Air conditioning system

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

Technical Field

[0001] The present disclosure relates to an air conditioner capable of performing a defrost operation.

Background Art

[0002] Conventionally, when frost forms on the heat exchanger of an outdoor unit during heating operation, an air conditioner that defrosts (removes frost) the heat exchanger has been proposed (see, for example, Patent Document 1).

[0003] In Patent Document 1, during heating operation, when there is a defrost request for any one of a plurality of heat exchangers of the outdoor unit, only the flow path switching mechanism of the heat exchanger with the defrost request is switched, and the high-temperature refrigerant discharged from the compressor is directly introduced into the heat exchanger with the defrost request to perform the defrost operation.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In Patent Document 1, during the defrost operation, since the throttle device of the indoor unit is open, the liquid refrigerant accumulated in the heat exchanger of the indoor unit during heating operation flows into the outdoor unit through the throttle device of the indoor unit. And when the inflow amount of the liquid refrigerant into the outdoor unit increases, there is a problem that liquid backflow occurs to the compressor of the outdoor unit.

[0006] The present disclosure has been made to solve the above problems, and an object thereof is to provide an air conditioner capable of suppressing liquid backflow to the compressor.

Means for Solving the Problems

[0007] The air conditioning system according to this disclosure includes 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 unit connected between the outdoor unit and the indoor unit, which switches the flow of refrigerant according to the operating conditions; a refrigerant circuit through which the refrigerant circulates, with the outdoor unit, the relay unit, and the indoor unit connected by piping; a control device for controlling the refrigerant circuit; a discharge temperature detection device for detecting the temperature of the refrigerant discharged from the compressor; a discharge pressure detection device for detecting the pressure of the refrigerant discharged from the compressor; an inlet temperature detection device for detecting the temperature of the refrigerant flowing into the accumulator; and a suction device for the compressor. The control device includes an intake pressure detection device that detects the pressure of the incoming refrigerant. During defrost operation, 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, and completely closes the throttle device. After returning from defrost operation to heating operation, the control device determines whether the difference between the temperature detected by the discharge temperature detection device and the condensation temperature calculated from the pressure detected by the discharge pressure detection device is greater than or equal to a first threshold value which is a preset value, and whether the difference between the temperature detected by the inlet temperature detection device and the evaporation temperature calculated from the pressure detected by the intake pressure detection device is greater than or equal to a second threshold value which is a preset value. Then, it is determined whether too much liquid refrigerant is returning to the outdoor unit. A first determination process is performed, and if the conditions of the first determination process are not met, the opening degree of the aperture device is reduced. This suppresses liquid backflow to the compressor. It is. [Effects of the Invention]

[0008] According to the air conditioning system described in this disclosure, 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 also completely closes the throttle device. After returning from defrost operation to heating operation, it performs a first determination process to determine whether too much liquid refrigerant has returned to the outdoor unit, and if the conditions of the first determination process are not met, it reduces the opening of the throttle device. In this way, by completely closing the throttle device of the indoor unit during defrost operation, the liquid refrigerant stored in the indoor unit does not flow to the outdoor unit, thus suppressing liquid backflow to the compressor. Furthermore, after returning from defrost operation to heating operation, if too much liquid refrigerant has returned from the indoor unit to the outdoor unit, reducing the opening of the throttle device of the indoor unit suppresses the return of too much liquid refrigerant from the indoor unit to the outdoor unit, thereby suppressing liquid backflow to the compressor. [Brief explanation of the drawing]

[0009] [Figure 1] This is a schematic diagram showing an example of the refrigerant circuit configuration of an air conditioning system according to an embodiment. [Figure 2] Figure 1 is a schematic diagram illustrating the refrigerant flow in the air conditioning system during full cooling operation. [Figure 3] Figure 1 is a schematic diagram illustrating the refrigerant flow in the air conditioning system during cooling-focused operation. [Figure 4] Figure 1 is a schematic diagram illustrating the refrigerant flow in the air conditioning system during full heating operation. [Figure 5] Figure 1 is a schematic diagram illustrating the refrigerant flow in an air conditioning system during heating-focused operation. [Figure 6] Figure 1 is a schematic diagram illustrating the refrigerant flow during defrost operation in the air conditioning system. [Figure 7] This flowchart shows the control process after the air conditioning system returns from defrost operation to heating operation according to the embodiment. [Modes for carrying out the invention]

[0010] Embodiments of this disclosure will be described below with reference to the drawings. However, this disclosure is not limited to the embodiments described below. Also, the size relationships of the components in the following drawings may differ from those of the actual components.

