Air conditioning system

Abstract

To provide an air conditioning system that can achieve low cost and energy efficiency. [Solution] The air conditioning system 101 includes a refrigerant circuit in which the refrigerant circulates in the order of a compressor, a first heat exchanger, a first expansion valve, a refrigerant container, a second expansion valve, and a second heat exchanger, and an expansion valve control unit that adjusts the opening degrees of the first expansion valve and the second expansion valve. When the rotational speed of the motor that drives the compressor is less than or equal to a predetermined value, the expansion valve control unit adjusts the opening degree of the first expansion valve so that the degree of subcooling of the first heat exchanger becomes a target degree of subcooling, and also adjusts the opening degree of the second expansion valve so that the discharge temperature of the compressor becomes a target discharge temperature.

Description

Technical Field

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[0001] The present invention relates to an air conditioner.

Background Art

[0002] There is an air conditioner including a refrigerant circuit in which a compressor, an outdoor heat exchanger, a first expansion valve, a refrigerant container, a second expansion valve, and an indoor heat exchanger are connected in this order in a refrigerant pipe, and an expansion valve control unit that adjusts the opening degrees of the first expansion valve and the second expansion valve (for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the air conditioner described in Patent Document 1, the opening degrees of the first expansion valve and the second expansion valve are respectively controlled using the outlet superheat degree of the indoor heat exchanger and the discharge temperature of the compressor. In order to obtain the outlet superheat degree of the indoor heat exchanger, it is necessary to provide a temperature sensor at the outlet of the indoor heat exchanger, which increases the cost.

[0005] Further, since the outlet superheat degree of the indoor heat exchanger is a small value, it is difficult to perform accurate control due to variations in the measured values by the temperature sensor.

[0006] Therefore, an object of the present invention is to provide an air conditioner capable of achieving low cost and energy saving.

Means for Solving the Problems

[0008] As described above, by adjusting the opening of the first expansion valve so that the degree of supercooling of the first heat exchanger reaches the target degree of supercooling, the opening of the first expansion valve can be adjusted without installing a temperature sensor at the outlet of the indoor heat exchanger, thus suppressing the cost increase that would result from installing a temperature sensor. Furthermore, since the value of the degree of supercooling is greater than the value of the outlet superheating, the influence of variability in the measured values ​​from the temperature sensor can be suppressed, allowing for accurate adjustment of the opening of the first expansion valve. This prevents the compressor from stopping due to an error in adjusting the opening of the first expansion valve, which would otherwise require restarting the compressor and thus require a large amount of power. Therefore, it is possible to provide an air conditioning system that can achieve low cost and energy efficiency.

[0009] In the above embodiment, the target degree of supercooling when the rotational speed is less than or equal to the predetermined value may be higher than the target degree of supercooling when the rotational speed is greater than the predetermined value.

[0010] In this embodiment, when the rotational speed of the motor driving the compressor drops below a predetermined value, the opening of the first expansion valve is adjusted to a smaller value in order to increase the degree of supercooling, thereby reducing the minimum capacity of the air conditioner. This prevents the compressor from stopping, thus alleviating the discomfort experienced by users due to the cessation of cooling or heating. Furthermore, it prevents the restart of the compressor, which requires a large amount of power, thus reducing the amount of electricity consumed by the air conditioning system.

[0011] In the above embodiment, the target discharge temperature when the rotational speed is less than or equal to the predetermined value may be higher than the target discharge temperature when the rotational speed is greater than the predetermined value.

[0012] In this embodiment, when the rotational speed of the motor driving the compressor drops below a predetermined value, the opening of the second expansion valve is adjusted to a smaller value in order to increase the discharge temperature of the compressor, thereby lowering the minimum capacity of the air conditioner. This prevents the compressor from stopping, thus reducing the discomfort experienced by users due to the cessation of cooling or heating. Furthermore, it prevents the restart of the compressor, which requires a large amount of power, thus reducing the amount of electricity consumed by the air conditioning system.

[0013] In the above embodiment, the first heat exchanger and the second heat exchanger may be an outdoor heat exchanger and an indoor heat exchanger, respectively.

[0014] According to this embodiment, the air conditioning system can be operated as a cooling system.

[0015] In the above embodiment, the first heat exchanger and the second heat exchanger may be an indoor heat exchanger and an outdoor heat exchanger, respectively.

[0016] According to this embodiment, the air conditioning system can be operated as a heating system.

[0017] An air conditioning system according to one aspect of the present invention comprises a compressor, a refrigerant circuit connected in the order of a first heat exchanger, a first expansion valve, a refrigerant container, a second expansion valve, and a second heat exchanger, a four-way switching valve that can selectively switch between a first connection state in which the discharge and suction portions of the compressor are connected to the first and second heat exchangers, respectively, and a second connection state in which the discharge and suction portions of the compressor are connected to the second and first heat exchangers, respectively, and an expansion valve control unit that adjusts the opening degree of the first and second expansion valves, wherein the expansion valve control unit drives the compressor When the rotational speed of the compressor is below a predetermined value, and the four-way switching valve switches to the first connection state, the opening of the first expansion valve is adjusted so that the degree of subcooling of the first heat exchanger becomes the target degree of subcooling, and the opening of the second expansion valve is adjusted so that the discharge temperature of the compressor becomes the target discharge temperature. When the four-way switching valve switches to the second connection state, the opening of the second expansion valve is adjusted so that the degree of subcooling of the second heat exchanger becomes the target degree of subcooling, and the opening of the first expansion valve is adjusted so that the discharge temperature of the compressor becomes the target discharge temperature.

