Control method of air conditioner

Abstract

The application discloses a control method of an air conditioner, and belongs to the technical field of air treatment. The air conditioner comprises a compressor, an outdoor heat exchanger, a first electronic expansion valve, a first indoor heat exchanger, a second electronic expansion valve and a second indoor heat exchanger; a fresh air module, a fresh air outlet of which is in communication with an indoor return air inlet; when the air conditioner is running, fresh air flows through the second indoor heat exchanger and then flows through the first indoor heat exchanger at the indoor return air inlet; the control method comprises the following steps: controlling the opening degree of the second electronic expansion valve to adjust the refrigeration temperature of the second indoor heat exchanger, so that the fresh air is dehumidified when flowing through the second indoor heat exchanger; and controlling the opening degree of the first electronic expansion valve or the frequency of the compressor to adjust the heating temperature of the first indoor heat exchanger, so that the fresh air is heated when flowing through the first indoor heat exchanger. The control method of the air conditioner can realize fresh air dehumidification.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of air treatment, and in particular to a control method of an air conditioner. BACKGROUND

[0002] Some air conditioners have a fresh air function, which improves the freshness of indoor air by sending outdoor air into the room. In spring and summer, weather phenomena such as back to the south and Huangmei days occur in southern and some coastal areas, although the air temperature is moderate, but the humidity is very high. The air conditioner will introduce this high-humidity fresh air into the room, which will result in poor comfort of people.

[0003] In related technologies, a dehumidification wheel is added to the fresh air module to achieve fresh air dehumidification by using the dehumidification wheel to absorb moisture from the fresh air.

[0004] However, this dehumidification method requires significant changes to the fresh air module and the structure of the air conditioner, so it is necessary to add a fresh air dehumidification function to the air conditioner from the perspective of control logic to reduce the changes to the structure of the air conditioner. SUMMARY

[0005] The present application provides a control method of an air conditioner, which can achieve fresh air dehumidification.

[0006] In one aspect of the present application, the air conditioner includes: a compressor, an outdoor heat exchanger, a first electronic expansion valve, a first indoor heat exchanger, a second electronic expansion valve, and a second indoor heat exchanger in a refrigerant circuit connected in series; a fresh air module, the fresh air outlet of the fresh air module being communicable with the indoor return air inlet of the air conditioner, so that the fresh air introduced by the fresh air module flows to the indoor return air inlet; and the air conditioner is configured to cause the fresh air to flow through the second indoor heat exchanger and then flow through the first indoor heat exchanger when the air conditioner is running.

[0007] The control method of the air conditioner includes: controlling the opening degree of the second electronic expansion valve according to the temperature of the second indoor heat exchanger and the relative humidity of the indoor return air to adjust the cooling temperature of the second indoor heat exchanger, so that the fresh air is cooled and dehumidified when flowing through the second indoor heat exchanger; and controlling the opening degree of the first electronic expansion valve or the frequency of the compressor according to the difference between the indoor return air temperature and the indoor target temperature or according to the difference between the indoor return air temperature and the outdoor environment temperature to adjust the heating temperature of the first indoor heat exchanger, so that the cooled fresh air is warmed when flowing through the first indoor heat exchanger.

[0008] In some embodiments, the air conditioner can run at least one of the following fresh air micro-cooling dehumidification mode, fresh air non-cooling dehumidification mode, and fresh air micro-warming dehumidification mode;

[0009] In the fresh air micro-cooling dehumidification mode, the fine temperature adjustment step includes judging the difference between the indoor return air temperature and the indoor target temperature, increasing the opening of the first electronic expansion valve when the difference is less than the lower limit value of the preset temperature difference interval, and decreasing the opening of the first electronic expansion valve when the difference is greater than the upper limit value of the preset temperature difference interval.

[0010] In the fresh air non-cooling dehumidification mode, the fine temperature adjustment step includes controlling the first electronic expansion valve to be fully open, judging the difference between the indoor return air temperature and the outdoor environment temperature, increasing the frequency of the compressor when the difference is less than the lower limit value of the preset temperature difference interval, and decreasing the frequency of the compressor when the difference is greater than the upper limit value of the preset temperature difference interval.

[0011] In the fresh air micro-warming dehumidification mode, the fine temperature adjustment step includes controlling the first electronic expansion valve to be fully open, judging the difference between the indoor return air temperature and the indoor target temperature, increasing the frequency of the compressor when the difference is less than the lower limit value of the preset temperature difference interval, and decreasing the frequency of the compressor when the difference is greater than the upper limit value of the preset temperature difference interval.

[0012] In some embodiments, when entering the fresh air micro-cooling dehumidification mode, the second electronic expansion valve is opened at an initial opening a 21 ;

[0013] When entering the fresh air non-cooling dehumidification mode, the second electronic expansion valve is opened at an initial opening a 21 lower than a 22 ;

[0014] When entering the fresh air micro-warming dehumidification mode, the second electronic expansion valve is opened at an initial opening a 22 lower than a 23 .

[0015] In some embodiments, when entering the fresh air non-cooling dehumidification mode, the compressor is controlled to operate at a second preset frequency f2;

[0016] When entering the fresh air micro-warming dehumidification mode, the compressor is controlled to operate at a third preset frequency f3 higher than f2.

[0017] In some embodiments, when entering the fresh air micro-cooling dehumidification mode, the outdoor fan is controlled to operate at a first preset speed n1;

[0018] When entering the fresh air non-cooling dehumidification mode, the outdoor fan is controlled to operate at a second preset speed n2 lower than n1;

[0019] When entering the fresh air micro-warming dehumidification mode, the outdoor fan is controlled to operate at a third preset speed n3 lower than n2.

[0020] In another aspect of this application, the air conditioner includes: a refrigerant circuit consisting of a compressor, an outdoor heat exchanger, a first electronic expansion valve, a first indoor heat exchanger, a second electronic expansion valve, and a second indoor heat exchanger connected in series; a fresh air module, the fresh air outlet of which can be connected to the indoor return air inlet of the air conditioner, so that the fresh air introduced by the fresh air module flows to the indoor return air inlet; when the air conditioner is running, the fresh air flows from the indoor return air inlet first through the second indoor heat exchanger and then through the first indoor heat exchanger;

[0021] The control method of the air conditioner includes: controlling the opening of the second electronic expansion valve to adjust the cooling temperature of the second indoor heat exchanger so that the fresh air is cooled and dehumidified when it flows through the second indoor heat exchanger; and controlling the opening of the first electronic expansion valve or the frequency of the compressor according to the difference between the indoor return air temperature and the indoor target temperature or the difference between the indoor return air temperature and the outdoor ambient temperature to adjust the heating temperature of the first indoor heat exchanger so that the cooled fresh air is heated when it flows through the first indoor heat exchanger.

