Heat pump unit and defrosting control method thereof

Abstract

The application discloses a heat pump unit and a defrosting control method thereof. The heat pump unit is provided with a heat accumulator between a first electronic expansion valve and an indoor heat exchanger. The outdoor heat exchanger is communicated with the heat accumulator through a second pipeline. A first interface of a four-way reversing valve is communicated with the indoor heat exchanger and communicated with the outdoor heat exchanger through a fifth pipeline. A pipeline from the heat accumulator is communicated with a second interface of the four-way reversing valve through a fifth electric valve and a second electronic expansion valve in sequence. The application establishes a new heat pump system through pipelines and valves, combines the heat accumulator, bypass defrosting and hot fluorine defrosting technology, stores low-grade condensing waste heat by using the phase change heat accumulator, and achieves the double purposes of ensuring indoor heating and saving energy consumption during defrosting.

Description

TECHNICAL FIELD

[0001] The present application relates to the air conditioning technical field, especially to a heat pump unit with a heat accumulator and a multi-strategy defrosting control method thereof. BACKGROUND

[0002] In China, the latitude of the high area is hot in summer and cold in winter, in order to improve the comfort of people in the room, the heat pump unit is widely used. The heat pump unit includes a compressor, a four-way reversing valve, an indoor heat exchanger, a throttling device and an outdoor heat exchanger. When refrigerating, the high-temperature and high-pressure refrigerant gas discharged by the compressor is introduced into the outdoor heat exchanger through the four-way reversing valve, and the condensed refrigerant in the outdoor heat exchanger becomes low-temperature and low-pressure liquid through the throttling device, and then is introduced into the indoor heat exchanger to exchange heat with the air, to supply cold to the room, and the gasified refrigerant is introduced into the compressor through the low-pressure suction pipe to circulate; when heating, the high-temperature and high-pressure refrigerant gas discharged by the compressor is introduced into the indoor heat exchanger through the four-way reversing valve to exchange heat with the air, to supply heat to the room, and the condensed refrigerant is introduced into the outdoor heat exchanger to exchange heat with the ambient air to be gasified, and the gasified refrigerant is returned to the compressor through the low-pressure suction pipe to circulate.

[0003] In northern China, the outdoor temperature is lower than 0℃ at night in winter, and the relative humidity is high. The surface of the outdoor heat exchanger is easy to frost in winter, and the heat exchange effect of the outdoor heat exchanger is poor, which leads to low efficiency of the heat pump unit. Therefore, the outdoor heat exchanger needs to be defrosted. The existing defrosting method is to reverse the four-way reversing valve to change the heat pump unit from heating operation to refrigeration operation, and the high-temperature and high-pressure gas discharged by the compressor is introduced into the outdoor heat exchanger to defrost, which is also called hot gas defrosting. During the defrosting process, the indoor heat exchanger acts as an evaporator, and after the outdoor heat exchanger is defrosted, the four-way reversing valve is controlled to reverse and run the heating cycle to supply heat to the room. During the defrosting operation, the refrigerant heating is suspended, and cold air is discharged to the room, which leads to a decrease in indoor temperature and reduces the comfort of the indoor personnel.

[0004] In addition, the skilled person finds that during the operation of the heat pump unit to supply heat to the room, a part of the condensing waste heat is directly discharged to the outdoor, causing waste of heat. SUMMARY

[0005] The present application provides a multi-strategy defrosting heat pump unit and a defrosting control method thereof to solve the technical problems of the prior art heat pump unit in defrosting operation, which reduces the indoor temperature and wastes the condensing waste heat.

[0006] The technical scheme adopted by the present application is to provide a heat pump unit, which comprises a four-way reversing valve, an indoor heat exchanger and an outdoor heat exchanger, a first electric valve, a heat accumulator, a first electronic expansion valve and a second electric valve are sequentially arranged on a first pipeline between the indoor heat exchanger and the outdoor heat exchanger, the outdoor heat exchanger is communicated with the heat accumulator through a second pipeline, a third electric valve is arranged on the second pipeline, a first interface of the four-way reversing valve is communicated with the indoor heat exchanger, and the four-way reversing valve is communicated with the outdoor heat exchanger through a fifth pipeline, a seventh electric valve is arranged on the fifth pipeline, a pipeline from the heat accumulator to the four-way reversing valve is communicated with a second interface of the four-way reversing valve through a fifth electric valve and a second electronic expansion valve in sequence, and when the heat pump unit meets defrosting conditions, a controller selects a heating and defrosting mode according to the temperature of the heat accumulator.

