Screw refrigerating unit energy saving method based on precise control over oil way pressure difference

Abstract

The invention discloses an energy-saving method for a screw refrigerating unit based on precise control of oil path pressure difference, which is characterized in that the traditional indirect control based on suction and exhaust pressure difference is changed into direct control based on oil low pressure difference for the first time; according to the method, the unit is controlled to be switched between an emergency shutdown mode, a risk avoiding mode, a safety mode and an energy-saving mode in a self-adaptive mode, and then the real state of the oil way pressure is accurately matched through cooperative execution of a cooling water flow bypass regulating valve, a cooling tower fan frequency converter and an electronic expansion valve, so that cooperative optimization control from indirect safety protection to safe energy conservation is realized; the problem of safety blind areas caused by an existing control mode is solved, the compression ratio can be reduced through adjustment, the unit comprehensive energy efficiency ratio (COP) is remarkably improved, and the problem that in the prior art, in order to guarantee safety under the efficient working condition, suction and exhaust air pressure difference is forced to be manually increased, and consequently continuous energy is wasted is fundamentally solved.

Description

Technical Field

[0001] This invention belongs to the field of refrigeration technology, and in particular relates to an energy-saving method for refrigeration units based on precise control of oil circuit pressure difference. Background Technology

[0002] The refrigeration unit mainly consists of an interconnected screw compressor, condenser, electronic expansion valve, and evaporator. The lubricating oil in the screw compressor is processed sequentially through an oil separator and oil filter before returning to its original position. The screw compressor's suction and discharge ports are equipped with suction pressure monitoring units and discharge pressure monitoring units, respectively, responsible for monitoring the suction and discharge pressures. The condenser's cooling water piping is equipped with a cooling water flow bypass regulating valve and a cooling tower fan frequency converter. Additionally, the refrigeration unit includes a control module to collect key data signals and perform corresponding control.

[0003] Existing screw chiller units generally employ a control mode that monitors the suction and discharge pressure difference and maintains a fixed high pressure differential threshold (e.g., 4 bar, commonly set in the industry to cope with extreme oil filter clogging). If a serious blockage or other fault occurs in the oil circuit, a mechanical oil filter differential pressure switch provides alarm and other safety protection. However, this system has the following drawbacks: First, a fixed high pressure differential threshold cannot adapt to the actual needs of different units and operating conditions. This forces units to artificially increase the suction and discharge pressure differential even under naturally efficient operating conditions, resulting in significant and continuous energy waste. For example, under efficient operating conditions with low natural suction and discharge pressure differentials (typically only 2-3 bar) such as low ambient temperatures (cooling water temperature ≤15℃ in winter), units must artificially increase discharge pressure by opening the cooling water flow bypass valve and reducing the cooling tower fan speed to meet the fixed high pressure differential threshold, leading to a decrease in the compressor's theoretical efficiency. Taking R134a refrigerant as an example, increasing the discharge pressure from 5.5 bar (a) to 7.5 bar (a) corresponds to an increase in the discharge saturation temperature from 19℃ to 29℃, a temperature rise of 10℃. According to thermodynamic principles such as the reverse Carnot cycle, an increase in discharge saturation temperature directly increases the compressor's compression ratio, leading to a decrease in the compressor's theoretical efficiency of up to 30%.

[0004] Secondly, the output of the mechanical oil filter differential pressure switch is a fixed-point, delayed switching signal, which cannot reflect the continuous changes in the oil circuit status in real time. It cannot actively adjust the operating parameters to maintain the optimal oil supply when the oil circuit resistance increases. It can only provide passive protection when the switch is finally triggered by a fault such as a serious blockage in the oil circuit. It has a blind spot in safety protection and lacks predictive and coordinated control capabilities based on the actual state of the oil circuit. In order to ensure safety, it can only be forced to increase the suction and discharge pressure difference, which further leads to a decrease in the theoretical efficiency of the compressor.

