A three-pipe multi-connected system and a control method thereof

Abstract

The application provides a three-pipe multi-connected system, which comprises an outdoor unit, a plurality of indoor units and a plurality of hydraulic modules connected by a gas pipe, a liquid pipe and a condensate water pipe; the outdoor unit comprises a compressor, a high-pressure pressure sensor, an oil separator, a first switching device, a second switching device, a third switching device, a fin heat exchanger, a compressor heat dissipation module, a plate heat exchanger, a first electronic expansion valve, a second electronic expansion valve, a charging needle valve, a gas-liquid separator, a low-pressure switch, a first electromagnetic valve, a second electromagnetic valve, a third electromagnetic valve, a fourth electromagnetic valve, a fifth electromagnetic valve, an outdoor unit fan and an outdoor unit temperature detection assembly; the indoor unit comprises an indoor unit heat exchanger, a third electronic expansion valve, an indoor unit fan and an indoor unit temperature detection assembly; and the hydraulic module comprises a refrigerant-water heat exchanger, a water pump, a water temperature detection sensor, a water flow switch, a sixth electromagnetic valve, a seventh electromagnetic valve and a fourth electronic expansion valve.

Description

Technical Field

[0001] This invention relates to the field of air conditioning technology, and in particular to a three-pipe multi-split air conditioning system and its control method. Background Technology

[0002] In existing three-pipe multi-split air conditioning systems using hydraulic modules for chilled and hot water preparation, when the air conditioning system is in heating mode, the refrigerant in the three refrigerant lines connecting the indoor unit and the hydraulic module is high-pressure refrigerant. To cut off the refrigerant supply to a particular hydraulic module, the solenoid valve and electronic expansion valve controlling that module need to be shut off. This leaves some high-pressure liquid refrigerant and compressor lubricating oil remaining in the hydraulic module, resulting in insufficient refrigerant and lubricating oil in the system and affecting system reliability. Simultaneously, in standby mode, the hydraulic module closes the solenoid valve and electronic expansion valve, leaving some high-pressure refrigerant in the line between the solenoid valve and electronic expansion valve. When the high-pressure liquid refrigerant remains in the hydraulic module... When refrigerant encounters drastic temperature changes, the piping between the solenoid valve and electronic expansion valve of the hydraulic module is equivalent to a sealed container. The refrigerant inside easily expands due to temperature changes, causing high internal pressure within the hydraulic module. When the pressure in the sealed section exceeds the maximum pressure the piping can withstand, it can easily cause damage to the piping and the hydraulic module. Furthermore, in existing three-pipe multi-split systems, the refrigerant in the three pipes connected to the indoor unit and the hydraulic module is high-pressure refrigerant, which prevents the hydraulic module from performing cooling during the heating process. This severely limits the application range of the three-pipe multi-split system and also prevents the recovery of cooling capacity, resulting in energy waste. Conventional three-pipe multi-split systems cannot use chilled water in heating mode, and therefore cannot utilize the chilled water hydraulic module for heat recovery and defrosting without shutting down the system. Summary of the Invention

[0003] This invention aims to at least solve one of the technical problems existing in the prior art. To this end, this invention proposes a three-pipe multi-split air conditioning system and its control method, which can avoid situations such as insufficient refrigerant or oil shortage in the system, while ensuring the reliability of system operation.

[0004] In a first aspect, embodiments of the present invention provide a three-pipe multi-split air conditioning system, the three-pipe multi-split air conditioning system comprising an outdoor unit connected by gas pipes, liquid pipes and condensate pipes respectively, multiple indoor units and multiple hydraulic modules; The outdoor unit includes: a compressor, a high-pressure sensor, an oil separator, a first switching device, a second switching device, a third switching device, a finned heat exchanger, a compressor cooling module, a plate heat exchanger, a first electronic expansion valve, a second electronic expansion valve, a charging needle valve, a gas-liquid separator, a low-pressure switch, a first solenoid valve, a second solenoid valve, a third solenoid valve, a fourth solenoid valve, a fifth solenoid valve, an outdoor unit fan, and an outdoor unit temperature detection assembly; The indoor unit includes: an indoor unit heat exchanger, a third electronic expansion valve, an indoor unit fan, and an indoor unit temperature detection component; The hydraulic module includes: a refrigerant-water heat exchanger, a water pump, a water temperature detection sensor, a flow switch, a sixth solenoid valve, a seventh solenoid valve, and a fourth electronic expansion valve.

