Multi-split air conditioning system

Abstract

The invention discloses a multi-split air conditioning system which comprises an outdoor unit, an air conditioning unit and a control unit. The indoor units are connected to the outdoor units through refrigerant piping and are provided with indoor throttling elements in a matched mode; a control device for controlling the outdoor unit and the plurality of indoor units; in the heating process, the control device receives a shutdown or shutdown instruction, evacuation operation is executed, and refrigerants on the indoor unit side move towards the outdoor unit side; the control unit is configured to execute the following control so that the pressure of the air suction side and the pressure of the exhaust side of the compressor can reach a balanced state: when evacuation operation is executed, the indoor throttling element is controlled to be in a valve opening state, and the outdoor throttling element is controlled to be in a set opening degree; and after the evacuation operation is finished, the indoor throttling element is kept in a valve opening state, the outdoor throttling element is kept in a set opening degree, and then the outdoor throttling element is controlled to work in a valve closing state. The multi-split air conditioning system is ensured to stably operate in the shutdown or shutdown process, and noise is remarkably restrained.

Description

Multi-split air conditioning system Technical Field

[0001] This invention relates to the field of refrigeration equipment technology, and more particularly to a multi-split air conditioning system. Background Technology

[0002] When a multi-split air conditioning system starts up, a large pressure difference between the intake and exhaust sides can lead to start-up failure, affecting the normal operation of the system and reducing its reliability. In multi-split air conditioning systems, when the compressor's starting pressure difference exceeds a certain range, the compressor's starting torque becomes less than the sum of the starting pressure difference torque and the frictional resistance torque, resulting in a stall phenomenon. This leads to abnormally high starting current and power. In this situation, on the one hand, the motor coils will overheat, affecting the insulation performance of the compressor's enameled wires and potentially burning out the coils; on the other hand, excessive power and current increase the load on the power supply and wiring, which, if exceeded, can also lead to accidents.

[0003] To address the aforementioned issues, existing technology incorporates a pressure balancing device between the intake and exhaust pipes of a multi-split air conditioning system. This pressure balancing device is a bypass branch consisting of a capillary tube, a solenoid valve, and a filter. Upon receiving a shutdown or stop signal, the solenoid valve on the bypass branch opens, ensuring rapid pressure balancing of the high and low pressures in the multi-split air conditioning system after the compressor stops operating.

[0004] However, when equalizing pressure through a bypass branch, the refrigerant flow noise suddenly becomes sharp, resulting in a poor user experience and even complaints.

[0005] The information disclosed in this background section is only intended to enhance the understanding of the background technology of this application, and therefore may include prior art that is not known to those skilled in the art. Summary of the Invention

[0006] To address the issue that the refrigerant flow noise suddenly becomes sharp when equalizing pressure through a bypass branch, resulting in a poor user experience and even complaints, this application designs and provides a multi-split air conditioning system.

[0007] To achieve the above-mentioned objectives, the present invention employs the following technical solution:

[0008] In some embodiments of this application, a multi-split air conditioning system is provided, including: an outdoor unit, in which a compressor and an outdoor throttling element are disposed; multiple indoor units connected to the outdoor unit via refrigerant piping, each indoor unit being equipped with an indoor throttling element; a control device for controlling the outdoor unit and the multiple indoor units; during heating, the control device receives a shutdown command or a stop command and performs a vacuum operation, causing the refrigerant on the indoor unit side to move to the outdoor unit side; the control device is further configured to perform the following control to achieve a balanced state between the suction and discharge pressures of the compressor: during the vacuum operation, the indoor throttling element is controlled to be in an open valve state, and the outdoor throttling element is controlled to be in a set opening degree; after the vacuum operation is completed, the indoor throttling element is kept in an open valve state, the outdoor throttling element is kept in a set opening degree, and then the outdoor throttling element is controlled to operate in a closed valve state.

[0009] The above technical solution has the following advantages or beneficial effects: In the multi-split air conditioning system provided in this application, after receiving a shutdown command or stop command, the control device performs vacuum operation. During and after vacuum operation, the indoor throttling element is kept in the open valve state, and the outdoor throttling element is kept at the set opening degree. This can effectively balance the pressure on the compressor suction side and discharge side, avoid sudden changes in refrigerant flow, reduce pressure fluctuations, and the stable refrigerant flow and pressure balance can reduce the vibration and noise sources of the refrigerant system, ensure the smooth operation of the multi-split air conditioning system during shutdown or stop, significantly suppress noise, and improve overall performance and user experience.

[0010] In one or more embodiments of this application, the control device is configured to set an opening degree according to the number of indoor units in the working state; the set opening degree corresponds to the number of indoor units in the working state, and the more indoor units in the working state, the larger the set opening degree.

[0011] The above technical solution has the following advantages or beneficial effects: by configuring the opening degree according to the number of indoor units in operation, the refrigerant shock borne by the indoor units can be assessed based on the distributed pressure difference, reducing refrigerant shock and flow noise under different operating conditions, thereby significantly improving the stability of the system and the user experience.

[0012] In one or more embodiments of this application, the control device is configured to: acquire the number of indoor units in operation; compare the number of indoor units in operation with a set number; when the number of indoor units in operation is higher than the set number, set a larger first set opening degree based on the number of indoor units in operation; control the outdoor throttling element to first operate at the first set opening degree and then operate in a closed valve state; when the number of indoor units in operation is not higher than the set number, set a smaller second set opening degree based on the number of indoor units in operation; control the outdoor throttling element to first operate at the second set opening degree and then operate in a closed valve state.

[0013] The above technical solution has the following advantages or beneficial effects: by comparing the number of indoor units in working condition with the set number, it can automatically select and generate the corresponding set opening degree, ensuring smooth refrigerant flow and improving the stability and user experience of the multi-split air conditioning system.

[0014] In one or more embodiments of this application, during heating, the control device receives a shutdown command and performs a vacuum operation, causing the refrigerant on the indoor unit side to move to the outdoor unit side; the control device is configured to control the indoor throttling element to be in an open valve state and control the outdoor throttling element to be in a shutdown set opening state during the vacuum operation; after the vacuum operation ends, the indoor throttling element is kept in an open valve state, the outdoor throttling element is kept in a shutdown set opening state, and then the outdoor throttling element is controlled to operate in a closed valve state; or

[0015] During heating, the control device receives a shutdown command and performs a vacuum operation, causing the refrigerant on the indoor unit side to move to the outdoor unit side. The control device is configured to keep the indoor throttling element in the open valve state and the outdoor throttling element in the shutdown set opening state during the vacuum operation. After the vacuum operation is completed, the indoor throttling element is kept in the open valve state and the outdoor throttling element is kept in the shutdown set opening state. Then, the outdoor throttling element is controlled to operate in the closed valve state.

