A method and equipment for intelligent control of high-temperature water source heat pump units

Abstract

This invention discloses an intelligent control method and device for a high-temperature water source heat pump unit. The method is differential pressure interval intelligent control, which divides the suction and exhaust pressure difference ΔP into three intervals based on a first and a second differential pressure threshold, and implements differentiated opening control of the electronic expansion valve (EEV) to actively utilize the high evaporation temperature characteristics of the high-temperature heat pump to increase the pressure difference. The device is a falling film evaporator with a bottom-inclined oil return port of 3-7°. Through differential pressure interval intelligent control and equipment structure optimization, this invention eliminates the pressure maintaining valve and regenerator required in existing technologies, achieving a comprehensive effect of improving energy efficiency by more than 5%, reducing failure points by more than 40%, and reducing the total life cycle cost by more than 7%. It can balance safety and energy efficiency, and also has the advantages of reducing costs, improving reliability, and expanding the unit's load adjustment range.

Description

Technical Field

[0001] This invention belongs to the technical field of high-temperature water source heat pump units, specifically relating to an intelligent control method and equipment for high-temperature water source heat pump units. Background Technology

[0002] In industrial production and residential heating equipment, high-temperature water source heat pump units have become one of the main alternatives to traditional fossil fuel heating due to their ability to efficiently recover low-grade heat energy and reduce carbon emissions. Typically, they operate under conditions where the heat source water temperature is 20-60℃ and the hot water outlet temperature is ≥55℃. The core power component is a semi-hermetic screw compressor, and its operational safety and energy efficiency directly determine the unit's industrial value. However, existing high-temperature water source heat pump units face several technical challenges in actual operation, including:

[0003] (I) Solutions for fuel supply security during startup and its energy efficiency losses

[0004] The lubricating oil circulation of a semi-hermetic screw compressor relies on the pressure difference between the suction and discharge pressures. This pressure difference delivers the lubricating oil to critical friction components such as bearings and the compression chamber, forming an oil film for lubrication and sealing. Insufficient pressure difference will lead to an interruption in lubricating oil supply, causing fatal malfunctions such as compressor seizure and rotor wear. For example, during initial startup, the hot water tank temperature is typically lower than the heat source water temperature (hot water temperature 30℃, heat source water temperature 45℃), creating an inverted operating condition. In this case, the suction and discharge pressure difference is too low to meet the oil supply requirements.

[0005] In actual operation, the control system can stabilize the suction and discharge pressure difference within the target range by adjusting the opening of the electronic expansion valve (EEV) in real time. Currently, there are various methods for calculating the target opening of the electronic expansion valve, such as a control algorithm based on the evaporator liquid level. This algorithm reduces the target opening of the electronic expansion valve when the liquid level is too high and increases it when the liquid level is too low. There are also methods that use the small temperature difference in the evaporator as a basis to correct the base opening of the electronic expansion valve. However, existing control methods have slow response times and cannot guarantee that the pressure difference will reach the target range in a short time. To ensure safe oil supply during startup, the industry commonly uses a pressure maintaining valve at the compressor discharge port. Its purpose is to open the discharge passage only when the suction and discharge pressure difference exceeds a set safety threshold, forcibly accumulating the pressure difference to ensure oil supply. However, the pressure maintaining valve not only incurs energy efficiency losses but also poses a risk of failure.

[0006] 1. The mechanical structure of the pressure maintaining valve generates a fixed discharge pressure drop of ≥0.5 bar, inevitably resulting in the following energy efficiency loss: According to thermodynamic principles and industry measurement data, for every 1°C increase in the compressor discharge saturation temperature, the operating efficiency decreases by approximately 3%. Taking the commonly used environmentally friendly refrigerant R1234ze(E) as an example, a 0.5 bar discharge pressure drop corresponds to an increase in discharge saturation temperature of approximately 1.4°C, directly leading to a 4.1% reduction in compressor efficiency, and consequently a decrease in the system's overall energy efficiency ratio (COP).

