EP2717002A1 - Method for determining thaw times - Google Patents

Abstract

The method involves providing a refrigeration unit with a refrigeration circuit flowing-through to a refrigerant with an evaporator, which is provided in a heat exchange relationship with the ambient air. The ambient air temperature (12) and the evaporation temperature (14) of the refrigerant are determined in the evaporator. The defrosting time (30) is determined in response to a temperature difference between the ambient air temperature and the evaporation temperature. A ventilator is provided with a rotational speed (20), which supplies ambient air to the evaporator. An independent claim is included for a refrigerator, particularly for a heat pump with a control unit.

Description

The present invention relates to a method for determining defrosting times for a refrigerating machine, in particular for a heat pump, wherein the refrigerating machine comprises a refrigerant circuit through which refrigerant flows with at least one evaporator, which is in heat exchange relationship with ambient air.

Refrigerators make it possible to extract heat from a first medium, such as air, and to supply this heat to a second medium. In particular, heat pumps are used to extract heat energy by means of an evaporator of the ambient air, the heat energy is used for example as heating energy. The ambient air is passed through an evaporator of the heat pump, wherein refrigerant is evaporated in the evaporator, thereby extracting energy from the ambient air.

Due to the energy withdrawal, the ambient air cools down, which can lead to the formation of ice on the evaporator, especially when cooled below 0 ° C. Such ice formation is undesirable because the evaporator is isolated from the ambient air by the ice and thus hinders the transfer of heat from the ambient air to the refrigerant.

In conventional heat pumps, therefore, a defrost is cyclically performed by the refrigeration cycle is operated inversely and Heat is thus supplied to the evaporator. Disadvantageously, each defrosting process degrades the energy balance of the heat pump because, on the one hand, energy is needed for the defrosting process itself and, on the other hand, during the defrosting process, no heat energy can be recovered from the ambient air.

To save unnecessary defrosting, known heat pumps use, for example, light sensors, air differential pressure measurements or structure-borne noise measurements to detect ice on the evaporator. However, the known methods for ice detection and thus the definition of defrosting times are complex and complex to carry out.

It is therefore an object of the invention to provide a method for determining defrosting times, which permits the simplest possible determination of the defrosting time.

This object is achieved by a method according to claim 1 and in particular by the fact that the temperature of the ambient air and the evaporation temperature of the refrigerant are determined in the evaporator and the defrosting times are determined in dependence on a difference between the temperature of the ambient air and the evaporation temperature.

The invention is therefore based on the idea of using the temperature difference between the ambient air and evaporation temperature of the refrigerant to detect whether ice has formed on the evaporator. In the ice-free state of the evaporator, the evaporation temperature of the refrigerant, which is also referred to as the saturation temperature, can approach the temperature of the ambient air theoretically. This is why possible because a very good heat transfer between ambient air and refrigerant through the ice-free evaporator is possible. If ice forms on the evaporator, the heat transfer from the ambient air to the refrigerant becomes more and more difficult as the thickness of the ice layer increases. Consequently, less heat can be transferred to the refrigerant than in the ice-free state. Accordingly, the pressure in the evaporator and thus the evaporation temperature of the refrigerant decreases. Due to the lowered evaporation temperature, the difference between the temperature of the ambient air and the evaporation temperature becomes greater. The greater the temperature difference, the sooner it can be assumed that ice formation on the evaporator.

The method according to the invention makes it possible to detect ice on the evaporator and to determine defrosting times for the refrigerating machine in dependence on parameters that have been recorded in any case, namely the evaporation temperature of the refrigerant and the temperature of the ambient air. The inventive method is thus easy and inexpensive to implement and perform. In addition, a control unit for carrying out the method according to the invention can be retrofitted with little effort in existing refrigerating machines.

Advantageous embodiments of the invention are described in the description, the subclaims and the drawings.

According to a first embodiment, one of the rotational speed of a fan, which supplies ambient air to the evaporator, and dependent on the evaporator power first correction value is determined and added to the temperature difference.

