Refrigeration cycle device and refrigerant amount detection method

Abstract

Provided are a device and a method capable of shortening the work time required for adding a refrigerant. The device circulates a refrigerant in a refrigerant circuit in which a compressor 21, a condenser, a supercooler 25, an expansion valve and an evaporator are connected in sequence by piping, branches a part of the refrigerant discharged from the condenser, expands the refrigerant using a bypass valve 27, and then supplies the refrigerant to the suction side of the compressor 21 via the supercooler 25. The device comprises: a control means 32 for controlling the operation in a refrigerant amount determination operation mode in which the compressor 21 operates at a predetermined frequency, the supercooler 25 is maintained at a constant cooling capacity, and a refrigerant superheating degree at the outputs of the evaporator is kept constant; a first detection means 30 for detecting the supercooling degree of the refrigerant at the outlet of the condenser; a second detection means 31 for detecting the cooling capacity of the supercooler 25; and a determination means 33 for determining an amount of refrigerant shortage in a stepwise manner on the basis of a combination of at least two of a first detection result of the first detection means, a second detection result of the second detection means, the opening degree of the bypass valve, and the opening degree of the expansion valve.

Description

Refrigeration cycle device and refrigerant amount detection method

[0001] The present invention relates to a refrigeration cycle device and a method for detecting the amount of refrigerant sealed in the refrigeration cycle device.

[0002] Refrigeration cycle devices such as air conditioners equipped with multiple indoor units must be able to handle a wide variety of installation situations, which requires the calculation and refilling of additional refrigerant amounts appropriate to the on-site installation piping and indoor unit capacity.

[0003] However, there are cases where the appropriate amount of refrigerant is not filled due to human error by on-site workers or unclear piping specifications that make it difficult to make accurate calculations.

[0004] Therefore, in order to ensure that the appropriate amount of refrigerant is charged, a method has been proposed for determining the amount of refrigerant charged in a multi-air conditioning system, which determines whether the amount of refrigerant charged is a gas low or overcharge based on the degree of subcooling at the condenser outlet and the opening degree of the indoor expansion valve and subcooling bypass expansion valve, etc. (See, for example, Patent Document 1).

[0005] Japanese Patent Application Laid-Open No. 2008-96051

[0006] In the conventional method described above, the amount of refrigerant can only be judged in three stages: overfill, adequate, and insufficient, so when manually filling a refrigerant shortage, the operator does not know how much to add. Therefore, the operator must add small amounts at a time while watching the situation to avoid overfilling, which is a time-consuming operation.

[0007] In view of the above problems, the present invention provides a refrigeration cycle device in which refrigerant circulates in a refrigerant circuit in which a compressor, a condenser, a subcooler, an expansion valve, and an evaporator are connected in that order by piping, and a portion of the refrigerant that has flowed out of the condenser is branched, expanded by a bypass valve, and then supplied to the suction side of the compressor via the subcooler, the refrigeration cycle device comprising: a control means that controls the compressor to operate at a predetermined frequency, maintains the subcooler at a constant cooling capacity, and operates in a refrigerant amount determination operation mode in which the degree of superheat of the refrigerant at the outlet of the evaporator is kept constant; a first detection means that detects the degree of subcooling of the refrigerant at the outlet of the condenser; a second detection means that detects the cooling capacity of the subcooler; and a determination means that determines the amount of refrigerant that is insufficient in a stepwise manner based on at least two or more combinations of a first detection result of the first detection means, a second detection result of the second detection means, the opening degree of the bypass valve, and the opening degree of the expansion valve.

[0008] According to the present invention, it is possible to reduce the time required for adding refrigerant.

[0009] 1 is a diagram showing an example of the configuration of a refrigeration cycle device; 2 is a diagram showing an example of the configuration of an air conditioner as a refrigeration cycle device according to the present embodiment; 3 is a flowchart showing an example of a process for determining the amount of refrigerant that is insufficient in stages; 4 is a diagram showing an example of setting the same degree of superheat for each evaporator when a refrigeration cycle device is equipped with multiple evaporators; and 5 is a diagram showing an example of setting different degrees of superheat for each evaporator when a refrigeration cycle device is equipped with multiple evaporators.

[0010] In a refrigeration cycle device, a refrigerant circulates in a refrigerant circuit that connects a compressor, a condenser, a subcooler, an expansion means, and an evaporator in that order with piping, and the circulating refrigerant exchanges heat with a fluid such as water or air to provide a cooled or heated fluid. The refrigeration cycle device may be any device that includes a refrigerant circuit, such as a refrigerator, a chiller, or an air conditioner.

[0011] The refrigerant filled in the refrigeration cycle device's refrigerant circuit may be R410A, which is the mainstream refrigeration system for refrigerators, freezers, and commercial air conditioners, or, for the purpose of preventing global warming, R1234yf, R1132(E), R1123, or the like, which have a low GWP value of approximately 1, may be used. R410A is an azeotropic refrigerant mixture containing 50% by mass each of R32 (difluoromethane) and R125 (pentafluoroethane). R1234yf is 2,3,3,3-tetrafluoropropene, R1132(E) is trans-1,2-difluoroethylene, and R1123 is trifluoroethylene.

[0012] FIG. 1 is a diagram showing an example of the configuration of a refrigeration cycle device. Hereinafter, the refrigeration cycle device will be described as an air conditioner, but the refrigeration cycle device is not limited to an air conditioner. The air conditioner includes an indoor unit and an outdoor unit. Note that the number of indoor units and outdoor units may be one each, one outdoor unit and two or more indoor units, or two or more indoor units and two or more outdoor units. In the example shown in FIG. 1, there are two indoor units and one outdoor unit.

