Outdoor unit, multi-connected air conditioning system and control method

Abstract

This invention relates to the field of air conditioning technology, specifically providing an outdoor unit, a multi-split air conditioning system, and a control method. The aim is to solve the problems of low heat exchange efficiency at the bottom of the outdoor unit's heat exchanger, low overall operating efficiency of the multi-split air conditioning system, and low steady-state heating capacity of the multi-split air conditioning system. To this end, the outdoor unit of this invention includes a heat exchanger and a fan. The total height of the heat exchanger is H, and the heat exchanger is divided into n equal parts from top to bottom. The total air volume Q required for heat exchange by the heat exchanger is... 总 The wind speed distribution in each equal part of the heat exchanger: a1, a2, a3, ... a n‑1 a n According to H, n, Q 总 a1, a2, a3, ... a n‑1 a n This invention determines the number of fan layers and the diameter of the fan blades. It can create a uniform airflow and improve the heat exchange efficiency at the bottom of the heat exchanger, thereby improving the overall operating efficiency of the multi-split air conditioning system. It can also improve the matching degree between the airflow of the heat exchanger and the refrigerant flow rate, thus enhancing the steady-state heating capacity of the multi-split air conditioning system.

Description

Technical Field

[0001] This invention relates to the field of air conditioning technology, specifically providing an outdoor unit, a multi-split air conditioning system, and a control method. Background Technology

[0002] Multi-split air conditioning systems evolved from traditional air conditioners and are a type of central air conditioning system for users. Commonly known as "one-to-many," it refers to a system where one outdoor unit is connected to two or more indoor units via piping. Multi-split air conditioning systems are increasingly widely used in small and medium-sized buildings and some public buildings.

[0003] Multi-split air conditioning systems typically use top-discharge or side-discharge outdoor units. In top-discharge units, the fan is located at the top of the heat exchanger, while the lower part of the heat exchanger is farther from the fan, resulting in greater air resistance and thus lower airflow or velocity. Consequently, the airflow in the outdoor heat exchanger experiences a significant vertical reduction. This uneven airflow is particularly pronounced when the heat exchanger is tall. Existing technology reduces the resistance at the top of the heat exchanger by decreasing the tube length, thereby increasing the refrigerant flow in the higher airflow section and decreasing it in the lower section. By altering the refrigerant flow in the upper and lower parts of the heat exchanger, the uneven airflow in top-discharge outdoor units can be improved, allowing the heat exchange capacity of the upper part of the heat exchanger to be fully utilized.

[0004] However, the refrigerant flow and air volume at the bottom of the heat exchanger are small, resulting in insufficient utilization of the heat exchange area and low heat exchange efficiency. This leads to low overall heat exchange efficiency of the outdoor unit's heat exchanger, and consequently, low overall operating efficiency of the multi-split air conditioning system. Furthermore, due to the poor uniformity of the airflow in the top-discharge outdoor unit, the outdoor unit's evaporation capacity is poor while meeting condensation requirements, resulting in low steady-state heating capacity of the multi-split air conditioning system.

[0005] Accordingly, there is a need in this field for a new outdoor unit, multi-split air conditioning system, and control method to solve the above problems. Summary of the Invention

[0006] The present invention aims to solve the above-mentioned technical problems, namely, to solve the problem that when the heat exchanger is high, the uniformity of the air field of the top-discharge outdoor unit is poor, resulting in low heat exchange efficiency at the bottom of the heat exchanger, which in turn leads to low overall heat exchange efficiency of the outdoor unit heat exchanger, low overall operating efficiency of the multi-split air conditioning system, and low steady-state heating capacity of the multi-split air conditioning system.

[0007] In a first aspect, the present invention provides an outdoor unit.

[0008] In the preferred technical solution of the outdoor unit described above, the outdoor unit includes a heat exchanger and a fan. The total height of the heat exchanger is H. The heat exchanger is divided into n equal parts from top to bottom. The total air volume Q required for heat exchange by the heat exchanger is... 总 The wind speed distribution in each equal part of the heat exchanger is as follows: a1, a2, a3, ... a n-1 a n ;

[0009] According to H, n, Q 总 a1, a2, a3, ... a n-1 a n The number of layers of the fan and the diameter of the fan are determined.

