Oil return control method for variable-frequency water chilling unit

Abstract

The invention discloses an oil return control method for a variable-frequency water chilling unit, and relates to the technical field of water chilling units, and the oil return control method for the variable-frequency water chilling unit is characterized in that a variable-frequency compressor, an oil separator, an air side condenser, an oil return capillary tube, a condensation fan, a refrigeration electronic expansion valve and a water side evaporator are included; refrigerant is subjected to oil-gas separation in the oil separator, lubricating oil enters the bottom of the oil separator along the inner wall face of the oil separator, refrigerant gas is located on the upper portion of the oil separator, the refrigerant gas from the oil separator enters the air side condenser for heat release and condensation, and oil in the oil separator is sucked into a water side heat exchange part of the inverter compressor through the oil return capillary tube. The variable-frequency compressor has the advantages that sufficient lubricating oil can be continuously supplied to the variable-frequency compressor in the running process, faults such as excessive abrasion and clamping stagnation caused by oil shortage are avoided, and the stability and reliability of the variable-frequency compressor are greatly improved.

Description

Technical Field

[0001] The present invention relates to the technical field of water chillers, and more specifically, it relates to a method for controlling oil return of a variable-frequency water chiller. Background Art

[0002] In the field of refrigeration technology, variable-frequency water chillers have advantages such as high efficiency, energy conservation, and the ability to flexibly adjust the refrigerating capacity according to load changes. However, during the operation of variable-frequency water chillers, the problem of oil return has always been one of the key factors affecting their performance and reliability. In the refrigeration cycle, the refrigerant gas discharged by the compressor usually carries a certain amount of lubricating oil. If the lubricating oil cannot be effectively returned to the compressor in a timely manner, a series of problems will occur. On the one hand, the lack of oil in the compressor will cause increased wear between components, reduce the service life of the compressor, and may even lead to the compressor shutting down due to failure, affecting the normal operation of the refrigeration system and bringing economic losses and inconveniences to users. On the other hand, the unreasonable distribution of lubricating oil in the refrigeration system will affect the flow and heat transfer performance of the refrigerant. For example, when the lubricating oil mixes into the refrigerant and enters the condenser and evaporator, an oil film will be formed on the heat transfer surface, increasing the thermal resistance and reducing the heat transfer efficiency, thereby resulting in a decrease in the refrigerating capacity of the refrigeration system and an increase in energy consumption.

[0003] The existing methods for controlling oil return of water chillers have certain limitations. Using a simple oil return device has poor adaptability to the oil return requirements under different working conditions and cannot ensure good oil return effects under various loads and operating conditions. Moreover, the oil return control cannot be dynamically adjusted according to the actual operating conditions, resulting in untimely or excessive oil return in some working conditions, affecting the stability and energy-saving effect of the system. Summary of the Invention

[0004] Aiming at the deficiencies of the existing technology, the purpose of the present invention is to provide a method for controlling oil return of a variable-frequency water chiller.

[0005] To achieve the above purpose, the present invention provides the following technical solutions:

[0006] A method for controlling oil return of a variable-frequency water chiller, including a variable-frequency compressor, an oil separator, an air-side condenser, an oil return capillary tube, a condensing fan, a refrigeration electronic expansion valve, and a water-side evaporator:

[0007] The refrigerant gas discharged from the outlet of the variable-frequency compressor enters the oil separator, where the refrigerant separates oil and gas. The lubricating oil enters the bottom of the oil separator along the inner wall surface of the oil separator. The refrigerant gas is at the upper part of the oil separator. The refrigerant gas from the oil separator enters the air-side condenser to release heat and condense. The oil return capillary tube sucks the oil in the oil separator into the water-side heat exchange part of the variable-frequency compressor. The condensing fan conducts convective heat exchange between the refrigerant and the air. The liquid refrigerant after releasing heat by condensation flows through the refrigeration electronic expansion valve to throttle down the pressure and temperature. The throttled refrigerant evaporates and absorbs heat in the water-side evaporator to achieve chilled water. The refrigerant gas flowing out of the water-side evaporator is compressed by the variable-frequency compressor.

[0008] Preferably, it further includes a refrigerant pipe, which is connected between the variable-frequency compressor and the oil separator. The refrigerant gas discharged from the outlet of the variable-frequency compressor enters the oil separator after passing through a plurality of refrigerant pipes.

[0009] Preferably, it further includes a water pipe and a circulating water pump. The return water enters the water-side evaporator through a plurality of water pipes and is pressurized by the circulating water pump to exchange heat and reduce the temperature.

[0010] Preferably, it further includes a variable-frequency chiller controller, which is used to control the variable-frequency compressor, the condensing fan, the circulating water pump and the refrigeration electronic expansion valve.

[0011] Preferably, when the variable-frequency compressor meets the oil return condition, the variable-frequency compressor performs oil return operation. When the oil return end condition is met during the oil return process of the variable-frequency compressor, the oil return of the variable-frequency compressor ends.

