A defrosting control method for refrigeration units with variable temperature difference and adaptive correction

Abstract

The present invention discloses a variable temperature difference adaptive correction defrost control method for a refrigeration unit, which measures and obtains evaporation temperature change information, analyzes and compares the evaporation temperature change information with the ideal evaporation temperature corresponding to the set storage temperature, judges the attenuation degree of the heat exchange capacity of the evaporator of the refrigeration unit, identifies the starting point of the defrost operation according to the attenuation degree, and automatically controls the defrost process; after each defrost, the defrost process is evaluated according to the defrost operation monitoring data, the control parameters are adaptively corrected, and the defrost process operation control is optimized, thereby effectively improving the energy efficiency of the refrigeration unit and the cold storage preservation quality, and improving the intelligent control level of the refrigeration unit.

Description

Technical Field

[0001] The present invention belongs to the field of refrigeration and cryogenic technology, and in particular relates to an intelligent defrosting control method for a low-temperature cold storage or a refrigeration unit for refrigeration and freezing. Background Art

[0002] The importance of cold chain logistics in modern society and people's lives has never been greater. The cold chain environment controlled by key equipment, refrigeration units, provides a low-temperature environment ideal for pre-cooling, freezing, refrigeration, storage, transportation, and distribution of agricultural and sideline products, preserving their quality and freshness while minimizing resource consumption. Furthermore, the storage and transportation of products such as biological vaccines require an even stricter cold chain environment to ensure their high quality.

[0003] Direct evaporative refrigeration units are widely used in small and medium-sized cold storages due to their smaller heat transfer losses. The cooling capacity generated by the refrigeration unit is transferred to the cooled space and the refrigerated objects through the evaporator. During the heat and mass exchange process, when the surface temperature of the evaporator is lower than the air dew point temperature, the water vapor in the air condenses on the surface of the evaporator. When the surface temperature of the evaporator is equal to or lower than 0℃, a frost layer is formed. As the refrigeration unit continues to operate at a low temperature, the frost layer continues to thicken. If defrosting is not performed in time, the air volume flowing through the evaporator will gradually decrease, the evaporation temperature and heat exchange rate will gradually decrease, the operating energy efficiency of the refrigeration unit will gradually decrease, the energy consumption will gradually increase, and it will easily cause the temperature in the cold storage to deviate excessively from the set value, affecting the quality of the stored food. If the defrosting control is improper, resulting in excessive or frequent defrosting, it will also lead to a significant increase in the energy consumption of the refrigeration unit and greater temperature fluctuations in the controlled space.

[0004] For direct evaporative refrigeration units used in cold storage, the frosting characteristics are mainly affected by the heat exchange surface temperature of the finned tube evaporator, the air humidity of the controlled space, and the air flow rate. They have dynamic changing characteristics and are difficult to express with precise numerical methods. Therefore, defrost control technology that can both reduce temperature fluctuations in the cold storage space and maximize energy saving has always been a difficult problem in the industry. At present, conventional refrigeration units generally adopt "timing" or "time + temperature" defrost control methods. Due to the time-varying nature of the objects to be preserved in the cold storage, the time-varying nature of the relative humidity of the cold storage space, and the variability of the frosting speed and frost layer density (high humidity, fast frosting humidity, low frost layer density; vice versa), it is easy to cause problems such as failure to defrost in time or excessive defrosting. How to accurately identify the start and stop points of the defrost operation has become the key to the research of defrost control technology. It is also one of the core technologies for improving the automatic control level of refrigeration units and the energy efficiency level of cold storage operations. Summary of the Invention

[0005] In order to avoid the deficiencies of the above-mentioned prior art, the present invention provides a variable temperature difference adaptive correction defrost control method for a refrigeration unit, which intelligently identifies the starting point and stopping point of the defrost operation, evaluates the defrost process based on the defrost operation monitoring data, adaptively corrects key control parameters, and realizes the optimization of the defrost operation process.

