CN112228972A - Multi-split air conditioning system - Google Patents

Multi-split air conditioning system Download PDF

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Publication number
CN112228972A
CN112228972A CN202011131794.7A CN202011131794A CN112228972A CN 112228972 A CN112228972 A CN 112228972A CN 202011131794 A CN202011131794 A CN 202011131794A CN 112228972 A CN112228972 A CN 112228972A
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China
Prior art keywords
refrigerant
pressure
indoor
dryness
current
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CN202011131794.7A
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CN112228972B (en
Inventor
董现
王战术
高玉泽
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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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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F24—HEATING; RANGES; VENTILATING
    • F24F—AIR-CONDITIONING; AIR-HUMIDIFICATION; VENTILATION; USE OF AIR CURRENTS FOR SCREENING
    • F24F3/00—Air-conditioning systems in which conditioned primary air is supplied from one or more central stations to distributing units in the rooms or spaces where it may receive secondary treatment; Apparatus specially designed for such systems
    • F24F3/06—Air-conditioning systems in which conditioned primary air is supplied from one or more central stations to distributing units in the rooms or spaces where it may receive secondary treatment; Apparatus specially designed for such systems characterised by the arrangements for the supply of heat-exchange fluid for the subsequent treatment of primary air in the room units
    • F24F3/065—Air-conditioning systems in which conditioned primary air is supplied from one or more central stations to distributing units in the rooms or spaces where it may receive secondary treatment; Apparatus specially designed for such systems characterised by the arrangements for the supply of heat-exchange fluid for the subsequent treatment of primary air in the room units with a plurality of evaporators or condensers
    • 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
    • F24F11/30—Control or safety arrangements for purposes related to the operation of the system, e.g. for safety or monitoring
    • 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
    • F24F11/50—Control or safety arrangements characterised by user interfaces or communication
    • F24F11/61—Control or safety arrangements characterised by user interfaces or communication using timers
    • 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
    • F24F11/62—Control or safety arrangements characterised by the type of control or by internal processing, e.g. using fuzzy logic, adaptive control or estimation of values
    • F24F11/63—Electronic processing
    • F24F11/64—Electronic processing using pre-stored data
    • 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
    • F24F11/83—Control systems characterised by their outputs; Constructional details thereof for controlling the temperature of the supplied air by controlling the supply of heat-exchange fluids to heat-exchangers
    • 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
    • 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
    • F24F11/87—Control systems characterised by their outputs; Constructional details thereof for controlling the temperature of the supplied air by controlling absorption or discharge of heat in outdoor units
    • F24F11/871—Control systems characterised by their outputs; Constructional details thereof for controlling the temperature of the supplied air by controlling absorption or discharge of heat in outdoor units by controlling outdoor fans
    • 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
    • F24F11/89—Arrangement or mounting of control or safety devices
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F24—HEATING; RANGES; VENTILATING
    • F24F—AIR-CONDITIONING; AIR-HUMIDIFICATION; VENTILATION; USE OF AIR CURRENTS FOR SCREENING
    • F24F13/00—Details common to, or for air-conditioning, air-humidification, ventilation or use of air currents for screening
    • F24F13/24—Means for preventing or suppressing noise
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F24—HEATING; RANGES; VENTILATING
    • F24F—AIR-CONDITIONING; AIR-HUMIDIFICATION; VENTILATION; USE OF AIR CURRENTS FOR SCREENING
    • F24F13/00—Details common to, or for air-conditioning, air-humidification, ventilation or use of air currents for screening
    • F24F13/24—Means for preventing or suppressing noise
    • F24F2013/247—Active noise-suppression

Abstract

The invention provides a multi-split air conditioning system, which can reduce the noise of a refrigerant without additionally arranging related parts, thereby simplifying the space structure of an indoor unit and reducing the production cost of a whole unit. The multi-split air conditioning system includes: the outdoor unit comprises an outdoor heat exchanger, a compressor, an outdoor throttling element and an outdoor fan; the indoor unit comprises a plurality of indoor units connected in parallel, wherein each indoor unit comprises an indoor heat exchanger and an indoor throttling element; the multi-split air conditioning system further includes: a controller configured to control a dryness x ≠ a of the refrigerant at the inlet of the indoor heat exchanger, wherein a is an equal dryness value corresponding to an equal dryness line in a pressure-enthalpy diagram of the refrigerant. The invention eliminates the flowing noise of the refrigerant by controlling the dryness x of the refrigerant at the inlet of the indoor heat exchanger (namely before flowing through the indoor heat exchanger) of the multi-split air-conditioning system by the controller, does not need to add other parts, simplifies the structure of the indoor unit, reduces the production cost of the whole unit and improves the competitiveness of the product cost.

