Variable frequency air source heat pump water chiller and parallel control method thereof

Abstract

The application provides a variable frequency air source heat pump water chiller and a parallel method thereof, the method comprising: setting the set water temperature of each subunit and obtaining the total outlet water temperature; judging whether the total outlet water temperature meets the first unloading condition according to the operation mode of the unit, if yes, controlling the subunit with the lowest operation frequency to execute the unloading action; obtaining the total outlet water temperature in real time and judging whether the total outlet water temperature meets the second unloading condition, if yes, controlling the subunit with the lowest operation frequency to execute the unloading action; judging whether the total outlet water temperature meets the start-up loading condition in real time, if yes, controlling the first subunit with the shortest cumulative operation time among the subunits executing the unloading action to execute the start-up loading action; judging whether the total outlet water temperature meets the start-up loading condition every interval of a specified time length. The application independently controls the operation frequency of each subunit, improves the energy utilization efficiency, and ensures that the unit capacity is sufficient to meet the required water temperature requirement.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of heat pump, in particular to a variable frequency air source heat pump water chiller and a parallel control method thereof. BACKGROUND

[0002] In the variable frequency air source heat pump water chiller, during the operation of the unit, the single unit in the whole parallel system is controlled to run at a uniform frequency, and the problem of stopping without frequency reduction occurs; when the water temperature of part of the units reaches the temperature, all the units are directly unloaded, which may cause part of the units to not reach the set temperature, but the capacity output of the unit is just balanced with the energy consumption, so that even if the unit is opened at the maximum output, the water temperature can only be maintained without decreasing or increasing, and the situation of stopping the unit in the parallel system without reaching the temperature occurs; on the other hand, in order to reach the set temperature, the compressor is restarted, which causes the compressor to start and stop frequently, shortens the service life of the compressor, and affects the service life of the whole system.

[0003] In addition, in the starting program of the parallel system, the number of units to be started is directly determined at the time of starting, and the units of the water system cannot directly reflect the specific demand of the end through the water temperature difference, so that part of the units are not started, which causes misjudgment of the system demand. SUMMARY

[0004] In view of the above problems, the present application provides a variable frequency air source heat pump water chiller and a parallel control method thereof, each sub-unit independently controls the running frequency of itself, so as to prevent the problem of stopping without frequency reduction, greatly improve the energy efficiency of the whole system, and achieve the purpose of energy saving. In addition, in the unloading program, it is judged whether there is a starting load demand, so as to ensure that the unit capacity is sufficient to meet the required water temperature requirement under the premise of meeting the use demand.

[0005] The present application provides a parallel control method of a variable frequency air source heat pump water chiller, the variable frequency air source heat pump water chiller comprises a plurality of sub-units arranged in parallel, and the parallel control method comprises the following steps:

[0006] Set the set water temperature of each sub-unit, and obtain the total outlet water temperature of the variable frequency air source heat pump water chiller;

[0007] According to the operation mode of the variable frequency air source heat pump water chiller, it is judged whether the total outlet water temperature meets the first unloading condition, if yes, the sub-unit with the lowest running frequency is controlled to execute the unloading action; the first unloading condition is: in the heating / living hot water mode, the total outlet water temperature is greater than or equal to the set water temperature minus (the number of sub-units started minus the first preset value); in the cooling mode: the total outlet water temperature is less than or equal to the set water temperature plus (the number of sub-units started minus the second preset value);

[0008] Real-time total outlet water temperature is acquired, and whether the total outlet water temperature meets the second unloading condition is judged, if yes, the subunit group with the lowest running frequency is controlled to execute the unloading action;

[0009] Real-time total outlet water temperature is acquired, and whether the total outlet water temperature meets the second unloading condition is judged, if yes, the subunit group with the lowest running frequency is controlled to execute the unloading action;

[0010] Real-time total outlet water temperature is acquired, and whether the total outlet water temperature meets the second unloading condition is judged, if yes, the subunit group with the lowest running frequency is controlled to execute the unloading action;

