阅读说明：本技术 用于冷水机组的控制方法 (Control method for water chilling unit ) 是由 张瑞台 任文臣 赵瑞昌 张虹 杨云龙 张捷 苗玉涛 于 2021-09-28 设计创作，主要内容包括：本发明涉及换热技术领域,具体提供一种用于冷水机组的控制方法。旨在解决现有冷水机组的单一控制方式难以实现高效运行的问题。为此,本发明的控制方法包括：在冷水机组启动后,获取冷冻水的初始进水温度；根据初始进水温度,确定电子膨胀阀的初始开度；在压缩机的启动阶段,获取压缩机的吸气压力和排气压力；如果排气压力和吸气压力的差值大于第一预设压差的持续时间达到第一预设时长,则直接根据冷媒循环回路的吸气过热度选择性地调节电子膨胀阀的开度；否则,根据压缩机的吸气压力选择性地调节电子膨胀阀的开度。本发明能够根据初始进水温度相应确定电子膨胀阀的初始开度,以便快速建立压缩机吸排气压差,进而有效提高机组运行的可靠性及能效。(The invention relates to the technical field of heat exchange, and particularly provides a control method for a water chilling unit. Aims to solve the problem that the single control mode of the existing water chilling unit is difficult to realize high-efficiency operation. To this end, the control method of the present invention includes: after the water chilling unit is started, acquiring the initial water inlet temperature of chilled water; determining the initial opening degree of the electronic expansion valve according to the initial water inlet temperature; at the starting stage of the compressor, acquiring the suction pressure and the exhaust pressure of the compressor; if the difference value between the exhaust pressure and the suction pressure is greater than the duration of a first preset pressure difference and reaches a first preset time, selectively adjusting the opening of the electronic expansion valve directly according to the suction superheat degree of the refrigerant circulation loop; otherwise, the opening degree of the electronic expansion valve is selectively adjusted according to the suction pressure of the compressor. The invention can correspondingly determine the initial opening of the electronic expansion valve according to the initial water inlet temperature so as to quickly establish the suction-exhaust pressure difference of the compressor, thereby effectively improving the reliability and the energy efficiency of the unit operation.)

1. The control method for the water chilling unit is characterized in that the water chilling unit comprises a refrigerant circulation loop and a chilled water circulation loop, wherein an evaporator, a compressor, an electronic expansion valve and a condenser are arranged on the refrigerant circulation loop, chilled water in the chilled water circulation loop can exchange heat with a refrigerant in the evaporator, and the control method comprises the following steps:

after the water chilling unit is started, acquiring the initial water inlet temperature of chilled water;

determining the initial opening degree of the electronic expansion valve according to the initial inlet water temperature;

at the starting stage of the compressor, acquiring the suction pressure and the discharge pressure of the compressor;

if the difference value between the exhaust pressure and the suction pressure is greater than the duration of a first preset pressure difference and reaches a first preset time, selectively adjusting the opening of the electronic expansion valve directly according to the suction superheat degree of the refrigerant circulation loop; otherwise, selectively adjusting the opening degree of the electronic expansion valve according to the suction pressure of the compressor.

2. The control method as claimed in claim 1, wherein the step of selectively adjusting the opening degree of the electronic expansion valve according to the suction superheat degree of the refrigerant circulation circuit comprises:

calculating the difference value of the suction superheat degree and the target superheat degree;

and selectively adjusting the opening degree of the electronic expansion valve according to the value range of the difference value of the suction superheat degree and the target superheat degree.

3. The control method according to claim 2, wherein the step of selectively adjusting the opening degree of the electronic expansion valve in accordance with the range of values within which the difference between the suction superheat and the target superheat is located specifically comprises:

if the difference value between the suction superheat degree and the target superheat degree is smaller than a first preset difference value or larger than a second preset difference value, adjusting the opening degree of the electronic expansion valve;

wherein the first preset difference is smaller than the second preset difference.

4. The control method according to claim 3, wherein the step of adjusting the opening degree of the electronic expansion valve if the difference between the suction superheat degree and the target superheat degree is smaller than a first preset difference or larger than a second preset difference further comprises:

and if the difference between the suction superheat degree and the target superheat degree is smaller than the first preset difference, the opening degree of the electronic expansion valve is reduced.

5. The control method according to claim 3, wherein the step of adjusting the opening degree of the electronic expansion valve if the difference between the suction superheat degree and the target superheat degree is smaller than a first preset difference or larger than a second preset difference further comprises:

and if the difference value between the suction superheat degree and the target superheat degree is larger than the second preset difference value, the opening degree of the electronic expansion valve is increased.

