Multi-connected system

Abstract

The application discloses a multi-connected system, determines the load rate of the indoor unit in operation; when the load rate of the indoor unit in operation is below the set load rate: the operating frequency of the compressor is controlled to be the first frequency; the exhaust pressure target value of the compressor is determined to be the first target exhaust pressure value, and the gear or rotating speed of the outdoor fan is controlled so that the exhaust pressure of the compressor reaches the first target exhaust pressure value or the threshold range of the first target exhaust pressure value; wherein the first target exhaust pressure value is a pressure value higher than the normal exhaust pressure value. When the load rate of the indoor unit in operation is low, the multi-connected system increases the exhaust pressure of the compressor and the pressure difference between the outdoor heat exchanger and the indoor expansion valve, so that the liquid refrigerant remaining at the bottom of the outdoor heat exchanger is reduced, more refrigerant flows out of the outdoor heat exchanger to participate in the refrigeration cycle, the actual refrigerant circulation amount of the multi-connected system is ensured, the refrigerant at the inlet of the indoor unit is in a supercooled state, and thus the refrigerant sound of the indoor unit when the load rate of the indoor unit in operation is low is reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the air conditioning technical field, and particularly to a multi-connected system. BACKGROUND

[0002] The compressor frequency of the multi-connected system is related to the load rate of the running indoor unit. When the load rate of the running indoor unit is small, the running frequency of the compressor is less adaptive. However, under the refrigeration working condition, when the compressor runs at a low frequency, the compressor provides less power to the refrigerant for circulation, and at the same time, due to the gravity, liquid refrigerant is left at the bottom of the outdoor heat exchanger, so that the actual amount of refrigerant participating in the refrigeration cycle is insufficient, which causes the refrigerant at the inlet of the indoor unit to be in a two-phase state, resulting in high refrigerant noise at the indoor expansion valve.

[0003] The above information disclosed in the background of the application is only used to increase the understanding of the background of the application, and therefore, it can include prior art known to those skilled in the art. SUMMARY

[0004] The present application provides a multi-connected system, which solves the problem of refrigerant noise at the indoor unit when the load rate of the running indoor unit is small and the compressor runs at a low frequency under the refrigeration working condition of the existing multi-connected system.

[0005] To achieve the above-mentioned application purposes, the present application adopts the following technical solutions:

[0006] A multi-connected system, comprising:

[0007] An outdoor unit, comprising a compressor, an outdoor heat exchanger, and an outdoor fan;

[0008] An exhaust pressure detection module for detecting the exhaust pressure of the compressor;

[0009] At least two indoor units, the multi-connected system further comprising:

[0010] A control module configured to determine the load rate of the running indoor unit;

[0011] When the load rate of the running indoor unit is below a set load rate:

[0012] The running frequency of the compressor is controlled to be a first frequency;

[0013] The target value of the exhaust pressure of the compressor is determined to be a first target exhaust pressure value, and the gear or speed of the outdoor fan is controlled so that the exhaust pressure of the compressor reaches the first target exhaust pressure value;

[0014] The first target exhaust pressure value is a value within a set threshold range of a standard exhaust pressure value, the standard exhaust pressure value is the exhaust pressure value corresponding to the standard working condition, the indoor unit is fully opened, and the compressor runs at a second frequency; the first frequency is less than the second frequency.

[0015] The technical scheme has the following advantages or beneficial effects: the multi-connected system comprises an outdoor unit, at least two indoor units, a compressor discharge pressure detection module, and a control module, the control module is configured to determine an on-machine indoor unit load rate; when the on-machine indoor unit load rate is below a set load rate: the control module controls a running frequency of the compressor to be a first frequency; the control module determines a target value of the discharge pressure of the compressor to be a first target discharge pressure value, and controls a gear or rotating speed of an outdoor fan so that the discharge pressure of the compressor reaches the first target discharge pressure value; the first target discharge pressure value is a value within a threshold range of a standard discharge pressure value, the standard discharge pressure value is a discharge pressure value corresponding to a standard working condition, full opening of the indoor unit, and running of the compressor at a second frequency; the first frequency < the second frequency. The multi-connected system optimizes the discharge pressure of the compressor when the on-machine indoor unit load rate is low: when the on-machine indoor unit load rate is below the set load rate and the compressor runs at the first frequency, the discharge pressure of the compressor is increased to the discharge pressure value corresponding to the standard working condition, full opening of the indoor unit, and running of the compressor at the second frequency, and the pressure difference between the outdoor heat exchanger and the indoor expansion valve is increased. The large pressure difference can reduce the liquid refrigerant remaining at the bottom of the outdoor heat exchanger, and more refrigerant flows out of the outdoor heat exchanger to participate in the refrigeration cycle under the action of the pressure difference, thereby ensuring the actual refrigerant circulation amount of the multi-connected system, realizing the supercooling state of the refrigerant at the inlet of the indoor unit, and reducing the indoor unit refrigerant sound when the refrigeration on-machine indoor unit load rate is low, thereby improving the user comfort.

[0016] In some embodiments, the first frequency is a frequency within a threshold range of a lower limit value of a normal running frequency range of the compressor.

[0017] The second frequency is a frequency within a threshold range of an upper limit value of the normal running frequency range of the compressor.

[0018] The technical scheme has the following advantages or beneficial effects: the setting of the first frequency can ensure that the frequency is adapted to the on-machine indoor unit load rate, and the setting of the second frequency can ensure that the discharge pressure of the compressor can completely avoid the indoor refrigerant sound.

[0019] In some embodiments, the multi-connected system comprises a storage module.

[0020] The storage module is configured to store different first target discharge pressure values corresponding to different on-machine indoor unit load rate intervals, or store a correlation between the on-machine indoor unit load rate and the first target discharge pressure value.

[0021] The control module is configured to determine the first target discharge pressure value according to the on-machine indoor unit load rate and the storage module.

[0022] The control module is configured to determine a first target discharge pressure value corresponding to the on-machine indoor unit load rate interval as the target discharge pressure value of the compressor according to the on-machine indoor unit load rate.