[0016] The power-off setting is less than the power-off setting.

[0017] The above technical solution has the following advantages or beneficial effects: When receiving a shutdown command, the multi-split air conditioning system is in standby mode. At this time, other equipment in the refrigerant system is not completely stopped; for example, some equipment may be in a low-power state. The operation of these devices helps maintain the high and low pressure difference at a relatively low level. Under these circumstances, a relatively large shutdown setting is allowed. Within the allowable noise range, the suction and discharge pressures of the compressor can reach equilibrium more quickly. At the same time, since some equipment is in a low-power state, it will also have a low level of noise, which will prevent the noise of refrigerant flow from suddenly becoming sharp, keeping it at a level acceptable to the user.

[0018] In one or more embodiments of this application, the outdoor unit further includes: an outdoor fan;

[0019] During heating, the control device receives a shutdown command and performs a vacuum operation, causing the refrigerant on the indoor unit side to move to the outdoor unit side; the control device is configured to stop the outdoor fan during and after the vacuum operation.

[0020] The above technical solution has the following advantages or beneficial effects: By executing the above steps, when the shutdown command (SW OFF) is received, the control device can effectively achieve the following control objectives: while making the pressure on the suction side and the exhaust side of the compressor reach a balance state quickly and controlling the noise at a low level, the outdoor fan is stopped in time, thereby avoiding the user from mistakenly believing that the indoor unit is still working and creating a false impression that it has not been shut down.

[0021] In one or more embodiments of this application, the indoor unit further includes: an indoor fan;

[0022] During heating, the control device receives a shutdown command and performs a vacuum operation, causing the refrigerant on the indoor unit side to move to the outdoor unit side; the control device is configured to stop the indoor fan during and after the vacuum operation.

[0023] The above technical solution has the following advantages or beneficial effects: By executing the above steps, when the shutdown command (SW OFF) is received, the control device can effectively achieve the following control objectives: while making the pressure on the suction side and the exhaust side of the compressor reach a balance state quickly and controlling the noise at a low level, the operation of the indoor fan is stopped in time to prevent low-temperature air from being sent into the air-conditioned room, and also to prevent users from mistakenly believing that the indoor unit is still working, creating the illusion that it has not been turned off.

[0024] In one or more embodiments of this application, the outdoor unit further includes: an outdoor fan;

[0025] During heating, the control device receives a shutdown command and performs a vacuum operation, causing the refrigerant on the indoor unit side to move to the outdoor unit side; the control device is configured to control the outdoor fan to stop operating during and after the vacuum operation.

[0026] The above technical solution has the following advantages or beneficial effects: After receiving the shutdown command (Thermo OFF), by executing the above steps, the control device can efficiently achieve the following objectives: quickly balance the pressure on the suction and discharge sides of the compressor, while keeping the noise at a low level, and promptly stop the operation of the outdoor fan, thereby preventing users from misunderstanding that the multi-split air conditioning system is still working and avoiding the illusion that it has not been shut down.

[0027] In one or more embodiments of this application, the indoor unit further includes: an indoor fan;

[0028] During heating, the control device receives a shutdown command and performs a vacuum operation, causing the refrigerant on the indoor unit side to move to the outdoor unit side; the control device is configured to control the indoor fan to operate at a set speed during and after the vacuum operation.

[0029] The above technical solution has the following advantages or beneficial effects: an indoor fan that operates at a set speed helps to reduce exhaust pressure and reduce the pressure difference between high and low pressure, thereby achieving pressure balance more quickly with lower noise.

[0030] In one or more embodiments of this application, a multi-split air conditioning system includes: an outdoor unit, in which a compressor and an outdoor electronic expansion valve are installed; multiple indoor units connected to the outdoor unit via refrigerant piping, each indoor unit being equipped with an indoor electronic expansion valve; a control device for controlling the outdoor unit and the multiple indoor units; during heating, the control device receives a shutdown command and performs a vacuum operation, causing the refrigerant on the indoor unit side to move to the outdoor unit side; the control device is further configured to perform the following control to balance the pressure on the compressor's suction and discharge sides: during the vacuum operation, the indoor electronic expansion valve is controlled to be in an open state, and the outdoor electronic expansion valve is controlled to be in a shutdown set opening degree; after the vacuum operation ends, the indoor electronic expansion valve is kept in an open state, the outdoor electronic expansion valve is kept in a shutdown set opening degree, and then the opening degree of the outdoor electronic expansion valve is gradually reduced over time until the outdoor electronic expansion valve reaches a closed state.

[0031] The above technical solution has the following advantages or beneficial effects: By controlling the vacuum operation, and keeping the indoor electronic expansion valve in the open state and the outdoor electronic expansion valve at the set opening degree during and after the vacuum operation, the pressure on the compressor suction and discharge sides can be effectively balanced. Furthermore, the opening degree of the outdoor electronic expansion valve is reduced in a stepwise manner over time, making the stepper motor deceleration process smoother and avoiding problems with accurate positioning. This can also effectively avoid sudden changes in refrigerant flow and reduce pressure fluctuations. Stable refrigerant flow and pressure balance can reduce vibration and noise sources in the refrigerant system, ensuring stable operation of the multi-split air conditioning system during shutdown or stoppage, significantly suppressing noise, and improving overall performance and user experience.

[0032] In one or more embodiments of this application, a multi-split air conditioning system includes: an outdoor unit, in which a compressor and an outdoor electronic expansion valve are installed; multiple indoor units connected to the outdoor unit via refrigerant piping, each indoor unit being equipped with an indoor electronic expansion valve; a control device for controlling the outdoor unit and the multiple indoor units; during heating, the control device receives a shutdown command and performs a vacuum operation, causing the refrigerant on the indoor unit side to move towards the outdoor unit side; the control device is further configured to perform the following control to balance the pressure on the compressor's suction and discharge sides: during the vacuum operation, the indoor electronic expansion valve is controlled to be in an open state, and the outdoor electronic expansion valve is controlled to be in a shutdown set opening degree; after the vacuum operation ends, the indoor electronic expansion valve is kept in an open state, the outdoor electronic expansion valve is kept in a shutdown set opening degree, and then the opening degree of the outdoor electronic expansion valve is gradually reduced over time until the outdoor electronic expansion valve reaches a closed state.

