GB2640100A

GB2640100A - Air-conditioning device

Info

Publication number: GB2640100A
Application number: GB2509442.6A
Authority: GB
Inventors: Masui Shintaro; Shinozaki Karoyoshi; Motomura Yuji
Original assignee: Mitsubishi Electric Corp
Current assignee: Mitsubishi Electric Corp
Priority date: 2023-02-09
Filing date: 2023-02-09
Publication date: 2025-10-08
Also published as: GB202509442D0; WO2024166276A1

Abstract

An air-conditioning device comprising: a compressor that compresses and discharges a refrigerant; a load-side heat exchanger that functions as a condenser during heating operation; a flow rate adjustment valve that adjusts the flow rate of the refrigerant flowing out of the load-side heat exchanger during heating operation; a heat source-side heat exchanger that functions as an evaporator during heating operation; and a control unit that controls the opening degree of the flow adjustment valve, wherein, during heating operation, the control unit adjusts, as a control parameter, the opening degree of the flow rate adjustment valve using the dryness degree of the refrigerant flowing into the heat source-side heat exchanger.

Description

DESCRIPTION Title of Invention

AIR-CONDITIONING DEVICE

Technical Field

[0001] The present disclosure relates to an air-conditioning apparatus that performs heating and cooling using a refrigeration cycle, and in particular to, the control of a flow control valve provided in an indoor unit.

Background Art

[0002] An air-conditioning apparatus using a refrigeration cycle includes a refrigerant circuit in which a heat source unit and an indoor unit are connected by pipes and refrigerant flows, the heat source unit including a compressor and a heat-source-side heat exchanger, the indoor unit including a flow control valve (hereinafter also referred to as load-side flow control valve) and a load-side heat exchanger. In the air-conditioning apparatus, in the load-side heat exchanger, when evaporating or condensing, the refrigerant receives or transfers heat from or to air, which is to be subjected to heat exchange, in an air-conditioning target space, whereby air-conditioning is performed while varying the pressure, temperature, and other conditions of the refrigerant that flows in the refrigerant circuit. Such air-conditioning apparatuses described above includes an air-conditioning apparatus that performs an SC target control to adjust the opening degree of the load-side flow valve using the degree of subcooling as a control parameter when controlling the condensation performance of the load-side heat exchanger during heating (see, for example, Patent Literature 1).

The degree of subcooling corresponds to the difference between a condensation temperature and a refrigerant temperature at the outlet of the load-side heat exchanger, which operates as a condenser. In the SC target control, the load-side flow control valve is controlled so that the degree of subcooling of the refrigerant at the outlet of the load-side heat exchanger operating as a condenser reaches a target value determined in advance. That is, when the SC target control is performed, refrigerant whose degree of subcooling becomes sufficient at the outlet of the load-side heat exchanger flows into the heat-source-side heat exchanger.

Citation List Patent Literature [0003] Patent Literature 1: Japanese Unexamined Patent Application Publication No. 2021-156563

Summary of Invention

Technical Problem [0004] However, in the air-conditioning apparatus of Patent Literature 1 in which the load-side flow control valve is controlled using, as a the control parameter, the degree of subcooling of the refrigerant at the outlet of the load-side heat exchanger operating as a condenser, during heating, the quality of refrigerant that flows into the heat-source-side heat exchanger operating as a evaporator easily lowers to a low value. In general, a gas-phase fluid flows at a higher velocity than a liquid-phase fluid because mainly of the difference between the densities of the gas-phase fluid and the liquid-phase fluid. Furthermore, in general, as the amount of refrigerant that circulates in the refrigerant circuit decreases to a small value, the flow velocity of the refrigerant also decreases.

Therefore, during a heating operation, in the case where a low load condition occurs where the amount of refrigerant circulating in the refrigerant circuit decreases, the flow velocity of the refrigerant at the inlet of the heat-source-side heat exchanger becomes extremely low due to the decrease in both the quality and the circulation amount of the refrigerant. Consequently, the refrigerant distribution from a distribution header provided at the inlet of the heat-source-side heat exchanger to refrigerant passages may not be uniform, leading to a significant decrease in a refrigerant distribution performance of the heat-source-side heat exchanger.

[0005] The present disclosure is applied to solve the above problem, and relates to an air-conditioning apparatus in which the refrigerant distribution performance of a heatsource-side heat exchanger under a low load condition during heating is improved. Solution to Problem [0006] An air-conditioning apparatus according to an embodiment of the present disclosure includes: a compressor configured to compress refrigerant and discharge the compressed refrigerant; a load-side heat exchanger configured to operate as a condenser during a heating operation; a flow control valve configured to adjust a flow rate of the refrigerant that flows out from the load-side heat exchanger during the heating operation; a heat-source-side heat exchanger configured to operate as an evaporator during the heating operation; and a controller configured to control an opening degree of the flow control valve. The controller is configured to adjust the opening degree of the flow control valve using, as a control parameter, a quality of the refrigerant that flows into the heat-source-side heat exchanger, during the heating operation.

Advantageous Effects of Invention [0007] In the air-conditioning apparatus according to the embodiment of the present disclosure, during the heating operation, the opening degree of the load-side flow control valve is adjusted using, as a control parameter, the quality of refrigerant that flows into the heat-source-side heat exchanger operating as an evaporator. Therefore, as compared with existing techniques, it is possible to reduce a decrease in the quality of the refrigerant that flows into heat-source-side heat exchanger even under a low load condition during the heating operation, and thus reduce a decrease in the flow velocity of the refrigerant. Accordingly, it is possible to provide an air-conditioning apparatus that is improved in the refrigerant distribution performance of the heat-source-side heat exchanger under a low load condition during the heating operation.

Brief Description of Drawings

[0008] [Fig. 1] Fig. 1 is a circuit diagram of an air-conditioning apparatus according to an embodiment of the present disclosure.

[Fig. 2] Fig. 2 is a block diagram indicating the functions of a controller of the air-conditioning apparatus according to the embodiment of the present disclosure.

[Fig. 3] Fig. 3 is a circuit diagram indicating the state of a cooling only operation of the air-conditioning apparatus according to the embodiment of the present disclosure.

[Fig. 4] Fig. 4 is a circuit diagram indicting the state of a heating only operation of the air-conditioning apparatus according to the embodiment of the present disclosure.

[Fig. 5] Fig. 5 is a circuit diagram indicating the state of a cooling main operation of the air-conditioning apparatus according to the embodiment of the present disclosure.

[Fig. 6] Fig. 6 is a circuit diagram indicating the state of a heating main operation of the air-conditioning apparatus according to the embodiment of the present disclosure.

[Fig. 7] Fig. 7 is a flowchart of an opening-degree adjustment method of a load-side flow control valve by the controller in the air-conditioning apparatus according to

the embodiment of the present disclosure.

[Fig. 8] Fig. 8 is a p-h diagram illustrating an example of variation of the state of refrigerant in the case where the opening degree of the load-side flow control valve is adjusted in the air-conditioning apparatus according to the embodiment of the present disclosure.

Description of Embodiments

[0009] Embodiment An air-conditioning apparatus according to an embodiment of the present disclosure will be described with reference to the drawings. The present disclosure is not limited to the embodiment, and various modifications can be made without departing from the gist of the present disclosure. Furthermore, in each of figures in the drawings, components that are the same as or equivalent to those in a previous figure or previous figures are denoted by the same reference signs. The same is true of the entire text of the specification. It should be noted that in each of the figures, a relationship or relationships in size, shape, or other points between components may be different from actual ones.

[0010] Fig. 1 is a circuit diagram of an air-conditioning apparatus 1 according to the embodiment of the present disclosure. The air-conditioning apparatus 1 will be described with reference to Fig. 1. As illustrated in Fig. 1, the air-conditioning apparatus 1 includes a heat source unit 100, a plurality of indoor units 300a and 300b, a relay unit 200 that distributes refrigerant supplied from the heat source unit 100 to the plurality of indoor units 300a and 300b, and a control unit 10.

[0011] The following description concerning the embodiment is made by referring to by way of example the case where two indoor units 300a and 300b are connected to one heat source unit 100. However, the number of heat source units 100 and that of indoor units in the air-conditioning apparatus 1 are not limited to the above numbers. For example, the number of the heat source units 100 may be two or more, and that of the indoor units may be three or more. Furthermore, the following description concerning the embodiment is also made with respect to the case where the relay unit 200 enables each of the indoor units to perform cooling operation or heating operation. However, the relay unit 200 may be configured to cause both or all the indoor units 30 and 300b to perform the same operation. Alternatively, the air-conditioning apparatus 1 may be configured such that no relay unit 200 is provided, and one indoor unit is connected to one heat source unit 100.

[0012] As illustrated in Fig. 1, the air-conditioning apparatus 1 is configured such that the heat source unit 100, the indoor units 300a and 300b, and the relay unit 200 are connected. The heat source unit 100 has a function of supplying heating energy or cooling energy to the indoor units 300a and 300b. The indoor units 300a and 300b are connected in parallel with each other and have the same configuration. In the following, the indoor unit 300a and the indoor unit 300b may each be referred to as the indoor unit 300 without being distinguished from each other. The indoor unit 300 has a function of heating or cooling the air-conditioning target space such as an indoor space, with the heating energy or cooling energy supplied from the heat source unit 100. The relay unit 200 is located between the heat source unit 100 and the plurality of indoor units 300a and 300b, and has a function of switching the flow direction of refrigerant that is supplied from the heat source unit 100 between plural flow directions in response to a request from each of the indoor units 300.

[0013] Furthermore, the air-conditioning apparatus 1 includes a load capacity detecting unit 20 that detects a cooling and heating load capacity of each of the indoor units 300a and 300b. The cooling and heating load capacity corresponds to a cooling load capacity and a heating load capacity of the indoor units 300a and 300b. The load capacity detecting unit 20 includes a plurality of liquid-pipe temperature detecting units 303a and 303b and a plurality of gas-pipe temperature detecting units 304a and 304b. [0014] The heat source unit 100 and the relay unit 200 are connected, on a high-pressure side, by a high-pressure pipe 402 through which high-pressure refrigerant flows, and are also connected, on a low-pressure side, by a low-pressure pipe 401 through which low-pressure refrigerant flows. Furthermore, the relay unit 200 and the indoor units 300a and 300b are connected by gas branch pipes 403a and 403b, respectively. Through the gas branch pipes 403a and 403b, primarily, gas-phase refrigerant flows. Also, the relay unit 200 is connected to the indoor units 300a and 300b by liquid branch pipes 404a and 404b, respectively. Through the liquid branch pipes 404a and 404b, primarily, liquid-phase refrigerant flows.

