Heat pump water heater and control method thereof

Abstract

The application belongs to the technical field of heat pumps, and particularly relates to a heat pump water heater and a control method thereof, which are used for solving the technical problem of pipeline leakage. The control method comprises determining a first target valve adjusting step number; wherein the first target valve adjusting step number is determined after a throttling device operates for a first preset time length according to an initial opening degree in a starting stage; when the first target valve adjusting step number is greater than 0 and the exhaust temperature of the compressor is less than or equal to a first preset exhaust temperature, a second target valve adjusting step number is determined according to the exhaust temperature of the compressor; after the second target valve adjusting step number is determined, the opening degree of the throttling device is adjusted according to the smaller one of the first target valve adjusting step number and the second target valve adjusting step number at a first preset period within a second preset time length. The application can reduce the risk of pipeline leakage and improve safety and reliability.

Description

Technical Field

[0001] This application relates to the field of heat pump technology, and in particular to a heat pump water heater and its control method. Background Technology

[0002] Heat pump technology is a new energy-saving technology that has attracted worldwide attention. A heat pump water heater utilizes the reverse Carnot cycle to transfer heat from a low-temperature object to high-temperature water using a refrigerant. The internal structure of a heat pump water heater mainly includes a compressor, condenser, throttling device, and evaporator. The throttling device is used to change the throttling cross-section or throttling length to control the flow rate of the refrigerant.

[0003] In related technologies, throttling devices typically employ electronic expansion valves and capillary tubes. Electronic expansion valves offer a wider adjustment range and superior energy efficiency and stability. Specifically, during the initial startup phase of a heat pump water heater, the initial opening of the electronic expansion valve is determined by detecting parameters such as water temperature, ambient temperature, and compressor frequency, and maintained for a fixed duration. Once the fixed duration of adjustment is met, superheat control is initiated, adjusting according to the valve adjustment steps required during normal operation of the heat pump water heater.

[0004] However, heat pump water heaters experience increased vibration during startup, posing a risk of pipe leaks and resulting in low safety and reliability. Summary of the Invention

[0005] This application provides a heat pump water heater and its control method, which can reduce the vibration of the heat pump water heater during the start-up phase, reduce the risk of pipeline leakage, and improve the safety and reliability of the heat pump water heater during operation.

[0006] To achieve the above objectives, this application provides the following technical solution:

[0007] In a first aspect, embodiments of this application provide a control method for a heat pump water heater, including:

[0008] Determine the first target valve control step number; wherein, the first target valve control step number is determined by the throttling device during the start-up phase after it has run for a first preset time based on the initial opening;

[0009] When the first target valve adjustment step number is greater than 0 and the compressor discharge temperature is less than or equal to the first preset discharge temperature, the second target valve adjustment is determined according to the compressor discharge temperature.

[0010] After determining the second target valve control step number, within the second preset time period, at a first preset cycle, the opening degree of the throttling device is adjusted according to the smaller of the first target valve control step number and the second valve control step number.

[0011] As an optional implementation, when the first target valve adjustment step number is greater than 0 and the compressor's discharge temperature is less than or equal to the first preset discharge temperature, determining the second target valve adjustment step number based on the compressor's discharge temperature specifically includes:

[0012] If the exhaust temperature of the compressor is less than or equal to the first preset exhaust temperature and greater than the second preset exhaust temperature, then the second target valve control step number is determined to be the first preset threshold, wherein the first preset threshold is greater than 0.

[0013] As an optional implementation, the first preset threshold is 3.

[0014] As an optional implementation, when the first target valve adjustment step number is greater than 0 and the compressor's discharge temperature is less than or equal to the first preset discharge temperature, determining the second target valve adjustment step number based on the compressor's discharge temperature specifically includes:

[0015] If the exhaust temperature of the compressor is less than or equal to the second preset exhaust temperature and greater than the third preset exhaust temperature, then the second target valve control step number is determined to be the second preset threshold; wherein the second preset threshold is less than the first preset threshold and the second preset threshold is greater than 0.

[0016] As an optional implementation, when the first target valve adjustment step number is greater than 0 and the compressor's discharge temperature is less than or equal to the first preset discharge temperature, determining the second target valve adjustment step number based on the compressor's discharge temperature specifically includes:

[0017] If the exhaust temperature of the compressor is less than or equal to the third preset exhaust temperature, then the second target valve control step number is determined to be the third preset threshold; wherein the third preset threshold is less than the second preset threshold and the third preset threshold is greater than 0.