[0033] The above technical solution has the following advantages or beneficial effects: By controlling the indoor electronic expansion valve to remain open after receiving a shutdown command, and gradually reducing the opening of the outdoor electronic expansion valve, the pressure on the compressor's suction and discharge sides reaches a balanced state. This stepwise control method effectively prevents damage to the compressor caused by pressure imbalance during shutdown, improves the system's reliability and stability, and also effectively suppresses noise, enhancing the user experience.

[0034] Other features and advantages of the present invention will become clearer after reading the detailed embodiments of the invention in conjunction with the accompanying drawings. Attached Figure Description

[0035] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0036] Figure 1 is a schematic diagram of the structure of a multi-split air conditioning system provided by one or more embodiments of the present invention;

[0037] Figure 2 is a schematic diagram of the refrigerant circulation during heating in a multi-split air conditioning system provided by one or more embodiments of the present invention;

[0038] Figure 3 is a schematic diagram of the structure of a multi-split air conditioning system provided by one or more embodiments of the present invention;

[0039] Figure 4 shows an example of the test curve for noise testing;

[0040] Figure 5 shows an example of the test curve for noise testing;

[0041] Figure 6 is a timing control diagram of the indoor throttling element in a multi-split air conditioning system provided by one or more embodiments of the present invention;

[0042] Figure 7 is a timing control diagram of the outdoor throttling element in a multi-split air conditioning system provided by one or more embodiments of the present invention;

[0043] Figure 8 is a timing control diagram of the outdoor throttling element in a multi-split air conditioning system provided by one or more embodiments of the present invention;

[0044] Figure 9 is a timing control diagram of the indoor throttling element in a multi-split air conditioning system provided by one or more embodiments of the present invention;

[0045] Figure 10 is a timing control diagram of the outdoor throttling element in a multi-split air conditioning system provided by one or more embodiments of the present invention;

[0046] Figure 11 is a timing control diagram of the outdoor throttling element in a multi-split air conditioning system provided by one or more embodiments of the present invention.

[0047] Figure 12 is a timing control diagram of the indoor electronic expansion valve in a multi-split air conditioning system provided by one or more embodiments of the present invention;

[0048] Figure 13 is a timing control diagram of the outdoor electronic expansion valve in a multi-split air conditioning system provided by one or more embodiments of the present invention;

[0049] Figure 14 is a timing control diagram of the indoor electronic expansion valve in a multi-split air conditioning system provided by one or more embodiments of the present invention;

[0050] Figure 15 is a timing control diagram of the outdoor electronic expansion valve in a multi-split air conditioning system provided by one or more embodiments of the present invention. Detailed Implementation

[0051] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0052] In the description of this application, it should be understood that the terms "center", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this application 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, and therefore should not be construed as a limitation of this application.

[0053] 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 technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, unless otherwise stated, "multiple" means two or more.

[0054] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "installation," "connection," and "linking" 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 between two components. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0055] 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" 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.

[0056] The following disclosure provides many different embodiments or examples for implementing various structures of the invention. To simplify the disclosure, specific examples of components and arrangements are described below. These are merely examples and are not intended to limit the invention. Furthermore, reference numerals and / or letters may be repeated in different examples; such repetition is for simplification and clarity and does not in itself indicate a relationship between the various embodiments and / or arrangements discussed. In addition, examples of various specific processes and materials are provided in this invention, but those skilled in the art will recognize the application of other processes and / or the use of other materials.

[0057] A multi-split air conditioning system is a system that performs a refrigeration cycle using a compressor (shown as 100 in Figure 1), a condenser, a throttling device, and an evaporator. The refrigeration cycle includes a series of processes involving compression, condensation, expansion, and evaporation to cool or heat an indoor space.

[0058] From a principle perspective, low-temperature, low-pressure refrigerant enters the compressor, which compresses it into a high-temperature, high-pressure refrigerant gas 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 the heat is released to the surrounding environment through the condensation process.

[0059] The throttling device expands the high-temperature, high-pressure liquid refrigerant that condenses in the condenser into a low-pressure liquid refrigerant. The evaporator evaporates the expanded refrigerant in the throttling device, returning the low-temperature, low-pressure refrigerant gas to the compressor. The evaporator achieves its cooling effect by utilizing the latent heat of refrigerant evaporation to exchange heat with the material being cooled. Throughout the cycle, the multi-split air conditioning system regulates the temperature of the indoor space.

[0060] The outdoor unit of a multi-split air conditioning system refers to the part of the refrigeration cycle that includes the compressor and the outdoor heat exchanger (as shown in Figure 1, 101). The indoor unit of the multi-split air conditioning system is located in the air-conditioned room and includes the indoor heat exchanger (as shown in Figure 1, 201). Throttling devices can be provided in both the indoor and outdoor units, i.e., outdoor throttling elements and indoor throttling elements. For example, in this embodiment, both the outdoor throttling element (as shown in Figure 1, 102) and the indoor throttling element (as shown in Figure 1, 202) are implemented by electronic expansion valves. More specifically, each indoor unit is equipped with an expansion valve, called an indoor electronic expansion valve, and an outdoor electronic expansion valve can also be installed in the outdoor unit.

[0061] Outdoor and indoor throttling elements can also be implemented by other valve elements or combinations of valve elements that can achieve the same function.

[0062] In one or more embodiments of this application, the electronic expansion valve is driven by a stepper motor (or other motor capable of performing the same function) disposed within it. Upon receiving a control signal, the stepper motor rotates according to a specified number of steps, driving the valve core to move, thereby changing the opening degree of the electronic expansion valve. Each step corresponds to a small change in the valve opening degree; the desired opening degree adjustment is achieved by accumulating the number of steps.

[0063] The indoor and outdoor heat exchangers are used as condensers or evaporators. When the indoor heat exchanger is used as a condenser, the multi-split air conditioning system acts as a heater in heating mode (i.e., during heating). When the indoor heat exchanger is used as an evaporator, the multi-split air conditioning system acts as a cooler in cooling mode (i.e., during cooling).

[0064] In one alternative implementation, each outdoor unit may be equipped with one or more compressors, and AC power is supplied to the compressors in operation via a frequency converter. When the output frequency of the frequency converter changes, the compressor speed changes, thereby achieving different air conditioning capacities.

