Heat pump hot water system and heat exchanger ice prevention method

Abstract

The application relates to a heat pump hot water system and a heat exchanger anti-icing method. The heat pump hot water system comprises an inner circulation pipeline, a heat exchanger, a drainage pipeline, a water feeding pipeline, a three-way valve, a waterway heater, a first temperature sensor, a second temperature sensor, a water pump, an electric stop valve, an ambient temperature sensor and a controller. The inner circulation pipeline comprises a first pipeline, a second pipeline and a connecting pipeline. The first end of the first pipeline is in communication with the water outlet of the heat exchanger, the second end of the first pipeline is in communication with the first water inlet of the three-way valve, one end of the drainage pipeline is in communication with the water outlet of the three-way valve, and the first end of the second pipeline is in communication with the water inlet of the heat exchanger. The circulating water is heated by the waterway heater, the heat is uniformly transferred to the whole heat exchanger through the water body, there is no local overheating phenomenon, and the risk of plate damage is completely avoided.

Description

Technical Field

[0001] This application relates to the field of heat pump systems, and more particularly to a heat pump hot water system and a method for preventing icing of the heat exchanger. Background Technology

[0002] In heat pump water heating systems, plate heat exchangers typically play a crucial role—serving as the condenser-side heat exchange element to achieve efficient heat exchange between the refrigerant and domestic hot water. Specifically, the high-temperature, high-pressure gaseous refrigerant discharged from the compressor enters the refrigerant channel of the plate heat exchanger, where it transfers heat to the flowing cold water on the other side via metal plates, thus producing hot water to meet the user's needs. Because plate heat exchangers can achieve a large heat exchange area within a relatively small volume, and the refrigerant and water flow in a near-countercurrent manner, their heat exchange efficiency is significantly higher than that of traditional shell-and-tube or coaxial heat exchangers, making them one of the core components of modern heat pump water heating units.

[0003] However, in practical engineering applications, the freeze resistance of plate heat exchangers has always been a recognized weakness in the industry. Unlike shell-and-tube heat exchangers, plate heat exchangers have narrow internal flow channels, small hydraulic diameters, and plate thicknesses typically only 0.4~0.6mm. Furthermore, the contact points between the plates are sealed using brazing (copper or nickel brazing) or rubber gaskets. Once the ambient temperature drops below freezing (0℃), if the heat pump unit unexpectedly shuts down due to malfunction, maintenance, power outage, or standby, and the water circuit is not forcibly evacuated before shutdown, the water remaining in the narrow channels of the plate heat exchanger will gradually freeze. The freezing process is accompanied by approximately 9% volume expansion. This expansion generates enormous internal stress within the confined gaps between the plates. This stress is sufficient to cause irreversible plastic deformation of the stainless steel plates, or even directly crack the brazing points or welds, leading to cross-contamination between the refrigerant and water, ultimately causing the entire heat pump system to fail.

[0004] To address the aforementioned freezing risks, existing technologies have proposed several anti-freezing measures. The most common approach is to directly attach or wrap electric heating tape (self-regulating or constant-power heating tape) to the outer surface of the plate heat exchanger. When energized, the heating tape heats up, conducting heat to the shell and residual water inside the plate heat exchanger, maintaining its temperature above freezing. While this method effectively prevents freezing, it also has several inherent drawbacks: First, as an independent external heating element, the heating tape requires additional power lines, temperature controllers, sensors, and protection devices, significantly increasing equipment costs and installation complexity. Second, the heating power distribution of the heating tape is difficult to achieve completely uniformly, easily leading to hot spots in the contact area with the plate, causing localized overheating. Long-term operation may accelerate the aging of the brazing material or even cause the plate to crack. Summary of the Invention

[0005] This application provides a heat pump water heating system and a method for preventing icing in a heat exchanger, in order to solve the technical problems mentioned in the background art.

[0006] In a first aspect, this application provides a heat pump water heating system, including an internal circulation pipeline, a heat exchanger, a drainage pipeline, a water supply pipeline, a three-way valve, a water heater, a first temperature sensor, a second temperature sensor, a water pump, an electric shut-off valve, an ambient temperature sensor, and a controller. The internal circulation pipeline includes a first pipeline, a second pipeline, and a connecting pipeline; the first end of the first pipeline is connected to the outlet of the heat exchanger, and its second end is connected to the first inlet of the three-way valve; one end of the drain pipeline is connected to the outlet of the three-way valve; the first end of the second pipeline is connected to the inlet of the heat exchanger; the second end of the second pipeline, one end of the water supply pipeline, and the first end of the connecting pipeline are connected; and the second end of the connecting pipeline is connected to the second outlet of the three-way valve. The electric shut-off valve is installed on the water supply pipeline, the water pump and the water heater are installed on the internal circulation pipeline, and the ambient temperature sensor is used to detect the ambient temperature; the ambient temperature sensor is used to detect the ambient temperature, the first temperature sensor is used to detect the water temperature on the outlet side of the heat exchanger, and the second temperature sensor is used to detect the water temperature on the inlet side of the heat exchanger. The ambient temperature sensor, the first temperature sensor, the second temperature sensor, the water pump, the three-way valve, and the water heater are all connected to the controller via signal connection.

[0007] According to one embodiment of this application, at least one water flow sensor is included, which is installed on the internal circulation pipeline for detecting the flow rate of water in the internal circulation pipeline.

[0008] According to one embodiment of this application, at least one drain valve is installed on the internal circulation pipeline, the drain valve being used to drain the water in the internal circulation pipeline and the water inside the heat exchanger.

[0009] According to one embodiment of this application, the second pipeline includes a first pipeline, a second pipeline, and a third pipeline. The first end of the first pipeline is connected to the inlet of the water pump, and the second end of the first pipeline, the first end of the connecting pipeline, and one end of the water delivery pipeline are connected by a tee joint. One end of the second pipeline is connected to the outlet of the water pump, and the other end is connected to the inlet of the heat exchanger. One end of the third pipeline is connected to an opening on the side wall of the second pipeline, and the other end is connected to the drain valve.

[0010] According to one embodiment of this application, the first pipeline includes a first pipe and a second pipe. One end of the first pipe is connected to the inlet of the three-way valve, and the other end is connected to the outlet of the water heater. One end of the second pipe is connected to the inlet of the water heater, and the other end is connected to the outlet of the heat exchanger.

[0011] According to one embodiment of this application, a heat pump system is included, the heat pump system including a refrigerant circulation line for connection to the heat exchanger.