[0007] 2. As a mechanical component, the pressure maintaining valve is susceptible to failures such as jamming and leakage. This not only increases system maintenance costs but may also cause unit shutdowns due to pressure maintaining valve failures, affecting continuous operation.

[0008] (II) Solutions for protection against liquid leakage during air intake and their energy efficiency losses

[0009] Existing high-temperature water source heat pumps generally use environmentally friendly refrigerants with low adiabatic indices, such as R515B, R245fa, R1234ze(E), and R1233zd(E). While these refrigerants meet environmental requirements, they have significant drawbacks under certain operating conditions. For example, when the hot water temperature is low, the heat source water temperature is high, and the unit is operating at full load, the refrigerant discharge volumetric flow rate increases significantly, leading to a decrease in the separation efficiency of the oil separator. A large amount of lubricating oil enters the evaporator along with the refrigerant. The lubricating oil entering the evaporator mixes with the liquid refrigerant, causing a surge in liquid foaming and a significant increase in the amount of liquid droplets (liquid entrainment) in the evaporator outlet gas. If this liquid-laden gas enters the compressor, it will trigger liquid compression, causing damage to the compressor valves, motor overload, and other malfunctions. To solve this safety problem, the conventional solution in existing technology is to add a regenerator to the system. This regenerator utilizes the heat from the high-temperature liquid refrigerant at the condenser outlet to heat the liquid-laden gas at the evaporator outlet, causing the droplets to vaporize before entering the compressor.

[0010] The core drawback of this solution is that the regenerator's piping design significantly increases the flow resistance of the evaporator's outlet piping, resulting in a decrease in suction pressure of approximately 0.3 bar, a corresponding decrease in suction saturation temperature of 1.8°C, and consequently a further decrease in compressor efficiency of 5.4%. Furthermore, the addition of the regenerator not only increases equipment procurement and assembly costs but also prolongs the system commissioning cycle and increases maintenance difficulty.

[0011] (iii) Design defects in the evaporator oil return structure

[0012] Existing high-temperature water source heat pumps mostly use flooded evaporators or falling film evaporators, and both of these have the following design flaws in the location of the oil return port:

[0013] The oil return port of a flooded evaporator is usually located about 100-200 mm below the centerline of the shell. When the system reduces the evaporation pressure to regulate the pressure difference (such as during startup or low-load conditions), the refrigerant level will be lower than the height of the oil return port. This causes the lubricating oil accumulated at the bottom of the evaporator to be unable to flow back to the oil reservoir through the oil return port, resulting in an oil accumulation problem. Although the oil return port of a falling film evaporator is located at the bottom of the shell, its tilt angle (the angle between the central axis and the vertical direction) is usually 15-30°. When there is almost no liquid level in the evaporator, it is difficult to ensure that the accumulated lubricating oil can be effectively ejected and flowed back, resulting in the same oil accumulation problem.

[0014] Oil buildup in the lubricating oil directly hinders heat exchange between the refrigerant and the heat exchange tubes, which not only further deteriorates the heat exchange efficiency of the evaporator, but also causes the oil level in the oil receiver to drop continuously, which may cause the unit to alarm due to low oil level, or even cause compressor failure due to lack of oil.

[0015] In summary, existing high-temperature water source heat pump units rely on a hardware combination of pressure maintaining valves and regenerators to solve the two major safety problems of insufficient start-up pressure differential and liquid carryover during suction. At the same time, they face the additional problem of difficulty in oil return from the evaporator. Ultimately, they not only fail to balance safety and energy efficiency, but also suffer from technical problems such as increased costs, reduced reliability, and limitations on the unit's load adjustment range. Summary of the Invention

[0016] The present invention aims to solve the above-mentioned technical problems existing in the prior art by providing an intelligent control method and equipment for high-temperature water source heat pump units.

