Heat pump defrosting control method

Abstract

The present application belongs to the technical field of heat pump, discloses a heat pump defrosting control method, which is applied to a heat pump unit. The heat pump unit comprises a condenser, an evaporator and a compressor connected in sequence to form a circulating loop. An electronic expansion valve is arranged between the evaporator and the condenser. The heat pump defrosting control method comprises entering a defrosting mode when a defrosting mode self-starting condition is met. After entering the defrosting mode, the compressor adjusts the frequency according to the water inlet temperature, and at the same time, the opening degree of the electronic expansion valve is adjusted from the opening degree before defrosting to the opening degree in the defrosting mode. The heat pump defrosting control method can automatically defrost according to the specific operating conditions of the heat pump unit, avoid the problems of insufficient heat production and shortened service life of the heat pump unit caused by excessive defrosting, and effectively reduce the operating cost of the heat pump unit.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of heat pump, in particular to a heat pump defrosting control method. BACKGROUND

[0002] Air source heat pump is an energy-saving device for realizing heat energy flow control by using heat source difference, which has the advantages of convenient heat source acquisition, high efficiency, simple operation, no pollution, etc. When the heat pump unit is running in heating mode in winter, frost may be formed on the fins as air flows through the fins, which affects the stability and thermal efficiency of the air source heat pump.

[0003] In the existing defrosting control scheme, the timed defrosting method is usually used. In order to effectively reduce the occurrence of frost, defrosting operation is often performed too frequently, which leads to insufficient heating capacity, high operating cost, and seriously affects the service life of the unit.

[0004] Therefore, it is urgent to propose a heat pump defrosting control method to solve the above problems. SUMMARY

[0005] The purpose of the present application is to provide a heat pump defrosting control method which can automatically defrost according to the specific operating conditions of the heat pump unit, avoid the problems of insufficient heating capacity and shortened service life of the heat pump unit caused by excessive defrosting, and effectively reduce the operating cost of the heat pump unit.

[0006] To achieve this purpose, the present application adopts the following technical scheme:

[0007] The heat pump defrosting control method is applied to a heat pump unit, which comprises a condenser, an evaporator and a compressor connected in sequence to form a circulating loop, an electronic expansion valve is arranged between the evaporator and the condenser, and the heat pump defrosting control method comprises that when the heat pump unit meets the self-starting condition of defrosting mode, it enters the defrosting mode.

[0008] After entering the defrosting mode, the compressor adjusts the frequency according to the water inlet temperature, and at the same time, the opening degree of the electronic expansion valve is adjusted from the opening degree K0 before defrosting to the opening degree K of the defrosting mode.

[0009] Optionally, the heat pump defrosting control method further comprises that when the heat pump unit meets the exit condition of defrosting mode, it exits the defrosting mode.

[0010] After exiting the defrosting mode, the opening degree of the electronic expansion valve is adjusted to the defrosting recovery opening degree K1, and the holding time of the defrosting recovery opening degree K1 is 50s-100s.

[0011] K1=K0+α*K0, α is 5%-15%.

[0012] Optionally, the compressor adjusts the frequency according to the water inlet temperature, comprising:

[0013] When the water inlet temperature is less than or equal to T1, the frequency of the compressor is f1;

[0014] When the water inlet temperature is greater than T1 and less than T2, the frequency of the compressor is f2;

[0015] When the water inlet temperature is greater than or equal to T2, the frequency of the compressor is f3;

[0016] T1 and T2 satisfy T1

[0017] Optionally, the defrosting mode opening degree is the maximum opening degree of the electronic expansion valve.

[0018] Optionally, the self-starting condition of the defrosting mode comprises case one:

[0019] (1) The temperature difference between the environment and the evaporator coil is greater than or equal to the preset evaporator coil and environment temperature difference value HST1 for entering the defrosting mode, and the cumulative running time of the compressor heating is greater than or equal to the preset cumulative running minimum time HSTM1 of the compressor heating for entering the defrosting mode, and the duration is greater than or equal to the preset time t; or,

[0020] (2) The temperature difference between the environment and the evaporator coil is greater than or equal to the preset evaporator coil and environment temperature difference value HST2 for entering the defrosting mode plus the preset evaporator coil and environment temperature difference correction value HSTSL, and the cumulative running time of the compressor heating is greater than or equal to the preset cumulative running time HSTM3 of the compressor heating for entering the defrosting mode, and the duration is greater than or equal to the preset time t;

[0021] (3) The water supply temperature is greater than or equal to 17℃ and the return water temperature is greater than or equal to 17℃;

[0022] (4) The heat pump unit has no shutdown fault.