[0065] The outdoor unit also includes an outdoor fan (shown as 103 in Figure 1) and a four-way valve (shown as 104 in Figure 1). In addition, other conventional components such as a gas-liquid separator (shown as 105 in Figure 1), a capillary tube (not shown), and an oil separator (not shown) can also be installed.

[0066] A gas-liquid separator is a shell-shaped component used to separate the refrigerant into gas and liquid components, and it is usually located on the suction side of the compressor.

[0067] An outdoor heat exchanger is configured to facilitate heat exchange between the refrigerant flowing through its internal heat exchange pipes and the air (or other medium) guided by the outdoor fan. The outdoor fan can be an axial fan, a cross-flow fan, or other optional fan type, and is usually located near the outdoor heat exchanger.

[0068] A four-way valve is used to switch the refrigerant flow direction according to the operating mode of a multi-split air conditioning system. In cooling mode, the compressor discharge side is connected to one end of the outdoor heat exchanger via a four-way valve and other piping, while the compressor suction side is connected to one end of the indoor heat exchanger via the same four-way valve and piping. Thus, the outdoor heat exchanger functions as a condenser, and the indoor heat exchanger functions as an evaporator. Similarly, in heating mode, the compressor discharge side is connected to one end of the indoor heat exchanger via a four-way valve and piping, while the compressor suction side is connected to one end of the outdoor heat exchanger via the same four-way valve and piping. Thus, the indoor heat exchanger functions as a condenser, and the outdoor heat exchanger functions as an evaporator.

[0069] The refrigerant circuit of a multi-split air conditioning system is connected sequentially to the compressor, outdoor heat exchanger, expansion valve, and indoor heat exchanger to allow the refrigerant to circulate.

[0070] The indoor electronic expansion valve and the outdoor electronic expansion valve, which are installed corresponding to the indoor unit, are valves that reduce the pressure of the refrigerant flowing into the valve body itself. They are installed on the piping through which liquid refrigerant or gas-liquid two-phase refrigerant flows.

[0071] An oil separator is used to separate lubricating oil from the refrigerant discharged from the compressor. It is usually installed on the discharge side of the compressor. The lubricating oil separated by the oil separator can be guided to a gas-liquid separator through a pipeline. A one-way valve can also be installed to guide the separated refrigerant to a four-way valve.

[0072] The outdoor unit is equipped with an outdoor control circuit. The outdoor control circuit is usually housed in a well-sealed electrical box.

[0073] The outdoor control circuit includes components such as a processor, storage unit, input / output interfaces, and communication interfaces. The processor can be a dedicated processor, a central processing unit (CPU), etc. The processor can access the storage unit to execute instructions or application programs stored therein to achieve related functions. The storage unit can include volatile memory and / or non-volatile memory. The input / output interfaces can communicate with various sensors installed in the outdoor unit to receive their detection values. The input / output interfaces can also communicate with devices such as frequency converters, compressors, outdoor fans, four-way valves, and outdoor electronic expansion valves to output control commands generated by the processor. The communication interfaces can support different wireless communication protocols, such as WiFi, Bluetooth, near-field communication, NB-IoT, etc., to communicate with other electronic devices, including but not limited to cloud servers, computers (host computers), smartphones, tablets, PDAs, intelligent control fixtures, wearable devices, and vehicle-mounted devices.

[0074] In one alternative implementation, the multi-split air conditioning system may include an outdoor unit.

[0075] In one alternative implementation, the multi-split air conditioning system may include multiple outdoor units, each of which may operate independently or be configured to operate in groups, such as two outdoor units as a group, four outdoor units as a group, and so on.

[0076] In one alternative implementation, each outdoor unit or group of outdoor units is paired with a corresponding indoor unit. Multiple indoor units are connected to the outdoor unit via refrigerant piping.

[0077] In one alternative implementation, the indoor unit can employ an independent air supply structure, such as a wall-mounted air supply structure, a floor-standing air supply structure, a ducted air supply structure, or an air supply structure embedded in the ceiling. The air supply structure includes a housing with a return air inlet for drawing in air and an air supply outlet for delivering the heat-exchanged air into the air-conditioned room. An indoor fan (shown as 203 in Figure 1) and an indoor heat exchanger are housed within the housing. The indoor fan is located near the indoor heat exchanger.

[0078] In one optional implementation, a wired controller is correspondingly installed in the indoor unit, and the wired controller is fixedly installed on the wall of the air-conditioned room. The wired controller is equipped with an operation interface for inputting the set temperature and operating mode, as well as a display interface for displaying the real-time temperature of the air-conditioned room and the operating status of the multi-split air conditioning system.

[0079] In one optional implementation, the indoor unit is equipped with a corresponding remote control, which is communicatively connected to the indoor unit. The remote control is equipped with buttons for inputting the set temperature and operating mode, as well as a display interface for displaying the real-time temperature of the air-conditioned room and the operating status of the multi-split air conditioning system.

[0080] In one optional implementation, the indoor unit is equipped with a corresponding mobile control terminal. The mobile control terminal is communicatively connected to the indoor unit and has an application interface. Users can input the set temperature and operating mode through the application interface and display the real-time temperature or operating status of the air-conditioned room.

[0081] In one alternative implementation, the mobile control terminal may be a computer, tablet computer, smartphone, wearable device, etc.

[0082] The indoor unit is equipped with an indoor unit control circuit, which preferably includes an indoor controller. The indoor controller is configured to drive the indoor fan, display various parameters on the display panel, provide human-machine interaction, receive and process sampling signals from various sensors, and perform necessary communication functions.

[0083] The indoor unit control circuit also includes electrical components such as storage units, processors, input / output interfaces, and communication interfaces.

[0084] The storage unit may include volatile memory and / or non-volatile memory. The storage unit is configured to store instructions or data associated with at least one component of the indoor unit, such as an application program. For example, the application program could be used to adjust the temperature of an air-conditioned room by adjusting different speed settings of the indoor fan.

[0085] An indoor processor can be a dedicated processor, a central processing unit (CPU), or the like. The indoor processor can access memory to execute instructions stored in the memory to perform related functions.

[0086] The input / output interface can communicate with various sensors installed in the indoor unit to receive their detection values. The input / output interface can be a serial communication interface. It can also communicate with components such as indicator lights, buzzers, and stepper motors to output control commands. The stepper motor can be the driving component for the air guide plate.

