A method of anti-freezing control for a grain cooling unit

Abstract

The present application relates to air conditioning technical field, especially a kind of freeze prevention control method of grain cooling unit, it is applied to the grain cooling unit including compressor, condenser, evaporator, outdoor fan and indoor fan, and indoor fan is single-speed fan, and compressor is fixed-frequency compressor;It includes the following steps: obtaining the motor type of outdoor fan, if the motor type is alternating-current motor, obtaining outdoor ambient temperature and condenser coil temperature, and according to the outdoor ambient temperature and condenser coil temperature, the speed gear of the outdoor fan is switched;If the motor type is direct-current motor, obtain indoor ambient temperature, outdoor ambient temperature and condenser coil temperature, and according to the indoor ambient temperature, outdoor ambient temperature and condenser coil temperature, the target speed of the outdoor fan is generated;The speed of the outdoor fan is adjusted to target speed.By the control of the outdoor fan speed, the risk of evaporator freezing can be reduced by the present scheme.

Description

Technical Field

[0001] This invention relates to the field of air conditioning technology, and in particular to an anti-freezing control method for grain cooling units. Background Technology

[0002] Grain cooling units are specialized devices used for refrigeration and cooling of grain silos. Their function is to maintain a suitable storage temperature for grain during cold seasons or in low ambient temperatures. During unit operation, when the indoor temperature is low and the unit is still in refrigeration mode, the evaporator surface is prone to frost, ice, or even freezing due to excessively low evaporation temperatures. Once the evaporator freezes, not only does the heat exchange efficiency drop sharply, resulting in poor cooling effect inside the silo, but it may also cause incomplete evaporation of the refrigerant on the compressor suction side, leading to the risk of liquid slugging and seriously affecting the reliability and lifespan of the refrigeration system.

[0003] To address the aforementioned issues, common anti-freeze protection measures in existing technologies mainly include increasing the indoor fan speed, reducing the compressor operating frequency, or directly shutting down the compressor. However, for grain chiller units using single-speed indoor fans and fixed-frequency compressors, the indoor fan cannot be speed-adjusted to enhance heat exchange, and the compressor cannot be frequency-reduced to adjust cooling capacity. Therefore, only shutdown is feasible among these measures. This results in the unit repeatedly starting and stopping during anti-freeze protection, leading to poor cooling performance and reduced system reliability.

[0004] In addition, some existing technologies attempt to determine the risk of freezing by detecting the temperature of the evaporator coil, triggering protection when the coil temperature falls below a certain threshold. However, this method of relying on the evaporator side temperature for post-event judgment often only takes action when freezing has already occurred or is about to occur, resulting in insufficient proactive protection and frequent activation due to temperature fluctuations.

[0005] In summary, existing technologies lack an anti-freezing control method that can effectively reduce the risk of evaporator freezing and avoid frequent start-stop of the unit for grain cooling units with single-speed indoor fans and fixed-frequency compressors. Summary of the Invention

[0006] This invention provides a method for preventing freezing in grain cooling units, which can reduce the risk of evaporator freezing in a timely manner and avoid frequent start-ups and shutdowns of the unit by controlling the speed of the outdoor fan.

[0007] To achieve the above objectives, this application provides the following technical solution:

[0008] A method for preventing freezing in a grain cooling unit, applied in the grain cooling unit, the grain cooling unit including a compressor, a condenser, an evaporator, an outdoor fan, and an indoor fan, the indoor fan being a single-speed fan, and the compressor being a fixed-frequency compressor; the method includes the following steps:

[0009] S100: Obtain the motor type of the outdoor fan. The motor type includes AC motor and DC motor. If the motor type is AC motor, then execute S200. If the motor type is DC motor, then execute S300.

[0010] S200: Obtain the outdoor ambient temperature and the condenser coil temperature, and switch the speed level of the outdoor fan according to the outdoor ambient temperature and the condenser coil temperature.

[0011] S300: Obtain the indoor ambient temperature, outdoor ambient temperature, and condenser coil temperature, and generate the target speed of the outdoor fan based on the indoor ambient temperature, outdoor ambient temperature, and condenser coil temperature; adjust the speed of the outdoor fan to the target speed.