[0023] (5) The evaporator coil temperature is less than or equal to the preset evaporator coil temperature value HST3 for entering the defrosting mode plus the preset evaporator coil and environment temperature difference correction value HSTSL, and the duration is greater than or equal to the preset time t;

[0024] Optionally, the self-starting condition of the defrosting mode comprises case two:

[0025] (1) The environment temperature is less than or equal to the preset environment temperature value HST4, and the duration is greater than or equal to the preset time t;

[0026] (2) The cumulative running time of the compressor heating is greater than or equal to the preset cumulative running maximum time HSTM2 of the compressor heating for entering the defrosting mode, or multiple low pressure faults occur within the preset time period;

[0027] (3) The water supply temperature is greater than or equal to 17℃ and the return water temperature is greater than or equal to 17℃;

[0028] (4) the heat pump unit has no stop failure.

[0029] Optionally, the self-starting condition of the defrosting mode includes case three:

[0030] (1) the evaporator coil temperature ≤ a preset evaporator coil temperature value HST3 for entering the defrosting mode, and the duration ≥ a preset time t;

[0031] (2) the ambient temperature ≤ a preset ambient temperature value HST4, and the duration ≥ a preset time t;

[0032] (3) the compressor heating cumulative running time ≥ a preset compressor heating cumulative running time HSTM3 for entering the defrosting mode;

[0033] (4) the temperature difference between the environment and the evaporator coil ≥ a preset temperature difference value HST2 between the evaporator coil and the environment for entering the defrosting mode, and the duration ≥ a preset time t;

[0034] (5) the water supply temperature ≥ 17℃ and the return water temperature ≥ 17℃;

[0035] (6) the heat pump unit has no stop failure.

[0036] Optionally, the self-starting condition of the defrosting mode includes case four:

[0037] (1) when the ambient temperature ≤ -20℃ and the compressor heating cumulative running time > 20 min, a low-pressure failure occurs;

[0038] (2) the water supply temperature ≥ 17℃ and the return water temperature ≥ 17℃;

[0039] (4) the heat pump unit has no stop failure.

[0040] Optionally, when the evaporator coil of the evaporator has no failure, the defrosting mode exit condition is one or more of the following cases:

[0041] (1) the defrosting mode running time ≥ a preset maximum defrosting mode running time HSRMTM;

[0042] (2) the evaporator coil temperature ≥ a preset evaporator coil temperature value HSECT for exiting the defrosting mode + 5℃, and the duration ≥ a preset first evaporator coil temperature duration HSECTM1 for exiting the defrosting mode;

[0043] (3) the evaporator coil temperature ≥ the preset evaporator coil temperature value HSECT for exiting the defrosting mode, and the duration ≥ a preset second evaporator coil temperature duration HSECTM2 for exiting the defrosting mode;

[0044] (4) the evaporator coil temperature is greater than or equal to the preset evaporator coil temperature value for exiting the defrosting mode HSECT-2℃, and the duration is greater than or equal to the preset third duration of the evaporator coil temperature for exiting the defrosting mode HSECTM3;

[0045] (5) the evaporator coil temperature is greater than or equal to the preset evaporator coil temperature value for exiting the defrosting mode HSECT-5℃, and the duration is greater than or equal to the preset fourth duration of the evaporator coil temperature for exiting the defrosting mode HSECTM4;

[0046] (6) the supply water temperature is less than or equal to 5℃ or the return water temperature is less than or equal to 5℃;

[0047] (7) the heat pump unit has a shutdown fault;

[0048] wherein HSECTM1

[0049] Optionally, when the evaporator coil of the evaporator has a fault, the defrosting mode exit condition is one or more of the following:

[0050] (1) the defrosting mode running time is greater than or equal to the preset defrosting mode timing time HSRTM;

[0051] (2) the supply water temperature is less than or equal to 5℃ or the return water temperature is less than or equal to 5℃;

[0052] (3) the heat pump unit has a shutdown fault.

