REFRIGERATION APPLIANCE WITH COMPARTMENT WHICH CAN BE USED IN A VARIABLE MANNER

Abstract

A refrigeration appliance with multiple storage compartments has a refrigerant circuit with a first expansion valve, a first heat exchanger, a second expansion valve, and a second heat exchanger connected in series between pressure and suction connections of a compressor. Each heat exchanger is associated with at least one storage compartment in order to control its temperature. A control unit controls the compressor rotational speed and positions of the expansion valves. The control unit has a continuously linear regulator for each storage compartment with a P-component for estimating a required temperature control output using a difference between actual and target temperatures. A model computing unit ascertains a target evaporation temperature for a first storage compartment controlled by the first heat exchanger, and for a second storage compartment controlled by the second heat exchanger. The heat exchangers are operated by selecting the compressor rotational speed and the valve positions of the expansion valves.

Claims

1-9. (canceled)

10. A refrigeration appliance, comprising: a plurality of storage compartments; a refrigerant circuit in which a first expansion valve, a first heat exchanger, a second expansion valve, and a second heat exchanger are connected in series between a pressure connection and a suction connection of a compressor; each of said heat exchangers being assigned at least one of said storage compartments in order to control a temperature thereof; a control unit for controlling a rotational speed of said compressor and for controlling respective valve positions of said expansion valves; said control unit including: a continuously linear regulator for each of said storage compartments, said regulator comprising at least one P component for estimating a required temperature control output using a difference between a target temperature and an actual temperature of the respective storage compartment; and a model computing unit configured to determine a target evaporation temperature for at least one first storage compartment of said storage compartments, the temperature of said first storage compartment being controlled by said first heat exchanger, and for a second storage compartment of said storage compartments, the temperature of said second storage compartment being controlled by said second heat exchanger, using the required temperature control output thereof; and to operate said first and second heat exchangers of said first and second storage compartments at the target evaporation temperatures by selecting the rotational speed of said compressor and the valve positions of said expansion valves.

11. The refrigeration appliance according to claim 10, wherein the target evaporation temperature of a respective storage compartment is calculated using an actual temperature of the storage compartment, corrected by a quotient of the required temperature control output and a heat transfer coefficient of the assigned said heat exchanger.

12. The refrigeration appliance according to claim 11, which comprises a fan assigned to said heat exchanger, and wherein the heat transfer coefficient of the heat exchanger is a function of an operating parameter of the fan.

13. The refrigeration appliance according to claim 12, wherein said control unit is configured to set the operating parameter of the fan using an evaporation temperature and a target air humidity of said storage compartment.

14. The refrigeration appliance according to claim 10, wherein said control unit is configured to calculate a mass flow of refrigerant for each of said storage compartments, an evaporation of which covers a required temperature control output of said storage compartment, to total the mass flows to form a total mass flow, and to select the rotational speed of said compressor such that said compressor provides the total mass flow.

15. The refrigeration appliance according to claim 14, which comprises a third heat exchanger of a third storage compartment arranged downstream of said second heat exchanger without an intermediate throttling point, and wherein said control unit is configured to take into consideration a cooling capacity of steam flowing in from said second heat exchanger during a calculation of the mass flow of refrigerant to be evaporated in said third heat exchanger.

16. The refrigeration appliance according to claim 15, wherein said control unit is configured to estimate a heat transfer coefficient of said third heat exchanger or a heat flux via said third heat exchanger as a function of a ratio between liquid and gaseous refrigerant at a transition between said second and third heat exchangers.

17. The refrigeration appliance according to claim 10, further comprising an internal heat exchanger, wherein said control unit is configured to iteratively take into consideration a contribution of said internal heat exchanger during a calculation of the evaporation enthalpy of the refrigerant.

18. The refrigeration appliance according to claim 10, wherein said refrigerant circuit comprises a plurality of parallel line sections, including one line section that contains said first expansion valve, said first heat exchanger and said second expansion valve, and at least one other said line section that contains a third expansion valve, a fourth heat exchanger and a fourth expansion valve.

19. The refrigeration appliance according to claim 10, configured as a household refrigeration appliance.

Description

[0014] Further features and advantages of the invention result from the following description of exemplary embodiments with reference to the appended figure, in which

[0015] FIG. 1 shows a block diagram of an inventive refrigeration appliance;

[0016] FIG. 2 shows a block diagram of a control unit of the refrigeration appliance.