[0005] According to some embodiments of the present invention, the outdoor unit temperature detection component includes an exhaust temperature sensor, an ambient temperature sensor, a condenser temperature sensor, and an outdoor unit heat exchanger temperature sensor.

[0006] According to some embodiments of the present invention, the indoor unit temperature detection component includes an indoor unit ambient temperature sensor, an indoor unit heat exchanger middle temperature sensor, and an indoor unit heat exchanger outlet temperature sensor.

[0007] According to some embodiments of the present invention, the first switching device, the second switching device and the third switching device are four-way valves.

[0008] According to some embodiments of the present invention, the device further includes a switching valve for external connection of the outdoor unit, the switching valve comprising a liquid-side shut-off valve, a gas-side shut-off valve, and a hydraulic module shut-off valve; wherein, The liquid-side shut-off valve is connected to the liquid pipes of the indoor unit and the hydraulic module; The gas-side shut-off valve is connected to the gas pipe of the indoor unit; The shut-off valve of the hydraulic module is connected to the air pipe of the hydraulic module.

[0009] According to some embodiments of the present invention, the first switching device, the second switching device, and the third switching device are provided with an A interface, a B interface, a C interface, and a D interface.

[0010] According to some embodiments of the present invention, the three-pipe heat recovery multi-split system according to claim 1 is characterized in that the compressor is a variable frequency compressor, a fixed speed compressor, or a digital compressor.

[0011] A control method for a three-pipe multi-split air conditioning system according to a second aspect of the present invention includes the following steps: detecting the operating mode of the indoor unit; When the indoor unit is in cooling mode, the system is controlled to operate according to the first mode; When the indoor unit is in heating mode, the control system operates according to the second mode.

[0012] According to some embodiments of the present invention, the system is further configured to operate in a first mode as follows: the first switching device is powered off; the second switching device is powered on or off according to the demand for cooling, hot water production, and chilled water; the third switching device is powered on; the fourth electronic expansion valve of the hydraulic module for cooling is opened, the sixth solenoid valve is opened, and the seventh solenoid valve is closed; the fourth electronic expansion valve of the hydraulic module for heating is opened, the seventh solenoid valve is opened, and the sixth solenoid valve is closed; the fourth electronic expansion valve of the hydraulic module for shutdown is closed, the sixth solenoid valve is opened, and the seventh solenoid valve is closed.

[0013] According to some embodiments of the present invention, the system is further configured to operate in a second mode as follows: a first switching device is powered on; a second switching device is powered on or off according to the demand for cooling, hot water production, and chilled water; a third switching device is powered off; the fourth electronic expansion valve of the hydraulic module for cooling is opened, the seventh solenoid valve is opened, and the sixth solenoid valve is closed; the fourth electronic expansion valve of the hydraulic module for heating is opened, the seventh solenoid valve is closed, and the sixth solenoid valve is opened; the fourth electronic expansion valve of the hydraulic module for shutdown is closed, the seventh solenoid valve is opened, and the sixth solenoid valve is closed.

[0014] By adopting the technical solution of the present invention, the following advantages are achieved: 1. By optimizing the air conditioning system and control logic, regardless of the cooling or heating mode, one of the three pipes connecting the outdoor unit, indoor unit, and hydraulic module will always be connected to the compressor return port at a low pressure. This allows the liquid refrigerant remaining in the hydraulic module when the system is off to flow back to the compressor through the low-pressure pipe, preventing the system from running out of refrigerant or oil and ensuring the reliability of the system operation. 2. The system and control logic ensure that one of the three pipes of the multi-split system is always in the low-pressure side connected to the compressor return port, so that the refrigerant in the hydraulic module during standby or shutdown can be drawn away through the above-mentioned pipes, avoiding the expansion of the liquid refrigerant in the hydraulic module pipes due to changes in ambient temperature, which could damage the hydraulic module pipe system. 3. The system and control logic ensure that at least one of the three pipes in the multi-split system is always in a low-pressure state connected to the compressor's return port. This allows the hydraulic module in the system to still provide chilled water even in indoor heating mode, thus broadening the application range of the multi-split system. Simultaneously, it enables the recovery of cooling capacity, achieving energy conservation and emission reduction. 4. Through system and control logic, ensure that one of the three pipes of the multi-split system is always in low pressure connected to the compressor return port. In the air conditioning heating mode, as long as the hydraulic module in the chilled water mode is present, the cooling capacity of the chilled water can be recovered, increasing the evaporation area and delaying the frosting of the outdoor unit heat exchanger. 5. Simultaneously, under the condition of having chilled water in the hydraulic module, the outdoor unit can defrost without stopping, avoiding the reversal of the four-way valve controlling the indoor unit and the hydraulic module, ensuring that the indoor unit and the hot water hydraulic module are not affected, avoiding changes in indoor temperature and hydraulic module water temperature; it also avoids the noise caused by the reversal of the indoor four-way valve, improving system reliability and user experience. Attached Figure Description

[0015] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying 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.