Description

Multi-split air conditioning system
Technical Field
The invention belongs to the technical field of air conditioners, and particularly relates to a multi-split air conditioning system capable of reducing noise of a refrigerant.
Background
The multi-split air conditioning system is one of central air conditioners and can be called as 'one split multiple', wherein one outdoor unit refers to one outdoor unit, a plurality of indoor units refer to a plurality of indoor units, the outdoor unit adopts an air cooling heat exchange mode, and the indoor unit adopts an evaporation heat exchange mode to realize indoor refrigeration, so that the multi-split air conditioning system is widely used in small and medium-sized buildings.
Refrigerant noise is generally present in the indoor unit during a cooling operation. The noise caused by the refrigerant is generally dependent on the phase and flow pattern of the refrigerant. In the refrigeration state of the multi-split air-conditioning unit, high-temperature and high-pressure gaseous refrigerant is efficiently subjected to heat exchange by the condenser and then is changed into high-pressure and super-cooled liquid refrigerant, and the liquid refrigerant is conveyed to the indoor unit through the indoor and outdoor unit connecting pipeline. Because the in-line resistance of fluid friction exists in the indoor and outdoor connecting pipelines of the multi-connected unit, the supercooling degree of the liquid refrigerant flowing into the indoor unit is lower than the supercooling degree of the outlet of the condenser, and if the in-line resistance of the indoor and outdoor connecting pipelines is large, the high-pressure supercooled refrigerant is even changed into a two-phase flow refrigerant. When the refrigerant passes through the electronic expansion valve of the indoor unit at a high speed, the refrigerant flows through the throttling component to generate a certain pressure drop and form turbulence and turbulence sound waves. The relevant research literature shows that when the dryness (i.e. the proportion of dry saturated vapor in wet vapor of the refrigerant) x = a (a is an equal dryness value corresponding to an equal dryness line in a pressure-enthalpy diagram of the refrigerant) of the refrigerant at the inlet of the indoor heat exchanger at the downstream of the electronic expansion valve, the noise of the refrigerant flow sound of the indoor unit in a refrigerating state is far higher than a normal level.
The refrigerant flows through the electronic expansion valve to generate two-phase flow refrigerant and turbulent sound wave, and the intensity of the flow noise of the refrigerant is mainly determined by the flow state of the two-phase flow and the intensity of the turbulent sound wave. The elimination of the flow noise of the refrigeration refrigerant in the multi-split air conditioner industry is mainly realized by reducing the dryness of the refrigerant by measures of adding a capillary tube, a special-shaped pipeline, a throttling part and the like. The capillary tube is added at the upstream or downstream of the electronic expansion valve to solve the noise of the flowing sound of the refrigerant, but the heating increasing capillary tube increases the on-way resistance of the indoor unit pipeline and reduces the heating capacity; meanwhile, the indoor unit is additionally provided with pipeline parts, so that the effective space loss of the indoor unit can be increased, the risk of reducing the effective heat exchange area of the indoor unit exists, the product cost can be increased by additionally arranging the pipeline parts, and the competitiveness of the product cost is weakened.
Disclosure of Invention
The invention provides a multi-split air conditioning system, which can reduce the noise of a refrigerant without additionally arranging related parts, thereby simplifying the space structure of an indoor unit and reducing the production cost of a whole unit.
In some embodiments of the present application, a multi-split air conditioning system includes:
the outdoor unit comprises an outdoor heat exchanger, a compressor, an outdoor throttling element and an outdoor fan;
the indoor unit comprises a plurality of indoor units connected in parallel, wherein each indoor unit comprises an indoor heat exchanger and an indoor throttling element;
the multi-split air conditioning system further includes: a controller configured to control a dryness x ≠ a of the refrigerant at the inlet of the indoor heat exchanger, wherein a is an equal dryness value corresponding to an equal dryness line in a pressure-enthalpy diagram of the refrigerant.
The refrigerant dryness x ≠ a at the inlet of the indoor heat exchanger (namely before flowing through the indoor unit) of the multi-split air-conditioning system is controlled by the controller to eliminate the flowing noise of the refrigerant, other parts do not need to be added, the space structure of the indoor unit is simplified, the production cost of the whole unit is reduced, and the product cost competitiveness is improved.
