Rotation speed control method and device of direct-current brushless motor and fan coil unit

Abstract

The invention discloses a rotating speed control method and device of a direct-current brushless motor and a fan coil unit. The fan coil unit comprises a direct-current brushless motor and a heat exchanger. The rotating speed control method comprises the steps that after the brushless direct current motor is started, the surface temperature of the heat exchanger is detected in real time; judging the operation condition of the fan coil unit according to the surface temperature; and the rotating speed of the direct-current brushless motor is controlled according to the surface temperature and the operation working condition of the fan coil unit. According to the rotating speed control method of the direct-current brushless motor, the operation working condition of the fan coil unit can be judged more accurately according to the surface temperature of the heat exchanger, so that the rotating speed of the direct-current brushless motor can be flexibly adjusted under different operation working conditions, and the air supply volume of the fan coil unit under different working conditions can be equivalent; particularly, when the fan coil unit operates in a refrigeration mode, the air volume can be increased by increasing the rotating speed of the direct-current brushless motor, and the refrigeration effect is improved.

Description

Technical Field

[0001] The present application relates to the technical field of air conditioning, and in particular to a speed control method and device of a brushless DC motor and a fan coil unit. Background Art

[0002] The fan coil unit is one of the ideal terminal products for central air conditioning, and its main functions are air supply, cooling, heating, etc. In the scenarios of the above-mentioned various functional applications, the state of the heat exchanger surface is often different. For different states, the wind resistance of the whole machine will be different, especially when cooling, the wind resistance will be greatly increased due to the generation of condensed water. Among them, the fluid (air) in the fan coil unit will produce friction with the wall of the heat exchanger during the flow process. This friction will hinder the flow of the fluid, thereby generating resistance, that is, wind resistance.

[0003] For fan coil units that use brushless DC motors, the control logic is fixed speed operation. At the same speed, the degree of air volume attenuation is different in environments with different wind resistance conditions. Especially when the fan coil unit is running the cooling function, the air volume attenuation is serious, affecting the cooling effect under this function. Summary of the invention

[0004] In view of this, the present application aims to solve one of the problems in the related art to at least a certain extent. To this end, the purpose of the present application is to provide a speed control method and device of a brushless DC motor and a fan coil unit.

[0005] The present application provides a speed control method of a brushless DC motor, which is applied to a fan coil unit. The fan coil unit includes the brushless DC motor and a heat exchanger, and the speed control method includes: after the brushless DC motor is started, real-time detection of the surface temperature of the heat exchanger; judging the operating condition of the fan coil unit according to the surface temperature; and controlling the speed of the brushless DC motor according to the surface temperature and the operating condition of the fan coil unit.

[0006] In some embodiments, the heat exchanger is provided with a temperature sensor, and the real-time detection of the surface temperature of the heat exchanger includes: after the brushless DC motor is started at a preset speed, real-time detection of the surface temperature by the temperature sensor.

[0007] In certain embodiments, determining the operating condition of the fan coil unit based on the surface temperature includes: comparing the surface temperature with a preset temperature critical value to determine the operating condition of the fan coil unit, the operating condition including a wet condition and a dry condition, the wet condition refers to the condition corresponding to when the heat exchanger surface is wet, and the dry condition refers to the condition corresponding to when the heat exchanger surface is dry.

[0008] In certain embodiments, comparing the surface temperature with a preset temperature critical value to determine the operating condition of the fan coil unit includes: after the DC brushless motor runs at a preset speed for a preset time, determining whether the initial value of the surface temperature is greater than or equal to a first temperature critical value; if the initial value of the surface temperature is greater than or equal to the first temperature critical value, determining that the fan coil unit is in the dry condition; if the initial value of the surface temperature is less than the first temperature critical value, determining that the fan coil unit is in the wet condition.

[0009] In some embodiments, controlling the speed of the brushless DC motor according to the surface temperature and the operating condition of the fan coil unit includes: when it is determined that the fan coil unit is in the dry condition, controlling the brushless DC motor to maintain operation at the preset speed; when it is determined that the fan coil unit is in the wet condition, controlling the brushless DC motor to operate at a first speed, wherein the first speed is greater than the preset speed.

[0010] In certain embodiments, after controlling the brushless DC motor to keep running at the preset speed when it is determined that the fan coil unit is in the dry condition, the speed control method further includes: real-time detection of the current temperature value of the surface temperature; comparing the current temperature value of the surface temperature with the lower limit value of the first temperature critical value; if the current temperature value of the surface temperature is less than or equal to the lower limit value of the first temperature critical value, determining that the fan coil unit is in the wet condition, and controlling the brushless DC motor to switch from the preset speed to the first speed; if the current temperature value of the surface temperature is greater than the lower limit value of the first temperature critical value, controlling the brushless DC motor to keep running at the preset speed.

[0011] In certain embodiments, after determining that the fan coil unit is in the wet condition and controlling the DC brushless motor to switch from the preset speed to the first speed, the speed control method further includes: comparing the current temperature value of the surface temperature with the upper limit value of the first temperature critical value; if the current temperature value of the surface temperature is greater than or equal to the upper limit value of the first temperature critical value, controlling the DC brushless motor to switch from the first speed to the preset speed; if the current temperature value of the surface temperature is less than the upper limit value of the first temperature critical value, controlling the DC brushless motor to keep running at the first speed.

[0012] In certain embodiments, after controlling the brushless DC motor to operate at the first speed when it is determined that the fan coil unit is in the wet condition, the speed control method further includes: detecting the current temperature value of the surface temperature in real time; comparing the current temperature value of the surface temperature with the upper limit value of the first temperature critical value; if the current temperature value of the surface temperature is greater than or equal to the upper limit value of the first temperature critical value, determining that the fan coil unit is in the dry condition, and controlling the brushless DC motor to switch from the first speed to the preset speed; if the current temperature value of the surface temperature is less than the upper limit value of the first temperature critical value, controlling the brushless DC motor to maintain operating at the first speed.

[0013] In certain embodiments, after determining that the fan coil unit is in the dry condition and controlling the DC brushless motor to switch from the first speed to the preset speed, the speed control method further includes: comparing the current temperature value of the surface temperature with the lower limit value of the first temperature critical value; if the current temperature value of the surface temperature is less than or equal to the lower limit value of the first temperature critical value, determining that the fan coil unit is in the wet condition and controlling the DC brushless motor to switch from the preset speed to the first speed; if the current temperature value of the surface temperature is greater than the lower limit value of the first temperature critical value, controlling the DC brushless motor to keep running at the preset speed.

