Air conditioner and air conditioner control method

Abstract

An air-conditioning apparatus (1) includes a refrigerant circuit (2) including an outdoor heat exchanger (30), expansion valve (42), indoor heat exchanger (50), compressor (10), and first switching mechanism, an internal heat exchanger (60) having a first channel leading to the first switching mechanism and the compressor (10) and a second channel leading to a bifurcation (33) of refrigerant pipes (32, 43, 44) and a second switching mechanism, and a controller (80). The controller (80) switches the second switching mechanism to connect the second channel to the expansion valve (42) and thus feed refrigerant after heat exchange in the internal heat exchanger (60) to the expansion valve (42) when the indoor heat exchanger (50) cools indoor air, or to disconnect the second channel from the expansion valve (42) and thus stop refrigerant flow from the second channel to the expansion valve (42) when the indoor heat exchanger (50) heats indoor air.

Description

Technical Field

[0001] The present invention relates to an air-conditioning apparatus and a method of controlling an air-conditioning apparatus.Background Art

[0002] Some air-conditioning apparatuses include an internal heat exchanger that cools the refrigerant output from an outdoor heat exchanger during a cooling operation.

[0003] For example, Patent Literature 1 discloses an air-conditioning apparatus including compressors that compress refrigerant, a bifurcation provided to a high-pressure liquid pipe through which the refrigerant output from an outdoor heat exchanger flows, and an internal heat exchanger disposed between the compressors and the bifurcation. The internal heat exchanger performs heat exchange between the refrigerant separated at the bifurcation and cooled through decompression by an expansion device and the refrigerant just separated at the bifurcation during a cooling operation, and thus cools the refrigerant just separated at the bifurcation, and then returns the refrigerant to the high-pressure liquid pipe.

[0004] The internal heat exchanger of the air-conditioning apparatus disclosed in Patent Literature 1 cools the refrigerant output from the outdoor heat exchanger during the cooling operation. This air-conditioning apparatus has improved cooling performance. The air-conditioning apparatus also includes two indoor heat exchangers, one of which functions as an evaporator and the other of which functions as a condenser. During an operation of heating the room including the other indoor heat exchanger, the air-conditioning apparatus closes a switching valve provided between the compressors and the bifurcation, and thus allows the internal heat exchanger to serve as a reservoir for excess refrigerant. The air-conditioning apparatus therefore has improved heating performance. Document WO 2016 / 047506 A1 discloses also an air-conditioning apparatus with a closed refrigerant circuit including an outdoor heat exchanger, an expansion valve, an indoor heat exchanger, a compressor, and a reversible four-way switching mechanism. The system further comprises a dual-channel internal heat exchanger in which refrigerant of a return channel and refrigerant of a bypass-controlled liquid channel exchange heat. A control valve selectively connects the second channel to the expansion valve, enabling targeted control of the internal heat-exchange operation.Citation ListPatent Literature

[0005] Patent Literature 1: Unexamined Japanese Patent Application Publication No. H4-257661 Patent Literature 2: WO2016 / 047506 A1 describing a gas-liquid separator. Patent Literature 3: US2014 / 123689 describing a heat pump and water heating circuit for a structure. Summary of InventionTechnical Problem

[0006] The air-conditioning apparatus disclosed in Patent Literature 1, however, has a complicated structure because of the expansion device included in the internal heat exchanger to decrease the pressure of the refrigerant.

[0007] An objective of the present invention, which has been accomplished to solve the above problem, is to provide an air-conditioning apparatus having improved cooling performance and improved heating performance with a simple structure, and a method of controlling the air-conditioning apparatus.Solution to Problem

[0008] In order to achieve the above objective, an air-conditioning apparatus according to the present invention comprises the features of claim 1..Advantageous Effects of Invention

[0009] According to the present invention, the controller switches the second switching mechanism such that the second channel is connected to the first expansion valve, and thus causes the refrigerant after the heat exchange performed by the internal heat exchanger to flow to the first expansion valve, in a process of causing the indoor heat exchanger to cool the indoor air. The refrigerant to flow via the first expansion valve to the indoor heat exchanger thus has a lower temperature. This configuration can therefore improve the cooling performance of the air-conditioning apparatus.

[0010] In addition, the controller switches the second switching mechanism such that the second channel is disconnected from the first expansion valve, and thus stops the flow of the refrigerant from the second channel to the first expansion valve, in a process of causing the indoor heat exchanger to heat the indoor air. The refrigerant that entered the second channel in the process of causing the indoor heat exchanger to heat the indoor air thus remains in the second channel. This configuration can prevent the refrigerant circuit from suffering from excess refrigerant during the heating operation. The configuration can therefore improve the heating performance of the air-conditioning apparatus.

[0011] Furthermore, the internal heat exchanger has the second channel leading to the bifurcation and the second switching mechanism. The bifurcation is included in a refrigerant pipe that couples the outdoor heat exchanger to the first expansion valve. The second switching mechanism is disposed at a position in the refrigerant pipe more adjacent to the first expansion valve than to the bifurcation and configured to switch the direction of a flow of the refrigerant. That is, the controller can connect or disconnect the second channel to or from the refrigerant pipe just by switching the second switching mechanism. This configuration can improve the cooling performance and the heating performance of the air-conditioning apparatus. The air-conditioning apparatus can therefore achieve improved cooling performance and improved heating performance with a simple structure.Brief Description of Drawings

[0012] FIG. 1 illustrates a refrigerant circuit of an air-conditioning apparatus according to an embodiment of the present invention; FIG. 2 illustrates a hardware configuration of a controller included in the air-conditioning apparatus according to the embodiment; FIG. 3 illustrates the refrigerant circuit with flows of refrigerant during a cooling operation in the air-conditioning apparatus according to the embodiment; and FIG. 4 illustrates the refrigerant circuit with flows of refrigerant during a heating operation in the air-conditioning apparatus according to the embodiment. Description of Embodiments

[0013] The following describes an air-conditioning apparatus and a method of controlling an air-conditioning apparatus according to an embodiment of the present invention in detail with reference to the accompanying drawings. In the drawings, the components identical or corresponding to each other are provided with the same reference symbol.

