Dishwasher with a heat pump circuit and operating method for such a dishwasher

Abstract

Dishwasher for cleaning dishes with washing liquid that is circulated in a washing circuit, comprising a heat pump circuit (7) for extracting heat from a water-filled evaporator tank (8) and transferring it to the washing circuit, wherein a sensor is provided for the evaporator tank (8) for detecting a degree of icing present in the evaporator tank, characterized in that the sensor for detecting the degree of icing is a capacitance sensor (13) that is arranged on the outside of the evaporator tank (8).

Description

[0001] The invention relates to a dishwasher, in particular a household dishwasher, for cleaning dishes with washing liquid circulated in a washing circuit. The dishwasher has a heat pump circuit for extracting heat from a, in particular closed, water-filled evaporator tank and transferring it to the washing circuit. A sensor is provided for the evaporator tank to detect the degree of icing. The invention further relates to an operating method for such a dishwasher with a heat pump circuit.

[0002] The use of heat pumps is known for reducing the energy consumption of dishwashers. For example, EP 2 682 038 A2 describes a dishwasher with an air-water heat pump that extracts energy from the ambient air to support energy-intensive steps of the washing program, such as heating the dishwashing liquid.

[0003] Dishwashers with a water-to-water heat pump are also known, in which heat is extracted from a water tank containing an evaporator of the heat pump circuit and fed into the washing circuit.

[0004] For example, EP 2 224 049 A1 describes a dishwasher in which the water tank from which the heat is extracted is a wastewater tank of the dishwasher. During the dishwasher's program run, heat is extracted from the wastewater tank until the water in the wastewater tank begins to freeze. At the end of the process, warm wastewater from the washing chamber is pumped into the wastewater tank, thawing the frozen wastewater there.

[0005] An anti-freeze sensor is installed in the wastewater tank to control the heat pump circuit to prevent the entire wastewater tank from freezing completely. Extracting heat until the water partially freezes makes sense, as a large amount of heat can be extracted during the conversion of water to ice. However, complete freezing could damage the wastewater tank due to the water's expansion during freezing. Furthermore, complete freezing would prevent the drainage of at least enough wastewater to absorb additional process water and then thaw the ice that has already formed.

[0006] To detect the onset of icing, the document describes the use of a temperature sensor or, alternatively, a conductivity sensor. However, the conductivity sensor must be installed inside the wastewater tank, which, due to sealing issues, increases the design and thus the manufacturing costs of the wastewater tank. Detecting the onset of icing using temperature measurement requires a precise measurement, which can also only be performed inside the wastewater tank.

[0007] Alternatively, icing could be detected optically, which is generally possible with an external sensor if the tank is made of sufficiently transparent material. The disadvantage, however, is that optically transparent plastic is generally more expensive and may not have the required mechanical properties.

[0008] In addition, deposits or other contamination can affect the transparency of the tank wall material over time, which may cause an optical sensor to no longer work reliably.

[0009] EP 2 692 937 A1 also describes a dishwasher with a heat pump circuit that extracts heat from an evaporator tank and transfers it to the washing circuit. The heat pump is stopped when the tank is largely frozen.

[0010] US 4 347 709 A discloses a capacitive sensor which monitors the formation of ice on the surface of an evaporator of a heat pump of a refrigeration unit and is used to control a defrosting cycle.

[0011] It is therefore an object of the present invention to provide a dishwasher of the type mentioned above with an icing sensor that is as easy to install and operates reliably as possible. A further object is to provide an operating method for a dishwasher with such an icing sensor.

[0012] This problem is solved by a dishwasher or an operating method having the features of the respective independent claim. Advantageous embodiments and further developments are the subject of the dependent claims.