[0022] The dehumidification process specifically includes:

[0023] S11, Based on indoor return air temperature T n Relative humidity of indoor return air φ n The return air dew point temperature T was calculated. L ;

[0024] Determine the coil temperature T of the second indoor heat exchanger P The interval to which T belongs: If T P If T ≤ 0℃, increase the opening of the second electronic expansion valve; if T P ≥T L If 0℃ < T, then reduce the opening of the second electronic expansion valve; P <T L Then proceed to S12;

[0025] S12. Determine the relative humidity φ of the indoor return air. n relative humidity φ of the target s The interval to which the difference belongs: If φ n -φ s If the humidity difference is less than the first preset threshold value, then increase the opening of the second electronic expansion valve; if φ n -φ s If the second preset humidity difference threshold is greater than or equal to φ, then the opening of the second electronic expansion valve is reduced; if the first preset humidity difference threshold is less than or equal to φ, then the opening of the second electronic expansion valve is reduced. n -φ s If the humidity difference is less than or equal to the second preset humidity difference threshold, the opening of the second electronic expansion valve remains unchanged.

[0026] In some embodiments, during the dehumidification step, when 0°C < T P <T Land the first preset humidity difference threshold value ≤ φ n -φ s ≤ the second preset humidity difference threshold value, entering the fine temperature adjustment step.

[0027] In some embodiments, in S11, after the opening of the second electronic expansion valve is increased or decreased, T is re-judged every first preset time interval Δt1 P belongs to the interval;

[0028] In S12, after the opening of the second electronic expansion valve is increased or decreased, T is re-judged every first preset time interval Δt1 in S11 P belongs to the interval;

[0029] In the fine temperature adjustment step, after the frequency of the compressor is increased or decreased, the interval of the difference value is judged every second preset time interval Δt2.

[0030] In some embodiments, in S11, the opening increment of the second electronic expansion valve is a first preset opening increment Δa 21 ;

[0031] In S12, the opening increment of the second electronic expansion valve is a second preset opening increment Δa 21 that is less than the first preset opening increment Δa 22 .

[0032] In some embodiments, in S11, the opening increment of the second electronic expansion valve is a first preset opening increment Δa 21 ;

[0033] In S11, the opening decrement of the second electronic expansion valve is a first preset opening decrement Δa 21 that is less than the first preset opening increment Δa 23 .

[0034] In some embodiments, in S12, the opening decrement of the second electronic expansion valve is a second preset opening decrement Δa 23 that is not greater than the first preset opening decrement Δa 24 . BRIEF DESCRIPTION OF DRAWINGS

[0035] Figure 1 A schematic diagram of an indoor unit of an air conditioner according to some embodiments is shown;

[0036] Figure 2 A schematic diagram of a fresh air module of an air conditioner according to some embodiments is shown;

[0037] Figure 3 A schematic diagram of a refrigerant circuit of an air conditioner according to some embodiments is shown;

[0038] Figure 4 A flow chart of a dehumidification mode of an air conditioner is shown according to some embodiments;

[0039] Figure 5 A flow chart of a fresh air slightly cooling dehumidification mode of an air conditioner is shown according to some embodiments;

[0040] Figure 6 A flow chart of a fresh air non-cooling dehumidification mode of an air conditioner is shown according to some embodiments;

[0041] Figure 7 A flow chart of a fresh air slightly heating dehumidification mode of an air conditioner is shown according to some embodiments;

[0042] In the above figures, 1, compressor; 2, four-way valve; 3, outdoor heat exchanger; 4, first electronic expansion valve; 5, first indoor heat exchanger; 6, second electronic expansion valve; 7, second indoor heat exchanger; 10, housing; 11, indoor return air inlet; 12, air outlet; 20, indoor heat exchanger; 30, indoor fan; 40, fresh air module; 41, fresh air module housing; 411, fresh air inlet; 412, fresh air outlet; 413, air guide part; 42, fresh air fan. DETAILED DESCRIPTION

[0043] In order to make the purpose and implementation of the present application more clear, the following will combine the drawings in the exemplary embodiments of the present application to clearly and completely describe the exemplary embodiments of the present application. Obviously, the described exemplary embodiments are only some of the embodiments of the present application, but not all the embodiments.

[0044] In the description of the present application, it needs to be understood that the terms "center", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the indicated device or element must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application.

[0045] The terms "first", "second" are only for the purpose of description, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined with "first", "second" can explicitly or implicitly include one or more of the features. In the description of the present application, unless otherwise stated, "a plurality of" means two or more.

[0046] In the description of the present application, it is necessary to explain that unless explicitly defined and limited, the terms "mount", "connect", "connection" should be understood in a broad sense, for example, it can be fixed connection, or detachable connection, or integrally connected; it can be mechanical connection, or electrical connection; it can be directly connected, or indirectly connected through intermediate medium, or the communication inside two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0047] The embodiments of the present application will be described in detail below with reference to the accompanying drawings.

[0048] In the present application, the air conditioner performs a refrigeration cycle of the air conditioner by using a compressor, a condenser, an expansion valve, and an evaporator. The refrigeration cycle includes a series of processes involving compression, condensation, expansion, and evaporation, and supplies a refrigeration amount to the air that has been adjusted and heat-exchanged.

[0049] The compressor compresses refrigerant gas in a low-temperature and low-pressure state and discharges the compressed refrigerant gas. The discharged refrigerant gas flows into the condenser. The condenser condenses the compressed refrigerant into a liquid phase, and heat is released to the surrounding environment through the condensation process.

[0050] The expansion valve expands the liquid-phase refrigerant in a high-temperature and high-pressure state condensed in the condenser into a low-pressure gas-liquid two-phase refrigerant. The evaporator evaporates the refrigerant expanded in the expansion valve and returns the refrigerant gas in a low-temperature and low-pressure state to the compressor. The evaporator can achieve a refrigeration effect by heat-exchanging with a material to be cooled using latent heat of evaporation of the refrigerant. Throughout the cycle, the air conditioner can adjust the temperature of the indoor space.

