Low-temperature oil return control method and equipment, heat pump unit and storage medium

Abstract

The invention discloses a low-temperature oil return control method and device, a heat pump unit and a storage medium, the method is used for the heat pump unit, the heat pump unit comprises a gas-liquid separator, at least one oil outlet hole is additionally formed in the upper portion of the gas-liquid separator, and the oil outlet hole is connected with a compressor through an oil outlet pipeline; the method comprises the steps that before a unit is started, at least one layering correlation characteristic parameter is detected, and whether lubricating oil and a refrigerant in a gas-liquid separator are layered or not is determined according to the layering correlation characteristic parameter; and when the layering condition occurs in the gas-liquid separator, before the compressor is started, the gas-liquid separator enters an oil return mode, so that lubricating oil enters the compressor through the oil outlet hole and the oil outlet pipeline. Aiming at the oil seal phenomenon, upper-layer oil is rapidly guided through the upper oil outlet hole, the problem that an oil return and gas return channel is blocked during low-temperature starting is fundamentally solved, it is ensured that the compressor can be lubricated in time when started under the severe working condition, abrasion caused by liquid impact and insufficient lubrication is effectively prevented, and the service life of the compressor is prolonged.

Description

Technical Field

[0001] This application relates to the technical field of heat pump systems, and in particular to a low-temperature oil return control method, equipment, heat pump unit, and storage medium. Background Technology

[0002] In heat pump systems, the compatibility of refrigerant and compressor oil (also known as refrigeration oil) is one of the key factors ensuring stable system operation. Both must maintain a good solubility state during system circulation to ensure the compressor's lubrication requirements and the refrigerant's heat exchange efficiency. For heat pump systems using high-density refrigerants, operational reliability in low-temperature environments faces particular challenges, especially when the system is left stagnant for extended periods in temperatures ranging from 0°C to -30°C, disrupting the phase equilibrium between the refrigerant and compressor oil.

[0003] Specifically, low temperatures significantly alter the solubility of high-density refrigerant and compressor oil. Combined with their inherent density difference, this makes stratification highly likely within the system. This stratification is particularly pronounced in the gas-liquid separator. As a core component in heat pump systems used to separate gaseous and liquid refrigerant and ensure compressor suction quality, the gas-liquid separator becomes the primary retention area for refrigerant and compressor oil, ultimately resulting in a stratified state where the denser refrigerant settles to the bottom layer and the compressor oil floats to the top.

[0004] In the existing technology, the structural design of conventional gas-liquid separators usually only has one air inlet and one air outlet at the top. This structure can meet the basic gas-liquid separation requirements under normal operating conditions where the refrigerant and refrigeration oil are fully mixed. However, when the aforementioned stratification phenomenon occurs after low-temperature settling, the upper layer of refrigeration oil forms a liquid seal-like covering layer on the surface of the lower layer of refrigerant. This structural defect directly leads to two fatal problems during the system startup phase: First, the covering layer formed by the upper oil layer obstructs the normal flow of gaseous refrigerant, causing poor gas return and excessively low pressure at the low-pressure end of the system. At the same time, the lower layer of liquid refrigerant cannot evaporate sufficiently, which not only leads to a significant decrease in compressor suction efficiency but also makes it very easy for the compressor to suck in unevaporated liquid refrigerant, causing liquid slugging and severely damaging compressor components. Second, because the stratification of refrigerant and refrigeration oil disrupts their dissolution balance, most of the refrigeration oil cannot flow back to the compressor with the refrigerant circulation. Long-term operation will lead to insufficient oil storage in the compressor crankcase, causing air-oil lubrication failure, which in turn causes severe wear on moving parts such as compressor pistons and bearings, ultimately leading to compressor failure and paralysis of the entire heat pump system. Summary of the Invention

[0005] The purpose of this application is to provide a low-temperature oil return control method, equipment, heat pump unit, and storage medium, which can solve the above-mentioned problems existing in the prior art.

[0006] To achieve the above objectives, this application adopts the following technical solution: On the one hand, a low-temperature oil return control method is provided for a heat pump unit, the method comprising: Before the unit is started, the stratification correlation characteristic parameters are detected, and the stratification correlation characteristic parameters are used to determine whether stratification occurs inside the gas-liquid separator. When stratification occurs in the gas-liquid separator, before the compressor starts or after a preset first time, the oil return mode is entered so that the lubricating oil in the upper layer of the gas-liquid separator is introduced into the compressor.

[0007] Furthermore, the hierarchical correlation feature parameters include temperature parameters and time parameters that characterize the hierarchical induction conditions.

[0008] Furthermore, the temperature parameter is the ambient temperature, and the time parameter is the downtime.

