air conditioner

Abstract

An air conditioner contains a refrigerant circuit with a compressor, a heat source-side heat exchanger that acts as an evaporator, a refrigerant flow switch, a load-side heat exchanger that acts as a condenser, and a load-side expansion device. The air conditioner includes a bypass line that routes the refrigerant delivered by the compressor to the heat source-side heat exchanger, a primary opening and closing device in the bypass line, and a control unit. The compressor, the heat source-side heat exchanger, the refrigerant flow switch, the bypass line, and the primary opening and closing device are housed in an outdoor unit.When defrosting the heat source-side heat exchanger, the control is designed to make a flow channel of the refrigerant flow switching device into a flow channel through which the refrigerant delivered by the compressor flows into the load-side heat exchanger, changes the first opening and closing device from the closed state to the open state, changes the load-side expansion device from the open state to the closed state, and allows the refrigerant delivered by the compressor to flow from the bypass line into the load-side heat exchanger.

Description

TECHNICAL FIELD

[0001] The present invention relates to an air conditioning device. STATE OF THE ART

[0002] In some air conditioning systems, such as a VRF (Variable Refrigerant Flow) system, an outdoor unit located outside a building as a heat source and an indoor unit located inside the building are connected by a piping system, forming a refrigerant circuit through which the refrigerant circulates. Furthermore, the target room of the air conditioner is heated by heating the indoor air using the heat dissipation of the refrigerant. Furthermore, the room to be air-conditioned is cooled by cooling the indoor air using the heat dissipation of the refrigerant.

[0003] During heating operation of such an air conditioner, a heat-source-side heat exchanger installed in the outdoor unit acts as an evaporator, allowing the low-temperature refrigerant and the outside air to exchange heat. As a result, the moisture contained in the outside air condenses on the fins and heat transfer tubes of the heat-source-side heat exchanger, forming frost on the heat-source-side heat exchanger. This frost formation on the heat-source-side heat exchanger leads to the clogging of an air passage in the heat-source-side heat exchanger, reducing the heat transfer area of ​​the heat-source-side heat exchanger that exchanges heat with the outside air, and thus resulting in insufficient heating performance.

[0004] This problem is typically solved by interrupting heating operation when frost forms on the heat-source-side heat exchanger and defrosting the heat-source-side heat exchanger by switching the refrigerant flow with a refrigerant flow switching device, so that the heat-source-side heat exchanger installed in the outdoor unit functions as a condenser. Performing such defrosting prevents a reduction in heating capacity. However, defrosting requires a smaller amount of refrigerant than heating and therefore generates excess refrigerant. Furthermore, the generation of excess refrigerant leads to liquid backflow into the compressor, which affects compressor reliability.

[0005] To solve this problem, some air conditioners have been proposed that reduce the liquid return flow to the compressor during defrosting mode (see Patent Document 1). The air conditioner described in Patent Document 1 includes two indoor heat exchangers connected in parallel. One of the two indoor heat exchangers is used as a heat exchanger in which the refrigerant accumulates during defrosting of a heat source-side heat exchanger. Furthermore, in the air conditioner described in Patent Document 1, when the heat source-side heat exchanger is defrosted, the refrigerant discharged from the compressor is supplied to the heat source-side heat exchanger via the other of the two indoor heat exchangers, thus defrosting the heat source-side heat exchanger.Thus, the air conditioner described in Patent Document 1 is designed to reduce the liquid return flow to the compressor by accumulating excess refrigerant in one of the two indoor heat exchangers during the defrosting mode of the heat source-side heat exchanger.

[0006] Patent Document 1: Japanese Patent Application JP 2020-056 515A SUMMARY OF THE INVENTION Problems to be solved by the invention

[0007] In the air conditioner described in Patent Document 1, the refrigerant flows through the same flow channel during both the defrosting mode and the cooling operation. That is, during the defrosting mode, the refrigerant discharged from the compressor flows through an indoor heat exchanger, further through a pipe connecting an indoor unit and an outdoor unit, and flows into the heat source-side heat exchanger. For this reason, in the air conditioner described in Patent Document 1, during the defrosting mode, a large pressure loss occurs in a flow channel through which the refrigerant discharged from the compressor flows into the heat source-side heat exchanger, so that the density of the refrigerant flowing into the heat source-side heat exchanger decreases. This causes the air conditioner described in Patent Document 1 to suffer from deterioration in defrosting performance.

[0008] The present invention is intended to solve the above-mentioned problem and aims to provide an air conditioner capable of reducing the liquid backflow to the compressor during the defrosting mode and also reducing the deterioration of the defrosting performance. Means to solve the problems

[0009] An air conditioner according to an embodiment of the present invention includes a refrigerant cycle having a compressor configured to compress and discharge refrigerant, a heat source-side heat exchanger configured to function as an evaporator in a heating-only mode in which all the operating units of the indoor unit perform heating operation, a refrigerant flow switching device configured to switch the flow channels of the refrigerant according to the mode of operation, a load-side heat exchanger configured to function as a condenser during the heating operation, and a load-side expansion device configured tothat the refrigerant flowing from the load-side heat exchanger acting as a condenser and flowing into the heat-source-side heat exchanger acting as an evaporator flows through the load-side expansion device formed by the compressor, the heat-source-side heat exchanger, the load-side expansion device, and the load-side heat exchanger, which are connected by a refrigerant line, and through which the refrigerant circulates; a bypass line, one end of which is an inlet-side end connected to a point in the refrigerant circuit located between an outlet of the compressor and the refrigerant flow switching device, and the other end of which is an outlet-side end connected to a point in the refrigerant circuit located between the load-side expansion device and the load-side heat exchanger; a first opening and closing device;which is provided in the bypass line and configured to open and close a refrigerant flow channel at a location where the first opening and closing device is installed; a controller configured to control the refrigerant flow switching device, the load-side expansion device, and the first opening and closing device; and an outdoor unit mounted with the compressor, the heat-source-side heat exchanger, the refrigerant flow switching device, the bypass line, and the first opening and closing device. The controller is configured to, when performing a defrost mode for defrosting the heat-source-side heat exchanger, cause a refrigerant flow channel through the refrigerant flow switching device to be a flow channel through which the refrigerant discharged from the compressor flows into the load-side heat exchanger.the first opening and closing device is moved from the closed state to the open state, the load-side expansion device is moved from the open state to the closed state, and the refrigerant discharged from the compressor flows from the bypass line into the heat source-side heat exchanger. Effect of the invention

[0010] The air conditioner according to an embodiment of the present invention is configured to retain excess refrigerant in the load-side heat exchanger during the defrosting mode of the heat-source-side heat exchanger, thus reducing liquid backflow to the compressor. Furthermore, in the air conditioner according to an embodiment of the present invention, during the defrosting mode for the heat-source-side heat exchanger, the refrigerant discharged from the compressor flows into the heat-source-side heat exchanger by flowing only within the outdoor unit. Therefore, the air conditioner according to an embodiment of the present invention can prevent the density of the refrigerant flowing into the heat-source-side heat exchanger from decreasing due to pressure loss during the defrosting mode of the heat-source-side heat exchanger and also reduce deterioration in defrosting performance. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic view showing a circuit configuration of an air conditioner according to Embodiment 1 and a diagram illustrating a state in which the air conditioner operates in a cooling-only mode; Fig. 2 is a schematic view showing the circuit configuration of an air conditioner according to Embodiment 1 and a diagram showing a state in which the air conditioner operates in a heating-only mode; Fig. 3 is a schematic view showing the circuit configuration of the air conditioner according to Embodiment 1 and a diagram showing a state in which the air conditioner operates in a defrost mode; Fig. 4 is a flowchart showing a control process in which a controller of the air conditioner according to Embodiment 1 executes the defrost mode; Fig. 5 is a schematic view showing a circuit configuration of another example of the air conditioner according to Embodiment 1 and a diagram illustrating a state in which the air conditioner operates in the defrost mode; Fig. 6 is a schematic view showing a circuit configuration of an air conditioner according to Embodiment 2 and a diagram illustrating a state in which the air conditioner operates in the defrost mode; Fig. 7 is a schematic view of a Mollier diagram showing the states of the refrigerant when the air conditioner according to Embodiment 2 operates in the heating-only mode; Fig. 8 is a schematic view of a Mollier diagram showing the states of the refrigerant when the air conditioner according to Embodiment 2 operates in the defrost mode; Fig. 9 is a flowchart showing a control process in which a controller of the air conditioner according to Embodiment 2 executes the defrost mode; Fig. 10 is a schematic view showing a circuit configuration of an air conditioner according to Embodiment 3 and a diagram illustrating a state in which the air conditioner operates in a cooling-only mode; Fig. 11 is a schematic view showing the circuit configuration of an air conditioner according to Embodiment 3, and a diagram showing a state in which the air conditioner operates in a main cooling mode; Fig. 12 is a schematic diagram of the circuit configuration of the air conditioner according to Embodiment 3 and a diagram showing a state in which the air conditioner operates in the heating-only mode; Fig. 13 is a schematic view showing the circuit configuration of the air conditioner according to Embodiment 3 and a diagram showing a state in which the air conditioner operates in a main heating mode; Fig. 14 is a schematic view showing the circuit configuration of the air conditioner according to Embodiment 3 and a diagram showing a state in which the air conditioner operates in the defrost mode; Fig. Fig. 15 is a schematic view showing a circuit configuration of an air conditioner according to Embodiment 4, and a diagram showing a state in which the air conditioner operates in the defrosting mode, wherein solid arrows indicate the flow direction of the refrigerant in Fig. 15 display, and Fig. 16 is a schematic view showing a circuit configuration of an air conditioner according to Embodiment 5 and a diagram illustrating a state in which the air conditioner operates in the defrost mode. Description of the embodiments

[0011] In each of the following embodiments, an example of an air conditioner according to the present invention will be described with reference to the drawings. Components designated by identical reference numerals in the drawings are identical or equivalent, and these reference numerals will be retained throughout the entire specification. Furthermore, the component shapes shown in the full specification are merely examples of air conditioners according to the present invention. The air conditioners according to the present invention are not limited to the component shapes shown in the full specification. Embodiment 1.[Configuration of the air conditioner 1001

[0012] Fig. 1 is a schematic view showing a circuit configuration of an air conditioner according to Embodiment 1 and a diagram illustrating a state in which the air conditioner operates in a cooling-only mode.

[0013] The air conditioner 100 is configured to perform air conditioning using a refrigerant circuit by circulating the refrigerant through a refrigerant circuit 101. The air conditioner 100 is configured to be selectively operated in the cooling-only mode, in which all indoor units 2 perform cooling operation, in the heating-only mode, in which all indoor units 2 perform heating operation, or in the defrost mode, in which a heat source-side heat exchanger 12 in an outdoor unit 1 is defrosted.

[0014] As in Fig. As shown in Figure 1, the air conditioner 100 includes the outdoor unit 1 and an indoor unit 2, and is configured such that the outdoor unit 1 and the indoor unit 2 are connected by a main line 111. As mentioned later, the components installed in the outdoor unit 1 and the indoor unit 2 are connected to each other by a refrigerant line 110, forming the refrigerant circuit 101. The main line 111 is a part of the refrigerant line 110. [Refrigerant Circuit Configuration 101]

[0015] The refrigerant cycle 101 includes a compressor 10, a refrigerant flow switching device 13, the heat source side heat exchanger 12, a load side heat exchanger 26, a load side expansion device 25, and an accumulator 19. In addition, the compressor 10, the refrigerant flow switching device 13, the heat source side heat exchanger 12, the load side heat exchanger 26, and the load side expansion device 25 are connected by the refrigerant line 110 and form the refrigerant cycle 101 through which the refrigerant circulates.

[0016] The compressor 10 is configured to compress and discharge the refrigerant. Specifically, the compressor 10 draws in the refrigerant and compresses it to a high-temperature, high-pressure state. The compressor 10 is, for example, a capacity-controlled inverter compressor or other device. The refrigerant flow switching device 13 is configured to switch the refrigerant flow channels depending on the operation mode. Specifically, the refrigerant flow switching device 13 switches between the refrigerant flow during the heating-only mode, the refrigerant flow during the cooling-only mode, and the refrigerant flow during the defrosting mode.

[0017] The heat source-side heat exchanger 12 is configured to function as an evaporator in the heating-only mode and as a condenser in the cooling-only mode and defrosting mode. In Embodiment 1, the heat source-side heat exchanger 12 is configured to exchange heat between the refrigerant flowing in the indoor and outdoor air. For this purpose, the air conditioner 100 according to Embodiment 1 includes a heat source-side air supply device 18 configured to supply the outdoor air to the heat source-side heat exchanger 12.

[0018] The load-side heat exchanger 26 is configured to function as a condenser in heating mode and as an evaporator in cooling mode. In Embodiment 1, the load-side heat exchanger 26 is configured to exchange heat between the refrigerant flowing inside and the indoor air. To this end, the air conditioner 100 according to Embodiment 1 includes a load-side air supply device (not shown) configured to supply the indoor air to the load-side heat exchanger 26. That is, the indoor air cooled by the load-side heat exchanger 26 serves as cooling air supplied to a target air-conditioned space. In addition, the indoor air heated by the load-side heat exchanger 26 serves as heating air supplied to the target air-conditioned space.

[0019] The load-side expansion device 25 has an opening degree that can be regulated, for example, continuously or in multiple stages. Usable examples of the load-side expansion device 25 are electronic expansion valves. The load-side expansion device 25 functions as a pressure reducing valve and an expansion valve. In other words, the load-side expansion device 25 decompresses and expands the refrigerant. The load-side expansion device 25 is located in the refrigerant circuit 101 and downstream of the load-side heat exchanger 26 when the load-side heat exchanger 26 functions as a condenser. In particular, the load-side expansion device 25 is configured such that the refrigerant exiting the load-side heat exchanger 26, which functions as a condenser, and flowing into the load-side heat exchanger 12, which functions as an evaporator, flows through the load-side expansion device 25.In Embodiment 1, the load-side expansion device 25 decompresses the refrigerant flowing into the load-side heat exchanger 26 during the cooling operation. That is, the load-side expansion device 25 is located in the refrigerant circuit 101 and upstream of the load-side heat exchanger 26 when the load-side heat exchanger 26 functions as an evaporator.

[0020] The accumulator 19 is configured to store the refrigerant. Specifically, the accumulator 19 is a liquid receiver mounted on the suction side of the compressor 10 and capable of storing excess refrigerant. The excess refrigerant is generated, for example, by a difference in the operating state during the heating-only mode, the cooling-only mode, and the defrosting mode. Furthermore, the excess refrigerant is generated, for example, by a temporary change in the operation of the air conditioner 100. [Outdoor Unit 1 Configuration]

[0021] The outdoor unit 1 is equipped with the compressor 10, the heat source-side heat exchanger 12, the heat source-side air supply device 18, the refrigerant flow switching device 13, and the accumulator 19. Furthermore, the outdoor unit 1 is equipped with a bypass line 16 and a first opening and closing device 11 containing the air conditioner 100.

[0022] The bypass line 16 is a line through which, in defrost mode, the high-temperature and high-pressure refrigerant discharged from the compressor 10 is supplied to the heat-source-side heat exchanger 12. That is, the bypass line 16 is a line through which the refrigerant flows to defrost the frost formed on the heat-source-side heat exchanger 12. The bypass line 16 has an inlet end 16a connected to a point in the refrigerant circuit 101 located between a pressure outlet of the compressor 10 and the refrigerant flow switching device 13. The other end of the bypass line 16 is an outlet end 16b connected to a point in the refrigerant circuit 101 located between the load-side expansion device 25 and the load-side heat exchanger 12.More specifically, the outlet-side end 16b, which is the other end of the bypass line 16, is connected to a portion of the refrigerant line 110 located between the load-side expansion device 25 and the heat-source-side heat exchanger 12 and closer to the heat-source-side heat exchanger 12 than the main line 111.

[0023] The first opening and closing device 11 is provided in the bypass line 16 and configured to open and close a refrigerant flow passage at a location where the first opening and closing device 11 is installed. That is, when the first opening and closing device 11 changes from the closed state to the open state, the high-temperature and high-pressure refrigerant discharged from the compressor 10 is supplied to the heat source-side heat exchanger 12. The first opening and closing device 11 may preferably be a device capable of opening and closing a refrigerant flow passage, such as a two-way valve, a solenoid valve, and an electronic expansion valve capable of adjusting the refrigerant flow rate.

[0024] In addition, the outdoor unit 1 is equipped with a heat source-side heat exchanger temperature sensor 43, an outlet temperature sensor 42, an outlet pressure sensor 40, and an outside air temperature sensor 46. The heat source-side heat exchanger temperature sensor 43, the outlet temperature sensor 42, and the outside air temperature sensor 46 are, for example, thermistors or other devices. In heating-only mode and defrosting mode, the heat source-side heat exchanger temperature sensor 43 detects the temperature of the refrigerant flowing out of the heat source-side heat exchanger 12. In addition, in cooling-only mode, the heat source-side heat exchanger temperature sensor 43 detects the temperature of the refrigerant flowing into the heat source-side heat exchanger 12. In addition, the heat source-side heat exchanger temperature sensor 43 outputs the thus detected temperature of the refrigerant as a detection signal to a downstream controller 60.The outlet temperature sensor 42 detects the temperature of the refrigerant discharged from the compressor 10. Furthermore, the outlet temperature sensor 42 outputs the detected refrigerant temperature as a detection signal to the downstream controller 60. The outlet pressure sensor 40 detects the pressure of the refrigerant discharged from the compressor 10. Furthermore, the outlet pressure sensor 40 outputs the detected refrigerant pressure as a detection signal to the downstream controller 60. The outside air temperature sensor 46 is installed in a part of the outdoor unit 1 through which air flows into the heat source-side heat exchanger 12. The outside air temperature sensor 46 detects, for example, the temperature of the outside air, i.e., the temperature of an area around the outdoor unit 1. Furthermore, the outside air temperature sensor 46 outputs the detected temperature as a detection signal to the downstream controller 60. [Configuration of indoor unit 2]

[0025] The indoor unit 2 is equipped with the indoor-side expansion device 25 and the load-side heat exchanger 26.

[0026] Furthermore, the indoor unit 2 is equipped with a first load-side temperature sensor 31 and a second load-side temperature sensor 32. The first load-side temperature sensor 31 and the second load-side temperature sensor 32 are, for example, thermistors or other devices. While the indoor unit 2 is cooling, the first load-side temperature sensor 31 detects the temperature of the refrigerant flowing into the load-side heat exchanger 26. While the indoor unit 2 is heating, the first load-side temperature sensor 31 detects the temperature of the refrigerant flowing out of the load-side heat exchanger 26. While the indoor unit 2 is cooling, the second load-side temperature sensor 32 detects the temperature of the refrigerant flowing out of the load-side heat exchanger 26.In addition, the second load-side temperature sensor 32 detects the temperature of the refrigerant flowing into the load-side heat exchanger 26 while the indoor unit 2 is operating in heating mode. Furthermore, the first load-side temperature sensor 31 and the second load-side temperature sensor 32 output the thus detected refrigerant temperatures as detection signals to the downstream controller 60.

