Air conditioner and control method

Abstract

To provide an air conditioner capable of storing a surplus refrigerant during a heating operation and a control method.SOLUTION: An air conditioner includes: a compressor 30 that compresses a refrigerant; a four-way valve 32 that switches a circulating direction of the compressed refrigerant; an indoor heat exchanger 20 that functions as a condenser for condensing the refrigerant during a heating operation; an outdoor heat exchanger 34 that functions as an evaporator for evaporating the refrigerant during the heating operation; a first outdoor expansion valve 33 that decompresses the refrigerant condensed by the indoor heat exchanger 20 during the heating operation; a sub cooler 37 disposed between the first outdoor expansion valve 33 and the outdoor heat exchanger 34; a second outdoor expansion valve 38 disposed between the sub cooler 37 and the outdoor heat exchanger 34; and detection means for detecting a state of the circulating refrigerant. During the heating operation, according to a detection result obtained by the detection means, the first outdoor expansion valve 33 is fully opened and by using the second outdoor expansion valve 38, the refrigerant condensed by the indoor heat exchanger 20 is decompressed.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to an air conditioner and a control method for controlling the amount of refrigerant circulating within the air conditioner. [Background technology]

[0002] An air conditioner is composed of an indoor unit and an outdoor unit, and refrigerant circulates between the indoor unit and the outdoor unit to perform cooling or heating operation. The capacity of the indoor unit and the outdoor unit depends on the volume of the heat exchanger that each unit has, and if the volume of the heat exchanger of the indoor unit and the volume of the heat exchanger of the outdoor unit differ significantly, a problem is likely to occur in which the appropriate amount of refrigerant charged to the air conditioner differs between cooling operation and heating operation.

[0003] When the optimum amount of refrigerant charged differs between cooling operation and heating operation, the refrigerant is charged according to the operation with the greater optimum amount, and the surplus refrigerant during operation can be stored in a receiver tank. However, depending on the air conditioner, there are cases where a receiver tank cannot be installed due to space constraints within the air conditioner.

[0004] In view of this, a technique has been proposed in which part of a heat exchanger provided in an air conditioner is used as a storage container for the refrigerant (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2012 / 081110 Summary of the Invention [Problem to be solved by the invention]

[0006] However, in the conventional technology described above, the use of part of the heat exchanger as a storage container for the refrigerant is limited to cooling operation, and there was a problem that surplus refrigerant could not be stored during heating operation. [Means for solving the problem]

[0007] In view of the above problems, the present invention provides a compressor for compressing a refrigerant, A switching means for switching the circulation direction of the refrigerant compressed by the compressor; an indoor heat exchanger that functions as a condenser that condenses the refrigerant during heating operation; An outdoor heat exchanger that functions as an evaporator that evaporates a refrigerant during heating operation; a first expansion valve that reduces the pressure of the refrigerant condensed by the indoor heat exchanger during heating operation; an auxiliary outdoor heat exchanger disposed between the first expansion valve and the outdoor heat exchanger; a second expansion valve disposed between the auxiliary exterior heat exchanger and the exterior heat exchanger; A detection means for detecting the state of the circulating refrigerant; Including, An air conditioner is provided in which, during heating operation, the first expansion valve is fully opened depending on the detection result of the detection means, and the second expansion valve reduces the pressure of the refrigerant condensed by the indoor heat exchanger. Effect of the Invention

