A multi-connected air conditioning system

Abstract

The present invention discloses a multi-split air-conditioning system, in which a refrigerant branch is added between the exhaust side of a compressor and an outdoor heat exchanger, and the refrigerant branch is controlled to be connected during heating of the multi-split air-conditioning system, so that a part of the high-temperature and high-pressure refrigerant discharged by the compressor enters the indoor heat exchanger to realize indoor heating by condensing and releasing heat, and a part of the refrigerant enters the outdoor heat exchanger from the refrigerant branch to be mixed with the refrigerant inside the outdoor heat exchanger, and the coil temperature of the outdoor heat exchanger is increased by its high temperature, thereby delaying the frosting speed of the outdoor heat exchanger, and the evaporation pressure and evaporation temperature of the outdoor heat exchanger can also be increased by the high-temperature and high-pressure refrigerant, thereby further delaying the frosting speed of the outdoor heat exchanger, ensuring high-frequency operation of the compressor, ensuring the heating capacity of the indoor heat exchanger, and being able to increase the heating time by reducing the frequency of defrosting operations, thereby stabilizing the heating capacity of the multi-split air-conditioning system to the greatest extent.

Description

Technical Field

[0001] The present invention relates to the technical field of air conditioning, and in particular to a multi-split air conditioning system. Background Art

[0002] When the multi-split air-conditioning system is in heating operation, the outdoor heat exchanger is prone to frost due to the low evaporation temperature. As the system runs, more and more frost will form, the heat exchange capacity of the outdoor heat exchanger will become worse and worse, and the low-pressure pressure of the system will become lower and lower, which will cause the compressor to reduce frequency, thereby affecting the heating capacity of the indoor heat exchanger and reducing the user experience.

[0003] The current multi-split air-conditioning systems are designed with defrost programs to deal with frosting. The coil temperature of the outdoor heat exchanger or the outdoor ambient temperature is used to determine when to start defrosting. After the defrost program is started, the four-way valve is used to switch to the refrigeration refrigerant circuit, converting the indoor heat exchanger into an evaporator and the outdoor heat exchanger into a condenser. The heat dissipated by the condenser is used to melt the frost on the surface of the outdoor heat exchanger.

[0004] This defrosting method will cause the indoor heat exchanger to absorb heat from the room as it is converted into an evaporator, causing the indoor ambient temperature to drop, giving the user an uncomfortable experience. Summary of the invention

[0005] The object of the present invention is to provide a multi-split air-conditioning system, in which an electronic expansion valve is used to establish a refrigerant branch between the high-pressure side of the system and the outdoor heat exchanger. While ensuring that the unloading amount is not large, the high-temperature and high-pressure refrigerant is mixed into the outdoor heat exchanger through the refrigerant branch, and mixed with the refrigerant in the outdoor heat exchanger to increase the evaporation pressure and coil temperature of the outdoor heat exchanger, thereby delaying the frosting speed of the outdoor heat exchanger and ensuring the heating capacity of the indoor heat exchanger.

[0006] In order to achieve the above-mentioned purpose, the present invention adopts the following technical solutions:

[0007] A multi-split air conditioning system is proposed, comprising:

[0008] An outdoor unit and an indoor unit; wherein the outdoor unit comprises a compressor, a four-way valve, and an outdoor heat exchanger connected in series;

[0009] A refrigerant branch connected between the exhaust side of the compressor and the outdoor heat exchanger;

[0010] The controller is configured as:

[0011] The refrigerant branch is connected during heating of the multi-split air-conditioning system so that part of the high-temperature and high-pressure refrigerant discharged from the compressor enters the outdoor heat exchanger from the refrigerant branch and mixes with the refrigerant in the indoor heat exchanger, thereby delaying frosting of the outdoor heat exchanger.

[0012] Compared with the prior art, the advantages and positive effects of the air-conditioning system are as follows: in the multi-split air-conditioning system proposed in the present invention, a refrigerant branch is added between the exhaust side of the compressor and the outdoor heat exchanger, and the refrigerant branch is controlled to be connected during the heating period of the multi-split air-conditioning system, so that a part of the high-temperature and high-pressure refrigerant discharged by the compressor enters the indoor heat exchanger to achieve indoor heating through condensation and heat release, and a part enters the outdoor heat exchanger from the refrigerant branch and mixes with the refrigerant inside the outdoor heat exchanger. The high temperature is used to increase the coil temperature of the outdoor heat exchanger, thereby delaying the frosting speed of the outdoor heat exchanger. The high-temperature and high-pressure refrigerant can also be used to increase the evaporation pressure and evaporation temperature of the outdoor heat exchanger, further delaying the frosting speed of the outdoor heat exchanger, ensuring high-frequency operation of the compressor, ensuring the heating capacity of the indoor heat exchanger, and being able to increase the heating time by reducing the frequency of defrosting operations, thereby stabilizing the heating capacity of the multi-split air-conditioning system to the greatest extent.

[0013] In some embodiments of the present invention, the controller is configured to adjust the unloading amount of the refrigerant branch circuit in combination with the coil temperature of the outdoor heat exchanger, the outdoor ambient temperature and the system low pressure.

[0014] When the multi-split air-conditioning system is operating in heating mode, the coil temperature of the outdoor heat exchanger, the outdoor ambient temperature and the system low pressure can all affect or reflect the frosting speed or degree of the outdoor heat exchanger. The unloading amount of the refrigerant branch can be adjusted based on the above parameters. The unloading amount can be dynamically changed to cope with different working conditions, and the frosting speed of the outdoor heat exchanger or the degree of frosting of the outdoor heat exchanger can be delayed as much as possible.

[0015] In some embodiments of the present invention, the refrigerant branch includes an unloading electronic expansion valve, and the controller is configured to adjust the opening of the unloading electronic expansion valve in combination with the coil temperature of the outdoor heat exchanger, the outdoor ambient temperature and the system low pressure, so as to adjust the unloading amount of the refrigerant branch by adjusting the opening of the unloading electronic expansion valve.

[0016] In some embodiments of the present invention, the opening of the unloading electronic expansion valve is adjusted according to EVX(n)=EVX(n-1)+ΔEVX, and 0≤EVX(n)≤1 / 2*EVXmax; wherein EVX(n) is the current opening of the unloading electronic expansion valve, EVX(n-1) is the opening of the unloading electronic expansion valve in the previous control cycle, ΔEVX is the adjustment amount of the opening of the unloading electronic expansion valve in each control cycle, and EVXmax is the maximum opening set for the unloading electronic expansion valve.

[0017] In each control cycle, the unloading electronic expansion valve is adjusted according to the adjustment amount ΔEVX based on the opening of the unloading electronic expansion valve in the previous control cycle, and half of the maximum opening set for the unloading electronic expansion valve is used as the adjustment limit to achieve a balanced distribution of refrigerant between ensuring heating performance and delaying frosting.