[0018] As an optional implementation, determining the first target valve control step number specifically includes:

[0019] Determine the actual suction superheat of the compressor;

[0020] The first target valve adjustment step number is determined based on the difference between the actual intake superheat and the target intake superheat.

[0021] As an optional implementation, determining the actual suction superheat of the compressor specifically includes:

[0022] Obtain the suction temperature and evaporation temperature of the compressor;

[0023] The actual intake superheat of the compressor is determined based on the difference between the intake temperature and the evaporation temperature.

[0024] As an optional implementation, determining the initial opening degree of the throttling device specifically includes:

[0025] Obtain ambient temperature, water temperature, and compressor frequency;

[0026] The initial opening degree of the throttling device is determined based on the ambient temperature, the water temperature, and the compressor frequency.

[0027] As an optional implementation, after determining the second target valve control step number, and adjusting the opening of the throttling device within the second preset time period at a first preset cycle using the smaller of the first target valve control step number and the second target valve control step number, the method further includes:

[0028] After the opening adjustment of the throttling device is completed within the second preset time period, the opening adjustment of the throttling device within the second preset time period is terminated, and the opening of the throttling device is adjusted at a second preset period; wherein, the first preset period is greater than the second preset period.

[0029] Those skilled in the art will understand that the control method for a heat pump water heater provided in this application includes: determining a first target valve adjustment step number; wherein, the first target valve adjustment step number is determined after the throttling device has run for a first preset time based on its initial opening during the start-up phase; when the first target valve adjustment step number is greater than 0, and the compressor's exhaust temperature is less than or equal to a first preset exhaust temperature, determining a second target valve adjustment step number based on the compressor's exhaust temperature; after determining the second target valve adjustment step number, adjusting the opening of the throttling device according to the smaller of the first target valve adjustment step number and the second target valve adjustment step number within a second preset time period at a first preset cycle. Through the above technical solution, the vibration of the heat pump water heater during the start-up phase can be reduced, thereby reducing the risk of pipe leakage and improving the safety and reliability of the heat pump water heater during operation.

[0030] Secondly, this application provides a heat pump water heater, comprising: a compressor, a first heat exchanger, a throttling device, and a second heat exchanger connected in sequence, wherein the first heat exchanger is connected to the exhaust port of the compressor, and the second heat exchanger is connected to the intake port of the compressor; when the heat pump water heater is turned on, the heat pump water heater adjusts the opening degree of the throttling device using the control method described in the above embodiment.

[0031] The heat pump water heater provided in this application has the same technical effects as the above embodiments, and will not be repeated here.

[0032] In addition to the technical problems solved by the embodiments of this application, the technical features constituting the technical solutions, and the beneficial effects brought about by the technical features of these technical solutions described above, other technical problems that can be solved by the heat pump water heater and its control method provided by the embodiments of this application, other technical features included in the technical solutions, and the beneficial effects brought about by these technical features will be further explained in detail in the specific implementation. Attached Figure Description

[0033] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0034] Figure 1 A flowchart illustrating the control method for a heat pump water heater provided in this application embodiment;

[0035] Figure 2 This is a schematic diagram of the structure of a heat pump water heater provided in an embodiment of this application.

[0036] Figure label:

[0037] 100-Heat pump water heater;

[0038] 110 - Compressor;

[0039] 120 - First heat exchanger;

[0040] 130 - Throttling device;

[0041] 140 - Second heat exchanger;

[0042] 150 - Control valve. Detailed Implementation

[0043] In related technologies, throttling devices typically employ electronic expansion valves and capillary tubes. Electronic expansion valves offer a wider adjustment range and superior energy efficiency and stability. When a heat pump water heater is first started, the initial opening of the electronic expansion valve is determined based on parameters such as water temperature, ambient temperature, and compressor frequency, and maintained for a fixed duration. Once the duration condition is met, conventional superheat control is initiated, allowing the electronic expansion valve to adjust its opening during normal operation. However, because the refrigerant system is transitioning from an unsteady state to a steady state upon startup, the electronic expansion valve typically opens rapidly for a short period before gradually closing during normal operation. This results in significant fluctuations in refrigerant flow, increasing compressor vibration. This increased compressor vibration, in turn, leads to increased vibration in the piping system, increasing the risk of pipe leaks and posing a technical problem of low safety and reliability.

