CN114857760B - Air conditioning unit - Google Patents

Air conditioning unit Download PDF

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Publication number
CN114857760B
CN114857760B CN202210620337.7A CN202210620337A CN114857760B CN 114857760 B CN114857760 B CN 114857760B CN 202210620337 A CN202210620337 A CN 202210620337A CN 114857760 B CN114857760 B CN 114857760B
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China
Prior art keywords
surge
air conditioning
compressor
rotating speed
centrifugal compressor
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CN202210620337.7A
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Chinese (zh)
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CN114857760A (en
Inventor
王锡元
朱海涛
李磊
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Qingdao Hisense Hitachi Air Conditioning System Co Ltd
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Qingdao Hisense Hitachi Air Conditioning System Co Ltd
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Priority to CN202210620337.7A priority Critical patent/CN114857760B/en
Publication of CN114857760A publication Critical patent/CN114857760A/en
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Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F24—HEATING; RANGES; VENTILATING
    • F24F—AIR-CONDITIONING; AIR-HUMIDIFICATION; VENTILATION; USE OF AIR CURRENTS FOR SCREENING
    • F24F11/00—Control or safety arrangements
    • F24F11/70—Control systems characterised by their outputs; Constructional details thereof
    • F24F11/80—Control systems characterised by their outputs; Constructional details thereof for controlling the temperature of the supplied air
    • F24F11/86—Control systems characterised by their outputs; Constructional details thereof for controlling the temperature of the supplied air by controlling compressors within refrigeration or heat pump circuits
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
    • F25B1/00—Compression machines, plants or systems with non-reversible cycle
    • F25B1/04—Compression machines, plants or systems with non-reversible cycle with compressor of rotary type
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
    • F25B49/00—Arrangement or mounting of control or safety devices
    • F25B49/02—Arrangement or mounting of control or safety devices for compression type machines, plants or systems
    • F25B49/022—Compressor control arrangements
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
    • F25B2600/00—Control issues
    • F25B2600/02—Compressor control
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
    • F25B2700/00—Sensing or detecting of parameters; Sensors therefor
    • F25B2700/19—Pressures
    • F25B2700/193—Pressures of the compressor
    • F25B2700/1931—Discharge pressures
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
    • F25B2700/00—Sensing or detecting of parameters; Sensors therefor
    • F25B2700/19—Pressures
    • F25B2700/193—Pressures of the compressor
    • F25B2700/1933—Suction pressures
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
    • Y02B30/00—Energy efficient heating, ventilation or air conditioning [HVAC]
    • Y02B30/70—Efficient control or regulation technologies, e.g. for control of refrigerant flow, motor or heating

Abstract

The application discloses an air conditioning unit, which is characterized in that when the air conditioning unit operates, the operation conditions of a plurality of centrifugal compressors are adjusted to be consistent; according to the suction pressure, the exhaust pressure and the opening degree of the guide vane of each centrifugal compressor, the surge rotating speed and the blocking rotating speed of each centrifugal compressor are obtained; when the air conditioning unit is loaded, if the rotating speed of one centrifugal compressor reaches the blocking rotating speed, acquiring the exhaust pressure and the suction pressure of one centrifugal compressor H with the highest blocking rotating speed; recalculating the blocking rotating speed of each centrifugal compressor according to the exhaust pressure and the suction pressure of the centrifugal compressor H; when the air conditioning unit is in load shedding, if the rotating speed of one centrifugal compressor reaches the surge rotating speed and the compressor surge does not occur, acquiring the exhaust pressure and the suction pressure of one centrifugal compressor L with the lowest surge rotating speed; the surge rotational speed of each centrifugal compressor is recalculated based on the discharge pressure and the suction pressure of the centrifugal compressor L. The application can ensure the consistent output of the compressor.

Description

Air conditioning unit
Technical Field
The application relates to the technical field of air conditioners, in particular to an air conditioner unit.
Background
The magnetic suspension centrifugal compressors are often applied to the same air conditioning system, and for operation safety, the compressors need to operate at the same rotating speed or frequency, and if the rotating speeds are different, some compressors can surge or be blocked under the same air conditioning working condition.
In order to more truly calculate the surge and blockage speeds, each compressor is generally provided with a set of suction and exhaust pressure sensors, but because of the manufacturing difference of the pressure sensors, the pressure data read out from the compressors are different, so that the calculated surge speeds or blockage speeds of each compressor are different, and the compressors of the same system can be operated at different speeds, because the actual speeds of the compressors are higher than the surge speeds and lower than the blockage speeds in order to avoid the surge and blockage.
In this way, in an air conditioning unit with multiple compressors, the output of each compressor is different, for example, when the compressors are loaded, if the output of the multiple compressors is different, the output cold (heat) quantity of the whole unit is reduced, so that a user feels that the refrigerating (heat) quantity of the unit is insufficient; when the load is reduced, if the output of the compressors is different, the load reduction of some compressors is insufficient, so that the compressors are frequently started and stopped to meet the smaller refrigeration (heat) meeting requirements, and the performance of the compressors is not exerted. If the pressure readings are inaccurate, it is possible for some compressors to fail due to bearing shake caused by surge.
Therefore, a solution is needed for balancing the load of a centrifugal compressor against the load imbalance of the centrifugal compressor caused by the pressure sensor bias, so that the centrifugal compressor is actually operated under the same load.
Disclosure of Invention
In order to solve the technical problems, the embodiment of the application provides an air conditioning unit, which can realize balanced load and ensure consistent output of a compressor by correcting the blocking rotating speed and the surging rotating speed of a centrifugal compressor.
