WO2015189010A1

WO2015189010A1 - Refrigeration device having hot gas defrosting, and defrosting method

Info

Publication number: WO2015189010A1
Application number: PCT/EP2015/061048
Authority: WO
Inventors: Adolf Feinauer; Niels Liengaard; Matthias Mrzyglod; Vitali ULRICH
Original assignee: BSH Hausgeräte GmbH
Priority date: 2014-06-11
Filing date: 2015-05-20
Publication date: 2015-12-17
Also published as: DE102014211108A1

Abstract

The invention relates to a refrigeration device, in particular a household refrigeration device, comprising at least one storage chamber (2), an evaporator (3) for cooling the storage chamber (2), a compressor (7) for driving a refrigerant flow through the evaporator (3), and a control unit (17) that is designed to supply the compressor (7) with current, and to switch between a normal cooling mode, wherein refrigerant passes a throttle point (12) on the way from the compressor (7) to the evaporator (3), and a defrosting mode, wherein the refrigerant bypasses the throttle point (12) on the way from the compressor (7) to the evaporator (3). The control unit (17) can also switch between a drive operation mode, wherein a current supplied by the control unit (17) to the compressor (7) causes a movement of the compressor (7) that drives the refrigerant flow, and a heating operation mode, wherein the compressor (7) is applied with current by the control unit without causing a movement of the refrigerant.

Description

Refrigerating appliance with hot gas defrosting and defrosting

The present invention relates to a refrigerator, in particular a domestic refrigerator such as a refrigerator or freezer, in which an evaporator can be deflated by passing warm refrigerant, and a method for defrosting the evaporator in such a refrigerator.

The defrosting of an evaporator by passing warm refrigerant is common in large refrigeration systems. It allows for energy-efficient defrosting, since the gas passed through it releases its heat predominantly at the coldest points of the evaporator, so that when the evaporator has iced and ice-free areas, the heat is given off mainly at the icy areas and unnecessary heating of already defrosted parts the evaporator can be largely avoided. For domestic refrigeration appliances, hot gas defrosting is not widespread because the waste heat from the high efficiency compressors installed in these appliances is generally insufficient to carry out a defrosting operation within a reasonable time, without excessive heating of the refrigerated product stored in the refrigerator, and because of faster defrosting necessary installation of a heater for heating the refrigerant causes additional costs that make such refrigerators unattractive to consumers.

Object of the present invention is to provide a refrigeration device, which is despite high energy efficiency of its compressor with minimal cost in a position to provide sufficient hot gas for a rapid defrosting, or specify a cost-implementable and efficient defrosting.

The object is achieved on the one hand, by a compressor, in particular a household refrigerator, with at least one storage chamber, an evaporator for cooling the storage chamber, a compressor for driving a refrigerant flow through the evaporator and a control unit which is configured to power the compressor supply and switch between a normal cooling mode in which refrigerant passes through the throttle on the way from the compressor to the evaporator, and a defrost mode in which the refrigerant, bypassing the throttle point - and consequently further absent the otherwise occurring cooling - passes to the evaporator, the control unit further switchable between a drive operating mode in which a current supplied to the compressor by the control unit causes the refrigerant flow driving movement of the compressor, and a Heizbetriebsmodus in which they energized the compressor without causing movement of the refrigerant. The electrical power fed into the compressor in heating mode can only be released as heat in the compressor, so that when refrigerant is recirculated from the compressor following the heating mode of operation, it will absorb the heat from the compressor and transport it to the evaporator. In order to be able to bypass the throttle, a refrigerant circuit of the refrigerator should include a shunt line connecting an output of the compressor to an inlet of the evaporator parallel to the choke point, and a shut-off valve located in the shunt line should be closed in the normal cooling mode and open in the defrost mode.

Another shut-off valve connected in series with the restriction and the evaporator may be closed in defrost mode to completely force the refrigerant onto the bypass line; However, this second shut-off valve is not absolutely necessary because, even if it is missing or open, the small cross section of the throttle is sufficient to direct the refrigerant over the shunt line predominantly.

