Patent Application
20190390882
The present invention relates to a refrigeration appliance, in particular a household refrigeration appliance, having a plurality of temperature zones, and a method for operating a refrigeration appliance of this kind.
DE 10 2013 226 341 A1 discloses a refrigeration appliance having a first and a second temperature zone, in which a refrigerant circuit includes a compressor, a first evaporator for cooling the first temperature zone and, connected in series with the first evaporator, a second evaporator for cooling the second temperature zone, and in which a controllable expansion valve is connected upstream of each evaporator in the refrigerant circuit.
In this known refrigeration appliance, if there is an unmet need for cooling in a temperature zone, throttling at the controllable expansion valve lying upstream of the evaporator for this temperature zone is increased, with the result that the evaporating temperature in the relevant evaporator falls. In order to prevent this measure from also having an effect on other evaporators downstream in the refrigerant circuit, throttling in an expansion valve downstream of the relevant evaporator is reduced as a counter-measure, with the result that throttling of the expansion valves connected in series remains unchanged: in this way, the mass flow of refrigerant in the refrigerant circuit also remains unchanged overall, with the result that cooling power that is additionally available in this way in the relevant temperature zone has to be withheld from the other temperature zones. If an unmet need for cooling then arises in another temperature zone, then the available cooling power is redistributed again, which results in undesired fluctuations in temperature. As a result of redistributing the cooling power, it is not possible to take account of the changing need for cooling in all the temperature zones which in practice unavoidably arises as a result of changes in temperature in the area surrounding the refrigeration appliance.
It is the object of the invention to develop a refrigeration appliance of the type known from DE 10 2013 226 341 A1, and to provide a method for operation of a refrigeration appliance, which enable simple and stable temperature control of the different temperature zones.
The object is achieved, in a first aspect, in that in a refrigeration appliance having at least a first and a second temperature zone and a refrigerant circuit that includes a compressor, a first evaporator for cooling the first temperature zone and a second evaporator for cooling the second temperature zone, wherein the first evaporator is connected in series with the second evaporator, downstream thereof in the refrigerant circuit, and a first controllable throttling point is connected in the refrigerant circuit upstream of the first evaporator and downstream of the second evaporator, a first regulator controls the degree of opening of the first controllable throttling point, independently of the temperature of the first temperature zone, by way of the temperature of the second temperature zone.
The basic concept here is that the mass flow in the refrigerant circuit is determined by the intake conditions (pressure and temperature) that prevail at a suction connector of the compressor and an outlet of the first evaporator leading to this suction connector. If the degree of opening of the first controllable throttling point is changed, it takes considerable time before this results in a change in the intake conditions (superheated gas at evaporation pressure) in the first evaporator, which lies between the first throttling point and the suction connector. As long as the intake conditions remain the same, adjustment of the degree of opening has no effect on the mass flow but does have an effect on the cooling power of the second evaporator, which lies upstream of the first controllable throttling point.
Only once there is a change to the intake conditions is there also a change in the cooling power of the first evaporator lying downstream of the first controllable throttling point. In order to counter this change, advantageously a compressor regulator, which controls adaptation of the compressor speed by way of the temperature of the first temperature zone, is provided. It is only this change in speed which also results in a change in the mass flow. Depending on the mass flow, the cooling power that can be distributed to the different temperature zones also changes, with the result that the change to the cooling power affecting the second evaporator need not be compensated, or at least not in its entirety, by a countering change in power at the first evaporator. Thus, it is possible to decouple regulation of the individual temperature zones in a simple manner. Because of inertia in the system, it is immaterial when a change to the total cooling power as a result of a briefly unmet need for cooling in an individual compartment occurs.
Independence of the temperature in the first temperature zone simplifies control of the first throttling point, since there is no need for two influencing variables to be taken into account at the same time.
The first regulator should be set up to increase the degree of opening of the first controllable throttling point when a setpoint temperature in the second temperature zone is exceeded, and to reduce the degree of opening of the first controllable throttling point when the temperature falls below a setpoint temperature in the second temperature zone. If for example the first regulator increases the degree of opening of the first controllable throttling point, then the pressure in the second evaporator falls, and the temperature thereof then also falls, with the result that the second temperature zone is cooled to a greater extent, as desired; conversely, the pressure and temperature of the second evaporator rise when the degree of opening of the first controllable throttling point is increased.