In order to achieve the aim of the application, the application is realized by adopting the following technical scheme:
the application provides an air conditioning unit, which is characterized by comprising a plurality of centrifugal compressors and a control unit, wherein the control unit is configured to:
when the air conditioning unit operates, the operation conditions of the centrifugal compressors are adjusted to be consistent;
according to the suction pressure, the exhaust pressure and the opening degree of the guide vane of each centrifugal compressor, the surge rotating speed and the blocking rotating speed of each centrifugal compressor are obtained;
when the air conditioning unit is loaded, if the rotating speed of one centrifugal compressor reaches the blocking rotating speed, acquiring the exhaust pressure and the suction pressure of one centrifugal compressor H with the highest blocking rotating speed of all the centrifugal compressors;
recalculating the blocking rotating speed of each centrifugal compressor according to the exhaust pressure and the suction pressure of the centrifugal compressor H;
when the air conditioning unit is in load shedding, if the rotating speed of one centrifugal compressor reaches the surge rotating speed and no compressor surge occurs, acquiring the exhaust pressure and the suction pressure of one centrifugal compressor L with the lowest surge rotating speed of all the centrifugal compressors;
the surge rotational speed of each centrifugal compressor is recalculated based on the discharge pressure and the suction pressure of the centrifugal compressor L.
In some embodiments of the present application, the operation conditions of the plurality of centrifugal compressors are adjusted to be consistent, specifically:
when the air conditioning unit is a multi-compressor co-fluoride unit, the opening degree of the guide vanes of other centrifugal compressors is adjusted to be consistent with the opening degree of the guide vanes of the centrifugal compressor with the highest rotating speed when the air conditioning unit is loaded, and the opening degree of the guide vanes of the other centrifugal compressors is adjusted to be consistent with the opening degree of the guide vanes of the centrifugal compressor with the lowest rotating speed when the air conditioning unit is unloaded;
when the air conditioning unit is an independent fluorine unit, the opening degree of the guide vane of the other centrifugal compressors is adjusted to be consistent with the opening degree of the guide vane of the centrifugal compressor with the highest rotating speed, the liquid level of the evaporator or the condenser corresponding to the other centrifugal compressors is adjusted to be consistent with the liquid level of the evaporator or the condenser corresponding to the centrifugal compressor with the highest rotating speed when the air conditioning unit is loaded, the opening degree of the guide vane of the other centrifugal compressors is adjusted to be consistent with the opening degree of the guide vane of the centrifugal compressor with the lowest rotating speed when the air conditioning unit is unloaded, and the liquid level of the evaporator or the condenser corresponding to the other centrifugal compressors is adjusted to be consistent with the liquid level of the evaporator or the condenser corresponding to the centrifugal compressor with the lowest rotating speed.
In some embodiments of the application, the control unit is further configured to:
the centrifugal compressor is calibrated for pressure sensors for detecting suction and discharge pressures.
In some embodiments of the application, the pressure sensor is calibrated, in particular:
recording unit parameters of the air conditioning unit under the working condition of maximum operation at intervals at the current refrigerating/heating Ji Shi;
respectively averaging the suction pressure and the exhaust pressure when the unit parameters are the same, and storing;
at the next cooling/heating Ji Shi, if the operating condition of the air conditioning unit is consistent with the recorded operating condition, comparing whether the first deviation between the current suction pressure and the stored average suction pressure and the second deviation between the current discharge pressure and the stored average discharge pressure are respectively within the preset ranges, if so, not correcting the current suction pressure and the discharge pressure, otherwise, correcting the current suction pressure by using the average suction pressure, and correcting the current discharge pressure by using the average discharge pressure.
In some embodiments of the present application, when the air conditioning unit is de-loaded, if the rotational speed of one centrifugal compressor reaches the surge rotational speed and the compressor is in surge, a surge avoidance process is required until the surge is eliminated.
In some embodiments of the application, the control unit is configured to:
detecting whether the opening degree of the guide vane of the centrifugal compressor reaches the maximum value, if not, gradually increasing the opening degree of the guide vane until the compressor gets rid of surge, if so, increasing the rotating speed of the compressor, and if the rotating speed of the compressor is increased to the blocking rotating speed and the compressor is not getting rid of surge, gradually increasing the hot gas bypass valve until the compressor gets rid of surge;
wherein, the hot gas bypass valve is arranged on a connecting pipe between a condenser and an evaporator of the air conditioning unit.
In some embodiments of the present application, the surge speed and the choke speed of each centrifugal compressor are obtained according to the suction pressure, the discharge pressure and the opening degree of the guide vane of each centrifugal compressor, specifically:
surge speed vs=a+bx -1 +cY+dX -2 +eY 2 +fYX -1 +gX -3 +hY 3 +iY2X -1 +jYX -2 ；
The blocking rotational speed vd=a '+b' X -1 +c'Y+d'X -2 +e'Y 2 +f'YX -1 +g'X -3 +h'Y 3 +i'Y2X -1 +j'YX -2 ；
Wherein a-j and a '-j' are debugging constants, X represents the opening degree of the guide vane, and Y represents the ratio of exhaust pressure to suction pressure.
Compared with the prior art, the air conditioning unit provided by the application has the following advantages and beneficial effects:
the surge rotating speed and the blocking rotating speed of the centrifugal compressor are corrected by correcting the exhaust pressure and the suction pressure of the centrifugal compressor, so that the compressor operates in the rotating speed range between the surge rotating speed and the blocking rotating speed, the load of each centrifugal compressor is balanced, the centrifugal compressors operate under the same load, the consistency of the output of each centrifugal compressor is ensured, and the safe and reliable operation of the centrifugal compressors is realized.