[0018] As described above, by adjusting the opening of the first or second expansion valve so that the degree of supercooling of the first or second heat exchanger reaches a target degree of supercooling, the opening of the first or second expansion valve can be adjusted without installing a temperature sensor at the outlet of the indoor heat exchanger, thus suppressing the cost increase caused by installing a temperature sensor. Furthermore, since the value of the degree of supercooling is greater than the value of the outlet superheating, the influence of variability in the measured values ​​from the temperature sensor can be suppressed, allowing for accurate adjustment of the opening of the first or second expansion valve. This prevents the compressor from stopping due to an error in adjusting the opening of the first or second expansion valve, which would otherwise require restarting the compressor and thus reduce the power consumption. Therefore, it is possible to provide an air conditioning system that achieves low cost and energy efficiency. In addition, in the air conditioning system described in Patent Document 1, the control of the opening of the first expansion valve using the outlet superheating of the indoor heat exchanger is only possible during cooling operation and cannot be performed during heating operation. In contrast, by using a four-way switching valve to switch between the first and second connection states, the opening degree of the first or second expansion valve can be adjusted using the degree of subcooling of the first or second heat exchanger, respectively, so that the air conditioning system can be operated as either a cooling system or a heating system. [Effects of the Invention]

[0019] According to the present invention, it is possible to provide an air conditioning system that can achieve low cost and energy efficiency. [Brief explanation of the drawing]

[0020] [Figure 1] This diagram shows an overview of the cooling operation of the air conditioning system 101 according to this embodiment. [Figure 2] This is a functional block diagram showing the functions of the control device 30 in the air conditioning system 101 according to this embodiment. [Figure 3] Table Tbl1 shows the relationship between the target degree of subcooling, target discharge temperature, and the opening degree of each valve during cooling operation. [Figure 4]It is a flowchart showing a method for adjusting the opening degree of an expansion valve executed by a control device 30 during a cooling operation according to this embodiment. [Figure 5] It is a diagram showing an overview of the heating operation of the air conditioner 101 according to this embodiment. [Figure 6] It is a table Tbl2 showing the relationship between the target subcooling degree, the target discharge temperature, and the operating states of the opening degrees of each valve during the heating operation. [Figure 7] It is a flowchart showing a method for adjusting the opening degree of an expansion valve executed by a control device 30 during the heating operation according to this embodiment.

Mode for Carrying Out the Invention

[0021] Hereinafter, embodiments of the present invention will be specifically described with reference to the drawings. Note that the embodiments described below are merely specific examples for implementing the present invention and do not limitatively interpret the present invention. Also, for ease of understanding the description, the same reference numerals are attached to the same constituent elements in each drawing as much as possible, and duplicate descriptions may be omitted.

[0022] [During Cooling Operation] FIG. 1 is a diagram showing an overview of the cooling operation of the air conditioner 101 according to this embodiment. As shown in FIG. 1, the air conditioner 101 includes an outdoor unit 21 and an indoor unit 22. The outdoor unit 21 includes a compressor 11, a four-way switching valve 12, an outdoor heat exchanger 13, an electronic expansion valve 14, a refrigerant container 15, an electronic expansion valve 16, operation valves 17 and 19, a control device 30, and temperature sensors 51, 52, 53, 54, and 57. The indoor unit 22 includes an indoor heat exchanger 18 and temperature sensors 55, 56, and 58.

[0023] During cooling operation, the refrigerant circulates in the refrigerant circuit 10 in the following order: compressor 11, four-way switching valve 12, outdoor heat exchanger 13 (an example of a "first heat exchanger"), electronic expansion valve 14 (an example of a "first expansion valve"), refrigerant container 15, electronic expansion valve 16 (an example of a "second expansion valve"), control valve 17, indoor heat exchanger 18 (an example of a "second heat exchanger"), control valve 19, four-way switching valve 12, and compressor 11.

[0024] In detail, the compressor 11 includes, for example, a motor 11c driven by power supplied from a control device 30. The rotational speed of the motor 11c is controlled by the control device 30.

[0025] The compressor 11 draws in low-temperature, low-pressure gaseous refrigerant through the refrigerant intake section 11b, compresses the drawn-in refrigerant, generates high-temperature, high-pressure gaseous refrigerant, and discharges it from the refrigerant discharge section 11a.

[0026] The four-way switching valve 12 can selectively switch between a first connection state in which the refrigerant discharge section 11a and refrigerant suction section 11b of the compressor 11 are connected to the outdoor heat exchanger 13 and the indoor heat exchanger 18, respectively, and a second connection state in which the refrigerant discharge section 11a and refrigerant suction section 11b of the compressor 11 are connected to the indoor heat exchanger 18 and the outdoor heat exchanger 13, respectively. The four-way switching valve 12 is switched to the first connection state during cooling operation.