[0011] Embodiment. The air conditioning system 100 according to the embodiment will now be described. In the following description, the air conditioning system 100 is installed in, for example, a building or apartment complex, and can perform cooling or heating operations using a refrigerant circuit 101 that circulates a refrigerant. In particular, the air conditioning system 100 according to the embodiment can perform cooling only, heating only, or both simultaneously for multiple air-conditioned spaces. Furthermore, the air conditioning system 100 according to the embodiment can perform a defrost operation to remove frost that has accumulated on the heat source side heat exchanger 13 during heating operation.

[0012] [Configuration of the air conditioning system 100] Figure 1 is a schematic diagram showing an example of the refrigerant circuit configuration of an air conditioning system 100 according to an embodiment. The air conditioning system 100 according to Embodiment 1 includes an outdoor unit 10, a plurality of indoor units 20a, 20b, a repeater 30, and a control device 40. In the example in Figure 1, the air conditioning system 100 is shown to consist of one outdoor unit 10, two indoor units 20a, 20b, and one repeater 30.

[0013] In the air conditioning system 100, the outdoor unit 10 and the repeater 30 are connected by the first main pipe 1 and the second main pipe 2. The repeater 30 and the indoor unit 20a are connected by the first branch pipe 5a and the second branch pipe 6a, and the repeater 30 and the indoor unit 20b are connected by the first branch pipe 5b and the second branch pipe 6b. In this way, the outdoor unit 10, the repeater 30, and the indoor units 20a and 20b are connected by their respective piping, forming 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. Similarly, the number of outdoor units 10 and repeater 30 may be two or more. Furthermore, the type of refrigerant used in the air conditioning system 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 used in existing products.

[0014] (Outdoor unit 10) The outdoor unit 10 is provided to supply heat to the indoor unit 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 is equipped with check valves 15a, 15b, 15c, 15d, a first connecting pipe 3, and a second connecting pipe 4 so that the flow of refrigerant into the relay unit 30 can be directed in a constant direction, regardless of the requirements of the indoor unit 20.

[0015] The compressor 11 draws in low-temperature, low-pressure gaseous refrigerant, compresses it to a high-temperature, high-pressure state, and discharges it. As the compressor 11, for example, an inverter compressor is used that can control the capacity, which is the amount of refrigerant delivered per unit time, by arbitrarily changing the drive frequency. The drive frequency of the compressor 11 is controlled by the control device 40.

[0016] Note that the 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. Further, the compressor 11 may be any compressor that can compress the inhaled refrigerant to a high pressure state, and is composed of various types such as reciprocating, rotary, scroll, or screw.

[0017] The flow path switching device 12 is, for example, a four-way valve, and switches the direction of the refrigerant flow to switch between cooling operation and heating operation. 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 a two-way valve or a three-way valve.

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

[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. Then, 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] Further, 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. Then, 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 located on the low-pressure side, which is the suction side of the compressor 11. The accumulator 14 stores excess refrigerant resulting from the difference in operating conditions between cooling operation and heating operation, as well as excess refrigerant due to transient changes in operation.

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

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

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

[0025] In the following explanation, when there is no need to distinguish between indoor units 20a and 20b, they will simply be referred to as "indoor unit 20" as appropriate. Also, since throttling devices 21a and 21b have the same configuration, and load-side heat exchangers 22a and 22b have the same configuration, the following explanation will use throttling device 21a and load-side heat exchanger 22a as examples.

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

[0027] The load-side heat exchanger 22a performs heat exchange between a fluid such as indoor air or water and a refrigerant. Specifically, during cooling operation, the load-side heat exchanger 22a functions as an evaporator, evaporating the refrigerant into a gas and absorbing heat from the outdoor air as latent heat of vaporization. During heating operation, the load-side heat exchanger 22a functions as a condenser, releasing the heat from the refrigerant into the indoor air and condensing the refrigerant into a liquid.

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

[0029] (Repeater 30) The relay unit 30 switches the flow of refrigerant according to the operating conditions, distributing 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 and 34b, and second on-off valves 35a and 35b. In the following description, when there is no need to distinguish between the first on-off valves 34a and 34b and the second on-off valves 35a and 35b, they will simply be referred to as "first on-off valve 34" and "second on-off valve 35" as appropriate.

