A three-pipe multi-connected system and control method

Abstract

The application provides a three-pipe multi-connected system and a control method. The three-pipe multi-connected system comprises a high-pressure gas pipe electromagnetic valve for controlling opening and closing of the high-pressure gas pipe; a main gas pipe switching bypass pipe for providing a bypass path; and a main gas pipe switching electromagnetic valve for controlling opening and closing of the bypass pipe. The control method of the three-pipe multi-connected system comprises the following steps: detecting a refrigeration load when operating in a pure refrigeration mode; if the refrigeration load reaches a first threshold value, closing the high-pressure gas pipe electromagnetic valve and opening the main gas pipe switching electromagnetic valve; opening low-pressure side switching valves and high-pressure side switching valves connected to indoor units in a branch box; and making low-pressure gas refrigerants evaporated in indoor heat exchangers flow to both sides of the low-pressure main gas pipe and the high-pressure main gas pipe, and then flow to the low-pressure gas pipe through the main gas pipe switching electromagnetic valve and be sucked into a compressor. The application solves the problem of how to prevent the refrigeration capacity of the three-pipe multi-connected system from decreasing when long pipes are installed.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of air conditioning, in particular to a three-pipe multi-connected system and a control method. BACKGROUND

[0002] With the continuous development of science and technology, air conditioner technology is also innovating, and there is a three-pipe multi-connected system that faces technical challenges when installed at a long distance. When the outdoor unit and the indoor unit are far apart (for example, 200 meters), the refrigerant density of the low-pressure main gas pipe becomes smaller, and the flow rate becomes faster, resulting in a significant increase in pressure drop (for example, more than 4 bars). The increase in pressure drop will cause the evaporation temperature of the indoor heat exchanger to rise, thereby reducing the evaporation capacity and overall refrigeration capacity (for example, more than 50% reduction). The traditional solution is to reduce the refrigerant flow rate by expanding the pipe diameter to reduce the pressure drop. Expanding the pipe diameter will increase the material and construction costs, especially when installed at a long distance. After expanding the pipe diameter, the refrigerant flow rate is reduced, which may cause the compressor oil to be unable to return effectively, ultimately resulting in insufficient compressor oil and damaging the compressor. Therefore, it is difficult to solve the technical problem of solving the pressure drop problem when installed at a long distance while considering the stability and reliability of the system. SUMMARY

[0003] The problem solved by the present application is how to prevent the refrigeration capacity of the three-pipe multi-connected system from decreasing when installed at a long distance.

[0004] To solve the above problems, the present application provides a three-pipe multi-connected system, comprising: an outdoor unit, a distribution box and an indoor unit, wherein the outdoor unit comprises: a compressor, a compressor discharge pipe, a compressor suction pipe, a four-way valve high-pressure main gas pipe connection part and a low-pressure main gas pipe connection part; the distribution box comprises a high-pressure side switching valve and a low-pressure side switching valve; the indoor unit comprises an indoor heat exchanger and an indoor expansion valve; a high-pressure main gas pipe is provided between the high-pressure main gas pipe connection part and the high-pressure side switching valve; a low-pressure main gas pipe is provided between the low-pressure main gas pipe connection part and the low-pressure side switching valve; wherein a high-pressure gas pipe electromagnetic valve is installed on the high-pressure gas pipe between the compressor discharge pipe and the high-pressure main gas pipe connection part, and the high-pressure gas pipe electromagnetic valve is used to control the opening and closing of the high-pressure gas pipe; the high-pressure gas pipe between the high-pressure gas pipe electromagnetic valve and the high-pressure main gas pipe connection part, and the low-pressure gas pipe between the four-way valve and the low-pressure main gas pipe connection part, are provided with a main gas pipe switching bypass pipe, and the main gas pipe switching bypass pipe provides a bypass path; a main gas pipe switching electromagnetic valve is installed in the main gas pipe switching bypass pipe, and the main gas pipe switching electromagnetic valve is used to control the opening and closing of the bypass pipe.

[0005] The technical effects achieved by the technical scheme are as follows: the high-pressure gas pipe electromagnetic valve installed on the high-pressure gas pipe can flexibly control the opening and closing of the high-pressure gas pipe, so that the system can adjust the working state according to the actual demand; the design of the main gas pipe switching bypass pipe and the main gas pipe switching electromagnetic valve provides an additional bypass path, which not only can maintain the normal operation of the system in some specific conditions, but also can optimize the air flow distribution in different working conditions, and improve the adaptability and reliability of the system.

[0006] Further, a compressor suction pressure sensor for measuring the compressor suction pressure is installed on the compressor suction pipe; and an indoor low-pressure gas pipe pressure sensor for measuring the indoor low-pressure gas pipe pressure is installed on the indoor machine side of the low-pressure main gas pipe.

[0007] The technical effects achieved by the technical scheme are as follows: the real-time monitoring of the key pressure values by the sensors can timely understand the running state of the system; the control based on the actually measured data improves the control accuracy and reliability.

[0008] Further, the evaporation temperature is measured by an evaporation temperature sensor installed on the refrigerant pipe between the indoor expansion valve of the indoor machine and the central part of the indoor heat exchanger.