[0027] It should be noted that Fig. 1 shows an indoor unit 2. However, the air conditioner 100 may include any number of indoor units 2. The air conditioner 100 may include two or more indoor units 2. For example, in the case where the air conditioner 100 includes multiple indoor units 2, each indoor unit 2 is connected in parallel to the outdoor unit 1.

[0028] The air conditioner 100 thus configured includes a controller 60 configured to perform each operation mode. The controller 60 controls the compressor 10, the heat source-side air supply device 18, the load-side air supply device (not shown), the refrigerant flow switching device 13, the load-side expansion device 25, the first opening and closing device 11, or other devices, for example, in accordance with input information from each sensor included in the air conditioner 100 and instructions from a remote controller (not shown). Specifically, the controller 60 controls the driving and stopping of the compressor 10. Furthermore, the controller 60 controls the driving and stopping of the heat source-side air supply device 18 and the load-side air supply device.Furthermore, the controller 60 controls the rotational frequencies of the heat source-side air supply device 18 and the load-side air supply device while the heat source-side air supply device 18 and the load-side air supply device are driven. Furthermore, the controller 60 switches the flow channels of the refrigerant flow switching device 13. Furthermore, the controller 60 controls the opening and closing of the load-side expansion device 25. Furthermore, the controller 60 controls the opening degree of the load-side expansion device 25 while the load-side expansion device 25 is in an open state. Furthermore, the controller 60 controls the opening and closing of the first opening and closing device 11.

[0029] Such a controller 60 is dedicated hardware or a central processing unit (CPU) configured to execute programs stored in memory. Note that the CPU is also referred to as a central processing apparatus, processing apparatus, computing apparatus, microprocessor, microcomputer, or processor.

[0030] In the case where the controller 60 is dedicated hardware, the controller 60 corresponds, for example, to a single circuit, a composite circuit, an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA), or a combination of the above. The functional units implemented by the controller 60 may be implemented by separate hardware components, or the functional units may be implemented by a single hardware component.

[0031] In the case where the controller 60 is a CPU, the functions performed by the controller 60 are implemented by software, firmware, or a combination of software and firmware. The software and firmware are described as programs and stored in memory. The CPU performs the functions of the controller 60 by reading and executing the programs stored in memory. Note that the memory may be, for example, non-volatile or volatile semiconductor memory such as RAM, ROM, flash memory, EPROM, and EEPROM.

[0032] It should be noted that some of the functions of the controller 60 may be implemented by the dedicated hardware and others may be implemented by the software or firmware.

[0033] Even if in Fig. 1, the controller 60 is mounted in the outdoor unit 1, this is merely an example. The controller 60 may also be mounted in the indoor unit 2. Furthermore, the controller 60 may be divided into parts mounted in the outdoor unit 1 and the indoor unit 2. In this case, the part of the controller 60 mounted in the outdoor unit 1 and the part of the controller 60 mounted in the indoor unit 2 may preferably be connected to each other either by cable or wirelessly and configured to be controlled together.

[0034] The controller 60 thus configured includes, for example, an input unit 61, an arithmetic unit 62, and a control unit 63 as functional units. The input unit 61 is a functional unit to which a detection signal representing a detection result from each sensor included in the air conditioner 100 is input. In addition, a command from the remote control (not shown) is also input to the input unit 61. The arithmetic unit 62 is a functional unit for calculating the information required for control based on the information input to the input unit 61. The arithmetic unit 62 converts, for example, the refrigerant pressure detected by the outlet pressure sensor 40 into the refrigerant saturation temperature.Furthermore, the arithmetic unit 62 calculates, for example, the degree of superheat and the degree of subcooling of the refrigerant using two pieces of temperature information included in the information supplied to the input unit 61 and the arithmetic unit 62. The control unit 63 is a functional unit configured to control the compressor 10, the heat source-side air supply device 18, the load-side air supply device (not shown), the refrigerant flow switching device 13, the load-side expansion device 25, the first opening and closing device 11, or other devices according to the information supplied to the input unit 61 and the arithmetic unit 62.

[0035] Next, each operation mode that the air conditioner 100 performs will be described.

[0036] Each operating mode is described below in relation to the refrigerant flow. [Pure cooling mode]

[0037] The cooling-only mode of operation performed by the air conditioner 100 will be described with reference to Fig. 1. As already mentioned, the pure cooling mode is an operating mode in which all indoor units 2 in operation perform cooling operation. In the Fig. 1, a cooling load is generated in the load-side heat exchanger 26 in the indoor unit 2. In Fig. 1 the flow direction of the refrigerant is shown by solid arrows.

[0038] In the pure cooling mode, the refrigerant flow switching device 13 is switched to a flow channel which is Fig. 1 is shown by solid lines. The first opening and closing device 11 is switched to the closed state to block the flow channel of the refrigerant.

[0039] When the compressor 10 is driven, the compressor 10 compresses low-temperature and low-pressure refrigerant into high-temperature and high-pressure refrigerant gas and discharges the high-temperature and high-pressure refrigerant gas through the outlet. The high-temperature and high-pressure refrigerant gas discharged from the compressor 10 passes through the refrigerant flow switching device 13 and flows into the heat source-side heat exchanger 12. The high-temperature and high-pressure refrigerant gas flowing into the heat source-side heat exchanger 12 transforms into high-pressure liquid refrigerant by releasing heat to the outside air at the heat source-side heat exchanger 12. The high-pressure liquid refrigerant flowing out of the heat source-side heat exchanger 12 flows out of the outdoor unit 1.

[0040] The high-pressure liquid refrigerant flowing out of the outdoor unit 1 flows through the main line 111 into the indoor unit 2 and is expanded by the load-side expansion device 25 into a low-temperature, low-pressure two-phase refrigerant. This two-phase refrigerant flows into the load-side heat exchanger 26, which acts as an evaporator, and converts into a low-temperature, low-pressure gaseous refrigerant, while cooling the indoor air by extracting heat from the indoor air. The gaseous refrigerant flowing out of the load-side heat exchanger 26 flows through the main line 111 and flows back into the outdoor unit 1. The gaseous refrigerant flowing into the outdoor unit 1 passes through the refrigerant flow switching device 13 and the accumulator 19 and is sucked back into the compressor 10.

[0041] The controller 60 controls the opening degree of the load-side expansion device 25 so that the degree of superheat, which results from the difference between the refrigerant temperature detected by the first load-side temperature sensor 31 and the refrigerant temperature detected by the second load-side temperature sensor 32, becomes constant. Note that the degree of superheat may also be referred to as "superheat." [Pure heating mode]

[0042] Fig. 2 is a schematic view showing the circuit configuration of the air conditioner according to Embodiment 1 and a diagram illustrating a state in which the air conditioner operates in the heating only mode.

[0043] The heating-only mode of operation performed by the air conditioner 100 will be described with reference to Fig. 2. As already mentioned, the heating-only mode is an operating mode in which all indoor units 2 in operation operate in the heating-only mode. Fig. In the case shown in Figure 2, a heating power is generated in the load-side heat exchanger 26 of the indoor unit 2. In Fig. 2 the flow direction of the refrigerant is shown by solid arrows.

[0044] In the pure heating mode, the refrigerant flow switching device 13 is set to a Fig. 2. The first opening and closing device 11 is switched to the closed state to block the flow channel of the refrigerant.

[0045] When the compressor 10 is driven, the compressor 10 compresses the low-temperature and low-pressure refrigerant into high-temperature and high-pressure refrigerant gas and discharges the high-temperature and high-pressure refrigerant gas through the outlet. The high-temperature and high-pressure refrigerant gas discharged from the compressor 10 passes through the refrigerant flow switching device 13 and flows out of the outdoor unit 1.

[0046] The high-temperature and high-pressure refrigerant gas flowing out of the outdoor unit 1 passes through the main line 111, flows into the indoor unit 2, and converts into liquid refrigerant while heating the indoor air by releasing heat to the indoor air at the load-side heat exchanger 26. The liquid refrigerant flowing out of the load-side heat exchanger 26 is expanded by the load-side expansion device 25 into a two-phase or low-temperature and low-pressure liquid refrigerant, which then flows into the outdoor unit 1 through the main line 111.

[0047] The low-temperature, low-pressure refrigerant flowing into the outdoor unit 1 flows into the heat-source-side heat exchanger 12. The refrigerant flowing into the heat-source-side heat exchanger 12 is converted into low-temperature, low-pressure gaseous refrigerant by extracting heat from the outside air, passes through the refrigerant flow switching device 13 and the accumulator 19, and is sucked into the compressor 10 again.

[0048] The controller 60 controls the opening degree of the load-side expansion device 25 so that the degree of subcooling, which is the difference between a value obtained by converting the refrigerant pressure detected by the outlet pressure sensor 40 into the refrigerant saturation temperature, and the temperature detected by the first load-side temperature sensor 31, becomes constant. Note that the degree of subcooling may also be referred to as "subcooling." [Defrosting mode]

[0049] As mentioned above, the defrost mode is a mode for defrosting the heat source-side heat exchanger 12 in the outdoor unit 1. The heat source-side heat exchanger temperature sensor 43 is located adjacent to an outlet of the heat source-side heat exchanger 12 in the heating-only mode in the refrigerant flow direction. That is, the heat source-side heat exchanger temperature sensor 43 is located in a position adjacent to an outlet of the heat source-side heat exchanger 12 through which the refrigerant flows out in a state where the heat source-side heat exchanger 12 operates as an evaporator. The defrost mode is executed when the temperature detected by the heat source-side heat exchanger temperature sensor 43 in the heating-only mode is lower than or equal to a predetermined temperature.That is, when the controller 60 is operating in heating-only mode and the temperature detected by the heat-source-side heat exchanger temperature sensor 43 is lower than or equal to the preset temperature, the controller 60 determines that a preset amount of frost has formed on the fins of the heat-source-side heat exchanger 12 and executes the defrost mode. The preset temperature is, for example, -10°C.

[0050] Alternatively, the heat source-side heat exchanger temperature sensor 43 may be provided at a position adjacent to the inlet of the heat source-side heat exchanger 12 through which the refrigerant flows in a state where the heat source-side heat exchanger 12 operates as an evaporator. That is, the heat source-side heat exchanger temperature sensor 43 only needs to be capable of detecting the evaporation temperature of the refrigerant flowing through the heat source-side heat exchanger 12 during the heating-only operation mode.

[0051] Furthermore, the above-described method for determining whether frost has formed on the heat source-side heat exchanger 12 is only an example. For example, if the saturation temperature of the refrigerant, which is converted from the pressure of the refrigerant sucked by the compressor 10, is lower than a preset outside air temperature by at least the predetermined temperature, it can be determined that the predetermined amount of frost has formed on the fins of the heat source-side heat exchanger 12. If the temperature difference between the outside air temperature and the evaporation temperature is greater than or equal to a predetermined value over a certain period of time, it can be determined that the predetermined amount of frost has formed on the fins of the heat source-side heat exchanger 12.

[0052] Fig. Fig. 3 is a schematic view showing the circuit configuration of the air conditioner according to Embodiment 1 and a diagram illustrating a state in which the air conditioner operates in the defrost mode. Fig. 3 the solid arrows indicate the flow direction of the refrigerant.

[0053] In the defrosting mode, the refrigerant flow switching device 13 is kept in the same state as the heating only mode, which is Fig. 2 is shown by solid lines. That is, in the defrost mode, the flow path of the refrigerant through the refrigerant flow switching device 13 is the same as the flow path through which the refrigerant discharged from the compressor 10 flows into the load-side heat exchanger 26. The load-side expansion device 25 changes from the open state to the closed state. The first opening and closing device 11 changes from the closed state to the open state to allow the refrigerant to flow through the bypass line 16. In addition, the heat source-side air supply device 18 and the load-side air supply device (not shown) are deactivated.

[0054] In Embodiment 1, when executing the defrosting mode, the controller 60 brings the load-side expansion device 25 into the closed state after bringing the first opening and closing device 11 into the open state. In this way, clogging of the refrigerant flow channels and excessive pressure increase in the refrigerant circuit 101 can be prevented.

[0055] The high-temperature and high-pressure refrigerant gas discharged from the compressor 10 flows through the bypass line 16 and flows into the heat-source-side heat exchanger 12. The high-temperature gaseous refrigerant flowing into the heat-source-side heat exchanger 12 flows through the heat-source-side heat exchanger 12 while defrosting the frost formed on the heat-source-side heat exchanger 12 and flows out of the heat-source-side heat exchanger 12. The refrigerant flowing out of the heat-source-side heat exchanger 12 may be a low-temperature gaseous refrigerant, a two-phase refrigerant, or a liquid refrigerant. The refrigerant flowing out of the heat-source-side heat exchanger 12 passes through the refrigerant flow switching device 13 and flows into the accumulator 19.Of the refrigerant flowing into the accumulator 19, the liquid refrigerant then remains in the accumulator 19, and the gaseous refrigerant flows into a suction unit of the compressor 10.

[0056] In Embodiment 1, the high-temperature and high-pressure refrigerant gas discharged from the compressor 10 is decompressed by the first opening and closing device 11 to such an extent that the saturation temperature for conversion is higher than 0 °C, and flows into the heat source side heat exchanger 12. The thus-decompressed high-temperature and medium-pressure refrigerant has a higher temperature than frost and flows into the heat source side heat exchanger 12 as a two-phase refrigerant. This enables the utilization of the latent heat of the refrigerant and leads to an improved defrosting effect.

[0057] For example, when any of the following conditions is met, defrosting of the heat source-side heat exchanger 12 is terminated based on the determination that the termination conditions are met. The decision to terminate the defrost mode is made, for example, by the control unit 63. Specifically, in the case where the time elapsed since the start of execution of the defrost mode is longer than or equal to a predetermined time, the defrost mode is terminated based on the determination that defrosting of the heat source-side heat exchanger 12 is completed. The predetermined time is, for example, 10 minutes. Note that the time elapsed since the start of execution of the defrost mode is calculated, for example, by the arithmetic unit 62.When the refrigerant temperature measured by the heat source-side heat exchanger temperature sensor 43 is higher than or equal to a specified temperature, the defrosting of the heat source-side heat exchanger 12 is considered complete, and the operation mode is terminated. The specified temperature is, for example, 5°C. Note that when introducing high-temperature refrigerant, in the case where frost has completely formed on the heat source-side heat exchanger 12, the aforementioned specified time may preferably be set longer than or equal to the time required for all the frost to melt.

[0058] Please note that the above-mentioned time period of 10 minutes is merely an example. The above-mentioned temperature of 5°C is also merely an example. Specific values ​​for the aforementioned time period and temperature need only be appropriately determined, taking into account the capacity of the heat source-side heat exchanger 12, the possible state of frost formation on the heat source-side heat exchanger 12, or other conditions, so that all the frost on the heat source-side heat exchanger 12 can defrost.

[0059] A flow passage for the high-temperature and high-pressure refrigerant gas discharged from the compressor 10 is connected to a flow passage of the load-side heat exchanger 26 via the main line 111. Furthermore, the pressure of the high-temperature and high-pressure refrigerant gas discharged from the compressor 10 is higher than the pressure of the refrigerant in the load-side heat exchanger 26. Furthermore, the load-side expansion device 25 is in a closed state in the defrost mode. Therefore, the pressure of the high-temperature and high-pressure refrigerant gas discharged from the compressor 10 in the defrost mode causes the refrigerant existing between the refrigerant flow switching device 13 and the load-side expansion device 25 during the heating-only mode to be retained between the refrigerant flow switching device 13 and the load-side expansion device 25.

[0060] It should be noted here that the load-side heat exchanger 26, which is located between the refrigerant flow switching device 13 and the load-side expansion device 25, functions as a condenser in the heating-only mode. For this reason, a large amount of refrigerant is contained in the load-side heat exchanger 26. This makes it possible to retain excess refrigerant in the load-side heat exchanger 26 by executing the defrosting mode shown in Embodiment 1, thereby reducing the amount of excess refrigerant remaining in the accumulator 19. Accordingly, the air conditioner 100 is configured to prevent the liquid refrigerant from overflowing from the accumulator 19 and being sucked into the compressor 10 during the defrosting mode. That is, during the defrosting mode, the air conditioner 100 is configured to reduce liquid backflow to the compressor 10.

[0061] Furthermore, in the air conditioner 100 according to Embodiment 1, during the defrosting mode, the high-temperature refrigerant discharged from the compressor 10 can flow into the heat-source-side heat exchanger 12 by flowing only within the outdoor unit 1. In other words, in the air conditioner 100 according to Embodiment 1, during the defrosting mode, the high-temperature refrigerant discharged from the compressor 10 can flow into the heat-source-side heat exchanger 12 without passing through the main pipe 111 or the indoor unit 2. For this reason, the air conditioner 100 according to Embodiment 1 is configured so that the density of the refrigerant flowing into the heat-source-side heat exchanger 12 does not decrease due to pressure loss during the defrosting mode.Thereby, the amount of refrigerant circulating between the compressor 10 and the heat source side heat exchanger 12 can be increased, so that the deterioration of the defrosting performance can also be reduced.

[0062] Furthermore, the air conditioner 100 according to Embodiment 1 is configured so that the target room of the air conditioner of the heating-only mode is heated shortly after the defrosting mode is completed, whereby the comfort of the user can be improved.

[0063] Specifically, upon resuming the heating-only mode after the defrosting mode is terminated, the control unit 63 of the controller 60 switches the load-side expansion device 25 from the closed state to the open state. As a result, the refrigerant begins to circulate through the refrigerant circuit 101. Furthermore, upon resuming the heating-only mode after the defrosting mode is terminated, the control unit 63 switches the first opening and closing device 11 from the open state to the closed state to prevent the refrigerant from flowing through the bypass line 16. Furthermore, upon resuming the heating-only mode after the defrosting mode is terminated, the controller 63 causes the heat-source-side air supply device 18 to rotate. As a result, the refrigerant flowing through the heat-source-side heat exchanger 12 is evaporated by extracting heat from the outside air.

[0064] When the heating-only operation is resumed after the defrosting mode is terminated, the excess refrigerant retained in the load-side heat exchanger 26 flows into the heat-source-side heat exchanger 12 through the load-side expansion device 25 and the main pipe 111 and evaporates by extracting heat from the outside air. That is, the excess refrigerant retained in the load-side heat exchanger 26 can be evaporated in the heat-source-side heat exchanger 12 immediately after the heating-only operation is resumed. For this reason, the air conditioner 100 according to Embodiment 1 allows more gaseous refrigerant to flow into the compressor 10 than in the case where the excess refrigerant does not flow into the heat-source-side heat exchanger 12 during the defrosting mode, thereby increasing the amount of refrigerant discharged from the compressor 10.Accordingly, in the air conditioner 100 according to Embodiment 1, a larger amount of high-temperature and high-pressure refrigerant gas can flow into the load-side heat exchanger 26 than in the case where the excess refrigerant does not flow into the load-side heat exchanger 12 during the defrosting operation. As a result, the air conditioner 100 according to Embodiment 1 is configured to heat the target room to be air-conditioned in the heating-only mode soon after the defrosting operation is completed, thereby improving user comfort.

