Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25D—REFRIGERATORS; COLD ROOMS; ICE-BOXES; COOLING OR FREEZING APPARATUS NOT OTHERWISE PROVIDED FOR
  • F25D21/00—Defrosting; Preventing frosting; Removing condensed or defrost water
  • F25D21/002—Defroster control
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25D—REFRIGERATORS; COLD ROOMS; ICE-BOXES; COOLING OR FREEZING APPARATUS NOT OTHERWISE PROVIDED FOR
  • F25D21/00—Defrosting; Preventing frosting; Removing condensed or defrost water
  • F25D21/06—Removing frost
  • F25D21/08—Removing frost by electric heating

Definitions

• the present invention relates to a diagnostic method for checking a defrost operation in a refrigeration system.
• the defrost operation is monitored by a controller of the refrigeration system by means of a defrost probe designed to detect the temperature of the thermal exchange surface.
• the controller reactivates the evaporator, thus resuming the refrigeration action.
• the defrost operation must be performed in such a way as to limit the heat transferred to the evaporator as much as possible and must also have a duration which is as limited as possible in order to avoid an unacceptable increase in temperature (given that as mentioned, the refrigeration action is interrupted during the defrost operation).
• a so-called "pull-down” step is envisaged, i.e. a sudden lowering of the temperature, which involves the activation of the evaporator at maximum cooling capacity to bring it back as quickly as possible to optimal working conditions and to restore the temperature of the compartment to be refrigerated.
• a possible positioning error of the defrost probe can compromise the quality and effectiveness of the defrost operation. Too long or too short intervals between two successive defrost operations can compromise the efficiency of the refrigeration system. For example, the defrost operation can be incomplete or infrequent, and therefore compromise the heat exchange at the thermal exchange surface of the evaporator. Conversely, the defrost operation can be too long or too frequent, causing too high temperature peaks at the thermal exchange surface, and therefore requiring a considerable increase in the cooling action to compensate for the excessive heating, and consequently leading to an excessive consumption of power.
• the object of the present invention is to improve the defrost efficiency of a refrigeration system, while allowing the identification of any malfunctions or incorrect configurations of the machine which could compromise the efficiency of the defrost operation.
• this diagnostic method it is possible to identify, in a simple but at the same time reliable way, conditions of incorrect execution of the defrost operation, whether due to malfunctions of the defrost probe or of the electrical resistances, to an incorrect positioning of the defrost probe, or to an incorrect setting of the defrost parameters (such as the time interval between two consecutive defrost operations, the duration of the defrost operation, the defrost operation end temperature, etc.), and also to propose - depending on the cause that generated an abnormal operating condition - one or more possible corrective actions aimed at eliminating this cause.
• the diagnostic method of the present invention also allows achieving a reduction in energy consumption, both during the defrost operation and in normal operation, since it ensures that the evaporator is always efficient. Furthermore, a better operating quality of the refrigeration system is obtained, with the operating temperatures always being kept within the optimal ranges, and therefore a better quality of the food products is ensured in the event the refrigeration system is a deep freezer for the preservation of food products.
• the refrigeration system controller cyclically controls a defrost operation of the evaporator, which is performed by heating, for example by means of electrical resistances, the thermal exchange surface of the evaporator so as to completely melt the layer of ice formed on this surface.
• the defrost operation is monitored by the controller by means of a defrost probe which is mounted in the coldest part of the evaporator, in contact with the thermal exchange surface thereof.
• Figure 1 of the attached drawings shows the typical time trend of the temperature measured by the defrost probe during a defrost operation in the case of a defrost probe functioning correctly and correctly positioned.
• the expression “during the defrost operation” is to be understood as during the time interval in which heat is supplied to the thermal exchange surface of the evaporator, for example by the activation of electrical resistances.
• the temperature detected by the defrost probe initially increases (time interval between the instants indicated in the diagram with t 0 and t 1 ), and then remains substantially constant at a given value (indicated with T melt ) for a certain time interval (between the instants indicated in the diagram with t 1 and t 2 ), and then increases again until the end of the defrost operation (time interval between instants t 2 and t 3 ).
• the time trend of the temperature therefore shows an inflection point at the temperature T melt in the interval between the time instants t 1 and t 2 , during which the phase transition of the ice from the solid to the liquid phase takes place.
• This temperature (hereinafter referred to as the "reference temperature”) represents the temperature measured by the defrost probe when the ice on the thermal exchange surface begins to melt.
