Treatment method for high exhaust temperature of heat pump fixed-frequency jet-enthalpy compressor during low-temperature starting

Abstract

The application discloses a processing method for high exhaust temperature of a low-temperature starting heat pump fixed-frequency jet-enthalpy compressor, and divides the process of the unit operation into two stages, and the control modes of the two stages are the same. In the starting stage, the unit selects a proper electronic expansion valve to open according to the ambient temperature and the water outlet temperature, and reasonably gives the initial opening degree of the electronic expansion valve, so that the exhaust temperature of the compressor can be quickly stabilized, the problem that the exhaust temperature rapidly rises in a short time during the gradual increase of the load of the unit is avoided, the exhaust protection unit shutdown caused by the high exhaust temperature during the starting of the compressor is avoided, and the exhaust temperature is prevented from greatly fluctuating in a short time, so that the unit can be stably started.

Description

Technical Field

[0001] This invention relates to the field of heat pumps, and more particularly to a method for dealing with excessively high exhaust temperature during low-temperature startup of a heat pump fixed-frequency injection enthalpy compressor. Background Technology

[0002] Current cryogenic compressors rely on liquid injection or enthalpy injection to ensure stable operation at low temperatures. Variable frequency units gradually increase the compressor load during startup by varying the frequency. However, fixed frequency compressors, lacking this adjustment, operate at full load from the start. Furthermore, because the refrigerant hasn't circulated before startup, the low ambient temperature and high water temperature result in even lower low pressure and higher high pressure. With limited refrigerant in the system and the system not yet stable during startup, the valve opening is still adjusting, leading to exceptionally high exhaust temperatures. Enthalpy-injected units, due to their less direct effect on reducing exhaust temperature, may experience the following two issues: 1. Significant fluctuations in exhaust temperature. 2. Excessively high start-up exhaust temperature triggering exhaust protection mechanisms.

[0003] Prior art, disclosed in patent application CN 110953757 A, describes a liquid-injection enthalpy-increasing heat pump unit and its control method. The unit includes a compressor, a four-way valve, a condenser, an economizer, and an evaporator connected in sequence. The economizer is also connected to the compressor's gas inlet for cooling the refrigerant in the unit's main cycle and for injecting gas to increase the compressor's enthalpy. The unit further includes a liquid-injection throttling element, one end connected to the economizer and evaporator, and the other end connected to the compressor's gas inlet, for injecting gaseous refrigerant, after being throttled, cooled, and depressurized by the economizer or evaporator, into the compressor to lower the compressor's exhaust temperature. In the specific control method disclosed in the specification, regardless of whether the unit is in heating or cooling mode, the liquid-injection enthalpy electronic expansion valve is first opened, and then the opening degree of the liquid-injection electronic expansion valve is controlled according to the compressor's exhaust temperature.

[0004] However, the existing technology does have the following problems: when the compressor and the electronic expansion valve are opened at the same time, the exhaust temperature is already low when the compressor is first turned on. Therefore, the opening of the electronic expansion valve will make the exhaust temperature even lower. Moreover, as the unit load starts, the compressor exhaust temperature will rise rapidly in a short period of time. If the exhaust temperature is used as the condition for controlling the opening of the electronic expansion valve, then when the unit starts, the compressor exhaust temperature will rise much faster than the adjustment speed of the electronic expansion valve. This will cause large fluctuations when the unit starts. Summary of the Invention

