Patent Application
20230296293
The present invention relates to a refrigeration appliance, particularly a household refrigeration appliance, with a refrigerant circuit, having a suction tube heat exchanger, and a method for operating such a refrigeration appliance.
A refrigeration appliance with an internal heat exchanger is known from DE 10 2016 202 565.
The object of the present invention is to provide a refrigeration appliance with two parallel evaporators or evaporator assemblies and a suction tube heat exchanger and a method for operating such a refrigeration appliance, in which an estimate of the mass flow of the refrigerant through an evaporator or an evaporator assembly in relation to the total mass flow of the refrigerant can be obtained.
The object is achieved by a refrigeration appliance and a method for operating a refrigeration appliance according to the independent claims.
The invention relates to a refrigeration appliance with a refrigerant circuit, having a compressor, a first evaporator assembly with at least one first evaporator and with a high-pressure tube connected upstream of the first evaporator assembly, a second evaporator assembly connected in parallel with the first evaporator assembly with at least one second evaporator, a low-pressure tube connected downstream of the first evaporator assembly and the second evaporator assembly, and a suction tube heat exchanger, in which a high-pressure tube section of the high-pressure tube and a low-pressure tube section of the low-pressure tube are coupled in a heat-conducting manner. The suction tube heat exchanger has three temperature sensors in three positions from a group of positions at the inlet and outlet of the low-pressure tube section, and at the inlet and outlet of the high-pressure tube section.
Such a refrigeration appliance is particularly a household refrigeration appliance, in which in various compartments normal household quantities of food items are stored at different temperatures and may undergo a temperature treatment. With evaporators, which are operated at various temperatures, storage compartments can be kept or operated at various temperatures.
The invention can be advantageously used in evaporators or evaporator assemblies connected in parallel, in which an evaporator assembly has evaporators each with a variably selectable temperature. A storage compartment, which can be operated with a variably selectable temperature is hereinafter referred to as a flex compartment, and the associated evaporator as a flex compartment evaporator.
The invention can be particularly advantageously used in evaporators or evaporator assemblies connected in parallel, in which a first evaporator or the evaporators of a first evaporator assembly are operated at low temperatures and the second evaporator or the evaporators of the second evaporator assembly are selectively operated at a temperature lower than the ambient temperature or at a temperature higher than the ambient temperature. In such an appliance a flex compartment can be set to temperatures within a particularly wide temperature range.
In its generality, the invention describes a refrigeration appliance with a refrigerant circuit with two parallel lines each with at least one evaporator. An important application is one in which in one or both lines respectively there is only one evaporator. Hereinafter, to simplify the description, the invention is described with regard to the first evaporator and the second evaporator. The person skilled in the art will recognize the generalization of the lines.
In the description of the invention the terms suction tube and low-pressure tube are used synonymously, and the terms suction tube heat exchanger and internal heat exchanger are also used synonymously. In such appliances the parallel evaporators typically each have an adjustable flow restriction point, particularly an expansion valve on the inlet and outlet of the evaporator. Hereinafter an expansion valve is mentioned as representative of an adjustable flow restriction point. Through the valve positions the pressure in the evaporator can be influenced in such a way that the associated compartment is cooled to a varying extent.
From the perspective of the refrigerant circuit, the evaporator assemblies are considered to be lines of the refrigerant circuit. Advantageously, the evaporators can be combined in assemblies such that in a first evaporator assembly there are exclusively evaporators which operate storage compartments at below the ambient temperature, and in a second evaporator assembly there are exclusively evaporators which operate storage compartments at either below or above the ambient temperature.
Storage compartments of the first evaporator assembly are, for example, a refrigeration compartment, a chiller compartment, a freezer compartment, or a basic flex compartment. Since all these compartments are cooled it is advantageous that the refrigerant line of the first evaporator assembly is part of an internal heat transfer system or suction tube heat transfer system.
A distinctive feature of the refrigerant line to the second evaporator assembly is that this is not part of the internal heat transfer systems in order to also heat a flex compartment with an extended temperature range by refrigerant liquefying in the flex compartment evaporator. The advantage of this is that the second evaporator can be supplied with warm or hot refrigerant at approximately condenser temperature.