Typically, the evaporator performance is increased by the use of a fan by the fan increases the flow rate of ambient air through the evaporator. In particular, the speed of the fan is increased with incipient icing. The detection of ice on the evaporator, and thus the determination of the defrosting times can be affected by the varying speeds of the fan, which is why the difference is added to the first correction value, which takes into account the varying speeds of the fan. The speed of the fan is usually greater when low ambient air temperatures are detected.

Preferably, the higher the rotational speed of the fan and the evaporator output, the greater the first correction value is selected. The first correction value may, for example, be in a range from 0 K to 3 K. The first correction value is advantageously determined specifically for each refrigerating machine or each series of refrigerating machines and can be stored, for example in the form of a look-up table, in a control unit of the refrigerating machine.

Advantageously, a second correction value dependent on the overheating of the refrigerant in the evaporator is determined and added to the temperature difference. By overheating a complete evaporation of the refrigerant is ensured in the evaporator, with a usual overheating, for example, between 0 K and 10 K. The higher the overheating, the more additional heat energy is removed from the ambient air, which may increase the likelihood of ice formation on the evaporator. This increased risk of icing is taken into account by the second correction value.

The second correction value can be greater, the greater the overheating of the refrigerant. Advantageously, a function of the second correction value in a predetermined range of overheating, for example between 6 K and 10 K, has a predetermined slope, e.g. a slope of 1. In the remaining areas, however, the function can be constant. The second correction value can be determined specifically for a specific chiller or a series of chillers.

According to a second embodiment, one of the rotational speed of a fan, which supplies ambient air to the evaporator, and dependent on the evaporator power first correction value is determined and subtracted from the temperature difference.

Furthermore, a second correction value which is dependent on the overheating of the refrigerant in the evaporator can also be determined and subtracted from the temperature difference.

In addition, a dependent on the evaporator power third correction value can be determined and subtracted from the temperature difference. A function describing the dependence of the third correction value on the evaporator output is advantageously stored in the chiller.

In both embodiments, a defrost timing may be present when the temperature difference or a difference corrected by at least one correction value exceeds a threshold. Thus, both the temperature difference, which is determined from the evaporation temperature and the temperature of the ambient air, and a difference corrected by one or more correction values can be used to define defrosting times to determine. Since the temperature difference is greater, the greater the thermal resistance of the evaporator, it can be assumed that the temperature difference of more insulating ice on the evaporator becomes larger. The threshold value may be selected depending on whether the correction values have been subtracted from the temperature difference or added to the temperature difference.

Simply, the threshold is an absolute temperature value. The threshold value can be specified, for example, in Kelvin or degrees Celsius, and in the case of the addition of correction values, for example, in a range from 5 K to 20 K. In the case of subtraction, for example, a defrost time may be present when the temperature difference minus the correction values exceeds 7K.

Alternatively, the threshold may be a time-dependent threshold. That is, the threshold may change over the operating time of the chiller, for example, and a function may be used for the threshold describing the time dependency. If defrosting is performed, the function can be reset. The time-dependent course can be determined empirically, for example. Alternatively, for example, the threshold may decrease linearly over time, which may force a defrost operation after a certain amount of time has elapsed.

According to a further embodiment, the threshold value is determined as a function of a difference minimum, which is achieved with an ice-free evaporator. For this purpose, the temperature difference is determined at which under normal operating conditions no ice still deposits on the evaporator. The temperature difference minimum may additionally be time-dependent, ie over the operating time of the chiller vary. The operating time of the chiller is reset at initial startup and after each defrost cycle.

Thus, a defrosting instant may be present when a determined temperature difference or a difference corrected by at least one correction value exceeds a respective difference minimum, which was determined in a predetermined time interval, by a predetermined threshold value. For this purpose, the temperature difference or the corrected difference is continuously monitored over a predetermined period of time and the minimum value is stored in each case. If the temperature difference or the corrected difference exceeds the respective minimum by the predetermined threshold value, for example 5 K, a defrosting time is present.

According to a further embodiment, the defrost times are additionally determined by an expiration timer. Thus, a defrosting operation is performed at fixed intervals regardless of the temperature difference or a threshold value. Thus, it is additionally ensured by a separate mechanism that the efficient heat exchange at the evaporator is not hindered by ice.