The control unit should be set to temporarily activate the heating operation mode before transitioning to the defrosting mode to achieve a high temperature of the refrigerant circulating in the evaporator in the defrosting mode, and thus a quick defrosting operation.

If necessary, if the available amount of heat for a fast defrost is not sufficient, can be switched back from the defrost mode temporarily in the heating operation mode; however, it is preferable to manage with a single heating operation phase before the start of the defrost mode, since at the beginning of the defrost mode, when the evaporator is frosted over a large area, the evaporator for the most part can not heat above 0 ° C, even though the refrigerant pumped through is considerably warmer, whereas in later stages of defrosting, when the evaporator is partially ice-free, a high refrigerant temperature may result in unnecessary heating of these ice-free areas. Therefore, it is advantageous for an energy-efficient defrosting operation when the temperature of the refrigerant is high at the transition to the defrost mode and decreases during the defrosting mode.

In the simplest case, the control unit can be set up to activate the heating operating mode before each transition into the defrosting mode. In order to further reduce the energy consumption during defrosting, however, the heating operating mode can also be linked to conditions. For example, the control unit may be configured to activate the heating operation mode only if the temperature of the compressor is below a limit before the transition to the defrost mode. To detect this temperature, the control unit should be connected to a temperature sensor on the compressor; As such a temperature sensor may serve a PTC element, which is conventionally present in many compressors to interrupt the operation of the compressor in case of overheating.

A low ambient temperature results in short periods of operation of the compressor, which are interrupted by long standstill phases, so that at low ambient temperatures there is a high probability that the compressor temperature is low and the compressor can not supply the amount of heat required for a defrosting operation. Therefore, the control unit may also be connected to an ambient temperature sensor to activate the heating mode of operation when the ambient temperature is below a threshold prior to the transition to the defrost mode.

As a drive unit, the compressor may have an asynchronous motor.

In some types of electric motors, especially in asynchronous motors, the energizing of a main winding is not sufficient to initiate a rotation, and it is an auxiliary winding needed to deflect when starting the engine from an equilibrium position and specify its direction of rotation. When in the heating mode, the auxiliary winding remains de-energized and consequently no direction of rotation is given, strong currents can be fed into the main winding and heat them up, without the rotation of the engine gets going.

Instead of leaving the auxiliary winding in the heating mode completely energized, can also be provided that it is continuously energized by the control unit, so as to use the auxiliary winding for heat generation.

In order to selectively suppress or maintain the energization of the auxiliary winding, a switch controlled by the control unit may be connected in series with the auxiliary winding.

Alternatively and in a manner known per se, a PTC element may be connected in series with the auxiliary winding in order to enable a current flow in the auxiliary winding, which is required for starting the rotation, when the motor is still cold when the PTC element is still cold but after a short time, as a result of the heating caused by the current flow of the PTC element, turn off or to reduce a not significantly affecting the movement of the motor current. In such a motor with a PTC element, the control unit may be configured to turn on the heating operation mode by first energizing the motor in the manner conventional for starting the engine to thereby heat the PTC element, then momentarily interrupting the energization that a possibly started movement of the motor can come to a standstill, and then resumes the energization, so that although the main winding is supplied with power and generates heat, in the absence of a significant current flow in the auxiliary winding of the engine, however, remains at a standstill. A start of the compressor can also be prevented by the fact that at the outlet of the compressor is too high pressure against which the compressor has to work. Therefore, regardless of the type of engine, it is also possible to activate the heating operation mode by operating the compressor for a short time to build up at its output a pressure high enough to stop when the compressor has been stopped for a short time prevent restarting.

The object is further achieved by a method for defrosting an evaporator, which in a normal cooling mode from a compressor via a throttle point with refrigerant be acted upon, comprising the steps of: a) operating the compressor in a heating mode in which the compressor is energized without driving a movement of refrigerant, then b) operating the compressor in a drive operating mode in which the refrigerant from the compressor Bypassing of the throttle is transported to the evaporator.

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

Fig. 1 is a schematic representation of an inventive

Household refrigerating appliance;

FIG. 2 is a block diagram of a control unit and a compressor motor of FIG

Refrigerating appliance according to a first embodiment;

3 is a block diagram analogous to FIG. 2 according to a second embodiment of the invention; and FIG. 4 shows a block diagram analogous to FIG. 2 according to a third embodiment of the invention

Invention.

