Heat pump air conditioning system and defrosting control method thereof

Abstract

The invention relates to the technical field of air conditioners, in particular to a heat pump air conditioning system and a defrosting control method thereof, and aims to solve the problem that the efficient operation of the system and the thermal comfort of a user are greatly influenced when an outdoor heat exchanger is defrosted by adopting reverse circulation defrosting. In order to achieve the purpose, the heat pump air conditioning system comprises a refrigerant loop, an economizer, an indoor heat exchanger and an outdoor heat exchanger, the refrigerant loop comprises a main path and a defrosting branch which are arranged in parallel, the indoor heat exchanger, the economizer and the outdoor heat exchanger are arranged on the main path, and the economizer communicates with the defrosting branch; a branch throttling element is arranged on the defrosting branch and can conduct throttling and pressure reduction on a refrigerant entering the economizer. One path of refrigerant flowing out of the indoor heat exchanger flows through the economizer through the main path, the other path of refrigerant flows through the branch throttling element and the economizer through the defrosting branch, and the two paths of refrigerant flow into the outdoor heat exchanger after being mixed and heated. The frosting period of the outdoor heat exchanger can be delayed, and the operation efficiency of the system and the thermal comfort of a user are improved.

Description

Technical Field

[0001] This invention relates to the field of air conditioning technology, specifically providing a heat pump air conditioning system and its defrosting control method. Background Technology

[0002] Heat pump air conditioning systems typically have cooling and heating modes. They supply appropriately priced air to the room by circulating refrigerant through a loop formed by the compressor, outdoor heat exchanger, throttling device, and indoor heat exchanger, meeting people's requirements for indoor temperature. When the air conditioner is in heating mode and the outside temperature is very low, the outdoor heat exchanger is prone to frosting. The presence of frost increases the thermal resistance of the outdoor heat exchanger surface, reduces the amount of air flowing through it, and lowers heat exchange efficiency. This leads to a decrease in the coefficient of performance (COP) of the heat pump air conditioning system, and in severe cases, compressor shutdown. Therefore, measures must be taken to defrost the heat exchanger surface.

[0003] In existing technologies, most heat pump air conditioning systems employ a reverse cycle process in heating mode to defrost the outdoor heat exchanger. In this mode, the outdoor heat exchanger becomes the condenser, and the indoor heat exchanger becomes the evaporator, allowing the system to extract heat from the indoor environment to melt the frost. However, this reverse cycle defrosting method deteriorates the indoor environment, affecting user thermal comfort. Furthermore, when the heat pump air conditioning system operates under high load, frequent reverse cycle defrosting significantly impacts the system's efficiency and user thermal comfort.

[0004] Accordingly, there is a need in the field for a new heat pump air conditioning system and its defrosting control method to solve the above problems. Summary of the Invention

[0005] The present invention aims to solve the above-mentioned technical problems, namely, to solve the problem that using reverse circulation defrosting to defrost the outdoor heat exchanger will cause the indoor environment to deteriorate and affect the thermal comfort of users, and that when the heat pump air conditioning system is operating at high load, reverse circulation defrosting will be performed frequently, which will have a significant impact on the efficient operation of the heat pump air conditioning system and the thermal comfort of users.

[0006] In a first aspect, the present invention provides a heat pump air conditioning system; the heat pump air conditioning system includes a refrigerant circuit, an economizer, at least one indoor heat exchanger and an outdoor heat exchanger, the refrigerant circuit includes a main circuit and a defrost branch circuit arranged in parallel, the indoor heat exchanger, the economizer and the outdoor heat exchanger are arranged sequentially on the main circuit, and the economizer is connected to the defrost branch circuit.

[0007] The defrosting branch is equipped with a branch throttling element, which can throttle and reduce the pressure of the refrigerant entering the economizer;

[0008] The refrigerant flowing out of the indoor heat exchanger flows through the defrost branch, passes through the branch throttling element and economizer, and then evaporates. The other refrigerant flows through the main branch, passes through the economizer, and then cools down. The two refrigerants mix, heat up, and then flow into the outdoor heat exchanger.