With parallel refrigerant lines the distribution of the mass flow is not dependent solely on the valve positions but also on the gas proportion or the subcooling at the respective valve inlet. The gas proportion and the subcooling are inaccessible for appliance control, meaning that the precise distribution of the mass flows between the individual evaporators is difficult to determine.
The invention is based on the idea that a ratio of mass flows in an internal heat exchanger with two lines can be determined if the two mass flows are substantially single-phase and at least three temperatures are known at the inlets and outlets of the internal heat exchanger. If four temperatures at inlets and outlets of the internal heat exchanger are known the calculation is simplified.
In the internal heat exchanger a refrigerant line transfers heat to the suction tube. Since different mass flows cause other temperatures of the suction gas on the hot and cold side, this can be used to determine the mass flow proportion flowing through the first evaporator, since this is substantially single-phase in the high-pressure tube section. The refrigerant in the suction tube should be completely vaporized and thus present in single-phase gas form.
The temperature distribution at the suction tube heat exchanger is thereby used as an internal heat transfer to infer the mass flow proportion through the first evaporator. On the warm side of this the refrigerant is liquid and on the suction tube side the refrigerant is gaseous, with the respective specific heat capacities. With the considerations from thermodynamics it is now possible to determine the ratio of the mass flows with good accuracy with three temperatures at inlets and outlets of the suction tube heat exchanger. See for example Grundlagen der Wärme-und Stoffübertragung, Vorlesungsskript Uni-Magdeburg, WS2009/2010.
In the case of a third evaporator, which follows the parallel evaporators and through which the entire mass flow of the refrigerant flows, and the suction tube of which leads directly to the suction tube heat exchanger, it is possible to use the temperature of the third evaporator for the temperature at the inlet of the suction tube line or to replace a temperature sensor on the inlet of the suction tube line by the temperature sensor in the third evaporator if no heat transfer takes place between the third evaporator and the suction tube.
Using the evaporation temperature in the third evaporator and the suction gas temperature at the outlet of the internal heat transfer system the suction gas density, and with the speed of the compressor, the delivery mass flow and thereby the total mass flow, can be determined. Thus, from the ratio of the mass flows and the total mass flow, this method also provides the absolute value of the mass flow flowing through the first evaporator line. The mass flow through the second evaporator line is then given by the difference to the total mass flow. In the event that the second evaporator line only has one evaporator, the mass flow is determined by means of this evaporator.
According to one embodiment of the invention the high-pressure tube section leads exclusively to the first evaporator assembly and does not lead to the second evaporator assembly. This has the advantage that the high-pressure tube section has precisely the mass flow that flows through the first evaporator assembly.
Since the high-pressure tube section follows the condenser it carries substantially liquid refrigerant. The mass flow through the high-pressure tube section is therefore substantially a mass flow of liquid refrigerant with at most a very small gas proportion.
According to a further embodiment of the invention a variably adjustable flow restriction element, particularly an expansion valve, is connected upstream and downstream respectively of the first evaporator and the second evaporator. The advantage of this is that in the first evaporator and in the second evaporator respectively a mass flow can be set independently of the other evaporator. Each of these evaporators can be operated as an evaporator with a variable temperature. The pressure of the refrigerant and thus the evaporator temperature can be adjusted for each of the evaporators independently of other evaporators.
According to a further embodiment of the invention the suction tube heat exchanger has a temperature sensor at each position of a group of positions. This has the advantage of simplifying calculation of the ratio of the mass flows.
According to a further embodiment of the invention the refrigeration appliance has a facility for determining a ratio of the mass flows in the high-pressure tube section and in the low-pressure tube section. Such a facility can be advantageously integrated in the refrigeration appliance controller.
According to another embodiment of the invention the refrigeration appliance has a facility for determining a ratio of the mass flows to the first evaporator assembly and the second evaporator assembly. This is based on the fact that the total mass flow is the sum of the mass flows to the first evaporator assembly and the second evaporator assembly.