In some embodiments of the present application, the method of controlling the refrigerant dryness x ≠ a is:
s1, initializing the cycle number n =1 of the system;
s2, obtainingTaking the refrigerant dryness x, comparing the refrigerant dryness x with a, and executing S6 if the refrigerant dryness x is not equal to a; if the refrigerant dryness x = a, increasing the rotation speed of the outdoor fan by delta R1The outdoor fan operates at the current rotating speed for a time t1Then obtaining the current refrigerant dryness x, Delta R1、t1Is a preset value;
s3, comparing the current refrigerant dryness x with a, and executing S6 if the current refrigerant dryness x is not equal to a; if the current refrigerant dryness x = a, reducing the rotation speed of the compressor by delta R2The opening degree of the indoor throttling element is kept unchanged, and the system stabilizes the running time t according to the current rotating speed of the outdoor fan and the current rotating speed of the compressor2Then obtaining the current refrigerant dryness x, Delta R2、t2Is a preset value;
s4, comparing the current refrigerant quality x with a, and if the current refrigerant quality x is not equal to a, executing S6, wherein the opening degree of the indoor throttling element is kept unchanged; if the current refrigerant quality x = a, n is increased by 1;
s5, judging whether N is equal to or less than N, wherein N is a preset cycle number and is a natural number, if N is equal to or less than N, returning to S2, or N is more than N, and executing S6;
and S6, finishing, keeping the current rotating speed of the outdoor fan and the current rotating speed of the compressor unchanged, and enabling the system to stably operate.
In some embodiments of the present application, 2 ≦ N ≦ 5.
In some embodiments of the present application, the method for obtaining the refrigerant dryness x is:
obtaining the current enthalpy value H of the refrigerant at the inlet of the indoor heat exchanger4；
Obtaining the current refrigerant pressure P at the inlet of the indoor heat exchanger4；
By using the enthalpy value H of the refrigerant in a pressure-enthalpy diagram4Refrigerant pressure P4And obtaining the refrigerant dryness x according to the one-to-one correspondence relationship of the refrigerant dryness x.
In some embodiments of the present application, the enthalpy value H of the refrigerant at the inlet of the indoor throttling element is obtained by obtaining the current enthalpy value H of the refrigerant3To obtain the enthalpy value H of the refrigerant4，H3=H4(ii) a In particular, the refrigerant enthalpy value H3The acquisition method comprises the following steps:
obtaining the current refrigerant temperature T at the inlet of the indoor throttling element3；
Obtaining the current refrigerant pressure P at the inlet of the indoor throttling element3；
Using refrigerant temperature T in pressure-enthalpy diagram3Refrigerant pressure P3With the enthalpy H of the refrigerant3To obtain the enthalpy value H of the refrigerant3。
In some embodiments of the present application, the refrigerant pressure P is calculated by the formula:
P3=Pd-△P1-△P2in which P isdFor the discharge pressure of said compressor, Δ P1For on-way pressure loss of the pipeline, Δ P2For the pressure loss, Δ P, of the outdoor heat exchanger1、△P2Is a set value.
In some embodiments of the present application, a high pressure sensor is provided at the discharge port of the compressor, PdObtained by the high pressure sensor.
In some embodiments of the present application, a temperature sensor is provided at the inlet of the indoor throttling element, and the refrigerant temperature T is3Obtained by the temperature sensor.
In some embodiments of the present application, the refrigerant pressure P4The calculation formula of (2) is as follows:
P4=PS+PS_setin which P isSIs the suction pressure of the suction side of the compressor, PS_setIs a suction side pressure loss compensation coefficient of the compressor, which is a set value.
In some embodiments of the present application, a low pressure sensor is provided at the suction port of the compressor, and the PSObtained by the low pressure sensor.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed to be used in the description of the embodiments or the prior art will be briefly introduced below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to these drawings without creative efforts.
Fig. 1 is a schematic diagram of a cycle of a multi-split air conditioning system according to an embodiment;
fig. 2 is a refrigerant pressure-enthalpy diagram of a multi-split air conditioning system according to an embodiment;
fig. 3 is a control flowchart of making the refrigerant dryness x ≠ a in the multi-split air conditioning system according to the embodiment.