[0011] The application judges whether the subunit group needs to be unloaded according to whether the subunit group meets the first unloading condition, and judges whether the subunit group needs to be further unloaded according to whether the subunit group meets the second unloading condition, that is, the number of unloaded subunit groups is adjusted in real time according to the real-time total outlet water temperature and the change of the total outlet water temperature, and the running of the subunit group is adjusted according to the total outlet water temperature, which improves the efficiency of the running of the subunit group, achieves the purpose of energy saving, each subunit group independently controls the running frequency of itself, prevents the problem of not reducing the frequency and stopping the machine, greatly improves the energy efficiency of the whole system, further realizes the purpose of energy saving. In addition, judging whether there is a start-up loading demand can avoid the situation that the water temperature does not reach the temperature in the parallel unit group although the subunit group is stopped, ensures the stability and reliability of the running of the unit group, ensures that the required water temperature requirement is met on the premise that the capacity of the unit group is sufficient, meets the use demand, the stop of the subunit group executing the start-up loading action is stopped according to the condition in the non-parallel mode, which can prevent the same subunit group from being unloaded, causes the subunit group to be frequently started and stopped in a short time, and improves the service life of the subunit group.

[0012] In the optional technical scheme of the application, the start-up loading condition is that, in the heating / living hot water mode, whether the total outlet water temperature is not higher than the set water temperature, and whether the total outlet water temperature rises in the first preset time period, if the total outlet water temperature is not higher than the set water temperature, and the total outlet water temperature does not rise in the first preset time period, the first subunit group with the shortest cumulative running time in the subunit group executing the unloading action is controlled to execute the start-up loading action;

[0013] In the refrigeration mode, whether the total outlet water temperature is not lower than the set water temperature, and whether the total outlet water temperature falls in the second preset time period, if the total outlet water temperature is not lower than the set water temperature, and the total outlet water temperature does not fall in the second preset time period, the first subunit group with the shortest cumulative running time in the subunit group executing the unloading action is controlled to execute the start-up loading action.

[0014] According to the technical scheme, in the unloading process, whether the total outlet water temperature meets the requirement is judged, and when the requirement is not met, a first sub-machine group with the shortest accumulated running time in the sub-machine group performing the unloading action is executed to perform the start-up loading action, so that the output capacity of the machine group is improved, and the total outlet water temperature meets the user requirement water temperature.

[0015] In the optional technical scheme of the application, the second unloading condition is that, in the heating / living hot water mode, the total outlet water temperature rises by a first specified temperature; and in the cooling mode, the total outlet water temperature drops by a second specified temperature.

[0016] According to the technical scheme, in different modes, the sub-machine group with the lowest unloading running frequency is reduced in energy waste on the basis of improving energy efficiency, so that the energy-saving purpose is achieved.

[0017] In the optional technical scheme of the application, it further includes judging whether the total outlet water temperature meets the highest / lowest water temperature limit condition, and if not, the temperature-reached shutdown processing is performed.

[0018] According to the technical scheme, the machine group water temperature can be controlled in a reasonable range, and the comfort of use and the reliability of machine group operation are improved.

[0019] In the optional technical scheme of the application, it further includes judging whether the sub-machine group meets the shutdown / shutdown condition, and if so, a sub-machine group is unloaded every interval of a specified time length according to the accumulated running time of the sub-machine group.

[0020] In the optional technical scheme of the application, it further includes a start-up control logic: according to the operation mode of the variable frequency air source heat pump cold water machine group, whether the total outlet water temperature meets the first start-up condition is judged, if so, the sub-machine group with the shortest accumulated running time in the shutdown state is started; the total outlet water temperature is acquired every interval of a first specified time length, and whether the difference of the total outlet water temperature in adjacent time intervals meets the second start-up condition is judged every interval of a second specified time length, if so, the sub-machine group with the shortest accumulated running time in the shutdown state is started; and if not, the sub-machine group is not started.

