Air conditioner

Abstract

An air conditioner (1) is provided with: a compressor (11); a condenser (16) connected to the compressor (11) via a discharge pipe (18); an evaporator (14) connected to the compressor (11) via a suction pipe (17); a main expansion valve (15) for decompressing the refrigerant supplied from the condenser (16) and then supplying the refrigerant to the evaporator (14); a bypass expansion valve (23) provided midway along a bypass path (22) for connecting the discharge pipe (18) and the suction pipe (17); and a control device (43) for controlling the bypass expansion valve (23) so as to switch the bypass expansion valve (23) between a first state in which the refrigerant does not flow through the bypass path (22) and a second state in which the refrigerant flows from the discharge pipe (18) to the suction pipe (17) via the bypass path (22) when the compressor (11) is compressing the refrigerant of the suction pipe (17) and discharging the compressed refrigerant to the discharge pipe (18).

Description

Technical Field

[0001] The technology disclosed in the present invention relates to an air conditioner. Background Art

[0002] An air conditioner is known that has a bypass path for hot gas bypass, and the hot gas bypass is to supply the refrigerant on the discharge side of the compressor to the suction side of the compressor (Patent Documents 1 to 3). This air conditioner can prevent liquid return and refrigerant retention by supplying the refrigerant on the discharge side of the compressor to the suction side of the compressor via the bypass path, thereby increasing the enthalpy of the refrigerant on the suction side.

[0003] Patent Document 1: Japanese Patent Application Publication No. 2018-112396

[0004] Patent Document 2: Japanese Patent Application Publication No. 2004-020064

[0005] Patent Document 3: Japanese Patent Application Publication No. 2003-156258 Summary of the invention

[0006] Even when the refrigerant is compressed at the same compression ratio, if the type of refrigerant is different, the discharge temperature of the refrigerant discharged from the compressor may be different. For example, due to its properties, the discharge temperature of R290 refrigerant is lower than that of R32 refrigerant even when compressed at the same compression ratio. In the air conditioner, a lower discharge temperature causes a smaller temperature difference with the air in the condenser, thereby reducing the amount of heat exchange. The air conditioner can increase the discharge temperature by increasing the speed of the compressor, thereby suppressing the reduction in the amount of heat exchange in the condenser. However, when the speed of the compressor is increased, the compression ratio may become larger, resulting in an increase in the load applied to the sliding part of the compressor and a problem of reduced reliability of the compressor. As in Patent Documents 1 to 3, by providing a bypass path for supplying the refrigerant on the discharge side of the compressor to the hot gas bypass on the suction side of the compressor, the discharge temperature can be increased without increasing the speed of the compressor, but the purpose is to suppress excessive increase in the discharge temperature, so there is room for improvement in the control method.

[0007] The disclosed technology has been made in view of the above-mentioned situation, and an object of the disclosed technology is to provide an air conditioner which can suppress an increase in the load on the compressor and increase the temperature of the refrigerant discharged from the compressor.

[0008] An air conditioner according to one aspect of the present disclosure includes: a compressor; a condenser connected to the compressor via a discharge pipe; an evaporator connected to the compressor via a suction pipe; a main expansion valve for reducing the pressure of refrigerant supplied from the condenser and supplying it to the evaporator; a bypass expansion valve provided in the middle of a bypass path for connecting the discharge pipe and the suction pipe; a discharge temperature sensor for detecting the temperature of the discharged refrigerant discharged from the compressor, namely, the discharge temperature; a condensation pressure calculation unit for calculating the pressure of the refrigerant flowing in the condenser, namely, the condensation pressure; and a control unit for controlling the bypass expansion valve to switch between a first state in which the refrigerant does not flow through the bypass path and a second state in which the refrigerant flows from the discharge pipe to the suction pipe via the bypass path, wherein when the refrigerant does not flow through the bypass path, the control unit controls the opening of the main expansion valve in such a way that the discharge temperature becomes a predetermined target discharge temperature, and when the refrigerant flows through the bypass path, the control unit controls the opening of the main expansion valve in such a way that the condensation pressure becomes a predetermined target condensation pressure.

[0009] The disclosed air conditioner can increase the temperature of the refrigerant discharged from the compressor while suppressing an increase in the load on the compressor. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 This is a circuit diagram of the air conditioner according to the first embodiment.

[0011] Figure 2 This is a block diagram showing the air conditioner of the first embodiment.

[0012] Figure 3 This is a flow chart showing the control of the main expansion valve and the bypass expansion valve.

[0013] Figure 4 This is a Mollier diagram showing the state change of the refrigerant when the refrigerant flows in the bypass path.

[0014] Figure 5 It is a Mollier diagram showing other state changes of the refrigerant when the refrigerant flows in the bypass path.

[0015] Figure 6 This is a flowchart showing control of the main expansion valve and the bypass expansion valve of the air conditioner according to the second embodiment. DETAILED DESCRIPTION

[0016] Hereinafter, the air conditioner of the embodiment disclosed in the present application will be described in detail with reference to the accompanying drawings. In addition, the technology disclosed in the present application is not limited to the following description. In addition, in the following description, the same structural elements are marked with the same symbols, and repeated descriptions are omitted.

[0017] Example 1

[0018] like Figure 1 As shown, the air conditioner 1 according to the first embodiment includes an outdoor unit 2 and an indoor unit 3 . Figure 1 1 is a circuit diagram of the air conditioner 1 according to the first embodiment. The outdoor unit 2 is installed outdoors. The indoor unit 3 is installed indoors to be cooled and heated by the air conditioner 1. The air conditioner 1 further includes a refrigerant circuit 5 and a water circuit 6. The refrigerant circuit 5 is arranged inside the outdoor unit 2. The refrigerant circuit 5 includes a compressor 11, a four-way valve 12, an outdoor heat exchanger 14, a main expansion valve 15, and an intermediate heat exchanger 16.