[0087] The communication interface can be a software interface that supports different wireless communication protocols, such as WiFi and Bluetooth.

[0088] The indoor unit control circuit is usually equipped with a power supply circuit to provide 12V and 5V voltage.

[0089] The outdoor unit control circuit and the indoor unit control circuit are connected for communication.

[0090] In some optional embodiments of this application, the outdoor unit control circuit and the indoor unit control circuit work together as a control device to control the multi-split air conditioning system.

[0091] In some optional embodiments of this application, the control device may also be a server or a host computer. The server or host computer is communicatively connected to the outdoor unit control circuit and the indoor unit control circuit.

[0092] Figure 1 is a structural schematic diagram of a multi-split air conditioning system provided in one or more embodiments of this application, and Figure 2 is a refrigerant circulation diagram of the multi-split air conditioning system provided in one or more embodiments of this application during heating, with the refrigerant flow direction shown as F in Figure 2. As shown in Figures 1 and 2, the multi-split air conditioning system includes multiple indoor units (as shown in Figures 20-1, 20-2, 20-3, and 20-4), and the multiple indoor units are respectively connected to an outdoor unit (as shown in Figure 10) via refrigerant piping.

[0093] As shown in Figure 3, the multi-split air conditioning system also includes a control device (as shown in Figure 30), which is used to control the outdoor unit and multiple indoor units.

[0094] When heating, the control device receives a shutdown command or stop command and performs a vacuum operation, causing the refrigerant on the indoor unit side to move to the outdoor unit side.

[0095] In one or more embodiments of this application, the power off command (SW OFF) refers to a command used to turn off the power switch. The power off command (SW OFF) is implemented through the power button on a wired controller, remote controller, or mobile control terminal.

[0096] In one or more embodiments of this application, a shutdown command (Thermo OFF) refers to a command to stop heating when the air-conditioned room reaches the set temperature. The shutdown command (Thermo OFF) is an command automatically generated based on the detection value of the temperature sensor (or thermostat).

[0097] In one or more embodiments of this application, pump down (or pump down operations) refers to controlling the compressor to continue running for a period of time after receiving a shutdown command (SW OFF) or a thermo OFF command, causing the refrigerant on the indoor unit side to move to the outdoor unit side, and recovering the remaining refrigerant and refrigeration oil in the low-pressure piping to the high-pressure side. In one or more embodiments of this application, pump down operations can be terminated based on pressure or temperature. For example, when the pressure or temperature reaches a preset value, the compressor is turned off, completing the pump down operation and ensuring that most of the refrigerant has been drawn back. The control conditions for exiting pump down operations are not the focus of this application; existing pump down operation control conditions can be used and will not be further described here. Pump down operations can ensure the safety and stability of the multi-split system when it is shut down or in standby mode, and can also prevent liquid return during startup or the occurrence of low compressor oil viscosity.

[0098] In one or more embodiments of this application, the control device is further configured to perform the following control to bring the pressure on the suction side and discharge side of the compressor into a balanced state:

[0099] During vacuum operation, the indoor throttling element is in the open state, and the outdoor throttling element is in the set opening state.

[0100] After the vacuuming operation is completed, keep the indoor throttling element in the open valve state, keep the outdoor throttling element in the set opening degree, and then control the outdoor throttling element to work in the closed valve state.

[0101] It should be noted that, in one or more embodiments of this application, the valve-closed state is not limited to the case where the electronic expansion valve is completely closed and the refrigerant flow is zero. The valve-closed state also includes the case where the electronic expansion valve operates at its minimum permissible opening. For some electronic expansion valves, the electronic expansion valve itself is designed with a minimum opening, allowing a very small flow even when the electronic expansion valve is operating in the closed state, to prevent refrigerant from accumulating at the valve and to avoid malfunctions such as liquid slugging and jamming.

[0102] In one or more embodiments of this application, the valve opening state includes fully open and nearly fully open. Fully open means that the electronic expansion valve is set to its maximum opening degree, the valve is fully open, and the refrigerant flow has almost no resistance. Nearly fully open means that the electronic expansion valve is set to its maximum opening degree, the valve is almost fully open, and the refrigerant flow experiences very little resistance.

[0103] In one or more embodiments of this application, the valve opening state also includes setting the opening degree to a predetermined large value, such as a boundary value of the reference range.

[0104] In one or more embodiments of this application, a balanced state refers to the pressure difference between the compressor's suction and discharge sides being within a reasonable range, ensuring the stable operation and high efficiency of the multi-split air conditioning system. That is, the pressure difference is within the range allowed by the design and operating specifications of the multi-split air conditioning system, avoiding excessively large or small pressure differences. In a pressure balanced state, the compressor can start and operate smoothly, avoiding overload or instability. For example, in a balanced state, the pressure difference between the compressor's suction and discharge sides is within 0.3 MPa. This 0.3 MPa range is merely an example; the range of pressure difference may vary depending on the design and operating specifications of the multi-split air conditioning system.

[0105] In one or more embodiments of this application, the indoor throttling element includes an indoor throttling element that is configured to be installed in conjunction with an indoor unit in an on-state (including a off-state) and an off-state.

[0106] In the multi-split air conditioning system provided in this application, after receiving a shutdown or stop command, the control device performs a vacuum operation. During and after the vacuum operation, the indoor throttling element is kept in the open valve state, and the outdoor throttling element is kept at the set opening degree. This can effectively balance the pressure on the compressor's suction and discharge sides, avoid sudden changes in refrigerant flow, reduce pressure fluctuations, and the stable refrigerant flow and pressure balance can reduce the vibration and noise sources of the refrigerant system. This ensures that the multi-split air conditioning system operates smoothly during shutdown or stop, significantly suppresses noise, and improves overall performance and user experience.

[0107] Figure 4 shows a comparison of measured noise levels. Without the above control measures, when one indoor unit receives a shutdown command, a stop command, or all indoor units receive a shutdown command, the refrigerant unloading sound suddenly becomes sharp within 3-4 seconds, then gradually decreases over 1 minute. This is particularly noticeable in wall-mounted indoor units and is unacceptable to listen to. However, with the above control method, the indoor units do not exhibit a sudden unloading impact sound, and the noise suppression effect is very significant.

[0108] In one or more embodiments of this application, the opening degree is set to be in the range of 20%-30% of the total opening degree.

[0109] For example, suppose the total opening of the electronic expansion valve is 500 pls, and the opening is set in the range of 100 pls-150 pls.