Preferably, an expiration time of the drain timer at ambient air temperatures in a predetermined range around 0 ° C, in particular in the range of -4 ° C to + 4 ° C and preferably between -20 ° C and + 10 ° C, shortened and at temperatures over a predetermined threshold, for example, + 10 ° C, extended. The drain timer can thus be adapted to the temperature of the ambient air and thus to varying operating conditions. In particular, in the area around 0 ° C is in the ambient air, a relatively high moisture content, which occurs when cooling the ambient air in the evaporator as ice on the evaporator precipitates. As a result, the evaporator freezes very quickly around 0 ° C, which is why the expiry time of the drainage timer in this area is shortened.

If the temperature of the ambient air falls below -20 ° C, only a small amount of moisture is contained in the ambient air, so that no rapid icing of the evaporator is to be expected. Below -20 ° C, the expiry time of the drain timer is therefore not extended.

Above + 10 ° C, cooling the ambient air in the evaporator to temperatures below 0 ° C is very unlikely, which is why icing of the evaporator at temperatures above + 10 ° C is also very unlikely. Thus, at ambient temperatures above + 10 ° C, the expiry time of the drain timer can be extended.

Defrosting can also be completely suppressed if the ambient air temperature exceeds + 15 ° C or if the evaporative temperature of the refrigerant is greater than 0 ° C. In both cases, no ice can precipitate on the evaporator, which is why no defrosting is necessary.

Advantageously, the expiration timer is reset if there is a defrost time. It is irrelevant whether the defrosting time was triggered by exceeding a threshold value, by expiry of the expiry timer or in another way. An unnecessary triggering of defrosting is thus prevented.

The defrost times are preferably additionally determined by a low-pressure alarm. A low pressure alarm is triggered when the evaporator performance decreases so much that in the evaporator only still a very small amount of refrigerant can be evaporated, the flow of refrigerant is throttled accordingly and the pressure in the evaporator drops sharply. A possible reason for such a low evaporator performance may be icing of the evaporator, which is why the evaporator is preemptively de-iced in a low pressure alarm. The low pressure alarm also determines a defrost time.

The invention further relates to a refrigerating machine, in particular a heat pump, comprising a refrigerant circuit through which refrigerant flows with at least one evaporator, which is in heat exchange relationship with ambient air, and a control unit, wherein the control unit with a temperature sensor for detecting the temperature of the ambient air and a pressure sensor for detecting the pressure of the refrigerant is connected in the evaporator. The control unit is designed to determine the evaporation temperature of the refrigerant in the evaporator and to determine defrosting in dependence on a difference between the temperature of the ambient air and the evaporation temperature.

Fig. 1

eine schematische Darstellung einer ersten Ausführungsform eines erfindungsgemäßen Verfahrens zur Bestimmung eines Abtauzeitpunkts;

Fig. 2

eine Abhängigkeit eines ersten Korrekturwerts von einer Verdampferleistung und einer Drehzahl eines Ventilators;

Fig. 3

eine Abhängigkeit der Drehzahl des Ventilators von einer Temperatur der Umgebungsluft;

Fig. 4

einen zweiten Korrekturwert in Abhängigkeit von einer Überhitzung in dem Verdampfer;

Fig. 5

eine Verlängerung oder Verkürzung einer Ablaufzeit eines Ablauftimers in Abhängigkeit von der Temperatur der Umgebungsluft;

Fig. 6

eine schematische Darstellung einer zweiten Ausführungsform eines erfindungsgemäßen Verfahrens zur Bestimmung eines Abtauzeitpunkts; und

Fig. 7

eine Abhängigkeit eines dritten Korrekturwerts von einer Verdampferleistung.

The invention will now be described purely by way of example with reference to possible embodiments with reference to the accompanying drawings. Show it:

Fig. 1

a schematic representation of a first embodiment of a method according to the invention for determining a defrost time;

Fig. 2

a dependence of a first correction value on an evaporator output and a rotational speed of a fan;

Fig. 3

a dependence of the speed of the fan on a temperature of the ambient air;

Fig. 4

a second correction value in response to overheating in the evaporator;

Fig. 5

an extension or shortening of an expiry time of a drain timer as a function of the temperature of the ambient air;

Fig. 6

a schematic representation of a second embodiment of a method according to the invention for determining a defrost time; and

Fig. 7

a dependence of a third correction value on an evaporator power.

