Screw water-cooled water chiller device and low-temperature operation method

Abstract

The present application relates to the field of data processing and air conditioning, and particularly relates to a screw water-cooled chiller device and a low-temperature operation method. The method comprises the following steps: obtaining monitoring data of the water-cooled chiller; calculating a condensation side performance attenuation index; calculating an evaporation side liquid supply stability index; multiplying the condensation side performance attenuation index and the evaporation side liquid supply stability index to determine a system coupling response index; calculating an oil circuit safety margin index; multiplying the reciprocal of the oil circuit safety margin index and the system coupling response index and performing normalization processing to obtain an adaptive compensation factor of the water-cooled chiller under low-temperature operation; multiplying the adaptive compensation factor and a preset maximum oil circuit adjustment amount to determine an adjustment compensation increment of the oil circuit system, and performing compensation adjustment on the oil circuit system according to the adjustment compensation increment. The present application can improve the operation safety and coordination of the screw water-cooled chiller.

Description

Technical Field

[0001] This invention relates to the fields of data processing and air conditioning, specifically to a screw-type water-cooled chiller unit and a low-temperature operation method. Background Technology

[0002] Screw-type water-cooled chillers are among the most widely used central air conditioning and process cooling equipment in industrial and commercial buildings. They utilize a screw compressor to drive refrigerant circulation, achieving water-side heat exchange and providing stable chilled water for various production equipment, clean environments, and comfort air conditioning systems in electronics manufacturing, precision machining, food refrigeration, chemical process control, and other applications requiring high cooling capacity and temperature stability. These units are widely used in many key fields due to their significant advantages, including high energy efficiency, wide load adjustment range, and high structural reliability.

[0003] However, when the unit operates in low-temperature environments (such as winter or cold regions), it faces a series of key technical challenges and operational risks caused by excessively low condensing pressure:

[0004] Uncontrolled condensing pressure and reduced energy efficiency: When the ambient temperature is too low, the cooling water temperature drops significantly, leading to excessive heat exchange in the condenser. This causes a sharp drop in refrigerant condensing pressure, forcing the compressor to operate under extremely low pressure ratios, making it difficult to maintain the condensing pressure within a reasonable, efficient operating range. Simultaneously, the reduced refrigerant vapor density at low condensing pressure results in a decrease in cooling capacity per unit volume, significantly reducing the efficiency of the entire refrigeration cycle and lowering the unit's cooling capacity.

[0005] Risks of Lubricating Oil Return Failure and Equipment Damage: More seriously, excessively low condensing pressure will directly lead to a drop in compressor discharge pressure, resulting in insufficient differential pressure driving force for the lubricating oil to return from the low-pressure side of the system to the compressor crankcase. Without effective lubricating oil return, internal moving parts of the compressor (such as bearings and screw rotors) will face lubrication failure, easily leading to serious mechanical failures such as oil film rupture and bearing dry friction, causing irreversible and severe damage to the unit and threatening the operational safety of the entire system.

[0006] Existing conventional control methods often struggle to effectively address the aforementioned coupling challenges simultaneously, resulting in low efficiency for unit optimization under low-temperature conditions. Summary of the Invention

[0007] This invention provides a screw-type water-cooled chiller unit and a low-temperature operation method to solve existing problems.

[0008] The low-temperature operation method of a screw-type water-cooled chiller unit of the present invention adopts the following technical solution:

[0009] One embodiment of the present invention provides a method for low-temperature operation of a screw-type water-cooled chiller unit, the method comprising the following steps:

[0010] In response to the cooling water temperature of the water-cooled chiller being lower than the condensation temperature of the currently operating refrigerant, the monitoring data of the water-cooled chiller is acquired.

[0011] Based on the pressure and temperature data of the condenser in the monitoring data, the condenser-side performance degradation index, which is used to characterize the degree of deterioration of the condenser's heat exchange performance, is calculated.

[0012] Based on the liquid refrigerant flow rate data at the evaporator inlet from the monitoring data, the evaporator-side liquid supply stability index, which characterizes the stability of the liquid refrigerant supply to the evaporator, is calculated.

[0013] The product of the condenser-side performance degradation index and the evaporator-side liquid supply stability index is determined as the system coupling response index used to characterize the sensitivity of the evaporator end to changes in the condenser end.

[0014] Based on the discharge pressure and return pressure data of the screw compressor in the monitoring data, the oil circuit safety margin index, which is used to characterize the stability of the lubricating oil return path, is calculated.

[0015] The adaptive compensation factor for low-temperature operation of the water-cooled unit is obtained by multiplying the reciprocal of the oil circuit safety margin index with the system coupling response index and then normalizing it.

[0016] The product of the adaptive compensation factor and the preset maximum oil circuit adjustment amount is determined as the adjustment compensation increment of the oil circuit system. The oil circuit system is then adjusted according to the adjustment compensation increment to maintain the stability of the lubricating oil return pressure.

[0017] Optionally, based on the pressure and temperature data of the condenser in the monitoring data, a condenser-side performance degradation index is calculated to characterize the degree of deterioration in the condenser's heat transfer performance, specifically including:

[0018] Based on the pressure and temperature data of the condenser, the phase change driving force deviation coefficient on the condenser side is calculated to characterize the degree of thermodynamic deviation of the refrigerant phase change.

[0019] Based on the temperature and pressure data of the condenser, the liquid phase generation rate decay parameter, used to characterize the liquid phase generation capability, is calculated.

[0020] The product of the liquid phase generation rate decay parameter and the deviation coefficient of the phase change driving force on the condensing side is determined as the condensing side performance decay index.

[0021] Optionally, the condenser pressure data is the pressure data within a preset observation time window. Based on the condenser pressure and temperature data, the condenser-side phase change driving force deviation coefficient, used to characterize the degree of thermodynamic shift in refrigerant phase transition, is calculated, specifically including:

[0022] The ratio of the average condensing pressure of the water-cooled chiller unit under the set reference operating conditions to the average pressure data over a preset time period is determined as the deviation amplification factor of the pressure data.

[0023] For each moment within the observation time window, based on the temperature at that moment, the theoretical saturation pressure value of the refrigerant is determined according to its thermodynamic properties, and the actual pressure value at that moment is obtained. The absolute value of the difference between the saturation pressure value and the actual pressure value is calculated as the instantaneous pressure deviation value at that moment.

[0024] Obtain the instantaneous pressure deviation values ​​at all times, and calculate the average value to obtain the average pressure deviation value;

[0025] The product of the deviation amplification factor and the average pressure deviation value is determined as the deviation coefficient of the phase change driving force on the condensing side.

[0026] Optionally, the temperature data of the condenser is the temperature data within a preset observation time window. Based on the temperature and pressure data of the condenser, a liquid phase generation rate decay parameter used to characterize the liquid phase generation capability is calculated, specifically including:

[0027] For each moment within the observation time window, based on the pressure at that moment, the theoretical saturation temperature value of the refrigerant is determined according to its thermodynamic properties, and the actual temperature value at that moment is obtained. The difference between the theoretical saturation temperature value and the actual temperature value is calculated, and the difference is normalized to obtain the normalized subcooling value at that moment.

