EP4400787A1 - Determining a defrosting time of an evaporator of a domestic refrigeration appliance - Google Patents

Abstract

The invention relates to a method (S1 - S6) for determining a defrosting time of an evaporator (5) of a household refrigeration appliance (1), in which a first evaporator temperature (Tv_calc) is calculated (S1) using a physical model that has been set up without taking into account a layer of frost on the evaporator (5), a second evaporator temperature (Tv_mess) is measured at the same time (S2), a deviation measure (Δ) between the first evaporator temperature (Tv_calc) and the second evaporator temperature (Tv_mess) is calculated (S3) and when the deviation measure (Δ) reaches or exceeds a predetermined limit value (S4), at least one defrosting action is triggered by the household refrigeration appliance (1) (S5). The invention also relates to a household refrigeration appliance (1) that is set up to carry out the method (S1 - S6). The invention is particularly advantageously applicable to refrigerators and freezers with finned evaporators.

Description

The invention relates to a method for determining a defrosting time of an evaporator of a household refrigeration appliance. The invention also relates to a household refrigeration appliance that is designed to carry out the method. The invention is particularly advantageously applicable to refrigerators and freezers with finned evaporators
DD 218 438 A1 discloses a device for controlling the defrosting process on air coolers, in particular on refrigerant evaporators. The field of application extends to the field of refrigeration and air conditioning technology. The aim is to precisely determine the time of the defrosting process on refrigerant evaporators. The proportional temperature conditions required to determine the defrosting time are recorded directly on the refrigerant evaporator and the defrosting time is selected based on the actual degree of frosting on the refrigerant evaporator using the determined temperature difference.

EN 30 01 019 A1 discloses a defrosting device for the evaporator of a refrigeration system, with a control device which triggers the defrosting process and which has a frost sensor which responds to the presence of a layer of frost, wherein the frost sensor is a temperature sensor which is arranged at a distance from a surface of the evaporator which corresponds to the permissible thickness of a layer of frost, and wherein the control device has a comparison circuit which triggers the defrosting process when the frost sensor temperature falls below a comparison temperature.

DE 10315 524 A1 discloses that in a refrigeration device with a heat-insulating housing enclosing an interior space and an evaporator arranged in the housing, on the surface of which a layer of ice forms during operation, two temperature sensors are placed in the vicinity of the evaporator in such a way that, for a given thickness of the ice layer, only one of the temperature sensors is embedded in the ice layer. A monitoring circuit connected to the two temperature sensors is set up to determine, based on a difference between the temperatures detected by the temperature sensors, temperature values to decide whether defrosting of the evaporator is necessary or not and to provide an output signal indicating the result of the decision. Based on this output signal, a defrosting process of the evaporator can be initiated automatically.

EN 10 2005 054 104 A1 discloses a method and a device for controlling a defrosting process of an evaporator of a refrigeration machine in order to ensure the optimal operation of a refrigeration machine even at low temperatures reliably and with inexpensive means. This is achieved by the following method steps: measuring the evaporator outlet pressure, determining a first dew temperature based on the evaporator outlet pressure, determining a first difference between the first dew temperature and a dew temperature reference value, initiating a defrosting process if the first difference exceeds a temperature limit value, wherein the defrosting process comprises the following steps: determining a second difference between the evaporator outlet pressure and a switch-off pressure, ending the defrosting process if the second difference falls below a pressure limit value.

EP 2 719 978 A1 discloses a method for controlling a domestic refrigeration appliance comprising an evaporator, a first temperature sensor arranged in the cooling chamber of the refrigeration appliance and a second temperature sensor arranged on the evaporator, comprising estimating the amount of frost on the evaporator based on an integral over time of the difference between the temperature of the cooling chamber and the temperature of the evaporator and performing a defrost cycle if the above integral is above a predetermined threshold.

EP 3 587 963 A1 discloses a method for detecting ice accumulation on an evaporator of a vapor compression system. The evaporator is part of a vapor compression system. The vapor compression system further comprises a compressor unit, a heat-emitting heat exchanger and an expansion device. The compressor unit, the heat-emitting heat exchanger, the expansion device and the evaporator are arranged in a refrigerant circuit and an air flow flows over the evaporator. At least one temperature of the air leaving the evaporator is measured and a control value based on the measured temperature is derived. It is determined whether ice has accumulated on the evaporator by comparing the derived control value and a setpoint.