6. The control method according to any one of claims 2 to 5, wherein an economizer is further provided on the refrigerant circulation circuit, and the control method further comprises:

acquiring the opening and closing state of the economizer;

under the condition that the economizer is started, further acquiring the supercooling degree of an outlet of the economizer;

calculating the difference value between the outlet supercooling degree and the target supercooling degree;

comparing the difference between the outlet supercooling degree and the target supercooling degree with a third preset difference;

and selectively correcting the target superheat degree according to the comparison result of the difference value between the outlet supercooling degree and the target supercooling degree and a third preset difference value.

7. The control method according to claim 6, wherein the step of selectively correcting the target degree of superheat based on the comparison result between the difference between the outlet supercooling degree and the target supercooling degree and a third preset difference specifically includes:

and if the difference value between the outlet supercooling degree and the target supercooling degree is smaller than the third preset difference value, increasing the target superheat degree.

8. The control method according to any one of claims 1 to 5, wherein the step of selectively adjusting the opening degree of the electronic expansion valve according to the suction pressure of the compressor specifically includes:

acquiring the change speed of the suction pressure of the two adjacent compressors;

and selectively adjusting the opening degree of the electronic expansion valve according to the change speed of the suction pressure of the compressor at two adjacent times.

9. The control method according to claim 8, wherein the step of selectively adjusting the opening degree of the electronic expansion valve according to the change speed of the suction pressure of the compressor in two adjacent times comprises:

if the current descending rate of the suction pressure is greater than a first preset descending rate and the last descending rate is greater than a second preset descending rate, or the current descending rate of the suction pressure is greater than the second preset descending rate, the opening degree of the electronic expansion valve is increased;

wherein the second predetermined drop rate is greater than the first predetermined drop rate.

10. The control method according to claim 9, wherein the step of selectively adjusting the opening degree of the electronic expansion valve according to the change speed of the suction pressure of the compressor in two adjacent times further comprises:

if the current descending rate of the suction pressure is less than or equal to the first preset descending rate, or the current descending rate of the suction pressure is greater than the first preset descending rate and less than or equal to the second preset descending rate, and the last descending rate is less than or equal to the second preset descending rate, the inlet water temperature of the chilled water is obtained again;

and selectively adjusting the opening degree of the electronic expansion valve according to the numerical range of the inlet water temperature of the chilled water and the numerical range of the suction pressure of the compressor, which are obtained again.

Technical Field

The invention relates to the technical field of heat exchange, and particularly provides a control method for a water chilling unit.

Background

The existing heat source tower heat pump unit has a wide operation range during heating operation, and the outlet water temperature of a heat source side can cover 15 ℃ to-20 ℃; the conventional water source heat pump unit has a small operation range during heating operation, and the water inlet temperature is between 5 and 15 ℃; however, the opening degrees of the electronic expansion valves of the two heat pump units are controlled by the suction superheat degree, and the single control mode often cannot meet the operation requirement of the heat pump units, so that the heat pump units cannot operate optimally under all working conditions, and the comprehensive energy efficiency is low. The refrigerant circulation sequence of the conventional water source heat pump unit is as follows: the refrigerant is compressed by the compressor, then flows to the condenser through the exhaust pipe, throttled by the expansion valve, then flows to the evaporator, evaporated by the evaporator, and then flows back to the compressor. The refrigerant circulation sequence of the heat source tower heat pump unit is as follows: the refrigerant is compressed by a compressor, then flows to a condenser through an exhaust pipe, throttled by an expansion valve, then flows to an evaporator, evaporated by the evaporator and then flows back to the compressor; the economizer is additionally arranged on a liquid path to cool a liquid path refrigerant, so that the degree of supercooling is improved, and the capacity and the energy efficiency of a unit are improved.

Conventional water source heat pump unit is through breathing in superheat degree control, still can satisfy the unit demand, however heat source tower heat pump unit when the operating heating operating mode under low temperature environment, especially open under the operating mode behind the economic ware, if still only control through breathing in superheat degree, then the unit is difficult to operate according to optimum operating mode, specifically as follows: when the conventional water source heat pump unit is started, the initial opening of the electronic expansion valve is fixed, and the problem is not easy to occur when the unit is started due to the small operation range of the conventional water source heat pump unit; however, if the heat source tower heat pump unit is started according to the uniform fixed initial opening, when the heat source tower heat pump unit is started at a low freezing water temperature, the establishment of suction and exhaust pressure difference is slow, and then faults such as pressure difference alarm or low exhaust superheat degree are easy to occur; when the air conditioner runs stably, the air suction superheat degree is uniformly controlled, and when the air conditioner runs at low freezing water temperature, the problems of low supercooling degree of a liquid path, more flash evaporation refrigerants, poor effect of an economizer and the like easily occur, so that the running energy efficiency of a unit is influenced.