[0028] For each moment within the observation time window except the last moment, calculate the ratio of the normalized supercooling value at that moment to the normalized supercooling value at the next moment, and obtain the instantaneous rate of change of liquid phase generation capacity at that moment.

[0029] The average value of the instantaneous change rate of liquid phase generation capacity at all times is obtained to obtain the liquid phase generation rate decay parameter.

[0030] Optionally, based on the liquid refrigerant flow rate data at the evaporator inlet from the monitoring data, an evaporator-side liquid supply stability index is calculated to characterize the stability of the liquid refrigerant supply to the evaporator, specifically including:

[0031] Based on a preset observation time window, the liquid refrigerant flow rate data at the evaporator inlet within the window is obtained, wherein the liquid refrigerant flow rate data is time-series data;

[0032] The average value of the liquid refrigerant flow rate data at all times within the current observation time window is taken as the average liquid refrigerant flow rate value within the current observation time window.

[0033] Obtain the reference liquid refrigerant flow rate value, and use the ratio of the reference liquid refrigerant flow rate value to the average liquid refrigerant flow rate value within the current observation time window as the flow rate reference deviation parameter for the current observation time window;

[0034] Based on liquid refrigerant flow data, calculate the transient flow fluctuation parameters to characterize the instantaneous fluctuation characteristics within the current observation time window;

[0035] The stability index of the evaporation-side liquid supply is obtained by multiplying the flow rate baseline deviation parameter and the flow rate transient fluctuation parameter within the current observation time window.

[0036] Optionally, based on the liquid refrigerant flow rate data, transient flow rate fluctuation parameters are calculated to characterize the instantaneous fluctuation characteristics within the current observation time window, specifically including:

[0037] Based on the liquid refrigerant flow data, calculate the instantaneous rate of change sequence of the data over time at each moment;

[0038] The average of the absolute values ​​of the differences between all adjacent instantaneous rate of change sequences is calculated and used as the transient fluctuation parameter of the flow rate.

[0039] Optionally, based on the discharge pressure and return pressure data of the screw compressor in the monitoring data, an oil circuit safety margin index is calculated to characterize the stability of the lubricating oil return path, specifically including:

[0040] Acquire the time-series data of the discharge oil pressure and return oil pressure of the screw compressor within a preset observation time window;

[0041] Based on the time series data, calculate the absolute value of the difference between the discharge pressure and the return pressure at each moment within the window, which is taken as the actual pressure difference at each moment;

[0042] Based on the actual pressure difference at all times, calculate the safety deviation coefficient, which characterizes the degree to which the average pressure difference deviates from the safety target;

[0043] Based on the time sequence of actual pressure difference, the pressure difference fluctuation coefficient is calculated to characterize its instantaneous fluctuation characteristics;

[0044] Multiplying the safety deviation coefficient and the differential pressure fluctuation coefficient yields the oil circuit safety margin index.

[0045] Optionally, based on the actual pressure difference at all times, a safety deviation coefficient is calculated to characterize the degree to which the average pressure difference deviates from the safety target, specifically including:

[0046] Calculate the average actual pressure difference over all time periods to obtain the average actual pressure difference;

[0047] Obtain the minimum safe target pressure differential value;

[0048] The reciprocal of the absolute value of the difference between the minimum safe target pressure difference and the average actual pressure difference is used as the safety deviation coefficient.

[0049] Optionally, based on the time sequence of the actual pressure difference, a pressure difference fluctuation coefficient is calculated to characterize its instantaneous fluctuation characteristics, specifically including:

[0050] Calculate the average of the absolute values ​​of the differences between all adjacent actual pressure differences in the actual pressure difference sequence, and use this as the average pressure difference fluctuation range;

[0051] Calculate the reciprocal of the average differential pressure fluctuation amplitude, and use it as the differential pressure fluctuation coefficient.

[0052] This invention proposes a screw-type water-cooled chiller unit, including a screw compressor, a condenser, an evaporator, a cooling tower, an oil circuit system, and a control system. The control system is used to execute a low-temperature operation method for the screw-type water-cooled chiller unit.

[0053] The beneficial effects of the technical solution of the present invention are:

[0054] In this embodiment of the invention, by real-time monitoring of the operating parameters of the condenser, evaporator and compressor lubrication oil circuit, a comprehensive index characterizing the performance degradation on the condenser side, the stability of the liquid supply on the evaporator side and the safety margin of the oil circuit is calculated. Based on the coupling analysis of the above index, an adaptive compensation factor is generated to dynamically adjust the oil circuit system to maintain stable lubrication oil pressure. This solves the problems of energy efficiency degradation and oil return failure caused by low condensation pressure under low temperature conditions, and achieves adaptive and coordinated optimization of unit safety and efficiency. Attached Figure Description

[0055] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0056] Figure 1 This is a flowchart illustrating a low-temperature operation method for a screw-type water-cooled chiller unit, as provided in one embodiment of the present invention. Detailed Implementation

[0057] To further illustrate the technical means and effects adopted by the present invention to achieve its intended purpose, the following, in conjunction with the accompanying drawings and preferred embodiments, details the specific implementation, structure, features, and effects of a low-temperature operation method for a screw-type water-cooled chiller unit proposed according to the present invention. In the following description, different "one embodiment" or "another embodiment" do not necessarily refer to the same embodiment. Furthermore, specific features, structures, or characteristics in one or more embodiments can be combined in any suitable form.

[0058] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0059] The following description, in conjunction with the accompanying drawings, details a specific scheme for a low-temperature operation method for a screw-type water-cooled chiller unit provided by the present invention.

[0060] This invention provides a screw-type water-cooled chiller unit and a low-temperature operation method. Please refer to [link / reference]. Figure 1 The diagram illustrates a flowchart of a low-temperature operation method for a screw-type water-cooled chiller unit according to an embodiment of the present invention. The method includes the following steps:

[0061] S101. In response to the cooling water temperature of the water-cooled chiller being lower than the condensation temperature of the currently operating refrigerant, acquire monitoring data of the water-cooled chiller.

[0062] For example, the monitoring data is obtained in the following way:

[0063] By installing ambient temperature sensors outside the unit and temperature sensors on the cooling tower outlet pipe, real-time data on ambient temperature and cooling water temperature are obtained, serving as a preliminary basis for determining whether the unit has entered a low-temperature operating condition.

[0064] Pressure sensors and temperature sensors are installed at the refrigerant inlet and outlet of the condenser and the refrigerant inlet and outlet of the evaporator, respectively, to synchronously collect the condensing pressure, evaporating pressure and corresponding temperature data of the refrigerant.

[0065] On screw compressors, current sensors, motor speed sensors, oil pressure sensors, and oil temperature sensors are used to monitor their operating load, lubrication oil pressure, and lubrication status. Simultaneously, flow meters and temperature sensors installed in the chilled water circuit acquire inlet and outlet water temperature and flow rate data to assess the unit's real-time cooling capacity.