Description of the drawings:
100-an outdoor unit; 110-outdoor heat exchanger; 120-a compressor; 130-an outdoor throttling element; 140-outdoor fan; 150-high pressure sensor; 160-low pressure sensor; 170-four-way valve; 180-exhaust temperature sensor;
200-indoor units; 210-an indoor unit; 211-indoor heat exchanger; 212-an indoor throttling element; 213-a temperature sensor;
300-trachea; 400-liquid tube; 500-a first shut-off valve; 600-second stop valve.
Detailed Description
The technical scheme of the invention is clearly and completely described in the following with reference to the accompanying drawings. In the description of the present invention, it should be noted that the terms "center", "upper", "lower", "horizontal", "inner", "outer", etc. indicate orientations or positional relationships based on those shown in the drawings, and are only for convenience of description and simplification of description, but do not indicate or imply that the referred device or element must have a specific orientation, be constructed in a specific orientation, and be operated, and thus should not be construed as limiting the present invention.
In the description of the present invention, it should be noted that, unless otherwise explicitly specified or limited, the terms "mounted," "connected," and "connected" are to be construed broadly, e.g., as meaning either a fixed connection, a removable connection, or an integral connection; they may be connected directly or indirectly through intervening media, or they may be interconnected between two elements. The specific meanings of the above terms in the present invention can be understood in specific cases to those skilled in the art.
In addition, the technical features involved in the different embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.
The multi-split air conditioning system is one of central air conditioners and can be called as 'one split multiple', wherein one outdoor unit refers to one outdoor unit, a plurality of indoor units refer to a plurality of indoor units, the outdoor unit adopts an air cooling heat exchange mode, and the indoor units adopt an evaporation heat exchange mode to realize indoor refrigeration.
The air conditioning system performs a refrigeration cycle of the air conditioner by using a compressor, a condenser, an expansion valve, and an evaporator in the present application. The refrigeration cycle includes a series of processes involving compression, condensation, expansion, and evaporation, and supplies refrigerant to the air that has been conditioned and heat-exchanged.
The compressor compresses a refrigerant gas in a high-temperature and high-pressure state and discharges the compressed refrigerant gas. 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.
When the refrigerant flows through the evaporator expansion valve, the refrigerant is changed into a low-pressure low-temperature two-phase flow refrigerant, and after the refrigerant absorbs heat from a room, the gas refrigerant in a low-temperature low-pressure state returns to the compressor. The evaporator can achieve a cooling effect by heat-exchanging with a material to be cooled using latent heat of evaporation of a refrigerant. The air conditioner can 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 and an outdoor heat exchanger, the indoor unit of the air conditioner includes an indoor heat exchanger, and an expansion valve may be provided in the indoor unit or the outdoor unit.
The indoor heat exchanger and the outdoor heat exchanger serve as a condenser or an evaporator. When the indoor heat exchanger is used as a condenser, the air conditioner is used as a heater in a heating mode, and when the indoor heat exchanger is used as an evaporator, the air conditioner is used as a cooler in a cooling mode.
Referring to fig. 1, the multi-split air conditioning system in the embodiment of the present disclosure includes an outdoor unit 100 and an indoor unit 200, where the outdoor unit 100 includes an outdoor heat exchanger 110, a compressor 120, an outdoor throttling element 130, an outdoor fan 140, a four-way valve 170, and the like; the indoor unit 200 comprises a plurality of indoor units 210 connected in parallel, each indoor unit 210 comprises an indoor heat exchanger 211 and an indoor throttling element 212, and the indoor throttling element 212 and the outdoor throttling element 130 are electronic expansion valves; the indoor unit 210 is connected to the outdoor unit 100 through an air pipe 300 and a liquid pipe 400, respectively, the air pipe 300 is provided with a first stop valve 500, and the liquid pipe 400 is provided with a second stop valve 600. In order to solve the problem of refrigerant flow noise of the indoor unit in a cooling state, in the multi-split air conditioning system in the embodiment, the dryness of the refrigerant (namely, the proportion of dry saturated vapor contained in wet vapor of the refrigerant) at the inlet of the indoor heat exchanger is controlled to be x ≠ a, wherein a is an equal dryness value corresponding to an equal dryness line in a pressure-enthalpy diagram of the system refrigerant.
When the dryness x = a of the refrigerant at the inlet of the indoor heat exchanger 211 at the downstream of the indoor throttling element 212 is far higher than the normal level, the dryness x ≠ a of the refrigerant at the inlet of the indoor heat exchanger 211 is controlled, namely, the dryness of the refrigerant flowing into the indoor unit 210 is far away from the isochronism line, so that the flow noise of the refrigerant under the refrigeration working condition is reduced.