[0005] In summary, the existing control mode based on the pressure difference between intake and exhaust not only sacrifices the unit's operating efficiency under most operating conditions, but its safety protection mechanism also suffers from lag in response and disconnection from energy efficiency control, leading to the refrigeration unit being trapped in a dilemma of high energy consumption to ensure safety for a long time. Summary of the Invention

[0006] This invention aims to address the technical problems of high energy consumption and inaccurate safety protection in existing technologies by providing an energy-saving method for screw chiller units based on precise control of oil circuit differential pressure.

[0007] The technical solution of this invention is: an energy-saving method for screw chiller units based on precise control of oil pressure difference. This method monitors the oil injection pressure P1 and suction pressure P2 of the oil filter in real time. Based on the low oil pressure difference ΔP1 = P1 - P2, it adaptively performs emergency shutdown, risk avoidance mode, safety mode, or energy-saving mode control. The risk avoidance mode aims to ensure that the low oil pressure difference ΔP1 is greater than the low oil pressure difference alarm threshold, prioritizing the adjustment of the cooling tower fan frequency converter, and then adjusting the cooling water flow bypass regulating valve. Both the safety mode and the energy-saving mode aim to minimize the total system energy consumption, collaboratively adjusting the cooling water flow bypass regulating valve, the cooling tower fan frequency converter, and the electronic expansion valve. The safety mode is constrained by the low oil pressure difference alarm threshold, while the energy-saving mode is constrained by the low oil pressure difference alarm threshold being less than the energy-saving threshold.

[0008] The preferred procedure is as follows: Step 1. Set the shutdown threshold Ts, the low oil differential pressure alarm threshold Ta, the energy saving threshold Te, and the duration threshold Tt, wherein the shutdown threshold Ts < the low oil differential pressure alarm threshold Ta < the energy saving threshold Te, and control the unit operation; Step 2. Real-time acquisition of injection pressure P1 and intake pressure P2, and calculation of low oil pressure difference ΔP1 = P1 - P2; Step 3. Based on the low oil pressure difference ΔP1, perform corresponding mode control: When the oil low pressure difference ΔP1 < shutdown threshold Ts or shutdown threshold Ts ≤ oil low pressure difference ΔP1 ≤ oil low pressure difference alarm threshold Ta, and the duration > duration threshold Tt, the unit is controlled to shut down urgently and the procedure ends. When the shutdown threshold Ts ≤ oil low pressure differential ΔP1 ≤ oil low pressure differential alarm threshold Ta, and the duration ≤ duration threshold Tt, the risk avoidance mode control is implemented, and step 4 is performed. When the oil low differential pressure alarm threshold Ta < oil low differential pressure ΔP1 ≤ energy saving threshold Te, safety mode control is activated, and step 4 is performed. When the oil low pressure difference ΔP1 > energy saving threshold Te, energy saving mode control is activated, and step 4 is performed. Step 4. Determine whether to end control. If yes, end; if no, return to step 2.

[0009] The preferred safety mode aims to minimize the total system energy consumption by prioritizing increasing the opening of the cooling water flow bypass regulating valve, and then adjusting the frequency of the cooling tower fan inverter and / or the opening of the electronic expansion valve, constrained by the oil low pressure difference ΔP1 being greater than the oil low pressure difference alarm threshold Ta. The energy-saving mode aims to minimize the total system energy consumption by prioritizing decreasing the opening of the cooling water flow bypass regulating valve, and then adjusting the frequency of the cooling tower fan inverter and / or the opening of the electronic expansion valve, constrained by the oil low pressure difference ΔP1 being greater than the energy-saving threshold Te.

[0010] Preferably, step 1 also requires setting the oil filter pressure drop threshold Tp, and step 2 also requires real-time acquisition of exhaust pressure P3, real-time calculation of oil filter pressure drop ΔP2 = P3-P1, and determination of whether oil filter pressure drop ΔP2 is greater than oil filter pressure drop threshold Tp. If yes, an oil filter clogging alarm signal is issued and step 3 is performed; otherwise, step 3 is performed directly.

