A multi-contact system and a control method of an electronic expansion valve for heating

Abstract

The application discloses a multi-connected system and a control method of an electronic injection enthalpy expansion valve during heating of the multi-connected system. The multi-connected system is started and enters a soft start stage. In the soft start stage, the electronic injection enthalpy expansion valve is closed, and after the multi-connected system runs for a time length A, the multi-connected system enters a normal control stage. In the normal control stage, when the frequency of the compressor reaches B, the multi-connected system determines whether the electronic injection enthalpy expansion valve is opened according to the ambient temperature and the indoor unit load rate, and the initial opening degree of the electronic injection enthalpy expansion valve after being opened. If the electronic injection enthalpy expansion valve is opened and maintained for a time length C, the multi-connected system determines a target high-pressure saturated temperature according to the current ambient temperature, and then adjusts the opening degree of the electronic injection enthalpy expansion valve according to the difference between the target high-pressure saturated temperature and the actual high-pressure saturated temperature. In this way, the electronic injection enthalpy expansion valve can be adjusted from multiple aspects, the state of the multi-connected system is detected in real time during the opening of the electronic injection enthalpy expansion valve, and the customer comfort and the system reliability are improved.

Description

Technical Field

[0001] This invention relates to the field of heat pump air conditioning, and more particularly to a multi-split system and a control method for the electronic expansion valve of the injection enthalpy during heating. Background Technology

[0002] In the air conditioning market, air conditioners are categorized into low-temperature models and normal-temperature models based on the user's environment. As is well known, refrigerant-based air conditioning systems exchange heat through the temperature difference between the refrigerant and the air. This means that when the temperature difference is small, the air conditioner's heat exchange capacity decreases significantly. In winter, temperatures in northern regions often drop below -15°C or even -20°C. At these temperatures, the refrigerant temperature is also very low, absorbing less heat from the outer circulation loop, resulting in a lower overall heating performance compared to when operating at slightly higher ambient temperatures. To address this issue, many manufacturers have begun developing enthalpy injection systems.

[0003] One type of enthalpy injection system (flash evaporation) builds upon the existing single-stage throttling process by adding refrigerant via the flash tank's nozzle after the throttling phase. This allows medium-pressure refrigerant to be directly supplied to the compressor, improving heating efficiency. Furthermore, the refrigerant supplied to the compressor also lowers the system's exhaust temperature, enhancing overall system reliability. Many manufacturers use solenoid valves or electronic expansion valves to control the enthalpy injection flow rate; however, considering the wider opening range of expansion valves, many manufacturers opt for electronic expansion valves.

[0004] However, because the manufacturer of this control part does not control the opening of the electronic expansion valve of the injection enthalpy in a very reasonable way, it will lead to: the expansion valve opening too large, the compressor returning liquid, the system reliability decreasing, and the compressor's service life being affected. Summary of the Invention

[0005] In order to solve the problems in the prior art, the purpose of this invention is to provide a multi-split system and a control method for the electronic expansion valve of the injection enthalpy during heating. This method can increase the system pressure to increase the heating capacity of the multi-split system, and can also avoid the risk of liquid backflow, thereby improving the user experience, the overall operational reliability of the machine, and extending the service life of the system.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: a control method for an electronic expansion valve for enthalpy injection during heating in a multi-split system, wherein an electronic expansion valve for enthalpy injection is installed at the enthalpy injection port of the compressor in the multi-split system; the multi-split system starts heating and enters a soft start phase; during the soft start phase, the electronic expansion valve for enthalpy injection is closed, and after the multi-split system has been running for a duration of A, it enters a normal control phase;

[0007] During the normal control phase, when the compressor frequency reaches B, the multi-split system determines whether the electronic expansion valve for enthalpy injection should be opened based on the ambient temperature and the indoor unit load rate, as well as the initial opening degree of the electronic expansion valve after opening. If the electronic expansion valve for enthalpy injection is opened and maintained for a duration of C, the multi-split system determines the target high-pressure saturation temperature based on the current ambient temperature, and then adjusts the opening degree of the electronic expansion valve based on the difference between the target high-pressure saturation temperature and the actual high-pressure saturation temperature.

