DE102006048880A1 - Method for controlling defrosting of an evaporating unit of a refrigerator comprises estimating the actual ice formation on the unit by measuring the ambient temperature and air moisture of the surroundings and further processing - Google Patents

Abstract

Method for controlling defrosting of an evaporating unit (V) of a refrigerator comprises estimating the actual ice formation on the evaporating unit by measuring the ambient temperature and air moisture of the surroundings (U), estimating a nominal ice formation on the evaporating unit for a nominal operating point of the refrigerator and determining the ratio of the estimated actual ice formation and the estimated nominal ice formation to determine a next defrosting date or to determine the type of defrost. Preferred Features: The actual ice formation is estimated by the difference of the air moisture at the inlet (E) to the evaporating unit and the air moisture at the outlet (A) of the evaporating unit.

Description

The The invention relates to a method for controlling the defrosting of a Evaporator of a refrigerated cabinet.

Cooling furniture will be For example, as an open sales cooling furniture for normal cooling or refrigeration of food in supermarkets or the like used. The evaporator of the refrigerator is used for Absorption of heat from the to be cooled Goods and the air surrounding the goods. This happens as a result the moisture contained in the ambient air over time icing of the evaporator, which undesirably reduces the efficiency of the device. Particularly serious is this ice formation on the evaporator at open Cooling furniture, at those constantly fresh ambient air and thus additional moisture to the Evaporator arrives. The evaporator must therefore regularly defrosted become.

This is it known, the evaporator with an optional activatable electric heater equip. Specially for the freezing is a so-called hot gas defrost known in the heated gaseous refrigerant through the heat exchanger tubes led the evaporator becomes.

Problematic However, the detection of the actual degree of icing of the Evaporator. Usually becomes dependent from the special furniture product according to predetermined Time intervals defrosted without the special installation or Environmental conditions of the furniture considered become. As a result, often unnecessarily often defrosted in practice. The defrost is therefore with an unnecessary Energy requirements a related party, and the stored in the refrigerator furniture can by too frequent or unnecessary Defrosting processes are affected. The degree of icing Although over the while the melting time measured for the defrost, which is the melting point of the ice batch needed becomes. The disadvantage of this, however, is that the judgment only for the past he follows.

It is therefore an object of the invention to provide a method through which the actual current Defrosting an evaporator of a refrigerated cabinet using as possible few additional probes determined with high accuracy.

These The object is achieved by a method having the features of the claim 1 solved, and in particular in that an actual ice formation on the evaporator by measuring at least the ambient temperature and the humidity appreciated the environment becomes; that a nominal ice formation on the evaporator for a rated operating point of the refrigerator is estimated, being for the rated operating point of the refrigerated cabinet Nominal icing rate - like for example, a nominal defrost interval - known; and that the estimated actual Ice formation and the estimated Nominal ice formation are related to each other in order to get out of the relationship and from the known nominal icing rate, a next defrost date or to define a defrost type.

It So two mathematical estimates are made. On the one hand becomes an actual ice formation on the evaporator, ie an amount of ice (mass or volume) or one Ice formation rate, estimated. For this will be at least the ambient temperature and the humidity of the environment (relative or absolute humidity) measured and taken into account. These measurements usually mean No significant additional expenditure, as for example in supermarkets with several refrigerators usually anyway, a central measurement of the ambient temperature and humidity takes place and these measured values to the respective control device of Refrigerated furniture or a central control device transmitted become.

To the another is a nominal ice formation on the evaporator according to a predetermined rated operating point of the refrigerator or its evaporator, namely at least according to one Nominal ambient temperature and / or a nominal air humidity estimated, whereby the determination of the nominal ice formation preferably analogous to the determination the aforementioned actual Ice formation is made. The named nominal operating point can, for example, the Nominal ambient temperature and / or the nominal air humidity of a climate class according to standard EN441 or equivalent (eg EN23953) correspond, e.g. 25 ° C and 60% relative humidity for the climate class "3".

