DE102021208510A1 - Method for operating a refrigeration device and refrigeration device with a defrost heater - Google Patents

Abstract

A refrigeration device (10) with a refrigerant circuit (27), which has an evaporator (18) with an electric defrost heater (26), the refrigeration device being intended for operation on a power supply system with a nominal mains voltage, has a control unit for operating a defrosting process, in which a predetermined necessary defrosting energy is introduced into the defrosting heater in a first defrosting phase, taking into account a current mains voltage. A method for carrying out a defrosting process has the following steps: a) determining the necessary defrosting energy for a first defrosting phase; b) operating the defrosting heater in a first defrosting phase with a supply voltage proportional to a current mains voltage; c) observing the current mains voltage; d) calculating a defrosting energy supplied in the first defrosting phase with the observed mains voltage; ande) ending the first defrosting phase when the defrosting energy supplied has reached the necessary defrosting energy.

Description

The present invention relates to a refrigeration appliance, in particular a household refrigeration appliance, with at least one storage compartment which is accessible through a door, a refrigerant circuit which has an evaporator with an electric defrost heater, and a control unit, and a method for operating a refrigeration appliance, with a defrosting process is carried out.

From the WO2010078998A2 a refrigerator with a defrost heater is known, with different defrost temperatures being generated during a defrosting process.

From the CN107726721A a refrigeration device with a defrost heater is known, with different final defrost temperatures being generated during a defrosting process.

IN03670CH2014A discloses a refrigerator with a defrost heater that is operated with voltage pulses during a defrosting process.

The object of the present invention is to provide a refrigeration device and an operating method for a refrigeration device with an improved defrosting process.

The object is achieved by a refrigeration device and a method for operating a refrigeration device according to the independent claims.

The invention relates to a refrigeration appliance with at least one storage compartment which is accessible through a door, a refrigerant circuit which has an evaporator with an electric defrost heater, and a control unit, the refrigeration appliance being intended for operation on a mains power supply with a nominal mains voltage, the Control is set up to carry out a defrosting process in such a way that a predetermined necessary defrosting energy is introduced into the defrosting heater in a first defrosting phase, taking into account a current mains voltage.

During operation of the refrigeration device, moisture is introduced into the storage compartment in connection with door operations, both through air exchange with room air from the environment and through the introduction of refrigerated goods. This moisture precipitates as frost in the evaporator when the refrigerant circuit is in operation. The evaporator and storage compartment are connected by an air duct. Air circulation between the evaporator and the storage compartment transports the moisture into the evaporator. The frost is removed by a defrosting process after a period of time, the defrosting interval.

During the defrosting process, the evaporator is heated by the electric defrosting heater. The evaporator is first heated and brought to a temperature close to 0 °C. When the temperature reaches 0 °C, the frost begins to melt. A further supply of energy at those points where frost is present on the evaporator does not increase the temperature but melts the frost. The melted frost forms water droplets on the surface of the evaporator, with small droplets sticking there and larger droplets flowing away by gravity.

The electric defrost heater is preferably installed in the lower area of the evaporator or under the evaporator in order to thaw a collecting channel for defrost water arranged under the evaporator at the beginning of the formation of defrost water.

In the vicinity of the defrost heater, the temperature value 0 °C is reached first. There the evaporator is first free of frost. The frost-free area of the evaporator can then continue to heat up. Higher temperatures can be reached here, so that water vapor forms from water droplets on the evaporator surface. The water vapor can now spread within the air duct and, in the worst case, even reach the storage compartment.

The air duct is usually not covered by the heater, as defrosting is not necessary there. A fan is arranged in the air duct, which drives the air circulation. The fan can be part of an evaporator unit. The fan can be heated by the defrost heater or have a separate heater or be unheated. The evaporator is usually arranged at a distance from the heater, so that it still has a very low temperature at least at the start of vapor formation.

When steam starts to form, the steam can possibly be prevented from spreading by an overlying layer of frost. At the moment when the frost layer thaws, a lot of vapor can be released and suddenly condense on the air duct or on the fan. The steam should only reach the fan in doses if possible.