Other features and advantages of the present application will become apparent upon review of the detailed description of the application in conjunction with the drawings.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings that are needed in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are some embodiments of the present application, and other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
FIG. 1 is a control flow chart I of an embodiment of an air conditioning unit according to the present application when loading/unloading;
FIG. 2 is a schematic block diagram I of an embodiment I of an air conditioning unit according to the present application;
FIG. 3 is a flow chart of the adjustment condition of the loading process of embodiment I of the air conditioning unit according to the present application;
FIG. 4 is a flow chart of the adjustment of unloading process of embodiment I of the air conditioning unit according to the present application;
FIG. 5 is a schematic block diagram II of an embodiment II of an air conditioning unit according to the present application;
FIG. 6 is a flow chart of the adjustment condition of the loading process of embodiment II of the air conditioning unit according to the present application;
FIG. 7 is a flow chart of the unloading process of embodiment II of the air conditioning unit according to the present application;
FIG. 8 is a control flow chart II of an embodiment of an air conditioning unit according to the present application when loading/unloading;
FIG. 9 is a flow chart illustrating surge avoidance during load shedding in accordance with one embodiment of the present application;
fig. 10 is a flowchart of calibrating a pressure sensor in an embodiment of an air conditioning unit according to the present application.
Detailed Description
The following description of the embodiments of the present application will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present application, but not all embodiments.
All other embodiments, which can be made by those skilled in the art based on the embodiments of the application without making any inventive effort, are intended to be within the scope of the application. In the description of the present application, it should be understood that the terms "center," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," and the like indicate orientations or positional relationships based on the orientation or positional relationships shown in the drawings, merely to facilitate describing the present application and simplify the description, and do not indicate or imply that the devices or elements referred to must have a specific orientation, be configured and operated in a specific orientation, and thus should not be construed as limiting the present application.
In the description of the present application, it should be noted that the terms "mounted," "connected," and "coupled" are to be construed broadly, as well as, for example, fixedly coupled, detachably coupled, or integrally coupled, unless otherwise specifically indicated and defined. The specific meaning of the above terms in the present application will be understood in specific cases by those of ordinary skill in the art. In the description of the above embodiments, particular features, structures, materials, or characteristics may be combined in any suitable manner in any one or more embodiments or examples.
The terms "first," "second," and the like, are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defining "a first" or "a second" may explicitly or implicitly include one or more such feature. In the description of the present application, unless otherwise indicated, the meaning of "a plurality" is two or more.
Basic operation principle of air conditioner
The air conditioner performs a cooling and heating cycle of the air conditioner by using a compressor, a condenser, an expansion valve, and an evaporator. The refrigerating and heating cycle includes a series of processes involving compression, condensation, expansion and evaporation, and refrigerating or heating an indoor space.
The low-temperature low-pressure refrigerant enters the compressor, the compressor compresses the refrigerant gas into a high-temperature high-pressure state, and the compressed refrigerant gas is discharged. The discharged refrigerant gas flows into the condenser. The condenser condenses the compressed refrigerant into a liquid phase, and heat is released to the surrounding environment through the condensation process.
The expansion valve expands the liquid-phase refrigerant in a high-temperature and high-pressure state formed by condensation in the condenser into a low-pressure liquid-phase refrigerant. The evaporator evaporates the refrigerant expanded in the expansion valve and returns the refrigerant gas in a low-temperature and low-pressure state to the compressor. The evaporator may achieve a cooling effect by exchanging heat with a material to be cooled using latent heat of evaporation of a refrigerant. The air conditioner may adjust the temperature of the indoor space throughout the cycle.
The outdoor unit of the air conditioner refers to a portion of a refrigeration cycle including a compressor, an outdoor heat exchanger, and an outdoor fan, the indoor unit of the air conditioner includes a portion of an indoor heat exchanger and an indoor fan, and a throttling device (e.g., a capillary tube or an electronic expansion valve) may be provided in the indoor unit or the outdoor unit.
The indoor heat exchanger and the outdoor heat exchanger function as a condenser or an evaporator. The air conditioner performs a heating mode when the indoor heat exchanger is used as a condenser, and performs a cooling mode when the indoor heat exchanger is used as an evaporator.
The mode of converting the indoor heat exchanger and the outdoor heat exchanger into a condenser or an evaporator generally adopts a four-way valve, and the arrangement of a conventional air conditioner is specifically referred to and will not be described herein.
The refrigeration working principle of the air conditioner is as follows: the compressor works to enable the interior of an indoor heat exchanger (in an indoor unit, an evaporator at the moment) to be in an ultralow pressure state, liquid refrigerant in the indoor heat exchanger is rapidly evaporated to absorb heat, air blown out by an indoor fan is cooled by an indoor heat exchanger coil and then changed into cold air to be blown into the indoor, the evaporated refrigerant is pressurized by the compressor and then condensed into liquid state in a high-pressure environment in an outdoor heat exchanger (in an outdoor unit, a condenser at the moment), heat is released, the heat is emitted to the atmosphere by the outdoor fan, and the refrigerating effect is achieved through circulation.
The heating working principle of the air conditioner is as follows: the gaseous refrigerant is pressurized by the compressor to become high-temperature high-pressure gas, and enters the indoor heat exchanger (a condenser at the moment), so that the gaseous refrigerant is condensed, liquefied and released heat to become liquid, and meanwhile, the indoor air is heated, so that the aim of improving the indoor temperature is fulfilled. The liquid refrigerant is decompressed by the throttling device, enters the outdoor heat exchanger (an evaporator at the moment), evaporates, gasifies and absorbs heat to become gas, and simultaneously absorbs heat of outdoor air (the outdoor air becomes colder) to become gaseous refrigerant, and enters the compressor again to start the next cycle.
Air conditioning unit
The centrifugal compressor in some embodiments of the application is a magnetic levitation centrifugal compressor, and the air conditioning unit comprises a plurality of centrifugal compressors and a control unit.
As follows, two characteristics of a centrifugal compressor are first described: surge and choke.