[0008] As a preferred option, during the typical control phase, the lower the ambient temperature, the lower the requirement for the indoor unit load rate when opening the electronic expansion valve, but the larger the initial opening degree of the electronic expansion valve.

[0009] Preferably, during the normal control phase, the electronic expansion valve for enthalpy injection is closed when the ambient temperature is >19°C.

[0010] Preferably, the lower the ambient temperature, the higher the target saturation temperature.

[0011] As a preferred option, during the control phase, if the actual high-pressure saturation temperature is lower than the target saturation temperature, the opening of the electronic expansion valve is periodically increased; the lower the ambient temperature, the greater the opening of the electronic expansion valve needs to be adjusted each time.

[0012] Preferably, during the control phase, when the actual high-pressure saturation temperature is higher than the target saturation temperature, the opening of the enthalpy-injected electronic expansion valve is periodically reduced; the lower the ambient temperature, the smaller the opening of the enthalpy-injected electronic expansion valve needs to be adjusted each time.

[0013] Preferably, during the control phase, if the actual high-pressure saturation temperature reaches the target saturation temperature and remains there for a duration of D, the opening of the enthalpy electronic expansion valve will no longer change.

[0014] As a preferred embodiment, in the multi-split system, a second gas separator is provided between the electronic expansion valve and the enthalpy injection port of the compressor, and a ball valve is installed at the inlet of the second gas separator. The multi-split system monitors the return gas superheat in real time. After the actual return gas superheat is lower than E and remains below F for a duration of F, the multi-split system enters the priority control stage. In the priority control stage, the electronic expansion valve immediately closes to step G, and the ball valve on the second gas separator immediately opens until the multi-split system re-enters the normal control stage or shuts down.

[0015] Preferably, during the priority control phase, if the real-time return gas superheat is greater than H and lasts for a duration of I, the ball valve closes and the multi-split system re-enters the normal control phase; during the priority control phase, if the real-time return gas superheat is lower than the corresponding target return gas superheat fault value and lasts for 30 seconds, the multi-split system is determined to be faulty, the multi-split system is shut down, and a fault message indicating low return gas superheat is displayed.

[0016] A multi-split air conditioning system that applies the control method of the electronic expansion valve for enthalpy injection during heating in a multi-split system as described above.

[0017] The beneficial effects of the technical solution of this invention are as follows: By limiting the conditions (ambient temperature, load rate, frequency) for opening the electronic expansion valve of the multi-split air conditioning system during heating, the impact of low ambient temperature conditions on the heating effect of the multi-split air conditioning system can be accurately judged; and after the electronic expansion valve of ... Attached Figure Description

[0018] Figure 1 This is a schematic diagram of a multi-split air conditioning system.

[0019] Reference numerals: 1. Compressor; 2. Exhaust temperature sensor; 3. Oil separator; 4. Four-way valve; 5. Second gas separator; 6. Ball valve; 7. Gas pipe; 8. Gas pipe shut-off valve; 9. First gas separator; 10. Injection enthalpy solenoid valve; 11. Flash evaporator; 12. Liquid pipe shut-off valve; 13. Liquid pipe; 14. Indoor unit electronic expansion valve; 15. Liquid pipe temperature sensor; 16. Indoor unit; 17. Gas pipe temperature sensor; 18. Outdoor unit; 19. Ambient temperature sensor; 20. Outdoor unit electronic expansion valve; 21. High pressure sensor; 22. Low pressure sensor; 23. Return gas temperature sensor. Detailed Implementation

[0020] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0021] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "clockwise," and "counterclockwise," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0022] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "a plurality of" means two or more, unless explicitly defined otherwise.

[0023] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0024] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature. Example

[0025] like Figure 1 The multi-split air conditioning system shown includes a compressor 1, an oil separator 3, a four-way valve 4, a second air separator 5, a flash evaporator 11, an outdoor unit 18, a first air separator 9, and multiple indoor units 16.

