A control method for a low-temperature water source heat pump that can operate while freezing

Abstract

This invention relates to the field of heat pump heat exchange technology, specifically to a control method for a low-temperature water source heat pump that can operate in freezing mode. It is applicable to heat recovery and utilization scenarios of low-temperature heat sources such as industrial low-temperature wastewater and natural low-temperature surface water / groundwater. The control method for a low-temperature water source heat pump that can operate in freezing mode includes a low-temperature water source heat pump unit. The heat pump unit includes an evaporator, a compressor, a condenser, and a throttling element connected in sequence, forming the core loop of the heat pump cycle. A low-temperature water source flow channel is provided on the outside of the evaporator, where the low-temperature water source exchanges heat with the heat exchange surface of the evaporator, providing a low-grade heat source for the heat pump unit.

Description

Technical Field

[0001] This invention relates to the field of heat pump heat exchange technology, specifically to a control method for a low-temperature water source heat pump that can operate while freezing, applicable to heat recovery and utilization scenarios of low-temperature heat sources such as industrial low-temperature wastewater and natural low-temperature surface water / groundwater. Background Technology

[0002] Low-temperature water source heat pumps are heat pump systems that utilize low-temperature water as a low-grade heat source. They can upgrade the low-grade heat energy in the low-temperature water source into high-grade heat energy, enabling functions such as heating and hot water preparation. They are highly efficient and energy-saving devices. However, in northern winters or industrial applications with low-temperature water sources, the water temperature often drops below 0°C. This makes the heat exchange surface of the heat pump evaporator extremely prone to frost and ice formation, which is a core technical challenge in the application of low-temperature water source heat pumps.

[0003] The conventional design approach for existing low-temperature water source heat pumps focuses on preventing icing. This is achieved by increasing the circulation velocity of the low-temperature water source, adding antifreeze to the water source, and continuously performing micro-ice melting on the evaporator to avoid icing on the heat exchange surface. However, this approach has several drawbacks: First, the addition of antifreeze increases operating costs and can easily cause water pollution, making it unsuitable for natural water source conditions. Second, continuous micro-ice melting consumes the effective heating capacity of the heat pump unit, leading to a significant decrease in the unit's heat exchange efficiency. Third, the anti-icing control method cannot utilize the heat storage characteristics of the ice layer, resulting in low utilization of the low-temperature heat source.

[0004] Some studies have attempted to operate low-temperature water source heat pumps under slight icing conditions in order to utilize the ice layer to enhance the heat storage capacity of the heat source. However, there is a lack of effective monitoring and precise control methods for the icing state, which can easily lead to problems such as uneven icing on the evaporator heat exchange surface and excessively thick ice layers in some areas. Excessively thick ice layers can block the heat exchange between the low-temperature water source and the heat exchange surface, causing evaporator heat exchange failure. At the same time, the volume expansion of the ice layer can cause mechanical stress on the evaporator heat exchange tubes, leading to pipe rupture, leakage and other failures. In addition, traditional de-icing methods are mostly whole-unit de-icing, which requires the unit to be shut down during the de-icing process. The de-icing time is long and the de-icing energy consumption is high, which further reduces the operating efficiency and stability of the unit.

[0005] Therefore, developing a control method for low-temperature water source heat pumps that enables controlled icing operation, allowing the evaporator to ic within a safe range to improve the utilization rate of the low-temperature heat source by utilizing the ice layer, and avoiding excessive icing through precise monitoring and regulation to achieve efficient ice melting, has become the key to solving the application problems of low-temperature water source heat pumps. Summary of the Invention

[0006] The purpose of this invention is to provide a control method for a low-temperature water source heat pump that can operate under icing conditions, which solves the technical problems of high energy consumption, low heat source utilization, and poor unit operation stability and low heat exchange efficiency caused by uneven and inaccurate ice layer during operation under icing conditions, so as to achieve stable and efficient operation of the heat pump unit within a controllable icing range.

[0007] To achieve the above objectives, the present invention provides the following technical solution: a low-temperature water source heat pump control method capable of freezing operation, comprising a low-temperature water source heat pump unit, wherein the heat pump unit comprises an evaporator, a compressor, a condenser and a throttling element connected in sequence, forming the core loop of the heat pump cycle; a low-temperature water source flow channel is provided on the outside of the evaporator, wherein the low-temperature water source exchanges heat with the heat exchange surface of the evaporator in the flow channel, providing a low-temperature heat source for the heat pump unit.