[0019] The refrigerant circuit 5 includes a suction pipe 17 and a discharge pipe 18. The compressor 11 includes a rotating body, and the gas-phase refrigerant supplied to the compressor 11 via the suction pipe 17 is compressed by the rotation of the rotating body, and the compressed gas-phase refrigerant is discharged to the discharge pipe 18. The higher the rotation speed of the rotating body, the greater the amount of refrigerant discharged by the compressor 11 per unit time. Refrigeration oil is stored inside the compressor 11. Refrigeration oil is used to lubricate the sliding parts provided inside the compressor 11 to prevent the sliding parts from wearing and cylinder jamming. Refrigeration oil is also used to seal the gap (small gap) formed inside the compressor 11 to prevent the refrigerant from leaking from the high-pressure side inside the compressor 11 to the low-pressure side through the gap.

[0020] The four-way valve 12 includes a first connection port 121, a second connection port 122, a third connection port 123, and a fourth connection port 124. The first connection port 121 is connected to the suction pipe 17, and is connected to the compressor 11 via the suction pipe 17. The second connection port 122 is connected to the discharge pipe 18, and is connected to the compressor 11 via the discharge pipe 18. The third connection port 123 is connected to the outdoor heat exchanger 14. The fourth connection port 124 is connected to the intermediate heat exchanger 16 via a refrigerant pipe. The four-way valve 12 includes a valve body, which is switched to the heating position by arranging the valve body in the heating position, and is switched to the cooling position by arranging the valve body in the cooling position. When the four-way valve 12 is switched to the heating position, the second connection port 122 is connected to the fourth connection port 124, and the third connection port 123 is connected to the first connection port 121. When the four-way valve 12 is switched to the cooling position, the second connection port 122 is connected to the third connection port 123, and the fourth connection port 124 is connected to the first connection port 121.

[0021] The outdoor heat exchanger 14 is connected to the main expansion valve 15 via a refrigerant pipe. The intermediate heat exchanger 16 is connected to the main expansion valve 15 via a refrigerant pipe. That is, the outdoor heat exchanger 14 is connected to the intermediate heat exchanger 16 via the main expansion valve 15. The main expansion valve 15 changes the flow rate of the refrigerant flowing between the outdoor heat exchanger 14 and the intermediate heat exchanger 16 via the main expansion valve 15 by adjusting the opening degree. The larger the opening degree of the main expansion valve 15, the greater the flow rate of the refrigerant flowing through the main expansion valve 15 per unit time.

[0022] The refrigerant circuit 5 also includes a bypass circuit 21. A bypass path 22 is formed in the bypass circuit 21. One end of the bypass path 22 is connected to the discharge pipe 18. The other end of the bypass path 22 is connected to the suction pipe 17. The bypass circuit 21 includes a bypass expansion valve 23. The bypass expansion valve 23 is provided in the middle of the bypass path 22. The bypass expansion valve 23 connects the discharge pipe 18 and the suction pipe 17 in a manner that allows the refrigerant to flow through the bypass path 22, or blocks the bypass path 22 in a manner that prevents the refrigerant from flowing through the bypass path 22. The bypass expansion valve 23 also changes the flow rate of the refrigerant flowing through the bypass path 22 per unit time by changing the opening degree. The larger the opening degree of the bypass expansion valve 23, the greater the flow rate of the refrigerant flowing through the bypass path 22 per unit time.

[0023] The water circuit 6 includes an indoor heat exchanger 25 and a pump 26. The indoor heat exchanger 25 is arranged inside the indoor unit 3. The indoor heat exchanger 25 is connected to the intermediate heat exchanger 16. The pump 26 is arranged inside the outdoor unit 2. The pump 26 is connected to the intermediate heat exchanger 16 and to the indoor heat exchanger 25. The pump 26 is used to circulate water in the water circuit 6 and supply the water supplied from the indoor heat exchanger 25 to the intermediate heat exchanger 16.

[0024] The air conditioner 1 further includes a discharge temperature sensor 31, an intermediate heat exchange temperature sensor 32, an outdoor heat exchange temperature sensor 33, an outdoor heat exchange gas side temperature sensor 34, an intake temperature sensor 35, a return temperature sensor 36, an outflow temperature sensor 37, an indoor temperature sensor 38, and an outlet temperature sensor 39. The discharge temperature sensor 31 is used to measure the temperature of the discharged refrigerant discharged from the compressor 11 to the discharge pipe 18. The intermediate heat exchange temperature sensor 32 is used to measure the temperature of the refrigerant flowing in the intermediate heat exchanger 16. The outdoor heat exchange temperature sensor 33 is used to measure the temperature of the refrigerant flowing in the outdoor heat exchanger 14. The outdoor heat exchange gas side temperature sensor 34 is used to measure the temperature of the outdoor heat exchange outlet refrigerant supplied from the outdoor heat exchanger 14 to the four-way valve 12 during the heating operation. The intake temperature sensor 35 is used to measure the temperature of the suction refrigerant supplied to the compressor 11 via the intake pipe 17. The return temperature sensor 36 is used to measure the temperature of the water supplied from the pump 26 to the intermediate heat exchanger 16. The outflow temperature sensor 37 measures the temperature of water supplied from the intermediate heat exchanger 16 to the indoor heat exchanger 25. The indoor temperature sensor 38 measures the temperature of the room in which the indoor unit 3 is arranged. The blow-out temperature sensor 39 measures the temperature of air blown out by the indoor unit 3 into the room.

[0025] The air conditioner 1 further includes a discharge pressure sensor 41 . The discharge pressure sensor 41 is for measuring the pressure of the refrigerant discharged from the compressor 11 to the discharge pipe 18 .