Surging means that when the flow is smaller than the design flow, the outlet pressure of the compressor is reduced, the pressure in the pipe network is larger than the outlet pressure of the compressor, the backflow is generated until the pressure in the pipe network is reduced below the outlet pressure of the compressor, at the moment, the compressor is restored to work normally, the air is exhausted to the pipe network with larger displacement, the pressure in the pipe network is increased along with the pressure, meanwhile, the outlet flow of the compressor is reduced, the backflow phenomenon is repeated, and periodic low-frequency high-amplitude pressure pulsation is generated in the pipe network system of the whole compressor repeatedly.
The condition when the flow reaches the maximum is the "blocking" condition, and there are two possibilities for this:
firstly, the air flow at the throat part of a certain flow passage is concentrated to reach a critical state, at the moment, the volume flow of the air is at a maximum value, and the flow cannot be increased even if the back pressure of the compressor is reduced, so that the working condition is also a blocking working condition.
And secondly, the critical state is not reached in the flow passage, namely the first working condition is not generated, but the compressor has great flow loss in the machine under the condition of larger flow, the provided exhaust pressure is very small and almost approaches zero energy, and the exhaust pressure can only be used for overcoming the resistance in the exhaust pipeline to maintain the large flow.
According to the characteristics, a manufacturer of the centrifugal compressor gives out a calculation formula of the surge rotating speed and the blocking rotating speed, and controls the centrifugal compressor to operate between the surge rotating speed and the blocking rotating speed at the working rotating speed when the centrifugal compressor works, so that the operation safety of the compressor is ensured.
In general, for each of a plurality of centrifugal compressors, the discharge pressure Pd and the suction pressure Ps of each compressor are detected and obtained by corresponding pressure sensors, and then the surge rotation speed Vs and the blockage rotation speed Vd are calculated by using the discharge pressure Pd, the suction pressure Ps and the vane opening of the centrifugal compressor.
Each centrifugal compressor is then controlled to operate in a rotational speed range between its corresponding surge speed Vs and choke speed Vd.
However, when the control unit issues a control command for matching the rotational speed demands to the plurality of centrifugal compressors, the pressure sensors for detecting the discharge pressure Pd and the intake pressure Ps of the compressors are different from each other in the detected pressures, so that the surge rotational speed Vs and the choke rotational speed Vd of the compressors are not matched, and the centrifugal compressors are limited to approach the surge rotational speed or the choke rotational speed, and the compressor outputs are not matched.
In order to solve the technical problem that the load unbalance is caused by the deviation of the pressure sensor to the operation of the compressor, the application provides an air conditioning unit.
The control unit is used for balancing the load of each centrifugal compressor, so that each centrifugal compressor works under the same load, and the output of each centrifugal compressor is consistent.
The specific implementation process is described below.
Referring to fig. 1, a flow chart of a control unit for balancing the load of each centrifugal compressor is shown.
S1: and adjusting the operation conditions of the centrifugal compressors to be consistent.
Before balancing loads of a plurality of centrifugal compressors, the operation conditions of the centrifugal compressors are adjusted to be consistent, so that the loads can be accurately balanced in the working process of the centrifugal compressors, and the consistent output of the centrifugal compressors is realized.
The present application relates to an air conditioning system having a plurality of centrifugal compressors (hereinafter referred to as centrifuges).
Referring to fig. 2-7, various conditions for adjusting operating conditions of an embodiment of an air conditioning unit are illustrated.
Multi-press fluorine-sharing unit
Referring to fig. 2, the air conditioning unit is a multi-press co-fluoridation unit, i.e., a plurality of centrifuges (centrifuge 1, centrifuge 2, centrifuge n) share an evaporator and a condenser.
Referring to fig. 3 and 4, when the air conditioning unit is a multi-press co-fluoride unit, the operation condition is adjusted by both loading and unloading.
Referring to fig. 3, when the air conditioning unit is loaded, the opening degree of the guide vanes of each centrifuge is detected first, and the opening degree of the guide vanes of the centrifuge (denoted as centrifuge a) with the highest rotation speed is determined.
And if the opening degrees of the guide vanes of the other centrifuges are not consistent with the opening degrees of the guide vanes of the centrifuges A, adjusting the opening degrees of the guide vanes of the other centrifuges to be consistent with the opening degrees of the guide vanes of the centrifuges A.
For the purpose of convenient and quick adjustment, if the number of centrifuges is more than two, the opening degree of the guide vane of each centrifuge with a small rotating speed (for example, the rotating speed is less than 1/3 of the highest rotating speed) can be adjusted to be consistent with the opening degree of the guide vane of the centrifuge A, and the opening degree of the guide vane of the rest centrifuges is not adjusted.
Referring to fig. 4, when the air conditioning unit is off-load, the opening degree of the guide vanes of each centrifuge is first detected, and the opening degree of the guide vanes of the centrifuge (denoted as centrifuge B) with the lowest rotation speed is determined.
And if the opening degrees of the guide vanes of the other centrifuges are not consistent with the opening degrees of the guide vanes of the centrifuges B, adjusting the opening degrees of the guide vanes of the other centrifuges to be consistent with the opening degrees of the guide vanes of the centrifuges B.
For the purpose of convenient and quick adjustment, if the number of centrifuges is more than two, the opening degree of the guide vane of each centrifuge with higher rotation speed (for example, the rotation speed is more than 2/3 of the lowest rotation speed) can be adjusted to be consistent with the opening degree of the guide vane of the centrifuge B, and the opening degree of the guide vane of the rest centrifuges is not adjusted.
Independent fluorine unit
Referring to fig. 5, the air conditioning unit is a separate fluorine unit, i.e., each of the plurality of centrifuges (centrifuge 1, centrifuge 2, centrifuge n) has one evaporator and one condenser.
Referring to fig. 6 and 7, when the air conditioning unit is an independent fluorine unit, the operation condition thereof is adjusted by both loading and unloading.