[0023] The control module is configured to determine the first target discharge pressure value according to the correlation between the on-machine indoor unit load rate and the first target discharge pressure value, and take the first target discharge pressure value as the target discharge pressure value of the compressor.

[0024] The above technical solution has the following advantages or beneficial effects: the first target discharge pressure value of the multi-split system is not a fixed value, but is determined by adjusting the on-machine indoor unit load rate, and the corresponding relationship between the on-machine indoor unit load rate and the first target discharge pressure value is determined in advance to avoid indoor refrigerant noise, so that the first target discharge pressure value can be more accurately adapted to the on-machine indoor unit load rate to better reduce indoor refrigerant noise under low load rate conditions.

[0025] In some embodiments, the on-machine indoor unit load rate interval is negatively correlated with the first target discharge pressure value, or the on-machine indoor unit load rate is negatively correlated with the first target discharge pressure value.

[0026] The above technical solution has the following advantages or beneficial effects: the first target discharge pressure value of the multi-split system is not a fixed value, but is determined by adjusting the on-machine indoor unit load rate, and the corresponding relationship between the on-machine indoor unit load rate and the first target discharge pressure value is determined in advance to avoid indoor refrigerant noise, so that the first target discharge pressure value can be more accurately adapted to the on-machine indoor unit load rate to better reduce indoor refrigerant noise under low load rate conditions.

[0027] In some embodiments, the multi-split system comprises:

[0028] The storage module is configured to store different outdoor fan gear positions or speeds corresponding to different first target discharge pressure values, or to store the correlation between the first target discharge pressure value and the outdoor fan gear position or speed.

[0029] The control module is configured to determine the outdoor fan gear position or speed according to the first target discharge pressure value and the storage module.

[0030] The control module is configured to determine the outdoor fan gear position or speed according to the correlation between the first target discharge pressure value and the outdoor fan speed, and control the outdoor fan to operate at the above gear position or speed.

[0031] The technical scheme has the advantages or beneficial effects that: the multi-connected system adjusts the compressor discharge pressure by adjusting the outdoor fan gear or rotating speed, and the corresponding relationship between the outdoor fan gear or rotating speed and the first target discharge pressure value is determined in advance, so that the compressor discharge pressure can quickly reach the required first target discharge pressure value, and the indoor unit is prevented from generating refrigerant sound.

[0032] In some embodiments, the outdoor fan gear or rotating speed is negatively related to the first target discharge pressure value.

[0033] The technical scheme has the advantages or beneficial effects that: the multi-connected system has a large outdoor fan gear or rotating speed when the first target discharge pressure value is small, and has a small outdoor fan gear or rotating speed when the first target discharge pressure value is large, so as to ensure that the compressor discharge pressure quickly reaches the required first target discharge pressure value.

[0034] In some embodiments, the control module is configured to control the operating frequency of the compressor to be a frequency lower than the first frequency when the on-machine indoor unit load rate is below the set load rate.

[0035] The technical scheme has the advantages or beneficial effects that: the multi-connected system can further reduce the operating frequency to be lower than the first frequency, and better adapt to the low on-machine indoor unit load rate demand by reducing the operating frequency.

[0036] In some embodiments, the first target discharge pressure value is between a first discharge pressure value and a second discharge pressure value; the control module is configured to limit the operating frequency of the compressor to be above a third frequency when the discharge pressure is below the second discharge pressure value, and to limit the operating frequency of the compressor to be above the first frequency when the discharge pressure is above the second discharge pressure value, during the process of increasing the discharge pressure; and the control module is configured to limit the operating frequency of the compressor to be above the first frequency when the discharge pressure is above the first discharge pressure value, and to limit the operating frequency of the compressor to be above the third frequency when the discharge pressure is below the first discharge pressure value, during the process of reducing the discharge pressure; the third frequency is lower than the first frequency.

[0037] The technical scheme has the advantages or beneficial effects that: the lower limit of the operating frequency of the compressor is associated with the discharge pressure of the compressor, which can ensure the reliability of the compressor drive, the noise of the compressor body, and the stress problem of the pipe, and the hysteresis is set between the first discharge pressure and the second discharge pressure, which can prevent frequency fluctuation.

[0038] In some embodiments, the indoor unit includes an indoor heat exchanger and an indoor expansion valve.

[0039] The system includes:

[0040] An exhaust temperature detection module is configured to detect the exhaust temperature of the compressor.

[0041] an indoor temperature detection module configured to detect an indoor temperature;

[0042] a set temperature acquisition module configured to acquire a set temperature;

[0043] The control module is configured to determine an indoor heat exchanger outlet superheat target value according to a difference between the discharge temperature of the compressor, the indoor temperature and the set temperature, and control the opening degree of the indoor expansion valve to make the indoor heat exchanger outlet superheat reach the indoor heat exchanger outlet superheat target value or a target value threshold range.

[0044] The above technical solution has the following advantages or beneficial effects: when the on-machine indoor unit load rate is below the set load rate, the opening degree of the indoor expansion valve is first controlled by taking the indoor unit heat exchanger outlet superheat as the control target, and the discharge temperature is also considered, so that the indoor unit refrigerant flow rate is ensured to match the actual on-machine indoor unit load rate, and the phenomenon of high refrigerant noise caused by the increase of the refrigerant flow rate is avoided. At the same time, the discharge temperature is also considered, and when the discharge temperature is too high, the indoor unit heat exchanger outlet superheat target value will be reduced to reduce the discharge temperature of the compressor and ensure the reliability of the unit operation.

[0045] In some embodiments, the indoor unit comprises:

[0046] an indoor heat exchanger temperature detection module configured to detect an indoor heat exchanger outlet temperature and an indoor heat exchanger inlet temperature;

[0047] The control module is configured to determine a current indoor heat exchanger outlet superheat according to the indoor heat exchanger outlet temperature and the indoor heat exchanger inlet temperature, determine a first difference value as a difference between the current indoor heat exchanger outlet superheat and the indoor heat exchanger outlet superheat target value, determine a second difference value as a difference between a last indoor heat exchanger outlet superheat and the indoor heat exchanger outlet superheat target value, and determine an opening degree adjustment value of the indoor expansion valve according to the first difference value and the second difference value.