[0013] One indoor unit 10 is installed in each space (room) to be air-conditioned. In the example shown in Fig. 1, one indoor unit 10 is installed in each of the two rooms. The indoor unit 10 includes an indoor heat exchanger 11 as heat exchange means, an indoor fan 12 as air supply means, and an indoor expansion valve 13 as pressure reducing means.

[0014] The indoor fan 12 takes in indoor air through an air intake port in the housing of the indoor unit 10, and blows the air heated or cooled in the indoor heat exchanger 11 out into the room through an air outlet port in the housing. The indoor fan 12 is driven by an indoor fan motor, and the rotation speed of the indoor fan motor is controlled by a control device. The air volume of the indoor fan 12 changes depending on the rotation speed of the indoor fan motor.

[0015] The indoor heat exchanger 11 has a heat transfer tube through which a refrigerant flows, and the air flowing outside the heat transfer tube comes into contact with the heat transfer tube, thereby indirectly exchanging heat between the refrigerant and the air. The indoor heat exchanger 11 functions as a condenser in the heating operation mode, heating the air taken in by the indoor fan 12, and as an evaporator in the cooling operation mode, cooling the air taken in by the indoor fan 12.

[0016] The opening degree of the indoor expansion valve 13 is controlled by a control device, and the indoor expansion valve 13 reduces the pressure of the refrigerant and adjusts the amount of refrigerant flowing to each indoor unit 10 .

[0017] The outdoor unit 20 includes a compressor 21 as compression means, an outdoor heat exchanger 22 as heat exchange means, an outdoor fan 23 as air supply means, an outdoor expansion valve 24 as pressure reduction means, a subcooler 25 as subcooling means, and a four-way valve 26 as switching means. The outdoor unit 20 is provided with a bypass valve 27 as expansion means for branching a portion of the refrigerant discharged from the condenser and expanding the portion of the branched refrigerant. The portion of the refrigerant expanded by the bypass valve 27 is supplied to the suction side of the compressor 21 via the subcooler 25.

[0018] The compressor 21, four-way valve 26, outdoor heat exchanger 22, outdoor expansion valve 24, subcooler 25, indoor expansion valve 13, indoor heat exchanger 11, four-way valve 26, and compressor 21 are each connected by piping to form a refrigerant circuit through which the refrigerant circulates.

[0019] The compressor 21 compresses the refrigerant and circulates it within the refrigerant circuit. The outdoor fan 23 takes in outdoor air (outside air) into the housing of the outdoor unit 20 through an air intake port in the housing, and blows the air heated or cooled in the outdoor heat exchanger 22 out to the outdoors through an air outlet port in the housing. The outdoor fan 23 is driven by an outdoor fan motor, and the rotation speed of the outdoor fan motor is controlled by a control device. The air volume of the outdoor fan 23 changes depending on the rotation speed of the outdoor fan motor.

[0020] The outdoor heat exchanger 22 has a heat transfer tube through which a refrigerant flows, and the air flowing outside the heat transfer tube comes into contact with the heat transfer tube, thereby indirectly exchanging heat between the refrigerant and the air. The outdoor heat exchanger 22 functions as an evaporator in the heating operation mode, cooling the air taken in by the outdoor fan 23, and functions as a condenser in the cooling operation mode, heating the air taken in by the outdoor fan 23.

[0021] The outdoor expansion valve 24 has its opening controlled by a control device, reduces the pressure of the refrigerant, and adjusts the amount of refrigerant flowing in the refrigerant circuit.

[0022] The subcooler 25 exchanges heat between the refrigerant flowing in the refrigerant circuit (mainstream refrigerant) and a portion of the refrigerant (bypass refrigerant) expanded by the bypass valve 27. The bypass refrigerant is a portion of the main stream refrigerant branched off, and its temperature drops due to adiabatic expansion by the bypass valve 27. Heat exchange occurs between this refrigerant and the main stream refrigerant, thereby subcooling the main stream refrigerant.

[0023] The refrigerant on the bypass side that has left the subcooler 25 merges with the refrigerant on the mainstream side on the suction side of the compressor 21 and is supplied to the compressor 21 .

[0024] The air conditioner has a cooling operation mode and a heating operation mode as operation modes, and may also have a dehumidifying operation mode, a fan operation mode, etc.

[0025] In the cooling operation mode, the user of the air conditioner selects "cooling" on the remote controller and issues a command to start the operation, which starts the cooling operation. Upon receiving the command to start the operation, the four-way valve 26 is switched so that the refrigerant flows in the direction indicated by the solid arrow in Figure 1, the compressor 21 starts, sucks in the refrigerant, increases the pressure to a predetermined level, and discharges it toward the outdoor heat exchanger 22, which functions as a condenser.

[0026] The outdoor heat exchanger 22 exchanges heat between the high-temperature gaseous refrigerant (also referred to as refrigerant gas or gas refrigerant) flowing inside the heat transfer tubes and the air that is taken in by the outdoor fan 23 and flows outside the heat transfer tubes. The refrigerant gas that enters the outdoor heat exchanger 22 is condensed by the outdoor heat exchanger 22 and is discharged as liquid refrigerant (also referred to as liquid refrigerant). The outdoor expansion valve 24 controls the flow rate of the liquid refrigerant that leaves the outdoor heat exchanger 22 and expands the liquid refrigerant.