[0053] Beneficial effects:

[0054] The heat pump unit provided by the application automatically enters the defrosting mode after meeting the self-starting condition. After entering the defrosting mode, the compressor adjusts the frequency according to the water inlet temperature and the electronic expansion valve adjusts the opening degree. Since the frequency of the compressor can be adjusted according to the real-time water inlet temperature, the energy of the heat pump unit is avoided from being wasted due to the excessively high frequency of the compressor, and the service life of the compressor is prolonged. The heat pump unit defrosts when meeting the preset self-starting condition of the defrosting mode, so that the effect of defrosting when there is frost and not defrosting when there is no frost is achieved, and the problem of insufficient heating capacity caused by frequent defrosting of the heat pump unit is effectively avoided. BRIEF DESCRIPTION OF DRAWINGS

[0055] In order to more clearly illustrate the technical solutions in the embodiments of the application, the drawings needed in the description of the embodiments of the application will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the application, and other drawings can be obtained by those skilled in the art according to the contents of the embodiments of the application and the drawings without creative labor.

[0056] Figure 1is a schematic diagram of a heat pump unit provided by the present application;

[0057] Figure 2 is a flow chart of a heat pump defrosting control method provided by the present application.

[0058] in the figure:

[0059] 100, condenser; 200, evaporator; 300, compressor; 400, electronic expansion valve; 500, four-way reversing valve; 600, heat exchanger. DETAILED DESCRIPTION

[0060] The technical solutions of the present application will be described clearly and completely below in conjunction with the drawings. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0061] In the description of the present application, it should be noted that the orientations or positional relationships indicated by the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. are based on the orientations or positional relationships shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and therefore cannot be understood as indicating or implying that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the present application. In addition, the terms "first", "second", etc. are only for the purpose of description, and cannot be understood as indicating or implying relative importance. Among them, the terms "first position" and "second position" are two different positions, and moreover, the "above", "upper" and "upper surface" of the first feature relative to the second feature include the vertical direction of the first feature above and obliquely above the second feature, or only indicate that the horizontal height of the first feature is higher than that of the second feature. The "below", "below" and "below" of the first feature relative to the second feature include the vertical direction of the first feature below and obliquely below the second feature, or only indicate that the horizontal height of the first feature is less than that of the second feature.

[0062] In the description of the present application, it should be noted that unless otherwise explicitly specified and limited, the terms "mounting", "connection", "connection" should be understood broadly, for example, it can be fixedly connected, or it can be detachably connected, or integrally connected; it can be mechanically connected, or it can be electrically connected; it can be directly connected, or it can be indirectly connected through an intermediate medium; it can be the communication inside two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0063] Embodiments of the present application are described below in detail with reference to the accompanying drawings, wherein the same or similar components are denoted by the same or similar reference numerals throughout the drawings. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to explain the present application, and should not be understood as limiting the present application.

[0064] The present embodiment provides a heat pump defrosting control method, applied to a heat pump unit, referring to Figure 1 , the heat pump unit comprises a condenser 100, an evaporator 200 and a compressor 300 connected in sequence to form a circulation loop, an electronic expansion valve 400 is arranged between the evaporator 200 and the condenser 100, and the heat pump defrosting control method comprises entering a defrosting mode when a defrosting mode self-starting condition is met. After entering the defrosting mode, the compressor 300 adjusts the frequency according to the water inlet temperature, and at the same time, the opening degree of the electronic expansion valve 400 is adjusted from the opening degree K0 before defrosting to the defrosting mode opening degree K.

[0065] The above heat pump unit automatically enters the defrosting mode after meeting the self-starting condition. After entering the defrosting mode, the compressor 300 adjusts the frequency according to the water inlet temperature and the electronic expansion valve 400 adjusts the opening degree. Since the frequency of the compressor 300 can be adjusted according to the real-time water inlet temperature, the problem of waste of energy of the heat pump unit due to too high frequency of the compressor 300 is avoided, and the service life of the compressor 300 is prolonged. The heat pump unit defrosts when the preset defrosting mode self-starting condition is met, achieving the effect of defrosting when there is frost and not defrosting when there is no frost, and effectively avoiding the problem of insufficient heating capacity caused by frequent defrosting of the heat pump unit.

