Air conditioner

Abstract

An air conditioner (1, 1A) comprises a refrigerant circuit (10), a temperature sensor (96), and a control device (100) configured to store a measured temperature that is measured by the temperature sensor (96) in a given period before the present time point and the amount of refrigerant circulating in the refrigerant circuit (10). The control device (100) is configured to control the operating frequency of a compressor (30) to a fixed frequency when the temperature measured by the temperature sensor (96) satisfies a stability condition with respect to a set temperature. The fixed frequency is determined on the basis of the moving average value of the refrigerant circulation amount in a fixed period.

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 including a compressor, a condenser, an expansion valve, and an evaporator, configured to circulate a refrigerant; a temperature sensor for detecting the temperature of a space to be air-conditioned; and a control device. The control device is configured to store the temperature measured by the temperature sensor over a fixed period of time from the current time and the amount of refrigerant circulating in the refrigerant circuit. 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 the stability condition for the target temperature, the control device is configured to control the operating frequency of the compressor to a fixed frequency. The fixed frequency is determined based on a moving average value of the amount of refrigerant circulating over the fixed period of time.

[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] FIG. 1 is a diagram showing the configuration of an air conditioner of embodiment 1 and the flow of refrigerant during cooling. FIG. 2 is a diagram showing the configuration of an air conditioner of embodiment 1 and the flow of refrigerant during heating. FIG. 3 is a diagram for explaining the relationship between the resolution of the temperature sensor of the air conditioner and hunting. FIG. 4 is a flowchart for explaining a specific control method for the air conditioner shown in FIG. 1. FIG. 5 is a diagram for explaining an example of determining the compressor frequency Fz_ave corresponding to the moving average value Gr_ave from past operating data. FIG. 6 is a diagram showing changes in temperature and refrigerant circulation flow rate when the control of FIG. 4 is executed. FIG. 7 is a diagram showing the configuration of an air conditioner of embodiment 2 and the flow of refrigerant during cooling. FIG. 8 is a diagram showing the relationship between the opening degree of the expansion valve and the flow coefficient.

[0009] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Although several embodiments will be described below, it was originally intended that the configurations described in each embodiment be combined as appropriate. Note that the same or corresponding parts in the drawings will be designated by the same reference numerals, and their description will not be repeated.

[0010] Embodiment 1. Figure 1 is a diagram showing the configuration of an air conditioner according to embodiment 1 and the flow of refrigerant during cooling. The air conditioner 1 shown in Figure 1 comprises 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 subject to air conditioning, and is equipped with a four-way valve 40, a compressor 30, a heat exchanger 50, an outdoor fan 51, an expansion valve 65, and a refrigerant flow sensor 97.

[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 the indoor space to be air-conditioned, and includes a heat exchanger 60, an indoor fan 61, a temperature sensor 96 that detects the indoor temperature, and refrigerant flow rate sensors 97 and 98. To measure the refrigerant flow rate, a sensor must be installed in the liquid phase, so the flow rate during cooling is measured by the refrigerant flow rate sensor 97, and the flow rate during heating is measured by the refrigerant flow rate sensor 98.

[0017] The refrigerant flow rate sensors 97 and 98 are not particularly limited, but ultrasonic flow meters, Coriolis flow meters, etc. may be used.

[0018] 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.

[0019] 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 .

[0020] 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.

[0021] 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.

[0022] 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).

[0023] 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.

[0024] 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.

[0025] Next, the conditions and flow of the refrigerant during heating operation will be described. Fig. 2 is a diagram showing the configuration of the air conditioner of the first embodiment and the flow of the refrigerant during heating.

[0026] 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.

[0027] 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.

[0028] FIG. 3 is a diagram for explaining the relationship between the resolution of the temperature sensor of the air conditioner and hunting.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] Here, the compressor frequency during steady operation when the room temperature Ta coincides with the set temperature Taset is defined as frequency Fset.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] 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 memory 102 together with the compressor operating frequency Fz at that time and refrigerant circulation flow rate data Gr, which is a measurement value from the refrigerant flow rate sensor 97 or 98. The refrigerant circulation flow rate data Gr is measured using the refrigerant flow rate sensor 97 during cooling operation and the refrigerant flow rate sensor 98 during heating operation. The stored acquired value Tain is also used as past temperature data to be used in step S2. Next, in step S2, the control device 100 reads from memory 102 past temperature data stored for a period up to X seconds before the present time. Note that the processing of step S2 may be executed between steps S3 and S4.