[0008] According to the present invention, it is possible to provide an air conditioner and a control method capable of storing surplus refrigerant during heating operation. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a diagram showing an example of the configuration of an air conditioning device. [Diagram 2] FIG. 2 is a diagram showing an example of the configuration of an indoor unit and an outdoor unit. [Diagram 3] FIG. 4 is a diagram for explaining control during normal heating operation. [Figure 4] FIG. 4 is a diagram for explaining control during heating operation when there is an excess of refrigerant. [Diagram 5] FIG. 4 is a diagram for explaining control during cooling operation. [Figure 6] pH (pressure-specific enthalpy) diagram of the refrigeration cycle. [Figure 7]FIG. 4 is a diagram showing the positions at which sensors for detecting the state of the refrigerant are attached. [Figure 8] 4 is a flowchart showing an example of control of the amount of refrigerant circulating in the air conditioning apparatus. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Fig. 1 is a diagram showing an example of the configuration of an air conditioner. The air conditioner 10 includes an indoor unit 11 installed in the space (indoors) where air conditioning is performed, and an outdoor unit 12 installed outdoors, and performs air conditioning by circulating a refrigerant between the indoor unit 11 and the outdoor unit 12 and exchanging heat with the indoor air. For this reason, the indoor unit 11 and the outdoor unit 12 are connected by two refrigerant pipes 13 and 14 for circulating the refrigerant.

[0011] The indoor unit 11 and the outdoor unit 12 may each be configured with two or more units, and two or more indoor units 11 may be connected to one outdoor unit 12. As the refrigerant, hydrofluorocarbons (HFCs) and hydrofluoroolefins (HFOs) can be used, and examples of HFCs include R-410A and R-32, and examples of HFOs include R-1234yf and R-1234ze.

[0012] The indoor unit 11 performs wired communication with a remote control 15 placed in the room, and receives various signals such as operation commands, stop commands, commands to change the set temperature, and commands to change the operation mode. The indoor unit 11 may also perform wireless communication using infrared rays or the like with the remote control 15 to receive various signals. The indoor unit 11 is connected to the outdoor unit 12 via a communication line, and works together with the outdoor unit 12 to condition the air in the room.

[0013] The indoor unit 11 starts up upon receiving an operation command from the remote control 15, and instructs the outdoor unit 12 to start up. After starting up, the outdoor unit 12 adjusts the compressor rotation speed and the opening degree of the expansion valve, etc., and controls the amount of refrigerant circulating, etc., so that the indoor temperature becomes the set temperature.

[0014] Fig. 2 is a diagram showing an example of the configuration of the indoor unit 11 and the outdoor unit 12. The arrows shown in Fig. 2 indicate the flow of the refrigerant during heating operation. Note that the direction of the refrigerant flow is reversed during cooling operation.

[0015] The indoor unit 11 includes an indoor heat exchanger 20, an indoor fan 21, and an indoor fan drive motor 22. The indoor fan 21 is driven by the indoor fan drive motor 22, takes in indoor air, and sends it to the indoor heat exchanger 20. The indoor heat exchanger 20 has multiple heat transfer tubes through which a refrigerant flows, and is configured so that the sent air comes into contact with the surfaces of the multiple heat transfer tubes and exchanges heat. The air that has undergone heat exchange by the indoor heat exchanger 20 is discharged into the room.

[0016] The indoor unit 11 may further include various sensors for measuring the indoor temperature, etc., an indoor expansion valve, etc.

[0017] The outdoor unit 12 includes a compressor 30, an accumulator 31, a four-way valve 32, a first outdoor expansion valve 33 as an outdoor expansion valve, an outdoor heat exchanger 34, an outdoor fan 35, and an outdoor fan drive motor 36. The compressor 30 is driven by the compressor drive motor, compresses a low-pressure refrigerant, and discharges it as a high-pressure refrigerant. The accumulator 31 is a container for storing liquid refrigerant generated when the suction refrigerant is a two-phase refrigerant, and adjusts the refrigerant to an appropriate dryness. The dryness is the proportion of steam in wet steam, which indicates the mixed state of steam and minute liquid droplets.

[0018] The four-way valve 32 functions as a switching means and is a valve that switches the direction of refrigerant flow depending on the operating state (operating mode) of the air conditioner 10. The operating modes are cooling mode, heating mode, ventilation mode, etc. The first outdoor expansion valve 33 is a valve that reduces the pressure of high-pressure refrigerant and expands it. The outdoor fan 35 is driven by an outdoor fan drive motor 36, takes in outdoor air, and sends it to the outdoor heat exchanger 34. Like the indoor heat exchanger 20, the outdoor heat exchanger 34 has multiple heat transfer tubes through which the refrigerant flows, and is configured so that the sent-in air comes into contact with the surfaces of the multiple heat transfer tubes and exchanges heat. The air that has been heat exchanged by the outdoor heat exchanger 34 is discharged to the outside.