[0010] In the preferred technical solution of the outdoor unit mentioned above, the fan diameter is D0 when using a single-layer fan, and when using a double-layer fan, the fan includes an upper fan and a lower fan, the fan diameter of the upper fan is D1, and the fan diameter of the lower fan is D2.

[0011] When a1 / a n When μ is less than or equal to 0, the fan is designed as a single-layer fan;

[0012] Where μ is a preset constant.

[0013] In the preferred technical solution of the outdoor unit described above, when the fan is designed as a single layer, the fan diameter of the fan satisfies the following relationship:

[0014]

[0015] In this context, α1, α2, and α3 are all constants.

[0016] In the preferred technical solution of the outdoor unit described above, when the height of the heat exchanger is higher than the set value, the wind speed at the k-th moment reaches a1 / a k <μ and a1 / a k →μ, simultaneously satisfying a1 / a k+1 >μ and a k+1 / a n When μ is less than or equal to 0, the fan is designed as a double-layer fan.

[0017] The lower-level fan is installed in the (k+1)th section and below of the heat exchanger, meaning the installation height of the lower-level fan is: H. 下 <(nk)H / n.

[0018] In the preferred technical solution of the outdoor unit described above, the fan diameters of the upper and lower fans should satisfy the following relationship:

[0019]

[0020] Among them, γ1, γ2, γ3, δ1, δ2 and δ3 are all constants.

[0021] In the preferred technical solution of the outdoor unit mentioned above, the heat exchanger is arranged to form an air duct, and in the case of a double-layer fan, both the upper fan and the lower fan are located inside the air duct.

[0022] The outdoor unit also includes a housing and a support frame. The heat exchanger is located inside the housing, and the support frame is mounted on the housing and located inside the air duct.

[0023] The support frame includes a fan cover and several columns mounted on the fan cover. The columns are connected to the housing, and the lower fan is mounted on the fan cover.

[0024] In the preferred technical solution of the outdoor unit described above, the support frame further includes a sound insulation layer disposed on the fan cover, the outdoor unit further includes a compressor, the compressor is connected to the heat exchanger through a pipeline, and the compressor is located in the space formed by the sound insulation layer, the column and the shell.

[0025] Secondly, the present invention provides a multi-split air conditioning system.

[0026] In the preferred embodiment of the multi-split air conditioning system described above, the multi-split air conditioning system includes an outdoor unit.

[0027] Thirdly, the present invention provides a control method for a multi-split air conditioning system.

[0028] In the preferred technical solution of the control method of the above-mentioned multi-split air conditioning system, the multi-split air conditioning system includes an outdoor unit, the outdoor unit includes a heat exchanger, an upper fan, a lower fan, a first defrost temperature sensor and a second defrost temperature sensor, the first defrost temperature sensor is located on the upper part of the heat exchanger, and the second defrost temperature sensor is located on the lower part of the heat exchanger.

[0029] The heat exchanger is arranged to form an air duct, and the upper fan and the lower fan are both located in the air duct. The lower fan is located below the upper fan and in the lower middle part of the air duct.

[0030] The control method includes the following steps:

[0031] The temperature Tdef1 of the first defrost temperature sensor and the temperature Tdef2 of the second defrost temperature sensor are obtained, and the speed of the upper and lower fans is controlled according to the difference between Tdef1 and Tdef2 to adjust the airflow of the outdoor unit.

[0032] In the preferred technical solution of the outdoor unit described above, "obtaining the temperature Tdef1 of the first defrost temperature sensor and the temperature Tdef2 of the second defrost temperature sensor, and controlling the speed of the upper and lower fans based on the difference between Tdef1 and Tdef2 to adjust the airflow of the outdoor unit" specifically includes the following steps:

[0033] When Tdef1-Tdef2>the first preset value, the speed of the lower fan is increased to increase the air volume at the bottom of the heat exchanger;

[0034] When Tdef1-Tdef2 < the second preset value, the rotational speed of the upper fan is increased to increase the air volume at the top of the heat exchanger.

