Four-pipe air-cooled heat pump unit and its control method

Abstract

This application relates to the field of heat pump air conditioners, in particular to a four-pipe air-cooled heat pump unit and its control method. The four-pipe air-cooled heat pump unit includes a compressor, a four-way valve, a finned coil, a hot water side heat exchanger, a cold water side heat exchanger, a three-way valve, a first electronic expansion valve, a second electronic expansion valve, and a gas-liquid separator. The finned coil includes a first heat exchange circuit on the air inlet side and a second heat exchange circuit on the air outlet side, and the heat exchange area of the second heat exchange circuit is larger than that of the first heat exchange circuit. For the four-pipe air-cooled heat pump unit of this application, according to the requirements of the environment and working conditions, by using different finned coil heat exchange circuits, when the ambient temperature is lower than the compressor suction saturation temperature, refrigerant will not accumulate in the finned coil, and as much refrigerant as possible can be made to participate in the cycle of the refrigeration system, preventing the evaporation temperature of the unit from dropping significantly due to the reduction in the circulating amount of the refrigerant participating in the work.

Description

Technical Field

[0001] The present application relates to the field of heat pump air conditioners, in particular to a four-pipe air-cooled heat pump unit and its control method. Background Art

[0002] Currently, there are more and more four-pipe air-cooled heat pump units on the market. However, when operating in the winter cooling + hot water mode, when the ambient temperature is lower than the compressor suction saturation temperature, the refrigerant will migrate into the finned coil, resulting in a reduction in the refrigerant circulation volume participating in the work, a significant drop in the evaporation temperature of the unit, affecting the operating efficiency of the unit, and seriously affecting the reliability of the unit operation in severe cases.

[0003] In view of the above problems, the prior art mostly uses valves to control the migration of the refrigerant to the finned coil. The specific solutions are as follows. Solution 1: An electric ball valve is arranged on the connecting pipe between the four-way valve and the finned coil. In the cooling + hot water mode, the electric ball valve is closed to prevent the refrigerant from migrating from the gas-liquid separator through the four-way valve into the finned coil. Solution 2: A check valve is arranged on the connecting pipe between the four-way valve and the gas-liquid separator. When the pressure in the gas-liquid separator is higher than the pressure in the finned coil, the migration of the refrigerant is blocked. For example, the application publication number of the applicant's prior application is: CN113446756A. However, the above solutions can only block the migration of the refrigerant to the finned coil to a certain extent, and they cannot drive the refrigerant that has already accumulated in the finned coil back into the refrigeration system to participate in the cycle. In addition, for the above Solution 2, in the single hot water mode, pressure loss may occur when the low-pressure return gas passes through the check valve, thereby affecting the performance of the compressor. Summary of the Invention

[0004] In view of the technical problems existing in the prior art, the present application provides a four-pipe air-cooled heat pump unit and its control method, and the heat pump unit has high operating efficiency and good reliability.

[0005] On the one hand, the present application proposes a four-pipe air-cooled heat pump unit, which includes a compressor, a four-way valve, a finned coil, a hot water side heat exchanger, a cold water side heat exchanger, a three-way valve, a first electronic expansion valve, a second electronic expansion valve, and a gas-liquid separator. The finned coil includes a first heat exchange circuit on the air inlet side and a second heat exchange circuit on the air outlet side, and the heat exchange area of the second heat exchange circuit is 1.5 - 5 times that of the first heat exchange circuit; the outlet of the compressor is connected to the interface D of the four-way valve, the interface C of the four-way valve is connected to the hot water side heat exchanger, the interface E of the four-way valve is connected to one end of the second heat exchange circuit of the finned coil, the gas-liquid separator is provided with two inlets and one outlet, one of the two inlets is connected to the interface S of the four-way valve, the other inlet is connected to the outlet of the cold water side heat exchanger, and the outlet of the gas-liquid separator is connected to the inlet of the compressor; the hot water side heat exchanger is connected to the interface A of the three-way valve, the interface B of the three-way valve is connected to one end of the first heat exchange circuit of the finned coil, and the other end of the first heat exchange circuit is connected in parallel with the interface C of the three-way valve and then connected to the first electronic expansion valve and the second electronic expansion valve respectively; the first electronic expansion valve is connected to the inlet of the cold water side heat exchanger, the second electronic expansion valve is connected to the other end of the second heat exchange circuit, and a bypass is also provided between the two and is connected to the first electronic expansion valve; in different operating modes, the first heat exchange circuit and the second heat exchange circuit are alternatively used as the outdoor heat exchanger.