[0019] The outdoor unit 12 is equipped with a subcooler 37 as an auxiliary outdoor heat exchanger arranged between the first outdoor expansion valve 33 and the outdoor heat exchanger 34, and a second outdoor expansion valve 38 as a second expansion valve arranged between the subcooler 37 and the outdoor heat exchanger 34.

[0020] The air conditioning apparatus includes a compressor 30, a four-way valve 32, an indoor heat exchanger 20, an outdoor heat exchanger 34, a first outdoor expansion valve 33, a subcooler 37, a second outdoor expansion valve 38, the outdoor heat exchanger 34, and an accumulator 31, which form a refrigerant circuit through which the refrigerant circulates.

[0021] During heating operation, the refrigerant discharged from the compressor 30 flows in this order through the four-way valve 32, the indoor heat exchanger 20, the first outdoor expansion valve 33, the subcooler 37, the second outdoor expansion valve 38, the outdoor heat exchanger 34, the four-way valve 32, and the accumulator 31, before returning to the compressor 30.

[0022] During cooling operation, the four-way valve 32 switches the direction of refrigerant flow, and the refrigerant discharged from the compressor 30 flows in this order: four-way valve 32, outdoor heat exchanger 34, second outdoor expansion valve 38, subcooler 37, first outdoor expansion valve 33, indoor heat exchanger 20, four-way valve 32, and accumulator 31, before returning to the compressor 30.

[0023] The outdoor unit 12 is equipped with a control device 39 that controls the rotation speed of the indoor fan drive motor 22, the rotation speed of the outdoor fan drive motor 36, the rotation speed of the compressor 30, the valve opening degree of the first outdoor expansion valve 33, the valve opening degree of the second outdoor expansion valve 38, etc. The control device 39 may be equipped in the indoor unit 11. Also, the function of the control device 39 may be divided into two, with a control device having one function being mounted in the indoor unit 11 and a control device having the other function being mounted in the outdoor unit 12.

[0024] Fig. 3 is a diagram explaining control during normal heating operation. The air conditioner 10 has an indoor fan 21 and an indoor fan drive motor 22 in the indoor unit 11, and an outdoor fan 35, an outdoor fan drive motor 36, and a control device 39 in the outdoor unit 12, but these devices are omitted in Fig. 3. This is also the case for Figs. 4, 5, and 7.

[0025] During normal heating operation, the refrigerant compressed by the compressor 30 passes through the four-way valve 32 and is sent to the indoor heat exchanger 20. The indoor heat exchanger 20 functions as a condenser and condenses the compressed refrigerant. The condensed refrigerant is reduced in pressure by the first outdoor expansion valve 33 and passes through the subcooler 37 and the second outdoor expansion valve 38, which is fully open, and is sent to the outdoor heat exchanger 34. The outdoor heat exchanger 34 functions as an evaporator and evaporates the condensed refrigerant. At this time, the subcooler 37 also functions as an evaporator.

[0026] The refrigerant evaporated in the outdoor heat exchanger 34 passes through the four-way valve 32 and is sent to the accumulator 31, where it is separated into liquid refrigerant and gas refrigerant. The compressor 30 draws in the refrigerant whose quality has been adjusted in the accumulator 31, compresses it to a predetermined pressure, and discharges it.

[0027] During normal heating operation, this process is repeated, and heat is exchanged in the indoor heat exchanger 20 between the refrigerant and the indoor air drawn in by the indoor fan 21, and the air warmed by the indoor heat exchanger 20 is blown out into the room.

[0028] During normal heating operation, the valve opening of the second outdoor expansion valve 38 is fully open, the pressure is reduced by the first outdoor expansion valve 33, and the valve opening of the first outdoor expansion valve 33 is controlled so that the dryness or superheat degree of the refrigerant sucked by the compressor 30 is within a predetermined range. The state of the sucked refrigerant may be directly sensed by the temperature, pressure, etc. of the sucked refrigerant, or may be estimated based on the information sensed by sensing the temperature, pressure, etc. of the discharged refrigerant. Here, the superheat degree refers to the temperature rise from the saturation temperature.