[0031] Furthermore, the relay unit 30 is provided with connecting pipes 7, 8, and 9. Connecting pipe 7 connects the gas side of the gas-liquid separator 31 to the first on-off valve 34 and is the pipe through which the gaseous refrigerant flows. Connecting pipe 8 connects the liquid side of the gas-liquid separator 31 to the indoor unit 20 and is the pipe through which the liquid refrigerant flows. Relay pipe 9 is provided to relay connecting pipes 7 and 8.

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

[0033] The first throttling device 32 is installed in the connecting pipe 8. The first throttling device 32 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 first throttling device 32 is composed of a valve whose opening degree can be controlled, such as an electronic expansion valve. In this case, the opening degree of the first throttling device 32 is controlled by the control device 40.

[0034] The second throttling device 33 is installed in the relay piping 9. The second throttling device 33 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 second throttling device 33 is composed of 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 and 34b are for controlling the supply of refrigerant to the indoor units 20a and 20b for each operating mode, and are installed between the connecting pipe 7 and the first branch pipes 5a and 5b. In other words, one of the first on-off valves 34a and 34b is connected to the gas-liquid separator 31, and the other is connected to the load-side heat exchangers 22a and 22b of the indoor units 20a and 20b, respectively, and by controlling their opening and closing, the refrigerant is supplied or not supplied.

[0036] The second on-off valves 35a and 35b are also used to control the supply of refrigerant to the indoor units 20a and 20b for each operating mode, and are installed between the first branch pipes 5a and 5b and the first main pipe 1. In other words, one end of the second on-off valves 35a and 35b is connected to the first main pipe 1, and the other end is connected to the load-side heat exchangers 22a and 22b of the indoor units 20a and 20b, respectively, and by controlling their opening and closing, the refrigerant is supplied or not supplied.

[0037] (Control device 40) The control device 40 controls the entire air conditioning system 100. For example, the control device 40 controls the flow path switching device 12, throttle devices 21a and 21b, first throttle device 32, second throttle device 33, first on-off valves 34a and 34b, and second on-off valves 35a and 35b, etc., according to the operating mode of the air conditioning system 100. The control device 40 is configured to perform various functions by executing software on a computing device such as a microcomputer, or by being composed of hardware such as circuit devices that perform various functions.

[0038] The refrigerant circuit 101 described above is equipped with a discharge temperature detection device 51, a discharge pressure detection device 52, an inlet temperature detection device 53, an suction pressure detection device 54, and condenser outlet temperature detection devices 55a and 55b. The discharge temperature detection device 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 detection device 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 detection device 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 detection device 54 is provided on the suction side of the compressor 11 and detects the pressure of the refrigerant being drawn into the compressor 11. The suction pressure detection device 54 may also be provided at the inlet of the accumulator 14. The condenser outlet temperature detection devices 55a and 55b are installed at the outlets when the load-side heat exchangers 22a and 22b function as condensers, and detect the temperature of the refrigerant that has flowed out when the load-side heat exchangers 22a and 22b function as condensers. The discharge temperature detection device 51, the inlet temperature detection device 53, and the condenser outlet temperature detection devices 55a and 55b are, for example, thermistors, and the discharge pressure detection device 52 and the suction pressure detection device 54 are, for example, pressure gauges.

[0039] [Refrigerant operation of air conditioning unit 100] Next, the operation of the refrigerant in the various operating modes of the air conditioning system 100 having the above configuration will be described. The air conditioning system 100 has the following operating modes: full cooling operation, cooling-dominant operation, full heating operation, heating-dominant operation, and defrost operation, and it performs one of these operations.

[0040] Full cooling operation is a type of cooling operation in which all indoor units 20 perform cooling on the air-conditioned space. Cooling-dominant operation is a type of cooling operation in which the cooling load of the indoor units 20 that perform cooling on the air-conditioned space exceeds the heating load of the indoor units 20 that perform heating on the air-conditioned space. Full heating operation is a type of heating operation in which all indoor units 20 perform heating on the air-conditioned space. Heating-dominant operation is a type of heating operation in which the heating load of the indoor units 20 that perform heating on the air-conditioned space exceeds the cooling load of the indoor units 20 that perform cooling on the air-conditioned space. Defrost operation is an operation performed to remove frost that has accumulated on the heat source side heat exchanger 13 during heating operation (full heating operation or heating-dominant operation).