[0066] Optionally, the heat pump unit in the present embodiment further comprises a heat exchanger 600 arranged between the condenser 100 and the evaporator 200 and a four-way reversing valve 500. The heat exchanger 600 and the four-way reversing valve 500 are conventional arrangements in the technical field, and will not be described here.

[0067] Further, the compressor 300 adjusts the frequency according to the water inlet temperature, which comprises:

[0068] When the water inlet temperature is less than or equal to T1, the frequency of the compressor 300 is f1;

[0069] When the water inlet temperature is greater than T1 and less than T2, the frequency of the compressor 300 is f2;

[0070] When the water inlet temperature is greater than or equal to T2, the frequency of the compressor 300 is f3;

[0071] T1, T2 satisfy T1

[0072] In the embodiment, T1 = 40℃, T2 = 48℃; f1 = 75Hz, f2 = 65Hz, f3 = 60Hz. That is, when the heat pump unit enters the defrosting mode, if the water inlet temperature is less than or equal to 40℃, the frequency of the compressor 300 is adjusted to 75Hz; if the water inlet temperature is greater than 40℃ and less than 48℃, the frequency of the compressor 300 is adjusted to 65Hz; if the water inlet temperature is greater than or equal to 48℃, the frequency of the compressor 300 is adjusted to 60Hz.

[0073] In other embodiments, the values of T1, T2, f1, f2 and f3 can be set according to specific conditions.

[0074] Further, the defrosting mode opening degree is the maximum opening degree of the electronic expansion valve 400. That is, if the maximum opening degree of the electronic expansion valve 400 is 480 steps, when the heat pump unit enters the defrosting mode, the opening degree of the electronic expansion valve 400 is adjusted to 480 steps.

[0075] Further, the defrosting mode self-starting condition includes case one ((1)-(4) are simultaneously satisfied): (1) the temperature difference between the environment and the evaporator coil is greater than or equal to a preset evaporator coil and environment temperature difference value HST1 for entering the defrosting mode, and the cumulative heating running time of the compressor 300 is greater than or equal to a preset minimum compressor 300 cumulative heating running time HSTM1 for entering the defrosting mode, and the duration is greater than or equal to a preset time t; or, the temperature difference between the environment and the evaporator coil is greater than or equal to a preset evaporator coil and environment temperature difference value HST2 for entering the defrosting mode plus a preset evaporator coil and environment temperature difference correction value HSTSL, and the cumulative heating running time of the compressor 300 is greater than or equal to a preset cumulative heating running time HSTM3 of the compressor 300 for entering the defrosting mode, and the duration is greater than or equal to a preset time t; (2) the evaporator coil temperature is less than or equal to a preset evaporator coil temperature value HST3 for entering the defrosting mode plus a preset evaporator coil and environment temperature difference correction value HSTSL, and the duration is greater than or equal to a preset time t; (3) the water supply temperature is greater than or equal to 17℃ and the water return temperature is greater than or equal to 17℃; (4) the heat pump unit has no shutdown fault. That is, when (1)-(4) are simultaneously satisfied, the defrosting mode is self-started.

[0076] Further, the defrosting mode self-starting condition includes case two ((1)-(4) are simultaneously satisfied): (1) the environment temperature is less than or equal to a preset environment temperature value HST4, and the duration is greater than or equal to a preset time t; (2) the cumulative heating running time of the compressor 300 is greater than or equal to a preset maximum compressor 300 cumulative heating running time HSTM2 for entering the defrosting mode, or, there are multiple low pressure faults in a preset time period; (3) the water supply temperature is greater than or equal to 17℃ and the water return temperature is greater than or equal to 17℃; (4) the heat pump unit has no shutdown fault. That is, when (1)-(4) are simultaneously satisfied, the defrosting mode is self-started.