[0009] In the preferred technical solution of the above-mentioned heat pump air conditioning system, the branch throttling element is one of an electronic expansion valve, a throttling tube, or a thermal expansion valve.

[0010] In the preferred technical solution of the above-mentioned heat pump air conditioning system, a compressor located on the main line is also included, and the compressor is a gas-injection enthalpy-increasing compressor;

[0011] The refrigerant circuit also includes a gas supply branch, the first end of which is connected to the defrost branch and located between the economizer and the outdoor heat exchanger, and the second end of which is connected to the gas supply port of the compressor.

[0012] In the preferred technical solution of the above-mentioned heat pump air conditioning system, a first shut-off valve is provided on the defrost branch, a second shut-off valve is provided on the gas supply branch, and the first end of the gas supply branch is located between the first shut-off valve and the economizer.

[0013] Secondly, the present invention provides a defrosting control method for a heat pump air conditioning system as described above; the defrosting control method for the heat pump air conditioning system includes the following steps:

[0014] Determine whether the heat pump air conditioning system requires defrosting;

[0015] Based on the assessment results, determine whether to activate the defrosting mode.

[0016] In the preferred embodiment of the above defrosting control method, the defrosting mode includes a first-level defrosting mode. If the heat pump air conditioning system needs defrosting, the first-level defrosting mode is activated.

[0017] In the preferred embodiment of the above defrosting control method, the primary defrosting mode includes:

[0018] Control the operation of the heat pump air conditioning system in heating mode;

[0019] Control the closing of the second shut-off valve and the opening of the first shut-off valve.

[0020] In the preferred embodiment of the above defrosting control method, the defrosting mode further includes a secondary defrosting mode, wherein the defrosting capacity of the secondary defrosting mode is greater than that of the primary defrosting mode.

[0021] The defrosting control method further includes:

[0022] If the coil temperature of the outdoor heat exchanger is not greater than the first preset temperature, the secondary defrosting mode is activated.

[0023] In the preferred embodiment of the above defrosting control method, the secondary defrosting mode includes:

[0024] Control the closure of the first and second shut-off valves;

[0025] Control the operation of the heat pump air conditioning system in cooling mode.

[0026] In the preferred embodiment of the above defrosting control method, after the step of "controlling the heat pump air conditioning system to operate in cooling mode", the secondary defrosting mode further includes:

[0027] Determine whether the heat pump air conditioning system needs to continue defrosting;

[0028] If defrosting is no longer required, exit the defrosting mode.

[0029] In the preferred embodiment of the above defrosting control method, "determining whether the heat pump air conditioning system needs to continue defrosting" specifically includes:

[0030] If the heat pump air conditioning system operates continuously in cooling mode for more than a second preset time, or if the coil temperature of the outdoor heat exchanger is greater than a second preset temperature, the heat pump air conditioning system does not need to continue defrosting.

[0031] By adding an economizer, a defrost branch, and a branch throttling element to the heat pump air conditioning system, this invention allows the high-temperature, high-pressure liquid refrigerant flowing from the indoor heat exchanger to be divided into two streams before defrosting the outdoor heat exchanger using reverse circulation. One stream of refrigerant flows through the defrost branch and is throttled by the branch throttling element before entering the economizer. In the economizer, it absorbs heat from the main stream refrigerant and evaporates into a medium-temperature, medium-pressure gaseous refrigerant. The other stream of refrigerant flows through the main stream and is cooled to a lower temperature. The two streams of refrigerant mix, heat up, and then flow into the outdoor heat exchanger, raising its temperature. This delays frosting on the outdoor heat exchanger and reduces the frequency of reverse circulation defrosting during high-load operation, thereby improving system efficiency and user thermal comfort. Furthermore, the reduction in heating capacity during the delay of outdoor heat exchanger frosting is minimal and does not affect user thermal comfort.