An advantage of the invention is that the amount of vapor released can be minimized. This is achieved by introducing a predetermined necessary defrosting energy into the defrosting heater in the first defrosting phase, taking into account the current mains voltage.

The necessary defrosting energy essentially corresponds to the energy that heats the evaporator to a temperature of 0 °C and melts an expected minimum amount of frost. The temperature of the evaporator at the start of the defrost is known, for example from a defrost temperature sensor.

The assumed minimum amount of frost can be set equal to zero, determined from experiments, or determined by an observation of user behavior. A larger assumed minimum amount of frost leads to an overall shorter defrosting process, but involves a risk that the actual amount of frost is less than the assumed minimum amount of frost.

To determine the assumed minimum amount of frost from observing user behavior of the refrigeration appliance, the amount of frost is estimated from observing the number of door openings, the ambient temperature and possible other parameters, and a minimum value that is most likely exceeded is determined for this purpose.

The door can be designed as a hinged door or as the front of a drawer.

The evaporator can be a finned evaporator that is installed horizontally or preferably vertically. With an evaporator installed upright, there is a risk that a very large vapor cloud will form, which can be avoided with the invention.

The evaporator advantageously has a temperature sensor with which the defrosting process is observed. This temperature sensor is preferably arranged at a location on the evaporator at which the frost melts last when the defrost heater is operated.

It is common and advantageous to monitor the temperature measured by this temperature sensor during the defrost phase. The moment the last frost melts, the temperature in this area of the evaporator begins to rise. One aim of defrosting is to end the defrosting process in such a way that on the one hand no frost remains in the evaporator and on the other hand the heating is switched off immediately as soon as the last frost has melted. Therefore, the defrosting process is usually and advantageously ended as soon as the temperature sensor determines a temperature value corresponding to a predetermined end of defrosting temperature.

With the invention it is possible on the one hand to carry out a comparatively short defrosting process and first to heat the evaporator with high heating power and melt off frost as long as there is most likely frost on the evaporator, but on the other hand to avoid vapor formation and to approach the point with low heating power approach where the last frost will probably melt.

The defrost heater can be a contact heater or preferably a radiant heater. The defrost heater can be designed for operation with mains voltage.

Since the performance of the defrost heater depends quadratically on the current mains voltage, the temperature target value of 0 °C for the minimum frosted evaporator can be achieved very precisely by taking into account the current mains voltage and thus mains voltage fluctuations.

According to the invention, heating can be carried out with maximum heat output in a first defrosting phase and the evaporator can be brought to the temperature value of 0° C. in the shortest possible time, with steam propagation in the air duct being reliably avoided.

The current mains voltage can be measured continuously or determined with several measurements and the formation of an average value. This can begin before the heater is turned on or when the heater is turned on. The formation of an average value can be regarded as sufficient since the mains voltage usually changes slowly.

According to one embodiment of the invention, the defrosting process is continued after the first phase with a second defrosting phase with a reduced heat output in relation to the first defrosting phase. The reduced heat output has the advantage that the temperature differences between the part of the evaporator that is still covered in frost and the part of the evaporator that has already been defrosted are lower and the temperature of the part of the evaporator that has already been defrosted is therefore lower, and therefore significantly less steam is formed.

in the second defrosting phase, a probably required defrosting energy can be determined. The probably necessary defrosting energy is the energy that is needed in the second phase to melt off an assumed probable amount of frost.

The assumed probable amount of frost can be derived from a user's observation behavior of the refrigeration appliance can be determined. For this purpose, the amount of frost is estimated from observation of the number of door openings, the ambient temperature and other possible parameters, as already used in a configuration above for the first defrosting phase.

The second defrosting phase can be divided into two partial phases. In the first partial phase, heating can take place with a progression of the heating power. In the second partial phase, heating can take place with a predetermined minimum heating power. This procedure allows heating in the first partial phase in such a way that the probable amount of frost is melted. In the second partial phase, a remaining amount of frost can be melted. Here, too, the formation of vapor is minimized by a low temperature in the area of the evaporator where the frost has already melted.

