EP1508007B1 - Freezer comprising a defrost function and operating method therefor - Google Patents

Abstract

A freezer includes a refrigeration surface that can be frozen, such as an evaporator surface, a heating device for heating the refrigeration surface, and a control circuit for controlling the operation of the heating device in accordance with a timer. The control circuit is configured to block the operation of the heating device for a time period that is defined by the timer. The timer is used to ensure that the refrigeration surface is only heated to defrost the freezer, if the refrigeration power requirement of the latter is low.

Description

The present invention relates to a freezer having a cooling surface on which an ice sheet can be formed in the course of operation of the freezer, and a heater for heating the cooling surface and thereby defrosting such an ice sheet.

Conventional freezers of this type, also referred to as frost-free devices, have a control device for controlling the operation of the heater, which automatically puts the heater into operation when detected by means of a timer runtime of the device or a compressor of the device a predetermined limit exceeds. In this way it is ensured that the cooling surface is defrosted from time to time even without the active intervention of a user, so that it can not form a layer of ice on it in a thickness that significantly affects the energy efficiency of the device.

document US 5,806,321 A1 describes a refrigeration system in which each time interval is determined after the next defrost is considered necessary. Depending on the operating parameters, the next defrost may be a partial or complete defrost. If the defrost is deemed necessary, it will definitely be done, the heater will be put into operation.

A problem with this technique is that it is unable to take into account whether refrigerated goods may have been freshly stored in the freezer shortly before initiating a defrosting process. If this is the case, such refrigerated goods should be frozen as quickly as possible, for which a high cooling capacity is required. However, automatic defrosting of the cooling surface at such a time causes freezing to take a long time, and in unfavorable circumstances could even cause the refrigerated goods already stored in the freezer to become so hot from the newly stored one, that this stored goods antaut.

Another disadvantage of this technique is that it is associated with relatively high energy costs because the increased power requirements of the freezer associated with defrosting can occur at any time of the day.

From the document US 3,164,969 is an air conditioner - but not a freezer - known, in which it comes to that a heat pump defrost control device is controlled by a timer in operation. By this timer, only the service life of the air conditioner is detected. After a cumulatively detected period of time by the relevant timer, the mentioned defrost control device is put into operation.

From the documents US 2,703,481 and US 1,979,103 refrigerators are known in which an automatic defrosting is done by initiating a defrost period at certain time intervals. Thus, a defrosting operation is performed only after a lapse of a certain period of time.

document US 2001/0002540 describes a vending machine with a dedustable cooling area in which a time interval is determined after the respective temperature change is determined. If this temperature change shows a completely abnormal behavior, a troubleshooting of the device is initiated. However, if the temperature change is in the normal range, then a dependent of the temperature change duration of the defrosting is determined. Once the need for defrosting has been determined and the duration of the defrosting operation is determined, defrosting is performed.

The object of the present invention is to provide a freezer and a method of operation for ensuring at any time a quick freezing newly stored refrigerated goods and also make it possible to minimize the energy costs associated with the operation of such a device.

The object is solved by the independent claims 1 and 15.

This freezer, however, need not necessarily be an automatic defrosting freezer; the timer according to the invention does not necessarily serve as in the conventional frost-free devices to trigger a defrosting after a certain time, but, on the contrary, to prevent this at certain, unfavorable times. The times when defrosting is considered necessary can be determined both automatically and by a user according to the present invention, as will be explained in more detail below.

According to a preferred embodiment of the freezer according to the invention, the time interval defined by the timer is a time interval, preferably one that lasts from 9:00 to 22:00, preferably at least from 1:00 to 5:00. This time interval setting is based on the assumption that at night, especially between 10:00 pm and 9:00 am, the likelihood of refrigerated goods being reloaded into the freezer is low because most users are shopping at an earlier time of day. The extension of the time interval in which the operation of the heater is locked at 5:00 clock the one day to 1:00 clock the next day, also has the advantage that in the then still available for defrosting period inexpensive night stream can be used for the defrosting process.