[0066] All the monitoring data collected by the above sensors are collected and preprocessed in a unified manner through a programmable logic controller (PLC) or a dedicated unit controller, and then uploaded to the control system integrated inside the unit or an external host computer platform.

[0067] Before data analysis, the collected raw data is filtered, denoised, and outlier removed to ensure that the data used for subsequent calculations and analysis is highly effective and reliable.

[0068] Furthermore, this embodiment primarily addresses the operation method of water-cooled chillers under low-temperature conditions, and the low-temperature condition can also be set below a certain fixed temperature. The main basis for setting the low-temperature condition in this embodiment—that the cooling water temperature of the water-cooled chiller is lower than the condensation temperature of the currently operating refrigerant—is as follows:

[0069] For example, during the peak summer season, if the unit's condensing temperature is already low (e.g., only 28°C) due to light load or design reasons, even if the cooling water temperature is 25°C, which does not reach the fixed "low temperature" threshold, the 25°C cooling water is actually lower than the 28°C condensing temperature. This can still lead to excessive heat exchange in the condenser, pressure drop, and the risk of oil return. Fixed thresholds cannot identify this risk of "relative overcooling."

[0070] In late autumn, the cooling water temperature is 10℃, which is far below the fixed threshold. However, if the unit's condensing temperature remains above 40℃ due to high load operation, the 10℃ cooling water is still within the normal heat exchange temperature range, and the unit operation is not risky. The fixed threshold may cause the system to make unnecessary compensation adjustments under these circumstances.

[0071] This embodiment employs a dynamic relationship that is directly compared to the real-time operating status of the unit. The focus is not on how "absolutely cold" the cooling water is, but rather on whether the cooling water has cooled to a level sufficient to pose a threat to the current operating status.

[0072] Furthermore, the refrigerant condensation temperature is the saturation temperature at which the refrigerant gas begins to condense into a liquid under the current condensation pressure. It represents the "target operating temperature" required to maintain normal phase change on the refrigerant side within the condenser. The cooling water temperature is the temperature of the medium used to remove heat from the condensation process. In a normal and efficient heat exchange process, the condensation temperature should always be higher than the cooling water temperature, maintaining a reasonable temperature difference between the two (e.g., 5-10°C). This temperature difference is the fundamental driving force for heat transfer from the refrigerant to the cooling water.

[0073] When the cooling water temperature drops to near or even below the condensing temperature, it signifies: An abnormally increased heat exchange driving force: The temperature difference between the two becomes extremely large, leading to excessive heat exchange capacity in the condenser. The refrigerant is "overcooled": Not only is the refrigerant completely condensed into a liquid, but its liquid temperature is further cooled to far below its saturation temperature, meaning the subcooling increases dramatically. This triggers a systemic chain reaction of risks: Over-condensation leads to the accumulation of liquid refrigerant in the condenser, reducing the gas phase and causing a rapid drop in condensing pressure. The drop in condensing pressure leads to a drop in compressor discharge pressure, which in turn reduces the compressor's operating pressure ratio. This reduced pressure ratio directly results in insufficient pressure differential driving force for the lubricating oil to return from the low-pressure side of the system to the compressor, a direct cause of lubrication failure.

[0074] Therefore, this embodiment continuously compares two key temperatures: first, the actual temperature of the cooling water measured in real time by a temperature sensor on the cooling tower outlet pipe; and second, the real-time condensation temperature of the refrigerant dynamically calculated based on the current operating status of the refrigeration system. The method for determining the real-time condensation temperature of the refrigerant is as follows: by reading the refrigerant condensation pressure measured by a pressure sensor installed at the condenser outlet or in the middle, and based on the inherent thermodynamic properties of this type of refrigerant, the current pressure value is converted into the corresponding saturation temperature value. This saturation temperature is then identified as the real-time condensation temperature of the system at the current moment.

[0075] When the control system determines through logical operations that the actual temperature of the cooling water is lower than the real-time condensing temperature of the refrigerant, it identifies a critical risk condition where the cooling water is too cold, which may lead to excessively low condensing pressure. At this point, the system automatically confirms that the unit has entered the "low-temperature operation target condition" that requires the activation of intelligent protection.

[0076] Once the target operating condition is entered, the control system immediately activates the preset high-frequency data acquisition and processing task, and collects various key operating monitoring data, including condenser pressure and temperature, evaporator inlet refrigerant flow rate, compressor discharge pressure and return pressure, in a comprehensive and synchronous manner according to the established process.

[0077] S102. Based on the pressure and temperature data of the condenser in the monitoring data, calculate the condenser-side performance degradation index, which is used to characterize the degree of deterioration of the condenser's heat exchange performance.

[0078] In this embodiment, based on the pressure and temperature data of the condenser in the monitoring data, a condenser-side performance degradation index is calculated to characterize the degree of deterioration in the condenser's heat transfer performance, specifically including:

[0079] Based on the pressure and temperature data of the condenser, the phase change driving force deviation coefficient on the condenser side is calculated to characterize the degree of thermodynamic deviation of the refrigerant phase change.

[0080] Based on the temperature and pressure data of the condenser, the liquid phase generation rate decay parameter, used to characterize the liquid phase generation capability, is calculated.

[0081] The product of the liquid phase generation rate decay parameter and the deviation coefficient of the phase change driving force on the condensing side is determined as the condensing side performance decay index.

[0082] The condenser pressure data is the pressure data within a preset observation time window. Based on the condenser pressure and temperature data, the condenser-side phase change driving force deviation coefficient, which characterizes the degree of thermodynamic shift in refrigerant phase transition, is calculated. Specifically, this includes:

[0083] The ratio of the average condensing pressure of the water-cooled chiller unit under the set reference operating conditions to the average pressure data over a preset time period is determined as the deviation amplification factor of the pressure data.

[0084] For each moment within the observation time window, based on the temperature at that moment, the theoretical saturation pressure value of the refrigerant is determined according to its thermodynamic properties, and the actual pressure value at that moment is obtained. The absolute value of the difference between the saturation pressure value and the actual pressure value is calculated as the instantaneous pressure deviation value at that moment.

[0085] Obtain the instantaneous pressure deviation values ​​at all times, and calculate the average value to obtain the average pressure deviation value;

[0086] The product of the deviation amplification factor and the average pressure deviation value is determined as the deviation coefficient of the phase change driving force on the condensing side.

[0087] The condenser temperature data are the temperature data within a preset observation time window. Based on the condenser temperature and pressure data, a liquid phase formation rate decay parameter, used to characterize the liquid phase formation capability, is calculated, specifically including:

[0088] For each moment within the observation time window, based on the pressure at that moment, the theoretical saturation temperature value of the refrigerant is determined according to its thermodynamic properties, and the actual temperature value at that moment is obtained. The difference between the theoretical saturation temperature value and the actual temperature value is calculated, and the difference is normalized to obtain the normalized subcooling value at that moment.

[0089] For each moment within the observation time window except the last moment, calculate the ratio of the normalized supercooling value at that moment to the normalized supercooling value at the next moment, and obtain the instantaneous rate of change of liquid phase generation capacity at that moment.