The course of the heating power in the first partial phase is preferably decreasing. In the first partial phase, the heat output can be equal to the maximum heat output from the first defrosting phase at the beginning. In the first partial phase, the heating output can be equal to the predetermined minimum heating output from the second partial phase. These properties of the heating power curve are advantageous with regard to the probability considerations for the expected amount of frost. At the beginning of the first partial phase, there is a high probability that there is an unmelted amount of frost on the evaporator. It is therefore advantageous to begin the first sub-phase with a heating output that is higher than the predetermined minimum. At the end of the first sub-phase, there is a high probability that only a little frost is left. It is therefore advantageous to end the second partial phase with a predetermined minimum heating output.

The course of the heating power in the first partial phase can be continuous or gradually decreasing. Alternatively, the profile can also be constant with an average heating power between the predetermined minimum heating power and the maximum heating power.

The heating during the second defrost phase can be done with a pulse train. The heating power can advantageously be generated with a pulse modulation of the heating voltage.

The course of the heating output can be determined with the help of the defrosting energy likely to be required for the second defrosting phase. The course of the heating power can then be determined in such a way that at the end of the first partial phase of the second defrosting phase, the defrosting energy that is probably required for the second defrosting phase is reached.

The heat output can be determined during at least a partial phase of the second defrosting phase using the mains voltage observed. In the first partial phase, this has the advantage that the expected amount of frost can be adjusted very precisely. In the second partial phase, it has the advantage that an increased mains voltage does not lead to vapor formation.

The method according to the invention for operating a refrigeration device is now formulated with method steps. The method relates to a refrigeration device with a refrigerant circuit, which has an evaporator with an electric defrost heater, the refrigeration device being provided for operation on a power grid with a mains voltage, with an actual mains voltage being able to deviate from a nominal mains voltage.

The method is used to carry out a defrosting process and begins with method step a) determining a necessary defrosting energy for a first defrosting phase. Here, a defrost energy is determined, which must be used in any case, even with a minimally frosted evaporator.

Now, in a first defrosting phase, method step b) operation of the defrosting heater with a supply voltage proportional to a current mains voltage follows. This step is for rapidly heating the evaporator to the point where frost begins to melt. In particular, the defrost heater can be operated with mains voltage.

In method step c), the current mains voltage is observed. This observation can take place before or during the first phase.

In method step d), a current defrosting energy supplied in the first defrosting phase is calculated using the mains voltage observed. Deviations from the nominal mains voltage are taken into account in this way.

The first defrosting phase is ended according to method step e) when the defrosting energy supplied has reached the necessary defrosting energy. After this process step, the evaporator is just warm enough to melt the minimum expected amount of frost. If the evaporator has a lot of frost, the temperature of the evaporator can still be less than 0 °C, but it will be close to 0 °C.

According to one embodiment of the method, in a further method step f) in a second defrosting phase, the defrosting heater with a reduced heat output in relation to the first operated defrosting phase. In this second defrosting phase, the accumulated frost is defrosted.

For this purpose, according to the further method step g), a probably necessary defrosting energy for the second defrosting phase can be determined. The probably required defrosting energy is determined from the probably existing amount of frost.

Another embodiment of the method provides in a first partial phase of the second defrosting phase according to method step h) heating with a course of heating power, and in a second partial phase of the second defrosting phase according to method step i) heating with a predetermined minimum heating power. In the first partial phase, the expected frost is melted off, the second partial phase serves to melt off a further quantity of frost that may exceed the expected quantity of frost.

In the further method step j), the course can be determined, in particular with decreasing heating power, with the probably necessary defrosting energy for the second defrosting phase.

Preferably, at the end of the first partial phase of the second defrosting phase, the defrosting energy that is likely to be necessary for the second defrosting phase has been reached.

The heat output is advantageously determined during at least a partial phase of the second defrosting phase using the mains voltage observed.

In a further method step k), the defrosting process can be ended when a predetermined end defrosting temperature is reached at the evaporator.

