EP3759405A1

EP3759405A1 - Refrigeration appliance comprising a defrost heater

Info

Publication number: EP3759405A1
Application number: EP19706582.4A
Authority: EP
Inventors: Andreas BABUCKE; Frank Cifrodelli
Original assignee: BSH Hausgeraete GmbH
Current assignee: BSH Hausgeraete GmbH
Priority date: 2018-02-28
Filing date: 2019-02-20
Publication date: 2021-01-06
Anticipated expiration: 2039-02-20
Also published as: EP3759405B1; WO2019166291A1; CN111788442B; DE102018202971A1; CN111788442A

Abstract

The invention relates to a refrigeration appliance, in particular a household refrigeration appliance, 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, a defrost heater (10) for defrosting the evaporator (7), and a control unit (18) for controlling the operation of the defrost heater (10), characterised in that the control unit (18) is designed to compare a variable (I) representative of a pressure drop at the evaporator with a limit value (I_end) and to start the defrost heater (10) when said limit value is exceeded.

Description

Refrigerating appliance with defrost heating

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. US 5 522 232 A describes a hoop sensor in which a first temperature sensor in a hermetically sealed chamber and a second temperature sensor is housed in a chamber communicating with its surroundings via slots, and the temperature difference between the sensors disappears when the slots are closed by frost.

EPO 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 to determine the representative quantity can be obtained via suitable circuits on an engine of the Fan and in particular be tapped at 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, a priori can be considered not known flow resistance of the storage chamber are 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 prior to compressor shutdown so that when the door is opened while the compressor is off, a meaningful representative value measurement is available.

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

a) detecting a representative of a pressure drop at the evaporator size, b) comparing the detected size with a limit value and

c) Start the defrost heater if the limit is exceeded. 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 shows a schematic section in the depth direction through an inventive

Household refrigerator;

Fig. 2: the relationship between pressure loss and fin spacing in one

Lamella evaporator;

Fig. 3: characteristics of a fan;

4 shows an exemplary temporal development of the pressure drop at the evaporator of the refrigerator of FIG. 1; and

5 shows a flow chart of a working method executed by a control unit of the refrigerator of FIG. 1.

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

The evaporator chamber 6 includes a fin evaporator 7 with arranged parallel to the sectional plane of Fig. 1 fins. In a lying below the finned evaporator 7 space 8 of the evaporator chamber 6, a defrost heater 10 for defrosting the finned evaporator 7 is housed. In a divided at the level of the freezer compartment 5 from the body 1 engine room, a compressor 19 for driving the flow of refrigerant through the finned evaporator 7 is housed. The space 8 forms here an inlet volume at an upstream side of the finned evaporator 7, which communicates with the freezer compartment 5 via an entrance slit 1 1.

The vertical partition wall 4 contains a distribution chamber 12, which communicates via an opening, on which a fan 13 is arranged, with a second, here downstream, free space 14 of the evaporator chamber 6 above the evaporator 7. A first outlet 15 of the distribution chamber 12 opens into the freezer compartment 5 close to the ceiling. Another outlet is formed by a line 16 extending in a wall of the body 1 to the normal cooling compartment 3. In this line 16, a controlled by a thermostat flap can be provided, which allows to suppress the cold air supply to the normal refrigeration compartment 3, if there is only 5 cooling needs in the freezer compartment. If there is a need for cooling in the normal cooling compartment 5 and the flap is therefore open, the cold air circulated by the fan 13 is distributed 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 via a gap or other passage passes into the normal refrigeration compartment and air is sucked from the normal refrigeration compartment in the evaporator.

Moisture, which is absorbed by the air when circulating through the storage chambers 3, 5, settles on the fins of the evaporator 7, thus reducing the free gap width between the fins. This gap width has a strong influence on the pressure loss of the circulating air. The pressure drop Dr at the evaporator 7 can be estimated by the following formula:

where L is the length of the evaporator 7 in the flow direction of the air flow, H is the height of the evaporator measured transversely to the flow direction in the plane of one of the slats, d is the free slit width between two slats, n is the number of slats, m is the dynamic viscosity of the air and V designates the volume flow. The pressure loss Dr 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. In order to measure the pressure loss Dr, a differential pressure sensor 21 may be connected to the two free spaces 8, 14. Since the pressure in the bearing chambers 3, 5 (at least under steady-state operating conditions when the doors 20 are closed long enough) does not deviate significantly from the atmospheric pressure, an absolute pressure sensor may alternatively be provided on one of the two free spaces 8, 14. A pressure sensor is not needed when the pressure loss Dr is estimated from electric operating quantities of the fan 13, as described below.