[0009] The technical effects achieved by the technical scheme are as follows: the indirect measurement of the low-pressure gas pipe pressure by the evaporation temperature simplifies the layout of the sensors; the control based on the saturation pressure calculated based on the evaporation temperature improves the control accuracy.

[0010] To solve the above problems, the application provides a control method of a three-pipe multi-split system, which is realized by any one of the above three-pipe multi-split systems, and the three-pipe multi-split system comprises an outdoor unit, a branch box and an indoor unit, wherein the outdoor unit comprises a compressor, a compressor discharge pipe, a compressor suction pipe, a four-way valve, a high-pressure main gas pipe connecting part and a low-pressure main gas pipe connecting part; the branch box comprises a high-pressure side switching valve and a low-pressure side switching valve; the indoor unit comprises an indoor heat exchanger and an indoor expansion valve; a high-pressure main gas pipe is arranged between the high-pressure main gas pipe connecting part and the high-pressure side switching valve; a low-pressure main gas pipe is arranged between the low-pressure main gas pipe connecting part and the low-pressure side switching valve; the control method of the three-pipe multi-split system comprises the following steps: detecting a refrigeration load when operating in a pure refrigeration mode; if it is detected that the refrigeration load reaches a first threshold value, closing a high-pressure gas pipe electromagnetic valve and opening a main gas pipe switching electromagnetic valve; opening a low-pressure side switching valve and a high-pressure side switching valve in the branch box connected to a refrigeration indoor unit; making low-pressure gas refrigerant evaporated in the indoor heat exchanger flow to both sides of the low-pressure main gas pipe and the high-pressure main gas pipe, and flow to the low-pressure gas pipe through the main gas pipe switching electromagnetic valve; and making the low-pressure gas refrigerant flowing through the low-pressure main gas pipe and the high-pressure main gas pipe merge in the low-pressure gas pipe and be sucked into the compressor.

[0011] The technical effects achieved after the technical scheme are as follows: through cooperation of the high-pressure gas pipe electromagnetic valve and the main gas pipe switching electromagnetic valve, the refrigerant flow path can be adjusted according to actual operation conditions, so that the system performance is optimized; when the refrigeration load is large, the pressure drop of the low-pressure main gas pipe can be effectively reduced through the bypass path, and the refrigeration efficiency is improved; the installed control valve improves the additional control means and enhances the flexibility and adaptability of the system; through reducing the pressure drop of the low-pressure main gas pipe, the evaporation temperature in the indoor heat exchanger can be prevented from rising, so that the refrigeration capacity is maintained at a high level; and the system stability and reliability under high load are ensured.

[0012] Further, the control method of the three-pipe multi-split system further includes: if it is detected that the refrigeration load does not reach the first threshold, opening the high-pressure gas pipe electromagnetic valve, closing the main gas pipe switching electromagnetic valve, opening the low-pressure side switching valve connected to the refrigeration indoor unit in the branch box, and closing the high-pressure side switching valve; and making the evaporated low-pressure gas refrigerant in the indoor heat exchanger of the refrigeration indoor unit only flow to the low-pressure main gas pipe.

[0013] The technical effects achieved after the technical scheme are as follows: under low refrigeration load, maintaining the traditional flow path can prevent oil retention caused by too slow flow rate; the lubrication of the compressor is ensured, and mechanical wear caused by insufficient oil amount is avoided; under low load, the system can operate with lower energy consumption, and the energy efficiency is improved.

[0014] Further, a compressor suction pressure sensor is installed on the compressor suction pipe for measuring the compressor suction pressure; and an indoor low-pressure gas pipe pressure sensor is installed at the indoor unit measurement position of the low-pressure main gas pipe for measuring the indoor low-pressure gas pipe pressure.

[0015] The technical effects achieved after the technical scheme are as follows: through real-time monitoring of key pressure values by the sensors, the operation condition of the system can be understood in time; control is performed based on actually measured data, and the control accuracy and reliability are improved; real-time monitoring helps to discover potential faults early, and the reliability and maintenance efficiency of the system are improved.

[0016] Further, the control method of the three-pipe multi-split system includes the following steps: calculating the low-pressure gas pipe pressure drop; if the low-pressure gas pipe pressure drop reaches a preset threshold, closing the high-pressure gas pipe electromagnetic valve, opening the main gas pipe switching electromagnetic valve, opening the low-pressure side switching valve connected to the refrigeration indoor unit in the branch box, and closing the high-pressure side switching valve; and if the low-pressure gas pipe pressure drop does not reach the preset threshold, opening the high-pressure gas pipe electromagnetic valve, closing the main gas pipe switching electromagnetic valve, opening the low-pressure side switching valve connected to the refrigeration indoor unit in the branch box, and closing the high-pressure side switching valve.

[0017] The technical effects achieved by the technical scheme are as follows: the pressure drop of the low-pressure gas pipe is effectively reduced by timely adjusting the flow path, the refrigeration efficiency is improved, the system can still operate efficiently under high load, and the overall performance is improved; the reduction of the pressure drop helps to maintain a lower evaporation temperature and maintain good refrigeration effect.

