WO2020103516A1

WO2020103516A1 - Evaporative cooling chiller unit heat-exchanging system and control method therefor

Info

Publication number: WO2020103516A1
Application number: PCT/CN2019/103290
Authority: WO
Inventors: 江集庆; 张海强; 孟庆超; 张捷
Original assignee: 青岛海尔空调电子有限公司
Priority date: 2018-11-21
Filing date: 2019-08-29
Publication date: 2020-05-28
Also published as: CN109631377A; CN109631377B

Abstract

Provided are an evaporative cooling chiller unit heat-exchanging system and a control method therefor. The chiller unit heat-exchanging system comprises a magnetic levitation centrifugal compressor (1), an evaporative condenser (2), a drying filter (3), an energy saver (5), a falling film evaporator (7), and a control system (12). An exhaust vent of the magnetic levitation centrifugal compressor (1) is in communication with an inlet of the evaporative condenser (2) via a pipework. An outlet of the evaporative condenser (2) is in communication with an inlet of the drying filter (3) via the pipework and is in communication with a cooling inlet of the magnetic levitation centrifugal compressor (1) via the pipework. The falling film evaporator (7) is in communication with the inlet of the magnetic levitation centrifugal compressor (1) via the pipework. The exhaust vent of the magnetic levitation centrifugal compressor (1) is also in communication with the falling film evaporator (7) via the pipework. A bypass solenoid valve (8) is connected in series on the pipework. The chiller unit heat-exchanging system, by means of the control of the bypass solenoid valve (8), implements the normal start of a low-pressure ratio compressor, and greatly increases the energy efficiency ratio of the unit.

Description

Evaporative cooling type water chiller heat exchange system and its control method

Technical field

The invention relates to the technical field of air conditioning, in particular to an evaporative cooling chiller heat exchange system and a control method thereof.

Background technique

At present, the chiller technology is currently in accordance with the relevant national regulations. The design conditions of the inlet / outlet water temperature of chilled water are 12/7 ℃, the refrigerant is clean water, and the ambient dry / wet bulb temperature is 35/24 ℃. Cooling mode, shut down in winter. And some areas, such as rail transit, edible fungus cultivation, etc., generally need to be the annual cooling mode.

The operating power of the evaporative cooling magnetic suspension chiller is proportional to the condensation temperature and the ambient temperature. The cooling capacity is proportional to the evaporation temperature and the chilled water temperature. How to make the unit operate under low condensing temperature and high evaporating temperature is the key to improving the unit's energy efficiency. While ordinary chillers are only designed for hot weather seasons, the cooling water temperature is limited by the temperature of the environment. The cooling water temperature can be lower in winter or transition season, and the lower the cooling water temperature, the more energy-efficient the unit will be. high.

Evaporative cooling type magnetic suspension chiller is an efficient and energy-saving chiller. The unit is matched with magnetic suspension compressor. In view of the centrifugal compression nature of magnetic suspension centrifugal compressor, the start, stop or minimum stable load depends on the pressure applied to the compressor by the chiller system ratio. When the magnetic levitation compressor is in the start, stop or low load operation phase, the system cannot meet the pressure ratio applied to the compressor, the magnetic levitation centrifugal compressor is operating under abnormal conditions, and the magnetic levitation centrifugal compressor cannot be operated under low load conditions. Long-term operation at low load is required to meet refrigeration requirements, and long-term repeated start / stop causes damage to the magnetic levitation centrifugal compressor.

Summary of the invention

The embodiment of the present invention provides an evaporative cooling type chiller heat exchange system and a control method thereof, so as to solve at least one of the technical problems existing in the prior art. In order to have a basic understanding of some aspects of the disclosed embodiments, a brief summary is given below. This summary is not a general comment, nor is it to identify key / important elements or to describe the scope of protection of these examples. Its sole purpose is to present some concepts in a simple form as a preface to the detailed description that follows.