[0014] In certain embodiments, after controlling the brushless DC motor to keep running at the preset speed when it is determined that the fan coil unit is in the dry condition, the speed control method further includes: real-time detection of the current temperature value of the surface temperature; determining whether the current temperature value of the surface temperature is greater than or equal to a second temperature critical value; if the current temperature value of the surface temperature is greater than or equal to the second temperature critical value, controlling the brushless DC motor to switch from the preset speed to a second speed, the second speed being greater than the preset speed; if the current temperature value of the surface temperature is less than the second temperature critical value, controlling the fan coil unit to keep running at the preset speed.

[0015] The present application also provides a speed control device for a brushless DC motor, which is applied to a fan coil unit. The fan coil unit includes the brushless DC motor and a heat exchanger, and the speed control device for the brushless DC motor includes a temperature detection module, a judgment module and a control module. The temperature detection module is used to detect the surface temperature of the heat exchanger in real time after the brushless DC motor is initially started; the judgment module is used to judge the operating condition of the fan coil unit according to the surface temperature; and the control module is used to control the speed of the brushless DC motor according to the surface temperature and the operating condition of the fan coil unit.

[0016] The present application also provides a fan coil unit, wherein the fan coil unit is used to execute the speed control method of a brushless DC motor described in any one of the above embodiments, or the brushless DC motor includes the speed control device of the brushless DC motor described in the above embodiments.

[0017] The present application also provides an air conditioning system, which includes the fan coil unit described in the above embodiment.

[0018] The speed control method of the brushless DC motor of the present application can more accurately judge the operating condition of the fan coil unit according to the surface temperature of the heat exchanger, so that the speed of the brushless DC motor can be flexibly adjusted under different operating conditions, and the air supply volume of the fan coil unit under different working conditions can be made equivalent. In particular, when the fan coil unit is operating in the cooling mode, the air volume can be increased by increasing the speed of the brushless DC motor to improve the cooling effect.

[0019] Additional aspects and advantages of the present application will be given in part in the description below, and in part will become apparent from the description below, or will be learned through the practice of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The above and / or additional aspects and advantages of the present application will become apparent and easily understood from the following description of the embodiments in conjunction with the accompanying drawings, in which:

[0021] Figure 1 is a flow chart of a speed control method of a brushless DC motor according to certain embodiments of the present application;

[0022] Figure 2 is a schematic structural diagram of a speed control device for a brushless DC motor according to certain embodiments of the present application;

[0023] Figure 3 is a flow chart of a speed control method of a brushless DC motor according to certain embodiments of the present application;

[0024] Figure 4 is a flow chart of a speed control method of a brushless DC motor according to certain embodiments of the present application;

[0025] Figure 5 is a flow chart of a speed control method of a brushless DC motor according to certain embodiments of the present application;

[0026] Figure 6 is a flow chart of a speed control method of a brushless DC motor according to certain embodiments of the present application;

[0027] Figure 7is a flow chart of a speed control method of a brushless DC motor according to certain embodiments of the present application;

[0028] Figure 8 is a flow chart of a speed control method of a brushless DC motor according to certain embodiments of the present application;

[0029] Fig. 9 is a flow chart of a speed control method of a brushless DC motor according to certain embodiments of the present application;

[0030] Fig.10 is a flow chart of a speed control method of a brushless DC motor according to certain embodiments of the present application;

[0031] Fig.11 is a curve diagram showing the relationship between the speed of the DC brushless motor and the surface temperature of the heat exchanger during the process of the operating condition of the fan coil unit of certain embodiments of the present application changing from a wet condition to a dry condition;

[0032] Fig.12 It is a curve diagram showing the relationship between the speed of the DC brushless motor and the surface temperature of the heat exchanger when the operating condition of the fan coil unit in certain embodiments of the present application changes from a dry condition to a wet condition. DETAILED DESCRIPTION

[0033] The embodiments of the present application are described in detail below, and examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present application, and cannot be understood as limiting the present application.

[0034] In the description of the present application, the terms "first" and "second" are used for descriptive purposes only and are not to 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 features. In the description of the present application, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0035] In the description of this application, it should be noted that, unless otherwise clearly specified and limited, the terms "installation" and "connection" should be understood in a broad sense, and may refer to fixed connection, detachable connection, or integral connection; mechanical connection, electrical connection, or mutual communication; direct connection, indirect connection through an intermediate medium, internal connection between two elements, or interaction between two elements. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0036] The disclosure below provides many different embodiments or examples to realize the different structures of the present application. In order to simplify the disclosure of the present application, 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 application. In addition, the present application can repeat reference numbers and / or reference letters in different examples, and this repetition is for the purpose of simplification and clarity, which itself does not indicate the relationship between the various embodiments and / or settings discussed.

[0037] The embodiments of the present application are described in detail below, and examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present application, and cannot be understood as limiting the present application.

[0038] See also Figure 1 The present application provides a speed control method of a brushless DC motor, which is applied to a fan coil unit. The fan coil unit includes a brushless DC motor and a heat exchanger, and the speed control method includes:

[0039] 01: After the brushless DC motor is started, the surface temperature of the heat exchanger is detected in real time;

[0040] 02: Determine the operating condition of the fan coil unit based on the surface temperature;

[0041] 03: Control the speed of the brushless DC motor according to the surface temperature and the operating conditions of the fan coil unit.

[0042] See also Figure 2 The present application also provides a speed control device 10 for a brushless DC motor, which is applied to a fan coil unit. The fan coil unit includes a brushless DC motor and a surface, and the speed control device for the brushless DC motor includes a temperature detection module 11, a judgment module 12 and a control module 13.

[0043] Step 01 can be implemented by the temperature detection module 11, step 02 can be implemented by the judgment module 12, and step 03 can be implemented by the control module 13. That is, the temperature detection module 11 is used to detect the surface temperature of the heat exchanger in real time after the DC brushless motor is started; the judgment module 12 is used to judge the operating condition of the fan coil unit according to the surface temperature; and the control module 13 is used to control the speed of the DC brushless motor according to the surface temperature and the operating condition of the fan coil unit.

[0044] Specifically, when the brushless DC motor is initially started, the surface temperature of the heat exchanger is detected in real time. That is to say, the present application determines the operating condition of the fan coil unit by detecting the surface temperature of the heat exchanger, which is more accurate than determining the operating condition of the fan coil unit by detecting the return air temperature.

[0045] The operating condition of the fan coil unit refers to the dry and wet state of the heat exchanger surface, which is divided into dry condition and wet condition. Wet condition refers to the condition corresponding to when the heat exchanger surface is wet, and dry condition refers to the condition corresponding to when the heat exchanger surface is dry. Specifically, when the surface temperature of the heat exchanger fin is higher than the dew point temperature of the return air, condensation will not form on the heat exchanger surface. At this time, the heat exchanger surface is dry, so it is called dry condition. On the contrary, when the surface temperature of the heat exchanger fin is lower than the dew point temperature of the return air, condensation will form on the heat exchanger surface. At this time, the heat exchanger surface is wet, so it is called wet condition.