[0014] The air-conditioning apparatus according to the embodiment is designed for conditioning the indoor air of a railway vehicle. This air-conditioning apparatus includes, as well as an indoor heat exchanger and an outdoor heat exchanger, an internal heat exchanger aimed at improving the cooling performance. The air-conditioning apparatus also includes a controller that switches three-way valves and thus causes refrigerant to flow to the internal heat exchanger during a cooling operation. The air-conditioning apparatus to be controlled by the controller is described below with reference to FIG. 1.

[0015] FIG. 1 illustrates a refrigerant circuit of an air-conditioning apparatus 1 according to an embodiment. FIG. 1 illustrates, in addition to the individual components of the air-conditioning apparatus 1, electrical connections between a controller 80 and the individual components with broken lines, in order to facilitate an understanding.

[0016] As illustrated in FIG. 1, the air-conditioning apparatus 1 includes a compressor 10 that compresses refrigerant, three-way valves 21 and 22 that switch the directions of refrigerant flows, an outdoor heat exchanger 30 that performs heat exchange between the refrigerant and the outdoor air, expansion valves 41 and 42 that expand the refrigerant, and an indoor heat exchanger 50 that performs heat exchange between the refrigerant and the indoor air. The compressor 10, the three-way valves 21 and 22, the outdoor heat exchanger 30, the expansion valves 41 and 42, and the indoor heat exchanger 50 are connected to each other in sequence and constitute a refrigerant circuit 2.

[0017] The compressor 10 compresses low-pressure refrigerant and thus converts the refrigerant into high-pressure refrigerant. The compressor 10 has an inlet and an outlet, which are not illustrated. The compressor 10 introduces low-pressure refrigerant through the inlet and discharges high-pressure refrigerant through the outlet. The inlet is coupled to an internal heat exchanger 60, which is described below. The outlet is coupled to the three-way valve 21 via a check valve 11, which allows refrigerant to flow in the direction from the compressor 10 toward the three-way valve 21 and does not allow refrigerant to flow in the opposite direction.

[0018] The three-way valves 21 and 22 are coupled in parallel to each other. In detail, the three-way valve 21 has three ports. The three ports include a first port coupled to a branch pipe of a refrigerant pipe 31 leading to the outdoor heat exchanger 30. The three ports include a second port coupled to a refrigerant pipe 12 extending from the compressor 10. The three ports further include a third port coupled to a branch pipe of a refrigerant pipe 51 leading to the indoor heat exchanger 50.

[0019] The three-way valve 22 also has a first port, a second port, and a third port. The first port is coupled to another branch pipe of the refrigerant pipe 31. The second port is coupled to a refrigerant pipe 63 extending from the internal heat exchanger 60. The third port is coupled to another branch pipe of the refrigerant pipe 51.

[0020] The three-way valves 21 and 22 are each a solenoid valve or a motorized valve, for example. The three-way valves 21 and 22 are electrically coupled to the controller 80, which is described below. The three-way valves 21 and 22 guide the refrigerant introduced from the compressor 10 through the refrigerant pipe 12, to the refrigerant pipe 31 leading to the outdoor heat exchanger 30, in response to a switching operation by the controller 80. The three-way valves 21 and 22 guide the refrigerant output from the indoor heat exchanger 50 through the refrigerant pipe 51, to the refrigerant pipe 63 leading to the internal heat exchanger 60. The three-way valves 21 and 22 thus turn the operation mode of the air-conditioning apparatus 1 into a cooling mode.

[0021] Also, the three-way valves 21 and 22 guide the refrigerant introduced from the compressor 10, to the refrigerant pipe 51 leading to the indoor heat exchanger 50, in response to another switching operation by the controller 80. The three-way valves 21 and 22 guide the refrigerant output from the outdoor heat exchanger 30 through the refrigerant pipe 31, to the refrigerant pipe 63 leading to the internal heat exchanger 60. The three-way valves 21 and 22 thus turn the operation mode of the air-conditioning apparatus 1 into a heating mode.

[0022] That is, the three-way valves 21 and 22 switch the directions of refrigerant flows in the refrigerant circuit 2, and thus achieve the cooling mode or the heating mode of the air-conditioning apparatus 1. The three-way valves 21 and 22 accordingly guide the refrigerant compressed by the compressor 10 to the outdoor heat exchanger 30 or the indoor heat exchanger 50.

[0023] The outdoor heat exchanger 30 has a finned tube structure. In detail, the outdoor heat exchanger 30 has multiple fins and tubes, which are not illustrated. The fins are fed with the outdoor air by a fan, which is not illustrated. The tubes allow the refrigerant from the compressor 10 to flow through the tubes during the cooling operation, or allow the refrigerant from an expansion valve 41 to flow through the tubes during the heating operation. The outdoor heat exchanger 30 having this structure performs heat exchange between the outdoor air fed to the fins and the refrigerant flowing through the tubes, and condenses the refrigerant during the cooling operation, or evaporates the refrigerant during the heating operation. The outdoor heat exchanger 30 thus functions as a condenser during the cooling operation, or functions as an evaporator during the heating operation. The outdoor heat exchanger 30 outputs the refrigerant to an expansion valve 42 illustrated in FIG. 1 during the cooling operation, or outputs the refrigerant to the three-way valves 21 and 22 during the heating operation.