[0110] Figure 5 shows a comparison of the measured noise levels. Compared to a valve opening of 39% (190 pls), the noise level decreased by 2.04 dB at a valve opening of 30% and by 5.1 dB at a valve opening of 20%.

[0111] Tables 1 to 3 show the test data of the compressor's suction side pressure Ps and discharge side pressure Pd after the above control was implemented, where AP = Pd - Ps.

[0112]

[0113] Table 1: First Received Shutdown Command

[0114]

[0115] Table 2: Second Received Shutdown Command

[0116]

[0117] Table 3: Third time receiving the shutdown command

[0118] After testing, the pressure difference between the intake and exhaust sides was within 0.3 MPa 3 minutes after shutdown, and the pressure on the intake and exhaust sides of the compressor reached a balanced state, which met the drive requirements.

[0119] In one or more embodiments of this application, the control device is configured to set an opening degree based on the number of indoor units in operation. The set opening degree corresponds to the number of indoor units in operation, and the more indoor units in operation, the larger the set opening degree.

[0120] In multi-split air conditioning systems, the number of indoor units connected has a significant impact on refrigerant flow and pressure distribution. When the pressure difference between the compressor's suction and discharge sides is the same, a higher number of connected indoor units means that the high and low pressure differences are distributed across each unit. This means that each indoor unit experiences a smaller pressure difference. Because the pressure difference is distributed, each indoor unit experiences less refrigerant impact when adjusting the outdoor throttling element's opening, resulting in smoother refrigerant flow. Therefore, even with a higher setting, the refrigerant flow noise remains within acceptable limits, and a higher setting allows for faster pressure equalization.

[0121] Conversely, if fewer indoor units are connected, the high and low pressure differences will be concentrated on fewer indoor units, meaning each indoor unit will experience a larger pressure difference. Due to this concentrated pressure difference, the refrigerant surge force experienced by each indoor unit when opening the valve will also increase, leading to unstable refrigerant flow and potentially generating significant refrigerant flow noise, negatively impacting the user experience. To reduce refrigerant surge and flow noise, when fewer indoor units are connected, the valve opening is set to be smaller to control the refrigerant flow, resulting in smoother refrigerant flow and reduced noise.

[0122] By configuring the opening degree according to the number of indoor units in operation, the refrigerant shock borne by the indoor units can be assessed based on the distributed pressure difference, reducing refrigerant shock and flow noise under different operating conditions, thereby significantly improving system stability and user experience.

[0123] In Figures 6 to 15, EVI opening is the opening of the indoor throttling element (indoor electronic expansion valve), and EVO opening is the opening of the outdoor throttling element (outdoor electronic expansion valve).

[0124] As shown in Figures 6 to 8, in one or more embodiments of this application, the control device is configured to perform the following control methods:

[0125] Obtain the number of indoor units that are in operation;

[0126] Compare the number of indoor units in operation with the set number;

[0127] When the number of indoor units in operation is higher than the set number, a larger first set opening degree is set according to the number of indoor units in operation (as shown by B1pls in Figure 8); the outdoor throttling element is controlled to first operate at the first set opening degree, and then operate in the closed valve state.

[0128] When the number of indoor units in operation is less than the set number, a smaller second set opening degree is set according to the number of indoor units in operation (as shown in Figure 7, A1pls); the outdoor throttling element is controlled to first operate at the second set opening degree, and then operate in the closed valve state.

[0129] As shown in Figures 7 and 8, if the number of indoor units in operation (number of connected indoor units) is not higher than the set number (e.g., less than or equal to a units), the outdoor throttling element is at the second set opening degree during the vacuuming operation (as shown by A1pls in Figure 7). After the vacuuming operation is completed, the outdoor throttling element is kept at the second set opening degree. After maintaining this for a T1 cycle (usually several minutes), the outdoor throttling element is controlled to work in the closed valve state (as shown by Opls in Figure 7).

[0130] When the number of indoor units in operation is higher than the set number (e.g., greater than a units), the outdoor throttling element is at the first set opening degree during the vacuuming operation (as shown by B1pls in Figure 8). After the vacuuming operation is completed, the outdoor throttling element is kept at the first set opening degree. After maintaining this for a T1 cycle (usually several minutes), the outdoor throttling element is controlled to work in the closed valve state (as shown by Opls in Figure 8).

[0131] By comparing the number of indoor units in operation with the set number, the system can automatically select and generate the corresponding set opening degree, ensuring smooth refrigerant flow and improving the stability and user experience of the multi-split air conditioning system.

[0132] In one or more embodiments of this application, the control device is configured to perform the following controls in response to different shutdown and stop commands.

[0133] During heating, the control unit receives a shutdown command (SW OFF) and performs a vacuum operation, causing the refrigerant on the indoor unit side to move to the outdoor unit side. The control unit is configured to keep the indoor throttling element in the open valve state and the outdoor throttling element at the shutdown set opening during the vacuum operation. After the vacuum operation is completed, the indoor throttling element remains in the open valve state, the outdoor throttling element remains at the shutdown set opening, and then the outdoor throttling element is controlled to operate in the closed valve state.

[0134] As shown in Figures 9 to 11, similarly, during heating, the control device receives a shutdown command (Thermo OFF) and performs a vacuum operation, causing the refrigerant on the indoor unit side to move to the outdoor unit side. The control device is configured to keep the indoor throttling element in the open valve state and the outdoor throttling element at the shutdown set opening degree during the vacuum operation (as shown by A2pls in Figure 10). After the vacuum operation ends, the indoor throttling element remains in the open valve state, the outdoor throttling element remains at the shutdown set opening degree, and then the outdoor throttling element is controlled to operate in the closed valve state.

[0135] The power-off setting opening A1pls is less than the shutdown setting opening A2pls.

[0136] When the number of connected devices is greater, the corresponding shutdown setting B1pls is also less than the stop setting B2pls, as shown in Figure 11.

[0137] When a shutdown command is received, the multi-split air conditioning system is in standby mode. At this time, other devices in the refrigerant system are not completely shut down; for example, some devices may be operating at low power. The operation of these devices helps maintain the high and low pressure difference at a relatively low level. In this case, a relatively large shutdown setting is allowed. Within the permissible noise range, this allows the compressor's suction and discharge pressures to reach equilibrium more quickly. At the same time, because some devices are operating at low power, they themselves will also generate low-level noise, preventing the refrigerant flow noise from suddenly becoming sharp and keeping it at an acceptable level for the user.