[0027] The refrigerant that has left the outdoor expansion valve 24 is branched, with the mainstream refrigerant being supplied to the subcooler 25 and the bypass refrigerant being supplied to the bypass valve 27. The bypass refrigerant expands through the bypass valve 27, its temperature is reduced, and it is supplied to the subcooler 25. In the subcooler 25, heat is exchanged between the mainstream refrigerant and the temperature-reduced bypass refrigerant, and the mainstream refrigerant is subcooled.

[0028] The refrigerant on the bypass side that has left the subcooler 25 is supplied to the suction side of the compressor 21 , and the refrigerant on the mainstream side is sent to the indoor unit 10 .

[0029] The refrigerant sent to the indoor unit 10 is sent via the indoor expansion valve 13 to the indoor heat exchanger 11, which functions as an evaporator. The indoor expansion valve 13 controls the degree of superheat at the outlet of the indoor heat exchanger 11 so that it remains constant. The refrigerant evaporates at a constant temperature (saturation temperature) corresponding to the pressure inside the indoor heat exchanger 11 and is discharged from the indoor heat exchanger 11 at a temperature higher than the saturation temperature. The degree of superheat is Δt when the refrigerant is discharged at a temperature Δt higher than the saturation temperature, and indicates the temperature rise from the saturation temperature. For this reason, a temperature sensor is provided at the outlet of the indoor heat exchanger 11 as a temperature detection means for detecting the refrigerant temperature.

[0030] The refrigerant that leaves the indoor heat exchanger 11 is sent to the outdoor unit 20 and returned to the compressor 21 via the four-way valve 26. A pipe that supplies bypass refrigerant is connected to the pipe connecting the four-way valve 26 and the compressor 21, and the mainstream refrigerant and the bypass refrigerant join at this connection and are sent to the compressor 21. An accumulator may be provided on the compressor 21 side of this connection as a refrigerant storage means. The accumulator separates liquid that did not completely evaporate in the indoor heat exchanger 11.

[0031] In the heating operation mode, the user of the air conditioner selects "heating" on the remote controller as the operating means and issues a command to start the operation, thereby starting the heating operation. Upon receiving the command to start the operation, the four-way valve 26 is switched so that the refrigerant flows in the direction indicated by the dashed arrow in Figure 1 (the opposite direction to the cooling operation), and the compressor 21 is started. In the heating operation mode, the refrigerant simply flows in the opposite direction to the cooling operation mode, so a detailed description thereof will be omitted.

[0032] The air conditioner is equipped with a control device that controls the rotation speed of the compressor motor of the compressor 21, the rotation speed of the indoor fan motor of the indoor fan 12, the opening degree of the indoor expansion valve 13, the rotation speed of the outdoor fan motor of the outdoor fan 23, and the opening degree of the outdoor expansion valve 24. The control device includes a controller equipped with a processor and memory, and is provided in the outdoor unit 20. Note that the control device may be provided in the indoor unit 10, or its functions may be divided into two and provided in both the indoor unit 10 and the outdoor unit 20.

[0033] When installing an air conditioner, the indoor unit 10 and the outdoor unit 20 are connected by piping to form an enclosed space in which the compressor 21, four-way valve 26, outdoor heat exchanger 22, outdoor expansion valve 24, subcooler 25, indoor expansion valve 13, indoor heat exchanger 11, four-way valve 26, and compressor 21 are connected by piping in this order, and the enclosed space is then filled with refrigerant. The length of the piping connecting the indoor unit 10 and the outdoor unit 20 varies depending on the installation position of the indoor unit 10 and the installation position of the outdoor unit 20, the capacity of the indoor unit 10 varies depending on the size of the room, the capacity of the outdoor unit 20 varies depending on the capacity and number of indoor units 10, and the size of the piping connecting the indoor unit 10 and the outdoor unit 20 varies depending on the capacity and number of indoor units 10 and the capacity of the outdoor unit 20. Therefore, the amount of refrigerant to be filled (also called the enclosed amount) when filling a sealed space needs to be changed depending on the construction situation, and to fill an appropriate amount of refrigerant, the minimum amount of refrigerant is estimated and that amount is filled, and in addition, the amount of refrigerant to be added on site is calculated and the calculated amount of refrigerant is added.

[0034] It would be ideal if the amount of refrigerant to be added on-site could always be calculated correctly, but there are cases where the calculation cannot be done correctly due to human error by on-site workers or unclear piping specifications. In such cases, the appropriate amount of refrigerant will not be charged.

[0035] In the refrigerant circuit, the compressor 21 converts the refrigerant into a high-temperature, high-pressure gas. For example, in cooling mode, the gas is converted into a liquid by the outdoor heat exchanger 22 (which functions as a condenser), then converted into a low-temperature, low-pressure liquid by the outdoor expansion valve 24, and the liquid is converted back into a gas by the indoor heat exchanger 11 (which functions as an evaporator). This cycle is repeated (refrigeration cycle). In this refrigeration cycle, the degree of subcooling of the refrigerant at the condenser outlet correlates with the amount of refrigerant charged in the refrigerant circuit, and a method for estimating the amount of refrigerant charged by measuring the degree of subcooling is commonly used. The degree of subcooling is the opposite of the degree of superheat described above. It is the value Δt when the refrigerant is discharged at a temperature approximately Δt lower than the saturation temperature, and indicates the temperature drop from the saturation temperature at that pressure.