It is important that a nominal icing rate of the evaporator is known for the rated operating point of the evaporator considered. This rated icing rate may be determined empirically by the operator for the particular refrigerated cabinet and / or specified by the refrigeration cabinet manufacturer. The named rated operating point of the evaporator is chosen in particular such that it corresponds to the worst-case expected environmental conditions (eg highest expected temperature and highest expected relative humidity at the installation site of the refrigerator). In turn, the associated rated icing rate is particular the icing rate that corresponds to these worst-case expected environmental conditions. The starting point for the process is therefore a nominal icing rate, the consideration of which is sufficient even for the most unfavorable environmental conditions to be expected (eg according to the ambient conditions according to a special climate class according to EN441) for a timely defrost. The stated nominal icing rate may be a defrost interval (ie a time interval between two consecutive defrosting dates) or else the specification of an ice formation volume or an ice formation mass per unit time.

Around a next one to determine the required deferral date and / or order for the next predetermined Defrost date (nominal defrost date) is a suitable type of defrost method determine the estimated (based on the measured values) actual Ice formation and the (on the basis of the corresponding nominal values) estimated Nominal ice formation relative to each other, for example - however not necessarily - by Quotient formation, and this ratio is in turn with the ratio mentioned above, for example by multiplication or division.

By this ratio formation will ultimately be a delay the determined deferral dates with respect to for the unfavorable expected icing rate or Defrosting dates effected, or it is thereby determined the proportion, around the the actual Ice formation differs from the nominal ice formation, in each case in dependence from the deviation of the measured real conditions from the nominal conditions.

One particular advantage of this method is the consideration one from the device manufacturer already specified climate class (whereby the nominal ambient temperature and the nominal air humidity are specified) or one for one such nominal operating point of the evaporator usually anyway already known nominal icing rate (e.g., nominal defrost interval). This is because the Consequence, that the volume or mass flow affecting the evaporator the ambient air indirectly taken into account can be, without having its own measurement of this volume or Mass flow is required. Only taking into account this volume or mass flow, however, is an accurate estimate of the evaporator per unit time accumulating condensate possible.

Possible configurations the method according to the invention will be explained below, for better understanding first the typical structure of the refrigerator affected here should be explained.

1 and 2 each show a schematic side view of a refrigerated cabinet with an evaporator and different air streams.

In 1 is a here on its front open cooling cabinet only shown schematically. The refrigerator has an evaporator V. This is integrated in a conventional manner in a known refrigerant circuit, ie, the evaporator V is connected in the flow direction of the refrigerant, for example with a compressor, a condenser and an expansion valve.

Furthermore, in 1 shown different air flows. That's how a stream of air gets 1 guided in the refrigerator to the evaporator V. The air is cooled at the evaporator V and leaves it as air flow 2 , At the top of the refrigerator, namely at an air outlet A, the cooled air is as air flow 3 output. The cooled air flows curtain-like down along the front of the cabinet (airflow 4 ), wherein the goods arranged in the refrigerated goods is cooled. In this air stream 4 air mixes from the environment U (air flow 5 ). The entering at the bottom air inlet E of the cabinet and the air flow 1 forming air is therefore a mixture of the cooled air flow 4 and the ambient airflow 5 , For a standard normal cooling, the air temperature at the outlet A, for example, about + 2 ° C and the air inlet E of the refrigerator furniture be about + 5 ° C.

In 1 In addition, the temperatures at the air outlet A, in the environment U, at the air inlet E and at the evaporator V prevailing temperatures T, the relative humidity rF and the absolute humidity (water content) x are shown. The measured values used in the context of the method according to the invention are each surrounded by a circle, wherein a solid line indicates a mandatory measured value and a dashed line indicates an optional measured value. A respective rectangular border indicates a calculated value, and optional calculations are again indicated by a dashed line. Specifically, the respective water content x (absolute humidity) can be taken as a function of the temperature T and the relative humidity rF the Mollier diagram, wherein simplifying a constant pressure can be assumed.

