Air conditioner

Abstract

An air conditioner (1) comprises: a refrigerant circuit (10); and a control device (100) configured to store a measured temperature from a temperature sensor (96), measured during a certain period before the present time point, and an operating frequency of a compressor (30). The control device (100) is configured such that, if the temperature measured by the temperature sensor (96) does not satisfy a stability condition with respect to a target temperature, the control device performs feedback control of the operating frequency of the compressor (30) such that the temperature measured by the temperature sensor (96) matches the target temperature. The control device (100) is configured to fix the operating frequency of the compressor (30) when the temperature measured by the temperature sensor (96) satisfies the stability condition with respect to the target temperature.

Description

air conditioner

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

[0002] A known air conditioner includes a control device that uses the indoor temperature and the indoor heat exchanger temperature as controlled variables and the compressor drive frequency and the indoor fan rotation speed as manipulated variables (see Japanese Patent Laid-Open Publication No. 9-119696). This control device includes a first controller and a second controller. The first controller manipulates either the drive frequency or the indoor fan rotation speed so as to match the indoor temperature with a target value. The second controller manipulates the other of the drive frequency and the indoor fan rotation speed so as to match the indoor heat exchanger temperature with a target value.

[0003] Japanese Patent Application Publication No. 9-119696

[0004] In a typical air conditioner, the temperature measured by a temperature sensor is compared with a target temperature, and the compressor is controlled based on the comparison result. However, if the resolution of the temperature sensor or the resolution of the A / D converter that acquires the temperature sensor output value is low, hunting occurs in the temperature, so there is room for improvement.

[0005] The present disclosure has been made to solve the above-mentioned problems, and has an object to provide an air conditioner that can suppress room temperature hunting more than conventional air conditioners.

[0006] The present disclosure relates to an air conditioner. The air conditioner includes a refrigerant circuit, a temperature sensor, and a control device. The refrigerant circuit includes a compressor, a condenser, an expansion valve, and an evaporator, and is configured to circulate a refrigerant. The temperature sensor detects the temperature of a space to be air-conditioned. The control device is configured to store the temperature measured by the temperature sensor over a certain period of time prior to the present and the operating frequency of the compressor. If the temperature measured by the temperature sensor does not satisfy a stability condition for a target temperature, the control device is configured to feedback-control the operating frequency of the compressor so that the temperature measured by the temperature sensor matches the target temperature. If the temperature measured by the temperature sensor satisfies a stability condition for the target temperature, the control device is configured to fix the operating frequency of the compressor.

[0007] According to the air conditioner of the present disclosure, hunting of room temperature can be suppressed more effectively than before even when the resolution of the temperature sensor or A / D converter is low.

[0008] 1 is a diagram showing the configuration of an air conditioner of the present embodiment and the flow of refrigerant during cooling. 2 is a diagram showing the configuration of an air conditioner of the present embodiment and the flow of refrigerant during heating. 3 is a diagram for explaining the relationship between the resolution of a temperature sensor of an air conditioner and hunting. 4 is a flowchart for explaining a specific control method for the air conditioner shown in FIG. 1. 5 is a diagram showing changes in temperature and compressor frequency when the control of FIG. 4 is executed.

[0009] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are designated by the same reference numerals, and description thereof will not be repeated.

[0010] Fig. 1 is a diagram showing the configuration of an air conditioner according to this embodiment and the flow of refrigerant during cooling. The air conditioner 1 shown in Fig. 1 includes an outdoor unit 300, an indoor unit 400, and a control device 100. The outdoor unit 300 and the indoor unit 400 are connected by extension pipes 21 and 22, and the refrigerant circulates between the outdoor unit 300 and the indoor unit 400.

[0011] The outdoor unit 300 is installed outdoors in an area that is not the target of air conditioning, and includes a four-way valve 40 , a compressor 30 , a heat exchanger 50 , an outdoor fan 51 , and an expansion valve 65 .

