REFRIGERATION APPLIANCE AND METHOD FOR INITIALISING A DEFROSTING OPERATION IN A REFRIGERATION APPLIANCE

Abstract

A method initializes a defrosting operation in a refrigeration appliance having a speed-controlled compressor. The method includes the steps of: a) starting up the compressor at a speed set to an initial value, b) adjusting the speed of the compressor in order to prevent a temperature in a storage chamber of the refrigeration appliance from deviating from a target temperature, c) monitoring a deviation between an adjusted speed and the initial value, and d) deciding that defrosting is necessary if the deviation exceeds a limit value.

Claims

1-11. (canceled)

12. A method for initializing a defrosting procedure in a refrigeration appliance with a variable speed compressor, which comprises the steps of: a) starting up the variable speed compressor with a rotational speed n.sub.t set to an initial value n.sub.0; b) adapting the rotational speed n.sub.t of the variable speed compressor, in order to prevent a temperature of a storage chamber of the refrigeration appliance from drifting from a setpoint temperature; c) monitoring a deviation between an adapted rotational speed n.sub.t and the initial value n.sub.0; and d) deciding that defrosting is necessary when the deviation exceeds a limit value.

13. The method according to claim 12, wherein the monitoring includes increasing the deviation, if the adapted rotational speed n.sub.t lies above the initial value n.sub.0.

14. The method according to claim 12, wherein the monitoring includes reducing the deviation, if the adapted rotational speed n.sub.t lies below the initial value n.sub.0.

15. The method according to claim 12, which further comprises ascertaining the deviation as a time integral of a difference between the adapted rotational speed n.sub.t and the initial value n.sub.0 or the time integral of the difference of one of a plurality of terms that are summed to form the deviation.

16. The method according to claim 12, wherein the adapting of the rotational speed n.sub.t of the variable speed compressor in step b) includes a lowering of the rotational speed n.sub.t in an event of falling below a first limit temperature of the storage chamber, and raising the rotational speed n.sub.t in an event of exceeding a second limit temperature of the storage chamber.

17. The method according to claim 12, wherein in step a), ascertaining the rotational speed which, in a starting phase of an operation after the defrosting procedure, proves to be suitable for preventing the temperature in the storage chamber of the refrigeration appliance from drifting from the setpoint temperature, and the initial value n.sub.0 is derived from a suitable rotational speed.

18. The method according to claim 12, wherein the initial value n.sub.0 is predefined as a function of an ambient temperature.

19. The method according to claim 18, wherein the initial value n.sub.0 is a function of an instantaneous ambient temperature.

20. The method according to claim 18, wherein the limit value is a decreasing function of a compressor runtime since a last defrosting procedure.

21. A refrigeration appliance, comprising: at least one storage chamber; a variable-speed compressor for cooling said at least one storage chamber; and a controller for regulating a rotational speed of said variable speed compressor on a basis of a temperature measured in said at least one storage chamber, said controller configured to initializing a defrosting procedure in the refrigeration appliance by said controller being programmed to: a) start up said variable speed compressor with the rotational speed n.sub.t set to an initial value n.sub.0; b) adapt the rotational speed n.sub.t of said variable speed compressor, in order to prevent the temperature of said at least one storage chamber of the refrigeration appliance from drifting from a setpoint temperature; c) monitor a deviation between an adapted rotational speed n.sub.t and the initial value n.sub.0; and d) decide that defrosting is necessary when the deviation exceeds a limit value.

22. The refrigeration appliance according to claim 21, wherein the refrigeration appliance is a household refrigeration appliance.

23. A non-transitory computer readable medium having computer readable instructions that enable a computer to carry out a method for initializing a defrosting procedure in a refrigeration appliance with a variable speed compressor, which comprises the steps of: a) starting up the variable speed compressor with a rotational speed n.sub.t set to an initial value n.sub.0; b) adapting the rotational speed n.sub.t of the variable speed compressor, in order to prevent a temperature of a storage chamber of the refrigeration appliance from drifting from a setpoint temperature; c) monitoring a deviation between an adapted rotational speed n.sub.t and the initial value n.sub.0; and d) deciding that defrosting is necessary when the deviation exceeds a limit value.

Description

[0027] Further features and advantages of the invention will emerge from the description of exemplary embodiments provided below, with reference to the attached drawings, in which:

[0028] FIG. 1 shows a refrigeration appliance in accordance with the present invention in schematic form;

[0029] FIG. 2 shows a flow diagram of a method in accordance with a first embodiment of the invention; and

[0030] FIG. 3 shows a flow diagram of a method in accordance with a second embodiment of the invention

[0031] FIG. 1 shows a schematic section through a household refrigeration appliance of a construction which is known per se. A thermally insulating carcass 1 and at least one door 2 delimit at least one storage chamber 3. Accommodated in a machine room 4 of the carcass 1 is a variable speed compressor 5, which is connected to a condenser (not shown), a choke point and at least one evaporator 6 in a coolant circuit and supplies the evaporator 6 with liquid coolant to cool the storage chamber 3.