[0024] The expansion valves 41 and 42 each have a valve body, which is not illustrated, to adjust the aperture of a flow path of refrigerant. The expansion valves 41 and 42 are each a solenoid valve or a motorized valve, for example. The expansion valves 41 and 42 are electrically connected to the controller 80 illustrated in FIG. 1, and adjust the apertures of the valve bodies that define the flow paths in accordance with the output from the controller 80. The expansion valves 41 and 42 decrease the pressure of the refrigerant by means of the apertures of the valve bodies. The expansion valves 41 and 42 decrease the pressure of the refrigerant to a pressure depending on the output from the controller 80 and thus expand the refrigerant.

[0025] The expansion valves 41 and 42 are aimed at expanding refrigerant during the heating operation and the cooling operation, respectively. The expansion valve 41 is coupled in parallel to a check valve 68, so that the expansion valve 41 is used only in the heating operation and not used in the cooling operation. The check valve 68 allows refrigerant to flow in the direction from a refrigerant pipe 32 having a bifurcation between the expansion valve 41 and the outdoor heat exchanger 30 toward the internal heat exchanger 60 or toward the indoor heat exchanger 50, and does not allow refrigerant to flow in the opposite direction. The expansion valve 42 is coupled in parallel to a check valve 46, so that the expansion valve 42 is used only in the cooling operation and not used in the heating operation. The check valve 46 allows refrigerant to flow in the direction from the indoor heat exchanger 50 toward the outdoor heat exchanger 30, and does not allow refrigerant to flow in the opposite direction.

[0026] The expansion valves 41 and 42 are controlled by the controller 80, such that the apertures of the individual valve bodies are adjusted depending on whether the current mode is the cooling mode or the heating mode. In the cooling mode, the expansion valve 42 expands refrigerant and outputs the expanded refrigerant to the indoor heat exchanger 50. In the heating mode, the expansion valve 41 expands refrigerant and outputs the expanded refrigerant to the outdoor heat exchanger 30.

[0027] The indoor heat exchanger 50 has a finned tube structure, like the outdoor heat exchanger 30. In detail, the indoor heat exchanger 50 has fins, which are not illustrated, like the outdoor heat exchanger 30. The fins are fed with the indoor air by a fan, which is not illustrated. The indoor heat exchanger 50 also has tubes, which are not illustrated. The tubes allow the refrigerant expanded by the expansion valve 42 to flow through the tubes during the cooling operation, or allow the refrigerant compressed by the compressor 10 to flow through the tubes during the heating operation. The indoor heat exchanger 50 having this structure performs heat exchange between the fed indoor air and the refrigerant flowing through the tubes. This indoor heat exchanger 50 functions as an evaporator that absorbs heat from the indoor air and evaporates the refrigerant during the cooling operation, or functions as a condenser that discharges heat to the indoor air and condenses the refrigerant during the heating operation. The indoor heat exchanger 50 accordingly cools the indoor air during the cooling operation, or heats the indoor air during the heating operation. The indoor heat exchanger 50 returns the refrigerant to the three-way valves 21 and 22 during the cooling operation, or outputs the refrigerant to the expansion valve 41 during the heating operation.

[0028] These components constitute the refrigerant circuit 2, which enables the air-conditioning apparatus 1 to perform the cooling operation or the heating operation. These operations basically require the condenser to discharge the heat absorbed from the air by the evaporator and the input heat generated by compression. The condenser thus must have heat exchange performance superior to that of the evaporator. The refrigerant contains a material existing in nature, in terms of environmental conservation. In detail, the refrigerant is made of carbon dioxide, that is, CO 2 .

[0029] CO 2 never transforms into liquid even in a supercritical state at a pressure exceeding the supercritical point. The outdoor heat exchanger 30 serving as a condenser during the cooling operation thus preferably has a large volumetric capacity like a heat exchanger called gas cooler. In view of such a background, the outdoor heat exchanger 30 is designed to have a volumetric capacity for accommodating refrigerant that is even larger than the volumetric capacity of the indoor heat exchanger 50 for accommodating refrigerant, in comparison to that of an air-conditioning apparatus using condensable refrigerant.

[0030] If the amount of refrigerant used in the refrigerant circuit 2 is determined appropriately for the volumetric capacity of the outdoor heat exchanger 30 serving as a condenser during the cooling operation, the indoor heat exchanger 50 having a smaller volumetric capacity than the outdoor heat exchanger 30 and serving as a condenser during the heating operation will suffer from excess refrigerant. Such excess refrigerant unintentionally increases the temperature and pressure of the refrigerant flowing through the indoor heat exchanger 50 during the heating operation, thereby impairing the heating performance of the air-conditioning apparatus 1. If such impairment of the heating performance of the air-conditioning apparatus 1 is reduced by the indoor heat exchanger 50 designed to have a volumetric capacity that is larger than the outdoor heat exchanger 30, this indoor heat exchanger 50 requires a larger amount of refrigerant and results in an increase in the size of the air-conditioning apparatus 1.

[0031] In order to solve these problems, the air-conditioning apparatus 1 further includes the internal heat exchanger 60 aimed at improving the cooling performance, and a three-way valve 70 that switches the direction of a refrigerant flow to the internal heat exchanger 60 and thus allows the internal heat exchanger 60 to reserve excess refrigerant during the heating operation.

[0032] The internal heat exchanger 60 has a shell-and-tube structure for performing heat exchange between two types of refrigerant in different states. In detail, the internal heat exchanger 60 includes multiple tubes 61 in communication with each other, and a hollow cylindrical shell 62 having the cylindrical shaft extending in the longitudinal direction of the tubes 61 and accommodating the tubes 61 therein.

[0033] The tubes 61 are coupled to the refrigerant pipe 63 leading to the second port of the three-way valve 22, which is described above, to introduce refrigerant to be subject to heat exchange, in detail, to introduce the low-temperature refrigerant flowing from the indoor heat exchanger 50 during the cooling operation, or to introduce the low-temperature refrigerant flowing from the outdoor heat exchanger 30 during the heating operation. The tubes 61 are also coupled to a refrigerant pipe 64 leading to the compressor 10, to output the introduced refrigerant.