[0007] In an embodiment, the heat pump unit further comprises a third pipeline, one end of the third pipeline is communicated with a pipeline between the second interface of the four-way reversing valve and the second electronic expansion valve outlet on the second pipeline, and the other end of the third pipeline is communicated with a pipeline between the outdoor heat exchanger and the third electric valve, and a fourth electric valve is arranged on the third pipeline.

[0008] In another embodiment, the heat pump unit further comprises a fourth pipeline, one end of the fourth pipeline is communicated with a pipeline between the four-way reversing valve and the indoor heat exchanger, and the other end of the fourth pipeline is communicated with a pipeline between the heat accumulator and the first electric valve, and a sixth electric valve is arranged on the fourth pipeline.

[0009] The defrosting mode of the heat pump unit comprises a heat accumulation and traditional defrosting mode, a heating and defrosting mode and a pause heating and defrosting mode.

[0010] In the heat accumulation and traditional defrosting mode, the first electric valve, the second electric valve and the fourth electric valve are opened, and the third electric valve, the fifth electric valve, the sixth electric valve and the seventh electric valve are closed.

[0011] In the heating and defrosting mode, the first electric valve, the third electric valve, the fifth electric valve and the seventh electric valve are opened, and the second electric valve, the fourth electric valve and the sixth electric valve are closed.

[0012] In the pause heating and defrosting mode, the second electric valve, the fourth electric valve and the sixth electric valve are opened, and the first electric valve, the third electric valve, the fifth electric valve and the seventh electric valve are closed.

[0013] Preferably, a one-way valve is arranged on an exhaust pipeline of the compressor, a fifth pipeline communicated with the outlet of the gas-liquid separator is led out between the compressor and the one-way valve, and an unloading electric valve is arranged on the fifth pipeline.

[0014] Preferably, the heat accumulator is a phase change heat accumulator, adopts a barrel structure, is internally provided with finned bent pipes, and is filled with heat storage materials, and the barrel is externally wrapped with a thermal insulation layer.

[0015] The application further provides a defrosting control method of the heat pump unit.

[0016] In an embodiment, the defrosting control method comprises the following steps:

[0017] Step 1: detecting the temperature of the outdoor heat exchanger, and determining whether the outdoor heat exchanger meets the defrosting condition; if not, maintaining the heating and heat storage mode; if yes, proceeding to step 2;

[0018] Step 2: determining whether the temperature of the heat accumulator is less than or equal to the temperature of the outdoor heat exchanger; if yes, proceeding to the heating and traditional defrosting mode; if not, proceeding to the heating and defrosting mode;

[0019] Step 3: determining whether the time of the heat pump unit in the heating and defrosting mode reaches the set time T; if not, maintaining the previous operation mode; if yes, and the heat pump unit still meets the defrosting condition, switching to the heating and defrosting suspension mode;

[0020] Step 4: when the temperature of the outdoor heat exchanger is greater than the defrosting temperature, exiting the defrosting mode.

[0021] Preferably, the set time T is 10 minutes.

[0022] Compared with the prior art, the technical scheme has the following beneficial effects:

[0023] 1. The phase change heat accumulator is added in the refrigeration system to store the condensing waste heat of the refrigeration unit, and the low-grade condensing waste heat is used for defrosting work, thereby saving energy consumption and avoiding releasing cold energy to the room during defrosting.

[0024] 2. The heat accumulator, bypass defrosting and traditional hot gas defrosting are combined through pipelines and valves to establish a new heat storage heating and defrosting system, and the low-grade condensing waste heat stored by the phase change heat accumulator is used to achieve the dual purposes of ensuring indoor heating and saving energy consumption during defrosting.