[0026] Multiple indoor units 16 are connected in parallel. One port of indoor unit 16 is connected to gas pipe 7, and the other port of indoor unit 16 is connected to liquid pipe 13. An indoor unit electronic expansion valve 14 is installed at the connection between any indoor unit 16 and liquid pipe 13. The outlet of compressor 1 is connected to one port of four-way valve 4 through oil separator 3. The inlet of compressor 1 is connected to the other port of four-way valve through first gas separator 9. The other port of four-way valve 4 is connected to gas pipe 7. The other port of four-way valve 4 is connected to outdoor unit 18. Outdoor unit 18 is connected to flash evaporator 11. Flash evaporator 11 is connected to the enthalpy injection port of compressor 1 through injection enthalpy solenoid valve 10. Flash evaporator 11 is connected to liquid pipe 13. A second gas separator 5 is installed on the pipeline between injection enthalpy electronic expansion valve 10 and compressor 1. A ball valve 6 is installed at the inlet of second gas separator 5.

[0027] A gas pipe temperature sensor 17 for monitoring gas pipe temperature Teoa is installed at the connection between indoor unit 16 and gas pipe 7. A liquid pipe temperature sensor 15 for monitoring liquid pipe temperature Teia is installed between indoor unit 16 and indoor unit electronic expansion valve 14. A middle temperature sensor for monitoring the middle temperature Tzba of indoor unit 16 is installed on indoor unit 16. An ambient temperature sensor 19 for detecting ambient temperature Tao is installed on outdoor unit 18. An exhaust temperature sensor 2 for monitoring exhaust temperature Tda is installed at the outlet of compressor 1. A low-pressure sensor 22 for monitoring low-pressure saturation temperature PS-t is installed on the pipeline between the first gas separator and the four-way valve. A return gas temperature sensor 23 for monitoring return gas temperature ts is installed on the pipeline between the first gas separator 9 and the four-way valve. A high-pressure sensor 21 for monitoring high-pressure saturation temperature Pd-t is installed on the pipeline between the oil separator and the four-way valve.

[0028] In this embodiment, an air pipe shut-off valve 8 is installed on the air pipe 7, a second air distributor 5 is located between the four-way valve 4 and the air pipe shut-off valve 8, and a filter is installed between the second air distributor 5 and the air pipe shut-off valve 8; a liquid pipe shut-off valve 12 is installed on the liquid pipe 13, and a filter is installed between the liquid pipe shut-off valve 12 and the flash evaporator 11; a filter is installed between the flash evaporator 11 and the enthalpy solenoid valve 10; an outdoor unit electronic expansion valve 20 is installed between the flash evaporator 11 and the outdoor unit 18, and a filter is installed between the outdoor unit electronic expansion valve 20 and the outdoor unit 18. Example

[0029] A control method for the electronic expansion valve of the injection enthalpy during heating in a multi-split system, which can be used to control a multi-split system as described in Example 1;

[0030] The specific control methods include: the multi-split system starts heating and enters the soft start phase; during the soft start phase, the electronic expansion valve for enthalpy injection is closed, and after the multi-split system has been running for a duration of A, it enters the normal control phase; where A is 3 minutes.

[0031] During the typical control phase, once the compressor frequency reaches point B, the multi-split system determines whether the electronic expansion valve (IEV) should open, and its initial opening degree, based on the ambient temperature and indoor unit load rate. If the IEV is open and maintained for duration C, the multi-split system determines the target high-pressure saturation temperature based on the current ambient temperature, and then adjusts the opening degree of the IEV based on the difference between the target and actual high-pressure saturation temperatures. Here, B is 65 Hz, and C is 1 minute 30 seconds.