It should be noted that, when the air conditioning unit is an independent fluorine unit, the operation condition of the centrifuges also considers the liquid level in the evaporator or the condenser, so, referring to fig. 5, a liquid level sensor is disposed in the condenser corresponding to each centrifuges, for example, a liquid level sensor a corresponding to the centrifuge 1, a liquid level sensor B corresponding to the centrifuge 2, and a liquid level sensor C corresponding to the centrifuge n.
Of course, a liquid level sensor may be provided in the evaporator, and only one of the evaporator and the condenser may detect the liquid level.
Referring to fig. 6, when the air conditioning unit is loaded, the opening degree of the guide vanes of each centrifuge is first detected, and the opening degree of the guide vanes of the centrifuge (denoted as centrifuge a') with the highest rotation speed is determined.
And if the opening degrees of the guide vanes of the other centrifuges are not consistent with the opening degrees of the guide vanes of the centrifuges A ', adjusting the opening degrees of the guide vanes of the other centrifuges to be consistent with the opening degrees of the guide vanes of the centrifuges A'.
For the purpose of convenient and quick adjustment, if the number of centrifuges is more than two, the opening degree of the guide vane of each centrifuge with a small rotation speed (for example, the rotation speed is less than 1/3 of the highest rotation speed) can be adjusted to be consistent with the opening degree of the guide vane of the centrifuge A', and the opening degree of the guide vane of the rest centrifuges is not adjusted.
In addition, it is necessary to detect the liquid level in each condenser and determine the liquid level in the condenser (denoted as condenser a) corresponding to the centrifuge a' having the highest rotation speed.
If the liquid levels in the condensers corresponding to the other centrifuges are inconsistent with the liquid level in the condenser A, the liquid levels in the other condensers are adjusted to be consistent with the liquid level in the condenser A.
For the purpose of convenient and quick adjustment, if the number of centrifuges is more than two, the liquid level in the condenser corresponding to each centrifuge with a smaller rotating speed (for example, the rotating speed is less than 1/3 of the highest rotating speed) can be adjusted to be consistent with the liquid level in the condenser A, and the liquid level in the condensers corresponding to the rest centrifuges is not adjusted.
Referring to fig. 7, when the air conditioning unit is de-loaded, the opening degree of the guide vanes of each centrifuge is first detected, and the size of the opening degree of the guide vanes of the centrifuge (denoted as centrifuge B') having the lowest rotation speed is determined.
And if the opening degrees of the guide vanes of the other centrifuges are not consistent with the opening degrees of the guide vanes of the centrifuges B ', adjusting the opening degrees of the guide vanes of the other centrifuges to be consistent with the opening degrees of the guide vanes of the centrifuges B'.
For the purpose of convenient and quick adjustment, if the number of centrifuges is more than two, the opening degree of the guide vane of each centrifuge with higher rotation speed (for example, the rotation speed is more than 2/3 of the lowest rotation speed) can be adjusted to be consistent with the opening degree of the guide vane of the centrifuge B', and the opening degree of the guide vane of the rest centrifuges is not adjusted.
In addition, it is necessary to detect the liquid level in each condenser and determine the liquid level in the condenser (denoted as condenser B) corresponding to the centrifuge B' having the lowest rotation speed.
If the liquid levels in the condensers corresponding to the other centrifuges are inconsistent with the liquid level in the condenser B, the liquid levels in the other condensers are adjusted to be consistent with the liquid level in the condenser B.
For the purpose of convenient and quick adjustment, if the number of centrifuges is more than two, the liquid level in the condenser corresponding to each centrifuge with higher rotation speed (for example, the rotation speed is more than 2/3 of the lowest rotation speed) can be adjusted to be consistent with the liquid level in the condenser B, and the liquid level in the condenser corresponding to the rest centrifuges is not adjusted.
The adjustment of the liquid level in the condenser is achieved by providing an expansion valve on the connecting line between the evaporator and the condenser.
For example, the opening degree of the expansion valve 1 is used for adjusting the liquid level in the condenser corresponding to the centrifuge 1, the opening degree of the expansion valve 2 is used for adjusting the liquid level in the condenser corresponding to the centrifuge 2, and the opening degree of the expansion valve n is used for adjusting the liquid level in the condenser corresponding to the centrifuge 1.
Thus, the operation condition adjustment of each centrifugal machine is completed, and the operation condition of each centrifugal machine is ensured to be consistent.
S2: whether or not loading is performed, if yes, proceeding to S3, otherwise proceeding to S6.
Since the rotational speed limit of the centrifuge is not the same when the air conditioning unit is loaded and unloaded, the balancing load is described in terms of both loading and unloading.
S3: and detecting whether the rotation speed of one compressor reaches the blocking rotation speed, if so, proceeding to S4, otherwise, returning to S2.
In some embodiments of the application, the blocking speed Vd is calculated from the discharge pressure Pd, suction pressure Ps and vane opening of the centrifuge.
The relationship between the exhaust pressure Pd, the suction pressure Ps, and the vane opening, and the blocking rotation speed Vd can be obtained by the following formula.
The blocking rotational speed vd=a '+b' X -1 +c'Y+d'X -2 +e'Y 2 +f'YX -1 +g'X -3 +h'Y 3 +i'Y2X -1 +j'YX -2 。
Wherein a 'to j' are debugging constants, X represents the opening degree of the guide vane, and Y represents the ratio of exhaust pressure to suction pressure.
The above formula is a formula fitted according to experimental test data.
The amount of data fitted by different centrifuge manufacturers is different, and the formulas to which the corresponding centrifuge manufacturers are fitted also have differences.
The obtained fitting formulas may also be different by using different fitting methods, so the above formulas are given as a calculation example only.
S4: and obtaining the exhaust pressure and the suction pressure of one centrifugal compressor with the highest blocking rotating speed of all the centrifugal compressors.