Accordingly, there is a need in the art for a new control method for a chiller to address the above-mentioned problems.

Disclosure of Invention

The invention aims to solve the technical problem that the single control mode of the existing water chilling unit is difficult to realize high-efficiency operation.

The invention provides a control method for a water chilling unit, wherein the water chilling unit comprises a refrigerant circulation loop and a chilled water circulation loop, wherein an evaporator, a compressor, an electronic expansion valve and a condenser are arranged on the refrigerant circulation loop, chilled water in the chilled water circulation loop can exchange heat with a refrigerant in the evaporator, and the control method comprises the following steps:

after the water chilling unit is started, acquiring the initial water inlet temperature of chilled water;

determining the initial opening degree of the electronic expansion valve according to the initial inlet water temperature;

at the starting stage of the compressor, acquiring the suction pressure and the discharge pressure of the compressor;

if the difference value between the exhaust pressure and the suction pressure is greater than the duration of a first preset pressure difference and reaches a first preset time, selectively adjusting the opening of the electronic expansion valve directly according to the suction superheat degree of the refrigerant circulation loop; otherwise, selectively adjusting the opening degree of the electronic expansion valve according to the suction pressure of the compressor.

In a preferred embodiment of the control method, the step of selectively adjusting the opening degree of the electronic expansion valve according to the suction superheat degree of the refrigerant circulation circuit includes:

calculating the difference value of the suction superheat degree and the target superheat degree;

and selectively adjusting the opening degree of the electronic expansion valve according to the value range of the difference value of the suction superheat degree and the target superheat degree.

In a preferred embodiment of the above control method, the step of "selectively adjusting the opening degree of the electronic expansion valve according to a value range of a difference between the suction superheat degree and the target superheat degree" specifically includes:

if the difference value between the suction superheat degree and the target superheat degree is smaller than a first preset difference value or larger than a second preset difference value, adjusting the opening degree of the electronic expansion valve;

wherein the first preset difference is smaller than the second preset difference.

In a preferred embodiment of the above control method, the step of adjusting the opening degree of the electronic expansion valve if the difference between the suction superheat degree and the target superheat degree is smaller than a first preset difference or larger than a second preset difference further comprises:

and if the difference between the suction superheat degree and the target superheat degree is smaller than the first preset difference, the opening degree of the electronic expansion valve is reduced.

In a preferred embodiment of the above control method, the step of adjusting the opening degree of the electronic expansion valve if the difference between the suction superheat degree and the target superheat degree is smaller than a first preset difference or larger than a second preset difference further comprises:

and if the difference value between the suction superheat degree and the target superheat degree is larger than the second preset difference value, the opening degree of the electronic expansion valve is increased.

In a preferred technical solution of the above control method, an economizer is further provided on the refrigerant circulation loop, and the control method further includes:

acquiring the opening and closing state of the economizer;

under the condition that the economizer is started, further acquiring the supercooling degree of an outlet of the economizer;

calculating the difference value between the outlet supercooling degree and the target supercooling degree;

comparing the difference between the outlet supercooling degree and the target supercooling degree with a third preset difference;

and selectively correcting the target superheat degree according to the comparison result of the difference value between the outlet supercooling degree and the target supercooling degree and a third preset difference value.

In a preferred technical solution of the above control method, the step of "selectively correcting the target superheat degree according to a comparison result between the difference between the outlet subcooling degree and the target subcooling degree and a third preset difference" specifically includes:

and if the difference value between the outlet supercooling degree and the target supercooling degree is smaller than the third preset difference value, increasing the target superheat degree.

In a preferred embodiment of the above control method, the step of "selectively adjusting the opening degree of the electronic expansion valve according to the suction pressure of the compressor" may specifically include:

acquiring the change speed of the suction pressure of the two adjacent compressors;

and selectively adjusting the opening degree of the electronic expansion valve according to the change speed of the suction pressure of the compressor at two adjacent times.