[0032] Here, the evaporator 6 is shown as a no-frost evaporator in an evaporator chamber 8 separated from the storage chamber by an intermediate wall 7. Here, a defrost heater 9 can be formed by a heating rod, which is mounted on an underside of the block-shaped evaporator 6 and heats said evaporator by physical contact, radiation and/or convection during defrosting. A passage 13 is provided at the bottom of the evaporator chamber 8, in order to drain condensation water from the evaporator 6 to the outside, typically into an evaporation pan 14 in the machine compartment 4.

[0033] A control circuit 10, typically a microprocessor system that controls the operation of the compressor 5 and the defrost heater 9, can be placed at any suitable place on the carcass 1. The control circuit 10 is connected to an internal temperature sensor 11 for detecting the temperature of the storage chamber 3; furthermore, an ambient temperature sensor 12 for detecting the ambient temperature can be connected to the control circuit 10.

[0034] FIG. 2 shows an operating method for the control circuit 10 in accordance with a first embodiment of the invention. This operating method does not require the ambient temperature sensor 12.

[0035] During normal operation, the control circuit 10 runs through a loop at regular time intervals, of which the first step S1, in the representation in FIG. 2, is the detection of the internal temperature Tin with the aid of the temperature sensor 11. This internal temperature Tin should be kept close to a setpoint temperature set on the control circuit 10 by the user. To this end, in step S2 the control circuit 10 compares the internal temperature Tin with a first limit temperature T1, which may be identical to the setpoint temperature, but preferably is a few degrees lower. In the event of falling below the limit temperature T1, then this indicates that the instantaneous rotational speed n.sub.t of the compressor 5 is higher than required to maintain the setpoint temperature; for this reason, in this case, the rotational speed n.sub.t is decremented (S3) by a predefined step size.

[0036] In step S4, the internal temperature Tin is compared with a second limit temperature T2, and in the event of T2 being exceeded, the rotational speed n.sub.t is decremented in step S5. The step sizes can be the same in step S3 and S5, but do not have to be. Likewise, the second setpoint temperature T2 can be identical to the setpoint temperature, but typically lies slightly higher, so that T1 and T2 define a temperature interval of a few degrees wide, within which the rotational speed n.sub.t is not changed.

[0037] In step S6, the difference between the instantaneous rotational speed n.sub.t of the compressor 5 and an initial value n.sub.0 is added to a control variable Int. Since, as the thickness of a layer of frost on the evaporator 6 increases, the compressor rotational speed needed to keep the storage chamber 3 at the setpoint temperature rises, this difference tends to assume values that are all the more positive, the longer it has been since the last defrosting procedure, meaning that the control variable Int rises over time.

[0038] As long as it is determined in step S7 that the control variable Int has not yet exceeded a threshold value thr, the method returns to the beginning, and the loop of steps S1 to S6 is repeated.

[0039] By contrast, if the threshold thr is exceeded, then the control circuit 10 switches off the defrost heater 9 and the compressor 5, in order to defrost (S8) the evaporator 6.

[0040] Following successful defrosting, the control variable Int is reset (S9) to a starting value that is lower than thr, typically to zero, and the compressor 5 is returned to operation.

[0041] The rotational speed when resuming operation can be a fixed standard value; it is also conceivable to resume operation with the rotational speed at which it was canceled in order to perform the defrosting. In the latter case, the rotational speed is usually higher than required to keep the storage chamber 3 at the setpoint temperature during continuous operation; however, this is also expedient in order to remove the heat, which has entered during the defrosting, from the storage chamber 3 again in a short period of time.

[0042] The temperature Tin of the storage chamber 3 is measured in step S10 and then compared with T1 in step S11. Due to the preceding interruption of the cooling operation and the unavoidable ingress of heat due to the defrosting, the temperature Tin will lie above T1 immediately after the resumption of the operation of the compressor, meaning that the steps S10, S11 are repeated until T1 is exceeded. If, as described above, the restart rotational speed of the compressor 5 has with certainty been chosen to be higher than necessary for maintaining the setpoint temperature, then it is sufficient to repeat the steps S10, S11; otherwise, it can be provided that the rotational speed is increased (S12) incrementally for as long as T1 has not yet been reached. In either case, at the point in time at which Tin falls below T1, the rotational speed n.sub.t is higher than necessary for maintaining the setpoint temperature.

[0043] Furthermore, the temperature Tin is also measured (S13) after falling below T1, and is compared (S14) with T1. If it remains below T1, then each time step S15 is repeated the rotational speed n.sub.t of the compressor 5 is decremented; additionally, a flag Fl− is set in order to indicate that T1 has been fallen below after restarting the compressor 5.