[0012] The four-way valve 40 includes connection ports 41, 42, 43, and 44. Connection port 41 is connected to the intake port of the compressor 30. Connection port 42 is connected to the heat exchanger 50 of the outdoor unit 300 via piping 17. Connection port 43 is connected to the discharge port of the compressor 30. Connection port 44 is connected to the indoor unit 400 via piping 12 and extension piping 21. The four-way valve 40 is configured to switch its internal communication state under the control of the control device 100. During cooling operation, as shown by the solid lines in FIG. 1 , the four-way valve 40 is controlled so that connection ports 41 and 44 are connected to each other and connection ports 42 and 43 are connected to each other.

[0013] The compressor 30 is configured to operate and stop, and to change its rotational speed during operation, under the control of the control device 100. The control device 100 arbitrarily changes the operating frequency Fz of the compressor 30. The compressor 30 changes its rotational speed in response to changes in the operating frequency Fz, thereby changing the amount of refrigerant discharged. Various types of compressors can be used for the compressor 30, and for example, a scroll type, a rotary type, a screw type, etc. can be used as the compressor 30.

[0014] Heat exchanger 50 exchanges heat between the outside air and the refrigerant using outdoor fan 51. One end of heat exchanger 50 is connected to connection port 42 of four-way valve 40 via piping 17. The other end of heat exchanger 50 is connected to one end of expansion valve 65 via piping 16. The other end of expansion valve 65 is connected to indoor unit 400 via piping 15 and extension piping 22.

[0015] The outdoor fan 51 is configured to operate and stop under the control of the control device 100, and further to change its rotation speed during operation.

[0016] The indoor unit 400 is installed in an indoor space to be air-conditioned, and includes a heat exchanger 60, an indoor fan 61, and a temperature sensor 96 that detects the indoor temperature.

[0017] The heat exchanger 60 of the indoor unit 400 exchanges heat between the indoor air and the refrigerant using an indoor fan 61. One end of the heat exchanger 60 is connected to the connection port 44 of the four-way valve 40 via a pipe 13, an extension pipe 21, and a pipe 12. The other end of the heat exchanger 60 is connected to the other end of the expansion valve 65 via a pipe 14, an extension pipe 22, and a pipe 15.

[0018] The indoor fan 61 is configured to operate and stop, and further to change the rotation speed during operation, under the control of the control device 100 .

[0019] The expansion valve 65 is, for example, an electronic expansion valve whose opening degree is adjusted under the control of the control device 100. The control device 100 is configured to adjust the amount of pressure reduction of the refrigerant by adjusting the opening degree of the expansion valve 65. Note that although the expansion valve 65 is arranged on the outdoor unit 300 side in FIG. 1 , it may also be arranged on the indoor unit 400 side.

[0020] The control device 100 includes a CPU 101 and a memory 102. The control device 100 is configured to control each actuator of the refrigerant circuit 10, such as the compressor 30, the expansion valve 65, the four-way valve 40, the outdoor fan 51, and the indoor fan 61. The control device 100 may be mounted in either the outdoor unit 300 or the indoor unit 400, or may be separate from the outdoor unit 300 and the indoor unit 400. The control device 100 may be distributed between the outdoor unit 300 and the indoor unit 400.

[0021] The CPU 101 is a computing entity that executes various programs to control the actuators of the refrigerant circuit 10. The CPU 101 has the function of executing various processes by executing the programs, but some or all of these functions may be implemented using dedicated hardware circuits such as an ASIC (Application Specific Integrated Circuit) or an FPGA (Field-Programmable Gate Array).

[0022] The memory 102 provides a storage area for storing program code, various variables, etc., when the CPU 101 executes various programs. The memory 102 may be one or more non-transitory computer-readable media. Examples of the memory 102 include volatile memory such as dynamic random access memory (DRAM) and static random access memory (SRAM), and non-volatile memory such as read-only memory (ROM) and flash memory. The CPU 101 controls each actuator of the refrigerant circuit 10 by executing the programs stored in the memory 102.