[0032] The defrosting branch is also connected to a gas supply branch. When the heat pump air conditioning system is operating in heating mode, the first shut-off valve is closed, and the branch throttling element and the second shut-off valve are opened, allowing medium-temperature, medium-pressure gaseous refrigerant to be supplied to the compressor to replenish its enthalpy. This enables the heat pump air conditioning system to improve its heating capacity and energy efficiency ratio, and also allows for more stable operation at lower temperatures. Attached Figure Description

[0033] The preferred embodiments of the present invention are described below with reference to the accompanying drawings, in which:

[0034] Figure 1 This is a schematic diagram of the heat pump air conditioning system of the present invention;

[0035] Figure 2 This is a flowchart of the main steps of the defrosting control method of the present invention;

[0036] Figure 3 This is a flowchart illustrating the specific steps of the defrosting control method of the present invention;

[0037] Figure label:

[0038] 1. Compressor; 2. Economizer; 3. Indoor heat exchanger; 4. Outdoor heat exchanger; 5. Four-way valve; 61. Main circuit; 62. Defrost branch circuit; 63. Gas supply branch circuit; 7. Indoor unit electronic expansion valve; 8. Outdoor unit electronic expansion valve; 9. Branch circuit throttling element; 10. First shut-off valve; 11. Second shut-off valve. Detailed Implementation

[0039] Preferred embodiments of the present invention will now be described with reference to the accompanying drawings. Those skilled in the art should understand that these embodiments are merely illustrative of the technical principles of the invention and are not intended to limit the scope of protection of the invention. Those skilled in the art can make adjustments as needed to adapt to specific applications.

[0040] It should be noted that in the description of this invention, terms such as "upper," "lower," "left," and "right," indicating directional or positional relationships, are based on the directional or positional relationships shown in the accompanying drawings. These are merely for ease of description and do not indicate or imply that the device or element must have a specific orientation, or be constructed and operated in a specific orientation; therefore, they should not be construed as limitations on this invention. Furthermore, the terms "first," "second," "third," and "fourth" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0041] Furthermore, it should be noted that, in the description of this invention, unless otherwise explicitly specified and limited, the terms "connected," "linked," and "connected" should be interpreted broadly. For example, they can refer to a fixed connection or a detachable connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0042] Example 1

[0043] To address the issue that using reverse circulation defrosting for outdoor heat exchangers deteriorates the indoor environment and affects user thermal comfort, and that frequent reverse circulation defrosting during high-load operation of the heat pump air conditioning system significantly impacts the efficient operation of the system and user thermal comfort.

[0044] like Figure 1 As shown, this embodiment discloses a heat pump air conditioning system, which includes a refrigerant circuit, a compressor 1, a four-way valve 5, an economizer 2, at least one indoor heat exchanger 3, an indoor unit electronic expansion valve 7, an outdoor heat exchanger 4, and an outdoor unit electronic expansion valve 8. In this embodiment, the number of indoor heat exchangers 3 and indoor unit electronic expansion valves 7 is taken as multiple, and the indoor heat exchangers 3 are arranged in parallel. The number of outdoor heat exchangers 4 and outdoor electronic expansion valves is taken as one. The compressor 1 is a gas-injection enthalpy-increasing compressor, and the economizer 2 is a plate heat exchanger. The economizer 2 can also be a shell-and-tube heat exchanger, a tubular heat exchanger, etc.

[0045] The refrigerant circuit includes a main circuit 61, a defrost branch circuit 62, and a make-up gas branch circuit 63. The compressor 1, four-way valve 5, indoor heat exchanger 3, indoor unit electronic expansion valve 7, economizer 2, outdoor unit electronic expansion valve 8, and outdoor heat exchanger 4 are sequentially arranged on the main circuit 61. The main circuit 61 is connected to the subcooling side passage of the economizer 2.