[0032] This configuration, by limiting the conditions (ambient temperature, load rate, frequency) under which the multi-split system opens the electronic expansion valve during heating, allows for an accurate assessment of the impact of low ambient temperature conditions on the heating performance of the multi-split system. Furthermore, the opening degree of the electronic expansion valve changes accordingly when the high pressure of the multi-split system changes after it opens. Additionally, the electronic expansion valve is controlled when there is a risk of liquid return. These control methods adjust the electronic expansion valve from multiple aspects, monitoring the status of the multi-split system in real time during enthalpy injection. When an anomaly occurs in the multi-split system, timely action is taken to maintain system reliability, thereby extending the unit's service life, reducing maintenance risks, and ultimately ensuring that this control method, when applied to multi-split systems, improves customer comfort and system reliability.

[0033] In this embodiment, as shown in Table 1, during the normal control phase, the lower the ambient temperature, the lower the requirement for the indoor unit load rate when the electronic expansion valve is opened, but the larger the initial opening of the electronic expansion valve is. With this setting, the multi-split system has a lot of load. When the load rate is not very high, the heat of the multi-split system will not be easily dissipated, and the heating effect of the multi-split system will be guaranteed. Therefore, when the load rate is not high, it is not necessary to open the electronic expansion valve to increase the high pressure. Specifically, as shown in Table 1, when the ambient temperature is greater than 15℃, the electronic expansion valve of the enthalpy injection system opens when the indoor unit compliance rate of the multi-split system is greater than 70%, and the opening degree of the electronic expansion valve of the enthalpy injection system is 40 steps; when the ambient temperature is between 7℃ and 15℃, the electronic expansion valve of the enthalpy injection system opens when the indoor unit compliance rate of the multi-split system is greater than 55%, and the opening degree of the electronic expansion valve of the enthalpy injection system is 60 steps; when the ambient temperature is less than 7℃, the electronic expansion valve of the enthalpy injection system opens when the indoor unit compliance rate of the multi-split system is greater than 40%, and the opening degree of the electronic expansion valve of the enthalpy injection system is 80 steps.

[0034] Ambient temperature Indoor unit load rate Initial opening of the electronic expansion valve for enthalpy injection Ambient temperature ≥15℃ ≥70％ 40 7℃ < T environment < 15℃ ≥55％ 60 Temperature ≤ 7℃ ≥40％ 80

[0035] Table 1. Opening conditions and initial opening degree of the electronic expansion valve for enthalpy injection

[0036] It is worth noting that during the normal control phase, when the ambient temperature is >19℃, it can be determined that the ambient temperature is relatively high and the pressure of the multi-split system is very high, which basically meets the heating effect. Therefore, it is no longer necessary to increase the high pressure through enthalpy injection, and the enthalpy injection electronic expansion valve will not open.

[0037] In this embodiment, the indoor unit load rate = number of horsepower of indoor unit in operation / number of horsepower of outdoor unit * 100%.

[0038] In this embodiment, as shown in Table 2, the lower the ambient temperature, the higher the target saturation temperature.

[0039] outer ambient temperature Target high pressure saturation temperature Ambient temperature ≥15℃ 49 7℃ < T environment < 15℃ 50 Temperature ≤ 7℃ 51

[0040] Table 2. Target Saturation Temperature Determination Table

[0041] In this embodiment, as shown in Table 3, during the normal control phase, if the actual high-pressure saturation temperature is lower than the target saturation temperature, the opening of the electronic expansion valve is periodically increased; wherein, the lower the ambient temperature, the greater the opening of the electronic expansion valve needs to be adjusted each time.

[0042] During the normal control phase, when the actual high-pressure saturation temperature is higher than the target saturation temperature, the opening of the enthalpy-injected electronic expansion valve is periodically reduced; the lower the ambient temperature, the smaller the opening of the enthalpy-injected electronic expansion valve needs to be adjusted each time.

[0043] During the normal control phase, if the actual high-pressure saturation temperature reaches the target saturation temperature and remains there for a duration of D, the opening of the electronic expansion valve for enthalpy injection will not change; where D is 2 minutes. With this setting, the ambient temperature affects the adjustment of the electronic expansion valve for enthalpy injection in real time. When the ambient temperature is high, the high-pressure of the multi-split system will also be higher, resulting in better heating performance. Although the high pressure may not reach the target, a large opening is not required at this point. Conversely, if the high-pressure is higher than the target high pressure, the enthalpy injection flow rate needs to be quickly reduced to ensure the stability of the multi-split system.

