A heat pump system and a defrosting control method thereof

Abstract

The present application relates to the technical field of heat pump control, and discloses a heat pump system and a defrosting control method thereof, the method comprising: obtaining operating parameters and calculating a ring fin difference; determining whether a frozen rain defrosting entry condition is met, and if so, entering a frozen rain defrosting mode, otherwise determining whether a ring fin difference defrosting entry condition is met; if the ring fin difference defrosting entry condition is met, entering a ring fin difference defrosting mode, otherwise not performing defrosting; exiting defrosting when a exit condition is met; correcting the next defrosting interval according to the running time after exiting the ring fin difference defrosting; the frozen rain defrosting condition involves the ambient temperature, the evaporation saturation temperature and the running time, and the evaporation saturation temperature threshold is corrected according to the water inlet temperature; the ring fin difference defrosting condition involves a ring fin difference threshold selected according to the ambient temperature in sections. The present application can accurately identify different frosting conditions by distinguishing the frozen rain defrosting mode from the ring fin difference defrosting mode, adjusting the defrosting interval in combination with the running time, realizing on-demand defrosting, and improving the defrosting accuracy and the unit operation stability.

Description

Technical Field

[0001] This invention relates to the field of heat pump control technology, and more specifically, to a heat pump system and its defrosting control method. Background Technology

[0002] When an air-source heat pump unit is operating in winter, if the surface temperature of the finned heat exchanger on the air side is lower than the dew point temperature of the surrounding air, water vapor in the airflow will condense into liquid water on the evaporator surface. If the evaporator temperature drops further below 0°C, the liquid water will freeze into frost. At this time, the unit will automatically defrost to remove the frost layer from the finned heat exchanger surface. However, when freezing rain or blizzards occur in winter, ice will form on the surface of the unit's finned heat exchanger. Since the unit defrosts at regular intervals, the ice layer on the finned heat exchanger can become very thick, making it difficult to remove completely. Over a long period of operation, the accumulation of ice will significantly reduce the heat exchange efficiency of the evaporator, increase the energy consumption of the refrigeration equipment, and may even cause equipment failure.

[0003] In current technology, air source heat pump units on the market defrost the unit at intervals by detecting the difference between the ambient temperature and the fin temperature. This defrosting technology can effectively remove frost from the evaporator in low-temperature, low-humidity environments. However, in freezing rain conditions below 0°C, ice forms on the surface of the finned heat exchanger. Since the unit defrosts at regular intervals, the accumulated ice layer becomes very thick, making complete removal difficult. If the defrosting interval is set too short, the unit may defrost without frost, resulting in poor heating capacity and a poor user experience. Summary of the Invention

[0004] The present invention aims to overcome at least one of the defects of the prior art and provide a heat pump system and its defrosting control method. The method can automatically detect and judge the temperature of the finned heat exchanger according to the change of ambient temperature, and the unit defrosts in time, thereby improving the heating efficiency of the heat pump and improving the reliability of the unit.

[0005] The defrosting control method for heat pump systems used in this invention includes: S1. Obtain the operating parameters of the heat pump unit, including the compressor cumulative running time, compressor frost running time, ambient temperature, fin temperature, evaporation saturation temperature TE, inlet water temperature Ti, and outlet water temperature; S2. Determine whether the conditions for entering the freezing rain defrosting mode are met. If they are met, control the unit to enter the freezing rain defrosting mode. If not, execute S4 directly. Preferably, the freezing rain defrosting entry condition is that the following conditions are met simultaneously: the ambient temperature is within the preset freezing rain temperature range; the evaporation saturation temperature TE is less than or equal to the preset freezing rain defrosting evaporation temperature TE1; the compressor's cumulative running time reaches the preset minimum freezing rain running time; and the compressor's frost accumulation running time reaches the freezing rain defrosting interval.

[0006] Preferably, the timing start condition for the compressor frost operation time is: the fin temperature is detected to be less than or equal to 0°C, and the duration exceeds the preset frost determination time; the timing start condition for the freezing rain defrosting interval is: the evaporation saturation temperature TE is detected to be less than or equal to the freezing rain defrosting evaporation temperature TE1.

[0007] Preferably, the freezing rain defrosting evaporation temperature TE1 is corrected according to the inlet water temperature Ti: When the inlet water temperature Ti is less than the first inlet water temperature threshold Ti1, the freezing rain defrosting evaporation temperature TE1 is the difference between the baseline value and the low water temperature freezing rain evaporation compensation. When the inlet water temperature Ti is greater than or equal to the first inlet water temperature threshold Ti1 and less than the second inlet water temperature threshold Ti2, the freezing rain defrosting evaporation temperature TE1 remains unchanged at the reference value. When the inlet water temperature Ti is greater than or equal to the second inlet water temperature threshold Ti2, the freezing rain defrosting evaporation temperature TE1 is the sum of the baseline value and the high water temperature freezing rain evaporation compensation.

[0008] S3. During operation, if the conditions for exiting the freezing rain defrosting mode are met, the freezing rain defrosting mode will be exited. Preferably, the freezing rain defrosting exit conditions include: when in freezing rain defrosting mode, if any of the following conditions are met: the defrosting time reaches the sum of the preset duration and the freezing rain defrosting delay time compensation, the fin temperature reaches the sum of the exit defrosting fin temperature and the freezing rain fin temperature compensation, or the outlet water temperature reaches the minimum defrosting water temperature, then the freezing rain defrosting mode is exited; after exiting the freezing rain defrosting mode, S4 is executed.

