Oil return control method of air conditioning system and three-way air conditioning system

Abstract

This invention provides a method for controlling oil return in an air conditioning system and a three-pipe air conditioning system, relating to the field of air conditioning technology. If the operating parameters meet the conditions for oil return entry, the oil return process begins. The air conditioning system is adjusted to a pure cooling mode for oil return, and the bypass valve connecting the high-pressure and low-pressure gas pipes is opened. During oil return, if the oil return parameters meet the conditions for oil return exit, the oil return process is exited. Compared to existing technologies, this invention rationally arranges the timing of oil return by defining oil return entry and exit conditions. By adopting a pure cooling mode for oil return and connecting the high-pressure and low-pressure gas pipes, the refrigerant in the high-pressure gas pipe is discharged into the low-pressure gas pipe, increasing the refrigerant flow rate. This allows the accumulated oil in the low-pressure gas pipe to circulate back to the compressor through the flow rate and pipe circulation, achieving better oil return efficiency and preventing long-term oil accumulation in the low-pressure gas pipe during operation, which could affect the reliability and heat exchange performance of the air conditioning system.

Description

Technical Field

[0001] This invention relates to the field of air conditioning technology, and more specifically, to an oil return control method for an air conditioning system and a three-pipe air conditioning system. Background Technology

[0002] A three-pipe air conditioning system is a system that can simultaneously cool and heat the indoor unit. In the past, the outdoor unit of the three-pipe system was designed with three four-way valves, which was complicated to control and prone to cross-flow of air between the four-way valves. The current design of the three-pipe outdoor unit is a single four-way valve design, which is simpler in design and control. It includes an outdoor unit system, a mode conversion device system, and an indoor unit system.

[0003] The inventor's research revealed that in current three-pipe air conditioning systems with a single four-way valve, both the high-pressure and low-pressure gas pipes flow in one direction: the high-pressure pipe flows from the outdoor unit to the indoor unit, and the low-pressure pipe flows from the indoor unit to the outdoor unit. When the outdoor unit is above the indoor unit, oil accumulation may occur in the low-pressure gas pipe during operation, affecting the reliability of the air conditioning system. Summary of the Invention

[0004] The problem addressed by this invention is how to improve the situation of oil accumulation in low-pressure gas pipes and ensure the reliability of the air conditioning system.

[0005] To solve the above problems, the present invention adopts the following technical solution.

[0006] In one aspect, the present invention provides an oil return control method for an air conditioning system, applicable to a three-pipe air conditioning system. The three-pipe air conditioning system includes an outdoor unit, a mode conversion device, and multiple indoor units located below the horizontal plane of the outdoor unit. The outdoor unit is connected to the mode conversion device via a high-pressure gas pipe, a low-pressure gas pipe, and a liquid pipe. The multiple indoor units are connected to the mode conversion device. The oil return control method includes:

[0007] Obtain the operating mode of the three-pipe air conditioning system, wherein the operating modes of the three-pipe air conditioning system include pure cooling, main cooling, pure heating and main heating;

[0008] Obtain the operating parameters of the three-pipe air conditioning system;

[0009] When the operating parameters meet the oil return entry conditions of the corresponding operating mode, the three-pipe air conditioning system is adjusted to pure cooling mode.

[0010] The bypass valve connecting the high-pressure gas pipe and the low-pressure gas pipe is kept open so that the refrigerant in the high-pressure gas pipe is discharged into the low-pressure gas pipe.

[0011] Obtain the oil return parameters of the three-pipe air conditioning system;

[0012] If the oil return parameters meet the oil return exit conditions of the corresponding operating mode, the three-pipe air conditioning system is adjusted to the initial operating mode or shut down.

[0013] The oil return control method for an air conditioning system provided in this embodiment of the invention, when the outdoor unit is higher than the indoor unit, firstly obtains the operating mode of the air conditioning system, then obtains the operating parameters of the air conditioning system, and compares the operating parameters with the oil return entry conditions of the corresponding operating mode. If the conditions are met, the oil return process is initiated, the air conditioning system is adjusted to a pure cooling mode for oil return, and the bypass valve connecting the high-pressure gas pipe and the low-pressure gas pipe is opened, allowing the refrigerant in the high-pressure gas pipe to be discharged into the low-pressure gas pipe. In the pure cooling mode, through flow rate and refrigerant circulation, the accumulated oil in the low-pressure gas pipe returns to the outdoor unit, realizing the unit's oil return. During the oil return process, the oil return parameters of the air conditioning system also need to be obtained. When the oil return parameters meet the oil return exit conditions of the corresponding operating mode, the oil return process is exited, the air conditioning system is adjusted to the initial operating mode or shut down, and the oil return is completed. Compared to existing technologies, the oil return control method provided in this invention rationally arranges the timing of oil return by defining oil return entry and exit conditions. It also employs a pure cooling mode for oil return and utilizes a bypass valve to connect the high-pressure and low-pressure gas pipes. This allows oil in the high-pressure gas pipe to be discharged into the low-pressure gas pipe and increases the refrigerant flow rate. This enables the accumulated oil in the low-pressure gas pipe to circulate back to the compressor in the outdoor unit through the flow rate and pipe circulation, achieving better oil return efficiency and preventing long-term oil accumulation in the low-pressure gas pipe during operation, which could affect the reliability and heat exchange performance of the air conditioning system.