[0034] In contrast, the shell 62 is coupled to a refrigerant pipe 65, to introduce the high-temperature refrigerant to be subject to heat exchange condensed by the outdoor heat exchanger 30 during the cooling operation. The refrigerant pipe 65 is coupled to a bifurcation 33 provided to the refrigerant pipe 32 that couples the outdoor heat exchanger 30 to the expansion valve 41. The refrigerant pipe 65 is provided with a filter 67 for removing water and contaminants from the refrigerant. The shell 62 is also coupled to a refrigerant pipe 66, to output the introduced refrigerant. This refrigerant pipe 66 is coupled to the joint between a refrigerant pipe 43 extending from the expansion valve 41 and a refrigerant pipe 44 extending from the expansion valve 42.

[0035] The refrigerant pipe 65 is provided with the check valve 68, which allows refrigerant to flow in the direction from the refrigerant pipe 32 toward the shell 62 and does not allow refrigerant to flow in the opposite direction, in order to define the above-described direction of refrigerant flow. The refrigerant pipe 65 has a middle portion 651 in the longitudinal direction. The middle portion 651 is coupled to a refrigerant pipe 45 branching from the refrigerant pipe 43 leading to the expansion valve 41, to introduce the refrigerant existing adjacent to the expansion valve 41. The refrigerant pipe 45 is provided with a check valve 69, which allows refrigerant to flow in the direction from the refrigerant pipe 43 to the shell 62 and does not allow refrigerant to flow in the opposite direction, in order to prevent occurrence of a reverse flow of refrigerant from the refrigerant pipe 65 to the expansion valve 41.

[0036] The shell 62 of the internal heat exchanger 60 has an internal space, in which the tubes 61 have gaps therebetween and against the inner wall of the shell 62. The tubes 61 are made of a metal, such as aluminum, having a high thermal conductivity. When the above-described coupling relationship causes low-temperature refrigerant to enter the tubes 61 from the indoor heat exchanger 50 and causes high-temperature refrigerant to enter the shell 62 from the outdoor heat exchanger 30 during the cooling operation, these refrigerants exchange heat with each other. This heat exchange cools the refrigerant that entered the shell 62 from the outdoor heat exchanger 30. The cooled refrigerant is output to the refrigerant pipe 66 extending from the shell 62. The refrigerant pipe 66 is provided with the three-way valve 70 to control whether to feed the output refrigerant to the indoor heat exchanger 50.

[0037] The three-way valve 70 leads to the refrigerant pipe 66 coupled to the shell 62 of the internal heat exchanger 60, the refrigerant pipe 43 coupled to the expansion valve 41, and the refrigerant pipe 44 coupled to the expansion valve 42. The three-way valve 70 is a solenoid valve or a motorized valve, for example, like the three-way valves 21 and 22. The three-way valve 70 is electrically connected to the controller 80. In response to a switching operation by the controller 80, the three-way valve 70 guides the cooled refrigerant, which is output from the shell 62 to the refrigerant pipe 66 during the cooling operation, to the refrigerant pipe 44 and thus feeds the refrigerant to the expansion valve 42. The refrigerant to be expanded by the expansion valve 42 thus has an even lower temperature. The indoor heat exchanger 50 therefore has still higher efficiency of cooling the indoor air.

[0038] In order to execute such switching operations of the three-way valve 70 depending on the cooling mode or the heating mode, the air-conditioning apparatus 1 includes the controller 80. The following describes a configuration of the controller 80 and a method of controlling the air-conditioning apparatus 1 executed by the controller 80, with reference to FIGS. 2 to 4.

[0039] FIG. 2 illustrates a hardware configuration of the controller 80 included in the air-conditioning apparatus 1. FIG. 3 illustrates the refrigerant circuit with flows of refrigerant during a cooling operation in the air-conditioning apparatus 1. FIG. 4 illustrates the refrigerant circuit with flows of refrigerant during a heating operation in the air-conditioning apparatus 1. FIG. 2 also illustrates the components electrically connected to the controller 80 in order to facilitate an understanding. FIGS. 3 and 4 include arrows indicating the directions of refrigerant flows along some segments of the refrigerant circuit 2. FIGS. 3 and 4 do not illustrate the controller 80 or electrical connections between the controller 80 and the individual components.

[0040] As illustrated in FIG. 2, the controller 80 includes an input / output (I / O) port 81. The I / O port 81 is electrically connected to the compressor 10, the three-way valves 21, 22, and 70, and the expansion valves 41 and 42 to be controlled by the controller 80, in order to achieve the above-described refrigerant flows.

[0041] The I / O port 81 is also electrically connected to pressure sensors 91 and 92 and a switch 93, which are illustrated in not FIG. 2 but FIGS. 1, 3, and 4.

[0042] The pressure sensor 91 measures a pressure of the refrigerant and determines whether the detected pressure has a significantly low value, which indicates leakage of refrigerant, during the activation of the air-conditioning apparatus 1 and during the deactivation of the air-conditioning apparatus 1. The pressure sensor 92 measures a pressure of the refrigerant and determines whether the detected pressure has a high value exceeding the allowable limit, during the activation of the air-conditioning apparatus 1. The switch 93 deactivates the air-conditioning apparatus 1 when the refrigerant pressure has a high value exceeding the allowable limit.

[0043] The controller 80 has a computer including a central processing unit (CPU) 82, a read-only memory (ROM) 83, and a random access memory (RAM) 84, as illustrated in FIG. 2. The CPU 82, the ROM 83, and the RAM 84 are electrically connected to the I / O port 81. The CPU 82 loads various programs stored in the ROM 83 into the RAM 84 and executes the programs, so that the controller 80 executes various processes for controlling the individual components of the air-conditioning apparatus 1. For example, when the CPU 82 executes a control program stored in the ROM 83, the controller 80 operates the compressor 10 electrically connected to the above-described I / O port 81, and opens or closes the three-way valves 21, 22, and 70 and the expansion valves 41 and 42 or adjusts their apertures.