[0025] 3. The multi-strategy defrosting method can select different defrosting circuits according to the temperature of the heat accumulator and the degree of frosting of the outdoor heat exchanger, and can achieve the purpose of not affecting indoor heating as much as possible during system defrosting. BRIEF DESCRIPTION OF DRAWINGS

[0026] The present application will be described in detail below in conjunction with the accompanying drawings and specific embodiments, wherein:

[0027] Figure 1 is a system diagram of the heat pump unit proposed by the present application;

[0028] Figure 2 is a schematic diagram of the phase change heat accumulator;

[0029] Figure 3 is a cross-sectional schematic diagram of the phase change heat accumulator;

[0030] Figure 4 is a schematic diagram of the refrigerant flow direction of the heat pump unit in the first defrosting mode;

[0031] Figure 5 is a schematic diagram of the refrigerant flow direction of the heat pump unit in the second defrosting mode;

[0032] Figure 6 is a schematic diagram of the refrigerant flow direction of the heat pump unit in the third defrosting mode;

[0033] Figure 7 is a defrosting control logic diagram of the heat pump unit.

[0034] wherein:

[0035] 1 compressor, 2 indoor heat exchanger, 3 heat accumulator, 4 outdoor heat exchanger, 5 oil separator, 6 gas-liquid separator, 7 four-way reversing valve, 8 first electronic expansion valve, 9 second electronic expansion valve;

[0036] 10 seventh electric valve, 11 second electric valve, 12 third electric valve, 13 fifth electric valve, 14 sixth electric valve, 15 first electric valve, 16 fourth electric valve, 17 check valve, 22 unloading electromagnetic valve;

[0037] 18 suction pressure sensor, 19 discharge pressure sensor, 20 suction temperature sensor, 21 discharge temperature sensor;

[0038] 23 thermal insulation layer; 24 heat storage material, 25 fin; 26 copper pipe;

[0039] 30 first pipeline; 31 second pipeline, 32 third pipeline, 33 fourth pipeline, 34 fifth pipeline, 35 sixth pipeline. DETAILED DESCRIPTION

[0040] In order to make the purpose, technical solutions and advantages of the present application more clear, the present application will be described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the following specific embodiments are only used to explain the present application and do not constitute limitation to the present application.

[0041] The terminology used in the present description is for the purpose of describing particular embodiments only and is not intended to limit the present application. Unless specifically defined in these embodiments, the relative arrangement of the components and the numerical expressions and values set forth in the specification do not limit the scope of the present application.

[0042] Techniques, methods, and equipment known to those of ordinary skill in the relevant art are not discussed in detail in this specification, but should be considered part of the specification, where appropriate. Any specific values set forth in this specification are only examples and do not limit the scope of the present application.

[0043] For ease of description, the terms used in the description to describe the position, such as "on", "left", "front", etc. are only used to describe the spatial relationship between the components of the embodiments shown in the drawings and other components, and the relative position will change when the components are placed in different positions, so the position relationship of the embodiment of the drawing should not be limited to the present application.

[0044] In addition, it should be noted that the use of "first", "second" and the like in the specification is only to distinguish similar components and does not imply a sequence, so it should not be understood as limiting the scope of protection of the present application.

[0045] In winter, when the heat pump unit supplies heat to the room for a long time, the outdoor heat exchanger is easy to frost. The method of using four-way valve to introduce high-temperature and high-pressure refrigerant discharged by the compressor into the outdoor heat exchanger for hot fluorine defrosting will cause the interruption of indoor heating, and the cold air is discharged to the indoor, thereby affecting the comfort of the indoor personnel. The idea of the present application is: to improve the existing heat pump unit, by adding a heat accumulator and re-planning the refrigerant flow path, to achieve the purpose of minimizing the impact on indoor temperature during defrosting, and the condensation waste heat can be recovered and utilized through the heat accumulator, thereby saving energy consumption.