[0017] FIG. 1 shows a block diagram of an inventive refrigeration appliance. In a heat-damping housing 1, at least three, here four storage compartments 2, 3, 4, 23, are cut out. Each of these storage compartments 2, 3, 4, 23 is assigned a heat exchanger 5, 6, 7, 24. The assignment can consist for instance in the heat exchanger being embedded in the manner of a cold wall evaporator between an inner container of the storage compartment and a layer of insulation material surrounding the inner container, or in the heat exchanger 5, 6, 7, 24 being assembled in the inner container 8 of the relevant storage compartment 2, 3, 4, 23. In the latter case, a separating wall 9 can be provided in the inner container, which separating wall subdivides the volume of the inner container into the storage compartment 2, 3, 4 and a heat exchanger chamber 10 which receives the heat exchanger 5, 6, 7.

[0018] Irrespective of how the heat exchanger 5, 6, 7, 24 is assigned to the storage compartment 2, 3, 4, 23, a fan 11 can be assigned to each heat exchanger 5, 6, 7, 24 in order to intensify the heat transfer between the storage compartment 2, 3, 4, 23 and its heat exchanger 5, 6, 7, 24. The rotational speed or output of such a fan 11 can be fixedly predetermined or, as explained again more precisely below, can be controlled.

[0019] Each storage compartment 2, 3, 4, 23 is equipped with a temperature sensor 12. Measured values of the temperature sensor 12 are detected by a control circuit 13.

[0020] A refrigerant circuit comprises, starting from a pressure connection of a compressor 14, in sequence a condenser 15, a pressure line 16, a first expansion valve 17, the heat exchanger 5, a second expansion valve 18, the second heat exchanger 6, the third heat exchanger 7 and a suction line 19, which leads to a suction connection of the compressor 14.

[0021] If, as shown in FIG. 1, a further fourth storage compartment 23 is provided, its heat exchanger 24, an upstream expansion valve 25 and a downstream expansion valve 26 can be arranged in a branch of the refrigerant circuit, which extends parallel to a branch, between two connection points 27, 28, which contains the expansion valves 17, 18 and the heat exchanger 5. If necessary, provision can be made for further parallel branches with in each case two expansion valves and a heat exchanger for controlling the temperature of further storage compartments.

[0022] The expansion valves 17, 18, 25, 26 are of a construction type known per se, not described here, and are designed to set an opening cross-section, predefined by a control signal, between the inlet and outlet. The source of the control signals is the control circuit 13.

[0023] The pressure line 16 and the suction line 19 run over one part of their length in a contrarotating manner in close contact with one another, in order thus to form an internal heat exchanger 22, in which the compressed refrigerant outputs residual heat to the vapor in the suction line 19 shortly before reaching the expansion valve 17.

[0024] The pressure difference occurring on the expansion valves 17, 25 is to a great extent variable. On the one hand, with a maximum opening of the expansion valve 17 (or 25) in the heat exchanger 5 (or 24), a pressure develops, which, if at all, only differs minimally from the pressure at the pressure connection of the compressor 14, so that condensation of refrigerant can take place in the heat exchanger 5 (or 24) and in the condenser 15, and the storage compartment 2 (23) can be operated at a target temperature above the ambient temperature, and refrigerant condensed in the condenser 15 and heat exchanger 5 and/or 24 is supplied to the heat exchangers 6 and 7 by way of the expansion valve 18. An upper limit of the temperature at which the storage compartment 2 or 23 can be operated should not amount to below +18° C.

[0025] In order to enable operation of the storage compartment 3 as a freezer compartment, even if the storage compartment 2 (and/or 23) is operated as a normal refrigeration compartment, a non-negligible drop in pressure at the expansion valve 18 is required. The maximum pressure difference at the expansion valve 18 should be enough to also then enable a freezer compartment operation of the storage compartment 3 if essentially the full outlet pressure of the compressor 14 is present at the input of the expansion valve 18.

[0026] There is no appreciable drop in pressure between the heat exchangers 6 and 7. In particular, both heat exchangers 6, 7 and a line connecting them can be manufactured from the same type of pipe with constant cross-sectional dimensions.

[0027] Target temperatures for all three storage chambers 2, 3, 4 can be set on a user interface 20 of the control circuit 13. If one of the storage chambers 2, 3, 4 has a fan 11, provision can also be made for the possibility to use the user interface 20 to select an air humidity value for the relevant storage chamber.