[0090] The average value of the instantaneous change rate of liquid phase generation capacity at all times is obtained to obtain the liquid phase generation rate decay parameter.

[0091] For example, by analyzing the refrigerant phase shift characteristics under condensation thermal drop conditions, the formation mechanism of condensation pressure deviation can be perceived and predicted. "Condensation thermal drop conditions" specifically refer to an operating state where the cooling water temperature rapidly or significantly drops below the current refrigerant condensation temperature, causing the condenser's heat exchange capacity to far exceed design requirements, thus triggering a sharp deviation of the system's thermal state from the normal range. Based on coupled monitoring data of condenser-side pressure and temperature, the trend of insufficient refrigerant phase change driving force due to excessively low cooling water temperature can be identified in advance, thus providing reliable data support for subsequent analysis.

[0092] In this embodiment, the length of the observation time window is not specifically limited and can be set according to actual needs, such as 5 minutes or 10 minutes.

[0093] First, a short observation window (e.g., 5 minutes) is set. This observation window is a continuous, fixed time period used for real-time data analysis and feature extraction, containing multiple data points collected at fixed frequencies. Pressure sensors are installed at the condenser outlet to collect refrigerant condensing pressure signals during chiller unit operation. The arithmetic mean of the condensing pressure during stable operation under set baseline conditions is recorded as follows: The arithmetic mean of the condensation pressure signal within the current observation time window is denoted as... "Set-benchmark operating conditions" typically refer to the operating conditions under which the unit can operate efficiently and stably under standard design conditions (such as specified cooling water inlet temperature, flow rate, and cooling load), and its parameters serve as a benchmark for evaluating whether current performance has deteriorated.

[0094] By combining the real-time temperature values ​​collected by the refrigerant temperature sensor at the condenser outlet, and based on the refrigerant's thermodynamic properties, the theoretical saturation pressure reference data corresponding to that temperature is dynamically matched and determined. "Refrigerant thermodynamic properties" refer to the inherent physical relationships between state parameters such as pressure, temperature, enthalpy, and entropy of a specific type of refrigerant, typically pre-stored in the control system in the form of a database or empirical formula. "Theoretical saturation pressure" refers to the pressure corresponding to the point at which a pure refrigerant begins to undergo a condensation phase change (i.e., gas-liquid two-phase equilibrium) at a given temperature; it is a theoretical value that is only related to temperature.

[0095] Then, the deviation coefficient of the condensation-side phase change driving force within the current observation time window is calculated. :

[0096] ;

[0097] in, This indicates the ideal pressure level under the set reference operating conditions, that is, the average value of the condensing pressure; This represents the average pressure data over a preset time period. This indicates the amplification factor for the deviation of the pressure data; It represents the theoretical saturation pressure determined by the thermodynamic properties of the refrigerant based on the measured temperature at the i-th sampling time. This represents the actual pressure value directly measured by the pressure sensor at the i-th sampling time. This represents the absolute difference between the theoretical saturation pressure required for the refrigerant to undergo a phase change at the current temperature and the actual pressure value actually reached by the system at each sampling moment. This represents the number of sampling moments within the current observation time window.

[0098] In the formula, This reflects the degree of imbalance between the driving force (theoretical value) and the actual resistance (leading to pressure increase) of the condensation process at that point in time. The larger the difference, the greater the heat transfer or flow resistance of the condenser at that moment, i.e., the worse the heat exchange performance. In the process, when the condenser's performance deteriorates due to overcooling or its own degradation, the refrigerant-side resistance increases, often manifesting as an increase in the current average pressure. An increase in the value of this ratio leads to an increase in the average pressure deviation term. Its effect is to amplify the subsequent average pressure deviation term. exist The contribution of this factor makes small, persistent pressure deviation trends more prominent in the calculation results, thus improving the sensitivity of the diagnosis. Condensation-side phase change driving force deviation coefficient This reflects the impact in two dimensions: first, the instantaneous deviation of the pressure-temperature matching relationship (i.e., the average pressure deviation term); and second, the magnitude of the increase in current operating pressure relative to the reference pressure (i.e., the deviation amplification factor). Therefore, an increase in the phase change driving force deviation coefficient on the condenser side directly means that the effective thermodynamic potential energy (driving force) provided by the condenser side to drive the phase change is insufficient, and the system may already be operating under a higher resistance state.

[0099] It should be noted that while the condenser-side phase change driving force deviation coefficient can effectively quantify the degree of thermodynamic deviation in refrigerant phase transition, its core calculation is based on the macroscopic deviation relationship between pressure and temperature, making it essentially a "result-based" indicator. It cannot directly distinguish the specific root cause of the deviation: that is, it cannot identify whether the performance deviation is a "passive" deviation caused by external conditions (excessively low cooling water temperature, i.e., subcooling) or an "active" performance degradation caused by the internal state of the condenser (such as deterioration of heat exchange and flow caused by fouling of heat exchange tubes, excessive oil content in the refrigerant, or the presence of non-condensable gases like air). Therefore, further comprehensive analysis in conjunction with other characteristic parameters (such as subcooling) is necessary.

[0100] After obtaining the phase change driving force deviation coefficient on the condenser side, it is necessary to further evaluate whether the liquid refrigerant generation capacity at the condenser outlet shows a declining trend, i.e., to calculate the liquid phase generation rate decline parameter. This parameter is used to quantify the dynamic deterioration of the condenser's liquid phase output capacity. The specific steps are as follows:

[0101] After calculating the deviation coefficient of the phase change driving force on the condenser side, it is necessary to further evaluate the dynamic generation capacity of the liquid refrigerant at the condenser outlet, i.e., calculate the liquid generation rate decay parameter. This parameter is used to quantify the decay trend of the liquid refrigerant supply capacity at the condenser outlet.

[0102] The first step is to obtain the normalized subcooling sequence. Temperature sensors are installed on the refrigerant line at the condenser outlet to continuously collect the actual temperature values ​​of the refrigerant. Simultaneously, based on the thermodynamic properties of the refrigerant, the theoretical saturation temperature corresponding to the current condensing pressure is determined in real time. For each sampling time i within the observation time window, calculate the difference between the theoretical saturation temperature and the actual temperature at that time. The difference is then normalized to obtain the normalized supercooling value at that moment, denoted as . .

[0103] The second step is to calculate the instantaneous rate of change of liquid phase generation capacity. For each sampling time i within the observation time window (except for the last sampling time), the normalized supercooling value is calculated. With the next time value The ratio, i.e., the instantaneous rate of change of liquid phase generation capacity, is calculated as follows: In the formula, This represents a small, non-zero constant that guarantees the calculation's significance. This ratio directly characterizes the relative rate of change in liquid phase formation capacity between two adjacent sampling times. If the ratio is greater than 1, it indicates that the supercooling at the later time step is less than that at the earlier time step (i.e.,...). This means that the ability to generate liquid phase is weakening, the condensation process is becoming incomplete, and the operational risk is increasing.