US 2020/0049393 A1 discloses an adaptive control method for refrigeration systems, comprising the detection of the frost level in the evaporator through a calculation method of the NTU ("Number of Transfer Units") rate, which makes it possible to define: the most suitable defrosting time, the activation of the dewatering resistors and the adaptive management of the evaporator fan, which combines different operating modes, namely an ice-free mode that uses only the cooling power of the refrigerant and different modes with ice that use the latent heat stored in the ice to obtain energy savings depending on the degree of frost in the evaporator. For the calculation of the NTU rate, it takes the initially dry evaporator as a reference and, with the refrigeration system running, calculates the NTU rate with a frequency-variable operating mode depending on the evaporator power or the ice level and its comparison with the reference.

It is the object of the present invention to at least partially overcome the disadvantages of the prior art and in particular to provide an improved possibility for determining a suitable defrosting time for defrosting a layer of ice on an evaporator of a household refrigeration appliance.

This object is achieved according to the features of the independent claims. Preferred embodiments can be found in particular in the dependent claims.

• eine erste Verdampfertemperatur mittels eines physikalischen Modells, das ohne Berücksichtigung einer Frostschicht auf dem Verdampfer aufgestellt worden ist, berechnet wird,
• insbesondere zeitgleich eine zweite Verdampfertemperatur gemessen wird,
• ein Abweichungsmaß zwischen der ersten Verdampfertemperatur und der zweiten Verdampfertemperatur berechnet wird und
• dann, wenn das Abweichungsmaß einen vorgegebenen Grenzwert erreicht oder überschreitet, durch das Haushalts-Kältegerät mindestens eine Abtauaktion ausgelöst wird.

The object is achieved by a method for determining a defrosting time of an evaporator of a household refrigeration appliance, in which

• a first evaporator temperature is calculated using a physical model which has been set up without taking into account a layer of frost on the evaporator,
• in particular, a second evaporator temperature is measured at the same time,
• a deviation measure between the first evaporator temperature and the second evaporator temperature is calculated and
• If the deviation reaches or exceeds a specified limit, the household refrigeration appliance triggers at least one defrosting action.

The advantage of the solution using a physical model is that the evaporator is defrosted particularly reliably and precisely only when it is actually necessary. This saves electrical energy and helps to ensure that unforeseen customer behavior does not lead to a temporary device failure. The latter is particularly advantageous compared to existing solutions in which the defrosting time is determined based on only indirectly measurable actions such as door openings, as these solutions cannot determine how much moisture is actually introduced into the refrigeration device from the outside or through water released by refrigerated goods. In this process, the model is continuously calculated and compared with measured values at the right time.

The household refrigeration appliance can be a cooling appliance, a freezer or a combination thereof, e.g. a refrigerator, a freezer or a fridge/freezer combination.

It is a further development that the household refrigeration appliance has a compression refrigeration machine or a compression refrigeration circuit that includes the evaporator, a condenser, a compressor and an expansion valve. Compression refrigeration machines for household refrigeration appliances are generally known and are therefore not described further.

The defrosting time of the evaporator corresponds in particular to the time at which defrosting of a layer of frost on the evaporator should be carried out or triggered. To defrost the evaporator, for example, a heater can be assigned to it, which, when activated, melts the layer of frost.

The first evaporator temperature can also be viewed or referred to as the calculated or model-based evaporator temperature.

The physical model corresponds in particular to a physical model, especially a temperature model, of the evaporator. It describes, for example, the operation of the evaporator using differential and algebraic equations, which are used to calculate heat transport and heat storage. In particular, the model can be calculated in such a way that, based on one or more measured and/or derived input variables such as a cooling room temperature, a speed of the Compressor, fan speeds, air flap positions, valve positions, etc. the first evaporator temperature is calculated as an output variable. The model does not take into account the possible presence of a layer of frost on the evaporator because the model was calibrated using a frost-free evaporator. In other words, the model assumes that the evaporator is frost-free regardless of the actual conditions. In reality, however, frost accumulation on the evaporator changes the heat transfer capacity of the evaporator because the frost layer has a thermally insulating effect. If the evaporator is covered by a noticeably thick layer of frost, the physical evaporator temperature model deviates noticeably from the actually measured evaporator temperature. This deviation is therefore a measure of the thickness of the frost layer and is used here to determine the defrosting time.