[0028] FIG. 2 shows a block diagram of the control unit 13. At the left edge of the diagram, inputs for the setpoint variables set by the user on the interface 20 are shown, namely the target temperatures T.sub.target, flex1 of the storage compartment 2, T.sub.target, fridge of the storage compartment 4 used as a normal cooling compartment and T.sub.target, freezer of the storage compartment 3 operated as a freezer compartment and facultatively T.sub.target, flex2 of the storage compartment 23 and target humidity values φ.sub.target, flex1 of the storage compartment 2 and φ.sub.target, flex2 of the storage compartment 23.

[0029] Each target temperature and the associated actual temperature measured by the sensor 12, e.g. the temperatures T.sub.target, flexI and T.sub.sensor, flexI, are present at the inputs of a differential circuit 29, in order to determine a target value difference which is in turn an input variable of a PID controller 30. Each PID controller 30 supplies an output signal, which is an estimated value for the required temperature control output {dot over (Q)}.sub.0,1, i∈{flex1, flex2, freezer, fridge}, i.e. for the cooling or heating output which has presumably to be fed to the relevant storage compartment 2, 3, 4 23 in order to bring it to or retain its target temperature.

[0030] A model computing unit 31 receives as input variables the required temperature control outputs {dot over (Q)}.sub.0,1 of the storage compartments 2, 3, 4, 23, the actual temperatures T.sub.F,i thereof measured by the sensors 12, boundary conditions such as for instance the condensation temperature T.sub.c in the condenser 15, the ambient temperature T.sub.∞, and, if a humidity controller of the compartments 2, 23 is provided, the rotational speeds n.sub.fan,i; of its fans 11.

[0031] The output variables of the model computing unit 31 are positions pos.sub.valve,i of the expansion valves 16, 17, 25, 26 and the rotational speed n.sub.compr of the compressor 14. These already afore-described components are combined in the diagram in FIG. 2 in a controlled system 32.

[0032] The model computing unit 31 uses the known required temperature control outputs {dot over (Q)}.sub.0,1, i∈{flex1, flex2, freezer, fridge} to calculate the evaporation temperatures in the compartments 2, 23, 4, the temperature difference between the compartment and evaporator is produced from the refrigerant power and heat transfer capacity of the evaporator.

[0033] The evaporation enthalpy Δh.sub.evap is produced from the evaporation temperature of the freezer compartment 3, T.sub.evap,freezer, the condensation temperature T.sub.c, an assumed subcooling ΔT.sub.sc and the transmitted enthalpy Δh.sub.IHX of the internal heat exchanger 22: the specific evaporation enthalpy is produced from the boiling/thawing line of condensation/evaporation temperature, the subcooling at the condenser end and the specific heat transfer of the inner heat exchanger.

[0034] The condensation temperature T.sub.c can be measured; alternatively it is estimated by the model computing unit 31 on the basis of the ambient temperature T.sub.∞ and the heat transfer coefficient kA.sub.c,eff of the condenser, wherein it is assumed that the heat output emitted by the condenser equates to the total of the required temperature control outputs absorbed by the heat exchangers 5, 6, 7, 24.

[0035] The enthalpy Δh.sub.IHX is a priori not known, here an empirical value can firstly be assumed from the past, which is then refined iteratively.

[0036] The evaporation rate in each of the heat exchangers 5, 6, 7, 24, i.e. how much refrigerant evaporates there per time unit (or in the case of the compartments 2, 23 possibly also condenses) is produced from the required temperature control output {dot over (Q)}.sub.0,1 of the assigned compartment 2, 3, 4 or 23 and the evaporation enthalpy determined according to (2). The evaporating mass flow is calculated for the flex compartments 2, 23 and the freezer compartment 3 from the required temperature output and the evaporation enthalpy.

[0037] In the cooling compartment 4, a calculation purely by way of the evaporation enthalpy would be insufficient since here also refrigerant vapor, which passes from the heat exchanger 6 of the freezer compartment 3 into that of the cooling compartment 4, contributes {dot over (Q)}.sub.0,gas to the cooling effect of the heat exchanger 7 and is produced from the heat transfer of a warming one-phase medium.

[0038] If this contribution {dot over (Q)}.sub.0,gas is already greater than the required temperature control output {dot over (Q)}.sub.0,fridge of the cooling compartment 4, the rotational speed of the fan 11 of the cooling compartment 4 is reduced. Otherwise, according to equation (6), the portion ζ.sub.2 phase of the heat exchanger 7 in which evaporation takes place is calculated.