[0044] To address the aforementioned technical problems, this application provides a heat pump water heater and its control method. By adding a buffer zone for opening adjustment between the initial opening stage and the normal operation stage of the throttling device, the opening adjustment of the throttling device during the start-up stage can be made smoother, reducing fluctuations and thus reducing the impact of refrigerant circulation flow changes on pipeline system vibration, thereby reducing the risk of pipeline leakage and improving safety and reliability.

[0045] 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.

[0046] Example 1

[0047] Figure 1 A flowchart illustrating the control method for a heat pump water heater provided in this application embodiment. See also... Figure 1 As shown in the embodiment of this application, the control method for a heat pump water heater includes the following steps:

[0048] Step S101: Determine the first target valve control step number; wherein, the first target valve control step number is determined by the throttling device during the start-up phase after running for a first preset time according to the initial opening.

[0049] The throttling device includes, but is not limited to, structures such as electronic expansion valves. In this application, an example of a throttling device including an electronic expansion valve will be used for description.

[0050] Optionally, the initial opening degree of the throttling device can be determined according to parameters such as ambient temperature, water temperature, and compressor frequency. When a start-up command is received, the throttling device opens to the initial opening degree and runs for a first preset duration. In this application, the first preset duration can be represented by T1.

[0051] It should be noted that the first preset duration is a fixed duration. The first preset duration can be set in advance by the throttling device at the factory; or it can be a custom setting by the user according to their needs.

[0052] After running for the first preset time based on the initial opening, the actual suction superheat of the compressor is determined.

[0053] Taking the properties of water and water vapor as an example, superheat refers to the degree to which the temperature of water vapor exceeds the saturation temperature at the corresponding pressure. In this application, the superheat control of the throttling device includes intake superheat control, exhaust superheat control, and control of both intake and exhaust superheat. In this application, intake superheat control is used to illustrate a method for adjusting the opening of the throttling device during the start-up phase.

[0054] Optionally, determine the actual suction superheat of the compressor, specifically including:

[0055] Obtain the compressor's suction temperature and evaporation temperature; determine the compressor's actual suction superheat based on the difference between the suction temperature and the evaporation temperature.

[0056] In some embodiments, the compressor’s suction temperature and evaporation temperature can be detected by a temperature sensor or other detection device, and the difference between the suction temperature and the evaporation temperature can be calculated. This difference is the compressor’s actual suction superheat.

[0057] After obtaining the actual suction superheat of the compressor, the first target valve control step number is determined based on the difference between the actual suction superheat and the target superheat.

[0058] The target intake superheat can be controlled based on the type of refrigerant controller used and its adjustment value.

[0059] In summary, the number of steps for the first target valve control can be calculated using the following formula:

[0060] △P1=(To-Te)-△t1 (1)

[0061] Where △P1 is the first target valve control step number; To is the intake temperature; Te is the steam temperature; and △t1 is the target intake superheat.

[0062] After determining the first target valve control step number, check whether the first target valve control step number is greater than 0.

[0063] The first target valve control step number may be greater than 0 or less than or equal to 0. When the first target valve control step number is less than or equal to 0, the throttling device adjusts according to the actual value of the first target valve control step number. For example, if the determined first target valve control step number is 0, -1, -2, etc., then the next target opening of the throttling device is the sum of the current actual opening of the throttling device and the first target valve control step number, as shown in the following formula:

[0064] P i+1 =P i +△P1 (2)

[0065] Among them, P i+1 P is the target opening degree of the throttling device for the next operation. i This represents the current actual opening degree of the throttling device.

[0066] Step S102: When the first target valve adjustment step number is greater than 0 and the compressor's exhaust temperature is less than or equal to the first preset exhaust temperature, determine the second target valve adjustment step number based on the compressor's exhaust temperature.

[0067] The number of steps for the second target valve control can be represented by ΔP2.

[0068] In some optional embodiments, when the first target valve adjustment step number is greater than 0 and the compressor's discharge temperature is less than or equal to the first preset discharge temperature, the second target valve adjustment step number is determined based on the compressor's discharge temperature, specifically including:

[0069] If the compressor's exhaust temperature is less than or equal to the first preset exhaust temperature, but greater than the second preset exhaust temperature, then the second target valve control step number is determined to be the first preset threshold; wherein, the first preset threshold is greater than 0.