[0006] The present invention adopts the following technical solutions to solve the technical problems:

[0007] The characteristics of the variable temperature difference adaptive correction defrost control method of the refrigeration unit of the present invention are: measuring and obtaining the evaporation temperature change information of the refrigeration unit, analyzing and comparing the evaporation temperature change information with the ideal evaporation temperature corresponding to the set storage temperature, judging the attenuation degree of the heat exchange capacity of the evaporator of the refrigeration unit, identifying the starting point of the defrost operation according to the attenuation degree, and automatically controlling the defrost process; after each defrost is completed, the defrost process is evaluated according to the defrost operation monitoring data, the control parameters are adaptively corrected, and the defrost process operation control is optimized.

[0008] The characteristics of the variable temperature difference adaptive correction defrosting control method for a refrigeration unit of the present invention are also as follows:

[0009] The refrigeration unit starts cooling operation and periodically collects the evaporation temperature T of the refrigeration unit. ZFC ; Based on the evaporation temperature T of the refrigeration unit ZFC Make the following controls:

[0010] At the evaporation temperature T ZFC When the temperature is ≤0℃, the non-defrosting operation time t of the refrigeration unit is obtained by timing. Y , set the minimum running time of the refrigeration unit without triggering defrost to t min ; Establish condition 1 represented by formula (1):

[0011] t Y -t min ≥ 0 (1)

[0012] If condition 1 is met, the defrost operation starting point identification is performed as follows:

[0013] First defrost operation start conditions:

[0014] Set the maximum operating time of the refrigeration unit without triggering defrost to t max , establish the second condition represented by formula (2):

[0015] t Y -t max ≥ 0 (2)

[0016] If condition 2 is met, the refrigeration operation of the refrigeration unit is terminated and hot gas defrosting operation is started;

[0017] Second defrost operation start conditions:

[0018] The evaporation temperature of the refrigeration unit is obtained in real time by measuring T ZFC , the ideal evaporation temperature is obtained by calculation as T ZFL , define the evaporation temperature T of the refrigeration unit ZFC With the ideal evaporation temperature T ZFL The difference is △T ZFC , set the defrost start temperature difference to △T ZFS , establish the third condition represented by formula (3):

[0019] T ZFL -T ZFC =△T ZFC ≥△T ZFS (3)

[0020] If condition three is met, the judgment result M is recorded as "1", otherwise the judgment result M is recorded as "0";

[0021] If the judgment result M is "1" for three consecutive measurement cycles, the refrigeration operation of the refrigeration unit is terminated and the hot gas defrosting operation is started;

[0022] For the refrigeration unit that has been put into hot gas defrost operation, the defrost operation control is carried out as follows:

[0023] Obtain the defrost operation time t by timing CSC , the evaporator outlet temperature is obtained in real time by measuring T IOC , set the evaporator outlet temperature to end the defrosting operation as T IOS , establish the fourth condition represented by formula (4):

[0024] T IOC -T IOS ≥0 (4)

[0025] If condition 4 is met, the judgment result N is recorded as "1", otherwise the judgment result N is recorded as "0";

[0026] If the judgment result N is "1" for three consecutive measurement cycles, the hot gas defrosting operation is terminated and the refrigeration unit returns to the cooling operation.

[0027] The characteristics of the variable temperature difference adaptive correction defrosting control method for a refrigeration unit of the present invention are also as follows:

[0028] The defrost start temperature difference given value △T ZFS Set the correction coefficient D, and D=(t CSL / t CSC ) A , where t CSL is the set ideal defrost time, A is the set parameter;

[0029] The corrected starting temperature difference △T is calculated by formula (5): ZFS’ ;

[0030] △T ZFS’ = D × △T ZFS (5)

[0031] During the cold storage operation control process, the corrected starting temperature difference △T is calculated using the operating parameters of the previous defrost cycle. ZFS’ , the corrected starting temperature difference △T ZFS’ Applied to the next defrost operation cycle to replace the defrost start temperature difference set value △T ZFS , to achieve adaptive correction; the defrost cycle refers to the complete process from the start of refrigeration of the refrigeration unit to the end of this defrost.

