A heat pump unit

Abstract

The present application relates to a kind of heat pump unit, using the method of refrigerant counter heat pump cycle to defrost outdoor heat exchanger, and based on this design a kind of defrosting control method, by the return water temperature and ambient temperature determined by acquisition maximum opening degree variation coefficient, minimum opening degree variation coefficient and ring temperature influence coefficient that influence electronic expansion valve opening degree, and combining the initial temperature of evaporator's coil contact point, limit temperature and real-time temperature calculated to obtain the current opening degree of electronic expansion valve, make the current opening degree of electronic expansion valve and the change demand of refrigerant flow of compressor in defrosting process match, reduce the risk of compressor refrigerant liquid hammer, while, improve the reliability of defrosting, prolong the service life of compressor.

Description

Technical Field

[0001] This invention relates to the field of heat pumps, and more particularly to a heat pump unit. Background Technology

[0002] Heat pump units are highly efficient energy-saving devices. However, when operating in outdoor environments with excessively low temperatures and high relative humidity, their outdoor heat exchangers are particularly prone to frosting, sometimes to the point of becoming unusable. This leads to a continuous decrease in the heating efficiency of the heat pump unit, reducing its overall energy efficiency. Therefore, it is necessary to set up defrost control to defrost the frosted outdoor heat exchanger.

[0003] Currently, heat pump units primarily employ a refrigerant reverse heat pump circulation method for defrosting the outdoor heat exchanger. This involves installing a four-way valve in the refrigerant circulation pipeline. During defrosting, the four-way valve is switched, allowing high-temperature refrigerant to enter the outdoor heat exchanger and release heat to melt the frost on its outer surface. For the unit system, during defrosting, the system circulates in reverse, causing the unit's condensing temperature to continuously change from low to high, and the refrigerant circulation volume to also change. However, current heat pump units mainly control the refrigerant flow and thus the entire defrosting process by controlling the fixed opening of the electronic expansion valve. A common control scheme for the electronic expansion valve opening during defrosting is shown below:

[0004] 1) When entering defrosting mode, the electronic expansion valve should be adjusted according to the following requirements:

[0005] A. If the return water temperature is >20℃, the electronic expansion valve is adjusted to a fixed opening, stabilized for 1 minute, and then adjusted to the current opening -100 and continuously operated until the defrosting time is set.

[0006] B. If the return water temperature is ≤20℃, adjust the electronic expansion valve to a fixed opening, stabilize for 1 minute, then adjust it to the current opening -50 and continue running until the defrost set time.

[0007] C. After defrosting is stopped, the electronic expansion valve will maintain its initial opening for 3 minutes before automatically adjusting.

[0008] 2) When defrosting begins, the electronic expansion valve is fixed at a certain opening.

[0009] The above solutions, due to the relatively long fixed setting of the electronic expansion valve opening during the defrosting process, are prone to causing compressor liquid return during defrosting. Summary of the Invention

[0010] Based on this, the purpose of the present invention is to provide a heat pump unit and its defrosting control method, which enables the heat pump unit to control the defrosting process in a low temperature and high humidity environment through real-time regulation of the electronic expansion valve, so that the opening degree of the electronic expansion valve can be adjusted in real time to match the changes in the refrigerant flow demand of the compressor, thereby reducing the risk of refrigerant liquid slugging in the compressor.

[0011] A heat pump unit includes a compressor, a four-way valve, an evaporator, an electronic expansion valve, and a condenser connected sequentially via a refrigerant circulation pipeline, and a controller electrically and / or communicatively connected to the compressor, the four-way valve, the electronic expansion valve, and multiple temperature sensors, characterized in that:

[0012] When the controller receives a command to enter defrosting operation but the heat pump unit has not yet entered defrosting operation, the controller acquires the initial state data of the heat pump unit; and determines the opening degree influence factor of the electronic expansion valve based on the initial state data, and calculates the initial opening degree of the electronic expansion valve based on the opening degree influence factor and the initial state data.

