Heat pump unit and defrosting control method thereof

Abstract

The invention discloses a heat pump unit and a defrosting control method thereof.According to the heat pump unit, a heat accumulator is arranged between a first electronic expansion valve and an indoor heat exchanger, an outdoor heat exchanger communicates with the heat accumulator through a second pipeline, and a first connector of a four-way reversing valve communicates with the indoor heat exchanger; and meanwhile, the second pipeline is communicated with the outdoor heat exchanger through a fifth pipeline, and the second pipeline is communicated with a second connector of the four-way reversing valve after passing through a fifth electric valve and a second electronic expansion valve in sequence from a pipeline coming out of the heat accumulator. The novel heat pump system is established through the pipeline and the valve, the heat accumulator, bypass defrosting and hot fluorine defrosting technologies are combined, low-grade condensation waste heat is stored through the phase change heat accumulator, and the dual purposes of guaranteeing indoor heating and saving energy consumption during defrosting are achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of air conditioning, and in particular to a heat pump unit with a heat accumulator and a multi-strategy defrosting control method thereof. Background Art

[0002] In China, the regions with higher latitudes are hot in summer and cold in winter. In order to improve people's requirements for indoor comfort, heat pump units are widely used. Heat pump units include compressors, four-way reversing valves, indoor heat exchangers, throttling devices and outdoor heat exchangers. During cooling, 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. The refrigerant condensed in the outdoor heat exchanger becomes a low-temperature and low-pressure liquid through the throttling device, and then introduced into the indoor heat exchanger to exchange heat with the air to provide cooling to the room. The vaporized refrigerant is introduced into the compressor circulation through the low-pressure suction pipe; during 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 provide heating to the room. The condensed refrigerant becomes a low-temperature and low-pressure liquid through the throttling device, and then introduced into the outdoor heat exchanger to exchange heat with the ambient air and vaporize. The vaporized refrigerant returns to the compressor circulation through the low-pressure suction pipe.

[0003] In the winter nights in the north, the outdoor temperature is below 0℃ and the relative humidity is high. The surface of the outdoor heat exchanger is prone to frost when working in winter. At this time, the heat exchange effect of the outdoor heat exchanger deteriorates, resulting in a very low working efficiency of the heat pump unit. Therefore, it is necessary to defrost the outdoor heat exchanger. The existing defrosting method generally switches the heat pump unit from heating operation to cooling operation through the four-way reversing valve, and introduces the high-temperature and high-pressure gas discharged from the compressor into the outdoor heat exchanger for defrosting. This defrosting method is also called hot fluorine defrosting. During the defrosting process, the indoor heat exchanger acts as an evaporator. After the outdoor heat exchanger is defrosted, the four-way reversing valve is controlled to reverse, and the heating cycle is operated to heat the room. During the defrosting operation, the refrigerant heating is suspended, and cold air is discharged into the room, causing the indoor temperature to drop and reducing the comfort of indoor personnel.

[0004] In addition, technicians found that when the heat pump unit was operating to provide indoor heating, a portion of the waste heat from condensation was directly discharged outdoors, resulting in heat waste. Summary of the invention

[0005] The present invention provides a heat pump unit with multi-strategy defrosting and a defrosting control method thereof, so as to solve the technical problems of reducing indoor temperature and wasting condensation waste heat in the defrosting operation of the heat pump unit in the prior art.

[0006] The technical solution adopted by the present invention is to propose a heat pump unit, including a four-way reversing valve, an indoor heat exchanger and an outdoor heat exchanger. The first pipeline between the indoor heat exchanger and the outdoor heat exchanger is provided with a first electric valve, a heat accumulator, a first electronic expansion valve and a second electric valve in sequence. The outdoor heat exchanger is connected to the heat accumulator through a second pipeline. A third electric valve is provided on the second pipeline. The first interface of the four-way reversing valve is connected to the indoor heat exchanger and is connected to the outdoor heat exchanger through a fifth pipeline. A seventh electric valve is provided on the fifth pipeline. The pipeline of the second pipeline coming out of the heat accumulator is connected to the second interface of the four-way reversing valve after passing through the fifth electric valve and the second electronic expansion valve in sequence. When the heat pump unit meets the defrosting conditions, the controller selects to enter the heating and defrosting mode according to the temperature of the heat accumulator.

[0007] In one embodiment, the heat pump unit also includes a third pipeline, one end of which is connected to the pipeline between the second interface 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, and a fourth electric valve is provided on the third pipeline.