According to the first aspect of the embodiments of the present invention, there is provided an evaporative cooling chiller heat exchange system;

In some optional embodiments, the evaporative cooling chiller heat exchange system includes; a magnetic suspension centrifugal compressor, an evaporative condenser, a drying filter, an energy saver, a falling film evaporator, and a control system;

The exhaust port of the magnetic levitation centrifugal compressor communicates with the inlet of the evaporative condenser through a first pipeline, and the outlet of the evaporative condenser communicates with the inlet of the drying filter through a second pipeline , The outlet of the evaporative condenser is also connected to the cooling inlet of the magnetic levitation centrifugal compressor through a sixth pipeline;

The outlet of the drying filter is connected to the inlet of the main liquid pipe of the economizer through a third pipeline, and the outlet of the main liquid pipe of the economizer is connected to the inlet of the falling film evaporator through a fourth pipeline Connected, the outlet of the falling film evaporator is connected to the inlet of the magnetic levitation centrifugal compressor through a fifth pipeline, and the exhaust port of the economizer is connected to the inlet of the magnetic levitation centrifugal compressor through an eighth pipeline Connected, the magnetic suspension centrifugal compressor is electrically connected to the control system through a cable; the exhaust port of the magnetic suspension centrifugal compressor is also connected to the falling film evaporator through a ninth pipeline, and the first Nine pipelines have bypass solenoid valves connected in series.

In some optional embodiments, further, the outlet of the drying filter is connected to the supercooled liquid inlet of the economizer through a seventh pipeline, and an energy-saving expansion valve is connected in series on the seventh pipeline.

In some optional embodiments, further, an electronic expansion valve is connected in series on the fourth pipeline.

In some optional embodiments, further, a liquid level gauge is provided on the falling film evaporator for detecting the liquid level in the falling film evaporator.

In some optional embodiments, further, the chilled water outlet and the chilled water inlet of the falling film evaporator are respectively provided with differential pressure switches.

In some optional embodiments, further, a filter is connected in series with the sixth pipeline.

According to a second aspect of the embodiments of the present invention, a control method is provided;

In some optional embodiments, the control method is directed to any of the foregoing optional implementation of the evaporative cooling chiller heat exchange system; including; Step S1, the magnetic suspension centrifugal compressor is started, and the evaporative cooling chiller meets the starting conditions If the absolute pressure ratio of the corresponding compressor is greater than 2.0 and continues to be maintained for N1 seconds, the compressor interlock switch needs to be closed, the bypass solenoid valve is opened to 100%, and the bypass solenoid valve is closed after the compressor is started;

Step S2, the magnetic suspension centrifugal compressor is turned off, and the evaporative cooling chiller meets the shutdown condition. If the absolute pressure ratio of the corresponding compressor is greater than 2.5 and lasts for N2 seconds, the compressor of the corresponding system enters the minimum capacity maintenance state, and the bypass solenoid valve is opened After a preset time, the compressor is turned off and the bypass solenoid valve is closed.

In some optional embodiments, further, in step S1, N1 is 3 seconds; in step S2, N2 is 30 seconds.

In some optional embodiments, further, in step S2, if the corresponding compressor absolute pressure ratio is less than 2.5, it is directly shut down.

In some optional embodiments, further, the method further includes;

Step S3, the magnetic suspension centrifugal compressor operates at low load, and the evaporative cooling chiller meets the logic of operating low load, but the compressor absolute pressure ratio cannot meet the system design requirements. The system determines the opening of the bypass solenoid valve according to the compressor absolute pressure ratio To ensure the normal operation of the magnetic suspension centrifugal compressor at low load and meet the minimum load operation requirements;

Step S4, if the chilled water temperature <target temperature-shutdown temperature difference + T, and after 3S, the bypass solenoid valve is opened to the initial set opening degree, after the bypass solenoid valve adjustment period, if the water temperature continues to meet the chilled water temperature ≤ target Temperature-Stop temperature difference + T, the bypass solenoid valve continues to open to the maximum opening according to the set adjustment range; or

If the chilled water temperature> target temperature-shutdown temperature difference + T + 0.2 ℃ for 3 seconds or the compressor exits the minimum capacity state for 30 seconds, the bypass solenoid valve starts to close according to the adjustment range; or

If the target temperature-shutdown temperature difference + T ℃ ≤ chilled water temperature ≤ target temperature-shutdown temperature difference + T + 0.2 ℃, the bypass solenoid valve opening remains unchanged.

The technical solutions provided by the embodiments of the present invention may include the following beneficial effects:

By adding a communication line that connects the suction port side and the exhaust port side at the compressor exhaust port, a bypass solenoid valve is added to the communication line, and the absolute pressure ratio of the magnetic suspension centrifugal compressor unit is controlled by the bypass solenoid valve. Judging the operation status of the magnetic levitation centrifugal compressor. During the start / stop phase of the magnetic levitation centrifugal compressor, the pressure ratio applied to the compressor by the chiller system can completely make the magnetic levitation centrifugal compressor start / stop steadily to ensure the normal start and stop of the unit; The magnetic levitation centrifugal compressor runs at low load, and the unit needs to run low load logic, but the compressor absolute pressure ratio cannot meet the system design requirements. The system determines the opening of the bypass solenoid valve according to the compressor absolute pressure ratio to ensure that the magnetic levitation centrifugal compressor is low The normal operation of the load meets the minimum load operation requirements of the unit, realizes the normal start of the low-pressure ratio compressor, protects the compressor from damage, enables the low-pressure ratio compressor to be applied, and greatly improves the energy efficiency ratio of the unit.