[0011] The preferred shutdown threshold Ts is 0.8~1.3 bar, the low oil differential pressure alarm threshold Ta is 1.4~2.4 bar, the energy saving threshold Te is 1.6~2.5 bar, the duration threshold Tt is 15~90 seconds, and the oil filter pressure drop threshold Tp is 0.5~1.5 bar.

[0012] Preferably, the real-time monitoring of the oil filter's injection pressure P1 involves installing an injection pressure sensor at a distance ≤50mm from the oil filter outlet to collect the pressure signal value of the injection pressure sensor in real time. The injection pressure sensor has a range of 0-30 bar and an accuracy of ±0.2% FS.

[0013] Preferably, the single adjustment range of the electronic expansion valve does not exceed 5% of the total opening.

[0014] This invention innovatively replaces traditional indirect control based on intake and exhaust pressure difference with direct control based on low oil pressure difference. By monitoring the low oil pressure difference in real time, the unit adaptively switches between emergency shutdown, emergency avoidance mode, safety mode, and energy-saving mode. Furthermore, through the coordinated execution of the cooling water flow bypass regulating valve, cooling tower fan frequency converter, and electronic expansion valve, it precisely matches the actual oil pressure state, achieving a shift from indirect safety-oriented control to a coordinated optimization of safety and energy saving. This not only solves the safety blind spots caused by existing control methods but also significantly improves the unit's overall energy efficiency ratio (COP) by adjusting and reducing the compression ratio. It fundamentally solves the problem of continuous energy waste caused by artificially increasing the intake and exhaust pressure difference under high-efficiency operating conditions to ensure safety in existing technologies.

[0015] Compared with existing technologies, the specific technical effects are as follows: 1. Excellent energy-saving effect: This invention releases energy efficiency by reducing the compressor compression ratio. The measured comprehensive energy efficiency ratio (COP) of the unit is significantly improved (by more than 25%). Taking a 110kW unit as an example, it can save 264,000 kWh of electricity by running for 8,000 hours a year. It fundamentally solves the problem of continuous energy waste caused by artificially increasing the intake and exhaust pressure difference under high-efficiency operating conditions in order to ensure safety in existing technologies. 2. Precise and reliable safety protection: This invention achieves a leap from indirect protection to direct safeguarding by directly monitoring the low oil pressure differential. Combined with the multi-dimensional threshold preset by the control module, it fundamentally eliminates the safety blind spot caused by the oil filter clogging, realizes accurate identification and protection against the risk of no oil, effectively avoids insufficient oil supply, and can extend the life of the compressor's core components by more than 30%. 3. Low implementation cost and good compatibility: The equipment of this invention does not change the main unit structure and the original refrigeration circuit. It only adds a low-cost oil injection pressure sensor (costing about 200 yuan) and does not require modification of the core program of the original control system. Only simple parameter configuration of the control module is required. There is no additional debugging cost. It is easy to promote and implement on new and old units, with a return on investment of more than 10 times.

[0016] 4. Intelligent self-adaptability and strong adaptability: This invention can automatically and seamlessly switch between safety and energy-saving modes based on the oil circuit status and external operating conditions without manual intervention; at the same time, different thresholds can be set within the threshold range to adapt to the needs of different power units, different refrigerant types, and different operating conditions (such as adapting to higher alarm thresholds for low temperature conditions and lower thresholds for normal temperature conditions), further improving the practicality and promotion value of the technical solution and reducing operation and maintenance costs. Attached Figure Description

[0017] Figure 1 This is a partial structural schematic diagram of the device according to an embodiment of the present invention.

[0018] Figure 2 This is a flowchart of the control method according to an embodiment of the present invention.