[0051] The outdoor unit of the air conditioner refers to the part of the refrigeration cycle including the compressor and the outdoor heat exchanger, the indoor unit of the air conditioner includes the indoor heat exchanger, and the expansion valve can be provided in the indoor unit or the outdoor unit.

[0052] The indoor heat exchanger and the outdoor heat exchanger are used as a condenser or an evaporator. When the indoor heat exchanger is used as a condenser, the air conditioner is used as a heater in a heating mode, and when the indoor heat exchanger is used as an evaporator, the air conditioner is used as a cooler in a cooling mode.

[0053] Referring to Figure 1 , the indoor unit of the air conditioner according to the embodiments of the present application includes a case 10 having an indoor return air inlet 11 and an air outlet 12, an indoor heat exchanger 20 performing heat exchange with air introduced into the case 10, and an indoor fan 30 circulating the air. The indoor unit of the air conditioner of the present application can be a wall-mounted air conditioner installed on a wall.

[0054] The indoor fan 30 is used to force air flow. Under the action of the indoor fan 30, air can enter the shell 10 from the indoor return air inlet 11, then flow through the indoor heat exchanger 20, and finally circulate to the indoor through the air outlet 12.

[0055] In combination Figure 2 , the indoor unit of the air conditioner of the present application further comprises a fresh air module 40 for introducing outdoor fresh air into the indoor. The fresh air module 40 comprises a fresh air module shell 41 having a fresh air inlet 411 and a fresh air outlet 412, and a fresh air fan 42 for introducing outdoor fresh air.

[0056] The fresh air inlet 411 is communicated with the outdoor through a fresh air duct, and the fresh air outlet 412 is provided with a wind guide part 413. The wind guide part 413 is used to guide the fresh air to the direction of the indoor return air inlet 11, so that the fresh air can flow from the fresh air outlet 412 to the indoor return air inlet 11.

[0057] Specifically, the wind guide part 413 is arc-shaped, which is connected to the side wall of the fresh air outlet 412 away from the indoor return air inlet 11. The arc-shaped opening of the wind guide part 413 faces the direction of the indoor return air inlet 11, so that the fresh air flowing out of the fresh air outlet 412 flows to the side of the indoor return air inlet 11 under the guidance of the wind guide part 413. In this way, as Figure 1 the arrow shows the direction of the fresh air flow, when the air conditioner introduces fresh air, the fresh air and the indoor return air mix inside the indoor return air inlet 11, flow through the indoor heat exchanger 20 together, and flow to the air outlet 12, so that the temperature and humidity of the fresh air are processed through the indoor heat exchanger 20.

[0058] In the present application, the indoor heat exchanger 20 comprises a first indoor heat exchanger 5 and a second indoor heat exchanger 7. On the air moving path from the indoor return air inlet 11 to the air outlet 12, the second indoor heat exchanger 7 is closer to the indoor return air inlet 11 than the first indoor heat exchanger 5, so that the air flows through the second indoor heat exchanger 7 first, and then flows through the first indoor heat exchanger 5.

[0059] In the present application, with reference to Figure 3 , the refrigerant circuit of the air conditioner comprises a compressor 1, a four-way valve 2, an outdoor heat exchanger 3, a first electronic expansion valve 4, a first indoor heat exchanger 5, a second electronic expansion valve 6, and a second indoor heat exchanger 7 connected in series in sequence.

[0060] In the refrigeration and dehumidification operation, the refrigerant flows through the compressor 1, the four-way valve 2, the outdoor heat exchanger 3, the first electronic expansion valve 4, the first indoor heat exchanger 5, the second electronic expansion valve 6, the second indoor heat exchanger 7, and then returns to the compressor 1 in sequence in the refrigerant circuit. The refrigerant releases heat in the outdoor heat exchanger 3 and changes from superheated vapor to two-phase flow, further releases heat in the first indoor heat exchanger 5, and absorbs heat in the second indoor heat exchanger 7 to change from two-phase flow to superheated vapor; the air flows through the second indoor heat exchanger 7 and the first indoor heat exchanger 5 in sequence, and after flowing through the second indoor heat exchanger 7, the temperature of the air is greatly reduced, and a large amount of condensed water is precipitated, thereby realizing the dehumidification of the air, and after flowing through the first indoor heat exchanger 5, the temperature of the air is increased to a suitable temperature and then sent to the indoor, thereby realizing the adjustment of the temperature of the fresh air supply.

[0061] The air conditioner of the present application can realize multiple dehumidification modes for fresh air / mixed air to meet different user requirements for comfort. The multiple dehumidification modes include a fresh air slightly-cooled dehumidification mode, a fresh air non-cooled dehumidification mode, and a fresh air slightly-heated dehumidification mode.

[0062] For example, when the outdoor humidity is relatively large, the user needs the air conditioner to dehumidify when introducing fresh air. In addition, if the outdoor temperature is slightly high, the user expects to reduce the temperature of the fresh air when introducing the fresh air, in which case the slightly-cooled dehumidification mode can be selected. If the outdoor temperature is relatively suitable, the user expects not to change the temperature of the fresh air, in which case the non-cooled dehumidification mode can be selected. If the outdoor temperature is slightly low, the user expects to increase the temperature of the fresh air when introducing the fresh air, in which case the slightly-heated dehumidification mode can be selected. The multiple dehumidification modes provide multiple choices for the user and can meet different user requirements for the temperature and humidity of the fresh air.

[0063] The control method of the air conditioner in the multiple dehumidification modes is described below.

[0064] The air conditioner of the present application further comprises a return air temperature and humidity sensor, an outdoor temperature sensor, and a second coil temperature sensor.