[0036] The degree of subcooling of the refrigerant is also correlated with the amount of refrigerant circulating within the refrigerant circuit. Therefore, the compressor 21 is operated at a constant frequency, and the constant frequency is maintained while the degree of subcooling of the refrigerant is measured. The degree of subcooling of the refrigerant can be measured by measuring the temperature at the outlet of the condenser using a temperature sensor as a temperature detection means. The pressure of the refrigerant can be measured by using a pressure sensor as a pressure detection means for detecting the discharge pressure attached to the compressor 21. The pressure of the refrigerant may be measured using a pressure sensor attached to the compressor 21 or a separate pressure sensor provided at the inlet or outlet of the condenser.

[0037] The saturation temperature of the refrigerant can be calculated from the refrigerant pressure measured by a pressure sensor. The degree of subcooling of the refrigerant can be calculated by subtracting the calculated saturation temperature from the refrigerant temperature measured by a temperature sensor at the condenser outlet. The temperature sensor that detects the temperature at the condenser outlet and the pressure sensor that detects the discharge pressure function as a first detection means for detecting the degree of subcooling at the condenser outlet.

[0038] When the amount of refrigerant charged is adequate, the refrigerant at the outlet of the condenser is completely condensed into liquid and reaches a certain level of subcooling. On the other hand, when the amount of refrigerant charged is insufficient, the suction pressure of the compressor 21 decreases, and the discharge pressure also decreases, but the discharge temperature increases, and the refrigerant at the outlet of the condenser becomes saturated, with some remaining in a gaseous state, resulting in increased pressure loss. Therefore, by detecting the degree of subcooling, it is possible to determine whether the amount of refrigerant is adequate or insufficient.

[0039] As the amount of refrigerant charged is reduced from a sufficient amount, the degree of subcooling of the refrigerant at the outlet of the condenser decreases and eventually becomes saturated. Accordingly, the refrigerant becomes saturated in the piping on the inlet side of the subcooler 25, which is closest to the condenser, followed by the piping on the outlet side.

[0040] As the degree of subcooling of the refrigerant at the outlet of the condenser decreases, the cooling efficiency of the subcooler 25 decreases, and therefore the opening of the bypass valve 27 is controlled to increase in order to maintain the cooling capacity of the subcooler 25. In this way, the subcooler 25 attempts to maintain its cooling capacity by controlling the opening of the bypass valve 27. The cooling capacity of the subcooler 25 can be detected by providing a temperature sensor as temperature detection means for detecting the temperature of the refrigerant at the outlet of the subcooler 25, and providing a pressure sensor as pressure detection means for detecting the pressure at the inlet or outlet of the subcooler 25, and detecting the degree of subcooling of the refrigerant at the outlet of the subcooler 25, similar to the above-mentioned degree of subcooling of the refrigerant at the outlet of the evaporator. However, the cooling capacity of the subcooler 25 is not limited to this, and a temperature sensor may be provided as temperature detection means for detecting the temperature of the refrigerant at the inlet of the subcooler 25, and the temperature may be detected from the temperatures of the refrigerant at the inlet and outlet of the subcooler 25. The temperature sensor or pressure sensor that detects the temperature of the refrigerant at the outlet of the above-mentioned supercooler 25, or the temperature sensor that detects the temperature of the refrigerant at the inlet and outlet of the supercooler 25, functions as a second detection means that detects the cooling capacity of the supercooler 25.

[0041] In this way, when the amount of refrigerant charged is reduced from a sufficient amount, the degree of subcooling at the outlet of the evaporator first decreases, and then the opening of the bypass valve 27 increases as the subcooler 25 tries to maintain its cooling capacity.

[0042] As the amount of refrigerant charged is further reduced and the opening of the bypass valve 27 is increased, the subcooler 25 gradually becomes unable to maintain its cooling capacity, the saturated refrigerant at the outlet of the condenser is no longer subcooled, and the degree of subcooling of the refrigerant at the outlet of the subcooler 25 decreases. When the opening of the bypass valve 27 reaches its maximum, the subcooler 25 becomes unable to maintain its cooling capacity, the saturated refrigerant at the outlet of the condenser passes through the subcooler 25 as is, and the refrigerant also becomes saturated at the outlet of the subcooler 25.

[0043] When the refrigerant leaving the subcooler 25 changes from a subcooled state to a saturated state, it changes from a liquid state to a mixture of liquid and gas, which increases the pressure loss and causes the opening of the expansion valve on the evaporator side to increase. In the cooling operation mode, the indoor heat exchanger 11 functions as an evaporator, so the expansion valve on the evaporator side is the indoor expansion valve 13. In the heating operation mode, on the other hand, the outdoor heat exchanger 22 functions as an evaporator, so the expansion valve on the evaporator side is the outdoor expansion valve 24.

[0044] A temperature sensor is provided at the outlet of the evaporator as a temperature detection means for detecting the temperature of the refrigerant at the outlet of the evaporator, and the expansion valve on the evaporator side is controlled to keep the degree of superheat calculated from the temperature detected by the temperature sensor constant and to maintain a constant ratio of gas in the evaporator. This prevents a phenomenon in which a large ratio of refrigerant accumulates in the evaporator in the refrigeration cycle, making it difficult to achieve a degree of supercooling at the outlet of the condenser.

[0045] For this reason, in addition to operation modes such as the cooling operation mode and the heating operation mode, a refrigerant amount determination operation mode is provided, in which the compressor 21 is maintained at a constant frequency, the cooling capacity of the subcooler 25 is maintained constant, and the degree of superheat of the refrigerant at the outlet of the evaporator is maintained constant. By detecting changes in the degree of subcooling of the refrigerant at the outlet of the condenser, the opening of the bypass valve 27, the cooling capacity of the subcooler 25, and the opening of the expansion valve on the evaporator side, it is possible to determine refrigerant shortage in stages.