[0012] Furthermore, the outdoor fan's speed settings include a high-speed setting, a low-speed setting, and a stop setting; S200 includes:

[0013] S201, Obtain the outdoor ambient temperature;

[0014] S202, Based on the outdoor ambient temperature, generate the initial speed setting of the outdoor fan;

[0015] S203, control the outdoor fan to run at the initial speed and obtain the first continuous running time of the outdoor fan at the initial speed; when the first continuous running time is greater than the first preset time, execute S204;

[0016] S204, with a second preset time period, acquires the real-time outdoor ambient temperature and condenser coil temperature;

[0017] S205, based on the real-time acquired outdoor ambient temperature and condenser coil temperature, switch the speed level of the outdoor fan.

[0018] Furthermore, in S202:

[0019] When the outdoor ambient temperature is greater than or equal to the first start-up temperature threshold, the initial gear is the high-speed gear;

[0020] When the outdoor ambient temperature is less than or equal to the second start-up temperature threshold, the initial gear is the shutdown gear;

[0021] When the outdoor ambient temperature is greater than the second start-up temperature threshold and less than the first start-up temperature threshold, the initial gear is the low speed gear.

[0022] The first startup temperature threshold is greater than the second startup temperature threshold.

[0023] Furthermore, in S205:

[0024] When the outdoor ambient temperature is greater than or equal to the first outdoor temperature threshold, if the condenser coil temperature is greater than or equal to the first switching temperature threshold, the outdoor fan is controlled to operate at high speed; if the condenser coil temperature is less than or equal to the second switching temperature threshold, the outdoor fan is controlled to operate at low speed; the first switching temperature threshold is greater than the second switching temperature threshold.

[0025] When the outdoor ambient temperature is less than or equal to the second outdoor temperature threshold, if the condenser coil temperature is greater than or equal to the third switching temperature threshold, the outdoor fan is controlled to operate at high speed; if the condenser coil temperature is less than or equal to the fourth switching temperature threshold, the outdoor fan is controlled to operate at low speed; the third switching temperature threshold is greater than the fourth switching temperature threshold.

[0026] The third switching temperature threshold is greater than the first switching temperature threshold, and the fourth switching temperature threshold is greater than the second switching temperature threshold.

[0027] When the outdoor ambient temperature is greater than the second outdoor temperature threshold and less than the first outdoor temperature threshold, the historical outdoor ambient temperature is obtained, and the speed of the outdoor fan is switched according to the historical outdoor ambient temperature and the condenser coil temperature.

[0028] Furthermore, the S300 includes:

[0029] S301, obtain the outdoor ambient temperature;

[0030] S302, Based on the outdoor ambient temperature, generate the initial rotational speed of the outdoor fan;

[0031] S303, control the outdoor fan to run at the initial speed, and obtain the second continuous running time of the outdoor fan at the initial speed; when the second continuous running time is greater than the third preset time, execute S304;

[0032] S304, with the fourth preset time as the cycle, acquires the real-time indoor ambient temperature, outdoor ambient temperature and condenser coil temperature.

[0033] S305, Based on the real-time acquired indoor ambient temperature, outdoor ambient temperature and condenser coil temperature, the target speed of the outdoor fan is generated;

[0034] S306, Adjust the speed of the outdoor fan to the target speed.

[0035] Furthermore, in S302:

[0036] When the outdoor ambient temperature is greater than or equal to the first start-up temperature threshold, the initial rotation speed is the preset maximum rotation speed;

[0037] When the outdoor ambient temperature is less than or equal to the second start-up temperature threshold, the initial speed is the preset minimum speed;

[0038] When the outdoor ambient temperature is greater than the second start-up temperature threshold and less than the first start-up temperature threshold, the initial speed is a preset medium speed.

[0039] The first startup temperature threshold is greater than the second startup temperature threshold.