[0046] like Figure 1 As shown, the defrost branch 62 is connected in parallel with the main branch 61, and the defrost branch 62 is connected to the evaporator-side channel of the economizer 2. The first end of the defrost branch 62 is located between the economizer 2 and the indoor heat exchanger 3, and the second end is located between the economizer 2 and the outdoor heat exchanger 4. A branch throttling element 9 is installed on the defrost branch 62 between the economizer 2 and the indoor heat exchanger 3. The branch throttling element 9 is one of an electronic expansion valve, a throttling tube, or a thermostatic expansion valve, which can throttle and reduce the pressure of the refrigerant in the defrost branch 62. In this embodiment, the branch throttling element 9 is an electronic expansion valve, which can not only throttle and reduce the pressure of the refrigerant in the defrost branch 62, but also regulate the flow rate of the refrigerant entering the defrost branch 62. A first shut-off valve 10 is installed on the defrost branch 62 between the economizer 2 and the outdoor heat exchanger 4. The first shut-off valve 10 can control whether the refrigerant in the defrost branch 62 can flow into the main branch 61.

[0047] A second shut-off valve 11 is installed on the gas supply branch 63. The first end of the gas supply branch 63 is connected to the defrost branch 62 and is located between the economizer 2 and the first shut-off valve 10. The second end of the gas supply branch 63 is connected to the gas supply port of the compressor 1.

[0048] When the heat pump air conditioning system is in cooling mode, the first shut-off valve 10, the second shut-off valve 11, and the branch throttling element 9 are all closed. The high-temperature and high-pressure refrigerant discharged from the compressor 1 flows sequentially through the four-way valve 5, the outdoor heat exchanger 4, the outdoor unit electronic expansion valve 8, the economizer 2, the indoor unit electronic expansion valve 7, the indoor heat exchanger 3, and the four-way valve 5 before returning to the compressor 1, completing the refrigeration cycle and cooling the indoor unit.

[0049] When the heat pump air conditioning system is in heating mode, the first shut-off valve 10 is closed, the second shut-off valve 11 is open, and the branch throttling element 9 is open. The high-temperature, high-pressure refrigerant discharged from the compressor 1 flows sequentially through the four-way valve 5, the indoor heat exchanger 3, and the indoor unit electronic expansion valve 7. After being throttled and depressurized by the indoor unit electronic expansion valve 7, the refrigerant is divided into two paths: one path flows through the main path 61, passes through the economizer 2 for cooling, and then flows through the outdoor unit electronic expansion valve 8 for throttling and depressurization, forming a low-temperature, low-pressure gas-liquid two-phase refrigerant. This then flows sequentially through the outdoor heat exchanger 4 and the four-way valve 5, returning to the compressor 1 to heat the indoor unit. The other path flows through the defrost branch 62, passes through the branch throttling element 9, and enters the economizer 2. In the economizer 2, it absorbs heat from the refrigerant in the main path 61 and evaporates into a medium-temperature, medium-pressure gaseous refrigerant. This gas then enters the compressor 1 through the gas replenishment branch 63 to replenish the compressor 1 and increase its enthalpy. This allows heat pump air conditioning systems to improve heating capacity and energy efficiency ratio, and also to operate more stably at lower temperatures.

[0050] Before starting the defrost mode, it is determined whether the heat pump air conditioning system needs defrosting. This is usually determined by the coil temperature of the outdoor heat exchanger 4. If the coil temperature of the outdoor heat exchanger 4 is not greater than the first preset temperature, it is considered that the heat pump air conditioning system needs to defrost, and the defrost mode is started.

[0051] The defrost mode includes a primary defrost mode and a secondary defrost mode. The primary defrost mode delays frost formation on the outdoor heat exchanger 4, while the secondary defrost mode has a greater defrost capacity than the primary mode and can defrost the outdoor heat exchanger 4. After the defrost mode is activated, the primary defrost mode runs first. Once the coil temperature of the outdoor heat exchanger 4 is no higher than the first preset temperature and remains at the first preset temperature for a certain period of time, the secondary defrost mode is activated. After defrosting is complete, the defrost mode is deactivated. After the defrost mode is deactivated, the heat pump air conditioning system closes the first shut-off valve 10, opens the second shut-off valve 11, and opens the branch throttling element 9. The heat pump air conditioning system then operates in heating mode to continue heating the indoor unit.