[0027] The outdoor heat exchanger 13 is through which the refrigerant, which is pressurized and supplied from the compressor 11 through the four-way switching valve 12, flows. In the outdoor heat exchanger 13, heat exchange occurs between the refrigerant, which is in a high-temperature, high-pressure gaseous state, and the outdoor air, which is at a lower temperature than the refrigerant. During this process, the temperature of the refrigerant decreases due to the heat exchange, and it undergoes a phase change from a gaseous state to a liquid state.

[0028] The electronic expansion valve 14 has a valve whose opening degree is variable according to the control of the control device 30. In this embodiment, the electronic expansion valve 14 sets the size of the refrigerant flow path to an opening degree corresponding to the level of the opening degree signal V1 received from the control device 30 via a signal line (not shown). The pressure and temperature of the refrigerant decrease as it passes through the electronic expansion valve 14. The refrigerant may be in a liquid state or a gas-liquid two-phase state downstream of the electronic expansion valve 14. Generally, it is in a gas-liquid two-phase state. The refrigerant container 15 temporarily stores the refrigerant in a liquid state. The refrigerant container 15 is provided as a refrigerant buffer tank and has the function of appropriately adjusting the amount of refrigerant in the refrigerant circuit.

[0029] The electronic expansion valve 16 has a valve whose opening degree is variable according to the control of the control device 30. In this embodiment, the electronic expansion valve 16 sets the size of the refrigerant flow path to an opening degree corresponding to the level of the opening degree signal V2 received from the control device 30 via a signal line (not shown). The pressure and temperature of the refrigerant decrease as it passes through the electronic expansion valve 16. The refrigerant is in a gas-liquid two-phase state downstream of the electronic expansion valve 16.

[0030] Indoor heat exchanger 18 is through which refrigerant drawn from the electronic expansion valve 16 to the compressor 11 via the four-way switching valve 12 flows. In indoor heat exchanger 18, heat exchange occurs between the low-temperature gas-liquid two-phase refrigerant and the indoor air, which is hotter than the refrigerant. At this time, the refrigerant undergoes a phase change from a gas-liquid two-phase state to a gaseous state due to the thermal energy received through heat exchange. Note that the temperature of the refrigerant may rise.

[0031] The refrigerant, in a low-temperature, low-pressure gaseous state, that has passed through the indoor heat exchanger 18 is compressed again by the compressor 11 and then pumped to the outdoor heat exchanger 13.

[0032] The operating valves 17 and 19 are used to seal refrigerant into the outdoor unit 21 side of the refrigerant circuit 10 when the outdoor unit 21 and indoor unit 22 are separated, such as when the product is shipped.

[0033] The temperature sensor 51 is attached to the compressor 11 and detects the temperature of the compressor 11 body. The temperature sensor 51 generates a temperature signal T1 indicating the detected temperature.

[0034] The temperature sensor 52 is attached to the piping connected to the refrigerant discharge section 11a of the compressor 11 and detects the temperature of the refrigerant discharged from the compressor 11 (hereinafter sometimes referred to as the discharge temperature). The temperature sensor 52 generates a temperature signal T2 indicating the detected discharge temperature.

[0035] The temperature sensor 53 is a plurality of pipes, one end of which is connected to the four-way switching valve 12 and the other end of which is connected to the electronic expansion valve 14. The sensor 53 is installed at approximately the middle position of any of the plurality of pipes included in the outdoor heat exchanger 13 and detects the temperature at the middle position (hereinafter sometimes referred to as the first middle position temperature). The temperature sensor 53 generates a temperature signal T3 indicating the detected first middle position temperature.

[0036] The temperature sensor 54 is attached to the piping connected to the inlet and outlet on the electronic expansion valve 14 side of the outdoor heat exchanger 13, and detects the temperature of the liquid side inlet and outlet of the outdoor heat exchanger 13 (hereinafter sometimes referred to as the first liquid side inlet and outlet temperature). The temperature sensor 54 generates a temperature signal T4 indicating the detected first liquid side inlet and outlet temperature.

[0037] The temperature sensor 55 is attached to the piping connected to the inlet and outlet on the electronic expansion valve 16 side of the indoor heat exchanger 18, and detects the temperature of the liquid side inlet and outlet of the indoor heat exchanger 18 (hereinafter sometimes referred to as the second liquid side inlet and outlet temperature). The temperature sensor 54 generates a temperature signal T5 indicating the detected second liquid side inlet and outlet temperature.

[0038] The temperature sensor 56 is a plurality of pipes, one end of which is connected to the four-way switching valve 12 and the other end of which is connected to the electronic expansion valve 16. The sensor 56 is mounted at approximately the middle position of any of the plurality of pipes included in the indoor heat exchanger 18 and detects the temperature at the middle position (hereinafter sometimes referred to as the second middle position temperature). The temperature sensor 56 generates a temperature signal T6 indicating the detected second middle position temperature.

[0039] The temperature sensor 57 is attached to the outdoor unit 21 and detects the temperature of the air before it passes through the outdoor heat exchanger 13. The temperature sensor 57 generates a temperature signal T7 indicating the detected air temperature.