[0016] Figure 1 This is a schematic diagram of the structure of the three-pipe multi-split air conditioning system provided by the present invention; Figure 2 The flowchart shows the control method for a three-pipe multi-unit air conditioning system provided by the present invention.

[0017] The diagram is labeled: 100 - Multi-split system; 1-Compressor, 2-High-pressure sensor, 3-Oil separator, 4-First switching device, 5-Second switching device, 6-Third switching device, 7-Finned heat exchanger, 8-Compressor cooling module, 9-Plate heat exchanger, 10-First electronic expansion valve, 11-Second electronic expansion valve, 12-Charging needle valve, 13-Gas-liquid separator, 14-Low-pressure switch, 15-First solenoid valve, 16-Second solenoid valve, 17-Third solenoid valve, 18-Fourth solenoid valve, 19-Fifth solenoid valve, and 20-Outdoor unit fan; 30-Indoor unit heat exchanger, 31-Third electronic expansion valve and 32-Indoor unit fan; 40-Refrigerant-water heat exchanger, 41-Water pump, 42-Water temperature sensor, 43-Flow switch, 44-Sixth solenoid valve, 45-Seventh solenoid valve and 46-Fourth electronic expansion valve; 50 - Liquid-side shut-off valve, 51 - Gas-side shut-off valve, and 52 - Hydraulic module shut-off valve. Detailed Implementation

[0018] Embodiments of the present invention are described in detail below. Examples of these embodiments are shown 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 are only used to explain the present invention, and should not be construed as limiting the present invention.

[0019] 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," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential," etc., indicating orientation or positional relationships, are based on the orientation or positional relationships shown in the accompanying drawings and are only for the convenience of describing the 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, and therefore should not be construed as a limitation of the invention. Furthermore, features defined with "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.

[0020] In the description of this invention, it should be noted that, unless otherwise explicitly 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 of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0021] This invention provides a three-pipe multi-split air conditioning system (100 units). Please refer to [link / reference needed]. Figure 1 As shown, the three-pipe multi-split air conditioner 100 system includes an outdoor unit, multiple indoor units, and multiple hydraulic modules, all connected by gas pipes, liquid pipes, and condensate pipes respectively. The outdoor unit includes: a compressor 1, a high-pressure sensor 2, an oil separator 3, a first switching device 4, a second switching device 5, a third switching device 6, a finned heat exchanger 7, a compressor heat dissipation module 8, a plate heat exchanger 9, a first electronic expansion valve 10, a second electronic expansion valve 11, a charging needle valve 12, a gas-liquid separator 13, a low-pressure switch 14, a first solenoid valve 15, a second solenoid valve 16, a third solenoid valve 17, a fourth solenoid valve 18, a fifth solenoid valve 19, an outdoor unit fan 20, and an outdoor unit temperature detection assembly; The indoor unit includes: an indoor unit heat exchanger 30, a third electronic expansion valve 31, an indoor unit fan 32, and an indoor unit temperature detection component; The hydraulic module includes: a chilled water heat exchanger 40, a water pump 41, a water temperature detection sensor 42, a flow switch 43, a sixth solenoid valve 44, a seventh solenoid valve 45, and a fourth electronic expansion valve 46.

[0022] The outdoor unit temperature detection component includes an exhaust temperature sensor, an ambient temperature sensor, a condenser temperature sensor, and an outdoor unit heat exchanger temperature sensor.

[0023] The indoor unit temperature detection component includes an indoor unit ambient temperature sensor, an indoor unit heat exchanger middle temperature sensor, and an indoor unit heat exchanger outlet temperature sensor.

[0024] The first switching device 4, the second switching device 5, and the third switching device 6 are four-way valves.