[0006] Specifically, a second check valve is provided at the outlet of the hot water side heat exchanger, the outlet of the second check valve is connected to a liquid receiver, and the liquid receiver is connected to the interface A of the three-way valve.

[0007] Specifically, the first heat exchange circuit is connected in parallel with the interface C of the three-way valve and then connected to a drying filter, and the outlet of the drying filter is connected to the first electronic expansion valve and the second electronic expansion valve respectively.

[0008] Specifically, a check valve is provided in the bypass, and the outlet of the first heat exchange circuit is connected in parallel with the interface C of the three-way valve and the outlet of the first check valve and then connected to the inlet of the drying filter.

[0009] Specifically, the three-way valve is an electric three-way valve.

[0010] On the other hand, the present application proposes a control method for the cooling + hot water mode of a four-pipe air-cooled heat pump unit. The four-pipe air-cooled heat pump unit is as described above. When the heat pump unit is operated in the cooling + hot water mode, the four-way valve shall not be energized, the three-way valve interface A and the interface B are connected, the second electronic expansion valve is closed, and the first electronic expansion valve is connected; the compressor discharges high-temperature and high-pressure gas through the four-way valve interface D and the interface C into the hot water side heat exchanger, and the heat generated during the condensation process is discharged to the hot water to heat it and then condense it into a high-pressure liquid. The high-pressure liquid refrigerant then flows through the first heat exchange circuit of the fin coil through the three-way valve, and then to the first electronic expansion valve to throttle and reduce the pressure to a low-temperature and low-pressure gas-liquid two-phase refrigerant and then enters the cold water side heat exchanger. The refrigerant absorbs heat from the chilled water flowing through the cold water side heat exchanger and cools it down. After the refrigerant evaporates and exchanges heat, it returns to the compressor suction port through the gas-liquid separator, and circulates back and forth.

[0011] In particular, when the load demand on the cold water side is large and the load demand on the hot water side is relatively small, the heat exchange fan of the fin coil can be turned on appropriately to exchange heat with the high-pressure liquid refrigerant flowing through the first heat exchange circuit of the fin coil close to the air outlet side to increase its subcooling, thereby increasing the cooling capacity of the unit, balancing the cold and hot loads, and reducing the frequent mode switching of the unit.

[0012] On the third aspect, the present application proposes a control method for the hot water mode of a four-pipe air-cooled heat pump unit. The four-pipe air-cooled heat pump unit is as described above. When the unit is operated in a single hot water mode, the four-way valve shall not be energized, the flow direction of the three-way valve is from A to C, the first electronic expansion valve is closed, and the second electronic expansion valve is turned on; the high-temperature and high-pressure gas discharged from the compressor enters the hot water side heat exchanger through the four-way valve to discharge heat to the hot water to heat it, and the refrigerant is condensed into a high-pressure liquid with a certain degree of supercooling, and then flows through the three-way valve to the second electronic expansion valve and is throttled into a low-temperature and low-pressure gas-liquid two-phase refrigerant, and then flows into the second heat exchange circuit of the fin coil, evaporates and exchanges heat into a low-pressure gas, and then flows through the four-way valve through the gas-liquid separator and returns to the compressor suction port, and so on.

