Oil return control method and system for multi-split air conditioning units

Abstract

This invention discloses a method and system for controlling oil return in a multi-split air conditioning unit. The air conditioning unit includes at least two compressors operating in parallel and a gas-liquid separator. A main oil return path is provided between the gas-liquid separator and an oil separator located at the compressor output end. The main oil return path includes a capillary tube and a bypass oil return path connected in parallel with the capillary tube. A control valve is installed on the bypass oil return path. The oil return control method includes: when the air conditioning unit executes a command to shut down the compressor, simultaneously opening the control valve and maintaining the control valve in the open state for a first preset time; when the air conditioning unit executes a command to start the compressor, simultaneously closing the control valve and the expansion valve on the air conditioning unit. Based on the above oil return control method, it is possible to effectively avoid malfunctions due to oil shortage during the startup of each compressor in the multi-split air conditioning unit, thereby enabling the compressor to respond quickly and effectively improving reliability.

Description

Technical Field

[0001] This invention relates to the field of air conditioning oil return control technology, and in particular to a method and system for controlling oil return in multi-split air conditioning units. Background Technology

[0002] Current air conditioning units can be categorized based on the number of compressors in the refrigeration system, including single-split air conditioners with one compressor and multi-split air conditioners with two or more compressors. Single-split air conditioners are technologically mature and low-cost; however, they also have several drawbacks. For example, the long-term operation of a single compressor can cause mechanical fatigue, shortening its lifespan. Therefore, they are not suitable for applications requiring continuous air conditioning use for extended periods.

[0003] Air conditioner compressors are filled with refrigerant and lubricating oil. When the compressor starts, before superheating is established, the amount of oil injected by the compressor is relatively high, causing the lubricating oil to circulate in the system along with the refrigerant. Therefore, an oil separator is installed at the output end of the compressor to separate the lubricating oil from the refrigerant injected by the compressor and return it to the compressor to prevent the compressor from losing lubricating oil.

[0004] However, although the air conditioning unit is equipped with an oil return line for the compressor, when the air conditioner stops, the valve body on the oil return line also closes immediately after the compressor stops, so that the lubricating oil separated by the oil separator cannot all flow back to the compressor. This results in insufficient lubricating oil when the compressor is restarted. If the starting frequency is high, it will cause the compressor to malfunction and alarm.

[0005] To address this, some air conditioning units reduce the compressor's starting frequency to decrease oil injection. While this ensures sufficient lubrication in the compressor, it also reduces the system's capacity and slows down startup. Additionally, some units have a solenoid valve that opens when shutting down to return the lubricating oil separated by the oil separator to the compressor itself. However, this only works for single-split air conditioners. For multi-split units, the lubricating oil separated by the oil separator may concentrate and flow back to one compressor, causing other compressors to run out of oil. This can lead to malfunctions when the compressor with insufficient oil is started first.

[0006] In summary, improvements are needed to the oil return control scheme for multi-split air conditioners. Summary of the Invention

[0007] The purpose of this invention is to provide a method and system for controlling the return oil of a multi-split air conditioning unit that collects lubricating oil from outside the compressor when the air conditioner is off and returns it to each compressor in a timely manner when the air conditioner is turned on.

[0008] To achieve the above objectives, this invention discloses a method for controlling oil return in a multi-split air conditioning unit. The air conditioning unit includes at least two compressors operating in parallel and a gas-liquid separator. Each compressor is connected to the gas-liquid separator via an independent oil supply pipeline. A main oil return line is provided between the gas-liquid separator and an oil separator located at the output end of the compressor. The main oil return line includes a capillary tube and a bypass oil return line connected in parallel with the capillary tube. A control valve is provided on the bypass oil return line. The oil return control method includes:

[0009] When the air conditioning unit receives a command to shut down the compressor, it performs the action of shutting down the compressor and at the same time opens the control valve, and keeps the control valve in the open state for a first preset time.

