METHOD FOR MANUFACTURING ICE PIECES

The present invention relates to a method for manufacturing ice pieces.

Ice-makers to be integrated in household refrigeration appliances are known, for example from DE 10 2005 003 237 A1, wherein the low temperatures of a freezer compartment of the household refrigeration appliance are used to freeze the water into ice pieces. To this end a tray is filled with water and placed in the freezer compartment. In the cold environment of the freezer compartment the water cools slowly and freezes into ice pieces. The time taken for the water to form ice pieces is generally more than 30 minutes.

Another method for producing ice pieces consists of storing water in a container, into which project metal fingers actively chilled by means of a coolant. The ice pieces result from an ice layer that develops on the metal fingers that are immersed in the water. Such an apparatus is known for example from WO 03/054458 A1.

The object of the invention is to manufacture ice pieces from water in an energy-efficient manner.

The object is achieved by a method with the features of claim 1.

The inventive method for the energy-efficient manufacture of ice pieces has at least the following steps:

filling a mold with water;

chilling the water using a refrigeration unit operated by a compressor at an initial compressor power;

reducing the compressor power at a time after the water starts to freeze.

The inventive method steps means that much less energy is required to manufacture ice pieces than with conventional methods. Producing ice from a mass of 1 kg water by placing a tray of water in a freezer compartment of a conventional household refrigeration appliance (e.g. according to DE 10 2005 003 237 A1) requires an energy of more than 0.4 kWh. Producing ice from a mass of 1 kg water by developing an ice layer on chilled metal fingers (e.g. according to WO 03/054458 A1) requires an energy of at least 0.27 kWh.

The inventive advantage of better energy efficiency is particularly evident in conjunction with an apparatus for the active production of ice in household appliances, which has at least one mold for holding water to be frozen, of which the inner wall facing the water is connected to a refrigeration unit. With such an apparatus, in contrast to the prior art, the heat is not dissipated by way of chilled metal fingers but by way of the chilled mold wall. The apparatus for the active production of ice in household appliances can comprise at least one water tray, in which the water to be chilled is stored, the water tray having a wall that can be chilled by direct contact with at least one coolant channel.

The relevant aspects of the apparatus can be described as follows. A tray is chilled by at least one coolant channel. The tray here can be an ice tray with internal coolant channels, which are determined by holes or the mold shape. It can however also be a tray that has a preferably flat base that is connected in a thermally conducting manner to a flat evaporator, e.g. a roll-bond plate. It can however also be a solid tray with half-open U-shaped channels on the lower face, into which a tube carrying coolant has been pressed. The apparatus can also have intermediate tray walls, which separate the individual ice pieces from one another. The coolant channels are located below the tray and are formed by a U-shaped tube. In principle the intermediate walls can also be hollow and carry coolant but this is not necessary because of the high thermal conductivity of the tray. The tray can be made of aluminum but extremely thermally conductive, in particular metal, materials, and also plastics can be used. The high thermal conductivity here allows a greater distance between water and coolant channel. However the apparatus can also be produced using a material with poorer thermal conductivity, in which case it would be expedient to provide a number of channels, preferably of complex shape, for example in the intermediate walls. The apparatus can have ejectors so that the tray can be mounted in a fixed manner, for example for safety reasons. If flexible coolant lines are used, the tray can be rotated so that ejectors are not required. The apparatus for the active production of ice insures high freezing capacity while at the same time using energy efficiently and taking up little space.

Compared with chilling by means of fingers immersed in the water, the apparatus described above has a larger contact surface between chilling facility and water, so that there is a better transfer of heat from the water to the mold. Mold according to the invention refers to any receptacle for the water that holds a specific quantity of water to be frozen into ice. The mold can be shaped differently depending on the desired contour shape of the ice piece. The mold can in particular be in the shape of a tray, e.g. in the shape of a hemisphere or segment of a circular disk. Chilling takes place here by way of the tray-shaped wall of the water receptacle.