[0070] For example, the first preset threshold can be 3.

[0071] In some alternative embodiments, when the first target valve adjustment step number is greater than 0 and the compressor's discharge temperature is less than or equal to the first preset discharge temperature, the second target valve adjustment step number is determined based on the compressor's discharge temperature, specifically including:

[0072] If the compressor's exhaust temperature is less than or equal to the second preset exhaust temperature, but greater than the third preset exhaust temperature, then the second target valve control step number is determined to be the second preset threshold; wherein, the second preset threshold is less than the first preset threshold and greater than 0.

[0073] For example, the second preset threshold is 2.

[0074] In some alternative embodiments, when the first target valve adjustment step number is greater than 0 and the compressor's discharge temperature is less than or equal to the first preset discharge temperature, the second target valve adjustment step number is determined based on the compressor's discharge temperature, specifically including:

[0075] If the compressor's exhaust temperature is less than or equal to the third preset exhaust temperature, then the second target valve control step number is determined to be the third preset threshold; wherein the third preset threshold is less than the second preset threshold and greater than 0.

[0076] For example, the third preset threshold is 1.

[0077] Among them, the first preset exhaust temperature, the second preset exhaust temperature, and the third preset exhaust temperature can all be exhaust temperature values ​​that are set in advance according to requirements.

[0078] Understandably, when the number of steps for the second target valve control is less than the number of steps for the first target valve control, the calculation formula for the next target opening of the throttling device is as follows:

[0079] P i+1 =P i +△P2 (3)

[0080] If the number of steps for the second target valve adjustment is greater than the number of steps for the first target valve adjustment, the formula for calculating the target opening degree of the throttling device in the next step is as follows:

[0081] P i+1 =P i +△P1 (4)

[0082] In other embodiments, when the first valve adjustment step number is greater than 0 and the current exhaust temperature of the compressor is greater than the first preset exhaust temperature, the throttling device adjusts the opening degree of the throttling device within a second preset time period according to the first target valve adjustment step number.

[0083] That is, the target opening degree of the throttling device next time is:

[0084] P i+1 =P i +△P1 (5)

[0085] Step S103: After determining the second target valve control step number, within the second preset time period, adjust the opening of the throttling device according to the smaller of the first target valve control step number and the second target valve control step number at a first preset cycle.

[0086] Specifically, after determining the second target valve control step number, it is determined whether the second target valve control step number is less than the first target valve control step number; if so, the opening of the throttling device is adjusted within a second preset time period and a first preset cycle according to the second target valve control step number; if not, the opening of the throttling device is adjusted within a second preset time period and a first preset cycle according to the first target valve control step number.

[0087] For example, if the first target valve adjustment step is 5 and the second target valve adjustment step is 3, then the opening of the throttling device is adjusted according to step 3. That is to say, the opening of the throttling device next time is the sum of the current actual opening of the throttling device and step 3.

[0088] The second preset duration (which can be represented by T2) is the transition period from the first preset duration of operation during the start-up phase to the normal operation of the heat pump water heater. This allows the throttling device to form a transition range from its initial opening to its normal operating opening. In this way, the opening of the throttling device can smoothly transition from its initial opening to its normal adjustment within the second preset duration, making the opening adjustment of the throttling device smoother and reducing fluctuations. This reduces the impact of refrigerant flow changes on the vibration of the pipeline system, thereby reducing the risk of pipeline leakage.

[0089] In addition, the adjustment of the throttling device opening is periodic within a second preset time period, which can be a first preset time period. For example, the second preset time period can be 10 minutes and the first preset time period can be 120 seconds. In this way, the throttling device adjusts its opening once every 120 seconds within 10 minutes until the 10 minutes are over.

[0090] Optionally, after determining the second target valve adjustment step number, and adjusting the opening of the throttling device within a second preset time period at a first preset cycle using the smaller of the first target valve adjustment step number and the second target valve adjustment step number, the method further includes:

[0091] After the throttling device finishes adjusting its opening within the second preset time period, it exits the adjustment process and adjusts the opening of the throttling device according to the second preset cycle; wherein, the first preset cycle is longer than the second preset cycle.