The household refrigerating appliance shown schematically in Fig. 1 comprises a heat-insulating housing 1, in which at least one storage chamber 2 is formed for refrigerated goods. An evaporator 3 for cooling the storage chamber 2 is typically housed in an evaporator chamber 4 separated from the storage chamber 2 and cools the storage chamber 2 by circulating air between the storage chamber 2 and the evaporator chamber 4 by means of a fan 5. An outlet of the evaporator 3 is connected via a suction line 6 to a suction port of a compressor 7. A pressure line 8 extends from an outlet of the compressor 7 via a branch 9, a condenser 10 and a shut-off valve 1 1 to a functioning as a throttle point 12 capillary. At a low pressure Line section 13 between the throttle point 12 and the evaporator 3, a confluence 14 is provided with an outgoing from the branch 9 shunt line 15. In the bypass line 15, a second shut-off valve 16 is arranged. The shut-off valves 1 1, 16, the fan 5 and the compressor 7 are controlled by an electronic control unit 17. In a conventional manner, the control unit 17 is connected to a temperature sensor 18 to the storage chamber 2 to decide whether the storage chamber 2 requires cooling or not and in the presence of cooling demand to operate the compressor 7 in a normal cooling mode in which the compressor 17 sucks refrigerant from the evaporator 3 and outputs under high pressure to the condenser 10. In this normal cooling mode, the shut-off valve 1 1 is open to admit liquid refrigerant from the condenser 10 via the throttle point 12 in the evaporator 3, the shut-off valve 16 is closed, and the fan 5 is in operation to the evaporator 3 cooled air in the storage chamber. 2 to distribute.

During the normal cooling mode, frost is deposited on the evaporator 3, which slows the heat exchange with the circulating through the evaporator chamber 4 air and thus affects the efficiency of the refrigerator. The control unit 17 is arranged to estimate the amount of frost on the evaporator 3 to, if it is large enough to significantly affect the heat exchange to initiate a defrosting of the evaporator 3 in the way. The amount of frost on the evaporator 3 can be estimated in different ways. In a simple manner, the control unit 17 detects the duration of successive phases in the normal cooling mode and determines the need for defrosting when the accumulated duration of these phases has exceeded a predetermined limit.

Since moist outside air enters the storage chamber 2 each time a door of the housing 1 is opened, it can be assumed that the amount of frost on the evaporator 3 is related to the number of door openings made since the last defrost, and the need for defrosting may be different Method, if this number exceeds a given value. More direct methods for detecting the frost on the evaporator 3 may be based, for example, on a time delay between the start of the normal cooling mode and a resulting cooling of the storage chamber 2 detected by the temperature sensor 18 or on the change of a resonant frequency of the evaporator 3 by the frost adhering to it.

As a result, when the control unit 17 has determined the necessity of defrosting, it can unconditionally first change over to a heating operation mode in order to stop the compressor 7 before the start of the defrosting operation; However, the decision as to whether such a heating is required, but can also be done taking into account operating conditions of the refrigerator. For example, a second temperature sensor 19 may be provided to detect the temperature in the environment of the refrigeration device. If it is above a threshold, it can be considered that before the present time, the compressor 7 has run long enough to contain the amount of heat needed for defrosting, so that in such a case the energy-intensive heating operation mode is not needed before the start of defrosting , Alternatively, the temperature sensor 19 could also be arranged directly on the compressor 7 in order to measure its temperature and thus estimate the amount of heat stored in it directly. In a simpler variant, the temperature sensor 19 can also be dispensed with, and the control unit 17 decides whether the amount of heat in the compressor 7 is sufficient for a defrosting operation on the basis of the duration of the immediately preceding normal cooling phase measured anyway.

In the heating operation mode, the control unit 17 supplies the compressor 7 with power, but the motor of the compressor 7 does not rotate, so that the supplied electrical energy in the compressor 7 is completely converted into heat. Depending on the design of the compressor 7, there may be different ways to energize this, without causing the engine rotates; Some of these options will be discussed in detail later.