In one exemplary arrangement of such an apparatus the electrical power required to freeze 100 grams of water to ice has been determined. In addition to the mold, i.e. the tray holding the water, the apparatus comprises an electrical refrigeration unit, having a compressor, the evaporator side of which is connected to the mold or tray. The apparatus was first operated according to a standard method. With the actively cooled tray the freezing process starts on the tray surface, i.e. the ice pieces freeze from the outside inward. At maximum compressor power the freezing process starts approx. 3 minutes after the water has been introduced. The initial temperature of the water is 20° Celsius. A powerful electric compressor is required to achieve the fasting freezing possible. In the exemplary arrangement a VEM Z 5C type compressor was used, supplying a refrigeration power of 146 watts at its maximum speed at a condensing temperature of 45° C. and an evaporator temperature of minus 20° Celsius. The coefficient of performance COP of this refrigeration unit is 1.81 at its operating point.

The COP, i.e. the ratio of refrigeration power to electrical power expended, describes the energy efficiency of the system. Assuming a certain quality of the technical equipment, this coefficient of performance is principally a function of the temperature rise between the useful cold supplied at the evaporator and the waste heat released at the condenser. The higher the COP, the better the energy efficiency. A COP of 3.6 or higher corresponds to energy efficiency class A for refrigeration appliances for example.

At maximum power the exemplary arrangement takes approximately 15 minutes for a complete cycle to freeze 100 grams of water into ice and then thaw and eject the ice pieces. This consumes approximately 0.02 kilowatt hours (kWh) of electrical energy. That makes 0.2 kWh/kg for 1 kilogram of water. Therefore compared with the known placing of a tray of water in a freezer compartment at approx. 0.4 kWh/kg and chilling using metal fingers at approx. 0.27 kWh/kg the exemplary arrangement requires much less energy.

However an estimation shows that in the most favorable instance only approximately 0.15 kWh/kg would be necessary for such a system; in other words a further 0.05 kWh/kg could be saved compared with the determined 0.2 kWh/kg, corresponding to an energy saving of 25%. The minimum quantity of energy theoretically required can be calculated from the characteristic variables of the exemplary arrangement:

Quantity of

Material or
Mass
T_START
T_END
Specific heat
heat

process
[g]
[° C.]
[° C.]
[J/g] or [J/gK]
Q[J]
Q[Wh]

Alu tray and
800
4
−10
0.896
10035
2.8

evaporator

Water
100
20
0
4.18
8360
2.3

Solidification
100
0
0
335.00
33500
9.3

Supercooling
100
0
−10
2.10
2100
0.6

ice

Sum of energy theoretically required for 100 g water/ice: 15.0 [Wh] The efficiency of the freezing process is therefore 0.15 kWh/kg.

Theoretically electrical energy consumption could be even lower, if the refrigeration power generated by the compressor with a COP higher than 1 could be introduced without loss into the mold, i.e. the aluminum tray (alu tray). However with the actual arrangement an at least small part of the refrigeration power is always lost to the environment.

However the energy for thawing the ice pieces, in other words the energy required to heat the mold (alu tray and evaporator) from minus 10 degrees Celsius to a temperature above zero degrees Celsius so that the ice pieces thaw and can be released from the mold, is not taken into account in the above consideration.