[0023] Next, the conditions and refrigerant flow during cooling operation will be described. Cooling operation with a set temperature of 27°C is assumed. The refrigerant compressed by the compressor 30 becomes a high-pressure gas refrigerant. The refrigerant discharged from the compressor 30 passes through the four-way valve 40 and flows into the heat exchanger 50 of the outdoor unit 300. The heat exchanger 50 functions as a condenser, exchanging heat with outdoor air. The refrigerant changes to liquid refrigerant by releasing heat to the outdoor air. The liquid refrigerant exiting the heat exchanger 50 enters the expansion valve 65 and is decompressed to become a two-phase gas-liquid refrigerant. The two-phase gas-liquid refrigerant flows into the heat exchanger 60 of the indoor unit 400. The heat exchanger 60 functions as an evaporator, where the refrigerant exchanges heat with the indoor air, changing from the two-phase gas-liquid refrigerant to a low-pressure gas refrigerant, while the indoor air is cooled by heat exchange with the refrigerant. Thereafter, the refrigerant passes through the four-way valve 40 again and enters the intake port of the compressor 30, where it is compressed to become high-pressure refrigerant again.

[0024] Next, the conditions and flow of refrigerant during heating operation will be described. Fig. 2 is a diagram showing the configuration of the air conditioner of this embodiment and the flow of refrigerant during heating.

[0025] Assume heating operation with a set temperature of 20° C. During heating operation, the four-way valve 40 is controlled so that the connection ports 41 and 42 communicate with each other and the connection ports 44 and 43 communicate with each other, as shown by the solid lines in FIG.

[0026] The refrigerant compressed by the compressor 30 becomes high-pressure gas refrigerant. The refrigerant discharged from the compressor 30 passes through the four-way valve 40 and flows into the heat exchanger 60 of the indoor unit 400. The heat exchanger 60 functions as a condenser, exchanging heat with the indoor air. The refrigerant changes to liquid refrigerant by releasing heat to the indoor air. The liquid refrigerant exiting the heat exchanger 60 enters the expansion valve 65, where it is decompressed and becomes a two-phase gas-liquid refrigerant. The two-phase gas-liquid refrigerant flows into the heat exchanger 50 of the outdoor unit 300. The heat exchanger 50 functions as an evaporator, where the refrigerant exchanges heat with the outdoor air, changing from the two-phase gas-liquid refrigerant to low-pressure gas refrigerant, while the outdoor air is cooled by the heat exchange with the refrigerant. The refrigerant then passes through the four-way valve 40 again and enters the suction port of the compressor 30, where it is compressed and becomes high-pressure refrigerant again.

[0027] FIG. 3 is a diagram for explaining the relationship between the resolution of the temperature sensor of the air conditioner and hunting.

[0028] A typical air conditioner uses feedback control of the compressor frequency to keep the room temperature at a target temperature. However, this type of control can cause periodic fluctuations in the room temperature (hunting). Such hunting will be explained below in the case of cooling operation, using Figures 1 and 3.

[0029] The output value of the temperature sensor 96 is A / D converted so that it can be acquired by a control device 100, such as a microcomputer, provided in the air conditioner 1. For this reason, the acquired value Tain has a resolution. Therefore, the air conditioner 1 can only grasp the indoor temperature using the acquired value Tain, which is a discrete numerical value.

[0030] Since the acquired indoor temperature value Tain is a discrete value, even if the indoor temperature Ta changes slightly, it cannot be detected in the feedback control of the compressor operating frequency Fz.

[0031] The indoor temperature Ta changes in accordance with changes in the compressor operating frequency Fz. However, the value Tain obtained from the temperature sensor 96 is a discrete value, resulting in a stepped waveform as shown in Fig. 3. In section K1, there is a difference between the indoor temperature Ta and the set temperature Taset, and the indoor temperature Ta gradually approaches the set temperature Taset, so the compressor 30 operates while lowering the operating frequency Fz.

[0032] At time t1, the indoor temperature Ta is higher than the set temperature Taset, but the acquired value Tain detected by the temperature sensor 96 matches the set temperature Taset, so the operating frequency Fz of the compressor does not fluctuate in section K2.

[0033] Here, the compressor frequency during steady operation when the room temperature Ta coincides with the set temperature Taset is defined as frequency Fset.