[0021] According to the technical scheme, after the start-up requirement is met, the total outlet water temperature is acquired in real time, and whether the temperature difference of the total outlet water temperature meets the second start-up condition is judged, so that the number of started sub-machine groups can be adjusted in real time according to the requirement of the machine group, and the accuracy of the number of started machine groups is improved. Further, whether to start up the machine group is judged by judging whether the total outlet water temperature rises / drops in a specified time interval before starting up, so that whether the machine group can quickly meet the set water temperature requirement is judged, the misjudgment of the requirement is avoided, and the frequent start-stop of the sub-machine group is avoided, so that the service life of the compressor in the sub-machine group is guaranteed, and energy waste is reduced.

[0022] In an optional technical solution of the present application, the first start-up condition is that, in the heating / living hot water mode, the total outlet water temperature is less than or equal to the difference between the set water temperature and the third preset value; and in the cooling mode, the total outlet water temperature is greater than or equal to the sum of the set water temperature and the fourth preset value.

[0023] The second start-up condition is that, in the heating / living hot water mode, the total outlet water temperature is less than or equal to the difference between the set water temperature and the third preset value, and the difference of the total outlet water temperature is less than or equal to the first temperature threshold; and in the cooling mode, the total outlet water temperature is greater than or equal to the sum of the set water temperature and the fourth preset value, and the difference of the total outlet water temperature is greater than or equal to the second temperature threshold.

[0024] According to the technical solution, in the heating / living hot water mode, the total outlet water temperature is lower than the set water temperature, and the total outlet water temperature has a small rising amplitude; and in the cooling mode, the total outlet water temperature is higher than the set temperature, and the total outlet water temperature has a small falling amplitude. The start-up loading action is performed, the output capacity of the unit is improved, and the total outlet water temperature and the rising / falling rate of the total outlet water temperature can meet the user demand.

[0025] In an optional technical solution of the present application, the total outlet water temperature is acquired every 5 minutes, whether the difference of the total outlet water temperature meets the second start-up condition is judged every 30 minutes, if yes, the sub-unit with the shortest accumulated running time in the shutdown state is started; and if no, the sub-unit is not started.

[0026] According to the technical solution, the unit can be avoided from being frequently started and stopped, and the reliability of the unit operation is improved.

[0027] In an optional technical solution of the present application, if the difference of the total outlet water temperature or the total outlet water temperature does not meet any start-up condition for a specified time length, and no unloading action of the sub-unit is detected during the time length, the sub-unit with the shortest accumulated running time is forcibly started.

[0028] According to the technical solution, under the above conditions, the sub-unit with the shortest accumulated running time is forcibly started, the output capacity of the unit is improved, and the total outlet water temperature can meet the user demand water temperature.

[0029] The present application further provides a variable frequency air source heat pump water chiller, which executes the parallel control method of the variable frequency air source heat pump water chiller. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 FIG. 1 is a schematic diagram of a shutdown control logic flow of the parallel control method of the variable frequency air source heat pump water chiller in the embodiment of the present application.

[0031] Figure 2 FIG. 2 is a schematic diagram of a start-up control logic flow of the parallel control method of the variable frequency air source heat pump water chiller in the embodiment of the present application. DETAILED DESCRIPTION

[0032] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative effort belong to the scope of protection of the present application.

[0033] As shown in Figure 1 The present application provides a parallel control method of a variable frequency air source heat pump water chiller, the variable frequency air source heat pump water chiller comprising a plurality of sub-units arranged in parallel, and the parallel control method comprising the following steps:

[0034] Setting a set water temperature TS of each sub-unit, and acquiring a total outlet water temperature T1 of the variable frequency air source heat pump water chiller.

[0035] According to the operation mode of the variable frequency air source heat pump water chiller, it is judged whether the total outlet water temperature T1 meets a first unloading condition, and if so, the sub-unit with the lowest operation frequency is controlled to perform an unloading action; as shown in the dashed box in Figure 1 The first unloading condition is that, in the heating / living hot water mode, the total outlet water temperature T1 is greater than or equal to the set water temperature TS minus a first preset value of the number of sub-units turned on; and in the cooling mode, the total outlet water temperature T1 is less than or equal to the set water temperature TS plus a second preset value of the number of sub-units turned on.