The diagram of Fig. 2 illustrates the pressure loss Dr, against which the fan 13 works, as a function of the gap width d. For a just-defrosted, ice-free evaporator 7, a free gap width d of 5 mm between the lamellae and for the circulation through the storage chambers 3, 5 is assumed to be independent of the gap width contribution to the pressure loss Dr of 15 Nm / m ² . A solid curve shows the evolution of the absolute pressure loss Dr at gap width d decreasing due to frost growth; a dashed curve shows the percentage change in the pressure loss Dr compared to the state at d = 5 mm. Halving the gap width d leads to a clearly measurable change in the pressure loss.

The electric motor of the fan 13 can react differently to the change in the pressure loss Dr depending on the design or operating point, 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 drop Dr of the fan 13 as a function of the volume flow V. The operating point of the fan 13 should be in the vicinity of a maximum of the efficiency n, shown as a solid curve. In this highlighted in the diagram of Fig. 3 area by hatching both the pressure loss Dr, shown as dashed curve, and the power P, shown as a dotted curve, unique functions of the volume flow V, so that from a measured power P of the fan 13th can be clearly concluded on the pressure drop Dr on the evaporator 7 and thus on the strength of the frost layer. At a fixed operating voltage of the fan 13, therefore, the knowledge of the current absorbed by the fan 13 is sufficient to estimate the thickness of the frost layer on the fins of the evaporator 7 can. The practical application of this idea will be explained with reference to FIGS. 4 and 5. FIG. 4 shows schematically a temporal development of the pressure drop at the evaporator 7 of the refrigeration device from FIG. 1; FIG. 5 shows a flowchart of a working method executed by a control unit 18 of the refrigeration device from FIG. 1.

The free gap width in the evaporator 7 is in each case a maximum, if eliminated by the operation of the defrost heater 10 all adhering to the fins of the evaporator 7 frost. In this case, the pressure loss Dr, against which the fan 13 must work, essentially determined by a flow resistance of the bearing chambers 3, 5. However, this is not known a priori, since in the storage chambers 3, 5 refrigerated goods placed depending on its amount and Arrangement, the flow of air can impede different degrees.

The description of the method therefore begins in FIG. 5 with the defrost heater 10 being switched off after complete defrosting of the evaporator 7 in step S1. This time corresponds to the time t = 0 in the diagram of FIG. 4.

In step S2, the control unit 18 sets the compressor 19 in motion to resume the cooling of the evaporator 7. At the same time, preferably slightly delayed after the onset of cooling of the evaporator 7, in step S3 and the fan 13 is turned on. If this has reached a stationary rotational speed after a few seconds, the current I detected by the fan 13 is detected as the quantity representative of the pressure loss Dr (S4). The measured value l _{0 obtained in this case} is stored in step S5. Its amount will generally vary from one defrosting operation to another since it depends on the distribution of the refrigerated goods in the chambers 3, 5.

Subsequently, a limit value l _en d of the amperage is set which, if exceeded, is assumed to have accumulated again so much frost on the evaporator 7 that defrosting is necessary. In order to ensure that even with different loading of the storage chambers 3, 5 with refrigerated goods at the same thickness of the frost layer is thawed, the limit l _en d is calculated in step S6 as the sum of the previously stored initial value l ₀ and a predetermined difference value D. In step 7, the current intensity I is again detected and compared in step S8 with the limit value l _en d. As long as the limit value l _en d has not yet been reached, the process branches to step S9 to check whether the door 20 of one of the storage chambers 3, 5 is open.

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

In the latter case, the last measured value l _{t of} the current intensity (which may be a value that has not been updated since the compressor 19 was switched off) is stored in step S1 1. The fan 13 is turned off S12, to prevent moist ambient air that passes through the open door 20 in the storage chamber 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 L in the diagram of FIG. 4. Since since the time t = 0, frost on the lamellae of the

Evaporator 7 is deposited, which is recorded by the fan 13

Current from l ₀ to increased. The remaining difference to the limit of

Current l _en d is calculated (S13) and stored as a new difference value D.

Subsequently, the processing unit waits until the door 20 is closed again at time t ₂ in FIG. 4, and then returns to step S3.

In the period [t _1; t ₂ ], in which the door 20 has been open, the user has invited fresh chilled goods into the chambers 3, 5, whereby the pressure loss Dr increases significantly, so that when step S5 is repeated, a significantly higher current intensity l ₂ as measured before opening the door.