[0048] The above technical solution has the following advantages or beneficial effects: the opening degree adjustment value of the indoor expansion valve is determined to gradually adjust the opening degree of the indoor expansion valve.

[0049] In some embodiments, the control module is configured to acquire a minimum value and a maximum value of the indoor heat exchanger inlet temperature, determine a correction coefficient according to the indoor heat exchanger inlet temperature, the maximum value and the minimum value, and correct the opening degree adjustment value of the indoor expansion valve by the correction coefficient.

[0050] The above technical solution has the following advantages or beneficial effects: the correction coefficient is determined by the indoor heat exchanger inlet temperature, the minimum value and the maximum value of the indoor heat exchanger inlet temperature, and the opening degree adjustment value of the indoor expansion valve is corrected by the correction coefficient, so as to further reduce the refrigerant noise and ensure the reliability of the unit operation.

[0051] Other features and advantages of the present application will become more apparent from the following detailed description when read in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF DRAWINGS

[0052] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description are some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained from these drawings without creative labor.

[0053] Fig. 1 Schematic diagram of a multi-connected system according to an embodiment;

[0054] Fig. 2 Principle block diagram of a multi-connected system according to an embodiment;

[0055] Fig. 3 Flowchart of a multi-connected system according to an embodiment;

[0056] Fig. 4 Principle block diagram of a multi-connected system according to an embodiment;

[0057] Fig. 5 Flowchart of a multi-connected system according to an embodiment;

[0058] Fig. 6 Correlation diagram of lower limit of compressor operating frequency and discharge pressure of a multi-connected system according to an embodiment;

[0059] Fig. 7 Flowchart of a multi-connected system according to an embodiment;

[0060] Fig. 8 Principle block diagram of a multi-connected system according to an embodiment;

[0061] Fig. 9 Flowchart of a multi-connected system for determining adjustment value of indoor expansion valve opening degree according to an embodiment;

[0062] Fig. 10 Flowchart of a multi-connected system for determining correction coefficient of adjustment value of indoor expansion valve opening degree according to an embodiment.

[0063] In the drawings,

[0064] 1. Compressor;

[0065] 2. Oil separator;

[0066] 3. Gas-liquid separator;

[0067] 4. Four-way valve;

[0068] 5. outdoor heat exchanger;

[0069] 6. outdoor fan;

[0070] 7. outdoor expansion valve;

[0071] 9. oil return capillary;

[0072] 10. gas side stop valve;

[0073] 11. liquid side stop valve;

[0074] 13. first indoor heat exchanger; 14. first indoor expansion valve; 15. first indoor fan;

[0075] 18. second indoor heat exchanger; 19. second indoor expansion valve; 20. second indoor fan;

[0076] 23. nth indoor heat exchanger; 24. nth indoor expansion valve; 25. nth indoor fan. DETAILED DESCRIPTION

[0077] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the present application.

[0078] In the description of the present application, it should be understood that the terms "center", "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the purpose of facilitating the description of the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application.

[0079] The terms "first", "second" are only for the purpose of description, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the technical features indicated. Therefore, the features defined with "first", "second" can explicitly or implicitly include one or more of the features. In the description of the present application, unless otherwise specified, "a plurality of" means two or more.

[0080] In the description of the present application, it is required to explain that the terms "mount", "connect", "connection" should be understood in a broad sense unless otherwise specifically defined and limited, for example, can be fixed connection, can be detachable connection, or integral connection; can be mechanical connection, can be electrical connection; can be direct connection, can be indirect connection through intermediate medium, can be internal communication of two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0081] In the present application, unless otherwise specifically defined and limited, the first feature "on" or "under" the second feature can include that the first and second features are in direct contact, or that the first and second features are not in direct contact but are in contact through another feature between them. Moreover, the first feature "on", "above" and "over" the second feature includes that the first feature is directly above and obliquely above the second feature, or only indicates that the first feature is higher in horizontal height than the second feature. The first feature "under", "below" and "under" the second feature includes that the first feature is directly below and obliquely below the second feature, or only indicates that the first feature is lower in horizontal height than the second feature.

[0082] The following disclosure provides many different embodiments or examples for implementing different structures of the present application. In order to simplify the disclosure of the present application, the components and settings of specific examples are described below. Of course, they are only examples, and the purpose is not to limit the present application. In addition, the present application can repeatedly refer to numbers and / or letters in different examples, and such repetition is for the purpose of simplification and clarity, which itself does not indicate the relationship between the various embodiments and / or settings discussed. In addition, the present application provides examples of various specific processes and materials, but those skilled in the art can realize the application of other processes and / or the use of other materials.

[0083] The multi-split system given in the present application performs a refrigeration cycle of an air conditioner by using a compressor, a condenser, a throttling device and an evaporator. The refrigeration cycle includes a series of processes involving compression, condensation, expansion and evaporation, and performs refrigeration or heating for an indoor space.

[0084] The low-temperature and low-pressure refrigerant enters the compressor, which compresses the refrigerant gas into 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.

[0085] The throttling device expands the high-temperature and high-pressure liquid-phase refrigerant condensed in the condenser into low-pressure liquid-phase refrigerant. The evaporator evaporates the refrigerant expanded in the throttling device and returns refrigerant gas in a low-temperature and low-pressure state to the compressor. The evaporator can achieve a refrigeration effect by exchanging heat with a material to be cooled using latent heat of evaporation of the refrigerant. Throughout the cycle, the air conditioner can adjust the temperature of the indoor space.

[0086] The outdoor unit of the multi V system refers to a portion of the refrigeration cycle including the compressor and the outdoor heat exchanger, and the throttling device is located in the outdoor unit.

[0087] The indoor unit of the multi V system includes an indoor heat exchanger, the multi V system includes at least two indoor units, and one indoor expansion valve is provided for each indoor unit, and the capacity of the indoor unit is adjusted by adjusting the opening degree of the indoor expansion valve.

[0088] The indoor heat exchanger and the outdoor heat exchanger are used 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 state, and when the indoor heat exchanger is used as an evaporator, the air conditioner is used as a cooler in a cooling state.