[0018] In some embodiments of the present invention, the controller is configured to: obtain the outdoor ambient temperature and the system low pressure, determine the ambient temperature interval in which the outdoor ambient temperature is located and the system low pressure interval in which the system low pressure is located; determine the adjustment amount of the opening of the unloading electronic expansion valve according to the ambient temperature interval and the system low pressure interval; adjust the opening of the unloading electronic expansion valve based on the determined adjustment amount when the execution condition is met, and stop adjusting the unloading electronic expansion valve when the exit condition is met; wherein the outdoor ambient temperature is divided into M ambient temperature intervals; N system low pressure intervals are divided for the system low pressure in each ambient temperature interval; each system low pressure interval is provided with an execution condition, an exit condition and the adjustment amount of the unloading electronic expansion valve; the execution condition and the exit condition are limited based on the minimum value of the coil temperature of the outdoor heat exchanger; the execution condition is set so that the minimum value of the coil temperature of the outdoor heat exchanger does not exceed the first specified value; the exit condition is configured so that the minimum value of the coil temperature of the outdoor heat exchanger is not lower than the second specified value.

[0019] In order to achieve precise control of the unloading amount of the refrigerant branch, the outdoor ambient temperature is divided into M ambient temperature intervals. In each ambient temperature interval, N system low-pressure pressure intervals are further divided according to the system low-pressure pressure. Corresponding to each system low-pressure pressure interval, execution conditions, exit conditions and adjustment amounts of the unloading electronic expansion valve are set. When adjusting the unloading electronic expansion valve, according to the ambient temperature interval in which the temperature in the current outdoor environment is located and the current system low-pressure pressure, when the execution conditions are met, the opening of the unloading electronic expansion valve is adjusted on the basis of the opening of the unloading electronic expansion valve in the previous control cycle according to the determined adjustment amount, and the adjustment is exited when the exit conditions are met. If the exit conditions are not met, the opening of the unloading electronic expansion valve is continuously adjusted on the basis of the opening of the unloading electronic expansion valve in the previous control cycle according to the determined adjustment amount; among them, the execution conditions and the exit conditions are both limited based on the minimum value of the coil temperature of the outdoor heat exchanger.

[0020] In some embodiments of the present invention, the system also includes: a memory, storing relationship data between the ambient temperature range, system low pressure, execution conditions, exit conditions and the adjustment amount of the opening of the unloading electronic expansion valve; the controller is configured to: query the relationship data in the memory, determine the adjustment amount of the opening of the unloading electronic expansion valve based on the ambient temperature range and the system low pressure range under the current operating conditions, obtain the execution conditions and exit conditions under the ambient temperature range and the system low pressure range, adjust the opening of the unloading electronic expansion valve on the basis of the opening of the unloading electronic expansion valve in the previous control cycle according to the determined adjustment amount when the execution conditions are met, and exit the adjustment when the exit conditions are met.

[0021] The present invention uses a memory to store relationship data between the ambient temperature range, the system low-pressure range, the execution condition, the exit condition and the adjustment amount of the opening of the unloading electronic expansion valve. During the system heating period, the system obtains the outdoor ambient temperature and the system low-pressure pressure, queries the relationship data in the memory, and determines the adjustment amount of the opening of the unloading electronic expansion valve based on the ambient temperature range and the system low-pressure pressure range under the current working conditions, obtains the execution conditions and exit conditions under the ambient temperature range and the system low-pressure pressure range, and adjusts the opening of the unloading electronic expansion valve according to the determined adjustment amount on the basis of the opening of the unloading electronic expansion valve in the previous control cycle when the execution conditions are met, and exits the adjustment when the exit conditions are met. If the exit conditions are not met, the opening of the unloading electronic expansion valve is continuously adjusted according to the determined adjustment amount on the basis of the opening of the unloading electronic expansion valve in the previous control cycle.

[0022] In some embodiments of the present invention, the controller is configured to: determine the ambient temperature range in which the outdoor ambient temperature is located; start defrosting according to the defrost execution conditions specified in the ambient temperature range, and exit defrosting when the defrost exit conditions specified in the ambient temperature range are met; wherein the defrost execution conditions include: the coil temperature of the outdoor heat exchanger is lower than the first defrost limit, the change in the system low pressure is lower than the first change, and the heating time meets the heating time limit, and all three must be met; the defrost exit conditions include: the coil temperature of the outdoor heat exchanger is higher than the second defrost limit, the system high pressure is higher than the high pressure limit, or the defrost time meets the defrost time limit, and at least one of the three must be met.

[0023] When the system is actually running, there is a situation where the relative humidity of the outdoor environment is relatively low, which makes the outdoor heat exchanger frost very slowly or not frost at all. However, if the conditions for entering defrost are determined based on the current outdoor ambient temperature and the coil temperature of the outdoor heat exchanger, unnecessary defrost procedures will be started, resulting in false defrost, which not only wastes energy but also reduces the indoor temperature and reduces the user experience. In view of this, considering that the heat exchange capacity of the outdoor heat exchanger will inevitably decrease when frosting occurs, the system low pressure will inevitably decrease, and finally the defrost will be entered. At this time, if the outdoor heat exchanger is frost-free, although the conditions of the outdoor ambient temperature and the coil temperature of the outdoor heat exchanger are met, the system low pressure will not drop significantly. Based on the present invention, the change in the system low pressure at different ambient temperatures is used to determine whether to enter defrost, which can avoid the system from entering false defrost, thereby not affecting the normal heating.

[0024] In some embodiments of the present invention, the controller is configured to increase the shortest time limit that the heating time in the defrost execution condition needs to meet when the defrost exit condition includes that the system high pressure exceeds the high pressure limit.

[0025] The present invention proposes a judgment condition that the system high pressure exceeds the high pressure limit in the defrost exit condition. If the system high pressure is too high during defrosting, it also illustrates the problem of frost-free defrosting of the outdoor heat exchanger, that is, false defrosting. In an embodiment of the present invention, when the defrost exit condition includes the system high pressure exceeding the high pressure limit, the shortest time limit that the heating time in the defrost execution condition must meet is increased, that is, the re-heating time after exiting defrost is increased, so as to improve the user comfort.

[0026] In some embodiments of the present invention, the system further includes: a diverter, whose input end is connected to the refrigerant branch, whose output end is connected to the outdoor heat exchanger, and whose output end includes at least two output ports, and the at least two output ports are connected to the outdoor heat exchanger at different parts of the outdoor heat exchanger.

[0027] The structure in which at least two output ports of the diverter are connected to the outdoor heat exchanger at different positions of the outdoor heat exchanger allows the high-temperature and high-pressure refrigerant discharged from the compressor to be evenly mixed with the refrigerant inside the outdoor heat exchanger, thereby improving the overall effect of delaying frost formation of the outdoor heat exchanger.