[0014] Furthermore, the step of obtaining the operating parameters of the three-pipe air conditioning system includes:

[0015] Obtain the cumulative operating time of the three-pipe air conditioning system;

[0016] Obtain the number of start-stop cycles of the three-pipe air conditioning system within a first preset time t1;

[0017] Obtain the operating ratio of the indoor units of the three-pipe air conditioning system.

[0018] The oil return control method for air conditioning systems provided in this invention monitors the operating status of the air conditioning system from multiple perspectives by acquiring the cumulative running time, number of start-stop cycles, and indoor unit start-up ratio of the air conditioning system. This allows for better judgment on when the air conditioning system needs to return oil, ensuring better oil return performance and minimizing the impact on the normal operating time of the air conditioning system.

[0019] Furthermore, the oil return entry condition is: the cumulative running time reaches the second preset time t2, and the indoor unit start-up ratio is less than or equal to the preset ratio;

[0020] Alternatively, the oil return entry condition is: the number of start-stop cycles reaches a preset number, and the indoor unit start-up ratio is less than or equal to a preset ratio.

[0021] The oil return control method for an air conditioning system provided in this invention sets the oil return entry conditions through multiple operating parameters, making the oil return entry conditions more reasonable and the oil return effect better. Simultaneously, the indoor unit operating ratio represents the indoor unit's operating load. As long as the indoor unit operating ratio meets the preset ratio, oil return is determined to begin once either the cumulative operating time or the number of start-stop cycles meets the condition. This avoids misjudgments of the air conditioning system and makes the control of the oil return timing more precise and reliable.

[0022] Furthermore, the first preset time t1 is 2 hours, the second preset time t2 in pure cooling or main cooling mode is 6 hours, and the second preset time t2 in pure heating or main heating mode is 2 hours; the preset number of times in pure cooling or main cooling mode is 4 times, and the preset number of times in pure heating or main heating mode is 2 times; the preset ratio in pure cooling or main cooling mode is 75%, and the preset ratio in pure heating or main heating mode is 100%.

[0023] The oil return control method for an air conditioning system provided in this embodiment of the invention addresses the issue that oil return is more difficult in heating mode. By reasonably setting different parameters for oil return in heating and cooling modes, the oil return process is made easier in heating mode, which conforms to the basic logic of oil return control, ensures the effectiveness of oil return control, and further avoids long-term oil accumulation.

[0024] Further, the step of obtaining the oil return parameters of the three-pipe air conditioning system includes:

[0025] Obtain the oil return operation time of the three-pipe air conditioning system;

[0026] Obtain the return gas pressure of the three-pipe air conditioning system;

[0027] Obtain the exhaust temperature of the three-pipe air conditioning system.

[0028] The oil return control method for an air conditioning system provided in this invention monitors the operating status of the air conditioning system during the oil return process from multiple perspectives by acquiring the oil return operation time, return gas pressure, and exhaust temperature. This allows for better monitoring of the oil return process and a more accurate determination of when to discontinue the oil return operation, ensuring better oil return performance and minimizing impact on the normal operating time of the air conditioning system. Furthermore, since the outdoor unit is located at the top, refrigerant flow is difficult upwards, thus preventing refrigerant overload. The oil return discontinuation conditions only require the oil return operation time, return gas pressure, and exhaust temperature to comprehensively monitor the oil return status.

[0029] Furthermore, the oil return exit conditions are: the oil return operation time reaches a third preset time t3, the return gas pressure is less than or equal to a preset pressure Ps, or the exhaust temperature is greater than or equal to a preset temperature Td.

[0030] The oil return control method for an air conditioning system provided in this invention sets oil return exit conditions through multiple oil return parameters, making the oil return exit conditions more reasonable and the oil return effect better. Furthermore, oil return can be exited as soon as any one of the conditions—oil return operation time, return gas pressure, or exhaust temperature—is met, enabling rapid exit of oil return, shortening the oil return time, and reducing the impact on the normal operation of the air conditioning system.

[0031] Furthermore, the third preset time t3 is 10 min, the preset temperature Td is 108℃, the preset pressure Ps in pure cooling or main cooling mode is 0.15 MPa, and the preset pressure Ps in pure heating or main heating mode is 0.1 MPa.

[0032] The oil return control method for an air conditioning system provided in this invention can shorten the oil return time while ensuring the oil return effect by reasonably setting the parameter standards for the exit conditions. Furthermore, since oil return is more difficult in heating mode, different return gas pressure standards are set for heating and cooling modes, resulting in a relatively longer oil return time in heating mode to achieve a better oil return effect.