In order to enable rapid adaptation of the degree of opening to a change in conditions, the first regulator should be a proportional regulator, preferably a PI controller—that is to say the change in the degree of opening caused by the first regulator should include a term that is proportional to the deviation between the actual and the setpoint temperature, and preferably also a term that is proportional to the duration of the deviation.
The second temperature zone should have a temperature sensor that is connected to an input to the first regulator. Further measurement variables are not required to control the first controllable throttling point—that is to say that this input may be the only input to the first regulator to receive a measurement variable.
Typically, there is no controllable throttling point connected downstream of the first evaporator. So that it is also possible to influence the temperature of this, it is possible, as mentioned above, to provide a compressor regulator that controls the speed of the compressor by way of the temperature and/or an unmet need for cooling of the temperature zone that comes last, as seen in the direction of flow.
The compressor regulator should be set up to increase the speed of the compressor when a setpoint temperature in the last temperature zone, as seen in the direction of flow, is exceeded, and to reduce the speed of the compressor when the temperature falls below a setpoint temperature in the last temperature zone, as seen in the direction of flow. Similarly to the manner in which the degree of opening the first controllable throttling point is increased, as explained above, increasing the speed brings about not only a reduction in the pressure and temperature in the first evaporator but at the same time also an increase in the mass flow of refrigerant, with the result that an additional cooling power that is required is provided in one of the temperature zones. Among other things, this favors rapid reinstatement of an energy-efficient steady operating state of the refrigeration appliance if the need for cooling has changed in all the temperature zones after a change in the ambient temperature.
The compressor regulator may be coupled to the first regulator and be set up to increase the speed when the degree of opening of the first controllable throttling point is increased and to reduce it when the degree of opening of the first controllable throttling point is reduced. In this way, a proactive adaptation of the compressor speed is already possible at a point in time before a change in the degree of opening of the first controllable throttling point has had any effect on the cooling power of the first evaporator.
The compressor regulator may also be a proportional or PI controller.
The principle of the invention may be extended to an indefinite number of evaporators connected in series, for example by connecting a third evaporator, which is for controlling the temperature of a third temperature zone, upstream of the second evaporator in the refrigerant circuit by way of a second controllable throttling point, and by providing a second regulator in order to control the degree of opening of the second controllable throttling point by way of the temperature of the third temperature zone independently of the temperature of the second temperature zone.
It goes without saying that the compressor regulator may in that case also be coupled to the second regulator in order to take account of a change to the degree of opening of the second controllable throttling point when the compressor speed is established.
The second regulator for controlling the second throttling point may operate entirely independently of the first regulator. In practice, in fact, both regulators may be implemented in the form of software on the same processor; the fact that they are mutually independent is seen in the fact that the two do not have access to the same temperature sensors, nor does one of the regulators use output data from the other as input data.
Between a pressure-side connector of the compressor and the evaporators there may be provided an upstream controllable throttling point. In order to control the distribution of refrigerant between the evaporators and a high-pressure portion of the refrigerant circuit, the degree of opening of this throttling point may be controlled by way of a drop in temperature at the first evaporator. A distribution regulator that is used for this purpose may in turn be independent, in the sense specified above, of the first, second and any further regulators.
For an efficient heat transfer between the evaporator and the associated temperature zone, there may be associated with at least one of the evaporators a ventilator for driving air current that streams over a surface of the evaporator.
In order to control the air humidity in the temperature zone, this ventilator may be capable of being switched between at least two operating modes of different speeds. One of these modes may be operation at high speed, which keeps the difference in temperature between the temperature zone and the evaporator small and accordingly has only a small dehumidifying effect on the circulated air at the evaporator. Although the evaporator temperature, relatively high in this mode, enables efficient generation of refrigeration, because of the high ventilator output it does not achieve an ideal level of efficiency. In a second mode, the ventilator can be switched off or operated at low speed, with the result that the evaporator reaches low temperatures which, although they are typically not of ideal energy efficiency either, have a pronounced air dehumidifying effect. In a further mode, the ventilator can be operated at medium speed in order to optimize the energy efficiency of the appliance.
