b for each operation mode, and are provided between the first branch pipes 5a, 5b and the first main pipe 1. That is, the second on-off valves 35a, 35b are connected on one side to the first main pipe 1 and on the other side to the load-side heat exchangers 22a, 22b of the indoor units 20a, 20b, respectively, and are controlled to allow or prevent the refrigerant from flowing through them.

[0037] (Control device 40) The control device 40 controls the entire air conditioning apparatus 100. For example, the control device 40 controls the flow path switching device 12, the throttling devices 21a and 21b, the first throttling device 32, the second throttling device 33, the first on-off valves 34a and 34b, and the second on-off valves 35a and 35b, etc., depending on the operation mode of the air conditioning apparatus 100. The control device 40 realizes various functions by executing software on a calculation device such as a microcomputer, or is composed of hardware such as circuit devices that realize various functions.

[0038] The refrigerant circuit 101 is equipped with a discharge temperature detector 51, a discharge pressure detector 52, an inlet temperature detector 53, a suction pressure detector 54, and condenser outlet temperature detectors 55a and 55b. The discharge temperature detector 51 is provided on the discharge side of the compressor 11 and detects the temperature of the refrigerant discharged from the compressor 11. The discharge pressure detector 52 is provided on the discharge side of the compressor 11 and detects the pressure of the refrigerant discharged from the compressor 11. The inlet temperature detector 53 is provided at the inlet of the accumulator 14 and detects the temperature of the refrigerant flowing into the accumulator 14. The suction pressure detector 54 is provided on the suction side of the compressor 11 and detects the pressure of the refrigerant drawn into the compressor 11. The suction pressure detector 54 may alternatively be provided at the inlet of the accumulator 14. The condenser outlet temperature detectors 55a, 55b are provided at the outlets of the load-side heat exchangers 22a, 22b when they function as condensers, and detect the temperatures of the refrigerant flowing out of the load-side heat exchangers 22a, 22b when they function as condensers. The discharge temperature detector 51, the inlet temperature detector 53, and the condenser outlet temperature detectors 55a, 55b are, for example, thermistors, and the discharge pressure detector 52 and the suction pressure detector 54 are, for example, pressure gauges.

[0039] [Refrigerant Operation in Air Conditioning Apparatus 100] Next, we will explain the operation of the refrigerant in various operation modes in the air conditioning apparatus 100 having the above configuration. The air conditioning apparatus 100 has the following operation modes: full cooling operation, cooling-dominated operation, full heating operation, heating-dominated operation, and defrost operation, and performs one of these operations.

[0040] The full cooling operation is a type of cooling operation in which all indoor units 20 cool the air-conditioned space. The cooling-dominated operation is a type of cooling operation in which the cooling load of the indoor units 20 that cool the air-conditioned space exceeds the heating load of the indoor units 20 that heat the air-conditioned space. The full heating operation is a type of heating operation in which all indoor units 20 heat the air-conditioned space. The heating-dominated operation is a type of heating operation in which the heating load of the indoor units 20 that heat the air-conditioned space exceeds the cooling load of the indoor units 20 that cool the air-conditioned space. The defrost operation is an operation performed to remove frost that has formed on the heat source-side heat exchanger 13 during heating operation (full heating operation or heating-dominated operation).

[0041] (Cooling only operation) Figure 2 is a schematic diagram for explaining the flow of refrigerant during cooling only operation in the air conditioning apparatus 100 of Figure 1. During cooling only operation, all indoor units 20a, 20b cool the air-conditioned space. In Figure 2, the arrows indicate the direction of refrigerant flow during cooling only operation.

[0042] In the cooling only operation, first, the flow path switching device 12 in the outdoor unit 10 is switched so that the discharge side of the compressor 11 is connected to the heat source side heat exchanger 13 and the suction side of the compressor 11 is connected to the first main pipe 1. In addition, the first on-off valves 34a and 34b are closed and the second on-off valves 35a and 35b are opened.

[0043] The low-temperature, low-pressure refrigerant is compressed by the compressor 11 and discharged as high-temperature, high-pressure gas refrigerant. The high-temperature, high-pressure gas refrigerant discharged from the compressor 11 flows into the heat source-side heat exchanger 13 via the flow switching device 12. The high-temperature, high-pressure gas refrigerant that has flowed into the heat source-side heat exchanger 13 exchanges heat with the outdoor air, condenses while releasing heat, and becomes high-pressure liquid refrigerant, which flows out of the heat source-side heat exchanger 13. The high-pressure liquid refrigerant that has flowed out of the heat source-side heat exchanger 13 passes through the second main pipe 2, flows out of the outdoor unit 10, and flows into the relay unit 30.