[0040] The temperature sensor 58 is attached to the indoor unit 22 and detects the temperature of the air before it passes through the indoor heat exchanger 18. The temperature sensor 58 generates a temperature signal T8 indicating the detected air temperature.

[0041] The temperature sensors 51 to 58 each output the temperature signals T1 to T8 they generate to the control device 30 via a signal line (not shown).

[0042] Figure 2 is a functional block diagram showing the functions of the control device 30 in the air conditioning system 101 according to this embodiment. As shown in Figure 2, the control device 30 includes a compressor control unit 31, a low-load operation determination unit 32, a subcooling degree acquisition unit 33, a discharge temperature acquisition unit 34, an expansion valve control unit 35, and a target temperature acquisition unit 36.

[0043] The compressor control unit 31 in the control device 30 controls the rotational speed of the motor 11c in the compressor 11. Specifically, the drive shaft of the motor 11c is connected to a rotating member included in the compressor 11. The rotating member is, for example, a shaft with a swash plate that causes a piston to reciprocate, a rotor with vanes attached, or a movable scroll. The rotational speed of the motor 11c is the rotational speed of the drive shaft of the motor 11c. The rotational speed of the motor 11c can also be rephrased as the rotational speed of the rotating member included in the compressor 11. The compressor control unit 31 has, for example, an inverter circuit that supplies power to the motor 11c. The compressor control unit 31 adjusts the frequency of the power supplied by the inverter circuit (hereinafter sometimes referred to as the power frequency) based on the operating mode, such as cooling and heating, and the room temperature. The motor 11c rotates at a rotational speed corresponding to the power frequency.

[0044] The low-load operation determination unit 32 determines whether the operating state of the air conditioner 101 is low-load operation. Specifically, the low-load operation determination unit 32 determines whether the operating state of the air conditioner 101 is low-load operation based on the relationship between the rotational speed of the motor 11c and a predetermined threshold value (an example of a "predetermined value").

[0045] In this embodiment, the low-load operation determination unit 32 monitors the rotational speed of the motor 11c, and if the rotational speed of the motor 11c is below a predetermined threshold, it determines that the operating state of the air conditioner 101 is low-load operation.

[0046] On the other hand, the low-load operation determination unit 32 determines that the operating state of the air conditioner 101 is normal operation if the rotational speed of the motor 11c is higher than a predetermined threshold. The low-load operation determination unit 32 outputs the determination result to the expansion valve control unit 35.

[0047] The supercooling degree acquisition unit 33 acquires the supercooling degree of the first heat exchanger. Specifically, during cooling operation, the supercooling degree acquisition unit 33 acquires the supercooling degree of the outdoor heat exchanger 13.

[0048] In detail, the subcooling degree acquisition unit 33 receives temperature signals T3 and T4 from temperature sensors 53 and 54, respectively, and acquires the first intermediate position temperature of the outdoor heat exchanger 13 indicated by temperature signal T3 and the first liquid side inlet / outlet temperature indicated by temperature signal T4. The subcooling degree acquisition unit 33 acquires the subcooling degree of the outdoor heat exchanger 13 by subtracting the first liquid side inlet / outlet temperature from the first intermediate position temperature and outputs it to the expansion valve control unit 35.

[0049] The discharge temperature acquisition unit 34 acquires the temperature of the refrigerant discharged from the compressor 11. Specifically, the discharge temperature acquisition unit 34 receives a temperature signal T2 from the temperature sensor 52, acquires the discharge temperature indicated by the temperature signal T2, and outputs it to the expansion valve control unit 35.

[0050] The target temperature acquisition unit 36 ​​acquires the target temperature of the discharge temperature. In this embodiment, for example, the target temperature acquisition unit 36 ​​receives temperature signals T3 and T6 from temperature sensors 53 and 56, respectively, and acquires the first intermediate position temperature of the outdoor heat exchanger 13 indicated by temperature signal T3 and the second intermediate position temperature of the indoor heat exchanger 18 indicated by temperature signal T6. The target temperature acquisition unit 36 ​​also acquires the rotational speed of the motor 11c based on the power frequency output by the compressor control unit 31.

[0051] Figure 3 is Table Tbl1, which shows the relationship between the target subcooling degree, target discharge temperature, and the opening degree of each valve during cooling operation. As shown in Table Tbl1, the target temperature acquisition unit 36 ​​acquires the target discharge temperature (hereinafter sometimes referred to as the target discharge temperature) based on the first intermediate position temperature, the second intermediate position temperature, the rotational speed of the motor 11c, and the operating state of the air conditioner 101.

[0052] Specifically, when the low-load operation determination unit 32 determines that the system has switched from normal operation to low-load operation, the target temperature acquisition unit 36 ​​raises the target discharge temperature by approximately 5 to 15°C. As an example of calculating the target discharge temperature, the target temperature acquisition unit 36 ​​acquires the temperature detected by temperature sensors 53 and 56 and the rotational speed of the motor 11c, and calculates the target discharge temperature based on a preset calculation formula into which the acquired temperature and rotational speed are input. On the other hand, when the low-load operation determination unit 32 determines that the system has switched from low-load operation to normal operation, the target temperature acquisition unit 36 ​​returns the target discharge temperature to the target discharge temperature corresponding to the operating state during normal operation. The target temperature acquisition unit 36 ​​outputs the target discharge temperature to the expansion valve control unit 35.