[0013] In the fourth aspect, the present application proposes 9. A control method for the refrigeration mode of a four-pipe air-cooled heat pump unit. The four-pipe air-cooled heat pump unit is as described above. When the unit is operated in a single refrigeration mode, the four-way valve is energized, the second electronic expansion valve is closed, the first electronic expansion valve is working, and there is no requirement for the flow direction of the three-way valve; the high-temperature and high-pressure gas discharged by the compressor enters the second heat exchange circuit of the fin coil through the four-way valve, and after dissipating the heat to the atmosphere, the refrigerant condenses and exchanges heat into a high-pressure liquid, and then flows through the bypass between the second electronic expansion valve and the second heat exchange circuit to the first electronic expansion valve, throttled into a low-temperature and low-pressure gas-liquid two-phase refrigerant, and then flows into the cold water side heat exchanger, and absorbs heat from the chilled water flowing through the cold water side heat exchanger, and after cooling the chilled water, the refrigerant evaporates and exchanges heat into a low-pressure superheated gas, and then returns to the compressor suction port through the gas-liquid separator, repeating the cycle.

[0014] Specifically, when the unit operates at an ambient temperature lower than -10°C and the set water temperature on the hot water side has reached or there is no hot water demand on the hot water side, the hot water flow rate in and out of the hot water side heat exchanger is closed. The four-way valve loses power and the flow direction is from the D interface to the C interface. The flow direction of the three-way valve is switched to from the A interface to the B interface. The high-temperature and high-pressure gaseous refrigerant discharged from the compressor only releases heat and condenses in the first heat exchange circuit with a smaller finned coil heat exchange area. The pressure in the condenser is increased, and the reliability of the unit's single refrigeration operation at ultra-low temperatures is ensured.

[0015] Based on common knowledge in the art, the above preferred conditions can be combined arbitrarily to obtain various preferred examples of this application.

[0016] The above technical solution has the following advantages or beneficial effects: The four-pipe air-cooled heat pump unit of this application can, according to the requirements of the environment and working conditions, by using different finned coil heat exchange circuits, when the ambient temperature is lower than the compressor suction saturation temperature, no refrigerant will accumulate in the finned coil, and as much refrigerant as possible can participate in the cycle of the refrigeration system, preventing the evaporation temperature of the unit from dropping significantly due to the reduction in the circulating amount of the refrigerant participating in the work. Description of the Drawings

[0017] In order to more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, for those skilled in the art, without creative efforts, other drawings can also be obtained based on the provided drawings.

[0018] Figure 1 It is a schematic structural diagram of a four-pipe air-cooled heat pump unit according to this application.

[0019] Figure 2 It is a schematic structural diagram of the finned coil according to this application.

[0020] Wherein, 1 - compressor; 2 - four-way valve; 3 - finned coil; 30 - first heat exchange tube; 31 - aluminum foil; 32 - end plate; 33 - flute-shaped liquid inlet tube; 311 - liquid inlet interface; 34 - flute-shaped intermediate liquid tube; 35 - flute-shaped liquid outlet tube; 312 - liquid outlet interface; 36 - distributor assembly; 322 - liquid-containing side interface; 313 - capillary liquid dividing tube; 37 - elbow; 38 - gas collecting pipe; 39 - second heat exchange tube; 4 - first check valve; 5 - dryer filter; 6 - first electronic expansion valve; 7 - cold water side heat exchanger; 8 - gas-liquid separator; 9 - hot water side heat exchanger; 10 - second check valve; 11 - accumulator; 12 - three-way valve; 13 - second electronic expansion valve. Detailed Embodiments

[0021] Combined with the accompanying drawings of the present application, the technical solutions in the embodiments of the present application will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present application, aiming to explain the inventive concept. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without creative efforts belong to the scope of protection of the present application.

[0022] The terms "first", "second", etc. used in the description are only for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, features defined with "first", "second" may explicitly or implicitly include one or more of such features. The meaning of the term "plural" is two or more, unless otherwise specifically defined.

[0023] Unless otherwise clearly specified and defined, the terms "connected", "communicated", etc. used in the description should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or integrated; it can be a mechanical connection, an electrical connection; it can be directly connected, indirectly connected through an intermediate medium; it can be the communication inside two components or the interaction relationship between two components. For those of ordinary skill in the art, the specific meanings of the above terms in the embodiments can be understood according to specific circumstances.