[0028] After reading the specific embodiments of the present invention in conjunction with the accompanying drawings, other features and advantages of the present invention will become more clear. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0030] Figure 1 A schematic diagram of the system architecture of the multi-split air conditioning system proposed by the present invention;

[0031] Figure 2 It is a schematic diagram of the refrigerant flow direction under the refrigeration condition of the multi-split air conditioning system proposed by the present invention;

[0032] Figure 3 The diagram is a schematic diagram of the refrigerant flow direction in the heating condition of the multi-split air conditioning system proposed by the present invention;

[0033] Figure 4 It is a schematic diagram of the refrigerant flow direction under the delayed frosting control in the heating condition of the multi-split air conditioning system proposed by the present invention;

[0034] Figure 5 The structure diagram of the multi-split air conditioning system provided in the first embodiment of the present invention is shown;

[0035] Figure 6 It is a schematic diagram of the structure of a multi-split air conditioning system provided in the second embodiment of the present invention;

[0036] Figure 7 This is a schematic diagram of the control of delaying frosting of a multi-split air conditioning system provided in the third embodiment of the present invention;

[0037] Figure 8 The control parameters for delaying frosting of a multi-split air conditioning system provided in the third embodiment of the present invention are shown;

[0038] Fig. 9 This is a schematic diagram of defrosting control of a multi-split air conditioning system provided in Embodiment 5 of the present invention;

[0039] Fig.10 This is a schematic diagram of control parameters for defrosting a multi-split air conditioning system provided in Embodiment 5 of the present invention;

[0040] Fig.11 This is a schematic diagram of defrosting control of a multi-split air conditioning system provided in Embodiment 6 of the present invention;

[0041] Fig.12 The figure is a schematic diagram of the structure of a multi-split air conditioning system provided in the seventh embodiment of the present invention. DETAILED DESCRIPTION

[0042] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0043] In the description of the present application, it should be understood that the terms "center", "up", "down", "front", "back", "top", "bottom", "inside", "outside", etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present application.

[0044] In the description of this application, it should be understood that the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the feature. In the description of this application, unless otherwise specified, "plurality" means two or more.

[0045] In the description of this application, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0046] In the present invention, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may include that the first and second features are in direct contact, or may include that the first and second features are not in direct contact but are in contact through another feature between them. Moreover, a first feature being "above", "above" and "above" a second feature includes that the first feature is directly above and obliquely above the second feature, or simply indicates that the first feature is higher in level than the second feature. A first feature being "below", "below" and "below" a second feature includes that the first feature is directly below and obliquely below the second feature, or simply indicates that the first feature is lower in level than the second feature.

[0047] The disclosure below provides many different embodiments or examples to realize different structures of the present invention. In order to simplify the disclosure of the present invention, the parts and settings of specific examples are described below. Of course, they are only examples, and the purpose is not to limit the present invention. In addition, the present invention can repeat reference numbers and / or reference letters in different examples, and this repetition is for the purpose of simplicity and clarity, which itself does not indicate the relationship between the various embodiments and / or settings discussed. In addition, the present invention provides various specific examples of processes and materials, but those of ordinary skill in the art can be aware of the application of other processes and / or the use of other materials.

[0048] The present invention aims to provide a multi-split air-conditioning system, in which an electronic expansion valve is used to establish a refrigerant branch between the high-pressure side of the system and the outdoor heat exchanger. While ensuring that the unloading amount is not large, the high-temperature and high-pressure refrigerant is mixed into the outdoor heat exchanger through the refrigerant branch and mixed with the refrigerant in the outdoor heat exchanger to increase the evaporation pressure and coil temperature of the outdoor heat exchanger, thereby delaying the frosting speed of the outdoor heat exchanger and ensuring the heating capacity of the indoor heat exchanger.

[0049] like Figure 1 As shown, the multi-split air conditioning system proposed by the present invention comprises:

[0050] An outdoor unit and an indoor unit; wherein the outdoor unit comprises a compressor (1), a four-way valve (2), and an outdoor heat exchanger (3) connected in series; and the indoor unit comprises at least one indoor heat exchanger (4).

[0051] The refrigerant branch (5) is connected between the exhaust side of the compressor (1) and the outdoor heat exchanger (3).

[0052] The controller (not shown in the figure) is configured to: during the heating period of the multi-split air conditioning system, control the connection of the refrigerant branch (5) so that the high-temperature and high-pressure refrigerant discharged from the compressor (1) enters the outdoor heat exchanger (3) from the refrigerant branch (5) and mixes with the refrigerant inside the indoor heat exchanger (3), thereby delaying the frosting of the outdoor heat exchanger (3).

[0053] The outdoor heat exchanger (3) and the indoor heat exchanger (4) are used as a condenser or an evaporator. When the indoor heat exchanger (4) is used as a condenser, the indoor unit is used as a heater in a heating mode, and the outdoor heat exchanger (3) is used as an evaporator in a heating mode to absorb heat from the outdoor environment. When the indoor heat exchanger (4) is used as an evaporator, the indoor unit is used as a cooler in a cooling mode, and the outdoor heat exchanger (3) is used as a heater in a cooling mode to release heat to the outdoor environment.

[0054] like Figure 2As shown, in the multi-split air conditioning system, under the cooling condition, the four-way valve (2) is controlled so that the exhaust side of the compressor (1) is connected to the outdoor heat exchanger (3), and the suction side is connected to the indoor heat exchanger (4). The compressor (1) compresses the sucked low-temperature and low-pressure gaseous refrigerant into high-temperature and high-pressure gaseous refrigerant and discharges it into the outdoor heat exchanger (3) through the four-way valve (1), releases heat in the outdoor heat exchanger (3), and condenses into high-pressure liquid refrigerant. The high-pressure liquid refrigerant enters the indoor heat exchanger (4) after pressure reduction and throttling by the indoor electronic expansion valve, absorbs heat in the indoor heat exchanger (4) and evaporates into gaseous refrigerant. The gaseous refrigerant returns to the suction side of the compressor (1) through the four-way valve (2).

[0055] like Figure 3 As shown, in the heating condition, the multi-split air conditioning system controls the four-way valve (2) so that the exhaust side of the compressor (1) is connected to the indoor heat exchanger (4), and the suction side is connected to the outdoor heat exchanger (3). The compressor (1) compresses the sucked low-temperature and low-pressure gaseous refrigerant into high-temperature and high-pressure gaseous refrigerant and discharges it into the indoor heat exchanger (4) through the four-way valve (1). The refrigerant releases heat in the indoor heat exchanger (4) and becomes high-pressure liquid refrigerant. The high-pressure liquid refrigerant enters the outdoor heat exchanger (3) after pressure reduction and throttling by the outdoor electronic expansion valve. The high-pressure liquid refrigerant absorbs heat in the outdoor heat exchanger (3) and evaporates into gaseous refrigerant. The gaseous refrigerant returns to the suction side of the compressor (1) through the four-way valve (2).

[0056] The indoor / outdoor electronic expansion valve expands the high-temperature and high-pressure liquid refrigerant condensed in the condenser into a low-pressure liquid refrigerant. The evaporator evaporates the refrigerant expanded in the expansion valve and returns the low-temperature and low-pressure refrigerant gas to the compressor. The evaporator can achieve a cooling effect by utilizing the latent heat of evaporation of the refrigerant to exchange heat with the material to be cooled. In the entire cycle, the multi-split air conditioning system adjusts the temperature of the indoor space.