[0036] The total outlet water temperature T1 is acquired in real time, and it is judged whether the total outlet water temperature T1 meets a second unloading condition, and if so, the sub-unit with the lowest operation frequency is controlled to perform an unloading action; as shown in the dashed box in Figure 1 The second unloading condition is that, in the heating / living hot water mode, the total outlet water temperature T1 rises by a first specified temperature a ℃, that is, it is judged whether the temperature difference value T1'-T1 of the total outlet water temperature in the interval between adjacent two temperature acquisition times is not less than a ℃, where T1' is the total outlet water temperature acquired this time, and T1 is the total outlet water temperature acquired last time; and in the cooling mode, the total outlet water temperature T1 falls by a second specified temperature a', that is, it is judged whether the temperature difference value T1'-T1 of the total outlet water temperature in the interval between adjacent two temperature acquisition times is not greater than-a ℃.

[0037] It is judged in real time whether the total outlet water temperature T1 meets a start-up loading condition, and if so, the first sub-unit with the shortest cumulative operation time among the sub-units performing the unloading action is controlled to perform a start-up loading action; and it is judged every interval of a specified time length whether the total outlet water temperature T1 meets the start-up loading condition, and if so, the sub-unit performing the start-up loading action is controlled, and the shutdown of the sub-unit is performed according to the condition in the non-parallel mode.

[0038] The application determines whether the sub-machine group needs to be unloaded according to whether the sub-machine group meets the first unloading condition, and determines whether the sub-machine group needs to be further unloaded according to whether the sub-machine group meets the second unloading condition, that is, the number of unloaded sub-machine groups is adjusted in real time according to the total outlet water temperature and the change of the total outlet water temperature, and the operation of the machine group is adjusted according to the total outlet water temperature, which improves the efficiency of the machine group operation and achieves the purpose of energy saving; and the set water temperature is compared with the total outlet water temperature combined with the number of started sub-machine groups, for example, in the heating / living hot water mode, when the number of started sub-machine groups is small, the total outlet water temperature may exceed the set water temperature to enter the unloading program, and when the number of started sub-machine groups is large, the total outlet water temperature may be lower than the set water temperature to enter the unloading program, which fully considers the influence of the number of started sub-machine groups on the change speed of the total outlet water temperature and improves the accuracy of unloading; each sub-machine group independently controls its own operation frequency, which prevents the problem of not reducing the frequency and stopping the machine, greatly improves the energy efficiency of the whole system, and further achieves the purpose of energy saving. In addition, the judgment of whether there is a start-up loading demand can avoid the situation that the water temperature does not reach the temperature in the parallel machine group with the sub-machine group stopped, ensure the stability and reliability of the machine group operation, and ensure that the required water temperature can be reached under the premise that the capacity of the machine group is sufficient, meet the use demand. The stop of the sub-machine group performing the start-up loading action is according to the condition of the non-parallel mode, which can prevent the same sub-machine group from being unloaded, causing the sub-machine group to be frequently started and stopped in a short time, and improve the service life of the sub-machine group. It should be noted that the set water temperature of the application is the set water temperature of each sub-machine group, and the set water temperatures of the sub-machine groups can be the same or different.

[0039] In the preferred embodiment of the application, as shown in the dashed box, Figure 1 In the heating / living hot water mode, whether the total outlet water temperature T1 is not higher than the set water temperature TS (T1≤TS), and whether the total outlet water temperature T1 rises within a first preset time period, if the total outlet water temperature T1 is not higher than the set water temperature TS (T1≤TS), and the total outlet water temperature T1 does not rise within the first preset time period, the first sub-machine group with the shortest cumulative running time in the sub-machine group performing the unloading action is controlled to perform the start-up loading action.