Hereinafter, a particularly accurate method for determining a defrosting deadline for the evaporator V according to 1 explained (so-called condensate model). In this process, the in 1 determined as optional measured values, and the calculations marked as optional are performed. Subsequently, a simplified embodiment of the method according to the invention is explained (so-called linear approach).

(a) Estimate the actual Ice formation on the evaporator V:

On the one hand, the (volume or mass specific) actual ice formation on the evaporator is estimated. For this purpose, at least the ambient temperature T _U and the relative humidity rF _{U of} the environment are measured. As a result, the water content x _U of the cooling air flow 4 mixed ambient air flow 5 known (Mollier diagram).

In the context of the so-called condensate model, a difference Δx between the absolute humidity x _E at the evaporator inlet E and the absolute humidity x _A at the air outlet A is ultimately determined for the estimation of the actual ice formation on the evaporator V, it being assumed that the heating of the cooling air between the Air outlet A (air flow 3 ) and the air inlet E (air flow 1 ) solely from the admixture of the ambient air (air flow 5 ) results.

The absolute humidity x _A at the air outlet A can be equated with the water content x _V at the evaporator V. The airflow 2 from the evaporator V to the air outlet A is indeed heated, ie the relative humidity RH changes. The absolute water content x remains constant. It can also be reasonably assumed that the air at the evaporator V cools down to the dew point or below the dew point (relative humidity rF _V at the evaporator V of 100%). Thus, the water content x _V or x _A can be determined directly from the temperature T _V at the evaporator V (Mollier diagram). This value in turn can be measured by means of the temperature sensor, which is usually present at the evaporator V anyway. Alternatively, neglecting the above-mentioned heating, the temperature T _A at the air outlet A can be used instead of the temperature T _V at the evaporator V.

The absolute humidity x _E at the air inlet E is - as already mentioned - determined taking into account the fact that the output at the air outlet A cooling air (air flow 3 ) an airflow 5 from the environment U is added. However, the respective mass flows are not known. The absolute humidity x _E is therefore determined according to a mixing rule (mixture of the air masses located at different temperature levels), the accumulating condensate quantities being specific, ie in each case based on a defined air mass (eg one kilogram).

For a better explanation of the mixing rule used on 2 referenced, in which the mass flows are drawn. It is assumed that the mass flow in the refrigeration cabinet is constant (m ₁ = m ₃ , m ₅ = m ₆ ). There is thus a mass exchange between the air flow 2 in the refrigerator and the surroundings U by the amount m ₆ = m ₅ instead. With this condition, the mass flow remains constant in the calculation.

After the mixing rule results for the air flow 1 at the air inlet E a mixing temperature T ₁ , which is initially from the temperatures T ₄ and T _{5 of} the air streams 4 and 5 and from the corresponding masses and heat capacities:

Here, c _i denotes the respective specific mixing heat capacity of the air and the water content at a given temperature and relative humidity. As explained above, it can be assumed that m ₄ = m ₃ -m ₆ = m ₃ -m ₅ . In addition, for the sake of simplicity, the respective proportion of water in the partial flows, which accounts for a maximum of about 2% of the total mass, is neglected. From equation (1):

The heat capacity c _i can be assumed to be constant as a simplification. It can be estimated that the errors caused by neglecting the unequal heat capacities of air and water are small and that the above simplifications only make equation (2) "safer". because they ultimately lead to larger calculated condensate quantities at the evaporator V.

From this, the compounding amount m ₅ can then ambient air will be approximately calculated as:

Due to the aforementioned equation (3), the mass ratio m ₅ / m _{3 is} known. The temperature T ₁ corresponds to that in connection with 1 said inlet temperature T _E and can be measured by means of a arranged at the air inlet E of the refrigerator furniture temperature sensor. The temperature T ₃ corresponds to the outlet temperature T _{A of} the air outlet A according to 1 ; An associated temperature sensor can also be provided for this purpose, or the outlet temperature T _A is equated with the temperature T _V at the evaporator V for the sake of simplicity. The temperature T ₅ finally corresponds to the ambient temperature T _U according to 1 , Thus, from the mentioned equation (3) by measuring the temperatures T _E , T _A (or T _V ) and T _U, the mass ratio m ₅ / m _{3 of} the proportionate admixture of the ambient air (air flow 5 according to 1 ) in the cooling air flow 3 known.

