DE102018202971A1 - Refrigerating appliance with defrost heating - Google Patents

Abstract

A refrigerator, in particular a domestic refrigerator, comprises an evaporator (7), a fan (13) for driving an air flow through the evaporator (7), a storage chamber cooled by the air flow (3, 5), a defrost heater (10) for defrosting the Evaporator (7) and a control unit (18) for controlling the operation of the defrost heater (10), characterized in that the control unit (18) is arranged, a representative of a pressure drop at the evaporator size (I) with a limit (I _end ) to compare and the defrost heater (10) to start when the limit is exceeded.

Description

The present invention relates to a refrigeration device with a defrost heater, in particular a household refrigeration appliance in no-frost construction, in which an evaporator to be defrosted by the defrost heater is housed in a separate evaporator chamber from a storage chamber and the storage chamber is cooled by an air flow from a fan is circulated between the evaporator chamber and the storage chamber.

Moisture released from refrigerated goods stored in the storage chamber or entering the storage chamber from the outside when a door of the storage chamber is opened, precipitates as frost on the evaporator over time. The increasing thickness of the frost layer over time obstructs both air circulation and heat exchange between the air circulating in contact with the evaporator and a refrigerant evaporating in the evaporator, so that with increasing thickness of the frost layer, an ever higher fan output is required, to maintain the air circulation between the evaporator chamber and the storage chamber, and an ever lower evaporator temperature is required to cool the circulating air to a desired temperature for the storage compartment. Both increase the energy consumption of the refrigerator.

In order to enable energy-efficient operation of the refrigerator, therefore, the frost layer must be removed from time to time. A simple solution is to operate the defrost heater at regular intervals. However, this leads to the defrost heater also being turned on unnecessarily if little or no frost has formed within the fixed time interval. In such a case, the energy expenditure for defrosting unnecessarily impairs the energy efficiency of the refrigeration appliance.

In order to achieve a demand-adapted and thus energy-efficient defrosting, various sensors have been proposed. In US 5 522 232 A there is described a hoop sensor in which a first temperature sensor is housed in a hermetically sealed chamber and a second temperature sensor in a chamber communicating with its surroundings via slots, and the temperature difference between the sensors disappears when the slots are closed by frost.

EP0 713 065 B1 describes the use of a capacitive sensor for detecting ice on an evaporator. There are also known optical and acoustic methods for detection. All of these methods have in common that additional, sometimes complex sensors for the rims detection are needed.

Object of the present invention is to provide a refrigeration device and an operating method for this, which allow simple and inexpensive means a needs-based control of the defrost heater.

The object is achieved on the one hand by a refrigerating appliance, in particular a household refrigeration appliance, with an evaporator, a fan for driving an air flow through the evaporator, a cooled by the air flow storage chamber, a defrost heater for defrosting the evaporator and a control unit for controlling the operation the defrost heater, the control unit is adapted to compare a representative of a pressure drop at the evaporator size with a limit and to start the defrost heater when the limit is exceeded.

According to a first embodiment of the invention, for this purpose the control unit may be connected to at least one pressure sensor which is exposed to the air pressure prevailing on an inlet side or an outlet side of the evaporator. If such a pressure sensor is already provided, for example, to control a door opening aid, it can be used at no additional cost for the control of the defrost heater.

According to a second preferred embodiment, the representative variable responsible for the pressure drop is an electrical quantity of the fan. Electrical quantities can be detected without the need for an additional sensor in the vicinity of the evaporator; The measurement data required for determining the representative size can be tapped via suitable circuits on a motor of the fan and in particular on a power supply of the fan.

In particular, the electric power of the fan can be used as a representative variable. Since the operating voltage of the fan is fixed and immutable in the simplest case, a measurement of the current consumed by the fan is equivalent to a determination of the power. In the case that the operating voltage of the fan is variable, the quotient of electric power and operating voltage can be equivalently determined as a representative quantity.

If the fan provides a tacho signal, the fan speed can also be used as the representative variable associated with the power.

The control unit should be set up to monitor the ratio of the representative size when the door of the storage chamber is closed and to interrupt monitoring when the door is open. There may be several reasons for such an interruption, for example, the operation of the fan may be coupled to the position of the door to prevent hot, humid air from entering the storage chamber when the door is open by turning off the fan when the door is open and their moisture can immediately settle on the evaporator. If the fan is off when the door is open, there is no meaningful measure of the horsepower output and fan speed.