[0046] It is understandable that in the related art, the operating condition of the fan coil unit is determined by detecting the return air temperature of the fan coil unit. Regardless of the cooling mode in summer or the heating mode in winter, the return air temperature of the fan coil unit may be detected as 25°C. In other words, in the related art, it is impossible to accurately determine whether the fan coil unit is in a wet condition or a dry condition by detecting the return air temperature of the fan coil unit.

[0047] In the implementation manner of the present application, in summer, the fan coil unit is in cooling mode. Since the water pipes of the heat exchanger contain cold water, it can be detected that the surface temperature of the heat exchanger is less than or equal to 15°C, or other values, which are not limited here. In winter, the fan coil unit is in heating mode. Since the water pipes of the heat exchanger contain hot water, it can be detected that the surface temperature of the heat exchanger is greater than or equal to 35°C, or other values, which are not limited here. In other words, the present application can more accurately determine whether the fan coil unit is in a wet condition or a dry condition by directly detecting the surface temperature of the heat exchanger, and the accuracy of the judgment is higher.

[0048] The speed control method of the brushless DC motor of the present application determines the operating condition of the fan coil unit according to the surface temperature of the heat exchanger, and then controls the speed of the motor according to the operating condition of the fan coil unit. In this way, the air volume of the fan coil unit under different working conditions can be made equivalent, especially when the fan coil unit is in a wet condition in the operating cooling mode, the air volume can be increased by increasing the speed of the motor to improve the cooling effect.

[0049] In this way, the speed control method of the brushless DC motor of the present application can more accurately judge the operating condition of the fan coil unit according to the surface temperature of the heat exchanger, so that the speed of the brushless DC motor can be flexibly adjusted under different operating conditions, and the air supply volume of the fan coil unit under different working conditions can be made equivalent. In particular, when the fan coil unit is operating in the cooling mode, the air volume can be increased by increasing the speed of the brushless DC motor to improve the cooling effect.

[0050] In some embodiments, a temperature sensor is provided on the heat exchanger, and step 01 includes:

[0051] 011: When the brushless DC motor starts at a preset speed, the surface temperature is detected in real time through the temperature sensor.

[0052] Please combine Figure 2 , step 01 can be implemented by the temperature detection module 11. That is, the temperature detection module 11 is used to detect the surface temperature in real time through the temperature sensor after the brushless DC motor is started at a preset speed.

[0053] Specifically, the preset speed can be as follows: Figure 3 The speed A shown, the specific operating speed setting can be set according to actual needs.

[0054] The temperature sensor can be specifically arranged on the fin surface of the heat exchanger or on the surface of the water inlet pipe of the heat exchanger. That is, the present application can more accurately judge the operating condition of the fan coil unit by detecting the surface temperature of the heat exchanger through the temperature sensor.

[0055] In some embodiments, step 02 includes:

[0056] 021: Compare the surface temperature with the preset temperature critical value to determine the operating condition of the fan coil unit. The operating conditions include wet conditions and dry conditions. The wet condition refers to the condition corresponding to when the heat exchanger surface is wet, and the dry condition refers to the condition corresponding to when the heat exchanger surface is dry.

[0057] Please combine Figure 2 , step 021 can be implemented by the judgment module 12. That is, the judgment module 12 is used to compare the surface temperature with the preset temperature critical value to judge the operating condition of the fan coil unit, and the operating condition includes a wet condition and a dry condition. The wet condition refers to the condition corresponding to when the heat exchanger surface is wet, and the dry condition refers to the condition corresponding to when the heat exchanger surface is dry.

[0058] Specifically, the preset temperature critical value may be 20° C., 21° C. or 22° C., which is not limited here. The preset temperature critical value may be determined in advance based on experiments.

[0059] That is, the speed control method of the brushless DC motor of the present application can more accurately determine whether the operating condition of the fan coil unit is in a dry condition or a wet condition by comparing the surface temperature of the heat exchanger with the preset temperature critical value, thereby accurately controlling the speed of the brushless DC motor under different operating conditions, thereby improving the cooling effect of the fan coil unit.

[0060] See also Figure 3 In some embodiments, step 021 includes:

[0061] 0211: After the brushless DC motor runs at a preset speed for a preset time, determining whether an initial value of the surface temperature is greater than or equal to a first temperature critical value;

[0062] 0212: If the initial value of the surface temperature is greater than or equal to the first temperature critical value, it is determined that the fan coil unit is in a dry condition;

[0063] 0213: If the initial value of the surface temperature is less than the first temperature critical value, it is determined that the fan coil unit is in a wet condition.

[0064] Please combine Figure 2 , step 0211, step 0212 and step 0213 can be implemented by the judgment module 12. That is, the judgment module 12 is used to judge whether the initial value of the surface temperature is greater than or equal to the first temperature critical value after the DC brushless motor runs at a preset speed for a preset time; if the initial value of the surface temperature is greater than or equal to the first temperature critical value, it is judged that the fan coil unit is in a dry condition; if the initial value of the surface temperature is less than the first temperature critical value, it is judged that the fan coil unit is in a wet condition.

[0065] Specifically, the first temperature critical value may refer to the return air dew point temperature. The first temperature critical value may be 20° C. as mentioned above, or other values, which are not limited here.

[0066] The preset speed can be 920 rpm, or other values, which are not limited here. The preset time can be 30S, 34S, 35S, 36S, 39S, 40S, 42S, 45S, 50S or 60S, which are not limited here. It can be understood that after the DC brushless motor runs at the preset speed for the preset time, the initial value of the surface temperature of the heat exchanger can be detected more stably, ensuring the accuracy of the subsequent judgment of the operating condition of the fan coil unit based on the initial value of the surface temperature.

[0067] See also Figure 4In one example, when the brushless DC motor starts to run at a preset speed A for n seconds, n is, for example, 60 seconds, that is, the preset time is 60 seconds, and the first temperature threshold is Tdw, Tdw may be 20°C, then at this time, the initial value T2 of the surface temperature of the heat exchanger can be detected by the temperature sensor installed on the heat exchanger. Therefore, at this time, it can be determined whether the initial value T2 of the surface temperature of the heat exchanger is greater than or equal to Tdw. Figure 4 The middle tube temperature is expressed as the surface temperature of the water inlet pipe of the heat exchanger, which can represent the surface temperature of the heat exchanger.