[0012] Secondly, this application provides a method for preventing icing of heat exchangers in the aforementioned heat pump water heating system. The method includes the following steps: Step 1: Use an ambient temperature sensor to obtain the ambient temperature and record the downtime of the heat pump system. Use the first temperature sensor and the second temperature sensor to detect the water temperature on the outlet side and the water temperature on the inlet side of the heat exchanger, respectively, and calculate the rate of change of water temperature on the inlet side of the heat exchanger per unit time. The second step involves generating an icing risk index based on the ambient temperature, the downtime of the heat pump system, and the water temperature change rate. Then, according to the risk level assigned to the icing risk index, an anti-icing strategy corresponding to that risk level is implemented. The anti-icing strategy includes at least the following: The first strategy is to execute the first strategy to make the water in the circulating water circuit formed by the internal circulation pipeline and the heat exchanger circulate. The second strategy involves implementing the second strategy to circulate the water in the circulating water circuit formed by the internal circulation pipe and the heat exchanger and intermittently heat the water in the circulating water circuit. The third strategy involves implementing the third strategy to circulate the water in the circulating water circuit formed by the internal circulation pipe and the heat exchanger, and continuously heating the water in the circulating water circuit until the water temperature in the circulating water circuit reaches a safe temperature.

[0013] According to one embodiment of this application, the first strategy includes: controlling the electric shut-off valve to close, controlling the three-way valve to switch to internal circulation mode, driving the water pump to operate at 10%~20% of the rated flow, and turning off the water circuit heater.

[0014] According to one embodiment of this application, the second strategy includes: controlling the electric shut-off valve to close, controlling the electric three-way valve to switch to internal circulation mode, driving the water pump to operate at 40%~60% of the rated flow rate, controlling the water circuit heater to operate in a periodic working mode, and dynamically adjusting the opening and closing time of the water circuit heater according to the water temperature change rate.

[0015] According to one embodiment of this application, the third strategy includes: controlling the electric shut-off valve to close, controlling the three-way valve to switch to internal circulation mode, driving the water pump to operate at 100% of the rated flow rate, and controlling the water circuit heater to continuously heat until the water temperature in the circulating water circuit reaches a preset safety threshold.

[0016] According to one embodiment of this application, the icing risk index is divided into three levels: low risk, medium risk, and high risk. When the ambient temperature is within the first temperature range, it is determined to be a low-risk level, and the first strategy is executed. When the ambient temperature is within the second temperature range and the water temperature change rate exceeds the first change rate threshold, it is determined to be at a medium risk level, and the second strategy is executed accordingly. When the ambient temperature is within the third temperature range and the water temperature change rate exceeds the second change rate threshold, it is determined to be at a high risk level, and the third strategy is executed accordingly; the first temperature range is greater than the second temperature range, the second temperature range is greater than the third temperature range, and the second change rate threshold is less than the first change rate threshold.

[0017] According to one embodiment of this application, the icing risk index is divided into three levels: low risk, medium risk, and high risk. When the ambient temperature is within the first temperature range, it is determined to be of low risk level, and the first strategy is executed. When the ambient temperature is within the second temperature range and the downtime of the heat pump system falls within the first downtime threshold, it is determined to be at a medium risk level, and the second strategy is executed accordingly. When the ambient temperature is within the third temperature range and the downtime of the heat pump system falls within the second downtime threshold, it is determined to be at a high risk level, and the third strategy is executed accordingly; the second downtime threshold is greater than the first downtime threshold.

[0018] The technical solutions provided in this application have the following advantages compared with the prior art: In the first aspect, when the ambient temperature sensor in the heat pump water heating system provided in this application detects a low temperature and the unit stops, the controller first controls the three-way valve to switch to the internal circulation mode, and at the same time the electric shut-off valve prevents water from flowing to the user side. Then, based on the water temperature and rate of change fed back by the first temperature sensor and the second temperature sensor, the freezing risk level is dynamically determined. When the risk is low, only the water pump is driven to maintain water flow at a low flow rate. When the risk is medium, the water heater is started to heat intermittently and the start-stop cycle is adjusted. When the risk is high, the water heater is continuously heated to a safe temperature. Throughout the process, the controller continuously collects the ambient temperature, water temperature and shutdown time without any manual intervention.

[0019] Compared with the solution of directly attaching electric heating tape to the outer surface of plate heat exchanger, it has at least the following advantages: First, electric heating tape requires additional power supply lines, thermostats, sensors and protection devices, resulting in high cost and complex installation. This embodiment directly utilizes the original water pump and piping system of the heat pump water heating system, only requiring simple modification to the piping system, adding only water heaters and a small number of low-cost valves and sensors. This design avoids the large number of external auxiliary devices required for electric heating tape, reducing the total equipment cost and installation complexity. Moreover, all added components are standardized, low-cost general-purpose parts, which are easy to mass-produce and maintain.

[0020] Secondly, unlike previous electric heating cables, which had uneven heating power distribution, local hot spots leading to overheating of the plates, aging of brazing materials, and even cracking, this embodiment uses a water heater to heat the circulating water. The heat is then evenly transferred to the entire heat exchanger via water convection, eliminating local overheating and completely avoiding the risk of plate damage.

[0021] In addition, this embodiment adopts a graded anti-icing strategy, which executes the corresponding strategy according to the real-time risk, significantly reducing standby power consumption compared to the continuous power supply of the electric heating tape.

[0022] The heat exchanger anti-icing method provided in the second aspect of this application generates an icing risk index based on ambient temperature, heat pump system downtime, and water temperature change rate. Based on the risk level that the icing risk index falls into, an anti-icing strategy corresponding to that risk level is executed. In this way, the optimal anti-icing action can be automatically switched according to the actual cooling rate, environmental severity, and heat pump downtime, achieving on-demand response and precise intervention. Attached Figure Description

[0023] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[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, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] One or more embodiments are illustrated by way of example with reference numerals in the accompanying drawings. These illustrations do not constitute a limitation on the embodiments. Elements with the same reference numerals in the drawings are denoted as similar elements. Unless otherwise stated, the figures in the drawings are not to be limited by scale.

[0026] Figure 1 A schematic diagram of a heat pump water heating system provided in an embodiment of this application; Figure 2 Connection diagram of heat exchanger, internal circulation pipeline, drainage pipeline and water supply pipeline provided for embodiments of this application; Figure 3 A schematic diagram showing the connection of the controller, ambient temperature sensor, first temperature sensor, second temperature sensor, water heater, electric three-way valve, water flow sensor, water pump, drain valve and electric shut-off valve provided for embodiments of this application; Figure 4 This is a schematic diagram of a heat exchanger anti-icing method provided in an embodiment of this application.