A second reason is that the performance of the fan is determined not only by the flow resistance of the evaporator, but also by that of the storage chamber. Therefore, due to the removal or addition of refrigerated goods in the storage chamber with the door open the flow resistance can change suddenly, without this being due to a change in the amount of frost on the evaporator.

In the simplest case, especially if the door is not opened for a long time, the limit may be the sum of the representative quantity immediately after defrosting of the evaporator and a predetermined deviation. By detecting the representative quantity immediately after defrosting, an a priori unknown flow resistance of the storage chamber can be taken into account; once the representative size has increased by the predetermined deviation, it can be considered that the frost layer from the evaporator has become thick enough to require defrosting.

Since most of the moisture precipitated as frost on the evaporator enters the storage chamber by opening the door, the case that the limit is exceeded without the door having been opened since the previous defrosting is quite rare in practice. In most cases the door is opened one or more times between two defrosts. In order to take into account the flow resistance of the storage chamber, which changes as a result of added or removed refrigerated goods, the control unit should be set up to update the limit value after closing the door

In particular, the control unit can be set up to detect the representative size before and after closing the door and to adjust the limit value based on the difference between these two detected variables, in particular to change it by this difference. This can prevent that changes in the representative size, which arise during the opening of the door by removal or addition of refrigerated goods, affect the control of the defrost heater.

Further, the control unit should be arranged to detect the representative size even before a compressor is turned off, so that when the door is opened while the compressor is off, a meaningful measurement of the representative size is available.

1. a) Erfassen einer für einen Druckabfall am Verdampfer repräsentativen Größe,
2. b) Vergleichen der erfassten Größe mit einem Grenzwert und
3. c) Starten der Abtauheizung bei Überschreitung des Grenzwerts.

The object is further achieved by a method for operating a refrigeration device, in particular as described above, with the steps:

1. a) detecting a variable representative of a pressure drop across the evaporator,
2. b) comparing the detected quantity with a limit value and
3. c) Start the defrost heater if the limit is exceeded.

• 1: einen schematischen Schnitt in Tiefenrichtung durch ein erfindungsgemäßes Haushaltskältegerät;
• 2: den Zusammenhang zwischen Druckverlust und Lamellenabstand in einem Lammellenverdampfer;
• 3: Kennlinien eines Ventilators;
• 4: eine exemplarische zeitliche Entwicklung des Druckabfalls am Verdampfer des Kältegeräts aus 1; und
• 5: ein Flussdiagramm eines von einer Steuereinheit des Kältegeräts der 1 ausgeführten Arbeitsverfahrens.

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

• 1 a schematic section in the depth direction by a household refrigerator according to the invention;
• 2 : the relationship between pressure loss and fin spacing in a sludge evaporator;
• 3 : Characteristics of a fan;
• 4 : an exemplary temporal evolution of the pressure drop at the evaporator of the refrigerator off 1 ; and
• 5 a flowchart of one of a control unit of the refrigeration device of 1 executed work procedure.

As an example of an inventive refrigeration device shows 1 a no-frost combination device in a schematic section in the depth direction. In a corpus 1 of the refrigerator are two cavities by a preferably made of plastic integrally deep-drawn inner container 2 limited. One of the cavities is a storage chamber, here a normal refrigerator 3 , The other cavity is through a vertical partition 4 in a second storage room, here a freezer 5 , and an evaporator chamber 6 divided. Both storage chambers 3 . 5 are each through a door 20 locked. The invention described below is of course also applicable to refrigerators with a single or more than two storage chambers.

The evaporator chamber 6 contains a finned evaporator 7 with parallel to the cutting plane of the 1 arranged slats. In one below the lamellar evaporator 7 lying space 8th the evaporator chamber 6 is a defrost heater 10 for defrosting the finned evaporator 7 accommodated. In one at the height of the freezer compartment 5 from the body 1 separated engine room is a compressor 19 for driving the refrigerant flow through the vane evaporator 7 accommodated.

The open space 8th here forms an inlet volume on an upstream side of the finned evaporator 7 that with the freezer 5 over an entrance gap 11 communicated.