[0065] It should be noted that the first opening and closing device 11 preferably has a size selected as follows. As already mentioned, the high-temperature and high-pressure refrigerant gas discharged from the compressor 10 is decompressed by the first opening and closing device 11 to such an extent that the saturation temperature is higher than 0 °C. If the first opening and closing device 11 is too small for the amount of circulating refrigerant, the pressure of the high-pressure refrigerant discharged from the compressor 10 may increase excessively. For this reason, the first opening and closing device 11 may preferably be selected to be large enough so that the pressure of the high-pressure refrigerant discharged from the compressor 10 is lower than the operating pressure, depending on the amount of circulating refrigerant. For example,A case will be described where the refrigerant used is R410A and the design pressure of the high-pressure side of the refrigerant circuit 101 is 4.15 MPa. Then, for example, a case will be described where an upper limit for the operating pressure on the high-pressure side of the refrigerant circuit 101 during the actual execution of the defrost mode is 3.8 MPa, which is lower than 4.15 MPa, in order to prevent the pressure from exceeding the limit. In this case, the first opening and closing device 11 only needs to be selected to be large enough so that the operating pressure during the actual execution of the defrost mode is less than or equal to 3.8 MPa.

[0066] Furthermore, it is advantageous for the control unit 63 to control the drive frequency of the compressor 10 during the defrost mode as follows. For example, when the frost on the heat source-side heat exchanger 12 defrosts during the defrost mode, there may be a path where the frost hardly defrosts due to the inflow of the amount of frost formed on each path of the heat transfer tubes of the heat source-side heat exchanger 12 and the difference in the flow rate of the refrigerant. In such a case, the temperature of the gaseous refrigerant flowing out of the heat source-side heat exchanger 12 rises above 0°C, which is the melting point of frost, and the temperature of the refrigerant sucked into the compressor 10 rises. This leads to an excessive increase in the temperature of the refrigerant discharged from the compressor 10.

[0067] The temperature of the refrigerant discharged from the compressor 10 influences the deterioration of the refrigerating oil or other phenomena. For this reason, the reliability of the air conditioner 100, such as preventing deterioration of the refrigerating oil, is ensured by setting an upper limit for the temperature of the refrigerant discharged from the compressor 10. The upper limit is, for example, 120°C. For this reason, it is preferable that the control unit 63 controls the drive frequency of the compressor 10 so that the temperature of the refrigerant discharged from the compressor 10 does not exceed the upper limit. In particular, it is desirable that the control unit 63 lower the drive frequency of the compressor 10 in the defrost mode when the temperature detected by the outlet temperature sensor 42 is higher than or equal to the specified temperature.For example, the control unit 63 lowers the drive frequency of the compressor 10 by 20%. The preset temperature is, for example, 110°C. By lowering the drive frequency of the compressor 10, the temperature of the refrigerant discharged from the compressor 10 can be lowered, allowing the defrost mode to be performed stably. The temperature of the refrigerant discharged from the compressor 10 may be referred to as the "discharge temperature of the compressor 10" hereinafter.

[0068] It should be noted that the upper limit value of 120°C for the discharge temperature and the set temperature value of 110°C for the compressor 10 are merely examples. Specific values ​​for the upper limit of the discharge temperature and the set temperature of the compressor 10 only need to be reasonably determined based on the reliability of the compressor 10 and the actual refrigeration oil used, or other conditions. Also, the amount by which the drive frequency of the compressor 10 decreases is not limited to 20%. The amount by which the drive frequency of the compressor 10 decreases can be arbitrarily large, provided the discharge temperature of the compressor 10 can be reduced.

[0069] The following describes a control that the controller 60 performs when executing the defrost mode.

[0070] Fig. 4 is a flowchart showing a control process in which the controller of the air conditioner according to Embodiment 1 executes the defrost mode.

[0071] In the case where the conditions for executing the defrost mode are met, the controller 60 starts the defrost mode in step CT1. In step CT2 following step CT1, the control unit 63 of the controller 60 sets the flow channel of the refrigerant flow switching device 13 to a defrost mode flow channel. Specifically, the control unit 63 causes the flow channel of the refrigerant flow switching device 13 to be the flow channel through which the refrigerant discharged from the compressor 10 flows into the load-side heat exchanger 26. In the case of Embodiment 1, the control unit 63 switches from the heating-only mode to the defrost mode. For this reason, in Embodiment 1, the controller 63 maintains the flow channel of the refrigerant flow switching device 13 equal to the heating-only mode flow channel.

[0072] In step CT3 following step CT2, the control unit 63 changes the first opening and closing device 11 from the closed state to the open state. In step CT4 following step CT3, the control unit 63 changes the load-side expansion device 25 from the open state to the closed state. This allows the refrigerant discharged from the compressor 10 to flow from the bypass line 16 into the heat source-side heat exchanger 12.

[0073] In step CT5, which follows step CT4, it is determined whether the drive frequency of the compressor 10 should be changed. Specifically, in step CT5, it is determined whether the outlet temperature of the compressor 10 is higher than or equal to the predetermined temperature. In other words, in step CT5, it is determined whether the temperature detected by the outlet temperature sensor 42 and input to the input unit 61 is higher than or equal to the predetermined temperature. This determination is made, for example, by the controller 63.

[0074] If the temperature detected by the outlet temperature sensor 42 and input to the input unit 61 is higher than or equal to the predetermined temperature in step CT5, the control unit 63 proceeds to step CT6, where the control unit 63 lowers the drive frequency of the compressor 10. For example, the control unit 63 lowers the drive frequency of the compressor 10 by 20%. This makes it possible to lower the outlet temperature of the compressor 10. After step CT6, the controller 60 returns to step CT5.

[0075] On the other hand, in the case where a temperature detected by the outlet temperature sensor 42 and input to the input unit 61 is not higher than or equal to the temperature set in step CT5, the controller 60 proceeds to step CT7 without changing the drive frequency of the compressor 10.

[0076] In step CT7, it is determined whether the conditions for terminating the defrost mode are met. For example, the arithmetic unit 62 calculates the time elapsed since the start of execution of the defrost mode. If the time elapsed since the start of execution of the defrost mode is greater than or equal to the specified time, the control unit 63 determines that the conditions for terminating the defrost mode are met. Conversely, if the time elapsed since the start of execution of the defrost mode is shorter than the specified time, the control unit 63 determines that the conditions for terminating the defrost mode are not met.If the temperature of the refrigerant flowing out of the heat source-side heat exchanger 12 is higher than or equal to the predetermined temperature, the control unit 63 determines that the conditions for ending the defrost mode are met. Conversely, if the temperature of the refrigerant flowing out of the heat source-side heat exchanger 12 is lower than the predetermined temperature, the control unit 63 determines that the conditions for ending the defrost mode are not met. The temperature of the refrigerant flowing out of the heat source-side heat exchanger 12 is a temperature detected by the heat source-side heat exchanger temperature sensor 43 and input to the input unit 61.It should be noted that the control unit 63 may consider at least one of the conditions for terminating the defrost mode based on the time elapsed since the start of execution of the defrost mode or the conditions for terminating the defrost mode based on the temperature of the refrigerant flowing out of the heat source-side heat exchanger 12 to be satisfied.

[0077] If the control unit 63 determines in step CT7 that the conditions for ending the defrost mode are met, the controller 60 ends the defrost mode in step CT8. Specifically, the control unit 63 switches the load-side expansion device 25 from the closed state to the open state. Subsequently, the control unit 63 switches the first opening and closing device 11 from the open state to the closed state. Then, the control unit 63 executes the heating-only operation.

[0078] However, if the control unit 63 determines in step CT7 that the conditions for terminating the defrost mode are not met, the controller 60 returns to step CT5. [Variation of Embodiment 1]

[0079] The air conditioner 100 described above is merely an example. Some modifications of the air conditioner 100 according to Embodiment 1 are presented below.

[0080] Fig. 5 is a schematic view showing a circuit configuration of another example of the air conditioner according to Embodiment 1 and a diagram illustrating a state in which the air conditioner operates in the defrost mode. Fig. 5 the flow direction of the refrigerant is shown by solid arrows.

[0081] In the Fig. In the air conditioner 100 shown in Fig. 5, the first opening and closing device 11 is an electronic expansion valve with which the flow rate of the refrigerant can be adjusted.

[0082] A case will now be described where, as the defrosting mode progresses, most of the frost on the heat source-side heat exchanger 12 melts, and some of the frost remains on the heat source-side heat exchanger 12. In such a situation, the heat source-side heat exchanger 12 is heated by the refrigerant, so an increase in the low pressure of the refrigerant circulating between the compressor 10 and the heat source-side heat exchanger 12 and an increase in the pressure of the high-pressure gas refrigerant discharged from the compressor 10 may occur.However, if an electronic expansion valve capable of controlling the flow rate of the refrigerant is used as the first opening and closing device 11, the control unit 63 may adjust the opening degree of the first opening and closing device 11 during the defrosting mode so that the pressure of the high-pressure refrigerant gas discharged from the compressor 10 becomes equal to a first predetermined pressure. The first specified pressure is, for example, 3.0 MPa. Furthermore, for example, during the defrosting mode, the control unit 63 increases the opening degree of the first opening and closing device 11 in the case where the pressure of the high-pressure refrigerant gas discharged from the compressor 10 becomes higher than or equal to a second predetermined pressure. The second specified pressure is, for example, 3.8 MPa.By using an electronic expansion valve capable of regulating the refrigerant flow rate as the first opening and closing device 11, the pressure of the high-pressure refrigerant discharged from the compressor 10 can be adjusted and a pressure increase of the high-pressure refrigerant discharged from the compressor 10 can be reduced. That is, by using an electronic expansion valve capable of controlling the refrigerant flow rate as the first opening and closing device 11, the defrosting mode can be stably performed.

[0083] In the above example, the air conditioner 100 includes the accumulator 19 as a container in which excess refrigerant can be accumulated. However, the container in which excess refrigerant is to be collected is not limited to the accumulator 19. A well-known example of a container in which excess refrigerant accumulates is a receiver tank arranged between the heat-source-side heat exchanger 12 and the load-side expansion device 25. The air conditioner 100 may also use a container other than the accumulator 19, such as the receiver tank, as the container for collecting the excess refrigerant. As mentioned above, the air conditioner 100 according to Embodiment 1 is configured to reduce the amount of liquid refrigerant that accumulates in the container in which the excess refrigerant is stored in the defrost mode.For this reason, in the air conditioner 100 according to Embodiment 1, it is advantageous that the capacity of the tank in which excess refrigerant accumulates is smaller than the volume of refrigerant charged into the refrigerant circuit 101 when all the refrigerant is in liquid form. This allows the outdoor unit 1 and the air conditioner 100 to be downsized.

[0084] In the case where excess refrigerant is generated only during the defrosting mode and the excess refrigerant can be retained in the load-side heat exchanger 26, the air conditioner 100 does not need to include a container such as the accumulator 19 in which excess refrigerant is collected.

[0085] In the above-mentioned example of the air conditioner 100, the load-side expansion device 25 is mounted in the indoor unit 2. However, the load-side expansion device 25 may be mounted anywhere. For example, the load-side expansion device 25 may be mounted in the outdoor unit 1. Furthermore, as shown in an embodiment described later, the air conditioner 100 may include a relay unit that connects the outdoor unit 1 to the indoor unit 2. In such a case, the load-side expansion device 25 may be mounted in the relay unit, for example.

[0086] In the above example of the air conditioner 100, the heat source-side heat exchanger 12 and the load-side heat exchanger 26 are configured so that refrigerant and air supplied from an air supply device exchange heat with each other. However, the heat source-side heat exchanger 12 and the load-side heat exchanger 26 can be configured in any manner, provided they can add or remove heat from the refrigerant. For example, the heat source-side heat exchanger 12 and the load-side heat exchanger 26 can be configured so that refrigerant and a heat transfer medium exchange heat with each other. The term "heat medium" refers to a liquid other than the refrigerant that circulates through the heat source-side heat exchanger 12 and the load-side heat exchanger 26, such as water and antifreeze. In addition, the load-side heat exchanger 26 can be, for example, a radiant heater.In the case where the load-side heat exchanger 26 is configured to effect heat exchange between refrigerant and a heat carrier, the load-side heat exchanger 26 is not limited to being installed in the indoor unit 2. The load-side heat exchanger 26 may also be installed in the outdoor unit 1, for example. Furthermore, if the air conditioner 100 includes a relay unit, the load-side heat exchanger 26 may be installed in the relay unit. The space to be air-conditioned can be cooled or heated by providing the indoor unit 2 with an indoor heat exchanger through which the heat medium subjected to heat exchange with the refrigerant in the load-side heat exchanger 26 flows, and supplying the indoor heat exchanger with the heat medium cooled or heated in the load-side heat exchanger 26.

[0087] Furthermore, in the above example, the air conditioner 100 includes a heat source side heat exchanger 12, a refrigerant flow switching device 13, a first opening and closing device 11, and a bypass line 16. Without being limited to this example, the air conditioner 100 may also include a plurality of heat source side heat exchangers 12, a plurality of refrigerant flow switching devices 13, a plurality of first opening and closing devices 11, and a plurality of bypass lines 16.

[0088] In the above example of the air conditioner 100, the refrigerant used is R410A. However, the refrigerant used in the air conditioner 100 is not limited to R410A. For example, any single-component refrigerant or mixed refrigerants with a two-phase gas-liquid state can be used in the air conditioner 100.

[0089] As mentioned above, an air conditioner 100 according to Embodiment 1 includes a refrigerant cycle 101 in which a compressor 10, a heat source-side heat exchanger 12, a refrigerant flow switching device 13, a load-side heat exchanger 26, and a load-side expansion device 25 are connected by a refrigerant pipe 110. Furthermore, the air conditioner 100 includes a bypass pipe 16, the inlet end 16a of which is connected to a point in the refrigerant cycle 101 located between an outlet of the compressor 10 and the refrigerant flow switching device 13, and the outlet end 16b of which is connected to a point in the refrigerant cycle 101 located between the load-side expansion device 25 and the heat source-side heat exchanger 12.The air conditioner 100 further includes a first opening and closing device 11 provided in the bypass line 16 and configured to open and close a refrigerant flow channel at a location where the first opening and closing device 11 is installed. Furthermore, the air conditioner 100 includes a controller 60 configured to control the refrigerant flow switching device 13, the load-side expansion device 25, and the first opening and closing device 11. Furthermore, the air conditioner 100 includes an outdoor unit 1 equipped with the compressor 10, the heat source-side heat exchanger 12, the refrigerant flow switching device 13, the bypass line 16, and the first opening and closing device 11.Furthermore, when executing the defrosting operation mode for defrosting the heat source-side heat exchanger 12, the controller 60 causes a flow channel of the refrigerant through the refrigerant flow switching device 13 to be a flow channel through which the refrigerant discharged from the compressor 10 flows into the load-side heat exchanger 26. Furthermore, the controller 60 changes the first opening and closing device 11 from the closed state to the open state, changes the load-side expansion device 25 from the open state to the closed state, and causes the refrigerant discharged from the compressor 10 to flow from the bypass line 16 into the load-side heat exchanger 12.

[0090] As already mentioned, the air conditioning unit 100 thus formed is also designed to reduce liquid return to the compressor 10 during the defrosting mode and also to reduce the deterioration of the defrosting performance. Embodiment 2

[0091] As shown in Embodiment 2, the air conditioner 100 may include a second opening and closing device 15. Note that the points not mentioned in Embodiment 2 are the same as those in Embodiment 1.

[0092] Fig. Fig. 6 is a schematic view showing a circuit configuration of an air conditioner according to Embodiment 2 and a diagram illustrating a state in which the air conditioner operates in the defrost mode. Fig. 6 the flow direction of the refrigerant is shown by solid arrows.

[0093] The air conditioner 100 according to Embodiment 2 includes a second opening and closing device 15. The second opening and closing device 15 is configured to open and close a flow channel for the refrigerant at a location where the second opening and closing device 15 is installed. The second opening and closing device 15 is provided in the refrigerant circuit 101 and at an inlet side of the heat source-side heat exchanger 12 through which the refrigerant flows into the heat source-side heat exchanger 12 when the heat source-side heat exchanger 12 functions as an evaporator, and faces the heat source-side heat exchanger 12 via a location to which the outlet-side end 16b of the bypass pipe 16 is connected. In Embodiment 2, the second opening and closing device 15 is mounted in the outdoor unit 1.The second opening and closing device 15 may preferably be a device capable of opening and closing a flow channel for the refrigerant, such as a two-way valve, a solenoid valve, and an electronic expansion valve capable of adjusting the flow rate of the refrigerant. The second opening and closing device 15 is controlled by the controller 60. Specifically, during the cooling-only mode and the heating-only mode, the control unit 63 of the controller 60 maintains the second opening and closing device 15 in an open state. Furthermore, when executing the defrosting mode, the controller 63 changes the second opening and closing device 15 from the open state to the closed state.

[0094] In the defrost mode, the high-temperature and high-pressure refrigerant gas discharged from the compressor 10 flows through the bypass line 16 and flows into the heat source side heat exchanger 12. When the second opening and closing device 15 is not provided, a part of the high-temperature and high-pressure refrigerant gas discharged from the compressor 10 flows toward the load-side expansion device 25 after exiting the bypass line 16. It should be noted that a portion of the refrigerant line 110 located between the second opening and closing device 15 and the load-side expansion device 25 has a lower temperature than the refrigerant discharged from the compressor 10.Therefore, when the refrigerant discharged from the compressor 10 flows into the portion of the refrigerant line 110 located between the second opening and closing device 15 and the load-side expansion device 25, the high-temperature and high-pressure refrigerant gas discharged from the compressor 10 may condense and stagnate.

[0095] However, by keeping the second opening and closing device 15 closed during the defrost mode, the refrigerant discharged from the compressor 10 can be prevented from flowing into the refrigerant line portion 110 located between the second opening and closing device 15 and the load-side expansion device 25. That is, by keeping the second opening and closing device 15 closed during the defrost mode, the high-temperature and high-pressure refrigerant gas discharged from the compressor 10 can be prevented from condensing or remaining in the refrigerant line portion 110 between the second opening and closing device 15 and the load-side expansion device 25.Accordingly, in the air conditioner 100 according to Embodiment 2, a larger portion of the high-temperature and high-pressure refrigerant gas discharged from the compressor 10 can flow into the heat source side heat exchanger 12, resulting in further improvement of the defrosting performance.