Fig. 1 1 shows an exemplary sequence of a first embodiment of a method for determining defrost times for a heat pump, which has a cooling circuit through which refrigerant flows, in which a compressor, a condenser, an expansion valve and an evaporator are arranged in succession. According to the invention, a temperature 12 of the ambient air and an evaporation temperature 14 of the refrigerant are first detected. Subsequently, a temperature difference Δ between the temperature 12 of the ambient air and the evaporation temperature 14 of the refrigerant is determined in a subtractor 10. The evaporation temperature 14 is determined by a control unit (not shown) from a pressure P _{evaporator of} the refrigerant in the evaporator calculated. For this purpose, the phase transition diagram of the refrigerant is stored in the control unit.

wobei $${\mathrm{T}}_{\mathrm{Verdampf}}=\mathrm{f}\left({\mathrm{P}}_{\mathrm{Verdampf}}\right)$$

ist. Die ermittelte Temperaturdifferenz Δ wird von dem Subtrahierer 10 an einen Normalisierer 16 weitergegeben, wobei der Normalisierer 16 neben der ermittelten Temperaturdifferenz Δ noch eine Verdampferleistung 18, die Drehzahl 20 eines dem Verdampfer zugeordneten Ventilators (nicht gezeigt) sowie die Überhitzung 22 des den Verdampfer durchströmenden Kältemittels berücksichtigt. Genauer gesagt addiert der Normalisierer 16 abhängig von der Drehzahl 20 des Ventilators und der Verdampferleistung 18 zu der Temperaturdifferenz Δ noch einen ersten Korrekturwert Δ_{Korrektur_Fan} hinzu. Weiterhin wird zu der Temperaturdifferenz Δ ein von der Überhitzung des Kältemittels abhängiger zweiter Korrekturwert Δ_{Korrektur_ÜH} hinzuaddiert. In dem Normalisierer 16 sind dazu die in Fig. 2 und Fig. 4 dargestellten Referenzkurven gespeichert.The subtracter 10 forms the temperature difference Δ between the ambient air temperature 12 and the evaporating temperature 14 according to the formula $$\mathrm{\Delta }={\mathrm{T}}_{\mathrm{Surroundings}}-{\mathrm{T}}_{\mathrm{Verbampf}}$$

in which $${\mathrm{T}}_{\mathrm{evaporator}}=\mathrm{f}\left({\mathrm{P}}_{\mathrm{evaporator}}\right)$$

is. The determined temperature difference Δ is forwarded by the subtractor 10 to a normalizer 16, wherein the normalizer 16 in addition to the determined temperature difference Δ still an evaporator capacity 18, the speed 20 of the evaporator associated fan (not shown) and the superheating 22 of the refrigerant flowing through the evaporator considered. More specifically, the normalizer 16 adds, depending on the speed 20 of the fan and the evaporator power 18, to the temperature difference Δ nor a first correction value Δ _{Korrektur_Fan} . Furthermore, a second correction value Δ _{Korrektur_ÜH, which is} dependent on the overheating of the refrigerant, is added to the temperature difference Δ. In the normalizer 16, the in Fig. 2 and Fig. 4 stored reference curves stored.

Fig. 2 Graphically shows the relationship between the evaporator power 18, which is plotted on the X-axis, and the first correction value Δ _{Korrektur_Fan} , which is plotted on the Y-axis. In Fig. 2 is a Functional set 24 shown, which includes several functions for different speeds 20 of the fan. Thus, for example, the graph 26a describes the relationship between the evaporator power 18 and the first correction value Δ _{Korrektur_Fan} at a speed of the fan of 50% of the maximum speed (FS = speed of the fan). A graph 26b shows the same relationship at a speed 20 of 60% of the maximum speed.

Generally, the rotational speed 20 is determined according to the in Fig. 3 controlled relationship, wherein on the X-axis, the temperature 12 of the ambient air and the Y-axis, the rotational speed 20 of the fan are plotted. It can be seen that the speed is increased at temperatures below 2 ° C in order to supply more heat energy to the evaporator. Above about 2 ° C, the fan is operated at a speed 20 of 50% of the maximum speed.

