GB2557058A

GB2557058A - Air conditioner

Info

Publication number: GB2557058A
Application number: GB1800859.9A
Authority: GB
Inventors: Koge Hirofumi; Okano Hiroyuki; okochi Kazuki
Original assignee: Mitsubishi Electric Corp
Current assignee: Mitsubishi Electric Corp
Priority date: 2015-06-24
Filing date: 2015-06-24
Publication date: 2018-06-13
Anticipated expiration: 2035-06-24
Also published as: WO2016207993A1; GB2557058B; GB201800859D0; GB2557058C; JP6391832B2; JPWO2016207993A1

Abstract

In the present invention, an air conditioner has a heat source device, a plurality of indoor devices, and a relay device connected between the heat source device and the plurality of indoor devices via refrigerant pipelines. A heat-source-side heat exchanger includes an upper-stage heat exchanger and a lower-stage heat exchanger that are connected in parallel to a compressor and disposed so as to be aligned in the vertical direction. The heat source device is provided with: a capacity control valve for controlling the flow of refrigerant into the upper-stage heat exchanger and lower-stage heat exchanger to control the capacity of the heat-source-side heat exchanger; a heat-source-side gas-liquid separator for separating the refrigerant flowing in from the relay device into a gas refrigerant and a liquid refrigerant; a first branch pipeline through which the refrigerant that has flowed into the heat-source-side gas-liquid separator is caused to flow through the capacity control valve; a second branch pipeline through which the refrigerant that has flowed into the heat-source-side gas-liquid separator is caused to flow into the lower-stage heat exchanger; and a flow-rate control device provided to the second pipeline, the flow-rate control device adjusting the rate at which refrigerant flows into the lower-stage heat exchanger via the second pipeline.

Description

(54) Title of the Invention: Air conditioner Abstract Title: Air conditioner (57) In the present invention, an air conditioner has a heat source device, a plurality of indoor devices, and a relay device connected between the heat source device and the plurality of indoor devices via refrigerant pipelines. A heat-source-side heat exchanger includes an upper-stage heat exchanger and a lower-stage heat exchanger that are connected in parallel to a compressor and disposed so as to be aligned in the vertical direction. The heat source device is provided with: a capacity control valve for controlling the flow of refrigerant into the upper-stage heat exchanger and lower-stage heat exchanger to control the capacity of the heat-source-side heat exchanger; a heat-source-side gas-liquid separator for separating the refrigerant flowing in from the relay device into a gas refrigerant and a liquid refrigerant; a first branch pipeline through which the refrigerant that has flowed into the heatsource-side gas-liquid separator is caused to flow through the capacity control valve; a second branch pipeline through which the refrigerant that has flowed into the heat-source-side gas-liquid separator is caused to flow into the lower-stage heat exchanger; and a flow-rate control device provided to the second pipeline, the flow-rate control device adjusting the rate at which refrigerant flows into the lower-stage heat exchanger via the second pipeline.

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DESCRIPTION

Title of Invention

AIR-CONDITIONING APPARATUS

Technical Field [0001]

The present invention relates to an air-conditioning apparatus that includes a heat source-side heat exchanger including a plurality of heat exchange units. Background Art [0002]

In an air-conditioning apparatus including a related-art refrigeration cycle (heat pump cycle), a heat source-side unit including a compressor and a heat source-side heat exchanger, and a load-side unit (indoor unit) including a flow control device and an indoor unit-side heat exchanger are connected by refrigerant pipes to form a refrigerant circuit through which refrigerant is circulated. When the refrigerant is evaporated or condensed in the indoor unit-side heat exchanger, the refrigerant removes heat from or rejects heat to air in an air-conditioned space with which the refrigerant exchanges heat, to thereby perform air conditioning while pressure, temperature, or other conditions related to the refrigerant in the refrigerant circuit are varied. Examples of refrigerants that are often used for such an air-conditioning apparatus include hydrofluorocarbon (HFC)-based refrigerants. There has also been proposed an air-conditioning apparatus that employs natural refrigerants such as carbon dioxide (CO2).

[0003]

Further, a fin-and-tube heat exchanger including a heat transfer tube and fins has been used as a heat source-side heat exchanger. As the heat transfer tube, there has been known, in addition to the heat transfer tube having a circular crosssectional shape as disclosed in Patent Literature 1, a flat tube having a crosssectional shape of a chamfered rectangle with a large aspect ratio as disclosed in Patent Literature 2. In Patent Literature 2, the outdoor heat exchanger is divided into three heat exchange units arrayed in a vertical direction, and a liquid-side connection member and a gas-side header are connected to each heat exchange unit such that refrigerant is diverted to each heat exchange unit from the liquid-side connection member or the gas-side header.

Citation List

Patent Literature [0004]

Patent Literature 1: Japanese Unexamined Patent Application Publication No. Hei 2-033595

Patent Literature 2: Japanese Unexamined Patent Application Publication No. 2012-163313

Summary of Invention

Technical Problem [0005]

When a heat source-side heat exchanger has a plurality of heat exchange units as described in Patent Literature 2, the heat exchange units may have different air velocity distribution. Thus, it is required that refrigerant be distributed corresponding to the air velocity distribution. In particular, when the heat transfer tube is a flat tube as described in Patent Literature 2, the overall performance of the heat exchanger may be degraded unless the flow rate of refrigerant to the upper heat exchanger is increased. When effective distribution of refrigerant to each heat exchange unit is to be achieved with a structure of the heat exchanger, there arises a problem in that the structure of the heat exchanger is increased in complexity.

[0006]

The present invention has been made to solve the above-mentioned problem, and has an object to provide an air-conditioning apparatus that enables effective distribution of refrigerant to each of the heat exchange units when the heat source2 side heat exchanger is divided into a plurality of heat exchange units, without employing a special structure for the heat source-side heat exchanger.

Solution to Problem [0007]

According to one embodiment of the present invention, there is provided an airconditioning apparatus including a heat source unit including a compressor configured to compress and discharge refrigerant and a heat source-side heat exchanger configured to perform heat exchange between the refrigerant discharged from the compressor and a heat source medium, a plurality of indoor units each including a use-side heat exchanger configured to perform heat exchange between refrigerant and a use-side medium and a heat source-side flow regulator connected to the use-side heat exchanger, and a relay unit connected between the heat source unit and the plurality of indoor units by refrigerant pipes, and configured to distribute refrigerant having flowed out from the heat source-side heat exchanger to the plurality of indoor units. The heat source-side heat exchanger includes an upper heat exchange unit and a lower heat exchange unit that are connected to the compressor in parallel to each other and arrayed in a vertical direction. The heat source unit includes a capacity control valve configured to control a capacity of the heat sourceside heat exchanger by controlling inflow of refrigerant to the upper heat exchange unit and the lower heat exchange unit, a heat source-side gas-liquid separator configured to separate refrigerant flowing in from the relay unit into gas refrigerant and liquid refrigerant, a first branched pipe configured to allow refrigerant having flowed into the heat source-side gas-liquid separator to flow into the capacity control valve, a second branched pipe configured to allow refrigerant having flowed into the heat source-side gas-liquid separator to flow into the lower heat exchange unit, and a flow control device arranged in the second branched pipe and configured to regulate a flow rate of refrigerant flowing into the lower heat exchange unit via the second branched pipe.

Advantageous Effects of Invention [0008]

In the air-conditioning apparatus according to one embodiment of the present invention, the flow control device configured to regulate the flow rate of refrigerant in the heat source-side heat exchanger is provided. Thus, effective distribution of refrigerant to each heat exchange unit is achieved by a simple structure without providing a special refrigerant distribution structure to the heat source-side heat exchanger itself.

Brief Description of Drawings [0009] [Fig. 1] Fig. 1 is a refrigerant circuit diagram for illustrating an example of an air-conditioning apparatus according to an embodiment of the present invention.

[Fig. 2] Fig. 2 is a refrigerant circuit diagram for illustrating a flow of refrigerant when a simultaneous cooling and heating operation that is mainly cooling is performed in the air-conditioning apparatus illustrated in Fig. 1.

[Fig. 3] Fig. 3 is a refrigerant circuit diagram for illustrating a flow of refrigerant when a simultaneous cooling and heating operation that is mainly heating is performed in the air-conditioning apparatus illustrated in Fig. 1.