[0046] The heat pump unit provided by the present application comprises a compressor 1, an oil separator 5, a four-way valve 7, an indoor heat exchanger 2, a first electronic expansion valve 8, an outdoor heat exchanger 4 and a gas-liquid separator 6. The discharge pipe of the compressor is provided with a discharge temperature sensor 21, a discharge pressure sensor 19 and a one-way valve 17. The outlet pipeline of the gas-liquid separator is provided with a suction temperature sensor 20 and a suction pressure sensor 18.

[0047] A first electric valve 15, a heat accumulator 3, a first electronic expansion valve 8, and a second electric valve 11 are sequentially installed on the first pipeline 30 between the indoor heat exchanger 2 and the outdoor heat exchanger 4. The outdoor heat exchanger 4 is connected to the heat accumulator 3 via a second pipeline 31, on which a third electric valve 12 is installed. The first port A of the four-way reversing valve 7 is connected to the indoor heat exchanger 2 and simultaneously to the outdoor heat exchanger 4 via a fifth pipeline 34, on which a seventh electric valve 10 is installed. The second port B of the four-way reversing valve 7 is connected to the pipeline between the outdoor heat exchanger 4 and the third electric valve 12 via a third pipeline 32, on which a fourth electric valve 16 is installed. After exiting the heat accumulator 3, the second pipeline sequentially passes through the fifth electric valve 13 and the second electronic expansion valve 9 before connecting to the third pipeline 32 between the fourth electric valve 16 and the four-way reversing valve 7. The third port C of the four-way reversing valve is connected to the compressor's suction pipe. A fourth pipe 33 is also led out from the pipe between the four-way reversing valve 7 and the indoor heat exchanger 2, connecting to the pipe between the heat accumulator 3 and the first electric valve 15. A sixth electric valve 14 is installed on the fourth pipe. A sixth pipe 35 is led out from the pipe between the compressor 1 and the one-way valve 17, connecting to the outlet pipe of the gas-liquid separator 6. An unloading electric valve 22 is installed on the sixth pipe.

[0048] like Figure 2 and Figure 3 As shown, the heat storage device 3 in the above embodiment is a phase change heat storage device, employing an outer cylindrical barrel with an inner copper bent tube design to save space and facilitate placement in the outdoor unit of a heat pump unit. The cylindrical barrel 23 contains an inner copper tube 26, which may have fins 25. The barrel is filled with heat storage material 24, and an insulation layer 23 surrounds the barrel. The insulation layer encloses the phase change heat storage material 24 to reduce heat loss, while the fins 25 increase heat dissipation from the copper tube within the heat storage material, facilitating heat transfer. During the phase change process, the heat storage material can absorb or release a large amount of latent heat, resulting in high energy density. Phase change materials can store more energy in a smaller volume, making them particularly suitable for applications with limited space. The outer shell, inner tubes, and heat storage material of the heat storage device can all be made of other suitable materials. Figure 1 and Figure 3 The structures in this example are for illustrative purposes only and do not constitute a limitation.

[0049] like Figure 1As shown, when the heat pump unit proposed in this invention provides heating, the high-temperature and high-pressure refrigerant gas discharged from the compressor 1 passes through the one-way valve 17, the oil separator 5, and the four-way reversing valve 7 in sequence before reaching the indoor heat exchanger 2 to release heat and provide heating to the room. The refrigerant coming out of the indoor heat exchanger passes through the heat storage tank 3 to further release the residual heat of condensation. The heat is stored by the heat storage material in the heat storage tank. Then, the liquid refrigerant passes through the first electronic expansion valve 8 to reduce the pressure to the corresponding evaporation pressure, and then passes through the second electric valve 11 to the outdoor heat exchanger 4 to absorb heat and vaporize. The gaseous refrigerant passes through the fourth electric valve 16, the four-way reversing valve 7, and the vapor-liquid separator 6 on the second pipeline 31 to ensure that no liquid enters the compressor. Then, the gaseous refrigerant returns to the compressor to complete one heating cycle.

[0050] The above heating mode is heating plus heat storage. This invention uses a phase change heat storage device to absorb and utilize the low-grade condensation waste heat in the room, increasing the subcooling degree and improving the heat absorption of the evaporator, thereby improving the heating capacity of the system.