[0077] Further, the defrosting mode self-starting condition includes case three ((1)-(6) are simultaneously satisfied): (1) the evaporator coil temperature is less than or equal to a preset evaporator coil temperature value HST3 for a duration greater than or equal to a preset time t; (2) the ambient temperature is less than or equal to a preset ambient temperature value HST4 for a duration greater than or equal to a preset time t; (3) the compressor 300 heating cumulative running time is greater than or equal to a preset compressor 300 heating cumulative running time HSTM3 for entering the defrosting mode; (4) the temperature difference between the environment and the evaporator coil is greater than or equal to a preset temperature difference value HST2 between the evaporator coil and the environment for entering the defrosting mode for a duration greater than or equal to a preset time t; (5) the water supply temperature is greater than or equal to 17°C and the return water temperature is greater than or equal to 17°C; and (6) the heat pump unit has no shutdown fault. That is, when (1)-(6) are simultaneously satisfied, the defrosting mode is self-started.

[0078] Further, the defrosting mode self-starting condition includes case four ((1)-(4) are simultaneously satisfied): (1) when the ambient temperature is less than or equal to -20°C and the compressor 300 heating cumulative running time is greater than 20 min, a low-pressure fault occurs; (2) the water supply temperature is greater than or equal to 17°C and the return water temperature is greater than or equal to 17°C; (4) the heat pump unit has no shutdown fault. That is, when (1)-(4) are simultaneously satisfied, the defrosting mode is self-started.

[0079] Referring to Figure 2 When any one of the above case one, case two, case three, and case four occurs, the heat pump unit enters the defrosting mode, the compressor 300 adjusts the frequency according to the water inlet temperature, and at the same time, the opening degree of the electronic expansion valve 400 is adjusted from the opening degree before defrosting to the opening degree in the defrosting mode.

[0080] Further, the heat pump defrosting control method further includes that when the heat pump unit satisfies a defrosting mode exit condition, the heat pump unit exits the defrosting mode, and after exiting the defrosting mode, the opening degree of the electronic expansion valve 400 is adjusted to a defrosting recovery opening degree K1, and the holding time of the defrosting recovery opening degree K1 is 50s-100s, wherein K1=K0+α*K0, and α is 5%-15%. Illustratively, the holding time of the defrosting recovery opening degree K1 can be 50s, 60s, 70s, 80s, 90s, or 100s, etc., and α can be 5%, 10%, or 15%, etc. Illustratively, when α is 10% and the opening degree K0 before defrosting is 100 steps, after exiting the defrosting mode, the opening degree of the electronic expansion valve 400 is 110 steps, and the holding time is 50s-100s. By gradually adjusting the opening degree of the electronic expansion valve 400, the running stability of the heat pump unit in the defrosting exit process is ensured.

[0081] When the evaporator coil has no fault, the defrosting mode exit condition is one or more of the following conditions:

[0082] (1) the defrosting mode running time is greater than or equal to a preset maximum defrosting mode running time HSRMTM;

[0083] (2) the evaporator coil temperature ≥ a preset evaporator coil temperature value for exiting the defrost mode HSECT+5°C, for a duration ≥ a preset evaporator coil temperature first duration for exiting the defrost mode HSECTM1;

[0084] (3) the evaporator coil temperature ≥ a preset evaporator coil temperature value for exiting the defrost mode HSECT, for a duration ≥ a preset evaporator coil temperature second duration for exiting the defrost mode HSECTM2;

[0085] (4) the evaporator coil temperature ≥ a preset evaporator coil temperature value for exiting the defrost mode HSECT-2°C, for a duration ≥ a preset evaporator coil temperature third duration for exiting the defrost mode HSECTM3;

[0086] (5) the evaporator coil temperature ≥ a preset evaporator coil temperature value for exiting the defrost mode HSECT-5°C, for a duration ≥ a preset evaporator coil temperature fourth duration for exiting the defrost mode HSECTM4;

[0087] (6) the supply water temperature ≤ 5°C or the return water temperature ≤ 5°C;

[0088] (7) the heat pump unit has a shutdown fault;

[0089] wherein HSECTM1 < HSECTM2 < HSECTM3 < HSECTM4.

[0090] With continued reference to Figure 2 in the event that the evaporator coil is not faulty, when any one or more of (1)-(7) above are satisfied, the heat pump unit will exit the defrost mode.