[0044] The high-pressure liquid refrigerant that has flowed into the relay unit 30 flows through the gas-liquid separator 31 into the first throttle device 32, where it is reduced in pressure and expanded to become intermediate-pressure liquid refrigerant. The intermediate-pressure liquid refrigerant then passes through the connecting pipe 8, is branched into the second branch pipes 6a and 6b, and flows out of the relay unit 30. The intermediate-pressure liquid refrigerant that has flowed out of the relay unit 30 passes through the second branch pipes 6a and 6b and flows into the indoor units 20a and 20b.

[0045] The intermediate-pressure liquid refrigerant that flows into the indoor unit 20a is decompressed and expanded by the expansion device 21a to become a low-temperature, low-pressure, two-phase gas-liquid refrigerant, which then flows into the load-side heat exchanger 22a. The low-temperature, low-pressure, two-phase gas-liquid refrigerant that flows into the load-side heat exchanger 22a exchanges heat with the indoor air, absorbing heat and evaporating, thereby cooling the indoor air, and then becomes a low-pressure gas refrigerant that flows out of the load-side heat exchanger 22a. The low-pressure gas refrigerant that flows out of the load-side heat exchanger 22a passes through the first branch pipe 5a, flows out of the indoor unit 20a, and flows into the relay unit 30.

[0046] The intermediate-pressure liquid refrigerant that flows into the indoor unit 20b also becomes low-pressure gas refrigerant through the expansion device 21b and the load-side heat exchanger 22b, just like the refrigerant that flows into the indoor unit 20a. The low-pressure gas refrigerant then passes through the first branch pipe 5b, flows out of the indoor unit 20b, and flows into the relay unit 30.

[0047] The low-pressure gas refrigerant that has flowed into the relay unit 30 reaches the first main pipe 1 via the second on-off valves 35a and 35b, flows out of the relay unit 30, and then flows into the outdoor unit 10. The low-pressure gas refrigerant that has flowed into the outdoor unit 10 passes through the flow path switching device 12 and the accumulator 14, and is sucked into the compressor 11. Then, the above-described circulation is repeated thereafter.

[0048] (Cooling-dominated operation) Figure 3 is a schematic diagram for explaining the flow of refrigerant during cooling-dominated operation in the air conditioning apparatus 100 of Figure 1. Here, an example will be described in which the indoor unit 20a cools the air-conditioned space and the indoor unit 20b heats the air-conditioned space. In Figure 3, the arrows indicate the direction of refrigerant flow during cooling-dominated operation.

[0049] In cooling-dominated operation, first, the flow path switching device 12 in the outdoor unit 10 is switched so that the discharge side of the compressor 11 is connected to the heat source-side heat exchanger 13 and the suction side of the compressor 11 is connected to the first main pipe 1. In addition, the first on-off valve 34a and the second on-off valve 35b are closed, and the first on-off valve 34b and the second on-off valve 35a are opened.

[0050] The low-temperature, low-pressure refrigerant is compressed by the compressor 11 and discharged as high-temperature, high-pressure gas refrigerant. The high-temperature, high-pressure gas refrigerant discharged from the compressor 11 flows into the heat source-side heat exchanger 13 via the flow switching device 12. The high-temperature, high-pressure gas refrigerant that has flowed into the heat source-side heat exchanger 13 exchanges heat with the outdoor air and condenses while releasing heat, becoming high-pressure two-phase gas-liquid refrigerant that flows out of the heat source-side heat exchanger 13. The high-pressure two-phase gas-liquid refrigerant that has flowed out of the heat source-side heat exchanger 13 passes through the second main pipe 2, flows out of the outdoor unit 10, and flows into the relay unit 30.

[0051] The high-pressure gas-liquid two-phase refrigerant that has flowed into the relay unit 30 flows into the gas-liquid separator 31 and is separated into high-pressure gas refrigerant and high-pressure liquid refrigerant. The high-pressure gas refrigerant separated by the gas-liquid separator 31 passes through the connecting pipe 7, then passes through the first branch pipe 5b via the first on-off valve 34b, and flows out of the relay unit 30. The high-pressure gas refrigerant that has flowed out of the relay unit 30 flows into the indoor unit 20b.

[0052] The high-pressure gas refrigerant that has flowed into the indoor unit 20b flows into the load-side heat exchanger 22b, where it exchanges heat with the indoor air and condenses while releasing heat, heating the indoor air, and then turns into high-pressure liquid refrigerant and flows out of the load-side heat exchanger 22b. The high-pressure liquid refrigerant that has flowed out of the load-side heat exchanger 22b is reduced in pressure and expanded by the expansion device 21b, becoming intermediate-pressure liquid refrigerant, which flows out of the indoor unit 20b and then flows into the relay unit 30.