[0005] To address the problem of high unit load and drastic exhaust temperature fluctuations during unit startup in low-temperature environments in existing technologies, the present invention aims to provide a method for handling excessively high exhaust temperature during low-temperature startup of a heat pump fixed-frequency injection enthalpy compressor, thereby ensuring a more appropriate opening of the electronic expansion valve and a more stable unit startup process in low-temperature environments.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: a method for handling excessively high exhaust temperature during low-temperature startup of a heat pump fixed-frequency enthalpy-injection compressor, applied to a heat pump unit, the unit comprising a compressor, a four-way valve, a condenser, an economizer, an evaporator, a liquid injection electronic expansion valve, and an enthalpy-injection electronic expansion valve; wherein, the main pipeline sequentially passes through the compressor, the four-way valve, the condenser, the economizer, and the evaporator, and then connects back to the compressor via the four-way valve to form a loop; the enthalpy-injection electronic expansion valve is installed on the enthalpy-injection pipeline, one end of which is connected to the main pipeline between the condenser and the economizer, and the other end of which is connected to the compressor's gas inlet via the economizer; the liquid injection electronic expansion valve is installed on the liquid injection pipeline, one end of which is connected to the main pipeline between the condenser and the economizer, and the other end of which is connected to the compressor's gas inlet; the specific control method is as follows:

[0007] When the compressor starts, the unit enters the start-up phase. The unit opens the liquid injection electronic expansion valve or the enthalpy injection electronic expansion valve according to the current ambient temperature or outlet water temperature, and then periodically adjusts the opening degree of the electronic expansion valve in the open state. The initial opening degree of the enthalpy injection electronic expansion valve is determined according to the current ambient temperature and the current outlet water temperature, while the initial opening degree of the liquid injection electronic expansion valve is a fixed number of steps S.

[0008] After M minutes of startup, the unit enters the formal operation phase.

[0009] Once the unit enters the formal operation phase, it determines whether to switch the opening state of the two electronic expansion valves based on the current exhaust temperature or the opening degree of the electronic expansion valve that is currently open, and then periodically adjusts the opening degree of the electronic expansion valve that is currently open.

[0010] Preferably, when the unit is in the startup phase, the conditions for determining whether the liquid injection electronic expansion valve or the enthalpy injection electronic expansion valve is open are as follows: 1) When the ambient temperature Tao is greater than or equal to the first set temperature, the startup is carried out using the enthalpy injection control method; 2) When the first set temperature is greater than or equal to the ambient temperature Tao, the unit determines whether the liquid injection electronic expansion valve or the enthalpy injection electronic expansion valve is open based on the outlet water temperature at the current ambient temperature; 3) When the ambient temperature Tao is less than the second set temperature, the liquid injection electronic expansion valve is opened.

[0011] Preferably, when the first set temperature > ambient temperature Tao ≥ the second set temperature, if c ≥ a, the liquid injection electronic expansion valve or the enthalpy injection electronic expansion valve is opened; otherwise, the enthalpy injection electronic expansion valve is opened. Wherein, the coefficient C = A*Tao + B*ToutAC, Tao is the current ambient temperature, ToutAC is the current outlet water temperature, and a is a constant.

[0012] Preferably, when the unit is in the start-up phase, if the electronic expansion valve is opened, the initial opening degree of the electronic expansion valve is V=[A*Tao+B*ToutAC]*F, where A is a constant, B is a constant, F is a constant, Tao is the current ambient temperature, and ToutAC is the current outlet water temperature.

[0013] Preferably, during the start-up phase, the unit adjusts the number of steps of the electronic expansion valve that is in the open state based on the difference between the current exhaust temperature and the target exhaust temperature.

[0014] As a preferred method, when the unit enters the formal operation phase, the method for determining whether to switch the opening state of the two electronic expansion valves is as follows: 1) When the current exhaust temperature Td ≥ the set value α, open the liquid injection electronic expansion valve and close the enthalpy injection electronic expansion valve; 2) If the set temperature α > the current exhaust temperature Td ≥ the set temperature β, if the enthalpy injection electronic expansion valve is in the open state, then continue to close the liquid injection electronic expansion valve; if the liquid injection electronic expansion valve is in the open state, then determine whether to close the liquid injection electronic expansion valve and open the enthalpy injection electronic expansion valve based on the current opening degree of the liquid injection electronic expansion valve; 3) If the current exhaust temperature Td < the set temperature β, then open the enthalpy injection electronic expansion valve and close the liquid injection electronic expansion valve.