[0029] FIG. 4 is a diagram for explaining control during cooling operation. During cooling operation, the four-way valve 32 switches the flow direction of the refrigerant compressed by the compressor 30 from that of the heating mode, and the refrigerant is sent to the outdoor heat exchanger 34. Unlike during heating operation, the outdoor heat exchanger 34 functions as a condenser and condenses the compressed refrigerant. The condensed refrigerant passes through the second outdoor expansion valve 38 and the subcooler 37, which are fully opened, is depressurized by the first outdoor expansion valve 33, and is sent to the indoor heat exchanger 20. At this time, the subcooler 37 also functions as a condenser. Unlike during heating operation, the indoor heat exchanger 20 functions as an evaporator and evaporates the condensed refrigerant.

[0030] The refrigerant evaporated in the indoor heat exchanger 20 passes through a four-way valve 32 and is sent to the accumulator 31, where it is separated into liquid refrigerant and gas refrigerant. The compressor 30 draws in the refrigerant whose quality has been adjusted in the accumulator 31, compresses it to a predetermined pressure, and discharges it.

[0031] During cooling operation, this process is repeated, and heat is exchanged in the indoor heat exchanger 20 between the refrigerant and the indoor air sucked in by the indoor fan 21, and the air cooled by the indoor heat exchanger 20 is blown out into the room.

[0032] Incidentally, the amount of refrigerant charged into the air conditioner may differ between cooling and heating. In cooling, the high-pressure side is from the compressor 30 through the outdoor heat exchanger 34 to the first outdoor expansion valve 33, and the low-pressure side is from the first outdoor expansion valve 33 through the indoor heat exchanger 20 to the compressor 30. On the other hand, in heating, the high-pressure side is from the compressor 30 through the indoor heat exchanger 20 to the first outdoor expansion valve 33, and the low-pressure side is from the first outdoor expansion valve 33 through the outdoor heat exchanger 34 to the compressor 30. Since the high-pressure side occupies most of the refrigerant during operation of the air conditioner 10, if the capacity from the compressor 30 through the outdoor heat exchanger 34 to the first outdoor expansion valve 33 during cooling is significantly different from the capacity from the compressor 30 through the indoor heat exchanger 20 to the first outdoor expansion valve 33 during heating, the appropriate amount of refrigerant will differ between cooling and heating.

[0033] For example, when the capacity of the indoor heat exchanger 20 of the indoor unit 11 and the capacity of the outdoor heat exchanger 34 of the outdoor unit 12 differ significantly, a problem is likely to occur in which the appropriate amount of refrigerant differs between cooling and heating.

[0034] In general, the indoor unit 11 tends to be small due to the load-bearing capacity and space constraints of the installation location, and the capacity of the indoor heat exchanger 20 also tends to be small. On the other hand, the outdoor unit 12 is installed outdoors where there is ample space, and tends to be large in order to provide sufficient capacity, and the capacity of the outdoor heat exchanger 34 also tends to be large. In addition, in an air conditioning apparatus, for example, multiple indoor units 11 are connected to one outdoor unit 12, and there are cases where only some of the multiple indoor units 11 are operating, and the indoor heat exchangers 20 of the indoor units 11 that are not operating do not function, and the difference between the total capacity of the active indoor heat exchangers 20 and the capacity of the outdoor heat exchanger 34 tends to be large.

[0035] The amount of refrigerant charged to the air conditioner depends on whether it is matched to the capacity of the indoor heat exchanger 20 or the capacity of the outdoor heat exchanger 34, i.e., whether cooling or heating is prioritized, and this determines whether an excess or shortage of refrigerant will occur in the cooling or heating mode.