[0065] The return air temperature and humidity sensor can be arranged at the indoor return air inlet 11 and used to detect the temperature Tn and the relative humidity φn of the indoor return air. n The outdoor temperature sensor can be arranged on the outdoor unit of the air conditioner or at the fresh air inlet 411 of the fresh air module 40 and used to detect the temperature To of the outdoor air. w The second coil temperature sensor can be arranged on the coil of the second indoor heat exchanger 7 and used to detect the coil temperature T7 of the second indoor heat exchanger. p

[0066] ​In the new air micro-cooling dehumidification mode, the first electronic expansion valve 4 and the second electronic expansion valve 5 are both in throttling state. The second electronic expansion valve 5 has a small opening degree, so that the temperature at the second indoor heat exchanger 7 is low, which is beneficial to the cooling and dehumidification of the new air by the second indoor heat exchanger 7; the first electronic expansion valve 4 has a relatively large opening degree, so that the temperature at the first indoor heat exchanger 5 is high, which is beneficial to the heating of the new air by the first indoor heat exchanger 5, and at the same time, due to the throttling effect of the first electronic expansion valve 4, the temperature at the first indoor heat exchanger 5 is lower than the temperature of the outdoor heat exchanger 3, so that the temperature of the new air is still lower than the initial temperature after rising, thereby realizing the micro-cooling and dehumidification of the new air.

[0067] The initial temperature of the new air T w is greatly reduced and dehumidified when passing through the second indoor heat exchanger 7, and the temperature is reduced to T w1 . w2 Then the temperature rises to T w2 when passing through the first indoor heat exchanger 5. w .

[0068] It can be understood that T w is allowed to have a fluctuation range, rather than a fixed value.

[0069] In the new air non-cooling dehumidification mode and the new air micro-heating mode, the first electronic expansion valve 4 is fully opened, and the second electronic expansion valve 5 is in throttling state. The second electronic expansion valve 5 has a small opening degree, so that the temperature at the second indoor heat exchanger 7 is low, which is beneficial to the cooling and dehumidification of the new air by the second indoor heat exchanger 7; the first electronic expansion valve 4 does not throttle, so that the temperature at the first indoor heat exchanger 5 is basically the same as that of the outdoor heat exchanger 3, which is beneficial to the heating of the new air by the first indoor heat exchanger 5, so that the temperature of the new air rises to the initial temperature or slightly higher than the initial temperature, thereby realizing the non-cooling dehumidification or micro-heating dehumidification of the new air.

[0070] The condensing pressure in the new air micro-heating mode is slightly higher than that in the new air non-cooling dehumidification mode, so as to realize the micro-heating of the new air.

[0071] <New air micro-cooling dehumidification>

[0072] After starting the new air micro-cooling dehumidification mode, the new air fan and the indoor fan operate at the user-set air speed. The outdoor fan operates at a first preset speed n1, the compressor operates at a first preset frequency f1, the initial opening degree of the first electronic expansion valve is a 11 , and the initial opening degree of the second electronic expansion valve is a 21 .

[0073] The air conditioner receives the user-set indoor target temperature T s and the indoor target humidity φ s.

[0074] The indoor return air temperature T n and the indoor relative humidity φ n can be obtained by the return air temperature and humidity sensor. p .

[0075] In the fresh air micro-cooling dehumidification mode, the opening degree of the second electronic expansion valve is adjusted according to the temperature T n and the humidity φ n of the indoor return air and the coil temperature T p of the second indoor heat exchanger, so as to adjust the refrigeration temperature of the second indoor heat exchanger, so that the fresh air is cooled and dehumidified when flowing through the second indoor heat exchanger; and the opening degree of the first electronic expansion valve is adjusted according to the indoor return air temperature T n and the indoor target temperature T s , so as to adjust the heating temperature of the first indoor heat exchanger, so that the cooled and dehumidified fresh air is warmed to the target temperature when flowing through the first indoor heat exchanger.

[0076] The dehumidification step specifically comprises: S11, calculating the return air dew point temperature T L according to the indoor return air temperature T n and the indoor return air relative humidity φ n ; judging the interval in which the coil temperature T P of the second indoor heat exchanger is located: if T P ≤0℃, the opening degree of the second electronic expansion valve is increased; if T P ≥T L , the opening degree of the second electronic expansion valve is decreased; if 0℃<T P <T L , step S12 is entered.

[0077] Since the dew point temperature T L is calculated according to the indoor return air temperature T n and the indoor return air relative humidity φ n , the calculation process is not described in detail here.

[0078] If the coil temperature T P of the second indoor heat exchanger is ≤0℃, it indicates that the coil temperature of the second indoor heat exchanger is too low and has the risk of frosting, therefore, the opening degree of the second electronic expansion valve needs to be increased, and the opening degree increment is the first preset opening degree increment Δa 21 .

[0079] If the coil temperature T P of the second indoor heat exchanger is ≥ the dew point temperature T LThis indicates that the temperature of the second indoor heat exchanger coil is too high, resulting in poor dehumidification. Therefore, the opening of the second electronic expansion valve needs to be reduced by the amount of the first preset opening reduction Δa. 23 If the coil temperature T of the second indoor heat exchanger P Satisfying 0℃ < T P <T L This indicates that at this temperature, the second indoor heat exchanger can dehumidify the fresh air and will not frost over, so proceed to step S12.

[0080] S12. Determine the relative humidity φ of the indoor return air. n relative humidity φ of indoor target s The interval containing the difference: if φ n -φ s If the humidity difference is less than the first preset threshold value, then increase the opening of the second electronic expansion valve; if φ n -φ s If the second preset humidity difference threshold is greater than or equal to φ, then the opening of the second electronic expansion valve is reduced; if the first preset humidity difference threshold is less than or equal to φ, then the opening of the second electronic expansion valve is reduced. n -φ s If the humidity difference is less than or equal to the second preset humidity difference threshold, the opening of the second electronic expansion valve remains unchanged.

[0081] In this step, if φ n -φ s If the humidity difference exceeds the first preset threshold, it indicates excessive dehumidification and a low coil temperature in the second indoor heat exchanger. This results in overly dry fresh air. Therefore, the opening of the second electronic expansion valve needs to be increased by an increment of Δa. 22 .

[0082] As the opening of the second electronic expansion valve increases, the coil temperature of the second indoor heat exchanger will rise, resulting in a reduction in the amount of fresh air dehumidified.

[0083] If φ n -φ s If the second preset humidity difference threshold is not met, it indicates that the dehumidification capacity is insufficient and the coil temperature of the second indoor heat exchanger is too high. Therefore, the opening of the second electronic expansion valve needs to be reduced by Δa. 24 .

[0084] When the opening of the second electronic expansion valve decreases, the coil temperature of the second indoor heat exchanger will drop, thereby increasing the dehumidification of the fresh air.