[0041] (Full air conditioning operation) Figure 2 is a schematic diagram illustrating the refrigerant flow in the air conditioning system 100 shown in Figure 1 during full cooling operation. In full cooling operation, all indoor units 20a and 20b cool the air-conditioned space. In Figure 2, the direction of refrigerant flow during full cooling operation is indicated by arrows.

[0042] In full cooling 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. Also, 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 a high-temperature, high-pressure gaseous refrigerant. The high-temperature, high-pressure gaseous refrigerant discharged from the compressor 11 flows into the heat source side heat exchanger 13 via the flow path switching device 12. The high-temperature, high-pressure gaseous refrigerant that flows into the heat source side heat exchanger 13 condenses while exchanging heat with the outdoor air and releasing heat, becoming a high-pressure liquid refrigerant that flows out of the heat source side heat exchanger 13. The high-pressure liquid refrigerant that flows out of the heat source side heat exchanger 13 passes through the second main pipe 2 and flows out of the outdoor unit 10 and into the relay unit 30.

[0044] The high-pressure liquid refrigerant flowing into the relay unit 30 flows into the first throttling device 32 via the gas-liquid separator 31, where it is depressurized and expanded to become liquid refrigerant at an intermediate pressure. The liquid refrigerant at an intermediate pressure then passes through the connecting pipe 8, splits into the second branch pipes 6a and 6b, and flows out from the relay unit 30. The liquid refrigerant at an intermediate pressure that flows out from 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 flowing into the indoor unit 20a is depressurized and expanded by the throttling device 21a to become a low-temperature, low-pressure gas-liquid two-phase refrigerant, which then flows into the load-side heat exchanger 22a. The low-temperature, low-pressure gas-liquid two-phase refrigerant flowing into the load-side heat exchanger 22a cools the indoor air by exchanging heat with it, absorbing heat and evaporating, and then flows out of the load-side heat exchanger 22a as a low-pressure gaseous refrigerant. The low-pressure gaseous refrigerant flowing out of the load-side heat exchanger 22a passes through the first branch pipe 5a and flows out of the indoor unit 20a, into the relay unit 30.

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

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

[0048] (Mainly air conditioning operation) Figure 3 is a schematic diagram illustrating the refrigerant flow during cooling-dominant operation in the air conditioning system 100 shown in Figure 1. Here, we will explain using the example where indoor unit 20a cools the air-conditioned space and indoor unit 20b heats the air-conditioned space. In Figure 3, the direction of refrigerant flow during cooling-dominant operation is indicated by arrows.

[0049] In cooling-focused operation, the flow path switching device 12 in the outdoor unit 10 is first 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. Also, 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 a high-temperature, high-pressure gaseous refrigerant. The high-temperature, high-pressure gaseous refrigerant discharged from the compressor 11 flows into the heat source side heat exchanger 13 via the flow path switching device 12. The high-temperature, high-pressure gaseous refrigerant that flows into the heat source side heat exchanger 13 condenses while exchanging heat with the outdoor air and releasing heat, becoming a high-pressure gas-liquid two-phase refrigerant and flowing out of the heat source side heat exchanger 13. The high-pressure gas-liquid two-phase refrigerant that flows out of the heat source side heat exchanger 13 passes through the second main pipe 2 and flows out of the outdoor unit 10 and into the relay unit 30.