[0015] Preferably, when the unit enters the formal operation phase, if the set temperature α > the current exhaust temperature Td ≥ the set temperature β, and the opening degree of the liquid injection electronic expansion valve ≤ the opening degree limit value V, then the liquid injection electronic expansion valve is opened and closed; if the set temperature α > the current exhaust temperature Td ≥ the set temperature β, and the opening degree of the liquid injection electronic expansion valve > the opening degree limit value V, then the liquid injection electronic expansion valve is opened and closed.

[0016] Preferably, when the unit enters the formal operation phase and the opening state of the two electronic expansion valves switches, if the injection enthalpy electronic expansion valve is opened, the initial opening degree of the injection enthalpy electronic expansion valve is determined according to the opening degree when the injection electronic expansion valve is closed.

[0017] Preferably, when the unit enters the formal operation phase and the opening state of the two electronic expansion valves switches, if the liquid injection electronic expansion valve is opened, the initial opening degree of the liquid injection electronic expansion valve is determined according to the opening degree when the liquid injection electronic expansion valve is closed.

[0018] As a preferred option, during the formal operation phase, the unit adjusts the number of steps of the electronic expansion valve that is in the open state based on the difference between the current exhaust temperature and the target exhaust temperature.

[0019] The beneficial effects of the technical solution of this invention are as follows: The above method divides the unit operation process into two stages, and the control methods for these two stages are different. During the start-up stage, the unit selects the appropriate electronic expansion valve to open based on the ambient temperature and outlet water temperature, and provides a reasonable initial opening degree for the electronic expansion valve. This allows the compressor's exhaust temperature to stabilize quickly, preventing a rapid rise in exhaust temperature during the gradual increase of load. This avoids the compressor starting up and triggering a shutdown due to excessively high exhaust temperature, and also prevents large fluctuations in exhaust temperature within a short period, ensuring a stable start-up. During the formal operation stage, the unit can select the appropriate electronic expansion valve to open based on the current operating status and dynamically adjust its opening degree, ensuring stability during both start-up and operation. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the heat pump unit.

[0021] Attached reference numerals: 1. Compressor; 2. Four-way valve; 3. Condenser; 4. Economizer; 5. Evaporator; 6. Main electronic expansion valve; 7. Main pipeline; 8. Liquid injection electronic expansion valve; 9. Liquid injection pipeline; 10. Enthalpy injection electronic expansion valve; 11. Enthalpy injection pipeline. Detailed Implementation

[0022] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0023] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "clockwise," and "counterclockwise," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to 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.

[0024] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "a plurality of" means two or more, unless explicitly defined otherwise.

[0025] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical 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.

[0026] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature. Example

[0027] like Figure 1The heat pump unit shown includes a compressor 1, a four-way valve 2, a condenser 3, an economizer 4, an evaporator 5, a main circuit electronic expansion valve 6, a liquid injection electronic expansion valve 8, and an enthalpy injection electronic expansion valve 10. The main circuit 7 sequentially passes through the compressor 1, four-way valve 2, condenser 3, economizer 4, and evaporator 5, and then connects back to the compressor 1 via the four-way valve 2 to form a loop. The main circuit electronic expansion valve 6 is installed on the main circuit 7 located between the condenser 3 and the economizer 4. The enthalpy injection electronic expansion valve 10... The enthalpy injection valve 10 is installed on the injection pipe 11. One end of the injection pipe 11 is connected to the main pipe 7 between the condenser 3 and the main electronic expansion valve 6, and the other end of the injection pipe 11 is connected to the gas supply port of the compressor 1 via the economizer 4. The liquid injection electronic expansion valve 8 is installed on the liquid injection pipe 9. One end of the liquid injection pipe 9 is connected to the injection pipe 11 located between the main pipe 7 and the injection pipe 10, and the other end of the injection pipe 11 is connected to the injection pipe 11 located between the compressor 1 and the economizer 4. This configuration allows the unit to reduce the exhaust temperature through at least two methods: enthalpy injection and liquid injection. The main electronic expansion valve 6 also opens after the unit starts.