[0025] According to some embodiments of the present invention, the system further includes a switching valve for external connection of the outdoor unit, the switching valve comprising a liquid-side shut-off valve 50, a gas-side shut-off valve 51, and a hydraulic module shut-off valve 52; wherein, The liquid-side shut-off valve 50 is connected to the liquid pipe of the indoor unit and the hydraulic module; The gas-side shut-off valve 51 is connected to the gas pipe of the indoor unit; The hydraulic module shut-off valve 52 is connected to the air pipe of the hydraulic module.

[0026] The first switching device 4, the second switching device 5, and the third switching device 6 are equipped with interfaces A, B, C, and D.

[0027] According to claim 1, the three-pipe heat recovery multi-unit system 100 is characterized in that the compressor 1 is a variable frequency compressor 1, or a fixed speed compressor 1, or a digital compressor 1.

[0028] Therefore, by optimizing the air conditioning system, regardless of cooling or heating mode, one of the three pipes connecting the outdoor unit, indoor unit, and hydraulic module will always maintain a low-pressure state connected to the compressor 1's return port. This allows the liquid refrigerant remaining in the hydraulic module when the system is off to flow back to compressor 1 through the low-pressure pipe, preventing situations where the system is short of refrigerant or oil, and ensuring the reliability of system operation. Simultaneously, the system ensures that one of the three pipes in the multi-split system 100 is always connected to the low-pressure side of the compressor 1's return port. In the low pressure range, the refrigerant in the standby or stopped hydraulic module can be drawn away through the above-mentioned pipes, avoiding the expansion of the liquid refrigerant in the hydraulic module pipes due to changes in ambient temperature, which could damage the hydraulic module pipe system. In the multi-split 100 system, one of the three pipes is always in the low pressure range connected to the low pressure side of the compressor 1 return port, so that the hydraulic module in the system can still provide chilled water in the indoor unit heating mode, thus broadening the application range of the multi-split 100 system. Simultaneously, it achieves the recovery of cooling capacity, realizing energy conservation and emission reduction. In the multi-split 100 system, one of the three pipes is always in low pressure connected to the return port of compressor 1. This allows for the recovery of cooling capacity of the chilled water in the air conditioning heating mode, as long as the hydraulic module in the chilled water mode is present. This increases the evaporation area and delays the frosting of the outdoor unit's heat exchanger. At the same time, under the condition that the chilled water in the hydraulic module is present, the outdoor unit can be defrosted without stopping. This avoids the reversal of the four-way valve controlling the indoor unit and the hydraulic module, ensuring that the indoor unit and the hot water hydraulic module are not affected, avoiding changes in indoor temperature and hydraulic module water temperature. It also avoids the noise caused by the reversal of the four-way valve on the indoor side, improving system reliability and user experience.

[0029] The control method of a three-pipe multi-split air conditioner 100 system according to a second aspect embodiment of the present invention, with reference to Figure 2 The flowchart of the control method for a three-pipe multi-split air conditioner 100 system provided by the present invention includes the following steps: Step S100: Detect the operating mode of the indoor unit; Step S110: When the indoor unit is in cooling mode, control the system to operate according to the first mode; Step S120: When the indoor unit is in heating mode, control the system to operate in the second mode; The system is controlled to operate in the first mode as follows: the first switching device 4 is de-energized; the second switching device 5 is energized or de-energized according to the demand for cooling, hot water, and chilled water; the third switching device 6 is energized; the fourth electronic expansion valve 46 of the hydraulic module for cooling is opened, the sixth solenoid valve 44 is opened, and the seventh solenoid valve 45 is closed; the fourth electronic expansion valve 46 of the hydraulic module for heating is opened, the seventh solenoid valve 45 is opened, and the sixth solenoid valve 44 is closed; the fourth electronic expansion valve 46 of the hydraulic module is closed when the hydraulic module is shut down, the sixth solenoid valve 44 is opened, and the seventh solenoid valve 45 is closed.

[0030] In this embodiment, if the indoor unit is in cooling mode, the first switching device 4 is de-energized, with interfaces A and C connected, and interfaces B and D connected. At this time, the refrigerant state in the pipeline at the gas-side shut-off valve 51 is low-pressure gaseous refrigerant. The second switching device 5 is energized or de-energized according to the demand for cooling, hot water, and chilled water, thereby allowing the outdoor unit's heat exchanger to select as either an evaporator or a condenser. The third switching device 6 is energized, with interfaces A and B connected, and interfaces C and D connected. At this time, the refrigerant state in the pipeline at the hydraulic module shut-off valve 52 is high-pressure gaseous refrigerant. The cooling hydraulic module's electronic expansion valve opens, the sixth solenoid valve 44 opens, and the seventh solenoid valve 45 closes. The hot water hydraulic module's fourth electronic expansion valve 46 opens, the seventh solenoid valve 45 opens, and the sixth solenoid valve 44 closes. When the unit is off, the hydraulic module's fourth electronic expansion valve 46 closes, the sixth solenoid valve 44 opens, and the seventh solenoid valve 45 closes.