In a preferred embodiment of the above control method, the step of "selectively adjusting the opening degree of the electronic expansion valve according to the change speed of the suction pressure of the compressor in two adjacent times" includes:

if the current descending rate of the suction pressure is greater than a first preset descending rate and the last descending rate is greater than a second preset descending rate, or the current descending rate of the suction pressure is greater than the second preset descending rate, the opening degree of the electronic expansion valve is increased;

wherein the second predetermined drop rate is greater than the first predetermined drop rate.

In a preferred embodiment of the above control method, the step of "selectively adjusting the opening degree of the electronic expansion valve according to the change speed of the suction pressure of the compressor in two adjacent times" further includes:

if the current descending rate of the suction pressure is less than or equal to the first preset descending rate, or the current descending rate of the suction pressure is greater than the first preset descending rate and less than or equal to the second preset descending rate, and the last descending rate is less than or equal to the second preset descending rate, the inlet water temperature of the chilled water is obtained again;

and selectively adjusting the opening degree of the electronic expansion valve according to the numerical range of the inlet water temperature of the chilled water and the numerical range of the suction pressure of the compressor, which are obtained again.

Under the condition of adopting the technical scheme, the water chilling unit comprises a refrigerant circulation loop and a chilled water circulation loop, wherein an evaporator, a compressor, an electronic expansion valve and a condenser are arranged on the refrigerant circulation loop, chilled water in the chilled water circulation loop can exchange heat with a refrigerant in the evaporator, and the control method comprises the following steps: after the water chilling unit is started, acquiring the initial water inlet temperature of chilled water; determining the initial opening degree of the electronic expansion valve according to the initial inlet water temperature; at the starting stage of the compressor, acquiring the suction pressure and the discharge pressure of the compressor; if the difference value between the exhaust pressure and the suction pressure is greater than the duration of a first preset pressure difference and reaches a first preset time, selectively adjusting the opening of the electronic expansion valve directly according to the suction superheat degree of the refrigerant circulation loop; otherwise, selectively adjusting the opening degree of the electronic expansion valve according to the suction pressure of the compressor. Based on the control mode, the invention can correspondingly determine the initial opening of the electronic expansion valve according to the difference of the initial water inlet temperature so as to quickly establish the suction-exhaust pressure difference of the compressor, thereby effectively improving the operation reliability and energy efficiency of the water chilling unit.

Drawings

Preferred embodiments of the present invention are described below with reference to the accompanying drawings, in which:

FIG. 1 is a schematic diagram of the overall construction of the water chiller of the present invention;

FIG. 2 is a flow chart of the main steps of the control method of the present invention;

FIG. 3 is a detailed step flow diagram of a preferred embodiment of the control method of the present invention;

reference numerals: 11. an evaporator; 12. a compressor; 13. an electronic expansion valve; 14. a condenser; 15. an economizer; 16. drying the filter; 17. a first ball valve; 18. a second ball valve; 19. an angle valve; 20. a one-way valve.

Detailed Description

Preferred embodiments of the present invention are described below with reference to the accompanying drawings. It should be understood by those skilled in the art that these embodiments are only for explaining the technical principle of the present invention, and are not intended to limit the scope of the present invention. And can be adjusted as needed by those skilled in the art to suit particular applications. It should be noted that in the description of the preferred embodiment, the terms of direction or positional relationship indicated by the terms "inside", "outside", and the like are based on the directions or positional relationships shown in the drawings, which are only for convenience of description, and do not indicate or imply that the device or element must have a specific orientation, be constructed in a specific orientation, and be operated, and thus should not be construed as limiting the present invention.

In addition, in the description of the present invention, unless otherwise explicitly specified or limited, the term "connected" is to be understood broadly, and may be, for example, directly connected, indirectly connected through an intermediate, or communicating between two elements. The specific meanings of the above terms in the present invention can be understood by those skilled in the art according to specific situations. Although the steps of the control method of the present invention are described herein in a particular order, the order is not limiting and those skilled in the art can perform the steps in a different order without departing from the basic principles of the invention.

It should be noted that in the description of the present invention, although the steps of the control method of the present invention are described in a specific order in the present application, the order is not limited, and those skilled in the art can perform the steps in a different order without departing from the basic principle of the present invention.