[0053] Furthermore, the target temperature acquisition unit 36 ​​acquires a target temperature for the degree of subcooling (hereinafter sometimes referred to as the target degree of subcooling). Specifically, when the judgment by the low-load operation determination unit 32 switches from normal operation to low-load operation, the target temperature acquisition unit 36 ​​increases the target degree of subcooling of the outdoor heat exchanger 13. Specifically, for example, when the target degree of subcooling of 5 to 10K switches to low-load operation, the target temperature acquisition unit 36 ​​increases it by 10K. As an example of calculating the target degree of subcooling, the target temperature acquisition unit 36 ​​acquires the temperatures detected by temperature sensors 53, 54, and 57, and calculates the target degree of subcooling based on a preset calculation formula into which each acquired temperature is input. On the other hand, when the judgment by the low-load operation determination unit 32 switches from low-load operation to normal operation, the target temperature acquisition unit 36 ​​returns the target degree of subcooling of the outdoor heat exchanger 13 to the target degree of subcooling corresponding to the operating state during normal operation. The target temperature acquisition unit 36 ​​outputs the target degree of subcooling to the expansion valve control unit 35.

[0054] The expansion valve control unit 35 receives the degree of subcooling and the target degree of subcooling from the subcooling degree acquisition unit 33 and the target temperature acquisition unit 36, respectively, and adjusts the opening degree of the electronic expansion valve 14 so that the degree of subcooling becomes the target degree of subcooling.

[0055] In this embodiment, the expansion valve control unit 35 generates an opening signal V1 to adjust the opening degree of the electronic expansion valve 14, and adjusts the opening degree of the electronic expansion valve 14 by outputting the opening signal V1 to the electronic expansion valve 14. The expansion valve control unit 35 adjusts the level of the opening signal V1 so that the degree of supercooling reaches the target degree of supercooling.

[0056] Furthermore, the expansion valve control unit 35 receives the discharge temperature and target discharge temperature from the discharge temperature acquisition unit 34 and the target temperature acquisition unit 36, respectively, and adjusts the opening degree of the electronic expansion valve 16 so that the discharge temperature becomes the target discharge temperature.

[0057] In this embodiment, the expansion valve control unit 35 generates an opening signal V2 to adjust the opening degree of the electronic expansion valve 16, and outputs the opening signal V2 to the electronic expansion valve 16 to adjust the opening degree of the electronic expansion valve 16. The expansion valve control unit 35 adjusts the level of the opening signal V2 so that the discharge temperature reaches the target discharge temperature.

[0058] [How to adjust the opening of the expansion valve] Next, we will explain in detail how to adjust the opening degree of the expansion valve during cooling operation. Figure 4 is a flowchart showing the method for adjusting the opening degree of the expansion valve performed by the control device 30 during cooling operation according to this embodiment. As shown in Figure 4, the method for adjusting the opening degree of the expansion valve includes steps S102 to S118, and each step is performed by the processor included in the control device 30.

[0059] First, the control device 30 monitors the rotational speed of the motor 11c and determines whether the operating state of the air conditioner 101 is low-load operation based on the relationship between the rotational speed of the motor 11c and a predetermined threshold. Specifically, the control device 30 determines that the operating state of the air conditioner 101 is low-load operation when the rotational speed of the motor 11c is below the predetermined threshold (YES in step S102).

[0060] Next, the control device 30 calculates a new target subcooling degree for the outdoor heat exchanger 13 (step S112). The new target subcooling degree is higher than the target subcooling degree before the operating state change if the operating state of the air conditioner 101 has just switched from normal operation to low-load operation (see Table Tbl1).

[0061] Next, the control device 30 adjusts the opening of the electronic expansion valve 14 so that the degree of subcooling of the outdoor heat exchanger 13 reaches a new target degree of subcooling (step S114). For example, immediately after the operating state of the air conditioner 101 has been switched from normal operation to low-load operation, the opening of the electronic expansion valve 14 after the switch in operating state is smaller than the opening before the switch in operating state (see Table Tbl1).

[0062] Next, the control device 30 calculates a new target discharge temperature (step S116). The new target discharge temperature is higher than the target discharge temperature before the operating state change, immediately after the operating state of the air conditioner 101 has switched from normal operation to low-load operation (see Table Tbl1).

[0063] Next, the control device 30 adjusts the opening of the electronic expansion valve 16 so that the discharge temperature reaches the new target discharge temperature (step S118). For example, immediately after the operating state of the air conditioner 101 has been switched from normal operation to low-load operation, the opening of the electronic expansion valve 16 after the operating state switch is smaller than the opening before the operating state switch (see Table Tbl1).

[0064] On the other hand, the control device 30 determines that the operating state of the air conditioner 101 is normal operation when the rotational speed of the motor 11c is higher than a predetermined threshold (NO in step S102).

[0065] Next, the control device 30 calculates the target degree of subcooling for the outdoor heat exchanger 13 (step S104). The target degree of subcooling is lower than the new target degree of subcooling before the operating state change, if the operating state of the air conditioner 101 has just switched from low-load operation to normal operation (see Table Tbl1).