[0057] like Figure 4As shown, during the heating period of the multi-split air conditioning system, the refrigerant branch (5) is controlled to be connected, so that a part of the high-temperature and high-pressure refrigerant discharged from the compressor (1) (as shown by the hollow arrow in the figure) enters the indoor heat exchanger (4) to release heat through condensation to achieve indoor heating; and a part (as shown by the black solid arrow in the figure) enters the outdoor heat exchanger (3) from the refrigerant branch (5) to mix with the refrigerant inside the outdoor heat exchanger (3), and uses its high temperature to increase the coil temperature of the outdoor heat exchanger (3), thereby delaying the frosting of the outdoor heat exchanger (3). speed; at the same time, the evaporation pressure and evaporation temperature of the outdoor heat exchanger (3) can be increased by high-temperature and high-pressure refrigerant, thereby further delaying the frosting speed of the outdoor heat exchanger (3), ensuring the high-frequency operation of the compressor (1), and ensuring the heating performance of the indoor heat exchanger (4); when the frosting speed of the outdoor heat exchanger (3) is delayed, the operating conditions for the multi-split air-conditioning system to enter the defrost mode are reduced, thereby being able to increase the heating time of the system by reducing the frequency of the defrost operation, thereby stabilizing the heating capacity of the multi-split air-conditioning system to the greatest extent.

[0058] The operation of the multi-split air conditioning system proposed by the present invention is described in detail below with reference to several specific embodiments.

[0059] Embodiment 1

[0060] The multi-split air conditioning system proposed in this embodiment includes:

[0061] An outdoor unit and an indoor unit; wherein the outdoor unit comprises a compressor (1), a four-way valve (2), and an outdoor heat exchanger (3) connected in series; and the indoor unit comprises at least one indoor heat exchanger (4).

[0062] The refrigerant branch (5) is connected between the exhaust side of the compressor (1) and the outdoor heat exchanger (3).

[0063] In this embodiment, the controller is configured to: during the heating period of the multi-split air conditioning system, control the connection of the refrigerant branch (5), and adjust the unloading amount of the refrigerant branch (5) in combination with the coil temperature of the outdoor heat exchanger (3), the outdoor ambient temperature and the system low pressure, so that the high-temperature and high-pressure refrigerant discharged from the compressor (1) enters the outdoor heat exchanger (3) from the refrigerant branch (5) at the adjusted unloading amount, and mixes with the refrigerant inside the indoor heat exchanger (3), thereby delaying the frosting of the outdoor heat exchanger (3).

[0064] In the cooling condition, the multi-split air conditioning system controls the four-way valve (2) so that the exhaust side of the compressor (1) is connected to the outdoor heat exchanger (3), and the suction side is connected to the indoor heat exchanger (4). The compressor (1) compresses the sucked low-temperature and low-pressure gaseous refrigerant into high-temperature and high-pressure gaseous refrigerant and discharges it into the outdoor heat exchanger (3) through the four-way valve (1), releases heat in the outdoor heat exchanger (3), and condenses into high-pressure liquid refrigerant. The high-pressure liquid refrigerant enters the indoor heat exchanger (4) after pressure reduction and throttling by the indoor electronic expansion valve, absorbs heat in the indoor heat exchanger (4) and evaporates into gaseous refrigerant. The gaseous refrigerant returns to the suction side of the compressor (1) through the four-way valve (2).

[0065] In the heating condition, the multi-split air conditioning system controls the four-way valve (2) so that the exhaust side of the compressor (1) is connected to the indoor heat exchanger (4), and the suction side is connected to the outdoor heat exchanger (3). The compressor (1) compresses the sucked low-temperature and low-pressure gaseous refrigerant into high-temperature and high-pressure gaseous refrigerant and discharges it into the indoor heat exchanger (4) through the four-way valve (1). The refrigerant releases heat in the indoor heat exchanger (4) and becomes high-pressure liquid refrigerant. The high-pressure liquid refrigerant enters the outdoor heat exchanger (3) after pressure reduction and throttling by the outdoor electronic expansion valve. The high-pressure liquid refrigerant absorbs heat in the outdoor heat exchanger (3) and evaporates into gaseous refrigerant. The gaseous refrigerant returns to the suction side of the compressor (1) through the four-way valve (2).

[0066] refer to Figure 5 As shown, during the heating period of the multi-split air conditioning system, the coil temperature Te of the outdoor heat exchanger (3), the outdoor ambient temperature Ta, and the system low pressure Ps are obtained, and the unloading amount of the high-temperature and high-pressure refrigerant discharged from the compressor (1) to the refrigerant branch (5) is determined according to the coil temperature Te, the outdoor ambient temperature Ta, and the system low pressure Ps. The controller is configured to: control the connection of the refrigerant branch (5) according to the determined unloading amount, and the high-temperature and high-pressure refrigerant enters the outdoor heat exchanger (3) from the refrigerant branch (5) and mixes with the refrigerant inside the outdoor heat exchanger (3), thereby increasing the outdoor heat exchange rate with its high temperature. The coil temperature of the outdoor heat exchanger (3) is increased, thereby slowing down the frosting speed of the outdoor heat exchanger (3). At the same time, the evaporation pressure and evaporation temperature of the outdoor heat exchanger (3) are increased by the high-temperature and high-pressure refrigerant, further slowing down the frosting speed of the outdoor heat exchanger (3), ensuring the high-frequency operation of the compressor (1), and ensuring the heating capacity of the indoor heat exchanger (4). When the frosting speed of the outdoor heat exchanger (3) is slowed down, the operating conditions for the multi-split air conditioning system to enter the defrost mode are reduced, thereby increasing the heating time of the system by reducing the frequency of the defrost operation, and stabilizing the heating capacity of the multi-split air conditioning system to the greatest extent.

[0067] When the multi-split air-conditioning system is operating under heating conditions, the outdoor heat exchanger (3) is an evaporator. At this time, the coil temperature Te and the outdoor ambient temperature Ta are relatively low. The outdoor heat exchanger (3) will gradually frost as the heating operation progresses, and the frost will accumulate thicker and thicker, affecting the heat exchange capacity of the outdoor heat exchanger, and ultimately affecting the low-pressure pressure Ps of the system, causing the compressor to reduce frequency, and ultimately affecting the heating performance of the indoor heat exchanger at the user end; therefore, the coil temperature Te of the outdoor heat exchanger (3), the outdoor ambient temperature Ta and the system low-pressure pressure Ps can all affect or reflect the frosting speed or degree of the outdoor heat exchanger (03). This embodiment determines the unloading amount of the refrigerant branch (5) based on the above parameters, and can respond to different working conditions with a dynamically changing unloading amount, thereby delaying the frosting speed of the outdoor heat exchanger or reducing the frosting degree of the outdoor heat exchanger as much as possible.

[0068] Specifically, limit values ​​can be set for the coil temperature Te of the outdoor heat exchanger (3), the outdoor ambient temperature Ta, and the system low pressure Ps, respectively, and the connection of the refrigerant branch (5) can be started by combining any one parameter, any two parameters, or a combination of three parameters. The technical personnel in this field set the limit value based on the actual operating conditions, experience or statistics, and this embodiment does not specifically limit it.

[0069] Embodiment 2

[0070] The multi-split air conditioning system proposed in this embodiment includes:

[0071] An outdoor unit and an indoor unit; wherein the outdoor unit comprises a compressor (1), a four-way valve (2), and an outdoor heat exchanger (3) connected in series; and the indoor unit comprises at least one indoor heat exchanger (4).

[0072] The refrigerant branch (5) is connected between the exhaust side of the compressor (1) and the outdoor heat exchanger (3).