[0040] Furthermore, S305 includes:

[0041] S3051, Calculate the actual temperature difference between the condenser coil temperature and the outdoor ambient temperature;

[0042] S3052, generate a target temperature difference based on the indoor ambient temperature and the outdoor ambient temperature;

[0043] S3053, Calculate the difference between the actual temperature difference and the target temperature difference to generate a temperature difference deviation value A;

[0044] S3054, retrieve the temperature difference deviation value generated in the previous cycle. Calculate the temperature difference deviation value A and the temperature difference deviation value of the previous cycle. The difference is used to generate the temperature difference deviation change B;

[0045] S3055, the target rotational speed of the outdoor fan is generated based on the temperature difference deviation value A and the temperature difference deviation change B.

[0046] The principles and advantages of this invention are as follows:

[0047] This solution reduces the risk of evaporator freezing by controlling the outdoor fan speed. Specifically, for grain chiller units with a single-speed indoor fan and a fixed-frequency compressor, the solution obtains the outdoor fan motor type and executes different control strategies based on the motor type, achieving differentiated control of the outdoor fan speed. This reduces the risk of evaporator freezing without increasing hardware costs. When the motor type is an AC motor, since AC motors typically have only a limited number of speed ranges, continuous adjustment is difficult. Therefore, this solution only obtains the outdoor ambient temperature and condenser coil temperature, and switches the outdoor fan speed range based on these two parameters. This control method matches the range characteristics of AC motors, and can avoid frequent start-stop cycles due to traditional anti-freeze protection in a simple and reliable way, reducing the number of repeated start-stop cycles. When the motor type is a DC motor, since DC motors have stepless speed regulation capabilities, this invention further obtains the indoor ambient temperature and combines it with the outdoor ambient temperature and condenser coil temperature to generate a target speed for the outdoor fan, and then adjusts the outdoor fan to this target speed. Introducing indoor ambient temperature can more comprehensively reflect the changes in the evaporator's heat load, thereby reducing the risk of evaporator freezing while maintaining continuous operation of the unit and avoiding control failures caused by insufficient parameters.

[0048] In summary, this solution selects the corresponding control strategy based on the motor type of the outdoor fan, and by controlling the speed of the outdoor fan, it reduces the risk of evaporator freezing and improves the operational reliability of the grain cooling unit. Attached Figure Description

[0049] Figure 1 This is a flowchart illustrating an embodiment of an anti-freezing control method for a grain cooling unit according to the present invention.

[0050] Figure 2 This is a schematic diagram of the refrigeration system of a grain cooling unit in an embodiment of the anti-freezing control method for a grain cooling unit according to the present invention. Detailed Implementation

[0051] The following detailed description illustrates the specific implementation method:

[0052] The markings in the accompanying drawings include: compressor 1, condenser 2, evaporator 3, outdoor fan 4, indoor fan 5, gas-liquid separator 6, first filter 7, second filter 8, expansion valve 9, low-pressure switch 10, and high-pressure switch 11.

[0053] Example 1:

[0054] A method for preventing freezing in grain cooling units, applied to grain cooling units, such as... Figure 2As shown, the grain cooling unit includes a compressor 1, a condenser 2, an evaporator 3, an outdoor fan 4, an indoor fan 5, a gas-liquid separator 6, a first filter 7, a second filter 8, an expansion valve 9, a low-pressure switch 10, and a high-pressure switch 11. The exhaust port of the compressor 1 is sequentially connected to the high-pressure switch 11, the condenser 2, the first filter 7, the expansion valve 9, the second filter 8, the evaporator 3, the low-pressure switch 10, and the gas-liquid separator 6, and then connected to the suction port of the compressor 1, forming a refrigerant circulation loop. The outdoor fan 4 is located at the condenser 2 for forced cooling of the condenser 2. The indoor fan 5 is located at the evaporator 3 for delivering cold air into the grain silo. The indoor fan 5 is a single-speed fan, and the compressor 1 is a fixed-frequency compressor 1. The grain cooling unit also includes a controller, which is electrically connected to the outdoor fan 4, the indoor fan 5, the compressor 1, and a temperature sensor for temperature detection, and is used to implement an anti-freezing control method.