[Fig. 4] Fig. 4 is a graph for showing a relationship between a flow regulator and heating performance when heating only operation is performed in the airconditioning apparatus illustrated in Fig. 1.

[Fig. 5] Fig. 5 is a flowchart for illustrating exemplary operation of a flow control device during simultaneous cooling and heating operation of the air-conditioning apparatus illustrated in Fig. 2 and Fig. 3.

[Fig. 6] Fig. 6 is a flowchart for illustrating exemplary operation of an on-off valve when the air-conditioning apparatus illustrated in Fig. 1 performs cooling operation.

Description of Embodiments [0010]

With reference to the drawings, description is made below of an airconditioning apparatus according to an embodiment of the present invention. Fig. 1 is a refrigerant circuit diagram for illustrating an example of an air-conditioning apparatus according to an embodiment of the present invention. An air-conditioning apparatus 1 illustrated in Fig. 1 is configured to perform cooling and heating operations with use of refrigerant circulation in a refrigeration cycle (heat pump cycle). In particular, the air-conditioning apparatus 1 according to the embodiment enables a plurality of indoor units to each perform a simultaneous cooling and heating operation, in which cooling and heating are performed simultaneously.

[0011]

The air-conditioning apparatus 1 includes a heat source unit 10, a relay unit 20, and a plurality of indoor units 30A and 30B. Those units are connected by refrigerant pipes. That is, the relay unit 20 configured to control the flow rate of refrigerant is arranged between the heat source unit 10 and each of the indoor units 30A and 30B. The indoor units 30A and 30B are connected to the relay unit 20 in parallel to each other.

[0012]

The heat source unit 10 and the relay unit 20 are connected to each other by a first main pipe 2, and a second main pipe 3 that is smaller in pipe diameter than the first main pipe 2. Refrigerant at a high pressure flows through the first main pipe 2 from the heat source unit 10 toward the relay unit 20 side. Refrigerant at a pressure lower than that of the refrigerant flowing through the first main pipe 2 flows through the second main pipe 3 from the relay unit 20 toward the heat source unit 10 side. In this case, whether a pressure is high or low is not determined in relation to a reference pressure (numerical value), but is expressed as a relative value (including an intermediate value) in the refrigerant circuit that results from application of pressure by the compressor 11, the control of the open-close state (opening degree) of each individual flow control device, or other factors. In this regard, refrigerant is at its highest pressure at the time when the refrigerant is discharged from the compressor 11, and then the pressure is reduced by a flow control device or other components. Thus, refrigerant is at its lowest pressure at the time of being sucked into the compressor 11.

[0013]

The relay unit 20 and each of the indoor units 30A and 30B are connected by first branch pipes 4 and second branch pipes 5. The pipe connection using the first main pipe 2, the second main pipe 3, the first branch pipes 4, and the second branch pipes 5 forms a refrigerant circuit through which the refrigerant is circulated between the heat source unit 10, the relay unit 20, and the indoor units 30Aand 30B.

[0014] [Heat Source Unit 10]

The heat source unit 10 includes the compressor 11, a flow switching unit 12, a heat source-side heat exchanger 13, an accumulator 14, and a flow path forming unit 15. The compressor 11 applies pressure to sucked refrigerant, and discharges the resulting refrigerant. The compressor 11 includes an inverter compressor that is capable of varying its discharge capacity, which represents the amount of refrigerant discharged by the compressor 11 as a whole per unit time, and also capable of varying its capability corresponding to discharge capacity. Further, the driving frequency of the compressor 11 can be varied in accordance with an instruction from a controller 60 by an inverter circuit (not shown).

[0015]

The flow switching unit 12 is connected to the discharge side of the compressor 11, and is configured to switch flow paths corresponding to the mode of cooling or heating in accordance with an instruction from the controller 60. The flow switching unit 12 is formed of a four-way valve. The flow switching unit 12 includes four ports that are connected to the discharge side of the compressor 11, the heat source-side heat exchanger 13, the accumulator 14, the outlet side of a check valve 15b, and the inlet side of a check valve 15c. The flow switching unit 12 switches the flow paths of refrigerant such that the flow path of refrigerant during cooling only operation, in which the indoor units 30Aand 30B are all performing cooling operation, and during cooling main operation, which is a type of simultaneous cooling and heating operation in which cooling is mainly performed, differs from the flow path of refrigerant during heating only operation, in which the indoor units 30Aand 30B are all performing heating operation, and during heating main operation, which is a type of simultaneous cooling and heating operation in which heating is mainly performed.

[0016]

The heat source-side heat exchanger 13 has a heat transfer tube through which refrigerant passes, and fins (not shown) used to increase the heat transfer area between the refrigerant flowing through the heat transfer tube and air (outside air).

The heat source-side heat exchanger 13 performs heat exchange between refrigerant and air (outside air). For example, during heating only operation and heating main operation, the heat source-side heat exchanger 13 acts as an evaporator to evaporate and gasify the refrigerant. During cooling only operation and cooling main operation, the heat source-side heat exchanger 13 acts as a condenser to condense and liquefy the refrigerant. The heat source-side heat exchanger 13 performs heat exchange between refrigerant flowing in the heat source-side heat exchanger 13, and refrigerant flowing in the heat source-side heat exchanger 13. The refrigerant flowing in the heat source-side heat exchanger 13 may be water or brine. The heat source unit 10 may be provided with a heat source unit-side air-sending device (not shown) configured to send air to the heat source-side heat exchanger 13 for efficient heat exchange between the refrigerant and air.

[0017]

The heat source-side heat exchanger 13 described above has an upper heat exchange unit 13a and a lower heat exchange unit 13b, which are arrayed in the vertical direction and connected in parallel to each other. One of the upper heat exchange unit 13a and the lower heat exchange unit 13b is connected to the flow switching unit 12, and the other is connected to the first main pipe 2. There is exemplified the case in which the heat source-side heat exchanger 13 is divided into two units, that is, into the upper heat exchange unit 13a and the lower heat exchange unit 13b. However, the heat source-side heat exchanger 13 may be divided into two or more units.

[0018]

In particular, the heat source-side heat exchanger 13 has a cross-sectional shape of a chamfered rectangle with a large aspect ratio. The heat source-side heat exchanger 13 has a structure in which a single heat exchanger is divided into upper and lower regions to form the upper heat exchange unit 13a and the lower heat exchange unit 13b. Further, the heat source-side heat exchanger 13 is formed of one or two rows of single-row flat tube heat exchangers that are coupled in the thickness direction. Each single-row flat tube heat exchanger includes a flat tube through which the refrigerant flows, and a plurality of plate-like fins into which the flat tube is inserted and that are joined at right angles to the flat tube. This configuration allows brazing or other operations to be performed from both sides of the heat exchanger, thereby improving ease of processing. The heat source-side heat exchanger 13 is not limited to a heat exchanger formed of one or two heat exchanger rows, but may be a heat exchanger formed of two or more heat exchanger rows. [0019]

The accumulator 14 is connected to the suction side of the compressor 11, and separates liquid refrigerant and supply gas refrigerant to the compressor 11. The flow path forming unit 15 ensures circulation of refrigerant along a path such that the refrigerant flows out from the first main pipe 2 into the second main pipe 3, irrespective of switching of flow paths performed by the flow switching unit 12. The flow path forming unit 15 has check valves 15a to 15c. The check valve 15a is located on the pipe between the heat source-side heat exchanger 13 and the first main pipe 2, and permits passage of refrigerant from the heat source-side heat exchanger 13 toward the first main pipe 2. The check valve 15b is located on the pipe between the flow switching unit 12 and the second main pipe 3, and permits passage of refrigerant from the second main pipe 3 toward the flow switching unit 12. The check valve 15c is located on the pipe between the flow switching unit 12 and the first main pipe 2, and permits passage of refrigerant from the flow switching unit 12 toward the second main pipe 3.