[0026] Figure 2 1 is a block diagram showing an air conditioner 1 according to Embodiment 1. The air conditioner 1 further includes an input device 42 and a control device 43. The input device 42 generates information such as cooling operation and heating operation start and stop instructions or changes in set temperatures by being operated by a user, and outputs the generated information to the control device 43.

[0027] The control device 43 is a computer, and includes a storage device 44 and a CPU 45 (Central Processing Unit). The storage device 44 is used to store the computer program installed in the control device 43, and to store information used by the CPU 45. The CPU 45 performs information processing by executing the computer program installed in the control device 43, and reads data from the storage device 44. The CPU 45 also receives information from the compressor 11, the four-way valve 12, the main expansion valve 15, the bypass expansion valve 23, the pump 26, the discharge temperature sensor 31, the intermediate heat exchange temperature sensor 32, the outdoor heat exchange temperature sensor 33, the indoor temperature sensor 38, the discharge pressure sensor 41, and the input device 42.

[0028] The operations performed by the air conditioner 1 include heating operation and cooling operation.

[0029] Heating operation

[0030] For example, when the air conditioner 1 is operated by the user to perform a heating operation, a heating operation is performed. When the air conditioner 1 performs a heating operation, the control device 43 controls the four-way valve 12, and switches the four-way valve 12 so that the first connection port 121 is connected to the third connection port 123 and the second connection port 122 is connected to the fourth connection port 124 (heating position). The control device 43 controls the compressor 11 to compress the low-pressure gas-phase refrigerant supplied via the suction pipe 17. The low-pressure gas-phase refrigerant is compressed by the compressor 11 to become a high-pressure gas-phase refrigerant. The compressor 11 then discharges the high-pressure gas-phase refrigerant to the discharge pipe 18. Since the four-way valve 12 is switched to the heating position, the high-pressure gas-phase refrigerant discharged to the discharge pipe 18 is supplied to the intermediate heat exchanger 16.

[0031] The intermediate heat exchanger 16 exchanges heat between the high-pressure gas-phase refrigerant supplied from the four-way valve 12 and the water circulating in the water circuit 6. The high-pressure gas-phase refrigerant releases heat to the water in the intermediate heat exchanger 16 and becomes a high-pressure liquid-phase refrigerant in a supercooled state. That is, when the air conditioner 1 performs heating operation, the intermediate heat exchanger 16 functions as a condenser. The high-pressure liquid-phase refrigerant flowing out of the intermediate heat exchanger 16 is supplied to the main expansion valve 15.

[0032] The main expansion valve 15 adjusts the flow rate of the refrigerant flowing from the intermediate heat exchanger 16 to the outdoor heat exchanger 14, so that the high-pressure liquid-phase refrigerant supplied from the intermediate heat exchanger 16 is decompressed. The high-pressure liquid-phase refrigerant is decompressed by the main expansion valve 15 to become a low-pressure gas-liquid two-phase refrigerant. The low-pressure gas-liquid two-phase refrigerant flowing out of the main expansion valve 15 is supplied to the outdoor heat exchanger 14.

[0033] The outdoor heat exchanger 14 exchanges heat between the low-pressure gas-liquid two-phase refrigerant supplied from the main expansion valve 15 and the outside atmosphere. The low-pressure gas-liquid two-phase refrigerant releases heat to the outside atmosphere in the outdoor heat exchanger 14 and becomes a low-pressure gas-phase refrigerant. That is, when the air conditioner 1 performs heating operation, the outdoor heat exchanger 14 functions as an evaporator. The low-pressure gas-phase refrigerant flowing out of the outdoor heat exchanger 14 is supplied to the four-way valve 12. Since the four-way valve 12 is switched to the heating position, the low-pressure gas-phase refrigerant supplied to the four-way valve 12 is supplied to the suction pipe 17 and is sucked into the compressor 11 via the suction pipe 17.

[0034] When the air conditioner 1 performs heating operation, the control device 43 further controls the pump 26 to supply water to the intermediate heat exchanger 16, so that the water circulates in the water circuit 6. The water heated in the intermediate heat exchanger 16 is supplied to the indoor heat exchanger 25. The indoor heat exchanger 25 exchanges heat between the heated water flowing through the indoor heat exchanger 25 and the air in the room where the indoor unit 3 is installed. The indoor unit 3 heats the room by blowing the air that has exchanged heat with the heated water in the indoor heat exchanger 25 into the room.

[0035] When the air conditioner 1 performs heating operation, the control device 43 further performs speed control of the compressor 11. In the speed control of the compressor 11, the control device 43 calculates a target speed based on the temperature difference between the set temperature input via the input device 42 and the indoor temperature measured by the indoor temperature sensor 38. For example, the larger the absolute value of the temperature difference, the larger the target speed. The control device 43 controls the compressor 11 in such a way that the speed of the compressor 11 becomes equal to the target speed.

[0036] When the air conditioner 1 performs the heating operation, the control device 43 further controls the main expansion valve 15 and the bypass expansion valve 23 . Figure 3 4 is a flow chart showing the control of the main expansion valve 15 and the bypass expansion valve 23. This control is performed during the heating operation. The control device 43 performs the discharge temperature control of the main expansion valve 15, closes the bypass expansion valve 23 to block the bypass path 22, and prevents the refrigerant from flowing in the bypass path 22 (step S1). During the discharge temperature control of the main expansion valve 15, the control device 43 uses the discharge temperature sensor 31 to measure the temperature of the discharged refrigerant discharged from the compressor 11 to the discharge pipe 18.