• the reference temperature T melt will not be equal to the melting temperature of the ice, i.e. 0° C.
• the detection of the inflection point in the time trend of the temperature measured by the defrost probe, and therefore the determination of the offset error of the probe can take place by constructing the normalized histogram of the temperature frequencies recorded by the probe at each defrost operation.
• the presence of an evident peak indicates the temperature value measured by the probe (in this example the temperature of -6.5° C) at which the ice melts.
• the construction of a second histogram is advantageously provided, the classes of which are offset by half of their amplitude. In this way it is possible to detect the melting temperature if it straddles two classes of the first histogram, and therefore if two close peaks, but of lower value, were present in this histogram.
• the offset error of the defrost probe is determined on a daily basis by examining all the defrost operations of the day in question and considering the average of the inflection point temperatures detected during these operations. For an inflection point to be considered valid, and therefore its temperature to be considered for the purpose of determining the offset error, the following two conditions must occur simultaneously:
• the last value detected in the defrost probe memory is searched. If this search is unsuccessful, a null offset error, and therefore a reference temperature value T melt equal to 0° C, is assumed.
• the diagnostic method can therefore include a step of verifying the correct configuration of the refrigeration system, which in the event of a positive result, consents to the possibility of verifying the correct execution of each individual defrost operation, while in the event of a negative result, provides a fault signal for requesting the intervention of an operator in order to restore the correct configuration of the refrigeration system.
• the aforementioned reference temperature T melt is used (which as said, represents the offset error of the defrost probe) and the temperatures of the refrigeration system are considered when it is operating, i.e. when there is a passage of coolant gas in the evaporator, and therefore a defrost operation is not in progress.
• this verifying step is carried out by taking into consideration the following temperatures in addition to the reference temperature T melt of the defrost probe:
• the constant values ⁇ 1 , ⁇ 2 , ⁇ 3 and ⁇ 4 can be fixed arbitrarily, either manually or by further automated analyses, to adapt the method to the particular refrigeration system to be controlled, even if it is preferable for them to be included in the range examples indicated above.
• S de is a score that assumes a real value between 0 and 1 and indicates how much the difference between the defrost temperature T def and the evaporation temperature T evp respects the expected conditions.
• the evaporation temperature T evp must be the lowest temperature inside the refrigeration system.
• S rd is a score that assumes a real value between 0 and 1 and indicates how much the difference between the operation temperature T reg of the refrigeration system and the defrost temperature T def respects the expected conditions.
• the defrost temperature T def must always be lower than the operation temperature T reg when the refrigeration system is in operation (i.e. far from the defrost operation steps).
• the lower of the two indices S de and S rd calculated on a daily basis is used as a compliance index I c of the refrigeration system.
• the value of the compliance index of the refrigeration system is higher than or equal to a threshold value C, then consent is given to the analysis of the individual defrost operations which took place on the same day for which the compliance of the system refrigerator was evaluated. If, on the other hand, the value of the compliance index of the refrigeration system is lower than the threshold value C, then the analysis of the individual defrost operations of that day is not performed.
• the sensitivity with which the refrigeration system is considered compliant for the analysis of the individual defrost operations depends on the threshold value C. It has been empirically found that a threshold value C comprised between 0.3 and 0.4 is optimal for correctly filtering refrigeration systems not compliant for analysis.
• This step of verifying the correct configuration of the refrigeration system is preferably carried out on a daily basis, i.e. considering all the samples acquired (for example with a frequency of one every minute) throughout the day. If the compliance index of the refrigeration system is lower than the threshold value C, for example due to malfunctioning or incorrect positioning of the defrost probe, the diagnosis process is interrupted and leads to the generation of a fault signal which informs the operator about the fault found.
• the diagnostic process therefore includes a verification step of each individual defrost operation in order to determine whether this operation has been performed correctly or not and, if not, to report the presence of a fault and preferably indicate one or more possible corrective actions to remedy this fault.
• This verification step is performed by checking the time trend of the temperature detected by the defrost probe during the defrost operation and verifying the respect of a series of conditions, as illustrated below.
• these performance indices must be higher than a given constant value, which means, with regards to the index S melt , that the ratio rt m-d must be higher than a given minimum threshold value, and with regards to the index S max , that the maximum temperature T max must be higher than a given minimum threshold but lower than a given maximum threshold value.