[0027] Explanation of reference numerals in the attached figures: 1. Heat pump system; 101. Refrigerant outlet pipe; 102. Refrigerant inlet pipe; 2. Heat exchanger; 3. First temperature sensor; 4. Second temperature sensor; 5. Water heater; 6. Water flow sensor; 7. Water pump; 8. Drain valve; 9. Electric three-way valve; 10. Electric shut-off valve; 11. Drainage pipe; 12. First pipe; 121. First pipeline; 122. Second pipeline; 13. Water supply pipe; 14. Second pipeline; 141. Pipe 1; 142. Pipe 2; 143. Pipe 3; 15. Connecting pipe; 16. T-joint; 17. Ambient temperature sensor; 18. Controller. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0029] The following disclosure provides numerous different embodiments or examples for implementing various structures of the invention. To simplify the disclosure, specific examples of heat pump water heating systems, control methods, and arrangements are described below. These are merely examples and are not intended to limit the invention. Furthermore, reference numerals and / or letters may be repeated in different examples. Such repetition is for simplification and clarity and does not in itself indicate a relationship between the various embodiments and / or arrangements discussed.

[0030] For ease of description, spatial relative terms may be used in the text to describe the relative position or movement of one element or feature relative to another element or feature, as shown in the figure. These relative terms include, for example, "inside," "outside," "middle," "outer," "below," "below," "above," "front," "back," etc. Such spatial relative terms are intended to include different orientations of the device in use or operation, other than those depicted in the figure. For example, if the device in the figure undergoes a positional flip, orientation change, or change of motion, these directional indications will change accordingly. For instance, an element described as "below other elements or features" or "below other elements or features" will subsequently be oriented "above other elements or features" or "above other elements or features." Therefore, the example term "below" can include both upper and lower orientations. The device may be otherwise oriented (rotated 90 degrees or in other directions), and the spatial relative descriptors used in the text will be interpreted accordingly.

[0031] The first aspect of this application provides a heat pump water heating system with anti-icing function, which can automatically prevent residual water inside the heat exchanger 2 from freezing under low-temperature shutdown conditions, thereby avoiding damage to the heat exchanger 2 due to freezing expansion. Specifically, the heat pump water heating system includes an internal circulation pipeline, a heat exchanger 2, a drain pipeline 11, a water supply pipeline 13, a three-way valve, a water heater 5, a first temperature sensor 3, a second temperature sensor 4, a water pump 7, an electric shut-off valve 10, an ambient temperature sensor 17, and a controller 18; the internal circulation pipeline includes a first pipeline 12, a second pipeline 14, and a connecting pipe 15; the first end of the first pipeline 12 is connected to the outlet of the heat exchanger 2, and its second end is connected to the first inlet of the three-way valve; one end of the drain pipeline 11 is connected to the outlet of the three-way valve; the first end of the second pipeline 14 is connected to the inlet of the heat exchanger 2; and the second end of the second pipeline 14 is connected to the water supply pipeline 15. One end of the pipeline 13 is connected to the first end of the connecting pipe 15, and the second end of the connecting pipe 15 is connected to the second outlet of the three-way valve; the electric shut-off valve 10 is installed on the water supply pipeline 13, the water pump 7 and the water heater 5 are installed on the internal circulation pipeline, and the ambient temperature sensor 17 is used to detect the ambient temperature; the first temperature sensor 3 is used to detect the water temperature on the outlet side of the heat exchanger 2, and the second temperature sensor 4 is used to detect the water temperature on the inlet side of the heat exchanger 2; the ambient temperature sensor 17, the first temperature sensor 3, the second temperature sensor 4, the water pump 7, the three-way valve and the water heater 5 are all connected to the controller 18 for signal transmission.

[0032] In this embodiment, when the ambient temperature sensor 17 detects a low temperature and the unit shuts down, The controller 18 first controls the three-way valve to switch to the internal circulation mode, so that the first pipeline 12, the connecting pipeline 15, the second pipeline 14 and the heat exchanger 2 form a closed circulation loop. At the same time, the electric shut-off valve 10 prevents water from flowing to the user side. Then, based on the water temperature and change rate fed back by the first temperature sensor 3 and the second temperature sensor 4, the freezing risk level is dynamically judged. When the risk is low, only the water pump 7 is driven to maintain water flow at a low flow rate. When the risk is medium, the water heater 5 is started to heat intermittently and the start-stop cycle is adjusted. When the risk is high, the water heater is continuously heated to a safe temperature. Throughout the process, the controller 18 continuously collects the ambient temperature, water temperature and downtime, without any manual intervention.

[0033] Compared with the solution of directly attaching electric heating tape to the outer surface of plate heat exchanger, this embodiment has at least the following advantages: First, electric heating tape requires additional power supply lines, thermostats, sensors and protection devices, resulting in high cost and complex installation. This embodiment directly utilizes the original water pump 7 and piping system of the heat pump water heating system, and only makes simple modifications to the piping system, adding only water heater 5 and a small number of low-cost valves and sensors. This design avoids the large number of external auxiliary devices required for electric heating tape, reduces the total equipment cost and installation complexity, and all added components are standardized, low-cost general-purpose parts, which are easy to mass-produce and maintain.

[0034] Secondly, unlike previous electric heating cables, which had uneven heating power distribution, local hot spots leading to overheating of the plates, aging of brazing materials, and even cracking, in this embodiment, the circulating water is heated by the water heater 5, and the heat is evenly transferred to the entire heat exchanger 2 through water convection, so there is no local overheating phenomenon and the risk of plate damage is completely avoided.

[0035] In addition, this embodiment adopts a graded anti-icing strategy, which executes the corresponding strategy according to the real-time risk, significantly reducing standby power consumption compared to the continuous power supply of the electric heating tape.

[0036] In this embodiment, when the ambient temperature sensor 17, the first temperature sensor 3, and the second temperature sensor 4 detect a risk of low-temperature shutdown, the controller 18 can control the three-way valve to switch to the internal circulation loop, drive the water pump 7 to continuously flow water in the heat exchanger 2 and the internal circulation pipeline, and start the water heater 5 as needed for compensatory heating. This completely avoids the additional component costs, local overheating damage to the plates, and energy waste caused by the electric heating tape. The heat pump water heating system also includes a heat pump system 1, which generates high-temperature, high-pressure refrigerant. Internally, it contains conventional components such as a compressor, condenser, expansion valve, and evaporator. The refrigerant circulation pipeline of the heat pump water heating system is connected to the refrigerant-side interface of the heat exchanger 2, providing a heat source to the heat exchanger 2. The heat exchanger 2 is equipped with an inlet and an outlet. The inlet receives low-temperature water from the internal circulation pipeline, and the outlet delivers the heated water after absorbing heat.

[0037] In normal heating mode, the high-temperature refrigerant from the heat pump system 1 enters the refrigerant channel of the heat exchanger 2 and transfers heat to the cold water flowing in the water channel. The cold water is heated and becomes hot water, which flows out from the outlet of the heat exchanger 2 and then flows into the drain pipe 11 through the first pipe 12 and the three-way valve.

[0038] Specifically, the refrigerant circulation pipeline of the heat pump system 1 includes a refrigerant outlet pipe 101 and a refrigerant inlet pipe 102. One end of the refrigerant outlet pipe is connected to the refrigerant inlet of the heat exchanger 2, and one end of the refrigerant inlet pipe 102 is connected to the refrigerant outlet of the heat exchanger 2.