[0009] Furthermore, determining whether stratification occurs inside the gas-liquid separator based on the stratification correlation feature parameters further includes: When the ambient temperature is lower than a preset temperature threshold and the shutdown duration is greater than or equal to a preset duration threshold, the oil return mode is entered.

[0010] Furthermore, the hierarchical correlation feature parameters include medium state parameters that characterize the hierarchical state.

[0011] Furthermore, the medium state parameter is the liquid level height inside the gas-liquid separator.

[0012] Furthermore, the upper part of the gas-liquid separator is provided with at least one oil outlet, the oil outlet is connected to the inlet end of the compressor through an oil outlet pipeline, and a control valve is provided on the oil outlet pipeline; In the oil return mode, the control valve is kept open for a preset second duration.

[0013] On the other hand, a low-temperature oil return control device is also provided, comprising: Memory and one or more processors; The memory is used to store one or more programs; When the one or more programs are executed by the one or more processors, the one or more processors perform the method described above.

[0014] On the other hand, a heat pump unit is also provided, including: a compressor, a condenser, a throttling device, an evaporator, and a gas-liquid separator connected in a circulation loop via pipelines. The outlet end of the compressor is connected to a four-way valve, which is also connected to the condenser, the evaporator, and the gas-liquid separator respectively. The upper part of the gas-liquid separator is provided with at least one oil outlet hole, which is connected to the inlet end of the compressor via an oil outlet pipeline. A control valve is provided on the oil outlet pipeline. The heat pump unit performs the method described above.

[0015] On the other hand, a storage medium for storing computer-executable instructions is also provided, which, when executed by a processor, are used to perform the methods described above.

[0016] The beneficial effects of this application are as follows: by setting an oil outlet hole and matching oil outlet pipeline and control valve at the top of the gas-liquid separator, and combining the pre-detection of layered correlation characteristic parameters and oil return mode control, it is possible to accurately break the liquid seal barrier formed by the upper layer of lubricating oil after low temperature standing, and smooth the return gas channel to ensure that the lower layer of liquid refrigerant evaporates fully, fundamentally avoiding the risk of compressor liquid slugging. At the same time, it can actively guide the upper layer of lubricating oil to the compressor without relying on oil refrigerant dissolution balance, effectively solving the problem of compressor air-oil lubrication failure, significantly extending the compressor service life, improving the start-up reliability and long-term operation stability of high-density refrigerant heat pump system under low temperature conditions, and its structure is simple and the transformation and implementation cost is low. Attached Figure Description

[0017] The present application will now be described in further detail with reference to the accompanying drawings and embodiments.

[0018] Figure 1 This is a flowchart of the low-temperature oil return control method described in the embodiments of this application; Figure 2 This is a schematic diagram of the cryogenic oil return control device described in the embodiments of this application; Figure 3 This is a schematic diagram of the heat pump unit described in the embodiments of this application. Detailed Implementation

[0019] To make the technical problems solved by this application, the technical solutions adopted, and the technical effects achieved clearer, the technical solutions of the embodiments of this application are further described in detail below. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0020] In the description of this application, unless otherwise expressly specified and limited, the terms "connected," "linked," and "fixed" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0021] In this application, unless otherwise expressly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature being directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature being directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0022] like Figure 1 As shown, this embodiment provides a low-temperature oil return control method for a heat pump unit. The heat pump unit includes a gas-liquid separator with two ports (one inlet and one outlet) at the top and at least one oil outlet at the top. The oil outlet is connected to the compressor via an oil outlet pipeline, and a control valve is installed on the oil outlet pipeline. The method includes: Step 101: Before the unit is started, at least one stratification correlation characteristic parameter is detected, and the stratification correlation characteristic parameter is used to determine whether the lubricating oil and refrigerant in the gas-liquid separator are stratified. Step 102: When stratification occurs in the gas-liquid separator, before the compressor starts or after a preset first time, the oil return mode is entered so that the lubricating oil enters the compressor through the oil outlet and the oil outlet pipeline.

[0023] Based on the above scheme, before unit startup, at least one stratification-related characteristic parameter (such as ambient temperature, liquid level in the gas-liquid separator, etc.) is detected to accurately determine whether there is a stratified state in the gas-liquid separator where lubricating oil floats on the upper layer and high-density refrigerant settles on the lower layer. This avoids ineffective intervention under normal operating conditions and ensures the targeted and accurate nature of the control strategy. For the liquid seal layer formed by the upper lubricating oil after stratification, the oil outlet hole set at the top of the gas-liquid separator is precisely aligned with the area of ​​lubricating oil floating on the upper layer to construct a dedicated oil return channel. Once stratification is confirmed, the oil return mode is activated by opening the control valve. Using the pressure difference generated by the compressor operation or the system's preset pressure difference mechanism, the upper lubricating oil is driven to flow directly to the compressor through the oil outlet hole and oil outlet pipeline, quickly eliminating the oil's coverage of the lower refrigerant and restoring the flow path of the gaseous refrigerant from the source, thus solving the problem of gas return obstruction caused by the oil seal.