It should be understood that the above general description and the following detailed description are only exemplary and explanatory, and do not limit the present invention.

BRIEF DESCRIPTION

The drawings herein are incorporated into and constitute a part of this specification, show embodiments consistent with the present invention, and are used to explain the principles of the present invention together with the specification.

Fig. 1 is a schematic flow chart of a heat exchange system of an evaporative cooling chiller according to an exemplary embodiment;

2 is a schematic flowchart of a control method according to another exemplary embodiment;

FIG. 3 is a schematic flowchart of a control method according to another exemplary another embodiment.

Reference mark:

1-magnetic suspension centrifugal compressor; 2-evaporative condenser, 3-dry filter, 4-energy saver expansion valve, 5-energy saver, 6-electronic expansion valve, 7-falling film evaporator, 8-bypass electromagnetic Valve, 9-differential pressure switch, 10-filter, 11-level gauge, 12-control system; 13-first line; 14-second line; 15-third line; 16-fourth tube Road; 17-fifth pipeline; 18-sixth pipeline; 19-seventh pipeline; 20-eighth pipeline; 21-ninth pipeline.

detailed description

The following description and drawings sufficiently illustrate specific embodiments of the present invention to enable those skilled in the art to practice them. Other embodiments may include structural, logical, electrical, process, and other changes. The examples represent only possible changes. Unless specifically required, individual components and functions are optional, and the order of operations may vary. Parts and features of some embodiments may be included in or substituted for parts and features of other embodiments. The scope of the embodiments of the present invention includes the entire scope of the claims, and all available equivalents of the claims. In this document, various embodiments may be individually or collectively expressed by the term "invention", which is for convenience only, and if in fact more than one invention is disclosed, it is not intended to automatically limit the scope of the application to any A single invention or inventive concept. In this article, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not require or imply that there is any actual relationship between these entities or operations or order. Furthermore, the terms "include", "include" or any other variant thereof are intended to cover non-exclusive inclusion, so that a process, method, or device that includes a series of elements includes not only those elements, but also other items not explicitly listed Elements, or also include elements inherent to such processes, methods, or equipment. Without more restrictions, the element defined by the sentence "include one ..." does not exclude that there are other identical elements in the process, method, or equipment that includes the element. The embodiments in this document are described in a progressive manner. Each embodiment focuses on the differences from other embodiments. The same and similar parts between the embodiments can be referred to each other. For the methods and products disclosed in the embodiments, since they correspond to the method parts disclosed in the embodiments, the description is relatively simple, and the relevant parts can be referred to the description in the method part.

As shown in FIG. 1, in some alternative embodiments, the evaporative cooling chiller heat exchange system includes: magnetic suspension centrifugal compressor 1, evaporative condenser 2, drying filter 3, energy saver 5, falling film evaporator 7 And control system 12;

The exhaust port of the magnetic levitation centrifugal compressor 1 communicates with the inlet of the evaporative condenser 2 through a first line 13 and communicates with the falling film evaporator 7 through a ninth line 21, The outlet of the evaporative condenser 2 communicates with the inlet of the drying filter 3 through the second pipeline 14, and the outlet of the evaporative condenser 2 also communicates with the cooling inlet of the compressor through the sixth pipeline ;

The outlet of the drying filter 3 communicates with the inlet of the main liquid pipe of the economizer 5 through the third pipeline 15, and the outlet of the main liquid pipe of the economizer 5 communicates with the drop through the fourth pipeline 16 The inlet of the membrane evaporator 7 is in communication, the outlet of the falling film evaporator 7 is in communication with the inlet of the compressor through a fifth pipeline 17, and the exhaust port of the economizer 5 is in communication with the eighth pipeline 20 The inlet of the compressor is connected, the compressor is electrically connected to the control system 12 through a cable, and the exhaust port of the magnetic suspension centrifugal compressor 1 is also connected to the falling film evaporator through a ninth pipeline 21 7 communicates, and a bypass solenoid valve 8 is connected in series on the ninth pipeline 21.