[0010] When the air conditioning unit receives a command to start the compressor, it performs the action of starting the compressor, and at the same time, it keeps the control valve and the expansion valve on the air conditioning unit in the closed state, and keeps the control valve in the closed state for a second preset time, and keeps the expansion valve in the closed state for a third preset time.

[0011] Preferably, the compressor has a variable frequency system, and when the air conditioning unit receives a command to shut down the compressor, the method for shutting down the compressor includes:

[0012] Based on the current frequency of the compressor, the frequency of the compressor is gradually reduced by a preset amount until the compressor is stopped.

[0013] Preferably, when the compressor is shut down by reducing its frequency, the reduction rate is proportional to the current operating frequency of the compressor.

[0014] Preferably, when the current operating frequency of the compressor is greater than or equal to 80Hz, the frequency reduction is 4Hz; when the current operating frequency of the compressor is greater than or equal to 60Hz but less than 80Hz, the frequency reduction is 3Hz; when the current operating frequency of the compressor is greater than or equal to 40Hz but less than 60Hz, the frequency reduction is 2Hz; and when the current operating frequency of the compressor is less than 40Hz, the frequency reduction is 1Hz.

[0015] Preferably, the first preset time T1 is: T1≥25s.

[0016] Preferably, the second preset time T2 is 35≤T2≤45s. When the duration exceeds the second preset time after the compressor starts, the state of the control valve is controlled according to the superheat of the compressor's exhaust.

[0017] Preferably, the second preset time T3 is: 15≤T3≤25s.

[0018] This invention also discloses a multi-split air conditioning unit oil return control system. The air conditioning unit includes at least two compressors operating in parallel and a gas-liquid separator. Each compressor is connected to the gas-liquid separator through an independent oil supply pipeline. An oil return main line is also provided between the gas-liquid separator and the oil separator located at the output end of the compressor. A capillary tube and an oil return bypass line connected in parallel with the capillary tube are provided on the oil return main line. A control valve is provided on the oil return bypass line. The oil return control system controls the operation of the air conditioning unit based on the above-described multi-split air conditioning unit oil return control method.

[0019] This invention also discloses another oil return control system for multi-split air conditioning units, comprising:

[0020] One or more processors;

[0021] Memory;

[0022] And one or more programs, wherein the one or more programs are stored in the memory and configured to be executed by the one or more processors, the programs including instructions for performing the multi-split air conditioning unit oil return control method as described above.

[0023] The present invention also discloses a computer-readable storage medium comprising a computer program that can be executed by a processor to perform the oil return control method for a multi-split air conditioning unit as described above.

[0024] Compared with the prior art, the oil return control method disclosed in the above technical solution of the present invention opens the control valve simultaneously when the air conditioning unit executes the shutdown command, and keeps the control valve in the open state for a certain period of time so that the lubricating oil sprayed by each compressor flows back to the gas-liquid separator. Then, when the air conditioning unit executes the start command, the control valve and the expansion valve are first controlled to be in the closed state, so that the lubricating oil in the gas-liquid separator flows back to each compressor, avoiding the compressor from malfunctioning due to lack of oil when starting, thereby enabling the compressor to respond quickly and effectively improving reliability. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the multi-split air conditioning unit in an embodiment of the present invention. Detailed Implementation

[0026] To illustrate the technical content, structural features, objectives, and effects of the present invention in detail, the following description is provided in conjunction with the embodiments and accompanying drawings.

[0027] This embodiment discloses a method for controlling the oil return of a multi-split air conditioning unit, which is used to control the shutdown and startup actions of the multi-split air conditioning unit, thereby ensuring that there is sufficient lubricating oil in the compressor when the air conditioner is turned on.

[0028] like Figure 1 In this embodiment, the air conditioning unit includes at least two compressors M operating in parallel and a gas-liquid separator Q. Each compressor M is connected to the gas-liquid separator Q via an independent oil supply line L1. A main oil return line L2 is also provided between the gas-liquid separator Q and the oil separator P located at the output end of the compressor M. A capillary tube G and a bypass oil return line L3 connected in parallel with the capillary tube G are provided on the main oil return line L2. A control valve V1 is provided on the bypass oil return line L3. In this embodiment, the air conditioning unit includes two compressors M. Each compressor M can be equipped with its own oil separator P, or the two compressors M can be equipped with a shared oil separator P. Furthermore, the main oil return lines L2 configured for the two compressors M are interconnected.