[0040] In the refrigeration mode, whether the total outlet water temperature T1 is not lower than the set water temperature TS, and whether the total outlet water temperature T1 falls within a second preset time period, if the total outlet water temperature T1 is not lower than the set water temperature TS, and the total outlet water temperature T1 does not fall within the second preset time period, the first sub-machine group with the shortest cumulative running time in the sub-machine group performing the unloading action is controlled to perform the start-up loading action.

[0041] According to different operation modes of the system, whether the total outlet water temperature meets the refrigeration water temperature demand or the heating / living hot water temperature demand is judged respectively, and the accuracy of the total outlet water temperature control is improved. In the unloading process, whether the total outlet water temperature T1 meets the water temperature demand is judged, and when the water temperature demand is not met, a start-up loading action is performed on the first sub-unit with the shortest accumulated running time in the sub-units performing the unloading action, which can improve the output capacity of the unit and make the total outlet water temperature T1 meet the user water temperature demand.

[0042] In the preferred embodiment of the application, it is further included that whether each sub-unit meets a single shutdown condition is judged, and if yes, the sub-unit is controlled to stop; specifically, the single shutdown condition is that the energy demand is equal to 0 or the over-temperature protection, and when the unit meets any shutdown condition, a shutdown action is performed,

[0043] In the preferred embodiment of the application, it is further included that whether the total outlet water temperature T1 meets the highest / lowest water temperature limit condition is judged, and if not, a temperature-reached shutdown treatment is performed. Through the above-mentioned manner, the unit water temperature can be controlled in a reasonable range, and the comfort of use and the reliability of unit operation are improved.

[0044] In the preferred embodiment of the application, it is further included that whether the sub-unit meets a shutdown condition is judged, and if yes, one sub-unit is unloaded every interval of a specified time length according to the accumulated running time of the sub-unit; specifically, when the sub-unit meets the shutdown condition, one sub-unit can be unloaded every interval of 10s according to the accumulated running time of the sub-unit.

[0045] As shown in FIG. 1, Figure 2 In the preferred embodiment of the application, it is further included that a start-up control logic is: according to the operation mode of the variable frequency air source heat pump water chiller unit, whether the total outlet water temperature T1 meets a first start-up condition is judged, and if yes, the sub-unit with the shortest accumulated running time in the shutdown state is started; the total outlet water temperature T1 is obtained every interval of a first specified time length, and whether the difference of the total outlet water temperature T1 in adjacent time intervals meets a second start-up condition is judged every interval of a second specified time length, and if yes, the sub-unit with the shortest accumulated running time in the shutdown state is started; and if not, the sub-unit is not started.

[0046] By the above manner, after meeting the start-up demand, the number of sub-units that are started is adjusted in real time according to the demand of the unit by acquiring the total outlet water temperature T1 in real time and judging whether the temperature difference of the total outlet water temperature T1 meets the second start-up condition, the accuracy of the number of units that are started is improved, and the sub-unit with the shortest cumulative running time length in the stopped state is started, which is beneficial to prolong the overall service life of the variable frequency air source heat pump chiller and reduce the use cost. Further, whether to continue to start the unit is judged by judging whether the unit can quickly meet the set water temperature demand by judging whether to start at intervals and judging the rising / falling amplitude of the total outlet water temperature before starting, so as to avoid misjudgment of the demand and frequent start-stop of the sub-unit, thereby ensuring the service life of the compressor in the sub-unit and reducing energy waste.

[0047] In the preferred embodiment of the present application, the first start-up condition is that, in the heating / living hot water mode, the total outlet water temperature T1 is less than or equal to the difference between the set water temperature TS and a third preset value (for example, T1≤TS-2); in the cooling mode, the total outlet water temperature T1 is greater than or equal to the sum of the set water temperature TS and a fourth preset value (for example, T1≥TS+6); and the second start-up condition is that, in the heating / living hot water mode, the total outlet water temperature T1 is less than or equal to the difference between the set water temperature TS and the third preset value, and the difference of the total outlet water temperature T1 is less than or equal to a first temperature threshold (for example, ΔT1 (ΔT1=the 10th min T1-the 5th min T1)≤5℃); in the cooling mode, the total outlet water temperature T1 is greater than or equal to the sum of the set water temperature TS and the fourth preset value, and the difference of the total outlet water temperature T1 is greater than or equal to a second temperature threshold (ΔT1 (ΔT1=the 10th min T1-the 5th min T1)≥-5℃).