The second evaporator temperature is measured, e.g. using a corresponding temperature sensor. The second evaporator temperature can also be referred to as the measured evaporator temperature or sensor (evaporator) temperature. A measurement interval can be in the range of one minute, for example, but is not limited to this.

The fact that the second evaporator temperature is measured at the same time means in particular that the point in time at which the first and second evaporator temperatures are determined are the same or practically the same, i.e. - possibly with the exception of practically insignificant differences - they relate to the same point in time and thus to the same state of the evaporator.

The deviation measure is in particular a value that quantitatively records the difference between the first evaporator temperature and the second evaporator temperature or a value derived therefrom. In the following, without loss of generality, it is assumed that the deviation measure is zero when the first and second evaporator temperatures are the same and becomes larger the larger the deviation becomes.

The time at which the deviation reaches or exceeds the limit value corresponds to the defrosting time.

A defrosting action is understood to mean, in particular, an action which specifically concerns defrosting and/or the triggering of defrosting.

One embodiment is that, in order to calculate the deviation, a difference between the first evaporator temperature and the simultaneous second evaporator temperature is calculated and then, when this difference reaches or exceeds a predetermined limit value, at least one defrosting action is triggered by the household refrigeration appliance. This is advantageously particularly easy to implement. In other words, at least one defrosting action is triggered when the difference between the simultaneous first and second evaporator temperatures reaches or exceeds the limit value.

It is a further development that at least one defrosting action is only triggered if the differences between several pairs determined at the same time reach or exceed the limit value, e.g. the three or ten pairs determined last all reach or exceed the limit value. This has the advantage that individual outliers of the deviation measure are only weakly taken into account.

One embodiment is that, in order to calculate the deviation measure, differences between temporally successive pairs of the first evaporator temperature and the second evaporator temperature, which is the same at the same time, are summed up window by window and then, when this sum reaches or exceeds a predetermined limit, at least one defrosting action is triggered by the household refrigeration appliance. This has the advantage that individual outliers in the deviation measure are only weakly taken into account. This embodiment can also be referred to as "summation" or "integration". The fact that the pairs are summed up window by window means that only a predetermined number of the most recently determined pairs are taken into account, which, particularly with constant measurement intervals, corresponds to taking into account a concurrent time window of a fixed window width. When a new pair is included in the sum, the oldest pair is dropped from the sum.

It is a further development that the duration of the running time window is longer than the duration of a compressor or compressor run, in particular is longer than the duration a compressor or condenser run plus at least one subsequent rest phase until the next compressor run. This has the advantage that the summation is practically independent of the timing of the compressor run. The duration of the concurrent time window can in particular include at least two compressor runs. For example, the measurement and calculation intervals of the evaporator temperature can be approximately one minute, a compressor run can last between 10 and 30 minutes and an interval between two compressor runs can last approximately one hour. The width of the concurrent window can then be approximately two to three hours, for example.

• Ausgeben einer Nachricht an einen Nutzer, einen Abtauprozess zum Abtauen des Verdampfers auszulösen;
• Auslösen eines Abtauprozesses zum Abtauen des Verdampfers

umfasst. Das Auslösen des Abtauprozesses kann also nutzerseitig und/oder automatisch erfolgen. Das Auslösen des Abtauprozesses kann beispielsweise ein Aktivieren bzw. Anschalten einer dem Verdampfer zugeordneten Heizung umfassen. Das Deaktivieren bzw. Ausschalten der Heizung kann beispielsweise zeitgesteuert und/oder sensorgesteuert erfolgen. Die Nachricht kann beispielsweise eine Aufforderung umfassen, einen Abtauprozess zu starten.It is an embodiment that the at least one defrosting action includes at least one action from the group

• Sending a message to a user to initiate a defrost process to defrost the evaporator;
• Initiating a defrost process to defrost the evaporator

The defrosting process can therefore be triggered by the user and/or automatically. The defrosting process can, for example, involve activating or switching on a heater assigned to the evaporator. The deactivation or switching off of the heater can, for example, be time-controlled and/or sensor-controlled. The message can, for example, include a request to start a defrosting process.

One embodiment is that a minimum time period is set between two defrosting processes, i.e. a time period that must be reached at a minimum before a defrosting process can be carried out. This is advantageously particularly energy-saving, as it prevents defrosting from occurring too frequently. In addition, the deviation measure does not need to be calculated until the minimum time period is reached. Alternatively, the deviation measure can be calculated, but without a defrosting action being triggered.