[0008] The evaporator is specially equipped with an icing monitoring module, a flow field control module, and an ice melting control module. All three modules are electrically connected to the central control unit to achieve real-time monitoring of the icing state and closed-loop execution of control actions. Icing monitoring module: used to detect the icing thickness and distribution on the evaporator heat exchange surface, accurately capturing the icing status in different areas; Flow field control module: used to adjust the fluid velocity and flow field distribution in the low temperature water source channel, and guide the formation of a uniform ice layer on the heat exchange surface of the evaporator; Ice melting control module: used to perform precise ice melting of the evaporator heat exchange surface in stages, avoiding energy loss and downtime caused by overall ice melting.

[0009] The core of the icing operation control method of this invention is to achieve controllable icing conditions through graded threshold setting, real-time status monitoring, dynamic flow field regulation, and graded precise ice melting. The specific steps are as follows: S1, Threshold setting: Based on the water quality (sand content, impurity content) and temperature conditions (static water temperature, flowing water temperature) of the low-temperature water source, a safe icing first threshold, a safe icing second threshold, and an ice melting trigger threshold are set for the evaporator heat exchange surface. The ice melting trigger threshold is greater than the safe icing first threshold, and the safe icing first threshold is greater than the safe icing second threshold. The safe icing first threshold is the optimal thickness threshold for icing operation, at which the ice layer possesses both heat storage and heat exchange characteristics. The safe icing second threshold is the ice melting termination threshold; when ice melting reaches this thickness, ice melting stops, and icing operation resumes. The ice melting trigger threshold is the limit threshold for icing operation; when this thickness is reached, ice melting must be initiated to avoid heat exchange failure.

[0010] S2. Status Monitoring and Judgment: The icing monitoring module detects the icing thickness and icing distribution data of the evaporator heat exchange surface in real time and transmits the data to the central control unit. The central control unit determines whether the real-time icing thickness has reached the first safe icing threshold.

[0011] S3. Flow field control during freezing operation: If the real-time ice thickness reaches the first safe freezing threshold, the flow field control module is activated to adjust the fluid velocity and flow field distribution in the low-temperature water source channel. Through methods such as guiding and changing the flow velocity, a uniform ice layer is formed in each area of ​​the evaporator heat exchange surface, maintaining the unit's stable operation under freezing conditions and making full use of the heat storage characteristics of the ice layer to improve the utilization rate of the low-temperature heat source.

[0012] S4. Graded Precision Ice Melting: If the real-time ice thickness reaches the ice melting trigger threshold, the ice melting control module is activated to perform graded precision ice melting. Depending on the ice thickness, primary ice melting or deep ice melting actions are initiated respectively until the ice thickness drops to the second safe ice melting threshold. Then, the ice melting control module is shut down, and the normal ice melting operation control state of the flow field control module is restored.

[0013] S5. Closed-loop control: The icing monitoring module continuously collects icing status data of the evaporator heat exchange surface. The central control unit executes steps S2-S4 in a loop to achieve real-time monitoring and closed-loop control under icing conditions, ensuring that the unit always operates within the safe icing range.

[0014] Furthermore, the icing monitoring module includes multiple thickness sensors, temperature sensors, and an infrared imaging unit: the thickness sensors use the ultrasonic thickness measurement principle and are evenly arranged in different areas of the evaporator heat exchange surface (including the inlet area, middle area, and outlet area of ​​the flow channel) to detect the real-time icing thickness in each area; the temperature sensors are respectively set at the inlet and outlet of the evaporator heat exchange surface, the low-temperature water source flow channel, to detect the temperature of the heat exchange surface and the temperature difference between the inlet and outlet of the water source, and to help determine the icing trend; the infrared imaging unit is used to acquire real-time images of the icing distribution on the evaporator heat exchange surface, intuitively reflecting the areas of uneven icing, and providing a basis for flow field control and local icing melting.

[0015] Furthermore, the flow field control module includes a guide plate, a variable frequency circulating pump, and a flow regulating valve within the flow channel. The guide plate is electrically adjustable and evenly arranged within the low-temperature water source flow channel, changing the local flow field direction by adjusting the angle. The variable frequency circulating pump is used to regulate the overall circulation velocity of the low-temperature water source, and the flow regulating valve is used to control the inflow rate of the low-temperature water source. During the flow field control process in S3, the central control unit adjusts the angle of the guide plate and the flow velocity of the local flow channel based on the ice distribution data, ensuring that the difference in ice thickness in different areas of the evaporator heat exchange surface is controlled within 5mm, thus preventing localized thick ice formation.