[0037] When the discharge temperature measured by the discharge temperature sensor 31 is higher than the predetermined target discharge temperature, the control device 43 reduces the opening of the main expansion valve 15. As the opening of the main expansion valve 15 becomes smaller, the flow rate of the low-pressure gas-liquid two-phase refrigerant supplied to the outdoor heat exchanger 14 decreases, and the pressure of the low-pressure gas-liquid two-phase refrigerant supplied to the outdoor heat exchanger 14 decreases. The target discharge temperature is calculated based on the detection value (condensation temperature) of the intermediate heat exchange temperature sensor 32 and the detection value (evaporation temperature) of the outdoor heat exchange temperature sensor 33. The evaporation temperature indicating the temperature of the refrigerant flowing in the outdoor heat exchanger 14 decreases due to the pressure reduction of the low-pressure gas-liquid two-phase refrigerant supplied to the outdoor heat exchanger 14. The temperature of the evaporator outlet refrigerant supplied from the outdoor heat exchanger 14 to the suction pipe 17 decreases due to the decrease in the evaporation temperature. The temperature of the suction refrigerant supplied from the suction pipe 17 to the compressor 11 decreases due to the decrease in the temperature of the evaporator outlet refrigerant. The temperature of the discharge refrigerant discharged from the compressor 11 decreases due to the decrease in the temperature of the suction refrigerant.

[0038] When the discharge temperature measured by the discharge temperature sensor 31 is lower than the target discharge temperature, the control device 43 increases the opening of the main expansion valve 15. As the opening of the main expansion valve 15 increases, the flow rate of the low-pressure gas-liquid two-phase refrigerant supplied to the outdoor heat exchanger 14 increases, so that the pressure of the low-pressure gas-liquid two-phase refrigerant supplied to the outdoor heat exchanger 14 increases. The evaporation temperature increases due to the increase in the pressure of the low-pressure gas-liquid two-phase refrigerant supplied to the outdoor heat exchanger 14. The temperature of the refrigerant at the evaporator outlet increases due to the increase in the evaporation temperature. The temperature of the suction refrigerant supplied from the suction pipe 17 to the compressor 11 increases due to the increase in the temperature of the evaporator outlet refrigerant. The temperature of the discharge refrigerant discharged from the compressor 11 increases due to the increase in the temperature of the suction refrigerant. That is, including when the discharge temperature is higher than the target discharge temperature, the temperature of the discharge refrigerant is brought close to the target discharge temperature by executing the discharge temperature control of the main expansion valve 15.

[0039] When executing the discharge temperature control of the main expansion valve 15, the control device 43 uses the discharge temperature sensor 31 to measure the temperature of the discharged refrigerant discharged from the compressor 11, and uses the intermediate heat exchange temperature sensor 32 to measure the condensation temperature of the refrigerant flowing in the intermediate heat exchanger 16. The control device 43 calculates the superheat of the discharged refrigerant, that is, the discharge superheat, based on the discharge temperature and the condensation temperature measured by the discharge temperature sensor 31. When the condensation temperature measured by the intermediate heat exchange temperature sensor 32 is lower than the condensation temperature threshold, or the discharge superheat is higher than the first superheat threshold (step S2: No), the control device 43 keeps the bypass path 22 blocked and continues to execute the discharge temperature control of the main expansion valve 15. The condensation temperature threshold is a condensation temperature of a compression ratio that may affect the reliability of the compressor 11, which is predetermined by experiments or the like. In addition, the first superheat threshold is a discharge superheat required to ensure a sufficient amount of heat exchange with water in the intermediate heat exchanger 16, which is predetermined by experiments or the like.

[0040] When the condensing temperature measured by the intermediate heat exchange temperature sensor 32 is above the condensing temperature threshold and the discharge superheat is below the first superheat threshold (step S2: yes), the control device 43 performs pressure control of the main expansion valve 15 and performs discharge temperature control of the bypass expansion valve 23 (step S3).

[0041] In the pressure control of the main expansion valve 15, the control device 43 uses the discharge pressure sensor 41 to measure the pressure of the discharged refrigerant discharged from the compressor 11 to the discharge pipe 18. The control device 43 calculates the condensing pressure indicating the pressure of the refrigerant flowing in the intermediate heat exchanger 16 based on the discharge pressure measured by the discharge pressure sensor 41. When the condensing pressure is higher than the predetermined target condensing pressure, the control device 43 increases the opening of the main expansion valve 15. As the opening of the main expansion valve 15 increases, the flow rate of the low-pressure gas-liquid two-phase refrigerant supplied from the intermediate heat exchanger 16 to the outdoor heat exchanger 14 increases, and thus the condensing pressure decreases.

[0042] When the condensing pressure is lower than the target condensing pressure, the control device 43 reduces the opening of the main expansion valve 15. As the opening of the main expansion valve 15 becomes smaller, the flow rate of the low-pressure gas-liquid two-phase refrigerant supplied from the intermediate heat exchanger 16 to the outdoor heat exchanger 14 decreases, and thus the condensing pressure rises. That is, including when the condensing pressure is higher than the target condensing pressure, the condensing pressure is brought close to the target condensing pressure by executing the pressure control of the main expansion valve 15.