[0015] Heat Source Unit 100 The heat source unit 100 includes a compressor 101 that is variable in capacity, a flow switching valve 102 that switches the flow direction of refrigerant that flows in the heat source unit 100, a heat-source-side heat exchange unit 120, an accumulator 104 that is connected to a suction side of the compressor 101 through the flow switching valve 102 and that stores liquid-phase refrigerant, and a heat-source-side flow-passage adjustment unit 140 that limits the flow direction of the refrigerant. The heat source unit 100 has a function of supplying heating energy or cooling energy to the indoor units 300a and 300b. It should be noted that Fig. 1 illustrates by way of example that the flow switching valve 102 is a four-way valve; however, the flow switching valve 102 may be formed as a combination of two-way valves or three-way valves.

[0016] The heat-source-side heat exchange unit 120 includes a main pipe 114, a heatsource-side heat exchanger 103, a heat-source-side fan 112, a bypass pipe 113, a heatsource-side flow control valve 109, a bypass flow control valve 110, and a gas-liquid separation unit 111.

[0017] The heat-source-side heat exchanger 103 operates as an evaporator or a condenser. In the case where the heat-source-side heat exchanger 103 is of air-cooled type, it causes heat exchange to be performed between the refrigerant and outdoor air. In the case where the heat-source-side heat exchanger 103 is of a water-cooled type, it causes heat exchange to be performed between the refrigerant and water or brine, for example. Although it is not illustrated, the heat-source-side heat exchanger 103 includes, for example, a plurality of heat transfer tubes and a header to which ends of the plurality of heat transfer tubes are connected. In the case where the heat-source-side heat exchanger 103 operates as an evaporator, the header corresponds to an inlet for the refrigerant, and operates as a distribution header that distributes refrigerant that is returned from the indoor units 300a and 300b to the heat source unit 100 to the plurality of heat transfer tubes (that is, a plurality of flow passages). The heat-source-side fan 112 changes the amount of air that is sent to the heat-source-side heat exchanger 103, thereby controlling a heat exchange capacity.

One of ends of the main pipe 114 is connected to the flow switching valve 102 and the other is connected to the high-pressure pipe 402. At the main pipe 114, the heatsource-side heat exchanger 103 and the heat-source-side flow control valve 109 are provided. One of ends of the bypass pipe 113 is connected to the flow switching valve 102 and the other is connected to the high-pressure pipe 402. The bypass pipe 113 is connected in parallel with the main pipe 114. Refrigerant that flows through the bypass pipe 113 does not pass through the heat-source-side heat exchanger 103; that is, it does not exchange heat in the heat-source-side heat exchanger 103.

[0018] The heat-source-side flow control valve 109 is connected in series to the heat-source-side heat exchanger 103 by the main pipe 114 to adjust the amount of refrigerant that flows through the main pipe 114. Specifically, the heat-source-side flow control valve 109 is provided, at the main pipe 114, between the heat-source-side heat exchanger 103 and the gas-liquid separation unit 111. In the following, at the main pipe 114, a pipe portion provided between the heat-source-side heat exchanger 103 and the heat-source-side flow control valve 109 may be referred to as a first refrigerant pipe 501. The heat-source-side flow control valve 109 is, for example, an electric expansion valve whose opening degree is variable. The bypass flow control valve 110 is provided at the bypass pipe 113 to adjust the amount of refrigerant that flows through the bypass pipe 113. The bypass flow control valve 110 is, for example, an electric expansion valve whose opening degree is variable.

[0019] The gas-liquid separation unit 111 separates liquid-phase refrigerant and gas-phase refrigerant from each other. The liquid-phase refrigerant flows through a liquid passage side of the gas-liquid separation unit 111, the gas-phase refrigerant flows through a gas passage side of the gas-liquid separation unit 111, and the gas-phase refrigerant and the liquid-phase refrigerant pass through a mixture side of the gas-liquid separation unit 111. To the liquid passage side of the gas-liquid separation unit 111, the main pipe 114 is connected: to the gas passage side of the gas-liquid separation unit 111, the bypass pipe 113 is connected; and to the mixture side of the gas-liquid separation unit 111, the low-pressure pipe 401 and the high-pressure pipe 402 are connected. When the refrigerant flows to the high-pressure pipe 402, the gas-liquid separation unit 111 merge refrigerant that flows through the main pipe 114 and refrigerant that flows through the bypass pipe 113 into single refrigerant, and causes the single refrigerant to flows to the high-pressure pipe 402; and when the refrigerant flows out from the low-pressure pipe 401, the gas-liquid separation unit 111 causes the refrigerant that flows out from the low-pressure pipe 401 to branch into refrigerant that flows through the main pipe 114 and refrigerant that flows through the bypass pipe 113. [0020] The gas-liquid separation unit 111 may be formed of, for example, a T-tube, or may be formed of a tube having a connection portion that is processed to allow gas-phase refrigerant to be easily let out. It should be noted that the gas-liquid separation unit 111 may separate the gas-phase refrigerant and the liquid-phase refrigerant at a separation efficiency of 100% or may separate the gas-phase refrigerant and the liquid-phase refrigerant at a separation efficiency of less than 100%, and it suffices that the gas-liquid separation unit 111 is configured to separate the gas-phase refrigerant and the liquid-phase refrigerant at a required separation efficiency depending on the product's specifications.

[0021] The heat-source-side flow-passage adjustment unit 140 includes a third check valve 105, a fourth check valve 106, a fifth check valve 107, and a sixth check valve 108. The third check valve 105 is provided at a pipe that connects the heat-sourceside heat exchange unit 120 and the high-pressure pipe 402, and allows the refrigerant to flow from the heat-source-side heat exchange unit 120 toward the high-pressure pipe 402. The fourth check valve 106 is provided at a pipe that connects the flow switching valve 102 of the heat source unit 100 and the low-pressure pipe 401, and allows the refrigerant to flow from the low-pressure pipe 401 toward the flow switching valve 102. The fifth check valve 107 is provided at a pipe that connects the flow switching valve 102 of the heat source unit 100 and the high-pressure pipe 402, and allows the refrigerant to flow from the flow switching valve 102 toward the high-pressure pipe 402.

The sixth check valve 108 is provided at a pipe that connects the heat-source-side heat exchange unit 120 and the low-pressure pipe 401, and allows the refrigerant from the low-pressure pipe 401 toward the heat-source-side heat exchange unit 120.

[0022] Furthermore, in the heat source unit 100, a discharge pressure detecting unit 126 is provided. The discharge pressure detecting unit 126 is provided at a pipe that connects the flow switching valve 102 and a discharge side of the compressor 101, and detects a discharge pressure of the compressor 101. The discharge pressure detecting unit 126 is, for example, a sensor, and transmits a signal indicating the detected discharge pressure to the control unit 10. It should be noted that the discharge pressure detecting unit 126 may include, for example, a storage device. In this case, the discharge pressure detecting unit 126 stores data on the detected discharge pressure in, for example, the storage device, for a predetermined time period, and transmits a signal including data on the detected discharge pressure to the control unit 10 at regular intervals determined in advance.

[0023] In addition, in the heat source unit 100, a suction pressure detecting unit 127 is provided. The suction pressure detecting unit 127 is provided at a pipe that connects the flow switching valve 102 and the accumulator 104, and is configured to detect a suction pressure of the compressor 101. The suction pressure detecting unit 127 is, for example, a sensor, and transmits a signal indicating the detected suction pressure to the control unit 10. It should be noted that the suction pressure detecting unit 127 may include, for example, a storage device. In this case, the suction pressure detecting unit 127 stores data on the detected suction pressure in, for example, the storage device, for a predetermined time period, and transmits a signal including the data on the detected suction pressure to the control unit 10 at regular intervals determined in advance. [0024] Indoor Units 300a and 300b The indoor units 300a and 300b include load-side heat exchangers 301a and 301 b each configured to operate as a condenser or an evaporator, and load-side flow control valves 302a and 302b configured to adjust the amount of refrigerant that flows in the indoor units 300a and 300b, respectively. Furthermore, the indoor units 300a and 300b include respective indoor fans (not illustrated) provided for the load-side heat exchangers 301a and 301b. The indoor units 300a and 300b have a function of cooling or heating respective air-conditioning target spaces such as indoor spaces with cooling energy or heating energy supplied from the heat source unit 100. In the following, the indoor units 300a and 300b may each be referred to as the indoor unit 300 without being distinguished from each other; the load-side flow control valves 302a and 302b may each be referred to as the load-side flow control valve 302 without being distinguished from each other; and the load-side heat exchangers 301a and 301b may each be referred to as the load-side heat exchanger 301 without being distinguished from each other.

[0025] The load-side flow control valves 302a and 302b are each, for example, an electric expansion valve whose opening degree is variable. During cooling, the load-side flow control valves 302a and 302b are controlled based on the superheat amounts, that is, the degrees of superheat at the outlets of the load-side heat exchangers 301a and 301b. Also, during heating, the load-side flow control valves 302a and 302b are controlled based on the subcooling amounts, that is, the degrees of subcooling at the outlets of the load-side heat exchangers 301a and 301b, or the quality of refrigerant that flows out from the load-side heat exchangers 301a and 301b and then flows into the heat-source-side heat exchanger 103. Control methods may be selectively applied such that for example, under a low load condition during a heating only operation, the load-side flow control valves 302a and 302b are controlled based on the quality of the refrigerant, and during a cooling main operation and under a condition other than the low load condition during the heating only operation, the load-side flow control valves 302a and 302b are controlled based on the degree of subcooling.