[0013] A dishwasher according to the invention of the type mentioned above is characterized in that the sensor for detecting the degree of icing is a capacitance sensor arranged on the outside of the evaporator tank. A capacitance sensor arranged on the outside of the evaporator tank also allows conclusions to be drawn about the dielectric constant of a medium in the tank in the area in front of the capacitance sensor. Since water's dielectric constant changes when it freezes, the onset and progression of freezing can be detected via the capacitance measurement. Positioning the sensor on the outside of the evaporator tank allows for easy installation without sealing problems. Furthermore, the capacitance measurement is less sensitive to deposits on the evaporator tank.

[0014] An operating method according to the invention for such a dishwasher comprises the following steps: The heat pump circuit is operated to extract heat from the closed, water-filled evaporator tank and transfer it to the washing circuit. During this process, a capacitance value is measured repeatedly and, if necessary, continuously by a capacitance sensor arranged on an outer side of the evaporator tank. If the measured capacitance value indicates a certain degree of icing, the heat pump circuit is stopped or throttled. In particular, the heat pump circuit is stopped or throttled if the capacitance value falls below a predetermined threshold. The method is based on the finding that the dielectric constant decreases during the transition from water to ice.

[0015] In an advantageous embodiment of the dishwasher, the capacitance sensor is positioned in an upper area on a side wall of the evaporator tank. Firstly, icing usually begins at the top of the tank. Secondly, a capacitance sensor in this position can be used not only as an icing sensor but also as a fill level sensor.

[0016] For this purpose, the following additional steps can be performed in the operating procedure before operating the heat pump circuit: A capacitance value is again determined by the capacitance sensor, and the evaporator tank is filled with water if and as long as the capacitance value is below a predefined additional threshold. This takes advantage of the fact that air has a dielectric constant that is approximately two orders of magnitude lower than water.

[0017] In a further advantageous embodiment of the dishwasher, the capacitance sensor has planar electrodes arranged side by side, facing the evaporator tank. The planar electrodes preferably comprise a central measuring electrode and an annular shielding electrode arranged around it. From these electrodes, an electric field measuring the dielectric constant penetrates a few millimeters to a few centimeters into the evaporator tank. This makes it possible to detect, in particular, icing that begins inside the evaporator tank and spreads toward the wall of the evaporator tank. Preferably, the heat pump circuit is stopped or throttled shortly before the icing limit reaches the wall. In this way, the latent heat of the water in the evaporator tank is effectively utilized without the risk of damaging the evaporator tank due to the volume expansion of the water or ice during freezing.

[0018] In a further advantageous embodiment of the dishwasher, the evaporator tank comprises evaporator tubes arranged in a plurality of loops at different heights. To detect the icing emanating from the evaporator tubes, the capacitance sensor is preferably arranged at a height on the evaporator tank that approximately corresponds to the height of one of the upper loops. Depending on the penetration depth of the electric field, the capacitance sensor is positioned, or the loops of the evaporator tube are laid, such that the capacitance sensor has a minimum distance of a few millimeters to a few centimeters from the evaporator tube.

[0019] In a further advantageous embodiment of the dishwasher, the capacitance sensor includes an evaluation unit. The evaluation thus takes place directly near the electrodes, enabling reliable measurement.

[0020] The invention is explained in more detail below using an exemplary embodiment with the aid of figures. The figures show: Fig. 1 a schematic block diagram of a dishwasher with a heat pump circuit; Fig. 2 is a schematic diagram of a capacitance sensor for use in a dishwasher; Fig. 3 an isometric view of an evaporator tank of the dishwasher according to Fig. 1; Fig. 4 the evaporator tank according to Fig. 3 with the housing open; and Fig. 5 a sectional view of the evaporator tank of the Fig. 3 and Fig. 4.

[0021] Fig. 1 shows a dishwasher in a schematic functional block diagram.