[0043] When the bypass expansion valve 23 is used for discharge temperature control, the control device 43 opens the bypass expansion valve 23 to connect the discharge pipe 18 and the suction pipe 17 so that the refrigerant flows in the bypass path 22. Before the bypass expansion valve 23 is opened, Figure 4 As shown, the compressor 11 compresses the evaporator outlet refrigerant 51 supplied from the outdoor heat exchanger 14 to the suction pipe 17 . Figure 4 It is a Mollier diagram showing the state change of the refrigerant when the refrigerant flows in the bypass path 22. The decompression process of the main expansion valve 15 and the bypass expansion valve 23 is schematically shown in the figure. The low-pressure gas phase refrigerant flowing out of the evaporator outlet refrigerant 51 is compressed by the compressor 11 to become the discharged refrigerant 52. Since the bypass expansion valve 23 is open, a part of the discharged refrigerant 52 discharged from the compressor 11 is supplied to the bypass expansion valve 23. The bypass expansion valve 23 adjusts the flow rate of the refrigerant flowing through the bypass path 22 so that a part of the discharged refrigerant 52 supplied to the bypass expansion valve 23 is decompressed. A part of the discharged refrigerant 52 is decompressed by the bypass expansion valve 23 to become the bypass refrigerant 53. The evaporator outlet refrigerant 51, and the bypass refrigerant 53 flowing through the bypass path 22 and supplied to the suction pipe 17 are mixed in the suction pipe 17 to become the suction refrigerant 54. The superheat of the suction refrigerant 54 is higher than the superheat of the evaporator outlet refrigerant 51. The compressor 11 compresses the suction refrigerant 54. The suction refrigerant 54 is compressed by the compressor 11 to become another discharge refrigerant 55. Since the superheat of the suction refrigerant 54 is higher than the superheat of the evaporator outlet refrigerant 51, the temperature of the discharge refrigerant 55 is higher than the temperature of the discharge refrigerant 52 before the bypass expansion valve 23 is opened.

[0044] When the discharge temperature of the bypass expansion valve 23 is controlled, the control device 43 further uses the discharge temperature sensor 31 to measure the temperature of the discharged refrigerant discharged from the compressor 11 to the discharge pipe 18. When the discharge temperature measured by the discharge temperature sensor 31 is lower than the target discharge temperature, the control device 43 increases the opening of the bypass expansion valve 23. The flow rate of the bypass refrigerant supplied to the suction pipe 17 via the bypass path 22 increases due to the larger opening of the bypass expansion valve 23. In the suction refrigerant supplied to the compressor 11, more bypass refrigerant is mixed due to the increase in the flow rate of the bypass refrigerant supplied to the suction pipe 17 via the bypass path 22. Since more bypass refrigerant is mixed in the suction refrigerant, the superheat of the suction refrigerant supplied to the compressor 11 increases. The temperature of the discharge refrigerant discharged from the compressor 11 increases due to the increase in the superheat of the suction refrigerant.

[0045] When the discharge temperature measured by the discharge temperature sensor 31 is higher than the target discharge temperature, the control device 43 reduces the opening of the bypass expansion valve 23. The flow rate of the bypass refrigerant supplied to the suction pipe 17 via the bypass path 22 is reduced due to the smaller opening of the bypass expansion valve 23. In the suction refrigerant supplied to the compressor 11, less bypass refrigerant is mixed due to the reduction in the flow rate of the bypass refrigerant supplied to the suction pipe 17 via the bypass path 22. As the amount of bypass refrigerant mixed in the suction refrigerant decreases, the superheat of the suction refrigerant supplied to the compressor 11 decreases. The temperature of the discharge refrigerant discharged from the compressor 11 decreases due to the decrease in the superheat of the suction refrigerant. That is, including when the discharge temperature is lower than the target discharge temperature, the temperature of the discharge refrigerant is brought close to the target discharge temperature by executing the discharge temperature control of the bypass expansion valve 23.

[0046] When executing the pressure control of the main expansion valve 15 and the discharge temperature control of the bypass expansion valve 23, the control device 43 uses the discharge temperature sensor 31 to measure the temperature of the discharged refrigerant discharged from the compressor 11, and uses the intermediate heat exchange temperature sensor 32 to measure the temperature of the refrigerant flowing in the intermediate heat exchanger 16. The control device 43 calculates the superheat of the discharged refrigerant, that is, the discharge superheat, based on the discharge temperature measured by the discharge temperature sensor 31 and the condensation temperature measured by the intermediate heat exchange temperature sensor 32.

[0047] When the condensing temperature measured by the intermediate heat exchange temperature sensor 32 is higher than the condensing temperature threshold, or the discharge superheat is lower than the predetermined second superheat threshold (step S4: No), the control device 43 continues to perform the pressure control of the main expansion valve 15 and the discharge temperature control of the bypass expansion valve 23. The second superheat threshold is set to a discharge superheat greater than the first superheat threshold. At this discharge superheat, even if the bypass expansion valve 23 is closed, the discharge superheat required to ensure a sufficient amount of heat exchange with water in the intermediate heat exchanger 16 can be ensured. When the condensing temperature is below the condensing temperature threshold and the discharge superheat is above the second superheat threshold (step S4: Yes), the control device 43 closes the bypass expansion valve 23 and performs the discharge temperature control of the main expansion valve 15 (step S1).

[0048] When the opening of the main expansion valve 15 becomes larger, Figure 5 As shown, the pressure of the refrigerant 61 flowing in the outdoor heat exchanger 14 is higher than the pressure of the evaporator outlet refrigerant 62 supplied from the outdoor heat exchanger 14 to the suction pipe 17 before the opening degree of the main expansion valve 15 becomes larger. Figure 5 It is a Mollier diagram showing other state changes of the refrigerant when the refrigerant flows in the bypass path 22. The temperature of the refrigerant 61 is in a state higher than the temperature of the refrigerant 63 flowing in the outdoor heat exchanger 14 before the opening degree of the main expansion valve 15 becomes larger. As the temperature of the refrigerant 61 increases, the absolute value of the temperature difference between the temperature of the refrigerant 61 and the temperature of the external atmosphere decreases, so that the performance of the outdoor heat exchanger 14 in heat exchange between the refrigerant 61 and the external atmosphere decreases. The reduction in the performance of the outdoor heat exchanger 14 in heat exchange may cause the superheat of the evaporator outlet refrigerant 64 supplied from the outdoor heat exchanger 14 to the suction pipe 17 to decrease, or the refrigerant 61 is not completely evaporated, and the evaporator outlet refrigerant 64 is in a humid state instead of a superheated state.