[0033] Furthermore, the step of adjusting the three-pipe air conditioning system to pure cooling mode includes:

[0034] Increase the compressor frequency of the outdoor unit to the oil return frequency;

[0035] Keep the outdoor expansion valve of the outdoor unit at its maximum opening;

[0036] Close the high-pressure valve in the mode switching device that connects to the high-pressure gas pipe;

[0037] Open the low-pressure valve in the mode switching device that connects to the low-pressure gas pipe;

[0038] Open the indoor expansion valve of the indoor unit to the oil return opening position.

[0039] The oil return control method for an air conditioning system provided in this embodiment of the invention can increase refrigerant circulation and ensure the oil return effect in pure cooling mode by controlling the opening and closing of various valves in the air conditioning system and increasing the compressor frequency to the oil return frequency.

[0040] Furthermore, prior to the step of obtaining the operating mode of the three-pipe air conditioning system, the oil return control method further includes:

[0041] When the three-pipe air conditioning system switches modes, the bypass valve connecting the high-pressure gas pipe and the low-pressure gas pipe is opened in advance.

[0042] The air conditioning system oil return control method provided in this embodiment of the invention requires switching the opening and closing of valves on the high-pressure and low-pressure gas pipes before mode switching. The pressure difference between the high-pressure and low-pressure gas pipes causes refrigerant whistling, resulting in noise in the air conditioning system and affecting the user experience. Therefore, by opening the bypass valve in advance, the pressure difference can be reduced, thereby eliminating noise and improving the user experience.

[0043] In another aspect, embodiments of the present invention provide a three-pipe air conditioning system applicable to the aforementioned oil return control method, comprising:

[0044] Outdoor unit;

[0045] Multiple indoor units, wherein the multiple indoor units are located below the horizontal plane of the outdoor unit;

[0046] The mode conversion device is configured to be connected to multiple indoor units via multiple liquid distribution pipes and multiple gas distribution pipes, and the mode conversion device is connected to the outdoor unit via a high-pressure gas pipe, a low-pressure gas pipe and a liquid pipe. The multiple liquid distribution pipes are connected to the liquid pipe, and each gas distribution pipe is connected to the high-pressure gas pipe or the low-pressure gas pipe.

[0047] A bypass valve is provided between the high-pressure gas pipe and the low-pressure gas pipe, and the bypass valve is used to selectively connect the high-pressure gas pipe and the low-pressure gas pipe. Attached Figure Description

[0048] Figure 1 A schematic diagram of a three-pipe air conditioning system provided in an embodiment of the present invention;

[0049] Figure 2 for Figure 1 Schematic diagram of the outdoor unit;

[0050] Figure 3 for Figure 1 A schematic diagram of the mode conversion device and the indoor unit;

[0051] Figure 4 A flowchart illustrating the steps of an oil return control method for an air conditioning system provided in an embodiment of the present invention.

[0052] Explanation of reference numerals in the attached figures:

[0053] 100 - Three-pipe air conditioning system; 110 - Outdoor unit; 111 - Compressor; 113 - Outdoor heat exchanger; 115 - Four-way valve; 117 - Subcooling electronic expansion valve; 119 - Outdoor expansion valve; 130 - Mode conversion device; 131 - High-pressure gas pipe; 133 - Low-pressure gas pipe; 135 - Liquid pipe; 150 - Indoor unit; 151 - Liquid distribution pipe; 153 - Gas distribution pipe; 155 - Low-pressure valve; 157 - High-pressure valve; 159 - Indoor expansion valve; 170 - Bypass valve. Detailed Implementation

[0054] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0055] Please refer to Figures 1 to 4 This invention provides an oil return control method for an air conditioning system, which can improve the oil accumulation in the low-pressure gas pipe 133 and ensure the reliability and heat exchange performance of the air conditioning system.

[0056] See Figure 1 The oil return control method for the air conditioning system provided in this embodiment is applicable to a three-pipe air conditioning system 100. The three-pipe air conditioning system 100 includes an outdoor unit 110, a mode conversion device 130, and multiple indoor units 150 located below the horizontal plane of the outdoor unit 110. The outdoor unit 110 is connected to the mode conversion device 130 through a high-pressure gas pipe 131, a low-pressure gas pipe 133, and a liquid pipe 135. The multiple indoor units 150 are connected to the mode conversion device 130. Specifically, the mode conversion device 130 is connected to multiple indoor units 150 via multiple liquid distribution pipes 151 and multiple gas distribution pipes 153. The mode conversion device 130 is also connected to the outdoor unit 110 via a high-pressure gas pipe 131, a low-pressure gas pipe 133, and a liquid pipe 135. Multiple liquid distribution pipes 151 connect to the liquid pipe 135, and each gas distribution pipe 153 connects to either the high-pressure gas pipe 131 or the low-pressure gas pipe 133. A bypass valve 170 is installed between the high-pressure gas pipe 131 and the low-pressure gas pipe 133 to achieve bypass control to prevent oil accumulation during operation and oil return control during the oil return process. During normal operation, when the corresponding indoor unit 150 is cooling, the corresponding low-pressure valve 155 is open and the high-pressure valve 157 is closed; when the corresponding indoor unit 150 is heating, the low-pressure valve 155 is closed and the high-pressure valve 157 is open. The bypass valve 170 and the electronic expansion valve are controlled as needed.