[0012] Preferably, when the variable-frequency compressor meets the oil return condition, the variable-frequency compressor performs oil return operation, which specifically includes the following steps:

[0013] Obtain the current operating frequency of the variable-frequency compressor and mark it as the real-time operating frequency F;

[0014] Compare the real-time operating frequency F of the variable-frequency compressor with the preset oil return critical frequency F1;

[0015] If the real-time operating frequency F is lower than the preset oil return critical frequency F1 within the predetermined time T1, the variable-frequency compressor performs oil return operation.

[0016] Preferably, it further includes the following steps:

[0017] During the oil return operation process or the oil return preparation operation process of the variable-frequency compressor, the variable-frequency compressor does not stop; when the variable-frequency compressor performs oil return operation, the condensing fan is automatically controlled; when the variable-frequency compressor starts to return oil, the frequency of the variable-frequency compressor is increased to the preset oil return frequency F2; the circulating water pump is in the operating state; and the opening degree of the refrigeration electronic expansion valve is adjusted to the maximum opening degree state.

[0018] Preferably, when the oil return end condition is met during the oil return process of the variable-frequency compressor, the oil return of the variable-frequency compressor ends, which specifically includes the following steps:

[0019] When the preset oil return time T2 is reached during the oil return process of the variable-frequency compressor, the oil return of the variable-frequency compressor ends.

[0020] Preferably, it further includes an oil level monitoring device, an oil temperature sensor, a pressure sensor, a flow sensor, an oil quality detection module, an environmental parameter monitoring unit, and an auxiliary oil return heating device;

[0021] The oil level monitoring device is installed on the oil separator, and the oil level monitoring device is used to monitor the oil level of the lubricating oil in the oil separator in real time;

[0022] The oil temperature sensor is installed at the bottom of the oil separator, and the oil temperature sensor is used to monitor the temperature of the lubricating oil in real time;

[0023] The pressure sensors are respectively installed at the inlet and outlet of the variable-frequency compressor, the inlet and outlet of the oil separator, and both ends of the oil return capillary. The pressure sensors are used to monitor the pressure at the corresponding positions in real time;

[0024] The flow sensor is installed on the oil return capillary, and the flow sensor is used to monitor the oil return flow in the oil return capillary in real time;

[0025] The oil quality detection module is installed at the oil outlet at the bottom of the oil separator, and the oil quality detection module is used to detect the quality of the lubricating oil;

[0026] The environmental parameter monitoring unit includes an environmental temperature sensor and an environmental humidity sensor, and the environmental parameter monitoring unit is used to monitor the temperature and humidity of the unit operating environment;

[0027] The auxiliary oil return heating device is installed outside the oil separator, and the auxiliary oil return heating device is used to assist in heating the lubricating oil in the oil separator.

[0028] Preferably, it further includes the following steps:

[0029] Dynamically adjust the operating frequency of the variable-frequency compressor and the opening degree of the refrigeration electronic expansion valve according to the oil return flow monitored by the flow sensor;

[0030] If the temperature of the lubricating oil monitored by the oil temperature sensor is lower than the preset optimal oil return temperature range, start the auxiliary oil return heating device to heat the lubricating oil;

[0031] If the environmental humidity monitored by the environmental parameter monitoring unit is higher than the preset humidity threshold, appropriately increase the opening degree correction coefficient of the refrigeration electronic expansion valve during the oil return process.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] The oil return control method of this application effectively separates the lubricating oil from the refrigerant gas through an oil separator. The lubricating oil flows along the inner wall surface of the oil separator into the bottom, and then is sucked into the water-side heat exchange part of the variable-frequency compressor through the oil return capillary. This process ensures that the variable-frequency compressor can continuously obtain sufficient lubricating oil supply during operation, avoiding faults such as excessive wear and jamming caused by lack of oil, greatly improving the stability and reliability of the variable-frequency compressor, extending the service life of the compressor, and thus ensuring the stable operation of the entire variable-frequency chiller.

[0034] After the refrigerant gas completes the oil-gas separation in the oil separator, the pure refrigerant gas enters the air-side condenser to release heat and condense, then passes through the refrigeration electronic expansion valve to throttle, depressurize and cool down, and finally evaporates and absorbs heat in the water-side evaporator. This clear and orderly process ensures that the refrigerant can efficiently circulate in the system, reducing the problem of reduced refrigeration efficiency that may be caused by the mixing of lubricating oil into the refrigerant, making the refrigeration cycle smoother, and thus improving the refrigeration capacity of the entire system.

[0035] The condensing fan promotes the convective heat exchange between the refrigerant and the air. Under the synergistic effect of the oil return control method, the state change of the refrigerant is more stable, and it can exchange heat with the air more fully, improving the heat exchange efficiency of the air-side condenser. At the same time, in the water-side evaporator, the throttled refrigerant can effectively evaporate and absorb heat to achieve the purpose of refrigerating water, further improving the overall refrigeration efficiency of the system.

[0036] The variable-frequency compressor can adjust its speed according to the actual refrigeration demand, and can reduce energy consumption under partial load conditions. At the same time, the oil return control method ensures that the variable-frequency compressor can maintain a good operating state under various working conditions, avoiding the extra work of the variable-frequency compressor caused by poor oil return, thereby reducing energy consumption. The entire oil return control process cooperates with components such as the refrigeration electronic expansion valve and the condensing fan, enabling the system to achieve an optimized operating state under different working conditions. Brief Description of the Drawings

[0037] Figure 1 It is a schematic diagram of a method for controlling oil return of a variable-frequency chiller proposed by the present invention.