[0036] In recent product development, the capacity of the outdoor heat exchanger 34 has been increased and the amount of refrigerant has been increased accordingly. However, there have been cases where excess refrigerant has been generated during heating operation, and a significant amount of development work has been required to establish product specifications that would ensure reliability and capacity.

[0037] For this reason, when there is an excessive amount of surplus refrigerant during heating operation, control is required to store the surplus refrigerant and circulate an appropriate amount of refrigerant.

[0038] Fig. 5 is a diagram for explaining control during heating operation when there is an excess of refrigerant. Excessive refrigerant during heating operation can be detected using a detection means for detecting the state of the refrigerant circulating in the refrigerant circuit. A specific detection method will be described later.

[0039] When an excess of surplus refrigerant is detected, control is switched from the first outdoor expansion valve 33 shown in Fig. 3 to control by the second outdoor expansion valve 38 shown in Fig. 5. The refrigerant compressed by the compressor 30 is sent to the indoor heat exchanger 20 through the four-way valve 32, and condensed in the indoor heat exchanger 20, as in the normal heating operation shown in Fig. 3.

[0040] The refrigerant leaving the indoor heat exchanger 20 is not depressurized by the first outdoor expansion valve 33, but passes through the subcooler 37 and is depressurized by the second outdoor expansion valve 38. At this time, the first outdoor expansion valve 33 is fully opened, and the subcooler 37 serves as a high-pressure side condenser and serves as a storage area for excess refrigerant. In other words, when there is an excess amount of refrigerant, the subcooler 37 is treated as the high-pressure side, thereby increasing the volume of the high-pressure side.

[0041] The surplus refrigerant is stored in the subcooler 37, and the required amount of refrigerant is decompressed by the second outdoor expansion valve 38 and sent to the outdoor heat exchanger 34. The refrigerant leaving the outdoor heat exchanger 34 is sent to the accumulator 31 through the four-way valve 32, as in the normal heating operation shown in Fig. 3, and the compressor 30 draws in the refrigerant stored in the accumulator 31, compresses it to a predetermined pressure, and discharges it.

[0042] Note that there are devices in which the outdoor unit is equipped with a subcooler and an outdoor expansion valve between the subcooler and the outdoor heat exchanger, and the indoor unit is equipped with an indoor expansion valve, but it is not realistic to reduce the pressure with the indoor expansion valve without providing a separate outdoor expansion valve equivalent to the first outdoor expansion valve 33. If the pressure is reduced with the indoor expansion valve, the refrigerant piping connecting the indoor unit and the outdoor unit becomes a low-pressure piping, reducing the volume of the high-pressure piping and encouraging the generation of excess refrigerant.

[0043] Also, in this case, the subcooler is placed in the outdoor unit closest to the indoor unit, but is installed at the bottom of the outdoor heat exchanger, through which the high-pressure refrigerant flows, and is used to prevent condensation of water that accumulates at the bottom of the outdoor unit. This subcooler must function as a condenser during heating operation, and cannot be used as the subcooler 37 of the air conditioner according to this embodiment, which can serve as an evaporator. Therefore, this device cannot be used as the air conditioner 10 according to this embodiment.

[0044] In the air conditioning apparatus 10 of this embodiment, when there is an excess of refrigerant during heating operation, the first outdoor expansion valve 33 is fully opened and control is switched to reducing the pressure of the condensed refrigerant in the second outdoor expansion valve 38, thereby allowing the excess refrigerant to be stored in the subcooler 37.

[0045] FIG. 6 is a ph (pressure-specific enthalpy) diagram of the refrigeration cycle. Specific enthalpy is the amount of energy per unit mass (kJ / kg). The ph diagram has isotherms at predetermined temperature intervals. During heating operation, the indoor heat exchanger 20 functions as a condenser, and the refrigerant condenses from gas to liquid, so that the pressure remains almost constant and the temperature drops to the saturation temperature from the high-pressure, high-temperature state discharged from the compressor 30, as shown by the bold line in FIG. 6. When the saturation temperature is reached, the gas condenses and is maintained at the saturation temperature until it is all liquid. When the refrigerant is all liquid, the temperature drops from the saturation temperature and becomes subcooled (supercooled).