[0085] In steps S11 and S12, each time the opening of the second electronic expansion valve is adjusted, it is necessary to return to step S11 after an interval of Δt1 to re-determine T. P Within the specified range, the opening degree of the second electronic expansion valve does not need to be changed.

[0086] In the present application, the opening of the second electronic expansion valve is adjusted according to whether the temperature of the coil of the second indoor heat exchanger is between 0℃ and the dew point temperature T L of the return air, so that the temperature of the second indoor heat exchanger has dehumidification capacity without frosting; the opening of the second electronic expansion valve is further adjusted according to whether the relative humidity difference (φ n -φ s ) of the return air is in a preset return air relative humidity difference range, so that the dehumidification amount of the second indoor heat exchanger to the fresh air is moderate.

[0087] In the above dehumidification step, Δa 23 ≥Δa 24 , so that the temperature T P of the coil of the second indoor heat exchanger decreases to the dew point temperature T L of the return air at a faster speed, and the temperature T P of the coil of the second indoor heat exchanger decreases to the dew point temperature T L of the return air as soon as possible, so that the second indoor heat exchanger dehumidifies the fresh air as soon as possible, and the temperature of the second indoor heat exchanger decreases at a slower speed when the dehumidification amount of the second indoor heat exchanger is increased, so that the dehumidification amount is not excessively large due to excessive decrease of the temperature.

[0088] Δa 21 >Δa 22 , and Δa 21 >Δa 23 , so that the temperature T p of the coil of the second indoor heat exchanger increases above 0℃ at the fastest speed, and frosting of the second indoor heat exchanger is avoided as soon as possible.

[0089] When the second electronic expansion valve does not need to be changed in the dehumidification step, i.e., 0℃ < T P < T L , and the first preset humidity difference threshold is less than or equal to φ n -φ s is less than or equal to the second preset humidity difference threshold, the fine temperature adjustment step is entered.

[0090] In the fresh air micro-dehumidification mode, the fine temperature adjustment step includes: judging the interval of the difference between the return air temperature T n and the indoor target temperature T s ; if T n -T s is less than the first preset temperature difference threshold, the opening of the first electronic expansion valve is increased; if T n -T s is greater than the second preset temperature difference threshold, the opening of the first electronic expansion valve is decreased; and if the first preset temperature difference threshold is less than or equal to T n -T s is less than or equal to the second preset temperature difference threshold, the opening of the first electronic expansion valve is kept unchanged.

[0091] If T n -T s The first preset temperature difference threshold indicates that the supply air temperature and the return air temperature are too low, and the coil temperature of the first indoor heat exchanger is too low, so the opening of the first electronic expansion valve needs to be increased, and the opening increment is a preset value Δa 11 ;

[0092] Increasing the opening of the first electronic expansion valve can increase the temperature of the first indoor heat exchanger, thereby increasing the temperature of the fresh air.

[0093] If T n -T s The second preset temperature difference threshold indicates that the supply air temperature and the return air temperature are too high, and the coil temperature of the second indoor heat exchanger is too high, so the opening of the first electronic expansion valve needs to be reduced, and the opening decrement is a preset value Δa 12 ;

[0094] Reducing the opening of the first electronic expansion valve can reduce the temperature of the first indoor heat exchanger, thereby reducing the temperature of the fresh air.

[0095] If the first preset temperature difference threshold ≤ T n -T s ≤ the second preset temperature difference threshold, it indicates that the return air temperature and the user set temperature are basically the same, and the coil temperature of the first indoor heat exchanger is moderate, so the opening of the first electronic expansion valve does not need to be changed.

[0096] In the above T n -T s interval judgment, each time the opening of the first electronic expansion valve is adjusted, the interval T n -T s is re-judged after a interval Δt2 time, until the first preset temperature difference threshold ≤ T n -T s ≤ the second preset temperature difference threshold, and the opening of the first electronic expansion valve is unchanged.

[0097] In the embodiments of the present application, when the opening of the first electronic expansion valve is adjusted in the fine tuning temperature step, i.e. the first preset temperature difference threshold ≤ T n -T s ≤ the second preset temperature difference threshold, the next round of humidity control step is entered according to the obtained real-time sensor detection data. The control process is running all the time after starting the fresh air micro-cooling dehumidification mode until the user turns off the fresh air micro-cooling dehumidification mode.

[0098] In the present application, the opening of the first electronic expansion valve is controlled by judging whether the difference between the indoor return air temperature and the indoor target temperature is in the preset return air temperature difference interval, so that the temperature of the first indoor heat exchanger is maintained within a suitable temperature range, thereby achieving the user set temperature.

[0099] <Fresh air non-cooling dehumidification mode>

[0100] After starting the fresh air non-cooling dehumidification mode, the fresh air fan and the indoor fan operate according to the user-set wind speed. The outdoor fan operates at the second preset speed n2, the compressor operates at the second preset frequency f2, the first electronic expansion valve is fully open, and the initial opening degree of the second electronic expansion valve is a 22 .

[0101] The air conditioner receives the user-set indoor target humidity φ s .

[0102] The indoor return air temperature T n and the indoor relative humidity φ n are obtained by the return air temperature and humidity sensor; the outdoor environment temperature T w is obtained by the outdoor temperature sensor; and the coil temperature T p of the second indoor heat exchanger is obtained by the second coil temperature sensor.

[0103] In the fresh air non-cooling dehumidification mode, the opening degree of the second electronic expansion valve is adjusted according to the temperature T n and the humidity φ n of the indoor return air and the coil temperature T p of the second indoor heat exchanger, so as to adjust the refrigeration temperature of the second indoor heat exchanger, so that the fresh air is cooled and dehumidified when flowing through the second indoor heat exchanger; and the frequency of the compressor is adjusted according to the return air temperature T n and the outdoor environment temperature T w , so as to adjust the heating temperature of the first indoor heat exchanger, so that the cooled and dehumidified fresh air is warmed to the outdoor environment temperature when flowing through the first indoor heat exchanger.

[0104] Since the control method of the fresh air non-cooling dehumidification mode and the fresh air micro-cooling dehumidification mode only differs in the fine temperature adjustment step, only the fine temperature adjustment step is described in detail here, and the dehumidification step can refer to the content in the fresh air micro-cooling dehumidification mode.