[0104] Optionally, in this embodiment You can add it or not, but generally, for the sake of the calculation formula's rationality, you will choose to add it during the calculation. .

[0105] The third step is to calculate the performance degradation index on the condenser side. The calculation formula can be shown below:

[0106] ;

[0107] in, This represents the deviation coefficient of the phase change driving force on the condensation side; This represents the liquid phase generation rate decay parameter, which is calculated by averaging the instantaneous change rate of liquid phase generation capacity at each sampling time. This represents the number of sampling moments within the current observation time window.

[0108] In the formula, This represents the arithmetic mean of the instantaneous rates of change of all liquid phase generation capacity within the entire observation window, i.e., the liquid phase generation rate decay parameter. The liquid phase generation rate decay parameter reflects the overall trend of liquid phase generation capacity during the observation period; the larger the average value, the more significant the decay trend. Furthermore, the condensation-side performance decay index... The deviation coefficient of the phase change driving force on the condensation side The product of the liquid phase formation rate decay parameter and the condensation side performance degradation index. As a composite index, it integrates two aspects of information: first, the overall severity of the shift in the thermodynamic state on the condenser side (reflected by the coefficient f); and second, the dynamic rate of decline in liquid phase generation capacity over time (reflected by the average rate of change). Therefore, when the thermodynamic conditions deteriorate significantly (large f value) and the rate of decline in liquid phase generation accelerates (large average rate of change), the product effect of these two factors will cause the parameter to... The value increases significantly, thus revealing the potential risk level of the system due to insufficient condensation more sensitively and comprehensively.

[0109] S103. Based on the liquid refrigerant flow data at the evaporator inlet in the monitoring data, calculate the evaporator-side liquid supply stability index, which characterizes the stability of the liquid refrigerant supply to the evaporator.

[0110] In this embodiment, based on the liquid refrigerant flow rate data at the evaporator inlet from the monitoring data, the evaporator-side liquid supply stability index, which characterizes the stability of the liquid refrigerant supply to the evaporator, is calculated, specifically including:

[0111] Based on a preset observation time window, the liquid refrigerant flow rate data at the evaporator inlet within the window is obtained, wherein the liquid refrigerant flow rate data is time-series data;

[0112] The average value of the liquid refrigerant flow rate data at all times within the current observation time window is taken as the average liquid refrigerant flow rate value within the current observation time window.

[0113] Obtain the reference liquid refrigerant flow rate value, and use the ratio of the reference liquid refrigerant flow rate value to the average liquid refrigerant flow rate value within the current observation time window as the flow rate reference deviation parameter for the current observation time window;

[0114] Based on liquid refrigerant flow data, calculate the transient flow fluctuation parameters to characterize the instantaneous fluctuation characteristics within the current observation time window;

[0115] The stability index of the evaporation-side liquid supply is obtained by multiplying the flow rate baseline deviation parameter and the flow rate transient fluctuation parameter within the current observation time window.

[0116] Based on liquid refrigerant flow data, transient flow fluctuation parameters are calculated to characterize the instantaneous fluctuations within the current observation time window. These parameters include:

[0117] Based on the liquid refrigerant flow data, calculate the instantaneous rate of change sequence of the data over time at each moment;

[0118] The average of the absolute values ​​of the differences between all adjacent instantaneous rate of change sequences is calculated and used as the transient fluctuation parameter of the flow rate.

[0119] For example, to assess the stability of the liquid refrigerant supply at the evaporator inlet under low-temperature operating conditions, it is necessary to calculate the evaporator-side liquid supply stability index. This calculation aims to identify evaporator-side liquid supply imbalances caused by deterioration in condenser-side performance and to provide a quantitative basis for subsequent system adjustments, thereby helping the unit maintain stable refrigerant flow on the evaporator side in low-temperature environments. The calculation steps are as follows:

[0120] The first step is to acquire time-series data of liquid refrigerant flow. Flow sensors are installed on the evaporator inlet pipe to collect time-series data of liquid refrigerant flow within the observation time window.

[0121] The second step is to calculate the flow rate reference deviation parameter. The arithmetic mean of the flow rate data within the previous observation time window immediately preceding the current observation window is denoted as the reference average flow rate value Y. The arithmetic mean of the flow rate data within the current observation time window is denoted as the average liquid refrigerant flow rate value y within the current observation time window. Calculation... This ratio is the flow rate baseline deviation parameter. The smaller the current average flow rate y, the more insufficient the liquid phase supply at the evaporation end. The larger the value, the more it amplifies the rate of decrease in flow, thus quantifying the average degree of loss in liquid supply.

[0122] Optionally, the reference liquid refrigerant flow rate value here, in a preferred embodiment, is the arithmetic mean of the flow rate data within the previous observation time window immediately adjacent to the current observation window. It can also be an ideal flow rate value set according to the actual situation, or a flow rate value obtained by other means. There are no specific limitations here.

[0123] The third step is to calculate the transient fluctuation parameters of the flow rate. The time-series data of the liquid refrigerant flow rate within the current observation window is analyzed. First, the instantaneous slope sequence of the flow rate data over time is calculated, and the slope value corresponding to each sampling time is denoted as k. This slope value... This represents the instantaneous rate of change of the flow rate at the j-th sampling time. Subsequently, the arithmetic mean of the absolute values ​​of the differences between all adjacent slope values ​​in this slope sequence is calculated, i.e. .in, Represents a small, non-zero constant that guarantees the calculation is meaningful. The difference between adjacent slopes. This represents the fluctuation range of the flow rate change rate. A larger fluctuation range indicates a more unstable supply of liquid refrigerant at the evaporator end, potentially leading to uneven distribution of the gas and liquid phases, thus increasing the risk of localized dry burning and friction. The average value calculated above is the transient flow rate fluctuation parameter, which quantifies the instantaneous instability of the liquid supply flow rate.

[0124] The fourth step is to calculate the stability index of the evaporation-side liquid supply. The calculation formula can be:

[0125] ;

[0126] in, Indicates the deviation parameter from the flow baseline; This represents the parameter indicating transient fluctuations in flow rate. It represents a non-zero small constant that guarantees the computation is meaningful.

[0127] In the formula, the flow rate baseline deviation parameter reflects the magnitude of the decrease (loss) in the average level of the liquid supply. The transient flow rate fluctuation parameter reflects the degree of instantaneous instability in the liquid supply process. The product of the two is the evaporation-side liquid supply stability index. The larger the value of this index d, the more severe the average loss of the liquid phase supply at the evaporation end, and the more severe the instantaneous fluctuation, that is, the worse the liquid supply stability.

[0128] The evaporator-side liquid supply stability index effectively quantifies the average loss and transient fluctuations in the liquid refrigerant supply at the evaporator end. However, this index primarily describes the liquid supply status of the evaporator side itself, making it a "conclusion-based" representation. It cannot directly reflect the sensitivity of the evaporator flow rate to the impact of the decline in the condenser-side liquid phase generation capacity (such as the liquid phase generation rate decline parameter g calculated earlier), nor can it independently characterize the dynamic response capability of the entire refrigeration system under the specific driving condition of low condensing pressure. Therefore, it is necessary to couple the evaporator-side liquid supply stability index with parameters reflecting the condenser-side status to evaluate the overall system response.