[0046] The surplus refrigerant can be stored in the accumulator 31, etc., but if the amount of surplus refrigerant becomes excessive, it becomes difficult to store the refrigerant even in the accumulator 31, etc. Therefore, the air conditioning device 10 according to this embodiment stores the surplus refrigerant in the subcooler 37 when there is an excess of surplus refrigerant.

[0047] The subcooling (supercooling) value is used as a guideline for detecting an excess of refrigerant. When the amount of excess refrigerant increases, it is no longer possible to store it in the accumulator 31, etc., and liquid refrigerant begins to be stored in the condenser. The temperature of the stored liquid then drops due to heat exchange with the indoor air, and the subcooling value gradually increases. Therefore, when the subcooling value becomes equal to or greater than a first threshold value, it is determined that there is an excess of refrigerant.

[0048] The first threshold value may be any value, for example, 10 K. The subcooling value can be calculated from the condensation temperature in the indoor heat exchanger 20 functioning as a condenser and the liquid temperature of the refrigerant at the outlet of the indoor heat exchanger 20 by detecting these temperatures. If the condensation temperature cannot be detected directly, and the pressure on the high pressure side can be detected, the saturation temperature at that pressure can be used.

[0049] FIG. 7 is a diagram for explaining the position of the detection means for detecting the state of the refrigerant. The detection means for detecting the state of the refrigerant may include a sensor for detecting the condensation temperature in the indoor heat exchanger 20 or a sensor for detecting the pressure on the high pressure side, and a sensor for detecting the liquid temperature of the refrigerant at the outlet of the indoor heat exchanger 20. In the example shown in FIG. 7, a pressure sensor 40 is attached as a sensor for detecting the pressure on the high pressure side, and a thermistor 23 is attached as a sensor for detecting the liquid temperature of the refrigerant. The sensor for detecting the condensation temperature may include a thermistor attached adjacent to the wall of the heat transfer tube at the approximate center of the refrigerant path in the indoor heat exchanger 20, that is, the heat transfer tube is formed by repeatedly going back and forth and turning back multiple times in the indoor heat exchanger 20. As long as the condensation temperature can be detected, the position is not limited to the approximate center of the refrigerant path.

[0050] As long as the pressure sensor 40 can detect the discharge pressure of the refrigerant discharged from the compressor 30 during heating operation, its installation position is not limited to the discharge side piping between the compressor 30 and the four-way valve 32 of the outdoor unit 12, but may be the piping between the four-way valve 32 and the indoor heat exchanger 20 in the outdoor unit 12, or the piping between the four-way valve 32 and the indoor heat exchanger 20 in the indoor unit 11. When the pressure sensor 40 is also used to detect the discharge pressure during cooling, the installation position of the pressure sensor 40 is preferably the discharge side piping between the compressor 30 and the four-way valve 32.

[0051] The thermistor 23 can be mounted adjacent to the pipe wall of the outlet side piping connected to the outlet side of the indoor heat exchanger 20 during heating operation, and the closer the mounting position is to the outlet side of the indoor heat exchanger 20, the more preferable it is.

[0052] Fig. 8 is a flow chart showing an example of control of the amount of refrigerant circulating inside the air conditioner. When a user sets the mode to heating mode or switches to heating mode and starts heating operation, control starts from step 100. This control is performed by the control device 39 shown in Fig. 2. When heating operation starts, the refrigerant is decompressed by the first outdoor expansion valve 33, the second outdoor expansion valve 38 is fully opened, and normal heating operation is performed.

[0053] In step 101, the pressure of the refrigerant is detected by the pressure sensor 40. If a sensor for detecting the condensation temperature of the indoor heat exchanger 20 is provided instead of the pressure sensor 40, the condensation temperature is detected in step 101. In step 102, the liquid temperature of the refrigerant is detected by the thermistor 23. Steps 101 and 102 may be performed in the reverse order or simultaneously.