[0019] Figure 1 The following are the definitions of the reference numerals in the attached diagram: 1. Oil separator, 2. Oil filter, 3. Control module, 4. Injection pressure sensor, 5. Screw compressor, 6. Discharge pressure monitoring unit, 7. Suction pressure monitoring unit, 8. Electronic expansion valve, 9. Condenser, 10. Evaporator. Detailed Implementation

[0020] The present invention discloses an energy-saving method for screw chiller units based on precise control of oil circuit differential pressure. Part of the equipment structure is shown below. Figure 1As shown, the system includes an oil separator 1, an oil filter 2, a control module 3, a screw compressor 5, an exhaust pressure monitoring unit 6, an intake pressure monitoring unit 7, an electronic expansion valve 8, a condenser 9, and an evaporator 10, similar to existing technologies. The exhaust end of the screw compressor 5 is equipped with an exhaust pressure monitoring unit 6, and the intake end of the screw compressor 5 is equipped with an intake pressure monitoring unit 7. The screw compressor 5, the exhaust pressure monitoring unit 6, the intake pressure monitoring unit 7, and the electronic expansion valve 8 are electrically connected to the control module 3. Also electrically connected to the control module 3 are a cooling water flow bypass regulating valve and a cooling tower fan frequency converter.

[0021] Taking a 110kW screw chiller unit (660kW cooling capacity, R134a refrigerant) as an example, the specific system configuration is as follows: The control module 3 adopts Siemens S7-200SMART and connects to various sensors and actuators via RS485 communication. It has built-in programs for calculating low oil pressure differential, threshold judgment, and energy-saving optimization.

[0022] The cooling water flow bypass regulating valve is a DN150 electric ball valve (regulation accuracy ±1%); the cooling tower fan frequency converter is Huichuan CA300 series (power 5.5kW); the electronic expansion valve 8 is a Carrera E6V model (diameter DN40), with an adjustment accuracy of ±1%, and its single adjustment range can be limited to ≤5% of the total opening by the control module.

[0023] The screw compressor model is RE-920A. Both the discharge pressure monitoring unit 6 and the suction pressure monitoring unit 7 use Carrera SPKT series pressure sensors (range 0-20 bar). The oil separator 1 has a volume of 120L, the oil filter 2 has a filtration accuracy of 10μm, the condenser 9 is a shell and tube type (heat exchange area 42m²), and the evaporator 10 is a falling film evaporator (heat exchange area 35m²).

[0024] Unlike existing technologies, an injection pressure sensor 4 is provided downstream of the oil filter 2. The injection pressure sensor 4 is electrically connected to the control module 3. Preferably, the injection pressure sensor 4 is a Carrera SPKT series pressure sensor (range 0-30 bar, accuracy ±0.2% FS). The installation position is preferably ≤50mm away from the outlet of the oil filter 2. If the distance is too close (<20mm), it is easily affected by the internal flow field disturbance of the oil filter. If the distance is too far (>100mm), it will introduce unnecessary pressure drop error along the pipeline. In this embodiment of the invention, the injection pressure sensor 4 is set at a distance of 40mm from the outlet of the oil filter 2.

[0025] The energy-saving method for screw chiller units based on precise control of oil pressure difference of the present invention monitors the oil injection pressure P1 and suction pressure P2 of the oil filter in real time. Based on the low oil pressure difference ΔP1=P1-P2, it adaptively performs emergency shutdown, risk avoidance mode, safety mode or energy-saving mode control. The risk avoidance mode aims to make the low oil pressure difference ΔP1 greater than the low oil pressure difference alarm threshold, and prioritizes adjusting the frequency converter of the cooling tower fan, and then adjusts the cooling water flow bypass regulating valve. The safety mode and energy-saving mode both aim to minimize the total energy consumption of the system, and coordinately adjust the cooling water flow bypass regulating valve, the frequency converter of the cooling tower fan and the electronic expansion valve. The safety mode is constrained by the low oil pressure difference alarm threshold, and the energy-saving mode is constrained by the low oil pressure difference alarm threshold being less than the energy-saving threshold.