[0051] The heat pump unit proposed in this invention has multiple defrosting modes, including: Mode 1, heat storage plus traditional defrosting mode; Mode 2, heating plus defrosting mode; and Mode 3, heating suspension defrosting mode. Different defrosting modes are controlled by electric valves controlling each circuit. When the heat pump unit meets the defrosting conditions, the controller selects the appropriate defrosting mode based on the temperature of the heat accumulator.

[0052] In one embodiment, the defrosting condition is that the outdoor heat exchanger temperature reaches the set defrosting temperature T. 化霜 At that time, the heat pump unit meets the defrosting conditions.

[0053] The defrosting control method proposed in this invention is as follows: real-time monitoring of the temperature of the outdoor heat exchanger; when the outdoor heat exchanger meets the defrosting conditions, the controller selects and controls the heat pump unit to enter the corresponding defrosting mode based on the temperature of the heat accumulator.

[0054] The different defrosting modes are described in detail below with reference to the accompanying drawings.

[0055] Figure 4 This is a heat storage combined with traditional defrosting mode, also known as heat storage heating refrigerant defrosting mode, or defrosting mode one mentioned above. In this mode, the second electric valve 11, the first electric valve 15, and the fourth electric valve 16 are open; the seventh electric valve 10, the third electric valve 12, the fifth electric valve 13, and the sixth electric valve 14 are closed. The high-temperature, high-pressure refrigerant discharged from the compressor passes through the one-way valve 17, the oil separator 5, and the four-way reversing valve 7, and is introduced into the outdoor heat exchanger 4 for defrosting. The refrigerant from the outdoor heat exchanger goes to the heat accumulator 3 to store the condensation waste heat, and then returns to the compressor 1 through the indoor heat exchanger 2, the four-way reversing valve 7, and the gas-liquid separator 6 for circulation. In the first defrosting mode, cold air is discharged into the room during defrosting, which will affect the indoor temperature. The advantage is that the heat accumulator recovers the condensation waste heat.

[0056] Figure 5 This is a system diagram for the heating and defrosting mode, also known as defrosting mode two mentioned above. In this mode, the system can maintain heating to the room while defrosting. The valves in this mode are controlled as follows: the seventh electric valve 10, the third electric valve 12, the fifth electric valve 13, and the first electric valve 15 are open; the second electric valve 11, the sixth electric valve 14, and the fourth electric valve 16 are closed. The high-temperature, high-pressure gaseous refrigerant discharged from the compressor is divided into two parts. One part flows through the seventh electric valve 10 to the outdoor heat exchanger 4 for defrosting, and the other part flows into the indoor heat exchanger 2 for indoor heating, achieving simultaneous indoor heating and outdoor defrosting. The refrigerant flowing from the outdoor heat exchanger 4 and the indoor heat exchanger 2 undergoes heat exchange in the heat accumulator 3, where the refrigerant absorbs the low-grade heat in the heat accumulator, which acts as an evaporator. Subsequently, the refrigerant returns to the compressor cycle through the fifth electric valve 13, the second electronic expansion valve 9, the four-way reversing valve 7, and the vapor-liquid separator 6.

[0057] The amount of high-temperature, high-pressure gaseous refrigerant flowing from the compressor into the outdoor heat exchanger 4 can be adjusted by the seventh electric valve 10 according to the degree of frost formation.

[0058] Defrost Mode 2 can provide indoor heating while defrosting, ensuring that the indoor temperature does not drop due to outdoor defrosting, resulting in a better user experience. Defrost Mode 2 is suitable for situations where the outdoor heat exchanger has only a light layer of frost.