[0049] The evaporator outlet refrigerant 64 and the bypass refrigerant 65 flowing through the bypass path 22 and supplied to the suction pipe 17 are mixed in the suction pipe 17 to become the suction refrigerant 66. That is, when the evaporator outlet refrigerant 64 is in an overheated state, the superheat degree of the suction refrigerant 66 is higher than the superheat degree of the evaporator outlet refrigerant 64, and even if the evaporator outlet refrigerant 64 is not in an overheated state, the evaporator outlet refrigerant 64 becomes the suction refrigerant 66 in an overheated state. The compressor 11 compresses the suction refrigerant 66. That is, even when the evaporator outlet refrigerant supplied from the outdoor heat exchanger 14 to the suction pipe 17 is not completely evaporated, the air conditioner 1 can prevent the refrigerant in a humid state from being supplied to the compressor 11, and can supply the refrigerant in an overheated state to the compressor 11. The air conditioner 1 can improve the reliability of the compressor 11 by preventing the refrigerant in a humid state from being supplied to the compressor 11.

[0050] Even when the discharge temperature of the refrigerant cannot be raised to the target discharge temperature by the process of step S1, the air conditioner 1 can raise the discharge temperature of the refrigerant to the target discharge temperature by executing the process of step S2. For example, when using R290 refrigerant having a lower discharge temperature than R32 refrigerant, the air conditioner 1 can raise the discharge temperature of the refrigerant to the target discharge temperature without increasing the rotation speed of the compressor 11. The air conditioner 1 can appropriately heat the room by raising the discharge temperature of the refrigerant to the target discharge temperature.

[0051] Refrigeration operation

[0052] For example, when the air conditioner 1 is operated by the user to perform cooling operation, the cooling operation is performed. When the air conditioner 1 performs cooling operation, the control device 43 controls the four-way valve 12 and switches the four-way valve 12 to the cooling position. The control device 43 controls the compressor 11 to compress the low-pressure gas-phase refrigerant supplied via the suction pipe 17. The low-pressure gas-phase refrigerant is compressed by the compressor 11 to become a high-pressure gas-phase refrigerant. The compressor 11 then discharges the high-pressure gas-phase refrigerant to the discharge pipe 18. Since the four-way valve 12 is switched to the cooling position, the high-pressure gas-phase refrigerant discharged to the discharge pipe 18 is supplied to the outdoor heat exchanger 14.

[0053] The outdoor heat exchanger 14 exchanges heat between the high-pressure gas-phase refrigerant supplied from the four-way valve 12 and the outside atmosphere, and releases heat from the high-pressure gas-phase refrigerant to the outside atmosphere. After the high-pressure gas-phase refrigerant releases heat in the outdoor heat exchanger 14, it becomes a high-pressure liquid-phase refrigerant in a supercooled state. That is, when the air conditioner 1 performs cooling operation, the outdoor heat exchanger 14 functions as a condenser. The high-pressure liquid-phase refrigerant is supplied to the main expansion valve 15.

[0054] The main expansion valve 15 adjusts the flow rate of the refrigerant flowing from the outdoor heat exchanger 14 to the intermediate heat exchanger 16, thereby reducing the pressure of the high-pressure liquid-phase refrigerant supplied from the outdoor heat exchanger 14. The high-pressure liquid-phase refrigerant is reduced in pressure by the main expansion valve 15 to become a low-pressure gas-liquid two-phase refrigerant. The low-pressure gas-liquid two-phase refrigerant is supplied to the intermediate heat exchanger 16.

[0055] The intermediate heat exchanger 16 exchanges heat between the low-pressure gas-liquid two-phase refrigerant supplied from the main expansion valve 15 and the water circulating in the water circuit 6. The low-pressure gas-liquid two-phase refrigerant absorbs heat from the water in the intermediate heat exchanger 16 and becomes a low-pressure gas-phase refrigerant. That is, when the air conditioner 1 performs cooling operation, the intermediate heat exchanger 16 functions as an evaporator. The low-pressure gas-phase refrigerant is supplied to the four-way valve 12. Since the four-way valve 12 is switched to the cooling position, the low-pressure gas-phase refrigerant is supplied to the suction pipe 17 and supplied to the compressor 11 via the suction pipe 17.

[0056] When the air conditioner 1 performs cooling operation, the control device 43 further controls the pump 26 to supply water to the intermediate heat exchanger 16 in a manner that the water circulates in the water circuit 6. The water cooled by the intermediate heat exchanger 16 is supplied to the indoor heat exchanger 25. The indoor heat exchanger 25 exchanges heat between the water circulating in the water circuit 6 and the air in the room where the indoor unit 3 is installed. The indoor unit 3 cools the room by blowing the air that has exchanged heat with the water in the indoor heat exchanger 25 into the room.

[0057] When the air conditioner 1 performs cooling operation, the control device 43 further performs the speed control of the compressor 11, just as when the air conditioner 1 performs heating operation. When the air conditioner 1 performs cooling operation, the control device 43 further performs the speed control of the compressor 11, just as when the air conditioner 1 performs heating operation. Figure 3 Control of the main expansion valve 15 and the bypass expansion valve 23.

[0058] When performing cooling operation, the air conditioner 1 can raise the discharge temperature of the refrigerant to the target discharge temperature, as in the case of heating operation. The air conditioner 1 can appropriately cool the room by raising the discharge temperature of the refrigerant to the target discharge temperature.