[0020]

Further, the heat source unit 10 includes a capacity control valve 41, a heat source-side gas-liquid separator 42, a first branched pipe 43a, a second branched pipe 43b, a third branched pipe 43c, and a flow control device 44. The capacity control valve 41 controls inflow of refrigerant into the upper heat exchange unit 13a and the lower heat exchange unit 13b, to thereby control the capacity of the heat source-side heat exchanger 13. The capacity control valve 41 has an upper control valve 41a connected to the upper heat exchange unit 13a, and a lower control valve 41 b connected to the lower heat exchange unit 13b. The upper control valve 41 a and the lower heat exchange unit 13b each include a solenoid valve. A check valve 41 x is arranged between the capacity control valve 41 and the flow switching unit 12. The check valve 41 x permits the passage of refrigerant from the flow switching unit 12 when a heating flow path is formed, and blocks the passage of refrigerant from the heat source-side gas-liquid separator 42 when a cooling flow path is formed. When the heat source-side heat exchanger 13 is divided into three or more units, the capacity control valve 41 is provided with a number of solenoid valves corresponding to the number of divisions.

[0021]

The heat source-side gas-liquid separator 42 separates the refrigerant flowing in from the relay unit 20 into gas refrigerant and liquid refrigerant. That is, the refrigerant having passed through each of the indoor units 30A and 30B flows into the heat source-side gas-liquid separator 42 via the relay unit. The heat source-side gas-liquid separator 42 is connected to the first branched pipe 43a, the second branched pipe 43b, and the third branched pipe 43c. The first branched pipe 43a allows the liquid refrigerant separated by the heat source-side gas-liquid separator 42 to flow into the capacity control valve 41. The first branched pipe 43a is provided with a check valve 16. The check valve 16 permits the flow of refrigerant through the first branched pipe 43a from the heat source-side gas-liquid separator 42 to the capacity control valve 41.

[0022]

The second branched pipe 43b allows the liquid refrigerant separated in the second heat source-side gas-liquid separator to flow into the lower heat exchange unit 13b. The second branched pipe 43b is provided with the flow control device 44 including an electronic expansion valve. The opening degree of the flow control device 44 is regulated. Consequently, the flow rate of refrigerant flowing into the lower heat exchange unit 13b is regulated.

[0023]

The third branched pipe 43c is connected between the flow switching unit 12 and the accumulator 14, and allows the gas refrigerant separated in the heat sourceside gas-liquid separator 42 to flow into the suction side of the compressor 11. The third branched pipe 43c is provided with an on-off valve 45 to control the inflow of refrigerant from the heat source-side gas-liquid separator 42 to the suction side of the compressor 11.

[0024]

While a cooling flow path is formed such that the heat source-side heat exchanger 13 acts as a condenser, opening of the on-off valve 45 causes the gas refrigerant separated by the heat source-side gas-liquid separator 42 to flow into the accumulator 14 via the third branched pipe 43c. When the on-off valve 45 closes, the refrigerant having flowed in from the relay unit 20 does not flow to the first branched pipe 43a, but flows toward the first branched pipe 43a and the second branched pipe 43b. In contrast, while a heating flow path is formed such that the heat source-side heat exchanger 13 acts as an evaporator, opening of the on-off valve 45 causes the refrigerant flowing to the accumulator 14 from the flow switching unit 12 to flow into the heat source-side gas-liquid separator 42 via the third branched pipe 43c.

[0025]

Further, the heat source unit 10 is provided with a connecting pipe 46 connecting between the flow switching unit 12 and the check valve 15a (second main pipe 3). The connecting pipe 46 is provided with a check valve 47. When a cooling flow path is formed, the refrigerant having flowed out from the heat source-side heat exchanger 13 flows into the accumulator 14 via the connecting pipe 46 and the check valve 47. When a heating flow path is formed, the check valve 47 blocks the flow of refrigerant to the connecting pipe 46.

[0026] [Relay Unit 20]

The relay unit 20 includes a relay unit-side gas-liquid separator 21, a first intermediate heat exchanger 22, a first relay-unit-side flow regulator 23, a second intermediate heat exchanger 24, a second relay-unit-side flow regulator 25, a first distributing unit 26, and a second distributing unit 27. The relay unit-side gas-liquid separator 21 separates the refrigerant flowing in from the second main pipe 3 into gas refrigerant and liquid refrigerant. The relay unit-side gas-liquid separator 21 is connected to a gas-phase pipe 21a to which the gas refrigerant flows, and a liquidphase pipe 21 b to which the liquid refrigerant flows. The gas-phase pipe 21a is connected to the first distributing unit 26, and the liquid-phase pipe 21b is connected to the first intermediate heat exchanger 22.

[0027]

The first intermediate heat exchanger 22 subcools liquid refrigerant and supplies the resulting refrigerant toward the indoor units 30Aand 30B in cooling only operation. The first intermediate heat exchanger 22 performs heat exchange between the refrigerant flowing from the relay unit-side gas-liquid separator 21 to the first relay-unit-side flow regulator 23, and the refrigerant flowing from the second intermediate heat exchanger 24 to the second main pipe 3.

[0028]

The first relay-unit-side flow regulator 23, which includes an electronic expansion valve, is arranged between the first intermediate heat exchanger 22 and the second intermediate heat exchanger 24. The first relay-unit-side flow regulator regulates the flow rate of refrigerant travelling from the first intermediate heat exchanger 22 to the second intermediate heat exchanger 24, and the pressure of the refrigerant. The opening degree of the first relay-unit-side flow regulator 23 is controlled by the controller 60.

[0029]

The second intermediate heat exchanger 24 performs heat exchange between the refrigerant flowing from the first relay-unit-side flow regulator 23 to the second distributing unit 27, and the refrigerant flowing through a first relay-unit-side bypass pipe 28 at a location downstream of the second relay-unit-side flow regulator 25 (the refrigerant having passed through the second relay-unit-side flow regulator 25). The first relay-unit-side bypass pipe 28 connects the second intermediate heat exchanger and the second distributing unit 27 to each other. Part of the refrigerant flowing between the second intermediate heat exchanger 24 and the second distributing unit 27 flows into the second intermediate heat exchanger 24 via the first relay-unit-side bypass pipe 28. The refrigerant having flowed out from the first relay-unit-side bypass pipe 28 via the second intermediate heat exchanger 24 flows into the first intermediate heat exchanger 22. As described above, the first intermediate heat exchanger 22 and the second intermediate heat exchanger 24 subcool liquid refrigerant and supply the resulting refrigerant toward the indoor units 30A and 30B in cooling operation.

[0030]

The second relay-unit-side flow regulator 25 includes, for example, an electronic expansion valve, and regulates the flow rate of refrigerant passing through the first relay-unit-side bypass pipe 28, and the pressure of the refrigerant. The opening degree of the second relay-unit-side flow regulator 25 is controlled by the controller 60.

[0031]

In cooling only operation or cooling main operation, the refrigerant having flowed out from the relay unit-side gas-liquid separator 21 flows into the second distributing unit 27 via the first intermediate heat exchanger 22, the first relay-unit-side flow regulator 23, and the second intermediate heat exchanger 24. Meanwhile, the refrigerant having passed through the second relay-unit-side flow regulator 25 and the first relay-unit-side bypass pipe 28 subcools refrigerant in the second intermediate heat exchanger 24 and the first intermediate heat exchanger 22, and then flows to the second main pipe 3.

[0032]

The first distributing unit 26 and the second distributing unit 27 distribute the refrigerant supplied from the heat source unit 10 to the indoor units 30Aand 30B.

The first distributing unit 26 has an on-off valve 26a for heating and an on-off valve 26b for cooling that are connected to each of the indoor unit 30A and the indoor unit 30B. The on-off valve 26a for heating is connected to the gas-phase pipe 21a, and the on-off valve 26b for cooling is connected to the second main pipe 3. When the indoor units 30A and 30B perform cooling operation, the on-off valve 26b for cooling is opened, so that the refrigerant flows from the indoor units 30A and 30B to the heat source unit 10 via the second main pipe 3. At this time, the on-off valve 26a for heating is closed. When the indoor units 30A and 30B perform heating operation, the on-off valve 26a for heating is opened, so that the refrigerant flows from the gasphase pipe 21a to the indoor units 30A and 30B. At this time, the on-off valve 26b for cooling is closed.