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

[0052] The high-pressure gaseous refrigerant that flows into the indoor unit 20b flows into the load-side heat exchanger 22b, where it exchanges heat with the indoor air, releasing heat while condensing and heating the indoor air. It then flows out of the load-side heat exchanger 22b as high-pressure liquid refrigerant. The high-pressure liquid refrigerant that flows out of the load-side heat exchanger 22b is depressurized and expanded by the throttling device 21b to become an intermediate-pressure liquid refrigerant, which flows out of the indoor unit 20b and then 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, then splits, with one portion 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 flowing into the indoor unit 20a is depressurized and expanded by the throttling device 21a to become a low-temperature, low-pressure gas-liquid two-phase refrigerant, which then flows into the load-side heat exchanger 22a. The low-temperature, low-pressure gas-liquid two-phase refrigerant flowing into the load-side heat exchanger 22a cools the indoor air by exchanging heat with it, absorbing heat and evaporating, and then flows out of the load-side heat exchanger 22a as a low-pressure gaseous refrigerant. The low-pressure gaseous refrigerant flowing out of the load-side heat exchanger 22a passes through the first branch pipe 5a and flows out of the indoor unit 20a, into the relay unit 30. The low-pressure gaseous refrigerant flowing 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 and flows into the first throttling device 32, where it is depressurized and expanded to become intermediate-pressure liquid refrigerant. The intermediate-pressure liquid refrigerant flowing out of the first throttling device 32 flows from the indoor unit 20b into the relay unit 30, where it merges with the intermediate-pressure liquid refrigerant that was separated, and passes through the relay pipe 9. The intermediate-pressure liquid refrigerant passing through the relay pipe 9 is depressurized 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 gaseous refrigerant passing through the first main pipe 1 via the second on-off valve 35a, and flows out from the relay unit 30.

[0056] The low-pressure refrigerant flowing out from 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 path switching device 12 and the accumulator 14 and is drawn into the compressor 11. The circulation described above is then repeated.

[0057] (Full heating operation) Figure 4 is a schematic diagram illustrating the refrigerant flow during full heating operation in the air conditioning system 100 shown in Figure 1. During full heating operation, all indoor units 20a and 20b provide heating to the air-conditioned space. In Figure 4, the direction of refrigerant flow during full heating operation is indicated by arrows.

[0058] In full heating 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. Also, the first on-off valves 34a and 34b are opened, and the second on-off valves 35a and 35b are closed. Furthermore, the first throttling device 32 is fully closed, and the second throttling device 33 is fully opened.

[0059] Low-temperature, low-pressure refrigerant is compressed by the compressor 11 and discharged as high-temperature, high-pressure gaseous refrigerant. The high-temperature, high-pressure gaseous 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 gaseous refrigerant that flows into the relay unit 30 passes through the gas-liquid separator 31, the connecting pipe 7, and the first on-off valves 34a and 34b, then passes through the first branch pipes 5a and 5b, before flowing out of the relay unit 30 and into the indoor units 20a and 20b.

[0060] The high-temperature, high-pressure gaseous refrigerant that flows into the indoor unit 20a flows into the load-side heat exchanger 22a, where it exchanges heat with the indoor air, releasing heat while condensing and heating the indoor air. It then becomes a high-pressure liquid refrigerant and 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 depressurized and expanded by the throttling device 21a to become a low-pressure liquid refrigerant. After flowing out of the indoor unit 20a, it flows into the relay unit 30 through the second branch pipe 6a.

[0061] The high-temperature, high-pressure gaseous refrigerant that flows into the indoor unit 20b, like the refrigerant that flows into the indoor unit 20a, becomes low-pressure liquid refrigerant via the load-side heat exchanger 22b and the throttling device 21b. 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 throttling 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 connecting 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, and flows out of the heat source side heat exchanger 13 as a low-temperature, low-pressure gaseous refrigerant. The low-pressure gaseous refrigerant that flows out of the heat source side heat exchanger 13 passes through the flow path switching device 12 and the accumulator 14 and is drawn into the compressor 11. The above circulation is then repeated.

[0063] (Mainly heating operation) Figure 5 is a schematic diagram illustrating the refrigerant flow during heating-dominant operation in the air conditioning system 100 shown in Figure 1. Here, we will explain using the example where indoor unit 20b provides heating to the air-conditioned space and indoor unit 20a provides cooling to the air-conditioned space. In Figure 5, the direction of refrigerant flow during heating-dominant operation is indicated by arrows.

[0064] In heating-focused 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. Also, 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 throttling device 32 and the second throttling device 33 are fully closed.

[0065] The low-temperature, low-pressure refrigerant is compressed by the compressor 11 and discharged as a high-temperature, high-pressure gaseous refrigerant. The high-temperature, high-pressure gaseous 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 gaseous refrigerant that flows into the relay unit 30 passes through the gas-liquid separator 31, the connecting pipe 7, and the first on-off valve 34b, then passes through the first branch pipe 5b, flows out of the relay unit 30, and flows into the indoor unit 20b.