[0091] in the event that the evaporator coil is faulty, the defrost mode exit conditions are one or more of:

[0092] (1) the defrost mode run time ≥ a preset defrost mode timing time HSRTM;

[0093] (2) the supply water temperature ≤ 5°C or the return water temperature ≤ 5°C;

[0094] (3) the heat pump unit has a shutdown fault.

[0095] With continued reference to Figure 2 in the event that the evaporator coil is faulty, when any one or more of (1)-(3) above are satisfied, the heat pump unit will exit the defrost mode.

[0096] Further, the preset entering defrost mode evaporator coil and environment maximum temperature difference value HST1, the preset entering defrost mode evaporator coil and environment temperature difference value HST2, the preset entering defrost mode evaporator coil temperature value HST3, the preset entering defrost mode compressor 300 heating cumulative running minimum time HSTM1, the preset entering defrost mode compressor 300 heating cumulative running maximum time HSTM2, the preset entering defrost mode compressor 300 heating cumulative running time HSTM3, the preset entering defrost mode environment temperature value HST4, the preset defrost mode maximum running time HSRMTM, the preset defrost mode timing time HSRTM, the preset defrost mode exit evaporator coil temperature value HSECT, the preset defrost mode exit evaporator coil temperature first duration HSECTM1, the preset defrost mode exit evaporator coil temperature second duration HSECTM2, the preset defrost mode exit evaporator coil temperature third duration HSECTM3, the preset defrost mode exit evaporator coil temperature fourth duration HSECTM4, the preset time t and the preset evaporator coil and environment temperature difference correction value HSTSL can refer to parameter table 1 and parameter table 2. In other embodiments, they can be set according to specific use needs, which are not limited here.

[0097] Parameter table 1

[0098]

[0099] Parameter table 2

[0100]

[0101] Obviously, the above embodiments of the present application are only examples for clearly illustrating the present application, and are not limited to the embodiments of the present application. For those skilled in the art, various obvious changes, readjustments and substitutions can be made without departing from the scope of the present application. Here, it is not necessary and impossible to exhaust all the embodiments. Any modification, equivalent substitution and improvement within the spirit and principle of the present application shall be included in the protection scope of the present application claims.

Claims

1. A heat pump defrosting control method applied to a heat pump unit, the heat pump unit comprising a condenser (100), an evaporator (200) and a compressor (300) connected in sequence to form a circulating loop, an electronic expansion valve (400) being arranged between the evaporator (200) and the condenser (100), characterized in that, The heat pump defrosting control method comprises that when the defrosting mode self-starting condition is met, the heat pump unit enters the defrosting mode; After entering the defrosting mode, the compressor (300) adjusts the frequency according to the water inlet temperature of the condenser (100), and meanwhile, the opening degree of the electronic expansion valve (400) is adjusted from the opening degree K0 before defrosting to the defrosting mode opening degree K; the defrosting mode opening degree is the maximum opening degree of the electronic expansion valve (400); The compressor (300) adjusts the frequency according to the water inlet temperature, which comprises: When the water inlet temperature is less than or equal to T1, the frequency of the compressor (300) is f1; When the water inlet temperature is greater than T1 and less than T2, the frequency of the compressor (300) is f2; When the water inlet temperature is greater than or equal to T2, the frequency of the compressor (300) is f3; T1, T2 satisfy T1 2. The heat pump defrost control method according to claim 1, wherein, The heat pump defrosting control method further comprises that when the defrosting mode exit condition is met, the heat pump unit exits the defrosting mode; After exiting the defrosting mode, the opening degree of the electronic expansion valve (400) is adjusted to the defrosting recovery opening degree K1, and the holding time of the defrosting recovery opening degree K1 is 50s-100s; K1=K0+α*K0, and α is 5%-15%.