[0129] S104. The product of the condenser-side performance degradation index and the evaporator-side liquid supply stability index is determined as the system coupling response index used to characterize the sensitivity of the evaporator end to changes in the condenser end.

[0130] For example, to comprehensively evaluate the overall impact of condenser-side performance degradation on the evaporator-side liquid supply status, it is necessary to fuse key parameters reflecting the states of both sides, i.e., calculate the system coupling response index F. This index is used to characterize the dynamic response sensitivity of the evaporator side to changes in the condenser-side state, and the resulting potential system-level risks.

[0131] The formula for calculating the system coupling response exponent F can be:

[0132] ;

[0133] in, Indicates the performance degradation index on the condenser side. This indicates the stability index of the liquid supply on the evaporation side.

[0134] In the formula, the condenser-side performance degradation index comprehensively characterizes the degree of deterioration in the condenser's heat exchange performance. The evaporator-side liquid supply stability index comprehensively characterizes the stability of the liquid refrigerant supply at the evaporator inlet. The system coupling response index directly correlates the states of the condenser and evaporator sides; the larger the value, the higher the systemic risk of evaporator-side liquid supply instability due to condenser-side deterioration, meaning the system is more sensitive to overall low-temperature disturbances. When the system coupling response index F increases, it indicates that the refrigerant circulation system is in a highly unstable state. This instability directly affects the compressor's suction operation, leading to a decrease in the system's core pressure difference (suction and discharge pressure difference), thereby weakening the driving force for lubricating oil return and posing a significant risk of mechanical damage to the equipment.

[0135] S105. Based on the discharge pressure data and return pressure data of the screw compressor in the monitoring data, calculate the oil circuit safety margin index used to characterize the stability of the lubricating oil return path.

[0136] In this embodiment, based on the discharge pressure data and return pressure data of the screw compressor in the monitoring data, the oil circuit safety margin index, which characterizes the stability of the lubricating oil return path, is calculated, specifically including:

[0137] Acquire the time-series data of the discharge oil pressure and return oil pressure of the screw compressor within a preset observation time window;

[0138] Based on the time series data, calculate the absolute value of the difference between the discharge pressure and the return pressure at each moment within the window, which is taken as the actual pressure difference at each moment;

[0139] Based on the actual pressure difference at all times, calculate the safety deviation coefficient, which characterizes the degree to which the average pressure difference deviates from the safety target;

[0140] Based on the time sequence of actual pressure difference, the pressure difference fluctuation coefficient is calculated to characterize its instantaneous fluctuation characteristics;

[0141] Multiplying the safety deviation coefficient and the differential pressure fluctuation coefficient yields the oil circuit safety margin index.

[0142] Based on the actual pressure difference at all times, a safety deviation coefficient is calculated to characterize the degree to which the average pressure difference deviates from the safety target. Specifically, this includes:

[0143] Calculate the average actual pressure difference over all time periods to obtain the average actual pressure difference;

[0144] Obtain the minimum safe target pressure differential value;

[0145] The reciprocal of the absolute value of the difference between the minimum safe target pressure difference and the average actual pressure difference is used as the safety deviation coefficient.

[0146] Based on the time-varying sequence of actual pressure differential, a pressure differential fluctuation coefficient is calculated to characterize its instantaneous fluctuation properties, specifically including:

[0147] Calculate the average of the absolute values ​​of the differences between all adjacent actual pressure differences in the actual pressure difference sequence, and use this as the average pressure difference fluctuation range;

[0148] Calculate the reciprocal of the average differential pressure fluctuation amplitude, and use it as the differential pressure fluctuation coefficient.

[0149] For example, to assess the stability of the compressor lubricating oil return path under low temperature and low pressure ratio conditions in real time and to identify potential risks in advance, it is necessary to monitor and quantify the oil circuit pressure difference in real time, i.e., calculate the oil circuit safety margin index D. This index aims to comprehensively reflect the real-time safety margin of the lubrication system by capturing the fluctuation characteristics of the pressure difference and its deviation from the safety target. The calculation process is as follows:

[0150] The first step is to obtain the actual pressure difference sequence. Pressure sensors are installed at the compressor's oil discharge port and oil return port, respectively. Within a set observation time window, pressure monitoring data from both locations are collected simultaneously. For each sampling time i within the window, the absolute value of the difference between the oil discharge pressure and the oil return pressure at that time is calculated and recorded as the actual pressure difference at that time. Calculate the arithmetic mean of all actual pressure differences within the entire window, denoted as . That is, the average actual pressure difference.

[0151] The second step is to define the minimum safe target differential pressure value. The minimum safe differential pressure threshold required to ensure reliable lubricant return is defined as the minimum safe target differential pressure value, denoted as [reference needed]. This value is a preset system security parameter.

[0152] Optionally, the minimum safe target differential pressure value here is a target value calculated based on the actual situation, and can be set or modified according to actual needs; there are no restrictions here.

[0153] The third step is to calculate the oil circuit safety margin index D. The calculation formula is:

[0154] ;

[0155] in, It represents the arithmetic mean of the absolute values ​​of the differences between all two adjacent pressure difference values ​​in the actual pressure difference sequence, that is, the average pressure difference fluctuation range. This represents the pressure difference fluctuation coefficient. It represents the absolute value of the difference between the minimum safe target pressure difference and the average actual pressure difference. Indicates the safety deviation coefficient. This represents a small, non-zero constant that guarantees the calculation's significance; its function is the same as the constants mentioned in the previous calculations. This indicates the number of moments within the observation time window.

[0156] The average differential pressure fluctuation amplitude characterizes the instantaneous fluctuation amplitude of the oil circuit differential pressure. According to fluid mechanics principles, when the lubricating oil return channel is obstructed or the flow is sluggish, the flow disturbance intensifies, inevitably leading to an increase in instantaneous pressure fluctuation, i.e. The value will increase. Therefore, the larger the average value, the worse the oil circuit stability, that is, the smaller the differential pressure fluctuation coefficient. The smaller the value, the closer the average differential pressure level of the system is to the safety requirements, that is, the lower the degree to which the differential pressure deviates from the safety target, and the better the basic safety.

[0157] The oil circuit safety margin index is composed of the product of two reciprocals. The first reciprocal reflects the evaluation of differential pressure fluctuation; the smaller the fluctuation, the larger the value. The second reciprocal reflects the evaluation of the safe proximity of the average differential pressure; the closer to the safety target, the larger the value. Therefore, the larger the value of the oil circuit safety margin index D, the more it indicates that the oil circuit differential pressure remains stable (small fluctuation) and is close to the safety target (small deviation), meaning that the safety margin of lubricating oil return is higher, and the safety of equipment operation at low temperatures is more guaranteed.

[0158] S106. Take the reciprocal of the oil circuit safety margin index, multiply it with the system coupling response index, and normalize it to obtain the adaptive compensation factor for low-temperature operation of the water-cooled unit.