To subsequently switch to the defrost mode, the control unit 17 closes the shut-off valve 1 1, opens the shut-off valve 16 and starts the motor of the compressor 7, so that the compressor 7 circulates refrigerant. The heated in the compressor 7 Refrigerant reaches the evaporator 7 via the bypass line 15, where it gives off its heat and flows back to the compressor 7.

The duration of the defrost mode can be fixed, preferably variable as needed. To achieve such a demand-dependent variability, z. B. the amount of frost on the evaporator 3 can be estimated based on their influence on the resonant frequency of the evaporator 3, or it can be provided on the suction line 6 or in the evaporator chamber 4, a temperature sensor to a temperature increase of the refrigerant flowing out of the evaporator or the temperature in the evaporator chamber 4 to conclude that the frost is completely thawed, and then to end the defrost mode.

2 shows a block diagram of the control unit 17 and the engine 7 of the compressor 7, which is controlled by it and denoted here by 20, according to a first embodiment. The control unit 17 is here divided into a logic unit 21, as described above, the operating mode of the compressor 7 - normal cooling mode, defrost mode, heating mode or sleep mode - sets and controls the valves 1 1, 16 and the fan 5, a relay 22 and a Inverter 23. The motor 20 is a known asynchronous motor with a main winding 24 articulated in three strands 25 on the stator and an auxiliary winding 26, which is energized at a start of the motor 20 to initiate the rotation and set their direction ,

The logic unit 21 may employ different methods of controlling the relay 22 and the inverter 23. As a result of a first of these methods, the relay 22 remains open during the heating mode of operation so that the auxiliary winding 26 remains de-energized, whereas the inverter 23 energizes the main winding 24. The order in which the inverter 23 supplies the individual strands 25 of the stator winding 24 with current can be the same as in the normal cooling operating mode. However, since there is no triggering of the rotation of the rotor via the auxiliary winding 26, rotation of the compressor 7 does not start during the heating operation mode, and the entire electric power supplied to the main winding 24 merely heats it up. As a result of a second method, the logic unit 21 keeps the relay 22 closed during the heating mode of operation, so that a continuous current flows through the auxiliary winding 26, which adds to the heat generation in the motor 20. In this method, the order in which the inverter 23 energizes the strings 25 should be variable under the control of the logic unit 21 to ensure that an order suitable for driving a rotation of the motor is generated only during the normal cooling mode, and so exclude that in heating mode, rotation is initiated. For this purpose, for example, the strands 25 are supplied with DC voltage, so that no rotating magnetic field in the motor 20 is formed, or the order of the output at the terminals U, V, W of the inverter 23 current pulses can be chosen so that the direction of rotation of it resulting magnetic field in the motor 20 changes faster than the rotor can follow.

When the motor 20 is energized at standstill, significantly higher currents occur in the main winding than when the motor 20 rotates in normal operation. The resulting heating, if it lasts too long, can lead to the destruction of the motor 20. To avoid this, conventional compressors usually have overheat protection, e.g. in the form of a PTC or bimetallic element that interrupts its power supply at too high a temperature of the motor 20. Such an overheat protection element 27 can also be provided on the compressor 7 as shown; the temperature at which it takes effect is lower than the temperature of the compressor 7 required for defrosting, so that it does not hinder the defrosting.

In the embodiment of FIG. 3, the logic unit 21 controls via a relay 28, the supply of both the inverter 23 and a series circuit of a PTC element 29 and the auxiliary winding 26 with operating voltage. The inverter 23 generates at its three connected to the strands 25 output terminals U, V, W suitable for driving a rotation of the motor 20 pulse train, as long as the supply voltage is applied. Consequently, when the compressor 7 has been turned off long enough to allow the PTC element 29 to cool, and the control unit 17 closes the relay 28, the inverter 23 starts to operate and at the same time a current flows through the PTC element 29 and the auxiliary winding 26, so that a rotation of the motor 20 comes into operation. The PTC element 29 is heated by the current flowing through it, so that its resistance increases rapidly after a short time and the current flow through the auxiliary winding 26 is so severely limited that the magnetic field of the auxiliary winding 26 has no influence on the operation of the motor 20.