[0013] When the heat pump unit enters the defrosting operation, the controller controls the electronic expansion valve to remain unadjusted for a first time period at the initial opening.

[0014] After the heat pump unit enters defrosting mode, the controller acquires the coil contact point temperature of the evaporator in real time and compares the coil contact point temperature with the defined coil contact point temperature in the initial state data.

[0015] If the coil contact point temperature is lower than the coil contact point limit temperature, the controller calculates the current opening of the electronic expansion valve based on the coil contact point temperature, the initial state data, and the opening influence factor; compares the current opening with the minimum opening of the electronic expansion valve and outputs the defrost opening; and controls the electronic expansion valve to remain unchanged within the defrost valve adjustment cycle at the defrost opening, while continuously acquiring the coil contact point temperature in real time.

[0016] If the temperature at the coil contact point is greater than or equal to the specified temperature at the coil contact point, the controller sends a frequency reduction command to the compressor and a valve switching command to the four-way valve to restore the unit's operating mode control for the compressor and electronic expansion valve, thereby ending the defrosting process of the heat pump unit.

[0017] Compared with the prior art, the heat pump unit of the present invention adjusts the current opening of the electronic expansion valve in real time by setting the opening influence factor of the electronic expansion valve and combining it with the real-time measured coil contact point temperature. This makes the opening of the electronic expansion valve of the heat pump unit during defrosting match the compressor's demand for refrigerant flow, reducing the risk of refrigerant liquid slugging in the compressor and extending the compressor's service life.

[0018] Furthermore, the initial opening is calculated according to the following formula:

[0019]

[0020] In the formula, K 0K represents the initial opening degree of the electronic expansion valve. MAX This indicates the maximum opening degree of the electronic expansion valve. F represents the coefficient of maximum opening variation determined based on return water temperature, e represents the ambient temperature influence coefficient determined based on ambient temperature, and F represents the coefficient of maximum opening variation determined based on return water temperature. t Indicates the operating frequency of the compressor. This indicates the initial defrosting frequency of the compressor.

[0021] Furthermore, the current opening degree is calculated according to the following formula:

[0022]

[0023] In the formula, K t K represents the current opening degree of the electronic expansion valve during the defrosting process of the heat pump unit. MAX K represents the maximum opening degree of the electronic expansion valve. MIN This indicates the minimum opening degree of the electronic expansion valve. This represents the coefficient of variation of the maximum opening degree determined based on the return water temperature. denoted by , the minimum opening variation coefficient determined based on the return water temperature; and 'e', ​​the ambient temperature influence coefficient determined based on the ambient temperature. This indicates the real-time temperature of the coil contact points after the heat pump unit enters defrosting mode. This indicates the initial temperature of the coil contact points when the controller receives the command to enter defrost operation, but the heat pump unit has not yet entered defrost operation. This indicates the set temperature limit for the coil contact points of the heat pump unit.

[0024] Furthermore, the maximum opening variation coefficient is determined according to the temperature range of the return water temperature in the following manner:

[0025] When the return water temperature is less than 20℃, the maximum opening variation coefficient

[0026] When the return water temperature is greater than or equal to 20℃ and less than 35℃, the maximum opening variation coefficient

[0027] When the return water temperature is greater than or equal to 35℃ and less than 45℃, the maximum opening variation coefficient

[0028] When the return water temperature is greater than or equal to 45℃ and less than 55℃, the maximum opening variation coefficient

[0029] Furthermore, the minimum opening variation coefficient is determined according to the temperature range of the return water temperature in the following manner:

[0030] When the return water temperature is less than 20℃, the minimum opening degree variation coefficient

[0031] When the return water temperature is greater than or equal to 20℃ and less than 35℃, the minimum opening variation coefficient

[0032] When the return water temperature is greater than or equal to 35℃ and less than 45℃, the minimum opening variation coefficient

[0033] When the return water temperature is greater than or equal to 45℃ and less than 55℃, the minimum opening variation coefficient