[0053] The intermediate-pressure liquid refrigerant that flows into the relay unit 30 passes through the second branch pipe 6b and then branches, with one branch passing through the second branch pipe 6a and flowing out of the relay unit 30. The intermediate-pressure liquid refrigerant that flows out of the relay unit 30 flows into the indoor unit 20a.

[0054] The intermediate-pressure liquid refrigerant that flows into the indoor unit 20a is decompressed and expanded by the throttling device 21a to become a low-temperature, low-pressure, two-phase gas-liquid refrigerant, which then flows into the load-side heat exchanger 22a. The low-temperature, low-pressure, two-phase gas-liquid refrigerant that flows into the load-side heat exchanger 22a exchanges heat with the indoor air, absorbing heat and evaporating, thereby cooling the indoor air, and then becomes a low-pressure gas refrigerant that flows out of the load-side heat exchanger 22a. The low-pressure gas refrigerant that flows out of the load-side heat exchanger 22a passes through the first branch pipe 5a, flows out of the indoor unit 20a, and flows into the relay unit 30. The low-pressure gas refrigerant that flows into the relay unit 30 reaches the first main pipe 1 via the second on-off valve 35a.

[0055] Meanwhile, the high-pressure liquid refrigerant separated by the gas-liquid separator 31 passes through the connecting pipe 8, then flows into the first throttling device 32, where it is decompressed and expanded to become intermediate-pressure liquid refrigerant. The intermediate-pressure liquid refrigerant flowing out of the first throttling device 32 merges with the intermediate-pressure liquid refrigerant that flowed from the indoor unit 20b into the relay unit 30 and was then diverted, and passes through the relay pipe 9. The intermediate-pressure liquid refrigerant passing through the relay pipe 9 is decompressed and expanded by the second throttling device 33 to become low-pressure liquid refrigerant. The low-pressure liquid refrigerant then reaches the first main pipe 1, where it merges with the low-pressure gas refrigerant passing through the first main pipe 1 via the second on-off valve 35a, and flows out of the relay unit 30.

[0056] The low-pressure refrigerant flowing out of the relay unit 30 flows into the outdoor unit 10 via the first main pipe 1. The low-pressure refrigerant flowing into the outdoor unit 10 passes through the flow switching device 12 and the accumulator 14, and is then drawn into the compressor 11. The above-described circulation is then repeated.

[0057] (Heating only operation) Figure 4 is a schematic diagram for explaining the flow of refrigerant during heating only operation in the air conditioning apparatus 100 of Figure 1. During heating only operation, all of the indoor units 20a, 20b heat the air-conditioned space. In Figure 4, the arrows indicate the direction of refrigerant flow during heating only operation.

[0058] In the heating only operation, first, the flow path switching device 12 in the outdoor unit 10 is switched so that the discharge side of the compressor 11 is connected to the first main pipe 1 and the suction side of the compressor 11 is connected to the heat source side heat exchanger 13. In addition, the first on-off valves 34a and 34b are opened and the second on-off valves 35a and 35b are closed. Furthermore, the first expansion device 32 is fully closed and the second expansion device 33 is fully opened.

[0059] The low-temperature, low-pressure refrigerant is compressed by the compressor 11 and discharged as high-temperature, high-pressure gas refrigerant. The high-temperature, high-pressure gas refrigerant discharged from the compressor 11 flows out of the outdoor unit 10 via the flow path switching device 12, the first main pipe 1, the first connecting pipe 3, and the second main pipe 2, and flows into the relay unit 30. The high-temperature, high-pressure gas refrigerant that has flowed into the relay unit 30 passes through the first branch pipes 5a, 5b via the gas-liquid separator 31, the connecting pipe 7, and the first on-off valves 34a, 34b, before flowing out of the relay unit 30 and flowing into the indoor units 20a, 20b.

[0060] The high-temperature, high-pressure gas refrigerant that flows into the indoor unit 20a flows into the load-side heat exchanger 22a, where it exchanges heat with the indoor air and condenses while releasing heat, heating the indoor air, and then turns into high-pressure liquid refrigerant, which flows out of the load-side heat exchanger 22a. The high-pressure liquid refrigerant that flows out of the load-side heat exchanger 22a is decompressed and expanded by the expansion device 21a, becoming low-pressure liquid refrigerant, and after flowing out of the indoor unit 20a, flows into the relay unit 30 through the second branch pipe 6a.

[0061] The high-temperature, high-pressure gas refrigerant that flows into the indoor unit 20b also becomes low-pressure liquid refrigerant through the load-side heat exchanger 22b and the expansion device 21b, just like the refrigerant that flows into the indoor unit 20a. After flowing out of the indoor unit 20b, the low-pressure liquid refrigerant flows into the relay unit 30 through the second branch pipe 6b.