The normalizer 16 can thus the first correction value Δ _{Korrektur_Fan} from the evaporator power 18 and the speed 20 of the fan with the aid of in Fig. 2 determine graphs 26 shown.

The second correction value Δ _{Korrektur_ÜH is} determined by the normalizer 16 from the in Fig. 4 shown diagram in which the second correction value Δ _{Korrektur_ÜH} is plotted against the superheat 22 of the refrigerant in the evaporator. In the event of overheating 22 of less than 6 K, the second correction value Δ _{Korrektur_ÜH is} constant -2 K. Between 6 K and 10 K, the second correction value Δ _{Korrektur_ÜH increases} linearly from -2 K to + 2 K. Above 10 K overheating 22, the second correction value Δ _{Korrektur_ÜH is} constant +2 K.

It is understood that in Fig. 2 to 4 numerical values shown are merely exemplary in nature and may vary from chiller to chiller.

After the normalizer 16 has determined the first correction value Δ _{Korrektur_ÜH} and the second correction value Δ _{Korrektur_ÜH} , the normalizer 16 calculates, as in FIG Fig. 1 shown a corrected difference Δ _Korr according to the formula $${\mathrm{\Delta }}_{\mathrm{corr}}=\mathrm{\Delta }+{\mathrm{\Delta }}_{\mathrm{Korrektur\_Fan}}+{\mathrm{\Delta }}_{\mathrm{Korrektur\_ÜH}}\mathrm{,}$$

The corrected difference Δ _Korr is then passed to an estimator 28, which compares the corrected difference Δ _Korr with a time-dependent threshold, which may be between 5 K and 20 K, for example. If the corrected difference Δ _{Korr is} greater than the currently valid threshold, there is a defrost time 30 which is signaled and triggers a defrost operation.

However, the estimator 28 determines the defrost time 30 not only based on the corrected difference _ΔCorr and the threshold, but also in response to a low pressure alarm 32 which is triggered when the pressure in the evaporator falls below a predetermined threshold. If a low pressure alarm 32 is signaled to the estimator 28, a defrost time 30 is immediately output.

The estimator 28 further includes an internal expiration timer 34, at the expiration of which a defrost time 30 is issued. An expiration time of the expiry timer 34 is determined according to the in Fig. 5 shown function of the temperature 12 of the ambient air by an adjustment value 36, which can shorten the expiration time of the drain timer 34 by a maximum of one hour or by two hours.

The estimator 28 is also supplied with the temperature 12 of the ambient air and the evaporation temperature 14 of the coolant, wherein the estimator 28 does not output defrosting times 30 when the ambient air temperature 12 is above + 15 ° C or the evaporation temperature 14 is above 0 ° C.

When a defrost time 30 is signaled by the estimator 28, the heat pump's refrigeration cycle is reversed, which generates heat at the evaporator and melts the ice present on the evaporator. Subsequently, the refrigeration cycle is again operated in the "normal" flow direction, and the determination of the next defrost time 30 begins.

A second embodiment of the method according to the invention is in Fig. 6 shown schematically. The second embodiment is substantially different from the first embodiment in that the temperature difference Δ in the normalizer 16 of the second embodiment is reduced by the subtraction of correction values.

Identical to the first embodiment of Fig. 1 is also in the second embodiment of Fig. 6 determined by the subtractor 10, the temperature difference Δ from the temperature 12 of the ambient air and the evaporation temperature 14. Also, the normalizer 16, the evaporator power 18, the speed 20 of the fan and the superheating 22 of the refrigerant are provided in the evaporator.

Unlike the first embodiment, in the second embodiment, a third, dependent on the evaporator power 18 correction value Δ _{Korrektur_VL} determined by means of a first logic unit 38a in addition. For this purpose, a function is stored in the logic unit 38a, which in Fig. 7 is shown and shows the relationship between evaporator power 18 and the third correction value Δ _{Korrektur_VL} . The third correction value Δ _{Korrektur_VL} is greater, the higher the evaporator power 18.

Both the third correction value Δ _{Korrektur_VL} and the overheating 22 are generated by a second logic unit 38b (FIG. Fig. 6 ) processed. As in the first embodiment, the second logic unit 38b determines from the overheating 22 a second correction value Δ _{Korrektur_ÜH} and adds this to the third correction value Δ _{Korrektur_VL} . The result of the addition is output as an intermediate result Δ _intermediate .