[0029] Furthermore, the main function of the vapor-liquid separator in this embodiment is to protect the compressor M when the refrigerant liquid returns after startup, operation, or defrosting (heat pump). The vapor-liquid separator Q provides additional internal volume to the low-pressure side of the system, which can temporarily store excess refrigerant liquid and lubricating oil flowing out of the oil separator, and also prevents excess refrigerant from flowing into the crankcase of the compressor M and causing oil dilution.

[0030] For air conditioning units with the above structure, the oil return control method in this embodiment includes:

[0031] When the air conditioning unit receives the instruction to shut down the compressor M, it executes the action of shutting down the compressor M, and at the same time opens the control valve V1, and keeps the control valve V1 in the open state for a first preset time, so that the lubricating oil in the oil separator P has enough time to flow back to the gas-liquid separator Q.

[0032] When the air conditioning unit receives the command to start the compressor M, it executes the action of starting the compressor M, and at the same time, it keeps the control valve V1 and the expansion valve V2 on the air conditioning unit in the closed state, and keeps the control valve V1 in the closed state for a second preset time, and keeps the expansion valve V2 in the closed state for a third preset time.

[0033] In the control method disclosed in this embodiment, when the air conditioning unit executes a shutdown command, the control valve V1 is opened at the same time, so that the lubricating oil in the oil separator P can bypass the capillary tube G through the return oil bypass L3 and then quickly flow into the gas-liquid separator Q, so as to ensure that the lubricating oil separated by the oil separator P is completely returned to the gas-liquid separator Q.

[0034] When the air conditioning unit executes the start command, the lubricating oil in the gas-liquid separator Q will quickly flow back to the two compressors M through the two oil pipelines L1.

[0035] It should also be noted that when compressor M starts, the opening of control valve V1 will cause the main oil return line L2 to be connected to the low-pressure side, which may cause the pressure difference of compressor M to fail to be established and result in start-up failure. Therefore, when compressor M starts, keeping control valve V1 closed can effectively ensure the normal start-up of compressor M.

[0036] Furthermore, since some or a large amount of liquid refrigerant may remain on the low-pressure side after the compressor M stops, if the expansion valve V2 is immediately given an initial opening upon startup, it will hinder the rapid vaporization of the liquid refrigerant in the gas-liquid separator Q. This will have the following effects:

[0037] First, the lubricating oil may float on top of the liquid refrigerant and cannot flow back to the compressor M in time;

[0038] Second, increased superheat leads to decreased efficiency, resulting in prolonged periods of low superheat and triggering alarm protection.

[0039] Third, low superheat leads to increased oil injection in compressor M, limiting compressor M's load.

[0040] Therefore, when compressor M starts, since control valve V1 and expansion valve V2 remain closed, the low pressure continues to drop and the saturation temperature drops. The liquid refrigerant in gas-liquid separator Q vaporizes, the oil is separated, and the lubricating oil flows back to compressor M. Compressor M is fully lubricated by the lubricating oil, and the superheat increases rapidly, so that the capacity output can be responded to quickly.

[0041] Furthermore, the first preset time T1 is: T1≥25s. In this embodiment, T1=30s.

[0042] The second preset time T2 is: 35≤T2≤45s. In this embodiment, T2=40s.

[0043] When the compressor M starts and the duration exceeds the second preset time, the state of the control valve V1 is controlled according to the exhaust superheat of the compressor M. Specifically, when the exhaust superheat is less than or equal to 10°C, the control valve V1 is opened; otherwise, the control valve V1 is closed.

[0044] The second preset time T3 is: 15≤T3≤25s. In this embodiment, T3=20s. When the compressor M starts for more than 20s, the opening degree of the expansion valve V2 is controlled according to the indoor / outdoor temperature and low pressure.