[0017] The technical solution of this invention is: an intelligent control method for a high-temperature water source heat pump unit, including a differential pressure range-based intelligent control step, which adjusts the opening of the electronic expansion valve according to a target opening value. The target opening value is obtained through the following operations: real-time monitoring of the compressor's suction and discharge pressure difference ΔP and the evaporator's minimum temperature difference, where the evaporator's minimum temperature difference is the difference between the evaporator outlet water temperature and the evaporation temperature; comparing ΔP with a first differential pressure threshold and a second differential pressure threshold; when ΔP > the second differential pressure threshold, calculating the basic opening of the electronic expansion valve and correcting it based on the evaporator's minimum temperature difference to obtain the target opening value; when the first differential pressure threshold ≤ ΔP ≤ the second differential pressure threshold, calculating the basic opening of the electronic expansion valve, i.e., obtaining the target opening value; when ΔP < the first differential pressure threshold, calculating the basic opening of the electronic expansion valve and reducing the basic opening based on the extent to which ΔP is lower than the first differential pressure threshold to obtain the target opening value; the first differential pressure threshold is 2.0 ~ 3.0 bar, and the second differential pressure threshold is 2.5 bar. ~3.5 bar, where the first differential pressure threshold is less than the second differential pressure threshold.

[0018] The preferred embodiment also includes a differential pressure safety protection linkage step, specifically as follows: if ΔP is less than the first differential pressure threshold and the opening of the electronic expansion valve has been adjusted according to the target opening value, and ΔP is still less than the first differential pressure threshold and reaches the preset duration, then the operating frequency of the hot water circulation pump is reduced simultaneously.

[0019] Preferably, the method also includes a step to prevent suction and liquid carryover, specifically as follows: after adjusting the opening of the electronic expansion valve according to the target opening value, the opening of the electronic expansion valve is then adjusted in a closed loop to maintain the exhaust superheat of 5~8°C. The exhaust superheat is the difference between the exhaust temperature and the saturation temperature corresponding to the exhaust pressure.

[0020] Preferably, the first differential pressure threshold is 2.0 to 3.0 bar, and the second differential pressure threshold is 2.5 to 3.5 bar.

[0021] Preferably, the first differential pressure threshold is 2.5 bar, and the second differential pressure threshold is 3.0 bar.

[0022] Preferably, the single adjustment range of the electronic expansion valve does not exceed 10% of its total opening.

[0023] The preferred preset duration is 1 minute.

[0024] Preferably, the adjustment range of the operating frequency of the synchronously reduced hot water circulation pump is 25~50Hz.

[0025] An equipment for the above-mentioned intelligent control method of high-temperature water source heat pump unit is provided with a falling film evaporator. The oil return port of the falling film evaporator is located at the bottom of the shell, and the angle between the central axis of the oil return port and the vertical direction is 3~7°.

[0026] This invention eliminates the need for passive hardware protection such as pressure maintaining valves and regenerators, solving three core problems inherent in existing technologies: insufficient start-up pressure differential, liquid carryover during air intake, and difficulty in oil return at low liquid levels. It completely eliminates energy efficiency losses caused by additional hardware, reduces equipment costs and maintenance complexity, and improves operational reliability. It is suitable for the intelligent control of high-temperature water source heat pump units equipped with semi-hermetic screw compressors and hot water outlet temperatures ≥55℃ and heat source water temperatures 20~60℃. Specific features are as follows:

[0027] 1. Safe and reliable operation with significantly reduced failure risk: The intelligent differential pressure regulation logic adopted in this invention, along with the active control mode that coordinates the frequency control of the hot water circulation pump, provides a fast response, reducing the time from unit startup to differential pressure stabilization above the safe threshold to within 2 minutes. This can replace mechanical pressure maintaining valves with high failure rates, fundamentally avoiding the risk of oil supply interruption caused by valve jamming and leakage. The electronic expansion valve based on closed-loop control of exhaust superheat can replace the regenerator, accurately suppressing liquid carryover during suction and protecting core components such as compressor valve plates and rotors from liquid compression damage. Utilizing the optimized falling film evaporator with a 3-7° tilt angle for the oil return port, reliable oil return is achieved under all operating conditions, including low liquid levels and low loads, completely solving the oil accumulation problem of existing evaporators and preventing compressor alarm shutdowns due to oil shortage. Based on 1000 hours of continuous operation test data, the system's failure points are reduced by more than 40%, and the mean time between failures (MTBF) is extended by 30%.