[0026] The indoor units 300a and 300b are provided with the gas-pipe temperature detecting units 304a and 304b, the liquid-pipe temperature detecting units 303a and 303b, and drawn-in temperature detecting units 305a and 305b, respectively. In the following, the gas-pipe temperature detecting units 304a and 304b may each be referred to as gas-pipe temperature detecting unit 304 without being distinguished from each other; the liquid-pipe temperature detecting units 303a and 303b may each be referred to as the liquid-pipe temperature detecting unit 303 without being distinguished from each other; and the drawn-in temperature detecting units 305a and 305b may each be referred to as drawn-in temperature detecting unit 305 without being distinguished from each other. The gas-pipe temperature detecting units 304a and 304b are provided between the load-side heat exchangers 301a and 301b and the relay unit 200, respectively, and are configured to detect the temperatures of refrigerant that flows through the gas branch pipes 403a and 403b that connect the load-side heat exchangers 301a and 301b and the relay unit 200. The gas-pipe temperature detecting units 304a and 304b are each, for example, a thermistor, and transmit a signal indicating the detected temperature to the control unit 10. It should be noted that the gas-pipe temperature detecting units 304a and 304b may each include, for example, a storage device. In this case, the gas-pipe temperature detecting units 304a and 304b each store data on the detected temperature in, for example, the storage device, and transmit a signal including the data on the detected temperature to the control unit 10 at regular intervals determined in advance.

[0027] The liquid-pipe temperature detecting units 303a and 303b are provided between the load-side heat exchangers 301a and 301 b and the load-side flow control valves 302a and 302b, respectively, and configured to detect the temperatures of refrigerant that flows through the liquid branch pipes 404a and 404b that connect the load-side heat exchangers 301 a and 301 b and the load-side flow control valves 302a and 302b, respectively. In the following, in the liquid branch pipes 404a and 404b, pipe portions located between the load-side heat exchangers 301a and 301 b and the load-side flow control valves 302a and 302b may be referred to as second refrigerant pipes 502a and 502b, respectively. The liquid-pipe temperature detecting units 303a and 303b are each, for example, a therm istor, and transmit a signal indicating a detected temperature to the control unit 10. It should be noted that the liquid-pipe temperature detecting units 303a and 303b may each include a storage device. In this case, the liquid-pipe temperature detecting units 303a and 303b each store data on the detected temperature in, for example, the storage device for a predetermined time period, and a signal including the data on the detected temperature to the control unit 10 at regular intervals determined in advance.

[0028] The drawn-in temperature detecting units 305a and 305b are provided in, for example, the housings of the indoor units 300a and 300b and configured to detect the temperatures of indoor air that is drawn into the housings. The drawn-in temperature detecting units 305a and 305b are each, for example, a thermistor, and transmit a signal indicating the detected temperature to the control unit 10. It should be noted that the drawn-in temperature detecting units 305a and 305b may each include, for example, a storage device. In this case, the drawn-in temperature detecting units 305a and 305b each store data on the detected temperature in, for example, the storage device, for a predetermined time period, and transmit a signal including the data on the detected temperature to the control unit 10 at regular intervals determined in advance [0029] The relay unit 200 includes a first branch portion 240, a second branch portion 250, a gas-liquid separator 201, a relay bypass pipe 209, a liquid-outflow-side flow control valve 204, a heat exchange unit 260, and a relay bypass flow control valve 205. The relay unit 200 is installed between the heat source unit 100 and the indoor units 300a and 300b, and has a function of switching the flow direction of refrigerant that is supplied from the heat source unit 100 between plural flow directions in response to a request from the indoor units 300a and 300b, and distributing the refrigerant supplied from the heat source unit 100 to the plurality of indoor units 300a and 300b.

[0030] One side of the first branch portion 240 is connected to the gas branch pipes 403a and 403b, another side of the first branch portion 240 is connected to the low-pressure pipe 401 and the high-pressure pipe 402, and in the first branch portion 240, the flow direction of the refrigerant in the cooling operation is different from that in the heating operation. The first branch portion 240 includes heating solenoid valves 202a and 202b and cooling solenoid valves 203a and 203b. One of ends of the heating solenoid valve 202a is connected to the gas branch pipe 403a and the other is connected to the high-pressure pipe 402; one of ends of the heating solenoid valve 202b is connected to the gas branch pipe 403b and the other is connected to the high-pressure pipe 402; and the heating solenoid valves 202a and 202b are opened in the heating operation and closed in the cooling operation. One of ends of the cooling solenoid valve 203a is connected to the gas branch pipe 403a and the other is connected to the low-pressure pipe 401; one of ends of the cooling solenoid valve 203b is connected to the gas branch pipe 403b and the other is connected to the low-pressure pipe 401; and the cooling solenoid valves 203a and 203b are opened in the cooling operation and closed in the heating operation.

[0031] One side of the second branch portion 250 is connected to the liquid branch pipes 404a and 404b; another side of the second branch portion 250 is connected to the low-pressure pipe 401 and the high-pressure pipe 402; and in the second branch portion 250, the flow direction of the refrigerant in the cooling operation is different from that in the heating operation. The second branch portion 250 includes first check valves 210a and 210b and second check valves 211a and 211b.

[0032] One of ends of the first check valve 210a is connected to the liquid branch pipe 404a and the other is connected to the high-pressure pipe 402; one of end of the first check valve 210b is connected to the liquid branch pipe 404b and the other is connected to the high-pressure pipe 402; and the first check valves 210a and 210b allow the refrigerant to flow from the high-pressure pipe 402 toward the liquid branch pipes 404a and 404b, respectively.

[0033] One of ends of the second check valve 211 a is connected to the liquid branch pipe 404a and the other is connected to the low-pressure pipe 401; one of ends of the second check valve 211b is connected to the liquid branch pipe 404b and the other is connected to the low-pressure pipe 401; and the second check valves 211a and 211 b allow the refrigerant to flow from the liquid branch pipes 404a and 404b toward the high-pressure pipe 402, respectively [0034] The gas-liquid separator 201 separates the gas-phase refrigerant and the liquid-phase refrigerant from each other, an inflow side of the gas-liquid separator 201 is connected to the high-pressure pipe 402, a gas outflow side of the gas-liquid separator 201 is connected to the first branch portion 240, and a liquid outflow side of the gas-liquid separator 201 is connected to the second branch portion 250. The relay bypass pipe 209 connects the second branch portion 250 and the low-pressure pipe 401. The liquid-outflow-side flow control valve 204 is connected to the liquid outflow side of the gas-liquid separator 201, and is, for example, an electric expansion valve whose opening degree is variable. The liquid-outflow-side flow control valve 204 adjusts the amount of liquid-phase refrigerant that flows out from the gas-liquid separator 201. [0035] The heat exchange unit 260 includes a first heat exchange unit 206 and a second heat exchange unit 207. The first heat exchange unit 206 is provided between the liquid outflow side of the gas-liquid separator 201 and the liquid-outflow-side flow control valve 204, and provided at the relay bypass pipe 209. The first heat exchange unit 206 causes heat exchange to be performed between liquid-phase refrigerant that flows out from the gas-liquid separator 201 and refrigerant that flows through the relay bypass pipe 209. The second heat exchange unit 207 is provided downstream of the liquid-outflow-side flow control valve 204 and provided at the relay bypass pipe 209. The second heat exchange unit 207 causes heat exchange to be performed between refrigerant that flows out from the liquid-outflow-side flow control valve 204 and refrigerant that flows through the relay bypass pipe 209.

[0036] The relay bypass flow control valve 205 is provided at the relay bypass pipe 209, connected to an upstream side of the second heat exchange unit 207, and is, for example, an electric expansion valve whose opening degree is variable. The relay bypass flow control valve 205 adjusts the flow rate of refrigerant that flows out from the second heat exchange unit 207 and flows into the relay bypass pipe 209.

[0037] An upstream side of each of the first check valves 210a and 210b is connected to a downstream side of the second heat exchange unit 207 and the relay bypass pipe 209. Thus, refrigerant that flows out from the second heat exchange unit 207 branches into refrigerant that flows toward the first check valves 210a and 210b and refrigerant that flows into the relay bypass pipe 209. In addition, a downstream side of each of the second check valves 211a and 211 b is connected between the liquid-outflow-side flow control valve 204 and the upstream side of the second heat exchange unit 207. That is, refrigerant that flows out from the second check valves 211a and 211 b branches into refrigerant that flows toward the first check valves 210a and 210b and refrigerant that flows into the relay bypass pipe 209 after flowing into the second heat exchange unit 207 and being subjected to heat exchange.

[0038] Furthermore, the relay unit 200 is provided with a liquid-outflow pressure detecting unit 231, a downstream-side liquid-outflow pressure detecting unit 232, and a relay-bypass temperature detecting unit 208. The liquid-outflow pressure detecting unit 231 is provided between the first heat exchange unit 206 and an upstream side of the liquid-outflow-side flow control valve 204, and detects the pressure of refrigerant on the liquid outflow side of the gas-liquid separator 201. The liquid-outflow pressure detecting unit 231 is, for example, a sensor and transmits a signal indicating the detected pressure to the control unit 10. It should be noted that the liquid-outflow pressure detecting unit 231 may include, for example, a storage device. In this case, the liquid-outflow pressure detecting unit 231 stores data on the detected pressure in, for example, the storage device, for a predetermined time period, and transmits a signal including the data on the detected pressure to the control unit 10 at regular intervals determined in advance.

[0039] The downstream-side liquid-outflow pressure detecting unit 232 is provided between a downstream side of the liquid-outflow-side flow control valve 204 and the second heat exchange unit 207, and detects the pressure of refrigerant that flows out from the liquid-outflow-side flow control valve 204. The downstream-side liquid-outflow pressure detecting unit 232 is, for example, a sensor and transmits a signal indicating the detected pressure to the control unit 10. It should be noted that the downstream-side liquid-outflow pressure detecting unit 232 may include, for example, a storage device. In this case, the downstream-side liquid-outflow pressure detecting unit 232 stores data on the detected pressure in, for example, the storage device for a predetermined time period, and transmits a signal indicating including the data on the detected pressure to the control unit 10. It should be noted that the opening degree of the liquid-outflow-side flow control valve 204 is adjusted in such a manner as to cause the difference between the pressure detected by the liquid-outflow pressure detecting unit 231 and that detected by the downstream-side liquid-outflow pressure detecting unit 232 to be constant.