The object is further achieved by a method for operating a refrigeration appliance having at least a first and a second temperature zone and a refrigerant circuit that includes a compressor, a first evaporator for cooling the first temperature zone and a second evaporator for cooling the second temperature zone, wherein the first evaporator is connected in series with the second evaporator, downstream thereof in the refrigerant circuit, and a first controllable throttling point is connected in the refrigerant circuit upstream of the first evaporator and downstream of the second evaporator, in which the temperature of the second temperature zone is measured and the degree of opening of the first controllable throttling point, independently of the temperature of the first temperature zone, is controlled by way of the temperature of the second temperature zone.
A variable speed of the compressor can be controlled by way of the measured temperature of the first temperature zone.
Further, if the degree of opening of the first (or the second, if present) controllable throttling point is increased the speed of the compressor may be increased, and if the degree of opening of the same controllable throttling point is reduced the speed of the compressor may be reduced.
Further features and advantages of the invention become apparent from the description of exemplary embodiments, given with reference to the attached figures, in which:
Each temperature zone 1, 2, 3, 4 has an evaporator 6, 7, 8 and 9 respectively, which are connected within a refrigerant circuit having a compressor 10 and a condenser 11. At least two evaporators, in this case the evaporators 6, 7, 8, are connected in series along a branch 13 of a refrigerant line 12; as shown, the refrigerant line 12 may have further branches 14 that are parallel to the branch 13 and supply further evaporators, in this case the evaporator 9.
Each evaporator 6, 7, 8, 9 and the condenser 11 are combined with a respective ventilator 25 for increasing the heat transfer output.
The temperature zones 1, 2, 3, 4 may each be divided, in a manner known per se, into a storage compartment and an evaporator chamber, which receives the evaporator 6, 7, 8 or 9, in which case the ventilator 25 drives the air exchange between the storage compartment and the evaporator chamber.
The temperature difference that must prevail between an evaporator and the storage compartment cooled thereby in order to be able to keep the storage compartment at its setpoint temperature depends on the extent of the air exchange between the storage compartment and the evaporator chamber. If this is small, then the evaporator temperature must be low, and since maintaining a low evaporator temperature requires a high output from the compressor 11 the energy efficiency of the appliance is limited. Because of the low evaporator temperature, almost all the water vapor reaching the evaporator chamber from the storage compartment is precipitated at the evaporator, so the air humidity in the storage compartment is low. Conversely, the temperature difference between the evaporator and the storage compartment can be kept small if the ventilator 25 provides a high exchange of air. In that case, the output requirements made of the compressor 10 are reduced, but in exchange more energy is consumed for operation of the fan 25. Because of the small difference in temperature, condensation on the evaporator is also small, and a high air humidity can be maintained in the storage compartment. Between these two extreme cases there is an optimum-efficiency operating mode in which the output of both the compressor 10 and the ventilator 25 is small but not minimal, and the sum of their outputs is at a minimum. It may be provided for the user to be able to select one of these operating modes for each temperature zone 1, 2, 3 or 4.
A high-pressure portion 15 of the refrigerant line 12 extends from a pressure-side connector 16 of the compressor 10, through the condenser 11 and, in this case, a branching point 17, to an upstream throttling point 18, 19. The upstream throttling point 18, 19 has a constant flow resistance. In this case, it is formed in each case in a manner known per se by a capillary that opens into the evaporator 8 and 9 respectively.
Connected in series downstream of the evaporator 8 there are a controllable throttling point 20, the evaporator 7, a further controllable throttling point 21 and the evaporator 6. Since the pressure in the refrigerant line 12 falls after each throttling point 18, 20, 21, zone 3 is the warmest of the temperature zones 1, 2, 3 and zone 1 is the coldest. In this way, the zone 3 may for example form a normal refrigerator compartment, the zone 2 may form a crisper compartment and the zone 1 may form a freezer compartment.
Downstream of the evaporator 6, the branches 13, 14 meet again at a merge point 22, and a low-pressure portion 23 of the refrigerant line 12 leads to a suction connector 24 of the compressor 10.
A plurality of regulators 27, 28, 29 are implemented on a microprocessor 26. The regulators 27, 28, 29 comprise utilities that share the processing power of the microprocessor 26 but do not access common data. Each regulator 27, 28, 29 receives and processes measurement values from one particular temperature sensor 30, 31 and 32 respectively.