[0028] 2. Significantly Improved Energy Efficiency and Outstanding Energy Saving and Carbon Reduction Benefits: Since the pressure maintaining valve and regenerator are eliminated, the ≥0.5 bar discharge pressure drop and ≥0.3 bar suction pressure drop caused by them are completely eliminated, fundamentally preventing the compressor's efficiency decline due to increased discharge temperature and decreased suction temperature. Actual measurements compared to existing units of the same specifications equipped with pressure maintaining valves and regenerators show that the overall energy efficiency ratio (COP) of this invention is improved by more than 5%. For a unit with a heating capacity of 800kW, based on 7500 hours of annual operation and an industrial electricity price of 0.8 yuan / kWh, annual electricity savings exceed 100,000 kWh, resulting in annual electricity cost savings of over 80,000 yuan. Simultaneously, the reduction in electricity consumption directly reduces carbon emissions, decreasing CO2 emissions by more than 80 tons annually, highlighting both environmental and economic value.

[0029] 3. Reduced life-cycle costs and significant economic advantages: At the hardware level, eliminating the need for two core outsourced components—the pressure maintaining valve and the regenerator—reduces material costs per 800kW unit by 3-5%, saving 15,000-30,000 RMB; at the assembly level, it reduces component installation and pipeline connection processes, improving assembly efficiency by 20% and reducing assembly costs by 8-10%; at the maintenance level, it eliminates maintenance needs for common faults such as pressure maintaining valve sticking and regenerator scaling, reducing annual maintenance costs by 25-30% and reducing inventory costs for vulnerable parts; at the commissioning level, it eliminates the need for complex adjustments to regenerator heat exchange matching and pressure maintaining valve threshold settings, shortening the commissioning cycle by 30% and further reducing project implementation costs. Detailed Implementation

[0030] The embodiments of the present invention are based on a system configuration of an 800kW high-temperature water source heat pump unit, the specific configuration of which is as follows:

[0031] Core components: Similar to existing technologies, it features a semi-hermetic screw compressor (model RC2-930G) using R1234ze(E) refrigerant; a falling film evaporator (shell size DN600) with an oil return port located at the bottom, having a diameter of DN10; an electronic expansion valve (model E6VB2A); a 7.5kW variable frequency centrifugal pump for hot water circulation (operating frequency adjustment range 25~50Hz); and an oil separator (separation efficiency ≥99.99%). The difference from existing technologies is that the central axis of the oil return port of the falling film evaporator forms a 5° angle with the vertical direction.

[0032] Control system: The system adopts existing technology, namely, using a PLC as the controller, and is equipped with a suction pressure sensor (range 0~2.0MPa, accuracy ±0.01MPa), an exhaust pressure sensor (range 0~3.0MPa, accuracy ±0.01MPa), an exhaust temperature sensor (range 0~150℃, accuracy ±0.1℃), and an evaporator outlet water temperature sensor (range 0~100℃, accuracy ±0.1℃).

[0033] Preset parameters: First differential pressure threshold 2.5 bar, second differential pressure threshold 3.0 bar; single adjustment range of electronic expansion valve (EEV) ≤10%; preset duration 1 minute; anti-liquidity control target exhaust superheat 7°C.

[0034] The control method of this invention first adjusts the opening of the electronic expansion valve according to a target opening value, which is obtained through the following operation:

[0035] The compressor's suction and discharge pressure difference ΔP and the evaporator's minimum temperature difference are monitored in real time. The evaporator's minimum temperature difference is the difference between the evaporator outlet water temperature and the evaporation temperature. ΔP is compared with 2.5 bar and 3.0 bar. When ΔP > 3.0 bar, the basic opening of the electronic expansion valve is calculated and corrected based on the evaporator's minimum temperature difference to obtain the target opening value. When 2.5 bar ≤ ΔP ≤ 3.0 bar, the basic opening of the electronic expansion valve is calculated, and the target opening value is obtained without correction. When ΔP < 2.5 bar, the basic opening of the electronic expansion valve is calculated and corrected by reducing the basic opening based on the extent to which ΔP is lower than the first pressure difference threshold to obtain the target opening value.