[0062] The low-pressure liquid refrigerant that flows into the relay unit 30 flows out of the relay unit 30 via the second expansion device 33 and the first main pipe 1. The low-pressure liquid refrigerant that flows out of the relay unit 30 flows into the outdoor unit 10 via the first main pipe 1. The low-pressure liquid refrigerant that flows into the outdoor unit 10 flows into the heat source side heat exchanger 13 via the second connection pipe 4 and the second main pipe 2. The low-pressure liquid refrigerant that flows into the heat source side heat exchanger 13 exchanges heat with the outdoor air, absorbs heat, and evaporates, becoming low-temperature, low-pressure gas refrigerant that flows out of the heat source side heat exchanger 13. The low-pressure gas refrigerant that flows out of the heat source side heat exchanger 13 passes through the flow switching device 12 and the accumulator 14, and is drawn into the compressor 11. The above-described circulation is then repeated.

[0063] (Heating-dominant operation) Figure 5 is a schematic diagram for explaining the flow of refrigerant during heating-dominant operation in the air conditioning apparatus 100 of Figure 1. Here, an example will be described in which the indoor unit 20b heats the air-conditioned space and the indoor unit 20a cools the air-conditioned space. In Figure 5, the arrows indicate the direction of refrigerant flow during heating-dominant operation.

[0064] In heating-dominated operation, first, the flow path switching device 12 in the outdoor unit 10 is switched so that the discharge side of the compressor 11 is connected to the first main pipe 1 and the suction side of the compressor 11 is connected to the heat source-side heat exchanger 13. In addition, the first on-off valve 34a and the second on-off valve 35b are closed, and the first on-off valve 34b and the second on-off valve 35a are opened. Furthermore, the first expansion device 32 and the second expansion device 33 are fully closed.

[0065] The low-temperature, low-pressure refrigerant is compressed by the compressor 11 and discharged as high-temperature, high-pressure gas refrigerant. The high-temperature, high-pressure gas refrigerant discharged from the compressor 11 flows out of the outdoor unit 10 via the flow path switching device 12, the first main pipe 1, the first connecting pipe 3, and the second main pipe 2, and flows into the relay unit 30. The high-temperature, high-pressure gas refrigerant that has flowed into the relay unit 30 passes through the first branch pipe 5b via the gas-liquid separator 31, the connecting pipe 7, and the first on-off valve 34b, then flows out of the relay unit 30 and flows into the indoor unit 20b.

[0066] The high-temperature, high-pressure gas refrigerant that has flowed into the indoor unit 20b flows into the load-side heat exchanger 22b, where it exchanges heat with the indoor air and condenses while releasing heat, heating the indoor air, and turns into high-pressure liquid refrigerant, which then flows out of the load-side heat exchanger 22b. The high-pressure liquid refrigerant that has flowed out of the load-side heat exchanger 22b is reduced in pressure and expanded by the expansion device 21b, becoming intermediate-pressure liquid refrigerant, which then flows out of the indoor unit 20b and flows into the relay unit 30 through the second branch pipe 6a.

[0067] The intermediate-pressure liquid refrigerant that flows into the relay unit 30 passes through the second branch pipe 6b and then the second branch pipe 6a, and flows out of the relay unit 30. The intermediate-pressure liquid refrigerant that flows out of the relay unit 30 flows into the indoor unit 20a.

[0068] The intermediate-pressure liquid refrigerant that flows into the indoor unit 20a is decompressed and expanded by the expansion device 21a to become a low-temperature, low-pressure, two-phase gas-liquid refrigerant, which then flows into the load-side heat exchanger 22a. The low-temperature, low-pressure, two-phase gas-liquid refrigerant that flows into the load-side heat exchanger 22a exchanges heat with the indoor air, absorbing heat and evaporating, thereby cooling the indoor air, and then becomes a low-pressure gas refrigerant that flows out of the load-side heat exchanger 22a. The low-pressure gas refrigerant that flows out of the load-side heat exchanger 22a passes through the first branch pipe 5a, flows out of the indoor unit 20a, and flows into the relay unit 30. The low-pressure gas refrigerant that flows into the relay unit 30 reaches the first main pipe 1 via the second on-off valve 35a. The low-pressure gas refrigerant then flows out of the relay unit 30 via the first main pipe 1.