According to a further embodiment of the invention the refrigeration appliance has a third evaporator between the first and second evaporators arranged in parallel and the low-pressure tube. This allows a further cooled compartment, preferably a compartment with a lower temperature than the preceding compartments.
According to a further embodiment of the invention with a third evaporator the refrigeration appliance has a further suction tube heat exchanger, in which a further high-pressure tube section of the high-pressure tube and a further low-pressure tube section of the low-pressure tube are coupled in a heat-conducting manner. This increases the energy efficiency. It should be noted, however, that the further suction tube heat exchanger cannot be used for mass flow determinations if no substantially single-phase flows are present.
According to a further embodiment of the invention with a third evaporator, the third evaporator has a temperature sensor, which replaces a temperature sensor at the inlet of the low-pressure tube section, and the outlet of the third evaporator is directly connected to the inlet of the suction tube heat exchanger. In this case, in which no further suction tube heat exchanger is disposed between the third evaporator and the suction tube heat exchanger, the refrigerant temperature in the third evaporator and at the inlet of the suction tube heat exchanger is the same. Therefore the temperature sensor for the temperature at the inlet of the suction tube line of the heat exchanger can also be disposed in the third evaporator. This is particularly advantageous in a no-frost evaporator, which normally already has a temperature sensor for controlling the defrosting process.
The third evaporator is preferably associated with a freezer compartment.
According to a further embodiment of the invention the refrigeration appliance has a fourth evaporator in the direction of flow of the refrigerant immediately before the third evaporator. This allows a further cooled compartment.
The fourth evaporator can advantageously be associated with a refrigeration compartment or a chiller compartment, which is supplied with a gaseous refrigerant from the preceding freezer compartment evaporator. This allows a very good energy efficiency.
According to a further embodiment of the invention the compressor is a permanently running compressor with variable speed. This has the advantage of allowing a constant temperature adjustment in the evaporators, which avoids the normal temperature hysteresis of an intermittently working compressor.
In further embodiments of the invention the evaporators of the first evaporator assembly do not necessarily have to be associated with flex compartments but can also be associated with compartments with a narrow target temperature range, for example a refrigeration compartment, a chiller compartment, or a freezer compartment.
The invention also relates to a method for determining a ratio of mass flows in a refrigeration appliance with a refrigerant circuit, having a compressor, a first evaporator assembly with at least one first evaporator and with a high-pressure tube connected upstream of the first evaporator assembly, a second evaporator assembly connected in parallel with the first evaporator assembly with at least one second evaporator, a low-pressure tube connected downstream of the first evaporator assembly and the second evaporator assembly, and a suction tube heat exchanger, in which a high-pressure tube section of the high-pressure tube and a low-pressure tube section of the low-pressure tube are coupled in a heat-conducting manner. The suction tube heat exchanger has a group of positions at the inlet and at the outlet of the low-pressure tube section, and at the inlet and outlet of the high-pressure tube section, and the method is carried out with the method steps
In the suction tube heat exchanger after a certain compressor running time a stationary state is reached, in which both the refrigerant flows and the temperatures at the inlets and outlets of the suction tube heat exchanger are constant. The temperature profiles in the two refrigerant tube sections of the heat exchanger are also constant and have an interdependence. This dependency known from thermodynamics can be used to determine the ratio of the refrigerant mass flows from the temperatures at the inlets and outlets. A further application of thermodynamics can be used to determine the ratio of the refrigerant mass flows from just three temperatures at the inlets and outlets.
One embodiment of the method contains the further method step of determining temperatures at all positions from the group of positions. With three temperatures ascertained by sensors, the fourth temperature can either be determined from a further sensor or estimated well by application of thermodynamics.
In a further embodiment of the method the determination of the ratio of the mass flow through the high-pressure tube section to the mass flow through the low-pressure tube section is carried out by means of specific thermal capacities of a refrigerant assuming a liquid refrigerant in the high-pressure tube section and a gaseous refrigerant in the low-pressure tube section.