[0048] By the above manner, in the heating / living hot water mode, the total outlet water temperature T1 is lower than the set water temperature TS, and the rising amplitude of the total outlet water temperature T1 is less than the third preset value; in the cooling mode, the total outlet water temperature T1 is higher than the set temperature, and the falling amplitude of the total outlet water temperature T1 is less than the fourth preset value, the start-up loading action is performed, which can improve the output capacity of the unit, so that the total outlet water temperature T1 and the rising / falling amplitude of the total outlet water temperature T1 can meet the user demand.

[0049] In the preferred embodiment of the present application, the total outlet water temperature T1 is acquired every 5 minutes, and whether the difference of the total outlet water temperature T1 meets the second start-up condition is judged every 30 minutes, if yes, the sub-unit with the shortest cumulative running time length in the stopped state is started; if not, the sub-unit in the stopped state is not started. By the above manner, the total outlet water temperature T1 is acquired in real time, which can timely understand the outlet water temperature of the unit, avoid too high or too low water temperature, and affect the operation reliability of the unit or the comfort of the user, and lengthening the time interval of judging whether to meet the second start-up condition can avoid frequent start-stop of the unit and improve the reliability of the operation of the unit.

[0050] In the preferred embodiment of the present application, if the difference of the total outlet water temperature T1 or the total outlet water temperature T1 does not satisfy any start condition for a specified duration, and no unloading action of the sub-units is detected during the specified duration, the sub-unit with the shortest cumulative running duration is forced to start. Under the above condition, the sub-unit with the shortest cumulative running duration is forced to start, which can improve the output capacity of the unit, so that the total outlet water temperature T1 can satisfy the user's demand water temperature.

[0051] In the preferred embodiment of the present application, each sub-unit can be operated according to the energy requirement of the single sub-unit during the specific operation process: for example, by setting the temperature difference between the water temperature TS and the total outlet water temperature T1, the running frequency of the sub-unit is increased or decreased at different speeds according to different temperature difference intervals.

[0052] In the preferred embodiment of the present application, before entering the unloading control logic and the start control logic, it further includes judging whether the variable frequency air source heat pump water chiller is a parallel unit, and in the start control logic, it further includes judging whether to start.

[0053] The present application further provides a variable frequency air source heat pump water chiller, which executes the parallel control method of the variable frequency air source heat pump water chiller as described above.

[0054] The above is only a preferred embodiment of the present application, and is not intended to limit the present application. Any modification, equivalent replacement and improvement within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A parallel control method of a variable frequency air source heat pump water chiller, the variable frequency air source heat pump water chiller comprising a plurality of sub-units arranged in parallel, characterized in that, The parallel control method comprises the following steps: setting a set water temperature of each of the sub-units, and acquiring a total outlet water temperature of the variable-frequency air source heat pump chiller; determining whether the total outlet water temperature meets a first unloading condition according to an operation mode of the variable-frequency air source heat pump chiller, and if yes, controlling the sub-unit with the lowest operation frequency to perform an unloading action; the first unloading condition is that, in a heating / living hot water mode, the total outlet water temperature is greater than or equal to the set water temperature minus a first preset value of the number of sub-units turned on; and in a refrigeration mode, the total outlet water temperature is less than or equal to the set water temperature plus a second preset value of the number of sub-units turned on; acquiring the total outlet water temperature in real time, and determining whether the total outlet water temperature meets a second unloading condition, and if yes, controlling the sub-unit with the lowest operation frequency to perform an unloading action; determining whether the total outlet water temperature meets a start-up loading condition in real time, and if yes, controlling the first sub-unit with the shortest cumulative operation time among the sub-units performing an unloading action to perform a start-up loading action; determining whether the total outlet water temperature meets the start-up loading condition every interval of a specified time length, and if yes, controlling the sub-unit performing the start-up loading action to stop according to a condition in a non-parallel mode.