[0033]

There is exemplified the case in which the first distributing unit 26 has the onoff valve 26a for heating and the on-off valve 26b for cooling. Alternatively, for example, a three-away valve may be provided to each of the indoor units 30A and 30B to switch its connection to the second main pipe 3 or the gas-phase pipe 21a. [0034]

The second distributing unit 27 includes a check valve 27a for heating and a check valve 27b for cooling that are connected to each of the indoor unit 30A and the indoor unit 30B. When the indoor units 30A and 30B perform cooling operation, the refrigerant subcooled in the second intermediate heat exchanger 24 flows to the indoor units 30A and 30B via the check valve 27b for cooling. When the indoor units

30A and 30B perform heating operation, the refrigerant flowing out from the indoor units 30A and 30B flows to a second relay-unit-side bypass pipe 29 via the check valve 27a for heating. The second relay-unit-side bypass pipe 29 connects the check valve 27a for heating, the first relay-unit-side flow regulator 23, and the second intermediate heat exchanger 24 to one another. There is exemplified the case in which the second distributing unit 27 includes a plurality of check valves. However, as with the first distributing unit 26, the second distributing unit 27 may include on-off valves.

[0035]

Further, in cooling main operation or heating main operation, the refrigerant having flowed out from the indoor unit 30Aor 30B performing heating via the second distributing unit 27 flows through the second relay-unit-side bypass pipe 29. Part or all of the refrigerant having passed through the second relay-unit-side bypass pipe 29 passes through the second intermediate heat exchanger 24 and the second distributing unit 27, and then flows to the indoor unit 30Aor 30B performing cooling operation. In contrast, in heating only operation, all of the refrigerant having flowed out from the indoor units 30Aand 30B performing heating via the second distributing unit 27 passes through the second relay-unit-side flow regulator 25 and the first relayunit-side bypass pipe 28, and flows to the second main pipe 3.

[0036]

The first distributing unit 26 and the second distributing unit 27 are connected to two indoor units 30A and 30B in the present case, and thus two sets of on-off valves and check valves are placed in the first distributing unit 26. The number of sets of on-off valves and check valves to be placed correspond to the number of indoor units 30Aand 30B being placed.

[0037] [Indoor Units 30A and 30B]

The indoor units 30A and 30B are connected to the relay unit 20 in parallel to each other. Each of the indoor units 30A and 30B has a use-side heat exchanger 31, and a use-side flow regulator 32 connected in series with the use-side heat exchanger 31. In Fig. 1, there is exemplified the case in which each of the indoor units 30A and 30B has a plurality of sets of use-side heat exchangers 31 and useside flow regulators 32 that are connected in parallel. However, each of the indoor units 30A and 30B may only need to have one or more sets of use-side heat exchangers 31 and use-side flow regulators 32.

[0038]

The use-side heat exchanger 31 performs heat exchange between air sent from an indoor air-sending device such as a fan (not shown) and refrigerant supplied from the relay unit 20, and generates heating air or cooling air that is to be supplied to the indoor space. The use-side flow regulator 32 includes a device with an adjustable opening degree, such as an electronic expansion valve. In cooling operation, the use-side flow regulator 32 reduces the pressure of the refrigerant supplied from the relay unit 20 to cause the refrigerant to expand, and supplies the resulting refrigerant to the use-side heat exchanger 31. The opening degree of the use-side flow regulator 32 is controlled by the controller 60.

[0039] [Controller 60]

The operation of the air-conditioning apparatus 1 described above is controlled by the controller 60. The controller 60 includes a microcomputer or a computer.

The controller 60 performs processes such as a determination process on the basis of, for example, various sensors arranged inside and outside the air-conditioning apparatus, or signals transmitted from various component devices (units) of the airconditioning apparatus 1. The controller 60 causes various devices to operate on the basis of the result of the determination process, to thereby control the overall operation of the air-conditioning apparatus 1, including operations of components such as the heat source unit 10, the relay unit 20, and the indoor units 30Aand 30B.

In Fig. 1, there is exemplified the case in which a single separate controller 60 is arranged independently from components such as the heat source unit 10, but the present invention is not limited to the example case. For example, the controller 60 may be built in the heat source unit 10, the relay unit 20, or each of the indoor units

30A and 30B, or the function of the controller 60 may be distributed among various devices.

[0040]

The controller 60 controls the overall operation of the air-conditioning apparatus 1 on the basis of information obtained by various sensors. That is, the heat source unit 10 has a compressor-outlet-temperature detection unit 51 that measures the temperature of refrigerant discharged from the compressor and includes a thermistor or other devices, a high-pressure detection unit 52 arranged between the compressor 11 and the flow switching unit 12 to measure the pressure of refrigerant, an outside-air-temperature detection unit 53 arranged in the heat source unit 10 to measure outside air, and a suction-side pressure detection unit 54 that measures the suction-side pressure (low pressure) of refrigerant flowing into the accumulator 14 (the suction side of the compressor 11). The controller 60 controls various devices on the basis of information from various sensors as described later. [0041]

The relay unit 20 includes a first relay-unit-side pressure sensor 55, a second relay-unit-side pressure sensor 56, a temperature detection unit 57, and an intermediate temperature detection unit 58. The first relay-unit-side pressure sensor 55 measures the pressure of refrigerant flowing between the first intermediate heat exchanger 22 and the first relay-unit-side flow regulator 23. The second relay-unitside pressure sensor 56 measures the pressure of refrigerant flowing between the first relay-unit-side flow regulator 23 and the second intermediate heat exchanger 24. The temperature detection unit 57 measures the temperature of refrigerant flowing from the first intermediate heat exchanger 22 to the first main pipe 2. The intermediate temperature detection unit 58 measures the intermediate temperature of the refrigerant at the outlet of the second intermediate heat exchanger 24, that is, the refrigerant flowing downstream of the second intermediate heat exchanger 24, and is formed of, for example, a thermistor. The controller 60 performs a control such that the difference between a first relay-unit-side pressure measured by the first relay-unitside pressure sensor 55 and a second relay-unit-side pressure measured by the second relay-unit-side pressure sensor 56 is equal to a target relay-unit-side pressure.

[0042]

Various sensors such as the compressor-outlet-temperature detection unit 51, the high-pressure detection unit 52, the outside-air-temperature detection unit 53, the suction-side pressure detection unit 54, the first relay-unit-side pressure sensor 55, the second relay-unit-side pressure sensor 56, the temperature detection unit 57, and the intermediate temperature detection unit 58 may directly transmit their measurements to the controller 60, or may accumulate their measurements for a given period of time and then transmit the accumulated measurements to the controller 60 at predetermined intervals of time.

[0043]

As described above, the air-conditioning apparatus 1 is capable of performing one of four modes of operation, including a cooling only operation, a heating only operation, and a simultaneous cooling and heating operation (including a cooling main operation and a heating main operation), by the flow switching unit 12 and the opening and closing action of the first distributing unit 26. The heat source-side heat exchanger 13 acts as a condenser in cooling only operation and in cooling main operation, and acts as an evaporator in heating only operation and in heating main operation. Description is made of an exemplary operation of the air-conditioning apparatus 1 and the flow of refrigerant in simultaneous cooling and heating operation (cooling main operation and heating main operation).

[0044] [Cooling Main Operation]

Fig. 2 is a refrigerant circuit diagram for illustrating the flow of refrigerant when a simultaneous cooling and heating operation that is mainly cooling is performed in the air-conditioning apparatus illustrated in Fig. 1. In Fig. 2, there is exemplified the case in which a cooling main operation is performed, which is a type of simultaneous cooling and heating operation with the indoor unit 30A performing heating operation and the indoor unit 30B performing cooling operation and in which the cooling load is greater than the heating load. In Fig. 2, the flow of refrigerant is indicated by the arrows. Of the check valves and on-off valves, portions through which refrigerant does not pass are indicated by the solid regions, and portions through which refrigerant passes are indicated by the hollow regions. In the case of the cooling main operation illustrated in Fig. 2, the controller 60 opens the on-off valve 26a for heating on the indoor unit 30A side that performs heating operation, and closes the on-off valve 26b for cooling on the indoor unit 30A side. Further, the controller 60 closes the on-off valve 26a for heating on the indoor unit 30B side that performs cooling operation, and opens the on-off valve 26b for cooling on the indoor unit 30B side.

[0045]

High-temperature high-pressure gas refrigerant compressed and discharged by the compressor 11 flows into the heat source-side heat exchanger 13 via the flow switching unit 12. The high-temperature high-pressure gas refrigerant exchanges heat with a heat source medium such as water in the heat source-side heat exchanger 13, and through this heat exchange, the high-temperature high-pressure gas refrigerant turns into high-temperature high-pressure gas refrigerant that is in a two-phase gas-liquid state. The high-temperature high-pressure gas refrigerant in two-phase gas-liquid state passes through the second main pipe 3 via the check valve 15a, and is supplied to the relay unit-side gas-liquid separator 21 of the relay unit 20. The first main pipe 2 is at a low pressure and the second main pipe 3 is at a high pressure. Consequently, due to the pressure difference between the two pipes, the refrigerant passes to the check valve 15a and the check valve 15b, but does not pass to the check valve 15c.