Preferably, the freezer according to the invention also uses low-cost night-time electricity in that - provided no defrosting takes place - the cooling surface operates at a higher cooling capacity in the defrosting period than during the blocked time interval. Thus, during normal operation of the freezer, energy demand is also shifted from the blocked time interval to the period in which defrosting is permitted and in which the cost of electrical energy is less than in the locked time interval.

According to an alternative embodiment of the invention, the timer is coupled to a sensor for detecting the opening of a door of the freezer, and the time interval set by the timer is a time interval from when the door is open. The effect of this embodiment is comparable to that described above. By the defrosting is blocked for the specified time interval in each case following the opening of the door, on the one hand it is achieved that newly stored refrigerated goods can be rapidly frozen during this time interval without the freezing process being interrupted or delayed by defrosting. The likelihood that the door of the freezer will remain closed for a long time interval on the order of several hours is, of course, higher at night than during the day, so that the freezer according to this alternative will defrost at a correspondingly high probability at night.

The timer for the control circuit can be constructed differently. First, it may be an autonomous timer that receives no external control signals. In particular, such a timer may include an oscillator for high accuracy accuracy at low cost, especially a quartz oscillator.

As a non-autonomous timer in particular a radio receiver for the reception of a radio time standard comes into consideration.

Of course, if the freezer is designed for operation in a data network, the interface to such a network can also be used to receive a time signal which is transmitted or interrogated on the network and to make it available to the control circuit.

A preferred application of the invention are devices such as the already mentioned frost-free devices, in which the control circuit is designed to detect at least one operating parameter of the freezer correlated with the degree of icing of the cooling surface and to put the heating device into operation outside the specified time interval if the at least one monitored operating parameter has exceeded a limit value.

Preferred examples of such operating parameters are the total time elapsed since the last operating phase of the heating device or the operating time of a compressor of the freezer which has since passed.

One parameter that does not require cumulative detection in contrast to the above two is the ratio of operating time to service life of a compressor of the freezer.

Another suitable parameter is the number of door openings counted since the last operating phase of the heater.

According to another, simpler embodiment of the invention, the control circuit is assigned an operating element for inputting a command for starting up the heating device. This control allows the user to enter a command to start up the heater at any time, if he determines that defrosting makes sense, especially if he has opened the door and thus recognized the need for defrosting. The blocking according to the invention prevents the defrosting process from being carried out at an unfavorable time.

Of course, such an operating element can also be provided in addition to a freezer with automatic defrosting.

1. a) Festlegen eines Sperrzeitintervalls, in welchem die Kühloberfläche nicht abgetaut werden darf,
2. b) Erfassen der Notwendigkeit, die Kühloberfläche abzutauen,
3. c) wenn der Zeitpunkt der Abtaunotwendigkeit in dem Sperrzeitintervall liegt, Abwarten des Endes des Sperrzeitintervalls, und nach Ablauf des Sperrzeitintervalls: Betreiben der Heizeinrichtung.

In the method according to the invention for controlling a freezer with an icing-capable cooling surface and a heating device for heating the cooling surface, the following steps are carried out:

1. a) setting a blocking time interval in which the cooling surface must not be defrosted,
2. b) detecting the need to defrost the cooling surface,
3. c) if the time of defrost need is in the lock time interval, waiting for the end of the lock time interval, and after expiration of the lock time interval: operating the heater.

Fig. 1

einen schematischen Schnitt durch ein Gefriergerät, an dem die vorliegende Erfin- dung anwendbar ist;

Fig. 2

ein Blockdiagramm einer ersten Ausgestaltung einer Steueranordnung für das Käl- tegerät;

Fig. 3

ein Flussdiagramm eines Arbeitsverfahrens für die Steueranordnung aus Fig. 2;

Fig. 4

ein Blockdiagramm einer zweiten Ausgestaltung der Steueranordnung;

Fig. 5

ein Flußdiagramm eines Arbeitsverfahrens für die Steueranordnung aus Fig. 4;

Fig. 6

eine Abwandlung des Steuerverfahrens aus Fig. 5;

Fig. 7

eine dritte Ausgestaltung einer Steueranordnung gemäß der Erfindung; und

Fig. 8

ein Flussdiagramm eines Arbeitsverfahrens für die Steueranordnung aus Fig. 7.