Referring to fig. 2, a pressure-enthalpy diagram, which refers to a graph of pressure versus enthalpy, is commonly used for refrigerant analysis in refrigeration engineering. The ordinate of the graph is the logarithmic value lgp of the absolute pressure (the value indicated in the graph is the absolute value of the pressure), and the abscissa is the specific enthalpy value H.
The meaning of the enthalpy diagram curve can be summarized by one point (critical point), two lines (saturated liquid line, saturated steam line), three regions (liquid phase region, two phase region, gas phase region), five states (supercooled liquid state, saturated liquid state, superheated steam state, saturated steam state, wet steam state) and eight lines (isobars, isenthalpics, saturated liquid line, saturated steam line, isocrycity line, isentropic line, geometric volume line, isotherm).
One point (critical point):
the critical point K is the intersection of two thick solid lines. At this point, the liquid and gaseous differences disappear.
Second line (saturated liquid line, saturated vapor line):
a thick solid line KA on the left of the point K is a saturated liquid line, and the state of any point on the KA line is saturated liquid with corresponding pressure; the thick solid line KB to the right of the point K is a saturated steam line, and the state at any point on the line KB is a saturated steam state, or dry steam.
And (3) three zones:
ka left side — supercooled liquid region C, in which the temperature is lower than the saturation temperature at the same pressure;
kb right-side-superheated steam zone D, in which the steam temperature is higher than the saturation temperature at the same pressure;
ka and Kb-a wet vapor area E, namely a gas-liquid coexisting area, wherein the refrigerant in the area is in a saturated state, and the pressure and the temperature are in one-to-one correspondence;
during refrigeration, the evaporation and condensation processes are mainly carried out in the wet vapor region, and the compression process is carried out in the superheated vapor region.
Six sets of isoparametric lines:
there are eight lines in the pressure-enthalpy (LgP-H) diagram: isobars (LgP), isenthalpic lines (enthalpies), Saturated Liquid lines (structured Liquid), isentropic lines (Entropy), isochoric lines (Volume), dry Saturated steam lines (structured Vapor), isocrycity lines (Quality), isotherms (Temperature);
(1) isobaric line I: horizontal thin solid lines parallel to the abscissa axis on the pressure-enthalpy diagram are all isobars, and the pressures of the same horizontal line are all equal;
(2) isenthalpic line ii: the thin solid line vertical to the abscissa axis on the pressure-enthalpy diagram is an equal enthalpy line, and the enthalpy values of the working media on the same equal enthalpy line are the same no matter how the working media are in the same state;
(3) isotherm iii: the pressure-enthalpy diagram is represented by dotted lines as isotherms, the isotherms have different changing shapes in different regions, and the isotherms are almost vertical to the abscissa axis in the supercooling region; the wet steam area is a horizontal line parallel to the abscissa axis; the superheated steam area is an inclined line which is sharply bent towards the lower right;
(4) isentropic line iv: a thin solid line inclined from left to right and above on the pressure-enthalpy diagram is an isentropic line, and the compression process of the refrigerant is carried out along the isentropic line, so that the isentropic line of the superheated steam zone is used more, and the isentropic line on the lgp-h diagram takes a saturated steam line as a starting point;
(5) an isochoric line V: the dotted line which inclines slightly upwards from left to right on the graph is an isovolumetric line which is flat compared with an isentropic line, and the specific capacity value of the suction point of the refrigeration compressor is searched by the isovolumetric line commonly used in refrigeration;
(6) and VI: starting from the critical point K, connecting the same dryness points of the wet steam area C to form a dotted line which is an equal dryness line and only exists in the wet steam area;
the pressure-enthalpy diagram of most refrigerants is known, and out of the six state parameters (pressure, temperature, specific volume, dryness, enthalpy and entropy), as long as any two state parameter values are known, the thermodynamic state of the refrigerant can be determined, and further, the state point of the refrigerant can be determined on the pressure-enthalpy diagram, and the other four state parameter values of the point can be found.