The vertical partition 4 contains a distribution chamber 12 , which has an opening, where a fan 13 is arranged, with a second, here downstream, free space 14 the evaporator chamber 6 above the evaporator 7 communicated. A first outlet 15 the distribution chamber 12 flows near the ceiling into the freezer compartment 5 , Another outlet is through one in a wall of the corpus 1 to the normal refrigerator 3 extending line 16 educated. In this line 16 may be provided by a thermostat controlled flap, which allows the cold air supply to the normal refrigeration compartment 3 to stop if only in the freezer 5 Cooling requirement exists. If in the normal refrigerated compartment 5 Cooling requirement exists and the flap is therefore open, which is distributed by the fan 13 circulated cold air to both storage chambers 3 . 5 ,

Alternatively, there is also a structure in which a fan in the evaporator cools air cooled into the freezer, air from the freezer through a gap or other passage passes into the normal refrigeration compartment and air is sucked from the normal refrigeration compartment in the evaporator.

wobei L die Länge des Verdampfers 7 in Flussrichtung der Luftströmung, H die quer zur Flussrichtung in der Ebene einer der Lamellen gemessene Höhe des Verdampfers, d die freie Spaltbreite zwischen zwei Lamellen, n die Zahl der Lamellen, µ die dynamische Viskosität der Luft und V̇ den Volumenstrom bezeichnet. Der Druckverlust Δp ist umgekehrt proportional zur dritten Potenz der freien Spaltbreite d und reagiert damit empfindlich auf die Dicke der Reifschicht auf den Lamellen.Moisture from the air when circulating through the storage chambers 3 . 5 is absorbed, hits the fins of the evaporator 7 down and thus reduces the free gap width between the slats. This gap width has a strong influence on the pressure loss of the circulating air. The pressure drop Δp at the evaporator 7 can be estimated by the following formula: $${\Delta }_p=\frac{12\mu L}{d^3\left(n+1\right)H}\dot{V}$$

where L is the length of the evaporator 7 in the flow direction of the air flow, H the height of the evaporator measured transversely to the flow direction in the plane of one of the slats, d the free slit width between two slats, n the number of slats, μ the dynamic viscosity of the air and V̇ the volumetric flow. The pressure loss Δp is inversely proportional to the cube of the free gap width d and thus reacts sensitively to the thickness of the frost layer on the lamellae.

To the pressure loss Ap can measure a differential pressure sensor 21 with the two open spaces 8th . 14 be connected. Because the pressure in the storage chambers 3 . 5 (at least under steady-state operating conditions when closing the doors 20 long enough) does not deviate significantly from the atmospheric pressure, alternatively, an absolute pressure sensor on one of the two free spaces 8th . 14 be provided. A pressure sensor is not required if the pressure loss Δp, as described below, based on electrical operating variables of the fan 13 is estimated.

The diagram of 2 illustrates the pressure loss Ap against which the fan 13 works as a function of the gap width d. For a just-defrosted, ice-free evaporator 7 is a free gap width d of 5 mm between the slats and for circulation through the storage chambers 3 . 5 an independent of the gap width contribution to the pressure loss Ap assumed from 15 Nm / m ² . A solid curve shows the evolution of the absolute pressure loss Ap with decreasing by ripening gap width d; a dashed curve shows the percentage change in pressure loss Ap compared to the condition at d = 5 mm. Halving the gap width d leads to a clearly measurable change in the pressure loss Δp.

The electric motor of the fan 13 can change the pressure loss Ap Depending on the design or operating point react differently, for example by slower running or by increased power consumption. 3 shows exemplary characteristic curves for the power P, the efficiency n and the pressure loss Ap of the fan 13 as a function of the volumetric flow V̇. The operating point of the fan 13 should be in the vicinity of a maximum of efficiency n, represented as a solid curve. In this in the diagram of the 3 The area highlighted by hatching is both the pressure loss Ap represented as a dashed curve, as well as the power P , shown as a dash-dotted curve, unique functions of the volume flow V̇, so that from a measured power P of the fan 13 clearly on the pressure loss Ap on the evaporator 7 and thus the strength of the frost layer can be deduced. At fixed operating voltage of the fan 13 Therefore, the knowledge of the fan is sufficient 13 absorbed current to the thickness of the frost layer on the fins of the evaporator 7 to be able to estimate.