[0105] The fine temperature adjustment step in the fresh air non-cooling dehumidification mode specifically includes: judging the interval of the difference between the indoor return air temperature T n and the outdoor environment temperature T w ; if T n -T w is less than a first preset temperature difference threshold, the frequency of the compressor is increased; if T n -T w is greater than a second preset temperature difference threshold, the frequency of the compressor is decreased; and if the first preset temperature difference threshold ≤ T n -T w ≤ the second preset temperature difference threshold, the frequency of the compressor is kept unchanged.

[0106] In this step, if T n -T w The first preset temperature difference threshold value indicates that the return air temperature is too low, and the first indoor heat exchanger coil temperature is too low, so the compressor frequency needs to be increased by Δf1. The increase in the compressor frequency can increase the temperature of the first indoor heat exchanger, thereby increasing the supply air temperature.

[0107] If T n -T w The second preset temperature difference threshold value indicates that the return air temperature is too high, and the first indoor heat exchanger coil temperature is too high, so the compressor frequency needs to be reduced by Δf2. The decrease in the compressor frequency can decrease the temperature of the first indoor heat exchanger, thereby decreasing the supply air temperature.

[0108] If the first preset temperature difference threshold value ≤ T n -T w The second preset temperature difference threshold value indicates that the return air temperature is too high, and the first indoor heat exchanger coil temperature is too high, so the compressor frequency needs to be reduced by Δf2. The decrease in the compressor frequency can decrease the temperature of the first indoor heat exchanger, thereby decreasing the supply air temperature.

[0109] In the above T n -T w interval determination, each time the compressor frequency is adjusted, the T n -T w interval is re-determined after an interval Δt2, until the first preset temperature difference threshold value ≤ T n -T w ≤ the second preset temperature difference threshold value, and the compressor frequency is unchanged.

[0110] In the embodiments of the present application, after the compressor frequency is adjusted in the fine temperature adjustment step, the next round of dehumidification step is entered according to the real-time detection data of the sensor. The control process is running all the time after the fresh air non-cooling dehumidification mode is started until the user turns off the fresh air non-cooling dehumidification mode.

[0111] In the present application, the compressor frequency is controlled by determining whether the temperature difference between the indoor return air temperature T n and the outdoor environment temperature T w is in the preset return air temperature difference interval, so that the first indoor heat exchanger coil temperature is maintained in an appropriate temperature range, the return air temperature is basically consistent with the outdoor air temperature, and the purpose of fresh air non-cooling dehumidification is achieved.

[0112] <New air micro-warming dehumidification mode>

[0113] After starting the fresh air slightly increased temperature dehumidification mode, the fresh air fan and the indoor fan operate according to the user set air speed. The outdoor fan operates at the third preset rotating speed n3, the compressor operates at the third preset frequency f3, the first electronic expansion valve is fully opened, and the initial opening degree of the second electronic expansion valve is a 23 .

[0114] The air conditioner receives the user set indoor target temperature T s and the indoor target humidity φ s .

[0115] The indoor return air temperature T n and the indoor relative humidity φ n are obtained by the return air temperature and humidity sensor; the second indoor heat exchanger coil temperature T p is obtained by the second coil temperature sensor.

[0116] In the fresh air slightly decreased temperature dehumidification mode, the second electronic expansion valve opening degree is adjusted according to the indoor return air temperature T n , the indoor return air humidity φ n and the second indoor heat exchanger coil temperature T p , to adjust the second indoor heat exchanger refrigeration temperature, so that the fresh air is dehumidified when flowing through the second indoor heat exchanger; the compressor frequency is adjusted according to the return air temperature T n and the indoor target temperature T s , to adjust the first indoor heat exchanger heating temperature, so that the dehumidified fresh air is increased to the target temperature when flowing through the first indoor heat exchanger.

[0117] Since the control method of the fresh air slightly increased temperature dehumidification mode and the fresh air slightly decreased temperature dehumidification mode only differs in the fine temperature adjustment step, only the fine temperature adjustment step is described in detail here, and the dehumidification step can refer to the content in the fresh air slightly decreased temperature dehumidification mode.

[0118] The fine temperature adjustment step in the fresh air slightly increased temperature dehumidification mode specifically includes: judging the interval of the difference between the indoor return air temperature T n and the indoor target temperature T s ; if T n -T s is less than a first preset temperature difference threshold, the compressor frequency is increased; if T n -T s is greater than a second preset temperature difference threshold, the compressor frequency is decreased; and if the first preset temperature difference threshold ≤ T n -T s ≤ the second preset temperature difference threshold, the compressor frequency remains unchanged.

[0119] In this step, T n -T sThe first preset temperature difference threshold indicates that the return air temperature is too low and the first indoor heat exchanger coil temperature is too low, so the compressor frequency needs to be increased by Δf1. The compressor frequency increase can increase the temperature of the first indoor heat exchanger, thereby increasing the supply air temperature.

[0120] If T n -T s is greater than the second preset temperature difference threshold, it indicates that the return air temperature is too high and the first indoor heat exchanger coil temperature is too high, so the compressor frequency needs to be reduced by Δf2. The compressor frequency reduction can reduce the temperature of the first indoor heat exchanger, thereby reducing the supply air temperature.

[0121] If the first preset temperature difference threshold is less than or equal to T n -T s is less than or equal to the second preset temperature difference threshold, it indicates that the return air temperature is basically the same as the user set temperature, and the first indoor heat exchanger coil temperature is moderate, so the compressor frequency does not need to be changed.

[0122] In the above T n -T s interval determination, each time the compressor frequency is adjusted, the T n -T s interval is re-determined after a time interval Δt2, until the first preset temperature difference threshold is less than or equal to T n -T s is less than or equal to the second preset temperature difference threshold, and the compressor frequency remains unchanged.

[0123] In the embodiments of the present application, after the compressor frequency is adjusted in the fine temperature adjustment step, the next round of dehumidification step is entered according to the real-time detection data of the sensor. The control process is running all the time after the fresh air micro-warming dehumidification mode is started until the user turns off the fresh air micro-warming dehumidification mode.

[0124] In the present application, the difference between the indoor return air temperature T n and the indoor target temperature T s is determined to control the compressor frequency, so that the first indoor heat exchanger coil temperature is maintained within an appropriate temperature range, the return air temperature is basically consistent with the user set temperature, and the purpose of fresh air micro-warming dehumidification is achieved.