[0066] The high-temperature, high-pressure gaseous refrigerant that flows into the indoor unit 20b flows into the load-side heat exchanger 22b, where it exchanges heat with the indoor air, releasing heat while condensing and heating the indoor air. It then flows out of the load-side heat exchanger 22b as a high-pressure liquid refrigerant. The high-pressure liquid refrigerant that flows out of the load-side heat exchanger 22b is depressurized and expanded by the throttling device 21b to become an intermediate-pressure liquid refrigerant. After flowing out of the indoor unit 20b, it 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, then through 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 flowing into the indoor unit 20a is depressurized and expanded by the throttling device 21a to become a low-temperature, low-pressure gas-liquid two-phase refrigerant, which then flows into the load-side heat exchanger 22a. The low-temperature, low-pressure gas-liquid two-phase refrigerant flowing into the load-side heat exchanger 22a cools the indoor air by exchanging heat with it, absorbing heat and evaporating, and then flows out of the load-side heat exchanger 22a as a low-pressure gaseous refrigerant. The low-pressure gaseous refrigerant flowing out of the load-side heat exchanger 22a passes through the first branch pipe 5a and flows out of the indoor unit 20a, into the relay unit 30. The low-pressure gaseous refrigerant flowing into the relay unit 30 reaches the first main pipe 1 via the second on-off valve 35a. The low-pressure gaseous 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 flowing 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 flowing into the heat source side heat exchanger 13 exchanges heat with the outdoor air, absorbs heat and evaporates, and flows out from the heat source side heat exchanger 13 as a low-temperature, low-pressure gaseous refrigerant. The low-pressure gaseous refrigerant flowing out from the heat source side heat exchanger 13 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.

[0070] (Defrost operation) Figure 6 is a schematic diagram illustrating the refrigerant flow during defrost operation in the air conditioning system 100 shown in Figure 1. In Figure 6, the direction of refrigerant flow during defrost operation is indicated by arrows.

[0071] In defrost operation, 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 throttling devices 21a, 21b are completely closed.

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

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

[0074] In defrost operation, the first on-off valves 34a and 34b and the second on-off valves 35a and 35b are closed, and the throttling devices 21a and 21b are fully closed, so the liquid refrigerant stored in the indoor units 20a and 20b remains in the indoor units 20a and 20b. In other words, the liquid refrigerant stored in the indoor units 20a and 20b does not flow to the outdoor unit 10, so it is possible to suppress the inflow of liquid refrigerant into the outdoor unit 10, which would cause the liquid refrigerant stored in the accumulator 14 to overflow and return to the compressor 11.

[0075] Furthermore, after returning from defrosting 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 re-accumulated 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 defrosting to heating operation will be slower. To address this, the refrigerant accumulated in the indoor units 20a and 20b is retained in the indoor units 20a and 20b and does not flow to the outdoor unit 10. By doing so, the start-up of heating capacity after returning from defrosting to heating operation can be improved, and heating capacity at low outdoor temperatures can be enhanced.

[0076] Figure 7 is a flowchart showing the control process after the air conditioning system 100 according to the embodiment returns from defrost operation to heating operation. In the air conditioning system 100 according to the embodiment, after returning from defrost operation to heating operation, the control process shown in Figure 7 is executed at a predetermined interval (for example, once every 30 seconds) for a period of several minutes (for example, for 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) calculated from the pressure detected by the discharge pressure detection device 52 is greater than or equal to a preset first threshold 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) calculated from the pressure detected by the suction pressure detection device 54 is greater than or equal to a preset second threshold 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; otherwise, 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 (condensation temperature) calculated from the pressure detected by the discharge pressure detection device 52 is greater than or equal to a preset third threshold A1 (>B1) (compressor discharge temperature - saturation temperature (condensation temperature) ≥ A1), and whether the difference between the temperature detected by the inlet temperature detection device 53 and the saturation temperature (evaporation temperature) calculated from the pressure detected by the suction pressure detection device 54 is greater than or equal to a preset fourth threshold A2 (>B2) (accumulator inlet temperature - saturation temperature (evaporation temperature) ≥ A2). If the conditions of the second determination process are met, the process proceeds to step S4; otherwise, the process proceeds to step S5.