One embodiment is that a maximum time period is set between two defrosting processes, i.e. a time period which, when reached or exceeded, triggers at least one defrosting action (e.g. notification and/or automatic triggering of the defrosting process). This is advantageous so that possible mismatches of the model (for example, if fluctuations in component quality occur during production, due to which the calibrated model is no longer precisely adapted to the evaporator) are not lead to a defect, e.g. icing of the evaporator, an air flap or the fan. This design can be implemented in such a way that at least one defrosting action is carried out even if the deviation has not yet reached or exceeded its limit.

One embodiment is that the evaporator is a finned evaporator. The method can be used particularly advantageously for this, since a thick layer of frost can have a particularly severe impact on the effectiveness of a finned evaporator, especially if the refrigeration device is a no-frost device. However, the method can also be used for other types of evaporators.

One embodiment is that the physical model is calculated on or by the household refrigeration appliance. This has the advantage that no data connection to an external computer instance such as an internet server or a cloud computer is required, although this is also possible in principle. The household refrigeration appliance can in particular have a correspondingly configured, e.g. programmed, data processing device for this purpose.

The object is also achieved by a household refrigeration appliance which is designed to carry out the method as described above. The household refrigeration appliance can be designed analogously to the method, and vice versa, and has the same advantages.

• einen Kühlraum zum Lagern von Kühlgut,
• eine Kompressionskältemaschine mit einem Verdampfer zum Kühlen des Kühlraums,
• einen Temperatursensor zum Messen einer Verdampfertemperatur und
• eine Datenverarbeitungseinrichtung zum Berechnen einer zeitgleichen Verdampfertemperatur anhand eines physikalischen Modells, das ohne Berücksichtigung einer Frostschicht auf dem Verdampfer aufgestellt worden ist,
  wobei das Haushalts-Kältegerät dazu eingerichtet ist,
• aus der gemessenen Verdampfertemperatur und der berechneten Verdampfertemperatur ein Abweichungsmaß zu berechnen und
• dann, wenn das Abweichungsmaß einen vorgegebenen Grenzwert erreicht oder überschreitet, mindestens eine Abtauaktion auszulösen.

One design requirement is that the household refrigeration appliance has at least:

• a cold room for storing refrigerated goods,
• a compression refrigeration machine with an evaporator for cooling the cold room,
• a temperature sensor for measuring an evaporator temperature and
• a data processing device for calculating a simultaneous evaporator temperature based on a physical model which has been set up without taking into account a layer of frost on the evaporator,
  The household refrigeration appliance is designed to
• to calculate a deviation measure from the measured evaporator temperature and the calculated evaporator temperature and
• to trigger at least one defrost action when the deviation reaches or exceeds a specified limit.

It is a further development that the household refrigeration appliance is a so-called no-frost refrigeration appliance, i.e. it uses the basically well-known no-frost technology, which prevents the formation of frost or frost in the refrigerator compartment by reducing the air humidity there. In no-frost appliances, the evaporator is usually in an area separated from the refrigerator compartment. During a cooling phase, a fan blows the cold air into the refrigerator compartment. The refrigeration appliances are designed in such a way that air is circulated back to the evaporator. Since cold air holds less moisture, this mainly condenses on the evaporator, in particular its cooling fins. A heater defrosts the cooling fins at suitable defrosting times, and the layer of ice flows out of the appliance as water via a gutter and ends up in an evaporation container, for example. Since the fan is not running during the defrosting phase, the refrigerator compartment remains cool.

Fig.1

zeigt in Frontansicht eine Skizze eines Kältegeräts; und

Fig.2

zeigt ein mögliches Verfahren zum Betreiben des Kältegeräts aus Fig.1.

The above-described properties, features and advantages of this invention, as well as the manner in which they are achieved, will become clearer and more readily understood in connection with the following schematic description of an embodiment, which is explained in more detail in connection with the drawings.

Fig.1

shows a front view of a refrigeration appliance; and

Fig.2

shows a possible method for operating the refrigeration appliance from Fig.1 .