[0092] Understandably, after the second preset time period ends, the refrigerant in the heat pump water heater changes from an unsteady state to a steady state, and the heat pump water heater enters a stable operating phase. At this time, the throttling device exits the state of adjusting the opening degree in the first preset cycle during the second preset time period. After entering the normal operating phase, the opening degree adjustment of the throttling device can be changed from the first preset cycle to the second preset cycle.

[0093] For example, the second preset period can be 90s, which can shorten the adjustment period of the throttling device opening and improve the sensitivity of the throttling device when adjusting the flow rate.

[0094] Understandably, the adjustment cycle of the throttling device within the second preset time period is longer than the adjustment cycle during normal operation. This avoids the problem of the throttling device opening too wide due to delayed execution when adjusting the opening within the second preset time period. In addition, by making different corrections to the target valve step number based on conditions such as exhaust temperature within the second preset time period, the smoothness of the throttling device during opening adjustment can be increased, fluctuations can be reduced, and the impact of changes in refrigerant flow on pipeline system vibration can be reduced, thereby reducing the risk of pipeline leakage and improving operational safety and reliability.

[0095] Example 2

[0096] Figure 2 A schematic diagram of the structure of a heat pump water heater provided in an embodiment of this application. See also... Figure 2 As shown in the embodiment of this application, a heat pump water heater 100 is also provided, including: a compressor 110, a first heat exchanger 120, a throttling device 130 and a second heat exchanger 140 connected in sequence. The first heat exchanger 120 is connected to the exhaust port of the compressor 110, and the second heat exchanger 140 is connected to the intake port of the compressor 110. When the heat pump water heater 100 is turned on, the heat pump water heater 100 adjusts the opening degree of the throttling device 130 using the control method in the above embodiment.

[0097] The control method of the heat pump water heater 100 has been described in detail in the above embodiments and will not be repeated here.

[0098] Optionally, the first heat exchanger 120 can be an outdoor unit, and the second heat exchanger 140 can be an indoor unit. During heating, the second heat exchanger 140 acts as a condenser, and the first heat exchanger 120 acts as an evaporator. Furthermore, it is understood that the control method described above for a heat pump water heater can also be applied to other devices with similar structures and operating principles to the heat pump water heater 100, such as devices equipped with electronic expansion valves, which can then be used for both cooling and heating. In this case, when the device similar to the heat pump water heater 100 is used for cooling, the first heat exchanger 120 acts as a condenser, and the second heat exchanger 140 acts as an evaporator.

[0099] When the heat pump water heater 100 is operating for heating, the exhaust port of the compressor 110 is connected to the second heat exchanger 140. The high-temperature and high-pressure refrigerant gas discharged by the compressor 110 is cooled by the second heat exchanger 140 to form a medium-temperature and high-pressure liquid refrigerant. In this way, the second heat exchanger 140 can release heat to the water to be heated in the heat pump water heater 100 to increase the water temperature. The medium-temperature and high-pressure liquid refrigerant is throttled and depressurized by the throttling device 130 to form a low-temperature and low-pressure gas-liquid mixture, which then enters the first heat exchanger 120. The first heat exchanger 120 absorbs heat from the air or circulating water to vaporize the low-temperature and low-pressure gas-liquid mixture, turning it into refrigerant gas, which then returns to the compressor 110 for further compression and continues to circulate for heating.

[0100] Optionally, the heat pump water heater 100 also includes a control valve 150. For example, the control valve 150 is a four-way valve. The compressor 110 is connected to the first heat exchanger 120 and the second heat exchanger 140 respectively through the control valve 150, and the connection of the heating circuit or other circuits is realized through the control valve 150.

[0101] This application provides a heat pump water heater and its control method. The control method for the heat pump water heater provided by this application includes: determining a first target valve adjustment step number; wherein, the first target valve adjustment step number is determined after the throttling device operates for a first preset time based on its initial opening during the start-up phase; when the first target valve adjustment step number is greater than 0, and the compressor's exhaust temperature is less than or equal to a first preset exhaust temperature, determining a second target valve adjustment step number based on the compressor's exhaust temperature; after determining the second target valve adjustment step number, adjusting the opening of the throttling device according to the smaller of the first and second target valve adjustment step numbers within a second preset time period at a first preset cycle. Through the above technical solution, the vibration of the heat pump water heater during the start-up phase can be reduced, thereby reducing the risk of pipe leakage and improving the safety and reliability of the heat pump water heater during operation.