This new measured value is again stored in step S5, and based on the difference value D updated in the previous step S13, the threshold value l _en d is recalculated in step S6. io

From the time t ₂ of closing the door, the fan 13 is running again, and the frost layer in the evaporator 7 continues to increase in thickness. As shown in FIG. 4, the current value can be exceeded the limit which was valid in the time interval [0, ti], without triggering a start of the defrost heater 10. At the time t ₃ , the door 20 is opened again, which the control unit 18 recognizes in step S9, the most recent interim current measured value is stored in step S1 1, and based on the stored value, the difference value D is updated again in step S13.

At time t ₄ , the door is closed again 20, so that the process returns to step S3. The storage chambers 3, 5 are vacated this time largely empty, so that contained refrigerated goods hardly contributes to the pressure loss Dr and now measured current strength l _{4 is} significantly lower than before the door opening. The limit value l _end is updated once more in step S6. Since the few chilled goods still containing only a small amount of moisture, the increase of the frost in the evaporator 7 is also reduced, which is reflected in a slower increase in the current intensity I from t ₄ compared to the time interval [t ₂ , t ₃ ].

At time t ₅ , the exceeding of the current limit value l _{end is} detected. The method now branches to step S15, in which the heater 10 is turned on. At the same time, unless previously done, compressor 19 and fan 13 are turned off. The difference value D is reset to a predetermined value D ₀ corresponding to a vaporizer 7 which has been completely freed of frost. If it is determined in step S17 that the defrosting operation is completed and refrigeration is required again in one of the storage chambers 3, 5, the process returns to step S2.

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

1 corpus

2 inner containers

3 normal refrigerated compartment

4 intermediate wall

5 freezer

6 evaporator chamber

7 (lamellar) evaporator

8 free space

9 lower edge

10 defrost heating

1 1 entrance gap

12 distribution chamber

13 fans

14 free space

15 outlet

16 line

17 flap

18 control unit

19 compressors

20 door

21 differential pressure sensor

Claims

1. Refrigerating appliance, in particular domestic refrigeration appliance, with an evaporator (7), a fan (13) for driving an air flow through the evaporator (7), a cooled by the air flow storage chamber (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 adapted to a representative of a pressure drop at the evaporator size (I) with a limit (l _en d ) and start the defrost heating (10) when the limit is exceeded.

2. Refrigerating appliance according to claim 1, characterized in that the control unit (18) is connected to at least one pressure sensor which is exposed to the prevailing at an inlet side or an outlet side of the evaporator (7) pressure.

3. Refrigerating appliance according to claim 1, characterized in that the representative size is an electrical size of the fan (13).

4. Refrigerating appliance according to claim 3, characterized in that the representative size of power and operating voltage of the fan (13) is derived.

5. Refrigerating appliance according to claim 3, characterized in that the representative size is the electric power or operating current (I) of the fan (13) for a given operating voltage.

6. Refrigerating appliance according to one of the preceding claims, characterized in that the representative size of the speed of the fan (13) is derived.

7. Refrigerating appliance according to one of claims 3 to 6, characterized in that the control unit (18) is arranged, with the door closed (20) of the storage chamber (3, 5) to monitor the representative size (I) and with the door open (20 ) to interrupt the monitoring.

8. Refrigerating appliance according to one of claims 3 to 7, characterized in that the limit value is the sum of the representative size immediately after defrosting of the evaporator (7) and a predetermined deviation (D).

9. Refrigerating appliance according to claim 8, characterized in that the control unit (18) is arranged after closing the door (20) to the limit value

To update.

10. Refrigerating appliance according to claim 9, characterized in that the control unit (18) is adapted to detect the representative size (I) before and after closing the door (20) and the limit value and the limit value (l _end ) based on the difference to adapt to these two parameters.

1 1. Refrigerating appliance according to one of claims 3 to 10, characterized in that the control unit (18) is adapted to detect the representative size (I) before turning off a compressor (19).

12. A method for operating a refrigerator, which comprises an evaporator (7), a fan (13) for driving an air flow through the evaporator (7), a cooled by the air flow storage chamber (3, 5) and a defrost heater (10) for defrosting of the evaporator (7), comprising the steps of:

a) detecting a pressure drop (Dr) at the evaporator (7)

representative size (I) (S4),

b) comparing the detected quantity with a limit value (l _end ) and c) starting the defrosting heater (10) when the limit value (l _end ) is exceeded