[0045] Furthermore, for compressor M with a variable frequency system, if compressor M rapidly reduces its operating frequency to the shutdown frequency during shutdown, it will cause a rise in low pressure, an increase in saturation temperature, and a decrease in superheat, which may pose a risk of liquid return in a short period of time. Therefore, a further improvement is made: when the air conditioning unit receives a command to shut down compressor M, it gradually reduces the frequency of compressor M by a preset amount based on the current frequency of compressor M until compressor M is in a shutdown state. Specifically, when shutting down compressor M by reducing its frequency, the reduction amount is proportional to the current operating frequency of compressor M.

[0046] For example, when the current operating frequency of compressor M is greater than or equal to 80Hz, the frequency reduction is 4Hz; when the current operating frequency of compressor M is greater than or equal to 60Hz but less than 80Hz, the frequency reduction is 3Hz; when the current operating frequency of compressor M is greater than or equal to 40Hz but less than 60Hz, the frequency reduction is 2Hz; and when the current operating frequency of compressor M is less than 40Hz, the frequency reduction is 1Hz.

[0047] In this embodiment, reducing the frequency of compressor M is beneficial to system safety.

[0048] In summary, this invention discloses an oil return control method for multi-split air conditioning units. When the air conditioning unit executes a shutdown command, control valve V1 is simultaneously opened and maintained in the open state for a certain period of time, so that the lubricating oil sprayed from each compressor M flows back into the gas-liquid separator Q. Then, when the air conditioning unit executes a startup command, control valve V1 and expansion valve V2 are first controlled to be closed, thereby returning the lubricating oil in the gas-liquid separator Q to each compressor M, avoiding compressor M failure due to lack of oil during startup, thus enabling compressor M to respond quickly and effectively improving reliability.

[0049] In another preferred embodiment of the present invention, a multi-split air conditioning unit oil return control system is also disclosed. The air conditioning unit includes at least two compressors M operating in parallel and a gas-liquid separator Q. Each compressor M is connected to the gas-liquid separator Q through an independent oil supply pipeline L1. A main oil return line L2 is also provided between the gas-liquid separator Q and an oil separator P located at the output end of the compressor M. A capillary tube G and a bypass oil return line L3 connected in parallel with the capillary tube G are provided on the main oil return line L2. A control valve V1 is provided on the bypass oil return line L3. The oil return control system controls the operation of the air conditioning unit based on the multi-split air conditioning unit oil return control method in the above embodiment.

[0050] This invention also discloses another multi-split air conditioning unit oil return control system, which includes one or more processors, a memory, and one or more programs, wherein the one or more programs are stored in the memory and configured to be executed by the one or more processors. The programs include instructions for executing the multi-split air conditioning unit oil return control method as described above. The processor can be a general-purpose central processing unit (CPU), a microprocessor, an application-specific integrated circuit (ASIC), or one or more integrated circuits, used to execute relevant programs to achieve the functions required by the modules in the multi-split air conditioning unit oil return control system of this application embodiment, or to execute the multi-split air conditioning unit oil return control method of this application method embodiment.

[0051] This invention also discloses a computer-readable storage medium comprising a computer program executable by a processor to perform the oil return control method for a multi-split air conditioning unit as described above. The computer-readable storage medium can be any available medium accessible to a computer or a data storage device such as a server or data center integrating one or more available media. The available medium can be read-only memory (ROM), random access memory (RAM), or magnetic media, such as floppy disks, hard disks, magnetic tapes, magnetic disks, or optical media, such as digital versatile discs (DVDs), or semiconductor media, such as solid-state disks (SSDs).

[0052] This application also discloses a computer program product or computer program, which includes computer instructions stored in a computer-readable storage medium. The processor of an electronic device reads the computer instructions from the computer-readable storage medium and executes the computer instructions, causing the electronic device to perform the aforementioned multi-split air conditioning unit oil return control method.