[0079] (Step S3) The control device 40 detects that too much liquid refrigerant is returning to the outdoor unit 10 and reduces the opening of the throttling devices 21a and 21b on the indoor units 20a and 20b. If too much liquid refrigerant returns from the indoor units 20a and 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. Also, 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 then re-accumulated in the indoor unit 20. Therefore, if a large amount of liquid refrigerant is accumulated in the accumulator 14, the start-up of the heating capacity after returning from defrost operation to heating operation will be delayed accordingly. For this reason, when too much liquid refrigerant is returning from the indoor units 20a and 20b to the outdoor unit 10, the opening of the throttling devices 21a and 21b on the indoor units 20a and 20b is reduced. This prevents excessive return of liquid refrigerant from indoor units 20a and 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, it improves the rise in heating capacity after returning from defrost operation to heating operation, thereby improving heating capacity at low outdoor temperatures.

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

[0081] (Step S5) The control device 40 controls the subcooling of the outlets of the load-side heat exchangers 22a and 22b, assuming that the opening degrees of the throttling devices 21a and 21b of the indoor units 20a and 20b are at the appropriate opening degrees. In other words, it controls the opening degrees of the throttling devices 21a and 21b so that the subcooling (degree of supercooling) at the outlets of the load-side heat exchangers 22a and 22b reaches a preset value. Here, the subcooling at the outlets of the load-side heat exchangers 22a and 22b is calculated 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] Note that A1 and B1 above are values ​​corresponding to the compression ratio, for example, A1 = 30°C and B1 = 25°C. Also, A2 and B2 above are values ​​that indicate whether or not superheating occurs at the inlet of the accumulator 14, for example, A2 = 5°C and B2 = 3°C.

[0083] As described above, the air conditioning system 100 according to the embodiment comprises an outdoor unit 10 having a compressor 11, a flow path switching device 12, a heat source side heat exchanger 13, and an accumulator 14; indoor units 20a and 20b having throttling devices 21a and 21b and load side heat exchangers 22a and 22b; a relay unit 30 connected between the outdoor unit 10 and the indoor units 20a and 20b, which switches the flow of refrigerant according to the operating conditions; and the outdoor unit 10, the relay unit 30 and the indoor units 20a and 20b The system includes a refrigerant circuit 101 through which the refrigerant circulates, a control device 40 that controls the refrigerant circuit 101, a discharge temperature detection device 51 that detects the temperature of the refrigerant discharged from the compressor 11, a discharge pressure detection device 52 that detects the pressure of the refrigerant discharged from the compressor 11, an inlet temperature detection device 53 that detects the temperature of the refrigerant flowing into the accumulator 14, and an suction pressure detection device 54 that detects the pressure of the refrigerant drawn 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 completely closes the throttling device 21. After returning from defrost operation to heating operation, 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) calculated from the pressure detected by the discharge pressure detection device 52 is greater than or equal to a first threshold value which is a preset value, and whether the difference between the temperature detected by the inlet temperature detection device 53 and the saturation temperature (evaporation temperature) calculated from the pressure detected by the suction pressure detection device 54 is greater than or equal to a second threshold value which is a preset value. If the conditions of the first determination process are not met, the control device 40 reduces the opening degree of the throttling device.

[0084] According to the air conditioning system 100 of this embodiment, 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 during defrost operation, and also completely closes the throttle devices 21a and 21b. After returning from defrost operation to heating operation, it performs a first determination process to determine whether too much liquid refrigerant has returned to the outdoor unit 10. If the conditions of the first determination process are not met, the opening of the throttle devices 21a and 21b is reduced. In this way, by completely closing the throttle devices 21a and 21b of the indoor units 20a and 20b during defrost operation, the liquid refrigerant stored in the indoor units 20a and 20b does not flow to the outdoor unit 10, thus suppressing liquid backflow to the compressor 11. Furthermore, if too much liquid refrigerant returns from indoor units 20a and 20b to the outdoor unit 10 after returning from defrosting operation to heating operation, reducing the opening of the throttling devices 21a and 21b on indoor units 20a and 20b suppresses excessive return of liquid refrigerant from indoor units 20a and 20b to the outdoor unit 10, thereby suppressing liquid backflow to the compressor 11. In addition, it is possible to improve the rise of heating capacity after returning from defrosting operation to heating operation, and to improve heating capacity at low outdoor temperatures.