[0009] S4. Determine whether the preset conditions for entering the annular fin differential defrosting mode are met. If the conditions are met, control the unit to enter the annular fin differential defrosting mode. If not, defrosting is not required, and return to S1 to continue monitoring. Preferably, the conditions for entering the annular-fin differential defrosting condition are met simultaneously as follows: the compressor's cumulative running time reaches the initial start-up running time; the compressor's frost accumulation running time reaches the defrosting interval; the difference between the ambient temperature and the fin temperature is greater than or equal to the annular-fin differential threshold; and the fin temperature is less than or equal to the frosting temperature threshold. Preferably, the method for determining the annular fin difference threshold includes: Based on the ambient temperature range, the corresponding ring fin difference thresholds are selected: when the ambient temperature is greater than or equal to 10℃, the unit does not enter defrosting mode; when the ambient temperature is greater than or equal to 3℃ and less than 10℃, the second ring fin difference threshold ΔT2 is selected; when the ambient temperature is greater than or equal to -5℃ and less than 3℃, the third ring fin difference threshold ΔT3 is selected; when the ambient temperature is greater than -15℃ and less than -5℃, the fourth ring fin difference threshold ΔT4 is selected; when the ambient temperature is ≤ -15℃, the fifth ring fin difference threshold ΔT5 is selected; wherein, ΔT2>ΔT3>ΔT4>ΔT5.

[0010] S5. During operation, when the conditions for exiting the ring-fin differential defrosting are met, exit the ring-fin differential defrosting mode and calculate the duration of this defrosting operation. Preferably, the conditions for exiting the ring-fin differential defrosting include: when in the ring-fin differential defrosting mode, if any one of the following conditions is met: the defrosting time reaches the preset duration, the fin temperature reaches the defrosting exit temperature, or the outlet water temperature reaches the minimum defrosting water temperature, then defrosting is exited; the freezing rain defrosting delay time and freezing rain fin temperature compensation are both greater than zero.

[0011] S6. After exiting the ring-fin differential defrosting mode, the defrosting interval time for the next defrosting is adjusted according to the duration of the current defrosting run. Preferably, the step of adjusting the defrosting interval for the next ring-fin differential defrosting based on the duration of the current ring-fin differential defrosting operation specifically includes: If the defrosting operation time is less than or equal to 3 minutes, the next defrosting interval will be adjusted to the current baseline interval t plus the time compensation value t. k sum; If the defrosting operation time is greater than 3 minutes and less than or equal to 5 minutes, the next defrosting interval will remain unchanged. If the defrosting operation time is greater than 5 minutes but less than 8 minutes, the next defrosting interval will be adjusted to the current baseline interval t plus the time compensation value t. k difference; If the defrosting operation time is greater than or equal to 8 minutes, the next defrosting interval will be adjusted to the preset fixed interval. Wherein, the time compensation value t k It is the product of the current reference interval time t and the preset parameter k.

[0012] The present invention also provides a heat pump system for implementing the above method, the system comprising: Compressor, four-way valve, plate heat exchanger, filter, main circuit electronic expansion valve, controller, finned heat exchanger, gas-liquid separator, high pressure sensor, low pressure sensor, finned temperature probe, outdoor fan, ambient temperature probe, outlet water temperature probe and inlet water temperature probe; The controller is used to receive signals from various sensors and control the compressor, four-way valve, outdoor fan and main electronic expansion valve to perform the above method; The compressor's exhaust port is connected to port D of the four-way valve, port C of the four-way valve is connected to the refrigerant inlet of the plate heat exchanger, the refrigerant outlet of the plate heat exchanger is connected to the inlet of the main electronic expansion valve via the filter, the outlet of the main electronic expansion valve is connected to the refrigerant inlet of the finned heat exchanger, the refrigerant outlet of the finned heat exchanger is connected to port E of the four-way valve, and port S of the four-way valve is connected to the compressor's return port via the gas-liquid separator, forming a refrigerant circulation loop. The low-pressure sensor is located between the compressor return port and the S port of the four-way valve, and is used to detect the evaporation pressure and calculate the evaporation saturation temperature TE; the high-pressure sensor is located on the compressor exhaust pipe, which is connected between the compressor exhaust port and the D port of the four-way valve. The fin temperature probe is installed on the fin heat exchanger and is used to detect the fin temperature; the outdoor fan is installed corresponding to the fin heat exchanger; the ambient temperature probe is used to detect the outdoor ambient temperature. The outlet water temperature probe and the inlet water temperature probe are respectively installed at the water-side outlet and inlet of the plate heat exchanger to detect the outlet water temperature and the inlet water temperature.

[0013] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention distinguishes between two modes: freezing rain defrosting and ring-fin differential defrosting. By setting specific freezing rain defrosting entry conditions, it can accurately identify frost conditions under special severe weather conditions such as freezing rain, avoiding the problem of incomplete defrosting or frequent false defrosting in extreme weather conditions caused by traditional single control logic, and improving the unit's adaptability to complex environments.

[0014] The defrosting method of this invention introduces a multi-dimensional correction mechanism: on the one hand, the evaporation temperature threshold for freezing rain defrosting is corrected according to the inlet water temperature to adapt to different water temperature conditions; on the other hand, different ring fin difference thresholds are selected in segments according to the ambient temperature range. This dynamic adjustment of the judgment criteria makes the defrosting judgment more consistent with the actual operating conditions, reducing misjudgments and omissions.

[0015] Furthermore, this invention establishes a feedback adjustment mechanism based on the defrosting runtime. By analyzing the duration of the current defrosting operation, the interval between the next defrosting operation is adjusted: a shorter defrosting time indicates less frost, so the interval is automatically extended; a longer defrosting time indicates more frost, so the interval is automatically shortened. This intelligent logic of defrosting on demand effectively avoids unnecessary energy waste, ensuring timely defrosting when frost is severe and reducing downtime when frost is mild, thereby improving overall heating efficiency and stability. Attached Figure Description

[0016] Figure 1 This is a schematic flowchart of the heat pump defrosting control method in Example 1.