[0040] The relay-bypass temperature detecting unit 208 is provided at the relay bypass pipe 209 and detects the pressure of refrigerant that flows through the relay bypass pipe 209. The relay-bypass temperature detecting unit 208 is, for example, a thermistor and transmits a signal indicating the detected temperature to the control unit 10. The relay-bypass temperature detecting unit 208 may include, for example, a storage device. In this case, the relay-bypass temperature detecting unit 208 stores data on the detected temperature in, for example, the storage device for a predetermined time period, and transmits a signal including the data on the detected temperature to the control unit 10 at regular intervals determined in advance. It should be noted that the opening degree of the relay bypass flow control valve 205 is adjusted based on at least one or more of the pressure detected by the liquid-outflow pressure detecting unit 231, that detected by the downstream-side liquid-outflow pressure detecting unit 232, and the temperature detected by the relay-bypass temperature detecting unit 208.

[0041] Refrigerant In the air-conditioning apparatus 1, refrigerant is filled in the pipe. The refrigerant is, for example, natural refrigerant such as carbon dioxide (CO2), hydrocarbons, and helium; chlorine-free alternative refrigerant for chlorofluorocarbon, such as HFC410A, HFC407C, and HFC404A; or fluorocarbon refrigerant for use in existing products, such as R22 and R134a. It should be noted that HFC407C is nonazeotropic mixed refrigerant in which R32, R125, and R134a that are HFCs are mixed in proportions of 23 wt%, 25 wt%, and 52 wt%, respectively. In addition, the piping of the air-conditioning apparatus 1 may be filled with a heat medium, not the refrigerant.

The heat medium is, for example, water or brine.

[0042] Control Unit 10 The control unit 10 controls the entire system of the air-conditioning apparatus 1, and is, for example, a microprocessor unit that includes, a CPU and a memory. The control unit 10 receives detection information (temperature information and pressure information) from various detecting units such as the gas-pipe temperature detecting units 304a and 304b, the liquid-pipe temperature detecting units 303a and 303b, the drawn-in temperature detecting units 305a and 305b, the liquid-outflow pressure detecting unit 231, the downstream-side liquid-outflow pressure detecting unit 232, the relay-bypass temperature detecting unit 208, the discharge pressure detecting unit 126, the suction pressure detecting unit 127, a discharge temperature detecting unit 128, and a suction temperature detecting unit 129. Furthermore, the control unit 10 receives an instruction from each of remote controls (not illustrated) supplied with the indoor units 300a and 300b. Based on the received detection information from each of the detecting units and the received instruction from the remote control, the control unit 10 controls, for example, the drive frequency of the compressor 101, the rotation speed of each of the heat-source-side fan 112 and an indoor fan (not illustrated), the switching operation of the flow switching valve 102, the opening/closing of each of the heating solenoid valves 202a and 202b, and the cooling solenoid valves 203a and 203b, the opening degree of each of the heat-source-side flow control valve 109, the bypass flow control valve 110, the load-side flow control valves 302a and 302b, the liquid-outflowside flow control valve 204, and the relay bypass flow control valve 205.

[0043] The control unit 10 includes a controller 141 provided in the heat source unit 100 and a controller 220 provided in the relay unit 200; however, the control unit 10 may be mounted in any of the heat source unit 100, the indoor units 300a and 300b, and the relay unit 200, or all the heat source unit 100, the indoor units 300a and 300b, and the relay unit 200 may be provided with respective control units 10. Furthermore the control unit 10 may be mounted in another unit other than the heat source unit 100, the indoor units 300a and 300b, and the relay unit 200. It should be noted that the controller 141 and the controller 220 are connected such that they can communicate with each other by wire and wirelessly, thereby receiving and transmitting various data.

Furthermore, the control unit 10 may include a single controller [0044] Fig. 2 is a block diagram indicating the functions of the control unit 10 of the air-conditioning apparatus 1 according to the embodiment of the present disclosure. As illustrated in Fig. 2, the control unit 10 includes a storage unit 11, a setting unit 12, and a component controlling unit 13.

[0045] Storage Unit 11 The storage unit 11 stores various setting values and other values. For example, the storage unit 11 stores an opening-degree table in which the cooling/heating load capacity of each of the plurality of indoor units 300a and 300b is associated with an opening-degree adjustment value of the bypass flow control valve 110 and an opening-degree adjustment value of the heat-source-side flow control valve 109 and an air-sending table in which the cooling/heating load capacity of each of the plurality of indoor units 300a and 300b is associated with the output of the heat-source-side fan 112. To be more specific, in the opening-degree table and the air-sending table, a load ratio between the cooling-load capacity and the heating-load capacity of each of the plurality of indoor units 300a and 300b is associated with a target temperature of the heat-source-side heat exchanger 103, and the target temperature is associated with the opening-degree adjustment value of the bypass flow control valve 110, the opening-degree adjustment value of the heat-source-side flow control valve 109, and the output of the heat-source-side fan 112. In addition, the storage unit 11 stores various formulas such as equations (1), (2) and (3).

[0046] Setting Unit 12 The setting unit 12 calculates a load ratio between the cooling load capacity and the heating load capacity from the values of various detection by the load capacity detecting unit 20, and switches an operation mode between plural operation modes, according to the load ratio. Furthermore, the setting unit 12 has a function of determining whether the air-conditioning apparatus 1 is in the cooling main operation or in the heating main operation. Furthermore, the setting unit 12 collates the cooling/heating load capacities of the indoor units 300a and 300b that are detected by the load capacity detecting unit 20 with the opening-degree table and the air-sending table stored in the storage unit 11, and sets the opening degree of the bypass flow control valve 110, the opening degree of the heat-source-side flow control valve 109, and the output of the heat-source-side fan 112.

[0047] Furthermore, in the heating only operation, the setting unit 12 calculates, using an arithmetic equation stored in the storage unit 11, a flooding multiplier C corresponding to the quality of refrigerant that flows into the heat-source-side heat exchanger 103, based on detection values from a plurality of detecting units that detect pressures and temperatures, such as the suction pressure detecting unit 127, the suction temperature detecting unit 129, the discharge pressure detecting unit 126, the discharge temperature detecting unit 128, the drawn-in temperature detecting units 305a and 305b, and the liquid-pipe temperature detecting units 303a and 303b. The setting unit 12 sets opening degrees of the load-side flow control valves 302a and 302b, according to the flooding multiplier C obtained by the above calculation. It should be noted that in the heating only operation, in the case of controlling the opening degrees of the load-side flow control valves 302a and 302b, different control methods may be applied under a low load condition and other conditions. In this case, only when the load in the heating only operation falls below a preset load, the setting unit 12 calculates the flooding multiplier C corresponding to the quality of the refrigerant flowing into the heatsource-side heat exchanger 103, and sets the opening degree of the load-side flow control valves 302a and 302b according to the calculated flooding multiplier C. [0048] Component Controlling Unit 13 The component controlling unit 13 controls the opening degree of the bypass flow control valve 110, the opening degree of the heat-source-side flow control valve 109, and the output of the heat-source-side fan 112 such that they are set to values set by the setting unit 12, that is, the set opening degree of the bypass flow control valve 110, the set opening degree of the heat-source-side flow control valve 109, and the set output of the heat-source-side fan 112. Furthermore, the component controlling unit 13 controls the opening degrees of the load-side flow control valves 302a and 302b such that they are set to the values set by the setting unit 12, that is, the set opening degrees of the load-side flow control valves 302a and 302b.

[0049] Next, operations of the air-conditioning apparatus 1 will be described. In the air-conditioning apparatus 1, the cooling only operation, the heating only operation, the cooling main operation, and the heating main operation are present. In the cooling only operation, both the indoor units 300a and 300b perform the cooling operation, and in the heating only operation, both the indoor units 300a and 300b perform the heating operation. In the cooling main operation, in a simultaneous cooling and heating operation, the capacity of the cooling operation is larger than that of the heating operation. In the heating main operation, in the simultaneous cooling and heating operation, the capacity of the heating operation is larger than that of the cooling operation.

[0050] Fig. 3 is a circuit diagram indicating the state of the cooling only operation of the air-conditioning apparatus 1 according to the embodiment of the present disclosure. Fig. 4 is a circuit diagram indicating the state of the heating only operation of the air-conditioning apparatus 1 according to the embodiment of the present disclosure. Fig. is a circuit diagram indicating the state of the cooling main operation of the air-conditioning apparatus 1 according to the embodiment of the present disclosure. Fig. 6 is a circuit diagram indicating the state of the heating main operation of the air-conditioning apparatus 1 according to the embodiment of the present disclosure. In Figs. 3 to 6, high-pressure refrigerant is indicated by solid arrows, and low-pressure refrigerant is indicated by dashed arrows.

[0051] Cooling Only Operation The cooling only operation will be described with reference to Fig. 3. In the air-conditioning apparatus 1, both the indoor units 300a and 300b perform the cooling operation. As illustrated in Fig. 3, high-temperature and high-pressure gas refrigerant discharged from the compressor 101 flows through the flow switching valve 102 and exchanges heat with outdoor air sent by the heat-source-side fan 112, at the heatsource-side heat exchanger 103, and is thus condensed and liquefied. Then, the condensed and liquefied refrigerant flows through the heat-source-side flow control valve 109, the gas-liquid separation unit 111, the third check valve 105, and the high-pressure pipe 402 and reaches the gas-liquid separator 201. Since the bypass flow control valve 110 is in the fully closed state, the refrigerant does not flow through the bypass pipe 113.

[0052] Then, the refrigerant is divided by the gas-liquid separator 201 into gas-phase refrigerant and liquid-phase refrigerant. The liquid-phase refrigerant flows out from a liquid outflow side, flows through the first heat exchange unit 206, the liquid-outflow-side flow control valve 204, and the second heat exchange unit 207 in this order, and branches, at the second branch portion 250, into refrigerant that flows into the indoor unit 300a through the first check valve 210a and the liquid branch pipe 404a, and refrigerant that flows into the indoor unit 300b through the first check valve 210b and the liquid branch pipe 404b.

[0053] The pressures of the refrigerants that have flowed into the indoor units 300a and 300b are reduced to low pressures by the load-side flow control valves 302a and 302b, which are controlled based on superheat amount at the outlet sides of the load-side heat exchangers 301 a and 301 b, respectively. The refrigerants whose pressures have been reduced flow into the load-side heat exchangers 301a and 301b, and exchange heat with indoor air in the load-side heat exchangers 301a and 301 b, respectively, to be evaporated and gasified. In this case, all the indoor spaces are cooled. Then, the gasified refrigerants flow through the gas branch pipes 403a and 403b and the cooling solenoid valves 203a and 203b of the first branch portion 240, and then join each other to combine into single refrigerant. The single refrigerant then flows through the low-pressure pipe 401.