[0026] The specific process is as follows: Figure 2 As shown, proceed as follows: Step 1. Set the shutdown threshold Ts, low oil differential pressure alarm threshold Ta, energy-saving threshold Te, and duration threshold Tt, wherein the shutdown threshold Ts < low oil differential pressure alarm threshold Ta < energy-saving threshold Te, to control the unit operation. The above thresholds can be selected within a range to adapt to the needs of different power units, different refrigerant types, and different operating conditions. The threshold ranges are as follows: shutdown threshold Ts = 0.8~1.3 bar, low oil differential pressure alarm threshold Ta = 1.4~2.4 bar, energy-saving threshold Te = 1.6~2.5 bar, duration threshold Tt = 15~90 seconds, and oil filter pressure drop threshold Tp = 0.5~1.5 bar. In this embodiment, the selected thresholds are shutdown threshold Ts = 1.3 bar, low oil differential pressure alarm threshold Ta = 1.8 bar, energy-saving threshold Te = 2.0 bar, duration threshold Tt = 45 seconds, and oil filter pressure drop threshold Tp = 1.0 bar. Step 2. Real-time acquisition of injection pressure P1, intake pressure P2, and exhaust pressure P3; calculation of oil low pressure differential ΔP1 = P1 - P2 and oil filter pressure drop ΔP2 = P3 - P1 (ΔP2 is used to assist in judging the oil filter clogging status); determination of whether the oil filter pressure drop ΔP2 is greater than the oil filter pressure drop threshold Tp; if yes, issue an oil filter clogging alarm signal to remind replacement of the oil filter and proceed to step 3; otherwise, proceed directly to step 3. Step 3. Based on the low oil pressure difference ΔP1, perform corresponding mode control: When the oil low pressure differential ΔP1 < 1.3 bar or 1.3 bar ≤ oil low pressure differential ΔP1 ≤ 1.8 bar, and the duration is > 45 seconds, the control unit will shut down urgently and the procedure will end. When 1.3 bar ≤ oil low pressure difference ΔP1 ≤ 1.8 bar and the duration ≤ 45 seconds, the emergency mode control is implemented. That is, the frequency of the cooling tower fan inverter is reduced first. If the oil low pressure difference ΔP1 is still not greater than 1.8 bar, the opening of the cooling water flow bypass regulating valve is adjusted until the oil low pressure difference ΔP1 is greater than 1.8 bar, and then step 4 is performed. When 1.8 bar < oil low pressure differential ΔP1 ≤ 2.0 bar, safety mode control is activated; The safety mode control aims to minimize the total system energy consumption. It prioritizes increasing the opening of the cooling water flow bypass regulating valve, and then, constrained by maintaining the low oil pressure difference ΔP1 greater than the alarm threshold Ta, uses an extreme value search method to adjust the frequency of the cooling tower fan inverter and / or the opening of the electronic expansion valve 8. This involves adjusting the frequency of the cooling tower fan inverter in small steps of 1-2 Hz and / or adjusting the opening of the electronic expansion valve 8 by no more than 5% of the total opening in a single adjustment. During the adjustment process, ΔP1 and exhaust pressure are monitored in real time. When the exhaust pressure stabilizes, the current frequency of the cooling tower fan inverter and / or the opening of the electronic expansion valve 8 are locked. Then, it is determined whether the oil filter pressure drop ΔP2 is greater than the oil filter pressure drop threshold Tp. If yes, an oil filter clogging alarm signal is issued to prompt replacement of the oil filter, and step 4 is performed. If no, step 4 is performed directly. When the oil low pressure difference ΔP1 > energy saving threshold Te, energy saving mode control is activated, and step 4 is performed. The energy-saving mode control aims to minimize the total system energy consumption. It prioritizes reducing the opening of the cooling water flow bypass regulating valve (reducing the bypass flow increases the amount of cooling water entering the condenser, thus lowering the exhaust pressure). Then, constrained by maintaining the low oil pressure difference ΔP1 greater than the energy-saving threshold Te, it uses an extreme value search method to adjust the frequency of the cooling tower fan inverter and the opening of the electronic expansion valve 8. The frequency of the cooling tower fan inverter is adjusted in small steps of 1-2 Hz, and the fan's own power consumption and the sum of the unit's compressor power consumption are monitored in real time. When the total energy consumption is reduced to the minimum and the exhaust pressure is stable, the current frequency is locked to optimize the exhaust pressure. The opening of the electronic expansion valve 8 is adjusted in increments not exceeding 5% of the total opening, and the evaporation pressure and the unit's COP are monitored in real time. When the unit's COP rises to the maximum and the suction pressure is stable, the current opening is locked to optimize the evaporation pressure. Due to unavoidable flow resistance in the suction pipeline, the suction pressure is usually slightly lower than the evaporation pressure numerically, but their trends are consistent. Therefore, by adjusting the electronic expansion valve 8 to optimize the evaporation pressure, the effect will be equivalently transmitted and reflected in the optimization of the suction pressure, thereby improving the unit's energy efficiency.