[0024] On the one hand, the oil return mode does not rely on the dissolution balance between refrigerant and lubricating oil. Through the active diversion method driven by the pressure difference, the residual lubricating oil can be quickly delivered to the compressor crankcase before or at the beginning of compressor startup, and the lubricating medium can be replenished in time before the system circulation is fully established. On the other hand, with the removal of the upper oil seal, the gaseous refrigerant in the gas-liquid separator can flow smoothly, the low-pressure end pressure remains stable, and the lower liquid refrigerant obtains sufficient evaporation space, which can be fully evaporated into gas before entering the compressor, avoiding the risk of liquid slugging caused by the suction of liquid refrigerant.

[0025] Based on the above working principle, the technical solution of this application has the following effects: (1) Completely solve the risks of poor gas return and liquid slugging during low-temperature start-up and ensure the safe operation of the compressor: Through the targeted design of the oil outlet at the top of the gas-liquid separator, the pressure difference-driven diversion mechanism and the active intervention of the oil return mode, the liquid seal barrier formed by the lubricating oil after stratification can be broken precisely and efficiently, so that the gaseous refrigerant flow path in the gas-liquid separator can be restored to smooth flow, effectively solving the problems of blocked gas return and excessively low pressure in the existing technology; at the same time, the liquid refrigerant in the lower layer obtains sufficient evaporation conditions, and can fully vaporize and enter the compressor suction port, fundamentally avoiding the compressor liquid slugging failure caused by liquid refrigerant suction, and significantly improving the operating safety of the compressor under low-temperature start-up conditions.

[0026] (2) Efficiently solves the problem of oil return after low temperature standing and avoids lubrication failure damage: The lubricating oil is directly drawn back by the pressure difference drive, without relying on the natural dissolution and mixing of refrigerant and lubricating oil. During the critical stage of compressor start-up, the lubricating oil remaining on the upper layer of the gas-liquid separator can be quickly transported to the compressor crankcase, ensuring that the crankcase always maintains a sufficient oil reserve. This completely solves the hidden danger of empty oil caused by the lubricating oil not being able to circulate back with the refrigerant in the existing technology, and provides continuous and reliable lubrication protection for the compressor piston, bearing and other moving parts, effectively avoiding the wear of parts caused by insufficient lubrication, significantly extending the service life of the compressor and reducing the unit failure maintenance cost.

[0027] (3) Precise control and strong adaptability, improving the reliability of the system under extreme conditions: By pre-detection and judgment of hierarchical associated characteristic parameters, the oil return mode can be started on demand. This not only does not interfere with the normal operation of the system under normal conditions, but also accurately adapts to the special conditions of high-density refrigerant heat pump system after long-term static operation in low-temperature environment from 0℃ to -30℃. This effectively fills the gap in the adaptation of existing technology to extreme low-temperature static operation conditions, greatly improves the start-up reliability and long-term operation stability of heat pump system under complex climatic conditions, and broadens the application scenarios of heat pump system.

[0028] (4) Simple structure and easy implementation, with significant engineering practical value: This application can fundamentally solve the low-temperature stratification problem simply by adding an oil outlet hole, matching oil outlet pipeline and control valve to the upper part of the gas-liquid separator, combined with the differential pressure driven oil return logic and intelligent control strategy, without the need for major modifications to the core components of the heat pump system (such as compressor, condenser, throttling device, etc.). Its structural design is simple and compact, with low modification difficulty and controllable implementation cost. Moreover, the differential pressure driven mode conforms to the conventional operating principle of the heat pump system, without the need for additional pressurization equipment, making it easy for industrial production and upgrading of existing units. It has broad application prospects and significant engineering practical value.

[0029] Furthermore, the stratification-related characteristic parameters include temperature and time parameters characterizing the stratification induction conditions. The temperature parameter directly relates to the solubility characteristics of the refrigerant and lubricating oil. The miscibility of high-density refrigerant and lubricating oil decreases significantly with decreasing temperature. When the detected ambient temperature or the gas-liquid separator body temperature is within the high-risk stratification range of 0℃ to -30℃, it can be determined that the system possesses the conditions for inducing oil refrigerant stratification, providing a core environmental basis for stratification status judgment. The time parameter corresponds to the duration of the system's low-temperature static state. Oil refrigerant stratification is a dynamic cumulative process. Only when the system is statically placed in a low-temperature environment for a preset critical duration can the refrigerant and lubricating oil complete sufficient gravity stratification, forming a stable oil-on-top, refrigerant-on-bottom stratified structure. By detecting the duration of the low-temperature environment, it can be determined whether the stratification phenomenon has developed to the point requiring intervention.