[0068] If T2 is greater than or equal to Tdw, it indicates that the surface temperature of the heat exchanger is relatively high at this time. When the surface temperature of the heat exchanger fins is higher than the dew point temperature of the return air, no condensation water will form on the surface of the heat exchanger. Therefore, it can be determined that the fan coil unit is in a dry condition at this time, that is, the surface of the heat exchanger is in a dry state.

[0069] If T2 is less than Tdw, it means that when the surface temperature of the heat exchanger fin is lower than the dew point temperature of the return air, condensed water will form on the surface of the heat exchanger. At this time, the surface of the heat exchanger is wet, and it is determined that the fan coil unit is in a wet condition, that is, the surface of the heat exchanger is wet.

[0070] In this way, the speed control method of the brushless DC motor of the present application can determine whether the fan coil unit is in a dry condition or a wet condition by judging whether the surface temperature of the heat exchanger is greater than or equal to the first temperature critical value after the brushless DC motor has run for a preset time.

[0071] See also Figure 5 In some embodiments, step 03 includes:

[0072] 031: When the fan coil unit is determined to be in dry condition, the brushless DC motor is controlled to run at a preset speed;

[0073] 032: When it is determined that the fan coil unit is in a wet condition, the brushless DC motor is controlled to operate at a first speed, wherein the first speed is greater than a preset speed.

[0074] Please combine Figure 2 , step 031 and step 032 can be implemented by the control module 13. That is, the control module 13 is used to control the DC brushless motor to keep running at a preset speed when it is determined that the fan coil unit is in a dry condition; and to control the DC brushless motor to run at a first speed when it is determined that the fan coil unit is in a wet condition, wherein the first speed is greater than the preset speed.

[0075] Specifically, please combine Figure 4As mentioned above, if T2 is greater than or equal to Tdw, it indicates that the surface temperature of the heat exchanger is relatively high. When the surface temperature of the heat exchanger fin is higher than the dew point temperature of the return air, no condensation will form on the surface of the heat exchanger. Therefore, it can be determined that the fan coil unit is in a dry condition, that is, the surface of the heat exchanger is dry, and the wind resistance of the fan coil unit is small. Therefore, the speed of the brushless DC motor can be kept unchanged at this time, and the brushless DC motor can be controlled to continue to run at the preset speed A.

[0076] If T2 is less than Tdw, it means that when the surface temperature of the heat exchanger fin is lower than the dew point temperature of the return air, condensed water will form on the surface of the heat exchanger. At this time, the surface of the heat exchanger is wet, and it is determined that the fan coil unit is in a wet condition, that is, the surface of the heat exchanger is wet. At this time, the wind resistance of the fan coil unit will become larger due to the presence of condensed water. Therefore, at this time, the speed of the DC brushless motor can be increased, and the DC brushless motor can be controlled to run at a first speed B greater than the preset speed A, thereby increasing the air volume and improving the heat exchange effect of the heat exchanger, thereby improving the cooling effect of the fan coil unit under the cooling function.

[0077] In this way, the speed control method of the brushless DC motor of the present application can increase the speed of the brushless DC motor and increase the air volume when it is determined that the fan coil unit is in a wet condition, thereby improving the cooling effect of the fan coil unit under the cooling function.

[0078] See also Figure 6 In some embodiments, after step 031, the speed control method further includes:

[0079] 041: Real-time detection of the current temperature value of the surface temperature;

[0080] 042: Compare the current temperature value of the surface temperature with the lower limit value of the first temperature critical value;

[0081] 043: If the current temperature value of the surface temperature is less than or equal to the lower limit value of the first temperature critical value, it is determined that the fan coil unit is in a wet condition, and the brushless DC motor is controlled to switch from a preset speed to a first speed;

[0082] 044: If the current temperature value of the surface temperature is greater than the lower limit value of the first temperature critical value, the brushless DC motor is controlled to keep running at a preset speed.

[0083] Please combine Figure 2, step 041 can be implemented by the temperature detection module 11. Step 042, step 043 and step 044 can all be implemented by the control module 13. That is to say, the temperature detection module 11 is used to detect the current temperature value of the surface temperature in real time; the control module 13 is used to compare the current temperature value of the surface temperature with the lower limit value of the first temperature critical value; if the current temperature value of the surface temperature is less than or equal to the lower limit value of the first temperature critical value, it is judged that the fan coil unit is in a wet condition, and the DC brushless motor is controlled to switch from the preset speed to the first speed; if the current temperature value of the surface temperature is greater than the lower limit value of the first temperature critical value, the DC brushless motor is controlled to keep running at the preset speed.

[0084] It can be understood that when the fan coil unit is in a dry condition by the initial value of the surface temperature of the heat exchanger being greater than or equal to the first temperature critical value, it indicates that the surface temperature of the heat exchanger is relatively high at this time, and the surface temperature of the heat exchanger is at least higher than the first temperature critical value. However, considering that the surface temperature of the heat exchanger detected by a temperature sensor or other technical means may not be a stable value.

[0085] For example, the value of the surface temperature detected at the current moment is 21°C, and the surface temperature of the heat exchanger may be detected as 19°C or 23°C in the next second. If the speed of the DC brushless motor is controlled by comparing the surface temperature value of the heat exchanger with the single value of the first temperature critical value, it may be that the fan coil unit is in a wet condition because the surface temperature of the heat exchanger detected in the next second is 19°C, which is less than the first temperature critical value of 20°C, and the speed of the DC brushless motor is switched to the first speed. In the next second, the surface temperature of the heat exchanger is detected to be 21°C, which is greater than the first temperature critical value of 20°C, and the fan coil unit is considered to be in a dry condition, and the speed of the DC brushless motor is switched to the preset speed. This will cause the speed switching frequency of the DC brushless motor to be too fast, which is easy to damage the DC brushless motor.

[0086] Therefore, the present application can set a lower limit value of the first temperature critical value corresponding to the surface temperature of a heat exchanger during the operation of the DC brushless motor, thereby avoiding frequent judgments that the fan coil unit is in dry conditions and wet conditions, which causes the speed switching frequency of the DC brushless motor to be too fast and damage the DC brushless motor, thereby ensuring the working stability of the DC brushless motor, extending the service life of the DC brushless motor, and improving the overall performance of the fan coil unit.

[0087] Specifically, in one example, the first temperature critical value is 20° C. If the dry and wet working condition judgment tolerance value is set to 2° C., the lower limit of the first temperature critical value is 18° C., and the upper limit of the first temperature critical value is 22° C. The preset speed A is 920 rpm, and the first speed B is 950 rpm.