[0008] In another embodiment, the heat pump unit further includes a fourth pipeline, one end of which is 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, and a sixth electric valve is provided on the fourth pipeline.

[0009] The defrosting modes of the heat pump unit include a heat storage plus traditional defrosting mode, a heating plus defrosting mode and a heating pause defrosting mode.

[0010] In the heat storage plus conventional defrost 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-plus-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 heating suspension 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 provided on the exhaust pipe of the compressor, and a fifth pipeline connected to the outlet of the gas-liquid separator is led out between the compressor and the one-way valve, on which an unloading electric valve is provided.

[0014] Preferably, the heat accumulator is a phase change heat accumulator, which adopts a cylindrical structure, has built-in finned elbows, and is filled with heat storage materials, and the outside of the cylindrical structure is wrapped with an insulation layer.

[0015] The present invention also proposes a defrost control method for the above-mentioned heat pump unit. When the outdoor heat exchanger meets the defrosting conditions, the controller controls the heat pump unit to enter the heat storage plus traditional defrost mode, the heating plus defrost mode, or the heating defrost mode is suspended according to the temperature of the heat storage device.

[0016] In one embodiment, the defrost control method includes:

[0017] 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 and heat storage mode. If not, proceed to step 2.

[0018] Step 2: Determine whether the temperature of the heat storage device is less than or equal to the temperature of the outdoor heat exchanger. If so, enter the heat storage plus traditional defrost mode; if not, enter the heating plus defrost mode;

[0019] Step 3. Determine whether the time for the heat pump unit to enter the heating and defrosting mode reaches the set time T. If not, maintain the current operation mode unchanged. If so, and the heat pump unit still meets the defrosting conditions, switch to the suspended heating and defrosting mode;

[0020] Step 4. When the temperature of the outdoor heat exchanger is greater than the defrost temperature, exit the defrost mode.

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

[0022] Compared with the prior art, the technical solution proposed by the present invention has the following beneficial effects:

[0023] 1. The present invention adds a phase change heat accumulator in the refrigeration system to store the condensation waste heat of the refrigeration unit, and uses the low-grade condensation waste heat for the defrosting of the system, which not only saves energy consumption but also avoids releasing cold to the room during defrosting.

[0024] 2. The present invention establishes a new type of heat storage heating and defrosting system through pipelines and valves, combines the heat storage device with bypass defrosting and traditional hot fluorine defrosting, and achieves the dual purpose of ensuring indoor heating and saving energy during defrosting by utilizing the low-grade condensation waste heat stored in the phase change heat storage device.

[0025] 3. The multi-strategy defrosting method proposed in the present invention can select different defrosting circuits according to the temperature of the heat storage device and the degree of frost on the outdoor heat exchanger, so as to achieve the purpose of not affecting indoor heating as much as possible when the system is defrosted. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments, wherein:

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

[0028] Figure 2 is a schematic diagram of a phase change heat storage device;

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

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

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

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

[0033] Figure 7 It is the defrost control logic diagram of the heat pump unit.

[0034] in:

[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 one-way valve, 22 unloading solenoid valve;

[0037] 18 intake pressure sensor, 19 exhaust pressure sensor, 20 intake temperature sensor, 21 exhaust temperature sensor;

[0038] 23 insulation layer; 24 heat storage material, 25 fins; 26 copper tube;

[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 solution and advantages of the present invention clearer, the present invention is 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 invention and do not constitute a limitation to the present invention.

[0041] The terms used in this specification are only for describing specific embodiments and are not intended to limit the present invention. Unless otherwise specifically stated, the relative arrangement of the components and steps, numerical expressions and numerical values ​​described in these embodiments do not limit the protection scope of the present invention.

[0042] The techniques, methods and equipment known to ordinary technicians in the relevant fields are not discussed in detail in this specification, but where appropriate, the techniques, methods and equipment should be considered as part of this specification. Any specific values ​​in this specification should be interpreted as being merely exemplary and not limiting the present invention.

[0043] For the convenience of description, the terms describing the position used in the specification, such as "above...", "to the left of...", "in front of...", etc., are only used to describe the spatial position relationship between a certain component and other components of the embodiment shown in the figure. When the position of the component is different, the relative position will change. Therefore, the position relationship of the embodiment of the drawing should not constitute a limitation to the present invention.

[0044] In addition, it should be noted that the terms "first" and "second" used in the specification are only used to distinguish similar components, and there is no order of precedence, so they cannot be understood as limiting the scope of protection of the present invention.