• the index S melt whose value varies between 0 and 1, indicates whether the time interval in which the ice melted during the defrost operation under analysis was long enough. This index will be maximum (equal to 1) in the case of ratio t melt /t def higher than the constant value ⁇ 2 .
• the index S max whose value varies between 0 and 1, will be maximum (equal to 1) when the maximum temperature T max during the defrost operation is comprised between ⁇ 2 and ⁇ 3 .
• the maximum temperature T max must exceed a given minimum value to ensure that all the ice inside the evaporator has melted, but at the same time is not to exceed a given maximum value to avoid unnecessary waste of energy as well as to avoid thermal shock to the food stored in the deep freezer in the event that the refrigeration system in question is a deep freezer.
• the defrost operation is considered correctly performed, and therefore no fault signal is generated, if the time trend of the defrost temperature T def during the defrost operation shows an inflection point at the reference temperature T melt and if both the following conditions are met: S melt > ⁇ 1 , and S max > ⁇ 2 , where ⁇ 1 and ⁇ 2 are positive constant values lower than 1.
• the ratio t melt /t def must be higher than a given minimum threshold value ⁇ min , which in the case of the S melt index calculated with the aforementioned "ramp" function, will be equal to ⁇ 1 + ⁇ 1 ⁇ ( ⁇ 2 - ⁇ 1 ), and on the other hand that the maximum temperature T max must be comprised between a minimum threshold value ⁇ min and a maximum threshold value ⁇ max , which in the case of the index S max calculated with the aforementioned "trapezoid” function, will be respectively equal to ⁇ 1 + ⁇ 2 ⁇ ( ⁇ 2 - ⁇ 1 ) and to ⁇ 4 - ⁇ 2 ⁇ ( ⁇ 4 - ⁇ 3 ).
• Figures 4 to 6 show respective examples of the time trend of the defrost temperature T def in the case of defrost operations performed incorrectly, for which the diagnostic method according to the invention therefore provides for the generation of a fault signal.
• the time trend of the defrost temperature T def shows an inflection point at the reference temperature T melt , but at least one of the performance indices S max and S melt is lower than the constant value ⁇ defined above.
• Figure 4 refers to a defrost operation in which S melt ⁇ ⁇ .
• This situation indicates a scarce presence of ice in the evaporator before the start of the defrost operation.
• there was an ice melting phase as shown by the fact that the defrost temperature trend T def shows an inflection point, but this phase was short-lived as the ice melted very quickly.
• the defrost operation was performed without any need for it, with consequent useless consumption of electricity.
• Reprogramming the time of the defrost operations is recommended as a corrective action in this case, with an increase in the time interval between two consecutive operations.
• Figure 5 shows an example of a defrost operation in which S max ⁇ ⁇ and T max ⁇ T melt + ⁇ 2 .
• This situation indicates the possibility that the ice inside the evaporator has not completely melted.
• the recommended corrective actions are checking the evaporator for any ice and if there is any, the forced execution of an additional defrost operation. Additionally or alternatively, increasing the duration t def of the defrost operation is recommended.
• Figure 6 shows an example of a defrost operation in which S max ⁇ ⁇ and T max ⁇ T melt + ⁇ 2 .
• This situation indicates that the ice inside the evaporator has completely melted, but that the maximum temperature has reached too high a value, for example due to an incorrect configuration of the defrost parameters (such as the duration of the defrost operation), thus leading to an unnecessary consumption of electricity.
• the recommended corrective actions are the reduction of the duration t def of the defrost operation and the setting of a lower temperature at the end of the defrost operation.
• Figures 7 to 9 show respective examples of the time trend of the defrost temperature T def in the case of defrost operations carried out incorrectly, for which the diagnostic method according to the invention therefore provides for the generation of a fault signal.
• the time trend of the defrost temperature T def does not show an inflection point at the reference temperature T melt in any of these examples, and therefore the performance index S melt is lower than the constant value ⁇ defined above.
• Figure 7 refers to a defrost operation in which T max ⁇ T melt + ⁇ 1 .
• T max ⁇ T melt + ⁇ 1 .
• the recommended corrective actions are the forced execution of an additional defrost operation, after checking the actual presence of residual ice inside the evaporator, and in addition or alternatively, increasing the duration t def of the defrost operation.
• Figure 8 relates to a defrost operation in which T max ⁇ T melt + ⁇ 1 .