[0088] like Figure 4As shown, when it is determined that the fan coil unit is in a dry condition, the DC brushless motor is controlled to maintain operation at a preset speed A of 920 rpm, and the current temperature value of the surface temperature can be detected in real time, and the current temperature value of the surface temperature can be compared with the lower limit value of the first temperature critical value. If the current temperature value of the surface temperature is 21°C, which is greater than the lower limit value of the first temperature critical value of 18°C, it means that the fan coil unit is still in a dry condition at this time, and condensed water will not form on the surface of the heat exchanger, so the DC brushless motor can be controlled to maintain operation at a preset speed A of 920 rpm.

[0089] If the current temperature value of the surface temperature is 17°C, which is less than or equal to the lower limit value of the first temperature critical value of 18°C, the fan coil unit is judged to be in a wet condition, and the DC brushless motor is controlled to switch from the preset speed A of 920rpm to the first speed B of 950rpm, thereby increasing the air volume, which can make the air supply volume of the fan coil unit equivalent under different working conditions, and improve the performance of the fan coil unit.

[0090] In this way, the speed control method of the present application can determine that the fan coil unit is in a dry condition and the DC brushless motor is running at a preset speed after the DC brushless motor is initially started for a preset time. By judging in real time whether the current temperature value of the surface temperature of the heat exchanger is less than or equal to the lower limit value of the first temperature critical value, it can be judged whether the fan coil unit has entered a wet condition from a dry condition state, thereby timely increasing the motor speed and improving the operating performance of the fan coil unit when the fan coil unit enters a wet condition state.

[0091] It should be noted that, since the fan coil unit cannot be in a wet condition in an instant when it is initially in a dry condition, it may take a period of time to be in a wet condition. Therefore, after the DC brushless motor is initially started for a preset time, when it is determined that the fan coil unit is in a dry condition and the DC brushless motor is running at a preset speed, it is also possible to detect the current temperature value of the surface temperature in real time after a preset time interval, for example, another 60S interval, and compare the current temperature value of the surface temperature with the lower limit value of the first temperature critical value, so as to determine whether the fan coil unit has entered a wet condition from a dry condition, and then control and adjust the motor speed accordingly to improve the control efficiency of the motor speed.

[0092] See also Figure 7 In some embodiments, after step 043, the speed control method further includes:

[0093] 045: Compare the current temperature value of the surface temperature with the upper limit value of the first temperature critical value;

[0094] 046: If the current temperature value of the surface temperature is greater than or equal to the upper limit value of the first temperature critical value, control the brushless DC motor to switch from the first speed to the preset speed;

[0095] 047: If the current temperature value of the surface temperature is less than the upper limit value of the first temperature critical value, the brushless DC motor is controlled to keep running at the first speed.

[0096] Please combine Figure 2 , step 045, step 046 and step 047 can all be implemented by the control module 13. That is, the control module 13 is used to compare the current temperature value of the surface temperature with the upper limit value of the first temperature critical value; if the current temperature value of the surface temperature is greater than or equal to the upper limit value of the first temperature critical value, the DC brushless motor is controlled to switch from the first speed to the preset speed; if the current temperature value of the surface temperature is less than the upper limit value of the first temperature critical value, the DC brushless motor is controlled to keep running at the first speed.

[0097] Specifically, when it is determined that the fan coil unit is in a wet condition and the DC brushless motor is controlled to switch from a preset speed A of 920 rpm to a first speed B of 950 rpm, the current temperature value of the surface temperature of the heat exchanger can be compared with the upper limit value of the first temperature critical value.

[0098] Please combine Figure 4 If the current temperature value of the surface temperature is 19°C, which is less than the upper limit of the first temperature critical value of 22°C, it indicates that the fan coil unit is continuously operating in a wet condition. At this time, it continues to operate at the first speed B of 950rpm to ensure the operating performance of the fan coil unit.

[0099] If the current temperature value of the surface temperature is 23°C, which is greater than or equal to the upper limit value of the first temperature critical value of 22°C, it indicates that the fan coil unit has entered the dry working state again from the wet working state, and the DC brushless motor is controlled to switch from the first speed B of 950rpm to the preset speed A of 920rpm, thereby reducing the speed and improving the operating efficiency of the fan coil unit.

[0100] In this way, the speed control method of the present application can determine whether the current operating state of the fan coil unit is in a wet condition and control the DC brushless motor to switch from a preset speed to a first speed. It can then determine in real time whether the current temperature value of the surface temperature of the heat exchanger is greater than or equal to the upper limit value of the first temperature critical value, thereby determining whether the fan coil unit has entered a dry condition from a wet condition. When the fan coil unit enters a dry condition, the motor speed can be reduced in time to improve the operating efficiency of the fan coil unit.

[0101] See also Figure 8In some embodiments, after step 032, the speed control method further includes:

[0102] 051: Real-time detection of the current temperature value of the surface temperature;

[0103] 052: Compare the current temperature value of the surface temperature with the upper limit value of the first temperature critical value;

[0104] 053: If the current temperature value of the surface temperature is greater than or equal to the upper limit value of the first temperature critical value, it is determined that the fan coil unit is in a dry condition, and the brushless DC motor is controlled to switch from the first speed to the preset speed;

[0105] 054: If the current temperature value of the surface temperature is less than the upper limit value of the first temperature critical value, the brushless DC motor is controlled to maintain running at the first speed.

[0106] Please combine Figure 2 , step 051 can be implemented by the temperature detection module 11. Step 052, step 053 and step 054 can all be implemented by the control module 13. That is to say, the temperature detection module 11 is used to detect the current temperature value of the surface temperature in real time; the control module 13 is used to compare the current temperature value of the surface temperature with the upper limit value of the first temperature critical value; if the current temperature value of the surface temperature is greater than or equal to the upper limit value of the first temperature critical value, it is judged that the fan coil unit is in a dry condition, and the DC brushless motor is controlled to switch from the first speed to the preset speed; if the current temperature value of the surface temperature is less than the upper limit value of the first temperature critical value, the DC brushless motor is controlled to maintain running at the first speed.

[0107] Specifically, when the fan coil unit is in a wet condition when the initial value of the surface temperature of the heat exchanger is less than the first temperature critical value, the DC brushless motor is controlled to run at the first speed, indicating that the surface temperature of the heat exchanger is low at this time, and the surface temperature of the heat exchanger is at least lower than the first temperature critical value. However, considering that the surface temperature of the heat exchanger detected by a temperature sensor or other technical means may not be a stable value.