[0038] 1. Variable-frequency compression; 2. Refrigerant pipe; 3. Oil separator; 4. Oil return capillary; 5. Air-side condenser; 6. Condensing fan; 7. Refrigeration electronic expansion valve; 8. Water-side evaporator; 9. Water pipe; 10. Circulating water pump; 11. Variable-frequency chiller controller. Detailed Embodiments

[0039] Refer to Figure 1 as shown.

[0040] Embodiment 1 further illustrates a method for controlling oil return of a variable-frequency water chiller proposed by the present invention.

[0041] A method for controlling oil return of a variable-frequency water chiller includes a variable-frequency compressor 1, an oil separator 3, an air-side condenser 5, an oil return capillary 4, a condensing fan 6, a refrigeration electronic expansion valve 7, and a water-side evaporator 8:

[0042] The refrigerant gas discharged from the outlet of the variable-frequency compressor 1 enters the oil separator 3, where the refrigerant undergoes oil-gas separation. The lubricating oil flows along the inner wall surface of the oil separator 3 into the bottom of the oil separator 3, and the refrigerant gas is in the upper part of the oil separator 3. The refrigerant gas from the oil separation enters the air-side condenser 5 to release heat and condense. The oil return capillary 4 sucks the oil in the oil separation into the water-side heat exchange part of the variable-frequency compressor 1. The condensing fan 6 promotes the convective heat exchange between the refrigerant and the air. The liquid refrigerant after condensing heat release flows through the refrigeration electronic expansion valve 7 to throttle down the pressure and lower the temperature. The throttled refrigerant evaporates and absorbs heat in the water-side evaporator 8 to achieve chilled water, and the refrigerant gas flowing out of the water-side evaporator 8 is compressed by the variable-frequency compressor 1.

[0043] The method for controlling oil return of this variable-frequency water chiller involves the variable-frequency compressor 1, the oil separator 3, the air-side condenser 5, the oil return capillary 4, the condensing fan 6, the refrigeration electronic expansion valve 7, and the water-side evaporator 8. The refrigerant gas discharged from the variable-frequency compressor 1 enters the oil separator 3 for oil-gas separation. The lubricating oil deposits at the bottom of the oil separator 3, and the refrigerant gas rises to the upper part. Subsequently, it enters the air-side condenser 5 to release heat and condense. The oil return capillary 4 sucks the oil in the oil separator into the water-side heat exchange part of the variable-frequency compressor 1. The condensing fan 6 promotes the convective heat exchange between the refrigerant and the air. The condensed liquid refrigerant is throttled down in pressure and temperature by the refrigeration electronic expansion valve 7, evaporates and absorbs heat in the water-side evaporator 8 for refrigeration, and the flowing-out refrigerant gas is compressed by the variable-frequency compressor 1 again, thus forming a cycle.

[0044] The variable-frequency compressor 1 of this application can automatically adjust the speed according to the actual load demand to achieve energy-saving operation. The equipped high-efficiency oil separator 3 can effectively separate the lubricating oil in the refrigerant gas. The oil return capillary 4 ensures that the lubricating oil can smoothly flow back to the variable-frequency compressor 1. The condensing fan 6 adopts variable-frequency speed control and can adjust the wind speed according to the heat load of the condenser. The refrigeration electronic expansion valve 7 has precise flow control ability and can quickly adjust the refrigerant flow according to the load change of the evaporator. The water-side evaporator 8 uses high-efficiency heat transfer tubes to improve the refrigeration efficiency.

[0045] Under the refrigeration condition, the variable-frequency compressor 1 runs at high speed and discharges a large amount of refrigerant gas. After these gases enter the oil separator 3, the lubricating oil is quickly separated and settles to the bottom of the oil separator 3 under the action of gravity and centrifugal force, while the refrigerant gas enters the air-side condenser 5, where the refrigerant gas exchanges heat with air and condenses into liquid. At this time, the oil return capillary 4 slowly sucks the lubricating oil at the bottom of the oil separator 3 into the water-side heat exchange part of the variable-frequency compressor 1 to supplement the lubricating oil required for the operation of the variable-frequency compressor 1. The condensed liquid refrigerant is throttled, depressurized and cooled by the refrigeration electronic expansion valve 7 and then enters the water-side evaporator 8. In the water-side evaporator 8, the liquid refrigerant absorbs the heat in the water and evaporates into gas, reducing the temperature of the water and realizing the refrigeration function. The evaporated refrigerant gas is sucked in and compressed by the variable-frequency compressor 1 again and enters the next cycle.

[0046] When the load decreases, the variable-frequency compressor 1 reduces its speed and the refrigerant circulation volume decreases. At this time, the oil-gas separation amount of the oil separator 3 also decreases accordingly, but the oil return capillary 4 can still ensure an appropriate amount of lubricating oil to flow back to the variable-frequency compressor 1 to maintain the normal lubrication of the compressor.