The inventive method is based on the knowledge described below. With the actively chilled tray the freezing process starts on the tray surface, in other words the ice pieces freeze from the outside inward. At maximum compressor power the freezing process starts approx. 3 minutes after the introduction of the water. The initial temperature of the water is 20° Celsius. The transfer of heat from the solidification front to the evaporator surface (mold wall) is increasingly impeded by the forming ice layer. This is due on the one hand to the lower thermal conductivity of the ice and on the other hand to the fact that the active surface for the transfer of heat from the water, i.e. the surface of the solidification front, is constantly decreasing due to the increasing thickness of the ice layer. The evaporation temperature of the coolant therefore drops and the available refrigeration power, i.e. the coefficient of performance COP, of the compressor decreases. After a further 8 to 9 minutes, in other words at cycle minute 11 to 12, more than 90% of the water has already frozen. At this time the evaporator is already colder than minus 15 degrees Celsius. Only after a further 2 to 3 minutes, in other words at cycle minute 13 to 15, is the remaining water in the center of the ice piece also frozen. The very low temperature means that the mold or alu tray must be heated from minus 15 degrees Celsius to above zero degrees Celsius to subsequently thaw the ice pieces. This process takes approx. 2 to 3 additional minutes, particularly because of the limited power of hot gas thawing. Generally speaking the freezing process is not extended to any significant degree given the much reduced energy consumption,

With the inventive method compressor power is reduced from the start of freezing. This means that the mold, i.e. the water receptacle or alu tray, is not chilled to an unnecessarily low temperature. With the exemplary arrangement the reduction of compressor power at a time after the water has started to freeze prevents the temperature of the mold or tray dropping to below minus 15 degrees Celsius. It has proven that despite diminished compressor power the process of freezing the water into ice is not noticeably delayed or impaired. At the same time when the ice pieces are subsequently thawed, the mold or tray only has to be heated from a less low temperature (approx. minus 12 degrees Celsius instead of minus 22 degrees Celsius) to above zero degrees Celsius so that less energy is also needed to heat or thaw the ice pieces.

Compressor power can be reduced immediately after the water starts to freeze. Compressor power should preferably be operated at a high and in particular maximum initial compressor power at least until the required amount of heat for solidification has been dissipated. The greatest energy saving therefore results when compressor power is reduced immediately after this. However a certain energy saving can also be achieved if compressor power is only reduced a certain time later. This also comes within the scope of the invention, with the inventive doctrine of reducing compressor power being utilized with such a less energy-efficient embodiment.

Compressor power can be reduced to a minimum compressor power of the compressor of the refrigeration unit used in each instance. In the described example (VEM Z 5C type compressor) the compressor power of 146 watts refrigeration power can be reduced to 74 watts for an evaporation temperature of minus 15 degrees Celsius and a condenser temperature of 35 degrees Celsius with a COP of 2.75. A reduced temperature difference also improves the COP of the compressor.

Generally speaking compressor power can therefore be reduced to approx. 50% of the initial compressor power. The compressor power reduction can be selected to be other than precisely 50% in a context that continues to insure the inventive advantages, in other words in particular between 40% and 60% or even beyond.

The time when compressor power is reduced can be set as a function of the design of an apparatus for manufacturing ice pieces, in particular from an empirical determination. To this end experiments can be carried out using the respective apparatus to determine the time when the water starts to freeze. This time, i.e. the time period from the start of a cycle according to the method, can then be implemented in an in particular electrical controller of an apparatus for manufacturing ice pieces.

Alternatively however a signal can also be generated during the method, in particular to prompt the electrical controller of the apparatus for manufacturing ice pieces to reduce the compressor power. The start of the reduction of compressor power can in particular be determined or controlled based on a measurement of the temperature of the mold, i.e. the tray, in which the water to be frozen into ice pieces is present. However other sensors that can determine the start of solidification of the water are also possible.

For example compressor power can be reduced when the measured temperature of the mold, i.e. the tray, reaches a predetermined setpoint temperature. A temperature below minus 10 degrees Celsius, in particular below minus 12 degrees Celsius, can in particular be predetermined as the setpoint temperature.

The mold or tray is also further chilled to significantly below the freezing point of water of zero degrees Celsius with reduced compressor power, typically to minus 15 degrees Celsius. In order not to have to heat for too long when thawing the ice pieces, in one development of the invention it is proposed to shut off the compressor at the end of the freezing process, i.e. when the required ice pieces have been produced from the water, and to wait for a time period before starting to heat the mold or tray to thaw the ice pieces.