[0039] If liquid coolant also flows into the heat exchanger 7, only a small portion is still available for the heat exchange with the converted steam; accordingly the contribution of the converted steam to the heat transfer coefficient of the heat exchanger 7 is reduced. This is taken into account by the evaporator region with a pure gas flow back into the calculation of the refrigeration power.

[0040] The mass flow evaporating in the cooling compartment heat exchanger is then produced from the difference between the refrigerant requirement and cooling power of the gas.

[0041] The total of the evaporating mass flows across all compartments produces the entire mass flow which the compressor conveys 14.

[0042] In a simple embodiment and as explained subsequently in more detail, the model computing unit 31 could now calculate and output the rotational speed of the compressor 14 required herefor. Here it would however have to neglect the influence of the internal heat exchanger 22.

[0043] For the enthalpy transmitted in the internal heat exchanger 22, is calculated from the difference between the high pressure temperature and exit temperature of the cooling compartment evaporator, the overall mass flow and the structure of the inner heat exchanger. The enthalpy at the exit of the KF evaporator calculates the enthalpy at the condenser exit, the enthalpy transfer of the inner heat exchanger and the quotient from the total of the temperature control outputs and mass flow. The temperature at the exit of the cooling compartment evaporator is then produced therefrom.

[0044] The determination of the compressor speed on the basis of the total mass flow is carried out on the basis of the suction gas density, an estimate for the service level and the compressor-specific displaced volume.

[0045] The evaporation temperatures or pressures determined from the above calculations, the specific enthalpies and thus the gas portions at the corresponding positions of the refrigerant circuit (and if parallel heat exchangers such as here 5 and 24 are available, the division of the mass flow hereto) are boundary conditions for a valve model, with which the model computing unit 31 calculates the correct positions of the expansion valves.

[0046] As mentioned above, there may be the option to predefine a desired air humidity in the compartment 2 or 23 on the user interface 20.

[0047] If a compartment i (2, 3, 4 or 23) is cooled, its heat exchanger 5, 6, 7 or 24 is the coldest point. The steam pressure of the water in the air of the compartment can therefore only be as high as that to which the saturation vapor pressure corresponds at the temperature of the heat exchanger. The greater the temperature difference between the storage area of the compartment and the evaporator, the lower therefore the relative air humidity in the storage area. In order to set a given target temperature in the compartment, the fan of the compartment can run fast with a small temperature difference or slowly with a high temperature difference; in one case there is a high air humidity and in the other a low air humidity. In order to reach a predefined relative air humidity in a compartment, the model computing unit 31 selects the evaporation temperature T.sub.evap,i of the heat exchanger assigned to the compartment so that the saturation vapor pressure P.sub.sat,i(T.sub.evap,i) of water produces the desired relative air humidity at this temperature at the target temperature of the compartment and controls the speed of the fan so that the target temperature of the compartment is reached.

[0048] If the difference between the actual and target temperature of the compartment exceeds a predefined limit value, this type of regulation can be discontinued and the fan can be set so that as efficient a cooling as possible of the compartment is achieved. This is generally a high fan speed, however for acoustic reasons this rotational speed can be lower than a specified maximum rotational speed of the fan.

REFERENCE CHARACTERS

[0049] 1 Housing [0050] 2 Storage compartment [0051] 3 Storage compartment [0052] 4 Storage compartment [0053] 5 Heat exchanger [0054] 6 Heat exchanger [0055] 7 Heat exchanger [0056] 8 Inner container [0057] 9 Separating wall [0058] 10 Heat exchanger chamber [0059] 11 Fan [0060] 12 Temperature sensor [0061] 13 Control circuit [0062] 14 Compressor [0063] 15 Condenser [0064] 16 Pressure line [0065] 17 Expansion valve [0066] 18 Expansion valve [0067] 19 Suction line [0068] 20 User interface [0069] 21 Fan [0070] 22 Internal heat exchanger [0071] 23 Storage compartment [0072] 24 Heat exchanger [0073] 25 Expansion valve [0074] 26 Expansion valve [0075] 27 Connection point [0076] 28 Connection point [0077] 29 Differential circuit [0078] 30 PID controller [0079] 31 Model computing unit [0080] 32 Controlled system