Further features and advantages of the invention will become apparent from the following description of exemplary embodiment with reference to the accompanying figures. Show it:

Fig. 1

a schematic section through a freezer to which the present invention is applicable;

Fig. 2

a block diagram of a first embodiment of a control device for the Käl- tegerät;

Fig. 3

a flowchart of a working method for the control arrangement Fig. 2 ;

Fig. 4

a block diagram of a second embodiment of the control arrangement;

Fig. 5

a flowchart of a working method for the control arrangement Fig. 4 ;

Fig. 6

a modification of the tax procedure Fig. 5 ;

Fig. 7

a third embodiment of a control arrangement according to the invention; and

Fig. 8

a flowchart of a working method for the control arrangement Fig. 7 ,

The construction of in Fig. 1 shown refrigerator is essentially known and will therefore be outlined only briefly.

A heat-insulating housing 1 and a similar door 2 define a freezer compartment 3 inside the housing 1. A wall 4 separates from the freezer compartment 3 from a chamber 5, at the rear wall serving as a cooling surface evaporator 6 is arranged. The evaporator 6 is part of a refrigerant circuit, together with a compressor 7 and a condenser 8. A fan 9 is arranged in a passage opening of the partition 4, to effect an air circulation between the freezer compartment 3 and the chamber 5.

Under normal operating conditions, the evaporator 6 is at temperatures below zero degrees Celsius. Moisture from the freezer compartment 3 in the chamber 5 circulated air condenses on the surface of the evaporator 6 and forms on this after prolonged use of an ice layer. In order to defrost this ice layer, a heater 10 is disposed in the chamber 5.

The invention is also applicable to freezers in which the evaporator 6 is not housed in a separate chamber, but is in direct thermal contact with the freezer compartment 3.

Fig. 2 shows a first embodiment of a control arrangement for the refrigeration device Fig. 1 , The control arrangement comprises a control circuit 11, for example a microprocessor or microcontroller, which is connected to an operating element 12, for example an electrical button attached to the housing 1, a temperature sensor 13 arranged on the evaporator 6 and a timer 14. The timer 14 is preferably implemented in the form of a quartz watch or a radio-controlled clock and periodically provides a quantitative, representative of the time signal. In the case of an "intelligent" freezer, which is also a terminal in a communications network, the timer 14 may also be the interface to such a network because in such networks time signals may be periodically transmitted or requested by the interface 14 from another terminal.

Fig. 3 shows a first example of a working method that can be processed by the control circuit 11 to defrost the evaporator 6 if necessary. In this method, it is assumed that a defrosting operation is not initiated automatically by the control circuit 11, but upon command of a user by pressing the key 12. If the control circuit 11 determines in step S1 that the key 12 has been pressed, it checks in the next step S2 the time supplied by the timer 14. If it is between 5:00 am and 1:00 am, the control circuit 11 first ignores the user's command and waits until 1:00 am in step S3. The time interval from 5:00 in the morning until 1:00 at night is therefore a blocking time interval in which no defrosting is performed. At 1:00 am, the control circuit 11 turns on the power of the heater 10 and simultaneously turns off the compressor 7 and the fan 9, if they were turned on. Alternatively, there is a possibility that, when the compressor 7 and blower 9 are turned on, the control circuit 11 waits to initiate the defrosting process until the operation phase is completed normally.

When the heater 10 has run so long that the sensor 13 detects a target temperature above zero degrees Celsius, which surely indicates that the evaporator 6 is completely defrosted, the power of the heater 10 is turned off and the normal cooling operation is restored in step S6 added.

The user can thus enter a defrost command via the key 12 at any convenient time, e.g. when it detects when defrosting or unloading refrigerated goods that defrosting is required. By limiting the defrost period to between 1:00 and 5:00 in the night, it is ensured that, until the defrosting process is initiated, any newly loaded refrigerated goods may have frozen safely.

As you can easily see, other limits could easily be set for the period in which a defrosting process can be initiated. It would also be readily possible to set a fixed time, e.g. 3:00 o'clock at night, at which a defrosting process can start.