In fig. 1, point 1 indicates the compressor suction inlet position, point 2 indicates the compressor discharge outlet position, point 3 indicates the position before the inlet of the indoor throttling element, and point 4 indicates the indoor heat exchanger refrigerant inlet position. When the theoretical multi-split air conditioning system performs refrigeration operation, a low-temperature low-pressure gaseous refrigerant is adiabatically compressed by the compressor 120 and then is changed into a high-temperature high-pressure gaseous refrigerant (1 → 2, namely, the refrigerant flows from 1 point to 2 points), the high-temperature high-pressure gaseous refrigerant is efficiently heat-exchanged by the outdoor heat exchanger 110 and then is changed into a super-cooled high-pressure liquid refrigerant (2 → 3, namely, the refrigerant flows from 2 points to 3 points), the high-pressure super-cooled liquid refrigerant is changed into a low-temperature low-pressure two-phase flow refrigerant (3 → 4, namely, the refrigerant flows from 3 points to 4 points) by the electronic expansion valve of the indoor unit, the low-temperature low-pressure two-phase flow refrigerant is changed into a low-temperature low-pressure gaseous refrigerant after. In addition, the approximately trapezoidal curve in fig. 2 is an inverse carnot cycle diagram of the refrigerant, and the meanings indicated by points 1, 2, 3, and 4 in fig. 2 are the same as those in fig. 1 during cooling, that is, point 1 indicates the compressor suction inlet position, point 2 indicates the compressor discharge outlet position, point 3 indicates the position before the inlet of the indoor throttling element, and point 4 indicates the indoor heat exchanger refrigerant inlet position.
Through experimental tests, the dryness of the refrigerant at the 4-point position is closely related to the rotating speed of the outdoor fan 140 and the rotating speed of the compressor 120. Specifically, referring to fig. 3, the control flow of the refrigerant dryness x ≠ a in the present embodiment is:
s1, initializing the cycle number n =1 of the system;
s2, acquiring the refrigerant dryness x, comparing the refrigerant dryness x with a, and executing S6 if the refrigerant dryness x is not equal to a; if the refrigerant dryness x = a, the rotation speed of the outdoor fan 140 is increased by Δ R1The outdoor fan 140 operates at the current rotation speed for a time t1Then obtaining the current refrigerant quality x, wherein delta R1、t1Is a preset value, Δ R in this embodiment1Preferably 25-65rpm, t1Preferably 1-5min, all measured by tests;
s3, comparing the current refrigerant dryness x with a, and executing S6 if the current refrigerant dryness x is not equal to a; if the current refrigerant quality x = a, the rotation speed of the compressor 120 is reduced by Δ R2The opening of the indoor throttling element 212 (i.e. the electronic expansion valve) is kept constant, and the system is stabilized at the current rotation speed of the outdoor fan 140 and the current rotation speed of the compressor 120 for the running time t2Then obtaining the current refrigerant dryness x, Delta R2、t2To a predetermined value,. DELTA.R2Preferably 5-15Hz, t2Preferably 1-5min, all measured by tests;
s4, comparing the current dryness x with a, and if the current dryness x is not equal to a, executing S6, wherein the opening degree of the indoor throttling element 212 (i.e. the electronic expansion valve) is kept unchanged; if the current refrigerant quality x = a, n is increased by 1;
s5, judging whether N is equal to or less than N, wherein N is a preset cycle number and is a natural number, if N is equal to or less than N, returning to S2, or N is more than N, and executing S6;
and S6, ending, keeping the current rotating speed of the outdoor fan 140 and the current rotating speed of the compressor 120 unchanged, and stably operating the system.
Wherein N is more than or equal to 2 and less than or equal to 5.
In detail, the method for acquiring the dryness x of the refrigerant at 4 points comprises the following steps:
obtaining the current enthalpy value H of the refrigerant at 4 points4；
Obtaining the current refrigerant pressure P at the inlet of the indoor heat exchanger4；
Utilizing preset stored enthalpy value H of refrigerant in pressure-enthalpy diagram1Refrigerant pressure P1And obtaining the refrigerant quality x at the current 4 points according to the one-to-one correspondence relation of the refrigerant quality x.
Due to the refrigerant temperature T at the inlet (i.e., 3 o' clock position) of the indoor restriction element 2123And refrigerant pressure P3Is easily obtained, and the corresponding enthalpy value H of the refrigerant3 Is easy to obtain. Meanwhile, as can be seen from the pressure-enthalpy diagram, the enthalpy value H of the refrigerant at 4 points4And the enthalpy value H of the refrigerant at the point 33Equal, i.e. H3= H4Then the enthalpy value H of the refrigerant at 3 points can be obtained3To obtain the enthalpy value H of the refrigerant at 4 points4And the method is easy to implement.