Referring first to fig. 1, the overall structure of the water chiller according to the present invention is schematically shown. As shown in fig. 1, the water chilling unit of the present invention includes a refrigerant circulation loop, a chilled water circulation loop and a heat exchange water circulation loop, wherein an evaporator 11, a compressor 12, an electronic expansion valve 13 and a condenser 14 are sequentially disposed on the refrigerant circulation loop, an economizer 15 is further disposed between the evaporator 11 and the condenser 14, a first ball valve 17 is further disposed between the evaporator 11 and the electronic expansion valve 13, a second ball valve 18 and a dry filter 16 are further disposed between the condenser 14 and the economizer 15, and an angle valve 19 and a check valve 20 are further disposed between the compressor 12 and the economizer 15; the chilled water in the chilled water circulation loop can exchange heat with a refrigerant in the evaporator 11, so that the chilled water can take away the cold energy of the evaporator 11 and is discharged to the outdoor environment through a heat source tower of the water chilling unit; the heat exchange water in the heat exchange water circulation loop can exchange heat with the refrigerant in the condenser 14, so that the heat of the condenser 14 can be taken away by the heat exchange water, and the indoor temperature is increased through the terminal equipment. In addition, it should be noted that the present invention does not limit the specific structure of the water chilling unit, and a technician may set the water chilling unit according to actual use requirements, as long as the water chilling unit includes a refrigerant circulation loop and a chilled water circulation loop.

Furthermore, the water chilling unit also comprises a plurality of temperature sensors, a plurality of pressure sensors and a controller, wherein the controller can acquire detection data of the plurality of temperature sensors and the plurality of pressure sensors; wherein, the exhaust temperature sensor and the exhaust pressure sensor are arranged at the exhaust port of the compressor 12, the suction temperature sensor and the suction pressure sensor are arranged at the suction port of the compressor 12, and the outlet temperature sensor and the outlet pressure sensor are arranged at the outlet of the economizer 15. In addition, the controller can also control the running state of the water chilling unit; for example, the opening/closing state and the opening degree of the electronic expansion valve 13 are controlled. It can be understood by those skilled in the art that the present invention does not limit the specific structure and model of the controller, and the controller may be the original controller of the water chilling unit, or may be a controller separately configured to execute the control method of the present invention, and the structure and model of the controller may be set by a technician according to actual use requirements.

Referring next to fig. 2, a flow chart of the main steps of the control method of the present invention is shown. As shown in fig. 2, based on the water chilling unit described in the above embodiment, the control method of the present invention mainly includes the following steps:

s1: after the water chilling unit is started, acquiring the initial water inlet temperature of chilled water;

s2: determining the initial opening degree of the electronic expansion valve according to the initial water inlet temperature;

s3: at the starting stage of the compressor, acquiring the suction pressure and the exhaust pressure of the compressor;

s4: if the difference value between the exhaust pressure and the suction pressure is greater than the duration of a first preset pressure difference and reaches a first preset time, selectively adjusting the opening of the electronic expansion valve directly according to the suction superheat degree of the refrigerant circulation loop; otherwise, the opening degree of the electronic expansion valve is selectively adjusted according to the suction pressure of the compressor.

Further, in step S1, the controller may obtain an initial inlet water temperature of the chilled water in the chilled water circulation loop after the chiller is started; next, in step S2, the controller is capable of determining an initial opening degree of the electronic expansion valve 13 according to the initial inlet water temperature, so as to determine an initial opening degree of the electronic expansion valve 13 according to the initial inlet water temperature, and thus quickly and effectively establish a suction-discharge air pressure difference of the compressor 12. It should be noted that the present invention does not limit the specific determination method, and the skilled person can set the determination method according to the actual use requirement.

Next, in step S3, the controller is capable of obtaining the suction pressure and the discharge pressure of the compressor 12 at the start stage of the compressor 12, so as to quickly establish a suction-discharge pressure difference of the compressor 12 based on the suction pressure and the discharge pressure of the compressor 12, thereby effectively ensuring the operation stability of the chiller.

Finally, in step S4, if the difference between the discharge pressure and the suction pressure of the compressor 12 is greater than the duration of the first preset pressure difference for the first preset time period, selectively adjusting the opening of the electronic expansion valve 13 directly according to the suction superheat of the refrigerant circulation loop; otherwise, the opening degree of the electronic expansion valve 13 is selectively adjusted according to the suction pressure of the compressor 12. It should be noted that, the invention does not limit the specific adjusting mode, and the technical personnel can set the adjusting mode according to the actual using requirement; in addition, the specific values of the first preset pressure difference and the first preset time length are not limited, and technicians can set the values according to actual use requirements.