[0022] The dishwasher has a washing chamber 1, into which the dishes can be placed and into which washing liquid is sprayed to clean the dishes. Rotating spray arms, for example, are provided to spray the washing liquid, one of which is located in the Fig. 1 is indicated schematically. Washing liquid dripping from the dishes or the walls of the washing cabinet 1 collects in a collecting pan 2 in a lower area of ​​the washing cabinet 1. From there, the washing liquid is pressurized by a circulation pump 3 and recirculated into the washing cabinet 1 for cleaning, thereby forming a washing circuit. The collecting pan 2, like the circulation pump 3, is generally arranged in a base of the dishwasher below the washing cabinet 1. A heating element for heating the washing liquid is also present in the collecting pan 2 or in the area of ​​the circulation pump 3.

[0023] In the illustrated embodiment, rinsing liquid that is no longer required is led directly into a drain 4 via a waste water pump. Furthermore, a fresh water tank 5 is provided, which is coupled to an inlet 6 via a valve. The fresh water tank 5 is generally arranged next to the washing chamber 1, so that the fresh water introduced can, prior to use in the washing chamber 1, be heated to a temperature higher than the temperature at the inlet 6, possibly due to the waste heat from the washing chamber 1 and also due to the ambient heat. Control elements such as valves (V), pump motors (M), temperature sensors (T) and pressure sensors (P) are included in the Fig. 1 are mostly not provided with reference symbols, but only identified by the given letters.

[0024] The dishwasher also features a heat pump circuit 7, through which heat is extracted from an evaporator tank 8 and supplied to a condenser tank 10. The condenser tank 10 communicates with the collecting tank 2 via the circulation pump 3, allowing water heated in the condenser tank 10 to be fed into the washing process. The heat pump circuit 7 thus forms a water-to-water heat pump.

[0025] An evaporator 9 of the heat pump circuit 7 is arranged in the preferably closed evaporator tank 8. A condenser 11 of the heat pump circuit 7 is arranged in the condenser tank 10. Further components of the heat pump circuit 7, such as the heat pump itself, are arranged in the Fig. 1 shown schematically, but not further described.

[0026] The evaporator tank 8 is filled with water, whose thermal capacity is utilized to supply heat to the rinsing process, thereby reducing the temperature of the water in the evaporator tank 8. During pauses until the next rinsing process, the temperature of the water in the evaporator tank 8 can then adjust to the ambient temperature again to make its thermal energy available for the next rinsing process. A fan 12 is arranged in the area of ​​the evaporator tank 8 to accelerate this temperature equalization and to remove condensate that may form on the evaporator tank 8 if its temperature falls below a dew point.

[0027] The evaporator tank 8 is connected to the fresh water tank 5 via lines and valves to allow for setting a desired fill level before the start of the process. Within the rinsing process itself, the evaporator tank 8, in the illustrated embodiment, represents a closed system.

[0028] During operation of the dishwashers, heat is extracted from the evaporator tank 8 via the heat pump circuit 7 at appropriate process times and supplied to the condenser tank 10, thereby heating the dishwashing liquid in an energy-saving manner. To prevent the water in the evaporator tank 8 from completely freezing and thereby damaging the evaporator tank 8 or the evaporator 9 located therein due to its expansion, a capacitance sensor 13 is arranged on the outside of the evaporator tank 8. This sensor determines a capacitance value (or a value correlated therewith) that depends on a dielectric constant of a medium located in the evaporator tank 8 in the region of the capacitance sensor 13.

[0029] Fig. 2 shows an example of a possible structure of the capacitance sensor 13. On a front side of the capacitance sensor 13, with which it is placed on the evaporator tank 8, there is a central and, for example, circular measuring electrode 131 and a preferably annular shielding electrode 132 arranged concentrically around it. The electrodes 131, 132 are connected to an evaluation unit 133, which determines a capacitance value of the arrangement of the electrodes 131, 132. Instead of a capacitance value, a value correlating therewith can also be determined. The evaluation unit 133 can, for example, comprise an oscillating circuit that oscillates at a frequency that is dependent on the capacitance value. The evaluation unit 133 can be designed to convert the measured frequency value into a capacitance value. However, it can also be provided to directly output the frequency value that is representative of the capacitance value.When a capacitance value is referred to below, this term also includes a value correlated with the capacitance value.