According to a further embodiment of the method, the defrosting process can have a preparatory phase before the first defrosting phase, in which the mains voltage can already be determined or in which an intensive cooling phase can take place, in which the storage chamber can be brought to a particularly low temperature so that the refrigerated goods during the first and second defrost phase does not exceed the maximum storage temperature.

The preferred application of the invention is an evaporator in a freezer compartment, but refrigerator compartments can also be equipped with frost-accumulating evaporators that have to be defrosted.

• 1 eine schematische Darstellung eines erfindungsgemäßen Kältegeräts;
• 2 eine schematische Darstellung eines Verlaufs einer Heizleistung gemäß einer Ausführungsform der Erfindung;
• 3 ein Flussdiagramm des erfindungsgemäßen Verfahrens; und
• 4 ein Flussdiagramm mit weiteren Ausführungsformen des erfindungsgemäßen Verfahrens.

Further features and advantages of the invention result from the following description of exemplary embodiments with reference to the attached figures. Show it:

• 1 a schematic representation of a refrigerator according to the invention;
• 2 a schematic representation of a course of a heating power according to an embodiment of the invention;
• 3 a flowchart of the method according to the invention; and
• 4 a flowchart with further embodiments of the method according to the invention.

1 shows a refrigerator 10 according to the invention schematically with two storage compartments 11, 12 which are accessible through a door 13, 14 respectively. The rear walls of the storage compartments are not shown, so you get a view of the evaporator units 15, 16, which are assigned to the storage compartments 12, 13. The evaporator units 15,16 each have an evaporator 17,18, a fan 19,20 above the evaporator 17,18, and a temperature sensor 21,22 on top of the evaporator 17,18. Both evaporators 17, 18 are designed as vertical lamellar evaporators. Additional temperature sensors for the compartment temperatures are not shown. A control unit 24 with a display unit is located in a front strip of the refrigeration device 10 .

The storage compartment 11 is designed as a refrigerated compartment and is illuminated by a lamp 25 .

The storage compartment 12 is designed as a freezer compartment. The evaporator 18 of the freezer compartment has a defrost heater 26 on its underside. The defrost heater 26 is designed as an electric radiant heater.

A collecting channel (not shown) for collecting and discharging condensed water is arranged under each evaporator.

The control unit 24 controls a refrigerant circuit 27, of which only the evaporator units 15, 16 and pipes 28 are shown. The controller 24 controls the defrosting process of the refrigeration device 10. The refrigeration device 10 is connected to a mains voltage and the defrost heater 26 can be operated at the mains voltage. The controller 24 controls the defrost heater 26 with a pulse modulation of the mains voltage.

The invention relates to an improved defrosting process for the evaporator 18 or the evaporator unit 16 of the freezer compartment in the refrigeration device 10 .

Frost accumulates in the evaporator 18 during operation of the refrigeration device 10 . The fan 20 drives air circulation between the storage compartment 12 and the evaporator 16, the storage compartment 12 and the evaporator 16 being connected to one another by an air duct, not shown. Warm, moist air flows from below into the evaporator 18, and the moisture settles in the evaporator 18 as frost. The cold, dry air leaves the evaporator 18 at the top and is drawn in by the fan 20 and conveyed into the storage compartment 12 via the air duct.

Due to the fact that the moist air flows into the evaporator 18 from below, the lower part of the evaporator 18 usually has more frost than the upper part of the evaporator 18. The defrost heater 26 is therefore arranged near the area of the evaporator 18 with the greatest frost.

The defrost heater 26 heats the evaporator 18 during the defrosting process. In this case, the evaporator 18 is first brought to the temperature of approximately 0° C. in a first defrosting phase. If the evaporator has very little frost, a minimal amount of frost may already have melted off. In a second defrosting phase, a further supply of energy causes the frost introduced by user behavior since the last defrosting to begin to melt, and the evaporator 18 maintains the temperature of approximately 0°C.