[0096] Fig. Fig. 7 is a schematic view of a Mollier diagram showing the conditions of the refrigerant when the air conditioner operates according to Embodiment 2 of the heating-only mode. Fig. 7, the horizontal axis represents the specific enthalpy h [kJ / kg]. In addition, the vertical axis shows in Fig. 7 the pressure P [MPa]. The distribution of the refrigerant quantity in the heating-only mode of the air conditioning unit 100 is determined by Fig. 7. In the case where the air conditioner 100 shown in the embodiment 1 also operates in the pure heating mode, the refrigerant is in conditions corresponding to the Fig. 7 are similar.

[0097] In Fig. 7, saturation lines are labeled i. On the right side of the right saturation line i, the refrigerant is in a single-phase gas state. On the left side of the left saturation line i, the refrigerant is in a single-phase liquid state. Furthermore, between the right and left saturation lines i, the refrigerant is in a two-phase gas-liquid state. In the single-phase liquid state, the refrigerant has a density about 30 times higher than in the single-phase gaseous state. For example, in the case where R410A has a pressure of 1.0 MPa, the density of the single-phase gaseous refrigerant is about 38 kg / m3 and the density of the single-phase liquid refrigerant is about 1,140 kg / cm3. For this reason, the required amount of refrigerant increases as the two-phase gas-liquid refrigerant approaches the left saturation line i.

[0098] In Fig. 7, the gaseous refrigerant discharged from the compressor 10 is in a state indicated by a point b. This gaseous refrigerant is condensed by the load-side heat exchanger 26 into liquid refrigerant, which is in a state indicated by a point c. This liquid refrigerant is decompressed by the load-side expansion device 25, flows through the main line 111, and becomes two-phase gas-liquid refrigerant, which is in a state indicated by a point d. This two-phase gas-liquid refrigerant is evaporated by the heat-source-side heat exchanger 12, passes through the accumulator 19, and is sucked as gaseous refrigerant into the compressor 10, which is in a state indicated by point a.Therefore, most of the refrigerant charged into the air conditioner 100 remains in the load-side heat exchanger 26, the main line 111, and the heat source-side heat exchanger 12, where it changes from a two-phase gas-liquid state to a liquid state.

[0099] Fig. Fig. 8 is a schematic view of a Mollier diagram showing the conditions of the refrigerant when the air conditioner according to Embodiment 2 operates in the defrost mode. Fig. 8 represents the horizontal axis, as in Fig. 7, represents the specific enthalpy h [kJ / kg]. In addition, the vertical axis in Fig. 8 represents the pressure P [MPa], as in Fig. 7. The distribution of the refrigerant quantity in the defrosting mode of the air conditioner 100 is determined by Fig. 8. In the case where the air conditioner 100 shown in Embodiment 1 also operates in the defrosting mode, the refrigerant is in conditions similar to those in Fig. 8 resemble.

[0100] Fig. 8 shows saturation lines i, which are identical to those in Fig. 7. That is, on the right side of the right saturation line i, the refrigerant is in a single-phase gas state. On the left side of the left saturation line i, the refrigerant is in a single-phase liquid state. Furthermore, between the right and left saturation lines i, the refrigerant is in a two-phase gas-liquid state. As mentioned earlier, the refrigerant in the single-phase liquid state has a density about 30 times higher than in the single-phase gaseous state. For this reason, the required amount of refrigerant increases as the two-phase gas-liquid refrigerant approaches the left saturation line i.

[0101] In Fig. 8, the gaseous refrigerant discharged from the compressor 10 is in a state indicated by a point b. This gaseous refrigerant is decompressed in the first opening and closing device 11 into gaseous refrigerant, which is in a state indicated by a point c. The gaseous refrigerant at point c is cooled by the defrosting of the frost formed on the heat source-side heat exchanger 12, passes through the accumulator 19, and is sucked as gaseous refrigerant into the compressor 10, which is in a state indicated by a point a. For this reason, the part of the refrigerant used in the heating-only mode that is no longer needed in the defrost mode remains as excess refrigerant in the load-side heat exchanger 26 and the accumulator 19.

[0102] Due to installation constraints, some air conditioners may have a long main pipe between an outdoor unit and an indoor unit. For example, a VRF (Variable Refrigerant Flow) system has an outdoor unit installed on the roof of a building and a plurality of indoor units installed on the lower floors of the building. In such a case, a main pipe between the outdoor unit and an indoor unit may be long. The air conditioner 100 according to Embodiment 2 may also have a long main pipe 111 between the outdoor unit 1 and the indoor unit 2 due to installation environment constraints. In such a case, where the main pipe 111 is long, the amount of refrigerant in the main pipe 111 increases.For this reason, by providing the second opening and closing device 15 and maintaining the second opening and closing device 15 in a closed state during the defrosting mode, a large amount of refrigerant can be accumulated in the main line 111. This makes it possible to reduce the amount of refrigerant that accumulates in the accumulator 19 during the defrosting mode. For this reason, it is advantageous for an air conditioner 100 having an accumulator 19 whose capacity is smaller than the volume of refrigerant charged into the refrigerant circuit 101 when all the refrigerant is in liquid form to be provided with a second opening and closing device 15.

[0103] The following describes a control operation that the controller 60 performs when the air conditioner 100 according to Embodiment 2 executes the defrost mode.

[0104] Fig. 9 is a flowchart showing a control in which the controller of the air conditioner according to Embodiment 2 executes the defrosting mode.

[0105] When the air conditioner 100 according to Embodiment 2 executes the defrosting mode, the control performed by the controller 60 includes a step CT9, which leads to the Fig. 4 of Embodiment 1. This step CT9 is executed between step CT3 and step CT4. Note that step CT9 only needs to occur between step CT3 and step CT5. For example, step CT9 may occur between step CT4 and step CT5.

[0106] Specifically, when executing the defrosting mode, the control unit 63 of the controller 60 changes the second opening and closing device 15 from the open state to the closed state in step CT9 following step CT3, and proceeds to step CT5. That is, when executing the defrosting mode, the controller 63 brings the first opening and closing device 11 to the open state before bringing the load-side expansion device 25 and the second opening and closing device 15 to the closed state, respectively. In this way, clogging of the refrigerant flow channels and excessive pressure increase in the refrigerant circuit 101 can be prevented. Embodiment 3

[0107] As mentioned above, the air conditioner 100 may include a relay unit that connects the outdoor unit 1 to the indoor unit 2. Embodiment 3 shows an example of an air conditioner 100 with a relay unit. It should be noted that things not mentioned in Embodiment 3 are similar to those mentioned in Embodiments 1 and 2. [Configuration of the air conditioner 100]

[0108] Fig. 10 is a schematic view showing a circuit configuration of an air conditioner according to Embodiment 3 and a diagram illustrating a state in which the air conditioner operates in the cooling only mode.

[0109] As in Fig. As shown in Figure 10, the air conditioner 100 includes an outdoor unit 1, a plurality of indoor units 2, and a relay unit 3. The relay unit 3 connects the outdoor unit 1 and the indoor units 2. The outdoor unit 1 and the relay unit 3 are connected by a plurality of main pipes 111 through which the refrigerant flows. The main pipes 111 are parts of the refrigerant pipe 110 of the refrigerant cycle 101. In addition, the relay unit 3 and each of the indoor units 2 are connected by corresponding branch pipes 112. The branch pipes 112 are parts of the refrigerant pipe 110 of the refrigerant cycle 101. The cooling or heating energy generated in the outdoor unit 1 is supplied to each indoor unit 2 via the relay unit 3.

[0110] In the following, the indoor units 2 can be distinguished from one another by a letter of the alphabet at the end of a reference number. Fig. 1 shows an indoor unit 2a, an indoor unit 2b, an indoor unit 2c, and an indoor unit 2d as the plurality of indoor units 2. Hereinafter, multiple components of the respective indoor units 2 may be distinguished from each other by an alphabetic letter at the end of a reference numeral. For example, as mentioned later, each indoor unit 2 is equipped with a load-side heat exchanger 26. In this case, the load-side heat exchanger 26 mounted in the indoor unit 2a may be referred to, for example, as "load-side heat exchanger 26a."

[0111] In Embodiment 3, the outdoor unit 1 and the relay unit 3 are connected by two main lines 111. Furthermore, the relay unit 3 and each of the indoor units 2 are connected by two branch lines 112. Specifically, the relay unit 3 and each of the indoor units 2 are connected by a branch line 112a and a branch line 112b. Since the outdoor unit 1 and the relay unit 3 are connected by two lines, and the relay unit 3 and each indoor unit 2 are connected by two lines, the air conditioner 100 can be easily installed. [Outdoor Unit 1 Configuration]

[0112] As in Embodiment 1, the outdoor unit 1 is equipped with a compressor 10, a refrigerant flow switching device 13, a heat source side heat exchanger 12, an accumulator 19, a first opening and closing device 11, a bypass line 16, and a heat source side air supply device 18.

[0113] In addition, the outdoor unit 1 is equipped with a backflow prevention device 14a, a backflow prevention device 14b, a backflow prevention device 14c, and a backflow prevention device 14d. The backflow prevention devices 14a to 14d are, for example, check valves. The backflow prevention device 14a is designed to prevent the high-temperature and high-pressure refrigerant gas discharged from the compressor 10 from flowing back to the heat source-side heat exchanger 12 during the heating-only mode and the subsequent main heating mode.The backflow prevention device 14b is configured to prevent high-pressure liquid refrigerant or two-phase gas-liquid refrigerant from flowing back to the accumulator 19 from a region of the refrigerant line 110 located adjacent to an outlet of the backflow prevention device 14a during the cooling-only mode, a main cooling mode. The backflow prevention device 14c is configured to prevent high-pressure liquid refrigerant or two-phase gas-liquid refrigerant from flowing back to the accumulator 19 from a region of the refrigerant line 110 located adjacent to an inlet of the backflow prevention device 14a during the cooling-only mode and the main cooling mode.The backflow prevention device 14d is configured to prevent high-temperature and high-pressure refrigerant gas from flowing back from a flow channel located adjacent to a discharge side of the compressor 10 to a main line 111 during the heating-only mode and the main heating mode.

[0114] The backflow prevention devices 14a to 14d allow the refrigerant flow flowing into the relay unit 3 to be directed in one direction, regardless of the operation requested by the indoor unit 2. Although the backflow prevention devices 14a to 14d used in Embodiment 3 are check valves, the backflow prevention devices 14a to 14d are not limited to this configuration as long as they are configured to prevent backflow of refrigerant. For example, opening and closing devices or expansion devices, each of which has a fully closing function, can be used as the backflow prevention devices 14a to 14d. [Configuration of indoor units 2a to 2d]

[0115] The indoor units 2, for example, are constructed identically to one another. Each indoor unit 2 has an indoor-side expansion device 70, which functions as a load-side expansion device 25, and a load-side heat exchanger 26. That is, the indoor unit 2a has an indoor-side expansion device 70a and a load-side heat exchanger 26a. The indoor unit 2b has an indoor-side expansion device 70b and a load-side heat exchanger 26b. The indoor unit 2c has an indoor-side expansion device 70c and a load-side heat exchanger 26c. The indoor unit 2d has an indoor-side expansion device 70d and a load-side heat exchanger 26d. Each of the load-side heat exchangers 26a to 26d is connected to the outdoor unit 1 via the branch lines 112, the relay unit 3, and the main lines 111.

[0116] Each of the load-side heat exchangers 26 is configured so that the refrigerant flowing inside and the indoor air exchange heat with each other. To this end, the air conditioner 100 according to Embodiment 3 includes load-side air supply devices (not shown) configured to supply the indoor air separately to each of the load-side heat exchangers 26. That is, the indoor air cooled by each of the load-side heat exchangers 26 serves as cooling air supplied to a target space to be air-conditioned. The indoor air heated by the load-side heat exchangers 26 serves as heating air supplied to the target space for air conditioning.

[0117] Each of the indoor expansion devices 70a has an opening degree that can be regulated, for example, continuously or in multiple stages. The indoor expansion devices 70a include, for example, an electronic expansion valve. Each of the indoor expansion devices 70a functions as a pressure reducing valve and an expansion valve. In other words, each of the indoor expansion devices 70a decompresses and expands the refrigerant. Each of the indoor expansion devices 70a is located in the refrigerant circuit 101 and downstream of a corresponding load-side heat exchanger 26 when the corresponding load-side heat exchanger 26 functions as a condenser. That is, during heating operation, each of the indoor expansion devices 70a decompresses the refrigerant flowing out of a corresponding load-side heat exchanger 26.During cooling operation, each of the indoor expansion devices 70a decompresses the refrigerant flowing into one of the load-side heat exchangers 26. That is, each of the indoor expansion devices 70a is arranged in the refrigerant circuit 101 and upstream of a corresponding load-side heat exchanger 26 when the corresponding load-side heat exchanger 26 functions as an evaporator.

[0118] In addition, each indoor unit 2 is equipped with a first load-side temperature sensor 31 and a second load-side temperature sensor 32. That is, the indoor unit 2a is equipped with a first load-side temperature sensor 31a and a second load-side temperature sensor 32a. The indoor unit 2b is equipped with a first load-side temperature sensor 31b and a second load-side temperature sensor 32b. The indoor unit 2c is equipped with a first load-side temperature sensor 31c and a second load-side temperature sensor 32c. The indoor unit 2d is equipped with a first load-side temperature sensor 31d and a second load-side temperature sensor 32d. Each first load-side temperature sensor 31 and each second load-side temperature sensor 32 are, for example, thermistors or other devices.While one of the indoor units 2 is performing a cooling operation, each first load-side temperature sensor 31 detects the temperature of the refrigerant flowing into one of the load-side heat exchangers 26. While one of the indoor units 2 is performing a heating operation, each first load-side temperature sensor 31 detects the temperature of the refrigerant flowing out of one of the load-side heat exchangers 26. While a corresponding indoor unit 2 is cooling, each second load-side temperature sensor 32 detects the temperature of the refrigerant flowing out of a corresponding load-side heat exchanger 26. Furthermore, each second load-side temperature sensor 32 detects the temperature of the refrigerant flowing into a corresponding load-side heat exchanger 26 while one of the indoor units 2 is operating in the heating operation.In addition, each first load-side temperature sensor 31 and each second load-side temperature sensor 32 outputs the thus detected refrigerant temperatures as detection signals to a controller 60.

[0119] It should be noted that in Fig. 10, four indoor units 2a to 2d are shown. However, the air conditioner 100 may also include two indoor units 2, three indoor units 2, or five or more indoor units 2. [Relay Unit 3 Configuration]

[0120] The relay unit 3 includes a gas-liquid separator 29, a plurality of “first opening and closing relay units” 23, a plurality of “second opening and closing relay units” 24, a “first expansion relay unit” 30, and a “second expansion relay unit” 27 as components of the refrigerant cycle 101.

[0121] The gas-liquid separator 29 is provided at an inlet of the relay unit 3 in the refrigerant flow. The gas-liquid separator 29 separates the refrigerant flowing in from the outdoor unit 1 into liquid refrigerant and gaseous refrigerant. A gaseous refrigerant outlet line 113, which is part of the refrigerant line 110, is connected to an outlet of the gas-liquid separator 29 for the gaseous refrigerant. Furthermore, one end of a liquid refrigerant outlet line 114, which is part of the refrigerant line 110, is connected to an outlet of the liquid refrigerant separator 29. Note that the other end of the liquid refrigerant outlet line 114 divides into branches connected to the respective indoor expansion devices 70.Specifically, in the main cooling mode described below, the gas-liquid separator 29 separates the two-phase high-pressure gas-liquid refrigerant generated in the outdoor unit 1 into liquid refrigerant and gaseous refrigerant. The gas-liquid separator 29 discharges the thus-separated liquid refrigerant into the liquid refrigerant outlet line 114, thereby supplying cooling energy to one or more of the indoor units 2. Furthermore, the gas-liquid separator 29 discharges the thus-separated gaseous refrigerant into the gaseous refrigerant outlet line 113, thereby supplying heating energy to one or more other indoor units 2.

[0122] One end of each of the "first opening and closing device relay unit" 23 is connected to the gas refrigerant outlet line 113. Furthermore, the "first opening and closing device relay unit" 23 is provided for the respective indoor units 2, and the other end of each of the "first opening and closing device relay unit" 23 is connected to the load-side heat exchanger 26 of a corresponding one of the indoor units 2. That is, the "first opening and closing device relay unit" 23a is connected to the load-side heat exchanger 26a of the indoor unit 2a. The "first opening and closing device relay unit" 23b is connected to the load-side heat exchanger 26b of the indoor unit 2b. The "first opening and closing device relay unit" 23c is connected to the load-side heat exchanger 26c of the indoor unit 2c.The "first opening and closing device relay unit" 23d is connected to the load-side heat exchanger 26d of the indoor unit 2d. Each "first opening and closing device relay unit" 23 is configured to open and close a flow channel for high-temperature and high-pressure refrigerant gas supplied to a corresponding indoor unit 2. The "first opening and closing device relay unit" 23 may be, for example, solenoid valves or other devices. The "first opening and closing device relay unit" 23 only needs to be capable of opening and closing flow channels and may be expansion devices, each of which has a complete closing function.

[0123] Each of the "second opening and closing device relay units" 24 is connected to a relay unit outlet pipe 115. The relay unit outlet pipe 115 is a pipe that is part of the refrigerant pipe 110 and through which the refrigerant flowing out of the relay unit 3 flows. Furthermore, the "second opening and closing device relay units" 24 are provided for the respective indoor units 2, and the other end of each of the "second opening and closing device relay units" 24 is connected to the load-side heat exchanger 26 of a corresponding one of the indoor units 2. That is, the "second opening and closing device relay unit" 24a is connected to the load-side heat exchanger 26a of the indoor unit 2a. The "second opening and closing device relay unit" 24b is connected to the load-side heat exchanger 26b of the indoor unit 2b.The "second opening and closing device relay unit" 24c is connected to the load-side heat exchanger 26c of the indoor unit 2c. The "second opening and closing device relay unit" 24d is connected to the load-side heat exchanger 26d of the indoor unit 2d. Each of the "second opening and closing device relay units" 24 is configured to open and close a flow channel for low-temperature and low-pressure refrigerant flowing out of one of the indoor units 2. The "second opening and closing device relay units" 24 are, for example, solenoid valves or other devices. The "second opening and closing device relay units" 24 only need to be capable of opening and closing flow channels and may be expansion devices, each of which has a complete closing function.

[0124] That is, the air conditioner 100 according to Embodiment 3 includes a plurality of devices each having an indoor unit 2, a “first opening and closing device relay unit” 23, and a “second opening and closing device relay unit” 24.