[0054] In step 103, the subcooling value is calculated from the detection results in steps 101 and 102, and in step 104, it is determined whether heating operation with an excess of refrigerant is being performed. That is, it is determined whether control is being performed to fully open the first outdoor expansion valve 33 and reduce the pressure by the second outdoor expansion valve 38.

[0055] If it is determined in step 104 that heating operation with excess refrigerant is not being performed, the process proceeds to step 105, where it is determined whether the subcooling value calculated in step 103 is equal to or greater than a first threshold. If it is determined that it is equal to or greater than the first threshold, the process proceeds to step 106, where the first outdoor expansion valve 33 is fully opened, and control is switched to one in which the second outdoor expansion valve 38 depressurizes the refrigerant (heating operation with excess refrigerant), the excess refrigerant is stored in the subcooler 37, and the amount of circulating refrigerant is reduced. Then, the process proceeds to step 109. If it is determined in step 105 that it is less than the first threshold, the process proceeds directly to step 109.

[0056] If it is determined in step 104 that heating operation with an excess of refrigerant is being performed, the process proceeds to step 107, where it is determined whether the subcooling value calculated in step 103 is equal to or less than the second threshold. If it is determined in step 107 that the subcooling value is equal to or less than the second threshold, the process proceeds to step 108, where the second outdoor expansion valve 38 is fully opened, and control is switched to reduce pressure by the first outdoor expansion valve 33, and normal heating operation is resumed. Then, the process proceeds to step 109. If it is determined in step 107 that the second threshold is exceeded, the process proceeds directly to step 109.

[0057] The second threshold value is a value smaller than the first threshold value, such as 3 K or 5 K. This is because if the value is smaller than the first threshold value but close to the first threshold value, then when the normal heating operation is resumed, the calculated value will again soon exceed the first threshold value, resulting in frequent switching.

[0058] In step 109, it is determined whether the stop of heating operation has been detected. The stop of heating operation is detected by stopping the air conditioning device or switching to an operation other than heating. If it is not detected, the process returns to step 101 and control continues. On the other hand, if it is detected, the process proceeds to step 110 and this control ends.

[0059] If the indoor unit 11 is equipped with an indoor expansion valve, during cooling operation, the second outdoor expansion valve 38 may be fully opened and the first outdoor expansion valve 33 may be used to reduce pressure. However, since pressure loss is likely to increase when the piping between the indoors and outdoors is on the low pressure side, it is preferable to fully open the first outdoor expansion valve 33 and the second outdoor expansion valve 38 and use the indoor expansion valve to reduce pressure.

[0060] If an existing air conditioning system is equipped with a subcooler 37, the control shown in Fig. 8 can be achieved by simply adding a second outdoor expansion valve 38, i.e., by adding one more part. Adding one expansion valve makes it possible to store surplus refrigerant in the subcooler 37 without the need for a receiver tank, which contributes to space saving of the product.

[0061] Although the air conditioning apparatus and control method of the present invention have been described in detail using the above-mentioned embodiments, the present invention is not limited to the above-mentioned embodiments, and can be modified within the scope of what a person skilled in the art can conceive, such as other embodiments, additions, modifications, deletions, etc., and any aspect is within the scope of the present invention as long as it achieves the functions and effects of the present invention. [Explanation of symbols]

[0062] 10...Air conditioning equipment 11...Indoor unit 12...Outdoor unit 13, 14…Refrigerant piping 15…Remote control 20…Indoor heat exchanger 21…Indoor fan 22...Indoor fan drive motor 23...Thermistor 30…Compressor 31…Accumulator 32...Four-way valve 33…First outdoor expansion valve 34…Outdoor heat exchanger 35…Outdoor fan 36...Outdoor fan drive motor 37…Subcooler 38…Second outdoor expansion valve 39...Control device 40...Pressure sensor

Claims

1. A compressor that compresses a refrigerant; A switching unit for switching a circulation direction of the refrigerant compressed by the compressor; an indoor heat exchanger that functions as a condenser that condenses the refrigerant during heating operation; an outdoor heat exchanger that functions as an evaporator that evaporates the refrigerant during heating operation; a first expansion valve that reduces the pressure of the refrigerant condensed by the indoor heat exchanger during a heating operation; an auxiliary outdoor heat exchanger disposed between the first expansion valve and the outdoor heat exchanger; a second expansion valve disposed between the auxiliary exterior heat exchanger and the exterior heat exchanger; A detection means for detecting the state of the circulating refrigerant; Including, the first expansion valve is fully opened and the second expansion valve reduces the pressure of the refrigerant condensed by the indoor heat exchanger in accordance with the detection result of the detection means during heating operation.