Due to the placement of the heater on one side of the evaporator and limited heat conduction within the evaporator, the areas of the evaporator near the heater are at a slightly higher temperature than the areas of the evaporator at an end of the evaporator opposite the heater. The temperature sensor of the evaporator is located on the side of the evaporator opposite the heater and during the defrosting process initially measures rapidly rising temperatures of up to around -1 °C in the first defrosting phase. Then, in the first partial phase of the second defrosting phase, the temperature at the temperature sensor rises only very slowly to around +1 °C while the frost in the evaporator melts. At the end of the defrosting process, the frost near the temperature sensor has also melted and the temperature there then rises quickly because the heater is still in operation. The heating is switched off as soon as a predetermined temperature significantly above +1 °C is reached at the temperature sensor.

In the vicinity of the defrost heater, the temperature value 0 °C is reached first and the frost starts to melt there. There, the evaporator first becomes free of frost, with water droplets from the melted frost remaining on the evaporator surface. Further energy supplied in the vicinity of the defrost heater will quickly heat up this area since the energy supplied is no longer absorbed as heat of fusion. Due to the higher temperature, water vapor forms from the water droplets.

The water vapor can be understood as a vapor cloud, which occupies the entire already melted area of the evaporator. The cloud of steam cannot escape upwards because the water vapor condenses on the frost above and contributes to the melting of this frost. At the end of the defrosting phase, when there is only a little frost left, the vapor cloud can still escape upwards. This can happen suddenly with a subsequent uncontrolled spread of steam.

It will now be described how this effect is minimized according to the invention while keeping rapid defrosting as a secondary objective. The defrosting process is divided into phases and a minimum amount of frost is determined. The minimum amount of frost can be assumed to be zero or better determined in experiments in order to record the residual moisture that is always present in practice. However, the minimum amount of frost can also be estimated if a probable amount of frost is known, which can be determined, for example, with the number of door openings and the ambient temperature.

2 shows in diagram 30 the course of the heating power of a complete defrosting process for an actual amount of frost that is greater than the estimated probable amount of frost. The time t is plotted on the abscissa and the heating power P on the ordinate. The defrosting process begins at time t ₀ with the heating power P ₁ in the first phase, where P ₁ =P _max , the heating power P ₁ is therefore in the first phase equal to the maximum heating power P _max .

In the first defrosting phase, the evaporator is heated with the heat output P ₁ until time t ₁ has the necessary defrosting energy has been introduced, which is necessary to heat the evaporator including the minimum amount of frost to 0 ° C and to melt the minimum amount of frost. When determining time t ₁ , the current mains voltage is taken into account in order to take into account a deviation of the current mains voltage from the nominal mains voltage. Since the minimum amount of frost has now melted, there is the possibility of vapor formation from t ₁ , but vapor formation has not yet started. Taking the current mains voltage into account enables this point in time t ₁ to be determined very precisely.

The embodiment shown provides that in a second defrosting phase, further heating takes place with a lower heating power P ₂ . The second defrosting phase is divided into two partial phases. Now, the probable amount of frost is taken back to calculate a probable necessary defrosting energy equal to the heat of fusion of the probable amount of frost. The heat output P ₂₁ is used for heating in the first partial phase of the second defrosting phase until at time t ₂ the defrosting energy that is probably required has been supplied to the evaporator.

The current mains voltage is also taken into account in the first partial phase of the second defrosting phase in order to determine as precisely as possible the point in time t ₂ at which the probable amount of frost introduced since the last defrosting process has melted.

In the first partial phase of the second defrosting phase, the heating power P ₂₁ decreases uniformly, beginning with P _max at time t ₁ and ending with P _min at time t ₂ . Such a linear progression can advantageously be achieved with a pulse modulation of the heating voltage. This curve uses the knowledge of the probable amount of frost, in that at the beginning of the second partial phase, when the probability of the presence of non-melted frost is high, a high heating output is started, and with decreasing probability of the presence of non-melted frost as well which decreases the heating capacity. This procedure enables a reasonably short defrosting time.