[0016] Furthermore, the ice-melting control module adopts a multi-branch composite ice-melting design, including the heat recovery ice-melting branch of the heat pump unit itself, the electric auxiliary ice-melting unit, and the low-temperature water source bypass ice-melting branch: The heat recovery de-icing branch is connected to the condenser. Through the switching valve, the condensing heat of the condenser (the waste heat of the heat pump unit) is extracted to de-ic the evaporator. No external energy is required, and the de-icing efficiency is high. The electric-assisted ice-melting unit is a patch-type heating element, which is evenly arranged in the areas of the evaporator heat exchange surface that are prone to thick ice formation (such as the flow channel outlet area and the heat exchange tube bends) as an auxiliary ice-melting method. The low-temperature water source bypass de-icing branch is used to introduce ambient temperature water (such as municipal tap water or industrial ambient temperature return water) to precisely de-ic the localized areas of excessively thick ice on the evaporator, with a fast de-icing speed.

[0017] Furthermore, the graded precision ice melting in S4 includes two levels: primary ice melting and deep ice melting, which are switched according to the ratio of real-time ice thickness to the ice melting trigger threshold. Primary ice melting: When the ice thickness reaches the ice melting trigger threshold but does not exceed 1.2 times the ice melting trigger threshold, only the heat recovery ice melting branch is activated to use the waste heat of the heat pump for gentle ice melting, avoiding sudden temperature changes on the heat exchange surface caused by excessively rapid ice melting. Deep ice melting: When the ice thickness exceeds 1.2 times the ice melting trigger threshold, the heat recovery ice melting branch and the electric auxiliary ice melting unit in the corresponding thick ice area are activated simultaneously; if the ice thickness in a local area exceeds 1.5 times the ice melting trigger threshold, the low temperature water source bypass ice melting branch is activated in addition to perform localized and precise ice melting in that area until the ice thickness drops to the second safe ice melting threshold.

[0018] Furthermore, considering the operating characteristics of the low-temperature water source heat pump, the basic value ranges for the thresholds are set as follows: the first safe freezing threshold is 3~8mm, the second safe freezing threshold is 1~3mm, and the ice-melting trigger threshold is 8~15mm. For extreme low-temperature conditions, the thresholds are dynamically adjusted: when the low-temperature water source temperature is below -5℃, the first safe freezing threshold is lowered by 1~2mm, and the ice-melting trigger threshold is lowered by 2~3mm to avoid malfunctions caused by rapid ice thickening under extreme low temperatures.

[0019] Furthermore, the heat pump unit is also equipped with a unit operation parameter monitoring module, which is used to detect the compressor's exhaust temperature, suction pressure, condenser's condensing temperature, and inlet and outlet pressure difference of the throttling element in real time, and incorporate the unit's core operating parameters into the icing control system: during the icing operation control in S3 and the de-icing control in S4, if the compressor exhaust temperature exceeds 110℃ or the suction pressure is lower than 0.1MPa, it indicates that the unit has experienced an operational abnormality. The icing promotion intensity of the flow field control module is immediately reduced, or the de-icing control module is activated in advance to prioritize the safe operation of the unit.

[0020] Furthermore, during the status monitoring process of S2, the central control unit has a built-in ice thickness-heat exchange efficiency correlation model. This model is obtained by fitting a large amount of experimental data. By substituting the real-time detected ice data into the model, the heat exchange efficiency of the unit under the current ice condition can be quickly determined. If the heat exchange efficiency drops by more than 20% compared with the ice-free condition, even if the ice thickness does not reach the ice melting trigger threshold, a local ice melting action is initiated to avoid excessive impact of the ice layer on the heat exchange efficiency.

[0021] Furthermore, the flow rate of the variable frequency circulating pump is positively correlated with the ice thickness of the evaporator: when the ice thickness is within the range of the first safe ice-forming threshold to the ice-melting trigger threshold, the circulation flow rate of the low-temperature water source gradually increases with the increase of the ice thickness, and the increase range is 1.1 to 1.5 times the initial flow rate. By increasing the flow rate, the heat exchange between the low-temperature water source and the ice layer is enhanced, and the heat storage of the ice layer is fully utilized.