Fig. 4 shows an example of a control arrangement that allows a fully automatic defrosting operation. Components of this arrangement, already with reference to Fig. 2 have been described, bear the same reference numerals and will not be described separately. The control circuit 11 of Fig. 4 In addition, it has a signal input 15 to which a control signal generated by a thermostat control circuit 16 for switching on and off the compressor 7 is applied.

A first example of a working method that can be carried out with this embodiment of the control arrangement is shown in FIG Fig. 5 shown. The method begins with an operating time counter t being set to zero after the freezer is switched on in step S11. As soon as the control circuit 11 recognizes that the compressor 7 is turned on (S12), it stores the current time t _akt in a buffer b (S13). Once it is determined that the compressor is turned off again, the value in the buffer b is subtracted from the now current time clock and stored again in the buffer b (S15). If the result is less than zero in step S16, the start and end of the compressor operation phase are different days, and 24 hours must be added to the value in buffer b (S17) to obtain the correct duration of the operation phase of the suspected , The duration thus obtained is added to t (S18), and it is checked (S19) whether the result is over a permissible total operating time t _{lim of} the compressor between two defrosting operations. If so, then defrosting is necessary and the process goes to step S21; if not, it is checked in step S 20 whether the user has pressed the key 12 and therefore a defrosting operation is necessary. If so, the method also proceeds to step S21, if not, a new operating phase of the compressor is awaited in step S12.

The subsequent steps S21 to S26 are identical to the steps S2 to S7 of Fig. 3 and will not be described again here.

In a simplified variant of the control method, instead of the compressor running time, the total operating time of the freezer since the last defrosting operation could be summarily measured and branched to step S21 as soon as the total operating time has exceeded a predetermined limit value.

A further embodiment of an operating method for the control arrangement Fig. 4 is determined by Fig. 6 treated. In this embodiment, the ratio between compressor running time and freezer running time is used as a criterion for the need for defrosting. This modification has the advantage that it does not work with parameters accumulated over the entire operating time of the last defrosting operation, so that the defrosting process can be triggered correctly even if parameter values stored as a result of a power failure or another fault have been lost.

The method begins in step S31 with the initialization of a parameter a representative of the ratio between the compressor running time and the device running time to a value a, which in principle can arbitrarily be selected below a predetermined limit value A. In step S32 is checked whether the compressor 7 is turned on or not. If not, the parameter a is multiplied by a "forgetting factor" 1-ε in step S34; otherwise, it is previously incremented in step S33. By repeating these steps frequently, a converges to a value proportional to the desired ratio. In step S 35 it is checked whether the limit A is exceeded. If not, the steps S32 to S34 are repeated, otherwise, it is determined that defrosting is required, and steps S21 to S26 are followed.

In the control arrangement of Fig. 6 is the signal input 15 of Fig. 4 replaced by a connection to a switch 17. This switch 17 is arranged in a conventional manner on the housing 1 to detect the opening and closing of the door 2 and, accordingly, the interior lighting of the freezer compartment 3 on and off. In this embodiment, the control circuit 11 counts the number of times the door 2 has been opened since the last defrosting operation or, alternatively, the total time during which the door 2 has been open since the last defrosting operation and compares the result with a threshold value. This method is not illustrated by way of a flow chart, as its operation may be evident by generalizing the examples given above. As soon as the limit value is exceeded, steps S21 to S26 are also carried out in this method.

An alternative, with the control arrangement off Fig. 7 feasible method is described with reference to Fig. 8 explained. In step S 41, the value of any suitable parameter is detected, eg the number or duration of the door openings, compressor operating time, total operating time, ratio of compressor operating time to total operating time, etc. If it is determined in step S 42 that the door 2 has been opened, then the timer 14 is started (S43), which does not serve to provide a time in this embodiment, but to indicate the elapse of a predetermined period of, for example, three hours. These steps are cyclically repeated unless it is determined in step S44 that the monitored parameter has exceeded the threshold. If this happens, then next (S45) it has to be checked whether the timer has expired, that is, whether the given time has elapsed since the last door open. If this is not the case, steps S41 to S44 are looped through until the timer has expired.

The expiry of the timer indicates that a defrosting process may now be initiated because sufficient time has elapsed since the last door was opened to safely freeze any newly stored refrigerated goods. The subsequent steps are identical to the steps S4 to S7 Fig. 3 and therefore need not be explained again.