To initiate a heating operation phase, the logic unit 21 reopens the relay 28 for a short time, typically a few seconds, to cause the motor 20 to stop. This short time is not sufficient to allow the PTC element 29 to cool down to such an extent that again a significant current flow via the auxiliary winding 26 is possible. Consequently, if the relay 28 is closed again after the interruption, the main winding 24 is energized by the converter 23, but in turn lacks the impulse via the auxiliary winding 26, which would initiate a rotation of the motor 20, so that in the main winding 24th fed electrical power only leads to heating.

In this way, when the compressor 7 is heated enough to allow rapid defrosting, the logic unit 21 re-opens the relay 28, this time long enough to allow the PTC element 29 to cool, so that when the relay 28 is closed again, also flows over the auxiliary winding 26 current and the rotation of the motor 20 comes into operation.

Fig. 4 shows a variant in which the logic unit 21 controls two relays, a relay 28, which supplies the inverter 23 with operating voltage, and a relay 30, the series circuit of auxiliary winding 26 and PTC element 29 optionally with the operating voltage or a source 31 connects a measuring voltage which is considerably lower than the operating voltage. In order to set the heating operation mode, the logic unit 21 first closes the relay 28 and supplies the PTC element 29 and the auxiliary winding 26 with the low measurement voltage insufficient to start the rotation of the motor 20. By measuring the current in the PTC element 29 by means of a measuring instrument 32, the logic unit 21 monitors the heating of the motor 20 and terminates the heating mode of operation when a temperature sufficient for defrosting is reached, i. the PTC element 29 functions here as the above-mentioned temperature sensor 19 on the evaporator 7.

The temperature sufficient for defrosting is significantly lower than that which the PTC element 29 assumes when it is supplied via the relay 30 with the operating voltage is charged. Therefore, in order to switch from the heating operation mode to the defrost mode, it is sufficient to switch the relay 30 so that the auxiliary winding 26 and the PTC element 29 are connected to the operating voltage and a current pulse is applied across the auxiliary winding 26 to start the rotation of the motor 20. As described above, in the case of an asynchronous motor having an auxiliary winding 26, control over whether energization of the motor 20 initiates rotation or not may be exercised via the drive of the auxiliary winding 26. Regardless of the type of engine 20 used in the compressor 7, a large pressure difference between the pressure line 8 and the suction line 6 can prevent the motor 20 from starting. Therefore, in such a case, the control unit 17 can bring about a heating operation mode in which it allows the compressor 7, possibly with closed shut-off valves 1 1 and 16, to run for a short time to build up a high pressure in the pressure line 8, then the compressor 7 for a short time Time switches off to let the engine 20 to rest. When the control unit 17 then energizes the motor 20 while the valves 11, 16 are still closed, the high pressure on the line 8 prevents the motor 20 from starting. In such a case, it suffices for the control unit 17 to open the shut-off valve 16 the engine 20 starts and the device transitions from the heating operation phase to the defrosting operation phase.

REFERENCE NUMBERS

1 housing

2 storage room

3 evaporators

4 evaporator chamber

5 fans

6 suction line

7 compressors

8 pressure line

9 branch

10 liquefier

1 1 shut-off valve

12 throttle point

13 low-pressure line section

14 confluence

15 shunt line

16 shut-off valve

17 control unit

18 temperature sensor

19 temperature sensor

20 engine

21 logic unit

22 relays

23 inverters

24 main winding

25 strand

26 auxiliary winding

27 Overheating protection element

28 relays

29 PTC element

30 relays

31 measuring voltage source 32 meter

Claims

Refrigerating appliance, in particular household refrigerating appliance, with at least one storage chamber (2), an evaporator (3) for cooling the storage chamber (2), a compressor (7) for driving a refrigerant flow through the evaporator (3) and a control unit (17) is to supply the compressor (7) with electricity and to switch between a normal cooling mode in which refrigerant passes on the way from the compressor (7) to the evaporator (3) a throttle point (12), and a defrost mode in which the refrigerant, bypassing the throttling point (12) from the compressor (7) passes to the evaporator (3), characterized in that the control unit (17) further between a drive operating mode in which a current to which the control unit (17) the compressor (7) applied, causes a refrigerant flow driving movement of the compressor (7), and a heating mode is switched, in which it pressurizes the compressor (7), without a movement of the refrigerant z u effect.