[0047] Embodiment 2

[0048] Based on Embodiment 1, the following technical features are added: It further includes a refrigerant pipe 2, which is connected between the variable-frequency compressor 1 and the oil separator 3. The refrigerant gas discharged from the outlet of the variable-frequency compressor 1 enters the oil separator 3 after passing through a number of refrigerant pipes 2.

[0049] The variable-frequency compressor 1 compresses the low-temperature and low-pressure refrigerant gas into a high-temperature and high-pressure gas. These gases are transported to the oil separator 3 through the refrigerant pipe 2. In the oil separator 3, the refrigerant gas is separated from the lubricating oil. The lubricating oil flows along the inner wall surface of the oil separator 3 into the bottom, while the refrigerant gas is located in the upper part. Then, the refrigerant gas enters the air-side condenser 5, where it exchanges heat with air in a convection manner under the action of the condensing fan 6 and releases heat to condense into liquid. The oil return capillary 4 sucks the oil at the bottom of the oil separator 3 into the water-side heat exchange part of the variable-frequency compressor 1. The liquid refrigerant is throttled, depressurized and cooled by the refrigeration electronic expansion valve 7 and enters the water-side evaporator 8 to evaporate and absorb heat to realize refrigeration. The refrigerant gas flowing out of the water-side evaporator 8 is compressed by the variable-frequency compressor 1 again, and so on in a cycle.

[0050] The refrigerant pipe 2 is made of high-strength and corrosion-resistant materials, and its pipe diameter is precisely calculated to ensure the minimum pressure loss of the refrigerant gas during transportation. The oil separator 3 has high-efficiency oil-gas separation performance, and the separation efficiency reaches more than 98%. The air-side condenser 5 adopts a large-scale finned structure to enhance the heat exchange effect. The condenser fan 6 adopts intelligent variable-frequency control and can automatically adjust the wind speed according to the temperature of the condenser. The refrigeration electronic expansion valve 7 has the characteristics of fast response and precise adjustment, and can adjust the refrigerant flow rate in real time according to the load of the evaporator. The water-side evaporator 8 adopts a high-efficiency heat exchange tube group to improve the refrigeration efficiency.

[0051] Embodiment Three

[0052] On the basis of Embodiment Two, the following technical features are added: It also includes a water pipe 9 and a circulating water pump 10. The return water passes through several water pipes 10 and then enters the water-side evaporator 8 through the pressurization of the circulating water pump 9 for heat exchange and cooling.

[0053] After the variable-frequency compressor 1 compresses the refrigerant gas, it is transported to the oil separator 3 through the refrigerant pipe 2 for oil-gas separation. The lubricating oil settles to the bottom of the oil separator 3, and the refrigerant gas enters the air-side condenser 5 and releases heat and condenses under the action of the condenser fan 6. The oil return capillary 4 sends the oil at the bottom of the oil separator 3 back to the water-side heat exchange part of the variable-frequency compressor 1. The condensed liquid refrigerant passes through the refrigeration electronic expansion valve 7 for throttling, pressure reduction and temperature reduction, and enters the water-side evaporator 8. At the same time, after the return water passes through several water pipes 9, it is pressurized by the circulating water pump 10 and enters the water-side evaporator 8 to exchange heat and cool down with the liquid refrigerant. The cooled water can be used to meet the refrigeration demand, and the refrigerant gas flowing out of the water-side evaporator 8 is compressed by the variable-frequency compressor 1 again, thus forming a complete circulation system.

[0054] The addition of the water pipe 9 and the circulating water pump 10 constructs a stable and efficient water circulation system. The circulating water pump 10 can accurately adjust the water flow rate according to the actual load, ensuring that the water fully exchanges heat with the refrigerant in the water-side evaporator 8 and improving the refrigeration efficiency. Compared with the unit without this water circulation system, the refrigerating capacity can be increased by 10%-15%, effectively meeting the requirements of large refrigeration demand places such as commercial complexes.

[0055] The variable-frequency control function of the circulating water pump 10 enables it to automatically adjust the rotation speed according to the load change, avoiding energy waste of traditional water pumps at low loads. At the same time, the coordinated and optimized operation of the entire system enables components such as the variable-frequency compressor 1 and the condenser fan 6 to work in a more energy-saving state. Through actual measurement, this improved version of the system can save 15%-20% of electric energy during the annual operation compared with the traditional system, reducing the operation cost.

[0056] Embodiment Four

[0057] On the basis of Embodiment 3, the following technical features are added: It further includes a variable-frequency chiller controller 11, which is used to control the variable-frequency compressor 1, the condenser fan 6, the circulating water pump 10, and the refrigeration electronic expansion valve 7.

[0058] The variable-frequency compressor 1 compresses the refrigerant gas, which is sent to the oil separator 3 through the refrigerant pipe 2 for oil-gas separation. The lubricating oil flows into the bottom of the oil separator 3, and the refrigerant gas enters the air-side condenser 5, where it releases heat and condenses under the action of the condenser fan 6. The oil return capillary 4 sends the lubricating oil at the bottom of the oil separator 3 back to the water-side heat exchange part of the variable-frequency compressor 1. The condensed liquid refrigerant enters the water-side evaporator 8 after throttling, depressurizing, and cooling through the refrigeration electronic expansion valve 7. At the same time, the return water passes through the water pipe 9 and is pressurized by the circulating water pump 10 and sent into the water-side evaporator 8 for heat exchange and cooling. The variable-frequency chiller controller 11 monitors the operating parameters of the system in real time and precisely controls the variable-frequency compressor 1, the condenser fan 6, the circulating water pump 10, and the refrigeration electronic expansion valve 7 according to the set control strategy.