When detecting that the rotation speed of one centrifuge reaches the blocking rotation speed, acquiring one centrifuge (marked as a centrifuge H) with the highest blocking rotation speed in all centrifuges.
At this time, the discharge pressure Pd and the suction pressure Ps of the centrifuge H are obtained.
S5: the blocking rotational speed of each centrifugal compressor is recalculated based on the discharge pressure and suction pressure of the centrifugal compressor H.
According to the above, when the discharge pressure Pd, the suction pressure Ps, and the vane opening degree of each centrifuge are known, the blocking rotation speed of the centrifuge can be recalculated to be known.
By using the blocking rotational speed before updating the blocking rotational speed, the blocking rotational speed of each compressor depends on the exhaust pressure Pd and the suction pressure Ps of the centrifugal machine H instead of the pressure indication detected by the pressure sensor of the centrifugal machine H, thereby avoiding the influence of the deviation of different pressure sensors on the blocking rotational speed of each centrifugal compressor.
In this way, when the operation conditions of the compressors are identical, the opening degrees of the guide vanes of the compressors are correspondingly adjusted, and the exhaust pressure and the suction pressure of the other centrifuges are correspondingly adjusted according to the exhaust pressure and the suction pressure of the one centrifuges with the highest blocking rotational speed, so that the blocking rotational speeds of all centrifuges can be ensured to be basically identical.
S6: if not, go to S7, if not, return to S2.
Since the rotational speed limit of the centrifuge is not the same when the air conditioning unit is loaded and unloaded, the balancing load is described in terms of both loading and unloading.
S7: and detecting whether the rotation speed of one compressor reaches the surge rotation speed, if so, proceeding to S8, otherwise, returning to S2.
In some embodiments of the application, the surge speed Vs is calculated from the discharge pressure Pd, the suction pressure Ps, and the vane opening of the centrifuge.
The relationship between the exhaust pressure Pd, the suction pressure Ps, the vane opening, and the surge rotation speed Vs can be obtained by the following formula.
Surge speed vs=a+bx -1 +cY+dX -2 +eY 2 +fYX -1 +gX -3 +hY 3 +iY2X -1 +jYX -2 。
Wherein a-j are debugging constants, X represents the opening degree of the guide vane, and Y represents the ratio of exhaust pressure to suction pressure.
The above formula is a formula fitted according to experimental test data.
The amount of data fitted by different centrifuge manufacturers is different, and the formulas to which the corresponding centrifuge manufacturers are fitted also have differences.
The obtained fitting formulas may also be different by using different fitting methods, so the above formulas are given as a calculation example only.
S8: when no compressor surge occurs, the exhaust pressure and the suction pressure of one centrifugal compressor with the lowest surge rotation speed of all the centrifugal compressors are obtained.
When the rotational speed of one of the centrifuges is detected to reach the surge rotational speed, one of the centrifuges (denoted as a centrifuge L) with the lowest surge rotational speed is obtained.
At this time, the discharge pressure Pd and the suction pressure Ps of the centrifuge L are obtained.
S9: the surge rotational speed of each centrifugal compressor is recalculated based on the discharge pressure and the suction pressure of the centrifugal compressor L.
According to the above, when the exhaust pressure Pd, the suction pressure Ps, and the vane opening degree of each centrifuge are known, the surge rotation speed of the centrifuge can be recalculated to be known.
The surge rotation speed before the surge rotation speed is updated is utilized, so that the surge rotation speed of each compressor depends on the exhaust pressure Pd and the suction pressure Ps of the centrifugal machine L instead of the pressure indication detected by the pressure sensor, and the influence of the deviation of different pressure sensors on the surge rotation speed of each centrifugal compressor is avoided.
In this way, when the operation conditions of the compressors are identical, the opening degrees of the guide vanes of the compressors are correspondingly adjusted, and the exhaust pressure and the suction pressure of the other centrifuges are correspondingly adjusted according to the exhaust pressure and the suction pressure of the one centrifuges with the lowest surge rotation speed, so that the surge rotation speeds of all centrifuges can be ensured to be basically identical.
Therefore, when the control unit issues a consistent rotation speed demand control command to the centrifuges, the centrifuges can be ensured to operate in a rotation speed range between the surge rotation speed and the blocking rotation speed, so that the rotation speeds of the centrifuges are basically consistent, the operation under the same load is realized, and the output of the centrifuges is ensured to be the same.
Surge avoidance process
In some embodiments of the present application, it is desirable to control the centrifuge operating speed to not be lower than its own surge speed Vs when the air conditioning unit is de-rated to avoid compressor surge.
Referring to fig. 8, there are more steps S10 and S11 than in fig. 1.
S10: it is determined whether or not the compressor is surging, and if so, the process proceeds to S11, and if not, the process proceeds to S8.
For example, it may be determined whether the compressor has surge by detecting the current or suction pressure/discharge pressure of the compressor.
For example, when the current reaches the current threshold, indicating that the compressor is surging, a current margin may be set to determine that the compressor is approaching surging when approaching the current threshold.
S11: surge avoidance processing.
When the unit is off-load, the running rotating speed of the compressor is controlled to be not lower than Vs, and when the rotating speed approaches Vs, the rotating speed is required to be kept to be V & gtVs+DeltaV.
The compressor rotation speed V can be increased or the surge rotation speed Vs can be reduced by keeping V not less than Vs+DeltaV.
There are various existing surge avoidance treatments, several of which are described by way of example below.
(1) By adopting the surge protection principle of a hot gas bypass valve
The hot gas bypass valve is used for surge protection, and the opening or closing of the hot gas bypass valve is controlled through a surge protection line, so that the unit is far away from a surge point, and the purpose of protection is achieved.