[0034] Furthermore, the ambient temperature influence coefficient is determined according to the temperature range of the ambient temperature using the following method:

[0035] When the ambient temperature is greater than or equal to 0℃ and less than 12℃, the ambient temperature influence coefficient e = 1.0;

[0036] When the ambient temperature is greater than or equal to -10℃ and less than 0℃, the ambient temperature influence coefficient e = 0.9;

[0037] When the ambient temperature is greater than or equal to -20℃ and less than -10℃, the ambient temperature influence coefficient e = 0.85;

[0038] When the ambient temperature is less than -20℃, the ambient temperature influence coefficient e = 0.8.

[0039] When designing the opening control parameters, we fully considered the different requirements of the maximum and minimum opening of the electronic expansion valve of the heat pump unit during defrosting: different return water temperatures; and the impact of different ambient temperatures on the opening of the electronic expansion valve when the external fan is not turned on and the heat pump unit is in static heat exchange during defrosting. This ensures that the real-time defrosting opening of the electronic expansion valve, after being corrected by the opening control parameters, can better match the changes in the compressor's demand for refrigerant flow during the defrosting process.

[0040] To better understand and implement this invention, the following detailed description is provided in conjunction with the accompanying drawings. Attached Figure Description

[0041] Figure 1 This is a schematic diagram of a heat pump unit under defrosting control according to an embodiment of the present invention;

[0042] Figure 2 This is a flowchart of a defrosting control method for a heat pump unit according to an embodiment of the present invention. Detailed Implementation

[0043] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings of the embodiments of the present invention.

[0044] The terminology used in the embodiments of this application is for the purpose of describing particular embodiments only and is not intended to limit the embodiments of this application. The singular forms “a,” “the,” and “the” used in the embodiments of this application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that, unless otherwise stated, “a plurality” means two or more; and the term “and / or” as used herein refers to and includes any or all possible combinations of one or more associated listed items.

[0045] In the following description, when referring to the accompanying drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this application. In the description of this application, it should be understood that the terms "first," "second," "third," etc., are used only for distinction and not to describe a specific order or sequence, nor should they be construed as indicating or implying relative importance. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0046] To address the issue of refrigerant backflow and liquid slugging during defrosting in heat pump units where the outdoor heat exchanger uses a refrigerant reverse heat pump circulation method with a fixed electronic expansion valve opening, the invention proposes a heat pump unit that employs an improved electronic expansion valve opening control method. By using designed electronic expansion valve opening control parameters and real-time measured coil temperature, the opening of the electronic expansion valve is adjusted in real-time during defrosting. This ensures the electronic expansion valve opening adapts to the compressor's refrigerant flow requirements during defrosting, reducing the risk of refrigerant liquid slugging and extending the compressor's lifespan.

[0047] For specific implementation details, please refer to [link / reference]. Figure 1The heat pump unit proposed in this invention includes a compressor 10, a four-way valve 20, an evaporator 30, an electronic expansion valve 40, a condenser 50, multiple temperature sensors (not shown), a controller (not shown), and other auxiliary pipes. The compressor 10, four-way valve 20, evaporator 30, electronic expansion valve 40, and condenser 50 are sequentially connected via refrigerant piping; the controller is electrically or communicatively connected to the compressor 10, four-way valve 20, electronic expansion valve 40, and multiple temperature sensors. Specifically, when the heat pump unit defrosts, the exhaust port A of the compressor 10, the inlet D of the four-way valve 20, the first working port E of the four-way valve 20, the evaporator 30, the electronic expansion valve 40, the condenser 50, the second working port C of the four-way valve 20, the return port S of the four-way valve 20, and the return port B of the compressor 10 are connected in sequence to form a refrigerant circulation pipeline. This allows the high-temperature and high-pressure gaseous refrigerant generated by the compressor 10 to flow through the evaporator 30, releasing heat to the evaporator 30 and heating and defrosting the frost on its outer surface.