[0035] When the above technical solution is adopted, during outdoor unit operation, the upper and lower fans are activated. Outside air, driven by the upper and lower fans, enters the casing through the air inlet and exchanges heat with the heat exchanger. The heat-exchanged air is then discharged from the air outlet of the duct. By adding a lower fan within the duct and positioning it in the lower middle part of the heat exchanger, the airflow at the bottom of the heat exchanger is increased, the airflow becomes more uniform, and the heat exchange efficiency at the bottom of the heat exchanger is improved. This, in turn, improves the overall heat exchange efficiency of the heat exchanger and consequently, the overall operating efficiency of the multi-split air conditioning system.

[0036] Furthermore, by adding a lower fan, the airflow of the outdoor unit becomes more uniform, thereby improving the matching degree between the airflow at the bottom of the heat exchanger and the refrigerant flow in each flow path at the bottom of the heat exchanger. This makes it less prone to frost formation at the bottom of the heat exchanger, thus enhancing the steady-state heating capacity of the multi-split air conditioning system. Attached Figure Description

[0037] The preferred embodiments of the present invention are described below with reference to the accompanying drawings, in which:

[0038] Figure 1 This is a schematic diagram of the outdoor unit in Embodiment 1 of the present invention;

[0039] Figure 2 This is a flowchart of the main steps of the control method for the multi-split air conditioning system in Embodiment 2 of the present invention;

[0040] Figure 3 This is a detailed flowchart of the control method for the multi-split air conditioning system in Embodiment 2 of the present invention;

[0041] 1. Shell; 2. Heat exchanger; 21. Air duct; 31. First fan; 32. First guide ring; 33. Second fan; 34. Second guide ring; 4. Lower fan; 51. Fan cover; 52. Column; 53. Sound insulation layer; 6. Compressor; 7. Base plate. Detailed Implementation

[0042] Preferred embodiments of the present invention will now be described with reference to the accompanying drawings. Those skilled in the art should understand that these embodiments are merely illustrative of the technical principles of the invention and are not intended to limit the scope of protection of the invention. Those skilled in the art can make adjustments as needed to adapt to specific applications.

[0043] It should be noted that in the description of this invention, terms such as "upper," "lower," "left," and "right," indicating directional or positional relationships, are based on the directional or positional relationships shown in the accompanying drawings. These are merely for ease of description and do not indicate or imply that the device or element must have a specific orientation, or be constructed and operated in a specific orientation; therefore, they should not be construed as limitations on this invention. Furthermore, the terms "first," "second," "third," and "fourth" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0044] Furthermore, it should be noted that, in the description of this invention, unless otherwise explicitly specified and limited, the terms "connected," "linked," and "connected" should be interpreted broadly. For example, they can refer to a fixed connection or a detachable connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0045] Example 1

[0046] To address the issue of low refrigerant flow and air volume at the bottom of the heat exchanger, resulting in low heat exchange efficiency at the bottom of the heat exchanger, which in turn leads to low overall heat exchange efficiency of the outdoor unit heat exchanger and consequently low overall operating efficiency of the multi-split air conditioning system.

[0047] like Figure 1 As shown, this embodiment discloses a multi-split air conditioning system, which includes a control system, an outdoor unit, and several indoor units. Each indoor unit is connected to the outdoor unit through pipes. The control system controls the outdoor unit and indoor units to cool or heat the indoor units. Specifically, the outdoor unit includes a casing 1, a heat exchanger 2, a fan, and a support frame. The casing 1 has an air inlet on its side (not shown in the figure), an air outlet on its top (not shown in the figure), and a base plate 7 fixed to the bottom of the casing 1 to form an installation space.

[0048] The heat exchanger 2 is located within the installation space and fixed to the base plate 7. The heat exchanger 2 forms an air duct 21, the cross-section of which is rectangular, but can also be circular or other shapes. A first defrost temperature sensor (not shown in the figure) is installed on the upper part of the heat exchanger 2, which can upload the temperature Tdef1 of the upper part of the heat exchanger 2 to the control system of the multi-split air conditioning system. A second defrost temperature sensor (not shown in the figure) is installed on the lower part of the heat exchanger 2, which can upload the temperature Tdef2 of the lower part of the heat exchanger 2 to the control system of the multi-split air conditioning system.