[0066] Next, the control device 30 adjusts the opening of the electronic expansion valve 14 so that the degree of subcooling of the outdoor heat exchanger 13 reaches the target degree of subcooling (step S106). For example, immediately after the operating state of the air conditioner 101 has switched from low-load operation to normal operation, the opening of the electronic expansion valve 14 after the switch in operating state is greater than the opening before the switch in operating state (see Table Tbl1).

[0067] Next, the control device 30 calculates the target discharge temperature (step S108). The target discharge temperature is lower than the new target discharge temperature before the operating state change, immediately after the operating state of the air conditioner 101 has switched from low-load operation to normal operation (see Table Tbl1).

[0068] Next, the control device 30 adjusts the opening degree of the electronic expansion valve 16 so that the discharge temperature reaches the target discharge temperature (step S110). For example, immediately after the operating state of the air conditioner 101 has switched from low-load operation to normal operation, the opening degree of the electronic expansion valve 16 after the operating state switch is greater than the opening degree before the operating state switch (see Table Tbl1).

[0069] Next, the control device 30 monitors the rotational speed of the motor 11c and determines whether the operating state of the air conditioner 101 is low-load operation based on the relationship between the rotational speed of the motor 11c and a predetermined threshold (step S102). Note that the determination of the operating state during low-load operation may be performed, for example, at set time intervals.

[0070] Furthermore, the processes in the flowchart above may be rearranged as long as it does not affect the operation. For example, the order of processes S104 to S110 in the flowchart above may be rearranged as long as S106 is performed after S104 and S110 is performed after S108.

[0071] Furthermore, the order of the processes S112 to S118 in the flowchart above may be changed, as long as S114 is performed after S112 and S118 is performed after S116.

[0072] [During heating operation] The following describes how to adjust the opening of the expansion valve during heating operation. Here, we will omit descriptions of aspects common to adjusting the expansion valve opening during cooling operation and only explain the differences. In particular, similar configurations and their corresponding effects will not be mentioned sequentially.

[0073] Figure 5 shows an overview of the air conditioning system 101 during heating operation according to this embodiment. As shown in Figure 5, during heating operation, the second flow path is set in the four-way switching valve 12.

[0074] During heating operation, the refrigerant circulates in the refrigerant circuit 10 in the following order: compressor 11, four-way switching valve 12, control valve 19, indoor heat exchanger 18 (an example of a "first heat exchanger"), control valve 17, electronic expansion valve 16 (an example of a "first expansion valve"), refrigerant container 15, electronic expansion valve 14 (an example of a "second expansion valve"), outdoor heat exchanger 13 (an example of a "second heat exchanger"), four-way switching valve 12, and compressor 11.

[0075] The four-way switching valve 12 is switched to the second connection state during heating operation. The indoor heat exchanger 18 is through which the refrigerant, which is pressurized and supplied from the compressor 11 through the four-way switching valve 12, flows. In the indoor heat exchanger 18, heat exchange occurs between the high-temperature, high-pressure gaseous refrigerant and the indoor air, which is at a lower temperature than the refrigerant. At this time, the temperature of the refrigerant decreases due to the heat exchange, and it undergoes a phase change from a gaseous state to a liquid state.

[0076] The refrigerant's pressure and temperature decrease as it passes through the electronic expansion valve 16. The refrigerant may be in a liquid state or a gas-liquid two-phase state downstream of the electronic expansion valve 16. Generally, it is in a gas-liquid two-phase state.

[0077] The refrigerant's pressure and temperature decrease as it passes through the electronic expansion valve 14. The refrigerant is in a gas-liquid two-phase state downstream of the electronic expansion valve 14.

[0078] The outdoor heat exchanger 13 is through which the refrigerant, which is drawn from the electronic expansion valve 14 to the compressor 11 via the four-way switching valve 12, flows. In the outdoor heat exchanger 13, heat exchange occurs between the low-temperature gas-liquid two-phase refrigerant and the outdoor air, which is hotter than the refrigerant. At this time, the refrigerant undergoes a phase change from a gas-liquid two-phase state to a gaseous state due to the thermal energy received through heat exchange. Note that the temperature of the refrigerant may rise.

[0079] The refrigerant, in a low-temperature, low-pressure gaseous state, that has passed through the indoor heat exchanger 18 is compressed again by the compressor 11 and then pumped back to the indoor heat exchanger 18.

[0080] As shown in Figure 2, the supercooling degree acquisition unit 33 acquires the supercooling degree of the indoor heat exchanger 18 during heating operation.

[0081] In detail, the subcooling degree acquisition unit 33 receives temperature signals T6 and T5 from temperature sensors 56 and 55, respectively, and acquires the second intermediate position temperature of the indoor heat exchanger 18 indicated by temperature signal T6 and the second liquid side inlet / outlet temperature indicated by temperature signal T5. The subcooling degree acquisition unit 33 acquires the subcooling degree of the indoor heat exchanger 18 by subtracting the second liquid side inlet / outlet temperature from the second intermediate position temperature and outputs it to the expansion valve control unit 35.