[0017] Figure 2 This is a schematic diagram of the heating operation principle of the heat pump system of the present invention.

[0018] Figure 3 This is a schematic diagram illustrating the working principle of the heat pump system of the present invention during unit cooling and defrosting.

[0019] In the diagram: 1. Compressor; 2. Four-way valve; 3. Plate heat exchanger; 4. Filter; 5. Main electronic expansion valve; 6. Finned heat exchanger; 7. Gas-liquid separator; 8. High-pressure sensor; 9. Low-pressure sensor; 10. Finned temperature probe; 11. Outdoor fan; 12. Ambient temperature probe; 13. Outlet water temperature probe; 14. Inlet water temperature probe. Detailed Implementation

[0020] The accompanying drawings are for illustrative purposes only and should not be construed as limiting the invention. To better illustrate the following embodiments, some parts in the drawings may be omitted, enlarged, or reduced, and do not represent the actual product dimensions; it is understandable to those skilled in the art that some well-known structures and their descriptions may be omitted in the drawings.

[0021] Example 1 like Figure 1 As shown in the figure, this embodiment provides a heat pump defrosting control method, the method is as follows: How to enter the heat pump freezing rain defrosting mode: If the following conditions are met simultaneously, the freezing rain defrosting mode will begin after a 30-second delay: A: When the ambient temperature is within the preset range, the preset range is the ambient temperature range where freezing rain is likely to occur, and the freezing rain temperature range is -5℃ to 0℃ (or determined according to the actual working conditions). B: Evaporation saturation temperature TE ≤ freezing rain defrost evaporation temperature TE1, parameter can be set; C: Compressor 1's cumulative running time is greater than or equal to the minimum running time during freezing rain; this parameter can be set. D: Compressor 1 frost accumulation running time ≥ freezing rain defrost interval, parameter can be set, wherein the timing of the freezing rain defrost interval must start from the evaporation saturation temperature TE ≤ freezing rain defrost evaporation temperature TE1; The parameters can be set specifically, including the freezing rain defrosting evaporation temperature TE1, low water temperature freezing rain evaporation compensation, and high water temperature freezing rain evaporation compensation, all of which are configurable parameters; the reference TE1 is obtained through prototype testing under freezing rain simulation conditions, and the compensation amount is determined based on the unit's heat exchange characteristics and the influence of inlet water temperature on the evaporation side conditions.

[0022] Specifically, the freezing rain defrosting evaporation temperature TE1 is differentiated based on the inlet water temperature Ti as follows: A: When the inlet water temperature Ti < Ti1, the corrected freezing rain defrosting evaporation temperature TE1 = baseline value - low water temperature freezing rain evaporation compensation; B: When Ti1≤inlet water temperature Ti<Ti2, the freezing rain defrosting evaporation temperature is not compensated and the freezing rain defrosting evaporation temperature TE1 is directly applied. C: When the inlet water temperature Ti≥Ti2, the corrected freezing rain defrosting evaporation temperature TE1 = baseline value + high water temperature freezing rain evaporation compensation; Ti1 and Ti2 are the inlet water temperature segmentation thresholds, used to divide the inlet water temperature into three segments to achieve segmented compensation for TE1: Ti1 is the boundary between the low water temperature segment and the middle water temperature segment, and Ti2 is the boundary between the middle water temperature segment and the high water temperature segment.

[0023] The above steps determine freezing rain weather based on ambient temperature. Since freezing rain typically occurs in the temperature range of -5℃ to 0℃, and ambient temperatures below -5℃ usually manifest as snowfall, if freezing rain is detected within the above-mentioned set temperature range, the unit must be controlled to perform rapid defrosting. Under this condition, the defrosting interval needs to be set shorter than the defrosting interval under non-freezing rain weather conditions. The purpose is to achieve rapid defrosting of the unit by shortening the defrosting cycle, preventing frost buildup and condensation on the surface of the finned heat exchanger 6, thereby avoiding defrosting failure or ineffective removal due to frost freezing into ice.

[0024] Furthermore, the evaporation saturation temperature TE varies depending on the inlet water temperature of the unit. Therefore, the value of the freezing rain defrosting evaporation temperature TE1 should be set according to the water temperature to more accurately determine whether it is freezing rain weather and avoid mistakenly entering the heat pump intelligent ring fin differential defrosting step.

[0025] How to exit the heat pump freezing rain defrosting mode: A: The actual operating time t for this freezing rain defrosting operation. f1 ≥ Freezing rain defrosting time t f2 + Freezing rain defrosting delay time compensation t f3 ; where t f2 t f3 All are calibrated based on the heat pump unit model and freezing rain test conditions, and can be debugged and modified. B: Fin temperature ≥ defrost exit fin temperature Td + freezing rain fin temperature compensation Td1, parameter can be set, and lasts for 10 seconds; C: Outlet water temperature ≤ minimum defrost water temperature Tk, parameter can be set, and lasts for 10 seconds; How to enter the heat pump intelligent ring-fin differential defrosting mode: Defrosting will begin after a 30-second delay if the following conditions are met simultaneously: A: T0 ≥ Initial startup time; The initial startup time is a configurable parameter, with a value range of 3 to 10 minutes; B: Compressor 1's frost accumulation time T2 ≥ defrost interval; C: Ambient temperature - fin temperature ≥ annular fin temperature difference, and lasts for 30 seconds; D: Fin temperature ≤ 0℃, and lasts for 30 seconds; Specifically, the timing of the compressor 1's frost accumulation operation time T2 begins when the temperature detected by the fin temperature probe 10 is ≤0℃ and the duration exceeds 3 minutes; Specifically, the defrosting interval is intelligently differentiated based on the ambient temperature as follows: When the ambient temperature is ≥10℃, the unit will not enter defrosting mode; With a high ambient temperature, it is difficult for a stable frost layer to form on the surface of the finned heat exchanger 6, so there is basically no risk of frost formation. The defrosting judgment logic is directly turned off to avoid accidental defrosting and loss of heating performance.