[0024] The term "a specific embodiment" used in the description means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in a suitable manner in any one or more embodiments or examples. In addition, without contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0025] Refer to Figure 1 , a specific embodiment of the present application discloses a four-pipe air-cooled heat pump unit, and the heat pump unit includes a compressor 1, a four-way valve 2, a finned coil 3, a hot water side heat exchanger 9, a cold water side heat exchanger 7, a three-way valve 12, a first electronic expansion valve 6, a second electronic expansion valve 13, and a gas-liquid separator 8. The three-way valve 12 is preferably an electric three-way valve.

[0026] The outlet of the compressor 1 is connected to the interface D of the four-way valve 2, the interface C of the four-way valve 2 is connected to the hot water side heat exchanger 9, the interface E of the four-way valve 2 is connected to the fin coil 3, and the gas-liquid separator 8 is provided with two inlets and one outlet, one of the two inlets of the gas-liquid separator 8 is connected to the interface S of the four-way valve 2, and the other inlet is connected to the outlet of the cold water side heat exchanger 7, and the outlet of the gas-liquid separator 8 is connected to the inlet of the compressor 1.

[0027] refer to Figure 2 A specific embodiment of the present application discloses a fin coil of a four-pipe air-cooled heat pump unit, wherein the fin coil 3 includes a shell composed of an end plate 32 and an aluminum foil 31, a heat exchange fan is arranged on one side of the shell, a first heat exchange tube 30 is arranged on the air inlet side of the shell, and a second heat exchange tube 39 is arranged on the air outlet side of the shell. A flute-shaped liquid inlet pipe 33 is connected in series with a plurality of first heat exchange tubes 30, a flute-shaped intermediate liquid pipe 34 and a flute-shaped liquid outlet pipe 35 to form a first heat exchange circuit, wherein a liquid inlet interface 311 of the flute-shaped liquid inlet pipe 33 is connected to an interface B of the three-way valve 12, and a liquid outlet interface 312 of the flute-shaped liquid outlet pipe 35 is connected to an interface C of the three-way valve 12 and an outlet of the first check valve 4 in parallel, and then connected to an inlet of a drying filter 5. The second heat exchange tube 39 is connected to the elbow 37 to form a group, and the distributor assembly 36, a plurality of capillary liquid separation tubes 313, a group of second heat exchange tubes 39, and a gas collecting pipe 38 are connected in series to form a second heat exchange loop, wherein the gas side interface 321 of the gas collecting pipe 38 is connected to the interface E of the four-way valve 2, and the liquid side interface 322 of the distributor assembly 36 is respectively connected to the inlet of the second electronic expansion valve 13 and the first check valve 4. The first heat exchange loop is a small auxiliary heat exchange zone, and the second heat exchange loop is a large main heat exchange zone. Preferably, the heat exchange area of the main heat exchange zone is 1.5-5 times that of the auxiliary heat exchange zone, and most preferably 2-3 times.

[0028] A second one-way valve 10 is provided at the outlet of the hot water side heat exchanger 9, the outlet of the second one-way valve 10 is connected to the liquid reservoir 11, the liquid reservoir 11 is connected to the interface A of the three-way valve 12, the interface B of the three-way valve 12 is connected to one end of the first heat exchange circuit of the fin coil 3, and the other end of the first heat exchange circuit is connected to the interface C of the three-way valve 12 and the outlet of the first one-way valve 4 and then connected to the inlet of the drying filter 5.

[0029] When the unit is operated in cooling + hot water mode, the four-way valve 2 is de-energized, the interface A of the three-way valve 12 is connected to the interface B, the second electronic expansion valve 13 is closed, and the first electronic expansion valve 6 is connected.