[0085] Furthermore, in the air conditioning system 100 according to the embodiment, the control device 40 performs a first determination process. If the conditions of the first determination process are met, 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 (condensation temperature) calculated from the pressure detected by the discharge pressure detection device 52 is greater than or equal to a third threshold value which is a preset value greater than the first threshold, and whether the difference between the temperature detected by the inlet temperature detection device 53 and the saturation temperature (evaporation temperature) calculated from the pressure detected by the suction pressure detection device 54 is greater than or equal to a fourth threshold value which is a preset value greater than the second threshold. If the conditions of the second determination process are met, the control device 40 increases the opening degree of the throttle devices 21a and 21b.

[0086] According to the air conditioning system 100 of the embodiment, a first determination process is performed, and if the conditions of the first determination process are met, a second determination process is performed to determine whether there is insufficient liquid return to the outdoor unit 10, and if the conditions of the second determination process are met, the opening of the throttling devices 21a and 21b is increased. In other words, if there is insufficient liquid return to the outdoor unit 10, increasing the opening of the throttling devices 21a and 21b of the indoor units 20a and 20b can suppress the decrease in pressure on the intake side, which reduces the intake density of the compressor 11 and prevents a decrease in heating capacity.

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

[0088] According to the air conditioning system 100 of the embodiment, by performing a first determination process to determine whether too much liquid refrigerant is returning to the outdoor unit 10 and a second determination process to determine whether insufficient liquid is returning to the outdoor unit 10 at the above timing, it is possible to efficiently resolve both excessive and insufficient liquid refrigerant returning to the outdoor unit 10. [Explanation of Symbols]

[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 Intermediate 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 Intermediate unit, 31 Gas-liquid separator, 32 First throttle device, 33 Second throttle device, 34 First shut-off valve, 34a First shut-off valve, 34b First shut-off valve, 35 Second shut-off valve, 35a Second shut-off valve, 35b Second shut-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 system, 101 Refrigerant circuit.

Claims

1. 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 throttling device and a load-side heat exchanger, A relay unit connected between the outdoor unit and the indoor unit, which switches the flow of refrigerant according to the operating conditions, The outdoor unit, the relay unit, and the indoor unit are connected by piping, and a refrigerant circuit through which the refrigerant circulates is provided. A control device for controlling the refrigerant circuit, A discharge temperature detection device for detecting the temperature of the refrigerant discharged from the compressor, A discharge pressure detection device for detecting the pressure of the refrigerant discharged from the compressor, An inlet temperature detection device for detecting the temperature of the refrigerant flowing into the accumulator, The compressor is equipped with an intake pressure detection device that detects the pressure of the refrigerant being drawn into the compressor, The control device is During defrost operation, The flow path 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 completely closed. After returning from the defrost operation to the heating operation, The first determination process determines whether too much liquid refrigerant is being returned to the outdoor unit, by determining whether the difference between the temperature detected by the discharge temperature detection device and the condensation temperature calculated from the pressure detected by the discharge pressure detection device is greater than or equal to a first threshold value which is a preset value, and whether the difference between the temperature detected by the inlet temperature detection device and the evaporation temperature calculated from the pressure detected by the suction pressure detection device is greater than or equal to a second threshold value which is a preset value. If the conditions of the first determination process are not met, the opening of the throttle device is reduced to suppress liquid backflow to the compressor. Air conditioning system.

2. The control device is If the conditions for the first determination process are met, A second determination process is performed to determine whether the liquid return to the outdoor unit is insufficient, by determining whether the difference between the temperature detected by the discharge temperature detection device and the condensation temperature calculated from the pressure detected by the discharge pressure detection device is greater than or equal to a third threshold value which is a preset value greater than the first threshold, and whether the difference between the temperature detected by the inlet temperature detection device and the evaporation temperature calculated from the pressure detected by the suction pressure detection device is greater than or equal to a fourth threshold value which is a preset value greater than the second threshold. If the conditions of the second determination process are met, the opening of the throttle device is increased to suppress the occurrence of a decrease in heating capacity. The air conditioning device according to claim 1.

3. The control device is If the conditions for the second determination process are not met, the opening degree of the throttle device is controlled so that the subcooling at the outlet of the load-side heat exchanger becomes a preset value. The air conditioning device according to claim 2.

4. The control device is The control process, including the first determination process and the second determination process, is performed at predetermined intervals for a predetermined period of time after returning from the defrost operation to the heating operation. The air conditioning device according to claim 3.

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