[0049] like Figure 1 As shown, depending on different operating conditions, the outdoor unit's fan can be configured as a single-layer or double-layer fan to improve the uniformity of the airflow inside the outdoor unit. This allows for more effective utilization of the heat exchange area at the bottom of heat exchanger 2, improving the heat exchange efficiency at the bottom of heat exchanger 2, thereby increasing the overall heat exchange efficiency of outdoor unit heat exchanger 2 and ultimately improving the overall operating efficiency of the multi-split air conditioning system.

[0050] Furthermore, whether the fan is designed as a single-layer or double-layer fan can be determined using the following method:

[0051] The total height of heat exchanger 2 is H. If heat exchanger 2 is divided into n equal parts from top to bottom, the total air volume Q required for heat exchanger 2 is... 总 The wind speed distribution in each equal part of heat exchanger 2: a1, a2, a3, ... a n-1 a n The wind speed distribution in each equal part of heat exchanger 2 can be obtained through fluid simulation calculations or experimental tests. Based on H, n, and Q... 总 a1, a2, a3, ... a n-1 a n Determine the number of floors in the fan and the diameter of the fan.

[0052] The fan diameter for a single-layer fan is D0; for a double-layer fan, the fan consists of an upper fan and a lower fan 4, with the upper fan diameter being D1 and the lower fan 4 diameter being D2; when a1 / a n When μ is less than or equal to μ, μ is a preset constant, and the fan is designed as a single layer (not shown in the figure in this case).

[0053] Specifically, the single-layer fan is mounted on the housing 1 via a guide ring and is located at the air outlet of the air duct 21. During operation, the single-layer fan is started, and outside air enters the housing 1 through the air inlet under the action of the fan, exchanging heat with the heat exchanger 2. The heat-exchanged air is then discharged from the air outlet of the housing 1. Because a1 / a n When the value is ≤μ, the airflow inside the outdoor unit is relatively uniform, and the heat exchange efficiency of the lower part of heat exchanger 2 is relatively high, which improves the overall heat exchange efficiency of heat exchanger 2 and thus improves the overall operating efficiency of the multi-split air conditioning system.

[0054] Furthermore, when the fan is designed as a single-layer structure, the fan diameter satisfies the following relationship:

[0055]

[0056] α1, α2, and α3 are all constants that can be obtained through fluid simulation calculations. This allows the diameter of the single-layer fan to better meet operational requirements and improve air intake efficiency.

[0057] Furthermore, when the height of heat exchanger 2 is higher than the set value, the wind speed at the k-th moment reaches a1 / a k <μ and a1 / a k →μ, simultaneously satisfying a1 / a k+1 >μ and a k+1 / a n When k ≤ μ, the fan is designed as a double-layer fan. The setpoint of heat exchanger 2 can be determined according to the actual situation, where k is any value from 1 to n.

[0058] like Figure 1 As shown, specifically, the upper fan can be installed inside the air duct 21 or at the air outlet of the air duct 21. In this embodiment, the upper fan is installed at the air outlet of the air duct 21. The lower fan 4 is installed inside the air duct 21 by a support frame, and is located in the lower middle part of the heat exchanger 2, so that the lower fan 4 and the upper fan form a series fan. When the outdoor unit is running, the upper fan and the lower fan 4 are started. Under the action of the upper fan and the lower fan 4, the outside air enters the housing 1 through the air inlet on the housing 1 and exchanges heat with the heat exchanger 2. Then, the heat-exchanged air is discharged from the air outlet of the housing 1.

[0059] Compared to existing technologies that rely solely on an upper fan to promote airflow, resulting in a large airflow at the top of heat exchanger 2 and a small airflow at the bottom, leading to low utilization of the heat exchange tubes at the bottom of heat exchanger 2, this embodiment adds a lower fan 4 to the lower middle part of heat exchanger 2. This increases the airflow at the bottom of heat exchanger 2, evens out the airflow, and improves the heat exchange efficiency at the bottom of heat exchanger 2, thereby improving the overall heat exchange efficiency of heat exchanger 2 and consequently improving the overall operating efficiency of the multi-split air conditioning system. Furthermore, the addition of the lower fan 4 makes the airflow of the outdoor unit more uniform, improving the matching degree between the airflow at the bottom of heat exchanger 2 and the refrigerant flow rate in each flow path at the bottom of heat exchanger 2. This makes the bottom of heat exchanger 2 less prone to frost formation, thus enhancing the steady-state heating capacity of the multi-split air conditioning system.