[0045] When the heat pump unit provides indoor heating for a long time in winter, the outdoor heat exchanger is prone to frost. The current method of using a four-way reversing valve to introduce the high-temperature and high-pressure refrigerant discharged from the compressor into the outdoor heat exchanger for hot fluorine defrosting will cause indoor heating to be interrupted and cold air to be discharged into the room, thereby affecting the comfort of indoor personnel. The concept of the present invention is to improve the existing heat pump unit, by adding a heat accumulator and re-planning the refrigerant flow path, so as to minimize the impact on the indoor temperature during defrosting, and at the same time, the condensation waste heat can be recovered and utilized through the heat accumulator to save energy.

[0046] The heat pump unit proposed in the present invention comprises a compressor 1, an oil separator 5, a four-way reversing valve 7, an indoor heat exchanger 2, a first electronic expansion valve 8, an outdoor heat exchanger 4 and a gas-liquid separator 6. An exhaust temperature sensor 21, an exhaust pressure sensor 19 and a one-way valve 17 are provided on the exhaust pipe of the compressor. An intake temperature sensor 20 and an intake pressure sensor 18 are provided on the outlet pipe of the gas-liquid separator.

[0047] The first pipeline 30 between the indoor heat exchanger 2 and the outdoor heat exchanger 4 is provided with a first electric valve 15, a heat accumulator 3, a first electronic expansion valve 8, and a second electric valve 11 in sequence. The outdoor heat exchanger 4 is connected to the heat accumulator 3 through a second pipeline 31, and a third electric valve 12 is provided on the second pipeline. The first interface A of the four-way reversing valve 7 is connected to the indoor heat exchanger 2, and is also connected to the outdoor heat exchanger 4 through a fifth pipeline 34, and a seventh electric valve 10 is provided on the fifth pipeline. The second interface 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 through a third pipeline 32, and a fourth electric valve 16 is provided on the third pipeline. After the second pipeline comes out of the heat accumulator 3, it passes through the fifth electric valve 13 and the second electronic expansion valve 9 in sequence and is connected to the third pipeline 32 between the fourth electric valve 16 and the four-way reversing valve 7. The third interface C of the four-way reversing valve is connected to the suction pipe of the compressor. The pipeline between the four-way reversing valve 7 and the indoor heat exchanger 2 also leads to a fourth pipeline 33 connected to the pipeline between the heat accumulator 3 and the first electric valve 15, and the fourth pipeline is provided with a sixth electric valve 14. The pipeline between the compressor 1 and the one-way valve 17 leads to a sixth pipeline 35 connected to the outlet pipeline of the gas-liquid separator 6, and the unloading electric valve 22 is provided on the sixth pipeline 35.

[0048] like Figure 2 and Figure 3 As shown, the heat accumulator 3 in the above embodiment is a phase change heat accumulator, which adopts the design of an outer barrel with a built-in copper bent pipe to save space and facilitate placement in the outdoor unit of the heat pump unit. The barrel 23 has a built-in copper tube 26, which may have fins 25. The barrel is filled with heat storage material 24, and the outer side of the barrel is wrapped with an insulation layer 23. The insulation layer wraps the phase change heat storage material 24 to reduce heat loss, and the fins 25 can increase the heat dissipation of the copper tube in the heat storage material, which is convenient for heat transfer. The heat storage material can absorb or release a large amount of latent heat during the phase change process, and has a high energy storage density. The phase change material can store more energy in a smaller volume, and is particularly suitable for use in occasions with limited space. The outer shell, built-in tube and heat storage material of the heat accumulator can all be made of other materials that meet the requirements, Figure 1 and Figure 3 The structures in are for illustration only and are not limiting.

[0049] like Figure 1As shown, when the heat pump unit proposed in the present 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 and then reaches the indoor heat exchanger 2 to release heat and provide heating to the indoor room; the refrigerant coming out of the indoor heat exchanger further releases the waste heat of condensation through the heat accumulator 3, and the heat is stored by the heat storage material in the heat accumulator. After that, the liquid refrigerant is throttled and reduced in pressure to the corresponding evaporation pressure through the first electronic expansion valve 8, 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, and then the gaseous refrigerant returns to the compressor to complete a heating cycle.

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

[0051] The heat pump unit proposed in the present invention has a multi-strategy defrosting mode, including: mode 1, heat storage plus traditional defrosting mode; mode 2, heating plus defrosting mode; mode 3, pause heating defrosting mode. Different defrosting modes are controlled by electric valves in each circuit. When the heat pump unit meets the defrosting conditions, the controller selects different defrosting modes according to the temperature of the heat storage tank.