[0055] The outdoor ambient temperature is detected by an outdoor ambient temperature sensor located on the condenser 2 side of the outdoor unit, the indoor ambient temperature is detected by an indoor ambient temperature sensor located on the evaporator 3 side of the indoor unit, and the condenser 2 coil temperature is detected by a coil temperature sensor located on the condenser 2 coil. All of the above temperature sensors are electrically connected to the controller to provide the corresponding temperature data in real time.

[0056] like Figure 1 As shown, the method includes the following steps:

[0057] S100: Obtain the motor type of the outdoor fan 4. The motor type includes AC motor and DC motor. If the motor type is AC motor, execute S200; if the motor type is DC motor, execute S300. In this embodiment, the motor type of the outdoor fan 4 is obtained using a DIP switch. Specifically, the outdoor fan 4 motor is equipped with a DIP switch, and the user or installer sets the DIP switch to the corresponding position according to the actual motor type. The controller identifies the motor type by reading the status signal of the DIP switch. In other embodiments of this application, the controller can also automatically identify the motor type by detecting the drive signal feedback of the outdoor fan 4: if the controller outputs an AC voltage drive signal and detects a zero-crossing signal, it is determined to be an AC motor; if the output is a DC voltage PWM drive signal, it is determined to be a DC motor.

[0058] S200: Acquire the outdoor ambient temperature and the condenser 2 coil temperature, and switch the speed range of the outdoor fan 4 according to the outdoor ambient temperature and the condenser 2 coil temperature; the speed range of the outdoor fan 4 includes a high speed range, a low speed range, and a stop range. S200 includes:

[0059] S201, obtain the outdoor ambient temperature.

[0060] S202, based on the outdoor ambient temperature, generates the initial speed setting for the outdoor fan 4. In S202:

[0061] When the outdoor ambient temperature is greater than or equal to the first start-up temperature threshold, the initial gear is the high-speed gear;

[0062] When the outdoor ambient temperature is less than or equal to the second start-up temperature threshold, the initial gear is the shutdown gear;

[0063] When the outdoor ambient temperature is greater than the second start-up temperature threshold and less than the first start-up temperature threshold, the initial gear is the low speed gear.

[0064] The first startup temperature threshold is greater than the second startup temperature threshold.

[0065] In this embodiment, the first start-up temperature threshold is 32°C, and the second start-up temperature threshold is 27°C. Through the aforementioned initial setting, after startup, the unit can set the outdoor fan 4 to high speed, low speed, or stop mode according to the specific range of the outdoor ambient temperature: when the outdoor ambient temperature is high, high speed is used to enhance the heat dissipation of the condenser 2 and ensure system energy efficiency; when the outdoor ambient temperature is low, stop mode is used, as the condensing pressure is already high enough, and stopping the outdoor fan 4 avoids excessive heat dissipation leading to a further drop in condensing pressure, thereby preventing the evaporator 3 from freezing due to excessively low evaporation temperature; when the outdoor ambient temperature is between these two, low speed is used to achieve a balance between anti-freezing and energy efficiency. This initial setting avoids excessively low evaporation temperatures due to improper mode selection, thereby reducing the risk of evaporator 3 freezing and reducing the likelihood of forced shutdown due to freeze protection.

[0066] S203: Control the outdoor fan 4 to operate at the initial speed and obtain the first continuous operating time of the outdoor fan 4 at the initial speed; when the first continuous operating time is greater than the first preset time, execute S204. In this embodiment, the first preset time is 10 seconds. The first preset time ensures the basic stability of the unit during the start-up phase and avoids accidental triggering of subsequent adjustments due to instantaneous fluctuations.

[0067] S204, the real-time outdoor ambient temperature and condenser 2 coil temperature are acquired using a second preset time period. In this embodiment, the second preset time period is 5 seconds. The period is the second preset time period.

[0068] S205: Based on the real-time acquired outdoor ambient temperature and condenser 2 coil temperature, the speed setting of the outdoor fan 4 is switched. In S205:

[0069] When the outdoor ambient temperature is greater than or equal to a first outdoor temperature threshold, if the temperature of the condenser 2 coil is greater than or equal to a first switching temperature threshold, the outdoor fan 4 is controlled to operate at high speed; if the temperature of the condenser 2 coil is less than or equal to a second switching temperature threshold, the outdoor fan 4 is controlled to operate at low speed; the first switching temperature threshold is greater than the second switching temperature threshold. In this embodiment, the first outdoor temperature threshold is 21°C, the first switching temperature threshold is 35°C, and the second switching temperature threshold is 30°C.