[0039] In this embodiment, the heat exchanger 2 is a brazed plate heat exchanger, which has the characteristics of compact structure and high heat exchange efficiency. Its interior is formed by multiple layers of stainless steel plates stacked to form alternating refrigerant channels and water channels.

[0040] In this embodiment, the internal circulation pipeline is a key component of the entire anti-icing system. Its function is to form a closed water circulation loop when anti-icing is required, so that residual water can continuously flow inside the heat exchanger 2 and in the pipeline, avoiding stagnant freezing; at the same time, when heating is required, the water flows through the water heater 5 during the circulation process and is heated.

[0041] It should be noted that the three-way valve has one inlet and two outlets. For ease of description, the port connected to the first pipe 12 is referred to as the inlet, the port connected to the drain pipe 11 is referred to as the first outlet, and the port connected to the connecting pipe 15 is referred to as the second outlet. In this embodiment, the first end of the first pipe 12 is connected to the outlet of the heat exchanger 2, the second end of the first pipe 12 is connected to the inlet of the three-way valve, one end of the drain pipe 11 is connected to the first outlet of the three-way valve, the first end of the second pipe 14 is connected to the inlet of the heat exchanger 2, the second end of the second pipe 14, one end of the water supply pipe 13, and the first end of the connecting pipe 15 are interconnected, and the second end of the connecting pipe 15 is connected to the second outlet of the electric three-way valve 9.

[0042] When the electric three-way valve 9 switches to the internal circulation mode, the inlet of the electric three-way valve 9 is connected to the second outlet. At this time, the hot water from the outlet of the heat exchanger 2 flows through the first pipe 12, the three-way valve, and the connecting pipe 15 in sequence, and then flows into the second pipe 14. Finally, it flows back to the inlet of the heat exchanger 2 through the second pipe 14, thus forming a closed internal circulation loop.

[0043] In some embodiments, the second end of the second pipeline 14, one end of the water supply pipeline 13, and the first end of the connecting pipeline 15 can be connected by a tee joint 16, or the three can be interconnected by welding or flaring.

[0044] In this embodiment, the three-way valve is preferably an electric three-way valve 9, whose valve core can rotate or translate under the control signal of the controller 18, thereby switching the internal flow channel to connect the inlet to the first outlet or to connect the inlet to the second outlet.

[0045] In this embodiment, the first pipeline 12 includes a first pipe 121 and a second pipe 122. One end of the first pipe 121 is connected to the inlet of the electric three-way valve 9, and the other end is connected to the outlet of the water heater 5. One end of the second pipe 122 is connected to the inlet of the water heater 5, and the other end is connected to the outlet of the heat exchanger 2.

[0046] Furthermore, the second pipeline 14 includes a first pipeline 141, a second pipeline 142, and a third pipeline 143. The first end of the first pipeline 141 is connected to the inlet of the water pump 7. The second end of the first pipeline 141, the end of the connecting pipeline 15 away from the electric three-way valve 9, and the end of the water supply pipeline 13 are connected by a three-way connector 16. One end of the second pipeline 142 is connected to the outlet of the water pump 7, and the other end is connected to the inlet of the heat exchanger 2. One end of the third pipeline 143 is connected to the opening on the side wall of the second pipeline 142, and the other end is connected to the drain valve 8.

[0047] In some embodiments, the water pump 7 is preferably a DC brushless centrifugal pump with multi-speed adjustment function and low power consumption standby capability.

[0048] In some embodiments, the water heater 5 is preferably an electric heating tube heater, which has a stainless steel heating tube and a flow cavity inside. Water is heated when it flows through the heater. The water heater 5 has a multi-level power adjustment function and can output different proportions of heating power according to control commands.

[0049] In some embodiments, the first temperature sensor 3 is installed near the outlet side of the heat exchanger 2, specifically on the second pipe 122 or inside the outlet port of the heat exchanger 2, for detecting the water temperature at the outlet side of the heat exchanger 2. The second temperature sensor 4 is installed near the inlet side of the heat exchanger 2, specifically on the second pipe 142 or inside the inlet port of the heat exchanger 2, for detecting the water temperature at the inlet side of the heat exchanger 2. The output signals of both the first temperature sensor 3 and the second temperature sensor 4 are connected to the analog input port of the controller 18 via signal lines.

[0050] In some embodiments, the first temperature sensor 3 and the second temperature sensor 4 may be NTC thermistors or PT1000 platinum resistance thermometers, with a measurement accuracy of not less than ±0.3℃.

[0051] In this embodiment, the ambient temperature sensor 17 is used to detect the atmospheric temperature of the environment in which the heat pump water heating system is located. The ambient temperature sensor 17 is usually installed on the shaded side of the unit casing, away from heat sources and air vents, so as to ensure that the measured value can accurately reflect the outdoor temperature. The ambient temperature sensor 17 also adopts the NTC or PT1000 type, and its output signal is connected to the controller 18.

[0052] In this embodiment, the controller 18 is the control core of the heat pump water heating system, and typically includes a central processing unit, memory, input / output interfaces, communication interfaces, and a power management module. The controller 18 has a pre-installed anti-icing control algorithm program, which can receive signals from the first temperature sensor 3, the second temperature sensor 4, and the ambient temperature sensor 17. After processing, it outputs control commands to the actuators such as the water pump 7, the electric three-way valve 9, the water heater 5, and the drain valve 8.

[0053] To monitor water flow, the heat pump water heating system also includes at least one water flow sensor 6. The water flow sensor 6 is installed on the internal circulation pipe, for example, on pipe 142 or near the outlet of the water pump 7. The controller 18 reads the signal from the water flow sensor 6 to determine whether the water flow rate in the internal circulation pipe is normal, thereby confirming whether the water pump 7 is working effectively and whether there is air blockage or leakage in the pipe. During the purging operation, the water flow sensor 6 can also be used to determine whether the accumulated water has been completely drained. When the purging valve 8 is opened, if the water flow sensor 6 detects that the flow rate continuously decreases to near zero and remains so for several seconds, it indicates that there is no residual water in the system.

[0054] Optionally, the water flow sensor 6 can be a turbine flow meter or a Hall effect flow switch, whose output pulse frequency or analog voltage is proportional to the instantaneous flow rate.

[0055] In some embodiments, the drain valve 8 is an electric solenoid valve with a normally closed characteristic, that is, it is closed when the power is off and opens when the power is on. When the controller 18 determines that a draining operation needs to be performed, it outputs AC power to the coil of the drain valve 8, the valve core is lifted, and the accumulated water can be discharged from the drain valve 8. After the draining is completed, the controller 18 cuts off the power supply to the drain valve 8, and the valve closes automatically.