[0032] Compared with the existing technology, the beneficial effects of the present invention are embodied in:

[0033] 1. The present invention is based on the positive correlation between the thickness of frost on the evaporator surface and the decrease in evaporation temperature during the operation of the refrigeration unit, and the ideal evaporation temperature T ZFL and real-time evaporation temperature T ZFC The difference △T ZFC , identify the attenuation degree of the evaporator's heat exchange capacity, and then determine the starting point of the defrost operation, scientifically solving the technical problem of identifying the starting point of the defrost operation.

[0034] 2. Based on the principle of positive correlation between the operating efficiency of compression refrigeration equipment and evaporation temperature, the present invention controls and reduces the operation of the refrigeration unit when the evaporation temperature is too low and deviates from the set storage temperature, thereby improving the energy efficiency of the cold storage operation and reducing operating costs.

[0035] 3. The present invention is based on the need to preserve the quality of biological vaccine products and the quality and freshness of frozen and refrigerated foods. By controlling the fluctuation range of evaporation temperature operation and rationally designing and controlling the defrosting operation time, the purpose of reducing the fluctuation range of storage temperature and improving the quality preservation and freshness preservation functions of cold storage is achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 is a flow chart of the control method of the present invention; DETAILED DESCRIPTION

[0037] The variable temperature difference adaptive correction defrost control method of the refrigeration unit in this embodiment is as follows: measuring and obtaining the evaporation temperature change information of the refrigeration unit, analyzing and comparing the evaporation temperature change information with the ideal evaporation temperature corresponding to the set storage temperature, judging the attenuation degree of the heat exchange capacity of the evaporator of the refrigeration unit, identifying the starting point of the defrost operation according to the attenuation degree, and automatically controlling the defrost process; after each defrost is completed, evaluating the defrost process according to the defrost operation monitoring data, adaptively correcting the control parameters, and optimizing the operation control of the defrost process.

[0038] See also Figure 1 In this embodiment, the variable temperature difference adaptive correction defrosting control method for the refrigeration unit is performed as follows:

[0039] If the refrigeration unit does not start cooling, the defrost start point identification will not be performed.

[0040] When the refrigeration unit starts cooling operation, the evaporation temperature T of the refrigeration unit is collected periodically. ZFC ; Based on the evaporation temperature T of the refrigeration unit ZFC Make the following controls:

[0041] At the evaporation temperature T ZFC When the temperature is ≤0℃, the non-defrosting operation time t of the refrigeration unit is obtained by timing. Y , set the minimum running time of the refrigeration unit without triggering defrost to t min ; Establish condition 1 represented by formula (1):

[0042] t Y -t min ≥0 (1)

[0043] If condition 1 is met, the defrost operation starting point identification is performed as follows:

[0044] First defrost operation start conditions:

[0045] Set the maximum operating time of the refrigeration unit without triggering defrost to t max , establish the second condition represented by formula (2):

[0046] t Y -t max ≥0 (2)

[0047] If condition 2 is met, the refrigeration operation of the refrigeration unit is terminated and hot gas defrosting operation is started;

[0048] Second defrost operation start conditions:

[0049] The evaporation temperature of the refrigeration unit is obtained in real time by measuring T ZFC , the ideal evaporation temperature is obtained by calculation as T ZFL , define the evaporation temperature T of the refrigeration unitZFC With the ideal evaporation temperature T ZFL The difference is △T ZFC , set the defrost start temperature difference to △T ZFS , establish the third condition represented by formula (3):

[0050] T ZFL -T ZFC =△T ZFC ≥△T ZFS (3)

[0051] If condition three is met, the judgment result M is recorded as "1", otherwise the judgment result M is recorded as "0";

[0052] If the judgment result M is "1" for three consecutive measurement cycles, the refrigeration operation of the refrigeration unit is terminated and the hot gas defrosting operation is started;

[0053] For the refrigeration unit that has been put into hot gas defrost operation, the defrost operation control is carried out as follows:

[0054] Obtain the defrost operation time t by timing CSC , the evaporator outlet temperature is obtained in real time by measuring T IOC , set the evaporator outlet set temperature to end the defrost operation as T IOS , establish the fourth condition represented by formula (4):

[0055] T IOC -T IOS ≥0 (4)

[0056] If condition 4 is met, the judgment result N is recorded as "1", otherwise the judgment result N is recorded as "0";

[0057] If the judgment result N is "1" for three consecutive measurement cycles, the hot gas defrosting operation is terminated and the refrigeration unit returns to the cooling operation.