[0030] By coupling temperature and time parameters for judgment, rather than judging based on a single parameter, interference from non-stratified operating conditions such as short-term low temperatures and long-term normal temperatures can be effectively eliminated. This ensures that the oil return mode is only activated when both the low-temperature environment and sufficient settling time are met. This judgment mechanism is precisely linked to the subsequent differential pressure-driven targeted oil return control logic, providing a reliable pre-judgment basis for the on-demand activation of the oil return mode.

[0031] Furthermore, the temperature parameter refers to the ambient temperature, and the time parameter refers to the downtime. Ambient temperature directly determines the thermodynamic environment of the system and is the core inducing factor for oil-refrigerant stratification. For heat pump systems using high-density refrigerants, when the ambient temperature is below the critical miscibility temperature of the refrigerant and compressor oil, and falls into the high-risk range of 0℃ to -30℃, their miscibility decreases sharply, the intermolecular dissolution equilibrium is broken, and the basic thermodynamic conditions for stratification are met. By detecting the ambient temperature, it is possible to directly determine whether the system is within the environmental threshold where stratification is likely to occur, providing a core environmental basis for stratification judgment. Moreover, ambient temperature detection does not require intrusion into the system, offering the inherent advantages of convenient implementation and low detection cost. Downtime corresponds to the cumulative static time of the system in a low-temperature environment. Oil-refrigerant stratification is a dynamic equilibrium process driven by gravity, not an instantaneous occurrence in low-temperature environments. It requires a certain amount of time to complete sufficient density stratification, forming a stable state where "lubricating oil floats on top and high-density refrigerant settles at the bottom." By detecting the downtime, the development stage of the stratification phenomenon can be accurately defined. When the downtime reaches the preset critical value, it indicates that the refrigerant and lubricating oil have completed sufficient stratification and formed a dense oil seal structure that requires intervention. If the downtime does not reach the critical value, even if the ambient temperature is low, there is only a potential risk of stratification, and stable stratification has not been formed, so there is no need to start the oil return mode.

[0032] A dual-criteria system is established by coupling ambient temperature and downtime for judgment. Before unit startup, the system first checks whether the ambient temperature falls within the high-risk range for stratification, and then determines whether the downtime reaches a critical value. Only when both conditions are met is stable stratification within the gas-liquid separator determined to exist. If either parameter is not met, such as an ambient temperature higher than the critical miscibility temperature, or a short downtime in a low-temperature environment, the system is judged to be in a non-stratification condition. This coupled judgment logic precisely connects to the subsequent oil return mode, ensuring that oil return intervention is only initiated under truly necessary conditions, avoiding ineffective intervention.

[0033] Specifically, when the ambient temperature is lower than a preset temperature threshold and the shutdown duration is greater than or equal to a preset duration threshold, the system enters the oil return mode. By using both the low-temperature threshold and the duration threshold, interference from various non-target operating conditions is effectively eliminated. On the one hand, this avoids false triggering in scenarios such as insufficient stratification due to short-term low temperatures or insufficient shutdown due to low temperatures, preventing increased energy consumption and ineffective wear of the control valve caused by ineffective oil return mode startup. On the other hand, it eliminates missed triggering in scenarios of sufficient stratification due to long-term low-temperature shutdown, avoiding faults such as poor air return, liquid slugging, and insufficient lubrication caused by untimely intervention, significantly improving the accuracy and reliability of the control strategy.

[0034] This judgment rule employs explicit threshold comparison logic, eliminating the need for complex algorithm calculations or multi-parameter fitting. The system can quickly complete detection and judgment, shortening the preparation time before unit startup and improving startup response efficiency. Simultaneously, the rigid dual-threshold condition reduces ambiguity in the judgment process, lowers judgment deviations caused by parameter fluctuations, enhances the stability of the control logic, and adapts to the fluctuating sensor signal characteristics in low-temperature environments. Furthermore, ambient temperature detection relies on the existing external temperature sensor of the heat pump system, and downtime can be obtained through the existing controller's timing module. Preset temperature and duration thresholds can be directly configured through system software parameters, without requiring additional dedicated detection equipment or modifications to the system hardware structure. This design is perfectly compatible with the existing unit's hardware and control architecture, significantly reducing implementation costs, modification difficulty, and debugging cycle, and significantly improving its engineering practicality and applicability.