[0034] At time t2, the operating frequency Fz is higher than the frequency Fset, so the room temperature Ta gradually decreases in the first half of section K3. Meanwhile, in the second half of section K3, the value Tain obtained from the temperature sensor 96 changes and becomes lower than the set temperature Taset, so the operating frequency Fz of the compressor decreases, and when Fz<Fset, the room temperature Ta begins to rise.

[0035] In section K4, the value Tain obtained from the temperature sensor 96 matches the set temperature Taset, so the compressor operating frequency Fz becomes a constant value, but since this operating frequency Fz is lower than the frequency Fset, the indoor temperature Ta gradually rises.

[0036] In section K5, the value Tain obtained by the temperature sensor 96 is higher than the set temperature Taset, so the operating frequency Fz of the compressor increases. As a result, when Fz>Fset, the indoor temperature Ta gradually decreases.

[0037] After section K5, the states of sections K2 to K5 occur repeatedly, resulting in a hunting phenomenon in which the indoor temperature Ta fluctuates periodically.

[0038] As described above, if the value Tain obtained from the temperature sensor 96 is a discrete value, fluctuations in the operating frequency Fz of the compressor occur, causing a hunting phenomenon in which the indoor temperature Ta periodically fluctuates. This hunting phenomenon can cause problems such as increased discomfort for people in the room, and can also cause an increase in power consumption due to fluctuations in the operating frequency.

[0039] Fig. 4 is a flowchart for explaining a specific control method for the air conditioner shown in Fig. 1. In the flowchart of Fig. 4, the control device 100 of Fig. 1 determines whether to execute feedback control or fixed processing while referring to past measurements of the temperature sensor 96 that have been stored in advance in the memory 102. In feedback control, the currently measured value is used and fed back to the compressor operating frequency. In fixed processing, the degree of temperature stability is determined from past measurements, and the compressor frequency is fixed if the stability condition is met.

[0040] First, in step S1, the control device 100 obtains an acquired value Tain from the temperature sensor 96. This acquired value Tain is stored in the memory 102 together with the operating frequency Fz of the compressor at that time. The stored acquired value Tain is also used as past temperature data to be used in step S2. Subsequently, in step S2, the control device 100 reads from the memory 102 the past temperature data stored for the period from the present time up to X seconds ago. Note that the processing of step S2 may be executed between steps S3 and S4.

[0041] Next, in step S3, it is determined whether the acquired value Tain corresponding to the current temperature is within a range of ±β from the set temperature Taset. If Taset-β<Tain<Taset+β is not true (NO in S3), the acquired value Tain is used as the input temperature, and the process of step S9 is executed. On the other hand, if Taset-β<Tain<Taset+β is true (YES in S3), the process proceeds to step S4.

[0042] In step S4, it is determined whether the average temperature Tain_ave, calculated from the past temperature data read out in step S2 and the current temperature (acquired value Tain), is within the range of ±α. The average temperature Tain_ave is calculated using the following formula: Tain_ave = (total value of acquired values ​​Tain recorded within a period) / (number of acquired value data). If Taset - α < Tain_ave < Taset + α is not true (NO in S4), the measured temperature (acquired value Tain) is used as the input temperature, and the process of step S9 is executed. On the other hand, if Taset - α < Tain_ave < Taset + α is true (YES in S4), the process proceeds to step S5.

[0043] The determination values ​​α and β used in steps S3 and S4 are preferably α<β, and for example, values ​​such as 0.3° C. for α and 0.5° C. for β may be used.

[0044] In step S5, it is determined whether or not the process of step S9 was executed to perform the feedback control when the process of the flowchart of Fig. 4 was executed last time. This is because, when a frequency is calculated the first time that the stability condition is satisfied, a fixed frequency is calculated at that time, and the fixed value used last time is continued to be used from the second time onward that the stability condition is satisfied.