Finally, referring to fig. 3, a detailed flow chart of the steps of the preferred embodiment of the control method of the present invention is shown. As shown in fig. 3, based on the water chilling unit described in the above preferred embodiment, the preferred embodiment of the control method of the present invention specifically includes the following steps:

after the water chilling unit is started, acquiring the initial water inlet temperature of chilled water; it should be noted that, the present invention does not limit the specific obtaining manner and obtaining time, and the technician can set the obtaining time according to the actual using requirement.

The controller can then determine the initial opening of the electronic expansion valve 13 based on the initial inlet water temperature. It should be noted that, this determination manner is not limited, and may be determined according to a preset relation, or may determine the initial opening degree of the electronic expansion valve 13 according to the numerical range of the initial inlet water temperature, and a technician may set the initial opening degree according to actual needs.

In the preferred embodiment, the initial opening degree of the electronic expansion valve 13 is determined by dividing four temperature ranges, specifically as follows:

if the initial inlet water temperature of the chilled water is less than-10 ℃, the initial opening degree of the electronic expansion valve 13 is determined as A%;

if the initial inlet water temperature of the chilled water is more than or equal to minus 10 ℃ and less than or equal to 0 ℃, the initial opening degree of the electronic expansion valve 13 is determined as B percent;

if the initial inlet water temperature of the chilled water is more than 0 ℃ and less than or equal to 5 ℃, the initial opening degree of the electronic expansion valve 13 is determined as C%;

if the initial inlet water temperature of the chilled water is more than 5 ℃, the initial opening degree of the electronic expansion valve 13 is determined as D%;

wherein, A is more than B and more than C and less than D.

It should be noted that the above temperature division ranges are only preferred, the present invention does not limit the specific division manner of the numerical range at all, and the skilled person can set the threshold of each temperature range according to the actual use requirement.

The controller can acquire the suction pressure and the discharge pressure of the compressor 12 after the compressor 12 has been started by 50%, that is, after the opening degree of the adjustable solenoid valve of the compressor 12 reaches 50% of the maximum opening degree. It should be noted that the above-mentioned acquisition timing is only a preferable acquisition timing, but is not limited thereto, and a skilled person may set the acquisition timing according to actual use requirements as long as the suction pressure and the discharge pressure of the compressor 12 are acquired at the start-up stage of the compressor 12.

Then, calculating the difference between the exhaust pressure and the suction pressure of the compressor 12, and judging whether the duration time that the difference between the exhaust pressure and the suction pressure of the compressor 12 is greater than 0.4Mpa reaches 2S, if so, selectively adjusting the opening degree of the electronic expansion valve 13 directly according to the suction superheat degree of the refrigerant circulation loop; otherwise, it is determined whether the adjustment process has continued for 5 minutes, i.e., since the chiller was started up this time, although this time period is not limiting. If yes, the opening degree of the electronic expansion valve 13 is selectively adjusted directly according to the suction superheat degree of the refrigerant circulation circuit, and if not, the opening degree of the electronic expansion valve 13 is further selectively adjusted according to the suction pressure of the compressor 12. It should be noted that, the values of the first preset pressure difference and the first preset time period are only preferable, but not restrictive, and the technical staff may set the values according to actual use requirements.

As a preferable configuration, the step of "selectively adjusting the opening degree of the electronic expansion valve according to the suction superheat degree of the refrigerant circulation circuit" includes:

firstly, acquiring the opening and closing state of the economizer 15 so as to judge whether the target superheat degree needs to be corrected or not; of course, the present invention does not impose any limitation on the specific value of the target superheat. Under the condition that the economizer 15 is started, further acquiring the supercooling degree of an outlet of the economizer 15; calculating the difference value between the outlet supercooling degree and the target supercooling degree; comparing the difference between the outlet supercooling degree and the target supercooling degree with the third preset difference; and selectively correcting the target superheat degree according to the comparison result of the difference value between the outlet supercooling degree and the target supercooling degree and the third preset difference value. Specifically, if the difference between the outlet supercooling degree and the target supercooling degree is smaller than the third preset difference, the target superheat degree is increased; and if the difference value between the outlet supercooling degree and the target supercooling degree is greater than or equal to the third preset difference value, maintaining the target superheat degree unchanged. It should be noted that, the specific value of the third preset difference is not limited in the present invention, and the technician can set the third preset difference according to the actual use requirement. In addition, if the economizer 15 is not turned on, the target superheat degree does not need to be corrected. The invention can selectively correct the target superheat degree according to the outlet supercooling degree of the economizer 15 under the condition that the economizer 15 is started, so that the water chilling unit can always operate under the optimal condition, and the problem of liquid path flash evaporation is effectively avoided.