[0028] The method for handling excessively high exhaust temperature during low-temperature start-up of the heat pump fixed-frequency injection enthalpy compressor 1 is used to solve the problem of excessively high exhaust temperature and large fluctuation range when the above-mentioned heat pump unit starts up under low ambient temperature conditions.

[0029] The specific steps of this method include a startup phase and a formal operation phase. The unit enters the startup phase when compressor 1 starts, and the unit enters the formal operation phase after the startup phase is completed.

[0030] During the start-up phase, the unit opens the liquid injection electronic expansion valve 8 or the enthalpy injection electronic expansion valve 10 according to the current ambient temperature or outlet water temperature, and then periodically adjusts the opening degree of the electronic expansion valve in the open state; wherein, the initial opening degree of the enthalpy injection electronic expansion valve 10 is determined according to the current ambient temperature and the current outlet water temperature, while the initial opening degree of the liquid injection electronic expansion valve 8 is a fixed number of steps S.

[0031] After M minutes of startup, the unit enters the formal operation phase.

[0032] After the unit enters the formal operation stage, it determines whether to switch the opening state of the injection enthalpy electronic expansion valve 10 and the injection liquid electronic expansion valve 8 based on the current exhaust temperature or the opening degree of the electronic expansion valve that is currently in the open state, and then periodically adjusts the opening degree of the electronic expansion valve that is in the open state.

[0033] Using the above method, the unit operation process is divided into two stages, and the control methods for these two stages are different. During the startup stage, the unit selects the appropriate electronic expansion valve to open based on the ambient temperature and outlet water temperature, and provides a reasonable initial opening degree for the electronic expansion valve. This allows the exhaust temperature of compressor 1 to stabilize quickly, preventing a rapid rise in exhaust temperature during the gradual increase of load. This avoids the unit shutting down due to excessively high exhaust temperature during compressor 1 startup, and also prevents large fluctuations in exhaust temperature within a short period, ensuring a stable startup. During the formal operation stage, the unit selects the appropriate electronic expansion valve to open based on the current operating status and dynamically adjusts its opening degree, ensuring stability during both startup and operation.

[0034] In this embodiment, when the unit is in the startup phase, the conditions for determining whether the liquid injection electronic expansion valve 8 or the enthalpy injection electronic expansion valve 10 is open are as follows: 1) When the ambient temperature Tao ≥ the first set temperature, the startup is performed using enthalpy injection control; 2) When the first set temperature > the ambient temperature Tao ≥ the second set temperature, the unit determines whether the liquid injection electronic expansion valve 8 or the enthalpy injection electronic expansion valve 10 is open based on the outlet water temperature at the current ambient temperature; 3) When the ambient temperature Tao < the second set temperature, the liquid injection electronic expansion valve 8 is opened. More preferably, when the first set temperature > the ambient temperature Tao ≥ the second set temperature, if c ≥ a, the liquid injection electronic expansion valve 8 or the enthalpy injection electronic expansion valve 10 is opened; otherwise, the enthalpy injection electronic expansion valve 10 is opened. Wherein, the coefficient C = A*Tao + B*ToutAC, Tao is the current ambient temperature, ToutAC is the current outlet water temperature, and a is a constant.

[0035] More preferably, when the unit is in the startup phase, if the electronic expansion valve 10 is opened, the initial opening degree of the electronic expansion valve 10 is V=[A*Tao+B*ToutAC]*F, where A is a constant, B is a constant, F is a constant, Tao is the current ambient temperature, and ToutAC is the current outlet water temperature. In this way, the ambient temperature and outlet water temperature can better reflect the unit's load and better predict whether the unit will encounter high temperature and high pressure conditions during subsequent operation, thereby ensuring a stable startup of the unit.