[0125] In some embodiments of the present application, the relationship between the second preset frequency f2 of the compressor in the fresh air non-cooling dehumidification mode and the third preset frequency f3 of the compressor in the fresh air micro-warming dehumidification mode satisfies f2 < f3. Since the fresh air needs to be micro-warmed in the fresh air micro-warming dehumidification mode, the required condensing pressure is relatively large, and therefore f3 is set to be relatively large, so that in the fresh air micro-warming dehumidification mode, the temperature of the fresh air can meet the supply air demand as soon as possible, avoiding the problem that the frequency of the compressor needs to be adjusted multiple times to meet the condensing demand at the start when the frequency is low; f2 is set to be relatively small, so as to avoid waste of energy.

[0126] In some embodiments of the present application, the relationship between the initial opening a of the second electronic expansion valve in the fresh air micro-cooling dehumidification mode, the initial opening a of the second electronic expansion valve in the fresh air non-cooling dehumidification mode, and the initial opening a of the second electronic expansion valve in the fresh air micro-warming dehumidification mode satisfies: a 21 > a 22 > a 23 > a 21 > a 22 > a 23 Since the required condensing temperature gradually increases and the high-low pressure difference gradually increases from the fresh air micro-cooling dehumidification mode to the fresh air non-cooling dehumidification mode to the fresh air micro-warming dehumidification mode, the required opening of the second electronic expansion valve gradually decreases, and a 21 > a 22 > a 23 The relationship can reduce the adjustment frequency of the second electronic expansion valve in the dehumidification step, and the opening of the second electronic expansion valve can be quickly adjusted, thereby improving the working efficiency of the system.

[0127] In some embodiments of the present application, the relationship between the first preset rotating speed n1 of the outdoor fan in the fresh air micro-cooling dehumidification mode, the second preset rotating speed n2 of the outdoor fan in the fresh air non-cooling dehumidification mode, and the third preset rotating speed n3 of the outdoor fan in the fresh air micro-warming dehumidification mode satisfies: n1 > n2 > n3. Since the required outdoor unit heat exchange gradually decreases from the fresh air micro-cooling dehumidification mode to the fresh air non-cooling dehumidification mode to the fresh air micro-warming dehumidification mode, the rotating speed of the outdoor fan is set to be correspondingly reduced, thereby avoiding waste of energy.

[0128] The first concept of the present application is that the fresh air module can supply air to the indoor return air outlet, so that the fresh air can enter the heat exchange air duct of the air conditioner, and the first indoor heat exchanger and the second indoor heat exchanger are arranged, so that the fresh air can reach a suitable supply air temperature while being dehumidified.

[0129] The second concept of the present application is that the air conditioner can realize multiple dehumidification modes for fresh air, so as to meet different user requirements for comfort and improve the user experience.

[0130] The third concept of this application is to adjust the opening of the second electronic expansion valve based on whether the temperature of the second indoor heat exchanger coil is between 0℃ and the return air dew point temperature TL, so that the temperature of the second indoor heat exchanger is within the fresh air dehumidification temperature range and frost will not form; based on the return air relative humidity difference (φ) n -φ s Whether it is within the preset return air relative humidity difference range, the opening of the second electronic expansion valve can be further adjusted so that the temperature of the second indoor heat exchanger is appropriate for the dehumidification of the fresh air.

[0131] The fourth concept of this application is to control the opening of the first electronic expansion valve by judging whether the difference between the indoor return air temperature and the indoor target temperature is within the preset return air temperature difference range, so that the temperature of the first indoor heat exchanger can be maintained within a suitable temperature range, thereby achieving the user-set temperature and realizing the micro-cooling and dehumidification of fresh air.

[0132] The fifth concept of this application is to determine the indoor return air temperature T. n With outdoor ambient temperature T w The compressor frequency is controlled by whether the temperature difference is within the preset return air temperature difference range, so that the temperature of the first indoor heat exchanger coil is kept within a suitable temperature range, and the return air temperature is basically the same as the outdoor air temperature, thereby achieving the purpose of dehumidifying the fresh air without cooling it.

[0133] The sixth concept of this application is to determine the indoor return air temperature T. n With indoor target temperature T s The compressor frequency is controlled by whether the temperature difference is within the preset temperature difference range, so that the temperature of the first indoor heat exchanger coil is kept within a suitable temperature range, and the return air temperature is basically consistent with the user-set temperature, thereby achieving the purpose of slightly heating and dehumidifying the fresh air.

[0134] The seventh concept of this application is due to the setting of Δa 23 ≥Δa 24 The coil temperature T of the second indoor heat exchanger can be adjusted during the adjustment process. P Drop to return air dew point temperature T L The following speeds are faster, T p Descend to the return air dew point temperature T as quickly as possible. L The following allows the second indoor heat exchanger to dehumidify the fresh air as quickly as possible. When the second indoor heat exchanger increases its dehumidification capacity, the temperature drops slowly, which can prevent the temperature from dropping too much and causing the dehumidification capacity to become too large.

[0135] The eighth concept of this application, due to the setting of Δa 21 >Δa 22 , Δa 21 >Δa 23 The coil temperature T of the second indoor heat exchanger can be adjusted during the adjustment process.p The speed of rising to above 0℃ is the fastest, and the frosting of the second indoor heat exchanger can be avoided as soon as possible.

[0136] The ninth concept of the application is that, since f2

[0137] The tenth concept of the application is that, since a 21 > a 22 > a 23 The number of adjustments of the second electronic expansion valve in the dehumidification step can be reduced, and the opening of the second electronic expansion valve can be quickly adjusted, thereby improving the working efficiency of the system.

[0138] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the application, and not to limit them; although the application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacement for part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the application.

[0139] In order to facilitate explanation, the above description has been made in combination with specific embodiments. However, the above exemplary discussion is not intended to exhaust or limit the embodiments to the specific forms disclosed above. Various modifications and variations can be derived according to the above teachings. The selection and description of the above embodiments are to better explain the principles and practical applications, so that those skilled in the art can better use the embodiments and various different modified embodiments suitable for specific use considerations.