[0089] In Fig. 1 , Fig. 2 Examples of the multi V system include an outdoor unit, at least two indoor units, a compressor discharge pressure detection module, and a control module.

[0090] The outdoor unit includes a compressor 1, an outdoor heat exchanger 5, and an outdoor fan 6.

[0091] The compressor discharge pressure detection module is configured to detect the discharge pressure of the compressor.

[0092] Each indoor unit includes an indoor heat exchanger and an indoor expansion valve.

[0093] The control module is configured to determine the on-load rate of the indoor unit;

[0094] When the on-load rate of the indoor unit is below the set load rate:

[0095] The control module controls the operating frequency of the compressor to be a first frequency;

[0096] The control module determines the target value of the discharge pressure of the compressor to be a first target discharge pressure value, and controls the gear or speed of the outdoor fan so that the discharge pressure of the compressor reaches the first target discharge pressure value;

[0097] The first target discharge pressure value is a value within a threshold range of a standard discharge pressure value, the standard discharge pressure value is a discharge pressure value corresponding to a standard operating condition, the indoor unit is fully on, and the compressor is operating at a second frequency; and the first frequency < the second frequency.

[0098] The standard working condition is a standard indoor temperature, outdoor temperature and indoor humidity specified in the air conditioning field.

[0099] Indoor 27 / 19, outdoor 35 / -. 27 and 35 are dry-bulb temperatures, and 19 is a wet-bulb temperature. The outdoor wet-bulb temperature is not specified.

[0100] The multi-split system optimizes the discharge pressure of the compressor when the load rate of the indoor unit in operation is low: when the load rate of the indoor unit in operation is below the set load rate and the compressor operates at the first frequency, the discharge pressure of the compressor is increased to the value corresponding to the standard working condition, full opening of the indoor unit and operation of the compressor at the second frequency, so as to increase the pressure difference between the outdoor heat exchanger and the indoor expansion valve by increasing the discharge pressure. The large pressure difference can reduce the liquid refrigerant remaining at the bottom of the outdoor heat exchanger. More refrigerant flows out of the outdoor heat exchanger to participate in the refrigeration cycle under the action of the pressure difference, ensuring the actual refrigerant circulation amount of the multi-split system and realizing the supercooling state of the refrigerant at the inlet of the indoor unit, thereby reducing the refrigerant sound of the indoor unit when the load rate of the indoor unit in operation is low and improving the user comfort.

[0101] In Fig. 1 Examples, the multi-split system includes an outdoor unit and one or more indoor units.

[0102] The outdoor unit includes a compressor 1, an oil separator 2, a gas-liquid separator 3, a four-way valve 4, an outdoor heat exchanger 5, an outdoor fan 6, an outdoor expansion valve 7, an oil return capillary tube 9, a gas-side stop valve 10, and a liquid-side stop valve 11.

[0103] The indoor unit 1 includes a first indoor heat exchanger 13, a first indoor expansion valve 14, and a first indoor fan 15.

[0104] The indoor unit 2 includes a second indoor heat exchanger 18, a second indoor expansion valve 19, and a second indoor fan 20.

[0105] The indoor unit n includes an n-th indoor heat exchanger 23, an n-th indoor expansion valve 24, and an n-th indoor fan 25.

[0106] After the multi-connected system is started and runs in the refrigeration mode, the compressor 1 discharges high-temperature and high-pressure refrigerant gas, which flows through the oil separator 2, enters the outdoor heat exchanger 5 through the four-way valve 4, and the lubricating oil separated in the oil separator 2 returns to the suction port of the compressor 1 through the oil return capillary tube 9. After being cooled by the outdoor heat exchanger 5, the refrigerant becomes a medium-temperature and high-pressure liquid, which then flows through the outdoor expansion valve 7 and the liquid-side stop valve 11, and is divided into n paths to flow into n indoor units. The medium-temperature and high-pressure refrigerant liquid is throttled by the expansion valves (for example, the first indoor expansion valve 14 of the indoor unit 1, the second indoor expansion valve 19 of the indoor unit 2, and the nth indoor expansion valve 24 of the indoor unit n) of the indoor units in operation, and forms low-temperature and low-pressure two-phase refrigerant, which then flows into the indoor heat exchanger to evaporate and absorb heat, and forms superheated refrigerant gas. Finally, the refrigerant gas returns to the suction port of the compressor 1 through the gas-side stop valve 10 and the four-way valve 4, and completes the refrigeration cycle.

[0107] In some embodiments, the starting indoor unit load ratio (LR) = total starting indoor unit capacity / outdoor unit capacity.

[0108] In some embodiments, the starting indoor unit load ratio (LR) = total starting indoor unit capacity / outdoor unit capacity.

[0109] In some embodiments, the set load ratio LR' is a value determined in advance through experiments.

[0110] In some embodiments, the first frequency is a frequency within a threshold range of the lower limit of the normal operating frequency range of the compressor.

[0111] The first frequency is the lower limit threshold of the normal operating frequency of the compressor ± c, and c is a constant determined in advance.

[0112] The second frequency is a frequency within a threshold range of the upper limit of the normal operating frequency range of the compressor.

[0113] The second frequency is the upper limit threshold of the normal operating frequency of the compressor ± d, and d is a constant determined in advance.

[0114] The first frequency can make the compressor run at a low frequency, and the setting of the first frequency can ensure that the frequency is suitable for the low starting indoor unit load ratio, and the setting of the second frequency can ensure that the exhaust pressure of the compressor can completely avoid indoor refrigerant noise. In some embodiments, the standard exhaust pressure value is e1, the first target exhaust pressure value is e2, e2 is a value within a threshold range of e1, that is, e2 is within a range of e1 ± b.