[0046] This begins with a decrease in the degree of subcooling of the refrigerant at the outlet of the condenser, followed by an increase in the opening of the bypass valve 27, followed by a decrease in the cooling capacity of the subcooler 25, and finally an increase in the opening of the expansion valve on the evaporator side.Since these phenomena occur in this order, by determining which stage the current situation is at, it is possible to determine how much refrigerant is in short supply.Since the amount of shortfall can be determined to some extent, the time required for the refrigerant charging operation can be shortened.

[0047] In addition to the operation modes, a refrigerant amount determination operation mode is provided, and in the refrigerant amount determination operation mode, it is possible to switch between cooling operation and heating operation.

[0048] Based on the above, as shown in FIG. 2, the air conditioner includes, in addition to the indoor unit 10 and outdoor unit 20 shown in FIG. 1, a first detection means 30 that detects the degree of subcooling of the refrigerant at the condenser outlet and a second detection means 31 that detects the cooling capacity of the subcooler. The air conditioner also includes a control means 32 that controls the air conditioner to operate in a refrigerant quantity determination operation mode, and a determination means 33 that determines the refrigerant quantity deficiency in stages based on at least two or more combinations of the first detection result of the first detection means, the second detection result of the second detection means, the opening degree of the bypass valve 27, and the opening degree of the evaporator-side expansion valve. The control means 32 can be realized by the above-mentioned control device, and the determination means 33 can be realized by the control device or a personal computer (PC), tablet terminal, smartphone, etc. that can communicate with the control device. The air conditioner can also include a notification means 34 that notifies the user of the determination result of the determination means 33. The notification means 34 may be a display device such as a display that displays the determination result, or a sound output device such as a speaker that notifies the determination result by voice.

[0049] A specific refrigerant amount detection process will be described in detail with reference to Fig. 3. The process starts from step 100, and in step 101, the refrigerant amount determination operation mode is activated, and operation begins in the refrigerant amount determination operation mode. At this time, the operation mode may be the cooling operation mode or the heating operation mode. Here, the cooling operation mode will be described.

[0050] In step 102, it is determined whether the refrigeration cycle has stabilized. Whether the refrigeration cycle has stabilized can be determined, for example, based on whether a predetermined time has passed since the start of operation, but this is not a limiting factor. Alternatively, the refrigeration cycle may be determined to have stabilized based on whether the temperature and pressure of the refrigerant circulating in the refrigerant circuit at each position are within a predetermined range and have remained so for a certain period of time.

[0051] In step 103, it is determined whether the opening degree of the evaporator-side expansion valve, i.e., the indoor expansion valve 13, which has the largest refrigerant shortage, is equal to or greater than a predetermined threshold. If it is equal to or greater than the predetermined threshold, the process proceeds to step 104, where the refrigerant shortage is determined to be "very large," and the process proceeds to step 112, where the determination result is displayed. If it is less than the predetermined threshold in step 103, the process proceeds to step 105, where it is determined whether the cooling capacity of the subcooler 25, which has the next largest refrigerant shortage, is smaller than a predetermined value and the bypass valve 27 is larger than a predetermined opening degree. If the cooling capacity is smaller than the predetermined value and larger than the predetermined opening degree, the process proceeds to step 106, where the refrigerant shortage is determined to be "large," and the process proceeds to step 112, where the determination result is displayed.

[0052] Here, it is determined whether the cooling capacity of the supercooler 25 is smaller than a predetermined value and the bypass valve 27 is larger than a predetermined opening degree, but it is also possible to determine only whether the cooling capacity of the supercooler 25 is smaller than a predetermined value. Note that, since the cooling capacity of the supercooler 25 starts to decrease when the opening degree of the bypass valve increases to a certain extent, these two may progress simultaneously. Therefore, it is more desirable to determine whether the cooling capacity of the supercooler 25 is smaller than a predetermined value and the bypass valve 27 is larger than a predetermined opening degree.

[0053] In step 107, it is determined whether the cooling capacity of the subcooler 25, which has the next largest refrigerant shortage, is equal to a predetermined value and whether the opening of the bypass valve 27 is greater than a predetermined value. If the cooling capacity is equal to the predetermined value and greater than the predetermined opening, the process proceeds to step 108, where the refrigerant shortage is determined to be a "medium amount," and the process proceeds to step 112, where the determination result is displayed.

[0054] Here, it is determined whether the cooling capacity of the supercooler 25 is equal to a predetermined value and the bypass valve 27 is greater than a predetermined opening degree, but it is also possible to determine only whether the bypass valve 27 is greater than a predetermined opening degree. In this case, too, the cooling capacity of the supercooler 25 begins to decrease when the opening degree of the bypass valve increases to a certain extent, and these may progress simultaneously. Therefore, it is more desirable to determine whether the cooling capacity of the supercooler 25 is equal to a predetermined value and the bypass valve 27 is greater than a predetermined opening degree. Note that the cooling capacity of the supercooler 25 being equal to a predetermined value includes not only equal to the predetermined value but also a value that is within a certain range of the predetermined value.

[0055] In step 109, it is determined whether the degree of subcooling of the refrigerant at the outlet of the evaporator, which is the smallest amount of refrigerant shortage, is smaller than a predetermined value. If it is smaller than the predetermined value, the process proceeds to step 110, where the amount of refrigerant shortage is determined to be "small," and the process proceeds to step 112, where the determination result is displayed.