[0053] The above-disclosed embodiments are merely preferred embodiments of the present invention and should not be construed as limiting the scope of the present invention. Therefore, any equivalent variations made in accordance with the claims of the present invention are still within the scope of the present invention.

Claims

1. A method for controlling oil return of a multi-connected air conditioning unit, characterized by, The air conditioning unit comprises at least two parallelly operated compressors and a gas-liquid separator, each of the compressors is connected with the gas-liquid separator through an independent oil delivery pipeline, an oil return main path is further arranged between the gas-liquid separator and an oil separator arranged at the output end of the compressor, a capillary tube and an oil return bypass parallelly connected with the capillary tube are arranged on the oil return main path, and a control valve is arranged on the oil return bypass; the oil return control method comprises: When the air conditioning unit receives an instruction to shut down the compressor, the action of shutting down the compressor is performed, and at the same time, the control valve is opened, and the control valve is maintained in the open state for a first preset time; When the air conditioning unit receives an instruction to start the compressor, the action of starting the compressor is performed, and at the same time, the control valve and an expansion valve on the air conditioning unit are in a closed state, the control valve is maintained in the closed state for a second preset time, and the expansion valve is maintained in the closed state for a third preset time.

2. The oil return control method of a multi-connected air conditioning unit according to claim 1, characterized by, The compressor has a variable frequency system, and when the air conditioning unit receives an instruction to shut down the compressor, the method of shutting down the compressor comprises: According to the current frequency of the compressor, the frequency of the compressor is gradually reduced at a preset amplitude until the compressor is in a shutdown state.

3. The oil return control method of a multi-type air conditioning unit according to claim 2, characterized by, When the compressor is shut down in the frequency reduction mode, the frequency reduction amplitude is proportional to the current operating frequency of the compressor.

4. The oil return control method of a multi-connected air conditioning unit according to claim 3, characterized by, When the current operating frequency of the compressor is greater than or equal to 80 Hz, the frequency reduction amplitude is 4 Hz, when the current operating frequency of the compressor is greater than or equal to 60 Hz and less than 80 Hz, the frequency reduction amplitude is 3 Hz, when the current operating frequency of the compressor is greater than or equal to 40 Hz and less than 60 Hz, the frequency reduction amplitude is 2 Hz, and when the current operating frequency of the compressor is less than 40 Hz, the frequency reduction amplitude is 1 Hz.

5. The oil return control method of a multi-connected air conditioning unit according to claim 1, wherein The first preset time T1 is T1≥25s.

6. The oil return control method of a multi-connected air conditioning unit according to claim 1, wherein The second preset time T2 is 35≤T2≤45s, and when the duration exceeds the second preset time since the start of the compressor, the state of the control valve is controlled according to the exhaust gas superheat degree of the compressor.

7. The oil return control method of a multi-connected air conditioning unit according to claim 1, wherein The second preset time T3 is 15≤T3≤25s.

8. A multi-connected air conditioning unit oil return control system, characterized by, The air conditioning unit comprises at least two parallelly operated compressors and a gas-liquid separator, each of the compressors is connected with the gas-liquid separator through an independent oil delivery pipeline, an oil return main path is further arranged between the gas-liquid separator and an oil separator arranged at the output end of the compressor, a capillary tube and an oil return bypass parallelly connected with the capillary tube are arranged on the oil return main path, and a control valve is arranged on the oil return bypass; the oil return control system controls the operation of the air conditioning unit based on the oil return control method of the multi-connected air conditioning unit according to any one of claims 1 to 7.

9. A multi-connected air conditioning unit oil return control system, characterized by, Comprise: One or more processors; Memory; And one or more programs, wherein one or more programs are stored in the memory and are configured to be executed by the one or more processors, the programs comprise instructions for executing the oil return control method of the multi-connected air conditioning unit according to any one of claims 1 to 7.

10. A computer-readable storage medium, characterized in that, The computer program can be executed by a processor to complete the oil return control method of the multi-connected air conditioning unit as claimed in any one of claims 1 to 7.

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