The intermediate result Δ _between and the rotational speed 20 are supplied to a third logic unit 38c, which, as in the first embodiment, determines a first correction value Δ _{Korrektur_Fan} from the rotational speed 20 and the evaporator power 18 and adds it to Δ _Zwischen . As a result, the third logic unit 38c _outputs a correction term Δ _Korr2 , which is calculated according to the following formula: $${\mathrm{\Delta }}_{\mathrm{corr}2}={\mathrm{\Delta }}_{\mathrm{Korrektur\_Fan}}+{\mathrm{\Delta }}_{\mathrm{Korrektur\_ÜH}}+{\mathrm{\Delta }}_{\mathrm{Korrektur\_VL}}$$

The correction term Δ _Korr2 is subtracted from the temperature difference Δ by means of a detection unit 40, the result of the subtraction representing a _trigger difference Δ _trigger : $${\mathrm{\Delta }}_{\mathrm{trigger}}=\mathrm{\Delta }-{\mathrm{\Delta }}_{\mathrm{corr}\mathrm{2}}$$

_During operation, the detection unit 40 also continuously stores a minimum _{trigger difference} Δ _{Trigger_min} , which is replaced by a new minimum _{trigger difference} Δ _{Trigger_min} as soon as a new _{trigger difference} Δ _{Trigger is} below the previous minimum _{trigger difference} Δ _{Trigger_min} .

oder wenn die Triggerdifferenz Δ_Trigger die minimale Triggerdifferenz Δ_{Trigger_min} um einen vorbestimmten Betrag übersteigt. Beispielsweise wird ein Abtausignal 42 ausgegeben, wenn $${\mathrm{\Delta }}_{\mathrm{Trigger}}-{\mathrm{\Delta }}_{\mathrm{Trigger\_min}}>5K$$

ist. Das Abtausignal 42 wird einem Schätzer 44 zugeleitet, der ähnlich wie bei der ersten Ausführungsform anhand der Temperatur 12 der Umgebungsluft und der Verdampfungstemperatur 14 überprüft, ob ein Abtauvorgang durchgeführt werden soll. Dies bedeutet, der Schätzer 44 überprüft, ob die Temperatur 12 der Umgebungsluft über +15°C oder die Verdampfungstemperatur 14 über 0°C liegt. Ist dies der Fall, wird das Abtausignal 42 verworfen. Andernfalls wird ein Abtauzeitpunkt 30 signalisiert. Zusätzlich überprüft der Schätzer 44 wie bei der ersten Ausführungsform, ob ein Abtauzeitpunkt 30 wegen eines abgelaufenen Ablauftimers 34 oder wegen eines Niederdruckalarms 32 signalisiert werden muss.The detection unit 40 outputs a defrost signal 42 when either the _trigger difference Δ _trigger exceeds a predetermined absolute threshold, that is, for example $${\mathrm{\Delta }}_{\mathrm{trigger}}>7K.$$

or when the _{trigger difference} Δ _trigger exceeds the minimum _{trigger difference} Δ _{Trigger_min} by a predetermined amount. For example, a defrost signal 42 is output when $${\mathrm{\Delta }}_{\mathrm{trigger}}-{\mathrm{\Delta }}_{\mathrm{Trigger\_min}}>5K$$

is. The defrost signal 42 is fed to an estimator 44 which, similarly as in the first embodiment, checks whether a defrosting operation is to be performed based on the ambient air temperature 12 and the evaporating temperature 14. This means that the estimator 44 checks whether the temperature 12 of the ambient air is above + 15 ° C. or the evaporation temperature 14 is above 0 ° C. If so, defrost signal 42 is discarded. Otherwise, a defrost time 30 is signaled. In addition, the estimator 44 checks, as in the first embodiment, whether a defrost time 30 must be signaled because of an expired timer 34 or because of a low pressure alarm 32.