[0046]

The high-temperature high-pressure gas refrigerant in two-phase gas-liquid state is separated in the relay unit-side gas-liquid separator 21 into gaseous refrigerant and liquid refrigerant, and the separated gaseous refrigerant flows into the first distributing unit 26. The gaseous refrigerant flowing into the first distributing unit 26 is supplied to, via the on-off valve 26a for heating, the indoor unit 30B that is being set to perform heating operation. In the use-side heat exchanger 31 of the indoor unit 30B, heating is performed as the refrigerant exchanges heat with a use-side medium, such as air, and the supplied gaseous refrigerant is condensed and liquefied. Then, the liquid refrigerant having been condensed and liquefied in the use-side heat exchanger 31 has its pressure reduced by the use-side flow regulator 32, and turns into refrigerant at an intermediate pressure that lies between high and low pressures. The refrigerant at the intermediate pressure flows into the second distributing unit 27. The refrigerant having flowed into the second distributing unit 27 passes toward the check valve 27a for heating, and flows into the second intermediate heat exchanger 24 via the second relay bypass pipe.

[0047]

Meanwhile, the liquid refrigerant separated in the relay unit-side gas-liquid separator 21 passes through the first intermediate heat exchanger 22 and the first relay-unit-side flow regulator 23, and is merged with the refrigerant having flowed out from the indoor unit 30A. The merged refrigerant flows into the second distributing unit 27, and flows into the indoor unit 30B from the check valve 27b for cooling corresponding to the indoor unit 30B. The liquid refrigerant having flowed into the indoor unit 30B has its pressure reduced to a low pressure by the use-side flow regulator 32, and the refrigerant in the low-pressure state is supplied to the use-side heat exchanger 31 of the indoor unit 30A. The liquid refrigerant supplied to the useside heat exchanger 31 exchanges heat with a use-side medium, such as water, causing the liquid refrigerant to evaporate and gasify.

[0048]

The gasified refrigerant flows into the first distributing unit 26 via the second branch pipes 5, and then travels from the on-off valve 26b for cooling into the heat source unit 10 via the second main pipe 3. The gas refrigerant flows into the check valve 15b side that is at a lower pressure than the check valve 16, flows into the accumulator 14 via the flow switching unit 12, and is sucked into the compressor 11. Through the above operation, a refrigeration cycle is formed, and cooling main operation is performed.

[0049]

Description is made below of the flow of refrigerant in the first intermediate heat exchanger 22 and the second intermediate heat exchanger 24. The refrigerant branched to the first relay-unit-side bypass pipe 28 from the second intermediate heat exchanger 24 passes through the second relay-unit-side flow regulator 25. Then, in the second intermediate heat exchanger 24 and the first intermediate heat exchanger 22, this refrigerant subcools the refrigerant flowing from the relay unit-side gas-liquid separator 21, and flows to the first main pipe 2. At this time, the liquid refrigerant having flowed into the second relay-unit-side flow regulator 25 has its pressure reduced to a low pressure, causing its evaporating temperature to decrease. The liquid refrigerant having a decreased evaporating temperature flows into the second intermediate heat exchanger 24 via the first relay-unit-side bypass pipe 28. In the second intermediate heat exchanger 24, this liquid refrigerant turns into refrigerant in two-phase gas-liquid state in heat exchange with the liquid refrigerant supplied from the first relay-unit-side flow regulator 23. The two-phase gas-liquid refrigerant then flows into the first intermediate heat exchanger 22.

[0050]

In the first intermediate heat exchanger 22, this refrigerant turns into gas refrigerant in heat exchange with the high-temperature high-pressure gas liquid refrigerant supplied from the relay unit-side gas-liquid separator 21. The gas refrigerant then flows into the first main pipe 2. The opening degree of the second relay-unit-side flow regulator 25 increases, and the flow rate of refrigerant through the first relay-unit-side bypass pipe 28 (refrigerant used for subcooling) increases.

Then, the amount of refrigerant that does not undergo evaporation increases excessively. Consequently, the controller 60 controls the degree of refrigerant superheat at the outlet of the first relay-unit-side flow regulator 23 by the second relay-unit-side flow regulator 25, such that the difference between the pressure measured by the first relay-unit-side pressure sensor 55 and the pressure measured by the second relay-unit-side pressure sensor 56 is equal to a predetermined value. As described above, the subcooled refrigerant flows toward the second distributing unit 27 to decrease enthalpy at the inlet side of refrigerant (the first branch pipes 4 in this case), thereby being capable of increasing the amount of heat exchange with air in the use-side heat exchangers 31.

[0051] [Heating Main Operation]

Fig. 3 is a refrigerant circuit diagram for illustrating the flow of refrigerant when a simultaneous cooling and heating operation that is mainly heating is performed in the air-conditioning apparatus illustrated in Fig. 1. In Fig. 3, there is exemplified the case in which a cooling main operation is performed, which is a type of simultaneous cooling and heating operation with the indoor unit 30A performing heating operation and the indoor unit 30B performing cooling operation and in which the cooling load is greater than the heating load. In Fig. 2, of the check valves and on-off valves, portions through which refrigerant does not pass are indicated by the solid regions, and portions through which refrigerant passes are indicated by the hollow regions.

In the case of the cooling main operation illustrated in Fig. 2, the controller 60 opens the on-off valve 26a for heating on the indoor unit 30A side, and closes the on-off valve 26b for cooling on the indoor unit 30A side. Further, the controller 60 closes the on-off valve 26a for heating on the indoor unit 30B side, and opens the on-off valve 26b for cooling on the indoor unit 30B side. In Fig. 3, the upper control valve 41 a of the capacity control valve 41 is closed and the lower control valve 41 b of the capacity control valve 41 is opened so that refrigerant does not pass to the upper heat exchange unit 13a.

[0052]

First, the high-temperature high-pressure gas refrigerant compressed and discharged by the compressor 11 flows through the flow switching unit 12 and the check valve 15c, passes through the second main pipe 3, and is supplied to the relay unit-side gas-liquid separator 21 of the relay unit 20. At this time, the first main pipe 2 is at a low pressure, and the second main pipe 3 is at a high pressure. Consequently, due to the pressure difference between the two pipes, the refrigerant passes to the check valve 15c, but does not pass to the check valve 15a and the check valve 15b.

[0053]

The high-temperature high-pressure gas refrigerant having flowed into the relay unit-side gas-liquid separator 21 is supplied to the first distributing unit 26 via the gasphase pipe 21a. The gas refrigerant supplied to the first distributing unit 26 flows into the on-off valve 26a for heating on the indoor unit 30A side, flows through the second branch pipe 5, and is supplied to the indoor unit 30Athat is being set to perform heating operation.

[0054]

In the indoor unit 30A, the refrigerant exchanges heat with a use-side medium, such as air, in the use-side heat exchanger 31, and thus the supplied gas refrigerant is condensed and liquefied. At this time, the opening degree of the use-side flow regulator 32 is controlled on the basis of the degree of subcooling at the outlet of the use-side heat exchanger 31. The liquid refrigerant having been condensed and liquefied in the use-side heat exchanger 31 has its pressure reduced by the use-side flow regulator 32, and turns into liquid refrigerant at an intermediate pressure that lies between high and low pressures. The liquid refrigerant at the intermediate pressure is then flowed into the second distributing unit 27.

[0055]

The liquid refrigerant having flowed into the second distributing unit 27 passes through the second relay-unit-side bypass pipe 29 and is merged with the liquid refrigerant having been separated in the relay unit-side gas-liquid separator 21.

Then, the liquid refrigerant passes through the second intermediate heat exchanger 24, and flows into the second distributing unit 27. At this time, after passing through the second intermediate heat exchanger 24, the liquid refrigerant is branched to the first relay-unit-side bypass pipe 28, and flows into the second intermediate heat exchanger 24 again. In the second intermediate heat exchanger 24, heat is exchanged between the liquid refrigerant at intermediate pressure and the liquid refrigerant at low pressure. At this time, the liquid refrigerant at low pressure has a low evaporating temperature, and thus the liquid refrigerant turns into gas refrigerant that flows into the first main pipe 2.