[0073] Uninstall the electronic expansion valve (6) and install it on the refrigerant branch (5). Figure 6 shown.

[0074] In this embodiment, the controller is configured to: during the heating period of the multi-split air conditioning system, control the connection of the refrigerant branch (5), and adjust the opening of the unloading electronic expansion valve (6) in combination with the coil temperature of the outdoor heat exchanger (3), the outdoor ambient temperature and the system low pressure, so as to adjust the unloading amount of the refrigerant branch (5) by adjusting the opening of the unloading electronic expansion valve (6), so that the high-temperature and high-pressure refrigerant discharged from the compressor (1) enters the outdoor heat exchanger (3) from the refrigerant branch (5) at the adjusted unloading amount, and mixes with the refrigerant inside the indoor heat exchanger (3), thereby delaying the frosting of the outdoor heat exchanger (3).

[0075] In the cooling condition, the multi-split air conditioning system controls the four-way valve (2) so that the exhaust side of the compressor (1) is connected to the outdoor heat exchanger (3), and the suction side is connected to the indoor heat exchanger (4). The compressor (1) compresses the sucked low-temperature and low-pressure gaseous refrigerant into high-temperature and high-pressure gaseous refrigerant and discharges it into the outdoor heat exchanger (3) through the four-way valve (1), releases heat in the outdoor heat exchanger (3), and condenses into high-pressure liquid refrigerant. The high-pressure liquid refrigerant enters the indoor heat exchanger (4) after pressure reduction and throttling by the indoor electronic expansion valve, absorbs heat in the indoor heat exchanger (4) and evaporates into gaseous refrigerant. The gaseous refrigerant returns to the suction side of the compressor (1) through the four-way valve (2).

[0076] In the heating condition, the multi-split air conditioning system controls the four-way valve (2) so that the exhaust side of the compressor (1) is connected to the indoor heat exchanger (4), and the suction side is connected to the outdoor heat exchanger (3). The compressor (1) compresses the sucked low-temperature and low-pressure gaseous refrigerant into high-temperature and high-pressure gaseous refrigerant and discharges it into the indoor heat exchanger (4) through the four-way valve (1). The refrigerant releases heat in the indoor heat exchanger (4) and becomes high-pressure liquid refrigerant. The high-pressure liquid refrigerant enters the outdoor heat exchanger (3) after pressure reduction and throttling by the outdoor electronic expansion valve. The high-pressure liquid refrigerant absorbs heat in the outdoor heat exchanger (3) and evaporates into gaseous refrigerant. The gaseous refrigerant returns to the suction side of the compressor (1) through the four-way valve (2).

[0077] refer to Figure 5 As shown, during the heating period of the multi-split air conditioning system, the coil temperature Te of the outdoor heat exchanger (3), the outdoor ambient temperature Ta, and the system low pressure Ps are obtained, and the unloading amount of the high-temperature and high-pressure refrigerant discharged from the compressor (1) to the refrigerant branch (5) is determined according to the coil temperature Te, the outdoor ambient temperature Ta, and the system low pressure Ps. The controller is configured to: determine the opening of the unloading electronic expansion valve (6) according to the determined unloading amount, and adjust the opening of the unloading electronic expansion valve (6) according to the opening, so that the refrigerant branch (5) is connected and the high-temperature and high-pressure refrigerant is discharged to the refrigerant branch (5) according to the determined unloading amount, and the high-temperature and high-pressure refrigerant enters the outdoor heat exchanger (3) from the refrigerant branch (5). ), is mixed with the refrigerant inside the outdoor heat exchanger (3), and its high temperature is used to increase the coil temperature of the outdoor heat exchanger (3), thereby delaying the frosting speed of the outdoor heat exchanger (3). At the same time, the evaporation pressure and evaporation temperature of the outdoor heat exchanger (3) are increased by the high-temperature and high-pressure refrigerant, further delaying the frosting speed of the outdoor heat exchanger (3), ensuring the high-frequency operation of the compressor (1), and ensuring the heating capacity of the indoor heat exchanger (4); when the frosting speed of the outdoor heat exchanger (3) is delayed, the operating conditions for the multi-split air-conditioning system to enter the defrost mode are reduced, thereby increasing the heating time of the system by reducing the frequency of the defrost operation, and stabilizing the heating capacity of the multi-split air-conditioning system to the greatest extent.

[0078] Embodiment 3

[0079] The multi-split air conditioning system proposed in this embodiment includes:

[0080] An outdoor unit and an indoor unit; wherein the outdoor unit comprises a compressor (1), a four-way valve (2), and an outdoor heat exchanger (3) connected in series; and the indoor unit comprises at least one indoor heat exchanger (4).

[0081] The refrigerant branch (5) is connected between the exhaust side of the compressor (1) and the outdoor heat exchanger (3).

[0082] The unloading electronic expansion valve (6) is installed on the refrigerant branch line (5).

[0083] In this embodiment, the controller is configured to: during the heating period of the multi-split air conditioning system, control the connection of the refrigerant branch (5), and adjust the opening of the unloading electronic expansion valve (6) in combination with the coil temperature Te of the outdoor heat exchanger (3), the outdoor ambient temperature Ta and the system low pressure Ps, so as to adjust the unloading amount of the refrigerant branch (5) by adjusting the opening of the unloading electronic expansion valve (6), so that the high-temperature and high-pressure refrigerant discharged from the compressor (1) enters the outdoor heat exchanger (3) from the refrigerant branch (5) at the adjusted unloading amount, and mixes with the refrigerant inside the indoor heat exchanger (3), thereby delaying the frosting of the outdoor heat exchanger (3).

[0084] refer to Figure 5 As shown, during the heating period of the multi-split air conditioning system, the coil temperature Te of the outdoor heat exchanger (3), the outdoor ambient temperature Ta, and the system low pressure Ps are obtained, and the unloading amount of the high-temperature and high-pressure refrigerant discharged by the compressor (1) to the refrigerant branch (5) is determined according to the coil temperature Te, the outdoor ambient temperature Ta, and the system low pressure Ps. The controller is configured as follows:

[0085] 1. Determine the opening degree of the unloading electronic expansion valve (6) according to the determined unloading amount.

[0086] 2. According to EVX(n)=EVX(n-1)+ΔEVX, and 0≤EVX(n)≤1 / 2*EVXmax, adjust the opening of the unloading electronic expansion valve (6).

[0087] Among them, EVX(n) is the current opening degree of the unloading electronic expansion valve (6), and EVX(n-1) is the previous

[0088] The opening of the unloading electronic expansion valve (6) in each control cycle, ΔEVX is the adjustment amount of the opening of the unloading electronic expansion valve in each control cycle, and EVXmax is the maximum opening of the unloading electronic expansion valve.

[0089] The control cycle is the time interval for adjusting the unloading of the electronic expansion valve (6), for example, in the heating condition, the unloading amount is determined and adjusted every five minutes.

[0090] In this embodiment, if Figure 7As shown, the controller is further configured as follows:

[0091] S1: Determine the ambient temperature range in which the outdoor ambient temperature is located and the system low pressure range in which the system low pressure is located.

[0092] S2: Determine the adjustment amount of the opening of the unloading electronic expansion valve according to the ambient temperature range and the system low pressure range.

