EP1332325A1

EP1332325A1 - Refrigerating device with an automatic defrosting system

Info

Publication number: EP1332325A1
Application number: EP01982413A
Authority: EP
Inventors: Hans-Georg Reisinger
Original assignee: BSH Bosch und Siemens Hausgeraete GmbH
Current assignee: BSH Hausgeraete GmbH
Priority date: 2000-10-27
Filing date: 2001-10-09
Publication date: 2003-08-06
Anticipated expiration: 2021-10-09
Also published as: DE50110072D1; CN1471622A; BR0114956A; DE10053422A1; ES2266279T3; WO2002035165A1; ATE329217T1; EP1332325B1; CN1471622B

Abstract

The invention relates to a refrigerating device comprising a refrigeratory (3) arranged on a refrigerating chamber (2), a first sensor (5) for detecting the temperature of the refrigerating chamber (3), a second sensor (6) for detecting the temperature(Tv) of the refrigerating agent, a third sensor (7) for detecting the external temperature (Te), a heating device (9) for the refrigeratory (3) and a control device (8) for operating the heating device (9) according to the temperatures (Ti, Tv) measured by the first and second sensors (5,6). The control device (8) activates the heating device (9) if the temperature (Tv) measured by the second sensor (5,6) falls below a threshold value (Tlim) which is set according to the temperatures (Ti, Te) measured by the first and third sensors (5, 7).

Description

Refrigeration device with automatic defrost

The present invention relates to a refrigerator with automatic defrost, also referred to as a no-frost refrigerator. Such refrigeration devices are e.g. used as household refrigerators or freezers. The evaporators of such refrigeration devices are equipped with heating devices which are operated from time to time in order to heat the evaporator to a temperature above 0.degree. C. and thus to melt frost, which is deposited on the evaporator during operation and the like Cooling performance affected.

In order to operate such a refrigerator economically, a compromise between contradicting requirements must be found. On the one hand, it is beneficial for a high cooling capacity of the evaporator if there is as little frost on it as possible, on the other hand considerable energy is required for the defrosting cycle to heat the evaporator above freezing, to defrost the frost and then to return the evaporator to its own Cool down operating temperature. In addition, the evaporator cannot cool during defrosting.

Measuring the thickness of a layer of frost directly on an evaporator in order to use it as a criterion for the need for a defrosting process is difficult and has not yet been used in practice. In most practical applications, therefore, to control the automatic defrost, the operating time of the refrigerator is measured, and a defrost process is initiated when a predetermined period of time has passed. A control system that is purely based on the operating time can of course not take into account the different application conditions of a refrigeration device. The amount of frost that accumulates in a household refrigerator in a given time can vary greatly, depending on how often and for how long the door of the refrigerator is opened and how high the moisture content of the outside air entering the refrigerator is. An adaptive method for defrosting has therefore been proposed in US Pat. No. 4,251,988, in which a control device draws conclusions from the duration of a defrosting process on the amount of frost or layer thickness that must have been present on the evaporator at the start of the defrosting process, and that the period between two defrosts is reduced if this amount has been greater than a limit, and the the time span is extended if this amount has been less than a limit value in order to ensure that defrosting always takes place at a predetermined layer thickness. The disadvantage of such a control is that it necessarily lags behind long-term changes in the operating conditions of a cold device B In summer, at relatively high outside temperatures and when there is generally no heating in an apartment in which such a cold appliance is installed, a relatively large amount of moisture enters the appliance each time it is opened Time on a relatively short time interval between two defrosting processes If heating is started again in the apartments in winter and the ambient temperature of such a refrigeration device is typically lower and the air humidity is lower, the moisture input is also lower and the automatic system gradually switches to longer tent intervals After two defrosts, optimal control is not available during the transition times

For larger refrigeration systems, a temperature-dependent control of the automatic defrost system is also used.For example, it is known to measure the evaporation temperature and the air temperature at the evaporator inlet or outlet of an evaporator through which air flows, and to trigger a defrost process whenever the difference between these two temperatures directly affects one initial value measured after a defrost process exceeds a predetermined percentage

Although this technique avoids incorrect regulation in the event that the amount of moisture entered into the cold device changes over time, it has the disadvantage that it is not able to take into account a change in the ambient temperature and thus the cooling requirement if the temperature in the vicinity of a refrigeration device controlled in this way, the heat input into its cooling chamber also increases, and with it the difference between the evaporation temperature and air temperature.In such a case, the automatic system triggers a defrosting process before it is actually necessary If the ambient temperature drops, so the defrosting process is delayed beyond what is economically reasonable

A similar problem arises when the controller position is changed. If this is set to a lower target temperature in the cooling chamber of the cold device, this also leads to an increase in the temperature difference, with the result that a defrosting process aisle and thus heating of the cold room is brought about when the user actually wanted to cool down more.

The object of the present invention is to provide a refrigeration device with automatic defrosting which also maintains a favorable time interval for the defrosting processes in the event of changes in the outside temperature or the desired temperature of the cooling space set by a user.