[0059] Effects of the air conditioner 1 of embodiment 1

[0060] The air conditioner 1 of Example 1 includes a compressor 11, an intermediate heat exchanger 16, an outdoor heat exchanger 14, a main expansion valve 15, a bypass expansion valve 23, a discharge temperature sensor 31, a discharge pressure sensor 41, and a control device 43. The intermediate heat exchanger 16 is connected to the compressor 11 via a discharge pipe 18. The outdoor heat exchanger 14 is connected to the compressor 11 via a suction pipe 17. The main expansion valve 15 is used to reduce the pressure of the refrigerant supplied from the intermediate heat exchanger 16 and supply it to the outdoor heat exchanger 14. The bypass expansion valve 23 is provided in the middle of a bypass path 22 for connecting the discharge pipe 18 and the suction pipe 17. The discharge temperature sensor 31 is used to measure the temperature of the discharged refrigerant discharged from the compressor 11, that is, the discharge temperature. The discharge pressure sensor 41 is used to measure the pressure of the discharged refrigerant discharged from the compressor 11. The control device 43 is used to control the bypass expansion valve 23 when the compressor 11 is compressing the refrigerant in the suction pipe 17 and discharging it to the discharge pipe 18, so that the bypass expansion valve 23 is switched between a first state in which the refrigerant does not flow through the bypass path 22 and a second state in which the refrigerant flows from the discharge pipe 18 to the suction pipe 17 via the bypass path 22. The control device 43 is also used to calculate the pressure of the refrigerant flowing through the intermediate heat exchanger 16, that is, the condensation pressure, based on the discharge pressure measured by the discharge pressure sensor 41. When the refrigerant does not flow through the bypass path 22, the control device 43 controls the opening of the main expansion valve 15 in such a way that the discharge temperature becomes a specified target discharge temperature, and when the refrigerant flows through the bypass path 22, the control device 43 controls the opening of the main expansion valve 15 in such a way that the condensation pressure becomes a specified target condensation pressure.

[0061] At this time, the air conditioner 1 of Embodiment 1 can increase the superheat of the suction refrigerant when a part of the discharge refrigerant is supplied to the suction pipe 17, and can increase the temperature of the discharge refrigerant without increasing the compression ratio of the compressor 11 compressing the refrigerant. Therefore, the air conditioner 1 of Embodiment 1 can reduce the load applied to the compressor 11 when increasing the temperature of the discharge refrigerant, thereby improving the reliability of the compressor 11.

[0062] In addition, when the refrigerant does not flow through the bypass path 22, and the temperature of the refrigerant flowing in the intermediate heat exchanger 16, that is, the condensation temperature, is above the condensation temperature threshold, and the superheat of the discharged refrigerant is below the first superheat threshold, the control device 43 of the air conditioner 1 of Example 1 controls the bypass expansion valve 23 so that the refrigerant flows through the bypass path 22. When the refrigerant flows through the bypass path 22, and the condensation temperature is below the condensation temperature threshold, and the superheat of the discharged refrigerant is above the second superheat threshold that is greater than the first superheat threshold, the control device 43 controls the bypass expansion valve 23 so that the refrigerant does not flow through the bypass path 22.

[0063] Furthermore, the control device 43 of the air conditioner 1 according to the first embodiment controls the bypass expansion valve 23 so that the discharge temperature becomes equal to or lower than the threshold value when the refrigerant flows in the bypass passage 22 .

[0064] Example 2

[0065] In the air conditioner 1 of the second embodiment, the above-mentioned Figure 3 The control of the main expansion valve 15 and the bypass expansion valve 23 is replaced by other control, and the other parts are the same as the air conditioner of Example 1. Figure 6 1 is a flowchart showing the control of the main expansion valve 15 and the bypass expansion valve 23 of the air conditioner of Example 2. This control is performed during heating operation. When the air conditioner of Example 2 performs heating operation, the control device 43 performs discharge temperature control of the main expansion valve 15, closes the bypass expansion valve 23 to block the bypass path 22, and prevents the refrigerant from flowing in the bypass path 22 (step S11), as in the air conditioner 1 of Example 1 described above.

[0066] When executing the control of the main expansion valve 15 and the bypass expansion valve 23, the control device 43 calculates the compression ratio of the compressor 11 compressing the refrigerant based on the condensing temperature as the detection value of the intermediate heat exchange temperature sensor 32 and the evaporating temperature as the detection value of the outdoor heat exchange temperature sensor 33. When the compression ratio is less than the first compression ratio threshold value (step S12: No), the control device 43 keeps the bypass path 22 blocked and continues to execute the discharge temperature control of the main expansion valve 15. The first compression ratio threshold value is a compression ratio predetermined by experiments, etc., and it is known that if the compressor 11 operates at a compression ratio exceeding this compression ratio, the reliability of the compressor 11 will be reduced. When the compression ratio is greater than the first compression ratio threshold value (step S12: Yes), the control device 43 executes the pressure control of the main expansion valve 15 and executes the discharge temperature control of the bypass expansion valve 23 (step S13).

[0067] When the compression ratio is greater than the second compression ratio threshold value (step S14: No), the control device 43 continues to perform the pressure control of the main expansion valve 15 and the discharge temperature control of the bypass expansion valve 23. The second compression ratio threshold value is set to a compression ratio smaller than the first compression ratio threshold value. At this compression ratio, even if the compression ratio increases, closing the bypass expansion valve 23 does not affect the reliability of the compressor 11. When the compression ratio is less than the second compression ratio threshold value (step S14: Yes), the control device 43 closes the bypass expansion valve 23 and performs the discharge temperature control of the main expansion valve 15 (step S11).

[0068] When the air conditioner of the second embodiment performs cooling operation, the control device 43 performs the same operation as the air conditioner of the second embodiment performs heating operation. Figure 6The main expansion valve 15 and the bypass expansion valve 23 are controlled. According to this control, the air conditioner of Example 2 can raise the discharge temperature of the refrigerant to the target discharge temperature without making the compression ratio greater than the specified value, as with the air conditioner 1 of Example 1 described above, thereby being able to appropriately cool and heat the room.