[0056]

The liquid refrigerant at intermediate pressure having flowed into the second distributing unit 27 flows into the indoor unit 30B via the check valve 27b for cooling connected to the indoor unit 30B. The liquid refrigerant having flowed into the indoor unit 30B has its pressure reduced to a low pressure by the use-side flow regulator 32, which is controlled corresponding to the degree of superheat at the outlet of the useside heat exchanger 31 of the indoor unit 30B. This causes the evaporating temperature of the liquid refrigerant to decrease, and the liquid refrigerant in this state is supplied to the use-side heat exchanger 31. In the use-side heat exchanger 31, the supplied liquid refrigerant having a lower evaporating temperature exchanges heat with a use-side medium, such as air, causing the liquid refrigerant to evaporate and gasify. The refrigerant having been gasified passes through the first main pipe 2, and flows into the first distributing unit 26. The gas refrigerant having flowed into the first distributing unit 26 passes through the on-off valve 26b for cooling connected to the indoor unit 30B, and flows into the first main pipe 2.

[0057]

The gas refrigerant having flowed into the first main pipe 2 flows into the heat source-side gas-liquid separator 42 that is at a lower pressure than the check valve 15b. Then, the gas refrigerant is branched in the heat source-side gas-liquid separator 42 to the first branched pipe 43a, the second branched pipe 43b, and the third branched pipe 43c. The refrigerant branched to the first branched pipe 43a passes through the check valve 16 and the lower control valve 41 b, and flows into the lower heat exchange unit 13b for heat exchange. The refrigerant branched to the second branched pipe 43b flows into the lower heat exchange unit 13b through the flow control device 44 for heat exchange. At this time, when the on-off valve 45 is open, the gas refrigerant branched to the third branched pipe 43c flows into the accumulator 14. After undergoing heat exchange, the refrigerant flows into the accumulator 14 via the check valve 47 and the flow switching unit 12. The refrigerant is then sucked into the compressor 11 via the accumulator 14. Through the above operation, a refrigeration cycle is formed, and heating main operation is performed.

[0058]

As the operation modes of the air-conditioning apparatus 1, there are exemplified the cooling main operation illustrated in Fig. 2 and the heating main operation illustrated in Fig. 3. However, the air-conditioning apparatus 1 is also capable of performing a cooling only operation in which all of the indoor units 30Aand 30B perform cooling and a heating only operation in which all of the indoor unit 30B perform heating. For the cooling only operation, the flow path of refrigerant in the heat source unit 10 is the same as the flow path of refrigerant illustrated in Fig. 2. However, in the relay unit 20, refrigerant does not flow from the indoor unit 30A that performs heating toward the indoor unit 30B that performs cooling as is the case with Fig. 2. Rather, the liquid refrigerant flowing from the relay unit-side gas-liquid separator 21 flows to both the indoor units 30A and 30B. For the heating only operation, the flow path of refrigerant in the heat source unit 10 is the same as the flow path of refrigerant illustrated in Fig. 3. However, in the relay unit 20, refrigerant does not flow from the indoor unit 30A that performs heating toward the indoor unit 30B that performs cooling as is the case with Fig. 3. Rather, the gas refrigerant flowing from the relay unit-side gas-liquid separator 21 flows to both the indoor units 30A and 30B.

[0059]

The controller 60 has the function of controlling operations of the capacity control valve 41, the flow control device 44, and the on-off valve 45 of the heat source unit 10 corresponding to the mode of operation. Specifically, in heating only operation, the controller 60 controls the opening degree of the flow control device 44 such that the ratio between the flow rate of refrigerant into the upper heat exchange unit 13a and the flow rate of refrigerant into the lower heat exchange unit 13b is equal to a set ratio. For example, the ratio between the flow rate of refrigerant into the upper heat exchange unit 13a and the flow rate of refrigerant into the lower heat exchange unit 13b is set at 8.5 to 9.5:5. At this time, a set opening degree that provides the set ratio is stored in the controller 60 in advance. When heating only operation is to be performed, the controller 60 fixes the opening degree of the flow control device 44 to the set opening degree. This allows high heating performance to be maintained for the air-conditioning apparatus 1 as a whole.

[0060]

Fig. 4 is a graph for showing the relationship between a flow regulator and heating performance when heating only operation is performed in the air-conditioning apparatus illustrated in Fig. 1. As shown in Fig. 4, when the opening degree of the flow control device 44 is set to a predetermined opening degree VPp or greater during heating only operation in which the heat source-side heat exchanger 13 acts as an evaporator, the flow rate of refrigerant into the lower heat exchange unit 13b increases. This leads to insufficient amount of heat exchange in the lower heat exchange unit 13b, causing liquid backflow to the accumulator 14. As a result, the pressure on the suction side ofthe compressor 11 decreases, resulting in decreased heating performance. Consequently, during heating only operation, the opening degree of the flow control device 44 is fixed to a set opening degree such that the flow rate of refrigerant into the lower heat exchange unit 13b satisfies the set ratio described above. This restricts the flow rate of refrigerant into the lower heat exchange unit 13b, with the result that the flow rate of refrigerant into the upper heat exchange unit 13a increases. This enables effective distribution of refrigerant to the upper heat exchange unit 13a and the lower heat exchange unit 13b.

[0061]

Further, the controller 60 has a function such that during simultaneous cooling and heating operation illustrated in each of Fig. 2 and Fig. 3, the controller 60 controls the opening degree of the flow control device 44 on the basis of the ratio between cooling and heating operations performed in a plurality of indoor units, the outside air temperature measured by the outside-air-temperature detection unit 53, and the suction-side pressure measured by the suction-side pressure detection unit 54.

[0062]

Fig. 5 is a flowchart for illustrating exemplary operation of a flow control device during simultaneous cooling and heating operation of the air-conditioning apparatus illustrated in each of Fig. 2 and Fig. 3. Specifically, as illustrated in Fig. 5, the controller 60 controls the opening degree of the flow control device 44 such that at the start of simultaneous cooling and heating operation, the opening degree of the flow control device 44 is fixed to a preset initial opening degree (Step ST 1). Then, the controller 60 determines whether the heating load is equal to or greater than the cooling load, whether the outside air temperature measured by the outside-airtemperature detection unit 53 is lower than an outside air temperature threshold (for example, 5 degrees Celsius), and whether the suction-side pressure measured by the suction-side pressure detection unit 54 is less than a pressure threshold (for example, 0.7 MPa) (Step ST2 to Step ST4). Further, the controller 60 determines whether the intermediate temperature measured by the intermediate temperature detection unit 58 is less than an intermediate temperature threshold (for example, 4 degrees Celsius) (Step ST5). Step ST2 to Step ST5 may not necessarily be performed in the order illustrated in Fig. 5, but may be performed in any order.

[0063]

When all the conditions in Step ST2 to Step ST5 are satisfied, the evaporating temperature of the indoor unit 30B that is performing cooling operation becomes equal to or less than a predetermined value, making it impossible to continue the cooling operation. Consequently, the controller 60 cancels the fixing of the opening degree of each flow control device 44, and controls such that the opening degree of the flow control device 44 is adjustable. At this time, the controller 60 regulates the flow control device 44 such that the evaporating temperature of the indoor unit 30B that is performing cooling does not become equal to or less than a predetermined value. In this case, the evaporating temperature is detected by an evaporating temperature detection unit 59 that detects the temperature of refrigerant flowing through each of the use-side heat exchangers 31. As a result, the simultaneous cooling and heating operation of the indoor units 30Aand 30B can be maintained. That is, when cooling main operation (heating load < cooling load) is performed, the opening degree of the flow control device 44 is fixed to a set opening degree, and when heating main operation (heating load > cooling load) is performed, the opening degree of the flow control device 44 is controlled to be adjustable when the abovementioned conditions are satisfied.

[0064]

Further, the controller 60 illustrated in Fig. 1 to Fig. 3 has a function such that in cooling only operation, the controller 60 controls the operation of the on-off valve 45 on the basis of the capacity of the heat source-side heat exchanger 13 and the degree of superheat at the compressor outlet. Specifically, the controller 60 calculates the degree of superheat at the compressor outlet on the basis of the compressor outlet temperature measured by the compressor-outlet-temperature detection unit 51, and the high pressure measured by the high-pressure detection unit 52. The controller 60 opens the on-off valve 45 when the lower control valve 41 b of the capacity control valve 41 is open and the degree of superheat at the compressor outlet, TdSH, is equal to or greater than a set degree of outlet superheat, SHref (for example, 20 degrees Celsius).