[0018] Further, an evaporation temperature sensor is installed on the refrigerant pipe between the indoor expansion valve of the indoor unit and the central part of the indoor heat exchanger to measure the evaporation temperature.

[0019] The technical effects achieved by the technical scheme are as follows: the low-pressure gas pipe pressure is indirectly measured by the evaporation temperature, and the sensor layout is simplified; the control is based on the saturation pressure calculated from the evaporation temperature, and the accuracy of the control is improved.

[0020] Further, the control method of the three-pipe multi-split system includes the following steps: calculating the evaporation pressure using the saturation pressure formula of the refrigerant, regarding the evaporation pressure as the indoor low-pressure gas pipe pressure; calculating the low-pressure pipe pressure drop; if the low-pressure gas pipe pressure drop reaches a preset threshold, closing the high-pressure gas pipe electromagnetic valve, opening the main gas pipe switching valve, and opening the low-pressure side switching valve and the high-pressure switching valve in the branch box connected to the refrigeration indoor unit.

[0021] The technical effects achieved by the technical scheme are as follows: ensuring normal operation of the system under high load, improving system efficiency; ensuring efficient operation of the system under high load, improving overall performance.

[0022] Further, if the low-pressure gas pipe pressure drop does not reach the preset threshold, the high-pressure gas pipe electromagnetic valve is opened, the main gas pipe switching electromagnetic valve is closed, and the low-pressure side switching valve connected to the refrigeration indoor unit in the branch box is opened, and the high-pressure side switching valve is closed.

[0023] The technical effects achieved by the technical scheme are as follows: ensuring normal operation of the system under low load, improving system efficiency; under low load, the system can operate with lower energy consumption, improving energy efficiency.

[0024] In summary, the above-mentioned technical schemes of the present application can have one or more of the following advantages or beneficial effects: i) the control valve precisely controls each pipe, and the system flexibility is improved. ii) the control accuracy is optimized with the help of various sensors in the system. iii) the service life of the components in the system is prolonged by precisely controlling the working state of the compressor. iv) this design allows fault diagnosis and maintenance of individual components without stopping the entire system, which not only reduces downtime but also reduces maintenance costs. v) more effective control is achieved by precisely calculating the refrigeration load. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1A first structure schematic diagram of a three-pipe multi-connected system in an embodiment of the present application;

[0026] Figure 2 A first flow chart of a three-pipe multi-connected system control method in an embodiment of the present application;

[0027] Figure 3 A second structure schematic diagram of a three-pipe multi-connected system in an embodiment of the present application;

[0028] Figure 4 A second flow chart of a three-pipe multi-connected system control method in an embodiment of the present application;

[0029] Figure 5 A third structure schematic diagram of a three-pipe multi-connected system in an embodiment of the present application;

[0030] Figure 6 A third flow chart of a three-pipe multi-connected system control method in an embodiment of the present application.

[0031] Explanation of reference signs:

[0032] 100-three-pipe multi-connected system; 110-outdoor unit; 111-high pressure gas pipe electromagnetic valve; 112-four-way valve; 113-main gas pipe switching electromagnetic valve; 114-main gas pipe switching bypass pipe; 115-compressor discharge pipe; 116-compressor suction pipe; 117-compressor; 118-high pressure main gas pipe connecting part; 119-low pressure main gas pipe connecting part; 120-distribution box; 121-low pressure side switching valve; 122-high pressure side switching valve; 130-indoor unit; 131-indoor heat exchanger; 132-indoor expansion valve; 140-high pressure main gas pipe; 150-low pressure main gas pipe; 160-compressor suction pressure sensor; 170-indoor side low pressure gas pipe pressure sensor; 180-evaporation temperature sensor; 190-main liquid pipe. DETAILED DESCRIPTION

[0033] The present application aims to provide a three-pipe multi-connected system and control method for realizing how to prevent the refrigeration capacity of a three-pipe multi-connected system from decreasing when long pipes are installed.

[0034] In order to make the above objectives, features and advantages of the present application more obvious and easy to understand, the specific embodiments of the present application are described in detail below with reference to the drawings.

[0035] Reference is made to Figure 1The application provides a three-tube multi-connected system 100, comprising an outdoor unit 110, a branch box 120 and an indoor unit 130, wherein the outdoor unit 110 comprises a compressor 117, a compressor exhaust pipe 115, a compressor suction pipe 116, a four-way valve 112, a high-pressure main gas pipe connecting part 118 and a low-pressure main gas pipe connecting part 119; the branch box 120 comprises a high-pressure side switch valve 122 and a low-pressure side switch valve 121; the indoor unit 130 comprises an indoor heat exchanger 131 and an indoor expansion valve 132; a high-pressure main gas pipe 140 is arranged between the high-pressure main gas pipe connecting part 118 and the high-pressure side switch valve 122; a low-pressure main gas pipe 150 is arranged between the low-pressure main gas pipe connecting part 119 and the low-pressure side switch valve 121; wherein a high-pressure gas pipe electromagnetic valve 111 is arranged on the high-pressure gas pipe between the compressor exhaust pipe 115 and the high-pressure main gas pipe connecting part 118, and the high-pressure gas pipe electromagnetic valve 111 is used for controlling the opening and closing of the high-pressure gas pipe; a main gas pipe switch bypass pipe 114 is arranged on the high-pressure gas pipe between the high-pressure gas pipe electromagnetic valve 111 and the high-pressure main gas pipe connecting part 118, a low-pressure gas pipe between the four-way valve 112 and the low-pressure main gas pipe connecting part 119, and the main gas pipe switch bypass pipe 114 provides a bypass path; a main gas pipe switch electromagnetic valve 113 is arranged in the main gas pipe switch bypass pipe 114, and the main gas pipe switch electromagnetic valve 113 is used for controlling the opening and closing of the bypass pipe; the four-way valve 112 is connected with the indoor unit 130 through a main liquid pipe 190.