[0093] S3: When the execution condition is met, adjusting the opening degree of the unloading electronic expansion valve based on the determined adjustment amount.

[0094] And, S4: stop regulating and unloading the electronic expansion valve when the exit condition is met.

[0095] That is, in this embodiment, the outdoor ambient temperature is divided into M ambient temperature intervals;

[0096] N system low-pressure pressure intervals are divided according to the system low-pressure pressure within the temperature interval; each system low-pressure pressure interval is set with an execution condition, an exit condition and an adjustment amount of the unloading electronic expansion valve.

[0097] The execution condition and the exit condition are limited based on the minimum value of the coil temperature of the outdoor heat exchanger.

[0098] like Figure 8 A specific embodiment is shown: Temin is the minimum value of the coil temperature of the outdoor heat exchanger (3), the execution condition is set to the minimum value of the coil temperature of the outdoor heat exchanger not exceeding the first specified value, and the exit condition is set to the minimum value of the coil temperature of the outdoor heat exchanger not lower than the second specified value. The parameters a, b, c and other parameters and the influencing factors d, e, f, g and other factors in the table can be obtained based on the experience or statistical values ​​of actual working conditions.

[0099] It can be seen that when the outdoor ambient temperature Ta ≥ 6°C, due to the good heat exchange capacity of the outdoor heat exchanger, the low-pressure pressure Ps of the system will also be relatively high. When the low-pressure pressure Ps of the system ≥ 0.65 Mpa, it can be basically defaulted that the outdoor heat exchanger frosts slowly or does not frost. At this time, the opening m% of the EVX will be relatively small, but it can still achieve the purpose of delaying frosting; when 0.60 < Ps < 0.65, there is a possibility that the outdoor heat exchanger will gradually frost, and the opening n% of the EVX will be slightly larger to achieve the effect of delaying the frosting speed of the outdoor heat exchanger; when the low-pressure pressure Ps of the system ≤ 0.6 Mpa, the frosting speed of the outdoor heat exchanger will be relatively fast. At this time, the opening control of the EVX will be relatively large, which can delay the frosting speed of the outdoor heat exchanger to a certain extent. As the outdoor ambient temperature and the low-pressure pressure of the system decrease, the user's demand for heating also increases, and the corresponding EVX control also gradually increases, delaying the frosting speed of the outdoor heat exchanger to a greater extent, ensuring the continuous heating time, maximizing the heating time and capacity, and improving the user's comfort.

[0100] In the above-mentioned embodiment, the outdoor ambient temperature is divided into M ambient temperature intervals. In each ambient temperature interval, the low-pressure pressure of the system is further divided into N low-pressure pressure intervals of the system. For each low-pressure pressure interval of the system, there are execution conditions, exit conditions, and the adjustment amount of the unloading electronic expansion valve. When adjusting the unloading electronic expansion valve, according to the ambient temperature interval where the current outdoor ambient temperature is located and the current low-pressure pressure of the system, when the execution conditions are met, the opening of the unloading electronic expansion valve is adjusted based on the opening of the unloading electronic expansion valve in the previous control cycle according to the determined adjustment amount, and the adjustment is exited when the exit conditions are met. If the exit conditions are not met, the opening of the unloading electronic expansion valve is continuously adjusted based on the opening of the unloading electronic expansion valve in the previous control cycle according to the determined adjustment amount, realizing the precise control of the refrigerant branch unloading amount.

[0101] Embodiment 4

[0102] This embodiment is implemented on the basis of Embodiment 3. The multi-connected air-conditioning system given includes:

[0103] An outdoor unit and an indoor unit; wherein, the outdoor unit includes a compressor (1), a four-way valve (2), and an outdoor heat exchanger (3) connected in series; the indoor unit includes at least one indoor heat exchanger (4).

[0104] A refrigerant branch (5) is connected between the exhaust side of the compressor (1) and the outdoor heat exchanger (3).

[0105] A unloading electronic expansion valve (6) is installed on the refrigerant branch (5).

[0106] The memory is used to store the relationship data between the ambient temperature range, the system low pressure, the execution condition, the exit condition and the adjustment amount of the opening of the unloading electronic expansion valve, such as the relationship data shown in Table 1 in Example 3.

[0107] The controller is configured to query the relational data in the memory, determine the adjustment amount of the opening of the unloading electronic expansion valve (6) based on the ambient temperature range and the system low pressure range under the current working conditions, obtain the execution conditions and exit conditions under the ambient temperature range and the system low pressure range, adjust the opening of the unloading electronic expansion valve (6) based on the opening of the unloading electronic expansion valve (6) in the previous control cycle according to the determined adjustment amount when the execution conditions are met, and exit the adjustment when the exit conditions are met.

[0108] In this embodiment, the memory stores the relationship data between the ambient temperature range, the system low-pressure range, the execution conditions, the exit conditions and the adjustment amount of the opening of the unloading electronic expansion valve. During the heating period of the system, the system obtains the outdoor ambient temperature and the system low-pressure pressure, queries the relationship data in the memory, determines the adjustment amount of the opening of the unloading electronic expansion valve based on the ambient temperature range and the system low-pressure pressure range under the current working conditions, obtains the execution conditions and the exit conditions under the ambient temperature range and the system low-pressure pressure range, and adjusts the opening of the unloading electronic expansion valve according to the determined adjustment amount on the basis of the opening of the unloading electronic expansion valve in the previous control cycle when the execution conditions are met, and exits the adjustment when the exit conditions are met. If the exit conditions are not met, the opening of the unloading electronic expansion valve continues to be adjusted according to the determined adjustment amount on the basis of the opening of the unloading electronic expansion valve in the previous control cycle.

[0109] Embodiment 5

[0110] Based on the implementation of any one of the above-mentioned embodiments 1 to 4, the speed of frosting of the outdoor heat exchanger can be delayed, but delay does not mean no frosting. In actual working conditions, if frosting occurs on the outdoor heat exchanger, the defrosting program still needs to be started to defrost the outdoor heat exchanger. The specific implementation of defrosting control is implemented according to the existing defrosting method, which is not specifically limited in this embodiment.

[0111] When the system is actually running, the relative humidity of the outdoor environment is low, which makes the outdoor heat exchanger frost very slowly or not frost at all. However, if the defrosting conditions are determined based on the current outdoor environment temperature Ta and the coil temperature Te of the outdoor heat exchanger, an unnecessary defrost program will be started, resulting in false defrosting, which not only wastes energy but also reduces the indoor temperature and reduces the user experience.

[0112] In view of this, considering that the heat exchange capacity of the outdoor heat exchanger will inevitably decrease when it is frosted, the system low pressure Ps will inevitably decrease, and finally it will enter defrosting. At this time, if the outdoor heat exchanger is frost-free, although the conditions of the outdoor ambient temperature Ta and the coil temperature Te of the outdoor heat exchanger are met, the system low pressure Ps will not drop significantly. Based on the measures given in this embodiment to determine whether to enter defrosting by using the change in the system low pressure at different ambient temperatures, it can avoid the system from entering false defrosting, thereby not affecting the normal heating.