[0042] 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.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] If it was previously determined that feedback control should be performed (YES in S5), the stability conditions of step S3 or S4 were not satisfied previously, 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 Gr_ave from the refrigerant circulation flow rate data Gr stored in memory 102 up to X seconds before the present time. The moving average value Gr_ave is calculated using the following formula: Gr_ave = (total value of Gr recorded within a period) / (number of Gr data points). The control device 100 then determines a compressor frequency Fz_ave corresponding to the moving average value Gr_ave from a relational expression calculated in advance. Note that the compressor frequency Fz_ave corresponding to the moving average value Gr_ave may also be determined from past operating data.

[0047] Fig. 5 is a diagram illustrating an example of determining the compressor frequency Fz_ave corresponding to the moving average value Gr_ave from past operating data. Each time the flowchart of Fig. 4 is executed, the temperature Tain, the refrigerant circulation flow rate Gr, and the operating frequency Fz are recorded in step S1. As shown in Fig. 6, on a plane with Gr as the vertical axis and Fz as the horizontal axis, interpolation is performed using a straight line passing through two points close to the refrigerant circulation flow rate Gr_ave, and the compressor frequency indicated by the point on the straight line corresponding to Gr_ave can be determined as the frequency Fz_ave. The two points used to determine the straight line can be, for example, two points between which Gr_ave is located. However, taking into account variations and the like, an approximation line can also be determined from two or more points close to the refrigerant circulation flow rate Gr_ave.

[0048] Returning to FIG. 4 again, if the process was not determined to execute feedback control last time (NO in S5), it means that the stability conditions that were satisfied last time are still satisfied this time. In this case, the frequency Fz_ave uses the previous value as is. This fixes the operating frequency Fz.

[0049] After the frequency Fz_ave is determined in step S6 or step S7, the control device 100 sets the compressor operating frequency Fz to the frequency 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 frequency 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.

[0050] Fig. 6 is a diagram showing changes in temperature and refrigerant circulation flow rate when the control of Fig. 4 is executed. The graph shown in Fig. 6 has the same initial state as the graph shown in Fig. 3, but hunting of the indoor temperature Ta is suppressed.

[0051] 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, and refrigerant circulates at a refrigerant circulation flow rate Gr corresponding to the operating frequency Fz.

[0052] 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. Therefore, in section K12, the operating frequency Fz of the compressor is fixed, and operation is performed with the refrigerant circulation flow rate Gr fixed at the moving average value Gr_ave at time t13.

[0053] However, in section K12, the refrigerant circulation flow rate Gr was greater than the circulation rate Grset corresponding to the set temperature Taset, so the indoor temperature Ta begins to gradually decrease from around the middle of section K12. Therefore, at time t14, the last point in section K12, the acquired value Tain from the indoor 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.

[0054] In section K13, the operating frequency Fz of the compressor decreases due to feedback control, and the refrigerant circulation flow rate Gr also decreases, so 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 refrigerant circulation flow rate Gr is fixed to Gr_ave calculated by the moving average at time t15.

[0055] 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.

[0056] After that, at time t17, Tain again coincides with Taset, and when it is determined that the state is stable, the operating frequency Fz of the compressor is fixed to the frequency Fz_ave corresponding to the moving average value Gr_ave calculated at time t17.

[0057] As described above, the refrigerant circulation flow rate Gr and the frequency Fz gradually stabilize, and the indoor temperature Ta can be maintained near the set temperature Taset while the frequency Fz remains constant.

[0058] 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.

[0059] Embodiment 2. In Embodiment 1, the refrigerant circulation flow rate Gr is measured by a sensor. On the other hand, in Embodiment 2, the refrigerant circulation flow rate Gr is calculated using information from a pressure sensor provided in the refrigerant circuit and the expansion valve opening.

[0060] Fig. 7 is a diagram showing the configuration of an air conditioner according to embodiment 2 and the flow of refrigerant during cooling. Air conditioner 1A shown in Fig. 7 includes pressure sensors 201 and 202 instead of refrigerant flow sensors 97 and 98 in the configuration of air conditioner 1 shown in Fig. 1. The configuration of other parts of air conditioner 1A according to embodiment 2 is the same as that of air conditioner 1 according to embodiment 1, and therefore description thereof will not be repeated here.

[0061] In the first embodiment, in step S1 of Fig. 4, the temperature Tain is measured and the refrigerant circulation flow rate Gr is directly measured by one of the refrigerant flow rate sensors 97, 98. In the second embodiment, in step S1 of Fig. 4, the control device 100 calculates the refrigerant circulation flow rate Gr based on the pressures P1, P2 detected by the pressure sensors 201, 202.