[0059] The addition of the variable-frequency chiller controller 11 realizes the precise control of the key components of the system. Through real-time monitoring and intelligent adjustment, it can make components such as the variable-frequency compressor 1, the condenser fan 6, the circulating water pump 10, and the refrigeration electronic expansion valve 7 work together to reach the best operating state, improving the refrigeration efficiency of the system. Compared with the previous embodiments, the refrigeration efficiency can be further increased by 10%-15%, effectively meeting the refrigeration requirements of high-heat-dissipation demand places such as data centers.

[0060] The controller 11 can precisely adjust the operating parameters of each device according to the actual load change, avoiding the over-operation of the devices at low loads. For example, when the load of the data center decreases, it timely reduces the operating frequency of the variable-frequency compressor, the wind speed of the condenser fan 6, and the rotation speed of the circulating water pump 10, greatly reducing the energy consumption. Through actual measurement, the energy-saving effect of this advanced version system can be improved by 20%-30% compared with the traditional system, effectively reducing the operation cost of the data center.

[0061] Through the real-time monitoring and fault diagnosis functions, the variable-frequency chiller controller 11 can timely detect abnormal situations in the system operation and take corresponding measures to deal with them, avoiding the expansion of faults. At the same time, the precise control also reduces the frequent start-stop and excessive wear of the devices, prolonging the service life of the devices and improving the stability and reliability of the system. In the application of the data center, the mean time between failures of the system is greatly extended, ensuring the stable operation of the data center.

[0062] The variable-frequency chiller controller 11 endows the entire system with a high degree of intelligence and automation. Without frequent manual intervention, the system can automatically adjust the operating parameters according to the actual operating conditions to adapt to different load changes. This not only reduces the workload of the operation and maintenance personnel, but also improves the response speed and control accuracy of the system, providing users with a more convenient and efficient usage experience.

[0063] Embodiment Five

[0064] On the basis of Embodiment Four, the following technical features are added: When the variable-frequency compressor 1 meets the oil return condition, the variable-frequency compressor 1 performs oil return operation, and when the oil return end condition is met during the oil return process of the variable-frequency compressor 1, the variable-frequency compressor 1 ends the oil return.

[0065] When the variable-frequency compressor 1 meets the oil return condition, the variable-frequency compressor 1 performs oil return operation, which specifically includes the following steps:

[0066] Obtain the current operating frequency of the variable-frequency compressor 1 and mark it as the real-time operating frequency F;

[0067] Compare the real-time operating frequency F of the variable-frequency compressor 1 with the preset oil return critical frequency F1;

[0068] If the real-time operating frequency F is lower than the preset oil return critical frequency F1 within the predetermined time T1, the variable-frequency compressor 1 performs oil return operation.

[0069] It also includes the following steps:

[0070] During the oil return operation process or the oil return preparation operation process of the variable-frequency compressor 1, the variable-frequency compressor 1 does not stop; when the variable-frequency compressor 1 performs oil return operation, the condenser fan 6 is automatically controlled; when the variable-frequency compressor 1 starts to return oil, the variable-frequency compressor 1 is frequency-increased to the preset oil return frequency F2; the circulating water pump 10 is in the operating state; and the opening degree of the refrigeration electronic expansion valve 7 is adjusted to the maximum opening degree state.

[0071] When the oil return end condition is met during the oil return process of the variable-frequency compressor 1, the variable-frequency compressor 1 ends the oil return, which specifically includes the following steps:

[0072] When the preset oil return time T2 is reached during the oil return process of the variable-frequency compressor 1, the variable-frequency compressor 1 ends the oil return.

[0073] The general principle of the refrigeration oil return control method for the chiller unit is as follows:

[0074] A. The refrigeration oil return operating frequency is [oil return frequency] F2. If a recoverable protection occurs, continue the oil return after restarting.

[0075] B. When the system performs the oil return operation, if it detects that the high pressure is too high or the exhaust temperature is too high, it will reduce the frequency according to "high pressure protection control" and "exhaust high temperature protection" respectively. If the current of the variable frequency compressor 1 is too high or the temperature of the radiator is too high, the compressor will perform the oil return operation at the current frequency (that is, the oil return frequency runs at the current frequency, and other operations still follow the normal oil return operation).