3. The heat pump defrost control method according to claim 1, wherein, The defrosting mode self-starting condition comprises case one: (1) the temperature difference between the environment and the evaporator coil is greater than or equal to a preset entering defrosting mode evaporator coil and environment temperature difference value HST1, and the compressor (300) heating cumulative running time is greater than or equal to a preset entering defrosting mode compressor (300) heating cumulative running minimum time HSTM1, and the duration is greater than or equal to a preset time t; Or, the temperature difference between the environment and the evaporator coil is greater than or equal to a preset entering defrosting mode evaporator coil and environment temperature difference value HST2+ a preset evaporator coil and environment temperature difference correction value HSTSL, and the compressor (300) heating cumulative running time is greater than or equal to a preset entering defrosting mode compressor (300) heating cumulative running time HSTM3, and the duration is greater than or equal to a preset time t; (2) the evaporator coil temperature is less than or equal to a preset entering defrosting mode evaporator coil temperature value HST3+ a preset evaporator coil and environment temperature difference correction value HSTSL, and the duration is greater than or equal to a preset time t; (3) the water supply temperature is greater than or equal to 17℃, and the return water temperature is greater than or equal to 17℃; (4) the heat pump unit has no shutdown fault.

4. The heat pump defrost control method according to claim 1, wherein, The defrosting mode self-starting condition comprises case two: (1) the environment temperature is less than or equal to a preset environment temperature value HST4, and the duration is greater than or equal to a preset time t; (2) the compressor (300) heating cumulative running time is greater than or equal to a preset entering defrosting mode compressor (300) heating cumulative running maximum time HSTM2, or, multiple low pressure faults occur within a preset time period; (3) the water supply temperature is greater than or equal to 17℃, and the return water temperature is greater than or equal to 17℃; (4) the heat pump unit has no shutdown fault.

5. The heat pump defrost control method according to claim 1, wherein, The defrosting mode self-starting condition comprises case three: (1) the evaporator coil temperature is less than or equal to a preset entering defrosting mode evaporator coil temperature value HST3, and the duration is greater than or equal to a preset time t; (2) the environment temperature is less than or equal to a preset environment temperature value HST4, and the duration is greater than or equal to a preset time t; (3) The compressor (300) heating cumulative running time ≥ preset compressor (300) heating cumulative running time HSTM3 entering defrost mode; (4) The temperature difference between the environment and the evaporator coil ≥ preset temperature difference HST2 between the evaporator coil and the environment entering defrost mode, and the duration ≥ preset time t; (5) The water supply temperature ≥ 17℃ and the return water temperature ≥ 17℃; (6) The heat pump unit has no shutdown failure.

6. The heat pump defrost control method according to claim 1, wherein, The defrost mode self-starting condition includes case four: (1) When the ambient temperature ≤ -20℃ and the compressor (300) heating cumulative running time > 20 min, a low pressure failure occurs; (2) The water supply temperature ≥ 17℃ and the return water temperature ≥ 17℃; (4) The heat pump unit has no shutdown failure.

7. The heat pump defrost control method according to claim 1, wherein, When the evaporator coil has no failure, the defrost mode exit condition is one or more of the following cases: (1) The defrost mode running time ≥ preset maximum defrost mode running time HSRMTM; (2) The evaporator coil temperature ≥ preset evaporator coil temperature HSECT for defrost mode exit + 5℃, and the duration ≥ preset first evaporator coil temperature duration HSECTM1 for defrost mode exit; (3) The evaporator coil temperature ≥ preset evaporator coil temperature HSECT for defrost mode exit, and the duration ≥ preset second evaporator coil temperature duration HSECTM2 for defrost mode exit; (4) The evaporator coil temperature ≥ preset evaporator coil temperature HSECT-2℃ for defrost mode exit, and the duration ≥ preset third evaporator coil temperature duration HSECTM3 for defrost mode exit; (5) The evaporator coil temperature ≥ preset evaporator coil temperature HSECT-5℃ for defrost mode exit, and the duration ≥ preset fourth evaporator coil temperature duration HSECTM4 for defrost mode exit; (6) The water supply temperature ≤ 5℃ or the return water temperature ≤ 5℃; (7) The heat pump unit has a shutdown failure; Wherein, HSECTM1 < HSECTM2 < HSECTM3 < HSECTM4.

8. The heat pump defrost control method according to claim 1, wherein, When the evaporator coil has a failure, the defrost mode exit condition is one or more of the following: (1) The defrost mode running time ≥ preset defrost mode timing time HSRTM; (2) The water supply temperature ≤ 5℃ or the return water temperature ≤ 5℃; (3) The heat pump unit has a shutdown failure.

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