[0108] For example, the value of the surface temperature detected at the current moment is 18°C, and the surface temperature of the heat exchanger may be detected as 19°C or 21°C in the next second. If the speed of the DC brushless motor is controlled by comparing the surface temperature value of the heat exchanger with the single value of the first temperature critical value, it may be that the fan coil unit is in a dry condition because the surface temperature of the heat exchanger detected in the next second is 21°C, which is greater than the first temperature critical value of 20°C, and the speed of the DC brushless motor is switched from the first speed to the preset speed. In the next second, if the surface temperature of the heat exchanger is detected to be 19°C, which is less than the first temperature critical value of 20°C, the fan coil unit is considered to be in a wet condition, and the speed of the DC brushless motor is switched to the first speed again. This will cause the speed switching frequency of the DC brushless motor to be too fast, which is easy to damage the DC brushless motor.

[0109] Therefore, the present application can set an upper limit value of the first temperature critical value corresponding to the surface temperature of a heat exchanger during the operation of the DC brushless motor, and judge whether the fan coil unit has truly entered the dry working state from the wet working state by comparing the current temperature value of the surface temperature with the upper limit value of the first temperature critical value. In this way, it can avoid frequent judgments that the fan coil unit is in the dry working state and the wet working state, which causes the DC brushless motor to switch speed too fast and damage the DC brushless motor, thereby ensuring the working stability of the DC brushless motor, extending the service life of the DC brushless motor, and improving the overall performance of the fan coil unit.

[0110] Specifically, in one example, the first temperature critical value is 20° C. If the dry and wet working condition judgment tolerance value is set to 2° C., the lower limit of the first temperature critical value is 18° C., and the upper limit of the first temperature critical value is 22° C. The preset speed A is 920 rpm, and the first speed B is 950 rpm.

[0111] like Figure 4 As shown, when it is determined that the fan coil unit is in a wet condition, the DC brushless motor is controlled to maintain operation at the first speed B of 950rpm, and the current temperature value of the surface temperature can be detected in real time, and the current temperature value of the surface temperature can be compared with the upper limit value of the first temperature critical value. If the current temperature value of the surface temperature is 19°C, which is less than the upper limit value of the first temperature critical value of 22°C, it means that the fan coil unit is still in a wet condition at this time, and condensed water will form on the surface of the heat exchanger, so the DC brushless motor can be controlled to maintain operation at the first speed B of 950rpm.

[0112] If the current temperature value of the surface temperature is 23°C, which is greater than or equal to the upper limit value of the first temperature critical value of 22°C, the fan coil unit is judged to be in a dry working state, and the DC brushless motor is controlled to switch from the first speed B of 950rpm to the preset speed A of 920rpm. This can make the air supply volume of the fan coil unit equivalent under different working conditions, thereby improving the working efficiency of the fan coil unit.

[0113] In this way, the speed control method of the present application can determine that the fan coil unit is in a wet operating state and the DC brushless motor is running at a preset speed after the DC brushless motor is initially started for a preset time. By judging in real time whether the current temperature value of the surface temperature of the heat exchanger is greater than or equal to the upper limit value of the first temperature critical value, it can be judged whether the fan coil unit has entered a dry operating state from a wet operating state, thereby timely reducing the motor speed when the fan coil unit enters a dry operating state to improve the working efficiency of the fan coil unit.

[0114] It should be noted that, since the fan coil unit cannot be in a dry working state in an instant when it is initially in a wet working state, it takes a period of time to be in a dry working state. Therefore, after the DC brushless motor is initially started for a preset time, when it is determined that the fan coil unit is in a wet working state and the DC brushless motor is running at the first speed, it is also possible to detect the current temperature value of the surface temperature in real time after another preset time, for example, another 60S, and compare the current temperature value of the surface temperature with the upper limit value of the first temperature critical value, so as to determine whether the fan coil unit has entered the dry working state from the wet working state, and then control and adjust the motor speed accordingly to improve the control efficiency of the motor speed.

[0115] See also Fig. 9 In some embodiments, after step 053, the speed control method further includes:

[0116] 054: Compare the current temperature value of the surface temperature with the lower limit value of the first temperature critical value;

[0117] 055: If the current temperature value of the surface temperature is less than or equal to the lower limit value of the first temperature critical value, it is determined that the fan coil unit is in a wet condition, and the brushless DC motor is controlled to switch from a preset speed to a first speed;

[0118] 056: If the current temperature value of the surface temperature is greater than the lower limit value of the first temperature critical value, the brushless DC motor is controlled to keep running at a preset speed.

[0119] Please combine Figure 2 , step 054, step 055 and step 056 can all be implemented by the control module 13. That is, the control module 13 is used to compare the current temperature value of the surface temperature with the lower limit value of the first temperature critical value; if the current temperature value of the surface temperature is less than or equal to the lower limit value of the first temperature critical value, it is determined that the fan coil unit is in a wet condition, and the DC brushless motor is controlled to switch from the preset speed to the first speed; if the current temperature value of the surface temperature is greater than the lower limit value of the first temperature critical value, the DC brushless motor is controlled to keep running at the preset speed.

[0120] Specifically, please combine Figure 4 When it is determined that the fan coil unit is in a dry condition and the DC brushless motor is controlled to switch from the first speed B of 950 rpm to the preset speed A of 920 rpm, the current temperature value of the surface temperature of the heat exchanger can be compared with the lower limit value of the first temperature critical value.

[0121] If the current temperature value of the surface temperature is 20°C, which is greater than the lower limit of the first temperature critical value of 18°C, it indicates that the fan coil unit is continuously operating in a dry condition. At this time, it continues to operate at a preset speed A of 920 rpm to ensure the operating efficiency of the fan coil unit.

[0122] If the current temperature value of the surface temperature is 17°C, which is less than or equal to the lower limit of the first temperature critical value of 18°C, it indicates that the fan coil unit has entered the wet condition again from the dry condition. The DC brushless motor is controlled to switch from the preset speed A of 920rpm to the first speed B of 950rpm to increase the speed and ensure the operating performance of the fan coil unit.

[0123] In this way, the speed control method of the present application can determine whether the fan coil unit is running in a dry condition after determining that the current operating state of the fan coil unit is in a dry condition and controlling the DC brushless motor to switch from the first speed to the preset speed. It can then determine in real time whether the current temperature value of the surface temperature of the heat exchanger is greater than or equal to the lower limit value of the first temperature critical value, thereby determining whether the fan coil unit is running in a wet condition from a dry condition. When the fan coil unit enters the wet condition, the motor speed can be increased in time to ensure the operating performance of the fan coil unit.

[0124] In detail, the solution of the present application is described below with an example of a complete motor speed control.