[0045] If the process was previously determined to execute feedback control (YES in S5), the stability conditions of step S3 or S4 were not satisfied last time, and the temperature has changed to satisfy the stability conditions of steps S3 and S4 this time. In this case, in step S6, the control device 100 calculates a moving average value Fz_ave from past frequency data stored in memory 102 up to X seconds before the current time. The moving average value Fz_ave is calculated using the following formula: Fz_ave = (total value of frequency Fz recorded within a period) / (number of frequency data). On the other hand, if the process was not previously determined to execute feedback control (NO in S5), the stability conditions satisfied last time continue to be satisfied this time. In this case, the previous value is used as the moving average value Fz_ave. This fixes the operating frequency Fz.

[0046] After the moving average value Fz_ave is determined in step S6 or step S7, the control device 100 sets the compressor operating frequency Fz to the moving average value Fz_ave in step S8. If the stability conditions of steps S3 and S4 are met by the processing of steps S3 to S8, the compressor operating frequency Fz is fixed to the moving average value Fz_ave calculated at that time, and operation continues at the same operating frequency until the stability conditions of step S3 or S4 are no longer met. Then, if the stability conditions of step S3 or S4 are no longer met (NO in S3 or NO in S4), the control device 100 feedback-controls the operating frequency Fz in step S9 so that the acquired value Tain matches the set temperature Taset.

[0047] Fig. 5 is a diagram showing changes in temperature and compressor frequency when the control of Fig. 4 is executed. The graph shown in Fig. 5 has the same initial state as the graph shown in Fig. 3, but hunting of the room temperature Ta and the operating frequency Fz is suppressed.

[0048] In section K11, there is no time when the acquired value Tain from the indoor temperature sensor and the moving average value Tain_ave of the indoor temperature sensor simultaneously become close to the set temperature Taset, so the operating frequency Fz of the compressor is controlled by feedback control as in the conventional method.

[0049] At time t13, the last time of section K11, the acquired value Tain becomes Tain = Taset, and the moving average value Tain_ave of the indoor temperature sensor falls within the range Taset - β < Tain_ave < Taset. Therefore, both the acquired value Tain and the moving average value Tain_ave are near the set temperature Taset, and the indoor temperature is determined to be stable. For this reason, in section K12, operation is performed with the compressor operating frequency Fz fixed at the moving average value Fz_ave of the compressor frequency at time t13.

[0050] However, in section K12, the operating frequency Fz of the compressor is higher than the frequency Fset corresponding to the set temperature Taset, so the room temperature Ta starts to gradually decrease from around the middle of section K12. Therefore, at time t14, the last time point of section K12, the acquired value Tain from the room temperature sensor is different from the set temperature Taset by β or more, so that in section K13, the compressor frequency is again feedback-controlled.

[0051] In section K13, the operating frequency Fz of the compressor is reduced by feedback control, and at time t15, Tain = Taset and Taset - β < Tain_ave < Taset, and it is determined that the indoor temperature is again stable. Therefore, in section K14, the operating frequency Fz of the compressor is fixed to Fz_ave calculated by the moving average at time t15.

[0052] Then, in section K15, at time t16, the acquired value Tain rises and moves away from the set temperature Taset, so the temperature is no longer stable. Therefore, in section K15, the operating frequency Fz of the compressor is feedback controlled in the same way as in section K13.

[0053] After that, at time t17, Tain again coincides with Taset, and it is determined that the state is stable, and the operating frequency Fz of the compressor is fixed to the moving average value Fz_ave calculated at time t17.

[0054] As described above, the frequency Fz gradually stabilizes, and the indoor temperature Ta can be maintained near the set temperature Taset while the frequency Fz is constant.

[0055] As described above, according to this embodiment, the moving average value Tain_ave is calculated while observing changes in the acquired value Tain from the temperature sensor, and the operating frequency Fz is fixed when the room temperature satisfies the stability condition. This makes it possible to suppress hunting of the room temperature and compressor frequency even when the resolution of the acquired temperature value is coarse.