[0057] Furthermore, in this embodiment, the indoor unit 150 is located below the horizontal plane where the outdoor unit 110 is located, meaning that multiple indoor units 150 are all located below the horizontal plane where the outdoor unit 110 is located. That is, the installation position of the outdoor unit 110 is higher than the installation positions of all indoor units. Multiple indoor units 150 can achieve simultaneous cooling and heating functions. Moreover, the three-pipe air conditioning system 100 includes four operating modes: pure cooling, pure heating, main cooling, and main heating. Pure cooling means that all operating indoor units 150 are in cooling mode. Pure heating means that all operating indoor units 150 are in heating mode. Main cooling means that more than half of the operating indoor units 150 are in cooling mode. Main heating means that more than half of the operating indoor units 150 are in heating mode.

[0058] See Figure 2 and Figure 3 The outdoor unit 110 includes a compressor 111, an outdoor heat exchanger 113, and a four-way valve 115. The compressor 111 is connected to the four-way valve 115, which has ports D, C, S, and E. A high-pressure gas pipe 131 leads from port D of the four-way valve 115 and is connected to a mode switching device 130 via the high-pressure gas pipe 131. Port C of the four-way valve 115 is connected to the outdoor heat exchanger 113 via a pipe. Ports E and S of the four-way valve 115 are connected via capillary tubes. Simultaneously, a liquid pipe 135 is connected to the outdoor heat exchanger 113, and a low-pressure gas pipe 133 is connected to port E. Furthermore, each liquid distribution pipe 151 is connected to the liquid pipe 135 via a one-way valve assembly, and each gas distribution pipe 153 is connected to the low-pressure gas pipe 133 via a low-pressure valve 155 and to the high-pressure gas pipe 131 via a high-pressure valve 157. The low-pressure valve 155 and the high-pressure valve 157 are selectively open. In this embodiment, the outdoor expansion valve 119 is installed on the liquid pipe 135 next to the outdoor heat exchanger 113, and the indoor expansion valve 159 is installed on the liquid distribution pipe 151 in the indoor unit 150.

[0059] The three-pipe air conditioning system 100 provided in this embodiment adds a bypass valve 170 to the existing single four-way valve 115 three-pipe air conditioning system. The bypass valve 170 is located between the high-pressure gas pipe 131 and the low-pressure gas pipe 133, and is used to selectively connect the high-pressure gas pipe 131 and the low-pressure gas pipe 133. This enables oil return control during the oil return process. The oil return control method of this three-pipe air conditioning system 100 will be described in detail below.

[0060] The oil return control method for an air conditioning system provided in this embodiment of the invention, when the outdoor unit 110 is higher than the indoor unit 150, firstly obtains the operating mode of the air conditioning system, then obtains the operating parameters of the air conditioning system, and compares the operating parameters with the oil return entry conditions of the corresponding operating mode. If the conditions are met, the oil return process is initiated, the air conditioning system is adjusted to a pure cooling mode for oil return, and the bypass valve 170 connecting the high-pressure gas pipe 131 and the low-pressure gas pipe 133 is opened, so that the refrigerant in the high-pressure gas pipe 131, which is not filled with oil, can be discharged into the low-pressure gas pipe 133. In the pure cooling mode, through flow rate and refrigerant circulation, the oil in the low-pressure gas pipe 133 returns to the outdoor unit 110, realizing the unit's oil return. During the oil return process, the oil return parameters of the air conditioning system also need to be obtained. When the oil return parameters meet the oil return exit conditions of the corresponding operating mode, the oil return process is exited, the air conditioning system is adjusted to the initial operating mode or shut down, and the oil return is completed.

[0061] See Figure 4 The oil return control method for the air conditioning system provided in this embodiment may specifically include the following steps:

[0062] S1: Obtain the operating mode of the three-pipe air conditioning system 100.

[0063] Specifically, the three-pipe air conditioning system 100 has four operating modes: pure cooling, main cooling, pure heating, and main heating. These modes can be directly determined by the controller. Pure cooling means all operating indoor units 150 are in cooling mode; pure heating means all operating indoor units 150 are in heating mode; main cooling means more than half of the operating indoor units 150 are in cooling mode, i.e., indoor units 150 have both cooling and heating modes, and the cooling demand is greater than the heating demand; main heating means more than half of the operating indoor units 150 are in heating mode, i.e., indoor units 150 have both cooling and heating modes, and the heating demand is greater than the cooling demand. In pure cooling and main cooling modes, the four-way valve 115 of the outdoor unit 110 is de-energized and in the OFF position. At this time, ports D and C are connected, ports S and E are connected, and the outdoor heat exchanger 113 is the condenser. In pure heating and main heating modes, the four-way valve 115 of the outdoor unit 110 is energized and in the ON position. At this time, ports C and S are connected, the low-pressure gas pipe 133 is connected to the outdoor heat exchanger 113, and the outdoor heat exchanger 113 is the evaporator.