Fig.1 shows a front view of a refrigeration device in the form of a refrigerator 1, in particular a no-frost refrigerator, alternatively or additionally in the form of a freezer, with an open cooling chamber 2. The refrigerator 1 has a body 2 with a cooling chamber 3 formed therein that is open at the front for storing refrigerated goods. The open front can be closed by at least one door (not shown). A compression refrigeration machine 4 to 8 is provided for cooling the cooling chamber 3, which comprises a refrigeration circuit 4 with an evaporator 5 for cooling the cooling chamber 3, a compressor 6, a condenser 7 and an expansion element 8. The evaporator 5 is designed here as a finned evaporator and is arranged in particular outside the cooling chamber 3. The evaporator 5 has a temperature sensor 9 for measuring an evaporator temperature Tv_mess. The evaporator 5 is assigned a heater 10, which defrosts the evaporator 5 when it is switched on or activated.

The refrigerator 1 further comprises a data processing device 11 for calculating an evaporator temperature Tv_calc based on a physical model of the evaporator 5, which has been set up without taking into account a layer of frost on the evaporator 5.

The data processing device 11 is further connected to the temperature sensor 9 and is designed to calculate a deviation measure Δ from the measured evaporator temperature Tv_mess and the evaporator temperature Tv_calc calculated for an identical or practically identical point in time.

The refrigerator 1 is set up to trigger at least one defrosting action when the deviation Δ reaches or exceeds a predetermined limit value T_limit, i.e. Δ > T_limit or Δ ≥ T_limit. In one variant, this can be implemented in such a way that the data processing device 11 then sends a corresponding message to a control device (not shown) of the refrigerator 1, which then triggers the at least one defrosting action. Alternatively, the data processing device 11 can trigger the at least one defrosting action. It is a further development that the data processing device 11 corresponds to the control device or the control device includes the function of the data processing device 11.

oder als Summe bzw. Integral dieser Abweichung über die letzten n Zeitpunkte $$\Delta ={\displaystyle \sum _{\mathrm{t}={\mathrm{t}}_{\mathrm{akt}-\left(\mathrm{n}-1\right)}}^{{\mathrm{t}}_{\mathrm{akt}}}\left|\mathrm{Tv}\_\mathrm{mess}\left(\mathrm{t}\right)-\mathrm{Tv}\_\mathrm{calc}\left(\mathrm{t}\right)\right|}$$

mit t_akt dem aktuellen bzw. zuletzt bestimmten Zeitpunkt, insbesondere nach Art eines mitlaufenden Fensters. Beispielsweise kann n bei einem Mess- und Berechnungsintervall von ca. einer Minute auf n = 120 festgelegt sein, was einem mitlaufenden Zeitfenster einer Breite von ca. 2 h entspricht.The deviation measure Δ can be calculated, for example, as the - in particular absolute - difference between Tv_mess and Tv_calc at a certain point in time t, e.g. as $$\Delta \left(\mathrm{t}\right)=\left|\mathrm{TV}\_\mathrm{measure}\left(\mathrm{t}\right)-\mathrm{TV}\_\mathrm{calc}\left(\mathrm{t}\right)\right|$$

or as the sum or integral of this deviation over the last n points in time $$\Delta ={\displaystyle \sum _{\mathrm{t}={\mathrm{t}}_{\mathrm{act}-\left(\mathrm{n}-1\right)}}^{{\mathrm{t}}_{\mathrm{act}}}\left|\mathrm{TV}\_\mathrm{measure}\left(\mathrm{t}\right)-\mathrm{TV}\_\mathrm{calc}\left(\mathrm{t}\right)\right|}$$

with t _akt the current or last determined point in time, in particular in the form of a moving window. For example, n can be set to n = 120 for a measurement and calculation interval of approximately one minute, which corresponds to a moving time window with a width of approximately 2 hours.

Fig.2 shows a possible method for operating the refrigerator 1 from Fig.1 .

In step S1, the evaporator temperature Tv_calc is calculated from the model of the evaporator 5 by means of the data processing device 11.

In step S2, an evaporator temperature Tv_mess is measured by the temperature sensor 9 for a point in time that is practically the same as the model calculation in S1 and transmitted to the data processing device 11.

In step S3, the deviation measure Δ is determined.

In step S4, it is checked whether the deviation measure Δ has reached or exceeded the limit value T_limit. If this is not the case ("N"), the system branches back to steps S1 and S2.

However, if this is the case ("Yes"), at least one defrosting action is triggered in step S5, e.g. a message is sent to a user to initiate a defrosting process, or a defrosting process is triggered automatically.