[0022] Furthermore, in order to reduce the adhesion between the ice layer and the heat exchange surface of the evaporator and reduce the residual ice slag after melting, the heat exchange surface of the evaporator is treated with an ultra-ice-repellent coating. The water contact angle of the ultra-ice-repellent coating is greater than 120°, and the ice layer is easy to detach. This facilitates the flow field control to form a uniform ice layer, improves the melting efficiency, and reduces the melting time. Beneficial effects

[0023] The icing-capable low-temperature water source heat pump control method of the present invention has the following significant advantages compared with the prior art: 1. Achieving controllable icing operation and improving the utilization rate of low-temperature heat sources: Breaking through the traditional anti-icing design concept, by setting graded thresholds and dynamic control, the evaporator is allowed to ic within a safe range, making full use of the heat storage characteristics of the ice layer and improving the heat recovery efficiency of low-temperature water sources (especially water sources below 0℃). Compared with the traditional anti-icing operation method, the unit's heating capacity is increased by 15%~30%. 2. Good ice layer uniformity and avoidance of local failures: The icing monitoring module accurately captures the ice distribution, and the flow field control module adjusts the flow velocity and flow field in the flow channel in a targeted manner, so that the difference in ice thickness in different areas of the evaporator heat exchange surface is controlled within 5mm, avoiding heat exchange failure and mechanical stress damage to heat exchange tubes caused by local thick ice, and greatly improving the safety of unit operation. 3. Precise, staged ice melting, reducing energy consumption: A composite ice melting method combining heat recovery, electric-assisted ice melting, and bypass ice melting is employed. Ice melting is staged according to ice thickness, prioritizing the use of waste heat from the heat pump. Electric-assisted and bypass ice melting are only activated when necessary, and localized ice melting is performed on thick ice areas without requiring a complete unit shutdown. Compared to traditional overall ice melting methods, ice melting energy consumption is reduced by 40%–60%, and ice melting time is shortened by 30%–50%. 4. Closed-loop intelligent control, strong adaptability: Real-time monitoring and closed-loop control of icing status and unit operating parameters are achieved through multiple monitoring modules and a central control unit. Thresholds can be dynamically adjusted according to the temperature and water quality of the low-temperature water source, making it suitable for various low-temperature heat source scenarios such as industrial low-temperature wastewater and natural surface water / groundwater, demonstrating strong versatility. 5. Super-hydrophobic coating enhances control effect: The super-hydrophobic coating on the evaporator heat exchange surface reduces the adhesion between the ice layer and the heat exchange surface, which facilitates the formation of a uniform ice layer by controlling the flow field, reduces residual ice slag after melting, improves melting efficiency, and further ensures the stability of the unit's icing operation. Attached Figure Description

[0024] 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 preferred embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 is a schematic diagram of the working principle of the low-temperature water source heat pump unit of the present invention; Figure 2 is a flowchart of the control method for the low-temperature water source heat pump that can operate in freezing mode according to the present invention. Detailed Implementation

[0026] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments and accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] To achieve the above objectives, the present invention provides the following technical solution: a low-temperature water source heat pump control method capable of freezing operation, comprising a low-temperature water source heat pump unit, wherein the heat pump unit comprises an evaporator, a compressor, a condenser and a throttling element connected in sequence, forming the core loop of the heat pump cycle; a low-temperature water source flow channel is provided on the outside of the evaporator, wherein the low-temperature water source exchanges heat with the heat exchange surface of the evaporator in the flow channel, providing a low-temperature heat source for the heat pump unit.

[0028] The evaporator is specially equipped with an icing monitoring module, a flow field control module, and an ice melting control module. All three modules are electrically connected to the central control unit to achieve real-time monitoring of the icing state and closed-loop execution of control actions. Icing monitoring module: used to detect the icing thickness and distribution on the evaporator heat exchange surface, accurately capturing the icing status in different areas; Flow field control module: used to adjust the fluid velocity and flow field distribution in the low temperature water source channel, and guide the formation of a uniform ice layer on the heat exchange surface of the evaporator; Ice melting control module: used to perform precise ice melting of the evaporator heat exchange surface in stages, avoiding energy loss and downtime caused by overall ice melting.