If it is determined in step S2 that the measured temperature is above the tolerance range, then there is clearly a need for greater cooling power in the temperature zone 8. In this case, the regulator 27 actuates the throttling point 20 in step S4 in order to reduce the flow resistance thereof by a fixed value OR. The extent of the reduction may be fixedly predetermined or be proportional to the discrepancy between the measured temperature and the setpoint temperature.
As a result of reducing the flow resistance, the evaporating temperature in the evaporator 8 falls, and cooling of the temperature zone 3 becomes more intense. At the same time, more liquid refrigerant arrives in the evaporator 7 although more refrigerant does not flow away therefrom, with the result that over time the pressure there rises and the cooling power falls.
If, after the waiting time Δt, step S2 is repeated and the measured temperature continues to be above the tolerance range, then the flow resistance of the throttling point 20 is reduced again. In this way, the flow resistance is varied in a manner proportional to the time integral of the standard deviation until the cooling requirement in the temperature zone 3 is sufficient and the temperature measured by the sensor 30 is within the tolerance range.
If, by contrast, the measured temperature in step S2 is below the tolerance range, then in step S5 the regulator increases the flow resistance of the throttling point 20 by the value OR such that the temperature of the evaporator 8 rises. Increasing the flow resistance may, again, be repeated in successive iterations of the method.
In the context of the method, there is no need to take into account the operating mode of the ventilator 25 that has been selected for the temperature zone 3; if the user changes the operating mode, this results initially in a change in the temperature measured by the sensor 30 and then, in the course of one or more iterations of the method described above, in an adjustment of the flow resistance, as a result of which the temperature zone 3 reaches its setpoint temperature again.
The operating method of the regulator 28 comprises the same steps as those illustrated in
Where a reduction has become necessary because, as a result of the increased need for cooling of the temperature zone 3, the regulator 27 has reduced the flow resistance of the throttling point 20 and so the temperature in the evaporator 7 has risen, the reduction of the flow resistance of the throttling point 21 contributes to meeting the need for cooling of the temperature zone 3 quickly.
Accordingly, where there is an increase in the flow resistance of the throttling point 21, the pressure in the evaporator 7 and, to a lesser extent, in the evaporator 8 rises.
If the temperature measured by the sensor 32 in the temperature zone 1 differs from the setpoint temperature, there is no throttling point downstream of the evaporator 6 which could be used to influence the evaporating temperature. For this reason, the regulator 29 performs a slightly modified method, in which, if the setpoint temperature is exceeded, the speed of the compressor 10 is increased in step S4 and, if the temperature falls below the setpoint temperature, it is reduced in step S5. As in the case of the regulators 27, 28, S4 results in a fall in the evaporating temperature in the associated evaporator 6 but at the same time an increase in the mass flow, so that overall more cooling power to be distributed to the different evaporators is available. Conversely, S5 raises the evaporating temperature while at the same time throttling the mass flow.
In this way, a change in the cooling requirement is propagated through the refrigeration appliance step by step: in the case of an increased need for cooling in the temperature zone 3, meeting the need by opening the throttling point 20 has the result, with some delay, that the need for cooling in the temperature zone 2 is no longer entirely met, and a correction in this respect of the degree of opening of the throttling point 21 results in heating the temperature zone 1 and a subsequent correction of the compressor speed.
In order to make convergence of the regulation faster, it may be provided for the compressor regulator 29 to be coupled to the regulators 27, 28 in order to receive therefrom information on a change in the flow resistance of the throttling points 20, 21 controlled thereby and to track the speed of the compressor 10 that corresponds to the change before the change in the flow resistance has taken effect as a change to the temperature in the temperature zone 1. A coupling of this kind may for example comprise, whenever one of the regulators 27, 28 has increased or reduced the flow resistance by OR step S4, having the compressor regulator 29 reduce or raise the speed of the compressor 10 by a corresponding increment AU.
In a modified embodiment, the capillaries at the throttling points 18, 19 in
In this case too, the regulators 28, 29 continue to operate by the method described in conjunction with
| Number | Date | Country | Kind |
|---|---|---|---|
| 102017205426.3 | Mar 2017 | DE | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2018/057009 | 3/20/2018 | WO | 00 |