[0060] Furthermore, a lower fan 4 is installed in the (k+1)th section and below of the heat exchanger 2, meaning the installation height of the lower fan 4 is: H. 下 <(nk)H / n.

[0061] By calculating the installation height of the lower fan 4, energy consumption of the lower fan 4 can be saved, and the airflow at the bottom of the heat exchanger 2 can be made more uniform, which can further improve the heat exchange efficiency at the bottom of the heat exchanger 2.

[0062] like Figure 1 As shown, specifically, the upper fan includes a first guide ring 32 and a first fan 31 mounted on the first guide ring 32. The first fan 31 is located at the air outlet of the air duct 21. The first fan 31 draws outside air into the air duct 21 from the air inlet of the housing 1 and discharges it from the air outlet of the air duct 21, where it exchanges heat with the heat exchanger 2. The first guide ring 32 is detachably mounted on the housing 1 by bolts, so that the first fan 31 can be removed for maintenance.

[0063] The lower fan 4 can be coaxially or non-coaxially arranged with the first fan 31. Both arrangements allow the first fan 31 and the lower fan 4 to form a series airflow, thereby increasing the speed at which outside air enters the air duct 21 and improving the heat exchange efficiency of the heat exchanger 2. Coaxial arrangement of the first fan 31 and the lower fan 4 provides better airflow guidance, reduces turbulence within the air duct 21, and lowers the noise generated during outdoor unit operation.

[0064] Furthermore, the upper fan also includes a second guide ring 34 and a second fan 33 mounted on the second guide ring 34. The second fan 33 is installed at the same height as the first fan 31. Both the second fan 33 and the first fan 31 are located at the air outlet of the air duct 21, thereby increasing the airflow at the top of the heat exchanger 2. Depending on the actual application conditions, the designer can increase or decrease the number of upper fans. In this embodiment, two upper fans are used for explanation. Specifically, the first fan 31 and the second fan 33 are not coaxially arranged with the lower fan 4, making the airflow from the first fan 31 and the second fan 33 more uniform. The second guide ring 34 is detachably mounted on the housing 1 to facilitate the removal of the second fan 33 for maintenance.

[0065] like Figure 1 As shown, within the air duct 21, the lower fan 4 is installed below the upper fan via a support frame, and the installation height H of the lower fan 4 is satisfied. 下 <(nk)H / n. By adding a lower fan 4, the airflow at the bottom of heat exchanger 2 can be increased, making the airflow of the outdoor unit more uniform. A more uniform airflow in the outdoor unit improves the heat exchange efficiency at the bottom of heat exchanger 2, thus increasing the overall heat exchange efficiency of heat exchanger 2 and consequently improving the overall operating efficiency of the multi-split air conditioning system. Furthermore, it improves the matching degree between the airflow at the bottom of heat exchanger 2 and the refrigerant flow in each flow path at the bottom of heat exchanger 2, making the bottom of heat exchanger 2 less prone to frost buildup, thereby enhancing the steady-state heating capacity of the multi-split air conditioning system.

[0066] Furthermore, when the fan is configured as a double-layer fan, the fan diameters of the upper fan and the lower fan 4 should satisfy the following relationship:

[0067]

[0068] Among them, γ1, γ2, γ3, δ1, δ2, and δ3 are all constants that can be obtained through fluid simulation calculations. The first fan 31 and the second fan 33 have the same diameter. The fan diameters of the upper fan and the lower fan 4 are selected by calculation using formulas to better meet operational requirements and improve air intake efficiency.

[0069] like Figure 1 As shown, the outdoor unit further includes compressor 6, gas-liquid separator, oil separator, four-way valve and refrigerant piping, which are essential components for realizing the basic functions of the multi-split air conditioning system. Compressor 6, gas-liquid separator, oil separator and four-way valve are all located in the space between the support frame and the base plate 7 to reduce the internal space occupied by the casing 1.