[0076] Oil return conditions:

[0077] ① After the unit is powered on and started, when the operating frequency of the variable frequency compressor 1 is lower than [oil return critical frequency] F1 and continuously accumulates for more than [oil return cumulative operating time] T1, it will enter the oil return state;

[0078] ② After the cumulative operating time since the last oil return operation reaches 4 hours, and the operating frequency of the variable frequency compressor 1 has been less than or equal to [oil return cycle reduction frequency] F3, the interval time changes from 6 hours to 4 hours;

[0079] ③ During the timing period, if the compressor operating frequency is greater than or equal to [oil return reset frequency] F4 and continuously runs for more than 4 minutes, the timing will be reset;

[0080] ④ During mode switching, normal shutdown or protective shutdown, the timing is not reset, and the timing continues after the compressor starts;

[0081] Oil return control content:

[0082] During the oil return operation or the preparation process of the oil return operation, the compressor does not stop.

[0083] Automatic control of the condenser fan during the oil return operation:

[0084] When the oil return of the variable frequency compressor 1 starts, the variable frequency compressor increases the frequency to [oil return frequency] F2;

[0085] The circulating water pump 10 is in the running state;

[0086] The opening of the refrigeration electronic expansion valve 7 is the largest;

[0087] Oil return end conditions:

[0088] When the oil return duration reaches [oil return time] T2 (including the frequency increase time), the oil return will exit.

[0089] The entire oil return process is that the frequency of the variable-frequency compressor 1 changes. The variable-frequency compressor 1 operates on the oil return frequency platform. The refrigerant system's air-cooled condenser 5, water-cooled evaporator 8, and the refrigeration auxiliary accessories bring the refrigerant oil back to the compressor. The refrigerant oil flows at high speed along the pipe wall, and the variable-frequency compressor 1 operates at a relatively high speed under the oil return platform, which is sufficient to drive the refrigerant oil back to the suction port of the variable-frequency compressor 1. The corresponding refrigerant electronic expansion valve 7 has the largest opening, and the condenser fan 6 is under automatic control. Although the oil return capillary 4 in the oil separator 3 returns oil at all times, when the variable-frequency compressor 1 operates at a low load and a low speed (low frequency) all the time, it is very difficult for the refrigerant oil in the refrigeration system to completely return to the variable-frequency compressor 1. Therefore, system oil return needs to be controlled. Generally, it is more appropriate for the refrigeration system of the chiller to return oil once every 6 hours of operation.

[0090] Variable-frequency Compressor Oil Return Control Parameter Table:

[0091] Parameter Unit Default Value Minimum Value Maximum Value F1 Hertz 30 20 50 F2 Hertz 70 50 90 F3 Hertz 20 20 50 F4 Hertz 60 50 90 T1 Hour 6 4 10 T2 Minute 3 2 10

[0092]

Oil Return Critical Frequency

[0093]

Oil Return Cumulative Operating Time

[0094]

Oil return frequency

[0095]

Oil return time

[0096]

Frequency for reducing oil return cycle

[0097]

Frequency of Oil Return Zeroing

[0098] Embodiment Six

[0099] On the basis of Embodiment Five, the following technical features are added: It also includes an oil - level monitoring device, an oil - temperature sensor, a pressure sensor, a flow sensor, an oil - quality detection module, an environmental - parameter monitoring unit, and an auxiliary oil - return heating device;

[0100] The oil - level monitoring device is installed on the oil separator 3, and the oil - level monitoring device is used to monitor the oil level of the lubricating oil in the oil separator 3 in real - time;

[0101] The oil - temperature sensor is installed at the bottom of the oil separator 3, and the oil - temperature sensor is used to monitor the temperature of the lubricating oil in real - time;

[0102] The pressure sensors are respectively installed at the inlet and outlet of the variable - frequency compressor 1, the inlet and outlet of the oil separator 3, and both ends of the oil - return capillary 4. The pressure sensors are used to monitor the pressure at the corresponding positions in real - time;

[0103] The flow sensor is installed on the oil - return capillary 4, and the flow sensor is used to monitor the oil - return flow rate in the oil - return capillary 4 in real - time;

[0104] The oil - quality detection module is installed at the oil outlet at the bottom of the oil separator 3, and the oil - quality detection module 16 is used to detect the quality of the lubricating oil;

[0105] The environmental - parameter monitoring unit includes an environmental - temperature sensor and an environmental - humidity sensor. The environmental - parameter monitoring unit is used to monitor the temperature and humidity of the operating environment of the unit;

[0106] The auxiliary oil - return heating device is installed outside the oil separator 3, and the auxiliary oil - return heating device is used to assist in heating the lubricating oil in the oil separator 3.

[0107] It also includes the following steps:

[0108] According to the oil - return flow rate monitored by the flow sensor, dynamically adjust the operating frequency of the variable - frequency compressor 1 and the opening degree of the refrigeration electronic expansion valve 7;

[0109] If the lubricating oil temperature monitored by the oil temperature sensor is lower than the preset optimal oil return temperature range, start the auxiliary oil return heating device to heat the lubricating oil.

[0110] If the ambient humidity monitored by the ambient parameter monitoring unit is higher than the preset humidity threshold, appropriately increase the opening correction coefficient of the refrigeration electronic expansion valve 7 during the oil return process.

[0111] The oil level monitoring device is installed on the oil separator 3 to monitor the oil level of the lubricating oil in the oil separator 3 in real time, providing key data for judging the oil return state of the system and the lubricating oil inventory.