[0159] For example, based on the aforementioned comprehensive analysis results of the condenser side, evaporator side and oil circuit system, the overall operating status of the unit at low temperature can be finally comprehensively evaluated, and the adaptive compensation factor can be generated to make decisions and execute precise oil circuit compensation adjustment, thereby effectively improving the operating stability and reliability of the unit in low temperature environment.

[0160] Adaptive compensation factor The calculation formula is:

[0161]

[0162] in, The system coupling response index, For oil circuit safety margin index, This is the normalization function.

[0163] The product of these factors essentially constitutes a "risk-demand ratio." A larger numerator indicates a higher instability risk on the refrigerant cycle side; a smaller denominator indicates a lower safety margin in the oil circuit. Therefore, a larger product indicates that the unit's current operating state deviates further from the safe and efficient range, making the need for compensation and adjustment of the oil circuit system more urgent, and requiring greater compensation. The adaptive compensation factor obtained after normalization is the adaptive compensation factor.

[0164] S107. The product of the adaptive compensation factor and the preset maximum oil circuit adjustment amount is determined as the adjustment compensation increment of the oil circuit system, and the oil circuit system is compensated and adjusted according to the adjustment compensation increment to maintain the stability of the lubricating oil return pressure.

[0165] For example, after obtaining the adaptive compensation factor, the oil circuit adjustment compensation increment can be determined and executed. The adjustment of the oil circuit system is a closed-loop process applied proportionally:

[0166] Obtain the adjustment reference: Obtain the pre-set maximum oil circuit adjustment amount allowed by the system design from the unit control system. (For example, the increase in the highest frequency of the oil pump or the change in the maximum opening of the regulating valve).

[0167] The calculated adaptive compensation factor and Multiply by this to obtain the actual incremental oil circuit adjustment compensation that needs to be performed within this control cycle. The larger the compensation factor (indicating higher risk), the larger the calculated compensation increment, ensuring that the adjustment is sufficient to cope with the current risk.

[0168] The calculated oil circuit adjustment compensation increment is sent to the actuator, such as the compressor's variable frequency oil pump control module or the electric regulating valve on the return oil line. Based on this increment command, the actuator precisely adjusts the oil pump output flow or the regulating valve opening, thereby changing the oil circuit resistance or driving force, so that the actual pressure difference between the compressor's oil discharge port and return oil port approaches the preset minimum safe target pressure difference value.

[0169] After completing this compensation adjustment, the control system continues to collect key operating data in real time, including compressor oil discharge / return pressure, evaporator inlet refrigerant flow rate and temperature. Based on this updated data, the system restarts all the aforementioned analysis steps, calculates a new adaptive compensation factor, and makes the next round of adjustment decisions and execution accordingly.

[0170] Optionally, in one specific embodiment of the present invention, in order to achieve the regulation of cooling water temperature and create a stable operating boundary for the implementation of the method in this embodiment, the cooling water system of the unit is configured as follows:

[0171] In this embodiment, a bypass pipe is added between the main cooling water inlet and outlet pipes of the condenser. A flow proportional electric regulating valve is installed on this bypass pipe. By adjusting the opening of this valve, the flow rate of cooling water diverted from the condenser can be precisely controlled, thereby effectively regulating the actual water flow rate and temperature entering the condenser in low-temperature environments.

[0172] Furthermore, this embodiment integrates a dedicated cooling water pressure and temperature control module into the unit's control system. This module can coordinate with the bypass regulating valve to maintain the cooling water parameters on the condenser side within the target range based on the real-time status of the condensing pressure or a preset strategy.

[0173] In addition, to cope with extremely cold weather, this embodiment is equipped with an immersion electric heater and a matching automatic control system installed in the cooling tower basin. When the cooling water temperature is detected to be lower than the safe operating limit, the heating system automatically starts to provide auxiliary heating to the cooling water in the basin, ensuring that the cooling water temperature output from the cooling tower meets the unit's minimum operating requirements.

[0174] The hardware configuration provided in this embodiment constitutes an active environmental temperature adaptation layer. It can significantly mitigate the direct impact of extreme low temperatures on the condenser side, reducing the frequency and intensity of the system triggering intelligent protection control thresholds. When the aforementioned hardware adjustment methods reach their limits or still need to operate under specific low-temperature conditions, the method in this embodiment will serve as the final and core technical defense line to ensure the safe, efficient, and stable operation of the unit. This system, combining "front-end hardware buffering" and "back-end intelligent closed-loop control," jointly achieves wide-range, safe, and efficient operation of the screw-type water-cooled chiller unit under complex climatic conditions throughout the year.

[0175] In summary, in this embodiment of the invention, by real-time monitoring of the operating parameters of the condenser, evaporator, and compressor lubrication circuits, a comprehensive index characterizing the performance degradation on the condenser side, the stability of the liquid supply on the evaporator side, and the safety margin of the oil circuit is calculated. Based on the coupling analysis of the above indices, an adaptive compensation factor is generated to dynamically adjust the oil circuit system to maintain stable lubrication oil pressure. This simultaneously solves the problems of energy efficiency degradation and oil return failure caused by excessively low condensation pressure under low temperature conditions, achieving adaptive and coordinated optimization of unit safety and efficiency.

[0176] A screw-type water-cooled chiller unit includes a screw compressor, a condenser, an evaporator, a cooling tower, an oil circuit system, and a control system. The control system is used to execute a low-temperature operation method for the screw-type water-cooled chiller unit.

[0177] It should be noted that the order of the above embodiments of the present invention is merely for descriptive purposes and does not represent the superiority or inferiority of the embodiments. The processes depicted in the accompanying drawings do not necessarily require a specific or sequential order to achieve the desired result. In some embodiments, multitasking and parallel processing are also possible or may be advantageous.

[0178] The various embodiments in this specification are described in a progressive manner. The same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on describing the differences from other embodiments.

[0179] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for low-temperature operation of a screw-type water-cooled chiller unit, characterized in that, The method includes: In response to the cooling water temperature of the water-cooled chiller being lower than the condensation temperature of the currently operating refrigerant, the monitoring data of the water-cooled chiller is acquired. Based on the pressure and temperature data of the condenser in the monitoring data, the condenser-side performance degradation index, which is used to characterize the degree of deterioration of the condenser's heat exchange performance, is calculated. Based on the liquid refrigerant flow rate data at the evaporator inlet from the monitoring data, the evaporator-side liquid supply stability index, which characterizes the stability of the liquid refrigerant supply to the evaporator, is calculated. The product of the condenser-side performance degradation index and the evaporator-side liquid supply stability index is determined as the system coupling response index used to characterize the sensitivity of the evaporator end to changes in the condenser end. Based on the discharge pressure and return pressure data of the screw compressor in the monitoring data, the oil circuit safety margin index, which is used to characterize the stability of the lubricating oil return path, is calculated. The adaptive compensation factor for low-temperature operation of the water-cooled unit is obtained by multiplying the reciprocal of the oil circuit safety margin index with the system coupling response index and then normalizing it. The product of the adaptive compensation factor and the preset maximum oil circuit adjustment amount is determined as the adjustment compensation increment of the oil circuit system. The oil circuit system is then adjusted according to the adjustment compensation increment to maintain the stability of the lubricating oil return pressure.