Wherein referring to fig. 2 and 5, a connection pipe is connected between the condenser and the evaporator, and a hot gas bypass valve is provided on the connection pipe, and when an operation point reaches a surge protection point but does not reach a surge point, the hot gas bypass valve is opened by a control system, and hot gas from the condenser is discharged to the evaporator, thereby reducing a pressure ratio and simultaneously increasing an exhaust gas amount, thereby avoiding the occurrence of surge.
This protection reduces the pressure ratio and thus the surge speed Vs.
(2) Varying compressor speed
When the unit is off-load, controlling the running rotating speed of the compressor to be not lower than Vs, and when the rotating speed is close to Vs, keeping the rotating speed to be V more than or equal to Vs+delta V; wherein DeltaV may be a value set according to the characteristics of the compressor in order not to let the compressor rotation speed V < Vs.
(3) Adjusting with rotating diffuser
When the flow is reduced, a severe rotational pull-off is typically first created in the diffuser, resulting in surge.
When the flow changes, if the inlet geometric angle of the flow passage of the diffuser can be correspondingly changed to adapt to the changed working condition, so that the attack angle is not very large, the performance curve can be greatly moved towards a small flow area, the stable working condition range is expanded, the surge flow is greatly reduced, and the purpose of anti-surge is achieved.
Of course, there are many ways of surge avoidance, and no limitation is made here.
Referring to fig. 9, a flow chart for surge avoidance in the present application is shown.
S111: and judging whether the opening degree of the guide vane of the centrifugal machine reaches 100 percent, if so, proceeding to S113, otherwise proceeding to S112.
When approaching surge, a surge avoidance process is required.
S112: the opening degree of the guide vane is gradually increased.
When the opening degree of the guide vane of the centrifugal machine is detected to be less than 100%, the opening degree of the guide vane is gradually increased until the centrifugal machine is separated from surge.
Specifically, the opening of the guide vane can be increased by a preset opening at a time, and after a delay time t1, the judgment is returned to judge whether the surge is approaching.
The specific approach to surge is determined as described above.
If the opening degree of the guide vane does not reach 100%, and still approaches to surge, the opening degree of the guide vane is continuously increased gradually until the guide vane is separated from surge, and the process is finished.
S113: whether or not the surge is released is judged, if so, the process is ended, and if not, the process proceeds to S114.
When the vane opening reaches 100%, but still does not deviate from surge, the process proceeds to S114.
When the opening of the guide vane reaches 100% and the surge is released, the process proceeds to the end.
S114: whether the centrifuge rotational speed reaches the clogging rotational speed is judged, if so, the process proceeds to S116, and if not, the process proceeds to S115.
S115: the compressor speed is gradually increased.
If the compressor speed does not reach the blocking speed and still does not break away from surge, the compressor speed starts to be gradually increased until the compressor speed breaks away from surge.
Specifically, the compressor speed may be increased one preset speed at a time, and after a delay of time t2, a return is made to determine whether to disengage from surge.
Until the surge is removed, and the process is finished.
S116: the opening degree of the hot gas bypass valve is gradually increased.
And if the rotation speed of the compressor reaches the blocking rotation speed and still does not break away from surge, starting to gradually increase the opening of the hot gas bypass valve until the hot gas bypass valve breaks away from surge.
Specifically, the opening of the hot gas bypass valve may be increased one preset opening at a time, and after a delay of time t3, a return is made to determine whether to disengage from surge.
Until the surge is removed, and the process is finished.
As above, surge avoidance is achieved.
Pressure sensor calibration
As described above, the discharge pressure Pd and the suction pressure Ps obtained by each centrifuge are obtained by the pressure sensor, and when the load of the centrifuge is corrected as described above, for example, when the air conditioning unit is loaded, the discharge pressure Pd and the suction pressure Ps of the other centrifuge are corrected depending on the discharge pressure Pd and the suction pressure Ps of the centrifuge having the highest clogging rotational speed, but the discharge pressure Pd and the suction pressure Ps of the centrifuge having the highest clogging rotational speed are obtained by the pressure sensor itself.
In the long-term running process of the unit, the pressure sensing components in the pressure sensor are semiconductor devices, so that certain drift can be generated and certain deviation can be generated between the pressure sensing components and the actual pressure value, and therefore, in order to ensure the accuracy of the indication of the pressure sensor, the pressure sensor is also necessary to be calibrated.
Referring to fig. 10, a flow chart for calibrating a pressure sensor is shown.
(1) At intervals t, the unit parameters of the air conditioning unit under the working condition with the maximum operation of the air conditioning unit are recorded at the current refrigerating/heating Ji Shi.
The unit parameters in the present application may include evaporator or condenser fluid level, chilled water temperature, cooling water temperature parameters, and the like.
It should be noted that the time t is not preferable to be too short, because the pressure measurement drift is a long-term process.
(2) Respectively averaging Ps of suction pressure and exhaust pressure when the unit parameters are the same Average of And an exhaust pressure Pd Average of And storing.
(3) At the next refrigerating/heating Ji Shi, if the operating condition of the air conditioning unit is consistent with the recorded operating condition, the current suction pressure Ps is recorded Currently, the method is that And an exhaust pressure Pd Currently, the method is that 。
(4) Judging and comparing the current suction pressure Ps Currently, the method is that And Ps Average of Whether or not the current exhaust pressure Pd is within the first deviation Currently, the method is that And Pd (Pd) Average of Whether within the second deviation.
If both are, the current suction pressure Ps is not Currently, the method is that And Ps Average of If not, the correction is performed by using the average suction pressure Ps Average of Correction of the current suction pressure Ps Currently, the method is that By means of average exhaust pressure Pd Average of Correcting the current exhaust pressure Pd Currently, the method is that 。
The first deviation and the second deviation are both freely set.
The air conditioning unit provided by the application can balance the load of the centrifugal machine by correcting the surge rotating speed and the blocking rotating speed, ensure that the centrifugal machine works under the same load, ensure the same output, ensure the working operation safety of the centrifugal machine and improve the working reliability of the air conditioning unit.