A further embodiment of the method contains the further method step of determining a mass flow through the low-pressure tube section from a delivery by the compressor. The delivery mass flow is a function of the speed, the displaced volume, the volumetric efficiency, and the suction gas density. The suction gas density is a function of the evaporation temperature of the evaporator before the suction tube heat exchanger and the temperature at the gas outlet of the suction tube heat exchanger. The volumetric efficiency is a function of the condenser pressure and the evaporator pressure.
A further embodiment of the method contains the further method step of determining a mass flow through the second evaporator assembly from the ratio of the mass flow through the high-pressure tube section to the mass flow through the low-pressure tube section and the mass flow through the low-pressure tube section. The determination of the mass flows therefore results from the ratio of the mass flows and the delivery mass flow. This has the advantage that an otherwise difficult to determine mass flow through the second evaporator assembly can be determined absolutely.
A further embodiment of the method contains the further method step of controlling the refrigeration appliance on the basis of the temperatures determined. If the mass flow through the second evaporator assembly or the second evaporator is known, this knowledge can be used to better control the second evaporator assembly or the second evaporator.
A further embodiment of the method contains the further method step of controlling the refrigeration appliance on the basis of the ratio of the mass flow through the high-pressure tube section to the mass flow through the low-pressure tube section. The refrigeration appliance can thereby be advantageously controlled with improved energy efficiency.
Further features and advantages of the invention are indicated by the following description of exemplary embodiments by reference to the attached figures.
These show as follows:
In the various embodiments functionally identical elements are provided with the same reference numerals, and similar elements with dashed reference numerals.
The compressor is a speed-controlled compressor with variable speed. The compressor is designed to work in continuous operation.
In the first evaporator assembly 26 the first evaporator 28 and the further evaporator 30 of the first evaporator assembly 26 are disposed parallel to each other. In the direction of flow before the first evaporator 28 an expansion valve 36 is disposed, which controls the refrigerant inflow into the evaporator 28. In the direction of flow after the first evaporator 28 an expansion valve 38 is disposed, which controls the refrigerant outflow from the first evaporator 28.
Before and after the further evaporator 30 of the first evaporator assembly 26 expansion valves 40 and 42 are also disposed. In the first evaporator assembly further evaporators of the first evaporator assembly could be disposed parallel to the first evaporator, to provide further storage compartments with their own evaporator.
The evaporators 28, 30 of the first evaporator assembly 26 are associated with storage compartments, which can be cooled to temperatures below the ambient temperature. Thus the first evaporator 28 is associated with a refrigeration compartment, and the further evaporator 30 of the first evaporator assembly 26 is associated with a simple flex compartment with variable temperature, so that this compartment can be operated optionally as a further refrigeration compartment, chiller compartment or freezer compartment. The variable temperatures of the evaporators of the first evaporator assembly 26 are made possible by the expansion valves before and after the evaporators, which allow an evaporating pressure of the refrigerant in the evaporator to be adjusted such that the desired temperatures are reached independently of temperatures in other evaporators.
In the second evaporator assembly 32, in the embodiment shown in
The second evaporator 34 of the second evaporator assembly 32 is associated with a flex compartment with an extended temperature range, which can be operated in a wide temperature range both below and above the ambient temperature. The variable temperatures of the second evaporator 34 are made possible by the expansion valves before and after the second evaporator 34, which allow an evaporating pressure of the refrigerant to be adjusted such that the desired temperatures are reached independently of temperatures in other evaporators.
The arrangement shown in
The refrigerant circuit 20 has a circulation system with pipelines that connect together the described elements of the refrigerant circuit 20. The refrigerant circuit 20 has a high-pressure range between the outlet of the compressor 22 and the expansion valves 36, 40 and 44. The refrigerant circuit 20 has a low-pressure range between the valves 36, 40 and 46 and the inlet of the compressor 22.