[0030] To output the capacitance value, an interface 134 is provided on the capacitance sensor 13, which outputs the capacitance value in analog and / or digital form. The evaluation unit 133 and the interface 134 can be configured in analog and / or digital form using a microcontroller.

[0031] In the Fig. 3-5 shows the evaporator tank 8 with the evaporator 9 and the capacity sensor 13 in more detail. Fig. 3 and Fig. 4 are isometric drawings, where the Fig. 3 shows the evaporator tank 8 in an overall view and the Fig. 4 shows the evaporator tank 8 partially opened to reveal its internal structure. In Fig. 5 shows a cross section through the evaporator tank 8 in the area of ​​the capacity sensor 13.

[0032] The evaporator tank 8 is formed from a lower part 81 and an upper part 82, which is attached and connected to the lower part in a watertight manner. The connection between the two housing parts 81, 82 can be achieved, for example, by a material-to-material bonding process. Preferably, the lower and upper parts 81, 82 are injection-molded plastic parts, the outer contours of which are adapted to the available space in the base of the dishwasher.

[0033] The evaporator 9 is formed by a meandering evaporator tube 91, which is guided in a plurality of loops through substantially the entire interior volume of the evaporator tank 8. Support elements 85 are inserted to hold individual loops of the evaporator tube 91 in their position.

[0034] The capacity sensor 13 is arranged on the outside of a side wall 83 in the upper area of ​​the evaporator tank 8. Furthermore, inlets and outlets 84 are formed on the lower and upper parts 81, 82, through which the evaporator tank 8 can be filled and emptied. In order to be able to represent the position of the capacity sensor 13 relative to the evaporator tube 91, Fig. 4 the capacitance sensor 13 is shown, although the upper part 82 to which it is attached is not shown.

[0035] In the sectional view of the Fig. 5 it can be seen that the capacity sensor 13 is positioned approximately at the height of an upper layer of loops of the evaporator tube 91. Schematically, Fig.5 shows an electric field 135 emanating from the electrodes 131, 132 of the capacitance sensor 13. The electric field 135 extends a few millimeters up to approximately one centimeter into the interior of the evaporator tank 8. This penetration depth corresponds approximately to the distance between the evaporator tube 91 and the wall of the evaporator tank 8 in this area where the capacitance sensor 13 is arranged.

[0036] The capacitance sensor 13 is advantageously used during operation of the dishwasher both as a fill level sensor and as an icing sensor. This takes advantage of the fact that the dielectric constant of water is many times greater than that of air and also greater than that of ice.

[0037] At the beginning of a rinsing process, a capacitance measurement can initially provide information about whether the area in front of the capacitance sensor 13 is filled with water or whether the water level in the evaporator tank 8 has dropped so low that the dielectric constant of air is effective and a correspondingly low capacitance value is measured. The evaporator tank 8 is then filled with water from the fresh water tank 8 by controlling the corresponding valves. As soon as the water reaches the lower end of the measuring range of the capacitance sensor 13, the capacitance value begins to rise until the upper end of the measuring range is reached.

[0038] Compared to the empty evaporator tank 8, the capacitance value of the filled evaporator tank 8 increases by approximately two orders of magnitude. Because the capacitance sensor 13 has a laterally extended measuring range, a desired fill level can be set for the water filling process by appropriately setting switching thresholds. Advantageously, the evaporator tank 8 is not completely filled with water, so that a certain volume of air remains above the evaporator tube 91, into which any ice forming can expand.

[0039] During the rinsing process, the heat pump circuit 7 is operated to extract heat from the water in the evaporator tank 8 and supply it to the rinsing process. This causes the water in the evaporator tank 8 to cool, which is also reflected by the capacitance sensor 13 in the form of a slight increase in the measured capacitance. This is due to a certain temperature dependence of the dielectric constant of liquid water.