[0069] The low-pressure liquid refrigerant flowing out from the relay unit 30 flows into the outdoor unit 10 via the first main pipe 1. The low-pressure liquid refrigerant that has flowed into the outdoor unit 10 flows into the heat source-side heat exchanger 13 via the second connecting pipe 4 and the second main pipe 2. The low-pressure liquid refrigerant that has flowed into the heat source-side heat exchanger 13 exchanges heat with the outdoor air, absorbs heat, and evaporates, becoming low-temperature, low-pressure gas refrigerant that flows out of the heat source-side heat exchanger 13. The low-pressure gas refrigerant that has flowed out of the heat source-side heat exchanger 13 passes through the flow switching device 12 and the accumulator 14, and is drawn into the compressor 11. The above-described circulation is then repeated.

[0070] (Defrosting Operation) Figure 6 is a schematic diagram for explaining the flow of refrigerant during defrosting operation in the air conditioning apparatus 100 of Figure 1. In Figure 6, the direction of refrigerant flow during defrosting operation is indicated by arrows.

[0071] In defrost operation, the heating operation (full heating operation or heating-dominant operation) is interrupted, and the flow path switching device 12 in the outdoor unit 10 is switched so that the discharge side of the compressor 11 is connected to the heat source-side heat exchanger 13 and the suction side of the compressor 11 is connected to the first main pipe 1. In addition, the first on-off valves 34a, 34b and the second on-off valves 35a, 35b are closed. Furthermore, the expansion devices 21a, 21b are fully closed.

[0072] When low-temperature, low-pressure gas refrigerant is drawn into the compressor 11, it is compressed by the compressor 11 and becomes high-temperature, high-pressure gas refrigerant, which is then discharged from the compressor 11. The gas refrigerant discharged from the compressor 11 passes through the flow switching device 12 and flows into the heat source-side heat exchanger 13. The high-temperature, high-pressure gas refrigerant that flows into the heat source-side heat exchanger 13 exchanges heat with the surrounding air and becomes liquid refrigerant. The heat source-side heat exchanger 13 functions as a condenser that radiates heat into the surrounding air and lowers the refrigerant temperature in the piping. Therefore, the heat radiated into the air by the heat source-side heat exchanger 13 melts frost adhering to the surface of the heat source-side heat exchanger 13. At this time, a blower (not shown) disposed near the heat source-side heat exchanger 13 is often stopped. The liquid refrigerant flowing out of the heat source-side heat exchanger 13 flows through the second main pipe 2 into the relay unit 30.

[0073] The liquid refrigerant that flows into the relay unit 30 passes through the connecting pipe 8, then flows into the first throttle device 32, where it is decompressed and expanded, and then passes through the relay pipe 9, where it is decompressed and expanded by the second throttle device 33, becoming a low-temperature, low-pressure gas. The low-temperature, low-pressure gas refrigerant then flows out of the relay unit 30 via the first main pipe 1. The low-temperature, low-pressure gas refrigerant that has flowed out of the relay unit 30 flows into the outdoor unit 10 via the first main pipe 1. The low-temperature, low-pressure gas refrigerant that has flowed into the outdoor unit 10 passes through the flow path switching device 12 and the accumulator 14, and is drawn into the compressor 11. The above-described circulation is then repeated.

[0074] In defrost operation, the first on-off valves 34a, 34b and the second on-off valves 35a, 35b are closed and the expansion devices 21a, 21b are fully closed, so the liquid refrigerant stored in the indoor units 20a, 20b is retained in the indoor units 20a, 20b as is. In other words, the liquid refrigerant stored in the indoor units 20a, 20b does not flow to the outdoor unit 10, so it is possible to prevent the amount of inflow to the outdoor unit 10 from increasing and causing the liquid refrigerant stored in the accumulator 14 to overflow and return to the compressor 11.

[0075] Furthermore, after returning from defrost operation to heating operation, a process occurs in which the liquid refrigerant accumulated in the accumulator 14 of the outdoor unit 10 is expelled and stored again in the indoor unit 20. Therefore, if a large amount of liquid refrigerant accumulates in the accumulator 14, the start-up of heating capacity after returning from defrost operation to heating operation will be delayed accordingly. Therefore, the refrigerant accumulated in the indoor units 20a, 20b is retained in the indoor units 20a, 20b and is prevented from flowing to the outdoor unit 10. This improves the start-up of heating capacity after returning from defrost operation to heating operation, and improves heating capacity at low outdoor temperatures.

[0076] 7 is a flowchart showing the control process after the air conditioning apparatus 100 according to the embodiment returns from defrost operation to heating operation. After returning from defrost operation to heating operation, the air conditioning apparatus 100 according to the embodiment executes the control process shown in FIG. 7 at preset intervals (e.g., once every 30 seconds) for several minutes (e.g., 10 minutes).