[0059] Figure 6 This is the defrosting mode, also known as defrosting mode three mentioned above. In this mode, the second electric valve 11, the sixth electric valve 14, and the fourth electric valve 16 are open; the seventh electric valve 10, the third electric valve 12, the fifth electric valve 13, and the first electric valve 15 are closed. The heat pump unit reverses the flow through the four-way reversing valve, introducing high-temperature, high-pressure refrigerant discharged from the compressor to defrost the outdoor heat exchanger 4. Subsequently, the refrigerant passes through the first electronic expansion valve 8 to cool and depressurize before entering the heat accumulator 3 for heat exchange. At this time, the heat accumulator acts as an evaporator, providing a heat source for the refrigerant to vaporize. The vaporized refrigerant then returns to the compressor for circulation through the four-way reversing valve 7 and the gas-liquid separator 6. This defrosting mode utilizes the heat accumulator 3 as an evaporator, shielding the indoor heat exchanger 2. No cooling is supplied to the room at this time, so the indoor temperature is not affected. This mode is suitable for situations where the outdoor heat exchanger is severely frosted. Because the indoor heat exchanger 2 is not in the working circuit in this defrosting mode, it does not provide cooling to the room, ensuring that the indoor temperature remains constant to the greatest extent possible. In extreme frosting conditions, when the heat in the accumulator is insufficient to provide enough heat for the refrigerant to vaporize, the system controller switches back to the traditional hot refrigerant defrosting mode for rapid defrosting.

[0060] The defrosting control method for heat pump units proposed in this invention is as follows: when the outdoor heat exchanger meets the defrosting conditions, the controller of the heat pump unit selects the heat pump unit to enter the heat storage plus traditional defrosting mode, the heating defrosting mode, or the suspended heating defrosting mode according to the temperature control of the heat storage unit.

[0061] The defrosting control method proposed in this invention specifically includes: firstly, determining whether the heat pump unit meets the defrosting conditions based on the temperature detected by the defrosting temperature sensor installed on the outdoor heat exchanger; if the defrosting conditions are met, then selecting a defrosting mode. Specifically, this selection includes determining the relationship between the temperature of the outdoor heat exchanger and the temperature of the heat storage unit. If the temperature of the heat storage unit is less than or equal to the temperature of the outdoor heat exchanger, then the refrigerant flowing from the outdoor heat exchanger will have no heat to absorb in the heat storage unit, and in this case, defrosting mode one (hot refrigerant defrosting) is selected. If the temperature of the heat storage unit is greater than the temperature of the outdoor heat exchanger, defrosting mode two is selected, simultaneously providing indoor heating and defrosting the outdoor heat exchanger. After the defrosting time in defrosting mode two reaches the set time (in this embodiment, the set time is ten minutes), if the heat pump unit still meets the defrosting conditions, the controller switches the heat pump unit to defrosting mode three, suspending the heating defrosting mode. This accelerates the defrosting process and ensures that no cold air flows into the indoor heat exchanger, minimizing the impact on the indoor temperature.

[0062] Figure 7 This is a flowchart of the defrosting control process. The defrosting control method proposed in this invention specifically includes:

[0063] Step 1. Detect the temperature of the outdoor heat exchanger to determine whether the outdoor heat exchanger meets the defrosting conditions. If not, maintain the heating plus heat storage mode. If not, proceed to Step 2.

[0064] Step 2. Determine if the temperature of the heat storage unit is less than or equal to the temperature of the outdoor heat exchanger. If yes, then enter the traditional defrosting mode; otherwise, enter the heating plus heat storage defrosting mode.

[0065] Step 3. Determine whether the time for the heat pump unit to enter the heating plus heat storage defrosting mode has reached the set time T. If not, maintain the current operating mode. If yes, switch to the suspended heating defrosting mode when the heat pump unit still meets the defrosting conditions.

[0066] Step 4. When the temperature of the outdoor heat exchanger is higher than the defrost temperature, exit the defrost mode.

[0067] The heat pump unit and its control method proposed in this invention establish a new type of heat pump system through pipelines and valves, combining heat accumulators, bypass defrosting and hot fluorine defrosting technology, and using phase change heat accumulators to store low-grade condensation waste heat, so as to achieve the dual purpose of ensuring indoor heating and saving energy during defrosting.

[0068] The above description is merely a specific embodiment of the present invention. It should be noted that any modifications, equivalent substitutions, and variations made within the spirit and framework of the present invention should be included within the protection scope of the present invention.