[0035] Specifically, a system is considered at risk of stratification when the ambient temperature is below 5℃, the downtime is ≥2 hours, and the system receives a start-up command. Based on experimental data on the miscibility of high-density refrigerant and compressor oil, 5℃ is the critical point where their miscibility significantly decreases. When the ambient temperature is below 5℃, the intermolecular solubility equilibrium between the high-density refrigerant and compressor oil is disrupted, and their miscibility decreases sharply. The system already possesses the thermodynamic basis for oil-refrigerant stratification. Compared to a broad low-temperature range, the specific threshold of 5℃ more closely matches the starting boundary of stratification risk in actual application scenarios, accurately identifying low-temperature environments with genuine stratification risks and avoiding invalid judgments due to overly broad thresholds. Furthermore, this temperature parameter can be acquired in real-time using the system's standard external ambient temperature sensor, eliminating the need for additional dedicated detection components, thus balancing accuracy and ease of implementation.

[0036] Refrigerant stratification is a dynamic settling process driven by gravity. Based on engineering data, high-density refrigerant and compressor oil require at least 2 hours of settling time in an environment below 5°C to fully stratify, forming a stable structure where lubricating oil floats on top and high-density refrigerant settles at the bottom. Setting the shutdown time threshold to 2 hours allows for precise determination of whether stratification has progressed to a stable stage requiring intervention. When the shutdown time is ≥2 hours, stratification is complete, and the upper lubricating oil forms a dense oil seal. If the shutdown time is less than 2 hours, even if the ambient temperature is below 5°C, stratification is still in its initial stage, and a stable oil seal structure has not yet formed. Therefore, activating the oil return mode is unnecessary, avoiding premature intervention and resource waste. This duration parameter can be accurately recorded by the system controller's timing module without additional adjustments.

[0037] The system receiving a startup command is the core trigger condition for judgment. Strongly linking the tiered risk judgment with the startup command ensures that the judgment action only occurs at critical points before the unit starts, avoiding invalid continuous judgments during shutdown and reducing system computing power consumption. Simultaneously, this trigger condition ensures precise integration of tiered risk judgment with subsequent startup procedures and oil return modes. When all three conditions are met simultaneously, the system can immediately initiate special oil return intervention before or at the beginning of startup, preventing direct unit startup under tiered operating conditions from causing malfunctions and ensuring the safety and continuity of the startup process.

[0038] The judgment criterion adopts a triple-coupling logic of "necessary condition + sufficient condition + triggering condition". An ambient temperature below 5℃ is a necessary thermodynamic prerequisite for stratification, a downtime of ≥2h is a sufficient condition for stratification stability, and the system receiving a start command is the trigger node for judgment and intervention. All three are indispensable. In actual operation, the system first monitors the ambient temperature and downtime in real time. Only when both meet the threshold requirements and a start command is received from the user or control system is the system finally judged as a stratification risk condition. If any condition is not met (e.g., ambient temperature ≥5℃, downtime <2h, no start command received), it is judged as a normal operating condition and operates according to the normal start-up procedure. This closed-loop logic ensures that the stratification risk judgment is accurately matched with the actual operating condition requirements, achieving the core control objective of intervention on demand.

[0039] In some embodiments, the stratification-related characteristic parameters include media state parameters characterizing the stratification state. These media state parameters, characterizing the stratification state, are core indicators directly reflecting whether a stable stratification has formed between the refrigerant and lubricating oil within the gas-liquid separator, distinct from indirect parameters such as ambient temperature and downtime. The core logic is that refrigerant stratification leads to significant abrupt changes in the physical distribution or properties of the media within the gas-liquid separator; detecting these abrupt changes directly verifies whether stratification has occurred. Typical media state parameters include the liquid level height, media density, dielectric constant, and pressure differential distribution within the gas-liquid separator. For example, after stratification, the density difference between the upper lubricating oil and the lower high-density refrigerant can cause a false stabilization of the liquid level (the liquid level height no longer changes with slight disturbances), or the density abrupt change between the upper and lower media can be directly detected by a density sensor; a dielectric constant sensor can accurately identify the existence of the stratification interface through the difference in dielectric properties between the refrigerant and lubricating oil.

[0040] Specifically, the medium state parameter refers to the liquid level height within the gas-liquid separator. When the oil refrigerant is not stratified, the refrigerant and lubricating oil in the gas-liquid separator are in a mixed state, and the liquid level in the accumulation area will fluctuate with the residual pressure of the system and show slight dynamic changes with minor disturbances in the medium. However, when the two are fully stratified in a low-temperature environment to form a stable structure where the lubricating oil floats on the upper layer and the high-density refrigerant settles in the lower layer, the stratification interface will form a physical barrier, so that the overall liquid level in the accumulation area will no longer change with slight external disturbances, and the final stable liquid level height will be significantly higher than the mixed medium liquid level when it is not stratified (because the medium molecules are more densely arranged after stratification, the volume contraction is smaller for the same mass, or because the medium settles sufficiently during the stratification process, and there are no suspended droplets in the accumulation area, causing the liquid level reference to rise). Based on this characteristic, the stable state and height threshold of the liquid level height can be directly used as the core criteria for determining whether stratification has formed.