[0070] When the outdoor ambient temperature is less than or equal to the second outdoor temperature threshold, if the temperature of the condenser 2 coil is greater than or equal to the third switching temperature threshold, the outdoor fan 4 is controlled to operate at high speed; if the temperature of the condenser 2 coil is less than or equal to the fourth switching temperature threshold, the outdoor fan 4 is controlled to operate at low speed. The third switching temperature threshold is greater than the fourth switching temperature threshold; the third switching temperature threshold is greater than the first switching temperature threshold; and the fourth switching temperature threshold is greater than the second switching temperature threshold. In this embodiment, the second outdoor temperature threshold is 17°C, the third switching temperature threshold is 38°C, and the fourth switching temperature threshold is 34°C.

[0071] When the outdoor ambient temperature is greater than the second outdoor temperature threshold and less than the first outdoor temperature threshold, i.e., between 17°C and 21°C, the historical outdoor ambient temperature is acquired, and the speed of the outdoor fan 4 is switched based on the historical outdoor ambient temperature and the coil temperature of the condenser 2. The historical outdoor ambient temperature refers to the last acquired outdoor ambient temperature before the real-time outdoor ambient temperature entered the current range, i.e., before it was greater than the second outdoor temperature threshold and less than the first outdoor temperature threshold. Specifically: if the historical outdoor ambient temperature is greater than or equal to the first outdoor temperature threshold, i.e., it was previously in a high-temperature zone, the switching is performed according to the rules for outdoor ambient temperatures greater than or equal to the first outdoor temperature threshold; if the historical outdoor ambient temperature is less than or equal to the second outdoor temperature threshold, i.e., it was previously in a low-temperature zone, the switching is performed according to the rules for outdoor ambient temperatures less than or equal to the second outdoor temperature threshold; if the grain cooling unit is powered on for the first time and the outdoor ambient temperature immediately falls into this range, the default switching is performed according to the rules for outdoor ambient temperatures less than or equal to the second outdoor temperature threshold, i.e., a low-temperature zone control threshold is used to prevent freezing risks.

[0072] The aforementioned AC motor control strategy fully utilizes the limited speed ranges of the AC fan. By comparing the switching thresholds of the condenser 2 coil temperature with different ambient temperature ranges, it effectively regulates the condensing pressure, thereby indirectly controlling the evaporation temperature and preventing frost formation on the evaporator 3. Compared to existing technologies that rely solely on compressor 1 shutdown protection, this solution maintains continuous compressor 1 operation under most conditions, avoiding forced shutdown due to evaporator 3 freezing, thus improving the stability of the cooling effect and the system reliability.

[0073] After switching, wait for the next cycle, then return to S204 to continue the loop execution.

[0074] S300: Acquire the indoor ambient temperature, outdoor ambient temperature, and condenser 2 coil temperature; generate the target speed of the outdoor fan 4 based on the indoor ambient temperature, outdoor ambient temperature, and condenser 2 coil temperature; adjust the speed of the outdoor fan 4 to the target speed. S300 includes:

[0075] S301, obtains the outdoor ambient temperature.

[0076] S302, based on the outdoor ambient temperature, generates the initial rotational speed of the outdoor fan 4. In S302:

[0077] When the outdoor ambient temperature is greater than or equal to the first start-up temperature threshold, the initial rotation speed is the preset maximum rotation speed;

[0078] When the outdoor ambient temperature is less than or equal to the second start-up temperature threshold, the initial speed is the preset minimum speed;

[0079] When the outdoor ambient temperature is greater than the second start-up temperature threshold and less than the first start-up temperature threshold, the initial speed is a preset medium speed.

[0080] The first startup temperature threshold is greater than the second startup temperature threshold.