[0115] The multi-connected system reduces the indoor refrigerant sound by optimizing the discharge pressure of the compressor under the condition of low load rate. Under the condition of low load rate, the compressor operates at a low frequency, the refrigerant flow is small, the flow rate is low, the kinetic energy is low, and the system discharge pressure is low. By adjusting the outdoor fan gear or speed to increase the discharge pressure of the compressor, the pressure difference between the outdoor heat exchanger and the indoor expansion valve is increased, the liquid refrigerant remaining at the bottom of the outdoor heat exchanger is reduced, and more refrigerant flows out of the outdoor heat exchanger to participate in the refrigeration cycle under the action of the pressure difference, thereby ensuring the actual refrigerant circulation amount of the multi-connected system and realizing the supercooling state of the refrigerant at the inlet of the indoor unit, thereby reducing the indoor refrigerant sound under the condition of low load rate of the refrigeration start-up indoor unit.

[0116] The multi-connected system also causes the refrigerant condensation temperature in the outdoor heat exchanger to be low under the condition of low load rate, the heat exchange temperature difference with the environment is small, the heat exchange amount is small, and the refrigerant at the inlet of the indoor unit has no supercooling degree. By adjusting the outdoor fan gear or speed to increase the discharge pressure of the compressor, the heat exchange amount of the refrigerant in the outdoor heat exchanger with the environment is also increased, the state of the refrigerant at the inlet of the indoor unit is changed from two-phase state to supercooling state, and the indoor refrigerant sound is reduced.

[0117] In some embodiments, when the ambient temperature is 35°C, the discharge pressure is 2.3 MPa, the corresponding saturation temperature is 39.7°C, and the heat exchange temperature difference between the refrigerant and the atmospheric environment is only 4.7°C; if the refrigerant discharge pressure is increased to 2.8 MPa, the corresponding saturation temperature is 47.66°C, the heat exchange temperature difference between the refrigerant and the atmospheric environment is increased to 12.66°C, the heat exchange amount is increased, the refrigerant in the outdoor unit heat exchanger is cooled by the atmospheric environment more obviously, the state of the refrigerant at the inlet of the indoor unit is changed from two-phase state to supercooling state, and the indoor refrigerant sound is reduced.

[0118] In the example of Fig. 3 The control method of the multi-connected system is as follows:

[0119] S1, refrigeration starts.

[0120] S2, determine the load rate LR of the start-up indoor unit.

[0121] S4, LR<LR', if yes, enter step S4, otherwise, enter step S7.

[0122] S4, the operating frequency of the compressor is the first frequency.

[0123] S5, determine the target value of the discharge pressure of the compressor as the first target discharge pressure value.

[0124] S6, control the gear or speed of the outdoor fan so that the discharge pressure of the compressor reaches the first target discharge pressure value or the threshold range of the first target discharge pressure value. Enter step S2.

[0125] S7, enter the normal refrigeration operation. Enter step S2.

[0126] In Fig. 4 In an example, the multi-connected system comprises a storage module.

[0127] The storage module is configured to store different first target exhaust pressure values corresponding to different on-machine indoor unit load rate intervals.

[0128] The control module is configured to determine the first target exhaust pressure value according to the on-machine indoor unit load rate and the storage module.

[0129] The control module is configured to determine the on-machine indoor unit load rate interval to which the on-machine indoor unit load rate belongs, and determine the first target exhaust pressure value corresponding to the on-machine indoor unit load rate interval as the target exhaust pressure value of the compressor.

[0130] In some embodiments, the storage module stores a correspondence table of different on-machine indoor unit load rate intervals and first target exhaust pressure values, as shown in the following table:

[0131] Start-up room indoor unit load ratio (LR) interval Target exhaust pressure LR < LR 1% e21 LR 1% < LR < LR 2% e22 LR 2% < LR < LR 3% e23

[0132] Wherein, e21≥e22≥e23.

[0133] In some embodiments, the storage module stores the association relationship between the on-machine indoor unit load rate and the first target exhaust pressure value.

[0134] The control module is configured to determine the first target exhaust pressure value according to the on-machine indoor unit load rate and the storage module.

[0135] The control module is configured to determine the first target exhaust pressure value according to the association relationship between the on-machine indoor unit load rate and the first target exhaust pressure value, and take the first target exhaust pressure value as the target exhaust pressure value of the compressor.

[0136] In some embodiments, the association relationship between the on-machine indoor unit load rate and the first target exhaust pressure value is a function relationship determined in advance.

[0137] The first target exhaust pressure value of the multi-connected system is not a fixed value, but is determined by adjusting the on-machine indoor unit load rate. The correspondence relationship between the on-machine indoor unit load rate and the first target exhaust pressure value determined in advance avoids indoor refrigerant noise. Therefore, the first target exhaust pressure value can be more accurately adapted to the on-machine indoor unit load rate, so that any on-machine indoor unit load rate can better reduce indoor refrigerant noise when the low load rate condition is met.

[0138] In some embodiments, the on-machine indoor unit load rate interval and the first target exhaust pressure value are negatively correlated; when the on-machine indoor unit load rate interval is a large interval, the first target exhaust pressure value is small; when the on-machine indoor unit load rate interval is a small interval, the first target exhaust pressure value is large.

[0139] In some embodiments, the starting indoor unit load rate is negatively correlated with the first target exhaust pressure value; the smaller the starting indoor unit load rate, the greater the first target exhaust pressure value; the greater the starting indoor unit load rate, the smaller the first target exhaust pressure value.

[0140] The first target exhaust pressure value of the multi-split system is greater when the starting indoor unit load rate is low and is smaller when the starting indoor unit load rate is high, so as to better reduce the indoor refrigerant sound at any starting indoor unit load rate, especially when the starting indoor unit load rate is low.

[0141] In some embodiments, the storage module is configured to store a plurality of different first target exhaust pressure values corresponding to outdoor fan gears or speeds.

[0142] The control module is configured to determine the outdoor fan gear or speed according to the first target exhaust pressure value and the storage module.

[0143] In some embodiments, the outdoor fan gear corresponding to the first target exhaust pressure value is shown in the following table:

[0144] First target exhaust pressure value Outdoor fan gear e21 Fo1 e22 Fo2 e23 Fo3

[0145] Wherein, Fo1≤Fo2≤Fo3.