The absolute humidity x _E at the air inlet E, ie the prevailing water content (g / kg), is the sum of the water content of the air streams 4 and 5 according to 1 , The absolute humidity x _E thus results from the product of the absolute humidity x _A at the air outlet A with the air mass m _{3 there} , from which the product of the absolute humidity x _A at the air outlet A with the mass m _{6 is} to be subtracted (to the environment discharged water quantity), in which case again the product of the absolute humidity x _U of the ambient air is to be added to the mass m ₅ supplied by the environment U, and wherein this function is of course to be standardized with respect to the total mass m ₁ = m ₃ :

Overall, it follows that the absolute humidity x _E can be calculated as a value related to the recirculated air mass. The absolute humidity x _A at the air outlet A can namely be set equal to the water content x _{V of} the air at the evaporator V, which in turn can be estimated from the measured at the evaporator V temperature T _V and from the assumption that the dew point is reached or fallen below as already explained above. The absolute humidity x _{U of} the ambient air can be calculated from the measured ambient temperature T _U and relative humidity rF _U (Mollier diagram). The aforementioned mass m ₆ corresponds to the mass m ₅ at a constant mass flow (cf. 2 ). The mass ratio m ₅ / m ₃ is obtained according to equation (3) from the measured temperatures T ₁ = T _E , T ₃ = T _A (or T ₃ = T _V ) and T ₅ = T _U.

Thus, the aforementioned difference .DELTA.x of the absolute humidity x _E and x _{A is} known, which corresponds to the condensation or ice formation on the evaporator V, namely as a relative to the circulated air mass value (eg g / kg). In other words, the actual ice formation .DELTA.x at the evaporator V has hitherto only been estimated as a volume or mass-specific value by taking account of the described mixing rule, namely based on the volume or the mass of the airflow circulating in the refrigeration appliance. However, this is not known and should not be measured if possible.

(b) Estimate a nominal ice formation at the evaporator:

Of the thus missing mass flow or volume flow in the refrigerator is therefore considered indirectly, namely in the form of a nominal icing rate of the refrigerator or its evaporator. This nominal icing rate, For example, a nominal defrost interval may be empirical by the operator of the refrigerator have been determined or - also based on empirical determination - specified by the refrigeration equipment manufacturer be. The nominal icing rate corresponds in particular to the most unfavorable expected real ambient conditions at the installation site of the refrigerator, and It can correspond to a special climate class according to the EN441 standard. The rated icing rate is the nominal operating point of the evaporator assigned a nominal ambient temperature and a nominal air humidity.

On the basis of this nominal ambient temperature and nominal air humidity, the nominal ice formation x _nominal is estimated at the evaporator V, with the actual ice formation being estimated analogously to the above-described estimation. Here, for example, only the actually measured ambient temperature T _U and humidity RH _U by the corresponding nominal values (Nom ambient temperature or nominal air humidity). The further calculation of the nominal ice formation x _nominal takes place as explained in detail above for the calculation of the actual formation of ice, in particular taking into account the same measured values (eg T _A , T _E , T _V ).

As an alternative to replacing the actual measured ambient temperature T _U and air humidity rF _U by the corresponding nominal values, only one of these measured values can be replaced by the corresponding nominal value of the nominal operating point of the evaporator. For example, it is sufficient to replace only the measured air humidity rF _{U of} the environment by the rated humidity of the cooling cabinet, ie for the calculation of nominal ice formation x _nominal analogous to the calculation of the actual ice formation, the measured ambient temperature T _U = T ₅ ( and not the nominal ambient temperature). This means according to the above equation (3) that of the same mass ratio m ₅ / m ₃ (ratio of the air flow supplied from the environment U 5 to the airflow 3 at the outlet A) is assumed as in the calculation of the actual ice formation, and not by a reduced such mass ratio at a higher temperature T ₅ .