[0026] When the ambient temperature is <10℃, the corresponding defrosting interval time shall be configured according to the different temperature ranges of the ambient temperature. A: Ambient temperature < 10℃ (general opening condition); B: 3℃≤Ambient temperature<10℃, defrost interval T4; This temperature range is characterized by high humidity, condensation, and the formation of thin frost / freezing rain / ice film. The air has a high moisture content, resulting in rapid frost formation, but the frost layer thickness increases relatively slowly. Therefore, an appropriate defrosting interval T4 is configured to balance timely defrosting with reducing the frequency of defrosting.

[0027] C: -5℃≤Ambient temperature<3℃, defrost interval T5; This is a typical operating condition range where heat pumps are most prone to rapid and thick frost buildup. The air humidity is high, and frost layers accumulate on the fins very easily and quickly, resulting in the highest frost growth rate. Therefore, the defrost interval T5 is set to the shortest value in this range to ensure timely defrosting and prevent rapid frost buildup from deteriorating heat exchange.

[0028] D: -15℃ < ambient temperature < 5℃, defrost interval T6; As the ambient temperature decreases further and the absolute humidity in the air drops, the frost formation rate slows down compared to the -5 to 3℃ range, and the frost layer formation rate becomes slower. Therefore, compared to T5, the defrosting interval T6 is appropriately lengthened to reduce unnecessary defrosting actions.

[0029] E: Ambient temperature ≤-15℃, defrost interval T7; In low-temperature and frigid conditions, the absolute humidity of the air is very low, which further reduces the frosting speed and slows down the formation of frost. A longer defrosting interval T7 can be used to reduce the frequency of defrosting and ensure the unit's continuous output of heating at low temperatures.

[0030] The above steps divide the defrost interval based on ambient temperature and configure the interval length in conjunction with the operating characteristics of the heat pump unit. Specifically, in the ambient temperature range corresponding to high humidity, the defrost interval is set to a shorter one to ensure that the unit can quickly remove the frost layer on the surface of the finned heat exchanger 6; in the ambient temperature range corresponding to low humidity, the defrost interval is set to a longer one. This setting can avoid unnecessary defrosting operations that reduce the unit's heating capacity, thereby ensuring a continuous and stable heating effect and improving the user experience.

[0031] Specifically, the method to exit the heat pump ring fin differential defrosting mode is as follows: The ring-fin differential defrosting function will be discontinued if any of the following conditions are met: A: Defrosting time t n1 ≥t n2 The parameters can be set; B: Fin temperature ≥ defrost exit temperature Td, parameter can be set, and lasts for 10 seconds; C: Outlet water temperature ≤ minimum defrost water temperature Tk, parameter can be set, and lasts for 10 seconds; Specifically, the exit time for the freezing rain defrosting mode needs to be longer than that for the ring-fin differential defrosting mode, and the defrosting termination fin temperature for the freezing rain defrosting mode is set higher than the corresponding temperature for the intelligent ring-fin differential defrosting mode. The purpose of these settings is to ensure that the ice layer on the surface of the finned heat exchanger 6 can be completely removed.

[0032] The exit time specifically refers to the minimum defrosting runtime threshold in the freezing rain defrosting mode; the minimum defrosting runtime threshold for the freezing rain defrosting mode is set to be greater than the minimum defrosting runtime threshold for the intelligent ring-fin differential defrosting mode. Under freezing rain conditions, an ice film forms on the heat exchanger surface, which is more difficult to melt than the frost layer under normal frosting conditions. By setting a longer minimum defrosting runtime threshold, and simultaneously using a higher defrosting termination fin temperature threshold for freezing rain defrosting, it is ensured that the ice layer on the surface of the finned heat exchanger 6 can be fully melted and removed, avoiding incomplete defrosting.

[0033] In each cycle, the defrost interval is intelligently calculated based on the time of the previous defrost cycle, using the following additive calculation: The initial value of the defrost interval is selected based on the ambient temperature. In heating mode, the defrost interval is calculated as follows each time defrosting is stopped: A: If the defrosting operation time is ≤3 minutes, the next defrosting interval will be adjusted to t+(t×K); (the parameter K can be set) B: If 3 minutes < defrost running time ≤ 5 minutes, the next defrost interval will remain the same as the previous defrost interval; C: When 5 minutes < defrost running time < 8 minutes, the next defrost interval will be reduced, i.e.: next defrost interval = t - (t × K); (the parameter K can be set) D: If the defrosting operation time is ≥8 minutes, the next defrosting interval will be adjusted to 30 minutes (30 minutes is the value taken in this embodiment, not the only one), and the t-(t×K) calculation will no longer be performed; The defrost interval self-correction logic is as follows: first, obtain the initial value t of the defrost interval based on the ambient temperature; after each defrost cycle ends, adjust the next defrost interval by adding or reducing it based on the actual defrost cycle duration.

[0034] Here, t is the defrost interval before this correction (i.e., the defrost interval that took effect in the previous round), not the original initial value of the ambient temperature; K is the correction coefficient, which can be set as a parameter.