In this embodiment, during the operation, the refrigerant of the evaporative cooling chiller is discharged from the exhaust port of the magnetic levitation compressor 1, enters from the inlet of the evaporative condenser 2 through the first pipeline 13, and the high-temperature and high-pressure gas refrigerant evaporates The condenser 2 is condensed into a high-temperature and high-pressure liquid refrigerant. The high-temperature and high-pressure liquid refrigerant flows through the second pipeline 14 through the drying filter 3, and after being dried by the drying filter 3, enters the economizer 5 main liquid pipe through the third pipeline 15 The inlet is cooled by the refrigerant in the supercooled liquid inlet during the flow through the economizer 5. The degree of supercooling increases. Part of the refrigerant flowing through the drying filter 3 enters the supercooled liquid inlet of the economizer 5 through the seventh line 19, During this process, it is throttled by the expansion valve 4 of the economizer, and the low-pressure liquid refrigerant evaporates and absorbs heat in the economizer 5 to form a refrigerant cooling of the supercooling inlet of the economizer 5. The supercooled liquid refrigerant passing through the economizer 5 is throttled by the electronic expansion valve 6 and enters the falling film evaporator 7 through the fourth pipeline 16. After the throttle, the refrigerant in the falling film evaporator 7 fully exchanges heat with the refrigerant It is discharged from the outlet of the falling film evaporator 7 and finally converges to the suction port of the compressor through the fifth pipeline 17. The refrigerant cooled by the motor is taken from the second pipeline 14 of the outlet of the evaporative condenser 2 and cooled by the motor. After the filter 10 on the pipeline is dry, it enters the magnetic levitation compressor 1 and cools the motor; when the compressor is in low-load operation, according to system requirements, a portion of the high-temperature high-pressure gaseous refrigerant is taken from the first pipeline 13 at the outlet of the magnetic levitation compressor 1 through the ninth The bypass solenoid valve 8 on the closed road is opened and discharged into the falling film evaporator 7, which facilitates the compressor to operate at low load.

In some optional embodiments, further, the outlet of the drying filter 3 communicates with the supercooled liquid inlet of the economizer 5 through a seventh pipeline 19, and the seventh pipeline 19 is connected in series There is an energy-saving expansion valve, which is convenient for drying and filtering the passing refrigerant.

In some optional embodiments, further, as shown in FIG. 1, a filter 10 is connected in series with the sixth pipeline. It is convenient to dry filter the passing refrigerant.

In some optional embodiments, further, as shown in FIG. 1, an electronic expansion valve 6 is connected in series on the fourth pipeline 16. Used to throttle the refrigerant passing through it.

In some optional embodiments, further, as shown in FIG. 1, a liquid level gauge 11 is provided on the falling film evaporator 7 for detecting the liquid level in the falling film evaporator 7 to facilitate Real-time monitoring of the liquid level in the membrane evaporator 7.

In some optional embodiments, further, as shown in FIG. 1, the chilled water outlet and the chilled water inlet of the falling film evaporator 7 are respectively provided with differential pressure switches 9 to improve the safety performance of the outlet and the inlet.

As shown in FIGS. 2 and 3, in some optional embodiments, the control method is directed to any of the foregoing optional implementation of the evaporative cooling chiller heat exchange system; including; Step S1, the magnetic suspension centrifugal compressor is started , The evaporative cooling chiller meets the starting conditions, if the corresponding compressor absolute pressure ratio is greater than 2.0 and continues to be maintained for N1 seconds, the compressor interlock switch needs to be closed, the bypass solenoid valve is opened to 100%, and the bypass is closed after the compressor is started The electromagnetic valve;

Step S2, the magnetic suspension centrifugal compressor is turned off, and the evaporative cooling chiller meets the shutdown condition. If the absolute pressure ratio of the corresponding compressor is greater than 2.5 and lasts for N2 seconds, the compressor of the corresponding system enters the minimum capacity maintenance state, and the bypass solenoid valve is opened. After a preset time, the compressor is turned off and the bypass solenoid valve is closed.

Optionally, in step S1, N1 is 3 seconds; in step S2, N2 is 30 seconds.

Optionally, step by step, in step S2, if the corresponding compressor absolute pressure ratio is less than 2.5, it is directly stopped.