[0125] The “first expansion device relay unit” 30 is provided in the liquid refrigerant outlet line 114 and is configured to decompress the refrigerant flowing through a location where the “first expansion device relay unit” 30 is installed. Specifically, the “first expansion device relay unit” 30 functions as a pressure reducing valve and an on-off valve. The “first expansion device relay unit” 30 is configured to decompress the liquid refrigerant to have a predetermined pressure and to open and close a liquid refrigerant flow channel. The “first expansion device relay unit” 30 has an opening degree that can be regulated, for example, either continuously or in multiple steps. Usable examples of the “first expansion device relay unit” 30 include an electronic expansion valve.

[0126] The "relay unit second expansion device" 27 is provided in the relay unit bypass line 116 and configured to decompress the refrigerant flowing through a location where the "relay unit second expansion device" 27 is installed. The relay unit bypass line 116 is a line that is part of the refrigerant line 110. One end of the relay unit bypass line 116 is connected to a location in the liquid refrigerant outlet line 114 located between the "relay unit first expansion device" 30 and the indoor expansion device 70. Furthermore, the other end of the relay unit bypass line 116 is connected to the relay unit outlet line 115. The "relay unit second expansion device" 27 functions as a pressure reducing valve and an on-off valve.The "second expansion device relay unit" 27 is configured to open and close a refrigerant flow channel in the heating-only mode. Furthermore, the "second expansion device relay unit" 27 is configured to regulate the flow rate of the refrigerant flowing through the relay unit bypass line 116 in the main heating mode, as mentioned above, depending on the indoor load. The "second expansion device relay unit" 27 has an opening degree that can be regulated, for example, continuously or in multiple steps. Suitable examples of the "second expansion device relay unit" 27 include an electronic expansion valve.

[0127] Furthermore, the relay unit 3 is equipped with an inlet-side pressure sensor 33 and an outlet-side pressure sensor 34. The inlet-side pressure sensor 33 is located in the liquid refrigerant outlet line 114 next to the inlet of the "first expansion device relay unit" 30. The inlet-side pressure sensor 33 is configured to detect the pressure of the high-pressure refrigerant. The outlet-side pressure sensor 34 is located in the liquid refrigerant outlet line 114 next to the outlet of the "first expansion device relay unit" 30. The outlet-side pressure sensor 34 is configured to detect the intermediate pressure of the liquid refrigerant at a position next to the outlet of the "first expansion device relay unit" 30 in the main cooling mode mentioned below.

[0128] The controller 60 of the air conditioner 100 according to Embodiment 3 performs each of the operations described below. As in Embodiment 1, the controller 60 according to Embodiment 3 controls the compressor 10, the heat source-side air supply device 18, the load-side air supply device (not shown), the refrigerant flow switching device 13, the first opening and closing device 11, or other devices, for example, in accordance with the input information from each sensor included in the air conditioner 100 and the instructions from a remote controller (not shown).

[0129] Furthermore, the controller 60 according to Embodiment 3 controls the indoor expansion devices 70, the "first opening and closing device relay unit" 23, the "second opening and closing device relay unit" 24, the "first expansion device relay unit" 30, the "second expansion device relay unit" 27, or other devices, for example, in accordance with input information from each sensor included in the air conditioner 100 and instructions from the remote controller (not shown). Specifically, the control unit 63 of the controller 60 controls the opening and closing of the indoor expansion devices 70. Furthermore, the control unit 63 controls the opening degrees of the indoor expansion devices 70 each in an open state.Furthermore, the control unit 63 controls the opening and closing of the "first opening and closing device relay unit" 23 and the "second opening and closing device relay unit" 24. In addition, the control unit 63 of the controller 60 controls the opening and closing of the "first expansion device relay unit" 30. In addition, the control unit 63 controls the opening degree of the "first expansion device relay unit" 30 in an open state. Furthermore, the control unit 63 of the controller 60 controls the opening and closing of the "second expansion device relay unit" 27. In addition, the control unit 63 controls the opening degree of the "second expansion device relay unit" 27 in an open state.

[0130] Even if in Fig. 10, the controller 60 is installed in the outdoor unit 1, but this is only an example. The controller 60 may also be installed in an indoor unit 2. The controller 60 may be installed in the relay unit 3. Furthermore, the controller 60 may be divided into parts installed in at least two of the outdoor unit 1, the indoor unit 2, and the relay unit 3.

[0131] Each operation mode performed in the air conditioner 100 will be described below. The controller 60 of the air conditioner 100 is capable of independently performing a cooling or heating operation in each of the indoor units 2a to 2d according to the instructions of the indoor units 2a to 2d. That is, the air conditioner 100 is configured to perform the same operation in all the indoor units 2a to 2d. Specifically, the air conditioner 100 is configured to perform a cooling operation in all the indoor units 2a to 2d. The air conditioner 100 is configured to perform a heating operation in all the indoor units 2a to 2d. Furthermore, the air conditioner 100 is configured to separately perform different operation modes in each of the indoor units 2a to 2d.

[0132] The operating modes implemented in the air conditioning device 100 can be roughly divided into cooling modes and heating modes. The cooling modes include the pure cooling mode and the main cooling mode.

[0133] The cooling-only mode is an operation mode in which all indoor units 2a to 2d perform cooling operation. That is, in the cooling-only mode, all load-side heat exchangers 26a to 26d function as evaporators. The main cooling mode is a mixed cooling-heating mode in which one or more of the indoor units 2a to 2d perform cooling operation and one or more of the indoor units 2a to 2d perform heating operation, and is an operation mode in which the cooling load is higher than the heating capacity. That is, in the main cooling mode, one or more of the load-side heat exchangers 26a to 26d function as evaporators and another or more of the load-side heat exchangers 26a to 26d function as condensers.

[0134] The heating modes include heating-only mode and main heating mode. Heating-only mode is an operation mode in which all operating indoor units 2a to 2d perform heating operation. That is, in heating-only mode, all load-side heat exchangers 26a to 26d function as condensers. Main heating mode is a mixed cooling and heating operation in which one or more of the indoor units 2a to 2d perform cooling operation and one or more of the indoor units 2a to 2d perform heating operation, and is an operation mode in which the heating capacity is higher than the cooling load. Each mode is described below. [Pure cooling mode]

[0135] The pure cooling mode that the air conditioner100 performs is determined by Fig. 10 described. Fig. Figure 10 illustrates the pure cooling mode using the example of a case in which cooling loads are generated only in the load-side heat exchanger 26a and the load-side heat exchanger 26b. That is, Fig. Figure 10 illustrates the cooling-only mode using the example of a case in which only the indoor unit 2a and the indoor unit 2b perform cooling operation. Fig. 10 the flow direction of the refrigerant is shown by solid arrows.

[0136] In the case of the pure cooling mode, the controller 60 switches the refrigerant flow switching device 13 of the outdoor unit 1 so that the refrigerant discharged from the compressor 10 flows into the heat source-side heat exchanger 12.

[0137] First, the compressor 10 compresses low-temperature and low-pressure refrigerant into high-temperature and high-pressure refrigerant gas and discharges the high-temperature and high-pressure refrigerant gas through the outlet. The high-temperature and high-pressure refrigerant gas discharged from the compressor 10 passes through the refrigerant flow switching device 13, flows into the heat-source-side heat exchanger 12, and then transforms into high-pressure liquid refrigerant while releasing heat to the outside air through the heat-source-side heat exchanger 12. The high-pressure liquid refrigerant flowing out of the heat-source-side heat exchanger 12 passes through the backflow prevention device 14a, flows out of the outdoor unit 1, passes through a main pipe 111, and flows into the relay unit 3.

[0138] The high-pressure liquid refrigerant flowing into the relay unit 3 passes through the gas-liquid separator 29, the liquid refrigerant outlet line 114, the “relay unit first expansion device” 30, and the branch lines 112b, and is expanded into a two-phase low-temperature, low-pressure gas-liquid refrigerant by the indoor-side expansion device 70a and the indoor-side expansion device 70b.

[0139] The refrigerant expanded into a two-phase gas-liquid state by the indoor expansion device 70a and the indoor expansion device 70b flows separately into the load-side heat exchanger 26a and the load-side heat exchanger 26b, which function as evaporators. The two-phase gas and liquid refrigerant flowing into the load-side heat exchanger 26a and the load-side heat exchanger 26b transforms into a low-temperature, low-pressure gaseous refrigerant while cooling the indoor air by removing heat from the indoor air. In this case, the opening degree of the indoor expansion device 70a is controlled so that the degree of superheat, which results from the difference between a temperature detected by the first load-side temperature sensor 31a and a temperature detected by the second load-side temperature sensor 32a, becomes constant.Similarly, the opening degree of the indoor-side expansion device 70b is controlled so that the degree of superheat resulting from the difference between a temperature detected by the first load-side temperature sensor 31b and a temperature detected by the second load-side temperature sensor 32b becomes constant.

[0140] The gaseous refrigerant flowing out of the load-side heat exchanger 26a and the gaseous refrigerant flowing out of the load-side heat exchanger 26b flow through branch pipes 112a and flow into the “second opening and closing device relay unit” 24a and the “second opening and closing device relay unit” 24b. Then, the gaseous refrigerant flowing out of the “relay unit second opening and closing device” 24a and the “relay unit second opening and closing device” 24b flows through the relay unit outlet pipe 115, flows out of the relay unit 3, passes through a main pipe 111, and flows into the outdoor unit 1 again. The refrigerant flowing into the outdoor unit 1 passes through the backflow prevention device 14d, passes through the refrigerant flow switching device 13 and the accumulator 19, and is sucked into the compressor 10 again.

[0141] Since it is not necessary to flow refrigerant through the load-side heat exchanger 26c and the load-side heat exchanger 26d, in which no thermal load is generated, the indoor expansion device 70c and the indoor expansion device 70d, which correspond to the load-side heat exchanger 26c and the load-side heat exchanger 26d, are each in a closed state. When a cooling load is generated in the load-side heat exchanger 26c or the load-side heat exchanger 26d, the indoor expansion device 70c or the indoor expansion device 70d is opened, allowing the refrigerant to circulate.In this case, the opening degree of the indoor-side expansion device 70c or the indoor-side expansion device 70d is controlled so that the degree of superheat resulting from the difference between a temperature detected by the first load-side temperature sensor 31 and a temperature detected by the second load-side temperature sensor 32 becomes constant, as in the described case of the indoor-side expansion device 70a or the indoor-side expansion device 70b. [Main operating mode: Cooling]

[0142] Fig. Fig. 11 is a schematic view showing the circuit configuration of the air conditioner according to Embodiment 3 and a diagram illustrating a state in which the air conditioner operates in a main cooling mode. Fig. In Figure 11, the flow direction of the refrigerant is indicated by solid arrows. Here, a case is described in which a cooling load is generated only in the load-side heat exchanger 26a and a heating load is generated only in the load-side heat exchanger 26b. That is, a case is described in which only the indoor unit 2a performs cooling operation and only the indoor unit 2b performs heating operation.

[0143] In the main cooling mode, the controller 60 switches the refrigerant flow switching device 13 so that the refrigerant discharged from the compressor 10 flows into the heat source-side heat exchanger 12.

[0144] The compressor 10 compresses low-temperature and low-pressure refrigerant into high-temperature and high-pressure refrigerant gas and discharges the high-temperature and high-pressure refrigerant gas through the outlet. The high-temperature and high-pressure refrigerant gas discharged from the compressor 10 passes through the refrigerant flow switching device 13, flows into the heat-source-side heat exchanger 12, and then transforms into a two-phase gas-liquid refrigerant while releasing heat to the outside air at the heat-source-side heat exchanger 12. The refrigerant flowing out of the heat-source-side heat exchanger 12 passes through the backflow prevention device 14a and a main line 111 and flows into the relay unit 3.

[0145] The two-phase gas-liquid refrigerant flowing into the relay unit 3 is separated into high-pressure gas refrigerant and high-pressure liquid refrigerant by the gas-liquid separator 29. The high-pressure gas refrigerant flows through the gas refrigerant outlet line 113, the relay unit first opening and closing device 23b, and a branch line 112a, and then flows into the load-side heat exchanger 26b, which functions as a condenser. The high-pressure gas refrigerant transforms into liquid refrigerant and heats the room air by releasing heat to the room air.In this case, the opening degree of the indoor expansion device 70b is controlled so that the degree of subcooling, which is the difference between a value obtained by converting a pressure detected by the inlet-side pressure sensor 33 into a saturation temperature and a temperature detected by the first load-side temperature sensor 31b, becomes constant. The liquid refrigerant flowing out of the load-side heat exchanger 26b is expanded by the indoor expansion device 70b and flows through a branch line 112b.

[0146] Subsequently, the liquid refrigerant separated by the gas-liquid separator 29 is expanded to medium pressure by the "first expansion device relay unit" 30, and the liquid refrigerant flowing through the indoor expansion device 70b joins the liquid refrigerant outlet line 114. In this case, the opening degree of the "first expansion device relay unit" 30 is controlled so that the pressure difference between a pressure detected by the inlet-side pressure sensor 33 and a pressure detected by the outlet-side pressure sensor 34 becomes equal to a predetermined pressure difference. The predetermined pressure difference is, for example, 0.3 MPa.

[0147] The combined refrigerant flows into the indoor unit 2a through a branch line 112b. The refrigerant expanded into a two-phase gas-liquid state by the indoor-side expansion device 70a of the indoor unit 2a flows into the load-side heat exchanger 26a, which functions as an evaporator, and transforms into a low-temperature, low-pressure gaseous refrigerant while cooling the indoor air by removing heat from the indoor air. In this case, the opening degree of the indoor-side expansion device 70a is controlled so that the degree of superheat, which results from the difference between a temperature detected by the first load-side temperature sensor 31a and a temperature detected by the second load-side temperature sensor 32a, remains constant.The gaseous refrigerant flowing out of the load-side heat exchanger 26a passes through a branch line 112a, the “relay unit second opening and closing device” 24a and the relay unit outlet line 115 and flows out of the relay unit 3.

[0148] The gaseous refrigerant flowing out of the relay unit 3 flows through a main pipe 111 and flows into the outdoor unit 1 again. The refrigerant flowing into the outdoor unit 1 passes the backflow prevention device 14d, passes through the refrigerant flow switching device 13 and the accumulator 19, and is sucked into the compressor 10 again.

[0149] Since it is not necessary to flow refrigerant through the load-side heat exchanger 26c and the load-side heat exchanger 26d, in which no thermal load is generated, the indoor expansion device 70c and the indoor expansion device 70d, which correspond to the load-side heat exchanger 26c and the load-side heat exchanger 26d, are each in a closed state. When a cooling load is generated in the load-side heat exchanger 26c or the load-side heat exchanger 26d, the indoor expansion device 70c or the indoor expansion device 70d is opened, allowing the refrigerant to circulate.In this case, the opening degree of the indoor-side expansion device 70c or the indoor-side expansion device 70d is controlled so that the degree of superheat resulting from the difference between a temperature detected by the first load-side temperature sensor 31 and a temperature detected by the second load-side temperature sensor 32 becomes constant, as in the described case of the indoor-side expansion device 70a.Further, in the case where heating power is generated in the load-side heat exchanger 26c or the load-side heat exchanger 26d, the opening degree of the indoor-side expansion device 70c or the indoor-side expansion device 70d is controlled so that the degree of subcooling, which is calculated as a difference between a value obtained by converting a pressure detected by the inlet-side pressure sensor 33 into a saturation temperature and a temperature detected by the load-side first temperature sensor 31, becomes constant, as in the described case of the indoor-side expansion device 70b. [Pure heating mode]

[0150] Fig. Fig. 12 is a schematic view showing the circuit configuration of the air conditioner according to Embodiment 3 and a diagram illustrating a state in which the air conditioner operates in the heating-only mode. Fig. In Figure 12, the flow direction of the refrigerant is indicated by solid arrows. Here, a case is described in which heating power is generated only in the load-side heat exchanger 26a and the load-side heat exchanger 26b. That is, a case is described in which only the indoor unit 2a and the indoor unit 2b perform heating operation.

[0151] In the case of the pure heating mode, the controller 60 switches the refrigerant flow switching device 13 so that the refrigerant discharged from the compressor 10 flows into the relay unit 3 without passing through the heat source-side heat exchanger 12.

[0152] First, the compressor 10 compresses the low-temperature, low-pressure refrigerant into high-temperature, high-pressure refrigerant gas and discharges the high-temperature, high-pressure refrigerant gas through the outlet. The high-temperature, high-pressure refrigerant gas discharged from the compressor 10 passes through the refrigerant flow switching device 13 and the backflow prevention device 14b and flows out of the outdoor unit 1. The high-temperature, high-pressure refrigerant gas discharged from the outdoor unit 1 flows through a main line 111 and into the relay unit 3.

[0153] The high-temperature and high-pressure refrigerant gas flowing into the relay unit 3 passes through the gas-liquid separator 29 and the gas refrigerant outlet line 113 and flows into the "relay unit first opening and closing device" 23a and the "relay unit first opening and closing device" 23b. The high-temperature and high-pressure refrigerant gas flowing into the "relay unit first opening and closing device" 23a and the "relay unit first opening and closing device" 23b flows through the branch lines 112a and then flows into the corresponding load-side heat exchanger 26a and the load-side heat exchanger 26b, which function as a condenser. The refrigerant flowing into the load-side heat exchanger 26a and the load-side heat exchanger 26b turns into liquid refrigerant while heating the room air by releasing the heat to the room air.The liquid refrigerant flowing out of the load-side heat exchanger 26a and the load-side heat exchanger 26b is expanded by the indoor-side expansion device 70a and the indoor-side expansion device 70b, passes through the branch pipes 112b, the relay unit bypass pipe 116, and the “relay unit second expansion device” 27 which is in an open state, and flows into the outdoor unit 1 again. In this case, the opening degree of the indoor-side expansion device 70a is controlled so that the degree of subcooling, which is the difference between a value obtained by converting a pressure detected by the inlet-side pressure sensor 33 into a saturation temperature, and a temperature detected by the first load-side temperature sensor 31a, becomes constant.Similarly, the opening degree of the indoor-side expansion device 70b is controlled so that the degree of subcooling, which is determined as the difference between a value obtained by converting a pressure detected by the inlet-side pressure sensor 33 into a saturation temperature and a temperature detected by the first load-side temperature sensor 31b, becomes constant.

[0154] The refrigerant flowing into the outdoor unit 1 passes the backflow prevention device 14c, converts into gaseous refrigerant with low temperature and low pressure while extracting heat from the outside air at the heat source side heat exchanger 12, passes the refrigerant flow switching device 13 and the accumulator 19, and is sucked into the compressor 10 again.