[0031] The system is controlled to operate in the second mode as follows: the first switching device 4 is powered on, the second switching device 5 is powered on or off according to the demand for cooling, hot water, and chilled water, the third switching device 6 is powered off, the fourth electronic expansion valve 46 of the hydraulic module for cooling is opened, the seventh solenoid valve 45 is opened, and the sixth solenoid valve 44 is closed; the fourth electronic expansion valve 46 of the hydraulic module for heating is opened, the seventh solenoid valve 45 is closed, and the sixth solenoid valve 44 is opened; the fourth electronic expansion valve 46 of the hydraulic module for shutdown is closed, the seventh solenoid valve 45 is opened, and the sixth solenoid valve 44 is closed.

[0032] In this embodiment, if the indoor unit is in heating mode, the first switching device 4 is powered on, with interfaces A and B connected, and interfaces C and D connected. At this time, the refrigerant state in the pipeline at the gas-side shut-off valve 51 is high-pressure gaseous refrigerant. The second switching device 5 is powered on or off according to the cooling and hot water demand, thereby allowing the outdoor unit's heat exchanger to select as either an evaporator or a condenser. The third switching device 6 is powered off, with interfaces A and C connected, and interfaces B and D connected. At this time, the refrigerant state in the pipeline at the hydraulic module shut-off valve 52 is low-pressure gaseous refrigerant. In hydraulic module cooling mode, the fourth electronic expansion valve 46 opens, the seventh solenoid valve 45 opens, and the sixth solenoid valve 44 closes. In hydraulic module heating mode, the fourth electronic expansion valve 46 opens, the seventh solenoid valve 45 closes, and the sixth solenoid valve 44 opens. In hydraulic module shutdown mode, the fourth electronic expansion valve 46 closes, the seventh solenoid valve 45 opens, and the sixth solenoid valve 44 closes.

[0033] In summary, by optimizing the control method of the air conditioning system, regardless of the cooling or heating mode, one of the three pipes connecting the outdoor unit, indoor unit, and hydraulic module will always maintain a low-pressure state connected to the compressor 1 return port. This allows the liquid refrigerant remaining in the hydraulic module when the system is off to flow back to compressor 1 through the low-pressure pipe, preventing situations where the system lacks refrigerant or oil, and ensuring the reliability of system operation. At the same time, the control logic ensures that one of the three pipes of the multi-split 100 system is always in a low-pressure state connected to the low-pressure side of the compressor 1 return port. This allows the refrigerant in the hydraulic module during standby or shutdown to be drawn away through the aforementioned pipe, preventing the liquid refrigerant remaining in the hydraulic module from expanding in the hydraulic module pipeline due to changes in ambient temperature, which could damage the hydraulic module pipeline system. The fact that one of the three pipes of the multi-split 100 system is always in a low-pressure state connected to the compressor 1 return port also allows the hydraulic module in the system to still have the potential to provide chilled water even when the indoor unit is in heating mode, thus broadening the application range of the multi-split 100 system. Simultaneously, it achieves the recovery of cooling capacity, realizing energy conservation and emission reduction. In the multi-split 100 system, one of the three pipes is always in low pressure connected to the return port of compressor 1. This allows for the recovery of cooling capacity of the chilled water in the air conditioning heating mode, as long as the hydraulic module in the chilled water mode is present. This increases the evaporation area and delays the frosting of the outdoor unit's heat exchanger. At the same time, under the condition that the chilled water in the hydraulic module is present, the outdoor unit can be defrosted without stopping. This avoids the reversal of the four-way valve controlling the indoor unit and the hydraulic module, ensuring that the indoor unit and the hot water hydraulic module are not affected, avoiding changes in indoor temperature and hydraulic module water temperature. It also avoids the noise caused by the reversal of the four-way valve on the indoor side, improving system reliability and user experience.