[0036] In the embodiment, the high-pressure gas pipe electromagnetic valve 111 is arranged on the high-pressure gas pipe, so that the opening and closing of the high-pressure gas pipe can be flexibly controlled, and the system can adjust the working state according to the actual demand; the design of the main gas pipe switch bypass pipe 114 and the main gas pipe switch electromagnetic valve 113 provides an additional bypass path, which not only can maintain the normal operation of the system in some specific conditions, but also can optimize the air flow distribution in different working conditions, and improve the adaptability and reliability of the system.

[0037] Specifically, this is a structural diagram of the first method. In the three-tube multi-connected system of the first invention, a high-pressure gas pipe electromagnetic valve 111 is arranged on the high-pressure gas pipe between the compressor exhaust pipe 115 and the high-pressure main gas pipe connecting part 118; a main gas pipe switch bypass pipe 114 is arranged, ranging from the high-pressure gas pipe between the high-pressure gas pipe electromagnetic valve 111 and the high-pressure main gas pipe connecting part 118 to the low-pressure gas pipe between the four-way valve 112 and the low-pressure main gas pipe connecting part 119. Then a main gas pipe switch electromagnetic valve 113 is arranged in the main gas pipe switch bypass pipe 114.

[0038] Referring to Figure 3 A compressor suction pressure sensor 160 for measuring the compressor suction pressure is arranged on the compressor suction pipe 116; an indoor side low-pressure gas pipe pressure sensor 170 for measuring the indoor side low-pressure gas pipe pressure is arranged on the indoor unit 130 side of the low-pressure main gas pipe.

[0039] In this embodiment, the key pressure values are monitored in real time by the sensors, so that the running condition of the system can be known in time; the control is based on the actually measured data, so that the precision and reliability of the control are improved.

[0040] Specifically, the compressor 117 suction pressure sensor 160 is installed on the compressor suction pipe 116; the indoor side low pressure gas pipe pressure sensor 170 is installed between the low pressure main gas pipe and the low pressure side switching valve 121; the pressure value is monitored in real time, the running condition of the system is known in real time, and the refrigerant circulation is controlled in time.

[0041] Referring to Figure 5 , the evaporation temperature is measured by the evaporation temperature sensor 180 installed on the refrigerant pipe between the indoor expansion valve 132 of the indoor unit 130 and the central part of the indoor heat exchanger 131.

[0042] In this embodiment, the low pressure gas pipe pressure is indirectly measured by the evaporation temperature, so that the layout of the sensor is simplified; the control is based on the saturated pressure calculated based on the evaporation temperature, so that the accuracy of the control is improved.

[0043] Specifically, the evaporation temperature sensor 180 is installed on the refrigerant pipe between the indoor expansion valve 132 of the indoor unit 130 and the central part of the indoor heat exchanger 131, the temperature is monitored in real time, and the refrigerant circulation is macroscopically regulated and controlled.

[0044] Referring to Figure 1 and Figure 2The application provides a control method of a three-tube multi-connected system 100, which is realized by the three-tube multi-connected system, and the three-tube multi-connected system 100 comprises an outdoor unit 110, a branch box 120 and an indoor unit 130. The outdoor unit 110 comprises a compressor 117, a compressor exhaust pipe 115, a compressor suction pipe 116, a four-way valve 112, a high-pressure main gas pipe connecting part 118 and a low-pressure main gas pipe connecting part 119. The branch box 120 comprises a high-pressure side switching valve 122 and a low-pressure side switching valve 121. The indoor unit 130 comprises an indoor heat exchanger 131 and an indoor expansion valve 132. The high-pressure main gas pipe connecting part 118 is provided with a high-pressure main gas pipe 140 between the high-pressure side switching valve 122. The low-pressure main gas pipe connecting part 119 is provided with a low-pressure main gas pipe 150 between the low-pressure side switching valve 121. The control method of the three-tube multi-connected system 100 comprises the following steps. When the system is in a pure refrigeration mode, the refrigeration load is detected. When the refrigeration load reaches a first threshold value, the high-pressure gas pipe electromagnetic valve 111 is closed, and the main gas pipe switching electromagnetic valve 113 is opened. The low-pressure side switching valve 121 and the high-pressure side switching valve 122 in the branch box 120 connected to the refrigeration indoor unit 130 are opened. The low-pressure gas refrigerant evaporated in the indoor heat exchanger 131 flows to both sides of the low-pressure main gas pipe 150 and the high-pressure main gas pipe 140, and flows to the low-pressure gas pipe through the main gas pipe switching electromagnetic valve 113. The low-pressure gas refrigerant flowing through the low-pressure main gas pipe 150 and the high-pressure main gas pipe 140 is merged in the low-pressure gas pipe and is sucked into the compressor 117.