[0030] When the unit is operated in the cooling + hot water mode, the refrigerant flow and its heat exchange are as follows: the compressor 1 discharges high-temperature and high-pressure gas through the four-way valve 2 interface D and interface C into the hot water side heat exchanger 9, and discharges a large amount of heat generated during the condensation process to the hot water to heat it up and then condense it into a high-pressure liquid. The high-pressure liquid refrigerant then flows into the liquid storage 11 through the second one-way valve 10, and the high-pressure liquid refrigerant then flows through the first heat exchange circuit of the fin coil 3, the drying filter 5 to the first electronic expansion valve 6 through the three-way valve 12, and enters the cold water side heat exchanger 7 after throttling and reducing the pressure to a low-temperature and low-pressure gas-liquid two-phase refrigerant. The refrigerant absorbs heat from the chilled water flowing through the cold water side heat exchanger 7 and cools it down. The refrigerant evaporates and exchanges heat into a low-pressure superheated gas, and then returns to the compressor suction port through the gas-liquid separator 8, and the cycle repeats.

[0031] When the ambient temperature is lower than the compressor suction saturation temperature, the high-pressure liquid refrigerant flows through the fin coil 3 and heats it, which can not only prevent the refrigerant in the system from migrating to the fin coil 3 through the gas-liquid separator 8, but also heat the refrigerant accumulated in the second heat exchange tube of the fin coil 3 to migrate to the gas-liquid separator 8 with relatively low pressure, so that these refrigerants participate in the refrigeration cycle. Furthermore, when the load demand on the cold water side is large and the load demand on the hot water side is relatively small, the heat exchange fan of the fin coil 3 can be properly turned on to exchange heat with the high-pressure liquid refrigerant flowing through the first heat exchange circuit of the fin coil 3 to increase its supercooling, increase the cooling capacity of the unit, balance the cold and hot loads, and reduce the frequent switching of the unit's modes.

[0032] When the unit is operated in single hot water mode, the four-way valve 2 is not energized, the flow direction of the three-way valve 12 is from A to C, the first electronic expansion valve 6 is closed, and the second electronic expansion valve 13 is turned on.

[0033] When the unit is operated in single hot water mode, the refrigerant process and its heat exchange are as follows: the high-temperature and high-pressure gas discharged from the compressor 1 enters the hot water side heat exchanger 9 through the four-way valve 2 to discharge a large amount of heat to the hot water to heat it. The refrigerant is condensed into a high-pressure liquid with a certain degree of supercooling and then flows into the liquid storage tank 11 through the second one-way valve 10, and then flows through the drying filter 5 to the second electronic expansion valve 13 through the three-way valve 12. After being throttled into a low-temperature and low-pressure gas-liquid two-phase refrigerant, it flows into the second heat exchange circuit of the fin coil 3 to evaporate and exchange heat into a low-pressure gas, and then flows through the four-way valve 2 through the gas-liquid separator 8 and returns to the compressor suction port, and so on.

[0034] When the temperature is low in winter and the mode is switched from hot water only to cooling + hot water mode, if there is slight frost residue on the fin coil, the high-pressure liquid refrigerant flowing through the first heat exchange circuit of the fin coil 3 can heat the surface of the fin coil and melt the frost layer, thereby reducing the defrosting frequency in the hot water only mode and improving the heating operation efficiency.

[0035] When the unit operates in the single refrigeration mode, the four-way valve 2 is energized, the second electronic expansion valve 13 is closed, the first electronic expansion valve 6 operates, and there is no requirement for the flow direction of the three-way valve 12.

[0036] When the unit operates in the single refrigeration mode, the refrigerant flow and its heat exchange conditions are as follows: The high-temperature and high-pressure gas discharged from the compressor 1 enters the finned coil 3 through the four-way valve 2. After discharging heat to the atmosphere, the refrigerant condenses and exchanges heat into high-pressure liquid, then flows through the first one-way valve 4 to the dryer filter 5, and then to the first electronic expansion valve 6. After throttling into a low-temperature and low-pressure gas-liquid two-phase refrigerant, it flows into the chilled water side heat exchanger 7, absorbs heat from the chilled water flowing through the chilled water side heat exchanger 7, and cools the chilled water. After that, the refrigerant evaporates and exchanges heat into low-pressure superheated gas, and then returns to the suction port of the compressor through the gas-liquid separator 8 for reciprocating cycle.