[0056] It should be noted that the above-mentioned pipeline connection uses multiple pipe sections and joints. In actual manufacturing, several pipe sections can be integrally formed or bends can be used to reduce the number of joints, depending on the spatial layout, as long as the fluid communication relationship is in accordance with the above description.

[0057] The working principle of the heat pump water heating system in this embodiment will be explained in detail below, combining the normal heating mode and the anti-icing mode.

[0058] Under normal heating conditions, the ambient temperature is usually above 5℃, so there is no risk of freezing. At this time, the electric shut-off valve 10 opens, and the controller 18 controls the electric three-way valve 9 to connect the inlet and the first outlet. The user's water enters the heat exchanger 2 through the water supply pipeline 13, passing through the first pipeline 141, the water pump 7, and the second pipeline 142. The water exchanges heat with the refrigerant inside the heat exchanger 2, and the temperature rises to form high-temperature water. Then, the high-temperature water flows into the drain pipeline 11 through the second pipeline 122, the first pipeline 121, the inlet of the electric three-way valve 9, and the first outlet of the electric three-way valve 9.

[0059] In anti-icing mode, the controller 18 executes different anti-icing strategies based on the icing risk level. These strategies will be described in detail in the second embodiment; here, only the system's response to control commands is explained.

[0060] When the first strategy (low risk) is executed, controller 18 controls the electric shut-off valve 10 to close, controls the electric three-way valve 9 to connect the inlet of the electric three-way valve 9 to the second outlet, shuts off the water heater 5, and adjusts the speed of water pump 7 to output only 10% to 20% of the rated flow. At this time, the water flows slowly in the internal circulation pipeline and heat exchanger 2, and the flowing water is less likely to form ice crystals, thus preventing the water inside heat exchanger 2 from freezing. Due to the very low flow rate, the power consumption of water pump 7 is low, making it very energy-efficient.

[0061] When the second strategy (medium risk) is implemented, the controller 18 also controls the electric shut-off valve 10 to close and switches the electric three-way valve 9 to internal circulation mode (i.e., controls the electric three-way valve 9 to connect the inlet of the electric three-way valve 9 to the second outlet). At the same time, the speed of the water pump 7 is increased to 40% to 60% of the rated flow rate, which speeds up the water circulation and facilitates uniform heat distribution. The controller 18 controls the water heater 5 according to a periodic working mode, for example, turning it on for 5 minutes and stopping it for 10 minutes, and dynamically adjusts the start-stop time ratio according to the water temperature change rate. When the water heater 5 is powered on, the circulating water flows through it and is heated, and the water temperature gradually rises, maintaining the water temperature above the freezing point.

[0062] When the third strategy (high risk) is executed, the controller 18 controls the electric shut-off valve 10 to close and switches the electric three-way valve 9 to the internal circulation mode, drives the water pump 7 to run at full speed with 100% rated flow, and controls the water heater 5 to continuously heat and raise the temperature of the circulating water. At this time, the controller 18 reads the value of the second temperature sensor 4 in real time. When the water temperature reaches the preset safe temperature (e.g., 8°C), it is considered that the water inside the heat exchanger 2 is completely safe and there is no risk of freezing. It should be noted that when the user is not at home, i.e., the heat pump water heating system is in a shutdown state, and the shutdown time is greater than 24 hours or 36 hours, regardless of whether the first, second, or third strategy mentioned above is executed, the drain valve 8 will be opened. Circulating water will enter the drain valve 8 from the internal circulation pipe under the action of gravity and system pressure and be discharged. The controller 18 monitors the drainage flow rate through the water flow sensor 6. When the flow rate is detected to be close to zero and remains so for 3 to 5 seconds, it determines that the water has been drained and immediately closes the drain valve 8, then controls the shutdown of all components (water heater 5, water pump 7). After the above operations, there is no liquid water residue in the heat exchanger 2 and the internal circulation pipe, and even if the ambient temperature drops to tens of degrees below zero, there will be no freezing damage.

[0063] In some embodiments, to further improve the reliability and automation of the system, the controller 18 can also be connected to a wireless communication module to send unit status and anti-icing action information to the user's mobile phone or cloud platform for remote monitoring and maintenance.

[0064] In summary, this heat pump hot water system has the following significant advantages: First, the system does not require additional electric heating tape and its matching power supply lines, dedicated thermostats, and protection devices. Instead, it directly reuses the original water pump 7 of the heat pump system. Only simple modifications are made to the pipeline, and a few low-cost standardized components such as a three-way valve, an electric shut-off valve 10, a drain valve 8, a first temperature sensor 3, a second temperature sensor 4, and an ambient temperature sensor 17 are added to achieve complete anti-icing function. This significantly reduces the total equipment cost and on-site installation difficulty, which is conducive to large-scale production and promotion. Second, traditional electric heating tapes are prone to forming hot spots in local areas in contact with the plate due to uneven heating power distribution. Long-term operation may lead to aging of the brazing material or even cracking of the plate. In this embodiment, the circulating water is heated by the water heater 5, and the heat is evenly transferred to the entire heat exchanger 2 through water convection. There is no risk of local overheating, which completely avoids plate damage. At the same time, the electric shut-off valve 10 in the internal circulation pipeline can effectively prevent hot water from flowing back to the user side, further improving system safety. Third, the controller 18 can generate an icing risk index based on the ambient temperature, water temperature change rate, and the downtime of the heat pump system 1, and automatically execute a graded anti-icing strategy. That is, in low-risk situations, only the water pump 7 is driven to maintain water flow at a low flow rate (extremely low power consumption); in medium-risk situations, the water heater 5 is started for intermittent heating and the start-stop cycle is dynamically adjusted (avoiding ineffective energy consumption); in high-risk situations, continuous heating is carried out to a safe temperature. This on-demand response working mode has a significant energy-saving effect compared to the passive heating method of continuously energizing the electric heating tape. Fourth, when the system is shut down for a long time, it can automatically perform forced evacuation to ensure that there is no liquid water residue in the heat exchanger 2 and the internal circulation pipeline. Even in extreme low temperatures, it will not be damaged by freezing expansion, thereby greatly extending the service life of the plate heat exchanger.

[0065] A second aspect of this application provides a method for preventing icing in a heat exchanger, used to prevent icing from occurring in the heat exchanger 2 of the heat pump hot water system in the first embodiment. The method is executed by a controller 18 and includes the following steps: Step 1: Use ambient temperature sensor 17 to obtain ambient temperature, record the downtime of heat pump system 1, use first temperature sensor 3 and second temperature sensor 4 to detect the water temperature on the outlet side and the water temperature on the inlet side of heat exchanger 2 respectively, and calculate the water temperature change rate. The second step involves generating an icing risk index based on the ambient temperature, the downtime of heat pump system 1, and the rate of water temperature change. Then, according to the risk level assigned to the icing risk index, an anti-icing strategy corresponding to that risk level is implemented. The anti-icing strategy includes at least the following: The first strategy is to execute the first strategy to make the water in the circulating water circuit formed by the internal circulation pipeline and heat exchanger 2 circulate. The second strategy is to implement the second strategy so that the water in the circulating water circuit formed by the internal circulation pipe and heat exchanger 2 circulates and intermittently heats the water in the circulating water circuit. The third strategy involves implementing the third strategy to circulate the water in the circulating water circuit formed by the internal circulation pipe and heat exchanger 2, and continuously heating the water in the circulating water circuit until the water temperature in the circulating water circuit reaches a safe temperature.