[0045] In the embodiment, the cooperation of the high-pressure gas pipe electromagnetic valve 111 and the main gas pipe switching electromagnetic valve 113 can adjust the refrigerant flow path according to the actual operating conditions, so as to optimize the system performance. When the refrigeration load is large, the bypass path can effectively reduce the pressure drop of the low-pressure main gas pipe 150 and improve the refrigeration efficiency. The installed control valve improves the additional control means and enhances the flexibility and adaptability of the system. By reducing the pressure drop of the low-pressure main gas pipe 150, the evaporation temperature in the indoor heat exchanger 131 can be prevented from rising, so as to maintain a high refrigeration capacity. The stability and reliability of the system under high load are ensured.

[0046] Specifically, referring to Figure 1 and Figure 2 , this is the first method. When the pure refrigeration operation is performed, the refrigeration load is detected. If the load is large, the high-pressure gas pipe electromagnetic valve 111 is closed, and the main gas pipe switching electromagnetic valve 113 is opened. At the same time, the low-pressure side switching valve 121 and the high-pressure side switching valve 122 in the branch box connected to the refrigeration indoor unit 130 are opened. Then, the ratio of the refrigeration load to the refrigeration indoor unit 130 operation capacity is determined. The formula for calculating the pressure drop is as follows

Formula 1

[0047]

Formula 1

[0048] △

[0049] △ : pressure drop [bar]

[0050] : pipe friction coefficient [-]

[0051] : pipe length [m]

[0052] : refrigerant density [kg / m3]

[0053] V: refrigerant flow rate [m / s]

[0054] : pipe inner diameter [m]

[0055] Preferably, the upper limit of the number of revolutions of the compressor 117 is 120 rps, and the number of revolutions of the compressor 117 is determined to be the cooling load when the number of revolutions of the compressor 117 is 84 rps or more.

[0056] Preferably, referring to Figure 3 , the low-pressure gas refrigerant evaporated in the indoor heat exchanger 131 of the cooling indoor unit 130 flows to both the low-pressure main gas pipe 150 and the high-pressure main gas pipe 140 and to the outdoor unit 110. Since the high-pressure gas pipe electromagnetic valve 111 is closed, the low-pressure gas refrigerant flowing through the high-pressure main gas pipe 140 flows to the low-pressure gas pipe through the main gas pipe switching electromagnetic valve 113. Here, the low-pressure gas refrigerant is mixed with the low-pressure gas refrigerant flowing through the low-pressure main gas pipe 150 and is sucked into the compressor 117. As a result, the flow rate of the refrigerant is slower than when the low-pressure gas refrigerant flows through only the low-pressure main gas pipe 150. Thus, the pressure drop in the low-pressure main gas pipe 150 can be reduced. For example, when the inner diameter of the low-pressure main gas pipe 150 is φ 26.6 mm and the inner diameter of the high-pressure main gas pipe 140 is φ 17.1 mm, the flow rate of the refrigerant in the low-pressure main gas pipe 150 can be slowed down by 19%. Finally, the pressure drop is reduced by 42%. Thus, when the outdoor unit 110 is installed far from the indoor unit 130, an increase in the pressure drop due to a large flow rate of the refrigerant in the low-pressure main gas pipe 150 can be prevented. Thus, a decrease in the cooling capacity due to an increase in the evaporation temperature in the indoor heat exchanger 131 can be prevented.

[0057] Preferably, referring to Figure 1 and Figure 2 , the control method of the three-pipe multi VRF system further includes: if it is detected that the cooling load does not reach the first threshold, opening the high-pressure gas pipe electromagnetic valve 111 and closing the main gas pipe switching electromagnetic valve 113; opening the low-pressure side switching valve 121 of the branch box 120 connected to the cooling indoor unit 130 and closing the high-pressure side switching valve 122; and causing the low-pressure gas refrigerant evaporated in the indoor heat exchanger 131 of the cooling indoor unit 130 to flow to only the low-pressure main gas pipe 150.

[0058] ​In this embodiment, under low refrigeration load, maintaining the traditional flow path can prevent oil retention problems caused by slow flow rate; ensure the lubrication of the compressor 117, avoid mechanical wear caused by insufficient oil; under low load, the system can run with lower energy consumption, improve energy efficiency.

[0059] Preferably, referring to Figure 4 When the refrigeration load is detected, open the high-pressure gas pipe electromagnetic valve 111, and close the main gas pipe switching electromagnetic valve 113. At the same time, open the low-pressure side switching valve 121 in the branch box connected to the indoor unit 130, and close the high-pressure side switching valve 122. After the above actions, as shown in Figure 4 The low-pressure gas refrigerant evaporated in the indoor heat exchanger 131 of the indoor unit 130 only flows to the low-pressure main gas pipe 150, and the refrigerant flow rate of the main gas pipe does not slow down. Therefore, oil retention and insufficient oil in the compressor 117 caused by slow refrigerant flow rate in the low-pressure main gas pipe 150 can be prevented.