[0056] [Summary] (Section 1) The present disclosure relates to an air conditioner 1. The air conditioner 1 includes a refrigerant circuit 10 including a compressor 30, a condenser (heat exchanger 50), an expansion valve 65, and an evaporator (heat exchanger 60) and configured to circulate a refrigerant; a temperature sensor 96 for detecting the temperature of a space to be air-conditioned; and a control device 100 configured to store the temperature measured by the temperature sensor 96 over a certain period of time prior to the present and the operating frequency Fz of the compressor 30. If the temperature measured by the temperature sensor 96 (acquired value Tain) does not satisfy a stability condition for a set temperature Taset, which is a target temperature, the control device 100 is configured to feedback-control the operating frequency Fz of the compressor 30 so that the temperature measured by the temperature sensor 96 (acquired value Tain) coincides with the set temperature Taset. If the temperature measured by the temperature sensor 96 (acquired value Tain) satisfies a stability condition for the set temperature Taset, the control device 100 is configured to fix the operating frequency Fz of the compressor 30.

[0057] (Clause 2) In the air conditioner described in clause 1, the stability condition is satisfied when the magnitude of the difference between the current temperature measured by the temperature sensor 96 and the set temperature Taset is smaller than a first value α, and the magnitude of the difference between the moving average value Tain_ave of the temperature measured by the temperature sensor 96 over a certain period of time and the set temperature Taset is smaller than a second value β.

[0058] (Clause 3) In the air conditioner described in clause 2, the second value β is smaller than the first value α.

[0059] (4) In the air conditioner described in 1, the control device 100 repeatedly determines (S6-S8) whether to perform feedback control (S9) or fix the operating frequency Fz of the compressor 30. The control device 100 uses, as the frequency at which to fix the operating frequency Fz of the compressor 30, the moving average value of the operating frequency of the compressor measured over a certain period of time at the time when the state transitions from not satisfying the stability condition to satisfying it (YES in S5) (S8).

[0060] (Item 5) In the air conditioner described in item 1, the temperature sensor 96 has a resolution, and the control device 100 is configured to acquire discrete detection values ​​from the temperature sensor 96 with the resolution as the smallest unit.

[0061] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of the present disclosure is defined by the claims, not by the description of the above embodiments, and is intended to include all modifications within the meaning and scope of the claims.

[0062] 1 Air conditioner, 10 Refrigerant circuit, 12, 13, 14, 15, 16, 17 Piping, 21, 22 Extension piping, 30 Compressor, 40 Four-way valve, 41, 42, 43, 44 Connection port, 50, 60 Heat exchanger, 51 Outdoor fan, 61 Indoor fan, 65 Expansion valve, 96 Temperature sensor, 100 Control device, 101 CPU, 102 Memory, 300 Outdoor unit, 400 Indoor unit.

Claims

1. An air conditioner comprising: a refrigerant circuit including a compressor, a condenser, an expansion valve, and an evaporator, and configured to circulate a refrigerant; a temperature sensor that detects the temperature of a space to be air-conditioned; and a control device configured to store the temperature measured by the temperature sensor during a certain period prior to the present time and the operating frequency of the compressor, wherein the control device is configured to feedback control the operating frequency of the compressor so that the temperature measured by the temperature sensor matches the target temperature when the temperature measured by the temperature sensor does not satisfy a stability condition for a target temperature, and wherein the control device is configured to fix the operating frequency of the compressor when the temperature measured by the temperature sensor satisfies the stability condition for the target temperature.

2. An air conditioner as described in claim 1, wherein the stability condition is satisfied when the magnitude of the difference between the current temperature measured by the temperature sensor and the target temperature is smaller than a first value, and the magnitude of the difference between the moving average value of the temperature measured by the temperature sensor over the certain period and the target temperature is smaller than a second value.

3. The air conditioner according to claim 2, wherein the second value is smaller than the first value.

4. The air conditioner of claim 1, wherein the control device repeatedly determines whether to execute the feedback control or fix the operating frequency of the compressor, and the control device adopts, as the frequency at which to fix the operating frequency of the compressor, a moving average value of the operating frequency of the compressor measured over the certain period at the point in time when the control device transitions from a state that does not satisfy the stability condition to a state that satisfies the stability condition.

5. The air conditioner according to claim 1, wherein the temperature sensor has a resolution, and the control device is configured to obtain discrete detection values ​​from the temperature sensor with the resolution as a minimum unit.

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