Such a method would follow the method steps as claimed in claim 1 and contain the following further steps:

shutting off the compressor once the ice pieces have been produced from the water,

leaving the ice pieces in the mold for a rest period segment,

heating the mold to thaw the ice pieces to facilitate the release of the ice pieces from the mold, after the end of the rest period segment.

The rest period segment can be between 1 and 3 minutes, in particular 2 minutes.

During the waiting period after the compressor has been shut off, i.e. during the rest period segment, the mold or tray heats up automatically, i.e. in particular due to the influence of ambient temperature, for example to approximately minus 5 degrees Celsius. While the mold is heating up from approx minus 15 degrees Celsius to minus 5 degrees Celsius, the freezing process continues apace in the center of the ice piece so that the compressor could for example also be shut off slightly before the ice pieces are completely frozen. Since the mold is no longer so cold at the start of the heating process, the thawing time is shortened considerably, i.e. by approx. 1 minute for example. Also less heating energy is required for thawing. Despite the diminished compressor power and the compressor break the overall cycle time is only slightly extended, for example from approx. 15 minutes to just 17 to 18 minutes approximately. The cycle here includes introducing the water, freezing into ice pieces, thawing and ejecting the finished ice pieces.

Overall the quantity of energy required drops from approx. 0.2 kWh/kg to approx. 0.15 kWh/kg, meaning a saving of 25%. Only a small loss of throughput has to be tolerated for the significant energy saving. Approx. 8.0 kg of ice can still be produced per day compared with a former approx. 9.6 kg ice per day. The much quieter operation due to the reduced compressor power and the introduction of rest time segments is advantageous. Lower compressor and fan speeds are required and the switching noise at the start of thawing is reduced. One subsidiary effect is that there are fewer cracks in the ice pieces produced, as the thawing to release the ice pieces from the mold is more gradual. The more gradual thawing with a prior rest time is less stressful for materials; in other words the fact that there is no sudden temperature rise from maximum refrigeration power to maximum heating power for thawing purposes means that in particular the connection between the evaporator and mold, i.e. alu tray, is less subject to mechanical strain due to temperature-induced material stresses.

An exemplary embodiment of an apparatus for the energy-efficient manufacture of ice pieces is illustrated in the following detailed description, in which the temperature profiles of an exemplary ice production cycle with such an apparatus is explained, to demonstrate the action of the inventive method. Further general features and advantages of the present invention will also emerge from the detailed description of this specific exemplary embodiment. In the drawings:

FIG. 1 shows a schematic diagram of the method as claimed in claim 1;

FIG. 2 shows a schematic diagram of the method as claimed in claim 9;

FIG. 3 shows a sectional view through an exemplary apparatus for the energy-efficient manufacture of ice pieces according to one of the inventive methods;

FIG. 4 shows a diagram of the temporal profile of temperatures during an inventive cycle.

FIG. 1 illustrates a method for the energy-efficient manufacture of ice pieces as claimed in claim 1. The method begins after the start with a first step S1, in which a mold is filled with water. In a second step S2 the water is chilled by means of a refrigeration unit operated by a compressor at an initial compressor power. The method ends with a third step S3 of reducing the compressor power at a time after the water starts to freeze. The method as claimed in claim 1 ends after step S3.

FIG. 2 illustrates a method for the energy-efficient manufacture of ice pieces as claimed in claim 9. The method again begins after the start with the first step S1, in which a mold is filled with water. In the second step S2 the water is chilled by means of a refrigeration unit operated by a compressor at an initial compressor power and in the third step S3 the compressor power is reduced at a time after the water starts to freeze. This third step S3 is then followed by a fourth step S4, in which the compressor is shut off once the ice pieces have been produced from the water. In a fifth step S5 the ice pieces are left in the mold for a rest period segment and in a sixth step S6 the mold is heated to thaw the ice pieces so that they can be released from the mold more easily, this taking place after the end of the rest period segment according to step S5. The method as claimed in claim 9 ends after step S6.