[0041] The liquid level parameter is not used in isolation, but rather forms a predictive-verification collaborative logic with ambient temperature and downtime. The specific judgment process is as follows: First, the system initially screens out operating conditions with potential stratification risks by checking whether the ambient temperature is below 5℃ and whether the downtime is ≥2h. Second, the system collects real-time liquid level data through a preset liquid level sensor in the gas-liquid separator, while simultaneously monitoring the stability of the liquid level. If the liquid level is stable and reaches the preset stratification threshold (this threshold is based on the unit's rated medium filling volume and the gas-liquid separator volume pre-calibrated), then it is finally determined to be a stratification operating condition, and the oil return mode is activated. If the triggering parameters are met but the liquid level does not reach the threshold or is still in a dynamic fluctuation state, then it is determined that a stable stratification has not formed, and the system is activated according to the normal procedure to avoid false triggering.

[0042] Throughout the entire stratification process, the liquid level exhibits a traceable pattern of change, further enhancing the accuracy of judgment. In the initial stage of stratification, the mixed medium begins to settle, and the liquid level rises slowly with minor fluctuations. During the stratification stabilization stage, the liquid level stops rising and enters a pseudo-stabilized state. In the stratification resolution stage, the liquid level fluctuates again and its height slowly decreases. Based on this pattern, the system can accurately identify the stage of stratification by continuously monitoring the trend of liquid level changes. The oil return mode is only activated when the liquid level enters the stabilization stage, ensuring optimal intervention timing. Simultaneously, liquid level changes can be monitored in real time during the oil return process. When the liquid level begins to fluctuate dynamically again and its height falls back to the normal mixed liquid level range, it is determined that stratification has been resolved, and the oil return mode is immediately shut off, achieving refined control of the oil return process.

[0043] Liquid level detection can be achieved by pre-installing a liquid level sensor (such as a float-type liquid level sensor or a capacitive liquid level sensor) in the liquid accumulation area from the middle to the bottom of the gas-liquid separator housing. The sensor installation height covers the entire range from the un-separated mixed liquid level to the stratified stable liquid level. This installation method is fully compatible with the existing gas-liquid separator structure, requiring no major modifications to the housing. Furthermore, the liquid level sensor signal can be directly connected to the system controller for collaborative calculation with ambient temperature and downtime data, without the need to reconstruct the core control logic, thus balancing detection accuracy and ease of engineering implementation.

[0044] It is worth mentioning that in the oil return mode, the control valve is kept open for a preset second duration. Specifically, the brief opening of the control valve in oil return mode can directly target and extract the upper layer of lubricating oil, quickly breaking the blockage of the oil film on the lower layer of refrigerant. Compared with existing technologies that rely on the natural dissolution of refrigerant through circulation, the sealing efficiency is significantly improved, creating sufficient conditions for the evaporation of the lower layer of refrigerant and fundamentally solving the problems of poor gas return, excessively low pressure, and liquid slugging risks. At the same time, the timing control of the brief opening avoids excessive flow and prevents the lower layer of liquid refrigerant from being sucked in, further improving the safety of compressor startup.

[0045] During normal operation, the control valve is closed, keeping the gas-liquid separator in its normal flow field structure and ensuring that the gas-liquid separation efficiency meets the standard. The normal oil return logic of the normal return gas pipeline conforms to the original circulation design of the system. It can achieve stable mixing and circulation of lubricating oil and refrigerant without additional intervention, ensuring stable system pressure and heat exchange efficiency, and avoiding the impact of adding an oil outlet structure on normal operating performance.

[0046] On the other hand, a heat pump unit is also provided, such as Figure 3As shown, it includes: a compressor 1, a condenser 2, a throttling device 4, an evaporator 3, and a gas-liquid separator 5 connected in a circulation loop via pipelines. The outlet end of the compressor 1 is connected to a four-way valve 7, which is also connected to the condenser 2, the evaporator 3, and the gas-liquid separator 5 respectively. The upper part of the gas-liquid separator 5 is provided with at least one oil outlet hole, which is connected to the inlet end of the compressor 1 via an oil outlet pipeline. A control valve 6 is provided on the oil outlet pipeline. The heat pump unit performs the method described above.

[0047] Meanwhile, an air inlet and an air outlet are provided on the top of the gas-liquid separator 5. The air inlet is connected to a four-way valve 7, and the air outlet is connected to the inlet of the compressor 1. A three-way valve 8 is provided on the pipeline, which is connected to the oil return pipeline, the air outlet and the compressor 1 respectively.

[0048] Furthermore, the hierarchical correlation feature parameters include temperature parameters and time parameters that characterize the hierarchical induction conditions.

[0049] Furthermore, the temperature parameter is the ambient temperature, and the time parameter is the downtime.