With the second evaporator 34, the association of the pipe region between the expansion valve 44 before the second evaporator 34 and the expansion valve 46 after the second evaporator 34 with the high-pressure range or the low-pressure range is dependent upon the respective operating condition of the second evaporator 34 and the prevailing pressure therein. If the second evaporator 34 is operated at a temperature higher than the ambient temperature, then in this operating condition it has the function of a condenser and can be operated at high pressure.
The refrigerant circuit 20 has a high-pressure tube 48, which is connected upstream of the evaporators of the first evaporator assembly. The high-pressure tube 48 terminates at the flow restrictors of the evaporators of the first evaporator assembly, and so here at the expansion valves 36 and 40.
The refrigerant circuit 20 has a low-pressure tube 49, which is connected downstream of the first evaporator assembly 26 and the second evaporator assembly 32. The low-pressure tube 49 runs between the expansion valves 38, and 46 and the inlet to the compressor 22.
The refrigerant circuit 20 also has a suction tube heat exchanger 50, in which a high-pressure tube section 52 of the high-pressure tube 48 and a low-pressure tube section 54 of the low-pressure tube 49 are coupled in a heat-conducting manner.
The suction tube heat exchanger 50 has four preferred positions for temperature sensors, namely position 56 at the inlet of the high-pressure tube section 52, position 58 at the outlet of the high-pressure tube section 52, position 60 at the inlet of the low-pressure tube section 54 and position 62 at the outlet of the low-pressure tube section 54. The reason these positions for temperature sensors are preferred, is because when the refrigeration appliance is in operation a maximum temperature difference of the refrigerant of the high-pressure tube section 52 occurs and between positions 60 and 62 a maximum temperature difference of the refrigerant of the low-pressure tube section 54 occurs in the heat exchanger 50 due to the heat exchange between positions 56 and 58.
In one embodiment of the invention, at each of the four positions 56, 58, 60 and 62 the refrigerant circuit 20 has a temperature sensor. This embodiment has the advantage that the temperature differences in the high-pressure tube section 52 and in the low-pressure tube section 54 can be determined by simple temperature measurements with the temperature sensors.
From these, the display and control unit 16 of the refrigeration appliance 10 can determine a ratio between the mass flows in the high-pressure section and the low-pressure section.
In the arrangement shown in
In another embodiment of the invention, at three positions from the group of positions 56, 58, 60 and 62, the refrigerant circuit 20 has a temperature sensor. This embodiment has the advantage that there is less need for a temperature sensor. The temperature at the position of the missing temperature sensor can be determined by considerations from thermodynamics. All four temperatures are thereby then known, and the ratios of mass flows can be determined as in the above-mentioned embodiment.
In the refrigerant circuit 20 represented in
Apart from that, the improvement in the energy efficiency made possible by the suction tube heat exchange is used in such a way that in addition the refrigerant, which is fed to the first evaporator assembly, is cooled by the suction tube heat exchange.
In the refrigerant circuit 20 the condenser 24 has a fan 66. The fan 66 has the task of preventing excessive condenser temperatures and is able to cool the condenser 24 if in the second evaporator assembly no evaporator in a heating mode is being operated to reach a temperature above the ambient temperature in the evaporator or in its flex compartment with extended temperature range.
The evaporators 28, 30 and 34 have fans 68, 70 and 72. These fans can be used both for improving the heat transfer between evaporator and the respective compartment or also for humidity control of the respective compartment.
In the second evaporator assembly further evaporators of the second evaporator assembly could be disposed parallel to the second evaporator, to provide further storage compartments, particularly flex compartments with an extended temperature range, with their own evaporator. The evaporators of these compartments are preferably disposed parallel to the second evaporator 34 and also with an expansion valve disposed before and an expansion valve after each evaporator, respectively.
Alternatively, it is possible to provide the positions for temperature sensors internally on the tube of the respective tube section.
A coordinate line 77 is for example indicated, with end points 78 and 79 and a section, along which in the suction tube heat exchanger 50 a heat exchange occurs. By means of the coordinate line 77 a temperature profile within the suction tube heat exchanger 50 can be determined using thermodynamics.