Claims

1. A heat pump unit, comprising a four-way reversing valve, an indoor heat exchanger, and an outdoor heat exchanger, characterized in that, The first pipeline between the indoor heat exchanger and the outdoor heat exchanger is sequentially equipped with a first electric valve, a heat accumulator, a first electronic expansion valve, and a second electric valve. The outdoor heat exchanger is connected to the heat accumulator via a second pipeline. The second pipeline is equipped with a third electric valve. The first port of the four-way reversing valve is connected to the indoor heat exchanger and simultaneously connected to the outdoor heat exchanger via a fifth pipeline. The fifth pipeline is equipped with a seventh electric valve. The pipe from the heat accumulator in the second pipeline passes sequentially through the fifth electric valve and the second electronic expansion valve before connecting to the second port of the four-way reversing valve. The heat pump unit also includes a third pipeline, one end of which is connected to the pipeline between the second port of the four-way reversing valve and the outlet of the second electronic expansion valve on the second pipeline, and the other end is connected to the pipeline between the outdoor heat exchanger and the third electric valve. The third pipeline is equipped with a fourth electric valve. The fourth pipeline is one end connected to the pipeline between the four-way reversing valve and the indoor heat exchanger, and the other end is connected to the pipeline between the heat accumulator and the first electric valve. The fourth pipeline is equipped with a sixth electric valve.

2. The heat pump unit as described in claim 1, characterized in that, The defrosting modes of the heat pump unit include heat storage plus traditional defrosting mode, heating plus defrosting mode, and heating suspension defrosting mode.

3. The heat pump unit as described in claim 2, characterized in that, In the heat storage plus conventional defrosting mode, the first electric valve, the second electric valve, and the fourth electric valve are open; the third electric valve, the fifth electric valve, the sixth electric valve, and the seventh electric valve are closed.

4. The heat pump unit as described in claim 2, characterized in that, In the heating and defrosting mode, the first electric valve, the third electric valve, the fifth electric valve, and the seventh electric valve are open; the second electric valve, the fourth electric valve, and the sixth electric valve are closed.

5. The heat pump unit as described in claim 2, characterized in that, In the suspended heating defrosting mode, the second electric valve, the fourth electric valve, and the sixth electric valve are open; the first electric valve, the third electric valve, the fifth electric valve, and the seventh electric valve are closed.

6. The heat pump unit as described in claim 1, characterized in that, The compressor's exhaust pipe is equipped with a one-way valve, and a sixth pipeline is led out between the compressor and the one-way valve and connected to the outlet of the gas-liquid separator, on which an unloading electric valve is installed.

7. The heat pump unit as described in claim 1, characterized in that, The heat accumulator is a phase change heat accumulator with a cylindrical structure. It has internal finned tubes and is filled with heat storage material. The cylinder is wrapped with an insulation layer.

8. The defrosting control method for a heat pump unit according to any one of claims 1-7, characterized in that, When the outdoor heat exchanger meets the defrosting conditions, the controller controls the heat pump unit to enter the heat storage plus traditional defrosting mode, the heating plus defrosting mode, or the suspended heating defrosting mode according to the temperature of the heat storage unit.

9. The defrosting control method as described in claim 8, characterized in that, include: Step 1. Detect the temperature of the outdoor heat exchanger to determine whether the outdoor heat exchanger meets the defrosting conditions. If not, maintain the heating plus heat storage mode. If not, proceed to Step 2. Step 2. Determine if the temperature of the heat storage unit is less than or equal to the temperature of the outdoor heat exchanger. If yes, then enter the heat storage plus traditional defrosting mode; otherwise, enter the heating plus defrosting mode. Step 3. Determine whether the time for the heat pump unit to enter the heating and defrosting mode has reached the set time T. If not, maintain the current operating mode. If yes, and the heat pump unit still meets the defrosting conditions, switch to the suspended heating and defrosting mode. Step 4. When the temperature of the outdoor heat exchanger is higher than the defrost temperature, exit the defrost mode.

10. The defrosting control method as described in claim 9, characterized in that, The set time T is 10 minutes.

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