[0036] More preferably, during the start-up phase, the unit adjusts the number of steps of the electronic expansion valve in the open state based on the difference between the current exhaust temperature and the target exhaust temperature. Specifically, after the liquid injection electronic expansion valve 8 opens, the adjustment number K per cycle of the liquid injection electronic expansion valve 8 is K = (current exhaust temperature Td - target exhaust temperature Td) * coefficient d; after the enthalpy injection electronic expansion valve 10 opens, the adjustment number L per cycle of the enthalpy injection electronic expansion valve 10 is L = (current exhaust temperature Td - target exhaust temperature Td) * coefficient e, when the current exhaust temperature Td ≥ the set value α. 1) Open the liquid injection electronic expansion valve 8 and close the enthalpy injection electronic expansion valve 10; 2) If the set temperature α > the current exhaust temperature Td ≥ the set temperature β, and the enthalpy injection electronic expansion valve 10 is open, then continue to close the liquid injection electronic expansion valve 8; if the liquid injection electronic expansion valve 8 is open, then determine whether to close the liquid injection electronic expansion valve 8 and open the enthalpy injection electronic expansion valve 10 based on the current opening degree of the liquid injection electronic expansion valve 8; 3) If the current exhaust temperature Td < the set temperature β, then open the enthalpy injection electronic expansion valve 10 and close the liquid injection electronic expansion valve 8. With this setting, after the unit enters the formal operation stage, the exhaust temperature of compressor 1 will not experience a rapid increase. Thus, by selecting the appropriate electronic expansion valve to open based on the current exhaust temperature of the unit, the exhaust temperature can be better controlled.

[0037] In this embodiment, when the unit enters the formal operation stage, if the set temperature α > the current exhaust temperature Td ≥ the set temperature β, and the opening degree of the liquid injection electronic expansion valve 8 ≤ the opening degree limit value V, then the liquid injection electronic expansion valve 10 is opened and the liquid injection electronic expansion valve 8 is closed; if the set temperature α > the current exhaust temperature Td ≥ the set temperature β, and the opening degree of the liquid injection electronic expansion valve 8 > the opening degree limit value V, then the liquid injection electronic expansion valve 8 is opened and the liquid injection electronic expansion valve 10 is closed.

[0038] In this embodiment, when the unit enters the formal operation phase and the opening states of the enthalpy-injected electronic expansion valve 10 and the liquid injection electronic expansion valve 8 switch, if the enthalpy-injected electronic expansion valve is opened, the initial opening of the enthalpy-injected electronic expansion valve 10 is determined based on the opening degree of the liquid injection electronic expansion valve 8 when it is closed; specifically, the initial opening degree of the enthalpy-injected electronic expansion valve 10 = N * the opening degree of the liquid injection electronic expansion valve 8 when it is closed + X. After the enthalpy-injected electronic expansion valve 10 is opened, its opening degree is dynamically adjusted in a 10-second cycle. Furthermore, the adjustment steps of the enthalpy-injected electronic expansion valve 10 per cycle are L = (current Td - target Td) * coefficient e / 3. If the difference between the current exhaust temperature and the target exhaust temperature is within ±3℃, the opening degree of the enthalpy-injected electronic expansion valve 10 is no longer adjusted.

[0039] In this embodiment, when the unit enters the formal operation phase and the opening states of the enthalpy injection electronic expansion valve 10 and the liquid injection electronic expansion valve 8 switch, if the liquid injection electronic expansion valve 8 is opened, the initial opening degree of the enthalpy injection electronic expansion valve 10 is determined based on the opening degree of the enthalpy injection electronic expansion valve 10 when it is closed; specifically, the initial opening degree of the liquid injection electronic expansion valve 8 = 1 / N enthalpy injection electronic expansion valve 10 + Y. After the liquid injection electronic expansion valve 8 is opened, its opening degree is dynamically adjusted in a 10-second cycle. Furthermore, the adjustment step K of the liquid injection electronic expansion valve 8 per cycle is K = (current Td - target Td) * coefficient d / 2. If the difference between the current exhaust temperature and the target exhaust temperature is within ±3℃, the opening degree of the liquid injection electronic expansion valve 8 is no longer adjusted.