[0069] The air conditioner of the second embodiment switches whether to allow the refrigerant to flow in the bypass path 22 based on the compression ratio, thereby more reliably preventing the compression ratio from exceeding a predetermined value. The air conditioner of the second embodiment can reduce the load applied to the compressor 11 by preventing the compression ratio from increasing, thereby improving the reliability of the compressor 11.

[0070] In the water circuit 6 of the air conditioner 1 of the above-mentioned embodiments 1 and 2, water is circulated, but other heat media different from water may also be circulated. Antifreeze is shown as an example of heat media. As with the air conditioners of embodiments 1 and 2, when other heat media different from water circulates in the water circuit 6, the air conditioner can also suppress the increase in the load of the compressor 11 and increase the temperature of the discharged refrigerant discharged from the compressor 11.

[0071] Example 3

[0072] In the air conditioner of embodiment 3, the water circuit 6 of the air conditioner 1 of embodiments 1 and 2 described above is omitted, the intermediate heat exchanger 16 is replaced by another indoor heat exchanger, and the other parts are the same as the air conditioner 1 of embodiment 1 described above. The indoor heat exchanger is arranged inside the indoor unit 3. One end of the indoor heat exchanger is connected to the fourth connection port 124 of the four-way valve 12, and the other end of the indoor heat exchanger is connected to the main expansion valve 15. The indoor heat exchanger performs heat exchange between the refrigerant circulating in the refrigerant circuit 5 and the indoor air.

[0073] As with the air conditioner 1 of the first embodiment described above, or as with the air conditioner 1 of the first embodiment described above, the control device 43 of the air conditioner of the third embodiment controls the main expansion valve 15 and the bypass expansion valve 23. Therefore, as with the air conditioners of the first and second embodiments described above, the air conditioner of the third embodiment can suppress the increase in the load of the compressor 11 and can increase the temperature of the discharged refrigerant discharged from the compressor 11.

[0074] Although the control device 43 described above calculates the condensing pressure based on the discharge pressure measured by the discharge pressure sensor 41, the condensing pressure may be calculated based on other physical quantities different from the discharge pressure. As an example of the physical quantity, the condensing temperature measured by the intermediate heat exchange temperature sensor 32 during the heating operation is shown. When the condensing pressure is calculated in this way, the air conditioner can suppress the increase in the load of the compressor 11 and can increase the temperature of the discharged refrigerant discharged from the compressor 11, as in the air conditioner of the embodiment described above.

[0075] The above embodiments are described, but the embodiments are not limited to the above contents. In addition, the above structural elements include structural elements that can be easily thought of by those skilled in the art, are substantially the same, and are within the so-called equivalent range. Further, the above structural elements can be appropriately combined. Further, at least one of the various omissions, replacements, and changes of the structural elements can be performed within the scope of the gist of the embodiments.

[0076] Explanation of symbols

[0077] 1 Air conditioner

[0078] 5 Refrigerant circuit

[0079] 6 Water circuit

[0080] 11. Compressor

[0081] 14 Outdoor heat exchanger

[0082] 15 Main expansion valve

[0083] 16 Intermediate heat exchanger

[0084] 17 Suction pipe

[0085] 18 Discharge pipe

[0086] 21 Bypass circuit

[0087] 22 Bypass path

[0088] 23 Bypass expansion valve

[0089] 31 Discharge temperature sensor

[0090] 43 Control Device

Claims

1. An air conditioner, characterized in that: have: compressor; a condenser connected to the compressor via a discharge pipe; an evaporator connected to the compressor via a suction pipe; a main expansion valve for reducing the pressure of the refrigerant supplied from the condenser and supplying the refrigerant to the evaporator; a bypass expansion valve disposed in the middle of a bypass path for connecting the discharge pipe and the suction pipe; a discharge temperature sensor for detecting the temperature of the discharged refrigerant discharged from the compressor, that is, the discharge temperature; a condensing pressure calculating unit for calculating the pressure of the refrigerant flowing in the condenser, that is, the condensing pressure; and a control unit that controls the bypass expansion valve to switch between a first state in which the refrigerant does not flow through the bypass path and a second state in which the refrigerant flows from the discharge pipe to the suction pipe via the bypass path, When the refrigerant does not flow through the bypass path, the control unit controls the opening degree of the main expansion valve so that the discharge temperature becomes a predetermined target discharge temperature. When the refrigerant flows through the bypass path, the control unit controls the opening degree of the main expansion valve so that the condensing pressure becomes a predetermined target condensing pressure.

2. The air conditioner according to claim 1, characterized in that: When the refrigerant does not flow through the bypass path, and the temperature of the refrigerant flowing in the condenser, that is, the condensation temperature, is above the condensation temperature threshold, and the superheat of the discharged refrigerant is below the first superheat threshold, the control unit controls the bypass expansion valve so that the refrigerant flows through the bypass path. When the refrigerant flows through the bypass path, and the condensation temperature is below the condensation temperature threshold, and the superheat of the discharged refrigerant is above a second superheat threshold that is greater than the first superheat threshold, the control unit controls the bypass expansion valve so that the refrigerant does not flow through the bypass path.

3. The air conditioner according to claim 1, characterized in that: When the refrigerant does not flow through the bypass path and the compression ratio of the compressor compressing the refrigerant is greater than a first threshold, the control unit controls the bypass expansion valve so that the refrigerant flows through the bypass path. When the refrigerant flows through the bypass path and the compression ratio is less than a second threshold value that is smaller than the first threshold value, the control portion controls the bypass expansion valve so that the refrigerant does not flow through the bypass path.

4. The air conditioner according to claim 1, characterized in that: Also available: The indoor heat exchanger is used to exchange heat between the other refrigerant circulating between the indoor unit and the outdoor unit and the indoor air. One of the condenser and the evaporator allows the refrigerant to exchange heat with the external atmosphere. The other of the condenser and the evaporator exchanges heat between the refrigerant and the other refrigerant.

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