[0044] These processes are described in more detail below. In response to a pushing manipulation on a power button, which is not illustrated, and a pushing manipulation on a mode selecting button, which is not illustrated, for selecting the cooling operation, the controller 80 operates the compressor 10. The controller 80 switches the coupling relationship between the individual ports of the three-way valves 21 and 22, and thus connects the refrigerant pipe 12 extending from the compressor 10, to the refrigerant pipe 31 leading to the outdoor heat exchanger 30, which are illustrated in FIG. 3. The controller 80 also connects the refrigerant pipe 51 extending from the indoor heat exchanger 50, to the refrigerant pipe 63 leading to the tubes 61 of the internal heat exchanger 60.

[0045] The controller 80 switches the coupling relationship between the individual ports of the three-way valve 70, and thus connects the refrigerant pipe 66 extending from the shell 62 of the internal heat exchanger 60, to the refrigerant pipe 44 leading to the expansion valve 42. In addition, the controller 80 closes the expansion valve 41 and opens the expansion valve 42.

[0046] The controller 80 controls these three-way valves 21, 22, and 70 and the expansion valves 41 and 42, and thus circulates refrigerant through the compressor 10, the three-way valve 21, the outdoor heat exchanger 30, the check valve 68, the filter 67, the shell 62 of the internal heat exchanger 60, the three-way valve 70, the expansion valve 42, the indoor heat exchanger 50, the three-way valve 22, the tubes 61 of the internal heat exchanger 60, and the compressor 10 in sequence, as illustrated with the arrows in FIG. 3. The controller 80 accordingly causes the outdoor heat exchanger 30 to function as a condenser and causes the indoor heat exchanger 50 to function as an evaporator. These functions achieve a cooling operation for cooling the indoor air.

[0047] During the cooling operation, the high-temperature refrigerant condensed by the outdoor heat exchanger 30 enters the shell 62 of the internal heat exchanger 60 through the refrigerant pipe 65. The low-temperature refrigerant evaporated by the indoor heat exchanger 50 enters the tubes 61 of the internal heat exchanger 60 through the refrigerant pipe 63. The high-temperature refrigerant flowing through the shell 62 and the low-temperature refrigerant flowing through the tubes 61 thus exchange heat with each other in the internal heat exchanger 60. This heat exchange cools the high-temperature refrigerant flowing through the shell 62. The refrigerant to be output from the shell 62 to the refrigerant pipe 66 and fed to the expansion valve 42 thus has an even lower temperature. Also, the refrigerant to be expanded by the expansion valve 42 and fed to the indoor heat exchanger 50 has an even lower temperature. The indoor heat exchanger 50 therefore has still higher efficiency of cooling the indoor air, resulting in higher cooling efficiency of the air-conditioning apparatus 1.

[0048] In contrast, in response to a pushing manipulation on the mode selecting button, which is not illustrated, for selecting the heating operation, the controller 80 switches the coupling relationship between the individual ports of the three-way valves 21 and 22, and thus connects the refrigerant pipe 12 extending from the compressor 10, to the refrigerant pipe 51 leading to the indoor heat exchanger 50, which are illustrated in FIG. 4. The controller 80 also connects the refrigerant pipe 31 extending from the outdoor heat exchanger 30, to the refrigerant pipe 63 leading to the tubes 61 of the internal heat exchanger 60.

[0049] The controller 80 switches the coupling relationship between the individual ports of the three-way valve 70, and thus disconnects the refrigerant pipe 66 extending from the shell 62 of the internal heat exchanger 60, from the refrigerant pipe 44 leading to the expansion valve 42, and connects the refrigerant pipe 44 to the refrigerant pipe 43 leading to the expansion valve 41. In addition, the controller 80 opens the expansion valve 41 and closes the expansion valve 42.

[0050] The controller 80 controls these three-way valves 21, 22, and 70 and the expansion valves 41 and 42, and thus circulates refrigerant through the compressor 10, the three-way valve 21, the indoor heat exchanger 50, the check valve 46, the three-way valve 70, the expansion valve 41, the outdoor heat exchanger 30, the three-way valve 22, the tubes 61 of the internal heat exchanger 60, and the compressor 10 in sequence, as illustrated with the arrows in FIG. 4. The controller 80 accordingly causes the outdoor heat exchanger 30 to function as an evaporator and causes the indoor heat exchanger 50 to function as a condenser. These functions achieve the heating operation for heating the indoor air.

[0051] During the heating operation, the three-way valve 70 closes the end, adjacent to the refrigerant pipes 43 and 44, of the refrigerant pipe 66 extending from the shell 62 of the internal heat exchanger 60. The refrigerant pipe 66 is thus separated from the refrigerant pipes 43 and 44. This structure can prevent the refrigerant inside the refrigerant pipe 66 within a region A1 illustrated in FIG. 4 from reaching the refrigerant pipes 43 and 44. The structure can also prevent the refrigerant inside the shell 62 from reaching the refrigerant pipes 43 and 44 through the refrigerant pipe 66.

[0052] The refrigerant pipe 65 leading to the shell 62 is provided with the check valve 68 that does not allow refrigerant to flow in the direction from the shell 62 to the refrigerant pipe 32 leading to the outdoor heat exchanger 30. The refrigerant pipe 45 coupled to the middle portion 651 of the refrigerant pipe 65 is provided with the check valve 69 that does not allow refrigerant to flow in the direction from the refrigerant pipe 65 to the refrigerant pipe 43 extending from the refrigerant pipe 45 and leading to the expansion valve 41. This structure can prevent the refrigerant inside the refrigerant pipe 65 and a part of the refrigerant pipe 45 within a region A2 illustrated in FIG. 4 from reaching the refrigerant pipes 32 and 43. The structure can also prevent the refrigerant inside the shell 62 from reaching the refrigerant pipes 32 and 43 through the refrigerant pipe 65.