[0040] Of the parameters above, NX and Y are settable parameters, and their specific values ​​are determined based on the ratio of the two selected valves and the exhaust effect.

[0041] In the description of this specification, references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0042] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention without departing from the principles and spirit of the present invention.

Claims

1. A method for handling excessively high exhaust temperature during low-temperature startup of a heat pump fixed-frequency injection enthalpy compressor, characterized in that: The heat pump unit includes a compressor (1), a four-way valve (2), a condenser (3), an economizer (4), an evaporator (5), an electronic expansion valve for liquid injection (8), and an electronic expansion valve for enthalpy injection (10). The main pipeline (7) passes through the compressor (1), the four-way valve (2), the condenser (3), the economizer (4), and the evaporator (5) in sequence, and then passes through the four-way valve (2) again to connect with the compressor (1) to form a loop. The electronic expansion valve (10) for injection enthalpy is installed on the injection enthalpy pipeline (11). One end of the injection enthalpy pipeline (11) is connected to the main pipeline (7) between the condenser (3) and the economizer (4). The other end of the injection enthalpy pipeline (11) is connected to the gas supply port of the compressor (1) through the economizer (4). The liquid injection electronic expansion valve (8) is installed on the liquid injection pipeline (9). One end of the liquid injection pipeline (9) is connected to the main pipeline (7) between the condenser (3) and the economizer (4), and the other end of the liquid injection enthalpy pipeline (11) is connected to the gas supply port of the compressor (1). The specific control methods are as follows: When the compressor (1) starts, the unit enters the start-up stage. The unit opens the liquid injection electronic expansion valve (8) or the enthalpy injection electronic expansion valve (10) according to the current ambient temperature or outlet water temperature, and then periodically adjusts the opening degree of the electronic expansion valve in the open state. The initial opening degree of the enthalpy injection electronic expansion valve (10) is determined according to the current ambient temperature and the current outlet water temperature, while the initial opening degree of the liquid injection electronic expansion valve (8) is a fixed number of steps S. After M minutes of startup, the unit enters the formal operation phase. After the unit enters the formal operation stage, it is determined whether to switch the opening state of the two electronic expansion valves based on the current exhaust temperature or the opening degree of the electronic expansion valve that is currently in the open state, and then the opening degree of the liquid injection electronic expansion valve (8) or the enthalpy injection electronic expansion valve (10) that is in the open state is periodically adjusted. When the unit is in the start-up phase, the conditions for determining whether the liquid injection electronic expansion valve (8) or the enthalpy injection electronic expansion valve (10) is open are as follows: 1) When the ambient temperature Tao is greater than or equal to the first set temperature, the start-up is carried out by enthalpy control; 2) When the first set temperature is greater than or equal to the ambient temperature Tao, the unit determines whether the liquid injection electronic expansion valve (8) or the enthalpy injection electronic expansion valve (10) is open based on the outlet water temperature at the current ambient temperature; 3) When the ambient temperature Tao is less than the second set temperature, the liquid injection electronic expansion valve (8) is opened.

2. The method for handling excessively high exhaust temperature during low-temperature startup of a heat pump fixed-frequency injection enthalpy compressor according to claim 1, characterized in that: When the first set temperature > ambient temperature Tao ≥ the second set temperature, if c ≥ a, the liquid spray electronic expansion valve (8) or the enthalpy spray electronic expansion valve (10) is opened; otherwise, the enthalpy spray electronic expansion valve (10) is opened; where, the coefficient C = A*Tao + B*ToutAC, Tao is the current ambient temperature, ToutAC is the current outlet water temperature, and a is a constant.