[0044] The consequence of decrementing the rotational speed n.sub.t is that T2 is exceeded again, sooner or later. As soon as this is identified in step S16, a second flag Fl+ is set (S17) in order to indicate the exceeding, and the rotational speed n.sub.t is incremented again. As soon as it is identified in step S18 that both flags Fl−, Fl+ are set, the loop of steps S13-S8 is canceled.

[0045] The rotational speed n.sub.t set at this point in time is specified as initial value n.sub.0 in step S19, after which the method returns to normal operation, i.e. the loop of step S1 to S7.

[0046] Since, in this way, a slightly lower value is chosen for n.sub.0 than is necessary to maintain the setpoint temperature, the difference n.sub.t−n.sub.0 is more often positive than negative during normal operation. This ensures that the control variable Int rises in the long term, and that sooner or later a new defrosting procedure is triggered. The faster that frost builds up on the evaporator 6, and for this reason the rotational speed n.sub.t is raised, the faster that the variable Int rises, and the faster that defrosting takes place once more.

[0047] FIG. 3 shows a flow diagram of an operating method in accordance with a second embodiment of the invention. The representation of the method begins here with a step of defrosting the evaporator 6. This step is identical to the step S8 of the method from FIG. 2, and for this reason is also referred to as S8. The subsequent step S9 of resetting the control variable Int is also identical.

[0048] This is followed by a step S20 of measuring the ambient temperature Tout with the aid of the sensor 12. A function F, which assigns a rotational speed of the compressor 5 to a measured ambient temperature Tout in each case, is stored in the control unit 10 in the form of a lookup table or a calculation rule. On the basis of this function F and the measured temperature Tout, an appropriate initial value n.sub.0 for the rotational speed when restarting the compressor 5 after the defrosting is specified in step S21. The function F can be defined such that it assigns each value of the ambient temperature Tout precisely the rotational speed that would be produced in stationary operation with a frost-free evaporator 6 for the ambient temperature in question when the steps S1-S5 described above are carried out repeatedly; in this case the compressor could theoretically run for any given length of time without defrosting, if the door 2 is not opened and also no moisture enters the storage chamber 3 in other ways that could condense as frost on the evaporator.

[0049] It is also conceivable, however, as described above in connection with FIG. 2, to choose the values of F to be slightly smaller in each case, in order thus to ensure that defrosting occurs after a finite runtime of the compressor 5, even without the rotational speed n.sub.t rising over time.

[0050] The same effect could also be achieved by the threshold value thr being reduced in a time-dependent manner, e.g. by a step of decrementing thr being added into the loop S1-S7.

[0051] After specifying the initial value n.sub.0, the temperature Tin of the storage chamber 3 is detected; this step is identical to the step S1 from FIG. 2 and therefore is also referred to as S1. The following steps S2-S7 are also the same as in FIG. 2 and are therefore not described once more here. If it emerges in step S7 that the control variable Int has exceeded the threshold value thr, then the method branches out to S8, in order to defrost the evaporator 6.

[0052] If the threshold value thr has not yet been reached in step S7, then a first variant of the method returns to step S1, in order once again to measure the temperature Tin, so that after repeatedly running through the loop S1-S7 the control variable Int approximates the integral

[00001]$\int n_t-n_0\mathrm{dt}$

where n.sub.0=F(Tout(t.sub.0)), i.e. is the value of F that corresponds to the temperature Tout at the point in time to of restarting operation of the compressor.

[0053] If the ambient temperature decreases or increases during an operating phase of the compressor 5, then this leads to a reduction or increase in the rotational speed n.sub.t over steps S2 or S4. A reduction would have the consequence that the control variable Int rises more slowly than if the ambient temperature were to remain the same, and that consequently a defrosting procedure is delayed, even if the frost on the evaporator 6 has already reached a thickness at which it would make sense to perform a defrosting; conversely, an increase in the ambient temperature can trigger a premature defrosting. In order to avoid this, if the threshold value thr has not yet been reached in step S7, according to a second variant, the method jumps back to step S21, i.e. the ambient temperature Tout is measured, and n.sub.0 is updated on the basis of the measured temperature: n.sub.0(t)=F(Tout(t)), where t is the current point in time in each case. In this way, the time period between two defrosting procedures can be made independent of fluctuations in the ambient temperature Tout.

REFERENCE CHARACTERS

[0054] 1 carcass [0055] 2 door [0056] 3 storage chamber [0057] 4 machine compartment [0058] 5 compressor [0059] 6 evaporator [0060] 7 intermediate wall [0061] 8 evaporator chamber [0062] 9 defrost heater [0063] 10 control circuit [0064] 11 internal temperature sensor [0065] 12 ambient temperature sensor [0066] 13 passage [0067] 14 evaporation pan