[0081] In this embodiment, the first start-up temperature threshold is 32°C, the second start-up temperature threshold is 27°C; the preset maximum speed is the maximum allowable speed RPM1 of the DC fan, the preset minimum speed is the minimum allowable speed RPM2 of the DC fan, and the preset medium speed is (RPM1+RPM2) / 2.

[0082] S303: Control the outdoor fan 4 to run at the initial speed and obtain the second continuous running time of the outdoor fan 4 at the initial speed; when the second continuous running time is greater than the third preset time, execute S304. In this embodiment, the third preset time is 5 minutes. The third preset time is also used to ensure stability during the start-up phase and avoid premature adjustment.

[0083] S304, the real-time indoor ambient temperature, outdoor ambient temperature, and condenser coil temperature are acquired at a fourth preset time interval. In this embodiment, the fourth preset time interval is 5 seconds.

[0084] S305, based on the real-time acquired indoor ambient temperature, outdoor ambient temperature, and condenser 2 coil temperature, generates the target rotational speed of the outdoor fan 4. S305 includes:

[0085] S3051, Calculate the temperature of the coil in condenser 2. outdoor ambient temperature actual temperature difference .

[0086] S3052, Generate a target temperature difference based on the indoor and outdoor ambient temperatures. Specifically: when the indoor ambient temperature is less than or equal to a first indoor temperature threshold, a first target temperature difference function is used; when the indoor ambient temperature is greater than or equal to a second indoor temperature threshold, a second target temperature difference function is used; when the indoor ambient temperature is greater than the first indoor temperature threshold and less than the second indoor temperature threshold, the target temperature difference function used in the previous cycle of the grain cooling unit is executed; if the unit is powered on for the first time and the indoor ambient temperature falls directly into this range, the second target temperature difference function is executed by default.

[0087] In this embodiment, the first indoor temperature threshold is 16℃, and the second indoor temperature threshold is 18℃. The first target temperature difference function is as follows: when the outdoor ambient temperature is ≤21℃, the target temperature difference is constant at 9℃; when the outdoor ambient temperature is ≥32℃, the target temperature difference is constant at 5℃; and when 21℃ < outdoor ambient temperature <32℃, the target temperature difference is constant at 7℃. The second target temperature difference function is as follows: when the outdoor ambient temperature is ≤21℃, the target temperature difference is constant at 11℃; when the outdoor ambient temperature is ≥32℃, the target temperature difference is constant at 7℃; and when 21℃ < outdoor ambient temperature <32℃, the target temperature difference is constant at 9℃.

[0088] The principle behind setting the target temperature difference is as follows: When the indoor temperature is low (≤16℃), the evaporator 3 has a small heat load and is prone to freezing. In this case, a higher target temperature difference is needed (i.e., the condenser 2 coil temperature should be significantly higher than the outdoor temperature) to ensure sufficient condensing pressure, thereby increasing the evaporating temperature. When the indoor temperature is high (≥18℃), the evaporator 3 has a larger heat load, and the risk of freezing is relatively low. A lower target temperature difference can be used, allowing for a slight reduction in condensing pressure, thus reducing the energy consumption of the outdoor fan 4. The target temperature difference decreases as the outdoor ambient temperature increases because the condensing pressure is naturally higher at higher outdoor temperatures. Therefore, an excessively high target temperature difference is not necessary to ensure the evaporating temperature does not drop too low, thus reducing fan energy consumption while preventing freezing.

[0089] It can be seen that the target temperature difference is negatively correlated with the outdoor ambient temperature, that is, the higher the outdoor temperature, the lower the target temperature difference. On the other hand, the target temperature difference is positively correlated with the indoor ambient temperature, that is, under the same outdoor ambient temperature, the higher the indoor temperature, the higher the target temperature difference.

[0090] S3053, Calculate the difference between the actual temperature difference and the target temperature difference to generate a temperature difference deviation value A; .

[0091] S3054, retrieve the temperature difference deviation value generated in the previous cycle. Calculate the temperature difference deviation value A and the temperature difference deviation value of the previous cycle. The difference is used to generate the temperature difference deviation change B; The period is the fourth preset time.