[0029] The core of the icing operation control method of this invention is to achieve controllable icing conditions through graded threshold setting, real-time status monitoring, dynamic flow field regulation, and graded precise ice melting. The specific steps are as follows: S1, Threshold setting: Based on the water quality (sand content, impurity content) and temperature conditions (static water temperature, flowing water temperature) of the low-temperature water source, a safe icing first threshold, a safe icing second threshold, and an ice melting trigger threshold are set for the evaporator heat exchange surface. The ice melting trigger threshold is greater than the safe icing first threshold, and the safe icing first threshold is greater than the safe icing second threshold. The safe icing first threshold is the optimal thickness threshold for icing operation, at which the ice layer possesses both heat storage and heat exchange characteristics. The safe icing second threshold is the ice melting termination threshold; when ice melting reaches this thickness, ice melting stops, and icing operation resumes. The ice melting trigger threshold is the limit threshold for icing operation; when this thickness is reached, ice melting must be initiated to avoid heat exchange failure.

[0030] S2. Status Monitoring and Judgment: The icing monitoring module detects the icing thickness and icing distribution data of the evaporator heat exchange surface in real time and transmits the data to the central control unit. The central control unit determines whether the real-time icing thickness has reached the first safe icing threshold.

[0031] S3. Flow field control during freezing operation: If the real-time ice thickness reaches the first safe freezing threshold, the flow field control module is activated to adjust the fluid velocity and flow field distribution in the low-temperature water source channel. Through methods such as guiding and changing the flow velocity, a uniform ice layer is formed in each area of ​​the evaporator heat exchange surface, maintaining the unit's stable operation under freezing conditions and making full use of the heat storage characteristics of the ice layer to improve the utilization rate of the low-temperature heat source.

[0032] S4. Graded Precision Ice Melting: If the real-time ice thickness reaches the ice melting trigger threshold, the ice melting control module is activated to perform graded precision ice melting. Depending on the ice thickness, primary ice melting or deep ice melting actions are initiated respectively until the ice thickness drops to the second safe ice melting threshold. Then, the ice melting control module is shut down, and the normal ice melting operation control state of the flow field control module is restored.

[0033] S5. Closed-loop control: The icing monitoring module continuously collects icing status data of the evaporator heat exchange surface. The central control unit executes steps S2-S4 in a loop to achieve real-time monitoring and closed-loop control under icing conditions, ensuring that the unit always operates within the safe icing range.

[0034] Furthermore, the icing monitoring module includes multiple thickness sensors, temperature sensors, and an infrared imaging unit: the thickness sensors use the ultrasonic thickness measurement principle and are evenly arranged in different areas of the evaporator heat exchange surface (including the inlet area, middle area, and outlet area of ​​the flow channel) to detect the real-time icing thickness in each area; the temperature sensors are respectively set at the inlet and outlet of the evaporator heat exchange surface, the low-temperature water source flow channel, to detect the temperature of the heat exchange surface and the temperature difference between the inlet and outlet of the water source, and to help determine the icing trend; the infrared imaging unit is used to acquire real-time images of the icing distribution on the evaporator heat exchange surface, intuitively reflecting the areas of uneven icing, and providing a basis for flow field control and local icing melting.

[0035] Furthermore, the flow field control module includes a guide plate, a variable frequency circulating pump, and a flow regulating valve within the flow channel. The guide plate is electrically adjustable and evenly arranged within the low-temperature water source flow channel, changing the local flow field direction by adjusting the angle. The variable frequency circulating pump is used to regulate the overall circulation velocity of the low-temperature water source, and the flow regulating valve is used to control the inflow rate of the low-temperature water source. During the flow field control process in S3, the central control unit adjusts the angle of the guide plate and the flow velocity of the local flow channel based on the ice distribution data, ensuring that the difference in ice thickness in different areas of the evaporator heat exchange surface is controlled within 5mm, thus preventing localized thick ice formation.

[0036] Furthermore, the ice-melting control module adopts a multi-branch composite ice-melting design, including the heat recovery ice-melting branch of the heat pump unit itself, the electric auxiliary ice-melting unit, and the low-temperature water source bypass ice-melting branch: The heat recovery de-icing branch is connected to the condenser. It is switched by a three-way valve to extract the condensing heat of the condenser (the waste heat of the heat pump unit) for de-icing the evaporator. No external energy is required, and the de-icing efficiency is high. The electric-assisted ice-melting unit is a patch-type heating element, which is evenly arranged in the areas of the evaporator heat exchange surface that are prone to thick ice formation (such as the flow channel outlet area and the heat exchange tube bends) as an auxiliary ice-melting method. The low-temperature water source bypass de-icing branch is used to introduce ambient temperature water (such as municipal tap water or industrial ambient temperature return water) to precisely de-ic the localized areas of excessively thick ice on the evaporator, with a fast de-icing speed.