[0035] If the defrosting cycle ends quickly (≤3min), it means that the frost layer on the fins is very thin and the frost formation rate is slow. Frequent defrosting is not necessary. The interval between the next defrosting should be lengthened proportionally: t + t×K. This will lengthen the defrosting cycle, reduce the frequency of defrosting, and protect the heating capacity.

[0036] If the defrosting time is longer than 5 minutes, it indicates a thick frost layer and rapid frost formation. The defrosting cycle needs to be shortened, and the next defrosting interval should be reduced proportionally: t t×K allows for earlier defrosting, preventing excessive frost buildup.

[0037] t + t×K is not calculated based on the initial value of the ambient temperature, but is a proportional correction based on the actual defrosting interval t used in the previous cycle; after multiple cycles, the defrosting interval will dynamically drift based on the initial value of the ambient temperature.

[0038] K is the correction factor, representing the percentage adjustment of the defrosting interval after each defrosting cycle.

[0039] Specifically, the selection of the K value is based on the following criteria: A large value for K (e.g., 0.3) results in a large adjustment range each time, responding quickly to changes in frost formation, but it can also cause the defrosting interval to oscillate back and forth. A small K value (e.g., 0.1) results in a gentle adjustment and a stable system, but it is slow to respond to changes in frosting conditions and requires multiple heating cycles to adjust the interval to the correct value.

[0040] In addition, the K value is also related to the type of unit. If it is a large commercial heat pump heat exchanger, or when used outdoors or in the open air, the heat pump is large in size and the frost inertia changes greatly, so the K value should be appropriately larger. For small-scale residential heat pumps, the K value should be appropriately reduced.

[0041] The technical effect of iteratively calculating the next defrost interval based on the previous defrost time is to avoid the unit consuming electricity for defrosting even though there is no frost, or failing to defrost even though there is frost because the interval has not been updated; if the defrost time of the previous cycle was long, it means that the ambient temperature and humidity were high at that time, and there was a lot of frost on the finned heat exchanger 6. In that case, the interval between the unit entering the defrost time in the next cycle should be shortened to ensure that the frost on the finned heat exchanger 6 does not accumulate into an ice layer.

[0042] The annular fin difference is intelligently differentiated based on the ambient temperature as follows: Ring-fin temperature difference = ambient temperature (TA) - fin temperature (TF); When the ambient temperature (TA) is ≥10℃, the unit will not enter the defrosting phase; A: 3℃≤TA<10℃, execute the second ring fin difference threshold ΔT2, the parameter can be set; B: -5℃≤TA<3℃, execute the third ring fin difference threshold ΔT3, the parameter can be set; C: -15℃ < TA < -5℃, execute the fourth ring fin difference threshold ΔT4, the parameter can be set; D: TA≤-15℃, execute the fifth ring fin difference threshold ΔT5, the parameter can be set; Specifically, A represents a high-humidity, frost-prone / freezing rain condition; the air has a high moisture content, and even a slight temperature difference can cause frost formation, so the corresponding annular fin difference threshold is used. B represents a typical heat pump condition with the highest frost formation rate, where thick frost forms most quickly, and the annular fin difference threshold in this range is configured to be the most sensitive. C represents a condition where the temperature decreases, the absolute humidity of the air decreases, and the difficulty of frost formation increases, so the annular fin difference threshold is adjusted to avoid false defrosting. D represents a severe cold and low-temperature condition where the water vapor content in the air is very low, making frost formation difficult; the annular fin difference threshold in this range is further adapted to the low-temperature characteristics to prevent false defrosting triggers.

[0043] The parameters ΔT2, ΔT3, ΔT4, and ΔT5 mentioned above are all settable parameters, obtained through frosting tests under different temperature and humidity conditions on the prototype. The specific calibration method for the ring fin difference threshold is as follows: In the calibration test, the heat pump prototype was placed in an environmental laboratory with controllable temperature and humidity (enthalpy difference laboratory). According to the above temperature range division, typical environmental temperature points in each range were selected one by one, and the relative humidity of the air was adjusted to the humidity conditions that are easy to frost in the temperature range through humidification equipment, so that the prototype could run continuously in heating mode under the corresponding temperature and humidity conditions. During the experiment, the ambient temperature TA and fin temperature TF were collected in real time and the annular-fin difference (TA-TF) was calculated. At the same time, the formation and growth of frost on the surface of the finned heat exchanger 6 were monitored. When the frost began to form and grow stably on the surface of the finned heat exchanger 6, that is, when the unit needed to defrost, the annular-fin difference at that moment was recorded as the critical annular-fin difference under the temperature and humidity conditions. Repeated tests were conducted under the same temperature and humidity conditions. After removing outlier data, the critical ring-fin difference recorded for each test was statistically analyzed (e.g., average value). Combined with the unit's defrosting capacity and a safety margin, the ring-fin difference threshold corresponding to the ambient temperature range was obtained. Calibration was performed for each temperature range using the same method: 3℃≤TA<10℃, -5℃≤TA<3℃, -15℃<TA<-5℃, and TA≤-15℃. The unit was then continuously operated for heating under the same temperature and humidity conditions. During operation, ambient temperature and fin temperature were simultaneously collected, and the fin temperature was observed. The frost formation on the heat exchanger surface is monitored. When frost begins to appear on the fin surface or accumulates to a preset thickness, the difference between the ambient temperature and the fin temperature is recorded. This difference is the critical value for the annular-fin temperature difference under that operating condition. The test is repeated multiple times for different temperature and humidity conditions within each temperature range. The average value of the recorded values ​​is then added to a preset safety margin to obtain the corresponding annular-fin temperature difference threshold for that temperature range. These are the second annular-fin temperature difference threshold ΔT2, the third annular-fin temperature difference threshold ΔT3, the fourth annular-fin temperature difference threshold ΔT4, and the fifth annular-fin temperature difference threshold ΔT5. Specifically, for temperature ranges with faster frost formation and greater frost thickness (e.g., -5℃≤TA<3℃), the corresponding annular-fin temperature difference threshold value is smaller, and the defrosting trigger is more sensitive. This ensures that the unit can defrost promptly and accurately under the corresponding operating conditions, guaranteeing the accuracy and consistency of defrosting timing determination under different temperature and humidity conditions.