[0048] The plurality of temperature sensors includes at least a first temperature sensor (not shown), a second temperature sensor (not shown), and a third temperature sensor (not shown); wherein, the first temperature sensor is disposed in the evaporator 30, and transmits the measured temperature signal of the coil contact point of the evaporator 30 to the controller; the second temperature sensor is disposed at the return water end of the condenser 50, and transmits the measured temperature signal of the water source flowing into the condenser 50 to the controller; the placement of the third temperature sensor is not limited in this application, as long as its placement allows it to transmit the ambient temperature signal to the controller.

[0049] The controller receives temperature signals from the first, second, and third temperature sensors, as well as the operating frequency and operating time signals of the compressor 10. It also acquires the initial defrost frequency table of the compressor set by the heat pump unit and the defined temperature of the evaporator coil contact point. The controller sends defrost start or defrost end signals to the compressor 10 and the four-way valve 20 via a defrost control program stored thereon, controlling the operating frequency of the compressor 10 and the valve switching of the four-way valve 20. Furthermore, it sends an adjustment signal to the electronic expansion valve 40 via a defrost opening control program stored thereon, controlling the opening adjustment of the electronic expansion valve 40.

[0050] Specifically, the controller controls the defrosting operation of the heat pump unit by controlling the opening of the electronic expansion valve, including the following steps.

[0051] S10 When the controller receives a command to enter defrost operation but the heat pump unit has not yet entered defrost operation, the controller acquires the initial state data of the heat pump unit, determines the opening degree influence factor of the electronic expansion valve based on the initial state data, and calculates the initial opening degree K based on the opening degree influence factor and the initial state data. 0 .

[0052] In practice, the controller obtains the initial opening degree of the electronic expansion valve 40 when the heat pump unit enters the defrosting operation through the following sub-steps.

[0053] S11 acquires the initial state data of the heat pump unit, the initial state data including: the initial temperature of the coil contact point measured by the first temperature sensor. The return water temperature T measured by the second temperature sensor h The third temperature sensor measures the ambient temperature T. E and the current operating frequency F of compressor 10 t And obtain the initial defrosting frequency of the compressor 10 set for defrosting operation in the heat pump unit. The temperature limit of the coil contact point of the evaporator 30 when it is out of defrost operation. And obtain the maximum opening degree K of the electronic expansion valve 40. MAX And the minimum opening K that has been experimentally verified to ensure normal defrosting of the heat pump unit. MIN .

[0054] S12 determines the opening influence factor of the electronic expansion valve based on the initial state data, the opening influence factor including the maximum opening variation coefficient. Minimum opening variation coefficient And the ambient temperature influence coefficient e.

[0055] Specifically, based on the return water temperature T in the initial state data h The maximum opening variation coefficient of the electronic expansion valve is determined according to the temperature range constant value method. As shown in Table 1, the maximum opening variation coefficient is... To meet the different return water temperatures T during defrosting. h Different maximum opening requirements for the electronic expansion valve of the heat pump unit.

[0056] Table 1

[0057]

[0058] Based on the return water temperature T in the initial state data h The minimum opening variation coefficient of the electronic expansion valve is determined according to the temperature range constant value method. As shown in Table 2, the minimum opening variation coefficient is... To meet the different return water temperatures T during defrosting. h For the electronic expansion valve of the heat pump unit, there are 40 different minimum opening degrees K MIN need.

[0059] Table 2

[0060]

[0061] Based on the ambient temperature T in the initial state data E The ambient temperature influence coefficient e is determined according to the temperature range fixed value method, as shown in Table 3. Since the external fan is not turned on during defrosting, the heat pump unit is in static heat exchange mode. Therefore, it is necessary to set calibration parameters at different ambient temperatures to correct the opening of the electronic expansion valve 40.