[0027] The extreme value search method includes, but is not limited to, conventional optimization techniques in the field of chiller unit control such as small-step iteration, PID self-tuning, and gradient descent. Its core logic is "small-step adjustment - real-time monitoring - feedback locking." Those skilled in the art can flexibly select the appropriate method based on the unit model and operating conditions, and it can be implemented through control module 3 without creative effort. This embodiment of the invention adopts the "small-step iteration method," which has simple logic and strong adaptability. It can be implemented simply by programming the adjustment step size, dwell time, and monitoring parameter thresholds, without the need for complex algorithm development.

[0028] Step 4. Determine whether to end control. If yes, end; if no, return to step 2.

[0029] The control process of step 3 of the present invention will be described in detail below for three scenarios: ΔP1 = 5.2 bar, ΔP1 = 1.9 bar, and ΔP1 = 1.5 bar, calculated in step 2, with a duration of <45 seconds.

[0030] 1. ΔP1 = 5.2 bar Since ΔP1 = 5.2 bar, which is greater than the energy-saving threshold Te = 2.0 bar, energy-saving mode control is executed, as follows: The cooling water flow bypass regulating valve is first closed from 30% to 0%. After the cooling water flow bypass regulating valve is adjusted to its proper position (0% opening), the adjustment is carried out using a "small-step iteration + energy consumption feedback" extreme value search method, with the constraint that the oil low pressure difference ΔP1 is greater than the energy-saving threshold (2.0 bar). Cooling tower fan frequency converter adjustment: Starting from 30Hz, the frequency is increased by 2Hz each time, and the total energy consumption (fan power consumption + compressor power consumption) is monitored for 30 seconds. The monitoring data is as follows: Total energy consumption 152kW at 30Hz → 148kW at 32Hz → 142kW at 35Hz → 139kW at 38Hz → 138kW at 40Hz → 139kW at 42Hz → 141kW at 45Hz. When the frequency is increased to 40Hz, the total energy consumption is the lowest (138kW), and the exhaust pressure is stable at 6.8bar (a), so the frequency is locked at 40Hz. Electronic expansion valve 8 adjustment: Starting from 40% opening, increase the opening by 5% each time, hold for 60 seconds to monitor COP. The monitoring data are as follows: 40% COP = 8.2 → 45% COP = 8.9 → 50% COP = 9.5 → 55% COP = 9.3. When the opening reaches 50%, the COP is the highest (9.5) and the evaporation pressure stabilizes at 4.1 bar (a), therefore the opening is locked at 50%.

[0031] After adjustment, the oil low pressure difference ΔP1 is maintained at 2.7 bar (higher than the energy-saving threshold of 2.0 bar), and the total system energy consumption is reduced to 138 kW, a reduction of 14 kW compared to the initial state.