[0054] Part of the refrigerant that passes through the second heat exchange unit 207 flows into the relay bypass pipe 209. The pressure of the refrigerant that has flowed into the relay bypass pipe 209 is reduced by the relay bypass flow control valve 205 to low pressure, and the refrigerant then exchanges heat, in the second heat exchange unit 207, with refrigerant that has passed through the liquid-outflow-side flow control valve 204, that is, refrigerant that has not yet branched to flow into the relay bypass pipe 209. Because of this heat exchange, the refrigerant evaporates. Furthermore, at the first heat exchange unit 206, the refrigerant exchanges heat with refrigerant that has not yet flowed into the liquid-outflow-side flow control valve 204 and is evaporated by this heat exchange. The evaporated refrigerant flows into the low-pressure pipe 401 and joins refrigerant that has flowed through the cooling solenoid valves 203a and 203b to combine into single refrigerant. The single refrigerant then flows through the fourth check valve 106, the flow switching valve 102, and the accumulator 104, and is sucked into the compressor 101.

[0055] It should be noted that in the cooling only operation, both the heating solenoid valves 202a and 202b are in the closed state. The cooling solenoid valves 203a and 203b are in the open state. Furthermore, since the pressure in the low-pressure pipe 401 is low and that in the high-pressure pipe 402 is high, the refrigerant flows into the third check valve 105 and the fourth check valve 106. In addition, since the pressures in the liquid branch pipes 404a and 404b are lower than that in the high-pressure pipe 402, the refrigerant does not flow to the second check valves 211 a and 211 b. Furthermore, since the bypass flow control valve 110 is in the closed state, the refrigerant does not flow through the bypass pipe 113.

[0056] Heating Only Operation Next, the heating only operation will be described with reference to Fig. 4. In the air-conditioning apparatus 1, both the indoor units 300a and 300b perform the heating operation. As illustrated in Fig. 4, high-temperature and high-pressure gas refrigerant discharged from the compressor 101 flows through the flow switching valve 102, the fifth check valve 107, and the high-pressure pipe 402 in this order, and reaches the gas-liquid separator 201. In this case, since the bypass flow control valve 110 is in the fully closed state, the refrigerant does not flow through the bypass pipe 113.

[0057] The refrigerant is divided by the gas-liquid separator 201 into gas-phase refrigerant and liquid-phase refrigerant. The gas-phase refrigerant flows out from the gas outflow side of the gas-liquid separator 201, and branches at the first branch portion 240, into refrigerant that flows into the indoor unit 300a through the heating solenoid valve 202a and the gas branch pipe 403a and refrigerant that flows into the indoor unit 300b through the heating solenoid valve 202b and the gas branch pipe 403b. The refrigerants that have flowed into the indoor units 300a and 300b exchange heat with indoor air in the load-side heat exchangers 301a and 301b, respectively, and are thus condensed and liquefied. Thus, the indoor spaces are both heated. Then, the condensed and liquefied refrigerants flow through the load-side flow control valves 302a and 302b that are controlled based on the quality of the refrigerant on the inlet side of the heat-source-side heat exchanger 103.

[0058] The refrigerants that have flowed through the load-side flow control valves 302a and 302b flow through the liquid branch pipes 404a and 404b and the second check valves 211a and 211b of the second branch portion 250, and join each other to combine into single refrigerant. The single refrigerant flows through the second heat exchange unit 207 and flows into the relay bypass pipe 209. Then, after the pressure of the refrigerant is reduced to low pressure, at the second heat exchange unit 207, the refrigerant exchanges heat with refrigerant that has flowed through the liquid-outflow-side flow control valve 204, that is, refrigerant that has not yet branched to flow into the relay bypass pipe 209, and is evaporated by this heat exchange. Furthermore, at the first heat exchange unit 206, the refrigerant exchanges heat with refrigerant that has not yet flowed into the liquid-outflow-side flow control valve 204, and is thus evaporated.

The evaporated refrigerant flows into the low-pressure pipe 401, flows through the sixth check valve 108, and flows into the gas-liquid separation unit 111. Then, after flowing out from the gas-liquid separation unit 111, the refrigerant is decompressed by the heatsource-side flow control valve 109, exchanges heat, at the heat-source-side heat exchanger 103, with outdoor air sent by the heat-source-side fan 112, and is thus evaporated and gasified. The gasified refrigerant is sucked into the compressor 101 through the flow switching valve 102 and the accumulator 104.

[0059] It should be noted that in the heating only operation, the heating solenoid valves 202a and 202b are in the open state. The cooling solenoid valves 203a and 203b are in the closed state. Furthermore, since the pressure in the low-pressure pipe 401 is low and that in the high-pressure pipe 402 is high, the refrigerant flows through the fifth check valve 107 and the sixth check valve 108. It should be noted that the liquidoutflow-side flow control valve 204 is in the closed state. In addition, since the pressures in the liquid branch pipes 404a and 404b are higher than that in the high-pressure pipe 402, the refrigerant does not flow through the first check valves 210a and 210b. Furthermore, since the bypass flow control valve 110 is in the closed state, the refrigerant does not flow through the bypass pipe 113.

[0060] Cooling Main Operation Next, the cooling main operation will be described with reference to Fig. 5. In the air-conditioning apparatus 1, a cooling request is made from the indoor unit 300a and a heating request is made from the indoor unit 300b. As illustrated in Fig. 5, high-temperature and high-pressure gas refrigerant discharged from the compressor 101 flows through the flow switching valve 102 and branches into refrigerant that flows into the main pipe 114 and refrigerant that flows into the bypass pipe 113. The refrigerant that has flowed into the main pipe 114 exchanges heat, at the heat-source-side heat exchanger 103, with outdoor air sent by the heat-source-side fan 112, and is thus condensed and liquefied. The condensed and liquefied refrigerant is then decompressed at the heat-source-side flow control valve 109 and reaches the gas-liquid separation unit 111. On the other hand, the refrigerant that has flowed into the bypass pipe 113 is decompressed at the bypass flow control valve 110 and reaches the gas-liquid separation unit 111. The refrigerant that has flowed into the heat-source-side heat exchanger 103 joins refrigerant that has flowed into the bypass pipe 113, at the gas-liquid separation unit 111, and then flows through the third check valve 105 and the high-pressure pipe 402, and reaches the gas-liquid separator 201. The refrigerant is divided by the gas-liquid separator 201 into gas-phase refrigerant and liquid-phase refrigerant.

[0061] The liquid-phase refrigerant that has flowed out from the gas-liquid separator 201 flows through the first heat exchange unit 206, the liquid-outflow-side flow control valve 204, and the second heat exchange unit 207, and reaches the second branch portion 250. The refrigerant flows through the first check valve 210a of the second branch portion 250 and the liquid branch pipe 404a, and flows into the indoor unit 300a. The pressure of the refrigerant that has flowed into the indoor unit 300a is reduced to low pressure by the load-side flow control valve 302a that is controlled based on the superheat amount on the outlet side of the load-side heat exchanger 301a. The refrigerant whose pressure has been reduced flows into the load-side heat exchanger 301 a, exchanges heat with indoor air at the load-side heat exchanger 301a, and is evaporated and gasified. At this time, the indoor space in which the indoor unit 300a is installed is cooled. The gasified refrigerant flows through the gas branch pipe 403a and the cooling solenoid valve 203a of the first branch portion 240 and flows into the low-pressure pipe 401.

[0062] On the other hand, the gas-phase refrigerant that has flowed out from the gas outflow side of the gas-liquid separator 201 passes through the heating solenoid valve 202b of the first branch portion 240 and flows into the indoor unit 300b through the gas branch pipe 403b. The refrigerant that has flowed into the indoor unit 300b exchanges heat with indoor air at the load-side heat exchanger 301 b and is thus condensed and liquefied. At this time, the indoor space in which the indoor unit 300b is installed is heated. Then, the condensed and liquefied refrigerant flows through the load-side flow control valve 302b that is controlled based on the subcooling amount on the outlet side of the load-side heat exchanger 301 b, thereby changing into intermediate-pressure liquid refrigerant the temperature of which is intermediate between a high pressure and a low pressure. The intermediate-pressure liquid refrigerant flows through the liquid branch pipe 404b and the second check valve 211b of the second branch portion 250, and flows into the second heat exchange unit 207.

[0063] Thereafter, the refrigerant flows into the relay bypass pipe 209; and after the pressure of the refrigerant is reduced to low pressure at the relay bypass flow control valve 205, the refrigerant exchanges heat, at the second heat exchange unit 207, with refrigerant that has passed through the liquid-outflow-side flow control valve 204, that is, refrigerant that has not yet branched to flow into the relay bypass pipe 209, and is evaporated by this heat exchange. Furthermore, the refrigerant exchanges heat, at the first heat exchange unit 206, with refrigerant that has not yet flowed into the liquid-outflow-side flow control valve 204, and is evaporated by this heat exchange. The evaporated refrigerant flows into the low-pressure pipe 401 joins refrigerant that flows through the cooling solenoid valve 203a to combine into single refrigerant. The single refrigerant flows through the fourth check valve 106, the flow switching valve 102, and the accumulator 104, and is sucked into the compressor 101.

[0064] It should be noted that in the cooling main operation, the heating solenoid valve 202a is in the closed state and the heating solenoid valve 202b is in the open state. The cooling solenoid valve 203a is in the open state and the cooling solenoid valve 203b is in the closed state. Furthermore, since the pressure in the low-pressure pipe 401 is low and that in the high-pressure pipe 402 is high, the refrigerant flows through the third check valve 105 and the fourth check valve 106. Furthermore, since the pressure in the liquid branch pipe 404a is lower than that in the high-pressure pipe 402, the refrigerant does not flow to the second check valve 211a. Furthermore, since the pressure in the liquid branch pipe 404b is higher than that in the high-pressure pipe 402, the refrigerant does not flow to the first check valve 210b.

[0065] Heating Main Operation Next, the heating main operation will be described with reference to Fig. 6. In the air-conditioning apparatus 1, a heating request is made from the indoor unit 300b and a cooling request is made from the indoor unit 300a. As illustrated in Fig. 6, high-temperature and high-pressure gas refrigerant discharged from the compressor 101 flows through the flow switching valve 102, the fifth check valve 107, and the high-pressure pipe 402 and reaches the gas-liquid separator 201. The refrigerant is divided by the gas-liquid separator 201 into gas-phase refrigerant and liquid-phase refrigerant.