[0037] Further, when the ambient temperature in winter is lower than -10°C or even lower and refrigeration is required, and the set water temperature on the hot water side has reached or there is no hot water demand on the hot water side, at this time, in the single refrigeration mode, since the heat exchange of the finned coil is too good to maintain sufficient condensation pressure, and the machine may have a low-pressure alarm and shut down, the following operations can be performed: Close the hot water flow rate in and out of the hot water side heat exchanger 9. The four-way valve 2 is de-energized, that is, the flow direction is switched from the D interface to the E interface to the D interface to the C interface, and the flow direction of the three-way valve 12 is switched to from the A interface to the B interface. At this time, the high-temperature and high-pressure gaseous refrigerant discharged from the compressor 1 only releases heat and condenses in the first heat exchange circuit with a smaller heat exchange area of the finned coil 3, the pressure in the condenser is increased, and the reliability of the unit operating in single refrigeration at ultra-low temperature is guaranteed.

[0038] Although the embodiments of the present application have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limiting the present application. Without departing from the spirit and scope of the present application, the present application will have various changes and improvements, and these changes and improvements all fall within the scope of the present application claimed.

Claims

1. Four-pipe air-cooled heat pump unit, comprising a compressor (1), a four-way valve (2), a finned coil (3), a hot water side heat exchanger (9), a cold water side heat exchanger (7), a three-way valve (12), a first electronic expansion valve (6), a second electronic expansion valve (13), and a gas-liquid separator (8), characterized in that: The finned coil includes a first heat exchange circuit on the air inlet side and a second heat exchange circuit on the air outlet side, and the heat exchange area of the second heat exchange circuit is 1.5 - 5 times that of the first heat exchange circuit; the first heat exchange circuit includes a flute-shaped liquid inlet pipe (33), a first heat exchange pipe (30), a flute-shaped intermediate liquid pipe (34), and a flute-shaped liquid outlet pipe (35) connected in series in sequence; the second heat exchange circuit includes a distributor assembly (36), a capillary liquid distribution pipe (313), a group of second heat exchange pipes (39), and a gas collector pipe (38) connected in series in sequence; the outlet of the compressor is connected to the interface D of the four-way valve, the interface C of the four-way valve is connected to the hot water side heat exchanger, the interface E of the four-way valve is connected to one end of the second heat exchange circuit of the finned coil, the gas-liquid separator is provided with two inlets and one outlet, one of the two inlets is connected to the interface S of the four-way valve, the other inlet is connected to the outlet of the cold water side heat exchanger, and the outlet of the gas-liquid separator is connected to the inlet of the compressor; the hot water side heat exchanger is connected to the interface A of the three-way valve, the interface B of the three-way valve is connected to one end of the first heat exchange circuit of the finned coil, and the other end of the first heat exchange circuit is connected in parallel with the interface C of the three-way valve and then connected to the first electronic expansion valve and the second electronic expansion valve respectively; the first electronic expansion valve is connected to the inlet of the cold water side heat exchanger, the second electronic expansion valve is connected to the other end of the second heat exchange circuit, and a bypass is also provided between the two and is connected to the first electronic expansion valve; in different operating modes, one of the first heat exchange circuit and the second heat exchange circuit is selected as the outdoor heat exchanger.

2. The four-pipe air-cooled heat pump unit according to claim 1, wherein: A second check valve (10) is provided at the outlet of the hot water side heat exchanger, and the outlet of the second check valve is connected to the liquid receiver (11), and the liquid receiver is connected to the interface A of the three-way valve.

3. The four-pipe air-cooled heat pump unit according to claim 1, wherein: The first heat exchange circuit is connected in parallel with the interface C of the three-way valve and then connected to the drier filter (5), and the outlet of the drier filter is connected to the first electronic expansion valve and the second electronic expansion valve respectively.