An alternative trajectory to the steadily decreasing trajectory is a degressively decreasing trajectory with a more rapid decrease at the beginning of the second defrost phase, preferably in the case where the likely amount of frost is associated with a large uncertainty. Another alternative course is a progressively decreasing course with a faster decrease towards the end of the second defrost phase, preferably in the case where the probable amount of frost is associated with a small uncertainty. These variants take into account the fact that the uncertainty of the probable amount of frost reflects the risk of vapor formation before time t ₂ by overestimating the actual amount of frost.

The evaporator is then further heated in a second partial phase of the second defrosting phase with a heating power P ₂₂ which corresponds to a minimum heating power P _min . The minimum heating power P _min is supplied until the predetermined defrost end temperature has been reached at time t ₃ . In the second partial phase of the second defrosting phase, a further actual amount of frost that goes beyond the probable amount of frost is melted off. Since this amount of frost is not known, the minimum heating power is supplied, since the frost must always be expected to be completely defrosted, which can only be detected with the temperature sensor, the point in time t ₃ being the result. Due to the minimal heating capacity, the part of the evaporator that has already been defrosted has only a low temperature and therefore only a minimal amount of steam is formed.

The current mains voltage is also taken into account in the second partial phase of the second defrosting phase, in order to prevent an unintentionally high temperature from occurring in the already defrosted part of the evaporator when the current mains voltage is greater than the normal mains voltage.

Overall, this procedure achieves a short and reliable defrosting process. If the actual amount of frost is less than the estimated probable amount of frost, the final defrosting temperature at the temperature sensor is already reached in the course of the first partial phase of the second defrosting phase, and the defrosting is then ended.

3 FIG. 4 shows a flow chart 40 of the method according to the invention for operating the refrigeration device 10 1 with the refrigerant circuit 27, which has an evaporator 18 with an electric defrost heater 26, wherein the refrigeration device 10 is connected to a power supply system with a nominal line voltage for operation. Points in time from Diagram 30 for individual process steps are given.

The method is used to carry out a defrosting process and begins with method step a) determining a necessary defrosting energy for a first defrosting phase. Here, a defrost energy is determined, which must be used in any case, even with a minimally frosted evaporator. The necessary defrosting energy can be determined as described above, when the refrigeration device is produced, or can be determined from an estimated amount of frost during operation of the refrigeration device.

Method step b) now follows in a first defrosting phase between t ₀ and t ₁ operation of the defrost heater with a supply voltage proportional to a current mains voltage. This step serves to rapidly heat the evaporator to the point where frost introduced since the last defrost begins to melt.

In method step c), the current mains voltage is observed. This observation can take place before or during the first phase.

In method step d), a current defrosting energy supplied in the first defrosting phase is calculated using the mains voltage observed. Deviations from the nominal mains voltage are taken into account in this way.

According to method step e), the first defrosting phase ends at time t ₁ when the defrosting energy supplied has reached the necessary defrosting energy. After this process step, the evaporator is just warm enough to melt the minimum expected amount of frost.

At time t ₁ after carrying out method step e), the result has been reached that a maximum amount of energy for heating the evaporator has been supplied to the evaporator in the shortest possible time and vapor formation in the evaporator has been avoided.

4 shows a flow chart 42 with further embodiments of the method following method step e). In a further method step f) in a second defrosting phase between t ₁ and t ₂ the defrosting heater is operated with a reduced heat output in relation to the first defrosting phase. In this second defrosting phase, the accumulated frost is defrosted.

For this purpose, according to the further method step g), a probably necessary defrosting energy for the second defrosting phase can be determined. The probably required defrosting energy is determined from the probably existing amount of frost. The amount of frost that is likely to be present can already have been determined using a suitable sensor system before the defrosting process is carried out; in particular, the decision to carry out a defrosting can have been made with this amount of frost that is likely to be present.

Another embodiment of the method provides in a first partial phase of the second defrosting phase according to method step h) heating with a course of heating power, and in a second partial phase of the second defrosting phase according to method step i) heating with a predetermined minimum heating power. In the first partial phase, the expected frost is melted off, the second partial phase serves to melt off a further quantity of frost that may exceed the expected quantity of frost.