[0062] Table 3

[0063] <![CDATA[Ambient temperature T E , °C]]> <![CDATA[12>T E ≥0]]> <![CDATA[0>T E ≥-10]]> <![CDATA[-10>T E ≥-20]]> <![CDATA[-20>T E ]]> e 1.0 0.9 0.85 0.8

[0064] S13 calculates the initial opening degree K based on the opening degree influence factor and the initial state data. 0 .

[0065] Specifically, the controller determines the maximum opening degree K of the electronic expansion valve 40 based on the initial state data. MAX The current operating frequency F of compressor 10 t The initial defrosting frequency of the compressor 10 is set. and the maximum opening degree variation coefficient in the opening degree influencing factors. The ambient temperature influence coefficient e is calculated according to equation (1) to obtain the initial opening degree K of the electronic expansion valve 40 when the heat pump unit enters the defrosting operation. 0 .

[0066]

[0067] The time period during which the controller receives the instruction to start defrosting but the heat pump unit has not yet started defrosting is the delay preparation phase. The delay preparation phase lasts for 3 to 5 minutes, during which the above steps S11-S13 are completed.

[0068] When the heat pump unit enters defrosting operation, the controller controls the electronic expansion valve 40 to maintain an initial opening degree K. 0 The valve remains unchanged for the first time period t0.

[0069] After the delayed preparation phase, the heat pump unit enters the defrost start-up procedure, which involves reducing the operating frequency of the compressor, stopping the external fan, and the controller sending a valve port switching command to the four-way valve 20 and controlling the electronic expansion valve 40 to adjust the opening.

[0070] Specifically, the controller calculates the initial opening degree K. 0 The electronic expansion valve 40 is sent a valve adjustment command at the set valve adjustment rate, causing the electronic expansion valve 40 to adjust its opening to the initial opening K according to the set valve adjustment rate. 0 When the controller receives a signal that the electronic expansion valve 40 has reached its initial opening degree K. 0 After receiving the information, a command is sent to the electronic expansion valve 40 to maintain the current opening degree for a period of time t1, so that the compressor maintains the initial opening degree K. 0 It will continue to run for a period of time, t1.

[0071] This application does not impose any restrictions on the conditions for initiating the defrost procedure of a heat pump unit. However, the following criteria can be used to determine the defrost start-up of a heat pump unit: 1) When the outdoor coil contact point temperature... ≤ Minimum set coil temperature And continue for more than 3 minutes; 2) and when the compressor runs continuously for ≥ 5 minutes; 3) and when the compressor runs for a cumulative time ≥ the set defrost interval time.

[0072] After the heat pump unit enters defrosting mode, the controller obtains the coil contact point temperature of the evaporator in real time. Temperature; and the temperature of the coil contact point Compare with the coil contact point defined temperature in the initial state data:

[0073] If the temperature at the coil contact point Less than the coil contact point temperature limit If so, then proceed to step S40;

[0074] If the temperature at the coil contact point Temperature greater than or equal to the coil contact point limit temperature If so, then step S50 is executed.

[0075] Specifically, when the heat pump unit enters defrosting mode, the compressor is at its initial opening degree K. 0 After running continuously for a period of time t1, the controller begins to acquire the coil contact point temperature measured by the first temperature sensor of the heat pump unit in real time. Real-time acquisition of coil contact point temperature The time interval for the data is set to be less than or equal to the defrost valve control cycle. The defrost valve control cycle t is different from the valve control cycle during normal operation of the unit and is a separate parameter value. This value is less than the normal valve control cycle value, preferably less than 10 seconds, to reflect the timeliness of the opening control during defrosting.

[0076] S40 The controller determines the temperature of the coil contact point based on the temperature of the coil contact point. The initial state data and the opening influence factor are used to calculate the current opening degree; the current opening degree is then compared with the minimum opening degree of the electronic expansion valve to output the defrost opening degree; the electronic expansion valve is controlled to remain unchanged within the defrost valve adjustment cycle at the defrost opening degree, and the process returns to step S30, continuously acquiring the coil contact point temperature in real time.