FIG. 3 shows a schematic section of a mold 1 for manufacturing an ice piece. An exemplary apparatus for the energy-efficient manufacture of ice pieces according to one of the inventive methods can in particular feature a number of such molds 1, which are disposed in spatially ordered proximity to one another in the manner of an ice cube tray, in particular possibly being combined in one structural unit. The mold 1 is configured as an aluminum tray for example, having a base body 2 made of aluminum and an inner wall 3 in the shape of half the tray. An ice layer 4 is shown adjacent to the inner wall 3 in the mold 1, said ice layer 4 currently forming and ending adjacent to a currently remaining quantity of water 5. A solidification front 6 is present at the boundary between ice layer 4 and quantity of water 5. A heat flow, shown as the arrow 7, flows from the quantity of water 5 to an evaporator plate 8, which is connected to a refrigeration unit (not shown). The heat from the quantity of water 5 is dissipated along the heat flow (arrow 7) into the evaporator plate 8, so that as chilling continues, the solidification front 6 grows further upward in FIG. 3 until all the quantity of water 5 has solidified to ice.

FIG. 4 shows a diagram of an example of the temporal profile of the temperatures during an inventive cycle for an apparatus according to FIG. 3. The temporal profile of the temperatures is executed for 100 grams of water. The two upper temperature lines predominantly in the region of plus degrees represent the temperature profiles in the water. The temperature profile shown right at the top represents the temperature profile over time of the water to be frozen without the inventive method, i.e. without compressor power reduction. Just below and overlapping in places is the temperature profile over time of the water to be frozen using the inventive method. The water temperatures were determined in the center of the water, in other words at a point where freezing occurs last in time. Both temperature profiles of the water start at the minute 0 with an initial temperature of approx. 20 to 21 degrees Celsius. In the minutes that follow both temperature profiles noticeably show almost identical behavior. The two temperature profiles only diverge at around minute 11.5. The temperature profile for continuing maximum compressor power at this point drops below the zero degrees Celsius limit, in other words the ice piece is completely frozen at this time. With an inventive reduction of compressor power, here by approx. 50%, the temperature profile only drops below the zero degrees Celsius limit at approx. minute 13.5, in other words the ice piece is completely frozen at this slightly later point. This profile shows the manufacturing process of the ice pieces and demonstrates that with the inventive method of reducing compressor power completely frozen ice pieces are produced only slightly later. The delay is only approx. 2 minutes of an overall total manufacturing period of approx. 15 to 17 minutes.

The two lower temperature lines predominantly in the region of minus degrees in FIG. 4 show the temperature profiles over time in the mold, i.e. in an aluminum tray. Initially both temperature profiles, with and without the inventive reduction of compressor power, start with the mold at approx. 12 to 13 degrees Celsius. The introduction of water at a temperature of approx. 20 to 21 degrees Celsius causes the mold temperature initially to rise briefly to approx. 15 to 16 degrees Celsius, after which it drops rapidly in both temperature profiles due to the maximum compressor power until minute 6.5. From minute 6.5 the essential difference between the prior art and the inventive method is shown in the two temperature profiles. While according to the prior art chilling continues at full compressor power even after minute 6.5, according to the invention compressor power is reduced at this time, in the exemplary instance by approx. 50%. This has the result that in a time segment between minute 12 and 13 the temperature of the mold does not drop to a value of approx. minus 20 degrees Celsius but simply levels off at around minus 10 degrees Celsius. The area between the temperature profiles of maximum compressor power and reduced compressor power here represents a proportion of the energy saving. In the temperature profile for maximum compressor power a bend results at approx. minute 13 due to the complete shutting off of the compressor. In the temperature profile for reduced compressor power an inventive compressor break follows between minutes 13.5 and 15.5 before the mold is heated.

METHOD FOR MANUFACTURING ICE PIECES

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