2. The parallel control method of a variable frequency air source heat pump chiller unit according to claim 1, characterized in that, the start-up loading condition is that, in the heating / living hot water mode, whether the total outlet water temperature is not higher than the set water temperature and whether the total outlet water temperature rises in a first preset time period, and if the total outlet water temperature is not higher than the set water temperature and the total outlet water temperature does not rise in the first preset time period, controlling the first sub-unit with the shortest cumulative operation time among the sub-units performing the unloading action to perform the start-up loading action; in the refrigeration mode, whether the total outlet water temperature is not lower than the set water temperature and whether the total outlet water temperature falls in a second preset time period, and if the total outlet water temperature is not lower than the set water temperature and the total outlet water temperature does not fall in the second preset time period, controlling the first sub-unit with the shortest cumulative operation time among the sub-units performing the unloading action to perform the start-up loading action.

3. The parallel control method of a variable frequency air source heat pump chiller unit according to claim 1, characterized in that, the second unloading condition is that, in the heating / living hot water mode, the total outlet water temperature rises by a first specified temperature; and in the refrigeration mode, the total outlet water temperature falls by a second specified temperature.

4. The parallel control method of a variable frequency air source heat pump chiller unit according to claim 1, characterized in that, further comprising: determining whether the total outlet water temperature meets a highest / lowest water temperature limit condition, and if not, performing a temperature-reached stop processing.

5. The parallel control method of a variable frequency air source heat pump chiller unit according to claim 1, wherein, further comprising: determining whether the sub-units meet a stop condition, and if yes, sequentially unloading one sub-unit every interval of a specified time length according to the cumulative operation time of the sub-units.

6. The parallel control method of a variable frequency air source heat pump chiller unit according to any one of claims 1 to 5, characterized in that, further comprising a start-up control logic: determining whether the total outlet water temperature meets a first start-up condition according to an operation mode of the variable-frequency air source heat pump chiller, and if yes, starting the sub-unit with the shortest cumulative operation time in a stop state; The total outlet water temperature is acquired every first specified time interval, and whether the difference of the total outlet water temperature in adjacent time intervals meets a second start condition is determined every second specified time interval, and if yes, the sub-unit with the shortest accumulated running time in the shutdown state is started; If not, the sub-unit is not started.

7. The parallel control method of a variable frequency air source heat pump chiller unit according to claim 6, characterized in that, The first start condition is that in the heating / living hot water mode, the total outlet water temperature is less than or equal to the difference between the set water temperature and a third preset value; and in the cooling mode, the total outlet water temperature is greater than or equal to the sum of the set water temperature and a fourth preset value. The second start condition is that in the heating / living hot water mode, the total outlet water temperature is less than or equal to the difference between the set water temperature and a third preset value, and the difference of the total outlet water temperature is less than or equal to a first temperature threshold value; and in the cooling mode, the total outlet water temperature is greater than or equal to the sum of the set water temperature and a fourth preset value, and the difference of the total outlet water temperature is greater than or equal to a second temperature threshold value. It also includes acquiring the total outlet water temperature every 5 minutes, determining whether the difference of the total outlet water temperature meets the second start condition every 30 minutes, and if yes, starting the sub-unit with the shortest accumulated running time in the shutdown state; if not, the sub-unit is not started.

8. The parallel control method of a variable frequency air source heat pump chiller unit according to claim 6, wherein, If the difference of the total outlet water temperature or the total outlet water temperature does not meet any start condition for a specified time interval, and during which no unloading action of the sub-unit is detected, the sub-unit with the shortest accumulated running time is forcibly started.

9. The parallel control method of a variable frequency air source heat pump chiller unit according to claim 6, wherein, A parallel control method of the variable frequency air source heat pump water chiller unit according to any one of claims 1 to 9 is executed.

10. A variable speed air source heat pump chiller unit, characterized by, ​

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