Specifically, the enthalpy value H of the refrigerant at 3 points3The acquisition method comprises the following steps:
acquiring the current refrigerant temperature T at 3 points3；
Acquiring the current refrigerant pressure P at the point 33；
Using refrigerant temperature T in pressure-enthalpy diagram3Refrigerant pressure P3With the enthalpy H of the refrigerant3To obtain the enthalpy value H of the refrigerant3。
More specifically, the current refrigerant pressure P at point 33Is calculated byThe formula is as follows:
P3=Pd-△P1-△P2in which P isdTo obtain the discharge pressure of the compressor 120, in the present embodiment, as shown in fig. 1, a high pressure sensor 150, P, is provided at the discharge outlet (i.e. at the 2-point) of the compressor 120dMeasured by high pressure sensor 150; delta P1For on-way pressure loss of the pipeline, Δ P2Is the pressure loss, Δ P, of the outdoor heat exchanger 1101、△P2The set value can be determined by experiments.
As a specific implementation manner, in the present embodiment, the following formulas are used to obtain Δ P1 and Δ P2, and are preset and stored in the controller storage unit.
Pipeline on-way pressure loss: delta P1=△P11 +△P12；
△P11: the pressure drop of the air pipe 300 from the discharge port of the compressor 120 to the outdoor heat exchanger 110;
△P11=ξ1×L11×ρ1×（VP×Fb）2×10-6/D1+P11_set；
wherein ξ1: a constant;
L11: the length of the air pipe 300 from the discharge port of the compressor 120 to the outdoor heat exchanger 110;
ρ1: discharge density, ρ, of the compressor 1201Can be based on the known compressor discharge pressure PdAnd compressor discharge temperature TdObtained by consulting in a refrigerant physical property parameter table or according to the known compressor discharge pressure PdAnd compressor discharge temperature TdObtained by using a median difference algorithm, the compressor discharge temperature TdMeasured by the discharge temperature sensor 180 at the discharge of the compressor 120 (i.e., at point 2);
VP: theoretical displacement of the compressor;
Fb: the rotational speed of the compressor;
D1: the diameter of the trachea;
P11_set: air pipe 300 pressure loss compensation factor;
△P12: pressure drop of the outdoor heat exchanger 110 to the indoor unit liquid pipe 400;
△P12=ξ2×L12×ρ2×（VP×Fb）2×10-6/D1+P12_set；
wherein ξ2: a constant;
L12: the length of the liquid pipe 400 from the outdoor heat exchanger 110 to the indoor unit;
ρ2: the density of the saturated liquid refrigerant in the outdoor heat exchanger 100, which can be obtained from the refrigerant physical property parameter table;
VP: theoretical displacement of the compressor;
Fb: the rotational speed of the compressor;
D2: the diameter of the liquid pipe is 400;
P12_set: the pressure loss compensation coefficient of the outdoor heat exchanger 110 to the liquid pipe 400.
Pressure loss of the outdoor heat exchanger 110: delta P2=ξ3×（Pdo-PTemin）+△P2_set；
Wherein ξ3: a constant;
Pdo: saturated gas pressure corresponding to compressor discharge pressure, compressor discharge pressure PdThe measured pressure is measured by the high pressure sensor 150, and the corresponding saturated gas pressure P is known by the pressure-enthalpy diagramdo；
PTemin: the saturation pressure corresponding to the saturated condensation temperature of the outdoor heat exchanger corresponds to the saturation pressure and the saturation temperature of the liquid refrigerant one by one according to the inherent properties of the refrigerant in thermodynamics;
△P2_set: and (4) compensating coefficient of pressure loss of the outdoor heat exchanger.
In this embodiment, as shown in fig. 1, a temperature sensor 213 is provided at the inlet of the indoor throttling element 212, and the refrigerant temperature T at the inlet (i.e. 3 o' clock) of the indoor throttling element 212 is set3By temperature sensingAnd obtained by the unit 213.
In the present embodiment, the refrigerant pressure P at 4 points4The calculation formula of (2) is as follows:
P4=PS+PS_setin which P isSIs the suction side suction pressure, P, of the compressor 120S_setIs the suction side pressure loss compensation factor of the compressor 120, which is a set value.
Further, a low pressure sensor 160, P, is provided at the suction port of the compressor 120SObtained by a low pressure sensor 160.
Finally, it should be noted that: the above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.