[0036] The above-mentioned calculation of the basic opening of the electronic expansion valve using ΔP is obtained using a conventional control algorithm based on the evaporator liquid level. The method of correcting the basic opening of the electronic expansion valve based on the small temperature difference in the evaporator employs existing technology. It reduces the basic opening of the electronic expansion valve based on ΔP being less than 2.5 bar. This reduction correction value is obtained based on a mapping relationship, which is implemented through preset rules. For example, linear correction can be used, i.e., reduction correction value = (first differential pressure threshold - ΔP) × correction coefficient K, where K is a preset constant based on the unit capacity and refrigerant characteristics; or the mapping relationship can be represented as a preset lookup table storing recommended reduction correction values ​​corresponding to different ΔP deviation ranges.

[0037] If ΔP is less than 2.5 bar and the opening of the electronic expansion valve has been adjusted according to the target opening value, but ΔP is still less than the first differential pressure threshold and continues for 1 minute, then the operating frequency of the hot water circulation pump will be reduced simultaneously.

[0038] After adjusting the opening of the electronic expansion valve according to the target opening value, the opening of the electronic expansion valve is then adjusted in a closed loop to maintain the exhaust superheat of 7°C. The exhaust superheat is the difference between the exhaust temperature and the saturation temperature corresponding to the exhaust pressure. Example 1

[0039] Test conditions: target hot water outlet temperature 70℃, heat source water temperature 45℃, and inverted conditions during startup (initial hot water temperature 30℃, heat source water temperature 45℃).

[0040] After startup, the real-time pressure difference ΔP is monitored at 3.0 bar (between the first and second preset thresholds). The base opening calculated using the conventional EEV opening control algorithm (based on evaporator level) is 41%, with no evaporator temperature difference signal correction, and the opening stabilizes at 40%. After one minute of operation, the pressure difference ΔP rises to 3.5 bar (greater than the second preset threshold). The base opening is then output using the conventional EEV opening control algorithm (based on evaporator level) with the evaporator temperature difference signal correction incorporated, and the EEV opening eventually stabilizes at 45%. The time from unit startup to the pressure difference ΔP stabilizing above 4 bar is one minute, with no pressure maintaining valve intervention throughout the process.

[0041] Comparative Experiment 1: Comparison of Pressure Difference ΔP Settlement Time and Energy Efficiency

[0042] The test conditions are the same as in Example 1. A 7,500-hour simulated annual operation test is conducted, and the operating data of the unit in this embodiment and the comparison unit are recorded simultaneously. The pressure difference ΔP establishment time and energy efficiency are compared.

[0043] Comparison of unit equipment: The 800kW high-temperature water source heat pump unit of the same specification, except for the pressure maintaining valve (set opening threshold of 4.0 bar) and the regenerator, and the oil return port tilt angle of the falling film evaporator is 15°, the other core components (compressor model, capacity, refrigerant type, etc.) are completely consistent with the unit of Embodiment 1 of the present invention to ensure the fairness of the comparison.

[0044] The control method of the comparison unit relies on the pressure maintaining valve after startup. The valve only opens when the pressure difference ΔP reaches 4.0 bar. It takes 15 minutes from the start of the unit to the pressure difference ΔP being above 4 bar. During operation, the inherent resistance of the pressure maintaining valve causes a 0.55 bar exhaust pressure drop, and the regenerator causes a 0.32 bar intake pressure drop. The superposition of the two pressure drops affects energy efficiency.