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

[0053] The defrost control method proposed in the present invention is: real-time monitoring of the temperature of the outdoor heat exchanger, when the outdoor heat exchanger meets the defrost conditions, the controller controls the heat pump unit to enter the corresponding defrost mode according to the temperature of the heat storage device.

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

[0055] Figure 4 It is a heat storage plus traditional defrost mode, also known as the heat storage heating fluorine defrost mode, which is the defrost mode 1 mentioned above. In this mode, the second electric valve 11, the first electric valve 15 and the fourth electric valve 16 are opened; 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 and high-pressure refrigerant discharged from the compressor is introduced into the outdoor heat exchanger 4 for defrosting through the one-way valve 17, the oil separator 5, and the four-way reversing valve 7. The refrigerant coming out of the outdoor heat exchanger goes to the heat accumulator 3 to store the condensation waste heat in the heat accumulator, and then returns to the compressor 1 for circulation through the indoor heat exchanger 2, the four-way reversing valve 7, and the gas-liquid separator 6. The first defrost mode will discharge cold air into the room during defrosting, which will affect the indoor temperature. The advantage is that the condensation waste heat is recovered by using the heat accumulator.

[0056] Figure 5 This is a system diagram of the heating and defrosting mode, which is also the defrosting mode 2 mentioned above. In the heating and defrosting mode, the system can maintain heating for the room while defrosting. The control of the valves in this mode is 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 and high-pressure gaseous refrigerant discharged by the compressor is divided into two parts, one part flows to the outdoor heat exchanger 4 through the seventh electric valve 10 for defrosting, and the other part flows into the indoor heat exchanger 2 for indoor heating, so that indoor heating and outdoor defrosting are carried out simultaneously. The refrigerant flowing out of the outdoor heat exchanger 4 and the indoor heat exchanger 2 is heat exchanged through the heat accumulator 3, and the refrigerant absorbs the low-grade heat in the heat accumulator, where the heat accumulator acts as an evaporator. Then the refrigerant returns to the compressor circulation 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 and 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.

[0058] Defrost mode 2 can provide heating to the room while defrosting, ensuring that the indoor temperature will not drop due to outdoor defrosting, providing a good user experience. Defrost mode 2 is used when the outdoor heat exchanger is slightly frosted.

[0059] Figure 6 It is the defrosting mode for suspending heating, which is also the 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 opened; 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 is switched by the four-way reversing valve, and the high-temperature and high-pressure refrigerant discharged by the compressor is introduced to defrost the outdoor heat exchanger 4. Then the refrigerant enters the heat accumulator 3 for heat exchange after cooling and reducing the pressure through the first electronic expansion valve 8. At this time, the heat accumulator acts as an evaporator to provide a heat source for the refrigerant to gasify. The gasified refrigerant returns to the compressor circulation through the four-way reversing valve 7 and the gas-liquid separator 6. This defrosting mode uses the heat accumulator 3 to act as an evaporator to shield the indoor heat exchanger 2. At this time, no cooling is provided to the room, and the indoor temperature will not be affected. This mode is suitable for the situation where the outdoor heat exchanger is severely frosted. Since the indoor heat exchanger 2 is not in the working circuit in this defrosting mode, it will not provide cooling to the room, which guarantees the indoor temperature to the greatest extent. In extreme frosting conditions, when the heat in the heat accumulator is insufficient to provide heat to vaporize the refrigerant, the system controller switches to the traditional hot fluorine defrost mode for rapid defrosting.

[0060] The defrost control method of the heat pump unit proposed in the present invention is: when the outdoor heat exchanger meets the defrost conditions, the controller of the heat pump unit controls the heat pump unit to enter the heat storage plus traditional defrost mode, the heating defrost mode, or the suspended heating defrost mode according to the temperature control of the heat accumulator.

[0061] The defrost control method proposed in the present invention specifically includes: first, judging whether the heat pump unit meets the defrost condition according to the temperature detected by the defrost temperature sensor set on the outdoor heat exchanger, and selecting the defrost mode if the defrost condition is met. The specific selection includes judging the relationship between the temperature of the outdoor heat exchanger and the temperature of the heat accumulator. If the temperature of the heat accumulator is less than or equal to the temperature of the outdoor heat exchanger, the refrigerant flowing out of the outdoor heat exchanger will have no heat to absorb in the heat accumulator, and the defrost mode 1 hot fluorine defrost is selected at this time; if the temperature of the heat accumulator is greater than the temperature of the outdoor heat exchanger, the defrost mode 2 is selected, and the outdoor heat exchanger is defrosted while heating the room; after the defrost time in the defrost mode 2 reaches the set time, the set time in this embodiment is ten minutes, if the heat pump unit still meets the defrost condition, the controller switches the heat pump unit to the defrost mode 3, suspends the heating and defrosting mode, and accelerates the defrost process at this time, and ensures that there is no cold inflow into the indoor heat exchanger, so as to minimize the impact on the indoor temperature.