[0040] When icing occurs in the evaporator tank 8, the capacity sensor 13 detects a sharp drop in the measured capacity value, whereupon the operation of the heat pump circuit 7 is either stopped or throttled with regard to its heat transfer. Icing can be detected based on absolute capacity values ​​and / or with the aid of a relative change or rate of change in the capacity value.

[0041] During operation, icing begins on the evaporator tubes 91. Starting at the evaporator tubes 91, an ice crust forms, the thickness of which increases. The growth of this ice crust can be observed by a decreasing capacity value. A threshold value for shutting down the heat pump circuit is preferably selected so that it shuts down shortly before the icing limit reaches the wall of the evaporator tank 8. For example, the threshold value can be selected so that it shuts down at approximately 90% ice volume. In this way, the latent heat of the water in the evaporator tank 8 is effectively utilized without the risk of damaging the evaporator tank 8 due to volume expansion during freezing. Reference symbol 1 dishwashing compartment 2 collection pot 3 Circulation pump 4 Procedure 5 Fresh water tank 6 Inlet 7 Heat pump circuit 8 Evaporator tank 81 Lower part 82 top 83 Side wall 84 Inlet / Outlet 85 support element 9 evaporators 91 Evaporator tube 10 Condenser tank 11 Condenser 12 fans 13 Capacitance sensor 131 measuring electrode 132 Shield electrode 133 Evaluation unit 134 Interface 135 electric field

Claims

[1] Dishwasher for cleaning dishes with washing liquid which is circulated in a washing circuit, comprising a heat pump circuit (7) for extracting heat from an evaporator tank (8) filled with water and transferring it to the washing circuit, wherein a sensor is provided for the evaporator tank (8) in order to detect a degree of icing present in the evaporator tank, characterized by that the sensor for detecting the degree of icing is a capacitance sensor (13) which is arranged on the outside of the evaporator tank (8). [2] Dishwasher according to claim 1, wherein the capacitance sensor (13) is positioned in an upper region on a side wall (83) of the evaporator tank (8). [3] Dishwasher according to claim 1 or 2, wherein the capacitance sensor (13) has planar electrodes arranged side by side, which point towards the evaporator tank (8). [4] Dishwasher according to claim 3, wherein the planar electrodes are a central measuring electrode (131) and a shielding electrode (132) arranged around it. [5] Dishwasher according to one of claims 1 to 4, wherein the capacitance sensor (13) comprises an evaluation unit (133). [6] Dishwasher according to one of claims 1 to 5, wherein in the evaporator tank (8) evaporator tubes (91) run in a plurality of loops at different heights. [7] Dishwasher according to claim 6, wherein the capacitance sensor (13) is arranged at a height on the evaporator tank (8) which corresponds approximately to the height of an upper one of the loops. [8] Dishwasher according to claim 6 or 7, wherein the capacitance sensor (13) is positioned such that it has a minimum distance of a few millimetres to a few centimetres from the evaporator tube (91). [9] Operating method for a dishwasher for cleaning dishes with washing liquid circulated in a washing circuit, with a heat pump circuit (7), comprising the following steps: - Operating the heat pump circuit (7) to extract heat from a closed evaporator tank (8) filled with water and transfer it to the rinsing circuit; - measuring a capacitance value by a capacitance sensor (13) arranged on an outer side (83) of the evaporator tank (8); - Stopping or throttling the heat pump circuit (7) when the measured capacity value indicates a certain degree of icing present in the evaporator tank. [10] Operating method according to claim 9, wherein the heat pump circuit (7) is stopped or throttled when the measured capacity value falls below a threshold value. [11] Operating method according to claim 9 or 10, with the following additional steps, which are carried out before operating the heat pump circuit (7): - measuring a capacitance value by the capacitance sensor (13); - Filling the evaporator tank (8) with water if and as long as the capacity value is below a predetermined threshold.

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