[0125] Assume that the preset speed of the fan coil unit is 920rpm, the first speed is 950rpm, the first temperature critical value of the dry and wet conditions is 20℃, and the dry and wet condition judgment tolerance value is 2℃, that is, the lower limit value of the first temperature critical value is 18℃, and the upper limit value of the first temperature critical value is 22℃.

[0126] The fan coil unit is powered on, and the DC brushless motor runs at a preset speed of 920 rpm. After a preset interval of 60 seconds, the surface temperature T2 of the heat exchanger is detected to be 30°C, and it is judged that T2 is greater than the first temperature critical value of 20°C, which means that it is in a dry condition at this time, so the DC brushless motor is controlled to maintain the preset speed of 920 rpm. After the second interval of 60 seconds, the surface temperature T2 of the heat exchanger is detected to be 27°C, and it is judged that T2 is greater than the lower limit of the first temperature critical value of 18°C, so the DC brushless motor is controlled to continue to run at a speed of 920 rpm. After the third interval of 60 seconds, if the surface temperature T2 of the heat exchanger is detected to be 16°C, and it is judged that the surface temperature T2 of the heat exchanger is less than the lower limit of the first temperature critical value of 18°C, it is judged that the operating condition of the fan coil unit has changed from a dry condition to a wet condition at this time, so the DC brushless motor can be controlled to switch from the preset speed of 920 rpm to the first speed of 950 rpm, increase the motor speed, increase the air volume, and improve the operating performance of the fan coil unit.

[0127] After the operating condition of the fan coil unit changes from dry condition to wet condition, after the fourth interval of 60 seconds, the tube temperature T2 is detected to be 14°C, and it is judged that the surface temperature T2 of the heat exchanger is less than the upper limit of the first temperature critical value of 22°C, and the operation at the first speed of 950rpm is continued. After the fifth interval of 60 seconds, the tube temperature T2 is detected to be 10°C, and it is judged that T2 is still less than the upper limit of the first temperature critical value of 22°C, and the operation at the first speed of 950rpm is continued, and so on.

[0128] See also Fig.10 In some embodiments, after step 031, the speed control method further includes:

[0129] 061: Real-time detection of the current temperature value of the surface temperature;

[0130] 062: Determine whether the current temperature value of the surface temperature is greater than or equal to the second temperature threshold value;

[0131] 063: If the current temperature value of the surface temperature is greater than or equal to the second temperature critical value, the brushless DC motor is controlled to switch from the preset speed to the second speed, and the second speed is greater than the preset speed;

[0132] 064: If the current temperature value of the surface temperature is less than the second temperature critical value, the fan coil unit is controlled to keep running at the preset speed.

[0133] Please combine Figure 2, step 061, step 062 and step 063 can all be implemented by the control module 13. That is, the control module 13 is used to detect the current temperature value of the surface temperature in real time; determine whether the current temperature value of the surface temperature is greater than or equal to the second temperature critical value; if the current temperature value of the surface temperature is greater than or equal to the second temperature critical value, control the DC brushless motor to switch from the preset speed to the second speed, and the second speed is greater than the preset speed; if the current temperature value of the surface temperature is less than the second temperature critical value, control the fan coil unit to keep running at the preset speed.

[0134] It is understandable that when the fan coil unit is in a dry condition, if the temperature on the heat exchanger is too high, for example, when the temperature of the water inlet pipe of the heat exchanger is higher than 35°C, the surface of the heat exchanger expands due to the high temperature, causing the gap between the fins on the surface of the heat exchanger to become smaller, resulting in greater wind resistance, and poor operating performance of the fan coil unit. Therefore, when it is detected that the surface temperature of the heat exchanger is higher than the preset temperature threshold, for example, higher than 35°C, the speed of the brushless DC motor can be increased to the second speed to increase the air volume and improve the operating performance of the fan coil unit.

[0135] That is, the second temperature critical value can be 35°C, the second temperature critical value can also be 35.1°C, 35.2°C, 35.3°C, 35.4°C, 35.6°C, 35.7°C, 35.8°C, 36°C, 37°C or 38°C, without limitation here.

[0136] As in the example described above, the preset speed A is 920rpm and the first speed B is 950rpm. The second speed can be the same value as the first speed, both are 950rpm. The second speed can also be different from the first speed, for example, it can be 960rpm, and there is no limitation here.

[0137] The present application can detect that the temperature on the heat exchanger is too high when the fan coil unit is in a dry condition, and when it is higher than a second temperature critical value, increase the speed of the DC brushless motor to increase the air volume and improve the operating performance of the fan coil unit.

[0138] The present application also provides a fan coil unit. The fan coil unit is used to execute the speed control method of a brushless DC motor described in any one of the above embodiments, or the brushless DC motor includes the speed control device 10 of the brushless DC motor described in the above embodiments.

[0139] Specifically, the steps and working principle of the speed control method of the brushless DC motor are as described above, which will not be repeated here. The structure of the speed control device 10 of the brushless DC motor is also as described above, which will not be repeated here.

[0140] See also Fig.11 and Fig.12 , Fig.11 The fan coil unit of the present application is in operation, and the speed of the DC brushless motor changes with the surface temperature of the heat exchanger during the process of the fan coil unit changing from a wet condition to a dry condition. Fig.12 The graph is a relationship between the speed of the DC brushless motor and the surface temperature of the heat exchanger during the operation of the fan coil unit, when the operating condition of the fan coil unit changes from a dry condition to a wet condition. Fig.11 and Fig.12 In the figure, Tdw is the first temperature critical value under dry and wet working conditions, in °C. dtT is the judgment tolerance value of dry and wet working conditions, that is, dtT is the absolute value of the difference between the first temperature critical value and the upper and lower limits of the first temperature critical value, in °C. Nd is the speed under dry working conditions, in rpm. Nw is the speed under wet working conditions, in rpm. Nd can be 920 rpm as mentioned above, and Nw can be 950 rpm as mentioned above.

[0141] In this way, the fan coil unit of the present application uses the above-mentioned DC brushless motor speed control method to more accurately judge the operating condition of the fan coil unit according to the surface temperature of the heat exchanger, so that the speed of the DC brushless motor can be flexibly adjusted under different operating conditions, and the air supply volume of the fan coil unit under different working conditions can be made equivalent. In particular, when the fan coil unit is operating in the cooling mode, the air volume can be increased by increasing the speed of the DC brushless motor to improve the cooling effect.

[0142] The present application also provides an air conditioning system, which includes the fan coil unit described in the above embodiment.

[0143] In this way, the fan coil unit in the air-conditioning system of the present application uses the above-mentioned DC brushless motor speed control method to more accurately judge the operating condition of the fan coil unit according to the surface temperature of the heat exchanger, so that the speed of the DC brushless motor can be flexibly adjusted under different operating conditions, and the air supply volume of the fan coil unit under different working conditions can be made equivalent. In particular, when the fan coil unit is operating in the cooling mode, the air volume can be increased by increasing the speed of the DC brushless motor to improve the cooling effect.