[0034] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0035] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A control method for a three-pipe multi-split air conditioning system, applied to a three-pipe multi-split air conditioning system, the three-pipe multi-split air conditioning system comprising an outdoor unit, multiple indoor units, and multiple hydraulic modules connected by gas pipes, liquid pipes, and condensate pipes respectively, characterized in that: The outdoor unit includes: a compressor (1), a high-pressure sensor (2), an oil separator (3), a first switching device (4), a second switching device (5), a third switching device (6), a finned heat exchanger (7), a gas-liquid separator (13), an outdoor unit fan (20), and an outdoor unit temperature detection assembly. The oil separator (3) is connected to the compressor (1). The indoor unit includes: an indoor unit heat exchanger (30), a third electronic expansion valve (31), an indoor unit fan (32), and an indoor unit temperature detection component. The indoor unit heat exchanger (30) is connected to the third electronic expansion valve (31). The hydraulic module includes: a refrigerant-water heat exchanger (40), a water pump (41), a water temperature detection sensor (42), a water flow switch (43), a sixth solenoid valve (44), a seventh solenoid valve (45), and a fourth electronic expansion valve (46). The fourth electronic expansion valve (46) is connected to one end of the refrigerant pipeline of the refrigerant-water heat exchanger (40), and the sixth solenoid valve (44) and the seventh solenoid valve (45) are respectively connected to the other end of the refrigerant pipeline of the refrigerant-water heat exchanger (40). The first switching device (4), the second switching device (5) and the third switching device (6) are four-way valves; The three-pipe multi-split air conditioning system also includes a switching valve for the outdoor unit's external connection, the switching valve including a liquid-side shut-off valve (50), a gas-side shut-off valve (51), and a hydraulic module shut-off valve (52); wherein, The liquid-side shut-off valve (50) is connected to the third electronic expansion valve (31) in the indoor unit and the fourth electronic expansion valve (46) in the hydraulic module, respectively. The gas-side shut-off valve (51) is connected to the indoor unit heat exchanger (30) in the indoor unit and the sixth solenoid valve (44) in the hydraulic module, respectively. The hydraulic module shut-off valve (52) is connected to the seventh solenoid valve (45) of the hydraulic module; The first switching device (4), the second switching device (5), and the third switching device (6) are provided with interfaces A, B, C, and D. All A interfaces are connected to the working fluid outlet of the compressor (1) via the oil separator (3); The B interface of the first switching device (4) is connected to the gas-side shut-off valve (51); The B interface of the second switching device (5) is connected to the compressor (1) via the gas-liquid separator (13); The B interface of the third switching device (6) is connected to the hydraulic module shut-off valve (52); The C interfaces of the first switching device (4) and the third switching device (6) are connected to the compressor (1) via the gas-liquid separator (13); The C interface of the second switching device (5) is connected to the liquid-side shut-off valve (50) via the finned heat exchanger (7); The D interfaces are all connected to the compressor (1) via the gas-liquid separator (13); The control method for the three-pipe multi-split air conditioning system includes the following steps: Detect the operating mode of the indoor unit; When the indoor unit is in cooling mode, the three-pipe multi-split system is controlled to operate in the first mode. When the indoor unit is in heating mode, the three-pipe multi-split air conditioning system is controlled to operate in the second mode. The control of the three-pipe multi-split air conditioning system to operate in the first mode is as follows: the first switching device (4) is de-energized, the second switching device (5) is energized or de-energized according to the demand for cooling, hot water and cooling water, and the third switching device (6) is energized; when the hydraulic module is cooling, the fourth electronic expansion valve (46) is opened, the sixth solenoid valve (44) is opened and the seventh solenoid valve (45) is closed; when the hydraulic module is heating, the fourth electronic expansion valve (46) is opened, the seventh solenoid valve (45) is opened and the sixth solenoid valve (44) is closed; when the hydraulic module is shut down, the fourth electronic expansion valve (46) is closed, the sixth solenoid valve (44) is opened and the seventh solenoid valve (45) is closed. The control of the three-pipe multi-split air conditioning system to operate in the second mode is as follows: the first switching device (4) is powered on, the second switching device (5) is powered on or off according to the demand for cooling, hot water and cooling water, and the third switching device (6) is powered off; when the hydraulic module is cooling, the fourth electronic expansion valve (46) is opened, the seventh solenoid valve (45) is opened and the sixth solenoid valve (44) is closed; when the hydraulic module is heating, the fourth electronic expansion valve (46) is opened, the seventh solenoid valve (45) is closed and the sixth solenoid valve (44) is opened; when the hydraulic module is shut down, the fourth electronic expansion valve (46) is closed, the seventh solenoid valve (45) is opened and the sixth solenoid valve (44) is closed.

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