[0044] outer ambient temperature Step control below the target high-pressure saturation temperature Step control above the target high pressure saturation temperature Ambient temperature ≥15℃ 4 steps per second Turn off 8 steps per second 7℃ < T environment < 15℃ Open 6 steps per second Reduce speed by 6 steps per second Temperature ≤ 7℃ 8 steps per second Reduce speed by 4 steps per second

[0045] Table 3. Control Logic Table of Electronic Expansion Valve during Normal Control Phase

[0046] In this embodiment, the multi-split system monitors the return gas superheat in real time. If the actual return gas superheat is lower than E and remains below F for a duration of F, it is determined that there is a risk of liquid return to the system. The valve needs to be closed slightly to reduce the refrigerant flow into the compressor, prioritizing preventing liquid return to the compressor. Then, the multi-split system enters a priority control phase. During the priority control phase, the injection enthalpy electronic expansion valve immediately closes to step G, and the ball valve on the second gas separator immediately opens until the multi-split system re-enters the normal control phase or shuts down. Here, E is 2°C, F is 1 min, and G is 30; where return gas superheat = return gas temperature ts - low-pressure saturation temperature PS - t.

[0047] In a further preferred embodiment, during the priority control phase, if the actual return gas superheat is greater than H and lasts for a duration of I, the ball valve closes, and the multi-split system re-enters the normal control phase; where H > G, H is 3°C, and I is 2 min.

[0048] Further preferably, during the priority control phase, if the actual return gas superheat is lower than the corresponding target return gas superheat fault value and this condition persists for 30 seconds, the multi-split system is deemed to be faulty, the multi-split system is shut down, and a low return gas superheat fault is indicated. The lower the ambient temperature, the lower the target return gas superheat fault value.

[0049] Taking a multi-split outdoor unit paired with three indoor units, with all three indoor units operating at 100% load (outside ambient temperature of 7°C):

[0050] The multi-split air conditioning system enters the soft-start control phase, with the enthalpy injection electronic expansion valve opening to 0 for 3 minutes. After this period, the system transitions to normal control, at which point the compressor frequency is 70Hz. According to Table 1, the enthalpy injection electronic expansion valve meets the opening conditions and opens to step 80, lasting 1 minute and 30 seconds. The detected high-pressure saturation temperature is then 50°C. According to Table 2, the target high-pressure saturation temperature at an ambient temperature of 7°C is 51°C. Table 3 indicates the enthalpy injection electronic expansion valve will open 8 steps per second. The following scenarios may occur: Scenario 1: After 5 seconds, the enthalpy injection electronic expansion valve opens to step 120, at which point the high-pressure saturation temperature is exactly 51°C, and this has lasted for 2 minutes and 10 seconds. In this case, the expansion valve maintains its current step count and does not change further. Scenario 2: When the enthalpy-injected electronic expansion valve opens to step 480, the high-pressure saturation temperature is exactly 50.8℃, and the enthalpy-injected electronic expansion valve will not continue to open further. In case three, after 5 seconds, when the number of steps of the enthalpy-injected electronic expansion valve reaches 120, the high-pressure saturation temperature is exactly 51℃, and the return gas superheat is 1.9℃, which lasts for 1 minute. In this case, the enthalpy-injected electronic expansion valve will not be controlled according to Table 3, and will enter the priority control stage. At this time, the ball valve opens, and the valve step of the enthalpy-injected expansion valve is reduced to 30 steps. After running for 5 minutes, the return gas superheat is 3.5℃, which lasts for another 2 minutes. At this time, the ball valve closes, and the enthalpy-injected electronic expansion valve continues to be controlled according to Table 3. In case four, when the return gas superheat is -0.4℃, which lasts for 35 seconds, the multi-split system will directly shut down for protection, and at the same time report a fault of low return gas superheat.