[0064] S2: Obtain the operating parameters of the three-pipe air conditioning system 100.

[0065] Specifically, the operating parameters may include the cumulative operating time, number of start-stop cycles, and indoor unit operating ratio of the three-pipe air conditioning system 100. Therefore, when executing step S1, the controller can directly read the relevant parameters from the relevant sensors or timers, first obtaining the cumulative operating time of the three-pipe air conditioning system 100, then obtaining the number of start-stop cycles of the three-pipe air conditioning system 100 within a first preset time t1, and simultaneously obtaining the indoor unit operating ratio of the three-pipe air conditioning system 100.

[0066] It is worth noting that the controller has preset oil return entry conditions. After acquiring the operating parameter information, it compares the operating parameters with the oil return entry conditions to determine whether oil return control needs to be activated. By acquiring the cumulative operating time, start-stop count, and indoor unit start-up ratio of the air conditioning system, the operating status of the air conditioning system is monitored from multiple perspectives. This allows for a better determination of when the air conditioning system needs oil return, ensuring better oil return performance and minimizing the impact on the normal operating time of the air conditioning system.

[0067] If the operating parameters meet the oil return entry conditions of the corresponding operating mode, execute step S3: adjust the three-pipe air conditioning system 100 to pure cooling mode.

[0068] Specifically, the control method for adjusting the three-pipe air conditioning system 100 to pure cooling mode is the same as the control method during normal cooling. In addition, the frequency of the compressor 111 of the outdoor unit 110 needs to be increased to the oil return frequency, such as adjusting it to 90Hz, to improve oil return capacity. The outdoor expansion valve 119 of the outdoor unit 110 is kept at its maximum opening to increase refrigerant circulation, and the fan of the outdoor unit 110 is adjusted normally according to the pressure. Simultaneously, the high-pressure valve 157 in the mode conversion device 130, which connects to the high-pressure gas pipe 131, is closed, and the low-pressure valve 155 in the mode conversion device 130, which connects to the low-pressure gas pipe 133, is opened, and the subcooling electronic expansion valve 117 of the outdoor unit 110 is closed. Finally, the indoor expansion valve 159 of the indoor unit 150 is opened to the oil return opening, such as 400P. The fan of the indoor unit 150, which was in cooling mode before the oil return, continues to run without being significantly affected, while the fan of the indoor unit 150, which was in heating mode before the oil return, stops running. By controlling the opening and closing of various valves in the air conditioning system and simultaneously increasing the compressor 111 frequency to the oil return frequency, the refrigerant circulation can be increased, ensuring the oil return effect in pure cooling mode.

[0069] The oil return entry condition here is: the cumulative running time reaches the second preset time t2, and the indoor unit's operating ratio is less than or equal to a preset ratio; or, the oil return entry condition is: the number of start-stop cycles reaches a preset number, and the indoor unit's operating ratio is less than or equal to a preset ratio. This oil return entry condition can be pre-programmed into the controller, and the specific criteria for the oil return entry condition will be adjusted accordingly under different operating modes. Setting the oil return entry condition through multiple operating parameters makes the oil return entry condition more reasonable and the oil return effect better. Simultaneously, the indoor unit's operating ratio represents the indoor unit's operating load. As long as the indoor unit's operating ratio meets the preset ratio, and either the cumulative running time or the number of start-stop cycles meets the condition, oil return is determined to begin, avoiding misjudgments of the air conditioning system and making the control of the oil return timing more precise and reliable.

[0070] Furthermore, regarding the oil return entry conditions, specifically, the first preset time t1 is 2 hours, the second preset time t2 in pure cooling or main cooling mode is 6 hours, and the second preset time t2 in pure heating or main heating mode is 2 hours; the preset number of times in pure cooling or main cooling mode is 4 times, and the preset number of times in pure heating or main heating mode is 2 times; the preset proportion in pure cooling or main cooling mode is 75%, and the preset proportion in pure heating or main heating mode is 100%.

[0071] In other words, referring to Table a below, if the cumulative operating time of the three-pipe air conditioning system 100 reaches 6 hours in pure cooling or main cooling mode, and the indoor unit operating rate is less than or equal to 75%, then the system is determined to need to enter the oil return phase. Alternatively, if the number of start-stop cycles of the three-pipe air conditioning system 100 reaches 4 times within 2 hours in pure cooling or main cooling mode, and the indoor unit operating rate is less than or equal to 75%, then the system is determined to need to enter the oil return phase.