[0102] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection between two components. Those skilled in the art will understand the specific meaning of the above terms in this application based on the specific circumstances.

[0103] The terms "first" and "second" used in the specification, claims, and accompanying drawings of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of this application described herein can be implemented, for example, in orders other than those illustrated or described herein.

[0104] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A control method of a heat pump water heater, characterized by, The method comprises the following steps: determining a first target valve step number; wherein the first target valve step number is determined after the throttling device operates for a first preset time length according to an initial opening degree; the determination of the first target valve step number comprises: determining an actual suction superheat degree of the compressor; determining the first target valve step number according to a difference between the actual suction superheat degree and a target suction superheat degree; when the first target valve step number is greater than 0 and the exhaust temperature of the compressor is less than or equal to a first preset exhaust temperature, determining a second target valve step number according to the exhaust temperature of the compressor; after determining the second target valve step number, adjusting the opening degree of the throttling device according to the smaller one of the first target valve step number and the second target valve step number at a first preset period within a second preset time length.

2. The control method of the heat pump hot-water supply unit according to claim 1, wherein The step of determining the second target valve step number according to the exhaust temperature of the compressor when the first target valve step number is greater than 0 and the exhaust temperature of the compressor is less than or equal to a first preset exhaust temperature specifically comprises: if the exhaust temperature of the compressor is less than or equal to the first preset exhaust temperature and greater than a second preset exhaust temperature, determining the second target valve step number as a first preset threshold value; wherein the first preset threshold value is greater than 0.

3. The control method of the heat pump hot-water supply unit according to claim 2, wherein The first preset threshold value is 3.

4. The control method of the heat pump hot-water supply unit according to claim 1, wherein The step of determining the second target valve step number according to the exhaust temperature of the compressor when the first target valve step number is greater than 0 and the exhaust temperature of the compressor is less than or equal to a first preset exhaust temperature specifically comprises: if the exhaust temperature of the compressor is less than or equal to a second preset exhaust temperature and greater than a third preset exhaust temperature, determining the second target valve step number as a second preset threshold value; wherein the second preset threshold value is less than the first preset threshold value and greater than 0.

5. The control method of a heat pump water heater according to claim 1, wherein The step of determining the second target valve step number according to the exhaust temperature of the compressor when the first target valve step number is greater than 0 and the exhaust temperature of the compressor is less than or equal to a first preset exhaust temperature specifically comprises: if the exhaust temperature of the compressor is less than or equal to a third preset exhaust temperature, determining the second target valve step number as a third preset threshold value; wherein the third preset threshold value is less than the second preset threshold value and greater than 0.

6. The control method of a heat pump water heater according to claim 1, wherein The step of determining the actual suction superheat degree of the compressor specifically comprises: obtaining the suction temperature and the evaporation temperature of the compressor; determining the actual suction superheat degree of the compressor according to the difference between the suction temperature and the evaporation temperature.

7. The control method of a heat pump hot-water device according to any one of claims 1 to 5, characterized by, The step of determining the initial opening degree of the throttling device specifically comprises: obtaining the ambient temperature, the water temperature and the compressor frequency; determining the initial opening degree of the throttling device according to the ambient temperature, the water temperature and the compressor frequency.

8. The control method of a heat pump hot-water supply apparatus according to any one of claims 1 to 3, characterized by, The step of adjusting the opening degree of the throttling device according to the smaller one of the first target valve step number and the second target valve step number at the first preset period within the second preset time length after determining the second target valve step number further comprises: The throttling device exits the opening degree adjustment of the throttling device within the second preset time length after the opening degree adjustment within the second preset time length is completed, and adjusts the opening degree of the throttling device at a second preset period; wherein the first preset period is greater than the second preset period.

9. A heat pump water heater, characterized by, Comprise: The compressor, the first heat exchanger, the throttling device and the second heat exchanger are connected in sequence, the first heat exchanger is connected with the exhaust port of the compressor, and the second heat exchanger is connected with the suction port of the compressor; when the heat pump water heater is started, the heat pump water heater adjusts the opening degree of the throttling device by using the control method in any one of the above claims 1-8.

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