[0044] Based on the heating operation characteristics of heat pump units, as the ambient temperature decreases, the fin temperature also decreases, and the heat exchange efficiency of the fins gradually weakens, resulting in different temperature differences between the ambient temperature and the fin temperature under different ambient temperatures. Therefore, by setting corresponding annular fin temperature difference thresholds for different ambient temperature ranges, the frosting state on the surface of the finned heat exchanger 6 can be accurately identified, thereby enabling the unit to quickly and accurately determine the defrosting timing.

[0045] Optionally, since the setting of the ring-fin difference threshold is physically related to the defrost interval in actual operation—that is, the smaller the threshold, the earlier the defrost is triggered, and the interval should be shortened accordingly; the larger the threshold, the later the defrost is triggered, and the interval should be extended accordingly—the next defrost interval is dynamically adjusted based on the ratio of the actual ring-fin difference to the threshold for this defrost operation.

[0046] in, To determine the next defrost interval after correction. This is the baseline defrosting interval corresponding to the current ambient temperature range. The actual ambient fin temperature difference (ambient temperature - fin temperature) at the time of this defrosting trigger; ΔT is the threshold value of the fin temperature difference in the current ambient temperature range; γ is the linkage coefficient, which is taken as γ = -0.5. A negative value indicates that the larger the actual temperature difference and the thicker the frost layer, the shorter the next interval should be. The extent to which the actual trigger temperature difference exceeds the threshold; when Since the ratio term is greater than 0, γ takes a negative value, therefore the calculation yields... This means the frost is thicker, the next interval should be shorter, and defrosting should be done earlier.

[0047] when The ratio term equals 0. Maintain the baseline interval unchanged; Theoretically, this situation will not occur because defrosting is only initiated when the threshold is met; however, actual operation is affected by sensor noise, so protection can be added: therefore, in a preferred embodiment, a condition can be added that the difference is not less than 0.

[0048] In one specific implementation, for example: when the current annular fin difference is 1.5 times the threshold, i.e. the frost layer is thicker, the next interval is adjusted as follows: = 45 (1 + (-0.5) (1.5 - 1)) = 45 0.75 = 33.75 min (25% reduction).

[0049] The above-mentioned optional method ensures the physical consistency of the threshold and the interval through the four-interval linkage setting, that is, the low temperature zone has high sensitivity and short interval, the high temperature zone has low sensitivity and long interval, and the linkage correction formula dynamically adjusts the interval according to the actual temperature difference, so that the interval correction not only depends on the defrosting operation time, but also takes into account the frost thickness signal.

[0050] In summary, this embodiment automatically detects and judges the temperature of the finned heat exchanger 6 based on changes in ambient temperature, enabling real-time determination of whether the unit needs defrosting, and can still defrost efficiently even in extreme freezing rain weather; in addition, it can also remove the ice layer from the finned heat exchanger 6 of the unit, achieving the technical effects of improving the heating efficiency of the heat pump and improving the reliability of the unit.

[0051] Example 2 In a preferred embodiment, based on Example 1, a transition control method for switching between the annular fin differential defrosting mode and the freezing rain defrosting mode during the heat pump defrosting process is provided, as follows: The positive transition steps from the annular fin difference mode to the freezing rain mode are as follows: Step 1: During operation in the ring-fin differential defrosting mode, the controller continuously monitors the freezing rain triggering conditions. When freezing rain conditions are detected, it is marked as a positive transition preparation state, but the switch is not made immediately.

[0052] Step 2: In the positive transition preparation state, the controller performs parallel preheating of freezing rain mode parameters, reads the current inlet water temperature Ti, and calculates freezing rain mode parameters such as evaporation saturation temperature threshold correction amount and defrost heating power correction coefficient, but does not output them to the actuator.

[0053] Step 3: After the current ring-fin differential defrosting is completed, or when the ring-fin differential mode interval expires, a 5-minute positive transition period begins.

[0054] Step 4: During the transition period, defrost is run with the parameters of freezing rain mode, but the exit condition adopts the "OR" logic of the exit conditions of the two modes, that is, the exit condition is triggered by the first condition reached between the ring fin difference mode and the freezing rain mode exit conditions.

[0055] Step 5: After the transition period ends, switch completely to freezing rain mode exit conditions.

[0056] The reverse transition steps from the freezing rain mode to the ring-fin difference mode are as follows: Step 1: During the operation of the freezing rain defrosting mode, the controller continuously monitors the freezing rain release conditions. When the freezing rain conditions are no longer met, it is marked as a reverse transition preparation state.

[0057] Step 2: After the freezing rain defrosting is completed, a 3-minute reverse transition period begins.

[0058] Step 3: During the transition period, the wing temperature exit target linearly transitions from the target value of the freezing rain mode to the target value of the ring-wing difference mode, and is interpolated linearly over time.

[0059] Step 4: After the transition period, fully switch to the ring-wing differential mode exit conditions and parameters.