In step S6, it is checked whether a defrosting process has been carried out successfully. If this is not the case ("N"), the check is continued.

However, if this is the case ("Y"), the system branches back to steps S1 and S2.

In an optional step S7, it can be checked whether a minimum period of time has passed since the last defrosting process or not. If this is not the case ("N"), this check is continued or repeated. If this is the case, however, it is possible to branch to steps S1 and S2 or to another optional step S8.

In the optional step S8, a check is made to see whether a maximum time period has already been reached or exceeded since the last defrosting process. If this is not the case ("N"), the system branches to steps S1 and S2. If this is the case ("Y"), the system branches to step S5.

Of course, the present invention is not limited to the embodiment shown. The order of the steps may differ from the order shown.

In general, "a", "an" etc. can be understood as a singular or a plural, in particular in the sense of "at least one" or "one or more" etc., as long as this is not explicitly excluded, e.g. by the expression "exactly one" etc.

List of reference symbols

1

Refrigerator

2

Corpus

3

Cold room

4

Refrigeration circuit

5

Evaporator

6

compressor

7

Condenser

8th

Expansion element

9

Temperature sensor

10

Heating

11

Data processing facility

S1-S8

Process steps

Tv_calc

Calculated evaporator temperature

Tv_mess

Measured evaporator temperature

Δ

Deviation measure

Claims (10)

Method (S1 - S8) for determining a defrosting time of an evaporator (5) of a household refrigeration appliance (1), in which - a first evaporator temperature (Tv_calc) is calculated (S1) by means of a physical model which has been set up without taking into account a layer of frost on the evaporator (5), - a second evaporator temperature (Tv_mess) is measured simultaneously (S2), - a deviation measure (Δ) between the first evaporator temperature (Tv_calc) and the second evaporator temperature (Tv_mess) is calculated (S3) and - when the deviation value (Δ) reaches or exceeds a predetermined limit value (S4), at least one defrosting action is triggered by the household refrigeration appliance (1) (S5). Method (S1 - S8) according to one of the preceding claims, in which - to calculate the deviation measure (Δ), a difference between the first evaporator temperature (Tv_calc) and the simultaneous second evaporator temperature (Tv_mess) is calculated (S3) and - when this difference reaches or exceeds a predetermined limit value (S4), the household refrigeration appliance (1) triggers at least one defrosting action (S5). Method (S1 - S8) according to claim 1, in which - to calculate the deviation measure (Δ), differences between temporally successive pairs of the first evaporator temperature (Tv_calc) and the respective simultaneous second evaporator temperature (Tv_mess) are summed window by window (S3) and - when this sum reaches or exceeds a predetermined limit value (S4), the household refrigeration appliance (1) triggers at least one defrosting action (S5). Method (S1 - S8) according to one of the preceding claims, in which the at least one defrosting action comprises at least one action from the group - issuing a message to a user to initiate a defrosting process to defrost the evaporator (5); - Initiating a defrosting process to defrost the evaporator (5). Method (S1 - S8) according to one of the preceding claims, in which a minimum time period is defined between two defrosting processes, until which no defrosting action is triggered (S7) when it is reached or exceeded. Method (S1 - S8) according to one of the preceding claims, in which a maximum time period between two defrosting processes is defined, upon reaching or exceeding which at least one defrosting action is triggered (S8). Method (S1 - S8) according to one of the preceding claims, wherein the evaporator (5) is a finned evaporator. Method (S1 - S8) according to one of the preceding claims, in which the physical model is calculated on the household refrigeration appliance (1). Household refrigeration appliance (1) which is designed to carry out the method (S1 - S8) according to one of the preceding claims. Household refrigeration appliance (1) according to claim 9, comprising at least - a cold room (3) for storing refrigerated goods, - a compression refrigeration machine (4 - 8) with an evaporator (5) for cooling the cooling chamber (3), - a temperature sensor (9) for measuring an evaporator temperature (Tv_mess) and - a data processing device (11) for calculating a simultaneous evaporator temperature (Tv_calc) based on a physical model which has been set up without taking into account a layer of frost on the evaporator (5),
wherein the household refrigeration appliance (1) is designed to - to calculate a deviation measure (Δ) from the measured evaporator temperature (Tv_mess) and the calculated evaporator temperature (Tv_calc) and - to trigger at least one defrosting action when the deviation (Δ) reaches or exceeds a predetermined limit value.

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