[0052] When the heat pump air conditioning system is in primary defrost mode, the first shut-off valve 10 and the branch throttling element 9 are open, and the second shut-off valve 11 is closed. The high-temperature and high-pressure refrigerant discharged from the compressor 1 flows sequentially through the four-way valve 5, the indoor heat exchanger 3, and the indoor unit electronic expansion valve 7. After being throttled and depressurized by the indoor unit electronic expansion valve 7, the refrigerant is divided into two paths: one path flows through the defrost branch 62, passes through the branch throttling element 9, and then enters the economizer 2. In the economizer 2, it absorbs heat from the refrigerant in the main path 61 and evaporates into a medium-temperature and medium-pressure gaseous refrigerant, which then flows back into the main path 61 through the defrost branch 62. The other path flows through the main path 61, passes through the economizer 2, is cooled, and then flows through the outdoor unit electronic expansion valve 8, where it is throttled and depressurized to form a low-temperature and low-pressure gas-liquid two-phase refrigerant. The two refrigerants mix and heat up before flowing into the outdoor heat exchanger 4, raising the temperature of the outdoor heat exchanger 4. This delays frosting on outdoor heat exchanger 4, reducing the frequency of reverse-cycle defrosting during high-load system operation, thereby improving system efficiency and user thermal comfort. Furthermore, the reduction in heating capacity during the delay of outdoor heat exchanger 4 is minimal and will not affect user thermal comfort.

[0053] When the heat pump air conditioning system operates in secondary defrost mode, the first shut-off valve 10, the second shut-off valve 11, and the branch throttling element 9 are closed, and the control system operates in cooling mode. Since the high-temperature and high-pressure refrigerant discharged from the compressor 1 first passes through the outdoor heat exchanger 4, the coil temperature of the outdoor heat exchanger 4 rises, thereby removing the frost layer on the outdoor heat exchanger 4.

[0054] In the first-level defrost mode, a mixture of medium-temperature, medium-pressure refrigerant and low-temperature, low-pressure refrigerant is flowed into the outdoor heat exchanger 4 to delay frost formation. In the second-level defrost mode, high-temperature, high-pressure refrigerant is flowed into the outdoor heat exchanger to defrost it, making the defrost capacity of the second-level mode greater than that of the first-level mode. By delaying frost formation on the outdoor heat exchanger 4 through the first-level defrost mode, the frequency of activation of the second-level defrost mode can be reduced, minimizing the impact on user thermal comfort and system efficiency.

[0055] Example 2

[0056] This embodiment discloses a defrosting control method for a heat pump air conditioning system. Based on the first embodiment, the heat pump air conditioning system in this embodiment also includes a temperature sensor. The temperature sensor is installed on the coil of the outdoor heat exchanger 4 and can detect the coil temperature of the outdoor heat exchanger 4.

[0057] like Figure 2 As shown, the defrosting control method of a heat pump air conditioning system mainly includes the following steps:

[0058] Determine whether the heat pump air conditioning system needs defrosting, and based on the determination result, determine whether to activate the defrosting mode;

[0059] If defrosting is required, activate the first-level defrosting mode.

[0060] Determine whether the coil temperature of outdoor heat exchanger 4 is not greater than the first preset temperature;

[0061] If the coil temperature of outdoor heat exchanger 4 is not greater than the first preset temperature, the control will start the second-level defrosting mode.

[0062] The first-level defrosting mode can delay the frosting of outdoor heat exchanger 4. The second-level defrosting mode has a greater defrosting capacity than the first-level defrosting mode. The second-level defrosting mode can defrost outdoor heat exchanger 4. By delaying the frosting of outdoor heat exchanger 4 through the first-level defrosting mode, the activation frequency of the second-level defrosting mode can be reduced when the system is running under high load, thereby improving the system's operating efficiency and the user's thermal comfort.

[0063] like Figure 3 As shown, the defrosting control method for a heat pump air conditioning system specifically includes the following steps:

[0064] S1. Obtain the coil temperature of outdoor heat exchanger 4.

[0065] S2. Determine if the coil temperature of the outdoor heat exchanger 4 is not greater than the first preset temperature. The first preset temperature can be -1℃, -2℃, or -3℃, etc., and the first preset time is 1, 2, or 3 minutes. Users can set it according to actual conditions. If the coil temperature is greater than the first preset temperature, the heat pump air conditioning system does not need to defrost and continues to operate in heating mode; if the coil temperature is not greater than the first preset temperature, execute S3.