[0058] In specific implementation, the corresponding technical measures also include:

[0059] The defrost start temperature difference set value △T ZFS Set the correction coefficient D, and D=(t CSL / t CSC ) A , where t CSL is the set ideal defrost time, A is the set parameter;

[0060] The corrected starting temperature difference △T is calculated by formula (5): ZFS’ ;

[0061] △T ZFS’ = D × △T ZFS (5)

[0062] During the cold storage operation control process, the corrected starting temperature difference △T is calculated using the operating parameters of the previous defrost cycle. ZFS’ , the corrected starting temperature difference △T ZFS’ Applied to the next defrost cycle to replace the defrost start temperature difference set value △T ZFS , to achieve adaptive correction; the defrost cycle refers to the complete process from the start of refrigeration of the refrigeration unit to the end of this defrost.

[0063] In this embodiment, the corresponding parameter values ​​are based on:

[0064] t min is a preset value, which means that at t min During the time when the refrigeration unit is running in the refrigeration condition, the thickness of the frost on the evaporator at the beginning does not reach the level that affects the operating efficiency of the refrigeration unit, and the defrost start point identification is not performed; usually t min The value can be set to 30-240 minutes, the relative humidity in the cold storage Φ KU The larger the value of t min The smaller the value.

[0065] t max It is a preset value, which refers to the evaporator temperature T ZFC Below or equal to 0℃, the refrigeration unit has no defrosting operation time reaching t max The refrigeration unit must perform a defrost operation to prevent the occurrence of unknown faults in the relevant system. Usually t max The value can be set to 720-2880 minutes, the relative humidity of the cold storage Φ KU The smaller the value of t max For defrosting that meets the first defrosting operation start condition, the cold storage operation manager should conduct relevant routine inspections, such as whether the temperature sensor is installed in the correct position or the temperature sensor is damaged, whether the temperature in the cold storage is abnormal, and other equipment failures; the defrosting start temperature difference set value △T ZFS This situation may also occur if the setting is too large, and it will be corrected and optimized after several defrost cycles.

[0066] Ideal evaporation temperature T ZFL The physical meaning is to maintain the cold storage set temperature T LKS , and maintain the evaporation temperature when the refrigeration unit is operating at a high efficiency; except for the initial frosting period, as the frost layer on the evaporator fin tubes continues to thicken, the evaporator's wind resistance increases, the air volume decreases, and the heat exchange capacity decays, the evaporation temperature of the refrigeration unit shows a downward trend. Ideal evaporation temperature T ZFL The value of is: T ZFL =T LKS-(3-8℃), which is related to the system matching characteristics of the refrigeration unit. For example, the larger the heat exchange area of ​​the evaporator, the larger the heat exchange coefficient or the larger the air flow, the higher the ideal evaporation temperature T ZFL The higher the value is; for the evaporator of the finalized refrigeration unit, its heat transfer area and heat transfer coefficient have been determined. When the overflow air volume is stable, the ideal evaporation temperature T ZFL Relatively certain. Maintain the cold storage set temperature T LKS The higher the average evaporation temperature of the refrigeration unit, the higher the operating efficiency of the refrigeration unit, and vice versa; the average evaporation temperature of the refrigeration unit refers to the statistical average of the evaporation temperature during the operation of the cold storage. For low-temperature cold storage at -40℃ or -60℃, in order to pursue higher cold storage energy efficiency, it is advisable to design a higher ideal evaporation temperature T ZFL In actual operation, the ideal evaporation temperature T ZFL The evaporation temperature can be taken when the cold storage runs stably at the set storage temperature for 15-30 minutes.