[0077] (Step S1) The control device 40 performs a first determination process to determine whether the difference between the temperature detected by the discharge temperature detection device 51 and the saturation temperature (condensation temperature) converted from the pressure detected by the discharge pressure detection device 52 is equal to or greater than a predetermined first threshold value B1 (compressor discharge temperature - saturation temperature (condensation temperature) ≧ B1), and whether the difference between the temperature detected by the inlet temperature detection device 53 and the saturation temperature (evaporation temperature) converted from the pressure detected by the suction pressure detection device 54 is equal to or greater than a predetermined second threshold value B2 (accumulator inlet temperature - saturation temperature (evaporation temperature) ≧ B2). If the conditions of the first determination process are met, the process proceeds to step S2. If the conditions of the first determination process are not met, the process proceeds to step S3.

[0078] (Step S2) The control device 40 performs a second determination process to determine whether the difference between the temperature detected by the discharge temperature detection device 51 and the saturation temperature (condensing temperature) converted from the pressure detected by the discharge pressure detection device 52 is equal to or greater than a predetermined third threshold A1 (> B1) (compressor discharge temperature - saturation temperature (condensing temperature) ≧ A1), and whether the difference between the temperature detected by the inlet temperature detection device 53 and the saturation temperature (evaporating temperature) converted from the pressure detected by the suction pressure detection device 54 is equal to or greater than a predetermined fourth threshold A2 (> B2) (accumulator inlet temperature - saturation temperature (evaporating temperature) ≧ A2). If the conditions of the second determination process are met, the process proceeds to step S4. If the conditions of the second determination process are not met, the process proceeds to step S5.

[0079] (Step S3) The control device 40 determines that too much liquid refrigerant is returning to the outdoor unit 10 and reduces the opening of the throttling devices 21a, 21b of the indoor units 20a, 20b. If too much liquid refrigerant returns from the indoor units 20a, 20b to the outdoor unit 10, the liquid refrigerant accumulated in the accumulator 14 may overflow and return to the compressor 11, potentially causing a malfunction. Furthermore, after returning from defrosting operation to heating operation, a process occurs in which the liquid refrigerant accumulated in the accumulator 14 of the outdoor unit 10 is expelled and then accumulated again in the indoor unit 20. Therefore, if the amount of liquid refrigerant accumulated in the accumulator 14 is large, the start-up of the heating capacity after returning from defrosting operation to heating operation will be delayed accordingly. Therefore, if too much liquid refrigerant is returning from the indoor units 20a, 20b to the outdoor unit 10, the opening of the throttling devices 21a, 21b of the indoor units 20a, 20b is reduced. This prevents excessive return of liquid refrigerant from the indoor units 20a, 20b to the outdoor unit 10, and prevents the liquid refrigerant accumulated in the accumulator 14 from overflowing and returning to the compressor 11. Furthermore, the start-up of heating capacity after returning from defrost operation to heating operation can be improved, and heating capacity at low outdoor temperatures can be improved.

[0080] (Step S4) The control device 40 determines that the liquid refrigerant returning from the indoor units 20a, 20b to the outdoor unit 10 is insufficient, and increases the opening of the throttling devices 21a, 21b of the indoor units 20a, 20b. If the liquid refrigerant returning from the indoor units 20a, 20b to the outdoor unit 10 is insufficient, the pressure on the suction side of the compressor 11 decreases, which reduces the suction density of the compressor 11 and causes a decrease in heating capacity. Therefore, by increasing the opening of the throttling devices 21a, 21b of the indoor units 20a, 20b when the liquid refrigerant returning from the indoor units 20a, 20b to the outdoor unit 10 is insufficient, the pressure on the suction side decreases, which reduces the suction density of the compressor 11 and prevents a decrease in heating capacity.

[0081] (Step S5) The control device 40 determines that the apertures of the throttling devices 21a and 21b of the indoor units 20a and 20b are appropriate, and performs subcooling control at the outlets of the load-side heat exchangers 22a and 22b. That is, the apertures of the throttling devices 21a and 21b are controlled so that the subcooling (degree of supercooling) at the outlets of the load-side heat exchangers 22a and 22b is a preset value. Here, the subcooling at the outlets of the load-side heat exchangers 22a and 22b is the saturation temperature (condensing temperature) converted from the pressure detected by the discharge pressure detection device 52 minus the temperature detected by the condenser outlet temperature detection devices 55a and 55b (SC = saturation temperature (condensing temperature) - condenser outlet temperature).

[0082] The above A1 and B1 are values ​​corresponding to the compression ratio, for example, A1=30° C. and B1=25° C. The above A2 and B2 are values ​​that determine whether or not superheat occurs at the inlet of the accumulator 14, for example, A2=5° C. and B2=3° C.