[0050] Furthermore, determining whether stratification occurs inside the gas-liquid separator 5 based on the stratification correlation feature parameters further includes: When the ambient temperature is lower than a preset temperature threshold and the shutdown duration is greater than or equal to a preset duration threshold, the oil return mode is entered.

[0051] Furthermore, the hierarchical correlation feature parameters include medium state parameters that characterize the hierarchical state.

[0052] Furthermore, the medium state parameter is the liquid level height inside the gas-liquid separator 5.

[0053] Furthermore, in the oil return mode, the control valve 6 is kept open for a preset second duration.

[0054] In this solution, the addition of a dedicated oil return branch allows the unit to directly target and extract the upper layer of lubricating oil after stratification, quickly breaking the oil film blockage and creating sufficient conditions for the evaporation of the lower layer of refrigerant. This fundamentally solves the risks of poor gas return, excessively low pressure, liquid slugging, and insufficient lubrication during low-temperature startup of existing units. Combined with precise stratification determination and timing control, intervention is only initiated when necessary, avoiding ineffective operations and significantly improving the safety and reliability of compressor 1 during low-temperature startup. The complete retention of the conventional circulation loop allows the unit to maintain its original stable cooling / heating functions under non-stratified operating conditions, and the conventional gas-liquid separation function of gas-liquid separator 5 remains unaffected. The control valve 6 of the dedicated oil return branch is closed during normal operation, avoiding interference from the new structure on the circulation flow field, ensuring that the refrigerant circulation efficiency and heat exchange efficiency are on par with the original unit, and guaranteeing that the unit's performance indicators meet the standards under normal operating conditions. Moreover, the dedicated oil return branch is achieved simply by adding an oil outlet hole, matching oil outlet pipeline and control valve 6 to the upper part of the gas-liquid separator 5, without the need for major modifications to core components such as compressor 1, condenser 2, and four-way valve 7, and is perfectly compatible with the existing heat pump unit's structural architecture; the added components have a simple structure and controllable cost, which facilitates the upgrading and transformation of existing units and the industrial production of new units.

[0055] In addition, the unit can not only operate stably under normal operating conditions such as normal temperature and short-term low temperature, but also accurately cope with the stratified start-up condition after long-term static placement in low temperature environments of 0℃ to -30℃. By adjusting parameters such as the stratification judgment threshold and preset duration, it can also be adapted to units with different types of high-density refrigerants and different specifications of heat exchange components, effectively expanding the low-temperature application scenarios of heat pump units and improving the adaptability of units under complex climatic conditions.

[0056] On the other hand, a low-temperature oil return control device is also provided, such as Figure 2 As shown, it includes: The device includes a processor 21, a memory 22, a communication module 23, an input device 24, and an output device 25. The cryogenic oil return control device may have one or more processors 21 and one or more memory units 22. The processor 21, memory 22, communication module 23, input device 24, and output device 25 of the cryogenic oil return control device can be connected via a bus or other means.

[0057] The memory 22, as a computer-readable storage medium, can be used to store software programs, computer-executable programs, and modules, such as the program instructions / modules corresponding to the low-temperature oil return control method described in any embodiment of this application. The memory 22 may mainly include a program storage area and a data storage area. The program storage area may store the operating system and at least one application program required for a function; the data storage area may store data created based on the use of the device, etc. Furthermore, the memory 22 may include high-speed random access memory 22, and may also include non-volatile memory 22, such as at least one disk storage device 22, flash memory device, or other non-volatile solid-state memory 22.

[0058] In some instances, memory 22 may further include memory 22 remotely located relative to processor 21, and these remote memories 22 may be connected to the device via a network. Examples of such networks include, but are not limited to, the Internet, corporate intranets, local area networks, mobile communication networks, and combinations thereof.

[0059] The communication module 23 is used for data transmission.

[0060] The processor 21 executes various functional applications and data processing of the device by running software programs, instructions and modules stored in the memory 22, thereby realizing the above-mentioned low-temperature oil return control method.

[0061] Input device 24 can be used to receive input digital or character information, and to generate key signal inputs related to user settings and function control of the device. Output device 25 may include display devices such as a display screen.

[0062] The low-temperature oil return control device provided above can be used to execute the low-temperature oil return control method provided in the above embodiments, and has corresponding functions and beneficial effects.

[0063] This application embodiment also provides a storage medium for storing computer-executable instructions. When executed by a computer processor 21, the computer-executable instructions are used to perform the following actions before the unit starts: detecting at least one layering-related characteristic parameter, and determining whether there is layering between the lubricating oil and refrigerant in the gas-liquid separator based on the layering-related characteristic parameter; when layering occurs in the gas-liquid separator, before the compressor starts or after a preset first time, entering the oil return mode so that the lubricating oil enters the compressor through the oil outlet and the oil outlet pipeline.