2. the detection means includes a first detection means for detecting a pressure of the refrigerant discharged from the compressor or a condensation temperature of the refrigerant condensed by the indoor heat exchanger, and a second detection means for detecting an outlet temperature of the refrigerant exiting the indoor heat exchanger during heating operation; 2. The air conditioning apparatus of claim 1, wherein when a value obtained by subtracting the outlet temperature from the saturation temperature or condensation temperature of the refrigerant at the pressure is equal to or greater than a first threshold value, the first expansion valve is fully opened and the second expansion valve reduces the pressure of the refrigerant condensed by the indoor heat exchanger.

3. 3. The air conditioning apparatus of claim 2, wherein the first detection means is a pressure sensor attached to a discharge side piping of the compressor for detecting the pressure of the refrigerant or a thermistor for detecting a condensation temperature of the refrigerant in the indoor heat exchanger, and the second detection means is a thermistor attached to an outlet side piping of the indoor heat exchanger for detecting an outlet temperature of the refrigerant during heating operation.

4. 4. The air conditioning apparatus of claim 2, wherein when the second expansion valve is performing control to reduce the pressure of the refrigerant condensed by the indoor heat exchanger, if the value obtained by subtracting the outlet temperature from the saturation temperature or the condensation temperature becomes equal to or lower than a second threshold value that is smaller than the first threshold value, the second expansion valve is fully opened and the control is switched to the first expansion valve being used to reduce the pressure of the refrigerant condensed by the indoor heat exchanger.

5. A method for controlling an amount of refrigerant circulating in an air-conditioning apparatus including a compressor that compresses a refrigerant, a switching means for switching a circulation direction of the refrigerant compressed by the compressor, an indoor heat exchanger that functions as a condenser that condenses the refrigerant during heating operation, an outdoor heat exchanger that functions as an evaporator that evaporates the refrigerant during heating operation, a first expansion valve that reduces the pressure of the refrigerant condensed by the indoor heat exchanger during heating operation, an auxiliary outdoor heat exchanger arranged between the first expansion valve and the outdoor heat exchanger, a second expansion valve arranged between the auxiliary outdoor heat exchanger and the outdoor heat exchanger, and a detection means for detecting a state of the circulating refrigerant, a step of fully opening the first expansion valve and decompressing the refrigerant condensed by the indoor heat exchanger through the second expansion valve in response to a detection result of the detection means during heating operation; A control method comprising:

6. the detection means includes a first detection means for detecting a pressure of the refrigerant discharged from the compressor or a condensation temperature of the refrigerant condensed by the indoor heat exchanger, and a second detection means for detecting an outlet temperature of the refrigerant exiting the indoor heat exchanger during heating operation; 6. The control method according to claim 5, wherein in the depressurizing step, when a value obtained by subtracting the outlet temperature from the saturation temperature or the condensation temperature of the refrigerant at the pressure is equal to or higher than a first threshold value, the first expansion valve is fully opened and the refrigerant condensed by the indoor heat exchanger is depressurized by the second expansion valve.

7. The control method according to claim 6, further comprising a step of fully opening the second expansion valve and switching to a control in which the first expansion valve reduces the pressure of the refrigerant condensed by the indoor heat exchanger when a value obtained by subtracting the outlet temperature from the saturation temperature or the condensation temperature becomes equal to or lower than a second threshold value that is smaller than the first threshold value while the second expansion valve is performing a control in which the second expansion valve reduces the pressure of the refrigerant condensed by the indoor heat exchanger.

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