[0032] Under this optimized operating condition, due to the significant reduction in exhaust pressure and the moderate increase in evaporation pressure, the compressor compression ratio decreases, resulting in a substantial drop in power consumption and an improvement in the unit's COP from 6.7 to 9.8. This fundamental improvement in energy efficiency stems from the significant reduction in the operating compression ratio: in this example, based on the monitored exhaust pressure decreasing from 8.9 bar(a) to 6.9 bar(a) and the intake pressure increasing from 3.7 bar(a) to 4.0 bar(a), the compression ratio decreased from 2.41 (8.9 / 3.7) to 1.73 (6.9 / 4.0). According to thermodynamic principles, the reduction in compression ratio directly leads to a significant decrease in the compressor's theoretical power consumption, thereby fully releasing the unit's inherent energy efficiency potential under superior operating conditions.

[0033] 2. ΔP1 = 1.9 bar Since ΔP1 = 1.9 bar, which is greater than the low oil differential pressure alarm threshold Ta = 1.8 bar and less than the energy-saving threshold Te = 2.0 bar, safety mode control is executed, as follows: First, increase the opening of the cooling water flow bypass regulating valve from its current position (e.g., from 0% to 20%). After the cooling water flow bypass regulating valve is adjusted, with the constraint that the oil low pressure difference ΔP1 is greater than the oil low pressure difference alarm threshold Ta=1.8bar, the extreme value search method of "small step iteration + energy consumption feedback" is used for adjustment: the frequency of the cooling tower fan inverter is reduced from 45Hz to 30Hz in small steps of 1~2Hz, the exhaust pressure is increased from 6.5bar (a) to 6.7bar (a), and the oil low pressure difference ΔP1 is restored to 2.1bar. Then, it is determined whether the oil filter pressure drop ΔP2 is greater than the oil filter pressure drop threshold of 1.0bar. If not, proceed to step 4.

[0034] 3. ΔP1 = 1.5 bar Since ΔP1 = 1.5 bar and the duration is < 45 seconds, it falls under the condition that 1.3 bar ≤ oil low pressure differential ΔP1 ≤ 1.8 bar and the duration is < 45 seconds. Therefore, the emergency control mode is activated. First, the frequency of the cooling tower fan inverter is adjusted, and the result is ΔP1 = 1.8. Since it is still not greater than the oil low pressure differential alarm threshold Ta = 1.8 bar, the opening of the current cooling water flow bypass regulating valve is adjusted until ΔP1 = 1.9 bar. Implementation effect

[0035] This invention, after 12 months of continuous operation across various real-world scenarios involving both low and high chilled water temperatures, showed that the unit's average COP increased from 6.25 to 9.2, resulting in annual energy savings of 264,000 kWh and an energy efficiency of 32.1%. Oil differential pressure remained stable between 1.8 and 4.0 bar, with no oil-related malfunctions. The oil filter replacement cycle was extended from 5 months to 10 months, reducing maintenance costs by 50%. The ineffective adjustment time of the cooling water flow bypass valve was reduced by 60% (due to priority adjustment of the bypass valve, avoiding the ineffective operation of "adjusting the fan / electronic expansion valve first" in existing technologies), and the ineffective operating time of the cooling tower fan was reduced by 40%, further reducing auxiliary energy consumption. During implementation, no abnormal wear was observed in core components such as compressor bearings and rotors, and their lifespan was extended by more than 30% compared to existing control technologies.

Claims

1. An energy-saving method for screw chiller units based on precise control of oil circuit differential pressure, characterized in that: The system monitors the oil injection pressure P1 and suction pressure P2 of the oil filter in real time. Based on the low oil pressure difference ΔP1 = P1 - P2, it adaptively performs emergency shutdown, risk avoidance mode, safety mode, or energy-saving mode control. The risk avoidance mode aims to make the low oil pressure difference ΔP1 greater than the low oil pressure difference alarm threshold, prioritizing the adjustment of the cooling tower fan frequency converter, and then adjusting the cooling water flow bypass regulating valve. The safety mode and energy-saving mode both aim to minimize the total system energy consumption, coordinating the adjustment of the cooling water flow bypass regulating valve, the cooling tower fan frequency converter, and the electronic expansion valve. The safety mode is constrained by the low pressure difference alarm threshold, and the energy-saving mode is constrained by the low oil pressure difference alarm threshold being less than the energy-saving threshold.