A by-product of this control is that the timer will usually expire at night, so the likelihood that the door will remain closed so long that the timer can expire is greatest. Therefore, even with the method of Fig. 8 For the defrosting process mostly cheap night-time electricity can be used.

Claims (16)

1. Freezing appliance with a cooling surface (6) capable of icing, a heating device (10) for heating the cooling surface (6) and a control circuit (11) for controlling operation of the heating device (10) in dependence on a time transmitter (14), wherein the control circuit (11) is arranged to block operation of the heating device (10) during a blocking time period which is fixed by the time transmitter (14) and in which the cooling surface (6) is not to be defrosted and to detect the need for defrosting the cooling surface (6), characterised in that the control circuit (11) is arranged to wait for the end of the blocking time period when the time instant of the need for defrosting lies in the blocking time period and to operate the heating device (10) after expiry of the blocking time period.
2. Freezing appliance according to claim 1, characterised in that the time period fixed by the time transmitter is a clock time period.
3. Freezing appliance according to claim 2, characterised in that the clock time period lasts at least from 0900 hours to 2200 hours, preferably at least from 0500 hours to 0100 hours of the following day.
4. Freezing appliance according to claim 2 or 3, characterised in that the mean cooling power of the cooling surface (6) is higher outside the clock time period than within the clock time period.
5. Freezing appliance according to claim 1, characterised in that the time transmitter (14) is coupled to a sensor (17) for detecting the opening of a door (2) of the freezing appliance and that the time period fixed by the time transmitter (14) is a time period from when the door (2) is in its open state.
6. Freezing appliance according to any one of claims 1 to 5, characterised in that the time transmitter (14) comprises an oscillator, particularly a quartz oscillator.
7. Freezing appliance according to any one of claims 1 to 5, characterised in that the time transmitter (14) comprises a radio receiver.
8. Freezing appliance according to any one of claims 1 to 5, characterised in that the time transmitter (14) comprises an interface to a data network.
9. Freezing appliance according to any one of the preceding claims, characterised in that the control circuit (11) is designed to detect at least one operating parameter, which is correlated with the depth of icing of the cooling surface (6), of the freezing appliance and to place the heating device (10) in operation outside the fixed time period if the parameter has exceeded a limit value.
10. Freezing appliance according to claim 9, characterised in that the operating parameter or one of the operating parameters is the time elapsed since the last operating phase of the heating device (10).
11. Freezing appliance according to claim 9 or 10, characterised in that one of the operating parameters is the operating time, which has elapsed since the last operating phase of the heating device (10), of a compressor (7) of the freezing appliance.
12. Freezing appliance according to any one of claims 9 to 11, characterised in that one of the operating parameters is the ratio of operating time to standstill time of a compressor (7) of the freezing appliance.
13. Freezing appliance according to any one of claims 9 to 12, characterised in that it comprises a door and a sensor (17) for detecting opening of the door and that one of the operating parameters is the number of door openings counted since the last operating phase of the heating device (10).
14. Freezing appliance according to any one of claims 9 to 13, characterised in that the control circuit (11) is associated with an operating element (12) for input of a command for placing the heating device (10) in operation.
15. Method of controlling a freezing appliance with a cooling surface (6) capable of icing and a heating device (10) for heating the cooling surface (6), comprising the steps:

    a) fixing a blocking time period in which the cooling surface (6) is not to be defrosted and

    b) detecting the need for defrosting (S1, S19, S20, S35) the cooling surface (6), characterised by,

    c) if the time instant of the need for defrosting lies in the blocking time period (S2, S21, S35), waiting for the end of the of the blocking time period (S3, S22) and, after expiry of the blocking time period, operating the heating device (S4, S23).
16. Method according to claim 15, characterised in that the need for defrosting is recognised

    - on the basis of input of a command by a user (S1),

    - by monitoring at least one operating parameter, which is correlated with the depth of the icing, of the freezing appliance (S13 to S18; S31 to S34; S41) and detecting the need (S19, S35, S44) if at least one of the operating parameters exceeds a limit value.

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