[0045] The results of comparative experiment 1 show that:

[0046] 1. In Embodiment 1 of the present invention, the time for the unit to establish a stable differential pressure ΔP above 4 bar from startup is 1 minute, while the comparative unit takes 15 minutes;

[0047] 2. The average COP of the unit in Embodiment 1 of the present invention is 4.2, while the average COP of the comparative unit is 3.9, representing a 7.7% improvement in COP. After 7,500 hours of operation, the power consumption of the unit in Embodiment 1 of the present invention is 1,428,571 kWh, while the power consumption of the comparative unit is 1,538,462 kWh. The unit in Embodiment 1 of the present invention can save 109,891 kWh (over 100,000 kWh), which translates to an annual power saving of 87,912.8 yuan based on an industrial electricity price of 0.8 yuan / kWh. Example 2

[0048] Simulated extreme conditions: The temperature of the heat source water increases to 50℃ and the temperature of the hot water outlet is 60℃, resulting in ΔP=2.0bar (lower than the first preset threshold).

[0049] The base opening calculated using the conventional EEV opening control algorithm (based on the evaporator liquid level) is 38%. This is then corrected to 33% based on a 0.5 bar decrease in differential pressure ΔP and a preset mapping relationship. After adjustment, the differential pressure ΔP remains at 2.2 bar for one minute, still below the first preset threshold. Therefore, the hot water circulation pump frequency is reduced to 35 Hz to decrease heat exchange intensity on the condenser side and quickly increase the exhaust pressure. After 40 seconds, ΔP rises back to 2.6 bar, and the linkage mode is exited. The entire process takes 1 minute and 40 seconds, less than 2 minutes. Oil supply remains stable throughout, with no compressor alarms.

[0050] Comparative Experiment 2: Experiment on the linkage effect of low pressure difference ΔP and reduced hot water circulation pump frequency

[0051] The test conditions were the same as in Example 2, and a 1000-hour continuous operation test was conducted, while the operating data of the unit in Example 2 and the comparative unit were recorded simultaneously.

[0052] The equipment of the comparison unit is the same as that in Comparative Experiment 1. Its control method is to open the pressure maintaining valve only to a small degree to maintain ΔP not lower than 4.0 bar, while at this time the pressure difference between the pressure after the discharge pressure maintaining valve and the intake pressure is about 2.0 bar.

[0053] The results of Comparative Experiment 2 show that under this operating condition, the compressor discharge pressure of Unit 2 of the present invention is 1.4 bar lower than that of the comparative unit, the discharge saturation temperature is about 4°C lower, and the unit's energy efficiency ratio is more than 10% higher. Example 3

[0054] Test conditions: heat source water temperature 48℃, unit operating at full load (800kW), continuous monitoring of exhaust superheat and return gas liquid carryover.

[0055] Based on Example 1, the exhaust superheat was calculated to be 5°C by converting the exhaust temperature (85°C) and exhaust pressure (1.9MPa) to the corresponding saturation temperature (80°C). Since this was lower than the target value of 7°C, the EEV opening was appropriately reduced from 45% to 38%. After 3 minutes, the exhaust superheat stabilized at 7°C. During operation, the exhaust superheat change rate was detected to be 0.6°C / min. Since the superheat was still within the target range of 5°C to 8°C, the EEV maintained its current opening, and there was no liquid carryover phenomenon during the entire process.

[0056] Comparative Experiment 3.1: Experiment on Anti-liquidation and Oil Return Effects

[0057] The test conditions were the same as in Example 3, and a 1000-hour continuous operation test was conducted to continuously monitor the exhaust superheat and liquid carryover in the return gas of the unit in Example 2 of this invention and the comparative unit.

[0058] The unit equipment was compared with that in Experiment 1; the control method was to force the exhaust superheat to be maintained above 10°C to avoid the risk of liquid carryover, but the presence of the regenerator caused the intake pressure drop to be maintained at 0.32 bar, and the intake saturation temperature to decrease by about 1°C.

[0059] Energy efficiency difference: The intake saturation temperature of the unit in Embodiment 3 of this invention is about 1°C higher than that of the control unit (corresponding to a decrease in intake pressure drop of 0.32 bar), thus improving the unit's energy efficiency ratio by about 3%.