[0062] When calculating the refrigerant circulation flow rate Gr, the control device 100 acquires the values ​​(P1, P2) of the pressure sensors 201, 202 provided before and after the expansion valve 65 during operation, and the opening degree LP of the expansion valve 65. The control device 100 calculates the flow coefficient Cv of the expansion valve 65 from the opening degree LP.

[0063] Fig. 8 is a diagram showing the relationship between the opening degree of the expansion valve and the flow coefficient. Characteristic data showing the relationship between the opening degree of the expansion valve and the flow coefficient as shown in Fig. 8 is stored in advance in memory 102, and control device 100 refers to the characteristic data to determine the flow coefficient Cv corresponding to opening degree LP.

[0064] The control device 100 then calculates the circulation flow rate Gr using the following formula: Gr=A×Cv×√(|P1−P2|) where A is a constant determined by the specifications of the expansion valve 65.

[0065] The control device 100 performs control based on the circulation flow rate Gr obtained from the above equation in the same manner as in embodiment 1. Specifically, the circulation flow rate Gr obtained from the above equation is used to calculate Gr_ave in step S6 of Fig. 4. The other processing is as described in the flowchart of Fig. 4, and therefore description thereof will not be repeated here.

[0066] In the air conditioner of embodiment 2, the operating frequency Fz is fixed when the room temperature satisfies the stable condition, as in embodiment 1. 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.

[0067] [Summary] (Section 1) The present disclosure relates to an air conditioner 1, 1A. The air conditioner 1, 1A 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 that detects the temperature of a space to be air-conditioned; and a control device 100. The control device 100 is configured to store the temperature measured by the temperature sensor 96 over a certain period of time prior to the present and the amount of refrigerant circulating in the refrigerant circuit 10. If the temperature acquisition value Tain measured by the temperature sensor 96 does not satisfy a stability condition for the set temperature Taset, which is a target temperature, the control device 100 is configured to feedback-control the operating frequency of the compressor 30 so that the temperature measured by the temperature sensor 96 (acquired value Tain) matches the set temperature Taset. The control device 100 is configured to control the operating frequency Fz of the compressor 30 to a fixed frequency when the temperature measured by the temperature sensor 96 (acquired value Tain) satisfies a stability condition with respect to the set temperature Taset. The fixed frequency is determined based on a moving average value of the refrigerant circulation amount over a certain period of time.

[0068] (2) In the air conditioner 1, 1A of 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.

[0069] (Term 3) In the air conditioner 1, 1A of term 2, the second value β is smaller than the first value α.

[0070] (4) In the air conditioner 1, 1A of the 1st paragraph, the control device 100 repeatedly determines whether to perform feedback control (S9) or to fix (S5-S8) the operating frequency Fz of the compressor 30. At the point in time when the state transitions from not satisfying the stability condition to satisfying it (YES in S5), the control device 100 adopts, as the fixed frequency, a frequency corresponding to the moving average value Gr_ave of the refrigerant circulation amount Gr for a certain period prior to that point in time.

[0071] (Item 5) The air conditioner 1A of item 1 further includes pressure sensors 201, 202 that detect a pressure difference before and after the expansion valve 65 in the refrigerant circuit 10. The control device 100 is configured to estimate the amount of refrigerant circulating based on the pressure difference and the opening degree of the expansion valve 65.

[0072] (Item 6) In the air conditioner 1, 1A of item 1, the temperature sensor 96 has a resolution, and the control device 100 is configured to acquire from the temperature sensor 96 discrete detection values ​​with the resolution as the smallest unit.

[0073] 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.

[0074] 1, 1A air conditioner, 10 refrigerant circuit, 12-17 piping, 21, 22 extension piping, 30 compressor, 40 four-way valve, 41-44 connection port, 50, 60 heat exchanger, 51 outdoor fan, 61 indoor fan, 65 expansion valve, 96 temperature sensor, 97, 98 refrigerant flow sensor, 100 control device, 101 CPU, 102 memory, 201, 202 pressure sensor, 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 fixed period from the present time and the amount of refrigerant circulating in the refrigerant circuit, 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 control the operating frequency of the compressor to a fixed frequency when the temperature measured by the temperature sensor satisfies the stability condition for the target temperature, and the fixed frequency is determined based on a moving average value of the amount of refrigerant circulating during the fixed period.

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 fixed frequency, a frequency corresponding to a moving average value of the refrigerant circulation volume for a certain period prior to the point at which the control device transitions from a state that does not satisfy the stability condition to a state that satisfies the stability condition.

5. An air conditioner as described in claim 1, further comprising a pressure detection device that detects the pressure difference before and after the expansion valve in the refrigerant circuit, and the control device is configured to estimate the amount of refrigerant circulating based on the pressure difference and the opening degree of the expansion valve.

6. 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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