The practical application of this idea is based on the 4 and 5 explained. 4 schematically shows a temporal evolution of the pressure drop at the evaporator 7 of the refrigeration device out 1 ; 5 shows a flowchart of one of a control unit 18 of the refrigerator off 1 executed work procedure.

The free gap width in the evaporator 7 is in each case maximum, if by the operation of the defrost heater 10 all on the fins of the evaporator 7 Adhesive hoop is eliminated. In this case, the pressure loss Ap against which the fan 13 must work, essentially determined by a flow resistance of the storage chambers 3 . 5 , However, this is not known a priori, as in the storage chambers 3 . 5 placed refrigerated depending on its quantity and arrangement, the flow of air can impede different degrees.

The description of the method is therefore in 5 with that in step S1 the defrost heater 10 after complete defrosting of the evaporator 7 is turned off. This time corresponds to the time t = 0 in the diagram of 4 ,

In step S2 sets the control unit 18 the compressor 19 in progress to cool the evaporator 7 to resume. At the same time, preferably somewhat delayed after the onset of cooling of the evaporator 7 , in step S3 also the fan 13 switched on. If it has reached a stationary speed after a few seconds, it is considered as for the pressure loss Ap representative size of the fan 13 absorbed current I detected (S4). The measured value I _{0 obtained} in this step is S5 saved. Its amount will generally vary from one defrosting operation to another, as it depends on the distribution of the refrigerated goods in the compartments 3 . 5 depends.

Subsequently, a limit I _{end of} the current is set, which, if exceeded, it is assumed that on the evaporator 7 again so much frost has accumulated that a defrost is necessary. To ensure that even with different loading of the storage chambers 3 . 5 is defrosted with refrigerated goods at the same thickness of the frost layer, the limit I _end in step S6 calculated as the sum of the previously stored initial value I ₀ and a predetermined difference value D.

In step 7 the current I is detected again and in step S8 compared with the limit I _end . As long as the limit I _end has not yet been reached, the method branches to step S9 to check if the door 20 one of the storage chambers 3 . 5 is open.

When the doors 20 are closed, next in step S10 checked if the compressor 19 - because the cooling demand in both storage compartments 3 . 5 is satisfied - is off. Then in the episode also the fan 13 turned off, so that no meaningful reading of the current I is more to win. In this case, the checks of the steps S9 . S10 repeated until either refrigeration needs in at least one of the storage compartments 3 . 5 causes the compressor 19 and subsequently also the fan 13 be turned on again and the procedure to step 7 or a user returns one of the doors 20 opens.

In the latter case, the last measured value is obtained I _t the amperage (which is a since switching off the compressor 19 can not act on the updated value) in step S11 saved. The ventilator 13 is switched off S12 To prevent humid ambient air coming through the open door 20 in the storage room 3 or 5 from there immediately to the evaporator 7 is pumped further and there contributes to the formation of frost. This phase corresponds, for example, to the time t ₁ in the diagram of FIG 4 , Since since the time t = 0, frost on the fins of the evaporator again 7 is the one from the fan 13 absorbed current of I ₀ on I ₁ grown. The remaining difference to the current value limit I _end is being computed ( S13 ) and as a new difference value D saved. Subsequently, the processing unit waits until the time t ₂ in 4 the door 20 closed again, then to step S3 to return.

During the period [ t ₁ . t ₂ ], in which the door 20 has been open, the user has fresh refrigerated goods in the chambers 3 . 5 Invited, causing the pressure loss Ap increased significantly, so when the step S5 is repeated, a significantly higher current I ₂ as measured before opening the door.

This new reading will turn into step S5 saved, and based on the previous step S13 updated difference value D is in step S6 the limit I _end recalculated.

From the moment t ₂ closing the door, the fan is running 13 again, and the frost layer in the evaporator 7 continues to increase in thickness. As in 4 shown, the current value can be exceeded, the limit, which was valid in the time interval [0, t ₁ ], without this being a start of the defrost heater 10 triggers. At the time t ₃ will be the door 20 reopened what the control unit 18 in step S9 detects, the most recent intermediate measured current value is in step S11 stored and based on the stored value is the difference value D in step S13 updated again.