[0060] Comparative Experiment 3.2: Low Liquid Level Oil Return Effect Experiment

[0061] Test conditions: heat source water temperature 50℃, hot water outlet temperature 60℃, no liquid level in the evaporator, unit running at full load (800kW) for 1000 hours continuously.

[0062] In Embodiment 3 of this invention, the unit utilizes a 5° tilt angle for the oil return port. Even when there is no liquid level in the evaporator, a slight accumulation of lubricating oil causes the oil level to rise to the oil return port. Under the force of high-pressure gas injection, the oil is continuously drawn into the oil return port and flows back to the compressor suction port. During 1000 hours of continuous operation, the oil level in the oil reservoir remains stable at 40-60%, with no oil level alarm, and the oil content in the oil separator exhaust is ≤80×10⁻⁶. -6 .

[0063] Compared with Experiment 1, the lubricating oil in the unit equipment is in the same way as in Experiment 2. Because the inclination angle of the oil return port of the falling film evaporator is 15°, a large amount of lubricating oil accumulates in the evaporator. After running for 2 hours, the oil level in the oil reservoir drops to the position that triggers the oil shortage alarm. Manual intervention is required to increase the opening of the EEV so that the liquid level rises above the oil return port, and the accumulated lubricating oil can reliably flow back by gravity.

[0064] Comparative Experiment 3.3: Comparative Experiment of Fault and Reliability Data

[0065] Unit 3 of this invention: During 1000 hours of continuous operation, only one non-core fault occurred (loose sensor wiring, repaired within 5 minutes), and there were no fault shutdown records;

[0066] Compared to the unit: During 1000 hours of continuous operation, 3 faults occurred (pressure maintaining valve failure 2 times, evaporator oil accumulation 1 time), with a total downtime of 8 hours for repair;

[0067] The results show that the number of fault points of the unit of the present invention is reduced by 66.7% compared with the traditional comparative unit, and the reduction rate of fault points is significantly higher than 40%. The estimated mean time between failures (MTBF) reaches 12,000 hours, which is 30.4% longer than the comparative unit (9,200 hours).

[0068] Other tests and verifications:

[0069] 1. Compatibility testing of different refrigerants

[0070] Two environmentally friendly refrigerants, R515B and R1234ze(E), were used respectively and operated under the same test conditions (condensing temperature 80℃, evaporating temperature 45℃). The control logic of this invention was preset according to the thermodynamic parameters of the corresponding refrigerants. The results are shown in Table 1.

[0071] Table 1

[0072]

[0073] The results showed that all refrigerants could operate stably, with COP increasing by more than 5%, and no control failures or performance abnormalities were caused by differences in refrigerant properties.

[0074] 2. Adaptation testing for different scenarios

[0075] Industrial waste heat recovery scenario: heat source water temperature 60℃, hot water outlet temperature 85℃, unit load 100%, running for 100 hours, pressure difference ΔP stabilizes at 3.2 bar, COP=3.8, no liquid carryover or oil accumulation issues;

[0076] Central heating scenario: heat source water temperature 20℃, hot water outlet temperature 65℃, unit load 50%, operation for 100 hours, pressure difference ΔP stabilizes at 2.8 bar, COP=4.5, oil return is normal.

[0077] 3. Lifecycle cost comparison and verification (5-year accounting period)

[0078] Taking an 800kW unit as an example, the total life cycle cost of the unit in Embodiment 1 of this invention is compared with that of the comparative unit. The total electricity cost over 5 years is calculated based on the annual electricity savings of 109,891kWh measured in Embodiment 1 and the industrial electricity price of RMB 0.8 / kWh, with a 5-year operating cycle. The results are shown in Table 2.

[0079] Table 2

[0080]

[0081] Note: The cost data in the table are exemplary calculations based on specific supply chains and labor hour standards. The differences in material procurement costs are mainly due to the omission of pressure maintaining valves (approximately RMB 3,000 / unit) and regenerators (approximately RMB 17,000 / unit), while the differences in maintenance costs are related to the fact that electronic control systems typically require more frequent maintenance compared to mechanical components (pressure maintaining valves).