[0062] Figure 7 The defrost control method proposed by the present 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 and heat storage mode. If not, proceed to step 2.

[0064] Step 2: Determine whether the temperature of the heat storage device is less than or equal to the temperature of the outdoor heat exchanger. If so, enter the traditional defrost mode; if not, enter the heating plus heat storage defrost 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 unchanged. If so, when the heat pump unit still meets the defrosting conditions, switch to the suspended heating defrosting mode;

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

[0067] The heat pump unit and control method thereof proposed in the present invention establish a new type of heat pump system through pipelines and valves, combining the heat accumulator, bypass defrosting and hot fluorine defrosting technology, and utilizing the phase change heat accumulator to store low-grade condensation waste heat, thereby achieving the dual purpose of ensuring indoor heating and saving energy consumption during defrosting.

[0068] The above description is only a specific implementation of the present invention. It should be pointed out that any modification, equivalent substitution and change made within the spirit and framework of the present invention should be included in 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: A first electric valve, a heat accumulator, a first electronic expansion valve and a second electric valve are sequentially arranged on the first pipeline between the indoor heat exchanger and the outdoor heat exchanger. The outdoor heat exchanger is connected to the heat accumulator through a second pipeline. A third electric valve is arranged on the second pipeline. The first interface of the four-way reversing valve is connected to the indoor heat exchanger and is connected to the outdoor heat exchanger through a fifth pipeline. A seventh electric valve is arranged on the fifth pipeline. The pipeline of the second pipeline coming out of the heat accumulator is sequentially connected to the second interface of the four-way reversing valve after passing through the fifth electric valve and the second electronic expansion valve. When the heat pump unit meets the defrosting conditions, the controller selects to enter the heating and defrosting mode according to the temperature of the heat accumulator.

2. The heat pump unit according to claim 1, characterized in that: It also includes a third pipeline, one end of which is connected to the pipeline between the second interface 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. A fourth electric valve is provided on the third pipeline.

3. The heat pump unit according to claim 2, characterized in that: It also includes a fourth pipeline, one end of which is 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. A sixth electric valve is arranged on the fourth pipeline.

4. The heat pump unit according to claim 3, characterized in that: The defrosting modes of the heat pump unit include a heat storage plus traditional defrosting mode, a heating plus defrosting mode and a heating pause defrosting mode.

5. The heat pump unit according to claim 4, characterized in that: In the heat storage plus conventional defrost 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.

6. The heat pump unit according to claim 4, characterized in that: In the heating-plus-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.

7. The heat pump unit according to claim 4, characterized in that: In the heating suspension 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.

8. The heat pump unit according to claim 1, characterized in that: A one-way valve is arranged on the exhaust pipe of the compressor, and a sixth pipeline connected with the outlet of the gas-liquid separator is led out between the compressor and the one-way valve, on which an unloading electric valve is arranged.

9. The heat pump unit according to claim 1, characterized in that: The heat accumulator is a phase change heat accumulator, which adopts a cylindrical structure, has a built-in finned bent pipe, is filled with heat storage material, and is wrapped with a heat preservation layer outside the cylindrical structure.

10. The defrost control method for a heat pump unit according to any one of claims 1 to 9, 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 defrost mode, the heating plus defrost mode, or suspend the heating defrost mode according to the temperature of the heat storage tank.

11. The defrosting control method according to claim 10, 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 and heat storage mode. If not, proceed to step 2. Step 2: Determine whether the temperature of the heat storage device is less than or equal to the temperature of the outdoor heat exchanger. If so, enter the heat storage plus traditional defrost mode; if not, enter the heating plus defrost mode; Step 3. Determine whether the time for the heat pump unit to enter the heating and defrosting mode reaches the set time T. If not, maintain the current operation mode unchanged. If so, 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 greater than the defrost temperature, exit the defrost mode.

12. The defrosting control method according to claim 11, characterized in that: The set time T is 10 minutes.

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