[0077] In practice, the controller obtains the defrost opening degree of the electronic expansion valve 40 after the heat pump unit defrosts through the following sub-steps.

[0078] S41 uses the initial temperature of the coil contact point from the acquired initial state data. Coil contact point temperature limit Maximum opening K MAX Minimum opening K MIN The coefficient of maximum opening degree variation of the opening degree influencing factor Minimum opening variation coefficient Ambient temperature influence coefficient e and real-time coil contact point temperature The current opening degree K of the electronic expansion valve 40 during the defrosting process of the heat pump unit is calculated using equation (2). t .

[0079]

[0080] S42 will specify the current opening degree K t With the minimum opening K MIN Compare the settings and output the defrost opening as follows:

[0081] If the current opening degree is K t Greater than or equal to minimum opening K MIN Then output the current opening degree as the defrost opening degree K = K t ;

[0082] If the current opening degree is K t Less than the minimum opening K MIN Then the minimum opening degree is output as the defrost opening degree K = K MIN .

[0083] S43 controls the electronic expansion valve 40 to remain unchanged within the valve adjustment cycle t at the defrost opening K, and returns to step S30.

[0084] Specifically, based on the defrost opening degree K output in step S42 and the set valve adjustment rate, the controller sends a valve adjustment command to the electronic expansion valve 40, causing the electronic expansion valve 40 to adjust its opening to the defrost opening degree K according to the set valve adjustment rate. When the controller receives information that the opening degree of the electronic expansion valve 40 has reached the defrost opening degree K, it sends a command to the electronic expansion valve 40 to maintain the current opening degree for a period of time t2, causing the compressor to run continuously at the defrost opening degree K for a period of time t, and continuing to monitor the current coil contact point temperature of the evaporator 30. This allows the heat pump unit to continuously defrost under the control of the controller.

[0085] The controller S50 sends a frequency reduction command to the compressor 10 and a valve switching command to the four-way valve 20 to restore the unit's operating mode control of the compressor 10 and the electronic expansion valve 40, so that the heat pump unit ends defrosting.

[0086] The heat pump unit of this invention employs a real-time adjustment method for the opening of the electronic expansion valve during the defrosting process. By combining designed opening control parameters with real-time monitoring and measurement of the coil temperature, the opening of the electronic expansion valve is adjusted in real time during defrosting. This ensures the opening of the electronic expansion valve adapts to the compressor's refrigerant flow requirements during defrosting, reducing the risk of refrigerant liquid slugging and extending the compressor's lifespan. The design of the opening control parameters fully considers the different requirements of varying return water temperatures on the maximum and minimum opening of the electronic expansion valve during defrosting; and the impact of different ambient temperatures on the opening of the electronic expansion valve when the external fan is not running and the heat pump unit is in a static heat exchange state. The real-time defrosting opening of the electronic expansion valve, corrected by the opening control parameters, better matches the compressor's refrigerant flow requirements during defrosting, thereby reducing the risk of refrigerant liquid slugging and improving defrosting reliability and energy efficiency.

[0087] The embodiments described above are merely examples of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and the present invention also intends to include these modifications and variations.