[0082] In summary, the specific embodiments of the present invention have been verified through a series of rigorous comparative tests and full-condition verifications. Compared with existing technical solutions that rely on pressure maintaining valves and regenerators, this invention achieves a comprehensive technological breakthrough by eliminating the need for two key externally purchased hardware components. This breakthrough results in an energy efficiency improvement of >5%, a reduction in failure points of >40%, and a reduction in total life cycle cost of >7%. It successfully resolves the long-standing core contradiction in the field of high-temperature water source heat pumps between ensuring safety and improving energy efficiency.

Claims

1. A method for intelligent control of a high-temperature water source heat pump unit, wherein the high-temperature water source heat pump unit adopts a semi-hermetic screw compressor and relies on the pressure difference between suction and discharge to achieve lubricating oil circulation and supply, including a pressure difference range-based intelligent control step during the start-up phase, which adjusts the opening of the electronic expansion valve according to a target opening value, characterized in that... The target opening value is obtained through the following operations: real-time monitoring of the suction and discharge pressure difference ΔP of the semi-hermetic screw compressor and the small temperature difference of the evaporator, wherein the small temperature difference of the evaporator is the difference between the evaporator outlet water temperature and the evaporation temperature; comparing ΔP with a first pressure difference threshold and a second pressure difference threshold; when ΔP > the second pressure difference threshold, calculating the basic opening of the electronic expansion valve and correcting the basic opening based on the small temperature difference of the evaporator to obtain the target opening value; when the first pressure difference threshold ≤ ΔP ≤ the second pressure difference threshold, calculating the basic opening of the electronic expansion valve, i.e., obtaining the target opening value; when ΔP < the first pressure difference threshold, calculating the basic opening of the electronic expansion valve and correcting the basic opening by reducing it according to the extent that ΔP is lower than the first pressure difference threshold to obtain the target opening value; the first pressure difference threshold is 2.0 ~ 3.0 bar, the second pressure difference threshold is 2.5 ~ 3.5 bar, and the first pressure difference threshold is less than the second pressure difference threshold.

2. The intelligent control method for high-temperature water source heat pump units according to claim 1, characterized in that... It also includes a differential pressure safety protection linkage step, as follows: if ΔP is less than the first differential pressure threshold and the opening of the electronic expansion valve has been adjusted according to the target opening value, and ΔP is still less than the first differential pressure threshold and reaches the preset duration, then the operating frequency of the hot water circulation pump will be reduced simultaneously.

3. The intelligent control method for high-temperature water source heat pump units according to claim 2, characterized in that... It also includes a liquid-preventing control step, as follows: after adjusting the opening of the electronic expansion valve according to the target opening value, the opening of the electronic expansion valve is then adjusted in a closed loop to maintain the exhaust superheat of 5~8°C. The exhaust superheat is the difference between the exhaust temperature and the saturation temperature corresponding to the exhaust pressure.

4. The intelligent control method for high-temperature water source heat pump units according to claim 1, 2, or 3, characterized in that: The first differential pressure threshold is 2.5 bar, and the second differential pressure threshold is 3.0 bar.

5. The intelligent control method for high-temperature water source heat pump units according to claim 4, characterized in that: The single adjustment range of the electronic expansion valve shall not exceed 10% of its total opening.

6. The intelligent control method for high-temperature water source heat pump units according to claim 2, characterized in that: The preset duration is 1 minute.

7. The intelligent control method for high-temperature water source heat pump units according to claim 2, characterized in that: The adjustment range for the synchronous reduction of the operating frequency of the hot water circulation pump is 25~50Hz.

8. An apparatus for intelligent control of a high-temperature water source heat pump unit as described in claim 1, comprising a falling film evaporator, wherein the oil return port of the falling film evaporator is located at the bottom of the casing, characterized in that: The angle between the central axis of the oil return port and the vertical direction is 3~7°.

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