[0083] As described above, the air conditioning apparatus 100 according to the embodiment includes the outdoor unit 10 having the compressor 11, the flow switching device 12, the heat source side heat exchanger 13, and the accumulator 14, the indoor units 20a, 20b having the expansion devices 21a, 21b and the load side heat exchangers 22a, 22b, the relay unit 30 connected between the outdoor unit 10 and the indoor units 20a, 20b and switching the refrigerant flow depending on the operating conditions, and the outdoor unit 10, the relay unit 30, and the indoor units 20a, 20b. the accumulator 14, and the like. The refrigerant circuit 101 is connected to the accumulator 14 by pipes and circulates a refrigerant therethrough; a control device 40 for controlling the refrigerant circuit 101; a discharge temperature detection device 51 for detecting the temperature of the refrigerant discharged from the compressor 11; a discharge pressure detection device 52 for detecting the pressure of the refrigerant discharged from the compressor 11; an inlet temperature detection device 53 for detecting the temperature of the refrigerant flowing into the accumulator 14; and a suction pressure detection device 54 for detecting the pressure of the refrigerant sucked into the compressor 11. Then, during defrost operation, the control device 40 switches the flow path switching device 12 so that the refrigerant discharged from the compressor 11 flows into the heat source side heat exchanger 13, and fully closes the throttling device 21.After returning from defrost operation to heating operation, the control device 40 performs a first judgment process to determine whether the difference between the temperature detected by the discharge temperature detection device 51 and the saturation temperature (condensation temperature) converted from the pressure detected by the discharge pressure detection device 52 is greater than or equal to a first threshold value, which is a predetermined value, and whether the difference between the temperature detected by the inlet temperature detection device 53 and the saturation temperature (evaporation temperature) converted from the pressure detected by the suction pressure detection device 54 is greater than or equal to a second threshold value, which is a predetermined value.If the conditions of the first judgment process are not met, the opening of the throttling device is reduced.

[0084] In the air conditioning apparatus 100 according to the embodiment, the control device 40 switches the flow path switching device 12 during defrost operation so that the refrigerant discharged from the compressor 11 flows into the heat source-side heat exchanger 13 and fully closes the throttling devices 21a, 21b, and after returning to heating operation from defrost operation, performs a first determination process to determine whether too much liquid refrigerant is returning to the outdoor unit 10. If the conditions of the first determination process are not met, the control device 40 reduces the opening degrees of the throttling devices 21a, 21b. In this way, by fully closing the throttling devices 21a, 21b of the indoor units 20a, 20b during defrost operation, the liquid refrigerant stored in the indoor units 20a, 20b does not flow to the outdoor unit 10, thereby suppressing liquid backflow to the compressor 11. Furthermore, if too much liquid refrigerant is returning from the indoor units 20a, 20b to the outdoor unit 10 after returning from defrost operation to heating operation, by reducing the opening of the throttling devices 21a, 21b of the indoor units 20a, 20b, it is possible to prevent too much liquid refrigerant from returning from the indoor units 20a, 20b to the outdoor unit 10 and to prevent liquid backflow to the compressor 11.Furthermore, it is possible to improve the start-up of heating capacity after returning from defrost operation to heating operation and to improve heating capacity at low outdoor temperatures.

[0085] Furthermore, in the air conditioning apparatus 100 according to the embodiment, the control device 40 performs a first judgment process, and if the conditions of the first judgment process are met, it performs a second judgment process to determine whether the difference between the temperature detected by the discharge temperature detection device 51 and the saturation temperature (condensation temperature) converted from the pressure detected by the discharge pressure detection device 52 is equal to or greater than a third threshold value that is a pre-set value greater than the first threshold value, and whether the difference between the temperature detected by the inlet temperature detection device 53 and the saturation temperature (evaporation temperature) converted from the pressure detected by the suction pressure detection device 54 is equal to or greater than a fourth threshold value that is a pre-set value greater than the second threshold value, and if the conditions of the second judgment process are met, it increases the opening of the throttling devices 21a, 21b.

[0086] According to the air conditioning apparatus 100 of this embodiment, a first determination process is performed, and if the conditions of the first determination process are satisfied, a second determination process is performed to determine whether or not there is insufficient liquid returning to the outdoor unit 10, and if the conditions of the second determination process are satisfied, the openings of the throttling devices 21a, 21b are increased. In other words, if there is insufficient liquid returning to the outdoor unit 10, by increasing the openings of the throttling devices 21a, 21b of the indoor units 20a, 20b, the pressure on the suction side decreases, the suction density of the compressor 11 decreases, and a decrease in heating capacity can be suppressed.