[0051] In the description of this specification, references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0052] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention without departing from the principles and spirit of the present invention.

Claims

1. A control method for an electronic expansion valve for enthalpy injection during heating in a multi-split system, characterized in that: In a multi-split air conditioning system, an electronic expansion valve for enthalpy injection is installed at the compressor's enthalpy injection port; The multi-split system starts heating and enters the soft start phase; during the soft start phase, the electronic expansion valve of the injection enthalpy is closed, and after the multi-split system has been running for a period of time A, it enters the normal control phase; During the normal control phase, when the compressor frequency reaches B, the multi-split system determines whether the electronic expansion valve for injection enthalpy is open and the initial opening degree of the electronic expansion valve for injection enthalpy is determined based on the ambient temperature and the indoor unit load rate. If the electronic expansion valve for enthalpy injection is opened and maintained for duration C, the multi-split system determines the target high-pressure saturation temperature based on the current ambient temperature, and then adjusts the opening degree of the electronic expansion valve for enthalpy injection based on the difference between the target high-pressure saturation temperature and the actual high-pressure saturation temperature. In a multi-split air conditioning system, a second gas separator is provided between the electronic expansion valve for enthalpy injection and the enthalpy injection port of the compressor, and a ball valve is installed at the inlet of the second gas separator. The multi-split system monitors the return gas superheat in real time. If the actual return gas superheat is lower than E and continues for a duration of F, the multi-split system enters the priority control phase. During the priority control phase, the injection enthalpy electronic expansion valve immediately closes to step G, and the ball valve on the second gas separator immediately opens until the multi-split system re-enters the normal control phase or shuts down. During the priority control phase, if the real-time return gas superheat is greater than H and continues for a duration of I, the ball valve closes, and the multi-split system re-enters the normal control phase. During the priority control phase, if the real-time return gas superheat is lower than the corresponding target return gas superheat fault value and continues for 30 seconds, the multi-split system is determined to be faulty, the multi-split system is shut down, and a fault message indicating low return gas superheat is displayed.

2. The control method for the electronic expansion valve of injection enthalpy during heating in a multi-unit system according to claim 1, characterized in that: During the typical control phase, the lower the ambient temperature, the lower the requirement for the indoor unit load rate when opening the electronic expansion valve, but the larger the initial opening degree of the electronic expansion valve.

3. The control method for the electronic expansion valve of the injection enthalpy during heating in a multi-unit system according to claim 1, characterized in that: During normal control, the electronic expansion valve for enthalpy injection is closed when the ambient temperature is >19℃.

4. The control method for the electronic expansion valve of the injection enthalpy during heating in a multi-unit system according to claim 1, characterized in that: The lower the ambient temperature, the higher the target saturation temperature.

5. The control method for the electronic expansion valve of injection enthalpy during heating in a multi-unit system according to claim 1, characterized in that: During the normal control phase, if the actual high-pressure saturation temperature is lower than the target saturation temperature, the opening of the electronic expansion valve is periodically increased; the lower the ambient temperature, the greater the opening of the electronic expansion valve needs to be adjusted each time.

6. The control method for the electronic expansion valve of injection enthalpy during heating in a multi-unit system according to claim 1, characterized in that: During the normal control phase, when the actual high-pressure saturation temperature is higher than the target saturation temperature, the opening of the enthalpy-injected electronic expansion valve is periodically reduced; the lower the ambient temperature, the smaller the opening of the enthalpy-injected electronic expansion valve needs to be adjusted each time.

7. The control method for the electronic expansion valve of injection enthalpy during heating in a multi-unit system according to claim 1, characterized in that: During the normal control phase, if the actual high-pressure saturation temperature reaches the target saturation temperature and remains there for a duration of D, the opening of the enthalpy electronic expansion valve will no longer change.

8. A multi-split air conditioning system that applies the control method of the electronic expansion valve for injecting enthalpy during heating as described in any one of claims 1-7.

Images