[0155] Since it is not necessary to flow refrigerant through the load-side heat exchanger 26c and the load-side heat exchanger 26d, in which no thermal load is generated, the indoor expansion device 70c and the indoor expansion device 70d, which correspond to the load-side heat exchanger 26c and the load-side heat exchanger 26d, respectively, are each in a closed state. When heating power is generated in the load-side heat exchanger 26c or the load-side heat exchanger 26d, the indoor expansion device 70c or the indoor expansion device 70d is opened, allowing the refrigerant to circulate.In this case, the opening degree of the indoor-side expansion device 70c or the indoor-side expansion device 70d is controlled so that the degree of subcooling, which is determined as a difference between a value obtained by converting a pressure detected by the inlet-side pressure sensor 33 into a saturation temperature and a temperature detected by the first load-side temperature sensor 31, becomes constant, as in the described case of the indoor-side expansion device 70a or the indoor-side expansion device 70b. [Main operating mode: heating]

[0156] Fig. Fig. 13 is a schematic view showing the circuit configuration of the air conditioner according to Embodiment 3 and a diagram illustrating a state in which the air conditioner operates in a main heating mode. Fig. 13, the flow direction of the refrigerant is indicated by solid arrows. Here, a case is described in which a cooling load is generated only in the load-side heat exchanger 26a and a heating load is generated only in the load-side heat exchanger 26b. That is, a case is described in which only the indoor unit 2a performs a cooling operation and only the indoor unit 2b performs a heating operation.

[0157] In the main heating mode, the controller 60 switches the refrigerant flow switching device 13 so that the refrigerant discharged from the compressor 10 flows into the relay unit 3 without passing through the heat source-side heat exchanger 12.

[0158] The compressor 10 compresses low-temperature and low-pressure refrigerant into high-temperature and high-pressure refrigerant gas and discharges the high-temperature and high-pressure refrigerant gas through the outlet. The high-temperature and high-pressure refrigerant gas discharged from the compressor 10 passes through the refrigerant flow switching device 13 and the backflow prevention device 14b and flows out of the outdoor unit 1. The high-temperature and high-pressure refrigerant gas discharged from the outdoor unit 1 flows through a main line 111 and flows into the relay unit 3.

[0159] The high-temperature and high-pressure refrigerant gas flowing into the relay unit 3 passes through the gas-liquid separator 29, the gaseous refrigerant outlet line 113, the relay unit first opening and closing device 23b, and a branch line 112a, and then flows into the load-side heat exchanger 26b, which functions as a condenser. The refrigerant flowing into the load-side heat exchanger 26b becomes liquid refrigerant and heats the room air by releasing heat to the room air. The liquid refrigerant flowing out of the load-side heat exchanger 26b is expanded by the indoor expansion device 70b, passes through a branch line 112b, and flows into the relay unit 3.Subsequently, a large portion of the refrigerant flowing into the relay unit 3 flows through a branch line 112b and is then expanded by the indoor expansion device 70a into a low-temperature, low-pressure two-phase gas-liquid refrigerant. A remaining portion of the refrigerant flowing into the relay unit 3 flows through the relay unit bypass line 116 and is expanded by the relay unit second expansion device 27 into a liquid or two-phase gas refrigerant, which then flows into the relay unit outlet line 115.

[0160] The refrigerant expanded into a two-phase gas-liquid state by the indoor expansion device 70a flows into the load-side heat exchanger 26a, which functions as an evaporator, and transforms into gaseous refrigerant while cooling the indoor air by extracting heat from the indoor air. The gaseous refrigerant flowing out of the load-side heat exchanger 26a flows through a branch line 112a and the "second opening and closing device relay unit" 24a, and joins the remaining portion of the refrigerant flowing out of the "second expansion device relay unit" 27 in the relay unit outlet line 115. The combined refrigerant flows out of the relay unit 3, passes through a main line 111, and flows back into the outdoor unit 1.The refrigerant flowing into the outdoor unit 1 passes through the backflow prevention device 14c and becomes a low-temperature, low-pressure gaseous refrigerant, while extracting heat from the outside air at the heat source-side heat exchanger 12. The gaseous refrigerant passes through the refrigerant flow switching device 13 and the accumulator 19 and is sucked back into the compressor 10.

[0161] In this case, the opening degree of the indoor expansion device 70b is controlled so that the degree of subcooling, which results from the difference between a value obtained by converting a pressure detected by the inlet-side pressure sensor 33 into a saturation temperature, and a temperature detected by the first load-side temperature sensor 31b, becomes constant. At the same time, the opening degree of the indoor expansion device 70a is controlled so that the degree of superheating, which results from the difference between a temperature detected by the first load-side temperature sensor 31a and a temperature detected by the second load-side temperature sensor 32b, becomes constant.

[0162] Furthermore, the opening degree of the "second expansion device relay unit" 27 is controlled so that a pressure difference between a pressure detected by the inlet-side pressure sensor 33 and a pressure detected by the outlet-side pressure sensor 34 becomes equal to a predetermined pressure difference. The predetermined pressure difference is, for example, 0.3 MPa.

[0163] Since it is not necessary to flow refrigerant through the load-side heat exchanger 26c and the load-side heat exchanger 26d, in which no thermal load is generated, the indoor expansion device 70c and the indoor expansion device 70d, which correspond to the load-side heat exchanger 26c and the load-side heat exchanger 26d, are each in a closed state. When a cooling load is generated in the load-side heat exchanger 26c or the load-side heat exchanger 26d, the indoor expansion device 70c or the indoor expansion device 70d is opened, allowing the refrigerant to circulate.In this case, the opening degree of the indoor-side expansion device 70c or the indoor-side expansion device 70d is controlled so that the degree of superheat resulting from the difference between a temperature detected by the first load-side temperature sensor 31 and a temperature detected by the second load-side temperature sensor 32 becomes constant, as in the described case of the indoor-side expansion device 70a.Further, in the case where heating power is generated in the load-side heat exchanger 26c or the load-side heat exchanger 26d, the opening degree of the indoor-side expansion device 70c or the indoor-side expansion device 70d is controlled so that the degree of subcooling, which is calculated as a difference between a value obtained by converting a pressure detected by the inlet-side pressure sensor 33 into a saturation temperature and a temperature detected by the load-side first temperature sensor 31, becomes constant, as in the described case of the indoor-side expansion device 70b. [Defrosting mode]

[0164] Fig. Fig. 14 is a schematic view showing the circuit configuration of the air conditioner according to Embodiment 3 and a diagram illustrating a state in which the air conditioner operates in the defrost mode. Fig. 14 the flow direction of the refrigerant is shown by solid arrows.

[0165] In the case where the conditions for executing the defrosting mode in the heating-only mode or in the main heating mode are met, the controller 60 starts the defrosting mode. In the defrosting mode, a flow channel of the refrigerant flow switching device 13 is maintained in the same state as in the heating-only mode, which is Fig. 12 is shown by solid lines, and in the main heating mode, which is shown in Fig. 13 is shown by solid lines. That is, in the defrosting mode, the flow path of the refrigerant through the refrigerant flow switching device 13 is the same as the flow path through which the refrigerant discharged from the compressor 10 flows into a load-side heat exchanger 26. The indoor-side expansion device 70, which functions as the load-side expansion device 25, is brought into the closed state when it is in an open state. The first opening and closing device 11 changes from the closed state to the open state to allow the refrigerant to flow through the bypass line 16. In addition, the heat source-side air supply device 18 and the load-side air supply device (not shown) are deactivated.In this case, the indoor expansion device 70 can preferably be brought into the closed state after the first opening and closing device 11 is brought into the open state. In this way, clogging of the refrigerant flow channels and excessive pressure increase in the refrigerant circuit 101 can be prevented.

[0166] The high-temperature and high-pressure refrigerant gas exiting the compressor 10 flows through the bypass line 16 and flows into the heat source-side heat exchanger 12. The high-temperature refrigerant gas flowing into the heat source-side heat exchanger 12 flows through the heat source-side heat exchanger 12 and defrosts the frost forming on the heat source-side heat exchanger 12.

[0167] Furthermore, a flow channel of the high-temperature and high-pressure refrigerant gas discharged from the compressor 10 is connected to the flow channel of a load-side heat exchanger 26, which functions as a condenser in the heating-only mode or the main heating mode, via the backflow prevention device 14b, a main line 111, the gas-liquid separator 29, the gas refrigerant outlet line 113, the "first opening and closing device relay unit" 23, and a branch line 112a. Furthermore, the pressure of the high-temperature and high-pressure refrigerant gas discharged from the compressor 10 is higher than the pressure of the refrigerant in the load-side heat exchanger 26.For this reason, the pressure of the high-temperature and high-pressure refrigerant gas discharged from the compressor 10 in the defrosting mode causes the refrigerant existing between the gas-liquid separator 29 and the indoor-side expansion device 70 during the heating-only mode or the main heating mode to be retained between the gas-liquid separator 29 and the indoor-side expansion device 70.

[0168] It should be noted that a large amount of refrigerant is present in the load-side heat exchanger 26, which functions as a condenser in the heating-only mode or the main heating mode. Therefore, by executing the defrost mode, it is possible to retain excess refrigerant in the load-side heat exchanger 26, which functions as a condenser in the heating-only mode or the main heating mode, and thus reduce the amount of excess refrigerant remaining in the accumulator 19. Accordingly, the air conditioner 100 according to Embodiment 3 is configured to prevent the liquid refrigerant from overflowing from the accumulator 19 and being sucked into the compressor 10 during the defrost mode, similar to the air conditioners 100 according to Embodiments 1 and 2.This means that the air conditioning unit 100 is designed to reduce the liquid return flow to the compressor 10 during the defrosting mode.

[0169] In particular, in the case where the main lines 111 are long due to the limitations of the environment in which the air conditioner 100 is installed, the amount of excess refrigerant increases. Therefore, by retaining the excess refrigerant in the load-side heat exchanger 26 as in Embodiment 1, the liquid refrigerant can be prevented from overflowing from the accumulator 19 and being sucked into the compressor 10 during the defrost mode better than other air conditioners.

[0170] Furthermore, in the air conditioner 100 according to Embodiment 3, the high-temperature refrigerant discharged from the compressor 10 can flow into the heat source-side heat exchanger 12 during the defrosting mode by flowing only within the outdoor unit 1, as in the air conditioners 100 according to Embodiments 1 and 2. For this reason, the air conditioner 100 according to Embodiment 3 is configured so that the density of the refrigerant flowing into the heat source-side heat exchanger 12 does not decrease due to pressure loss during the defrosting mode, similarly to the air conditioners 100 according to Embodiments 1 and 2.That is, similar to the air conditioners 100 according to Embodiments 1 and 2, the air conditioner 100 according to Embodiment 3 makes it possible to increase the amount of refrigerant circulating between the compressor 10 and the heat source side heat exchanger 12, which can also reduce the deterioration of the defrosting performance.

[0171] Furthermore, in the air conditioner 100 according to Embodiment 3, the excess refrigerant retained in the load-side heat exchanger 26 can be evaporated in the heat-source-side heat exchanger 12 immediately after switching from the defrost mode to the heating-only mode or the main heating mode, as in the air conditioners 100 according to Embodiments 1 and 2. For this reason, the air conditioner 100 according to Embodiment 3 allows more gaseous refrigerant to flow into the compressor 10 than in the case where the excess refrigerant does not flow into the heat-source-side heat exchanger 12 during the defrost mode, thereby increasing the amount of refrigerant discharged from the compressor 10, similar to the air conditioners 100 according to Embodiments 1 and 2.Accordingly, the air conditioner 100 according to Embodiment 3 is configured to heat the target room of the air conditioner earlier after the defrosting mode is completed than in the case where the excess refrigerant does not flow into the heat source side heat exchanger 12 during the defrosting mode, thereby making it possible to improve user comfort, similarly to the air conditioners 100 according to Embodiments 1 and 2.

[0172] It should be noted that a portion of the refrigerant line 110 including a main line 111 from an outlet side of the relay unit 3 to the backflow prevention device 14c has a lower temperature than the refrigerant discharged from the compressor 10. When the refrigerant discharged from the compressor 10 flows into the portion of the refrigerant line 110, the high-temperature and high-pressure refrigerant gas discharged from the compressor 10 may condense and stagnate. In the defrost mode, the following two flow channels are the flow channels through which the refrigerant discharged from the compressor 10 flows into the portion of the refrigerant line 110 including the main line 111 from the outlet side of the relay unit 3 to the backflow prevention device 14c.

[0173] The first flow passage is a flow passage through which the refrigerant discharged from the compressor 10 and flowing into the relay unit 3 flows through the gas-liquid separator 29, the gas refrigerant outlet passage 113, the “relay unit first opening and closing device” 23, the “relay unit second opening and closing device” 24, and the relay unit outlet passage 115, and flows into the refrigerant passage area 110 including the main passage 111 from the outlet side of the relay unit 3 to the backflow prevention device 14c. By keeping the “relay unit second opening and closing device” 24 closed during the defrosting mode, the refrigerant discharged from the compressor 10 can be prevented from flowing through the first flow channel into the area of ​​the refrigerant line 110 including the main line 111 from the outlet side of the relay unit 3 to the backflow prevention device 14c.The second flow passage is a flow passage through which the refrigerant discharged from the compressor 10 and flowing into the relay unit 3 flows through the gas-liquid separator 29, the liquid refrigerant outlet passage 114, the “relay unit first expansion device” 30, the relay unit bypass passage 116, the “relay unit second expansion device” 27, and the relay unit outlet passage 115, and flows into the refrigerant passage portion 110 including the main passage 111 from the outlet side of the relay unit 3 to the backflow prevention device 14c.By bringing at least one of the “first expansion device relay unit” 30 and the “second expansion device relay unit” 27 into the closed state, the refrigerant discharged from the compressor 10 can be prevented from flowing through the second flow channel into the area of ​​the refrigerant line 110 including the main line 111 from the outlet side of the relay unit 3 to the backflow prevention device 14c.

[0174] Accordingly, it is advantageous for the control unit 63 of the controller 60 to close the "second opening and closing device relay unit" 24 and close at least one of the "first expansion device relay unit" 30 and the "second expansion device relay unit" 27 when executing the defrosting mode. In this way, the high-temperature and high-pressure refrigerant gas discharged from the compressor 10 can be prevented from condensing or stagnating in the refrigerant line 110 including the main line 111 from the outlet side of the relay unit 3 to the backflow prevention device 14c. This allows a larger portion of the high-temperature and high-pressure refrigerant gas discharged from the compressor 10 to flow into the heat source-side heat exchanger 12, thereby further improving the defrosting performance of the air conditioner 100.

[0175] When executing the defrosting mode, the control unit 63 of the controller 60 can bring the entire "first expansion device relay unit" 30, the "second expansion device relay unit" 27, the "first opening and closing device relay unit" 23, the "second opening and closing device relay unit" 24, and the indoor expansion device 70 into the closed state, respectively. Such a configuration can also prevent the high-temperature and high-pressure refrigerant gas discharged from the compressor 10 from condensing or stagnating in the refrigerant line 110 including the main line 111 from the outlet side of the relay unit 3 to the backflow prevention device 14c.As a result, a larger portion of the high-temperature and high-pressure refrigerant gas discharged from the compressor 10 can flow into the heat source-side heat exchanger 12, thereby further improving the defrosting performance of the air conditioner 100.

[0176] It should be noted here that in the heating-only mode and the main heating mode, the refrigerant flowing out of the load-side heat exchanger 26, which functions as a condenser, and flowing into the heat-source-side heat exchanger 12, which functions as an evaporator, flows through the "second expansion device relay unit" 27. For this reason, in the air conditioner 100 according to Embodiment 3, the "second expansion device relay unit" 27, like the indoor-side expansion device 70, functions as the load-side expansion device 25. For this reason, the "second expansion device relay unit" 27 can be used as the load-side expansion device 25. Specifically, when executing the defrosting mode, the control unit 63 of the controller 60 can set the "second expansion device relay unit" 27 to the closed state instead of the indoor-side expansion device 70.In this way, similar effects can be achieved in the defrosting mode as in the defrosting mode described above, in which the interior-side expansion device 70 is in a closed state.

[0177] In the case where the "second expansion device relay unit" 27 is used as the load-side expansion device 25 to perform the defrosting mode, the above-mentioned first flow channel is a flow channel through which the refrigerant discharged from the compressor 10 flows into the refrigerant line 110 including the main line 111 from the outlet side of the relay unit 3 to the backflow prevention device 14c. For this reason, in the case where the "second expansion device relay unit" 27 is used as the load-side expansion device 25 to perform the defrosting mode, it is preferable that the control unit 63 of the controller 60 bring the "second opening and closing device relay unit" 24 into the closed state.This prevents the high-temperature and high-pressure refrigerant gas discharged from the compressor 10 from condensing or stagnating in the refrigerant line 110, including the main line 111, from the outlet side of the relay unit 3 to the backflow prevention device 14c. This allows a larger portion of the high-temperature and high-pressure refrigerant gas discharged from the compressor 10 to flow into the heat source-side heat exchanger 12, further improving the defrosting performance of the air conditioner 100.

[0178] In the case where the "second expansion device relay unit" 27 is also used as the load-side expansion device 25 to perform the defrosting mode, the control unit 63 of the controller 60 can bring the entire "first expansion device relay unit" 30, the "second expansion device relay unit" 27, the "first opening and closing device relay unit" 23, the "second opening and closing device relay unit" 24, and the indoor-side expansion device 70 into the closed state, respectively. Such a configuration can also prevent the high-temperature and high-pressure refrigerant gas discharged from the compressor 10 from condensing or stagnating in the refrigerant line 110 including the main line 111 from the outlet side of the relay unit 3 to the backflow prevention device 14c.As a result, a larger portion of the high-temperature and high-pressure refrigerant gas discharged from the compressor 10 can flow into the heat source-side heat exchanger 12, thereby further improving the defrosting performance of the air conditioner 100. Embodiment 4

[0179] An air conditioner 100 according to Embodiment 4 is configured such that the air conditioner 100 shown in Embodiment 3 includes the second opening and closing device 15 shown in Embodiment 2. It should be noted that things not mentioned in Embodiment 4 are similar to those mentioned in any of Embodiments 1 to 3.

[0180] Fig. Fig. 15 is a schematic view showing a circuit configuration of an air conditioner according to Embodiment 4 and a diagram illustrating a state in which the air conditioner operates in the defrost mode. Fig. 15 the flow direction of the refrigerant is shown by solid arrows.

[0181] The air conditioner 100 according to Embodiment 4 includes a second opening and closing device 15. The second opening and closing device 15 is configured to open and close a flow channel for the refrigerant at a position where the second opening and closing device 15 is installed. The second opening and closing device 15 is provided in the refrigerant circuit 101 and at an inlet side of the heat source-side heat exchanger 12 through which the refrigerant flows into the heat source-side heat exchanger 12 when the heat source-side heat exchanger 12 functions as an evaporator, and faces the heat source-side heat exchanger 12 at a position to which the outlet-side end 16b of the bypass pipe 16 is connected. In Embodiment 4, the second opening and closing device 15 is mounted in the outdoor unit 1.