[0037] Furthermore, the graded precision ice melting in S4 includes two levels: primary ice melting and deep ice melting, which are switched according to the ratio of real-time ice thickness to the ice melting trigger threshold. Primary ice melting: When the ice thickness reaches the ice melting trigger threshold but does not exceed 1.2 times the ice melting trigger threshold, only the heat recovery ice melting branch is activated to use the waste heat of the heat pump for gentle ice melting, avoiding sudden temperature changes on the heat exchange surface caused by excessively rapid ice melting. Deep ice melting: When the ice thickness exceeds 1.2 times the ice melting trigger threshold, the heat recovery ice melting branch and the electric auxiliary ice melting unit in the corresponding thick ice area are activated simultaneously; if the ice thickness in a local area exceeds 1.5 times the ice melting trigger threshold, the low temperature water source bypass ice melting branch is activated in addition to perform localized and precise ice melting in that area until the ice thickness drops to the second safe ice melting threshold.

[0038] Furthermore, considering the operating characteristics of the low-temperature water source heat pump, the basic value ranges for the thresholds are set as follows: the first safe freezing threshold is 3~8mm, the second safe freezing threshold is 1~3mm, and the ice-melting trigger threshold is 8~15mm. For extreme low-temperature conditions, the thresholds are dynamically adjusted: when the low-temperature water source temperature is below -5℃, the first safe freezing threshold is lowered by 1~2mm, and the ice-melting trigger threshold is lowered by 2~3mm to avoid malfunctions caused by rapid ice thickening under extreme low temperatures.

[0039] Furthermore, the heat pump unit is also equipped with a unit operation parameter monitoring module, which is used to detect the compressor's exhaust temperature, suction pressure, condenser's condensing temperature, and inlet and outlet pressure difference of the throttling element in real time, and incorporate the unit's core operating parameters into the icing control system: during the icing operation control in S3 and the de-icing control in S4, if the compressor exhaust temperature exceeds 110℃ or the suction pressure is lower than 0.1MPa, it indicates that the unit has experienced an operational abnormality. The icing promotion intensity of the flow field control module is immediately reduced, or the de-icing control module is activated in advance to prioritize the safe operation of the unit.

[0040] Furthermore, during the status monitoring process of S2, the central control unit has a built-in ice thickness-heat exchange efficiency correlation model. This model is obtained by fitting a large amount of experimental data. By substituting the real-time detected ice data into the model, the heat exchange efficiency of the unit under the current ice condition can be quickly determined. If the heat exchange efficiency drops by more than 20% compared with the ice-free condition, even if the ice thickness does not reach the ice melting trigger threshold, a local ice melting action is initiated to avoid excessive impact of the ice layer on the heat exchange efficiency.

[0041] Furthermore, the flow rate of the variable frequency circulating pump is positively correlated with the ice thickness of the evaporator: when the ice thickness is within the range of the first safe ice-forming threshold to the ice-melting trigger threshold, the circulation flow rate of the low-temperature water source gradually increases with the increase of the ice thickness, and the increase range is 1.1 to 1.5 times the initial flow rate. By increasing the flow rate, the heat exchange between the low-temperature water source and the ice layer is enhanced, and the heat storage of the ice layer is fully utilized.

[0042] Furthermore, in order to reduce the adhesion between the ice layer and the heat exchange surface of the evaporator and reduce the residual ice slag after melting, the heat exchange surface of the evaporator is treated with an ultra-ice-repellent coating. The water contact angle of the ultra-ice-repellent coating is greater than 120°, and the ice layer is easy to detach. This facilitates the flow field control to form a uniform ice layer, improves the melting efficiency, and reduces the melting time. Beneficial effects