Then, calculating the difference value between the suction superheat degree and the target superheat degree; the opening degree of the electronic expansion valve 13 is selectively adjusted according to the numerical range in which the difference between the suction superheat degree and the target superheat degree is located. Specifically, if the difference between the suction superheat degree and the target superheat degree is smaller than the first preset difference or larger than the second preset difference, the opening degree of the electronic expansion valve is adjusted; wherein the first preset difference is smaller than the second preset difference. Further, if the difference between the suction superheat degree and the target superheat degree is smaller than the first preset difference, the opening degree of the electronic expansion valve 13 is decreased at a first preset speed; if the difference between the suction superheat degree and the target superheat degree is larger than the second preset difference, the opening degree of the electronic expansion valve 13 is increased at a second preset speed; otherwise, the current opening degree of the electronic expansion valve 13 may be maintained. In addition, it should be noted that, the present invention does not limit the specific values of the first preset speed and the second preset speed, and a technician can set the values according to actual use requirements.

In addition, the controller can also acquire the change speed of the suction pressure of the two adjacent compressors 12, and selectively adjust the opening degree of the electronic expansion valve 13 according to the change speed of the suction pressure of the two adjacent compressors 12; of course, the present invention does not limit the frequency of the acquisition, and the technician can set the frequency according to the actual use requirement.

If the current decreasing rate of the suction pressure is greater than the first preset decreasing rate and the last decreasing rate is greater than the second preset decreasing rate, or the current decreasing rate of the suction pressure is greater than the second preset decreasing rate, the opening degree of the electronic expansion valve 13 is increased, and the second preset decreasing rate is greater than the first preset decreasing rate. Preferably, the opening is increased at a rate of 2% per 1 second (i.e. 2% of the maximum opening), and the maximum opening of the adjustment process is set according to the specific conditions of the water chilling unit. Then, whether the increasing times of the electronic expansion valve 13 in the current adjusting process reaches 3 times is judged, if so, the current opening degree is maintained for 10 seconds, and then a judgment frame of whether the adjusting process is maintained for 5 minutes is executed, and of course, the values of the times and the duration are not restrictive; if not, the decision block "whether the adjustment process is maintained for 5 minutes" is directly executed again. Preferably, the first predetermined descent rate is 0.002Mpa/s and the second predetermined descent rate is 0.003 Mpa/s.

If the current descending rate of the suction pressure is less than or equal to the first preset descending rate, or the current descending rate of the suction pressure is greater than the first preset descending rate and less than or equal to the second preset descending rate, and the last descending rate is less than or equal to the second preset descending rate, the inlet water temperature of the chilled water is obtained again; and selectively adjusting the opening degree of the electronic expansion valve 13 according to the obtained numerical range of the inlet water temperature of the chilled water and the obtained numerical range of the suction pressure of the compressor 12.

Specifically, the following four different determination paths are correspondingly performed according to the four temperature ranges divided in the above preferred embodiment:

1. if the inlet water temperature of the obtained chilled water is less than-10 ℃, judging whether the suction pressure of the compressor 12 is greater than P1Mpa, if so, reducing the opening degree of the electronic expansion valve 13, preferably reducing the opening degree by 1 percent (namely 1 percent of the maximum opening degree) every 2 seconds, and setting the minimum opening degree of the regulating process according to the specific conditions of the water chilling unit; if not, further judging whether the suction pressure of the compressor 12 is less than P2Mpa, if so, increasing the opening degree of the electronic expansion valve 13, preferably at a speed of increasing the opening degree by 1 percent (namely 1 percent of the maximum opening degree) every 1 second, wherein the maximum opening degree in the adjusting process is set according to the specific condition of the water chilling unit; if not, the current opening degree of the electronic expansion valve 13 is maintained unchanged. It should be noted that, the invention does not limit the specific values of P1 and P2, as long as P1 is greater than P2; as a preferable embodiment, P1 is set to 0.26MPa, and P2 is set to 0.22 MPa.