[0182] The second opening and closing device 15 is controlled by the controller 60. Specifically, the control unit 63 of the controller 60 maintains the second opening and closing device 15 in an open state during the cooling-only mode, the main cooling mode, the heating-only mode, and the main heating mode. Furthermore, when executing the defrost mode, the controller 63 switches the second opening and closing device 15 from the open state to the closed state.

[0183] In the defrosting mode, the high-temperature and high-pressure refrigerant gas discharged from the compressor 10 flows through the bypass line 16 and flows into the heat source-side heat exchanger 12. When the second opening and closing device 15 is not provided, a portion of the high-temperature and high-pressure refrigerant gas discharged from the compressor 10 flows through the backflow prevention device 14a, a main line 111, the relay unit 3, and a branch line 112, and flows toward the indoor-side expansion device 70 after flowing out of the bypass line 16. In a portion of the refrigerant line 110 forming a flow passage from the second opening and closing device 15 to the indoor-side expansion device 70, there is a line having a lower temperature than the refrigerant discharged from the compressor 10.Therefore, when the refrigerant discharged from the compressor 10 flows into the portion of the refrigerant pipe 110 that forms the flow passage from the second opening and closing device 15 to the indoor expansion device 70, the high-temperature and high-pressure refrigerant gas discharged from the compressor 10 may condense and remain at a low-temperature pipe portion.

[0184] However, by keeping the second opening and closing device 15 closed during the defrosting mode, the refrigerant discharged from the compressor 10 can be prevented from flowing into the portion of the refrigerant line 110 that forms the flow channel from the second opening and closing device 15 to the indoor expansion device 70. That is, by keeping the second opening and closing device 15 closed during the defrosting mode, the high-temperature and high-pressure refrigerant gas discharged from the compressor 10 can be prevented from condensing in the portion of the refrigerant line 110 that forms the flow channel from the second opening and closing device 15 to the indoor expansion device 70, or from remaining at a low temperature in a portion of the line.Accordingly, in the air conditioner 100 according to Embodiment 4, a larger portion of the high-temperature and high-pressure refrigerant gas discharged from the compressor 10 can flow into the heat source-side heat exchanger 12, resulting in further improvement of the defrosting performance.

[0185] Although in Fig. 15 As the second opening and closing device 15, an electronic expansion valve is shown which is capable of regulating the flow rate of the refrigerant, the second opening and closing device 15 may also be an opening and closing device which is capable of blocking the flow of the refrigerant, such as a two-way valve and a solenoid valve. Embodiment 5

[0186] As mentioned above, the load-side heat exchanger 26 can be configured to effect heat exchange between the refrigerant and a heat carrier. Embodiment 5 shows an example of an air conditioner 100 with a load-side heat exchanger 26 configured to effect heat exchange between the refrigerant and a heat carrier. It should be noted that things not mentioned in Embodiment 5 are similar to those mentioned in any of Embodiments 1 to 4.

[0187] Fig. 16 is a schematic view showing a circuit configuration of an air conditioner according to Embodiment 5 and a diagram illustrating a state in which the air conditioner operates in the defrost mode.

[0188] Like the air conditioner 100 described in Embodiment 3, the air conditioner 100 according to Embodiment 5 executes four operation modes. The first operation mode is the cooling-only mode in which all operating indoor units 2 are enabled for cooling operation. The second operation mode is the heating-only mode in which all operating indoor units 2 are enabled for heating operation. The third operation mode is the main cooling mode, which is executed in the case of mixed cooling and heating operation in which the cooling load is higher than the heating capacity. The fourth operation mode is the main heating mode, which is executed in the case of mixed cooling and heating operation in which the heating capacity is higher than the cooling load.

[0189] As in Fig. As shown in Fig. 16, the load-side heat exchanger 26 is configured so that refrigerant and a heat medium exchange heat with each other. The term "heat medium" refers to a liquid, such as water and antifreeze, which is different from the refrigerant circulating through the heat source-side heat exchanger 12 and the load-side heat exchanger 26. The load-side heat exchanger 26 is mounted in the relay unit 3. The indoor unit 2 is equipped with an indoor heat exchanger 71 connected to the load-side heat exchanger 26 via a heat medium passage 120 through which the heat medium flows, which exchanges heat with the refrigerant in the load-side heat exchanger 26.That is, the load-side heat exchanger 26 forms the refrigerant cycle 101 by connecting to the heat-source-side heat exchanger 12 and other devices via the refrigerant line 110, and forms a heat medium cycle 102 by connecting to the indoor heat exchanger 71 and other devices via the heat medium line 120. Specifically, a refrigerant line of the load-side heat exchanger 26 is connected to the refrigerant line 110, and a heat medium line of the load-side heat exchanger 26 is connected to the heat medium line 120. Note that the air conditioner 100 according to Embodiment 5 includes a plurality of indoor units 2. In . Fig. 16, an indoor unit 2a, an indoor unit 2b, an indoor unit 2c and an indoor unit 2d are shown in this order from bottom to top.

[0190] The outdoor unit 1 and the relay unit 3 are connected by a plurality of main lines 111 through which the refrigerant flows. The main lines 111 are parts of the refrigerant line 110 of the refrigerant circuit 101. Furthermore, the relay unit 3 and each of the indoor units 2 are connected by corresponding branch lines 121. The branch lines 121 are parts of the heat transfer medium line 120 of the heat transfer medium circuit 102. [Relay Unit 3]

[0191] The relay unit 3 is configured with a load-side heat exchanger 26, a load-side expansion device 25, and a relay unit flow switching mechanism 35 as components of the refrigerant cycle 101. In Embodiment 5, the relay unit 3 further includes two sets, each comprising a load-side heat exchanger 26 and a load-side expansion device 25, to achieve mixed cooling and heating operation. Specifically, the relay unit 3 includes a load-side heat exchanger 26a, a load-side heat exchanger 26b, a load-side expansion device 25a connected to the load-side heat exchanger 26a via the refrigerant line 110, and a load-side expansion device 25b connected to the load-side heat exchanger 26b via the refrigerant line 110.

[0192] Furthermore, the relay unit 3 is equipped with a plurality of pumps 41, a plurality of first heat-medium flow switching devices 50, a plurality of second heat-medium flow switching devices 51, and a plurality of heat-medium flow controllers 52 as components of the heat-medium circuit 102. Note that the pumps 41 are required for the respective load-side heat exchangers 26. For this reason, the relay unit 3 in Embodiment 5 includes two pumps 41. Specifically, the relay unit 3 includes a pump 41a connected to the load-side heat exchanger 26a via the heat-medium line 120, and a pump 41b connected to the load-side heat exchanger 26b via the heat-medium line 120. In addition, the first heat carrier flow switching devices 50, the second heat carrier flow switching devices 51 and the heat carrier flow controllers 52 are required for the respective indoor units 2.For this reason, the relay unit 3 in Embodiment 5 includes four first heat-carrying medium flow switching devices 50, four second heat-carrying medium flow switching devices 51, and four heat-carrying medium flow controllers 52.

[0193] The load-side heat exchanger 26a and the load-side heat exchanger 26b function as a condenser or evaporator. The load-side heat exchanger 26a and the load-side heat exchanger 26b perform heat exchange between the refrigerant and the heat transfer medium to transfer the cooling or heating energy generated in the outdoor unit 1 and stored in the refrigerant to the heat transfer medium. In pure cooling mode, the load-side heat exchanger 26a and the load-side heat exchanger 26b function as evaporators to cool the heat transfer medium. In pure heating mode, the load-side heat exchanger 26a and the load-side heat exchanger 26b function as condensers to heat the heat transfer medium. In mixed cooling and heating mode, the load-side heat exchanger 26a functions as condensers to heat the heat transfer medium. In addition, the load-side heat exchanger 26b acts as an evaporator for cooling the heat transfer medium during mixed cooling and heating operation.

[0194] The "flow switching mechanism relay unit" 35 is configured to switch between connection destinations for the load-side expansion devices 25a and 25b and between connection destinations for the load-side heat exchangers 26a and 26b depending on the operating mode. The "flow switching mechanism relay unit" 35 includes a refrigerant supply line 117, a "first opening and closing device relay unit" 36a, a refrigerant discharge line 118, a "second opening and closing device relay unit" 36b, a "flow switching device relay unit" 39a, and a "flow switching device relay unit" 39b.

[0195] The refrigerant inlet line 117 connects an inlet of the refrigerant relay unit 3 to the load-side expansion devices 25. Specifically, one end of the refrigerant inlet line 117 is connected to the refrigerant inlet of the relay unit 3. The other end of the refrigerant inlet line 117 branches off to connect to the load-side expansion device 25a and the load-side expansion device 25b. The refrigerant inlet line 117 is a line through which the refrigerant flows and is also part of the refrigerant line 110. The "relay unit first opening and closing device" 36a is a two-way valve or other device.The “relay unit first opening and closing device” 36a is provided in the refrigerant inlet line 117 to open and close a flow channel of the refrigerant at a position where the “relay unit first opening and closing device” 36a is installed.

[0196] One end of the refrigerant outlet line 118 is connected to a location in the refrigerant inlet line 117 located between the "first opening and closing device relay unit" 36a and the load-side expansion devices 25. The other end of the refrigerant outlet line 118 is connected to an outlet of the refrigerant relay unit 3. The refrigerant outlet line 118 is a line through which the refrigerant flows and is also part of the refrigerant line 110. The "second opening and closing device relay unit" 36b is a two-way valve or other device. The "second opening and closing device relay unit" 36b is provided in the refrigerant outlet line 118 to open and close a refrigerant flow channel at a location where the "second opening and closing device relay unit" 36b is installed.

[0197] The "flow switching relay unit" 39a is a four-way valve or other device. The "flow switching relay unit" 39a is configured to switch between the connection of the load-side heat exchanger 26a to the inlet of the refrigerant relay unit 3 and the connection of the load-side heat exchanger 26a to the outlet of the refrigerant relay unit 3. Specifically, the "flow switching relay unit" 39a switches between connection destinations for one end of the load-side heat exchanger 26a opposite in a refrigerant flow channel to the other end to which the load-side expansion device 25a is connected. The "flow switching relay unit" 39b is a four-way valve or other device.The "flow switching relay unit" 39b is configured to switch between the connection of the load-side heat exchanger 26b to the inlet of the refrigerant relay unit 3 and the connection of the load-side heat exchanger 26b to the outlet of the refrigerant relay unit 3. Specifically, the "flow switching relay unit" 39b switches between connection destinations for one end of the load-side heat exchanger 26b opposite in a refrigerant flow channel to the other end to which the load-side expansion device 25b is connected.

[0198] Depending on the operating mode, the control unit 63 of the controller 60 switches the corresponding components of the “flow switching mechanism relay unit” 35 in the following manner.

[0199] For example, when executing the cooling-only operation mode, the controller 63 sets the "first opening and closing device relay unit" 36a to the open state and the "second opening and closing device relay unit" 36b to the closed state. Furthermore, the controller 63 switches a flow passage of the "flow switching device relay unit" 39a to a flow passage through which the load-side heat exchanger 26a and the refrigerant outlet of the relay unit 3 are connected. Furthermore, the controller 63 switches a flow channel of the "flow switching device relay unit" 39b to a flow channel through which the load-side heat exchanger 26b and the refrigerant outlet of the relay unit 3 are connected.By switching the respective components of the "relay unit flow switching mechanism" 35 in this way, the refrigerant discharged from the compressor 10 and condensed by the heat source-side heat exchanger 12 functioning as a condenser flows through the refrigerant inlet of the relay unit 3 into the refrigerant inlet line 117, and then into the load-side expansion device 25a and the load-side expansion device 25b. The refrigerant flowing into the load-side expansion device 25a is expanded by the load-side expansion device 25a and flows into the load-side heat exchanger 26a functioning as an evaporator. Furthermore, the refrigerant flowing into the load-side expansion device 25b is expanded by the load-side expansion device 25b and flows into the load-side heat exchanger 26b functioning as an evaporator.The refrigerant that cools the heat carrier while evaporating in the load-side heat exchanger 26a and the load-side heat exchanger 26b flows out of the relay unit 3 through the refrigerant outlet of the relay unit 3 and returns to the outdoor unit 1. This makes it possible to supply the indoor heat exchanger 71 of each indoor unit 2 with the heat medium cooled in the load-side heat exchanger 26a and the load-side heat exchanger 26b, enabling the cooling-only operation mode to be performed.

[0200] When executing the heating-only mode, for example, the control unit 63 closes the "first opening and closing device relay unit" 36a and opens the "second opening and closing device relay unit" 36b. Furthermore, the control unit 63 switches the flow passage of the "flow switching device relay unit" 39a to a flow passage connecting the load-side heat exchanger 26a and the refrigerant inlet of the relay unit 3. Furthermore, the control unit 63 switches the flow passage of the "flow switching device relay unit" 39b to a flow passage connecting the load-side heat exchanger 26b and the refrigerant inlet of the relay unit 3.By switching the respective components of the "flow switching relay unit mechanism" 35 in this way, the refrigerant discharged from the compressor 10 flows through the refrigerant inlet of the refrigerant relay unit 3 into the load-side heat exchanger 26a and the load-side heat exchanger 26b, which function as condensers. The refrigerant flowing into the load-side heat exchanger 26a heats the heat medium upon condensation and flows out of the load-side heat exchanger 26a. The refrigerant flowing out of the load-side heat exchanger 26a is expanded by the load-side expansion device 25a. The refrigerant flowing into the load-side heat exchanger 26b heats the heat medium upon condensation and flows out of the load-side heat exchanger 26b. The refrigerant flowing out of the load-side heat exchanger 26b is expanded by the load-side expansion device 25b.The refrigerant flowing out of the load-side expansion device 25a and the load-side expansion device 25b joins together, passes through the refrigerant inlet line 117 and the refrigerant outlet line 118, flows out of the relay unit 3 through the refrigerant outlet of the relay unit 3, and returns to the outdoor unit 1. This makes it possible to supply the indoor heat exchanger 71 of each indoor unit 2 with the heat medium heated in the load-side heat exchanger 26a and the load-side heat exchanger 26b, so that the operation mode is pure heating operation.

[0201] When executing the main cooling mode and the main heating mode, for example, the control unit 63 brings the "first opening and closing device relay unit" 36a into the closed state and brings the "second opening and closing device relay unit" 36b into the closed state. Furthermore, the control unit 63 switches the flow channel of the "flow switching device relay unit" 39a to the flow channel through which the load-side heat exchanger 26a and the inlet of the refrigerant relay unit 3 are connected. Furthermore, the control unit 63 switches the flow channel of the "flow switching device relay unit" 39b to the flow channel through which the load-side heat exchanger 26b and the outlet of the refrigerant relay unit 3 are connected.Switching the corresponding components of the "relay unit flow switching mechanism" 35 causes the refrigerant flowing into the relay unit 3 through the refrigerant inlet of the relay unit 3 to flow into the load-side heat exchanger 26a, which functions as a condenser. The refrigerant flowing into the load-side heat exchanger 26a heats the heat medium while condensing and flows out of the load-side heat exchanger 26a. The refrigerant flowing out of the load-side heat exchanger 26a flows through the load-side expansion device 25a and then through the load-side heat exchanger 26b. At this time, the refrigerant is expanded by the load-side expansion device 25b. The refrigerant expanded by the load-side expansion device 25b flows into the load-side heat exchanger 26b, which functions as an evaporator.The refrigerant, which cools the heat transfer medium while evaporating in the load-side heat exchanger 26b, flows out of the relay unit 3 through the refrigerant outlet of the relay unit 3 and returns to the outdoor unit 1. This makes it possible to permit heating operation in one or more indoor units 2 by supplying the indoor heat exchanger 71 of one or more indoor units 2 with the heat transfer medium heated in the load-side heat exchanger 26a. This also makes it possible to permit cooling operation in the other indoor unit(s) 2 by supplying the indoor heat exchanger 71 of one or more other indoor units 2 with the heat transfer medium cooled in the load-side heat exchanger 26b.

[0202] Pump 41a and pump 41b pressurize the heat transfer medium flowing through heat transfer line 120 and ensure circulation of the heat transfer medium. Pump 41a is provided in a region of heat transfer line 120 that connects load-side heat exchanger 26a to the plurality of second heat transfer flow switching devices 51. Pump 41b is provided in a region of heat transfer line 120 that connects load-side heat exchanger 26b to the plurality of second heat transfer flow switching devices 51. Pump 41a and pump 41b are, for example, power-controlled pumps.

[0203] The four first heat-transfer flow switching devices 50 are three-way valves or other devices and switch flow channels of the heat-transfer medium. Each of the four first heat-transfer flow switching devices 50 has three ends, one of which is connected to the load-side heat exchanger 26a, another to the load-side heat exchanger 26b, and the other to a corresponding heat-transfer flow controller 52. Furthermore, each of the four first heat-transfer flow switching devices 50 is provided on an outlet side of a heat-transfer flow channel in the indoor heat exchanger 71 of a corresponding unit of the indoor unit 2. It should be noted that Fig. 16 shows a first heat-medium flow switching device 50a, a first heat-medium flow switching device 50b, a first heat-medium flow switching device 50c, and a first heat-medium flow switching device 50d, which are arranged in this order from bottom to top corresponding to the indoor units 2.

[0204] The four second heat-transfer flow switching devices 51 are three-way valves or other devices and switch the flow paths of the heat transfer medium. Each of the four second heat-transfer flow switching devices 51 has three ends, one of which is connected to the load-side heat exchanger 26a, another to the load-side heat exchanger 26b, and the other to one of the corresponding indoor heat exchangers 71. Furthermore, each of the four second heat-transfer flow switching devices 51 is provided on an inlet side of the heat-transfer flow channel in the indoor heat exchanger 71 of a corresponding one of the indoor units 2. It should be noted that Fig. 16 shows a second heat-medium flow switching device 51a, a second heat-medium flow switching device 51b, a second heat-medium flow switching device 51c, and a second heat-medium flow switching device 51d, which are arranged in this order from bottom to top corresponding to the indoor units 2.

[0205] The four heat-medium flow controllers 52 are two-way valves or other devices capable of controlling the opening areas and flow rates through the heat-medium line 120. Each of the four heat-medium flow controllers 52 has two ends, one of which is connected to a corresponding indoor heat exchanger 71 and the other to a corresponding first heat-medium flow switching device 50. Furthermore, each of the four heat-medium flow controllers 52 is provided on the outlet side of the heat-medium flow channel in the indoor heat exchanger 71 of a corresponding unit of the indoor unit 2. Fig. 16 shows a heat medium flow controller 52a, a heat medium flow controller 52b, a heat medium flow controller 52c, and a heat medium flow controller 52d, which are arranged in this order from bottom to top corresponding to the indoor units 2. Alternatively, each of the four heat medium flow controllers 52 may be provided on the inlet side of the heat medium flow channel in the indoor heat exchanger 71 of the corresponding one of the indoor units 2.