Claims

1. A heat pump unit, comprising a compressor, a four-way valve, an evaporator, an electronic expansion valve, and a condenser connected sequentially via a refrigerant circulation pipeline, and a controller electrically and / or communicatively connected to the compressor, the four-way valve, the electronic expansion valve, and a plurality of temperature sensors, characterized in that: When the controller receives a command to enter defrosting operation but the heat pump unit has not yet entered defrosting operation, the controller acquires the initial state data of the heat pump unit; and determines the opening influence factor of the electronic expansion valve based on the initial state data, and calculates the initial opening of the electronic expansion valve based on the opening influence factor and the initial state data; wherein: The initial state data includes the ambient temperature, the condenser return water temperature, and the initial temperature of the evaporator coil contact point. and the set temperature limit of the coil contact point The operating frequency of the compressor and the set initial defrosting frequency The maximum opening degree of the electronic expansion valve and minimum opening ; The opening degree influencing factor is determined by using the temperature range constant value method based on the return water temperature to determine the maximum opening degree variation coefficient. and minimum opening variation coefficient The ambient temperature influence coefficient is determined according to the ambient temperature range fixed value method. ; When the heat pump unit enters the defrosting operation, the controller controls the electronic expansion valve to remain unadjusted for a first time period at the initial opening. After the heat pump unit enters defrosting mode, the controller acquires the coil contact point temperature of the evaporator in real time. ; and the temperature of the coil contact point Temperature defined by the coil contact point in the initial state data Comparison: If the temperature at the coil contact point Less than the coil contact point temperature limit At that time, the controller calculates the current opening degree of the electronic expansion valve based on the coil contact point temperature, the initial state data, and the opening degree influence factor. : ； The current opening degree is compared with the minimum opening degree of the electronic expansion valve to output the defrost opening degree; the electronic expansion valve is controlled to remain unchanged within the defrost valve adjustment cycle under the defrost opening degree, and the temperature of the coil contact point is continuously acquired in real time. If the temperature at the coil contact point Temperature greater than or equal to the coil contact point limit temperature At this time, the controller sends a frequency reduction command to the compressor and a valve switching command to the four-way valve, restoring the unit's operating mode control for the compressor and electronic expansion valve, thus ending the defrosting process of the heat pump unit.

2. The heat pump unit according to claim 1, characterized in that, The initial opening is calculated according to the following formula: In the formula, This indicates the initial opening degree of the electronic expansion valve. This indicates the maximum opening degree of the electronic expansion valve. This represents the coefficient of variation of the maximum opening degree determined based on the return water temperature. This represents the ambient temperature influence coefficient, determined based on the ambient temperature. Indicates the operating frequency of the compressor. This indicates the initial defrosting frequency of the compressor.

3. The heat pump unit according to claim 1 or 2, characterized in that, The maximum opening variation coefficient is determined according to the temperature range of the return water temperature using the following method: When the return water temperature is less than 20℃, the maximum opening variation coefficient =0.5; When the return water temperature is greater than or equal to 20℃ and less than 35℃, the maximum opening variation coefficient =0.6; When the return water temperature is greater than or equal to 35℃ and less than 45℃, the maximum opening variation coefficient =0.8; When the return water temperature is greater than or equal to 45℃ and less than 55℃, the maximum opening variation coefficient =1.

0.

4. The heat pump unit according to claim 1 or 2, characterized in that, The ambient temperature influence coefficient is determined according to the temperature range of the ambient temperature using the following method: When the ambient temperature is greater than or equal to 0℃ and less than 12℃, the ambient temperature influence coefficient =1.0; When the ambient temperature is greater than or equal to -10℃ and less than 0℃, the ambient temperature influence coefficient =0.9; When the ambient temperature is greater than or equal to -20℃ and less than -10℃, the ambient temperature influence coefficient =0.85; When the ambient temperature is below -20℃, the ambient temperature influence coefficient =0.

8.

5. The heat pump unit according to claim 1, characterized in that, The minimum opening variation coefficient is determined according to the temperature range of the return water temperature using the following method: When the return water temperature is less than 20℃, the minimum opening degree variation coefficient =0.5; When the return water temperature is greater than or equal to 20℃ and less than 35℃, the minimum opening variation coefficient =0.6; When the return water temperature is greater than or equal to 35℃ and less than 45℃, the minimum opening variation coefficient =0.7; When the return water temperature is greater than or equal to 45℃ and less than 55℃, the minimum opening variation coefficient =0.

9.

6. The heat pump unit according to claim 1, characterized in that, The period during which the controller receives the instruction to start defrosting but the heat pump unit has not yet started defrosting is a delay preparation phase, which lasts for 3 to 5 minutes.

7. The heat pump unit according to claim 1, characterized in that, The defrosting valve cycle is shorter than the valve cycle during normal unit operation.

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