[0113] Specifically, the multi-split air conditioning system proposed in this embodiment includes:

[0114] An outdoor unit and an indoor unit; wherein the outdoor unit comprises a compressor (1), a four-way valve (2), and an outdoor heat exchanger (3) connected in series; and the indoor unit comprises at least one indoor heat exchanger (4).

[0115] The refrigerant branch (5) is connected between the exhaust side of the compressor (1) and the outdoor heat exchanger (3).

[0116] The unloading electronic expansion valve (6) is installed on the refrigerant branch line (5).

[0117] like Fig. 9 As shown, the controller is configured as:

[0118] S91: Determine the ambient temperature range in which the outdoor ambient temperature is located.

[0119] S92: Start defrosting according to the defrost execution conditions specified within the ambient temperature range.

[0120] In this embodiment, the defrosting execution conditions include: 1) the coil temperature Te of the outdoor heat exchanger is lower than

[0121] The first defrost limit; 2) the change in the system low pressure Ps is lower than the first change; 3) the heating time meets the heating time limit. All three must be met.

[0122] The change of the system low pressure Ps is obtained according to Ps-Ps_start, where Ps-Ps_start is the system low pressure after the system enters the heating condition and stabilizes. For example, ten minutes after the system switches to the heating condition, the heating operation enters a stable state, and the system low pressure value at this time is obtained as Ps-Ps_start. Thereafter, when determining whether to switch to the defrost condition, the change of the system low pressure is calculated based on Ps_start.

[0123] S93: Exit defrost when the defrost exit conditions specified within the ambient temperature range are met.

[0124] The defrost exit conditions include: 1) The coil temperature of the outdoor heat exchanger is higher than the second defrost limit.

[0125] value; 2) the system high pressure is higher than the high pressure limit; 3) or the defrost time meets the defrost time limit. At least one of the three is met.

[0126] like Fig.10 A specific embodiment shown: Ps(n)-Ps_start is determined every set time, Pd is the high pressure during defrosting, and the shortest z is the shortest time that the heating time meets under the heating condition. Only when this short time is met can the defrosting be entered. When the ambient temperature is high, due to the good heat exchange capacity of the outdoor heat exchanger, the change of the system low pressure can be set larger, the shortest heating time is longer, and the system is not easy to enter false defrosting. As the outdoor ambient temperature decreases, the possibility of frost on the outdoor heat exchanger increases, the change of the system low pressure is set to decrease, and the shortest heating time also begins to decrease, avoiding the inability to implement effective defrosting.

[0127] The relationship data among the outdoor ambient temperature, the defrost execution conditions, and the defrost exit conditions shown in the figure are stored in the memory for query by the controller.

[0128] Embodiment 6

[0129] This embodiment is implemented on the basis of the fifth embodiment. Fig.11 As shown, when the defrost exit condition includes the situation that the system high pressure exceeds the high pressure limit, the controller is configured as follows:

[0130] S94: Increase the minimum time limit z that the heating time must meet in the defrost execution condition.

[0131] For example, when the defrost exit condition includes the system high pressure Pd ≥ 3.0Mpa, it means that the high pressure is too high during the defrost process, which can also indicate the problem of frost-free outdoor heat exchanger. At this time, the shortest time limit that the heating time must meet in the defrost execution condition can be increased, that is, z=z+Δt, where Δt can be given based on experience or statistical values.

[0132] Embodiment 7

[0133] like Fig.12 As shown, the multi-split air conditioning system provided in this embodiment includes:

[0134] An outdoor unit and an indoor unit; wherein the outdoor unit comprises a compressor (1), a four-way valve (2), and an outdoor heat exchanger (3) connected in series; and the indoor unit comprises at least one indoor heat exchanger (4).

[0135] The refrigerant branch (5) is connected between the exhaust side of the compressor (1) and the outdoor heat exchanger (3).

[0136] The controller (not shown in the figure) is configured to: during the heating period of the multi-split air conditioning system, control the connection of the refrigerant branch (5) so that the high-temperature and high-pressure refrigerant discharged from the compressor (1) enters the outdoor heat exchanger (3) from the refrigerant branch (5) and mixes with the refrigerant inside the indoor heat exchanger (3), thereby delaying the frosting of the outdoor heat exchanger (3).

[0137] The unloading electronic expansion valve (6) is installed on the refrigerant branch line (5).

[0138] The flow divider (7) has an input end connected to the refrigerant branch (5), and an output end connected to the outdoor heat exchanger (3), and the output end includes at least two output ports, and at least the two output ports are connected to the outdoor heat exchanger (3) at different locations of the outdoor heat exchanger (3).

[0139] The outdoor heat exchanger (3) and the indoor heat exchanger (4) are used as a condenser or an evaporator. When the indoor heat exchanger (4) is used as a condenser, the indoor unit is used as a heater in a heating mode, and the outdoor heat exchanger (3) is used as an evaporator in a heating mode to absorb heat from the outdoor environment. When the indoor heat exchanger (4) is used as an evaporator, the indoor unit is used as a cooler in a cooling mode, and the outdoor heat exchanger (3) is used as a heater in a cooling mode to release heat to the outdoor environment.

[0140] In the cooling condition, the multi-split air conditioning system controls the four-way valve (2) so that the exhaust side of the compressor (1) is connected to the outdoor heat exchanger (3), and the suction side is connected to the indoor heat exchanger (4). The compressor (1) compresses the sucked low-temperature and low-pressure gaseous refrigerant into high-temperature and high-pressure gaseous refrigerant and discharges it into the outdoor heat exchanger (3) through the four-way valve (1), releases heat in the outdoor heat exchanger (3), and condenses into high-pressure liquid refrigerant. The high-pressure liquid refrigerant enters the indoor heat exchanger (4) after pressure reduction and throttling by the indoor electronic expansion valve, absorbs heat in the indoor heat exchanger (4) and evaporates into gaseous refrigerant. The gaseous refrigerant returns to the suction side of the compressor (1) through the four-way valve (2).

[0141] In the heating condition, the multi-split air conditioning system controls the four-way valve (2) so that the exhaust side of the compressor (1) is connected to the indoor heat exchanger (4), and the suction side is connected to the outdoor heat exchanger (3). The compressor (1) compresses the sucked low-temperature and low-pressure gaseous refrigerant into high-temperature and high-pressure gaseous refrigerant and discharges it into the indoor heat exchanger (4) through the four-way valve (1). The refrigerant releases heat in the indoor heat exchanger (4) and becomes high-pressure liquid refrigerant. The high-pressure liquid refrigerant enters the outdoor heat exchanger (3) after pressure reduction and throttling by the outdoor electronic expansion valve. The high-pressure liquid refrigerant absorbs heat in the outdoor heat exchanger (3) and evaporates into gaseous refrigerant. The gaseous refrigerant returns to the suction side of the compressor (1) through the four-way valve (2).

[0142] The indoor / outdoor electronic expansion valve expands the high-temperature and high-pressure liquid refrigerant condensed in the condenser into a low-pressure liquid refrigerant. The evaporator evaporates the refrigerant expanded in the expansion valve and returns the low-temperature and low-pressure refrigerant gas to the compressor. The evaporator can achieve a cooling effect by utilizing the latent heat of evaporation of the refrigerant to exchange heat with the material to be cooled. In the entire cycle, the multi-split air conditioning system adjusts the temperature of the indoor space.