[0067] Defrost start temperature difference set value △T ZFS It is an important defrost control parameter, △T ZFS The larger the value is, the lower the evaporation temperature of the refrigeration unit is allowed to be, the greater the thickness of the frost is allowed to be, and the actual evaporation temperature of the refrigeration unit is different from the set temperature T of the cold storage. LKS The larger the allowable deviation value is, the lower the average operating efficiency of the refrigeration unit is, and the cold storage temperature T KU The larger the fluctuation range, the lower the frequency of defrost operation. ZFS The smaller the value, the smaller the allowed frost thickness and the higher the frequency of defrosting operation. Although the average operating efficiency of the refrigeration unit during refrigeration is high, excessively frequent defrosting will increase the extra defrosting energy consumption. Therefore, in this embodiment, the defrost start temperature difference △T is set to ZFS To intelligently correct parameters and achieve the purpose of optimizing defrost process control through intelligent correction.

[0068] The frosting characteristics are affected by the evaporator heat exchange surface temperature, the controlled space air humidity and the air flow rate, and have dynamic changing characteristics. In this embodiment, according to the positive correlation between the thickness of the frost on the evaporator heat exchange surface and the decrease in evaporation temperature during the operation of the refrigeration unit, the ideal evaporation temperature T is adopted. ZFL and real-time evaporation temperature T ZFC The difference △T ZFC This method can be used to identify the degree of attenuation of the evaporator's heat exchange capacity and, in turn, determine the defrost start point, scientifically resolving the technical challenge of identifying the defrost start point. Furthermore, based on the principle of a positive correlation between the operating efficiency and evaporation temperature of compression refrigeration equipment, this embodiment controls and reduces the operating conditions of the refrigeration unit when the evaporation temperature is too low and deviates from the set storage temperature, thereby improving the energy efficiency of the cold storage and reducing operating costs.

[0069] The key performance parameters of compression refrigeration units are cooling capacity and energy efficiency ratio. All thermodynamic systems possess self-balancing energy. Their commonality is that, under certain condensing temperatures, the higher the evaporation temperature, the greater the cooling capacity and energy efficiency; and vice versa. The purpose of this invention is to achieve a higher average evaporation temperature for the refrigeration unit through proper defrosting and minimize temperature fluctuations within the cold storage, ultimately achieving both high efficiency and maintaining quality and freshness.

[0070] End of defrosting operation evaporator outlet set temperature T IOS It is a preset value with a range of 12-25°C. During operation, the evaporator outlet temperature can be taken as the value when all the water on the evaporator surface is evaporated.

[0071] For vaccine cold storage, the ideal defrost time t CSL The value is 6-9 minutes, t CSL The larger the value, the greater the temperature fluctuation in the cold storage, affecting the quality of the frozen and refrigerated objects; CSL A smaller value will cause frequent defrosting, which is not advisable. For ordinary medium and low temperature food cold storage, the ideal defrosting time t CSL The value range is 7-12 minutes.

[0072] The value of parameter A is set based on the ratio (t CSL / t CSC )’s actual meaning, for example: (t CSL / t CSC ) is too small, indicating that the actual defrost time t CSC Much longer than the ideal defrost time t CSL , that is, the thickness of frost on the evaporator is too large, which can be further understood as a large attenuation of the evaporation temperature or a low average efficiency of the refrigeration unit. This is due to the defrost start temperature difference △T ZFS The optimization direction is to reduce the defrost start temperature difference △T ZFS On the contrary, if (t CSL / t CSC ) is too large, that is, the frost thickness of the evaporator is too small, and defrosting is performed when it is not necessary. This situation is likely to cause frequent defrosting, so the optimization direction is to increase the defrost start temperature difference △T ZFS In a specific implementation, the value of parameter A is set to 0.05-0.2.