[0056] In step 111, it is determined that there is no shortage, and the process proceeds to step 112, where the determination result is displayed, and then to step 113, where the refrigerant amount detection process is terminated.

[0057] The judgment result may be displayed as the above-mentioned "very large amount," "large amount," "medium amount," or "small amount," or the amount of refrigerant that needs to be added may be presented in a specific range, such as "A or more," "B or more but less than A" corresponding to "large amount," "C or more but less than B" corresponding to "medium amount," or "less than C" corresponding to "small amount," as the refrigerant amount corresponding to "very large amount."

[0058] In the example shown in Fig. 3, the refrigerant shortage is judged in four stages, but it is possible to detect the extent of the refrigerant shortage if it can be judged in at least two of the four stages. Note that by judging the refrigerant shortage in three stages instead of two stages, or in four stages instead of three stages, the amount of refrigerant shortage can be detected in more detail.

[0059] In this case, the determination means 33 determines the amount of refrigerant shortage in stages by determining at least two or more combinations of whether the first detection result of the first detection means 30 is smaller than a predetermined value, whether the second detection result of the second detection means 31 is equal to the predetermined value and the bypass valve 27 is larger than a predetermined opening, whether the second detection result is smaller than the predetermined value and the bypass valve 27 is larger than a predetermined opening, and whether the opening of the expansion valve on the evaporator side is equal to or larger than a predetermined threshold.

[0060] During operation in the refrigerant quantity determination operation mode, the operation is affected by the ambient air temperature. To mitigate this effect, it is desirable to change the rotation speed of the fan motors of the condenser-side fan as the first air supply means and the evaporator-side fan as the second air supply means, depending on the ambient air temperature.

[0061] Specifically, when the ambient temperature of the condenser-side fan is low, the rotation speed of the fan motor of the condenser-side fan is reduced, and when the ambient temperature of the evaporator-side fan is low, the rotation speed of the fan motor of the evaporator-side fan is increased. In this way, the amount of air supplied by each fan can be adjusted according to the ambient temperature. Here, the rotation speed of the fan motor is controlled according to the ambient temperature, but this is not limited to this. For example, the rotation speed of each fan motor may be controlled so that the refrigerant pressure on the high-pressure side and the low-pressure side, where the refrigerant pressure is high and low, respectively, divided by the compressor 21 and the outdoor expansion valve 24 of the refrigerant circuit, reaches a target value. The high-pressure side pressure is, for example, the discharge pressure of the compressor 21, and the low-pressure side pressure is, for example, the pressure of the refrigerant at the point where the refrigerant exits the outdoor expansion valve 24 in the cooling operation mode, or the pressure of the refrigerant at the point where the refrigerant exits the indoor expansion valve 13 in the heating operation mode.

[0062] The refrigeration cycle apparatus may include a plurality of evaporators. When the refrigeration cycle apparatus is an air conditioner, the air conditioner may include a plurality of indoor units.

[0063] As described above, the control device controls the degree of superheat to be constant so as to maintain a constant ratio of gas in the evaporator, but if the refrigeration cycle device has multiple evaporators, the same degree of superheat may be set for all evaporators, or different degrees of superheat may be set as the control target value for each evaporator. Also, even if there is only one evaporator, the same degree of superheat may be set regardless of the volume of the evaporator, or the degree of superheat may be changed depending on the volume of the evaporator.

[0064] The volume of the evaporator is the volume of the portion of the evaporator that can store refrigerant, and the volume of the heat transfer tubes provided in the evaporator accounts for the majority of the volume.

[0065] Fig. 4 shows an example in which the same degree of superheat is set for all evaporators. In Fig. 4, the evaporators are indoor heat exchangers 11, and the different capacities of the two indoor heat exchangers 11 are shown by the lengths of the heat transfer tubes provided in each indoor heat exchanger 11. Because the degree of superheat is set to a value greater than 0, the refrigerant is supplied in a liquid state, and some of it evaporates along the way, becoming a two-phase liquid-gas state. After that, all of the refrigerant vaporizes and is discharged in a gaseous state.

[0066] When the same degree of superheat is set for the two indoor heat exchangers 11, the ratios of the liquid state section (liquid region length: a, a'), two-phase state section (two-phase region length: b, b'), and gas state section (gas region length: c, c') existing in each indoor heat exchanger 11 are approximately equal. That is, a:b:c ≒ a':b':c'.

[0067] However, since the volumes of the two indoor heat exchangers 11 are different, the indoor heat exchanger 11 with a larger container receives a larger absolute amount of liquid refrigerant than the indoor heat exchanger 11 with a smaller volume, resulting in a larger amount of refrigerant as an evaporator.

[0068] Fig. 5 shows an example in which different degrees of superheat are set for each evaporator. Similar to Fig. 4, Fig. 5 also shows the indoor heat exchangers 11 as evaporators, with the different capacities of the two indoor heat exchangers 11 being represented by the lengths of the heat transfer tubes provided in each indoor heat exchanger 11. In this example, the degree of superheat is set to a value greater than 0, so the refrigerant is supplied in a liquid state, but some of it evaporates along the way, becoming a two-phase liquid-gas state. Then, all of the refrigerant vaporizes and is discharged in a gaseous state.