[0066] In this embodiment, the controller 18 uses the ambient temperature obtained by the ambient temperature sensor 17, denoted as Ta. The ambient temperature value detected by the ambient temperature sensor 17 reflects the atmospheric temperature at the location of the unit and is the primary factor in determining the risk of icing. Considering that the sensor may be affected by solar radiation or wind, the controller 18 can perform median filtering on multiple consecutive sampled values ​​to eliminate instantaneous disturbances.

[0067] In this embodiment, in the first step, the controller 18 uses the second temperature sensor 4 to detect the water temperature on the inlet side of the heat exchanger 2, denoted as T_in. The second temperature sensor 4 should be installed close to the inlet of the heat exchanger 2. The controller 18 uses the first temperature sensor 3 to detect the water temperature on the outlet side of the heat exchanger 2, denoted as T_out. The first temperature sensor 3 should be installed close to the outlet of the heat exchanger 2.

[0068] The water temperature change rate is calculated as follows: Controller 18 calculates the water temperature change rate dT / dt based on the time series of T_in or T_out. Specifically, every sampling period Δt (in minutes), the difference ΔT between the current water temperature T_now and the water temperature T_prev of the previous period is calculated. The change rate dT / dt = ΔT / Δt, in °C / min. In this embodiment, the change rate of the inlet water temperature T_in is preferred because the inlet side is closer to the ambient cold source and is more sensitive to changes. It is important to know that the water temperature change rate is a key indicator for predicting the freezing trend; the larger the negative value (i.e., the faster the drop), the sooner the freezing point will be reached if no intervention is provided.

[0069] In the first step, the controller 18 also records the downtime t_off of the heat pump system 1. It should be noted that the downtime is accumulated from the moment when the compressor of the heat pump system 1 stops running.

[0070] Specifically, the controller 18 integrates a timer module that accumulates counts in seconds. The controller 18 monitors the compressor operating status of the heat pump system 1 in real time (obtained through compressor contactor feedback signals or current detection). When the controller 18 detects that the compressor has stopped running, it determines that the unit has entered a shutdown standby state, and at this time, the shutdown timer starts accumulating.

[0071] In some embodiments, due to noise in water temperature changes, the moving average method is typically used to calculate the average water temperature change rate over the most recent 3 to 5 periods.

[0072] In this embodiment, in the second step, the icing risk index is divided into three levels: low risk, medium risk, and high risk. This embodiment provides two specific implementation methods for determining the level corresponding to the icing risk index, as follows: The first method is based on a threshold for the rate of change of water temperature: First: When the ambient temperature Ta is within the first temperature range, it is determined to be of low risk level, and the first strategy is implemented.

[0073] In one alternative embodiment, the first temperature range is between 0°C and 2°C, i.e., the ambient temperature is greater than 0°C and less than 2°C.

[0074] Second, when the ambient temperature Ta is within the second temperature range and the water temperature change rate dT / dt exceeds the first change rate threshold, it is determined to be at a medium risk level, and the second strategy is implemented.

[0075] In one optional embodiment, the second temperature range is between -5°C and 0°C, i.e., the ambient temperature is greater than -5°C and less than 0°C. The first rate of change threshold is set to -0.1°C / min.

[0076] Third, when the ambient temperature Ta is within the third temperature range and the water temperature change rate dT / dt exceeds the second change rate threshold, it is judged as a high-risk level and the third strategy is implemented.

[0077] In one optional embodiment, the third temperature range is an ambient temperature Ta ≤ -5℃, and the second rate of change threshold is -0.5℃ / min.

[0078] In this embodiment, the second rate of change threshold is less than the first rate of change threshold, and the first temperature range, the second temperature range, and the third temperature range decrease sequentially, that is, the lower limit of the first temperature range is greater than the upper limit of the second temperature range, and the lower limit of the second temperature range is greater than the upper limit of the third temperature range.

[0079] The second method is based on the threshold of the downtime of heat pump system 1: First, when the ambient temperature Ta is within the first temperature range, it is determined to be of low risk level, and the first strategy is implemented.

[0080] In one alternative embodiment, the first temperature range is between 0°C and 2°C.

[0081] Second, when the ambient temperature Ta is within the second temperature range and the downtime t_off falls within the first downtime threshold, it is determined to be of medium risk level and the second strategy is executed.

[0082] In one optional embodiment, the second temperature range is between -5°C and 0°C. The first downtime threshold is set to 2 hours, meaning it is triggered when the downtime reaches or exceeds 2 hours.

[0083] Third, when the ambient temperature Ta is within the third temperature range and the downtime t_off falls within the second downtime threshold, it is judged as a high-risk level and the third strategy is executed.

[0084] In one optional embodiment, the third temperature range is ≤-5℃, and the second downtime threshold is set to 6 hours, i.e., it is triggered when the downtime reaches or exceeds 6 hours.

[0085] In this embodiment, the second shutdown time threshold is greater than the first shutdown time threshold, and the first temperature range, the second temperature range, and the third temperature range decrease sequentially.

[0086] It is important to note that the second downtime threshold is obtained by accumulating downtime based on the first downtime threshold. When the downtime reaches the first downtime threshold, triggering a medium-risk level, the system executes the second strategy, using intermittent heating to maintain the water temperature within a certain temperature range above freezing, ensuring the water remains in a liquid state. When the downtime further accumulates to the second downtime threshold, and the ambient temperature falls within the third temperature range, the water will still not freeze, but a high-risk level will be triggered, and the third strategy will be executed.

[0087] In this embodiment, executing the first strategy specifically includes the following operations: Controller 18 controls the electric shut-off valve 10 to close, ensuring the circulating water circuit is closed. Simultaneously, controller 18 controls the electric three-way valve 9 to switch to internal circulation mode. Then, controller 18 drives water pump 7 to operate at a first percentage of the rated flow rate. At this time, controller 18 shuts off the water circuit heater 5, preventing heating of the circulating water.

[0088] In one alternative embodiment, the first flow rate percentage is 10% to 20% of the rated flow rate.

[0089] It should be noted that the internal circulation mode means that the inlet of the electric three-way valve 9 is connected to the second outlet, and the first outlet is closed, so that the water flow forms a closed circulation between the heat exchanger 2, the first pipeline 12, the connecting pipeline 15, and the second pipeline 14.