[0073] The present invention's variable temperature differential adaptive defrost control method for refrigeration units is primarily applicable to direct evaporative refrigeration units in medium and small cold storage facilities. This technology introduces high-temperature compressed vapor from the compressor directly into the evaporator for defrosting, a process known as hot gas defrosting. Hot gas defrosting offers advantages such as uniform heating of the evaporator's heat exchange fins, minimal thermal interference with the air inside the cold storage, rapid defrosting, convenient operation, full automation, and energy conservation, making it a promising method for widespread application.

Claims

1. A variable temperature difference adaptive correction defrost control method for a refrigeration unit, characterized by: The evaporation temperature change information of the refrigeration unit is measured and obtained, and the evaporation temperature change information is analyzed and compared with the ideal evaporation temperature corresponding to the set storage temperature to determine the degree of attenuation of the heat exchange capacity of the evaporator of the refrigeration unit. The starting point of the defrost operation is identified according to the attenuation degree, and the defrost process is automatically controlled. After each defrost, the defrost process is evaluated based on the defrost operation monitoring data, and the control parameters are adaptively corrected to optimize the defrost process operation control. The variable temperature difference adaptive correction defrost control method of the refrigeration unit is as follows: The refrigeration unit starts cooling operation and periodically collects the evaporation temperature T of the refrigeration unit. ZFC ; Based on the evaporation temperature T of the refrigeration unit ZFC Make the following controls: At the evaporation temperature T ZFC When the temperature is ≤0℃, the non-defrosting operation time t of the refrigeration unit is obtained by timing. Y , set the minimum running time of the refrigeration unit without triggering defrost to t min ; Establish condition 1 represented by formula (1): t Y -t min ≥ 0 (1) If condition 1 is met, the defrost operation starting point identification is performed as follows: First defrost operation start conditions: Set the maximum operating time of the refrigeration unit without triggering defrost to t max , establish the second condition represented by formula (2): t Y -t max ≥ 0 (2) If condition 2 is met, the refrigeration operation of the refrigeration unit is terminated and hot gas defrosting operation is started; Second defrost operation start conditions: The evaporation temperature of the refrigeration unit is obtained in real time by measuring T ZFC , the ideal evaporation temperature is obtained by calculation as T ZFL , define the evaporation temperature T of the refrigeration unit ZFC With the ideal evaporation temperature T ZFL The difference is △T ZFC , set the defrost start temperature difference to △T ZFS , establish the third condition represented by formula (3): T ZFL -T ZFC =△T ZFC ≥△T ZFS (3) If condition three is met, the judgment result M is recorded as "1", otherwise the judgment result M is recorded as "0"; If the judgment result M is "1" for three consecutive measurement cycles, the refrigeration operation of the refrigeration unit is terminated and the hot gas defrost operation is started; For the refrigeration unit that has been put into hot gas defrost operation, the defrost operation control is carried out as follows: Obtain the defrost operation time t by timing CSC , the evaporator outlet temperature is obtained in real time by measuring T IOC , set the evaporator outlet temperature to end the defrosting operation as T IOS , establish the fourth condition represented by formula (4): T IOC -T IOS ≥0 (4) If condition 4 is met, the judgment result N is recorded as "1", otherwise the judgment result N is recorded as "0"; If the judgment result N is "1" for three consecutive measurement cycles, the hot gas defrost operation is terminated and the refrigeration unit returns to cooling operation; The defrost start temperature difference given value △T ZFS Set the correction coefficient D, and D=(t CSL / t CSC ) A , where t CSL is the set ideal defrost time, A is the set parameter; The corrected starting temperature difference △T is calculated by formula (5): ZFS’ ; △T ZFS’ = D×△T ZFS (5) During the cold storage operation control process, the corrected starting temperature difference △T is calculated using the operating parameters of the previous defrost cycle. ZFS’ , the corrected starting temperature difference △T ZFS’ Applied to the next defrost operation cycle to replace the defrost start temperature difference set value △T ZFS , to achieve adaptive correction; the defrost cycle refers to the complete process from the start of refrigeration of the refrigeration unit to the end of this defrost.

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