[0066] The gas-phase refrigerant that has flowed out from the gas outflow side of the gas-liquid separator 201 flows through the heating solenoid valve 202b of the first branch portion 240 and flows into the indoor unit 300b through the gas branch pipe 403b. The refrigerant that has flowed into the indoor unit 300b exchanges heat with indoor air at the load-side heat exchanger 301 b and is thus condensed and liquefied.

At this time, the indoor space in which the indoor unit 300b is installed is heated. The condensed and liquefied refrigerant flows through the load-side flow control valve 302b that is controlled based on the subcooling amount on the outlet side of the load-side heat exchanger 301 b, thereby changing into intermediate liquid refrigerant the pressure of which is intermediate between a high pressure and a low pressure. The intermediate liquid refrigerant flows through the liquid branch pipe 404b and the second check valve 211b of the second branch portion 250, and flows into the second heat exchange unit 207. At this time, the refrigerant joins liquid refrigerant that has flowed out from the liquid outflow side of the gas-liquid separator 201 and flowed through the first heat exchange unit 206 and the liquid-outflow-side flow control valve 204 to combine into single refrigerant. The single refrigerant branches into refrigerant that flows into the second branch portion 250 and refrigerant that flows into the relay bypass pipe 209.

[0067] The refrigerant that has flowed into the second branch portion 250 flows through the first check valve 210a of the second branch portion 250 and the liquid branch pipe 404a and flows into the indoor unit 300a. Then, the pressure of the refrigerant that has flowed into the indoor unit 300a is reduced to low pressure by the load-side flow control valve 302a that is controlled based on the superheat amount on the outlet side of the load-side heat exchanger 301a. The refrigerant the pressure of which has been reduced flows into the load-side heat exchanger 301a, exchanges heat with indoor air at the load-side heat exchanger 301a and is thus evaporated and gasified. At this time, the indoor space in which the indoor unit 300a is installed is cooled. Then, the gasified refrigerant flows through the gas branch pipe 403a and the cooling solenoid valve 203a of the first branch portion 240 and flows into the low-pressure pipe 401.

[0068] On the other hand, the pressure of the refrigerant that has flowed into the relay bypass pipe 209 is reduced to low pressure at the relay bypass flow control valve 205, and the refrigerant exchanges heat, at the second heat exchange unit 207, with refrigerant that has flowed through the liquid-outflow-side flow control valve 204, that is, refrigerant that has not branched to flow into the relay bypass pipe 209, and is evaporated by this heat exchange. Furthermore, at the first heat exchange unit 206, the refrigerant exchanges heat with refrigerant that has not yet flowed into the liquidoutflow-side flow control valve 204, and is evaporated by this heat exchange. The evaporated refrigerant flows into the low-pressure pipe 401 and joins refrigerant that has flowed through the cooling solenoid valve 203a to combine into single refrigerant. Then, the single refrigerant flows through the sixth check valve 108 and flows into the gas-liquid separation unit 111. The refrigerant is divided by the gas-liquid separation unit 111 into gas-phase refrigerant and liquid-phase refrigerant.

[0069] The refrigerant that has flowed out from the liquid outflow side of the gas-liquid separation unit 111 into the main pipe 114 is decompressed by the heat-source-side flow control valve 109, exchanges heat, at the heat-source-side heat exchanger 103, with outdoor air sent by the heat-source-side fan 112, and is thus evaporated and gasified. On the other hand, the refrigerant that has flowed out from the gas outflow side of the gas-liquid separation unit 111 into the bypass pipe 113 is decompressed by the bypass flow control valve 110, and then joins refrigerant that has flowed out from the main pipe 114 to combine into single refrigerant. The single refrigerant is sucked into the compressor 101 through the flow switching valve 102 and the accumulator 104.

[0070] It should be noted that in the heating main operation, the heating solenoid valve 202b is in the open state and the heating solenoid valve 202a is in the closed state. The cooling solenoid valve 203a is in the open state and the cooling solenoid valve 203b is in the closed state. Furthermore, since the pressure in the low-pressure pipe 401 is low and that in the high-pressure pipe 402 is high, the refrigerant flows through the fifth check valve 107 and the sixth check valve 108. In addition, since the pressure in the liquid branch pipe 404a is lower than that in the high-pressure pipe 402, the refrigerant does not flow to the second check valve 211a. Furthermore, since the pressure in the liquid branch pipe 404b is higher than that in the high-pressure pipe 402, the refrigerant does not flow to the first check valve 210b.

[0071] Method for Controlling Load-side Control Valve Based on Quality The following description is made with respect to an opening-degree adjustment function of the load-side flow control valves 302a and 302b, each of which uses, as a control parameter, the quality of refrigerant that flows into the heat-source-side heat exchanger 103 (which will be referred to as refrigerant quality Q at an inlet portion of the heat-source-side heat exchanger 103 or simply as refrigerant quality Q). The opening-degree adjustment function of the load-side flow control valves 302a and 302b, each of which uses, as a control parameter, the refrigerant quality Q at the inlet portion of the heat-source-side heat exchanger 103, is one of the functions of the control unit 10, and becomes effective in, for example, the heating only operation (hereinafter also referred to "during heating"). It should be noted that with respect to the control method for controlling the opening degree of each of the load-side flow control valves 302a and 302b during the heating only operation, a control method that varies depending on whether the condition is the low load condition or other conditions may be applied.

Specifically, the opening-degree adjustment function of the load-side flow control valves 302a and 302b, each of which uses the refrigerant quality Q as a control parameter, may be set to become effective only under the low load condition during the heating only operation. Since a high-efficiency operation is possible under low load conditions, an improvement in the seasonal efficiency of the air-conditioning apparatus 1 can be expected.

[0072] Fig. 7 is a flowchart indicating the opening-degree adjustment method of the load-side flow control valve 302 by the control unit 10 in the air-conditioning apparatus 1 according to the embodiment of the present disclosure. Fig. 8 is a p-h diagram illustrating an example of variation of the state of the refrigerant in the case where the opening degree of the load-side flow control valve 302 is adjusted in the air-conditioning apparatus 1 according to the embodiment of the present disclosure. In Fig. 8, a circuit portion between the load-side heat exchanger 301 and the heat-source-side heat exchanger 103 is simplified. In an example illustrated in Figs. 1 and 3 to 6, at this circuit portion, the load-side flow control valve 302, the liquid-outflow-side flow control valve 204, and the heat-source-side flow control valve 109 are provided, and strictly speaking, the refrigerant quality Q of the inlet portion of the heat-source-side heat exchanger 103 is affected by the above three flow control valves In the following, in order that descriptions be easily understood, it is assumed that only the load-side flow control valve 302 is provided at the circuit portion. A flow of controls of the load-side flow control valves 302a and 302b that are performed by the control unit 10 during heating will be described with reference to Figs. 7 and 8, referring to Fig. 4. As illustrated in Fig. 7, first, temperatures and pressures of components are detected by various detecting units (step ST11).

[0073] Next, a discharge refrigerant flow rate Gr [Kg/h] of the compressor 101, a specific enthalpy of a discharge part of the compressor 101, and a condensation performance of each of the indoor units 300a and 300b are calculated (step ST12). The discharge refrigerant flow rate Gr of the compressor 101 is calculated by multiplying a refrigerant density at a suction part of the compressor, which is computed from a low pressure detected by the suction pressure detecting unit 127 and a refrigerant temperature detected by the suction temperature detecting unit 129, by the frequency and displacement volume of the compressor 101. The specific enthalpy of the discharge part of the compressor 101 can be calculated from a high pressure detected by the discharge pressure detecting unit 126 and a refrigerant temperature detected by the discharge temperature detecting unit 128. The condensation performance of the indoor units 300a and 300b is calculated by multiplying an actually measured value or a specification value of an air volume of the indoor units 300a and 300b by differences between temperatures of indoor air that are detected by the drawn-in temperature detecting units 305a and 305b of the indoor units 300a and 300b and refrigerant temperatures detected by the liquid-pipe temperature detecting units 303a and 303b that correspond to blowing temperatures of the indoor units 300a and 300b. In the case of calculating the condensation performance of the indoor units 300a and 300b, corrections may be made in consideration of the amount of heat generation and bypass factors and bypass factors of the indoor units 300a and 300b.

[0074] Then, the refrigerant quality of inflow part of the heat-source-side heat exchanger 103 is calculated (step ST13). The refrigerant quality Q of inlet part of the heat-source-side heat exchanger 103 is calculated from the pressure or temperature and the specific enthalpy at the second refrigerant pipes 502a and 502b. With respect to the second refrigerant pipes 502a and 502b through which refrigerant flowing out from the load-side heat exchangers 301 a and 301 b flows, during heating, and the first refrigerant pipe 501 through which refrigerant flowing into the heat-source-side heat exchanger 103 flows, during heating, if minor thermal losses are ignored, it is determined that only pressure losses occur, and the specific enthalpies of the above portions are equal to each other. The specific enthalpy of the first refrigerant pipe 501 can be calculated from the difference between the specific enthalpy of the discharge part of the compressor 101 that is calculated in step ST12 and a value obtained by dividing the condensation performance of the indoor units 300a and 300b by the discharge refrigerant flow rate Gr of the compressor 101.

[0075] Next the gas flow velocity ug and liquid flow velocity ul of two-phase refrigerant that flows into the heat-source-side heat exchanger 103 are calculated according to the following equations (1) and (2) (step ST14).

[0076] [Math. 1] oginvislfkg/h1)4(Dgikgi'n [0077] [Math. 2] sj /IDI[kgtm A[rnmei]*$.6 ation (2) [0078] As indicated in the equation (1), the gas flow velocity ug can be calculated from the discharge refrigerant flow rate Gr[Kg/h] of the compressor 101, the refrigerant quality Q of the inlet part of the heat-source-side heat exchanger, a gas saturation density Dg [kg/m3] , and a section area A [mm2]. Furthermore, as indicated in the equation (2), the liquid flow velocity ul can be calculated from the discharge refrigerant flow rate Gr[Kg/h] of the compressor 101, the refrigerant quality Q of the inlet part of the heat-source-side heat exchanger 103, a liquid saturation density DI [kg/m31, and the section area A [mm2]. It should be noted that the gas saturation density Dg is a refrigerant density at the boundary between a two-phase state and a gas state (see Fig. 8), and the liquid saturation density DI is a refrigerant density at the boundary between a liquid state and the two-phase state (see Fig. 8). Each of the gas saturation density Dg and the liquid saturation density DI can be calculated from a low pressure detected by the suction pressure detecting unit 127.