[0072] If the cumulative operating time of the three-pipe air conditioning system 100 reaches 2 hours in pure heating or main heating mode, and the indoor unit operating rate is less than or equal to 100%, then the system is determined to need to enter oil return mode. Alternatively, if the three-pipe air conditioning system 100 starts and stops twice within 2 hours in pure heating or main heating mode, and the indoor unit operating rate is less than or equal to 100%, then the system is determined to need to enter oil return mode.

[0073] Table-a

[0074]

[0075] It should be noted that in this embodiment, the outdoor unit 110 is located above the indoor unit 150. Due to gravity, oil return is more difficult. Therefore, the oil return entry condition is set more easily, while the oil return exit condition is set more difficult, thereby extending the oil return time and ensuring the oil return effect.

[0076] It should also be noted that the conditions for heating mode and cooling mode are distinguished here. Since it is more difficult for the system to return oil in heating mode, by reasonably setting different parameters for oil return in heating mode and cooling mode, it is easier to return oil in heating mode, which is in line with the basic logic of oil return control, ensures the effect of oil return control, and further avoids long-term oil accumulation.

[0077] S4: Continuously open the bypass valve 170 connecting the high-pressure gas pipe 131 and the low-pressure gas pipe 133 so that the refrigerant in the high-pressure gas pipe 131 is discharged into the low-pressure gas pipe 133.

[0078] Specifically, during step S3, step S4 can be executed simultaneously to open the bypass valve 170, close the high-pressure valve 157, and open the low-pressure valve 155. This allows the refrigerant in the high-pressure pipe 131 to be discharged into the inner side and the low-pressure pipe 133, improving the oil return capacity of the low-pressure pipe 133. Through this oil return operation, the accumulated oil in the low-pressure pipe 133 can return to the compressor 111 of the outdoor unit 110 through flow rate and refrigerant circulation, thereby realizing the unit's oil return function.

[0079] It should be noted that in this embodiment, since the outdoor unit is on top, oil will accumulate in the low-pressure gas pipe 133 due to gravity, while oil will not accumulate in the high-pressure gas pipe 131. Therefore, when the system determines that it needs to enter the oil return operation, it enters the pure cooling mode to return oil.

[0080] S5: Obtain the oil return parameters of the three-pipe air conditioning system 100.

[0081] Specifically, the method for obtaining the oil return parameters is similar to that for the operating parameters. They can be obtained by reading parameters from the corresponding sensors through the controller. Here, the oil return parameters include the oil return operating time, return gas pressure, and exhaust temperature of the three-pipe air conditioning system 100. Therefore, when executing step S5, it is first necessary to obtain the oil return operating time of the three-pipe air conditioning system 100, simultaneously obtain the return gas pressure, and then obtain the exhaust temperature. By obtaining the oil return operating time, return gas pressure, and exhaust temperature of the air conditioning system, the operating status of the air conditioning system during the oil return process can be monitored from multiple perspectives. This allows for better monitoring of the oil return process, enabling a better judgment on when the air conditioning system needs to exit the oil return process, ensuring better oil return performance, and minimizing the impact on the normal operating time of the air conditioning system. Furthermore, since the outdoor unit is located at the top, refrigerant flow upwards is difficult, so there is no problem of excessive refrigerant. The oil return exit condition only needs to include the oil return operating time, return gas pressure, and exhaust temperature, providing a sufficiently comprehensive monitoring of the oil return status.

[0082] If the oil return parameters meet the oil return exit conditions of the corresponding operating mode, execute step S6: adjust the three-pipe air conditioning system 100 to the initial operating mode or shut it down.

[0083] Specifically, when performing step S6, the operating mode of the three-pipe air conditioning system 100 can be adjusted to the mode before oil return, so as to minimize the impact on the air conditioning user experience. The control method is the same as the control method during normal operation, and the bypass valve 170 needs to be closed.

[0084] The oil return exit conditions here are: the oil return operation time reaches the third preset time t3, the return gas pressure is less than or equal to the preset pressure Ps, or the exhaust temperature is greater than or equal to the preset temperature Td. These oil return exit conditions can also be pre-programmed into the controller, and the specific criteria for the oil return exit conditions will be adjusted accordingly in different operating modes. Setting the oil return exit conditions through multiple oil return parameters makes the exit conditions more reasonable and the oil return effect better. Furthermore, the oil return can be terminated as soon as any one of the conditions—oil return operation time, return gas pressure, or exhaust temperature—is met, allowing for rapid termination after the oil return process is completed and minimizing the impact on the normal operation of the air conditioning system.