2. If the initial inlet water temperature of the chilled water obtained again is less than or equal to 0 ℃ below zero and less than or equal to 10 ℃, judging whether the suction pressure of the compressor 12 is greater than P3Mpa, if so, reducing the opening degree of the electronic expansion valve 13, preferably reducing the opening degree by 1 percent (namely 1 percent of the maximum opening degree) every 2 seconds, and setting the minimum opening degree in the adjusting process according to the specific condition of the water chilling unit; if not, further judging whether the suction pressure of the compressor 12 is less than P4Mpa, if so, increasing the opening degree of the electronic expansion valve 13, preferably at a speed of increasing the opening degree by 1% every 1 second (namely 1% of the maximum opening degree), wherein the maximum opening degree in the adjusting process is set according to the specific conditions of the water chilling unit; if not, the current opening degree of the electronic expansion valve 13 is maintained unchanged. It should be noted that, the invention does not limit the specific values of P3 and P4, as long as P3 is greater than P4; as a preferable embodiment, P3 is set to 0.27MPa, and P4 is set to 0.23 MPa.

3. If the initial inlet water temperature of the chilled water obtained again is less than or equal to 5 ℃ below 0 ℃, judging whether the suction pressure of the compressor 12 is greater than P5Mpa, if so, reducing the opening degree of the electronic expansion valve 13, preferably reducing the opening degree by 1 percent (namely 1 percent of the maximum opening degree) every 2 seconds, and setting the minimum opening degree in the regulating process according to the specific conditions of the water chilling unit; if not, further judging whether the suction pressure of the compressor 12 is less than P6Mpa, if so, increasing the opening degree of the electronic expansion valve 13, preferably at a speed of increasing the opening degree by 1 percent (namely 1 percent of the maximum opening degree) every 1 second, wherein the maximum opening degree in the adjusting process is set according to the specific condition of the water chilling unit; if not, the current opening degree of the electronic expansion valve 13 is maintained unchanged. It should be noted that, the invention does not limit the specific values of P5 and P6, as long as P5 is greater than P6; as a preferable embodiment, P5 is set to 0.28MPa, and P6 is set to 0.24 MPa.

4. If the initial inlet water temperature of the obtained chilled water is more than 5 ℃, judging whether the suction pressure of the compressor 12 is more than P7Mpa, if so, reducing the opening degree of the electronic expansion valve 13, preferably reducing the opening degree by 1 percent (namely 1 percent of the maximum opening degree) every 2 seconds, and setting the minimum opening degree in the regulating process according to the specific conditions of the water chilling unit; if not, further judging whether the suction pressure of the compressor 12 is less than P8Mpa, if so, increasing the opening degree of the electronic expansion valve 13, preferably at a speed of increasing the opening degree by 1% every 1 second (namely 1% of the maximum opening degree), wherein the maximum opening degree in the adjusting process is set according to the specific conditions of the water chilling unit; if not, the current opening degree of the electronic expansion valve 13 is maintained unchanged. It should be noted that, the invention does not limit the specific values of P7 and P8, as long as P7 is greater than P8; as a preferable embodiment, P7 is set to 0.29MPa, and P8 is set to 0.25 MPa.

As a preferable setting mode, the smaller the temperature range of the initial inlet water temperature of the obtained chilled water is, the smaller the preset value of the suction pressure is, namely P1 < P3 < P5 < P7.

Under the condition of adjusting the opening degree of the electronic expansion valve 13, judging whether the adjusting frequency of the electronic expansion valve 13 in the current adjusting process reaches 5 times, if so, maintaining the current opening degree for 10 seconds, and then executing a judgment frame of 'whether the adjusting process is maintained for 5 minutes', wherein the values of the frequency and the duration are not restrictive; if not, the decision block "whether the adjustment process is maintained for 5 minutes" is directly executed again.

Under the condition of maintaining the current opening degree of the electronic expansion valve 13 unchanged, the controller can obtain the difference value between the exhaust pressure and the suction pressure of the compressor 12 again, and judge whether the duration of the difference value between the exhaust pressure and the suction pressure of the compressor 12 being greater than 0.43Mpa reaches 5S, if so, the opening degree of the electronic expansion valve 13 is selectively adjusted directly according to the suction superheat degree of the refrigerant circulation loop; otherwise, a decision block of "whether the adjustment process is maintained for 5 minutes" is executed again.

So far, the technical solutions of the present invention have been described in connection with the preferred embodiments shown in the drawings, but it is easily understood by those skilled in the art that the scope of the present invention is obviously not limited to these specific embodiments. Equivalent changes or substitutions of related technical features can be made by those skilled in the art without departing from the principle of the invention, and the technical scheme after the changes or substitutions can fall into the protection scope of the invention.