In this embodiment, the operation of the magnetic levitation centrifugal compressor is judged by the absolute pressure ratio of the magnetic levitation centrifugal compressor unit through the control of the bypass solenoid valve, and the chiller system is applied to the compressor during the start / stop phase of the magnetic levitation centrifugal compressor. The pressure ratio can completely make the magnetic levitation centrifugal compressor start and stop steadily, ensuring the normal start and stop of the unit; when the magnetic levitation centrifugal compressor runs at low load, the unit needs to run low load logic, but the compressor absolute pressure ratio cannot meet the system design requirements. The system determines the opening of the bypass solenoid valve according to the absolute pressure ratio of the compressor, to ensure the normal operation of the magnetic levitation centrifugal compressor at low load, to meet the minimum load operation requirements of the unit, to achieve the normal start of the low pressure ratio compressor, to protect the compressor from damage, so that The use of low-pressure ratio compressors has greatly improved the energy efficiency ratio of the unit.

As shown in FIG. 3, in some optional embodiments, further, the method further includes;

In a specific embodiment of this embodiment, as shown in FIG. 3, the operation steps of the method are as follows,

Step S1, the magnetic suspension centrifugal compressor is started, the evaporative cooling chiller meets the starting conditions, if the corresponding compressor absolute pressure ratio is greater than 2.0 and continues to be maintained for 3 seconds, the compressor interlock switch needs to be closed, and the bypass solenoid valve is opened to 100%. Close the bypass solenoid valve after the compressor is started;

Step S2, the magnetic levitation centrifugal compressor is turned off, and the evaporative cooling chiller meets the shutdown condition. If the absolute pressure ratio of the corresponding compressor is greater than 2.5 and lasts for 30 seconds, the compressor of the corresponding system enters the minimum capacity maintenance state, and the bypass solenoid valve is opened. After the preset time, the compressor is turned off and the bypass solenoid valve is closed;

Step S4, if the chilled water temperature <target temperature-shutdown temperature difference + T, and after 3S, the bypass solenoid valve is opened to the initial set opening degree, after the bypass solenoid valve adjustment period, if the water temperature continues to meet the chilled water temperature ≤ target Temperature-shutdown temperature difference + T, the bypass solenoid valve continues to open to the maximum opening according to the set adjustment range; or if the chilled water temperature> target temperature-shutdown temperature difference + T + 0.2 ℃ for 3 seconds or the compressor exits the minimum capacity The state continues for 30 seconds, the bypass solenoid valve starts to close according to the adjustment range; or if the target temperature-shutdown temperature difference + T ℃ ≤ chilled water temperature ≤ target temperature-shutdown temperature difference + T + 0.2 ℃, the bypass solenoid valve opening degree stay the same.

Judging the operation status of the magnetic levitation centrifugal compressor by the absolute pressure ratio of the magnetic levitation centrifugal compressor unit. During the start / stop phase of the magnetic levitation centrifugal compressor, the pressure ratio applied to the compressor by the chiller system can completely make the magnetic levitation centrifugal compressor start / stop steadily To ensure the normal start and stop of the unit; when the magnetic levitation centrifugal compressor runs at low load, the unit needs to run low load logic, but the compressor absolute pressure ratio cannot meet the system design requirements. The system determines the bypass solenoid valve according to the compressor absolute pressure ratio The opening degree ensures the normal operation of the magnetic suspension centrifugal compressor at low load. By reducing the compressor suction and discharge pressure ratio during the startup process, a lower system compression ratio is achieved, which protects the compressor from high pressure ratio. Failure or damage, so that the evaporative cooling unit can use a low-pressure compressor.

The indoor unit of the air conditioner provided in the second aspect has the evaporative cooling type chiller heat exchange system provided in the first aspect, so it has all the beneficial effects of the evaporative cooling type chiller heat exchange system provided in the first aspect. Repeat.

Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention, rather than limiting it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: The technical solutions described in the foregoing embodiments can still be modified, or some or all of the technical features can be equivalently replaced; and these modifications or replacements do not deviate from the essence of the corresponding technical solutions of the technical solutions of the embodiments of the present invention range. In addition, those skilled in the art can understand that although some of the embodiments described herein include certain features included in other embodiments but not other features, the combination of features of different embodiments is meant to be within the scope of the present invention And form different embodiments. For example, in the above claims, any one of the claimed embodiments can be used in any combination. The information disclosed in this background section is only intended to deepen the understanding of the overall background of the present invention and should not be taken as an acknowledgement or in any way suggesting that this information constitutes prior art that is well known to those skilled in the art.