[0143] During the heating period of the multi-split air conditioning system, the refrigerant branch (5) is controlled to be connected, so that a part of the high-temperature and high-pressure refrigerant discharged from the compressor (1) (as shown by the hollow arrow in the figure) enters the indoor heat exchanger (4) to achieve indoor heating through condensation and heat release; a part (as shown by the black solid arrow in the figure) enters the diverter (7) from the refrigerant branch (5), and is diverted from different positions to enter the outdoor heat exchanger (3), where it is evenly mixed with the refrigerant inside the outdoor heat exchanger (3), and its high temperature is used to increase the coil temperature of the outdoor heat exchanger (3), thereby delaying the outdoor heat exchange. The frosting speed of the outdoor heat exchanger (3) is reduced; at the same time, the evaporation pressure and evaporation temperature of the outdoor heat exchanger (3) can be increased by using a high-temperature and high-pressure refrigerant, thereby further delaying the frosting speed of the outdoor heat exchanger (3), ensuring the high-frequency operation of the compressor (1), and ensuring the heating performance of the indoor heat exchanger (4); when the frosting speed of the outdoor heat exchanger (3) is delayed, the number of conditions in which the multi-split air-conditioning system enters the defrost mode is reduced, thereby increasing the heating time of the system by reducing the frequency of the defrost operation, and stabilizing the heating capacity of the multi-split air-conditioning system to the greatest extent.

[0144] In this embodiment, at least two output ports of the diverter (7) are connected to the outdoor heat exchanger (3) at different locations of the outdoor heat exchanger (3), so that the high-temperature and high-pressure refrigerant discharged from the compressor (1) is evenly mixed with the refrigerant inside the outdoor heat exchanger (3), thereby improving the overall effect of delaying frost formation of the outdoor heat exchanger.

[0145] In the description of the above embodiments, specific features, structures, materials or characteristics may be combined in a suitable manner in any one or more embodiments or examples.

[0146] The above is only a preferred embodiment of the present invention, and does not limit the present invention in other forms. Any technician familiar with the profession may use the above disclosed technical content to change or modify it into an equivalent embodiment with equivalent changes. However, any simple modification, equivalent change and modification made to the above embodiment according to the technical essence of the present invention without departing from the technical solution of the present invention still belongs to the protection scope of the technical solution of the present invention.

Claims

1. A multi-split air conditioning system, comprising: An outdoor unit and an indoor unit; wherein the outdoor unit comprises a compressor, a four-way valve, and an outdoor heat exchanger connected in series; Characterized in that the system further comprises: A refrigerant branch connected between the exhaust side of the compressor and the outdoor heat exchanger; The controller is configured as: During the heating period of the multi-split air conditioning system, the refrigerant branch is connected so that part of the high-temperature and high-pressure refrigerant discharged from the compressor enters the outdoor heat exchanger from the refrigerant branch and mixes with the refrigerant in the indoor heat exchanger, thereby delaying the frosting of the outdoor heat exchanger; The controller is further configured to: adjust the unloading amount of the refrigerant branch circuit in combination with the coil temperature of the outdoor heat exchanger, the outdoor ambient temperature and the system low pressure; The refrigerant branch includes an unloading electronic expansion valve; the controller is further configured to: adjust the opening of the unloading electronic expansion valve in combination with the coil temperature of the outdoor heat exchanger, the outdoor ambient temperature and the system low pressure; The controller is configured to: According to EVX(n)=EVX(n-1)+ΔEVX, and 0≤EVX(n)≤1 / 2*EVXmax, the opening degree of the unloading electronic expansion valve is adjusted; Among them, EVX(n) is the current opening of the unloading electronic expansion valve, EVX(n-1) is the opening of the unloading electronic expansion valve in the previous control cycle, ΔEVX is the adjustment amount of the opening of the unloading electronic expansion valve in each control cycle, and EVXmax is the maximum opening of the unloading electronic expansion valve; The controller is configured to: Obtain the outdoor ambient temperature and the system low pressure, and determine the ambient temperature range of the outdoor ambient temperature and the system low pressure range of the system low pressure; Determine the adjustment amount of the opening of the unloading electronic expansion valve according to the ambient temperature range and the system low pressure range; When an execution condition is met, adjusting the opening of the unloading electronic expansion valve based on the determined adjustment amount, and when an exit condition is met, stopping adjusting the unloading electronic expansion valve; Among them, the outdoor ambient temperature is divided into M ambient temperature intervals; in each ambient temperature interval, N system low pressure intervals are divided for the system low pressure; each system low pressure interval is provided with an execution condition, an exit condition and an adjustment amount of the unloading electronic expansion valve; the execution condition and the exit condition are limited based on the minimum value of the coil temperature of the outdoor heat exchanger; The execution condition is set to that the minimum value of the coil temperature of the outdoor heat exchanger does not exceed a first specified value; and the exit condition is set to that the minimum value of the coil temperature of the outdoor heat exchanger is not lower than a second specified value.

2. The multi-split air conditioning system according to claim 1, characterized in that: The system further comprises: A memory for storing relationship data between an ambient temperature range, a system low pressure range, an execution condition, an exit condition, and an adjustment amount of an opening of an unloading electronic expansion valve; The controller is configured to: query the relational data in the memory, determine the adjustment amount of the opening of the unloading electronic expansion valve based on the ambient temperature range and the system low-pressure range under the current operating conditions, obtain the execution conditions and exit conditions under the ambient temperature range and the system low-pressure range, adjust the opening of the unloading electronic expansion valve based on the opening of the unloading electronic expansion valve in the previous control cycle according to the determined adjustment amount when the execution conditions are met, and exit the adjustment when the exit conditions are met.

3. The multi-split air conditioning system according to claim 1, characterized in that: The controller is configured to: Determine the ambient temperature range of the outdoor ambient temperature; The defrost is started according to the defrost execution conditions defined in the ambient temperature range, and the defrost is exited when the defrost exit conditions defined in the ambient temperature range are met; Among them, the defrost execution conditions include: the coil temperature of the outdoor heat exchanger is lower than the first defrost limit, the change in the system low pressure is lower than the first change, and the heating time meets the heating time limit, all three must be met; the defrost exit conditions include: the coil temperature of the outdoor heat exchanger is higher than the second defrost limit, the system high pressure exceeds the high pressure limit, or the defrost time meets the defrost time limit, at least one of the three must be met.

4. According to the multi-split air conditioning system according to claim 3, it is characterized in that: The controller is configured to: Obtain the current system low pressure and the first system low pressure after the set time of switching to heating mode; A change in the system low pressure is obtained based on a difference between the current system low pressure and the first system low pressure.

5. According to the multi-split air conditioning system according to claim 3, it is characterized in that: The controller is configured to: When the defrost exit condition includes the system high pressure exceeding the high pressure limit, the minimum time limit that the heating time in the defrost execution condition must meet is increased.

6. The multi-split air conditioning system according to claim 1, characterized in that: The system further comprises: The diverter has an input end connected to the refrigerant branch, an output end connected to the outdoor heat exchanger, and an output end thereof includes at least two output ports, and the at least two output ports are connected to the outdoor heat exchanger at different locations of the outdoor heat exchanger.

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