[0146] In some embodiments, when LR 1%≤LR<LR 2%, the target exhaust pressure is e22 and the outdoor fan gear is Fo2. When LR=e22, the outdoor fan gear remains unchanged at Fo2; when LR<e22, the fan gear is reduced to Fo1; and when LR>e22, the fan gear is increased to Fo3.

[0147] In some embodiments, the storage module is configured to store a correlation between the first target exhaust pressure value and the outdoor fan gear or speed.

[0148] The control module is configured to determine the outdoor fan gear or speed according to the first target exhaust pressure value and the storage module.

[0149] The control module is configured to determine the outdoor fan gear or speed according to the correlation between the first target exhaust pressure value and the outdoor fan speed, and control the outdoor fan to operate at the above gear or speed.

[0150] The multi-split system adjusts the compressor exhaust pressure by adjusting the outdoor fan gear or speed, and determines the corresponding relationship between the outdoor fan gear or speed and the first target exhaust pressure value in advance, so that the compressor exhaust pressure can quickly reach the required first target exhaust pressure value, and the indoor unit can avoid generating refrigerant sound.

[0151] In some embodiments, the outdoor fan gear or speed is inversely related to the first target discharge pressure value.

[0152] The outdoor fan gear or speed is high when the first target discharge pressure value is low and is low when the first target discharge pressure value is high, so as to ensure that the compressor discharge pressure quickly reaches the required first target discharge pressure value.

[0153] In Fig. 5 In an example, the control method of the multi-connected system is as follows:

[0154] S1, start of refrigeration.

[0155] S2, determine the on-load indoor unit load rate LR.

[0156] S4, LR < LR', if yes, go to step S4, otherwise, go to step S7.

[0157] S4, the operating frequency of the compressor is the first frequency.

[0158] S5, determine the first discharge pressure target value of the compressor according to LR and the content stored in the storage module.

[0159] S6, determine the gear or speed of the outdoor fan according to the first discharge pressure target value of the compressor and the content stored in the storage module, and control the outdoor fan. Go to step S2.

[0160] S7, enter normal refrigeration operation. Go to step S2.

[0161] In some embodiments, the control module is configured to control the operating frequency of the compressor to be a frequency lower than the first frequency when the on-load indoor unit load rate is below a set load rate.

[0162] The multi-connected system can further reduce the operating frequency to be lower than the first frequency, and better adapt to the low on-load indoor unit load rate requirement by reducing the operating frequency.

[0163] In some embodiments, the lower limit threshold of the normal operating frequency range of the compressor is a1.

[0164] When the compressor is in stable state operation, in order to ensure the refrigeration pull-down speed and take into account noise and pipe vibration problems, the stable operating frequency is set to a lower limit, which is a1. When operating under low load rate conditions, the compressor operates at the lower limit of the operating frequency a1, and when the load rate is very small, the theoretically required frequency of the compressor is very small, but due to the limitation of the lower limit of the operating frequency a1, the compressor can only operate at a frequency a1 greater than the theoretically required frequency, thus causing the refrigerant flow rate to be large, the refrigerant sound to be high, and the energy consumption to increase. Therefore, the method of reducing the operating frequency of the compressor of the heat pump system adjusts the lower limit of the operating frequency of the compressor to a2, a2 < a1.

[0165] If the compressor discharge pressure is too high after the compressor operation frequency lower limit is adjusted to a2, the reliability of the compressor drive may be at risk, and the risk of problems such as compressor body noise and piping stress may increase. Therefore, when lowering the compressor operation frequency lower limit, the compressor discharge pressure Pd should be associated. When the compressor discharge pressure Pd is too high, the original operation frequency lower limit a1 is maintained.

[0166] In some embodiments, the first target discharge pressure value is between the first discharge pressure value Pd1 and the second discharge pressure value Pd2, Pd1 < Pd2.

[0167] In the example of Fig. 6 , the control module is configured to, during the process of increasing the discharge pressure, limit the operation frequency of the compressor to be above the third frequency a2 when the discharge pressure is below the second discharge pressure value Pd2, and limit the operation frequency of the compressor to be above the first frequency a1 when the discharge pressure is above the second discharge pressure value Pd2; during the process of reducing the discharge pressure, limit the operation frequency of the compressor to be above the first frequency a1 when the discharge pressure is above the first discharge pressure value Pd1, and limit the operation frequency of the compressor to be above the third frequency a2 when the discharge pressure is below the first discharge pressure value Pd1.

[0168] Associating the compressor operation frequency lower limit with the compressor discharge pressure can ensure the reliability of the compressor drive, the noise of the compressor body, and the piping stress problem. Setting a hysteresis between the first discharge pressure and the second discharge pressure can prevent frequency fluctuations.

[0169] In the example of Fig. 7 , the control method of the multi-split system is:

[0170] S1, start refrigeration.

[0171] S2, determine the on-machine indoor unit load rate LR.

[0172] S4, LR < LR', if yes, go to step S4, otherwise, go to step S12.

[0173] S4, the operation frequency of the compressor is the third frequency a2.

[0174] S5, determine the target value of the compressor discharge pressure as the first target discharge pressure value.

[0175] S6, control the gear or speed of the outdoor fan so that the discharge pressure of the compressor reaches the first target discharge pressure value or the threshold range of the first target discharge pressure value.

[0176] S7, detecting the discharge pressure of the compressor. In the process of the discharge pressure of the compressor rising, entering step S8, in the process of the discharge pressure of the compressor falling, entering step S11.

[0177] S8, the discharge pressure Pd < Pd2, if yes, entering step S9, otherwise, entering step S10.

[0178] S9, the operating frequency of the compressor is the third frequency a2. Entering step S2.

[0179] S10, the operating frequency of the compressor is the first frequency a1. Entering step S2.

[0180] S11, the discharge pressure Pd > Pd1, if yes, entering step S10, otherwise, entering step S9.

[0181] S12, entering the normal refrigeration operation. Entering step S2.

[0182] In some embodiments, the opening of the indoor expansion valve is controlled to avoid indoor refrigerant sound.

[0183] In the prior art, in the stable state of the multi-split system refrigeration operating condition, the opening of the indoor expansion valve is adjusted to control the discharge temperature Td of the compressor to be in the normal range, and the discharge temperature of the compressor is controlled by adjusting the refrigerant flow.