2. The low-temperature operation method for a screw-type water-cooled chiller unit according to claim 1, characterized in that, The calculation of the condenser-side performance degradation index, which characterizes the degree of deterioration in the condenser's heat transfer performance, based on the pressure and temperature data of the condenser in the monitoring data, specifically includes: Based on the pressure and temperature data of the condenser, the phase change driving force deviation coefficient on the condenser side is calculated to characterize the degree of thermodynamic deviation of the refrigerant phase change. Based on the temperature and pressure data of the condenser, the liquid phase generation rate decay parameter, used to characterize the liquid phase generation capability, is calculated. The product of the liquid phase generation rate decay parameter and the deviation coefficient of the phase change driving force on the condensing side is determined as the condensing side performance decay index.

3. A method for low-temperature operation of a screw-type water-cooled chiller unit according to claim 2, characterized in that, The pressure data of the condenser is the pressure data within a preset observation time window. Based on the pressure and temperature data of the condenser, the condenser-side phase change driving force deviation coefficient, which characterizes the degree of thermodynamic shift in refrigerant phase transition, is calculated, specifically including: The ratio of the average condensing pressure of the water-cooled chiller unit under the set reference operating conditions to the average pressure data over a preset time period is determined as the deviation amplification factor of the pressure data. For each moment within the observation time window, based on the temperature at that moment, the theoretical saturation pressure value of the refrigerant is determined according to its thermodynamic properties, and the actual pressure value at that moment is obtained. The absolute value of the difference between the saturation pressure value and the actual pressure value is calculated as the instantaneous pressure deviation value at that moment. Obtain the instantaneous pressure deviation values ​​at all times, and calculate the average value to obtain the average pressure deviation value; The product of the deviation amplification factor and the average pressure deviation value is determined as the deviation coefficient of the phase change driving force on the condensing side.

4. A method for low-temperature operation of a screw-type water-cooled chiller unit according to claim 2, characterized in that, The temperature data of the condenser is the temperature data within a preset observation time window. Based on the temperature and pressure data of the condenser, the calculation of the liquid phase formation rate decay parameter, used to characterize the liquid phase formation capability, specifically includes: For each moment within the observation time window, based on the pressure at that moment, the theoretical saturation temperature value of the refrigerant is determined according to its thermodynamic properties, and the actual temperature value at that moment is obtained. The difference between the theoretical saturation temperature value and the actual temperature value is calculated, and the difference is normalized to obtain the normalized subcooling value at that moment. For each moment within the observation time window except the last moment, calculate the ratio of the normalized supercooling value at that moment to the normalized supercooling value at the next moment, and obtain the instantaneous rate of change of liquid phase generation capacity at that moment. The average value of the instantaneous change rate of liquid phase generation capacity at all times is obtained to obtain the liquid phase generation rate decay parameter.

5. A method for low-temperature operation of a screw-type water-cooled chiller unit according to claim 1, characterized in that, The calculation of the evaporator-side liquid refrigerant supply stability index, which characterizes the stability of the liquid refrigerant supply to the evaporator, based on the liquid refrigerant flow rate data at the evaporator inlet from the monitoring data, specifically includes: Based on a preset observation time window, the liquid refrigerant flow rate data at the evaporator inlet within the window is obtained, wherein the liquid refrigerant flow rate data is time-series data; The average value of the liquid refrigerant flow rate data at all times within the current observation time window is taken as the average liquid refrigerant flow rate value within the current observation time window. Obtain the reference liquid refrigerant flow rate value, and use the ratio of the reference liquid refrigerant flow rate value to the average liquid refrigerant flow rate value within the current observation time window as the flow rate reference deviation parameter for the current observation time window; Based on liquid refrigerant flow data, calculate the transient flow fluctuation parameters to characterize the instantaneous fluctuation characteristics within the current observation time window; The stability index of the evaporation-side liquid supply is obtained by multiplying the flow rate baseline deviation parameter and the flow rate transient fluctuation parameter within the current observation time window.

6. A method for low-temperature operation of a screw-type water-cooled chiller unit according to claim 5, characterized in that, The calculation of transient flow fluctuation parameters based on liquid refrigerant flow data, used to characterize the instantaneous fluctuations within the current observation time window, specifically includes: Based on the liquid refrigerant flow data, calculate the instantaneous rate of change sequence of the data over time at each moment; The average of the absolute values ​​of the differences between all adjacent instantaneous rate of change sequences is calculated and used as the transient fluctuation parameter of the flow rate.

7. A method for low-temperature operation of a screw-type water-cooled chiller unit according to claim 1, characterized in that, The oil circuit safety margin index, which characterizes the stability of the lubricating oil return path, is calculated based on the discharge and return oil pressure data of the screw compressor from the monitoring data. Specifically, this includes: Acquire the time-series data of the discharge oil pressure and return oil pressure of the screw compressor within a preset observation time window; Based on the time series data, calculate the absolute value of the difference between the discharge pressure and the return pressure at each moment within the window, which is taken as the actual pressure difference at each moment; Based on the actual pressure difference at all times, calculate the safety deviation coefficient, which characterizes the degree to which the average pressure difference deviates from the safety target; Based on the time sequence of actual pressure difference, the pressure difference fluctuation coefficient is calculated to characterize its instantaneous fluctuation characteristics; Multiplying the safety deviation coefficient and the differential pressure fluctuation coefficient yields the oil circuit safety margin index.

8. A method for low-temperature operation of a screw-type water-cooled chiller unit according to claim 7, characterized in that, The calculation of the safety deviation coefficient, which characterizes the degree to which the average pressure difference deviates from the safety target, based on the actual pressure difference at all times, specifically includes: Calculate the average actual pressure difference over all time periods to obtain the average actual pressure difference; Obtain the minimum safe target pressure differential value; The reciprocal of the absolute value of the difference between the minimum safe target pressure difference and the average actual pressure difference is used as the safety deviation coefficient.

9. A method for low-temperature operation of a screw-type water-cooled chiller unit according to claim 7, characterized in that, The calculation of the pressure difference fluctuation coefficient, which characterizes the instantaneous fluctuation characteristics, based on the sequence of actual pressure difference changes over time, specifically includes: Calculate the average of the absolute values ​​of the differences between all adjacent actual pressure differences in the actual pressure difference sequence, and use this as the average pressure difference fluctuation range; Calculate the reciprocal of the average differential pressure fluctuation amplitude, and use it as the differential pressure fluctuation coefficient.

10. A screw-type water-cooled chiller unit, comprising a screw compressor, a condenser, an evaporator, a cooling tower, an oil circuit system, and a control system, characterized in that, The control system is configured to perform the low-temperature operation method for screw-type water-cooled chillers as described in any one of claims 1 to 9.

Images