[0138] In one or more embodiments of this application, the control device is configured to receive a shutdown command (SWOFF) and perform a vacuum operation during heating, causing the refrigerant on the indoor unit side to move to the outdoor unit side. The control device is also configured to control the outdoor fan to stop operating during and after the vacuum operation.

[0139] By executing the above steps, upon receiving the shutdown command (SW OFF), the control device can effectively achieve the following control objectives: while rapidly balancing the pressure on the compressor's suction and discharge sides and controlling the noise at a low level, it can promptly stop the operation of the outdoor fan, thereby preventing users from mistakenly believing that the indoor unit is still working and creating the illusion that it has not been shut down.

[0140] In one or more embodiments of this application, the control device is configured to receive a shutdown command (SWOFF) and perform a vacuum operation during heating, causing the refrigerant on the indoor unit side to move to the outdoor unit side. The control device is also configured to control the indoor fan to stop operating during and after the vacuum operation.

[0141] By executing the above steps, upon receiving the shutdown command (SW OFF), the control device can effectively achieve the following control objectives: while rapidly balancing the pressure on the compressor's suction and exhaust sides and controlling the noise at a low level, it can promptly stop the operation of the indoor fan to prevent low-temperature air from being sent into the air-conditioned room and to prevent users from mistakenly believing that the indoor unit is still working, thus creating the illusion that the unit has not been shut down.

[0142] In one or more embodiments of this application, the control device is configured to receive a shutdown command (Thermo OFF) and perform a vacuum operation during heating, causing the refrigerant on the indoor unit side to move to the outdoor unit side. The control device is also configured to control the outdoor fan to stop operating during and after the vacuum operation.

[0143] Upon receiving a shutdown command (Thermo OFF), the control device can efficiently achieve the following objectives by executing the above steps: quickly balancing the suction and discharge pressures of the compressor, maintaining a low noise level, and promptly stopping the operation of the outdoor fan, thereby preventing users from mistakenly believing that the multi-split air conditioning system is still working and avoiding the illusion that it has not been shut down.

[0144] In one or more embodiments of this application, the control device is configured to receive a shutdown command (Thermo OFF) and perform a vacuum operation during heating, causing the refrigerant on the indoor unit side to move to the outdoor unit side. The control device is also configured to control the indoor fan to operate at a set speed, such as the lowest fan speed, during and after the vacuum operation.

[0145] Indoor fans operating at a set speed help reduce exhaust pressure and decrease the pressure difference between high and low pressure, thereby achieving pressure balance more quickly with lower noise.

[0146] In one or more embodiments of this application, upon receiving a shutdown command, the control device is configured to perform the following control to achieve a balanced state between the suction and discharge pressures of the compressor: during vacuum operation, the indoor electronic expansion valve is controlled to be in the open state, and the outdoor electronic expansion valve is controlled to be in the shutdown set opening degree; after the vacuum operation ends, the indoor electronic expansion valve is kept in the open state, the outdoor electronic expansion valve is kept in the shutdown set opening degree, and then the opening degree of the outdoor electronic expansion valve is reduced stepwise over time until the outdoor electronic expansion valve reaches the closed state.

[0147] As shown in Figures 12 and 13, in the multi-split air conditioning system provided in this application, after receiving a shutdown command, the control device is configured to perform the following control to achieve a balance between the suction and discharge pressures of the compressor:

[0148] During vacuum operation, the indoor electronic expansion valve is in the open position, and the outdoor electronic expansion valve is in the off-set opening position (e.g., A1pls).

[0149] After the vacuuming operation is completed, keep the indoor electronic expansion valve in the open state and keep the outdoor electronic expansion valve at the shutdown set opening (e.g., A1pls). After reaching time T1, reduce the opening of the outdoor electronic expansion valve for the first time according to the preset adjustment amount, and keep the outdoor electronic expansion valve at the reduced opening. After reaching time T2, reduce the opening of the outdoor electronic expansion valve again according to the preset adjustment amount. Repeat the above steps until the outdoor electronic expansion valve reaches the closed state, for example, at time T4, it reaches 0pls.

[0150] By controlling the vacuum operation, and keeping the indoor electronic expansion valve open and the outdoor electronic expansion valve at a set opening during and after the vacuum operation, the pressure on the compressor's suction and discharge sides can be effectively balanced. Furthermore, the opening of the outdoor electronic expansion valve is gradually reduced over time, resulting in a smoother deceleration process for the stepper motor and eliminating problems with accurate positioning. This effectively prevents sudden changes in refrigerant flow and reduces pressure fluctuations. Stable refrigerant flow and pressure balance reduce vibration and noise sources in the refrigerant system, ensuring smooth operation of the multi-split air conditioning system during shutdown or stoppage, significantly suppressing noise, and improving overall performance and user experience.

[0151] In one or more embodiments of this application, upon receiving a shutdown command, the control device is configured to perform the following control to balance the pressure on the suction and discharge sides of the compressor: during vacuum operation, the indoor electronic expansion valve is controlled to be in the open state, and the outdoor electronic expansion valve is controlled to be in the shutdown set opening degree; after the vacuum operation ends, the indoor electronic expansion valve is kept in the open state, the outdoor electronic expansion valve is kept in the shutdown set opening degree, and then the opening degree of the outdoor electronic expansion valve is gradually reduced over time until the outdoor electronic expansion valve reaches the closed state.

[0152] As shown in Figures 14 and 15, in the multi-split air conditioning system provided in this application, after receiving a shutdown command, the control device is configured to perform the following control to balance the pressure on the compressor's suction and discharge sides:

[0153] During vacuum operation, the indoor electronic expansion valve is in the open position, and the outdoor electronic expansion valve is in the shutdown set opening position (e.g., A2pls).

[0154] After the vacuuming operation is completed, keep the indoor electronic expansion valve in the open state and keep the outdoor electronic expansion valve at the shutdown set opening (e.g., A2pls). After reaching time T1, reduce the opening of the outdoor electronic expansion valve for the first time according to the preset adjustment amount, and keep the outdoor electronic expansion valve at the reduced opening. After reaching time T2, reduce the opening of the outdoor electronic expansion valve again according to the preset adjustment amount. Repeat the above steps until the outdoor electronic expansion valve reaches the closed state, for example, at time T4, it reaches 0pls.