[0053] That is, the shell 62 of the internal heat exchanger 60 is separated from the refrigerant pipes 32, 43, and 44 during the heating operation. The refrigerant is prevented from flowing from the shell 62 to the refrigerant pipes 32, 43, and 44. The refrigerant that entered the shell 62 during the cooling operation is thus trapped inside the shell 62. The shell 62 accordingly reserves excess refrigerant caused by the difference in the amount of necessary refrigerant between the heating operation and the cooling operation. In other words, the excess refrigerant is reserved in the internal heat exchanger 60. This reservation can prevent the excess refrigerant from inducing a temperature rise and pressure rise in the refrigerant in the inner heat exchanger 50 during the heating operation, resulting in a reduction in impairment of the heating performance of the air-conditioning apparatus 1.

[0054] During the heating operation, the low-temperature refrigerant evaporated by the outdoor heat exchanger 30 enters the tubes 61 of the internal heat exchanger 60. This low-temperature refrigerant cools the refrigerant inside the shell 62 and thus decreases the pressure of the refrigerant inside the shell 62. When the refrigerant flowing through the refrigerant pipes 32 and 43 has a higher pressure than the refrigerant inside the shell 62, the higher-pressure refrigerant flows through the check valves 68 and 69 to the refrigerant pipe 65 and the shell 62 coupled to the refrigerant pipe 65. The shell 62 thus reserves a larger amount of refrigerant. The shell 62, which reserves a larger amount of excess refrigerant during the heating operation, further reduces impairment of the heating performance of the air-conditioning apparatus 1.

[0055] In order to terminate the cooling operation or the heating operation, a user of the air-conditioning apparatus 1 pushes the power button, which is not illustrated, again. The controller 80 then forcibly shuts down the above-described process, followed by deactivation of the air-conditioning apparatus 1.

[0056] The expansion valve 42 in the above-described embodiment is an example of a first expansion valve in the present invention. The expansion valve 41 is an example of a second expansion valve in the present invention. The three-way valves 21, 22, and 70, which switch the directions of refrigerant flows, are also called switching mechanisms. The three-way valves 21 and 22 are an example of a first switching mechanism in the present invention. The three-way valve 70 is an example of a second switching mechanism in the present invention.

[0057] The refrigerant pipe 63, the tubes 61, and the refrigerant pipe 64 are an example of a first channel included in the internal heat exchanger 60 in the present invention. The refrigerant pipe 65, the shell 62, and the refrigerant pipe 66 are an example of a second channel included in the internal heat exchanger 60 in the present invention. The refrigerant pipe 45 is an example of a branch pipe in the present invention. The check valve 46 is an example of a first check valve in the present invention. The check valve 69 is an example of a second check valve in the present invention. The check valve 68 is an example of a third check valve in the present invention.

[0058] As described above, the controller 80 of the air-conditioning apparatus 1 according to the embodiment switches the three-way valve 70 during the cooling operation, and thus connects the refrigerant pipe 66 extending from the shell 62 of the internal heat exchanger 60, to the refrigerant pipe 44 leading to the expansion valve 42. The refrigerant cooled through the heat exchange in the shell 62 is thus guided to the expansion valve 42. The refrigerant to flow via the expansion valve 42 to the indoor heat exchanger 50 accordingly has a lower temperature. This indoor heat exchanger 50 has higher efficiency of cooling the indoor air, resulting in improved cooling performance of the air-conditioning apparatus 1.

[0059] In addition, the controller 80 switches the three-way valve 70 during the heating operation, and thus disconnects the refrigerant pipe 66 from the refrigerant pipe 44 and stops the refrigerant flow from the shell 62 to the expansion valve 42. The refrigerant that entered the shell 62 during the cooling operation is thus reserved in the shell 62 during the heating operation. This reservation can reduce excess refrigerant in the refrigerant circuit 2 during the heating operation. In other words, the refrigerant in a gas state or supercritical state during the cooling operation transforms into a liquid state during the heating operation, and the shell 62 can reserve an amount of refrigerant corresponding to the difference in density between the states. This reservation can prevent excess refrigerant to induce a pressure rise and temperature rise in the refrigerant in the indoor heat exchanger 50. The air-conditioning apparatus 1 therefore has improved heating performance.

[0060] Since the reservation prevents excess refrigerant to induce a pressure rise during the heating operation, the refrigerant discharged from the compressor 10 has a lower temperature. The compressor 10 thus has higher compression efficiency.

[0061] The controller 80 can improve the cooling performance of the air-conditioning apparatus 1 in the cooling operation and improve the heating performance of the air-conditioning apparatus 1 in the heating operation, just by switching the three-way valve 70. That is, the air-conditioning apparatus 1 can achieve improved cooling performance and improved heating performance with a simple structure. Such an air-conditioning apparatus 1 can be readily fabricated.

[0062] The air-conditioning apparatus 1 preferably executes a heating operation for at least a short period after termination of the cooling operation. This heating operation allows a larger amount of refrigerant to be reserved in the internal heat exchanger 60, and can thus prevent refrigerant from transforming into liquid and remaining in the compressor 10 during the deactivation of the air-conditioning apparatus 1.

[0063] The air-conditioning apparatus 1 and the method of controlling the air-conditioning apparatus 1 according to the embodiment of the present invention described above are mere examples.

[0064] Although the refrigerant in the embodiment is CO 2 , this refrigerant is a mere example. The refrigerant may be other refrigerant generally used in the air-conditioning apparatus. The refrigerant is only required to have a difference between the volume during the cooling operation and the volume during the heating operation and yield excess refrigerant, because the air-conditioning apparatus 1 reserves excess refrigerant in the internal heat exchanger 60 during the heating operation. For example, the refrigerant may be a material having different volumes depending on whether the temperature is high or low.