[0184] When the multi-split system operates under low load rate, the compressor operates at the first frequency. At this time, due to the oil return of the oil separator 2, the suction temperature of the compressor is higher than that at the liquid side stop valve 11, the suction temperature and the suction superheat degree are increased, causing the discharge temperature of the compressor to rise. In order to ensure the stability of the discharge temperature Td of the compressor, the opening of the indoor expansion valve is increased, the refrigerant flow is increased, and the refrigerant at the outlet of the indoor heat exchanger is in a two-phase state, so as to reduce the refrigerant temperature at the suction port of the compressor and the suction superheat degree, and further reduce the discharge temperature Td of the compressor. In order to maintain the stability of the discharge temperature Td of the compressor, the existing control method makes the refrigerant at the outlet of the indoor heat exchanger in a two-phase state, increases the refrigerant flow, and makes the actual refrigerant flow greater than the theoretically required flow, which aggravates the high refrigerant sound phenomenon of the indoor unit. Therefore, a new control strategy of the indoor expansion valve is proposed, and the primary control target of the indoor expansion valve is changed from the discharge temperature Td of the compressor to the superheat degree at the outlet of the indoor heat exchanger.

[0185] In Fig. 8 Examples of the multi-split system include:

[0186] A discharge temperature detection module is configured to detect the discharge temperature Td of the compressor.

[0187] An indoor temperature detection module is configured to detect the indoor temperature.

[0188] The setting temperature acquisition module is configured to acquire a setting temperature.

[0189] The control module is configured to determine the indoor heat exchanger outlet superheat target value according to the difference between the discharge temperature of the compressor, the indoor temperature and the setting temperature, and control the opening degree of the indoor expansion valve to make the indoor heat exchanger outlet superheat reach the indoor heat exchanger outlet superheat target value or the target value threshold range.

[0190] When the on-machine indoor unit load rate is below the set load rate, the indoor expansion valve opening degree first takes the indoor unit heat exchanger outlet superheat as the control target, and the discharge temperature is also considered, so that the indoor unit refrigerant flow rate is ensured to match the actual on-machine indoor unit load rate, and the phenomenon of high refrigerant noise caused by the increase of the refrigerant flow rate is avoided. At the same time, the discharge temperature is also considered, and when the discharge temperature is too high, the indoor unit heat exchanger outlet superheat target value will be reduced to reduce the compressor discharge temperature and ensure the reliability of the unit operation.

[0191] The indoor unit comprises:

[0192] The indoor heat exchanger temperature detection module is configured to detect the indoor heat exchanger outlet temperature and the indoor heat exchanger inlet temperature.

[0193] The control module is configured to determine the current indoor heat exchanger outlet superheat according to the indoor heat exchanger outlet temperature and the indoor heat exchanger inlet temperature, determine the difference between the current indoor heat exchanger outlet superheat and the indoor heat exchanger outlet superheat target value as a first difference, determine the difference between the last indoor heat exchanger outlet superheat and the indoor heat exchanger outlet superheat target value as a second difference, and determine the opening degree adjustment value of the indoor expansion valve according to the first difference and the second difference.

[0194] The opening degree adjustment value of the indoor expansion valve is determined to gradually adjust the opening degree of the indoor expansion valve.

[0195] The control module is configured to acquire the minimum value and the maximum value of the indoor heat exchanger inlet temperature, determine a correction coefficient according to the indoor heat exchanger inlet temperature, the maximum value and the minimum value, and correct the opening degree adjustment value of the indoor expansion valve through the correction coefficient.

[0196] The correction coefficient is determined through the indoor heat exchanger inlet temperature, the minimum value and the maximum value of the indoor heat exchanger inlet temperature, and the opening degree adjustment value of the indoor expansion valve is corrected through the correction coefficient, so as to further reduce the refrigerant noise and ensure the reliability of the unit operation.

[0197] In some embodiments, the indoor unit heat exchanger outlet superheat target value Shx is related to the difference between the indoor temperature and the setting temperature and the discharge temperature Td, as shown in the following table, wherein t1, t2 and t3 are related to the difference between the indoor temperature and the setting temperature Tdm, Tdn are empirical values related to the compressor discharge temperature Td and the compressor reliability, where Tdm < Tdn, and Shx (x = 1, 2,..., 12) are empirical values.

[0198]

[0199] Indoor expansion valve opening degree adjustment value

[0200] wherein, wherein, SH is the actual indoor unit heat exchanger outlet superheat, and Shx is the indoor unit heat exchanger outlet superheat target value, the last calculated value.

[0201] The actual indoor unit heat exchanger outlet superheat SH is calculated as the difference between the indoor heat exchanger refrigerant outlet temperature Tg and the indoor heat exchanger refrigerant inlet temperature Tl, SH = Tg - Tl.

[0202] A and B are coefficients, and C is a coefficient related to the indoor heat exchanger refrigerant outlet temperature Tg and the indoor unit heat exchanger refrigerant inlet temperature Tl, and is calculated as follows:

[0203] C = D * exp[1 - (Tl - Tl_min) / (Tl_max - Tl_min)] + E.

[0204] wherein, Tl_min and Tl_max are the minimum and maximum values of the indoor unit heat exchanger refrigerant inlet temperature Tl, and D and E are fitting coefficients.

[0205] In the example of Fig. 9 , the process for determining the indoor expansion valve opening degree adjustment value is as follows:

[0206] S1, start.

[0207] S2, obtain the set temperature, detect the compressor discharge temperature, indoor temperature, and detect the indoor heat exchanger outlet temperature and inlet temperature.

[0208] S3, determine the current indoor heat exchanger outlet superheat based on the indoor heat exchanger outlet temperature and inlet temperature, and determine the indoor heat exchanger outlet superheat target value based on the difference between the compressor discharge temperature, indoor temperature, and set temperature.

[0209] S4, determine the difference between the current indoor heat exchanger outlet superheat and the indoor heat exchanger outlet superheat target value as a first difference, and determine the difference between the last indoor heat exchanger outlet superheat and the indoor heat exchanger outlet superheat target value as a second difference.