4. The four-pipe air-cooled heat pump unit according to claim 3, characterized in that: A first check valve (4) is provided in the bypass, and the outlet of the first heat exchange circuit is connected in parallel with the interface C of the three-way valve and the outlet of the first check valve and then connected to the inlet of the drier filter.

5. The four-pipe air-cooled heat pump unit according to claim 3, characterized in that: The three-way valve is an electric three-way valve.

6. Control method for the four-pipe air-cooled heat pump unit in the refrigeration + hot water mode. The four-pipe air-cooled heat pump unit is as described in claim 1, characterized in that: When the heat pump unit operates in the refrigeration + hot water mode, the four-way valve is not energized, the interface A and the interface B of the three-way valve are conducted, the second electronic expansion valve is closed, and the first electronic expansion valve is conducted; the high-temperature and high-pressure gas discharged by the compressor enters the hot water side heat exchanger through the interface D and the interface C of the four-way valve, and the heat generated during the condensation process is discharged to the hot water to heat it up and then it is condensed into a high-pressure liquid. The high-pressure liquid refrigerant then flows through the first heat exchange circuit of the finned coil through the three-way valve, and then reaches the first electronic expansion valve to be throttled and depressurized into a low-temperature and low-pressure gas-liquid two-phase refrigerant and then enters the cold water side heat exchanger. The refrigerant absorbs heat from the chilled water flowing through the cold water side heat exchanger and cools it down. After the refrigerant evaporates and exchanges heat, it returns to the suction port of the compressor through the gas-liquid separator, and the cycle repeats.

7. Control method for the hot water mode of a four-pipe air-cooled heat pump unit, the four-pipe air-cooled heat pump unit being as described in claim 1, characterized in that: When the unit operates in the single hot water mode, the four-way valve is de-energized. The flow direction of the three-way valve is from A to C. The first electronic expansion valve is closed, and the second electronic expansion valve is turned on. The high-temperature and high-pressure gas discharged by the compressor enters the hot water side heat exchanger through the four-way valve, releases heat to the hot water to heat it up, and the refrigerant is condensed into a high-pressure liquid with a certain degree of subcooling. Then it flows through the three-way valve to the second electronic expansion valve, where it is throttled into a low-temperature and low-pressure gas-liquid two-phase refrigerant. Then it flows into the second heat exchange circuit of the finned coil, evaporates and exchanges heat into a low-pressure gas, and then flows through the four-way valve and the gas-liquid separator to return to the suction port of the compressor, and this cycle repeats.

8. Control method for refrigeration mode of four-pipe air-cooled heat pump unit, the four-pipe air-cooled heat pump unit being as described in claim 1, characterized in that: When the unit operates in the single refrigeration mode, the four-way valve is energized. The second electronic expansion valve is closed, and the first electronic expansion valve works. The high-temperature and high-pressure gas discharged by the compressor enters the second heat exchange circuit of the finned coil through the four-way valve. After discharging the heat to the atmosphere, the refrigerant condenses and exchanges heat into a high-pressure liquid. Then it flows through the bypass between the second electronic expansion valve and the second heat exchange circuit to the first electronic expansion valve, where it is throttled into a low-temperature and low-pressure gas-liquid two-phase refrigerant and then flows into the cold water side heat exchanger. It absorbs heat from the chilled water flowing through the cold water side heat exchanger and cools the chilled water. After that, the refrigerant evaporates and exchanges heat into a low-pressure superheated gas, and then returns to the suction port of the compressor through the gas-liquid separator, and the cycle repeats.

9. The control method for the refrigeration mode of the four-pipe air-cooled heat pump unit according to claim 8, characterized in that: When the ambient temperature of the unit is lower than -10°C and the set water temperature on the hot water side has reached or there is no hot water demand on the hot water side, the hot water flow rate into and out of the hot water side heat exchanger is closed. The four-way valve is de-energized, and the flow direction is from the D interface to the C interface. The flow direction of the three-way valve is switched to from the A interface to the B interface. The high-temperature and high-pressure gaseous refrigerant discharged by the compressor only releases heat and condenses in the first heat exchange circuit of the finned coil.

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