This object is achieved in a refrigeration device with a cooling space, an evaporator for a refrigerant arranged on the cooling space, a first sensor for detecting a temperature of the cooling space and a second sensor for detecting a temperature of the refrigerant, a heating device for the evaporator and a control device for operation of the heating device as a function of the temperatures measured by the two sensors, in that a third sensor is provided for detecting an outside temperature, and in that the control circuit is set up to activate the heating device if the temperature measured by the second sensor falls below a limit value , which is determined as a function of the temperatures measured by the first and third sensors.

The control circuit can be implemented in a simple manner with a memory which records values of the limit value for different pairs of outside and cold room temperature. In order to be able to keep the size of this memory small and still achieve a sensitive regulation of the time of defrosting, the control circuit can further comprise an interpolation unit for calculating the limit value for pairs of temperatures measured by the first and third sensors on the basis of the values recorded in the memory.

The limit values for all pairs of outside and cold room temperature are preferably selected such that they correspond to a predetermined frost layer thickness on the evaporator. These values can be measured, for example, on a prototype of the refrigeration device under standardized operating conditions, and the limit values thus obtained are stored in the control devices of the refrigeration devices supplied by the manufacturer, According to a simple embodiment, these limit values can be predetermined, but it is also conceivable to design the control device in such a way that it is able to change these limit values

The control device is preferably able to measure the time required by the heating device to defrost the evaporator and thus to draw a conclusion about the amount or layer of frost actually present on the evaporator if the time required for defrosting deviates from a desired value corresponding to the optimal amount of frost , the control device changes the limit values of the second sensor so that the time required for defrosting converges to the setpoint value. That is, if the defrost takes too long, the limit value of the temperature difference is reduced, if it does not last long enough, it is increased

Such an adjustment of the limit values is preferably carried out selectively only for those limit values which are assigned to pairs of outside and cold room temperature which are only a short distance from the outside temperature-cold room temperature pair at which the defrosting time was measured. This selective readjustment acquires a cold device according to the invention during its operation a set of limit values of the second temperature sensor, which is adapted absolutely flexibly to the specific conditions of use of the cold device

Further features and advantages of the invention result from the following description of an exemplary embodiment with reference to the attached figures

Fig. 1 is a highly schematic representation of a cold device according to the invention, and

2 shows a flow chart of a control method carried out by the control device of the cold device

1 shows a highly schematic illustration of a cold device with an insulating housing 1, which encloses a cooling chamber 2. From a cold medium circuit of the cold device, an evaporator 3 inside the cooling room and a compressor 4 are shown in the figure, which evaporator 3 contains liquefied refrigerant supplied and extracted evaporated refrigerant therefrom A first sensor 5 is in the cold room for detection arranged from its temperature Ti. A second temperature sensor 6 is located on the evaporator 3 in the vicinity of the refrigerant inlet in order to measure the evaporating temperature T _{v of} the refrigerant. A third sensor 7 for measuring the outside temperature T _e is arranged outside the housing 1. All three sensors are connected to a control device, here a microprocessor 8. The microprocessor 8 regulates the operation of the compressor 4 on the basis of the temperature Ti measured by the first sensor 5, and it controls the operation of a heating element 9 arranged on the evaporator 3 on the basis of the temperatures measured by all three sensors 5, 6, 7 and a set of limit values, the memory 10 connected in another microprocessor 8 is stored.

The method performed by the microprocessor 8 to control the operation of the heater 9 is described with the flow chart of FIG. 2.

In a first step S1, the microprocessor 8 detects the temperatures Ti of the interior, T _{e of} the surroundings and T _{v of} the evaporator measured by the sensors 5, 6, 7. In step S2, he determines a limit value Tu ,, assigned to the measured values of T,, T _e , of the evaporator temperature. This determination can be carried out, for example, by storing the microprocessor 8 among the pairs of inside and outside temperature for which a limit value is stored in the memory 10, which determines the one closest to the measured pair of inside and outside temperature and assumes its limit value as the assigned limit value. It is also conceivable to round the measured temperature values to the next higher or lower temperature value, for which a limit value is present in the memory 10.

An alternative is that the microprocessor 8 for a pair (T ,, T _e ) of measured inside and outside temperatures those four pairs (Ti-, T _e .), (Tj., T _{e +} ), (T _{i +} , T _e .) and (Tj +, T _e +) determined for the Tj. (T _e .) Is the temperature value closest to T, (T _e ) and T, ₊ (T _{e +} ) the temperature value next to T, (T _e ), for which a limit value is stored in the memory 10, and that the Microprocessor sets the limit for (Ti, T _e ) by interpolating the limits to (T,., T _e .), (T,., T _{e +} ), (T _{i +} , T _e .) And (T _{i +} , T _{e +} ) certainly,