[0082] Figure 6 is Table Tbl2, which shows the relationship between the target subcooling degree, target discharge temperature, and valve opening degree during heating operation. As shown in Table Tbl2, the target temperature acquisition unit 36 ​​increases the target subcooling degree of the indoor heat exchanger 18 when the judgment by the low-load operation determination unit 32 switches from normal operation to low-load operation. Specifically, for example, the target temperature acquisition unit 36 ​​increases the target subcooling degree of 5-10K by 10K when switching to low-load operation. As an example of calculating the target subcooling degree, the target temperature acquisition unit 36 ​​acquires the temperatures detected by temperature sensors 55, 56, and 58, and calculates the target subcooling degree based on a preset calculation formula into which each acquired temperature is input. On the other hand, when the judgment by the low-load operation determination unit 32 switches from low-load operation to normal operation, the target temperature acquisition unit 36 ​​returns the target subcooling degree of the indoor heat exchanger 18 to the target subcooling degree corresponding to the operating state during normal operation. The target temperature acquisition unit 36 ​​outputs the target degree of subcooling to the expansion valve control unit 35.

[0083] [How to adjust the opening of the expansion valve] Next, the method for adjusting the opening degree of the expansion valve during heating operation will be described in detail. Figure 7 is a flowchart showing the method for adjusting the opening degree of the expansion valve performed by the control device 30 during heating operation according to this embodiment. As shown in Figure 7, the method for adjusting the opening degree of the expansion valve includes steps S202 to S218, each of which is performed by the processor included in the control device 30.

[0084] First, the control device 30 determines that the operating state of the air conditioner 101 is low-load operation when the rotational speed of the motor 11c is below a predetermined threshold (YES in step S202).

[0085] Next, the control device 30 calculates the new target subcooling degree of the indoor heat exchanger 18 (step S212). The new target subcooling degree is higher than the target subcooling degree before the operating state change when the operating state of the air conditioner 101 has just switched from normal operation to low-load operation (Table Tbl2).

[0086] Next, the control device 30 adjusts the opening of the electronic expansion valve 16 so that the degree of subcooling of the indoor heat exchanger 18 reaches a new target degree of subcooling (step S214). For example, immediately after the operating state of the air conditioning system 101 has been switched from normal operation to low-load operation, the opening of the electronic expansion valve 16 after the switch in operating state is smaller than the opening before the switch in operating state (see Table Tbl2).

[0087] Next, the control device 30 calculates a new target discharge temperature (step S216). The new target discharge temperature is higher than the target discharge temperature before the operating state change, immediately after the operating state of the air conditioner 101 has switched from normal operation to low-load operation (see Table Tbl2).

[0088] Next, the control device 30 adjusts the opening of the electronic expansion valve 14 so that the discharge temperature reaches the new target discharge temperature (step S218). For example, immediately after the operating state of the air conditioner 101 has been switched from normal operation to low-load operation, the opening of the electronic expansion valve 14 after the operating state switch is smaller than the opening before the operating state switch (see Table Tbl2).

[0089] On the other hand, the control device 30 determines that the operating state of the air conditioner 101 is normal operation when the rotational speed of the motor 11c is higher than a predetermined threshold (NO in step S202).

[0090] Next, the control device 30 calculates the target degree of subcooling for the indoor heat exchanger 18 (step S204). The target degree of subcooling is lower than the new target degree of subcooling before the operating state change, if the operating state of the air conditioner 101 has just switched from low-load operation to normal operation (see Table Tbl2).

[0091] Next, the control device 30 adjusts the opening of the electronic expansion valve 16 so that the degree of subcooling of the indoor heat exchanger 18 reaches the target degree of subcooling (step S206). For example, immediately after the operating state of the air conditioning system 101 has switched from low-load operation to normal operation, the opening of the electronic expansion valve 16 after the switch in operating state is greater than the opening before the switch in operating state (see Table Tbl2).

[0092] Next, the control device 30 calculates the target discharge temperature (step S208). The target discharge temperature is lower than the new target discharge temperature before the operating state change, immediately after the operating state of the air conditioner 101 has switched from low-load operation to normal operation (see Table Tbl2).

[0093] Next, the control device 30 adjusts the opening of the electronic expansion valve 14 so that the discharge temperature reaches the target discharge temperature (step S210). For example, immediately after the operating state of the air conditioner 101 has switched from low-load operation to normal operation, the opening of the electronic expansion valve 14 after the operating state switch is greater than the opening before the operating state switch (see Table Tbl2).

[0094] Next, the control device 30 monitors the rotational speed of the motor 11c and determines whether the operating state of the air conditioner 101 is low-load operation based on the relationship between the rotational speed of the motor 11c and a predetermined threshold (step S202). Note that the determination of the operating state during low-load operation may be performed, for example, at set time intervals.

[0095] Furthermore, the processes in the flowchart above may be rearranged as long as it does not affect the operation. For example, the order of processes S204 to S210 in the flowchart above may be rearranged as long as S206 is performed after S204 and S210 is performed after S208.

[0096] Furthermore, the order of the processes S212 to S218 in the flowchart above may be changed, as long as S214 is performed after S212 and S218 is performed after S216.