[0206] In addition, the relay unit 3 is equipped with various types of sensors (not shown). The sensors output detection results as detection signals to the controller 60 mentioned below. [Configuration of multiple indoor units 2]

[0207] The plurality of indoor units 2 are, for example, identically configured. Each of the plurality of indoor units 2 has an indoor heat exchanger 71. A plurality of the indoor heat exchangers 71 are each connected to the relay unit 3 via a branch line 121a and a branch line 121b. In each of the indoor heat exchangers 71, the air supplied from the load-side air supply device (not shown) undergoes heat exchange with the heat transfer medium, thereby generating cooling or heating air, which is supplied to the target room to be air-conditioned. It should be noted that Fig. 16 shows an indoor heat exchanger 71a, an indoor heat exchanger 71b, an indoor heat exchanger 71c and an indoor heat exchanger 71d arranged in this order from bottom to top corresponding to the indoor units 2. [Defrosting mode]

[0208] The defrosting mode that the air conditioner 100 performs is now determined by Fig. 16. In Fig. 16 the flow direction of the refrigerant is shown by solid arrows.

[0209] In the case where the conditions for executing the defrosting mode are met in the heating-only mode or in the main heating mode, the controller 60 starts the defrosting mode. In the defrosting mode, the refrigerant flow switching device 13 is in the same state as in the heating-only mode. That is, in the defrosting mode, as in Fig. 16, a flow passage of the refrigerant through the refrigerant flow switching device 13 is the same as a flow passage through which the refrigerant discharged from the compressor 10 flows into a load-side heat exchanger 26. Furthermore, the load-side expansion device 25a and the load-side expansion device 25b are each brought into the closed state. The first opening and closing device 11 changes from the closed state to the open state to allow the refrigerant to flow through the bypass passage 16. Furthermore, the heat source-side air supply device 18 and the load-side air supply device (not shown) are deactivated. In this case, the load-side expansion device 25a and the load-side expansion device 25b may each preferably be brought into the closed state after the first opening and closing device 11 is brought into the open state.In this way, clogging of the refrigerant flow channels and excessive pressure increase in the refrigerant circuit 101 can be prevented.

[0210] The high-temperature and high-pressure refrigerant gas exiting the compressor 10 flows through the bypass line 16 and flows into the heat source-side heat exchanger 12. The high-temperature refrigerant gas flowing into the heat source-side heat exchanger 12 flows through the heat source-side heat exchanger 12 and defrosts the frost forming on the heat source-side heat exchanger 12.

[0211] The pressure of the high-temperature and high-pressure refrigerant gas discharged from the compressor 10 also allows excess refrigerant to be retained in a load-side heat exchanger 26, which functions as a condenser in the heating-only mode or the main heating mode, thereby reducing the amount of excess refrigerant remaining in the accumulator 19. Accordingly, the air conditioner 100 according to Embodiment 5 is configured to prevent the liquid refrigerant from overflowing from the accumulator 19 and being sucked into the compressor 10 during the defrost mode, similar to the air conditioners 100 according to Embodiments 1 to 4. That is, during the defrost mode, the air conditioner 100 is configured to reduce liquid backflow to the compressor 10.

[0212] Also, in the air conditioner 100 according to Embodiment 5, the high-temperature refrigerant discharged from the compressor 10 can flow into the heat source-side heat exchanger 12 during the defrosting mode by flowing only within the outdoor unit 1, as in the air conditioners 100 according to Embodiments 1 to 4. For this reason, the air conditioner 100 according to Embodiment 5 is also configured so that the density of the refrigerant flowing into the heat source-side heat exchanger 12 does not decrease due to pressure loss during the defrosting mode, similarly to the air conditioners 100 according to Embodiments 1 to 4.That is, similar to the air conditioners 100 according to Embodiments 1 to 4, in the air conditioner 100 according to Embodiment 5, the amount of refrigerant circulating between the compressor 10 and the heat source side heat exchanger 12 can be increased, so that the deterioration of the defrosting performance can also be reduced.

[0213] Also, in the air conditioner 100 according to Embodiment 5, the excess refrigerant retained in the load-side heat exchanger 26 can be evaporated in the heat-source-side heat exchanger 12 immediately after switching from the defrost mode to the heating-only mode or the main heating mode, as in the air conditioners 100 according to Embodiments 1 to 4. For this reason, the air conditioner 100 according to Embodiment 5 also allows more gaseous refrigerant to flow into the compressor 10 than in the case where the excess refrigerant does not flow into the heat-source-side heat exchanger 12 during the defrost mode, thereby increasing the amount of refrigerant discharged from the compressor 10, similar to the air conditioners 100 according to Embodiments 1 to 4.Accordingly, the air conditioner 100 according to Embodiment 5 is also configured to heat the target room of the air conditioner earlier after the defrosting mode is completed than in the case where the excess refrigerant does not flow into the heat source side heat exchanger 12 during the defrosting mode, whereby user comfort can be improved, similarly to the air conditioners 100 according to Embodiments 1 to 4.

[0214] As mentioned above, the "relay unit flow switching mechanism" 35 of the air conditioner 100 according to Embodiment 5 includes the refrigerant supply line 117, the "relay unit first opening and closing device" 36a, the refrigerant outlet line 118, and the "relay unit second opening and closing device" 36b. In the case where an air conditioner 100 having such a "relay unit flow switching mechanism" 35 performs the defrosting mode, when the "relay unit first opening and closing device" 36a and the "relay unit second opening and closing device" 36b are each in an open state, the refrigerant discharged from the compressor 10 may condense and remain in the refrigerant line 110 including the main line 111 from the outlet side of the relay unit 3 to the backflow prevention device 14c.For this reason, when an air conditioner 100 having such a "relay unit flow switching mechanism" 35 performs the defrosting mode, it is preferable that the "relay unit first opening and closing device" 36a be always closed. This can prevent the refrigerant discharged from the compressor 10 from flowing into the refrigerant line 110 including the main line 111 from the outlet side of the relay unit 3 to the backflow prevention device 14c, thereby preventing the condensed refrigerant from remaining in the refrigerant line 110. This allows a larger portion of the high-temperature and high-pressure refrigerant gas discharged from the compressor 10 to flow into the heat source-side heat exchanger 12, further improving the defrosting performance of the air conditioner 100.

[0215] As in Fig. As shown in Figure 16, the air conditioner 100 according to Embodiment 5 includes a second opening and closing device 15, similar to the air conditioner 100 shown in Embodiment 4. For this reason, the air conditioner 100 according to Embodiment 5, similar to the air conditioner 100 according to Embodiment 4, can prevent the high-temperature and high-pressure refrigerant gas discharged from the compressor 10 and flowing out of the bypass line 16 from flowing in a direction opposite to the heat source-side heat exchanger 12. That is, the air conditioner 100 according to Embodiment 5 makes it possible to prevent the high-temperature and high-pressure refrigerant gas discharged from the compressor 10 from condensing or remaining in a low-temperature piping region during the defrosting operation mode, similar to the air conditioner 100 shown in Figure 16. Fig.4. For this reason, the air conditioner 100 according to Embodiment 5 further improves the defrosting performance, similar to the air conditioner 100 shown in Embodiment 4.

[0216] Although examples of air conditioners according to the present invention have been described in Embodiments 1 to 5 above, the air conditioner according to the present invention is not limited to the configurations shown in Embodiments 1 to 5. For example, each of the air conditioners 100 shown in Embodiments 3 to 5 is configured such that the outdoor unit 1 and the relay unit 3 are connected by two main lines 111. However, the outdoor unit 1 and the relay unit 3 may be connected by a variety of well-known configurations. In one configuration, for example, the outdoor unit 1 and the relay unit 3 may be connected by three main lines 111. The above-mentioned effects are also achieved when an air conditioner according to the present invention is configured in this manner.Furthermore, an air conditioner according to the present invention can of course also be formed by combining the configurations described in the various embodiments. List of reference symbols 1 outdoor unit 2 (2a, 2b, 2c, 2d) indoor unit 3 Relay unit 10 Compressor 11 first opening and closing device 12 heat source side heat exchanger 13 Refrigerant flow switching device 14a, 14b, 14c, 14d Backflow prevention device 15 second opening and closing device 16 Bypass line 16a inlet end 16b outlet end 18 heat source side air supply device 19 Accumulator 23 (23a, 23b, 23c, 23d) “Relay unit first opening and closing device” 24 (24a, 24b, 24c, 24d) “Relay unit second opening and closing device” 25 (25a, 25b) load-side expansion device 26 (26a, 26b, 26c, 26d) load-side heat exchanger 27 “Relay unit second expansion device” 29 Gas-liquid separators 30 “Relay unit first expansion device” 31 (31a, 31b, 31c, 31d) first load-side temperature sensor 32 (32a, 32b, 32c, 32d) second load-side temperature sensor 33 inlet pressure sensor 34 outlet-side pressure sensor 35 “Relay unit flow switching mechanism” 36a “Relay unit first opening and closing device” 36b “Relay unit second opening and closing device” 39a “Relay unit flow switching device” 39b “Relay unit flow switching device” 40 Outlet pressure sensor 41 (41a, 41b) Pump 42 Outlet temperature sensor 43 heat source side heat exchanger temperature sensor 46 Outside air temperature sensor 50 (50a, 50b, 50c, 50d) first heat carrier flow switching device 51 (51a, 51b, 51c, 51d) second heat carrier flow switching device 52 (52a, 52b, 52c, 52d) Heat carrier flow control 60 Control 61 Input unit 62 Arithmetic Unit 63 Control unit 70 (70a, 70b, 70c, 70d) interior expansion device 71 (71a, 71b, 71c, 71d) Interior heat exchanger 100 air conditioners 101 Refrigerant circuit 102 Heat transfer circuit 110 Refrigerant line 111 Main line 112 (112a, 112b) branch line 113 Outlet line for gaseous refrigerant 114 Outlet line for liquid refrigerant 115 Relay unit outlet line 116 Relay unit bypass line 117 Refrigerant inlet line 118 Refrigerant outlet line 120 heat transfer line 121 (121a, 121b) branch line QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] JP 2020-056 515A

[0006]

Claims

[1] Air conditioning unit having: a refrigerant circuit comprising a compressor configured to compress and discharge refrigerant, a heat source-side heat exchanger configured to function as an evaporator in a heating-only mode in which all the operating indoor units perform heating operation, a refrigerant flow switching device configured to switch flow passages of the refrigerant according to an operation mode, a load-side heat exchanger configured to function as a condenser during heating operation, and a load-side expansion device configured such that the refrigerant flowing from the load-side heat exchanger functioning as a condenser and flowing into the heat source-side heat exchanger functioning as an evaporator flows through the load-side expansion device formed by the compressor, the heat source-side heat exchanger,the load-side expansion device and the load-side heat exchanger are formed, which are connected by a refrigerant line and through which the refrigerant circulates; a bypass line, one end of which is an inlet-side end connected to a point in the refrigerant cycle located between an outlet of the compressor and the refrigerant flow switching device, and the other end of which is an outlet-side end connected to a point in the refrigerant cycle located between the load-side expansion device and the heat-source-side heat exchanger; a first opening and closing device provided in the bypass line and configured to open and close a flow channel of the refrigerant at a position where the first opening and closing device is installed; a controller configured to control the refrigerant flow switching device, the load-side expansion device, and the first opening and closing device; and an outdoor unit mounted with the compressor, the heat source side heat exchanger, the refrigerant flow switching device, the bypass line and the first opening and closing device, wherein the controller is configured to, when performing a defrosting mode for defrosting the heat source-side heat exchanger, cause a flow channel of the refrigerant through the refrigerant flow switching device to be a flow channel through which the refrigerant discharged from the compressor flows into the load-side heat exchanger, bring the first opening and closing device from the closed state to the open state, bring the load-side expansion device from the open state to the closed state, and cause the refrigerant discharged from the compressor to flow from the bypass line into the heat source-side heat exchanger; [2] The air conditioner according to claim 1, wherein the controller is configured to, when performing the defrosting mode, bring the load-side expansion device into the closed state after bringing the first opening and closing device into the open state; [3] The air conditioner according to claim 1 or 2, further comprising: an outlet temperature sensor configured to measure the temperature of the refrigerant discharged from the compressor, wherein the controller is designed to control a drive frequency of the compressor, and the controller is designed to reduce the drive frequency of the compressor in defrost mode when a temperature detected by the outlet temperature sensor is higher than or equal to a certain temperature; [4] The air conditioner according to any one of claims 1 to 3, further comprising: a second opening and closing device provided in the refrigerant circuit and at an inlet side of the heat source-side heat exchanger, through which the refrigerant flows into the heat source-side heat exchanger when the heat source-side heat exchanger functions as an evaporator, and which is opposed to the heat source-side heat exchanger at a position to which the outlet-side end of the bypass pipe is connected, wherein the controller is designed to control the second opening and closing device, and the control is designed such that when the defrosting mode is carried out, it changes the second opening and closing device from the open state to the closed state; [5] The air conditioner according to claim 4, wherein the controller is configured to, when performing the defrosting mode, bring the first opening and closing device into the open state before bringing the load-side expansion device and the second opening and closing device into the closed state, respectively; [6] An air conditioning device according to any one of claims 1 to 5, further comprising a container in which an excess of the refrigerant can be collected, the capacity of the container being smaller than the volume of the refrigerant charged into the refrigerant circuit when all of the refrigerant is in liquid form; [7] An air conditioner according to any one of claims 1 to 6, further including an indoor unit mounted with the load-side expansion device and the load-side heat exchanger. [8] An air conditioning unit according to any one of claims 1 to 6, further comprising: an indoor unit provided with the load-side expansion device and the load-side heat exchanger; and a relay unit that connects the outdoor unit to the indoor unit, whereby The relay unit contains the following components of the refrigerant circuit: a gas-liquid separator that separates the refrigerant flowing in from the outdoor unit into liquid refrigerant and gaseous refrigerant, an outlet line for gaseous refrigerant, which is part of the refrigerant line and is connected to an outlet of the gas-liquid separator for the gaseous refrigerant, a liquid refrigerant outlet line forming part of the refrigerant line, one end of which is connected to an outlet of the gas-liquid separator for the liquid refrigerant and the other end of which is connected to the load-side expansion device, a ‘first opening and closing device relay unit’, one end of which is connected to the gaseous refrigerant outlet line and the other end of which is connected to the load-side heat exchanger, a relay unit outlet line, which is part of the refrigerant line and through which the refrigerant flowing out of the relay unit flows, a "relay unit second opening and closing device" of which one end is connected to the relay unit outlet line and the other end is connected to the load-side heat exchanger, a “first expansion device relay unit” provided in the liquid refrigerant outlet line and configured to decompress the refrigerant flowing through a location where the “first expansion device relay unit” is installed, a relay unit bypass line forming part of the refrigerant line, one end of which is connected to a point in the liquid refrigerant outlet line located between the “relay unit first expansion device” and the load-side expansion device, and the other end of which is connected to the relay unit outlet line, and a “relay unit second expansion device” provided in the relay unit bypass line and configured to decompress the refrigerant flowing through a location where the “relay unit second expansion device” is installed, wherein the air conditioner includes a plurality of sets each comprising the indoor unit, the “first opening and closing device relay unit” and the “second opening and closing device relay unit”, and the control is designed such that, when carrying out the defrosting mode, it brings at least either the “first expansion device relay unit” or the “second expansion device relay unit” into the closed state and brings the “second opening and closing device relay unit” into the closed state; [9] An air conditioning unit according to any one of claims 1 to 6, further comprising: an indoor expansion device configured to decompress the refrigerant flowing out of the load-side heat exchanger during heating operation; an indoor unit connected to the indoor expansion device and the load-side heat exchanger; and a relay unit that connects the outdoor unit to the indoor unit, whereby The relay unit has the following components of the refrigerant circuit: a gas-liquid separator that separates the refrigerant flowing in from the outdoor unit into liquid refrigerant and gaseous refrigerant, an outlet line for gaseous refrigerant, which is part of the refrigerant line and is connected to an outlet of the gas-liquid separator for the gaseous refrigerant, a liquid refrigerant outlet line forming part of the refrigerant line, one end of which is connected to an outlet of the gas-liquid separator for the liquid refrigerant and the other end of which is connected to the indoor expansion device, a ‘first opening and closing device relay unit’, one end of which is connected to the gaseous refrigerant outlet line and the other end of which is connected to the load-side heat exchanger, a relay unit outlet line, which is part of the refrigerant line and through which the refrigerant flowing out of the relay unit flows, a "relay unit second opening and closing device" of which one end is connected to the relay unit outlet line and the other end is connected to the load-side heat exchanger, a “first expansion device relay unit” provided in the liquid refrigerant outlet line and configured to decompress the refrigerant flowing through a location where the “first expansion device relay unit” is installed, and a relay unit bypass line which is part of the refrigerant line, one end of which is connected to a point in the liquid refrigerant outlet line located between the “relay unit first expansion device” and the indoor-side expansion device, and the other end of which is connected to the relay unit outlet line, and in which the load-side expansion device is provided, wherein the air conditioner includes a plurality of sets each comprising the indoor unit, the “first opening and closing device relay unit” and the “second opening and closing device relay unit”, and the control is designed to bring the “second opening and closing device relay unit” into the closed state when the defrosting mode is carried out; [10] The air conditioning device according to any one of claims 1 to 6, wherein the load-side heat exchanger is a heat exchanger in which the refrigerant circulating through the refrigerant circuit and a heat carrier exchange heat with each other, the air conditioning device further comprising: an indoor heat exchanger through which the heat medium subjected to heat exchange with the refrigerant in the load-side heat exchanger flows; an indoor unit mounted with the indoor heat exchanger; and a relay unit mounted with the load-side expansion device and the load-side heat exchanger, connecting the outdoor unit to the indoor unit; [11] Air conditioning device according to claim 10, wherein the relay unit includes, as components of the refrigerant circuit, a “relay unit flow switching mechanism” which is designed to switch between connection destinations for the load-side expansion device and between connection destinations for the load-side heat exchanger, wherein the “flow switching mechanism relay unit” comprises: a refrigerant inlet line connecting an inlet of the relay unit for the refrigerant to the load-side expansion device, a “relay unit first opening and closing device” provided in the refrigerant inlet line and configured to open a flow channel of the refrigerant at a location and closes on which the “first opening and closing device relay unit” is installed, a refrigerant outlet line, one end of which is connected to a point in the refrigerant inlet line located between the “first opening and closing device relay unit” and the load-side expansion device, and the other end of which is connected to an outlet of the refrigerant relay unit, and a “second opening and closing device relay unit” provided in the refrigerant outlet line and configured to open and close a flow channel of the refrigerant at a location where the “second opening and closing device relay unit” is installed, and wherein the controller is designed to bring the “first opening and closing device relay unit” into the closed state when a defrosting mode for defrosting the heat source-side heat exchanger is carried out.

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