[0069] When different degrees of superheat are set for the two indoor heat exchangers 11, one possible approach is to make the liquid volumes the same. That is, the lengths of the liquid regions among the liquid state section (liquid region length: a, a'), two-phase state section (two-phase region length: b, b'), and gas state section (gas region length: c, c') present in each indoor heat exchanger 11 are made approximately the same. In other words, a ≒ a'. By making the lengths of the liquid regions the same in this way, the indoor heat exchanger 11 with the larger volume has a longer gas region length and is heated for a longer period of time, resulting in a higher degree of superheat than the indoor heat exchanger 11 with the smaller volume.

[0070] As described above, by determining the amount of refrigerant in stages and notifying the determination result, the worker can roughly grasp the amount of refrigerant to be added, thereby shortening the work time required to add the refrigerant.

[0071] The refrigeration cycle device and refrigerant amount detection method of the present invention have been described in detail using the above-mentioned embodiments, but 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 imagine, such as other embodiments, additions, modifications, deletions, etc., and any aspect is included in the scope of the present invention as long as it achieves the functions and effects of the present invention.

[0072] Therefore, according to the present invention, (1) a refrigeration cycle apparatus can be provided in which a refrigerant circulates in a refrigerant circuit that connects a compressor, a condenser, a subcooler, an expansion valve, and an evaporator in that order with piping, and a portion of the refrigerant that has flowed out of the condenser is branched and expanded by a bypass valve, and then supplied to the suction side of the compressor via the subcooler, the refrigeration cycle apparatus including: a control means that controls the compressor to operate at a predetermined frequency, the subcooler to maintain a constant cooling capacity, and to operate in a refrigerant amount determination operation mode in which the degree of superheat of the refrigerant at the outlet of the evaporator is kept constant; a first detection means that detects the degree of subcooling of the refrigerant at the outlet of the condenser; a second detection means that detects the cooling capacity of the subcooler; and a determination means that determines the amount of refrigerant that is insufficient in a stepwise manner based on at least two or more combinations of a first detection result of the first detection means, a second detection result of the second detection means, the opening degree of the bypass valve, and the opening degree of the expansion valve.

[0073] According to the present invention, (2) it is possible to provide the refrigeration cycle apparatus described above in (1), in which the determination means determines the amount of refrigerant shortage in a stepwise manner by determining at least two or more combinations of whether the first detection result is smaller than a predetermined value, whether the second detection result is equal to a predetermined value and the bypass valve is larger than a predetermined opening, whether the second detection result is smaller than a predetermined value and the bypass valve is larger than a predetermined opening, and whether the opening of the expansion valve is equal to or larger than a predetermined threshold.

[0074] According to the present invention, (3) it is possible to provide the refrigeration cycle device described in (1) or (2) above, which includes a notification means for notifying the determination result determined in stages by the determination means.

[0075] According to the present invention, (4) it is possible to provide the refrigeration cycle device according to any one of (1) to (3) above, including a switching means for switching the circulation direction of the refrigerant circulating in the refrigerant circuit, and a second expansion valve for decompressing the refrigerant after passing through the subcooler when the circulation direction of the refrigerant is switched by the switching means.

[0076] According to the present invention, (5) it is possible to provide a refrigeration cycle device according to any one of (1) to (4) above, which includes a first air supply means for supplying first air that exchanges heat with the refrigerant in the condenser, and a second air supply means for supplying second air that exchanges heat with the refrigerant in the evaporator, and the control means adjusts the amount of air supplied by the first air supply means according to the temperature of the first air, and adjusts the amount of air supplied by the second air supply means according to the temperature of the second air.

[0077] According to the present invention, (6) it is possible to provide a refrigeration cycle device described in any one of (1) to (5) above, in which the control target value of the degree of superheat of the refrigerant at the outlet of the evaporator is changed according to the volume of the evaporator.

[0078] According to the present invention, (7) it is possible to provide the refrigeration cycle apparatus according to any one of (1) to (6) above, wherein the refrigeration cycle apparatus is an air conditioning apparatus including a plurality of indoor units and outdoor units, and each of the indoor units includes an indoor heat exchanger that functions as the evaporator during cooling operation, an indoor expansion valve that functions as the expansion valve, and an indoor fan that functions as the second air supply means, and the outdoor unit includes the compressor, the switching means, the subcooler, and the bypass valve, and includes an outdoor heat exchanger that functions as the condenser during cooling operation, an outdoor expansion valve that functions as the second expansion valve, and an outdoor fan that functions as the first air supply means.

[0079] According to the present invention, (8) a method for detecting a refrigerant amount using a refrigeration cycle device in which a refrigerant circulates in a refrigerant circuit connecting a compressor, a condenser, a subcooler, an expansion valve, and an evaporator in that order with piping, and a portion of the refrigerant leaving the condenser is branched, expanded by a bypass valve, and then supplied to the suction side of the compressor via the subcooler, the method including the steps of controlling the compressor to operate in a refrigerant amount determination operation mode in which the compressor is operated at a predetermined frequency, the subcooler is maintained at a constant cooling capacity, and the degree of superheat of the refrigerant at the outlet of the evaporator is kept constant; detecting the degree of subcooling of the refrigerant at the outlet of the condenser; detecting the cooling capacity of the subcooler; and determining in a stepwise manner the amount of refrigerant deficiency based on at least two or more combinations of the detected degree of subcooling, the detected cooling capacity, the opening of the bypass valve, and the opening of the expansion valve.