[0087] Furthermore, in the air conditioning apparatus 100 according to the embodiment, the control device 40 executes the control process including the first determination process and the second determination process at predetermined intervals for a predetermined time after returning from defrost operation to heating operation.

[0088] According to the air conditioning apparatus 100 of the embodiment, by performing the first determination process to determine whether too much liquid refrigerant is returning to the outdoor unit 10 and the second determination process to determine whether insufficient liquid is returning to the outdoor unit 10 at the above-mentioned timing, it is possible to efficiently eliminate excessive return of liquid refrigerant to the outdoor unit 10 and insufficient return of liquid refrigerant to the outdoor unit 10.

[0089] 1 First main pipe, 2 Second main pipe, 3 First connecting pipe, 4 Second connecting pipe, 5a First branch pipe, 5b First branch pipe, 6a Second branch pipe, 6b Second branch pipe, 7 Connecting pipe, 8 Connecting pipe, 9 Relay pipe, 10 Outdoor unit, 11 Compressor, 12 Flow path switching device, 13 Heat source side heat exchanger, 14 Accumulator, 15a Check valve, 15b Check valve, 15c Check valve, 15d Check valve, 20 Indoor unit, 20a Indoor unit, 20b Indoor unit, 21a Throttle device, 21b Throttle device, 22a Load side heat exchanger, 22b Load side heat exchanger, 30 Relay unit, 31 Gas-liquid separator, 32 First throttle device, 33 Second throttle device, 34 First opening / closing valve, 34a First opening / closing valve, 34b First opening / closing valve, 35 Second on-off valve, 35a Second on-off valve, 35b Second on-off valve, 40 Control device, 51 Discharge temperature detection device, 52 Discharge pressure detection device, 53 Inlet temperature detection device, 54 Suction pressure detection device, 55a Condenser outlet temperature detection device, 55b Condenser outlet temperature detection device, 100 Air conditioning device, 101 Refrigerant circuit.

Claims

1. an outdoor unit having a compressor, a flow switching device, a heat source side heat exchanger, and an accumulator; an indoor unit having a throttling device and a load-side heat exchanger; A relay unit that is connected between the outdoor unit and the indoor unit and switches the flow of the refrigerant depending on an operating condition; a refrigerant circuit in which the outdoor unit, the relay unit, and the indoor units are connected by piping and in which a refrigerant circulates; A control device for controlling the refrigerant circuit; a discharge temperature detection device that detects the temperature of the refrigerant discharged from the compressor; a discharge pressure detection device that detects the pressure of the refrigerant discharged from the compressor; an inlet temperature detector that detects the temperature of the refrigerant flowing into the accumulator; a suction pressure detection device that detects the pressure of the refrigerant sucked into the compressor, The control device includes: During defrost operation, a flow switching device is switched so that the refrigerant discharged from the compressor flows into the heat source side heat exchanger, and the throttle device is fully closed; After returning from the defrost operation to the heating operation, a first determination process for determining whether or not an excessive amount of liquid refrigerant is returning to the outdoor unit by determining whether or not a difference between the temperature detected by the discharge temperature detection device and a condensation temperature converted from the pressure detected by the discharge pressure detection device is equal to or greater than a first threshold value which is a preset value, and whether or not a difference between the temperature detected by the inlet temperature detection device and an evaporation temperature converted from the pressure detected by the suction pressure detection device is equal to or greater than a second threshold value which is a preset value; When the condition of the first determination process is not satisfied, the opening degree of the throttling device is reduced to suppress liquid backflow to the compressor. Air conditioning units.

2. The control device includes: When the first determination process is performed and the condition of the first determination process is satisfied, a second determination process is performed to determine whether or not the difference between the temperature detected by the discharge temperature detection device and the condensation temperature converted from the pressure detected by the discharge pressure detection device is equal to or greater than a third threshold value that is a preset value greater than the first threshold value, and whether or not the difference between the temperature detected by the inlet temperature detection device and the evaporation temperature converted from the pressure detected by the suction pressure detection device is equal to or greater than a fourth threshold value that is a preset value greater than the second threshold value, and to determine whether or not the liquid returning to the outdoor unit is insufficient; When the condition of the second determination process is satisfied, the opening degree of the expansion device is increased to suppress the occurrence of a decrease in heating capacity. The air conditioning apparatus according to claim 1.

3. The control device includes: The second determination process is performed, and if the condition of the second determination process is not satisfied, the opening degree of the expansion device is controlled so that the subcooling at the outlet of the load side heat exchanger becomes a preset value. The air conditioning apparatus according to claim 2.

4. The control device includes: A control process including the first determination process and the second determination process is executed at predetermined intervals for a predetermined time after returning from the defrost operation to the heating operation. The air conditioning apparatus according to claim 3.