[0144] The above embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the present application. It should be pointed out that, for a person of ordinary skill in the art, several modifications and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the present application shall be subject to the attached claims.

Claims

1. A speed control method for a brushless DC motor, applied to a fan coil unit, characterized in that: The fan coil unit includes the brushless DC motor and a heat exchanger, and the speed control method includes: When the brushless DC motor is started, the surface temperature of the heat exchanger is detected in real time; determining the operating condition of the fan coil unit according to the surface temperature; The rotation speed of the brushless DC motor is controlled according to the surface temperature and the operating condition of the fan coil unit.

2. The speed control method of a brushless DC motor according to claim 1, characterized in that: The heat exchanger is provided with a temperature sensor, and the real-time detection of the surface temperature of the heat exchanger includes: When the brushless DC motor is started at a preset speed, the surface temperature is detected in real time by the temperature sensor.

3. The speed control method of a brushless DC motor according to claim 2, characterized in that: The step of judging the operating condition of the fan coil unit according to the surface temperature includes: The surface temperature is compared with a preset temperature critical value to determine the operating condition of the fan coil unit, wherein the operating condition includes a wet condition and a dry condition. The wet condition refers to the condition corresponding to when the heat exchanger surface is wet, and the dry condition refers to the condition corresponding to when the heat exchanger surface is dry.

4. The speed control method of a brushless DC motor according to claim 3, characterized in that: The step of comparing the surface temperature with a preset temperature threshold to determine the operating condition of the fan coil unit includes: After the brushless DC motor runs at a preset speed for a preset time, determining whether the initial value of the surface temperature is greater than or equal to a first temperature threshold value; If the initial value of the surface temperature is greater than or equal to the first temperature critical value, it is determined that the fan coil unit is in the dry condition; If the initial value of the surface temperature is less than the first temperature critical value, it is determined that the fan coil unit is in the wet condition.

5. The speed control method of a brushless DC motor according to claim 4, characterized in that: The controlling the rotation speed of the brushless DC motor according to the surface temperature and the operating condition of the fan coil unit comprises: When it is determined that the fan coil unit is in the dry condition, controlling the brushless DC motor to keep running at the preset speed; When it is determined that the fan coil unit is in the wet condition, the brushless DC motor is controlled to run at a first speed, wherein the first speed is greater than the preset speed.

6. The speed control method of a brushless DC motor according to claim 5, characterized in that: After controlling the brushless DC motor to keep running at the preset speed when it is determined that the fan coil unit is in the dry condition, the speed control method further includes: Real-time detection of the current temperature value of the surface temperature; Comparing the current temperature value of the surface temperature with the lower limit value of the first temperature critical value; If the current temperature value of the surface temperature is less than or equal to the lower limit value of the first temperature critical value, it is determined that the fan coil unit is in the wet working condition, and the brushless DC motor is controlled to switch from the preset speed to the first speed; If the current temperature value of the surface temperature is greater than the lower limit value of the first temperature critical value, the DC brushless motor is controlled to keep running at the preset speed.

7. The speed control method of a brushless DC motor according to claim 6, characterized in that: After determining that the fan coil unit is in the wet condition and controlling the brushless DC motor to switch from the preset speed to the first speed, the speed control method further includes: Comparing the current temperature value of the surface temperature with the upper limit value of the first temperature critical value; If the current temperature value of the surface temperature is greater than or equal to the upper limit value of the first temperature critical value, controlling the brushless DC motor to switch from the first speed to the preset speed; If the current temperature value of the surface temperature is less than the upper limit value of the first temperature critical value, the brushless DC motor is controlled to keep running at the first speed.

8. The speed control method of a brushless DC motor according to claim 5, characterized in that: When it is determined that the fan coil unit is in the wet condition, after controlling the brushless DC motor to run at a first speed, the speed control method further includes: Real-time detection of the current temperature value of the surface temperature; Comparing the current temperature value of the surface temperature with the upper limit value of the first temperature critical value; If the current temperature value of the surface temperature is greater than or equal to the upper limit value of the first temperature critical value, it is determined that the fan coil unit is in the dry condition, and the brushless DC motor is controlled to switch from the first speed to the preset speed; If the current temperature value of the surface temperature is less than the upper limit value of the first temperature critical value, the brushless DC motor is controlled to maintain running at the first speed.

9. The speed control method of a brushless DC motor according to claim 8, characterized in that: After determining that the fan coil unit is in the dry condition and controlling the brushless DC motor to switch from the first speed to the preset speed, the speed control method further includes: Comparing the current temperature value of the surface temperature with the lower limit value of the first temperature critical value; If the current temperature value of the surface temperature is less than or equal to the lower limit value of the first temperature critical value, it is determined that the fan coil unit is in the wet working condition, and the brushless DC motor is controlled to switch from the preset speed to the first speed; If the current temperature value of the surface temperature is greater than the lower limit value of the first temperature critical value, the DC brushless motor is controlled to keep running at the preset speed.

10. The speed control method of a brushless DC motor according to claim 5, characterized in that: After controlling the brushless DC motor to keep running at the preset speed when it is determined that the fan coil unit is in the dry condition, the speed control method further includes: Real-time detection of the current temperature value of the surface temperature; Determining whether the current temperature value of the surface temperature is greater than or equal to a second temperature threshold value; If the current temperature value of the surface temperature is greater than or equal to the second temperature threshold value, the brushless DC motor is controlled to switch from the preset speed to a second speed, and the second speed is greater than the preset speed; If the current temperature value of the surface temperature is less than the second temperature critical value, the fan coil unit is controlled to keep running at the preset speed.

11. A speed control device for a brushless DC motor, applied to a fan coil unit, characterized in that: The fan coil unit includes the brushless DC motor and a heat exchanger, and the speed control device of the brushless DC motor includes: A temperature detection module, used for detecting the surface temperature of the heat exchanger in real time after the brushless DC motor is initially started; a judging module, configured to judge the operating condition of the fan coil unit according to the surface temperature; and A control module is used to control the rotation speed of the brushless DC motor according to the surface temperature and the operating condition of the fan coil unit.

12. A fan coil unit, characterized in that: The fan coil unit is used to execute the speed control method of the brushless DC motor described in any one of claims 1 to 10, or the brushless DC motor includes the speed control device of the brushless DC motor described in claim 11.

13. An air conditioning system, characterized in that: The air conditioning system comprises the fan coil unit according to claim 12.

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