[0080] According to the present invention, (9) it is possible to provide the method according to (8) above, wherein in the determining step, the amount of refrigerant shortage is determined in stages by determining at least two or more combinations of whether or not the first detection result is smaller than a predetermined value, whether or not the second detection result is equal to a predetermined value and the bypass valve is larger than a predetermined opening, whether or not the second detection result is smaller than a predetermined value and the bypass valve is larger than a predetermined opening, and whether or not the opening of the expansion valve is equal to or larger than a predetermined threshold.

[0081] According to the present invention, (10) it is possible to provide the method according to (8) or (9) above, which includes a step of notifying the determination result determined step by step in the determining step.

[0082] According to the present invention, (11) it is possible to provide the method according to any one of (8) to (10) above, including: a step of switching a circulation direction of the refrigerant circulating in the refrigerant circuit; and a step of decompressing the refrigerant that has passed through the subcooler by a second expansion valve when the circulation direction of the refrigerant has been switched in the switching step.

[0083] According to the present invention, (12) it is possible to provide a method according to any one of (8) to (11) above, including the steps of: supplying first air that exchanges heat with the refrigerant in the condenser; supplying second air that exchanges heat with the refrigerant in the evaporator; adjusting the amount of air supplied by the first air supply means according to the temperature of the first air; and adjusting the amount of air supplied by the second air supply means according to the temperature of the second air.

[0084] DESCRIPTION OF SYMBOLS 10... Indoor unit 11... Indoor heat exchanger 12... Indoor fan 13... Indoor expansion valve 20... Outdoor unit 21... Compressor 22... Outdoor heat exchanger 23... Outdoor fan 24... Outdoor expansion valve 25... Subcooler 26... Four-way valve 27... Bypass valve 30... First detection means 31... Second detection means 32... Control means 33... Determination means 34... Notification means

Claims

1. A refrigeration cycle device in which refrigerant circulates in a refrigerant circuit that connects a compressor, a condenser, a subcooler, an expansion valve, and an evaporator in that order with piping, and in which a portion of the refrigerant that has flowed out of the condenser is branched and expanded in a bypass valve before being supplied to the suction side of the compressor via the subcooler, the refrigeration cycle device comprising: a control means that controls the compressor to operate at a predetermined frequency, the subcooler to maintain a constant cooling capacity, and to operate in a refrigerant amount determination operation mode that keeps the degree of superheat of the refrigerant at the outlet of the evaporator constant; a first detection means that detects the degree of subcooling of the refrigerant at the outlet of the condenser; a second detection means that detects the cooling capacity of the subcooler; and a determination means that determines the amount of refrigerant that is insufficient in stages based on at least two or more combinations of a first detection result of the first detection means, a second detection result of the second detection means, the opening degree of the bypass valve, and the opening degree of the expansion valve.

2. The refrigeration cycle device of claim 1, wherein the determination means determines the amount of refrigerant shortage in stages by determining at least two or more combinations of whether the first detection result is smaller than a predetermined value, whether the second detection result is equal to a predetermined value and the bypass valve is larger than a predetermined opening, whether the second detection result is smaller than a predetermined value and the bypass valve is larger than a predetermined opening, and whether the opening of the expansion valve is equal to or larger than a predetermined threshold.

3. The refrigeration cycle device according to claim 1 or 2, further comprising a notification means for notifying the result of the stepwise determination made by said determination means.

4. A refrigeration cycle device according to claim 1 or 2, comprising: a switching means for switching the circulation direction of the refrigerant circulating within the refrigerant circuit; and a second expansion valve for decompressing the refrigerant after passing through the subcooler when the circulation direction of the refrigerant is switched by the switching means.

5. A refrigeration cycle device as described in claim 4, including a first air supply means for supplying first air that exchanges heat with the refrigerant in the condenser, and a second air supply means for supplying second air that exchanges heat with the refrigerant in the evaporator, wherein the control means adjusts the amount of air supplied by the first air supply means according to the temperature of the first air, and adjusts the amount of air supplied by the second air supply means according to the temperature of the second air.

6. The refrigeration cycle device according to claim 5, wherein a control target value of the degree of superheat of the refrigerant at the outlet of the evaporator is changed according to the volume of the evaporator.

7. The refrigeration cycle device is an air conditioning device including a plurality of indoor units and outdoor units, each of the indoor units including an indoor heat exchanger that functions as the evaporator during cooling operation, an indoor expansion valve that functions as the expansion valve, and an indoor fan that functions as the second air supply means, and the outdoor unit including the compressor, the switching means, the subcooler, and the bypass valve, and including an outdoor heat exchanger that functions as the condenser during cooling operation, an outdoor expansion valve that functions as the second expansion valve, and an outdoor fan that functions as the first air supply means. The refrigeration cycle device described in claim 6.

8. A method for detecting a refrigerant amount using a refrigeration cycle device in which a refrigerant circulates in a refrigerant circuit in which a compressor, a condenser, a subcooler, an expansion valve, and an evaporator are connected in that order by piping, and a portion of the refrigerant that has flowed out of the condenser is branched, expanded by a bypass valve, and then supplied to the suction side of the compressor via the subcooler, the method comprising the steps of controlling the compressor to operate at a predetermined frequency, maintaining the subcooler at a constant cooling capacity, and operating in a refrigerant amount determination operation mode in which the degree of superheat of the refrigerant at the outlet of the evaporator is kept constant; detecting the degree of subcooling of the refrigerant at the outlet of the condenser; detecting the cooling capacity of the subcooler; and determining in stages the amount of refrigerant deficiency based on at least two or more combinations of the detected degree of subcooling, the detected cooling capacity, the opening degree of the bypass valve, and the opening degree of the expansion valve.

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