[0079] In general, the flow velocity of a gas-phase fluid is higher than that of a liquid-phase fluid, primarily due to the difference in density between the liquid-phase fluid and the gas-phase fluid. Therefore, the greater the proportion of gas-phase refrigerant in two-phase refrigerant that flows into the heat-source-side heat exchanger 103, that is, the higher the refrigerant quality at the inlet part of the heat-source-side heat exchanger 103, the higher the flow velocity of the refrigerant at the inflow part of the heat-sourceside heat exchanger 103 (which operates as an evaporator during heating). Furthermore, the higher the flow velocity of the refrigerant at the inflow part of the heat-source-side heat exchanger 103, the further the refrigerant distribution performance at the heat-source-side heat exchanger 103 is improved.

[0080] At step ST14, after the gas flow velocity ug and the liquid flow velocity ul at the inlet part of the heat-source-side heat exchanger 103 are calculated, the control unit 10 calculates the current flooding multiplier C according to the following equation (3), using known variables calculated in steps ST12 to ST14 (step ST15).

[0081] [Math. 3] C niga 0, 1;11 a5 jg = ug [m s] *(Dg[kgieml/( l[kg/rn g[ .);t 05 equat j1 ul [rn is] *0 l[kg/m9 /((:)(0 I [kWnici-D -0,5 [0082] To be more specific, the current flooding multiplier C is calculated from the gas flow velocity ug and the liquid flow velocity ul at the inlet part of the heat-source-side heat exchanger 103, the gas saturation density Dg, the liquid saturation density DI, and the refrigerant quality Q of the inlet part of the heat-source-side heat exchanger 103.

[0083] Next, the control unit 10 determines whether the current flooding multiplier C calculated in step ST15 coincides with a predetermined target value Ct (for example, 2.8) or not (step ST16). When the current flooding multiplier C coincides with the target value Ct (YES in step ST16), the control ends. When the current flooding multiplier C does not coincide with the target value Ct (NO in step ST16), the processing proceeds to step ST17, and the opening degrees of the load-side flow control valves 302a and 302b are adjusted as control, and the processing returns to step ST11. [0084] In order to avoid hunting of the opening degrees of the load-side flow control valves 302a and 302b, it is advisable to add hysteresis with respect to the target value Ct for the flooding multiplier C. [0085] The case where it is determined in step ST16 that the current flooding multiplier C does not coincide with the target value Ct corresponds to the case where the current flooding multiplier C is greater than the target value Ct or the case where the current flooding multiplier C is smaller than the target value Ct. Regarding each of these cases, adjustment of the opening degrees of the load-side flow control valves 302a and 302b in step ST17 is performed as follows: [0086] In the case where the current flooding multiplier C is greater than the target value Ct, in order to reduce the refrigerant quality Q at the inlet part of the heat-source-side heat exchanger 103, the control unit 10 causes the opening degrees of the load-side flow control valves 302a and 302b to be smaller than the current opening degrees. As a result, the flow velocity of the refrigerant after the adjustment falls below that before the adjustment.

[0087] By contrast, in the case where the current flooding multiplier C is smaller than the target value Ct, in order to raise the refrigerant quality Q at the inlet part of the heat-source-side heat exchanger 103, the control unit 10 causes the opening degrees of the load-side flow control valves 302a and 302b to be greater than the current opening degrees. As a result, the flow velocity of the refrigerant after the adjustment exceeds that before the adjustment.

[0088] In such a manner, in such a control as indicated in Fig. 7, in order that the refrigerant quality Q of the inlet part of the heat-source-side heat exchanger 103 reach a quality set as a target value (which will be hereinafter referred to as target quality), the opening degrees of the load-side flow control valves 302a and 302b are adjusted in such a manner as to cause the current flooding multiplier C to be closer to the target value Ct. It should be noted that the method for controlling the refrigerant quality 0 of the inlet pad of the heat-source-side heat exchanger 103 is not limited to the control method using the flooding multiplier C as indicated by way of example in Fig. 7.

[0089] It is advisable to set the target quality to the quality of the refrigerant at the time when a reduction rate n of the distribution loss is maximized (for example, when the flooding multiplier C is 2.8). Furthermore, if the distribution performance deteriorates, the low-pressure pressure decreases, as a result of which frost formation easily occurs and the performance deteriorates. Therefore, it is advisable to set the target dryness in consideration of the low-pressure limit for frost formation.

[0090] The distribution loss of the heat-source-side heat exchanger 103 that operates as an evaporator during heating varies depending on, for example, the size or shape of the heat-source-side heat exchanger 103. It is therefore advisable to set the target value Ct of the flooding multiplier C based on, for example, the size or shape of an employed evaporator. The target value Ct of the flooding multiplier C may be determined, for example, as a constant that causes the distribution loss of the employed evaporator to be stabilized. Alternatively, the control unit 10 may make a calculation to set the target value Ct to a value based on the operating state of the air-conditioning apparatus 1. It should be noted that the operating state corresponds to, for example, detection values obtained by various detecting units and used in calculation of the flooding multiplier C or a driving frequency of the compressor 101. Also, note that a table in which target values Ct are associated with operating states may be stored in the storage unit 11 of the control unit 10.

[0091] In such a manner, from temperatures and pressures of components that are detected by the various detecting units of the air-conditioning apparatus 1 according to the embodiment of the present disclosure, the air-conditioning apparatus 1 calculates the refrigerant quality Q of the inlet part of the heat-source-side heat exchanger 103 and the flooding multiplier C at that time. Then, the air-conditioning apparatus 1 controls the refrigerant quality Q of the inlet part of the heat-source-side heat exchanger 103 by adjusting the opening degrees of the load-side flow control valves 302a and 302b, until the calculated flooding multiplier C reaches the target value Ct.

[0092] In an example illustrated in Fig. 7, the refrigerant quality Q and the current flooding multiplier C can be calculated from detection values obtained by known detecting units for use in an existing control that are the suction pressure detecting unit 127, the suction temperature detecting unit 129, the discharge pressure detecting unit 126, the discharge temperature detecting unit 128, the drawn-in temperature detecting units 305a and 305b, and the liquid-pipe temperature detecting units 303a and 303b. It should be noted that another detecting unit or other detecting units may be further provided in addition to known detecting units in order to more accurately detect the refrigerant quality Q and the current flooding multiplier C. [0093] Next, advantages obtained by adjustment of the opening degrees of the load-side flow control valves 302a and 302b that is performed by the control unit 10 in the case where the current flooding multiplier C is smaller than the target value Ct will be described with reference to the p-h diagram of Fig. 8.

[0094] Refrigerant that flows out from each of the load-side heat exchangers 301 that operate as a condenser is decompressed by the load-side flow control valve 302 and flows into the heat-source-side heat exchanger 103 that operates as an evaporator. In the case where the current flooding multiplier C is smaller than the target value Ct, the control unit 10 adjusts and increases the opening degree of each of the load-side flow control valves in order to raise the refrigerant quality Q of the inlet part of the heat-source-side heat exchanger 103. In an example illustrated in Fig. 8, after the adjustment, the refrigerant quality of refrigerant C20 that flows into the heat-source-side heat exchanger 103 (refrigerant that flows through the first refrigerant pipe 501 as illustrated in Fig. 4) is higher than that of refrigerant C2 that flows into the heat-sourceside heat exchanger 103 before the adjustment. When the refrigerant quality Q of the inlet part of the heat-source-side heat exchanger 103 rises, that is, when the ratio of the gas-phase refrigerant in two-phase refrigerant that flows into the heat-source-side heat exchanger 103 increases, the flow velocity of refrigerant that flows into the heat-sourceside heat exchanger 103 increases, that is, the refrigerant flows at a higher velocity. [0095] As described above, when the opening degrees of the load-side flow control valves 302 are adjusted and increased to raise the refrigerant quality Q at the inlet part of the heat-source-side heat exchanger 103, the refrigerant quality Q of refrigerant C10 that flows out from each of the load-side heat exchangers 301 (refrigerants that flows through the second refrigerant pipes 502a and 502b as illustrated Fig. 4) is increased higher than that of refrigerant C1 that flows out from each of the load-side heat exchangers 301, before adjustment.

[0096] Incidentally, in a configuration in which an SC target control is performed during heating as in existing techniques, when a control to ensure the degree of subcooling of refrigerant that flows out from the load-side heat exchanger 301 is performed under the low load condition during the heating operation, the refrigerant quality Q at the inlet part of the heat-source-side heat exchanger 103 lowers as in, for example, the refrigerant C2 before adjustment as illustrated in Fig. 8. Thus, in the configuration in which the SC target control is performed during heating as in the existing techniques, the flow velocity of refrigerant that flows into the heat-source-side heat exchanger 103 under the low load condition during heating is lower than in the embodiment according to the present disclosure, and the refrigerant distribution performance of the heat-source-side heat exchanger 103 is deteriorated.

[0097] In the air-conditioning apparatus 1 according to the embodiment of the present disclosure, as described above, the opening degree of the load-side flow control valve 302 is adjusted using, as a control parameter, the refrigerant quality Q of two-phase refrigerant (refrigerant C20) at the inlet part of the heat-source-side heat exchanger 103 during heating. As a result, the refrigerant quality Q at the inlet part of the heat-source-side heat exchanger 103 is prevented from extremely lowering, even under the low-load condition in which the amount of refrigerant circulating in the refrigerant circuit is small and the flow velocity of the refrigerant easily lowers, whereby lowering of the flow velocity is reduced and deterioration of the refrigerant distribution performance of the heat-source-side heat exchanger 103 is reduced, as compared with the existing techniques. Accordingly, it is also possible to reduce lowering of an evaporation performance that is caused by the distribution loss of the heat-source-side heat exchanger 103.