[0085] Furthermore, regarding the oil return exit conditions, specifically, the third preset time t3 is 10 minutes, the preset temperature Td is 108°C, the preset pressure Ps in pure cooling or main cooling mode is 0.15 MPa, and the preset pressure Ps in pure heating or main heating mode is 0.1 MPa. By reasonably setting the parameter standards for the exit conditions, the oil return time can be shortened while ensuring the oil return effect. Moreover, since oil return is more difficult in heating mode, different return gas pressure standards are set for heating and cooling modes, resulting in a relatively longer oil return time in heating mode, thus achieving a better oil return effect. Additionally, because the outdoor unit is located on top, gravity affects the oil return capacity; therefore, the oil return exit conditions are set more stringently to ensure the oil return effect as much as possible.

[0086] It should be noted that the first preset pressure Ps in pure cooling or main cooling mode is 0.15 MPa, which means that the first preset pressure Ps in pure cooling or main cooling mode is 0.15 MPa before oil return. Similarly, the first preset pressure Ps in pure heating or main heating mode is 0.1 MPa, which means that the first preset pressure Ps in pure heating or main heating mode is 0.1 MPa before oil return.

[0087] In other words, as shown in Table b below, if the oil return operation time reaches 10 minutes, or the return gas pressure is less than or equal to 0.15 MPa, or the exhaust temperature is greater than or equal to 108°C under pure refrigeration or main refrigeration conditions, then the system needs to stop the oil return operation.

[0088] If the oil return operation time reaches 10 minutes under pure heating or main heating conditions, or the return gas pressure is less than or equal to 0.1 MPa, or the exhaust temperature is greater than or equal to 108°C, then the system needs to disconnect the oil return operation.

[0089] Table-b

[0090]

[0091] In some other embodiments, before performing step S1, the oil return control method further includes:

[0092] When the three-pipe air conditioning system 100 switches modes, step S11 is executed: the bypass valve 170 connecting the high-pressure gas pipe 131 and the low-pressure gas pipe 133 is opened in advance.

[0093] Specifically, the bypass valve 170 can be opened 1 minute before mode switching. Before mode switching, the valves on the high-pressure gas pipe 131 and the low-pressure gas pipe 133 need to be switched, and there is a pressure difference between the high-pressure gas pipe 131 and the low-pressure gas pipe 133, which will generate a refrigerant whistling sound, resulting in noise from the air conditioning system and affecting the user experience. Therefore, by opening the bypass valve 170 in advance, the pressure difference can be reduced, thereby eliminating noise and improving the user experience.

[0094] In summary, the oil return control method and three-pipe air conditioning system 100 provided in this embodiment, when the outdoor unit 110 is higher than the indoor unit 150, firstly, obtains the operating mode of the air conditioning system, then obtains the operating parameters of the air conditioning system, and compares the operating parameters with the oil return entry conditions of the corresponding operating mode. If the conditions are met, the oil return process is initiated, the air conditioning system is adjusted to pure cooling mode for oil return, and the bypass valve 170 connecting the high-pressure gas pipe 131 and the low-pressure gas pipe 133 is opened, so that the refrigerant in the high-pressure gas pipe 131 can be discharged into the low-pressure gas pipe 133. In pure cooling mode, through flow rate and refrigerant circulation, the oil accumulated in the low-pressure gas pipe 133 returns to the outdoor unit 110, realizing the unit's oil return. During the oil return process, it is also necessary to obtain the oil return parameters of the air conditioning system. When the oil return parameters meet the oil return exit conditions of the corresponding operating mode, the oil return process is exited, the air conditioning system is adjusted to the initial operating mode or shut down, and the oil return is completed. Compared to existing technologies, the oil return control method provided in this embodiment of the invention rationally arranges the timing of oil return by setting oil return entry and exit conditions. It also adopts a pure cooling mode for oil return and uses a bypass valve 170 to connect the high-pressure gas pipe 131 and the low-pressure gas pipe 133. This allows the oil in the high-pressure gas pipe 131 to be discharged into the low-pressure gas pipe 133 and increases the refrigerant flow rate. This allows the accumulated oil in the low-pressure gas pipe 133 to return to the compressor 111 of the outdoor unit 110 through the flow rate and pipe circulation, thus achieving better oil return effect and avoiding long-term oil accumulation in the low-pressure gas pipe 133 during operation, which would affect the reliability and heat exchange performance of the air conditioning system.

[0095] While the present invention has been disclosed above, it is not limited thereto. Any person skilled in the art can make various modifications and alterations without departing from the spirit and scope of the invention; therefore, the scope of protection of the present invention should be determined by the scope defined in the claims.