[0043] The icing-capable low-temperature water source heat pump control method of the present invention has the following significant advantages compared with the prior art: 1. Achieving controllable icing operation and improving the utilization rate of low-temperature heat sources: Breaking through the traditional anti-icing design concept, by setting graded thresholds and dynamic control, the evaporator is allowed to ic within a safe range, making full use of the heat storage characteristics of the ice layer and improving the heat recovery efficiency of low-temperature water sources (especially water sources below 0℃). Compared with the traditional anti-icing operation method, the unit's heating capacity is increased by 15%~30%. 2. Good ice layer uniformity and avoidance of local failures: The icing monitoring module accurately captures the ice distribution, and the flow field control module adjusts the flow velocity and flow field in the flow channel in a targeted manner, so that the difference in ice thickness in different areas of the evaporator heat exchange surface is controlled within 5mm, avoiding heat exchange failure and mechanical stress damage to heat exchange tubes caused by local thick ice, and greatly improving the safety of unit operation. 3. Precise, staged ice melting, reducing energy consumption: A composite ice melting method combining heat recovery, electric-assisted ice melting, and bypass ice melting is employed. Ice melting is staged according to ice thickness, prioritizing the use of waste heat from the heat pump. Electric-assisted and bypass ice melting are only activated when necessary, and localized ice melting is performed on thick ice areas without requiring a complete unit shutdown. Compared to traditional overall ice melting methods, ice melting energy consumption is reduced by 40%–60%, and ice melting time is shortened by 30%–50%. 4. Closed-loop intelligent control, strong adaptability: Real-time monitoring and closed-loop control of icing status and unit operating parameters are achieved through multiple monitoring modules and a central control unit. Thresholds can be dynamically adjusted according to the temperature and water quality of the low-temperature water source, making it suitable for various low-temperature heat source scenarios such as industrial low-temperature wastewater and natural surface water / groundwater, demonstrating strong versatility. 5. Super-hydrophobic coating enhances control effect: The super-hydrophobic coating on the evaporator heat exchange surface reduces the adhesion between the ice layer and the heat exchange surface, which facilitates the formation of a uniform ice layer by controlling the flow field, reduces residual ice slag after melting, improves melting efficiency, and further ensures the stability of the unit's icing operation.

[0044] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments.

Claims

1. A control method for a low-temperature water source heat pump capable of freezing operation, comprising a low-temperature water source heat pump unit, wherein the heat pump unit includes an evaporator, a compressor, a condenser, and a throttling element connected in sequence, characterized in that, The evaporator is equipped with a low-temperature water source channel on its outer side, and the evaporator is equipped with an ice-forming monitoring module, a flow field control module, and an ice-melting control module. The ice-forming monitoring module is used to detect the ice thickness and ice distribution on the heat exchange surface of the evaporator. The flow field control module is used to adjust the fluid velocity and flow field distribution in the low-temperature water source channel. The ice-melting control module is used to precisely melt the ice on the heat exchange surface of the evaporator. The control method for enabling icing operation is as follows: S1. Based on the water quality and temperature conditions of the low-temperature water source, set a first safe icing threshold, a second safe icing threshold, and a melting trigger threshold for the evaporator heat exchange surface. The melting trigger threshold is greater than the first safe icing threshold, and the first safe icing threshold is greater than the second safe icing threshold. S2. The icing monitoring module detects the icing thickness and icing distribution data of the evaporator heat exchange surface in real time to determine whether the real-time icing thickness has reached the first safe icing threshold. S3. If the real-time ice thickness reaches the first safe ice-forming threshold, the flow field control module is activated to adjust the fluid velocity and flow field distribution in the low-temperature water source channel, so that a uniform ice layer is formed on the heat exchange surface of the evaporator, and the unit is maintained to operate under ice-forming conditions. S4. If the real-time ice thickness reaches the ice-melting trigger threshold, start the ice-melting control module to perform graded and precise ice melting until the ice thickness drops to the second safe ice-melting threshold. Then, shut down the ice-melting control module and restore the normal ice-melting operation control state of the flow field control module. S5. Continuously monitor the ice-melting state of the evaporator heat exchange surface and execute S2-S4 in a loop to achieve closed-loop control under ice-melting conditions.

2. The control method for a low-temperature water source heat pump capable of freezing operation according to claim 1, characterized in that, The icing monitoring module includes multiple thickness sensors, temperature sensors, and an infrared imaging unit. The thickness sensors are evenly distributed in different areas of the evaporator heat exchange surface. The temperature sensors are respectively set on the evaporator heat exchange surface, the inlet and outlet of the low-temperature water source channel, and the infrared imaging unit is used to acquire images of the icing distribution on the evaporator heat exchange surface in real time.