3. The method for handling excessively high exhaust temperature during low-temperature startup of a heat pump fixed-frequency injection enthalpy compressor according to claim 1, characterized in that: When the unit is in the start-up phase, if the electronic expansion valve (10) is opened, the initial opening degree of the electronic expansion valve (10) is V=[A*Tao+B*ToutAC]*F, where A is a constant, B is a constant, F is a constant, Tao is the current ambient temperature, and ToutAC is the current outlet water temperature.

4. A method for handling excessively high exhaust temperature during low-temperature startup of a heat pump fixed-frequency injection enthalpy compressor according to claim 1, characterized in that: During the startup phase, the unit adjusts the number of steps of the electronic expansion valve, which is in the open state, based on the difference between the current exhaust temperature and the target exhaust temperature.

5. A method for handling excessively high exhaust temperature during low-temperature startup of a heat pump fixed-frequency injection enthalpy compressor according to claim 1, characterized in that: When the unit enters the formal operation stage, the method for determining whether to switch the opening state of the two electronic expansion valves is as follows: 1) When the current exhaust temperature Td ≥ the set value α, the liquid injection electronic expansion valve (8) is opened and the enthalpy injection electronic expansion valve (10) is closed; 2) If the set temperature α > the current exhaust temperature Td ≥ the set temperature β, and the enthalpy injection electronic expansion valve (10) is in the open state, the liquid injection electronic expansion valve (8) is closed; if the liquid injection electronic expansion valve (8) is in the open state, the liquid injection electronic expansion valve (8) is closed and the enthalpy injection electronic expansion valve (10) is opened according to the current opening degree of the liquid injection electronic expansion valve (8); 3) If the current exhaust temperature Td < the set temperature β, the enthalpy injection electronic expansion valve (10) is opened and the liquid injection electronic expansion valve (8) is closed.

6. A method for handling excessively high exhaust temperature during low-temperature startup of a heat pump fixed-frequency injection enthalpy compressor according to claim 1, characterized in that: When the unit enters the formal operation stage, if the set temperature α > the current exhaust temperature Td ≥ the set temperature β, and the opening degree of the liquid injection electronic expansion valve (8) ≤ the opening degree limit value V, then the liquid injection electronic expansion valve (10) is opened and the liquid injection electronic expansion valve (8) is closed; if the set temperature α > the current exhaust temperature Td ≥ the set temperature β, and the opening degree of the liquid injection electronic expansion valve (8) > the opening degree limit value V, then the liquid injection electronic expansion valve (8) is opened and the liquid injection electronic expansion valve (10) is closed.

7. A method for handling excessively high exhaust temperature during low-temperature startup of a heat pump fixed-frequency injection enthalpy compressor according to claim 1, characterized in that: When the unit enters the formal operation stage and the opening state of the two electronic expansion valves is switched, if the injection enthalpy electronic expansion is opened, the initial opening degree of the injection enthalpy electronic expansion valve (10) is determined according to the opening degree of the injection liquid electronic expansion valve (8) when it is closed.

8. A method for handling excessively high exhaust temperature during low-temperature startup of a heat pump fixed-frequency injection enthalpy compressor according to claim 1, characterized in that: When the unit enters the formal operation stage and the opening state of the two electronic expansion valves is switched, if the liquid injection electronic expansion valve (8) is opened, the initial opening degree of the liquid injection electronic expansion valve (10) is determined according to the opening degree when the liquid injection electronic expansion is closed.

9. A method for handling excessively high exhaust temperature during low-temperature startup of a heat pump fixed-frequency injection enthalpy compressor according to claim 1, characterized in that: During the formal operation phase, the unit adjusts the number of steps of the electronic expansion valve that is in the open state according to the difference between the current exhaust temperature and the target exhaust temperature.

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