[0060] Referring to Figure 3 and Figure 4 A compressor suction pressure sensor 160 is installed on the compressor suction pipe 116 to measure the compressor suction pressure; an indoor low-pressure gas pipe pressure sensor 170 is installed at the indoor unit 130 side of the low-pressure main gas pipe 150 to measure the indoor low-pressure gas pipe pressure.

[0061] In this embodiment, by real-time monitoring of key pressure values, the system's operating conditions can be understood in a timely manner; based on actual measurement data, the control accuracy and reliability are improved; real-time monitoring helps to discover potential faults early, and improves the reliability and maintenance efficiency of the system.

[0062] Specifically, referring to Figure 3 and Figure 4 This is the second method. A compressor suction pressure sensor 160 is installed on the compressor suction pipe 116 to measure the compressor suction pressure At the same time, an indoor low-pressure gas pipe pressure sensor 170 is installed at the indoor unit 130 side of the low-pressure main gas pipe 150 to measure the indoor low-pressure gas pipe pressure Here, the indoor low-pressure gas pipe pressure sensor 170 can be installed inside the branch box or outside. When performing pure refrigeration operation, the low-pressure gas pipe pressure drop Δ is calculated by the compressor suction pressure and the indoor low-pressure gas pipe pressure according to the following

Formula 2

[0063]

Formula 2

[0064] Δ = -

[0065] △ : low pressure gas pipe pressure drop [bar]

[0066] : compressor suction pressure [bar]

[0067] : indoor low pressure gas pipe pressure [bar]

[0068] See Figure 1 and Figure 2 , the control method of the three-tube multi-connected system comprises the following steps: calculating the low pressure gas pipe pressure drop; if the low pressure gas pipe pressure drop reaches a preset threshold, closing the high pressure gas pipe electromagnetic valve 111, opening the main gas pipe switching electromagnetic valve 113, and opening the low pressure side switching valve 121 and the high pressure side switching valve 122 in the branch box 120 connected to the cold indoor unit 130; if the low pressure gas pipe pressure drop does not reach the preset threshold, opening the high pressure gas pipe electromagnetic valve 111, closing the main gas pipe switching electromagnetic valve 113, and opening the low pressure side switching valve 121 in the branch box 120 connected to the refrigeration indoor unit 130, and closing the high pressure side switching valve 122.

[0069] In this embodiment, by timely adjusting the flow path, the pressure drop of the low pressure gas pipe is effectively reduced, the refrigeration efficiency is improved; it is ensured that the system can still operate efficiently under high load, and the overall performance is improved; reducing the pressure drop helps to maintain a lower evaporation temperature and maintain good refrigeration effect.

[0070] Specifically, when the calculated △ reaches a certain value, for example, more than 1 bar, the high pressure gas pipe electromagnetic valve 111 is closed, and the main gas pipe switching electromagnetic valve 113 is opened. At the same time, the low pressure side switching valve 121 and the high pressure side switching valve 122 in the branch box connected to the refrigeration indoor unit 130 are also opened. Through the above actions, the same effect as when the refrigeration load is large in the first invention can be achieved, that is, to prevent the refrigeration capacity from being reduced due to the increase of the evaporation temperature in the indoor heat exchanger 131.

[0071] When the calculated △ does not reach a certain value, for example, less than 1 bar, the high pressure gas pipe electromagnetic valve 111 is opened, and the main gas pipe switching electromagnetic valve 113 is closed. At the same time, the low pressure side switching valve 121 in the branch box connected to the refrigeration indoor unit 130 is opened, and the high pressure side switching valve 122 is closed. Through the above actions, the same effect as when the refrigeration load is small in the first invention can be achieved, that is, to prevent oil retention and insufficient oil in the compressor 117 caused by the slow flow rate of the low pressure main gas pipe 150.

[0072] In addition, since the low-pressure gas pipe pressure increase is not calculated from the refrigeration load or the number of revolutions of the compressor 117, but is calculated from the measured value of the pressure, the determination accuracy of the low-pressure gas pipe pressure increase can be improved. Thus, it is possible to prevent a decrease in the refrigeration capacity due to a large low-pressure gas pipe pressure increase, or a decrease in the oil amount of the compressor 117 due to a decrease in the refrigerant flow rate of the low-pressure main gas pipe 150.

[0073] Referring to Figure 1 and Figure 2 An evaporation temperature sensor 180 is installed on the refrigerant pipe between the indoor expansion valve 132 of the indoor unit 130 and the central portion of the indoor heat exchanger 131, and measures the evaporation temperature.

[0074] In this embodiment, the low-pressure gas pipe pressure is indirectly measured by the evaporation temperature, and the sensor layout is simplified. The control is performed based on the saturation pressure calculated from the evaporation temperature, and the accuracy of the control is improved.