The above embodiments are only for illustrating the technical solution of the present application, and are not limiting; although the application has been described in detail with reference to the foregoing embodiments, it will be apparent to one skilled in the art that modifications may be made to the technical solutions described in the foregoing embodiments, or equivalents may be substituted for some of the technical features thereof; such modifications and substitutions do not depart from the spirit and scope of the corresponding technical solutions.

Claims (6)

1. An air conditioning assembly comprising a plurality of centrifugal compressors and a control unit configured to:
when the air conditioning unit operates, the operation conditions of the centrifugal compressors are adjusted to be consistent;
according to the suction pressure, the exhaust pressure and the opening degree of the guide vane of each centrifugal compressor, the surge rotating speed and the blocking rotating speed of each centrifugal compressor are obtained;
when the air conditioning unit is loaded, if the rotating speed of one centrifugal compressor reaches the blocking rotating speed, acquiring the exhaust pressure and the suction pressure of one centrifugal compressor H with the highest blocking rotating speed of all the centrifugal compressors;
recalculating the blocking rotating speed of each centrifugal compressor according to the exhaust pressure and the suction pressure of the centrifugal compressor H;
updating the previous blocking rotational speed of each centrifugal compressor with the recalculated blocking rotational speed;
when the air conditioning unit is in load shedding, if the rotating speed of one centrifugal compressor reaches the surge rotating speed and no compressor surge occurs, acquiring the exhaust pressure and the suction pressure of one centrifugal compressor L with the lowest surge rotating speed of all the centrifugal compressors;
re-calculating the surge rotation speed of each centrifugal compressor according to the exhaust pressure and the suction pressure of the centrifugal compressor L;
updating a previous surge speed of each centrifugal compressor with the recalculated surge speed;
wherein, the operating condition of adjustment many centrifugal compressors keeps unanimous, specifically does:
when the air conditioning unit is a multi-compressor co-fluoride unit, the opening degree of the guide vanes of other centrifugal compressors is adjusted to be consistent with the opening degree of the guide vanes of the centrifugal compressor with the highest rotating speed when the air conditioning unit is loaded, and the opening degree of the guide vanes of the other centrifugal compressors is adjusted to be consistent with the opening degree of the guide vanes of the centrifugal compressor with the lowest rotating speed when the air conditioning unit is unloaded;
when the air conditioning unit is an independent fluorine unit, the opening degree of the guide vane of the other centrifugal compressors is adjusted to be consistent with the opening degree of the guide vane of the centrifugal compressor with the highest rotating speed, the liquid level of the evaporator or the condenser corresponding to the other centrifugal compressors is adjusted to be consistent with the liquid level of the evaporator or the condenser corresponding to the centrifugal compressor with the highest rotating speed when the air conditioning unit is loaded, the opening degree of the guide vane of the other centrifugal compressors is adjusted to be consistent with the opening degree of the guide vane of the centrifugal compressor with the lowest rotating speed when the air conditioning unit is unloaded, and the liquid level of the evaporator or the condenser corresponding to the other centrifugal compressors is adjusted to be consistent with the liquid level of the evaporator or the condenser corresponding to the centrifugal compressor with the lowest rotating speed.
2. The air conditioning unit of claim 1, wherein the control unit is further configured to:
the centrifugal compressor is calibrated for pressure sensors for detecting suction and discharge pressures.
3. Air conditioning unit according to claim 2, characterized in that the pressure sensor is calibrated, in particular:
recording unit parameters of the air conditioning unit under the working condition of maximum operation at intervals at the current refrigerating/heating Ji Shi;
respectively averaging the suction pressure and the exhaust pressure when the unit parameters are the same, and storing;
at the next cooling/heating Ji Shi, if the operating condition of the air conditioning unit is consistent with the recorded operating condition, comparing whether the first deviation between the current suction pressure and the stored average suction pressure and the second deviation between the current discharge pressure and the stored average discharge pressure are respectively within the preset ranges, if so, not correcting the current suction pressure and the discharge pressure, otherwise, correcting the current suction pressure by using the average suction pressure, and correcting the current discharge pressure by using the average discharge pressure.
4. The air conditioning unit of claim 1, wherein when the air conditioning unit is de-rated, if the rotational speed of one centrifugal compressor reaches a surge rotational speed and compressor surge occurs, a surge avoidance process is required until surge is eliminated.
5. The air conditioning unit of claim 4, wherein the control unit is configured to:
detecting whether the opening degree of the guide vane of the centrifugal compressor reaches the maximum value, if not, gradually increasing the opening degree of the guide vane until the compressor gets rid of surge, if so, increasing the rotating speed of the compressor, and if the rotating speed of the compressor is increased to the blocking rotating speed and the compressor is not getting rid of surge, gradually increasing the hot gas bypass valve until the compressor gets rid of surge;
wherein, the hot gas bypass valve is arranged on a connecting pipe between a condenser and an evaporator of the air conditioning unit.
6. The air conditioning assembly of claim 1, wherein the surge speed and the choke speed of each centrifugal compressor are obtained from the suction pressure, the discharge pressure and the vane opening of each centrifugal compressor, specifically:
surge speed vs=a+bx -1 +cY+dX -2 +eY 2 +fYX -1 +gX -3 +hY 3 +iY2X -1 +jYX -2 ；
The blocking rotational speed vd=a '+b' X -1 +c'Y+d'X -2 +e'Y 2 +f'YX -1 +g'X -3 +h'Y 3 +i'Y2X -1 +j'YX -2 ；
Wherein a-j and a '-j' are debugging constants, X represents the opening degree of the guide vane, and Y represents the ratio of exhaust pressure to suction pressure.
CN202210620337.7A 2022-06-02 2022-06-02 Air conditioning unit Active CN114857760B (en)

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