Claims

1. A method for controlling oil return in an air conditioning system, applicable to a three-pipe air conditioning system, the three-pipe air conditioning system comprising an outdoor unit (110), a mode conversion device (130), and a plurality of indoor units (150) located below the horizontal plane of the outdoor unit (110), the outdoor unit (110) being connected to the mode conversion device (130) via a high-pressure gas pipe (131), a low-pressure gas pipe (133), and a liquid pipe (135), and the plurality of indoor units (150) being connected to the mode conversion device (130), characterized in that, The oil return control method includes: Obtain the operating mode of the three-pipe air conditioning system, wherein the operating modes of the three-pipe air conditioning system include pure cooling, main cooling, pure heating and main heating; Obtain the operating parameters of the three-pipe air conditioning system; When the operating parameters meet the oil return entry conditions of the corresponding operating mode, the three-pipe air conditioning system is adjusted to pure cooling mode. The bypass valve (170) connecting the high-pressure gas pipe (131) and the low-pressure gas pipe (133) is continuously opened so that the refrigerant in the high-pressure gas pipe (131) is discharged into the low-pressure gas pipe (133); Obtain the oil return parameters of the three-pipe air conditioning system; If the oil return parameters meet the oil return exit conditions of the corresponding operating mode, the three-pipe air conditioning system is adjusted to the initial operating mode or shut down.

2. The method for controlling oil return in an air conditioning system according to claim 1, characterized in that, The steps for obtaining the operating parameters of the three-pipe air conditioning system include: Obtain the cumulative operating time of the three-pipe air conditioning system; Obtain the number of start-stop cycles of the three-pipe air conditioning system within a first preset time t1; Obtain the operating ratio of the indoor units of the three-pipe air conditioning system.

3. The method for controlling oil return in an air conditioning system according to claim 2, characterized in that, The oil return entry condition is: the cumulative running time reaches the second preset time t2, and the indoor unit start-up ratio is less than or equal to the preset ratio; Alternatively, the oil return entry condition is: the number of start-stop cycles reaches a preset number, and the indoor unit start-up ratio is less than or equal to a preset ratio.

4. The method for controlling oil return in an air conditioning system according to claim 3, characterized in that, The first preset time t1 is 2 hours, the second preset time t2 in pure cooling or main cooling mode is 6 hours, and the second preset time t2 in pure heating or main heating mode is 2 hours; the preset number of times in pure cooling or main cooling mode is 4 times, and the preset number of times in pure heating or main heating mode is 2 times; the preset ratio in pure cooling or main cooling mode is 75%, and the preset ratio in pure heating or main heating mode is 100%.

5. The method for controlling oil return in an air conditioning system according to claim 1, characterized in that, The steps for obtaining the oil return parameters of the three-pipe air conditioning system include: Obtain the oil return operation time of the three-pipe air conditioning system; Obtain the return gas pressure of the three-pipe air conditioning system; Obtain the exhaust temperature of the three-pipe air conditioning system.

6. The method for controlling oil return in an air conditioning system according to claim 5, characterized in that, The conditions for exiting the oil return process are: the oil return operation time reaches the third preset time t3, the return gas pressure is less than or equal to the preset pressure Ps, or the exhaust temperature is greater than or equal to the preset temperature Td.

7. The method for controlling oil return in an air conditioning system according to claim 6, characterized in that, The third preset time t3 is 10 min, the preset temperature Td is 108℃, the preset pressure Ps in pure cooling or main cooling mode is 0.15 MPa, and the preset pressure Ps in pure heating or main heating mode is 0.1 MPa.

8. The method for controlling oil return in an air conditioning system according to claim 1, characterized in that, The steps for adjusting the three-pipe air conditioning system to pure cooling mode include: Increase the frequency of the compressor (111) of the outdoor unit (110) to the oil return frequency; Keep the outdoor expansion valve (119) of the outdoor unit (110) at its maximum opening; Close the high-pressure valve (157) in the mode switching device (130) that connects to the high-pressure gas pipe (131); Open the low-pressure valve (155) in the mode switching device (130) that is used to connect the low-pressure gas pipe (133); Open the indoor expansion valve (159) of the indoor unit (150) to the oil return opening.

9. The method for controlling oil return in an air conditioning system according to claim 1, characterized in that, Before the step of obtaining the operating mode of the three-pipe air conditioning system, the oil return control method further includes: When the three-pipe air conditioning system switches modes, the bypass valve (170) connecting the high-pressure gas pipe (131) and the low-pressure gas pipe (133) is opened in advance.

10. A three-pipe air conditioning system, applicable to the oil return control method of the air conditioning system as described in any one of claims 1-9, characterized in that, include: Outdoor unit (110); Multiple indoor units (150) are located below the horizontal plane where the outdoor unit (110) is located; A mode conversion device (130) is provided, which is connected to multiple indoor units (150) via multiple liquid distribution pipes (151) and multiple gas distribution pipes (153), and is connected to the outdoor unit (110) via a high-pressure gas pipe (131), a low-pressure gas pipe (133) and a liquid pipe (135). The multiple liquid distribution pipes (151) are connected to the liquid pipe (135), and each gas distribution pipe (153) is connected to the high-pressure gas pipe (131) or the low-pressure gas pipe (133). A bypass valve (170) is provided between the high-pressure air pipe (131) and the low-pressure air pipe (133), and the bypass valve (170) is used to selectively connect the high-pressure air pipe (131) and the low-pressure air pipe (133).

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