[0090] In this embodiment, executing the second strategy specifically includes the following operations: controller 18 controls the electric shut-off valve 10 to close, and controller 18 controls the electric three-way valve 9 to switch to internal circulation mode. The controller 18 drives the water pump 7 to operate at a second percentage of the rated flow rate, and at the same time, the controller 18 controls the water heater 5 to operate in a periodic working mode.

[0091] It should be noted that the periodic working mode includes alternating on and off periods. For example, the on duration is set to 5 minutes and the off duration is set to 10 minutes, which means maintaining an alternating working mode of being on for 5 minutes and then off for 10 minutes.

[0092] In one alternative embodiment, the second flow rate percentage is 40% to 60% of the rated flow rate.

[0093] In some embodiments, the controller 18 dynamically adjusts the on-time and off-time of the water heater 5 based on the water temperature change rate dT / dt. For example, during the off-time of the water heater 5, if the water temperature change rate dT / dt is greater than -0.05℃ / min, indicating a slow decrease in water temperature, the off-time is extended and the on-time is shortened. Conversely, if the water temperature decreases rapidly, the off-time is shortened and the on-time is extended.

[0094] In this embodiment, the execution of the third strategy includes the following specific operations: the controller 18 controls the electric shut-off valve 10 to close, the controller 18 controls the electric three-way valve 9 to switch to the internal circulation mode, the controller 18 drives the water pump 7 to operate at the third flow percentage of the rated flow, and the controller 18 controls the water heater 5 to continuously heat until the water temperature in the circulating water circuit reaches the preset safety threshold.

[0095] In an optional embodiment, the third flow percentage is 100%, meaning that pump 7 operates at 100% of its rated flow rate.

[0096] In one optional embodiment, the preset safety threshold is 8°C.

[0097] It should be noted that when the total downtime of heat pump system 1 reaches or exceeds 24 hours or 36 hours, regardless of which strategy is currently being implemented, controller 18 will immediately interrupt the current strategy and execute a forced evacuation procedure.

[0098] The purging procedure includes: Controller 18 detects the water temperature T_in on the inlet side of heat exchanger 2. If T_in is below 2℃, it first performs short-term heating to raise the water temperature to the purging safety temperature, such as 5℃, and then opens the purging valve 8 to drain the water. If T_in is not lower than the forced purging heating threshold, it directly opens the purging valve 8 to drain the water. After purging is completed, controller 18 closes the purging valve 8, stops the water pump 7, shuts down the water heater 5, sets the electric three-way valve 9 to the fully closed state, and clears the total downtime accumulation variable to zero. The system then enters deep standby mode.

[0099] This forced evacuation mechanism ensures that the system is completely evacuated when the system is not in use for a long time, achieving zero-energy standby and fundamentally eliminating the risk of icing.

[0100] The numerical parameters mentioned in the above embodiments are all optional specific implementation methods and are not intended to limit the present invention. Those skilled in the art can adjust these values ​​within a reasonable range according to the actual application environment, such as a first temperature range, a second temperature range, a third temperature range, a first rate of change threshold, a second rate of change threshold, a first downtime threshold, and a second downtime threshold.

[0101] In summary, the heat exchanger anti-icing method proposed in Embodiment 2 achieves full-scenario, low-power, and high-reliability anti-icing protection for the plate heat exchanger 2 through the hierarchical decision algorithm embedded in the controller 18, and has the following significant advantages: First, the method uses ambient temperature Ta, water temperature change rate dT / dt, and unit shutdown time t_off as core criteria to construct a three-level icing risk index model of "low-risk, medium-risk, and high-risk," and dynamically selects the first strategy (low-speed internal circulation), the second strategy (intermittent heating and dynamic adjustment of start-stop cycle), or the third strategy (continuous heating to a safe temperature followed by complete evacuation) based on real-time data. This mechanism completely eliminates the timed or constant-temperature control mode of traditional solutions, and can automatically switch to the optimal anti-icing action according to the actual cooling rate, environmental severity, and user's absence time, truly achieving on-demand response and precise intervention.

[0102] Secondly, during low-risk conditions, only water pump 7 operates at 10% to 20% of its rated flow, consuming only a few watts. During medium-risk conditions, intermittent heating is used, and the heating duty cycle is compressed or extended in real time according to the water temperature change rate to avoid ineffective heating. Compared with the continuous power supply of electric heating tape, this method can prevent ice and consume less energy.

[0103] Third, the method introduces dual triggering conditions (temperature threshold + rate of change threshold / downtime threshold), so that even if a sensor is abnormal, the other condition can still trigger the corresponding level strategy.

[0104] Fourth, the forced evacuation mechanism will unconditionally evacuate when the total downtime exceeds 24 hours (or the user-defined value), completely eliminating the risk of freezing caused by sensor drift, heater failure or abnormal low temperature. It can ensure that the system is completely evacuated when no one is using it for a long time, achieving zero-energy standby.

[0105] In summary, the anti-icing method of this embodiment improves passive antifreeze to proactive intelligent decision-making with low control costs, achieving minimum energy consumption, minimal user intervention, and maximum environmental adaptability while ensuring the absolute safety of the heat exchanger.

[0106] It should be understood that the terminology used herein is for the purpose of describing particular exemplary embodiments only and is not intended to be limiting. Unless the context clearly indicates otherwise, the singular forms “a,” “an,” and “described” as used herein may also mean including the plural forms. The terms “comprising,” “including,” “containing,” and “having” are inclusive and therefore indicate the presence of the stated features, steps, operations, elements, and / or heat pump water heating systems and control methods, but do not exclude the presence or addition of one or more other features, steps, operations, elements, heat pump water heating systems and control methods, and / or combinations thereof. The method steps, processes, and operations described herein are not construed as requiring them to be performed in a specific order as described or illustrated, unless the order of performance is explicitly indicated. It should also be understood that additional or alternative steps may be used.

[0107] Although terms such as first, second, third, etc., may be used in this document to describe multiple components, heat pump water heating systems and control methods, areas, layers, and / or sections, these components, heat pump water heating systems and control methods, areas, layers, and / or sections should not be limited by these terms. These terms may be used only to distinguish one component, heat pump water heating system and control method, area, layer, or section from another area, layer, or section. Unless the context clearly indicates otherwise, terms such as "first," "second," and other numerical terms used herein do not imply order or sequence. Therefore, the first component, heat pump water heating system and control method, area, layer, or section discussed below may be referred to as a second component, heat pump water heating system and control method, area, layer, or section without departing from the teachings of the exemplary embodiments.