[0092] S3055, based on the temperature difference deviation value A and the temperature difference deviation change B, generates the target rotational speed of the outdoor fan 4. S3055 includes:

[0093] Based on the temperature difference deviation value A and the temperature difference deviation change B, the speed change is generated in conjunction with the preset fuzzy control rule table. The fuzzy control rule table is shown in Table 1.

[0094] Table 1 Fuzzy Control Rules

[0095]

[0096] Get the rotational speed of outdoor fan 4 in the previous cycle. And based on the change in rotational speed The target speed for this cycle is the same as the speed of outdoor fan 4 in the previous cycle. ; If the calculated If the speed exceeds the allowable speed range [RPM2, RPM1] of outdoor fan 4, then limit it to the boundary value.

[0097] Therefore, the fan speed can be dynamically adjusted based on the temperature difference deviation and its changing trend: when the actual temperature difference is much lower than the target temperature difference, i.e., A is negative and has a large absolute value, the fan speed needs to be significantly increased to improve the condensing pressure; when the actual temperature difference is too high, i.e., A is positive and large, the fan speed can be appropriately reduced to save energy; the introduction of the temperature difference deviation change B makes the adjustment smoother and avoids drastic fluctuations in speed. Using this control method, the DC fan can continuously adjust its speed, ensuring that the evaporator 3 does not freeze, and maintaining the continuous operation of the compressor 1 as much as possible, avoiding forced shutdown of the compressor 1 due to the freezing of the evaporator 3, thus improving the reliability of the refrigeration system and the cooling effect of the grain silo.

[0098] S306, adjust the speed of the outdoor fan 4 to the target speed. After adjustment, wait for the next cycle, then return to S304 to continue the cycle.

[0099] In summary, this solution targets grain cooling units where the indoor fan 5 is single-speed and the compressor 1 is fixed-frequency. Depending on the motor type of the outdoor fan 4, a control strategy of gear switching or continuous speed regulation is adopted to effectively regulate the condensing pressure, thereby reducing the risk of evaporator 3 freezing in a timely manner and avoiding forced shutdown of compressor 1 due to evaporator 3 freezing, thus ensuring the cooling effect and system reliability.

[0100] The above are merely embodiments of the present invention. Commonly known structures and characteristics are not described in detail here. Those skilled in the art are aware of all common technical knowledge in the field prior to the application date or priority date, are aware of all existing technologies in that field, and have the ability to apply conventional experimental methods prior to that date. Those skilled in the art can, under the guidance of this application, improve and implement this solution in combination with their own capabilities. Some typical known structures or methods should not be obstacles for those skilled in the art to implement this application. It should be noted that those skilled in the art can make several modifications and improvements without departing from the structure of the present invention. These should also be considered within the scope of protection of the present invention, and will not affect the effectiveness of the implementation of the present invention or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A method for preventing freezing in a grain cooling unit, applied in the grain cooling unit, the grain cooling unit comprising a compressor, a condenser, an evaporator, an outdoor fan, and an indoor fan, characterized in that: The indoor fan is a single-speed fan, and the compressor is a fixed-frequency compressor; the method includes the following steps: S100: Obtain the motor type of the outdoor fan. The motor type includes AC motor and DC motor. If the motor type is AC motor, then execute S200. If the motor type is DC motor, then execute S300. S200: Obtain the outdoor ambient temperature and the condenser coil temperature, and switch the speed level of the outdoor fan according to the outdoor ambient temperature and the condenser coil temperature. S300: Obtain the indoor ambient temperature, outdoor ambient temperature, and condenser coil temperature, and generate the target speed of the outdoor fan based on the indoor ambient temperature, outdoor ambient temperature, and condenser coil temperature; adjust the speed of the outdoor fan to the target speed.

2. The anti-freezing control method for a grain cooling unit according to claim 1, characterized in that: The outdoor fan has speed settings including high speed, low speed, and stop; S200 includes: S201, Obtain the outdoor ambient temperature; S202, Based on the outdoor ambient temperature, generate the initial speed setting of the outdoor fan; S203, control the outdoor fan to run at the initial speed and obtain the first continuous running time of the outdoor fan at the initial speed; when the first continuous running time is greater than the first preset time, execute S204; S204, with a second preset time period, acquires the real-time outdoor ambient temperature and condenser coil temperature; S205, based on the real-time acquired outdoor ambient temperature and condenser coil temperature, switch the speed level of the outdoor fan.