[0097] Furthermore, although this embodiment describes a configuration in which cooling operation and heating operation can be switched by a four-way switching valve 12, it is not limited to this. The air conditioning system 101 may also be configured in a way that does not include a four-way switching valve 12, and only cooling operation or heating operation is performed. Specifically, when the refrigerant discharge section 11a and refrigerant suction section 11b of the compressor 11 are connected to the outdoor heat exchanger 13 and the indoor heat exchanger 18, respectively, the air conditioning system 101 operates as a cooling system. On the other hand, when the refrigerant discharge section 11a and refrigerant suction section 11b of the compressor 11 are connected to the indoor heat exchanger 18 and the outdoor heat exchanger 13, respectively, the air conditioning system 101 operates as a heating system.

[0098] Furthermore, the control of the opening degrees of the electronic expansion valves 14 and 16 is not limited to the order described in the embodiment. The control of the opening degree of the electronic expansion valve 14 may be performed in the order of controlling the opening degree of the electronic expansion valve 16, or in the order of controlling the opening degree of the electronic expansion valve 16, or each control may be performed simultaneously.

[0099] Furthermore, the extent to which the target discharge temperature and target subcooling degree are increased during low-load operation may be set to increase by n% compared to the previous target discharge temperature and target subcooling degree, depending on the operating capacity of the air conditioner 101, which is indicated by the set room temperature, the previous target discharge temperature, the previous target subcooling degree, and the rotational speed of the motor 11c, etc., when low-load operation is determined. In other words, the extent to which the target discharge temperature and target subcooling degree are increased during low-load operation varies each time low-load operation is determined, depending on the operating capacity of the air conditioner 101 at that time (for example, at the time of determination).

[0100] The embodiments described above are provided to facilitate understanding of the present invention and are not intended to limit its interpretation. The elements, arrangement, materials, conditions, shapes, and sizes of the embodiments are not limited to those exemplified and can be modified as appropriate. Furthermore, it is possible to partially substitute or combine the configurations shown in different embodiments. [Explanation of Symbols]

[0101] 10…Refrigerant circuit 11… Compressor 11a...refrigerant discharge part 11b... Refrigerant intake 11c…motor 12…Four-way switching valve 13...Outdoor heat exchanger 14…Electronic expansion valve 15… Refrigerant container 16…Electronic expansion valve 17, 19... Operating valves 18…Indoor heat exchanger 21…Outdoor unit 22…Indoor unit 30...Control device 31…Compressor control unit 32...Low-load operation determination unit 33...Supercooling degree acquisition section 34...Discharge temperature acquisition section 35...Expansion valve control unit 36...Target temperature acquisition section 51, 52, 53, 54, 55, 56, 57, 58… Temperature sensors 101... Air conditioning system

Claims

1. A refrigerant circuit in which the refrigerant circulates in the following order: compressor, first heat exchanger, first expansion valve, refrigerant container, second expansion valve, and second heat exchanger. The system comprises an expansion valve control unit that adjusts the opening degree of the first expansion valve and the second expansion valve, The expansion valve control unit adjusts the opening of the first expansion valve so that the degree of subcooling of the first heat exchanger becomes the target degree of subcooling, and adjusts the opening of the second expansion valve so that the discharge temperature of the compressor becomes the target discharge temperature, when the rotational speed of the motor driving the compressor is below a predetermined value. Air conditioning system.

2. When the rotational speed is less than or equal to the predetermined value, the target degree of supercooling is higher than the target degree of supercooling when the rotational speed is greater than the predetermined value. The air conditioning device according to claim 1.

3. When the rotational speed is less than or equal to the predetermined value, the target discharge temperature is higher than the target discharge temperature when the rotational speed is greater than the predetermined value. The air conditioning device according to claim 1.

4. The first heat exchanger and the second heat exchanger are an outdoor heat exchanger and an indoor heat exchanger, respectively. The air conditioning device according to claim 1.

5. The first heat exchanger and the second heat exchanger are an indoor heat exchanger and an outdoor heat exchanger, respectively. The air conditioning device according to claim 1.

6. Compressor and, A refrigerant circuit consisting of a first heat exchanger, a first expansion valve, a refrigerant container, a second expansion valve, and a second heat exchanger connected in that order, A four-way switching valve that can selectively switch between a first connection state in which the discharge and suction sections of the compressor are connected to the first heat exchanger and the second heat exchanger, respectively, and a second connection state in which the discharge and suction sections of the compressor are connected to the second heat exchanger and the first heat exchanger, respectively, The system comprises an expansion valve control unit that adjusts the opening degree of the first expansion valve and the second expansion valve, When the rotational speed of the motor driving the compressor is below a predetermined value, the expansion valve control unit adjusts the opening of the first expansion valve so that the degree of subcooling of the first heat exchanger becomes the target degree of subcooling, and adjusts the opening of the second expansion valve so that the discharge temperature of the compressor becomes the target discharge temperature, when the four-way switching valve switches to the second connection state, and adjusts the opening of the second expansion valve so that the degree of subcooling of the second heat exchanger becomes the target degree of subcooling, and adjusts the opening of the first expansion valve so that the discharge temperature of the compressor becomes the target discharge temperature. Air conditioning system.

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