[0098] In the configuration in which the SC target control is performed as in the existing techniques, the refrigerant at the outlet part of the load-side heat exchanger 301 is subcooled liquid refrigerant. However, in the embodiment of the present disclosure, since the quality of refrigerant (refrigerant quality Q) at the inlet part of the heat-sourceside heat exchanger 103 is controlled, the refrigerant C10 at the outlet part of the load-side heat exchanger 301 may be two-phase refrigerant.

[0099] As described above, the air-conditioning apparatus 1 according to the embodiment of the present disclosure includes: the compressor 101 that compresses and discharges refrigerant; the load-side heat exchanger 301 that operates as a condenser during the heating operation; the flow control valve (the load-side flow control valve 302) that adjusts the flow rate of refrigerant that flows out from the load-side heat exchanger 301, during the heating operation; and the heat source unit 100 provided with the heat-source-side heat exchanger 103 that operates as an evaporator during the heating operation heating. The air-conditioning apparatus 1 further includes the control unit 10 that controls the opening degree of the load-side flow control valve 302. The control unit 10 adjusts the opening degree of the load-side flow control valve 302, using the quality (refrigerant quality Q) of refrigerant that flows into the heat-source-side heat exchanger 103, as a control parameter, during the heating operation.

[0100] In the air-conditioning apparatus 1 according to the embodiment of the present disclosure, during the heating operation, the opening degree of the load-side flow control valve 302 is adjusted using, as a control parameter, the quality of refrigerant (refrigerant quality Q) that flows into the heat-source-side heat exchanger 103 that operates as an evaporator. As a result, lowering of the quality (refrigerant quality Q) of refrigerant that flows into the heat-source-side heat exchanger 103 is reduced even under a low load condition during the heating operation, as compared with the existing techniques. It is therefore possible to provide an air-conditioning apparatus 1 in which the refrigerant distribution performance of the heat-source-side heat exchanger 103 under a low load condition during the heating operation is improved.

[0101] It should be noted that in the air-conditioning apparatus 1, the refrigerant distribution performance can be considered to be improved by change of the number of passages or a header structure of the heat-source-side heat exchanger 103; however, in this case, the heat-source-side heat exchanger 103 itself needs to be changed in structure, and there are thus remaining issues in terms of manufacturability. By contrast, as compared with the case where the structure of the heat-source-side heat exchanger 103 itself is changed, in the air-conditioning apparatus 1 according to the embodiment of the present disclosure, the refrigerant distribution performance under the low load condition can be improved, and the issues regarding manufacturability can be solved.

[0102] Furthermore, the air-conditioning apparatus 1 includes the discharge temperature detecting unit 128 and the discharge pressure detecting unit 126 that detect the temperature and pressure of refrigerant that is discharged from the compressor 101 and the suction temperature detecting unit 129 and the suction pressure detecting unit 127 that detect the temperature and pressure of refrigerant that is sucked into the compressor 101. Furthermore, the air-conditioning apparatus 1 includes the drawn-in temperature detecting unit 305 that detects the temperature of air that has not yet exchanged with refrigerant at the load-side heat exchanger 301 and the liquid-pipe temperature detecting unit 303 that detects the temperature of refrigerant that has flowed out from the load-side heat exchanger 301 and has not yet flowed into the load-side flow control valve 302 during the heating operation. The control unit 10 adjusts the opening degree of the load-side flow control valve 302 based on a value (for example, the flooding multiplier C) calculated according to an arithmetic equation including the quality (refrigerant quality Q) as a variable, from detection values obtained by the discharge temperature detecting unit 128, the discharge pressure detecting unit 126, the suction temperature detecting unit 129,the suction pressure detecting unit 127, the drawn-in temperature detecting unit 305, and the liquid-pipe temperature detecting unit 303.

[0103] Thus, even in the case where the opening degree of the load-side flow control valve 302 is adjusted using the refrigerant quality Q as a control parameter, it is possible to use a detecting unit provided in a common air-conditioning apparatus 1 and it is not necessary to add further detection, whereby the cost can be reduced.

[0104] During the heating operation, the control unit 10 calculates the flooding multiplier (C) based on the liquid flow velocity ul and the gas flow velocity ug of refrigerant that flows into the heat-source-side heat exchanger 103, and adjusts the opening degree of the load-side flow control valve 302 such that the calculated flooding multiplier C reaches the target value Ct corresponding to a target quality determined in advance.

[0105] The target value Ct of the flooding multiplier C is a constant. It is therefore possible to simplify an operation for adjustment of the opening degree of the load-side flow control valve 302 and reduce the load on the control.

[0106] Furthermore, the control unit 10 makes a calculation to set the target value Ct of the flooding multiplier C based on the operating state. As a result, the set target value Ct is optimal for an actual operating state, and the opening degree of the load-side flow control valve 302 can be controlled suitable for the operating state.

[0107] When the calculated flooding multiplier C is greater than the target value Ct, the control unit 10 causes the opening degree of the load-side flow control valve 302 to be smaller than the current opening degree thereof. When the calculated flooding multiplier C is smaller than the target value Ct, the control unit 10 causes the opening degree of the load-side flow control valve 302 to be greater than the current opening degree thereof.

[0108] Therefore, the opening degree of the load-side flow control valve 302 is controlled so that the calculated flooding multiplier C approaches the target value Ct, and it is therefore possible to set the flow velocity to an optimal flow velocity by adjusting the quality of refrigerant that flows into the heat-source-side heat exchanger 103, and improve the refrigerant distribution performance.

Reference Signs List [0109] 1: air-conditioning apparatus, 10: control unit 11: storage unit, 12: setting unit, 13: component controlling unit, 20: load capacity detecting unit, 30: indoor unit, 100: heat source unit, 101: compressor, 102: flow switching valve, 103: heat-source-side heat exchanger, 104: accumulator, 105: third check valve, 106: fourth check valve, 107: fifth check valve, 108: sixth check valve, 109: heat-source-side flow control valve, 110: bypass flow control valve, 111: gas-liquid separation unit, 112: heat-source-side fan, 113: bypass pipe, 114: main pipe, 120: heat-source-side heat exchange unit, 126: discharge pressure detecting unit, 127: suction pressure detecting unit, 128: discharge temperature detecting unit, 129: suction temperature detecting unit, 140: heat-sourceside flow-passage adjustment unit, 141: controller, 200: relay unit, 201: gas-liquid separator, 202a, 202b: heating solenoid valve, 203a, 203b: cooling solenoid valve, 204: liquid-outflow-side flow control valve, 205: relay bypass flow control valve, 206: first heat exchange unit, 207: second heat exchange unit, 208: relay-bypass temperature detecting unit, 209: relay bypass pipe, 210a, 210b: first check valve, 211a, 211b: second check valve, 220: controller, 231: liquid-outflow pressure detecting unit, 232: downstream-side liquid-outflow pressure detecting unit, 240: first branch portion, 250: second branch portion, 260: heat exchange unit, 300, 300a, 300b: indoor unit, 301, 301 a, 301 b: load-side heat exchanger, 302, 302a, 302b: load-side flow control valve, 303, 303a, 303b: liquid-pipe temperature detecting unit, 304, 304a, 304b: gas-pipe temperature detecting unit, 305, 305a, 305b: drawn-in temperature detecting unit, 401: low-pressure pipe, 402: high-pressure pipe, 403a, 403b: gas branch pipe, 404a, 404b: liquid branch pipe, 501: first refrigerant pipe, 502a, 502b: second refrigerant pipe, A: section area, C: flooding multiplier, Ct: target value, Dg: gas saturation density, Dl: liquid saturation density, Gr: discharge refrigerant flow rate, Q: refrigerant quality, ug: gas flow velocity, ul: liquid flow velocity, q: reduction rate of distribution loss

Claims

CLAIMS[Claim 1] An air-conditioning apparatus comprising: a compressor configured to compress refrigerant and discharge the compressed refrigerant; a load-side heat exchanger configured to operate as a condenser during a heating operation; a flow control valve configured to adjust a flow rate of the refrigerant that flows out from the load-side heat exchanger during the heating operation; a heat-source-side heat exchanger configured to operate as an evaporator during the heating operation; and a controller configured to control an opening degree of the flow control valve, wherein the controller is configured to adjust the opening degree of the flow control valve using, as a control parameter, a quality of the refrigerant that flows into the heat-source-side heat exchanger, during the heating operation.
[Claim 2] The air-conditioning apparatus of claim 1, further comprising: a discharge temperature detecting unit configured to detect a temperature of the refrigerant discharged from the compressor and a discharge pressure detecting unit configured to detect a pressure of the refrigerant discharged from the compressor; a suction temperature detecting unit configured to detect a temperature of the refrigerant that is sucked into the compressor and a suction pressure detecting unit configured to detect a pressure of the refrigerant that is sucked into the compressor; a drawn-in temperature detecting unit configured to detect a temperature of air that has not yet exchanged heat with the refrigerant at the load-side heat exchanger; a liquid-pipe temperature detecting unit configured to detect a temperature of the refrigerant that has flowed out from the load-side heat exchanger and that has not yet flowed into the flow control valve, during the heating operation, wherein the controller is configured to adjust an opening degree of the flow control valve based on a value that is calculated according to an arithmetic equation including the quality as a variable, from detection values obtained by the discharge temperature detecting unit, the discharge pressure detecting unit, the suction temperature detecting unit, the suction pressure detecting unit, the drawn-in temperature detecting unit, and the liquid-pipe temperature detecting unit.
[Claim 3] The air-conditioning apparatus of claim 1 or 2, wherein the controller is configured to, during the heating operation, calculate a flooding multiplier based on a liquid flow velocity and a gas flow velocity of the refrigerant that has not yet flowed into the heatsource-side heat exchanger, and adjust an opening degree of the flow control valve to cause the calculated flooding multiplier to reach a target value corresponding to a target quality determined in advance.
[Claim 4] The air-conditioning apparatus of claim 3, wherein the flooding multiplier is a constant.
[Claim 5] The air-conditioning apparatus of claim 3, wherein the controller is configured to make a calculation to set the target value of the flooding multiplier based on an operating state.
[Claim 6] The air-conditioning apparatus of any one of claims 3 to 5, wherein the controller is configured to: decrease the opening degree of the flow control valve to a smaller value than a current opening degree of the flow control valve when the calculated flooding multiplier is greater than the target value; and increase the opening degree of the flow control valve to a greater value than the current opening degree when the calculated flooding multiplier is smaller than the target value.