3. The anti-freezing control method for a grain cooling unit according to claim 2, characterized in that: In S202: When the outdoor ambient temperature is greater than or equal to the first start-up temperature threshold, the initial gear is the high-speed gear; When the outdoor ambient temperature is less than or equal to the second start-up temperature threshold, the initial gear is the shutdown gear; When the outdoor ambient temperature is greater than the second start-up temperature threshold and less than the first start-up temperature threshold, the initial gear is the low speed gear. The first startup temperature threshold is greater than the second startup temperature threshold.

4. The anti-freezing control method for a grain cooling unit according to claim 2, characterized in that: In S205: When the outdoor ambient temperature is greater than or equal to the first outdoor temperature threshold, if the condenser coil temperature is greater than or equal to the first switching temperature threshold, the outdoor fan is controlled to operate at high speed; if the condenser coil temperature is less than or equal to the second switching temperature threshold, the outdoor fan is controlled to operate at low speed; the first switching temperature threshold is greater than the second switching temperature threshold. When the outdoor ambient temperature is less than or equal to the second outdoor temperature threshold, if the condenser coil temperature is greater than or equal to the third switching temperature threshold, the outdoor fan is controlled to operate at high speed; if the condenser coil temperature is less than or equal to the fourth switching temperature threshold, the outdoor fan is controlled to operate at low speed; the third switching temperature threshold is greater than the fourth switching temperature threshold. The third switching temperature threshold is greater than the first switching temperature threshold, and the fourth switching temperature threshold is greater than the second switching temperature threshold. When the outdoor ambient temperature is greater than the second outdoor temperature threshold and less than the first outdoor temperature threshold, the historical outdoor ambient temperature is obtained, and the speed of the outdoor fan is switched according to the historical outdoor ambient temperature and the condenser coil temperature.

5. The anti-freezing control method for a grain cooling unit according to claim 1, characterized in that: The S300 includes: S301, obtain the outdoor ambient temperature; S302, Based on the outdoor ambient temperature, generate the initial rotational speed of the outdoor fan; S303, control the outdoor fan to run at the initial speed, and obtain the second continuous running time of the outdoor fan at the initial speed; when the second continuous running time is greater than the third preset time, execute S304; S304, with the fourth preset time as the cycle, acquires the real-time indoor ambient temperature, outdoor ambient temperature and condenser coil temperature. S305, Based on the real-time acquired indoor ambient temperature, outdoor ambient temperature and condenser coil temperature, the target speed of the outdoor fan is generated; S306, Adjust the speed of the outdoor fan to the target speed.

6. The anti-freezing control method for a grain cooling unit according to claim 5, characterized in that: In S302: When the outdoor ambient temperature is greater than or equal to the first start-up temperature threshold, the initial rotation speed is the preset maximum rotation speed; When the outdoor ambient temperature is less than or equal to the second start-up temperature threshold, the initial speed is the preset minimum speed; When the outdoor ambient temperature is greater than the second start-up temperature threshold and less than the first start-up temperature threshold, the initial speed is a preset medium speed. The first startup temperature threshold is greater than the second startup temperature threshold.

7. The anti-freezing control method for a grain cooling unit according to claim 5, characterized in that: S305 includes: S3051, Calculate the actual temperature difference between the condenser coil temperature and the outdoor ambient temperature; S3052, generate a target temperature difference based on the indoor ambient temperature and the outdoor ambient temperature; S3053, Calculate the difference between the actual temperature difference and the target temperature difference to generate a temperature difference deviation value A; S3054, retrieve the temperature difference deviation value generated in the previous cycle. Calculate the temperature difference deviation value A and the temperature difference deviation value of the previous cycle. The difference is used to generate the temperature difference deviation change B; S3055, the target rotational speed of the outdoor fan is generated based on the temperature difference deviation value A and the temperature difference deviation change B.

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