[0155] Upon receiving a shutdown command, the indoor electronic expansion valve is kept open while the opening of the outdoor electronic expansion valve is gradually reduced, thus achieving pressure balance between the compressor's suction and discharge sides. This stepwise control method effectively prevents compressor damage caused by pressure imbalance during shutdown, improves system reliability and stability, effectively suppresses noise, and enhances the user experience.

[0156] In the description of the above embodiments, specific features, structures, materials, or characteristics may be combined in any suitable manner in one or more embodiments or examples.

[0157] The above are merely specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. Multi-split air conditioning system, including: The outdoor unit contains a compressor and an outdoor throttling element; Multiple indoor units are connected to the outdoor unit via refrigerant piping. Each indoor unit is equipped with an indoor throttling element and a control device for controlling the outdoor unit and the multiple indoor units. During heating, the control device receives a shutdown command or a stop command and performs a vacuum operation, causing the refrigerant on the indoor unit side to move towards the outdoor unit side. The control device is further configured to perform the following control to balance the pressure on the compressor's suction and discharge sides: during vacuum operation, the indoor throttling element is controlled to be in an open valve state, and the outdoor throttling element is controlled to be at a set opening degree. After the vacuuming operation is completed, keep the indoor throttling element in the open valve state and keep the outdoor throttling element in the set opening degree, and then control the outdoor throttling element to work in the closed valve state.

2. The multi-split air conditioning system according to claim 1, characterized in that, The control device is configured to set the opening degree according to the number of indoor units in the working state; the set opening degree corresponds to the number of indoor units in the working state, and the more indoor units in the working state, the larger the set opening degree.

3. The multi-split air conditioning system according to claim 2, characterized in that: The control device is configured to: acquire the number of indoor units in operation; compare the number of indoor units in operation with a set number; when the number of indoor units in operation is higher than the set number, set a larger first set opening degree based on the number of indoor units in operation; control the outdoor throttling element to first operate at the first set opening degree, and then operate in a closed valve state; when the number of indoor units in operation is not higher than the set number, set a smaller second set opening degree based on the number of indoor units in operation; control the outdoor throttling element to first operate at the second set opening degree, and then operate in a closed valve state.

4. The multi-split air conditioning system according to claim 1, characterized in that: During heating, the control device receives a shutdown command and performs a vacuum operation, causing the refrigerant on the indoor unit side to move to the outdoor unit side; the control device is configured to control the indoor throttling element to be in the open valve state and control the outdoor throttling element to be in the shutdown set opening degree when performing the vacuum operation. After the vacuum operation is completed, the indoor throttling element is kept in the open valve state, and the outdoor throttling element is kept at the shutdown set opening degree. Then, the outdoor throttling element is controlled to work in the closed valve state. Alternatively, during heating, the control device receives a shutdown command and performs vacuum operation, causing the refrigerant on the indoor unit side to move to the outdoor unit side. The control device is configured to control the indoor throttling element to be in the open valve state and control the outdoor throttling element to be at the shutdown set opening degree when performing vacuum operation. After the vacuuming operation is completed, keep the indoor throttling element in the open valve state, keep the outdoor throttling element in the shutdown setting opening degree, and then control the outdoor throttling element to work in the closed valve state; wherein, the shutdown setting opening degree is less than the shutdown setting opening degree.

5. The multi-split air conditioning system according to claim 4, characterized in that: The outdoor unit further includes an outdoor fan; during heating, the control device receives a shutdown command and performs a vacuum operation, causing the refrigerant on the indoor unit side to move to the outdoor unit side; the control device is configured to control the outdoor fan to stop operating during and after the vacuum operation.

6. The multi-split air conditioning system according to claim 5, characterized in that: The indoor unit also includes an indoor fan; during heating, the control device receives a shutdown command and performs a vacuum operation, causing the refrigerant on the indoor unit side to move to the outdoor unit side; the control device is configured to control the indoor fan to stop operating during and after the vacuum operation.

7. The multi-split air conditioning system according to claim 4, characterized in that: The outdoor unit also includes an outdoor fan; during heating, the control device receives a shutdown command and performs a vacuum operation, causing the refrigerant on the indoor unit side to move to the outdoor unit side; the control device is configured to control the outdoor fan to stop operating during and after the vacuum operation.

8. The multi-split air conditioning system according to claim 5, characterized in that: The indoor unit also includes an indoor fan; during heating, the control device receives a shutdown command and performs a vacuum operation, causing the refrigerant on the indoor unit side to move to the outdoor unit side; the control device is configured to control the indoor fan to operate at a set speed during and after the vacuum operation.

9. Multi-split air conditioning system, including: The outdoor unit contains a compressor and an outdoor electronic expansion valve; Multiple indoor units are connected to the outdoor unit via refrigerant piping, and each indoor unit is equipped with an indoor electronic expansion valve. A control device is used to control the outdoor unit and the plurality of indoor units; during heating, the control device receives a shutdown command and performs a vacuum operation to move the refrigerant on the indoor unit side to the outdoor unit side; characterized in that the control device is further configured to perform the following control to balance the pressure on the suction side and the discharge side of the compressor: during the vacuum operation, the indoor electronic expansion valve is controlled to be in the open state, and the outdoor electronic expansion valve is controlled to be in the shutdown set opening degree; After the vacuuming operation is completed, keep the indoor electronic expansion valve in the open state and keep the outdoor electronic expansion valve at the shutdown set opening degree. Then, gradually reduce the opening degree of the outdoor electronic expansion valve over time until the outdoor electronic expansion valve reaches the closed state.

10. Multi-split air conditioning system, including: The outdoor unit contains a compressor and an outdoor electronic expansion valve; Multiple indoor units are connected to the outdoor unit via refrigerant piping, and each indoor unit is equipped with an indoor electronic expansion valve; a control device is used to control the outdoor unit and the multiple indoor units; during heating, the control device receives a shutdown command and performs a vacuum operation, causing the refrigerant on the indoor unit side to move to the outdoor unit side; characterized in that the control device is further configured to perform the following control to achieve a balanced state between the suction and discharge pressures of the compressor: during the vacuum operation, the indoor electronic expansion valve is controlled to be in the open state, and the outdoor electronic expansion valve is controlled to be in the shutdown set opening degree; After the vacuuming operation is completed, keep the indoor electronic expansion valve in the open state and keep the outdoor electronic expansion valve at the shutdown set opening degree. Then, gradually reduce the opening degree of the outdoor electronic expansion valve over time until the outdoor electronic expansion valve reaches the closed state.

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