In the further method step j), the course can be determined, in particular with decreasing heating power, with the probably necessary defrosting energy for the second defrosting phase. This process step can be carried out within process step h).

At the end of the first partial phase of the second defrosting phase, the defrosting energy that is probably required for the second defrosting phase has been reached.

The heat output is determined during both sub-phases of the second defrosting phase using the mains voltage observed.

In a further method step k), the defrosting process is terminated at time t ₃ when a predetermined end of defrosting temperature is reached at the evaporator.

Reference List

10

refrigeration device

11, 12

storage compartment

13, 14

door

15, 16

evaporator units

17, 18

Evaporator

19, 20

fan

21, 22

temperature sensor

24

control unit

25

lamp

26

defrost heater

27

Refrigerant circulation

28

piping

30

diagram

P

Performance

t

Time

40, 42

flow chart

QUOTES INCLUDED IN DESCRIPTION

This list of documents cited by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent Literature Cited

• WO 2010078998 A2 [0002]
• CN 107726721A [0003]

Claims (15)

Method for operating a refrigeration device (10) with a refrigerant circuit (27) which has an evaporator (18) with an electric defrost heater (26), the refrigeration device being intended for operation on a power supply system with a nominal mains voltage, characterized by the method steps for Carrying out a defrosting process a) determining a necessary defrosting energy for a first defrosting phase; b) in a first defrosting phase, operating the defrosting heater with a supply voltage proportional to a current mains voltage; c) observing the current mains voltage; d) calculating a defrosting energy supplied in the first defrosting phase using the mains voltage observed; and e) ending the first defrosting phase when the defrosting energy supplied has reached the necessary defrosting energy. procedure after claim 1 , characterized in that the necessary defrosting energy essentially corresponds to an energy which heats the evaporator (18) to a temperature of 0 °C and melts an expected minimum amount of frost. Procedure according to one of claim 2 , characterized in that the expected minimum amount of frost is assumed to be zero, or is determined in experiments or by observing user behavior. Method according to one of the preceding claims, characterized in that the current mains voltage is determined using a number of measurements and the formation of an average value therefrom. Method according to one of the preceding claims, characterized by the further method step f) in a second defrosting phase, operating the defrosting heater with a reduced heat output in relation to the first defrosting phase. procedure after claim 5 , characterized by the further method step g) determining a probably necessary defrosting energy from an estimated amount of frost. procedure after claim 5 or 6 , characterized by the further method steps h) in a first partial phase of the second defrosting phase, heating with a course of the heating power; i) in a second partial phase of the second defrosting phase, heating with a predetermined minimum heat output. procedure after claim 7 , characterized by the further method step j) determining the course, in particular with decreasing heating power, with the defrosting energy probably required for the second defrosting phase. procedure after claim 8 , characterized in that at the end of the first sub-phase of the second defrosting phase, the probably required defrosting energy is reached. Procedure according to one of Claims 7 until 9 , characterized in that the heating power is determined during at least a partial phase of the second defrosting phase with the observed mains voltage. Procedure according to one of Claims 5 until 10 , characterized in that the heating takes place during the second defrosting phase with a pulse train. Procedure according to one of Claims 1 until 11 , characterized by the further method step k) ending the defrosting process when a predetermined final defrosting temperature is reached at the evaporator (18). Refrigeration appliance (10) with at least one storage compartment (11, 12) which is accessible through a door (13, 14), a refrigerant circuit (27) which has an evaporator (18) with an electric defrost heater (26), and a control unit (24), the refrigerating appliance (10) being intended for operation on a power supply system with a nominal supply voltage, characterized in that the control unit (24) is set up to carry out a defrosting process in such a way that a predetermined necessary defrosting energy in a first defrosting phase is taken into account a current mains voltage is introduced into the defrost heater. refrigeration device Claim 13 , characterized in that the controller is set up to carry out the defrosting process in a second defrosting phase with a reduced heat output in relation to the first defrosting phase. refrigeration device Claim 14 , characterized in that the evaporator (18) has a radiant heater (26).

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