Claims (10)

1. A multi-split air conditioning system comprising:
the outdoor unit comprises an outdoor heat exchanger, a compressor, an outdoor throttling element and an outdoor fan;
the indoor unit comprises a plurality of indoor units connected in parallel, wherein each indoor unit comprises an indoor heat exchanger and an indoor throttling element;
it is characterized in that the multi-split air conditioning system further comprises:
a controller configured to control a dryness x ≠ a of the refrigerant at the inlet of the indoor heat exchanger, wherein a is an equal dryness value corresponding to an equal dryness line in a pressure-enthalpy diagram of the refrigerant.
2. The multi-split air conditioning system as claimed in claim 1, wherein the method of controlling the refrigerant dryness x ≠ a is:
s1, initializing the cycle number n =1 of the system;
s2, acquisition SystemComparing the refrigerant dryness x with a, and executing S6 if the refrigerant dryness x is not equal to a; if the refrigerant dryness x = a, increasing the rotation speed of the outdoor fan by delta R1The outdoor fan operates at the current rotating speed for a time t1Then obtaining the current refrigerant dryness x, Delta R1、t1Is a preset value;
s3, comparing the current refrigerant dryness x with a, and executing S6 if the current refrigerant dryness x is not equal to a; if the current refrigerant dryness x = a, reducing the rotation speed of the compressor by delta R2The opening degree of the indoor throttling element is kept unchanged, and the system stabilizes the running time t according to the current rotating speed of the outdoor fan and the current rotating speed of the compressor2Then obtaining the current refrigerant dryness x, Delta R2、t2Is a preset value;
s4, comparing the current refrigerant quality x with a, and if the current refrigerant quality x is not equal to a, executing S6, wherein the opening degree of the indoor throttling element is kept unchanged; if the current refrigerant quality x = a, n is increased by 1;
s5, judging whether N is equal to or less than N, wherein N is a preset cycle number and is a natural number, if N is equal to or less than N, returning to S2, or N is more than N, and executing S6;
and S6, finishing, keeping the current rotating speed of the outdoor fan and the current rotating speed of the compressor unchanged, and enabling the system to stably operate.
3. A multi-split air conditioning system as set forth in claim 2,
2≤N≤5。
4. the multi-split air conditioning system as claimed in claim 2, wherein the refrigerant quality x is obtained by:
obtaining the current enthalpy value H of the refrigerant at the inlet of the indoor heat exchanger4；
Obtaining the current refrigerant pressure P at the inlet of the indoor heat exchanger4；
By using the enthalpy value H of the refrigerant in a pressure-enthalpy diagram4Refrigerant pressure P4One to one with refrigerant quality xIn response, the refrigerant quality x is obtained.
5. A multi-split air conditioning system as claimed in claim 4,
by obtaining the current enthalpy value H of the refrigerant at the inlet of the indoor throttling element3To obtain the enthalpy value H of the refrigerant4，H3=H4Enthalpy value H of said refrigerant3The acquisition method comprises the following steps:
obtaining the current refrigerant temperature T at the inlet of the indoor throttling element3；
Obtaining the current refrigerant pressure P at the inlet of the indoor throttling element3；
Using refrigerant temperature T in pressure-enthalpy diagram3Refrigerant pressure P3With the enthalpy H of the refrigerant3To obtain the enthalpy value H of the refrigerant3。
6. A multi-split air conditioning system as claimed in claim 5, wherein the refrigerant pressure P3The calculation formula of (2) is as follows:
P3=Pd-△P1-△P2in which P isdFor the discharge pressure of said compressor, Δ P1For on-way pressure loss of the pipeline, Δ P2For the pressure loss, Δ P, of the outdoor heat exchanger1、△P2Is a set value.
7. A multi-split air conditioning system as claimed in claim 6,
the air outlet of the compressor is provided with a high-pressure sensor, and P isdObtained by the high pressure sensor.
8. A multi-split air conditioning system as set forth in claim 5,
a temperature sensor is arranged at the inlet of the indoor throttling element, and the temperature T of the refrigerant3Obtained by the temperature sensor.
9. A multi-split air conditioning system as claimed in claim 4, wherein the refrigerant pressure P4The calculation formula of (2) is as follows:
P4=PS+PS_setin which P isSIs the suction pressure of the suction side of the compressor, PS_setIs a suction side pressure loss compensation coefficient of the compressor, which is a set value.
10. A multi-split air conditioning system as recited in claim 9,
the air suction port of the compressor is provided with a low-pressure sensor, and P isSObtained by the low pressure sensor.
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