[0060] To prevent the two modes from switching too frequently, this embodiment also provides an anti-oscillation mechanism, specifically: Set minimum lock time T after mode switch lock = 30 minutes, during which reverse switching is not allowed: Within 30 minutes after a forward switch, even if the freezing rain conditions are lifted, the switch will not revert to the ring-wing differential mode; only the freezing rain condition status will be recorded. Within 30 minutes after a reverse switch, even if the freezing rain conditions are met again, the switch will not revert to the freezing rain mode. If the reverse conditions are met for more than 15 minutes during the lockout period, the switch will be executed immediately at the end of the lockout period.

[0061] The OR logic exit condition during the transition period in this preferred embodiment avoids defrosting interruptions caused by parameter mutations, ensuring the continuity of defrosting during the transition period. Furthermore, the parameter preheating mechanism ensures that the freezing rain mode parameters are ready before switching, and only pre-calculated results need to be output during switching, reducing switching delay. In addition, the 30-minute minimum lock-in time effectively prevents mode oscillations, ensuring the system's operational stability under critical conditions. The linear transition of the fin temperature target avoids abrupt changes in the exit condition during reverse switching, making the fin temperature recovery process smoother.

[0062] Example 3 In one specific implementation, such as Figure 2 and Figure 3 As shown, this embodiment provides a heat pump system.

[0063] The system includes a compressor 1, a four-way valve 2, a plate heat exchanger 3, a filter 4, a main electronic expansion valve 5, a controller, a finned heat exchanger 6, a gas-liquid separator 7, a high-pressure sensor 8, a low-pressure sensor 9, a finned temperature probe 10, an outdoor fan 11, an ambient temperature probe 12, an outlet water temperature probe 13, and an inlet water temperature probe 14. Figure 2 In the middle, the arrows indicate the direction of the heating refrigerant flow; Figure 3 In the image, the arrow indicates the direction of refrigerant flow during defrosting.

[0064] The controller is used to receive signals from various sensors and control the compressor 1, four-way valve 2, outdoor fan 11 and main electronic expansion valve 5 to perform the method described in Example 1; The exhaust port of the compressor 1 is connected to port D of the four-way valve 2, port C of the four-way valve 2 is connected to the refrigerant inlet of the plate heat exchanger 3, the refrigerant outlet of the plate heat exchanger 3 is connected to the inlet of the main circuit electronic expansion valve 5 via the filter 4, the outlet of the main circuit electronic expansion valve 5 is connected to the refrigerant inlet of the finned heat exchanger 6, the refrigerant outlet of the finned heat exchanger 6 is connected to port E of the four-way valve 2, and port S of the four-way valve 2 is connected to the return port of the compressor 1 via the gas-liquid separator 7, forming a refrigerant circulation loop; The low-pressure sensor 9 is located between the return port of the compressor 1 and the S port of the four-way valve 2, and is used to detect the evaporation pressure and calculate the evaporation saturation temperature TE; the high-pressure sensor 8 is located on the exhaust pipe of the compressor 1, and the exhaust pipe is connected between the exhaust port of the compressor 1 and the D port of the four-way valve 2. The fin temperature probe 10 is disposed on the fin heat exchanger 6 and is used to detect the fin temperature; the outdoor fan 11 is disposed corresponding to the fin heat exchanger 6; the ambient temperature probe 12 is used to detect the outdoor ambient temperature. The outlet water temperature probe 13 and the inlet water temperature probe 14 are respectively installed at the water-side outlet and inlet of the plate heat exchanger 3 to detect the outlet water temperature and the inlet water temperature.

[0065] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the technical solution of the present invention, and are not intended to limit the specific implementation of the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the claims of the present invention should be included within the protection scope of the claims of the present invention.

Claims

1. A defrosting control method for a heat pump system, characterized in that, Includes the following steps: S1. Obtain the operating parameters of the heat pump unit, including the compressor cumulative running time, compressor frost running time, ambient temperature, fin temperature, evaporation saturation temperature TE, inlet water temperature Ti, and outlet water temperature; the ambient temperature and fin temperature are used to calculate the ring-fin difference, that is, the difference between the ambient temperature and the fin temperature. S2. Determine whether the conditions for entering the freezing rain defrosting mode are met. If they are met, control the unit to enter the freezing rain defrosting mode. If not, execute S4 directly. S3. During operation, if the conditions for exiting the freezing rain defrosting mode are met, then exit the freezing rain defrosting mode; after exiting the freezing rain defrosting mode, execute S4. S4. Determine whether the preset conditions for entering the annular fin differential defrosting mode are met. If the conditions are met, control the unit to enter the annular fin differential defrosting mode. If not, defrosting is not required, and return to S1 to continue monitoring. S5. During operation, when the conditions for exiting the ring-fin differential defrosting are met, exit the ring-fin differential defrosting mode and calculate the duration of this defrosting run. S6. After exiting the ring-fin differential defrosting mode, the defrosting interval time for the next defrosting is adjusted according to the duration of the current defrosting run.

2. The method according to claim 1, characterized in that, The freezing rain defrosting entry condition described in S2 is that the following conditions must be met simultaneously: The ambient temperature is within the preset freezing rain temperature range; the evaporation saturation temperature TE is less than or equal to the preset freezing rain defrosting evaporation temperature TE1; the compressor's cumulative running time reaches the preset minimum freezing rain running time; and the compressor's frost accumulation running time reaches the freezing rain defrosting interval.

3. The method according to claim 2, characterized in that, The timing start condition for the compressor's frost accumulation operation time is: the fin temperature is detected to be less than or equal to 0°C, and the duration exceeds the preset frost accumulation judgment time; The timing start condition for the freezing rain defrosting interval is: the evaporation saturation temperature TE is detected to be less than or equal to the freezing rain defrosting evaporation temperature TE1.