Thus, the nominal ice formation x _nominal is now available as a volume or mass-specific value (eg g / kg).

(c) Ratio of the actual Ice formation and the nominal ice formation at the evaporator:

Finally, the (volume or mass specific) estimated actual ice formation Δx at the evaporator and the (volume or mass specific) estimated nominal ice formation x _nominal are set in relation to each other, for example by quotient Δx / x _nominal . By taking account of the aforementioned nominal icing rate, the missing knowledge of the air volume flow or air mass flow is taken into account.

Thus, a ratio V of the actual ice formation X to the estimated nominal ice formation X _nominal, which is no longer dependent on the volume flow or mass flow, can be formed from the corresponding volume- or mass-specific quantities Δx or x _nominal as follows:

With V . Here, the volume flow (m ³ / min) is referred to in the refrigerator. ρ _Air is the density of the air (kg / m ³ ). It can be seen that the specific values of the actual ice formation Δx and the nominal ice formation x _nominal relate to a mass (eg 1 kg of air) circulating around the refrigerated cabinet. Since the calculation of the actual ice formation X and the calculation of the nominal ice formation X _{nominal are} analogous to one another and the volume flow and the density of the air shorten out of the calculation of the ratio V, the volume flow and the density of the air can change without this affects the ratio V The volume flow and the density of the air need not be known.

The ratio V thus corresponds to a degree of icing. It indicates the ratio of actual ice formation to nominal ice formation. The nominal ice formation, in turn, is assigned to the nominal icing rate. The ratio V thus denotes the proportion by which the rated icing rate has fallen below due to the (more favorable) real conditions or a nominal defrost interval T _defrost can be exceeded.

The ratio V can be determined periodically, for example, with the individual determined values V _{i being} added up. The estimated actual ice formation and the estimated nominal ice formation are therefore cumulated. Preferably, the individual determined values V _i (or the sum formed) are additionally normalized with regard to the nominal icing rate, in particular by forming a ratio with the rated icing rate. For example, the determined values V _i can be multiplied by the ratio of the respective measurement interval Δt _{meas, i} (time duration between two measurements) to the nominal defrost interval T _defrost (defrost interval for nominal conditions):

Instead of a summation can of course also carried out an integration.

Once this accumulated (or integrated) and normalized degree of icing V (n) a vorbe If the threshold reaches or exceeds the threshold value, for example, 100%, the next defrost will be initiated, either immediately or after a programmed defrost release deadline has been reached (for example, to allow defrost only at certain night or weekend times). Thus, if more favorable environmental conditions exist than the nominal conditions, one or even several nominal defrosting dates are skipped. The comparison of the degree of icing V (n) normalized with respect to the nominal icing rate with a predetermined threshold value (such as 100%) indirectly corresponds to a comparison of the degree of icing with the nominal icing rate (eg with the nominal defrost interval T _defrost ).

It is also possible to convert the currently determined degree of icing into a time prognosis of the next actually required defrosting date, for example by the icing _{degree being set} in relation to the nominal defrost interval T _defrost .

alternative to the above Initiate the next Defrosting can also be provided that, regardless of the determined degree of icing the predetermined regular defrosting appointments (nominal defrosting appointments) are retained - thus not skipped. However, depending on of the determined degree of icing only the type of defrosting changed become. In this case, there is a summation of the degrees of icing so not over several nominal defrost intervals. In particular, if - upon elapse of a nominal defrost interval the determined degree of icing has a threshold value of 100% (calculated from the last defrost) exceeded wears an otherwise non-energetic defrosting procedure an energetic defrosting process can be selected. For example - especially in case of plus cooling (> 0 ° C) - for the expected Ambient conditions at the respective nominal defrosting date A circulating air defrost provided (temporary shutdown of the cooling, that is, only the circulating in the refrigerator Air ensures a defrosting of the evaporator). If, however, unfavorable environmental conditions set (which to an increased determine the degree of icing), so at the nominal defrost date instead of the recirculation defrost a Carried out electro-defrosting. In this case, the evaporator, for example, electrical cal heating energy supplied; So it will be an increased Energy consumption, however, is more effective Ensure de-icing, i.e. the evaporator becomes reliable Completely de-iced.