Claims

An evaporative cooling type chiller heat exchange system is characterized by comprising: a magnetic suspension centrifugal compressor, an evaporative condenser, a drying filter, an energy saver, a falling film evaporator and a control system;

The exhaust port of the magnetic levitation centrifugal compressor communicates with the inlet of the evaporative condenser through a first pipeline, and the outlet of the evaporative condenser communicates with the inlet of the drying filter through a second pipeline , The outlet of the evaporative condenser is also connected to the cooling inlet of the magnetic levitation centrifugal compressor through a sixth pipeline;

The outlet of the drying filter is connected to the inlet of the main liquid pipe of the economizer through a third pipeline, and the outlet of the main liquid pipe of the economizer is connected to the inlet of the falling film evaporator through a fourth pipeline Connected, the outlet of the falling film evaporator is connected to the inlet of the magnetic levitation centrifugal compressor through a fifth pipeline, and the exhaust port of the economizer is connected to the inlet of the magnetic levitation centrifugal compressor through an eighth pipeline Connected, the magnetic suspension centrifugal compressor is electrically connected to the control system through a cable; the exhaust port of the magnetic suspension centrifugal compressor is also connected to the falling film evaporator through a ninth pipeline, and the first Nine pipelines have bypass solenoid valves connected in series.
The evaporative cooling chiller heat exchange system according to claim 1, characterized in that

The outlet of the drying filter communicates with the supercooled liquid inlet of the economizer through a seventh pipeline, and an energy-saving expansion valve is connected in series on the seventh pipeline.
The evaporative cooling chiller heat exchange system according to claim 1, characterized in that

An electronic expansion valve is connected in series on the fourth pipeline.
The evaporative cooling chiller heat exchange system according to claim 1, characterized in that

The falling film evaporator is provided with a liquid level gauge for detecting the liquid level in the falling film evaporator.
The evaporative cooling chiller heat exchange system according to claim 4, characterized in that

The chilled water outlet and the chilled water inlet of the falling film evaporator are respectively provided with differential pressure switches.
The evaporative cooling chiller heat exchange system according to claim 1, characterized in that

A filter is connected in series on the sixth pipeline.
A control method, characterized in that it is applied to the evaporative cooling chiller heat exchange system according to any one of claims 1 to 6, comprising;

Step S1, the magnetic suspension centrifugal compressor is started, and the evaporative cooling chiller meets the starting conditions. If the corresponding compressor absolute pressure ratio is greater than 2.0 and continues to be maintained for N1 seconds, the compressor interlock switch needs to be closed and the bypass solenoid valve is opened to 100%. Close the bypass solenoid valve after the compressor is started;

Step S2, the magnetic suspension centrifugal compressor is turned off, and the evaporative cooling chiller meets the shutdown condition. If the absolute pressure ratio of the corresponding compressor is greater than 2.5 and lasts for N2 seconds, the compressor of the corresponding system enters the minimum capacity maintenance state, and the bypass solenoid valve is opened. After a preset time, the compressor is turned off and the bypass solenoid valve is closed.
The control method according to claim 7, wherein:

In step S1, N1 is 3 seconds; in step S2, N2 is 30 seconds.
The control method according to claim 7, wherein:

In step S2, if the corresponding absolute pressure ratio of the compressor is less than 2.5, it will directly stop.
The control method according to claim 7, further comprising;

Step S3, the magnetic suspension centrifugal compressor operates at low load, and the evaporative cooling chiller meets the logic of operating low load, but the compressor absolute pressure ratio cannot meet the system design requirements. The system determines the opening of the bypass solenoid valve according to the compressor absolute pressure ratio To ensure the normal operation of the magnetic suspension centrifugal compressor at low load and meet the minimum load operation requirements;

Step S4, if the chilled water temperature <target temperature-shutdown temperature difference + T, and after 3S, the bypass solenoid valve is opened to the initial set opening degree, after the bypass solenoid valve adjustment period, if the water temperature continues to meet the chilled water temperature ≤ target Temperature-Stop temperature difference + T, the bypass solenoid valve continues to open to the maximum opening according to the set adjustment range; or

If the chilled water temperature> target temperature-shutdown temperature difference + T + 0.2 ℃ for 3 seconds or the compressor exits the minimum capacity state for 30 seconds, the bypass solenoid valve starts to close according to the adjustment range; or

If the target temperature-shutdown temperature difference + T ℃ ≤ chilled water temperature ≤ target temperature-shutdown temperature difference + T + 0.2 ℃, the bypass solenoid valve opening remains unchanged.