In step S3, the found limit value T _{m is} compared with the evaporator temperature T _v . If the evaporator temperature is higher than the limit, it is concluded that defrosting is not yet necessary and the process returns to the beginning. If the evaporator temperature T _{v is} lower than the limit value, it is assumed that a frost layer has formed on the evaporator which must be defrosted. As a result, the microprocessor 8 sets a timer to 0 in step S4 and starts supplying the heater 9 with power to defrost the evaporator 3. As soon as the temperature T _v measured by the second sensor rises above 0 ° C, it is assumed that the evaporator has defrosted, the power supply to the heating device 9 is interrupted and the microprocessor 8 reads out the timer in order to find out the duration t of the defrosting process (step S5). In step S6, the duration t is compared with a first limit value. If the duration t is greater than this limit value liml, the limit value read from the memory 10 in step S2 is reduced in step S7. All other limit values in the memory remain unchanged. If t is smaller than the target value liml, a comparison of the time period t with a smaller target value Iim2 follows in step S8. If the time period t falls below this target value, the limit value Tii _m determined in step S2 is increased in the memory 8 in step S9.

If t lies between the two limit values liml and Iim2, this means that the defrosting time is in the desired, predetermined frame, and T | _{! m} remains unchanged. Reducing or increasing T | _in steps S7 or S9 can be done by subtracting or adding a fixed, small positive value or by subtracting or adding a value proportional to the difference between t and the setpoint liml or Iim2. A reduction or enlargement by multiplying or dividing by a predetermined fixed factor or a factor proportional to the difference is also possible. Alternatively, there is also the possibility of using a single setpoint instead of the two setpoints liml and Üm2, and of carrying out step S7 if t exceeds the setpoint and of step S9 if t falls below the setpoint.

If the limit T | _in as has been indicated above, determined by interpolation, all the limit values in the memory 10 which are received in the interpolation, adapted in the manner described above. The extent to which a limit value is adapted is expediently proportional to the weight with which the limit value was included in the interpolation. With the method described above, a limit value T | becomes over time for each operating condition of the cold device defined by a pair (of an outside temperature T _e and an inside or cold room temperature T 1) _{lm obtained} for the evaporator temperature, which corresponds exactly to a predetermined target thickness of a frost layer on the evaporator 3, changes in the operating conditions, be it due to fluctuations in the outside temperature T _e or because a user sets a changed cooling chamber temperature T between two defrosting processes can no longer cause problems in the Carry out the rhythm of the defrosting processes since the suitable evaporator limit temperature T _v is stored as a limit value in the memory 10 for all combinations of these temperatures. The defrost control is therefore completely independent of time. the door of the cold appliance is not opened and no moisture can penetrate inside and frost can form on the evaporator. If the door remains open for a longer period of time and accordingly more moisture than usual penetrates into the appliance, defrosting will occur more often This does not entail a change in the behavior of the control, which could lead to an inappropriate control during subsequent normal operation

Claims

claims

Cold device with a cooling space (2), an evaporator (3) for a refrigerant arranged on the cooling space (2), a first sensor (5) for detecting a temperature (T,) of the cooling space (2) and a second sensor (6) for Detecting a temperature (T _v ) of the refrigerant, a heating device (9) for the evaporator (3) and a control device (8) for operating the heating device (9) as a function of those of the first (5) and the second sensor (6 ) measured temperatures (T „T _v ), characterized in that it further comprises a third sensor (7) for detecting an outside temperature (T _e ), and in that the control device (8) is set up to activate the heating device (9), if the temperature (T _v ) measured by the second sensor (6) falls below a limit value which is determined as a function of the temperatures (T "T _e ) measured by the first (5) and third sensor (7)

Cold appliance according to claim 1, characterized in that the control device (8) comprises a memory (10) which _records values of the limit value (T | _ιm ) for different pairs of outside and cold room temperature

Cold device according to claim 2, characterized in that the control device (8) has an interpolation unit for calculating the limit value for pairs of temperatures (T "T _e ) measured by the first (5) and third sensor (7) on the basis of the data stored in the memory (10). recorded values

Cold appliance according to one of the preceding claims, characterized in that the limit values (T | _ιm ) for all pairs of outside and cold room temperature (T ,, T _e ) are selected such that they correspond to a predetermined frost thickness on the evaporator (3)

Cold device according to one of the preceding claims, characterized in that the limit values (T | _ιm ) of the second temperature sensor (6) are fixed Cold device according to one of claims 1 to 4, characterized in that the limit values (T |, _m ) of the second temperature sensor (6) can be changed by the control device (8)

Cold device according to claim 6, characterized in that the control device (8) is able to measure the time (t) required by the heating device (9) for defrosting the evaporator (3) and if this time deviates from a desired value (Iιm1 , Iιm2) to change the limit values (T | _im ) of the second sensor (6) in such a way that the time (t) required for defrosting converges to the target value

Cold device according to claim 7, characterized in that if, for a given pair of outside and cold room temperatures (Tj, T _e ), the time (t) required for defrosting deviates from the desired value (Iιm1, Iιm2), the control device (8) the limit values of the given pair of adjacent temperature pairs changed more than those of more distant ones