[0066] S3. Determine whether the duration for which the coil temperature of the outdoor heat exchanger 4 is not higher than the first preset temperature exceeds the first preset time. The first preset time is 1, 2, or 3 minutes, which can be set by the user according to the actual situation. If not, execute S1; if yes, the heat pump air conditioning system needs to defrost, and the first-level defrosting mode is started.

[0067] S4. Control the heat pump air conditioning system to continue operating in heating mode. At this time, the branch throttling element 9 is in the open state, and control the second shut-off valve 11 to close and the first shut-off valve 10 to open. The high-temperature and high-pressure refrigerant discharged from the compressor 1 flows sequentially through the four-way valve 5, the indoor heat exchanger 3, and the indoor unit electronic expansion valve 7. The refrigerant that has been throttled and depressurized by the indoor unit electronic expansion valve 7 is divided into two paths: one path of refrigerant flows through the defrost branch 62 and is throttled by the branch throttling element 9 before entering the economizer 2. In the economizer 2, it absorbs the heat of the refrigerant in the main path 61 and evaporates into a medium-temperature and medium-pressure gaseous refrigerant, which then flows into the main path 61 through the defrost branch 62.

[0068] The other refrigerant, flowing through the main circuit 61 and cooled after passing through the economizer 2, then throttled and depressurized after passing through the outdoor unit's electronic expansion valve 8, forms a low-temperature, low-pressure gas-liquid two-phase refrigerant. The two refrigerants mix and heat up before flowing into the outdoor heat exchanger 4, raising its temperature. This delays frosting on the outdoor heat exchanger 4, reducing the frequency of reverse-cycle defrosting during high-load system operation, thus improving system efficiency and user thermal comfort. Furthermore, the reduction in heating capacity during the delay of frosting on the outdoor heat exchanger 4 is minimal and does not affect user thermal comfort.

[0069] S5. Determine whether the coil temperature of outdoor heat exchanger 4 is not greater than the first preset temperature. If the coil temperature is greater than the first preset temperature, continue to run the first-level defrost mode; if the coil temperature is not greater than the first preset temperature, execute S6.

[0070] S6. Determine whether the duration for which the coil temperature of the outdoor heat exchanger 4 exceeds the first preset temperature exceeds the first preset time. If not, execute S4; if yes, start the second-level defrosting mode.

[0071] S7. Control the closure of the first shut-off valve 10 and the second shut-off valve 11 to control the heat pump air conditioning system to operate in cooling mode. The high-temperature and high-pressure refrigerant discharged from the compressor 1 first passes through the four-way valve 5 and the outdoor heat exchanger 4, raising the coil temperature of the outdoor heat exchanger 4 and removing the frost layer on the outdoor heat exchanger 4. Then it passes through the subcooling side channel of the economizer 2, the indoor heat exchanger, and the four-way valve, returning to the compressor.

[0072] S8. Obtain the continuous operating time of the heat pump air conditioning system in cooling mode.

[0073] S9. Determine whether the continuous running time in cooling mode is greater than the second preset time. The second preset time can be 6 minutes, 8 minutes, or 10 minutes, etc., and the user can set it according to the actual situation. If it is not greater than the second preset time, proceed to S10; if it is greater than the second preset time, proceed to S12.

[0074] S10. Determine if the coil temperature of the outdoor heat exchanger 4 is greater than the second preset temperature. The second preset temperature can be 13℃, 15℃, or 17℃, and the user can set it according to the actual situation. If it is not greater than the second preset temperature, the heat pump air conditioning system continues to operate in cooling mode; if it is greater than the second preset temperature, execute S11.

[0075] S11. Determine whether the duration for which the coil temperature of the outdoor heat exchanger 4 exceeds the second preset temperature exceeds the first preset time. If not, execute S8; if yes, execute S12.

[0076] S12, Control the exit from defrost mode.