2. The energy-saving method for screw chiller units based on precise control of oil circuit differential pressure according to claim 1, characterized in that... Follow these steps: Step 1. Set the shutdown threshold Ts, the low oil differential pressure alarm threshold Ta, the energy saving threshold Te, and the duration threshold Tt, wherein the shutdown threshold Ts < the low oil differential pressure alarm threshold Ta < the energy saving threshold Te, and control the unit operation; Step 2. Real-time acquisition of injection pressure P1 and intake pressure P2, and calculation of low oil pressure difference ΔP1 = P1 - P2; Step 3. Based on the low oil pressure difference ΔP1, perform corresponding mode control: When the oil low pressure difference ΔP1 < shutdown threshold Ts or shutdown threshold Ts ≤ oil low pressure difference ΔP1 ≤ oil low pressure difference alarm threshold Ta, and the duration > duration threshold Tt, the unit is controlled to shut down urgently and the program ends. When the shutdown threshold Ts ≤ oil low pressure differential ΔP1 ≤ oil low pressure differential alarm threshold Ta, and the duration ≤ duration threshold Tt, the risk avoidance mode control is implemented, and step 4 is performed. When the oil low differential pressure alarm threshold Ta < oil low differential pressure ΔP1 ≤ energy saving threshold Te, safety mode control is activated, and step 4 is performed. When the oil low pressure difference ΔP1 > energy saving threshold Te, energy saving mode control is activated, and step 4 is performed. Step 4. Determine whether to end control. If yes, end; if no, return to step 2.

3. The energy-saving method for screw chiller units based on precise control of oil circuit differential pressure according to claim 2, characterized in that... The safety mode aims to minimize the total system energy consumption by prioritizing increasing the opening of the cooling water flow bypass regulating valve, and then adjusting the frequency of the cooling tower fan inverter and / or the opening of the electronic expansion valve, with the oil low pressure difference ΔP1 being greater than the oil low pressure difference alarm threshold Ta as a constraint. The energy-saving mode aims to minimize the total system energy consumption by prioritizing decreasing the opening of the cooling water flow bypass regulating valve, and then adjusting the frequency of the cooling tower fan inverter and / or the opening of the electronic expansion valve, with the oil low pressure difference ΔP1 being greater than the energy-saving threshold Te as a constraint.

4. The energy-saving method for screw chiller units based on precise control of oil circuit differential pressure according to claim 3, characterized in that: Step 1 also requires setting the oil filter pressure drop threshold Tp. Step 2 also requires real-time acquisition of the exhaust pressure P3, real-time calculation of the oil filter pressure drop ΔP2 = P3 - P1, and determination of whether the oil filter pressure drop ΔP2 is greater than the oil filter pressure drop threshold Tp. If yes, an oil filter clogging alarm signal is issued and step 3 is performed; otherwise, step 3 is performed directly.

5. The energy-saving method for screw chiller units based on precise control of oil circuit differential pressure according to claim 4, characterized in that: The shutdown threshold Ts = 0.8~1.3 bar, the low oil differential pressure alarm threshold Ta = 1.4~2.4 bar, the energy saving threshold Te = 1.6~2.5 bar, the duration threshold Tt = 15~90 seconds, and the oil filter pressure drop threshold Tp = 0.5~1.5 bar.

6. The energy-saving method for screw chiller units based on precise control of oil circuit differential pressure according to claim 1, 2, 3, 4 or 5, characterized in that... The real-time monitoring of the oil filter's injection pressure P1 involves installing an injection pressure sensor at a distance ≤50mm from the oil filter outlet to collect the pressure signal value of the injection pressure sensor in real time. The injection pressure sensor has a range of 0-30 bar and an accuracy of ±0.2% FS.

7. The energy-saving method for screw chiller units based on precise control of oil circuit differential pressure according to claim 6, characterized in that: The single adjustment range of the electronic expansion valve shall not exceed 5% of the total opening.

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