3. The control method for a low-temperature water source heat pump capable of freezing operation according to claim 1, characterized in that, The flow field control module includes a guide plate, a variable frequency circulating pump, and a flow regulating valve in the flow channel. The guide plate has an adjustable angle structure, the variable frequency circulating pump is used to adjust the circulation velocity of the low temperature water source, and the flow regulating valve is used to control the inflow velocity of the low temperature water source. In S3, the flow field control module adjusts the angle of the guide plate and the flow velocity of the local flow channel according to the ice distribution data, so that the difference in ice thickness in each area of ​​the evaporator heat exchange surface is controlled within 5 mm.

4. The control method for a low-temperature water source heat pump capable of freezing operation according to claim 1, characterized in that, The ice-melting control module includes a heat recovery ice-melting branch of the heat pump unit itself, an electric auxiliary ice-melting unit, and a low-temperature water source bypass ice-melting branch. The heat recovery ice-melting branch is connected to the condenser and extracts the condensation heat of the condenser for ice melting of the evaporator. The electric auxiliary ice-melting unit is a patch-type heating element, which is evenly arranged in the area of ​​the heat exchange surface of the evaporator that is prone to thick ice formation. The low-temperature water source bypass ice-melting branch is used to introduce room temperature water to locally melt ice in the evaporator.

5. The control method for a low-temperature water source heat pump capable of freezing operation according to claim 4, characterized in that, The graded precision ice melting in S4 includes primary ice melting and deep ice melting: when the ice thickness reaches the ice melting trigger threshold but does not exceed 1.2 times the ice melting trigger threshold, primary ice melting is initiated, and only the heat recovery ice melting branch is activated; when the ice thickness exceeds 1.2 times the ice melting trigger threshold, deep ice melting is initiated, and the heat recovery ice melting branch and the electric auxiliary ice melting unit for the corresponding thick ice area are activated simultaneously. If the ice thickness in a local area exceeds 1.5 times the ice melting trigger threshold, the low-temperature water source bypass ice melting branch is activated to perform local ice melting.

6. The control method for a low-temperature water source heat pump capable of freezing operation according to claim 1, characterized in that, The first threshold for safe icing is in the range of 3~8mm, the second threshold for safe icing is in the range of 1~3mm, and the threshold for triggering ice melting is in the range of 8~15mm. When the temperature of the low-temperature water source is below -5℃, the first threshold for safe icing is lowered by 1~2mm, and the threshold for triggering ice melting is lowered by 2~3mm.

7. The control method for a low-temperature water source heat pump capable of freezing operation according to claim 1, characterized in that, The heat pump unit is also equipped with a unit operation parameter monitoring module, which is used to detect the compressor's exhaust temperature, suction pressure, condenser's condensing temperature, and the inlet and outlet pressure difference of the throttling element in real time. During the control process of S3 and S4, if the compressor's exhaust temperature exceeds 110℃ or the suction pressure is lower than 0.1MPa, the icing promotion intensity of the flow field control module is immediately reduced, or the de-icing control module is activated in advance.

8. The control method for a low-temperature water source heat pump capable of freezing operation according to claim 1, characterized in that, In step S2, the icing monitoring module transmits the real-time icing data to the central control unit. The central control unit uses a preset icing thickness-heat exchange efficiency correlation model to determine the unit's heat exchange efficiency under the current icing condition. If the heat exchange efficiency drops by more than 20% compared to the ice-free condition, a local icing action is initiated even if the icing thickness has not reached the icing trigger threshold.

9. The control method for a low-temperature water source heat pump capable of freezing operation according to claim 3, characterized in that, The variable frequency circulating pump's flow rate is positively correlated with the evaporator's ice thickness. When the ice thickness is within the range of the first safe ice-forming threshold to the ice-melting trigger threshold, the circulating flow rate of the low-temperature water source gradually increases with the increase in ice thickness, with an increase range of 1.1 to 1.5 times the initial flow rate.

10. The control method for a low-temperature water source heat pump capable of freezing operation according to claim 1, characterized in that, The heat exchange surface of the evaporator is treated with an ultra-ice-repellent coating. The contact angle of the ultra-ice-repellent coating is greater than 120°. During the flow field control and ice melting control process, the adhesion between the ice layer and the heat exchange surface is reduced, and the residual ice slag after ice melting is reduced.

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