• This situation indicates a possible absence of ice in the evaporator prior to the start of the defrost operation, but in any case the achievement of a defrost temperature high enough to guarantee the absence of residual ice in the evaporator at the end of the defrost operation.
• the recommended corrective action also in this case is reprogramming the time of the defrost operations with an increase in the time interval between two consecutive operations.
• Figure 9 shows an example of a defrost operation in which S max ⁇ ⁇ and T max > T melt + ⁇ 2 .
• This situation indicates a possible absence of ice in the evaporator prior to the start of the defrost operation, together with the achievement of a maximum temperature which is too high, and therefore an unnecessary consumption of electricity.
• the recommended corrective actions also in this case are the reduction of the duration t def of the defrost operation and the setting of a lower temperature at the end of the defrost operation.
• Figures 10 and 11 show (divided into two parts) the flow chart of an implementation example of the diagnostic method described above, in which all the steps described above are envisaged.
• step 2 the aforementioned step of verifying the correct configuration of the refrigeration system (indicated as "step 2" in the part of the flow chart shown in Figure 10 ) might not be carried out.
• the verification step (indicated as "step 3" in Figures 10 and 11 ) would be carried out at each defrost operation, aiming to identify the presence of an inflection point in the time trend of the defrost probe temperature, as well as to verify how the maximum value of the defrost temperature during the defrost operation relates in relation to the reference temperature T melt , in order to assess whether the defrost operation has been performed correctly or not and, in this second case, generate a fault signal and recommend one or more corrective actions according to the type of fault found.
• the step of verifying the correct configuration of the refrigeration system is advantageously carried out and meeting the aforementioned condition for the compliance index value of the refrigeration system not to be lower than the threshold value C constitutes a necessary precondition for the subsequent verification step of the correct execution of the defrost operation to be carried out.
• the verification step of the correct execution of the defrost operation is not carried out, rather a fault signal is generated which invites the operator to check the correct configuration of the refrigeration system, in particular the correct positioning of the defrost probe and/or its correct functioning.
• step 1 for calculating the offset error of the temperature probe, i.e. calculating the reference temperature T melt
• this value can also be optional.
• this calculation step is advantageously performed in such a way as to ensure the reliability of the aforementioned checking and verification steps, since these both use the reference temperature T melt and are therefore affected by a possible offset error of the defrost probe.
• the diagnostic method described above is advantageously performed by a special software installed in the controller of the refrigeration system or in a remote control system connected remotely with the refrigeration system and communicating with it through a communication network, in particular over the Internet.
• the method allows a way to simply and reliably identify conditions of the incorrect execution of the defrost operation, whether due to malfunctions of the defrost probe or of the electrical resistances, to an incorrect positioning of the defrosting probe or to an incorrect setting of the defrost parameters (such as the time interval between two consecutive defrost operations, the duration of the defrost operation, the temperature at the end of the defrost operation, etc.), while also proposing - depending on the cause that generated an abnormal operating condition - one or more possible corrective actions aimed at eliminating this cause.
• the method also makes it possible to achieve a reduction in energy consumption, both during the defrost operation and during normal operation, since it ensures that the evaporator is always efficient. Furthermore, a better operating quality of the refrigeration system is obtained, with the operating temperatures always being kept within the optimal ranges, and therefore a better quality of the food products is ensured in the event the refrigeration system is a deep freezer for the preservation of food products.

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• Engineering & Computer Science (AREA)
• Chemical & Material Sciences (AREA)
• Combustion & Propulsion (AREA)
• Physics & Mathematics (AREA)
• Mechanical Engineering (AREA)
• Thermal Sciences (AREA)
• General Engineering & Computer Science (AREA)
• Defrosting Systems (AREA)
• Devices That Are Associated With Refrigeration Equipment (AREA)

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• 2021
  • 2021-02-16 IT IT102021000003485A patent/IT202100003485A1/it unknown
• 2022
  • 2022-02-16 WO PCT/IB2022/051375 patent/WO2022175834A1/en not_active Ceased
  • 2022-02-16 ES ES22709393T patent/ES3060496T3/es active Active
  • 2022-02-16 EP EP22709393.7A patent/EP4295094B1/en active Active
  • 2022-02-16 PL PL22709393.7T patent/PL4295094T3/pl unknown
  • 2022-02-16 AU AU2022223750A patent/AU2022223750A1/en active Pending

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