[0112] The oil temperature sensor is located at the bottom of the oil separator 3 to monitor the temperature of the lubricating oil in real time, ensuring that the lubricating oil is within a suitable working temperature range to guarantee the oil return effect and the normal lubrication of the compressor.

[0113] The pressure sensors are respectively installed at the inlet and outlet of the variable frequency compressor 1, the inlet and outlet of the oil separator 3, and both ends of the oil return capillary 4 to monitor the pressure at each position in real time, which helps to analyze the pressure balance and oil return resistance of the system.

[0114] The flow sensor is installed on the oil return capillary 4 to monitor the oil return flow in the oil return capillary 4 in real time, providing a basis for dynamically adjusting the system operation parameters.

[0115] The oil quality detection module is set at the oil outlet at the bottom of the oil separator 3 to detect the quality of the lubricating oil, and timely discover problems such as pollution and deterioration of the lubricating oil, so as to take corresponding maintenance measures.

[0116] The ambient parameter monitoring unit consists of an ambient temperature sensor and an ambient humidity sensor to monitor the temperature and humidity of the unit operation environment, considering the influence of environmental factors on the oil return process.

[0117] The auxiliary oil return heating device is installed outside the oil separator 3. When the oil temperature sensor monitors that the lubricating oil temperature is lower than the preset optimal oil return temperature range, start this device to assist in heating the lubricating oil in the oil separator 3, improve the fluidity of the lubricating oil, and promote oil return.

[0118] According to the oil return flow monitored by the flow sensor, the variable frequency chiller controller 11 dynamically adjusts the operating frequency of the variable frequency compressor 1 and the opening of the refrigeration electronic expansion valve 7. If the oil return flow is low, appropriately increase the operating frequency of the variable frequency compressor 1 to increase the refrigerant circulation volume, and at the same time adjust the opening of the refrigeration electronic expansion valve 7 to optimize the oil return effect.

[0119] When the lubricating oil temperature monitored by the oil temperature sensor is lower than the preset optimal oil return temperature range, the auxiliary oil return heating device is started to heat the lubricating oil. After the oil temperature reaches the appropriate range, the oil return operation is carried out or the normal operation continues.

[0120] If the environmental humidity monitored by the environmental parameter monitoring unit is higher than the preset humidity threshold, during the oil return process, the controller 11 appropriately increases the opening correction coefficient of the refrigeration electronic expansion valve 7 to compensate for the influence of environmental humidity on the system performance and ensure the stability of the oil return process.

[0121] A high-precision oil level monitoring device is installed on the oil separator 3 to accurately measure the change of the oil level. An oil temperature sensor with high sensitivity is selected and installed at a suitable position at the bottom of the oil separator 3. The preset optimal oil return temperature range is 30 - 40 °C. Pressure sensors are installed at key positions such as the variable frequency compressor 1, the oil separator 3, and the oil return capillary 4 to monitor the pressure data in real time. A flow sensor is installed on the oil return capillary 4 to accurately monitor the oil return flow rate. An oil quality detection module is installed at the oil outlet at the bottom of the oil separator 3 to regularly detect the quality of the lubricating oil. An environmental parameter monitoring unit is deployed, and the preset humidity threshold is 70%. An auxiliary oil return heating device is installed outside the oil separator 3, which can be automatically started and stopped according to the oil temperature.

[0122] When the environmental humidity exceeds 70%, the environmental parameter monitoring unit feeds the data back to the variable frequency chiller controller 11, and the controller 11 automatically increases the opening correction coefficient of the refrigeration electronic expansion valve 7 during the oil return process to ensure smooth oil return. If the oil temperature sensor monitors that the lubricating oil temperature is lower than 30 °C, the auxiliary oil return heating device is automatically started to heat the lubricating oil in the oil separator 3. When the oil temperature rises above 30 °C, the heating device stops working. The flow sensor monitors the oil return flow rate in real time. If it is found that the oil return flow rate is low, the controller 11 appropriately increases the operating frequency of the variable frequency compressor 1 and adjusts the opening of the refrigeration electronic expansion valve 7 to increase the refrigerant circulation amount and improve the oil return effect. The oil level monitoring device continuously monitors the oil level in the oil separator 3. When the oil level is too low, an alarm is issued to remind the staff to replenish the lubricating oil in time. The oil quality detection module regularly detects the quality of the lubricating oil. Once it is found that the lubricating oil deteriorates, the maintenance personnel are notified to replace it in time.

[0123] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements for some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A variable frequency chiller oil return control method, characterized in that: It includes a variable frequency compressor (1), an oil separator (3), an air side condenser (5), an oil return capillary (4), a condensing fan (6), a refrigeration electronic expansion valve (7) and a water side evaporator (8): The refrigerant gas discharged from the outlet of the variable frequency compressor (1) enters the oil separator (3), and the refrigerant is separated from the oil and gas in the oil separator (3). The lubricating oil enters the bottom of the oil separator (3) along the inner wall surface of the oil separator (3). The refrigerant gas is in the upper part of the oil separator (3). The refrigerant gas from the oil separation enters the wind side condenser (5) to release heat and condense. The oil return capillary (4) sucks the oil in the oil separation into the water side heat exchange part of the variable frequency compressor (1). The condensing fan (6) convects the refrigerant and the air for heat exchange. The liquid refrigerant after condensation and heat release flows through the refrigeration electronic expansion valve (7) to throttle, reduce pressure and reduce temperature. The throttled refrigerant evaporates and absorbs heat in the water side evaporator (8) to achieve refrigeration of water. The refrigerant gas flowing out of the water side evaporator (8) is compressed by the variable frequency compressor (1).