[0075] Specifically, referring to Figure 5 and Figure 6 this is the third method. The evaporation pressure is calculated, and this pressure is regarded as the indoor-side low-pressure gas pipe pressure. This value is obtained because the indoor heat exchanger 131 in which evaporation is performed is close to the indoor-side low-pressure gas pipe, and the pressure drop is small to the extent that it can be ignored. The evaporation pressure is measured from the evaporation temperature, and the saturation pressure of the evaporation temperature is regarded as the evaporation pressure. For example, the saturation pressure of the refrigerant R410A is calculated from the refrigerant temperature using the general approximation formula shown in the following

Formula 3

[0076]

Formula 3

[0077] = 0.050 + 0.2024 + 7.2242

[0078] : saturation temperature [bar]

[0079] : refrigerant temperature [°C]

[0080] Preferably, the same effects as those of the first and second methods can be obtained by the above operation, that is, it is possible to prevent a decrease in the refrigeration capacity due to an increase in the evaporation temperature in the indoor heat exchanger 131. It is also possible to prevent the phenomenon of oil stagnation and a decrease in the oil amount of the compressor 117 due to a decrease in the refrigerant flow rate of the low-pressure main gas pipe 150.

[0081] Referring to Figure 5 and Figure 6The control method of the three-tube multi-connected system includes the following steps: calculating the evaporation pressure using a saturated pressure formula of refrigerant, taking the evaporation pressure as the indoor low-pressure gas pipe pressure; calculating the low-pressure pipe pressure drop; if the low-pressure gas pipe pressure drop reaches a preset threshold, closing the high-pressure gas pipe electromagnetic valve 111, opening the main gas pipe switching valve, and opening the low-pressure side switching valve 121 and the high-pressure switching valve in the branch box 120 connected to the refrigeration indoor unit 130;

[0082] In this embodiment, the system is ensured to operate normally under high load or low load, and the system efficiency is improved; the system is ensured to operate efficiently under high load, and the overall performance is improved; under low load, the system can operate with lower energy consumption, and the energy efficiency is improved.

[0083] Specifically, in the third inventive mode, the evaporation pressure is calculated, and the pressure is taken as the indoor low-pressure gas pipe pressure This is because the indoor heat exchanger 131 performing the evaporation operation is close to the indoor low-pressure gas pipe, and the pressure drop is small enough to be ignored. The evaporation pressure is measured by measuring the evaporation temperature, which is the temperature of the refrigerant at the outlet of the indoor expansion valve 132. The saturated pressure of the refrigerant is taken as the evaporation pressure. The calculation of the saturated pressure uses a general approximation formula similar to

Formula 4

[0084] Referring to Figure 5 and Figure 6 , if the low-pressure gas pipe pressure drop does not reach the preset threshold, the high-pressure gas pipe electromagnetic valve 111 is opened, the main gas pipe switching electromagnetic valve 113 is closed, and the low-pressure side switching valve 121 of the branch box 120 connected to the refrigeration indoor unit 130 is opened, and the high-pressure side switching valve 122 is closed.

[0085] In this embodiment, the system is ensured to operate normally under low load, and the system efficiency is improved; under low load, the system can operate with lower energy consumption, and the energy efficiency is improved.

[0086] When the present application is used for pure refrigeration operation, the operation capacity ratio of the refrigeration indoor unit 130 to the outdoor unit capacity is detected [%] as follows

Formula 4

[0087]

Formula 4

[0088]

[0089] : Outdoor unit operating capacity [HP]

[0090] : Total capacity of refrigeration indoor units [HP]

[0091] : operating capacity ratio [%]

[0092] Specifically, the refrigeration load can be determined by the number of revolutions of the compressor 117 [rps].

[0093] While the application has been disclosed with reference to the above embodiment, the application is not limited to the details shown. Any modification and changes along with other implementations can occur to one skilled in the art without departing from the spirit and scope of the application. Therefore, the scope of the application should be limited only by the appended claims.

Claims

1. A three-pipe multi-split air conditioning system, characterized in that, include: The system comprises an outdoor unit, a distribution box, and an indoor unit. The outdoor unit includes a compressor, a compressor discharge pipe, a compressor suction pipe, a four-way valve, a high-pressure main gas pipe connection, and a low-pressure main gas pipe connection. The distribution box includes a high-pressure side switching valve and a low-pressure side switching valve. The indoor unit includes an indoor heat exchanger and an indoor expansion valve. A high-pressure main gas pipe is provided between the high-pressure main gas pipe connection and the high-pressure side switching valve. A low-pressure main gas pipe is provided between the low-pressure main gas pipe connection and the low-pressure side switching valve. A high-pressure gas pipe solenoid valve is installed on the high-pressure gas pipe between the compressor exhaust pipe and the high-pressure main gas pipe connection. The high-pressure gas pipe solenoid valve is used to control the opening and closing of the high-pressure gas pipe. A main gas pipe switching bypass pipe is provided from the high-pressure gas pipe between the high-pressure gas pipe solenoid valve and the high-pressure main gas pipe connection to the low-pressure gas pipe between the four-way valve and the low-pressure main gas pipe connection. The main gas pipe switching bypass pipe provides a bypass path. A main gas pipe switching solenoid valve is installed in the main gas pipe switching bypass pipe. The main gas pipe switching solenoid valve is used to control the opening and closing of the bypass pipe.