[0070] The support frame includes a fan cover 51, a sound insulation layer 53 fixed to the fan cover 51, and several columns 52. The lower fan 4 is installed on the fan cover 51, and the end of the column 52 away from the fan cover 51 is fixed to the base plate 7, which allows the lower fan 4 to be installed more stably in the air duct 21. The sound insulation layer 53 is bonded to the fan cover 51. The sound insulation layer 53 can be a layered structure made of polyester fiber sound insulation cotton, centrifugal glass wool, or damping sound-absorbing material. The sound insulation layer 53 reduces the noise emitted by the compressor 6, gas-liquid separator, and oil separator, thereby reducing the noise transmitted to the environment by the outdoor unit during operation.

[0071] As another preferred embodiment, a sound insulation layer 53 can also be adhered to the outer wall of the compressor 6, the gas-liquid separator and the oil separator to reduce vibration and noise transmission, thereby further reducing the noise generated by the outdoor unit during operation.

[0072] Example 2

[0073] This embodiment discloses a control method for a multi-split air conditioning system, wherein the multi-split air conditioning system is the one described in Embodiment 1. Figure 2 As shown, the control method of the multi-split air conditioning system includes the following steps: obtaining the temperature Tdef1 of the first defrost temperature sensor and the temperature Tdef2 of the second defrost temperature sensor, and controlling the speed of the upper fan and the lower fan 4 according to the difference between Tdef1 and Tdef2 to adjust the air field of the outdoor unit.

[0074] This ensures that the amount of refrigerant passing through the upper and lower parts of heat exchanger 2 is better matched with the air volume in the upper and lower parts of heat exchanger 2, thereby enabling the upper and lower parts of heat exchanger 2 to better exert their heat exchange capacity, improving the overall heat exchange efficiency of heat exchanger 2, and thus making the multi-split air conditioning system operate more efficiently.

[0075] The control method includes the following specific steps:

[0076] like Figure 3 As shown, the temperatures Tdef1 and Tdef2 of the first and second defrost temperature sensors are obtained, and the speeds of the upper and lower fans 4 are controlled based on the difference between Tdef1 and Tdef2 to adjust the airflow of the outdoor unit and make the airflow more uniform. In the initial state, the upper and lower fans 4 are started and rotated at a set speed, wherein the first fan 31 and the second fan 33 of the upper fan start and stop simultaneously, and their speeds are the same.

[0077] When Tdef1-Tdef2>1℃, in this embodiment the first preset value is selected as 1℃. That is, when Tdef1-Tdef2>1℃, the temperature of the upper part of the heat exchanger 2 is higher than the temperature of the lower part of the heat exchanger 2. In other words, the refrigerant flow rate and air volume of the lower part of the heat exchanger 2 are not well matched. Therefore, the speed of the lower fan 4 is increased to increase the air volume of the lower part of the heat exchanger 2, so as to improve the matching degree of refrigerant flow rate and air volume of the lower part of the heat exchanger 2 and improve the heat exchange efficiency of the lower part of the heat exchanger 2.

[0078] When Tdef1-Tdef2 < the second preset value, in this embodiment the second preset value is selected as -1℃. That is, when Tdef1-Tdef2 < -1℃, the temperature of the upper part of the heat exchanger 2 is lower than the temperature of the lower part of the heat exchanger 2. In other words, the refrigerant flow rate and air volume of the upper part of the heat exchanger 2 are not well matched. Therefore, the speed of the upper fan is increased to increase the air volume of the upper part of the heat exchanger 2, so as to improve the matching degree of refrigerant flow rate and air volume of the upper part of the heat exchanger 2 and improve the heat exchange efficiency of the upper part of the heat exchanger 2.

[0079] The technical solution of the present invention has been described above with reference to the preferred embodiments shown in the accompanying drawings. However, it will be readily understood by those skilled in the art that the scope of protection of the present invention is obviously not limited to these specific embodiments. Without departing from the principles of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after such changes or substitutions will all fall within the scope of protection of the present invention.