2. A variable frequency chiller oil return control method according to claim 1, characterized in that: It also includes a refrigerant pipe (2), which is connected between the variable frequency compressor (1) and the oil separator (3). The refrigerant gas discharged from the outlet of the variable frequency compressor (1) passes through a plurality of refrigerant pipes (2) and then enters the oil separator (3).

3. The oil return control method of a variable frequency chiller according to claim 1, characterized in that: It also includes a water pipe (9) and a circulating water pump (10). Return water passes through a plurality of water pipes (10) and is pressurized by the circulating water pump (9) before entering the water-side evaporator (8) for heat exchange and cooling.

4. A variable frequency chiller oil return control method according to claim 3, characterized in that: It also comprises a variable frequency chiller controller (11), wherein the variable frequency chiller controller (11) is used to control the variable frequency compressor (1), the condensing fan (6), the circulating water pump (10) and the refrigeration electronic expansion valve (7).

5. A variable frequency chiller oil return control method according to claim 4, characterized in that: When the variable frequency compressor (1) meets the oil return condition, the variable frequency compressor (1) performs oil return operation, and when the oil return end condition is met during the oil return process of the variable frequency compressor (1), the oil return of the variable frequency compressor (1) ends.

6. A variable frequency chiller oil return control method according to claim 5, characterized in that: When the variable frequency compressor (1) meets the oil return condition, the variable frequency compressor (1) performs oil return operation, which specifically includes the following steps: Obtain the current operating frequency of the variable frequency compressor (1) and mark it as the real-time operating frequency F; comparing the real-time operating frequency F of the variable frequency compressor (1) with a preset oil return critical frequency F1; If the real-time operating frequency F is lower than the preset oil return critical frequency F1 within the predetermined time T1, the variable frequency compressor (1) performs oil return operation.

7. A variable frequency chiller oil return control method according to claim 6, characterized in that: The following steps are also included: When the variable frequency compressor (1) is in the process of oil return operation or oil return preparation operation, the variable frequency compressor (1) is kept running; when the variable frequency compressor (1) is in the process of oil return operation, the condensing fan (6) is automatically controlled; when the variable frequency compressor (1) starts to return oil, the frequency of the variable frequency compressor (1) is increased to a preset oil return frequency F2; the circulating water pump (10) is in operation; and the opening of the refrigeration electronic expansion valve (7) is adjusted to a maximum opening state.

8. A variable frequency chiller oil return control method according to claim 7, characterized in that: When the oil return end condition is met during the oil return process of the variable frequency compressor (1), the oil return of the variable frequency compressor (1) ends, which specifically includes the following steps: When a preset oil return time T2 is reached during the oil return process of the variable frequency compressor (1), the oil return of the variable frequency compressor (1) is completed.

9. The oil return control method of a variable frequency chiller according to claim 1, characterized in that: It also includes an oil level monitoring device, an oil temperature sensor, a pressure sensor, a flow sensor, an oil quality detection module, an environmental parameter monitoring unit and an auxiliary oil return heating device; The oil level monitoring device is installed on the oil separator (3), and is used to monitor the lubricating oil level in the oil separator (3) in real time; The oil temperature sensor is installed at the bottom of the oil separator (3), and is used to monitor the temperature of the lubricating oil in real time; The pressure sensors are respectively installed at the inlet and outlet of the variable frequency compressor (1), the inlet and outlet of the oil separator (3) and both ends of the oil return capillary (4), and the pressure sensors are used to monitor the pressure at the corresponding positions in real time; The flow sensor is installed on the oil return capillary (4), and the flow sensor is used to monitor the return oil flow in the oil return capillary (4) in real time; The oil quality detection module is installed at the oil outlet at the bottom of the oil separator (3), and the oil quality detection module (16) is used to detect the quality of the lubricating oil; The environmental parameter monitoring unit includes an environmental temperature sensor and an environmental humidity sensor, and the environmental parameter monitoring unit is used to monitor the temperature and humidity of the unit operating environment; The auxiliary oil return heating device is installed outside the oil separator (3), and is used to perform auxiliary heating on the lubricating oil in the oil separator (3).

10. A variable frequency chiller oil return control method according to claim 9, characterized in that: The following steps are also included: Dynamically adjusting the operating frequency of the variable frequency compressor (1) and the opening degree of the refrigeration electronic expansion valve (7) according to the return oil flow monitored by the flow sensor; If the lubricating oil temperature monitored by the oil temperature sensor is lower than the preset optimal oil return temperature range, the auxiliary oil return heating device is started to heat the lubricating oil; If the ambient humidity monitored by the environmental parameter monitoring unit is higher than a preset humidity threshold, the opening correction coefficient of the refrigeration electronic expansion valve (7) is appropriately increased during the oil return process.

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