(d) Summary of the condensate model:

In summary, the assumptions underlying the condensate model explained above should once again be mentioned:
It is assumed that the air pressure is constant (eg 1 bar). The heating of the air between the outlet and the entrance to the refrigerator is done only through the ambient air. The coldest point of the air circulation in the refrigerator is measured by means of a temperature sensor, at which point the relative humidity is 100%. The mass flow in the refrigerator is constant. The temperature and humidity of the ambient air are known or measured.

By Using a mass mixing rule, the amount of condensate can be on the evaporator V mass or volume specific calculate, namely based on the circulating in the refrigerator Air. By consideration a device-specific Nominal icing rate with assigned nominal ambient temperature and Nominal humidity can be the mass flow or volume flow of the circulating Air, i. the time dependence the esteemed Condensation taken into account become.

The Considered condensate model lower evaporation temperatures (i.e., lower than normal operating conditions accordingly) with a larger amount of condensate (former Abtautermin). Covered refrigerated cabinets or Times when the refrigerated cabinets are temporarily covered or is closed sen, be with a smaller amount of condensate considered (later Abtautermin).

(e) Linear Approach:

The estimation of ice formation can also be made according to a simplified linear approach, so that the in 1 dashed bordered values do not necessarily have to be measured or determined. For this purpose, the actual formation of ice on the evaporator V is estimated on the basis of the absolute humidity x _{U of} the ambient air U. This is calculated on the basis of the measured ambient temperature T _U and the measured relative humidity rF _{U of} the environment. In addition, a nominal ice formation on the evaporator V is estimated by calculating a reference humidity x _Ref for a nominal ambient temperature and / or a nominal air humidity. These nominal conditions can in turn correspond to a climate class according to the standard EN441. It is important that these nominal conditions are assigned a known nominal icing rate.

The estimated actual ice formation (actual moisture x _U ) is then related by quotient formation to the nominal ice formation (reference moisture x _Ref ) and the value obtained is compared with the nominal icing rate. As a result, for example - as in the illustrated condensate model - a degree of icing can be determined in order to initiate a defrosting process when an ice degree of 100% is reached.

Especially is a current degree of icing by summing and normalizing the measured values formed, or it is, for example, by integration a time average of the estimated actual ice formation is determined and taken into account.

In addition, at the quotient correction parameters are provided, in particular a slope correction value and / or an offset correction value.

Finally is Note that both in the illustrated condensate model as even with the simplified linear approach by appropriate measurement the ambient pressure taken into account can be an even higher Accuracy of the underlying estimates.

1-5

airflow

A

air outlet

e

air inlet

U

Surroundings

V

Evaporator

Claims (21)