[0064] The storage medium is any type of memory device 22 or storage device. The term "storage medium" is intended to include: mounting media, such as CD-ROM, floppy disk, or magnetic tape devices; computer system memory 22 or random access memory 22, such as DRAM, DDRRAM, SRAM, EDORAM, Rambus RAM, etc.; non-volatile memory 22, such as flash memory, magnetic media (e.g., hard disk or optical storage); registers or other similar types of memory elements 22, etc. The storage medium may also include other types of memory 22 or combinations thereof. Furthermore, the storage medium may reside in a first computer system in which the program is executed, or it may reside in a different second computer system connected to the first computer system via a network (such as the Internet). The second computer system can provide program instructions to the first computer for execution. The term "storage medium" may include two or more storage media residing in different locations (e.g., in different computer systems connected via a network). The storage medium may store program instructions (e.g., specifically implemented as a computer program) executable by one or more processors 21.

[0065] Of course, the computer-executable instructions stored in the storage medium provided in the embodiments of this application are not limited to the cryogenic oil return control method as described above, but can also execute related operations in the cryogenic oil return control method provided in any embodiment of this application.

[0066] The cryogenic oil return control device and storage medium provided in the above embodiments can execute the cryogenic oil return control method provided in any embodiment of this application. For technical details not described in detail in the above embodiments, please refer to the cryogenic oil return control method provided in any embodiment of this application.

[0067] In the description herein, it should be understood that the terms "upper," "lower," "left," "right," and other orientations or positional relationships are used only for ease of description and simplification of operation, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application. Furthermore, the terms "first" and "second" are used merely for descriptive distinction and have no special meaning.

[0068] In the description of this specification, references to terms such as "an embodiment," "example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this application. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example.

[0069] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style of the specification is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

[0070] The technical principles of this application have been described above with reference to specific embodiments. These descriptions are merely for explaining the principles of this application and should not be construed as limiting the scope of protection of this application in any way. Based on this explanation, those skilled in the art can readily conceive of other specific embodiments of this application without inventive effort, and these embodiments will all fall within the scope of protection of this application.

Claims

1. A low-temperature oil return control method for heat pump units, characterized in that, The method includes: Before the unit is started, the stratification correlation characteristic parameters are detected, and the gas-liquid separator is determined to be stratified based on the stratification correlation characteristic parameters. When the gas-liquid separator is internally layered, it enters the oil return mode before the compressor starts or after a preset first time, so that the lubricating oil in the upper layer of the gas-liquid separator is introduced into the compressor.

2. The low-temperature oil return control method according to claim 1, characterized in that, The hierarchical correlation feature parameters include temperature parameters and time parameters that characterize the hierarchical induction conditions.

3. The low-temperature oil return control method according to claim 2, characterized in that, The temperature parameter is the ambient temperature, and the time parameter is the downtime.

4. The low-temperature oil return control method according to claim 3, characterized in that, The step of determining whether stratification occurs inside the gas-liquid separator based on the stratification correlation feature parameters further includes: When the ambient temperature is lower than a preset temperature threshold and the shutdown duration is greater than or equal to a preset duration threshold, the oil return mode is entered.

5. The low-temperature oil return control method according to any one of claims 1-4, characterized in that, The hierarchical correlation feature parameters include medium state parameters that characterize the hierarchical state.

6. The low-temperature oil return control method according to claim 5, characterized in that, The medium state parameter is the liquid level height inside the gas-liquid separator.

7. The low-temperature oil return control method according to any one of claims 1-4, characterized in that, The gas-liquid separator is provided with at least one oil outlet at its upper part. The oil outlet is connected to the inlet end of the compressor through an oil outlet pipeline, and a control valve is provided on the oil outlet pipeline. In the oil return mode, the control valve is kept open for a preset second duration.

8. A low-temperature oil return control device, characterized in that, include: Memory and one or more processors; The memory is used to store one or more programs; When the one or more programs are executed by the one or more processors, the one or more processors implement the method as described in any one of claims 1-7.

9. A heat pump unit, characterized in that, include: A compressor, condenser, throttling device, evaporator, and gas-liquid separator are connected in a circulation loop via pipelines. The outlet end of the compressor is connected to a four-way valve, which is also connected to the condenser, the evaporator, and the gas-liquid separator. The upper part of the gas-liquid separator is provided with at least one oil outlet hole, which is connected to the inlet end of the compressor via an oil outlet pipeline. A control valve is provided on the oil outlet pipeline. The heat pump unit performs the method as described in any one of claims 1-7.

10. A storage medium for storing computer-executable instructions, characterized in that, The computer-executable instructions, when executed by a processor, are used to perform the method as described in any one of claims 1-7.

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