4. The method according to claim 2, characterized in that, The freezing rain defrosting evaporation temperature TE1 is corrected based on the inlet water temperature Ti: When the inlet water temperature Ti is less than the first inlet water temperature threshold Ti1, the freezing rain defrosting evaporation temperature TE1 is the difference between the baseline value and the low water temperature freezing rain evaporation compensation. When the inlet water temperature Ti is greater than or equal to the first inlet water temperature threshold Ti1 and less than the second inlet water temperature threshold Ti2, the freezing rain defrosting evaporation temperature TE1 remains unchanged at the reference value. When the inlet water temperature Ti is greater than or equal to the second inlet water temperature threshold Ti2, the freezing rain defrosting evaporation temperature TE1 is the sum of the baseline value and the high water temperature freezing rain evaporation compensation.

5. The method according to claim 1, characterized in that, The conditions for entering the ring-fin differential defrosting process described in S4 are that the following conditions must be met simultaneously: The compressor's cumulative running time reaches the initial start-up running time; the compressor's frosting running time reaches the defrosting interval; the difference between the ambient temperature and the fin temperature is greater than or equal to the ring-fin temperature difference threshold; the fin temperature is less than or equal to the frosting temperature threshold. The initial power-on time is obtained at the moment when the entire machine is powered off and then powered on again.

6. The method according to claim 5, characterized in that, The method for determining the annular fin difference threshold includes: Select the corresponding ring-fin difference threshold based on the ambient temperature range: When the ambient temperature is greater than or equal to 10℃, the unit will not enter defrosting mode; When the ambient temperature is greater than or equal to 3℃ and less than 10℃, the second ring fin difference threshold ΔT2 is selected. When the ambient temperature is greater than or equal to -5℃ and less than 3℃, the third ring fin difference threshold ΔT3 is selected. When the ambient temperature is greater than -15℃ and less than -5℃, the fourth ring fin difference threshold ΔT4 is selected. When the ambient temperature is ≤-15℃, select the fifth ring fin difference threshold ΔT5; Among them, ΔT2>ΔT3>ΔT4>ΔT5.

7. The method according to claim 1, characterized in that, The freezing rain defrosting exit conditions described in S3 include: When in freezing rain defrosting mode, freezing rain defrosting will exit if any of the following conditions are met: the defrosting time reaches the sum of the preset duration and the freezing rain defrosting delay time compensation; the fin temperature reaches the sum of the exit defrosting fin temperature and the freezing rain fin temperature compensation; or the outlet water temperature reaches the minimum defrosting water temperature. The freezing rain defrosting delay time and the freezing rain fin temperature compensation are both greater than zero.

8. The method according to claim 1, characterized in that, The conditions for exiting the ring-fin differential defrosting described in S5 include: When in the ring-fin differential defrosting mode, defrosting will exit if any of the following conditions are met: the defrosting time reaches the preset duration, the fin temperature reaches the defrosting exit temperature, or the outlet water temperature reaches the minimum defrosting water temperature.

9. The method according to claim 1, characterized in that, The step of adjusting the defrosting interval for the next ring-fin differential defrosting based on the duration of the current ring-fin differential defrosting operation specifically includes: If the defrosting operation time is less than or equal to 3 minutes, the next defrosting interval will be adjusted to the current baseline interval t plus the time compensation value t. k sum; If the defrosting operation time is greater than 3 minutes and less than or equal to 5 minutes, the next defrosting interval will remain unchanged. If the defrosting operation time is greater than 5 minutes but less than 8 minutes, the next defrosting interval will be adjusted to the current baseline interval t plus the time compensation value t. k difference; If the defrosting operation time is greater than or equal to 8 minutes, the next defrosting interval will be adjusted to the preset fixed interval. Wherein, the time compensation value t k It is the product of the current reference interval time t and the preset parameter k.

10. A heat pump system, characterized in that, The system includes a compressor, a four-way valve, a plate heat exchanger, a filter, a main electronic expansion valve, a controller, a finned heat exchanger, a gas-liquid separator, a high-pressure sensor, a low-pressure sensor, a finned temperature probe, an outdoor fan, an ambient temperature probe, an outlet water temperature probe, and an inlet water temperature probe. The controller is used to receive signals from various sensors and control the compressor, four-way valve, outdoor fan and main electronic expansion valve to perform the method described in any one of claims 1 to 9; The compressor's exhaust port is connected to port D of the four-way valve, port C of the four-way valve is connected to the refrigerant inlet of the plate heat exchanger, the refrigerant outlet of the plate heat exchanger is connected to the inlet of the main electronic expansion valve via the filter, the outlet of the main electronic expansion valve is connected to the refrigerant inlet of the finned heat exchanger, the refrigerant outlet of the finned heat exchanger is connected to port E of the four-way valve, and port S of the four-way valve is connected to the compressor's return port via the gas-liquid separator, forming a refrigerant circulation loop. The low-pressure sensor is located between the compressor return port and the S port of the four-way valve, and is used to detect the evaporation pressure and calculate the evaporation saturation temperature TE; the high-pressure sensor is located on the compressor exhaust pipe, which is connected between the compressor exhaust port and the D port of the four-way valve. The fin temperature probe is installed on the fin heat exchanger and is used to detect the fin temperature; the outdoor fan is installed corresponding to the fin heat exchanger; the ambient temperature probe is used to detect the outdoor ambient temperature. The outlet water temperature probe and the inlet water temperature probe are respectively installed at the water-side outlet and inlet of the plate heat exchanger to detect the outlet water temperature and the inlet water temperature.

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