[0065] Although the three-way valves 21 and 22 switch the directions of refrigerant flows in the refrigerant circuit 2 in the embodiment, the air-conditioning apparatus 1 may have other configuration. The three-way valves 21 and 22 in the air-conditioning apparatus 1 may be other switching mechanisms for switching the directions of flows of the refrigerant compressed by the compressor 10. For example, the three-way valves 21 and 22 may be replaced with a four-way valve.

[0066] Although the internal heat exchanger 60 has a shell-and-tube structure in the embodiment, this internal heat exchanger 60 is a mere example. The internal heat exchanger 60 is only required to have a structure for performing heat exchange between the refrigerant flowing through the first channel and the refrigerant flowing through the second channel. For example, the internal heat exchanger 60 may have a double-pipe structure, in which a pipe accommodates another pipe therein. The internal heat exchanger 60 may also have a spiral structure made of a plate bent into a spiral. Alternatively, the internal heat exchanger 60 may have a stacked structure made of a stack of plates.

[0067] Although the air-conditioning apparatus 1 is designed for conditioning the indoor air of a railway vehicle in the embodiment, this air-conditioning apparatus 1 is a mere example. The present invention can be applied to any general air-conditioning apparatus. For example, the air-conditioning apparatus 1 may be designed for conditioning the indoor air of a building.

[0068] Although the control program is stored in the ROM 83 in the embodiment, the control program may also be stored in a non-transitory computer-readable recording medium, such as flexile disc, compact disc read-only memory (CD-ROM), digital versatile disc (DVD), or magneto-optical disc (MO), and distributed. In this case, the control program stored in the non-transitory recording medium may be installed in a computer to configure the controller 80 that executes the control process.

[0069] The control program may also be stored in a disk drive included in a server device on a communication network, such as the Internet, and may be downloaded into a computer by being superimposed on a carrier wave, for example.

[0070] The foregoing describes some example embodiments for explanatory purposes. Accordingly, the specification and drawings are to be regarded in an illustrative rather than a restrictive sense. This detailed description, therefore, is not to be taken in a limiting sense, and the scope of the invention is defined only by the included claims, along with the full range of equivalents to which such claims are entitled.Reference Signs List

[0071] 1 Air-conditioning apparatus 2 Refrigerant circuit 10 Compressor 11 Check valve 12 Refrigerant pipe 21, 22Three-way valve 30 Outdoor heat exchanger 31, 32 Refrigerant pipe 33 Bifurcation 41, 42Expansion valve 43, 44, 45 Refrigerant pipe 46 Check valve 50 Indoor heat exchanger 51 Refrigerant pipe 60 Internal heat exchanger 61 Tube 62 Shell 63-66 Refrigerant pipe 67 Filter 68, 69 Check valve 70 Three-way valve 80 Controller 81 I / O port 82 CPU 83 ROM 84 RAM 91, 92Pressure sensor 93 Switch 651 Middle portion A1, A2 Region

Claims

1. An air-conditioning apparatus (1), comprising: a refrigerant circuit (2) including an outdoor heat exchanger (30) to perform heat exchange between refrigerant and outdoor air, a first expansion valve (42) to expand the refrigerant, an indoor heat exchanger (50) to perform heat exchange between the refrigerant and indoor air, a compressor (10) to compress the refrigerant, and a first switching mechanism (21, 22) to switch a direction of a flow of the refrigerant, the outdoor heat exchanger (30), the first expansion valve (42), the indoor heat exchanger (50), and the first switching mechanism (21, 22) being coupled to each other in sequence, the compressor (10) being coupled to the first switching mechanism (21, 22); an internal heat exchanger (60) including a first channel (61, 63, 64) leading to the first switching mechanism (21, 22) and the compressor (10), and a second channel (62, 65, 66) leading to a bifurcation (33) and a second switching mechanism (70), the bifurcation (33) being included in a refrigerant pipe (32, 43, 44) that couples the outdoor heat exchanger (30) to the first expansion valve (42), the second switching mechanism (70) being disposed at a position in the refrigerant pipe (32, 43, 44) more adjacent to the first expansion valve (42) than to the bifurcation (33) and configured to switch a direction of a flow of the refrigerant, the internal heat exchanger (60) being configured to perform heat exchange between the refrigerant flowing through the first channel (61, 63, 64) and the refrigerant flowing through the second channel (62, 65, 66); a first check valve (46) coupled in parallel to the first expansion valve (42), the first check valve (46) being configured to allow the refrigerant to flow in a direction from the indoor heat exchanger (50) toward the outdoor heat exchanger (30) and not to allow the refrigerant to flow in an opposite direction; a second expansion valve (41) disposed at a position in the refrigerant pipe (32, 43, 44) more adjacent to the outdoor heat exchanger (30) than to the second switching mechanism (70), and configured to expand the refrigerant; a branch pipe (45) branching from a position in the refrigerant pipe (32, 43, 44) between the second switching mechanism (70) and the second expansion valve (41), the branch pipe (45) leading to the second channel (62, 65, 66); a second check valve (69) provided to the branch pipe (45), the second check valve (69) being configured to allow the refrigerant to flow in a direction toward the second channel (62, 65, 66) and not to allow the refrigerant to flow in an opposite direction; and a controller (80) to (i) switch the second switching mechanism (70) such that the second channel (62, 65, 66) is connected to the first expansion valve (42), and thus cause the refrigerant after the heat exchange performed by the internal heat exchanger (60) to flow to the first expansion valve (42), and (ii) close the second expansion valve (41) and open the first expansion valve (42), and thus cause the refrigerant flowing through the first expansion valve (42) to expand, in a process of causing the indoor heat exchanger (50) to cool the indoor air, and (i) switch the second switching mechanism (70) such that the second channel (62, 65, 66) is disconnected from the first expansion valve (42), and thus stop the flow of the refrigerant from the second channel (62, 65, 66) to the first expansion valve (42), and (ii) close the first expansion valve (42) and open the second expansion valve (41), and thus cause the refrigerant flowing through the second expansion valve (41) to expand, in a process of causing the indoor heat exchanger (50) to heat the indoor air.