Method for controlling the defrosting of an evaporator (V) of a refrigerated appliance, characterized in that (a) an actual ice formation on the evaporator is estimated by measuring at least the ambient temperature (T _U ) and the relative humidity (rF _U ) of the environment (U); (b) estimating a nominal ice formation on the evaporator for a rated operating point of the refrigeration appliance, wherein a nominal icing rate - such as a nominal defrost interval - is known for the nominal operating point; and (c) correlating the estimated actual ice formation and the estimated nominal ice formation to determine from the ratio and the known nominal ice rate a next defrost date or define a defrost type. A method according to claim 1, characterized in that for the estimation of the actual ice formation, a difference of the air humidity (x _E ) at the evaporator inlet (E) and the humidity (x _A ) at the evaporator outlet (A) is determined. A method according to claim 2, characterized in that for determining the air humidity (x _E ) at the evaporator inlet (E) at least the ambient temperature (T _U ) and the humidity (rF _U ) of the environment (U) are taken into account. Method according to one of claims 2 or 3, characterized in that the determination of the humidity (x _E ) at the evaporator inlet (E) takes place according to a mass mixing rule, wherein additionally at least the temperature (T _E ) at the evaporator inlet (E), and the temperature ( T _A ) be taken into account at the evaporator outlet or temperature (T _V ) on the evaporator. Method according to claim 4, characterized in that the mass mixing rule comprises an admixture of ambient air ( 5 ) in a cooling air flow ( 4 ) of the refrigerator. Method according to one of claims 2 to 5, characterized in that for determining the air humidity (x _A ) at the evaporator outlet, the temperature (T _V ) at the evaporator or the temperature (T _A ) at the evaporator outlet (A) is taken into account, wherein a relative Humidity (RH _V ) at the evaporator (V) or at the evaporator outlet (A) of substantially 100% is assumed. Method according to one of the preceding claims, characterized in that the estimating the actual ice formation is air volume specific or air mass specific. Method according to one of the preceding claims, characterized marked that for appreciating the actual Ice formation in addition considered the ambient air pressure becomes. Method according to one of the preceding claims, characterized in that the estimation of the nominal ice formation is analogous to the estimation of the actual ice formation, wherein - the measured ambient temperature (T _U ) is replaced by a nominal ambient temperature, or - the measured air humidity (rF _U ) the environment is replaced by a nominal humidity, or - the measured ambient temperature (T _U ) is replaced by a nominal ambient temperature and the measured ambient air humidity (rF _U ) by a nominal air humidity. Method according to one of the preceding claims, thereby in that the rated operating point of the refrigerator is at least - by a nominal ambient temperature, or - by a nominal air humidity, or - by a nominal ambient temperature and a nominal air humidity is specified. Method according to one of the preceding claims, characterized characterized in that the rated operating point of the refrigerated cabinet is the unfavorable at the installation site of the refrigerator expected ambient conditions. Method according to one of the preceding claims, characterized characterized in that the rated icing rate is a Nominal defrost interval, or an ice formation volume or an ice formation mass per unit time is. Method according to one of the preceding claims, characterized characterized in that the ratio of estimated actual Ice formation and estimated Ratio of nominal ice formation to the nominal icing rate will be the next Define defrost date or determine the type of defrost. Method according to one of the preceding claims, characterized characterized in that the estimated actual Ice formation and the estimated Nominal ice formation can be cumulated from the last defrost, or that the ratio from esteemed actual Ice formation and estimated Nominal ice formation is cumulated from the last defrost. Method according to one of the preceding claims, characterized characterized in that the estimated actual Ice formation and the estimated Nominal ice formation are normalized on the basis of the nominal icing rate, or that the ratio from esteemed actual Ice formation and estimated Nominal ice formation is normalized by the nominal icing rate. Method according to one of the preceding claims, characterized characterized in that the ratio of estimated actual Ice formation and estimated Nominal ice formation is normalized with regard to the nominal icing rate, being this normalized ratio is compared with a threshold. Method according to one of the preceding claims, characterized characterized in that the ratio of estimated actual Ice formation and estimated Nominal ice formation is cumulated from the last defrost, the cumulative ratio in terms of nominal icing rate normalized, and wherein this cumulative and normalized relationship with is compared to a threshold value. Method according to one of the preceding claims, characterized marked that the next Defrost date or defrost type is determined by the condition that the esteemed actual Ice formation of the esteemed Is nominal ice formation or exceeds the rated ice formation. Method according to one of the preceding claims, characterized characterized in that due to the ratio of estimated actual Ice formation and estimated Nominal ice formation and based on the nominal icing rate a next defrost date determined which deviates from a nominal deferral date, which is the nominal operating point of the Cooling furniture corresponds. Method according to one of the preceding claims, characterized characterized in that due to the ratio of estimated actual Ice formation and estimated Nominal ice formation and due to the nominal icing rate one of several predetermined Defrosting is set, which is a different degrees of de-icing effect of the evaporator. Method according to one of the preceding claims, characterized characterized in that due to the ratio of estimated actual Ice formation and estimated Nominal ice formation and due to the nominal icing rate between an energetic one and a non-energetic type of defrost is selected.