LIST OF REFERENCE NUMBERS

10

subtractor

12

temperature

14

Evaporation temperature

16

normalizer

18

evaporator capacity

20

number of revolutions

22

overheating

24

family of functions

26a, 26b

graph

28

valuer

30

defrost time

32

Low pressure alarm

34

countdown timer

36

adjustment value

38a, 38b, 38c

logic unit

40

detection unit

42

defrost

44

valuer

Δ

temperature difference

Δ _corr

corrected difference

Δ _Corr2

correction term

Δ _trigger

trigger difference

Δ _{correction_fan}

First correction value

Δ _{Correction_ÜH}

Second correction value

Δ _{correction_VL}

Third correction value

Claims (14)

Method for determining defrosting times (30) for a refrigerating machine, in particular for a heat pump, the refrigerating machine comprising a refrigerant circuit through which refrigerant flows, with at least one evaporator which is in heat exchange relationship with ambient air,
characterized in that the temperature of the ambient air (12) and the evaporation temperature (14) of the refrigerant in the evaporator are determined and the defrost times (30) in dependence on a temperature difference (Δ) between the temperature of the ambient air (12) and the evaporation temperature ( 14). Method according to claim 1,
characterized in that one of the rotational speed (20) of a fan which supplies the evaporator ambient air, and the evaporator power (18) dependent first correction value (Δ _{Korrektur_Fan} ) is determined and added to the temperature difference (Δ). Method according to one of the preceding claims,
characterized in that a second correction value (Δ _{Korrektur_ÜH} ) dependent on the overheating (22) of the refrigerant in the evaporator is determined and added to the temperature difference (Δ). Method according to claim 3,
characterized in that a function of the second correction value (Δ _{Korrektur_ÜH} ) in a predetermined range of superheating (22), for example between 6 K and 10 K, has a predetermined slope, preferably a slope of 1, and constant in other areas. Method according to claim 1,
characterized in that one of the rotational speed (20) of a fan, which supplies the evaporator ambient air, and the evaporator power (18) dependent first correction value (Δ _{Korrektur_Fan} ) is determined and subtracted from the temperature difference (Δ). Method according to claim 5,
characterized in that one of the superheating (22) of the refrigerant in the evaporator dependent second correction value (Δ _{Korrektur_ÜH} ) is determined and subtracted from the temperature difference (Δ). Method according to claim 5 or 6,
characterized in that a dependent of the evaporator power (18) dependent third correction value (Δ _{Korrektur_VL} ) and is subtracted from the temperature difference (Δ). Method according to one of the preceding claims,
characterized in that there is a defrosting time when the temperature difference (Δ) or a difference (Δ _Korr , Δ _trigger ) corrected by at least one correction value exceeds a threshold value. Method according to claim 8,
characterized in that the threshold value is an absolute temperature value or a time-dependent threshold value and / or
the threshold is determined as a function of a minimum of the temperature difference that is achieved in an ice-free evaporator. Method according to one of the preceding claims,
characterized in that a defrosting is present when the temperature difference (Δ) or a corrected by at least one correction value difference (Δ _Korr , Δ _trigger ) exceeds a respective difference minimum, which was determined in a predetermined time interval by a predetermined threshold. Method according to one of the preceding claims,
characterized in that the defrost times are additionally determined by an expiration timer, and in particular the expiry timer is reset when a defrost time (30) is present. Method according to claim 11,
characterized in that an expiration time of the drain timer at ambient air temperatures (12) in a predetermined range around 0 ° C, in particular in the range of -4 ° C to + 4 ° C, preferably between -20 ° C and + 10 ° C. , is shortened and extended at temperatures (12) above a predetermined threshold, for example + 10 ° C. Method according to one of the preceding claims,
characterized in that the defrosting times (30) are additionally determined by a low pressure alarm (32). Refrigerating machine, in particular heat pump, comprising a refrigerant circuit through which refrigerant flows with at least one evaporator, which is in heat exchange relationship with ambient air, and a control unit,
characterized in that
the control unit is connected to a temperature sensor for detecting the temperature of the ambient air (12) and a pressure sensor for detecting the pressure of the refrigerant in the evaporator, wherein the control unit is adapted to determine the evaporation temperature (14) of the refrigerant in the evaporator and in Dependence on a difference (Δ) between the temperature of the ambient air (12) and the evaporation temperature (14) to determine defrosting times (30).

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