2. The air-conditioning apparatus (1) according to claim 1, wherein the outdoor heat exchanger (30) has a volumetric capacity for accommodating the refrigerant that is larger than a volumetric capacity of the indoor heat exchanger (50) for accommodating the refrigerant.

3. The air-conditioning apparatus (1) according to claim 1 or 2, wherein the second channel (62, 65, 66) includes a third check valve (68) adjacent to the bifurcation (33), the third check valve (68) being configured to allow the refrigerant to flow in a direction from the bifurcation (33) toward the second switching mechanism (70).

4. The air-conditioning apparatus (1) according to any one of claims 1 to 3, wherein the first switching mechanism (21, 22) includes two three-way valves (21, 22) coupled in parallel to each other.

5. The air-conditioning apparatus (1) according to any one of claims 1 to 3, wherein the first switching mechanism (21, 22) includes a four-way valve.

6. The air-conditioning apparatus (1) according to any one of claims 1 to 5, wherein the controller (80) switches the first switching mechanism (21, 22) such that the first switching mechanism (21, 22) guides the refrigerant compressed by the compressor (10) to the outdoor heat exchanger (30) and guides the refrigerant exiting the indoor heat exchanger (50) to the first channel (61, 63, 64), and thus causes the indoor heat exchanger (50) to cool the indoor air, and switches the first switching mechanism (21, 22) such that the first switching mechanism (21, 22) guides the refrigerant compressed by the compressor (10) to the indoor heat exchanger (50) and guides the refrigerant exiting the outdoor heat exchanger (30) to the first channel (61, 63, 64), and thus causes the indoor heat exchanger (50) to heat the indoor air.

7. A method of controlling an air-conditioning apparatus (1), the air-conditioning apparatus (1) including a refrigerant circuit (2) including an outdoor heat exchanger (30) to perform heat exchange between refrigerant and outdoor air, a first expansion valve (42) to expand the refrigerant, an indoor heat exchanger (50) to perform heat exchange between the refrigerant and indoor air, and a first switching mechanism (21, 22) to switch a direction of a flow of the refrigerant compressed by a compressor (10), the outdoor heat exchanger (30), the first expansion valve (42), the indoor heat exchanger (50), and the first switching mechanism (21, 22) being coupled to each other in sequence, an internal heat exchanger (60) including a first channel (61, 63, 64) leading to the first switching mechanism (21, 22) and the compressor (10), and a second channel (62, 65, 66) leading to a bifurcation (33) and a second switching mechanism (70), the bifurcation (33) being included in a refrigerant pipe (32, 43, 44) that couples the outdoor heat exchanger (30) to the first expansion valve (42), the second switching mechanism (70) being disposed at a position in the refrigerant pipe (32, 43, 44) more adjacent to the first expansion valve (42) than to the bifurcation (33) and configured to switch a direction of a flow of the refrigerant, the internal heat exchanger (60) being configured to perform heat exchange between the refrigerant flowing through the first channel (61, 63, 64) and the refrigerant flowing through the second channel (62, 65, 66), a first check valve (46) coupled in parallel to the first expansion valve (42), the first check valve (46) being configured to allow the refrigerant to flow in a direction from the indoor heat exchanger (50) toward the outdoor heat exchanger (30) and not to allow the refrigerant to flow in an opposite direction, a second expansion valve (41) disposed at a position in the refrigerant pipe (32, 43, 44) more adjacent to the outdoor heat exchanger (30) than to the second switching mechanism (70), and configured to expand the refrigerant, a branch pipe (45) branching from a position in the refrigerant pipe (32, 43, 44) between the second switching mechanism (70) and the second expansion valve (41), the branch pipe (45) leading to the second channel (62, 65, 66), and a second check valve (69) provided to the branch pipe (45), the second check valve (69) being configured to allow the refrigerant to flow in a direction toward the second channel (62, 65, 66) and not to allow the refrigerant to flow in an opposite direction, the method comprising: causing the indoor heat exchanger (50) to cool the indoor air by switching the first switching mechanism (21, 22) such that the first switching mechanism (21, 22) guides the refrigerant compressed by the compressor (10) to the outdoor heat exchanger (30) and guides the refrigerant exiting the indoor heat exchanger (50) to the first channel (61, 63, 64); and causing the indoor heat exchanger (50) to heat the indoor air by switching the first switching mechanism (21, 22) such that the first switching mechanism (21, 22) guides the refrigerant compressed by the compressor (10) to the indoor heat exchanger (50) and guides the refrigerant exiting the outdoor heat exchanger (30) to the first channel (61, 63, 64), wherein the causing the indoor heat exchanger (50) to cool the indoor air includes (i) switching the second switching mechanism (70) such that the second channel (62, 65, 66) is connected to the first expansion valve (42), and thus guiding the refrigerant after the heat exchange performed by the internal heat exchanger (60) to the first expansion valve (42), and (ii) closing the second expansion valve (41) and opening the first expansion valve (42), and thus causing the refrigerant flowing through the first expansion valve (42) to expand, and the causing the indoor heat exchanger (50) to heat the indoor air includes (i) switching the second switching mechanism (70) such that the second channel (62, 65, 66) is disconnected from the first expansion valve (42), and thus stopping the flow of the refrigerant from the second channel (62, 65, 66) to the first expansion valve (42), and (ii) closing the first expansion valve (42) and opening the second expansion valve (41), and thus causing the refrigerant flowing through the second expansion valve (41) to expand.

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