[0210] S5, determine the opening degree adjustment value of the indoor expansion valve based on the first difference and the second difference.

[0211] In Fig. 10 In the example of the indoor expansion valve opening degree adjustment value correction coefficient determination process, the process is as follows:

[0212] S1, start.

[0213] S2, detect the indoor heat exchanger inlet temperature.

[0214] S3, obtain the minimum value and the maximum value of the indoor heat exchanger inlet temperature.

[0215] S4, determine the correction coefficient according to the indoor heat exchanger inlet temperature, the maximum value and the minimum value.

[0216] When the multi-connected system operates under a low load rate condition, the indoor heat exchanger outlet superheat degree is first taken as the control target, and the compressor discharge temperature Td is considered, so that the indoor unit refrigerant flow rate is ensured to be matched with the actual load flow rate, and the phenomenon of high refrigerant sound caused by the increase of the refrigerant flow rate is avoided. At the same time, the Td is considered, and when the discharge temperature Td is too high, the indoor heat exchanger outlet superheat degree target value is reduced to reduce the compressor discharge temperature Td, and the reliability of the unit operation is ensured.

[0217] In the description of the above embodiments, specific features, structures, materials or characteristics can be combined in any one or more embodiments or examples in a suitable manner.

[0218] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto, any person skilled in the art can easily think of changes or replacements within the technical range disclosed by the present application, which should be covered within the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A multi-split air conditioning system, comprising: The outdoor unit includes the compressor, outdoor heat exchanger, and outdoor fan; At least two indoor units; The exhaust pressure detection module is used to detect the exhaust pressure of the compressor; Its characteristic is that it further includes: The control module is configured to determine the load rate of the indoor unit when it is turned on. When the indoor unit load rate is below the set load rate: The compressor's operating frequency is controlled to the first frequency; The target value for the compressor's discharge pressure is determined to be the first target discharge pressure value. The setting or speed of the outdoor fan is controlled to make the compressor's discharge pressure reach the first target discharge pressure value. Wherein, the first target exhaust pressure value is a value within the threshold range of the standard exhaust pressure value, and the standard exhaust pressure value is the exhaust pressure value corresponding to standard operating conditions, indoor unit fully open, and compressor running at the second frequency; the first frequency < the second frequency; The multi-unit system includes a storage module; The storage module is used to store different first target exhaust pressure values ​​corresponding to several different indoor unit load rate ranges, or to store the correlation between the indoor unit load rate and the first target exhaust pressure value. The control module is configured to determine the first target exhaust pressure value based on the indoor unit load rate and the storage module. The indoor unit load rate range is negatively correlated with the first target exhaust pressure value, or the indoor unit load rate is negatively correlated with the first target exhaust pressure value.

2. The multi-unit air conditioning system according to claim 1, characterized in that, The first frequency is a frequency within the lower limit threshold range of the compressor's normal operating frequency range; The second frequency is the frequency within the upper limit threshold range of the compressor's normal operating frequency range.

3. The multi-unit air conditioning system according to claim 1, characterized in that, The multi-unit system includes: The storage module is used to store different outdoor fan speeds or rotation speeds corresponding to different first target exhaust pressure values, or to store the correlation between the first target exhaust pressure value and the outdoor fan speed or rotation speed. The control module is configured to determine the outdoor fan speed or rotation speed based on the first target exhaust pressure value and the storage module. The outdoor fan speed or rotation speed is negatively correlated with the first target exhaust pressure value.

4. The multi-unit air conditioning system according to claim 1, characterized in that, The control module is configured to control the compressor to operate at a frequency lower than the first frequency when the load rate of the indoor unit is below the set load rate.

5. The multi-unit air conditioning system according to claim 4, characterized in that, The first target exhaust pressure value is located between the first exhaust pressure value and the second exhaust pressure value; The control module is configured such that, during the process of increasing exhaust pressure, when the exhaust pressure is below the second exhaust pressure value, the compressor's operating frequency is limited to a third frequency or higher, and when the exhaust pressure is above the second exhaust pressure value, the compressor's operating frequency is limited to a first frequency or higher; during the process of decreasing exhaust pressure, when the exhaust pressure is above the first exhaust pressure value, the compressor's operating frequency is limited to a first frequency or higher, and when the exhaust pressure is below the first exhaust pressure value, the compressor's operating frequency is limited to a third frequency or higher; the third frequency < the first frequency.

6. The multi-split air conditioning system according to any one of claims 1-5, characterized in that, The indoor unit includes an indoor heat exchanger and an indoor expansion valve; The system includes: The exhaust temperature detection module is used to detect the exhaust temperature of the compressor. Indoor temperature detection module, used to detect indoor temperature; The set temperature acquisition module is used to acquire the set temperature; The control module is configured to determine the target value of the superheat at the outlet of the indoor heat exchanger based on the compressor's exhaust temperature, the difference between the indoor temperature and the set temperature, and control the opening of the indoor expansion valve so that the superheat at the outlet of the indoor heat exchanger reaches the target value or the target value threshold range.

7. The multi-unit air conditioning system according to claim 6, characterized in that, The indoor unit includes: The indoor heat exchanger temperature detection module is used to detect the outlet and inlet temperatures of the indoor heat exchanger. The control module is configured to determine the current superheat of the indoor heat exchanger outlet based on the outlet temperature and inlet temperature of the indoor heat exchanger, determine the difference between the current superheat of the indoor heat exchanger outlet and the target value of the superheat of the indoor heat exchanger outlet as the first difference, determine the difference between the previous superheat of the indoor heat exchanger outlet and the target value of the superheat of the indoor heat exchanger outlet as the second difference, and determine the opening adjustment value of the indoor expansion valve based on the first difference and the second difference.

8. The multi-unit air conditioning system according to claim 7, characterized in that, The control module is configured to acquire the minimum and maximum values ​​of the indoor heat exchanger inlet temperature, determine a correction coefficient based on the indoor heat exchanger inlet temperature, maximum and minimum values, and correct the opening adjustment value of the indoor expansion valve using the correction coefficient.

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