[0065]

Fig. 6 is a flowchart for illustrating exemplary operation of an on-off valve when the air-conditioning apparatus illustrated in Fig. 1 is performing cooling. It is assumed that the on-off valve 45 is closed at the start of cooling only operation. As illustrated in Fig. 6, at the start of cooling only operation, the controller 60 determines whether the lower control valve 41 b is closed (Step ST11). When the lower control valve 41 b is closed (YES in Step ST11), the controller 60 controls the flow control device 44 such that the opening degree of the flow control device 44 is fixed to a predetermined value (Step ST12). This causes refrigerant to flow into the lower heat exchange unit 13b from the first branched pipe at a predetermined flow rate, and the refrigerant existing in the lower heat exchange unit 13b is returned to the accumulator 14.

[0066]

When the lower control valve 41b is open (NO in Step ST11), it is determined whether the degree of outlet superheat TdSH of the compressor 11 is equal to or greater than the set degree of outlet superheat SHref (Step ST 14). When the degree of outlet superheat TdSH is equal to or greater than the set degree of outlet superheat SHref (YES in Step STM), the on-off valve 45 is opened (Step ST15). Then, a portion of the refrigerant flowing from the relay unit 20 toward the accumulator 14 flows into the lower heat exchange unit 13b via the third branched pipe 43c, the heat source-side gas-liquid separator 42, the second branched pipe 43b, and the flow control device 44. As a result, low pressure loss due to piping can be reduced. This causes the evaporating temperature of the indoor units 30A and 30B (evaporators) to rise, thus allowing high cooling performance to be maintained. When the degree of outlet superheat TdSH is less than the set degree of outlet superheat SHref, the on-off valve 45 is closed (Step ST16). As a result, even when gas refrigerant flows into the lower heat exchange unit 13b at the time of opening of the lower control valve 41 b, liquid expansion of the refrigerant is prevented.

[0067]

According to the above-mentioned embodiment, the heat source-side heat exchanger 13 is divided into a plurality of units including the upper heat exchange unit 13a and the lower heat exchange unit 13b. The flow control device 44 is arranged to enable regulation of the flow rate of refrigerant into the lower heat exchange unit 13b. The opening degree of the flow control device 44 is decreased to cause more refrigerant to flow into the upper heat exchange unit 13a.

[0068]

For example, when the heat exchanger in which heat is exchanged with air is of a structure that blows out air upward (so-called top-flow structure), the velocity of air in the upper heat exchange unit 13a is greater than the velocity of air in the lower heat exchange unit 13b. Consequently, decrease in opening degree of the flow control device 44 causes the flow rate of refrigerant into the lower heat exchange unit 13b to be restricted. This in turn results in increased flow rate of refrigerant into the upper heat exchange unit 13a. In this way, refrigerant is caused to flow into each of the upper heat exchange unit 13a and the lower heat exchange unit 13b at an appropriate flow rate corresponding to the velocity of air. This enables uniform heat exchange in the heat source-side heat exchanger 13, allowing for improved performance of the heat source-side heat exchanger 13.

[0069]

In particular, the flow control device 44 is connected not to the upper heat exchange unit 13a, but to the lower heat exchange unit 13b to ensure that the flow rate of refrigerant into the upper heat exchange unit 13a is reliably increased. That is, under a state in which the flow control device 44 is connected to the upper heat exchange unit 13a, refrigerant tends to move downward due to gravity. Thus, although it may be possible to reduce the flow rate of refrigerant into the upper heat exchange unit 13a by decreasing the opening degree of the flow control device 44, it is difficult to increase the flow rate of refrigerant into the upper heat exchange unit 13a by increasing the opening degree of the flow control device 44. This tendency becomes particularly pronounced when a heating flow path that causes the heat source-side heat exchanger 13 to act as an evaporator is formed, because in this case liquid refrigerant is caused to flow into the heat source-side heat exchanger 13. Consequently, connection of the flow control device 44 to the upper heat exchange unit 13a ensures that the flow rate of refrigerant into the upper heat exchange unit 13a is reliably increased by decreasing the opening degree of the flow control device 44.

[0070]

That is, with a heat exchanger employing a flat tube, the channel crosssectional area of the heat transfer tubes is generally smaller than that of a circular tube heat exchanger. This leads to increased flow velocity inside the heat transfer tube in comparison to a circular tube heat exchanger, with an associated increase in pressure loss. An increase in pressure loss causes a decrease in the suction density of the compressor, leading to degradation in performance and efficiency. Thus, with the heat exchanger employing a flat tube, the number of heat exchanger passes is required to be increased.

[0071]

When a heat exchanger has a multi-row construction to increase heat transfer area under the constraint of limited unit space, pressure loss decreases when a product length necessary for the heat exchanger is provided. Thus, it is desirable to minimize the product length of heat transfer tubes. One way to achieve this would be to connect lead pipes from between heat exchanger rows. However, use of lead pipes leads to more complex pass geometry required to prevent interference between the lead pipes. This causes, for example, a problem that may not be addressed by automation due to constraints on facilities or equipment, such as brazing to be performed in situations such as when the size of the header pipe connected to the lead pipes becomes larger than the size in the depth direction of the heat exchanger. This results in degraded production efficiency of heat exchangers as well as increased cost.

[0072]

Further, under a state in which the heat source-side heat exchanger has a configuration such that flat tubes arranged side by side in the vertical direction are connected at one end to a first header collection pipe, and connected at the other end to a second header collection pipe 70, to reduce the difference in refrigerant flow rate between a plurality of heat exchange units when the heat exchanger acts as a condenser, only refrigerant supplied to some of the heat exchange units is caused to flow into each communication space inside the second header collection pipe.

Further, to reduce pressure loss in the evaporator, it would be conceivable to allow the direction of flow inside the second heat tube to be changed only once.

[0073]

However, when the heat source-side heat exchanger acts as a condenser, refrigerant flows into a plurality of spaces, resulting in decreased area to be filled with liquid refrigerant. When the amount of refrigerant is small, the influence of the header becomes dominant. Consequently, smooth flow of refrigerant is impeded, and performance of the heat exchanger is degraded. Further, the above-mentioned configuration requires communication spaces defined by a plurality of partition plates that partition the heat collection pipe of the flat tube heat exchanger, with an associated increase in the number of pipes to be connected. Consequently, routing of pipes becomes difficult, and structural complexity is also increased. Further, an associated increase in the number of brazed joints also leads to degraded productivity and increased cost.

[0074]

In contrast, the presence of the flow control device 44 connected to the lower heat exchange unit 13b as in the above-mentioned embodiment enables effective distribution of refrigerant to the upper heat exchange unit 13a and the lower heat exchange unit 13b, without adding complexity to the structure of the heat source-side heat exchanger as is the case with related art. This allows for improved productivity and reduced cost.

[0075]

Further, the controller 60 controls the operation of the flow control device 44 corresponding to each operation mode. As a result, even when cooling operation or heating operation is performed in a plurality of use-side heat exchangers 31 during simultaneous cooling and heating operation, stable control can be achieved at low cost without degrading performance. Thus, both comfort and productivity can be maintained at the same time.

[0076]

Further, when the controller 60 controls the opening degree of the flow control device 44 such that the flow rate of refrigerant into the upper heat exchange unit 13a and the flow rate of refrigerant into the lower heat exchange unit 13b have a set ratio during heating operation, it is possible to restrict the flow rate of refrigerant into the lower heat exchange unit 13b and increase the flow rate of refrigerant into the upper heat exchange unit 13a. This allows for effective distribution of refrigerant.

[0077]

As illustrated in Fig. 5, the controller 60 controls the opening degree of the flow control device 44 on the basis of the ratio between cooling and heating operations during simultaneous cooling and heating operation of the indoor units 30A and 30B, outside air temperature, and suction-side pressure. Further, after the fixing of the opening degree of the flow control device 44 is cancelled, the controller 60 controls the opening degree of the flow control device 44 such that the evaporating temperature of the use-side heat exchanger 31 is equal to or higher than a set evaporating temperature. This ensures that the evaporating temperature of the indoor unit 30B that is performing cooling during simultaneous cooling and heating operation does not become equal to or lower than a predetermined value, thus preventing decreases in cooling capacity.