Refrigerating appliance according to claim 1, characterized in that the power consumption of the compressor (7) in the heating operation mode is at least as high as in the drive operating mode.

Refrigerating appliance according to claim 1 or 2, characterized in that a refrigerant circuit comprises a bypass line (15) which connects parallel to the throttle point (12) an output of the compressor (7) with an input of the evaporator (3), and that in the shunt line (15) arranged shut-off valve (16) is closed in the normal cooling mode and open in defrost mode.

Refrigerating appliance according to claim 1, 2 or 3, characterized in that the control unit (17) is arranged to activate the heating operation mode temporarily before a transition to the defrost mode. Refrigeration appliance according to claim 4, characterized in that the control unit (17) is adapted to activate the heating operation mode, if before the transition to the defrost mode, the temperature of the compressor (7) is below a limit value; or the ambient temperature is below a threshold; or the duration of the last phase in the drive operating mode is below a limit.

Refrigerating appliance according to one of claims 1 to 5, characterized in that the compressor (7) has an asynchronous motor.

Refrigerating appliance according to one of claims 1 to 6, characterized in that a motor (20) of the compressor (7) in the drive operating mode constantly energized main winding (24) and energized only at the beginning of the drive operating mode auxiliary winding (26) and that in the heating mode of operation Auxiliary winding (26) remains energized.

Refrigerating appliance according to one of claims 1 to 6, characterized in that a motor (20) of the compressor (7) in the drive operating mode constantly energized main winding (24) and energized only at the beginning of the drive operating mode auxiliary winding (26) and that in the heating mode of operation Auxiliary winding (26) is energized continuously.

Refrigerating appliance according to claim 7 or 8, characterized in that a by the control unit (17) controlled switch (28; 30) with the auxiliary winding (26) is connected in series.

Refrigerating appliance according to one of claims 1 to 6, characterized in that a motor (20) of the compressor has a main winding (24) and parallel to the main winding (24) connected to a PTC element (29) in series auxiliary winding (26) and in that the control unit (17) is set up to switch on the heating operating mode by energizing the motor (20) in order to heat the PTC element (29), interrupt the current supply and resume it. Refrigerating appliance according to one of the preceding claims, characterized in that the compressor (7) is capable of generating at its output a pressure against which a start-up of the compressor (7) is not possible, and that the control unit (17) established is to activate the heating operation mode by temporarily stopping the compressor (7) and then energizing it again before the pressure at its output has dropped to a value at which startup is possible.

Refrigerating appliance according to one of claims 1 to 1 1, characterized in that the control unit (17) comprises an inverter (23).

Refrigerating appliance according to one of the preceding claims, characterized in that the compressor (7) has at least three connecting terminals (U, V, W) which are to be energized in a first order in order to drive a rotation of the compressor (7) in a working direction, and in that the control unit (17) is set up in the heating operation mode to energize the connection terminals (U, V, W) in a second order deviating from the first order.

Refrigerating appliance according to claim 13, characterized in that winding strands (25) of a motor (20) of the compressor (7) are connected to the connection terminals (U, V, W) in such a way that they are energized when the terminals (U, V, W) are energized. generate in the first order a rotating with a first direction of rotation magnetic field, and that the second order is selected so that a rotating magnetic field with alternating rotation, a stationary or an oscillating magnetic field is generated.

A method for defrosting an evaporator (3), which in a normal cooling mode of a compressor (7) via a throttle point (12) can be acted upon with refrigerant, comprising the steps of: a) operating the compressor (7) in a heating mode in which the compressor (7) is energized without driving a movement of refrigerant, then b) operating the compressor (7) in a drive mode of operation in which the the refrigerant from the compressor (7), bypassing the throttle point (12) for

Evaporator (3) is transported.