At the time t ₄ the door is closed again 20, so that the procedure to step S3 returns. The storage chambers 3 . 5 are this time vacated largely empty, so that contained refrigerated goods hardly contribute to the pressure loss Δp and the now measured current I ₄ is significantly lower than before the door opening. The limit I _end will be _repeated one more time in step S6 updated. Since the few refrigerated goods still contained only low moisture, is also the increase of the frost in the evaporator 7 diminished, which in one compared to the time interval [ t ₂ . t ₃ ] slower increase of the current I from t ₄ reflects.

At the time t ₅ the excess of the current limit I _{end is} detected. The process now branches to step S15 in which the heating 10 is turned on. At the same time, unless previously done, compressors 19 and fan 13 switched off. The difference value D gets onto a given, completely frost-free evaporator 7 corresponding value D ₀ reset. When in step S17 it is determined that the defrosting process is completed and again refrigeration needs in one of the storage chambers 3 . 5 the process returns to step S2 ,

With the method described above can be ensured that, despite changing loading of the storage chambers 3 . 5 a defrost each as needed for a given thickness of the frost layer in the evaporator 7 is triggered without the installation of sensors in the storage chambers 3 . 5 or the evaporator chamber 6 is required.

LIST OF REFERENCE NUMBERS

1

corpus

2

inner container

3

Normal refrigeration compartment

4

partition

5

freezer

6

evaporator chamber

7

(Lamellar) Evaporator

8th

free space

9

lower edge

10

defrost heater

11

entrance slit

12

distribution chamber

13

fan

14

free space

15

outlet

16

management

17

flap

18

control unit

19

compressor

20

door

21

Differential Pressure Sensor

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been 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.

Cited patent literature

• US 5522232 A [0004]
• EP 0713065 B1 [0005]

Claims (12)

Refrigerating appliance, in particular household refrigerating appliance, with an evaporator (7), a fan (13) for driving an air flow through the evaporator (7), a storage chamber (3, 5) cooled by the air flow, a defrosting heater (10) for defrosting the evaporator ( 7) and a control unit (18) for controlling the operation of the defrost heater (10), characterized in that the control unit (18) is adapted to compare a representative of a pressure drop at the evaporator size (I) with a limit value (I _end ) and the defrost heater (10) to start when the limit is exceeded. Refrigeration device after Claim 1 , characterized in that the control unit (18) is connected to at least one pressure sensor which is exposed to the pressure prevailing on an inlet side or an outlet side of the evaporator (7). Refrigeration device after Claim 1 , characterized in that the representative quantity is an electric quantity of the fan (13). Refrigeration device after Claim 3 , characterized in that the representative quantity is derived from power and operating voltage of the fan (13). Refrigeration device after Claim 3 , characterized in that the representative quantity is the electrical power or operating current (I) of the fan (13) at a given operating voltage. Refrigerating appliance according to one of the preceding claims, characterized in that the representative size of the speed of the fan (13) is derived. Refrigerating appliance according to one of Claims 3 to 6 , characterized in that the control unit (18) is adapted, with the door closed (20) of the storage chamber (3, 5) to monitor the representative size (I) and to interrupt the monitoring with the door open (20). Refrigerating appliance according to one of Claims 3 to 7 , characterized in that the limit value is the sum of the representative quantity immediately after a defrost of the evaporator (7) and a predetermined deviation (D). Refrigeration device after Claim 8 , characterized in that the control unit (18) is arranged to update the limit value after closing the door (20). Refrigeration device after Claim 9 characterized in that the control unit (18) is arranged to detect the representative quantity (I) before and after closing the door (20) and to adjust the limit value and the limit value (I _end ) based on the difference between these two detected quantities , Refrigerating appliance according to one of Claims 3 to 10 , characterized in that the control unit (18) is arranged to detect the representative variable (I) before switching off a compressor (19). A method of operating a refrigerator, comprising an evaporator (7), a fan (13) for driving an air flow through the evaporator (7), a storage chamber (3, 5) cooled by the air flow, and a defrost heater (10) for defrosting the evaporator (7), comprising the steps of: a) detecting a variable (I) (S4) representative of a pressure drop (Δp) on the evaporator (7), b) comparing the detected variable with a limit value (I _end ) and c) starting the defrost heater (10) when exceeding the limit (I _end ).

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