In this embodiment the refrigerant circuit has a third evaporator 82 between the first and second evaporator assemblies 26′, 32 disposed in parallel and the low-pressure tube 49′. In the direction of flow of the refrigerant the third evaporator 82 follows the evaporators 28, 34 of the parallel evaporator assemblies 26′, 32 in series.
The low-pressure tube 49′ runs from the third evaporator 82 to the compressor 22. A low-pressure tube section 54′ of the low-pressure tube 49′ is located in the suction tube heat exchanger 50′.
The refrigerant circuit 80 has an optional further internal heat transfer system 84, in which a further tube section 81 of the low-pressure tube 49′ and a refrigerant tube section 83 at the outlet of the first evaporator 28 are coupled in a heat-conducting manner. However, the further internal heat transfer system 84 does not provide any information regarding a mass flow distribution that at the outlet of the evaporator 28 the refrigerant is two-phase. The suction gas then sees in the further internal heat transfer system 84, as it were, an isothermal heat source.
The refrigerant circuit 80 is suitable for a refrigeration appliance 10 according to
The refrigerant circuit 80 advantageously uses the low suction pressure of the compressor 22 for an evaporator 82 disposed in series, which is associated with a particularly cold compartment.
The evaporator 82 is associated with a cold compartment, preferably a freezer compartment, and has a temperature sensor 86.
Together with the temperature sensor 86 the refrigerant circuit 80 has the following advantage. At the location of the temperature sensor 86 for the entire refrigerant mass flow the temperature and pressure are known, and from these, using a temperature sensor at the end of the low-pressure tube section, position 62′, the suction gas density there can be determined. In turn, by means of the compressor speed, from the delivery of the compressor, the absolute total mass flow can thereby be determined.
This, in turn, allows a determination of the absolute mass flow through the evaporator 34.
An embodiment of the invention without the further internal heat exchanger 84 furthermore allows, instead of a temperature sensor at the inlet of the low-pressure tube section 54′ the temperature sensor 86 at position 60′ to be used to determine the temperature at the inlet to the low-pressure tube section 54′.
The third evaporator 82′ has a blower 85′ and the fourth evaporator 88 has a blower 90.
In this arrangement the evaporator 86′ is operated as a freezer compartment evaporator for the supply of a freezer compartment and the additional evaporator 88 is operated as an evaporator for a chiller compartment or a refrigeration compartment. Control of the refrigeration appliance with this refrigerant circuit takes place in such a way that the refrigerant fed to the evaporator 86′ is substantially evaporated in the evaporator 86′ and the next evaporator 88 is cooled with cold gaseous refrigerant.
In turn, the temperature sensor 86′ is in the coldest compartment, and therefore the temperature and evaporating pressure at its position can be determined based on the prevailing temperature there and with this information with a temperature sensor at the end of the low-pressure tube section, position 62′, the suction gas density there can be determined. In turn, by means of the compressor speed, from the delivery of the compressor, the absolute total mass flow can thereby be determined.
The method has the method steps:
One embodiment of the method, instead of the method step a), contains the method step
The determination of a temperature at one of the positions at the suction tube heat exchanger normally takes place using a temperature sensor at the position at the suction tube heat exchanger. Alternatively, however, the determination of the temperature can also take place with a temperature sensor at an adjacent position on the suction tube in the refrigerant circuit outside the suction tube heat exchanger, if no heat transfer takes place from or to the suction tube between the two positions. Then it can reasonably be concluded that the prevailing temperature at both positions is the same.
In a further method step
If the refrigerant circuit 20, when the refrigeration appliance 10 is in operation, is in a stationary state, and so the temperatures in the evaporators 28, 30, 34 and in the suction tube heat exchanger 50 are substantially constant, the entire mass flow of the refrigerant delivered by the compressor 22 flows through the low-pressure tube section 52 of the suction tube heat exchanger 50. The entire mass flow can then be determined from the delivery by the compressor 22.
In a further method step
Alternatively to method step e),
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2020 207 648.0 | Jun 2020 | DE | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2021/065288 | 6/8/2021 | WO |