[0108] The above description is merely a specific embodiment of the present invention, enabling those skilled in the art to understand or implement the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the present invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A heat pump water heating system, characterized in that, It includes an internal circulation pipeline, a heat exchanger (2), a drainage pipeline (11), a water supply pipeline (13), a three-way valve, a water heater (5), a first temperature sensor (3), a second temperature sensor (4), a water pump (7), an electric shut-off valve (10), an ambient temperature sensor (17), and a controller (18). The internal circulation pipeline includes a first pipeline (12), a second pipeline (14), and a connecting pipeline (15); the first end of the first pipeline (12) is connected to the outlet of the heat exchanger (2), and its second end is connected to the first inlet of the three-way valve; one end of the drain pipeline (11) is connected to the outlet of the three-way valve; the first end of the second pipeline (14) is connected to the inlet of the heat exchanger (2); the second end of the second pipeline (14), one end of the water supply pipeline (13), and the first end of the connecting pipeline (15) are connected; the second end of the connecting pipeline (15) is connected to the second outlet of the three-way valve. The electric shut-off valve (10) is installed on the water supply pipeline (13), the water pump (7) and the water heater (5) are installed on the internal circulation pipeline, the ambient temperature sensor (17) is used to detect the ambient temperature; the ambient temperature sensor (17) is used to detect the ambient temperature, the first temperature sensor (3) is used to detect the water temperature of the water outlet side of the heat exchanger (2), and the second temperature sensor (4) is used to detect the water temperature of the water inlet side of the heat exchanger (2); The ambient temperature sensor (17), the first temperature sensor (3), the second temperature sensor (4), the water pump (7), the three-way valve, and the water heater (5) are all connected to the controller (18) via signal connection.

2. The heat pump water heating system according to claim 1, characterized in that, It includes at least one water flow sensor (6), which is installed on the internal circulation pipeline to detect the flow rate of water in the internal circulation pipeline.

3. The heat pump water heating system according to claim 1, characterized in that, At least one drain valve (8) is installed on the internal circulation pipeline. The drain valve (8) is used to drain the water in the internal circulation pipeline and the water inside the heat exchanger (2).

4. The heat pump water heating system according to claim 3, characterized in that, The second pipeline (14) includes a first pipeline (141), a second pipeline (142), and a third pipeline (143). The first end of the first pipeline (141) is connected to the inlet of the water pump (7). The second end of the first pipeline (141), the first end of the connecting pipeline (15), and one end of the water supply pipeline (13) are connected by a tee joint (16). One end of the second pipeline (142) is connected to the outlet of the water pump (7), and the other end is connected to the inlet of the heat exchanger (2). One end of the third pipeline (143) is connected to the opening on the side wall of the second pipeline (142), and the other end is connected to the drain valve (8).

5. The heat pump water heating system according to claim 1, characterized in that, The first pipeline (12) includes a first pipe (121) and a second pipe (122). One end of the first pipe (121) is connected to the inlet of the three-way valve, and the other end is connected to the outlet of the water heater (5). One end of the second pipe (122) is connected to the inlet of the water heater (5), and the other end is connected to the outlet of the heat exchanger (2).

6. The heat pump water heating system according to claim 1, characterized in that, The system includes a heat pump system (1), which includes a refrigerant circulation pipeline for connecting to the heat exchanger (2).

7. A method for preventing ice formation in a heat exchanger, characterized in that, To prevent icing of the heat exchanger (2) in any of the heat pump water heating systems described in claims 1-6, the method comprises the following steps: Step 1: Use the ambient temperature sensor (17) to obtain the ambient temperature, record the downtime of the heat pump system (11), use the first temperature sensor (3) and the second temperature sensor (4) to detect the water temperature of the outlet side of the heat exchanger (2) and the water temperature of the inlet side of the heat exchanger (2) respectively, and calculate the rate of change of water temperature of the inlet side of the heat exchanger (2) per unit time. The second step is to generate an icing risk index based on the ambient temperature, the downtime of the heat pump system (11) and the water temperature change rate, and to execute an anti-icing strategy corresponding to the risk level according to the risk level to which the icing risk index falls. The anti-icing strategy includes at least: The first strategy is to execute the first strategy to make the water in the circulating water circuit formed by the internal circulation pipeline and the heat exchanger (2) circulate. The second strategy is to execute the second strategy so that the water in the circulating water circuit formed by the internal circulation pipe and the heat exchanger (2) circulates and intermittently heats the water in the circulating water circuit. The third strategy is to implement the third strategy to make the water in the circulating water circuit formed by the internal circulation pipe and the heat exchanger (2) circulate and continuously heat the water in the circulating water circuit until the water temperature in the circulating water circuit reaches a safe temperature.

8. A heat exchanger anti-icing method according to claim 7, characterized in that: The first strategy includes: controlling the electric shut-off valve (10) to close, controlling the three-way valve to switch to internal circulation mode, driving the water pump (7) to run at 10%~20% of the rated flow, and turning off the water circuit heater (5).

9. A heat exchanger anti-icing method according to claim 7, characterized in that: The second strategy includes: controlling the electric shut-off valve (10) to close, controlling the electric three-way valve to switch to internal circulation mode, driving the water pump (7) to run at 40%~60% of the rated flow, controlling the water circuit heater (5) to run in a periodic working mode, and dynamically adjusting the opening and closing time of the water circuit heater (5) according to the water temperature change rate.

10. A heat exchanger anti-icing method according to claim 7, characterized in that: The third strategy includes: controlling the electric shut-off valve (10) to close, controlling the three-way valve to switch to internal circulation mode, driving the water pump (7) to run at 100% rated flow, and controlling the water heater (5) to continuously heat until the water temperature in the circulating water circuit reaches the preset safety threshold.

11. A heat exchanger anti-icing method according to claim 7, characterized in that: The icing risk index is divided into three levels: low risk, medium risk, and high risk. When the ambient temperature is within the first temperature range, it is determined to be a low-risk level, and the first strategy is executed. When the ambient temperature is within the second temperature range and the water temperature change rate exceeds the first change rate threshold, it is determined to be at a medium risk level, and the second strategy is executed accordingly. When the ambient temperature is within the third temperature range and the water temperature change rate exceeds the second change rate threshold, it is determined to be at a high risk level, and the third strategy is executed accordingly; the first temperature range is greater than the second temperature range, the second temperature range is greater than the third temperature range, and the second change rate threshold is less than the first change rate threshold.

12. A heat exchanger anti-icing method according to claim 7, characterized in that: The icing risk index is divided into three levels: low risk, medium risk, and high risk. When the ambient temperature is within the first temperature range, it is determined to be of low risk level, and the first strategy is executed. When the ambient temperature is within the second temperature range and the downtime of the heat pump system (11) falls within the first downtime threshold, it is determined to be of medium risk level and the second strategy is executed accordingly. When the ambient temperature is within the third temperature range and the downtime of the heat pump system (11) falls within the second downtime threshold, it is determined to be at a high risk level and the third strategy is executed accordingly; the first temperature range is greater than the second temperature range, the second temperature range is greater than the third temperature range, and the second downtime threshold is greater than the first downtime threshold.

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