2. The three-pipe multi-split air conditioning system according to claim 1, characterized in that, A compressor suction pressure sensor for measuring compressor suction pressure is installed on the compressor suction pipe; an indoor low-pressure gas pipe pressure sensor for measuring indoor low-pressure gas pipe pressure is installed on the indoor unit side of the low-pressure main gas pipe.

3. The three-pipe multi-split air conditioning system according to claim 2, characterized in that, The evaporation temperature is measured by an evaporation temperature sensor installed on the refrigerant piping between the indoor expansion valve and the central part of the indoor heat exchanger of the indoor unit.

4. A control method for a three-pipe multi-split air conditioning system, characterized in that, This is achieved through a three-pipe multi-split air conditioning system as described in any one of claims 1 to 3. The three-pipe multi-split air conditioning system includes an outdoor unit, a branch box, and an indoor unit. The outdoor unit includes: a compressor, a compressor discharge pipe, a compressor suction pipe, a four-way valve high-pressure main gas pipe connection, and a low-pressure main gas pipe connection. The branch box includes a high-pressure side switching valve and a low-pressure side switching valve. The indoor unit includes an indoor heat exchanger and an indoor expansion valve. A high-pressure main gas pipe is provided between the high-pressure main gas pipe connection and the high-pressure side switching valve. A low-pressure main gas pipe is provided between the low-pressure main gas pipe connection and the low-pressure side switching valve. The control methods for a three-pipe multi-split air conditioning system include: When operating in pure cooling mode, detect the cooling load; If the cooling load is detected to reach the first threshold, the high-pressure gas pipe solenoid valve will be closed and the main gas pipe switching solenoid valve will be opened. Open the low-pressure side switching valve and the high-pressure side switching valve connected to the indoor unit of the refrigeration unit in the branch box; The low-pressure gas refrigerant evaporated in the indoor heat exchanger flows to both sides of the low-pressure main gas pipe and the high-pressure main gas pipe, and flows to the low-pressure gas pipe through the main gas pipe switching solenoid valve. The low-pressure refrigerant flowing through the low-pressure main pipe and the high-pressure main pipe is mixed in the low-pressure pipe and then drawn into the compressor.

5. The control method for a three-pipe multi-split air conditioning system according to claim 4, characterized in that, Also includes: If the cooling load is detected to be below the first threshold, the high-pressure gas pipe solenoid valve will be opened and the main gas pipe switching solenoid valve will be closed. Open the low-pressure side switching valve connected to the indoor unit of the cooling unit in the branch box, and close the high-pressure side switching valve; This ensures that the low-pressure refrigerant evaporating in the indoor heat exchanger of the refrigeration indoor unit flows only to the low-pressure main gas pipe.

6. The control method for a three-pipe multi-split air conditioning system according to claim 4, characterized in that, A compressor suction pressure sensor is installed on the compressor suction pipe to measure the compressor suction pressure; An indoor low-pressure gas pipe pressure sensor is installed on the indoor unit side of the low-pressure main gas pipe to measure the indoor low-pressure gas pipe pressure.

7. The control method for a three-pipe multi-split air conditioning system according to claim 6, characterized in that, Includes the following steps: Calculate the low-pressure tracheal pressure drop; If the low-pressure gas pipe pressure drop reaches the preset threshold, the high-pressure gas pipe solenoid valve will be closed, the main gas pipe switching solenoid valve will be opened, and the low-pressure side switching valve and the high-pressure side switching valve connected to the indoor unit in the branch box will be opened. If the low-pressure gas pipe pressure drop does not reach the preset threshold, open the high-pressure gas pipe solenoid valve, close the main gas pipe switching solenoid valve, open the low-pressure side switching valve connected to the indoor unit of the cooling unit in the branch box, and close the high-pressure side switching valve.

8. The control method for a three-pipe multi-split air conditioning system according to claim 6, characterized in that, An evaporation temperature sensor is installed on the refrigerant piping between the indoor expansion valve and the central part of the indoor heat exchanger of the indoor unit to measure the evaporation temperature.

9. The control method for a three-pipe multi-split air conditioning system according to claim 8, characterized in that, Includes the following steps: The evaporation pressure is calculated using the refrigerant saturation pressure formula, and the evaporation pressure is regarded as the pressure of the low-pressure gas pipe on the indoor side. Calculate the pressure drop in the low-pressure pipe; If the low-pressure gas pipe pressure drop reaches the preset threshold, then close the high-pressure gas pipe solenoid valve, open the main gas pipe switching valve, and open the low-pressure side switching valve and high-pressure switching valve connected to the indoor unit of the cooling unit in the branch box.

10. The control method of the three-pipe multi-split air conditioning system according to claim 8, if the pressure drop of the low-pressure gas pipe does not reach the preset threshold, then the high-pressure gas pipe solenoid valve is opened, the main gas pipe switching solenoid valve is closed, and the low-pressure side switching valve connected to the indoor unit of the branch box is opened, while the high-pressure side switching valve is closed.

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