Claims

1. An outdoor unit, characterized in that, The heat exchanger (2) includes a heat exchanger (2) and a fan. The total height of the heat exchanger (2) is H. The heat exchanger (2) is divided into n equal parts from top to bottom. The total air volume Q required for heat exchange by the heat exchanger (2) is... 总 The wind speed distribution of each equal part of the heat exchanger (2) is as follows: a1, a2, a3, ... a n-1 a n ; According to H, n, Q 总 a1, a2, a3, ... a n-1 a n Determine the number of layers of the fan and the diameter of the fan. When the height of the heat exchanger (2) is higher than the set value, the wind speed at the kth moment reaches a1 / a k <µ and a1 / a k →µ, simultaneously satisfying a1 / a k+1 >µ and a k+1 / a n When the value is ≤µ, the fan is designed as a double-layer fan; In the case of a double-layer fan, the fan includes an upper fan and a lower fan, the fan diameter of the upper fan is D1, and the fan diameter of the lower fan (4) is D2; The fan diameters of the upper and lower fans (4) should satisfy the following relationship: Among them, γ1, γ2, γ3, δ1, δ2 and δ3 are all constants.

2. The outdoor unit according to claim 1, characterized in that, The fan diameter for a single-layer fan is D0; when a1 / a n When μ ≤ µ, the fan is designed as a single layer; where μ is a preset constant.

3. The outdoor unit according to claim 2, characterized in that, When the fan is designed as a single layer, the fan diameter satisfies the following relationship: In this context, α1, α2, and α3 are all constants.

4. The outdoor unit according to claim 1, characterized in that, The lower fan (4) is installed in the (k+1)th part and below of the heat exchanger (2), that is, the installation height of the lower fan (4) is: H 下 <(nk)H / n.

5. The outdoor unit according to claim 1, characterized in that, The heat exchanger (2) is arranged to form a duct (21). When there is a double-layer fan, the upper fan and the lower fan (4) are both located in the duct (21). The outdoor unit also includes a housing (1) and a support frame. The heat exchanger (2) is located inside the housing (1), and the support frame is located on the housing (1) and inside the air duct (21). The support frame includes a fan cover (51) and several columns (52) disposed on the fan cover (51). The columns (52) are connected to the housing (1). The lower fan (4) is disposed on the fan cover (51).

6. The outdoor unit according to claim 5, characterized in that, The support frame also includes a sound insulation layer (53) on the fan cover (51), and the outdoor unit also includes a compressor (6). The compressor (6) is connected to the heat exchanger (2) through a pipeline, and the compressor (6) is located in the space formed by the sound insulation layer (53), the column (52) and the shell (1).

7. A multi-split air conditioning system, characterized in that, Includes the outdoor unit as described in any one of claims 1-6.

8. A control method for a multi-split air conditioning system, characterized in that, The multi-split air conditioning system includes the outdoor unit as described in claim 1, 4, 5 or 6; The outdoor unit also includes a first defrost temperature sensor and a second defrost temperature sensor. The first defrost temperature sensor is located on the upper part of the heat exchanger (2), and the second defrost temperature sensor is located on the lower part of the heat exchanger (2). The heat exchanger (2) is arranged to form an air duct (21). The upper fan and the lower fan (4) are both located in the air duct (21). The lower fan (4) is located below the upper fan and is located in the lower middle part of the air duct (21). The control method includes the following steps: The temperature Tdef1 of the first defrost temperature sensor and the temperature Tdef2 of the second defrost temperature sensor are obtained, and the speed of the upper fan and the lower fan (4) is controlled according to the difference between Tdef1 and Tdef2 to adjust the wind field of the outdoor unit.

9. The control method for a multi-split air conditioning system according to claim 8, characterized in that, "Obtaining the temperatures Tdef1 of the first defrost temperature sensor and Tdef2 of the second defrost temperature sensor, and controlling the rotational speeds of the upper and lower fans (4) based on the difference between Tdef1 and Tdef2 to adjust the airflow" specifically includes the following steps: When Tdef1-Tdef2>the first preset value, the speed of the lower fan (4) is increased, and the air volume at the bottom of the heat exchanger (2) is increased; When Tdef1-Tdef2 < the second preset value, the rotation speed of the upper fan is increased, and the air volume at the top of the heat exchanger (2) is increased.

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