[0078]

Further, as illustrated in Fig. 6, when the controller 60 controls the operation of the on-off valve 45 on the basis of the capacity of the heat source-side heat exchanger 13 and the degree of outlet superheat TdSH during cooling operation, the controller 60 directs refrigerant to each of the upper heat exchange unit 13a and the lower heat exchange unit 13b at an appropriate flow rate corresponding to the velocity of air. This enables uniform heat exchange in the heat source-side heat exchanger 13, allowing for improved performance of the heat source-side heat exchanger 13. [0079]

The present invention is not limited to the above-mentioned embodiment, but capable of various modifications. For example, description is made of one example in a case in which there is a single heat source unit 10 and there are two indoor units 30A and 30B. However, the present invention is not limited to the configuration.

For example, there may be two or more indoor units. Further, for example, there may be a plurality of heat source units 10, or there may be a plurality of relay units 20. [0080]

Further, in Fig. 4, there is exemplified the case in which the opening degree of the flow control device 44 is fixed to a set opening degree. However, the opening degree may be controlled to be adjustable corresponding to the velocity of air in each of the upper heat exchange unit 13a and the lower heat exchange unit 13b. This may be accomplished by the following configuration, for example. An upper temperature sensor and a lower temperature sensor are provided to respectively measure the temperature of refrigerant flowing through the upper heat exchange unit 13a and the temperature of refrigerant flowing through the lower heat exchange unit 13b, and on the basis of the temperature measured by each of the upper and lower temperature sensors, the controller 60 detects the corresponding air velocity (amount of heat exchange), to thereby control the opening degree of the flow control device 44.

Reference Signs List [0081] air-conditioning apparatus 2 first main pipe 3 second main pipe 4 first branch pipe 5 second branch pipe 10 heat source unit 11 compressor 12 flow switching unit 13 heat source-side heat exchanger 13a upper heat exchange unitl 3b lower heat exchange unit 14 accumulator 15 flow path forming unit 15a, 15b, 15c, 16 checkvalve20 relay unit 21 relay unitside gas-liquid separator 21a gas-phase pipe 21b liquid-phase pipe 22 first intermediate heat exchanger 23 second relay-unit-side flow regulator 24 second intermediate heat exchanger 25 second relay-unit-side flow regulator 26 first distributing unit 26a on-off valve for heating 26b on-off valve for cooling 27 second distributing unit 27a check valve for heating 27b check valve for cooling 28 first relay-unit-side bypass pipe 29 second relayunit-side bypass pipe 30A, 30B indoor unit 31 use-side heat exchanger 32 use-side flow regulator 41 capacity control valve 41a upper control valve

41b lower control valve 41 x checkvalve 42 heat source-side gas-liquid separator 43a first branched pipe 43b second branched pipe 43c third branched pipe 44 flow control device 45 on-off valve 46 connecting pipe checkvalve 51 compressor-outlet-temperature detection unit 52 high-pressure detection unit 53 outside-air-temperature detection unit 54 suction-side pressure detection unit 55 first relay-unit-side pressure sensor 56 57 temperature detection unit 58 59 evaporating temperature detection second relay-unit-side pressure sensor intermediate temperature detection unit unit 60 controller outlet superheat

VPp

SHref set degree of outlet superheatTdSH degree of predetermined opening degree

Claims

CLAIMS [Claim 1]

An air-conditioning apparatus, comprising:

a heat source unit including a compressor configured to compress and discharge refrigerant and a heat source-side heat exchanger configured to perform heat exchange between the refrigerant discharged from the compressor and a heat source medium;

a plurality of indoor units each including a use-side heat exchanger configured to perform heat exchange between refrigerant and a use-side medium and a heat source-side flow regulator connected to the use-side heat exchanger; and a relay unit connected between the heat source unit and the plurality of indoor units by refrigerant pipes, and configured to distribute refrigerant having flowed out from the heat source-side heat exchanger to the plurality of indoor units, the heat source-side heat exchanger including an upper heat exchange unit and a lower heat exchange unit, the upper heat exchange unit and the lower heat exchange unit being connected to the compressor in parallel to each other and arrayed in a vertical direction, the heat source unit including a capacity control valve configured to control a capacity of the heat source-side heat exchanger by controlling inflow of refrigerant to the upper heat exchange unit and the lower heat exchange unit, a heat source-side gas-liquid separator configured to separate refrigerant flowing in from the relay unit into gas refrigerant and liquid refrigerant, a first branched pipe configured to allow refrigerant having flowed into the heat source-side gas-liquid separator to flow into the capacity control valve, a second branched pipe configured to allow refrigerant having flowed into the heat source-side gas-liquid separator to flow into the lower heat exchange unit, and a flow control device arranged in the second branched pipe, and configured to regulate a flow rate of refrigerant flowing into the lower heat exchange unit via the second branched pipe.
[Claim 2]

The air-conditioning apparatus of claim 1, further comprising a controller configured to control operations of the heat source unit and the relay unit to perform a simultaneous cooling and heating operation in which a cooling operation and a heating operation are performed simultaneously, wherein the controller is configured to control an opening degree of the flow control device corresponding to an operation mode.
[Claim 3]

The air-conditioning apparatus of claim 2, wherein the controller is configured to control the opening degree of the flow control device such that a flow rate of refrigerant into the upper heat exchange unit and a flow rate of refrigerant into the lower heat exchange unit during the heating operation have a set ratio.
[Claim 4]

The air-conditioning apparatus of claim 2 or 3, further comprising: an outside-air-temperature detection unit arranged in the heat source unit, and configured to measure an outside air temperature; and a pressure detection unit arranged on a suction side of the compressor, and configured to measure a suction-side pressure of refrigerant flowing to the suction side of the compressor, wherein the controller is configured to control the opening degree of the flow control device on a basis of a ratio between the cooling operation and the heating operation during the simultaneous cooling and heating operation of the plurality of indoor units, the outside air temperature measured by the outside-air-temperature detection unit, and the suction-side pressure measured by the pressure detection unit.
[Claim 5]

The air-conditioning apparatus of claim 4, wherein the controller is configured to fix the opening degree of the flow control device to a set opening degree at start of the simultaneous cooling and heating operation, and, when a heating load is greater than a cooling load, the outside air temperature is lower than an outside air temperature threshold, and the suction-side pressure is less than a pressure threshold, the controller is configured to cancel fixing of the opening degree of the flow control device, and control such that the opening degree of the flow control device is adjustable.
[Claim 6]

The air-conditioning apparatus of claim 5, wherein, when the fixing of the opening degree of the flow control device is cancelled, the controller is configured to control the opening degree of the flow control device such that an evaporating temperature of the use-side heat exchanger is equal to or higher than a set evaporating temperature.
[Claim 7]

The air-conditioning apparatus of any one of claims 1 to 6, wherein the heat source unit further includes a third branched pipe configured to allow the gas refrigerant having been separated by the heat source-side gas-liquid separator to flow into a suction side of the compressor, and an on-off valve arranged in the third branched pipe, and configured to control inflow of the gas refrigerant from the heat source-side gas-liquid separator to the suction side of the compressor.
[Claim 8]

The air-conditioning apparatus of claim 7, further comprising a controller configured to control an opening and closing operation of the on-off valve during a cooling operation on a basis of the capacity of the heat source-side heat exchanger

5 and a degree of compressor outlet superheat.
[Claim 9]

The air-conditioning apparatus of claim 8, wherein the controller for controlling the opening and closing operation of the on-off valve is configured to open the on-off

10 valve when a control valve of the capacity control valve that corresponds to the lower heat exchange unit is open, and when the degree of compressor outlet superheat is equal to or greater than a set degree of outlet superheat.
[Claim 10]

15 The air-conditioning apparatus of any one of claims 1 to 9, wherein the heat source-side heat exchanger has a cross-sectional shape of a chamfered rectangle with a large aspect ratio, and wherein the heat source-side heat exchanger comprises one or two rows of single-row flat tube heat exchangers that are coupled in a thickness direction of the

20 heat source-side heat exchanger, the single-row flat tube heat exchangers each including a flat tube through which refrigerant passes, and a plurality of plate-like fins joined at right angles to the flat tube.