[0077] The technical solution of the present invention has been described above with reference to the preferred embodiments shown in the accompanying drawings. However, it will be readily understood by those skilled in the art that the scope of protection of the present invention is obviously not limited to these specific embodiments. Without departing from the principles of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after such changes or substitutions will all fall within the scope of protection of the present invention.

Claims

1. A heat pump air conditioning system, characterized in that, It includes a refrigerant circuit, an economizer (2), at least one indoor heat exchanger (3) and an outdoor heat exchanger (4). The refrigerant circuit includes a main circuit (61) and a defrost branch circuit (62) arranged in parallel. The indoor heat exchanger (3), the economizer (2) and the outdoor heat exchanger (4) are arranged sequentially on the main circuit (61), and the economizer (2) is connected to the defrost branch circuit (62). The defrosting branch (62) is provided with a branch throttling element (9), which can throttle and reduce the pressure of the refrigerant entering the economizer (2); The refrigerant flowing out of the indoor heat exchanger (3) flows through the defrost branch (62) and then through the branch throttling element (9) and the economizer (2) to evaporate. The other refrigerant flows through the main branch (61) and then through the economizer (2) to cool down. The two refrigerants mix and heat up before flowing into the outdoor heat exchanger (4).

2. The heat pump air conditioning system according to claim 1, characterized in that, The branch throttling element (9) is one of an electronic expansion valve, a throttling tube, or a thermostatic expansion valve.

3. The heat pump air conditioning system according to claim 1, characterized in that, It also includes a compressor (1) installed on the main road (61), the compressor (1) being a gas-injection enthalpy-increasing compressor; The refrigerant circuit also includes a gas supply branch (63), the first end of which is connected to the defrost branch (62) and located between the economizer (2) and the outdoor heat exchanger (4), and the second end of which is connected to the gas supply port of the compressor (1).

4. The heat pump air conditioning system according to claim 3, characterized in that, The defrosting branch (62) is provided with a first shut-off valve (10), and the air supply branch (63) is provided with a second shut-off valve (11). The first end of the air supply branch (63) is located between the first shut-off valve (10) and the economizer (2).

5. A defrosting control method for a heat pump air conditioning system as described in any one of claims 1-4, characterized in that, The defrosting control method for the heat pump air conditioning system includes the following steps: Determine whether the heat pump air conditioning system requires defrosting; Based on the assessment results, determine whether to activate the defrosting mode.

6. The defrosting control method according to claim 5 of claim 4, characterized in that, The defrosting mode includes a first-level defrosting mode. If the heat pump air conditioning system needs defrosting, the first-level defrosting mode is activated.

7. The defrosting control method according to claim 6, characterized in that, The first-level defrosting mode includes: Control the operation of the heat pump air conditioning system in heating mode; The control closes the second shut-off valve (11) and opens the first shut-off valve (10).

8. The defrosting control method according to claim 7, characterized in that, The defrosting mode also includes a secondary defrosting mode, the defrosting capacity of which is greater than that of the primary defrosting mode; After the step of "controlling the activation of the first-level defrosting mode", the defrosting control method further includes: If the coil temperature of the outdoor heat exchanger (4) is not greater than the first preset temperature, the secondary defrosting mode is activated.

9. The defrosting control method according to claim 8, characterized in that, The secondary defrosting mode includes: Control the closure of the first shut-off valve (10) and the second shut-off valve (11); Control the operation of the heat pump air conditioning system in cooling mode.

10. The defrosting control method according to claim 9, characterized in that, After the step of "controlling the heat pump air conditioning system to operate in cooling mode", the secondary defrosting mode further includes: Determine whether the heat pump air conditioning system needs to continue defrosting; If defrosting is no longer required, exit the defrosting mode.

11. The defrosting control method according to claim 10, characterized in that, "Determining whether the heat pump air conditioning system needs to continue defrosting" specifically includes: If the heat pump air conditioning system runs continuously in cooling mode for longer than a preset time, or if the coil temperature of the outdoor heat exchanger (4) is greater than a second preset temperature, the heat pump air conditioning system does not need to continue defrosting.

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