Claims

1. A control method of an air conditioner, wherein the air conditioner comprises: a refrigerant circuit in which a compressor, an outdoor heat exchanger, a first electronic expansion valve, a first indoor heat exchanger, a second electronic expansion valve and a second indoor heat exchanger are connected in series; and a fresh air module, a fresh air outlet of the fresh air module being connected to an indoor return air inlet of the air conditioner, so that fresh air introduced by the fresh air module flows to the indoor return air inlet; the air conditioner is configured to cause the fresh air to flow through the second indoor heat exchanger and then the first indoor heat exchanger when the air conditioner is running; and the control method of the air conditioner comprises: a dehumidification step of controlling an opening degree of the second electronic expansion valve to adjust a refrigeration temperature of the second indoor heat exchanger, so that the fresh air is dehumidified when flowing through the second indoor heat exchanger; and a fine temperature adjustment step of controlling an opening degree of the first electronic expansion valve or a frequency of the compressor to adjust a heating temperature of the first indoor heat exchanger, so that the dehumidified fresh air is heated when flowing through the first indoor heat exchanger, according to a difference between an indoor return air temperature and an indoor target temperature or according to a difference between the indoor return air temperature and an outdoor environment temperature; wherein the dehumidification step comprises: controlling the opening degree of the first electronic expansion valve to increase when the difference between the indoor return air temperature and the indoor target temperature is less than a lower limit value of a preset temperature difference interval, and controlling the opening degree of the first electronic expansion valve to decrease when the difference between the indoor return air temperature and the indoor target temperature is greater than an upper limit value of the preset temperature difference interval; the air conditioner is configured to run at least one of a fresh air micro-cooling dehumidification mode, a fresh air non-cooling dehumidification mode and a fresh air micro-heating dehumidification mode; in the fresh air micro-cooling dehumidification mode, the fine temperature adjustment step comprises: increasing the opening degree of the first electronic expansion valve when the difference between the indoor return air temperature and the indoor target temperature is less than the lower limit value of the preset temperature difference interval, and decreasing the opening degree of the first electronic expansion valve when the difference between the indoor return air temperature and the indoor target temperature is greater than the upper limit value of the preset temperature difference interval; in the fresh air non-cooling dehumidification mode, the first electronic expansion valve is fully opened after the fresh air non-cooling dehumidification mode is started, and the fine temperature adjustment step of the fresh air non-cooling dehumidification mode comprises: increasing the frequency of the compressor when the difference between the indoor return air temperature and the outdoor environment temperature is less than the lower limit value of the preset temperature difference interval, and decreasing the frequency of the compressor when the difference between the indoor return air temperature and the outdoor environment temperature is greater than the upper limit value of the preset temperature difference interval; in the fresh air micro-heating dehumidification mode, the first electronic expansion valve is fully opened after the fresh air micro-heating dehumidification mode is started, and the fine temperature adjustment step of the fresh air micro-heating dehumidification mode comprises: increasing the frequency of the compressor when the difference between the indoor return air temperature and the indoor target temperature is less than the lower limit value of the preset temperature difference interval, and decreasing the frequency of the compressor when the difference between the indoor return air temperature and the indoor target temperature is greater than the upper limit value of the preset temperature difference interval. 3.The control method of the air conditioner according to claim 1, wherein the compressor is controlled to run at a second preset frequency f2 when the fresh air non-cooling dehumidification mode is entered; and the compressor is controlled to run at a third preset frequency f3 higher than f2 when the fresh air micro-heating dehumidification mode is entered. 4.The control method of the air conditioner according to claim 1, wherein an outdoor fan is controlled to run at a first preset rotating speed n1 when the fresh air micro-cooling dehumidification mode is entered; the outdoor fan is controlled to run at a second preset rotating speed n2 lower than n1 when the fresh air non-cooling dehumidification mode is entered; and the outdoor fan is controlled to run at a third preset rotating speed n3 lower than n2 when the fresh air micro-heating dehumidification mode is entered. 6.The control method of the air conditioner according to claim 1, wherein ​ ​ ​ S11, based on the indoor return air temperature T n and the indoor return air relative humidity Φ n The return air dew point temperature T L is calculated determining whether the temperature T of the coil of the second indoor heat exchanger is in a predetermined range P If T P ≤ 0°C, the opening degree of the second electronic expansion valve is increased; if T P ≥ T L , the opening degree of the second electronic expansion valve is decreased; if 0°C < T P < T L , the process proceeds to S12; S12, judging relative humidity Φ of indoor return air n and target relative humidity Φ s belongs to interval: if Φ n -Φ s < first preset humidity difference threshold, then increasing the opening of the second electronic expansion valve; if Φ n -Φ s > second preset humidity difference threshold, then reducing the opening of the second electronic expansion valve; if first preset humidity difference threshold ≤ Φ n -Φ s ≤ second preset humidity difference threshold, then keeping the opening of the second electronic expansion valve unchanged; ​ ​ ​ ​ 2. The control method of the air conditioner according to claim 1, characterized by, When entering the fresh air micro-cooling dehumidification mode, the second electronic expansion valve is opened at an initial opening degree a 21 On; When entering the fresh air non-cooling dehumidification mode, the second electronic expansion valve is opened at an initial opening degree a 21 lower than a 22 . Upon entering the fresh air micro-warming dehumidification mode, the second electronic expansion valve is opened at an initial opening degree a 22 lower than a 23 . ​ ​ ​ ​ ​ ​ ​ 5. The control method of the air conditioner according to claim 1, wherein In the dehumidification step, when 0℃ < T P <T L and the first preset humidity difference threshold value ≤ Φ n -Φ s ≤ the second preset humidity difference threshold value, the fine temperature adjustment step is entered. ​ In S11, the opening degree of the second electronic expansion valve is re-judged once every first preset time At1 after each change P of the belonging interval; In S12, the opening degree of the second electronic expansion valve is returned to S11 to rejudge T after each change for a first preset time interval At1 P to which the temperature T belongs.

7. The control method of an air conditioner according to claim 1, wherein In S11, the opening degree increment of the second electronic expansion valve is a first preset opening degree increment Δa 21 , the opening degree decrement of the second electronic expansion valve is a first preset opening degree decrement Δa 21 that is smaller than the first preset opening degree increment Δa 23 . In S12, the opening degree increment of the second electronic expansion valve is smaller than the first preset opening degree increment Da 21 the second preset opening degree increment Da 22 .

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